Gas Exchange Potential Ratio – A Quantitative Evaluation Parameter for Fully Variable, Time-Based Valve Train Concepts

The research and development of variable valve train concepts increase the DOF of their functionalities. Beginning with discrete switching between two valve timings (Alfa Romeo: “Variatore di Fase Dinamico”), also the discrete variability of the valve lift (Honda: “VTEC”) was introduced in the 1980s. Increasing the variability to continuous camshaft phasing in the 1990s (Porsche: “VarioCam”) and lift control in the 2000s (BMW: “VALVETRONIC”) an almost fully variable electrohydraulic valve train concept for the inlet valves has been introduced (Alfa Romeo: “MultAir”). Regardless of whether in future a fully variable free valve concept will be introduced or not, a quantitative characterization of the variability of valve trains seems to be necessary to compare different valve train designs with each other. More, the operational parameter of electromagnetic (e.g. voltage, current) or electrohydraulic (e.g. hydraulic pressure, switching times) can be characterized with such a quantity. Based on measurements of a developed and designed electrohydraulic valve train, a suitable quantity has been devised: The Gas Exchange Potential Ratio (GEPR). This parameter describes and evaluates the variability of gas exchange valves and is based on their valve lift curves, which are influenced by the two following main control parameters: the hydraulic operation pressure and valve opening time of a hydraulic switch valve. The introduced quantity is dimensionless and applicable for any valve train, whereby the advantages of the GEPR are primary at time-based valve trains.