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

COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

TITLE OF THE INVENTION
“COMPOSITE FORK BOLT ASSEMBLY FOR A 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 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 relates to a fork bolt assembly of the front telescopic suspension system. More particularly the invention relates to a composite fork bolt assembly adapted to be used in suspension of saddle type vehicles employing the upper bracket and under bracket for fixing the suspension unit to the vehicle.

Background of the Invention

[002] Fork bolt is an essential components of the suspension units as it is used to seal the fork pipes of the suspension units from the top. Despite serving the critical function of keeping the shock absorber safe from environmental conditions, the fork bolts have not been explored for technical improvements by the industry experts as of now.

[003] Since, the fork bolts are mounted at the top of the fork pipes, the fork bolts experience compressive load during the compression stroke of the shock absorber of the vehicle and the tensile load during the rebound stroke of the vehicle suspension. The compressive and tensile load requirements may reach up to 13KN during operation and/or running of a vehicle. Owing to the aggressive load requirements, the fork bolts are currently being made from EN8M carbon steel.

[004] The conventional fork bolts made in carbon steel thus impose the problems such as high cost, increased weight, and extra machining time. Thus, there is a long pending unmet requirement to overcome the above mentioned problems and provide a solution which is easy to manufacture, cost effective and do perform at par with the conventional fork bolts.
Objectives of the Present Invention

[005] The main object of the present invention is to develop a fork bolt assembly. More particularly, the objective of the invention is to develop a composite fork bolt having a plastic body molded around a metallic washer assembly.

[006] Another main object of the present invention is to provide a composite fork bolt assembly adapted to be used in suspension systems of saddle type vehicles wherein the front fork suspension assembly is affixed to the steering of the vehicle with the help of a triple clamp assembly.

[007] Another objective of the present invention is to composite fork bolt assembly which is light weight, durable and sustain the rigorous loading conditions during the operation of the vehicle.

[008] Still another objective of the present invention is to provide a composite fork bolt assembly with insert molding process, without any extra machining being performed on the fork bolt.

[009] Yet another objective of the present invention is to provide a composite fork bolt assembly with reduced production cycle time, cost effective and yet imparting at par performance.

Brief Description of Drawings

[0010] 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

[0011] Figure 1 discloses an assembled cut-sectional view of the front fork suspension having a conventional fork bolt (prior art).

[0012] Figure 2 describes an assembled cut-sectional view of the front fork suspension employing a composite fork bolt assembly as per the present invention.

[0013] Figures 3 and 4 disclose a perspective and a cut-section view, respectively of the composite fork bolt assembly as per the present invention.

[0014] Figures 5 and 6 presents the perspective and a cut-section view of the metallic washer assembly of composite fork bolt assembly according to the present invention.

[0015] Figures 7a, 7b and 7c discloses perspective view, cut-sectional view and top view, respectively of the metallic disc of the composite fork bolt in accordance with the present invention.

[0016] Figure 8 presents tensile strength characteristics of the composite fork bolt assembly of the present invention tested as per the standard 5140Z-GHA-6700.

Detailed Description of the Present Invention

[0017] 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.
[0018] Referring to Fig. 1, the conventional front fork suspension (500’) comprises of a triple clamp assembly (20) having an upper bracket (20U) and an under bracket (20L), a steering rod (15) of a saddle type vehicle, a pair of conventional fork bolt (200’), a pair of flange nut (10’), a pair of O-Rings (50), a pair of main spring (40), a pair of outer tubes (not shown) and a pair of fork pipe (45). The triple clamp assembly (20) holds the fork pipes (45) and the steering rod (15) of the saddle vehicle in a manner such that the upper bracket (20U) is fastened to the fork pipes (45) with the help of the flange nuts (10’). The steering rod (15) at its top end is fixedly connected to the said upper bracket (20U) in a manner such that the steering rod (15) is able to be rotated about a rotational axis in accordance with operation of a handlebar. The under bracket (20L) of the triple clamp assembly (20) holds fork pipes (45) and the steering rod (15) at its bottom end with the help of clamping means (35) provided on the said under bracket (20L). The said conventional fork bolt (200’) is fitted to the top end of the fork pipes (45) with the help of a circlip (50) in such a manner that the said circlip (50) snuggly fits within a groove provided in the fork pipes (45) and a corresponding matching groove provided in the fork bolts (200’). The main springs (40) are positioned within the fork pipes (45) in a manner such that the top end of the said springs (45) abuts with the bottom face of the fork bolts (200’) and the bottom end of the said springs (45) is housed within the outer tubes (not shown).

[0019] Referring to Figs. 2 - 4, the composite fork bolt assembly (200) of the present invention comprises of a fork bolt body (50) made in plastic and a metallic washer assembly (150). The fork bolt body (50) is made up of plastic selected from the group of thermoplastic materials, preferably polyamide and more preferably polyamide with glass filled so as to effectively compensate with the mechanical properties required for the purpose. The said fork bolt body (50) is configured to have a cylindrical cup-shaped profile and is molded around the metallic washer assembly (150) wherein the molding is performed by insert molding method. The said fork bolt body (50) is configured to have an annular skirt (50S) having a frustum shaped cavity (75). The annular skirt (50) has a pair of oil seal fins (70) formed at its lower outer circumferential surface and an O-Ring projection (65) formed just above the oil seal fins (70). The said oil seal fins (70) helps in evenly distributing the oil pressure within the fork suspension assembly and the O-Ring projection (65) helps in avoiding the oil leakage therefrom. Further, the fork bolt body (50) is configured to have a groove (60) and an annular tab (55) formed in a manner such that the groove (60) is positioned in between the O-Ring projection (65) and the annular tab (55) wherein the annular tab (55) is in axially upward direction in relation to the O-Ring projection (65). The said groove (60) is configured to accommodate an O-ring (30) therein so as to seal the interference between the inner surface of the fork pipe (45) and the outer surface of the fork bolt body (50) thus eliminating the leakage of oil thereby. The said annular tab (55) facilitates the inhibition of the vertical upside movement of the composite fork bolt assembly (200) relative to the fork pipe (45) of the front fork suspension system (500).

[0020] The metallic washer assembly (150) comprises of a metallic disc (100) and a cylindrical metallic sleeve (130) wherein the said metallic sleeve (130) is press fitted in the central opening (125) of the metallic disc (100) followed by welding. The metallic disc (100) is configured to have a thorough opening (125) to receive the said metallic sleeve (130) wherein the said opening (125) is formed by piercing the metallic disc (100). The forming of said opening (125) is done by any of the known conventional sheet metal processes such as blanking, punching etc. Further, the metallic disc (100) has an annular base portion (105), a stepped portion (110) and an annular collar (115) formed by metal forming process wherein the metal forming is performed after the piercing operation. The said portions of the metallic disc (100) are formed in a manner so as to have the uniform thickness (y). The stepped portion (110) is configured to have a plurality of thorough holes (120) formed on its top surface wherein the said holes (120) facilitates the flow of the molten plastic material during insert molding of the composite fork bolt assembly (200). The number of holes (120) is preferably selected from four to six and are positioned at an equiangular distance to each other in order to assure the desired volume flow of molten plastic during the insert molding process. The preferred cross sectional profile of the thorough holes is circular. However, said profile of the thorough holes (120) may vary from triangular to polygonal and/or the combination of thereof. Further, the holes (120) of the stepped portion (110) of the metallic disc are formed in such a manner that the center of said holes (120) lies on an imaginary base circle of radius Rb. The said imaginary circle maintains relation denoted in the subsequent section of this description so as serve the technical purpose in accordance with the ambit of the present invention.
Rb = k1 * Ra.
wherein,
Rb is the base circle radius
Ra is radius of the outer edge of the stepped portion of the metallic disc
k1 is the correction constant ranging from 0.1 - 0.5

[0021] The annular collar (115) along with the stepped portion (110) of the metallic disc (100) acts as to guide the metallic sleeve (130) by the virtue of the guide length (2y) during the fitment of the metallic sleeve (130) within the opening (125) of the metallic disc (100). The base portion (105) of the metallic disc (100) acts as the main load bearing portion embedded within the annular tab portion (55) of the fork bolt body (50) thus imparting the required strength to the composite fork bolt assembly (200).

[0022] The metallic sleeve (130) is a hollow cylindrical body configured to have female threads formed over its inner peripheral surface. The inner threaded surface of the metallic sleeve (130) receives the flange nut (10) in order to fix the composite fork bolt assembly (200) with the upper bracket (20U) of the triple clamp assembly (20). The metallic disc (100) and the metallic sleeve (130) are selected from a group of metals such as Steel, Aluminum (Ferrous & Non-Ferrous), etc. but the most preferably it is selected from E34 steel grade. Further, the metallic sleeve (130) of the metallic washer assembly (150) is configured to have the outer diameter Ds such that Ds = k2* 2Rc. It is to be noted that Rc can be selected as per the diameter of the fork pipe (45) where, Rc is the radius of the base portion (105) of the metallic disc and k2 is a constant ranging from 0.5 – 0.8.

[0023] The metallic washer assembly (150) is formed by welding the metallic sleeve (130) to the metallic disc (100) thus forming the weld spots (WS) at the interface formed between the top inner edge of the annular collar (115) and the outer peripheral surface of the sleeve (130) and the inner peripheral edge of the stepped portion (110) and outer peripheral surface of the sleeve (130). The guide length (2y) of the annular portion (115) and stepped portion (110) of the metallic disc (100) facilitates avoidance of distortion of the vertical axis of the metallic sleeve (130) with respect to the metallic disc (100) during welding process due to the formation of Heat Affected Zone (HAZ). The guide length (2y) the annular portion (115) and stepped portion (110) of the metallic disc (100) for the metallic sleeve (130) mandatorily maintains the below mentioned relation with the total length (l) of the metallic sleeve in order to impart the desired effects without deviating from the technical scope of the invention:
2y = k3*l
wherein,
y is the thickness of the metallic disc
l is the total length of the metallic sleeve
k3 is variation constant within the range 1.0-2.0

[0024] The metallic washer assembly (150) is placed in a die (not shown) so as to form the composite fork bolt assembly (200) according to the present invention by the insert molding process. Further, the location/placement of metallic washer assembly (150) is provided in a manner to maintain the below mentioned empirical relations:
x = c1*y
y = c2*z
where,
x = distance of the top face of the base portion of the metallic disc from top face of the fork bolt body;
y = thickness of the base portion of the metallic disc;
z = distance of the bottom face of the fork bolt body from the bottom face of the base portion of the metallic disc; and
c1 & c2 are the constants ranging from 2.5 to 3.5 and 0.1 to 0.3, respectively.

[0025] The composite fork bolt assembly (200) in accordance with the disclosed embodiment provides the following technical advantages that contributes to the technical advancement in the domain of fork bolt technology:
- Composite fork bolt of the invention exhibits enhanced tensile strength characteristics as shown in Fig. 8 when the said fork bolt was tested for tensile strength as per the test standard 5140Z-GHA-6700.
- It provides a light weight, compact and durable fork bolt solution for a two/three wheeler suspension.
- It provides system a cost effective solution of fork bolt for the two/three wheeler suspension without compromising the efficiency and performance of the suspension system.
- It reduces the machining time drastically thereby leading reduction in overall effective cost and cycle time of fork bolt and consequently the suspension unit incorporating the said fork bolt.
- It provides excellent durability against environmental impacts such as rain, dust, corrosion etc.

[0026] 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 composite fork bolt assembly (200) for a front suspension of a vehicle comprising of a fork bolt body (50) made in plastic and a metallic washer assembly (150) wherein,
- the fork bolt body (50) is configured to have a cylindrical cup-shaped profile having an annular skirt (50S) forming a frustum shaped cavity (75), a pair of oil seal fins (70) formed at its lower outer circumferential surface, an O-Ring projection (65) formed just above the oil seal fins (70), a groove (60) and an annular tab (55) wherein the groove (60) is positioned in between the O-Ring projection (65) and the annular tab (55) and the annular tab (55) is in axially upward direction in relation to the O-Ring projection (65);
- the metallic washer assembly (150) comprises of a metallic disc (100) and a cylindrical metallic sleeve (130) wherein the said metallic sleeve (130) is press fitted in the thorough opening (125) of the metallic disc (100) followed by welding; and
- said the fork bolt body (50) is insert molded around the metallic washer assembly (150) to form the fork bolt assembly (200).

2. The composite fork bolt assembly (200) for a front suspension of a vehicle as claimed in claim 1, wherein
- the metallic disc (100) is configured to have a thorough opening (125) to receive the metallic sleeve (130), and said opening (125) of the metallic disc (100) is formed by forming process selected from piercing, blanking, and punching;
- the metallic disc (100) has an annular base portion (105), a stepped portion (110) and an annular collar (115) formed by metal forming process wherein the metal forming is performed after the piercing operation;
- said portions annular base portion (105), a stepped portion (110) and an annular collar (115) of the metallic disc (100) are formed in a manner so as to have the uniform thickness (y); and
- the stepped portion (110) is configured to have a plurality of thorough holes (120) formed on its top surface so as to efficiently facilitate the flow of the molten plastic material during insert molding of the composite fork bolt assembly (200).

3. The composite fork bolt assembly (200) for a front suspension of a vehicle as claimed in claim 2, wherein
- the number of said thorough holes (120) varies from four to six and are positioned at an equiangular distance to each other in order to assure the desired flow rate of molten plastic during the insert molding process; and
- the cross sectional profile of said thorough holes (120) of the metallic washer assembly (150) is selected from circular, triangular, polygonal and the combination of thereof.

4. The composite fork bolt assembly (200) for a front suspension of a vehicle as claimed in claim 2, wherein
- the metallic sleeve (130) of the metallic washer assembly (150) is a hollow cylindrical body and is configured to have female threads formed over its inner peripheral surface to receive a flange nut (10) in order to fix the composite fork bolt assembly (200) with an upper bracket (20U) of a triple clamp assembly (20); and
- said metallic sleeve (130) is press fitted with the metallic disc (100) followed by spot welding at the interface formed between the top inner edge of the annular collar (115) of the metallic disc (100) and the outer peripheral surface of the sleeve (130), and the inner peripheral edge of the stepped portion (110) of the metallic disc (100) and the outer peripheral surface of the sleeve (130).

5. The composite fork bolt assembly (200) for a front suspension of a vehicle as claimed in claim 4, wherein the metallic disc (100) and the metallic sleeve (130) are formed from the metals selected from Steel, Aluminum (Ferrous & Non-Ferrous), and E34 steel.

6. The composite fork bolt assembly (200) for a front suspension of a vehicle as claimed in claim 5, wherein
- the metallic disc (100) having the annular collar (115) along with the stepped portion (110) is configured to guide the metallic sleeve (130) by the virtue of the guide length (2y) during the fitment of the metallic sleeve (130) within the opening (125) of said metallic disc (100);
- the guide length (2y) of the annular portion (115) and stepped portion (110) of the metallic disc (100) is configured to avoid distortion of the vertical axis of the metallic sleeve (130) with respect to the metallic disc (100) during welding process due to the formation of Heat Affected Zone (HAZ); and
- the base portion (105) of said metallic disc (100) is configured to act as the main load bearing portion embedded within the annular tab portion (55) of the fork bolt body (50) thus imparting the required strength to the composite fork bolt assembly (200).

7. The composite fork bolt assembly (200) for a front suspension of a vehicle as claimed in claim 3, wherein
- the thorough holes (120) on the stepped portion (110) of the metallic disc (100) are configured to form an imaginary base circle of radius Rb.; and
- the said imaginary base circle of radius Rb is configured to maintain a relation with the radius Ra of stepped portion of the metallic disc (100) as Rb = k1 * Ra., where Rb is the radius of the imaginary base circle, Ra is the radius of the stepped portion (110) of the metallic disc (100) and k1 is the correction constant ranges from 0.1 to 0.5.

8. The composite fork bolt assembly (200) for a front suspension of a vehicle as claimed in claim 6, wherein
- the guide length (2y) of the annular portion (115) and stepped portion (110) of the metallic disc (100) for the metallic sleeve (130) is configured to maintain a relation with the total length (l) of the metallic sleeve as 2y = k3*l; where, y is the thickness of the metallic disc (100), l is the total length of the metallic sleeve and k3 is variation constant ranging from 1.0 to 2.0; and
- said metallic sleeve (130) of the metallic washer assembly (150) is configured to have the outer diameter Ds maintaining a specific relation with the radius Rc of the base portion (105) as Ds = k2* 2Rc, where Rc is the radius of the base portion (105) of the metallic disc and k2 is the constant ranging from 0.5 to 0.8.

9. The composite fork bolt assembly (200) for a front suspension of a vehicle as claimed in claim 8, wherein
- the fork bolt assembly (200) is manufactured by positioning the metallic washer assembly (150) in a die and said positioning of the metallic washer assembly (150) is configured to maintain the empirical relations the thickness (y) of the base portion (105) of the metallic disc (100) as x = c1*y and y = c2*z, wherein “x” is distance of the top face of the base portion (105) of the metallic disc (100) from top face of the fork bolt body (50), “y” is the thickness of the base portion (105) of the metallic disc (100), “z” is the distance of the bottom face (80) of the fork bolt body (50) from the bottom face of the base portion of the metallic disc (100), and “c1” and “c2” are the constants ranging from 2.5 to 3.5 and from 0.1 to 0.3, respectively.

10. The composite fork bolt assembly (200) for a front suspension of a vehicle as claimed in claim 9, wherein
- the fork bolt body (50) of the fork bolt assembly (200) is made of plastic selected from glass filled polyamide so as to effectively compensate with the mechanical properties required for the purpose;
- the groove (60) of said fork bolt body (50) of the fork bolt assembly (200) is configured to accommodate an O-ring (30) therein so as to seal the interference between the inner surface of a fork pipe (45) and the outer surface of the fork bolt body (50) thus eliminating the leakage of oil thereby; and
- the annular tab (55) of said fork bolt body (50) of the fork bolt assembly (200) is configured to inhibit the vertical upside movement of the composite fork bolt assembly (200) relative to the fork pipe (45) of the front fork suspension system (500).

Dated this 6th day of Jan. 2025

Sahastrarashmi Pund
Head – IPR
Endurance Technologies Ltd.

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