Comparative analysis of stiffness measurement methods for lamination stacks in electric machines

Abstract

With the increasingly strict global regulations on vehicle emissions, the demand for electromobility has risen due to its potential to reduce local emissions. However, designing an electric motor for use in passenger cars poses significant challenges. The e-motor should operate reliably in various climates with good mechanical and electrical characteristics, be lightweight, withstand repetitive thermal and structural loads, be cost-effective, and - last but not least - exhibit good noise and vibration properties. To meet these requirements, virtual testing through simulations has become the most efficient and economical approach, enabling the identification of weaknesses and unwanted behaviors before physical prototyping. This paper focuses on the testing of lamination stacks, a critical component of electric motors. Two methods of stiffness measurement for such parts are compared: static stiffness determination and dynamic analysis. The former involve compressing the specimen and measuring the force-displacement response, while dynamic method uses the restoring force surface method to obtain the stiffness and damping characteristics. The study highlights the importance of considering nonlinearity in stiffness measurements. The stiffness of lamination stacks varies depending on the pretension state, and a significant hysteresis exists between the loading and unloading curves. The paper discusses the experimental procedures for each method. The findings emphasize the necessity of accurate stiffness characterization for different applications, such as structural strength, modal analysis, dynamic analysis, and noise-vibration-harshness (NVH) studies. The research contributes to the development of electric machines by providing insights into effective stiffness measurement techniques for lamination stacks.