Innovation and Future of Electric Steering Systems for Commercial Vehicles
Amid the wave of vehicle electrification and intelligence, the automotive industry is entering a critical transition period from functional vehicles to intelligent vehicles. This transformation has driven the rapid development of numerous cutting-edge technologies, among which steer-by-wire chassis technology-one of the core foundations of intelligent driving-signals the arrival of a new automotive era. The realization of high-level autonomous driving in the future will largely depend on steer-by-wire chassis technology.
Steer-by-wire technology replaces traditional mechanical connections with electrical signal transmission, breaking the limitations of conventional steering mechanisms and bringing revolutionary changes to vehicle control. A steer-by-wire chassis typically integrates five key systems: steering, braking, suspension, drive, and shifting. Its main advantages include a compact structure, strong controllability, and fast response.
Next, we focus on the core domain of steer-by-wire technology. Compared with passenger vehicles, commercial vehicles face more demanding challenges in steering systems, such as heavy loads, long wheelbases, and multi-axle steering requirements. At present, the primary function of commercial vehicle steering systems is still limited to providing basic steering assistance. Advanced features such as speed-sensitive assistance adjustment, automatic return-to-center, active steering control, and autonomous adjustment of assistance modes remain in the stages of research, development, and pilot installation.
Hydraulic power steering continues to be the mainstream solution for commercial vehicles. However, it has long-standing drawbacks, including high noise levels, non-adjustable assistance characteristics, and the inability to support electronic control or steer-by-wire functions.
With the rapid advancement of electronic control and intelligent technologies, commercial vehicle steering systems are gradually transitioning toward electronically controlled steering and steer-by-wire solutions. This shift has led to the development of technologies such as Electro-Hydraulic Power Steering (EHPS), Electric Power Steering (EPS), and various new steering gear configurations. These electronically controlled steering systems not only address the inherent limitations of traditional hydraulic systems but also significantly enhance steering performance, active control capability, driving safety, and overall driving experience.
The Electro-Hydraulic Power Steering (EHPS) system combines a traditional Hydraulic Power Steering (HPS) system with an electric motor and can remain compatible with the original HPS interface of the vehicle. EHPS systems are widely applied in light-duty, medium-duty, and heavy-duty trucks, as well as in medium-sized and large buses.
With the rapid growth of new energy commercial vehicles-such as buses, logistics vehicles, and sanitation vehicles-the power source of traditional hydraulic steering systems has gradually shifted from internal combustion engines to electric motors. Meanwhile, onboard high-voltage battery systems have enabled the application of high-power electric pumps. The EHPS system discussed here is essentially a hydraulic power steering system driven by a high-power electric pump.
On May 12, 2020, the national mandatory standard GB 38032-2020 Safety Requirements for Electric Buses was officially issued. Article 4.5.2 of this standard introduces new requirements for power assistance control during driving: if an abnormal Class B high-voltage disconnection occurs while the vehicle is in motion and the vehicle speed exceeds 5 km/h, the steering system must maintain power assistance for at least 30 seconds. To comply with this regulation, most electric pumps used in current electric buses adopt a dual power supply control strategy.
In light-duty commercial vehicles, Electric Power Steering (EPS) systems have gradually become the mainstream solution. These systems typically adopt an electric recirculating ball steering gear. Compared with traditional EHPS systems, EPS eliminates complex hydraulic components such as pumps, oil reservoirs, and pipelines, resulting in a simpler structure. As a result, EPS systems are lighter, offer faster response, and provide more precise control.
In EPS systems, steering assistance is provided by an electric motor instead of hydraulic pressure. The controller precisely regulates motor output based on steering wheel rotation signals. When the driver turns the steering wheel, sensors capture angle and torque data in real time and transmit them to the controller. After processing, the controller sends control signals to drive the motor and provide appropriate assistance. When the steering wheel is not in operation, the assistance system enters a dormant state, consuming no additional energy and thus improving energy efficiency.
Currently, some low-tonnage commercial vehicle models on the market have begun adopting EPS solutions, including light-duty commercial vehicles independently developed by our company. The development of electric steering technology is becoming increasingly diversified. New steering gear configurations, such as straight tie-rod designs, are under development and have made steady progress to meet the high torque demands of commercial vehicles.
At present, universities and manufacturers worldwide have developed a variety of electric steering gear configurations capable of delivering the large torque required by commercial vehicles. These innovations have injected new momentum into the advancement of electric steering technology for commercial vehicles. Among them, the planetary gear electric steering gear has attracted significant attention. It integrates key components such as a power-assist motor, cylindrical gear reduction mechanism, planetary gear reduction mechanism, and worm gear transmission. By combining planetary and cylindrical gear reduction mechanisms, this design effectively reduces motor speed while increasing output torque, thereby meeting high-torque requirements.
Meanwhile, the worm gear transmission mechanism ensures smooth transmission of steering wheel feedback torque and road resistance loads. The cycloidal pinwheel electric steering gear integrates a motor, a cycloidal pinwheel reducer, and a bevel gear reducer. The motor drives the cycloidal pinwheel reducer, which then connects to the bevel gear reducer, and finally transmits motion to the steering input shaft. This configuration features a compact and sophisticated structure while delivering high torque output, ensuring light and responsive steering for commercial vehicles.
The electromagnetic power steering gear utilizes electromagnetic principles to achieve power-assisted steering. Its core components include a rack-and-nut assembly on the steering input shaft, which meshes with a sector rocker shaft housed within the steering gear assembly. A permanent magnet is mounted on the rack-and-nut assembly, while DC electromagnetic coils are installed in the upper and lower cover assemblies. In addition, sensors on the steering input shaft monitor steering status in real time.
When the steering gear ECU receives signals related to steering angle, speed, and torque, it supplies current of appropriate magnitude and direction to the DC electromagnetic coils. Based on the principle that like magnetic poles repel and opposite poles attract, the rack-and-nut assembly is driven to move, thereby rotating the sector rocker shaft and providing steering assistance.
With the continuous advancement of autonomous driving technologies, higher demands are being placed on safety redundancy in steer-by-wire systems. Currently, autonomous driving demonstration vehicles typically adopt both software and hardware redundancy strategies to ensure operational safety. However, these technologies have not yet been widely applied in mass-produced commercial vehicles.
In summary, the selection of steer-by-wire technologies for commercial vehicles varies depending on factors such as vehicle load, layout constraints, and technology maturity. Multiple technical routes are converging toward electric steering solutions, marking a clear trend in the future development of commercial vehicle steering systems.
