On Thermal EHL Behavior Of Tilting And Skew Rollers In Rolling Bearings

Machinery elements such as rolling bearings, gears, and cams are widely used in practice. Roller tilting and skew are caused by the applied load, and will have effects on the elastohydrodynamic lubricating performance. Thermal effects can not be neglected in high-speed condition. With non-Newtonian fluid, the surface temperature effects of the solid, the tilting and skew effects of the roller under thermal condition are investigated. To reduce the tilting and skew effects, profile modification for rollers is carried out under thermal elastohydrodynamic lubrication(EHL) condition.Firstly, based on line contact EHL problem formed by two cylindrical rollers, a power law non-Newtonian fluid model is assumed, thermal effect and non-Newtonian effect are investigated in line contact EHL considering the surface temperature. Results show that, the effect of the surface temperature can not be neglected for power-law non-Newtonian thermal EHL. Similar to the Newtonian fluid, the central film thickness for the shear thinning and shear thickening fluid is determined by the effective viscosity at the inlet which is affected by the surface temperature. When the surface temperature is different from the oil-supply temperature, the film thickness will increase with the increasing rheological index. As the velocity parameter is fixed, the film temperature decreases with the increasing effective environmental viscosity of the power law fluid.Secondly, with the Eyring fluid, a finite line contact thermal EHL model formed between a tilting coupled with skew roller and races has been built, and a full numerical solution is obtained. The non-Newtonian lubricating performance for a roller-outer race or inner race is provided respectively. Results show that, compared to the ideal roller status, thermal effect is more obvious and the distribution of the lubricating behavior along the axial direction is more uneven when the roller is at the tilting and skew status. Comparison to the tilting and skew roller-inner race, the frictional coefficient is much higher, and the load-offset distance is larger for the tilting-inner race because of the skew roller-inner race can decrease the edge effect and tilting effect. The characteristic shear stress has an influence on the frictional coefficient and the oil temperature, but has little influence on the film thickness.Finally, profile modification for the roller generatrix is carried out in order to reduce the tilting and skew effect of the roller. The non-Newtonian finite line contact thermal EHL problem for profiled roller is investigated, and the effects of the profile modification for the roller generatrix on the thermal EHL are discussed under the four conditions: the ideal, the tilting, the skew, and the tilting coupled with skew roller status. Results show that, when the roller is at the ideal, the tilting, the skew or the tilting coupled with the skew status, the profile modification for the roller generatrix can reduce the edge effect and the tilting or the skew effect. In addition, an optimum value of the profile modification for the roller generatrix exists at the four kinds of status. The method is simple and feasible, which a profile modification function has been added on the straight roller generatrix, and a new idea for the engineering application of the roller profile modification is provided.