The Dueling Cooling Technologies

Have you thought it would be great to own an all-electric vehicle such as the Nissan LEAF™ or a not-totally-electric car like the Chevrolet Volt? Have you thought it would be awesome not to have to buy gas ever for the LEAF or only occasionally for the Volt, especially at today’s prices of more than $3.00/gal? Have you thought that either of these vehicles would let you do your small part in helping to reduce carbon emissions? If you answered yes to these questions, then before you buy, look a little deeper into the differences in the cooling technology for the batteries in these cars.

Depending on a number of factors, the LEAF offers a driving distance of about 73 miles before recharging while the Volt can go approximately 35 miles before the gasoline engine kicks in to extend the range up to 375 miles. Nissan has published three different driving scenarios with corresponding distances: highway driving in the summer, a crosstown commute on a hot day, and winter stop-and-go in a traffic jam, all with the climate control on. The driving distances are stated as 70, 68, and 62 miles, respectively.

The LEAF and Volt use lithium-ion batteries that have not yet stood the test of time for reliability in the extreme automotive environment. Yet that has not deterred either company as each one grants a 100,000-mile, eight-year warranty on its battery. As reported in the Dec. 7 issue of MIT Technology Review, “The Electric Cooling Battery Test” by Kevin Bullis, both companies use lithium manganese oxide as the electrode material that is said to store more energy and has better stability compared to other electrode materials.

The similarities end when it comes to cooling (and heating, as necessary) for the battery. According to the article, “Nissan has opted for a simple design, using a fan to cool its batteries. It says that the flat shape of the battery cells makes additional cooling unnecessary. GM’s design is more complex.”

As presented on the website dated Dec. 9, the Volt has not one but four independent cooling systems: the power electronics coolant loop, the high-voltage battery cooling/heating system, the engine cooling system and heater loop, and the electric drive unit cooling and lubrication system. Each system has its own radiator, and all are mounted in the front of the engine.

The power electronics coolant loop includes the power inverter module that converts DC into AC to power the motor generator and the plug-in battery charger that rectifies the household AC to charge the battery. The high-voltage battery cooling/heating loop provides coolant to the battery which flows between the individual Li-ion cells. Additionally, the coolant can be heated to warm the cells for cold-weather operation.

The engine cooling and heater loop functions similar to nonelectric vehicles by providing cooling to the gasoline engine and heat to the passengers in the car. The electric drive unit cooling and lubrication system cools the transaxle which has two motor generators that drive the vehicle. This unit also delivers lubrication to a number of gears and bearings in the vehicle.

As can be seen, the cooling system for the Volt is more complicated than the LEAF’s, and this dichotomy has fueled much discussion in the industry. It’s interesting to note that the Tesla Motors sports car and its upcoming sedan use liquid cooling as will the 2011 Ford Focus Electric. It seems that Nissan is the only automaker staying with fan-based-only cooling.

You are invited to offer your comments. Please send an e-mail to me.

Paul Milo
Editorial Director
[email protected]

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