本文介绍了轮缘与钢轨接触几何学、运动学、蠕滑机理以及研究车轮在稳态滚动条件下初始爬轨时如何应用这些理论来计算脱轨系数Y/Q。文章还指出在小冲角,大的纵向蠕滑力以及减小轮缘与钢轨接触处椭圆半轴a/b之比值,脱轨系数可以超出Nadal极限值,而并不危及行车安全。当冲角ψ增大、纵向蠕滑力很小或趋近于零时,根据蠕滑理论计算所得之脱轨系数与用Nadal公式计算所得结果甚为接近。 This paper introduces how the theory of contact geometry, kinematics and creep between rims and rails and how to apply the theories to calculate the derailment coefficient Y / Q when the wheels are initially climbing under steady-state rolling conditions. The article also points out that at small angles of attack, large longitudinal creep forces, and the ratio of a / b to the elliptical half-shaft at the wheel-rail contact, the derailment factor can exceed the Nadal limit without jeopardizing traffic safety. When the angle of attack ψ increases and the longitudinal creep force is small or close to zero, the derailment coefficient calculated by creep theory is very close to that calculated by Nadal formula.