Maximizing Efficiency: The Next Frontier in Electric Motor Technology

Motor Efficiency Benefits from Thermal Management Improvements

While electric drivetrains have fewer mechanical elements than traditional combustion engine architectures -- producing less heat and offering durability benefits for other systems -- EV motors still generate a considerable amount of heat during operation which, in turn, leads to energy losses. These losses are primarily caused by resistance encountered by the flow of electric current through various components in the motor, leading to the generation and dissipation of energy in the form of heat. Iron losses due to magnetization hysteresis and eddy currents as well as mechanical losses are additional loss types inherent to electrical motors and contributing to further heat generation.

Although today's motors are 90% efficient in more than 90% of the operating points, the question of reducing these losses remains high on the agenda. This can be achieved via advanced thermal management technologies, to improve the efficiency, longevity and performance of EV motors. For the various components within an EV motor to operate at their optimal temperatures, and to avoid altering the motor's thermal conductivity, causing demagnetization or material degradation, the motor should be kept at less than 180 C (356 F).

Currently, most motors are cooled via indirect methods, using an external water jacket. While this approach enables an increase in the continuous torque supply, it doesn't alter the fact that the heat is being produced within the active parts of the motor. As such, we're seeing a greater focus on the development of direct cooling methods, particularly for high-performance drivetrains, using oil to dissipate heat from the windings, stator and rotors.

These methods include:

• manifold dripping cooling - cooling fluid is precisely directed onto the motor winding heads
• shaft centrifugal cooling - the rotor's central shaft is used to spray oil to the head windings
• shaft splashing cooling - the shaft's rotation force is used to distribute oil along the winding heads.

Internally-cooled electric motors, though still undergoing further optimization, are starting in large EVs before eventually being democratized through all EVs.

In addition to minimizing heat losses, utilizing direct cooling methods such as these also enables the removal of the external water jacket seen in indirect motor cooling solutions, delivering a smaller, lighter and more affordable package, without compromising the power output.