Understanding Electric Power Steering Systems: Types and Key Differences
Understanding Electric Power Steering Solutions: Types and Key Differences The power steering system is a crucial component of a vehicle, serving as an important connection between the driver and the car. It has evolved alongside the overall development of vehicles and the emergence of new technologies. Initially, there was mechanical steering, followed by hydraulic power steering systems (HPS), electro-hydraulic power steering systems (EHPS), electric power steering systems (EPS), and now the latest steer-by-wire (SBW) technology. Depending on the location of the assist motor, electric power steering systems (EPS) are classified into C-EPS, P-EPS, DP-EPS, and R-EPS. Each type has its own unique functional and performance characteristics. Different Types of Electric Power Steering Systems 1. Column Assist Type Electric Power Steering (C-EPS) Motor placement: the motor and reduction gears are mounted on the steering column. The motor’s torque works together with the driver’s input to rotate the steering column, which then transmits force through the intermediate shaft and pinion to the rack, providing steering assistance. Applicable vehicle types: particularly suitable for compact vehicles that do not require excessive assistance. Structural characteristics: compact design, easy installation, and minimal required installation space. Driving experience: lightweight steering at low speeds, stable handling at high speeds, and excellent self-centering performance. Additional features: equipped with self-diagnosis and safety control functions, highly adaptable, allowing for customization of electric power steering columns and controllers based on different vehicle models. 2. Pinion Assist Type Electric Power Steering (P-EPS) Motor placement: the motor provides assistance directly to the pinion of the rack-and-pinion steering system, combining the precise adjustability of electric power steering with the strong road feedback typical of hydraulic power steering. System performance: equipped with a waterproof, compact, lightweight, high-performance integrated motor-ECU unit, the system delivers high rigidity and excellent dynamic steering performance. Structural characteristics: the compact, integrated housing structure enhances the precision of component manufacturing and improves overall product reliability. Cost: P-EPS is more expensive compared to C-EPS. 3. Dual-Pinion Assist Type Electric Power Steering (DP-EPS) Motor placement: an additional assist motor is placed on another part of the rack, applying steering force to the tie rod via a pinion. Together with the pinion on the intermediate shaft and tie rod, this forms a dual pinion structure. Applicable vehicle types: suitable for mid-size SUVs, large SUVs, MPVs, pickups, and other passenger vehicles, meeting the requirements for ADAS (Advanced Driver Assistance Systems). Performance advantages: the servo motor only operates when steering assistance is needed, reducing fuel consumption by 3-5%. It complies with ISO 26262 functional safety standards at the ASIL D level. The system is designed with high robustness to handle complex driving conditions, with high steering precision to support driving assistance at high speeds. Redundant design: the fully redundant DP-EPS system includes redundancy in power supply, communication, sensors, electronic control, and motor output, significantly enhancing the reliability and safety of the system. 4. Rack Assist Type Electric Power Steering (R-EPS) Motor placement: the motor typically applies force to the rack through a timing belt or ball screw. In some configurations, a coaxial motor directly provides assistance via a roller screw. Structural characteristics: the structure is relatively compact, making it suitable for scenarios where front axle loads are increasing and the steering system is positioned farther from the driver. Driving experience: it offers an enhanced steering feel and higher efficiency, making it more suitable for premium vehicles. Performance advantages: with a finely tuned steering feel and excellent NVH performance, it fully meets the steering needs of vehicles ranging from mid-size sedans to luxury MPVs. It also supports Level 2+ autonomous driving, including features like Lane Keep Assist (LKA), Automated Parking Assist (APA), and Remote Control Steering (RCS). Safety: the entire product platform is developed following ISO 26262 processes, ensuring functional safety at ASIL-D level. Key Differences of Electric Power Steering Systems After gaining a basic understanding of the different EPS structures, let’s take a look at the performance differences and suitable applications for each type: 1. Assist Effect and Applicable Vehicle Types EPS Type Maximum Assist Force Applicable Vehicle Types C-EPS 11 kN Compact cars, small SUVs P-EPS 12 kN Midsize cars, SUVs DP-EPS 13 kN Midsize/large SUVs, MPVs, pickups R-EPS 16 kN Luxury cars, large SUVs, performance vehicles C-EPS, with its compact structure, is typically used for vehicles that require moderate steering assistance. P-EPS, by applying assist force to the pinion, provides stronger assistance and is suitable for heavier vehicles. DP-EPS, with its dual-pinion design, offers even greater assist force to meet the needs of larger vehicles. R-EPS generally delivers the strongest assist, making it ideal for luxury and performance vehicles. 2. Energy Consumption and Efficiency by EPS Type EPS Type Energy Consumption Efficiency C-EPS Low Moderate P-EPS Moderate Relatively High DP-EPS Moderate to High High R-EPS High (operates only when needed) Very High While DP-EPS and R-EPS have relatively higher energy consumption, their servo motors only operate when steering assistance is required, effectively reducing fuel consumption in real-world use. Additionally, these systems generally exhibit higher efficiency, converting electrical energy into steering assistance more effectively. 3. Response Speed and Precision by EPS Type EPS Type Response Speed Precision C-EPS Moderate Moderate P-EPS Relatively Fast High DP-EPS Fast High R-EPS Very Fast Very High R-EPS typically exhibits the fastest response speed and highest precision, thanks to its advanced control algorithms and precise mechanical structure. DP-EPS also performs well, while C-EPS and P-EPS are comparatively slower and less precise. 4. Noise Levels and NVH Performance by EPS Type EPS Type Noise Level NVH Performance C-EPS Moderate Moderate P-EPS Lower High DP-EPS Very Low High R-EPS Very Low Very High Among these types, only C-EPS has the motor located in the passenger cabin, making it the noisiest and has the worst NVH experience. In contrast, P-EPS, DP-EPS, and R-EPS have their motors in the front compartment, resulting in better noise performance. Additionally, R-EPS benefits from its force transmission structure, offering the best NVH performance. 5. Redundancy Design and Safety by EPS Type EPS Type Redundancy Design Safety Level C-EPS Minimal
