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Cooling Complexity

December 13, 2022

The automotive industry has increasingly focused its attention on making eMobility architectures safe, efficient, and convenient. Since there are considerable pressures to make electric vehicles (EVs) more attractive to consumers, the industry has focused on three particular aspects that would make EVs as convenient as internal combustion engine (ICE) vehicles: range, battery life, and charging speed. Very few EVs on the market are capable of the range of a typical gasoline or diesel vehicle, and while an ICE vehicle can be fully refueled in just a few minutes, it can take considerably longer to charge an EV. A direct current fast charger can take 20–60 minutes to provide only 80% charge. And an EV’s battery pack has a limited lifespan because a lithium-ion battery loses a little of its capacity each time it is charged and discharged.

Since these factors are foremost on consumer’s minds, OEMs seem to have geared their thermal management efforts to help overcome these challenges. One of the keys to getting the best performance out of batteries and charging systems is to keep them at their optimal operating temperatures. Since the current produced by these systems results in a great deal of heat, keeping them cool is the primary consideration. However, effective thermal management involves much more than just keeping batteries and charging systems cool. There are a host of ancillary systems that must be kept at proper operating temperatures such as power inverters, electric motors, and electronic modules. Heating and cooling of the passenger cabin adds even more complexity to an EV’s thermal management needs. While these systems generally require less cooling than the battery, attention still needs to be paid.

Despite the evolving complexity of an EV’s thermal management needs, OEMs have often designed what might be called “static” thermal management systems with off-the-shelf components. These static systems are in many ways not too different from what might be found on a typical ICE vehicle—a pump circulates coolant through the entire system in a simple loop, using a small number of valves.

While existing systems have been used with a certain level of success, they are not without problems. For instance, these static systems have some limitations as to how effective they are at keeping batteries within their optimal operating temperature range. As coolant enters the battery pack and begins circulating, the coolant itself is very cool and able to draw excess heat effectively. But as that coolant makes its way to the downstream portions of the battery pack, it is often too hot to provide effective cooling to the remaining battery cells. The cells that receive less effective cooling tend to degrade more rapidly, shortening the life of the battery pack and providing less-than-optimal battery performance.

Static Thermal Management

In addition to this, thermal management is about more than just keeping systems from getting too hot. It is also about warming systems that are too cold. OEMs work hard to try to maximize vehicle performance for a wide range of environments so that harsh winters will not adversely affect performance any more than blazing summers. The static type of thermal management systems currently being used may not be the ideal way to properly deal with the complexities of both warming and cooling various EV components and systems in extreme temperatures.

For example, lithium-ion batteries perform best when kept within a certain temperature band. Excessive heat can degrade the battery. Cold temperatures cause slower chemical reactions in the battery’s electrolyte solution. This significantly reduces range and charging capacity and increases charging times. Cold temperatures also cause an EV to use more energy to heat the passenger cabin and warm the battery and other systems, further reducing vehicle range.

The issue of coolant being too hot by the time it reaches the far end of the battery pack may be mirrored in colder temperatures. If hot coolant is used to keep the battery warm, the hot coolant entering the battery pack at one end may lose some heat as it flows through the pack, resulting in uneven heating of the cells and diminished performance.

OEMs may wish to consider a more highly engineered, dynamic approach to thermal management to better cope with these challenges. A thermal management system that provides targeted variable coolant flow to individual systems and components could be the key. Various types of proportional valves could be used to deliver different flow volumes and rates as needed. This approach may provide more precise heating and cooling of not only the battery but also the power inverter, electric motor, and other secondary systems.

As an alternative to the static approach to thermal management that can result in uneven cooling of the battery, a dynamic approach could include a multiport proportional valve that directs targeted coolant flow to different sections of the battery pack. This could keep the battery within its optimal temperature band across all its cells, improving longevity and performance. This same cooling benefit could be equally harnessed to use hot coolant to warm the battery more effectively in cold temperatures.

Dynamic Thermal Management Tbnl

This approach could also help reduce the high demand for power that cabin heaters place on an EV’s system in cold weather. A potential solution is to use waste heat from ancillary systems to heat the passenger cabin. A dynamic thermal management system is one way to achieve this.

Proportional valves that take advantage of latching technology to actuate will also be important for keeping thermal management systems as energy efficient as possible. Latching actuators do not require constant power to maintain a commanded position and need only a short pulse of power to change state. This yields a significant energy savings over valves that need constant power to hold position. Valves using this technology can also be equipped with a fail-safe circuit that returns the valve to a designated safe position to prevent accidental overheating or underheating of whichever system it serves.

Effective and efficient thermal management systems are crucial for the future of eMobility. The existing static thermal management systems will have difficulty supporting the ever-increasing challenges resulting from evolving vehicle systems. Looking to more dynamic designs that use energy-efficient proportional valves may be the best solution.

This article was originally published by Automotive Powertrain Technology International in January 2023

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