Electric-motor-driven oil pump control system

1. An electric-motor-driven oil pump used for supplying working oil through a sub-working-oil passage to a transmission of an automotive vehicle employing an automatic engine-stop system configured to automatically stop an engine, and driven by an electric motor for hydraulic pressure supply from the sub-working-oil passage through a check valve to the transmission, at least when hydraulic pressure supplied to the transmission is dropping under a stopped state of a mechanical oil pump driven by the engine, comprising:

a motor current detector for detecting a motor current flowing through the electric motor; and

a controller configured to temporarily execute a preliminary operation of the electric-motor-driven oil pump when a length of time, elapsed from a point of time when the electric motor becomes stopped, exceeds a predetermined time length and a vehicle speed becomes less than a given vehicle-speed threshold value, the controller further configured to output an enabling signal to the automatic engine-stop system for permitting a mode shift to an automatic engine-stop mode when a motor current value, detected by the motor current detector during the preliminary operation, rises from zero to a high current value once and then turns to a drop, and thereafter rises again, and the controller still further configured to output an inhibiting signal to the automatic engine-stop system for inhibiting a mode shift to an automatic engine-stop mode when the motor current value, detected by the motor current detector during the preliminary operation, is continuously kept high or continuously kept low.

2. The electric-motor-driven oil pump as claimed in claim 1 , wherein:

the preliminary operation is executed only for a given execution time, and terminated upon expiration of the given execution time.

3. The electric-motor-driven oil pump as claimed in claim 1 , wherein:

the preliminary operation is terminated after the motor current value, detected by the motor current detector during the preliminary operation, has risen from zero to a high current value once and then turned to a drop, and thereafter has risen again.

4. The electric-motor-driven oil pump as claimed in claim 1 , wherein:

after the preliminary operation, a main operation of the electric-motor-driven oil pump is executed depending on a line pressure of working oil supplied to the transmission.

5. The electric-motor-driven oil pump as claimed in claim 4 , wherein:

the main operation of the electric-motor-driven oil pump is initiated, when the line pressure reduces to below a first threshold value under a condition where the mode shift to the automatic engine-stop mode has been permitted after the preliminary operation.

6. The electric-motor-driven oil pump as claimed in claim 5 , wherein:

after the preliminary operation, the main operation of the electric-motor-driven oil pump is initiated when the line pressure reduces to below the first threshold value, and continuously executed in such a manner as to maintain a pressure level corresponding to a second threshold value lower than the first threshold value, and thereafter terminated when the line pressure reaches a pressure level corresponding to a third threshold value lower than the first threshold value and higher than the second threshold value.

7. The electric-motor-driven oil pump as claimed in claim 1 , wherein:

a subsequent execution cycle of preliminary operation is initiated, when there is no occurrence of the mode shift to the automatic engine-stop mode upon expiration of a given period of time after one execution cycle of the preliminary operation.

8. The electric-motor-driven oil pump as claimed in claim 1 , wherein:

the electric motor comprises a direct-current brush motor.

9. An electric-motor-driven oil pump control system with automatic engine-stop system interaction, comprising:

an electric-motor-driven oil pump used for supplying working oil through a sub-working-oil passage to a transmission of an automotive vehicle employing an automatic engine-stop system configured to automatically stop an engine, and driven by an electric motor for hydraulic pressure supply from the sub-working-oil passage through a check valve to the transmission, at least when hydraulic pressure supplied to the transmission is dropping under a stopped state of a mechanical oil pump driven by the engine;

a motor current detector for detecting a motor current flowing through the electric motor; and

a controller configured to temporarily execute a preliminary operation of the electric-motor-driven oil pump when a length of time, elapsed from a point of time when the electric motor becomes stopped, exceeds a predetermined time length and a vehicle speed becomes less than a given vehicle-speed threshold value, the controller further configured to output an enabling signal to the automatic engine-stop system for permitting a mode shift to an automatic engine-stop mode when a motor current value, detected by the motor current detector during the preliminary operation, rises from zero to a high current value once and then turns to a drop, and thereafter rises again, and the controller still further configured to output an inhibiting signal to the automatic engine-stop system for inhibiting a mode shift to an automatic engine-stop mode when the motor current value, detected by the motor current detector during the preliminary operation, is continuously kept high or continuously kept low.

10. The electric-motor-driven oil pump control system as claimed in claim 9 , wherein:

the preliminary operation is executed only for a given execution time, and terminated upon expiration of the given execution time.

11. The electric-motor-driven oil pump control system as claimed in claim 9 , wherein:

the preliminary operation is terminated after the motor current value, detected by the motor current detector during the preliminary operation, has risen from zero to a high current value once and then turned to a drop, and thereafter has risen again.

12. The electric-motor-driven oil pump control system as claimed in claim 9 , wherein:

after the preliminary operation, a main operation of the electric-motor-driven oil pump is executed depending on a line pressure of working oil supplied to the transmission.

13. The electric-motor-driven oil pump control system as claimed in claim 12 , wherein:

the main operation of the electric-motor-driven oil pump is initiated, when the line pressure reduces to below a first threshold value under a condition where the mode shift to the automatic engine-stop mode has been permitted after the preliminary operation.

14. The electric-motor-driven oil pump control system as claimed in claim 13 , wherein:

after the preliminary operation, the main operation of the electric-motor-driven oil pump is initiated when the line pressure reduces to below the first threshold value, and continuously executed in such a manner as to maintain a pressure level corresponding to a second threshold value lower than the first threshold value, and thereafter terminated when the line pressure reaches a pressure level corresponding to a third threshold value lower than the first threshold value and higher than the second threshold value.

15. The electric-motor-driven oil pump control system as claimed in claim 9 , wherein:

a subsequent execution cycle of preliminary operation is initiated, when there is no occurrence of the mode shift to the automatic engine-stop mode upon expiration of a given period of time after one execution cycle of the preliminary operation.

16. The electric-motor-driven oil pump control system as claimed in claim 9 , wherein:

the electric motor comprises a direct-current brush motor.