Diagnostic apparatus and method for motor driven power-assisted steering system

• US 20010053952A1
• Filed: 06/15/2001
• Published: 12/20/2001
• Est. Priority Date: 06/16/2000
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Unisia Jecs Corporation (Hitachi, Ltd.)
• Inventors: Yamano, Kazuya, Kodaka, Takeshi
• Granted Patent: US 6,459,972 B2
• Time in Patent Office: Days
• US Class Current: 701/43
• CPC Class Codes: B62D 5/0484 for reaction to failures, e.g. limp home
• CPC Class Codes: B62D 5/0493 detecting processor errors, e.g. plausibility of steering direction

Abstract

In diagnostic apparatus and method for a motor-driven power-assisted steering system, an abnormality determining section detects a state in which the detected normal/reverse drive current indicates an opposite to a direction of the normal/reverse revolution drive torque and determines whether the state is in excess of a predetermined abnormality determination criterion so as to determine an occurrence in abnormality of the power-assisted steering system, the abnormality determining section comprising a sensitivity reducing section that varies a sensitivity of the abnormality determination criterion in a decrease direction as an absolute value of the detected normal/reverse drive current becomes smaller.

Claims

1. A diagnostic apparatus for a motor driven power-assisted steering system of an automotive vehicle, comprising:

a control section that regulates a magnitude of a drive torque and a direction of the drive torque to be applied to an electric motor in a form of a normal/reverse drive torque command current;

a drive current detection circuit to detect a normal/reverse drive current to be supplied to the motor;

an abnormality determining section that detects a state in which the detected normal/reverse drive current indicates an opposite to a direction of the normal/reverse drive torque command current and determines whether the state is in excess of a predetermined abnormality determination criterion so as to determine an occurrence in abnormality of the power-assisted steering system, the abnormality determining section comprising a sensitivity reducing section that varies a sensitivity of the abnormality determination criterion in a decrease direction as an absolute value of the detected normal/reverse drive current becomes smaller.

2. A diagnostic apparatus for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 1

, wherein the predetermined abnormality determination criterion is a number of times the normal/reverse drive current which is reverse to the normal/reverse drive torque command current is developed and the abnormality determining section determines whether the number of times the normal/reverse drive current which is reverse to the normal/reverse torque command current is developed has exceeded a predetermined number of times so as to determine whether the abnormality occurs in the power-assisted steering system.

3. A diagnostic apparatus for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 2

, wherein the abnormality determining section determines the occurrence in the abnormality of the motor-driven power-assisted steering system by determining whether a total of the number of times the normal/reverse drive current which is reverse to the normal/reverse drive torque command current is developed and which is counted for each predetermined sampling time is in excess of another predetermined number of times.

4. A diagnostic apparatus for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 3

, wherein the abnormality determining section repeats the abnormality determination for a predetermined time longer than a product of the other predetermined number for the abnormality determination by the sampling time.

5. A diagnostic apparatus for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 2

, wherein the sensitivity reducing section varies the sensitivity in the abnormal determination criterion in the decrease direction by varying an incremental count number on the number of times the normal/reverse drive current which is reverse to the normal/reverse drive torque command current is developed in the decrease direction, as compared with a case of a larger absolute value of the normal/reverse drive current, when the absolute value of the normal/reverse drive current becomes smaller.

6. A diagnostic apparatus for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 2

, wherein the sensitivity reducing section varies the sensitivity in the abnormal determination criterion in the decrease direction by varying the abnormality determination criterion in a larger direction, as compared with a case of a larger absolute value of the normal/reverse drive current, when the absolute value of the normal/reverse drive current becomes smaller.

7. A diagnostic apparatus for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 3

, wherein the abnormality determining section comprises a counter to count the number of times the normal/reverse drive current which is reverse to the normal/reverse drive torque command current has been developed for each predetermined sampling time in an accumulation manner, the counter being reset to zero when the normal/reverse drive current whose direction is the same as the normal/reverse drive command current is developed.

8. A diagnostic apparatus for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 1

, wherein the normal/reverse drive torque command value is generated by a microcomputer and is supplied to a motor drive circuit comprising an H bridge circuit with the electric motor.

9. A diagnostic apparatus for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 8

, wherein the abnormality determining section comprises a diagnostic circuitry installed in the microcomputer together with the control section and the drive current detection section comprises a voltage difference measuring section that measures a voltage difference between both ends of a resistor interposed between the motor and converts the voltage difference therebetween into a current value I which is caused to flow through the motor.

10. A diagnostic method for a motor driven power-assisted steering system of an automotive vehicle, comprising:

regulating a magnitude of a drive torque and a direction of the drive torque to be applied to an electric motor in a form of a normal/reverse drive torque command current;

detecting a normal/reverse drive current to be supplied to the motor,

detecting a state in which the detected normal/reverse drive current indicates an opposite to a direction of the normal/reverse drive torque command current;

determining whether the state is in excess of a predetermined abnormality determination criterion so as to determine an occurrence in abnormality of the power-assisted steering system; and

varying a sensitivity of the abnormality determination criterion in a decrease direction as an absolute value of the detected normal/reverse drive current becomes smaller.

11. A diagnostic method for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 10

, wherein the predetermined abnormality determination criterion is a number of times the normal/reverse drive current which is reverse to the normal/reverse drive torque command current is developed and, at the abnormality determining step, a determination is made of whether the number of times the normal/reverse drive current which is reverse to the normal/reverse torque command current is developed has exceeded a predetermined number of times so as to determine whether the abnormality occurs in the power-assisted steering system.

12. A diagnostic method for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 11

, wherein, at the abnormality determining step, the occurrence in the abnormality of the motor-driven power-assisted steering system is determined by determining whether a total of the number of times the normal/reverse drive current which is reverse to the normal/reverse drive torque command current is developed and which is counted for each predetermined sampling time is in excess of another predetermined number of times.

13. A diagnostic method for a motor driven power-assisted steering system of on automotive vehicle as claimed in

claim 11

, wherein, at the abnormality determining step, the abnormality determination is repeated for a predetermined time longer than a product of the other predetermined number for the abnormality determination by the sampling time.

14. A diagnostic method for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 11

, wherein, at the abnormality determining step, the sensitivity in the abnormal determination criterion is varied in the decrease direction by varying an incremental count number on the number of times the normal/reverse drive current which is reverse to the normal/reverse drive torque command current is developed in the decrease direction, as compared with a case of a larger absolute value of the normal/reverse drive current, when the absolute value of the normal/reverse drive current becomes smaller.

15. A diagnostic method for a motor driven power-assisted steering system of an automotive vehicle as claimed in

claim 11

, wherein, at the abnormality determining step, the sensitivity in the abnormal determination criterion is varied in the decrease direction by varying the abnormality determination criterion in a larger direction, as compared with a case of a larger absolute value of the normal/reverse current, when the absolute value of the normal/reverse drive current becomes smaller.