變(bian)速箱(xiang)(xiang)是車輛上非常(chang)重要的部件，它可以改變(bian)傳(chuan)(chuan)(chuan)動(dong)(dong)比，擴大驅動(dong)(dong)輪轉矩(ju)和(he)轉速的作用(yong)。隨(sui)著(zhu)現(xian)(xian)代科技的發展，變(bian)速箱(xiang)(xiang)也有(you)了升級，從最初的手動(dong)(dong)變(bian)速箱(xiang)(xiang)，到現(xian)(xian)在無級變(bian)速箱(xiang)(xiang)，從無同步器到有(you)同步器，操控(kong)越來越方便。目前工程機械(xie)上廣泛(fan)采(cai)用(yong)柴油機，其轉矩(ju)與轉速變(bian)化范圍小(xiao)，不能滿(man)足車輛在各種(zhong)工況(kuang)下對牽(qian)引力(li)和(he)行駛(shi)速度的要求，需采(cai)用(yong)變(bian)速箱(xiang)(xiang)來解決這種(zhong)矛盾。變(bian)速箱(xiang)(xiang)性(xing)能的優劣是衡量工程機械(xie)動(dong)(dong)力(li)性(xing)、經濟性(xing)及駕駛(shi)性(xing)的關鍵。目前的變(bian)速系統主要有(you)：機械(xie)傳(chuan)(chuan)(chuan)動(dong)(dong)、液(ye)力(li)傳(chuan)(chuan)(chuan)動(dong)(dong)、靜液(ye)壓傳(chuan)(chuan)(chuan)動(dong)(dong)。變(bian)速箱(xiang)(xiang)有(you)人力(li)換擋(dang)和(he)動(dong)(dong)力(li)換擋(dang)，結構有(you)定軸(zhou)式和(he)行星式。