傳動比(bi)(bi)是機(ji)構(gou)中兩轉(zhuan)動構(gou)件(jian)(jian)角速(su)度的(de)比(bi)(bi)值，也稱速(su)比(bi)(bi)。構(gou)件(jian)(jian)a和(he)(he)(he)構(gou)件(jian)(jian)b的(de)傳動比(bi)(bi)為i=ωa/ ωb=na/nb，式中ωa和(he)(he)(he) ωb分(fen)別(bie)為構(gou)件(jian)(jian)a和(he)(he)(he)b的(de)角速(su)度（弧度/秒）；na和(he)(he)(he)nb分(fen)別(bie)為構(gou)件(jian)(jian)a和(he)(he)(he)b的(de)轉(zhuan)速(su)（轉(zhuan)/分(fen)）。

當式中的角速(su)度為瞬(shun)時(shi)(shi)(shi)(shi)值(zhi)時(shi)(shi)(shi)(shi)，則求得的傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)比為瞬(shun)時(shi)(shi)(shi)(shi)傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)比。當式中的角速(su)度為平(ping)均值(zhi)時(shi)(shi)(shi)(shi)，則求得的傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)比為平(ping)均傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)比。理論上對于大(da)多數漸開線齒廓正(zheng)確的齒輪傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)，瞬(shun)時(shi)(shi)(shi)(shi)傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)比是(shi)(shi)不(bu)變的；對于鏈傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)和(he)摩(mo)擦輪傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)，瞬(shun)時(shi)(shi)(shi)(shi)傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)比是(shi)(shi)變化的。對于嚙合傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)，傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)比可(ke)用a和(he)b輪的齒數Za和(he)Zb表(biao)示，i=Zb/Za；對于摩(mo)擦傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)，傳(chuan)(chuan)動(dong)(dong)(dong)(dong)(dong)比可(ke)用a和(he)b輪的直徑Da和(he)Db表(biao)示，i=Db/Da。

計算方法：

傳動(dong)比(bi)=使(shi)用(yong)扭矩÷9550÷電(dian)機(ji)功(gong)率×電(dian)機(ji)功(gong)率輸入轉數÷使(shi)用(yong)系(xi)數

傳動(dong)比(bi)=主動(dong)輪轉(zhuan)速除(chu)以從動(dong)輪轉(zhuan)速的(de)值(zhi)=它們分度圓(yuan)直徑比(bi)值(zhi)的(de)倒數(shu)。即(ji)：i=n1/n2=D2/D1

i=n1/n2=z2/z1（齒輪的）

對于多級齒輪傳動：1.每兩軸之間的傳動比按(an)照上面的公式計算。 2.從(cong)第一軸到(dao)第n軸的總(zong)傳動比等于各級傳動比之積