Development of an Optimization Process for Engine NVH Performance

<div class="section abstract"><div class="htmlview paragraph">The constant evolution in the automotive sector to achieve more eco-friendly vehicles has induced the development of more efficient systems with new components and innovative materials. To evaluate the impact of these technologies or to improve them in terms of NVH performances, acoustic engineers rely on experimental tests and numerical computations. In this context, the use of experimental noise sources identification and characterization methods can provide interesting approaches. However, classical methods usually used in industry like the Nearfield Acoustical Holography (NAH) or the Beamforming techniques are quickly limited, in particular in terms of precision in localization, for such analysis support. The presented method, named M-iPTF for Mixed inverse Patch Transfer Functions, is more suitable as it is able to localize and quantify all acoustic source fields directly on the real geometry of a complex structure. As a result, it offers a more accurate noise sources identification, the possibility of ranking sources by the computation of the radiated power by parts, and a more efficient coupling between experiments and simulations to upgrade a model or to reuse experimental data in a larger virtual model. The M-iPTF principle is based on an inverse acoustic problem, formulated from the application of the Green’s identity on a closed virtual volume defined around the source. It only needs simple pressure measurements, which can be performed in an uncontrolled environment, coupled to a numerical modelling. This article will briefly present the theoretical background of the method, before illustrating its benefits as an analysis support technique in an industrial application: a reduced engine block excited by an electrodynamic shaker.</div></div>

<div class="htmlview paragraph">Low frequency torsional vibrations can be a significant source of objectionable vehicle vibrations and in-vehicle boom, especially with changes in engine operation required for improved fuel economy. These changes include lower torque converter lock-up speeds and cylinder deactivation.</div> <div class="htmlview paragraph">This paper has two objectives: <ol class="list nostyle"> <li class="list-item"><span class="li-label">1)</span><div class="htmlview paragraph">Examine the effect of increased torsional vibrations on vehicle NVH performance and ways to improve this performance early in the program using test and simulation techniques. The important design parameters affecting vehicle NVH performance will be identified, and the trade-offs required to produce an optimized design will be examined. Also, the relationship between torsional vibrations and mount excursions, will be examined.</div></li> <li class="list-item"><span class="li-label">2)</span><div class="htmlview paragraph">Investigate the ability of simulation techniques to predict and improve torsional vibration NVH performance. Evaluate the accuracy of the analytical models by comparison to test results.</div></li> </ol> </div> <div class="htmlview paragraph">A simple model is presented which gives fairly accurate results and can be included in a full vehicle finite element model to calculate vehicle level NVH responses. A procedure to calculate the loads to be applied to the model is also presented.</div>

<div class="htmlview paragraph">The use of graphical dynamic system simulation software is becoming more popular as automotive engineers strive to reduce the time to develop new control systems. The use of model-based control methods designed to meet future emission and diagnostic regulations has also increased the need for validated engine models. A previously validated, nonlinear, mean-torque predictive engine model<span class="xref">*</span> is converted to MATLAB / SIMULINK<span class="xref"><sup>†</sup></span> to illustrate the benefits of a graphical simulation environment. The model simulates a port-fuel-injected, spark-ignition engine and includes air, fuel and EGR dynamics in the intake manifold as well as the process delays inherent in a four-stroke cycle engine. The engine model can he used in five ways:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"><div class="htmlview paragraph">As a nonreal-time engine model for testing engine control algorithms</div> </li> <li class="list-item"><div class="htmlview paragraph">As a real-time engine model for hardware-in-the-loop testing</div> </li> <li class="list-item"><div class="htmlview paragraph">As an embedded model within a control algorithm or observer</div> </li> <li class="list-item"><div class="htmlview paragraph">As a system model for evaluating engine sensor and actuator models</div> </li> <li class="list-item"><div class="htmlview paragraph">As a subsystem in a powertrain or vehicle dynamics model</div> </li> </ul> </div> <div class="htmlview paragraph">Although developed and validated for a specific engine, the model is generic enough to be used for a wide range of spark-ignition engines. Modular programming techniques reduce model complexity by dividing the engine and control system into hierarchical subsystems.</div>

<div class="section abstract"><div class="htmlview paragraph">While designing the exhaust system of passenger car on one hand there is stringent emission regulations, packaging constraints, high NVH performance requirement. On the other hand with lightweight vehicle design there is tremendous pressure on weight reduction of exhaust system while keep the same NVH performance levels. Exhaust system consist of muffler, bellows, pipes and hangers. For muffler design both acoustic (transmission loss, pass-by noise, tail pipe noise etc.) and non-acoustic (backpressure) parameters needs to be considered.</div><div class="htmlview paragraph">In the current paper, methodology for muffler design optimization using 1D acoustic simulation software is presented. The baseline exhaust design consist of two mufflers; main muffler and post muffler. Simulation methodology is developed to optimize main muffler design in order to eliminate post muffler requirement while achieving the same performance of baseline exhaust design. For this purpose a DOE study is conducted by varying primary muffler internal pipe dimensions, baffle location, perforation etc. to achieve transmission loss (TL) and backpressure (BP) of the baseline design.</div><div class="htmlview paragraph">Based on simulation study a physical prototype is made for optimized exhaust design consisting of only main muffler (with modified design compared to baseline main muffler). Transmission loss and backpressure is measured physically and confirmed that the optimized exhaust design is able to deliver the same NVH performance as that of the baseline exhaust design. Furthermore, a vehicle level physical test is conducted to compare the pass-by noise for optimized exhaust design and compared with baseline exhaust design. It is observed that the optimized exhaust design with one muffler is able to maintain the same pass-by noise level as that of the baseline exhaust design with two mufflers.</div></div>

<div class="section abstract"><div class="htmlview paragraph">An Air intake system (AIS) is a duct system which leads the airflow going into the internal combustion engine. Combustion requires oxygen, and the more oxygen is provided into the combustion process the more power it will produce. The lower the air temperature, the higher its density, and hence there is more oxygen in a unit volume. The quality of air entering engine can be measured with the air temperature.</div><div class="htmlview paragraph">AIS design and routing influence the air charge temperature (ACT) at intake manifold runners and ACT is normally measured at AIS throttle body in reality. Higher ACT lead to inefficient combustion and can lead to spark retard. Optimization of AIS designs and reduction of ACT can improve engine performance and vehicle fuel economy.</div><div class="htmlview paragraph">High ACT can be a result of two different phenomena: <ul class="list disc"><li class="list-item"><div class="htmlview paragraph">Recirculation - Hot air from the underhood environment ingested into the dirty side of the air intake system. This is the result of the AIS snorkel not being isolated or sealed from the engine compartment hot air.</div></li><li class="list-item"><div class="htmlview paragraph">Underhood temperature rise - Air inside AIS is heated by the ducts walls because it is routed through a hot underhood environment. The longer the length and larger the diameter of the air induction system, and the higher duct skin temperatures, the worse the temperature rise.</div></li></ul></div><div class="htmlview paragraph">In this paper, it is planned to simulate and study the effects of following factors on ACT with CFD using a FCA production vehicle: <ul class="list disc"><li class="list-item"><div class="htmlview paragraph">Snorkel location: snorkel sucking fresh air at side air guide or snorkel sucking underhood hot recirculation air.</div></li><li class="list-item"><div class="htmlview paragraph">Exhaust hot end at front of an east-west engine or at the rear of the engine; these two arrangements will result in different underhood air temperatures and radiation to AIS surfaces.</div></li><li class="list-item"><div class="htmlview paragraph">Heat shield effects on ACT: heat shield blocks radiation from exhaust system to AIS surfaces, and hence reduces charge air heat pick from AIS duct walls.</div></li><li class="list-item"><div class="htmlview paragraph">The effects of other measures such as cutting holes on hood or fenders to lower engine compartment air temperatures.</div></li></ul></div><div class="htmlview paragraph">Although the airflow in vehicle AIS duct is transient in nature, steady CFD simulations will be performed to study the above cases for simplification, and CFD approach will be discussed in details. Vehicle test data will be used to validate the CFD models.</div><div class="htmlview paragraph">Finally, general practices of AIS development will be discussed, and future work on this topic will be outlined.</div></div>

<div class="htmlview paragraph">In order to reduce the weight of an engine, aluminum has been increasingly used as a material for the intake manifold --an engine component formerly made of a heavier metallic material. Recently, with the aim of further reducing the engine weight, more and more intake manifolds are being made of plastics. To bring the plastic manifold into practical use, a number of methods have been proposed and put into practice; these methods include melt core molding, injection molding and blow molding.</div> <div class="htmlview paragraph">Formerly, the melt core molding process had to be used to obtain a solid plastic intake manifold port section having a large curvature. The newly developed intake manifold does not need that process to form its solid port section having a large curvature. Instead, it employs a new process for solid injection molding in which the core is drawn out while it is rotated. This has made it possible to improve the smoothness of the port interior surface and reduce the weight and cost of the intake manifold.</div> <div class="htmlview paragraph">In this paper we discuss studies of plastic materials, and summarize result of our analysis of molding methods using CAE technology. We also report on the results of our study of the newly-developed product, focusing primarily on vibration noise and engine performance.</div>

<div class="section abstract"><div class="htmlview paragraph">The increasing trend toward electric and hybrid-electric vehicles (HEVs) has created unique challenges for NVH development and refinement. Traditionally, characterization of in-vehicle powertrain noise and vibration has been assessed through standard operating conditions such as fixed gear engine speed sweeps at varied loads. Given the multiple modes of operation which typically exist for HEVs, characterization and source-path analysis of these vehicles can be more complicated than conventional vehicles.</div><div class="htmlview paragraph">In-vehicle NVH assessment of an HEV powertrain requires testing under multiple operating conditions for identification and characterization of the various issues which may be experienced by the driver. Generally, it is necessary to assess issues related to IC engine operation and electric motor operation (running simultaneously with and independent of the IC engine), under both motoring and regeneration conditions. Additionally, mode transitions, including IC engine start/stop must be assessed.</div><div class="htmlview paragraph">An analysis is presented here, which explores the differences in NVH performance of multiple HEVs currently available in the US-market. Measurements were conducted on these vehicles to assess noise and vibration at the powertrain-level and vehicle interior. Two of the vehicles included in this investigation were then chosen for a more in-depth comparative analysis. The analysis of these two vehicles included assessment of source level excitations and vehicle NVH sensitivities, in the context of boundary conditions driven by their hybrid system architectures.</div><div class="htmlview paragraph">Based on the powertrain and vehicle NVH performance assessments, methods were explored for developing powertrain level NVH targets. For the initial phase of this target cascading process, the analysis was limited to full load (IC engine operational) and part load (EV-only) modes. Based on in-vehicle performance, and vehicle sensitivity information, test procedures and targets were defined for powertrain radiated noise and mount vibration content.</div></div>

<div class="htmlview paragraph"><b>T</b>HE CFR Full-Scale Engine Group was organized by engine men representing the major classifications of automotive-type diesel engines. This original group, with the cooperation of the representatives of the petroleum industry, the government agencies, and colleges, has carried on extensive series of tests on commercial diesel engines.</div> <div class="htmlview paragraph">The purpose of the investigation was to determine the influence of fuel properties such as cetane number, viscosity, volatility, and gravity on the engine performance. The following relationships are indicated:</div> <div class="htmlview paragraph">Starting and engine smoothness are dependent upon the ignition quality of the fuel.</div> <div class="htmlview paragraph">Smoke and engine deposits vary with the volatility and viscosity.</div> <div class="htmlview paragraph">Exhaust odor varies with ignition quality and cetane number.</div> <div class="htmlview paragraph">Power output and fuel consumption vary with the heat value of the fuel.</div> <div class="htmlview paragraph">At a given pump setting, viscosity may have an independent effect on the power output because of plunger leakage.</div> <div class="htmlview paragraph">The limited number of fuels used in this series of tests made it impossible to isolate all fuel properties and their effect on fuel performance, but the results obtained will guide future investigations.</div>

<div class="section abstract"><div class="htmlview paragraph">The ergonomic design of automobiles has changed over in the last years. It is increasingly being transferred from the usage of two-dimensional templates of the human shape to computer-aided manmodels. So far these models were mainly used for static anthropometric investigations on the drivers workplace. Dynamic questions can be answered only very insufficiently.</div><div class="htmlview paragraph">In the context of this work a methodology was developed to precalculate target directed human movements in a motor vehicle environment with the CAD-manmodel RAMSIS.</div><div class="htmlview paragraph">A new two-piece model was developed. In this model dynamic boundary conditions, so called dynamic restrictions, for any movement in a car are determined, concerning outside parameters. In the following, the entire bodyposture is determined by a statistical posture probability model, considering these dynamic restrictions.</div><div class="htmlview paragraph">A control theory of human movements was derived from the field of neurophysiology. It was adapted to the problems for the application in a manmodel. This theory is used, to generate the necessary dynamic restrictions.</div><div class="htmlview paragraph">For the first time, a statistical angle probability model is used to make the posture prognosis. The model was generated in a preceding work and its suitability to answer dynamic questions was validated within two test series.</div><div class="htmlview paragraph">Altogether 12 different experiments, with in each case 15 test subjects, were carried out within all fields of this work. More than 500 “dynamic “ postures were measured and analysed as well as more than 2500 movements.</div><div class="htmlview paragraph">Within this report the developed strategy, that enables a technical designer to precalculate movements of humans within the manmodel RAMSIS realistically, will be shown. This enables the designer to regard also dynamic questions for the ergonomic design of an automobile.</div></div>

<div class="htmlview paragraph">One of the most vital factors in combustion control is Air-to-Fuel Ratio (AFR) control and estimation. Various parameters such as intake air mass flow rate, fuel injection quantity and (Exhaust Gas Recirculation) EGR flow rate are affecting the AFR magnitude. In this study a detailed mathematical, nonlinear and control oriented model of dynamic processes of turbocharged diesel engines is presented for the purpose of AFR control. It is an attempt to describe the two main subsystems of compression ignition engines called intake manifold and fuel injection systems.</div> <div class="htmlview paragraph">The intake model itself consists of compressor, intercooler, intake manifold, EGR circuit, valve section and cylinder subsystems. This model has been developed for study of the air intake system in a turbocharged diesel engine, using physical equations. Experimental data has also been used to adjust the model. The output variable of this submodel (air mass flow) is a significant parameter in calculations of engine power, emission and AFR control. Of the methods of assisted aspiration, the exhaust gas driven turbocharger is by far the most widely used. Varying the rate of gas flow through the turbine by means of Variable Geometry Turbine (VGT) is a method by which the exhaust gas flow through turbine can be limited at high engine speeds. Therefore, turbocompound in this model is considered to have VGT.</div> <div class="htmlview paragraph">Common Rail Injection (CRI) that is a fully flexible fuel injection system in which quantity, timing and pressure of injection are controllable (based on electronic control) separately is chosen in this study. Fuel injection system is comprised of solenoid, working chamber and needle subsystems. A one-dimensional, transient and compressible flow model of CRI, based on Kirchhoff's law, mass and momentum conservation equations and the equilibrium of forces is derived.</div> <div class="htmlview paragraph">AFR control of diesel engine is performed make use of fuzzy logic methodology. Fuzzy logic is a control structure which emulates the way humans arrive at decisions, given a certain set of circumstances. This method improves the control and simplifies the development process. The fuzzy logic controller achieves this by considerably reduced complexity and lack of tedious mathematical derivation associated with modern control theory methods.</div> <div class="htmlview paragraph">All above-mentioned models are programmed in Matlab/Simulink software environment. The simulation results are then compared with available data to check the accuracy of the model.</div>

<div class="htmlview paragraph">The charge air cooler must be considered not only as a means of decreasing the temperature of the charge air, but also as a means of increasing the density of the air into the intake manifold.</div> <div class="htmlview paragraph">The density increase can be evaluated from a thermodynamic point of view.</div> <div class="htmlview paragraph">Using this information, the persformances of different cooling configurations are compared: air to air and air to water coolers.</div> <div class="htmlview paragraph">These can then be compared in terms of location and cost.</div> <div class="htmlview paragraph">Finally, we will see how recent evolutions in compressor design and engine bay geometry influence the conception of a charge air cooler.</div>

<div class="htmlview paragraph">Recent market trends show growing demands for automobile engines to attain better fuel economy and higher output while meeting the emission standards.</div> <div class="htmlview paragraph">To cope with these demands, Toyo Kogyo has made numerous improvements year by year on the rotary engine (<span class="xref">1</span>)<span class="xref">*</span>.</div> <div class="htmlview paragraph">A new engine that guarantees well-balanced fuel economy and vehicle performance has been developed.</div> <div class="htmlview paragraph">This engine uses a new induction system which incorporates the following technologies: 1) A variable intake port mechanism called the 6-Port Induction system (<span class="xref">2</span>). 2) A newly-developed intake passage which improves volumetric efficiency, utilizing the induction pressure variation generated in the intake manifold.</div> <div class="htmlview paragraph">This new induction system is simple in design, lightweight, and low in cost. It allows considerable improvement in performance over the entire engine speed range, without trading away fuel economy in normal vehicle operation.</div>

<div class="htmlview paragraph">Supplementing a “more miles per gallon” movement in 1919, a series of experiments outlined by the S. A. E. Committee on Utilization of Present Fuels was undertaken by the Bureau of Standards, in May, 1920, which included measurements of engine performance under conditions of both steady running and rapid acceleration with different temperatures of the intake charge secured by supplying heated air to the carbureter from a hot-air stove, by maintaining a uniformly heated intake manifold and by using a hot-spot manifold, fuel economy being determined for both part and full-throttle operation. A typical six-cylinder engine was used, having a two-port intake manifold with a minimum length of passage within the cylinder block, an exhaust manifold conveniently located for installing special exhaust openings, rather high peak-load speed and conventional general design. The carbureter was selected with the requirements in view of securing definite and measurable conditions of the intake charge and accurate measurements of the behavior of the charge as indicated by fuel consumption in pounds per brake-horsepower-hour. Provision was made for an unusually complete series of measurements. These are described, the most unique being the construction of the tee portion of the manifold of Pyrex glass. Motion pictures of the manifold were taken during operation, but in only one run were the walls completely dry, and a surprising amount of directly applied heat was required to accomplish this.</div> <div class="htmlview paragraph">The main series of runs was made with the exhaust-jacket manifold, in an attempt to determine how best to obtain low fuel consumption and rapid acceleration and how this result was influenced by changes in the amount of heat furnished the intake charge or in the method of supplying this heat. The fuel consumption tests were made at both full and half load at speeds of 650 and 1200 r.p.m. Full details of the tests are then stated, the results are presented in charts, and these are discussed. The results obtained are then summarized as follows:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">(1)</span> <div class="htmlview paragraph">At constant speed, mixture ratio and power output fuel consumption in pounds of fuel per brake-horsepower-hour are independent of the temperatures and methods of heating the intake charge within the range tested</div> </li> <li class="list-item"> <span class="li-label">(2)</span> <div class="htmlview paragraph">The rate at which an engine will accelerate with a given mixture ratio, or carbureter setting, is markedly affected by the amount of heat supplied to the charge and its method of application. Within the limits of this work, the greater the amount of heat supplied to the charge and the higher its temperature at the intake port, the more rapidly the engine would accelerate</div> </li> </ol> </div>

<div class="section abstract"><div class="htmlview paragraph">NVH predictions have gained importance since last few decades due to increased focus on ride comfort as competitive advantage within cost target. Hence, NVH CAE has become integral part of product development process for early issue identification and solutions. To make NVH simulation robust, continuous improvement is required in existing CAE processes.</div><div class="htmlview paragraph">In automobile powertrains, components are connected with each other through fasteners. Gaskets are sandwiched at periphery between two mating components, while the components are bolted together with required torque. Gaskets are used to prevent leakage of oil and gases into the atmosphere while operation. NVH CAE modeling practices globally are evolved with considering gaskets as one of the less important modelled components. However, these practices miss to consider its effects considerably on NVH performance.</div><div class="htmlview paragraph">Scope of this paper is to address the gaps present in the existing powertrain modeling techniques with the introduction of gasket. First the impact of gasket inclusion is studied at the experimental level. Then modified CAE modeling process is proposed with modal correlations perspective.</div></div>

<div class="htmlview paragraph">In accident reconstruction, the distance a pedestrian has been projected by an impact may be used to provide an estimate of the speed of the striking vehicle. With tyre marks becoming less common, as ABS braking is introduced, the method is gaining in importance.</div> <div class="htmlview paragraph">Speed estimation from throw distance rests on an empirical basis of field studies, which relate the distance projected to the speed of the vehicle. However field studies by themselves provide no understanding of the physical process. That understanding is important in the consideration of the effects of site characteristics, such as gradient or coefficient of friction.</div> <div class="htmlview paragraph">The paper presents the equation of motion for an idealised particle, travelling over a surface where the upward reaction from the surface varies from moment to moment, including times when the particle is airborne and the reaction is zero. A simple formula is derived linking the minimum initial speed, the coefficient of friction and the total distance travelled:-</div> <div class="htmlview paragraph"> <div id="FD1" class="formula"> <div class="graphic-wrapper"><img class="article-image equation block" src="930659_fig0001.jpg" alt="No Caption Available"/></div> </div> </div> <div class="htmlview paragraph">A series of tests was carried out to check this relationship experimentally. A dummy was projected on an airborne trajectory and the distance travelled was measured. It was found that whilst there were differences from the simple formula, those differences were small. For most practical purposes the simple formula provides a speed estimate of sufficient accuracy.</div> <div class="htmlview paragraph">This speed estimate is for the minimum speed at which the pedestrian must have been projected. The average speed will be slightly higher and the speed of the striking vehicle higher again. Comparison with the results of field studies suggests that these effects add on some 20% or so.</div>