Abstract: In a transmission system, a solenoid controlled electro-hydraulically actuated creeper gear coupler permits selection of very low speeds and provision is made to prevent creeper gear engagement/disengagement unless conrolled by the operator and then only if specified conditions exist. Current flow through the solenoid which actuates the creeper gear is monitored at all times to provide a controlled engagement/disengagement of the creeper gear in the event the monitoried conditions are not within prescribed limits. The current is monitored as the creeper solenoid is energized to insure sufficient pull-in current and while it is energized to insure sufficient hold-in current. The solenoid current is also monitored when the solenoid is not energized. Short or open circuit conditions are detected before they can cause an unexpected engagement or disengagement of the creeper gear.

Abstract: In a transmission system having range shift levers mechanically linked to couplers and shiftable between first and second positions to select ranges of gears and electro-hydraulic powershift clutches for selecting a gear within the range selected by the range shift lever, the powershift clutches are located on each side of at least one of the couplers, between the input shaft and the coupler and between the output shaft and the coupler. A dump solenoid is controlled by operation of a clutch pedal to release fluid from the powershift clutches as the clutch pedal is depressed but before it reaches the fully depressed position so that the coupler is not being driven when coupler shifting takes place.

Abstract: A safety valve includes a movable piston which functions to prevent actuation of fluid operated drive conditioning clutches of a vehicle transmission unless the selector valve means are passed through a neutral position. Such safety valve spool also acts as a load piston for a pressure modulating relief valve of the system.

Abstract: A compact combination of planetary gear sets together with a torque converter and drive conditioning clutches and brakes provides for a broad range of output speeds in either mechanical or converter drive with a nearly constant small step ratio between speeds and with a relatively small variation of transmitted power throughout a very broad range of output speeds.

Abstract: A control system for a vehicular drive train including a slipping clutch for proportioning power from a prime mover to implements and a primary output shaft of the vehicle including a manual control conditioned by a manual selector to vary engagement of the slipping clutch through a regulating valve in a first mode of vehicle operation and to regulate acceleration of the prime mover in a second mode of vehicle operation.