FIELD OF THE INVENTION
[001] The present invention relates to shock absorber of a motorcycle suitable for use
in a motorcycle or the like.
BACKGROUND OF THE INVENTION
[002] Shock absorbers for vehicles such as motorbikes, cars, coaches, etc. are widely
used in suspension system wherein it is provided with a piston sliding in a cylindrical
chamber containing damping fluid, which produces viscous damping of the stresses applied to
the suspension of the vehicle during driving and the piston is mounted on a guide rod which
projects from the cylindrical chamber and is secured onto the vehicle chassis. The movement
of the rod in the chamber, owing to the stresses while driving the vehicle, cause variations in
the volume of the damping fluid in the chamber. For the piston to move within the shock
body, the fluid within the fluid filled cavity of the shock body must travel through the piston.
Therefore passages are formed through piston to control the fluid flow between each section
of the shock body. The passages are typically aligned with the longitudinal axis of the piston.
The openings of some of these passages may be covered with leaf valves while the remainder
of the openings may be uncovered to thus serve as by-pass passages. The only restriction in
the by-pass passages is the viscosity of the fluid itself and the diameter of the passages.
[003] The shock rod/piston assembly and the shock body that includes the cylindrical
wall and both the end caps move in relation to one another upon the application of forces to the shock absorber. The relative movement between the shock rod/piston assembly and the shock body results in the movement of the piston through the fluid which provides the

hydraulic damping for the shock absorber. As a result, the shock forces that are applied to the vehicle component to which the shock absorber is coupled are at least partially absorbed by the shock absorber. Accordingly the shock forces that are applied to the vehicle chassis are dissipated by the shock absorber.
[004] The movement of the shock rod/piston assembly within the fluid-filled cavity
of the shock body occurs in two stages, a compression stage followed by a rebound stage.
[005] When the vehicle moves over an un-even terrain, shock forces are applied to
the vehicle component to which the shock absorber is mounted. These shock forces cause the vehicle component to move from a steady state position to a position where the vehicle component has compressed relative to the chassis. Since the shock absorber is disposed between the vehicle component and chassis, as the components move toward one another, the shock absorber compresses, the shock rod/piston assembly moves inwardly relative to the shock body, within the fluid filled cavity of the shock body. As a result, the piston moves within the fluid filled cavity of the shock body toward the first end cap. During this compression stage, the shock absorber slows or dampens the rate at which the vehicle component compresses toward the chassis.
[006] The rebound stage follows the compression stage. The rebound stage results
from the resilient expansion of the spring associated with the shock absorber, which pushes the vehicle component away from the vehicle chassis to the original steady state position. The force exerted by the spring is usually quite low by comparison with the compressive force, because in the rebound stage, the force of the spring only needs to be high enough to overcome the combined weight of the vehicle and the rider. This spring force causes the shock absorber to extend resulting in the shock rod/piston assembly extending outwardly

relative to the shock body. During the rebound stage, the piston moves within the fluid filled cavity away from the first end cap toward the second end cap. The shock absorber, as a result, slows or dampens the rate at which the vehicle component moves relative to the chassis during the rebound stage.
[007] Considering the system dynamics and existing vehicle design, it becomes
necessary to have a spring on either side of the vehicle. There also exists a need to design a shock absorber which is low in cost and weight.
SUMMARY
Present twin shock absorbers have a damper as well as spring on both sides of the vehicle. The spring performs the function of absorbing the shocks produced due to uneven profile of the road, while the primary function of the damper is dissipation of these absorbed energy into the surrounding environment. Considering the system dynamics and existing vehicle design, it is necessary to have a spring on either side of the vehicle. However, there is no absolute necessity that the energy dissipation also has to occur on both the sides. The present subject matter discloses a shock absorber which generates damping force in only one of the two legs of the shock absorber while no viscous damping in the other. This optimized design negates the requirement of a number of components in the shock absorber leg that has no viscous damping. This also leads to reduction in production cycle time and also reduces the cost and weight of the shock absorber. The shock absorber of the present invention decreases the asymmetric loading that would otherwise be created by the use of only a single side damping assembly.

BRIEF DESCRIPTION OF THE DRAWINGS
[008] The present invention will become more fully understood from the detailed
description given herein below and the accompanying drawings which are given by way of
illustration only and thus are not limitative of the present invention.
[009] Figure 1 is a schematic side view of the motorcycle including a shock absorber
system according to an embodiment of the present invention.
[0010] Figure 2 is a schematic representation of the shock absorber found in the prior
art.
[0011] Figure 3 is a cut sectional view of the shock absorber found in the prior art.
[0012] Figure 4 is a schematic representation of the shock absorber according to an
embodiment of the present invention.
[0013] Figure 5 is a cut sectional view of the shock absorber with mono tube structure
according to an embodiment of the present invention.
[0014] Figure 6 is a cut sectional view of the shock absorber with twin tube structure
according to an embodiment of the present invention.
[0015] Figure 7 is a cut sectional view of the gas charged shock absorber according to
an embodiment of the present invention.
[0016] Figure 8 shows a graphical representation of the shock absorber travel during
handling event of the motorcycle.
[0017] Figure 9 shows a graphical representation of the shock absorber travel during
ride event of the motorcycle.

DETAILED DESCRIPTION OF THE DRAWINGS
[0018] For the purposes of understanding the principles of the present invention,
reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is 'thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
[0019] Referring now specifically to the drawings, Figure 1 shows a schematic view
of a typical motorcycle 20 on which a shock absorber 10() is steerably mounted on a lower rear portion of the motorcycle 20 in a vertically swingable manner. The motorcycle 20 uses two legs of the shock absorbers 100, with one shock absorber located on each side of a rear wheel 40. The motorcycle has other conventional components which are not represented for convenience.
[0020] The drawing of a shock absorber 100A found in the prior art is represented by
Figure 2. The shock absorber 100A includes a pair of springs 62A and damper 64A assemblies, each having an upper portion and a lower portion configured to absorb relative shocks observed by the motorcycle 20 thereto. The upper portion is secured to a sprung mass (mass of a motorcycle body) 60A and the lower portion is secured to an unsprung mass (mass of a wheel assembly) 66A. The sprung mass 60A and the unsprung mass 66A translate with each other due to a combined effect of spring 62A and damper 64A.

[0021] Reference is now made to Figure 3 for a detailed description of the shock
absorber 100A, generally found in prior art. The shock absorber 100A comprises an outer
tube 110A and an inner tube 107A concentrically inserted within the outer tube 110A.
Pressurized damping fluid such as oil 105A is filled into the inner tube 107A to dissipate a
stored energy into the surrounding environment. Damping fluid 105A flows in and out of a
reservoir 112A through a base valve assembly 109A during compression and rebound cycles
respectively. A piston 103A is slidably mounted in the inner tube 107A and is provided
thereof with a piston valve 106A to restrict flow of damping fluid through an orifice 114A
during the compression and rebound cycles. A piston rod 102A is integrally connected to the
piston 103A, and extends outwardly through a rod guide 113A. A damping fluid seal 104A is
disposed on the top of the outer tube 110A to prevent leakage of damping fluid there through.
A main spring 101A rested on a spring seat 108A thereto performs the function of absorbing
the energy produced due to uneven profile of the road on which the motorcycle 20 traverses.
[0022] The reference now is being made to the Figure 4, which represent the shock
absorber 100 according to an embodiment of the present invention. The shock absorber 100 constitutes a right shock absorber unit 300 and a left shock absorber unit 200. The right shock absorber unit 300 and the left shock absorber unit 200 are made different from each other with respect to at least the internal structure and the design parameters. The left shock absorber unit 200 is constituted of a left spring 72 and a damper 64, and the right shock absorber unit 300 is constituted only of right spring 62. The right shock absorber unit 300 does not constitute damper, hence reducing the required parts thereto and simplifying the construction. The damper 64 in the left shock absorber unit generates a double or increased damping to absorb the same amount of energy as in the shock absorber consisting dampers on both

sides. Hence overall damping achieved by shock absorber 100 of the present invention is same as achieved in shock absorber of the prior art.
[0023] In Figure 5, 5a and 5b represent a cross sectional view of the left shock
absorber unit 200 and the right shock absorber unit 300 respectively, according to the present invention. The left shock absorber unit 200 includes an outer tube 110 secured on a mounting ring 115 which is at the bottom of the left shock absorber unit 200. An outer tube 110 has the hollow structure with the lower end. being closed by a bottom cap 132. The upper end of the outer tube 110 is closed by the means of a rod guide 113. An inner tube 107 is secured within the outer tube 110 and is filled with damping fluid 105. A left spring 72 performs the function of absorbing the energy produced due to uneven profile of the road on which the motorcycle 20 traverses. In left shock absorber unit 200, portions except for the outer tube 110, the inner tube 107 and the left spring 72, that is, portions which generate compression damping and rebound damping due to a piston 103, a piston valve 106, an orifice 114, a base valve assembly 109 and a piston rod 102 constitute the damper 64 (represented in Figure 4). The orifice 114 is such as to dampen movement of the piston 103 in the inner tube 107 and is responsive to changes in piston velocity to provide orifice control for the left shock absorber unit 200. Additional damping is provided by the piston valve 106 during compression and rebound cycles. Thus, left shock absorber unit 200 includes both the left spring 72 and the damper 64 on same side.
[0024] The right shock absorber unit 300, shown in Figure 5b is single tube or
cylinder type having relatively simple and inexpensive construction. The right shock absorber unit 300 includes either an unitary tube or an outer tube 110, the right spring 62 rested on a spring seat 108, the piston 103 connected to the piston rod 102. The outer tube 110 is

completely filled with free air 142 instead of damping fluid (oil). This substantially negates the requirement of number of components used for damping, like damping fluid, the damping fluid seal, the base valve assembly and the piston valve. Thus, right shock absorber unit 300, of the present invention generates no damping forces during the compression and rebound cycles of the piston 103.
[0025] Further, reference is made to the Figure 6 and Figure 7, which depict variations
made in the invention owing to applicability. The shock absorber with only single side damping which is already discussed above can also be used in the twin-tube shock absorber as well as in the gas charged shock absorber known in the art. In the Figure 6a, left shock absorber unit 200 is the twin tube type shock absorber which generates increased damping forces. In the Figure 6b, the right shock absorber unit 300 is also the twin tube type shock absorber but generates no damping forces during the compression and rebound cycles of the piston. Figure 7a shows the left shock absorber unit 200 which is gas charged type of shock absorber and generates increased damping. Figure 7b depicts the right shock absorber unit 300 which does not generate any damping.
[0026] Reference is now made to the Figure 8, which shows graphical representation
of travel of the shock absorber of the prior art and the shock absorber of the present invention, during the ride evaluation. According to Figure 8a, both the dotted line and the solid line depict the travelling of the two legs of the shock absorber as shown in Figure 2 (Prior Art). Further, according to Figure 8b, the dotted line depicts the travel of the right shock absorber unit (300 according to the Figure 4) while the bold line indicates the travel of the left shock absorber unit (200 according to the Figure 4). Thus, the values associated with the travelling of both the right shock absorber unit and left shock absorber unit are same. It indicates that

there is no adverse effect on ride and handling experience of the user because of the increased
damping on one side according to the present invention.
[0027] Further, the Figure 9 shows graphical representation of travel of the shock
absorber of the prior art and the shock absorber of the present invention, during the handling
events of the motorcycle. According to Figure 9a, both the dotted line and the solid line depict
the travelling of the two legs of the shock absorber as shown in Figure 2 (Prior Art). Further,
according to Figure 9b, the dotted line depicts the travel of the right shock absorber unit (300
according to the Figure 4) while the bold line indicates the travel of the left shock absorber
unit (200 according to the Figure 4) during the handling events.
[0028] Thus the results obtained in relation to the performance of the present
invention are comparable to that obtained in the prior art as illustrated in Figure 8 & 9.
[0029] It is only for the convenience that the increased damping shock absorber unit
and no damping shock absorber unit are depicted as left shock absorber unit and right shock
absorber unit respectively. However interchanging the same would not affect the overall
performance and would still satisfy the purpose of the invention.
[0030] The use of damper in only one of the units of shock absorber is advantageous
for reducing both the cost and the weight of shock absorber system. Also the overall cycle
time required for production of shock absorber is reduced. The shock absorber of the present
invention decreases the asymmetric loading that would otherwise be created by the use of
only a single side damping assembly.
[0031] While the invention has been illustrated and described in detail in the drawings
and description, the same is to be considered as illustrative and not restrictive in character, it
being understood that only the preferred embodiment has been shown and described and that

all changes and modifications that come within the spirit of the invention are desired to be protected.

CLAIMS
We claim:
1. A pair of hydraulic shock absorber for a rear suspension for a motorcycle comprising;
a first shock absorber unit having a spring assembly; and
a second shock absorber unit having said spring assembly, wherein a damping assembly is provided in either of said first shock absorber unit or said second shock absorber unit.
2. The pair of hydraulic shock absorber for a rear suspension for a motorcycle as claimed in claim 1, wherein said spring assembly comprises a spring, a spring seat, and said damping assembly comprises a base valve assembly, piston valve assembly, a damping fluid and a damping fluid seal.
3. The pair of hydraulic shock absorber for a rear suspension for a motorcycle as claimed in claim 1, wherein said first shock absorber have a twin tube structure and said second shock absorber may have either a mono tube or a twin tube structure.
4. The pair of hydraulic shock absorber for a rear suspension for a motorcycle as claimed in claim 1, wherein said first shock absorber have a mono tube structure and said second shock absorber may have either a mono tube or a twin tube structure.
5. A motorcycle having said shock absorber as claimed in claim 1.