Patent ID: 7244209
Filing Date: 2007-07-17
Classification: F16H,Y10T

Abstract:
1. A hydraulic control apparatus for controlling an automatic transmission which includes two hydraulically operated frictional coupling devices of a first group and a plurality of hydraulically operated frictional coupling devices of a second group, and which is arranged to establish a selected one of a plurality of gear positions thereof having respective different speed ratios, by simultaneous engaging actions of the two frictional coupling devices of the first group, or simultaneous engaging actions of one of the frictional coupling devices of the first group and one of the frictional coupling devices of the second group, said hydraulic control apparatus comprising: a second-group-engaging switching valve which is arranged to receive a plurality of second engaging hydraulic pressures generated to respectively engage the plurality of hydraulically operated frictional coupling devices of the second group and which is operable, upon reception of at least one of said second engaging hydraulic pressures, to generate a second-group-engaging pilot hydraulic pressure other than said at least one of said second engaging hydraulic pressures; and a fail-safe valve which is arranged to receive at least one of two first engaging hydraulic pressures generated to respectively engage the two hydraulically operated frictional coupling devices of the first group and which is operable, upon simultaneous reception of the first engaging hydraulic pressure generated to engage one of said two frictional coupling devices of the first group and said second-group-engaging pilot hydraulic pressure, to prevent application of the first engaging hydraulic pressure to the other of said two frictional coupling devices of the first group.