GB2064712A

GB2064712A - Hydraulic shock absorber with pressure relief valve

Info

Publication number: GB2064712A
Application number: GB8035543A
Authority: GB
Original assignee: Ringfeder GmbH
Current assignee: Ringfeder GmbH
Priority date: 1979-11-17
Filing date: 1980-11-05
Publication date: 1981-06-17
Also published as: DE2946462A1

Abstract

A hydraulic shock absorber comprises a cylinder 13 and a piston 7 sealed at 7a with respect to the cylinder and having a piston rod 2 sealed at 2a with respect to the cylinder which has a portion 1 of reduced diameter which passes through an annular partition 6, the space 5, 5a between the seals 7a, 2a of the piston and the piston rod accommodating a damping liquid, wherein the reduced diameter portion 1 contains a flow duct 3 which has a large diameter in relation to the gap between the partition 6 and the reduced diameter portion 1, the flow duct having an over-pressure valve 4 opening in the direction of contraction of the unit to connect the spaces 5, 5a. <IMAGE>

Description

SPECIFICATION Hydraulic shock absorber The present invention relates to a hydraulic shock absorber, in particular for use in combination with a buffer spring, e.g. a friction spring, of a rail vehicle, essentially of the type comprising a cylinder and a piston arranged therein and sealed with respect to the cylinder and having a piston rod which extends into the cylinder and is sealed and which has a portion of reduced diameter which extends at least over the length of the stroke path in the region of a ring disc extending from the inner wall of the cylinder in the vicinity of the piston, wherein the opening diameter of the ring disc is smaller than the diameter of the full piston rod, but larger than the diameter of the reduced diameter portion of the piston rod, the space between the seals of the piston and the piston rod accommodating a damping liquid.

A hydraulic shock absorber having the aforementioned features is known from DE-OS 26 1 2 639 and is suitable above all for assisting the effect of a friction spring of a buffer for rail vehicles. In contrast to the friction spring the spring force of which increases approximately proportionally during dynamic actuation of the spring, the hydraulic shock absorber has progressive characteristic curves dependent upon the respective shock velocity. For this reason the characteristic curve of the shock absorber may exceed on a short spring path the force for which the cylinder of the shock absorber or the buffer support of the vehicle is maximally designed, when high speeds occur, for example during unskilled marshalling operations; damage to the absorber, or to vehicle and goods, respectively, may then occur.

The present invention provides a hydraulic shock absorber, comprising a cylinder and a piston arranged therein and sealed with respect to the cylinder and having a sealed piston rod which extends into the cylinder and which has a portion of reduced diameter extending at least over the length of the stroke path in the region of a ring disc extending from the inner wall of the cylinder in the vicinity of the piston, wherein the opening diameter of the ring disc is smaller than the diameter of the full piston rod, but larger than the diameter of the reduced diameter portion of the piston rod, the space between the seals of the piston and the piston rod accommodating a damping liquid, wherein the reduced diameter portion of the piston rod contains a flow duct which has a large diameter in relation to the gap between the ring disc and the reduced diameter portion of the piston rod, the said flow duct having an over-pressure valve opening in the direction of shock of the damping liquid and, when the said valve is open, connecting the space between the seal of the piston rod and the ring disc on the one hand to the space between the ring disc and the seal of the piston on the other hand.

During the operating stroke of the hydraulic shock absorber, the damping liquid is pushed by the inwardly travelling piston rod over the annular shoulder thereof which exists towards the reduced diameter portion into the interior of the cylinder. Thereby a pressure is produced in the space between the seal of the piston rod and the ring disc, which pressure depends upon the velocity of the shock and which is broken down by the energy-consuming flowing process of the damping liquid through the annular gap between the ring disc and the reduced diameter portion of the piston rod into the other space loacted behind the ring disc. A further energy consumption takes place in this other space by deflection of the damping liquid at the front end of the piston.By means of the flow duct which is provided in the reduced diameter portion of the piston rod in a simple and space-saving manner, as well as by the over-pressure valve, the pressures occurring in the cylinder at high inward travel speeds of the piston rod may be limited to that for which the cylinder, and correspondingly the buffer as well as the buffer support of the vehicle, are designed.

When the over-pressure valve is open, the damping liquid travels additionally through the relatively large flow duct with considerably reduced restriction into the rear space of the absorber. Advantageously the friction spring operates parallel to the hydraulic shock absorber over the entire stroke path; this would not be the case without the flow duct and the over-pressure valve. Therefore the hydraulic shock absorber, the driving mechanism and the cargo are protected against damage.

The piston of the hydraulic shock absorber may have a cavity, for example for housing a spring-loaded inner piston for compensating for changes of volume in consequence of temperature fluctuations, which is in communication with the space between the ring disc and the seal of the piston. In this construction a particularly easy production of the flow duct and a space-saving attachment of the overpressure valve are obtained when the flow duct terminates in the cavity of the piston, the over-pressure valve being arranged axially in the flow duct.

In order to permit the shock absorber, in particular a vehicle buffer equipped therewith, to be adjusted to the largest extent to the respective prevailing strength conditions of the buffer support on the vehicle, the overpressure valve may be constructed to be adjustable in respect of its response pressure.

The invention will be further described, by way of example only, with reference to the accompanying drawing, which is a longitudinal section view of an unloaded buffer pro vided with a hydraulic shock absorber according to the invention.

The casing of the buffer shown in the drawing consists substantially of an outer casing member 8 with a buffer plate 8a and an inner casing member 9 with a rectangular base place 9a which is engaged by screws (located outside the plane of the drawing) for attaching the buffer to the corresponding support of a rail vehicle. A slit ring 10 is attached by welding to the open end of the outer casing member 8 and together with a collar 9b of the inner casing member 9 it forms a displacement limitation for the buffer. Moreover a sealing slide bush 11 lies between the casing members 8 and 9.

In the casing which is constructed in this form and which is insensitive to deformations and the ingress of moisture or dust, a friction spring 1 2 which comprises double-conical outer and inner rings in the usual manner, and a hydraulic shock absorber are disposed in a paraliel effective manner.

The hydraulic shock absorber has the following construction. A piston 7 is arranged in a cylinder 1 3 and has a piston rod 2 which has a portion 1 of reduced diameter. This portion 1 penetrates through a ring disc 6 which extends from the inner wall of the cylinder 1 3 and the opening diameter of which is larger than the diameter of the reduced diameter portion 1 of the piston rod 2.

The gap thus formed serves for energy-consuming flow of a damping liquid from a space 5 between a seal 2a of the piston rod 2 and the ring disc 6 on the one hand into a space 5a between the ring disc 6 and a seal 7a of the piston 7 on the other hand, wherein the space 5a includes a cavity 7b of the piston 7 connected through bores 7cwith the remainder of the space 5a. In other respects, the cavity 7b accommodates a spring-loaded inner piston 14.

The reduced diameter portion 1 of the piston rod 2 contains a flow duct 3 which has a diameter which is large in relation to the gap between the ring disc 6 and the reduced diameter portion 1. An over-pressure valve 4 is arranged axially in this flow duct 3, and opens in the shock direction of the damping liquid. When the valve 4 is open, the spaces 5 and 5a are connected to each other through the flow duct 3 in addition to through the gap between the ring disc 6 and the reduced diameter portion 1.

Claims

1. A hydraulic shock abosrber, comprising a cylinder and a piston arranged therein and sealed with respect to the cylinder and having a sealed piston rod which extends into the cylinder and which has a portion of reduced diameter extending at least over the length of the stroke path in the region of a ring disc extending from the inner wall of the cylinder in the vinicity of the piston, wherein the opening diameter of the ring disc is smaller than the diameter of the full piston rod, but larger than the diameter of the reduced diameter portion of the piston rod, the space between the seals of the piston and the piston rod accommodating a damping liquid, wherein the reduced diameter portion of the piston rod contains a flow duct which has a large diameter in relation to the gap between the ring disc and the reduced diameter portion of the piston rod, the said flow duct having an over-pressure valve opening in the direction of shock of the damping liquid and, when the said valve is open, connecting the space between the seal of the piston rod and the ring disc on the one hand to the space between the ring disc and the seal of the piston on the other hand.

2. A hydraulic shock absorber as claimed in Claim 1, wherein the piston has a cavity which is in communication with the space between the ring disc and the seal of the piston, wherein the flow duct terminates in the said cavity of the piston, and wherein the over-pressure valve is arranged axially in the flow duct.

3. A hydraulic shock absorber as claimed in Claim 2, wherein the said cavity of the piston houses a spring-loaded inner piston for compensating for changes of volume in consequence of temperature fluctuations.

4. A hydraulic shock absorber as claimed in any of Claims 1 to 3, wherein the overpressure valve is constructed to be adjustable in respect of its response pressure.

5. A hydraulic shock absorber according to Claim 1, substantially as herein described with reference to, and as shown in, the accompanying drawing.