Spring Loaded Rotor Shafts as New Flexible Shaft Hub Joint for E-Rotors

To improve the performance and range of electrified cars, the power density of the electric machines has to be increased, which is possible by increasing the rotational speed. However, the maximum rotational speed is limited by the radial expansion of the lamination stack due to centrifugal forces and radial temperature gradients. Improper centrifugal expansions may cause a loss of contact between shaft and lamination stack as well as a loss of radial centering of the lamination stack on the rotor shaft.

Hence, Mubea developed and presents a revolutionary spring loaded tubular rotor shaft, whose innovation is a defined radial spring stiffness. This radial spring-like behavior results in a significantly reduced sensitivity of the transmitted torque with regard to the rotational speed, since the spring loaded shaft compensates the centrifugal deformations of the stack. This ability is new in the state of the art including interlocking connections. In addition, the spring behavior results in lower sensitivities regarding tolerances, the needlessness of fine machining the press fit surfaces and the avoidance of thermal joining. Also, the mechanical load on the stack is on average reduced by approximately 50%, which results in better electromagnetic properties. Tests and simulations show the high robustness with respect to transmitted torque and radial centering of the stack, also beyond 25.000 rotations per minute. Inner cooling of the shaft is easily applicable due to a relatively large contact surface.