Cooling method and cooling device of electric motor

1. An electric motor cooling method for cooling an electric motor by using a first refrigerant, the electric motor cooling method comprising:

cooling the first refrigerant by heat exchange with a second refrigerant having a cooling target that is different from the first refrigerant;

supplying the first refrigerant to the electric motor after being cooled by heat exchange;

reducing a flow rate of the supply of the first refrigerant to the electric motor when a temperature of the first refrigerant is less than a first prescribed temperature as compared to when the temperature of the first refrigerant is greater than or equal to the first prescribed temperature, and

continuously reducing the flow rate of the supply of the first refrigerant as long as a temperature of the second refrigerant is less than a second prescribed temperature even after the temperature of the first refrigerant reaches the first prescribed temperature.

2. The electric motor cooling method according to claim 1 , further comprising

detecting a temperature of the electric motor, and

determining whether the temperature of the first refrigerant is greater than or equal to the first prescribed temperature based on the temperature that was detected.

3. The electric motor cooling method according to claim 1 , wherein

the supplying of the first refrigerant to the electric motor is supplied by a discharge from an oil pump,

detecting an operating state of the oil pump, and

determining whether the temperature of the first refrigerant is greater than or equal to the first prescribed temperature based on the operating state that was detected.

4. The electric motor cooling method according to claim 1 , wherein

the flow rate of the supply of the first refrigerant is increased more than the flow rate of the supply after the reduction where the temperature of the first refrigerant is greater than or equal to a third prescribed temperature, which is higher than the first prescribed temperature.

5. The electric motor cooling method according to claim 1 , wherein

the flow rate of the supply of the first refrigerant is increased more than the flow rate of the supply after the reduction where the temperature of the electric motor is greater than or equal to a fourth prescribed temperature.

6. The electric motor cooling method according to claim 1 , wherein

an amount of reduction is commensurate with a decrease in the temperature of the first refrigerant where the flow rate of the supply of the first refrigerant is reduced.

7. The electric motor cooling method according to claim 1 , wherein

the flow rate of the supply of the first refrigerant is increased more than the flow rate of the supply after a reduction, regardless of the temperature of the first refrigerant where the temperature of the second refrigerant is greater than or equal to the temperature of the first refrigerant.

8. The electric motor cooling method according to claim 1 , wherein

the flow rate of the supply of the first refrigerant to the electric motor is decreased more than the flow rate of the supply of the first refrigerant, regardless of the temperature of the first refrigerant where the temperature of the second refrigerant is less than a fifth prescribed temperature, which is below the second prescribed temperature.

9. The electric motor cooling method according to claim 1 , wherein

the flow rate of the supply of the first refrigerant is increased more than the flow rate of the supply after a reduction, regardless of the temperature of the first refrigerant where the temperature of the second refrigerant is greater than or equal to a sixth prescribed temperature, which is higher than the second prescribed temperature.

10. The electric motor cooling method according to claim 1 , wherein

the supplying of the first refrigerant to the electric motor is supplied by a discharge from an oil pump,

a rotational speed of the oil pump is decreased, or the oil pump is operated intermittently where the flow rate of the supply of the first refrigerant is reduced.

11. The electric motor cooling method according to claim 1 , wherein

the second refrigerant is an engine cooling water, and

the cooling target of the second refrigerant includes an engine provided in a vehicle as a drive source.

12. The electric motor cooling method according to claim 1 , wherein

a circulation path of the second refrigerant includes a radiator, and

the first refrigerant is cooled by using the second refrigerant after being cooled by heat exchange in the radiator.

13. An electric motor cooling device comprising:

a first refrigerant system includes an oil pump that supplies a first refrigerant discharged from the oil pump to an electric motor;

a second refrigerant system that circulates a second refrigerant to a cooling target that is different from the first refrigerant;

a heat exchanger interposed between the first refrigerant and the second refrigerant to cool the first refrigerant by heat exchange with the second refrigerant; and

a controller that controls an operation of the oil pump,

the controller being configured to

set an operating condition of the oil pump in each of a case where a temperature of the first refrigerant is less than a first prescribed temperature, and a case where the temperature of the first refrigerant is greater than or equal to the first prescribed temperature,

set the operating condition of the oil pump to reduce a supply flow rate of the first refrigerant to the electric motor where the temperature of the first refrigerant is less than the first prescribed temperature as compared to where the temperature of the first refrigerant is greater than or equal to the first prescribed temperature, and

set the operating condition of the oil pump to continuously reduce the supply flow rate of the first refrigerant as long as a temperature of the second refrigerant is below a second prescribed temperature even after the temperature of the first refrigerant reaches the first prescribed temperature.