Method and apparatus for dynamic leveling of a vehicle using an active suspension system

A suspension system for a motor vehicle comprising:

• a hydraulic actuator operably connected at each corner of the vehicle between the sprung and unsprung portions thereof;
• means for detecting movement of the sprung and unsprung portions of the motor vehicle and for deriving a force signal for each actuator in response thereto;
• and
• a valving arrangement for causing said hydraulic actuator to generate a desired output force in response to said force signal, said valving arrangement including first valving means operable for generating said output force by selectively varying the damping characteristics of said hydraulic actuator when said force signal is within a predetermined range, and second valving means for selectively controlling the supply and discharge of hydraulic fluid from said hydraulic actuator for generating said output force when said force signal is outside of said predetermined range.

An active suspension system for a motor vehicle comprising:

• a source of high pressure damping fluid;
• a hydraulic damper operably connected between the unsprung and sprung portions of the vehicle at each corner thereof, said hydraulic damper forming a working chamber operable to store damping fluid therein and secured to one of the sprung and unsprung portions of the vehicle, and a piston and rod assembly disposed for translational movement within said working chamber with opposite sides of said piston defining first and second portions thereof, said rod secured at an end opposite said piston to the other of the sprung and unsprung portions of the vehicle;
• sensor means for sensing the dynamic movement of said sprung and unsprung portions of the vehicle and generating sensor output signals in response thereto;
• semi-active valving means for selectively regulating the damped resistance to movement of said piston within said working chamber between a minimum limit and a maximum limit;
• flow control means fluidly connecting one of said first and second portions of said working chamber to said source of high pressure fluid for controlling the flow of damping fluid therebetween;
• an accumulator in fluid communication with the other of said first and second portions of said working chamber;
• and
• controller means for calculating a commanded force signal in response to said sensor output signals, said control means further operable to selectively actuate said semi-active valving means for generating an actuator output force when said commanded force signal is between said minimum and maximum limits and for actuating said flow control means in conjunction with said semi-active valve means when said commanded force signal is outside of said limits.

A method of dynamically leveling the attitude of a motor vehicle comprising the steps of:

• connecting a hydraulic actuator at each corner of the vehicle between its sprung and unsprung portions;
• sensing movement of the sprung and unsprung portions of the vehicle and generating sensor output signals in response thereto;
• calculating a demanded force signal for each actuator in response to said sensor output signals;
• leveling the attitude of the vehicle by regulating the damped resistance to movement between said sprung and unsprung portions when said demanded force signal is within a predetermined range;
• and
• leveling the attitude of the vehicle by controlling the flow of pressurized fluid between said hydraulic actuator and a central fluid pressure source when said demanded force signal is outside of said predetermined range.

A method of dynamically leveling the attitude of a vehicle in response to changes in the dynamic behavior of the sprung and unsprung portions of the vehicle, said method comprising the steps of:

• connecting a hydraulic actuator between the sprung and unsprung portions at each corner of the vehicle, said hydraulic actuator having a piston and rod assembly disposed for translational movement within a working chamber filled with damping fluid such that said piston defines first and second portions of said working chamber;
• connecting said first portion of said working chamber for each actuator to a closed-loop fluid source having a pump and a reservoir;
• connecting first valving means between said fluid source and each of said actuators for controlling the flow of damping fluid between said first portion of said working chamber and said fluid source;
• connecting an accumulator to said second portion of said working chamber for each of said actuator;
• providing second valving means for controlling the flow of damping fluid between said first and second portions of said working chamber;
• sensing the dynamic movement of the sprung and unsprung portions of the vehicle at each corner thereof and generating sensor output signals in response thereto;
• calculating a force signal for each actuator in response to said sensor output signals;
• actuating said second valving means for generating a desired actuator force in response to said force signal;
• and
• actuating said first valving means for providing a fluid communication path between said fluid source and said hydraulic actuator for cumulatively generating said actuator force whenever said force signal is outside of the limits of said second valving means.

A method of adapting the gains of a full feedback control system for an active suspension system, said system having an actuator connected between the sprung and unsprung mass of the vehicle, said method comprising the steps of:

• providing a control circuit adapted to receive output signals from sensor means for generating a state variable vector X.sub.n defining the velocity and displacement of the vehicle's sprung and unsprung masses, said control circuit having a feedback gain matrix G.sub.n defining stiffness and damping characteristics based on predetermined vehicle performance requirements so as to generate a demanded output force signal U=G.sub.n (X.sub.n);
• identifying disturbances represented by variations in the frequency and amplitude of the vehicle's relative suspension velocity;
• calculating a linear combination matrix "G" of a first feedback gain matrix G.sub.soft and a second feedback gain matrix G.sub.firm ;
• and
• inputting said weighted linear combination "G" into said feedback gain matrix G.sub.n for continuously modifying said demanded output force signal "U".