48 classic questions about motor technology

1. What is a motor? A motor is a component that converts battery energy into mechanical energy to drive the wheels of an electric vehicle.

2. What is winding? The armature winding is the core part of the DC motor. It is a coil wound with copper enameled wire. When the armature winding rotates in the magnetic field of the motor, it will generate electromotive force.

3. What is magnetic field? It refers to the force field around a permanent magnet or electric current and the space or range of magnetic force that can be reached.

4. What is magnetic field strength? The magnetic field strength of an infinitely long wire carrying a current of 1 ampere at a distance of 1/2 meter from the wire is 1A/m (ampere/meter, SI); in the CGS unit system (centimeter-gram-second), in order to commemorate Oersted's contribution to electromagnetism, the magnetic field strength of an infinitely long wire carrying a current of 1 ampere at a distance of 0.2 cm from the wire is defined as 10e (Oersted), 10e=1/4.103/m, and the magnetic field strength is usually expressed in H.

5. What is Ampere's law? Hold the wire with your right hand, with your extended thumb pointing in the same direction as the current. Then the direction pointed by the bent four fingers is the direction of the magnetic flux lines.

6. What is magnetic flux? Magnetic flux is also called magnetic flux: suppose there is a plane perpendicular to the direction of the magnetic field in a uniform magnetic field, the magnetic induction intensity of the magnetic field is B, and the area of ​​the plane is S. We define the product of the magnetic induction intensity B and the area S as the magnetic flux passing through this plane.

7. What is a stator? The part of a brushless or brushless motor that does not rotate when it is working. The motor shaft of a hub-type brushless or brushless gearless motor is called a stator. This type of motor can be called an internal stator motor.

8. What is a rotor? The part that rotates when a brushed or brushless motor is working. The outer shell of a hub-type brushed or brushless gearless motor is called a rotor, and this type of motor can be called an external rotor motor.

9. What is a carbon brush? A brush is placed on the surface of the commutator in a motor. When the motor rotates, it transmits electrical energy to the coil through the commutator. Since its main component is carbon, it is called a carbon brush and is easy to wear. It should be regularly maintained and replaced, and carbon deposits should be cleaned.

10. What is a brush holder? A mechanical guide groove that holds and maintains the position of the carbon brushes in a brushless motor.

11. What is a commutator? Inside a brushed motor, there are mutually insulated strip metal surfaces. As the motor rotor rotates, the strip metal alternately contacts the positive and negative poles of the brushes, achieving alternating positive and negative changes in the direction of the motor coil current, completing the commutation of the brushed motor coil.

12. What is phase sequence? The order in which the brushless motor coils are arranged.

13. What is magnet? It is generally used to refer to magnetic materials with high magnetic field strength. Electric vehicle motors all use neodymium iron boron rare earth magnets.

14. What is electromotive force? It is generated by the rotor of the motor cutting the magnetic lines of force. Its direction is opposite to that of the external power supply, so it is called back electromotive force.

15. What is a brushed motor? When the motor is working, the coil and commutator rotate, while the magnet and carbon brush do not rotate. The alternating change of the coil current direction is achieved by the commutator and brushes that rotate with the motor. In the electric vehicle industry, brushed motors are divided into high-speed brushed motors and low-speed brushed motors. There are many differences between brushed motors and brushless motors. From the word, it can be seen that brushed motors have carbon brushes, while brushless motors do not.

16. What is a low-speed brushed motor? What are its characteristics? In the electric vehicle industry, a low-speed brushed motor refers to a hub-type, low-speed, high-torque, gearless brushed DC motor. The relative speed of the motor stator and rotor is the speed of the wheel. There are 5 to 7 pairs of magnets on the stator, and the number of slots on the rotor armature is 39 to 57. Since the armature winding is fixed in the wheel housing, the heat can be easily dissipated with the help of the rotating housing. The rotating housing is woven with 36 spokes, which is more conducive to heat conduction. Jicheng Training WeChat account is worth your attention!

17. What are the characteristics of brushed gear motors? Because brushed motors have brushes, their main hidden danger is "brush wear". Users should note that brushed motors are divided into two types: geared and non-geared. Currently, many manufacturers use brushed gear motors, which are high-speed motors. The so-called "gear" means that the motor speed is reduced through the gear reduction mechanism (because the national standard stipulates that the speed of electric vehicles shall not exceed 20 kilometers per hour, so the motor speed should be around 170 revolutions per minute).

Since the high-speed motor is decelerated by gears, the rider feels strong power when starting and has strong climbing ability. However, the electric wheel hub is closed and only filled with lubricant before leaving the factory, so it is difficult for users to perform daily maintenance. In addition, the gears themselves also have mechanical wear. After about a year, insufficient lubrication will cause the gears to wear more, the noise will increase, and the current will increase during use, affecting the life of the motor and battery.

18. What is a brushless motor? Because the controller provides direct current with different current directions to achieve the alternating change of the current direction of the coil inside the motor. There are no brushes and commutators between the rotor and stator of the brushless motor.

19. How does the motor achieve phase commutation? When a brushless or brushed motor is rotating, the direction of the current flowing through the coil inside the motor needs to be changed alternately so that the motor can rotate continuously. The phase commutation of a brushed motor is completed by the commutator and the brushes, while the phase commutation of a brushless motor is completed by the controller.

20. What is phase loss? In the three-phase circuit of a brushless motor or brushless controller, one phase cannot work. Phase loss is divided into main phase loss and Hall phase loss. The manifestation is that the motor cannot work due to shaking, or it rotates weakly and makes loud noises. The controller is easy to burn out when working in the phase loss state.

21. What are the common types of motors? Common motors include: brushed geared hub motors, brushless geared hub motors, brushless geared hub motors, brushless gearless hub motors, side-mounted motors, etc.

22. How to distinguish high-speed and low-speed motors from the type of motor? A Brushed geared hub motors and brushless geared hub motors are high-speed motors; B Brushless geared hub motors and brushless gearless hub motors are low-speed motors.

23. How is the power of a motor defined? The power of a motor refers to the ratio of the mechanical energy output by the motor to the electrical energy provided by the power supply.

24. Why do we need to choose the power of the motor? What is the significance of choosing the power of the motor? The selection of the rated power of the motor is a very important and complex issue. When under load, if the rated power of the motor is too large, the motor will often run under light load, and the capacity of the motor itself cannot be fully utilized, becoming a "big horse pulling a small cart". At the same time, the motor has low operating efficiency and poor performance, which will increase operating costs.

On the other hand, if the rated power of the motor is too small, it will be like "a small horse pulling a big cart". If the motor current exceeds the rated current, the internal loss of the motor will increase. Low efficiency is a minor issue, but the important thing is that it affects the life of the motor. Even if the overload is not too large, the life of the motor will be greatly reduced; if the overload is too large, the insulation performance of the motor insulation material will be damaged or even burned. Of course, if the rated power of the motor is small, it may not be able to drag the load at all, and the motor will be in the starting state for a long time and overheated and damaged. Therefore, the rated power of the motor should be selected strictly according to the operation of the electric vehicle.

25. Why do brushless DC motors generally have three Hall sensors? In short, in order for a brushless DC motor to rotate, there must always be a certain angle between the magnetic field of the stator coil and the magnetic field of the rotor permanent magnet. The process of rotor rotation is also the process of changing the direction of the rotor magnetic field. In order to make the two magnetic fields have an angle, the direction of the magnetic field of the stator coil must change after a certain degree. So how do you know when to change the direction of the stator magnetic field? That depends on the three Hall sensors. It can be considered that the three Hall sensors are responsible for telling the controller when to change the direction of the current.

26. What is the approximate power consumption range of the brushless motor Hall? The approximate power consumption range of the brushless motor Hall is 6mA-20mA.

27.At what temperature can a motor normally work? At what temperature can a motor withstand at most? If the temperature of the motor cover is measured to be more than 25 degrees higher than the ambient temperature, it indicates that the temperature rise of the motor has exceeded the normal range. Generally, the temperature rise of the motor should be below 20 degrees. Generally, the motor coil is wound with enameled wire, and when the temperature of the enameled wire is higher than about 150 degrees, the paint film will fall off due to the high temperature, causing the coil to short-circuit. When the coil temperature is above 150 degrees, the temperature of the motor shell is about 100 degrees, so if the shell temperature is used as the basis, the maximum temperature that the motor can withstand is 100 degrees.