Application of Electrohydraulic Control Valves to Automatic Transmissions - - An Approach to Improving Shift Quality

The hydromechanical control systems conventionally used in passenger car automatic transmissions have been replaced in recent years with electrohydraulic control systems in order to improve shift quality and expand the range of control freedom. The electrohydraulic control valves employed in automatic transmissions today are generally built with either PWM control switching valves or proportional control valves. The major performance requirements that these electrohydraulic actuators must satisfy include good hydraulic response, hydraulic stability and suppression of surge pressure. This paper presents different examples of specific problems that have been encountered when these two types of electrohydraulic actuators have been applied to transmission control systems. Several measures for improving the performance of electrohydraulic actuators are then described based on simulation results and experimental validation. Finally, the results of an experiment conducted with a control system built with an improved electrohydraulic actuator are presented to show the high level of advanced shift control that was obtained.