Electric power steering apparatus

• US 10,286,949 B2
• Filed: 09/15/2016
• Issued: 05/14/2019
• Est. Priority Date: 09/18/2015
• Status: Active Grant

• Current Assignee: NSK Limited
• Original Assignee: NSK Limited
• Inventors: Sugawara, Takayoshi, Sawada, Hideki, Minaki, Ryo
• Primary Examiner(s): Carrasquillo, Jorge L
• Application Number:
  US15/751,315
• Publication Number:
  US 20180229764A1
• Time in Patent Office: 971 Days
• Field of Search: 318724, 31840007, 31840015
• CPC Class Codes: B62D 5/043 characterised by clutch means between driving element, e.g. motor, and driven element, e.g. steering column or steering gear
• CPC Class Codes: B62D 5/0484 for reaction to failures, e.g. limp home
• CPC Class Codes: B62D 5/0487 detecting motor faults B62D5/0496 takes precedence
• CPC Class Codes: B62D 5/049 detecting sensor failures
• CPC Class Codes: B62D 6/10 characterised by means for sensing or determining torque
• CPC Class Codes: H02P 25/22 Multiple windings; Windings for more than three phases
• CPC Class Codes: H02P 27/085 wherein the PWM mode is adapted on the running conditions of the motor, e.g. the switching frequency
• CPC Class Codes: H02P 29/028 the motor continuing operation despite the fault condition, e.g. eliminating, compensating for or remedying the fault
• CPC Class Codes: H02P 29/032 Preventing damage to the motor, e.g. setting individual current limits for different drive conditions
• CPC Class Codes: H02P 6/17 and for generating speed information
• CPC Class Codes: H02P 6/18 without separate position detecting elements

Abstract

[Problem]

An object of the present invention is to provide an electric power steering apparatus that can perform an angle estimating by using a motor regenerative current so as to accurately perform an angle estimating even in a low speed steering.

[Means for Solving the Problem]

The present invention is the electric power steering apparatus that calculates a current command value based on at least a steering torque, driving-controls a motor, which applies an assist torque to a steering system based on the current command value, by an inverter with respective phase duties of a PWM, and detects an angle of the steering system or the motor, comprising: an angle estimating section to estimate the angle when a detecting system of the angle is failed, wherein the electric power steering apparatus performs an assist-control based on an estimating angle that is estimated at the angle estimating section. The present invention can be also adapted to the control of the motor having multi-system windings.

Claims

1. An electric power steering apparatus that calculates a current command value based on at least a steering torque, driving-controls a motor, which applies an assist torque to a steering system based on said current command value, by an inverter with respective phase duties of a pulse width modulation (PWM) via a gate driving circuit, detects phase currents of said motor via motor current detecting circuit, and detects an angle of said steering system or said motor, comprising:

a processor that is configured to execute at least one software section, comprising

an angle estimating section to fix said respective phase duties, detect currents and estimate said angle when a detecting system of said angle has failed,

wherein said angle estimating section fixes said respective phase duties to 0% or 100% depending on a connection relation between said motor current detecting circuit and said inverter or motor phases, detects a regenerative current of said motor via said motor current detecting circuit while all of said phase duties are fixed, and estimates said angle from said detected regenerative current, and

wherein said electric power steering apparatus performs an assist-control based on an estimating angle that is estimated by said angle estimated section.

2. The electric power steering apparatus according to claim 1, wherein fixed duties are 0% in a case that a motor current detecting circuit is connected to lower-stage switching devices of said inverter.

3. The electric power steering apparatus according to claim 1, wherein fixed duties are 100% in a case that a motor current detecting circuit is connected to upper-stage switching devices of said inverter.

4. The electric power steering apparatus according to claim 1, wherein fixed duties are selected from 0% or 100% in a case that a motor current detecting circuit is disposed on a motor phase.

5. The electric power steering apparatus according to claim 1, wherein said angle estimating section corrects an estimating angle from a rotational direction of a steering shaft angle.

6. The electric power steering apparatus according to claim 1, wherein said angle estimating section uses a sign of said steering torque or a sign of a differential value of said steering torque instead of a rotational direction of a steering shaft angle.

7. The electric power steering apparatus according to claim 1, wherein a fixed time of said respective phase duties is changeable depending on circumstances such as a steering velocity and an assist torque.

8. The electric power steering apparatus according to claim 1, wherein said angle estimating section drives said motor by passing a current to said motor via said gate driving circuit in a circumstance that said motor is not rotated, and just after performs an angle estimating by detecting a current by means of fixing said respective phase duties.

9. An electric power steering apparatus that calculates a current command value based on at least a steering torque, driving-controls a motor, which has dual-system windings and applies an assist torque to a steering system based on said current command value, by respective system inverters with respective phase duties of a pulse width modulation (PWM) via respective gate driving circuits, detects phase currents of said motor via motor current detecting circuits of respective systems, and detects an angle of said steering system or said motor, comprising:

a processor that is configured to execute at least one software section, comprising

an angle estimating section for respective systems to fix said respective phase duties, detect currents and estimate said angle when a detecting system of said angle is failed,

wherein said angle estimating section of said respective systems fixes said respective phase duties to 0% or 100% depending on a connection relation between said motor current detecting circuits of said respective systems and said inverter of said respective systems or motor phases of said respective systems, detects a regenerative current of said motor via said motor current detecting circuits of said respective systems while all of said phase duties are fixed, and estimates said angle from said detected regenerative current, and

wherein said electric power steering apparatus performs an assist-control for respective systems based on an estimating angle that is estimated by said angle estimating section.

10. The electric power steering apparatus according to claim 9, wherein fixed duties are 0% in a case that a motor current detecting circuit of said respective systems is connected to lower-stage switching devices of said respective system inverters.

11. The electric power steering apparatus according to claim 9, wherein fixed duties are 100% in a case that a motor current detecting circuit of said respective systems is connected to upper-stage switching devices of said respective system inverters.

12. The electric power steering apparatus according to claim 9, wherein fixed duties are selected from 0% or 100% in a case that a motor current detecting circuit of said respective systems is disposed on a motor phase of said respective system.

13. The electric power steering apparatus according to claim 9, wherein said assist-control is performed by dual-systems and one system stops said assist-control only when an angle estimating is required.

14. The electric power steering apparatus according to claim 9, wherein a deficient assist amount while said assist-control is performed by one system and an angle estimating is performed by other system, is compensated by increasing an assist amount of said one system which performs said assist-control.

15. The electric power steering apparatus according to claim 9, wherein a motor release relay controls a turning-ON or a turning-OFF such that a regenerative current of a system which performs an angle estimating is not excess.

16. The electric power steering apparatus according to claim 9, wherein a duty fixed mode and a zero ampere [A] control alternately switches with a high speed such that a regenerative current of a system which performs an angle estimating is not excess.

17. The electric power steering apparatus according to claim 9, wherein one system which performs said assist-control generates an assist torque so as to cancel each other a brake torque that is generated from the other system which performs an angle estimating.