Land vehicles – Suspension modification enacted during travel – Lateral vehicle disposition
Reexamination Certificate
1999-08-02
2001-07-24
Mai, Lanna (Department: 3619)
Land vehicles
Suspension modification enacted during travel
Lateral vehicle disposition
C280S124159, C280S124106, C280S005508, C701S037000, C701S038000
Reexamination Certificate
active
06264212
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a vehicle suspension system.
In order to provide good vehicle ride behaviour, it is well known that a relatively soft vehicle suspension is desirable. A consequence of using soft suspension is that the vehicle roll stiffness is reduced leading to higher roll angles in cornering manoeuvres. Vehicle designers frequently resort to the use of anti-roll bars or similar devices to increase the vehicle roll stiffness. Soft suspension may also result in more severe vehicle pitch oscillations.
In some cases, the use of devices such as anti-roll bars degrade the performance of the suspension system. For example, vehicles designed for good off-road mobility sometimes employ independent suspension with a long wheel travel capability. In this case, the use of an anti-roll bar increases the suspension stiffness, even in the absence of body roll, when the wheels on opposite sides of the vehicle are moving in different directions in response to the terrain, thus reducing the independence of the wheel movements.
In the prior art, Patent Specification No. U.S. Pat. No. 4,693,493 describes a system for vehicle body roll control using steering angle detection. In British Patent Specification No. GB 2313346, there is described a pneumatic anti-roll system for vehicles.
Active control systems have been proposed which counter body roll and pitch in response to signals from sensors that detect body attitude, velocities, or accelerations. An active suspension system typically uses a power source external to the suspension system to drive an hydraulic pump that transfers fluid from a reservoir through a servo valve into a pressurised part of the suspension system. Because the pump must raise the pressure of the hydraulic fluid from reservoir pressure to system pressure, and because of the metering action of the servo valves, such systems often involve a significant power loss. Such systems are also relatively complex and expensive.
The present invention is directed towards overcoming these problems.
SUMMARY OF THE INVENTION
According to the invention, there is provided a suspension system for a pair of spaced-apart wheels on a vehicle, the system comprising:
a spring means and a damping means associated with each wheel and working in parallel such that their forces are additive,
a hydraulic actuator mounted in series with the spring means such that the force in the actuator equals either the spring force or the sum of the spring force and damping force,
each hydraulic actuator connected between the wheel and a chassis of the vehicle so as to transmit a force from the wheel to the chassis,
each hydraulic actuator having a variable volume fluid chamber, said fluid chamber being filled with a substantially incompressible hydraulic fluid,
an hydraulic fluid transfer line communicating between the fluid chambers of both hydraulic actuators,
a pump mounted in the hydraulic fluid transfer line, said pump having a fluid inlet and a fluid outlet,
fluid control valve means associated with the pump mounted in the fluid transfer line,
said control valve means being operable to isolate both hydraulic actuator fluid chambers from each other and from the pump or to selectively connect a first hydraulic actuator fluid chamber to an inlet of the pump and connect a second hydraulic actuator fluid chamber to an outlet of the pump,
means for sensing at least one vehicle attitude parameter, the sensing means being operatively connected to a controller,
said controller having means for regulating operation of the control valve means in response to said sensed vehicle attitude parameter or parameters to counteract one or both of lateral roll and longitudinal pitch of the vehicle.
It will be appreciated that the invention provides a roll and/or pitch control suspension system for a vehicle in which high pressure hydraulic fluid is pumped directly between hydraulic actuators in a controlled manner to counteract sensed roll and/or pitch of the vehicle. This arrangement advantageously helps minimise the power requirement and provides a relatively simple system with a view to minimising manufacturing cost and providing reliability in operation.
In one embodiment, the spring means is an hydraulic accumulator connected to the hydraulic actuator fluid chamber by a fluid line and the damping means is a flow restrictor mounted in the fluid line between the fluid chamber and the accumulator.
In another embodiment, the spring means is a mechanical spring and the damping means is a mechanical damper.
In a further embodiment, the spring means comprises a main piston incorporating a gas chamber and an oil chamber separated by a separator piston, said main piston forming a piston of the hydraulic actuator which slides within a complementary actuator cylinder and the damping means is a flow restrictor between the oil chamber in the main piston and the fluid chamber in the actuator cylinder.
In another embodiment, the hydraulic actuators are mounted at wheels on opposite sides of the vehicle. In a further embodiment, the hydraulic actuators are mounted at wheels on a common axle of the vehicle. In another embodiment the hydraulic actuators are mounted at wheels which are longitudinally spaced apart on the vehicle.
In a further embodiment, the hydraulic actuator is of two part construction comprising a piston slidably mounted in a complementary cylinder to provide the variable volume hydraulic fluid chamber, one part being attached to the wheel and the other part being attached to the vehicle chassis. In another embodiment of the invention, one of said parts has a spring and/or damper mounted between said part and the wheel or chassis.
In a further embodiment, means is provided for adjustment of the quantity of gas within the accumulator or gas chamber.
In another embodiment, means is provided for the gradual adjustment of the quantity of hydraulic fluid in the system.
Preferably, the control valve is a servo valve.
Conveniently, means may be provided for adjusting the quantity of hydraulic fluid in each accumulator.
In a further embodiment, the impedance of each flow restrictor is adjustable.
In another embodiment, the sensing means is operable to sense one or more of the vehicle attitude parameters selected from the group: lateral acceleration, roll angle, roll rate, braking, steering angle, pitch angle or pitch rate. In a further embodiment, the sensing means includes means for sensing the vehicle speed. Preferably, the sensing means includes means for sensing the longitudinal acceleration of the vehicle. Conveniently also, the sensing means includes means for sensing wheel displacement relative to the chassis.
In another embodiment, each hydraulic actuator comprises a forward hydraulic actuator and a rearward hydraulic actuator mounted on a forward axle and a rearward axle on the same side of the vehicle, the fluid chambers of the actuators on each side of the vehicle communicating with a common hydraulic accumulator.
In a further embodiment, each suspension system having the first and second hydraulic actuator mounted at longitudinally spaced-apart wheels on opposite sides of the vehicle.
Conveniently in this arrangement the pair of suspension systems may be interconnected by an equalising valve connected between the fluid transfer lines of the different systems, said equalising valve being operable to allow the slow bleed of hydraulic fluid between the systems in response to a sensed difference in averaged extension of hydraulic actuators in the two systems.
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patent: 2313346 (1997-11-01), None
Jacobson Price Holman & Stern PLLC
Jasmin Lynda
Mai Lanna
Technology Investments Limited
LandOfFree
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