Working Principle of Electric Power Steering (EPS)

The Electric Power Steering (EPS) system is a technology that uses an electric motor to replace the traditional hydraulic pump to provide steering assistance.

Working Principle

Electric Motor Drive
The core component of the electric power steering system is the electric motor. Unlike the traditional hydraulic power steering system, EPS does not rely on hydraulic oil and pumps but instead uses an electric motor to provide power. When the driver turns the steering wheel, sensors in the system detect the steering force and send signals to the Electronic Control Unit (ECU).

Electronic Control Unit (ECU)
The ECU processes the signals from the sensors and calculates the appropriate level of steering assistance. It then controls the electric motor’s operational state and adjusts the motor’s power output to provide the corresponding assistance. The ECU also adjusts the assistance level based on factors like vehicle speed and steering angle, usually providing more assistance at low speeds and less assistance at high speeds to enhance handling.

Electric Motor and Steering System Integration
The electric motor is connected to the steering system via gears, belts, or shafts. When the electric motor provides assistance to the steering system, it makes it easier for the driver to turn the steering wheel, reducing the steering effort.

Feedback Mechanism
In the EPS system, in addition to providing assistance, there is a feedback mechanism that simulates the road feel of traditional steering systems. By adjusting the output of the electric motor, the system maintains appropriate road feedback during steering, improving vehicle stability and comfort.

When the driver is not turning the steering wheel, the assistive electric motor does not operate.

When the driver turns the steering wheel, the torque (steering angle) sensor connected to the steering shaft continuously measures the torque applied to the steering shaft (direction) and converts it into an electrical signal. The vehicle speed sensor generates a speed signal that is sent to the ECU. The ECU processes these two signals and issues control instructions to the clutch and the electric motor, outputting an appropriate current. When the clutch engages, the electric motor generates a torque, which is reduced by the reduction mechanism and then applied to the output shaft. The lower end of the output shaft is connected to a small gear in the gear-rack steering assembly. The torque generated by the electric motor is finally applied to the vehicle’s steering mechanism through the gear-rack steering system, providing steering assistance that is appropriate for the operating conditions.