MCE-5 VCRi: Pushing back the fuel consumption reduction limits

Its service life
is not compatible with that of a vehicle

Today, a vehicle’s service life must be roughly 300,000 km. Depending on the vehicle’s usage conditions, all of its components don’t age at the same speed so that some need to be changed during its service life. Under normal usage conditions, the engine must provide service without replacement. The MCE‑5 VCRi was designed to meet this need.

The MCE‑5 VCRi has been designed to provide
a totally safe usage on vehicles over
at least 300,000 km

The MCE‑5 VCRi gear system is the heart of the
innovation. After a normal running-in that
consummes a fraction of micron of material,
its contact surfaces are no longer
subjected to any wear

Simulation, testing under severe conditions,
validation on single and multi-cylinder test engines
are at the core of the numerous investigations that
enabled us to guarantee MCE‑5 VCRi service life

It’s only the MCE‑5 VCRi gears that make it different from conventional engines. The other components (connecting rod, crankshaft, piston) are highly loaded as is the case for modern Diesels but their sizing brings them into line with normal fatigue strength criteria. Their service life therefore remains identical to the one sold today. For their part, the MCE‑5 VCRi teeth offer a high fatigue strength and are unwearable.

The service life of any gear system is determined by the lubrication of its teeth, their fatigue resistance to bending and to surface pitting or micro pitting.

Faulty lubrication can lead to the rapid destruction of the MCE‑5 VCRi teeth due to seizing. No car engine can function for more than a few minutes without lubrication and the MCE‑5 VCRi is no exception. The proper lubrication of the MCE‑5 VCRi teeth has never been challenged, regardless of the engine’s usage conditions.

The resistance to repeated or alternating bending particularly concerns the gear teeth root: this root is subjected to strong tensile and compression stress. A well-designed and properly dimensioned gear has an almost “unlimited” service life for these criteria, as long as its fatigue resistance limit is not reached.

For optimum safety, we can consider that the material’s fatigue resistance limit is equal to 50% of its elastic limit. We can nevertheless get away from this reference by proceeding with fatigue tests. These tests are generally carried out on 107 cycles repeated one to three times. Alternating stress is the most severe (in one direction and then the other). At 6000 rpm, 107 cycles corresponds to 27 hours of operation of the MCE‑5 VCRi engine. There has never been a failure of the MCE‑5 VCRi observed on this point, after more than 3000 hours of testing.

Another point is the resistance of the teeth to pitting, which is a result of the Hertz pressure exerted on the teeth surface due to the lineic contact between the teeth (very localized contact). This contact pressure shears the material in the sub-layer, which must be able to resist the resulting stress. The maximum shear depth is an essential criterion to determine the material’s carburizing depth.

To limit the effects of Hertz pressure, the design of the local geometry of the tooth is vital, as is the alignment of the teeth with regard to each other. Many geometrical details can give the teeth a better fatigue resistance, in particular reducing the edge effects or the consequences of a possible misalignment. The alignment of the MCE‑5 VCRi teeth always remains “ideal” given the ability of the rack to “self-orient” with respect to the gearwheel. The optimization of the MCE‑5 VCRi tooth profile progressively led to ensuring the teeth’s excellent resistance to tangential stress and an optimum distribution of Hertz pressure all along their contact line and line of action.

In the end, the MCE‑5 VCRi gear transmission system has safety factors similar or higher to those usually selected for conventional engine moving parts. The MCE‑5 VCRi meshing and bearing system is the “strong link” in its powertrain.

The other MCE‑5 VCRi components such as the connecting rod, piston and crankshaft have a service life in line with that of the conventional engines.