本文通过分析变齿厚的双导程圆柱蜗杆传动的实质,得知这是一种变模数和变蜗杆特征系数的复合的相对变位蜗杆传动。根据这一相对变位原理,可导出确定该传动主要参数的公式。从而解释了这种传动的蜗轮的大模数面首先发生根切的原因,并给出根切的验算公式和避免根切的压力角设计公 In this paper, by analyzing the essence of double-lead cylindrical worm gear with variable tooth thickness, we know that it is a compound relative variable-displacement worm gear with variable modulus and variable worm coefficient. Based on this principle of relative displacement, a formula for determining the main parameters of the transmission can be derived. Which explains why the large modulus plane of the worm gear of this kind of transmission is undergone the root cause first, and gives the formula of the root cut and the design of the pressure angle to avoid the undercut