Yamaha Previews XMAX SPHEV Hybrid

While electric vehicles have yet to take over the roads, the steppingstone of hybrids, which combine electric motors and conventional combustion engines, has become vastly popular among car manufacturers and customers. Motorcycle companies have taken note too, with Kawasaki getting in on the action with its Ninja 7 Hybrid and Z7 Hybrid machines, and Yamaha looks like it could be next to join the fray.

Yamaha has released a video demonstrating its prototype hybrid XMAX SPHEV, which takes the form of a midsize scooter and uses a series-parallel hybrid system that can combine combustion engine power and electric drive in a variety of ways.

Just like Kawasaki’s hybrids, the Yamaha machine can work as a zero-emissions, all-electric machine—for example, in cities with zero-emission zones—or use the combustion engine to directly drive the rear wheel, like a conventional scooter. Beyond that, it can also use the combustion engine as a generator, disengaging it from the wheel but using it at a fuel-efficient, low-emissions constant speed to recharge the battery, or like the Kawasakis, it can combine the output of both the electric motor and the combustion engine for more performance than either powertrain could provide on its own.

The layout, illustrated in Yamaha’s video, includes a simple single-cylinder engine, mounted just ahead of the swingarm pivot with its cylinder parallel to the ground. It’s connected to the rear wheel via a clutch and a belt drive on one side, and to a generator on the other end of its crankshaft. The electric drive motor is attached at the back of the swingarm, connected directly to the rear wheel, and doubles as another generator to provide a regenerative braking effect, replenishing the battery under deceleration. The battery itself is toward the front of the bike, between the rider’s feet, along with an inverter and control electronics.

Just like a hybrid car, the bike’s advantages are the ability to minimize fuel consumption and emissions but with a much smaller, lighter battery than an all-electric vehicle could use. Because it can run using the combustion engine rather like a conventional bike, with the electric motor to assist it (parallel hybrid), and that engine can also charge the battery like a range extender (series hybrid), the system is known as series-parallel hybrid.

Kawasaki might be the only major bike company with a hybrid on the market at the moment, but Yamaha has been working on hybrids for at least the last 20 years. As long ago as 2005 the company revealed the Gen-Ryu concept bike at the Tokyo Motor Show, using a four-cylinder R6 engine alongside a hybrid battery and transmission, and in 2009 a nearer-production hybrid called the HV-X was unveiled at the same event, complete with video of it in action. Both those machines used epicyclic transmissions like the design in the Toyota Prius to cleverly blend ICE and electric power and provide a continuously variable gear ratio.

More recently, Yamaha has filed patents for a pure series hybrid motorcycle, with the combustion engine as a range extender on an otherwise all-electric powertrain, but the new design, with its series-parallel setup, could be a best-of-both-worlds solution. It’s also simple, which should help keep costs down if the project makes the step from prototype to production.