Application of Neodymium Magnets in Aerospace Industry

Rare earth permanent magnet motors (REPM) are mainly used in aircraft for various electric actuation systems. The electric actuation system is a driving system with a motor as its actuator. It is widely used in the flight control system, environmental control system, braking system, fuel and starting system of aircraft. Because of the excellent magnetic properties of rare earth permanent magnets, a strong permanent magnetic field can be established without additional energy after magnetization. The rare earth permanent magnet motor made by replacing the electric field of the traditional motor is not only efficient, but also simple in structure, reliable in operation, small in size and light in weight. It can not only achieve the high performance (such as super high efficiency, super high speed, super high response speed) that traditional electric excitation motors cannot match but also make special motors which can meet the specific operational requirements, such as elevator traction motor, automobile special motor, etc. There are four kinds of actuation systems used in the aircraft: hydraulic, electric, pneumatic and mechanical. The hydraulic actuation system is the most widely used one, but the most promising one is the electric actuation system. With the development of permanent magnets, high power semiconductors and microprocessors, electric actuation systems have developed to compete with hydraulic actuation systems.

(1) Flight Control System The electric actuating system used in the flight control system is also called power telex actuator, which is mainly used for the operation of wing and rudder. It is mainly divided into an electro-hydraulic actuator and electro-mechanical actuator. In the mid-1970s, the frequent failures of the hydraulic system of American helicopters in important international events prompted them to research and develop rare earth permanent magnet electric actuators. Neodymium permanent magnet brushless DC motor (NdFeB PMBLDCM) technology is used in the electro-hydraulic actuator developed by General Electric Company, Vickers Company and HR Dextran Company for the next generation of flight control rudder. The developed electromechanical actuator uses high voltage permanent magnet brushless DC motor technology and pulse width modulation power converter technology. The motor controller receives the control instructions from the flight control computer on the aircraft, and through the signal processing, synthesis, and amplification of the servo amplifier of the three-channel rudder loop system, then drives the output angle of the corresponding rudder to control the rudder and aileron of the aircraft, thus changing the attitude and direction of the aircraft and realizing the automatic control of the flight control system to the aircraft.

(2) Electric Environmental Control System Electric environmental control system adopts electromechanical actuation technology, which is characterized by the high-power, high-speed variable-speed drive motor. Since 1982, the U.S. has developed an electric steam cycle environmental control system and tested it on a P-3 anti-submarine aircraft. The system uses a variable speed high voltage rare earth permanent magnet brushless DC motor of 30000-70000 r/min to drive the compressor. The samarium cobalt permanent magnet motor can output 34 at 45 000 r/min. 3 kW power.

(3) Air Oxygen Production System The oxygen concentrator is an important airborne equipment of advanced aircraft, which provides pilots with life-sustaining ability. At present, only four countries, such as the United States, have the technology. Our country has ranked among the internationally advanced ranks in this technology and successfully developed oxygen concentrators. The motor used is a low-speed and high-precision brushless DC motor speed stabilization system. Samarium cobalt permanent magnet excitation is used to drive the valve to rotate 6r/min.

(4) Electric brake system The electric brake system was successfully developed in 1982 in the United States and tested on the A-10 attack aircraft. In 1990, the third generation of the electric brake system was completed. Strong moment samarium cobalt permanent magnet brushless DC motor and pulley worm actuator were adopted. In 1998, the F-16 fighter flew a new electric brake system. Four rare earth permanent magnet brushless DC motors are used in the electric actuator of the system. Due to the use of the brushless motor and low inertia components, the response frequency of the electromechanical actuator is 20 ~ 30 Hz, while that of the hydraulic actuator is only 10 Hz. With this electric brake system, the fighter aircraft can be reduced by 22.5-45 kg.

(5) Fuel system In the past, most of the hydraulic pumps and valves used to be driven by brush DC motors. A Brushless DC motor is now used. The motor works with the pump immersed in fuel, and the controller and the magnet rotor body are installed in the same shell, completely sealed. The motor is made of a NdFeB magnet or SmCo magnet with high-temperature resistance and 1J22 high permeability stator core material. It has the function of speed closed loop and soft start with digital control.