Now, more and more multi-pole oriented magnet be the first choice magnets for EPS motors for they can bring better performance.
What is EPS System?
Electronic power steering (EPS), 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 affects the handling stability, comfort and driving safety of the vehicle. In the design of the steering system, most commercial vehicles and 50% of saloon cars adopt a power steering system in order to alleviate the contradiction between the steering lightness and the steering sensitivity.
Since the 1950s, the power steering system has gone through three development stages: conventional hydraulic power steering system (HPS), electro-hydraulic power steering system (EHPS), and electric power steering system (EPS). And there is a trend of continuing to electronic and intelligent development.
The composition of EPS system
The EPS system is based on the traditional mechanical steering system, according to the torque signal on the steering wheel and the driving speed signal of the car, using the electronic control device to make the motor generate auxiliary power of the corresponding size and direction to assist the driver in steering operations. It can easily realize different boosting effects provided to the motor at different vehicle speeds, ensuring that the car is light and flexible when steering at low speeds, and has sufficient road feel when steering 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, an electric 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:
1. Brushed Motors :
The brushed motor switches the current while the brushes and commutator rotate, and can rotate when the power is turned on, and the cost is low. However, the windings of the brushed motor are arranged on the rotor side. As the output power increases, the moment of inertia of the motor increases, and it is necessary to solve the problem of the deterioration of the steering sensitivity.
2. Brushless Motors :
The brushless motor itself does not have a rectifier function, so it needs a built-in angle sensor to switch the current corresponding to the angle signal through a circuit, so it has a complex structure and a high cost. However, the windings of the brushless motor are arranged on the stator side, and the rotor is a permanent magnet. Even if the output power increases, the inertia moment problem can be suppressed.
Permanent Magnets for EPS Motors
EPS system has very high requirements for the performance, weight, and volume of permanent magnet motors. Therefore, the permanent magnets in the EPS system are mainly high-performance neodymium magnets and currently are mainly sintered neodymium magnets. Common grades are 45H, 48H, 38SH, 40SH, 42SH, 48SH, 35UH, etc.
As the production process of multi-pole oriented magnet gradually matures, EPS motors are using this magnet as the first choice because it can help the motor achieve better performance:
- As a rotor, can achieve uniform magnetic density flux distribution.
- Fastening the magnet is simple, enabling assembly-related cost reductions.
- Highly reliability due to enabling rotor construction from a single magnet.
- Can obtain sine surface inductive flux distribution