Durability Testing of a Polymer Worm Gear Used in a Vehicle Steering System

Polymer worm gears are increasingly utilized in electric power steering (EPS) systems due to their favorable manufacturing features and performance. Ensuring consistent mechanical properties under various operating conditions is critical for steering reliability throughout a vehicle's lifespan. This study investigates the durability of injection-molded polyamide 66 worm gears within a Pinion-EPS configuration, where torque from the assist motor is transmitted through a worm-worm gear set to the rack and ultimately to the vehicle wheels. Given the complexity of steering maneuvers and the absence of mechanical integrity in steer-by-wire systems, durability testing becomes essential to understand if the considered worm gear for a certain steering system application provides safety and the needed performance within a specified product service life. This paper compares multiple testing methodologies. Traditional approaches, such as maximum torque and rotational speed, prove insufficient for comprehensive durability assessment, especially considering the thermal sensitivity of polymer materials. The findings highlight the limitations of conventional testing methods and emphasize the need for application-specific testing methods that reflect real-world boundary conditions. This research contributes to the development of more accurate and reliable evaluation techniques for polymer gear components in modern EPS systems, with implications for both conventional and autonomous vehicle platforms.