Time Optimum Cam Synthesis With Manufacturing and Operation Constraints

Abstract

Traditionally, cam profiles have been described in terms of harmonic functions or splines that are optimized to provide low residual oscillations and avoid constraints such as pressure angle. For automotive cams used in internal combustion engines, the designer usually manually manipulates the control points of the spline functions and checks for constraint violations by feeding the obtained cam profile through a dynamic simulation of the valve train. This is a lengthy and iterative process that cannot guarantee that the obtained cam profile is truly optimal, since constraint boundaries are usually only met at a few distinct points along the cam profile. However, a truly time optimal cam profile will need to follow constraints during the complete motion. This paper then shows a reverse design procedure, where cam profiles are defined in terms of the constraint functions. A valve lift profile is assembled that moves along the boundary of the feasible valve lift space. The resulting cam motion is constrained at all times and represents a time optimum cam profile in terms of the selected constraints. The proposed methodology is computationally efficient and runs effectively on standard office computers. Automotive cam designers can use the results of this approach as an initial starting point for their cam shape optimization.