Infiniti’s Variable Compression Engine – A World First

Infiniti has produced the world’s first production variable compression ratio engine. Called the VC-Turbo, this remarkable engine simultaneously achieves high efficiency and high power within the same block. By utilizing a sophisticated multi-link system, the VC-Turbo continuously varies piston positions. This makes it the world’s first production engine to achieve both high power and high fuel efficiency – two characteristics that ordinarily oppose each other.

Variable compression makes it possible

The folks at Warren Henry Infiniti (Miami) explained the technical details to us. They said that with gasoline engines, higher compression ratios yields greater efficiency; however, there is a limit to the compression ratio that can be used. This is because pre-ignition can occur due to the rise of mixture air temperature.

With a conventional engine, because the pistons and crankshaft are connected directly by the connecting rod, the compression ratio is fixed. However, with Infiniti’s VC-Turbo engine, a multi-link system in place of a traditional connecting rod and an actuator motor changes the system endpoints in order to vary the pistons’ reach thereby chnging the compression ratio. All this mechanical magic makes it possible to vary the compression ratio continuously as needed within the range of 8:1 (for high load) to 14:1 (for low load).

Now add a turbo

Infinit’s VC-Turbo engine also sports a newly developed high-efficiency, wide-range turbocharger and electric waste gate. This allows precise control of the boost pressure with minimal turbo lag to generate on-demand output. Under low load, the electric Valve Timing Control (VTC) continuously adjusts valve timing to reduce pumping loss. It realizes high fuel efficiency in combination with higher compression ratio.

Decades of research

Research for the VC-Turbo was started by Infiniti in 1998. Several methods were tested to change compression ratios “on the fly.” The winning system used mechanical links with precision part shapes and high-precision heat treatments.

The remarkable VC-Turbo engine will first appear in the 2019 Infiniti Qx50 models.

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