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Research

  • Analysis of a Dual Mass Flywheel System for Engine Control Applications

    Year: 2004

    Author: Nicolò Cavina, Gabriele Serra

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    Dual Mass Flywheel (DMF) systems are today widely adopted in compression ignition automotive powertrains, due to the well-known positive effects on vehicle drivability and fuel consumption.
    This work deals with the analysis of undesirable effects that the installation of a DMF may cause to engine and transmission dynamics, with the objective of understanding the causes and of determining possible solutions to be adopted. The main results of an experimental and simulation analysis, focused on the rotational dynamics of a powertrain equipped with a DMF system, are presented in the paper.
    A mathematical model of the physical system has been developed, validated, and used to investigate, in a simulation environment, the anomalous behavior of the powertrain that had been experimentally observed under specific conditions.
    Particular attention has been devoted to two aspects that are considered critical: engine cranking phase; interactions between powertrain dynamics and idle speed control. Experimental tests have initially been carried out in a laboratory environment, to characterize the performance (both static and dynamic) of the DMF system under study. On-board tests have subsequently been performed on a vehicle whose powertrain is equipped with the same DMF. During on-board tests, signals preprocessed by the Electronic Control Unit have been recorded together with analog signals sampled at higher frequency with an external device.

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  • Residual Gas Fraction Estimation: Application to a GDI Engine with Variable Valve Timing and EGR

    Year: 2004

    Author: Nicolò Cavina, Carlo Siviero, Rosanna Suglia

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    The paper presents an original review and extension of existing mathematical models for on-line residual gas fraction estimation. The resulting model has first of all been extended to take into account also the presence of externally recirculated exhaust gas (external EGR), and then critically analyzed to highlight the importance of a correct Intake Valve Opening and Exhaust Valve Closing effective position identification. As shown in the paper, such quantities may be evaluated by using experimental data, either acquired in the test-cell or on a valve flow bench.
    The main objective is to obtain a simple and reliable model (that could be run in real time within the engine control unit) also in presence of Variable Valve Timing (VVT, both on intake and exhaust valves) and external Exhaust Gas Recirculation (EGR) systems. In fact, the two main contributions to residual gas fraction (backflow of the burned gas during the valve overlap period, and amount of gas trapped within the cylinder) are strongly affected by intake and exhaust valves timing, and EGR flow should be taken into account in order to determine the total exhaust gas mass within the cylinder at IVC. Therefore, real time estimation of residual gas mass and composition is crucial for designing VVT and EGR management strategies that allow an optimal control of the combustion process.
    The new model has been applied to experimental data acquired on a 3.2 liter V6 GDI engine, equipped with intake and exhaust Variable Valve Timing systems. Tests were performed throughout the engine operating range for different combinations of intake and exhaust valve timings, while varying EGR flow. Model results are in good agreement with other measured quantities (such as Spark Advance angle and NO x emissions), and the proposed approach therefore represents a powerful tool for on-board optimal combustion control.

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  • Modeling and Diagnostic Constraints of Missing Combustion Phenomena

    Year: 2004

    Author: Enrico Corti

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    Missing combustions phenomena have been studied for a long time, in order to achieve on board diagnosis capability, due to their effect on emissions and after treatment system life. A detailed analysis of missing combustion causes can be used beyond the On Board Diagnostic (OBD) regulations observance aim, both for modeling and diagnostic purposes.
    The combustion taking place in a faulty cylinder right after the fault happens is usually different with respect to a standard one: both the residual gas fraction and the fuel film effect have strong influences on post-faulty combustions. Parameters used to describe these phenomena can then be evaluated analyzing the engine post-faulty behavior. The same analysis may lead to a better fault description, thus improving diagnosis performance.
    Residual gas fraction can be evaluated by means of models or with direct measurements: on one hand models always need to be validated, on the other hand the setup needed for the experimental evaluation is costly, and tests are time-consuming. A possible alternative approach could be based on the observation of residual gas fraction consequences on measured signals during particular operating conditions: missing combustion tests can be used for this purpose. Such a methodology can be easily used to validate models results, carrying out misfiring tests by means of a programmable Engine Control Unit (ECU) or a malfunction induction system. The same philosophy can be used, for example, for the calibration of the fuel film model parameters.
    The paper shows how observations of the engine faulty behavior can be used, in order to improve physical models describing standard running conditions. Diagnostic capabilities can as well take advantage of models improvement.
    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 faults whose consequences have been analyzed.

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  • 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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