Daihatsu to Launch Most Fuel-efficient Gasoline Vehicle

Jul 23, 2013
Motohiko Hamada, Nikkei Automotive Technology

Daihatsu Motor Co Ltd announced that it will use new technologies other than the "e:S Technology" for its "Mira e:S" light car, which will be partially remodeled and released in August 2013.

Together with the e:S Technology, the new technologies will realize a two-wheel-drive (2WD) vehicle that has a fuel efficiency of 33.4km/L (approx 78.6mpg) under the JC08 test mode, which is the highest efficiency of gasoline vehicles and higher than the efficiency of Suzuki Motor Corp's "Alto" (33.0km/L, the second highest efficiency), according to Daihatsu.

For the engine of the new vehicle, Daihatsu lowered intake-air temperature by cooling EGR (exhaust gas recirculation) gas. The company did not disclose whether the engine is cooled by water or air. It improved fuel efficiency by preventing abnormal combustion and advancing ignition timing to reduce the amount of injected gasoline. In addition, Daihatsu purified exhaust gas by lowering combustion temperature. And it changed the shape of the back side of the timing chain from a linear shape to a curved shape so that the area where it contacts the chain guide becomes smaller.

For the CVT (continuously variable transmission), Daihatsu made improvements to its operation so that it is used at lower reduction ratios.

Aerodynamic control
Daihatsu employed a design called "aero corner" for the front bumper so that wind coming from the front side smoothly flows to the rear side. With tire deflectors, the company prevented air from flowing around the front tires. Also, for the 2WD model, Daihatsu lowered its height by 10mm to reduce the amount of air coming under the vehicle and employed a floor cover to prevent air turbulence under the floor.

Idling stop
The previous model of the Mira e:S has an idling stop function that is activated when the vehicle slows down to 7km/h (approx 4.3mph) or 9km/h. This time, Daihatsu made changes to the restart operation of the engine. As a result, the engine of the new model can be stopped from a speed of 11km/h. When the gas pedal is released, fuel injection stops.

Daihatsu used an alternator having a high power generation efficiency to increase the amount of electricity generated at the time of deceleration. Also, the amount of electricity generated at the time of acceleration or constant speed running was decreased to reduce engine load.

4WD model
This time, Daihatsu even improved the fuel efficiency of the four-wheel-drive (4WD) model. It improved the final reduction gear on the rear side and replaced its hypoid bevel wheel with a spiral bevel wheel. Because the new gear does not have offset, it became possible to reduce the sizes of the components that cause slippery wheel surface and reduce frictional resistance. And the company replaced the high-viscosity lubricant inside the final reduction gear with a low-viscosity one to reduce resistance to stirring. When a spiral bevel wheel is used, the height of the propeller shaft becomes high. In consideration of this drawback, it can be said that Daihatsu took drastic measures, giving priority to fuel efficiency.