bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of a multivariable interval dynamic model from measurements in the frequency domain
Authors: Zhang Y M
Published: October 2002

Frequently, manufacturing processes cannot be accurately described using a model with fixed parameters. Interval models for which the parameters are within certain intervals may be more effective in describing such processes. In this paper, an algorithm is proposed to identify interval models of multivariable systems from measurements in the frequency domain. The intervals are minimized with membership constraints. The numerical aspects for implementing the proposed algorithm are also addressed. Simulation examples are given to show the effectiveness of the proposed algorithm.
Optimization of the fuel input to an industrial heating plant
Authors: Ford J , Griffiths A J , Brandon J A
Published: October 2002

The paper describes the calculation of the minimum amount of fuel required to warm a simple model of a batch heating plant that has an active temperature constraint on the furnace gas. The method of calculation combines optimal control theory and a direct search with a downhill simplex to place the temperatures of the multiple nodes of the load inside a target envelope. The split boundary value problem is solved by shooting. Shooting is facilitated by omitting from the plant model the thermal storage of the gas enclosed within the plant. The purpose of the calculation is to illustrate that minimizing a linear integral of fuel flow does not lead to bang-bang control and that the constraint on the gas temperature is easily handled by treating it as a control constraint.
Analysis of hydraulic components using computational fluid dynamics models
Authors: Borghi M , Cantore G , Milani M , Paoluzzi R
Published: October 2002

This paper presents some results obtained during the computational fluid dynamics (CFD) analysis of internal flows inside a hydraulic component, using a scaling technique applied to numerical pre- and post-processing. The main aim of the work is to demonstrate the reduction of computational work needed for a complete analysis of component behaviour over a wide range of operating conditions. This result is achieved through the adoption of a methodology aimed at giving the highest level of generality to a non-dimensional solution, thereby overcoming the two major limitations encountered in the use of CFD in fluid power design: computer resources and time. In the case study, the technique was applied to a hydraulic distributor and computations were performed with a commercial computational fluid dynamics code. The key factor of this technique is the evaluation, for a given distributor opening, of the Reynolds number of the flow in the metering region. Provided that this number is high enough to ensure that the discharge coefficient has reached its asymptotic value, the characterization of the flow by a single non-dimensional numerical run can be shown. The theoretical contents of the analysis of the re-scaling technique, which focuses on the engineering information necessary in component design, are described in detail. The bases for its subsequent application to actual cases are then outlined. Finally, a fairly close correlation between numerical results and experimental data is presented.
Two-phase momentum flux in pipes and its application to incompressible flow in nozzles
Authors: McNeil D A
Published: October 2002

The pressure drop produced when a single-phase gas or liquid flows through a nozzle can be reasonably well estimated from inviscid flow theory. A similarly based model, taking the slip with entrained liquid fraction approach, has been developed for two-phase gas—liquid flows. Fundamental to the model is the constraint that the nozzle flow depends on the entry conditions, particularly the momentum flux. At low qualities the tendency was for fractions of the liquid flow to be accelerated with the gas phase to maintain uniform momentum flux across the nozzle flow area. At higher qualities the gas core of the annular flow, along with its associated droplets, was found to contract with negligible interaction with the surrounding liquid film. The model has been compared with data sources and other models available in the literature and shown to perform well.
Errors of the dynamically tuned strapdown gyroscope to constant and harmonic rate inputs
Authors: Lee S-K , Lee C-W
Published: October 2002

The drift errors for constant and harmonic rotational rate inputs are derived for the dynamically tuned strapdown gyroscope with a single gimbal and orthogonally placed double gimbals. To account for the recent design tendencies of higher rate input, higher acceleration capability and smaller size, the analytic expressions for the drift errors, which include the influences of gimbal moments of inertia, asymmetries of flexure stiffnesses and rotor moments of inertia, and higher order terms related to misalignments, are presented. The drift errors are classified according to the sources and the characteristics of each error are investigated. The compensation and design to develop a more accurate sensor by reducing the drift errors are also discussed.
On the performance of a cascade of turbine rotor tip section blading in wet steam Part 3: Wake traverses
Authors: Bakhtar F , Mashmoushy H , Jadayel O C
Published: October 2002

During the course of expansion of steam in turbines the fluid first supercools and then nucleates to become a two-phase mixture. The liquid phase consists of a large number of extremely small droplets which are difficult to generate except by nucleation. To reproduce turbine two-phase flow conditions requires a supply of supercooled vapour which can be achieved under blow-down conditions by the equipment employed. This paper is the third of a set describing an investigation into the performance of a cascade of rotor tip section profiles in wet steam and presents the results of the wake traverses.
The effect of longitudinal microstriations and their profiles on the drag of flat plates
Authors: Parker K , Sayers A T
Published: October 2002

The use of surface modifications as a means of reducing viscous drag on a body has potential aerodynamic and hydrodynamic applications. V-grooves of specific dimensions are machined in a longitudinal direction onto the surface of a smooth plate and the resulting effect on the drag force of the plate is observed. Experiments show that V-grooves (riblets) could reduce turbulent skin friction drag by up to 7 per cent, depending on the size of the groove. The drag-reducing performance of riblets with aspect ratios, h/s, of 0.22 and 1 are examined. A boundary layer analysis of the turbulent flow characteristics over the smooth surface and the riblet surfaces indicated an increase in the laminar sublayer thickness and local Reynolds number while reducing the boundary layer thickness for the ribbed surfaces. A maximum drag reduction of 6.83 per cent was recorded for the surface covered with the symmetric riblet, at a Reynolds number of 117 101. It is felt that riblets hamper the momentum and turbulent energy exchange from regions of high velocity to lower-velocity regions. Riblets impede the cross-flow of stream-wise vortices that prevail in the viscous sublayer of a turbulent boundary layer. By suppressing these streamwise vortices, turbulent mixing and hence turbulent shear stress are reduced. Results obtained agree with results suggested from research elsewhere.
Computation of the series impedance matrix
Authors: Whalley R , Ebrahimi M , Mitchell D
Published: October 2002

The series decomposition analysis of impedance matrix models for linear systems of arbitrary degree and dimension using recursive computation is considered. Formulation of the series-admittance description for multi-input, multi-output system models is discussed together with typical applications. A particularly simple, recursive, computationally effective procedure is outlined. Thereafter when, as in most engineering problems, the impedance form results in a matrix quadratic structure, further computational efficiency is possible. Finally, the controllability—observability aspects of series models are investigated and illustrative problems are provided for comparison with conventional assessment procedures.
Walking machine leg design: The effect of leg geometry on knee torque
Authors: Howard D , Zhang S J , Sanger D J , Chen J Q
Published: October 2002

The authors have been studying the fundamental mechanics of legged vehicles with the aim of establishing generic principles for their mechanical design. The approach to date has been to consider overall machine design and leg mechanism design separately. In leg design there is inevitably a trade-off between workspace (reach) and leg weight for given loading conditions. To understand this trade-off, the effects of leg geometry on both kinematic workspace and leg weight must be investigated. Leg weight is largely a function of the hip and knee design torques; the former is determined by the overall machine design which has been discussed elsewhere.

This paper considers the effect of leg geometry on the total design torque that the knee must support through both its structure and the knee actuator. The actuator design torque is also considered. The leg geometry varied includes link lengths and knee twist angles. The necessary mathematical analyses are developed and data presented showing the relationship between knee or actuator torque and leg geometry.
Evaluation of exhaust gas recirculation as a technique for reducing diesel engine NOx emissions
Authors: Lapuerta M , Hernandez J. J. , Gimenez F
Published: October 2002

The aim of this work is to evaluate the potential of exhaust gas recirculation (EGR) to reduce NO x emissions, through the most significant parameters, and to delimit the application range of this technique. Therefore, a detailed analysis of experimental results on NO x formation and emissions is presented, and the mechanisms by which EGR affects them are explained. A collection of five different automotive diesel engines, all of them from Nissan, was tested, so it was possible to distinguish the combined effect of EGR and their main characteristics, such as supercharging, intercooling, size, compression ratio and combustion chamber type [direct injection (DI) and indirect injection (IDI)]. The engines were tested in a set of steady conditions, trying to reproduce the different operating modes of the European transient urban/extra-urban certification cycle. In this way, comparisons between different engine emissions provided conclusions directly related to the emission certification limits.
Airbag head restraint system
Authors: Latchford J , Chirwa E. C.
Published: October 2002

The function of a head restraint system is to prevent injurious hyperextension of the occupant's neck in the event of a road vehicle rear end impact, and thus it must have adequate stiffness to limit the movement of the head relative to the torso. Also, it should absorb the kinetic energy progressively so that the head does not sustain any injury and does not roll on the cushion. Practically, a well-designed head restraint will have an optimum balance of these features and thereby offer adequate protection for both the head and the neck.

This paper presents some pioneering thinking on head restraint design and develops criteria for qualifying the systems. It presents an airbag head restraint system that has optimum stiffness and good potential for reducing head and neck injuries suffered through rear end collisions. It also presents the results of experimental tests conducted on this novel airbag head restraint system and on several randomly selected existing head restraints. Furthermore, analysis of energy absorption capabilities, head injury criterion (HIC) values and a new criterion, called the equivalent impact power criterion (EIPC), is developed in order to quantify the relation between the rate at which energy is imparted to the head during the impact cycle and injury severity. Current test results show that, the lower the EIPC, the better is the head restraint system and the less is the risk of whiplash and head injuries. Moreover, the work has quantified a number of variables, including the optimum stiffness, as the factors governing the severity of injury to the occupant in a rear impact scenario.
Technical Note: Exhaust emissions from an indirect injection dual-fuel engine
Authors: Abd Alla G. H. , Badr O. A. , Soliman H. A. , Rabbo Abd M. F.
Published: October 2002

Diesel engines operating on gaseous fuels are commonly known as dual-fuel engines. In the present work, a single-cylinder, compression ignition, indirect injection research (Ricardo E6) engine has been installed at United Arab Emirates University for investigation of the exhaust emisssions when the engine is operating as a dual-fuel engine. The influence of changes in major operating and design parameters, such as the concentration of gaseous fuel in the cylinder charge, pilot fuel quantity, injection timing and intake temperature, on the production of exhaust emissions was investigated. Diesel fuel was used as the pilot fuel, while methane or propane was used as the main fuel which was inducted in the intake manifold and mixed with the intake air. The experimental investigations showed that the poor emissions at light loads can be improved significantly by increasing the concentration of gaseous fuel (total equivalence ratio), employing a large pilot fuel quantity, advancing the injection timing of the pilot fuel and increasing the intake temperature. It is demonstrated that, in general, any measure that tends to increase the size of the combustion regions within the overly lean cylinder charge will reduce markedly the concentrations of unburned hydro- carbons and carbon monoxide in the exhaust gases.
Fluid-structure interaction in crash simulation
Authors: Meywerk M , Decker F , Cordes J
Published: October 2002

In the automotive industry crash simulation plays an important role in decreasing development costs and in improving cars. To increase the reliability of crash simulation the modelling of parts of vehicles, which has been neglected in the past, becomes more important. One of these parts is the fuel tank together with the fuel inside the tank. An important aspect of a fuel tank in crash simulation is its kinematic behaviour as a result of the interaction with the fuel. To obtain good results in the simulation it is necessary to take into consideration the fluid properties of the fuel. The ability of crash simulation software to model fluid-structure interaction including free surfaces has been limited until now. Therefore, it is helpful to obtain some insight into modelling capabilities and to compare them with other sophisticated simulation techniques. In this paper three modelling techniques for fluid-structure interaction of fluids with free surfaces are presented. These results are compared with an experiment. It is shown that the simplest modelling technique is precise enough for reliable crash simulations.
Flow characteristics of misfired gas in the exhaust manifold of a spark ignition engine
Authors: Chung Y , Kim H , Choi S , Bae C
Published: October 2002

Misfiring in spark ignition engines should be avoided, otherwise unburned fuel and oxygen are brought into the catalyst, and subsequent combustion greatly increases the temperature, possibly resulting in immediate damage to the catalyst. As a new concept of misfire detection method, the signal fluctuation of a wide-range oxygen sensor has been introduced to monitor the fluctuation of the oxygen concentration at the exhaust manifold confluence point. The current research aims to develop a tool that is capable of predicting the variation in oxygen concentration at the exhaust manifold confluence point, and to investigate the flow characteristics of the misfired gas in the exhaust manifold under misfiring conditions in a cylinder. The oxygen concentration at the confluence point could be predicted by comparing the gas flowrate from the misfiring cylinder with the total exhaust gas flowrate. The gas flowrates from each of the cylinders were calculated using a one-dimensional engine cycle simulation including a gas dynamic model of the intake and exhaust systems. The variation in oxygen concentration was also determined experimentally using a fast-response hydrocarbon analyser. The trend of the oxygen concentration fluctuation calculated by the analytical model was compared with the experimental results. The analytical model could duplicate the measured trend of the fluctuation of oxygen concentration at the confluence point, which was characterized by twin peaks for one misfiring. The twin peaks are mainly caused by the mixing of the misfired gas with the burned gas from normally operating cylinders. The effects of engine load and speed on the characteristics of the variation in oxygen concentration were also investigated analytically and experimentally.
Measurements of cycle resolved air-fuel ratio near the spark plug in a spark ignition engine
Authors: Cho H , Lee J , Lee K
Published: October 2002

Mixture preparation is a key contributor to both the combustion and emissions of the automotive gasoline engine. The air-fuel ratio near the spark plug may have an effect on combustion characteristics, especially at low load, since it is related to flame development. Therefore, measurements of the cycle-resolved equivalence ratio near the spark plug are particularly important for a better understanding of their contribution to combustion and emissions.

This paper describes how the in-cylinder equivalence ratio was determined from the measured hydrocarbon concentrations near the spark plug using a fast response flame ionization detector (FRFID). The procedures established were then applied to a limited range of engine operating conditions, and the cycle-resolved equivalence ratio near the spark plug was determined from the measured hydrocarbon concentration.

The results showed that with premixed propane fuel the cyclic variation in equivalence ratio near the spark plug was quite small and corresponded to the overall equivalence ratio from the universal exhaust gas oxygen (UEGO) sensor signal. However, with gasoline fuel the equivalence ratio near the spark plug varied by up to 10 per cent and did not coincide with the UEGO sensor signal on a cyclic basis. The variation in equivalence ratio near the spark plug affected the heat release rate, which in turn affected the indicated mean effective pressure (i.m.e.p.). The equivalence ratio excursions and its effects during acceleration and deceleration are strongly related to the exhaust emissions, fuel economy and so on. With this in mind, the quantitative measurement method using the measured hydrocarbon concentrations was studied for detailed analysis during transient conditions. It was also observed that cyclic variation in the equivalence ratio near the spark plug might be one cause of cycle-by-cycle variation.
Development of a general-purpose program based on the concept of subsystem assembly for the analysis of dynamic characteristics of a power transmission system
Authors: Jo H-S , Jang W-J , Lim W-S , Lee J-M , Park Y-I
Published: October 2002

This paper presents the main algorithms of POTAS-MSM (POwer Transmission Analysis Software for MultiSlipping Mechanism), which are based on the concept of subsystem assembly and the self-determination technique for the system degrees of freedom. This software allows users quickly and easily to model the various and complex configurations of power transmission systems and their components. With these dynamic models, the program can be used to evaluate system performances, transient phenomena such as shift, and other dynamic problems. The program has features for effective handling of non-linear models, rapid examination of the various changes in system behaviour caused by design modification, and provision of stable responses to an arbitrary operating condition or control logic. The ability of the developed program is demonstrated through simulations and experiments of a transmission model.
The effect of reduced contact area on the occurrence of disc brake squeals for an automotive brake pad
Authors: Bergman F , Eriksson M , Jacobson S
Published: October 2002

Three sets of brake pads were subjected to a series of squeal tests. The pad area in contact with the brake disc was successively reduced down to 50 per cent of the original by removal of friction material either at the leading and trailing edges, at the outer and inner edges or spotwise removal of interior area by drilling. The pad surface geometry strongly affected the occurrence of brake squeals, with a significant reduction for all three pads with 50 per cent contact area. However, the average squeal noise level seems to be controlled by the pad contact length in the sliding direction.
A new type of internal combustion engine based on the porous-medium combustion technique
Authors: Durst F. , Weclas M.
Published: October 2002

At present, the emissions of internal combustion engines can only be improved by catalytic treatments of the exhaust gases. Such treatments, however, result in high costs and relatively low conversion efficiency. This suggests that a new combustion technique should be developed to yield improved primary combustion processes inside the engine with drastically reduced exhaust gas emissions. In this paper, the authors report on such a technique that is applicable to direct injection, internal combustion engines, either diesel or gasoline fuelled. This technique is based on the porousmedium (PM) combustion technology previously developed in the authors’ laboratory for steady state household and industrial combustion processes.

It is shown that the PM combustion technique can be applied to internal combustion engines, i.e. it is demonstrated that improvements obtained in steady state combustion are also realizable in unsteady combustion processes. Theoretical considerations are presented for internal combustion engines, indicating that an overall improvement in thermal efficiency can be achieved for the PM engine. This is explained and the general performance of the new PM engine is demonstrated for a single-cylinder, air-cooled, direct injection diesel engine. Verification experiments are described that were carried out as part of the present study. Initial results are presented and an outlook is given on how the present developments might continue in the future.
Enhancement of vehicle handling characteristics by suspension kinematic control
Authors: Lee S H , Lee U K , Han C S
Published: October 2002

In this paper, the enhancement of vehicle handling characteristics through the active kinematic control system (AKCS) is investigated. AKCS can improve the stability and ride comfort of a vehicle by automatically controlling suspension geometry in accordance with the running conditions of a vehicle. The variable roll centre suspension concept in a McPherson strut suspension is proposed, and lateral acceleration feedback control is derived to calculate the control input. The independent rear wheel steering system, which controls both rear wheels independently and actively, is also proposed. To achieve this, three suggested positions for controlling the suspension geometry are considered. The first position is between the mounting point of the lower arm of a McPherson front suspension and the vehicle body. The second position is between the mounting point of the strut and the vehicle body. The third position is between the mounting point of the lateral link of the multilink rear suspension and the vehicle body. In order to evaluate the handling performance, a 15 degrees of freedom full vehicle model is constructed using the commercial multibody analysis program ADAMS. The control inputs for integrated control of the front and rear suspensions are defined, and roll centre migration and vehicle behaviour are investigated. In step steering and double lane change manoeuvres, the simulation results demonstrate that integrated kinematic control can adjust the roll centre migration, by which the handling characteristics of the AKCS vehicle such as roll angle, lateral acceleration and yaw rate are much improved.
Gear rattle modelling and analysis for automotive manual transmissions
Authors: Wang M Y , Manoj R , Zhao W
Published: October 2002

This paper describes a model for torsional vibration of automotive manual transmissions and its subsequent analysis. The model is developed for the purpose of analysis and prediction of gear rattles. Efforts have been made to include as many components of power train as possible and to study the rattle responses of all the speeds. Elements of the model include engine, clutch, flywheel, laden and unladen gears, and shafts. Numerical methods available in MATLAB for solving the ordinary differential equations are employed for the dynamic analysis. Results are presented to show the effectiveness of the modelling and analysis scheme. A software package has also been developed to build and analyse any power train model. The package was used to analyse the Daimler-Chrysler T350 transmission and the results are presented in the paper. It is shown that the gear rattle may exhibit three major modes of double-sided, single-sided or irregular impacts. A rattle index has been used to compare the rattle levels produced by different gear pairs. This could be very useful for the purpose of tuning the clutch for the best rattle noise reduction.
The design of an active suspension force controller using genetic algorithms with maximum stroke constraints
Authors: Tsao Y J , Chen R
Published: October 2002

A novel control scheme is proposed for force control in an active vehicle suspension design using genetic algorithms with a half-car model. The new approach incorporates the constraints of maximum suspension strokes in the objective function to evaluate the compactness of the suspension working space, as opposed to the traditional integral quadratic form of suspension displacement. Genetic algorithms are employed in the design to obtain a more effective search for optimum control parameters. Force cancellation, virtual damper, skyhook damper and road-following concepts are employed in the scheme to achieve a satisfactory performance. Computer simulations are performed to verify the proposed control scheme.
A study of the influence of humidity on the friction and squeal generation of automotive brake pads
Authors: Eriksson M. , Lundqvist A. , Jacobson S.
Published: October 2002

In order to clarify the influence of humidity on the coefficient of friction and brake squeal generation, a series of brake rig tests has been performed. The influence of both air humidity and pad humidity was evaluated. The results show that, between 20 and 80 per cent relative humidity, air humidity has a limited influence on the coefficient of friction. Nevertheless, in a humid atmosphere the friction coefficient was considerably lower than in a wet environment for two of the pads and higher for one pad. This is believed to be an effect of different mechanisms of tribofilm formation on the pad surfaces. The tribofilm observed on the pads mainly consists of iron oxide originating from the disc. The film is more easily formed in dry environments and preferentially by the pads with low metal content. The friction increase often seen during each individual stop is slightly lower at high air humidity. This effect is more pronounced for the pads with high metal content. Generally, the pads with smooth surfaces were less sensitive to changes in humidity. Only a limited correlation was found between relative humidity and brake squeal generation. One of the pads generated considerably more squeal in low humidity. None of the pads showed the opposite behaviour.
Turbocharger motor-generator for improvement of transient performance in an internal combustion engine
Authors: Panting J. , Pullen K. R. , Martinez-Botas R. F.
Published: October 2002

Turbocharging of internal combustion engines is an established technology used for the purpose of increasing both power density and in some cases the cycle efficiency of diesel engines relative to naturally aspirated engines. However, one significant drawback is the inability to match the characteristics of the turbocharger to the engine under full load and also to provide sufficiently good transient response. Under many conditions this results in reduced efficiency and leads to higher exhaust emissions. The design of turbocharger components must be compromised in order to minimize these drawbacks throughout the entire operating range. However, when shaft power can be either added to or subtracted from the turbocharger shaft by means of a direct drive motor-generator, an additional degree of freedom is available to the designer to achieve a better turbocharger-engine matching. Both engine efficiency and transient response can be significantly improved by means of this method, normally described as hybrid turbocharging. This paper describes the results of a theoretical study of the benefits of hybrid turbocharging over a basic turbocharged engine in both steady state and transient operation. The new system and its benefits are described and four different engine-turbocharger systems are analysed in addition to the baseline engine. The main conclusion of the paper is that a significant increase in design point cycle efficiency can be afforded by re-matching the turbocharger components under steady state conditions while at the same time improving full throttle transient performance. Emissions are not considered in this paper.
Transient air-fuel ratio control of a multi-point injection engine with an integration-type ultrasonic flowmeter
Authors: Kim J. , Kang T. , Kauh S. K.
Published: October 2002

An integration-type flowmeter, composed of an ultrasonic flowmeter and an integration circuit, is used to measure the air mass for transient air-fuel ratio (AFR) control of a port fuel injection (PFI) spark ignition engine. Also, the air mass and required fuel mass in the cylinder are accurately calculated for precise AFR control. The proposed method can significantly improve the accuracy of measuring air mass inducted through a throttle valve. Air mass passing into a cylinder is estimated using the measured air mass at the throttle valve and intake manifold pressure. A simple two-constant fuel model is used for a dynamic fuel model. Control parameters from the air and fuel dynamics are applied to minimize AFR excursions, and a four-cylinder, 1.51 PFI engine was used to demonstrate this AFR control strategy. Results show that the AFR followed a command value with a peak error of 4 per cent during throttle transients at various operating points.
Performance enhancement of a sliding mode wheel slip controller by the yaw moment control
Authors: Bang M. S. , Lee S. H. , Han C. S. , Maciuca D. B. , Hedrick J. K.
Published: October 2002

A sliding mode wheel slip controller is the subject of this paper. The proposed wheel slip controller was based on a quarter-car model and a friction force observer was applied to ensure the robustness of the controller with respect to the estimation error. It was applied to a non-linear full vehicle model. This controller showed good longitudinal performance in tracking reference slip ratio regardless of modelling errors and disturbances. However, when cornering was combined with braking or there was a yaw moment disturbance due to a μ-split road, it was difficult to achieve the desired performance using this controller. In this case, lateral motion must be considered in maintaining the control of the vehicle. A yaw moment control method using the modified reference yaw rate was investigated. The effectiveness of this control theory was verified through simulations of emergency manoeuvres using a developed non-linear full vehicle Simulink model.
Design of continuously variable power split transmission systems for automotive applications
Authors: Mucino V. H. , Lu Z. , Smith J. E. , Kimcikiewicz M. , Cowan B.
Published: October 2002

The continuously variable power split transmission (CVPST) concept is presented in the context of an automotive application. The system consists of a variable pulley set (variator) coupling two of the three rotating elements of a planetary gear train, namely the sun and the ring gears. The arrangement is such that a ‘power split’ feature is attained in which the input shaft delivers power to the sun gear as well as to the driving pulley, which in turn drives the ring gear of the planetary through the variator.

Because the input shaft delivers the input power at two locations (at the sun gear and at the driving pulley), the variator carries only a fraction of the total power flowing through the input shaft. The third rotating element of the planetary gear set (the planet carrier) collects the power flows from the ring and the sun gears, delivering the total power output to the vehicle.

This feature allows an increased engine power envelope for potential automotive applications. This feature also reduces the power losses associated with power transmission, especially at the low speed-high torque modes, while providing continuously variable transmission ratio capability.

A term dubbed the ‘cross-over coefficient’ is established which can be used to prescribe both the fraction of total power flowing through the variable element and the velocity ratio span for the transmission. An extension of this can be obtained by means of an external gearbox, allowing a stepless span in the optimum range of both engine and transmission.

Design procedures are presented for an automotive application in which a stepless extension (synchronized variator) of the useful transmission ratio span is achieved by means of an external step-up gearbox. The two-stage system allows operation in the optimum range of both engine and transmission.
Prediction of wet band brake dynamic engagement behaviour Part 1: Mathematical model development
Authors: Fujii Y. , Tobler W. E. , Snyder T. D.
Published: October 2002

A wet (oil-lubricated) band brake is a critical component in the operation of automatic transmission systems in automotive applications. Its engagement characteristics significantly affect the quality of automatic shifting. During the automatic transmission design process, it is important to characterize band engagement behaviour accurately under a wide range of operating conditions. This paper describes a mathematical model which predicts the dynamic engagement behaviour of the wet band brake. The space-time-dependent model includes the effects of squeeze film, asperity deformation, porous oil diffusion, heat transfer and loading pressure distribution caused by a self-energizing mechanism. The model can be readily implemented and efficiently executed on a computer as a standalone program or as a subroutine for automatic transmission shift simulations. Knowledge of band engagement obtained through the model is expected to lead to improved band design and automatic transmission shift calibration processes.
The design of overlapped crankshafts Part 1: Crankpin fillets
Authors: Warrior N. A. , Sime A. P. , Hyde T. H. , Fessler H.
Published: October 2002

The finite element (FE) technique, with two-dimensional (plane strain) and three- dimensional meshes, has been used to determine the surface stress distributions in 19 shapes of undercut crankpin fillets under radial bending due to the connecting rod force and under pure torsion. In radial bending, two-dimensional analyses are as valid as three-dimensional ones. The stress concentration factors (SCFs) are compared with symmetrically notched and shouldered bars in pure bending. The information in this paper helps the designer to obtain low stress concentration factors in multi-circular arc or spiral fillets of chosen axial and radial extents.
A practical approach for rapid catalyst light-off by means of strategic engine control
Authors: Chan S. H.
Published: October 2002

Cold-start emissions pollution from gasoline engines has always been an issue in the urban driving cycle as it contributes a significant share of the overall engine emissions in a typical car journey. Rapid engine warm-up and catalyst light-off are two important factors deciding the overall exhaust emissions in a gasoline-powered electronic fuel injection (EFI) engine. This paper presents a practical approach for rapid catalyst light-off by means of strategic engine control. An existing engine control unit (ECU) was replaced by a programmable engine management system (EMS) so that idling speed, excess-air factor and spark timing can be optimized for improved catalyst light-off at the engine cold-start phase. Results show that with a proper high value of ignition retard (HVIR) control strategy the catalyst light-off time can be shortened to about 40 s with idle speed set at 1750 r/min. Compared with the normal spark timing setting, the cumulative tailpipe emissions during the cold-start phase have been decreased by 90 per cent for CO, 80 per cent for hydrocarbons and 65 per cent for NOx with HVIR implementation. A further increase in the idle speed to 2000 r/min, if allowable, could reduce the catalyst light-off time to less than 30 s from engine cold-start.
Development of a track tension monitoring system in tracked vehicles on flat ground
Authors: Huh K. , Cho B. H. , Choi J. H.
Published: October 2002

The mobility of tracked vehicles is mainly influenced by the characteristics of the track assembly and by the interaction between tracks and soil. In particular, the track tension is closely related to the manoeuvrability of tracked vehicles and the durability of chassis components. In order to minimize the excessive load on the tracks and to prevent the peel-off of tracks from the sprocket, it is necessary to maintain the optimum track tension throughout the manoeuvre. However, the track tension cannot be easily measured owing to limitations in sensor technology, harsh environment, etc. In this paper an indirect track tension monitoring system is developed for tracked vehicles on flat ground based on idler assembly models, a geometric relation around the idler and the estimated tractive force using the extended Kalman filter technique. The performance of the tension monitoring system is verified with the results obtained from the multibody dynamics tool and an experimental set-up.
Analysis of the air flow in the radial engine cooling fan of a combat vehicle
Authors: Širok B. , Trenc F. , Novak M. , Jere F.
Published: October 2002

Results of an optimizing procedure that led to better understanding of the sophisticated flow pattern and better aerodynamic characteristics of a modified inlet section of an engine cooling fan for a combat vehicle are presented in this paper. The highly turbulent air flow of the original cooling system configuration was the result of inadequate design and position of the cooling fan in the vehicle and especially its inlet configuration. Experimental analysis of the rotor flow velocity profiles was performed with a five-hole Pitot-Prandtl probe at the rotor exit section and by the computer-aided visualization of the turbulent flow within the baseline and new ‘flow improving’ coaxial leading vanes at the rotor inlet. The kinematic performance of the rotor inlet section was thus changed and was quantified by visualization and analysis of the measuring thread's agility in the air flow. Time-based averaging of the consecutive frames within a photograph shot of particular measuring threads determined the direction of the incoming flow, whereas the appropriate standard deviation of the thread's agility was estimated as the proportional variable that determined the intensity of turbulence in the incoming flow. This relatively simple method was subsequently tested and compared with the results of two-dimensional laser Doppler anemometry velocity measurements. It was also proved to be a suitable technique for flow analyses in complex and less accessible flow channels.
Sensitivity of rearward amplication control of a truck/full trailer to tyre cornering stiffness variations
Authors: Ei-Gindy M. , Mrad N. , Tong X.
Published: October 2002

Highway safety and vehicle performance are two important considerations in the design of a heavy vehicle combination. In this paper a performance measure called the ‘rearward amplification ratio’ (RWA) is used as a control criterion in the design of a vehicle-handling controller. This approach is different to conventional control techniques. The RWA is defined as the ratio of the peak lateral acceleration at the rearmost trailer's centre of gravity (CG) to that of the lead unit during a lane-change manoeuvre. The vehicle under consideration is a six-axle truck/full trailer, which usually exhibits a high level of RWA leading to roll-over during obstacle avoidance manoeuvres.

In this study, several control strategies are examined, namely active yaw control at the truck CG, active yaw control at the dolly CG and active yaw control at the trailer CG. These could be employed individually or in combination. The effect of an active control torque applied to various vehicle units is examined by using an optimal linear quadratic regulator approach combined with a simplified four degrees-of-freedom linear vehicle model. The controller performance index parameters are determined for the vehicle based on acceptable RWA target values. The sensitivity of the controller to tyre cornering stiffness variation is further evaluated.

Simulation results indicate that the RWA can be reduced without significant change of the uncontrolled vehicle trajectory when active yaw torque is applied to the dolly. The controller can be more effective in improving the dynamic performance and roll stability of this type of commercial vehicle, if applied to the lead unit (truck) or to the last unit (trailer). However, the path of the vehicle will be strongly influenced and driving difficulties can be experienced. For active yaw control at the dolly CG, the optimal controller is found to be most sensitive to the dolly's tyres' cornering stiffness variations and least sensitive to steering axle from the RWA point of view. It is also found that the controller is most sensitive to steering axle parameter variations for path following.
A direct transform method for the analysis of laser Doppler anemometry engine data
Authors: Roberts J. B. , Hilton A. D. M.
Published: October 2002

A new, computationally efficient method of fitting a specific parametric stochastic model of in-cylinder flow to real laser Doppler anemometry (LDA) internal combustion engine data, obtained either at a single position in space or over a range of spatial positions at effectively one point in the engine cycle (scanning data) is proposed. The model, which is fully specified in terms of a set of parameters, assumes that the velocity variations can be modelled as the sum of an ensembleaveraged mean component, a non-stationary ‘turbulence’ component and a random ‘cycle-to-cycle’ component, the last of these being phase locked to the engine cycles. The fitting technique is based on a direct transform of the velocity data obtained in each cycle and leads to an identification of the mean-square magnitudes of the turbulence and cycle-to-cycle components. A unique advantage of this approach is that it is possible to determine, theoretically, confidence limits for the estimates of the statistics of the fluctuation components. This provides a theoretical means of designing experiments to achieve a prescribed level of accuracy. The estimation method, and the theoretical determination of confidence limits, is validated initially through application to some simulated data which fully capture all the characteristics inherent in real data. Finally some results of analysing real in-cylinder LDA data, of the scanning type, are presented. Although the approach proposed here is applied to a particular model of in-cylinder flow it is, in principle, extendable to other models.
Unsteady in-cylinder heat transfer in a spark ignition engine: Experiments and modelling
Authors: Nijeweme D J Oude , Kok J. B. W. , Stone C. R. , Wyszynski L
Published: October 2002

Instantaneous heat flux measurements have shown that, in the expansion stroke, heat can flow from the wall into the combustion chamber, even though the bulk gas temperature is higher than the wall temperature. This unexpected result has been explained by modelling of the unsteady flows and heat conduction within the gas side thermal boundary layer. This modelling has shown that these unsteady effects change the phasing of the heat flux, compared with that which would be predicted by a simple convective correlation based on the bulk gas properties. Twelve fast response thermocouples have been installed throughout the combustion chamber of a pent roof, four-valve, single-cylinder spark ignition engine. Instantaneous surface temperatures and the adjacent steady reference temperatures were measured, and the surface heat fluxes were calculated for motoring and firing at different speeds, throttle settings and ignition timings. To make comparisons with these measurements, the combustion system was modelled with computational fluid dynamics (CFD). This was found to give very poor agreement with the experimental measurements, so this led to a review of the assumptions used in boundary layer modelling. The discrepancies were attributed to assumptions in the law of the wall and Reynolds analogy, so instead the energy equation was solved within the boundary layer. The one-dimensional energy conservation equation has been linearized and normalized and solved in the gas side boundary layer for a motored case. The results have been used for a parametric study, and the individual terms of the energy equation are evaluated for their contribution to the surface heat flux. It was clearly shown that the cylinder pressure changes cause a phase shift of the heat flux forward in time.
An experimental study of unsteady vehicle aerodynamics
Authors: Passmore M. A. , Richardson S , Imam A
Published: October 2002

The transient response of a vehicle to a wind disturbance is of importance to car drivers since low level inputs can result in poor vehicle refinement, and extreme effects can result in path deviation. This paper investigates the use of an oscillating aerofoil gust generator to simulate the transient aerodynamic effects produced on a car-type bluff body during a simplified sinusoidal side gust interaction. A simplified bluff body was exposed to a range of sinusoidal cross-wind excitations corresponding to a reduced frequency of between 0.09 and 0.71 based on the model length. Unsteady measurements of surface pressure are processed to determine the side force and yaw moment and the aerodynamic magnification (χa) is calculated by comparing the transient response with a quasi-steady prediction. The transient yaw moment response is shown to exceed the quasi-steady by as much as 30 per cent. The transient side force is generally significantly less than the quasi-steady value except at the lowest frequency tested. The change in response is attributed to changes in the strength of the front and rear pillar vortices and to changes in phase relative to the quasi-steady response.
Kinematic analysis of a two-degree-of-freedom steering mechanism used in rigid-axle vehicles
Authors: Simionescu P. A. , Tempea I , Loch N. E.
Published: October 2002

The paper presents a kinematic analysis of a two-degree-of-freedom (2-DOF) steering mechanism based on the Ackermann principle and of a type found in rigid-axle vehicles. Using an iterative approach to solve the equations of constraint, major features of the mechanism are investigated, e.g. sensitivity to geometry changes, steering errors induced by axle displacement, motion and force transmission functions. This approach enables the performance and characteristics of the proposed mechanism to be assessed easily and quickly, and a case study is given of a light agricultural tractor.