1 Gear noise test experiment 11 Test conditions and test instrument The object to be tested is a hanging wheel mechanism consisting of 3 standard involute gears in an old C630 lathe head box. The number of teeth is z1=z3=72, z2= 100, modulus m = 225, as shown. The test instrument is the signal acquisition system (including signal processing software) and signal amplifier of ND2 type precision sound level meter, Oriental Vibration and Noise Technology Research Institute. Figure 2 shows the signal acquisition process.
12 Experimental conditions and experimental instruments (1) Among the three gears, the outer ring of the intermediate gear of the hanging wheel is the largest (the basic structural size is shown in 3), and its ability to radiate noise is also stronger. Therefore, the idler is selected as the test object. Firstly, it is removed and suspended separately. The precision sound level meter microphone is pointed to the gear along the center position of the gear axis, and the distance is maintained at about 700 mm, and the gear is struck with a hammer. The recorded waveform is acquired by a signal acquisition system.
(2) Install the gear back on the lathe and tap the stationary gear with a hammer to record the noise waveform.
(3) Select the spindle speed of the lathe to rotate at 600r/min. When the noise tester reads stable, record the noise data and record the waveform with the signal acquisition system.
(4) Spread the configured lubricating fluid evenly on the tooth side of the three gears, the lathe spindle runs at a lower speed, so that the lubricating oil evenly infiltrates each tooth, and the lathe stops running for a few minutes to stabilize the lubricating fluid on the gear. Turn the lathe speed back to 600r/min. After the noise tester pointer is stable, record the reading and collect the data record waveform. It should be pointed out that the lubricating oil has been tested by the friction pendulum device and has a good effect of suppressing the friction excitation.
2 Experimental results and analysis 21 Experimental results The noise time domain signal is collected and subjected to FFT processing, and the spectrum result is obtained as shown in FIG.
The spectra of 4 and 5 obtain the natural frequency of the body when the gear is stationary. When the gear is stationary, it can be understood as the free state of the inner and outer boundaries. When the gear is statically mounted and fixed on the hanging frame, it can be understood as the outer boundary free. The state of the boundary attached constraint.
In order to obtain the noise spectrum when the spindle speed is 600r/min, the sound pressure level measured by the noise meter is 8993dB(A); the noise spectrum obtained after applying the lubricant, and the noise meter measured at this time. It becomes 8892dB(A). At this time, the changes of the frequency components and the corresponding amplitudes before and after the application of the lubricant can be observed by comparison. The mode shape when the gear rotates is a coupling of a plurality of modes, so that it is difficult to describe it simply.
The spectrogram obtained above has a sampling frequency of 2560 Hz, a coherence coefficient of 1, and a phase of 0, which is obtained by cross-power spectrum analysis.
The frequency components of the various vibration conditions and the corresponding magnitudes are compared.
1 Analysis and discussion of the main frequency components and their amplitudes of various vibration conditions. The peak frequency component of 25 Hz is the result of the overall oscillation of the gears when the free-spinning gear is struck; when the gears are installed, again This frequency component automatically disappears during tapping and subsequent testing. Therefore, there should actually be only 4 peak frequencies in the natural frequency of the gear.
The idler shown in Fig. 3 can be approximated as three rings. The 58mm42mm ring of the interface is difficult to excite, so the actual vibration should be a ring with a thickness of 13mm in the middle and a ring with an outer thickness of 20mm and air-coupled radiated noise. It is thus conceivable that the frequency component of 1325 Hz is mainly related to the middle ring. For the annular plate, regardless of the boundary conditions of the plate, the natural frequency of the lateral vibration is calculated as follows:
f=ans2a2DA where: ans is the frequency constant; D is called the bending stiffness, D=Eh312(1-2), where E is the elastic modulus of the plate, h is the thickness of the plate, and is the Poisson's ratio of the material; The outer circle radius of the disc; A is the area density of the board.
It can be found from the spectrogram that the frequency of the gear is 1325 Hz when the gear is separately suspended and the knocking wheel is struck. However, after the gear is rotated, the frequency component becomes 1350 Hz. When the number of pitch diameters is n=2, the mode frequency of the inner and outer boundaries is free at 13224 Hz when the number of pitch circles is s=0; and the mode frequency of the inner boundary of the inner boundary is 13494 Hz when n=2, s=0, which is 13494 Hz. Very close to the actual measured value. Since the shape of the gear is not a standard disk, the equivalent thickness h=14489m is used here, and the equivalent areal density A=113739kg/m2. (According to material properties, =032, E=201011MPa). The reason why this frequency component changes before and after the rotation is that at the time of rotation, since the gear rotates together with the shaft, the gear has a torsional deformation, and the gear vibration mode exhibits a vibration mode in which the inner boundary is simply supported and the outer boundary is free. At 3150 Hz and 4450 Hz, the approximate frequency components are not calculated, which may be related to the vibrations associated with the two. After the gear is installed, the idler gear meshes with the master and slave wheels at the same time, so that the outer ring vibration is hindered, so the 4450 Hz of the suspension gear is changed to 4475 Hz after installation. The component of 3150 Hz becomes 3125 Hz after the gear rotates.
The frequency component of 5550 Hz mainly depends on the outer ring. Since the tapping part before and after installation is mainly the outer ring, the frequency of 5550 Hz is not affected.
When the spindle of the lathe rotates at 600r/min, the headstock system and the hanging wheel system vibrate at the same time, and the noise peak increases more. Since the microphone of the sound level meter is facing the idler of the hanging wheel mechanism, the noise component associated with the gear can be completely recorded. The meshing frequency of the gear is equal to the product of the gear speed and the number of teeth, that is, fz=nz60 where: n is the rotational speed of the gear (r/min); z is the number of gear teeth. From the lathe rotation speed and the number of the driving gear teeth of the hanging wheel mechanism, it can be seen that the meshing frequency is f1=6007260=720Hz and the meshing frequency of the idler gear is 2 times, that is, f2=2f1=1440Hz will cause friction excitation according to the engagement and withdrawal engagement. From the point of view, the friction excitation frequency of the idler is twice the meshing frequency, that is, fM2 = 2f2 = 2880 Hz. It is known that there is a maximum amplitude of 2625 Hz. This frequency is very close to the nominal value of the calculated friction excitation frequency. Considering that the spindle speed of the lathe is obtained according to the tachometer gear, the actual speed and the nominal value must be different. Based on this understanding, the author believes that there is reason to judge that 2625Hz is the friction excitation. This high frequency frictional excitation causes high frequency noise between the tooth flanks.
In addition, the 1800 Hz that appears after the application of lubricating oil should be an evolution of 2125 Hz when no lubricating oil is applied. Because some properties of the flank are changed after the lubricant is applied, some constraints are partially reduced, so that a certain mode determined by 2125 Hz is more easily excited, and the constraint is changed to reduce the frequency of the step to 1800 Hz. In addition, it can be seen that the frequency component of 3175 Hz is superimposed on the basis of 3125 Hz, and has a certain relationship with the deformation frequency of the support shaft (or mandrel) of the idler.
After the noise-reducing oil is applied, the variation of the frictional force is greatly reduced when the tooth surfaces are engaged and disengaged, so that the noise peak caused by this excitation is also significantly reduced. The test results show that the noise peak of the friction excitation frequency after the tooth surface is lubricated is almost reduced by 60, and the noise of the higher frequency component caused by the friction excitation also has a corresponding decrease or is completely suppressed.
It can be seen that the test results obtained by spectrum analysis are much more accurate than the octave analysis method. The above data and facts show that in the involute gear transmission, there is indeed a friction excitation frequency twice the meshing frequency, and at the same time, higher frequency noise is excited. For the high-frequency noise of the gear caused by friction, the friction excitation is controlled by the noise-reducing oil, and the suppression effect of the friction excitation frequency component is very significant. Such noise reducers can be used for the control of high frequency noise associated with frictional excitation, such as the control of the whistling sound produced by the railway as it passes through a curve.
In the field, the A sound level measurement is performed with the ND2 type precision sound level meter, and the lubricating oil is applied to the gear teeth of the hanging wheel system, which can reduce the noise of the whole machine by about 2 dB. Although the overall noise reduction range is small, the octave analysis and The results of the spectrum analysis show that the high-frequency component noise values ​​have decreased. However, the spectrum analysis results are different from the octave analysis. The noise amplitude of 3125 Hz is greatly increased due to the coating of lubricating oil. This phenomenon has not been discovered in the octave analysis, and there may be some contingency. This frequency is undoubtedly a natural frequency of the gear body, but after reducing the influence of the friction excitation, the vibration of the gear body is intensified because the objective existence of the change of the tooth stiffness causes the other natural frequency components to be constrained. After that, it is not possible to constrain the mode shape, and the friction excitation frequency is similar to it, thus promoting the enhancement of the second-order vibration.
3 Conclusions (1) The conclusion that the friction excitation frequency is twice the meshing frequency is further proved by the more advanced technical method of noise spectrum analysis. And it is considered that the friction excitation frequency is not directly related to the natural frequency.
(2) The new lubricating noise reducer configured by the friction pendulum experimental device has a good inhibitory effect on the friction excitation, thereby effectively reducing the vibration of the system and reducing the noise.
(3) Due to the use of lubricating noise reducer, the vibration of the friction excitation frequency component is obviously suppressed, and the vibration mode of the overall gear system is changed, which has an effect on a certain natural frequency component, but the noise reduction effect is generally achieved. . As for the inhibition and influence of other components, there is a certain relationship and the effect of the rotation speed and load on the use of the lubricant to suppress the friction excitation is not clear, and further research is needed later.
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