Toyota Makes Progress on Hybrid Motorcycle Technology

Motorcycling would benefit from this new hybrid engine technology.

Toyota motor diagram

Because space on motorcycles is scarce, there has been little talk of hybrid motorcycles, which must add battery, electric motor, and power supply to what is already there. But a project from Toyota caught my eye because of its compactness.

This free-piston linear motor/generator would power a serial hybrid, which is one driven only by an electric motor but with a combustion-powered generator to charge its battery. In this case, the bulky conventional pistons-and-crank engine, clutch, and transmission would be deleted and its space taken by a modest-sized battery, electric motor, and the log-shaped linear motor/generator.

Such a vehicle would have the same range as any other combustion-powered vehicle, as its power would come from conventional energy-dense hydrocarbon fuel. It would not carry the bulky 200-pound battery of an all-electric bike, as its smaller battery is kept charged by operation of the free-piston linear generator.

When we think of generators or alternators, the rotary machines found on cars, trucks, and bikes naturally come to mind. But the essence of generating electric current is simply to move a wire through a magnetic field, and this can be accomplished by a variety of geometries.

Toyota motor generator diagram

In Toyota’s hybrid motorcycle concept, a piston driven by a simple two-stroke combustion cycle would move a permanent magnet back and forth inside a wire coil assembly to produce 50- or 60-cycle alternating current. Think of this as a solenoid (a linear motor) operating “in reverse” as an alternator. To eliminate vibration, two pistons could move opposite each other in a single cylinder, meeting in a central combustion chamber, each driving its own permanent magnet/coil assembly. There would be no rotating parts.

To start this linear motor, DC power from the battery would be transformed into AC by the power supply and sent to the coils around each piston’s permanent magnet. This would cause the pistons to bounce back and forth, fuel would be injected between them, spark ignition supplied, and the linear motor would start.

All who have experienced electric motorcycles have enjoyed their smooth, controllable power delivery. The problem has been that battery development has not kept pace with expectation, keeping range disappointingly short and charging times long. While we wait for improved batteries, the auto industry has turned to hybrids as the practical way to achieve future fuel-economy levels.

So far, fuel-economy standards are not changing motorcycles as they have cars. If they do one day, the first big reduction in fuel consumption will come from cutting highway engine rpm with an overdrive gearbox ratio or two (some cars now have eight or even nine speeds). Higher-tech measures, such as adopting hybrid power or Craig-Vetter-like full streamlining, would intrude more deeply into the motorcycle’s established “image.”