Brakes – Internal-resistance motion retarder – Valve structure or location
Patent
1993-05-17
1995-03-21
Oberleitner, Robert J.
Brakes
Internal-resistance motion retarder
Valve structure or location
188299, 188317, B60G 1308, F16F 1100
Patent
active
053987888
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention refers to the use of a displacement machine known a pressure control valve.
BACKGROUND OF THE INVENTION
The control of the flow of a liquid usually is gained by restricting the flow in a restriction in some kind of valve, usually a seat slide valve. In such valves it is required, however, a very small area change for providing a very great change of the pressure drop, is the pressure drop varies exponentially with the change of the position of the valve body. When slightly opening seat valves the flow velocity becomes very high and the liquid pressure locally becomes so low that the liquid tends to be vaporized, giving rise to cavitation. In order to avoid this it would be desirable to provide a control device operating, if possible, in an entirely proportional manner.
For the control of flows the use of rotary-dynamic machines is previously known in various connections. Thus, in U.S. Pat. No. 3,709,245 a control valve is disclosed in which a rotor is brought to rotate by means of a whirling rotation of a fluid flow. Energy then can be tapped from the rotor in various ways, for example by the generation of electric current or the like. Due to the inherent characteristics of the rotary-dynamic machines they are, however, not suited for a more exact control of a fluid flow and particularly the pressure thereof.
Displacement machines also have been used as flow meters. Such flow meters also have been used such that the output controls a valve or the like for providing a flow control, see DE-A-2 440 078. Furthermore, it is also known to use a displacement machine having a rotary member mounted in a liquid conduit for controlling the flow and/or the pressure of the liquid by braking the rotary member. In this respect it might be referred to; for example, DE-B-2 840 134, DE-A-3 210 098, FR-A-2 380 585 and U.S. Pat. No. 4,815,278.
Quite surprisingly it has now been found that a particular use of a displacement machine as a pressure control valve in connection with motor vehicle shock absorbers allows the achievement of unexpected advantages hitherto not obtainable with known shock absorber valve structures.
SUMMARY OF THE INVENTION
The main object of the present invention thus is to suggest the use of a known displacement machine as a pressure control valve for the liquid in a vehicle shock absorber in order to provide a direct proportional pressure control and hence a desired damping force of the latter, the displacement machine being mounted within the piston of the cylinder together with associated actuation means operable from the outside of the cylinder in response to a pressure sensor inside the cylinder.
With the present invention a very desirable and entirely proportional control action thus can be obtained by applying a braking action on the rotary member of the displacement machine mounted within the piston. This manner of controlling the liquid pressure is of particular advantage in connection with motor vehicle shock absorbers.
In a preferred embodiment of the present invention the displacement machine is a screw pump, particularly of so-called IMO-type. By the use of such a screw pump it can be obtained a pressure control which is proportional to the braking momentum exerted on the rotary member of the machine. This implies that the control action becomes independent of the viscosity of the fluid or liquid and the great equivalent flow area eliminates the risks of cavitation. However, the present invention also might be advantageously used in connection with other kinds of hydraulic cylinders.
It is also to be mentioned that in known displacement machines of screw-type which are used as flow or volume meters the rotary members have no output shaft but the rotary speed is registered by, for example, an inductive sensor. When using the displacement machine for the control of the pressure of a liquid according to the present invention the machine now also includes braking means and a pressure sensor for setting the pressure to a desired value. The inve
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Oberleitner Robert J.
Poon Peter M.
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