Planetary gear shaft of automobile gearbox failure analysis

Automobile transmission planetary gear shaft fracture failure analysis of 2020 - 04 - 25 upon, Jeff li ( Gerth lakshmi ( Jiangxi) The transmission system co. , LTD. ) Differential is mainly composed of differential shell, planetary gear, axle shaft gear, the driven bevel gear, adjusting washers, bearings and planetary gear shaft and so on, is the role of planetary gear shaft torque to the planetary gear, realize the torque distribution, thereby achieve the wheel differential operation, in the process of running, planet gear bearing torque and bending force. 1. Differential durability test is described in this paper, the transmission, detection of parts service life. Test process, the gearbox in sound, immediately stop the test, after unpacking inspection, found that of casing damage, planetary gear shaft fracture. Planetary gear shaft material is 42 crmo spring steel, material standards GB/T3077 alloy structural steel. To ensure the abrasion resistance and fatigue strength of planetary gear shaft, this paper parts heat treatment process: gas nitriding quenching + tempering, surface. 2. The results and discussion ( 1) Macro analysis transmission differential durability test in the process of sound, split open a case analysis found that planetary gear shaft fracture, differential has been damaged, as shown in figure 1, dotted arrow logo for planetary gear shaft fracture. Figure 2 for overall shaft fracture morphology, fracture source is located in the circular surface, and serious wear and tear, outside-in extension, terminal area is located in the center of the shaft. Figure 1 failure of the differential assembly figure 2 planetary gear shaft fracture morphology ( 2) Microscopic analysis using the spectrum analyzer ( 斯派克/实验室LAVM10) Evaluate the material chemical composition in the planetary gear shaft, the test results are shown in table 1, planetary gear shaft material chemical composition are in line with the GB/T3077 alloy structural steel technical requirements. Planetary gear shaft material chemical composition (table 1 The mass fraction) （ %） The vickers hardness tester, 未来, 科技/ LC - 200 rb) Measuring planetary gear shaft fracture, matrix hardness, surface hardness test using standard test block before calibration; Fracture of shaft fracture metallographic sample, the Mosaic, after grinding, polishing, etching, using the optical microscope ( 蔡司/ HAL100) Microscopic microstructure test, the results are shown in table 2, the surface hardness, matrix hardness, nitride layer depth, nitrides and brittle level all conform to the technical requirements, but the loose surface reach level 4, does not meet the technical requirements, this directly led to the decrease of the strength of parts surface, in use process is easy to crack, reduce the fatigue life of parts. Table 2 planetary gear shaft hardness and microstructure of surface microstructure (figure 3 500× ） Using scanning electron microscope and SEM ( EVO18） For further analyzing, fracture figure 4 as a source of fracture crack morphology, surface fatigue striations, See the convex 4 b white arrow) And fatigue grain direction is along the circumference of a circle, in the entire circumference direction to form a layer of crack, about 1 mm from the surface, the main reason is that the planet gear shaft by rotation in transmission torque, and form a nitride layer on the surface of parts after nitriding organization, brittle matrix relatively large. Figure 4 fracture crack source SEM morphology figure 5 and figure 6 respectively spreading area and transient breaking SEM morphology, main show is cleavage fracture, suggests that larger parts by external, fast fracture. Figure 5 fracture extension area SEM morphology figure 6 fracture transient breaking area SEM morphology in figure 7, table 3 is crack source energy spectrum detecting position and the results, the spectrum is shown in figure 1, 2, 4 testing parts for nitride compound layer area, including spectrum figure 1 and figure 4 can be obviously a large pore area, energy spectrum analysis, the oxygen content of the area is obviously greater than spectrum figure 2 and figure 3 area, and most close to the surface spectral figure 4 area, oxygen content is highest, far more than other area, the loose parts after nitriding surface area by oxidation, reduce the surface strength and fatigue performance, cause parts test in the process of fracture. Figure 7 fracture crack source energy spectrum detecting position (table 3 energy spectrum test result The mass fraction) （ %） 3. Conclusion planetary gear shaft after nitriding, the surface of compound floor is unqualified, loose organization by external test process, form the source of crack, and further expand to the central area completely broken. Source: the metal processing ( Hot working) 》