Credit: Toyota/Charged EVs
Generators make electricty by moving a conductor near a magnet. Or the other way round. Just so long as the conductor & magnet move relative to one another. Usually, a number of magnets are arranged in a circle & the coil spins on a shaft inside the circle of magnets.
Less commonly, a linear generator has a magnet moving back & forth inside a conductive coil.
A free-piston engine is an internal combustion engine (ICE) without a crankshaft. Without a crankshaft, there will be no rotary motion, but by incorporating a linear generator, an engine/generator with no rotary motion is produced.
By eliminating the crankshaft & separate generator, friction is reduced. Up to 40% efficiency has been claimed for the Toyota unit.
Laboratory measurements of ICE efficiency are not usually equalled in practice. This is substantially because outside a very narrow range of engine speed & load, ICE efficiency falls quickly. In an electric vehicle range extender, an ICE operating at a constant speed can build up a small cushion of charge in the battery to cope with changing demands for power without changing ICE speed. In this way an ICE range extender has the potential to operate at its peak efficiency all of the time.
Toyota is not the first to experiment with a free piston engine, but it's interesting to to see a major manufacturer, without an electric vehicle on the market, developing such a device.
http://chargedevs.com/newswire/toyota-developing-free-piston-engine-linear-generator-for-electric-drive-vehicles/ / Toyota Central R&D Labs developing development prototype Free Piston Engine Linear Generator FPEG SAE 2014 World Congress in Detroit internal combustion engine ICE propel propels drive shaft FPEG designed generate electricity directly two stroke two-stroke combustion chamber linear generator gas spring chamber piston moved combustion gas magnets attached linear coil converting kinetic energy electrical energy Toyota FPEG double piston system combustion chamber adjustable gas spring chamber returning piston combustion event power stroke kinetic energy piston stored gas spring extracted return stroke combustion chamber side magnetic mover mounted outer periphery piston linear generator permanently excited synchronous machine stationary coil mover neodymium-iron-boron magnets piston iron-core stator power electronics drive machine motor generator video animation of Toyota’s FPEG researchers achieved output power 10 kW 42% thermal efficiency B/C segment electric drive vehicles prototype cooling lubrication lubricating problems /
