In-depth understanding of the internal structure of electric vehicle motors
Many car enthusiasts are not very clear about the internal structure of the motor . Next, let's go inside the motor and see what these internal components are all about.
First, let's start with the magnets, which are of most concern to car enthusiasts. There are many types of magnets, but the three most common are ferrite, AlNiCo, and Neodymium Iron Boron (NdFeB). As a rare-earth permanent magnet material, NdFeB can release a strong magnetic energy product within a limited volume, making the miniaturization of DC motors possible. Therefore, except for the earliest ferrite motors, NdFeB has become the dominant material in electric vehicle motors. We won't go into detail about the magnets here. Magnets are commodities, and like any commodity, they vary in quality. So how do we distinguish between good and bad magnets? First, there's the grade. Magnet grades, from highest to lowest, are EH, UH, SH, H, M, and N, corresponding to temperature coefficients of 200°C, 180°C, 150°C, 120°C, 100°C, and 80°C, respectively. The higher the temperature resistance coefficient, the better, since motors generate heat, which can cause demagnetization and shorten their lifespan. The magnet grade is usually preceded by a number, typically 35, 38, or 40. While these numbers are technically complex, the basic principle is that a higher number indicates stronger magnetism. Currently, most motors on the market use 38M magnets with a temperature resistance of 100 degrees Celsius; standard H-grade magnets are extremely rare.
Once the material is determined, consider the height. Since the working principle of an electric motor is simply electromagnetic conversion, sufficient power is required for adequate speed or load capacity, necessitating a sufficiently large magnet. Currently, motor manufacturers typically only specify the height, neglecting to indicate thickness and width. However, magnet demagnetization is closely related to thickness (for example, a 3mm thick magnet will demagnetize by no more than 3% in 2 hours at 100 degrees Celsius, a 2.5mm thick magnet demagnetizes by 5-8% under the same conditions, and both thicknesses demagnetize by over 10%). In comparison, width has less impact on the motor, and some substandard motors have already appeared on the market). Therefore, be cautious.
Having discussed the magnets, let's talk about the iron core. Early motors were made by stacking single silicon steel sheets at the motor factory, so some people still refer to them as silicon steel sheets—the two are essentially the same. The iron core material is generally cold-rolled steel (hot-rolled steel was used before 2006), with grades ranging from 800, 600, 470, 400, 350, to 300, from highest to lowest. What do these grades mean? Taking cold-rolled 470 as an example, it indicates an iron loss value of 4.7 W/kg. A detailed explanation might be complex, but just know that this iron loss value is not good for motors; the lower the better. Of course, lower grades also mean more expensive steel, and the quality varies between steel mills. In China, for the same grade, Wuhan Iron and Steel (WISCO) is the best, followed closely by Baosteel and Taiyuan Iron and Steel (TISCO). The best steel is still imported from Germany or Japan, but it's not used in the electric vehicle motor industry.
Next, let's look at enameled wire. Generally, only two grades of enameled wire are used in electric vehicle motors: 130-2 or 180-1. How do we understand these numbers? 130 and 180 refer to the operating temperature resistance of the enameled wire, with 180 being naturally better. -1 and -2 refer to thin and thick enamel films, respectively, which is a matter of surface thickness. Without further ado, if the motor uses 180-1, the performance will be better than 130-2.
Next is the eight-core wire, commonly known as the lead wire. The "XX square millimeters" indicated by the motor manufacturer refers to the cross-sectional area of the three phase wires, generally following this pattern: below 800W, 1.5 square millimeters; 800-1000W, 2 square millimeters; 1000-1500W, 2.5 or 3 square millimeters; 1500-2000W, 6 square millimeters; 2000-2500W, 8 square millimeters; 2500-3000W, 10 square millimeters; and above 3000W, preferably 16 square millimeters. If your motor is rated 1500W but only has 1.5 square millimeters, this motor may be overstating its power rating, as this power rating combined with this lead wire has a high probability of causing it to burn out.
Finally, we need to analyze the components that both motor manufacturers struggle with: bearings and Hall effect sensors. Let's start with the simpler bearings. Bearings are widely used in the machinery industry, so what kind of bearing is most suitable? First, the motor's power is closely related to the bearing size. Experienced mechanics can see this clearly after disassembling the motor cover. What you need to know is that electric motorcycle motors (around 1500W) require at least a 6004 (42mm outer diameter) standard bearing to guarantee a lifespan of about three years. Furthermore, increased power requires even larger bearings to handle the motor's torque. Electric bicycle motors are much simpler; a 6203 (40mm outer diameter) will suffice. Now, let's talk about the grade. Manufacturers generally avoid discussing this because bearing prices are determined by grades Z1-Z4. If you use a Z4 group 6203, the price will exceed that of a Z1 group 6005 (47mm outer diameter)! This is the trick; those who are discerning can pay attention to this issue when buying a motorcycle. As for the final brand, I dare not say much. Three-quarters of the national production capacity of these small bearings is concentrated in Cixi, Zhejiang. If you can use the Z3 group bearings from here, you have already made a profit. As for boasting about Haval or Renben, it is not entirely impossible, but it is best to see for yourself, because the price of these bearings is 3-8 times that of ordinary bearings, so the possibility is very low.
The Hall effect sensor is like the front door of your house; it's simply a gateway for communication between the motor and the controller. It either opens or closes (this is the basic principle of electronic commutation). As long as the motor is properly designed and the controller is matched correctly, the Hall effect sensor isn't easily damaged or burned out. So why do many car owners experience repeated Hall effect sensor burnouts? Firstly, it's a matter of controller matching. With increasing motor power, controllers have also become more powerful, increasing the possibility of burnout. Intelligent controllers, upon detecting potential overheating and oil burnout in components, automatically cut off external signals, whether from the battery or the motor. The problem is that the motor isn't intelligent; it doesn't stop. The motor continues to operate as a generator until it stops. If the Hall effect sensor happens to be located at the point of stoppage, then it's doomed—this is one of the biggest reasons for Hall effect sensor burnout.
Analysis of the internal structure of electric vehicles
Electric vehicles mainly consist of three parts: the electric drive system, the energy system, and the auxiliary operating system. The electric drive system is the "central brain" of the electric vehicle and is the most significant difference between it and a gasoline-powered car. Its function is to convert the electrical energy stored in the battery into kinetic energy for driving, and it also plays a role in regenerative braking (that is, recovering and utilizing the kinetic energy during deceleration and returning it to the battery). The energy system is like the car's "digestive system," converting externally acquired "food" (electrical energy or other forms of energy) into battery energy for storage, providing a continuous energy source for the car's operation. The auxiliary operating system acts as the "car's attendant," providing functions such as air conditioning, lighting, and auxiliary power sources, which improve the overall operability of the car and the driver's comfort. This part is basically similar to that of a conventional gasoline-powered car.
Simplified diagram of the internal structure of an electric vehicle
1. Drive motor
The function of a drive motor is to convert electrical energy from the battery into mechanical energy, which then drives the vehicle through the transmission system. Simultaneously, in most electric vehicles, the motor also acts as a "generator" during braking, feeding excess mechanical energy back to the battery to recharge it. Motors on the market can be categorized into DC motors, asynchronous motors, permanent magnet synchronous motors, and switched reluctance motors. For example, Tesla uses an asynchronous motor, which provides faster acceleration from a standstill and is noiseless; the BAIC EU260 uses a permanent magnet synchronous motor because it is lightweight and easy to install.
2. Electric controller
An electric motor controller is designed for the speed change and direction adjustment of electric vehicles. Its function is to control the voltage or current of the electric motor, thereby controlling the driving torque and rotation direction of the motor. By uniformly changing the terminal voltage of the motor, the current of the motor is controlled, thus achieving stepless speed regulation of the motor. This process is called thyristor chopper speed regulation.
In the rotation direction control of electric vehicles, DC motors achieve rotation direction change by altering the direction of the armature or magnetic field current through contactors. When an AC asynchronous motor is used, changing the motor's direction only requires changing the phase sequence of the three-phase magnetic field current, simplifying the control circuit. Furthermore, using AC motors and their variable frequency speed control technology makes regenerative braking control of electric vehicles more convenient and the control circuit simpler.
3. Transmission and travel device
The function of the electric vehicle's transmission is to transmit the driving torque of the electric motor to the vehicle's drive shaft, and then the running gear (wheels, tires, and suspension, etc.) converts it into force on the ground, thereby driving the wheels. The electric motor can start under load, eliminating the need for a clutch, which is typically found in gasoline-powered vehicles. Furthermore, the drive motor's rotation direction can be changed via circuit control, thus eliminating the need for a reverse gear in gasoline-powered transmissions. Compared to gasoline-powered vehicles, electric vehicles are even simpler because, with continuously variable speed control of the electric motor, a transmission can be omitted; and with electric wheel drive, a differential can be eliminated, significantly simplifying the internal structure of electric vehicles.
4. Braking system
The braking system is also known as the "brake system". However, electric vehicles also have electromagnetic braking devices, which can convert the excess kinetic energy during braking and store it in the battery, effectively recovering and utilizing energy.
5. Storage battery
Batteries are the energy source for all the functions of an electric vehicle, converting electrical energy into kinetic energy for propulsion, and powering all other onboard devices. The market offers a wide variety of batteries, including lead-acid, nickel-metal hydride, lithium iron phosphate, lithium manganese oxide, lithium titanate, ternary lithium batteries, and multi-component composite batteries. Ternary lithium batteries are the mainstream for pure electric passenger vehicles, accounting for up to 76% of installed capacity; in electric buses, lithium iron phosphate batteries are even more dominant, accounting for over 60% of installed capacity. The basic considerations for installing batteries in electric vehicles are typically high energy density, mature charging technology, short charging time, high continuous discharge rate, low self-discharge rate, adaptability to the vehicle's operating environment, safety and reliability, long lifespan, and ease of maintenance.
6. Energy Management System
The energy management system acts as an "energy coordinator," effectively allocating and managing energy during vehicle operation, coordinating the operation of various components to maximize energy utilization. It also participates in energy recovery during braking, assisting control devices and improving the electric vehicle's range. Simultaneously, it monitors battery parameters such as temperature, terminal voltage, and discharge current in real time to prevent overcharging and over-discharging, effectively extending battery life.
7. Charger
The charger converts the alternating current from the external power grid into direct current of the corresponding voltage, which is then stored in the battery, while simultaneously controlling the charging current. The three stages of the charging process—constant current, constant voltage, and float charging—are all controlled by this device.
8. Power Steering System
The steering system is designed to enable a car to turn, and it consists of a steering wheel, steering gear, steering mechanism, and steering wheels. To improve driver operability, an electronic power steering system (EPS) can be used.
