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

It’s robust and reliable

Automobile internal combustion engines must have three essential qualities: robustness, reliability and durability. Robustness expresses the engine’s ability to deal with exceptional operating conditions without failures. Reliability reflects the number of failures or breakdowns per kilometer or per year. Durability reflects the ability of the engine to ensure a service over a high level of mileage.

Single cylinder and multi-cylinder MCE‑5 VCRi
engines are subjected to severe endurance
tests and extreme loads

Highly advanced simulation tools are used to
maximize the service life and resistance to extreme
loads of MCE‑5 VCRi specific components

Various specific test benches made is possible
to isolate and study MCE‑5 VCRi sub-assemblies

The endurance limits of MCE‑5 VCRi components are
studied using specific test benches capable
of largely surpassing targeted max loads

These three notions are potentially interlinked. For example, will the engine remain reliable after having operated in exceptional conditions? Will its life cycle be reduced because of this? Do breakdowns result in a reduction in life cycle? These are questions that will have to be answered upstream to avoid that end users face disappointments.

Engine validation is necessary in order to answer these questions early on. This means that endurance tests must be run in different load, power and temperature conditions. These tests can either represent final usage, be run in severe conditions or be destructive. Destructive tests make it possible to evaluate the available safety margins. There exist all types of alternatives in these three test categories. However, even when these tests have been completed, the risk of failure unfortunately still remains, which is why car mechanics exist. These residual risks must be minimized in any way possible.

Robustness, reliability and durability are very serious topics that no carmakers would take risks with, since their profitability (warranty insurance), reputation and market share depend on them.

We often associate complexity with the loss of reliability, which can sometimes be the case but in the automotive industry, it’s generally the opposite. Today, cars are much more complex than they were in the past and yet they are also much more reliable. When we think of the past, we remember cars on the side of the road when the weather was too hot, too cold or too damp. Many “complex” solutions have resulted in clear improvements in reliability. For example, when we electrified cooling fans, we made them more complex compared with simple fan blades fixed to an engine pulley. By doing this, we improved engine reliability by avoiding any overheating leading to a breakdown. We also considerably reduced the energy loss linked to this function. There are hundreds of similar examples in automotive technology.

Tests are not the sole elements in the reliability process. Computing advances and new numerical simulation tools now allow us to largely anticipate the reliability of the mechanical parts before they are made. The development of MCE‑5 VCRi was massively based on these tools and, moreover, the MCE‑5 VCRi mechanism could not have been built without them. Once the MCE‑5 VCRi parts made, they were duly tested to characterize their fatigue strength and safety margins. The tests enabled us to recalibrate the numerical models to continuously improve the reliability of the simulations. These processes led to the excellent behavior of the MCE‑5 VCRi mechanical components.

Robustness, reliability and durability have always been at the focus of the MCE‑5 VCRi R&D process, especially since hard downsizing-downspeeding is the main objective of VCR, which leads to high mechanical and thermal loads. These severe operating conditions demonstrate the relevance of the MCE‑5 VCRi technology.

Indeed, under high load, MCE‑5 VCRi offers decisive advantages compared with standard engines. Firstly, the MCE‑5 VCRi piston and cylinder are protected from the side forces exerted by the conrod. This is due to the mechanical dissociation of two essential functions: gas thrust is applied to the piston, and then transformed into torque available on the crankshaft through a pure rolling system. As the MCE‑5 VCRi is a highly-loaded engine, these dissociated functions allow it to bear both high BMEP (Brake Mean Effective Pressure) and high maximum in-cylinder pressure without harming the durability or reliability of the piston-liner assembly and without increasing FMEP (Friction Mean Effective Pressure). The task of the MCE‑5 VCRi piston is therefore simplified: it’s a simple “pushrod”. Consequently, parasite movements and piston distortion are reduced, which favors the correct operation of the ring pack. Another positive point: the MCE‑5 VCRi piston is naturally better cooled due to its architecture.

People are generally concerned about the robustness, reliability and durability of the MCE‑5 VCRi gear system and yet this system is its strong point. The MCE‑5 VCRi gear system is sized in terms of fatigue to ensure service for several billion cycles, i.e. well beyond the service life of an engine. What’s more, this system has proven its ability to take on very high exceptional loads, of over 250 bar, and yet in a commercialized engine, these exceptional loads are hard to reach in practice. Even if the endurance tests are still underway and not completely finished, thousands of hours of testing of MCE‑5 VCRi on a test bench have already provided maximum guarantees.

For all of these reasons, MCE‑5 VCRi is intrinsically very robust and highly reliable. It is designed for a long service life, at least equivalent to those of modern gasoline and Diesel engines.