Friction Power Loss Research Articles

Frictional power losses on spur gears with tip reliefs. The friction coefficient role

In this proposal, the effect of the friction coefficient on the efficiency of spur gears with tip reliefs was analysed. For this purpose, the efficiency values using an average friction coefficient along the mesh cycle were compared with those obtained implementing an enhanced friction coefficient formulation, which is based on elastohydrodynamic lubrication fundamentals. In this manner, it can be established the differences between both formulations in the efficiency and friction coefficient values, as well as the advantages of using this enhanced friction coefficient with respect to formulations implemented in traditional approaches of efficiency calculation. In addition to studying the impact of the friction coefficient choice on efficiency, the profile modifications influence on the friction coefficient and efficiency was also assessed. In this regard, three tip relief case studies were set out; pinion tip reliefs, driven wheel tip reliefs and profile modifications in both gears. From the results, it was inferred that the choice of friction coefficient formulation clearly influences the efficiency in gear transmissions with tip reliefs, obtaining discrepancies between both formulations with regard to which tip relief case study provides the lowest efficiency values.

An integrated model for the performance of piston ring pack in internal combustion engines

Piston rings are important components in internal combustion engines. Their primary function is to seal dynamically the gap between moving piston and cylinder liner surface in order to prevent the combustion gases from penetrating into the crankcase. The rings also control the oil leakage from the crankcase to the combustion chamber. The performance of the piston ring pack impacts the engine efficiency, durability and emissions. The recognition of the impact of the ring-pack performance on the engine design resulted in a sustained effort of research and development aimed at understanding the operation of the piston ring pack. Most of the published models developed in this field are two-dimensional assuming that the ring and liner are perfect circles for the purpose of modelling the axial and radial dynamics. Although this approach has proved to be useful, there exist a number of asymmetrical characteristics of the power cylinder system that can be crucial to the ring-pack performance and therefore it is considered to be appropriate. In this work, an integrated methodology that handles the complex ring-pack mechanism is presented. The physics of the ring-pack mechanism covers the three-dimensional piston ring dynamics of asymmetric engine cylinder due to bore distortion, the mixed lubrication at ring running face as well as the ring flanks and the interring gas dynamics. The modelling method is verified in two steps. In the first step, the dynamic behaviour of the three-dimensional ring model is verified against a commercial finite element software by comparing the eigenmodes up to a frequency of about 1 kHz. In the second step, the ring-pack modelling approach using three-dimensional ring models is also verified against a commercial ring dynamics program, which is based on the two-dimensional modelling. It is shown that the three-dimensional ring dynamics modelling method has advantages over the two-dimensional modelling approach as it facilitates studying the influence of the non-uniform twist along its circumference (ring winding), the effect of bore distortion on blow-by, ring friction, friction power losses and wear.

Coefficient of friction and wear rate effects of different composite nanolubricant concentrations on Aluminium 2024 plate

Wear of sliding parts and operational machine consistency enhancement can be avoided with good lubrication. Lubrication reduce wear between two contacting and sliding surfaces and decrease the frictional power losses in compressor. The coefficient of friction and wear rate effects study were carried out to measure the friction and anti-wear abilities of Al2O3-SiO2 composite nanolubricants a new type of compressor lubricant to enhanced the compressor performances. The tribology test rig employing reciprocating test conditions to replicate a piston ring contact in the compressor was used to measure the coefficient of friction and wear rate. Coefficient of friction and wear rate effects of different Al2O3-SiO2/PAG composite nanolubricants of Aluminium 2024 plate for 10-kg load at different speed were investigated. Al2O3 and SiO2 nanoparticles were dispersed in the Polyalkylene Glycol (PAG 46) lubricant using two-steps method of preparation. The result shows that the coefficient friction and wear rate of composite nanolubricants decreased compared to pure lubricant. The maximum reduction achievement for friction of coefficient and wear rate by Al2O3-SiO2 composite nanolubricants by 4.78% and 12.96% with 0.06% volume concentration. Therefore, 0.06% volume concentration is selected as the most enhanced composite nanolubricants with effective coefficient of friction and wear rate reduction compared to other volume concentrations. Thus, it is recommended to be used as the compressor lubrication to enhanced compressor performances.

A new coupling tribodynamic model of crosshead slipper-guide system and piston skirt-liner system of low-speed marine diesel engines

In this paper, considering the coupling effects of the crosshead slipper-guide system and the piston skirt-liner system, a new tribodynamic model is established for the low-speed two-stroke marine diesel engine. Firstly, a dynamic model including the crosshead slipper, the piston, the piston rod, and the crosshead pin is proposed. Then, considering the disciplinary coupling between the dynamic model and the lubrication models, the stiff and nonlinear tribodynamic model is solved with the modified extended backward differentiation formulae (MEBDF). Finally the tribodynamic performances of the crosshead slipper and the piston skirt are analyzed. The simulation results show that the crosshead slipper bears the thrust force and its friction power loss is obviously larger than that of the piston skirt.

Comprehensive model of a hermetic reciprocating compressor

A comprehensive simulation model is presented to predict the performance of a hermetic reciprocating compressor and to reveal the underlying mechanisms when the compressor is running. The presented model is composed of sub-models simulating the in-cylinder compression process, piston ring/journal bearing frictional power loss, single phase induction motor and the overall compressor energy balance among different compressor components. The valve model, leakage through piston ring model and in-cylinder heat transfer model are also incorporated into the in-cylinder compression process model. A numerical algorithm solving the model is introduced. The predicted results of the compressor mass flow rate and input power consumption are compared to the published compressor map values. Future work will focus on detailed experimental validation of the model and parametric studies investigating the effects of structural parameters, including the stroke-to-bore ratio, on the compressor performance.

Effect of partial grooving on the performance of hydrodynamic journal bearing

PurposeThis study aims to improve the performance of hydrodynamic journal bearings through partial grooving on the bearing surface.Design/methodology/approachBearing performance analysis is numerically carried out using the thin film flow physics of COMSOL Multiphysics 5.0 software. Initially, the static performance analysis is carried out for hydrodynamic journal bearing system with smooth surface, and the results of the same are validated with results from the literature. In the later part of the paper, the partial rectangular shape micro-textures are modeled on bearing surface. The effects of partial groove pattern on the bearing performance parameters, namely, fluid film pressure, load carrying capacity, frictional power loss and frictional torque, are studied in detail.FindingsThe numerical results show that the values of maximum fluid film pressure, load carrying capacity, frictional power loss and frictional torque are considerably improved due to deterministic micro-textures. Bearing surface with partial groove along 90°-180° region results in 81.9 per cent improvement in maximum fluid film pressure and 75.9 per cent improvement in load carrying capacity as compared with smooth surface of journal bearing, with no increase in frictional power loss and frictional torque. Maximum decrease in frictional power loss and frictional torque is observed for partially grooving along 90°-360° region. The simulations are supported by proof-of-concept experimentation.Originality/valueThis study is useful in the appropriate selection of groove parameters on bearing surface to the bearing performance characteristics.

An Efficient Algorithm for the Real-Time Generation of Synchronous Reference Signals

Discontinuous reference signals reduce the performances of feedback control systems. This paper proposes an algorithm which generates smooth and synchronous set-points for electromechanical systems, starting from rough input signals. This result is achieved by filtering the discontinuous signals through a set of nonlinear filters whose output is given by smooth profiles subject to velocity and acceleration constraints. The reference synchronization is obtained by acting on the velocity bounds and can be customized to accomplish alternative tasks. In this paper, for example, it is used to reduce friction power losses which affect electromechanical systems. The proposed algorithm is extremely compact and efficient, so that it can be implemented on control boards having limited memory and limited computational capabilities.

Effect of teeth micro-geometrical form modification on contact kinematics and efficiency of high performance transmissions

Light weight, compactness and efficiency are key objectives in high performance vehicular transmission systems, which are subject to large variations in torque and power. Pitch line velocities of up to 52 m/s and teeth pair contact pressures of up to 3 GPa are routinely encountered under race conditions. Contact patch asymmetry due to angular misalignments between input and output shafts leads to the generation of high edge stress discontinuities on gear flanks, inducing fatigue spalling which affects system durability. Crowning is widely used as a palliative measure to mitigate these undesired effects. These problems can be further exacerbated by contact footprint truncation. The paper presents a new approach to modelling the kinematics and contact micro-geometry of meshing conjunctions of involute spur gears with profile and lead modifications. A time-efficient analytical method is presented to accurately determine the contact footprint and kinematics, leading to the solution of highly loaded non-Newtonian mixed thermo-elastohydrodynamic contact under the extreme prevalent conditions of high performance vehicular transmissions. The effect of tooth form modification on contact footprint truncation, contact kinematics and generated frictional power loss is investigated. This approach has not hitherto been reported in literature.

Frictional analysis of deep-groove ball bearings with varying circumference radial preloads

Circumference radial preload due to the interference fit is of a great significant influence on rolling frictional power loss of bearing and service life of machinery. In this article, an analytical method where circumference radial preload is first involved is presented for determining the value of rolling friction power loss of ball bearing (SKF-6205). The experiments under different operating conditions for the bearing were carried out which verify the validity of our proposal. The work described in this article can be regarded as a foundation for the accuracy thermal modeling and friction power loss analysis of the deep-groove ball bearings in machinery.

Piston ring–liner lubrication and tribological performance evaluation: A review

Internal combustion engines are at present used as the major power sources for transportation and power generator. Improvement of the internal combustion engine efficiency is expected due to strict environmental standards and energy costs. Any reduction in oil consumption, friction power losses and emissions results in improving engines’ performance and durability. Automotive industries have intense passion to increase engines’ efficiency to meet the fuel economy and emission standards. Many studies have been conducted to develop reliable approaches and models to understand the lubrication mechanisms and calculate power losses. This review paper summarizes the synthesis of the main technical aspects considered during modeling of piston ring–liner lubrication and friction losses investigations. The literature review highlights the effects of piston ring dynamics, components geometry, lubricant rheology, surface topography and adopted approaches, on frictional losses contributed by the piston ring-pack.

In situ Measurement of Journal Bearing Lubricant Viscosity by Means of a Novel Ultrasonic Measurement Technique Using Matching Layer

ABSTRACTAn ultrasonic viscometer was used to measure the circumferential viscosity variation in a journal bearing noninvasively. This sensing technique is based on the reflection of a shear wave at a solid–liquid boundary that depends on the viscosity of the liquid and the acoustic properties of the solid. Very little ultrasonic energy can propagate into the oil at a metal–oil interface because the acoustic mismatch is significant. Interleaving a matching layer between the metal and the lubricant enables accurate ultrasonic viscosity measurements (M. Schirru, et al., Tribology Leters, Vol. 60, No. 3, 2015). This technique has been used to build a miniaturized ultrasonic viscometer that is accommodated inside a journal to obtain the circumferential viscosity profile. Four viscosity regions are identified due to the variations in the localized temperatures and loads. The results are compared with the isothermal solution of the Reynolds equations for hydrodynamic lubricated bearings. The ultrasonic viscometer locates the angle at which the maximum load occurs and the length of the loaded contact with good accuracy. Finally, the viscosity results are used to estimate the frictional power losses. It is shown that over 70% of the total losses in the journal bearing occur in the region where the load is maximum.

A Theoretical Tribological Comparison Between Soft and Hard Coatings of Spur Gear Pairs

A thermal elastohydrodynamic lubrication (TEHL) model is developed for a coated spur gear pair to investigate the effect of soft coatings and hard coatings on the tribological behavior of such a gear pair during meshing. The coating properties, i.e., the ratio of the Young's modulus between the coating and the substrate, and the coating thickness, are represented in the calculation of the elastic deformation. Discrete convolution, fast Fourier transform (DC-FFT) is utilized for the fast calculation of the surface deformation. The variation of the radius of curvature, the rolling speed, the slide-to-roll ratio, and the tooth load along the line of action (LOA) during meshing is taken into account and the transient squeeze effect is considered in the Reynolds equation. Energy equations of the solids and the oil film are derived. The temperature field and the pressure field are solved iteratively. The tribological behavior is evaluated in terms of the minimum film thickness, the maximum pressure, the temperature rise, the coefficient of friction, and the frictional power loss of the tooth contact during meshing. The results show discrepancies between the soft coating results and hard coating results.

Tribological characteristics of piston rings in a single-piston hydraulic free-piston engine

PurposeA free-piston engine (FPE) is an unconventional engine that abandons the crank system. This paper aims to focus on a numerical simulation for the lubricating characteristics of piston rings in a single-piston hydraulic free-piston engine (HFPE).Design/methodology/approachA time-based numerical simulation program was built using Matlab to define the piston motion of the new engine. And a lubrication mode of piston rings was built which is based on the gas flow equation, hydrodynamic lubrication equation and the asperity contact equation. The piston motion and the lubrication model are coupled, and then the finite difference method is used to obtain the piston rings lubrication performances of the FPE. Meanwhile, the lubrication characteristics of the new engine were compared with those of a corresponding conventional crankshaft-driven engine.FindingsThe study results indicate that compared with the traditional engine, the expansion stroke of the HFPE is longer, and the compression stroke is shorter. Lubrication oil film of the new engine is thicker than the traditional engine during the initial stage of compression stroke and the final stage of the power stroke. The average friction force and power of the hydraulic free piston engine are slightly lower than those of the traditional engine, but the peak friction power of the FPE is significantly greater than that of the traditional engine. With an increase in load, the friction loss power and friction loss efficiency decrease, and with a decrease in equivalence ratio, the friction power loss reduces, but the friction loss efficiency decreases first and then increases.Research limitations/implicationsIn this paper, only qualitative analysis was performed on the tribological difference between conventional crankshaft engine and HFPE, instead of a quantitative one.Practical implicationsThis paper contributes to the tribological design method of HFPE.Social implicationsNo social implications are available now, as the HFPE is under the development phase. However, the authors are positive that their work will be commercialized in the near future.Originality/valueThe main originality of the paper can be introduced as follows: the lubrication and friction characteristics of the new engine (HFPE) were investigated and revealed, which have not been studied before; the effect of the HFPE’s special piston motion on the tribological characteristics was considered in the lubrication simulation. The results show that compared with the traditional crankshaft engine, the new engine shows a different lubrication performance because of its free piston motion.

Frictional power losses on spur gears with tip reliefs. The load sharing role

The load sharing impact on the efficiency of spur gears with modified profile was assessed in this work. The aim was to analyse the influence of the profile modifications on the load sharing, which also considers the effect of the torque level on the system deflections, and how these load sharing variations affected the system efficiency. Due to the frictional effect importance on power losses, in the operating conditions considered, sliding friction between teeth in presence of lubricant was studied in this proposal. The results established that tip relief improves the efficiency of the system due to the reduction of effective contact ratio. Moreover, there is a tip relief which makes optimal the efficiency in specific operating conditions, corresponding to the unit value of the effective contact ratio. Thus, the main conclusion of this work is that the tip relief which makes optimal the efficiency coincides with the theoretical dynamic optimum of the transmission.

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.

Thermal analysis of hydrodynamic lubricated journal bearings in internal combustion engines

Hydrodynamic journal bearings are essential components in the internal combustion engines. The prediction of their reliability, durability, and economy, and also of their friction loss power and wear, are of highest importance. For an appropriate representation of the hydrodynamic load-carrying capacity and also the friction behavior, the multibody dynamics of the contacting components, the shape of the contacting component surfaces, the amount of the available lubricant, and the properties of the lubricant itself are of importance. A Reynolds-averaged equation with laminar flow conditions in combination with a dry asperity contact model and a multibody dynamic simulation of the structural components is a typical modeling approach for that purpose. Furthermore, this paper shows a newly developed model for the temperature distribution in the lubricant and the bearing structures. It includes thermal interface conditions between these domains, which incorporates the asperity energy source and predicts the temperature in supply areas. The presented method is applied for a typical engineering task of a sensitivity analysis for oils with different viscosity index improvers in a main bearing of a four-cylinder inline diesel engine. The influence of the oil film temperature on the oil film viscosity and, therefore, on the load-carrying capacity is shown. Furthermore, the simplified two-dimensional approach is compared with a three-dimensional approach in terms of the obtained result. The presented results show similar accuracy of the two-dimensional approach compared to the equivalent three-dimensional case.

The effect of cylinder liner operating temperature on frictional loss and engine emissions in piston ring conjunction

Despite extensive research into alternative methods, the internal combustion engine is expected to remain as the primary source of vehicular propulsion for the foreseeable future. There are still significant opportunities for improving fuel efficiency, thus directly reducing the harmful emissions. Consequently, mitigation of thermal and frictional losses has gradually become a priority. The piston-cylinder system accounts for the major share of all the losses as well as emissions. Therefore, the need for an integrated approach, particularly of a predictive nature is essential. This paper addresses this issue, particularly the role of cylinder liner temperature, which affects both thermal and frictional performance of the piston-cylinder system. The study focuses on the top compression ring whose critical sealing function makes it a major source of frictional power loss and a critical component in guarding against further blow-by of harmful gasses. Such an integrated approach has not hitherto been reported in literature. The study shows that the cylinder liner temperature is critical in mitigating power loss as well as reducing Hydrocarbon (HC) and Nitrogen Oxide (NOx) emissions from the compression ring – cylinder liner conjunction. The results imply the existence of an optimum range for liner working temperature, independent of engine speed (at least in the studied cases) to minimise frictional losses. Combined with the study of NOx and HC emissions, the control of liner temperature can help to mitigate frictional power loss and reduce emissions.

승용차용 터보과급기의 저속 영역 마찰 손실 측정 장치 개발

본 연구에서는 터보과급기의 성능을 저해하는 주요 인자 중 하나인 마찰손실에 대한 연구를 수행하였다. 실제 엔진에서 빈번하게 사용되는 저속 구간에서의 승용차용 터보과급기의 마찰손실 측정 장치를 개발하고, 30,000~90,000rpm의 저속 영역에서 작동하는 터보과급기의 마찰손실을 측정하였다. 플로팅 베어링 타입의 승용차용 터보과급기를 실험 대상으로 선정하였으며, 마찰손실 측정 장치는 구동 모터, 오일 공급 시스템, 커플링으로 구성되었다. 실제 차량의 저속 운전 상황을 모사할 수 있도록 설계, 제작되었고, 회전속도, 오일 온도 및 압력을 실험 변수로 선정하였다. 또한, 마찰손실 측정 장치는 로드셀을 사용하여 발생하는 마찰 토크를 직접 측정하여 마찰손실을 산출하였으며, 마그네틱 커플링을 통해 구동 모터의 동력을 터보과급기 축에 전달하고, 오일 공급 시스템을 오일 온도 및 압력을 조절하였다. 온도 <TEX>$60^{\circ}C$</TEX>와 <TEX>$90^{\circ}C$</TEX>, 압력 4bar의 오일을 공급하는 상태에서 터보과급기가 회전수 30,000~90,000rpm으로 작동할 때 터보과급기 회전속도 증가할 때 마찰손실은 증가하며, 대략적으로 과급기 회전속도의 1.4~1.8 지수승에 비례함을 보이고 있다. 또한 오일온도가 <TEX>$60^{\circ}C$</TEX>에서 <TEX>$90^{\circ}C$</TEX>로 증가할 때 마찰손실은 최소 41%, 최대 63% 감소하였다. Turbocharging is widely used in diesel and gasoline engines as an effective way to reduce fuel consumption. But turbochargers have turbo-lag due to mechanical friction losses. Bearing friction losses are a major cause of mechanical friction losses and are particularly intensified in the lower speed range of the engine. Current turbochargers mostly use oil bearings (two journal bearings and one thrust bearing). In this study, we focus on the bearing friction in the lower speed range. Experimental equipment was made using a drive motor, load cell, magnetic coupling, and oil control system. We measured the friction losses of the turbocharger while considering the influence of the rotation speed, oil temperature, and pressure. The friction power losses increased exponentially when the turbocharger speed increased.

Preliminary Study of Frictional Power Losses in Spur Geared Transmissions

Preliminary Study of Frictional Power Losses in Spur Geared Transmissions

The Evolution of Reliability and Efficiency of Aerospace Bearing Systems

The worldwide air traffic underwent a rapid development in recent decades. Between the early 70s and the late 90s of the last century civil air traffic doubled every 15 years. The civil aviation market will continue to grow with 4% - 5% each year within the next 20 years. This enormous growth represents major challenges for airframers, engine makers, suppliers, airlines, air traffic management and ground infrastructure. In addition, the public debate on the worldwide civil air traffic is dominated by environmental and climate issues, even though only 2% of the man-made carbon dioxide (CO2) emissions are due to air transportation. Therefore the aerospace industry will have to focus on a low-emission and quite air traffic, and on the conservation of natural resources and our environment. The end-use consumer and environmental policy requirements for aircrafts of the next generation translate into components with improved efficiency and reliability. Rolling bearings are one of these components which significantly determine the reliability and mechanical efficiency of aerospace applications such as aircraft and rotorcraft engines and transmission systems. They have to withstand very demanding operating conditions. Especially main shaft bearings in modern aircraft engines experience high rotational speeds andtemperatures. Furthermore aerospace bearings have to meet the highest reliability standards and require low-weight design solutions. These operating conditions and requirements present a continuous challenge for improvements in all fields of bearing technology. This article presents solutions in aspects of materials, design, analysis, and surface technologies in order to meet the environmental, reliability, and economical requirements of advanced aerospace bearing systems. State of the art bearing analysis and advanced bearing design solutions contributing to lower friction power losses and increased systems efficiency are discussed. Weight, functional, and maintenance benefits are presented with the example of highly integrated aircraft engine main shaft bearings. It is also shown that the progress in bearing materials and surface technology development is the basis for weight and friction energy reduction in aerospace bearing systems.