There are many ways to achieve a variation in TDC. The Gomecsys VCR system uses an eccentric between the crankpin and each conrod to achieve the desired variation in TDC.
The compression ratio can be varied by adjusting the position of this eccentric in TDC firing.
In full load operation the eccentricity is inline with the conrod during peak combustion pressure, minimizing gear load and maximizing durability.
To create a true 4 stroke cycle with several efficiency improving functions the eccentrics are driven to continuously rotate around the crankpin at half the speed of the crankshaft. This means that in addition to the adjustment of the CR position of the eccentric in TDC firing, the eccentrics are always running around the crankpin with half the crankshaft speed.
At max compression ratio the eccentric is in its highest position when in TDC firing, but one crankshaft revolution further the eccentric will thus be in its lowest position in TDC gas exchange. See cycle (5). This gives 2 advantages: 1 = internal EGR, 2 = it gives more freedom for the valves to move in TDC gas exchange.
The eccentrics running at half the crankshaft speed means that the eccentric rotates only 180 degrees per crankshaft revolution. When the eccentric is at its mid-range position (0 degrees) in TDC firing it will be at its lowest possible BDC position at the end of the expansion stroke and at its highest BDC position at the beginning of the compression stroke (7) and thus creating true overexpansion.
In part load the intake stroke is reduced and the expansion stroke increased. When the eccentric is in its 45 degrees position (6) in TDC firing, the intake stroke is at its minimum and the expansion stroke at its maximum.
When the eccentric is at its lowest position in TDC firing the intake volume is at its maximum (8).
zero impact on existing engine architecture
fully variable, high speed actuation
8% CO₂ reduction in the WLTC at low cost
minimum additional production costs
very low load on VCR gears
no additional friction
true 4-stroke cycle
more power at low compression ratio
no gear noise
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 782767.
