Durability of a refrigeration compressor

Refrigeration compressors are commonly mounted directly to automobile motors without any vibration decoupling. Thus, they are exhibited to high vibrations at excitation frequencies up to 2 [kHz]. This places high demands to the mechanical design of the contained inverter electronics and the busbars.

For the analysis and optimization of the structural durability, an FEA model of the inverter was created as shown in the top figure. This model contains the housing, the boards, the relevant electronic devices, the busbars and the housing cover, which is partly shown in the figure.

The material properties and coupling conditions were determined by a step-by-step correlation between experimental and numerical modal analyses for single components, subassemblies and the complete inverter system. As an example, the mid figure shows the comparison of a single transfer function obtained from measurement and simulation.

The correlated FEA model was used to predict the durability during the qualifying vibration tests. For this, the prescribed foot point excitations were applied to the mounting positions of the inverter housing. The resulting stresses are simulated and compared with strength data.

As an example result from this procedure, the bottom figure shows the failure index of some connection pins due to random excitation in z direction.

By this analysis, design weaknesses were identified and targeted redesign measures were developed, so that the serial product passed the challenging vibration tests.