[001] Field of the invention
[002] The present invention relates to bottom case of a shock absorber and more particularly to variable topology bottom case of a telescopic and inverted shock absorber of a two and three wheeler vehicle.
[003] Description of the prior art
[004] A conventional prior art shock absorber such as front fork shock absorber comprises a cylinder which is adapted at one end for attachment to the sprung or un-sprung mass of a vehicle. A piston is slideably disposed within the cylinder with the piston separating the interior of the cylinder into two fluid chambers. A piston rod is connected to the piston and extends out of one end of the cylinder where it is adapted for attachment to the other of the sprung or unsprung mass of the vehicle.
[005] Various conventional motorcycles employ, as a means for supporting a front wheel, a telescopic front fork including two sets of axially slidable inner and outer tubular members, each set of the tubular members including a fork pipe and a bottom case, respectively, and a hydraulic system interposed between the two tubular members for providing a shock absorbing action. Upon braking of such conventional motorcycles, displacement of the centre of gravity, a force of inertia, etc., act in a direction to contract the front fork. Particularly, upon sudden braking, the front fork will come to assume the fully contracted position thereof.
[006] A front wheel suspension system for a motorcycle is already known which includes a contraction restraining mechanism for intercepting, upon braking of a front wheel of the motorcycle, a main oil communicating passage between a fork pipe and a bottom case to restrain axially contracting motion

between the fork pipe and the bottom case in order to prevent a front part of the motorcycle from diving or moving down by sudden braking operation of the front wheel.
[007] In such a conventional front wheel suspension system for a motorcycle, generally, the front tube is made of high strength steel tubing. The bottomcase is generally manufactured in aluminium through casting process. Over considerable length at the topside of the bottomcase, it has an overlap with „ the front tube as illustrated in Figure 3a and Figure 3b. The lower end of the bottomcase experiences very high stress due to transfer of braking loads from wheel to the vehicle chassis. In the said overlap region, there is considerably lower load on the bottomcase than the lower end of the bottomcase. Despite of such a high variation of loads at the top and bottom side of the bottomcase, the cross section topology of the bottomcase is generally kept the same. The cross section is either uniformly circular or oval with a constant thickness. This makes the bottomcase either under designed or overdesigned without practical realisation.
[008] Few patent applications in prior art, such as WO2013185578 illustrates a scooter with variable cross section tubular frame. It relates to a scooter with a variable cross section tube frame through processes of hydroforming and suppression tailor welding. However, such processes is not sustainable in manufacturing of bottom case of front forks owing to manufacturing constrains and design limitations.
[009] Hence, there exists a need to obviate the lacunae in the prior art and to provide a simple optimized bottom case of a front fork, saving material as well as resources for its manufacturing. Therefore the objective of the present

invention is to provide an optimized variable topology bottomcase in front forks in motorcycles that facilitates optimized bottomcase in either inverted or telescopic front fork of two and three wheelers.
[0010] The second objective of the present invention is to provide an optimized bottomcase that saves considerable amount of metal for its manufacturing as well as processing costs.
[0011] Summary of the invention
[0012] The present invention relates to telescopic shock absorber such as a front fork of a two or a three wheeler. The bottom case of the lower front fork tube may be subdivided in various regions according to the loads/stress experienced by them. Basing on the loads/stress concentrations, different topologies can be assigned to the regions. For example, the region A of the bottom case where it has overlap with upper fork tube, experiences lesser load and stress, thus topology of the section is in the form of hollow ribbed section. The selective thickness of the rib is maximum at the mid length and gradually reduces towards the topside of the bottom case. The next region B experiences high bending load and stress. As a result, a different topology may be adopted for the bending stress concentrated area. Here the topology is quite uniform for handling higher loads and bending stress concentration over the next region C. The bending load reduces gradually as we move towards the bottom. Hence section of bottom case reduces accordingly. Here the topology can either be constant or variable. The bottom region D of bottom case experiences higher braking load. This region experiences high stress because of braking where it transfers the braking loads, cross section is with another suitable topology accordingly.

[0013] Brief description of drawings
[0014] The invention will now be explained in relation to the accompanying
drawings, in which: [0015] Figure 1 illustrates side view of a two-wheeler with a front fork
assembly according to the present invention. [0016] Figure 2 illustrates a telescopic front fork assembly with variable
topology bottom case according to the present invention. [0017] Figure 3a and 3b illustrates cross-sectional view of leg assembly of
braking side and non-braking side respectively of front fork according to the
prior art. [0018] Figure 5 illustrates braking side bottomcase for a vehicle with disc
brakes according to the present invention. [0019] Figure 6 illustrates non-braking side bottomcase for a vehicle with drum
brakes according to the present invention. [0020] Figure 7 illustrates alternate designs of braking side bottomcase
according to the present invention. [0021] Figure 8 illustrates alternate designs of non-braking side bottomcase
according to the present invention. [0022] Figure 9 illustrates the axle boss according to the present invention
[0023] Detailed description of the invention
[0024] A front fork assembly (101) is provided on a motorcycle and made up of a pair of telescopic shock absorber such as front fork members (figure 1 and figure 2), each secured to the steering stem (not shown) of the

motorcycle at or adjacent to the top of the front fork member. Each front fork member is made up of an upper fork tube (102) closed by a cap (104) at the top thereof and a bottom case (110, 111) or which is telescopically, sealably movable with respect to the upper fork tube (102). The lower fork tubes (110 &111) are provided with axel bosses (105) on whom the motorcycle front wheel is mounted on a hub (100). The front fork assembly may either be telescopic or inverted.
[0025] A main spring (106) (Figure 3) is positioned between the top of the damper piston (109) and the cap (104) which closes the upper end of the upper fork tube (102) to hold the front fork member in extended position and return it to extended position after compression (figure 3a). On one of the sides of the wheel hub (100, shown in figure 1) of the front wheel there are integrally mounted brakes which may be either disc or drum type (not shown in figure). The bottom case (110 &111), (Figure 3a, Figure 3b) present on the side where the brake disc or drum (not shown in figure) is mounted is termed the braking side (110) and the other front fork tube is termed as non-braking side (111, Figure 3b) respectively as illustrated in Figure 3a and Figure 3b. Mostly, the braking side (110) transfers the braking loads from the wheel to the chassis of vehicle (not shown in figure).
[0026] Figure 5 illustrates the bottom case (110) of braking side according to the present invention. The bottom case (110) may be subdivided in various regions according to the loads/stress experienced by them. Basing on the loads/stress magnitudes, different topologies can be assigned to the regions. For example, the region A of the bottomcase (110) where it has overlap with upper fork tube (102), experiences lesser loads and stress, thus the cross

section across X-X1 is with topology 1 (Figure 5a), which is in the form of hollow ribbed section. The next region B experiences high bending stress and load. As a result, a different topology may be adopted for the bending stress concentrated area. The selective thickness of the rib is maximum at the mid length and gradually reduces towards the topside of the bottomcase. Topology 2 (Figure 5b) is for the middle bending stress concentrated area B along section Y-Y1. For the next region C, the topology is quite uniform for handling higher loads and bending stress concentration. The bending load reduces gradually as we move towards the bottom of the region C. In region C, the cross section of bottomcase reduces accordingly. Here the topology can be variable. The bottom region D of bottomcase experiences higher braking load. This region D experiences high stress because of braking where it transfers the braking loads, cross section Z-Z1 is with topology 3 as illustrated in Figure 5c. [0027] Figure 6 illustrates the topologies in the non-braking side bottom case (111) according to the present invention. Since there is a marked difference between the braking side (110) and the non -braking side (111) owing to the presence of a lug (112)(Figure 3a) to accommodate the brake mount, both in drum and disc brake types. The topologies 1, 2 & 3 have been taken across cross sections A-A1, B-B1 and C-C1 respectively. There exists difference in the topologies in Figure 5c and Figure 6c (topologies 3) of said braking side (110) and non-braking side (111). Further, the loads/stress on the Topology 3 (Figure 5c) of bottom case (110) of braking side is more than that of Topology 3 (Figure 6c) of bottom case (111) of non-braking side, hence there is such difference of construction of this part.

[0028] Figure 7 and Figure 8 illustrates non-limitive alternative designs for braking and non-braking sides of bottom case respectively. The alternate designs can be of various combinations of different topologies in a bottom case as illustrated in said figures. For example, in Alternate Design A of Figure 7, topology 1 (Figure 7a) is a ribbed section, topology 2 (Figure 7b) is a circular section and topology 3 (Figure 7c) is a ribbed section. The ribbed section in topology 3 (Figure 7c) provides reduction in mass of the bottom case. In the region of topology 2 (Figure 7b), the support from inner tube ends, hence to distribute the stresses uniformly, a circular section is mostly given. In Alternate Design B of figure 7, topology 1 (Figure 7d) is an oval/elliptical section, topology 2 (Figure 7e) is a circular section and topology 3 (Figure 7f) is oval/elliptical section. The oval/elliptical section in topology 1 and topology 3 (Figure 7d & 7f), are proposed for increasing directional stiffness. In Alternate Design C of Figure 7, topology 1 (Figure 7g) is an oval/elliptical section, topology 2 (Figure 7h) is a circular section and topology 3 (Figure 7i) is a ribbed section. Alternate Design D of Figure 7, topology 1 (Figure 7j) is a ribbed section, topology 2 (Figure 7k) is a circular section and topology 3 (Figure 71) is an oval/elliptical section. Topology 1 (Figure 7a, Figure 7d, Figure 7g, Figure 7j), topology 2 (Figure 7b, Figure 7e, Figure 7h, Figure 7k) and topology 3 (Figure 7j, Figure 7k, Figure 71) are taken from cross section D-D1, E-E1 ,F-F1 respectively. For alternated designs C and D, they have the combined benefits of both oval/elliptical and ribbed section as illustrated in alternate designs A and B.
[0029] Similarly, in Alternate Design A of Figure 8 (Non braking side), topology 1 (Figure 8a) is a ribbed section, topology 2 (Figure 8b) is a circular section

and topology 3 (Figure 8c) is a ribbed section. The ribbed section in topology 3 (Figure 8c) provides reduction in mass of the bottom case. In the region of topology 2 (Figure 8b), the support from inner tube ends, hence to distribute the stresses uniformly, a circular section is mostly given. In Alternate Design B of figure 8, topology 1 (Figure 8d) is an oval/elliptical section, topology 2 (Figure 8e) is a circular section and topology 3 (Figure 8f) is oval/elliptical section. The oval/elliptical section in topology 1 and topology 3 (Figure 8d & 8f), are proposed for increasing directional stiffness. In Alternate Design C of Figure 8, topology 1 (Figure 8g) is an oval/elliptical section, topology 2 (Figure 8h) is a circular section and topology 3 (Figure 8i) is a ribbed section. Alternate Design D of Figure 8, topology 1 (Figure 8j) is a ribbed section, topology 2 (Figure 8k) is a circular section and topology 3 (Figure 81) is an oval/elliptical section. Topology 1 (Figure 8a, Figure 8d, Figure 8g, Figure 8j), topology 2 (Figure 8b, Figure 8e, Figure 8h, Figure 8k) and topology 3 (Figure 8j, Figure 8k, Figure 81) are taken from cross section G-G1, H-H1 ,l-l1 respectively
[0030] Further, the axel boss (105) of the bottom case (110 and 111) of both braking side (107) and non-braking side (108) are also provided with an optimised elevation where considerable mass of material is saved. The required configuration of axle clamping loads on the axle boss are met with the optimised elevation with sectored configuration (113) as shown in figure 9
[0031] While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other

modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. [0032] Brief references used in the drawings
100 Wheel Hub 109 Damper piston
101 Front fork assembly 110 Bottom case of braking side
Cap 111 Bottom case of non braking
Axel bosses side
Main spring 112 Lug
Braking side 113 Sectors on the boss
Non braking side

Claims
We claim:
A front fork shock absorber for two or three wheeler vehicle, having a braking side and a non- braking side, comprising an upper fork tube closed by a cap and a bottom case which is movable with respect to said upper fork tube, characterised by a bottom case having variable thickness.
A front fork shock absorber for two or three wheeler vehicle, having a braking side and a non- braking side, comprising an upper fork tube closed by a cap and a bottom case which is movable with respect to said upper fork tube, characterised by a bottom case having side walls of variable thickness.
A front fork shock absorber for two or three wheeler vehicles as claimed in claim 1, wherein two or more sectors of its bottom are thicker than other sectors.
A front fork shock absorber for two or three wheeler vehicles as claimed in claim 2, wherein the thickness of the side wall of the bottom case is maximum in the mid-length, gradually reducing towards top and the bottom of said bottom case.
A front fork shock absorber for two or three wheeler vehicle, as claimed in claim 1, wherein said braking side of a variable thickness bottom case has a hollow ribbed section followed by a circular section and further followed by a circle with single lug section cross section.
A front fork shock absorber for two or three wheeler vehicle, as claimed in claim 1, wherein said variable thickness for braking side and non-braking side bottom case for non-braking side comprises a hollow ribbed section followed
by a circular cross section

A front fork shock absorber for two or three wheeler vehicle, as claimed in claim 1, wherein said optimised variable thickness for braking side and non-braking side bottom case comprises a hollow ribbed section followed by a circular section and further followed by a hollow ribbed cross section.
A front fork shock absorber for two or three wheeler vehicle, as claimed in claim 1, wherein said variable thickness for braking side and non-braking side bottom case comprises a hollow elliptical section followed by a circular section and further followed by a hollow elliptical cross section.
A front fork shock absorber for two or three wheeler vehicle, as claimed in claim 1, wherein said variable thickness for braking side and non-braking side bottom case comprises a hollow ribbed section followed by a circular section and further followed by a hollow elliptical cross section.
A bottom case of a shock absorber for two and three wheelers comprising an axel boss with sectored configuration.