DESC:PISTON ROD ASSEMBLY FOR SHOCK ABSORBER

Field of the invention

The present invention relates to a suspension system of an automobile, more particularly, the present invention relates to a piston rod assembly for a shock absorber, specifically, to a bush in rod guide to avoid metal to metal contact, reduce friction and increase shock absorber life.

Background of the invention

Generally all shock absorbers such as hydraulic twin tube, mono tube, canister type shock absorber include a rod guide assembly with a bimetal bearing. Figures 1a and 1b show a typical rod guide assembly with bimetal bearing of the shock absorber. The assembly includes a piston rod (1) and a rod guide (2) separated by a bimetal bearing (3). The bimetal bearing (3) is used in shock absorber assembly to avoid direct metal to metal contact between the piston rod (1) and a rod guide (2) to reduce friction and wear.

The bimetal bearing (3) is a rolled piece of metal with a coating inside and with a gap/slit (4) in between the ends. The slit (4) in the bimetal bearing (3) provides cleavage for contaminant accumulation. The accumulated contaminant and sharp edge of the slit (4) may create scratches on the piston rod (10) during movement thereof. The slit (4) is unavoidable due to usage of sheets during manufacturing.

The bimetal bearing (3) is made up with alloy impregnated steel sheets and chamfer is generated during sheet cutting. Hence, chamfer cannot be controlled. The thickness of coating/ alloy thickness in the bimetal bearing (3) on an inner surface is about 0.2 to 0.4 mm. Hence, if this layer peels off either by the way of wear and tear or by the way of rubbing, the base metal of bearing/ back steel comes in direct contact with the piston rod (1) and creates scratch marks on the piston rod (1). Also, because of lesser thickness of the bimetal bearing (3), contaminant particle remain on surface and make scratch mark on the piston rod (1) while reciprocation motion thereof.

Accordingly, there exist a need to provide a piston rod assembly for a shock absorber that overcomes the above mentioned drawbacks of the prior art.

Objects of the invention

An object of the present invention is to avoid metal to metal contact in a rod guide and a piston rod.

Another object of the present invention is to reduce friction between the rod guide and the piston rod which increases life of a shock absorber.

Summary of the invention

Accordingly, the present invention provides a piston rod assembly for a shock absorber. The piston rod assembly comprises a piston rod, a rod guide and a bearing bush. The piston rod is capable of undergoing reciprocating movement. The rod guide is adapted for guiding the reciprocating movements of the piston rod there through. The bearing bush is fitted for example by press fitting to the rod guide for separating the piston rod from the rod guide. The bearing bush is made up of a polymer material as a single continuous piece without any slit and without any coating on an inner surface thereof to reduce contaminant accumulation as well as friction between the piston rod and the rod guide thereby minimizing the scoring mark on the piston rod and thus resulting in an improved shock absorbers life.

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,
Figures 1a and 1 b show a typical rod guide assembly with a bimetal bearing for a shock absorber of the prior art; and

Figures 2a and 2b show a piston rod assembly for a shock absorber, in accordance with the present invention.

Detailed description of the invention

The foregoing objects of the 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 embodiment.

The present invention provides a piston rod assembly for a shock absorber. The piston rod assembly includes a polymer plain bearing guide bush in a rod guide to avoid metal to metal contact, reduce friction between the rod guide and a piston rod and increase shock absorber life.

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 2a and 2b, there is shown a piston rod assembly (100) for a shock absorber, in accordance with the present invention. The piston rod assembly (100) comprises a piston rod (10), a rod guide (20) and a bearing bush (30). The piston rod (10) is capable of undergoing reciprocating movements in response to undulations of the road. The rod guide (20) is adapted for guiding the reciprocating movements of the piston rod (10) there through. In an embodiment, the piston rod (10) is made up of low carbon steel material and the rod guide (20) is made up of sintered steel material.

The bearing bush (30) is fitted to the rod guide (20) to act as a guide to the piston rod (10). In an embodiment, the bearing bush (30) is press fitted to the rod guide (20) using a hydraulic press (not shown). The bearing bush (30) is adapted for separating the piston rod (10) from the rod guide (20). Specifically, the bearing bush (30) is made up of a polymer material as a single continuous piece without any slit/break and without any coating on an inner surface (not numbered) thereof. In a preferred embodiment, the bearing bush (30) is made up of a plastic polymer material having a thickness of about 2 mm.

The bearing bush (30) with no slit reduces dust / contaminant accumulation on the piston rod (10). Since the bearing bush (30) is made up of polymer which being a softer material than the piston rod material (low carbon steel) avoids metal to metal contact and reduces friction between the piston rod (10) and the rod guide (20) during reciprocating movement of the piston rod (10). Thus, the slit-lacking polymer bearing bush minimizes the scoring mark on the piston rod (10) and thus results in an improved shock absorbers life.

Advantages of the invention

1. The piston rod assembly (100) includes the bearing bush (30) which causes no exposure of hard material in case of wear as complete part is made up by homogenous polymer material.
2. The bearing bush (30) has no slit in part and no sharp edges.
3. The piston rod assembly (100) causes the contaminant particle to penetrate deep inside the bearing bush (30) and preventing them from remaining on surface. This reduces scratching of the rod guide (20) while reciprocation motion.

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 assembly (100) for a shock absorber, the piston rod assembly (100) comprising:
a piston rod (10) being capable of undergoing reciprocating movement;
a rod guide (20) adapted for guiding the reciprocating movements of the piston rod (10) there through; and
a bearing bush (30) fitted to the rod guide (20) for separating the piston rod (10) from the rod guide (20),
characterized in that the bearing bush (30) being made up of a polymer material as a single continuous piece without any slit and without any coating on an inner surface thereof to reduce contaminant accumulation as well as friction between the piston rod (10) and the rod guide (20) thereby minimizing the scoring mark on the piston rod (10) and thus resulting in an improved shock absorbers life.

2. The piston rod assembly (100) as claimed in claim 1, characterized in that the bearing bush (30) is press fitted to the rod guide (20).

3. The piston rod assembly (100) as claimed in claim 1, characterized in that the bearing bush (30) is made up of a plastic polymer material.