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

Carmakers already
have working VCR solutions available

It’s very easy to imagine a VCR system whose only given constraint is to vary the volume of the engine’s combustion chamber. It is however difficult to imagine a VCR system that meets all the functional, economic and industrial criteria.

As relevant as it is, the multilink solution is
not enough to make a real difference
for conventional engines

When we imagine a VCR engine, we’re immediately tempted to take the simplest and shortest route to reach the final result, with front-facing solutions. These solutions generally take the shape of engine block lifting systems with slide rails or hinge joints, a piston introduced in the combustion chamber, various eccentrics or multiple conrods (multilink).

Multilink engines appear to be the most effective solution evaluated to date and carmakers’ most developed VCR engines are based on this principle. As relevant as it is, the multilink solution is not enough to make a real difference for conventional engines: they are overly sensitive to friction and load. An optimized GDI turbo engine will potentially be better and the gain obtained from VCR will be potentially very low or nil.

The emission reductions that we hope to achieve from VCR are not as high as we imagine compared with an optimized GDI turbo engine of the near future. For small vehicles, we’re talking about 8 to 10g of CO2/km. For large vehicles, the decrease will range from 25 to 30g of CO2/km. These few grams of CO2/km not emitted will nevertheless have a decisive value in future. No technology other than VCR is able to reach for those last grams of CO2/km, and there will be some very attractive savings for both the end user and the carmaker.

The MCE‑5 VCRi meets all the main criteria determining the effectiveness of VCR

The elimination of these last grams of CO2/km is based on a particularly high difference in the specific performance between conventional GDI turbo and VCR. We would have to reach 35 to 40 bar of BMEP (Brake Mean Effective Pressure) instead of 23 to 25 for fixed compression ratio GDI turbo engines. We would also have to obtain 130kW/L or 150 kW/L and even more with in-cylinder pressures in the order of 120 to 130 bar, which becomes more difficult for conventional engines to reach if they maintain an acceptable compression ratio and remain within a normal speed range. Despite these specific performance ambitions, VCR engine friction losses must not increase in comparison with those of conventional engines.

When we list the characteristics that a VCR engine must have, there is very little room to maneuver and the functional needs are important. It’s the main reason why no VCR engines have been industrialized to date. The other reason is that it was urgent to first produce GDI turbo engines, to push them to their efficiency limits and then to produce VVL systems (variable valve lift). It was only then that the time came for VCR, subject to the availability of a technological solution making it worthwhile.

Carmakers do indeed have VCR solutions that work and are available. It’s not sure that they work well enough to justify their mass production. Solid guarantees are necessary in order to produce millions of VCR engines. These guarantees have not yet been provided by any other VCR engine and this is what makes MCE‑5 VCRi technology so important. MCE‑5 VCRi technology provides these guarantees since it was built on two lessons learned from other VCR engines: “what must be done” and “what must absolutely be avoided”. Empowered by the application of these two lessons, MCE‑5 VCRi technology is by far the most effective VCR technology that exists.

The strength of MCE‑5 VCRi is the way it meets all the functional
expectations of VCR, regardless of the strategies implemented