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齒輪傳動(dòng)是機(jī)械設(shè)備中最常見的傳動(dòng)方式，現(xiàn)代機(jī)械對(duì)齒輪傳動(dòng)的要求日益提高，即要求齒輪能在高速、重載、特殊介質(zhì)等惡劣環(huán)境條件下工作，又要求齒輪裝置具有較高的平穩(wěn)性、高可靠性和結(jié)構(gòu)緊湊等良好的工作性能，由此使得齒輪發(fā)生故障的因素越來越多，而齒輪異常又是誘發(fā)機(jī)器故障的重要因素。因此，齒輪故障診斷技術(shù)的應(yīng)用研究是非常重要的。
齒輪由于制造、操作、維護(hù)以及齒輪材料、熱處理、運(yùn)行狀態(tài)等因素不同，產(chǎn)生異常的形式也不同，齒輪常見的故障形式有如下幾種：
1、齒的斷裂
齒的斷裂分疲勞斷裂和過負(fù)荷斷裂。疲勞斷裂是齒輪重復(fù)受載后由于應(yīng)力集中產(chǎn)生的。當(dāng)齒輪副進(jìn)入嚙合狀態(tài)時(shí)，最危險(xiǎn)的瞬間是接觸點(diǎn)位于齒輪的頂部，此時(shí)在齒根部產(chǎn)生的彎曲應(yīng)力為最大，存在較嚴(yán)重的應(yīng)力集中，當(dāng)載荷超過設(shè)計(jì)值，或者齒輪在周期性交變載荷作用下，經(jīng)過一定的載荷循環(huán)后，齒的根部有可能產(chǎn)生裂紋。齒輪繼續(xù)工作，裂紋向根部縱深發(fā)展，當(dāng)裂紋削弱的根部不能承受彎曲應(yīng)力時(shí)，齒就發(fā)生斷裂。
過負(fù)荷斷裂是由于機(jī)械系統(tǒng)速度的急劇變化，軸系共振，軸承破損，軸的彎曲等原因，使齒輪產(chǎn)生不正常的一端接觸，載荷集中到齒面的一端而引起的，其原因主要是由于裝配不良，機(jī)器運(yùn)轉(zhuǎn)時(shí)存在其他故障問題。
齒的斷裂是齒輪最嚴(yán)重的故障，常因此造成設(shè)備停機(jī)，或者引起機(jī)器其他零部件的故障。
2、齒的磨損
磨損是指金屬的整個(gè)齒面上連續(xù)不斷地?fù)p耗，從而在齒面上產(chǎn)生金屬的研磨狀。齒輪在嚙合過程中，往往在輪齒接觸表面上出現(xiàn)材料摩擦損傷的現(xiàn)象。如果磨損量不影響齒輪在其壽命內(nèi)應(yīng)具備的功能的磨損，我們稱之為正常磨損，其特征是齒面光滑，沒有宏觀擦傷，各項(xiàng)公差在允許范圍內(nèi)。如果由于齒輪用材不當(dāng)，或在接觸面間存在硬質(zhì)顆粒，以及潤(rùn)滑油供應(yīng)不足或不清潔，往往以其齒輪的早期磨損，有微小的顆粒分離出來，接觸表面發(fā)生尺寸變化，嚴(yán)重?fù)p失，并使齒形改變，齒厚邊薄，甚至出現(xiàn)“刀片”狀齒尖；嚙合間隙增大；噪聲增大；嚴(yán)重磨損的結(jié)果將導(dǎo)致齒輪失效。齒的磨損情況有下列幾類：
1）粘著磨損
粘著磨損是油膜被破壞而發(fā)生齒面金屬的直接接觸形成的。產(chǎn)生粘著磨損的原因可能是齒輪工作在低速、重載、高溫、潤(rùn)滑油黏度太低、供油不足和齒面粗糙等情況。
2）磨粒磨損
由于潤(rùn)滑油中夾雜直徑大于30um以上的顆粒，或者油污、金屬屑末、塵埃和砂粒等進(jìn)入齒的工作表面，引起磨粒磨損。磨粒磨損多發(fā)生在齒根、齒頂處地滑動(dòng)接觸部位，而在節(jié)園處較少發(fā)生。
3）腐蝕磨損
潤(rùn)滑油中含有酸、堿和水等易對(duì)金屬產(chǎn)生腐蝕的化學(xué)物質(zhì)，與齒面發(fā)生化學(xué)反應(yīng)，有腐蝕導(dǎo)致齒面損傷。
除了上述三類磨損情況外，由于不對(duì)中、聯(lián)軸節(jié)磨損，裝配不良以及扭轉(zhuǎn)共振，在齒輪嚙合點(diǎn)引起很大的扭矩變化，使齒輪嚙合時(shí)的沖擊加大，這些因素也將加速齒的磨損。此外，齒輪金屬材料的熱處理質(zhì)量差也容易發(fā)生齒的磨損故障。
3、齒面疲勞
齒輪在嚙合過程中，既有相對(duì)滾動(dòng)，又有相對(duì)滑動(dòng)。在滾動(dòng)中齒面接觸區(qū)內(nèi)的正壓力使表面層深處產(chǎn)生剪應(yīng)力，另一方面，齒面的相對(duì)滑動(dòng)，又會(huì)使表面產(chǎn)生拉應(yīng)力。在兩種力的作用下，就會(huì)導(dǎo)致齒輪表面層深處產(chǎn)生脈動(dòng)循環(huán)變化的剪應(yīng)力。當(dāng)這種剪應(yīng)力超過了齒輪材料的剪切疲勞極限，或者說齒面上脈動(dòng)循環(huán)變化的接觸應(yīng)力超過齒面的接觸疲勞極限時(shí)，齒面將會(huì)出現(xiàn)疲勞裂紋。隨著裂紋的擴(kuò)展，最終使齒面出現(xiàn)小塊金屬剝落，在齒面上形成小坑，稱為點(diǎn)蝕。當(dāng)點(diǎn)蝕進(jìn)一步擴(kuò)大，連成一片時(shí)，就會(huì)形成齒面上大塊的金屬剝落。這就是所謂的接觸疲勞剝落。它一般總是發(fā)生在輪齒根部靠近節(jié)圓處，嚴(yán)重剝落時(shí)就會(huì)影響齒輪的正常工作，甚至造成輪齒折斷。很多情況下，由于輪齒材質(zhì)的不均勻，或有局部擦傷等，就容易在某一輪齒上首先出現(xiàn)接觸疲勞，產(chǎn)生剝落。
發(fā)生點(diǎn)蝕的常見原因是齒表面硬度不夠，點(diǎn)蝕一般都發(fā)生在靠近節(jié)線的齒根部分，局部性點(diǎn)蝕現(xiàn)象并不危險(xiǎn)，齒輪實(shí)際上還能繼續(xù)長(zhǎng)期工作，這種局部性點(diǎn)蝕是由于存在齒面局部突起部分，在突起部分上面開始承受的載荷很高，因而發(fā)生強(qiáng)烈點(diǎn)蝕，但局部點(diǎn)蝕結(jié)果使原來不傳遞載荷的表面也參加工作，因而是突起表面上接觸應(yīng)力下降，這樣局部點(diǎn)蝕也就停止發(fā)展。
點(diǎn)蝕一般可用肉眼進(jìn)行定期檢查，由于電視面積的增長(zhǎng)率是與負(fù)荷的循環(huán)次數(shù)有關(guān)，利用這個(gè)關(guān)系，可定期檢測(cè)齒面點(diǎn)蝕的面積率，就能預(yù)測(cè)到需要維修的時(shí)間，此外，隨著點(diǎn)蝕面積率的增加，齒面必然成為剝離狀態(tài)，因此，定期檢查潤(rùn)滑油中混雜的剝離片，也可預(yù)測(cè)到齒輪需要維修的時(shí)間。
4、齒面膠合和劃痕
對(duì)于重載和高速的齒輪傳動(dòng)，如果潤(rùn)滑條件不良，兩個(gè)嚙合的齒面在相對(duì)滑動(dòng)時(shí)油膜破裂，在摩擦和表面壓力的作用下產(chǎn)生高溫，使處于接觸區(qū)內(nèi)的金屬出現(xiàn)局部熔焊，并且在齒面上形成垂直于節(jié)線的劃痕和膠合。
齒面擦傷就是齒表面接觸部分瞬間溫度升高，發(fā)生金屬之間的膠合現(xiàn)象，即一個(gè)齒面上的部分材料膠合到另一齒面上，并在此留下坑穴，因而與后面的齒嚙合時(shí)，這部分膠合的材料造成其他齒面的擦傷與溝痕。齒面的劃痕是擦傷的一種形式，它是由于潤(rùn)滑不足，嚙合齒面在相對(duì)滑動(dòng)時(shí)發(fā)生油膜破壞，從而引起金屬接觸表面熔融粘著并剝落而發(fā)生的損傷。
這類故障是驟然出現(xiàn)的，產(chǎn)生的條件相同于粘著磨損。一般來說，當(dāng)新齒輪未經(jīng)跑合時(shí)，常常會(huì)在某一局部產(chǎn)生齒面擦傷現(xiàn)象。另一方面，潤(rùn)滑油粘度過低，運(yùn)行溫度過高，齒面單位面積載荷過大，相對(duì)滑動(dòng)速度過高，以及接觸面積過小，也會(huì)使油膜易于破裂而造成齒面劃痕。
除了上述幾類故障外，還有齒輪的塑性變形（由于齒面硬度低而載荷大，齒面接觸應(yīng)力超過材料抗剪屈服限，造成齒面金屬的塑性流動(dòng)），齒輪咬入異物以及化學(xué)腐蝕等因素引起的故障，但上述四類故障是主要的。據(jù)統(tǒng)計(jì)，上述四類故障所占故障比例為：齒的斷裂為41%；齒面疲勞為31%；齒面劃痕為10%；齒面磨損為10%；其余故障僅占8%。
2.2 齒輪振動(dòng)機(jī)理分析
齒輪及齒輪箱在運(yùn)行中，其運(yùn)行狀態(tài)與故障征兆主要由齒輪傳送軸的扭振、轉(zhuǎn)距、齒輪箱的振動(dòng)、齒輪齒根應(yīng)力分布等構(gòu)成，每個(gè)量都從各自的角度反映了齒輪箱的狀態(tài)。但是由于工業(yè)現(xiàn)場(chǎng)測(cè)試的條件和技術(shù)所限，在復(fù)雜紛亂的信號(hào)中提取所需的征兆并不是一件容易的事情。相對(duì)來說，齒輪的振動(dòng)信號(hào)是目前最常用的也是最有效的提取量。在振動(dòng)信號(hào)中包含了各種故障信息，只要齒輪箱中的齒輪、滾動(dòng)軸承和軸系的工作狀態(tài)發(fā)生了變化，必然會(huì)從振動(dòng)信號(hào)中反映出來。對(duì)齒輪箱主要零部件的振動(dòng)值如位移、速度、加速度、轉(zhuǎn)速及相位值進(jìn)行測(cè)定，再與標(biāo)準(zhǔn)值進(jìn)行比較，就可以宏觀的對(duì)齒輪箱的運(yùn)行狀況進(jìn)行評(píng)定。對(duì)測(cè)得的上述振動(dòng)量進(jìn)行特征分析，就可以確定各種故障的原因和部位。
所以，研究齒輪及齒輪箱振動(dòng)的產(chǎn)生機(jī)理，分析其振動(dòng)信號(hào)的頻率成分，對(duì)于齒輪箱故障診斷來說有著十分重要的意義。
2.2.1 齒輪產(chǎn)生振動(dòng)的原因及特征
齒輪在運(yùn)行過程中產(chǎn)生的振動(dòng)是比較復(fù)雜的，由于齒輪所受的激勵(lì)不同，從而使齒輪產(chǎn)生的振動(dòng)類型也不同。其中齒輪的內(nèi)部激勵(lì)是指輪齒在嚙合過程中由于缺陷或故障產(chǎn)生的輪齒周節(jié)誤差、齒形誤差、齒輪偏心、質(zhì)量不平衡、軸線不對(duì)中等故障，還有運(yùn)行中產(chǎn)生的齒面疲勞、磨損、擦傷和斷裂等故障，這些故障帶給齒輪的激勵(lì)屬系統(tǒng)的內(nèi)部激勵(lì)。而外部激勵(lì)則與齒輪本身問題無關(guān)，是齒輪外部輸入的激勵(lì)，但也影響到齒輪的振動(dòng)情況，下面分別介紹一下各種振動(dòng)類型產(chǎn)生的原因及其特征：
1、齒輪嚙合過程中由于周節(jié)誤差、齒形誤差或均勻磨損等都會(huì)使齒與齒之間發(fā)生撞擊，撞擊頻率就是它的嚙合頻率。齒輪在此周期撞擊力的激勵(lì)下產(chǎn)生了以嚙合頻率為振動(dòng)頻率的強(qiáng)迫振動(dòng)，頻率范圍一般在幾百到幾千赫茲內(nèi)。
2、由于齒輪嚙合過程中輪齒發(fā)生彈性變形，使剛剛進(jìn)入嚙合的輪齒發(fā)生撞擊，因而產(chǎn)生沿著嚙合線方向作用的脈動(dòng)力，于是也會(huì)產(chǎn)生以嚙合頻率為頻率的振動(dòng)。對(duì)于齒廓為漸開線的齒輪，在節(jié)點(diǎn)附近為單齒嚙合，而在節(jié)點(diǎn)兩側(cè)為雙齒嚙合，故其剛度是非簡(jiǎn)的周期函數(shù)，而且還有嚙合頻率的高次諧波振動(dòng)。
3、齒與齒之間的摩擦在一定條件下會(huì)誘發(fā)自激振動(dòng)，主要與齒面加工質(zhì)量及潤(rùn)滑條件有關(guān)，自激振動(dòng)的頻率接近齒輪的固有頻率。
4、齒與齒之間撞擊時(shí)一種瞬態(tài)激勵(lì)，它使齒輪產(chǎn)生衰減自由振動(dòng)，振動(dòng)頻率就是齒輪的固有頻率，通常固有頻率在1～10kHz內(nèi)。
5、齒輪、軸、軸承等零件由于不同心、不對(duì)稱、材料不均勻等會(huì)產(chǎn)生偏心、不平衡，其離心慣性力使齒輪軸系統(tǒng)產(chǎn)生強(qiáng)迫振動(dòng)，振動(dòng)的頻率等于軸的轉(zhuǎn)動(dòng)頻率及其諧頻。
6、由于齒面的局部損傷而產(chǎn)生的激勵(lì)，其相應(yīng)的強(qiáng)迫振動(dòng)頻率等于損傷的齒數(shù)乘以軸的轉(zhuǎn)動(dòng)頻率。
綜上所述，齒輪的振動(dòng)頻率基本上可歸納為三類：即軸的轉(zhuǎn)動(dòng)頻率及其諧頻，齒輪的嚙合頻率及其諧頻，齒輪自身的各階固有頻率。而齒輪的實(shí)際振動(dòng)往往是上述各類振動(dòng)的某種組合。
2.2.2 理想齒輪振動(dòng)模型
齒輪及齒輪箱的振動(dòng)系統(tǒng)是一個(gè)十分復(fù)雜的彈性機(jī)械系統(tǒng)，在力的作用下將產(chǎn)生振動(dòng)響應(yīng)，并且這是一個(gè)非線性系統(tǒng)?，F(xiàn)在我們把要研究的齒輪看成指制造、安裝無誤差，齒面載荷均勻的理想齒輪。理想齒輪轉(zhuǎn)動(dòng)時(shí)，輪齒表面既有滑動(dòng)，又有滾動(dòng)，滑動(dòng)摩擦力在節(jié)點(diǎn)處會(huì)改變方向，形成節(jié)線沖擊。另外，每對(duì)輪齒在進(jìn)入嚙合或脫離嚙合時(shí)，輪齒上的載荷和變形突然增大或減少，形成嚙合沖擊。節(jié)線沖擊和嚙合沖擊組成的動(dòng)載荷，激發(fā)了齒輪的嚙合振動(dòng)，嚙合振動(dòng)是齒輪傳動(dòng)中固有的動(dòng)態(tài)特性，和齒輪有無缺陷無關(guān)。理想齒輪嚙合時(shí)，嚙合的齒對(duì)沿齒輪傳動(dòng)的線速度方向及切線方向振動(dòng)，其振動(dòng)的動(dòng)力學(xué)模型可簡(jiǎn)化為圖1所示的形式。根據(jù)振動(dòng)理論，其動(dòng)力學(xué)方程為：
式中：
x—在齒輪接觸力作用下沿作用線產(chǎn)生的齒輪相對(duì)位移；
M—齒輪副的等效質(zhì)量，，為小齒輪等效質(zhì)量；為大齒輪等效質(zhì)量；
C—齒輪嚙合阻尼；
K（t）—齒輪嚙合剛度，嚙合剛度隨時(shí)間t變化；
—齒輪受載荷后的平均彈性變形；
—齒輪轉(zhuǎn)動(dòng)誤差和故障激勵(lì)所引起兩齒輪間的相對(duì)位移。
圖1 理想齒輪嚙合
齒輪嚙合是間歇性的，因此輪齒的承載是脈動(dòng)的，每一輪齒從嚙入開始受載，嚙出停止受載，就齒而上某一點(diǎn)來講也是周期脈動(dòng)的，它遵循赫芝應(yīng)力分布，在接觸區(qū)壓力呈半圓形分布，壓力大小從零開始至最大再至零。最大尖峰載荷的頻率，即載荷脈動(dòng)頻率為：
式中：
—載荷脈動(dòng)周期；
n—齒輪轉(zhuǎn)度；
z—齒輪齒數(shù)。
這一載荷脈動(dòng)頻率就是齒輪嚙合頻率，相應(yīng)地，嚙合剛度、傳動(dòng)誤差引起的附加載荷都是以這個(gè)頻率為基頻周期變化的。
2.2.3 齒輪的傳動(dòng)誤差
傳動(dòng)誤差的定義是指齒輪在恒定的傳遞轉(zhuǎn)距下，因各種制造、安裝缺陷和使用過程中的故障問題所產(chǎn)生的誤差和變形，在輸出軸上實(shí)際的齒廓形狀和角位置與理論形狀和角位置之間的差值。這個(gè)差值可以用角位移表示，也可以沿壓力線用基圓半徑或節(jié)圓半徑上的線位移表示。傳動(dòng)誤差大，則齒輪運(yùn)轉(zhuǎn)過程中由于進(jìn)入和脫離嚙合時(shí)的碰撞加劇，產(chǎn)生較高的振動(dòng)峰值，并且形成短暫時(shí)間的幅值變化和相位變化。
現(xiàn)在我們?cè)O(shè)假設(shè)齒廓為理想形狀，并且輪齒剛度為絕對(duì)剛性，兩個(gè)齒輪嚙合時(shí)，主動(dòng)輪轉(zhuǎn)過角度，從動(dòng)輪則轉(zhuǎn)過角度，如圖2所示。與的關(guān)系是：
圖2 齒輪傳動(dòng)誤差
兩個(gè)相嚙合的齒輪按照這樣的關(guān)系均勻地回轉(zhuǎn)，但是實(shí)際齒輪不是絕對(duì)剛性的，而且由于各種因素，如齒輪制造誤差、齒面溫升、磨損等等，使得相嚙合的兩個(gè)齒輪相對(duì)角速度不均勻，從動(dòng)輪產(chǎn)生角加速度。這時(shí)從動(dòng)輪的轉(zhuǎn)角為：
其中是從動(dòng)輪轉(zhuǎn)角的相對(duì)偏差量，稱為傳動(dòng)誤差，也叫嚙合誤差，它是一個(gè)綜合誤差。
齒輪運(yùn)行狀態(tài)發(fā)生惡化，直接反映在齒輪傳動(dòng)誤差上，如齒輪軸的松動(dòng)、偏心、局部齒根疲勞裂紋或斷齒等將影響傳動(dòng)誤差的長(zhǎng)周期(與轉(zhuǎn)頻相關(guān))誤差成份；齒面發(fā)生過度磨損、膠合、點(diǎn)蝕等損傷時(shí)，傳動(dòng)誤差的短周期(與齒輪嚙合頻率相關(guān))成份加大，所有這些都使動(dòng)載荷加大，振動(dòng)也相應(yīng)加大。
2.2.4 嚙合剛度
對(duì)于齒輪振動(dòng)的產(chǎn)生，齒輪嚙合剛度是一個(gè)復(fù)雜的、重要的參量，它是研究齒輪動(dòng)態(tài)性能的基礎(chǔ)。齒輪的嚙合剛度受很多因素的影響，如傳遞載荷、載荷分布、輪齒變形和嚙合位置等。輪齒彈簧剛度的周期變化使系統(tǒng)的平移和回轉(zhuǎn)振動(dòng)具有相應(yīng)的周期性波動(dòng)，其振動(dòng)能量經(jīng)軸、軸承傳到齒輪箱箱體上。
直齒輪的嚙合剛度隨時(shí)間變化情況如圖3（a）所示；斜齒輪的情況如圖3（b）所示。與直齒輪相比，斜齒輪重合度大，其嚙合剛度波動(dòng)較平緩，波形近似正選波，這也是斜齒輪傳動(dòng)平穩(wěn)的原因之一。在相同的精度和工況下，斜齒輪傳動(dòng)的振動(dòng)比直齒輪傳動(dòng)小，輻射的噪聲也較小。
圖3 齒輪嚙合剛度變化曲線
通常情況下輪齒的剛度是穩(wěn)定的，當(dāng)齒根疲勞裂紋產(chǎn)生時(shí)，在嚙合過程中輪齒剛度會(huì)發(fā)生瞬時(shí)的變動(dòng)，產(chǎn)生一個(gè)低頻脈沖；當(dāng)齒輪發(fā)生損傷時(shí)，如膠合、過度磨損等，輪齒剛度也將發(fā)生變化，這一變化也會(huì)在振動(dòng)信號(hào)中反映出來。
2.3 齒輪的振動(dòng)類型
齒輪在運(yùn)轉(zhuǎn)過程中產(chǎn)生的振動(dòng)是比較復(fù)雜的，由于齒輪所受的激勵(lì)不同，從而使齒輪產(chǎn)生的振動(dòng)類型也不同。
1、齒輪嚙合過程中由于周節(jié)誤差、齒形誤差或非均勻磨損等都會(huì)使齒與齒之間發(fā)生撞擊，撞擊的頻率就是它的嚙合頻率。齒輪在此周期撞擊力的激勵(lì)下產(chǎn)生了以嚙合頻率為振動(dòng)頻率的強(qiáng)迫振動(dòng)，頻率范圍一般在幾百到幾千赫茲。
2、由于齒輪嚙合過程中輪齒發(fā)生彈性變形，使剛剛進(jìn)入嚙合的輪齒發(fā)生撞擊，因而產(chǎn)生沿著嚙合線方向作用的脈動(dòng)力，于是也會(huì)產(chǎn)生以嚙合頻率為頻率的振動(dòng)。對(duì)于齒廓為漸開線的齒輪，在節(jié)點(diǎn)附近為單齒嚙合，而在節(jié)點(diǎn)兩側(cè)為雙齒嚙合，故其剛度是非簡(jiǎn)諧的周期函數(shù)，所產(chǎn)生的強(qiáng)迫振動(dòng)與上述的一種情況相同，不僅有以嚙合頻率為頻率的基頻振動(dòng)，而且還有嚙合頻率的高次諧波振動(dòng)。
3、齒與齒之間的磨擦在一定條件下會(huì)誘發(fā)自激振動(dòng)，主要與齒面加工質(zhì)量及潤(rùn)滑條件有關(guān)，自激振動(dòng)的頻率接近齒輪的固有頻率。
4、齒與齒之間撞擊是一種瞬態(tài)激勵(lì)，它使齒輪產(chǎn)生衰減自由振動(dòng)，振動(dòng)頻率就是齒輪的固有頻率。
5、齒輪、軸、軸承等元件由于不同心、不對(duì)稱、材料不均勻等會(huì)產(chǎn)生偏心、不平衡，其離心慣性力使齒輪軸系統(tǒng)產(chǎn)生強(qiáng)迫振動(dòng)，振動(dòng)的頻率等于軸的轉(zhuǎn)動(dòng)頻率及其諧頻。
6、由于齒面的局部損傷而產(chǎn)生的激勵(lì)，其相應(yīng)的強(qiáng)迫振動(dòng)頻率等于損傷的齒數(shù)乘以軸的轉(zhuǎn)動(dòng)頻率。
綜上所述，齒輪的振動(dòng)頻率基本上可歸納為三類:即軸的轉(zhuǎn)動(dòng)頻率及其諧頻，齒輪的嚙合頻率及其諧頻，齒輪自身的各階固有頻率。而齒輪的實(shí)際振動(dòng)往往是上述各類振動(dòng)的某種組合。
Chapter II Forms of gear failure
2.1 The form of gear failure
Machinery and equipment in the gear transmission is the most common transmission mode,and the increasing demand gear of the modern machinery .The gear is not only required in high-speed, heavy, special media, and work in other harsh environmental conditions, but also required a high stable , high reliability and compact structure, good performance, so arouse more and more factors of failure. The gear fault is an important factor in inducing mechanical fault.Therefore, the gear fault diagnosis technology research is very important.
Gear because of different factors such as manufacturing, operation, maintenance and gear material, heat treatment,running state and so on , will produce different of abnormal forms.The common faults in gear have the following categories:
1.tooth fracture
Tooth fracture divide fatigue fracture and overload fracture.The fatigue fracture due to stress concentration which because of the gear repeat under load generated.When the gear into meshing state, the most dangerous moment is the contact point at the top of the gear. This time in the tooth root bending stress generated by the maximum, occur a more severe stress concentration. when the load exceeds the design value, or the gears under the cycle line of variable loads, after a certain load cycles, the roots of teeth may crack.The gear continue to work, the crack depth to the root of the development when the crack weaken the root can not afford to bending stress, the tooth to fracture.
Overload fault is due to dramatic changes in the speed of mechanical systems, shaft resonance, bearing damage, shaft bending and other reasons, so that caused by one end of gear abnormal contact with the load concentrated at one end to the tooth surface.The reason was mainly due to topoor assembly, machine operation when there are other failure.
Gear tooth fracture is the most serious failure, often resulting equipment downtime, or caused the machine of other parts fault.
2.tooth wear
Wear is the surface of the metal continuously throughout the loss of teeth, resulting in tooth-like surface grinding of metal.In meshing process, the gear often appears friction injury phenomenon on the surface of the tooth contact.If wear does not affect the life of the gear should have the function of the wear, we call normal wear, which characterized by a smooth tooth surface, there is no macro-scratches, the tolerances within the allowable range.If the gear timber improper or at the contact surface existence the hard particles, and the oil fall short of supply or dirty, often wear their gear early, with small particles separated from,the surface size changes, serious loss, and the profile changes, tooth thickness become thin, and even "Blade"-like cusps; engagement gap increases; noise increases; the results of serious wear will lead to the gear failure .Tooth wear any of the following categories:
1)adhesive wear
Adhesive wear is formed the occurrence of oil film is destroyed lead to the direct contact with the surface of metal tooth . Produce adhesive wear may be due to work in low gear, heavy duty, high temperature, low viscosity lubricating oil, oil shortages and tooth surface roughness and so on.
2)abrasive wear
As oil mixed with particles of diameter larger than 30um above, or oil, metal chipping, dust and sand and so on,these entering the teeth of the work surface, causing abrasive wear. Abrasive wear occurred in the tooth, the tooth to the top of sliding contact at the site, while less frequent in the pitch cercle.
3)corrosion and wear
Oil containing acid, alkali and water is easy on metal corrosion chemicals, chemical reaction with the tooth surface, form corrosion lead to tooth surface corrosion damage.
In addition to these three types of wear, because of the misalignment, coupling wear, poor assembly, and reverse the resonance, caused by the gear meshing point of the torque changes greatly, so that when the gears to increase the impact of these factors will accelerate the teeth wear and tear. In addition, the poor heat treatment of metal gear is also prone to tooth wear failure.
3.the tooth surface fatigue
Gear meshing process, both the relative rolling and relative sliding.Tooth contact of rolling pressure area is generated deep in the surface layer of shear stress, on the other hand, the relative sliding tooth surface, but also makes the surface tensile stress.Under the action of the two forces will result in the surface layer of deep pulsating gear change of the shear stress cycle.When this shear stress exceeds the shear fatigue limit of gears, or pulsating cyclic changes in tooth surface contact stress over the contact tooth surface fatigue limit, the tooth surface fatigue cracks will appear.With the crack and eventually peel off the metal tooth appears small, the formation of pits in the tooth surface, known as pitting.When pitting further expansion, even into one, it will form a large piece of metal falling off the surface of teeth.This is called the contact fatigue spalling.It generally occurs in the tooth roots are always close to the pitch at the severe spalling of gear when the work will affect and even cause teeth to break.In many cases, because uneven tooth material, or a local scratches, it is easy on the first appeared in a tooth contact fatigue, resulting in peeling.
Common cause of pitting is not enough tooth surface hardness, generally pitting near the section line in the tooth root portion, localized pitting is not dangerous, the gear is actually able to continue long-term work, this localized pittingtooth surface due to the presence of local protrusions in the upper part of the above began to bear the load is high, so that a strong pitting, localized pitting, but does not pass the results to the original surface of the load to work, and therefore decrease the contact stress on the surface processesThis will stop the development of local pitting.
Pitting regular eye checks are generally available, the television area of the growth rate is related with the load cycles, the use of this relationship can be regularly test pitting of tooth surface area ratio, can predict the time in need of repair, in addition, with thethe increase in the rate of pitting area of tooth surface is bound to become stripped state, therefore, regularly check the oil in the mixed peel, are also in need of repair can predict the time gear.
4.bonding and tooth surface scrathes
For the heavy and high-speed gear transmission, if the poor lubrication conditions, the two mating tooth surfaces in relative sliding film rupture, the surface friction and high temperature under pressure, so that the region is in contact with a partial fusion of metal,formed in the tooth surface and perpendicular to the section of line scratches and glue.
Tooth abrasion is the tooth surface contact part of the instantaneous temperature, a metal bonding between the phenomenon that is part of a tooth surface of the tooth surface material glued to another, and left in the pits, and therefore the backgear meshing, this part of the bonding material cause other tooth surface scratches and grooves.Scratches on the tooth surface is a form of scratches, which is due to insufficient lubrication, meshing tooth surfaces in relative sliding film damage occurs, causing molten metal contact surface adhesion and spalling damage occurred.
Such failures are suddenly appear, resulting in the same conditions on the adhesive wear.In general, when the new gear without running timely, often local produce in a tooth surface abrasions.On the other hand, oil viscosity is too low, too high operating temperature, load per unit area of tooth surface is too large, the relative sliding velocity is too high, and the contact area is too small, too easy to rupture the oil film will result in tooth surface scratches.
In addition to these types of failures, there are gear plastic deformation (due to tooth surface hardness of low load, tooth surface contact stress exceeds the material shear yield limit, causing the plastic flow of metal tooth surface), bite into gear, and chemical corrosion of foreign bodycaused by factors such failure, but these four are the main fault.According to statistics, the share of fault ratio of four faults:41% of broken teeth;31% of tooth surface fatigue;10% of tooth surface scratches;10% of tooth surface wear; only 8% of the remaining faults.
2.2Gear Vibration Analysis
Gears and gear boxes in operation, the operation status and fault indication transmitted mainly by the gear shaft torsional vibration, torque, vibration of the gearbox, the gear tooth root stress distribution, etc., and each volume is reflected from their point of view of the gearbox state.However, due to the conditions of industrial and technical field testing constraints, the complexity of chaotic signals to extract the required sign is not an easy thing.In contrast, the gear vibration signal is the most commonly used is the extraction of the most effective.The vibration signal contains a variety of fault information, as long as the gear box of gears, bearings and shaft of the working conditions change, will inevitably be reflected from the vibration signals.The main components of the gear vibration, such as displacement, velocity, acceleration, speed and phase values were measured, and then compared with the standard value, can the macro operational status of the gear to be assessed.Of measured to characterize the vibration analysis can identify the causes and location.
Therefore, research gear and gear box vibration generation mechanism, the frequency of the vibration signal components, for gearbox fault diagnosis is of great significance.
2.2.1 gear causes and characteristics of vibration
Gear vibration generated during operation is more complex, due to the different incentives suffered gear, so that the vibration of gear types are also different.One motivation is the internal gear teeth in the meshing process because of the defect or malfunction resulting tooth pitch error, profile error, gear eccentricity, unbalance, misalignment secondary failure, there is tooth surface generated by the operation of fatigue, wear, scratches and breakage failures, these failures is a system of incentives to bring gears internal incentives.The external excitation is nothing to do with the gear itself is the incentive gear external input, but also affect the vibration of the gear, the following types are introduced about the causes of various vibrations and their characteristics:
1. Gear meshing process because of pitch error, profile error, or even wear and so will the impact between the teeth and the teeth, meshing impact frequency is its frequency. Gear in this cycle, inspired by the force of impact generated by meshing frequency of the vibration frequency of the forced vibration, the frequency range is generally within a few hundred to several thousand Hertz.
2. Since the gear tooth meshing occurs during elastic deformation, so that occurred just crash into the meshing of the teeth, resulting in the direction along the meshing line of the role of pulse power, so also have to engage the frequency of the vibration frequency.The involute tooth profile as cogs in the vicinity of the single tooth meshing nodes, and in the nodes on both sides of a double tooth meshing, so the stiffness of non-simple periodic function, but also the high frequency harmonic meshing vibration
3. The friction between the teeth and the teeth, under certain conditions can induce self-excited vibration, and the tooth surface and lubrication conditions of processing quality, self-excited vibration frequency close to the natural frequency of the gear.
4. When the collision between the teeth and the teeth of a transient excitation, which produces attenuation of the gear free vibration, the vibration frequency is the natural frequency of the gear, usually natural frequency within the 1~ 10kHz.
5. Gears, shafts, bearings and other parts due to different heart, asymmetry, and other materials, will produce uneven eccentric, unbalanced, and its centrifugal force to the gear shaft system to produce forced vibration, the vibration frequency is equal to the shaft rotation frequency and itsharmonic.
6. The tooth surface of the local damage and the incentive, the corresponding vibration frequency is equal to force multiplied by the number of teeth damage the shaft rotation frequency.
In summary, the gear is essentially the vibration frequency can be summarized into three categories: the axis of rotation frequency and its harmonics, the gear mesh frequency and its harmonics, the gear natural frequencies of its own.The actual vibration of the gear vibration often some combination of the above categories.
2.2.2 gear vibration model of an ideal
The vibration of gear and gear box system is a very complex flexible mechanical system, under the action of forces will produce vibration, and this is a nonlinear system.Now we have to study as means of gear manufacturing, installation, error-free, ideal uniform tooth load gear.Ideal gear rotates, both the sliding tooth surfaces, there are rolling, sliding friction will change direction in the node, forming section line impact.In addition, each of the teeth into or out of meshing engagement, the teeth on the load and deformation of a sudden increase or decrease the formation of meshing impact.Section line impact and dynamic load consisting of meshing impact, stimulate the gear meshing vibration, gear meshing vibration is inherent in the dynamic characteristics, and the gear has nothing to do with or without defects.Ideal gear meshing, the meshing gear tooth on the line along the velocity direction and tangential direction of vibration, the vibration of the dynamic model can be simplified to the form shown in Figure 2-1.According to vibration theory, the kinetic e