Kawasaki’s Semi-automatic Transmission Revealed

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As seen at the Suzuka 8 Hours roadrace, Kawasaki is deep into development on a hybrid motorcycle. (Auto-By Magazine/)

Kawasaki recently previewed its upcoming hybrid-powered production bike at the Suzuka 8 Hours race in early August, and one of that bike’s notable features was the lack of a clutch lever or a gearshifter. Now, a new patent application from the company shows how that was achieved, and gives us a clear look at the layout of the bike’s twin-cylinder engine and the electric motor that should give it 650cc-class performance with the economy and emissions of a bike with much less displacement.

While other companies have dabbled in hybrid-bike concepts before—notably Piaggio, which sent the MP3 Hybrid to production way back in 2009 but later discontinued it, and Yamaha, which has shown several hybrid concepts—Kawasaki’s take on the idea is the most intriguing yet. Rather than targeting scooter riders or tech-mad early adopters, it appears to be intended as a machine that offers genuine advantages over the status quo for the future of motorcycling.

Related: Yamaha Back in the Hybrid Game

Patent drawings show the combined internal combustion engine and electric motor. (Kawasaki/)

At the moment, Kawasaki is steadfastly refusing to release any technical information about the machine, but a near-production-ready version is expected to appear at the EICMA show later this year. What we can gather from the two prototypes that have been seen in public so far—one last year, and a more finished version at Suzuka—is that it uses a parallel-twin engine that appears to come straight from the Ninja 400 and Z400, bolstered by an electric motor that looks large enough to offer a big performance boost when engaged.

The new patent application gives a detailed look at the powertrain unit, including both the combustion engine and electric motor. Combined as a single unit, the powertrain starts to make more sense, taking up little more space than the combustion engine alone, while adding the potential of much more power when the electric motor is thrown into the mix. While the patent doesn’t show the battery pack needed to run the motor, we know from seeing the prototype that it’s not large. As with many hybrid cars, the intention isn’t to be able to run for hundreds, or even dozens of miles in electric-only mode. Instead, it will have the ability to cover short distances at relatively low speeds on battery power alone, ideal for short hops in the city, while allowing the combustion engine to operate in scenarios like higher-speed cruising where it can work in its most efficient range and simultaneously recharge the battery. And when you need all the power, both can work together.

A side view shows where the electric motor that operates the servo controls resides. (Kawasaki/)

From the new patent application, it appears that the liquid-cooled electric-drive motor (marked “M” in the drawings) which sits atop the transmission, is geared to the transmission’s input shaft, like the combustion engine, so both powertrains drive through the same six-speed gearbox. That’s why Kawasaki has implemented a semi-auto, push-button gearshift rather than a conventional hand-operated clutch and foot-controlled lever. The idea is that, thanks to the bike’s on-board computer, the electric power and combustion-engine power can be juggled automatically, and by using a computer-controlled clutch and shifter you should get smooth gear changes regardless of what combination is being used.

The clutch and gearshift themselves are relatively conventional, just with servo controls. The shifter has an additional electric motor, mounted low down behind the transmission (labeled “30″). It drives through a series of six reduction gears to multiply its torque, ending with a fan-shaped partial gear (G6) that’s attached to the gear change shaft where you’d normally expect to find a foot-operated lever. The fan shape of that final gear is chosen because, like a normal gear lever, it only has to move a few degrees in either direction to change ratios, so there’s no need for it to be a full circle.

The fan-shaped partial gear attaches to the shift shaft where a traditional foot-operated lever would normally be. (Kawasaki/)

The real key to the system will be the computer controller that operates it. We’ve seen in previous patents how Kawasaki has developed a “boost” button to use on the right-hand bar, allowing you to manually engage both the electric motor and combustion engine together for maximum performance, but in other scenarios the switch between gas and electric power is expected to be automatic. With the semi-auto, servo-controlled shifter and clutch it should be possible to make a fully automatic mode where the bike changes ratios itself, but Kawasaki’s prototype also has buttons on the left-hand bar for manual gear changes. During shifts, the throttle, fueling, and clutch of the combustion engine will have to be controlled, but so will the torque output of the electric motor, so the computer’s ability to do both in a manner that the power delivery feels smooth and predictable will be one of the key challenges to making the system unobtrusive, while retaining the high level of rider control that we’ve come to expect from conventional manual transmissions.

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