柴油机配气机构两种凸轮型线的设计及性能对比

利用几何法和函数法对4125柴油机配气机构的凸轮型线进行设计,通过计算和比较两种凸轮型线下挺柱运动的位移、速度和加速度曲线得出:几何凸轮型线的换气时面值大,有利于提高发动机的充量系数,但在气门开启和关闭的瞬间以及速度的绝对值达到最大时,挺柱的加速度均发生突变,因此,采用几何凸轮的配气机构将产生较大的振动和噪声；函数凸轮挺柱的加速度连续光滑变化,在整个工作阶段,无加速突变,并且其最大加速度的绝对值约为几何凸轮挺柱最大加速度绝对值的1/2,所以,采用函数凸轮的配气机构工作平稳,产生的振动和噪声小,但对进气充量有不利影响,可通过增大气门直径或采用多气门等工程上常用的措施加以改善.

Design and Performance Comparison of Two Kinds of Cam Profile in Diesel Valve Mechanism

Based on geometric method and function method, cam profile design for 4125 diesel valve mechanism was done. Through calculation and analysis of displacement, velocity and acceleration of cam-tappet movement for the two kinds of cam profile, it was found the time area for air exchange of geometric cam profile was better to improve volumetric efficiency of the diesel engine, but that the acceleration of cam-tappet would change suddenly at the moment of the valve opening, closing and the maximum absolute value of velocity did lead to worse vibration and noises of valve mechanism. The acceleration of cam-tappet for function cam changed continuously, smoothly and no acceleration gust in the all working stages. Moreover, the maximum absolute value of acceleration for function cam was about half of that for geometric cam, so this cam would generate less vibration and noises, but was negative on volumetric efficiency. However, this can be improved by increasing the diameter of intake valves or the number of intake valves.