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Kawasaki is Looking at Hybrid Powertrains for Motorcycles

Combining Petrol and Electricity Is the Best of Both Worlds

While hybrid powertrains are common in cars, they have yet to catch on in motorcycles. Kawasaki has been working on the idea for some time and the surprising thing is that the petrol engine is actually a two-stroke.

The Rise Of The Hybrid Motorcycle

Kawasaki is Looking at Hybrid Powertrains for Motorcycles
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Kawasaki Hybrid
Using a petrol engine and an electric motor gives the best of both worlds, without the need for heavy batteries

You can’t open a motorcycle magazine these days without news of someone trying to reinvent the wheel. Or, in this case, the engine.

Kawasaki seems to be reinventing the 2-stroke. Not only that but they are thinking strongly about a hybrid option as well as supercharging…on the same engine.

There are two types of hybrid engine; series and parallel. In a parallel hybrid, the electric motors assist the combustion engine, which remains the primary motive power.

In a series hybrid, the electric motors alone drive the wheels, and the combustion engine acts solely as a generator to provide the electricity. This is the method Kawasaki is using.

The problem with that, is that often the engine isn’t running at optimum speed and therefore efficiency as it tops up the battery. Kawasaki’s solution is different in that it is a high performance engine that can be vastly more efficient and cleaner running because it will constantly operate at its most efficient speed.

But, hang on; if the engine is two stroke, isn’t that a ‘dirty’ engine? Not in Kawasaki’s new design. To understand this, we need to understand how a 2-stroke traditionally works.

In conventional 2 stroke designs, the downward motion of the piston pressurises the air/fuel/oil mixture in the crankcase which then is transferred via ports in the cylinder wall into the combustion chamber ready to be squeezed by the rising piston (hence ‘2-stroke’- two strokes of the piston making up a power stroke, as opposed to four strokes of the piston making a power stroke in a four-stroke engine).

Kawasaki is Looking at Hybrid Powertrains for Motorcycles
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The Kawasaki design uses conventional ‘poppet’ valves and twin overhead camshafts to operate them, as found on a four-stroke engine. But it’s still a 2-stroke and it’s the supercharger that makes all the difference here.

The supercharger performs the same role as the downward motion of the piston in a conventional 2-stroke, by compressing the air before it enters the combustion chamber whilst forcing the exhaust gases out of the chamber at the same time. To do this, both intake and exhaust valves need to be open at the same time which, in turn, means that direct fuel injection is needed, to inject the fuel when both valves are closed, meaning no possibility of unburned fuel escaping the chamber through an open exhaust valve. It also means that a conventional lubrication system can be used so no lubricating oil is burned.

Being a two stroke, there is a power stroke every 360° of crankshaft rotation as opposed to every 720°.

Now there’s a new complication. If we assume a four-cylinder engine, using a traditional flat-plane crankshaft, two cylinders would fire simultaneously, which increases vibration and stress on the engine due to the very short firing intervals between the two pairs of cylinders.

By adopting a cross-plane crank, all the combustion events are spread evenly, with one cylinder firing every 90° of rotation of the crankshaft, smoothing things out considerably.

So far, so good. But we all know that it is the batteries of an electric vehicle that weigh the most, so where’s the advantage? Well, by carrying your generator with you, you don’t need large batteries. In fact, you don’t need batteries at all; set of super capacitors - in effect, a short-period storage solution - can be used. So, instead of a clutch and gearbox running off the end of the crankshaft, the engine has a generator at each end of the crankshaft, producing electricity to power an electric motor attached to the rear wheel. To take this bit further, you could also have an electric motor on the front wheel as well, making the bike a 2X2.

We know that the internal combustion engine’s days are numbered, but a system such as this could be a stay of execution. A four-stroke engine’s efficiency is said to be around 50%, i.e. it converts half the energy stored in fuel to propulsion. Experts believe that a two-stroke engine can reach 60-70% efficiency. Combine that with external factors such as electricity generation, distribution and battery charging for electric-only vehicles and the hybrid system could reach parity with the 95% efficiency of electric motors (that is, converting 95% of energy into propulsion).

Not only that, but a hybrid solves all the problems of range by eliminating re-charge times. With technology such as this, maybe the future of personal transport isn’t as clear-cut as we think!

Harry Fisher
Harry Fisher
Motorcycling Contributor
Born and raised in England, he has lived in South Africa with his family since 2002. Harry has owned examples of Triumph, Norton, BSA, MV Agusta, Honda, BMW, Ducati, Harley Davidson, Kawasaki and Moto Morini motorcycles. He regrets selling all of them.  Read full bio
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