METHOD FOR DETERMINING THE CURRENT TRIMMING OF THE INTAKE TRACT OF AN INTERNAL COMBUSTION ENGINE DURING OPERATION

Abstract

In a method, dynamic pressure oscillations in the intake tract or outlet tract of a respective internal combustion engine are measured during normal operation, and from these measured oscillations, a corresponding pressure oscillation signal is generated. A crankshaft phase angle signal is determined at the same time. From the pressure oscillation signal, an actual value of at least one characteristic of at least one selected signal frequency of the measured pressure oscillations in relation to the crankshaft phase angle signal is determined, and the current trimming of the intake tract is determined on the basis of the determined actual value, taking into consideration reference values of the corresponding characteristic of the respectively identical signal frequency for different trimmings of the intake tract.

Claims

1. A method for determining the current trimming of the intake tract of an internal combustion engine during operation, comprising: measuring dynamic pressure oscillations, assignable to one cylinder of the internal combustion engine, in an intake tract or in an outlet tract of the internal combustion engine at a defined operating point during normal operation, generating a corresponding pressure oscillation signal from the measured pressure oscillations, and at the same time determining a crankshaft phase angle signal of the internal combustion engine, from the pressure oscillation signal and using discrete Fourier transformation, determining at least one actual value of at least one characteristic of at least one selected signal frequency of the measured pressure oscillations in relation to the crankshaft phase angle signal, and determining current trimming of the intake tract of the internal combustion engine on the basis of the at least one determined actual value of the respective characteristic, based upon reference values of the respectively corresponding characteristic of the respectively identical signal frequency for different trimmings of the intake tract.

2. The method as claimed in claim 1, wherein the reference values of the respective characteristic as a function of the trimming of the intake tract are made available in at least one respective reference value characteristic map, or at least one respective algebraic model function for the mathematical determination of the respective reference value of the respectively corresponding characteristic is made available, the model representing a relationship between the characteristic and the trimming of the intake tract.

3. The method as claimed in claim 2, wherein the determination of the actual value of the respective characteristic of the selected signal frequency and the determination of the current trimming of the intake tract of the internal combustion engine are performed by an electronic processing unit assigned to the internal combustion engine, wherein the respective reference value characteristic map or the respective algebraic model function is stored in at least one memory assigned to the electronic processing unit.

4. The method as claimed in claim 2, wherein the reference values of the respective characteristic for at least one selected signal frequency are determined in advance on a reference internal combustion engine as a function of different trimmings of the intake tract.

5. The method as claimed in claim 4, wherein a model function representing the relationship between the characteristic of the selected signal frequency and the trimming of the intake tract is in each case derived from the reference values of the respective characteristic of the selected signal frequency and the assigned trimmings of the intake tract.

6. The method as claimed in claim 5, wherein the determination in advance of the reference values of the respective characteristic of the respectively selected signal frequency is based on the measurement of a reference internal combustion engine at at least one defined operating point while specifying certain reference trimmings of the intake tract, wherein, to determine the reference values of the respective characteristic of the respectively selected signal frequency, the dynamic pressure oscillations, assignable to one cylinder of the reference internal combustion engine, in the intake tract or in the outlet tract are measured during operation, and a corresponding pressure oscillation signal is generated, wherein, at the same time, a crankshaft phase angle signal is determined, the reference values of the respective characteristic of the respectively selected signal frequency of the measured pressure oscillations in relation to the crankshaft phase angle signal is determined from the pressure oscillation signal by means of discrete Fourier transformation, and the determined reference values are stored as a function of the associated trimming of the intake tract in reference value characteristic maps.

7. The method as claimed in claim 1, wherein a phase position or an amplitude, or a phase position and an amplitude of at least one selected signal frequency is used as the at least one characteristic of the measured pressure oscillations.

8. The method as claimed in claim 1, wherein the trimming of the intake tract is adjusted or set by at least one variable intake manifold, by at least one adjustable swirl flap, by at least one resonator component, or by a combination of a plurality of the at least one variable intake manifold, the at least one adjustable swirl flap, and the at least one resonator component.

9. The method as claimed in claim 1, wherein the selected signal frequencies are the intake frequency or a multiple of the intake frequency.

10. The method as claimed in claim 1, wherein, the current trimming of the intake tract of the internal combustion engine is determined based on at least one of a temperature of the intake medium in the inlet tract, a temperature of a coolant used for cooling the internal combustion engine, and an engine speed of the internal combustion engine.

11. The method as claimed in claim 1, wherein the dynamic pressure oscillations in the intake tract are measured by a standard pressure sensor.

12. The method as claimed in claim 1, wherein a crankshaft position feedback signal is determined by a toothed gear and a Hall sensor.

13. The method as claimed in claim 3, wherein the electronic processing unit is part of an engine control unit for controlling the internal combustion engine, and an adaptation of further control variables or control routines for control of the internal combustion engine is performed by the engine control unit as a function of the determined current trimming of the intake tract.

14. An electronic processing unit for at least partly controlling an internal combustion engine, the electronic processing unit configured to perform a method comprising: measuring dynamic pressure oscillations, assignable to one cylinder of the internal combustion engine, in an intake tract or in an outlet tract of the internal combustion engine at a defined operating point during normal operation, generating a corresponding pressure oscillation signal from the measured pressure oscillations, and at the same time determining a crankshaft phase angle signal of the internal combustion engine, from the pressure oscillation signal and using discrete Fourier transformation, determining at least one actual value of at least one characteristic of at least one selected signal frequency of the measured pressure oscillations in relation to the crankshaft phase angle signal, and determining current trimming of the intake tract of the internal combustion engine on the basis of the at least one determined actual value, based upon reference values of a corresponding characteristic of an identical signal frequency for different trimmings of the intake tract.

15. The electronic processing unit of claim 14, wherein the reference values of the corresponding characteristic as a function of the trimming of the intake tract are made available in at least one reference value characteristic map, or at least one algebraic model function for a mathematical determination of the reference value of the corresponding characteristic is made available, the model representing a relationship between the characteristic and the trimming of the intake tract.

16. The electronic processing unit of claim 15, wherein the reference value characteristic map or the respective algebraic model function is stored in at least one memory assigned to the electronic processing unit.

17. The electronic processing unit of claim 15, wherein the reference values are determined in advance on a reference internal combustion engine as a function of different trimmings of the intake tract.

18. The electronic processing unit of claim 17, wherein a model function representing the relationship between the characteristic of the selected signal frequency and the trimming of the intake tract is in each case derived from the reference values and the assigned trimmings of the intake tract.

19. The electronic processing unit of claim 18, wherein the determination in advance of the reference values of the corresponding characteristic is based on a measurement of the reference internal combustion engine at at least one defined operating point while specifying certain reference trimmings of the intake tract, wherein, to determine the reference values of the corresponding characteristic, the dynamic pressure oscillations, assignable to one cylinder of the reference internal combustion engine, in the intake tract or in the outlet tract thereof are measured during operation, and a corresponding pressure oscillation signal is generated, wherein, at the same time, a crankshaft phase angle signal is determined, the reference values of the corresponding characteristic in relation to the crankshaft phase angle signal is determined from the pressure oscillation signal by discrete Fourier transformation, and the determined reference values are stored as a function of the associated trimming of the intake tract in reference value characteristic maps.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] To explain the functioning of an internal combustion engine underlying the invention and the relationships between the trimming of the intake tract and the characteristics, phase position and amplitude of the pressure oscillation signal measured in the intake tract or outlet tract for certain selected signal frequencies, and to describe particularly advantageous exemplary embodiments, details or developments of the subject matter of the invention, as per the dependent claims, reference is made below to the figures, although there is no intention to restrict the subject matter of the invention to these examples. In the drawings:

[0036] FIG. 1 is a simplified illustration of a reciprocating-piston internal combustion engine, referred to here in shortened form as internal combustion engine, with pertinent functional components;

[0037] FIG. 2a and 2b are two further-simplified illustrations of the internal combustion engine according to FIG. 1 intended to illustrate the trimming of the intake tract by means of the intake manifold length, wherein the intake manifold length is shown in a shortened setting in FIG. 2a, and the intake manifold length is shown in the maximum setting in FIG. 2b;

[0038] FIG. 3 shows a diagram intended to illustrate an example of the dependency between the phase position of the pressure oscillation signal and the intake manifold length at various signal frequencies;

[0039] FIG. 4 shows a diagram intended to illustrate an example of the dependency between the amplitude of the pressure oscillation signal and the intake manifold length at various signal frequencies;

[0040] FIG. 5 shows a diagram intended to illustrate reference phase positions of a signal frequency as a function of the trimming of the intake tract and the determination of a specific value of the trimming of the intake tract, based on a currently determined value of the phase position of a pressure oscillation signal; and

[0041] FIG. 6 shows a block diagram for schematic illustration of one embodiment of the method according to the invention.

DETAILED DESCRIPTION

[0042] Items of identical function and designation are denoted by the same reference signs throughout the figures.

[0043] FIGS. 1 and 2 have already been thoroughly explored in the above description of the principle of operation of an internal combustion engine and for the explanation of the trimming of the intake tract.

[0044] In the implementation of the method according to the invention, it is assumed, as already mentioned above, that the relationship or the dependency of the stated variables between or on one another is uniquely known. The relationships are explained below for the pressure oscillation signal measured in the intake tract, but are similarly applicable to the pressure oscillation signal in the outlet tract too.

[0045] FIG. 3 shows this relationship by way of example with reference to the characteristic comprising the phrase position of the pressure oscillation signal in the intake tract as a function of the trimming of the intake tract, in this case, by way of example, with reference to a variable intake manifold length in %, at various signal frequencies. It has been found here that it is quite possible for different profiles of the values of the phase position to be obtained at different signal frequencies as the intake manifold length increases. Interpolation between the individual measurement points results in each case in a continuous curve, wherein curve 101 has a rising profile with an increasing intake manifold length at the intake frequency, curve 102 has an initially falling and then almost constant profile at twice the intake frequency, and curve 103 has a falling profile with an increasing intake manifold length at three times the intake frequency. In this case, said curves 101, 102 and 103 intersect approximately in the region of 45% of the intake manifold length.

[0046] FIG. 4 shows the relationship, likewise by way of example, with reference to the characteristic comprising the amplitude of the pressure oscillation signal in the intake tract as a function of the variable intake manifold length in % as a parameter of the trimming of the intake tract, once again at various signal frequencies. Here too, interpolation between the individual measurement points results in each case in a continuous curve, wherein curve 201 has a rising profile with an increasing intake manifold length at the intake frequency, curve 202 has a profile which rises with a shallower gradient than curve 201 at twice the intake frequency, and curve 203 has an almost constant profile with an increasing intake manifold length at three times the intake frequency.

[0047] In the case of both characteristics, namely the phase position and the amplitude, it is found in this example that the accuracy and explanatory power of the method according to the invention may depend on the selection of an advantageous signal frequency for the determination of the trimming of the intake tract.

[0048] In one embodiment of the method according to the invention, the reference values of the respective characteristic as a function of the trimming of the intake tract are made available in at least one respective reference value characteristic map. A reference value characteristic map of this kind contains, for example, reference values for the phase position as a function of values for the trimming of the intake tract for different signal frequencies, as illustrated in FIG. 3, or reference values for the amplitude as a function of values for the trimming of the intake tract for different signal frequencies, as illustrated in FIG. 4. Here, a plurality of such characteristic maps can in each case be made available for different operating points of the internal combustion engine. Thus, a corresponding, more comprehensive characteristic map may, for example, include corresponding reference value curves for different operating points of the internal combustion engine and different signal frequencies.

[0049] The determination of the current trimming of the intake tract of the internal combustion engine can then be performed in a simple manner, as illustrated in FIG. 5 by the example of the phase position, in such a way that, proceeding from the determined actual value of a characteristic of the pressure oscillation signal, in this case a value of about 52.5 of the phase position, for a selected signal frequency, in this case the first harmonic 101, i.e. intake frequency, the associated point 105 on the reference curve of the first harmonic 101 is determined during normal operation of the internal combustion engine, and proceeding from this in turn, the associated trimming of the intake tract, in this case about 50% of the maximum intake manifold length, is determined, as visually illustrated on the basis of the dashed line in FIG. 5. Thus, the current trimming of the intake tract can be determined during operation in a particularly simple manner and with little computational effort.

[0050] As an option, at least one respective algebraic model function, characterizing the corresponding reference curve, for the mathematical determination of the respective reference value of the respectively corresponding characteristic is made available instead or as a supplementary measure, said model representing the relationship between the characteristic and the trimming of the intake tract. The determined actual value of the respective characteristic is specified, and the trimming of the intake tract is then calculated in real time. The advantage of this alternative lies in the fact that, overall, less memory capacity has to be made available.

[0051] The execution of the method according to the invention, i.e. the determination of the actual value of the respective characteristic of the selected signal frequency and the determination of the current trimming of the intake tract of the internal combustion engine, is advantageously performed with the aid of an electronic processing unit assigned to the internal combustion engine, which is preferably part of an engine control unit. Here, the respective reference value characteristic map and/or the respective algebraic model function are/is stored in at least one memory area assigned to the electronic processing unit, said area preferably likewise being part of the engine control unit. This is illustrated in simplified form with the aid of the block diagram in FIG. 6. An engine control unit 50 containing the electronic processing unit 53 is illustrated symbolically here by the frame in dashed lines, which contains the individual steps/blocks of one embodiment of the method according to the invention and the electronic memory area 54.

[0052] One particularly advantageous possibility for carrying out the method according to the invention involves the use of an electronic processing unit 53 assigned to the internal combustion engine, which is, for example, part of the central engine control unit 50, also referred to as a central processing unit or CPU, which is used to control the internal combustion engine 1. In this case, the reference value characteristic maps or the algebraic model functions can be stored in at least one electronic memory area 54 of the CPU 50.

[0053] In this way, the method according to the invention can be carried out automatically, very quickly and repeatedly during the operation of the internal combustion engine, and an adaptation or correction of further control variables or control routines for controlling the internal combustion engine as a function of the determined trimming of the intake tract can be performed directly by the engine control unit.

[0054] This firstly has the advantage that no separate electronic processing unit is required, and there are thus also no additional interfaces, which are possibly susceptible to failure, between multiple processing units. Secondly, the method according to the invention can thus be made an integral constituent part of the control routines of the internal combustion engine, whereby a fast adaptation of the control variables or control routines for the internal combustion engine to the current trimming of the intake tract is possible.

[0055] As already indicated above, it is assumed that the reference values of the respective characteristic for different trimmings of the intake tract are available for the implementation of the method.

[0056] For this purpose, in an enhancement of the method according to the invention, the reference values of the respective characteristic for at least one selected signal frequency are determined in advance on a reference internal combustion engine as a function of different trimmings of the intake tract. This is illustrated symbolically in the block diagram in FIG. 6 by the blocks denoted by B10 and B11, wherein block B10 indicates the measurement of a reference internal combustion engine (Vmssg_Refmot) and block B11 symbolizes the collation of the measured reference values of the respective characteristic at selected signal frequencies to form reference value characteristic maps (RWK_DSC_SF_1 . . . X). Here, the reference internal combustion engine is an internal combustion engine of identical design to the corresponding internal combustion engine series, and in which, in particular, it is ensured that no behavior-influencing structural tolerance deviations are present. This is intended to ensure that the relationship between the respective characteristic of the pressure oscillation signal and the trimming of the intake tract can be determined as accurately as possible and without the influence of further disturbance factors.

[0057] The determination of corresponding reference values is possible by means of the reference internal combustion engine at different operating points and with presetting or variation of further operating parameters such as the temperature of the intake medium, the coolant temperature or the engine speed. The reference value characteristic maps thus generated, see FIGS. 3 and 4 for example, can then advantageously be made available in all internal combustion engines of identical design in the series, in particular stored in an electronic memory area 54 of an electronic engine control unit 50 assignable to the internal combustion engine.

[0058] As a continuation of the abovementioned prior determination of the reference values of the respective characteristic of the selected signal frequencies, it is possible, from the determined reference values of the selected signal frequency and the associated trimmings of the intake tract, to derive a respective algebraic model function which represents at least the relationship between the respective characteristic of the selected signal frequency and the trimming of the intake tract. This is symbolized in the block diagram in FIG. 6 by the block denoted by B12. Here, it is optionally also possible for the abovementioned further parameters to also be incorporated. An algebraic model function (Rf(DSC_SF_1 . . . X) is thus generated with which, with presetting of the phase position and possible incorporation of the abovementioned variables, the value of the respective trimming of the intake tract can be calculated in real time.

[0059] The model function can then advantageously be made available in all internal combustion engines of identical design in the series, in particular stored in an electronic memory area 54 of an electronic engine control unit 50 assignable to the internal combustion engine. The advantages lie in the fact that the model function requires less memory space than comprehensive reference value characteristic maps.

[0060] In an implementation example, the determination in advance of the reference values of the respective characteristic of the selected signal frequency can be performed by the measurement of a reference internal combustion engine (Vmssg_Refmot) at at least one defined operating point while specifying certain reference trimmings of the intake tract. This is symbolized in the block diagram in FIG. 7 by the block denoted by B10. Here, for the determination of the reference values of the respective characteristic of the selected signal frequency, the dynamic pressure oscillations, assignable to one cylinder of the reference internal combustion engine, in the intake tract or in the outlet tract are measured during operation, and a corresponding pressure oscillation signal is generated.

[0061] At the same time as, i.e. in association in terms of time with, the measurement of the dynamic pressure oscillations, a crankshaft phase angle signal is determined. Subsequently, reference values of the respective characteristic of the selected signal frequency of the measured pressure oscillations in relation to the crankshaft phase angle signal are determined from the pressure oscillation signal by means of discrete Fourier transformation.

[0062] The determined reference values are then stored as a function of the associated trimming of the intake tract in reference value characteristic maps (RWK_DSC_SF_1 . . . X). This allows reliable determination of the dependence between the respective characteristic of the pressure oscillation signal of the selected signal frequency and the trimming of the intake tract.

[0063] In all the abovementioned embodiments and developments of the method according to the invention, a phase position or an amplitude or, alternatively, a phase position and an amplitude of at least one selected signal frequency can be used as the at least one characteristic of the measured pressure oscillations. The phase position and the amplitude are the essential basic characteristics which can be determined by means of discrete Fourier transformation in relation to individual selected signal frequencies. In the simplest case, precisely one actual value, e.g. of the phase position at a selected signal frequency, e.g. of the 2nd harmonic, is determined at a particular operating point of the internal combustion engine, and the associated value for the trimming of the intake tract is determined by assigning this value to the corresponding reference value of the phase position in the stored reference value characteristic map, at the same signal frequency.

[0064] However, it is also possible for a plurality of actual values, e.g. for the phase position and the amplitude and at different signal frequencies, to be determined and combined in order to determine the trimming of the intake tract, e.g. by averaging. In this way, it is advantageously possible to increase the accuracy of the determined value for the trimming of the intake tract.

[0065] According to another embodiment of the method according to the invention it is envisaged that the trimming of the intake tract can be set by means of at least one variable intake manifold or by means of at least one adjustable swirl flap or by means of at least one resonator component. However, it is also possible to provide a combination of a plurality of the abovementioned components, by means of which the trimming of the intake tract can be adjusted or set. For this purpose, an actuating unit which is driven by means of actuator and by means of which the length of one or more intake manifolds or the position of one or more swirl flaps can be varied in accordance with the respective operating point of the internal combustion engine can be provided, for example. This has the advantage that the trimming of the intake tract can be set and, where applicable regulated, in an optimized manner for the respective operating point in the course of operation.

[0066] It has proven to be advantageous for the intake frequency or a multiple of the intake frequency, i.e. the 1st harmonic, the 2nd harmonic, the 3rd harmonic etc., to be chosen as selected signal frequencies. At these signal frequencies, the dependence of the respective characteristic of the pressure oscillation signal on the trimming of the intake tract is particularly clearly evident.

[0067] In order, in a refinement of the method, to further increase the accuracy of the determination of the value of the trimming of the intake tract in an advantageous manner, it is possible for additional operating parameters of the internal combustion engine to be taken into consideration in the determination of the trimming of the intake tract. For this purpose, at least one of the further operating parameters [0068] temperature of the intake medium in the inlet tract, [0069] temperature of a coolant used for cooling the internal combustion engine and [0070] engine speed of the internal combustion engine,
may be taken into consideration in the determination of the trimming of the intake tract.

[0071] The temperature of the intake medium, that is to say substantially of the intake air, directly influences the speed of sound in the medium and thus the pressure propagation in the intake tract. This temperature can be measured in the inlet tract and is therefore known. The temperature of the coolant can also influence the speed of sound in the intake medium owing to heat transfer in the intake tract and in the cylinder. This temperature is generally also monitored and, for this purpose, measured, and is thus available in any case and can be taken into consideration in the determination of the current trimming of the intake tract.

[0072] The engine speed is one of the variables that characterizes the operating point of the internal combustion engine, and influences the time available for the pressure propagation in the intake tract. The engine speed is also constantly monitored and is thus available for the determination of the trimming of the intake tract.

[0073] The abovementioned additional parameters are thus available in any case, or can be determined in a straightforward manner. The respective influence of the stated parameters on the respective characteristic of the selected signal frequency of the pressure oscillation signal is in this case assumed to be known, and, as already noted above, has been determined for example during the measurement of a reference internal combustion engine and jointly stored in the reference value characteristic maps. Incorporation by means of corresponding correction factors or correction functions in the calculation of the current values of the trimming of the intake tract by means of an algebraic model function also constitutes a possibility for taking these additional, further operating parameters into consideration in the implementation of the method according to the invention.

[0074] For the implementation of the method according to the invention, it is furthermore advantageously possible for the dynamic pressure oscillations in the intake tract to be measured by means of a standard pressure sensor, e.g. directly in the intake manifold. This has the advantage that no additional pressure sensor is required, which represents a cost advantage.

[0075] In a further embodiment example, for the implementation of the method according to the invention, the crankshaft position feedback signal may be determined by means of a toothed gear and a Hall sensor, wherein this is a customary sensor arrangement, which is possibly present in the internal combustion engine in any case, for detecting the crankshaft revolutions, i.e. the speed of the internal combustion engine. The toothed gear is in this case arranged for example on the outer circumference of a flywheel or of the crankshaft timing adapter 10 (see also FIG. 1). This has the advantage that no additional sensor arrangement is required, which represents a cost advantage.

[0076] FIG. 6 illustrates an embodiment of the method according to the invention for determining the current trimming of the intake tract of an internal combustion engine during operation, once again in the form of a simplified block diagram showing the significant steps.

[0077] The border shown by dashed lines around the corresponding blocks B1 to B6 and 54 in the block diagram symbolically represents the boundary between an electronic, programmable engine control unit 50, e.g. of an engine control unit referred to as a CPU, of the respective internal combustion engine, on which the method is executed. This electronic engine control unit 50 contains, inter alia, the electronic processing unit 53 and the electronic memory area 54 for executing the method according to the invention.

[0078] At the start, dynamic pressure oscillations, assignable to the respective cylinder, of the intake air in the intake tract and/or of the exhaust gas in the outlet tract of the respective internal combustion engine are measured during operation and a corresponding pressure oscillation signal (DS_S) is generated from these, and a crankshaft phase angle signal (KwPw_S) is determined at the same time, i.e. in time dependence, as illustrated by the blocks arranged in parallel, which are denoted by B1 and B2.

[0079] Then, using discrete Fourier transformation symbolized by the block denoted by B3, an actual value (IW_DSC_SF_1 . . . X) of at least one characteristic of at least one selected signal frequency of the measured pressure oscillations in relation to the crankshaft phase angle signal (KwPw_S) is determined from the pressure oscillation signal (DS_S), this being illustrated by the block denoted by B4.

[0080] On the basis of the at least one determined actual value (IW_DSC_SF_1 . . . X) of the respective characteristic, intake tract trimming determination (ET_Trm_EM) is then carried out in block B5. This is accomplished taking into consideration reference values (RW_DSC_SF_1 . . . X) of the respectively corresponding characteristic of the respectively identical signal frequency for different trimmings of the intake tract, which are made available in the memory area denoted by 54 or are determined in real time with the aid of the algebraic model functions stored in the memory area 54. The current value, determined in this way, of the trimming of the intake tract (Trm_ET_akt) of the internal combustion engine is then made available in block B6.

[0081] FIG. 6 furthermore shows, in blocks B10, B11 and B12, the steps which precede the method described above. In block B10, a reference internal combustion engine (Vmssg_Refmot) is measured in order to determine reference values of the respective characteristic of the respectively selected signal frequency of the measured pressure oscillations in relation to the crankshaft phase angle signal from the pressure oscillation signal by means of discrete Fourier transformation. In block B11, the determined reference values are then collated in reference value characteristic maps (RWK_DSC_SF_1 . . . X) as a function of the associated values of the trimming of the intake tract and are stored in the electronic memory area 54 of the engine control unit 50 denoted by CPU.

[0082] The block denoted by B12 contains the derivation of algebraic model functions (Rf(DSC_SF_1 . . . X)), which, as reference value functions, reproduce, for example, the profile of the respective reference value curves of the respective characteristic of the pressure oscillation signal for a respective signal frequency as a function of the trimming of the intake tract, on the basis of the previously determined reference value characteristic maps (RWK_DSC_SF_1 . . . X). It is then likewise possible, as an alternative or in addition, for these algebraic model functions (Rf(DSC_SF_1 . . . X)) to be stored in the electronic memory area 54, denoted by 54, of the engine control unit 50 denoted by CPU, where they are available for implementing the above-explained method according to the invention.

[0083] Summarized briefly once again, the essence of the method according to the invention for determining the current trimming of the intake tract of an internal combustion engine is a method in which dynamic pressure oscillations in the intake tract or outlet tract of the respective internal combustion engine are measured during normal operation, and from these, a corresponding pressure oscillation signal is generated. At the same time, a crankshaft phase angle signal is determined and set in relation to the pressure oscillation signal. From the pressure oscillation signal, an actual value of at least one characteristic of at least one selected signal frequency of the measured pressure oscillations in relation to the crankshaft phase angle signal is determined, and the current trimming of the intake tract or a value for the current trimming of the intake tract is determined on the basis of the determined actual value taking into consideration reference values of the corresponding characteristic of the respectively identical signal frequency for different trimmings of the intake tract.