bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electric-hydrostatic drive—an innovative energy-saving power and motion control system
Authors: Helduser S 
Published: October 2002

The paper describes investigations of an electric-hydrostatic drive system, its components and its application in the clamp of a plastics injection moulding machine. The aim of the research work was to reveal the potential advantages and challenges of the new direct pump control concept as well as the suitability of hydraulic pumps for variable-speed operation. Measurements of component efficiency have proven that hydraulic components have very good efficiency compared with variable-speed electric motors. Therefore, the total efficiency of the electric-hydrostatic drive at a high load (close to corner power) cannot be expected to be noticeably better than the conventional drive system comprising an asynchronous electric motor and variable-displacement hydraulic pump, although fixed-displacement pumps can have better efficiency than variable-displacement pumps have. Improvements may be seen at part-load. The major advantages of the new motor-pump concept are reduction in power losses and noise during part-load and during idling. This was demonstrated in a test cycle. The design of hydraulic pumps applied in an electric-hydrostatic drive has to be carefully evaluated for suitability. Some piston pumps and internal gear pumps without gap compensation seem to work well under the specific load conditions of variable-speed drives, but not all units worked sufficiently during endurance testing. Owing to the high overload capability of rare earth electric motors, the dynamic performance of the electric-hydrostatic drive can be compared with that of many standard variable-displacement pumps. This was evaluated with performance tests of the clamp unit of a plastics injection moulding machine. The dry cycle time (Euromap 6 standard) achieved (1.8 s for a machine with a 1600 kN clamping force) proved the excellent controllability of the electric-hydrostatic drive and the high dynamic performance capability. The combination of a speed-controlled a. c. servomotor and fixed-displacement pump increases the number of direct pump control concepts that a hydraulic project engineer can apply to design competitive hydraulic systems for customer applications.
Multigrid techniques: A fast and efficient method for the numerical simulation of elastohydrodynamically lubricated point contact problems
Authors: Venner C. H. , Lubrecht A. A. 
Published: October 2002

The introduction and further development of algorithms based on multigrid (multilevel) techniques has resulted in fast and efficient solvers for elastohydrodynamically lubricated (EHL) point contact problems. As a result the capability to simulate steady state and transient point contact problems numerically has greatly increased in the past decade. This has led to an increased understanding of the mechanisms controlling film formation and pressure in the contact in relation to the operating conditions. In this article an overview is given of the essential ingredients of an efficient multigrid algorithm for an EHL point contact problem. Results are presented for some characteristic problems that illustrate today's numerical simulation capability. It is concluded that, with respect to EHL, one of the main questions of the last part of the century has been answered, i.e. how to solve efficiently the modelling equations such that realistic and highly loaded situations can be simulated. The challenge that researchers and engineers now face is how to translate the new insights into simple rules for design and engineering, and to establish clearly the limits of validity of the models that are used in simulations both on the scale of the contact as a whole as well as on a subcontact scale.
Grease soap particles passing through an elastohydrodynamic contact under side slip conditions
Authors: Eriksson P , Wikström V , Larsson R 
Published: October 2002

In a previous investigation, grease thickener fibres were tracked as they passed through an elastohydrodynamic (EHD) contact in pure rolling using interferometry in a standard ball-and-disc apparatus. In order to capture single thickener fibres, a high-speed video camera was used. Here, the experiments have been repeated introducing different amounts of side slip for different rolling speeds and a faster video camera capable of capturing 4500 frames/s. The contact was lubricated with a continuous supply of grease. Two greases, based on the same synthetic poly(α-olefin) but thickened with Li-12-OH and lithium complex soap respectively, were studied. It was observed that the thickener fibres were stretched both before entering the contact and as they passed through it. Fibres seem to avoid the minimum film thickness regions and, if they enter, the film is restored immediately after passage.
Lubricant thermal conductivity and heat capacity under high pressure
Authors: Larsson R , Andersson O 
Published: October 2002

The thermal conductivity λ and the heat capacity per unit volume, ρ c p, have been measured for a number of common lubricating oils. The oils tested were paraffinic and naphthenic mineral oils and a 50/50 blend of these. Poly-α-olefin, polyglycol, Santotrac, ester and rapeseed oils have also been tested. The measurements, using the transient hot-wire method, were carried out under isothermal conditions over a pressure range from atmospheric to 1.1 GPa and at two temperatures, 295 and 380K (22 and 107 °C respectively). The temperature had only a marginal effect on thermal conductivity; however, the thermal conductivity was doubled as the pressure was increased to 1 GPa. The heat capacity per unit volume was influenced by both the pressure and the temperature. Some of the lubricants solidified as the pressure increased and the transition from a fluid to a solid state could be detected in the measurements of ρ c p. The relationship between the thermodynamic properties and the pressure and temperature are described by two empirical equations. These equations can be used in thermal elastohydrodynamic analyses.
Investigation of the ball-bearing temperature rise under an oil-air lubrication system
Authors: Jeng Y-R , Gao C-C 
Published: October 2002

Ball-bearings are widely used on many high-speed rotating systems. However, heat generation and dynamic loading caused by high-speed operation have been the limiting factors for increasing the speed limit of many high-speed ball-bearing applications. Therefore, providing proper lubrication and preload to reduce heat generation effectively is a major task for high-speed ball-bearings. Recently, oil-air lubrication has been used on high-speed ball-bearings because of precise oil quantity control and high cooling efficiency. However, the fluctuation in oil supply resulting from the periodic oil feeding is unfavourable. In this study, equipment for measuring the fluctuation in the oil supply was established. The operation parameters affecting the stability of the oil supply for an oil-air lubrication system were experimentally studied. A test rig for high-speed ball-bearings was also developed. Tests were conducted to study the effects of the preload, oil quantity, air flowrate and rotating speed on the bearing temperature rise. The operating conditions that provide a stable oil supply and low bearing temperature rise were established.
Design functions for hydrodynamic bearings
Authors: Ståhl J , Jacobson B. O. 
Published: October 2002

Designing hydrodynamic bearings usually requires a total numerical analysis of the pressure distribution and corresponding design quantities such as the load capacity, load position, oil flowrate, power loss, coefficient of friction and relative power loss. Another option is to determine the design quantities from design diagrams, which may give rise to inaccurate results, especially if interpolation between the curves is needed. Instead, it would have been better to have functions describing the design quantities. The objective of this work is to determine curve-fitted functions describing each design quantity, by following a well-defined procedure. Three different kinds of geometry are analysed: rectangular tilting-pad thrust bearings, sector-shaped tilting-pad thrust bearings and journal bearings with two axial oil grooves. In addition, an optimum analysis is performed. The approximate design functions obtained in this work show very good resemblance to the numerically calculated results, and they are valid for a wide range of the geometric parameters. The intention is to use the functions in programmable pocket calculators or implemented short computer programs, making them a very fast and accurate alternative to a complete numerical analysis in bearing design. Finally, the functions concerning the optimum analysis saves a large amount of time compared with a traditional analysis.
Analysis of grease lubrication of a ball bearing using acoustic emission measurement
Authors: Miettinen J , Andersson P , Wikströ V 
Published: October 2002

The behaviour of grease lubrication in a rolling bearing is less known than that of oil in the same type of tribological system. In recent years the research of grease lubrication has shown several features of the grease lubrication that differ from the classical elastohydrodynamic lubrication theory of oil lubrication, notably that starvation is more prominent under grease-lubricated conditions. The goal of the present investigation was to clarify, by using a real bearing installation and realistic running conditions, how the fundamental properties of the lubricating grease influence the lubrication in a rolling bearing. The fundamental properties of the greases considered in the study were thickener concentration, base oil viscosity, base oil bleeding rate and consistency. Results obtained with grease lubrication were verified with pure oil lubrication. The analysis of grease lubrication in the present investigation is based on the relative differences in the pulse count rate of the acoustic emission (AE) generated by the running of the bearing. In order to make the correct decisions about the lubrication situation of a bearing, the fundamentals of the behaviour of grease lubrication in rolling bearings and its influence on the AE signal have to be known. Moreover, AE has proven to be a good tool to study grease lubrication in situ in a bearing. The results show that starvation of the lubrication situation increases with increasing thickener content and decreases with lowered base oil viscosity. This is in agreement with film thickness measurements made in ball-and-disc type equipment.
Application of analysis of variance to wet clutch engagement
Authors: Mansouri M , Khonsari M. M. , Holgerson M. H. , Aung W 
Published: October 2002

Factorial design is applied to a wet clutch in automatic transmission in order to study and predict the effects of operating conditions on its engagement. The analysis relies on a series of experimental measurements and computer simulations to compute process responses. Included in the simulations are the drive torque, friction coefficient, system inertia, applied load, engagement time, developed energy, maximum brake torque, maximum power requirement and maximum temperature rise. Analysis of variance (ANOVA) is performed to quantify realistically the main and interaction effects of the system parameters on process responses. ANOVA results are effectively compiled into charts complemented with prediction models, which could be used as a valuable tool to facilitate learning for a novice trainee and to allow a designer to evaluate quickly and effectively the effects of operating conditions on, and prediction of, performance parameters. The scope of this analysis tool, as applied to wet-clutch engagement, is not limited to operating conditions and could be extended to include materials selection, and to explore ideas not yet fully tested.
Dynamic behaviour of elastic engine main bearings: Theory and measurements
Authors: Moreau H , Maspeyrot P , Chomat-Delalex A. M. , Bonneau D , Frene J 
Published: October 2002

The design of crankshaft bearings is carried out with software using many assumptions on the geometrical and operating bearing parameters. The calculation results are thus more or less close to reality according to the assumptions used. In order to know the level of accuracy of the theoretical results, it is necessary to compare these results with those obtained by experimentation. This paper describes the experimental measurements and the theoretical calculations of oil-film thickness in a dynamically loaded crankshaft main bearing. Four eddy current gap sensors for each bearing are used to measure the oil-film thickness and to deduce the shaft trajectories. The elastohydrodynamic model considers the bearings, housing and crankshaft elastic deformations. The calculation process uses the finite element method and the Newton-Raphson method for the numerical analysis. Comparisons of the load effects and crankshaft speed are made between the experiment and the theory.
The design of lubricious oil-in-water emulsions
Authors: Ratoi-Salagean M , Spikes H , Hoogendoorn R 
Published: October 2002

Oil-in-water emulsions, as used in metal working and fire-resistant hydraulic fluids, often show poor lubricating performance and one reason for this is their inability to form effective elastohydrodynamic films. This paper considers how the composition of an oil-in-water emulsion contributes to its lubricating properties. A key factor in oil-in-water emulsion performance lies in the ability of the dispersed oil droplets to wet polar metal surfaces and thus promote full elastohydrodynamic lubrication, without starvation, up to high speeds. In this paper it is shown how this ability can be quantified in terms of measurable surface chemical parameters. Based on this work, three rules for designing lubricious oil-in-water emulsions are proposed. Where possible (a) the emulsifier concentration used should be just below its critical micelle concentration value, (b) the base oil should be polar and (c) the base oil should be viscous. The first two of these factors will promote oil-phase surface wetting while the third will ensure thick-film formation in the full elastohydrodynamic regime.
Sliding wear and friction of Si3N4-SiC-based ceramic composites containing hexagonal boron nitride
Authors: Westergård R , Åhlin A , Axén N , Hogmark S 
Published: October 2002

The friction and wear behaviour of a series of new Si3N4-SiC-based ceramic composites, intended for face seal applications, has been investigated with cylinder-on-disc equipment. In particular, the influence of water and vapour on the friction, wear and tribo-film formation has been studied. The ceramics consisted of Sis3N4 and SiC in the proportions 7:3, to which 0, 4 or 8 wt% of hexagonal boron nitride was added as a solid lubricant. All specimens were produced by hot isostatic pressing. X-ray diffraction and scanning electron microscopy were used to reveal the phase composition and microstructure respectively. The hardness was assessed using Vickers indentation. The chemical composition of the tribo-films was studied with X-ray photoelectron spectroscopy. The major results are that both friction and wear showed distinct low and high levels. The high friction level corresponded to friction coefficients between 0.4 and 0.9 and wear rates between 104 and 105 μm3/Nm. The low level corresponded to friction coefficients between 0.02 and 0.1, and wear rates between 10 and 103 μm3/Nm. When water or saturated vapour was present in the tribo-system, both friction and wear were low. All surfaces produced in the low level were smooth, covered by a thin well-adhering tribo-film while the high level resulted in strongly oxidized and patchy tribo-film covered by wear particles.
Computational fluid dynamics modelling of non-premixed combustion in direct injection diesel engines
Authors: Barths H , Hasse C , Peters N 
Published: October 2002

An overview over flamelet modelling for turbulent non-premixed combustion is given. A short review of previous contributions to simulations of direct injection (DI) diesel engine combustion using the representative interactive flamelet concept is presented. A surrogate fuel consisting of 70 per cent (liquid volume) n-decane and 30 per cent α-methyl-naphthalene is experimentally compared to real diesel fuel. The resemblance of their physical and chemical properties is shown to result in very similar combustion and pollutant formation for both fuels. In order to account for variations of the scalar dissipation rate within the computational domain, a method using multiple flamelets, called the Eulerian particle flamelet model, is used. A strategy is described for subdividing the computational domain and assigning the resulting subdomains to different flamelet histories represented by Eulerian marker particles. Experiments conducted with an Audi DI diesel engine and diesel fuel are compared to simulations using the surrogate fuel. The use of multiple flamelets, each having a different history, significantly improves the description of the ignition phase, leading to a better prediction of pressure, heat release and exhaust emissions of soot and NOx. The effect of the number of flamelet particles on the predictions is discussed.
The internal flow of diesel fuel injector nozzles: A review
Authors: Schmidt D. P. , Corradini M. L. 
Published: October 2002

Diesel fuel injector nozzles have a significant effect on the quality of spray and charge preparation. However, the mechanism and degree of this effect is unclear. The complexity of the internal nozzle flow has hindered the study of the fuel injection process. Diesel fuel injector nozzle flows are highly turbulent and usually two-phase. Several experiments have shown the presence of cavitation in the nozzles to be a dominating effect. Recent experimental work has revealed new qualitative details about the cavitation in fuel injector nozzles. The cavity tends to be smooth near the inlet, transitioning to a more ruffled appearance downstream. These flows are also strongly asymmetric in realistic geometries. Additionally, photographs have shown string cavitation inside the sac volume extending into the nozzles. The strings appear to be a form of stratified two-phase flow, like the cavities near the inlet corner. Like the cavities, the strings break down into bubbly flow near the exit of the nozzle. Future experiments in this field should address the exact nature of the two-phase flow at the exit. In spite of these difficulties, useful models for the flow in fuel injector nozzles have been developed. Analytical models work very well for the steady state behaviour of axisymmetric nozzles. Multi-dimensional models have proved to be useful for more general geometries and attempt to predict transient behaviour. There is currently no consensus on the basic physics behind the multi-dimensional models. Despite this controversy, there are several models available that have succeeded in predicting gross cavitation behaviour. The implications of the recent experimental investigations are that future cavitation models should include the ability to simulate more than one kind of cavitation. Typically, a model assumes that the cavitation is either a smooth cavity or a bubbly mixture. In general, the ideal cavitation model must capture either kind of behaviour.
Evaluation of temporal and spatial distribution of nanometric particles in a diesel engine by broadband optical techniques
Authors: Corcione F E , Merola S S , Vaglieco B M 
Published: October 2002

In the last few years, there has been an increasing concern about the emissions of ultrafine particles in the atmosphere. A detailed study of the formation and oxidation of these particles in the environment of the diesel engine cylinder presents many experimental difficulties due to the high temperatures, pressures and extremely reactive intermediate species. To allow investigation of the different phases of the diesel combustion process, high temporal and spatial resolution optical techniques were applied in the optically accessible chamber of a diesel engine at fixed engine speed and air-fuel ratio. Simultaneous extinction, scattering and flame chemiluminescence measurements from the ultraviolet to the visible region were carried out in order to study the diesel combustion process from the soot inception to the formation of soot particles, through the growth of their precursors. These species were characterized as carbonaceous nanometric structures and their sizes were evaluated by the Mie theory.
Polymerization of t-Butyl Vinyl Ether Mediated by an Aluminum Lewis Acid–TrF System and Its Complex Structure–Tacticity Correlation
Authors: Oishi Masataka , Yamamoto Hisashi 
Published: October 2002

Abstract
A variety of aluminum (aryloxide)s were used with triphenylmethyl fluoride (TrF) initiator for the isoselective cationic polymerization of t-butyl vinyl ether. This contribution discusses the relationship between polymer tacticity and counteranion structure, which changed according to the bulkiness, strength and chirality of the Lewis acid combined with TrF so as to make the ionic pair more interactive in the polymerization process. Newly developed organoaluminum activators, 15 and 22, showed mm = 55–57%, which is a more than 10% increase in mm compared with achiral aluminum compounds.
Simultaneous Removal of NO and N2O over Pd-ZSM-5 Catalysts and FT-IR Observations of their Decomposition Routes to N2
Authors: Izumi Yasuo , Kizaki Tetsuro , Aika Ken-ichi 
Published: October 2002

Abstract
Simultaneous removal of nitrogen monoxide and dinitrogen oxide with propene was investigated over Pd-H-ZSM-5 catalysts. Results were compared with reports of simultaneous removal of NO and N2O in the presence of O2 over Co-ZSM-5 and Fe-MFI. The N2O conversion was suppressed in the presence of NO, and the simultaneous removal rates were essentially the same as the NO conversion rates over Co-ZSM-5 and Fe-MFI. In contrast, the simultaneous removal in the presence of O2 was found to be accelerated over Pd-H-ZSM-5 and conventional Pd/SiO2 compared to the sum of the corresponding individual removal rates of NO and N2O. An intense FT-IR peak of NO±0 ligated to the Pd cation inside the ZSM-5 cage was observed at 1868 cm−1 in the promoted simultaneous removal reactions. Under the conditions for the individual removal of NO or N2O and the unpromoted simultaneous removal of NO + N2O, only a weak peak at 1842 cm−1 was observed. The oxygen atom that dissociates from N2O should be the key to promoted catalysis in the coexistence of NO and N2O in order to maintain the Pd cation site clear. The oxygen controls the concentration of surface carbonaceous species to effectively decompose NO, and so as not to inhibit the NO activation.
Supplement to ‘Third‐order transport due to internal waves and non‐local turbulence in the stably stratified surface layer’
Authors: Soomere Tarmo , Zilitinkevich Sergej S. 
Published: October 2002

AbstractA linear theory of internal gravity waves (IGWs) is applied to consider the IGW‐induced vertical fluxes of kinetic energy, pressure and squared density (or buoyancy) in non‐turbulent stably stratified fluid characterized by the Brunt–Väisälä frequency, N. These fluxes are required in modelling distant links and non‐local transports in the atmosphere. Investigations of the vertical flux of kinetic energy have shown that this flux, caused by the wave component performing the most efficient vertical transport, is proportional to N3. As far as the authors know, the flux of the squared density fluctuations was not systematically investigated. It is shown to be proportional to N5. Copyright © 2002 Royal Meteorological Society.