Optimal Design of Cams

Abstract

We present a methodology to design cams for motor engine valve trains using a constrained optimization algorithm. The imposed constraints are the maximum valve lift and timings while the objective function is to maximize the time integral of the valve area opened to gas flow. A piecewise analytically defined acceleration is imposed, so that the time instants controlling the profile of accelerations are used as variables for optimization. The strategy takes into account some geometrical constraints, e.g. to avoid interference between intake and exhaust valves, and between valves and piston. Also, minimum and maximum levels of acceleration are limited to avoid excessive forces in the mechanisms chain, and to prevent the possibility of separation between cam and follower. Once an optimal lift profile is determined, the cam shape is computed using an inverse kinematics analysis that takes into account all the geometric nonlinearities introduced by the kinematical chain. Finally, the whole mechanism is verified in a dynamics analysis to check satisfaction of the criteria for design. Comparisons with standard profiles of motion were made. Also, the profile was evaluated in an experimental device, where the actual valve displacement was measured.