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Research

  • Vehicle Simulation on the Test Bench

    Year: 2004

    Author: Enrico Corti

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    International emission tests (EPA, SFTP, MVEG-B, J-10.15, etc.) are carried out with vehicles running on the rolls dynamometer. Results, in terms of total emissions, are influenced by vehicles parameters such as mass, gear ratios, front surface, drag coefficient, etc. It would be useful, in the automobiles design phase, to have information about the impact of these parameters on total emissions. The obvious solution would be to build up a complete vehicle model to simulate performance and emission levels. Engine pollutants production modeling is the weak point, since it is difficult to obtain reliable results. Anyway it is possible to avoid pollutants production simulation, testing the actual engine under the same operating condition it would face inside the car’s hood. This paper describes a methodology whose aim is to test the engine on a standard test bench, simulating on-board operating conditions. An equivalence condition has to be satisfied in order to guarantee the methodology effectiveness: engine speed and Manifold Absolute Pressure (MAP) must always match for the two types of test performed on the same driving cycle. Engine speed and torque can be controlled through the bench actuators, their values depending on the simulated vehicle motion: once the car dynamics are simulated by means of a model, engine speed and torque corresponding to the given driving cycle can in fact be evaluated. The model is solved in real time, its output being the brake load torque value satisfying the equivalence condition. The brake controller, used as a slave, regulates the engine operating conditions consequently. The global model incorporates tires, aerodynamic forces, clutch, gearbox and driveline behaviors simulation: its response has been first validated comparing its outputs with data measured on board, and then it has been used to control an eddy current brake, for vehicle test simulation on the test bench. Two different control philosophies can be used: either a human driver or an automatic controller can ride the simulated car. The influence of vehicle parameters and gearshift mode on fuel consumption and pollutant emissions can be investigated.

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  • Model-Based Idle Speed Control for a High Performance Engine

    Year: 2003

    Author: Nicolò Cavina, Giorgio Minelli, Michele Caggiano, Riccardo Parenti, Stefano Mazzetti, Massimo Ceccarani

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    This paper shows the main results of a research activity carried out in order to investigate the impact of different hybridization concepts on vehicle fuel economy during standard homologation cycles (NEDC, FTP75, US Highway, Artemis). Comparative analysis between a standard passenger vehicle and three different hybrid solutions based on the same vehicle platform is presented. The following parallel hybrid powertrain solutions were investigated: Hybrid Electric Vehicle (HEV) solution (three different levels of hybridization are investigated with respect to different Electric Motor Generator size and battery storage/power capacity), High Speed Flywheel (HSF) system described as a fully integrated mechanical (kinetic) hybrid solution based on the quite innovative approach, and hydraulic hybrid system (HHV). In order to perform a fare analysis between different hybrid systems, analysis is also carried out for equal system storage capacities. All hybrid powertrain architectures include state-of-the-art hybrid components and are analyzed from the aspects of fuel economy related to the overall system efficiency, load point moving of the internal combustion engine due to energy flow control strategy operation, and regenerative braking (applying realistic drivability constraints). The simulations were performed within the IAV-VeLoDyn software environment. VeLoDyn (Vehicle Longitudinal Dynamics Simulation) is a modular and highly flexible Simulink-based software tool, which offers a straightforward simulation of longitudinal vehicle dynamics with special considerations on the driveline and model management functionality. In order to provide control and management of the hybrid powertrain system, a cycle-independent control strategy has been implemented into the supervisory hybrid control unit model, based on Equivalent Consumption Minimization Strategy (ECMS) approach. Due to the modular nature of the simulation tool, the control strategy was effectively implemented in all analyzed hybrid models with marginal modifications. In order to determine energy flows and validate hybrid powertrain behavior, a cycle-based energetic analysis was carried out, and the main results are presented in the paper.

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  • An Approach for Misfire Diagnosis in Critical Zones of the Operating Range of a High Performance Engine

    Year: 2003

    Author: Davide Moro, Fabrizio Ponti, Giovanni Cipolla, Marco Mammetti, Luca Poggio

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    The optimization of a high performance engine in order to achieve maximum power at full load and high speed can cause an unstable behavior when the engine is running at different conditions, thus making a robust combustion diagnosis for on board diagnostic EOBD/OBD II purposes (misfiring detection) particularly challenging. In fact, when a misfire occurs, its detection can be critical because of the high background noise due to high indicated mean effective pressure (IMEP) cyclic variability.
    A partial reduction of the high IMEP variability had been achieved by optimizing control parameters of a new prototype high performance V8/4.2 l engine. Spark advance and VVT phasing maps had in fact been re-designed based on in-cylinder pressure variability (cycle by cycle and cylinder by cylinder) analysis.
    In this paper the focus is the analysis of innovative misfire diagnosis techniques (such as joint time-frequency analysis of the engine speed signal) to make the new prototype V8 engine compliant with EOBD/OBD II regulations.
    The instantaneous engine speed signal has been recorded during experimental tests while inducing various misfire patterns. Both test rig investigations (i.e., off-line data processing) and real time analysis for OBD purposes have been carried out.
    The basic misfire detection algorithm has been modified by introducing a pre-processing of the experimental data, allowing to improve the effectiveness of the misfire detection also at higher engine speed operating conditions.

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  • Eddy Current Brake Control for Test Cycles Simulation

    Year: 2003

    Author: Enrico Corti

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    On-vehicle (rolls dynamometer or road) tests are usually more expensive and time-consuming than test bench ones. Furthermore, sometimes results would be useful during vehicles design phase. The paper aim is to present a methodology that allows simulating the vehicle on an engine test cell, by properly controlling the bench actuators. Engine operating conditions mainly depend on speed and load, which are determined by the vehicle driving conditions: the speed-time trend assigned for the vehicle must be converted into equivalent speed-time and load-time trends for the engine, and used for feedback control of brake and accelerator actuators. To evaluate the engine load torque it is necessary to know vehicle characteristics (mass, gear ratios, wheels radius, drag coefficient, frontal area, etc.) and driving conditions: the real vehicle can thus be substituted with a virtual vehicle. The methodology has been applied to simulate an ECE-EUDC driving cycle, which is usually carried out on the rolls dynamometer, as imposed by regulations. During such test the vehicle has to follow an assigned speed-time trajectory, while road load and vehicle inertia are simulated and calibrated using a standard procedure. The test is subject to human error, since the driver does not follow exactly the theoretical speed trend, while using robot-drivers increases the setup cost. The same test has been reproduced on a standard engine bench. This setup would be useful to tune the engine correctly and to study the effects of vehicle characteristics variation, thus allowing to determine the correct strategy for emissions reduction, or to estimate the vehicle emission performance, before it is available for chassis dynamometer tests. The same system could be used for real time implementation of control strategies involving both the vehicle and the engine, such as traction control algorithms. Furthermore driving conditions simulations, executed by electronically controlling engine speed and load trajectories, would be more repeatable than human driving on the chassis dynamometer, and their cost would be substantially smaller. The paper shows how the vehicle speed trend can be converted into engine speed and load trends with a physical system model, and then used to control the bench using a real time control system, thus performing a vehicle driving cycle simulation.

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  • Missing Combustion Diagnosis: Distinguishing Between Misfire and Misfuel

    Year: 2003

    Author: Enrico Corti

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    On-Board Diagnostics (OBD) regulations impose missing combustions detection within a wide portion of the engine operating range. Missing combustions can be caused either by ignition (misfire) or injection (misfuel) system failures. Missing combustions can damage the catalyst and cause abrupt pollutants increases (especially HC), but misfuels are not as detrimental as misfires, both from the emissions and the after treatment system life point of view. It would be important for the Electronic Control Unit (ECU) to be informed not only about the fault event, but also about its type, for the purpose of setting the right recovery strategy. The aim of this paper is to analyze missing combustion phenomena, in order to find out if a fault recognition strategy able to distinguish between misfire and misfuel can be setup. Different approaches can be found in the literature to diagnose missing combustions: many of them are based on the speed signal analysis, both in time and frequency domains, others use the knock accelerometer signal, or the exhaust manifold pressure information. A Universal Exhaust Gas Oxygen (UEGO) sensor can also be used. Usually diagnosis methodologies consist in observing signals perturbations subsequent to the malfunction event. Observable consequences of missing combustions are, for example, a sudden lack of indicated torque, causing vibrations and speed fluctuations, an increasing in exhaust gases Oxygen content, anomalous exhaust pressure ripples, etc. Many phenomena interact influencing in different ways the engine behavior, during and after the fault event: their effect can depend on the fault cause, thus helping the recognition. The first combustion taking place in the faulty cylinder after a misfire (post-misfiring cycle) usually leads to higher indicated pressure and torque levels if compared to standard values for the same operating conditions, while the same cannot be said for the post-misfueling combustion. On the other side, Air-Fuel Ratio (AFR) assumes different trends during the misfiring and post-misfiring cycles, with respect to misfueling and post-misfueling cycles. A 4 cylinders 1.2 liters spark ignition port injected engine, equipped with a programmable Electronic Control Unit (ECU) has been tested on the test bench, inducing both misfires and misfuels, over a wide engine operating range, while monitoring the engine faulty behavior. Misfire and misfuel-related phenomena have been analyzed showing their “signature” on indicated pressure and torque, engine speed and Air-Fuel Ratio measured signals, in order to define the most reliable recognition strategy.

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  • Comparison between Formula 1 and CART Acoustic Emission Analysis

    Year: 2002

    Author: Nicolò Cavina

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    The paper presents the application of signal processing algorithms to racing engines acoustic emission signals. The proposed methodology has shown to be effective in extracting from such signals information related to the main powertrain performance parameters, such as engine speed, gear ratios and driver's strategy. The objective of the paper is to compare performance parameters of racing engines that have participated in two different Championships, FIA Formula One World Championship (Formula 1) and CART Champ Car Series (CART). The comparison is quite interesting, since the two formulas differ not only in terms of regulations (and therefore in terms of admissible powertrain layouts), but also in terms of circuits where the races take place. For example, ovals are quite common in CART, and that is not the case of Formula 1: This fact is reflected in the different way the engine and the gearbox are operated during the race.

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  • Misfire Detection Based on Engine Speed Time-Frequency Analysis

    Year: 2002

    Author: Nicolò Cavina, Enrico Corti, Giorgio Minelli, Gabriele Serra

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    The paper presents the development of a methodology for detecting the misfire event using the time-frequency analysis of the instantaneous engine speed signal. The diagnosis of this type of malfunctioning operating condition is enforced by OBD requirements over the whole operating range of the engine, and many different approaches have been developed in the past in order to solve this problem.

    The novel approach presented here is based on the observation that the misfire causes an impulsive lack of torque acting on the engine crankshaft, and thus it causes the excitation of damped torsional vibrations at frequencies characteristic of the system under study. In order to enlighten the presence of this torsional vibration (and therefore detect the misfire event), information contained in the instantaneous crankshaft speed fluctuations have been processed in the time-frequency domain. A misfire detection parameter has then been defined showing a good capability of diagnosing the misfire occurrence.

    The procedure has been setup and validated running a supercharged 2 liter V6 SI engine in an engine test cell; in-cylinder pressure signals have been acquired together with the instantaneous engine speed, in order to verify the capability of the methodology.

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  • Formula 1 Engine Evolution Analysis Using the Engine Acoustic Emission

    Year: 2002

    Author: Fabrizio Ponti

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    This paper presents some results of a methodology capable of extracting instantaneous engine speed information from acoustic emission measurements, obtained from Formula 1 (F1) vehicles during qualifying or race sessions, from the early races in 50s-60s until present days. The results presented in the paper show that, from this signal, it is possible to gain information regarding the instantaneous engine speed (that in racing engines is strongly related to the power developed by the engine itself), but also regarding the way the combustions are distributed within an engine cycle, the time needed for a gear shift, the gear ratios employed, the driving strategy and so on.
    The analysis conducted in this work is applied to acoustic emission data recorded by microphones placed on-board the investigated cars. In recent years each F1 vehicle has been equipped with its own microphone while, in early races, in-car microphones had not been systematically used. It is anyway possible to find in the literature some recordings coming from microphones placed on board, during tests or even qualifying and race sessions.
    The analysis has shown to be insensitive from the type of microphone employed and from its position on-board the vehicle; even the signal coming from a low-cost microphone showed to be good enough for successfully applying the developed methodology. This made possible a useful comparison between the information obtained from all the engine acoustic emission signals available in the literature, thus allowing to analyze F1 powertrain evolution over the last four decades.

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