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Technical Paper

Drive Rattle Elastodynamic Response of Manual Automotive Transmissions

2011-05-17
2011-01-1586
Modern automotive industry is driven by improved fuel efficiency, whilst simultaneously increasing output power and reducing size/weight of vehicle components. This trend has the drawback of inducing various Noise, Vibration and Harshness (NVH) concerns in the drivetrain, since fairly low energy excitation often suffices to excite natural modes of thin walled structures, such as the transmission bell housing. Transmission rattle is one of the many undesired NVH issues, originating from irregularities in engine torque output. The crankshaft speed fluctuations are transferred through the transmission input shaft. Transmission compactness also allows repetitive interaction of conjugate loose gear pairs. The engine fluctuations disturb the otherwise unintended, but orderly meshing of these loose gears. This often leads to radiation of a characteristic air-borne noise from the impact sites.
Technical Paper

Analytical Evaluation of Fitted Piston Compression Ring: Modal Behaviour and Frictional Assessment

2011-05-17
2011-01-1535
Piston compression rings are thin, incomplete circular structures which are subject to complex motions during a typical 4-stroke internal combustion engine cycle. Ring dynamics comprises its inertial motion relative to the piston, within the confine of its seating groove. There are also elastodynamic modes, such as the ring in-plane motions. A number of modes can be excited, dependent on the net applied force. The latter includes the ring tension and cylinder pressure loading, both of which act outwards on the ring and conform it to the cylinder bore. There is also the radial inward force as the result of ring-bore conjunctional pressure (i.e. contact force). Under transient conditions, the inward and outward forces do not equilibrate, resulting in the small inertial radial motion of the ring.
Technical Paper

Interaction Between Ceramic Matrix Composite and Organic Pad Materials and its Impact on the Friction Performance

2011-09-18
2011-01-2350
Ceramic matrix composites (CMC) have been increasingly used as alternative materials of the rotors of friction brakes. However there is still a need for a better understanding of fundamentals of CMC rotors and their associated friction materials. In this paper, the friction performance at the initial stage was characterized by testing on a laboratory-scale dynamometer and a car for brakes consisting of rotors made of carbon-fiber-reinforced carbon-silicon carbide (Cf/C-SiC) composite, and pads with organic liners. The characteristics of friction surface and its evolution were studied through focused imaging on the surface of the rotor after testing on the dynamometer. Both dynamometer and vehicle tests showed that bedding was essential to reach the required coefficient of friction (CoF). Sustainable transfer layer was successfully deposited on the surface of silicon in the early stage of bedding, but the deposition became difficult on that of carbon constituents and silicon carbide.
Journal Article

Aerodynamic Drag Reduction on a Simple Car-Like Shape with Rear Upper Body Taper

2013-04-08
2013-01-0462
Various techniques to reduce the aerodynamic drag of bluff bodies through the mechanism of base pressure recovery have been investigated. These include, for example, boat-tailing, base cavities and base bleed. In this study a simple body representing a car shape is modified to include tapering of the rear upper body on both roof and sides. The effects of taper angle and taper length on drag and lift characteristics are investigated. It is shown that a significant drag reduction can be obtained with moderate taper angles. An unexpected feature is a drag rise at a particular taper length. Pressure data obtained on the rear surfaces and some wake flow visualisation using PIV are presented.
Technical Paper

The Impact of Underbody Roughness on Rear Wake Structure of a Squareback Vehicle

2013-04-08
2013-01-0463
In this paper the effects of a rough underbody on the rear wake structure of a simplified squareback model (the Windsor model) is investigated using balance measurements, base pressure measurements and two and three component planar PIV. The work forms part of a larger study to develop understanding of the mechanisms that influence overall base pressure and hence the resulting aerodynamic drag. In the work reported in this paper the impact of a rough underbody on the base pressure and wake flow structures is quantified at three different ground clearances. The underbody roughness has been created through the addition of five roughness strips to the underbody of the model and the effects on the wake at ground clearances of 10.3%, 17.3% and 24.2% of the model height are assessed. All work has been carried out in the Loughborough University Large Wind Tunnel with a ¼ scale model giving a blockage ratio of 4.4% for a smooth under-body or 4.5% with the maximum thickness roughness strips.
Journal Article

Real-Time Optimal Energy Management of Heavy Duty Hybrid Electric Vehicles

2013-04-08
2013-01-1748
The performance of energy flow management strategies is essential for the success of hybrid electric vehicles (HEVs), which are considered amongst the most promising solutions for improving fuel economy as well as reducing exhaust emissions. The heavy duty HEVs engaged in cycles characterized by start-stop configuration has attracted widely interests, especially in off-road applications. In this paper, a fuzzy equivalent consumption minimization strategy (F-ECMS) is proposed as an intelligent real-time energy management solution for heavy duty HEVs. The online optimization problem is formulated as minimizing a cost function, in terms of weighted fuel power and electrical power. A fuzzy rule-based approach is applied on the weight tuning within the cost function, with respect to the variations of the battery state-of-charge (SOC) and elapsed time.
Technical Paper

Non-Thermal Particulate Filter Regeneration Using Rapid Pulse Electric Discharges

2013-04-08
2013-01-0518
This research introduces a new, novel approach to reverse flow particulate filter regeneration enabled by rapidly pulsed electric discharges. The discharges physically dislodge particulate matter (PM) from the filter substrate and allow a very low reverse air flow to transport it to a soot handling system. The system is operable independent of filter temperature, does not expose the filter to high thermal stresses or temperatures, has no apparent upper limit for filter PM-mass level (regeneration of a filter up to 17 g/L has been demonstrated), and does not require any catalyst. The system is inherently scalable allowing application to monolithic filters of any size or shape and can be tailored to suit specific application requirements such as limits on maximum regeneration time or power consumption. For example a light duty application would require as little as 200-500W electrical power to regenerate a filter in less than ten minutes (i.e. passenger car GPF or DPF).
Technical Paper

The Potential of Fuel Metering Control for Optimising Unburned Hydrocarbon Emissions in Diesel Low Temperature Combustion

2013-04-08
2013-01-0894
Low temperature combustion (LTC) in diesel engines offers attractive benefits through simultaneous reduction of nitrogen oxides and soot. However, it is known that the in-cylinder conditions typical of LTC operation tend to produce high emissions of unburned hydrocarbons (UHC) and carbon monoxide (CO), reducing combustion efficiency. The present study develops from the hypothesis that this characteristic poor combustion efficiency is due to in-cylinder mixture preparation strategies that are non-optimally matched to the requirements of the LTC combustion mode. In this work, the effects of three key fuel path parameters - injection fuel quantity ratio, dwell and injection timing - on CO and HC emissions were examined using a Central Composite Design (CCD) Design of Experiments (DOE) method.
Technical Paper

Using Pneumatic Hybrid Technology to Reduce Fuel Consumption and Eliminate Turbo-Lag

2013-04-08
2013-01-1452
For the vehicles with frequent stop-start operations, fuel consumption can be reduced significantly by implementing stop-start operation. As one way to realize this goal, the pneumatic hybrid technology converts kinetic energy to pneumatic energy by compressing air into air tanks installed on the vehicle. The compressed air can then be reused to drive an air starter to realize a regenerative stop-start function. Furthermore, the pneumatic hybrid can eliminate turbo-lag by injecting compressed air into manifold and a correspondingly larger amount of fuel into the cylinder to build-up full-load torque almost immediately. This paper takes the pneumatic hybrid engine as the research object, focusing on evaluating the improvement of fuel economy of multiple air tanks in different test cycles. Also theoretical analysis the benefits of extra boost on reducing turbo-lag to achieve better performance.
Journal Article

Large Eddy Simulation of Premixed Combustion in Spark Ignited Engines Using a Dynamic Flame Surface Density Model

2013-04-08
2013-01-1086
In this work, cyclic combustion simulations of a spark ignition engine were performed using the Large Eddy Simulation techniques. The KIVA-4 RANS code was modified to incorporate the LES capability. The flame surface density approach was implemented to model the combustion process. Ignition and flame kernel models were also developed to simulate the early stage of flame propagation. A dynamic procedure was formulated where all model coefficients were locally evaluated using the resolved and test filtered flow properties during the fully developed phase of combustion. A test filtering technique was adopted to use in wall bounded systems. The developed methodology was then applied to simulate the combustion and associated unsteady effects in a spark ignition engine. The implementation was validated using the experimental data taken from the same engine.
Technical Paper

The State of the Art in Selective Catalytic Reduction Control

2014-04-01
2014-01-1533
Selective Catalytic Reduction (SCR) is a leading aftertreatment technology for the removal of nitrogen oxide (NOx) from exhaust gases (DeNOx). It presents an interesting control challenge, especially at high conversion, because both reagents (NOx and ammonia) are toxic, and therefore an excess of either is highly undesirable. Numerous system layouts and control methods have been developed for SCR systems, driven by the need to meet future emission standards. This paper summarizes the current state-of-the-art control methods for the SCR aftertreatment systems, and provides a structured and comprehensive overview of the research on SCR control. The existing control techniques fall into three main categories: traditional SCR control methods, model-based SCR control methods, and advanced SCR control methods. For each category, the basic control technique is defined. Further techniques in the same category are then explained and appreciated for their relative advantages and disadvantages.
Journal Article

Crankcase Sampling of PM from a Fired and Motored Compression Ignition Engine

2011-09-11
2011-24-0209
Crankcase emissions are a complex mixture of combustion products and aerosol generated from lubrication oil. The crankcase emissions contribute substantially to the total particulate matter (PM) emitted from an engine. Environment legislation demands that either the combustion and crankcase emissions are combined to give a total measurement, or the crankcase gases are re-circulated back into the engine. There is a lack of understanding regarding the physical processes that generate crankcase aerosols, with a paucity of information on the size/mass concentrations of particles present in the crankcase. In this study the particulate matter crankcase emissions were measured from a fired and motored 4-cylinder compression ignition engine at a range of speeds and crankcase locations.
Technical Paper

The Value of Component in the Loop Approaches to Exhaust Energy Management in Hybrid Vehicles

2012-04-16
2012-01-1024
Recent work on thermo-electric (TE) systems has highlighted the need for refined heat transfer design as well as the long standing need for improved materials performance. Recent work on heat transfer for TE systems has shown that enhanced heat transfer is needed over and above what would normally be seen in a vehicle exhaust system. In particular a better understanding of flow development and boundary layer behaviour is needed to support new design proposals. In the meantime, recent work in TE materials suggests that with the use of skutterudites significant performance benefits can accrue over existing materials. The current generation of TE materials have non-dimensional thermoelectric figure of merit (ZT) values of around 1. Skutterudites have been demonstrated to have ZT values of about 1.4 and can maintain these values over a wider temperature range than do existing materials through the engineering of the TE device.
Technical Paper

Challenges and Potential of Intra-Cycle Combustion Control for Direct Injection Diesel Engines

2012-04-16
2012-01-1158
The injection timing of a Diesel internal combustion engine typically follows a prescribed sequence depending on the operating condition using open loop control. Due to advances in sensors and digital electronics it is now possible to implement closed loop control based on in cylinder pressure values. Typically this control action is slow, and it may take several cycles or at least one cycle (cycle-to-cycle control). Using high speed sensors, it becomes technically possible to measure pressure deviations and correct them within the same cycle (intra-cycle control). For example the in cylinder pressure after the pilot inject can be measured, and the timing of the main injection can be adjusted in timing and duration to compensate any deviations in pressure from the expected reference value. This level of control can significantly reduce the deviations between cycles and cylinders, and it can also improve the transient behavior of the engine.
Technical Paper

Surface Conditioning of Carbon-Fiber Ceramic Rotors against Organic Pads

2012-09-17
2012-01-1833
Previous research has highlighted that the formation of a sustained friction film, desired for stable and predictable friction performance, is highly dependent upon the region of the substrate (CMC) being examined. In attempt to improve the friction performance, notably bedding-in, research at LU has been developing coatings aimed at ensuring friction film development across the substrate. This paper focuses on the performance of one of these coating formulations, and examines the performance of this on a laboratory scale dynamometer. Subsequently, the coating has then been applied to a full size brake disc, as used on a prestige vehicle, for dynamometer testing at an industry scale for comparative purposes. On both lab and full scale samples the bedding performance shows improvements over the standard material, and at the full scale the coating indicates improved stability of subsequent friction performance through a modified AK Master test schedule.
Technical Paper

Optical Diagnostics and CFD Validation of Jacket Cooling System Filling and the Occurrence of Trapped Air

2012-04-16
2012-01-1213
This paper reports the findings from an experimental investigation of the engine cooling jacket filling process for a medium duty off-highway diesel engine to characterise the physical processes that lead to the occurrence of trapped air. The motivation for the project was to provide knowledge and data to aid the development of a computational design tool capable of predicting the amount and location of trapped air in a cooling circuit following a fill event. To quantify the coolant filling process, a transparent replica of a section of the cylinder head cooling core was manufactured from acrylic to allow the application of optical diagnostic techniques. Experimentation has characterised the coolant filling process through the use of three optical techniques. These include the two established methods of High-Speed Imaging and Particle Image Velocimetry (PIV), as well as a novel approach developed for tracking the liquid-air interface during the fill event.
Technical Paper

Explicit Model Predictive Control of the Diesel Engine Fuel Path

2012-04-16
2012-01-0893
For diesel engines, fuel path control plays a key role in achieving optimal emissions and fuel economy performance. There are several fuel path parameters that strongly affect the engine performance by changing the combustion process, by modifying for example, start of injection and fuel rail pressure. This is a multi-input multi-output problem. Linear Model Predictive Control (MPC) is a good approach for such a system with optimal solution. However, fuel path has fast dynamics. On-line optimisation MPC is not the good choice to cope with such fast dynamics. Explicit MPC uses off-line optimisation, therefore, it can be used to control the system with fast dynamics.
Journal Article

An Investigation into the Wake Structure of Square Back Vehicles and the Effect of Structure Modification on Resultant Vehicle Forces

2011-06-09
2011-37-0015
A large contribution to the aerodynamic drag of a vehicle (30%(1) or more depending on vehicle shape) arises from the low base pressure in the wake region, especially on square-back configurations. A degree of base pressure recovery can be achieved through careful shape optimization, but the flow structures and mechanisms within the wake that cause these base pressure changes are not well understood. A more complete understanding of these mechanisms may provide opportunities for further drag reductions from both passive shape changes and in the future through the use of active flow control technologies. In this work surprisingly large changes in drag and lift coefficients of a square-back style vehicle have been measured as a result of physically small passive modifications. Tests were performed at quarter scale using a simplified vehicle model (Windsor Model) and at full scale using an MPV. The full scale vehicle was tested with and without a flat floor.
Technical Paper

Study on Optimization of Regenerative Braking Control Strategy in Heavy-Duty Diesel Engine City Bus using Pneumatic Hybrid Technology

2014-04-01
2014-01-1807
Recovering the braking energy and reusing it can significantly improve the fuel economy of a vehicle which is subject to frequent braking events such as a city bus. As one way to achieve this goal, pneumatic hybrid technology converts kinetic energy to pneumatic energy by compressing air into tanks during braking, and then reuses the compressed air to power an air starter to realize a regenerative Stop-Start function. Unlike the pure electric or hybrid electric passenger car, the pneumatic hybrid city bus uses the rear axle to achieve regenerative braking function. In this paper we discuss research into the blending of pneumatic regenerative braking and mechanical frictional braking at the rear axle. The aim of the braking function is to recover as much energy as possible and at the same time distribute the total braking effort between the front and rear axles to achieve stable braking performance.
Technical Paper

A Direct Comparison between Numerical and Experimental Results for Airborne Noise Levels in Automotive Transmission Rattle

2014-04-01
2014-01-1756
In this paper, a direct correlation between transmission gear rattle experiments and numerical models is presented, particularly focusing on the noise levels (dB) measured from a single gear pair test rig. The rig is placed in a semi-anechoic chamber environment to aid the noise measurements and instrumented with laser vibrometers, accelerometers and free field microphones. The input torsional velocity is provided by an electric motor, which is controlled by a signal generator, aiming to introduce an alternating component onto the otherwise nominal speed; thus, emulating the engine orders found in an internal combustion engine. These harmonic irregularities are conceived to be the triggering factor for gear rattle to occur. Hence, the rig is capable of running under rattling and non-rattling conditions. The numerical model used accounts for the gear pair's torsional dynamics, lubricated impacts between meshing teeth and bearing friction.
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