Patent ID: 7261662
Filing Date: 2007-08-28
Classification: F16H,Y10T

Abstract:
1. A hydraulic control apparatus for use with an automatic transmission of a vehicle, the automatic transmission establishing each of a plurality of speed steps having respective different speed ratios, according to a corresponding one of a plurality of combinations of respective selective engaging and releasing of a plurality of hydraulically operated frictional coupling devices, the hydraulic control apparatus comprising: a plurality of transmission-related solenoid valves which correspond to the hydraulically operated frictional coupling devices, respectively, and each of which has an input port to which a first hydraulic pressure is inputted, an output port from which a second hydraulic pressure is outputted, and a drain port from which a hydraulic fluid is drained, and includes a solenoid which changes a state in which the input port, the output port, and the drain port communicate with each other, so that said each transmission-related solenoid valve outputs, from the output port thereof, the second hydraulic pressure and thereby causes the engaging of a corresponding one of the hydraulically operated frictional coupling devices; and a fail-safe switch valve which has at least one escape-related output port connected to the drain port of at least one transmission-related solenoid valve corresponding to at least one escape-related frictional coupling device of the hydraulically operated frictional coupling devices that is to establish at least one escape-related speed step, and additionally has at least one escape-related input port to which a third hydraulic pressure is inputted, and at least one drain port from which the hydraulic fluid is drained, wherein the fail-safe switch valve is selectively switchable to a normal communication state thereof in which said at least one escape-related output port and said at least one drain port are communicated with each other and said at least one escape-related input port is shut off, and to a fail-related communication state thereof in which said at least one escape-related output port and said at least one escape-related input port are communicated with each other, and said at least one drain port is shut off, so that a fourth hydraulic pressure is supplied from said at least one escape-related output port of the fail-safe switch valve to the drain port of said at least one transmission-related solenoid valve corresponding to said at least one escape-related frictional coupling device.