Noise analysis in electric motor bearings
The manifestation of noise during the operation of electric motor bearings has always been a factor of concern for motor users and engineering technicians. Often, noise measurement is one of the commonly used methods for diagnosing and analyzing the operating conditions of engine bearings.
In fact, the root cause of noise is vibration. The sounds we hear in everyday life are simply vibrations within a certain frequency range, which are transmitted through the air to the eardrum and perceived by our auditory senses.
Therefore, the quantitative noise analysis method essentially aligns with that of vibration.
However, due to the influences of the measurement environment and human perceptual capabilities, it has certain unique characteristics.
Abnormal noise from engine bearings
Firstly, the engine bearings, once operational, generate a certain level of noise due to internal vibrations. Any mechanical device generates noise during operation due to the vibrations it produces.
There is no such thing as a completely silent bearing, so there is inherent noise from the engine bearings in operation. This noise is a result of the bearing structure.
Additionally, this noise is related to the finish and design of the bearing. This noise does not indicate the presence of possible bearing failures, therefore it is considered normal.
As a user of engine bearings, it is not possible to change or eliminate this inherent normal noise. As this noise does not indicate any fault, it does not require extra attention.
However, if there is a bearing defect or failure, the additional vibration caused by these defects will generate more noise during operation. This noise is an external manifestation of internal bearing failures.
This is an area of concern for engine engineers in practical applications and should be eliminated. Therefore, the noise mentioned in engine bearing fault diagnosis refers to the noise that reflects internal bearing failures, often referred to as abnormal engine bearing noise.
Abnormal engine bearing noise is noise caused by faults in the engine, bearings or related components. Removing the fault can eliminate this noise. Consequently, abnormal noise in engine bearings can be eliminated.
Likewise, this noise generally indicates the presence of an engine failure. Therefore, abnormal noises in engine bearings can be used as a determining factor in the diagnosis and analysis of engine bearing failures.
An engine's abnormal noise varies depending on the type of failure, but the normal noise pattern of engine bearings is relatively consistent. Normal engine bearing noise is easier to remember.
Limitations of Engine Bearing Noise Diagnosis and Analysis
Noise from engine bearings is perceived by the human ear after being transmitted through the air from the source of vibratory excitation. This transmission occurs over a considerable distance.
If there are other interfering noises in this space, the sound that reaches the human ear is a mixture. It is challenging for the human ear to separate this mixed noise.
Even test equipment can produce inaccurate results under certain interference conditions. Therefore, engine bearing noise measurements require a strictly controlled environment to eliminate interference caused by ambient noise.
On the other hand, a motor works as a whole and produces not only bearing noises, but also noises from components such as the fan and electromagnetic elements, among others. These noises are part of the general noise of the engine and are inseparable during its operation, adding to the interference in the analysis of engine bearing noise.
Therefore, when carrying out noise tests on motor bearings, the above-mentioned tuning factors and limitations often need to be taken into consideration. Due to these factors, engine bearing noise analysis can be difficult to quantify on site.
Methods for noise analysis in engine bearings
We mentioned earlier that noise and vibration from engine bearings have the same origin. If we can effectively capture engine bearing noise using superior equipment and experimental conditions, the analysis method will be consistent with vibration analysis. This includes time domain and frequency domain analysis.
In fact, under ideal conditions for motor bearing noise testing, analyzing motor bearing noise in the frequency domain can help exclude interference factors such as motor electromagnetic noise and fan noise, thereby identifying the spectrum of unique bearing noise.
Field application of diagnosis and analysis of noise in engine bearings
Given the stringent conditions for quantitative analysis of engine bearing noise, it is often difficult to achieve in general practical scenarios. Therefore, on-site analysis generally involves qualitative analysis of engine bearing noise, with quantitative analysis being less common.
This so-called qualitative analysis involves using the “correct method” to listen to engine bearing noise performance. This process involves making qualitative judgments by comparing it to normal noise or estimates for certain fault noises. Diagnosis and analysis of engine bearing failures are carried out in conjunction with other diagnostic and analysis methods.
In this process, experienced engineers often rely on memory. Some devices now store examples of typical noises, which helps field technicians make comparisons.
However, human comparisons still vary due to experience and auditory perception. Therefore, in real-world engineering, noise analysis often serves as a supplementary tool for qualitative judgment.
