MIT Electric Vehicle Team Porsche designing a cooling system for the AC24 electric motor

Abstract

In this thesis I worked on the design and analysis of a cooling system for the electric motor of the MIT Electric Vehicle Team's Porsche 914 Battery Electric Vehicle. The vehicle's Azure Dynamics AC24 motor tended to overheat (up to around 140C), which caused the motor controller to limit the maximum power of the motor. The maximum operating temperature of the motor is listed as 55C. The power limitation prevented the vehicle from achieving its top possible speeds, reaching only 87mph when it should get to over 100mph. To solve this problem, I designed a heat-exchanger system that runs coolant (a mix of water and ethylene glycol) through aluminum passages over the motor surface. The coolant then enters a heat-sink apparatus which consists of winding copper pipes attached to an aluminum array of fins (the heat sink) which convect away the heat into the moving ambient air. I found that with this system, at an ambient temperature of 50C, the maximum motor temperature would be about 72.61C. Even if the air temperature is 32C (89.6F), the maximum motor temperature will only be 54.7C, which is within the listed operating temperature of the motor and meets our goal. The total cost of this system is estimated to be $646.91.