Method and apparatus for dynamic leveling

An apparatus for use with an active suspension system of a motor vehicle having a central high pressure fluid source, comprising:

• hydraulic actuators adapted to be operably connected between the vehicle suspension and body at each corner thereof, each of said hydraulic actuators having a pressure cylinder forming a working chamber operable to store damping fluid therein and secured to one of the suspension and body of the vehicle, and a piston and rod assembly coaxially disposed within said pressure cylinder for translational movement therein with opposite sides of said piston defining first and second portions of said working chamber, said rod secured at an end opposite said piston to the other of the suspension and body portions of the vehicle;
• variable flow restriction means for varying the flow of damping fluid between said first and second portions of said working chamber;
• flow control means associated with said actuator and fluidly connecting said actuator to the central high pressure fluid source for controlling the flow of damping fluid therebetween, said flow control means adapted to fluidly communicate with one of said first and second portions of said working chamber;
• and
• an accumulator associated with said actuator and in fluid communication with the other of said first and second portions of said working chamber.

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

• connecting a hydraulic actuator between the suspension and body at each corner of the vehicle, said actuator having a piston and rod assembly disposed within a pressure cylinder such that said piston defines first and second portions of a working chamber adapted for storing damping fluid within said pressure cylinder;
• connecting said first portion of said working chamber for each actuator to a high pressure fluid source having a pump and a reservoir;
• connecting flow control means intermediate said high pressure fluid source and each of said actuators for controlling the addition or release of fluid from said first portion of said working chamber;
• connecting an accumulator to said second portion of said working chamber for each of said actuator;
• providing a variable flow restriction for varying the flow of damping fluid between said first and second portions of said working chamber said flow restriction being variable between an upper and lower limit;
• sensing the dynamic behavior of the suspension and body at each corner of the vehicle for generating an electrical sensor output signal in response thereto;
• calculating a desired suspension force "U" signal for each actuator in response to said sensor output signals;
• inputting said suspension force signal "U" to an actuator controller adapted for controlling actuation of said flow control means and said variable flow restriction for generating a desired output force F.sub.actuator from each actuator;
• actuating said variable flow restriction for generating said actuator force F.sub.actuator when said desired suspension force signal "U" is within said upper and lower limits of said variable flow restriction;
• and
• actuating said variable flow restriction to be set at either its upper o lower limit and concurrently actuating said flow control means for intermittently opening and closing a fluid communication path between said high pressure fluid source and said actuator for adding and subtracting energy to and from said actuator respectively, whereby substantially concurrent actuation generates said actuator force F.sub.actuator whenever said desired suspension force "U" is outside of said limits of said flow restriction.

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 closed-loop dynamic leveling control circuit adapted to receive output signals from a plurality of transducers for generating a state variable vector X.sub.n defining the velocity and displacement of the vehicle's sprung and unsprung mass, said dynamic leveling 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 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 gain weighting coefficient (.alpha.) based on the frequency content of said disturbances;
• calculating a linear combination matrix "G" of a first feedback gain matrix G.sub.soft and a second feedback gain matrix G.sub.firm according to the equation
• g=(1-(.alpha.))g.sub.soft +(.alpha.)g.sub.firm where:
• 0<(.alpha.)<1;
• and
• inputting said weighted linear combination "G" into said feedback gain matrix G for continuously calculating modified demanded output force signals "U".

A dynamic leveling control system for a low power fully active suspension system for generating a commanded force output signal "U" for input to an actuator controller system, comprising:

• sensor means for sensing the dynamic motion of the suspension and body of a vehicle and generating sensor output signals in response thereto;
• signal processing means for processing said sensor output signals so as to generate a state variable vector X.sub.n representing the dynamic motion of said vehicle's suspension and body, said signal processing means including estimating means for estimating at least one state variable of state variable vector X.sub.n from said sensor output signals;
• vehicle controller means having a feedback gain matrix G.sub.n defining stiffness and damping characteristics for said state variable vector X.sub.n based on predetermined vehicle dynamic performance requirements such that said vehicle controller means receives an output from said signal processing means for calculating "U.sub.dyn " according to the following state matrix equation:
• U.sub.dyn =-G.sub.n (X.sub.n).