Game-Changing Lightweight E-Motor Design Enables Unrivalled In-Wheel Drives and Other Applications

Abstract

This paper presents latest developments and applications of a new electrical motor design which delivers highest power and torque density, while keeping weight and cost at a minimum. This allows for direct drive applications like wheel-hub motors or other mobile drives, where very low weight is mandatory. The motor’s air-gap-winding design reduces the amount of iron and copper and consequently it’s weight and cost significantly. Slotless design completely avoids cogging torque and shows a very smooth operation. The simple geometric design based on two thin-walled hollow cylinders, supports an automated production, which also contributes to very low cost. A flat slotless stator design stands for a homogenous temperature distribution and very efficient cooling, which allows high shortterm overload. In a first application a 40-kW wheel-hub-motor for a 15-inch rim was developed, built and tested. It delivers nominal torque of 300 Nm over the complete range of speed up to 1350 rpm. Total weight of this prototype is only 20 kg. Further applications for an E-Scooter, a Wheel-Hub Generator, an E-Flyboat and an E-Motorbike will be presented. Combining air-gap winding with an additional slot winding boosts torque and power of the motor substantially, without any relevant increase of weight and cost. Both windings share the already existent permanent magnetic field and cooling system, and both contribute to the torque. Converting an existing wheel-hub motor of generation 1 showed a proof of concept by delivering a nominal torque of 450 Nm and nominal power of 60 kW keeping the same size and nearly the same weight. First generation 2 prototypes providing a nominal torque of 600 Nm in a 16-inch wheel rim and a power of 70 kW is designed, built and validated on test stand.