Line pressure control system for automotive automatic transmission

Claim 1

In an automatic transmission driven by an engine of an automotive vehicle and including friction elements for changing speed ratios of the vehicle when actuated, a hydraulic control system in which fluid having a line pressure is flowing for selectively actuating the friction elements, and an output shaft for applying a driving force to the vehicle, an electronic control system for electronically controlling a pressure level of said line pressure approximately in dependence upon torque transmitted from the engine to the transmission, said electronic control system comprising: a pair of torque-detecting means detecting torque of said output shaft in terms of torsion between two spaced portions on said output shaft for generating two AC voltage waves respectively representative of rotation characteristics of said two spaced portions; a pair of phase-difference-detecting means respectively connected with said torque-detecting means for generating a square wave having a width proportional to the phase difference due to said torsion; integrating means connected with said phase-difference-detecting means for integrating said square wave into a DC voltage having a magnitude proportional to the width of said square wave; at least one voltage dividing means connected with said integrating means for dividing said DC voltage into DC voltages respectively corresponding to one of said speed ratios at which said vehicle is running; electrohydraulic converting means for converting a voltage applied thereto into the pressure level of said line pressure in dependence upon a magnitude of said voltage; and at least one switch means for interconnecting said electrohydraulic converting means with one of said voltage dividing means and applying to said electrohydraulic converting means one of said DC voltages corresponding to said one speed ratio at which said vehicle is running.