基于齿面移动法的齿轮飞溅润滑性能数值分析与验证

Gear splash lubrication numerical simulation and validation based on teeth-face-moving method

由于齿轮传动系统飞溅润滑过程中润滑油流动的复杂性,近年来数值仿真分析方法已逐渐成为评价飞溅润滑性能的重要手段。为解决齿轮飞溅润滑数值建模过程中由于啮合位置间隙太小而带来网格划分困难的问题,该文提出了采用齿面移动法对齿轮进行处理,即在保留所有轮齿和不改变齿轮安装位置的基础上,通过改变轮齿厚度来增大啮合区域间隙,以便于流体域网格划分。该文对不同处理方法获得的飞溅润滑仿真结果进行了对比分析,并结合试验数据,说明了齿面移动法相对于现有文献中的齿轮建模处理方法获得的润滑油飞溅效果更符合实际情况,搅油功耗计算结果误差在8%以内,且工程适用性更好。该研究为进一步分析车辆变速箱、驱动桥等齿轮传动系统的润滑状况提供了参考。

In recent years numerical simulation has become one of the most important means to study the complex oil flow within gearbox. Since the gap between tooth surfaces near the gear mesh zone is quite tiny, it’s difficult to get high quality mesh grid near such zone. Further numerical divergence frequently occurs along iterative process with dynamic mesh. To overcome this predicament, some researchers have tried different gear modeling methods to simplify the gear model, such as none-teeth method, cutting-teeth method or gear-separation method. Nevertheless these methods have certain limitation. This paper attended to provide a new practical gear modeling methods called teeth-face-moving method. The method was operated by moving each tooth surface slightly. As the tooth thickness was marginally reduced, the gap between tooth surfaces near the mesh zone was increased to 0.5-1 mm, so that mesh generation in the gap became feasible, which was different from the previous methods, i.e. all of teeth profiles and the center distance of 2 gears were kept as same as the original when using the teeth-face-moving method. To certify the reasonability of this new method, a numerical model for splash lubrication in gearbox was built with different gear modeling methods. The volume of fluid （VOF） method was applied to track the air and oil two-phase flow. And RNG k-ε model was introduced to describe turbulence flow considering high fluid strain rate and high bending degree of flow line. Standard wall function was applied to deal with the flow near wall region and low Reynolds number flow. Dynamic mesh method with the spring-based smoothing and local remeshing was used to adapt the motion of gears. Due to more concentrating upon mesh zone, the gear-separation method and the teeth-face-moving method required more grid elements and computational resource than other methods. The numerical results of oil distribution and gears’ churning loss were comparatively analyzed. Also the simulated results were made a comparison with the existed experiment data. It was easily observed the quantity of oil splashed by gears with none-teeth method or cutting-teeth methods was obviously less than that with gear-separation method or teeth-face-moving method. The similar phenomenon was acquired from churning loss results as well. The churning loss computed with none-teeth method or cutting-teeth method was far less than the related experimental result. On the contrary the churning loss computed with gear-separation method or teeth-face-moving method showed good agreement with the related experimental result. The direct reason was tip diameter and teeth profile had a strong influence on the oil flow in the gearbox. So cutting all or partial teeth may lead unreliable simulation result for splash oil flow. It seemed that the gear-separation method got the result close to the teeth-face-moving method. Unfortunately the center distance of 2 gears had to be increased for the gear-separation method. This was unacceptable in real engineering case because changing the position of gear may lead to related bearings or shaft intersected with other structures, such as bearing base and gearbox housing. So the conclusion is drawn that the teeth-face-moving method not only provides more credible prediction for oil flow in the gearbox, but also has more practicability for complicated engineering situation and hence is superior to the previous gear modeling methods. The teeth-face-moving gear modeling method is quite beneficial to lubrication simulation for real engineering gear system, such as truck axle or vehicle transmission. And further work of applying this new method on complicated machinery is underway.