Better Gas Engines for Plug-in Hybrids On the Way

By · May 31, 2012

Mahle range extender engine

Mahle range extender engine

Will we ever see a long-range electric car? The upcoming Tesla model S, promising 300 miles of range, will have a battery pack weighing about 1,500 pounds. We're all waiting for better batteries, and there are several hints telling us that they're on the way, but right now in Europe, Chevrolet sells its Cruze compact with a diesel engine that provides 700 miles of range. There's just no way a car running on batteries can beat that with today's tech. But there's a hope with plug-in hybrids.

When the Chevrolet Volt was introduced, I asked why it didn't come with a larger fuel tank to give it the same range as a diesel. I was told that meeting diesel-levels of range was not the point. The Chevrolet Volt is intended to be plugged in everyday. It's a fantastic car if you do so, but I later found out that its fuel economy with the battery discharged is only average. Could it be better with a better gas engine? Some people think so.

Lotus range extender engine

Lotus range extender engine

Engineers are working on purpose-built range extenders. These are internal combustion engines that would be very poor if used in conventional cars, but which would be great when used with the sole purpose of generating electricity working at a fixed RPM. The first company which began looking into the subject was Lotus, the British company which built all the Tesla roadsters. It asked its engineers to design a 3-cylinder 1.2 liter, a very compact unit because of its revolutionary design with the whole engine, block, cylinder head and exhaust manifold integrated into one single casting. I've seen this engine in the back of a Lotus sports car, and I know it has also been tested in a large Jaguar XJ sedan.

A serial hybrid, that car had a 145-kW electric motor with a 2-speed transmission, and a 8.7 kWh battery with the small Lotus engine hooked to a generator behind it. It provided a 35 kW current when needed. I know this car could offer zero-to-60 mph in less than 8 seconds with excellent fuel economy, but sadly it won't turn into a production model. Development has been completed but the engineers have moved on to another project. I guess performance was deemed to be too low for a luxury car as top speed was only 112 mph, and it could only drive three minutes at that speed. We can expect a plug-in hybrid from Jaguar sometimes, but it take a different form.

Jaguar XJ plug-in hybrid prototype

Jaguar XJ plug-in hybrid prototype

The Germans are know looking into the field, and Mahle, the engine specialists have unveiled a new range-extender ICE. Few people know Mahle outside of the auto industry, but if one looks closely on Ford's latest Ecoboost engine, the pistons, the bearings, the camshafts and all the small internal parts are built by Mahle. This new engine is a very, very small unit, with only two cylinders. Displacement? 0.9 liter and it puts out 30 kW. Its most important characteristic is its weight. The complete engine with the generator hooked to it and a 6 gallons fuel tank weighs only 200 pounds. That's totally unbeatable with batteries. Mahle explains it has worked a lot to make its engine vibration-free and quiet. This engine can be installed horizontally or vertically, the engine and generator combo measuring 481 x 416 x 327 mm. It would take only half the space in the trunk of a Nissan LEAF and would fully recharge the battery in one hour with the car parked. Sounds good?

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