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Nth-degree harmonic cam optimal design with random search technique
Abstract
The paper presents a modified model to design an Nth-degree harmonic cam profile, with the point control strategy plus section control strategy to reduce its design parameters. An optimal random search technique was adopted to solve the Nth-degree harmonic cam design problem whose control indexes and design parameters has no certain correlations. It is proved that the random search method is most adaptive to solve the problem. Analytical results show that the range of length of the negative acceleration section is extremely small, and point control of that makes spring-inertia force match characteristics and constant curvature radius control in the corresponding section more effectively. As a result, the lifter-cam lubrication and fatigue-resistant properties are improved without lowering the valve train jump-up-camshaft-speed.
Metabolomics is a new omics technology which is developed after the genomics, transcriptomics, and proteomics. Metabolomics has characteristics of integrity, systematization, and comprehensiveness which just coincide with the whole view, dynamic concept, and dialectic approach of the traditional Chinese medicine theories. This study reviews the application of metabolomics in effective material bases and quality evaluation of Chinese Materia Medica (CMM). An integral research idea of quality control has also been put forward on the basis of metabolomics technology because of the deficiency of current quality control methods in CMM. That is, the technology and methods of metabolomics are used to ascertain the effective material bases of CMM and factors affecting the metabolic change of chemical constituents in medicinal plant. Then, a quality control method can be established to ensure the safety and effectiveness of CMM in clinical practice.
In this paper, the design method of a cam with Nth-degree harmonics is discussed and a new cam profile with constant curvature radius of Nth-degree harmonics is proposed. This cam is suitable for high speed automotive engines, the plane tappets of which are widely used.
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.