DESC:Field of the invention
The present invention relates to a shock absorber system of a vehicle, and more particularly, the present invention relates to a piston rods being used in the shock absorber and method of manufacture thereof.
Background of the invention
Shock absorbers such as hydraulic twin tube, mono tube, canister type shock absorber includes a piston rod at bottom portion thereof. The piston rod is typically a hard chrome-plated piece of cold-rolled steel which attaches to the piston and extends from the cylinder through the rod-end head. In cylinders, the actuator has a rod extending from a side of the piston and out of the barrel. The piston rod connects the hydraulic actuator to the machine component doing the work. This connection can be in the form of a machine thread or a mounting attachment.
Light weight vehicle is an important measure to save fuel. The existing piston rods are heavy as weight of each solid piston rod is around a kilogram. Further, the bending strength of the existing piston rod is comparatively lower. The weight of the existing piston rods requires raw material of higher cost.
Accordingly, there exists a need to provide a piston rod that overcomes the drawbacks of the prior art.
Objects of the invention
An object of the present invention is to reduce weight of the piston rod.

Another object of the present invention is to reduce cost of manufacturing of the piston rod.
Summary of the invention
The present invention provides a piston rod for a shock absorber. The piston rod comprises of a hollow pipe having solid ends joined on each end of the hollow pipe thus configuring the hollow pipe there between. In another aspect, the present invention provides a method for manufacture of hollow piston rod. The method includes holding a hollow pipe in a fixture and keeping solid rod ends in cryogenic cooling chamber to allow them to shrink, wherein the solid rod ends are cooled to the temperature between -170 oC to -190oC. Furthermore, the method includes keeping the cooled solid rod ends within open ends of the hollow rod in an assembly fixture and pressing. Specifically, each end of the hollow rod is pressed one by one to form a hollow piston rod.
Brief description of the drawings
The objectives and advantages of the present invention will become apparent from the following description read in accordance with the accompanying drawings wherein,
Figure 1 shows a cross sectional view of a hollow piston rod, in accordance with the present invention.
Figure 2 shows a flowchart for a method of manufacturing the hollow piston rod, in accordance with the present invention.

Detailed description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.
The present invention provides a hollow piston rod and a method of manufacture thereof. The hollow piston rod of the present invention is light in weight and cost of raw material required is also less as compared to piston rods of the prior art.
The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in bracket in the following description.
Referring to figure 1, there is shown a hollow piston rod (100). The hollow piston rod (100) includes a hollow pipe (10) with both open ends. The open ends of the hollow pipe (10) accommodate solid rod ends (12a, 12b) therein. In an embodiment, the solid rod ends (12a, 12b) are fixed into the open ends of the hollow pipe (10) by cryogenic cooling of the solid rod ends (12a, 12b) and pressing them. However, it may be evident to those skilled in the art to any other suitable method to fix the solid rod ends (12a, 12b) into open ends of the hollow pipe (10).
Referring now to figure 2, a method (hereinafter referred to as ‘the method (200)’) for manufacture of hollow piston rod (100) in accordance with the present invention is shown.
At step (110), the method (200) includes holding the hollow pipe (10) in a fixture (not shown).
At step (120), the method (200) includes keeping solid rod ends (12a, 12b) in cryogenic cooling chamber to allow them to shrink, wherein the solid rod ends (12a, 12b) are cooled to the temperature between -170 oC to -190oC.

At step (130), the method (200) includes keeping the cooled solid rod ends (12a, 12b) within open ends of the hollow pipe (10) in an assembly fixture and pressing. Specifically, each end of the hollow pipe (10) is pressed one by one to form a hollow piston rod (100).
In an embodiment, the hollow pipe (10) is made of low-carbon structural steel. Further, the solid rod ends (12a, 12b) are made of the same material.
Advantages of the invention
• The hollow piston rod has pull out strength of rod ends which surpass the standard requirement.
• The process of making the hollow piston rod is cleaner and efficient process.
• The costs making the hollow piston rod of the present invention is lesser than friction welding / laser welding of solid rod ends.
• The hollow piston rod of the present invention requires no filler material to join two parts.
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiment. Detailed descriptions of the preferred embodiment are provided herein; however, it is to be understood that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure, or matter. The embodiments of the invention as described above and the methods disclosed herein will suggest further modification and alterations to those skilled in the art. Such further modifications and alterations may be made without departing from the spirit and scope of the invention.

,CLAIMS:We claim:
1. A piston rod (100) for a shock absorber, the piston rod (100) comprising of
a) a hollow pipe (10) selected from low carbon steel; and
b) solid rod ends (12a, 12b) capable of joining on each ends of the hollow pipe (10) to configure the hollow tube (10) therebetween;
wherein, the solid rod ends (12a, 12b) are shrunk by cooling in a cooling chamber and are fixed into the open ends of the hollow pipe (10) by pressing.
2. The hollow piston rod (100) as claimed in claim 1 wherein the solid rod ends are cooled in a cryogenic cooling chamber.
3. The hollow piston rod (100) as claimed in claim 1 wherein the solid rod ends are cooled to the temperature between -170oC to – 190oC.
4. A method (200) for fabricating a hollow piston rod (100), the method (200) comprising the steps of:
holding the hollow rod (10) in a fixture at a position to configure the hollow pipe (10) between two solid rod ends (12a, 12b);
keeping solid rod ends (12a, 12b) in a cooling chamber to allow them to shrink; and
keeping the cooled solid rod ends (12a, 12b) within open ends of the hollow pipe (10) in an assembly fixture and pressing;
wherein, each end of the hollow pipe (10) is pressed one by one to form a hollow piston rod (100).
5. The method (200) for manufacturing a hollow piston rod (100) as claimed in claim 4 wherein the solid rod ends are cooled in a cryogenic cooling chamber.
6. The method (200) for manufacturing a hollow piston rod (100) as claimed in claim 4 wherein the solid rod ends are cooled to the temperature between -170oC to -190oC