Prediction of cogging torque level in PM motors due to assembly tolerances in mass‐production

Abstract

Purpose

The purpose of this study is to estimate the sensitivity of cogging torque in permanent magnet (PM) motor designs due to PM assembly tolerance and/or PM imperfections and to evaluate how such faults can be reliably detected in simulated and measured cogging torque signals.

Design/methodology/approach

PM motors exhibit inherent cogging torque, which creates torque ripple and prevents smooth rotation of the rotor, resulting in undesirable vibration and noise. While cogging torque minimization is necessary to improve PM motor performance, several FEM models have been developed to study and present data demonstrating the sensitivity of cogging torque to PM assemblies and/or PM imperfections. Some procedures that would predict and evaluate cogging torque components relative to measured PM positions on assembled PM motors were proposed.

Findings

On the basis of numerous performed simulations using different FEM models and experimental results on rotors from mass‐production, it was found and proved that PM assembly tolerance and/or PM imperfections cause the phenomenon of additional cogging torque harmonic components. Considering the presented theoretical aspects motor designers can predict which additional harmonic components will comprise the cogging torque, as a result of which the appropriate technique for minimizing native and additional harmonic components can be applied.

Research limitations/implications

The presented research of cogging torque sensitivity in different PM motor designs to assembly tolerance and/or PM imperfections should in future also consider stator irregularities and different methods of lamination stacking such as notches, welding, and interlocking.

Practical implications

By utilizing the presented method and considering recommendations, advanced motor designers have a reliable tool for predicting the order and level of additional harmonic components in total cogging torque. Thus, adequate critical manufacturing tolerances can be defined in order to achieve minimal waste in produced PM motors.

Originality/value

The originality of the paper is explained by the theoretical aspects and analytical equations of additional harmonic components in cogging torque of PM motors. Also original are the expressions for amplitude calculation of additional harmonic components influenced by manufacturing tolerances.

Citation

Gašparin, L., Černigoj, A., Markič, S. and Fišer, R. (2008), "Prediction of cogging torque level in PM motors due to assembly tolerances in mass‐production", COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, Vol. 27 No. 4, pp. 911-918. https://doi.org/10.1108/03321640810878333