DE102008054690B4 - Method and device for calibrating partial injections in an internal combustion engine, in particular a motor vehicle - Google Patents

Abstract

Method for calibrating the injection quantity of at least one partial injection (300) provided in addition to a main injection (310) in an injection system (30) of an internal combustion engine (10), characterized in that a correction value for the partial injection (300) in an individual cylinder of the internal combustion engine is performed Stimulation of at least two injection patterns is determined, values for the torque curve being determined from the speed signal of the internal combustion engine, and that by comparing the torque curve of a combustion with a single injection and a combustion with a multiple injection comprising the partial injection (300) it is determined whether the injection quantity of the Partial injection (300) deviates from a predetermined value.

Description

State of the art

The invention relates to a method for calibrating the injection quantity of a partial injection in an injection system of an internal combustion engine and a corresponding device according to the preambles of the respective independent claims.

In modern fuel injection systems, especially self-igniting internal combustion engines, the fuel quantities injected into combustion chambers by means of injectors are divided into several partial injections, which are arranged closely in time and consist, for example, of one or more pre-injections applied before a main injection. The time interval between two partial injections is defined by the pause between two consecutive electrical control pulses of the injectors, by a crankshaft angle or by a combination of these two variables.

These partial injections enable improved mixture preparation and thus lower exhaust gas emissions from the internal combustion engine, reduced noise development during combustion and increased mechanical power output by the internal combustion engine. For the simultaneous optimization of noise and exhaust gas, for example, in the case of pre-injections, very small injection quantities are specified, some of which are in the range of the smallest fuel quantity that can be represented by a named injector.

In order to be able to guarantee the exact adherence to the injection quantity, e.g. a pre-injection, in the event of a drift of the injector behavior over the duration of the injector, functions are necessary that allow the pre-injection quantities to be calibrated while the internal combustion engine is operating (fired). So goes from the DE 103 43 759 A1 a method in which, when an internal combustion engine is idling, a preinjection is switched off in one or more cylinders and the preinjection quantity is deduced from the control quantities of an idle regulator and a quantity compensation regulator on the basis of cylinder-specific corrections.

From the DE 196 32 650 C1 a method for suppressing torque jumps during the operation of an internal combustion engine is known. When a pilot injection is switched on / off, the difference between the fuel quantity to be injected and the pilot quantity is formed. A correction factor is then applied to this, which brings about the torque adjustment. This difference quantity represents the main injection quantity.

The DE 10 2005 052 024 A1 describes an injection quantity control. This citation also describes switching between different numbers of partial injections.

Summary of the invention

The present invention is based on the idea of determining a correction value for the partial injection into a single cylinder (ie individual cylinder) by stimulating at least two injection patterns in a calibration method concerned here, with a speed signal of the internal combustion engine based on a characteristic of the combustion physical variable it is determined whether the partial injection was too small or too large. Said stimulation takes place with a first injection pattern with a single injection, preferably a main injection (HE), and a combustion with a multiple injection, preferably a double injection composed of a pre-injection (VE) and a main injection (HE).

It should be emphasized that the order of the at least two injection patterns is arbitrary, i. the aforementioned first injection pattern and the second injection pattern can also be applied in reverse chronological order. It is also understood that the pre-injection mentioned there is only preferred and the method according to the invention can accordingly also be used for calibrating post-injections or the like.

According to a first embodiment of the method according to the invention, the torque curve is determined or reconstructed from the speed signal of the internal combustion engine, with a comparison of the torque curves thus determined for a combustion with a first injection pattern with a single injection (HE) and a combustion with a multiple injection, preferably a double injection (VE + HE), it is determined whether the partial injection (or pre-injection) was too small or too large. The necessary calculation of the course of the combustion torque from the speed course of the internal combustion engine is in the unpublished prior application DE 10 2006 056 708 disclosed and will be described in detail below.

According to a second embodiment, the calibration according to the invention of the injection quantity of a partial injection takes place on the basis of an energy-based speed evaluation, with those for a single injection and a multiple injection instead of the aforementioned torque curves converted physical energy or work can be compared with one another. A corresponding physical feature is preferably calculated from the time profile of the speed signal, which provides information about the difference between the converted energy or work of the single injection and the multiple injection.

According to a further embodiment, the activation duration or the duration of the VE is changed until the torques resulting from both injection patterns or the values of the physical energy or work resulting from both injection patterns are the same or as similar as possible.

The invention enables a cylinder-specific determination of the torque or the energy or work from the speed, which results in a higher accuracy and an improved robustness of the calibration. Because with the described evaluation in the frequency range, all cylinders have an influence on the calibration, which can cause interference. Furthermore, a multiple injection can excite other frequencies than a single injection, even with the same injection quantity. The invention eliminates these residual errors during the calibration and the calibration becomes less sensitive to the disturbances mentioned.

Correspondingly, this eliminates the further disadvantage of the prior art that when calculating the effect of the respective injection pattern with the aid of the discrete Fourier transform (DFT) method, the information of all cylinders is averaged, which is a considerable disadvantage, since cylinders on which the called injection pattern is not controlled, act as a disturbance variable, which is superimposed on the actual useful signal. There is an additional advantage if the absolute information (torque or combustion position) is not sought, but only the difference between two successive injections.

In addition, the values of the mentioned features determined from the speed signal can be physically better interpreted and the calibration can be carried out in a shorter time.

The method according to the invention enables the partial injection quantity to be precisely calibrated in the fired operation of an internal combustion engine or in the ongoing driving operation of an underlying motor vehicle, specifically not necessarily when the internal combustion engine is idling or in steady-state operation. Since a cylinder compensation function is not required in the proposed method, the method can advantageously be used in engines with unequal ignition intervals and in single-cylinder engines.

Compared to the method described at the outset, the approach according to the invention does not require overrun operation or even stationary idling operation of the internal combustion engine. It should be emphasized here that, with the methods known in the prior art, there must not be a change in the load torque during calibration in idle operation, since this falsifies the calibration result. Therefore, the known calibration methods can only be carried out in a workshop with the necessary precision. In addition, a quantity compensation control is no longer required for the correction of the partial injection quantity to be achieved. The calibration according to the known method is acoustically perceptible especially when idling and therefore leads to a loss of comfort when the internal combustion engine is operating.

In addition, the said overrun operation cannot be applied in all applications of diesel engines, e.g. B. in the off-road area, with stationary engines or automatic transmissions, no or only very rarely overrun. In addition, according to the current state of the art, the aforementioned quantity compensation regulations are only possible for engines with the same ignition intervals, and in particular not for single-cylinder engines.

drawing

The invention is explained in more detail below with the aid of preferred exemplary embodiments and with reference to the drawing, from which further features, features and advantages of the invention emerge.

• 1 eine schematische Darstellung eines Kraftstoffzumesssystems einer Brennkraftmaschine gemäß dem Stand der Technik, bei dem die vorliegende Erfindung eingesetzt werden kann;
• 2 eine detaillierte Darstellung der an sich bekannten Berechnung von Ansteuerdauern eines in der 1 gezeigten elektrisch betätigten Ventils;
• 3 einen typischen Einspritzverlauf mit einer Vor- und Haupteinspritzung, anhand dessen die erfindungsgemäße Umlagerung der Einspritzmenge zwischen Vor- und Haupteinspritzung illustriert wird; und
• 4 ein kombiniertes Block-/Flussdiagramm eines bevorzugten Ausführungsbeispiels der Erfindung zur zylinder-individuellen Korrektur von Voreinspritzungen.

Show in detail

• 1 a schematic representation of a fuel metering system of an internal combustion engine according to the prior art, in which the present invention can be used;
• 2 a detailed representation of the known calculation of control durations in the 1 shown electrically operated valve;
• 3 a typical injection curve with a pilot and main injection, on the basis of which the rearrangement according to the invention of the injection quantity between the pilot and main injection is illustrated; and
• 4th a combined block / flow diagram of a preferred exemplary embodiment of the invention for the individual cylinder correction of pilot injections.

Description of exemplary embodiments

The 1 shows a block diagram of the essential elements of a fuel metering system of an internal combustion engine. The internal combustion engine 10 received from a fuel metering unit 30th metered a certain amount of fuel at a certain point in time. Different sensors 40 record measured values 15th , which characterize the operating state of the internal combustion engine, and forward them to a control unit 20th . The control unit 20th are also different output signals 25th further sensors 45 forwarded. The recorded measured values 15th characterize the state of the fuel metering unit such as the driver's request. The control unit 20th calculated on the basis of these measured values 15th and the other sizes 25th Control pulses 35 with which the fuel metering unit 30th is applied.

The internal combustion engine is preferably a direct-injection and / or a compression-ignition internal combustion engine. The fuel metering unit 30th can be designed in different ways. For example, a distributor pump can be used as the fuel metering unit in which a solenoid valve determines the point in time and / or the duration of the fuel injection.

Furthermore, the fuel metering unit can be designed as a common rail system. As is known, a high-pressure pump compresses fuel in a reservoir. The fuel then reaches the combustion chambers of the internal combustion engine from this store via injectors. The duration and / or the start of the fuel injection is controlled by means of the injectors. The injectors preferably contain a solenoid valve or a piezoelectric actuator.

The control unit 20th calculates the amount of fuel to be injected into the internal combustion engine in a manner known per se. This calculation is based on various measured values 15th , such as the speed n, the engine temperature, the actual start of injection and possibly other variables 25th that characterize the operating state of the vehicle. These other variables are, for example, the position of the accelerator pedal or the pressure and temperature of the ambient air. The control unit 20th then converts the required amount of fuel into corresponding triggering pulses for the injectors.

In the case of the internal combustion engines mentioned, one or more small amounts of fuel are often metered into the cylinder shortly before the actual main injection. This can significantly improve the noise behavior of the engine. This injection is referred to as the pilot injection and the actual injection as the main injection. Furthermore, it can be provided that a small amount or several amounts of fuel are metered in after the main injection. This is then referred to as post-injection. Furthermore, it can be provided that the individual injections are divided into further partial injections.

The problem with such fuel metering systems is that the electrically actuated valves can meter different amounts of fuel with the same control signal. In particular, the activation time during which fuel is being metered depends on various factors. This minimum control period leads to an injection, whereas control periods shorter than the minimum control period do not lead to an injection. This minimum control duration depends on various factors, such as the temperature, the type of fuel, the service life, the rail pressure, manufacturing tolerances of the injectors and other influences. In order to be able to achieve precise fuel metering, this minimum activation period must be known.

A device for controlling the fuel metering in an internal combustion engine is in the 2 shown. Already in 1 elements described are denoted by corresponding reference symbols. Signals from the sensors 45 and other sensors, which are not shown, arrive at a quantity specification 110 . This quantity specification 110 calculates a fuel quantity QKW that corresponds to the driver's request. This quantity signal QKW arrives at a node 115 , at the second input the output signal QKM of a second synchronization 155 is applied. The output signal of the first connection point 115 comes to a second connection point 130 , which in turn is a control duration calculation 140 applied. At the second input of the second connection point 130 the signal QKO is a zero quantity correction 142 at.

In the two connection points 115 and 130 the quantity signals are preferably linked additively. The control duration calculation 140 calculated on the basis of the output signal of the connection point 130 the control signal for applying a fuel metering unit 30th . The activation duration calculation calculates the activation duration with which the electrically operated valves are acted upon.

On a transmitter wheel 120 various markings are arranged by a sensor 125 are scanned. In the illustrated embodiment, the encoder wheel is a so-called segment wheel, which is one of the The number of markings corresponds to the number of cylinders, in the illustrated embodiment there are four. This encoder wheel is preferably arranged on a crankshaft of the internal combustion engine, not shown. This means that a number of pulses is generated per engine revolution that corresponds to twice the number of cylinders. The sensor 125 delivers a corresponding number of pulses to a first synchronization 150 .

The first synchronization 150 acts on a first regulator 171 , a second regulator 172 , a third regulator 173 and a fourth regulator 174 . The number of regulators corresponds to the number of cylinders. The output signals of the four controllers then arrive at the aforementioned second synchronization 155 .

Such a facility that does not require zero quantity correction 142 is equipped is in the DE 195 27 218 shown in more detail. This facility works as follows. Based on various signals, such as a signal that characterizes the driver's request, determines the amount specified 110 the fuel quantity request signal QKW, which is required to provide the torque desired by the driver. In addition to the driver's request signal, other signals can also be processed. In particular, in addition to the driver's request signal, the speed signal and various temperature and pressure values are also processed. Furthermore, there is the possibility that signals are transmitted from other control units to the quantity specification, which request a torque request and / or a quantity request. Such a further control device can, for. B. be a transmission control that influences the torque from the engine during the shifting process.

Due to tolerances, especially of the fuel metering unit 30th there are deviations between the desired injection quantity and the actually injected fuel quantity. The individual cylinders of the internal combustion engine usually meter different amounts of fuel with the same control signal. These variations between the individual cylinders are usually compensated for with a quantity compensation control (MAR). Such a volume equalization scheme is shown schematically in the upper part of the 2 shown. A regulator is assigned to each cylinder of the internal combustion engine to regulate the quantity compensation. So the first regulator is the first cylinder 171 , the second cylinder the second regulator 172 , the third cylinder is the third regulator 173 and the fourth cylinder the fourth regulator 174 assigned. It can also be provided that only one controller is provided, which is alternately assigned to the individual cylinders. Using the sensor 125 and the sender wheel 120 determines the first synchronization 150 a setpoint and an actual value for each individual controller. It is provided that to compensate for tolerances of the encoder wheel and to compensate for torsional vibrations, a special filtering of the sensor signal 125 he follows. The output signals of the controller 171 to 174 become a second synchronization 155 supplied, which provides a correction amount QKM with which the desired amount QKW is corrected.

This volume compensation control is designed in such a way that the controllers regulate the volume metered to the individual cylinders to a common mean value. If a cylinder allocates an increased amount of fuel due to tolerances, a negative amount of fuel QKM is added to the driver's desired amount QKW for this cylinder. If a cylinder meters too little fuel quantity, a positive fuel quantity QKM is added to the driver's desired quantity QKW. With such quantity errors, a rotational nonuniformity occurs. This has the effect that vibrations are superimposed on the speed signal, the frequency of which corresponds to the camshaft frequency and / or a multiple of the camshaft frequency. These components in the speed signal with camshaft frequency characterize the rotational irregularity and are adjusted to zero by the quantity compensation control.

Quantity average errors cannot be corrected with this quantity balancing rule. In particular, errors that are based on the fact that no fuel is metered below the specified minimum control duration cannot be corrected with such a quantity compensation control.

In the 3 a typical injection pattern, consisting of a pilot injection and a main injection, is now shown schematically. The upper diagram shows the control of an injector, the current control being neglected. The lower diagram shows the time-delayed fuel flow through the injector nozzle resulting from the aforementioned control. The areas under the respective curves of the fuel flow correspond to the amount of fuel injected.

• - „Lernmodus“: Ermitteln des Korrekturwerts durch Stimulation des Einspritzmusters und Ausregeln der Drehzahlschwingung
• - „Anwendungsmodus“: Aufsteuern des ermittelten Korrekturwerts im normalen Motorbetrieb

The calibration method according to the invention now has the two working phases or operating modes already mentioned:

• - "Learning mode": Determination of the correction value by stimulating the injection pattern and regulating the speed oscillation
• - "Application mode": Activation of the correction value determined in normal engine operation

In the “learning” mode, the method according to the invention is stored for one cylinder and with half the camshaft frequency, the pre-injection quantity between the pre-injection and the main injection, preferably recurring cyclically. Such a rearrangement cycle is preferably repeated more than once, but in the simplest case can also only be implemented by a single cycle, ie a single rearrangement, since a single cycle can already cause a specified speed oscillation.

It should be emphasized that the injection pattern described herein of the rearrangement of a pre-injection in relation to a main injection is only an example and, in principle, other injection patterns are also conceivable by means of which a named speed oscillation can be excited. Instead of a pre-injection, a post-injection can be rearranged accordingly or an even more complex "rearrangement pattern", in which more than one partial injection is rearranged, can be generated.

In the in the 3 The embodiment shown is the amount of fuel provided for the pilot injection 300 alternately as the amount of fuel 305 to the main injection 310 steered up. It goes without saying, however, that other forms of rearrangement are also possible, such as, for example, the rearrangement of the fuel quantity of a pre-injection with a post-injection that is separated in time from the main injection.

The present invention is based on the knowledge that only in cases in which the quantities of fuel physically deposited during the cyclical rearrangement 300 , 305 are the same, no speed oscillation occurs. But as already with the 1 has been described, it can happen that the electrically operated valves of the injectors meter different amounts of fuel with the same control signal. It is therefore not automatically guaranteed that the two fuel quantities will be used if the activation duration is the same 300 and 305 to match. Even with injectors that have drifted or the calibration procedure that has not been learned in, the fuel quantities are 300 , 305 naturally unequal and the speed oscillations described above occur. The control objective of the calibration process is therefore to regulate these speed fluctuations to a minimum. The manipulated variable for this is a corrective intervention on the control duration of the pre-injection 300 .

It goes without saying that the concept according to the invention can not only be applied to the calibration of pre-injections, but in principle to the calibration of partial injections which are carried out in addition to a main injection, that is to say for example also to post-injections or the like.

In the 4th A preferred exemplary embodiment of the present invention is shown using a combined flow / block diagram, by means of which the cylinders of the internal combustion engine can be individually calibrated.

In step or block 600 First the already described inventive setting of an injection pattern and the specification of a rail pressure in the case of a common rail injection system take place. With the dashed line 605 preferred steps for the above-mentioned calculation of the torque from a speed signal are now outlined, which are described in the previously cited prior application DE 10 2006 056 708 are described in greater detail and which are described here only to the extent necessary for the present invention.

For a given injection pattern (ie combustion with or without pre-injection), a block / step 610 first a current speed signal of the internal combustion engine is recorded or possibly read out from a control unit. In block / step 615 there is an elimination or compensation of transverse influences on the present speed signal, such as the influence of a “dragged” engine behavior, the influence of oscillating masses or the influence of a torsion of the crankshaft. Based on these influencing factors, there is now a block / step 620 a differential torque curve of the combustion is determined or reconstructed and from this difference curve in block / step 625 calculates an average indexed moment.

In block / step 630 are compared with the at least two different injection patterns resulting torque curves and in block / step 635 the control duration of the partial injection is changed until the at least two torque curves are as similar as possible or even identical. It should be noted that instead of comparing the combustion torque profiles, suitable features of this profile such as an average torque, the combustion position or the maximum torque can also be used for the comparison.

As an alternative to the described comparison of torque curves in block / step 630 Sizes or features such as increment times of encoder wheel increments of a encoder wheel provided on the internal combustion engine or the resulting total torque, possibly including a compression torque, can also be used. Segment times or sub-segment times of the aforementioned encoder wheel can also be used. It should be emphasized that the variables mentioned are assigned to the respective cylinder to be calibrated and can therefore be compared directly with one another (in the manner described).

It can also be provided that the results of a calibration cycle from block / step 630 , ie the results from 2 revolutions of the crankshaft, can be filtered in a manner known per se in order to reduce the noise.

Furthermore, a feature can be calculated from the measured speed signal, preferably from individual tooth times of a 60-2 encoder wheel, specifically for the cylinder to be calibrated, which provides information about the difference in the converted physical energy or work between the single and multiple injection includes. For this purpose, the energy of the crankshaft system is calculated from the speed signal at a selected point in time or crankshaft angle φ before and after the combustion of the relevant cylinder, and the difference is calculated therefrom.

This difference value represents a measure for the physical energy or work converted by the respective combustion. This value can be converted into the unit, Pmi ‛(indexed mean pressure, English IMEP). The injection quantities of two such injection patterns are equal if the energy characteristics are identical, i.e. the corresponding difference is zero. For this purpose, it is advantageous to carry out an averaging over a specific number of injections when determining the energy or work in order to suppress the noise. Another advantage of the feature calculated here in the form of the Pmi difference is that this difference value is physically easy to interpret and the adjustment of the injection quantity, i.e. the adjustment of this difference can be done much faster.

As a result of the 4th The blocks or steps shown are then a calibration of the injection quantity of the partial injection.

Claims (13)

Method for calibrating the injection quantity of at least one partial injection (300) provided in addition to a main injection (310) in an injection system (30) of an internal combustion engine (10), characterized in that a correction value for the partial injection (300) in an individual cylinder of the internal combustion engine is performed Stimulation of at least two injection patterns is determined, values for the torque curve being determined from the speed signal of the internal combustion engine, and that by comparing the torque curve of a combustion with a single injection and a combustion with a multiple injection comprising the partial injection (300) it is determined whether the injection quantity of the Partial injection (300) deviates from a predetermined value. Procedure according to Claim 1 , characterized in that values for the physical energy and / or work converted in a single injection and a multiple injection comprising the partial injection (300) are determined from the speed signal of the internal combustion engine, and by comparing the resulting values of these physical variables it is determined whether the injection quantity of the partial injection (300) deviates from a predetermined value. Procedure according to Claim 2 , characterized in that the physical energy and / or work is calculated from the time profile of the speed signal, which provides information about the difference in the converted energy or work of the single injection and the multiple injection. Method according to one of the Claims 1 to 3 , characterized in that the duration of the partial injection (300) is varied until the torques resulting from the at least two injection patterns and / or the resulting values of the physical energy or work are equal or as equal as possible. Method according to one of the preceding claims, characterized in that for the individual cylinder with a fraction of the camshaft frequency, preferably with a camshaft frequency (n + ½), where n = 0, 1, 2, ..., a predetermined injection quantity of the partial injection (300) is rearranged between a pre-injection or post-injection and a main injection (310). Method according to one of the preceding claims, characterized in that the calibration takes place in at least two work phases, with a correction value of a cylinder in the first work phase by the said stimulation of the at least two injection patterns and the said evaluation of the resulting torque curves and / or the resulting values of the Energy or work is determined and the correction value determined in this way is controlled up to a currently present control variable of the pilot injection during operation of the internal combustion engine. Device, in particular a control device, for calibrating the injection quantity of a partial injection (300) provided in addition to a main injection (310) in an injection system (30) of an internal combustion engine (10), characterized by computing means or control means for determining a correction value for the partial injection (300) in a single cylinder of the internal combustion engine (10) based on a stimulation of at least two injection patterns, one of a Speed signal of the internal combustion engine is based on values determined for the torque curve, and that the computing means or control means stimulate a combustion with a first injection pattern with a single injection and a combustion with a second injection pattern with a multiple injection comprising the partial injection (300) and based on from the speed signal the internal combustion engine determined values for the torque curve in the two stimulated injection patterns determine whether the injection quantity of the partial injection (300) deviates from a predetermined value. Device according to Claim 7 , characterized in that said computing means or control means stimulate a combustion with a first injection pattern with a single injection and a combustion with a second injection pattern with a multiple injection comprising the partial injection (300) and based on values determined from the speed signal of the internal combustion engine for the two stimulated injection patterns each implemented physical energy and / or work determine whether the injection quantity of the partial injection (300) deviates from a predetermined value. Device according to one of the Claims 7 to 8th , characterized in that said computing or control means vary the duration of the partial injection (300) until the values of the torque and / or the physical energy or work resulting from the at least two injection patterns are equal or as equal as possible. Device according to one of the Claims 7 to 9 , characterized in that said computing or control means for the individual cylinder a predetermined injection quantity of the partial injection (300) with a fraction of the camshaft frequency, preferably with a camshaft frequency (n + ½), where n = 0, 1, 2, ... is to rearrange between a pre-injection or post-injection and a main injection (310). Device according to one of the Claims 7 to 10 , characterized in that said computing or control means provide two work phases, wherein in the first work phase a correction value of a cylinder is determined by said stimulation of the at least two injection patterns and by said evaluation of the resulting torque curves and / or energy or work, and wherein the correction value determined in this way is controlled up to a currently present control variable of the pilot injection during operation of the internal combustion engine. Internal combustion engine with a control unit according to one of the Claims 7 to 11 . Computer program with program code for performing all steps according to one of the Claims 1 to 6th when the program is executed in a computer or a control unit of the internal combustion engine.

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