Friction losses

VCR engines are inevitably more complex than conventional engines. However, despite their complexity, VCR engines must present friction losses that are at least comparable or even lower than those of conventional engines. If it is not the case, additional friction losses will reduce Fuel Consumption provided by VCR strategy, particularly when operating at low loads (most of the time).

Two main strategies exist for controlling Compression Ratio:

	1)	Controlling the engine Compression Ratio by moving its static parts (cylinder head, crankcase, bearings line): this permits keeping conventional engines’ moving parts. In this case, added friction losses will remain restricted to those generated by the CR actuator. This strategy has been retained on articulated cylinder heads, crankshafts on eccentrics, or additional pistons in cylinder head.
	2)	Redesigning the engine’s moving parts to allow CR control: this can be the opportunity to increase their mechanical efficiency. This approach can compensate for VCR complexity and CR actuation and can lead to reduced friction losses compared to those of conventional engines.

Whatever the strategy for designing moving parts, it is necessary to implement low energy consuming Compression Ratio actuators on VCR engines.

Conclusion

Because of possible additional friction losses, Variable Compression Ratio strategy Fuel Consumption reduction will not be the same depending on the chosen VCR engine design and associate actuators. Friction losses induced by VCR engines complexity and CR actuation could be compensated or even over-compensated by replacing conventional moving parts by high efficiency mechanisms.

Whatever the case, low energy consuming actuators are required.

(see: The MCE-5 technology response to VCR engines’ friction losses requirements)