Micro Thermal Ehl Numerical Analysis of Low-speed Heavy-duty Gear and Experimental Study of Tooth Surface Polishing
|Course||Mechanical Design and Theory|
|Keywords||thermal elastohydrodynamic lubrication surface roughness effects wind power gear box phosphate multi-grid method|
Gear transmission is the most important and most widely used form of transmission. In common, there is great different for contact strength design of gears based on Hertz elastic contact theory, which is just used for static contact as so smooth surface with no lubrication. However, in the process of gear lubrication, elastohydrodynamic oil film thickness is about 1μm or smaller, which is almost in the same order of magnitude with tooth surface roughness formed by cutting. Under this condition, it is an frequency of tooth surface asperity collisions, which is leaded to plastic deformation and metal migration. A large number of experiments show that tooth surface damage is caused by lubrication failure, such as pitting, excessive wear and glue, etc., especially in low speed heavy gear failure in the lubrication failure accounted for more than 60%. Therefore, there is higher theoretical and practical value for low-speed heavy gear lubrication of thermoelastic. These detailed studies are as follows:1) First of all, the mathematical model for micro-thermal elastohydrodynamic lubrication based on gear engagement theory, surface roughness effect and the non-Newtonian behavior is set up. Owe to complexity of second-order nonlinear characteristics of partial differential equations, Some challenging numerical calculation methods are adopted such as multi-grid method (Multi-Grid Method) to solve the pressure distribution of time-varying solution, multiple grid integration method to elastic deformation and the column scanning method to temperature distribution and then several major factors impacting low-speed EHL are discussed. the results show that under certain conditions, the greater the roughness, the greater the resulting local pressure peaks, while the film thickness correspondingly decreases and the maximum temperature rise also increased to some extent; When speed is becoming geater, film thickness is increasing with the corresponding parallel part of the film shortening, the position of the second pressure peak gradually is shifting to the entrance area, and even the largest film pressure is gradually reduced; oil viscosity is mainly reflected in the film shape, The higher the oil viscosity, the greater the formation of film thickness, while oil film shear heat generated by the more strongly; when larger loads, the pressure distribution gradually close to the Hertz contact pressure distribution, while the load is smaller, the pressure distribution is similar with the result calculated by classical lubrication theory. 2) The reference to gear parameters and load conditions of a company’s wind power growth of low-level box planetary gear, a mathematical model is established to solve gear complete thermal EHL numerical solutions for sun gear, planetary gear and ring and then the relationship between film pressure and film thickness of planetary gear system and damage and wear is analyzied. The results show that the ring gear and planet gear with Ra = 0.8μm work in abnormal state, whose degree of tooth injury up to 10% on account of the oil film thickness less than 1.5.3) The papar proposed gear running programs under the oxidation and phosphate conditions, and analyzed chemical reaction of the gears in phosphate solution: gear in reaction with solution is formed on the surface softening membrane of crystalline phosphate conversion layer, which is wiped by friction when gear is meshing. Over and over again roughness peak of gear tooth surface is decreased. Then by comparing the treated and untreated gears in the two kinds of programs, oil temperature of gear with lower roughness is great lower than anothers.