DESCRIPTION
LUBRICATING OIL COMPOSITION
Technical Field
[0001] The present invention relates to a lubricating oil composition suitably used for wet-type clutches or 4-stroke engines of two-wheeled vehicles ; more particularly, the invention relates to a lubricating oil composition used for wet-type clutches or 4-stroke engines of two-wheeled vehicles, which exhibits excellent power transmission performance in wet-type clutches and excellent fuel saving performance.
Background Art
[0002] In view of recent environmental issue, particularly reduction of carbon dioxide emission, improvement of automobile fuel efficiency is one of the major issues; in order to solve the issue, weight saving of vehicles, improvement of combustion, reduction of engine friction, development and improvement of power train, and so on have been studied.
[0003] For example, with regard to the reduction of engine friction, development of lean-burn engine and direct fuel-injection engine as well as adoption of fuel-efficient engine oil have been performed together with improvement of valve train, reduction of number of piston-rings, and improvement of material like decrease of surface roughness of slide member.
[0004] As for power train, not only material-level friction of manual transmission, automatic transmission, and so on has

been reduced, but also new technologies showing excellent power transmission performance has been developed, such as automatic transmission having slip-controlled lock-up clutch and metal belt-type, toroidal-type, or etc. continuously variable transmission. Thus, fuel saving performance has been improved. [0005] Further, these days, a transmission fluid, which has fuel saving performance by reducing both viscosity and friction and which has adequate frictional property that enables to exhibit excellent power transmission performance about wet-type clutches and metal belt, is demanded.
[0006] Moreover, with respect to the lubricating oil used for 4-stroke engines of two-wheeled vehicles in which not only an engine but also a transmission as well as a power transmission portion of the transmission (i.e. wet-type clutches) are incorporated in one crankcase, it is necessary to satisfy the required performance of both engine oil and transmission fluid; same as above, demand for fuel saving performance has been increasing.
[0007] The above engine and power train as well as 4-stroke engines of two-wheeled vehicles have been further developed to attain reduction in size and weight as well as high power. Due to this, heat load to the lubricating oil used for these becomes higher than ever before; thus, deterioration of the lubricating oil is accelerated. Therefore, in view of reducing waste oil, maintenance of initial property for a long period of time becomes a significant concern.
[0008] On the other hand, about gasoline-powered vehicle, particularly diesel-powered vehicle or two-wheeled vehicle these

days, for the purpose of exhausu-gas purification, EGR device and catalytic converter such as three-way catalyst, oxidation catalyst, N0X storage/reduction type catalyst, and diesel particulate filter (DPF) are started to be mounted. In order to maintain the performance of these catalytic converters, sulfur content reduction of gasoline and diesel fuel has been developed. Together with this, for the same purpose as above, further reduction of ash and phosphorus about engine oil has been studied. [0009] In the reduction of ash and phosphorus of engine oil, attempts like reduction of dosage of metallic detergent and zinc dithiophosphate to be added as excellent antioxidant and anti-wear agent or nonuse thereof have been carried out. However these attempts are possibly damage performance of the conventional engine oils; thus, reduction of ash and phosphorus is an extremely difficult problem.
[0010] As the fuel-efficient engine oil, for example, Patent document 1 proposes an engine oil composition which includes: a particular lubricant base oil; and a predetermined dosage of particular additives (alkali earth metal salicylate detergent, molybdenum dithiocarbamate friction reducer, and etc.). In addition, Patent document 2 proposes an oil composition for 4-stroke engines of two-wheeled vehicles which saves oil consumption by containing a particular base oil and additives (metallic detergent, friction modifier, and etc.) therein and which exhibits excellent fuel saving performance at an engine revolution of 3000 to 13000 rpm.
[0011] However, when these fuel-efficient engine oils as it is are applied in the 4-stroke engines of two-wheeled vehicles,

slippage of wet-type clutches is significant; power transmission performance of the clutch is poor, but also overheat, burning, wear, damage, and etc. of friction materials and deterioration of shift feeling are anticipated. Whereby, it has been a common-sense view among the persons skilled in the art that compatibility between fuel saving performance and slippage inhibitory effect of wet-type clutches is extremely difficult. [0012] Therefore, these fuel-efficient engine oils are only used for special two-wheeled vehicles to which slippage inhibitory measures is provided; an oil for 4-stroke engines of two-wheeled vehicles, which is widely-usable and which exhibits excellent in fuel saving performance and frictional property in wet-type clutches, has been demanded.
[0 013] From these points of view, Patent documents 3 and 4 propose oil compositions for 4-stroke engines of two-wheeled vehicles, which can strike a balance between fuel saving performance and slippage inhibitory effect in wet-type clutches and which is classified as MA-class (causing no clutch slippage) in the category in accordance with JASO T 903-98 (JASO: Japanese Automobile Standards Organization).
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 08-302378
Patent Document 2: JP-A No. 2000-087070 Patent Document 3: JP-A No. 2001-214184 Patent Document 4: JP-A No. 2003-041283
Disclosure of the Invention
Problems to be solved by the Invention

[0014] However, these proposed compositions are individually contain zinc dithiophosphate as the essential component so that there is still room for improvement in view of shift feeling and extending the life of lubricating oil.
[0015] Accordingly, the present invention is to provide a lubricating oil composition for wet-type clutches or 4-stroke engines of two-wheeled vehicles, which exhibits excellent power transmission performance in wet-type clutches and/or fuel saving performance even when zinc dithiophosphate is not used. Another object of the present invention is to provide a lubricating oil composition for 4-stroke engines of two-wheeled vehicles having a wet-type clutch, which exhibits excellent power transmission performance in wet-type clutch and which attains reduction of engine friction and exhibits excellent fuel saving performance.
Means for Solving the Problems
[0016] The inventors of the present invention had been seriously studied the above problems. As a result, they discovered the fact that a lubricating oil composition containing predetermined dosage of a certain phosphorus compound and metallic detergent can solve the above problems, and they completed the present invention.
[0017] The present invention is a lubricating oil composition for wet-type clutches or 4-stroke engines of two-wheeled vehicles, which includes: a lubricant base oil containing a mineral base oil and/or a synthetic base oil; and to the total mass of the composition,
(A) 0.01-0.2 mass % of a metal salt of phosphorus-containing acid

represented by the general formula (a) or (b) as the phosphorus content, (B) 0 .005-0 . 5 mass % of a metallic detergent as the metal content, and (C) 0.01-0.4 mass % of an ashless dispersant as the nitrogen content. [0018]
(a)
(Wherein, R1 is a C1-C30 hydrocarbon group,- R2 and R3 may be the same or different and are independently a hydrogen atom or a C1-C30 hydrocarbon group; and p is an integer of 0 or 1.) [0019]
(b)
(Wherein, R4 is a C1-C30 hydrocarbon group; R5 and R6 may be the same or different and are independently a hydrogen atom or a CT -C3n hydrocarbon group; and q is an integer of 0 or 1.)
[0020] According to the invention, it is capable of providing a lubricating oil composition which can improve frictional property of the wet-type clutches and which exhibits excellent power transmission performance.
[0021] In the present invention, mass ratio (M/P) of the metal content (M) and the phosphorus content (P) in the metal salt of the (A) phosphorus-containing acid is preferably 1 to 3 and more preferably 1.2 to 1. 8 . By setting the ratio within the range, anti-wear property can be improved.

[0 022] In the invention, concent of zinc dithiophosphate, to the total mass of the composition, is preferably below 0.01 mass % equivalent to phosphorus element or is not substantially contained. By setting the content like this, deterioration of lubricating oil is inhibited even under a severe deterioration condition so that longer-life lubricating oil can be obtained; it is also capable of enhancing the shift feeling. [0023] In the invention, the lubricating oil composition preferably does not contain (El) an organomolybdenum compound selected from molybdenum dithiophosphate and molybdenum dithiocarbamate. By doing so, it is capable of obtaining a composition which exhibits excellent frictional property and power transmission performance in wet-type clutches. [0024] Moreover, in the invention, the lubricating oil composition preferably contains (E) an organomolybdenum compound. By doing so, reduction of engine friction can be attained and fuel saving effect can be further improved. In addition to these, shift feeling can also be improved.
[0025] Further, in the invention, the (C) ashless dispersant includes a boron-containing succinimide and a boron-free mono-and/or bis-succinimide, and the content of the boron-containing succinimide, to the total mass of the composition, is preferably 0.005-0.2 mass % equivalent to boron element. By doing so, it is capable of obtaining a composition which can further improve the frictional property in wet-type clutches and which exhibits excellent high-temperature detergency and thermal resistance. [0026] Still further, in the invention, sulfated ash content in the lubricating oil composition, to the total mass of the

composition, is preferably 1 mass % or less. By setting the content within the range, impact on the catalytic converter can be reduced.
Effects of the Invention
[0027] By the present invention, since a metal salt of a specific phosphorus-containing acid is used instead of using the zinc dithiophosphate conventionally used as an essential additive, it is capable of providing a lubricating oil composition which can improve the frictional property in wet-type clutches and which exhibits excellent power transmission performance. Even in a case where molybdenum dithiocarbamate and molybdenum dithiophosphate are not used, reduction of engine friction can be attained and fuel saving performance can also be improved. In addition, in case where the molybdenum dithiocarbamate and the molybdenum dithiophosphate are used, the composition can attain a substantial reduction of engine friction and exhibits excellent fuel saving performance even in an engine without having a wet-type clutch. Moreover, even when the molybdenum dithiocarbamate and the molybdenum dithiophosphate are used, since frictional property in wet-type clutches can be maintained at high level, it is capable of providing an excellent lubricating oil composition which attains fuel saving from aspects of both power transmission performance and reduction of engine friction. Therefore, the lubricating oil composition of the invention is useful as a lubricating oil composition for apparatus including a wet-type clutch, particularly, oil for 4-stroke engines of two-wheeled vehicles having a wet-type clutch. Further, the

lubricating oil composition of the invention is also useful for apparatus having no wet-type clutch, such as 4-stroke engines of two-wheeled vehicles having no wet-type clutch.
Best Mode for Carrying Out the Invention
[0028] Hereinafter, the lubricating oil composition of the present invention will be described in detail.
As the lubricant base oil used for the lubricating oil composition of the present invention (hereinafter, simply refer to as "lubricating oil composition". ) , as long as it is a mineral base oil and/or a synthetic base oil used for normal lubricating oil, any kind of lubricant base oil can be used without specific restriction.
[0029] As the mineral base oil, specifically, there may be: an oil obtained by refining a lubricating oil fraction, which is obtained by vacuum distillation of topped crude obtained by topping of crude oil, by using one or more treatment such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, and hydrorefining; a wax-isomerized mineral oil; and a lubricant base oil produced by isomerization of GTL WAX (Gas to Liquid Wax) manufactured by Fischer-Tropsch process or the like.
[0030] The total aromatic fraction of the mineral base oil, but not specifically limited, is preferably 40 mass % or less, more preferably 3 0 mass % or less. The total aromatic fraction may be 0 mass %,- however, in view of solubility of additives, it is preferably 1 mass % or more, more preferably 2 mass % or more. When the total aromatic fraction of the base oil exceeds

40 mass %, oxidation stability of the lubricating oil composition is deteriorated; hence it is not preferable.
[0031] It should be noted that the total aromatic fraction means the content of aromatic fraction measured in accordance with ASTM D2549. Usually, the aromatic fraction includes-, not only alkyl benzene and alkyl naphthalene; but also anthracene, phenanthrene, and the alkylated product thereof; compounds in which four or more benzene rings are condensed; and compounds having he teroaromatic compound (s) such as pyridines , quinolines, phenols, and naphthols.
[0032] Sulfur content in the mineral base oil, but not specifically limited, is preferably 1 mass % or less, more preferably 0.5 mass % or less, and furthermore preferably 0.2 mass % or less. By reducing sulfur content of the mineral base oil, it is possible to attain antioxidant characteristic and to reduce impact on catalytic converter.
[0033] Specific examples of synthetic base oil include: polybutene or the hydrogenated product thereof; poly-a-olefin such as 1-octene oligomer and 1-decene oligomer, or the hydrogenated product thereof; diester such as ditridecyl glutalate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, and di-2-ethylhexyl sebacate; polyol ester such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol pelargonate; copolymer of dicarboxylic acids and C2-C30 a-olefin, such as dibutyl maleate; and aromatic synthetic oil such as alkyl naphthalene, alkyl benzene, aromatic ester or the mixtures thereof.

[0034] In the invention, examples of the lubricant base oil include: mineral base oils, synthetic base oils, or an optional mixture of two or more lubricating oils selected from these lubricating oil. For example, there may be one or more mineral base oils, one or more synthetic base oils, and the mixtures of one or more mineral base oils and one or more synthetic base oils. [0035] Viscosity of the lubricant base oil of the invention is not specifically limited; the lower limit of the kinematic viscosity at 100 degree C is preferably 2 mm2/s and more preferably 3 mm2/s. On the other hand, the upper limit of the kinematic viscosity at 100 degree C is preferably 10 mm2/s and more preferably 8 mm2/s. By setting the lower limit of the kinematic viscosity at 100 degree C of the lubricant base oil to 2 mm2/s or more, it is capable of obtaining a lubricating oil composition which can sufficiently form oil film and which exhibits superior lubricity, lower evaporation loss of the base oil at high temperature conditions (namely, oil consumption becomes less). While, by setting the upper limit of the kinematic viscosity at 100 degree C to 10 mm2/s or less, since fluid resistance becomes less so that it is capable of obtaining a lubricating oil composition which exhibits less friction resistance at the lubrication points, as it were, a lubricating oil composition which exhibits excellent fuel saving performance. [0036] Viscosity index of the lubricant base oil of the present invention, but not specifically limited, is preferably 80 or more, more preferably 100 or more. The lubricating oil composition desirably contains a lubricant base oil whose viscosity index is 120 or more at an amount of preferably 15 mass %

or more , more preferably 50 mass % or more , furthermore preferably 70 mass % or more; among them, the lubricating oil composition is particularly preferably a lubricant base oil whose viscosity index is 12 0 or more. The upper limit of viscosity index is not specifically limited. Examples of oil may be: base oils having viscosity index of about 135-189 such as n-paraffin, slack wax, and GLT wax, or iso-paraf f inic mineral oil obtained by isomerizing these base oils; and other base oils having viscosity index of about 150-250 such as complex ester base oil or HVI-PAO base oil. By setting the viscosity index to 80 or more, it becomes possible to obtain a lubricating oil composition which exhibits excellent fuel saving performance and lower evaporation loss under high temperature conditions.
[0037] NOACK volatility of the lubricant base oil of the invention is preferably 2 0 mass % or less, more preferably 16 mass % or less, and particularly preferably 5-15 mass %. By setting NOACK volatility of the lubricant base oil to 20 mass % or less, it is capable of obtaining a lubricating oil composition in which the evaporation loss under high-temperature conditions is lower and which enables to avoid adverse influence caused by accumulation of oil in the catalytic converter, pistons, and combustion chambers. It should be noted that the NOACK volatility means volatility measured in accordance with CEC L-40-T-87.
[0038] The lubricating oil composition of the invention contains, as (A) component, a metal salt of phosphorus-containing acid of the general formula (a) or (b) . By using the (A) component, compared with the conventional zinc dithiophosphate-containing

lubricating oil composition for 4-stroke engines of two-wheeled vehicles, clutch meeting is improved thereby shift feeling tends to be improved.
[0 03 9] As the (A) component, there may be a metal salt obtained by reacting a phosphorus-containing acid of the general formula (a) or (b) with a metal base such as metal oxide, metal hydroxide, metal carboxylate, and metal chloride. [0040]
(a)
(In the formula, R1 is a Ci-C30 hydrocarbon group,- R2 and R3 may be the same or different and are independently a hydrogen atom or a Ci-C30 hydrocarbon group; and p is an integer of 0 or 1.)
[0041]
(b)
(In the formula, R4 is a Ci-C30 hydrocarbon group,- R5 and R6 may be the same or different and are independently a hydrogen atom or a C1-C30 hydrocarbon group; and q is an integer of 0 or 1.)
[0042] In the general formulae (a) and (b), specific examples of Ci-C30 hydrocarbon substituent represented by R1-R6 are particularly preferably hydrocarbon group such as alkyl group, cycloalkyl group, alkenyl group, alkyl-substituted cycloalkyl group, aryl group, alkyl-substituted aryl group, and aryl alkyl group. As long as the hydrocarbon substituent includes the above

hydrocarbon group, it may be a group having in the molecule at
least one or a combination of two or more selected from the group consisting of: sulfur, nitrogen, and oxygen.
[0043] Examples of the above alkyl group include: methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl (the alkyl group may be linear or branched and may be primary alkyl group, secondary alkyl group, or tertiary alkyl group.).
[0044] Examples of the cycloalkyl group include: C5-C7 cycloalkyl group such as cyclopentyl, cyclohexyl, and cycloheptyl. Examples of the alkyl cycloalkyl group include: C6-Cn alkyl cycloalkyl group such as methyl cyclopentyl, dimethyl cyclopentyl, methylethyl cyclopentyl, diethyl cyclopentyl, methyl cyclohexyl, dimethyl cyclohexyl, methylethyl cyclohexyl, diethyl cyclohexyl, methyl cycloheptyl, dimethyl cycloheptyl, methylethyl cycloheptyl, and diethyl cycloheptyl (substitution position of alkyl group in the cycloalkyl group is also arbitrary.).
[0045] Examples of the alkenyl group include: butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, and octadecenyl (the alkenyl group may be linear or branched and the position of double bond is arbiltrary.).
[0046] Examples of the aryl group include: phenyl and naphthyl. In addition, examples of the alkyl aryl group include: C7-CiS alkyl aryl group such as tolyl, xylyl, ethyl phenyl, propyl phenyl, butyl phenyl, pentyl phenyl, hexyl phenyl, heptyl phenyl,

octyl phenyl, nonyl phenyl, decyl phenyl, undecyl phenyl, dodecyl phenyl (these alkyl may be linear or branched and the substitution position to aryl group may be arbitrary.).
[0047] Examples of aryl alkyl group include: C7-Ci2 aryl alkyl group such as benzyl, phenyl ethyl, phenyl propyl, phenyl butyl, phenyl pentyl, and phenyl hexyl (the alkyl group may be linear or branched.).
[0048] Ci-C30 hydrocarbon group represented by the above R1 to R6 is preferably Ci-C30 alkyl group or C6-C24 aryl group, more preferably C3-C18 alkyl group, furthermore preferably C4-Ci2 alkyl group, and particularly preferably Ce-Ci0 alkyl group.
[0049] Examples of phosphorus-containing acid of the general formula (a) include: phosphite monoester and
(hydrocarbyl) phosphonous acid, these of which have one of the above Ca-Cso hydrocarbon group; phosphite diester and
(hydrocarbyl) phosphonous acid monoester, these of which have two of the above Ci-C30 hydrocarbon group; phosphite triester and
(hydrocarbyl) phosphonous acid diester, these of which have three of the above C;L-C3O hydrocarbon group; and the mixtures thereof.
[0050] Examples of phosphorus-containing acid of the general formula (b) include: phosphate monoester and
(hydrocarbyl) phosphonic acid, these of which have one of the Ci-C30 hydrocarbon group,- phosphate diester and (hydrocarbyl) phosphonate monoester, these of which have two of the CX-CBO hydrocarbon group; phosphate triester and (hydrocarbyl) phosphonic acid diester, these of which have three of the C1-C30 hydrocarbon group; and the mixtures thereof. It should be noted that the term "hydrocarbyl" in the examples of the general

formulae (a) and (b) means a C-.-C30 hydrocarbon substituent. [0051] Metal salt of phosphorus-containing acid of the general formula (a) or (b) can be obtained by reacting the phosphorus-containing acid of the general formula (a) or (b) with a metal base such as metal oxide, metal hydroxide, metal carboxylate, and metal chloride and then neutralizing a part of or the entire remaining acidic hydrogen.
[0052] Examples of metal in the metal base include: alkali metal such as lithium, sodium, potassium, and cesium; alkali earth metal such as calcium, magnesium, and barium; and heavy metal such as zinc, copper, iron, lead, nickel, silver, molybdenum, and manganese. Among these, alkali earth metal like calcium and magnesium as well as molybdenum and zinc are preferable; zinc is particularly preferable.
[0053] The metal salt of the phosphorus compound has various structures depending on the valence of the metal or number of OH-group in the phosphorus compound; therefore, structure of the metal salt of the phosphorus compound is not restricted at all. For example, when 1 mol of zinc oxide is reacted with 2 mol of phosphate diester (a compound having one OH-group) , it is thought that a compound represented by the formula (c) is obtained as the main component, polymerized molecules are also thought to be existed. [0054]

(In the formula, R is independently a hydrogen atom or a C2-C^o hydrocarbon group.)
[0055] Alternatively, when 1 mole of zinc oxide is reacted with 1 mol of phosphate monoester (a compound having two OH-groups), it is thought that a compound represented by the formula (d) is obtained as the main component, polymerized molecules are also thought to be existed. [0056]
(d)
(In the formula, R is a hydrogen atom or a C1-C30 hydrocarbon group . )
[0057]In the invention, the metal salt of the phosphorus-containing acid may be used alone or may be a combination of two or more thereof.
[0058] More preferable examples regarding the metal salt of phosphorus-containing acid of the invention include: a zinc salt of phosphite diester having two C3-Cie alkyl or aryl groups, a zinc salt of phosphate monoester having one C3-Ci8 alkyl or aryl groups, a zinc salt of phosphate diester having two C3-Ci8 alkyl or aryl groups, a zinc salt of (hydrocarbyl) phosphonous acid having one C1-C18 alkyl or aryl group, a zinc salt of (hydrocarbyl) phosphonous acid monoester having two C1-C18 alkyl or aryl groups, a zinc salt of (hydrocarbyl) phosphonic acid having one C1-C18 alkyl or aryl group, and a zinc salt of (hydrocarbyl) phosphonate monoester having two C1-C18 alkyl or aryl groups; among them, a zinc salt of phosphate monoester and/or phosphate diester having C3-Ci8 alkyl group, preferably C4-Ci2 alkyl group is preferable

and a zinc salt of phosphate diester having C:.-C1S alkyl group, preferably C1-C18 alkyl group is particularly preferable. [0059] As the most preferable (A) component of the invention, in addition to the effect of the present invention, in view of excellent balance between solubility to the lubricant base oil and anti-wear performance, it is preferably a metal salt of phosphate monoester and/or phosphate diester having C4-Ci2 alkyl, preferably C6-C10 alkyl group and the mass ratio (M/P) of the metal content (M) and the phosphorus content (P) is preferably 1-3; it is more preferably a metal salt of mixture of a phosphate monoester and a phosphate diester and the M/P ratio is preferably 1.1-2.5, more preferably 1.2-1.8.
[0060] In the lubricating oil composition of the invention, content of the (A) component, to the total mass of the composition, is usually 0.01-0.2 mass %, preferably 0.02-0.15 mass %, more preferably 0.04-0.12 mass % equivalent to phosphorus element. When the content of the (A) component equivalent to phosphorus element is below 0.01 mass %, durability of transmission and gear tend to become insufficient; when the content exceeds 0.2 mass %, effect in propotion to the additive amount cannot be obtained and the solubility often becomes insufficient. [0061] The lubricating oil composition of the invention contains a metallic detergent as the (B) component. Examples of metallic detergent, but not limited to, include: a known alkali metal or alkali earth metal sulfonate detergent, alkali metal or alkali earth metal phenate detergent, alkali metal or alkali earth metal salicylate detergent, alkali metal or alkali earth metal naphthenate detergent, alkali metal or alkali earth metal

phosphonate detergent, and the mixture of two or more thereof (including complex-type).
[0062] The alkali metal as described above includes sodium and potassium; and the alkali earth metal as above includes calcium, magnesium, and barium. Alkali earth metal is preferable; calcium or magnesium is particularly referable. It should be noted that total base number and additive amount of these metallic detergents can be optionally selected depending on the required performance of the lubricating oil. [0063] Examples of alkali metal or alkali earth metal sulfonate include an alkali metal salt or an alkali earth metal salt of alkyl aromatic sulfonic acid obtained by sulfonation of alkyl aromatic compounds having molecular mass of 300-1500, preferably 400-700, it is particularly magnesium salt and/or calcium salt; calcium salt is preferably used. [0064] Examples of the above alkali metal or alkyl aromatic sulfonic acid may specifically be the so-called "petroleum sulfonic acid" and "synthetic sulfonic acid". [0065] As the petroleum sulfonic acid, in general, a compound obtained by sulfonation of alkyl aromatic compounds of mineral lubricating oil fraction or the so-called "mahogany acid" and the like obtained as a by-product in the manufacturing of white oil.
[0066] On the other hand, examples of the synthetic sulfonic acid may be a material obtained by sulfonating alkyl benzene having linear or branched alkyl, which is, for example, obtained as a by-product from plant manufacturing alkylbenzene for the raw material of detergent or is obtained by alkylation of

polyolefin into benzene; or another material obtained by
sulfonating alkyl naphthalene like dinonylnaphthalene.
[0067] The sulfonating agents to sulfonate these alkyl aromatic compounds are not particularly limited; usually, fuming sulfuric acid and anhydrous sulfate are used.
[0068] In the invention, among these alkali metal sulfonates or alkali earth metal sulfonates, petroleum-derived sulfonates exhibit an effect to particularly improve fuel saving performance at moderate high temperature and static frictional property in wet-type clutches; synthetic sulfonates exhibit an effect to particularly improve fuel saving performance at high temperature, dynamic frictional property, and property in braking time. The petroleum-derived sulfonates and the synthetic sulfonates can be selectively-used, as required.
[0069] In the invention, in view of excellent low-frictional property as well as excellent anti-wear property when used together with the (A) component, an alkali metal salt or an alkali earth metal salt of alkyl aromatic sulfonic acid having an ethylene oligomer-derived C6-C4o/ preferably Cio-C30/ more preferably C14-C20 or C2o-C26 alkyl group is preferably exemplified. Desirably, examples of the ethylene oligomer-derived C6-C40 alkyl group, in view of excellent friction-reducing effect, include preferably Ci0-C30 alkyl group. These compounds can be obtained by reacting an alkyl aromatic sulfonic acid, which is obtained by firstly performing alkylation of aromatic compound such as benzene or naphthalene using ethylene oligomer-derived C6-C40/ preferably C0-C30, more preferably C14-C20 or C2o-C2e linear a-olef in and then sulfonating the resultant using fuming sulfuric

acid or sulfuric acid, with metal base such as oxide or hydroxide of alkali metal or alkali earth metal; these also can be obtained by forming an alkali metal salt such as sodium salt or potassium salt or by substituting an alkali metal salt for an alkali earth metal salt.
[0070] Examples of these alkali metal sulfonate or alkali earth metal sulfonate not only include the above neutral metal sulfonate but also include: a basic alkali earth metal sulfonate obtained by heating a mixture of the above neutral alkali earth metal sulfonate and excessive alkali earth metal salt or alkali earth metal base (hydroxide and oxide) in the presence of water; carboxylate over-basic alkali earth metal sulfonate, and borate over-basic alkali earth metal sulfonate, both of which can be obtained by reacting the above neutral alkali earth metal sulfonate with base of alkaili earth metal in the presence of carbon dioxide and/or boric acid or borate. These neutral alkali earth metal sulfonate, basic alkali earth metal sulfonate, over-basic alkali earth metal sulfonate, and the mixture thereof can be preferably used.
[0071] In the invention, metal ratio of the alkali metal sulfonate or alkali earth metal sulfonate is not specifically limited; the one having the ratio of 1-40 can be usually used. In view of excellent anti-wear property, an alkali metal or alkali earth metal sulfonate detergent having a metal ratio of 2 or more is preferably used; the one having a metal ratio 6-20 is preferable and having a metal ratio of 8-15 is particularly preferable. It should be noted that the metal ratio in this context is shown by.

[valency of metal element in the metallic detergent] x
[metal-element content (mol %)]/[soap content (mol %)].
The "soap" means an opponent organic group forming metal salt, it may be a sulfonic acid-containing group in an alkali metal or a sulfonate.
[0072] The base-number of the alkali metal sulfonate or alkali earth metal sulfonate is arbitorary; it is usually 0-500 mgKOH/g. In view of excellent improving effect in high-temperature detergency and anti-wear property per content, a sulfonate of which base-number is preferably 100-450 mgKOH/g and particularly preferably 200-400 mgKOH/g is desirably used. The "base-number" means a base-number as measured by perchloric acid method in accordance with No. 7 in JIS K 2501 "Petroleum products and lubricating oil - Determination of neutralization number".
[0073] Examples of alkali metal phenate or alkali earth metal phenate include: an alkyl phenol sulfide obtained by reacting sulfur with an alkylphenol having at least one C4-C4o, preferably C6-C18 linear or branched alkyl group; or an alkali metal salt or alkali earth metal salt, particularly magnesium salt and/or calcium salt, and so on, of Mannich reaction product of alkylphenol obtained by reacting the alkylphenol with formaldehyde. Examples of alkali metal phenate or alkali earth metal phenate include: an alkylphenol sulfide obtained by reacting sulfur with an alkylphenol having at least one ethylene oligomer-derived C6-C40, preferably C10-C18 alkyl group; or an alkali metal salt or alkali earth metal salt, particularly magnesium salt and/or calcium salt, and so on, of Mannich reaction

product of alkylphenol obtained by reacting the alkylphenol with
formaldehyde are preferably used.
[0074] Examples of alkali metal phenate or alkali earth metal phenate further include: a basic salt obtained by adding further excessive alkali metal salt or alkali earth metal salt and alkali metal base or alkali earth metal base (hydroxide or oxide of alkali metal or alkali earth metal) to alkali metal phenate or alkali earth metal phenate (neutral salt) obtained in the above manner and heating the mixture in the presence of water; and an over-basic salt obtained by reacting the above neutral salt with a base such as hydroxide of alkali metal or alkali earth metal in the presence of carbon dioxide and/or boric acid or borate.
[0075] These reactions are usually carried out in solvent
(aliphatic hydrocarbon solvent like hexane, aromatic hydrocarbon solvent like xylene, and light lubricant base oil, etc.), and the metal content is preferable 1.0-20 mass %, preferably 2.0-16 mass %.
[0076] The base-number of the alkali metal phenate or alkali earth metal phenate to be used is usually 0-500 mgKOH/g, preferably 20-450 mgKOH/g.
[0077] In the invention, these alkali metal phenates or alkali earth metal phenates can be preferably used as it can improve fuel saving performance from low to high temperature and frictional property in wet-type clutches.
[0078] Structure of the alkali metal salicylate or alkali earth metal salicylate is not particularly limited; it is preferably a salicylic acid metal salt having one or two C1-C10

alkyl groups, preferably the alkali metal salt or alkali earth metal salt, particularly the magnesium salt and/or calcium salt. Moreover, examples of alkali metal salicylate or alkali earth metal salicylate preferably include an alkali metal salt or alkali earth metal salt of alkyl salicylic acid having ethylene oligomer-derived Cs-C4o alkyl group.
[0079] About the alkali metal salicylate or alkali earth metal salicylate usable for the lubricating oil composition of the present invention, in view of excellent property of low-temperature viscosity, a salicylate whose component ratio of monoalkyl salicylate metal salt is higher is preferable; for instance, it is preferably an aikyl salicylate metal salt and/or the (over-) basic salt thereof, in which component ratio of the monoalkyl salicylate metal salt is 85-100 mol %, component ratio of the dialkyl salicylate metal salt is 0-15 mol %, and component ratio of the 3-alkyl salicylate metal salt is 40-100 mol %. In addition, in view of excellent high-temperature detergency and base-number retention, the salicylate detergent preferably contains dialkyl salicylate metal salt.
[0080] Here, "monoalkyl salicylate metal salt" means alkyl salicylate metal salt having one alkyl group such as 3-alkyl salicylate metal salt, 4-alkyl salicylate metal salt, and 5-alkyl salicylate metal salt. The component ratio of monoalkyl salicylate metal salt, to 100 mol % of alkyl salicylate metal salt, is 85-100 mol %, preferably 88-98 mol %, and more preferably 90-95 mol %; the component ratio of alkyl salicylate metal salt other than the monoalkyl salicylate metal salt, e.g., component ratio of dialkyl salicylate metal salt, is 0-15 mol %, preferably

2-12 mol %, and more preferably 5-10 mol %. Moreover, component ratio of 3-alky1 salicylate metal salt, to 100 mol % of alkyl salicylate metal salt, is 40-100 mol %, preferably 45-80 mol %, and more preferably 50-60 mol %. The component ratio of sum of 4-alkyl salicylate metal salt and 5-alkyl salicylate metal salt, to 100 mol % of alkyl salicylate metal salt, is equivalent to the component ratio where the component ratios of the above 3-alkyl salicylate metal salt and dialkyl salicylate metal salt are substracted, namely, 0-60 mol %, preferably 20-50 mol %, more preferably 30-45 mol %. If small dosage of dialkyl salicylate metal salt is contained, it is capable of obtaining a composition which exhibits excellent high-temperature detergency, low-temperature properties, and property of base-number retention. By setting the component ratio of 3-alkylsalicylate at 40 mol % or more, it is possible to relatively lower the component ratio of 5-alkyl salicylate metal salt, which improves the oil solubility of the composition.
[0081] Further, examples of alkyl group of alkyl salicylate metal salt constituting the alkali metal salicylate or alkali earth metal salicylate may be C6-C40, preferably C10-C19 or C2o-C3o, more preferably C4-C18 or C2o-C26 alkyl group, particularly preferably Ci4-Ci8 alkyl group. Examples of C10-C40 alkyl group include: decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, henicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl, nonacosyl, and triacontyl. These alkyl groups may be linear or branched and may be primary alkyl group, secondary alkyl group, or tertiary alkyl group; in the present

invention, so as to easily obtain the above desirable salicylate metal salt, secondary alkyl group is particularly preferable. [0082] Examples of metal for alkyl salicylate metal salt are preferably alkali metal such as sodium and potassium as well as alkali earth metal such as calcium and magnesium. Among them, calcium and magnesium are preferable, and calcium is particularly preferable.
[0083] The alkali metal salicylate or alkali earth metal salicylate can be produced by conventional methods and the method is not particularly restricted. It can be obtained, for example: by reacting a metallic base such as an oxide, a hydroxide, or the like, of alkali metal or alkali earth metal with alkyl salicylic acid which contains a monoalkyl salicylic acid, as the main component, obtained by a method including alkylation of 1 mol of phenol with 1 mol or more of C6-C40 olefin having a polymer or copolymer of ethylene, propylene, butane, preferably 1 mol or more of linear a-olefin derived from ethylene oligomer and followed by carboxylation with carbon dioxide and so on, obtained by another method including alkylation of 1 mol of salicylic acid with 1 mol or more of the olefin, preferably the linear a-olefin, or the similar methods; by converting the monoalkyl salicylic acid into an alkali metal salt such as sodium salt and potassium salt; or by substituting the alkali metal salt with alkali earth metal salt. Here, by controlling the response rate of phenol or salicylic acid with olefin to preferably e.g., 1:1-1.15 (mole ratio), more preferably 1:1.05-1.1 (mole ratio), it is capable of controlling the component ratio between monoalkyl salicylate metal salt and dialkyl salicylate metal salt to the desirable

ratio. In addition, by using, as an olefin, linear a-olefin obtained by ethylene ligomer, it is capable of controlling the
component ratio among 3-alky1 salicylate metal salt, 5-alky1
salicylate metal salt, and so on to the desirable ratio and capable of obtaining an alkyl salicylate metal salt having preferable
secondary alkyl as the main component; thereby it is particularly preferable.
[0084] Examples of preferably used alkali metal salicylate or alkali earth metal salicylate include: a basic salt obtained by adding further excessive alkali metal salt or alkali earth metal salt and alkali metal base or alkali earth metal base
(hydroxide or oxide of alkali metal or alkali earth metal) to the alkali metal salicylate or alkali earth metal salicylate
(neutral salt) obtained in the above method and then heating the mixture in the presence of water; and an over-basic salt obtained by reacting the neutral salt with a base such as hydroxide of alkali metal or alkali eairth metal in the presence of carbon dioxide and/or boric acid or borate.
[0085] These reactions are usually carried out in a solvent
(e.g., aliphatic hydrocarbon solvent like hexane, aromatic hydrocarbon solvent like xylene, and light lubricant base oil, etc.) , and the metal content thereof is preferably 1.0-20 mass %, preferably 2.0-16 mass %.
[0086] In view of excellent balance among high-temperature detergency, base-number retention, and property of low-temperature viscosity, examples of the most preferable alkali metal salicylate or alkali earth metal salicylate include: an alkyl salicylate metal salt and/or the (over-) basic salt in which

component ratio of the monoalkyl salicylate metal salt is 85-95 mol %, component ratio of the dialkyl salicylate metal salt is 5-15 mol %, component ratio of the 3-alkyl salicylate metal salt is 50-60 mol %, component ratio of sum of the 4-alky1 salicylate metal salt and 5-alkyl salicylate metal salt is 35-45 mol %. The alkyl group described herein is particularly preferably secondary alkyl group.
[0087] The base-number of the alkali metal salicylate or alkali earth metal salicylate is usually 0-500 mgKOH/g, it is preferably 20-300 mgKOH/g, and particularly preferably 100-200 mgKOH/g. One or a combination of two or more of the above alkali metal salicylate or alkali earth metal salicylate can be used. The "base-number" described herein means a base-number as measured by perchloric acid method in accordance with No. 7 in JISK2501 "Petroleum products and lubricating oil - Determination of neutralization number".
[0088] In the invention, content of the (B) metallic detergent, to the total mass of the composition, equivalent to metal, is 0.005-0.5 mass %; it is preferably 0.05-0.4 mass %, more preferably 0.1-0.3 mass %, particularly preferably 0 .15-0 . 25 mass %.
[0089] The lubricating oil composition of the invention contains 0 . 01-0 .4 mass % of the (C) ashless dispersant as nitrogen content. The examples of ashless dispersant include a known ashless dispersant used for lubricating oil such as succinimide-based ashless dispersant, polyaminic ashless dispersant, benzyl aminic ashless dispersant, and succinic acid ester-based ashless dispersant. The examples also include:

boron compound, phosphorus compound, sulfur compound, and modified oxygen-containing organic compound described in the following column of "boron-free succinimide". Example thereof may be the one which includes at least one hydrocarbon group usually having 700-3500 of number average molecular mass.
[0090] As the ashless dispersant of the present invention, a succinimide-based ashless dispersant (hereinafter, it may be simply referred to as "succinimide" or "succinimide-based dispersant".) may be preferably used; a boron-containing succinimide and/or a boron-free succinimide are/is preferably contained.
[0091] The examples of boron-free succinimide include: mono-succinimide of the following general formula (e), bis-succinimide of the general formula (f), and a succinimide obtained by modifying these with oxygen-containing organic compound.
[0092]

[0094] In the formula (e) or (f), R7, R8, and R9 are independently polybutenyl group, and n is an integer of 2 to 7.

[0095] Number average molecular mass of the polybutenyl group represented by R7, R8, and R9 is preferably 700 or more, more preferably 900 or more; it is also preferably 3500 or less, more preferably 1500 or less.
[0096] By setting the number average molecular mass to 700 or more, it is capable of obtaining a lubricating oil composition which exhibits superior detergency and dispersiveness. Meanwhile, by setting the number average molecular mass to 3 50 0 or less, it is also capable of obtaining a lubricating oil composition which exhibits superior cold flow property.
[0097] Moreover, in view of excellent sludge inhibiting effect, the lower limit of n is 2, preferably 3; on the other hand, the upper limit of n is 7, preferably 6.
[00 98] Here, polybutenyl group can be derived from polybutene (poly iso-butene) obtained by polymerizing a mixture of 1-butene and iso-butene or high-purity iso-butene in the presence of catalyst like aluminum chloride and boron fluoride; in the polybutene mixture, a compound whose end has vinylidene structure is usually contained at the amount of 5-100 mol %.
[0099] As the polybutene (poly-iso-butene) to be used, the one in which a minute amount of fluorine and chloride attributed to the catalyst in the manufacturing process is removed by the adequate treatment can be used. Therefore, polybutenes whose content of halogen such as fluorine and chloride is preferably 50 mass ppm or less, more preferably 10 mass ppm or less, furthermore preferably 5 mass ppm or less, and particularly preferably 1 mass ppm or less.
[0100] Method for producing succinimide of the general

formula (e) or (f) is not particularly limited. It may be a method by reacting a polyamine such as diethylene triamine, triethylene tetramine, tetraethylene pentamine, or pentaethylene hexamine with the above chlorinated polybutene, preferably a polybutenyl succinic acid which is obtained by reacting maleic anhydride with a polybutene whose fluorine and chloride are preferably sufficiently removed at a temperature between 100-200 degree C. [0101] When producing the bis-succinimide, dosage of the polybutenyl succinic acid may be twice (mol ratio) as much as polyamine. When producing the monosuccinimide, the polybutenyl succinic acid and polyamine may be reacted in equal proportions (mol ratio).
[0102] The boron-free succinimide may be a compound which is obtained by reacting the compounds of the general formula (e) or (f) with an oxygen-containing organic compound and so on to neutralize or to amidate a part of or all of remaining amino group and/or imino group.
[0103] Specific examples of oxygen-containing organic compound include : Ci-C30 mono-carboxylic acid such as formic acid, acetic acid, glycolic acid, propionic acid, lactic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, oleic acid, nonadecanoic acid, eicosanic acid; C2-C30 polycarboxylic acid such as oxalic acid, phthalic acid, trimellitic acid, pyromellitic acid, or the anhydride thereof, or the ester compound thereof; C2-C6 alkylene oxide; and hydroxyl (poly) oxyalkylene carbonate.

'1104] By reacting such an oxygen-containing organic compound, it is assumed that, for example, a part of or all of remaining amino group and/or imino group in the compound of the general formula (e) or (f) become a structure represented by the following general formula (g). [0105]

[0106] In the formula, R10 is a hydrogen atom, C1-C24 alkyl group, alkenyl group, alkoxy group, or hydroxy (poly) oxyalkylene group represented by -0- (R1:L0) mH; R11 is Ci-C4 alkylene group; m is an integer of 1 to 5.
[0107] The boron-containing succinimide is obtained by reacting a compound of the general formula (e) or (f) with a boron compound. The examples of boron compound may be boric acid, borate, boric acid ester.
[0108] The specific examples of boric acid include orthoboric acid, metaboric acid, and tetraboric acid.
[0109] The examples of borate include alkali metal salt, alkali earth metal salt, or ammonium salt of boric acid; more specifically, lithium borate such as lithium metaborate , lithium tetraborate, lithium pentaborate, and lithium perborate; sodium borate such as sodium metaborate, sodium diborate, sodium tetraborate, sodium pentaborate, sodium hexaborate, and sodium octaborate,- potassium borate such as potassium metaborate, potassium tetraborate, potassium pentaborate, potassium hexaborate, and potassium octaborate; calcium borate such as

calcium metaborate, calcium diborate, tricalcium tetraborate, pentacalcium tetraborate, and calcium hexaborate; magnesium borate such as magnesium metaborate, magnesium diborate, trimagnesium tetraborate, pentamagnesium tetraborate, and magnesium hexaborate; and ammonium borate such as ammonium metaborate, ammonium tetraborate, ammonium pentaborate, and ammonium octaborate.
[0110] In addition, the borate ester may be an ester of boric acid and preferably a C1-C6 aliphatic alcohol; more specific examples include: monomethyl borate, dimethyl borate, trimethyl borate, monoethyl borate, diethyl borate, triethyl borate, monopropyl borate, dipropyl borate, tripropyl borate, monobutyl borate, dibutyl borate, and tributyl borate.
[0111] Mass ratio (B/N ratio) between boron content and nitrogen content of the boron-containing succinimide used for the invention is not particularly limited. The lower limit is 0.2, preferably 0.3, more preferably 0.5; on the other hand, the upper limit is 1.2, preferably 1, more prefereably 0.9. When the B/N ratio is below the lower limit, effect of the present invention is small; meanwhile, when the B/N ratio exceeds the upper limit, the invention is poor in oxidation stability. Thereby, these cases are not preferable.
[0112] In the invention, as the succinimide-based dispersant, the above boron-containing succinimide and boron-free mono- and/or bis-succinimide may be used alone or may be used in combination thereof. So as to enhance frictional property in wet-type clutches, single use of the boron-containing succinimide or a combination use of the boron-containing

succinimide and the boron-free mono- and/or bis-succinimide is preferable. As a preferable mixing ratio (mass ratio) of the boron-containing succinimide and boron-free succinimide, when combining these two, (the former) : (the latter) is 100:0 to 20:80, more preferably 90 :10 to 40 : 60 , and particularly preferably 70:30 to 45:55.
[0113] About the content of the succinimide-based dispersant in the invention, to the total mass of the composition, equivalent to nitrogen element, the lower limit is 0.01 mass %, preferably 0.05 mass %, more preferably 0.08 mass %; on the other hand, the upper limit is 0.4 mass %, preferably 0.3 mass %, more preferably 0.2 mass %. When the content of the succinimide-based dispersant in the invention, to the total mass of the composition, equivalent to nitrogen element, is the lower limit or more, fuel saving performance in moderate high temperature and frictional property in wet-type clutches can be sufficiently improved; meanwhile, when the content of the same, to the total mass of the composition, equivalent to nitrogen element, exceeds the upper limit, fuel saving performance, property of low-temperature viscosity, and emulsion-inhibiting effect tend to be deteriorated.
[0114] Further, due to the similar reason, the lower limit of content of the boron-containing succinimide, to the total mass of the composition, equivalent to boron element, is preferably 0.005 mass %, more preferably 0 . 01 mass %, furthermore preferably 0.02 mass %. While, the upper limit, to the total mass of the composition, equivalent to boron element, is preferably 0 . 2 mass % , preferably 0.1 mass %, more preferably 0.08 mass %, and

particularly preferably 0.0 5 mass %. When the content of boron-containing succinimide exceeds the upper limit, together with the above reason, impact on catalytic converter is expected; thereby it is not preferable.
[0115] The lubricating oil composition of the present invention may contain an organomolybdenum compound as the (E) component. The examples of organomolybdenum compound include:
(El) an organomolybdenum compound selected from molybdenum dithiophosphate and molybdenum dithiocarbamate; and (E2) an organomolybdenum compound other than molybdenum dithiophosphate and molybdenum dithiocarbamate. The (E2) component is an organomolybdenum compound other than the (El), the examples thereof include an organomolybdenum compounds containing sulfur as the constitutent element and an organomolybdenum compound which does not contain sulfur as the constituent element.
[0116] When the lubricating oil composition contains an organomolybdenum compound like the (El) component, engine friction is significantly reduced whereby fuel saving performance can be improved; when the lubricating oil composition contains an organomolybdenum compound like the (E2) component, improvement of oxidation stability and inhibition of viscosity increase can be performed, whereby frictional property in initial wet-type clutches or frictional property in initial engine can be maintained for a long time. Particularly, by containing the organomolybdenum compound like the (El) component, engine friction can be significantly reduced while maintaining frictional property in wet-type clutches in the lubricating oil composition at a high level; therefore, from the both aspect,

i-provement of fuel saving performance can be expected. In the invention, since engine friction-reducing effect is large so that it is particularly desirable to contain the (El) component as an essential constituent.
[0117] Examples of the molybdenum dithiophosphate may be a compound of the following general formula (h).
r m T oi
[0119] In the formula (h) , R12, R13, R14, and R15 are the same or different and are respectively a hydrocarbon group such as C2-C30, preferably C5-C18, more preferably C5-C12 alkyl group, or Cs-Ci8, preferably C10C15 (alkyl) aryl group. In addition, Y1, Y2, Y3, and Y4 are independently a sulfur atom or an oxygen atom.
[0120] Preferable examples of alkyl group include: ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl; these may be primary alkyl group, secondary alkyl group, or tertiary alkyl group and may be linear or branched.
[0121] Preferable examples of (alkyl) aryl group include: phenyl, tolyl, ethylphenyl, propylphenyl, butylphenyl, pentylphenyl, hexylphenyl, octylphenyl, nonylphenyl, decylphenyl, undecylphenyl, and dodecylphenyl; these alkyl groups may be primary alkyl group, secondary alkyl group, or tertiary alkyl group and may be linear or branched. The (alkyl) aryl group contains all types of substituted isomers in which

substitution site of alkyI group in the aryl group is different.
[0122] Specific examples of dithiophosphate include: molybdenum sulfide diethyl dithiophosphate, molybdenum sulfide dipropyl dithiophosphate, molybdenum sulfide dibutyl dithiophosphate, molybdenum sulfide dipentyl dithiophosphate, molybdenum sulfide dihexyl dithiophosphate, molybdenum sulfide dioctyl dithiophosphate, molybdenum sulfide didecyl dithiophosphate, molybdenum sulfide didodecyl dithiophosphate, molybdenum sulfide di (butylphenyl) dithiophosphate, molybdenum sulfide di (nonylphenyl) dithiophosphate, oxymolybdenum sulfide diethyl dithiophosphate, oxymolybdenum sulfide dipropyl dithiophosphate, oxymolybdenum sulfide dibutyl dithiophosphate, oxymolybdenum sulfide dipentyl dithiophosphate, oxymolybdenum sulfide dihexyl dithiophosphate, oxymolybdenum sulfide dioctyl dithiophosphate, oxymolybdenum sulfide didecyl dithiophosphate, oxymolybdenum sulfide didodecyl dithiophosphate, oxymolybdenum sulfide di (butylphenyl) dithiophosphate, oxymolybdenum sulfide di (nonylphenyl) dithiophosphate (these alkyls may be linear or branched; binding position of alkyl group in the alkylphenyl group is arbitorary.); and the mixtures thereof. As these molybdenum dithiophosphate , a compound having hydrocarbon group of different carbon number and/or structures in one molecule may be preferably used.
[0123] As the specific examples of molybdenum dithiocarbamate, a compound of the following general formula (i) can be used.
[0124]

[0125] In the formula (i) , R16, R17, R18, and R19 are the same or different and are hydrocarbon group such as C2-C24, preferably C4-C13 alkyl group or C6-C24, preferably Ci0-Ci5 (alkyl) aryl group. In addition, Y5, Y6, Y7, and Y8 are independently a sulfur atom or an oxygen atom.
[0126] Preferable examples of alkyl group include: ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl. These may be primary alkyl group, secondary alkyl group, or tertiary alkyl group and may be linear or branched.
[0127] Preferable examples of (alkyl) aryl group include: phenyl, tolyl, ethylphenyl, propylphenyl, butylphenyl, pentylphenyl, hexylphenyl, octylphenyl, nonylphenyl, decylphenyl, undecylphenyl, and dodecylphenyl. The alkyl group may be primary alkyl, secondary alkyl, or tertiary alkyl and may be linear or branched. The (alkyl) aryl group contains all types of substituted isomers in which substitution site of alkyl group in the aryl group is different. Moreover, molybdenum dithiocarbamate having a structure different from the above may be a compound having a structure in which a dithiocarbamate is coordinated to the thio- or polythio-trinuclear molybdenum as shown in WO 98/26030 or WO 99/31113.
[0128] Preferable examples of molybdenum dithiocarbamate specifically include: molybdenum sulfide diethyl

dithiocarbamate, molybdenum sulfide dipropyl dithiocarbamate, molybdenum sulfide dibutyl dithiocarbamate, molybdenum sulfide dipentyl dithiocarbamate, molybdenum sulfide dihexyl dithiocarbamate, molybdenum sulfide dioctyl dithiocarbamate, molybdenum sulfide didecyl dithiocarbamate, molybdenum sulfide didodecyl dithiocarbamate, molybdenum sulfide di (butylphenyl) dithiocarbamate, molybdenum sulfide di (nonylphenyl) dithiocarbamate, oxymolybdenum sulfide diethyl dithiocarbamate, oxymolybdenum sulfide dipropyl dithiocarbamate, oxymolybdenum sulfide dibutyl dithiocarbamate, oxymolybdenum sulfide dipentyl dithiocarbamate, oxymolybdenum sulfide dihexyl dithiocarbamate, oxymolybdenum sulfide dioctyl dithiocarbamate, oxymolybdenum sulfide didecyl dithiocarbamate, oxymolybdenum sulfide didodecyl dithiocarbamate, oxymolybdenum sulfide di
(butylphenyl) dithiocarbamate, oxymolybdenum sulfide di
(nonylphenyl) dithiocarbamate (these alkyls may be linear or branched; binding position of alkyl group in the alkyl phenyl group is arbitorary.); and the mixtures thereof. As these molybdenum dithiocarbamate, a compound having hydrocarbon group of different carbon number and/or structures in one molecule may be preferably used.
[0129] Examples of the (E2) organomolybdenum compounds other than molybdenum dithiophosphate and molybdenum dithiocarbamate may be organomolybdenum compounds other than the
(El) and containing sulfur as the constitutent element. Examples of the organomolybdenum compounds containing sulfur as the constitutent element include: complex and the like of molybdenum compounds (e.g. , molybdenum oxide such as molybdenum dioxide and

molybdenum trioxide; molybdic acid such as orthomolybdic acid, paramolybdic acid, and (poly) molybdenum sulfide, salt of these molybdic acids like metal salt and ammonium salt of molybdic acid, molybdenum sulfide such as molybdenum disulfide, molybdenum trisulfide, molybdenum pentasulfide, and molybdenum polysulfide,- sulfurized molybdic acid; metal salt or amine salt of molybdenum sulfide; and molybdenum halide like molybdenum chloride) and sulfur-containing organic compound (e.g., alkyl
(thio) xanthate, thiadiazole, mercapto thiadiazole, thiocarbonate, tetrahydrocarbyl thiuramdisulfide, and bis (di
(thio) hydrocarbyl dithiophosphonate) disulfide, organic (poly) sulfide, and sulfurized ester) and other organic compound; complex of sulfur-containing molybdenum compound (such as the above molybdenum sulfide, sulfurized molybdic acid, or sulfide of molybdenum oxide) and sulfur-free (as the constituent element) organic compounds such as amine compound, succinimide, organic acid, alcohol, or the like which will be described in the column below; or sulfur-containing organomolybdenum compounds and the like obtained by reacting below-mentioned sulfur-free (as the constituent element) molybdenum compound, the sulfur-free organic compound, and sulfur source (e.g., element sulfur, hydrogen sulfide, phosphorous pentasulfide, sulfur oxide, inorganic sulfide, hydrocarbyl (poly)sulfide, sulfurized olefin, sulfurized ester, sulfurized wax, sulfurized carboxylic acid, alkylphenol sulfide, thioacetamide, and thiourea). About these sulfur-containing organomolybdenum compounds, detailed manufacturing methods are described in e.g. Japanese Patent Application Laid-Open No. S56-10591 and US Patent No. 4263152.

I'.llZt As the (E2) organomolybdenum compounds other than
molybdenum dithiophosphate and molybdenum dithiocarbamate, sulfur-free (as the constituent element) organomolybdenum compounds can be used.
[0131] As the sulfur-free (as the constituent element) organomolybdenum compounds, specific examples include: molybdenum-amine complex, molybdenum-succinimide complex, molybdenum salt of organic acid, and molybdenum salt of alcohol; among them, molybdenum-amine complex, molybdenum salt of organic acid, and molybdenum salt of alcohol are preferable. [0132] Examples of molybdenum compound constituting the above molybdenum-amine complex include-, sulfur-free molybdenum compounds such as molybdenum trioxide or the hydrate thereof (Mo03-nH20) , molybdic acid (H2Mo04) , alkali metal salt of molybdic acid (M2Mo04; "M" indicates alkali metal.), ammonium molybdate ( (NH4)2Mo04 or (NH4) S [Mo7024] ' 4H20) , MoCl5, MoOCl4, Mo02Cl2/ Mo02Br2, and Mo203Cl6. Among these molybdenum compounds, from the viewpoint of yield of molybdenum-amine complex, hexavalent molybdenum compounds are preferable. Further, in view of availability, among the hexavalent molybdenum compounds, molybdenum trioxide or the hydrate thereof, molybdic acid, alkali metal salt of molybdic acid, and ammonium molybdate are preferable.
[0133] Moreover, amine compound constituting the molybdenum-amine complex is not particularly limited. Specific examples of nitrogen compound include: monoamine, diamine, polyamine, and alkanolamine. More specific examples include: alkylamine having Ci-C30 alkyl (these alkyls may be linear or

branched. ) , such as methylamine, ethyiamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, heptadecylamine, octadecylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, diundecylamine, didodecylamine, ditridecylamine, ditetradecylamine, dipentadecylamine, dihexadecylamine, diheptadecylamine, dioctaidecylamine, methyl ethyl amine, methylpropylamine, methylbutylamine, ethylpropylamine, ethylbutylamine, and propylbutylamine; alkenylamine having C2-C30 alkenyl (these alkenyls may be linear or branched.) such as ethenylamine, propenylamine, butenylamine, octenylamine, and oleylamine; alkanolamine having C!-C3o alkanol (these alkanols may be linear or branched.) , such as methanolamine, ethanolamine, propanolamine, butanolamine, pentanolamine, hexanolamine, heptanolamine, octanolamine, nonanolamine, methanol-ethanolamine, methanol-propanolamine, methanol-butanolamine, ethanol-propanolamine, ethanol-butanolamine, and propanol-butanolamine; alkylene diamine having Ci-C30 alkylene, such as methylenediamine, ethylenediamine, propylenediamine, and butylenediamine; polyamine such as diethylene triamine, triethylene tetramine, tetraethylene pentamine, and pentaethylene hexamine; heterocycle compounds such as imidazoline or compounds having C8-C20 alkyl or alkenyl group with the above monoamine, diamine, and polyamine, such as undecyl diethylamine, undecyl

cL-r-hanoIamine, dodecyl dipropanolamine, oleyl diethanolamine, oleyl propylene diamine, stearyl tetraethylene pentamine; alkylene oxide adduct of these compounds; and the mixtures thereof. Among these amine compounds, primary amine, secondary amine, and alkanolamine are preferable.
[0134] Carbon number of hydrocarbon group which exist in amine compound constituting the molybdenum-amine complex is preferably 4 or more, more preferably 4-30, and particularly preferably 8-18. When the carbon number of hydrocarbon group in the amine compound is below 4, the solubility tends to be deteriorated. Meanwhile, when the carbon number of the amine compound is set to 30 or less, it is capable of relatively enhancing molybdenum content in the molybdenum-amine complex and small dosage thereof can further enhance the effect of the present invention.
[0135] The molybdenum-succinimide complex may be a complex of sulfur-free molybdenum compound listed in the above description of molybdenum-amine complex with succinimide having alkyl or alkenyl group of carbon number 4 or more. Examples of succinimide include: succinimide having at least one C4-C40o alkyl or alkenyl group described in the column of ashless dispersant below in the molecule or the derivatives thereof; and succinimide having C4-C39, preferably C8-C18 alkyl or alkenyl group. When the carbon number of alkyl or alkenyl group in the succinimide is below 4, the solubility tends to be deteriorated. Alternatively, another succinimide having alkyl or alkenyl group of carbon number over 30 and 400 or less can be used; by setting the carbon number of the alkyl or alkenyl group to 30 or less, it is capable of

relatively enhancing molybdenum content in the
molybdenum-succinimide complex and small dosage thereof can
further enhance the effect of the present invention.
[0136] As the molybdenum salt of the organic acid, salts of organic acid with molybdenum oxide listed in the above description of the molybdenum-amine complex or molybdic base such as molybdenum hydroxide, molybdenum carbonate or molybdenum chloride. As organic acid, it is preferably sulfur-free phosphorus-containing acid listed in the column of the above (A) component, and carboxylic acid.
[0137] As carboxylic acid constituting molybdenum salt of carboxylic acid, it may be either monobasic acid or polybasic acid.
[0138] The monobasic acid is usually a C2-C30, preferably C4-C24 fatty acid; the fatty acid thereof may be linear or branched and may be saturated or unsaturated. Specific examples include: a saturated fatty acid such as acetic acid, propionic acid, linear or branched butanoic acid, linear or branched pentanoic acid, linear or branched hexanoic acid, linear or branched heptanoic acid, linear or branched octanoic acid, linear or branched nonanoic acid, linear or branched decanoic acid, linear or branched undecanoic acid, linear or branched dodecanoic acid, linear or branched tridecanoic acid, linear or branched tetradecanoic acid, linear or branched pentadecanoic acid, linear or branched hexadecanoic acid, linear or branched heptadecanoic acid, linear or branched octadecanoic acid, linear or branched hydroxyoctadecanoic acid, linear or branched nonadecanoic acid, linear or branched icosanoic acid, linear or branched

her._;?3anoic acid, linear or branched docosanoic acid, linear or branched tricosanoic acid, linear or branched tetracosanoic acid; an unsaturated fatty acid such as acrylic acid, linear or branched butenoic acid, linear or branched pentenoic acid, linear or branched hexenoic acid, linear or branched heptenoic acid, linear or branched octenoic acid, linear or branched nonenoic acid, linear or branched decenoic acid, linear or branched undecenoic acid, linear or branched dodecenoic acid, linear or branched tridecenoic acid, linear or branched tetradecenoic acid, linear or branched pentadecenoic acid, linear or branched hexadecenoic acid, linear or branched heptadecenoic acid, linear or branched octadecenoic acid, linear or branched hydroxyocta decenoic acid, linear or branched nonadecenoic acid, linear or branched icosenoic acid, linear or branched henicosenoic acid, linear or branched docosenoic acid, linear or branched tricosenoic acid, linear or branched tetracosenoic acid; and the mixtures thereof.
[0139] Further, as the monobasic acid, other than the above fatty acids, monocyclic or polycyclic carboxylic acid (it may have hydroxyl groups.) may be used; the carbon number may be preferably 4-30, more preferably 7-30. Examples of monocyclic or polycyclic carboxylic acid include: aromatic carboxylic acid or cycloalkyl carboxylic acid, and etc. each having zero to three, preferably one to two Ci-C30 linear or branched alkyl group, preferably Ci-C20 alkyl group. More specific examples include: (alkyl) benzene carboxylic acid, (alkyl) naphthalene carboxylic acid, and (alkyl) cycloalkyl carboxylic acid. Preferable examples of monocyclic or polycyclic carboxylic acid include:

benzoic acid, salicylic acid, alkyl benzoic acid, alkyl salicylic acid, and cyclohexane carboxylic acid.
[0140] As the polybasic acid, there may be a dibasic acid, a tribasic acid, and a tetrabasic acid. The polybasic acid may be either linear polybasic acid or cyclic polybasic acid. In addition, in case of linear polybasic acid, it may be either linear or branched, and saturated or unsaturated. As the linear polybasic acid, C2-Ci6 linear dibasic acid is preferable. The specific examples include: ethanedioic acid, propanedioic acid, linear or branched butanedioic acid, linear or branched pentanedioic acid, linear or branched hexanedioic acid, linear or branched heptanedioic acid, linear or branched octanedioic acid, linear or branched nonanedioic acid, linear or branched decanedioic acid, linear or branched undecanedioic acid, linear or branched dodecanedioic acid, linear or branched tridecanedioic acid, linear or branched tetradecanedioic acid, linear or branched heptadecanedioic acid, linear or branched hexadecanedioic acid, linear or branched hexenedioic acid, linear or branched heptenedioic acid, linear or branched octenedioic acid, linear or branched nonenedioic acid, linear or branched decenedioic acid, linear or branched undecenedioic acid, linear or branched dodecenedioic acid, linear or branched tridecenedioic acid, linear or branched tetradecenedioic acid, linear or branched heptadecenedioic acid, linear or branched hexadecenedioic acid, alkenyl succinic acid, and the mixtures thereof . Further, the examples of cyclic polybasic acid include : alicyclic dicarboxylic acid such as 1, 2 -cyclohexane dicarboxylic acid and 4-cyclohexene-1,2-dicarboxylic acid; aromatic

dicarboxylic acid like phthalic acid; aromacic tricarboxylic acid like trimellitic acid; and aromatic tetracarboxylic acid like pyromellitic acid.
[0141] As molybdenum salt of alcohol, there may be a salt of alcohol with sulfur-free molybdenum compound listed in the above description of molybdenum-amine complex; the alcohol may be any one of monovalent alcohol, polyvalent alcohol, partial ester or partial ether compounds of polyvalent alcohol, and a nitrogen compound (e.g. alkanolamine) having hydroxy1 group. The molybdic acid is strong acid and it forms ester by reaction with alcohol; this ester formed by the molybdic acid and alcohol is also contained in the molybdenum salt of alcohol of the present invention.
[0142] As the monovalent alcohol, usually Ci-C24, preferably C1-C12, more preferably Ci-C8 monovalent alcohol are used; such an alcohol may be linear or branched and saturated or unsaturated. The specific examples of C1-C24 alcohol include: methanol, ethanol, linear or branched propanol, linear or branched butanol, linear or branched pentanol, linear or branched hexanol, linear or branched heptanol, linear or branched octanol, linear or branched nonanol, linear or branched decanol, linear or branched undecanol, linear or branched dodecanol, linear or branched tridecanol, linear or branched tetradecanol, linear or branched pentadecanol, linear or branched hexadecanol, linear or branched heptadecanol, linear or branched octadecanol, linear or branched nonadecanol, linear or branched icosanol, linear or branched henicosanol, linear or branched tricosanol, linear or branched tetracosanol, and the mixtures thereof.

[Cl-^~ As polyvalent alcohol, usually, divalent to decavalent alcohol, preferably divalent to hexavalent alcohols are used. The specific examples of divalent to decavalent alcohols include: divalent alcohol such as ethylene glycol, diethyleneglycol, polyethylene glycol (trimer to pentadecamer of ethyleneglycol), propylene glycol, dipropyleneglycol, polypropyleneglycol (trimer to pentadecamer of propyleneglycol), 1,3-propanediol, 1,2-propanediol, 1,3-butanediol, 1,4-butandiol, 2-methyl-1,2-propanediol,
2-methyl-1,3-propanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, neopentylglycol; polyvalent alcohol such as glycerin, polyglycerin (dimer to octomer of glycerin, e.g. diglycerin, triglycerin, tetraglycerin), trimethylol alkane (e.g. trimethylol ethane, trimethylol propane, trimethylol butane) and the dimer to octomer thereof, pentaerythritol and the dimer to tetramer thereof, 1,2,4-butanetriol, 1,3,5-pentanetriol, 1,2,6-hexanetriol, 1,2,3,4-butanetetrol, sorbitol, sorbitan, sorbitol glycerin condensation, adonitol, arabitol, xylitol, and mannitol,- sugar group such as xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, and sucrose,- and the mixtures thereof. [0144] Furthermore, as the partial ester of polyvalent alcohol, there may be compounds in which a part of hydroxyl groups of the polyvalent alcohol listed in the above description of polyvalent alcohol is esterified by hydrocarbyl; among them, glycerin monoolate, glycerin diolate, sorbitan monoolate, sorbitan diolate , pentaerythritol monoolate, polyethyleneglycol

monoolate , and polyglycerin monoolate are preferable.
[0145] As partial ether of polyvalent alcohol, there may be compounds in which a part of hydroxyl groups of the polyvalent alcohol listed in the above description of polyvalent alcohol is etherif iedby hydrocarbyl, or compounds (sorbitan condensation, etc.) in which ether bonds are formed by condensation of polyvalent alcohol. Among them, 3-octadecyloxy-1, 2-propanediol, 3-octadecenyloxy-1,2-propanediol, and polyethyleneglycol alkylether are preferable.
[0146] Examples of nitrogen compound having hydroxyl group include: alkanolamine listed in the above description of the molybdenum-amine complex,- and alkanolamide (diethanolamide, etc.) in which amino group of the alkanol is amidated. Among them, stearyl diethanolamine, polyethyleneglycol stearylamine, polyethyleneglycol dioleylamine, hydroxyethyl laurylamine, oleic diethanolamide, and so on are preferable.
[0147] As the (E) organomolybdenum compounds, in view of excellent initial friction-reducing effect, one or a combination of two or more of sulfur-containing organomolybdenum compounds
(El) selected from molybdenum dithiophosphate and molybdenum dithiocarbamate are preferably used. By the synergic effect with other components, fuel saving performance from low to high temperature and frictional property in wet-type clutches can be significantly enhanced so that the (E) organomolybdenum compound is particularly preferably molybdenum dithiocarbamate. Moreover, in view of excellent high-temperature detergency, capability to inhibit increase of viscosity and to keep the fuel saving performance for a long time, the (E2) organomolybdenum

compound other than molybdenum dithiophosphate and molybdenum dithiocarbamate should be preferably used. As the (E2) component, among the compounds listed above, preferable examples thereof include : complex or salt of sulfur-containing molybdenum compound (e.g. molybdenum sulfide, molybdenum oxysulfide, and sulfide of molybdic acid) and sulfur-free (as the constitutent element) organic compound (e.g. amine compound, succinimide, alcohol, carboxylic acid); complex or salt of sulfur-free (as the constitutent element) molybdenum compound (e.g. oxymolybdenum and molybdic acid) and sulfur-free (as the constitutent element) organic compound (e.g. amine compound, succinimide, alcohol, carboxylic acid); and one or a combination of two or more of organomolybdenum compounds selected from organomolybdenum compounds obtained by reacting sulfur-containing molybdenum compound or sulfur-free (as the constitutent element) molybdenum compound with sulfur-free (as the constitutent element) organic compound, and sulfur source.
[0148] When the (E) organomolybdenum compound is contained in the present invention, the content is not particularly limited; the content to total mass of the composition, equivalent to molybdenum element, is preferably 0.001 mass % or more, more preferably 0.005 mass % or more, furthermore preferably 0.01 mass % or more, and particularly preferably 0.03 mass % or more. It is also preferably 0.2 mass % or less, more preferably 0.1 mass % or less, furthermore preferably 0.06 mass % or less, and particularly preferably 0.05 mass % or less. When the content is below 0.001 mass %, engine friction-reducing effect and antioxidation improvement or effect for inhibiting increase of

visrr-siry are small . On the other hand, when the content exceeds 0.2 mass %, effect proportional to the content cannot be obtained and storage stability of the lubricating oil composition tends to be deteriorated.
[0149] When the (E) organomolybdenum compound is contained in the composition of the present invention, mass ratio of the nitrogen equivalent of the succinimide-based dispersant to the molybdenum equivalent attributed to the organomolybdenum compound (though the lower limit is not particularly restricted to) is preferably 1 or more, more preferably 1.5 or more, and furthermore preferably 1. 8 or more, and particularly preferably 2 .1 or more. On the other hand, the upper limit of the mass ratio is not particularly restricted, it is usually 100 or less, preferably 10 or less, more preferably 5 or less, and particularly preferably 4 or less. By setting the mass ratio within the above range, it is capable of obtaining a composition which exhibits excellent frictional property in wet-type clutches and/or fuel saving performance.
[0150] Another preferable mode of the present invention is the (El) component-free lubricating oil composition. By excluding the (El) component, a lubricating oil composition which exhibits excellent frictional property in wet-type clutches and power transmission performance can be obtained. It should be noted that the frictional property in wet-type clutches described herein, for instance, is frictional property in accordance with MA class (causing no clutch slippage)in the performance classification of below-described JASO T 903-98; the lubricating oil composition hardly causes clutch slippage and exhibits

excellent power transmission performance so than fuel saving performance can be improved. Moreover, compared with the conventional 4-stroke engine oil of two-wheeled vehicles containing a zinc dithiophosphate as the main component, clutch meeting of the composition becomes better and shift feeling tends to be improved.
[0151] Because of the above constitution, the lubricating oil composition of the present invention is excellent in power transmission performance in wet-type clutches and/or fuel saving performance; in order to further improve the performance, a known lubricating oil additives can be added to the composition of the invention. Examples of these additives include: extreme pressure agent and anti-wear agent both other than the (A) component of the present invention; friction modifier other than molybdenum dithiocarbamate and molybdenum dithiophosphate; ashless dispersant other than succinimide-based dispersant; antioxidant; viscosity index improver; pour-point depressant; rust inhibitor; corrosion inhibitor; demulsifier; metal deactivator; defoamant; coloring agent; and rubber swelling agent. These may be used alone or may be used in combination of two or more thereof.
[0152] Examples of extreme pressure agent and anti-wear agent both other than the (A) component include: zinc dithiophosphate, phosphate/phosphite ester compounds, sulfur-based extreme pressure agent.
[0153] Specific examples of zinc dithiophosphate include: zinc dihydrocarbyl dithiophosphate having Ci-C30, pref erably C3-C8 hydrocarbon group. The Ci-C30 hydrocarbon group described herein

means the same as C-_-C3C hydrocarbon group described in the column of the (A) component, the preferable examples and range are also the same. Specific examples thereof may be alkyl group, cycloalkyl group, alkenyl group, alkyl-substituted cycloalkyl group, aryl group, alkyl-substituted aryl group, and aryl alkyl group,- among them, C3-C8 alkyl group is most preferable. These zinc dialkyl dithiophosphates may be compounds having alkyls of different carbon number and/or structures in one molecule. [0154] Specific examples of particularly preferable compound as zinc dithiophosphate include: zinc dipropyl dithiophosphate, zinc dibutyl dithiophosphate, zinc dipentyl dithiophosphate, zinc dihexyl dithiophosphate, zinc diheptyl dithiophosphate, zinc dioctyl dithiophosphate (these alkyls may be linear or branched. ) , and the mixtures of two or more selected from these at an arbitrary mixing ratio.
[0155] In the invention, zinc dithiophosphate may be zinc dithiophosphate having primary alkyl group (primary ZDTP) or zinc dithiophosphate having secondary alkyl group (secondary ZDTP); the mixture thereof is preferable. The mixing ratio (mass ratio) is preferably 5:95 to 50:50 (primary ZDTP:secondary ZDTP), more preferably 10:90 to 40:60. By setting the mixing ratio within the above preferable range, it is capable of obtaining a composition which exhibits excellent anti-wear property. [0156] The upper limit of zinc dithiophosphate content to total mass of the composition, equivalent to phosphorus element, is 0.2 mass %, preferably 0.1 mass %, and furthermore preferably 0.06 mass %. When zinc dithiophosphate is contained, molybdenum disulfide tends to be produced on the sliding surface by

interaction with crganomolybdenum compound so that it is capable of obtaining a composition which exhibits excellent engine friction-reducing effect; in case where the content of the zinc dithiophosphate to total mass of the composition, equivalent to phosphorus element, exceeds the upper limit, impact on catalytic converter by phosphorus and zinc is expected and fuel saving performance at high temperature and frictional property in wet-type clutches tend to be poor.
[0157] In the lubricating oil composition of the present invention, zinc dithiophosphate is contained at an amount of below 0.01 mass % to total mass of the composition equivalent to phosphorus element, or preferably is not substantially contained. By using the (A) component as the main component instead of using zinc dithiophosphate, it is capable of obtaining a lubricating oil which exhibits excellent anti-wear property and which keeps a longer life in inhibiting deterioration of the lubricating oil even under a severe deteriorating condition. In addition, the present invention can improve frictional property in wet-type clutches at the same level as the conventional level or more without using zinc dithiophosphate and the invention can enhance the shift feeling furthermore, which is a remarkable effect that is never expected by the conventional art using zinc dithiophosphate as the essential component. The phrase "is not substantially contained" described herein means a state where zinc dithiophosphate is not aggressively added as an additive to the lubricating oil composition; this includes a state where zinc dithiophosphate contaminates unintendedly as impurities and the like of the other additives.

[1155. Examples of phosphate/phosphite compounds include: phosphate monoesters, phosphate diesters, phosphate triesters, phosphite monoesters, phosphite diesters, phosphite triesters, thiophosphate esters, dithiophosphate esters, trithiophosphate esters, thiophosphite esters, dithiophosphite esters, trithiophosphite esters, and the salts thereof. These compounds usually contains C2-C30, preferably C3-C2o hydrocarbon group; specific examples of C2-C20 hydrocarbon group maybe alkyl group, cycloalkyl group, alkenyl group, aryl group, and arylalkyl group
(these may have substituent (s) .) described in the column of (A) component.
[0159] Preferable examples of phosphate/phosphite ester compounds are specifically shown as follows:
[0160] Monoalkyl phosphate (the alkyl group may be linear or branched. ) such as monopropyl phosphate, monobutyl phosphate, monopentyl phosphate, monohexyl phosphate, monopeptyl phosphate, and monooctyl phosphate; mono (alkyl) aryl phosphate such as monophenyl phosphate and monocresyl phosphate; dialkyl phosphate
(the alkyl group may be linear or branched.) such as dipropyl phosphate, dibutyl phosphate, dipentyl phosphate, dihexyl phosphate, dipeptyl phosphate, and dioctyl phosphate; di (alkyl) aryl phosphate such as diphenyl phosphate and dicresylphosphate; trialkyl phosphate (the alkyl group may be linear or branched.) such as tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate , tripeptyl phosphate , and trioctyl phosphate; tri (alkyl) aryl phosphate such as triphenyl phosphate and tricresyl phosphate;
[0161] Monoalkyl phosphite (the alkyl group may be linear

branched such as monopropyl phosphite, monobutyl phosphite, monopenryl phosphite, monohexyl phosphite, monopeptyl phosphite, and monooctyl phosphite; mono (alkyl) aryl phosphite such as monophenyl phosphite and monocresyl phosphite; dialkyl phosphite (the alkyl group may be linear or branched.) such as dipropyl phosphite, dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, dipeptyl phosphite, and dioctyl phosphite; di (alkyl) aryl phosphite such as diphenyl phosphate and dicresylphosphite; trialkyl phosphite (the alkyl group may be linear or branched.) such as tripropyl phosphite, tributyl phosphite, tripentyl phosphite, trihexyl phosphite, tripeptyl phosphite , and trioctyl phosphite; tri (alkyl) aryl phosphite such as triphenyl phosphate and tricresyl phosphite; and the mixtures thereof. [0162] Specific examples of salts of phosphates/phosphites include: phosphate monoester, phosphate diester, phosphate triester, phosphite monoester, phosphite diester, and a salt obtained by reacting phosphite triester with a nitrogen-containing compound like ammonia or an amine compound in which Ci-C20 hydrocarbon group or a hydroxyl-containing hydrocarbon group is only contained in the molecule and followed by neutralizing a part of or all of the remaining acidic hydrogen. [0163] Specific examples of nitrogen-containing compound may be as follows:
ammonia; alkylamine (the alkyl group may be linear or branched.) such as monomethyl amine, monoethyl amine, monopropyl amine, monobutyl amine, monopentyl amine, monohexyl amine, monoheptyl amine, monooctyl amine, dimethyl amine, methylethyl amine, diethyl amine, methylpropyl amine, ethylpropyl amine,

dipropi amine, methylbutyl amine, ethylbutyl amine, propylbutyl amine, dibutyl amine, dipentyl amine, dihexyl amine, diheptyl amine, and dioctyl amine; alkanolamine (the alkanol maybe linear or branched.) such as monomethanol amine, monoethanol amine, monopropanol amine, monobutanol amine, monopentanol amine, monohexanol amine, monoheptanol amine, monooctanol amine, monononanol amine, dimethanol amine, methanol-ethanol amine, diethanol amine, methanol-propanol amine, ethanol-propanol amine, dipropanol amine, methanol-butanol amine, ethanol-butanol amine, propanol-butanol amine, dibutanol amine, dipentanol amine, dihexanol amine, diheptanol amine, and dioctanol amine; and the mixtures thereof.
[0164] These phosphate/phosphite compounds can be used alone or can used as a mixture of two or more thereof arbitrary. In the invention, the phosphate/phosphite compounds are preferably at least one selected from the group consisting of: phosphate monoesters, phosphate diesters, phosphite monoesters, phosphite diesters, thiothosphates , thiphosphites , and the salts thereof; it is more preferably at least one selected from the group consisting of: phosphate/phosphite monoesters, phosphate/phosphite diesters, and the salts thereof. The carbon number of hydrocarbon group constituting these phosphate/phosphite compounds is preferably 4-20, more preferably 6-18.
[0165] When containing the phosphate/phosphite compounds in the lubricating oil composition of the invention, it is observed that the lubricating oil composition attains further fuel saving performance at low engine revolution (e.g., 1,0 00 rpm) and high

engine revolution (e.g., over 10,COO rpm) in 4-stroke engines of two-wheeled vehicles; thus it is preferably contained.
[0166] When the phosphate/phosphite compounds are contained in the lubricating oil composition of the invention, the preferable lower limit equivalent to phosphorus element, to total mass of the composition, is 0.005 mass %, more preferably 0.01 mass %; on the other hand, the upper limit equivalent to phosphorus element, to total mass of the composition, is 0.1 mass %, preferably 0.08 mass %, and more preferably 0.04 mass %. When the content of phosphate/phosphite compounds exceeds the upper limit, effect proportional to the content cannot be obtained and also reduction of phosphorus to a lower level cannot be attained; thereby it is not preferable.
[0167] Examples of sulfur-based extreme pressure agent include: sulfur-containing compounds like disulfides, polysulfides, sulfurized olefins, sulfurized oils, sulfurized ester, dithiocarbamate, and zinc dithiocarbamate.
[0168] As other anti-wear agents, a known anti-wear agent like borate ester, ashless anti-wear agent, metallic anti-wear agent can be used.
[0169] When these sulfur-based extreme pressure agent and other anti-wear agents are contained in the lubricating oil composition of the invention, the content thereof to total mass of the composition is usually 0.01 to 10 mass % and preferably 0.1 to 5 mass %.
[0170] Examples of friction modifier other than molybdenum dithiocarbamate and molybdenum dithiophosphate, include: a friction modifier having C6-C30 alkyl or alkenyl group such as

aliphatic alcohol, fatty acid, metal salt of fatty acid, fatty acid ester, aliphatic amine, aliphatic amine salt, and aliphatic amide.
[0171] In case where these friction modifier are used instead of the organomolybdenum compound of the present invention or are used together with the organomolybdenum compound, it is capable of obtaining a composition which exhibits excellent fuel saving performance and frictional property in wet-type clutches. [0172] As the antioxidant, any kind of antioxidant generally used in the lubricating oil like ashless antioxidant such as phenolic antioxidant and aminic antioxidant, as well as organometallic antioxidant can be used. By adding antioxidant, antioxidant characteristic of the lubricating oil composition can be further enhanced; oxidation stability, high-temperature detergency, and base-number retention of the composition of the invention can be further enhanced.
[0173] Preferable examples of phenolic antioxidant include: 4,4'-methylene bis (2,6-di-tert-butylphenol), 4,4'-bis (2,6-di-tert-butylphenol), 4,4'-bis (2-methyl-6-tert-butylphenol), 2,2'-methylene bis (4-ethyl-6-tert-butylphenol), 2,2'-methylene bis (4-methyl-6-tert-butylphenol), 4,4'-butylidene bis (3-methyl-6-tert-butylphenol), 4,4'-isopropylidene bis (2,6-di-tert-butylphenol), 2,2'-methylene bis (4-methyl-6-nonylphenol), 2,2'-isobutylidene bis (4,6-dimethylphenol) , 2,2'-methylene bis (4-methyl-6-cyclohexylphenol), 2,6-di-tert-butyl-4-methylphenol,

2,6-di-"e" -bucyl-4-ethylphenol,
2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-a-dimethyl amino-p-cresol, 2 , 6-di-tert-butyl-4- (N,N' -dimethyl aminomethyl phenol), 4,4'-thiobis (2-methyl-6-tert-butylphenol), 4;4'-thiobis (3-methyl-6-tert-butylphenol), 2,2'-thiobis
(4-methyl-6-tert-butylphenol), bis
(3-methyl-4-hydroxy-5-tert-butyl benzyl) sulfide, bis
(3,5-di-tert-butyl-4-hydroxy benzyl) sulfide, 2,2'-thio-diethylenebis
[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], tridecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, pentaerythrityl-tetrakis
[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and 3-methyl-5-tert-butyl-4-hydroxyphenyl substituted fatty acid esters. These can be used in combination of two or more thereof.
[0174] Examples of aminic antioxidant include: phenyl-a-naphtylamine, alkylphenyl-cx-naphtylamine, and dialkyl diphenylamine. These may be used in combination of two or more thereof.
[0175] As the organometallic antioxidant, a known organometallic antioxidant which contains metal and shows antioxidant effect can be used; among the above described organomolybdenum compound, the (E2) component is preferably used.
[0176] The phenolic amtioxidant, aminic antioxidant, and organometallic antioxidant may be mixed.

[0177] When antioxidant is contained in the lubricating oil composition of the invention, the content, to the total mass of the lubricating oil composition, is usually 0.01-20 mass %, preferably 0 .1-10 mass %, and more preferably 0 . 5-5 mass % . When the content exceeds 20 mass %, sufficient performance propotional to the mixing amount cannot, be obtained; thus it is not preferable. [0178] As the viscosity index improver, nondispersant viscosity index improver and dispersant viscosity index improver can be used; specific examples thereof include: nondispersant or dispersant polymethacrylate, olefin copolymer, polyisobutene, polystyrene, ethylene-propylene copolymer, styrene-diene copolymer, and the hydrogenated product thereof. The mass-average molecular mass thereof is generally 5,000-1,000,000, so as to enhance fuel saving performance, the viscosity index improver having a mass-average molecular mass of 100,000-1,000,000, preferably 200 , 000-900,000, and particularly preferably 400,000-800,000 can be desirably used. [0179] When the lubricating oil composition of the present invention is used for 4-stroke engines of two-wheeled vehicles, as it is necessary to enhance shear stability, olefin copolymer-based, viscosity index improver like
ethylene-propylene copolymer, styrene-diene copolymer, and the hydrogenated product thereof are preferably used. In addition, so as to enhance the viscosity index while favorably maintaining the shear stability and to enhance the fuel saving performance, high-temperature detergency, and sludge dispersancy, olefin copolymer-based viscosity index improver and dispersant polymethacrylate viscosity index improver are particularly

preferablv used at the same time.
[0180] Content of the viscosity index improver when it is contained, to total mass of the composition, is usually 0.1-20 mass %, preferably 1-15 mass %, more preferably 3-12 mass %, and particularly preferably 8-12 mass %. The mixing ratio of olefin copolymer-based viscosity index improver and dispersant polymethacrylate-based viscosity index improver when these are contained at the same time is not specifically limited; the mixing mass ratio is preferably 95:5 to 20:80 and more preferably 90 :10 to 60:40.
[0181] As pour-point depressant, polymethacrylate-based polyer, alkylated aromatic compound, fumarate-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, these of which are compatible with the lubricant base oil to be used, can be used; it is preferably polymethacrylate whose mass-average molecular mass is over 50,000 and 150,000 or less, preferably 80,000-120,000.
[0182] Examples of rust inhibitor include: alkenylsuccinic acid, alkenyl succinate, polyvalent alcohol ester, petroleum sulfonate, alkyl benzene sulfonate, and dinonylnaphthalene sulfonate.
[0183] Examples of corrosion inhibitor include benzotriazole-based, thiadiazole-based, and imidazole-based compounds.
[0184] Examples of demulsifier include: polyalkylene glycolic nonionic surfactant such as polyoxyethylene alkylether, polyoxyethylene alkylphenylether, and polyoxyethylene alkylnaphthyl ether.

[Cl = 5] Examples of metal deactivator include: imidazoline, pyrimidine derivatives, alkylthiadiazole, mercapto benzothiazole, benzotriazole or derivatives thereof, 1,3,4-thiadiazole polysulfide,
1,3,4-thiadiazolyl-2,5-bisdialkyl dithiocarbamate, 2- (alkyldithio) benzimidazole, and (3- (o-carboxybenzylthio) propionitrile.
[0186] As the defoamant, any kind of compounds usually used as defoamant for lubricating oil are available; for instance, silicones such as dimethyl silicone and fluoro silicone.
A certain amount of one or a combination of two or more compounds optionally selected from the above may be blended. Examples of defoamant include: silicone oil; alkenyl succinic acid derivatives; ester of polyhydroxy aliphatic alcohol and long-chain fatty acid; aromatic amine salt of methylsalicylate with o-hydroxybenzyl alcohol, aluminum stearate, potassium oleate, N-dialkyl-allylamine nitroaminoalkanol, or isoamyloctyl phosphate; alkylalkylene diphosphate; metal derivatives of thioether; metal derivatives of disulfide; fluorine compound of aliphatic hydrocarbon; triethyl silane; dichlorosilane; alkylphenyl polyethyleneglycol ethersulfide; and fluoroalkylether.
[0187] As coloring agent, any kind of usually used compounds may be available, and a certain dosage thereof can be blended. The dosage to total mass of the composition is usually 0.001-1.0 mass %.
[0188] When these additives are contained in the lubricating oil composition of the invention, to total mass of the composition,

usually, the dosage of corrosion inhibitor, rust inhibitor, demulsifier, and rubber swelling agent is respectively 0.005-5 mass %; the dosage of metal deactivator is 0.005-1 mass %; dosage of pour-point depressant is 0.01-1 mass %; dosage of defoamant is 0.0001-1 mass %; and dosage of coloring agent is 0.001-1.0 mass %.
[0189] The lubricating oil composition of the present invention not only exhibits excellent frictional property in wet-type clutches and/or fuel saving performance but also shows excellent performance such as anti-wear property, high-temperature oxidation stability, and detergency. It also shows sufficient performance compatible with JASO standard of the 4-stroke gasoline engine oil for the two-wheeled vehicles
(JASO T 903-98) . One of the regulations requires that the sulfated ash content of the composition to total mass of thecomposition is 1.2 mass % or less; the composition of the invention can be a low-ash type lubricating oil whose sulfated ash content is preferably 1.0 mass % or less, more preferably 0.8 mass % or less, and particularly preferably 0.7 mass % or less. It should be noted that the term "sulfated acid ash" described herein means a sulfated acid ash as measured in accordance with JIS K2272, namely, it is constant-mass ash obtained by adding sulfuric acid to carbonized residue produced by burning test samples.
[0190] Phosphorus content in the lubricating oil composition of the invention to total mass of the composition is preferably 0.2 mass % or less, more preferably 0.12 mass % or less; by adjusting other components, phosphorus content can

be set within the range of 0 . 1 mass % or less, further, 0.05 mass % or less.
[0191] These low-ash type, low-phosphorus type lubricating oil composition of the invention can minimize impact on catalytic converter, therefore these can be advantageously used for vehicles on which catalytic converter such as three-way catalyst, oxidation catalyst, NOx storage/reduction type catalyst, EGR device, and DPF is mounted.
[0192] Kinematic viscosity at 100 degree C of the lubricating oil composition of the invention is preferably 5.6 mm2/s or more, more preferably 9.3 mm2/s or more. On the other hand, kinematic viscosity at 100 degree C is preferably 21.9 mm2/s or less, more preferably 16.3 mm2/s or less, and particularly preferably 12.5 mm2/s or less. By setting kinematic viscosity of the lubricating oil composition within the above range, high fuel saving performance can be imparted.
[0193] TBS viscosity at 150 degree C of the lubricating oil composition of the present invention is preferably set at 2.9 mPa's or more; it is normally 5 mPa- s or less, preferably 4 . 5 mPa-s or less, more preferably 3.7 mPa-s or less, and furthermore preferably 3.2 mPa-s or less. By setting TBS viscosity at 2. 9 mPa-s or more, lubricity of transmissions and gear can be favorably maintained; by setting the same at 4 . 5 mPa-s or less, particularly 3.7 mPa*s or less, it is capable of obtaining a composition which exhibits excellent fuel saving performance. It should be noted that the term "TBS (Tapered bearing simulator) viscosity" described herein means an effective viscosity under a condition of high-temperature and high-shear; it can be measured

zy a method in accordance with ASTM D4683 (Standard Test Method for Measuring Viscosity at High Shear Rate and High Temperature by Tapered Bearing Simulator) at 150 degree C and a shear-rate of 10s/s.
[0194] Since the lubricating oil composition of the present invention exhibits excellent frictional property in wet-type clutches and/or fuel saving performance, it is suitably used for power train having a wet-type clutch or 4-stroke engines of two-wheeled vehicles; it is particularly preferable for 4-stroke engines of two-wheeled vehicles having a wet-type clutch. The lubricating oil composition can also be used as a lubricating oil of which fuel saving performance is required, e.g. lubricating oil for internal-combustion engine like gasoline engine, diesel engine, and gas engine, particularly lubricating oil for internal-combustion engine on which catalytic converter is mounted and various lubricating oil of which friction-modifying performance is required.
Examples
[0195] Hereinafter, the invention will be more specifically described by way of the following examples. However, the invention is not restricted by the examples.
[0196] Based on the composition shown in Table 2, lubricating oil compositions of the present invention (Examples 1 and 2), lubricating oil compositions as comparisons
(Comparative examples 1 and 2) , and lubricating oil composition as a reference (Reference example 1) were prepared such that the TBS viscosities at 15 0 degree C were 2.9-3.2 mPa*s. Ratio of the

base oil was determined based on the total mass of base oil, and additive dosage of the various additives was determined based on the total mass of the composition. About these compositions, below-described SRV friction test and frictional property test in wet-type clutches were carried out; and then, fuel saving performance and frictional property in wet-type clutches were evaluated. The evaluation results are also shown in Table 2.
[0197] [SRV friction test]
SRV friction test was carried out using SRV friction tester at a load of 400 N, a frequency of 50 Hz, an amplitude of 1.5 mm, an oil temperature of 40 degree C. The lower the friction coefficient, the more excellent the friction-reducing effect and fuel saving performance aire. Particularly, a lubricating oil composition having lower friction coefficient at 40 degree C shows improvement of fuel saving performance at a time of engine starting.
[0198] [Frictional property test in clutch]
Performance classification about clutch frictional property was carried out in accordance with JASO standard of the 4-stroke gasoline engine oil for the two-wheeled, vehicles (JASO T 903-98) . As it were, dynamic friction coefficient, static friction coefficient, and braking time were measured in accordance with the testing condition of JASO T 904-98, and then, dynamic friction index, static friction index, and index of braking time were calculated by the following calculation method; thereafter, these index were classified into MA or MB based on the criteria shown in Table 1. The compositions classified into MA can be seen that these compositions exhibit excellent

performance in all dynamic friction coefficient, static friction
coefficient, and braking time. On the other hand, the
composition classified into MB can be seen that any one of the
indexes of this composition are below the criteria; whereby
slippage inhibitory effect of the wet-type clutches is poor.
[0199] Calculation method (e.g.: dynamic friction index)
Dynamic friction index = 1+[ud(s)-ud(B)]/[ud(A)-ud(B)]
ud(s): dynamic friction coefficient of test oil
lid (A): dynamic friction coefficient of JAFRE-A
(high-frictional standard oil)
ud(B): dynamic friction coefficient of JAFRE-B (friction
modifier-containing low-frictional standard oil)
Static friction index and index of braking time were also
calculated by the same caluculation method.
[0200] (Table 1)
(Table 1)

[0202] As clearly seen from Table 2, the lubricating oil composition of Comparative example 1 which contains zinc dithiophosphate as the main component and does not contain molybdenum dithiocarbamate and molybdenum dithiophosphate shows high SRV friction coefficient. On the other hand, the

composition of Example 1 containing a particular metal salt of phosphorus-containing acid instead of using zinc dithiophosphate not only shows lower SRV friction coefficient but also shows improvement of frictional property in wet-type clutches in view of comprehensive evaluation of each index.
[0203] With regard to the conventional fuel-efficient engine oil of Comparative example 2 which contains zinc dithiophosphate as the main component and also contains molybdenum dithiocarbamate, although it shows low SRV friction coefficient, the frictional property in wet-type clutches is significantly poor; thereby the power transmission performance in wet-type clutches is poor. On the other hand, the composition of Example 2, in which various additives were optimized using particular metal salt of phosphorus-containing acid instead of zinc dithiophosphate, shows sufficiently low SRV friction coefficient and shows remarkable improvement regarding frictional property in wet-type clutches. Hence, the composition of Example 2 is an excellent composition which can improve fuel saving performance from both aspect of reduction of engine friction and power transmission performance in wet-type clutches. It is observed that there is a 50% or more reduction in SRV friction coefficient at 80 degree C of the composition of Example 2 to that of the composition of Example 1. This means that the composition of Example 2 , compared with that of Example 1, is a superior one which can significantly lower the engine friction while maintaining frictional property in wet-type clutches at a high level. [0204] The composition of Reference example 1 is an

excellent composition (See Japanese Parent Application Laid-Open No. 2003-41283.) which contains molybdenum dithiocarbamate and in which zinc dithiophosphate and various additives are optimized by the present inventors to attain compatibility between inhibition of clutch slippage and reduction of engine friction. The composition of Example 2 not only shows similar level of SRV friction coefficient but also shows further improvement of frictional property in wet-type clutches, without using zinc dithiophosphate as the essential component of the above publication (JP-A No. 2003-41283).
[0205] The above has described the present invention associated with the most practical and preferred embodiments thereof. However, the invention is not limited to the embodiments disclosed in the specification. Thus, the invention can be appropriately varied as long as the variation is not contrary to the subject substance and conception of the invention which can be read out from the claims and the whole contents of the specification. It should be understood that the lubricating oil composition with such an alternation are included in the technical scope of the invention.
Industrial Applicability
[0206] Since the lubricating oil composition of the present
invention is excellent in frictional property in wet-type
clutches and/or fuel saving performance, it can be suitably used
for power train having wet-type clutches or 4-stroke engines of
two-wheeled vehicles, it is particularly suitably used for
4-stroke engines of two-wheeled vehicles having wet-type clutches .

Cther than these, the lubricating oil composition can also be used for a lubricating oil which requires fuel saving performance, for a lubricating oil for internal-combustion engine like gasoline engine, diesel engine, and gas engine, particularly-internal -combust ion engine on which catalytic converter is mounted and various lubricating oil of which friction-modifying performance is required.

CLAIMS
1. A lubricating oil composition for wet-type clutches or 4-stroke engines of two-wheeled vehicles comprising:
a lubricant base oil containing a mineral base oil and/or a synthetic base oil; and
to the total mass of the composition,
(A) 0.01-0.2 mass % of a metal salt of phosphorus-containing acid
represented by the general formula (a) or (b) as the phosphorus
content,
(B) 0.005-0.5 mass % of a metallic detergent as the metal content,
and
(C) 0.01-0.4 mass % of an ashless dispersant as the nitrogen
content.
(a)
(wherein, R1 is a C1-C30 hydrocarbon group, R2 and R3 may be the same or different and are independently a hydrogen atom or a C1-C30 hydrocarbon group, and p is an integer of 0 or 1.)
(b)
(wherein, R4 is a Ci-C30 hydrocarbon group, R5 and R6 may be the same or different and are independently a hydrogen atom or a Ci-C30 hydrocarbon group, and q is an integer of 0 or 1.)

2. The _lubriating oil composition according to claim 1, wherein mass ratio (M/P) of the metal content (M) and the phosphorus content (P) in the metal salt of the (A) phosphorus-containing acid is 1 to 3.
3. The lubricating oil composition according to claim 1, wherein mass ratio (M/P) of the metal content (M) and the phosphorus content (P) in the metal salt of the (A) phosphorus-containing acid is 1.2 to 1.8.
4. The lubricating oil composition according to any one of claims 1 to 3, wherein content of zinc dithiophosphate, to the total mass of the composition, is below 0.01 mass % as the phosphorus content or substantially free.
5. The lubricating oil composition according to any one of claims 1 to 4, which does not contain (El) an organomolybdenum compound selected from molybdenum dithiophosphate and molybdenum dithiocarbamate.
6. The lubricating oil composition according to any one of claims 1 to 4, which contains (E) an organomolybdenum compound.
7. The lubricating oil composition according to any one of claims 1 to 6,
wherein the (C) ashless dispersant comprises a boron-containing succinimide and a boron-free mono- and/or bis-succinimide, and

where"-~- content of the boron-containing succinimide, to the -otal mass of the composition, is 0.0 05-0.2 mass % as the boron content.
8. The lubricating oil composition according to any one of claims 1 to 7, wherein sulfated ash content in the lubricating oil composition, to the total mass of the composition, is 1 mass % or less.