Method and apparatus for controlling an electric assist steering system using an adaptive blending torque filter

• US 5,504,403 A
• Filed: 05/20/1994
• Issued: 04/02/1996
• Est. Priority Date: 05/11/1994
• Status: Expired due to Term

• Current Assignee: TRW Inc. (Northrop Grumman Corporation)
• Original Assignee: TRW Inc. (Northrop Grumman Corporation)
• Inventors: McLaughlin, Kevin M.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Masih, Karen
• Application Number:
  US08/246,947
• Time in Patent Office: 683 Days
• Field of Search: 318/432, 318/433, 318/434, 180/79.1, 180/79, 180/6.2, 180/197, 364/724.01, 73/116
• US Class Current: 318/432
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input
• CPC Class Codes: B62D 6/10 characterised by means for sensing or determining torque

Abstract

A steering assist system (10) providing assist in response to a steering control signal includes a vehicle speed sensor (56) for sensing vehicle speed and for providing a speed signal having a value indicative of the sensed vehicle speed and a torque sensor (44) operatively connected to a vehicle hand wheel (12) for providing a torque signal indicative of applied steering torque. A blending filter (70, 71) is connected to the torque sensor and provides a blended filtered torque signal having a non-linear characteristic at torque frequencies less than a blending frequency and a linear characteristic at torque frequencies greater than the blending frequency. The blending filter establishing the blending frequency at a value functionally related to vehicle speed. Steering assist motor (28) provides steering assist in response to a control signal. The control signal is provided in response to the blended filtered torque signal. The blending filters filtering the torque signal so as to maintain a selectable system bandwidth during system operation.

Claims

1. An apparatus for controlling a steering assist system, said steering assist system providing assist in response to a steering control signal, said apparatus comprising:

torque sensing means operatively connected to a vehicle hand wheel for providing a torque signal indicative of applied steering torque;

blending filter means connected to said torque sensing means for providing a blended filtered torque signal having a first functional characteristic at torque frequencies less than a blending frequency and a second functional characteristic at torque frequencies greater than said blending frequency;

steering assist means for providing steering assist in response to a control signal; and

control means operatively connected to said blending filter means for providing said control signal to said steering assist means in response to said blended filtered torque signal, said blending filtering means filtering said torque signal so as to maintain a selectable system bandwidth during system operation.

2. The apparatus of claim 1 wherein said first functional characteristic of said blending filter is non-linear and wherein said second functional characteristic is linear.

3. The apparatus of claim 1 wherein said control means further includes adaptive filter means for filtering said blended filtered torque signal so as to maintain system stability at all vehicle speeds.

4. The apparatus of claim 1 wherein said blending filter means includes low pass filter means for passing the torque signal with frequencies less than said blending frequency.

5. An apparatus for controlling a steering assist system, said steering assist system providing assist in response to a steering control signal, said apparatus comprising:

vehicle speed sensing means for sensing vehicle speed and for providing a speed signal having a value indicative of the sensed vehicle speed;

torque sensing means operatively connected to a vehicle hand wheel for providing a torque signal indicative of applied steering torque;

blending filter means connected to said torque sensing means and to said vehicle speed sensing means for providing a blended filtered torque signal having a first functional characteristic at torque frequencies less than a blending frequency and a second functional characteristic at torque frequencies greater than said blending frequency, said blending filter means further establishing said blending frequency at a value functionally related to vehicle speed;

steering assist means for providing steering assist in response to a control signal; and

control means operatively connected to said blending filter means for providing said control signal to said steering assist means in response to said blended filtered torque signal, said blending filtering means filtering said torque signal so as to maintain a selectable system bandwidth during system operation.

6. The apparatus of claim 5 wherein said first functional characteristic of said blending filter is non-linear and wherein said second functional characteristic is linear.

7. The apparatus of claim 5 wherein said control means further includes adaptive filter means for filtering said blended filtered torque signal so as to maintain system stability at all vehicle speeds.

8. The apparatus of claim 5 wherein said blending filter means includes high pass filter means for passing the torque signal with frequencies greater than said blending frequency.

9. The apparatus of claim 5 wherein said blending filter means includes low pass filter means for passing the torque signal with frequencies less than said blending frequency.

10. A method for controlling a steering assist system that provides steering assist in response to a steering control signal, said method comprising the steps of:

measuring applied steering torque and providing a torque signal indicative of the measured applied steering torque;

filtering said torque signal so as to have a first functional characteristic at torque frequencies less than a blending frequency and a second functional characteristic at torque frequencies greater than said blending frequency so as to maintain a selectable system bandwidth during system operation;

providing steering assist in response to a steering control signal; and

providing the control signal in response to the filtered torque signal.

11. The method of claim 10 wherein said filtering step includes filtering said torque signal so as to have a first non-linear characteristic at torque frequencies less than the blending frequency and a linear characteristic at torque frequencies greater than said blending frequency.

12. The method of claim 10 wherein said step of filtering includes further filtering said filtered torque signal so as to maintain system stability at all vehicle speeds.

13. The method of claim 10 further including the step of establishing said blending frequency value one decade lower than the system'"'"'s open loop zero db crossover frequency.

14. An apparatus for controlling a steering assist system, said steering assist system providing assist in response to a steering control signal, said apparatus comprising:

torque sensing means operatively connected to a vehicle hand wheel for providing a torque signal indicative of applied steering torque;

blending filter means connected to said torque sensing means for providing a blended filtered torque signal having a first functional characteristic at torque frequencies less than a blending frequency and a second functional characteristic at torque frequencies greater than said blending frequency;

steering assist means for providing steering assist in response to a control signal; and

control means operatively connected to said blending filter means for providing said control signal to said steering assist means in response to said blended filtered torque signal, said blending filtering means filtering said torque signal so as to maintain a selectable system bandwidth during system operation;

wherein said blending filter means includes means for establishing a blending frequency value one decade lower than the system'"'"'s open loop zero db crossover frequency.

15. An apparatus for controlling a steering assist system, said steering assist system providing assist in response to a steering control signal, said apparatus comprising:

torque sensing means operatively connected to a vehicle hand wheel for providing a torque signal indicative of applied steering torque;

blending filter means connected to said torque sensing means for providing a blended filtered torque signal having a first functional characteristic at torque frequencies less than a blending frequency and a second functional characteristic at torque frequencies greater than said blending frequency, and including high pass filter means for passing the torque signal with frequencies greater than said blending frequency;

steering assist means for providing steering assist in response to a control signal; and

control means operatively connected to said blending filter means for providing said control signal to said steering assist means in response to said blended filtered torque signal, said blending filtering means filtering said torque signal so as to maintain a selectable system bandwidth during system operation.

16. An apparatus for controlling a steering assist system, said steering assist system providing assist in response to a steering control signal, said apparatus comprising:

vehicle speed sensing means for sensing vehicle speed and for providing a speed signal having a value indicative of the sensed vehicle speed;

torque sensing means operatively connected to a vehicle hand wheel for providing a torque signal indicative of applied steering torque;

blending filter means connected to said torque sensing means and to said vehicle speed sensing means for providing a blended filtered torque signal having a first functional characteristic at torque frequencies less than a blending frequency and a second functional characteristic at torque frequencies greater than said blending frequency, said blending filter means further establishing said blending frequency at a value functionally related to vehicle speed and one decade lower than the system'"'"'s open loop zero db crossover frequency;

steering assist means for providing steering assist in response to a control signal; and

control means operatively connected to said blending filter means for providing said control signal to said steering assist means in response to said blended filtered torque signal, said blending filtering means filtering said torque signal so as to maintain a selectable system bandwidth during system operation;

wherein said blending filter means further includes means for establishing said blending frequency value.