Research on the time-varying mesh stiffness and dynamic characteristics of steel–POM gear pair with off-line meshing

Plastic gears have been widely used in fields such as instruments, meters, and automotive electronics. In particular, metal–plastic gear pairs are commonly used in the low-speed stages of multi-stage gear transmissions to enhance load capacity and achieve lightweight design. However, due to the small elastic modulus and significant temperature sensitivity of plastic gears, off-line meshing phenomenon occurs in metal–plastic gear pairs during operation, which affects the overall system stiffness and dynamic behavior. Therefore, this study takes 45# steel-POM gear pair as the object of study, and considers the effect of temperature on the modulus of elasticity of the gear and the effect of out-of-line meshing on the time-varying stiffness of the gear pair , in which the 45# steel-POM gear pair refers to the combination of the steel and plastic gear pairs, with the pinion gear consisting of 45# steel gears, and the large gear made of POM gears. A lumped parameter method is used to establish a single-degree-of-freedom model of the gear transmission system, and the effect of load on the system’s dynamic behavior is investigated. Experimental validation shows that the stiffness varies linearly with the load, and the dynamic performance of the system deteriorates with increasing load. In the experimental study described in this article, as the load increased from 5 to 10 N m, the maximum dynamic transmission error increased by 62%. Under the same load, the system with consideration of off-line meshing exhibits better transmission accuracy compared to the one without consideration. Disregarding the dominant frequency of the system when there is no external meshing, the dominant frequency of the system increases by 1.4 times when considering external meshing. This study provides a theoretical basis for the design and transmission of plastic gears in the future.