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
“VARIABLE PRE-COMPRESSION ADJUSTING SYSTEM FOR FRONT FORK SUSPENSION OF A VEHICLE”

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

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

Field of Invention

The present invention is related to a front fork suspension of a two wheeled vehicle. More particularly, the present invention relates to a variable pre-compression adjusting system for front fork suspension of a two wheeled vehicle configured to change the precompression of the spring as per user requirement with a simple and optimized system of a fork bolt within the fork pipe.

Background of the Invention

In a two wheeled vehicle, a front wheel is attached to a front fork having two legs connected to the front part of the vehicle body, and a rear wheel is attached to a rear suspension. When the vehicle is running, the impact caused by the vertical movement of the front and rear wheels that are in contact with the ground is transmitted to the vehicle body through the front fork and the rear suspension. It is necessary to minimize the impact that is transferred from the ground to the vehicle body in order to enhance the ride comfort of the rider while riding the vehicles.

In the front fork, the pre-compression of main spring of a front fork determines how well a front fork suspension will help the wheels of a motor vehicle in following the profile of the road surface irregularities while maintaining the motor vehicle body at a desired level in different road conditions. In the conventional front fork, when there is requirement of minor change in precompression of the main spring, then the spacer tube is changed for achieving such pre-compression. Such alterations are only possible in the factory at the time of assembly of such front fork suspensions, but not possible at user ends.

To solve the above mentioned problem, a screw based mechanism is developed for adjusting the pre-compression of the main spring in both fork legs of the front fork. In such arrangements, the user / rider can change the pre-compression of the main spring of the front fork as per the requirement to navigate with the road irregularity. However, these screw based mechanism of pre-compressing the main spring has its own limitation as this mechanism completely fails to pre-compress the main spring equally with equal and uniform pre-compression in both the legs of front fork suspension which consequently leads to generate undesirable stresses in the front fork body during running condition of the vehicle on the irregularity of road surfaces. Due to these undesirable stresses, the child components of the front fork suspension are more prone to damage and wear and tear leading to the concern of durability of front fork suspension system. Further, the adjustment of the pre-compression in the front fork using screw based mechanism requires skilled user to set the pre-compression of the main spring.

Therefore, there is a long pending unmet need to address the aforementioned technical problems and provide an intelligent, very simple and easy to operate solution that will ensure an accurate and uniform pre-compression in both the fork legs of suspension system as per the user requirement at an economical cost.

Objectives of the Invention

The main objective of the present invention is to provide a variable pre-compression adjusting system for front fork suspension of a two wheeled vehicle.

Another objective of the present invention is to provide a variable pre-compression adjusting system for front fork of a two wheeled vehicle, where an unskilled user can easily alter the pre-compression of the main spring as per their requirement.

Yet, another objective of the present invention is to provide a variable pre-compression adjusting system for front fork of a two wheeled vehicle, which allows equal amount of pre-compression adjustment to be made accurately in both the fork legs of a front fork suspension of the vehicle.

Yet, another objective of the present invention is to provide a variable pre-compression adjusting system for front fork of a two wheeled vehicle that solves the problem of development of undesirable stresses during operation of front fork having unevenly adjusted main spring pre-compression.

Yet, the objective of the present invention is to provide a variable pre-compression adjusting system for front fork of a two wheeled vehicle that is very simple, easy to operate, easy to manufacture and is an economical solution for altering the pre-compression of the main spring of front fork.

Still another objective of the present invention is to provide a variable pre-compression adjusting system for front fork of a two wheeled vehicle that leads to improve reliability of the system and the working life of the fork legs of the suspension system.

Further objective of the present invention is to provide better ride comfort to the user / rider of the vehicle by eliminating the issue of noise, vibrations and harshness (NVH) by ensuring uniform compression of the main spring in both the fork legs of the suspension unit.

Brief Description of the Drawings

This invention is illustrated in the accompanying drawings, throughout which like reference letters / numerals 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 shows a leg of the suspension system with the cut-view at its top end disclosing the variable pre-compression adjusting system for front fork of a two wheeled vehicle in accordance with the present invention.

Figure 2 shows an exploded view of a variable pre-compression adjusting system for front fork of a two wheeled vehicle in accordance with the present invention.

Figure 3 shows an exploded cut view of a variable pre-compression adjusting system for front fork of a two wheeled vehicle in accordance with the present invention.

Figure 4 shows a cut section of fork pipe for front fork of a two wheeled vehicle in accordance with the present invention.

Figure 5 shows an isometric view of circlip, Figure 6 shows front view of the fork bolt and Figure 7 shows an enlarged cut section of upper end of the fork pipe for front fork of a two wheeled vehicle in accordance with the present invention.
Figure 8 shows an enlarged isometric cut view of a variable pre-compression adjusting system for front fork of a two wheeled vehicle in accordance with 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 3, the present invention discloses a variable pre-compression adjusting system (900) for a front fork of two wheeled vehicles. The front fork suspension of a vehicle has a pair of fork legs (1000), where an upper end of these legs (1000) are mounted on a triple clamp bracket (not shown) and connected to the handle bar of a vehicle through a steering rod of said triple clamp bracket. The lower end of these legs are mounted on the axle (not shown) of the wheel. Each of these fork legs (1000) of the front fork suspension of the two wheeler comprises of an outer tube (100), a fork pipe (200), a main spring (300), a spacer tube (400), a fork bolt (500), a circlip (600) and an O-ring (OR).

The said outer tube (100) is a cylindrical hollow body and is configured to have a lower end (100L) and an upper end (100U). The lower end (100L) of outer tube (100) is closed and is configured to have an axle hole (105) for receiving the axle shaft in order to fixing it with the wheel axle. The upper end (100U) of the outer tube (100) is configured to have longitudinal bore traversing up to the closed end of the lower end (100L) of the outer tube (100). The said longitudinal bore of the outer tube (100) is configured to accommodate the working fluid, a seat pipe, and allows a portion of the fork pipe (200) to slide coaxially therein. A sealing assembly (S) is provided in the annular space of the inner periphery of the outer tube (100) and outer periphery of the fork pipe (200) in the mouth (100U) of the outer tube (100). The said sealing assembly (S) comprises of a dust seal and an oil seal and is configured to prevent the ingressment of the foreign particles inside the working chamber of the fork leg (1000).

The said fork pipe (200) is a cylindrical hollow body and is configured to have an upper end (200U) and a lower end (200L). The lower end (200L) of the fork pipe (200) is configured to accommodate the seat pipe, a rebound assembly and is axially / telescopically slideable within the outer tube (100). The main spring (300) is positioned inside the fork pipe (200) in a manner such that the top end (300T) of the said main spring (300) axially abuts with the lower end (400L) of a spacer tube (400) and the bottom end (not shown) of the said main spring (300) rests over the sliding head of the seat pipe.

The fork bolt (500) is positioned inside the fork pipe (500) at its upper end (200U) thereby closing the upper end of the fork pipe. Said fork bolt has a groove on its outer peripheral surface and said groove houses an O-ring (OR) therein so as to prevent the leakage of working fluid from the fork pipe (200). Further, the circlip (600) is positioned above the fork bolt (500) within a groove provided on the inner peripheral surface of the upper end (200U) of the fork pipe (200). The said circlip (600) is configured to tightly hold the fork bolt (500) at its positions under the set compressed position of the main spring (300). The said circlip (600) is configured to have a circular ring shape. However, the circlip (600) may be selected from tapered ring circlip, flat circlip, snap ring circlip, push on ring circlip, and like. The bottom flat surface at the lower end (500L) of the fork bolt (500) is in communication with the spacer tube (400) and said fork bolt (500) is configured adjust the desired load on the main spring (300) via spacer tube (400) as per the requirement of rider depending on the irregularity of the road surface. The spacer tube (400) is a hollow cylindrical body having two ends i.e. lower end (400L) and upper end (400U).

The upper end (200U) of fork pipe (200) at its inner peripheral surface is configured to have a stepped profile (S) and said stepped profile (S) houses the fork bolt (500) therein. The said stepped profile (S) has a first plain portion (P1) followed by a plurality of profiled grooves (G1, G2, …, and Gn) followed by a second plain portion (P2). The said profiled grooves (G1, G2, …, and Gn) are intelligently positioned in between the first plain portion (P1) and the second plain portion (P2). The first plain portion (P1) is positioned at upper end of the stepped profile (S) and the second plain portion (P2) is positioned at lower end of the stepped profile (S) thereby sandwiching the plurality of profiled grooves (G1, G2, …, and Gn) therein. Each of the said grooves portion (G1, G2, …, and Gn) is configured to have a tapered hook profile (HP) wherein the said hook shaped profile is formed by a combination of a circular arc (C) of radius (R) and a tapered line segment (T). The said tapered line segment (T) is inclined towards inner periphery of the fork pipe (200) forming a tangent to the said circular arc (C) of radius (R). The said radius (R) of the said circular arc (C) is proportional to the radius (Rc) of the said circular circlip (600). The said grooves (G1, G2, …, and Gn) of the fork pipe (200) are provided at regular vertical distance in both legs (1000) of the front fork.

The inclination of the tapered line segment (T) is configured to have an angle (a) from the tangent of the circular arc (C) wherein the said line segment (T) is configured to provide a smooth transition of the circular circlip (600) from one groove portion to other groove portion. The angle (a) is intelligently optimized with respect to the radius (Rc) of the circlip (600) so as to make the smooth transition of the circlip (600) from groove to groove thereby changing the position of the fork bolt which consequently compresses or decompresses the main spring in line with positive or negative axial travel of the fork bolt. The optimized relation between the angle (a) and the radius (Rc) of the circlip (600) is calculated from the below mentioned relation so as to impart the desired pre-compression of the spring and provide positive locking to the circlip as well.
a=k 2pRc/3.6

where,
‘a’ is the inclination angle (in radians) of the tapered line segment (T) of the groves (G1, G2, …, and Gn) of the fork pipe (200);
k is the constant ranging from 0.5 to 1.0; and
Rc is the radius of the circlip.

The said inclination of the tapered line segment (T) is optimized to lie in the range of 30 degrees to 45 degrees and it can be varied in accordance with the above mentioned relation to suit the fork pipes of different configurations. The inclination of the tapered line segment (T) from the tangent of the said circular arc (C) provides smooth transition of the said circular circlip (600) from one groove to its successive groove. The plain portion (P1) is configured to merge with the first profiled groove (G1) and the plain portion (P2) is configured to merge with the last profiled groove (Gn); and said plain portions (P1, P2) are configured to provide a play area / buffer for the axial movement of the fork bolt (500) during compression or decompression of the main spring (300). The diameter (Ds) of inner periphery of the plain portion (P1) of the stepped portion (S) is optimized in such a manner that the flanges (F1 and F2) of the fork bolt (500) can easily slide therein without any interference. The end portion of the plain portion (P2) is converged towards the inner periphery of the fork pipe (200) and forms a chamfer portion (C1).

The fork bolt (500) has a solid cylindrical body and is configured to have two shank portions (510 and 520), two flanges (F1 and F2) and a groove (515) formed in between said flanges (F1 and F2). The shank portion (510) is at upper side of the fork bolt (500) and configured to merge with the flange (F1) whereas the shank portion (520) is provided at lower side of the fork bolt (500) and merges with the flange (F2) forming a chamfer portion (C2) at their merging interface. The diameter (Df) of the both shank portions (510 and 520) are same. The flanges (F1 and F2) along with the groove (515) are sandwiched between the shank portions (510 and 520) thereby forming a unitary / single piece structure of the fork bolt. The diameter of each of the flanges (F1, F2) is less than the inner diameter of stepped portion (S) in the upper end (200U) of the fork pipe (200) and greater than the diameter of the shank portions (510, 520) of fork bolt (500). The said diameter (Df) of the shank portion (510 and 520) of the fork bolt (500) and the inner diameter (Ds) of the stepped profile (S) which is provided at upper end (200U) of the fork pipe (200) need to maintain the below mentioned relations in order to receive the circlip (600) of optimized diameter of for the positive locking between the fork pipe (200) and fork bolt (500). Thus, the ratio of the inner diameter (Ds) of the stepped profile (S) to the diameter (Df) of the shank portion (510, 520) of the fork bolt (500) is in the range of 1.0 to 1.5.
Ds=Q*Df
Where,
Ds is the inner diameter of the stepped portion (S) of fork pipe (200),
Df is the diameter of the shanks (510, 520) of fork bolt (500), and
Q is the constant and it is in the range of 1.0 to 1.5

The flange (F1) and the shank portion (510) while merging with each other forms a merging arc (RS) at their merging interface and the radius of said merging arc (RS) is proportional to the radius (R) of the circular arc (C) of the hook profiled grooves (G1, G2, …, and Gn). The circlip (600) is positioned on the flange (F1) of the fork bolt (500) and is configured to get locked any of the tapered hook profiled grooves (G1, G2, …, and Gn) in the stepped profile (S) of the fork pipe (200) thereby fixing the position of the fork bolt (500). This arrangement provides a positive locking of the fork bolt (500) in the upper end (200U) of the fork pipe (200). Thus, this positive locking of the circlip (600) in any of the grooves (G1, G2, …, and Gn) is configured to position the fork bolt at variable location with respect to the respective profiled groove (G1 to Gn). Further, the groove (515) is provided radially between the flanges (F1 and F2) of the fork bolt (500) is configured to receive the O-ring (OR) and said O-ring (OR) restrict the leakage of the working fluid outside the fork pipe (200), if any, from the working chamber.

During adjustment of the pre-compression/pre-load of the main spring (300) of the front fork leg (1000), firstly the user has to press the fork bolt (500) manually in downward axial direction thereby compressing the main spring (300) as per requirement and then the circlip (600) positioned over the flange (F1) is released from the circlip holding tool so that it gets expanded to get fitted in a desired groove of the profiled grooves (G1, G2, …, and Gn). When the circlip (600) is locked in the first groove (G1), the main spring (300) is under least compression load but when the circlip is locked in the last groove (Gn), the main spring (300) is under maximum possible load as per the intent of the invention. Thus, the fork bolt (500) is configured to apply the pre-load on the main spring (300) via spacer tube (400) in accordance with the selected locking position of the circlip (600) within any of the selected grooves (G1, G2, …, and Gn). Similarly, during the reduction of the pre-compression/pre-load of main spring (300), a small amount of force will be applied of the fork bolt (500) and then loosen the circlip (600) using the tool and move circlip into the upper groove, e.g. positioning the circlip (600) from the groove (G3) to groove (G2).

This unique and very simple construction of adjusting the preload on the main spring imparts following technical advantages which leads to establishment of inventive step over the prior art solutions.
The system disclosed by the present invention allows an unskilled user to easily alter the pre-compression of the main spring as per their requirement.
It allows equal amount of pre-compression adjustment to be made accurately to both fork legs of a front fork of the vehicle, thereby the development of undesirable stresses during operation will be reduced.
The variable pre-compression adjusting system as discussed in the present invention is very simple and easy to manufacture, thereby it is an economical solution for altering the pre-compression of the main spring of front fork.
It provides better ride comfort to the user / rider of the vehicle by eliminating the issue of noise, vibrations and harshness (NVH).
It improves the durability and reliability of the front fork.

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

1. A variable pre-compression adjusting system (900) for a front fork suspension of two wheeled vehicle comprising of a pair of fork legs (1000), said fork legs connected to the handle bar of a vehicle through triple clamp assembly, and each of the fork legs (1000) having an outer tube (100), a fork pipe (200), a main spring (300), a spacer tube (400), a fork bolt (500), a circlip (600) and an O-ring (OR) wherein,
the said fork pipe (200) is a cylindrical hollow body having an upper end (200U) and a lower end (200L), and said upper end (200U) of fork pipe (200) is configured to have a stepped profile (S) at its inner periphery for accommodating the fork bolt (500);
the said stepped profile (S) has a first plain portion (P1) followed by a plurality of profiled grooves (G1, G2, …, and Gn) followed by a second plain portion (P2) and said profiled grooves (G1, G2, …, and Gn) are intelligently positioned in between the first plain portion (P1) and the second plain portion (P2);
the fork bolt (500) is configured to have a solid cylindrical body having two shank portions (510 and 520), two flanges (F1 and F2) and a groove (515) formed in between said flanges (F1 and F2), wherein the shank portion (510) is configured to merge with the flange (F1) and the shank portion (520) merges with the flange (F2) forming a chamfer portion (C2) at their merging interface;
the main spring (300) is positioned inside the fork pipe (200) having its top end (300T) to axially abut with the lower end (400L) of a spacer tube (400) and the bottom end (not shown) to rest over the sliding head of the seat pipe;
the spacer tube (400) having a cylindrical body is positioned in between the main spring (300) and the fork bolt (500) so that the lower end (500L) of the fork bolt (500) is in communication with the top end (400U) of the spacer tube (400);
the circlip (600) is positioned on the flange (F1) of the fork bolt (500) and is configured to get locked any of the profiled grooves (G1, G2, …, and Gn) in the stepped profile (S) of the fork pipe (200) thereby fixing the position of the fork bolt (500); and
the fork bolt (500) is configured to apply the pre-load on the main spring (300) via spacer tube (400) in accordance with the selected locking position of the circlip (600) within any of the selected grooves (G1, G2, …, and Gn).

2. The variable pre-compression adjusting system (900) as claimed in claim 1 wherein,
the first plain portion (P1) is positioned at upper end of the stepped profile (S) and the second plain portion (P2) is positioned at lower end of the stepped profile (S) thereby sandwiching the plurality of profiled grooves (G1, G2, …, and Gn) therein;
each of the said grooves portion (G1, G2, …, and Gn) is configured to have a tapered hook profile (HP) wherein the said hook shaped profile is formed by a combination of a circular arc (C) of radius (R) and a tapered line segment (T);
said tapered line segment (T) is inclined towards inner periphery of the fork pipe (200) forming a tangent to the said circular arc (C) of radius (R); and
the said radius (R) of the said circular arc (C) is proportional to the radius (Rc) of the said circular circlip (600).

3. The variable pre-compression adjusting system (900) as claimed in claim 2, wherein
the inclination of the tapered line segment (T) is configured to have an angle (a) from the tangent of the circular arc (C) wherein the said line segment (T) is configured to provide a smooth transition of the circular circlip (600) from the one profiled groove into the successive profiled groove;
the angle (a) is intelligently optimized with respect to the radius (Rc) of the circlip (600) so as to make the smooth transition of the circlip (600) from groove to groove thereby changing the position of the fork bolt which consequently compresses or decompresses the main spring in line with positive or negative axial travel of the fork bolt (500);
said angle (a) is in relation with the radius (Rc) of the circlip (600) in line with the below mentioned equation
a=k 2pRc/3.6

where,
‘a’ is the inclination angle (in radians) of the tapered line segment (T) of the groves (G1, G2, …, and Gn) of the fork pipe (200);
k is the constant ranging from 0.5 to 1.0; and
Rc is the radius of the circlip.

4. The variable pre-compression adjusting system (900) as claimed in claim 3, wherein
the said circlip (600) is configured to have a profile selected from circular ring, tapered ring circlip, flat circlip, snap ring circlip, and push on ring circlip; and
the inclination of the tapered line segment (T) that makes angle (a) is optimized to lie in the range of 30 degrees to 45 degrees; and
said angle (a) is configured to make smooth transition of said circular circlip (600) from one groove to its successive groove (G1 to Gn) in the stepped profile (S) of the fork pipe (200).

5. The variable pre-compression adjusting system (900) as claimed in claim 4, wherein
the first profiled groove (G1) in the stepped profile (S) is configured to merged with the plain portion (P1) and the plain portion (P2) is configured to merge with the last profiled groove (Gn);
said plain portions (P1, P2) are configured to provide a play area / buffer for the axial movement of the fork bolt (500) during compression or decompression of the main spring (300);
the end portion of the plain portion (P2) is converged towards the inner periphery of the fork pipe (200) forming a chamfer portion (C1); and
the diameter (Ds) of inner periphery of the plain portion (P1) of the stepped portion (S) is optimized to slide the flanges (F1, F2) of the fork bolt (500) therein without any interference.

6. The variable pre-compression adjusting system (900) as claimed in claim 5, wherein
the flanges (F1, F2) do have the diameter less than the inner diameter of stepped portion (S) in the upper end (200U) of the fork pipe (200) and greater than the diameter of the shank portions (510, 520) of fork bolt (500);
the flanges (F1 and F2) along with the groove (515) are sandwiched between the shank portions (510 and 520) thereby forming a unitary / single piece structure of the fork bolt (500);
the shank portions (510 and 520) have same diameter (Df) and said diameter (Df) of the shank portion (510 and 520) and the inner diameter (Ds) of the stepped profile (S) are configured to maintain the below mentioned relation in order to receive the circlip (600) of optimized diameter for the positive locking between the fork pipe (200) and fork bolt (500)
Ds=Q Df
where,
Ds is the inner diameter of the stepped portion (S) of fork pipe (200),
Df is the diameter of the shanks (510, 520) of fork bolt (500), and
Q is the constant and it is in the range of 1.0 to 1.5

7. The variable pre-compression adjusting system (900) as claimed in claim 6, wherein the ratio of the inner diameter (Ds) of the stepped profile (S) to the diameter (Df) of the shank portion (510, 520) of the fork bolt (500) is in the range of 1.0 to 1.5.

8. The variable pre-compression adjusting system (900) as claimed in claim 7, wherein
the shank portion (510) is configured to merge with the flange (F1) forming a merging arc (RS) at their merging interface and the radius of said merging arc (RS) is proportional to the radius (R) of the circular arc (C) of the tapered hook profiled grooves (G1, G2, …, and Gn); and
said tapered hook profiled grooves (G1, G2, …, and Gn) is configured to have positive locking of the circlip (600) in any of the grooves (G1, G2, …, and Gn) positioning the fork bolt (500) at variable location with respect to the respective profiled groove (G1 to Gn).

9. The variable pre-compression adjusting system (900) as claimed in claim 8, wherein the fork bolt (500) is configured the groove (515) formed by the flanges (F1 and F2) and said groove (515) on the outer peripheral surface of the fork bolt houses the O-ring (OR) so as to restrict the leakage of the working fluid outside the fork pipe (200), if any, from the working chamber.

10. The variable pre-compression adjusting system (900) for a front fork suspension of two wheeled vehicles as claimed in claim 9, wherein
the fork pipe (200) is configured to telescopically slide inside the outer tube (100);
said outer tube (100) is a cylindrical hollow body having a lower end (100L) and an upper end (100U); said lower end (100L) of outer tube (100) is closed and is configured to have an axle hole (105) for receiving the axle shaft in order to fixing it with the wheel axle;
the upper end (100U) of the outer tube (100) is configured to have longitudinal bore traversing up to the closed lower end (100L) of the outer tube (100);
said longitudinal bore of the outer tube (100) is configured to accommodate the working fluid, a seat pipe and a sealing assembly (S) wherein said sealing assembly (S) is positioned in the annular space of the inner periphery of the outer tube (100) and outer periphery of the fork pipe (200) in the mouth (100U) of the outer tube (100); and
said sealing assembly (S) having a dust seal and an oil seal is configured to prevent the ingressment of the foreign particles inside the working chamber of the fork leg (1000).

Dated this 6th day of Mar. 2025

Sahastrarashmi Pund
Head – IPR
Endurance Technologies Ltd.

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