How to ensure the long-term stability of magnetic properties in automotive permanent magnet motor accessories under high-temperature environments?
Publish Time: 2025-11-12
With the rapid development of new energy vehicles and intelligent driving technologies, permanent magnet motors have become core components of drive systems due to their high efficiency, high power density, and excellent dynamic response performance. The permanent magnet, a key component of the permanent magnet motor, directly determines the overall performance of the motor. However, during vehicle operation, especially under high-speed operation, frequent start-stop, or high-load conditions, the internal temperature of the motor can rapidly rise to 150℃ or even above 200℃. High temperatures not only cause reversible flux loss in the permanent magnet but may also lead to irreversible demagnetization, seriously affecting the motor's lifespan and safety. Ensuring the long-term stability of magnetic properties in permanent magnet motor accessories under high-temperature environments has become a key technological challenge in the research and development and manufacturing of automotive parts.
The first line of defense for ensuring stable magnetic properties at high temperatures is material selection. Currently, automotive permanent magnets mainly use sintered neodymium iron boron magnets due to their extremely high remanence and maximum energy product. However, ordinary NdFeB magnets exhibit a significant decrease in coercivity at high temperatures, making them prone to demagnetization. Therefore, the industry commonly employs "heavy rare earth element doping" technology, which involves adding heavy rare earth elements such as dysprosium or terbium to NdFeB magnets. These elements can significantly improve the coercivity and Curie temperature of the material, allowing it to maintain good magnetic properties even at 180℃ or even 200℃. For example, high-performance NdFeB magnets used in electric vehicle drive motors typically require operating temperature ratings of H, SH, UH, and even EH. Furthermore, while Samarium-Cobalt magnets are more expensive, their inherent excellent high-temperature stability and oxidation resistance make them commonly used in special vehicles or aerospace applications where reliability requirements are extremely high.
2. Optimizing Microstructure and Grain Boundary Diffusion Process
Besides compositional control, the microstructure of the material is equally crucial for high-temperature stability. Modern permanent magnet manufacturing widely utilizes "grain boundary diffusion" technology. This process diffuses heavy rare earth elements only to the surface layer of the magnet grains, rather than doing them throughout the entire structure. This significantly improves coercivity while reducing the amount of expensive heavy rare earth elements used, balancing performance and cost. Simultaneously, by controlling the sintering temperature, cooling rate, and heat treatment parameters, grain size can be refined, impurity phases reduced, and a dense, uniform microstructure formed. This suppresses the movement of magnetic domain walls at high temperatures and slows down the demagnetization process.
3. Scientific Magnetic Circuit Design and Thermal Management
The demagnetization of permanent magnets is not only affected by temperature but also closely related to the external reverse magnetic field. During the motor design phase, engineers need to optimize the magnetic circuit structure through finite element simulation to ensure that the demagnetizing magnetic field strength experienced by the permanent magnet is below its high-temperature coercivity threshold under various operating conditions. Furthermore, an efficient thermal management system is indispensable. By rationally arranging cooling channels and using oil or water cooling, the temperature rise of the motor windings and permanent magnet area can be controlled within a safe range, fundamentally preventing the magnet from being exposed to critical high-temperature environments for extended periods. Some high-end models even integrate temperature sensors inside the rotor to monitor the temperature of the permanent magnet area in real time, achieving intelligent temperature control protection.
4. Surface Protection and Encapsulation Technology
High temperatures are often accompanied by chemical degradation processes such as oxidation and corrosion. Neodymium iron boron magnets are particularly susceptible to moisture and oxygen corrosion, leading to surface powdering and accelerated magnetic performance decay. Therefore, permanent magnets must undergo rigorous surface treatment before assembly, such as electroplating with nickel, copper, or nickel, aluminum ion plating, epoxy resin spraying, or phosphating, to form a dense protective layer. In the motor assembly, permanent magnets are typically firmly embedded in the rotor core slots and prevented from shifting using high-strength adhesives or mechanical fixation, while simultaneously isolating them from the external environment. This "physical + chemical" dual protection strategy significantly improves the long-term reliability of the magnets in harsh automotive environments such as high temperature, high humidity, and salt spray.
5. Aging Testing and Reliability Verification
To ensure the stable magnetic performance of permanent magnet motor accessories throughout the vehicle's 10-year or even longer lifespan, manufacturers must perform stringent aging and reliability tests. This includes high-temperature and high-humidity storage tests, high-temperature demagnetization cycle tests, and durability bench tests simulating actual operating conditions. By comparing changes in magnetic flux before and after testing, the long-term stability of material and structural designs is evaluated, providing data support for product finalization.
Ensuring the long-term stability of the magnetic properties of automotive permanent magnet motor accessories under high-temperature environments is a systematic engineering project involving materials science, electromagnetic design, thermal management, and manufacturing processes. Only through multi-dimensional collaboration of high-performance material selection, advanced preparation processes, intelligent thermal control strategies, and rigorous reliability verification can permanent magnet motors maintain their magnetic force even under extreme operating conditions, providing a solid guarantee for the safe, efficient, and long-lasting operation of new energy vehicles.
