无节气门负荷控制策略对汽油机性能影响的研究

Effect of Throttle-Free Load Control Strategies on a SI Engine Performance

在汽油机上取消节气门,采用可变气门升程和气门定时控制进气量,继而控制发动机负荷,实现汽油机的无节气门负荷控制。针对一台4缸汽油机采用可变气门驱动负荷控制方式建立了无节气门汽油机仿真模型,并得到试验验证。在此基础上研究了不同负荷控制方式对汽油机性能的影响。结果表明,采用可变气门开启持续期(VET)负荷控制方式可以有效降低汽油机部分负荷泵气损失,最大降低幅度达到57%,同时比油耗降低了5.63%。VET同样可以使全负荷时低速转矩和高速功率得到提高,其中低速转矩提升达到了27.8%。但VET实现汽油机怠速控制较为困难,需要同时采用降低气门升程的(VVL)控制方式,该控制方式下泵气损失有所提高,但是气门升程降低造成进气流通特性的改变使燃油雾化及燃烧得到改善。

Throttle-free load control represents one of the most important developments in spark ignition gasoline engines. With throttle-free load control, the pumping loss at the partial load operation can be reduced remarkably. The throttle-free load control of SI engine can be realized by regulating the valve lift and the closing time of the inlet valve. The simulation model for a four-cylinder SI engine is built and validated by the experimental results. The effects on engine performance with different methods of engine load controlling are studied with this model. Simulation results show that the load control method with variable event timing （VET） can effectively decrease the pumping loss at engine partial load condition up to 57%, and the brake specific fuel consumption is improved by 5.63%. The VET load control method can also improve the torque at low speed and the power at high speed in which the torque at low speed increases by 27.8%. However, VET is difficult to make the idling controlling and needs the combination with the variable valve lift （VVL） method. VVL will improve the inlet flow characteristics and fuel atomization as well as combustion with the penalty of some increase in pumping loss.