Abstract: This article aims at the abnormal noise of the chassis when the car turns at low speed, and uses the human ear and stethoscope to identify the abnormal sound source to determine the approximate location and sound attributes of the abnormal sound. Then use the special vibration and noise testing equipment to collect the characteristics of the abnormal sound problem and analyze the characteristics to determine the source of the abnormal sound. The source of the abnormal sound is verified by the single variable method, and the parts that have the abnormal sound problem are locked. Make a sample of the manual solution for verification and determine the cause of the problem. The scope of the optimal solution is gradually narrowed down through the rapid verification method, and the optimal solution is obtained by combining the manufacturing process and assembly process. Lock the design parameters of the parts, make the plan parts and carry them on the whole vehicle for verification. The result is that the abnormal noise problem disappears, the plan is effective, and the problem is solved.
1.Introduction
With the rapid development of the automotive industry, customers have higher and higher requirements for automotive performance. Among them, the abnormal sound performance of automobiles is particularly prominent. It is a direct, superficial, and easily perceived performance dimension by customers, and has become one of the important basis for judging the performance and grade of automobiles. In the process of automobile development, the abnormal sound of the chassis is a key core technical issue in the development of automobile performance and a key issue affecting the quality of the automobile. In recent years, major car companies have paid more and more attention to the abnormal noise performance of cars, and the proportion of investment has continued to increase.
The automobile chassis system is mainly composed of suspension, sub-frame, brakes, wheels, drive shaft and so on. Among them, suspension, brakes, and drive shafts are the parts that account for a large proportion of chassis abnormal noise. For chassis abnormal noise control, CAE methods can be used in the early stage, including DMU inspection, modal design, stiffness and strength design, stress feature analysis, avoiding historical problems and outstanding market problems, etc. In the mid-term, abnormal noise can be adjusted on the actual prototype to identify abnormal In the later stage, the quality of parts and the consistency control of production process should be strengthened. After listing, it should mainly optimize the abnormal noise problem reported by the market.
The above is a relatively conventional way of solving the problem of abnormal noise in cars, but the abnormal noise is often beyond people's expectations. Even if the preliminary work is done well, it is difficult to guarantee that there will be no abnormal noise in the real car later. For the abnormal noise problem of real vehicles, we should mainly start with the common and serious abnormal noise problems, and give priority to solving the abnormal noise problems that trouble customers. For the outstanding abnormal noise problem, it can be extracted from the main line of abnormal sound development separately, and it can be treated as a technical problem dedicated to solving it. The cycle meets the development needs, and the problem can be solved and returned to the main development line. The solution to the chassis abnormal noise problem is the same as other abnormal noise problems, but the chassis abnormal noise problem is more complicated than other abnormal noise problems, and it takes more time and resources.
2.Chassis Abnormal Noise Troubleshooting and Analysis
2.1 Description of Abnormal Noise Phenomenon
When a vehicle is running normally on the road, when turning at low speed (15-20km/h), there will occasionally be a "click" sound from the front chassis, and the frequency of occurrence is irregular. In response to this problem, the vehicle was driven around a figure 8 on the test site. When the steering was switched in reverse during driving, the "click" sound at the front chassis reappeared, and the working conditions where the sound occurred were when the steering was switched, and the working conditions were relatively Stablize.
2.2 Abnormal sound troubleshooting
The front chassis of the vehicle is mainly a McPherson suspension structure, as shown in Figure 1. First.
use a stethoscope to narrow the range of abnormal noise sources, and arrange sensors on the following component structures (as shown in Figure 2): stabilizer bar (channel 1), swing arm (channel 2), brake (channel 3), steering knuckle (Channel 4), subframe (Channel 5), shock absorber (Channel 6), stabilizer bar (Channel 1), brake (Channel 3) and steering knuckle (Channel 4) are measured to be relatively loud. Continuing to narrow the range, the brake (channel 3) and steering knuckle (channel 4) sounds are more obvious.
After using the stethoscope to narrow down the location of the sound source, it is no longer possible to continue to analyze and determine the cause of the problem and the sound characteristics. Therefore, the NVH professional testing equipment LMS Test.Lab is used to continue to investigate the abnormal sound problem, and the vibration sensor is used for layout (as shown in Figure 3. Shown)
through vibration data collection, spectrum analysis, measured vibration conversion spectrum features, as shown in Figure 4.
By analyzing the data measured by the sensor, it can be concluded that: (1) the vibration source is the brake end; (2) according to the sound characteristics, it is determined that the abnormal sound is the impact sound of metal parts.
According to the troubleshooting, the source of abnormal locking noise is the brake (as shown in Figure 5).
Combined with the brake structure and the problem waterfall diagram, it is preliminarily suspected that this problem may occur at both the installation position of the brake caliper and the outer ring of the brake bearing.
Verification scheme 1: Disassemble the brake caliper (as shown in Figure 6)
and verify whether the problem recurs. Conclusion: After the brake caliper is disassembled, the abnormal noise still exists, and the abnormal noise caused by the caliper is ruled out.
Verification scheme 2: Weld the joint between the brake bearing outer ring and the steering knuckle bearing hole firmly (see Figure 7 for the welding position)
and verify whether the problem recurs. Conclusion: After the joint between the outer ring of the brake bearing and the bearing hole of the steering knuckle is welded firmly, the abnormal sound problem has not reappeared.
In order to confirm the validity of the verification plan, another three vehicles with this problem were welded firmly at this position, and the abnormal sound was not reproduced. From this, it can be determined that the root cause of the abnormal sound of the chassis when the vehicle is turning at low speed is the problem in the cooperation between the outer ring of the brake bearing and the bearing hole of the steering knuckle. Return the brake bearing outer ring and the steering knuckle bearing hole of the problem car to the factory for quality analysis, and both parts meet the design requirements. It follows that there is a design problem with this structure.
Through further verification, it can be seen that the outer ring of the brake bearing of the original car and the steering knuckle bearing are interference fit (the fit between the outer ring of the brake bearing and the steering knuckle bearing hole is shown in Figure 8)
and the design tolerance of the steering knuckle bearing hole is ∅80(-0.044, -0.073), the brake bearing outer ring tolerance ∅80 (0, -0.012).
Verification scheme: Make 3 sets of new samples for verification, so that the tolerance of the steering knuckle bearing hole is ∅80 (-0.07, -0.1). Verification result: After the new sample is installed on the whole vehicle, there is no such abnormal sound problem.
From the model in question, it is known that this model is a traditional fuel car that has undergone an oil-to-electric design. It is an oil-to-electric model. The curb weight of the vehicle has increased by 362kg. The joint bearings are used in traditional fuel vehicles and there is no such problem in fuel vehicles.
Based on vehicle information, changes in lateral force, and combined with troubleshooting conclusions, it can be concluded that the root cause of chassis abnormal sound when turning at low speed is that the outer ring of the brake bearing and the bearing hole of the steering knuckle are slippery due to the lateral force when the vehicle is turning. Move the impact. The reason for slippage and impact is that the outer ring of the brake bearing and the steering knuckle bearing hole have insufficient interference. The easiest solution is to eliminate this rattling problem by optimizing the dimensional tolerances of the steering knuckle bearing bore.
3.Optimization plan formulation
Due to the tight schedule of the project, it is necessary to use the rapid verification method to formulate the optimization scheme. Make 20 sets of steering knuckle outer ring bearings (the dimensional tolerances of steering knuckle bearing holes are shown in Table 2)
|
NO |
Dimensional tolerance |
|
1 |
∅80(-0.050,-0.078) |
|
2 |
∅80(-0.050,-0.080) |
|
3 |
∅80(-0.053,-0.080) |
|
4 |
∅80(-0.053,-0.082) |
|
5 |
∅80(-0.055,-0.085) |
|
6 |
∅80(-0.055,-0.088) |
|
7 |
∅80(-0.061,-0.080) |
|
8 |
∅80(-0.061,-0.085) |
|
9 |
∅80(-0.065,-0.085) |
|
10 |
∅80(-0.065,-0.088) |
|
11 |
∅80(-0.065,-0.090) |
|
12 |
∅80(-0.068,-0.090) |
|
13 |
∅80(-0.068,-0.095) |
|
14 |
∅80(-0.068,-0.097) |
|
15 |
∅80(-0.070,-0.095) |
|
16 |
∅80(-0.070,-0.097) |
|
17 |
∅80(-0.073,-0.095) |
|
18 |
∅80(-0.073,-0.097) |
|
19 |
∅80(-0.073,-0.1) |
|
20 |
∅80(-0.075,-0.1) |
and load them into vehicles for verification (select the full-load working condition of the vehicle to ensure the maximum lateral force of the vehicle, and select this working condition for the verification conditions below. conditions),narrowing the tolerance range. Verification conclusion: No. 1, 2, 3, 4, 5, 6, and 7 samples were carried on the whole vehicle for verification, and the abnormal noise problem was not significantly improved; Elimination of abnormal noise; samples of serial numbers 14, 15, 16, 17, 18, 19, and 20 are carried on the vehicle for verification, and the abnormal noise is eliminated, but the installation is stuck, which is inconvenient for loading and unloading.
According to the verification conclusion above, the implementable dimensional tolerance range is reduced to ∅80 (-0.061, -0.095) for further loading verification. In order to avoid that the abnormal sound is not obvious due to the small slip of the sample and is not recognized by the human ear, this verification uses LMS equipment to collect the vibration signal of the steering knuckle bearing end, and monitors whether there is a relative gap between the steering knuckle bearing hole and the outer ring of the brake bearing. sports. The layout of steering knuckle bearings is shown in Figure 9.
Verification conclusion: After the serial number 8 sample is loaded on the whole vehicle, there is relative motion between the steering knuckle bearing hole and the outer ring of the brake bearing, which is consistent with the problem characteristics; There is relative movement in the outer ring of the brake bearing.
Determination of the optimization scheme: According to the above verification conclusions, the dimensional tolerance of the steering knuckle bearing hole is determined to be ∅80 (-0.065, -0.095). within the control switching cycle. The optimized vibration characteristic waterfall diagram is shown in Fig. 10.
4 Real vehicle verification of steering knuckle bearing
According to the optimization plan, the dimensional tolerance of the steering knuckle bearing hole is optimized from ∅80 (-0.044, -0.073) to ∅80 (-0.065, -0.095), which increases the interference between the outer ring of the brake bearing and the steering knuckle bearing hole. The optimized fit between the brake bearing outer ring and the steering knuckle bearing hole is shown in Figure 11.
According to the optimization results, the soft film data was frozen, and 3 sets of manual samples were produced. The precision of the sample production met the design requirements. After the parts were tested and passed, it was mounted on a real vehicle for real vehicle verification (see Figure 12 for the real vehicle brake).
Verification conclusion: None of the 3 sets of manual samples had this abnormal sound problem.After the manual workpiece verification scheme is effective, the dura mater data is frozen, and the dura mater is opened to make 3 sets of tooling samples. After the parts are tested and passed, they are mounted on a real vehicle for real vehicle verification. None of the 3 sets of dura mater tooling samples has this abnormal sound problem. , it is comprehensively judged that this scheme can be mass-produced, and the subsequent batches of vehicles are equipped with this scheme's tooling parts, and there is no such abnormal sound problem.
5 Conclusion
As the automobile industry pays more attention to the performance of automobile abnormal noise, the abnormal noise development technology in the field of automobile development has achieved rapid development. This paper combines theoretical analysis and actual vehicle verification to analyze the influence of the lateral force generated when the vehicle turns on the cooperation between the steering knuckle bearing hole and the outer ring of the brake bearing. Through the troubleshooting of abnormal noise vehicles, the scope of the problem is gradually narrowed down, and then verified by manual schemes. Lock down the source of the abnormal sound problem. Make a sample of the solution to verify the abnormal noise problem, and then optimize the problem sample through rapid verification methods to obtain the optimal solution to the problem. According to the optimization plan, make a soft film manual sample for verification. After verifying that there is no problem, make a hard film tooling sample for verification. After verifying that there is no problem, proceed to mass production and switching.
Through the whole process of identification, investigation, analysis, plan formulation, engineering, and batching of this abnormal sound problem, a lot of experience has been gained. In the subsequent project development process, it is necessary to learn from this experience, especially in the early design stage of the vehicle, to fully simulate the force distribution of the vehicle and the stress on parts under various working conditions, and to confirm whether there are abnormal noise problems in key parts Risk, if there is a problem, it needs to be avoided in time.