Predicting the Fatigue Life of a Commercial Vehicle X-EPS Steering Gear with a Rigid–Flexible Coupling Dynamics Method

Commercial X-EPS steering gears are characterized by high torque output, torque—with increasing capabilities, high reliability, and excellent handling precision. Among them, the screw–nut pair in the steering gear is subjected to complex working loads, and its raceways are prone to fatigue failure. To more accurately and effectively predict the fatigue life of the screw–nut pair in the steering gear, a method for dynamic simulation and fatigue life prediction of commercial X-EPS steering gears is proposed based on virtual prototyping technology and finite element theory. That is, a rigid–flexible coupling dynamic model of the X-EPS steering gear is established to obtain the load spectra of the screw and nut, and a finite-element static model is also established. Then, combined with the material S-N curve, the fatigue life is predicted through the NOCDE fatigue “five-block diagram”. The research results show that the screw and nut raceways are the key components prone to fatigue failure in the steering gear. The minimum numbers of fatigue life cycles are 1.028 × 105 times and 2.9695 × 105 times, respectively. Subsequently, a fatigue life bench test was conducted for verification. The results show that the error between the fatigue life analysis model of the XEPS recirculating ball steering gear and the test is less than 5%, meeting the requirements of the fatigue life test standard and design standard.