Toyota Claims 13% Fuel Economy Gain with Atkinson/Otto Engine

Toyota Motor Corp. has introduced a 2.0-liter gasoline for its Corolla sedan in Europe that runs on an Atkinson cycle at low speed and automatically switches to conventional Otto cycle operation at higher speeds.

The system, coupled with a 6-speed automatic that replaces the previous 4-speed gearbox, is 13% more fuel efficient than the outgoing powertrain, according to the company.

The new engine features a variable valve timing "intelligent wide" system that uses a camshaft lock mechanism to retard the powerplant's otherwise continuously variable valve timing. The effect is to reduce the compression ratio but retain the expansion ratio, something a traditional Atkinson cycle engine does with an articulated piston connecting rod.

To improve fuel efficiency, the Toyota engine uses roller rocker arms, a low-friction timing chain and a fuel system that employs direct fuel injection alone or in combination with port injection, depending on engine speed.

Revised combustion chamber architecture improves cylinder block and head cooling, enhances anti-knock performance and enables a 12.8:1 compression ratio, Toyota says.