Friction losses

Thanks to its innovative arrangement, the MCE-5 VCR engine-block gives new opportunities to reduce main engines’ friction losses sources.

The MCE-5 provides a first friction reduction source thanks to its exclusive roller-guided piston: instead of beeing guided only by a skirt as it is the case for conventional engines, the MCE-5 piston is also guided by a synchronized roller located below in the crankcase.

Conventional piston	MCE-5 skirt contact area and synchronized roller contact surface
MCE-5 piston

This arrangement permits highly reducing the heigth of the piston skirt. As a result, piston skirt energy consumption coming from hydrodynamic resistance is reduced. On the other hand, as rod thrust is assumed by a synchronized roller instead of the skirt, piston slap and piston radial stress are eliminated.

Both piston slap and piston radial stress generate friction losses. The following graphs show the difference between the piston radial stress generated by a conventional modern 2L SI engine (max. power 100 kW) and that of a MCE-5 1.5 L engine (max. power160 kW):

Modern 2L SI engine: rod mass 570 g, piston+pin mass: 400 g, bore: 86 mm, stroke: 86 mm.
MCE-5 1.5 L engine: piston mass: 753 g, roller mass: 66 g, bore: 75 mm, stroke: 84 mm)

From the friction generation point of view, it is interesting to compare the respective product of piston radial stress by piston speed generated by the two engine concepts:

As the MCE-5 roller-guided piston eliminates piston radial stress and piston slap, it reduces cylinder wear and distortion and gives new opportunities to reduce rings’ tension. This approach is highly efficient to reduce friction losses, particularly when applied to the oil ring:

The opportunity to reduce rings’ tension and resulting friction losses is mainly due to the fact that the MCE-5 roller-guided piston preserves bore cylindricity: this ensures a well distributed ring/cylinder pressure and an improved sealing and oil consumption control during the whole engine life:

Another potential friction reduction source is due to the big-overlap and rigid MCE-5 crankshaft (its crank radius is reduced by half). Indeed, hydrodynamic bearings diameter could be reduced thanks to an improved natural crankshaft rigidity (this opportunity is under study).

However, the MCE-5 mechanism adds a new friction losses source that doesn’t exist on conventional engines: gears. Depending on instantaneous tangential stress applied to their teeth, the MCE-5 spur gears present an efficiency that always remains between 99.2 and 99.7%. Thanks to their high efficiency, the MCE-5 spur gears guarantee an advantageous final friction losses balance to the entire engine block.

Conclusion

The MCE-5 VCR technology opens the way to several strategies to reduce friction losses:

	1)	Ultra-short skirt
	2)	No piston radial stress
	3)	No piston slap
	4)	Low-tension rings (potentially)
	5)	Smaller diameter bearings (potentially)

(see: VCR engines’ requirements for mass-production: friction losses challenges)