Research On OHC Valve System Of Vehicle's Engine

The high speed engine widely uses the rocker arm style OHC valve. This paper aims at the characteristic of K157FMI motorcycle engine valve train, conduct the thorough research on the rocker arm style OHC valve, and improve the cam profile design. Get the better engine air admission performance, enhanced the engine power performance.First, according to the cam lift date of K157FMI engine, introduce the method of valve theoretic movement rules, owing to the fact that the rocker arm ratio of OHC valve train is variable; three measures are adopted for raising the calculation precision. The first is fitting the valve theoretic lift date which is calculated according to the cam lift data. The second is dividing the whole lift curve into two sections, the transition and working section which are fitted singly. The third is fitting the working section by using the methods of optimization and the least squares. The calculation results indicate that the counted precision of this new mathematical method is higher. It has the important reference value to analyse the dymamics of the valve and the main design factor of the cam.Second, use the polynomial profile to design the cam of valve train. The desirable configuration and major parameters of the acceleration curve could be obtained by setting the maximum velocity and maximum acceleration to expected position. The calculation process is simple and can modify for the characteristic parameters of the cam easily while mainting the merit of higher derivative continuity for the integral type function cam. The calculation results indicate that a perfect ample factor of cam lift and a better dymamics of the value train could be obtained by this design. Third, according to the optimization design, analize the lift errorwhich produces in the manufacture process. This paper with the cam position of the 0⁰ reference X₁ and 0 lifting reference X₂ as the design variable, with the sum of squares of measured cam points lifting error Ri as objective function, establishes the mathematical model of optimization to analyze cam lifting error by optimization method. Indicate through the actual computation: compared with the sensitive point method, the cam lifting error calculated with the optimized design method may accurately reflect the cam contour shape, enhance the erroneous precision by 37.9%. This method has a simple, feasible and practical merit. It has an important significance to accurately determinate cam processing error.Finally through the experiment confirme the effective influence after the improvement designs. The results indicate that, the new development timing mechanism has the better gasification performance and dynamicsperformance.