Lockup controlling system for variable speed, automatic transmission

Abstract

An electronic control system is provided which controls the locking and unlocking of a variable speed automatic transmission. A hydraulic control circuit comprising a plurality of hydraulic pressure controlling valves, a plurality of flow path switching means and a plurality of solenoid valves is provided to control the engagement of the clutches and brakes of the automatic transmission. The electronic control system detects a slope, modifies a portion of standard data in a manner corresponding to the detected slope to produce shift reference data which is then written into a read-write memory, compares the actual speed stage, throttle opening and vehicle speed against the shift reference data to determine the speed stage to which the transmission is to be shifted and controls the energization of the solenoid valves to change or shift the speed stage. Additionally, the electronic control system reads the minimum vehicle speed required to establish lockup and the maximum vehicle speed for unlocking which correspond to the actual speed stage and the throttle opening from lockup controlling reference data, compares them against the actual vehicle speed to determine the necessity of lockup or unlocking and controls the energization of the solenoid valves in accordance with the determination to establish a lockup or an unlocked condition.