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Research

  • Fast Algorithm for Individual Cylinder Air-Fuel Ratio Control

    Year: 2005

    Author: Nicolò Cavina

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    Individual cylinder Air-to-Fuel Ratio (AFR) control has been proposed by many authors in recent years as a technique of controlling the AFR of the various cylinders individually, based on a single lambda measurement for each engine bank. Most of such works describe theoretical and experimental efforts to develop and identify an observer, able to estimate the AFR of each cylinder separately.

    In this paper, a simple individual cylinder AFR controller is described, based on the observation that any type of AFR disparity between the various cylinders is reflected in a specific harmonic content of the AFR signal spectrum. In particular, any type of AFR disparity will be reflected on a limited number of frequencies, or harmonics, multiple of the engine cycle frequency. As a consequence, a way to reduce such disparity is to use a closed-loop controller (for example a PI controller) that modifies each cylinder injection duration until the amplitude of the harmonics that are excited by the AFR disparity is reduced under a certain level. At the same time, a second closed-loop controller, slower and identical for all the engine cylinders, guarantees the desired AFR mean value.

    The proposed AFR individual cylinder closed-loop controller has been tested in real time, by implementing it in a virtual Electronic Control Unit, using rapid control prototyping techniques. The results observed on a 4 cylinder Spark Ignition 1.2 liter engine are encouraging, since in most of the engine operating conditions the controller is able to guarantee AFR inequality below 0.01 lambda.

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  • Spark Advance Control based on a Grey Box Model of the Combustion Process

    Year: 2005

    Author: Nicolò Cavina, Rosanna Suglia

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    In order to reduce emissions and improve fuel economy, most recent SI engines are equipped with several subsystems that deeply influence the combustion process. For example, the quality and the quantity of the fluid within the cylinder at Intake Valve Closing may be controlled by acting on Variable Valve Timing systems, external EGR, variable geometry intake systems, and of course on the throttle. On the other hand, tumble/swirl components of the intake flow may be influenced by acting on specifically designed devices. To achieve maximum efficiency, the Spark Advance (SA) controller should therefore compensate for different combustion speeds, in order to control cylinder pressure peak (or 50% mass fraction burnt) position at a constant value.
    On one hand closed-loop SA control is still not feasible in most production systems, and on the other open-loop algorithms should take into account the influence of several subsystems that may be present, such as Variable Valve Timing, external Exhaust Gas Recirculation, variable intake/exhaust geometry, and tumble/swirl control devices.
    The paper presents one way of dealing with such complexity, by analyzing separately each subsystem's contribution to combustion duration. Optimal SA control is then achieved by feeding black-box combustion duration models with residual gas fraction estimations performed using a simple and reliable model of the gas exchange process. The overall algorithm has been designed by considering Electronic Control Unit constraints in terms of computational effort.
    Experimental data have been acquired on a 3.2 liter V6 GDI engine, equipped with intake and exhaust VVT systems. Tests were performed throughout the engine operating range for different combinations of intake and exhaust valve timings, while varying EGR flow and tumble device position.

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  • Cylinder by Cylinder Torque Production non-Uniformity Evaluation

    Year: 2005

    Author: Fabrizio Ponti

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    The paper presents the development of a model study whose results enable to evaluate the torque production non-uniformity between the cylinders of an Internal Combustion Engine (ICE). This non-uniformity can be due, for example, to different air breathing into the cylinders, to different injector characteristics, or to pathological operating conditions such as misfires or misfuels, as well as to other abnormal operating conditions. Between the nominal torque production and the one corresponding to the absence of combustion there exist, in fact, a series of possible intermediate conditions, each of them corresponding to a value of produced torque between the nominal value and the one corresponding to the lack of combustion (due for example to statistical dispersion in manufacturing, or aging in the injection system).
    The diagnosis of this type of non-uniformity is a very important issue in today's engine control strategies design. The use of the developed study should in fact allow the control strategy to adopt the appropriate interventions if the diagnosed non-uniformity is for example related to different behavior of the injectors.
    In order to evaluate this torque production variability, cylinder by cylinder, information contained in the instantaneous crankshaft speed fluctuations has been processed using a suitable model. The procedure has been validated on an L4 engine in an engine test cell; the in-cylinder pressure signals have been acquired together with the instantaneous engine speed in order to determine the indicated torque produced by each cylinder, and thus evaluate the real cylinder by cylinder torque non-uniformity.
    The procedure is able to diagnose abnormal combustions that do not necessarily involve lack of combustion, with the accuracy needed for on-board use. Control interventions to injection and ignition time commands of one or more cylinders should re-establish the torque production uniformity.

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  • Indicated Torque Estimation Using a Torsional Behavior Model of the Engine

    Year: 2005

    Author: Indicated Torque Estimation Using a Torsional Behavior Model of the Engine

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    Effective and precise torque estimation is a great opportunity to improve actual torque-based engine management strategies. Modern ECU often already implement algorithms to estimate on-board the torque that is being produced by the engine, even if very often these estimation algorithms are based on look-up tables and maps and cannot be employed for example for diagnostic purposes; In other cases the obtained precision is not very high.
    This work presents the development of a torque estimation procedure based on the instantaneous engine speed measurement. The steps that allowed defining this procedure are briefly explained in the following.
    The definition of a model that describes the torsional behavior of the engine-load system made first possible to analyze the relationship between the corresponding frequency components of the instantaneous engine speed fluctuations and the indicated torque developed by the cylinders. This enabled the development of an indicated torque frequency component estimation algorithm based on the analysis of the instantaneous engine speed fluctuation.
    Studying the nature of the relationship of the indicated torque mean value over an engine cycle and the amplitude of its frequency components, allowed defining the final estimation algorithm that reconstructs the indicated torque mean value starting from the instantaneous engine speed fluctuation analysis.
    The developed approach has been applied with success to an L4 engine mounted on a test bench. The algorithm can be applied without limitations also to an engine mounted on the vehicle and to other engine configurations as it will be discussed in detail in the paper. The obtained precision is compatible with onboard application, like for example torque-based engine management strategies.

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  • Rapid Control Prototyping System for Combustion Control

    Year: 2005

    Author: Enrico Corti, Luca Solieri

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    Combustion control is one of the keys to obtain better performance and pollutants emission, both for diesel, spark ignition and HCCI engines. This paper presents a low-cost and high performance system based on commercially available hardware and software, which allows the implementation of control and diagnostic strategies based on combustions analysis, with the typical Rapid Control Prototyping (RCP) advantages (user friendly development tools, real time calibration, etc.).
    Information on the combustion process can be accessed by means of an indicating sensor such as an in-cylinder pressure transducer, or a ionization current measurement system, depending on the application. The signal must be sampled with a fast sampling system within a given crank angle window. It is then possible to process the input signal, in order to evaluate diagnostic or control indexes which can be calculated before the end of the same engine cycle, and finally used to correct the engine control parameters.
    A knock detection strategy for engine mapping applications has been defined and implemented on the system. Standard equipment Variable Reluctance Sensors (VRS) were used for crankshaft and camshaft position detection, while both in-cylinder pressure sensors and accelerometers were considered as knock sensitive signals. The crankshaft and camshaft position signals are necessary for the windowing task, limiting the analysis of knock related signals to a precise portion of the engine cycle. Many different techniques have been compared, in order to find out whether it is possible to define an index whose critical (knocking) values are independent of the engine operating range (and hopefully independent of the engine characteristics).
    The system proved to be efficient, being able to analyze up to 4 signals at a time, over different windows: there aren't limitations on the windows position and dimension nor on the engine speed.
    The same system can be used for other purposes, such as 50% Mass Fuel Burned (MFB) crank angle determination, or heat release analysis for combustion control in diesel or Homogeneous Charge Compression Ignition (HCCI) engines.

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