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1 The transmission is the most basic device in the machine, and the gear is the basic original in the transmission.
The gear may have some malfunction during operation. After the gear is faulty, its transmission quality drops sharply, causing large vibration and noise, which will degrade the working performance of the transmission, and may even lose its working ability. Therefore, the diagnosis of the gear fault can improve the working capacity of the transmission and reduce the vibration of the gear. And noise is very important. Gear failures have historically been judged by experienced operators listening directly to the changes in the sound of the running gear with their ears. The success of the method depends entirely on the actual experience of the operator. In recent years, due to the continuous development and improvement of testing methods, it has become possible to accurately diagnose the fault of the gear.
2 Gears may fail 2.1 Gears caused by gear manufacturing errors Inevitably there are errors in the manufacturing process, but we can take measures to limit gear manufacturing tolerances to the allowable range. If the gear manufacturing error is outside the allowable range, the vibration and noise of the gear will increase. Although this failure does not seriously affect the gear operation, it does not work well.
2.2 Failure caused by gear installation error Due to the manufacturing error of the box hole and the error generated during the assembly process, it directly affects the mutual position accuracy of the gear pair, which will cause vibration and noise during the operation of the transmission.
2.3 Gear tooth damage due to gear manufacturing error, poor configuration or operation under inappropriate conditions, such as gears subjected to multiple repeated loads and impacts, long-term work under heavy load and poor lubrication, etc. The teeth produce various kinds of damage, which can be divided into the following four according to the occurrence state of the damage of the gear:
(1) wear; (2) surface fatigue; (3) plastic deformation; (4) tooth fracture.
Gear tooth damage is a serious gear failure, and once it occurs, the working conditions will deteriorate sharply. The gears that produce the above faults are capable of generating large vibrations and noises, and can reflect certain characteristics in the vibration and noise spectrum. Therefore, analyzing the vibration and noise spectrum maps can diagnose gear faults.
3 Basic characteristics of gear failure Gear failure is divided into large cycle failure and small cycle failure. A large cycle fault is a fault characterized by the rotational frequency of the gear as a fundamental frequency. Such as eccentricity, cracks and broken teeth, some of them affect the spectrum in the form of error, and some affect the response in the form of sudden stiffness.
Small cycle faults refer to faults such as gluing, pitting and wear that are characterized by the meshing frequency of the teeth as the fundamental frequency. Most of them affect the spectrum in the form of variable phase errors. The basic characteristics are as follows: (1) The amplitude of the gear with large period fault at the gyro frequency and its harmonics increases with the deterioration of the fault, while the amplitude of the gear with small period fault at the meshing frequency and its harmonics Increase with the deterioration of the fault.
(2) A gear having a large cycle fault generates a sideband family at intervals of the rotational frequency of the faulty gear at the meshing frequency and its harmonics, and is aggravated as the fault deteriorates.
(3) For gears with large cycle faults, the amplitude at the meshing frequency and its harmonics has little to do with the fault, while the gear with small cycle fault has no amplitude at the gyro frequency and its harmonics. The noise frequency characteristics of the faulty gear are shown.
4 Gear Fault Diagnosis Method The gear fault method has time signal observation method and spectrum analysis method, but the time signal observation method is relatively rough, and it is difficult to perform accurate diagnosis. The spectrum analysis method overcomes the above shortcomings and is a widely used method. The following describes several methods for troubleshooting using spectrum analysis.
4.1 Method of Observing Energy at a Specific Frequency The normal spectrum of a gear mechanism is determined. The energy change during operation is not very large. Usually, the energy of the normal spectrum plus the energy of the noise is used as a criterion to distinguish the fault signal. Hogg gives a formula for judging the abnormal signal, that is, Ac(f)=C1(1.5-n)+A(f) where: f- important frequency Ac(f)-test spectrum amplitude C1-constant n-noise level A (f) - The measured spectral amplitude is at the important frequency of the measured spectrogram. If the amplitude exceeds Ac(f), it is determined that the gear is faulty, otherwise it is normal.
4.2 Spectral amplitude comparison method When the frequency components are very rich, and the amplitude changes are fierce, it is difficult to observe the specific frequency amplitude on the spectrogram, and the frequency has a slight change, and the spectral line changes greatly. In order to observe this situation and judge the failure, a three-point method is adopted. If the amplitude corresponding to the frequency value is the largest in three consecutive points, the envelope is used as a criterion to judge the fault of the gear. If the envelope exceeds the envelope, it is a fault, otherwise it is normal.
4.3 Sideband method In the noise test, the frequency components of the measured spectrum map are often rich. When the gear has eccentricity or circumferential error, there will be a modulation phenomenon, which is reflected in the spectrum diagram, and many edges appear near the meshing frequency. frequency.
The larger the eccentricity or the pitch error, the more the edge spectral lines appear. For example, the sinusoidal signal f(t)=Bcos(2πfct+¢) where: f(t)-time function signal fc-carrier frequency B-signal amplitude ¢-phase considers amplitude modulation, then B is a function of time, ie B(t)=A(1+nmntnfa2cos) where: A-constant fm-modulation frequency an-amplitude modulation factor, so the amplitude modulation signal is: f(t)=A[(1+nmntnfacos)cos(2πfct+¢)] The phenomenon before and after modulation is drawn into the graph (2 and 3). It can be seen that the frequency components before and after modulation are not the same. After the modulation, several frequency components are added, and the upper and lower side frequencies appear. If there are two gears engaged, the pinion shaft frequency is f1, the large gear shaft frequency is f2, and the meshing frequency is f3. When the modulation frequency interval is X, the fault exists on the pinion. The frequency of the sideband after modulation is: the upper limit sideband is fc+f1, the second is fc+2f1, the third is fc+3f1..., the lower sideband is fc-f1, the second is fc-2f1, and the third is fc-3f1.
Similarly, if the defect exists on the large gear, the side-frequency spacing is f2. Therefore, in this way, the information of the gear defect can be found on the spectrogram.
5 Diagnostic Examples Tables 1 and 2 show the meshing frequencies of the respective gears in the transmission and the frequencies of the respective rotating shafts.
It is the noise spectrum of the transmission's hollow gear. As can be seen from the figure, there are many frequency conversions around the frequency 793HZ, and the frequency conversion spacing is 21.4HZ. According to Table 1 and Table 2, the 793HZ is the meshing frequency of a pair of permanent meshing teeth in the transmission, and 21.4HZ is the intermediate shaft. Axis frequency.
Therefore, according to the variable frequency belt analysis method, it is known that there is a failure of the driven gear in a pair of normally meshing gears in the transmission.
It is known from the basic characteristics of the gear fault that the noise spectrum of the normal gear and the fault gear is significantly different. The peak of the meshing frequency on the normal gear spectrum is prominent, and the harmonic peak is attenuated at a large speed. After the gear wears, the amplitude of the gear meshing frequency and its harmonics increase a lot, especially the harmonic amplitude increases more. As the degree of wear increases, higher order harmonics become more prominent. It can be seen that the harmonic amplitude of the meshing frequency 793HZ is large, and it can be concluded that one of the causes of the failure of the driven gear in the constant meshing gear is the tooth surface wear.
It can also be seen from the spectrogram that the modulation phenomenon near 793HZ is more serious.
According to the basic characteristics of the gear failure, it can be concluded that the driven gear in the constant meshing gear may have a large eccentricity or a peripheral error. It has been verified that the gear has an eccentric fault.
Through the above analysis, it is concluded that there is a fault in the driven gear in the constant meshing gear in the transmission, and the fault is caused by the gear eccentricity and the wear of the gear tooth surface.