Dynamic analysis and optimal design of over-head cam systems.

Abstract

High speed valve train systems for automotive engines are the subject of this research. The primary concern is the determination of cam profiles which give good performance in high speed engines. In the first part of this study, the valve train systems have been modeled and analyzed in order to describe the dynamic characteristics of the existing systems. The time step integration methods from Newmark algorithms have been used for the solution of the nonlinear simultaneous differential equations. Subsequently, the decoupling technique and the mode superposition technique are applied to determine the valve spring reaction force. The parameters which most significantly affect the high speed performances of valve train systems are determined from the sensitivity analysis of the multi-degree of freedom model. The second part of this study begins with the problem of moving a mass from one position to another without initiating a vibration in the mass being moved. Next, the motion of a mass initiated by another mass is evaluated, and the force required to move the system in question is determined. In the third part of this study, a design methodology is proposed for the optimal cam profiles using the model and analysis methods obtained in the first part of the study. These cam profiles have been designed using the rational B-spline. In addition, the rational B-spline functions are used to satisfy the arbitrary prescribed displacement, velocity and acceleration constraints in a least squares sense. A random search method has been applied to obtain the global optimization of the cam shape that gives the lowest output residual vibration amplitude. In conclusion, an optimized cam was successfully designed and numerically tested for increased maximum operating speeds. The computer model of the optimized cam showed improved dynamic characteristics.