電子系統散熱風扇噪音之改善研究

A Noise Reduction Study for the Cooling Fan of Electronic Systems

許哲維(Che-Wei Hsu)

指導教授 ： 陳永樹

元智大學/工程學院/機械工程學系/碩士(2006年)

https://doi.org/10.6838/YZU.2006.00181

摘要

為提高電子產品之散熱效能，故散熱風扇多朝高轉速設計。但在轉速上升的同時，噪音也相對地提高。而散熱風扇品質良窳，常以散熱效能及噪音來做為依據。因此，在提高轉速增加散熱效能的前提下，對於噪音的要求亦為風扇在設計時必需考量之重要議題。有鑑於此，本文將針對電腦散熱風扇之噪音問題，就扇葉結構與直流無刷驅動馬達之電磁噪音進行分析研究，並提出可行之改善方案。

風扇流場與噪音有最直接之影響，而軸流式風扇之葉型設計對於風扇流場影響甚鉅。為改善風扇流場達到降低噪音的目的，本研究首先以變更風扇動葉上圓弧角幾何尺寸，並於無響室中進行噪音值量測，了解圓弧角參數對風扇噪音之影響，並找出最佳之圓弧角尺寸。此外，亦在前後軸承處置入不同數目之墊片，以提高轉子及定子間之軸向力，降低風扇軸向振動，改善風扇因振動所產生之噪音。電磁噪音改善部分，由文獻得知頓轉扭矩為影響風扇噪音因素之一，較小之頓轉扭矩值具較小之噪音。因此，以MagneForce電磁分析軟體對風扇內轉子與定子間氣隙與定子開口槽寬度的參數，進行數值分析，了解在不同參數尺寸與頓轉扭矩值間之關聯性。

研究結果顯示，在最佳圓弧角幾何尺寸之設計變更方案，約可降低1.5 dB之風扇噪音，且風扇性能測試遠比初始風扇佳。此外，在軸承處置入墊片確具降低噪音效果。而電磁分析中，歸納出頓轉扭矩值隨氣隙尺寸增大而降低，當氣隙大小在0.5 mm時之頓轉扭矩與原始模型比較降低約23 %。定子開口槽寬度部份，縮減寬度至1.0 mm降低頓轉扭矩約49 %，而在實際風扇設計上，較低之頓轉扭矩值相對具較小之噪音值。綜合以上，將模型中氣隙變更為0.5 mm與開口槽寬度縮減至1.0 mm，其頓轉扭矩與原始模型比較之下降低約57 %。

關鍵字

風扇 ； 軸流式風扇 ； 噪音 ； 直流無刷馬達 ； 頓轉轉矩 ； 氣隙

並列摘要

In order to increase the heat dissipation capability of the electronic system, the cooling fan is often designed with high rotational speed recently. The accompanying noise becomes louder then ever before relatively. However, both the heat dissipation efficiency and the noise it generates are key indices of the cooling fan quality. Therefore, reducing the noise is an important factor that must be taken into consideration for the fan design of high rotational speed and better heat dissipation efficiency. The study then aimed at reducing the fan noise through a series of fan blade structure redesign and the analysis of the electromagnetic noise of its brushless DC motor. Some of the feasible improvement schemes are also presented after the study.

The air flow field relates to the fan noise directly. And the design of the blade geometry for the axial flow fan affects the air flow field remarkably. In order to improve the flow fields so as to reduce the noise, the study starts from modifying the dimensions of fan blade’s arc angle on the rotor blade. Then, by measuring the noise in a semi-anechoic chamber thereafter, the effects of the arc angle parameter on the fan noise are then understood and the best arc angle dimension is thus determined. In addition, different number of pieces of the shim at the rear and the front bearings are inserted for increasing the axial forces and then improving the vibration which brings out the noise between the rotor and stator. Regarding the electromagnetic noise, it is based on the literatures that the dominate factor influencing the electromagnetic fan noise is the cogging torque. It is emphasized that the less cogging torque, the less noise. Therefore, the parameters of the slot opening size on the stator and the air gap between the rotor and the stator are analyzed with the MagneForce electromagnetic analysis software. The corresponding relations between different parameters on the cogging torque are fully investigated.

The results show that one of the modification design for the best arc angle geometry can reduce the fan noise around 1.5dB, and the performance is even much better than the original fan. Moreover, shims insertion at the bearing locations did reduce the noise. In the electromagnetic analysis, it is found that the cogging torque decreases with the increase of the air gap. When the air gap size is 0.5 mm, the reduction of the cogging torque is about 23% when comparing with the original model. In the stator slot open sizes study, it is observed that when the slot opening size is decreased to 1.0 mm, the cogging torque is reduced about 49 %. In reality, less cogging torque causes less noise. It is then concluded for all the cases studied that while the air gap is set as 0.5 mm, and the slot opening is decreased to 1.0 mm, it can be reduced 57% of the cogging torque by comparing to the original model.

並列關鍵字

Axial Flow Fan ； Air Gap ； BLDC ； Fan ； Cogging Torque ； Noise

參考文獻

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