1. School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China 2. Northwest Institute of Mechanical and Electrical Engineering, Xianyang 712099, China
In order to accurately obtain the dynamic characteristics of the pinion and rack under grease lubrication condition, a structure-grease film coupling meshing stiffness model was presented, which took both the structural time-varying meshing stiffness and transient thermal elastohydrodynamic lubrication stiffness during the meshing process of the rack and pinion into account, the dynamics equations of the pinion and rack stroke-increment mechanism involving the friction were formulated. The dynamic characteristics of pinion and rack mechanism and grease film were analyzed, the numerical results showed that total meshing stiffness between gear teeth was lower than the time-varying meshing stiffness of structure when the transient thermal elastohydrodynamic effect of grease was considered. With the decreasing of the normal meshing force, the total stiffness also reduced. Generally speaking, with the increase of the equivalent radius of curvature, the center film thickness became more thicker and the center pressure decreased. Both of them showed high frequency fluctuation characteristics. The worst lubrication state occurred on the gear tooth flank near the base circle where the temperature rise and pressure of the grease film were the highest, thickness were the thinnest. The friction coefficient was lower in the middle period with higher rack and pinion drive velocity than that in start and end periods, and it decreased obviously when the meshing point was close to pitch point.
Zhi-qun CHEN,Lin-fang QIAN,Yi-cheng ZHU. Dynamic characteristics of pinion and rack stroke-increment mechanism with grease lubrication. Journal of ZheJiang University (Engineering Science), 2022, 56(9): 1833-1844.
Tab.3Rheological parameters of grease with temperature of 303 K and thermodynamic parameters of rack and pinion drive systems
Fig.5Flowchart of solving dynamic model of pinion and rack with grease lubrication
Fig.6Displacement curve and velocity curve of upper rack
Fig.7Meshing state characteristics during second tooth meshing cycle of gear and upper rack
Fig.8Meshing state characteristics during eighth tooth meshing cycle of gear and upper rack
Fig.9Total friction coefficient of upper rack
Fig.10Variation of friction coefficient during second tooth meshing process
Fig.11Finite element model of engagement of tooth and pinion engagement
Fig.12Comparison of meshing stiffness of second tooth
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