ELECTRIC POWER STEERING DEVICE FOR VEHICLE

• US 20150314804A1
• Filed: 01/24/2013
• Published: 11/05/2015
• Est. Priority Date: 01/24/2013
• Status: Active Grant

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: AOKI, Kenichiro, SHIBATA, Kenji, TSUJIMOTO, Takayoshi
• Granted Patent: US 10,137,929 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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

Abstract

An electric power steering device for a vehicle includes a plurality of assist systems electromagnetically driving an electric motor. When a first or second assist system malfunctions, a malfunction state assist amount calculation part calculates an assist amount while decreasing a limit value at the vehicle stopping, to an amount smaller than a limit value at the vehicle moving. When a malfunction such as a disconnection or a fixing of the switching elements occurs in the first or second assist systems on the basis of a judgment result of a malfunction judgment function, an assist amount switching part supplies an assist amount received from the malfunction state assist amount calculation part to first and second motor drive control parts. When a malfunction occurs in one of the first and second assist systems, one of the first and second motor drive control parts drives the motor by using the assist amount.

Claims

1. An electric power steering device for a vehicle, comprising:

at least one electric motor for adding a predetermined assist force for assisting a steering wheel manipulation by a driver;

a plurality of assist systems including said electric motor, said assist systems electromagnetically driving said electric motor;

assist control means for calculating an assist amount representing said predetermined assist force by using a manipulation force input by said driver via a steering wheel and controlling an assist to said steering wheel manipulation by using at least one of said assist systems on the basis of said calculated assist amount,

wherein when a malfunction occurs in at least one of said assist systems, said assist control means is configured to;

calculate an assist amount at one of vehicle stopping and moving while controlling a maximum assist amount at the vehicle stopping representing a maximum assist force added by said electric motor at the vehicle stopping to an amount smaller than a maximum assist amount at the vehicle moving representing a maximum assist force added by said electric motor at the vehicle moving; and

control the assist to said steering wheel manipulation by using said assist system under a normal state other than said assist system under a malfunction state on the basis of said calculated assist amount at the vehicle stopping or moving.

2. The electric power steering device for the vehicle of claim 1, wherein said maximum assist amount at the vehicle moving is determined as an amount smaller than or equal to an assist amount representing an upper limit of the assist force capable of being generated by said electric motor included in said assist system under the normal state.

3. The electric power steering device for the vehicle of claim 1, wherein when a malfunction occurs in at least one of said assist systems, said assist control means calculates one of the assist amounts at the vehicle stopping and moving on the basis of a relationship between the manipulation force input by said driver and the assist amount representing the assist force added by said electric motor and applied to between said maximum assist amounts at the vehicle stopping and moving.

4. The electric power steering device for the vehicle of claim 3, wherein a relationship between the manipulation force and the assist amount under a state where no malfunction occurs in said assist systems is employed as said relationship between the manipulation force input by said driver and the assist amount representing the assist force added by said electric motor.

5. The electric power steering device for the vehicle of claim 1, wherein when an acquired temperature acquired at a portion which generates heat due to the driving of said electric motor included in at least said assist system under the normal state of said assist systems exceeds a predetermined temperature, said assist control means calculates one of the assist amounts at the vehicle stopping and moving while decreasing said maximum assist amount at the vehicle stopping and moving as said acquired temperature rises.

6. The electric power steering device for the vehicle of claim 5, wherein said assist control means sets the same amount to said maximum assist amounts at the vehicle stopping and moving, respectively only when said acquired temperature is lower than a predetermined temperature for judging if said maximum assist amount at the vehicle stopping should be decreased.

7. The electric power steering device for the vehicle of claim 6, wherein said assist control means determines said maximum assist amounts at the vehicle stopping and moving as an assist amount representing an upper limit of the assist force capable of being generated by said electric motor included in said assist system under the normal.

8. The electric power steering device for the vehicle of claim 6, wherein said predetermined temperature for judging if said maximum assist amount at the vehicle stopping should be decreased is determined as a temperature lower than said predetermined temperature for judging if said maximum assist amount at the vehicle moving should be decreased.

9. The electric power steering device for the vehicle of claim 8, wherein said predetermined temperature for judging if said maximum assist amount at the vehicle moving is determined as a temperature judged that said acquired temperature cannot reach within a predetermined target time period by the manipulation of said steering wheel by said driver at the vehicle stopping on the basis of the balance of heat generation and radiation amounts at a portion which generates heat due to the driving of said electric motor.

10. The electric power steering device for the vehicle of claim 1, wherein said assist systems include a plurality of wire winding groups provided in said electric motor and drive circuits connected to said wire winding groups, respectively.