Electromagnetic Noise Investigation Of Permanent Magnet Dc Motor For Automotive Cooling Fan

With the increasing of people's demand for automotive quality and comfort, interior noise of vehicles has become an important influencing factors among all the elements. Interior noise control issues become more prominent. The noise mainly from the engine, Chassis and cooling fan when Vehicle is in motion. It is intolerable that the noise still exists after flameout, and it will appear howling when the motor speed down to a specific speed region. The study found that howling is electromagnetic noise. This will seriously affect the evaluation of the quality of vehicle. Permanent magnet DC motor(PMDC) is one of the main types of fan motors. In this thesis, the research of electromagnetic noise after the PMDC for cooling fan power off is based on both electro-magnetic exciting force and structural dynamic response.Because of the wide variation range of the motor speed, time-stepping finite element method is selected to calculate various of parameters of the permanent magnet dc motor ,such as harmonic flux densities generated by the stator and rotor, torque ripple and unbalanced magnetic pull. On this basis, the variation of the electromagnetic force amplitude following rotational speed is analyzed, and the parameters influenced by the electromagnetic force amplitude, order and frequency are concerned in the study, which lays a foundation on noise optimization of cooling fan motor.In the research of structural dynamic response of the motor, the modal analysis and harmonic response analysis of PMDC is carried out by finite element method. The impact of the components on the intrinsic mode is studied. The precise method of electromagnetic force with spatial and temporal distribution is put forward. On this basis , structural dynamic response under the given electro-magnetic exciting force is calculated. Finally, numerical calculation method of acoustic radiation is resolved based on FEM and BEM, and the variation of electromagnetic noise following rotational speed is also computed .The electromagnetic noise produced in PMDC used in automotive cooling fan is experimental researched. Vibration spectrum is analyzed according to the vibration data under different rotational speed. By experimental methods, the variation law of the electromagnetic noise with speed is studied. Hammering method modal experiment is adopted to test the natural model of the motor structure, verified the accuracy of material property definitions in dynamic structural analysis.The study found that howling produced by PMDC used in automotive cooling fan is electromagnetic noise, mainly due to resonance. Taking into account the economics and power index of motor, the best way to optimize motor noise include improving the order of electromagnetic waves, reducing electromagnetic force amplitude and restraining motor structural dynamic response.