a compact hydraulic system to move a transmission from one state to another.

摘要

Means for applying fluid pressure to selected pairs of the drive conditioning devices of a vehicle transmission in response to control lever movement includes a pressure modulating valve for establishing a gradual pressure rise at the selected drive devices and a safety differential spool valve provides for a delayed lesser pressure rise at the one of the devices which re-establishes drive through the transmission. The safety differential spool valve performs the further function of blocking fluid pressure from one of the selected devices if the vehicle engine should be started up with the control levers at a position other than neutral. Two valves thus provide transmission control functions which have heretofore required more complex valving assemblies.