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At present, the scroll compressor has been widely used in the United States, Japan and other countries, especially in the field of air conditioning, which can achieve the level of micro vibration and silence. Compared with the application of scroll compressor in China, its development prospects are considerable. There are many researches on the vibration of reciprocating and centrifugal compressors in China, but few on the vibration of scroll compressors. For the application of scroll compressor in our country, improving the machining accuracy can play a great role. At the same time, it is an effective way to establish a reasonable assembly process based on the analysis of vibration signals obtained in practice.
1 Vibration source analysis of scroll compressor The power transmission chain of scroll compressor (without radial variable mechanism) is shown in Figure 1. The following assumptions are established:
(1) Ignore the influence of motor vibration
(2) Under good lubrication conditions, the influence of cross slide can be ignored
(3) As a whole, the influence of the vibration system composed of the scroll compressor and the support base is ignored
(4) Ignore the influence caused by the air flow pulsation at the inlet and outlet.
As the second link in the transmission chain, the moving scroll plate is also the key component of the scroll compressor. Its operation directly affects the performance of the machine, which is the focus of research.
The vibration of the crankshaft is regarded as a vibration system with finite degrees of freedom. In order to make the simplified analysis model shown in the figure reflect the actual vibration of the crankshaft, several conditions for equivalent treatment must be followed: the mass of each section is equal to the corresponding concentrated mass, and the moment of inertia of each section is equal to the moment of inertia of the corresponding disk. The center of mass of the corresponding concentrated mass of each section is distributed on the same centerline. The stiffness (torsional stiffness and flexural stiffness) between adjacent sections is equal to the stiffness between two particles.
The bending stiffness is the crankshaft torsional vibration equation: in the equation, the resistance moment of the crank pin M is respectively the moment of inertia of each equivalent disc and the torsional stiffness of each segment is respectively the rotation angle of each segment length relative to the static balance position of each disc. It can be seen from the equation that the gas resistance moment M has a greater impact on the crankshaft torsional vibration.
The data used in the frequency domain analysis of the vibration of the scroll compressor are obtained from the following experiments. The equipment and devices used in the experiment are as follows: the scroll compressor performance test bench of the Scroll Research Institute of Gansu University of Technology, the 5h vertical scroll compressor, three piezoelectric acceleration sensors,
Determine the vibration direction of the moving scroll plate with a frequency component of 121 Hz. It can be seen from Table 1 that the amplitude of this component in the signals measured by the middle sensor is relatively large (the top sensor measures the longitudinal vibration signal of the scroll compressor, and the middle and bottom sensors measure the transverse vibration signal of the scroll compressor), so the author thinks that it is constructed by the radial flexible machine.
There are two reasons for this frequency component: one is the axial vibration of the moving scroll plate, and the other is the radial flexible mechanism.
The author thinks that this component is of great benefit to the vibration reduction of scroll compressor.
In addition, the analysis shows that the component with a frequency of 2.5 Hz in the table is caused by interference and improper fixation of the signal transmission line of the sensor.
1) The vibration of scroll compressor is mainly caused by the instability of gas force and gas resistance torque. The instability of the resistance torque will inevitably lead to the instability of the driving torque, which will make the working performance of the scroll compressor worse.
2) Through frequency domain analysis, we have a certain understanding of the actual vibration of the scroll compressor, which provides a basis for targeted vibration reduction, and also provides a good method for fault diagnosis of the scroll compressor.