Electrically assisted power steering apparatus

• US 5,979,587 A
• Filed: 06/06/1997
• Issued: 11/09/1999
• Est. Priority Date: 06/06/1997
• Status: Expired due to Term

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Liubakka, Michael Kenneth, Zaremba, Alexander Timofeevich
• Primary Examiner(s): Oberleitner, Robert J.
• Assistant Examiner(s): YEAGLEY, DANIEL S
• Application Number:
  US08/869,288
• Time in Patent Office: 886 Days
• Field of Search: 180/446, 701/42
• US Class Current: 180/446
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input

Abstract

An electronically assisted power steering system (10) for providing assist in response to a steering control signal includes a steering torque sensor (30) operatively connected to a vehicle hand wheel (12) for providing a torque signal indicative of applied steering torque. An electric motor control module (50) is connected to the torque sensor (30) and to an electric motor (32). The electric motor control module (50) includes an outer loop controller for generating a desired torque signal responsive to the applied steering torque. The outer loop controller includes a phase lag network in series with a second order network for compensating the desired torque signal. The electric motor control module (50) also includes an inner loop controller for generating a motor drive signal responsive to the desired torque signal output from the outer loop controller. The inner loop applies a motor drive signal to the electric motor to generate the required assistive torque.

Claims

1. An electrically assisted power steering apparatus for steering a motor vehicle, said electrically assisted power steering apparatus comprising:

a steering mechanism;

a steering torque sensor for detecting a steering torque applied to a steering wheel and generating a steering torque signal;

an electric motor for generating an assistive steering torque for said steering mechanism;

an outer loop controller for generating a desired torque signal responsive to said steering torque signal, said outer loop controller comprising;

a phase lag network; and

a lead-lag network in series with said phase lag network, said lead-lag network being characterized by having complex lead zeros; and

an inner loop controller for generating a motor drive signal responsive to said desired torque signal and applying said motor drive signal to said electric motor.

2. An electrically assisted power steering apparatus for steering a motor vehicle as set forth in claim 1, further comprising a vehicle speed sensor for detecting a vehicle speed of the motor vehicle and generating a vehicle speed signal used by said outer loop controller for generating a desired torque signal responsive to said steering torque signal and said vehicle speed signal.

3. An electrically assisted power steering apparatus for steering a motor vehicle as set forth in claim 1, wherein said phase lag network is characterized by the following relationship:

##EQU4## where values for β and

ω

_I are established based on the characteristics of the steering apparatus.

4. An electrically assisted power steering apparatus for steering a motor vehicle as set forth in claim 1, wherein said lead-lag network is characterized by the following relationship:

##EQU5## where values for ξ

_n and (ω

_p /ω

_n)² are established based on the characteristics of the steering apparatus.

5. An electrically assisted power steering apparatus for steering a motor vehicle as set forth in claim 1, further comprising a steering wheel position sensor for detecting a steering wheel angle and generating a steering wheel angle signal used by said outer loop controller for generating a desired torque signal responsive to said steering torque signal, said vehicle speed signal and said steering wheel angle signal.

6. An electrically assisted power steering apparatus for steering a motor vehicle, said electrically assisted power steering apparatus comprising:

steering wheel for accepting driver input;

a steering shaft having a first end connected to said steering wheel;

a steering pinion attached to a second end of said steering shaft opposite said first end;

a steering rack matingly engaged with said steering pinion;

a steering torque sensor for detecting a steering torque applied to said steering wheel and generating a steering torque signal;

an electric motor for generating an assistive steering torque to supplement said driver input to said steering rack;

an outer loop controller for generating a desired torque signal responsive to said steering torque signal, said outer loop controller comprising;

a phase lag network; and

a lead-lag network cooperating with said phase lag network, said lead-lag network being characterized by having complex lead zeroes; and

an inner loop controller for generating a motor drive signal responsive to said desired torque signal and applying said motor drive signal to said electric motor.

7. An electrically assisted power steering apparatus for steering a motor vehicle as set forth in claim 6, wherein said assistive torque generated by said electric motor is applied to said steering shaft.

8. An electrically assisted power steering apparatus for steering a motor vehicle as set forth in claim 6, wherein said assistive torque generated by said electric motor is applied to said steering rack.

9. An electrically assisted power steering apparatus for steering a motor vehicle as set forth in claim 6, further comprising a vehicle speed sensor for detecting a vehicle speed of the motor vehicle and generating a vehicle speed signal used by said outer loop controller for generating a desired torque signal responsive to said steering torque signal and said vehicle speed signal.

10. An electrically assisted power steering apparatus for steering a motor vehicle as set forth in claim 6, wherein said phase lag network is characterized by the following relationship:

##EQU6## where values for β and

ω

_I are established based on the characteristics of the steering apparatus.

11. An electrically assisted power steering apparatus for steering a motor vehicle as set forth in claim 6, wherein said lead-lag network is characterized by the following relationship:

##EQU7## where values for ξ

_n and (ω

_p /ω

_n)² are established based on the characteristics of the steering apparatus.

12. An electrically assisted power steering apparatus for steering a motor vehicle as set forth in claim 6, further comprising a steering wheel position sensor for detecting a steering wheel angle and generating a steering wheel angle signal used by said outer loop controller for generating a desired torque signal responsive to said steering torque signal, said vehicle speed signal and said steering wheel angle signal.