FORM 2
THE Patent Act, 1970
(39 of 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
Shock absorber with a gas canister
Endurance Technologies Pvt Ltd R&D, E 92, MIDC Industrial Area, Waluj, Aurangabad, Maharashtra-431136
The following specification describes the invention

Field of the invention
The present invention relates to "Shock absorber with a gas canister" and more particularly to a low weight, easy fit gas canister that includes a gas chamber to accommodate fluid displacement caused by the entry of a shock rod into shock body.
Background of the invention
Gas 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 oil, 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 oil 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 bypass passages is the viscosity of the fluid itself and the diameter of the passages.
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.
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.
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.
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.
As the shock rod/piston assembly moves inwardly within the shock body during the compression stroke, the shock rod displaces a volume of fluid within the shock body that is equal to the volume of the shock rod that has extended in the shock body. To accommodate this displacement of fluid, an external or internal gas-filled reservoir is typically used in association with the shock absorber. Apart from providing housing to gas cap and gas membrane, external gas filled reservoir which is also called gas canister also provides leak proof joint with the hydraulic reservoir assembly of the damper. Additionally, it acts as a shock absorber mounting link with the vehicle frame. Mostly this canister which houses the external gas filled reservoir is made of metal typically aluminium. In other words, a gas canister made of aluminium adds up the dead weight to the suspension system in addition to higher manufacturing cost. Additionally, aluminium canisters are prone to leakage caused due to porosity in the castings.
Hence to obviate the lacunae in the prior art the objective of the present invention is to provide a canister which is easy to manufacture and weighs significantly less.
Another objective of the present invention is to eliminate leakage in the canister owing to porosity in the metal casting.

Summary of the invention
According to the first aspect of the present invention, the canister is of split design with at least two parts. One of said part is made of metal, preferably aluminium which provides a leak proof joint with the hydraulic reservoir assembly of the damper. Additionally said part also acts as a shock absorber mounting link on the vehicle. The other part of the canister is made of non-metal preferably plastic or synthetic resin or any composite material that houses the gas cap or said diaphragm. The split parts are joined through insert moulding process which makes the. assembly as a single unit. Additionally, the split parts may be joined through other means also like threading, snap-fit or easy fit attachments, et. al. As a result of the above invention, there is considerably reduction of the weight. Moreover, leakage from the canister due to porosity in the aluminium castings is avoided due to elimination of pores and blow holes as in case of aluminium moulding.
Brief description of the drawings
Figure 1 illustrates an isometric view of a general suspension unit.
Figure 2 illustrates an expanded view of a general suspension unit.
Figure 3 illustrates an exploded view of canister assembly according to the present invention.
Figure 4 and 5 illustrates a close up view of the present invention
Figure 6 illustrates the portion having gas membrane used in canister assembly according to the present invention

Figure 7 illustrates the portion with mounting bracket used in canister assembly of a shock absorber according to the present invention.
Detailed description of the invention
A selected illustrative embodiment of the present invention will be now described with respect to the accompanying figures 1,2,3, 4, 5, 6 and 7. An exemplary shock absorber/suspension unit constructed in accordance with an embodiment of the invention is identified generally by the reference numeral in figure 1 and figure 2, The shock absorber 1 is designed to be positioned between a vehicle chassis, and a wheel-carrying hub in a manner known in the art. The suspension unit 1 includes a cylinder assembly or housing 2 which is provided with a first end wall or cap 3. The end wall 3 carries a bracket 4 so as to provide a pivotal connection to the vehicle chassis.
The cylinder housing 2 having a longitudinal axis includes a cylinder bore that is closed at one end by the end wall and at the other end by the gland. The opposite end of the cylinder housing is enclosed by an end wall or cap 3 that carries a sealing gland. A piston rod assembly 5 extends through the sealing gland out of an aperture formed in the wall in a sealing arrangement while providing a translational guide or an inner tube 6 for the rod to allow the rod to translate within the cylinder housing 2. The rod has an elongated portion on which is carried a yoke 7 that provides the connection to the wheel-carrying hub. A coil compression spring 8 encircles the cylinder housing and the exposed end external to the housing of the piston rod 5. One end of this spring rests against a collar 9 that is connected to the cylinder housing 2. The opposite end of the spring 8 rests against a spring retainer 10 that is carried by the piston rod assembly 5 and is adjacent, to the yoke 7. In this arrangement, the spring 8 will be loaded as the piston rod moves relative to the

cylinder housing 2 upon suspension movement of the wheel or hub relative to the chassis of the vehicle. A snubber 11 is carried by the spring retainer 10 and will engage with the end cap 3 so as to provide a cushioned, yet positive stop, providing a limit to the total compression of the shock absorber 1.
An elastic gas chamber 17 (figure 3) is contained within a bore of a canister assembly 13 which is integrated with the end wall cap 3. An inert gas such as nitrogen may be filled in gas chamber 17 or a diaphragm 17 formed in the canister 13 so as to maintain a fluid pressure on the fluid in the shock absorber chambers. The inert gas may be inserted through a non return valve 16. The diaphragm is secured in the canister assembly 13 with the help of a gas cap 18. According to the first aspect of the present invention (figure 4 and figure 5), the canister 13 is of split design with at least two parts 14 & 15. One of said part 15 is made of metal, preferably aluminium which provides a leak proof joint with the hydraulic reservoir assembly of the damper. Additionally said part 15 also acts as a shock absorber mounting link through a bracket 4 on the vehicle. The other part of the canister 14 is made of non-metal preferably plastic or synthetic resin or any composite material that houses the gas cap or said diaphragm 17. The split parts 14 & 15 (illustrated in figure 6 and figure 7) are joined through insert moulding process which makes the assembly 13 as a single unit. Additionally, the split parts 14 & 15 may be joined through other means also like threading; snap-fit or easy fit 16 attachments, et. al. As a result of the above invention, there is considerably reduction of the weight. The oil path 19 from the metallic part of canister 15 is provided with a path which communicates with oil channel 19a in said non metallic canister part 14. Additionally a structural member 20 and its receiver 20a is provided in metallic and non metallic part 15& 14 respectively. Moreover,

leakage from the canister 13 due to porosity in the aluminium castings is avoided due to elimination of pores and blow holes as in case of aluminium moulding. Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained therein.

Claims
We claim:
1. A gas canister assembly for a shock absorber, with a mounting bracket on its end cap, comprising at least two parts, first part attached to said mounting bracket and a second part with a gas diaphragm, coupled to said first part.
2. A gas canister assembly for a shock absorber, with a mounting bracket on its end cap, as claimed in claim 1, wherein said two parts are joined together through insert moulding process.
3. A gas canister assembly for a shock absorber, with a mounting bracket on its end cap, as claimed in claim 1, wherein said two parts are joined together through thread fitting.
4. A cas canister assembly for a shock absorber, with a mounting bracket on its end cap, as claimed in claim 1, wherein said two parts are joined together through snap fitting or easy fitting.
5. A gas canister assembly for a shock absorber, with a mounting bracket on its end cap, as claimed in claim 1, wherein said first part is preferably metal and second part is preferably non metal.
6. A gas canister assembly for a shock absorber, with a mounting bracket on its end cap, as claimed in claim 1, wherein said first part is preferably non-metal and second part is preferably metal.
7. A gas canister assembly for a shock absorber, with a mounting bracket on its end cap, as claimed in claim 1, wherein atleast a pair of structural member and a receiver is provided on said first part and said second part respectively.
8. A shock absorber with said gas canister as claimed in claim 1..