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

• Current Assignee: Deutsche Telekom AG
• Original Assignee: Deutsche Telekom AG
• Inventors: Ackermann, Jurgen
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): LOUIS JACQUES, JACQUES H
• Application Number:
  US08/338,175
• Time in Patent Office: 545 Days
• Field of Search: 364/424.05, 364/426.02, 364/426.03, 364/424.06, 364/426.01, 180/142, 180/140, 180/79.1, 180/197, 180/141, 180/178, 180/170, 280/91, 303/100, 303/95, 303/96, 303/9.62, 303/103, 303/111, 477/108, 477/903, 73/182, 73/861.66, 73/146.2
• US Class Current: 701/41
• CPC Class Codes: B60G 2400/0523 Yaw rate
• CPC Class Codes: B60G 2400/204 Vehicle speed
• CPC Class Codes: B60G 2400/41 Steering angle
• CPC Class Codes: B60G 2400/61 Load distribution
• CPC Class Codes: B60G 2800/016 Yawing condition
• CPC Class Codes: B60G 2800/24 Steering, cornering
• CPC Class Codes: B60G 2800/702 Improving accuracy of a sensor signal
• CPC Class Codes: B60G 2800/962 Four-wheel steering
• CPC Class Codes: B62D 7/159 characterised by computing methods or stabilisation processes or systems, e.g. responding to yaw rate, lateral wind, load, road condition

Abstract

A control system for steering a road vehicle having front-wheel and rear-wheel steering, comprising a wheel base l (in m), a rear cornering stiffness c_h (in N/rad), a center of gravity distance l_v (in m) from the front axle and a mass m (in kg) and provided with a decoupled control circuit, a predetermined yaw damping D_G is adjusted according to a damping parameter ##EQU1## via the steering of the rear wheels through an angle δ_h (in rad). Herewith the yaw rate r (in rad/s), travelling velocity v (in m/s) and steering wheel angle δ_L (in rad) are measured and the angle δ_h =(l/v-k_D) (w_h -r) is calculated by a microprocessor, whereby w_h is formed as command variable from the measured steering wheel angle (δ_L) by a prefilter (F_h) associated with the rear-wheel steering.

Claims

1. A steering system for a road vehicle which vehicle has

steerable 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 l_v (in m) behind the front axle; and

a rear cornering stiffness c_h (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 incorporating

a first calculation for calculating δ

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

_L only, the first calculation including compensation for the yaw signal r, and

means 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 W_h 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 K_D is a parameter, and

means 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.

2. The steering system according to claim 1, wherein W_h is calculated from δ

_L by a prefilter transfer function (F_h) associated with rear-wheel steering.

3. The steering system according to claim 1, wherein ##EQU14##

4. The steering system according to claim 3, further comprising;

a manual control accessible to a driver of the vehicle; and

parameter input means for varying the parameter K_D according to a setting of the manual control.

5. The steering system according to claim 3, further comprising;

automatic control means for varying the parameter k_D.

6. The steering system according to claim 1, wherein the yaw signal is proportional to a yawing angular acceleration of the vehicle.

7. The steering system according to claim 1, wherein the first process integrates r with respect to time.