Method for determining at least one injection parameter of an internal combustion engine, and internal combustion engine

Abstract

A method for determining at least one injection parameter of an internal combustion engine, including the following steps: detecting a pressure profile in a time-resolved manner in an injection system of an internal combustion engine at least during an injection; providing a reference pressure profile for at least one operating point of the injection system; comparing the detected pressure profile with the reference pressure profile, and ascertaining at least one injection parameter as a function of the comparison.

Claims

1. A method for determining at least one injection parameter of an internal combustion engine, comprising the steps of: detecting a pressure profile in a time-resolved manner in an injection system of the internal combustion engine at least during an injection; providing a reference pressure profile for at least one operating point of the injection system; comparing the detected pressure profile with the reference pressure profile; and ascertaining at least one injection parameter as a function of the comparison, wherein in each case one reference pressure profile is provided for a plurality of operating points, wherein the detected pressure profile is compared with more than one reference pressure profile, and wherein a comparison value is optimized, and, wherein a correlation coefficient of the detected pressure profile with the reference pressure profile is calculated as a comparison value, wherein the correlation coefficient is maximized by comparing the detected pressure profile with more than one reference pressure profile iteratively in a loop, wherein an injection quantity is defined as the injection quantity which is assigned to the reference pressure profile with a maximum correlation coefficient.

2. The method as claimed in claim 1, wherein the reference pressure profile is provided as a function of a setpoint injection quantity.

3. The method as claimed in claim 2, wherein the reference pressure profile is provided as a function of a pressure in a common high pressure accumulator of the injection system.

4. The method as claimed in claim 3, wherein the reference pressure profile is provided as a function of a start-of-injection pressure.

5. The method as claimed in claim 1, wherein a start of injection and/or an injection quantity is/are ascertained as an injection parameter/injection parameters as a function of the comparison.

6. The method as claimed in claim 1, wherein the pressure profile is detected in an individual accumulator of an injector of the internal combustion engine, in a common high pressure accumulator of the injection system or in a fuel line leading to the injector.

7. The method as claimed in claim 6, wherein the pressure profile is detected downstream of a restrictor that separates the injector from the common high pressure accumulator.

8. The method as claimed in claim 1, wherein the comparison is carried out by calculating a cross-correlation function of the detected pressure profile with the reference pressure profile, wherein a start of injection is ascertained from shifting of the profiles relative to one another.

9. The method as claimed in claim 1, wherein the reference pressure profile is provided as a compressed data set, wherein the compressed data set is expanded before the comparing step.

10. The method as claimed in claim 9, wherein the compressed data set is calculated by a main component analysis based on the reference pressure profile, wherein the compressed data set is expanded by an inverse main component analysis.

11. An internal combustion engine, comprising: an injection system that includes at least one injector; a pressure sensor for detecting a pressure profile in a time-resolved manner in the injection system during an injection; and a control unit configured to carry out a method according to claim 1.

12. The internal combustion engine as claimed in claim 11, wherein the control unit has at least one memory area, wherein at least one reference pressure profile for at least one operating point of the injection system is stored in the memory area, wherein the control unit is operatively connected to the pressure sensor for detecting the pressure profile, wherein the control unit includes a comparison unit configured to carry out a comparison of the detected pressure profile with the at least one reference pressure profile, wherein the control unit includes a unit for ascertaining at least one injection parameter as a function of the comparison.

13. The internal combustion engine as claimed in claim 11, wherein the injection system has a common high pressure accumulator and a plurality of injectors, wherein a fuel line leads from the common high pressure accumulator to each injector, wherein each fuel line has a restrictor between the high pressure accumulator and the injector assigned to the fuel line.

14. The internal combustion engine as claimed in claim 13, wherein the pressure sensor is arranged to detect a pressure in an individual accumulator of the injector, in the fuel line or in the common high pressure accumulator.

15. The internal combustion engine as claimed in claim 14, wherein the pressure sensor is arranged to detect the pressure in the fuel line, downstream of the restrictor.

16. The internal combustion engine as claimed in claim 13, further comprising an additional pressure sensor for detecting a pressure in the common high pressure accumulator, wherein the control unit is configured to determine an operating point of the injection system as a function of the pressure in the common high pressure accumulator.

17. The internal combustion engine as claimed in claim 11, wherein the control unit is configured to predefine an operating point of the injection system and to select a first reference pressure profile as a function of the operating point.

18. The internal combustion engine as claimed in claim 17, wherein the control unit is configured to actuate the at least one injector as a function of the operating point.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a schematic illustration of an exemplary embodiment of an internal combustion engine;

(2) FIG. 2 shows a schematic illustration of the provision of a compressed data set for reference pressure profiles within the scope of an embodiment of the method, and

(3) FIG. 3 shows a schematic illustration of the determination of injection parameters within the scope of the embodiment of the method according to FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

(4) FIG. 1 shows a schematic illustration of an exemplary embodiment of an internal combustion engine 1. The latter has an injection system 3 which comprises at least one injector 5. The internal combustion engine 1 or the injection system 3 preferably comprises a multiplicity of injectors, and in particular the internal combustion engine 1 is preferably embodied as a reciprocating piston machine with a multiplicity of cylinders, wherein each cylinder is assigned an injector 5. In this respect, by way of example just one injector 5 is illustrated in FIG. 1 merely for the sake of simpler illustration.

(5) However, it is not ruled out that an exemplary embodiment of the internal combustion engine 1 has just one injector 5, in particular just one cylinder, with an injector 5 which is assigned thereto.

(6) A pressure sensor 7 for detecting a pressure profile in a time-resolved manner in the injection system 3 during an injection is provided, which pressure sensor 7 is arranged directly on the injector 5 in the exemplary embodiment illustrated in FIG. 1. The pressure sensor 7 is preferably embodied as a strain gauge.

(7) The internal combustion engine 1 also comprises a control unit 9 which is configured to carry out a method according to one of the previously described embodiments of the method, or of an embodiment of the method which is still to be described below.

(8) The control unit 9 comprises a memory area 11 in which reference pressure profiles are preferably stored for a multiplicity of operating points of the injection system 3, wherein each operating point of the injection system 3 is assigned a reference pressure profile. In particular, the reference pressure profiles are stored as a function of a setpoint injection quantity, preferably a setpoint injection volume, and a start-of-injection pressure, wherein all the reference pressure profiles have a corresponding start of injection. The reference pressure profiles are stored as a compressed data set in the memory area 11, which data set is acquired by means of a main component analysis on the basis of the reference pressure profiles which are preferably measured in test bench trials and/or calculated, in particular, in simulation calculations.

(9) The control unit 9 is operatively connected to the pressure sensor 7 for detecting the pressure profile, which is indicated here schematically by a first operative connection 13. The first operative connection 13 can be established by means of cable or else in a cableless fashion.

(10) The control unit 9 has a comparison means 15, wherein the comparison means 15 is configured to carry out a comparison of the detected pressure profile with at least one subset of the reference pressure profiles, wherein the reference pressure profiles which are used for the comparison lie, for example, in a predetermined area surrounding a starting operating point which is predefined by means of the control unit 9 at the start of the comparison for the selection of the first reference pressure profile to be compared.

(11) The control unit 9 also has means 17 for ascertaining at least one injection parameter as a function of the comparison. In the exemplary embodiment illustrated in FIG. 1, the control unit 9 is designed to ascertain an injection quantity, in particular an injection volume and a start of injection as a function of the comparison, wherein the injection quantity is determined by maximizing a correlation coefficient within the scope of the comparison of the detected pressure profile with a multiplicity of reference pressure profiles as that injection quantity which is assigned as a setpoint injection quantity to that reference pressure profile which has the maximum correlation coefficient with the detected pressure profile, wherein the start of injection is ascertained relative to the constant start of injection of the reference pressure profiles on the basis of the shift of the detected pressure profile relative to the reference pressure profile with the maximum correlation coefficient.

(12) The injection system 3 has a common high pressure accumulator 19 and is in this respect embodied as an injection system 3 with a common rail or as a common rail injection system. In this context, a fuel line 21 leads from the high pressure accumulator 19 to each injector 5 and is assigned to said injector 5, and a restrictor 23 is preferably arranged in said fuel line 21, downstream of the high pressure accumulator 19 and upstream of the injector 5 which is assigned to the fuel line 21. The restrictor 23 serves here to bring about hydraulic decoupling of the injector 5 from the rest of the injection system 3, in particular from the high pressure accumulator 19 and from further injectors 5 (not illustrated in FIG. 1). It is preferably provided here that a length of the fuel line 21 from the restrictor 23 as far as the injector 5 is the same for all injectors 5.

(13) In the exemplary embodiment illustrated in FIG. 1, the injector 5 has an individual accumulator 25. The fuel volume which is to be injected is extracted here directly from the individual accumulator 25 during the injection, which contributes to particularly good hydraulic decoupling of the injector 5 from the rest of the injection system 3, in particular from the high pressure accumulator 19 and from the other injectors 5. The pressure sensor 7 is arranged here on the injector 5 in such a way that it can detect the pressure in the individual accumulator 25.

(14) In one preferred exemplary embodiment of the internal combustion engine 1 which comprises a multiplicity of injectors 5, each injector 5 is assigned a pressure sensor 7 which is operatively connected to the control unit 9, with the result that the method can be carried out on an injector-specific and preferably also cylinder-specific basis. It is then possible to carry out, within the scope of the method, an injector-specific and preferably also cylinder-specific regulating process of the injection by means of the method. In particular, injection parameters can be adjusted to setpoint values, wherein the start of injection and/or the injection quantity are/is preferably adjusted. The setpoint injection parameters are predefined here by the control unit 9 as a function of an operating point of the internal combustion engine 1. The injection parameters which are actually present are ascertained by means of the method on the basis of the comparison of the detected pressure profile with the reference pressure profile.

(15) An additional pressure sensor 27 is provided which, in the illustrated exemplary embodiment, is arranged directly on the high pressure accumulator 19, wherein a pressure in the high pressure accumulator 19 can be detected by means of the pressure sensor 27. The control unit 9 is for this purpose operatively connected to the further pressure sensor 27, which is illustrated schematically here by means of a second operative connection 29, which can be established by means of cable or in a cableless fashion. The control unit 9 is preferably configured to determine an operating point of the injection system 3 as a function of the pressure in the high pressure accumulator 19.

(16) A high pressure pump 31 is provided which delivers fuel from a tank (not illustrated in FIG. 1) into the high pressure accumulator 19 and maintains the pressure in the high pressure accumulator 19 at a predetermined setpoint value, preferably by means of a regulating device which acts in return on the further pressure sensor 27. The pressure sensor 27 serves, alternatively or additionally with respect to the control or regulation of the high pressure in the high pressure accumulator 19, also to detect a start-of-injection pressure which corresponds to the pressure in the high pressure accumulator 19 at the start of an injection. Since no fuel flows from the high pressure accumulator 19 into the individual accumulator 25 or to the injector 5 via the fuel line 21 and the restrictor 23 just before the start of the injection, it can be assumed that the pressure which is detected as a start-of-injection pressure in the high pressure accumulator 19 also corresponds to the pressure in the fuel line 21, in the injector 5 and/or in the individual accumulator 25.

(17) The control unit 9 is preferably configured to predefine an operating point of the injection system 3 and to select a first reference pressure profile as a function of this operating point. Furthermore, the control unit 9 is preferably operatively connected to the injector 5 in order to actuate it, which is illustrated schematically in FIG. 1 by means of a third operative connection 33, which can be established by means of cable or in a cableless fashion.

(18) The control unit 9 predefines a setpoint operating point and actuates the injector 5 via the operative connection 33 in such a way that the injection is carried out with a start of injection which corresponds to the setpoint operating point, and an injection quantity which corresponds to said start of injection. During the injection, the pressure profile is detected in a time-resolved manner by the pressure sensor 7 and transferred to the control unit 9 via the operative connection 13. Said control unit 9 determines, as a function of the setpoint operating point, a first reference pressure profile with which the detected pressure profile is compared. A comparison value is then optimized or a correlation coefficient is maximized, in order to ascertain a reference pressure profile in which the comparison value becomes optimal or the correlation coefficient assumes its maximum value. The comparison is preferably carried out by cross-correlating the detected pressure profile with the respective reference pressure profile. If a reference pressure profile with an optimum comparison value, in particular with a maximum correlation coefficient, has been found, the actual start of injection is ascertained as a time shift of the detected pressure profile relative to the reference pressure profile. The injection quantity is defined as that injection quantity which is assigned to the reference pressure profile with the optimum comparison value, in particular with the optimum correlation coefficient, which has been found.

(19) An embodiment of the method will be described in more detail below:

(20) FIG. 2 shows the provision of a multiplicity of reference pressure profiles as a compressed data set in an embodiment of the method in a schematic illustration. In a step S1, reference pressure profiles are provided on the basis of measurements, in particular test bench measurements, and/or on the basis of calculations, in particular simulation calculations, which can be carried out analytically or numerically. Said simulation calculations are subjected, in a step S2, to a main component analysis from which, in a step S3, a compressed data set results which preferably comprises mean values and standard deviations of the original data, in particular averaged over operating points of the injection system 3, the main components resulting from the main component analysis and the inverses of the coefficients of the main components. The compressed data set is stored in the control unit 9, in particular in the memory area 11.

(21) FIG. 3 shows a schematic illustration of the determination of injection parameters of the internal combustion engine 1 within the scope of the embodiment of the method according to FIG. 2. In a step S4, the compressed data set is read out from the memory area 11, and in a step S5 it is subjected to an inverse main component analysis in order to obtain a reference pressure profile in a step S6. In this context, the control unit 9, which preferably carries out the inverse main component analysis in the step S5, predefines a setpoint operating point for which the correspondingly assigned reference pressure profile is ascertained in the steps S5, S6.

(22) In a step S7, a pressure profile which is detected by the pressure sensor 7 is provided.

(23) In a step S8, the control unit 9 calculates a cross-correlation function between the reference pressure profile provided in the step S6 and the detected pressure profile provided in the step S7, wherein at least one correlation coefficient results from the cross correlation in a step S9.

(24) On the basis of the first reference pressure profile, at least one correlation coefficient is then maximized iteratively in a loop 35 by means of a search algorithm which is illustrated as step S10, wherein within the loop in the step S5 a new reference pressure profile is always provided in the step S6 by means of an inverse main component analysis, which reference pressure profile is compared with the detected pressure profile in step S8, as a result of which at least one new correlation coefficient results in step S9. The loop 35 is run through until a maximum value of the correlation coefficient is found. Once this is the case, in a step S11 at least one injection parameter is ascertained on the basis of the comparison of the detected pressure profile with the reference pressure profile which yields the maximum correlation coefficient. In this context, a start of injection and an injection quantity are, in particular, preferably detected on the basis of the comparison in a way already described.

(25) It is, in particular, possible for deviations of the start of injection and/or of the injection quantity from the setpoint values predefined by the control unit 9 to be determined in the step S11. The injection is then preferably regulated on the basis of these detected deviations.

(26) Alternatively or additionally it is possible to use the at least one injection parameter ascertained in step S11 for an on-board diagnosis of the injection system 3, in order, in particular, to ascertain injector-specific faults of the injection system and to assign them to the faulty injectors.

(27) The search algorithm which is carried out in step S10 is preferably carried out as a local search in a surrounding area of the setpoint operating point which is defined by the control unit 9. In this context, in one preferred embodiment of the method what is referred to as the hill climbing algorithm or some other suitable local search method is used. In another preferred embodiment, a global maximum is performed over all the reference pressure profiles included in the compressed data set, wherein a static search method is preferably applied.

(28) Overall it becomes apparent that the method and the internal combustion engine can be used to determine at least one injection parameter of the internal combustion engine 1 very accurately and in a simple, cost-effective and fast way.