DESC:FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules, 2005

COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

TITLE OF THE INVENTION
“TWIN TUBE TYPE SHOCK ABSORBER”

Endurance Technologies Limited
E-92, M.I.D.C. Industrial Area, Waluj,
Aurangabad – 431136, Maharashtra, India

The following specification describes the nature of the invention and the manner in which it is to be performed.

Field of Invention

The present invention relates to the rear shock absorber for a two / three wheeled vehicle. More particularly the invention relates to a twin tube gas filled type shock absorber adapted to withstand and dampen the forces of damping fluid in the vicinity of sealing assembly and thereby protect the oil seal from damage.

Background of the Invention

A twin tube type shock absorber typically comprises of an inner tube and an outer tube wherein a piston assembly is telescopically disposed within the said inner tube and a rod guide is fitted in between the outer tube and the inner tube so as to close the top end of the inner tube. The said rod guide is further fitted with an oil seal at its top end wherein the said oil seal is serves to seal the shock absorber. The said oil seal also works as a non-return valve during the compression stroke of the shock absorber thus preventing the flow of the damping fluid from the outer tube to the inner tube thereby.

The rebound stroke in the conventional twin tube type shock absorbers causes the damping fluid to flow from the inner tube to the outer tube by following the fluid path from the functional clearance in between the piston rod and the guide bush where it enters into the outer tube via deflecting the NRV (non-return valve) lips of the oil seal and flowing through the drainage passage provided in the rod guide. When the fluid enters from the inner tube to the area in between the rod guide and the oil seal, it acts as high velocity jet due to sudden decrease in the effective flow area at the interface of the piston rod and the guide bush. The high velocity jet impinges directly over the functional lip of the oil seal wherein the said functional lip intends to prevent the leakage of the damping fluid from the interface in between the piston rod and the functional lip of the oil seal. The said high jet impingement thus leads to an early failure of the oil seal ultimately leading to the failure of whole shock absorber unit. Hence there is a pressing need to develop a twin tube shock absorber that addresses the lacunae of the conventional shock absorbers.

Objectives of the Present Invention

The main object of the present invention is to develop a twin tube shock absorber. More particularly, the objective of the invention is to develop a gas filled high damping twin tube shock absorber.

Another objective of the present invention is to provide a twin tube shock absorber adapted to withstand high velocity jet impacts of the damping fluid generated during the rebound stroke of the shock absorber.

Yet another objective of the present invention is to develop a twin tube shock absorber being able to withstand and dampen the high velocity jet impacts of the damping fluid generated during the rebound stroke by the virtue of normal / side load.

Yet another objective of the present invention is to provide a uniquely profiled rod guide for a twin tube type shock absorber wherein the said rod guide is adapted to accumulate and drain the required amount of the damping fluid so as to prevent the seal lips of the oil seal from being damaged.
Still another objective of the present invention is to provide a check valve assembly configured to prevent the flow of the damping fluid from the outer tube of the shock absorber to the inner tube during the compression stroke.

Brief Description of Drawings

This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein and advantages thereof will be better understood from the following description when read with reference to the following drawings, wherein

Figure 1 illustrates the front view of the twin tube shock absorber of the present invention.

Figure 2 shows the cut sectional diagram of piston rod assembly of the twin tube shock absorber in accordance with the present invention.

Figure 3 depicts the cut sectional diagram of outer tube assembly of the twin tube shock absorber in accordance with the present invention.

Figure 4 illustrates the front cut sectional view of the twin tube shock absorber of the present invention.

Figures 5 and 5a presents the side cut section view of the twin tube shock absorber and the detailed view of the check valve assembly, respectively as per the present invention.
Figures 6 illustrates the cut sectional view of the rod guide of the twin tube shock absorber of the present invention.

Figure 7 illustrates the top view of the washer of the check valve assembly of twin tube shock absorber of the present invention.

Detailed Description of the Present Invention

The invention will now be described in detail with reference to the accompanying drawings which must not be viewed as restricting the scope and ambit of the invention. Referring to Figs.1 to 4, the twin tube shock absorber (500) comprises of a piston rod assembly (100), an outer tube assembly (150), a top cap (80) and a check valve assembly (CV). The piston rod assembly (100) further comprises of a piston rod (10), an oil seal (20), a rod guide (30), a DU bush (35), a rebound spring (40), a support plate (50), a piston (60), a piston support plate (65) and a nut (70).

Referring to Fig. 2, the piston rod (10) of the piston rod assembly (100) is configured to have a cylindrical stepped profile throughout its length forming three portions viz. a proximal portion (10P1), a central portion (10P2) and a distal portion (10P3). The rod guide (30) in accordance with the present invention (refer Figs. 2 and 6) is made from a metal preferably selected from aluminum and is configured to have a stepped cylindrical body having a first cylindrical body portion (30A) and a second cylindrical body portion (30B). The said second cylindrical body portion (30B) of the rod guide (30) has a lesser outer diameter than the outer diameter of the first cylindrical body portion (30A) of the rod guide (30). The first cylindrical body portion (30A) is configured to have a circular cavity (30R) bored therein wherein the said cavity (30R) forms a trapezoidal cross-section having gradually increasing diameter from its lower end to its top end. This cavity (30R) works as the reservoir for the damping fluid and has a plurality of thorough passages (30P) bored therein to extend across the first cylindrical body portion (30A). The thorough passages (30P) of the reservoir (30R) of the rod guide (30) are formed in an inclined manner such that the geometrical axis (A-A) of the passage (30P) is at an angle a with respect to the vertical axis (X-X) of the piston rod (10) and said angle a is in the range of 8° to 15° from the vertical axis (X-X) of the piston rod (10). The said thorough passages are configured to facilitate the flow of the damping fluid from the inner tube (120) to the outer tube (110) and the number of said passages (30P) varies from minimum three passages to maximum of five passages formed at equiangular orientation to each other.

The second cylindrical body portion (30B) of the rod guide (30) is configured to have a concentric stepped opening (30SP) formed therein to allow the passage of the piston rod (10) of the piston rod assembly (100). The said stepped opening (30SP) is configured to have a chamfer (30F) at its mouth and a step (30ST) formed proximal to the reservoir (30R) of the rod guide (30). Thus, the stepped opening (30SP) of the second cylindrical body portion (30B) seamlessly merges with the cavity (30R) the first cylindrical body portion (30A) through the step (30ST) of the said stepped opening (30SP). The chamfer (30F) allows the smooth entry of the piston rod (10) and the step (30ST) of the stepped opening (30SP) is configured to house the guide bush (35) snuggly fitted therein. The inner diameter stepped opening (30SP) of the second cylindrical body portion (30B) of the rod guide (30) is configured to guide the piston rod (10) there through and outer peripheral surface of the first cylindrical body portion (30A) of the rod guide (30) guides the outer tube (110) while the outer peripheral surface of the second cylindrical body portion (30B) guides the inner tube (120) thereon.
The piston (60) of the piston rod (10) of the piston rod assembly (100) is fitted on the distal portion (10P3) of the piston rod (10) and is locked into its position by the nut (70). A set of shims (60S1 and 60S2) is placed above and below the piston (60) in a manner to partially cover a plurality of oil passages (60P) formed in the piston (60). The piston support plate (65) is positioned in between the nut (70) and the set of shims (60S2) and the support plate (50) is positioned in between the set of shims (60S1) and the piston (60) at the distal portion (10P3) of the piston rod (10). The rebound spring (40) is sleeved over the piston rod (10) at its central portion (10P2) in a manner such that the lower face of the said spring (40) abuts with the support plate (50) and the top face of the said spring (40) abuts with the rod guide (30). The oil seal (20) is positioned in a press-fit manner over the first cylindrical body portion (30A) of the rod guide (30) so as to cover the reservoir cavity (30R) of the rod guide (30). The DU bush (35) is snuggly fitted in the stepped opening (30SP) of the second cylindrical body portion (30B) of the rod guide (30) and the outer peripheral surface of the piston rod (10). The said DU bush (35) is adapted to reduce the friction and facilitate the smooth movement of the piston rod (10) over the rod guide (30).

Referring to Fig. 3, the outer tube assembly (150) comprises of an outer tube (110), an inner tube (120), a base valve (140) and a bottom cap (130). The outer tube (110) is configured to have a step (110S) formed at its top end. The bottom cap (130) is configured to have a body portion (130B) and an integral gas canister (130C) wherein the said body portion (130B) is connected to the said canister (130C) with the help of an extending arm (130A). The said extending arm (130A) has an internal passage (130P) fluidly connecting the internal regions of the gas canister (130C) and the body portion (130B) of the bottom cap (130). The intelligent connection of gas canister (130C) with the bottom cap (130) is configured to keep the damping fluid under sufficient pressure at all times thereby avoiding foaming of damping fluid/cavitation in the shock absorber (500) unit during its operation. The outer tube (110) is fixed at its bottom end with the body portion (130B) of the bottom cap (130) with the help of threaded joint. The base valve (140) is mounted at the inner bottom surface of the bottom cap (130) and the inner tube (120) is press fitted with the base valve (140) in a manner such that the inner tube (120) is concentrically located within the outer tube (110), and thus forming the twin tube structure of the shock absorber.

The uniquely constructed check valve assembly (CV) has a washer (170), a check valve spring (135) and a check valve (125). The said check valve assembly (CV) is positioned in the annular space between the inner tube (120) and the outer tube (110) of the outer tube assembly (150) exactly below the rod guide (30). The washer (170) is a circular disc configured to have a plurality of thorough slots (170S) formed at its inner circumferential surface. The said slots (170S) are formed in a number ranging from four slots to six slots positioned at equiangular distance with respect to each other.

The twin tube shock absorber (500) is assembled by positioning the washer (170) of the check valve assembly (CV) at the stepped portion (110S) of the outer tube (110) of the outer tube assembly (150). The check valve spring (135) is concentrically positioned over the washer (170) in between the inner peripheral surface of the outer tube (110) and the outer peripheral surface of the inner tube (120). The check valve (125) is placed at the top end of the check valve spring (135) and the outer tube assembly (150) is then filled with the damping fluid followed by the positioning of the piston rod assembly (100) within the outer tube assembly (150) in a manner such that the piston rod (10) of the piston rod assembly (100) is able slide within the inner tube (120) along with the rebound spring (40) and the piston (60). The outer tube (110) is closed at its top end by spinning and/or crimping process in a manner such that the folded end of said outer tube (110) is placed over the oil seal (20). The top cap (80) is fixed to the top end of the outer tube (110) by press fitting so as to close the said twin tube shock absorber (500) from the top end.

The said shock absorber (500) is configured to form a plurality of fluid chambers in its assembled condition viz. chamber I, chamber II, chamber III, chamber IV and the chamber V. The chamber I is formed in between the piston (60) and the base valve (140) and the chamber II is formed in between the support plate (50) and the rod guide (30). The chamber III is formed in between the annular space of the inner peripheral surface of the outer tube (110) and the outer peripheral surface of the inner tube (120) and the chamber IV is formed at the circular cavity (30R) of the rod guide (30) and the oil seal (20). The chamber V is formed in between the space below the base valve (140) and the passage (130P) of the extending arm (130A) of the gas canister (130C).

During the compression stroke of the shock absorber (500), the piston rod (10) slides within the inner tube (120) of the outer tube assembly (150) along with the piston (60). The piston (60) causes to displace the damping fluid from chamber-I to the chamber II by the virtue of the oil passages (60P) provided in the piston (60) while some of the damping fluid also passes from the chamber-I to the chamber-III and from the chamber-I to chamber-V through the base valve (140). The damping fluid is not allowed to pass from the chamber-III to the chamber-IV during the compression stroke since the check valve (125) is pressurized by the compressive forces of the check valve spring (135) against the passage (30P) of the rod guide (30), acted upon by the washer (170) due to fluid pressure in the chamber-III. Thus, the check valve assembly (CV) acts as a non-returning valve in this condition.

During the rebound stroke of the shock absorber (500), the piston (60) of the piston rod assembly (100) retraces back to its original position. This causes the displacement of the damping fluid from the chamber-II to the chamber-I by the virtue of the oil passages (60P) provided in the piston (60) and from chamber-V to chamber-I through the base valve (140). Also, the damping fluid passes from the chamber-II to the chamber-IV through the functional clearance in between the DU bush (35) and the piston rod (10). The fluid from the chamber-IV further passes to the chamber-III through the passage (30P) by deflecting the check valve (125).

As a fact to be noted, the rod guide (30) is intelligently optimized in a manner to prevent the damage of the functional lips of the oil seal from the high velocity jet of damping fluid impinging in the chamber-IV. It is a well-known fact that the velocity of the jet (damping fluid) is increased as soon as the damping fluid enters from the chamber-II to the chamber-IV due to the reduction in flow area as laid down by the continuity equation which states
A1V1 = A2V2
wherein ,
A1 = Area of the chamber-II;
A2 = Area of the chamber-IV;
V1 = Velocity of damping fluid in the chamber-II; and
V2 = Velocity of damping fluid in the chamber-IV

Thus, the rod guide (30) is designed to have the reservoir (30R) optimized in a manner such that it accumulates a certain required amount of the damping fluid while also allowing the drainage of the damping fluid simultaneously. The following equation depicts the rate of accumulation being the subtractive unit of the rate of influx and rate of efflux of the damping fluid in and out of the reservoir (30R), considering the reservoir (30R) to be the control volume,
dq/dt+?Sj.dS=?
wherein ,
q = total amount of the fluid in control volume;
S = an imaginary closed surface, that encloses a volume;
?S dS = surface integral over that closed surface;
j = flux of q;
t = time; and
S = net rate that q is being produced inside the volume.

The accumulation of the damping fluid within the oil reservoir / cavity (30R) dampens the energy of the high velocity jet of damping fluid in the said reservoir / cavity (30R) of the rod guide (30) thus preventing the damage of the seal lip of the oil seal (20) thereby. Thus, optimum amount of the damping fluid to be accumulated within the reservoir (30R) for dampening the energy of high velocity jet of damping fluid in being followed / controlled by the following relations:
Dm=k1*Di
Dm=k2*3dm
wherein ,
k1 = volume influx constant and k1 ~ 1.5 - 2.5;
k2 = volume efflux constant and k2 ~ 3.5 – 4.5;
Dm = mean diameter of the reservoir of the rod guide;
Di = internal diameter of the second cylindrical portion of the rod guide; and
dm = mean diameter of the passage of the reservoir of the rod guide.

Thus, the unique construction of rod guide (30) having a uniquely profiled thorough passages (30P) formed at the reservoir (30R) and the said reservoir (30R) having a mean diameter (Dm) is so optimized that it always maintains / accumulates the required amount of damping fluid in the said reservoir (30R) to dampen the energy of high velocity jet of damping fluid while allowing some of the fluid to be drained therefrom. This unique rod guide having the rate of accumulation greater that the rate of discharge of the damping fluid leads to prevent the damage to the seal lips and thereby leads to prevent the failure of the oil seal (20). This unique construction of rod guide (30) leads to improved life of oil seal (20) by 12 to 20% thus increasing the overall life of the shock absorber (500) as compared to conventional shock absorbers. Further, the check valve assembly (CV) of the shock absorber (500) helps achieving the required damping force during the rebound stroke of the shock absorber (500).

The disclosed invention hence overcomes the limitation of the known solutions of high damping twin tube shock absorbers. The shock absorber (500) of a vehicle having the uniquely profiled rod guide (30) and the check valve assembly (CV) as described above, has an excellent capability to withstand the high damping forces of the damping fluid. A person skilled in the art can change positioning of the said check valve assembly (CV) or the profile of the reservoir (30R) of the rod guide (30) without carrying out any significant change to the features of the shock absorber (500). Hence, such changes must not be viewed as taking the emerging variants/embodiments out of the scope of claims of the disclosed invention.

The twin tube shock absorber (500) in accordance with the disclosed embodiment provides the following technical advantages that contributes to the advancement of technology and thereby establishes the inventive step:
It enhances the life of damper and oil seal in terms of oil leakage.
It provides consistent gas load pressure contributing to generate consistent damping.
It provides improved damping characteristic curve for required damping conditions.
It reduces the DF (damping force) losses by the virtue of the uniquely profiled and intelligently positioned check valve assembly.
It provides an economical solution for preventing the damage to seal lips and thereby enhancing the life of oil seal wherein the high damping forces / jets are generated in a twin tube type shock absorber.

The disclosed invention hence overcomes the limitation of the systems forming state of the art. 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. ,CLAIMS:We Claim

A twin tube type shock absorber (500) comprising of
a piston rod assembly (100) having a uniquely profiled rod guide (30), a piston rod (10), an oil seal (20), a DU bush (35), a rebound spring (40), a support plate (50), a piston (60), a piston support plate (65) and a nut (70);
an outer tube assembly (150) having an outer tube (110), an inner tube (120), a base valve (140) and a bottom cap (130); a check valve assembly (CV) having a washer (170), a check valve spring (135) and a check valve (125); and
a top cap (80)
wherein,
said rod guide (30) of the piston rod assembly (100) is configured to have a stepped cylindrical body having a first cylindrical body portion (30A) and a second cylindrical body portion (30B) and the said second cylindrical portion (30B) has an outer diameter lesser than the outer diameter of first cylindrical body portion (30A);
said first cylindrical body portion (30A) has an annular cavity /reservoir (30R) with a trapezoidal cross section having gradually increasing diameter from its lower end to its top end;
said first cylindrical body portion (30A) of the rod guide (30) is configured to guide the outer tube (110) and the outer peripheral surface of the second cylindrical body portion (30B) is configured to guide the inner tube (120) when the said rod guide (30) is positioned in the outer tube assembly (150);
the check valve assembly (CV) of the outer tube assembly (150) is positioned in between the inner tube (120) and the outer tube (110) of the outer tube assembly (150);
said piston rod assembly (100) is telescopically positioned within the outer tube assembly (150) and said outer tube assembly (150) has the damping fluid filled therein;
said outer tube (110) of the outer tube assembly (150) is closed at its top end by spinning and/or crimping process and the top cap (80) is fixed to the top end of the outer tube (110) by press fitting so as to close the said twin tube shock absorber (500) from the top end; and
said shock absorber (500) is configured to form a plurality of fluid chambers in its assembled condition namely chamber-I, chamber-II, chamber-III, chamber-IV and the chamber-V.

The twin tube type shock absorber (500) as claimed in claim 1, wherein
the chamber-I is formed in between the piston (60) and the base valve (140) whereas the chamber-II is formed in between the support plate (50) and the rod guide (30);
the chamber-III is formed in between the annular space of the inner peripheral surface of the outer tube (110) and the outer peripheral surface of the inner tube (120) whereas the chamber-IV is formed at the circular cavity (30R) of the first cylindrical body (30A) of the rod guide (30) and the oil seal (20); and
the chamber-V is formed in between the space below the base valve (140) and a passage (130P) of an extending arm (130A) of a gas canister (130C) of the bottom cap (130).
The twin tube type shock absorber (500) as claimed in claim 2, wherein
the first cylindrical body portion (30A) of the rod guide (30) is configured to have a plurality of thorough passages (30P) bored therein and passages (30) extend across the first cylindrical body portion (30A);
said thorough passages (30P) of the rod guide (30) are formed in an inclined manner and the geometrical axis (A-A) of the passages (30P) is at an angle a with respect to the vertical axis (X-X) of the piston rod (10);
said thorough passages (30P) are configured to facilitate the flow of the damping fluid from the inner tube (120), particularly the chamber-IV to the outer tube (110), particularly the chamber-III;
the second cylindrical portion (30B) of the rod guide (30) is configured to have a stepped opening (30SP) formed therein to allow the passage of the piston rod (10) of the piston rod assembly (100);
said stepped opening (30SP) is configured to have a chamfer (30F) at its mouth and a step (30ST) formed proximal to the reservoir (30R) of the rod guide (30); and
said chamfer (30F) is configured to allow the smooth entry of the piston rod (10) and the step (30ST) is configured to house the guide bush (35) snuggly fitted therein.

The twin tube type shock absorber (500) as claimed in claim 3, wherein
the angle a made by the through passages (30P) with the vertical axis (X-X) of the piston rod (10) ranges from 8° to 15°;
the thorough passages (30P) of the rod guide (30) ranges from minimum three passage to maximum of five passages and each of the passages (30P) are at equiangular orientation to each other; and
the stepped opening (30SP) of the second cylindrical body portion (30B) is configured to seamlessly merge with the cavity (30R) the first cylindrical body portion (30A) through the step (30ST) of the said stepped opening (30SP).

The twin tube type shock absorber (500) as claimed in claim 4, wherein the rod guide (30) has an optimized cavity / reservoir (30R) configured to accumulate optimum amount of the damping fluid while simultaneously allowing the drainage of the damping fluid and the rate of accumulation being the subtractive unit of the rate of influx and rate of efflux of the damping fluid in and out being controlled by said cavity / reservoir (30R) and is represented as
dq/dt+?Sj.dS=?
wherein ,
q = total amount of the fluid in control volume;
S = an imaginary closed surface, that encloses a volume;
?S dS = surface integral over that closed surface;
j = flux of q;
t = time; and
S = net rate that q is being produced inside the volume.

The twin tube type shock absorber (500) as claimed in claim 5, wherein
the cavity / reservoir (30R) of the rod guide (30) of the piston rod assembly (100) is configured to accumulate optimum amount of the damping fluid and accumulation of the damping fluid within the oil reservoir / cavity (30R) is configured to dampen the energy of the high velocity jet of damping fluid in the said reservoir / cavity (30R) of the rod guide (30) thereby preventing the damage of the seal lip of the oil seal (20); and
the optimum amount of the damping fluid to be accumulated within the reservoir (30R) for dampening the energy of high velocity jet of damping fluid in being followed / controlled by the following relations
Dm=k1*Di
Dm=k2*3dm
where, k1 is the volume influx constant and ranges from 1.5 to 2.5; k2 is the volume efflux constant ranging from 3.5 – 4.5; Dm is the mean diameter of the reservoir of the rod guide; Di is the internal diameter of the stepped opening of the second cylindrical portion of the rod guide; and dm is the mean diameter of the passage of the reservoir of the rod guide.

The twin tube type shock absorber (500) as claimed in claim 6, wherein
the piston rod assembly (100) along with the piston (60) is configured to displace the damping fluid from chamber-I to the chamber-II by the virtue of the oil passages (60P) of the piston (60); and from the chamber-I to the chambers III and V through the base valve (140) during the compression stroke of the shock absorber (500); and
the check valve (125) is configured to act as a non-returning valve and prevent the passage of damping fluid from the chamber-III to the chamber-IV during the compression stroke by the virtue of the compressive forces of the check valve spring (135) against the passage (30P) of the rod guide (30) acted upon by the washer (170) of the check valve assembly (CV) due to fluid pressure in the chamber-III.

The twin tube type shock absorber (500) as claimed in claim 7, wherein
the washer (170) of the check valve assembly (CV) is a circular disc configured to have four thorough slots (170S) formed at its inner circumferential surface and is positioned a stepped portion (110S) of the outer tube (110) of the outer tube assembly (150);
the check valve spring (135) of the check valve assembly (CV) is concentrically positioned over said washer (170) in between the inner peripheral surface of the outer tube (110) and the outer peripheral surface of the inner tube (120); and
the check valve (125) is positioned at the top end of said check valve spring (135).

The twin tube type shock absorber (500) as claimed in claim 8, wherein
the inner tube (120) of the outer tube assembly (150) is press fitted with the base valve (140) at its bottom end and said base valve (140) is mounted at the inner bottom surface of the bottom cap (130) in a manner that the inner tube (120) is concentrically located within the outer tube (110);
said bottom cap (130) is configured to have a body portion (130B) and an integral gas canister (130C) wherein the said body portion (130B) is connected to the said canister (130C) with the help of an extending arm (130A);
said outer tube (110) is fixed at its bottom end with the body portion (130B) of the bottom cap (130) with the help of threaded joint;
said extending arm (130A) has an internal passage (130P) fluidly connecting the internal regions of the gas canister (130C) and the body portion (130B) of the bottom cap (130); and
said gas canister (130C) so connected with the bottom cap (130) is configured to keep the damping fluid under pressure at all times thereby avoiding foaming of damping fluid/cavitation in the shock absorber (500) unit during its operation.

The twin tube type shock absorber (500) as claimed in claim 9, wherein
the inner tube (120) of outer tube assembly (150) is configured to house the piston rod (10) along with the rebound spring (40) and the piston (60) of the piston rod assembly (100) in a sliding manner;
said piston rod (10) of the piston rod assembly (100) is configured to have a cylindrical stepped profile throughout its length forming three portions namely a proximal portion (10P1), a central portion (10P2) and a distal portion (10P3);
said piston (60) of the piston rod (10) of the piston rod assembly (100) is fitted on the distal portion (10P3) of the piston rod (10) and locked into its position by the nut (70);
a set of shims (60S1 and 60S2) is positioned above and below the piston (60) to partially cover a plurality of oil passages (60P) of the piston (60);
the piston support plate (65) is positioned in between the nut (70) and the set of shims (60S2) and the support plate (50) is positioned in between the set of shims (60S1) and the piston (60) at the distal portion (10P3) of the piston rod (10);
the rebound spring (40) is sleeved over the piston rod (10) at its central portion (10P2) abutting the lower face of the said spring (40) with the support plate (50) and the top face of the said spring (40) with the rod guide (30);
the oil seal (20) is positioned in a press-fit manner over the rod guide (30) so as to cover the cavity / reservoir (30R) of the rod guide (30); and
the DU bush (35) is snuggly fitted in the stepped opening (30SP) of the second cylindrical portion (30B) of the rod guide (30) and is configured to reduce the friction and facilitate the smooth movement of the piston rod (10) through the rod guide (30).

Dated this 22nd day of Mar. 2025

Sahastrarashmi Pund
Head – IPR
Endurance Technologies Ltd.

To,
The Controller of Patents,
The Patent Office, at Mumbai