如何降低引擎之振動及噪音一直係一項重要的議題。而引擎各元件之間是利用螺栓鎖附，螺栓之鎖緊預力與模擬對引擎振動噪音之影響必須釐清。

本研究係以有限元素法建立整體引擎之數值模型，研究結果顯示，凸輪軸與曲軸建入有限元素模型後，整體引擎之各自然頻率會因受到此二軸對不同模態的影響而有所變化，因而導致模態出現次序之改變。至於曲軸之不同旋轉角度也會造成引擎質量慣性矩之改變，而因而使自然頻率有所升降。而由分析螺栓鎖緊預力之結果顯示，有無螺栓鎖緊預力之自然頻率差異小於0.45%，故於一般分析時，可忽略螺栓鎖緊預力，以減少分析時間。而由改變螺栓材料以模擬剛性元素之分析結果可知，以剛性元素模擬螺栓為不合理之設置，不能僅逕以剛性元素之設置做為調校模擬值與實驗值間之差異的依據。

最後針對整機之第一及第二模態，可藉由模態圖及應變圖以增加肋條的方式強化結構，以達減少振幅及改變自然頻率之目標。

How to reduce vibration and the noise of engine has been an important issue. Because the components of engine are locked by bolts, impacts from bolt-preload and simulation on engine vibration and noises have to be clarified.
This study used the finite element method to establish a numerical model for the engine. The study findings revealed that after including camshaft and crankshaft into the finite element model, the natural frequency of the engine changed due to impacts from these two shafts on the various modes, consequently the occurrence sequence of the modes varied. In addition, different rotation angle of the crankshaft can change the moment of inertia, and that will alter the natural frequency as well. Results from analyzing the bolt-preload indicate a less than 0.45% difference in natural frequency between the presence and the absence of bolt-preload. Therefore, for time-saving, bolt-preload can be neglected for general analysis. And by analysis results of change the bolt material to simulate the rigid element , when simulation the Young's modulus change to 1000 times of bolt material ,the results of analysis will close to result of bolt simulation rigid body element. However, the simulation and actualy of Young's modulus difference is too large. Therefore, the rigid element simulation of the set bolt is unreasonably.
In terms of the first and the second modes of the engine, one can stiffen the structure by increasing the number of ribs according to the mode shape and the strain diagram so the amplitude can be reduced and the natural frequency altered.

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