200842248 九、發明說明 【發明所屬之技術領域】 本發明有關一用於冷卻電氣零組件等之軸向流風扇。 【先前技術】 日本專利公告第05- 1 64089號（下文稱爲專利文件1) 揭示一包括風扇外殼、具有複數葉片之葉輪、轉子、定 子、及馬達殼體的軸向流風扇。該轉子包括一旋轉軸桿及 複數轉子磁極，該等轉子磁極係由永久磁鐵所形成及設置 在該旋轉軸桿的一圓周方向中，且被固定至該葉輪。該定 子包括一定子鐵心及激磁線圈。該定子鐵心包括複數在該 旋轉軸桿的徑向中面朝該轉子磁極之定子磁極。該激磁線 圈係分別纏繞著該等定子磁極。該馬達殼體包括一軸承支 撐圓柱形部份。在該軸承支撐圓柱形部份內側，配置支撐 該轉子之旋轉軸桿的軸承。該定子鐵心係以一穿透孔所形 成，該軸承支撐圓柱形部份係裝入該穿透孔。該定子係固 定至該軸承支撐圓柱形部份，使該軸承支撐圓柱形部份裝 入此穿透孔。 在專利文件1中所揭示之此型式的軸向流風扇中，當 該轉子被旋轉時所產生之震動係帶至或抵達該風扇外殻。 爲此緣故’震動之增加造成噪音。於該傳統之軸向流風扇 中，當用於該轉子之轉數係小的，或該轉子係在低速旋轉 時，抵達該風扇外殼之震動增加。 200842248 【發明內容】 本發明的一目的係因此提供一軸向流風扇，其能夠遍 及一轉子之整個速率範圍限制被帶至風扇外殼之震動。 一軸向流風扇之改良係本發明所瞄準之目的，該軸向 流風扇包括一風扇外殼、葉輪、轉子、定子、馬達殼體、 及軸承。該風扇外殼包括一具有二開口之空氣通道’即一 開口與另一開口。該葉輪係設置在該空氣通道內側及包括 複數葉片。該轉子包括一旋轉軸桿及複數由永久磁鐵所構 成之轉子磁極。該等轉子磁極係設置在該旋轉軸桿之圓周 方向中。該定子包括一具有複數定子磁極之定子鐵心，及 分別纏繞著該等定子磁極之激磁線圈。該等定子磁極在該 旋轉軸桿的一徑向中面朝該等轉子磁極。該馬達殼體包括 位在該一開口的側面上之底部壁面部份，一以該底部壁面 部份連續地形成及朝向該另一開口延伸之周邊壁面部份， 及一設在該底部壁面部份及朝向該另一開口延伸之軸承支 撐圓柱形部份。該等軸承設置在該軸承支撐圓柱形部份內 側，且支撐該旋轉軸桿。該定子鐵心係形成有一穿透孔， 該軸承支撐圓柱形部份係裝入該穿透孔。該定子係固定至 該軸承支撐圓柱形部份，使該軸承支撐圓柱形部份裝入該 穿透孔。 在本發明中，構成該轉子、該定子、該葉輪、該風扇 外殼、及該馬達殼體，以致在當旋轉該轉子時被帶至該風 扇外殼之震動中所包括的複數頻率分量之中，藉由齒隙轉 矩所造成之複數頻率分量（下文稱爲齒隙轉矩頻率分量）的 -6 - 200842248 全部値（Ο ·Α·)變得比藉由該轉子之不平衡所造成的複數頻 率分量（下文稱爲不平衡頻率分量）之全部値（0·Α.)較小。 該等“齒隙轉矩頻率分量之全部値（〇.A.[f(m*n)D，，在此 被界定爲藉由該震動的頻率分析所獲得之頻率分量之中的 齒隙轉矩頻率分量之頻譜的一合成値。該等“不平衡頻率 分量之全部値（O.A.[f(n)])，，在此被界定爲藉由該震動的 頻率分析所獲得之頻率分量之中的不平衡頻率分量之頻譜 的一合成値。該“總共全部値，，係齒隙轉矩頻率分量之全 部値與不平衡頻率分量之全部値的總和。 該等發明家已硏究當該轉子旋轉時被帶至或抵達該風 扇外殼之震動，並已注意到：當該風扇外殼具有8公分之 側面的一小巧之軸向流風扇係在等於或超過2 5 0 0轉/分鐘 之高速旋轉時，齒隙轉矩頻率分量之全部値係比不平衡頻 率分量之全部値較小。當該小巧之軸向流風扇係在少於 2 5 00轉/分鐘之低速旋轉時，該齒隙轉矩頻率分量之全部 値係大於不平衡頻率分量之全部値。然後，該等發明家已 發現在低速旋轉的齒隙轉矩頻率分量之全部値越大，則被 帶至該風扇外殼之震動增加越多。據此，在本發明中，構 成該轉子、定子、葉輪、風扇外殼、及馬達殼體，以致在 包括於當該轉子旋轉時被帶至該風扇外殻的震動中之頻率 分量之中，該等齒隙轉矩頻率分量之全部値變得比不平衡 頻率分量之全部値較小。其結果是，遍及一包括低速及高 速旋轉區域之整個速率範圍，該馬達之震動可被有效地限 制。 -7- 200842248 可構思一些用於造成該齒隙轉矩頻率分量之全部値比 不平衡頻率分量之全部値較小的方法。假設該定子鐵心之 厚度被界定爲TSt，如在平行於該旋轉軸桿之軸向的方向 中所測量，且該風扇外殼之厚度被界定爲TFr，如在平行 於該軸向的方向中所測量，界定該定子及風扇外殼之形狀 及尺寸，以致TSt/TFr之比率可採取百分之8至百分之25 的値。當TSt/TFr之比率超過百分之25時，該齒隙轉矩 φ 頻率分量之全部値在該軸向流風扇之低速旋轉傾向於比不 平衡頻率分量之全部値較大。當TSt/TFr之比率落在低於 百分之8時，該馬達之輸出係減少，這將導致增大之耗電 量、增加之震動、及該軸向流風扇之開始故障。 在這些情況之下，應該要考慮該轉子及該定子間之平 衡。當該轉子之轉子磁極的厚度被界定爲TMg，如在平行 於該軸向之方向中所測量時，其較佳的是該TSt/TMg之 比率可採取百分之40至百分之70的値。 φ 再者’應該要考慮通過該空氣通道的空氣之數量。當 該空氣通道之最小內徑被界定爲Rmin，且該馬達殼體之 外徑被界定爲Rm時，其較佳的是該風扇外殼及該周邊壁 面部份可被四連結板所連接，且Rm/Rmin之比率可採取 百分之35至百分之55的値。 當該等軸承係由一對設置在該軸承支撐圓柱形部份內 側之滾珠軸承所構成’該對中之滾珠軸承係於該軸向中呈 間隔地配置時，其較佳的是配置該定子鐵心及該對滾珠軸 承，以致該定子鐵心在該軸承支撐圓柱形部份上之安裝位 -8- 200842248 胃’可爲坐落在設置於該軸承支撐圓柱形部份內側之該對 ?袞珠軸承的位置之間。以此配置，由該定子所產生之震動 係分佈與接著被帶至該對軸承。再者，藉由該轉子的旋轉 所產生之震動係不會輕易地與由該定子所產生之震動結 合。據此，大震動係不會輕易局部地產生。如此，震動可 被減少及該等滾珠軸承之使用壽命可被延伸。 根據本發明，構成該轉子、定子、葉輪、風扇外殻、 及馬達殼體，以致在包括於當該轉子旋轉時被帶至該風扇 外殻的震動中之頻率分量之中，該等齒隙轉矩頻率分量之 全部値變得比不平衡頻率分量之全部値較小。據此，遍及 轉子包括該低速及高速旋轉區域之整個速率範圍，該馬達 之震動可被有效地限制。 【實施方式】 下面將參考該等圖面詳細地敘述本發明之具體實施例 的一軸向流風扇。圖1 A至1 C分別係本發明之具體實施 例的軸向流風扇之正面圖、側視圖、及後視圖。圖2係本 發明之具體實施例的軸向流風扇之橫截面視圖。參考圖1 及2，軸向流風扇1包括風扇外殼3、馬達殼體5、葉輪 7、轉子9、及定子1 1。該風扇外殼3包括在一將稍後敘 述的旋轉軸桿37之軸向的一側面上之環狀吸入側凸緣 i 3、及一在該軸向的另一側面上之環狀排放側凸緣1 5。 於此具體實施例中’該風扇外殻的一側面之長度係8公 分。該風扇外殻3包括一在該等凸緣1 3及1 5間之圓柱形 -9- 200842248 部份1 7。一空氣通道2 1係藉由該吸入側凸緣1 3、排放側 凸緣1 5、及圓柱形部份1 7之個別內部空間所形成。該空 氣通道21具有分別位於其任一側面上之開口 i 9a及 1 9b。該空氣通道2 1的一內側表面係由該圓柱形部份的一 內部周邊表面23、及錐形表面25及26所形成，該等錐 形表面係與該內部周邊表面23連續的及在該軸向流風扇 的一徑向地朝外方向中延伸。固定不動之葉片2 8係與形 成在該排放側凸緣1 5內側之錐形表面26 —體成形。 該馬達殻體5包括底部壁面部份27、周邊壁面部份 29、及軸承支撐圓柱形部份3 1。該底部壁面部份27係位 在一開口 1 9a之側面上。該周邊壁面部份29係與該底部 壁面部份27連續地形成，且朝向該另一開口 19b延伸。 該軸承支撐圓柱形部份3 1係設在該底部壁面部份27及朝 向該另一開口 1 9b延伸。在該軸承支撐圓柱形部份3 1內 側’設置支撐該旋轉軸桿3 7之二軸承3 2。該風扇外殼 3、該馬達殼體5、及該周邊壁面部份2 9被四連結板3 3 所連接。該風扇外殻3、該馬達殼體5、及該四連結板3 3 係由合成之樹脂材料一體地形成。該四連結板3 3之外側 端部的每一個係在一位置一體地連接至該排放側凸緣 1 5 ’該位置係比該排放側凸緣1 5的一對應側面之中心位 置較接近至該排放側凸緣15之角落。然後，界定在該等 連結板3 3之端部內側連接至該馬達殼體的位置，致使通 過每一連結板3 3之外面及內側端部的虛擬直線不能通過 該馬達殼體之中心，且鄰接二連結板的個別虛擬直線之間 -10- 200842248 所形成的角度可爲90度。 於此具體實施例中，當該馬達殻體5之外徑被界定爲 Rm，且該空氣通道21之一最小內徑被界定爲Rmin時， 界定該馬達殼體5及該風扇外殼3之形狀及尺寸’以致 Rm/Rmin之比率可採取百分之35至百分之55的値。 該葉輪7包括一像杯子之葉片固定構件35及安裝至 該葉片固定構件35上之七葉片36。該葉輪7係設置在該 風扇外殻3之空氣通道21內。該葉片固定構件35係經由 一由黃銅所形成之環狀構件34固定至該旋轉軸桿37的一 端部。 在該葉片固定構件35內側，固定一由磁導性材料所 形成之環狀磁鐵固定環構件3 8。然後，由複數永久磁鐵 所構成之複數轉子磁極3 9被固定至該磁鐵固定環構件3 8 的一內部周邊部份’以致該等轉子磁極3 9被配置於該旋 轉軸桿37的一圓周方向中。在本發明中，該轉子9包括 該旋轉軸桿3 7、葉片固定構件3 5、磁鐵固定環構件3 8、 及轉子磁極39。如此，該葉輪7係固定在該轉子9之外 側。 該定子1 1包括一定子鐵心4 1及複數激磁線圏43。 該定子鐵心4 1係於該旋轉軸桿3 7之軸向中藉由複數電磁 鋼板之層疊所形成。該定子鐵心41包括複數於該旋轉軸 桿3 7之徑向中面朝該轉子磁極3 9之定子磁極4 1 a。該等 激磁線圈43係分別纏繞著該等定子磁極41a。該定子鐵 心4 1係形成具有一穿透孔4 1 b，該軸承支撐圓柱形部份 -11 - 200842248 31係裝入該穿透孔。該定子11被固定至該軸承支撐圓柱 形部份3 1，使該軸承支撐圓柱形部份3 1被裝入該穿透孔 4 1 b。該等激磁線圈43係連接至一固定在該馬達殻體5內 之電路基板45。一用於將激磁電流供給至該激磁線圈43 之電路被安裝在該電路基板45上。 於此具體實施例中，當該定子鐵心4 1之厚度被界定 爲TSt，如在平行於該旋轉軸桿3 7的軸向中所測量，且 該風扇外殼3之厚度被界定爲TFr，如平行於該軸向所測 量時，界定該定子11及該風扇外殼3之形狀及尺寸，以 致TSt/TFr之比率可採取百分之8至百分之25的値。再 者，當該轉子9的轉子磁極39之厚度被界定爲TMg，如 平行於該軸向所測量時，界定該轉子9及該定子1 1之形 狀及尺寸，以致TSt/TMg之比率可採取百分之40至百分 之70的値。於此具體實施例之軸向流風扇中，在包括當 該轉子9旋轉時被帶至該風扇外殼3的震動中之複數頻率 分量之中，遍及包括低速及高速旋轉區域之整個速率範圍 (有計畫的迴轉數或轉速之整個範圍），藉由齒隙轉矩所造 成之複數頻率分量（齒隙轉矩頻率分量）的全部値變得比藉 由該轉子的不平衡所造成之複數頻率分量（不平衡頻率分 量）的全部値較小。 其次，此具體實施例之軸向流風扇及一比較範例之軸 向流風扇被旋轉，且關於兩軸向流風扇硏究一頻率及震動 之加速度間之關係。圖3 A及3 B顯示當此具體實施例之 軸向流風扇與該比較範例之軸向流風扇係在1，9〇〇轉/分 -12- 200842248 鐘之低速下旋轉時的測量之結果。在此被用於該測試的具 體實施例之軸向流風扇中，TSt/TFr之比率係百分之20， TSt/TMg之比率係百分之67，且Rm/Rmin之比率係百分 之45。在被用於該測試的比較範例之軸向流風扇中’ TSt/TFr之比率係百分之28，TSt/TMg之比率係百分之 72，且Rm/Rmin之比率係百分之56。關於異於這些比率 之態樣，該比較範例之軸向流風扇具有與此具體實施例之 軸向流風扇相同的結構。 參考圖3A及3B，fn(在此η係一整數，譬如，fd指 示一不平衡頻率分量之頻譜，且fmn(在此η係一整數，譬 如，fm ϊ )指示一齒隙轉矩頻率分量之頻譜。其已由圖3 A 發現在此具體實施例之軸向流風扇中，在包括當該轉子在 該低速旋轉時被帶至該風扇外殻的震動中之頻率分量之 中，藉由以下式子所獲得之齒隙轉矩分量的全部値（源自 漢尼窗（Hanning Window) (HF = 2/3)之均方總和）、對該總共 全部値（齒隙轉矩頻率分量之全部値及不平衡頻率分量的 全部値之總和）的比率係百分之1 3。於以下之式子中，該 等齒隙轉矩頻率分量的頻譜（震動加速度）之合成値係如該 全部値般獲得。據此，於該以下式子中之fn指示該頻譜 fn中之頻率分量的一震動加速度値。該以下之式子獲得震 動加速度値之均方總和。於該以下之式子中，（2/3)係該漢 尼窗（Hf)的一係數。 [式子1] __ aA[/(m *")]=豕2 + Λ,22 + 九32 + …+ 网 -13- 200842248 藉由以下式子所獲得之不平衡頻率分量的全部値（源 自漢尼窗（HF = 2/3)之均方總和）對該總共全部値之比率係 百分之87。 [式子2] 0.4/⑻]=^(/;2 + Λ2 + Λ2 + …+ Λ2) ♦ (2/3) 其由圖3 B發現於該比較範例之軸向流風扇中，齒隙 轉矩頻率分量之全部値對該總共全部値的比率係百分之 66，且不平衡頻率分量之全部値對該總共全部値的比率係 百分之34。 由這些測量結果，其能看出當該比較範例之軸向流風 扇係在該低速旋轉時，齒隙轉矩頻率分量之全部値變得大 於不平衡頻率分量之全部値。其亦可看出當此具體實施例 之軸向流風扇係在該低速旋轉時，齒隙轉矩頻率分量之全 部値變得比不平衡頻率分量之全部値較小。當圖3 A係與 圖3 B比較時，其能看出於此具體實施例之軸向流風扇 中，齒隙轉矩頻率分量之全部値變得比不平衡頻率分量之 全部値較小，且因此該軸向流風扇可大致上超過該比較範 例之軸向流風扇限制震動。 圖4A及4B分別顯示當此具體實施例之軸向流風扇 與該比較範例之軸向流風扇係在3,800轉/分鐘之高速下 旋轉時的測量之結果。其已由圖4A發現於此具體實施例 之軸向流風扇中，在包括當該轉子在該高速旋轉時被帶至 -14- 200842248 該風扇外殻的震動中之複數頻率分量之中，藉由該前述式 子所獲得之齒隙轉矩頻率分量的全部値對該總共全部値之 比率係百分之6，且藉由該前述式子所獲得之不平衡頻率 分量的全部値對該總共全部値之比率係百分之9 4 °其已 由圖4B發現於該比較範例之軸向流風扇中’在包括當該 轉子在該高速旋轉時被帶至該風扇外殼的震動中之複數頻 率分量之中，藉由前述式子所獲得之齒隙轉矩頻率分量的 全部値對該總共全部値的比率係百分之3 5，且藉由前述 式子所獲得之不平衡頻率分量的全部値對該總共全部値之 比率係百分之65。 其次，TSt/TFr之比率、亦即該定子鐵心41在與該旋 轉軸桿3 7的軸向平行所測量之厚度T S t對該風扇外殼3 在與該旋轉軸桿3 7的軸向平行所測量之厚度TFr的比率 係變化。然後，以下之關係被硏究：當該軸向流風扇係在 1，900轉/分鐘之低速下旋轉時，TSt/TFr之比率及齒隙轉 矩頻率分量之全部値對該總共全部値的比率間之關係、與 TSt/TFr之比率及不平衡頻率分量之全部値對該總共全部 値的比率間之關係。亦硏究以下之關係：當該軸向流風扇 係在3,800轉/分鐘之高速下旋轉時，TSt/TFr之比率及齒 隙轉矩頻率分量之全部値對該總共全部値的比率間之關 係，與TSt/TFr之比率及不平衡頻率分量之全部値對該總 共全部値的比率間之關係。圖5顯示這些關係之測量的結 果。其可由圖5看出當該軸向流風扇係在低速旋轉，且 TSt/TFr之比率係由百分之8至百分之25，齒隙轉矩頻率 -15- 200842248 分量之全部値變得比不平衡頻率分量之全部値較小’換句 話說，齒隙轉矩頻率分量之全邰値纟彳該總共全部値的比率 變得比不平衡頻率分量之全部値對該總共全部値的比率較 小。其已確認當TSt/TFr之比率係低於百分之8時’該馬 達之輸出減少，其將導致增大之耗電量、增加之震動、及 該馬達之開始故障。據此，該下限係百分之8。其亦可看 出當該軸向流風扇係在高速下旋轉及TSt/TFr之比率等於 或少於百分之3 5時，齒隙轉矩頻率分量之全部値變得比 不平衡頻率分量之全部値較小，換句話說，齒隙轉矩頻率 分量之全部値對該總共全部値之比率變得比不平衡頻率分 量之全部値對該總共全部値的比率較小。 其次，TSt/TMg之比率、亦即該定子鐵心41在與該 旋轉軸桿3 7的軸向平行所測量之厚度TSt、對與該轉子9 的轉子磁極3 9之軸向平行所測量之厚度TMg係變化的。 然後，硏究以下之關係：當該軸向流風扇係在1，9〇〇轉/ 分鐘之低速下旋轉時，TSt/TMg之比率及齒隙轉矩頻率分 量之全部値對該總共全部値的比率間之關係、與TSt/TMg 之比率及不平衡頻率分量之全部値對該總共全部値的比率 間之關係。亦硏究以下之關係：當該軸向流風扇係在 3,8 00轉/分鐘之高速下旋轉時，TSt/TMg之比率及齒隙轉 矩頻率分量之全部値對該總共全部値的比率間之關係，與 TSt/TMg之比率及不平衡頻率分量之全部値對該總共全部 値的比率間之關係。圖6顯示這些關係之測量的結果。其 可由圖6看出當該軸向流風扇係在低速下旋轉時及 -16- 200842248 TSt/TMg之比率係由百分之40至百分之70，齒隙轉矩頻 率分量之全部値變得比不平衡頻率分量之全部値較小，換 句話說，齒隙轉矩頻率分量之全部値對該總共全部値的比 率變得比不平衡頻率分量之全部値對該總共全部値的比率 較小。 其次，Rm/Rmiri之比率，換句話說，該馬達殻體5之 外徑對該空氣通道2 1的最小內徑Rmi η之比率係變化 的。然後，硏究以下之關係：當該軸向流風扇係在1，900 轉/分鐘之低速下旋轉時，Rm/Rmin之比率及齒隙轉矩頻 率分量之全部値對該總共全部値的比率間之關係、與 Rm/Rmin之比率及不平衡頻率分量之全部値對該總共全部 値的比率間之關係。亦硏究以下之關係：當該軸向流風扇 係在3,800轉/分鐘之高速下旋轉時，Rm/Rmin之比率及 齒隙轉矩頻率分量之全部値對該總共全部値的比率間之關 係，與Rm/Rmin之比率及不平衡頻率分量之全部値對該 總共全部値的比率間之關係。圖7顯示這些關係之測量的 結果。其可由圖7看出當該軸向流風扇係在低速下旋轉及 Rm/Rmin之比率係由百分之32至百分之55時，齒隙轉矩 頻率分量之全部値變得比不平衡頻率分量之全部値較小， 換句話說，齒隙轉矩頻率分量之全部値對該總共全部値的 比率變得比不平衡頻率分量之全部値對該總共全部値的比 率較小。考慮圖8 C所示之震動加速度，其將稍後被敘 述，Rm/Rmin之較佳範圍係百分之35至百分之55。 圖 8A、8B 及 8C 分別顯示 TSt/TFr、TSt/TMg、及 -17- 200842248 R m / R m i η比率之關係的測重結果’並使該風扇外威之震動 加速。如由這些圖示所已知，於TSt/TFr、TSt/TMg、及 Rm/Rmin之較佳數値範圍中，該風扇外殼之震動力卩速度係 少於百分之1〇〇’其指示限制被帶至該風扇外殼之震動。 於圖8 A至8 c中，在用於該比較範例之軸向流風扇的震動 加速度係百分之1 〇 〇的假定之下’測量代表爲縱坐標之軸 心的震動加速度。 雖然已用某一細節之程度參考該等圖面敘述本發明之 較佳具體實施例，以上面之教導的觀點，明顯之修改及變 化係可能的。因此應了解在所附申請專利之範圍內，本發 明可異於如所特別敘述者被實現。 【圖式簡單說明】 當關於所附圖面考慮時，本發明之這些及其它目的與 許多所附優點將被輕易地體會，因它們藉由參考以下之詳 細敘述變得更佳了解。 圖1 A係本發明的一具體實施例之軸向流風扇的正面 圖。 圖1 B係本發明之具體實施例的軸向流風扇之側視 圖。 圖1 c係本發明之具體實施例的軸向流風扇之後視 圖。 圖2係本發明之具體實施例的軸向流風扇之橫截面視 圖。 -18- 200842248 圖3 A係一曲線圖，顯示當該具體實施例之軸向流風 扇係在1，900轉/分鐘之低速下旋轉時，該具體實施例之 軸向流風扇的震動之頻率及加速度間之關係。 圖3 B係一曲線圖，顯示當一比較範例之軸向流風扇 係在1，900轉/分鐘之低速下旋轉時，該比較範例之軸向 流風扇的震動之頻率及加速度間之關係。 圖4A係一曲線圖，顯示當該具體實施例之軸向流風 扇係在3,800轉/分鐘之高速下旋轉時，該具體實施例之 軸向流風扇的震動之頻率及加速度間之關係。 圖4 B係一曲線圖，顯示當一比較範例之軸向流風扇 係在3,800轉/分鐘之高速下旋轉時，該比較範例之軸向 流風扇的震動之頻率及加速度間之關係。 圖5係一曲線圖，顯示當一定子鐵心之厚度被界定爲 TSt，如在平行於該旋轉軸桿之軸向中所測量，且風扇外 殼之厚度被界定爲TFr，如在平行於該軸向中所測量，且 該TSt/TFr之比率係變化的時，硏究以下之關係的測量之 結果：當該具體實施例之軸向流風扇係在1，900轉/分鐘 之低速下旋轉時，TSt/TFr之比率及齒隙轉矩頻率分量對 總共全部値的比率間之關係、與TSt/TFr之比率及不平衡 頻率分量之全部値對總共全部値的比率間之關係，以及當 該具體實施例之軸向流風扇係在3,800轉/分鐘之高速下 旋轉時，TSt/TFr之比率及齒隙轉矩頻率分量之全部値對 總共全部値的比率間之關係、與TSt/TFr之比率及不平衡 頻率分量之全部値對總共全部値的比率間之關係。 -19- 200842248 圖6係一曲線圖，顯示當該定子鐵心之厚度被界定爲 T St，如在平行於該旋轉軸桿之軸向中所測量，一轉子之 轉子磁極的厚度被界定爲TMg，如在平行於該軸向中所測 量，且該TSt/TFr之比率係變化的時，硏究以下之關係的 測量之結果：當該軸向流風扇係在1，9 00轉/分鐘之低速 下旋轉時，TSt/TMg之比率及齒隙轉矩頻率分量之全部値 對總共全部値的比率間之關係、與TSt/TMg之比率及不 平衡頻率分量之全部値對總共全部値的比率間之關係，以 及當該軸向流風扇係在3,800轉/分鐘之高速下旋轉時， TSt/TMg之比率及齒隙轉矩頻率分量之全部値對總共全部 値的比率間之關係、與TSt/TMg之比率及不平衡頻率分 量之全部値對總共全部値的比率間之關係。 圖7係一曲線圖，顯示當一馬達殻體之外徑被界定爲 Rm，一空氣通道之最小內徑被界定爲Rmin，及Rm/Rmin 之比率係變化的時，硏究以下之關係的測量之結果：當該 軸向流風扇係在1，900轉/分鐘之低速下旋轉時，Rm/Rmin 之比率及齒隙轉矩頻率分量之全部値對總共全部値的比率 間之關係、與Rm/Rmin之比率及不平衡頻率分量之全部 値對總共全部値的比率間之關係，以及當該軸向流風扇係 在3,800轉/分鐘之高速下旋轉時，Rm/Rmin之比率及齒 隙轉矩頻率分量之全部値對總共全部値的比率間之關係、 與Rm/Rmin之比率及不平衡頻率分量之全部値對總共全 部値的比率間之關係。 圖8A、8B、及8C係曲線圖，分別顯示硏究 -20- 200842248 TSt/TFr、TSt/TMg、及Rm/Rmin比率之關係的測量之結 果，並使該風扇外殼之震動加速。 【主要元件符號說明】 1 :軸向流風扇 3 :風扇外殼 5 :馬達殼體 7 :葉輪 9 :轉子 1 1 :定子 1 3 :凸緣 1 5 :凸緣 1 7 :圓柱形部份 19a :開□ 19b :開□ 21 :空氣通道 2 3 :內部周邊表面 2 5 :錐形表面 2 6 :錐形表面 27 :底部壁面部份 28 :葉片 29 :周邊壁面部份 3 1 :圓柱形部份 3 2 :軸承 -21 - 200842248 連結板 環狀構件 葉片固定構件 葉片 軸桿 磁鐵固定環構件 轉子磁極 定子鐵心 :定子磁極 :穿透孔 激磁線圈 電路基板 >22-200842248 IX. Description of the Invention [Technical Field] The present invention relates to an axial flow fan for cooling an electrical component or the like. [Prior Art] Japanese Patent Publication No. 05-1648 (hereinafter referred to as Patent Document 1) discloses an axial flow fan including a fan casing, an impeller having a plurality of blades, a rotor, a stator, and a motor casing. The rotor includes a rotating shaft and a plurality of rotor poles formed by permanent magnets and disposed in a circumferential direction of the rotating shaft and fixed to the impeller. The stator includes a certain sub-core and an excitation coil. The stator core includes a plurality of stator poles facing the rotor poles in a radial direction of the rotating shaft. The exciting coils are wound around the stator poles, respectively. The motor housing includes a bearing support cylindrical portion. Inside the cylindrical portion of the bearing support, a bearing that supports the rotating shaft of the rotor is disposed. The stator core is formed by a penetration hole into which the cylindrical portion of the bearing support is fitted. The stator is fixed to the cylindrical portion of the bearing support such that the bearing support cylindrical portion is fitted into the through hole. In the axial flow fan of this type disclosed in Patent Document 1, the vibration generated when the rotor is rotated is brought to or reaches the fan casing. For this reason, the increase in vibration caused noise. In the conventional axial flow fan, when the number of revolutions for the rotor is small, or the rotor is rotated at a low speed, the vibration reaching the fan casing is increased. SUMMARY OF THE INVENTION It is an object of the present invention to provide an axial flow fan that is capable of limiting the shock that is carried to the fan casing throughout the entire rate range of a rotor. An improvement of an axial flow fan is directed to the object of the present invention. The axial flow fan includes a fan casing, an impeller, a rotor, a stator, a motor housing, and a bearing. The fan casing includes an air passage having two openings, i.e., an opening and another opening. The impeller is disposed inside the air passage and includes a plurality of blades. The rotor includes a rotating shaft and a plurality of rotor poles formed of permanent magnets. The rotor poles are disposed in the circumferential direction of the rotating shaft. The stator includes a stator core having a plurality of stator poles, and an exciting coil wound around the stator poles, respectively. The stator poles face the rotor poles in a radial direction of the rotating shaft. The motor housing includes a bottom wall portion on a side of the opening, a peripheral wall portion continuously formed by the bottom wall portion and extending toward the other opening, and a bottom wall portion disposed on the bottom wall portion The portion and the bearing extending toward the other opening support the cylindrical portion. The bearings are disposed on the inner side of the cylindrical portion of the bearing support and support the rotating shaft. The stator core is formed with a through hole, and the bearing supporting cylindrical portion is fitted into the through hole. The stator is fixed to the bearing support cylindrical portion such that the bearing support cylindrical portion is fitted into the penetration hole. In the present invention, the rotor, the stator, the impeller, the fan casing, and the motor casing are configured such that among the plurality of frequency components included in the vibration of the fan casing when the rotor is rotated, -6 - 200842248 by the complex frequency component caused by the backlash torque (hereinafter referred to as the backlash torque frequency component) becomes 复 (Ο ·Α·) becomes a complex number caused by the imbalance of the rotor The total 値(0·Α.) of the frequency component (hereinafter referred to as the unbalanced frequency component) is small. All of the "backlash torque frequency components" (〇.A.[f(m*n)D,, herein defined as the backlash transition among the frequency components obtained by the frequency analysis of the vibration a composite of the spectrum of the moment frequency components. The total 値 (OA[f(n)]) of the "unbalanced frequency components" is defined herein as the frequency component obtained by the frequency analysis of the vibration. a composite of the spectrum of the unbalanced frequency components. The total of all, ,, the sum of all the 値 and unbalanced frequency components of the backlash torque frequency component. The inventors have studied the rotor The vibration that is brought to or reaches the fan casing when rotated, and it has been noted that when the fan casing has a side of 8 cm, a compact axial flow fan is rotated at a speed equal to or exceeding 2,500 rpm. When all of the backlash torque frequency components are smaller than the total unbalanced frequency components, the backlash is turned when the compact axial flow fan is rotated at a low speed of less than 2 500 rpm. All of the moments of the moment frequency component are greater than the total of the unbalanced frequency components. Then, the inventors have found that the greater the total value of the backlash torque frequency component at the low speed rotation, the more the vibration is brought to the fan casing. Accordingly, in the present invention, the rotor and the stator are constructed. The impeller, the fan casing, and the motor casing such that among the frequency components included in the vibrations brought to the fan casing when the rotor rotates, all of the backlash torque frequency components become The total frequency of the unbalanced frequency components is small. As a result, the vibration of the motor can be effectively limited throughout the entire rate range including the low speed and high speed rotation regions. -7- 200842248 It is conceivable to create some of the backlash. a method in which all of the torque frequency components are smaller than the total of the unbalanced frequency components. It is assumed that the thickness of the stator core is defined as TSt, as measured in a direction parallel to the axial direction of the rotating shaft, and The thickness of the fan casing is defined as TFr, as measured in a direction parallel to the axial direction, defining the shape and size of the stator and the fan casing such that the ratio of TSt/TFr can be taken as a percentage Between 8 and 25 percent. When the ratio of TSt/TFr exceeds 25 percent, the total value of the backlash torque φ frequency component tends to be lower than the unbalanced frequency component at the low speed rotation of the axial flow fan. All of the turns are larger. When the ratio of TSt/TFr falls below 8 percent, the output of the motor is reduced, which will result in increased power consumption, increased vibration, and the axial flow fan. In this case, the balance between the rotor and the stator should be considered. When the rotor pole thickness of the rotor is defined as TMg, as measured in a direction parallel to the axial direction, Preferably, the ratio of TSt/TMg can be from 40 to 70 percent. φ Again, the amount of air passing through the air passage should be considered. When the minimum inner diameter of the air passage is defined as Rmin, and when the outer diameter of the motor casing is defined as Rm, it is preferable that the fan casing and the peripheral wall portion can be connected by four connecting plates, and the ratio of Rm/Rmin can be 35 percent. Up to 55 percent. When the bearings are formed by a pair of ball bearings disposed inside the cylindrical portion of the bearing support, the ball bearings of the pair are spaced apart in the axial direction, preferably the stator is disposed a core and the pair of ball bearings, such that the stator core is mounted on the cylindrical portion of the bearing support -8- 200842248; the stomach ' can be located on the inner side of the cylindrical portion of the bearing support Between the locations. With this configuration, the vibrations generated by the stator are distributed and subsequently brought to the pair of bearings. Moreover, the vibration generated by the rotation of the rotor is not easily combined with the vibration generated by the stator. Accordingly, the large vibration system does not easily occur locally. Thus, the vibration can be reduced and the service life of the ball bearings can be extended. According to the present invention, the rotor, the stator, the impeller, the fan casing, and the motor casing are constructed such that the backlash is included in a frequency component included in the vibration of the fan casing when the rotor rotates The total 値 of the torque frequency component becomes smaller than the total 値 of the unbalanced frequency component. Accordingly, the vibration of the motor can be effectively limited throughout the entire rate range in which the rotor includes the low speed and high speed rotating regions. [Embodiment] An axial flow fan of a specific embodiment of the present invention will be described in detail below with reference to the drawings. 1A to 1C are a front view, a side view, and a rear view, respectively, of an axial flow fan of a specific embodiment of the present invention. Figure 2 is a cross-sectional view of an axial flow fan in accordance with a particular embodiment of the present invention. Referring to Figures 1 and 2, the axial flow fan 1 includes a fan casing 3, a motor casing 5, an impeller 7, a rotor 9, and a stator 11. The fan casing 3 includes an annular suction side flange i 3 on one side of an axial direction of a rotary shaft 37 to be described later, and an annular discharge side convex on the other side in the axial direction. Edge 1 5. In this embodiment, the length of one side of the fan casing is 8 cm. The fan casing 3 includes a cylindrical portion -9-200842248 portion 17 between the flanges 13 and 15. An air passage 21 is formed by the individual inner spaces of the suction side flange 13, the discharge side flange 15, and the cylindrical portion 17. The air passage 21 has openings i 9a and 19b on either side thereof. An inner side surface of the air passage 21 is formed by an inner peripheral surface 23 of the cylindrical portion, and tapered surfaces 25 and 26, the tapered surfaces being continuous with the inner peripheral surface 23 and A radially outwardly extending direction of the axial flow fan. The stationary blade 28 is integrally formed with a tapered surface 26 formed on the inside of the discharge side flange 15. The motor housing 5 includes a bottom wall portion 27, a peripheral wall portion 29, and a bearing support cylindrical portion 31. The bottom wall portion 27 is positioned on the side of an opening 19a. The peripheral wall portion 29 is formed continuously with the bottom wall portion 27 and extends toward the other opening 19b. The bearing support cylindrical portion 31 is disposed on the bottom wall portion 27 and extends toward the other opening 19b. A bearing 3 2 supporting the rotating shaft 37 is disposed on the inner side of the bearing support cylindrical portion 31. The fan casing 3, the motor casing 5, and the peripheral wall portion 29 are connected by four connecting plates 3 3 . The fan casing 3, the motor casing 5, and the four coupling plates 3 3 are integrally formed of a synthetic resin material. Each of the outer end portions of the four webs 3 3 is integrally connected to the discharge side flange 15 5 at a position that is closer to a center position of a corresponding side of the discharge side flange 15 to The corner of the discharge side flange 15. Then, a position connected to the motor housing inside the end portions of the connecting plates 33 is defined such that a virtual straight line passing through the outer and inner ends of each of the connecting plates 3 3 cannot pass through the center of the motor housing, and The angle formed by the individual virtual straight lines adjacent to the two webs may be 90 degrees. In this embodiment, when the outer diameter of the motor housing 5 is defined as Rm and the minimum inner diameter of one of the air passages 21 is defined as Rmin, the shape of the motor housing 5 and the fan housing 3 are defined. And the size 'so that the ratio of Rm / Rmin can take 35 to 55 percent of the enthalpy. The impeller 7 includes a cup-like blade fixing member 35 and seven blades 36 mounted to the blade fixing member 35. The impeller 7 is disposed within the air passage 21 of the fan casing 3. The blade fixing member 35 is fixed to one end portion of the rotating shaft 37 via an annular member 34 formed of brass. Inside the blade fixing member 35, a ring-shaped magnet fixing ring member 38 formed of a magnetically conductive material is fixed. Then, a plurality of rotor poles 39 composed of a plurality of permanent magnets are fixed to an inner peripheral portion of the magnet fixing ring member 38 such that the rotor poles 39 are disposed in a circumferential direction of the rotating shaft 37. in. In the present invention, the rotor 9 includes the rotating shaft 37, the blade fixing member 35, the magnet fixing ring member 38, and the rotor magnetic pole 39. Thus, the impeller 7 is fixed to the outside of the rotor 9. The stator 11 includes a fixed sub-core 41 and a plurality of exciting wires 43. The stator core 41 is formed by laminating a plurality of electromagnetic steel sheets in the axial direction of the rotating shaft 37. The stator core 41 includes a plurality of stator poles 4 1 a facing the rotor poles 39 in the radial direction of the rotating shaft 37. The excitation coils 43 are wound around the stator poles 41a, respectively. The stator core 41 is formed with a through hole 4 1 b, and the bearing supporting cylindrical portion -11 - 200842248 31 is fitted into the penetration hole. The stator 11 is fixed to the bearing support cylindrical portion 301, so that the bearing support cylindrical portion 31 is fitted into the penetration hole 4 1 b. The exciting coils 43 are connected to a circuit board 45 fixed in the motor casing 5. A circuit for supplying an exciting current to the exciting coil 43 is mounted on the circuit substrate 45. In this embodiment, when the thickness of the stator core 41 is defined as TSt, as measured in an axial direction parallel to the rotating shaft 37, and the thickness of the fan casing 3 is defined as TFr, such as The shape and size of the stator 11 and the fan casing 3 are defined parallel to the axial direction such that the ratio of TSt/TFr can be from 8 to 25 percent. Furthermore, when the thickness of the rotor pole 39 of the rotor 9 is defined as TMg, as measured parallel to the axial direction, the shape and size of the rotor 9 and the stator 11 are defined such that the ratio of TSt/TMg can be taken 40% to 70% of the total. In the axial flow fan of this embodiment, the entire frequency range including the low speed and high speed rotation regions is included in the plurality of frequency components including the vibrations brought to the fan casing 3 when the rotor 9 rotates (there are The entire range of the number of revolutions or speeds of the project), the total frequency of the complex frequency component (the backlash torque frequency component) caused by the backlash torque becomes larger than the complex frequency caused by the imbalance of the rotor The total 値 of the component (unbalanced frequency component) is small. Next, the axial flow fan of this embodiment and a comparative example axial flow fan are rotated, and the relationship between the acceleration of a frequency and the vibration is investigated with respect to the two axial flow fans. 3A and 3B show the results of measurements when the axial flow fan of this embodiment and the axial flow fan of the comparative example are rotated at a low speed of 1,9 rpm/min-12-200842248 sec. . In the axial flow fan of the specific embodiment used in this test, the ratio of TSt/TFr is 20%, the ratio of TSt/TMg is 67%, and the ratio of Rm/Rmin is 100%. 45. In the axial flow fan of the comparative example used in this test, the ratio of 'TSt/TFr was 28%, the ratio of TSt/TMg was 72%, and the ratio of Rm/Rmin was 56%. Regarding the aspect different from these ratios, the axial flow fan of this comparative example has the same structure as the axial flow fan of this embodiment. Referring to Figures 3A and 3B, fn (where η is an integer, for example, fd indicates the spectrum of an unbalanced frequency component, and fmn (where η is an integer, for example, fm ϊ ) indicates a backlash torque frequency component The spectrum of the axial flow fan of this embodiment, as found in Figure 3A, includes the frequency component of the vibration that is brought to the fan casing when the rotor is rotated at the low speed. The total value of the backlash torque component obtained by the following equation (from the mean square sum of the Hanning Window (HF = 2/3)), for the total total 値 (the backlash torque frequency component) The ratio of the total sum of all 値 and unbalanced frequency components is 13%. In the following equation, the synthesis of the spectrum (vibration acceleration) of the backlash torque frequency components is all According to this, fn in the following expression indicates a vibration acceleration 値 of the frequency component in the spectrum fn. The following equation obtains the mean square sum of the vibration acceleration 。. In the following equation , (2/3) is a coefficient of the Hanni window (Hf). [Formula 1] __ aA[/(m *")]=豕2 + Λ,22 + 九32 + ...+ net-13- 200842248 The total 値 of the unbalanced frequency components obtained by the following equation (from the Hanni window ( The sum of the mean squares of HF = 2/3) is 87% of the total total 。. [Formula 2] 0.4/(8)]=^(/;2 + Λ2 + Λ2 + ...+ Λ2) ♦ ( 2/3) It is found in Fig. 3B that in the axial flow fan of the comparative example, the ratio of the total value of the backlash torque frequency component to the total total enthalpy is 66%, and the total of the unbalanced frequency components The ratio of 値 to the total 値 is 34. From these measurements, it can be seen that when the axial flow fan of the comparative example is rotated at the low speed, the total frequency component of the backlash torque becomes It is greater than the total 不 of the unbalanced frequency component. It can also be seen that when the axial flow fan of this embodiment is rotated at the low speed, the total 値 of the backlash torque frequency component becomes more than the unbalanced frequency component. When Fig. 3A is compared with Fig. 3B, it can be seen that in the axial flow fan of this embodiment, the frequency component of the backlash torque is completely transformed. The total 値 is smaller than the unbalanced frequency component, and thus the axial flow fan can substantially exceed the axial flow fan limiting vibration of the comparative example. Figures 4A and 4B show the axial flow fan of this embodiment, respectively. The result of the measurement when the axial flow fan of the comparative example is rotated at a high speed of 3,800 rpm. It has been found in the axial flow fan of this embodiment by FIG. 4A, including when the rotor is in the When rotating at high speed, it is brought to -14- 200842248. Among the complex frequency components in the vibration of the fan casing, the ratio of the total 齿 of the backlash torque frequency component obtained by the above equation to the total 値 is 6 percent, and the ratio of the total enthalpy of the unbalanced frequency component obtained by the foregoing equation to the total total enthalpy is 9 4 ° which has been found in the axial flow of the comparative example by FIG. 4B Among the plurality of frequency components in the fan including the vibration that is brought to the fan casing when the rotor is rotated at the high speed, all of the backlash torque frequency components obtained by the foregoing equation are all Awkward ratio Line 35 percent, and by all the frequency components of the unbalanced Zhi formulas obtained for the ratio of the total of all the lines Zhi 65 percent. Next, the ratio of TSt/TFr, that is, the thickness TS t of the stator core 41 measured in parallel with the axial direction of the rotating shaft 37, is parallel to the axial direction of the rotating shaft 33 to the fan casing 3. The ratio of the measured thickness TFr is varied. Then, the following relationship is considered: when the axial flow fan is rotated at a low speed of 1,900 rpm, the ratio of the TSt/TFr and the frequency component of the backlash torque are all 値The relationship between the ratio, the ratio to the TSt/TFr, and the ratio of the total of the unbalanced frequency components to the total ratio of all 値. The following relationship is also considered: when the axial flow fan is rotated at a high speed of 3,800 rpm, the relationship between the ratio of TSt/TFr and the frequency component of the backlash torque to the total ratio of all turns is also considered. The relationship between the ratio of TSt/TFr and the ratio of all unbalanced frequency components to the total ratio of all 値. Figure 5 shows the results of measurements of these relationships. It can be seen from FIG. 5 that when the axial flow fan is rotated at a low speed, and the ratio of TSt/TFr is from 8 to 25 percent, the total value of the backlash torque frequency is -15-200842248. All of the ratios of the unbalanced frequency components are smaller. In other words, the ratio of the total frequency of the backlash torque frequency components to the total total turns becomes the ratio of the total of the unbalanced frequency components to the total total turns. Smaller. It has been confirmed that when the ratio of TSt/TFr is less than 8 percent, the output of the motor is reduced, which will result in increased power consumption, increased vibration, and the start of the motor. Accordingly, the lower limit is 8 percent. It can also be seen that when the axial flow fan is rotated at a high speed and the ratio of TSt/TFr is equal to or less than 35%, the total frequency of the backlash torque frequency component becomes larger than the unbalanced frequency component. All 値 is small, in other words, the ratio of the total 値 of the backlash torque frequency component to the total 値 becomes smaller than the ratio of all of the unbalanced frequency components to the total 値. Next, the ratio of TSt/TMg, that is, the thickness TSt measured by the stator core 41 in parallel with the axial direction of the rotating shaft 37, and the thickness measured parallel to the axial direction of the rotor pole 39 of the rotor 9 The TMg system is variable. Then, the following relationship is considered: when the axial flow fan is rotated at a low speed of 1,9 rpm, the ratio of the TSt/TMg and the frequency component of the backlash torque are all 値The relationship between the ratios, the ratio of TSt/TMg, and the ratio of all unbalanced frequency components to the total ratio of all 値. Also consider the following relationship: When the axial flow fan is rotated at a high speed of 3,800 rpm, the ratio of the ratio of TSt/TMg and the frequency component of the backlash torque to the total total 値The relationship between the ratio of TSt/TMg and the ratio of all unbalanced frequency components to the total ratio of all 値. Figure 6 shows the results of measurements of these relationships. It can be seen from Fig. 6 that when the axial flow fan rotates at a low speed and the ratio of -16-200842248 TSt/TMg is from 40 to 70 percent, the total frequency of the backlash torque frequency component is changed. It is smaller than the total 値 of the unbalanced frequency component, in other words, the ratio of the total 値 of the backlash torque frequency component to the total 値 is higher than the ratio of the total 不 of the unbalanced frequency component to the total 値small. Next, the ratio of Rm/Rmiri, in other words, the ratio of the outer diameter of the motor casing 5 to the minimum inner diameter Rmi η of the air passage 2 1 varies. Then, the following relationship is investigated: when the axial flow fan is rotated at a low speed of 1,900 rpm, the ratio of the Rm/Rmin ratio and the backlash torque frequency component to the total total enthalpy ratio The relationship between the relationship between the ratio, the ratio of Rm/Rmin, and the ratio of all unbalanced frequency components to the total ratio of all 値. The following relationship is also considered: when the axial flow fan is rotated at a high speed of 3,800 rpm, the relationship between the ratio of Rm/Rmin and the frequency component of the backlash torque to the total ratio of all turns is also considered. The relationship between the ratio of Rm/Rmin and the ratio of all unbalanced frequency components to the total ratio of all 値. Figure 7 shows the results of measurements of these relationships. It can be seen from FIG. 7 that when the axial flow fan rotates at a low speed and the ratio of Rm/Rmin is from 32 to 55 percent, the total frequency of the backlash torque frequency component becomes more than unbalanced. The total 値 of the frequency components is small, in other words, the ratio of the total 値 of the backlash torque frequency component to the total 値 becomes smaller than the ratio of the total 不 of the unbalanced frequency component to the total 値. Consider the vibration acceleration shown in Fig. 8C, which will be described later, and the preferred range of Rm/Rmin is 35 to 55 percent. Figures 8A, 8B, and 8C show the results of the weight measurement of the relationship of Tst/TFr, TSt/TMg, and -17-200842248 R m / R m i η, respectively, and accelerate the vibration of the fan. As is known from these figures, in the preferred range of TST/TFr, TSt/TMg, and Rm/Rmin, the vibration force of the fan casing is less than 1% of the indication. Limit the vibration that is brought to the fan casing. In Figs. 8A to 8c, under the assumption that the vibration acceleration of the axial flow fan used in the comparative example is 1 〇 百分之, the vibration acceleration representing the axis of the ordinate is measured. Although the preferred embodiment of the present invention has been described with reference to the details of the details of the present invention, it is obvious that modifications and variations are possible. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and many of the advantages of the present invention will be readily appreciated by the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A is a front elevational view of an axial flow fan in accordance with an embodiment of the present invention. Figure 1B is a side elevational view of an axial flow fan of a particular embodiment of the present invention. Figure 1 c is a rear view of an axial flow fan of a particular embodiment of the present invention. Figure 2 is a cross-sectional view of an axial flow fan in accordance with an embodiment of the present invention. -18- 200842248 Fig. 3A is a graph showing the frequency of vibration of the axial flow fan of the embodiment when the axial flow fan of the embodiment is rotated at a low speed of 1,900 rpm. And the relationship between acceleration. Fig. 3B is a graph showing the relationship between the vibration frequency and the acceleration of the axial flow fan of the comparative example when a comparative example axial flow fan is rotated at a low speed of 1,900 rpm. Fig. 4A is a graph showing the relationship between the frequency of vibration of the axial flow fan of the embodiment and the acceleration when the axial flow fan of the embodiment is rotated at a high speed of 3,800 rpm. Fig. 4B is a graph showing the relationship between the vibration frequency and the acceleration of the axial flow fan of the comparative example when a comparative example axial flow fan is rotated at a high speed of 3,800 rpm. Figure 5 is a graph showing that when the thickness of a certain core is defined as TSt, as measured in an axial direction parallel to the axis of rotation, and the thickness of the fan casing is defined as TFr, as in parallel to the axis When measured in the middle and the ratio of the TSt/TFr is varied, the result of the measurement of the following relationship is considered: when the axial flow fan of the specific embodiment is rotated at a low speed of 1,900 rpm , the relationship between the ratio of TSt/TFr and the ratio of the backlash torque frequency component to the total total enthalpy, the ratio to the TSt/TFr, and the ratio of the total of the unbalanced frequency components to the total 値, and When the axial flow fan of the specific embodiment is rotated at a high speed of 3,800 rpm, the relationship between the ratio of TSt/TFr and the frequency component of the backlash torque to the total ratio of all turns, and the relationship between TSt/TFr The relationship between the ratio of the ratio and the unbalanced frequency component to the total ratio of all 値. -19- 200842248 Figure 6 is a graph showing that when the thickness of the stator core is defined as T St , as measured in the axial direction parallel to the rotating shaft, the thickness of the rotor pole of a rotor is defined as TMg As measured parallel to the axial direction, and the ratio of the TSt/TFr is varied, the result of the measurement of the following relationship is considered: when the axial flow fan is at 1,900 rpm When rotating at low speed, the ratio of the ratio of TSt/TMg and the frequency component of the backlash torque to the total ratio of all 値, the ratio of TSt/TMg and the ratio of all unbalanced frequency components to the total total 値The relationship between the ratio of the TSt/TMg and the frequency component of the backlash torque to the total ratio of all turns, and the TSt, when the axial fan is rotated at a high speed of 3,800 rpm. The relationship between the ratio of /TMg and the ratio of all unbalanced frequency components to the total ratio of all 値. Figure 7 is a graph showing the relationship between when the outer diameter of a motor housing is defined as Rm, the minimum inner diameter of an air passage is defined as Rmin, and the ratio of Rm/Rmin is varied. Measurement result: When the axial flow fan is rotated at a low speed of 1,900 rpm, the relationship between the ratio of Rm/Rmin and the frequency component of the backlash torque to the total ratio of all turns, and The relationship between the ratio of Rm/Rmin and the ratio of all the unbalanced frequency components to the total enthalpy ratio, and the ratio of Rm/Rmin and backlash when the axial flow fan is rotated at a high speed of 3,800 rpm The relationship between the total ratio of the torque frequency components to the ratio of total 値, the ratio to Rm/Rmin, and the ratio of all of the unbalanced frequency components to the total 値 ratio. Figs. 8A, 8B, and 8C are graphs showing the results of the measurement of the relationship between the TSt/TFr, TSt/TMg, and Rm/Rmin ratios, respectively, and accelerating the vibration of the fan casing. [Main component symbol description] 1 : Axial flow fan 3 : Fan case 5 : Motor case 7 : Impeller 9 : Rotor 1 1 : Stator 1 3 : Flange 1 5 : Flange 1 7 : Cylindrical portion 19a : Opening 19b: opening 21: air passage 2 3 : inner peripheral surface 2 5 : tapered surface 2 6 : tapered surface 27 : bottom wall portion 28 : blade 29 : peripheral wall portion 3 1 : cylindrical portion 3 2 : bearing-21 - 200842248 connecting plate annular member blade fixing member blade shaft magnet fixing ring member rotor magnetic pole stator core: stator magnetic pole: penetration hole excitation coil circuit substrate > 22-