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The development history of a 30cc 2-stroke engine power unit in the covered rear wheel for retrofit into standard bicycle chassis. The rear wheel acts as cooling fan for the air cooled long stroke engine with catalyst exhaust system, autochoke carburetor, autolube oil pump, electric start and inertia start, single speed automatic transmission and 7 speed hub final drive. The space in the rear wheel contains intake air filter, exhaust system, fuel tank, oil tank and engine with drive train, the complete engine being only 94mm wide. The complete covered power unit is nearly undetectable as the rear wheel covers resemble road racing bicycles. There is very low stationary and pass-by noise (64 db[A]), no exhaust gas opacity or smell, very low vibration level and very good fuel economy up to 133 km/l.

A new hybrid concept is applied to a small carburetted lean burn 2-stroke engine where, according to the underlying patent, the asynchronous motor is mounted on the ICE crankshaft, to provide increased torque during acceleration, lower and stabilise idle speed, replace the electric starter, act as a speed limiter, recover energy during deceleration and to provide the power for the electrically heated catalyst. The paper describes the mechanical development, the redesign of the thermodynamic parts of the donor engine, the light-off optimisation of the electrically heated catalyst, the electric and electronic development including ECU, power electronics, sensors, battery management, mapped ignition system and control strategies. The results show acceleration performance at par of a 50% bigger engine, ULEV level emissions including cold start, and no visible smoke or smell and very low particulate emissions very short after the cold start.