Patent ID: 7377373

Claim:
A hydraulic control apparatus for a hydraulic power transmission with a lock-up clutch, where the lock-up clutch operates in accordance with a pressure difference between an engagement-side oil chamber and a disengagement-side oil chamber, comprising: (a) a lock-up relay valve which is switched between a first position and a second position by a switching electromagnetic solenoid, wherein: when the first position of the lock-up relay valve is selected hydraulic pressure is supplied to the engagement-side oil chamber; and when the second position of the lock-up relay valve is selected hydraulic pressure is supplied to the disengagement-side oil chamber; and (b) a linear solenoid valve, which includes a spool valve element driven using an electromagnetic force, that adjusts hydraulic pressure output from the linear solenoid valve, wherein: an oil passage is provided through which the hydraulic pressure output from the linear solenoid valve is supplied to the disengagement-side oil chamber via the lock-up relay valve when the lock-up relay valve is in the first position; and oil passages are respectively provided through which hydraulic pressure in the engagement-side oil chamber is applied to one end of the spool valve element of the linear solenoid valve, and hydraulic pressure in the disengagement-side oil chamber is applied to the other end of the spool valve element.