本文研究機車振動包含兩部分；第一部分為探討車架幾何形狀及其振動模態之關係，使用ANSYS 14.5 Workbench進行結構分析；而模型建構時發現，當中網格品質會影響到自然頻率的準確性，因此將實體元素大小設為2mm。比較以速可達機車排氣量作區分，125c.c.的LHJ3型、CYGNUS型及300 c.c.的LEA7型、XMAX型。
因車架上有些較大或較長之零件，如同懸臂樑固定於牆上，模擬結果會產生局部模態；然而相較於局部模態，整體車架變形才是最重要的，故車架模態分析不包含零件的振動模態，再與組內合作同學所進行的實驗數據對照，以驗證模擬之可行性。四台車架最大位移量為車頭及車尾處，排氣量300c.c.則受尾部重量、車體寬度影響，易有扭轉的模態；相同大小車架來說，在100Hz之前，其自然頻率和振動模態極為相近。
第二部分以LEA7型速可達引擎為研究對象，以往只討論速可達引擎怠速情形，探討其在高轉速下之搖撼力及搖撼力矩，將引擎假設為定轉速狀態與定扭力狀態下，最後進行離散傅立葉轉換，作為機車行走中簡諧分析的輸入振動源；發現三種不同轉速下，以定扭力分析比起以定轉速分析會更貼近引擎真實運轉情況，且搖撼力集中於U方向力。雖然搖撼力矩與轉速無明顯關係，但同方向搖撼力大小會與曲軸轉速平方成正比，若要預測其他轉速下之搖撼力，可利用正比關係，約略推算搖撼力大小。

In order to research the relation between the geometry of the frames of motorcycles and the natural frequencies and the natural modes, this thesis used the software “ANSYS 14.5” to analyze the structures of motorcycles. Mesh quality in the software would affect the precision of results in natural frequencies when constructing the motorcycles’ model. Therefore, the size of solid elements was set up in 2mm. To compare the difference of motorcycles’ frames, the engine displacement was used to classify them. They were divided into two groups that contained the 125c.c. type and the 300c.c. type. In the 125c.c. type engines, two models of 125c.c. type were denoted as LHJ3 and CYGUNS. Two models of 300c.c. type were denoted as LEA7 and XMAX.

Since some of the components of the motorcycles’ frame are slender, they can be considered as the cantilever beam, and the natural modes related to these components are considered as local mode. However, the whole motorcycles’ frame of deformation is the most important object. In the following discussion, the local modes were excluded from the result, when comparing with the experimental data. The biggest displacement appeared on the front and tail of four frames. In the 300c.c. type, the modes twisted due to the weight of the tail and the width of the frame. For the same engine displacement type, the natural frequencies and the modes were identical when the natural frequencies below 100Hz.

The second part of the paper is concerned with the 300c.c. type engine, denoted as LEA7, to study the shaking force and the shaking moment with high angular velocity which is in riding condition. Assume that the engine status as constant torque or constant angular velocity, and then use the Discrete Fourier Transform to transform the shaking force and the shaking moment which is used as a local vibration resource in the motorcycle harmonic analysis during the riding. With three different angular velocities, which are 6000rpm, 7000rpm and 8000rpm, the result showed that the engine in the constant torque condition would be closer to the real situation than the one in the constant angular velocity condition. At the same time, the shaking force was concentrated on U-direction, and the magnitude of the shaking force was proportioned to the square of the angular velocity. If someone analyzes the engine with other angular velocities, the shaking force will be predicted due to the same relationship.

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