Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
1993-02-02
2001-07-10
Teska, Kevin J. (Department: 2123)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S048000, C701S082000, C703S008000, C280S791000
Reexamination Certificate
active
06259982
ABSTRACT:
TECHNICAL FIELD
The present invention is directed to a vehicle active suspension system and is particularly directed to a method and apparatus for controlling the active suspension system.
BACKGROUND ART
Vehicle suspension systems are well known in the art. Such suspension systems have as their goal the control of the relative motion between the sprung mass (the vehicle chassis) and the unsprung mass (the suspension arms, wheels, tires, etc.) of the vehicle. Passive suspension systems, such as shock absorbers, absorb and dissipate some of the energy and motion produced in an automotive vehicle by road surface irregularities when a vehicle is driven over such irregular road surface.
Passive suspension systems provide good vibration isolation at a relatively narrow range of vibration frequencies. A linear response of a passive suspension system can be altered by (i) adding an advantageous nonlinear attribute, such as direction dependant damping, and (ii) minimizing an objectionable effect, such as stiction, i.e., stick slip friction characteristics of the suspension system including the shock absorber. Passive systems, however, react only to applied forces from below the unsprung mass, i.e., from the road surface, and from above the unsprung mass, i.e., from inertia of the sprung mass or vehicle body. Ideally, the suspension system should appear “soft” in reacting to road surface induced inputs, (“road noise”) and stiff when reacting to vehicle body accelerations and motions, (“inertia inputs”). Since a passive system cannot distinguish between the origin of the two types of vibration, an engineering compromise is made.
An active suspension system uses power from the vehicle engine to actively move the vehicle wheels over an irregular road surface usually with the objective of maintaining a constant force between the vehicle wheel and the road surface. Rather than a shock absorber, as is found in passive suspension system, an active suspension system uses a hydraulic servo-actuator, i.e., a hydraulic motor, to move, or control the forces in, the vehicle wheel. A plurality of sensors, for detecting impact, force, acceleration, velocity and displacement, are located at various vehicle locations. A controller, e.g., a microcomputer, monitors the sensor outputs and controls operation of the hydraulic actuator for the vehicle wheels and suspension located at each vehicle corner through an associated electrically controlled hydraulic servo valve. Through a control algorithm, the controller controls reaction to road noise and inertia inputs and controls relative motion of the sprung and unsprung masses.
In an active suspension system, the servo valve, actuator, and controller function as an energy control device. The servo valve connects the energy source, i.e., a pump, to the energy consumer, i.e., an actuator. The difference between power in and power out is converted to heat energy by the servo valve.
In a fully active suspension system, the actuator is operated so as to move the wheel up and down relative to the vehicle body as necessary to provide a desired “ride feel” and “handling characteristic” of the vehicle. The hydraulic pump provides energy in terms of fluid flow at system pressure. The servo valves remove energy at a rate to provide fluid flow and pressure so as to move an associated wheel at a velocity needed to achieve a desired ride feel and handling characteristics. Control of fluid flow with the servo valve controls actuator direction of movement and velocity. Control of fluid pressure, in turn, controls actuator force. The control signal output to the servo valve is referred to as a valve drive signal.
SUMMARY OF THE INVENTION
The present invention provides a hybrid control arrangement for an active suspension system. An analog force closed loop control arrangement controls an actuator as a function of a difference between a measured force value and a desired force value for a selected vehicle corner. The closed loop arrangement includes a variable gain feature wherein gain is controlled as a function of the frequency of changes in the force difference between measured and desired values. A digital network measures actuator displacement and calculates actuator displacement in response to the force difference value. The digital network adds the difference between actual and calculated displacement to the control signal used to control the actuator.
In accordance with the present invention, an apparatus is provided for controlling a vehicle suspension having a sprung mass and an unsprung mass. The apparatus comprises a plurality of actuators, each corner of the vehicle having an associated actuator operatively connecting the sprung mass with its associated unsprung mass. Means are provided for sensing at least one operating characteristic of a selected corner. Means provides a desired actuator drive signal in response to the at least one sensed operating characteristic for achieving a desired operating characteristic. The apparatus further includes means for determining the difference between the at least one sensed operating characteristic and the desired operating characteristic for a selected corner. Control means responsive to the determined difference provides an actuator control signal having a value which is functionally related to the determined difference. The control means has a variable gain amplifier means for outputting the actuator control signal, wherein the gain of said amplifier means is controlled in response to the frequency of variations of the determined difference. The Apparatus further includes actuator control means for driving the actuator in response to the actuator control signal.
In accordance with a preferred embodiment, the control means for sensing at least one operating parameter includes a plurality of load sensors, each corner having an associated load sensor operatively connected between the sprung mass and its associated unsprung mass. The load sensor provides a signal having a value indicative of the force on the actuator at that corner. The desired operating characteristic is force. The determining means determines the difference between the desired force in the actuator with the sensed force therein, the difference providing an error signal. The variable gain amplifier amplifies the error signal. The apparatus further includes a hub accelerometer, means for determining hub velocity from the hub accelerometer, a chassis accelerometer, means for determining chassis velocity from the chassis accelerometer, and means for summing the determined hub velocity and chassis velocity with the amplified error signal. The summation of the determined hub velocity with the amplified error signal serves to undamp the unsprung mass of the selected corner from the sprung mass. The summation of the determined chassis velocity with the amplified error signal serves to damp the sprung mass of the selected corner. The apparatus further includes a plurality of displacement sensors, each actuator having an associated displacement sensor for sensing the actuator displacement which is functionally related to the distance between the sprung mass and its associated unsprung mass for the selected corner. Means are provided for calculating the displacement of the actuator based upon the force error signal and providing a displacement error signal having a value equal to the difference between the calculated displacement and the measured displacement. The apparatus further includes means for summing the displacement error signal with the control signal. Each of the actuators is preferably a hydraulic motor and the actuator control means includes an electric servo valve, each actuator having an associated servo valve. Each electric servo valve is operatively connected between a pump and reservoir and its associated actuator. Means are provided for sensing the end of stroke of the actuator and reducing the variable gain when the actuator nears its end of stroke.
In accordance with another aspect of the present invention, a method for controlling a vehicle suspe
Ghaphery Abraham H.
Williams Daniel E.
Phan Phai
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
Teska Kevin J.
TRW Inc.
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