Increasing the Reliability of the Ball-Screw Hydraulic Power Steering with an Axial Drive Structure

The purpose of this article is to improve the performance and reliability of ball-screw hydraulic power steering systems (BSHPS), which are widely used in heavy vehicles, buses, and construction machinery. Despite decades of operational success, classical designs of BSHPS have remained largely unchanged since the 1980s and still exhibit technical drawbacks. The main problem addressed is the occurrence of a tipping moment on the piston, caused by the misalignment between the rack transmission plane and the line of action of the hydraulic force resultant. This misalignment leads to excessive wear and a reduction in the efficiency of the steering mechanism. The aim of this study is to develop a new BSHPS design in which the piston and screw axes are aligned to eliminate this drawback and increase the system's efficiency. The research is based on the principles of theoretical mechanics, materials resistance theory, and hydraulic drive theory. A comprehensive program was developed, including the analysis of load distribution in conventional BSHPS designs, mathematical modeling of efficiency with respect to all frictional resistance forces, and a comparative evaluation of mechanical efficiency losses due to the tipping moment. The proposed design introduces modifications to the gear teeth of the rack and sector, allowing for the installation of the screw axis within the initial plane of the rack transmission. This structural improvement eliminates the misalignment of the piston and screw, thereby reducing parasitic friction forces. Analytical derivations confirmed that this design results in decreased sliding friction, minimized wear, and improved energy transmission efficiency. The load diagrams and derived equations support a quantitative assessment of performance gains over conventional systems. The key outcome of the research is the elimination of the tipping moment, which reduces the wear of piston and housing surfaces and increases the efficiency of the steering mechanism by 5.9%. This is achieved through the axial alignment of the piston and screw within the rack transmission plane. Furthermore, the design ensures lower friction losses and higher durability. The proposed groove geometry in the rack and sector gears minimizes the contact area and ensures reduced contact stress. These improvements collectively contribute to increased operational reliability and longer service life of the steering system.