Patent ID: 8317655

Claim:
A hydraulic pressure control apparatus for a torque converter in which a turbine runner is rotated by operational fluid outputted from a pump impeller rotating in a hydraulic power transmission chamber, comprising: a relay valve switching levels of a hydraulic pressure in the hydraulic power transmission chamber to be a higher pressure or a lower pressure and establishing selective connections between a cooler and the hydraulic power transmission chamber or between the cooler and a hydraulic pressure supply source of which a flow amount of the operational fluid is regulated by a first orifice, the relay valve connecting the cooler and the hydraulic power transmission chamber when the hydraulic pressure in the hydraulic power transmission chamber is higher than a predetermined level and connecting the cooler and the hydraulic pressure supply source when the hydraulic pressure in the hydraulic power transmission chamber is lower than the predetermined level; a solenoid valve operating the relay valve in accordance with an energization state; an electronic control unit controlling the solenoid valve; a hydraulic pressure declination determining portion provided in the electronic control unit for judging whether the hydraulic pressure of the hydraulic pressure supply source is lower than a threshold value based on a predetermined vehicle state; and a switching command outputting portion provided in the electronic control unit for outputting a command to connect the cooler and the hydraulic pressure supply source by the relay valve when the hydraulic pressure declination determining portion determines that the hydraulic pressure of the hydraulic pressure supply source is lower than the threshold value.