Steer-by-wire steering system for motorized vehicles

• US 6,219,604 B1
• Filed: 12/28/1999
• Issued: 04/17/2001
• Est. Priority Date: 12/29/1998
• Status: Expired due to Fees

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Sauer, Thomas, Janetzke, Helmut, Harter, Werner, Yuan, Bo, Muller, Bernd, Allgeier, Thorsten, Pfeiffer, Wolfgang, Ries-Mueller, Klaus, Cao, Chi-Thuan, Ahner, Peter, Nguyen, Ngoc-Thach, Lohner, Herbert, Dominke, Peter, Hess, Werner, Blessing, Peter, Dilger, Elmar
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Marc-Coleman, Marthe Y.
• Application Number:
  US09/473,375
• Time in Patent Office: 476 Days
• Field of Search: 701/41, 701/42, 180/422, 180/443, 180/446
• US Class Current: 701/41
• CPC Class Codes: B62D 6/003 in order to control vehicle yaw movement, i.e. around a vertical axis B62D6/007 takes precedence
• CPC Class Codes: B62D 6/008 Control of feed-back to the steering input member, e.g. simulating road feel in steer-by-wire applications

Abstract

A steer-by-wire steering system comprised of an electronically regulated steering positioner mounted to the steering gear of the front axle or to both front wheels of a vehicle together with an electronic steering regulator and a feedback actuator. A sensor senses the driver'"'"'s selected direction from the steering wheel. Road feedback can be relayed to the driver through a feedback actuator via the steering wheel. The loss of road feel caused by the absence of the steering column, which normally strongly influences the driver'"'"'s directional wish, is recreated by the feedback actuator.

Claims

1. A steer-by-wire steering system for a motorized vehicle, said vehicle including a front axle, a plurality of steerable wheels connected to said axle, an electronically controlled steering positioner, a steering gear, and a steering wheel, said system comprising:

a steering wheel sensor for sensing a driver'"'"'s selected direction from the steering wheel;

a feedback actuator connected to the steering wheel for providing road feedback to a driver, said actuator including a steering wheel positioner and steering wheel regulator;

a torque sensor and a current sensor, both said torque sensor and current sensor connected to said steering wheel regulator for determining aligning torques and aligning currents;

a steering regulator connected to said steering positioner;

a nominal value generator connected to said steering regulator, said steering regulator and nominal value generator modifying a driver'"'"'s selected direction as a function of a moving vehicle'"'"'s handling dynamics and generating a nominal value for the steering positioner, said steering regulator determining a nominal manual torque for a driver as a function of simulated aligning torques derived from one of aligning torques and aligning currents, from signals measured by said steering wheel sensor and from operational status signals of said vehicle including driving speed, the co-efficient of friction between the road and vehicle, and wherein the nominal manual torque is used as the basis of the manual torque transferred to the steering wheel through the steering wheel positioner.

2. The steer-by-wire steering system according to claim 1 wherein the electronic steering regulator produces a variable steering angle transmission ratio as a function of the driver'"'"'s selected direction in accordance with the following relation:

3. The steer-by-wire steering system according to claim 1 wherein the electronic steering regulator varies the steering angle transmission ratio by means of a function which is a monotonous function of driving speed.

4. The steer-by-wire steering system according to claim 1 including a yaw regulator connected to the steering regulator, said yaw regulator modifying the driver'"'"'s selected direction as a function of the dynamics of the moving vehicle whereby the desired yaw behavior of the vehicle if obtained.

5. The steer-by-wire steering system according to claim 1 wherein the yaw regulator connected to a reference generator which provides a default for the desired yaw behavior according to the following relation:

${\mathrm{\omega <br><br>}}_{\mathrm{ref}}=\left[\frac{v}{l<br><br>\left(1+\frac{v^2}{v_{\mathrm{ch}}^2}\right)}·<br><br>\frac{{\mathrm{\delta <br><br>}}_H}{i_s}\right]·<br><br>\frac{1}{1+T_{\mathrm{ref}}<br><br>s}$$\mathrm{wherein}$$\begin{array}{cc}\begin{array}{c}{\mathrm{\omega <br><br>}}_{\mathrm{ref}}=\mathrm{nominal}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{yaw}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{velocity}\\ v=\mathrm{speed}\\ v_{\mathrm{ch}}=\mathrm{characteristic}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{speed}\end{array}& \begin{array}{c}l=\mathrm{wheel}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{base}\\ T_{\mathrm{ref}}=\mathrm{time}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{constant}\\ s=\mathrm{Laplace}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{operator}\end{array}\end{array}$$\left(\approx <br><br>60<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>100<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{km}/h\right)$

6. The steer-by-wire steering system according to claim 1 including two steering positioners for controlling individual wheels, the yaw regulator executing the modification of the driver'"'"'s selected direction as a function of the geometry of the inside-curve and outside-curve wheels according to the following relation:

$\begin{array}{c}\mathrm{Inside}<br><br>\text{;<br><br>}\\ {\mathrm{\delta <br><br>}}_{H,i}^{*}=\left[\frac{R}{R-\left(\frac{b}{2}\right)}\right]·<br><br>{\mathrm{\delta <br><br>}}_H^{*}\\ \mathrm{Outside}<br><br>\text{;<br><br>}\\ {\mathrm{\delta <br><br>}}_{H,a}^{*}=\left[\frac{R}{R+\left(\frac{b}{2}\right)}\right]·<br><br>{\mathrm{\delta <br><br>}}_H^{*}\end{array}$

wherein b is the equidistance of the wheels, the circular radius R can be determined and based on speeds V1, Va, according to the following relation;

$R=\frac{b<br><br>\left(v_a+v_i\right)}{2<br><br>\left(v_a-v_i\right)}.$

7. Steer-by-wire steering system according to claim 1 wherein a feedback simulator calculates the yaw behavior of the vehicle as a function of the driving speed and the steering angle, calculates the slip angles of the wheels, and calculates the aligning torque on the front wheels, and wherein a steering column model rear-mounted to a vehicle model calculates a nominal manual torque on the steering wheel, taking into account friction and elasticity present in the steering wheel.

8. Steer-by-wire steering system according to claim 1 wherein a feedback simulator stores a map with characteristic parameters for a rear-mounted model of steering characteristics, and calculates respective nominal manual torques for communication to the steering wheel positioner on the basis of diverse driving situations.

9. Steer-by-wire steering system according to claim 1 wherein, in order to determine a nominal manual torque, the steering wheel regulator converts one of the aligning torque measured at the front wheels and the aligning current measured at the steering positioner and relays it to a steering column model that is rear-mounted to the steering wheel regulator, which calculates the nominal manual torque relayed to the steering wheel positioner.

10. Steer-by-wire steering system according to claim 1 wherein the steering wheel regulator limits the resulting manual torque to a specific maximum value in order to convey the kind of driving feeling that is customary in power steering systems.

11. Steer-by-wire steering system according to claim 1 wherein the steering wheel regulator signal overloads of the steering positioner by means of a tactile signal relayed to the steering wheel via the steering wheel positioner.

12. Steer-by-wire steering system according to claim 1 wherein the vehicle and the control of other functions of the vehicle are adapted to be accomplished by one of an antilock, an automatic traction control, a straight-line stability and adaptive control constraint, an engine management, a chassis steering, chassis control recorder, and a tire inflation pressure recorder, whereby the steering wheel regulator is fed data generated by the control unit, while the nominal manual torque continues to be determined based on these values.

13. Steer-by-wire steering system according to claim 12 wherein the chassis steering and the chassis regulating system control the distance between the body and the wheels of the vehicle and the suspension and shock absorption properties of the suspension systems between the body and the wheels, and the nominal manual torque is determined as a function of a distance, a suspension property and a shock absorption property, whereby the nominal manual torque is increased as the shock absorption and the suspension hardness is diminished.

14. Steer-by-wire steering system according to claim 12 wherein the chassis steering and the chassis regulating system control the distance between the body and the wheels of the vehicle and the suspension and shock absorption properties of the suspension systems between the body and the wheels, and that the steering wheel regulator is adapted to modify the manual torque transmitted to the steering wheel positioner as a function of distance of distance, suspension property and shock absorption property.

15. Steer-by-wire steering system according to claim 12 including a tire inflation gauge which reads the current air pressure in the vehicle tires, and the nominal manual torque is determined on the basis of the recorded air pressure.

16. Steer-by-wire steering system according to claim 15 wherein the steering wheel regulator is adapted to modify the manual torque relayed to the steering wheel positioner as a function of the recorded air pressure, whereby vibration and jerking motion on the steering wheel if the air pressure is below a specifiable or default threshold value and falls at a specifiable rate are inhibited.

17. Steer-by-wire steering system according to claim 1 wherein the steering wheel regulator is adapted to modify the manual torque relayed to the steering wheel positioner on the basis of a friction coefficient of the road surface as determined by an antilock system control unit under slippery road conditions.

18. Steer-by-wire steering system according to claim 1 wherein the steering wheel regulator is adapted to modify the manual torque relayed to the steering wheel positioner on the basis of data generated in an electronic control unit which warns of the danger of the vehicle overturning or going into a skid.

19. Steer-by-wire steering system according to claim 1 wherein the steering wheel regulator is adapted to modify the manual torque relayed to the steering wheel positioner when the antilock system control unit identifies poor road conditions.

20. Steer-by-wire steering system according to claim 1 wherein the steering wheel regulator is adapted to generate a signal by means of the manual torque to indicate improper handling conditions of the vehicle selected from the maximum RPM'"'"'s, the maximum speed of the vehicle is exceeded, and when it is driven on a nearly empty tank.