Automotive Engineer

The likelihood that future cars will rely on more than one power source is increasing. GM has already shown that combining a gasoline engine, electric motor and battery pack is a legitimate technology as OEMs try to reduce tailpipe emissions.

But GM’s powertrain is based on an engine that hasn’t been specifically designed for powering an electrical generator, and is probably happier feeding power direct to the wheels. 

It is only the first generation, and GM is working on improving the technology. Other OEMs and Tier One suppliers are also developing range-extender engines. It’s likely to be a growth market.

Lotus began its initial research project in 2009 as part of an electric city concept car for Proton called the Emas. It used a 1.2-litre, three-cylinder gasoline engine which produced 35kW of power. The vehicle was also equipped with a 16.5kWh lithium-polymer battery and an electric motor. The range was nearly 50km under battery power alone, and the total range using the range-extender engine was more than 500km. 

But preparing the engine for series production required further development. There are now two versions – a 38kW naturally aspirated and a 55kW supercharged version, and the monoblock design has been replaced.

Lotus chief product engineer Lee Jeffcoat says: “We’ve moved away from the monoblock because it’s perceived as a risk by customers. So we’ve become more conventional with a separate cylinder head and block, but we have been able to integrate other components. We’ve integrated the exhaust manifold and inlet manifold too.”

The original concept had a 6kg inlet manifold which Jeffcoat and his engineers thought was too heavy.

Capacity has also been increased to 1.3 litres, which allowed the runner length to be brought down to only 200mm. Size is an important aspect of the engine’s new design. 

Lotus, with manufacturing partner Fagor Ederlan, foresee production of up to 10,000 units a year, with interest received from both passenger and commercial vehicle manufacturers – although they don’t say who. “Cost and package are key issues,” says Jeffcoat. “In terms of size, the big change is the length, which has decreased by about 60mm. Part of that is because we’ve used an off-centre oil pump, which has given us 21mm alone.