FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
AN IMPROVED OLEO-PNEUMATIC SHOCK ABSORBER FOR LAND VEHICLES AND THE LIKE
ENDURANCE TECHNOLOGIES PRIVATE LIMITED.
an Indian Company, of E-92, M.I.D.C Industrial Area, Waluj Aurangabad - 431136,
Maharashtra, India.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

This application is a patent of addition of Indian Patent Application No. 1015/MUM/2003 filed on September 29th, 2003, and now a Granted Indian Patent No. IN210922, the entire contents of which are specifically incorporated herein by reference.
FIELD OF THE DISCLOSURE
This invention relates to an improved oleo-pneumatic shock absorber for land vehicles and the like.
BACKGROUND
The conventional oleo-pneumatic shock absorber for land vehicles and the like, known in the art, are of three types namely the oleo-pneumatic twin tube shock absorber wherein the gas/air is injected after filling the oil in the shock absorber, the oleo-pneumatic mono tube shock absorber wherein a floating separator is provided inside the mono tube to separate the gas/air from the oil filled in the shock absorber and the oleo-pneumatic mono tube canister attached shock absorber wherein the gas/air is filled in a collapsible chamber enclosed in the canister that is separated from the oil filled in the mono tube, canister attached shock absorber. Each of these types of oleo-pneumatic shock absorbers is fitted in the land vehicles for dampening the shocks exerted to the vehicle due to road conditions
The conventional oleo-pneumatic twin tube shock absorber consists of an outer tube housing an inner tube fitted with a piston rod assembly and a base valve assembly. High-pressure gas/air is injected in the shock absorber from the oil seal fitted on the top end of the outer tube. The gas/air and oil filled in

the shock absorber have no separator between them and the gas/air and the oil are in constant contact with each other. Due to clearance, although very minute, between the oil seal and the piston rod by virtue of relative movement between both, the gas/air filled in the shock absorber escapes though the oil seal and reduces the pressure inside the shock absorber. The reduction of gas/air pressure inside the shock absorber lowers the dampening force in compression. The escaped gas/air cannot be re-charged. Also due to constant movement of the piston, while dampening the exerted shocks, the oil and the gas/air, being in direct contact with each other get emulsified. Since the emulsion has a very low density as compared to the oil filled in the shock absorber it results in heavy loss of dampening force when it passes through the piston valve or base valve. The continuous escape of the gas/air filled in the shock absorber over a period of time lowers the dampening force in compression and emulsification effects of oil ultimately reduces the performance of the shock absorber of this type to an unacceptable limit.
The second conventional oleo-pneumatic mono tube shock absorber consists of a single tube that is first put in the high-pressure gas/air medium. A floating separator is inserted in the tube to separate the gas/air from the oil The oil is filled in the tube, piston rod assembly and sealing assembly are inserted in the tube and open end of the tube is sealed. There is no base valve in the mono tube shock absorber hence the dampening force in compression is generated through the gas/air pressure inside the tube. Due to leakage of gas/air, over a period of time, across the sealing area of the floating separator, the escaped gas/air reaches the oil chamber of the shock absorber. The escaped gas/air comes in direct contact with the oil filled in the shock absorber and due to constant movement of the piston, while dampening the

exerted shocks, the oil and the escaped gas/air get emulsified. Since the emulsion has a very low density as compared to the oil filled in the shock absorber it results in heavy loss of dampening force when it passes through the piston valve. Further due to clearance, although very minute, between the oil seal and the piston rod by virtue of relative movement between both, the escaped gas/air also leaks through the oil seal and reduces pressure inside the tube. The escaped gas/air can never be re-charged. The absence of the base valve in the mono tube, the continuous escape of gas/air filled in the shock absorber over a period of time, from the sealing area of the floating separator and also from the oil seal, the emulsification of the oil with gas/air and the fall in dampening force in compression ultimately reduces the performance of the shock absorber of this type drastically.
In the third conventional oleo-pneumatic canister attached mono tube shock absorber, the mono tube is attached to the canister. A collapsible chamber is enclosed in the canister and sealed with a circlip. The oil is filled in the mono tube attached to the canister, piston rod assembly and sealing assembly are inserted in the tube and the open end of the tube is sealed. High-pressure gas/air is filled in the collapsible chamber enclosed in the canister attached to the mono tube of the shock absorber. There is no base valve in the mono tube shock absorber hence the dampening force in compression is generated through the gas/air pressure filled in the collapsible chamber enclosed in the canister. The gas/air filled in the collapsible chamber enclosed in the canister eliminates the contact of the gas/air with the oil filled in the shock absorber hence the emulsification of oil and gas/air is eliminated securing the density of the oil intact. However the gas/air filled in the collapsible chamber enclosed in the canister escapes

over a period of time and reduces the pressure inside the shock absorber. The escaped gas/air can however be re-charged. The absence of base valve in the mono tube and the reduction of gas/air pressure inside the shock absorber, over a period of time, lowers the dampening force in compression ultimately reduces the performance of the shock absorber of this type drastically.
It is an object of this invention to provide an oleo-pneumatic shock absorber for land vehicles and the like which obviates the aforesaid drawbacks and increases the life of the shock absorber.
SUMMARY
An improved oleo-pneumatic shock absorber for land vehicles and the like is disclosed in accordance with an embodiment of the present disclosure. The improved oleo-pneumatic shock absorber includes a twin tube. The twin tube includes outer tube housing and an inner tube. The inner tube is fitted with a base valve. A piston rod fitted in a piston inserted in the inner tube. The top open end of the outer tube is sealed with a sealing device including a seal shield. A canister is attached to the outer tube at its bottom end characterized in that a collapsible chamber having a cap is provided inside the canister. A hollow screw having a seal at its one end and female threads at its other end is provided on the cap. Another screw with male threads is provided to engage the female threads on the hollow screw and the collapsible chamber inserted in the canister is sealed with a circlip, characterized in that improved oleo-pneumatic shock absorber comprising a bump stop concentrically disposed at an operative top end of the main

suspension spring for taking up a portion of suspension load acting on the main suspension spring. The canister includes a floating separator piston adapted to slide inside the canister due to fluid pressure exerted thereon by the oil filled in the inner tube
Typically, the seal provided on the hollow screw is made of rubber or the like material.
Generally, the bump stop is made of polyurethane material.
BRIEF DESCRIPTION OF THE FIGURES
Other aspects of the invention will become apparent by consideration of the accompanying drawing and their description stated below, which is merely illustrative of a preferred embodiment of the invention and does not limit in anyway the nature and scope of the invention.
Figure 1 illustrates a cross sectional view of a twin tube, canister attached oleo-pneumatic shock absorber in accordance with one embodiment;
Figure 2 illustrates an enlarged cross sectional view of the portion marked 'X X1 of the twin tube, canister attached oleo-pneumatic shock absorber of Figure 1;
Figure 3 illustrate an oleo-pneumatic shock absorber fitted with a canister, housing a collapsible chamber therein in accordance with another embodiment of the present disclosure; and

Figure 4 illustrates an enlarged view of a canister having an air column defined therein by a floating piston sliding inside the canister in accordance with another embodiment of the present disclosure.
DETAILED DESCRIPTION
The invention will now be described with reference to the embodiment shown in the accompanying drawings, The embodiment does not limit the scope and ambit of the invention. The description relates purely to the exemplary preferred embodiment of the invention and its suggested applications.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The description herein after, of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be

comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The improved oleo-pneumatic shock absorber for land vehicles and the like, according to the present invention, consists of a twin tube comprising an outer tube housing an inner tube, the inner tube is fitted with a base valve and has got inserted in it a piston rod fitted with a piston, the top open end of the outer tube is sealed with a sealing device including a seal shield, a canister is attached to the outer tube at its bottom end, characterized in that a collapsible chamber having a cap is provided inside the canister, a hollow screw having a seal at its one end and female threads at it's other end is provided on the cap, another screw with male threads is provided to engage the female threads on the hollow screw and the collapsible chamber inserted in the canister is sealed with a circlip.
According to a preferred embodiment of this invention the seal provided on the hollow screw is made of rubber or the like material.
The oil is filled in the inner tube fitted with a base valve, the outer tube and the canister attached to the outer tube of the shock absorber. The piston rod fitted with a piston and sealing device are inserted in the inner tube and the open end of the outer tube is sealed with the sealing device that includes a

seal shield. High-pressure gas/air is filled in the collapsible chamber enclosed in the canister through a gas/air filling nozzle by piercing the seal provided in the hollow screw fitted in the cap of the collapsible chamber after unscrewing the screw with the male threads engaged in the female threads on the hollow screw. The oil filled in the shock absorber does not come in contact with the gas/air filled in the collapsible chamber; the emulsification of oil is eliminated securing the density of the oil intact. The gas/air filled in the collapsible chamber that escapes over a period of time can be easily recharged through gas/air filling nozzle by piercing the seal provided in the hollow screw after unscrewing the screw with male threads from the female threads on the hollow screw. The seal provided in the hollow screw when damaged due to frequent piercing to recharge the gas/air can be replaced. Having recharged the gas/air re-screwing the screw with the male threads in the female threads on the hollow screw seals the collapsible chamber. The dampening force in compression is generated through the base valve provided in the inner tube that is supplemented by the gas/air pressure to absorb and dampen the shocks in compression due to bad road conditions.
As shown in the accompanying drawings, Figure 1 is the cross sectional view and illustrates the twin tube canister attached oleo-pneumatic shock absorber (100) for land vehicles and the like, according to the present invention that consists of an outer tube (1) that houses an inner tube (2). A piston rod (4) fitted with the piston (5) is inserted in the inner tube (2) fitted with a base valve (6). The top open end of the outer tube (1) is sealed with a sealing device (7) including a seal shield. A canister (3) is attached to the outer tube (1) at its bottom end. A collapsible chamber (8) having a cap (9) is provided inside the canister (3). A hollow screw (12), provided with a seal

(11), preferable made of rubber or the like material, at its one end and female threads at its other end, is provided on the cap (9) through an "Coring (15). Another screw (10) with male threads is provided in the female threads on the hollow screw (12) through an "0"-ring (14). The collapsible chamber (8) fitted with the cap (9) is inserted in the canister (3) and sealed with a circlip (13).
Figure 2 is the enlarged cross sectional view illustrating the portion of the oleo-pneumatic shock absorber (100) marked "X X" in Figure 1.
Figure 3 illustrate an oleo-pneumatic shock absorber (200) fitted with a canister (112) that is housing a collapsible chamber therein in accordance with another embodiment of the present disclosure. The oleo-pneumatic shock absorber (200) includes an outer tube (101) that houses an inner tube (102). A piston rod (103) that is connected to a piston assembly (104) inserted in the inner tube (102). The oleo-pneumatic shock absorber (200) includes a bump stop (105), an outer coil spring (106), an oil seal (107) closing one end of the inner tube (102), a rod guide (108), a spring pre-load adjuster (109) and a base valve assembly (110). The oleo-pneumatic shock absorber (200) further includes a mounting block bush (111) for facilitating mounting of the oleo-pneumatic shock absorber (200) on the vehicle. The outer tube (101) of the oleo-pneumatic shock absorber (200) is attached to the canister (112) at its bottom end. The canister (112) includes a collapsible gas chamber/membrane (113), wherein the collapsible gas chamber/membrane (113) is closed by a gas cap (114) and a gas seal (115). The oleo-pneumatic shock absorber (200) includes a bump stop. (105). The bump stop. (105) acts as a parallel spring acting in parallel to the main

suspension spring in the rear mono suspension structure. The main spring takes up 65-75 percent of the suspension load while 25-35 percent of the suspension load at the end of the stroke is taken by the bump stop. (105). Such a configuration of the oleo-pneumatic shock absorber (200) reduces the mass of the spring and reduces space requirement within the suspension as the gas chamber has been shifted to a side location rather than in series.
In accordance with another embodiment, the canister (212) includes a floating separator piston (216) sliding inside the canister (212) (illustrated in Figure 4), the floating separator piston (216) slides inside the canister (212) under action of the fluid pressure exerted thereon by the oil filled in said inner tube (102) for defining the gas chamber/membrane (213) inside the canister (212). The canister (212) further includes a gas cap (214) and a gas seal (215) for closing the other end of the canister (212). Such a configuration of the canister (212) facilitates the shock absorber fitted therewith in withstanding higher gas pressures, thereby enabling the oleo-pneumatic shock absorber fitted with the canister (212) to support higher magnitude of damping forces and preventing foaming of the oil as is in case of conventional shock absorbers. The oleo-pneumatic shock absorber (200) in accordance with the present disclosure finds application in suspension system for motorcycles, particularly, rear mono-suspension motorcycles.
TECHNICAL ADVANTAGES
The advantages of the oleo-pneumatic shock absorbers for land vehicles and the like, according to this invention, having a canister attached to the outer tube and the base valve attached to the inner tube of the shock absorber are

the base valve provided in the inner tube dampens the shocks in compression. Secondly, the shocks are further dampened in compression progressively due to gas/air pressure filled in the collapsible chamber provided in the canister attached to the outer tube of the shock absorber. Thirdly, the oil filled in the shock absorber does not come in contact with the gas/air filled in the collapsible chamber; the emulsification of oil is eliminated securing the density of the oil intact. Fourthly, the escape of the gas/air filled in the collapsible chamber provided in the canister over a period of time, can be re-charged through gas/air filling nozzle by piercing the seaJ provided in the hollow screw after unscrewing the screw with male threads from the female threads on the hollow screw Having recharged the gas/air re screwing the screw with male threads in the female threads on the hollow screw seals the collapsible chamber. Fifthly the seal provided in the hollow screw when damaged due to frequent piercing to recharge the gas/air, can be replaced. Sixthly, when the efficiency of the shock absorber is reduced below permissible limits, the performance can be corrected by recharging the gas/air and/or replacing the seal at minimum costs without incurring the heavy costs of replacing the entire shock absorber. These advantages thus not only enhance the performance but also increase the life of the shock absorbers for land vehicles and the like.
Since many apparently different embodiments of the present invention could be made without departing from the scope and spirit thereof as will be apparent to those skilled in the art, it is intended that the description of the invention herein be interpreted as being illustrative only and not limiting in any manner.

In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only. The numerical values given of various physical parameters and dimensions are only approximations and it is envisaged that the values higher or lower than the numerical values assigned to the parameters, dimensions and quantities fall within the scope of the invention.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We Claim:
1. An improved oleo-pneumatic shock absorber for land vehicles and the like comprising a twin tube consisting of an outer tube housing and an inner tube, the inner tube is fitted with a base valve; a piston rod fitted in a piston inserted in the inner tube, the top open end of the outer tube sealed with a sealing device including a seal shield; a canister attached to the outer tube at its bottom end characterized in that a collapsible chamber having a cap is provided inside the canister, a hollow screw having a seal at its one end and female threads at its other end is provided on the cap, another screw with male threads is provided to engage the female threads on the hollow screw and the collapsible chamber inserted in the canister is sealed with a circlip, characterized in that improved oleo-pneumatic shock absorber comprising a bump stop concentrically disposed at an operative top end of said main suspension spring for taking up a portion of suspension load acting on said main suspension spring and said canister comprising a floating separator piston adapted to slide inside said canister due to fluid pressure exerted thereon by the oil filled in said inner tube.
2. The oleo-pneumatic shock absorber as claimed in claim 1, wherein the seal provided on the hollow screw is made of rubber or the like material.
3. The oleo-pneumatic shock absorber for land vehicles and the like
substantially as herein described and illustrated in the accompanying
drawings.

4. The oleo-pneumatic shock absorber as claimed in claim 1, wherein the bump stop is made of polyurethane material.