In general, drive motors for eco-friendly vehicles are used to implement a traveling mode in which EVs (Electric Vehicles) are driven by motors alone and a traveling mode in which HEVs (Hybrid Electric Vehicles) are driven by combination of motors and engines.
These eco-friendly vehicles are hybrid vehicles, and includes EVs (Electric Vehicles), HEVs (Hybrid Electric Vehicles), PHEVs (Plug-in Hybrid Electric Vehicles), FCEVs (Fuel Cell Electric Vehicles), MHEVs (Mild Hybrid Electric Vehicles), etc.
Such a drive motor includes a stator around which a coil is wound and which is coupled in a motor housing, and a rotor that is disposed in the stator with a predetermined gap interposed therebetween. The drive motor is provided with a cooling structure that cools heat generated by the current applied to the coil and the eddy current due to counter electromotive force.
This cooling structure uses indirect and direct cooling methods that are classified according to the method of cooling main heating parts and parts required for intensive cooling, such as a stator, a bearing, and a magnet of a drive motor.
For example, the indirect cooling method is a method of circulating coolant to a stator, a bearing, and a magnet of a drive motor to indirectly cool the inside of the drive motor. The indirect cooling method enables the cooling efficiency of the stator to be enhanced while enabling the drive motor to have a simple structure in which a coolant channel in a motor housing is used
For example, the direct cooling method is a method of circulating oil within a drive motor and a reducer, to main heating parts and parts required for cooling to directly cool the inside of the drive motor. The direct cooling method enables the cooling efficiency of a bearing and a magnet to be enhanced by a coolant channel formed in the drive motor while enabling a stator to be cooled by forming an oil path in the drive motor.
Accordingly, in the eco-friendly vehicles, it is possible to prevent damage to the drive motor due to deterioration during driving of the drive motor and maintain the performance of the drive motor by applying one or both of the indirect and direct cooling methods to the drive motor.
However, among the part required for intensive cooling, it is difficult for the indirect cooling method to secure the cooling performance of the bearing and the magnet compared to the stator. It is advantageous for the direct cooling method to secure the cooling performance of the stator, the bearing, and the magnet, but it is necessary to sufficiently secure a flow rate of oil.
Therefore, a separate cooling system has to be provided to the drive motor to which the combination of the indirect and direct cooling methods is applied.
For example, an HEV vehicle, which uses an engine and a motor together, requires an ATF (Auto Transmission Fluid) motor circulation system to supply ATF to the motor. For another example, an EV vehicle, which uses only a motor, requires a cooling system including an oil cooler to cool oil in the motor and a reducer.
For this reason, the application of the drive motor, to which the combination of the indirect and direct cooling methods is applied, to the HEV or EV vehicle causes an increase in cost due to the additional system, which may lead to a decrease in the price competitiveness of the eco-friendly vehicle.