可变气门相异升程4气门汽油机稳态流动特性

Steady Flow Characteristics of 4-Valve Gasoline Engine with Variable Valve Dissimilitude Lift

4气门汽油机在双进气门全开的情况下只存在滚流,当关闭其中一个气门后会得到较强的涡流,但流通能力比双进气门全开差.提出可变进气门相异升程概念,研制了可变进气门相异升程凸轮轴.使汽油机在双气门全开的过程中不仅存在滚流,而且在流通能力基本不变情况下得到较强涡流,综合表现出斜轴涡流特性,并可通过调整进气凸轮相异角实时改变两个进气门的升程差,满足汽油机不同工况对缸内大尺度气体运动的不同需求.试验表明:在不同相异角、相同凸轮轴转角下,流通系数变化不大;相同凸轮轴转角下,涡流比、滚流比和无因次斜轴涡流比随着相异角的增加而增大,斜轴涡流倾角随着相异角增加而减小;进气过程中产生两次方向相反的涡流和斜轴涡流.

A tumble in cylinder is generated when two intake valves are opened. Strong swirl is produced when one valve of two intake valves is closed but flow capacity is less than that when both valves are opened. Variable valve dissimilitude lift （WDL）was put forward and a variable valve dissimilitude lift camshaft was manufactured, which can make the existence of tumble and swirl in cylinder when two in- take valves are opened with no change in flow capacity. Comprehensive result is the inclined swirl charac- teristics, so the demand of different working conditions on air motion can be satisfied by changing the difference of two intake valve lifts via adjusting intake cam dissimilitude angle in a real-time way. Experi- ments show that the change in flow coefficient is small for different dissimilitude angles. At same cam angle, the swirl ratio, tumble ratio, inclined swirl ratio increase with increasing the dissimilitude angle. Inclined swirl angle decreases with increasing the dissimilitude angle. Two times of swirl and inclined swirl with opposite direction are generated during the intake process.