Dynamics Analysis And Cam Profile Optimization Of Valve Train System For Gasoline Engine

Valve train system plays an important role in the engine. It controls the intake and exhaust of the cylinder by opening and closing valves at proper times. Good valve train system lets engine not only work at good conditions, but have good volumetric efficiency, high power output and low emission as well. It’s necessary for valve train system to have great dynamical behavior, low vibration, low noise and low wear. Domestic research on valve train system has made a substantial step with the development of the computer technology. Current research focuses on the system itself. Valve train system is a subsystem in engine working with other system. The camshaft torque is the input load of timing system. It has a great influence on timing system. The research about the influence on other systems is rare. Therefore, this paper do the dynamical analysis and optimization of valve train system for gasoline engine regarding the camshaft torque. The main contents are as follows:Some parameters that evaluate the characteristics of valve train system and the equations of these parameters are presented. The performance of the system must meet the requirements of these parameters. In this paper, the tappet is flat. Then the geometrical motion of valve with flat tappet is presented. Considering the valve train system has a great impact on timing system, the theory calculation method of camshaft torque is introduced through kinematic analysis. The camshaft torque of the valve train system is calculated which offers data support.The paper has established the dynamical model of single valve train and whole valve train. The performance parameters are gotten in the analysis of single valve train. The camshaft torque of intake and exhaust camshaft in different engine speed is gotten through the whole valve train analysis. By comparing the dynamical results and the theory calculation of camshaft torque, this paper has studied the influence of the dynamical analysis.The method of designing cam profile is described. Base circle, ramp and working part consist of the cam profile. Because of the structure of the cylinder head, the optimization of base circle is limit. Therefore, this paper put emphasize on the redesign of ramp and working part of the cam profile. The reasons to set ramp and the equation of ramp height are mentioned. There are different kinds of ramp curve type using in different conditions. The Polydyne acceleration curve is used as the working part curve by comparing different curves. After the optimization of the cam profile, run the dynamical analysis of the valve train system. The simulation results include the lift, velocity, acceleration, fullness coefficient, contact stress, lubrication coefficient and jerk which are all in the permissible range. The camshaft torque fluctuation in the open period of the valve has declined significantly by using new cam profile.The research results of the paper have important theoretical significance and practical engineering value in the design, dynamical analysis and optimization of valve train system for gasoline engine.