Hydrodynamic lubrication characteristics of planet gear thrust washer used in high-speed planetary transmission

For the washer in planetary transmission with spur gears, in order to reduce wear between the thrust washer and planet gear due to the force in the axis direction, hydrodynamic lubrication design was presented by machining rectangular grooves in the radial direction into one side of thrust washer. Such grooves can result in a hydrodynamic pressure to separate the contact surfaces and reduce the wear accordingly when there is a relative movement between the planet gear and thrust washer. Rectangular grooves were chosen due to their symmetrical structure, two rotational directions and easily to be machined. A steady Reynolds equation was set up and the finite volume method (FVM) was used to obtain its numerical solutions. The effects of number of grooves, ratio of groove angle to periodic groove angle, depth of grooves and radial width etc on carrying capacity of hydrodynamic washer, oil flow rate and temperature rise were studied. Considering feasibility of application, the lubrication characteristic was analyzed for the cases with less number of grooves (2-12). The results show that when the number of grooves is about 20, the carrying capacity of oil film is the highest. When the number of grooves is in the range of 10 to 60, if the ratio of groove angle to periodic groove angle is about 0.5, the carrying capacity will be better. Moreover, the wider the radial width of washer, the higher the carrying capacity. More number of grooves, deeper groove depth and wider groove radial width increase the oil flow rate or vice versa. Larger ratio of groove angle to periodic groove angle results in a low oil flow rate. The measures of decreasing temperature rise are more number of grooves, wider radial width to make sure the groove depth is 10-40 μm.