bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling and validation of a fast switching valve intended for combustion engine valve trains
Authors: Pohl J , Sethson M , Krus P , Palmberg J-O
Published: October 2002

In recent years much research has been done in the area of variable-valve actuation in order to improve the efficiency of combustion engines. Currently, a number of different concepts for variable-valve actuation are under development or at a prototype stage. Hydraulic actuation has been an obvious candidate, but the lack of sufficiently fast switching valves with appropriate flowrates has been the major shortcoming. Design of such highly dynamic systems requires accurate models of the actual included components.

In this paper a model of a fast 2/2 switching valve is presented, where both the magnetic path as well as the spool assembly are modelled. The model presented here is primarily aimed at system simulations; therefore it has to be kept simple with the number of parameters low.

Some of the parameters are often hard to obtain, especially when it comes to magnetic material properties. In this study, an optimization strategy has been utilized in order to parameterize the model against measured data. However, even for major deviations from the operational point used for the model adaptation, the model predicts the valve response sufficiently accurately.
Robust polynomial eigenstructure assignment using dynamic feedback controllers
Authors: White B A
Published: October 2002

This paper presents a dynamic controller format for use in polynomial eigenstructure assignment. It formulates the controller in singular-value decomposition format, which enables the designer to use simple SISO (single-input, single-output) compensators, together with direction matrices to construct the controller. The technique utilizes the root locus to evaluate stability and performance. It also introduces several metrics for decoupling, disturbance rejection, actuator movement and stability robustness in a graphical manner that allows a systematic design to be carried out. The paper also includes a two-input, two-output design example to illustrate the technique.
Robust adaptive neural network control for a class of non-linear systems
Authors: Ge S S , Lee T H
Published: October 2002

In this paper, a general framework for robust parallel adaptive neural network (NN) control design is presented for a class of non-linear systems motivated by the work in references (14) and (15). The controller is based on applying direct adaptive techniques to an additional parallel neural network to provide adaptive enhancements to a basic fixed controller and incorporating a sliding mode term for robustness. It is shown that if bounded basis function (BBF) networks are used for the additional parallel NN, uniformly stable adaptation is assured and asymptotic tracking of the reference signal is achieved. Because of the introduction of the GL (Ge-Lee) matrices and operator, the results presented here are more general than the existing results.
Evolutionary adaptive active vibration control
Authors: Hossain M A , Tokhi M O
Published: October 2002

This paper presents an investigation into the development of an adaptive active control mechanism for vibration suppression using genetic algorithms (GAs). GAs are used to estimate the adaptive controller characteristics, where the controller is designed on the basis of optimal vibration suppression using the plant model. This is realized by minimizing the prediction error of the actual plant output and the model output. A MATLAB GA toolbox is used to identify the controller parameters. A comparative performance of the conventional recursive least-squares (RLS) scheme and the GA is presented. The active vibration control system is implemented with both the GA and the RLS schemes, and its performance assessed in the suppression of vibration along a flexible beam structure in each case.
Measurement of the longitudinal transmission characteristics of fluid-filled hoses
Authors: Drew J E , Longmore D K , Johnston D N
Published: October 2002

Flexible hoses used within a hydraulic circuit can reduce the levels of both pressure fluctuations and structural vibration. An important application is in automotive power steering where tubular inserts and restrictors are often used inside a hose to enhance the reduction of pressure ripple. The performance of a hose assembly in the frequency domain is usually specified by an impedance matrix relating pressure and flow ripple at the ends. However, these quantities are coupled to fluctuating axial tension and motion of the hose walls and it is desirable to have a 4 × 4 impedance matrix relating the complex amplitudes of all these quantities. A convenient method of experimentally measuring this matrix is presented. As well as allowing investigation of the main structural and fluid transmission from the hose assembly to the subsequent pipework, the 4 × 4 impedance matrix provides a way of obtaining the dynamic properties of hose walls under realistic conditions for use in further studies.
Genetic algorithms with variable mutation rates: Application to fuzzy logic controller design
Authors: Pham D T , Karaboga D
Published: October 2002

Three variable mutation rate strategies for improving the performance of genetic algorithms (GAs) are described. The problem of optimizing fuzzy logic controllers is used to evaluate a GA adopting these strategies against a GA employing a static mutation regime. Simulation results for a second-order time-delayed system controlled by fuzzy logic controllers (FLCs) obtained using the different GAs are presented.
An enhanced computed-torque control algorithm for robot manipulators
Authors: Li Q , Tso S K , Poo A N
Published: October 2002

An enhanced computed-torque control approach, which is developed based on the intuitive design concept of the internal model control structure, is proposed in this paper. Both theoretical analyses and simulation studies on a two-link robot prove that the robustness of this enhanced algorithm can surpass that of the conventional computed-torque control scheme by a large extent.
Output prediction in systems with backlash
Authors: Schenker B , Agarwal M
Published: October 2002

Systems exhibiting backlash pose a challenging prediction problem, since they involve state multiplicity for finite-order input-output models. Future outputs, given future inputs, cannot adequately be predicted using only a few past outputs and inputs, but are critically dependent on the internal state of these systems. In case the presence of steady state multiplicity is not known, a reliable predictor should be able to handle it without this explicit knowledge; in case the presence is known, the predictor would do well to be able to benefit from this knowledge even when the rest of the process might not be known.

Conventional empirical models such as feedforward neural networks cannot accurately represent systems that entail state multiplicity for their intrinsically limited input—output system representation. This work employs a state-feedback neural network structure, previously proposed by the authors, as an attractive solution to the problem of reliable output prediction for systems with hysteresis or backlash. By generating a state-space mapping of the system, the proposed network structure is able to store the relevant information in the state, thereby avoiding the information loss incurred by the input-output predictor. The feedback structure also yields more accurate multistep predictions.

The presented results for a simulation example of a backlash system demonstrate the superiority of the feedback structure over the feedforward network for achieving satisfactory prediction accuracy without explicit knowledge of the presence of backlash.
Real-time implementation of an algorithm for self-repairing control systems based on LQG optimization
Authors: Caliskan F
Published: October 2002

In this paper a self-repairing real-time control (SRC) system based on LQG (Linear Quadratic Gaussian) optimization is proposed. Its transputer implementation and a real-time aircraft application are presented. The SRC system is composed of the monitoring of the control system, the detection and diagnosis of the failure and the reconfiguration of the control laws. The proposed SRC system is suitable for real-time operation because of the parallel nature of its architecture. The INMOS multitransputer implementation of the SRC applied to an aircraft model provides 56 per cent efficiency compared to a single-transputer implementation.
Proportional-integral-plus (PIP) control of time delay systems
Authors: Taylor C J , Chotai A , Young P C
Published: October 2002

The paper shows that the digital proportional-integral-plus (PIP) controller formulated within the context of non-minimum state space (NMSS) control system design methodology is directly equivalent, under certain non-restrictive pole assignment conditions, to the equivalent digital Smith predictor (SP) control system for time delay systems. This allows SP controllers to be considered within the context of NMSS state variable feedback control, so that optimal design methods can be exploited to enhance the performance of the SP controller. Alternatively, since the PIP design strategy provides a more flexible approach, which subsumes the SP controller as one option, it provides a superior basis for general control system design. The paper also discusses the robustness and disturbance response characteristics of the two PIP control structures that emerge from the analysis and demonstrates the efficacy of the design methods through simulation examples and the design of a climate control system for a large horticultural glasshouse system.
Discrete-time least-squares Padé order reduction: A stability preserving method
Authors: Lucas T N , Smith I D
Published: October 2002

A new stability preservation property is proved for the least-squares Padé order reduction method when applied to discrete-time systems. It is shown that the property depends on which free reduced model parameter is chosen to be unity. Clarification is also given on how the system is actually approximated using this method. An example illustrates the enhanced appeal of the method as a result of the stability preservation property.
Mechanical system regulation using matrix quadratic models—a review
Authors: Whalley R
Published: October 2002

Matrix quadratic descriptions for series coupled mechanical systems are used in the synthesis of controllers generating prescribed closed-loop pole configurations. Three-term control action is introduced to improve the load disturbance rejection properties of the system while maintaining the specified set-point response. Conditions maximizing the closed-loop model's steady state determinant value, constraining thereby the error to load disturbances, are derived and a study illustrating this feature is presented. The interaction between the transient and steady state performance of the system is commented upon.
Robot torque and position control using an electrorheological actuator
Authors: Brookfield D J , Dlodlo Z B
Published: October 2002

An electrorheological (ER) clutch driven from a constant speed motor provides a steady torque independent of shaft angle and can be controlled by control of the applied field. Such an actuator avoids the ‘cogging’ variation in torque observed in d.c. servo-motors and is thus well suited to robot control applications, particularly in view of the very rapid time response of ER clutches (≍ 10−3s). However, the relationship between applied field and torque is difficult to model, being both non-linear and time varying. Whereas the non-linearity can be shown to be relatively small, the time-varying characteristic has remained a problem.

In most controlled plants, a non-linear or time-varying characteristic can be mitigated by providing a closed control loop around the plant. A PID (proportional plus integral plus derivative)-based torque controller was developed and tested. This was shown to be stable with at least critical damping and to exhibit low steady state error. Design of the controller was facilitated by the identification of the open-loop transfer function of the ER actuator.

The ER actuator with torque feedback was used to position a small robot link. A second PID control loop responding to the error in the link position and tuned using the standard Ziegler and Nichols method was designed and tested. A steady state error of less than 0.75 mm was achieved with a 2 per cent settling time of 2.0 s. Finally, the link position was controlled using a single-loop controller with no torque feedback and a similar steady state error achieved with a 2 per cent settling time of 1.4 s. It is argued that the ER torque actuator is ideally suited to the actuation of robot joints where precise smooth movement is required.
A representation for planar point contact joints in the multibody mechanical bond graph library
Authors: Favre W , Scavarda S
Published: October 2002

In this paper a bond graph representation of the point contact joint between two bodies with any outline curves and in planar motion is proposed. The body geometry and frames are described, the kinematic constraints attached to the point contact joint are identified and the bond graph junction structure is deduced. The example of an elliptic cam-follower is used to illustrate the bond graph representation. In particular this shows the need for the simulation to add strong damping and very stiff elements to the system.
Theoretical analysis of pressure and flow ripple in flexible hoses containing tuners
Authors: Drew J E , Longmore D K , Johnston D N
Published: October 2002

In automotive power steering systems it is common practice to include highly expandible hoses containing tubular inserts, referred to as tuners, to minimize the pump-generated pressure ripple. A theoretical model of a flexible hose containing a tuner is described, which can be used to compute the fluid-borne noise characteristics of complete systems.

Excellent agreement with experimental measurements is obtained. Leakage through the tuner wall is shown to have a strong effect on the results. With the common type of spiral wound tuner, most of the damping present is obtained from this leakage and from energy loss in the hose wall, and for low-viscosity fluids it may be acceptable to ignore the effect of fluid viscosity.
Application of non-linear H∞ control to the Tetrabot robot manipulator
Authors: Postlethwaite I , Bartoszewicz A
Published: October 2002

In this paper, an application of a non-linear H∞ control law for an industrial robot manipulator is presented. Control of the manipulator motion is formulated into a non-linear H∞ optimization problem, namely optimal tracking performance in the presence of modelling uncertainties and external disturbances. Analytical solutions for this problem are implemented on a real robot. The robot under consideration is the six-degrees-of-freedom GEC Tetrabot. Investigations are made into the selection of weights for the H∞ controller and it is shown how different selections of weights affect the Tetrabot performance. The authors believe this to be the first robotic application of nonlinear H∞ control. Comparisons of the proposed control strategy with conventional proportional-derivative and proportional-integral-derivative controllers show favourable performance of the Tetrabot under the new non-linear H∞ control scheme.
Modelling and identification of a wire-cable vibration isolator via a cyclic loading test
Authors: Ni Y Q , Ko J M , Wong C W , Zhan S
Published: October 2002

In Part 1 of the study, two improved Bouc-Wen models have been proposed to describe the hysteretic behaviour of a wire-cable vibration isolator. In this part, a frequency-domain parametric identification procedure is presented to determine the model parameters from the experimental data of the cyclic loading test. Making use of the rate-independent nature of the hysteretic behaviour, the measured quasi-periodic data sequences are modulated to periodic signals. Then the model parameters are identified from a one-stage estimate scheme using the acquired harmonic components of the displacement and restoring force signals. The identification results give rise to a good representation of the experimental hysteresis loops. After performing the modelling, the dynamic response behaviour of a wire-cable isolation system is evaluated with reference to the shear, the roll and the tension-compression modes respectively. The frequency-response characteristics in the tension-compression mode are found to be greatly different from those in shear and roll modes.
Parametric model development and quantitative feedback design for automotive torque converter bypass clutch control
Authors: Thompson D F , Kremer G G
Published: October 2002

Customer demands for large high-performance vehicles in the face of increasingly stringent fuel economy targets have led automobile makers to seek innovative ways of meeting these requirements, especially in the North American market. One of the most critical elements in automotive powertrain systems is the torque converter bypass clutch which is now in almost universal use in automatic transmission-equipped vehicles. The clutch is used to bypass the fluid coupling of the torque converter during steady state conditions (i.e. highway cruise), thus eliminating a 15–20 percent loss of efficiency. Generally, the clutch is disengaged during dynamic events (e.g. vehicle launch, braking and gear changes) when the torque converter functionality is required. Further gains in fuel economy can now be realized through modulation of the bypass clutch in some situations where it had been considered necessary that the clutch be disengaged (i.e. during gear changes). In this case, the clutch is operated in a state of continuous slip; the transmitted torque is controlled through modulation of the clutch apply pressure. The dynamics of this system, however, exhibit considerable complexity. Characterization of this behaviour has been of considerable interest among automobile makers in recent years. However, investigation of the non-linear dynamics of this system is beyond the scope of this paper; a more in-depth treatment generally requires bifurcation analysis and/or exhaustive simulation studies. The focus in this paper is upon the detailed development of a linear parametric differential equation model and the design of a linear robust feedback control system. Parametric uncertainty is included to capture the effects of variations in system damping, bulk modulus, coefficient of friction and constants of linearization. Based upon a specific operating point, a linear robust controller is developed using the quantitative feedback theory (QFT) technique. The QFT methodology is aimed at designing feedback controllers so that pointwise frequency response specifications on closed-loop tracking and disturbance rejection are met in spite of large parametric plant uncertainty. The local stability and performance of the non-linear feedback system are subsequently verified by simulation. Since the feedback design is based upon a linear parametric model, no specific guarantees can be made as to the performance of the non-linear closed-loop system, although the results are found to be satisfactory in this case.
Neural networks and hydraulic control—from simple to complex applications
Authors: Burton R T , Ukrainetz P R , Nikiforuk P N , Schoenau G J
Published: October 2002

The control of hydraulic servo-systems has been the focus of intense research over the past decades. The highly non-linear behaviour of these devices makes them ideal subjects for applying different types of sophisticated controllers. This paper considers the application of neural networks to the control of hydraulic servo-systems subjected to either non-linear friction or highly coupled loads. Three applications are considered: a very simple quasi-open-loop pattern follower, a proportional-integral-derivative (PID) multiple-gain neural controller and a neural-based controller for a very complex multiple-input multiple-output system. A major factor in these applications is the fact that the neural network controllers have been applied to real-time control of experimental systems. In all cases, these controllers showed superior performance over conventional-type PID controllers.
Non-linear dynamic systems fault detection and isolation using fuzzy observers
Authors: Chen J , Lopez-Toribio C J , Patton R J
Published: October 2002

This paper presents a novel fault detection and isolation scheme for non-linear dynamic systems. This scheme utilizes a fuzzy observer to generate the diagnostic residual signal for fault detection and isolation. This fuzzy observer, based upon the idea of Takagi-Sugeno fuzzy models, comprises a number of locally linear observers and the final state estimate is a fuzzy fusion of all local observer outputs. To ensure good estimation performance, the eigenvalues of the fuzzy observer are assigned in a pre-defined region in the complex plane. The stability as well as eigenvalue constraint conditions for the fuzzy observer design are presented and solved in the linear matrix inequality framework in this paper. Finally, the paper demonstrates the application of fuzzy observers in detecting and isolating intermittent faults in the induction motor of a railway traction system using a real-time test-rig implementation.
A hybrid artificial neural network inverse kinematic solution for accurate robot path control
Authors: Lou Y F , Brunn P
Published: October 2002

Artificial neural networks (ANNs) have recently become the focus of considerable attention in many disciplines, including robot control, where they can be used to solve highly nonlinear control problems. One of these ANN applications is that of the inverse kinematic problem, which is important in robot path planning. This paper outlines an iterative approach, using the offset error compensation method, to improve the accuracy of the inverse kinematic solution by using an ANN and the forward kinematic model of the robot. The method can be used as a feedforward position controller to generate accurate inverse kinematic information for general-purpose robotic manipulators.
Hydraulic actuator control with open-centre electrohydraulic valve using a cerebellar model articulation controller neural network algorithm
Authors: Pinsopon U , Hwang T , Cetinkunt S , Ingram R , Zhang Q , Cobo M , Koehler D , Ottman R
Published: October 2002

Real-time learning control of a hydraulic actuator is studied using a cerebellar model articulation controller (CMAC) neural network architecture. Experiments are conducted on a one-degree-of-freedom hydraulic cylinder. The main applications considered are the earth-moving equipment applications. The electrohydraulic valve used to control the flow in the hydraulic circuit is an open-centre non-pressure-compensated type of valve, the type used in most earth-moving vehicles. Large hysteresis and dead band are observed in the hydraulic system which result in a large delay and poor dynamic tracking performance. A comparison of the experimental results on the control of the hydraulic actuator for the CMAC controller and a conventional proportional-integral controller with a model-based feedforward valve transform is made.
Amplitude reduction of waviness in elastohydrodynamic lubrication using an Eyring fluid model
Authors: Jacod B , Lugt P. M. , Dumont M. L. , Tripp J. H. , Venner C. H.
Published: October 2002

This paper presents a first extension of the amplitude reduction approach, where the deformation of harmonic components of the roughness is considered, to non-Newtonian elastohydrodynamic lubrication (EHL) line contact. The amplitude reduction of one-sided waviness is computed as a function of the slide-roll ratio. Non-Newtonian effects result in an increase in the deformation for positive slide-roll ratios. This contrasts with published results using a Newtonian fluid where the deformation decreased for such conditions. Moreover, the amplitude reduction varies significantly throughout the contact, requiring an additional parameter for the characterization of the amplitude reduction. An explanation of these differences based on the velocity profile of the lubricant inside the contact concludes the paper.
Spherical surface generation mechanism in the grinding of balls for ultraprecision ball bearings
Authors: Zhang B , Nakajima A
Published: October 2002

Ultraprecision ball bearings are necessary for high-precision machines and/or high-speed machines since the vibration caused by ball bearings determines the precision of machines as a whole and may make high-speed machines fail to work. To produce ultraprecision ball bearings, it is necessary to clarify spherical surface generation mechanism in the grinding of balls. This paper is the first attempt to investigate the contact trace distribution on the ball surface, which is crucial to spherical surface generation. The kinematic analysis of the contact trace shows that the contact trace is a fixed circle on the ball surface and the contact points are not uniformly distributed on the ball surface. Experimental observation of the contact trace was also carried out. The observation is in good agreement with the analysis. Suggestions on how to distribute the contact trace over the whole ball surface and therefore to improve the precision of balls are given.
Magnetic and electron microscopy analysis of wear products of sliding tribo-conjugations
Authors: Gorkunov E. S. , Kharlamov V. V. , Sytnik S. V. , Veselov I. N. , Zadvorkin S. M. , Kogan L Kh
Published: October 2002

To evaluate the friction and wear parameters and to establish the residual lifetime of heavily loaded tribo-conjugations on samples of steel 40 (0.4 wt% C, 0.27 wt% Si, 0.63 wt% Mn, 0.24 wt% Cr and 0.17wt% Ni, with Fe being the balance) and steel 20XH3A, studies of the changes in the electromagnetic characteristics in surface layers of tribo-conjugations, lubricant performance characteristics after each testing stage in a friction machine and size distribution of wear particles were carried out. The presence of correlations between the amount of wear, eddy-current device readings and particle size distribution curves were found. The results obtained allow the stage of tribo-conjugation wear to be defined and its residual lifetime to be predicted.
On the concentrated contact as a viscometer
Authors: Bair S
Published: October 2002

Lubricant viscosities from published concentrated contact-based measurements are compared with measurements by conventional viscometry for overlapping pressures and viscosities. Contrary to published claims there are important differences. The greater than exponential pressure-viscosity behaviour, which is known to occur at high pressures, is absent from contact measurements. Deficiencies in contact-based techniques are probably due to assumed constitutive behaviour and are not related to time scale. In general, contact-based methods are poorly conditioned for the measurement of pressure-viscosity coefficients.
Kinematics of transverse real roughness in elastohydrodynamically lubricated line contacts using Fourier analysis
Authors: Morales-Espejel G. E. , Venner C. H. , Greenwood J. A.
Published: October 2002

A model is presented that facilitates prediction of the transient solution for the pressure and film thickness in an elastohydrodynamically lubricated line contact for the case of arbitrary surface microgeometry (roughness) under the assumption of Newtonian lubricant behaviour and small roughness amplitude. In the model the two parts of the transient solution (particular integral and complementary function) are calculated for each Fourier component of a surface real roughness and combined to obtain the complete transient solution. As no time-consuming numerical simulations are required, the computational scheme forms a simple and efficient tool for use in a practical engineering environment. To validate the approach, first simple cases such as single dents and harmonic waviness were considered. The predictions obtained for these cases are compared with the results of full numerical simulations, showing good agreement. Subsequently the results obtained for a realistic roughness profile are presented.
Lubrication studies of head-disk interfaces in a controlled environment Part 2: Degradation mechanisms of perfluoropolyether lubricants
Authors: Zhao X , Bhushan B , Kajdas C
Published: October 2002

The decomposition mechanisms of the perfluoropolyether (PFPE) lubricants were studied in this paper using several experimental approaches. The PFPE lubricant film can be bonded to disk surface by illuminating the lubricant film with ultraviolet (UV) light; then the durability of the head-disk interface can be improved. However, during the sliding process, the illumination with UV light can accelerate the decomposition of the lubricant, reducing the head-disk interface durability and causing more gaseous fragments because low-energy electrons created by the illumination interact with the lubricant molecules, activating and breaking up the molecules. A decomposition mechanism of the lubricant with the effect of low-energy electrons was proposed. Mechanical shear is also found to have an important effect on the decomposition of the lubricant. The partial pressures of the gaseous fragments of the lubricant increase rapidly with increase in the sliding velocity. No obvious effect of ambient temperature up to 70 °C on the decomposition of the PFPE lubricant was observed, although higher temperatures are expected to be detrimental.
Analysis of stain formation and wear mechanisms in a linear tape drive
Authors: Kattner M , Bhushan B
Published: October 2002

Magnetic reliability of a linear tape drive is intimately related to the tribology at the head-tape interface because an increase in the spacing between the read element of the head and the magnetic particles in the tape reduces the strength of the magnetic signal read from the tape. In this study, Co-γ-Fe2O3 tape was worn against magnetoresistive (MR) heads in a modified commercial tape drive. Friction, the head output and the number of drop-outs were used to determine the wear mechanisms at the head-tape interface. Additionally, atomic force microscope (AFM) measurements, Auger material composition analysis and stain thickness measurement using a nanoindentation scratch test were used to support the friction and magnetic data. Using these methods, it was found that three different wear mechanisms occur at the head-tape interface, which first involves adhesion building a stain on the head surface, followed by the cyclic wearing and accumulation of the stain. Finally, the tape binder is sufficiently worn away, causing the stain to be permanently removed by abrasion of the hard magnetic particles. The life of the head-tape interface can be improved by cleaning the stain from the head with an abrasive tape before the stain becomes too thick. Therefore, if only one tape was used in the lifetime of the head, the head would need to be cleaned only once because the tape has a finite amount of stain-producing material available. However, if the stain thickness is reduced too much, the head-tape interface will not function without an increase in stain material because the presence of the stain provides lubrication without which the friction at the head-tape interface exceeds the motor force, causing the drive to stop.
A fractal analysis of adhesive friction between rough solids in gentle sliding
Authors: Sahoo P , Roy Chowdhury S. K.
Published: October 2002

Studies of adhesive friction have always relied on careful experiments, and many plausible theories based on the observations now exist to describe the fundamental causes of interfacial bonding between rough solids. In this regard, an analytical model based on surface forces that operate within short ranges is probably not out of place. The analysis of friction is closely associated with that of adhesion between rough solids. Such analyses of adhesion and friction using a random rough surface model have already been described elsewhere. Adhesive bonds may occur at the peaks of nanometric size asperities even though the microscopic roughness would inhibit the surfaces from approaching close separation. It is therefore necessary to account for the effect of asperities ranging from nanometre to micrometre level for a true representation of asperity interactions at the interface and this essentially requires a scale-independent model such as a fractal approach.

The paper describes friction between rough solids using a fractal model and the results are compared with those using a conventional approach. The results explain some of the earlier experimental observations. It also seems that the variation in the fractal dimension D may produce a broad spectrum of results which may explain phenomenologically some of the experimental observations, hitherto not explained.
Digraph and matrix method for the selection, identification and comparison of metal-cutting fluids
Authors: Rao R Venkata , Gandhi O. P.
Published: October 2002

This paper presents a methodology to select a cutting fluid for a given machining application using the digraph and matrix method. A cutting fluid index is proposed which evaluates and ranks cutting fluids for a given machining application. The index is obtained from the cutting fluid function, obtained from the cutting fluid attributes digraph. The digraph is developed considering cutting fluid attributes and their relative importance for the considered operation. Coefficients of similarity and dissimilarity and the identification sets are also proposed. These are obtained from the cutting fluid function and are useful for easy storage and retrieval of the cutting fluid data. An example is included to illustrate the approach.
Technical Note: Some theoretical aspects of structure functions, fractal parameters and related subjects
Authors: Whitehouse D. J.
Published: October 2002

The use of structure functions in surface metrology started in 1970. It was originally used as an adjunct to correlation theory but some favourable properties have led to its being used to estimate the parameters of fractal surfaces. This note investigates some of the properties of structure functions and proposes some extensions. From these some very simple techniques for fractal analysis are developed.
Interferometry-based measurements of oil-film thickness
Authors: Marklund O , Gustafsson L
Published: October 2002

Measurement of the thickness of thin lubricant films separating rotating surfaces in elastohydrodynamic experiments presents some challenging problems. The nature of the experimental apparatus inhibits the use of most commonly applied interferometric phase measurement methods. Also the absolute thickness of the separating film must be determined, as opposed to relative distances that would be sufficient in most other measurement scenarios where interferometry methods are used. In this paper, computer-based analysis of interferograms recorded using an elastohydrodynamic lubrication Fitzeu interferometer (a so-called ball-and-disc apparatus) is discussed, the main objective being to extract the absolute oil-film thickness. Intensity based methods (most importantly, calibration look-up procedures where colour parameters from recorded dynamic interferograms are compared with table values corresponding to known film thicknesses, but also a phase measurement approach based on multi-channel interferometry using trichromatic light) are described. A discussion regarding compensation for measurement errors due to the pressure dependence of the refractive index of the lubricant is also included.
Study on cavitation inception in hydraulic oil flow through a long two-dimensional constriction
Authors: Washio S , Takahashi S , Uda Y , Sunahara T
Published: October 2002

It is known that the traditional ‘nucleus’ theory for cavitation is incompatible with certain facts physically and experimentally recognizable in oil hydraulic flows. In order to re-examine this issue, cavitation of hydraulic oil flow through a long two-dimensional acrylic constriction was observed by various techniques: stroboscopic photography with a microscope, laser beam transmission, pressure and noise measurements, and luminescence and electrical charge detection. It was revealed that, at the incipient stage of cavitation, one stationary microscopic cavity always emerges suddenly on the inlet edge. Light emission was also observed in the cavitation together with electrostatic charge. All the findings taken together, which cannot be consistently explained by nucleus theory, lead to the following hypothesis: at the separation point a tensile force rips a liquid particle from the wall, leaving behind a vacuum space, which forms the incipient stationary cavity on the edge.
Dynamic behaviours of piston rings and their practical impact. Part 2: Oil transport, friction and wear of ring/liner interface and the effects of piston and ring dynamics
Authors: Tian T
Published: October 2002

The paper discusses several important processes that have great impact on the lubrication between the top two rings and the liner. The analysis is conducted on the basis of the calculation results on a heavy-duty (HD) diesel engine using theoretical models. Oil supply mechanisms to different liner regions are analysed, and emphasis is given to the oil transport to the top liner region that is found critical to friction, wear and oil consumption in HD diesel engines. Additionally, the paper discusses the oil supply to the second ring, its uncertainties and the effect on the prediction of the performance of the top two rings. Furthermore, the effects of dynamics of the piston and rings on friction, wear and oil transport are illustrated and the effects of bore distortion on oil transport are discussed.

For practical purposes, a formula to describe the second ring running surface profile is given based on simple geometrical constraint. A new truncation method is rendered for plateau surface roughness in order to effectively use the existing mixed lubrication models.
Static and dynamic behaviours of pure squeeze films in couple stress fluid-lubricated short journal bearings
Authors: Lin J-R
Published: October 2002

On the basis of microcontinuum theory, this paper theoretically investigates the rheological effects of couple stress fluids on the static and dynamic behaviours of pure squeeze films in journal-bearing systems. The general modified Reynolds equation with no journal rotation is derived by using the Stokes constitutive equations to account for the couple stress effects resulting from lubricants containing additives or suspended particles. The cases of short bearings under a constant applied load and an alternating load are analysed. The solutions for film pressure in a closed form are shown, from which the squeeze film characteristics are determined. According to the results evaluated, the effects of couple stresses significantly increase the film pressure and then the load-carrying capacity is compared with the Newtonian lubricant case. Under a cyclic load the couple stress effects provide a reduction in the velocity of the journal centre as well as an increase in the minimum permissible height of the squeeze film. As a consequence, the bearing with a couple stress fluid as the lubricant improves the squeeze film characteristics and results in a longer bearing life.
Mechanical seal face materials
Authors: Nau B. S.
Published: October 2002

Mechanical seal face materials are described with an explanation of the properties affecting performance and the significance of surface texture including bi-Gaussian surface statistics. Aspects of seal behaviour attributable to face materials are discussed in detail, including random fluctuations of friction and thermal excursions. Boundary lubrication mechanisms of carbon-graphites and other ceramics are described. The role of tribolayers and transfer layers is highlighted. Failure modes are discussed including structural fracture, surface crazing, pitting and scoring, blistering, solids deposition and ‘squeal’ (‘ringing’). Many references are given.
Tribological effects of roughness and running-in on oil-lubricated line contacts
Authors: Chou C. C. , Lin J. F.
Published: October 2002

A gear/cam adapter was employed to study various aspects of line-contact lubrication, using oil with extreme-pressure additive at two different concentrations. The effect of run-in on the tribological performance of rollers with two different surface roughnesses was investigated in terms of friction coefficient, wear loss, oil temperature, specimen roughness and electrical resistance. The relation between roller wear loss and the time rate of electrical resistance change was established. Electrical resistance versus oil temperature underwent a dramatic change during testing, a period of rising oil temperature and relatively constant low electrical resistance abruptly becoming a period of relatively constant oil temperature and rising electrical resistance, low wear rates correlating strongly with the second period. The run-in effect on roller wear loss in smooth rollers ( Ra = 0.076 μm) is opposite to that in rough rollers ( Ra = 0.463 μm). The asperity height of the smooth rollers was increased by wear testing irrespective of run-in; however, run-in enhanced the increase in surface roughness. The extreme-pressure additive concentration instead of run-in was the decisive factor in electrical resistance. Friction coefficients during testing showed a strong positive relation with composite surface roughness.
Contact analysis of non-Gaussian random surfaces
Authors: Chilamakuri S. K. , Bhushan B
Published: October 2002

Surfaces produced by machining processes such as grinding, shaping and turning and some magnetic disk texturing processes such as sputtering and laser processing are frequently non-Gaussian. Most of the contact models developed in the past three decades assume Gaussian distribution of surface heights in their analyses. In the present paper, contact analysis of non-Gaussian surfaces has been conducted. A computer program was developed to generate non-Gaussian surfaces with specified standard deviation, autocorrelation length, skewness and kurtosis. Contact area, maximum contact pressure and relative meniscus force as a function of skewness and kurtosis were studied at different values of σ and β*. In these studies, it is observed that a surface with slight positive skewness and kurtosis in the range of 4-7.5 results in an optimum surface with a minimum contact area and meniscus force. Further, stiction of a surface with high kurtosis is somewhat insensitive to liquid film thickness. A surface with negative skewness and/or kurtosis of less than 3 will lead to severe friction/stiction problems and a surface with very high kurtosis and σ may lead to plastic deformation. Non-Gaussian surfaces offer promise for the design of interface roughness to provide low friction/stiction and wear.
Elastohydrodynamic analysis of one-layered journal bearings
Authors: Lahmar M , Haddad A , Nicolas D
Published: October 2002

Steady state and dynamic solutions to the problem of isothermal elastohydrodynamic lubrication of single-layered journal bearings are derived and presented. The mathematical problem comprises two parts: fluid and elasticity. The elasticity problem is governed by the elastostatic equations which are solved by application of a complex variable approach using the complex Kolosov-Muskhelishvili potentials. The fluid problem is described by the two-dimensional Reynolds equation which is discretized using a finite difference approach and solved by application of the Gauss-Seidel scheme with the Swift-Stieber boundary conditions. The fluid-structure coupling is achieved by an iterative procedure with an under-relaxation algorithm. The dynamic coefficients are obtained by use of a first-order perturbation approach. The results obtained show that the proposed elasticity model permits a fast solution of the problem, particularly under dynamic conditions. They also show that, under the effect of coating elastic deformation, the contact geometry is modified and the load-carrying capacity decreases while the stability margin of the journal bearing system increases.
Rapid and globally convergent method for dynamically loaded journal bearing design
Authors: Hirani H , Athre K , Biswas S
Published: October 2002

An approximate analytical pressure expression for dynamically loaded journal bearings is proposed. This approximation is applied to the solution of the finite journal bearing with a π-extent film. The starting and ending angular positions of the pressure curve are predicted by simple algebraic equations. The journal orbit is determined by treating it as an ‘inverse problem’ and evaluated by using the globally convergent Newton-Raphson method. To illustrate the validity of the present study, the Ruston and Hornsby big-end connecting rod bearing and an engine main bearing are analysed. The accuracy of the minimum film thickness and maximum film pressure values obtained by the proposed methodology is comparable to the more elaborate and time consuming finite element analysis, while the execution time is comparable to that required for the short bearing approximation.
Two-dimensional lubrication study of the piston ring pack
Authors: Liu K , Xie Y. B. , Gui C. L.
Published: October 2002

Based on the two-dimensional average flow model and asperity contact model, a theoretical model for the non-axisymmetrical analysis of piston ring lubrication has been suggested in this paper. The two-dimensional distribution of oil-film thickness between the piston rings and cylinder wall is obtained. Results show that the oil-film thickness along the circumference is non-uniform. Starvation is also considered in the model. The effect of secondary motion of piston assemblies on the lubrication property of the piston ring pack has also been studied.
Mid-life scuffing failure in automotive cam-follower contacts
Authors: Bell J. C. , Willemse P. J.
Published: October 2002

There are several practically important engineering systems that fail by scuffing long after the initial running-in has been completed. A common feature of these systems is repeated contact between the same points on the mating surfaces. The processes leading up to such mid-life scuffing failures have been examined by monitoring the development of cam follower surface roughness and wear at regular intervals during a series of valve train wear tests in a fired engine. By the application of both statistical and numerical models for the elastic contact of rough surfaces, the following stages in the scuffing process have been identified: (a) surface roughening in the mild-wear regime, which progressively increased maximum asperity contact pressures until (b) the elastic shakedown limit was exceeded, causing plastic deformation wear, accelerated roughening and enlargement of valleys, leading eventually to (c) a transition to high rates of wear, probably resulting from hydrodynamic pressure loss and oil-film collapse.
An investigation on thrust bearing tilting pads
Authors: Bassani R , Ciulli E , Forte P
Published: October 2002

The present work regards the first stage of a research activity aimed at the understanding of the phenomena involved in the working of thrust bearing tilting pads. Three pads of the same shape and dimensions with different pivot positions have been studied. An experimental investigation is carried out on the pads using a particularly versatile test rig. Simultaneous measurements of film thickness, pad tilt and frictional force are made; in particular the tilt angle is measured by optical interferometry with monochromatic light. Experimental results are compared with numerical data. A finite element method code is used to calculate the pressure field of the finite thrust pad. For a given pivot film thickness an iterative procedure yields the tilt angle using the condition of zero moment about the pivot. First results indicate the way to future investigations.