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Control system for steering a road vehicle having both front-wheel steering and rear wheel steering

  • US 5,515,275 A
  • Filed: 11/09/1994
  • Issued: 05/07/1996
  • Est. Priority Date: 03/03/1992
  • Status: Expired due to Fees
First Claim
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1. A steering system for a road vehicle which vehicle hassteerable front wheels disposed proximal a front axle;

  • steerable rear wheels disposed behind the front wheels a distance l (in m), said distance being the wheel base;

    a steering wheel rotatable to a steering wheel angle δ

    L (in rad);

    a mass m (in kg);

    a center of mass located a distance lv (in m) behind the front axle; and

    a rear cornering stiffness ch (in N/rad);

    said steering system comprising;

    a front actuator means for controlling a front wheel steering angle δ

    v in rad;

    a rear actuator means for controlling a rear wheel steering angle δ

    h in rad;

    a yaw sensor means for generating a yaw signal r proportional to a yawing angular rotation rate of the vehicle (in rad/s);

    a steering wheel angle sensor means for measuring the steering wheel angle δ

    L (in rad);

    a speedometer sensor for measuring vehicle velocity v in m/s; and

    a processor means for accepting the r, δ

    L, and v from said yaw sensor means, said angle sensor means and said speedometer and for controlling the front actuator and the rear actuator based thereon;

    the processor means incorporatinga first calculation for calculating δ

    v as a first function of r such that a front axle transverse acceleration av (in m/s) is a function of δ

    L only, the first calculation including compensation for the yaw signal r, andmeans for causing the front actuator to dispose the front wheels to δ

    v, whereby steering is decoupled from yaw rate;

    a second calculation for calculating a command variable Wh and calculating δ

    h as a second function
    
    
    space="preserve" listing-type="equation">δ

    .sub.h =(l/v-K.sub.D)(W.sub.h -r) (in rad)where KD is a parameter, andmeans for causing the rear actuator to dispose the rear wheels to δ

    h ;

    the first calculation and the second calculation being decoupled;

    whereby yaw damping is independent of v and the yaw control does not affect the transfer function from the steering wheel to the front axle tracking.

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