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
“FRONT FORK ASSEMBLY FOR A TWO AND THREE WHEELED VEHICLES”

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

The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed.
Field of Invention

[001] The present invention is related to suspension system for a motor vehicle. More particularly, the invention is related to front fork leg assembly for a vehicle, wherein the assembly has a pressure tube so intelligently placed in the bottom case in such a way that it drastically reduces the requirement of the oil and makes the front fork leg assembly leak proof.

Background of the Invention

[002] Suspension is one of the important systems of the vehicle architecture as it contributes to vehicle handling and provides safety and comfort by keeping the vehicle user comfortably isolated from road bumps and vibrations. Various forms of Suspension Systems have been proposed and developed for bikes, scooters and three wheelers over the period of time. The most common form of front fork assembly of the suspension system comprises a pair of telescopic assemblies between which the front wheel is mounted. Each telescoping assembly comprises an outer tube, and an inner tube which is free to move in and out of the outer tube and is cushioned in some manner, as by springs and/or a hydraulic System.

[003] The conventional front fork construction having inner tube, outer tube, oil seal, dust seal, cap oil lock, main spring, seat pipe, fork bolt, socket headed bolt, etc. experiences the leakage of oil after its usage for a specific period of time, which leads to deterioration of the suspension performance and life of the front fork. The oil leakage prone points/sources in this conventional construction are oil seal (due to dent on fork pipe and/or contamination in oil), copper washer at socket headed bolt (due to the clearance between bottom case and socket headed bolt), O-ring at the joinery of fork bolt and fork pipe (due to press fit clearance between fork pipe and fork bolt), and the bottom case (due to casting porosity, if any). Several pro-active measures have been taken by the industry experts to improve the oil seal material so as to withstand higher abuse due to all external factors in the front forks available in public domain. Also the measures are taken to curtail the oil contamination to the minimal level. Still there is a huge gap to address the leakage issues of front fork particularly at the fork bolt, at the socketed bolt and from the bottom case. Therefore, in order to address this issue of oil leakage in front fork, the present invention is being proposed to provide the leak proof front fork.

Objectives of the Invention

[004] The main object of the present invention is to provide a front fork leg assembly for a two and three wheeled vehicles.

[005] Another object of the present invention is to provide a front fork leg assembly that drastically reduces the number of components making the front fork very simple and light weight.

[006] Still another object of the present invention is to provide a front fork leg that drastically reduces the oil requirement and yet imparting the superior damping performance.
[007] Yet the object of the present invention is to provide a front fork leg assembly that blocks all the possible leakage sources and thereby provides a leak proof front fork.

[008] It is yet another objective of the invention to provide a front fork leg assembly with a unique construction of the pressure tube that totally eliminates the contact of the oil with the fork pipe and the bottom case making it leak proof.

[009] Further, the objective of the invention to provide a front fork leg assembly that imparts superior performance, improves the life of front fork and provides cost effective and easy to manufacture solution.

Brief Description of the Drawings

[0010] This invention is illustrated in the accompanying drawings, throughout which like reference letters / numerals indicate corresponding parts in the various figures. The embodiment herein and advantages thereof will be better understood from the following description when read with reference to the following drawings, wherein

[0011] Figure 1a discloses an isometric cut view of the front fork suspension assembly in accordance with the present invention.

[0012] Figure 1b discloses an isometric view of the front fork leg in accordance with the present invention.

[0013] Figure 2 presents the exploded view of the front fork leg assembly of the present invention.

[0014] Figure 3 depicts the cut view of the piston rod assembly of the present invention.

[0015] Figures 4a, 4b and 4c show a cut sectional view of the front fork leg assembly in fully free condition, enlarged view disclosing the fitment of the rod guide and pressure tube and the enlarged view disclosing the fitment of the adaptor and pressure tube, respectively in accordance with the embodiment of the present invention.

[0016] Figures 5a and 5b show a cut sectional views of a front fork leg in fully free condition and fully compressed condition, respectively in accordance with the embodiment of the present invention.

Detailed Description of the Present Invention

[0017] Referring to Fig. 1a, the front fork suspension assembly (600) comprises of a pair of leg assemblies (500), a triple clamp assembly (625) and a steering shaft (650). The fork legs (500) are joined with each other through the triple clamp assembly (625) and the triple clamp assembly is in mechanical communication with the handle of a vehicle through the steering shaft (650). Referring to Figs. 1b to 4, the front fork leg assembly (500) comprises of a fork pipe (10), a bottom case (20), a pressure tube (30), a top cap (40), a main spring (50), a sealing assembly (60), a fork bolt (70), a piston rod assembly (80), an adaptor (90) and a rubber bump stop (95). The piston rod assembly (80) comprises of a piston rod (82) and a piston assembly (85). The piston assembly (85) comprises of an oil seal (86), a rod guide (87), a rebound spring (88), a washer (W), a set of shims (85S) and a piston (89).

[0018] The fork bolt (70) is fitted at the top end of the fork pipe (10) through the threaded joinery and the fork pipe (10) is telescopically disposed within the bottom case (20). The piston rod (82) of the piston assembly (80) is configured to have a proximal end (82P) and a distal end (82D). The proximal end (82P) of the piston rod (82) is fitted with the fork bolt (70) through the threaded joint and locked there with the help of a nut (83). The nut (83) not only locks the piston rod (82) with the fork bolt (70) but also it works as a guide for the main spring (50).

[0019] The pressure tube (30) at its one end (E1) is fitted with the bottom case (20) at its lower end through the adaptor (90) and a socketed bolt (92). The adaptor (90) is press fitted with an O-ring (91) inside the pressure tube (30) at its lower end and the socketed bolt (92) locks the pressure tube (30) with the bottom case (20) through its threaded joinery with the adaptor (90). The rubber bump stop (95) is concentrically located within the bottom case (20) and fixed at the lower end of the pressure tube (30) around its outer peripheral surface and inside the bottom case (20). The other end (E2) of the pressure tube (30) is fitted with the top cap (40) concentrically mounted over it from the outer side through the treaded joinery. The rubber bump stop (95) absorbs the shock load from the fork pipe (10) and prevents the bottoming of the fork pipe (10) during the extreme compression stroke of the fork leg (500).

[0020] The piston rod (82) passes through the top cap (40) inside the pressure tube (30) and is fitted with the piston assembly (85) at its distal end (82D). Thus, the top inner space of the pressure tube (30) houses the piston assembly (85) mounted on the distal end (82D) of the piston rod (82). The piston assembly (85) has a washer (W) mounted at the top followed by the oil seal (86) followed by the rod guide (87). The rod guide (87) is configured to have a depression (87D) on its outer surface and the said depression (87D) receives the projections (30P) given on the inner surface of pressure tube (30). The depression (87D) and the matching projections (30P) locks the rod guide (87) with the inner surface of the pressure tube (30) at that location. The rod guide (87) has a central opening to allow the piston rod (82) to pass through it and the inner surface of the rod guide (87) has a groove to accommodate an O-ring (87R) that seals the passage of oil with the piston rod (82) when the piston is sliding in the pressure tube (30) through the central opening of the rod guide (87) during the operating condition of the front fork leg assembly.

[0021] The distal end (82D) of the piston rod (82) is configured to have a stepped profile and said stepped profile portion of the piston rod (82) is mounted with a piston (89) thereon with the help of rod bush (89B) and a nut (89N). The set of shims (89S) is placed in between the rod bush (89B) and the piston (89) and the rebound spring (88) is positioned in between the rod guide (87) and the rod bush (89B). The piston (89) is configured to have at least two orifices (89S) to allow the passage of the damping fluid through it. The outer peripheral surface of the piston (89) is configured to have a groove to accommodate a piston ring (89R) and said piston ring (89R) blocks the passage of oil with the inner surface of the pressure tube (30) and thereby avoids the leakage of the oil, if any, from the pressure tube (30). The said pressure tube (30) is partially filled with the damping fluid, particularly the oil; and the piston (89) of the piston assembly (85) of the piston rod assembly (80) divides the region within the pressure tube (30) into two fluid compartments viz. a fluid compartment (II) and the fluid compartment (III). The fluid compartment (II) lies above the piston (89) and the fluid compartment (III) lies below the piston (89). The rebound spring (88) is placed concentrically over the piston rod inside the pressure tube in between the rod bush (89B) and the rod guide (87).

[0022] In the fork leg assembly (500) of the present invention, the fork pipe (10) is configured to slide inside the bottom case (20) and over the top cap (40) mounted on the pressure tube (30). The main spring (50) is positioned concentrically around the piston rod (82) and in between the fork bolt (70) and the top cap (40). At the interface surface of the top cap (40) with the fork pipe (10), said top cap (40) is configured to have serrated profiled structure (D) creating the serrated gap/space with the fork pipe (10). This serrated gap/space is filled with the synthetic fluoro polymer particularly with Poly Tetra Fluoro Ethylene (PTTE) coating to reduce the friction between the cap (40) and the fork pipe (10). The sealing assembly (60) of the front fork is placed at the open end of the bottom case (20) and the lips of the sealing assembly (60) blocks the entry of dust and any other foreign material into the bottom case (20).
[0023] During normal full length compression when the wheel of the motor vehicle hits a big road surface irregularity, the front fork leg (500) of the present invention is so compressed such that the main spring (50) undergoes compression due to the sliding of the fork pipe (10) inside the bottom case (20). This pushes the piston rod (82) inside the pressure tube making the piston (89) to slide inside the pressure tube (30) compressing the fluid compartment (II) and enlarging the fluid compartment (III) between the rebound spring and the rod guide. In this action, the oil from the fluid compartment (II) passes to the fluid compartment (III) through the orifices (89P) provided in the piston (89) imparting the superior damping performance. During the expansion, the order of damping fluid flow is reversed in the fluid compartments.

[0024] In the present invention, the damping is generated in the pressure tube (30) which is first of its kind in the domain of front fork suspension assembly. Further, to prevent oil leakage from the pressure tube (30), an O-ring (87R) is mounted on a rod guide (87) to take care of excess oil pressure, if any, on the oil seal lip. In the bottom side end (E1) of the pressure tube (30), an adaptor bush (90) and O-ring (91) are mounted in such way that the adaptor bush (90) is fitted with the pressure tube (30) through Loctite and threading which will prevent oil leakage from bottom side of the Front Fork. The rod guide (87) is crimped with the pressure tube (30) so as to ensure positive locking. Further, the rod guide (87) is configured to have a uniquely formed oil sump (87S) to store the excess scraped oil from oil seal.

[0025] As far as the working of the front fork assembly of the present invention is concerned, when the vehicle is subjected to irregularity of the road (refer Fig. 5b), the piston rod assembly (80) slides downward inside the pressure tube (30). This is called as compression stroke. In this stroke, the fluid compartment (II) which is partially filled with damping fluid, gets compressed and the damping fluid from this compartment (II) passes to the fluid compartment (III) through the orifices provided in the piston assembly (85) and/or by deflecting the shims (89S) provided in the piston assembly (85). These actions happening in the pressure tube (30) of the bottom case (20) lead to smoothly absorbing the jerks created by the irregularity of the road and thereby provides comfortable ride to the rider / user. When the vehicle comes out of the irregularity of the road, i.e. runs on smooth road, the piston rod assembly (80) inside the pressure tube (30) travels back to its original position (refer Fig. 5a). This is called as the rebound stroke. During this stroke, the damping fluid from the fluid compartment (III) passes back to the fluid compartment (II) through the orifices provided in the piston assembly (85) and/or by deflecting the shims (89S) provided in the piston assembly (85), thereby compressing the fluid compartment (III) and enlarging the fluid compartment (II).

[0026] Thus, the novelty of this invention lies in intelligent placement of the uniquely profiled pressure tube (30) along with the top cap (40) within the bottom case (20) and said pressure tube (30) along with the piston rod assembly (85) therein forming two fluid chambers (II and III); and the fork pipe (10) having no damping fluid at all therein. This novel construction of the front fork totally eliminates the requirement number of child parts namely oil seal stopper, DU bush, DU bush washer, cap oil lock, oil lock collar, valve seat, seat pipe, etc. unlike the conventional front forks leading the front fork of the invention very simple, light weight and efficient thereby establishing the inventive step. Due to novel and inventive construction of the pressure tube (30) in the front fork assembly of the invention, the contact of the oil with the fork pipe (10) and the bottom case (20) is totally eliminated thereby eliminating the leakage of oil from the front fork assembly. Thus, the present invention addresses the issue of leakage from the front fork assembly by providing the leak proof front fork assembly for two and three wheeled vehicles.

[0027] The front fork of the present invention leads to 70% saving of damping fluid / oil as compared to the conventional telescopic front fork assemblies available in the public domain. The unique construction of front fork with damper assembly and the rod guide eliminates the leakage of oil, impart superior damping performance, leads to part and weight reduction, improves the life of front fork and provides cost effective and simple to manufacture solution thereby contributing to technical advancement. The damper assembly is fitted vertically into the bottom case assembly to form a single front fork assembly leading to elimination of oil seal, oil seal stopper, DU bush, DU bush washer, Cap oil lock, Oil lock collar, Valve seat, Seat pipe, etc. The adaptor bush and O-ring are mounted in the bottom side of front fork in such way that it facilitates to prevent oil leakage from bottom side of the Front Fork.

[0028] The foregoing description of the specific embodiment of the invention 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 embodiment. Further, 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 embodiment/s herein have been described in terms of preferred embodiment, 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

1. A front fork assembly (600), having a pair of leg assemblies (500), for two and three wheeled vehicles; front fork leg assembly (500) comprises of a fork pipe (10), a bottom case (20), a pressure tube (30), a top cap (40), a main spring (50), a sealing assembly (60), a fork bolt (70), a piston rod assembly (80), an adaptor (90) and a rubber bump stop (95);
wherein,
- the pressure tube (30) is configured to have two ends (E1 and E2) and projections (30P) on its inner surface towards the end (E2) of said pressure tube (30).
- the pressure tube (30) at its end (E1) is fitted with the bottom case (20) through the adaptor (90) and a socketed bolt (92);
- said adaptor (90) having an O-ring (91) is press fitted inside the pressure tube (30) at its end (E1) and the socketed bolt (92) is configured to lock the pressure tube (30) with the bottom case (20) through its threaded joinery with the adaptor (90);
- the other end (E2) of the pressure tube (30) is fitted with the top cap (40) concentrically mounted over it from the outer side through the treaded joinery;
- said pressure tube (30) is partially filled with the damping fluid, particularly the oil; and
- the piston assembly (85) of the piston rod assembly (80) housed inside the pressure tube (30) is configured to divide the region within the pressure tube (30) into two fluid compartments viz. a fluid compartment (II) and the fluid compartment (III).

2. The front fork assembly (600) as claimed in claim 1, wherein
- at the interface surface of the top cap (40) with the fork pipe (10), said top cap (40) is configured to have a serrated profiled structure (D) creating the serrated gap/space with the fork pipe (10); and
- said serrated gap/space is filled with the synthetic fluoro polymer particularly with Poly Tetra Fluoro Ethylene (PTTE) coating configured to reduce the friction between the cap (40) and the fork pipe (10).

3. The front fork assembly (600) as claimed in claim 1, wherein the fluid compartment (II) is sandwiched between the piston (89) and the adaptor (90); and the fluid compartment (III) is sandwiched between the piston (89) and a rod guide (87).

4. The front fork assembly (600) as claimed in claim 3, wherein
- the rod guide (87) is configured to have a depression (87D) on its outer peripheral surface, a central opening to allow the piston rod (82) to pass through it, and a groove on its inner peripheral surface to accommodate an O-ring (87R); and
- said depression (87D) on the rod guide (87) is configured to receive the projections (30P) given on the inner surface of the pressure tube (30).
5. The front fork assembly (600) as claimed in claim 4, wherein
- the rod guide (87) is configured to have a uniquely formed oil sump (87S) to store the excess scraped oil from oil seal; and
- said rod guide (87) is crimped with the pressure tube (30) so as to ensure positive locking.

6. The front fork assembly (600) as claimed in claim 3, wherein the adaptor bush (90) is fitted with the pressure tube (30) through Loctite and threaded joinery which is configured to prevent oil leakage from bottom side of the Front Fork.

7. The front fork assembly (600) as claimed in claim 1, wherein
- the piston rod assembly (80) comprises of a piston rod (82) and a piston assembly (85);
- said piston rod (82) of the piston assembly (80) is configured to have a proximal end (82P) and a distal end (82D);
- the proximal end (82P) of the piston rod (82) is fitted with the fork bolt (70) through the threaded joint and locked there with the help of a nut (83);
- the distal end (82D) of the piston rod (82) passes through the top cap (40) inside the pressure tube (30) and is fitted with the piston assembly (85); and
- said piston assembly (85) comprises of an oil seal (86), a rod guide (87), a rebound spring (88), a washer (W), a set of shims (85S) and a piston (89).
8. The front fork assembly (600) as claimed in claim 7, wherein
- the distal end (82D) of the piston rod (82) is configured to have a stepped profile and said stepped profile portion of the piston rod (82) is mounted with a piston (89) thereon with the help of rod bush (89B) and a nut (89N);
- a set of shims (89S) is placed in between the rod bush (89B) and the piston (89) and the rebound spring (88) is positioned in between the rod guide (87) and the rod bush (89B);
- the piston (89) is configured to have at least two orifices (89S) to allow the passage of the damping fluid through it;
- the outer peripheral surface of the piston (89) is configured to have a groove to accommodate a piston ring (89R) and said piston ring (89R) blocks the passage of oil with the inner surface of the pressure tube (30) and thereby avoids the leakage of the oil from the pressure tube (30); and
- the rebound spring (88) is positioned concentrically over the piston rod (82) inside the pressure tube (30) in between the rod bush (89B) and the rod guide (87).

9. The front fork assembly (600) as claimed in claim 8, wherein
- the main spring (50) is positioned concentrically around the piston rod (82) and in between the fork bolt (70) and the top cap (40);
- the sealing assembly (60) of the front fork is placed at the open end of the bottom case (20) and the lips of the sealing assembly (60) are configured to block the entry of dust and any other foreign material into the bottom case (20).

10. The front fork assembly (600) as claimed in claim 9, wherein
- the fork bolt (70) is fitted at the top end of the fork pipe (10) through the threaded joinery and said fork pipe (10) is configured to telescopically dispose within the bottom case (20);
- said bottom case (20) is configured to concentrically house the rubber bump stop (95) around its outer peripheral surface of the pressure tube (30) at its lower end (E1); and
- said rubber bump stop (95) is configured to prevent the bottoming of the fork pipe (10) during the extreme compression stroke of the fork leg (500).

Dated this 21st day of March 2024

Sahastrarashmi Pund
Head – IPR
Endurance Technologies Ltd.

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