背锥和当量齿轮o ACBO1O2r1r212r1、 r2分度圆半径1、 2分度圆锥角 两轴交角o ACBO1O2r1r212两轮的分度圆锥的立体图r1r2o ACBO1O2r1r212R大端齿廓位于以锥距R为半径的球面上。o ACBO1O2r1r212Ro ACBO1O2r1r212R由于球面齿形无法展成平面图形，故应作以下近似处理。o ACBO1O2r1r212R*背锥(back cone)过两分度圆锥的底圆与球面相切的圆锥。齿廓向背锥的锥面上投影，作为其近似齿形。该近似齿形可展成平面图形而便于设计计算。o ACBO1O2r1r212RoACBO1O2r1r2R21将背锥展开，得到两个扇形的平面不完全齿轮。oACBO1O2r1r2R21 当量齿轮的模数和压力角即圆锥齿轮大端的模数和压力角。*当量齿轮(equivalent spur gear)将背锥近似齿形展开的扇形不完全齿轮补全的直齿轮。当量齿数ZV Z（实际齿数）oACBO1O2r1r2R211 2r1/cos 1r2/cos 2oACBO1r1r2R21rV2rV1rV2=r2/cos 2rV1=r1/cos 1rV =r/co
