Electric power steering apparatus

• US 8,977,433 B2
• Filed: 07/26/2011
• Issued: 03/10/2015
• Est. Priority Date: 11/18/2010
• Status: Active Grant

• Current Assignee: NSK Limited
• Original Assignee: NSK Limited
• Inventors: Kojima, Atsushi
• Primary Examiner(s): Olszewski, John R
• Assistant Examiner(s): MERLINO, DAVID P
• Application Number:
  US13/202,917
• Publication Number:
  US 20130261894A1
• Time in Patent Office: 1,323 Days
• Field of Search: None
• US Class Current: 701/41
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input
• CPC Class Codes: B62D 5/0484 for reaction to failures, e.g. limp home
• CPC Class Codes: B62D 5/049 detecting sensor failures
• CPC Class Codes: B62D 6/00 Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits means for initiating a change in direction B62D1/00; steering valves B62D5/06; combined with means for inclining the vehicle body or wheels on bends B62D9/00

Abstract

An electric power steering apparatus includes a first torque calculating unit for calculating a first torque command based on a steering torque detected by the steering torque detecting unit, a second torque command calculating unit for calculating a second torque command based on the wheel rotation speed, an emergency switching unit for outputting the second torque command instead of the first torque command when error of the rotation torque is detected, a wheel rotation speed error detecting unit for detecting an error of the wheel rotation speed based at least on the wheel rotation speed, the steering torque in a normal state and the motor rotation information, and an emergency command limiting unit for liming the second torque command when normal and the motor rotation information, and where error of the wheel rotation speed is detected, when the second torque command is selected by the emergency switching unit.

Claims

1. An electric power steering apparatus comprising:

a steering torque detecting unit configured to detect a steering torque input to a steering mechanism;

a first torque command calculating unit configured to calculate a first torque command based on the steering torque detected by the steering torque detecting unit;

an electric motor configured to generate a steering assist torque to be supplied to the steering mechanism;

a torque detecting unit error detecting unit configured to detect error of the steering torque detecting unit;

a wheel rotation speed detecting unit configured to detect a wheel rotation speed of a vehicle;

a motor rotation information detecting unit configured to detect motor rotation information of the electric motor;

a second torque command calculating unit configured to calculate a second torque command based on the wheel rotation speed detected by the wheel rotation speed detecting unit;

an emergency switching unit configured to select the first torque command, when an error of the torque detecting unit is not detected by the torque detecting unit error detecting unit, and configured to select the second torque command, when an error of the torque detecting unit is detected by the torque detecting unit error detecting unit;

a motor control unit configured to drive control the electric motor based on the torque command selected by the emergency switching unit;

a wheel rotation speed error detecting unit configured to detect an error of the wheel rotation speed based on at least one of the wheel rotation speed detected by the wheel rotation speed detecting unit, the steering torque detected when the steering torque detecting unit is normal, and the motor rotation information detected by the motor rotation information detecting unit; and

an emergency command limiting unit configured to limit the second torque command when the second torque command is selected by the emergency switching unit, where the error of the wheel rotation speed is detected by the wheel rotation speed error detecting unit, wherein

where the error of the wheel rotation speed is detected when the second torque command is selected, the emergency command limiting unit limits the second torque command to a limiting value calculated as a function of a deviation between a threshold and a left and right wheel rotation speed difference detected by the wheel rotation speed detecting unit.

2. The electric power steering apparatus according to claim 1, wherein when the second torque command is selected instead of the first torque command, the emergency switching unit gradually changes a command from the first torque command to the second torque command.

3. The electric power steering apparatus according to claim 1, wherein the second torque command calculating unit comprises a self-aligning torque estimating unit configured to estimate a self-aligning torque applied to the steering mechanism based on the wheel rotation speed, and calculates the second torque command based on the self-aligning torque estimated by the self-aligning torque estimating unit.

4. The electric power steering apparatus according to claim 3, wherein when the second torque command is selected instead of the first torque command, the emergency switching unit gradually changes a command from the first torque command to the second torque command.

5. The electric power steering apparatus according to claim 3, wherein the self-aligning torque estimating unit comprises a vehicle sideslip angle estimating unit configured to estimate a wheel sideslip angle based on the wheel rotation speed, and estimates the self-aligning torque based on the vehicle sideslip angle estimated by the vehicle sideslip angle estimating unit.

6. The electric power steering apparatus according to claim 5, wherein the vehicle sideslip angle estimating unit estimates the vehicle sideslip angle based on the wheel rotation speed and to correct the estimated sideslip angle based on the motor rotation information detected by the motor rotation information detecting unit.

7. The electric power steering apparatus according to claim 5, wherein when the error of the wheel rotation speed is detected, the emergency command limiting unit stops an output of the second torque command when the second torque command is selected.

8. The electric power steering apparatus according to claim 5, wherein where the error of the wheel rotation speed is detected, when the second torque command is selected, the emergency command limiting unit sets, as a second torque command, the second torque command before the error is detected.

9. The electric power steering apparatus according to claim 3, wherein the self-aligning torque estimating unit estimates the self-aligning torque based on the wheel rotation speed and the motor rotation information detected by the motor rotation information detecting unit.

10. The electric power steering apparatus according to claim 9, wherein when an error of the wheel rotation speed is detected, the emergency command limiting unit stops an output of the second torque command when the second torque command is selected.

11. The electric power steering apparatus according to claim 9, wherein where the error of the wheel rotation speed is detected, when the second torque command is selected, the emergency command limiting unit sets, as a second torqued command, the second torque command before the error is detected.

12. The electric power steering apparatus according to claim 1, wherein when the error of the wheel rotation speed is detected, the emergency command limiting unit stops an output of the second torque command when the second torque command is selected.

13. The electric power steering apparatus according to of claim 1, wherein where the error of the wheel rotation speed is detected, when the second torque command is selected, the emergency command limiting unit sets, as a second torqued command, the second torque command before the error is detected.

18. The electric power steering apparatus according to claim 8, wherein the gain adjusting unit determines whether in which steering states a vehicle is among a wheel over-turning sate, a wheel turning-back state, and a wheel holding state based on either of the vehicle speed calculated based on the motor rotation information detected by the motor rotation information detecting unit and the self-aligning torque estimated by the self-aligning torque estimating unit, and

wherein the gain adjusting unit comprises at least one of a steering state gain adjusting unit configured to adjust steering state sensitive gain based on the determined result of the steering, a vehicle speed gain adjusting unit configured to adjust vehicle speed sensitive gain based on either of the vehicle speed calculated based on the wheel rotation speed detected by the wheel rotation speed detecting unit or the vehicle speed detected by the vehicle speed detecting unit, a self-aligning torque gain adjusting unit configured to adjust the self-aligning torque gain on the basis of a deviation between the motor rotation information detected by the motor rotation information detecting unit and the vehicle rotation speed detected by the wheel rotation speed detecting unit, and the self-aligning torque estimating value estimated by the self-aligning torque estimating unit, and a driving wheel slip gain adjusting unit configured to estimate a driving wheel slip state based on the wheel rotation speed detected by the wheel rotation speed detecting unit, and configured to adjust driving wheel slip sensitive gain based on the estimated driving wheel slip state.

19. The electric power steering apparatus according to claim 18, wherein when the second torque command is selected instead of the first torque command, the emergency switching unit gradually changes a command from the first torque command to the second torque command.

14. An electric power steering apparatus comprising:

a steering torque detecting unit configured to detect a steering torque input to a steering mechanism;

a first torque command calculating unit configured to calculate a first torque command based on the steering torque detected by the steering torque detecting unit;

an electric motor configured to generate a steering assist torque to be supplied to the steering mechanism;

a torque detecting unit error detecting unit configured to detect error of the steering torque detecting unit;

a wheel rotation speed detecting unit configured to detect a wheel rotation speed of a vehicle;

a motor rotation information detecting unit configured to detect motor rotation information of the electric motor;

a second torque command calculating unit configured to calculate a second torque command based on the wheel rotation speed detected by the wheel rotation speed detecting unit;

an emergency switching unit configured to select the first torque command, when an error of the torque detecting unit is not detected by the torque detecting unit error detecting unit, and configured to select the second torque command, when an error of the torque detecting unit is detected by the torque detecting unit error detecting unit;

a motor control unit configured to drive control the electric motor based on the torque command selected by the emergency switching unit;

a wheel rotation speed error detecting unit configured to detect an error of the wheel rotation speed based on at least one of the wheel rotation speed detected by the wheel rotation speed detecting unit, the steering torque detected when the steering torque detecting unit is normal, and the motor rotation information detected by the motor rotation information detecting unit; and

an emergency command limiting unit configured to limit the second torque command when the second torque command is selected by the emergency switching unit, where the error of the wheel rotation speed is detected by the wheel rotation speed error detecting unit, wherein

the second torque command calculating unit comprises a self-aligning torque estimating unit configured to estimate a self-aligning torque applied to the steering mechanism based on the wheel rotation speed, and a gain adjusting unit configured to calculate the second torque command by multiplying gain with the self-aligning torque estimated by the self-aligning torque estimating unit, and

where the error of the wheel rotation speed is detected when the second torque command is selected, the emergency command limiting unit limits the second torque command to a limiting value calculated as a function of a deviation between a threshold and a left and right wheel rotation speed difference detected by the wheel rotation speed detecting unit.

15. The electric power steering apparatus according to claim 14, wherein the gain adjusting unit determines in which steering states a vehicle is in from a wheel over-turning state, a wheel turning-back state, and a wheel holding state based on either of a vehicle speed calculated based on the motor rotation information detected by the motor rotation information detecting unit or the self-aligning torque estimated by the self-aligning torque estimating unit, and

wherein the gain adjusting unit comprises at least one of a steering state gain adjusting unit configured to adjust steering state sensitive gain based on the determined result of the steering, a vehicle speed gain adjusting unit configured to adjust a vehicle speed sensitive gain based on either of the vehicle speed calculated based on the wheel rotation speed detected by the wheel rotation speed detecting unit or the vehicle speed detected by the vehicle speed detecting unit, a self-aligning torque gain adjusting unit configured to adjust the self-aligning torque gain on the basis of a deviation between the motor rotation information detected by the motor rotation information detecting unit and the vehicle rotation speed detected by the wheel rotation speed detecting unit, and the self-aligning torque estimating value estimated by the self-aligning torque estimating unit, and a driving wheel slip gain adjusting unit configured to estimate a driving wheel slip state based on the wheel rotation speed detected by the wheel rotation speed detecting unit, and configured to adjust driving wheel slip sensitive gain based on the estimated driving wheel slip state.

16. The electric power steering apparatus according to claim 15, wherein when the second torque command is selected instead of the first torque command, the emergency switching unit gradually changes a command from the first torque command to the second torque command.

17. An electric power steering apparatus comprising:

a steering torque detecting unit configured to detect a steering torque input to a steering mechanism;

a first torque command calculating unit configured to calculate a first torque command based on the steering torque detected by the steering torque detecting unit;

an electric motor configured to generate a steering assist torque to be supplied to the steering mechanism;

a torque detecting unit error detecting unit configured to detect error of the steering torque detecting unit;

a wheel rotation speed detecting unit configured to detect a wheel rotation speed of a vehicle;

a motor rotation information detecting unit configured to detect motor rotation information of the electric motor;

a second torque command calculating unit configured to calculate a second torque command based on the wheel rotation speed detected by the wheel rotation speed detecting unit;

an emergency switching unit configured to select the first torque command, when an error of the torque detecting unit is not detected by the torque detecting unit error detecting unit, and configured to select the second torque command, when an error of the torque detecting unit is detected by the torque detecting unit error detecting unit;

a motor control unit configured to drive control the electric motor based on the torque command selected by the emergency switching unit;

a wheel rotation speed error detecting unit configured to detect an error of the wheel rotation speed based on at least one of the wheel rotation speed detected by the wheel rotation speed detecting unit, the steering torque detected when the steering torque detecting unit is normal, and the motor rotation information detected by the motor rotation information detecting unit; and

an emergency command limiting unit configured to limit the second torque command when the second torque command is selected by the emergency switching unit, where the error of the wheel rotation speed is detected by the wheel rotation speed error detecting unit, wherein

the second torque command calculating unit comprises a self-aligning torque estimating unit configured to estimate a self-aligning torque applied to the steering mechanism based on the wheel rotation speed, a gain adjusting unit configured to calculate the second torque command by multiplying gain with the self-aligning torque estimated by the self-aligning torque estimating unit, and a torque control unit configured to limit the second torque command calculated by the gain adjusting unit on the basis at least on either of a vehicle speed calculated based on the wheel rotation speed detected by the wheel rotation speed detecting unit or a vehicle speed detected by a vehicle speed detecting unit, and a motor angular velocity calculated by a motor angular velocity calculating unit, and

where the error of the wheel rotation speed is detected when the second torque command is selected, the emergency command limiting unit limits the second torque command to a limiting value calculated as a function of a deviation between a threshold and a left and right wheel rotation speed difference detected by the wheel rotation speed detecting unit.