傳動(dong)比(bi)是機(ji)構中兩轉動(dong)構件(jian)角(jiao)速度(du)的(de)比(bi)值，也稱速比(bi)。構件(jian)a和構件(jian)b的(de)傳動(dong)比(bi)為(wei)i=ωa/ ωb=na/nb，式中ωa和 ωb分別為(wei)構件(jian)a和b的(de)角(jiao)速度(du)（弧(hu)度(du)/秒）；na和nb分別為(wei)構件(jian)a和b的(de)轉速（轉/分）。

當式中(zhong)的(de)(de)(de)(de)角速度(du)為瞬(shun)時(shi)值(zhi)時(shi)，則求得(de)的(de)(de)(de)(de)傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)比(bi)為瞬(shun)時(shi)傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)比(bi)。當式中(zhong)的(de)(de)(de)(de)角速度(du)為平均值(zhi)時(shi)，則求得(de)的(de)(de)(de)(de)傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)比(bi)為平均傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)比(bi)。理論上對于大多(duo)數漸開線齒(chi)廓正確(que)的(de)(de)(de)(de)齒(chi)輪(lun)(lun)傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)，瞬(shun)時(shi)傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)比(bi)是不變的(de)(de)(de)(de)；對于鏈傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)和(he)摩(mo)擦(ca)輪(lun)(lun)傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)，瞬(shun)時(shi)傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)比(bi)是變化的(de)(de)(de)(de)。對于嚙合傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)，傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)比(bi)可(ke)用(yong)a和(he)b輪(lun)(lun)的(de)(de)(de)(de)齒(chi)數Za和(he)Zb表示(shi)，i=Zb/Za；對于摩(mo)擦(ca)傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)，傳(chuan)(chuan)(chuan)動(dong)(dong)(dong)比(bi)可(ke)用(yong)a和(he)b輪(lun)(lun)的(de)(de)(de)(de)直(zhi)徑Da和(he)Db表示(shi)，i=Db/Da。

計算方法：

傳動比=使用扭矩÷9550÷電機功(gong)率×電機功(gong)率輸入轉數÷使用系數

傳動(dong)比(bi)=主動(dong)輪(lun)轉(zhuan)速除以(yi)從動(dong)輪(lun)轉(zhuan)速的值(zhi)=它們分度圓直徑比(bi)值(zhi)的倒數(shu)。即：i=n1/n2=D2/D1

i=n1/n2=z2/z1（齒(chi)輪的）

對(dui)于多(duo)級齒輪傳動：1.每兩軸(zhou)之間的(de)傳動比(bi)按照上面的(de)公式計算。 2.從第(di)一軸(zhou)到(dao)第(di)n軸(zhou)的(de)總傳動比(bi)等于各(ge)級傳動比(bi)之積