傳動(dong)比(bi)是機構中兩轉(zhuan)動(dong)構件角(jiao)速(su)度的比(bi)值，也稱(cheng)速(su)比(bi)。構件a和(he)(he)構件b的傳動(dong)比(bi)為i=ωa/ ωb=na/nb，式中ωa和(he)(he) ωb分(fen)別為構件a和(he)(he)b的角(jiao)速(su)度（弧度/秒(miao)）；na和(he)(he)nb分(fen)別為構件a和(he)(he)b的轉(zhuan)速(su)（轉(zhuan)/分(fen)）。

當(dang)式中(zhong)的(de)(de)角速度為(wei)瞬時(shi)值時(shi)，則求得的(de)(de)傳(chuan)(chuan)動(dong)(dong)(dong)比(bi)為(wei)瞬時(shi)傳(chuan)(chuan)動(dong)(dong)(dong)比(bi)。當(dang)式中(zhong)的(de)(de)角速度為(wei)平均值時(shi)，則求得的(de)(de)傳(chuan)(chuan)動(dong)(dong)(dong)比(bi)為(wei)平均傳(chuan)(chuan)動(dong)(dong)(dong)比(bi)。理論上(shang)對于(yu)(yu)大(da)多數(shu)漸開線齒廓正確的(de)(de)齒輪傳(chuan)(chuan)動(dong)(dong)(dong)，瞬時(shi)傳(chuan)(chuan)動(dong)(dong)(dong)比(bi)是不變(bian)(bian)的(de)(de)；對于(yu)(yu)鏈傳(chuan)(chuan)動(dong)(dong)(dong)和摩擦輪傳(chuan)(chuan)動(dong)(dong)(dong)，瞬時(shi)傳(chuan)(chuan)動(dong)(dong)(dong)比(bi)是變(bian)(bian)化的(de)(de)。對于(yu)(yu)嚙合(he)傳(chuan)(chuan)動(dong)(dong)(dong)，傳(chuan)(chuan)動(dong)(dong)(dong)比(bi)可用a和b輪的(de)(de)齒數(shu)Za和Zb表示，i=Zb/Za；對于(yu)(yu)摩擦傳(chuan)(chuan)動(dong)(dong)(dong)，傳(chuan)(chuan)動(dong)(dong)(dong)比(bi)可用a和b輪的(de)(de)直徑Da和Db表示，i=Db/Da。

計算方法：

傳(chuan)動比=使用扭矩÷9550÷電(dian)(dian)機功率×電(dian)(dian)機功率輸入轉數÷使用系數

傳動(dong)比=主動(dong)輪轉速除(chu)以從動(dong)輪轉速的(de)(de)值(zhi)(zhi)=它們分(fen)度(du)圓(yuan)直徑(jing)比值(zhi)(zhi)的(de)(de)倒數。即：i=n1/n2=D2/D1

i=n1/n2=z2/z1（齒(chi)輪(lun)的）

對(dui)于多級(ji)齒輪傳(chuan)動(dong)：1.每兩軸之間(jian)的傳(chuan)動(dong)比按(an)照上面(mian)的公式計算(suan)。 2.從第一軸到第n軸的總傳(chuan)動(dong)比等于各(ge)級(ji)傳(chuan)動(dong)比之積