Mechanical Power Losses Research Articles

Piston dynamics, lubrication and tribological performance evaluation: A review

Mechanical power loss of lubricated and bearing surfaces serves as an attractive domain for study and research in the field of internal combustion engines. Friction reduction at lubricated and bearing surface is one of the most cost-effective ways to reduce gas emission and improve internal combustion engines’ efficiency. This thus motivates automotive industries and researchers to investigate tribological performance of internal combustion engines. Piston secondary motion has prime importance in internal combustion engines and occurs due to unbalanced forces and moments in a plane normal to the wrist pin axis. Consequently, piston executes small translations and rotations within the defined clearance during the piston reciprocating motion. Mechanical friction power loss and lubrication at piston skirt/liner and radiated engine noise are dramatically affected by piston secondary dynamics. The lubrication mechanism, piston secondary motion and tribological performance are affected by piston design parameters (piston/liner clearance, wrist pin offset, skirt profile, etc.), lubricant rheology, oil transport mechanism and operating conditions. Therefore, this review is devoted to summarize the synthesis of main technical aspects, research efforts, conclusions and challenges that must be highlighted regarding piston skirt/liner lubrication and piston dynamics and slap.

Experimental and Numerical Investigation on Windage Power Losses in High Speed Gears

Enhancing the efficiency of gearing systems is an important topic for the development of future aero-engines with low specific fuel consumption. An evaluation of its structure and performance is mandatory in order to optimize the design as well as maximize its efficiency. Mechanical power losses are usually distinguished into two main categories: load-dependent and load-independent losses. The former are all those associated with the transmission of torque, while the latter are tied to the fluid dynamics of the environment, which surrounds the gears. The relative magnitude of these phenomena is dependent on the operative conditions of the transmission: load-dependent losses are predominant at slow speeds and high torque conditions, load-independent mechanisms become prevailing in high speed applications, like in turbomachinery. A new test rig was designed for investigating windage power losses resulting by a single spur gear rotating in a free oil environment. The test rig allows the gear to rotate at high speed within a box where pressure and temperature conditions can be set and monitored. An electric spindle, which drives the system, is connected to the gear through a high accuracy torque meter, equipped with a speedometer providing the rotating velocity. The test box is fitted with optical accesses in order to perform particle image velocimetry (PIV) measurements for investigating the flow field surrounding the rotating gear. The experiment has been computationally replicated, performing Reynolds-averaged Navier–Stokes (RANS) simulations in the context of conventional eddy viscosity models, achieving good agreement for all of the speed of rotations.

평행축 기어트레인을 갖는 변속기의 마찰 및 쳐닝 동력 손실 예측

평행축 기어트레인을 갖는 변속기의 마찰 및 쳐닝 동력 손실 예측

Efficiency of application of direct-drive circuit for improvement of starting characteristics of gas turbine engine

The effectiveness of measures to improve the starting characteristics of gas turbine engines (GTE) is considered. To improve the reliability of the GTE launch, it is proposed to use the so-called gearless GTE scheme, created for a “more electric aircraft”, which uses an integrated high-speed starter generator and electric drive units for fuel, oil and other life support of gas turbine engines. With the help of a nonlinear dynamic mathematical startup model, the effect of the magnitude of the given moment of inertia of the rotor on the starting characteristics of the gas turbine engine is evaluated. Change it in the direction of reduction was carried out by replacing the gearbox with attachments to one unit a high-speed starter-generator, installed coaxially with the rotor. Determination of the value of the given moment of inertia of the rotor, aggregates, bearings was carried out using the developed 3-DCAD-models. In the mathematical model of start-up, the thermal state of the oil system, the mechanical power losses for rotating aggregates, bearings, gears are taken into account. The quantitative dependence of the starting characteristics on the moment of inertia of the GTE rotor and other factors is established. For comparison of the basic APU and APU of the direct-drive circuit simulation of the start in the most stressful operating conditions P H = 101,3 kPa at low negative temperatures t H = -40 °C and under normal conditions P H = 101,3 kPa and t H = +15 °C, for “cold” and “hot” state of the engine before starting was made. The tendencies of the moment of inertia of the rotors of the executed and newly created GTE are analyzed. It is shown that the gearless APU in comparison with the basic APU due to the reduction of the moment of inertia by 9,68 % and the reduction of the oil pumped volume in the oil system has a significant improvement in the launch characteristics under ground launch conditions ( P H = 101,3 kPa).

Power Loss and Thermal Analysis of a MW High-Speed Permanent Magnet Synchronous Machine

High-speed permanent magnet synchronous machines (PMSMs) have attracted much attention due to their high power density, high efficiency, and compact size for direct-drive applications. However, the consequent power loss density is high, and hence heat dissipation is a major technical challenge. This is particularly the case for high-speed operation. In this paper, a MW level high-speed PMSM is designed and its electromagnetic and mechanical power losses comprehensively investigated using finite element analysis. The transient machine demagnetization performance is studied, and a composite rotor structure is proposed to improve machine antidemagnetization capability. The temperature distribution of the proposed high-speed PMSM is also analyzed using a fluid-thermal coupling method with calculated power loss. Experiments conducted on a prototype of the high-speed PMSM demonstrate the effectiveness of the numerical models developed and validate the results obtained.

해석적 접근을 통한 기어 마찰 동력 손실 예측 및 최소화

해석적 접근을 통한 기어 마찰 동력 손실 예측 및 최소화

A mixed finite element and analytical method to predict load, mechanical power loss and improved efficiency in non-standard spur gear drives

A reasonably accurate estimation of gear power loss is desirable to maximize gear performance. The load share by teeth pair, contact stress, sliding speed, elastohydrodynamic film thickness and coefficient of friction are some of the most important contributing factors which determine frictional power losses in gears. This paper presents an improvement concept to minimize the load-related power losses (sliding and rolling power losses), which will lead to an enhancement in gear efficiency by selection of non-standard gears. The tooth thickness at the pitch circle of the pinion and gear is different in non-standard gears (kpπm > 0.5 πm and kgπm < 0.5 πm), whereas it is equal in standard gears (kpπm = kgπm = 0.5 πm). In this work, the load share-based frictional power loss and the respective mechanical efficiency have been determined for comparative performance of standard and non-standard gears. Finally, the influence of various gear and drive parameters such as gear ratio, pressure angle pinion teeth number and addendum height factor on gear efficiency has also been investigated and the results of the parametric study are discussed.

Modelling of steady-state mechanical power losses in planetary gear trains of automatic transmissions

Modelling of steady-state mechanical power losses in planetary gear trains of automatic transmissions

INFLUENCE OF LUBRICANT TEMPERATURE, TORQUE AND ROTATIONAL SPEED ON THE LOSS MECHANISMS IN A TWO-SPEED AUTOMATIC TRANSMISSION

The efficiency of the transmission system is of great significance to the overall efficiency of electric vehicles. However, many of energy losses are incurred during power transmission. Thus, it is much more demanding to increase the efficiency pertaining to the transmission system of electric vehicles, and this is also why computational models are required to predict friction-related mechanical dynamic efficiency. Individual power losses from gear meshes are analyzed in the efficiency model with bearing losses and oil churning to determine the total mechanical power losses of the transmission. Experimental work has been undertaken to investigate the load losses at a range of lubricant temperatures. This paper will discuss the observation from the experimental work, in particular the influence of many operating conditions like lubricant temperature torque and the rational speed on the individual loss mechanisms. Comprehensive comparisons are conducted on the experimental results and the computational ones in order to demonstrate the feasibility and superiority the proposed power loss prediction model.

Development and Validation of an Automotive Axle Power Loss Model

ABSTRACTThis study proposes a methodology to predict power losses of automotive axle units, including both load-dependent (mechanical) and load-independent (spin) loss components. This methodology combines a mechanical hypoid gear mesh power loss model, a new tapered roller bearing mechanical power loss model, a gear drag loss model, and empirical viscous bearing power loss formulae to determine the total power loss of an axle unit. The proposed methodology captures the effects of operating conditions (speed and torque and oil temperature and level), contact surface roughness amplitudes, as well as bearing preload on power loss. The model is employed to simulate published axle efficiency experiments. Direct comparisons between measured and predicted power losses are presented to demonstrate the accuracy of the proposed modeling methodology.

A semi-empirical method for assessing the performance of an open-drive screw refrigeration compressor

A semi-empirical modeling procedure for twin-screw compressor performance simulation is proposed in this paper. In detail, the compression process is split into a number of stages, taking into account fluid leakages, heat transfers as well as heat and power losses. Compared to the simplified models reported in technical literature for other positive-displacement units, a different formulation for ambient heat loss is proposed, while mechanical power losses are modeled according to torque losses depending on both load and viscous friction effects. The proposed model applies to open-drive compressors, so three specific units for refrigeration applications with medium-high evaporation temperature are selected as the test cases for model tuning and validation, based on manufacturer's catalog data. After the identification of eight parameters, the model is able to compute the mass flow rate, the shaft power and the fluid discharge temperature, as well as volumetric and compressor efficiencies and ambient heat losses.Contrary to geometric models, the semi-empirical procedure proposed in this study does not take the presence of lubricating oil into account, as (i) oil injection with no external cooling results in a thermal neutral process; (ii) the compression work for the oil is negligible in comparison with the one required by the refrigerant fluid; and (iii) even injecting oil at a lower temperature, no considerable saving in refrigerant specific work can be achieved. Actually, this hypothesis does not significantly affect the output of the model. As a matter of fact, referring to the first test case with the larger displacement volume and to the identification of the eight model parameters based on eight convenient data points, the mass flow rate delivered by the compressor is predicted with a maximum error up to 2.44%, and the shaft power is predicted with an even limited error, except for few points with the lowest and highest pressure ratios, where the shaft power is under-estimated by 5%. Moreover, fluid temperature at the compressor exhaust is calculated with an error within ±1 K for pressure ratios up to 7.5. Similarly interesting results are achieved for the other two test case compressors, with absolute values of the errors in mass flow rate and shaft power predictions always less than 3% and 5% respectively.Finally, further considerations on the actual possibility of generalizing the model to semi-hermetic units are suggested.

Mechanical power losses of full-complement needle bearings of planetary gear sets: Model and experiments

Full-complement (loose) needle bearings are used widely in automatic transmissions as planetary gear set planet bearings due to their cost advantages and high load-carrying capacity. This study provides theoretical and experimental investigations of the efficiency performance of full-complement needle bearings in a planetary gear set. An experimental setup is introduced to measure planetary gear set power losses. A number of full-complement needle bearing variations as well as a baseline caged needle bearing arrangement are tested within ranges of speed, torque, and oil temperature as well as key bearing parameters such as needle diameter and number of needle rows. A mechanical power loss model of full-complement needle bearings is proposed next. The model employs an elastohydrodynamic lubrication formulation for rolling power losses and includes the effects of needle skewing and needle-to-needle sliding. Predicted mechanical power losses are compared to measurements to assess the accuracy of the model. Results indicate that (i) full-complement needle bearings are consistently less efficient than the corresponding caged-needle baseline design, and (ii) double-row bearings have higher efficiency than their single-row counterparts, while the influence of the needle diameter on power loss is somewhat secondary.

A thermal tribo-dynamic mechanical power loss model for spur gear Pairs

This study proposes a formulation for the description of the gear mesh mechanical power loss under the thermal tribo-dynamic condition. A six degree-of-freedom motion equation set and the thermal mixed elastohydrodynamic lubrication governing equations are coupled to model the mechanical power loss under the condition where the gear dynamics and tribology disciplines interact. The important role of the gear thermal tribo-dynamics in power loss is demonstrated by comparing the predictions of the proposed model to those under the thermal quasi-static condition, and those under the iso-thermal tribo-dynamic condition. Considering an example spur gear pair, the impacts of the lubricant inlet temperature, input torque, and surface roughness on gear mesh mechanical power loss under the thermal tribo-dynamic condition are also investigated.

Axial piston pumps slippers with nanocoated surfaces to reduce friction

This paper shows the experimental results obtained using a nanocoating (developed by ISTEC-C.N.R.) applied to the slippers of an axial piston pump to reduce the friction losses in order to improve the pump overall efficiency map. It is well known that the mechanical power losses in a hydraulic pump come from the friction between parts in relative motion. The need to provide, especially at low rotational speed, hydrodynamic lift causes power losses in terms of volumetric and mechanical efficiency, due to the contrasting need to increase leakage to provide lubrication and to keep a minimum clearance in meatus to limit the volumetric losses. The application of special surface treatments have been exploited in pioneering works in the past, trying different surface finishing or adding ceramic or heterogeneous metallic layers, but the potential of structured coatings at nanoscale, with superhydrophobic and oleophobic characteristics, has never been exploited. Using a dedicated test rig developed at IMAMOTER-C.N.R., able to ensure hydrostatic working condition during the mutual rotation between the slippers and the swash plate, the functional performance of the nanocoated slippers’ surface have been studied. In the first part of the paper, the functionalization method is presented; in the second part, a comparison between the experimental performances of coated and uncoated surfaces is showed.

Resistive Power Loss Analysis of PV Modules Made From Halved 15.6 × 15.6 cm2 Silicon PERC Solar Cells With Efficiencies up to 20.0%

In photovoltaic (PV) modules, the interconnection of solar cells is critical in terms of mechanical stability and resistive power losses. In this study, we analyze the interconnection of large-area 15.6 × 15.6 cm 2 industrial p-type passivated emitter and rear cell (PERC) solar cells in terms of resistive losses. For our analysis, we prepare a 3 × 3 minimodule from PERC solar cells with soldering pads and efficiencies up to 20.0%. We measure a significant cell-to-module (CTM) power loss of 8% at this module. For comparison, we prepare a 3 × 6 module consisting of halved 7.8 × 15.6 cm 2 PERC solar cells. Using a nanosecond laser to cut the finished solar cell in two pieces, no additional power loss is introduced by cutting. The CTM factor of 1.0 determined at the 3 × 6 module is explained using an analytical model describing the series resistance of the module interconnection. Using this model, we estimate for our current PERC cell generation and module process an output power of 275 W for 60 full-size cells and 285 W for 120 halved cells.

Analysis on Transmission Efficiency of Planetary Gear Reducer

A transmission efficiency calculation model of planetary geared reducer was proposed in this paper. The power losses of meshed surfaces of sun-planet gears and planet-ring gears were analyzed in detail. Finally, the mechanical power losses and transmission efficiency of the planetary gear reducer were simulated to illustrate the influence of rotational speed and torque on mechanical power loss and transmission efficiency.

A Tridimensional CFD Analysis of the Oil Pump of an High Performance Motorbike Engine

The main target of nowadays engine designers is to focus on exhaust emissions, fuel consumption and engine performance, so during the design phase of a new internal combustion engine, all the aspects related to friction and mechanical power loss must be deeply considered. And then, also the friction related to engine lubrication system must be analyzed and studied.In this paper a tridimensional CFD analysis of the lubrication circuit oil pump of a modern high-performance engine manufactured by Aprilia will be shown. The model was build up with PumpLinx®, a commercial CFD 3D code by Simerics Inc.®, taking into account all the phenomena associated to the fluid cavitation. The model was validated by data of an experimental campaign performed on a hydraulic test bench, at the Industrial Engineering Department of the University of Naples, Federico II.

Design of a New Medium-temperature Stirling Engine for Distributed Cogeneration Applications

This paper presents and discusses the design and first prototype realization for a brand new generation of Stirling engines. This unit is realized within the DiGeSPo Project, in which it is coupled with a small-size parabolic trough concentration solar field. The engine is conceived for working with low-temperature heat sources (200-300̊C), in order to match the typical temperatures for the solar field itself.The first part presents the thermodynamic design, which is realized by using models and simulations, and give the specifications for each component, including pistons dimensions; the number, length, diameter for the heat exchangers tubes; regenerators porosity, length and diameter. Four independent and equally working spaces were chosen, as a compromise between the compactness of the overall system, limits imposed by the maximum charging pressure, and the target electrical power (3kW). The parameters of the overall system were optimized during this phase with an iterative procedure, taking into account different concurrent constraints, such as the heat exchange requirements, mechanical friction power losses, and small dead spaces. The engine has been subsequently arranged in a double-acting mechanical configuration, in which the cylinders are opposed as in a boxer engine. This configuration gives the advantages of reducing leaking losses and can work with four pistons. The heat exchangers, which are the most crucial and complex components, have been realized by the Selective Laser Melting (SLM) manufacturing technique.The specific scientific and technical details related to a low-temperature Stirling engine, and the solutions adopted, are discussed and presented trough the paper, and finals recommendations are provided.

Prediction of Mechanical Power Loss of Planet Gear Roller Bearings Under Combined Radial and Moment Loading

A modeling methodology is proposed to predict load-dependent (mechanical) power loss of cylindrical roller bearings under combined radial and moment loading with focus on planetary gear set planet bearings. This methodology relies on two models. The first model is a bearing load distribution model to predict load intensities along rolling element contacts due to combined force–moment loading. This model takes into account planet bearing macrogeometry as well as micromodifications to the roller and race surfaces. The second model is an elastohydrodynamic lubrication (EHL) model employed to predict rolling power losses of bearing contacts with load intensities predicted by the load distribution model. The bearing mechanical power loss methodology is applied to bearings of an automotive planetary gear set to quantify the sensitivity of mechanical power loss to key bearing, lubrication and surface parameters as well as operating speed, load and temperature conditions.

An Analytical Approach to Maximum Power Tracking and Loss Minimization of a Doubly Fed Induction Generator Considering Core Loss

To get maximum output power from a doubly fed induction generator (DFIG), it is essential to extract maximum mechanical power from the wind turbine and to minimize generator losses. The goal of maximum power tracking and minimum loss is usually achieved through vector control of rotor current. In other words, the d-axis and q-axis rotor currents I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dr</sub> and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">qr</sub> must be properly controlled as wind speed changes with time. In this paper, an analytical approach is developed to determine proper rotor current commands I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dr</sub> * and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">qr</sub> * which give maximum mechanical power and minimum loss based on the measured generator speed. The proposed analytical approach is more efficient than the exhaustive search approach proposed in a previous study and is, therefore, more suitable for real-time performance improvements. In addition, core loss component, which was usually neglected in previous studies, is included in the DFIG model in order to have more accurate results. The effectiveness of the derived analytical formulas is demonstrated by an example.