Control apparatus for motor-driven power steering system of motor vehicle

In a motor-driven power steering system of a motor vehicle which includes a steering mechanism for steering said motor vehicle, an electric motor for generating an assist torque to be applied to said steering mechanism for facilitating steering operation of said motor vehicle, and electromagnetic clutch means for transmitting said assist torque to said steering mechanism, said electromagnetic clutch means being of such a type that a magnitude of a coupling effort thereof can continuously and controllably be changed at least over a range from a partially energized state of said electromagnetic clutch means to a fully energized state thereof, wherein in said fully energized state of said electromagnetic clutch means, said assist torque generated by said motor is transmitted to said steering mechanism at a maximum level, while in said partially energized state of said electromagnetic clutch means, the transmission of said assist torque to said steering mechanism is limited to such an extent that said steering mechanism can manually be manipulated independent of the state of said electric motor;

• an apparatus for controlling said electromagnetic clutch means, comprising:
• clutch control means adapted for controlling said coupling effort of said electromagnetic clutch means over said range;
• abnormal torque detecting means for detecting an abnormally large torque applied to said steering mechanism, to thereby output an abnormal torque detection signal;
• motor fault monitor/control means operatively connected to said abnormal torque detecting means and responsive to said abnormal torque detection signal for thereby causing said clutch control means to control said electromagnetic clutch means so that said electrical energization of said electromagnetic clutch means is continuously decreased to a level corresponding to said partially energized state,
• vehicle speed detecting means for detecting a speed of said motor vehicle to generate a vehicle speed detection signal;
• steering torque detecting means for detecting a steering torque applied to said steering mechanism to generate a steering torque detection signal;
• reference torque value storing means (32) for storing reference torque values determined previously in correspondence to predetermined vehicle speeds, respectively;
• reference torque value decision means responsive to said vehicle speed signal to thereby read out from said reference torque value storing means one of said reference torque values which corresponds to a vehicle speed indicated by said vehicle speed detection signal;
• motor current detecting means for detecting a motor current flowing through said electric motor to generate a motor current signal;
• load torque arithmetic means for determining a load torque acting on said steering system on the basis of said steering torque detection signal and said motor current signal to thereby generate a load torque signal;
• and
• comparison means for comparing said load torque with said reference torque value read out from said reference torque value storing means to thereby output said abnormal torque detection signal when said load torque exceeds said reference torque value;
• wherein said motor fault monitor/control means responds to said abnormal torque detection signal for controlling said electromagnetic clutch means so that said electrical energization of said electromagnetic clutch means is continuously decreased to a level corresponding to said electrically partially energized state.

A control apparatus for a motor-driven power steering system of a motor vehicle, comprising:

• vehicle speed detecting means for detecting a vehicle speed of said motor vehicle;
• steering torque detecting means for detecting a steering torque applied to said steering system;
• current calculating/driving means for outputting a motor current command value on the basis of said vehicle speed detected by said vehicle speed detecting means and said steering torque detected by said steering torque detecting means;
• an assist torque generating electric motor operatively coupled to a steering mechanism through the medium of an electromagnetic clutch means and generating an assist torque to be applied to said steering system on the basis of said motor current command value;
• clutch control means for controlling a coupling effort of said electromagnetic clutch means;
• abnormal torque decision reference value arithmetic means for arithmetically determining an abnormal torque and a vehicle speed corresponding to said abnormal torque during a predetermined reference period to thereby output an abnormal torque decision reference value indicating said abnormal torque corresponding to the vehicle speed detected by said vehicle speed detecting means;
• load torque arithmetic means for arithmetically determining a load torque value indicating a sum of the steering torque detected by said steering torque detecting means and said assist torque generated by said electric motor;
• torque comparison means for comparing said load torque value with said abnormal torque decision reference value;
• and
• motor fault monitor/control means responsive to a result of said comparison indicating that said load torque value is greater than said abnormal torque decision reference value, to thereby control said clutch control means so that the coupling effort of said electromagnetic clutch means is lowered in a continuous manner to a predetermined coupling effort which permits manual operation of said steering system.

A control apparatus for a motor-driven power steering system of a motor vehicle, comprising:

• vehicle speed detecting means for detecting a vehicle speed of said motor vehicle;
• steering torque detecting means for detecting a steering torque applied to said steering system;
• current calculating/driving means for outputting a motor current command value on the basis of said vehicle speed detected by said vehicle speed detecting means and said steering torque detected by said steering torque detecting means;
• an assist torque generating electric motor coupled to said steering system through the medium of an electromagnetic clutch means and generating an assist torque to be applied to said steering system on the basis of said motor current command value;
• clutch control means for controlling a coupling effort of said electromagnetic clutch means;
• abnormal torque decision reference value arithmetic means for arithmetically determining an abnormal torque and a vehicle speed corresponding to said abnormal torque for a predetermined reference temporal duration to thereby output both an abnormal torque decision reference value indicating said abnormal torque corresponding to said vehicle speed detected by said vehicle speed detecting means and said reference temporal duration;
• load torque arithmetic means for arithmetically determining both a load torque value indicating a sum of said steering torque detected by said steering torque detecting means and said assist torque generated by said electric motor and a temporal duration of said load torque;
• torque comparison means for comparing said load torque value with said abnormal torque decision reference value and comparing said temporal duration of said load torque value with said reference temporal duration;
• and
• motor fault monitor/control means responsive to results of said comparisons indicating that said load torque value is greater than said abnormal torque decision value and that the temporal duration of said load torque value is not shorter than said reference temporal duration, to thereby control said clutch control means so that the coupling effort of said electromagnetic clutch means is lowered in a continuous manner to a predetermined coupling effort which permits manual steering.

In a motor-driven power steering system of a motor vehicle which includes a steering mechanism for steering said motor vehicle, an electric motor for generating an assist torque to be applied to said steering mechanism for facilitating steering operation of said motor vehicle, and electromagnetic clutch means for transmitting said assist torque to said steering mechanism, said electromagnetic clutch means being of such a type that magnitude of a coupling effort thereof can continuously and controllably changed at least over a range from an electrically partially energized state of said electromagnetic clutch means to an electrically fully energized state thereof, wherein in said electrically fully energized state of said electromagnetic clutch means, said assist torque generated by said motor can be transmitted to said steering mechanism at maximum, while in said electrically partially energized state of said electromagnetic clutch means, transmission of said assist torque to said steering mechanism is limited to such extent that said steering mechanism can manually be manipulated independent of the state of said electric motor;

• a method for controlling said electromagnetic clutch means, comprising the steps of:
• storing reference torque values determined previously in correspondence to predetermined vehicle speeds, respectively;
• detecting a current vehicle speed;
• detecting a steering torque being applied to said steering mechanism;
• reading out from said stored reference torque values a reference torque value which corresponds to said current vehicle speed;
• detecting a motor current flowing through said electric motor to generate a motor current signal;
• determining a load torque acting on said steering system on the basis of said detected steering torque and said motor current to thereby decide a load torque;
• comparing said load torque with said reference torque value as read out to thereby output an abnormal torque signal when said load torque exceeds said reference torque value;
• and
• controlling said electromagnetic clutch means in response to the abnormal torque signal so that said electrical energization of said electromagnetic clutch means is continuously decreased to a level corresponding to said electrically partially energized state.