Abstract: As an important component for transmitting power in a vehicle, the NVH performance of the transmission shaft seriously affects the NVH performance of the vehicle. The article introduces the process of handling the problem of abnormal noise in the transmission shaft of a light truck, and conducts troubleshooting from aspects such as dynamic balance of the transmission shaft, system resonance, and transmission shaft angle, and finally solves the problem of abnormal noise.
Keywords: Abnormal noise; Resonance; Transmission shaft angle
Preface
With the development of society, users have increasingly high requirements for the comfort of automotive products, especially the NVH performance of automobiles, which is receiving increasing attention from users. The transmission shaft, as an important component for transmitting power in the entire vehicle, its NVH performance seriously affects the NVH performance of the vehicle. During the development and verification of a certain light truck, a problem of abnormal noise was found in the entire vehicle. After analysis and confirmation, it was determined that the source of the abnormal noise in the entire vehicle was the transmission shaft.
1 Fault phenomenon
During the validation of the new car, the experimenters found that there was a "buzzing" noise when driving at high speeds (above 60km/h), and as the speed increased, the noise gradually increased. After professional evaluators evaluated and confirmed multiple systems, it was found that the source of the vehicle's abnormal noise was the transmission shaft.
2 Fault investigation
There are usually three reasons for abnormal noise in the transmission shaft: 1. Poor dynamic balance of the transmission shaft; 2. Resonance between transmission shaft and power system; 3. The included angle of the transmission shaft is unreasonable.
2.1 Troubleshooting of poor dynamic balance
The dynamic balance of the faulty vehicle's transmission shaft was tested and it was found that the transmission shaft met the design requirements, with a dynamic imbalance of less than 40gcm. All light truck transmission shaft products comply with this dynamic balance standard, and there are no adverse phenomena, so the factor of poor dynamic balance is ruled out.
2.2 Resonance troubleshooting of transmission shaft and power system
Calculate the critical speed of the transmission shaft. According to the Automotive design [1], the critical speed of the transmission shaft is calculated according to formula (1):
Where, D is the outer diameter of the transmission shaft tube, d is the inner diameter of the transmission shaft tube, and L is the length of the transmission shaft. After calculating the outer diameter of the transmission shaft of 69mm, the inner diameter of 63mm, and the length of 850mm, the critical speed of the transmission shaft is 15518rpm. Considering the Factor of safety of 1.5, the small critical speed of Z can reach 10345rpm.
Simultaneously calculate the Z-major frequency of the transmission shaft operation [2].
Among them, Vmax is the Z high speed, ig is the transmission ratio of the gearbox Z high gear, io is the main reducer transmission ratio, K is the main harmonic order of the engine torque (for a four cylinder four stroke engine, the main harmonic order is 2), and r is the wheel rolling radius.
Substitute Vmax=120km/h, ig=0.77, io=6.142, K=2, r=0.360m into equation (2), and calculate f=158Hz. The converted speed is 9480rpm, which is less than the critical speed of the transmission shaft of 10345rpm.
Therefore, the factor of resonance between the transmission shaft and the power system is excluded.
2.3 Investigation of unreasonable angle between transmission shafts
Check the included angle of the transmission shaft [1], and the schematic diagram of the included angle of the transmission shaft is shown in Figure 1.
Figure 1 Schematic diagram of transmission shaft angle
After verification, the included angle of the transmission shaft under various working conditions is shown in Table 1, and the equivalent included angle reaches 3.9 ° under no load, which is greater than the recommended allowable equivalent included angle of 3°in the design. Therefore, an excessive equivalent angle in the design of the transmission shaft may be the cause of abnormal noise in the transmission shaft.
Based on the above theoretical analysis, optimize the design of the transmission shaft angle.
Based on the previous theoretical analysis of the transmission shaft angle, analyze and adjust the rear axle elevation angle to reduce α 3. It can reduce the equivalent included angle φ。 The original design state has a rear axle elevation angle of 7.5 °, and after adjusting the rear axle elevation angle to 8.5 °, the verification results are shown in Table 2. The verification results show that when the rear axle elevation angle increases to 8.5 °, the individual included angle of the transmission shaft α 2 α 3 reduction, equivalent included angle φ Significantly reduced, only 1.9 ° under no-load condition. Compared to the original design state, it is reduced by 2 °.
Table 2: Theoretical included angle of the transmission shaft when adjusting the rear axle elevation angle to 8.5 °
Adjust the rear axle elevation angle to 8.5 ° for verification: add 1 ° inclined pad iron at the rear axle steel bracket, adjust the rear axle elevation angle to 8.5 °, and test install 2 vehicles for verification; Testers have reported that the abnormal noise is more pronounced and worse than the old state.
The above verification results differ significantly from the theoretical analysis. Therefore, it was decided to measure the included angle of the transmission shaft. The transmission shaft angle measurement was conducted using three coordinates for one offline vehicle in its original state and two vehicles in the adjusted rear axle elevation state. The test results are shown in Table 3.
Table 3: Actual included angle of the transmission shaft when adjusting the rear axle elevation angle to 8.5 °
The above measured results differ greatly from the theoretical analysis. From the measured results, it can be seen that the actual equivalent angle of the vehicle in its original design state reached 6.2 °, far exceeding the general requirement of 3 °.
After investigating the deviation between the above physical and theoretical conditions, it was found that the engine position is in the Z direction, and the actual state is 12mm lower than the theoretical state. Due to the short wheelbase (2800mm) of the problematic model, the design length of the front transmission is only 472mm, and the included angle of the transmission shaft is greatly affected by the installation position deviation (the actual state is 2.6 ° different from the theoretical state).
According to the physical condition, the angle between the transmission shaft was adjusted by adding a 10mm pad iron at the hanging point in the middle of the transmission shaft, and measured. The results are shown in Table 4.
Table 4 Adjusting the included angle of the transmission shaft based on the measured results
Therefore, it can be determined that the abnormal noise of the transmission shaft is caused by the excessive angle between the transmission shafts. After reducing the included angle of the transmission shaft, especially the equivalent included angle of the transmission shaft, the abnormal noise is significantly improved.
3 Conclusion
1) The investigation of abnormal noise in the transmission shaft should be systematically investigated, including dynamic balance, system resonance, and transmission shaft angle;
2) When analyzing problems, it is necessary to combine theory with actual testing (measurement) to avoid making incorrect judgments based solely on theoretical values;
3) The angle between the transmission shaft is unreasonable, which is often prone to batch production issues. It is necessary to conduct sufficient verification and evaluation during the design and development verification stage to avoid batch user complaints after the product is launched;
4) Through fault handling, it is more fully demonstrated the necessity of requiring an equivalent angle of less than 3°or the transmission shaft.
More about VAFEM Agricultural bearings：
Agricultural machinery requires better seals for contaminated conditions, provisions for misalignment, and economical mountings for shafts and housings. VAFEM offers bearings for disc harrows, planters, mowers, rakes, all types of balers, tillage, seeding and forage harvester equipment, combines, cotton pickers/stripers, and other agricultural equipment like silo unloaders and grain elevators.
We also offer a complete line of insert ball bearings, shaft mounted with either tapered adapters or locking collar or set screws. Our proven seal designs include low torque shields to heavy-duty triple lip seals. Disc harrow bearings are also available with either round, square, or hexagonal bores. All bearings are available with or without re-lubrication holes.
https://www.vafem.com/products/Agricultural-Bearings/775.html
2023-07-11