Brakes – Internal-resistance motion retarder – Having a thrust member with a variable volume chamber
Patent
1990-09-25
1993-02-09
Oberleitner, Robert J.
Brakes
Internal-resistance motion retarder
Having a thrust member with a variable volume chamber
18832215, F16F 934
Patent
active
051847035
DESCRIPTION:
BRIEF SUMMARY
INTRODUCTION
The present invention relates to a shock absorber, comprising a cylinder with damping fluid, a piston rod, which is displaceable in the cylinder and having a piston attached thereto which bounds a central aperture running in the axial direction of the cylinder, said central aperture being shut off at the end away from the piston rod, the piston being provided with at least two duct systems having different damping characteristics, said duct systems connect by means of an aperture or group of apertures to the central aperture, such that damping fluid can flow through the central aperture, to spaces in the cylinder on either side of the piston, and a sleeve, which is axially displaceable in the central aperture for controlling the fluid flow through the central aperture by opening or closing off one or more of the apertures or groups of apertures.
BACKGROUND OF THE INVENTION
A shock absorber of this type is known from European patent application 0,221,602.
The purpose of controlling the fluid flow in a shock absorber is to adapt the damping properties thereof as far as possible in an optimum manner to the momentary traveling conditions of a vehicle equipped with one or more of such shock absorbers. In motor vehicles it is for example important to keep the wheels in constant contact with the road as far as possible during moving off, acceleration, sudden sharp braking or when the motor vehicle leans to the side. It goes without saying that the type of road surface also plays an important role in the selection of the damping characteristics of the shock absorber. In general, if the road surface is good and fairly even, relatively little damping will be selected, while in the case of a poor, uneven road surface the shock absorbers have to be set with relatively great damping effect.
In the known shock absorber the sleeve is displaceable in axial direction of the central aperture by electrically controlled means, such as an electromagnet having a coil in which a core is movably arranged. The core is axially connected to the sleeve in its center. The sleeve has axial through flow channels, having cross-section dimensions such that the flow of damping fluid through the central aperture is not or in a neglectable manner impeded.
The damping characteristics of this know shock absorber are determined by the position of the sleeve in the central aperture, in other words, through which duct system(s) fluid can flow to the spaces on either side of the piston in the cylinder. With this arrangement the damping characteristics of the shock absorber can be controlled proportionally, independently of the speed of travel or direction of movement of the piston. Depending on the number of duct systems and their respective flow characteristics, the final damping characteristic of the shock absorber can be set proportionally over a wide range of speeds of travel of the piston.
The choice of the cross-section dimensions of the through flow channels in the sleeve or in general a sleeve-type element for the control of the fluid flow in the central aperture, is also based on the effort to make the response speed of the control as far as possible independent of the fluid pressure in the aperture.
As is well known, the response time of an electromagnet depends on the speed with which a magnetic force of sufficient strength can be built up to move the core. Generally, the response time of an electromagnet decreases if the magnet has to provide for an increased magnetic strength. However, for an effective control of the damping characteristics of shock absorbers there is a need for a response time of the order of few tenths of milliseconds or less. Such a response time cannot be achieved by a shock absorber having an electromagnet as the means for displacement of the sleeve.
From the European patent application 0,236,204 a shock absorber is known, having a piston with a first duct system which is shut off by means of spring-loaded valves which open or close under the influence of the speed of travel and the direction of
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patent: 4799577 (1989-01-01), de Carbon
ITT Corporation
Lewis J. Gordon
Muratori Alfred
Oberleitner Robert J.
Seitter Robert P.
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