OREANDA-NEWS. The Prius retains its 1.8-liter VVT-i equipped Atkinson cycle petrol engine (2ZR-FXE), which is perfectly for highway driving needs. However, the engine has been completely re-engineered, with remarkable results in terms of performance, fuel economy, and reductions to size and weight.

The new engine achieves a maximum thermal efficiency of 40 percent?the world's highest level in a mass-produced gasoline engine (as of October 2015, according to in-house research). This improvement was enabled in part through the use of a large-volume exhaust gas recirculation (EGR) system and improvements in combustion efficiency. Additionally, a redesigned air intake port improves airflow inside the combustion chamber, while the coolant passages have been redesigned to optimize internal engine temperature. The friction created by the piston skirts, rotating parts and the oil pump has been reduced, while the use of low-viscosity oil reduces friction between sliding engine components.

Key components of the hybrid system?including the motors, transaxle, power control unit and hybrid batteries?are now smaller and lighter, improving fuel efficiency and making excellent use of space.

The transaxle also boasts a more compact design, and achieves approximately 20 percent loss reduction compared to the current Prius. This was made possible due to multi-shaft positioning of the motors, along with the relocation of the final drive reduction gear onto the same axis as the drive motor.

The two all-new motor-generators in the Prius boast higher output density, with size and weight reduced to suit the multi-shaft transaxle design without affecting fuel economy. Both motors feature an innovative rolling-coil structure.

Improvements to the power control unit, including the use of low-loss components, have resulted in a 20 percent reduction in electrical losses, and a more compact design enables the unit to be positioned directly above the transaxle. The auxiliary battery has been relocated from the luggage area to the engine compartment. The relocation of the hybrid batteries to the space under the rear seats also increases the capacity of the luggage area by 56 liters, bringing the new total to 502 liters.

For the first time, the Prius has market-specific hybrid batteries?either Nickel-Metal Hydride or Lithium-ion. Positioned under the rear seats, these high-performance, compact batteries contribute to improvements in fuel efficiency.

Fuel efficiency is also boosted by improvements to heating performance. An automatic grille shutter has been added to open and close the grille as necessary in response to outside temperatures. The exhaust heat recirculation system has also been improved and made more compact. This recycles exhaust heat from the engine into the coolant to be reused in the heaters and to warm the engine. Cold weather fuel efficiency has also been improved by introducing an engine coolant selector valve and adding a new system which accelerates engine heating.