Car starter is a key component for starting car engines. Vibrations, that are constantly presented during engine operation, are transmitted to the starter and consequently affect its operation. Knowledge of the dynamic properties is thus crucial for determining the motor speeds at which the starter resonates, for optimizing the geometry and providing the function. When modeling the problem, we encounter the question of how to define the contacts between the components and replace the spring model with a prestress force, in order to get as close as possible to the real state. In the final task, to simplify the simulation, we assumed that all components are glued together. The helical spring holding the brush in contact with the commutator was modeled as a prestressing force, considering both the condition before and after brush wear. A model analysis was performed for 4 different models, which differ in the presence of commutator influence, prestressing force, and brush wear. The first ten non-zero natural frequencies of each model and the corresponding natural forms were obtained. Contact stiffness between the components was determined to have the greatest influence on the calculated results. Furthermore, the components on which the largest deformations occur at a certain natural frequency and their values were recorded.
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