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

Combustion piston

The MCE‑5 piston is very different from conventional pistons. In the worst case, it is subjected to a radial stress 5 times lower than what conventional pistons are subjected to, and this stress is on average 20 times lower and about 100 times lower at low loads. It is no longer oriented by a high piston skirt but by a shorter one with a specific profile that cooperates with the MCE5 synchronized roller. The MCE‑5 piston does not rotate around a pin like conventional pistons do, but is directly screwed onto the piston rack. This allows easy angular positioning of the piston during assembly, using an interface fixing sleeve and an internal stud bolt working in traction in the plastic range like a cylinder head screw. This assembly is highly robust and enables durable piston operation without any risk of loosening.

As opposed to conventional pistons, the MCE‑5 piston is not subject to tilting or piston slap. Piston tilting can impair the correct operation of the ring pack and lubrication and can also damage the cylinder. Tilting and piston slap increase noise, blow-by and oil consumption with different consequences on combustion (knock sensitivity) and pollutant emissions. It’s important to eliminate piston slap in a VCR engine since the vertical position of ring turnaround varies with respect to the cylinder, as a function of the compression ratio. This problem is eliminated by MCE‑5 technology.

The MCE‑5 VCRi piston is subjected to
an extremely low radial stress and is
not longer subjected to any piston slap

The MCE‑5 piston has a circular shape and is equipped with support wings that contribute to its cooling. Its regular shape limits heterogeneous and local distortions and their impact on the operation of the skirt and the ring pack. Combined with the elimination of tilting and piston slap, these characteristics should in future allow a reduction in ring tension. The MCE‑5 piston support wing is a heat sink directly positioned under the piston crown, making the MCE‑5 piston naturally cooler than a conventional piston and with better support under its hottest section. This feature is appreciable on engines with high specific power, such as VCR engines. The MCE‑5 piston is currently cooled by oil jets but thanks to its specific thermal characteristics, it could limit the use of this type of cooling system, with substantial gains in terms of the sizing and energy consumption of the engine’s oil pump.

The MCE‑5 piston has a standard ring pack. Its crown can accommodate any bowl shape or geometric particularity without impacting the engine height since the bowl cannot interfere with a pin (this notably explains the height of Diesel pistons). The MCE‑5 piston is currently made of the aluminum-silicon alloy normally used in the piston industry.

Different thermomechanical studies and tests have made it possible to better understand the MCE‑5 piston’s functional and behavioral characteristics and have led to an effective solution. This work was carried out taking into account all of the industrial and economic impacts to make its mass production possible in the short term.

The stud bolt and column mounting make it possible
to easily control the piston's final height and
rotational position, with no risk of loosening

The MCE‑5 VCRi piston is naturally "cold".
This provides it with excellent
thermo-mechanical resistance

The main characteristics of the MCE‑5 VCRi piston