在1台直喷增压汽油机上应用可变进气凸轮技术，研究了不同凸轮型线对发动机部分负荷工况经济性的影响。研究所用的可变凸轮由长行程凸轮和短行程凸轮组成，长、短行程凸轮切换通过电磁阀控制实现。研究结果表明，短行程凸轮通过进气门早关实现米勒循环，进气压力提升后有利于降低泵气损失和缸内残余废气系数。短行程凸轮应用在不同负荷下降低燃油消耗率1.9%~3.4%，不同工况下节油机理不尽相同。对于非爆震限制工况，如平均有效压力为0.5 MPa工况，短行程凸轮应用导致燃烧持续期延长，而油耗降低的主要影响因素为未燃损失下降和机械损失降低；对于爆震限制工况，如平均有效压力为0.8~1.7 MPa工况，短行程凸轮应用明显改善燃烧相位，油耗降低的主要影响因素是燃烧定容度增加导致的指示热效率提高。

A variable intake cam was applied on a turbocharged gasoline direct injection engine to study its effects on engine fuel economy at partial load. The cam was composed of a long travel cam and short travel cam, the switch between them was realized by an ECU controlled electromagnetic valve. The results show that short travel cam can realize miller cycle through early intake valve closing (EIVC) with the reduction of pumping loss and incylinder residual burned gas due to higher intake pressure. Applying short travel cam can reduce brake specific fuel consumption by 1.9%-3.4% at different loads based on different mechanisms of fuel economy. For restricted operating conditions of non-knock such as the average effective pressure of 0.5 MPa, short travel cam will prolong combustion duration and the main reason of fuel consumption improvement are the reduction of unburned loss and mechanical loss. For restricted operating conditions of knock such as the average effective pressure of 0.8-1.7 MPa, short travel cam will improve combustion phase obviously, and the fuel consumption improvement is due to improved indicated thermal efficiency led by the increase of combustion constant volume.