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Mounting brackets vibration tests

Operational Stability

Mounting brackets for vibration tests

Refrigeration compressors are commonly mounted to automobile engines without any vibration decoupling. On a motor test bench the operating vibrations were measured at the location of the compressor. Additional enhancement factors due to the number of probes, testing time and nonlinearities were considered in order to obtain excitation spectra for qualifying vibration tests on a shaker. Frequencies up to 2 [kHz] appear to be relevant for the durability of the compressor.

For mounting the compressor on the shaker, a suitable bracket is required. The bracket must be sufficiently stiff, so that the shaker translations are transferred to the mounting positions of the compressor without the influence of resonances up to 2 [kHz]. The mass of the bracket may not exceed a fixed limit. Otherwise the force of the shaker would not be sufficient to achieve the projected maximum acceleration. Additionally, the installation space is limited. Furthermore, in order to minimize test times, it is favorable to test several compressors simultaneously.

The FE analysis accompanying the design process showed that within the given restraints it is not possible to raise all natural frequencies of the test setup beyond 2 [kHz].

However, by a symmetric design of the bracket and a symmetric loading with compressors, it can be achieved that these vibration modes are excited only very weakly and won’t influence the test results.

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