Toyota Prius

A new hybrid system and platform enable the vehicle to compete with its combustion engine rivals

Range boosted

The new software allows the vehicle to draw more on its electric power as the range in which the electric motor is used exclusively has increased, and it also means that acceleration in low revs is possible.

As well as the motor is a 1.8-litre, four-cylinder gasoline engine. The third-generation Prius had the same unit, except that in several areas it has been improved.

The heat recovery system now makes use of the spent exhaust gas to speed up the warming of the engine. This means that the engine can be stopped earlier and more often when it is not needed to power the vehicle.

A large exhaust gas recirculation system with an EGR cooler lowers the temperature of the recirculated gas and contributes to thermal efficiency levels of 40%. That figure is an increase on the 38.5% of the 1.8-litre engine of the outgoing model, while the introduction of a water jacket spacer helps control cylinder wall temperatures in the combustion chamber, helping to minimise knocking.

Friction falls

Friction has been reduced through the use of thin-section, resin-coated rod bearings and low-friction camshaft chain, while the adoption of new springs has cut the valvetrain load.

The various measures have combined to make for an even more efficient engine, with the result that fuel consumption is at 3 litres/100km on the combined cycle and only 70g of CO2 are emitted every kilometre.

Engineers were able to redesign the transaxle so that it is 59mm shorter and allows for the auxiliary battery to be relocated to the engine compartment.

A DC/DC converter replaces the belt-driven alternator used previously to recharge the 12V auxiliary battery using energy from the hybrid battery.

Two completely new motor-generators are smaller and lighter than the ones replaced, but with higher motor speed and forced water-convection cooling efficiency they help the electric drive motor to deliver 53kW of power and 163Nm of torque.

Another major change in the development of the vehicle this time around concerned its architecture. It was the first model to have its chassis built on Toyota’s brand-new GA-C platform, which enabled engineers to make some significant improvements to the Prius.

Whereas before engineers would put considerable effort into millimetre adjustments to pack components most favourably, the new platform simplifies vehicle design.

Toyoshima was given licence to oversee the design of the platform on which the Prius was built. “I had the fortune to be allowed to start the Prius project before the platform existed,” he says.

“The chief executive told me that I should work on both the vehicle and the development of the platform so that we could create an even better car.

“I had the challenge that we had to catch up with European competitors in terms of driving performance and feel.”

tags: June 2016 Toyota Hybrids & EVs