| Gear is the key component of automobile transmission.Its transmission performance and fatigue life have an important impact on the critical performance index of transmission,such as the reliability.Especially now the electric vehicle market is gradually formed,and its power transmission system is developing towards high speed,high load-carrying capacity,lightweight,miniaturization,which puts forward stricter requirements for the load-carrying capacity of transmission gears.Fatigue pitting is one of the most common failure modes of gear tooth flank.It not only affects the transmission accuracy of the gear,but also produces hard particles which may reduce the life of other friction pairs.However,the pitting mechanism is complicated,which is related to gear material,surface treatment,lubrication status and so on.It is the result of several factors,so it has been one of the important research subjects in the field of gear transmission.Surface coating technology is regarded as an effective means to improve the anti-fatigue pitting performance of gears and has a good development prospect.In this paper,the Manganese phosphate conversion coating was deposited on the helical gear pair by phosphating treatment technology,which was the first gear pair of a seven-speed dual clutch transmission(7DCT).The contact fatigue experiments of the gear pairs were conducted on the power recirculation gear fatigue test rig.And the strengthening mechanism of the coating was investigated.The main work of the present study is as follows:(1)Based on Hertz contact theory,the contact stress of helical gears was calculated.The contact finite element analysis model of the gear pair was established.Then the influence of input torque on contact stress and surface shear stress was studied on the condition of static contact,and the numerical solutions were compared with the analytical solutions.(2)The rigid-flexible coupling models of gearboxes with different supporting span were presented,and the accuracy of the models was verified by the contact pattern results of experiment and simulation.The meshing misalignment and transmission error of the gear pair under different working conditions were calculated.Moreover,the variation of the load per unit length and the maximum shear stress distribution on the subsurface with torques under different supporting spans were investigated.(3)Viewing the helical gear meshing as the contact between two reverse-direction conical rollers,the finite-length line contact thermal elastohydrodynamic lubrication(TEHL)model of helical gears was established.The pressure was solved by multigrid method,and the temperature was solved by sequential scanning method.The distribution of oil film pressure,thickness and temperature field at different meshing positions was obtained.And the influence of operating parameters on the lubrication characteristics was researched.(4)The micro-morphology and surface roughness of manganese phosphate conversion coating were tested and analyzed.The contact fatigue experiments of uncoated gear pair and coated gear pair were carried out on the power recirculation gear fatigue test rig.The anticontact fatigue performances of the two pairs were compared.Meanwhile,the crack morphologies at different stages were observed by scanning electron microscope(SEM).The mechanism of fatigue pitting was studied in terms of load character,tooth friction and relative motion,lubricant and non-metallic inclusions.The strengthening mechanism of manganese phosphate coating on gear transmission was investigated by analysing the micro-morphology of coating surface after test. |
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