Nuisance coming from the vehicle motorized accessories have a significant impact on the noise perceived inside the automotive interior. This work focuses on the vibroacoustic behavior of an electric gear motor which equips each door of automotive vehicles in order to allow driver to go up and down the window.

The window-lift gear motor consists of a DC motor and a worm gear. The DC motor includes steel and plastic housings (stator) and a rotational part (rotor). The stator supports diametrically opposed ferrites inducing a permanent magnetic field, journal bearings guiding the rotor and a cage containing two brushes which supply electrical power to the rotor. It is attached to the door of the automotive vehicle at three fixation points. The rotor consists of a shaft on which coils are wound (number of coils: N=10) and connected to the N blades of a rotating commutator. The current flowing in the coils positioned within the magnetic field, generates tangential electromagnetic forces, input torque and consequently rotating motion of the rotor. A worm gear is machined in the steel rotor and meshes with a helical gear wheel in order to reduce the rotation speed and increase the motor output torque. The worm gear is designed such as the mesh frequency fm is equal to the rotor frequency fr. Finally, the gear wheel goes up and down the window via a mechanical clutch and a drum and cables mechanism.

Under operating conditions, the window-lift gear motor is submitted to various excitation sources. The following are considered:

- The fluctuation of the input electrical current at the contact between commutator and brushes and the periodic motion of the rotating coils through the permanent magnetic field generate periodic fluctuation of the input torque. The corresponding excitation is periodic at every blade or coil passage frequency (10 fr).

- Asymmetry of the rotor and assembly errors are responsible of shaft misalignment and mechanical imbalance. The corresponding excitation is periodic at the rotor frequency (fr).

- The meshing between the worm and the gear wheel is the source of a static transmission error (STE) fluctuation and a gear mesh stiffness fluctuation which generates a parametric excitation of the mechanical system. The corresponding excitation is periodic at the mesh frequency (fm=fr).

This work is focused on the multiphysics coupling between the gearmesh excitation and the excitation sources associated with the upstream electric motor. They mix high and low frequency phenomena. A spectral iterative methodology is used and allows a fast resolution of the parametric equations of motion in the spectral domain. The numerical simulations performed allow the prioritization of the different excitation sources. Moreover, the multiphysics coupling between excitations and the gearmesh stiffness fluctuation generates a frequency enrichment of the dynamic response reflected by the emergence of numerous lateral components on the spectrograms describing the dynamic response. These last have a significant impact on the nature of noise radiated directly by the gearmotor itself and indirectly by the vehicle door supporting the gearmotor.