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Through the bench test, the vibration characteristics of the front right support of the inline four-cylinder diesel engine is analyzed, and the MATLAB simulations and verifications are performed to the differential equation of 1 / 4 vibration model established by using the front right support as the research object. Experimental and simulation results show that the exciting force performs as basic frequency and second frequency and, the acceleration performs as basic frequency and low-frequency at low speed engine vibration; when it is in the high speed vibration, the exciting force is mainly manifested in the second frequency and the acceleration in high-frequency. The motion equation of 1/4 vibration model can reflect the status of the engine vibration well in the second frequency.

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Abstract. The combination of increased strain rate and thermal softening of the workpiece at higher cutting speeds will cause the change of cutting force coefficients. In this paper, a vibration model for milling process, which can consider the variable cutting force coefficients (VCFC) with the spindle speed and the variable pitch angle was proposed after some experimental investigations which mainly pay attention to the connection between spindle speed and cutting force coefficients. Then, an updated semi-discretization method is used to predict the stability of such system. The method is also applied to examine the stability trend for different radial immersion ratios and speed regions. Results show that VCFC has great effect on the stability lobes, especially for higher-speed region and smaller radial immersion ratios, whether milling process with uniform or variable pitch angle.