Power comes from the same 4-cylinder, 1.8-liter VVT-i gasoline engine, but in this latest application it has been thoroughly revised and offers a thermal efficiency of 40% which according to Toyota is comparable to a diesel engine. This was possible by implementing a dual cooling system that automatically reduces the volume of coolant flow in the engine to achieve a quicker warm-up. In addition, the engine uses low-viscosity oil to lower frictions between the components. The engineers also fitted a coolant water selector valve that boosts engine warm-up during cold days while keeping the cabin heater performance.
In terms of output, the four-cylinder DOHC combustion engine is capable of developing 97 bhp (72 kW) at 5,200 rpm and 142 Nm (105 lb-ft) of torque at 3,600 rpm. It uses newly developed piston and air intake port designs that create a bigger tumble swirl inside the cylinder while the volume of the exhaust gas recirculation has been increased as well.
Toyota redesigned the transaxle and 73 bhp (53 kW) electric motor to lower mechanical losses through friction by approximately 20% thanks to a new multi-axle design. The transaxle’s length is now shorter and this was possible by installing the drive motor and electric motor/generator over multiple axles. There’s a loss-reduction device within the power control unit which has lowered losses by around 20% and thanks to its more compact design it now sits above the transaxle.
As far as the battery is concerned, it’s a new nickel-metal (NiMH) pack that now sits beneath the rear seats and it does not affect the trunk’s capacity which in this fourth generation has grown to 502 liters also helped by the fact that Toyota moved the auxiliary batteries from the trunk to the engine compartment.
Toyota has announced the all-new Prius will be on display starting October 28 at the Tokyo Motor Show in Japan.