Noise emissions

The MCE-5 noise emissions can be summed up in 3 main points:

	1)	MCE-5 eliminates two major noise emissions sources: Piston slap; Cylinder-liner excitation.
	2)	MCE-5 doesn’t change or even reduces noise emissions coming from: Engine block (highly rigid); Crankshaft (highly rigid).
	3)	MCE-5 adds a new noise emissions source: Gears.

As a result, main studies related to MCE-5 noise emissions focused on gears.

There is a strong relation between MCE-5 gears noise emissions and gear teeth normal backlash: the higher the normal backlash (mechanical play), the higher the noise emissions. This fact is well illustrated in the following graphs resulting from various vibroacoustic measurements:

The challenge for MCE-5 is to reduce as far as possible the normal backlash. To reach this objective, high precision is required for gears (7 quality class - ISO norm 1328). To keep a sufficient room for maneuver, mass-production costs have been calculated for 5 quality class gears (a higher quality class).

Several geometrical optimizations are required for the MCE-5 gears to reach an ultra-small normal backlash. These optimizations are described in a SAE paper available on the SAE website (www.sae.org). This publication is titled «Gear design and dimensioning study for a Variable Compression Ratio engine» and results from studies carried out under collaboration between the MCE-5 Development Company and the CETIM (French Industrial and Mechanical Technical Center).

If a 0.03 mm operational normal backlash is required to reach noise level comparable to that of conventional engines, the normal backlash target for MCE-5 mass-production is between 0.015 and 0.02 mm: such a small play presents no problem because the MCE-5 racks are self-oriented.

An additional challenge for noise control is to minimize the wheel clearance «C» (which also determines the gear teeth normal backlash), taking into account thermal expansion differential between the engine block and the moving parts:

A simple nut-locknut system permits compensating all components machining variations when assembling the engine. This system now integrates a new function to automatically compensate for thermal expansion differential without generating overload or unexpected stress. This permits reaching ultra-small final operational normal backlash for gears.

Ultra-low play ensures the MCE-5 a near-to-silent operation.

Conclusion

Thanks to the absence of piston slap and liner excitation, the MCE-5 eliminates a major noise emissions source. Its rigid crankcase and crankshaft are favorable to low noise emissions, and its gears emit ultra-low noise below a 0.02 normal backlash:

The MCE-5 could become one of the most silent existing engines.

(see: VCR engines’ requirements for mass-production: noise emissions)