No abstract

In this dissertation, energy efficient hydraulic systems are studied. The research focuses on solutions for linear actuators in mobile applications, with emphasis on construction machines. Alongside the aspect of energy efficiency, the thesis deals with competing aspects in hydraulic system design found in the development of construction machines. Simulation models and controls for different concepts are developed, taking the whole machine into account. In line with this work, several proof of concept demonstrators are developed. In the thesis three main system topologies are covered:First, pump controlled systems are studied and a novel concept based on an open-circuit pump configuration is conceived. Special consideration is paid to multi-mode capabilities that allow for a broadened operating range and potential downsizing of components. Simulation models and controls are developed and the system is experimentally validated in a wheel loader application.Second, the possibility for energy recuperation in valve-controlled systems is investigated. In such solutions, a hydraulic motor, added to the meter-out port, is used for energy recovery during load lowering and in multi-function operation. Recuperated energy is either used momentarily or stored in a hydraulic accumulator. The proposed solution means an incremental improvement to conventional systems, which is sometimes attractive to machine manufacturers due to fewer uncertainties in reliability, safety and development cost. The energy recovery system is studied on a conceptual level where several alternative systems are proposed and a concept based on a two-machine hydraulic transformer is selected for a deeper control study followed by experimental validation.Third, so-called common pressure rail systems are considered. This technique is well established for rotary drives, at least for the industrial sector. However, in applying this technique to mobile hydraulics, feasible solutions for linear actuators are needed. In this dissertation, two approaches to this problem are presented. The first one focuses on hydraulic pressure transformers and the second one on secondary controlled multi-chamber cylinders. i ii Populärvetenskaplig sammanfattningHuvudtemat för denna avhandling är energieffektivisering av hydraulsystem. Forskningen rör främst linjära rörelsesystem inom mobila tillämpningar, med fokus på anläggningsmaskiner. Avhandlingen berör åtskilliga aspekter av systemdesign, där simulering och styrning av dynamiska system samt helfordonsmodellering är återkommande inslag. Ett led i forskningsstudien har varit att bygga in och utvärdera framtagna koncept genom fullskaliga demonstratorer. Ett flertal nya hydraulsystem har studerats inom tre huvudsakliga inriktningar: En första inriktning är mot så kallade pumpstyrda system, där ett nytt koncept baserat på pumpar anslutna i en öppen krets har utvecklats. Inom detta har smart reglering av ventiler visat sig vara central för att uppnå en hög energieffektivitet över ett brett arbetsområde. Konceptet vali...

No abstract

No abstract

This paper outlines an extended analysis on how multi-chamber actuators can improve the efficiency of valve-controlled systems. Resistive control is a major source of energy losses in valve-controlled systems that share the same pump to drive multiple loads. By combining different chambers, the load on multi-chamber actuators can be transformed into different pressure and flow rate levels. This allows the adaptation of its load to the loads on other actuators. This can lead to a reduction of resistive control energy losses that occur between pump and actuators when driven simultaneously. As a case study to highlight how the system efficiency can be improved, a load sensing system with a conventional and a multi-chamber actuator is analysed. The equations that describe the system steady state behaviour are presented to evaluate the effect of the load transformations on the system efficiency. A disadvantage of such architecture is the fact that load transformations result in different actuator speeds. To reduce this effect, a compensation factor for the command signal to the proportional valve is presented. The highlight from this paper is the potential for efficiency improvement enabled by the adoption of multi-chamber actuators in a valve-controlled architecture. Further research is required for the selection of number of chambers and their areas since they directly affect the system efficiency.