Low-speed steering returnability analysis and improvements through mathematical modeling and CAE simulation for SUV

In driving, steering serves as the input mechanism to control the vehicle's direction. The driver adjusts the steering input to guide the vehicle along the desired path. During maneuvers such as parking or U-turns, the steering wheel is often turned fully from lock to lock and then released. It is expected that the steering wheel quickly returns to its original position. Steering returnability is defined as the ratio of the difference between the steering wheel position at lock to lock and the steering wheel angle after 3 seconds of release, to the steering wheel angle at the lock position, under steady-state cornering conditions at 10 km/h. Industry standards dictate that the steering system should achieve 75% returnability under these conditions within 3 seconds. Achieving proper steering returnability characteristics is a critical aspect of vehicle design. Vehicles equipped with Electric Power-Assisted Steering (EPS) systems can more easily meet returnability targets since the electric motor in EPS can apply torque in the opposite direction, helping the steering wheel return to its neutral position after the driver releases it. However, SUVs, due to their higher axle weights and greater steering effort requirements, necessitate a high assist force. Meeting these demands with EPS often requires a larger motor, which poses packaging challenges. Consequently, most large SUVs utilize hydraulic-assisted power steering systems, which employ a hydraulic pump and fluid lines to assist the steering mechanism. However, hydraulic systems can only deliver torque in one direction, and they are generally more complex and less efficient compared to EPS. In this paper, we present a novel methodology to analyze and improve steering returnability performance. This approach includes mathematical modeling, Computer-Aided Engineering (CAE) simulations, friction analysis, and targeted design modifications. The proposed methodology is validated through physical testing at the vehicle level to ensure compliance with returnability targets.