Land vehicles – Suspension modification enacted during travel – Lateral vehicle disposition
Reexamination Certificate
1999-05-26
2001-03-27
Johnson, Brian L. (Department: 3618)
Land vehicles
Suspension modification enacted during travel
Lateral vehicle disposition
C280S005506
Reexamination Certificate
active
06206383
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to hydraulically actuated suspension control systems for vehicles, and in particular for roll control systems.
BACKGROUND OF THE INVENTION
It is known, for example from WO 98/26948, EP 0 512 358 and U.S. Pat. No. 5,529,324, to provide roll control systems. In particular it is known from U.S. Pat. No. 5,529,324 to disclose a vehicle suspension system comprising a hydraulic actuator, a source of hydraulic pressure and a drain, a pressure control valve for controlling the flow of hydraulic fluid from the source to the drain thereby to control the hydraulic pressure drop between the source and the drain, at least one actuation control valve for connecting the actuator between the source and the drain such that said pressure drop controls the magnitude of an actuating force produced by the actuator, and control means arranged to operate the valves in response to at least one input defining a desired actuating force.
However it can be a problem with such systems that the pressure control valve, even when fully open, creates a minimum pressure drop across itself defined partly by the cross section of the flow path through the valve when open and partly the viscosity of the fluid. Therefore a minimum pressure which can be applied across the actuator and a minimum roll control correction force which can therefore be applied. The present invention aims to minimize this problem.
SUMMARY OF THE INVENTION
The present invention provides a vehicle suspension system comprising a hydraulic actuator, a source of hydraulic pressure and a drain, a pressure control valve for controlling the flow of hydraulic fluid from the source to the drain thereby to control the hydraulic pressure drop between the source and the drain, at least one actuation control valve for connecting the actuator between the source and the drain such that said pressure drop controls the magnitude of an actuating force produced by the actuator, and control means arranged to operate the valves in response to at least one input defining a desired actuating force, wherein the control means is arranged to connect the actuator only when the desired actuating force is greater than a minimum value corresponding to a minimum pressure drop which can be produced by the pressure control valve, and to determine the minimum pressure drop from measurement of the temperature of a part of the hydraulic system.
Preferably the control means is arranged to obtain the measurement of said temperature by monitoring a temperature dependent characteristic of the drive current by which it controls at least one of the valves. Alternatively a separate thermometer can be provided.
Preferably the actuator is a roll control actuator arranged to control roll of a vehicle and the value of the minimum actuating force defines a deadband of low lateral accelerations for which roll control cannot be provided.
Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings.
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Davis & Bujold. P.L.L.C.
Johnson Brian L.
Rover Group Limited
Winner Tony
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