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Downsizing and downspeeding are two efficient strategies to reduce vehicles CO2 emission, provided that high BMEP can be achieved at any engine speed under clean, safe, stable and efficient combustion. With a 6:1 minimum compression ratio, the MCE-5 VCRi achieves 40 bar peak BMEP at 1200 rpm with no irregular combustion. If peak BMEP is maintained below 35 bar, fuel enrichment is no longer necessary. When running at part loads, the engine operates at high compression ratios (up to 15:1) to minimize BSFC and maximize the sweet spot area on the map. Next generation MCE-5 VCRi engines will combine VCR and stoichiometric charges, highly diluted with external cooled EGR, in order to improve part loads efficiency by means of both the reduction in heat and pumping losses, and the optimization of compression-expansion ratio. This strategy, added to downsizing-donwspeeding, requires high-energy ignition systems to promote repeatable, stable, rapid and complete combustion.

The MCE-5 VCR engine includes a gear mechanism, which transmits the piston motion to the crankshaft via the connecting rod. This arrangement reaches main VCR engines requirements in respect of conventional engines characteristics such as piston kinematics, combustion chamber shape, or vehicle integration. In addition, the MCE-5 design includes a roller-guided piston, which allows for a significant friction losses reduction while ensuring a great compatibility with high supercharging pressures on high mileage. To ensure a safe operation and to meet all operational requirements, different studies have been carried out to design appropriate safe high loaded gears. Several hundred hours of tests have been carried out on test bench under various operating conditions to validate the gear fatigue resistance and lubrication of the gear MCE-5 device. Positive results lead to various gear improvements and mass production perspectives.

At the end of four years Research & Development programme, the bench test results for the MCE-5 VCR engine are presented. Downsized supercharged Variable Compression Ratio engines allow for a 30% fuel consumption reduction while providing high power and torque and opening the way to numerous pollutants emissions reduction strategies. In this context, piston to crankshaft transmission by means of gears gives new opportunities for future mass production of rigid and robust low friction engines that conform to VCR requirements while improving piston and rings operation. Through development programmes, the MCE-5 gear-based compression ratio control device proved its robustness and reliability, as well as its ability to allow the design of compact and efficient VCR engines which are easy to integrate into all vehicles.