Hybrid Alternatives For Motorcycles

After I worked on the chassis design for the Mission R electric bike, I decided to look at the possibility of a "hybrid" motorcycle. Most hybrid vehicles have two drive systems—internal combustion and electric—and on motorcycles this imposes serious weight and packaging compromises. At this point, I don't think conventional hybrid motorcycles would be very good.

But there’s another hybrid technology under development that could work well to create very interesting high-performance motorcycles. Starting in 2009, Formula 1 car racing allowed a hybrid system that provided supplemental horsepower, called KERS (Kinetic Energy Recovery System). Electrical (or mechanical) energy generated under braking is stored and then used to provide additional power under acceleration for short periods.

In 2014, a second hybrid element was introduced. In addition to the KERS motor/generator, there is now a second motor/generator, this one attached to the engine’s turbocharger. Under deceleration, when reduced exhaust flow reduces turbo speed, this motor spins up to maintain turbo rpm and keep boost near maximum. Turbo lag, the time needed for turbos to speed up enough to provide boost, has always been the turbo’s weak point. The new hybrid application virtually eliminates it.

At high engine and turbo revs, the electric motor attached to the turbo becomes a generator, generating electricity while working to slow the turbo and thus limit boost from becoming destructive to the engine. (A conventional wastegate is also used as a backup.) The electricity charges the battery for when the motor needs to keep the turbo’s speed up (or to help with the KERS energy distribution).

The illustration shows the Renault F1 battery (left), engine (center), and turbo (right). Nested in the engine’s vee is the turbo’s motor/generator, called the MGU-H by Renault.

Will we see such a system on motorcycles soon? Probably not, as the F1 setup is astronomically expensive. But there’s another version, using parallel ideas, that’s closer to production—the Volvo High Performance Drive-E Concept.

This engine is a 2-liter inline-four, with two small, conventional, exhaust-driven turbos mounted close to the exhaust ports for best efficiency. There’s also a third turbo (or at least the compressor half), but this one is exclusively electrically driven to eliminate turbo lag when the engine is at low revs and the exhaust-driven turbos would not be providing enough boost.

How well does it work? It makes 450 hp from 2 liters and has the bottom-end torque it needs to pull a heavy car around. What would something like this look like in, say, a Yamaha FZ-07? Although its engine is less than half the displacement of the Volvo project, mechanically it's much like half of the Volvo with its two cylinders, two cams, and four valves per cylinder. It would get one small exhaust-driven turbo and a smaller version of the Volvo electrically driven turbo. Add an intercooler and various upgrades to take the additional power and we'd have a little superbike.

At the power-per-displacement number of the Volvo, the little 689cc “FZE-07” would put out 155 hp and would likely have significantly more bottom-end torque than any literbike.

The lesson here is that this alternative hybrid technology can liberate turbocharging from its dependence on exhaust flow and engine rpm and do for bottom-end power what turbocharging has always done for top-end power. We can perhaps see the super-efficient F1 approach to hybrid turbocharging as the preferred future system, but Volvo has shown that we don’t have to wait to take that approach—we can have a workable system now.

Audi is also working with turbo company Valeo on what they call an electric supercharger. With Audi's involvement with Ducati, would that be a possible route to seeing hybrid turbos on motorcycles? Interesting times ahead.