Maximizing energy efficiency is crucial for improving EV performance, and Subaru’s latest patent aims to do just that. The automaker has filed a patent with the United States Patent and Trademark Office for a system that uses the heat from the transmission oil that would normally go to waste to heat up the battery. Similar to how a turbocharger harnesses exhaust energy in a combustion engine, this innovation could enhance battery efficiency, improve cold-weather performance, and optimize overall energy use.
Harnessing Transmission Heat
All EVs have transmissions, typically a constant-mesh single-speed unit that reduces the electric motor’s output for the wheels. Some, like certain VW Group EVs, use a two-speed transmission. As these gears spin, the transmission oil heats up, which is usually wasted or dissipated through a cooler.
The main traction battery needs to be heated for optimal performance, whether for high power demands, efficient charging, or cold-weather operation. Subaru’s new patent proposes a smarter approach whereby waste heat from the transmission fluid is captured and used to warm the battery. Instead of discarding this heat and wasting even more energy by heating the battery up in alternative ways, Subaru’s system repurposes it, improving overall efficiency and reducing energy waste.
Components And Operation
Subaru’s system consists of several key components working together to efficiently transfer waste heat from the transmission to the battery:
- Heat-retaining transmission oil tank – Stores heated oil for use when needed.
- Heat exchanger – Transfers heat from the oil to the battery.
- Oil flow-control valve – Regulates oil flow based on heating requirements.
- Temperature sensor – Monitors system temperatures to optimize performance.
- Electronic control unit (ECU) – Manages the entire process, controlling the clutch mechanism and oil flow to ensure efficient battery heating.
As the transmission operates, its oil heats up and is stored in the tank. When battery heating is required, the system directs the warmed oil to the heat exchanger. The ECU fine-tunes the process, adjusting oil flow and clutch engagement to optimize heating efficiency.
While Subaru’s patent doesn’t specify what happens when battery heating isn’t needed, it’s likely that excess heat is dissipated through the heat exchanger. According to Subaru, this method provides the most efficient way to precondition a battery, improving cold-weather performance while extending battery lifespan.
