Noise generation mechanisms in claw pole alternators

Noise of claw pole alternators, generated electromagnetically and structurally radiated, has been the subject of an extensive research program. The goal has been to identify and reduce noise radiation mechanisms in claw pole (Lundell) alternators used in automotive applications. Two approaches have been followed. In the first, electromagnetic sources of noise have been investigated by lumped parameter and magnetically equivalent circuit modeling and simulation, and by related experimentation. This is the subject of separate papers. The second, concurrent study reported here has investigated machine and mount responses to an electromagnetically generated torque ripple. Modeling and experimentation has led to the conclusion that there exists a high correlation between electromagnetic sources, torque ripple, and radiated noise. Experimentation also has led to the conclusion that noise characteristics of a given machine are substantially altered by modification of the mounting configuration. The work reported here involves modeling, simulation, and experiment to isolate machine dynamic characteristics and mounting geometries which contribute to strong coupling between torque ripple and machine/mount dynamic response. A low-order model of the alternator which includes shaft flexibility, gyroscopic effects, shaft bearing asymmetry, mounting lug geometry, and mounting structure dynamics has been created. The model provides a rapid simulation of dynamic response in the form of a transfer function between torque ripple and mounting forces. Generic studies of a simplified mounting structure coupled to the machine model are presented here. Acoustic testing of several machine configurations on a production mount has been carried out to investigate 36th order noise in three phase machines and 72nd order noise in six-phase machines. Electromagnetic modeling and dynamic response simulations suggest that the six-phase machine is inherently quieter. This is supported by experimental results. A test fixture for the measurement of torque ripple has been developed. Experimentation shows that the relative amplitudes of torque ripple in three- and six-phase machines correlates with relative noise levels. In addition, in torque ripple measurements, machine mounting characteristics are substantially altered and a predictably large reduction in radiated noise is realized.