The development of automotive electronics requires magnetic materials
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Generally, the requirements for magnetic materials for automobiles are requirements for permanent magnet materials of various types of motors.
Magnets used as permanent magnet motors generally require high magnetic properties, resulting in large air gap magnetic fields; good magnetic properties and low temperature coefficient; high operating temperature to prevent demagnetization at high temperatures; Good mechanical properties and low prices. Depending on the type and structure of the permanent magnet motor, the starting point to consider when selecting a permanent magnet is different.
Permanent magnet motors for automobiles generally consider more price. Therefore, ferrite magnets and high-performance rare-earth NdFeB magnets are used. Due to their high magnetic properties, the volume of magnets is correspondingly smaller. Magnetic prices continue to decline, and more and more automotive motors use NdFeB rare earth permanent magnet materials.
When the permanent magnet is mounted on the motor, it must generate an air gap (usually 0.5 to 1 mm) with a certain distance from the rotor or stator of the motor. Therefore, magnetic poles are inevitably generated on the surface of the permanent magnets on both sides of the air gap. This magnetic pole generates a demagnetizing magnetic field inside the magnet, and its direction is opposite to the direction of the external magnetic field when the original magnetization is performed, and the larger the air gap, the stronger the demagnetizing field. That is to say, the permanent magnet works under the action of demagnetizing magnetic field, and it works at a certain point of the demagnetization curve. Therefore, it is hoped that the permanent magnet can maintain high magnetic induction intensity under the action of demagnetizing magnetic field, that is, the HCB is required to be large, and the HCB is more Large means that the ability to resist demagnetization is greater.
The key factors for measuring the application of permanent magnet materials in electric motors are: remanence (Br), coercivity (Hc), magnetic energy product (BH) m, shape of demagnetization curve, temperature stability of magnets, size, volume and weight, manufacturing Cost, etc.
General requirements for permanent magnet materials in automotive permanent magnet motors:
1. The high HCB can ensure the required magnetomotive force of the motor output, make the working point of the motor close to the maximum magnetic energy product, and make full use of the capability of the magnetic steel;
2, high Br, to ensure that the motor has a higher speed, large output torque and high power;
3, high HCJ, can ensure the motor's strong overload, demagnetization and anti-aging, low temperature resistance;
4. High (BH)m, (BH)m is higher, indicating that the working coefficient of the permanent magnet in the actual operation of the motor is better;
5. The larger the magnetic flux, the better, which will greatly improve the working efficiency of the motor;
With the development of lightweight, small, and high-efficiency automotive motors, magnet thickness is required to be thinner and thinner. To ensure the stability of magnetic performance and the stability of motor output power and voltage, HCB and HCJ are more demanding.
Table 1 The highest temperature of each part of the car
Car part maximum temperature engine 150°C instrument panel 140°C chassis 85°C exterior 121°C instrument panel (top) 113°C instrument panel (other parts) 85°C tail panel 107°C loading room 85°C
The requirements for permanent magnet materials vary depending on the position, structure and function of the motor in the vehicle. For example, the temperature of each part of the car is different, and the heat resistance requirements of the materials used are also different. The heat resistance standard generally means that the irreversible demagnetization is less than 3%. This requires the material to have a high intrinsic coercivity. This is due to the fact that the magnetic components are related to the normal operation of the car and the implementation of various functions. Therefore, heat resistance is one of the important indicators for preventing traffic accidents and ensuring the safety of people and property. Table 1 lists the maximum temperatures for various parts of the car.
Due to its rich raw materials, low price, high Curie temperature, low temperature coefficient and good corrosion resistance, it is suitable for automotive motor applications where the working environment is harsh. Therefore, the permanent magnet ferrite in the motor still accounts for a large proportion at present or in the future. In particular, the performance of permanent magnet ferrite materials has been continuously improved in recent years, and can better meet the needs of the development of automotive motors. The trend in the future is that the middle and low-grade ferrites will be replaced by high-grade permanent magnet ferrites, and the miniaturized and high-performance permanent magnet motors will continue to increase. The magnetic materials used will be increasingly reduced with the price of NdFeB materials. The more used, the requirement for NdFeB is that it is better in corrosion resistance and heat resistance.
A brief analysis of the requirements of ferrites for several major motors is now available.
Starter motor
Since the starter motor is mounted on the engine, it must face a severe working environment, such as high temperature, low temperature, dust or salt water. Only the ferrite material can be fully applied. Therefore, about 95% of the starting motor is made of tile-shaped permanent ferrite. According to the starting motor electromagnetic torque formula (M=cmφIa), the electromagnetic torque is large, and the magnet has a high (BH)max and Br value. In addition, since the magnet is affected by temperature changes, it is required that the magnetic flux irreversible loss ≤ 5% (some manufacturers require ≤ 3%), and therefore the magnet is required to have a high HCJ value. Now, the ferrite magnetic properties of the starting motor are generally above 380 mT, and the HCJ is at least 358 kA/m. As automakers have increased the requirements for starting motor characteristics and reduced the size and quality of the starting motor, some motor manufacturers have used permanent magnet ferrite tiles with a Br of 430 mT and a HCJ of 395 kA/m.
Wiper motor
The wiper motor has a high value for the magnetic performance HCJ. Although there is no high starting motor, it is also required to perform the low temperature impact demagnetization test. Most users require a flux change of less than 5%, and some users require less than 3%. The volume and mass ratio of the wiper motor in the future. It is now about 20% smaller, so magnets with a Br value of 450mT will be used on the wiper motor.
Fuel pump motor
Since the fuel pump is operated continuously and smoothly, and is immersed in the steam (wood) oil as a whole, the working temperature is stable, so the requirements for HCJ are lower than the above two. However, the fuel pump has a small volume and requires a high magnetic flux, so the Br and (BH)max values ​​are required to be higher. At present, the general demand for large quantities of Br reaches 420 mT, and the (BH)max requirement reaches 33 kJ/m3. Since the fuel pump motor is integrally installed in the fuel tank, the appearance and cleanliness of the magnetic tile are strictly required, and red powder, corners and debris are not allowed to appear. The company has used a 460 mT magnetic tile for the fuel pump motor to further reduce the volume.
With the advancement of automotive electronics technology, more and more soft magnetic materials are used in electronic control systems, sound systems, imaging systems, and the like in automobiles. The total requirements for soft magnetic materials and components of these devices are high magnetic permeability, high saturation magnetic flux density, low loss at high frequencies, high output power, high temperature operation stability, etc., in car navigation, radar recognition and global positioning system. The focus should be on the electromagnetic interference resistance of soft magnetic devices, and the choice of high performance and high reliability EMI (EMC) materials.
Since there are usually 20,000 auto parts, and there are as many as thousands of magnetic components, this article does not specifically analyze their requirements. In addition, with the rapid development of automotive electronics, new electronic device configurations in automobiles will have new requirements for new applications of magnetic materials and devices.
Application of permanent magnet materials in automotive electronic devices
Today, 40 to 70 permanent magnets are used in every car, most of which are used in motors, actuators and sensors. Taking automobile motors as an example, the average number of permanent magnet motors used per vehicle is currently more than 30. Permanent magnet motors with permanent magnet materials can help the car achieve electronic power control, brake control, driving operations and other functions. Future control functions generally require the use of permanent magnet materials and permanent magnet motors. The main drive on the car will use more computer control. These features require the addition of many small motors to take advantage of various control functions such as fuel or Throttling control, etc. High-performance permanent magnets have no excitation loss and do not generate heat. Adding more flexibility to the motor design, changing the conventional design, including the design of the disc motor and the outer rotor type motor, due to its low inertia and low reactance, it can achieve better dynamic characteristics and high speed capability, completely Meet the high reliability requirements of modern vehicles for high power and electronic systems.
The continuous development of permanent magnet materials has brought good news to the automotive motor industry. With the development of miniaturization, light weight and high efficiency of automotive permanent magnet motors, high-performance rare-earth permanent magnet materials represented by NdFeB, especially bonded NdFeB permanent magnet materials, have gradually replaced some traditional ones due to falling prices. Ferrite permanent magnet motors, such as starter motors, generators, automatic brakes, and oil pump motors, air conditioner motors, etc., will be widely used in operating systems in the future. Since the late 1980s, General Motors has used NdFeB bonded magnets to start motors in some models. Under the equivalent output torque, the weight of the NdFeB starter motor is reduced by half, the volume is reduced by 1/3, and the efficiency is improved. At present, permanent magnet materials in automobiles are mainly used for motors, actuators and sensors. Taking the motor as an example, more than 30 mid- and low-end cars are used, and more than 70 luxury cars are used, and some even have more than 100. The permanent magnet materials used in automobiles today generally include permanent magnet ferrite, NdFeB permanent magnet, SmCo permanent magnet and AlNiCo permanent magnet. The following analysis describes its main applications.
Typical application of permanent ferrite
Starter motor, wiper motor, engine cooling fan motor, voltage regulator wiper arm motor, seat automatic adjustment motor, air conditioner motor, steering linkage fog lamp motor, headlamp correction device motor, electric Permanent magnet ferrites are required for auto parts such as speedometer motors, electric steering brushless motors, electric water pumps, electric oil pumps, electronic air conditioners, speakers, sensors (position, speed, pressure, etc.). The specific application is shown in Table 2 (for details, see Magnetic Materials and Application Industry Information, 2005, issue 11).
The main application of NdFeB permanent magnets
NdFeB permanent magnet brushless DC motor for hybrid electric vehicles
In recent years, due to the increasingly prominent resources and environmental problems around the world, oil prices have soared, countries are stepping up the implementation of electric vehicle research and development plans, hybrid vehicles (HEV) and fuel cell vehicles (FCEV) have become new hot spots. Hybrid electric vehicles also have motor drives and engine drive systems, and this new type of vehicle that uses a mix of oil and electricity will be popular. Rare earth permanent magnet brushless DC motor is its core component, which is the key to achieve various working modes, directly affecting the performance of electric vehicles. The basic structure of the brushless motor is the same as that of the ordinary brushless motor. It is mainly composed of a permanent magnet motor body, a power electronic commutator and a rotor position sensor. The main features are small axial thickness, light weight, high output power and high efficiency. It integrates electric, power generation and braking functions, and can perform reversible work on electric and power generation frequently.
Power generation unit
With the development of the rural economy, the output of China's agricultural transport vehicles has been increasing, with an annual output of more than 3 million vehicles. At present, the generators used in small-scale agricultural vehicles are mainly permanent-magnet alternators, which have the problem of poor lighting performance at low speeds, which is easy to cause traffic accidents when such vehicles are driving at night or poor road conditions, and cannot be directly driven by vehicles. The shed's wiper, heater, etc. provide DC power. Therefore, the rare earth permanent magnet power generation device emerges as the times require, and its voltage output is stable, the cost is low, and the performance is reliable. The device includes an electronic regulator, a generator cover, a stator (consisting of a core, a coil), and a rotor (consisting of a shaft, a core, and NdFeB permanent magnets). The power generation device that integrates the generator and the electronic voltage regulator and uses the high-performance rare earth permanent magnet as the magnetic pole can realize DC constant voltage output, small volume, light weight, low cost, safe and reliable use, and solves the night illumination of the automobile. , DC power required for steering instructions, electric horns, wipers, heaters, etc.
With the development of NdFeB resist technology, the cost performance has decreased, and the application of NdFeB in automobiles has also increased.
AlNiCo and SmCo
Since they all contain strategic materials Co, they are limited in applications in automobiles. However, since the magnetic properties of AlNiCo are superior to those of ferrite and the corrosion resistance is superior to that of NdFeB, some components still use it. Table 2 lists the application of the above materials in the motor of each component of the automobile.
With the development of miniaturization, light weight and high efficiency of automotive permanent magnet motors, high-performance rare earth permanent magnet materials represented by NdFeB (especially bonded NdFeB) permanent magnet materials have gradually replaced some traditional irons due to falling prices. Oxygen permanent magnet motors, such as starter motors, generators, automatic brakes, and oil pump motors, air conditioner motors, etc., will be widely used in operating systems in the future.
In addition, the requirements for high speed, safety and comfort of the car make it more and more electronic. More and more magnetic materials are needed in automobiles. For example, in the vehicle millimeter wave system, electronic control system, communication system, car audio, television, multimedia, roadside camera and other equipment, it is necessary to use permanent magnet magnetic field, permanent magnet sensor, actuator, magnetic nail, permanent magnet bearing, permanent Magnetic support and fixtures, new functional micromotors, etc.
Application of soft magnetic materials in automotive electronic devices
With the development of automotive technology and electronic technology, high-frequency, micro, ultra-thin, anti-EMI/RFI, low-power, component, intelligent and other automotive magnetic components have emerged to meet the needs of energy saving, Environmental protection and electronic information equipment are digital, versatile, intelligent, lightweight, and smart. Soft magnetic materials, especially amorphous ultrafine crystals and magnetic films, are of great use here. The following is a brief introduction to the application of soft magnetic materials in automobiles.
Induction motor
Although most of the current use of permanent magnet materials, the United States and Europe's electric vehicles, many high-frequency low-loss metal soft magnetic materials for the magnetic core of the induction motor, its maximum output power is 70 ~ 100kW.
sensor
There are dozens of hundreds of sensors in a regular car, and the number of sensors on a luxury car can be as many as 200. There are generally more than 30 kinds, and there are more than 100 kinds. The application of soft magnetic materials is also indispensable, such as temperature sensors using thermal ferrite and metal materials, dew sensors, thermal switches, hot spring relays, and electromagnetic induction coils.
Vehicle millimeter wave system
Most of the power sources used here are switching power supplies. The main transformer, choke coil and noise filter can be used as high-power ferrite, high-conductivity soft ferrite or amorphous soft magnetic alloy and iron-based nanocrystalline alloy. . Such as a variety of inductors, transformers, relays, circulators, isolators, filters, switches, modulators, oscillators, phase shifters, and so on. In communication, the main functions of soft magnetic components are: adding inductance coils, reducing information attenuation, increasing communication distance; making channel filters, selecting and separating channel signals to prevent distortion; making linear broadband converters and pulse transformers, separating Potential, regulate voltage and conversion efficiency; act as a choke to filter out unwanted high frequency currents;
Lighting system
Lighting high voltage transformers, ballasts and oscillator transformers require a soft magnetic material as the core.
Car audio, TV, imaging system
A large number of inductors, filters, common mode chokes, transformers, etc. are needed here. Use a variety of ferrite core series, such as BB, RH, T, SH, DR, EE, ER series.
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