大配缸间隙活塞外圆型线对发动机NVH性能的影响

Influence of piston cylindrical profile with large cylinder clearance on NVH

为降低冷起动时大配缸间隙活塞的噪声,提高其噪声、振动、声振粗糙度(noise vibration harshness,NVH)性能,应用活塞动态分析软件PIMO3D,建立活塞弹性流体动力学模型,计算分析冷起动状态下大配缸间隙的活塞外圆型线对NVH性能的影响。分析结果表明:噪声主要产生在做功冲程初始阶段(上止点后曲轴转角为20°~60°),产生原因为活塞换向导致主推力侧裙部上端对缸套的拍击;NVH性能与主推力侧裙部下端接触点到裙部上端敲击点的高度差有关,敲击点越靠近活塞最大外圆位置,撞击产生的振动速度级越小。重新设计活塞裙部基础型线,在型线最大外圆的上、下方各增加一个凹面,形成双凹面型线。仿真验证结果表明:双凹面型线可以有效控制活塞裙部与缸套接触点的位置及接触点的落差,降低大配缸间隙活塞的噪声。

In order to reduce the noise of the piston with large cylinder clearance during cold start,improve the performance of noise,vibration and harshness(NVH),the piston dynamic analysis software PIMO3D is used to establish an elastic fluid dynamics model of the piston,and the influence of the piston outer circular profile with large cylinder clearance on NVH performance is calculated and analyzed under cold start conditions.The analysis results show that the noise mainly occurred in the initial stage of the power stroke(the crankshaft angle after top dead center is 20°~60°),and the reason for its occurrence is the slap of the upper end of the main thrust side skirt on the cylinder liner caused by the piston changing direction.The NVH performance is related to the height difference between the contact point at the lower end of the main thrust side skirt and the impact point at the upper end of the skirt.The closer the impact point is to the maximum outer circle position of the piston,the smaller the vibration velocity level generated by the impact.Redesign the basic profile of the piston skirt by adding a concave surface above and below the maximum outer circle of the profile,forming a double concave surface profile.The simulation verification results show that the double concave profile could effectively control the position and drop of the contact point between the piston skirt and the cylinder liner,and reduce the noise of the piston with large cylinder clearance.