US 4,789,040 AGranted

Motor-driven power steering system for a vehicle

AssigneeMitsubishi Denki Kabushiki Kaisha

InventorsMitsuharu Morishita, Shinichi Kohge

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Abstract

A motor-driven power steering system for a vehicle capable of preventing a motor-related element such as a motor itself, power elements for controlling power supply to the motor or the like from being damage due to an abnormal temperature rise or overheating thereof, thereby substantially avoiding or reducing resultant unsureness or instability in the operator's steering feeling upon change in steering mode as well as improving safety in steering operation. The motor is operatively connected with a steering rack and energizable by a power source for power assisting the steering motion caused by the operator through a steering wheel. A temperature sensor detects the temperature of the motor-related element. An electromagnetic switching clutch is interposed between the motor and the steering rack for selectively establishing and interrupting the transmission of power assisting force from the motor to the steering rack in accordance with the travelling speed of the vehicle. A control uint is provided for controlling the operation of the motor in such a manner such that when the detected temperature of the motor-related element is higher than a prescribed level, the current supplied to the motor through the motor-related element is gradually reduced to lower the temperature of the motor-related element.

Claims10

Dependent claims

A motor-driven power steering system for a vehicle having a steering wheel operatively connected to steer steerable road wheels in response to force exerted thereon by an operator, said motor-driven power steering system comprising:

a torque sensor connected to detect operator-induced steering torque resulting from steering force exerted on said steering wheel by the operator and generating an output signal representative of measured steering torque;
a vehicle-speed sensor to detect vehicle speed and generating an output signal representative of measured vehicle speed;
a motor operatively connected with said steerable road wheels and adapted to be energized by a power source to transmit a force to said steerable road wheels, thereby power assisting steering motion caused by the operator through said steering wheel;
a temperature sensor to detect temperature of a motor-related element and generating an output signal representative of detected temperature;
a clutch means interposed between said motor and said steerable road wheels for selectively establishing and interrupting the transmission of power assisting force from said motor to said steerable road wheels in accordance with the vehicle speed;
and
a control unit connected to the power source and supplying current to said motor, said control unit being connected to receive output signals from said torque sensor, said vehicle-speed sensor, and said temperature sensor, said control unit being operated by a control program to determine an increase or a decrease in current supplied to said motor to vary the power assisting force on the basis of measured vehicle speed and steering torque when the detected temperature of said motor-related element is equal to or less than a prescribed level and being operated by the control program to determine a decrease in current supplied to said motor on the basis of high detected temperature of said motor-related element only when
(a) said unit control determines an increase on the basis of measured vehicle speed and steering torque and
(b) said control unit determines the detected temperature of said motor-related element is higher than the prescribed level
to lower the temperature of said motor-related element to within an allowable range, thereby preventing damage to said motor due to overheating thereof.

7 more elements

a torque sensor connected to detect operator-induced steering torque resulting from steering force exerted on said steering wheel by the operator and generating an output signal representative of measured steering torque;
a vehicle-speed sensor to detect vehicle speed and generating an output signal representative of measured vehicle speed;
a motor operatively connected with said steerable road wheels and adapted to be energized by a power source to transmit a force to said steerable road wheels, thereby power assisting steering motion caused by the operator through said steering wheel;
a temperature sensor to detect temperature of a motor-related element and generating an output signal representative of detected temperature;
a clutch means interposed between said motor and said steerable road wheels for selectively establishing and interrupting the transmission of power assisting force from said motor to said steerable road wheels in accordance with the vehicle speed;
and
a control unit connected to the power source and supplying current to said motor, said control unit being connected to receive output signals from said torque sensor, said vehicle-speed sensor, and said temperature sensor, said control unit being operated by a control program to determine an increase or a decrease in current supplied to said motor to vary the power assisting force on the basis of measured vehicle speed and steering torque when the detected temperature of said motor-related element is equal to or less than a prescribed level and being operated by the control program to determine a decrease in current supplied to said motor on the basis of high detected temperature of said motor-related element only when
(a) said unit control determines an increase on the basis of measured vehicle speed and steering torque and
(b) said control unit determines that the temperature of said motor-related element is higher than the prescribed level on the basis of a current in excess of a prescribed level being continuously supplied to said motor over a duration longer than a predetermined period of time to lower the temperature of said motor-related element to within an allowable range, thereby preventing damage to said motor due to overheating thereof.

6 more elements

Dependencies are inferred from the claim text.