Image Number 7 for United States Patent #4102222.
A control system changes the gear ratio in an automatic transmission when engine torque is transferred from one member to another member of a three member planetary gear set. This transfer is accomplished through friction elements engaged and released by hydraulic pressure, without the use of one-way clutches. 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 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 closed loop circuit includes two pulse width modulation circuits for regulating operation of the two control valves. The system calculates the value of the engine acceleration torque for the shift, subtracts this value from the initial output torque value to obtain the desired torque level for the shift, and uses this desired torque level to regulate the shift.