01 Electric Hydraulic Power Steering System
As shown in Figure 1, the Electric Hydraulic Power Steering (EHPS) system is composed of hydraulic power steering (HPS) and an electric motor, which supports the original HPS system interface. The EHPS system is suitable for light-duty, medium-duty, and heavy-duty trucks, as well as medium and large coaches. With the rapid development of new energy commercial vehicles (such as buses, logistics, and sanitation), the power source of the traditional hydraulic power steering system’s hydraulic pump has changed from the engine to the motor, and the high-voltage battery system on the vehicle makes it possible to use a high-power electric pump. The EHPS system refers to the hydraulic power steering system that uses a high-power electric pump.
As the national concern for the safety and quality of new energy vehicles increases, the mandatory national standard “GB38032-2020 Electric Bus Safety Requirements” was issued on May 12, 2020. Section 4.5.2 added control requirements for the power-assisted system during driving. That is, during the vehicle’s driving process, when the whole vehicle experiences an abnormal situation of class B high-voltage power interruption, the steering system should maintain power-assisted state or at least maintain power-assisted state for 30 seconds when the vehicle speed is greater than 5 km/h. Therefore, currently, electric buses mostly use a dual-source power supply control mode to meet regulatory requirements. Other electric commercial vehiclesfollow the “GB 18384-2020 Electric Vehicle Safety Requirements.” The composition of the EHPS system for commercial vehicles is shown in Figure 2. Currently, all vehicles with a weight of 4.5 tons or more from YI use the HPS system, and the self-developed chassis reserves space for EHPS.
02 Electric Power Steering System
The Electric Power Steering (EPS) system for light-duty commercial vehicles mostly uses an electric circulating ball steering gear (as shown in Figure 3), which eliminates components such as an electric hydraulic pump, oil tank, and oil pipe compared to the EHPS system. It has the advantages of a simple system, reduced weight, fast response, and precise control. The power steering has been changed from hydraulic to electric, and the controller directly controls the electric motor to generate power assistance. When the driver turns the steering wheel, the sensor transmits the steering angle and torque signals to the controller. After receiving the steering angle, torque signals, and other information, the controller calculates and outputs control signals to control the electric motor to generate power assistance. When the steering wheel is not turned, the power-assisted steering control unit does not send signals, and the power-assisted motor does not work. The common composition of the electric circulating ball steering system is shown in Figure 4. Currently, YI uses an EPS scheme for self-developed small-tonnage models.
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Post time: May-23-2023
