Pressure Control in Hydraulic Power Steering Systems

Abstract

There is a clear trend in the vehicle industry to implement more safetyrelated functions, where the focus is on active safety systems and today the steering system is also involved. Steering-related active safety functions can only be realised with a steering system that allows electronic control of either the road wheel angle or the torque required to steer the vehicle, called active steering. The high power requirement of heavy vehicles means they must rely on hydraulic power to assist the driver. The system is a pure hydro-mechanical system with an open-centre circuit activated by the driver's steering action and suffers from poor energy efficiency. The main task of the hydraulic system is to control the pressure in the assistance cylinder in such a way that it eases the load on the driver.This work suggests a way to design and evaluate a self-regulating pressure control valve for use as actuator in the steering system. This valve can be made small and fast and is electronically controlled to enable active steering. It is based on a closed-centre circuit and has therefore the potential to improve energy efficiency. The aim of this work has been to investigate the possibility for the valve to perform as the original open-centre valve. The suggested approach is a model-based design and evaluation process where an optimisation routine is used to design the valve. Together with a validated model of the steering system, the new concept is compared with the original system. A hardware-inthe-loop simulation test rig has also been designed and built with the possibility to test a closed-centre steering system. It has partly been used to support the modelling process and partly to verify that a closedcentre steering system is a feasible solution. The simulation results have shown that the designed valve can perform sufficiently well compared to the original system.

Review of the Progress of Energy Saving of Hydraulic Control Systems

“…By collecting real-time steering wheel torque and hydraulic cylinder pressure signals during the steering process to control the opening and closing of the hydraulic valve, the overflow loss that existed during the steering process was eliminated and the throttling loss was reduced. Compared with traditional steering systems, the energy loss was reduced by 2.3 times, improving the machine's productivity by 22.6%; not only does it reduce the energy consumption of the steering system, but it also improves the stability during the steering process [56,57]. Zhao et al [58] proposed a valve-controlled hydraulic energysaving system based on a hydraulic transformer to address the problem of low energy utilization efficiency in the valve-controlled hydraulic system of hydraulic excavators and studied its energy-saving effect.…”

A contribution to the theoretical-experimental investigation of transverse vibrations of the controlling lever of a commercial motor vehicle

“…It should be noted that transfer functions depend on a large number of design parameters, the values of which are unknown because they are often protected by patents. Since the aforementioned transfer functions are described in detail in [13][14][15][16][17], it will not be done here.…”

Modeling, Simulation, and Experimental Investigation of an Electrohydraulic Closed-Center Power Steering System

“…1. Parameters needed for the model, such as friction levels and stiffness, are measured on the test rig, as described in [33], where also intial parts of the modelling procedure is presented.…”