New Atkinson-cycle engine has tumble-flow inlet ports and sky-high compression ratio.

Toyota City, Japan - Toyota has created a new series of highly fuel-efficient engines by focusing on combustion and loss-reduction technologies it's been refining for use in dedicated hybrid engines in cars such as the Prius.

The new engines will be used in models scheduled for mid-life upgrades and revision in the near future, with 14 new engine variations scheduled to be introduced globally by 2015; Toyota claims they will achieve fuel-consumption figures at least 10 percent better than current models.

One of the new engines is a 1.3-litre petrol engine using the Atkinson cycle - an old technology that Toyota has brought up to date specifically for dedicated hybrid engines. It uses a very high compression ratio (typically 13.5:1) to increase its expansion ratio and reduce waste heat, for improved thermal efficiency.


It also has inlet ports specially shaped to generate a strong tumble flow, whereby the air-fuel mixture flows in a vertical swirl, as used in Suzuki's Twin Swirl Combustion Chamber motorcycle engines of the late 1970s, combined with a cooled exhaust gas recirculation system and electronically-controlled 'intelligent' variable valve timing.

The aim is to use as much energy as possible to push down on the piston and send as little as possible down the exhaust pipe as heat and noise - which is simply pulses of vibration in the exhaust-gas flow.


Toyota is quoting near-record thermal efficiency of 38 percent for the new engines - i.e. 38 percent of the energy produced by burning the fuel is converted into work; the rest is lost as friction, and wasted to the air through the hot exhaust gases and the cooling system.

It says these features, combined with idle stop and other functions will reduce fuel-consumption by about 15 percent compared to current vehicles.

Meanwhile, sister company Daihatsu has come up with a one-litre engine using a similarly-shaped inlet tract, a high compression ratio and a cooled exhaust gas recirculation system to achieve maximum thermal efficiency of 37 percent.

Using idle-stop and various other fuel consumption reduction technologies, the small-engine specialist is forecasting a 30 percent reduction in fuel consumption compared to current models.