Investigations on Ventilation Strategies for SI Cylinder Deactivation Based on a Variable Valve Train 2016-01-2346
Advanced SI engines for passenger cars often use the cylinder deactivation technology for dethrottling and thus achieving a reduction of fuel consumption. The gas exchange valves of the deactivated cylinders are closed permanently by a zero lift of the cams. The solutions for cylinder deactivation can vary in the kind of gas composition included in the deactivated cylinders: charge air, exhaust gas or vacuum. All these strategies have in common the frequent loss of captured charge mass from cycle to cycle. Their two-stroke compression-expansion cycle additionally intensifies this phenomenon. Thus, a significant decrease of the minimum cylinder pressure can cause an undesired entry of lubricant into the combustion chamber. The idea was to ventilate the generally deactivated cylinders frequently to compensate the loss of captured cylinder charge mass. The task was to keep the minimum cylinder pressure above a certain limit to prevent the piston rings from a failure. However, a compromise has to be found about the value of IMEP the deactivated cylinders perform in dependence of the included charge mass. The experimental design for this investigation contains a large variety of parameters: type of inclusion, choice of ventilation valves, phase, intensity and frequency of ventilation. Some parametric combinations can be an interesting compromise. They use a ventilation phase at BDC_HP 180°CA before firing TDC in contact to the intake manifold or at BDC_GE 180°CA after firing TDC in contact to the exhaust manifold. Both advantageous strategies use small valve lift curves and low ventilation frequencies.