DESC:TECHNICAL FIELD
[0001] The present subject matter relates generally to an internal combustion engine. More particularly, the present invention relates to a connecting rod assembly employed in the engine.

BACKGROUND
An internal combustion engine converts thermal energy obtained from burning of a fuel with an oxidizer (air) into mechanical energy, which can be used to do some kind of mechanical work. It is used in a wide range of applications including providing motive force for movement of a vehicle. The main parts of the engine include a cylinder head, a reciprocating piston on a cylinder block and a connecting rod which connects the piston to the reciprocating crankshaft. The connecting rod in the engine transfers power generated by the reciprocating piston in the cylinder block of the engine and converts it into rotary motion of the crankshaft together forming a slider crank mechanism. Typically, the connecting rod is made of a stem which is a narrow long portion of the connecting rod whose cross section varies depending on the design like I-beam, H-beam, A-beam and like, a small end bore at one end of the stem which attaches to the piston through a gudgeon pin which enables it to swivel in the piston and a big end bore at the other end of the stem connected to a crankpin of the crankshaft through a bearing (usually a needle bearing). The connecting rod also has a small oil groove at one end of the stem towards the big end bore to permit flow of oil for lubrication and at least one oil hole drilled through an externally facing circumferential surface of the small end facing towards the piston for lubrication. Conventionally, the design of the connecting rod included two types. In a split-type connecting rod design, the big end bore is split into a rod portion which continues from the connecting rod stem, and a cap portion which is coupled to the connecting rod portion with bolts over the bearing journal. This is used in an integral crankshaft design where the crankshaft is not split into two separate halves. In a integral connecting rod design, the big end bore is integrally attached to one end of the stem and the bearing journal is inserted into the big end bore in the transverse plane. This is used in a split crankshaft design. Conventionally steel alloy is the material used for making the connecting rod.

BRIEF DESCRIPTION OF THE DRAWINGS
[0002] The detailed description is described with reference to the accompanying figures. The same numbers are used throughout the drawings to reference like features and components.
[0003] Fig. 1 illustrates a two wheeled vehicle employing the internal combustion engine according to an embodiment of the present invention.
[0004] Fig. 2 illustrates a side view of an internal combustion engine of a two wheeled vehicle according to the embodiment of the present invention.
[0005] Fig. 3 illustrates a cross sectional view of the internal combustion engine according to the embodiment of the present invention.
[0006] Fig. 4 illustrates the exploded view of a crankshaft assembly employing the connecting rod assembly according to the embodiment of the present invention.
[0007] Fig. 5 illustrates the isometric view of the connecting rod assembly according to the embodiment of the present invention.
[0008] Fig. 6a illustrates the front view of a connecting rod according to the embodiment of the present invention.
[0009] Fig. 6b illustrates the side view of a connecting rod according to the embodiment of the present invention.
[00010] Fig. 6c illustrates the cross section of the small end bore of the connecting rod according to the embodiment of the present invention.
[00011] Fig. 6d illustrates the cross section of the big end bore according to the embodiment of the present invention.
[00012] Fig. 7 illustrates the connecting rod assembly in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION
[00013] Various other features and embodiments of the present invention here will be discernible from the following further description thereof, set out hereunder. In the ensuing exemplary embodiments, the engine is a four stroke single cylinder internal combustion engine. However it is contemplated that the disclosure in the present invention may be applied to any engine capable of accommodating the present subject matter without defeating the spirit of the invention. Further "front" and "rear", and "left" and "right" referred to in the ensuing description for the illustrated embodiments refer to front and rear, and left and right directions as seen from the rear of the engine and looking forward. Furthermore, a "longitudinal" axis refers to a front to rear axis relative to the engine, while a "lateral" axis refers generally to a side to side, or left to right axis relative to the engine. The detailed explanation of the constitution of parts other than the invention which constitutes an essential part has been omitted at suitable places.
[00014] Connecting rod design and assembly is a very important aspect of the design of the engine since, the connecting rod plays a crucial role in transfer and conversion of power from reciprocatory motion of the piston to rotary movement of the crankshaft. The various design considerations for a connecting rod include, the capacity of the combustion chamber, the torque required, weight of the reciprocating parts, the cross section of the rods and the material used. In this regard, one of the most crucial design factor in consideration of the connecting rod is its strength, reliability, structural rigidity, and ability to withstand bearing failure and buckling failure as these factors are largely responsible for noise and vibration in vehicles. Additionally, these factors also help to analyse catastrophic engine failures that may occur due to fracture of the connecting rod.
[00015] Engine noise, vibration and engine failures mainly occur due to reciprocating mass, which causes a reciprocating unbalance force which acts along the piston axis. This unbalanced mass is mainly contributed by the piston and connecting rod. The connecting rod is under tremendous stress from the reciprocating load represented by the piston, which actually is being stressed and being compressed with every rotation and hence subjected to cyclic loads. Thus there is a chance for catastrophic engine failure to occur. Hence, any well designed connecting rod involves balancing the reciprocating mass and reducing noise and vibration. These include redesign of parts or by changing low density material without compromising the strength and functional requirement of the connecting rod.
[00016] Conventionally steel alloy is the material used for making a connecting rod, because steel alloy increases strength reduces brittleness and improves the overall structural rigidity of the rod. But the density of steel is high, hence the mass of the connecting rod is also more and it contributes to the reciprocating mass in the engine.
[00017] Connecting rods made of light materials with lesser density compared to steel alloy, such as aluminium alloys are known in art to reduce the reciprocating mass and hence reduce vibration and noise produced. But using such connecting rods gives rise to problems such as reduced structural rigidity which when acted upon by cyclic loads in a reciprocating motion may lead to bearing failure or buckling failure. Also, hardness of aluminium alloys is less, hence when high loads are applied on connecting rods made of aluminium alloy, there maybe dig or cavity formation by a roller bearing or journal bearing on the internally facing circumferential surface of the connecting rod. Also, the heat produced due to the inner surface being in contact with the bearing may cause the big end bore to expand due to heat thereby causing slip in the contact between the bearing and the inner surface. This may result in loss of power and also blockage of oil groove present in the junction between the rod stem and the big end bore. Also, structural rigidity is high in steel, hence connecting rods made of steel withstand large loads especially concentrated at the big end bore and small end bore, whereas in a rod made of lighter materials such as aluminium, application of such loads may lead to buckling failure or bearing failure. Also, to obtain same properties as that provided by using steel as a material, connecting rods made of lighter materials such a aluminium have to be designed with larger dimensions, thus causing layout constraints in the engine crankcase.
[00018] Hence it is the object of the present invention to design a connecting rod assembly made of light materials such as aluminium alloys, yet provide all the advantages of a connecting rod made of steel. Such design not only reduces mass to reduce vibration and noise but it provides all the functional advantages of a regular connecting rod made of steel alloy such as improved structural rigidity and avoids bearing and buckling failure.
[00019] Another object of the present invention is to eliminate the bearing and surface contact of such a connecting rod made of lighter materials such as aluminium, hence eliminating the problem of cavity formation due to relative motion, to avoid expansion of the big end bore of the connecting rod due to heat and prevent slip between the two surfaces in constant contact, and blocking of oil groove at the big end bore.
[00020] Another object of the present invention is to avoid big end and small end bore surface wear due application of high loads on a connecting rod made of lighter materials such as aluminium.
[00021] Another object of the present invention is to eliminate engine layout constraints by replacing connecting rods made of steel to rods made of lighter materials, hence ensuring that least design changes are made to other components of the engine.
[00022] With the above design changes, the following advantages can be obtained, such as the connecting rod mass reduction, reduced noise and vibration without affecting strength and functional requirement, minimises stress due to less sectional thickness, no layout changes required in the engine crankcase and is applicable to all applications which use the internal combustion engine including a straddle type motorcycle, the scooter type motorcycle and a three wheeled vehicle.
[00023] These and other advantages of the present subject matter would be described in greater detail in conjunction with the figures in the following description.
[00024] Fig. 1 illustrates a two wheeled vehicle (100), having an internal combustion engine (101) in accordance with one embodiment of the present invention. The vehicle further includes, a front wheel (110), a rear wheel (103), a body frame, a fuel tank (107) and seat (106). Body frame includes a head pipe (111), a main tube (112), a down tube (113), and seat rails (not shown). The head pipe (111) supports a steering shaft (not shown) with two brackets – upper bracket and lower bracket at each end. Two telescopic front suspension (114) is attached to the lower bracket on which is supported the front wheel (110). The upper portion of the front wheel (110) is covered by a front fender (115) mounted to the lower portion of a front fork at the end of the steering shaft. A handlebar (108) is fixed to upper bracket and can rotate to both sides. A head light (109) is arranged on an upper portion of the front fork. Down tube (113) is located in front of the engine (101) and stretches slantingly downward from head pipe (111). A bracket (116) is provided at the lower end of down tube (113) for supporting the internal combustion engine (101). Main tube (112) is located above the engine and stretches rearward from head pipe (111) and connects the rear of the engine. A vertical pipe (117) is joined to the rear end of main tube and stretches downward from the point where the main tube joins the seat rails (not shown). Seat rails are joined to main tube (112) and stretch rearward to support a seat (106) disposed above seat rails.
Left and right rear swing arm bracket portions (not shown) support a rear swing arm (not shown) to swing vertically, and a rear wheel (103) is connected to rear end of the rear swing arm. Generally, two rear wheel suspensions (102) is arranged between rear swing arm. A tail light unit (104) is disposed on the rear cover. A grab rail (105) is also provided on the rear of the seat rails. Rear wheel (103) is arranged below seat (106) and rotates by the driving force of the internal combustion engine (101) transmitted through a chain drive (118) from the engine (101). There is front brake (119) and back brake (not shown) arranged on the front wheel (110) and back wheel (103) respectively.
[00025] Fig. 2 illustrates the side view of the engine (101) in accordance with the embodiment of the present invention. The engine is made up of a cylinder head assembly (201), cylinder block (202) and crankcase (203).
[00026] Fig. 3 illustrates a cross sectional view of the engine (X-X) showing the main parts of the engine which include a reciprocating piston (306), a cylinder block (309), a rotatable crankshaft (405a) and the connecting rod assembly (301) according to one embodiment of the present invention, which connects the reciprocating piston (306) to the rotatable crankshaft (405a) . The cylinder head assembly (201) consists of at least one inlet valve (311) and at least one outlet valve (312) which are operated by means of rocker arms (308a and 308b) and a camshaft (not shown) which consists of at least one inlet cam lobe 304 and at least one outlet cam lobe (310) which actuates the rocker arms (308a and 308b) when required. A cam-chain (not shown) is meshed between gears (not shown) in the crankshaft (405a) and camshaft (not shown) in order to drive the camshaft in the cylinder head (201). The inlet air fuel mixture from the carburetor (not shown) is connected to an inlet portion of the engine (not shown) in the cylinder head and an exhaust system including a muffler (not shown) is connected to the outer portion of the cylinder head (201). The crankcase (203) houses the crankshaft assembly (Fig. 4), clutch assembly (not shown), starter assembly (not shown) and gearbox assembly (not shown) and other ancillary systems which include lubrication system (not shown), cooling system (not shown) and exhaust system (not shown) all housed in the main engine body.
[00027] The connecting rod assembly (301), including the connecting rod (501) whose small end bore (504) according to the embodiment of the present invention is connected to the piston (306) through a gudgeon pin (307) at one end, which reciprocates in the cylinder block (202).
[00028] Fig. 4 illustrates the exploded view of the crankshaft (405) of the engine (101) employing the embodiment of the present invention and housed in the crankcase (203). In this embodiment, the crankshaft (405) employed is a split crankshaft, which comprises of two ends, magneto side (405c) and clutch side (405b). A crankpin (404) is inserted through the big end bore (505) of the connecting rod assembly (301) over a roller bearing (403) and frictionally engaged on both sides of the crankshaft through holes present in the crankweb (405a and 405b). The connecting rod assembly (301), the roller bearing (403) and crankpin (404) are assembled in such a way that Internally facing circumferential surface of the insert (401) acts as a bearing running zone for roller bearing with equal hardness.
[00029] Fig. 5 illustrates the exemplary working of the embodiment of the present invention. In a preferred embodiment of the present invention, light material such as aluminium alloy material is used for connecting rod (501) design in place of steel alloy material. The aluminium connecting rod (501) comprises of a stem (510), a small end bore (504) and a big end bore (505). The big end bore (505) has a series of grooves such as those present in splines (505a) which are lined up continuously across the internally facing circumferential surface of the big end bore
[00030] The connecting rod assembly (401) according to the embodiment also has an insert (401), made of a material with good strength compared to the material of connecting rod. Such materials include steel alloy. The insert (401) has series of projections such as those present in spline (401a) is capable to mating exactly in the grooves of splines (505a) provided in the big end bore (505). Preferably, the insert (401) having spline (401a), is frictionally engaged at the big end bore splines (505a) of the connecting rod (501) by an interference fit above 60 micron tight to avoid slippage. Hence, Inner circumferential surface of the insert acts as a bearing running zone for roller bearing with equal hardness. The roller bearing in turn is mounted on the crankpin (404) of the crankshaft as shown in Fig. 4.
[00031] The connecting rod assembly (301) also has a bush (402), made of harder materials such steel or brass which is pressed on the small end bore (504) in for frictional engagement with the small end bore (504). This arrangement avoids small end bore wear due to application of high loads on lighter materials such aluminium alloy of which the connecting rod (501) is made.
[00032] Fig. 6a and Fig. 6b illustrates the front view and side view of the connecting rod assembly (301) according to the embodiment of the present invention. Accordingly, to provide improved strength and to avoid any layout constraint in the engine due to change in design of connecting rod, additionally an elongated structural member such as ribs are disposed continuously and radially and extending axially along the externally facing circumferential surface of the big end bore (502) and small end bore (506) of the connecting rod (501). Fig. 6c illustrates the cross section of the connecting rod (501) with elongated structural member such as ribs on the small end bore. Fig. 6d illustrates the cross section of the connecting rod (501) with elongated structural member such as ribs on the big end bore. As it is seen from the cross section structure, such elongated structural member provide additional strength to the connecting rod (501) while enabling least design changes in other parts of the engine.
[00033] Many modifications and variations of the present subject matter are possible in the light of above disclosure. Therefore, within the scope of claims of the present subject matter, the present disclosure may be practiced other than as specifically described.
,CLAIMS:We Claim:
1. An internal combustion engine (101) comprising:
a reciprocating piston (306), a cylinder block (309), a rotatable crankshaft (405), and a connecting rod assembly (301) connecting the reciprocating piston (306) to the rotatable crankshaft (405);
wherein,
said connecting rod assembly (301) comprising:
a connecting rod (501), said connecting rod (501) comprising a small end bore (504) at one end, and a big end bore (505) having a plurality of grooves (505a) at another end, said plurality of grooves (505a) disposed on an internally facing circumferential surface of the big end bore (505); and
an insert (401), said insert (401) comprising a plurality of projections (401a), said plurality of projections (401a) disposed on an externally facing circumferential surface of the insert (401), and said insert (401) capable of mating with said plurality of grooves (505a) disposed on the corresponding big end bore (505) of the connecting rod (501).

2. The internal combustion engine (101) as claimed in claim 1, wherein said connecting rod (501) comprises of an elongated structural element (502, 506) disposed continuously and radially, and extending axially along the externally facing circumferential surface of the big end bore (505), and the externally facing circumferential surface of the small end bore (504).
3. The internal combustion engine (101) as claimed in claim 1, wherein the connecting rod (501) is made of aluminum alloy.
4. The internal combustion engine (101) as claimed in claim 1, wherein the insert (401) is made of steel alloy.
5. The internal combustion engine (101) as claimed in claim 1, wherein the plurality of projections on the insert (401) is a spline (401a) that is configured to mate with its corresponding plurality of grooves (505a) in the bigger end bore (505).
6. The internal combustion engine (101) as claimed in claim 1, wherein the plurality of projections on the insert (401) is a serration that is configured to mate with its corresponding plurality of grooves that is also a serration in the bigger end bore (505).
7. The internal combustion engine (101) as claimed in claim 1, wherein the plurality of grooves on the big end bore (505) is a slot (702a) that mates with its corresponding plurality of projections (703a) in the insert (401).
8. The internal combustion engine (101) as claimed in claim 1, wherein the small end bore (504) of the connecting rod (501) is configured to accommodate a wear resistant bush (402).
9. The internal combustion engine (101) as claimed in claim 1, wherein the connecting rod (501) is an integral type connecting rod.
10. A two wheeled vehicle (100) including said internal combustion engine (101) as claimed in claims 1 to 9.