Torque-split control system for four-wheel-drive vehicles

Abstract

An active torque-split control system for a four-wheel-drive vehicle comprises a transfer clutch, and sensors for detecting a wheel-speed difference between a primary drive wheel and a secondary drive wheel, a throttle opening, a vehicle speed, depressed or undepressed states of a brake pedal. The system is capable of executing both a feedback control based on the wheel-speed difference and a feedforward control based on the throttle opening. The system is responsive to at least a feedback control signal from the feedback control system and an anticipating correction signal from the feedforward control system for determining a distribution ratio of driving torque of the secondary drive wheel to the primary drive wheel depending on the highest one of the feedback control signal value and the anticipating correction signal value. When accelerated from a standing start with the brake pedal depressed, the system operates to rise a secondary-drive-wheel distribution torque up to a predetermined driving-torque value regardless of the feedback control signal and the anticipating correction signal, and to decrease the driving torque, which torque is risen to the predetermined driving-torque value, at a predetermined rate of change, when the brake pedal is shifted to the undepressed state.