Relay valve with latch area for controlling a friction device

摘要

A powertrain has a multi-speed transmission with an electro-hydraulic control system for establishing the operating conditions of the transmission. The control system has a plurality of shift or relay valves that are each alternatively positioned by a spring or a solenoid controlled pressure bias. One of the relay valves, which controls two friction devices, has a latching mechanism which will retain the valve in the pressure set condition until the pressure in one of the friction devices is decreased below a predetermined pressure. The latch mechanism will also serve to retain the transmission in a low forward ratio if an electrical discontinuance should occur when the transmission is conditioned for the low forward ratio. The control will also permit retention in the highest forward ratio if electrical discontinuance occurs during operation in this ratio. Following an engine shutdown and restart, the transmission can be selectively operated in a reverse ratio, a neutral condition or the third forward ratio.