Logic valving for a transmission control.

摘要

A transmission control has a plurality of solenoid controlled hydraulic valves that are selectively operable to control the establishment of various drive ratios in a six speed transmission. A logic valve (18), comprised of two valve spools (46,68) and a solenoid (36), is disposed between the solenoid controlled hydraulic valves and some of the friction drives (C1-C5) in the transmission which establish the various drive ratios. The valve spools are operable to establish the fourth ratio if an electrical malfunction occurs during operation in the fourth or fifth ratios, or to establish the fifth ratio if electrical malfunction occurs while operating in the sixth ratio, or to establish the third ratio if an electrical malfunction occurs while operating in the first, second or third forward speed ratios. In the alternative, the valve spools can be controlled to establish fourth ratio whenever an electrical malfunction occurs when the transmission is operating in the second through fifth ratios.