Constructive Optimization of a Mechanism of Variable Valve Control

摘要

The mechanisms of variable valve control are frequently used on thermal engines which equip usual automobiles. In our paper we present such a solution consisting in a cam in rotational motion, a triad and a follower in plane-parallel motion. For this solution we perform the synthesis of cam and the kinematic analysis of the mechanism. The used methods are classical analytical ones of analysis and synthesis of cam, as well as CAD methods. The synthesis of cam by a CAD method assumes: the positioning of the raw material that materializes the cam, construction with solids of the follower as well as its positioning, extraction of the follower from the raw material, rotation by one degree of the obtained solid and the repeating of the procedure for the new angle. These operations are realized with an AutoLisp function which is not influenced by the complexity of the mechanism. The principle of the method of positional analysis by a CAD method consists in the modeling of the cam and follower with solids, variation of the rotational angle of the cam with the aid of an AutoLisp function until the follower is in contact with the cam and, finally, determination of the displacement of the valve of mechanism. In the end of the paper we present the constructive optimization of the cam mechanism by heuristic methods. The used algorithm has four steps, resulting finally the shape of the follower and the optimized cam.