Permanent Magnet in Automotive EPS
The full English name of EPS is Electronic Power Steering, that is, electronic power steering system, which uses the power generated by the electric motor to assist the driver in power steering. As an important part of the whole vehicle, the steering system is one of the key systems that affect the handling stability, comfort and driving safety of the vehicle.
In the design of the steering system, in order to alleviate the contradiction between the steering portability and steering sensitivity of the car, most commercial vehicles and 50% of the cars use power steering systems. Since the 1950s, the power steering system has gone through three development stages: conventional hydraulic power steering system (HPS), electrohydraulic power steering system (EHPS), and electric power steering system (EPS), and has continued to be electronic and intelligent. development trend.
From a global perspective, the percentage of EPS installed in automobiles has exceeded 50%. About 63% of the passenger cars sold in my country use HPS, and about 35% use EPS. However, the EPS loading rate of my country’s own brand cars is only about 20%, and the future development potential is huge. Since 2015, China has surpassed Europe, the United States and Japan to become the world’s largest EPS market.
The composition of the EPS system
Based on the traditional mechanical steering system, the EPS electronic power steering system uses the electronic control device to make the motor generate auxiliary power of corresponding magnitude and direction according to the torque signal on the steering wheel and the vehicle speed signal to assist the driver in steering operation. It can easily provide different assisting effects to the electric motor at different speeds, ensuring that the car is light and flexible when turning at low speeds, and has enough road feeling when turning at high speeds, and is stable and reliable.
Although different cars have different structural components, the structure of the EPS system is generally the same. It is generally composed of a torque (steering) sensor, an electronic control unit, a motor, a reducer, a mechanical steering gear, and a battery power supply.
The motors used in EPS are divided into brushed motors and brushless motors:
The brushed motor switches the current while the brush and the commutator are rotating, and it can rotate when the power is turned on. The cost is low, but the winding of the brushed motor is arranged on the rotor side. As the output power increases, the moment of inertia of the motor increases. It is necessary to solve the problem of poor steering operation sensitivity. Permanent Magnet in Automotive EPS
The brushless motor itself does not have a rectification function, so a built-in rotation angle sensor is required to switch the current corresponding to the rotation angle signal through a circuit, and the structure is complicated and the cost is high. However, the winding of the brushless motor is arranged on the stator side, and the rotor is a permanent magnet, which can suppress the inertia moment problem even if the output power increases.
Permanent magnet materials in EPS motors
EPS has high requirements on the performance, weight and volume of permanent magnet motors, so the permanent magnet materials mainly use high-performance NdFeB magnets, currently mainly sintered NdFeB magnets. Common grades are 45H, 48H, 38SH, 40SH, 42SH, 48SH, 35UH, etc. In the future, hot-pressed NdFeB is expected to replace sintered NdFeB in EPS, but the current technology is not yet mature, and the cost is still high, and sintered NdFeB is still the mainstream.
Permanent Magnet in Automotive EPS