Patent ID: 7510496

Claim:
An electro-hydraulic control system for an automatically shiftable transmission having first, second, and third selectively engageable torque transmitting mechanisms, wherein the automatically shiftable transmission is operable in a plurality of modes of operation including at least one reverse range, a neutral mode of operation, and a plurality of forward ranges, the electro-hydraulic control system comprising: a main source of fluid pressure; first, second, and third trim valves operable to effect the engagement of respective first, second, and third torque transmitting mechanisms; a latch valve in fluid communication with the first torque transmitting mechanism; an interlock valve in selective fluid communication with the latch valve; wherein said first trim valve is in fluid communication with said main source of fluid pressure; wherein said latch valve and said interlock valve are in fluid communication with said main source of fluid pressure; wherein said first trim valve is operable to selectively and variably communicate fluid pressure to said latch valve to effect engagement of the first torque transmitting mechanism; wherein said interlock valve is operable to selectively communicate fluid pressure to one of said second and third trim valve to effect engagement of the respective second and third torque transmitting mechanism; and wherein the electro-hydraulic control system is operable to receive control signals from an electronic control unit and, based upon an interruption of said control signals, the electro-hydraulic control system is operable to default to one of a pair of default modes of operation, including: a first default mode that is the same for each of the plurality of forward ranges; and a second default mode that is the same for each of the at least one reverse range and the neutral mode of operation.