Nissan Variable Compression Engine

Nissan has developed a new engine mechanism that enables both high power of turbo engine and low fuel consumption of non-turbo engine.

	The newly developed piston/crank mechanism (multi-link type) enables optimum compression ratio control.
	For example, the fuel economy of a non-turbo engine and the power output of a turbocharged engine can be achieved in one engine.
	By the ideal piston motion of multi - link, significant vibration reduction has been obtained.

New piston crank mechanism
By applying multi-link mechanism, significant improvement of engine vibration coupled with friction reduction (basic condition of engine mechanism) have been obtained. And in addition, function of variable compression ratio control under engine running condition has been achieved.

Example of CR control (turbo engine)

The highest compression ratio is used in city driving to increase thermal efficiency for improved fuel economy. The system shifts to a low compression ratio for super charging when accelerating or climbing hills. This enables also higher turbocharging for much power while suppressing engine knock.

Low vibration nature of multilink mechanism

Piston motion in the conventional mechanism is essentially asymmetrical, with rapid motion occurring at top dead center. That unbalance deteriorates engine vibration in the case of conventional 4-cylinder engines.With the multilink VCR mechanism, the piston’s reciprocal action achieves ideal simple harmonic motion, resolving the unbalance. This enable low vibration property of in-line 4 cylinder engine close to that of V type 6 cylinder engines.

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Saab Variable Compression

Saab is now launching an entirely new engine concept named SVC, which stands for Saab Variable Compression. Owing to the SVC engine's unique design, it offers performance on a par with units twice its size but with the fuel consumption of a small engine. The SVC engine is a five-cylinder 1.6 litre unit producing 225 bhp, and it delivers no less than 305 Nm of torque.

What is unique about the SVC engine is that it features variable compression. In other words, the ratio between the piston's displacement volume and the volume of the combustion chamber is not constant, as it is in a conventional engine. Instead, the SVC registers current needs and decides how much the mixture of fuel and air is to be compressed in the cylinder prior to ignition. The upper part, the mono-head, can be inclined up to four degrees to achieve optimum compression, which means that the engine always works at its most efficient level.

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