Abstract
Hydraulic steering systems for mechanical devices, for example, manipulators or vehicle steering systems, should be able to achieve high positioning precision with high energy efficiency. However, this condition is very often not met in practical applications. This is usually due to the stiffness of the hydraulic system being too low. As a result, additional corrections are required to achieve the required positioning precision. Unfortunately, this means additional energy losses in the hydraulic control system. In this study, this problem is presented using the example of a hydraulic steering system for an articulated frame steer vehicle. This hydraulic steering system should provide the required directional stability for road traffic safety reasons. So far, this issue, connected mainly with the harmful phenomenon of so-called vehicle snaking behaviour, has not been solved sufficiently practically. To meet the needs of industrial practice, taking into account the current global state of knowledge and technology, Wrocław University of Science and Technology is performing comprehensive experimental and computational studies on the snaking behaviour of an articulated frame steer wheeled commercial vehicle. The results of these tests and analyses showed that the main cause of problems that lead to the snaking behaviour of this vehicle class is the effective torsional stiffness of the hydraulic steering system. For this reason, a novel mathematical model of the effective torsional stiffness was developed and validated. This model comprehensively took into account all important mechanical and hydraulic factors that affect the stiffness of a hydraulic system, resulting in the examined snaking behaviour. Because of this, it is possible at the design stage to select the optimal parameters of the hydraulic steering system to minimise any adverse influence on the snaking behaviour of articulated frame steer wheeled vehicles. This leads to minimising the number of required corrections and minimising energy losses in this hydraulic steering system. The innovative model presented in the article can be used to optimise positioning accuracy, for example, in manipulators and any mechanical system with hydraulic steering of any system of any mechanical parts.
Highlights
The calculations based on the model, as presented above, confirmed that at a constant oil volume, a linear increase in effective torsional stiffness ks with an increase in the surface area of the hydraulic cylinder (Figure 17)
The calculations showed that an increase in the capacitance c of the hydraulic steering system and an increase in the undissolved air content Ein the oil were accompanied by a significant decrease in effective torsional stiffness ks (Figure 18)
Based on the experimental and simulation studies, it was shown that the stiffness of the steering system played a very significant role on the directional stability and energy demand of the steering system
Summary
The first publications in the field of AFSWV’s snaking behaviour [17] include a mathematical model of an AFSWV with three degrees of freedom, with which the authors presented a steering hydraulic system as an equivalent torsion spring with dampening In this model, some important parameters affecting the stiffness of this mechanism were omitted, namely, nonlinear elasticity parameters of hydraulic hoses and nonlinear dependence between modulus of elasticity of the liquid and its gas content. As well as in other subsequent publications [18,19,20,21,22], it was shown that the main causes of the AFSWV’s snaking behaviour are low stiffness and dampening of the steering system; mass distribution and inertia of the members of the vehicle; dynamic properties of the vehicle’s tyres; front-, rear-, or all-wheel drive; and the speed of the vehicle. The design of the internal tank strongly influences the air release process
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