Hydraulic control apparatus

A hydraulic control apparatus comprising:

• a piston provided so as to be movable between a first position and a second position;
• a plurality of control valves including a first control valve, a second control valve, a third control valve and a fourth control valve, the first control valve and the second control valve being respectively switched so as to exert a first hydraulic pressure and a second hydraulic pressure on the piston to press the piston toward the first position, the third control valve and the fourth control valve being respectively switched so as to exert a third hydraulic pressure and a fourth hydraulic pressure on the piston to press the piston toward the second position;
• a first failure detection device that detects a failure of the second control valve;
• a second failure detection device that detects a failure of the fourth control valve;
• a movement detection device that detects a movement of the piston from the second position to the first position;
• and
• an electronic control unit including a microprocessor and a memory connected to the microprocessor, wherein
• the microprocessor is configured to perform
• controlling the plurality of control valves,
• the controlling including executing a first process controlling the plurality of control valves so that the first hydraulic pressure, the second hydraulic pressure and the third hydraulic pressure are exerted on the piston while the fourth hydraulic pressure is not exerted, or a second process controlling the plurality of control valves so that the second hydraulic pressure is exerted on the piston while the first hydraulic pressure, the third hydraulic pressure and the fourth hydraulic pressure are not exerted, when the piston is moved from the second position to the first position, and
• the microprocessor is further configured to perform
• determining that the first control valve is failed when the movement of the piston to the first position is not detected by the movement detection device in spite of an execution of the first process, and determining that the third control valve is failed when the movement of the piston to the first position is not detected by the movement detection device in spite of an execution of the second process, under a situation where the failure of the second control valve is not detected by the first failure detection device and the failure of the fourth control valve is not detected by the second failure detection device.