Thermal Management Solutions for Electric and Hybrid Vehicles
Electrification is a Megatrend, not only for passenger cars and light-duty vehicles but also increasingly for construction equipment, agricultural applications, and logistics. Requirements are very different for working machinery than for passenger cars as utilization time, load rates and charging requirements are significantly more challenging. Here at AKG, we have developed high-performance thermal management systems for various applications with the objective to increase lifecycle, passenger comfort and in accordance with the company’s DNA using the latest advanced technical solutions.
We are a global heat exchanger manufacturer and supplier of thermal management systems. The company’s objective is to supply high performing solutions to the market, especially to those applications requiring these technologies: high-end sports cars, off-road heavy working machinery (construction, agricultural or mining equipment), railway applications, and many others.
In general, the thermal management of an EV is more complex than of an ICE-vehicle, due to the fact, that less heat is available and the temperature ranges for various components are reduced and rather strict.
Most electric components, motors, batteries, electronics, converters have an efficiency of 80-90%, so heat rejection is not significant. Nevertheless, to heat or cool the cabin and supply energy for secondary purposes, this low amount of heat has to be recovered and is called “heat harvesting”. The utilization of this “waste heat” is necessary due to the fact that if cabin heating is done by electricity, this utilization will reduce autonomy dramatically. It may be acceptable for a light passenger car with low requirements on comfort, but certainly will not be an appropriate solution for a high-end passenger car, tractor, or other machinery.
Also, the temperature regime for a Li-Ion battery is very strict, the battery should be kept in a temperature zone around 25-35°C. Same as the cabin, the battery has to be heated or cooled, depending on utilization.
The efficient fulfilling of these demanding challenges have impacted AKG’s design of new heat exchangers and the adoption of existing ones. Today we have all the necessary components available for optimized thermal management for BEV’s and Hybrid Vehicles thus increasing overall performances, autonomy, and comfort by reducing aging and thermal stress.
With the charging speed and power density of the latest lithium-ion batteries, active and passive cooling is becoming a key factor in electric vehicle battery life. We collaborated with FH Aachen and RWTH Aachen University to find the best combination of cooling technology for a 48 V high-power battery module. For an ideal temperature gradient across the battery, we use a combination of side-cooling, inter-cell cooling, and thermally conductive fill material.
The research used computational fluid dynamics (CFD) and finite element analysis (FEA) to test various configurations. The goal was to find a solution to keep the average temperatures of individual cells – not just the average temperature of the battery module – between 15 and 40 degrees Celsius. Analyses included 280 W, 560 W, and 840W heat generation rates. Along with maintaining an ideal temperature range, maintaining a small temperature gradient across each cell would further improve the outcome.
Figure 1: Example of thermal analysis of an 18-650 cell-style battery before and after adding thermal management methods. [Source: Wu Z., Stawarski A., Kemper H. “Thermal analysis of cooling effects of different cooling principles in 48V automotive battery module,” EEHE 2017 Bamberg, Mai 17-18, 2017.]
Using active cooling with water-glycol on the sides of the cells, and passive internal cooling plates, both temperature maximum, and temperature gradient are managed cost-effectively. The addition of suitable fill material for high-power battery applications significantly improves the heat transfer to the cooling system, allowing the design to exceed its goal.
The successful design optimization project was presented at the EVS 31 & EVTeC 2018 joint event in Japan on October 2. A full copy of the paper “Optimal Cooling Solution for High-Power Automotive Battery Module” is available through the Society of Automotive Engineers of Japan, Inc.