Electric Power Steering System
Electric Power Steering (EPS) is a power steering system that directly relies on the motor to provide auxiliary torque. Compared with the traditional hydraulic power steering system HPS (Hydraulic Power Steering), EPS has many advantages. EPS is mainly composed of torque sensor, vehicle speed sensor, motor, reduction mechanism and electronic control unit (ECU).
The basic principle of EPS is: the torque sensor is connected to the steering shaft (pinion shaft). When the steering shaft rotates, the torque sensor starts to work and converts the relative rotation angle displacement generated by the input shaft and the output shaft under the action of the torsion bar into an electrical signal to the ECU. The ECU determines the rotation direction of the motor and the size of the power current according to the signals of the vehicle speed sensor and the torque sensor, thereby completing real-time control of the power steering. Therefore, it can easily provide different power assistance effects of the motor at different vehicle speeds, ensuring that the car is light and flexible when steering at low speeds and stable and reliable when steering at high speeds.
The electric power steering system is developed on the basis of the traditional mechanical steering system. It uses the power generated by the motor to help the driver perform steering operations. The system is mainly composed of three parts: signal sensing device (including torque sensor, angle sensor and vehicle speed sensor), steering power mechanism (motor, clutch, reduction transmission mechanism) and electronic control device. The motor only works when power is needed. When the driver operates the steering wheel, the torque angle sensor generates a corresponding voltage signal according to the input torque and the steering angle. The vehicle speed sensor detects the vehicle speed signal. The control unit gives instructions to control the operation of the motor according to the voltage and vehicle speed signals, thereby generating the required steering power.
Compared with the traditional hydraulic power steering system, the electric power steering system has the following advantages:
1. The motor only provides power when steering, which can significantly reduce fuel consumption
The engine drives the traditional hydraulic power steering system to drive the steering oil pump, and part of the engine power is consumed regardless of steering or not. The electric power steering system only provides power when steering, and does not consume energy when not steering. Therefore, the electric power steering system can reduce the fuel consumption of the vehicle.
Comparative tests with hydraulic power steering systems show that when not steering, electric power steering can reduce fuel consumption by 2.5%; when steering, it can reduce fuel consumption by 5.5%.
2. The size of the steering assist can be adjusted by software, which can take into account the lightness of steering at low speed and the handling stability at high speed, and has good return performance. The size of the steering assist provided by the traditional hydraulic power steering system cannot change with the increase of vehicle speed. In this way, although the vehicle has good steering lightness at low speed, the steering wheel is too light at high speed, resulting in the phenomenon of "floating" steering, and the driver lacks a significant "road sense", which reduces the vehicle stability and the driver's sense of security at high speed.
The size of the assist provided by the electric power steering system can be easily adjusted by software. At low speed, the electric power steering system can provide greater steering assist and provide the vehicle with light steering; as the speed increases, the steering assist provided by the electric power steering system can be gradually reduced, and the steering force required by the driver when steering will gradually increase, so that the driver can feel a significant "road sense" and improve the stability of the vehicle.
The electric power steering system can also apply a certain additional return torque or damping torque, so that the steering wheel can accurately return to the middle position at low speed, and can suppress the oscillation and overshoot of the steering wheel during high-speed return, taking into account the return performance of the vehicle at high and low speeds.
3. Compact structure, light weight, good assembly of production line, easy maintenance
The electric power steering system eliminates the hydraulic steering oil pump, oil cylinder, hydraulic pipeline, oil tank and other components, and the motor and reduction mechanism can be made into a whole with the steering column and steering gear, making the entire steering system compact, light, good assembly on the production line, saving assembly time, and easy maintenance.
4. Through program settings, the electric power steering system is easy to match with different models, which can shorten the production and development cycle.
Due to the above advantages of the electric power steering system, it has been more and more widely used in recent years.
The electric power steering system is based on the mechanical steering system, with the addition of a motor and a reduction mechanism, a torque angle sensor, a vehicle speed sensor and an ECU electronic control unit.
