What is Inside an Electric Hub Motor?

After the hub motor is energized, the motor converts electrical energy into mechanical energy, thereby driving the wheels to rotate and driving the vehicle forward. Hub motors are mainly composed of 6 structures: stator core, stator winding, machine base, rotor core, rotor winding, and other accessories of phase asynchronous motor. Now ATO will tell you the details of electric hub motor structures.

1. Stator core

The stator core is part of the motor magnetic circuit, and on which the stator winding is placed. It is generally made of 0.35~0.5mm thick silicon steel sheet with an insulating layer on the surface, laminated, and evenly distributed slots are punched in the inner circle of the core to embed the stator winding.

• Semi-closed slot: the efficiency and power factor of the motor are higher, but the winding embedding and insulation are more difficult. Generally used in small low-voltage motors.
• Semi-open type slot: it can be embedded with formed windings, generally used in large and medium-sized low-voltage motors. The so-called forming winding that winding can be insulated beforehand and then put into the slot.
• Open type slot: used to embed forming windings, insulation method is convenient, mainly used in high-voltage motors.

2. Stator winding

The stator winding is the circuit part of the electric hub motor, which is connected to the three-phase alternating current to produce the rotating magnetic field. It is connected by three identical windings with the same structure, which are spatially separated by 120°electric angle and arranged in a team. The coils of these windings are embedded in each slot of the stator according to a certain rule to ensure reliable insulation between the conductive parts of the winding and the core and between the winding itself.

• Insulation to ground: insulation between the stator winding as a whole and the stator core.
• Inter-phase insulation: insulation between the stator windings of each phase.
• Turn-to-turn insulation: insulation between the turns of each stator winding in each phase.

3. Machine base

The base is usually cast iron, and the base of a large asynchronous motor is generally welded with steel plate, and the base of the micromotor is made of cast aluminum, which fixes the stator core and the front and rear end cover to support the rotor, and plays the role of protection and heat dissipation. The enclosed motor has heat dissipation bars outside the base to increase the heat dissipation area, and the protective motor has ventilation holes on both end caps to enable direct convection of air inside and outside the motor to facilitate heat dissipation.

4. Rotor core

The rotor core of the three-phase asynchronous motor is used as part of the magnetic circuit of the motor and the rotor winding is placed in the core slot, and the material used is the same as the stator, which is made of 0.5 mm thick silicon steel sheet punched and laminated. The outer circle of the silicon steel sheet is punched with evenly distributed holes to place the rotor windings. The inner circle of the silicon steel sheet after the stator core is punched is usually used to punch the rotor core. Generally, the rotor core of the small asynchronous motor is pressed directly on the rotor shaft, while the rotor core of the large and medium-sized asynchronous motor (rotor diameter above 300~400mm) is pressed on the rotor shaft with the help of a rotor bracket.

5. Rotor winding

The rotor winding of a three-phase asynchronous motor cuts the stator rotating magnetic field to produce induction electric potential and current, and form electromagnetic torque to make the motor rotate. It is divided into a squirrel-cage rotor and wire-wound rotor. The structure of the wire-wound motor is more complicated and not as widely used as a squirrel-cage motor, but the additional resistors and other components are strung in the rotor winding circuit through current collecting ring and brush to improve the starting and braking performance and speed regulation performance of asynchronous motor, so it is used in the equipment requiring smooth speed regulation within a certain range, such as crane, elevator, air compressor and so on.

• Squirrel cage rotor: the rotor winding consists of multiple guide bars inserted into the rotor slot and two end rings in a circular row. If the rotor core is removed, the shape of the whole winding is like a squirrel cage, so it is called cage winding. Small cage-type motors use cast aluminum rotor winding, and for motors above 100KW, copper strips and copper end rings are welded together.
• Winding rotor: winding rotor winding is similar to the stator winding, it is also symmetrical three-phase winding, generally connected into a star shape, and the three outgoing heads are connected to the three collector rings of the rotor shaft, and then connected to the external circuit through brushes.

6. Other accessories of phase asynchronous motor

• End cover: support role.
• Bearing: connect the rotating part with the immovable part.
• Bearing end cover: protect the bearing.
• Fan: cooling the motor.