Also among the many debuts at Geneva Motor Show, Toyota unveiled its new 1.5-liter VVT-i engine, which powers the latest Yaris model. This four-cylinder petrol engine replaces the current 1.33-liter unit, developed in anticipation of future Euro 6c emissions standard and RDE homologation requirements.
In the new Yaris the naturally aspirated 1,496cc engine develops a maximum 110ps/82kW and peak torque of 136Nm at 4,400rpm. Compared to the 1.33-liter unit, it is 0.8 seconds quicker in acceleration from 0 to 62mph (11.0 versus 11.8), while at overtaking speed in fifth gear the improvement is more than a second, moving from 50 to 75mph in 17.6 seconds compared to 18.8.
The powerplant is said to have a 38.5% thermal efficiency value, achieved using a high, 13.5:1 compression ratio, a cooled EGR system and extension of the variable valve timing operation so that the engine can switch from the Otto to the Atkinson cycle to gain optimum efficiency in different driving conditions.
The higher compression ratio has been made possible by the combustion chamber design and new pistons, which promote a homogenous air/petrol mixture and rapid combustion. Cooled EGR reduces combustion temperature and also helps prevent engine knocking. Furthermore, the volume of reinjected inert gases allows for a reduction in pumping losses at low and medium loads, improving overall engine efficiency.
