The model of road roughness is extremely important to the analysis of vehicle ride comfort and handling stability. In terms of hybrid vehicles, it is fateful in particular. IFFT(Inverse Fast Fourier Transform) theory was described in this paper. Simulation programs were compiled with Matlab software, and the results were compared with the same class of standard power spectral density. The paper had fitted the power spectral density of the same set of data with different window functions, compared the difference of the outcomes, and discussed why the difference occured. At the same time, results of IFFT and trigonometric series method were also contrasted. Overall, IFFT is of robustness, rigorous mathematical derivation ideal accuracy and easy to use. It can provide theoretical basis for road safety, indoor bench, optimal control strategy and dynamic load calculations.

The surface/subsurface damage of engineering ceramics after machining has a great influence on the service performance of parts. In order to obtain a high grinding surface quality of engineering ceramics, and take silicon nitride ceramic as a research object, a series of grinding experiments were carried out. The effects of grinding parameters on longitudinal crack propagation depth and the surface residual stress of silicon nitride ceramics were analyzed by grinding experiments, and the residual stress at the location of crack propagation was obtained. The variation in the grinding temperature under different grinding parameters was explored. The influences of the grinding temperature on crack propagation depth and surface residual stress were clarified, the distribution of residual stress along the depth direction was discussed, and the relationship between the residual stress and crack propagation was revealed. The results show that the residual compressive stress on the surface of silicon nitride ceramics decreases with the increase in the depth of crack propagation and the degree of surface brittle spalling. The residual stress at the location of the crack propagation was residual tensile stress. The crack propagation depth increased with the increase in the residual tensile stress. The research provides a reference for the realization of high-quality surfaces in the grinding of silicon nitride ceramics.

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This paper designs a kind of fuzzy temperature controller, which is suitable for high vacuum annealing furnace. Based on the high vacuum diffusing heat process's special characteristics, which are radiation only; the uneven temperature distribution inside furnace; the slow speed of work piece's temperature response; and easy to produce large overshoot, the paper designs a fuzzy inference in this controller. This fuzzy inference can adjust parameter of controller automatically on line through system error and error change. Through this fuzzy inference, controller can adapt to different control objects and various states. The results of experiment show that the temperature controller has several specific characteristics, which include: high control precision, small overshoot and better adaptive control etc. This controller can definitely satisfy the request of crystal annealing technology in high vacuum.