Abstract: In a transmission control system for a multiple speed ratio powershift transmission having a speed control valve and a plurality of fluid pressure operated clutches adapted to establish torque ratio changes, an electronic speed sensing system and downshift valve means for automatically shifting the transmission one step from a higher speed ratio to a lower speed ratio at a first predetermined vehicle ground speed by diverting the fluid for pressurizing a higher speed ratio clutch to a lower speed ratio clutch and then automatically shifting the transmission from the lower speed ratio back to the higher speed ratio at a second higher predetermined vehicle ground speed by ceasing the diverting of the pressurized fluid, with the fluid diverting being possible only when the speed control valve setting corresponds with the higher speed ratio.

Abstract: In a transmission control system for a multiple speed ratio powershift transmission having a plurality of fluid pressure operated clutches adapted to establish torque ratio changes and also including an electronic speed sensing system and downshift valve means for automatically shifting the transmission from a higher speed ratio to a lower speed ratio at a first predetermined vehicle ground speed, the addition of a downshift inhibitor or delay circuit for prohibiting downshifts from the higher speed ratio to the lower speed ratio while the vehicle undergoes a full throttle directional reversal.

Abstract: Control valve assemblies for a lock-up clutch in a vehicle drive system, wherein a torque converter normally couples a prime mover with a transmission, vary the degree of engagement of the lock-up clutch with respect to prime mover rotational speed within a predetermined speed range. In the control valve assemblies, a centrifugal valve selectively communicates the fluid pressure operated lock-up clutch with a source of pressure and a fluid drain, with the centrifugal valve having rotor means drivably interconnected with the prime mover. Spool means slidably received within a rotor bore are outwardly displaceable with a first force while resilient bias means oppose and equalize this first force when the prime mover reaches a first predetermined speed, with valve means regulating the flow of pressurized fluid from the rotor means.