Dynamics Optimization Of Cam Profile In Valve Trains

A valve train is one of the most important mechanisms in internal combustion engines,in which the cam profile has a significant influence on the performances of internal combustion engines.The aim of designing a cam profile is to get a larger charging coefficient and a stable movement of valve train.But both objects are usually contradictive,so cam profile design is focuses on achieving the best matching between the two contradictive goals.Cam profile optimization based on traditional function cam profiles,such as polynomial function cam profile,cosine function cam profile,et al,usually obtained the incomplete solution limited to a certain functions type.In this paper,a B-spline curve was adopted to design the cam profile,because the B-spline is more flexible by defining the profile with controlled vertexes,and is easy to implement standardized programming.The cam profile design method based on B-spline could adjust the tappet profiles of displacement,velocity,and acceleration effectively,and obtain the displacement profile with second-order and even higher-order continuity.Moreover,a single-mass dynamics model of engine valve train was established to evaluate the dynamical performances of a cam profile.Then the complex method was used to optimize the cam profile,taking the charging coefficient as the optimization target and the contact stress between cam and tappet as the optimization constraint.Additionally,an application software for cam profile optimization of engine valve train was developed.Using this software,results of the cam profile optimization of a certain diesel engine showed that the charging coefficient was increased significantly while there was no significant change of the valve train dynamic performances.