Design and analysis of skip fire valve strategies based on electromagnetic valve train

Skip fire strategy is an effective technology to improve spark ignition engines' efficiency at part load. However, it is difficult to achieve skip fire strategy based on variable valve train, because valves require to be controlled stroke by stroke for switching frequently between valve deactivation and normal operation. While the application of moving coil electromagnetic valve train (EMVT) on engine intake and exhaust system, as a fully flexible variable valve train, provides a feasible approach to actualize skip fire strategy. Firstly, four new valve strategies, including two strategies of trapped exhaust gas, one strategy of trapped fresh air and one strategy of keeping exhaust valve open, are proposed to achieve skip fire strategy based on EMVT. Then the optimum valve timing and lift with the minimum pumping losses of four valve strategies are achieved according to the GT-Power engine model. Finally, by the comprehensive evaluations of the average BMEP and the difficulty of valve control, the strategy of keeping exhaust valve open is identified as the optimum skip fire strategy. At the condition of 1200 rpm, results show the fuel economy has been improved 10-23% compared with the prototype when the break mean effective pressure (BMEP) decreases from 0.42 MPa to 0.215 MPa.