EPS integrates mechanical steering, electronic sensing, control and drive technologies. It is mainly composed of the following components: mechanical steering system, steering torque sensor, vehicle speed sensor, electronic control unit (ECU), motor and reduction mechanism.
- Motor: The critical core component that significantly affects EPS performance. It is responsible for generating the torque required for steering assist. Depending on the system configuration, it can be mounted on the steering column or integrated into the steering rack. The motor is controlled by the ECU and outputs torque matching the required assist. At present, permanent magnet synchronous motors (PMSM) and brushless direct current motors (BLDC) are widely used in various EPS systems due to their unique advantages such as simple structure, reliable operation, convenient maintenance, high operating efficiency, no excitation loss and excellent speed regulation performance.
- Torque Sensor: Detects the force applied by the driver on the steering wheel. It serves as the key basis for the ECU to judge "the magnitude of required assist force". Meanwhile, it can identify the steering direction to ensure that the assist direction is consistent with the driver's operation.
- Vehicle Speed Sensor: Measures the vehicle speed. Generally, an electromagnetic induction sensor is installed on the gearbox. It transmits pulse signals of the primary and secondary systems to the ECU according to changes in vehicle speed.
- Electronic Control Unit (ECU): The "brain" of the electric power steering system. It processes input signals from various sensors including the torque sensor and calculates the assist force that the motor needs to provide. The ECU runs sophisticated algorithms such as model-based and adaptive algorithms to ensure optimal steering feel and responsiveness under different driving conditions.
- Reduction Gear: Connects the motor with the steering column/rack. By reducing the motor speed and increasing torque, it ensures that the steering assist is stable and sufficient to help the driver turn the wheels easily.
The working principle of EPS is relatively complex, yet it boasts high efficiency. During operation, sensors detect the movement of the steering wheel (direction, speed, angle) and transmit the data to the MCU. After processing, signals are sent to the motor driver. The motor rotates and drives the steering gear to reduce the torque required by the driver. The motor is equipped with a rotor position sensor, as well as torque and angle sensors with SENT interfaces to guarantee accurate data collection.
