Oil pressure control device for transmission and control method thereof

1. An oil pressure control device for a transmission, which engages or disengages a frictional engagement element of the transmission by controlling an oil pressure supplied from a mechanical oil pump driven by a power source for driving a vehicle and an electric oil pump driven by an electric motor, comprising:

an air entering determining unit which determines whether or not air enters the electric oil pump; and

an air discharging unit which, when an ignition switch of the power source is switched from an ON state to an OFF state after the air entering determining unit has determined that air enters the electric oil pump, drives the electric oil pump such that the air entering the electric oil pump is discharged from the electric oil pump together with an oil.

2. The oil pressure control device for the transmission as defined in claim 1 , wherein the air entering determining unit determines whether or not air enters the electric oil pump when the power source is automatically stopped.

3. The oil pressure control device for the transmission as defined in claim 1 , wherein the air discharging unit starts the electric oil pump at the same time as the ignition switch is switched to the OFF state.

4. The oil pressure control device for the transmission as defined in claim 1 , wherein the air discharging unit starts the electric oil pump when a discharge pressure of the electric oil pump increases beyond a discharge pressure of the mechanical oil pump.

5. A method of controlling an oil pressure control device for a transmission, which engages or disengages a frictional engagement element of the transmission by controlling an oil pressure supplied from a mechanical oil pump driven by a power source for driving a vehicle and an electric oil pump driven by an electric motor, comprising:

determining whether or not air enters the electric oil pump;

driving the electric oil pump when an ignition switch of the power source is switched from an ON state to an OFF state after air is determined to enter the electric oil pump; and

discharging the air entering the electric oil pump from the electric oil pump together with an oil.

6. The method of controlling the oil pressure control device for the transmission as defined in claim 5 , wherein the determining is performed when the power source is automatically stopped.

7. The method of controlling the oil pressure control device for the transmission as defined in claim 5 , wherein the driving the electric oil pump is started at the same time as the ignition switch is switched to the OFF state.

8. The method of controlling the oil pressure control device for the transmission as defined in claim 5 , wherein the driving the electric oil pump is started when a discharge pressure of the electric oil pump increases beyond a discharge pressure of the mechanical oil pump.

9. An oil pressure control device for a transmission, which engages or disengages a frictional engagement element of the transmission by controlling an oil pressure supplied from a mechanical oil pump driven by a power source for driving a vehicle and an electric oil pump driven by an electric motor, comprising:

air entering determining means for determining whether or not air enters the electric oil pump; and

air discharging means for driving the electric oil pump such that the air entering the electric oil pump is discharged from the electric oil pump together with an oil, when an ignition switch of the power source is switched from an ON state to an OFF state after the air entering determining means has determined that air enters the electric oil pump.

10. The oil pressure control device for the transmission as defined in claim 9 , wherein the air entering determining means determines whether or not air enters the electric oil pump when the power source is automatically stopped.

11. The oil pressure control device for the transmission as defined in claim 9 , wherein the air discharging means starts the electric oil pump at the same time as the ignition switch is switched to the OFF state.

12. The oil pressure control device for the transmission as defined in claim 9 , wherein the air discharging means starts the electric oil pump when a discharge pressure of the electric oil pump increases beyond a discharge pressure of the mechanical oil pump.