GB2347395A - Vehicle suspension dampers - Google Patents

Abstract

A hydraulic vehicle suspension damper 10 has secondary chambers 22, 24 formed at the ends of its cylinder 12 with gas spring spheres 30 in them and apertures 26 connecting them to the working chambers 16, 18 of the damper. These apertures 26 are wider than those 20 interconnecting the two working chambers 16, 18 such than, over small amplitudes, the piston can move with less damping force than is produced for large amplitudes.

Description

Vehicle Suspension Dampers The present invention relates to hydraulic dampers such as those used in vehicle suspensions.

The damping force provided by most dampers is simply dependent on the relative velocity of the two components which they operate between. In a vehicle suspension damper, this is the vertical velocity of the wheel relative to the body. required at lower frequencies (and higher amplitudes) of wheel movement than at higher frequencies (and lower amplitudes).

A similar problem has been addressed in GB2270049, which discloses hydropneumatic suspension system in which a limited volume of fluid can flow between the two hydraulic chambers of each suspension unit, bypassing the damper which controls the flow of larger volumes of fluid.

The present invention provides a hydraulic damper comprising a cylinder and a piston slidable therein, and dividing the cylinder into two working chambers wherein a first passage is provided to allow the flow of fluid between the chambers with a first level of damping and fluid transfer means is provided to allow a limited volume of fluid to flow into and out of each of the chambers with a second level of damping and without passing through the passage, the second level of damping being lower than the first.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawing which as a schematic section through a damper according to the invention.

Referring to the drawing, a damper 10 comprises a cylinder 12 and a piston 14 slidable in the cylinder and dividing the cylinder into two working chambers 16, 18. The piston 14 has passages 20 formed through it which form fluid transfer means allowing fluid to flow between the chambers 16,18 as the piston 14 moves along the cylinder 12. The dimensions of the passages 20 determine the level of damping of fluid flow between the chambers.

At each end of the cylinder a secondary chamber 22,24 is formed, each being connected to a respective one of the working chambers 16,18 by fluid transfer means in the form of apertures 26 in the wall 28 between the working chamber 16, 18 and the secondary chamber 22,24. The dimensions of these apertures 26 determine the level of damping of fluid flow between the working chambers 16,18 and the secondary chambers 22,24, and are arranged so that they provide less damping than the passages 20 through the piston 14, for any given rate of movement of the piston 14 in the cylinder 12. Gas springs in the form of resilient gas spheres 30 are located in each of the secondary chambers which tend to resist the flow of fluid out of the working chambers 16,18 into the secondary chambers 22,24, and urge the fluid from the secondary chambers 22,24 out into the working chambers 16,18.

The damper will, when in use, operate between two parts 32,34 of a vehicle, such as the body and an axle or suspension arm, so that it is compressed by upward movement of a vehicle wheel relative to the vehicle body. A suspension spring 36 is provided which generally supports the weight of the vehicle body and operates in parallel with the damper.

In use, when the vehicle wheel is moving at high frequencies, and low amplitudes, relative to the vehicle body, the movement of the piston 14 in the cylinder 12 can be accommodated by flow of fluid through the apertures 26 into and out of the secondary chambers 22,24. Because these apertures are relatively wide compared with the passages 20 through the piston and provide less resistance to fluid flow, the damping, or resistance to such movement, is relatively low. For lower frequency, higher amplitude wheel movements fluid has to flow through the passages 20 in the piston 14 and so the amount of damping is relatively high. Also during high amplitude movements, the fluid pressure in the two working chambers 16,18 will tend to equal out as fluid flows between them, and the gas spheres 30, assuming they are all the same size, will tend to even out their volumes and hence even out the capacity of the two secondary chambers 22, 24 to receive fluid from the working chambers 16,18. Therefore lightly damped low amplitude vibration about any wheel position is possible.

It will be appreciated that various modifications could be made to the embodiment described, for example the design of the gas springs could take various other known forms, or the gas springs could be replaced by a piston biased by a spring.

Claims (4)

1. CLAIMS 1. A hydraulic damper comprising a cylinder and a piston slidable therein, and dividing the cylinder into two working chambers wherein main fluid transfer means is provided to allow the flow of fluid between the chambers producing a first level of damping of such flow, and two secondary chambers are provided each arranged to receive a limited volume of fluid from a respective one of the working chambers against the resistance of a resilient spring means through secondary fluid transfer means which provides less damping of the flow of fluid between the chambers than the main fluid transfer means.
2. 2. A damper according to claim 1 wherein the secondary chambers are formed in the ends of the cylinder.
3. 3. A damper according to claim 1 or claim 2 wherein the resilient spring means comprises a gas spring.
4. 4. A damper substantially as hereinbefore described with reference to the accompanying drawings.