An integrated gear tribodynamics model is proposed for the study of EV powertrains' performance. The model considers the transient effects of lubrication regimes, non-Newtonian shear thinning, inlet shear heating, deformation... more
An integrated gear tribodynamics model is proposed for the study of EV powertrains' performance. The model considers the transient effects of lubrication regimes, non-Newtonian shear thinning, inlet shear heating, deformation states of asperities in mixed regime of lubrication and contact temperature using a set of analytical routines, which are computationally efficient. The proposed gear tribodynamics model provides a breakdown of the interdependency of these attributes and studies their impact on the performance of gear contacts. The results indicate that up to 30% of the contact load can be carried by asperities, of which 80% undergo elastoplastic deformation. In addition, the contribution of lubricant to contact stiffness can be greater than that of surface asperities by an order of magnitude.
Research Interests: Mechanical Engineering, Electric Vehicles, Lubrication, Gears, Automotive NVH, and 15 morePowertrain, Gearbox, Mechanical Vibrations, Atuomobile Powertrain System, Lubrication and Friction, Stiffness, Elastohydrodynamics, Electric Cars, Friction, Electric Vehicle, Electrical Vehicles, Gearbox Dynamic, Elastohydrodynamic Lubrication, Drivetrain Dynamics, and Mesh Stiffness
Since Euler's original gyro-dynamic analysis nearly two and a half centuries ago, the use of multi-body dynamics (MBD) has spread widely in application scope from large displacement rigid body dynamics to infinitesimal amplitude... more
Since Euler's original gyro-dynamic analysis nearly two and a half centuries ago, the use of multi-body dynamics (MBD) has spread widely in application scope from large displacement rigid body dynamics to infinitesimal amplitude elastodynamics. In some cases, MBD has become a multi-physics multi-scale analysis, comprising contact mechanics, tribo-dynamics, terramechanics, thermodynamics, biomechanics, etc. It is an essential part of all analyses in many engineering disciplines, including vehicle engineering. This paper provides an overview of historical developments with emphasis on vehicle development and investigation of observed phenomena, including noise, vibration and harshness. The approach undertaken is comprehensive and provides a uniquely focused perspective, one which has not hitherto been reported in the literature.
Research Interests: Mechanical Engineering, Vehicle Dynamics, Multiscale Modelling, Tribology, Multidisciplinary, and 15 moreAutomotive NVH, Powertrain, Gearbox, Atuomobile Powertrain System, IC ENGINES, Lubrication and Friction, Multibody Dynamics, Elastodynamics, Clutch Systems, Multibody Vehicle Dynamics, Multiphysics modeling, Automotive Powertrain, Rigid Body Dynamics, Shuffle Mode, and Vehicle Powertrain Dynamics
Accurate prediction of constant velocity joint transient contact loading and complex kinematics is necessary to improve joint design and prevent incurring failure from rolling contact fatigue. A detailed multibody dynamic model is... more
Accurate prediction of constant velocity joint transient contact loading and complex kinematics is necessary to improve joint design and prevent incurring failure from rolling contact fatigue. A detailed multibody dynamic model is presented for cross groove constant velocity joints used in high performance automotive racing applications, hitherto not reported in the open literature. The developed model includes detailed contact mechanics and friction models for all contacts made between the components. A novel semi-Hertzian contact model is adopted for the cage-race conjunction. Local contact kinematics is evaluated based on a methodology used in tribological analysis. The proposed model is validated against available computational models provided in literature for cross groove designs. Using the model, contact pressures occurring in the ball-race and ball-cage contacts are shown to reach levels as high as 4 and 5 GPa, respectively. The assumed value of friction coefficient is shown to have a strong influence on the predicted contact forces. Local contact motions are presented for the ball-race and ball-cage contacts, demonstrating complex motion which varies between pure rolling and pure sliding within a single cycle.
Research Interests: Mechanical Engineering, Vehicle Dynamics, Theory Of Mechanisms, Mechanism Design, Kinetics And Mechanistic Studies, and 15 moreAutomobile, Contact Mechanics, Tribology, Formula One, Automotive Engineering, Powertrain, Multibody Dynamics, Kinematics of Machines, Friction, Automotive Technology, Joints, Automotive Powertrain, Formula One car, Drivetrain Dynamics, and CVJ
In the quest for decarbonisation, alternative clean fuels for propulsion systems are sought. There is definite advantage in retaining the well-established principles of operation of combustion engines at the core of future developments... more
In the quest for decarbonisation, alternative clean fuels for propulsion systems are sought. There is definite advantage in retaining the well-established principles of operation of combustion engines at the core of future developments with hydrogen as a fuel. Hydrogen is envisaged as a clean source of energy for propulsion of heavy and off-road vehicles, as well as in marine and construction sectors. A source of concern is the unexplored effect of hydrogen combustion on dilution and degradation of engine lubricants and their additives, and consequently upon tribology of engine contact conjunctions. These potential problems can adversely affect engine efficiency, durability, and operational integrity. Use of different fuels and their method of delivery, produces distinctive combustion characteristics that can affect the energy losses associated with in-cylinder components and their durability. Therefore, detailed predictive analysis should support the developments of such new genera...
Research Interests: Engineering, Thermodynamics, Hydrogen, Heat Transfer, Internal Combustion Engines, and 15 moreLubrication, Tribology, Internal Combustion Engine, Engine, Multiphysics Simulation, Hydrogen Fuel, IC ENGINES, Viscosity, Lubrication and Friction, Gas Dynamics, Friction, Piston Rings, Engine tribology, Hydrogen Combustion, and Hydrogen Internal Combustion Engine
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Energy efficiency and Noise, Vibration and Harshness (NVH) have been in the centre of attention for automotive manufacturers during the last decades. Energy losses occur in different forms, such as friction, impacts and noise. Physical... more
Energy efficiency and Noise, Vibration and Harshness (NVH) have been in the centre of attention for automotive manufacturers during the last decades. Energy losses occur in different forms, such as friction, impacts and noise. Physical understanding of the mechanisms that lead to aggressive dynamics and noise generation is a key in order to design more efficient systems with better NVH performance. In the current study, impact energy is calculated at the lubricated piston-liner conjunctions combining dynamics and tribology. The vibration power at the engine block surface is converted into sound pressure level (SPL) at any desired location analytically. Then, a technique is presented to reduce the severity of impact dynamics by controlling piston's secondary motion, comprising vibration absorbers with nonlinear characteristics. The piston secondary motion dynamics are studied and the absorber effectiveness on vibration reduction is discussed.
Although alternative power sources are getting well-established, transportation will remain primarily dependent on IC engines using fossil fuels for at least a few more decades. The IC engines typically employ reciprocating pistons to... more
Although alternative power sources are getting well-established, transportation will remain primarily dependent on IC engines using fossil fuels for at least a few more decades. The IC engines typically employ reciprocating pistons to convert the combustion pressure into mechanical work required by the vehicle. Engine NVH issues make their appearance at the piston-cylinder interface in the form of impulsive vibration signals. The piezo-viscous nature of the lubricant at the piston-cylinder conjunction can change the dynamic response of the impacting structures. Much of the published research to date has excluded the elasto-hydrodynamic effects of the lubricant on piston impact noise. Even when these effects were studied, the research focus has been primarily on the tribology of the contact. Thus, an accurate methodology is required to identify and predict piston impact noise using real in-cylinder conditions, especially at the lubricated piston-cylinder conjunction. [Continues.]
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The piston impacts against the cylinder liner are the most significant sources of mechanical noise in internal combustion engines. Conventionally, the severity of impacts is reduced through the modification of physical and geometrical... more
The piston impacts against the cylinder liner are the most significant sources of mechanical noise in internal combustion engines. Conventionally, the severity of impacts is reduced through the modification of physical and geometrical characteristics of components in the piston assembly. These methods effectively reduce power losses at certain engine operating conditions. Moreover, the conditions leading to the reduction in power losses inversely increase the engine noise due to piston impacts. An alternative control method that is robust to fluctuations in engine operating conditions is anticipated to improve the engine’s NVH performance whilst exacerbation in power loss remains within the limits of the conventional methods. The concept of Targeted Energy Transfer (TET) through the use of Nonlinear Energy Sinks (NES) has not been applied yet in automotive powertrains. Numerical studies have shown a potential in reducing the severity of impact dynamics by controlling piston’s second...
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The impulsive behavior of piston plays a key role in the Noise, Vibration and Harshness (NVH) of internal combustion engines. There have been several studies on the identification and quantification of piston impacting action under... more
The impulsive behavior of piston plays a key role in the Noise, Vibration and Harshness (NVH) of internal combustion engines. There have been several studies on the identification and quantification of piston impacting action under various operation conditions. In the current study, the dynamics of piston secondary motion are briefly explored, since this is fundamental to understanding the aggressive oscillations, energy loss and noise generation. Concepts of controlling piston secondary motion (and thus, impacts) are investigated and a new passive control approach is presented based on the nonlinear energy absorption of the highly transient oscillations. The effectiveness of this new method on the improvement of piston impact behavior is discussed, using a preliminary optimization exercise (with respect to engine excitation/speed, damping and stiffness of the nonlinear oscillator) that leads to the conceptual design of a nonlinear energy absorber.Copyright © 2015 by ASME
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In applications requiring high load carrying capacity, conforming contacting pairs with a relatively large contact footprint are used. These include circular arc, Novikov, and Wildhaber gears found, for example, in helicopter rotors.... more
In applications requiring high load carrying capacity, conforming contacting pairs with a relatively large contact footprint are used. These include circular arc, Novikov, and Wildhaber gears found, for example, in helicopter rotors. Closely conforming contacts also occur in many natural endo-articular joints, such as hips, or their replacement arthroplasty. The main determining factors in contact fatigue are the sub-surface shear stresses. For highly loaded contacts, classical Hertzian contact mechanics is used for many gears, bearings, and joints. However, the theory is essentially for concentrated counterforming contacts, where the problem is reduced to a rigid ellipsoidal solid penetrating an equivalent semi-infinite elastic half-space. Applicability is limited though, and the theory is often used inappropriately for contacts of varying degrees of conformity. This paper presents a generic contact mechanics approach for the determination of sub-surface stresses, which is applicab...
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Turbochargers are progressively used in modern automotive engines to enhance engine performance and reduce energy loss and adverse emissions. Use of turbochargers along with other modern technologies has enabled development of... more
Turbochargers are progressively used in modern automotive engines to enhance engine performance and reduce energy loss and adverse emissions. Use of turbochargers along with other modern technologies has enabled development of significantly downsized internal combustion engines. However, turbochargers are major sources of acoustic emissions in modern automobiles. Their acoustics has a distinctive signature, originating from fluid-structure interactions. The bearing systems of turbochargers also constitute an important noise source. In this case, the acoustic emissions can mainly be attributed to hydrodynamic pressure fluctuations of the lubricant film. The developed analytical model determines the lubricant pressure distribution in the floating journal bearings used mainly in the modern turbocharges. This allows for an estimation of acoustic emissions. The use of such an analytical approach is computationally efficient when compared with full numerical analysis approaches, whilst also providing reliable predictions. The results from the developed analytical model are used to determine the power loss as well as sound pressure levels generated in the turbocharger bearings due to oil flow which can be correlated with the acoustic emissions of turbochargers.
Research Interests: Acoustic Modelling, Tribology (Engineering), Internal Combustion Engines, Automobile, Lubrication, and 12 moreTribology, Acoustic Emission, SAE, Turbocharger, Noise Pollution, Automotive Technology, Lubricants, Vibration and Acoustics, Journal Bearing, Turbochargers, Turbocharging, and Noise Emissions
A novel integrated multi-physics assessment of the piston top compression ring of an internal combustion engine under normal operation mode, as well as subjected to cylinder deactivation is carried out. The methodology comprises... more
A novel integrated multi-physics assessment of the piston top compression ring of an internal combustion engine under normal operation mode, as well as subjected to cylinder deactivation is carried out. The methodology comprises ring-liner thermo-mixed hydrodynamics, elastodynamics of ring, as well as combustion gas blow-by and emissions. Therefore, the analysis provides prediction of ring-liner contact's energy losses and gas power leakage across the piston and ring crevices, as well as the resulting emissions. Cylinder deactivation (CDA) technology reduces the unburnt fuel entering the ring-pack crevices, as well as the emissions. It is also shown that the frictional and gas leakage power losses are exacerbated under CDA by as much as 20%. Although this is much lower than the potential gains in fuel usage when using CDA. The optimisation of the piston compression ring would provide further fuel efficiency and improved emissions, an issue which has not hitherto received the att...
Research Interests: Mechanical Engineering, Materials Science, Tribology (Engineering), Internal Combustion Engines, Automobile, and 13 moreTribology, Energy efficiency, Automotive Engineering, Lubrication and Friction, Energy Saving, Fuel economy, Friction, Automotive Technology, Fuel efficiency, Energy Efficiency, Cylinder Liner, CO Emissions, and Piston Rings
The viscosity and tribological behavior of nanofluids formed by dispersed nano-diamond particles within Poly-Alpha-Olefin (PAO6) lubricant is studied at different concentrations. The variation of coefficient of friction with nanoparticle... more
The viscosity and tribological behavior of nanofluids formed by dispersed nano-diamond particles within Poly-Alpha-Olefin (PAO6) lubricant is studied at different concentrations. The variation of coefficient of friction with nanoparticle concentration is measured using pin-on-disc tribometry under boundary, mixed, and hydrodynamic regimes of lubrication. A multi-scale multi-physics thermo-mixed lubrication model is developed to provide fundamental understanding of the measured tribometric results. The analytical approach combines continuum contact mechanics, thermal-mixed lubrication comprising the interaction of rough surfaces, as well as a thermal network heat transfer model. In particular, Einsteinʹs viscosity model for dispersed hard particles together with Vogel's viscosity-temperature dependence model for fluid viscosity containing nanoparticles represent new contributions to knowledge. This integrated numerical-experimental study of nanofluid thermal and tribological asse...
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Research Interests: Engineering, Economics, Nanocomposites, Internal Combustion Engines, Internal Combustion Engine, and 12 moreAutomotive Engineering, Surface Coatings, Lubrication and Friction, Fuel economy, Friction, Carbon Emissions, Automotive Technology, Applied Energy, DLC, Power Losses, CO Emissions, and Piston Rings
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The developed model for thermal conductivity of nanofluids integrates the interfacial Kapitza resistance, the characteristics of the nanolayer, convective diffusion and surface energy with capillary condensation.
Research Interests: Materials Science, Physical Chemistry, Nanofluidics, Nanomaterials, Heat Transport, and 13 moreNanoparticles, Nanotechnology, Nanochemistry, Nanofluids, Nanoscience, Nanophysics, Nanofluid, RSC, Thermal Conductivity, Nanofluid Heat Transfer, Heat Trasnfer, Theory of Molecular Self-assembly, and Nanolayer
Piston impacts against the cylinder liner are the most significant sources of mechanical noise in internal combustion (IC) engines. Traditionally, the severity of impacts is reduced through the modification of physical and geometrical... more
Piston impacts against the cylinder liner are the most significant sources of mechanical noise in internal combustion (IC) engines. Traditionally, the severity of impacts is reduced through the modification of physical and geometrical characteristics of components in the piston assembly. These methods effectively reduce power losses at certain engine operating conditions. Frictional losses and piston impact noise are inversely proportional. Hence, the reduction in power loss leads to louder piston impact noise. An alternative method that is robust to fluctuations in the engine operating conditions is anticipated to improve the engine's noise, vibration and harshness (NVH) performance, while exacerbation in power loss remains within the limits of conventional methods. The concept of targeted energy transfer (TET) through the use of nonlinear energy sink (NES) is relatively new and its application in automotive powertrains has not been demonstrated yet. In this paper, a TET device...
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The impulsive behavior of the piston in the cylinder liner plays a key role in the noise, vibration, and harshness (NVH) of internal combustion engines. There have been several studies on the identification and quantification of piston... more
The impulsive behavior of the piston in the cylinder liner plays a key role in the noise, vibration, and harshness (NVH) of internal combustion engines. There have been several studies on the identification and quantification of piston impact action under various operation conditions. In the current study, the dynamics of the piston secondary motion are initially explored in order to describe the aggressive oscillations, energy loss, and noise generation. The control of piston secondary motion (and thus, impacts) is investigated using a new passive approach based on energy transfer of the highly transient oscillations to a nonlinear absorber. The effectiveness of this new method for improving the piston impact behavior is discussed using a preliminary parametric study that leads to the conceptual design of a nonlinear energy absorber.
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Research Interests: Mechanical Engineering, Hydraulics, Internal Combustion Engines, Hydro Power, Surface Roughness, and 15 moreInternal Combustion Engine, Automotive Engineering, Automotive, Heavy Duty Diesel Engine, Multibody Dynamics Analysis, Lubrication and Friction, Multibody Dynamics, Surface topography, Friction, Clutch Systems, Off Highway and Auto Components Design and Analysis, Coefficient of Friction, Off Road Vehicle, Heavy Duty Diesel Engines, and Friction Coefficient
Fluid media such as water and ethylene glycol are usually quite poor conductors of heat. Nanoparticles can improve the thermal properties of fluids in a remarkable manner. Despite a plethora of experimental and theoretical studies, the... more
Fluid media such as water and ethylene glycol are usually quite poor conductors of heat. Nanoparticles can improve the thermal properties of fluids in a remarkable manner. Despite a plethora of experimental and theoretical studies, the underlying physics of heat transport in nanofluids is not yet well understood. Furthermore, the link between nanoscale energy transport and bulk properties of nanofluids is not fully established. This paper presents a thermal conductivity model, encapsulating solid-liquid interfacial thermal resistance, particle shape factor and the variation of thermal conductivity across a physisorbed fluidic layer on a nanoparticle surface. The developed model for thermal conductivity integrates the interfacial Kapitza resistance, the characteristics of a nanolayer, convective diffusion and surface energy with capillary condensation. In addition, the thickness of the nanolayer is predicted using the Brunauer-Emmett-Teller (BET) isotherms and micro/nano-menisci generated pressures of condensation. Such a comprehensive model for thermal conductivity of nanoparticles and systematic study has not hitherto been reported in the literature. The thermal conductivity model is evaluated using experimental data available in open literature.
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ABSTRACT An analytical/numerical methodology is presented to calculate the radiated noise due to internal combustion engine piston impacts on the cylinder liner through a film of lubricant. Both quasi-static and transient dynamic analyses... more
ABSTRACT An analytical/numerical methodology is presented to calculate the radiated noise due to internal combustion engine piston impacts on the cylinder liner through a film of lubricant. Both quasi-static and transient dynamic analyses coupled with impact elasto-hydrodynamics are reported. The local impact impedance is calculated, as well as the transferred energy onto the cylinder liner. The simulations are verified against experimental results for different engine operating conditions and for noise levels calculated in the vicinity of the engine block. Continuous wavelet signal processing is performed to identify the occurrence of piston slap noise events and their spectral content, showing good conformance between the predictions and experimentally acquired signals.
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This study aims at introducing the potential to utilise transfer learning methods in the training of artificial neural networks for tribological applications. Artificially enhanced surfaces through surface texturing, as an example, are... more
This study aims at introducing the potential to utilise transfer learning methods in the training of artificial neural networks for tribological applications. Artificially enhanced surfaces through surface texturing, as an example, are investigated under hydrodynamic regime of lubrication. The performance of these surface features is assessed in terms of load carrying capacity and friction. A large performance dataset including bearing load carrying capacity and friction is initially obtained for a specific category of textures with rectangular cross-sectional profile through analytical methods. The produced bearing performance are used to train a neural network. This neural network was then trained further by a minimal set of performance measure data from an intended category of textures with triangular cross-sectional profiles. It is shown that the resulting neural network performs with acceptable level of confidence for those intended texture profiles when trained with such relatively low number of performance data points. The results indicate that fast analytical methods can potentially produce a large volume of training datasets, which effectively allows for use of relatively lower number of training data sets from the intended category, where creating data for trainings can be more complex or time consuming. Use of transfer learning method in tribological applications and use of bearing performance parameters, as opposed to bearing design parameters, for training the neural networks are the major novel contributions of this study, which has not hitherto been reported elsewhere.
Research Interests: Computer Science, Artificial Intelligence, Transfer Learning, Lubrication, Surface Texturing, and 15 moreTribology, Surface Engineering, Artificial Neural Networks, Lubrication and Friction, Surface Design, Surface topography, Friction, Bearings, Laser Surface Texturing, Surface treatment, Hydrodynamic Lubrication, Artificial Neural Network, Load Carrying Capacity, Surface Pattern Design, and Surface Texture
In this paper, a mathematical model of a rotor-bearing system is presented. The model includes modal elastodynamics of a flexible rotor as well as the in-plane radial dynamics of the bearing with a flexible outer race. Elastodynamics of... more
In this paper, a mathematical model of a rotor-bearing system is presented. The model includes modal elastodynamics of a flexible rotor as well as the in-plane radial dynamics of the bearing with a flexible outer race. Elastodynamics of the flexible shaft utilises a solution based on Green's function to provide a computationally efficient approach. The flexible bearing outer race is modelled using Timoshenko beam theory. The system model also includes detailed lubricated contact mechanics of balls-to-races contacts with viscous friction. Therefore, the rotor-bearing analysis represents a detailed multi-physics tribodynamics and modal elastodynamic responses of the system which closely represents broad-band vibration response of such systems in practice, an approach not hitherto reported in the literature. It is also demonstrated that the outer race flexibility changes the location of the stability orbital centres, as well as the spread of limit cycle vibrations. Furthermore, it accentuates the occurrence of multiples of ball pass frequency. The importance of integrated system dynamics and lubricated contact mechanics is highlighted, showing that although the elastodynamic response of the rotor's flexible elements may not be clear in the acquired vibration signal, its effect on energy efficiency of the system can be quite important.
Research Interests: Mechanical Engineering, Nonlinear dynamics, Rotordynamics, Lubrication, Tribology, and 15 moreNonlinear vibrations, Energy efficiency, Automotive NVH, Mechanical Vibrations, Lubrication and Friction, Elastodynamics, Rolling element bearings, Friction, Lubricated Friction, Modal, Bearings, Timoshenko Beam, Nonlinear system, Ball bearings, and Energy Efficiency
Noise, vibration, and harshness (NVH) issues pose considerable challenges for electric vehicle powertrain engineers. Gear vibrations generate an intrusive gear whine noise, with significant impact on the sound quality of electric... more
Noise, vibration, and harshness (NVH) issues pose considerable challenges for electric vehicle powertrain engineers. Gear vibrations generate an intrusive gear whine noise, with significant impact on the sound quality of electric powertrains. Dynamic transmission error (DTE) is the most quantitative indicator for gear NVH. Backlash, time variable meshing stiffness and damping contribute to DTE. Hence, a better understanding of these excitation sources is essential. A gear tribodynamics model is developed using potential energy method to estimate time variable meshing stiffness (TVMS). A fully analytical time-efficient model is proposed for lubricated contact stiffness based on transitions in the regimes of lubrication. The model accounts for the combined effects of surface elasticity and lubricant stiffness. Film thickness and damping coefficients are transiently updated at each instant during meshing cycle. The predictions from this model are compared with measured results from the literature and predicted results from Hertz contact model. The lubricated contact model successfully shows the contribution of the lubricant stiffness to TVMS and its variations with elasticity and viscosity parameters during meshing cycle. Gear harmonic and super-harmonic resonances are accurately estimated in terms of amplitude, frequencies and stiffness softening nonlinearities. Time history responses and phase-displacement diagrams show good agreement with the gear dynamics response at the main harmonic and second super-harmonic frequencies. The proposed model has a reasonable accuracy, significantly better than those from Hertzian contact models, and is considerably time efficient in comparison to numerical EHL solvers.
Research Interests: Nonlinear dynamics, Electric Vehicles, Lubrication, Gears, Automotive Engineering, and 15 morePowertrain, Gearbox, Mechanical Vibrations, Atuomobile Powertrain System, Lubrication and Friction, Stiffness, Sound and Vibration, Acoustics and Vibration, Hybrid Electric Vehicles, Electric Vehicle, Nonlinear system, Electrical Vehicles, Gearbox Dynamic, Plug In Hybrid Electric Vehicles, and harshness
Constant Velocity Joint (CVJ) mechanisms enable torque transmission between two shafts at a fixed or variable angle. Cross groove CVJs are typically used in high performance automotive applications due to their versatility and light... more
Constant Velocity Joint (CVJ) mechanisms enable torque transmission between two shafts at a fixed or variable angle. Cross groove CVJs are typically used in high performance automotive applications due to their versatility and light weight. Critical failure modes, such as pitting or abrasive wear, occur due to the harsh tribological conditions at ball reversals. In this research, an existing mathematical model is developed further for the case of cross groove CVJs including an accurate contact mechanics model. The developed model is validated against a published data set from literature. Surface topography of worn raceways are experimentally measured and the results from the developed model are corroborated with the measured surface parameters. This improved model shows the correlations between predicted contact force variation and wear scar depths during ball reversals, hitherto not reported in the literature.
Research Interests: Mechanical Engineering, Mechanics, Vehicle Dynamics, Contact Mechanics, Tribology, and 15 moreVehicle Engineering, Automotive NVH, Automotive Engineering, Automotive, Atuomobile Powertrain System, Contact forces, Auto Racing, Mechanism, Automotive Technology, Friction and wear, Automotive Powertrain, Torque, Vehicle Powertrain Dynamics, Joint contact force, and CVJ
Meshing teeth pairs of involute spur gears often form the final drive of high-performance motorsport transmissions. They are subject to high normal and shear loading. Under transient conditions pertaining to a meshing cycle, the contact... more
Meshing teeth pairs of involute spur gears often form the final drive of high-performance motorsport transmissions. They are subject to high normal and shear loading. Under transient conditions pertaining to a meshing cycle, the contact conditions alter from the onset of teeth pair engagement through to maximum normal loading, followed by contact separation. Sliding motion only ceases instantaneously at the pitch point. The regime of lubrication remains mostly in non-Newtonian thermo-elastohydrodynamic conditions. The results show that a starved inlet boundary is attained throughout most of the meshing cycle which leads to the diminution of the pressure spike at the exit from the contact conjunction. The reversing sub-surface shear stresses are the main source of the onset of any inelastic deformation, which is dominated by the primary pressure peak in compliance with the Hertzian maximum pressure. The shear stress field is supplemented by an induced field due to the presence of the...
Research Interests: Tribology (Engineering), Contact Mechanics, Lubrication, Tribology, Gears, and 13 moreGearbox, Non-Newtonian Rheology, Lubrication and Friction, Elastohydrodynamics, Thermal modelling, Shear Stress, High performance, Gear Design, Spur Gears Parameter Modelling, Lubricants, Surface stresses in solids, Gears Modeling, and Pitting
Supplementary information files for 'Influence of advanced cylinder coatings on vehicular fuel economy and emissions in piston compression ring conjunction'<br>Abstract:IC engines contribute to global warming through... more
Supplementary information files for 'Influence of advanced cylinder coatings on vehicular fuel economy and emissions in piston compression ring conjunction'<br>Abstract:IC engines contribute to global warming through extensive use of fossil fuel energy and emission of combustion by‐products. Innovative technologies such as cylinder de‐activation (CDA), after‐exhaust heat treatment, surface texturing and coatings are proposed to improve fuel economy and reduce emissions of the vehicle fleet. Therefore, study of coating technology through a comprehensive multi‐physics analytical model of engine top compression ring is important to ascertain ways of promoting energy savings. This paper presents a multi‐scale, multi‐physics model of the compression ring‐cylinder bore conjunction, using three alternative bore surfaces. The model comprises ring dynamics, contact tribology, heat transfer and gas blow‐by. Tribological and thermal properties of advanced coatings, such as Nickel...
Supplementary Information Files for 'An assessment of gas power leakage and frictional losses from the top compression ring of internal combustion engines'<br>Abstract:A multi-physics integrated analysis of piston top... more
Supplementary Information Files for 'An assessment of gas power leakage and frictional losses from the top compression ring of internal combustion engines'<br>Abstract:A multi-physics integrated analysis of piston top compression ring of a high-performance internal combustion engines is presented. The effects of transient ring elastodynamics, thermal gas flow through piston crevices upon chamber leakage pressure and parasitic frictional losses are investigated. The multi-physics analysis comprises integrated flexible ring dynamics, ring-liner thermo-mixed hydrodynamics and gas blow-by, an approach not hitherto reported in literature. The predictions show close conformance to frictional measurements under engine motored dynamometric conditions. It is shown that power losses due to gas leakage can be as much as 6 times larger than frictional losses, which are usually considered as the main sources of inefficiency.<br>
A novel integrated multi-physics assessment of the piston top compression ring of an internal combustion engine under normal operation mode, as well as subjected to cylinder deactivation is carried out. The methodology comprises... more
A novel integrated multi-physics assessment of the piston top compression ring of an internal combustion engine under normal operation mode, as well as subjected to cylinder deactivation is carried out. The methodology comprises ring-liner thermo-mixed hydrodynamics, elastodynamics of ring, as well as combustion gas blow-by and emissions. Therefore, the analysis provides prediction of ring-liner contact’s energy losses and gas power leakage across the piston and ring crevices, as well as the resulting emissions. Cylinder deactivation (CDA) technology reduces the unburnt fuel entering the ring-pack crevices, as well as the emissions. It is also shown that the frictional and gas leakage power losses are exacerbated under CDA by as much as 20%. Although this is much lower than the potential gains in fuel usage when using CDA. The optimisation of the piston compression ring would provide further fuel efficiency and improved emissions, an issue which has not hitherto received the attenti...
Research Interests: Mechanical Engineering, Materials Science, Internal Combustion Engines, Automobile, Tribology, and 12 moreEnergy efficiency, Automotive Engineering, Lubrication and Friction, Energy Saving, Fuel economy, Friction, Automotive Technology, Fuel efficiency, Energy Efficiency, Cylinder Liner, CO Emissions, and Piston Rings
The study of textured surface performance is one of the highly researched topics in recent times. This is mainly due to the advantages that such surfaces can potentially provide in practice, in mitigating adverse tribological conditions,... more
The study of textured surface performance is one of the highly researched topics in recent times. This is mainly due to the advantages that such surfaces can potentially provide in practice, in mitigating adverse tribological conditions, such as friction and wear. However, considering the complexities found in practice, a methodological analysis and evaluation procedure is essential in order to gain an understanding of the benefits from utilising such features in a given contact. The current study provides a combined analytical and experimental approach towards an enhanced understanding of the behaviour of textured surfaces relative to their untextured counterparts. The developed analytical models are invaluable in providing an insight into the relationship between the many parameters involved in defining even simple surface texture feature geometry and the expected outcomes in practice, when corroborated with experimental results. The current study reports on such an endeavour. Wit...
Research Interests: Engineering, Materials Science, Tribology (Engineering), Lubrication, Surface Texturing, and 12 moreTribology, Surface Engineering, Lubrication and Friction, Friction, Bearings, Surface texture modelling, Lubricants, Sliding Bearings, Hydrodynamic Lubrication, slider Bearing, Piston Rings, and Surface Texture
The viscosity and tribological behavior of nanofluids formed by dispersed nano-diamond particles within Poly-Alpha-Olefin (PAO6) lubricant is studied at different concentrations. The variation of coefficient of friction with nanoparticle... more
The viscosity and tribological behavior of nanofluids formed by dispersed nano-diamond particles within Poly-Alpha-Olefin (PAO6) lubricant is studied at different concentrations. The variation of coefficient of friction with nanoparticle concentration is measured using pin-on-disc tribometry under boundary, mixed, and hydrodynamic regimes of lubrication. A multi-scale multi-physics thermo-mixed lubrication model is developed to provide fundamental understanding of the measured tribometric results. The analytical approach combines continuum contact mechanics, thermal-mixed lubrication comprising the interaction of rough surfaces, as well as a thermal network heat transfer model. In particular, Einstein’s viscosity model for dispersed hard particles together with Vogel’s viscosity-temperature dependence model for fluid viscosity containing nanoparticles represent new contributions to knowledge. This integrated numerical-experimental study of nanofluid thermal and tribological assessme...
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Research Interests: Mechanical Engineering, Tribology (Engineering), Internal Combustion Engines, Lubrication, Tribology, and 11 moreEnergy efficiency, Internal Combustion Engine, Automotive Engineering, Lubrication and Friction, Gas Dynamics, Friction, Energy Efficiency, Power Losses, Elsevier, Power Loss, and Piston Rings
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In the present paper, a new 2-D Van der Pol structural oscillator model is introduced for the vortex induced vibrations of circular cylinders.The main purpose of this task is to control the recently introduced model by means of modern... more
In the present paper, a new 2-D Van der Pol structural oscillator model is introduced for the vortex induced vibrations of circular cylinders.The main purpose of this task is to control the recently introduced model by means of modern control definitions in state space. In order to control the system, the whole model is linearized about its equilibrium point by deriving state-space matrices. Then, the linear transfer function is obtained and controlled by pole-placement technique which is based on the state variables feedback. Afterwards, this linear controller is applied to the nonlinear system about its equilibrium point by assuming that there is no uncertainty in both physical and mathematical models. Eventually,the results for linear and nonlinear systems are compared.
An analytical EHL model suitable for highly loaded point contacts operating in mixed and boundary regimes of lubrication is presented. The results are compared and validated with the experimental measurements of friction coefficient from... more
An analytical EHL model suitable for highly loaded point contacts operating in mixed and boundary regimes of lubrication is presented. The results are compared and validated with the experimental measurements of friction coefficient from an MTM tribometer. Measurements are carried out upon a PAO40 oil at medium to high temperatures. In general, a good agreement in trend and magnitude over a wide range of operating conditions is observed. Both the experimental findings and the model predictions show an inverse relationship between friction and contact load in mixed and boundary regimes of lubrication, an effect not hitherto reported in literature.
Research Interests: Rheology, Tribology (Engineering), Contact Mechanics, Lubrication, Tribology, and 15 moreViscosity, Lubrication and Friction, Elastohydrodynamics, Rolling element bearings, Friction, Elasto-Hydrodynamic Lubrication, Thermal Analysis, Analytical Model, Ball bearings, Lubricants, Boundary Lubrication, EHD Lubrication, Friction Coefficient, Traction, and MTM
Machines operate under increasingly harsher contact conditions, causing significant wear and contact fatigue. Sub-surface stresses are responsible for the premature contact fatigue of rolling element bearings, meshing gears, and... more
Machines operate under increasingly harsher contact conditions, causing significant wear and contact fatigue. Sub-surface stresses are responsible for the premature contact fatigue of rolling element bearings, meshing gears, and cam-follower pairs. Surface protection measures include hard, wear-resistant coatings. Traditionally, contact integrity has been predicted using classical Her ian contact mechanics. However, the theory is only applicable when the contact between a pair of ellipsoidal solids of revolution may be considered as a rigid indenter penetrating a semi-infinite elastic half-space. Many coatings act as thin bonded elastic layers that undergo considerably higher pressures than those predicted by the classical theory. Furthermore, inelastic deformation of bonded solids can cause plastic flow, work-hardening, and elastoplastic behaviour. This paper presents a comprehensive, integrated contact mechanics analysis that includes induced sub-surface stresses in concentrated counterformal finite line contacts for all the aforementioned cases. Generated pressures and deformation are predicted for hard coated surfaces, for which there is a dearth of relevant analysis. The contact characteristics, which are of particular practical significance, of many hard, wear-resistant advanced coatings are also studied. The paper clearly demonstrates the importance of using efficient semi-analytical, detailed holistic contact mechanics rather than the classical idealised methods or empirical numerical ones such as FEA. The novel approach presented for the finite line contact of thin-layered bonded solids has not hitherto been reported in the open literature.
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An integrated gear tribodynamics model is proposed for the study of EV powertrains' performance. The model considers the transient effects of lubrication regimes, non-Newtonian shear thinning, inlet shear heating, deformation states of... more
An integrated gear tribodynamics model is proposed for the study of EV powertrains' performance. The model considers the transient effects of lubrication regimes, non-Newtonian shear thinning, inlet shear heating, deformation states of asperities in mixed regime of lubrication and contact temperature using a set of analytical routines, which are computationally efficient. The proposed gear tribodynamics model provides a breakdown of the interdependency of these attributes and studies their impact on the performance of gear contacts. The results indicate that up to 30% of the contact load can be carried by asperities, of which 80% undergo elastoplastic deformation. In addition, the contribution of lubricant to contact stiffness can be greater than that of surface asperities by an order of magnitude.
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Accurate prediction of constant velocity joint transient contact loading and complex kinematics is necessary to improve joint design and prevent incurring failure from rolling contact fatigue. A detailed multibody dynamic model is... more
Accurate prediction of constant velocity joint transient contact loading and complex kinematics is necessary to improve joint design and prevent incurring failure from rolling contact fatigue. A detailed multibody dynamic model is presented for cross groove constant velocity joints used in high performance automotive racing applications, hitherto not reported in the open literature. The developed model includes detailed contact mechanics and friction models for all contacts made between the components. A novel semi-Hertzian contact model is adopted for the cage-race conjunction. Local contact kinematics is evaluated based on a methodology used in tribological analysis. The proposed model is validated against available computational models provided in literature for cross groove designs. Using the model, contact pressures occurring in the ball-race and ball-cage contacts are shown to reach levels as high as 4 and 5 GPa, respectively. The assumed value of friction coefficient is shown to have a strong influence on the predicted contact forces. Local contact motions are presented for the ball-race and ball-cage contacts, demonstrating complex motion which varies between pure rolling and pure sliding within a single cycle.
Research Interests: Vehicle Dynamics, Theory Of Mechanisms, Tribology (Engineering), Mechanism Design, Kinetics And Mechanistic Studies, and 15 moreAutomobile, Contact Mechanics, Tribology, Formula One, Automotive Engineering, Powertrain, Multibody Dynamics, Kinematics of Machines, Friction, Automotive Technology, Joints, Automotive Powertrain, Formula One car, Drivetrain Dynamics, and CVJ
In the quest for decarbonisation, alternative clean fuels for propulsion systems are sought. There is definite advantage in retaining the well-established principles of operation of combustion engines at the core of future developments... more
In the quest for decarbonisation, alternative clean fuels for propulsion systems are sought. There is definite advantage in retaining the well-established principles of operation of combustion engines at the core of future developments with hydrogen as a fuel. Hydrogen is envisaged as a clean source of energy for propulsion of heavy and off-road vehicles, as well as in marine and construction sectors. A source of concern is the unexplored effect of hydrogen combustion on dilution and degradation of engine lubricants and their additives, and consequently upon tribology of engine contact conjunctions. These potential problems can adversely affect engine efficiency, durability, and operational integrity. Use of different fuels and their method of delivery, produces distinctive combustion characteristics that can affect the energy losses associated with in-cylinder components and their durability. Therefore, detailed predictive analysis should support the developments of such new generation of eco-friendly engines. Different fundamental physics underpin the various aspects of a pertinent detailed analysis. These include thermodynamics of combustion, in-cylinder tribological interactions of contacting surfaces, and blowby of generated gasses. This paper presents such an integrated multi-physics analysis of internal combustion engines with focus on hydrogen as the fuel. Such an in-depth and computationally efficient analysis has not hitherto been reported in the literature. The results show implications for lubricant degradation due to the use of hydrogen in the performance of in-cylinder components and the underlying physical principles.
Research Interests: Thermodynamics, Hydrogen, Heat Transfer, Tribology (Engineering), Internal Combustion Engines, and 15 moreLubrication, Tribology, Internal Combustion Engine, Multiphysics Simulation, Hydrogen Fuel, IC ENGINES, Viscosity, Lubrication and Friction, Gas Dynamics, Friction, Tribology (Engineering) Internal combustion engine, Piston Rings, Engine tribology, Hydrogen Combustion, and Hydrogen Internal Combustion Engine
A multi-physics integrated analysis of piston top compression ring of a high-performance internal combustion engines is presented. The effects of transient ring elastodynamics, thermal gas flow through piston crevices upon chamber leakage... more
A multi-physics integrated analysis of piston top compression ring of a high-performance internal combustion engines is presented. The effects of transient ring elastodynamics, thermal gas flow through piston crevices upon chamber leakage pressure and parasitic frictional losses are investigated. The multi-physics analysis comprises integrated flexible ring dynamics, ring-liner thermo-mixed hydrodynamics and gas blow-by, an approach not hitherto reported in literature. The predictions show close conformance to frictional measurements under engine motored dynamometric conditions. It is shown that power losses due to gas leakage can be as much as 6 times larger than frictional losses, which are usually considered as the main sources of inefficiency.
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A common strategy to reduce engine parasitic power losses is to decrease pumping and viscous friction losses through use of a low viscosity engine oil. However, reducing lubricant viscosity can also decrease the contact load carrying... more
A common strategy to reduce engine parasitic power losses is to decrease pumping and viscous friction losses through use of a low viscosity engine oil. However, reducing lubricant viscosity can also decrease the contact load carrying capacity, thus exacerbating direct interaction of contacting surfaces. This leads to boundary frictional losses in contacts prone to mixed regime lubrication. As a result, detailed experimental and modelling studies of engine component frictional behaviour is required to ensure the engine level trade-offs. This paper presents a combined experimental and numerical investigation of frictional behaviour of three-piece piston oil control rings. A bespoke tribometer replicates kinematics of the contact between a full oil control ring and the cylinder liner. The three-piece oil control ring is composed of two segments, separated by a waveform type expander. The experimental results indicate the dominance of mixed regime of lubrication throughout the stroke. This is particularly the case when the experiments are conducted at 80 °C; a typical engine sump temperature, when compared with the case of 20 °C (a typical engine start-up temperature in the UK in the Spring). A mixed hydrodynamic numerical model of the oil control ring-cylinder liner tribological interface is employed to apportion frictional contributions with their physical underlying mechanisms. The combined experimental-predictive approach provides key information for engine designers when considering the efficiency trade-offs.