Development and application of vibration test syst

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Development and application of vibration test system for brushless fan of automobile air conditioner

DC brush fan is widely used in domestic automobile air conditioner before h, but DC brush fan has low efficiency, high noise, short service life of electric brush, and often needs maintenance and repair. Due to the adoption of electronic commutation technology, which must comprehensively consider the energy efficiency, environmental protection and product quality, the DC brushless motor eliminates the rectifier and brush in the DC brush motor, which has great room for the improvement of the efficiency and speed of the motor and the extension of the service life. In addition, the noise of the motor is also reduced. Therefore, using brushless motor instead of brush motor in automotive air conditioning is the trend of technological development. At present, a company in Fuzhou has completed the development of the first brushless DC fan for automotive air conditioning in China. In order to further improve the reliability, comfort, energy conservation and environmental protection performance of existing products and improve the anti vibration performance of fans, it is necessary to conduct vibration test on existing prototype products, find out the local factors affecting their vibration, and study effective measures to reduce fan vibration, so that fans can be applied in practice

1 development of test system

1.1 prototype structure

the structure of the prototype of DC brushless fan for automotive air conditioning provided by a company in Fuzhou is shown in Figure 1 and Figure 2. As can be seen from figure L, the fan is mainly composed of the following parts: brushless DC motor, integral outward rotating impeller, rotating shaft, rolling bearing, bearing shaft, upper and lower frames, upper and lower shock pads, flange, etc. Figure 2 is the physical drawing of the prototype of the automobile air range DC brushless fan provided by it

1.2 testing principle

in the measurement and analysis of vibration and noise signals, we should first use the sensor to convert the sound pressure signal or acceleration signal into electrical signal, and then measure and analyze it after amplification and processing. The signal is easy to produce signal distortion in the process of quantification and interception, so we should comply with the sampling theorem in the sampling process; In the process of measurement, some interference signals will inevitably infiltrate, which requires signal amplification, filtering and other pretreatment to filter the interference components in the signal, so as to extract useful information Finally, the signal is analyzed by spectrum. The amplitude spectrum or power spectrum obtained after spectrum analysis can provide the following vibration information:

1) what frequency components and harmonic components are mainly composed of in the vibration signal

2) which component of harmonic component has relatively prominent amplitude, which reflects that the vibration of this frequency component is relatively large

l.3 development of test system

the block diagram of the vibration test system designed according to the structure of the prototype product is shown in Figure 3

the test system mainly includes two parts:

1) signal acquisition and conditioning

including piezoelectric acceleration sensor and filter integral amplifier. The sensor obtains the measured vibration acceleration signal and converts it into a charge signal. Then, the signal is sent to filter. Famous chemical manufacturers such as DuPont, Cargill, BASF, etc. continue to enter this market by means of mergers and acquisitions and joint ventures to amplify and low-pass filter

2) signal analysis and processing

including signal acquisition instrument and computer data processing system. The conditioned signal can be identified by the computer after being converted into a digital signal by the aid of the data acquisition instrument, and the upper computer uses the software system to analyze and process it

due to the special structure and vibration type of the fan, in order to obtain accurate test data, the key to the design of the test system is the selection of test parts and the installation of sensors

1) selection of test parts

the rotor of the prototype is a high-speed rotating component, and it is not easy to install a sensor directly on the rotor to test it. During the movement, the visible vibration of rotor 1 will be transmitted to the bearing and flange through the rotating shaft, so, During the test, the vibration of the fan will be realized by testing the vibration of the flange at the same measuring point of the new product "Taiping Ying1 life insurance (Universal)" launched by Taiping Life Insurance

2) installation of sensor

the sensor is installed with a magnet base. The advantage of the magnet base is that it does not damage the measured object, and it is convenient and reliable. The installation method of vibration test is shown in Figure 4

1.4 test system entity

the test system for fan vibration test designed is shown in Figure 5

2 application example

assemble the prototype impeller after dynamic balancing to the whole machine and place it on the vibration test system platform. In view of the great impact of radial vibration on the fan, the soil should collect the radial sensor signal during the test and analyze it to obtain the waveform h and spectrum diagram of the radial vibration test of the fan at the speed of 2000 R/rain and 3000 R/rain (as shown in Figure 6 and Figure 7)

1) from the test spectrum figure 6, Figure 7 and the corresponding numerical analysis, it can be concluded that when the fan operates at 1200 R/min to 3000 R/min, the frequency component in the radial response spectrum is dominated by the l-fold frequency of the rotor speed, accompanied by 2, 3 and 4-fold frequency components. The vibration energy is mainly concentrated in the l-fold frequency of the speed, which is exactly the power frequency component corresponding to the working speed, and the vibration of other frequency components is small. The main soil factors that cause the vibration of these frequency components may be: the same frequency centrifugal force; Other exciting forces are caused by their natural frequencies. By analyzing the structural characteristics and processing technology of the rotor of the prototype, it is found that these frequency characteristics are consistent with the unbalance characteristics of the rotor. Therefore, it is considered that the serious mass unbalance of the fan is a major factor affecting its vibration

2) it can also be seen from the spectrum diagrams 6 and 7 that in addition to the obvious component of the vibration energy at the l-fold frequency of the rotating speed, there is also a large amplitude at the l-fold frequency of the rotating speed. Through analysis, it is found that the frequency at the l-fold frequency of the rotating speed is exactly equal to the commutation pulsation frequency and the cogging pulsation frequency of the brushless DC motor in the fan structure, Therefore, the commutation pulsation and cogging pulsation of brushless motor also have a great impact on the vibration of the fan

through the fan. After some improvement measures, such as re performing precise dynamic balance on the fan impeller, improving the assembly process of yoke and magnetic tile, yoke assembly and impeller, and improving the machining accuracy of important parts, ran carried out vibration test on the fan, and it was found that the vibration of the fan during operation was significantly reduced

3 conclusion

to sum up, putting the fan on the vibration test bench for vibration test can find out the main factors affecting the fan vibration. After targeted improvement, the fan vibration can be effectively reduced, which shows that the design of the test system is feasible and reasonable, and the application effect is good

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