GB2092707A

GB2092707A - Telescopic hydraulic shock absorber with hydraulic rebound stop

Info

Publication number: GB2092707A
Application number: GB8103615A
Authority: GB
Original assignee: Jonas Woodhead Ltd
Current assignee: Jonas Woodhead Ltd
Priority date: 1981-02-05
Filing date: 1981-02-05
Publication date: 1982-08-18
Also published as: GB2092707B

Abstract

A telescopic hydraulic shock absorber has a piston rod 3 with a portion 8 of reduced diameter on which is mounted an auxiliary check piston 21 comprising a disc 24 and a sleeve 23 of the same outer diameter as the main part of the piston rod, the sleeve containing a through duct 26 connecting opposite sides of the check piston and closable by one end of the duct 26 entering the piston rod guide 4. No bores are required in the piston rod, while the hydraulic stop is provided without any necessity to increase the dead length of the shock absorber. <IMAGE>

Description

SPECIFICATION Telescopic hydraulic shock absorber This invention relates to hydraulic checks or stops for telescopic hydraulic shock absorbers and may be applied either to monotube shock absorbers or to two-tube shock absorbers but is particularly directed to shock absorbers of the two-tube type in which the pressure tube is surrounded by a tube affording an annular reservoir.

It is often desirable to reduce rapidly the piston speed as the piston approaches the end of the cylinder during the rebound stroke and two forms of hydraulic stop have been proposed. In the first of these, of which that shown in our British Patent Specification No. 1 132 038 is an example, a reduced portion of the damping piston or a subsidiary or check piston enters a reduced portion of the working cylinder or a subsidiary cylinder. In the second, of which that shown in our British Patent Specification No. 1 411 21 8 is an example, flow to the damping piston is via passages within the piston rod that are closed when openings in the surface of the piston rod leading to these passages enter the piston rod guide.The first form of stop has the penalty that the shock absorber dead length is increased significantly, i.e. by about the length of the hydraulic stop action. The second form of stop requires the formation of passages in the piston rod which is difficult and expensive and substantially reduces the strength of the piston rod.

According to the present invention, a telescopic hydraulic shock absorber comprises a cylinder and a damping piston reciprocatable within the cylinder and carried by a piston rod having one end extending through a piston rod guide adjacent one end of the cylinder, the piston rod having between the damping piston and the said one end a portion of reduced diameter on which is mounted hydraulic rebound check means comprising: a check piston which extends out to the inner wall of the cylinder and a sleeve the outer surface of which is of at least approximately the same diameter as the piston rod between the reduced portion and the said one end, a duct being formed in the hydraulic rebound check means and extending from a first opening in the outer surface of the sleeve axially spaced from the check piston towards the said one end of the piston rod to a second opening on the opposite side of the check piston. With this construction, it is necessary to form the piston rod with a portion of reduced diameter but this is simple compared with the formation of passages therein particularly as the reduced diameter portion may simply be an extension of the spigot usually provided for mounting of the damping piston.Thus it is possible to take advantage of the invention using a shock absorber of existing design merely by enlarging the spigot and adding the hydraulic rebound check means without any modification to the cylinder, the damping piston or the valving components.

For ease of manufacture, the sleeve and the check piston may be integral with one another, for example by being constituted by a sintered component. The duct may be at least partially formed by a groove in the inner surface of the sleeve so that it will be bounded partly by the outer surface of the piston rod; in this way, the sleeve does not have to be drilled axially. Radial drillings can be avoided by forming the first and second openings by notches in the ends of the sleeve.

The invention may be carried into practice in various ways but one shock absorber embodying the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a fragmentary longitudinal section of the shock absorber; and Figure 2 is an isometric view of the rebound check piston forming part of the shock absorber.

The drawings show a shock absorber for an automotive vehicle which is for the most part of conventional construction. It includes a pressure tube 1 forming a working cylinder in which reciprocates a piston 2 carried on one end of a piston rod 3 which passes at the upper end of the cylinder through a piston rod guide 4 and a piston rod seal 5. The pressure tube 1 is surrounded by a second tube 6 to form an annular reservoir 7, communication between the working cylinder and the reservoir being through a base valve (not shown) which is of conventional construction and is located at the bottom of the working cylinder.

The piston 2 is retained on a spigot 8 of reduced diameter at the lower end of the piston rod 3 by a nut 9 and has extending through it inner and outer pairs of arcuate slots 11 and 12 respectively providing compression and rebound ports respectively. Flow through the outer or compression ports 1 2 is controlled by a valve disc 1 3 which is biased in the closing direction by its own rigidity and by a spring disc 14 which bears against a washer 1 5. Flow downwardly through the inner or rebound ports 11 is controlled by discs 1 6 which are biased towards a closed position by a compression coil spring 1 7. Access to the upper end of the ports 11 is through holes (not shown) in the disc 1 3.

A rebound check piston 21 which is of sintered metal and whose shape can be more clearly seen from Figure 2 is located on the spigot 8 between the washer 15 and a shoulder 22 at the upper end of the spigot and is clamped by the nut 9. The check piston is mainly comprised of a sleeve portion 23 and a disc portion 24 forming a flange projecting from the sleeve portion adjacent to the lower end thereof. There is a bore 25 extending through the check piston and this is formed with three spaced grooves 26 on its inner circumference so that three axially extending passages are formed between the check piston and the spigot 8.Notches 27 in the upper end of the sleeve portion 23 provide access between the space 28 surrounding the piston rod 3 and the upper ends of the grooves 26 while notches 29 in the lower end of the sleeve portion 23 provide access to the lower ends of the grooves from the space 31 between the flange portion 24 and the working piston 2. It will be noted that the portions 32 of the sleeve portion 23 remaining between the notches 29 provide spacers holding the flange portion 24 away from the washer 15.

The flange portion 24 contains two arcuate slots 33 providing communication between the two sides of the flange portion and the slots are closed on the upper side by a valve disc 34 which is held in position by a spring clip 35 which snaps into a groove 36 in the outer surface of the sleeve portion 23. There is some degree of axial clearance in the groove so that the disc 34 is able to move upwardly a short distance away from the upper surface of the flange portion 24 and in addition the disc 34 is resilient so that it can distort upwardly, thus permitting flow upwardly through the flange portion. Bleed notches 37 are provided to form a bypass around the disc 34 for limited flow downwardly through the slots 33.

Operation of the shock absorber when the working piston 2 is oscillating in its mid range as shown is largely conventional and flow around the flange portion 24 can take place freely through the passages afforded by the grooves 26. However, on excessive extension of the shock absorber, the notches 27 affording the upper access to the grooves 26 will pass into the bore of the piston rod guide 4 and will be largely closed off.

Resistance to further upward movement of the working piston will be substantially increased since flow out of the space 28 above the working piston will be able to take place only through the following restricted passages: a) the necessary clearance between the sleeve portion 23 and the piston rod guide 4 into the notches 27, b) through the bleed notches 37, and c) around the outer circumference of the flange portion 24, this flow being controlled by a piston ring 38 which may or may not be provided.

On reversal of the direction of movement of the piston, recuperation into the space 28 above the flange portion 24 can take place relatively freely through the slots 33 by the disc 34 moving axially and bending away from the flange portion 24.

While the resistance provided by the hydraulic check means described is determined by passages of constant cross-section as listed above, it would be possible to provide a resistance-limiting valve in a port extending through the flange portion 24 arranged to open when the pressure in the chamber 28 above the flange portion exceeds the pressure at which the valve is arranged to open.

Although the invention has been described in relation to a two-tube shock absorber it will be apparent that it can also be applied to a monotube shock absorber having a piston rod guide which is suitable to obturate the openings afforded by the notches 27.

Claims

1. A telescopic hydraulic shock absorber comprising a cylinder and a damping piston reciprocatable within the cylinder and carried by a piston rod having one end extending through a piston rod guide adjacent one end of the cylinder, the piston rod having between the damping piston and the said one end a portion of reduced diameter on which is mounted hydraulic rebound check means comprising: a check piston which extends out to the inner wall of the cylinder and a sleeve the outer surface of which is of at least approximately the same diameter as the piston rod between the reduced portion and the said one end, a duct being formed in the hydraulic rebound check means and extending from a first opening in the outer surface of the sleeve axially spaced from the check piston towards the said one end of the piston rod to a second opening on the opposite side of the check piston.

2. A shock absorber as claimed in Claim 1 in which the sleeve and the check piston are integral with one another.

3. A shock absorber as claimed in Claim 1 or Claim 2 in which the duct is at least partially formed by a groove in the inner surface of the sleeve.

4. A shock absorber as claimed in Claim 3 in which the first opening is formed by a notch in one end of the sleeve.

5. A shock absorber as claimed in Clairn 3 or Claim 4 in which the sleeve extends beyond the check piston on the side remote from the said one end of the piston rod and the second opening is formed by a notch in the end of the sleeve remote from the said one end of the piston rod.

6. A shock absorber as claimed in any of the preceding claims which includes a port through the check piston and a valve permitting but resisting flow through the port when the damping piston moves in the compression direction.

7. A shock absorber as claimed in any of the preceding claims in which the piston rod is formed with a spigot on which the hydraulic rebound check means and the damping piston are mounted and retained by a nut screwed on to a threaded portion of the spigot, part of the spigot forming the said portion of reduced diameter.

8. A telescopic hydraulic shock absorber substantially as described herein with reference to the accompanying drawings.