System for controlling a transfer clutch of a four-wheel drive vehicle

Claim 1

In a control system for a four-wheel drive vehicle having an engine having a throttle valve operatively connected with an accelerator pedal, a transmission operatively connected to the engine, main drive wheels operatively connected to an output shaft of the transmission, auxiliary drive wheels, a transfer clutch actuated by pressurized oil for continuously transmitting the output of the transmission to the auxiliary drive wheels, first speed sensing means for operatively detecting an output of the transmission for sensing speed of the main drive wheels for producing a first speed signal dependent on said speed, second speed sensing means operatively detecting an output of the transfer clutch for sensing speed of the auxiliary drive wheels for producing a second speed signal dependent thereon, and means for controlling torque of the transfer clutch in accordance with driving condition of the vehicle, the improvement in the system which comprises throttle position sensing means for detecting an opening degree of the throttle valve, speed ratio calculating means responsive to the output signals of the first and second sensing means for calculating a speed ratio of the first and second speed signals for producing a speed ratio signal depending on the driving condition of the vehicle, mode detecting means for deciding a straight driving mode, and a steering mode and a slipping mode by comparing said speed ratio signal with a maximum steering angle value predetermined by a characteristic of the vehicle for producing a straight driving mode signal, a steering mode signal and a slipping mode signal, respectively, clutch torque decision means responsive to said second speed signal and an output signal of the throttle position sensing means for deciding a clutch torque dependent on load ranges of the vehicle for producing a clutch torque signal, and correcting means responsive to the mode signal of the mode detecting means for correcting said clutch torque signal dependent on each respective mode, so as to continuously control the pressurized oil supplied to said transfer clutch depending on the driving condition of the vehicle of straight driving, cornering driving by steering, and slipping of the wheels.