Electronic Power Steering and NdFeb

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%. Among the passenger models sold in China, about 63% use HPS, and about 35% use EPS. Since 2015, China has surpassed Europe, the United States and Japan to become the world's largest EPS market.

Motors used in EPS are classified 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.

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.

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.