Land vehicles – Wheeled – Running gear
Reexamination Certificate
1999-11-08
2002-08-06
Mai, Lanna (Department: 3619)
Land vehicles
Wheeled
Running gear
C280S124100, C280S124159, C280S124160, C280S124161
Reexamination Certificate
active
06428024
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally directed to vehicle suspension systems, and in particular, to control arrangement for such suspension systems. The present invention will be described in relation to the Applicant's vehicle suspension systems. It is however envisaged the present invention also has general application in vehicle suspension systems.
2. Description of the Related Art
The applicant has developed vehicle suspension systems which utilize lateral stabilizer bars which can be used in conjunction with fluid circuits to thereby provide roll stabilization while facilitating free cross-axle articulation for the suspension system (the cross-axle articulation mode in a common direction with respect to the body, and the other pair of wheels move in the opposite direction. This mode of wheel motion is commonly referred to as warp). Suspension system of this type are described in U.S. Pat. Nos. 6,302,417 and 6,217,047, details of which are incorporated herein by reference. The suspension systems have the advantage of being passive systems which do not require an external energy source to operate properly. By comparison, active suspension systems typically require at least a fluid pump to supply fluid to actuators controlling the wheel motions.
There are however circumstances which make it advantageous to provide a control arrangement to adjust the volume of fluid within the fluid circuits of the Applicant's vehicle suspension systems.
The volume of fluid in the fluid circuits may need to be adjusted for at least the following reasons:
1) To permit levelling of the roll attitude of the vehicle body with respect to the wheels without introducing a bias in one direction in the fluid circuit; and
2) To prevent fluid expansion caused by temperature rises causing over pressure in the fluid circuits. This can be a problem since there is little resilience in the conduits of the fluid circuits and accumulators are normally not provided in the fluid circuits. The addition of accumulators can detract from the roll control of the vehicle where they are provided to accommodate fluid expansion within the fluid circuit because this can result in variation of the roll rates of the vehicle.
The extent of this temperature related problem, can be understood from the following case. When the vehicle is started in the city the system can be set with the correct volume of fluid for the essentially cold start. As it is run at low speed or under stop-start conditions within the city, the temperature in the fluid circuit rises resulting in an increase in the fluid volume therein. It is therefore preferred in this situation, that fluid be released from the circuit. Leaving the city, speeds increase, providing increased air flow over the components of the fluid circuit thereby cooling them down. The fluid then contracts which can leave the suspension system with reduced roll control since any small air bubbles in the fluid circuit can expand resulting in an initial additional compliance about the roll axis of the vehicle. To keep the roll rate constant, the pressure of the fluid in the roll system therefore preferably needs to be kept at an average design pressure.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a control arrangement for controlling the fluid volume and therefore the pressure within the fluid circuit of a vehicle suspension system.
With this in mind, there is provided a vehicle suspension control system for a vehicle,
the vehicle having at least one forward pair of wheels and at least one rearward pair of wheels connected to the body of the vehicle to allow substantially vertical relative motion of each wheel with respect to the body,
the suspension system of the vehicle including front and rear resilient support means for supporting the vehicle body with respect to the wheels, a front roll stabilisation assembly interconnecting at least one said forward pair of transversely spaced wheels and a rear roll stabilisation assembly interconnecting at least one said rearward pair of transversely spaced wheels, each roll stabilisation assembly including at least one lateral torsion bar and a double-acting hydraulic actuator interconnected to the at least one lateral torsion bar, the front and rear hydraulic actuators being interconnected by first and second fluid conduits such that
roll moments applied to the vehicle body generate pressure within the fluid conduits thereby transmitting the roll moment into each lateral torsion bar to react against at least a portion of said roll moment, and
warp motions of the wheels with respect to the vehicle body generate flow along the fluid conduits resulting in a displacement of one said hydraulic actuator in a proportional and opposite direction to the other said hydraulic actuator,
the front and rear roll stabiliser assemblies thereby providing roll stiffness during both roll and warp motions of the wheels with respect to the body while at the same time providing substantially zero warp stiffness,
wherein the control system includes an hydraulic fluid supply means and fluid conduit valve means for selectively communicating the fluid conduits with the hydraulic fluid supply means to thereby regulate the average pressure in both the first and second fluid conduits.
This control system does not require a fluid pump as fluid is vented from the fluid conduits to the reservoir, or is returned to the fluid conduits from the tank by controlling the valves in each fluid line.
A flow restricting means may be provided for each valve means for preventing rapid discharge of fluid from the fluid conduits.
The valve means may be in the form of an electric solenoid valve having “flow on” and “flow off” positions. The valve may normally be in the flow off position and may be moved to the flow on position when venting fluid from the fluid circuit or when supplying fluid to the fluid circuit is required.
Non-return valve means may optionally be provided in a bypass line bypassing the valve means. The non-return valve means allows the ingress of fluid when the pressure in the fluid circuit falls below a design pressure, for example when there is a drop in temperature in the fluid circuit.
Accumulators may also optionally be provided on each fluid conduit for providing a degree of resilience in the operation of the fluid circuit. This can provide a reduced roll stiffness zone around the level position and reduce the effect of temperature changes on the roll system pressure.
It should be noted that empirical testing has shown that the design pressure of the fluid circuit can be atmospheric (plus whatever head is provided by the position of the fluid tank). This can be desirable for reasons of cost, complexity and reliability. By keeping the design pressures of the hydraulic roll control system low when reacting roll moments on the vehicle body, the amount of additional resilience introduced by the expansion of the flexible hydraulic hoses in roll can be reduced.
Pressure sensing means may be provided for measuring pressure changes in the fluid circuit. The pressure sensing means may be located on the fluid conduits or on the fluid line communicating the valve means with the fluid conduits.
Releasing fluid can be controlled hydraulically or electronically. The electronic option is preferred due to the increased intelligence which can be built in to prevent too much fluid being released from one fluid conduit (the pressure change in the fluid circuit due to temperature effects being determined at least in part by the total volume of fluid in the fluid circuit). For example, to reduce pressure and maintain body roll attitude, fluid should preferably be released from both conduits in the correct proportions. Releasing fluid from just one conduit will reduce pressure, but may also cause the body roll attitude to change. This can be used intelligently to correct for roll attitude errors (although the fluid volume changes due to temperature are small). The method of control for
Heslewood Ray
Heyring Christopher B.
Longman Michael J
Monk Richard
Kinetic Limited
Mai Lanna
Royal, Jr. Paul
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