DE102005006997A1 - Method for regulation of operation of internal combustion engine, involves obtaining index for current combustion condition of internal combustion engine from rotational speed acceleration as observation window of crankshaft angle - Google Patents

Abstract

The method involves obtaining an index (X) for current combustion condition of internal combustion engine (20) from rotational speed acceleration as observation window of crankshaft angle and used as feedback signal. The observation window encloses at least one interval of crankshaft angle around upper dead center between compression and combustion cycle of piston of combustion engine. An independent claim is also included for the regulating system.

Description

The The invention relates to a method for controlling the operation of a Internal combustion engine, in particular a diesel engine. Further concerns The invention relates to a control system for carrying out such a method is trained.

The precise Control of the operation of an internal combustion engine is important to specified Achieve performance and emissions targets. So, for example in diesel engines to achieve extremely low NOx emissions Operation with homogeneous combustion and compression ignition or a Combustion be carried out at low temperatures. Compared to a conventional one Diesel combustion requires such high combustion modes Exhaust gas recirculation rate as well as a very early one Fuel injection. The ignition delay, which as a time period between the start of activation of the fuel injectors and the beginning of the combustion is defined, can be much longer than in conventional combustion modes where the fuel injection is within a few degrees of the crankshaft angle around top dead center. Since diesel engines achieve the achievement of given targets (emissions, desired Torque) primarily from the timing of the charge ignition and depends on the composition of the charge, requires a reliable control combustion an observation of the air supply respectively the exhaust gas recirculation as well the combustion behavior.

• – Abschätzung des gewünschten Drehmomentes aus zwei primären Eingangssignalen, der Motordrehzahl und der Gaspedalposition;
• – Berechnung der notwendigen Kraftstoffmenge zur Erzielung des gewünschten Drehmomentes;
• – Festlegung der Injektions-Zeitsteuerung zur Erreichung der Zielvorgaben in Bezug auf Emissionen und Geräuschpegel.

The internal combustion engine controls conventionally used in the prior art focus on the fuel injection means but not on the combustion itself. These control systems are designed to control the fuel injectors to supply the engine with the right amount of fuel at the right time , For this purpose, the number of injections per engine cycle, the start of the injector activation and the pulse width of the injector, which determines the amount of fuel injected per engine cycle, calculated, the calculation based on an open loop and predetermined maps and essentially in the following three steps:

• - estimation of the desired torque from two primary input signals, the engine speed and the accelerator pedal position;
• - calculating the amount of fuel required to achieve the desired torque;
• - Determination of the injection timing to achieve the emission and noise emission targets.

In front Against this background, it was an object of the present invention, means for simple and improved control of the operation of an internal combustion engine provide.

These The object is achieved by a method having the features of the claim 1 and by a control system with the features of the claim 10 solved.

advantageous Embodiments are included in the subclaims.

The inventive method is used to control the operation of an internal combustion engine, in which it may in particular be a diesel engine. The procedure is characterized in that a characteristic size, which hereafter referred to as "index" for the current one Combustion state of the internal combustion engine obtained and as a feedback signal for the Regulation is used. The index is obtained based on the speed acceleration of the internal combustion engine during a predetermined observation window of the crankshaft angle (where the observation window also consists of several separate subintervals can exist). The observation window can in particular at least an interval of crankshaft angle about top dead center between Compression stroke and combustion stroke of a piston of the internal combustion engine include (for example ± 20 ° around top dead center around). Furthermore, the speed acceleration is preferably at the flywheel the internal combustion engine determines, according to the inertial mass the flywheel in this case, the torque output by the engine reflects.

The method described can be realized with simple means, since it only requires the determination of the speed acceleration of the internal combustion engine. Surprisingly, however, a very meaningful index can be calculated from this one signal, which one on the observation of the burn Self-based, feedback control of the internal combustion engine allows. The method can thus contribute significantly to achieving predetermined objectives with respect to the performance of the internal combustion engine and an emission reduction.

The Determining the speed acceleration of the internal combustion engine can in principle done in different ways. Preferably, the Crankshaft angle of the internal combustion engine measured and thereby (two-fold) derivative calculates the speed acceleration. sensors for detecting the crankshaft angle are well known and in vehicles usually anyway available. By processing (derivative) of them supplied signals can therefore without additional sensor, the speed acceleration be determined.

According to one preferred embodiment of the method becomes the speed acceleration determined from measurements filtered and / or normalized before going for the determination of an index is used. This is especially true if - as above mentioned - the speed acceleration is calculated by derivation from the crankshaft angle, since in In this case, the discharges may be considerable noisy signal arises. By a bandpass filtering can from such Signal, however, still a useful value of the speed acceleration be won.

For the definition a meaningful Indexes based on the speed acceleration are in principle various possibilities open. Preferably, the index is calculated from an energy signal which depends on the current crankshaft angle and out of the square of (belonging to this crankshaft angle) speed acceleration is calculated. Physically, the square reflects the speed acceleration the actual kinetic energy of the rotating engine components including the flywheel, with this kinetic energy in turn through the combustion process in of the internal combustion engine and is given. In this way, information about the Combustion process in the Motor into the energy signal and thus reach the calculated index.

For the calculation of the energy signal from the square of the speed acceleration are it also different definition possibilities. Preferably the energy signal from the over a subsection of the observation window accumulated square the speed acceleration calculated. The square of the speed acceleration can, for example, over a short interval of the crankshaft angle, which within the observation window is integrated, in which case the Value of this integral is the energy signal of the integration interval represents (and usually a selected one Point of the integration interval is assigned, for example its center).

Of Further exist for the definition of the index as a function of an energy signal various possibilities. Preferably, the index is defined as the crankshaft angle, where the energy signal exceeds a predetermined percentage for the first time. This percentage is typically set at 50%, which is why the associated one Index may also be called "(Energy) Balance Index" or "Energy Center". As will be explained in more detail in connection with the description of the figures, is a so-defined index for different influencing variables of a Combustion process sensitive, for example, the exhaust gas recirculation rate or the beginning of fuel injection.

Of the the combustion process in the engine characterizing index can in diverse Way for the control of the internal combustion engine can be used. Preferably are based on the index parameters for fuel injection (for example Start of fuel injection, number of fuel injections per engine cycle, amount of injected fuel, etc.), parameters for air supply (Throttle position, boost pressure, etc.) and / or parameters for exhaust gas recirculation (open position an exhaust gas recirculation valve etc.) changed.

The Invention further relates to a control system for an internal combustion engine, especially for a diesel engine, which is designed to a method of the type described above. That is, the control system an index for the current combustion state of the internal combustion engine from the Speed acceleration during an observation window of the crankshaft angle is calculated and this as a feedback signal used. The control system can in particular with a speed sensor - for example a Hall sensor on the flywheel of the internal combustion engine - coupled be to determine the crankshaft angle and therefrom by derivation to calculate the speed acceleration. Regarding the others Details, advantages and further developments of the control system Reference is made to the above description of the associated method.

in the The invention will be explained in more detail by way of example with reference to the figures. It demonstrate:

1 schematically the use of a control system according to the present invention;

2 a schematic diagram for obtaining a speed acceleration from the measurement of the crankshaft angle at the flywheel;

3 Measurements of heat output in the engine at 20% exhaust gas recirculation rate and different starting points of fuel injection;

4 to the measurements of 3 associated index X depending on the starting point of the fuel injection;

5 Measurements accordingly 3 at 35% exhaust gas recirculation rate;

6 to the measurements of 5 associated index X depending on the starting point of the fuel injection;

7 Measurements of the heat emission in the engine and the position of the associated index X _ref for a reference operation;

8th Data accordingly 7 for additional exhaust gas recirculation, and

9 Data accordingly 7 for an additional pilot injection of fuel.

führt. 1 shows schematically the use of a control system according to the invention on an internal combustion engine 20 , which may be, for example, a diesel engine, but without the invention being limited thereto. The illustrated arrangement initially comprises a conventional engine control unit 10 , which can be realized in particular as a microprocessor with appropriate software. The control unit 10 uses as input signals the (time-averaged) speed n of the engine and the driver-specified position P _{acc of} the accelerator pedal to block out 11 to calculate the settings for the fuel injection. The mentioned settings are sent to the engine 20 transmitted where they are in the combustion system 21 Determine the combustion process. The latter in turn has an effect on the torque T thus generated, which is on the flywheel 22 acts and there to a momentary spin

leads.

des Schwungrades berech net (Block 31). Wie nachfolgend näher erläutert wird, berechnet Block 32 aus der Drehzahlbeschleunigung

einen Index X für den aktuellen Verbrennungszustand des Motors 20, welcher in Block 33 mit Leistungsvorgaben verglichen wird. Basierend auf diesem Vergleich wird dann in Block 11 des Motorreglers 10 Einfluß auf die Einstellungen der Injektionsparameter genommen.In a feedback loop 30 gets out of the flywheel 22 measured crankshaft angle θ the speed acceleration

of the flywheel (block 31 ). As will be explained in more detail below, Block calculates 32 from the speed acceleration

an index X for the current combustion state of the engine 20 which is in block 33 is compared with performance specifications. Based on this comparison is then in block 11 of the engine governor 10 Influence on the settings of the injection parameters taken.

beeinflussen.The system described allows a feedback control of the combustion, since a measurement or estimation of the combustion state of the internal combustion engine 20 is used. The function of the system is based on the fact that changes in the timing of combustion, the instantaneous engine torque T and thus the speed acceleration

influence.

detaillierter dargestellt. Zunächst wird am Schwungrad 22 z. B. mit einem Halleffekt-Sensor 23 dessen momentane Drehgeschwindigkeit gemessen. In Block 34 der nachgeschalteten Signalverarbeitung wird das ursprünglich mit einer Auflösung von beispielsweise 6° Kurbelwellenwinkel (CA) vorliegende Signal des Kurbelwellenwinkels θ durch Interpolation auf eine Auflösung von 0.5° CA heraufgesetzt. Anschließend wird durch Zeitableitung in Block 35 die Drehgeschwindigkeit

und durch weitere Zeitableitung in Block 36 die gesuchte Drehzahlbeschleunigung

berechnet.In 2 is the acquisition of the speed acceleration

shown in more detail. First, the flywheel 22 z. B. with a Hall effect sensor 23 measured its instantaneous rotational speed. In block 34 In the downstream signal processing, the signal of the crankshaft angle θ which was originally present with a resolution of, for example, 6 ° crankshaft angle (CA) is increased by interpolation to a resolution of 0.5 ° CA. Subsequently, by time derivation in block 35 the rotational speed

and by further time derivation in block 36 the desired speed acceleration

calculated.

beziehungsweise der damit verknüpften (kinetischen) Energie liegt ein wichtiges Signal zur Abschätzung des Verbrennungsverhaltens vor. Da durch die zweifachen Ableitungen in den Blöcken 35, 36 von 2 ein Rauschen in die Signale eingeführt wird, wird die berechnete Drehzahlbeschleunigung

vor ihrer weiteren Verwendung vorzugsweise zunächst digital bandpaßgefiltert und normiert, was das Signal

ergibt. Letzteres kann beispielsweise gemäß folgender Formel berechnet werden:

With the speed acceleration

or the associated (kinetic) energy is an important signal for estimating the combustion behavior. Because of the double derivatives in the blocks 35 . 36 from 2 a noise is introduced into the signals, the calculated speed acceleration

before their further use, preferably first digitally bandpass filtered and normalized, which is the signal

results. The latter can be calculated, for example, according to the following formula:

ermittelt werden, um hieraus einen (einzigen) Index für den Verbrennungszustand zu berechnen. Das Beobachtungsfenster I umfaßt üblicherweise ein Kurbelwellenwinkel-Fenster um den oberen Totpunkt einer jeden individuellen Verbrennung in den Zylindern herum (beispielsweise ein Intervall von ±20° um den oberen Totpunkt). Die Begrenzung der Messungen auf ein derartiges Fenster um den oberen Totpunkt herum begrenzt das Rauschen, welches durch andere Ereignisse im Motor (beispielsweise die Verbrennung in anderen Zylindern, das Öffnen und Schließen der Einlaß-/Auslaßventile etc.) verursacht wird.Herein, I means the observation window during which the speed accelerations

to calculate a (single) index of the combustion state. The observation window I typically includes a crankshaft angle window around the top dead center of each individual combustion in the cylinders (eg, an interval of ± 20 ° around top dead center). Limiting the measurements to such a window around top dead center limits the noise caused by other events in the engine (eg, combustion in other cylinders, opening and closing of the intake / exhaust valves, etc.).

The function F _BP in equation (1) represents the band-pass filter, which may be either the forward type or the forward / backward type. Forward type filters only filter a signal in the forward direction, that is, the angle θ incrementally increases in such a filter. For this reason, forward filters require less computation and can be used for online calculations, for example, for calculations of current events. Due to the nature of these filters, however, they lead to a phase shift of the input signal. On the other hand, forward / reverse type filters filter a signal in both the forward and reverse directions so that they can compensate for phase shifts. However, they usually require more computational effort than corresponding forward filters and can only be used offline, for example in calculations between combustion events.

berechnet (hier und im Folgenden wird dabei der Index * weggelassen und vorausgesetzt, daß es sich bei θ,

um gefilterte und normierte Größen handelt). Das Energiesignal kann dabei insbesondere gemäß folgender Formel aus der quadrierten und über ein (θ enthaltendes) Teilintervall [CA_begin, CA_end] des Beobachtungsfensters I akkumulierten Drehzahlbeschleunigung

berechnet werden:

In a next processing step, for each angle θ of the observation window I, an energy signal E (θ) based on the speed acceleration

calculated (here and below, the index * is omitted and provided that at θ,

filtered and normalized quantities). In this case, the energy signal can in particular be calculated according to the following formula from the speed acceleration squared and a partial interval [CA _begin , CA _end ] of the observation window I accumulated over a (θ containing)

be calculated:

In a further step, an index X which characterizes the entire observation window I is calculated from the energy signals E (.theta.), Which is also referred to as the "energy center index". It is defined as the crankshaft angle at which 50% of the maximum energy signal is reached for the first time, that is

Of the Index X characterizes the effects of combustion timing on the flywheel in relation to the length of the observation window I. The center of gravity position in the index follows the largest combustion effect, e.g. the maximum pressure gradient leading to a maximum acceleration of the Flywheel leads, and less sudden changes in the combustion, as for example in the knock detection in gasoline engines is the case.

From the energy signals E (θ) can further be defined according to an energy signal vector (E (θ 1 ), ... E (θ N )) (5), where θ ₁ , ... θ _{N are} the sampling points in the observation window I.

The 3 to 9 show the results of practical examinations of the concept explained above, with all measurements being carried out on a V6 diesel engine (Ford Lion).

In the measurements of 3 to 6 the engine was operated at 2000 rpm and 6 bar indicated mean pressure (IMEP). To provide two different EGR rates became the Air Force material ratio kept constant and accordingly increases the boost pressure in the case of higher EGR rates. For each EGR rate, the start of activation (BOA: Begin Of Activation) of the injector needles was varied in the range of 5 ° to 18 ° before top dead center (BTDC).

The 3 and 5 show calculated heat outputs in the cylinders based on in-cylinder pressure measurements at 20% EGR ( 3 ) and at 35% EGR ( 5 ). Each BOA operating point was calculated for 15 consecutive engine cycles and for two cylinders.

4 shows the calculated index X (square symbols) depending on the BOA settings. In addition, the indices are marked in the diagram by triangles or circles, which correspond to 10% or 90% of the energy level analogously to equation (4).

Of the The line of the index X follows the BOA behavior: An enlargement of the BOA leads to an earlier Combustion, as the rest Engine operating parameters unchanged stay.

The same result results from the 5 and 6 in the case of a 35% EGR. That is, the index X, regardless of whether the EGR rate is 20% or 35%, follows the combustion variation by the BOA.

The 7 to 9 show in diagrams of the heat release the results of further investigations of the control method according to the invention. These measurements were based on the values listed in Table 1 below for three operating modes "Reference", "EGR" and "Pilot". The reference mode has no exhaust gas recirculation and no pilot injection. In contrast, the EGR mode has an exhaust gas recirculation rate of 40% and, accordingly, less air intake into the cylinders. The pilot mode has no exhaust gas recirculation, but a pilot fuel injection at 18 ° before top dead center, with the main fuel injection remaining the same as in the reference mode, ie 9 ° before top dead center. The other operating parameters of the engine correspond to 1500 rpm and 6 bar IMEP.

Table 1:

The Table 2 below gives the calculated index X for the different ones tested operating modes again, with the indices each over twelve consecutive Motor cycles were averaged and the resulting standard deviation Std is also reproduced. From the values of the standard deviation let yourself conclude that the Indexes for the different engine operating parameters tested are distinguishable from each other are observable.

Table 2:

The indices according to the above table are in the heat emission diagrams of 7 to 9 entered as vertical lines for the three tested operating modes. It turns out that they behave like the expected timing of combustion.

Thus, in the reference mode according to 7 combustion within a few degrees of top dead center TDC (360 °). The absence of exhaust gas recirculation and pilot injection results in a very short and rapid onset of combustion corresponding to a strong premixed combustion phase.

In the 8th the addition of an exhaust gas recirculation and the resulting reduction of the air supply leads to a delayed start of the combustion. The associated index X _AGR is compared to the reference situation of 7 shifted to the right, that is, the combustion effect later affects the flywheel.

In the pilot mode of 9 takes place without exhaust gas recirculation a pilot injection at 18 ° crankshaft angle before top dead center. The associated index X _pilot is compared to the reference situation of 7 shifted to the left, that is, the combustion effect affects earlier on the flywheel.

Out The measurements can be concluded that the index X for both a variation the exhaust gas recirculation as also the parameter of the fuel injection is sensitive. The index can therefore be used for surveillance The strategy of fuel injection can be used for compensation drifts in the behavior of the injectors over time, as well to interact with the air-EGR strategy. An advantage of the featured Process is in particular that it can be realized at low cost, since no additional Sensor needed becomes.

Claims (10)

Method for controlling the operation of an internal combustion engine ( 20 ), in particular a diesel engine, characterized in that an index (X) for the current combustion state of the internal combustion engine ( 20 ) from the speed acceleration (

) during an observation window of the crankshaft angle (θ) and used as a feedback signal. Method according to Claim 1, characterized in that the observation window has at least one interval of the crankshaft angle (θ) about top dead center between the compression stroke and the combustion stroke of a piston of the internal combustion engine ( 20 ). Method according to Claim 1 or 2, characterized in that the crankshaft angle (θ) of the internal combustion engine ( 20 ) and from this by derivation the speed acceleration (

) is calculated. Method according to Claim 3, characterized in that the speed acceleration (

) is filtered and / or normalized. Method according to at least one of Claims 1 to 4, characterized in that the index (X) is based on an energy signal which is dependent on the crankshaft angle (θ) and consists of the square of the speed acceleration (

) is calculated. Method according to Claim 5, characterized in that the energy signal is calculated from the square of the speed acceleration (C) accumulated over a subinterval of the observation window (

) is calculated. Method according to claim 5 or 6, characterized that the Index (X) is defined as the smallest crankshaft angle (θ) at which the Energy signal a predetermined percentage, preferably 50% of his Exceeds maximums in the observation window. Method according to at least one of Claims 1 to 7, characterized in that the speed acceleration (

) on the flywheel ( 22 ) of the internal combustion engine ( 20 ) is determined. Method according to at least one of claims 1 to 8, characterized in that based on the index (X) parameters for the fuel injection, the air supply and / or the exhaust gas recirculation rate changed become. Regulatory system ( 10 . 30 ) for an internal combustion engine ( 20 ), characterized in that it is adapted to carry out a method according to at least one of claims 1 to 9.