摘要
动力机械的辐射噪声取决于结构表面振动,通过控制振动来降低辐射噪声是机械工程师长期追求的目标。本文以YC6113柴油机为研究对象,对柴油机辐射噪声进行了全面系统的理论分析和试验研究。其主要研究内容和成果如下:
首先在外特性下测试了发动机的整机噪声声压级,计算得到了声功率级。结果表明:在标定工况发动机的整机噪声声压级达到了97.21 dB(A)。测量结果表明:齿轮室面的噪声声压级明显高于其他测点,对整机噪声声功率级贡献最大;其次是进气侧、排气侧和顶面;飞轮侧的噪声值最低,对整机噪声的贡献最小。其次利用全声息技术和屏蔽消元法对发动机进气侧、排气侧、齿轮室侧以及顶面进行噪声源识别的测试,找出各个噪声辐射面噪声较大的地方。结果表明油底壳、齿轮室盖板以及缸盖罩等零部件辐射的噪声较大。
针对油底壳、齿轮室盖板以及缸盖罩等薄壁零部件辐射噪声较大的试验结果,应用有限元法对上述三薄壁零部件进行了模态计算和低噪声结构优化。
缸盖罩的模态计算表明其第四阶固有频率发生共振;因齿轮室盖板设计空间的限制,采用加筋和增加凸台的优化方案,优化后固有频率提高不多;对齿轮室盖板采用屏蔽措施。台架试验结果表明,屏蔽齿轮室盖板后发动机前端和整机噪声声压级在标定工况分别下降了1.40dB(A)和1.31dB(A)。
油底壳模态计算表明,油底壳模态密集,整体刚度小;油底壳深底面、油底壳浅底面、油底壳侧面、油底壳浅底面以及连接深底面和浅底面的中间位置局部振动比较强烈。对上述四个部位采用增加冲压槽的优化方案,优化后一阶固有频率增加了17.4Hz,其它阶固有频率都有所增加。考虑到汽车在行驶中机油液面变化不能太大,油底壳增加了一块挡油板,并对挡油板进行低噪声结构优化。增加挡油板后固有频率进一步提高。试验结果表明,优化油底壳后柴油机在外特性转速下整机噪声声压级最大下降了0.56dB(A)。
缸盖罩模态计算表明缸盖罩顶板的局部振动强烈,刚度最差,并且第八阶固有频率发生了共振。对顶板处采取了增加筋的宽度和筋的个数,并在顶板处增加迷宫盖板。增加筋的宽度和条数后固有频率有所提高;增加迷宫盖板后固有频率有所下降,但是其振动主要发生在迷宫盖板上,迷宫盖板对缸盖罩内部噪声有屏蔽作用。试验结果表明,优化缸盖罩后顶面和整机噪声最大下降了0.5dB(A)和0.54dB(A)。
台架试验表明,通过以上方案的改进发动机噪声在标定工况整机噪声只有95.30dB(A),比原来降低了1.51dB(A),取得了良好的效果,达到了控制柴油机结构噪声辐射的目的。本文的研究方法,对现代发动机及其薄壁件低噪声结构设计具有重要的工程参考意义。
The radiated noise of the dynamical mechanism comes from its surface vibration. It is mechanical engine's aim to decrease the radiated noise through controlling vibration. This paper gives theoretic analyzed and experimental study to the radiated noise on YC6113.The main contents and productions are maintained as follow:
This paper takes YC6113 diesel engine as research object. We first measure the pressure level of sound and acoustical power of the engine under the mode external characteristic. The study shows the whole pressure level of sound achieves 97.21 dB (A) at the demarcate point. The noise of gear is higher than other's, so it gives the most contribution to the noise of engine; The order of the noise from high to low are intake side, exhaust side and top side; the noise of flywheel is the lowest, it gives the least contribution to the noise of engine. Then we measure the intake side, exhaust side, gear and top side of the engine in order to identify the source of the noise, using the acoustic holography by electro beam scanning and shield technique, to find out where is the place the noise radiates extrusive. It is showed that the parts of oil pan, gear cover and valve mechanism cover give larger noise radiation.
According to the experimentation, the shell components such as oil pan、gear cover and valve mechanism cover give larger noise radiation. Then using finite element method, we put up mode calculation and structure optimization to the shell components above-mentioned to decrease their radiated noise.
The mode calculation of the gear cover shows that the fourth mode frequency is sympathetic vibration. On account of the limited space of gear cover, we only use the optimize method of adding rib and convexity, the inherence frequency optimized fore-and-aft increase few, the noise of the whole engine changes few too. After shielding the gear cover, the noise of the front-engine and the whole engine decrease 1.40dB(A) and 1.31 dB(A) respectively at the demarcate point.
The mode calculation of the oil pan shows that the mode of oil pan is dense, the whole rigidity is small, vibration of the deep-underside、side face、shallow- underside of the oil pan, and the middle part which joint the deep-underside and the shallow- underside is strong. We use optimize method which adding punch trough to the four sides above-mentioned, the first inherence frequency increases 17.4Hz,other inherence frequency also increase. Considering the lubricating oil level can't fluctuate too intensively, we add a oil baffle-plate on the oil pan, and then optimize it. The inherence frequency increases farther after adding a oil baffle-plate. The experimentation result shows that the pressure level of sound of noise of the whole engine decreases 0.56 dB(A) at the demarcate point.
The mode calculation of valve mechanism cover shows that vibration of the top-board of valve mechanism cover is intense, the rigidity is the worst, and the eighth inherence frequency arise sympathetic vibration. Then we take methods as increasing width and number of rib and adding labyrinth-board on the top-board. The inherence frequency increases after increasing width and number of rib, and the inherence frequency decreases after adding labyrinth-board. But vibration centralizes on the labyrinth-board. The noise of top side and the whole engine noise descend 0.5dB (A) and 0.54dB (A) respectively.
Thought the amelioration of the scheme upwards, the noise of the whole engine is 95.30dB (A), which is 1.51dB (A) lower relative to the original engine, the effect is salience. It is feasible to control the noise of diesel engine by using structure optimization. It will have the reference meaning in the optimize design of the modern engine and its device.
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