Safety related development of an electro-hydraulic active steering system

Research Task/Objectives

Increasing demand for driving comfort and reduced burden of the operator require the use of electro-hydraulic steering systems in construction and agricultural machines.
Comparable steering systems, which are currently available, already offer the advantages of semi and fully automated driver-assisted systems, but are limited to off-road use only. The reason is a  potentially dangerous behavior in case of system failure. The implementation of the active steering system with separate meter-in and meter-out valves shall maintain benefits of currently available systems and  additionally enable steering and comfort functions for on-road use. This is possible through a compensation of individual failures inside the extended valve structure.

Approach/Results

Based on an extensive risk assessment, corresponding to DIN EN ISO 12100, the development of the steering system has to consider aspects of functional safety (DIN 13849/ EN ISO 25119). The design of an integral safety and control concept is the goal of this consideration. Therefore, safety functions are defined and  measures for fault detection and fault  reaction are taken. For testing the safety related control concept, a three-stage validation is realized: using a simulation model, a test rig and a demonstration vehicle, which is operating under real environmental conditions. By means of the extensive validation, potentials and limits of the analyzed concept can be shown.

Supported by the European Union with funds from the European Regional Development Fund (ERDF) (V-630-1-309-2013/245).