The new Boon and Passo were released by Daihatsu Motor Co Ltd and Toyota Motor Corp, respectively, April 12, 2016. The fuel efficiency of 28.0km/L (approx 65.9mpg in the US) was realized by using fuel-saving technologies that Daihatsu developed for light cars. It is 1.5% higher than the fuel efficiency of the previous models.
This time, the compression ratio of the engine was increased from 11.5 to 12.5, significantly contributing to the improvement of fuel efficiency. It was realized by employing the “Dual Injector” and improving the “EGR (exhaust gas recirculation) System,” which improves fuel efficiency by recirculating exhaust gas.
The engine of the new vehicles is the “1KR-FE” 1.0L in-line three-cylinder engine, which is the same as the engine of the previous models. But the Dual Injector, which is used for the engine of Daihatsu’s “Mira e:S” light car, was employed. It injects fuel into the combustion chamber by using two injectors per cylinder.
The number of injection ports of the previous models’ engine is six per injector, but the number was increased to eight for the new models. As a result, the particle size of injected fuel was reduced. The shape of the suction port was changed so that strong tumble flows (longitudinal vortexes of air-fuel mixture in cylinders) can be generated.
Also, the Atkinson cycle was employed, and friction loss was reduced by changing the piston shape. Furthermore, the responsiveness of the EGR valve was improved to increase the amount of reused exhaust gas. The maximum output and maximum torque of the new engine are 51kW and 92N·m, respectively, which are the same as those of the previous models’ engine despite the improvement in fuel efficiency.