METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE, CONTROL UNIT FOR AN INTERNAL COMBUSTION ENGINE, AND INTERNAL COMBUSTION ENGINE

Abstract

A method for operating an internal combustion engine, the method including the steps of: (a) actuating an injector to introduce a pre-injection amount of a fuel into a combustion chamber of the internal combustion engine; (b) determining, for an operating cycle of the combustion chamber in which the injector was actuated in the step (a), a pressure gradient characteristic value which is characteristic of a combustion chamber pressure gradient in the combustion chamber; (c) repeating the steps (a) and (b) a plurality of times; (d) determining a skew of a distribution of a plurality of pressure gradient characteristic values determined in the step (c); and (e) changing or maintaining an actuation of the injector depending on the skew determined in the step (d).

Claims

1. A method for operating an internal combustion engine, the method comprising the steps of: (a) actuating an injector to introduce a pre-injection amount of a fuel into a combustion chamber of the internal combustion engine; (b) determining, for an operating cycle of the combustion chamber in which the injector was actuated in the step (a), a pressure gradient characteristic value which is characteristic of a combustion chamber pressure gradient in the combustion chamber; (c) repeating the steps (a) and (b) a plurality of times; (d) determining a skew of a distribution of a plurality of pressure gradient characteristic values determined in the step (c); and (e) changing or maintaining an actuation of the injector depending on the skew determined in the step (d).

2. The method according to claim 1, wherein, if the actuation of the injector is changed in the step (e), the steps (a) to (e) are repeated with a changed actuation.

3. The method according to claim 1, wherein, if the actuation of the injector is changed in the step (e), the method includes repeating the steps (a) to (e) with a changed actuation, the repeating being iterated until the actuation of the injector in the step (e) is maintained.

4. The method according to claim 1, wherein a directional change in the actuation of the injector is selected in the step (e) depending on whether a last change in the actuation of the injector has led to a greater change in the pressure gradient characteristic value than a penultimate change in the actuation of the injector.

5. The method according to claim 1, wherein a directional change in the actuation of the injector is selected in the step (e) depending on whether a last change in the actuation of the injector has led to a greater change in an average pressure gradient characteristic value than a penultimate change in the actuation of the injector.

6. The method according to claim 1, wherein the skew of the distribution is compared in the step (e) to a predetermined skew threshold value, wherein the actuation of the injector is changed if the skew is less than the predetermined skew threshold value, and wherein the actuation of the injector is maintained if the skew is greater than or equal to the predetermined skew threshold value.

7. The method according to claim 1, wherein the skew is determined as a measured value of the skew.

8. The method according to claim 1, wherein the skew is determined as a measured value of the skew, (i) from the distribution of the plurality of pressure gradient characteristic values, or (ii) directly from a plurality of pressure gradient characteristic values which are determined.

9. The method according to claim 1, wherein a combustion chamber pressure value or a structure-borne sound value is used as the pressure gradient characteristic value.

10. The method according to claim 1, wherein a combustion chamber pressure value or an integral of a structure-borne sound sensor measured value is used as the pressure gradient characteristic value.

11. The method according to claim 1, wherein the method is conducted in predetermined time intervals or in an event-driven manner during an operation of the internal combustion engine.

12. A control unit for an internal combustion engine, the control unit comprising: the control unit, which is configured for conducting a method for operating the internal combustion engine, the method comprising the steps of: (a) actuating an injector to introduce a pre-injection amount of a fuel into a combustion chamber of the internal combustion engine; (b) determining, for an operating cycle of the combustion chamber in which the injector was actuated in the step (a), a pressure gradient characteristic value which is characteristic of a combustion chamber pressure gradient in the combustion chamber; (c) repeating the steps (a) and (b) a plurality of times; (d) determining a skew of a distribution of a plurality of pressure gradient characteristic values determined in the step (c); and (e) changing or maintaining an actuation of the injector depending on the skew determined in the step (d).

13. An internal combustion engine, comprising: at least one combustion chamber; an injector which is assigned to the combustion chamber in order to supply the combustion chamber with a fuel; a control unit, the injector being operatively connected with the control unit of the internal combustion engine and thereby the control unit is configured for activating the injector; a pressure gradient sensor which is operatively connected with the control unit, the pressure gradient sensor being configured for detecting a measured value, the control unit being configured for determining a pressure gradient characteristic value from the measured value which is characteristic for a combustion chamber pressure gradient in the combustion chamber, the control unit being configured for carrying out a method for operating the internal combustion engine, the method comprising the steps of: (a) actuating the injector to introduce a pre-injection amount of the fuel into the combustion chamber of the internal combustion engine; (b) determining, for an operating cycle of the combustion chamber in which the injector was actuated in the step (a), the pressure gradient characteristic value which is characteristic of the combustion chamber pressure gradient in the combustion chamber; (c) repeating the steps (a) and (b) a plurality of times; (d) determining a skew of a distribution of a plurality of pressure gradient characteristic values determined in the step (c); and (e) changing or maintaining an actuation of the injector depending on the skew determined in the step (d).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0042] FIG. 1 is a schematic illustration of a design example of an internal combustion engine with a design example of a control unit;

[0043] FIG. 2 is a plot of a pressure gradient characteristic value against a pre-injection amount which explains the theoretical background of an embodiment of a method for operating the internal combustion engine; and

[0044] FIG. 3 is a schematic illustration of an embodiment of the method in the form of a flow chart.

[0045] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0046] FIG. 1 shows a schematic illustration of a design example of an internal combustion engine 1, which includes at least one combustion chamber 3. Internal combustion engine 1 is herein shown in the optional design of a reciprocating piston engine, with a reciprocating piston 5 assigned to combustion chamber 3. Internal combustion engine 1 includes optionally a plurality of—in particular—identically designed combustion chambers 3.

[0047] Combustion chamber 3 has assigned to it an injector 7 which is designed to introduce fuel into combustion chamber 3. Injector 7 can in particular be actuated to introduce a pre-injection amount of the fuel into combustion chamber 3.

[0048] Internal combustion engine 1 moreover includes a control unit 9 which is operatively connected with injector 7 in order to actuate injector 7, in particular in such a way that injector 7 can be actuated by way of control unit 9 in order to introduce the pre-injection amount of fuel into combustion chamber 3.

[0049] Internal combustion engine 1 moreover includes a pressure gradient sensor 11 which is operatively connected with control unit 9 and which is designed to detect a measured value from which control unit 9 can determine a pressure gradient characteristic value which is characteristic for a combustion chamber pressure gradient in combustion chamber 3. In an optional arrangement, pressure gradient sensor 11 is a structure borne sound sensor.

[0050] Control unit 9 is optionally designed to specify a duration of energization for injector 7.

[0051] Control unit 9 is moreover designed to conduct a method which is described in further detail below:

[0052] Injector 7 is actuated a) in order to introduce the pre-injection amount into combustion chamber 3; wherein b) the compression gradient characteristic value is determined for one operating cycle of combustion chamber 3 in which injector 7 was actuated in step a); wherein c) steps a) and b) are repeated multiple times; wherein in d) a skew of a distribution of the pressure gradient characteristic values which were determined in step c) is established and; wherein actuation of injector 7 is changed or maintained depending on the skew established in step d).

[0053] In particular, if actuation of injector 7 is altered in step c), steps a) through e) are repeated with the changed actuation, wherein this is iterated until the actuation in step e) is maintained for the first time.

[0054] A direction of the change in the actuation of injector 7 in step e) is optionally selected depending on whether a preceding change in actuation—in the immediately preceding iteration—has influenced the pressure gradient characteristic value in the direction of a smaller or in the direction of a greater combustion chamber pressure gradient.

[0055] The skew of the distribution is optionally compared to a predetermined skew threshold value in step e), wherein the actuation of injector 7 is changed if the skew is less than the pre-specified skew threshold value, and wherein the actuation of injector 7 is maintained if the skew is greater than or equal to the pre-specified skew threshold value.

[0056] The skew is optionally determined as a measured value of the skew, in particular from the distribution of the pressure gradient characteristic values themselves, or in an especially optional design, directly from the ascertained pressure gradient characteristic values in particular without explicit determination of the distribution.

[0057] In an optional arrangement, a combustion chamber pressure value, or a structure-borne sound value, in particular an integral of a structure-borne sound sensor measured value, is used as the pressure gradient characteristic value.

[0058] The method is optionally conducted in predetermined time intervals or in an event-driven manner during operation of the internal combustion engine.

[0059] FIG. 2 shows a diagrammatic plot of a pressure gradient characteristic value D in arbitrary units against a pre-injection amount V, also in arbitrary units, wherein pre-injection amount V is in particular an amount of fuel introduced into combustion chamber 3 by way of pre-injection by way of injector 7. Pressure gradient characteristic value D follows a curve K depending on the pre-injection amount, which—at a certain pre-injection amount V.sub.min—exhibits a minimum and increases on the one hand to pre-injection amounts less than the specified pre-injection amount V.sub.min and on the other hand to pre-injection amounts greater than the specified pre-injection amount V.sub.min. Curve K is flat within the range of the minimum, which makes a classic minimum search more difficult.

[0060] The concept of the minimum search based on the skew of the distribution of the pressure gradient characteristic values and thereby the theoretical background of the method proposed herein will be explained in more detail below with reference to FIG. 2.

[0061] If—in order to inject a pre-injection amount V—injector 7 is activated multiple times with the same actuation, in particular the same energization duration, the result is a pre-injection amount distribution of the pre-injection amounts V actually introduced into combustion chamber 3. This pre-injection amount distribution can be assumed to be symmetrical; in particular, this pre-injection amount distribution can assume the form of a bell curve, especially a Gaussian bell curve.

[0062] FIG. 2 illustrates a first pre-injection distribution VV1 which results from an actuation of injector 7 in the range of the minimum of curve K. The maximum of the first pre-injection amount VV1 is shown in particular on the specified pre-injection amount V.sub.min. Now, based on the progression of curve K, the result is a corresponding first pressure gradient characteristic value distribution DV1. This shows a pronounced skew with a pronounced shift of its maximum towards small pressure gradient characteristic values, especially since most of the pre-injection amount values within the first pre-injection amount distribution VV1 lead to pressure gradient characteristic values in the minimum range. In addition, there is the pronounced asymmetry as well as the flat progression of curve K towards greater pre-injection amounts, which ultimately leads to the fact that virtually the entire right branch of the first pre-injection amount distribution VV1 is mapped onto comparatively small pressure gradient characteristic values.

[0063] If, in contrast we consider a second pre-injection amount distribution VV2, the maximum of which is a much greater pre-injection amount, this enters in particular into a range in which curve K rises almost linearly. Accordingly, based on the progression of curve K a corresponding second pressure gradient distribution DV2 results, which is at least essentially symmetrical, and whose shape essentially corresponds to the shape of the second pre-injection amount distribution VV2.

[0064] Based on FIG. 2 it becomes immediately clear that the skew of the distribution of the pressure gradient characteristic values is a suitable measure for determining how close a specified actuation of injector 7 brings the pre-injection amount V introduced by the latter into the minimum range of the pressure gradient characteristic value.

[0065] FIG. 3 is a schematic illustration of one embodiment of a process for operating internal combustion engine 1 in the form of a flow chart. The process starts in first step S1. In second step S2 a duration of energization BD for injector 7 is initialized with a pre-specified starting value BDstart.

[0066] In third step S3, injector 7 is actuated with duration of energization BD in order to introduce a pre-injection amount of fuel into combustion chamber 3. In fourth step S4, a pressure gradient characteristic value DKW is specified for the operating cycle of combustion chamber 3 in which injector 7 was previously actuated in third step S3, wherein pressure gradient characteristic value DKW is characteristic for a combustion chamber gradient in combustion chamber 3.

[0067] In fifth step S5 it is queried whether a pre-specified number n of repeats of steps S3, S4 were conducted. As long as this is not yet the case, the process is continued in third step S3; in other words, steps S3 to S5 are repeated until the pre-specified number n of repeats is reached. The pre-specified number n may for example be 100. Thus, in this respect n pressure gradient characteristic values and in this respect also—either explicitly or at least implied—a distribution of the pressure gradient characteristic values are obtained.

[0068] On reaching the pre-specified number n of repeats, the process is continued in step S6, where a skew S of the distribution of pressure gradient characteristic values DKW is determined. Determination of skew S may occur either after having established the distribution from the distribution itself, or without explicit determination of the distribution. Skew S is optionally calculated as an empirical skew v according to equation (1) provided above.

[0069] In seventh step S7, skew S is compared with a pre-specified skew threshold value SSW. If it is observed that skew S is not greater than the pre-specified skew threshold value SSW, a sign for an otherwise optional constant, in particular pre-determined change value DeltaBD for changing the duration of energization BD is determined in step S8. In step S9, the duration of energization BD is newly defined as a sum of the previous value of the duration of energization BD and change value DeltaBD for the duration of energization, inclusive of the sign; in other words, change value DeltaBD itself is signed. The process is then continued in third step S3 with the new value for the energization duration BD determined in ninth step S9; in other words, injector 7 is actuated with the new value for energization duration BD.

[0070] The sign for change value DeltaBD is selected in step S8, in particular depending on whether the last change in actuation has resulted in a greater change of the pressure gradient characteristic value—in particular of the average pressure gradient characteristic value—than the penultimate change in actuation. In particular, the sign is changed compared to the sign selected in the last change step if the last change made to the energization duration resulted in a greater change in the pressure gradient characteristic value than the penultimate change made to the energization duration. In contrast, the sign is maintained compared to the last change if the last change in the energization duration did not lead to a greater change of the pressure gradient characteristic value than the penultimate change of the energization duration. This is based on the idea that curve K according to FIG. 2 displays a pronounced curvature originating from its minimum, so that the gradient of curve K changes in both directions, originating from the minimum and becomes larger in both directions in particular with increasing distance from the minimum. Thus, on the basis of constant change values DeltaBD, there is a growing change in the pressure gradient characteristic value with increasing distance from the minimum, so that this behavior indicates that the sign of change value DeltaBD should be changed to move along curve K in the direction of the minimum.

[0071] If no previous cycles of the process are yet available for evaluation in step S8, the sign for change value DeltaBD is optionally randomly selected or initialized in a predetermined manner.

[0072] The amount of change value DeltaBD and/or the amount of start value BDStart is/are optionally parameterizable. Likewise, the skew threshold SSW is optionally parameterizable.

[0073] If it is observed in step S7 that skew S is greater than the pre-specified skew threshold value SSW, the process ends in a tenth step S10.

[0074] The entire process is repeated optionally during operation of internal combustion engine 1 at predetermined time intervals or in an event-driven manner.

[0075] While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.