Control apparatus for motor-driven power steering system in which power suppy to an electric clutch is reduced upon detection of a malfunction

Claim 2

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a vehicle speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor in dependence on said vehicle speed, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value which corresponds to the vehicle speed detected by said vehicle speed detecting means; load torque arithmetic means for arithmetically determining a load torque on the basis of at least a steering torque detected by said steering torque detecting means; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value while decreasing the coupling effort of said coupling effort control means wherein said coupling effort control means comprises an electric clutch and wherein when the coupling effort of said coupling effort control means is decreased, said electric clutch assumes a semi-coupling state.

Claim 3

A control apparatus according to claim 1, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein when said motor rotation decision means decides that said electric motor is rotating, operation of said motor fault monitor/control means is inhibited.

Claim 4

A control apparatus according to claim 1, further comprising: motor voltage detecting means for detecting a voltage applied to said electric motor; motor current detecting means for detecting a motor current flowing through said electric motor; and motor rotation decision means for estimating rotation number of said electric motor on the basis of said motor voltage and said motor current to thereby decide whether or not said electric motor rotates; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 5

A control apparatus according to claim 1, further comprising: motor regeneration voltage detecting means for detecting a voltage generated by said electric motor; and motor rotation decision means for deciding on the basis of said voltage whether or not said electric motor is rotating; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 6

A control apparatus according to claim 1, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein for a predetermined time from the time point when said motor rotation decision means decided that said electric motor was rotating, operation of said motor fault monitor/control means is inhibited.

Claim 7

A control apparatus according to claim 1, wherein said coupling effort control means is constituted by a disk type electromagnetic clutch having a clutch gap substantially equal to zero.

Claim 8

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value in dependence on the vehicle speed detected by said vehicle speed detecting means; assist torque determining means for determining assist torque applied by said electric motor; load torque arithmetic means for arithmetically determining a load torque on the basis of a steering torque detected by said steering torque detecting means and on the determined assist torque; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value while decreasing the coupling effort of said coupling effort control means.

Claim 9

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value in dependence on the vehicle speed detected by said vehicle speed detecting means; assist torque determining means for determining assist torque applied by said electric motor; load torque arithmetic means for arithmetically determining a load torque on the basis of a steering torque detected by said steering torque detecting means and on the determined assist torque; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value while decreasing the coupling effort of said coupling effort control means.

Claim 10

A control apparatus for a motor-driven power steering system according to claim 7, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein when said motor rotation decision means decides that said electric motor is rotating, operation of said motor fault monitor/control means is inhibited.

Claim 11

A control apparatus according to claim 7, further comprising: motor voltage detecting means for detecting a voltage applied to said electric motor; motor current detecting means for detecting a motor current flowing through said electric motor; and motor rotation decision means for estimating rotation number of said electric motor on the basis of said motor voltage and said motor current to thereby decide whether or not said electric motor rotates; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 12

A control apparatus according to claim 7, further comprising: motor regeneration voltage detecting means for detecting a voltage generated by said electric motor; and motor rotation decision means for deciding on the basis of said voltage whether or not said electric motor is rotating; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 13

A control apparatus according to claim 7, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein for a predetermined time from the time point when said motor rotation decision means decided that said electric motor was rotating, operation of said motor fault monitor/control means is inhibited.

Claim 14

A control apparatus according to claim 7, wherein said coupling effort control means is constituted by a disk type electromagnetic clutch having a clutch gap substantially equal to zero.

Claim 15

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value and a reference time in dependence on the vehicle speed detected by said vehicle speed detecting means; load torque arithmetic means for arithmetically determining a load torque on the basis of at least a steering torque detected by said steering torque detecting means; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operating of said electric motor when said load torque exceeds said abnormal torque decision reference value and when in duration in which said load torque exceeds said abnormal torque decision reference value is longer than said reference time, while decreasing the coupling effort of said coupling effort control means.

Claim 16

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value and a reference time in dependence on the vehicle speed detected by said vehicle speed detecting means; load torque arithmetic means for arithmetically determining a load torque on the basis of at least a steering torque detected by said steering torque detecting means; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operating of said electric motor when said load torque exceeds said abnormal torque decision reference value and when in duration in which said load torque exceeds said abnormal torque decision reference value is longer than said reference time, while decreasing the coupling effort of said coupling effort control means.

Claim 17

A control apparatus according to claim 13, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein when said motor rotation decision means decides that said electric motor is rotating, operation of said motor fault monitor/control means is inhibited.

Claim 18

A control apparatus according to claim 13, further comprising: motor voltage detecting means for detecting a voltage applied to said electric motor; motor current detecting means for detecting a motor current flowing through said electric motor; and motor rotation decision means for estimating rotation number of said electric motor on the basis of said motor voltage and said motor current to thereby decide whether or not said electric motor rotates; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 19

A control apparatus according to claim 13, further comprising: motor regeneration voltage detecting means for detecting a voltage generated by said electric motor; and motor rotation decision means for deciding on the basis of the voltage whether or not said electric motor is rotating; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 20

A control apparatus according to claim 13, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein for a predetermined time from the time point when said motor rotation decision means decided that said electric motor was rotating, operation of said motor fault monitor/control means is inhibited.

Claim 21

A control apparatus according to claim 13, wherein said coupling effort control means is constituted by a disk type electromagnetic clutch having a clutch gap substantially equal to zero.

Claim 22

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value and a reference time in dependence on the vehicle speed detected by said vehicle speed detecting means; assist torque determining means for determining assist torque applied by said electric motor; load torque arithmetic means for arithmetically determining a load torque on the basis of a steering torque detected by said steering torque detecting means and on the determined assist torque; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value and when duration in which said load torque exceeds said abnormal torque decision reference value is longer than said reference time while decreasing the coupling effort of said coupling effort control means.

Claim 23

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value and a reference time in dependence on the vehicle speed detected by said vehicle speed detecting means; assist torque determining means for determining assist torque applied by said electric motor; load torque arithmetic means for arithmetically determining a load torque on the basis of a steering torque detected by said steering torque detecting means and on the determined assist torque; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value and when duration in which said load torque exceeds said abnormal torque decision reference value is longer than said reference time while decreasing the coupling effort of said coupling effort control means.

Claim 24

A control apparatus according to claim 19, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein when said motor rotation decision means decides that said electric motor is rotating, operation of said motor fault monitor/control means is inhibited.

Claim 25

A control apparatus according to claim 19, further comprising: motor voltage detecting means for detecting a voltage applied to said electric motor; motor current detecting means for detecting a motor current flowing through said electric motor; and motor rotation decision means for estimating rotation number of said electric motor on the basis of said motor voltage and said motor current to thereby decide whether or not said electric motor rotates; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 26

A control apparatus according to claim 19, further comprising: motor regeneration voltage detecting means for detecting a voltage generated by said electric motor; and motor rotation decision means for deciding on the basis of the voltage whether or not said electric motor is rotating; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 27

A control apparatus according to claim 19, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein for a predetermined time from the time point when said motor rotation decision means decided that said electric motor was rotating, operation of said motor fault monitor/control means is inhibited.

Claim 28

A control apparatus according to claim 19, wherein said coupling effort control means is constituted by a disk type electromagnetic clutch having a clutch gap substantially equal to zero.

Claim 29

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value in dependence on the vehicle speed detected by said vehicle speed detecting means; load torque arithmetic means for arithmetically determining a load torque on the basis of at least a steering torque detected by said steering torque detecting means; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value while controlling the coupling effort of said coupling effort control means so that the steering torque value detected by said steering torque detecting means does not exceed a predetermined value at which a steering wheel of said motor vehicle can be manipulated by a driver wherein said coupling effort control means comprises an electric clutch and wherein when the coupling effort of said coupling effort control means is decreased, said electric clutch assumes a semi-coupling state.

Claim 30

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value in dependence on the vehicle speed detected by said vehicle speed detecting means; load torque arithmetic means for arithmetically determining a load torque on the basis of at least a steering torque detected by said steering torque detecting means; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value while controlling the coupling effort of said coupling effort control means so that the steering torque value detected by said steering torque detecting means does not exceed a predetermined value at which a steering wheel of said motor vehicle can be manipulated by a driver wherein said coupling effort control means comprises an electric clutch and wherein when the coupling effort of said coupling effort control means is decreased, said electric clutch assumes a semi-coupling state.

Claim 31

A control apparatus according to claim 25, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein when said motor rotation decision means decides that said electric motor is rotating, operation of said motor fault monitor/control means is inhibited.

Claim 32

A control apparatus for a motor-driven power steering system according to claim 25, further comprising: motor voltage detecting means for detecting a voltage applied to said electric motor; motor current detecting means for detecting a motor current flowing through said electric motor; and motor rotation decision means for estimating rotation number of said electric motor on the basis of said motor voltage and said motor current to thereby decide whether or not said electric motor rotates; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 33

A control apparatus according to claim 25, further comprising: motor regeneration voltage detecting means for detecting a voltage generated by said electric motor; and motor rotation decision means for deciding on the basis of said voltage whether or not said electric motor is rotating; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 34

A control apparatus according to claim 25, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein for a predetermined time from the time point when said motor rotation decision means decided that said electric motor was rotating, operation of said motor fault monitor/control means is inhibited.

Claim 35

A control apparatus for a motor-driven power steering system according to claim 25, wherein said coupling effort control means is constituted by a disk type electromagnetic clutch having a clutch gap substantially equal to zero.

Claim 36

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value in dependence on the vehicle speed detected by said vehicle speed detecting means; assist torque determining means for determining assist torque applied by said electric motor; load torque arithmetic means for arithmetically determining a load torque on the basis of a steering torque detected by said steering torque detecting means and on the determined assist torque; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value while controlling the coupling effort of said coupling effort control means so that the steering torque value detected by said steering torque detecting means does not exceed a predetermined value at which a steering wheel of said motor vehicle can be manipulated by a driver.

Claim 37

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value in dependence on the vehicle speed detected by said vehicle speed detecting means; assist torque determining means for determining assist torque applied by said electric motor; load torque arithmetic means for arithmetically determining a load torque on the basis of a steering torque detected by said steering torque detecting means and on the determined assist torque; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value while controlling the coupling effort of said coupling effort control means so that the steering torque value detected by said steering torque detecting means does not exceed a predetermined value at which a steering wheel of said motor vehicle can be manipulated by a driver.

Claim 38

A control apparatus according to claim 31, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein when said motor rotation decision means decides that said electric motor is rotating, operation of said motor fault monitor/control means is inhibited.

Claim 39

A control apparatus according to claim 31, further comprising: motor voltage detecting means for detecting a voltage applied to said electric motor; motor current detecting means for detecting a motor current flowing through said electric motor; and motor rotation decision means for estimating rotation number of said electric motor on the basis of said motor voltage and said motor current to thereby decide whether or not said electric motor rotates; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 40

A control apparatus according to claim 31, further comprising: motor regeneration voltage detecting means for detecting a voltage generated by said electric motor; and motor rotation decision means for deciding on the basis of said voltage whether or not said electric motor is rotating; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 41

A control apparatus according to claim 31, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein for a predetermined time from the time point when said motor rotation decision means decided that said electric motor was rotating, operation of said motor fault monitor/control means is inhibited.

Claim 42

A control apparatus for a motor-driven power steering system according to claim 31, wherein said coupling effort control means is constituted by a disk type electromagnetic clutch having a clutch gap substantially equal to zero.

Claim 43

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value and a reference time in dependence on the vehicle speed detected by said vehicle speed detecting means; load torque arithmetic means for arithmetically determining a load torque on the basis of at least a steering torque detected by said steering torque detecting means; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value and when duration in which said load torque exceeds said abnormal torque decision reference value is longer than said reference time while controlling the coupling effort of said coupling effort control means so that the steering torque value detected by said steering torque detecting means does not exceed a predetermined value at which a steering wheel of said motor vehicle can be manipulated by a driver.

Claim 44

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value and a reference time in dependence on the vehicle speed detected by said vehicle speed detecting means; load torque arithmetic means for arithmetically determining a load torque on the basis of at least a steering torque detected by said steering torque detecting means; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value and when duration in which said load torque exceeds said abnormal torque decision reference value is longer than said reference time while controlling the coupling effort of said coupling effort control means so that the steering torque value detected by said steering torque detecting means does not exceed a predetermined value at which a steering wheel of said motor vehicle can be manipulated by a driver.

Claim 45

A control apparatus according to claim 37, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein when said motor rotation decision means decides that said electric motor is rotating, operation of said motor fault monitor/control means is inhibited.

Claim 46

A control apparatus according to claim 37, further comprising: motor voltage detecting means for detecting a voltage applied to said electric motor; motor current detecting means for detecting a motor current flowing through said electric motor; and motor rotation decision means for estimating rotation number of said electric motor on the basis of said motor voltage and said motor current to thereby decide whether or not said electric motor rotates; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 47

A control apparatus according to claim 37, further comprising: motor regeneration voltage detecting means for detecting a voltage generated by said electric motor; and motor rotation decision means for deciding on the basis of said voltage whether or not said electric motor is rotating; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 48

A control apparatus according to claim 37, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein for a predetermined time from the time point when said motor rotation decision means decided that said electric motor was rotating, operation of said motor fault monitor/control means is inhibited.

Claim 49

A control apparatus for a motor-driven power steering system according to claim 37, wherein said coupling effort control means is constituted by a disk type electromagnetic clutch having a clutch gap substantially equal to zero.

Claim 50

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value in dependence on the vehicle speed detected by said vehicle speed detecting means; assist torque determining means for determining assist torque applied by said electric motor; load torque arithmetic means for arithmetically determining a load torque on the basis of at least a steering torque detected by said steering torque detecting means and on the determined assist torque; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value and when duration in which said load torque exceeds said abnormal torque decision reference value is longer than said decision reference time while controlling the coupling effort of said coupling effort control means so that the steering torque value detected by said steering torque detecting means does not exceed a predetermined value at which a steering wheel of said motor vehicle can be manipulated by a driver.

Claim 51

In a motor-driven power steering system for a motor vehicle which includes vehicle speed detecting means for detecting a speed of said motor vehicle, steering torque detecting means for detecting a steering torque applied to a steering mechanism of said motor vehicle, and an electric motor operatively coupled to said steering mechanism through the medium of coupling effort control means, wherein an assist torque is applied to said steering mechanism by driving said electric motor, an apparatus for controlling said motor-driven power steering system, comprising: abnormal torque decision reference value arithmetic means for determining an abnormal torque decision reference value in dependence on the vehicle speed detected by said vehicle speed detecting means; assist torque determining means for determining assist torque applied by said electric motor; load torque arithmetic means for arithmetically determining a load torque on the basis of at least a steering torque detected by said steering torque detecting means and on the determined assist torque; torque comparison means for comparing said load torque with said abnormal torque decision reference value; and motor fault monitor/control means for stopping operation of said electric motor when said load torque exceeds said abnormal torque decision reference value and when duration in which said load torque exceeds said abnormal torque decision reference value is longer than said decision reference time while controlling the coupling effort of said coupling effort control means so that the steering torque value detected by said steering torque detecting means does not exceed a predetermined value at which a steering wheel of said motor vehicle can be manipulated by a driver.

Claim 52

A control apparatus for a motor-driven power steering system according to claim 43, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein when said motor rotation decision means decides that said electric motor is rotating, operation of said motor fault monitor/control means is inhibited.

Claim 53

A control apparatus according to claim 43, further comprising: motor voltage detecting means for detecting a voltage applied to said electric motor; motor current detecting means for detecting a motor current flowing through said electric motor; and motor rotation decision means for estimating rotation number of said electric motor on the basis of said motor voltage and said motor current to thereby decide whether or not said electric motor rotates; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 54

A control apparatus according to claim 43, further comprising: motor regeneration voltage detecting means for detecting a voltage generated by said electric motor; and motor rotation decision means for deciding on the basis of said voltage whether or not said electric motor is rotating; wherein operation of said motor fault monitor/control means is inhibited when said motor rotation decision means decides that said electric motor is rotating.

Claim 55

A control apparatus according to claim 43, further comprising: motor rotation decision means for deciding whether said electric motor is rotating or not; wherein for a predetermined time from the time point when said motor rotation decision means decided that said electric motor was rotating, operation of said motor fault monitor/control means is inhibited.

Claim 56

A control apparatus according to claim 43, wherein said coupling effort control means is constituted by a disk type electromagnetic clutch having a clutch gap substantially equal to zero.