Why is there an air gap between the motor rotor and stator?

In order to ensure that the rotor can rotate freely in the stator cavity during the operation of the motor, an air gap must be maintained between the rotor core and the stator core. Although there is no direct electromagnetic connection between the rotor and the stator, when the stator winding is energized, similar to the principle of a transformer, there is an electromagnetic connection between the rotor and the stator, thus realizing the energy conversion function between electrical energy and mechanical energy.

Let me remind you that the size of the air gap has a great influence on the performance and operating reliability of the asynchronous motor.

An excessively large air gap will greatly increase the magnetic resistance, thereby increasing the excitation loss, the excitation current will also increase, the power factor of the motor will also decrease, and the performance of the motor will deteriorate. In order to reduce the excitation current and improve the power factor, the air gap should be minimized.

However, if the air gap is too small, the harmonic magnetic field of the air gap will increase, the stray loss and noise of the motor will increase, and the maximum torque and starting torque will decrease. At the same time, if the air gap is too small, it is easy for the running rotor and stator to collide, resulting in a sweep phenomenon, which makes starting difficult, thereby reducing the reliability of operation and causing difficulties in assembly. Generally, the air gap of small asynchronous motors is approximately between 0.25~1.5mm, and that of medium-sized asynchronous motors is approximately between 0.75~2mm.

The gap between the stator and the rotor of the motor has been determined during the production process of the motor. Unless the gap becomes larger due to various reasons such as rotor scanning during use, this is generally impossible. There are many reasons for the large current of the motor. Here is a brief summary for you:

1, deviation of positioning magnet, treatment method: re-bonding;

2, the gap between the carbon brushes is uneven, the solution is: correct the carbon brush gap;

3, there is a short circuit between the positive and negative poles of the battery. Solution: eliminate the short circuit;

4, inter-turn short circuit, solution: re-change the wires;

5, the commutator segment is short-circuited, the treatment method is: clean and polish the commutator segment;

6, the fit between the shaft and the bearing is too tight, solution: grind the shaft;

7, electric vehicle zero start, handling method: try to avoid it while driving;

8, the load is large or the vehicle has large driving resistance, solution: manual assistance.

(Source: Today’s Motor)