Axial flux motor manufacturing technology

The core technical advantage of axial flux motors is that the rotating rotor is located on the side of the stator (rather than inside the stator) in structure, so the rotor has a larger diameter size, and torque = force x radius, so it can obtain higher torque output under the same force.

This means that higher torque output can be obtained under the premise of providing the same permanent magnet material and copper wire material. Generally, the design using new axial flux motors can improve the torque density by more than 30% compared with the design using traditional radial flux motors.

In the field of automotive electric drive using permanent magnet synchronous motors or induction motors, traditional radial flux motors are being widely developed for weight and cost optimization, but there is very limited room for further improvement in technology.

Therefore, turning to a completely different type of motor may be a good alternative. Due to the technical characteristics of axial flux motors with compact structure, flat and ultra-thin, small size, light weight and high power density, many developers have worked hard to improve the technology in the past decade to make it gradually suitable for new application scenarios such as electric motorcycles, airport pods, cargo trucks, electric vehicles, and even electric aircraft.

Axial flux motors have the inherent advantage of high power density. At present, the research hotspots (i.e., technical trends) for this type of motor in the field of new energy vehicles are to improve efficiency, reduce costs, system integration, and improve NVH. The innovation of axial flux motor technology mainly lies in structural design, and the technical difficulty lies in thermal management, advanced materials, and batch production processes.

Key technologies of axial flux motors

Different from traditional radial flux motors, axial flux motors include 5 key technologies

1、 Topological configuration research

According to the number of stators and rotors, relative positions, and main magnetic circuit classification, the basic topological structures can be divided into 4 types, namely single stator single rotor structure, double stator single rotor structure, single stator double rotor structure, and multi-disc structure. The appropriate structural topology should be selected based on the specific application scenario, process, and cost factors. At present, the automotive electric drive industry has conducted a comprehensive analysis of the performance, process feasibility, and cost of the topological structures of various types of axial flux motors, and concentrated on using two structural topologies: double stator single rotor and single stator double rotor.

2、 3D performance design of new motors

The flux path of traditional radial flux motors follows a nonlinear 2D path, while the flux path of new axial flux motors is a 3D path. Therefore, the difference between the two must be taken into account when performing performance simulation design, and models must be built based on their respective characteristics to improve the accuracy of the models. For new flux motors, 3D multi-physics field joint simulation and multi-objective comprehensive optimization design of electromagnetic solutions can be used. Continuously improve the design calculation efficiency of axial flux motors and improve the ability of accurate virtual modeling and simulation. Figure 3 shows the 3D performance design of axial flux motors.

3、 New material application development technology

Develop high-strength, high-insulation polyetheretherketone (PEEK) materials for stator skeleton;

Develop high-strength, high-thermal conductivity epoxy resin potting filling materials for heat dissipation and cooling to increase the heat dissipation capacity of the motor body and prevent the permanent magnet from demagnetizing at high temperatures;

Develop high-permeability, low-loss sheet molding compound (SMC) composite materials, amorphous alloy materials, and oriented silicon steel for stator and rotor cores. SMC materials are easy to form and have simple heat treatment processes, making them suitable for mass production. At the same time, due to their easy-to-form properties, they can also be used in 3D printing technology, making the motor innovation design more flexible and diverse;

Develop carbon fiber winding and fixing reinforcement processes for high-strength stators and rotors to cope with the physical properties of the poor tensile strength of the permanent magnets themselves.

4、 Research on advanced manufacturing processes

Develop rectangular cross-section copper conductors, spiral concentrated windings, and multi-pole continuous winding processes for windings;

Develop low-loss segmented fixed installation and pole shoe demagnetization protection processes for permanent magnets;

Develop yokeless segmented armature splicing, boltless fixing with end covers, and powder metallurgy manufacturing processes for stator cores;

Develop stator and rotor automated assembly technology, flat conductor forming coil automated production, and flexible automated production line processes for batch production needs

5、 Research on torque control and weak magnetic control strategies

Study the mathematical model of stator and rotor coordinate coefficients, build a system simulation model, study the new dual-vector model predictive torque control strategy, reduce torque pulsation, and improve torque control performance. For the axial flux motor permanent magnet surface-mounted structure, the motor's AC and DC axis inductances are equal and very small, vector control is difficult, and the magnetic circuit is easy to saturate, develop a control strategy to improve weak magnetic performance.