GM, U-Mich Patent Linear Engine for Extended-Range Hybrids

A recently patented powertrain system would extend the range of electric vehicles and hybrids by replenishing their batteries with power from linear alternators powered by four free-piston engines.

The U.S. Patent Office granted a patent for the technology to General Motors Co.'s Global Technology Operations LLC and the regents of the Univ. of Michigan.

Each engine consists of a cylinder containing a two-headed piston ringed by permanent magnets. The pistons are driven back and forth between combustion chambers at each end of the cylinder. The cylinder is lined with a stator and coils that produce electricity as the magnet-covered piston passes.

The developers say each engine would be configured with a separate bore and stroke to operate at a single optimized speed. Thus one engine/alternator might be tuned to produce 10 kW, a second unit 20 kW, a third unit 30 kW and a fourth unit 40 kW.

The engines would be switched on or off as needed, operating singly or in combinations to produce the required power. Such a scheme would help maximize efficiency, according to the researchers.

The system is designed to supply power to the vehicle's battery, electric propulsion motor or both, depending upon operating conditions. The linear engines would not power the vehicle's wheels directly.