Patent ID: 8066595
Filing Date: 2011-11-29
Classification: F16H,Y10T

Abstract:
1. A hydraulic control system for a vehicular power transmitting mechanism including a hydraulically operated continuously variable transmission of a belt-and-pulley type which includes a transmission belt and a speed ratio of which is continuously variable, and a hydraulically operated frictional coupling device which is capable of being engaged, for running of a vehicle, to establish a power transmitting path partially defined by the continuously variable transmission, said hydraulic control system comprising: a first linear solenoid-operated valve operable to generate a first control pressure for regulating a belt-tensioning hydraulic pressure for applying a tension to said transmission belt of said continuously variable transmission; a second linear solenoid-operated valve operable to generate a second control pressure for regulating a transient coupling hydraulic pressure to be applied to said frictional coupling device in a process of an engaging action from a fully released state to a fully engaged state; a line-pressure regulating valve operable to regulate a line pressure used for hydraulically operated devices of the vehicular power transmitting mechanism; a hydraulic-circuit switching device operable to switch hydraulic circuits such that, (i) for placing said hydraulically operated frictional coupling device in said fully engaged state, the hydraulic pressure of said hydraulically operated frictional coupling device and the line pressure are controlled by the second linear solenoid-operated valve, and the belt-tensioning hydraulic pressure is controlled by the first linear solenoid-operated valve, and (ii) during said hydraulically operated frictional coupling device being in the process of said engaging action, the belt-tensioning hydraulic pressure and the line pressure are controlled by the first linear solenoid-operated valve, and said second control pressure outputted from the second linear solenoid-operated valve is supplied to said frictional coupling device as said transient coupling hydraulic pressure; and a coupling-pressure regulating valve operable to generate a coupling hydraulic pressure to be applied to said frictional coupling device placed in said fully engaged state, wherein said hydraulic-circuit switching device includes a control-pressure switching valve which is arranged to receive said first control pressure, said second control pressure and said coupling hydraulic pressure, and which has: 1) a normal state in which said second control pressure is applied to said line-pressure regulating valve and said coupling-pressure regulating valve while said coupling hydraulic pressure is applied to said frictional coupling device, and 2) a control state in which said first control pressure is applied to said line-pressure regulating valve while said second control pressure is applied to said frictional coupling device as said transient coupling hydraulic pressure, said hydraulic-circuit switching device further including a switching control portion operable (i) to judge said fully engaged state and said process of said engaging action of said first linear solenoid-operated valve, and (ii) to switch said control-pressure switching valve to said normal state when placement of said frictional coupling device in said fully engaged state is judged, and (iii) to switch said control-pressure switching valve to said control state when process of said engaging action of said frictional coupling device is judged.