Contents
2 Testing process
3 Test disassembly and analysis
4 Conclusion
The reducer is an important part of the transmission components in the new energy vehicle, which can transmit the output torque of the motor to the output shaft through the reducer to drive the vehicle tires by increasing the torque.
The transmission performance of the reducer directly affects the efficiency, smoothness and driving power of the vehicle.
The maximum transmission torque of the reducer is directly influenced by its body material, structural strength and gear performance.
The maximum static torque of the reducer is analyzed through tests to ensure the reliable operation of the reducer in operation.
A new energy vehicle parallel shaft reducer was studied, and the static torque test was conducted by increasing the input torque at a constant speed until abnormal failure occurred, and the failure principle was analyzed.
The results show that the static torsional safety factor of the gearbox is 2.56, which meets the design requirements of the gearbox half-shaft gear and planetary gear metallographic and hardness are in accordance with the design requirements.
1 Introduction of the reducer
The object of the test is a parallel shaft reducer for the secondary drive of a new energy passenger car, as shown in Figure 1.
The input end is a splined shaft with input, and the output end is a differential gear connecting the two half shafts for output support bearings are ball bearings.
The reducer design rated torque, rated speed and other parameters are shown in Table 1
At the beginning of the design, the strength and life of the components were checked, and they were all within the design range, where the static torsional strength of each key component was above 2.5 times the maximum input torque and some components were above 3 times.
2. Test procedure
2.1 Test method
The input end of the reducer is connected to the drive motor through the adapter and universal coupling, and the spline of the differential output is connected to the two output half-shafts and fixed to the tooling base, as shown in Figure 2.
2.2 Preliminary analysis of the test
The gear teeth are subjected to the squeezing force of the bearing, the bending force at the engagement, the bending force of the drive shaft, the squeezing force of the bearing at the drive shaft, and the bending stress of the bevel gear at the engagement inside the differential housing during the static torsion test.
Therefore, the static torsion test continuous loading can lead to the failure of one or several different parts of different parts of the test in the range of 125.1 ° drive shaft rotation produced 3 times the peak torque and accompanied by 3 times the sound of collapse
Therefore, it can be judged that at least 3 parts should have broken or failed
3. Test disassembly and analysis
3.1 Disassembly and inspection
After the reducer is removed from the test bench, the input shaft can rotate freely and drive the differential shaft to rotate, and the two output half shafts of the differential can rotate at the same speed in the same direction, but cannot carry out differential speed, so the preliminary judgment is that the gear teeth of the reducer drive gear have not failed and broken, and the failure site is inside the differential.
Disassembly and inspection found that there is no crack at the root of the transmission gear teeth, and there is no obvious extrusion marks at the tooth surface involved in the engagement.
The bearings rotated smoothly without any obvious abnormalities such as stalling
No indentation and deformation in the bearing holes of the case
No cracks and deformation of the drive shaft
The transmission shaft is under static torsion, which means the transmission gear, bearing, case and strength of the gearbox are sufficient.
No obvious deformation and failure of the differential gear housing, as shown in Figure 4
Disassemble the differential gear and find that the teeth of the two half-shaft gears of the differential gear have cracks, and the differential gears are subjected to fluorescent magnetic particle inspection and flaw detection.
There were two cracks in the half-shaft gear I, which was located at the position of the two planetary gears, and the two cracks at the root of the teeth at the crack ① were very large, and the cracks were clearly visible, and the cracks were cracked along the root of the gear teeth, and there were also cracks on the tooth end face and tooth side as shown in Figure 5
The crack at ② is small and difficult to find with the naked eye, and the crack exists at the root and side of the two teeth, as shown in Figure 6.
There are also two cracks in the half shaft gears, which are also located at the meshing position with the two planetary gears, and the two cracks at the root of the teeth at crack ① are obvious and visible to the naked eye, and there is also a crack on the tooth end face, as shown in Figure 7.
Crack ② is more obvious and visible to the naked eye, and there are cracks on the tooth root, tooth end face and tooth side as shown in Figure 8
The planetary gear has a crack, the crack is not obvious, the naked eye can not see clearly under the fluorescent magnetic particle inspection can be found, the crack is on the tooth end face, as shown in Figure 9
Cracks in descending order: half shaft gear I crack ① half shaft gear work crack ① half shaft gear work crack ②, half shaft gear I crack ②, planetary gear I wheel crack
3.2 Failure analysis
3.2 Cause analysis
The cracks produced on the tooth surface and tooth root are bending fracture cracks
In the static torsion test, the differential gear is meshed with the half-shaft gear through its planetary gear, and the torque is transmitted to the half-shaft gear and then to the fixed tooling.
Therefore, in this process, the gear teeth at the mesh are mainly subjected to bending stress, thus the gear teeth at the mesh are prone to bending fracture
The reason for 3 torque peaks in static torque loading is that the differential bevel wheel has more than 4 pairs of bevel gears involved in each mesh.
The first time the torque peak is reached, the root of one of the half-shaft gear teeth involved in the mesh breaks off and the drive torque is then unloaded
The second reloading of the first cracked half-shaft gear gear teeth under load continues to expand at the cracked place while squeezing the other three gears until one of the gear teeth collapse, followed by drive torque unloading the third time the same principle as the second time, squeezing the other two gears until the third gear teeth collapse
3.2.2 Fracture analysis
The differential half-shaft gear and planetary gear materials are 20CrMo carburized fire steel, surface hardness requirements for 58 ~ 62HRC, the core hardness requirements for 30 ~ 42HRC
Anatomical analysis, the test results are shown in Table 2, all meet the design requirements
The most serious failure of the half-shaft gear I crack ① ((Figure 5) for fracture analysis of the root crack crack cracking serious existence of five cracks crack at the root are not obvious plastic deformation, two of which are located in the root of the tooth, a crack is located near the transition of the inner spline tooth root, another crack is located in the tooth root transition of the outer edge of the tooth groove, the outer edge of the tooth groove thickness is thin, especially with the minimum thickness of the tooth transition.
The other three smaller cracks exist on the tooth end face and tooth side face
One of the cracks with a larger opening at the transition of the tooth root on the outer edge of the tooth groove was cut and removed manually to open it, and the macroscopic morphology of the open fracture is shown in Figure 10, the overall fracture is silvery gray metallic luster, there are obvious radial stripes, and the direction of the radial stripes can be seen from the chamfer of the transition between the outer edge of the tooth groove and the gear teeth, where the thickness is the thinnest
Figure 11-14 shows the crack source Figure 13 (i.e. Figure 11 interrupted I area) microscopic morphology along the crystal morphology, fracture source at the chamfer surface machining marks deeper, no slag, sparse and old day crack defect characteristics.
Figure 14 (i.e. Figure 11 fracture II area) microscopic morphology, dominated by tough nest morphology
Cut the complete tooth groove outer edge and the chamfer of the gear tooth transition cross-sectional specimens for metallographic examination metallographic as shown in Figure 15, according to GB/T10561-2005 assessment of its non-metallic inclusions level: A1.0, D0.5 indicates that its material purity is good
In summary, the gear crack has the characteristics of overload brittle cracking, the crack source is located in the structure of the stress concentration of the outer edge of the tooth groove and the chamfer of the tooth transition, the fracture source is not seen at the slag sparse and old crack defects.
3.2.3 Safety factor
The static torsional safety factor of the reducer is S = M/ Mmax = 667 /260 = 2.56 where:Mmax is the maximum input torque of the reducer M is the torque of the reducer in case of failure.
According to QC/T1022-2015 "Technical conditions for pure electric passenger car reducer assembly" 5.2.9, the static torsional strength reserve factor should be not less than 2.5, and the safety factor meets the design requirements
4. Conclusion
(1)The gear inside the differential in the static torsion test broke apart and failed, and the rest of the parts were normal.
(2) The differential half-shaft, gear planetary gear metallographic and hardness are in accordance with the design requirements, the fracture fracture is brittle fracture.
(3)The torque safety factor of the reducer in static torsion test is 2.56, which meets the design requirements.
Through the static torque test and analysis of the reducer, the weak points of the reducer are reflected, which provide the basis for further improvement of the design and performance of the product.