Patent US 4,131,036

A control system to change gear ratio in an automatic transmission through friction elements engaged by hydraulic pressure. A closed loop electrical circuit is completed between a transducer, which provides an electrical signal related to the output torque of the transmission, and a pair of control valves, to vary the pressure applied to a friction element by each control valve. A circuit for computing reaction torque is coupled between the transducer and a logic control circuit, which provides logic command signals for controlling operation of components in the closed loop circuit. The system computes an output torque ramp when a downshift is called for by the shift point computer and uses controllers which react oppositely to control engagement of a clutch and brake in response to error signals of torque output compared to a desired ramp to produce a proper shift.