Method and apparatus for determining faults in an electric assist steering system

• US 20060122796A1
• Filed: 12/08/2004
• Published: 06/08/2006
• Est. Priority Date: 12/08/2004
• Status: Active Grant

• Current Assignee: TRW Automotive USLLC (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: TRW Automotive USLLC (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: McLaughlin, Kevin M., Miller, Joseph D.
• Granted Patent: US 7,483,796 B2
• Time in Patent Office: Days
• US Class Current: 702/58
• CPC Class Codes: G01R 31/006 on road vehicles, e.g. automobiles or trucks testing of ignition installations peculiar to internal combustion engines F02P17/00
• CPC Class Codes: G01R 31/343 in operation
• CPC Class Codes: H02P 29/0241 the fault being an overvoltage

Abstract

A method and apparatus for determining a fault in an electric motor (50) determines a calculated star voltage (V_star—calc) of the electric motor. The calculated star voltage (V_star—calc) is compared to a measured star voltage (V_star—meas) of the electric motor (50) to determine a star voltage error (V_star—err). The fault in the electric motor (50) is determined when the star voltage error (V_star—err) exceeds a predetermined maximum star voltage error (V_{star—err—max}).

Claims

1. A method for determining a fault in a system including an electric motor, said method comprising the steps of:

determining a calculated star voltage of the electric motor;

determining a measured star voltage of the electric motor;

comparing said calculated star voltage to said measured star voltage of the electric motor to determine a star voltage error; and

determining the fault in the system when said star voltage error exceeds a predetermined maximum star voltage error.

2. The method recited in claim 1, wherein said step of determining a calculated star voltage comprises the steps of:

determining phase voltages to apply to the phases of the electric motor; and

determining the sum of said phase voltages, said calculated star voltage being equal to one-third of said sum of said phase voltages.

3. The method as recited in claim 2, wherein the system is an electric assist steering system and the electric motor is an electric assist motor for providing steering assist torque for helping to steer steerable wheels of a vehicle, said step of determining phase voltages comprising the steps of:

determining a required steering assist torque as a function of a sensed applied steering torque and a sensed vehicle speed; and

determining said phase voltages as a function of said required steering assist torque and a sensed rotor position of the electric motor.

4. The method as recited in claim 1, wherein said step of comparing said calculated star voltage comprises the step of determining an absolute difference between said calculated star voltage and said measured star voltage.

5. The method as recited in claim 1, wherein the electric motor is a three-phase permanent magnet AC motor.

6. The method as recited in claim 1, wherein said step of determining a measured star voltage comprises the step of measuring voltage between a star connection point of the electric motor and ground.

7. The method as recited in claim 1, further comprising the step of disabling the electric motor when the fault is determined.

8. The method as recited in claim 1, further comprising the step of providing at least one of a visual and audible indication when the fault is determined.

9. The method as recited in claim 1, further comprising the step of disabling FETs of a drive circuit for said electric motor.

10. A method for determining a fault in an electric motor, said method comprising the steps of:

determining a calculated star voltage of the electric motor;

determining a measured star voltage of the electric motor;

comparing said calculated star voltage to said measured star voltage of the electric motor to determine a star voltage error; and

determining the fault in the electric motor when said star voltage error exceeds a predetermined maximum star voltage error.

11. Apparatus for determining a fault in a system including an electric motor, said apparatus comprising:

means for determining a calculated star voltage of the electric motor;

means for determining a measured star voltage of the electric motor;

means for comparing said calculated star voltage to said measured star voltage of the electric motor to determine a star voltage error; and

means for determining the fault in the system when said star voltage error exceeds a predetermined maximum star voltage error.

12. The apparatus recited in claim 11, wherein said means for determining a calculated star voltage comprises:

means for determining phase voltages to apply to the phases of the electric motor; and

means for determining the sum of said phase voltages, said calculated star voltage being equal to one-third of said sum of said phase voltages.

13. The apparatus as recited in claim 12, wherein the system is an electric assist steering system and the electric motor is an electric assist motor for providing steering assist torque for helping to steer steerable wheels of a vehicle, said means for determining phase voltages comprising:

means for determining a required steering assist torque as a function of a sensed applied steering torque and a sensed vehicle speed; and

means for determining said phase voltages as a function of said required steering assist torque and a sensed rotor position of the electric motor.

14. The apparatus as recited in claim 11, wherein said means for comparing said calculated star voltage comprises means for determining an absolute difference between said calculated star voltage and said measured star voltage.

15. The apparatus as recited in claim 11, wherein the electric motor is a three-phase permanent magnet AC motor.

16. The apparatus as recited in claim 11, wherein said measured star voltage is measured between a star connection point of the electric motor and ground.

17. The apparatus as recited in claim 11, further comprising means for disabling the electric motor when the fault is determined.

18. The method as recited in claim 11, further comprising means for providing at least one of a visual and audible indication when the fault is determined.

19. The method as recited in claim 11, further comprising means for disabling FETs of a drive circuit for said electric motor.

20. Apparatus for determining a fault in an electric motor, said apparatus comprising:

means for determining a calculated star voltage of the electric motor;

means for determining a measured star voltage of the electric motor;

means for comparing said calculated star voltage to said measured star voltage of the electric motor to determine a star voltage error; and

means for determining the fault in the electric motor when said star voltage error exceeds a predetermined maximum star voltage error.

21. Apparatus comprising:

an electric motor;

a voltage monitor operatively connected to said electric motor, said voltage monitor determining a measured star voltage of said electric motor; and

an electronic control unit for controlling operation of said electric motor, said electronic control unit being operatively connected to said electric motor and said voltage monitor, said electronic control unit comprising;

a circuit for determining a calculated star voltage of the electric motor;

a circuit for comparing said calculated star voltage to said measured star voltage to determine a star voltage error; and

a circuit for determining a fault when said star voltage error exceeds a predetermined maximum star voltage error.

22. An electric assist steering system comprising:

a vehicle steering gear operable to effectuate movement of steerable vehicle wheels upon application of an applied steering torque;

an electric assist motor for providing steering assist torque for assisting said applied steering torque;

means for sensing said applied steering torque and providing a sensed applied steering torque;

means for controlling said electric assist motor, said means for controlling being operatively connected to said means for sensing to receive said sensed applied steering torque, said means for controlling being operative to determine a motor voltage command;

means for providing electric current to said electric assist motor in accordance with said motor voltage command; and

means for determining a fault in the electric assist steering system when a calculated star voltage differs from a measured star voltage to a predetermined degree.

23. Apparatus as recited in claim 22, wherein said means for determining a fault in the electric assist steering system comprises:

means for determining said calculated star voltage of said electric assist motor;

means for determining said measured star voltage of said electric assist motor;

means for comparing said calculated star voltage to said measured star voltage of said electric assist motor to determine a star voltage error; and

means for determining the fault when said star voltage error exceeds a predetermined maximum star voltage error.

24. Apparatus for controlling an electric motor, said apparatus comprising:

an electronic control unit, said electronic control unit including a motor control circuit operative to determine a motor voltage command;

a drive circuit operatively connected to said electronic control unit and the electric motor, said drive circuit being operative to provide electric current to the electric motor in accordance with said motor voltage command; and

a voltage monitor operatively connected to the electric motor and said electronic control unit, said voltage monitor being operative to determine a measured star voltage of the electric motor and provide said measured star voltage to the electronic control unit,

said electronic control unit further including a fault detection circuit operative to determine a calculated star voltage of the electric motor, said fault detection circuit being operative to determine a fault when said calculated star voltage differs from said measured star voltage to a predetermined degree.

25. Apparatus as recited in claim 24, wherein the fault comprises a fault in at least one of said electric motor, said electronic control unit, and said drive circuit.

26. Apparatus comprising:

an electric motor;

an electronic control unit for controlling operation of said electric motor;

a drive circuit operatively connected to said electric motor and said electronic control unit, said drive circuit being operative to provide voltage to said electric motor in accordance with a motor control output determined by said electronic control unit,

said electronic control unit being operative to determine a calculated star voltage of the electric motor and compare said calculated star voltage to a measured star voltage to determine a star voltage error, said electronic control unit being operative to determine a fault when said star voltage error exceeds a predetermined maximum star voltage error.

27. Apparatus as recited in claim 26, wherein the fault comprises a fault in at least one of said electric motor, said electronic control unit, and said drive circuit.