Study On Stress And Temperature Field Of Automatic Transmission Gears With Coating Based On Fractal Theory

As the core transmission part of automobile transmission,gear is required to improve its performance and reliability with the increase of torque and speed.The application of surface coating technology to the automobile high strength gear,the preparation of modified coating on the surface of the gear,can effectively improve the pitting fatigue strength of the gear,improve the fatigue life of the gear,provides a way to solve this problem,has a broad development prospect.However,the mechanism of improving the working condition of the gear has not been fully understood and mastered after the coating is applied on the surface of the gear.Due to its self-similarity and scale-free property,fractal theory is expected to get rid of the influence of instrument resolution and realize more accurate theoretical modeling of rough surface,so as to accurately analyze the coated gear.The m-b fractal contact model based on the w-m fractal function and the island area distribution can well characterize the rough surface under different fractal states,simulate the real contact state,and then calculate the contact stress between the rough surfaces more accurately.Based on the m-b fractal contact model and the hertz-hertz elastic contact model,this paper introduces the fractal contact model of a gear in an automatic transmission by adding the surface contact coefficient.The influence of the main fractal parameters on the fractal contact model is analyzed.The contact stress between the uncoated gear and the gear coated with manganese phosphate is calculated by using the model.It is found that the coating can reduce the contact stress of the gear pair.The effects of different fractal dimensions and surface roughness on the results of stress calculation are discussed.Based on the stress calculation results of the fractal contact model and the gear temperature field theory,the temperature field simulation of the uncoated and coated gear is carried out.It is found that the coating can reduce the temperature field of the gear body,but it has no effect on the temperature distribution.Through dynamic circular gear fatigue testing of two kinds of gear fatigue tests are carried out,using high-definition infrared thermal imager to collect the temperature information of gear,by surface roughness measuring machine to test the gear profile measurement,using a scanning electron microscope to observe of gear,from the temperature,the reinforcement mechanism of the surface morphology and microstructure of the coating are analyzed.Results show that manganese phosphate conversion coating by covering on the surface of the gear cutting corrugated,a reduction in the number of surface wave trough and depth,reduce the friction factor between the meshing pair,lower the temperature of the gear mesh at the same time,reduce the thermal stress of the gear,to improve the gear contact state,improve gear pitting fatigue life,improve the work performance of the gear,and then improve the reliability of the transmission.