Electro-Hydraulic Variable-Speed Drive Networks—Idea, Perspectives, and Energy Saving Potentials

Electro-hydraulic differential cylinder drives with variable-speed displacement units as their central transmission element are subject to an increasing focus in both industry and academia. A main reason is the potential for substantial efficiency increases due to avoidance of throttling of the main flows. Research contributions have mainly been focusing on appropriate compensation of volume asymmetry and the development of standalone self-contained and compact solutions, with all necessary functions onboard. However, as many hydraulic actuator systems encompass multiple cylinders, such approaches may not be the most feasible ones with respect to efficiency or commercial feasibility. This article presents the idea of multi-cylinder drives, characterized by electrically and hydraulically interconnected variable-speed displacement units essentially allowing for completely avoiding throttle elements, while allowing for hydraulic and electric power sharing as well as the sharing of auxiliary functions and fluid reservoir. With drive topologies taking offset in communication theory, the concept of electro-hydraulic variable-speed drive networks is introduced. Three different drive networks are designed for an example application, including component sizing and controls in order to demonstrate their potentials. It is found that such drive networks may provide simple physical designs with few building blocks and increased energy efficiencies compared to standalone drives, while exhibiting excellent dynamic properties and control performance

Elderly Hospitalized Home-Patients in the Cross-Sectoral Team Care at North Zealand Hospital’s Emergency Department

Background: With an increasing- and an increasingly aging population, the elderly morbidity burden is growing. This raises the question of how we can effectively respond to this health-care challenge in a hospital setting where more patients are both old and comorbid. Consequently, North Zealand Hospital’s (NOH’s) Emergency Department (E.D.) has launched a pilot project that explores the value of having a cross-sectoral team (CST) to specifically manage old (65+ y.o.), complexly ill, and vulnerable patients on a hospital-at-home (HaH) basis. The purpose of this study was to classify and categorize the CST’s elderly HAH patients (not formally discharged from NOH’s E.D. but receive home visits by the E.D.’s HaH nurses). Methods: Data regarding the HaH CST-patients at NOH were prospectively gathered during February 2021. Microsoft Excel software was then used to categorize and analyze the data. Numeric data are given as means ± SEM.Results: There were 227 HaH CST-interventions. Of these, 186 (81.9%) were elderly patients. The number of unique HaH elderly CST-patients (uHaHe-CSTps) was 108 (56 male and 52 female) aged 81 ± 0.8 years. The uHaHe-CSTps were categorized into age groups as following: 10 (65-69 y.o.), 18 (70-70 y.o.), 20 (75-79 y.o.), 17 (80-84 y.o.), 27 (85-89 y.o.), 13 (90-94 y.o.), 3 (95-97 y.o.). Of the uHaHe-CSTps, 93% were multimorbid, 82% had polypharmacy, 33.3% were readmitted patients within 2 weeks after ended HaH CST-intervention, and 4.6% died while in HaH CST-care. Conclusion: NOH’s E.D. has vulnerable, elderly, and complexly ill patients who may benefit from the medical care of the CST’s HaH function. Furthermore, the HaH CST assists NOH’s E.D. and the municipality by taking care of issues that can be handled effectively at the patient's home

Data based root cause analysis for improving logistic key performance indicators of a company's internal supply chain

The manufacturing industry faces an increasingly complex and dynamic environment due to shorter product life cycles, advanced production structures and expanding customer services. It is imperative that logistic key performance indicators (KPIs) be considered along with product costs and product quality to obtain a competitive advantage. Numerous companies possess an internal supply chain that fails to meet logistic performance goals set by the management. The measurables for logistic performance include logistic KPIs such as delivery time as well as cost relevant figures including work-in-process or the utilization of employees. In a case of unsatisfactory logistic KPIs, it is pertinent to identify the root causes before attempting to rectify the situation. Increasing digitalization within industry means a substantial volume of confirmation data is available regarding the core processes of a company's internal supply chain. This study discloses a model-based analysis of confirmation data to identify the root causes of unsatisfactory logistic KPIs. A framework for the analysis is constructed by defining generic cause-and-effect relationships between the relevant logistic KPIs and influencing as well as disturbing factors. The results produced by the model-based analysis and the interpretation of the confirmation data show the occurring cause-and-effect relationships for particular use cases and deduce the root causes for insufficient logistic KPIs. From there, companies can develop and implement suitable steps to increase the logistic KPIs by focusing on the newly-identified root causes instead of non-related, but recurring, complications. A case study is included to show the practicality of the presented method. The root cause analysis provides the basis for advanced logistics controlling systems to automatically identify weak-points and propose counteractive measures and therefore continuously improve and adapt the supply chain to changing conditions

A Self-Contained Cylinder Drive with Indirectly Controlled Hydraulic Lock

This paper presents a self-contained pump-controlled hydraulic linear drive including an innovative load holding sub-circuit. For safety critical applications such as crane manipulators, locking valves or load holding valves are enforced by legislation, but the load holding functionality may also be used actively to decrease the energy consumption for applications where the load is kept stationary for longer periods of time. The system proposed in this paper is based on a simple hydraulic architecture using two variable-speed electric motors each connected to a fixed-displacement pump. This architecture is well-known in academic literature, but in this paper a novel load holding sub-circuit has been included. To control this load holding functionality, the low chamber pressure needs to be controlled accurately, while still being able to control the motion of the cylinder piston as well. Due to strong cross-couplings between cylinder piston motion and chamber pressures this task is non-trivial. The control for opening the locking valves is indirect in the sense that it is controlled via the chamber pressures, which are actively controlled. The fundamental control strategy presented in this paper is based on transforming the highly coupled physical states to virtual states, significantly reducing cross-couplings.publishedVersio

Energy Saving Potential in Knuckle Boom Cranes using a Novel Pump Controlled Cylinder Drive

This paper is considering the application of a novel pump controlled cylinder drive, the so-called Speed-variable Switched Differential Pump (SvSDP), for knuckle boom crane actuation. Especially the control system for the SvSDP drive is considered, and aiming on improving energy efficiency a refinement of the existing control structure is proposed. An energy efficient sizing algorithm for the SvSDP drive is developed, and fundamental differences between the achievable operating range for the SvSDP drive compared to a conventional valve-cylinder drive are discussed. A case study is conducted with knuckle boom crane actuation, and compared to a conventional valve actuation. Simulation results show that the motion tracking performance is on a similar level compared to the valve actuation approach, while the energy consumption is drastically decreased. For the given test trajectory the valve actuation system consumes 0.79 kWh of electrical energy, while the SvSDP drive consume 0.06 kWh, if ideal energy recovery and storage is assumed

Bootstrap reservoir concepts for electro-hydraulic compact cylinder drives

This paper presents a conceptual study aiming to improve the compactness of electro-hydraulic compact drives (ECD ). In most current ECD architectures, gas accumulators are used as volume compensators for the flow imbalance emerging whenever asymmetric single rod cylinders are used. To stay within a required reservoir pressure range typically from two to four bar, a large gas volume is required, compromising system compactness. Combining conventional ECD architectures with a bootstrap reservoir offers a greater degree of freedom in system design, which enables downsizing or avoidance of the gas volume. Another potential benefit by including a bootstrap reservoir is the possibility of elevating the backpressure of the ECD thus enhancing drive stiffness, expanding the application range and market acceptance. Based on an open analysis of the solution space occurring when introducing a bootstrap reservoir, three system architectures are selected for a conceptual study. The results show that the downsizing potential is strongly dependent on the maximum friction force and the area ratio of the bootstrap reservoir pistons, while a linear analysis reveals that for some system architectures the bootstrap reservoir may severely influence the system dynamics. Simulation results confirm the functionality of the proposed system architectures, and show that a potential for downsizing/avoiding the gas volume, as well as increasing the ECD stiffness is present

Alcohols as a Means to Inhibit the Formation of Precipitates in Blends of Biodiesel and Fossil Diesel Fuel

The European diesel fuel specification limits the biodiesel content to 7 %. It is, however, desirable to increase the amount of renewables in the transport sector; therefore blending with a higher biogenic fuel content is of interest. Blending of fuels can lead to chemical reactions between fuel components and may result in undesired products. In detail, aged biodiesel from unsaturated FAME and fossil diesel fuels can form oligomers and precipitations with a maximum in the range of B10 to B20. Precursors are oligomers that can be separated from the biodiesel or the blends in an amount of up to 20 %. These oligomers seem to have potency for chemical reactions with fuel components or the engine oil. To prevent tentative problems in the fuel filter, the injecting system and the combustion process itself, the formation of oligomers should be disabled in blends. Alcohols have been proven and tested to dis-solve precipitations in the fuel. However, flash point problems occur, in case the alcohols have too low boiling points. In our tests, some alcohols could be identified to reach the demands of the diesel fuel standard EN 590. As acceptable monovalent alcohols, the longer-chained alcohols 1-octanol, 3-methyl-1-butanol (isoamyl alcohol) and 2-hexyldecan-1-ol were found. The blends with these alcohols both showed acceptable flashpoints according to DIN EN 590 and could prevent the occurrence of precipi-tates when added in a rather low concentration of about 6 to 8 %. Additionally, engine tests were carried out to monitor regulated and non-regulated emissions. The emissions of selected blends (B10+6OctOH, B10+8IsoamylOH, B10+8HexdecOH) were analyzed by using a single cylinder test engine (Farymann Diesel 18W, TIER 4, agricultural 5-mode test). All of these blends showed less NOx emissions than the pure B10 blend without addition of alcohol. For the CO, HC and PM emissions, no remarkable changes could be found. In the case of non-regulated emis-sions, no relevant changes were observed in carbonyl and PAH emissions, relative to the B10 blend without addition of alcohol. In the result, some blends from biodiesel, diesel fuel and alcohols tend to be appropriate to suppress chemical reactions in the fuel and probably in the engine oil. Further research is necessary to explain the chemical interactions that are responsible for the formation of oligomers and their reaction products. Not only chemical but physical bonds can play important roles and are in the focus of current research

Energy Efficient Excavator Functions Based on Electro-hydraulic Variable-speed Drive Network

Electrification of mobile working machines is subject to increasing focus in both industry andacademia. At this stage, focus has been the replacement of conventional internal combustion engineswith cable or battery fed electric motors driving the main pump(s), and the replacement of rotaryfunctions with electro-mechanical drive solutions. However, the linear functions remain controlledby hydraulic control valves resulting in substantial throttle losses, which in turn necessitates largebattery sizes and/or low machine uptimes. Alternatively, the valve-controlled hydraulic cylinders maybe replaced with electro-mechanical solutions in applications with limited forces, whereas heavy dutyworking machines such as medium/large excavators may benefit from standalone electro-hydraulicprimary controlled drives, i.e., variable-speed standalone drives. The use of such solutions willsubstantially increase efficiency due to the absent/limited throttle control and the ability to sharepower through the electric supply/DC-bus. A main drawback is that each axis needs to be designedto meet both the maximum force and maximum speed, hence in the case of using single motorstandalone drives, each motor and associated inverter needs to be designed to meet both the maximumforce and maximum speed, potentially rendering these somewhat large. Alternatively, dual motorstandalone drives can be applied, enabling power distribution via more motors. However, the use ofnumerous motors requires more extensive system integration and potentially large motor powerinstallations considering industrially available non-specialized components. This paper presents anovel so-called electro-hydraulic variable-speed drive network, applied for actuation of three linearfunctions of an excavator implement. Cylinder chamber short-circuiting’s and electro-hydraulicvariable-speed units constitute a drive network allowing both electric and hydraulic power sharing.The drive network is realized with Bosch Rexroth A2 displacement units and eLION electric motorsas its core components. Results demonstrate that the proposed drive network is realizable with similarenergy efficiency as a standalone dual motor electro-hydraulic drive solution, but with less motorpower and with fewer motors, displacement units and integration effort, rendering this a moresustainable and cost-efficient solution. Finally, it is shown that the proposed drive network is superiorin terms of installed displacement, electric motor power and energy efficiency, compared to a separatemetering valve drive supplied by a battery fed electro-hydraulic pump