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Technology File - Safety Technology

Engine (Atkinson-cycle)

<Maximum Thermal Efficiency> Global Top Level1

High thermal efficiency engine produces world-class fuel efficiency.

Toyota’s hybrid vehicles have the Atkinson-cycle engine, which offers superb thermal efficiency. They feature a wide lineup of Atkinson-cycle engines, from 1.5-liter engines to 3.5-liter engines. Among these, the 1.8-liter 2ZR-FXE engine used in the newest Prius (2015) has greatly improved thermal efficiency thanks to its increased cooled exhaust gas recirculation (EGR)2 flow, redesigned intake port shape, and cool air duct. It also uses the Atkinson cycle’s ability to increase the engine’s basic compression ratio, which determines the thermal efficiency, resulting in a compression ratio of 13.0 despite using regular gasoline.

  1. As of December 2015. Internal measurement value.
  2. EGR: Exhaust Gas Recirculation

The same engine is used in plug-in hybrid vehicles.

Cooled EGR

The flow volume of the exhaust gas is cooled by the electric EGR valve and is channeled into the intake manifold, decreasing pumping loss and engine cooling loss in the engine. In the new (2015) Prius the ERG distribution channels in the intake manifold have been redesigned to increase and equalize the amount of the recirculated EGR distributed into each cylinder, resulting in more efficient combustion.

Intake port shape optimization

The intake port provides cylinders with the air they need for combustion. In the new (2015) Prius, the shape of the intake port has been optimized to produce a more direct flow of air into the cylinder, strengthening its tumble flow3. At the same time, the piston head shape has been changed to maintain the same tumble flow strength while increasing combustion speed.

  1. Vertical swirl of air that promotes air-fuel mixture. The flow in the direction of the piston’s stroke is called tumble flow.

Cool air duct

Thermal efficiency is increased by efficiently drawing dense, cold air into the engine. The new (2015) Prius uses a compact, lower positioned air cleaner to support vehicle bodies with lower hoods. It also has a dedicated intake opening for drawing in large amounts of air when driving at high speeds.

Engine (Atkinson-cycle)
  1. The piston is depressed while the throttle is open, eliminating wasteful resistance.
  2. Valve delayed closure
    Excess intake is adjusted by delaying the timing of valve closure.
  3. Compression stroke/expansion stroke
    Highly efficient system which enables a longer expansion stroke than compression stroke.
* Conceptual image.

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