Energy efficiency has become a major research issue in all fields of engineering. Opportunities of utilizing electric servo drives in the control of hydraulic lifting systems directly by an ...electric-servomotor-driven hydraulic machine and enabling energy recovery in them are studied. In this paper, the modelling and testing of an electro-hydraulic lifting and lowering system and a forklift with two lifting zones are carried out and analyzed. The efficiencies and energy-saving ratios of the experimental drive system are determined for the free lift and the second lift zones of a modified industrial forklift with different speeds and payloads. The maximum achieved energy-saving value in the Potential Energy Recovery System (PERS) was 50% for a maximum tested payload of 1000kg and a maximum fork velocity of 0.5m/s for the second lift zone. The efficiencies and energy consumptions of the experimental drive system and its components are determined.
► Differences between the two different lift zones of the forklift were analyzed. ► The maximum achieved energy-saving value was 50% for the second lift zone. ► In the free lift zone, the energy-saving ratio varies from 0 to 36%. ► The test results favored the second lift zone from the energy-saving point of view. ► The test shows that the direct electric pump drive system has numerous advantages.
Energy efficient pulse-width modulation inverters are widely used to control electrical machines accurately for process needs. The pulse-width modulation, however, has also adverse effects and ...produces additional losses in the motor. These losses increase the motor temperature and result in derating of the machine power in converter use. A reliable and reasonably accurate loss model of an induction motor drive system is important for the performance prediction of a variable-speed drive. A two-level frequency converter main circuit model is coupled to a finite-element method motor model. The drive model is controlled by closed-loop direct torque control. The frequency converter losses are calculated analytically, and the finite-element method motor model provides an analysis of the motor losses. The simulation results are compared with measurement results.
Powertrain electrification continues to be a growing trend in vehicular applications. Electric powertrains have numerous advantages over traditional mechanical and hydraulic powertrains but there are ...still important challenges to overcome for long-term commercial success. This research presents a technological assessment of present and future developments of powertrain electrification in non-road mobile machinery (NRMM). The challenges and opportunities of NRMM electrification are described in detail. The trends and drivers related to technological development such as regulations, policies and market development are analyzed, and technology enablers are highlighted. Future scenarios are formulated based on the prevailing trends and drivers, development of key components, scientific literature and status of the non-road mobile machinery industry. Some recommendations are also given in relation to the development of hybrid and electric powertrains for NRMM. The key findings of this research indicate that the electrification of NRMM is slowly started and the progress is demonstrated by hybridization of some specific, successful mobile machines. In short-term, high component and technology development costs remain the main barrier for higher adoption of electric and hybrid powertrains. In the long-term scenario, many NRMM can operate autonomously and powertrain electrification has become mainstream technology.
The energy efficiency of an electro-hydraulic forklift is significantly improved by using a permanent-magnet-synchronous-motor-servo-drive-based direct pump control to control the position of the ...fork without control valves. This paper provides a short evaluation of the hydraulic system and a more detailed analysis of the losses of the electric machine drive system. A theoretical approach is taken and the results are verified by practical measurements. Finally, possible improvements of the energy efficiency in the suggested system are discussed.
Effective heat transfer and protection against high operating temperatures are important, lifetime-affecting items in the design and operation of batteries, especially those intended for hybrid ...mobile working machines, where the peak power and current demands are high. This paper describes a methodology for the modeling of the electrical and thermal behavior of lithium ion pouch cells for hybrid mobile working machines. The model is produced by coupling the equivalent electrical circuit of the pouch cell and the 3-D pouch cell thermal model. The temperature dependence of the battery operation parameters is added to the model in order to analyze the influence of temperature on heat generation during battery operation. Determination of the parameters of the thermal model is carried out empirically based on the presented methodology, which allows the construction of a 3-D thermal model of a pouch cell without requiring detailed information about the battery chemistry. The validity of the modeling procedure is demonstrated experimentally for a 60 Ah lithium titanate pouch cell.
This article proposes a simple method to calculate a current vector trajectory for the enhanced operation of the electric power generation system based on a synchronous reluctance machine (SynRM). ...Owing to magnetic saturation and cross magnetization, the performance and the torque capability of a SynRM vary according to the position and the value of the stator current. State-of-the-art control methods usually assume parameters with constant values, especially the inductance, neglecting saturation, leading to possible uncertainty in the machine operation. Therefore, a current vector trajectory to operate this type of machine, as a generator, in an extended speed range, with enhanced performance and considering magnetic saturation is proposed. A straightforward algorithm based on the inductance characteristic of the machine is used to calculate the trajectory of the stator current vector. This trajectory is evaluated via the numerical simulation of an experimentally validated finite-element model of a SynRM. The results show that the proposed current vector trajectory can improve the torque capability to 5% concerning the estimated trajectory without considering saturation. Experimental results are also provided to demonstrate the enhanced operation of the generator.
The energy efficiency of non-road mobile machinery can be improved by using e.g., an electric drive system as a servo controller of a hydraulic machine to get an efficient electro-hydraulic (EH) ...converter. However, the cooling of EH devices require more understanding and new innovations. This work presents a design of a 7-kW integrated EH machine and studies its electric motor heat transfer phenomena both experimentally and numerically. Further, to better match the torque and speed performances of the permanent magnet synchronous motor (PMSM) and the hydraulic machine a planetary step-down gear is utilized to triple the output torque of the PMSM. The integrated motor and gear system is then connected to a bent axis piston hydraulic machine, which is capable of operating both as a motor and a pump. Two different electric motor cooling approaches are investigated. The first cooling approach is to use some hydraulic oil inside the motor-gear chamber to let it flow freely as a result of the rotor rotation and move the losses to the surface of the converter cover, which is equipped with some air cooling fins. In the second approach, the oil flows through the converter and removes the losses more effectively. Motor losses and thermal behaviour are studied within these two cooling approaches. Computational fluid dynamic (CFD) simulations are performed to find how the coolant is distributed inside the machine and how heat is distributed in the device.
Novel high power density integrated electro-hydraulic machine for electrical hybrid working vehicles is presented. The machine is dedicated to be used as a mechanical power source for hydraulic ...actuators with possibility of electrical energy recuperation. Advantages of using such a machine in mobile environments are discussed. The efficiency of the device is studied and compared with the traditional valve controlled systems.
Hybridization of heavy off-highway working vehicles brings considerable energy savings in the form of a downsized internal combustion engine (ICE) by means of reduced no-load losses. In this paper, a ...novel energy saving opportunity in working hydraulics at the end of long booms of working vehicles is proposed. In traditional off-highway working vehicles, the working hydraulics is supplied through pipes, hoses, and valves by a hydraulic pump located near the main engine. A significant amount of energy is lost in long pipelines and hoses as well as in valve throttles. A new topology is introduced to supply the power along the long boom; the power for a hydraulic actuator is supplied by an integrated electro-hydraulic energy converter (IEHEC), which is located at the boom end. The electrical energy to the converter is supplied through electrical cables, which have negligible losses compared with a conventional fluid power supply with long pipelines. The converter transforms the electrical energy into hydraulic energy at the end of the boom, and may also recover energy for additional energy savings.
•Novel component for energy saving in long boom working vehicles is proposed.•Energy saving achieved by using an integrated electro-hydraulic energy converter•Energy saving up to 53% in comparison with conventional fluid power system•The total efficiency of the original system is only 29% and new system reaches 62% efficiency.
In this paper, electric and hydraulic regeneration methods of recovering potential energy from an electro-hydraulic forklift truck are studied. Two similar forklift setups equipped with either ...electric or direct hydraulic energy storage are compared. In the first setup, the forklift lifting system is controlled directly with an electric servomotor drive. The servomotor drives a hydraulic pump capable of also operating as a hydraulic motor during lowering motion. In the second setup, the hydraulically operated forklift is equipped with an energy recovery system consisting of pressure accumulators for storing energy and a hydraulic digital valve package for precise leakage free flow control. This paper describes the arrangements of the experimental setups. The results of the proposed systems are then compared from the energy efficiency point of view. Energy-savings ratios for electric and hydraulic test systems were calculated for different fork velocities and payloads. Keywords: digital flow control unit, electric energy recovery, energy storage, forklift, hydraulic energy recovery, hydraulics, lead-acid battery, hydraulic accumulator, permanent magnet synchronous machine, reach truck, supercapacitor Cilj predstavljenega dela je analiza moznosti za regeneracijo energije pri elektrohidravlicnih vilicarjih. Namen studije je primerjava energijskega izkoristka elektricnih in neposrednih hidravlicnih sistemov za shranjevanje energije. Clanek preucuje metode elektricne in hidravlicne regeneracije shranjene potencialne energije pri elektrohidravlicnem vilicarju. Podana je primerjava dveh podobnih vilicarjev, opremljenih z elektricnim oz. neposrednim hidravlicnim sistemom za shranjevanje energije. Prvi vilicar ima elektricni servomotorni pogon za dviganje. Servomotor poganja hidravlicno crpalko, ki lahko med spuscanjem deluje tudi kot hidromotor. Drugi vilicar ima hidravlicni sistem za shranjevanje energije s tlacnimi akumulatorji in blok digitalnih hidravlicnih ventilov z natancnim krmiljenjem pretoka brez uhajanja. Z meritvami je bilo dokazano, da je mozna regeneracija potencialne energije pri sistemih s hidravlicnim in elektricnim shranjevanjem energije. Preucen je sistem za shranjevanje energije in podana je teoreticna analiza izkoriscanja energije pri elektrohidravlicnem vilicarju. Clanek opisuje pripravo eksperimenta in primerjavo rezultatov dveh sistemov z vidika energijske ucinkovitosti. Izracunan je tudi delez prihranjene energije za elektricni in hidravlicni testni sistem pri razlicnih hitrostih vilic in obremenitvah. Rezultati kazejo, da je najvecji 45-odstotni prihranek energije v obmocju prostega dviganja dosezen pri optimiziranih tlacnih akumulatorjih z neposrednim hidravlicnim shranjevanjem energije. V praksi pa se pri neposrednem sistemu pojavlja tezava zaradi potrebe po nadzorovanju tlaka predobremenitve hidravlicnega akumulatorja ali zahteve po izbiri fiksne vrednosti tlaka predobremenitve, zato so realne povprecne vrednosti lahko tudi precej manjse. Najvecji delez prihranjene energije pri elektricnem vilicarju je bil 36%. Prihranek razocara v primerjavi z rezultati za isti vilicar v obmocju delovanja drugega cilindra. Avtorji so skusali zagotoviti podobne delovne pogoje za dva nekoliko razlicna regalna vilicarja. Najenostavnejsa resitev ob upostevanju omejitev in podobnosti obeh sistemov je bila z izvedbo preskusov v obmocju prostega dviga in z dodatno omejitvijo hoda na 1,6 m. Razmeroma kratek gib prinasa nekaj odstotkov prednosti pri prihranku za hidravlicni sistem, saj je bila kapaciteta hidravlicnega akumulatorja pri preskusu omejena na 16 litrov. Z izbiro obmocja prostega dviga namesto obmocja drugega cilindra se je zmanjsal dosegljivi prihranek energije za oba sistema. Za manjso rabo energije stroja je treba bodisi izboljsati ucinkovitost komponent ali pa z regeneracijo izkoristiti energijo, ki bi se sicer izgubila v procesu. V zadnjem primeru je pogosto mozno ponovno uporabiti kineticno oz. potencialno energijo stroja ali njegovega podsistema. Odvisno od sistema in procesa lahko shranjevanje energije prinese pomembno skupno zmanjsanje rabe energije in daljsi cas delovanja mobilnih strojev. V clanku je zato podana primerjava neposrednega hidravlicnega in elektricnega sistema za shranjevanje energije. Neposredni hidravlicni sistem za shranjevanje energije odpravlja potrebo po pretvorbi energije iz hidravlicne v elektricno obliko v fazi shranjevanja in obratno v fazi regeneracije. Raziskava je sicer izpostavila hidravlicni sistem shranjevanja pri testnih vilicarjih, kljub temu pa ima tudi elektricni pogonski sistem stevilne prednosti. Ne zahteva namrec predobremenjevanja in uravnavanja shranjevanja energije za doloceno breme ali dvizno visino. Pristop z neposrednim hidravlicnim shranjevanjem energije zato ni prakticen tam, kjer so bremena razlicnih tez in se premikajo na razlicne visine. V tem primeru ima prednost elektricni ali posredni sistem za hidravlicno shranjevanje energije. Kljucne besede: Elektricna regeneracija energije, shranjevanje energije, vilicar, hidravlicna regeneracija energije, hidravlika, svincevo-kislinski akumulator, indukcijski motor (IM), hidravlicni akumulator, sinhronski motor s trajnimi magneti (PMSM), regalni vilicar
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