Control apparatus for reversible motor and motor-driven power steering system for motor vehicle using the same

A motor-driven power steering control system of a motor vehicle for assisting a driver in manipulating a steering wheel by making use of an assist torque generated by a reversible motor which is operatively coupled to a steering mechanism of said motor vehicle, comprising:

• a) electromagnetic clutch means for disconnectably coupling an output of said reversible motor to said steering mechanism;
• b) clutch control means for controlling operation of said electromagnetic clutch means;
• c) torque sensor means for detecting a steering torque applied to said steering wheel by the driver to thereby generate a steering torque signal;
• d) vehicle speed sensor means for detecting a speed of said motor vehicle to thereby generate a vehicle speed signal;
• e) control means for generating a control signal on the basis of said steering torque signal and said vehicle speed signal;
• f) DC power source means supplying electric energy to said reversible motor and said electromagnetic clutch means via said clutch control means;
• g) switching driver circuit means interposed between said DC power source means and said reversible motor for controlling said reversible motor in accordance with said control signal;
• h) relay switch means interposed between said DC power source means on one hand and said electromagnetic clutch means and said switching driver circuit means on the other hand;
• i) terminal voltage detecting means connected in parallel to said reversible motor for detecting terminal voltages at both terminals of said reversible motor to thereby generate a first detection signal of a first level when both of said terminal voltages are substantially at a zero level and generating a second detection signal of a second level when both of said terminal voltages are not substantially at a zero level;
• and
• j) fail-safe signal generating means connected to an output of said terminal voltage detecting means for generating a fault indication signal in response to said first detection signal;
• k) wherein said control means responds to said fault indication signal generated by said fail-safe signal generating means by interrupting power supply to said electromagnetic clutch means via said clutch control means and power supply to said switching driver circuit means by opening said relay switch means.

A control apparatus for a motor-driven power steering system of a motor vehicle, wherein said power steering system includes an electric reversible motor connected to a steering system of a motor vehicle through electromagnetic clutch means, motor driving means, switching drive means for driving said electric reversible motor in forward or reverse directions under the control of said motor driving means, and clutch control means for controlling said electromagnetic clutch means;

• said control apparatus comprising:
• motor voltage detecting means for detecting terminal voltages at both terminals of said electric reversible motor during normal operation thereof for thereby generating a voltage signal of a high level and subsequently a fail-safe voltage signal of a low level on the basis of said high-level voltage signal when both of said terminal voltages are approximately zero, while generating a voltage signal of a low level and subsequently a fail-safe voltage signal of a high level on the basis of said low-level voltage signal when both of said terminal voltages are not approximately zero;
• switch means connected between an electric power source and said switching drive means and said clutch control means;
• and
• control means for fetching said fail-safe voltage signal from said motor voltage detecting means to thereby open said switch means to interrupt power supply to said electric reversible motor and said clutch control means when said fail-safe voltage signal is at said low level.