To smoothly operate a transmission by operating a proportional solenoid control valve with an electronic controller, operationally connecting the control valve to a proportional retarder spool valve, and operationally connecting the proportional retarder spool valve to a fluid-operated retarder.
An electronic control module 40 serving as an electronic controller receives the input signal from a retarder control level switch 46 and controls the operation of a proportional solenoid control valve 77. The proportional solenoid control valve 77 maintains a fluid sufficient to keep the control level of a retarder proportional to a solenoid current between it and a proportional retarder spool valve 70. The deceleration level by the proportional command signal of the electronic control module 40 fed to the proportional solenoid control valve 77 is controlled by a fluid-operated retarder 15 to adjust the quantity of the fluid flowing into the proportional retarder spool valve 70.
DANIEL P SIMON
KENNETH P KIESENER
