In this work, an optimal cam profile design method for an OHV-type cam-valve train is studied considering the dynamic characteristics of the valve system. When designing a cam profile for an internal combustion engine, it is desirable to make the valve lift area be as large as possible and the valve peak acceleration and seating velocity be as low as those can be within the cam-event angle. But, as we know, those features conflict with one another. An optimal design must strike a compromise between the two. Another important factor in valve train design is avoiding abnormal valve motions such as jump and bounce. It is known that jump and bounce are closely related to valve train dynamic characteristics.
In this paper, a two-step optimization technique to design an optimal cam profile is proposed. In the first step, an attempt was made to maximize valve lift area without causing abnormal valve motions while satisfying all the given constraints such as cam-event angle, maximum valve acceleration, and cam displacements at both ends of the cam-event angle. Then, in the second step, minor modifications of the cam developed in the first step were made in order to reduce the cam acceleration while maintaining the maximized valve lift area and satisfying constrains obtained in the first step.
In order to prove the effectiveness of the optimization method, the valve motion driven by the optimized cam was not only simulated with a four degree of freedom model but was also tested experimentally. It was found that the measured valve motions agree quite well with the simulation results. Comparing the valve motions of the optimized cam with those of the original cam, it was found that the optimized cam can increase the valve-lift area by 8.6 percent while reducing the peak cam acceleration by 28.7 percent. Also, it was noted that the optimized cam increases the cam-valve train operating speed at which jump and bounce occur.
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Jeon, H.S., Park, K.J. & Park, Y.S. An optimal cam profile design considering dynamic characteristics of a cam-valve system. Experimental Mechanics 29, 357–363 (1989). https://doi.org/10.1007/BF02323851