Bearing Friction Losses Research Articles

Theoretical and Numerical Investigation of Reduction of Viscous Friction in Circular and Non-Circular Journal Bearings Using Active Lubrication

Reducing friction losses is one of the most common ways to improve fluid film bearings, whose adjustable design provides additional opportunities to improve their dynamic and tribological properties. Previous studies have shown the possibility of reducing viscous friction in actively lubricated bearings by adjusting the rotor position. This work provides a theoretical justification for the mechanism of this effect for the cases of purely laminar lubricant flows in journal bearings. The operating modes connected with the transition to turbulent phenomena and the occurrence of Taylor vortices are beyond the scope of this paper. Conditions that ensure the minimization of friction losses in hydrodynamic and hybrid bearings with hydrostatic parts are determined based on the equations describing viscous friction in a fluid film. In non-adjustable plain hydrodynamic bearings, the minimum of friction is achieved with the centered shaft position that is actually unstable due to the resulting forces configuration. In actively lubricated hybrid bearings, a further reduction in viscous friction is possible by combining film thickness and pressure distributions. Recombining them, along with adjustment of the shaft position, allows the optimization of the distribution of shear stresses in the fluid film. As a result, the shear stresses caused by the rotation of the shaft can be partially compensated by the stresses caused by the pressure gradient, reducing the torque-resisting rotation. In addition, additional benefits can be obtained in the minimum friction state by the reduced lubricant flow and power losses to its pumping. A series of numerical calculations for elliptical, 3-, and 4-lobe bearings show that non-circular bores provide additional variability in film thickness distribution and a premise for optimizing the bearing tribological parameters. Four-lobe bearing demonstrated the best ability for reducing viscous friction among the considered designs. The results obtained can be used as a basis for further optimization of the geometry of fluid film bearings of both active and passive designs by reducing power losses due to viscous friction.

A study on the dynamic contact feature of four-contact-point ball bearing

Four-contact-point ball bearing (FCPBB), with a special double half inner ring structure, presents dynamic multi-point contact characteristics in service. The dynamic contact feature, such as 2-point, 3-point or even 4-point contact phenomena between balls and bearing raceway, lead to completely different bearing friction, heat generation and wear rates. Considering the oil film traction effect, the traction and contact equations for ball and four raceways were proposed, and the changes of bearing dynamic contact feature with complex operating conditions, such as high speed-slight load, combined axial-radial load, were investigated. As bearing preload increases, the interaction between the ball and raceway gradually changes from 3-point to 2-point contact. In this process, the PV factor in outer sub-contact area first increases and then decreases, which is the key factor in bearing friction loss. In case of combined load, the ball may experience 2-point contact, 3-point contact and 4-point contact in one revolution. Besides, when two-point contact occurs, the main-contact area has the largest PV value; when four-point contact occurs, the sub-contact area has the largest PV value.

Evolutionary Optimisation of the Thrust Bearing Considering Multiple Operating Conditions in Turbomachinery

Thrust bearings are an essential part of rotating machines, significantly impacting their overall efficiency. The bearings must be designed to have optimal properties under the preferred operating conditions and be able to operate under off-design operating conditions occurring exceptionally. The available literature presents various possibilities for optimising bearing performance, but a method of including various operating conditions has not been introduced. The presented solution uses an optimisation of the thrust bearing that is based on genetic algorithms in combination with an efficient computational model of thrust bearing lubrication and heat transfer. The presented evolutionary optimisation approach makes it possible to design a bearing with exceptional performance under both specific and extreme operating conditions. The optimisation approach is applied in the development of a prototype thrust bearing and bearing friction losses decreased by approximately 30% compared to a serial bearing. At the same time, there is no significant decrease in the bearing ability to operate under off-design operating conditions. The prototype bearing designed using this approach reduced the mechanical losses of the entire turbocharger by approximately 20%.

Analysis of Standby Losses and Charging Cycles in Flywheel Energy Storage Systems

Aerodynamic drag and bearing friction are the main sources of standby losses in the flywheel rotor part of a flywheel energy storage system (FESS). Although these losses are typically small in a well-designed system, the energy losses can become significant due to the continuous operation of the flywheel over time. For aerodynamic drag, commonly known as windage, there is scarcity of information available for loss estimation since most of the publications do not cover the partial vacuum conditions as required in the design of low loss energy storage flywheels. These conditions cause the flow regime to fall between continuum and molecular flow. Bearings may be of mechanical or magnetic type and in this paper the former is considered, typically hybridized with a passive magnetic thrust bearing. Mechanical bearing loss calculations have been extensively addressed in the open literature, including technical information from manufacturers but this has not previously been presented clearly and simply with reference to this application. The purpose of this paper is therefore to provide a loss assessment methodology for flywheel windage losses and bearing friction losses using the latest available information. An assessment of windage losses based on various flow regimes is presented with two different methods for calculation of windage losses in FESS under rarefied vacuum conditions discussed and compared. The findings of the research show that both methods closely correlate with each other for vacuum conditions typically required for flywheels. The effect of the air gap between the flywheel rotor and containment is also considered and justified for both calculation methods. Estimation of the bearing losses and considerations for selection of a low maintenance, soft mounted, bearing system is also discussed and analysed for a flywheel of realistic dimensions. The effect of the number of charging cycles on the relative importance of flywheel standby losses has also been investigated and the system total losses and efficiency have been calculated accordingly.

Investigation of the power losses in induction machines with rotor eccentricity

Due to manufacturing tolerances and bearing ageing, rotor eccentricity is inevitable in electrical machines. The existence of rotor eccentricity in electrical machines will cause unbalanced magnetic pull (UMP), which would increase bearing friction losses. In addition, the additional magnetic flux harmonics caused by rotor eccentricity may incur additional copper and iron losses. Here, induction machines are analysed as they are more sensitive to rotor misalignment due to smaller air gap compared to other types of machines. The magnetic flux distribution and UMP for both squirrel cage and wound rotor induction machines are discussed, as they have a dissimilar rotor configuration. The existence of rotor eccentricity would increase rotor copper loss in squirrel cage induction machines and would increase iron losses in wound rotor induction machines, where the additional power losses are a function of the degree of eccentricity. Analytical models are used to estimate the additional power losses, and they were validated using finite element analysis. Finally, we investigated the impact of power losses when implementing the slip control method which is proposed in our previous literature, in order to reduce UMP.

Performance and Loss Analysis of Squirrel Cage Induction Machine Based Flywheel Energy Storage System

Flywheel energy storage systems (FESS) are one of the earliest forms of energy storage technologies with several benefits of long service time, high power density, low maintenance, and insensitivity to environmental conditions being important areas of research in recent years. This paper focusses on the electrical machine and power electronics, an important part of a flywheel system, the electrical machine rotating with the flywheel inertia in order to perform charge-discharge cycles. The type of machine used in the electrical drive plays an important role in the characteristics governing electrical losses as well as standby losses. Permanent magnet synchronous machine (PMSM) and induction machines (IM) are the two most common types of electric machines used in FESS applications where the latter has negligible standby losses due to its lower rotor magnetic field until energised by the stator. This paper describes research in which the operational and standby losses of a squirrel-cage induction machine-based flywheel storage system (SCIM-FESS) are modelled as a system developed in MATLAB/Simulink environment inclusive of the control system for the power electronics converters. Using the proposed control algorithm and in-depth analysis of the system losses, a detailed assessment of the dynamic performance of the SCIM-FESS is performed for different states of charging, discharging, and standby modes. The results of the analysis show that, in presence of system losses including aerodynamic and bearing friction losses, the SCIM-FESS has satisfactory characteristics in energy regulation and dynamic response during load torque variations. The compliance of FESS and its conversion between the generating and motoring mode within milliseconds show the responsiveness of the proposed control system.

The Performance Analysis of R32 Rotary Compressor Used for Room Air Conditioners

R32 has been used as an alternative refrigerant of R410A in room air conditioners for its zero ODP, low GWP, and high performance. In this study, performance of R32 hermetic rotary compressor with high pressure shell was analyzed with a more comprehensive theoretical model. The simulation results showed good agreement with the experimental results. Besides, in order to improve the accuracy, in the theoretical model, the two phase leakage model was chosen in the leakage passage of radial clearance, and the gas leakage was considered in the side of sliding vane when the height of oil level is lower than the upper end face of cylinder. The analysis results show that the main factors that influence the cooling capacity are heating loss and leakage loss, and the main factors that influence the input power are discharge pressure loss, suction heating loss, clearance volume loss, bearing friction loss and sliding vane friction loss. The theoretical model would have great useful for designation and performance optimization of rotary compressor.

Experimental Analysis and Modeling of the Effects of Oil–Air Lubrication Parameters on Bearings Friction Loss of High-Speed Motorized Spindle

The friction loss of an angular contact ball bearing is a key factor restricting the development of a high-speed motorized spindle. To quantitatively calculate the effects of the oil–air lubrication parameters on the friction loss of high-speed bearings, the drag resistance and the churning resistance generated by the movement of the rolling elements in the lubricant are theoretically modeled and the percentage volume of the lubricant in the bearing cavity (XCAV) is used to characterize the effects. The friction loss of bearings is tested by two novel methods: the free deceleration method and the energy-balance method. The experimental results show that the viscous resistance loss is a major component of bearing friction loss and oil–air lubrication parameters have important influence on it. A comparison of the theoretical calculations and the experimental results is used for deriving the empirical formula of XCAV with respect to the lubricant flow, gas pressure, rotating speed, and pitch diameter. The research results of this study have important significance for the measurement, prediction and reduction of the friction loss of high-speed bearings.

A holistic methodology to correct heat transfer and bearing friction losses from hot turbocharger maps in order to obtain adiabatic efficiency of the turbomachinery

Turbocharger performance maps provided by manufacturers are usually far from the assumption of reproducing the isentropic performance. The reason being, those maps are usually measured using a hot gas stand. The definition of the effective turbocharger efficiency maps include the mechanical losses and heat transfer that has occurred during the gas stand test for the turbine maps and only the heat transfer for the compressor maps. Thus, a turbocharger engine model that uses these maps provides accurate results only when simulating turbocharger operative conditions similar to those at which the maps are recorded. However, for some critical situations such as Worldwide harmonized Light vehicles Test Cycles (WLTC) driving cycle or off-design conditions, it is difficult to ensure this assumption. In this article, an internal and external heat transfer model combined with mechanical losses model, both previously developed and calibrated, has been used as an original tool to ascertain a calculation procedure to obtain adiabatic maps from diabatic standard turbocharger maps. The turbocharger working operative conditions at the time of map measurements and geometrical information of the turbocharger are necessary to discount both effects precisely. However, the maps from turbocharger manufacturers do not include all required information. These create additional challenges to develop the procedure to obtain approximated adiabatic maps making some assumptions based on SAE standards for non-available data. A sensitivity study has been included in this article to check the validity of the hypothesis proposed by changing the values of parameters which are not included in the map data. The proposed procedure becomes a valuable tool either for Original Equipment Manufacturers (OEMs) to parameterize turbocharger performance accurately for benchmarking and turbocharged engine design or to turbocharger manufacturers to provide much-appreciated information of their performance maps.

Design of High Power Density and High Efficiency Wound-Field Synchronous Motor for Electric Vehicle Traction

This paper deals with a design method to improve the power density and energy efficiency of a wound-field synchronous motor (WFSM) using hairpin type rectangular wire for electric vehicle traction. First, the prototype is analyzed via experiments to come up with plans to improve it. In addition, mechanical loss of the prototype including the bearing and brush friction losses is obtained and used for designing the improved motor. After then, an analytical approach is presented for the magnetic circuit design to minimize magnetic resistance in the motor core. Also, the analytical methods are proposed to predict the resistance of the field and armature windings. At this step, rectangular wire is considered for the armature winding to reduce the copper loss. Moreover, the calculation process is presented to estimate the iron loss considering harmonics. The performances such as power density and efficiency of the improved WFSM are analyzed and compared with those of the prototype. In addition, the energy efficiency of the motors in the new European drive cycle (NEDC) is analyzed. Finally, the performances of the improved WFSM are compared with the experimental results to verify the validity of the proposed design process.

Determining the Coefficient of Efficiency for the Drives of Centrifugal and Piston Compressors

A formula of the coefficient of efficiency for the drives of centrifugal and piston compressors was derived. It takes into consideration the adiabatic work of gas compression, friction losses in compressor bearings and gas pressure losses in the compressor. In the past, gas pressure losses in the compressor were not taken into account and these arise due to the friction of compressed gas flows, and due to the fact that the gas needs to overcome local resistances and the bends in compressor cavities. The computation formula of the coefficient of efficiency of the compressor was converted and it is used for a separate computation of the two coefficients of efficiency of the drive, in particular the coefficient of efficiency that takes into account the adiabatic work of gas compression and the friction losses in the bearings and the coefficient of efficiency that takes into account only gas pressure losses in the compressor. The plots for the coefficient of efficiency of the drive that takes into consideration only gas pressure losses in the compressor were constructed for centrifugal and piston compressors. Practical computations of the coefficient of efficiency of the drive that depends only on gas pressure losses in the compressor were done for centrifugal and piston compressors. For the centrifugal compressor this coefficient of efficiency can reach the value of 0.01 and for the piston compressor this value can be equal to 0.02. The values of the second order should be taken into account when calculating and estimating the coefficient of efficiency of the drive of centrifugal and piston compressors.

On the benchmarking of friction in timing chains

This paper is dealing with the evaluation of friction in timing chains. Benchmarking friction is based on the experimentally determined friction losses in basic chain drives with transmission ratio i=1. This friction is not including friction losses in bearings. These results should be used, in the simplest manner, in order to evaluate friction in timing chains (i = 2). We are presenting the theoretical approach and experimental validation that have been developed for the timing chain drives, with transmission ratio i = 2. Friction losses are presented as resistant friction torques at the input shaft, depending on input rotational speed and tensioning force in the chain drive.

Measurement of Journal Bearing Friction Loss of Turbocharger in a Passenger Vehicle

Measurement of Journal Bearing Friction Loss of Turbocharger in a Passenger Vehicle

The effect of oil feed pressure on the friction torque of plain bearings under light, steady loads

Abstract Friction losses in plain bearings can be reduced by reducing the pressure of the oil feed. The role of increased film cavitation has been investigated experimentally under light, steady loads for a bearing with a 180° groove, using an SAE 5W-30 oil. Friction torque was reduced by up to 18% by increased cavitation which reduces the film area and the eccentricity ratio. The latter reduces the surface shear stress in the load-bearing region of the film and overall, the circumferential average. As load increases, the reduction in film area accounts for an increasing proportion of the friction torque reduction.

Influence of Non-Linear Rotor Dynamics on the Bearing Friction of Automotive Turbochargers

One of the possibilities to increase the efficiency of an internal combustion engine is to enhance its interaction with the charging system. With the help of new advanced simulation tools, the rotor dynamic behavior and bearing friction losses of turbochargers (TC) can be quantified in the early stage of the development process. This procedure enables virtual bearing development, leading to shortened development times and reduced testing costs. This paper presents a detailed view of the findings in current research; focusing on rotor dynamic simulations with emphasis on the non-linear dynamics (oil whirl; oil whip) and their impact on bearing friction losses. In order to obtain a detailed understanding of these effects; elastic multibody simulations (EMBS) with elastic hydrodynamic bearing (EHD) analysis including a mass-conservative approach are used. Measurement data is obtained using a unique test bench which is designed to quantify the bearing friction losses by means of a drag test. Additionally, hot gas test bench measurements are carried out to assess the non-linear rotor dynamics during steady state operation using shaft motion measurement equipment. In the first step; a multibody simulation model of a common automotive TC is set up; and a model of the friction test bench is mapped into it. The author will show that there is a high agreement between simulated and measured friction losses. In the second step; the TC model is detached from the virtual test bench and a variation of the essential parameters are carried out to identify the influence of the non-linear rotor dynamics on the bearing friction. A final model validation is obtained by comparing the measured shaft orbits for the TC hot gas test bench with the results from the multibody simulation.

Rotordynamic and Friction Loss Measurements on a High Speed Laval Rotor Supported by Floating Ring Bearings

Floating ring bearings are the commonly used type of bearing for automotive turbochargers. The automotive industry continuously investigates how to reduce the bearing friction losses and how to create silent turbochargers. Many of these studies involve creating a numerical model of the rotor-bearing system and performing validation on a test bench on which a turbocharger is driven by hot gases. This approach, however, involves many uncertainties which diminish the validity of the measurement results. In this study, we present a test setup in which these uncertainties are minimized. The measurement results show the behavior of the floating ring bearing as a function of oil feed pressure, oil feed temperature, rotor unbalance and bearing clearances. Next to an increased validity, the test setup provides measurement data with good repeatability and can therefore represent a case study which can be used for validation of rotor-bearing models.

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.

Numerical modelling of twin-screw pumps based on computational fluid dynamics

Increasing demands for high-performance screw pumps in oil and gas as well as other applications require deep understanding of the fluid flow field inside the machine. Important effects on the performance such as dynamic losses, influence of the leakage gaps and presence and extent of cavitation are difficult to observe by experiments. However, it is possible to study such effects using well-validated computational fluid dynamics models. The novel-structured numerical mesh consisting of a single-computational domain for moving screw pump rotors was developed to allow three-dimensional computational fluid dynamics simulation of such machine possible. Based on finite volume method, the instantaneous mass flow rates, rotor torque, local pressure field, velocity field and other performance indicators including the indicated power were predicted. A calculation model for the bearing friction losses was introduced to account for mechanical losses. The geometry of the inlet and outlet passages and piping system are taken into consideration to evaluate their influences on the pressure distribution and shaft power. The paper also shows the influence of rotor clearances on the pump performance. The computational fluid dynamics model was validated by comparing the numerical results with the measured performance obtained in the experimental test rig through the comprehensive experiment performed for a set of discharge pressures and rotational speeds. Validation includes comparison of mass flow rates, shaft power and efficiency under variety of speeds and discharge pressure. It has been found that the predicted results match well with the measurements. The results also showed that the radial clearances have larger influence on the mass flow rate than the interlobe clearance. The correct design of the flow passages within the screw pump plays significant role in minimizing required power consumption. The analysis presented in this paper contributes to better understanding of the working process inside the screw pump and offers a good reference to improve design and optimize such machines in terms of clearance selection, shape of the ports, piping system, etc. In future, this model will be used for analysis of cavitating flows and determining performance of other multiphase screw pumps.

Microstructuring the surface of silicon carbide ceramic by laser action for reducing friction losses in rolling bearings

A possibility of microstructuring the surface of silicon carbide ceramic by pulse-periodic laser treatment was determined for reducing the coefficient of friction under actual contact stress conditions that occur in elements of the rolling bearing in operation. Temperature rate conditions for the laser treatment with pulse duration in the millisecond range were found, which lead to a change in the surface microrelief of silicon carbide ceramic obtained by diamond grinding after hot isostatic pressing. The determination of the coefficient of sliding friction was conducted with using the ball-on-disk tribometer at normal loads, which corresponds to the values of contact stresses of (0.5–1)×109Pa. When the load was increased to the upper limit of measuring range, the friction coefficient decrease after laser treatment was more than 30% compared to the initial structure. Significant reduction of friction in rolling bearings up to this level provides an opportunity to improve efficiency of various machines.

Heat Analysis of Vehicle Drive Axle

The vehicle drive axle is one of the main sources of power loss in drivetrain system, and its improvements can have a significant impact on vehicle fuel economy. Gears churning loss, bearing friction loss and engaging friction loss all make a great contribution to the heat generation. The temperatures of lubricants, the gear tooth contacting surfaces, and the bearing surfaces are critical to the overall axle performance in terms of power losses, fatigue life, and wear. So it is important to understand the heat generation and dissipation in automotive drive axle. However, the quantities of understandings of drive axle temperature is limited and published information is deficient.In this paper, we establish the mathematical model of heat generation and dissipation to investigate the connection between thermal behavior and power loss. Power loss is consist of churning loss, bearing friction loss and engaging friction loss. And also we simulate the model to get the conclusion and then conduct the experiments to verify the correctness of the theories and models.