CN117090685A

CN117090685A - Method for detecting knocking in a combustion chamber of a cylinder

Info

Publication number: CN117090685A
Application number: CN202310555649.9A
Authority: CN
Inventors: N·迪尼兹内托; M·切尔迪克; 保罗·卡普斯
Original assignee: AVL List GmbH
Current assignee: AVL List GmbH
Priority date: 2022-05-18
Filing date: 2023-05-17
Publication date: 2023-11-21
Also published as: DE102023112971A1; AT525903A4; AT525903B1

Abstract

The invention relates to a method (400) for detecting knocking in a combustion chamber (13) of a cylinder (14) of an internal combustion engine having a crankshaft, comprising the following steps: a) Measuring a cylinder pressure curve (24, 24a,24 b) with respect to a crankshaft angle parameter, wherein the cylinder pressure curve (24, 24a,24 b) comprises a high-frequency superimposed signal (27) and a low-frequency base signal (25); b) Determining a derivative (28 a,28 b) of the superimposed signal; c) Adjusting the derivative (28 a,28 b) of the superimposed signal by reversing the negative value of the derivative (28 a,28 b) of the superimposed signal; d) Determining a first value (310) of a crank angle parameter at which the adjusted superimposed signal derivative (312) reaches a maximum value (314); e) Determining a second value (316) of the crankshaft angle parameter, at which the base signal (25) reaches a maximum value; f) Determining an integral curve (318) of the adjusted superimposed signal derivative (312); g) Determining a combustion intensity value from the integral curve (318); and h) determining the relative combustion angle value as a difference between the first value (310) of the crank angle parameter and the second value of the crank angle parameter.

Description

Method for detecting knocking in a combustion chamber of a cylinder

Technical Field

The invention relates to a method for detecting knocking in a cylinder combustion chamber of an internal combustion engine having a crankshaft, and to a measuring device and an internal combustion engine based on the method.

Background

It is known in the art of internal combustion engines that uncontrolled combustion of fuel in the combustion chamber of a cylinder can cause knocking characterized by combustion noise. Runaway combustion associated with knocking is detrimental to the combustion process and the service life of the internal combustion engine components and can be avoided by adjustment of the engine controller. The first step for adjusting the engine control unit is to detect the knock signal.

The knock recognition method is disclosed by the prior art, for example EP0722562 A1. In this method, a knock sensor is used for knock detection, which senses the engine noise and adjusts the threshold of the engine noise in order to also detect knocking in the event of loud engine sounds.

DE102013109742 A1 discloses a knock detection method for an internal combustion engine of a motor vehicle. In this method, combustion noise of the internal combustion engine is detected over a plurality of combustion cycles and a reference value is ascertained on the basis of the combustion noise over the plurality of combustion cycles. The threshold value for the current combustion noise is then ascertained and adjusted based on the reference value and based thereon a knock recognition is performed.

This known method allows knock recognition under a simple internal combustion engine. But the new and improved internal combustion engine has special features related to the knock characteristics. However, in modern internal combustion engines under development, in addition to the desired combustion process, not only the knock signal but also the rapid combustion process occur. In the case of a rapid combustion process, the in-cylinder pressure is rich in harmonics, which cause pressure fluctuations during propagation of the flame front. The vibration impairs the signal-to-noise ratio because the background noise level increases significantly. This characteristic interferes with known knock recognition methods. In addition, rapid combustion processes also occur many times in new internal combustion engines. The rapid combustion process also involves vibrations, but is not as disadvantageous for internal combustion engines and combustion processes as knocking. In modern internal combustion engines, too, knocking needs to be avoided, wherein a rapid combustion process can be tolerated. The distinction between these two processes is therefore advantageous.

Disclosure of Invention

The problem on which the invention is based is to improve the knock detection in an internal combustion engine.

This problem is solved by a method according to claim 1.

The invention is based on the recognition of how flame front propagation acts on cylinder pressure fluctuations during rapid combustion. According to the invention, the envelope of the high-frequency cylinder pressure curve is extracted cycle by cycle under the knock condition, wherein the knock intensity and the knock position, which are associated with the flame front pressure angle and a significantly lower background noise than in the current state of the art, can be identified from the envelope.

According to a first aspect, the invention provides a method for cylinder knock detection in a cylinder combustion chamber of an internal combustion engine having a crankshaft, comprising the steps of:

a) Measuring a cylinder pressure curve for a crankshaft angle parameter, wherein the cylinder pressure curve comprises a high frequency superimposed signal and a low frequency base signal;

b) Determining a derivative of the superimposed signal;

c) Adjusting the derivative of the superimposed signal by reversing the negative value of the derivative of the superimposed signal;

d) Determining a first value of the crankshaft angle parameter, wherein the derivative of the adjusted superimposed signal reaches a maximum value;

e) Determining a second value of the crankshaft angle parameter, wherein the base signal reaches a maximum value;

f) Determining an integral curve of the derivative of the adjusted superimposed signal;

g) Determining a combustion intensity value from the integral curve; and is also provided with

h) The relative combustion angle value is determined as a difference between a first value of the crank angle parameter and a second value of the crank angle parameter.

The internal combustion engine may in particular be an external ignition internal combustion engine. The high frequency superimposed signal has a higher frequency than the base signal. In the same way, the low frequency base signal has a lower frequency than the superimposed signal. The signals are thus high frequency or low frequency in relation to each other.

The crankshaft angle parameter is a parameter which is associated with the crankshaft angle in a correspondingly associable manner, in particular a parameter from which the crankshaft angle can be determined. The crankshaft angle parameter may preferably be the crankshaft angle itself. Alternatively, the crankshaft angle parameter may be, for example, a relative time, by means of which the crankshaft angle can be determined for a later time with the aid of the engine speed and the crankshaft starting angle or the cylinder position. According to the specific selection of the crank angle parameters, the parameters related to the cylinder pressure curve can be respectively derived. The crank angle will thus be derived over time according to the invention. The relative times can thus be derived from the crankshaft angle according to the invention. As a crankshaft angle parameter, an acceleration signal measured at the engine housing can also be used, from which the crankshaft angle can be derived. Alternatively or additionally, the crankshaft angle parameter may also be an acoustic signal, provided that the crankshaft angle can be derived therefrom.

The cylinder pressure curve includes a signal from which the cylinder pressure can be derived. They are signals that are at least correlated with cylinder pressure. The base signal in this case in principle has a higher intensity than the superimposed signal to which the base signal is superimposed.

The negative of the derivative of the superimposed signal can be reversed mathematically by squaring all values and then squaring with the quadratic root of the squared values. The method step corresponds to applying an absolute value function to all values of the superimposed signal.

The first value of the crankshaft angle parameter that maximizes the derivative of the superimposed signal may be the value at which the crankshaft angle parameter reaches an absolute maximum.

The combustion intensity is preferably the maximum pressure that occurs during combustion. The signal may be identified as a knock signal or a non-knock signal from the combustion intensity value and/or the relative combustion angle value.

Preferably, it can be provided that the method further comprises the following steps:

i) The superimposed signal is assigned to a set of knock signals or a set of acoustic vibrations in dependence on the combustion intensity values and/or the relative combustion angle values.

By determining the combustion angle value and the combustion intensity value, in principle, the identification of the knock signal can be achieved. The differentiation of the knock signal from the acoustic vibrations allows a more accurate analysis of the combustion process in the engine for the corresponding assignment of one of the groups. For many acquired signals, it is sufficient to focus only on the combustion intensity value or the relative combustion angle value for differentiation. A particularly low combustion intensity indicates acoustic vibrations. A particularly high combustion intensity or a small relative combustion angle may indicate the presence of a knock signal. However, for a particularly reliable distribution, it is advantageous to evaluate the two values, namely the combustion intensity value and the relative combustion angle value. Acoustic vibrations refer to all high-frequency superimposed signals of the cylinder pressure curve which are not assigned to the knock signal. Acoustic vibrations may have different origins and in principle have a lower signal strength than the knock signal.

Preferably, it may be provided that step b) further comprises the steps of:

b1.1 Determining a derivative of the cylinder pressure curve; and is also provided with

b1.2 Separating the derivative of the superimposed signal from the derivative of the base signal with at least one filter; or alternatively

b2.1 Separating the superimposed signal from the base signal with at least one filter;

b2.2 Deriving the separated superimposed signal.

The two alternatives b 1) and b 2) allow to perform step b) of the method at low computational cost.

A further advantage is obtained when in this method the integral curve is calculated only up to the first value of the crankshaft angle parameter.

The calculation costs for determining the combustion intensity value and the combustion angle value are significantly reduced by limiting the calculation of the integral curve, but without reducing the accuracy of the knock recognition.

It is particularly advantageous if the combustion intensity value is determined as the maximum slope of the integral curve at the first value of the crankshaft angle parameter.

The combustion intensity value can thus be determined with high accuracy at low calculation costs. In particular, it can be provided that the slope of the integration curve is calculated from two measuring points, one of which is located at the first value of the crankshaft angle parameter determined in step d), and the second measuring point is the measuring point immediately preceding the first value of the crankshaft angle parameter. The spacing of the dots is therefore dependent on the measurement frequency. At a first value of the crankshaft angle parameter, the superimposed signal is maximum. The slope of the superimposed signal also increases as it gets closer to the maximum slope. In order to determine the slope with sufficient accuracy, it is sufficient to select two measurement points. These two measurement points can have a time difference of less than 1ms, preferably less than 0.1ms, particularly preferably less than 0.05 ms.

Further advantages are obtained when the filter is specified to be a high pass filter and/or a low pass filter.

With a high-pass filter or a low-pass filter, the base signal can be separated from the superimposed signal in a very simple manner. The filter may be designed as a digital filter or as an analog filter.

Further advantages are obtained when in the method the filter is provided with a filtering frequency between 3kHz and 5kHz, preferably 4kHz.

If, for example, in the case of a high-pass filter, all signals having a frequency below a value of between 3kHz and 5kHz, preferably 4kHz, are filtered out, the method is particularly well suited for cylinder knock detection in many internal combustion engines having a wide range of applications, for example in many engines in passenger cars. For many modes of operation of such engines, signal filtering and thus knock detection by means of this frequency is particularly effective.

A further advantage is provided when in the method provision is made for a pressure sensor in the combustion chamber for measuring the cylinder pressure curve.

A high measurement accuracy is obtained by means of a pressure sensor in the combustion chamber. Alternative methods (for example acceleration sensors used for example on the internal combustion engine housing) can also infer the pressure present in the combustion chamber, but may involve higher measurement errors. This particular embodiment of the invention results in a lower number of false positive and/or false negative identified knock signals due to the lower measurement error.

Further advantages are obtained when it is provided in the method that the method has the following further steps:

j) The superimposed signals corresponding to the group of knock signals are divided into groups of knock signals with low intensity, groups of knock signals with medium intensity or groups of knock signals with high intensity depending on the combustion intensity value and/or the relative combustion angle value.

By precisely corresponding assigning the superimposed signal identified as the knock signal, a more accurate analysis of the combustion process in the engine is allowed.

According to a second aspect, the invention provides a measuring device which is set up for using the method according to one of claims 1 to 8.

According to a third aspect, the invention provides an internal combustion engine comprising a sensor for measuring a cylinder pressure curve and a measuring device according to claim 9 which is signally connected to the sensor.

The sensor may be in particular a pressure sensor in the combustion chamber of a cylinder.

Drawings

Further advantages and features of the invention come from the following figures. In this case schematically shown:

fig. 1 shows a section of an internal combustion engine cylinder during a normal combustion process (fig. 1 (a)) and during knock combustion (fig. 1 (b));

fig. 2 shows a plot of pressure changes within a cylinder combustion chamber during knock combustion (fig. 2 (a)) and during flash combustion (fig. 2 (b));

FIG. 3 shows a plot of pressure changes within a cylinder combustion chamber and parameters derived therefrom;

fig. 4 shows the steps of a knock recognition method according to a particular embodiment of the invention;

fig. 5 shows a corresponding map of the number of signals with respect to acoustic vibrations and the various different knock signal strengths.

Detailed Description

Fig. 1 shows sections 10, 12 of a cylinder 14 of an internal combustion engine during a combustion process. Fig. 1 (a) shows a first step 10 during an externally ignited combustion process, in which only externally ignited combustion 16, which is caused by ignition means 11, takes place in combustion chamber 13. Fig. 1 (b) shows a second step 12 during the external ignition combustion process, in which a further self-initiating ignition core 18 is present in addition to the external ignition combustion 16 caused by the ignition means 11 in the combustion chamber 13. The fuel runaway combustion is known as knock combustion, where such an additional self-initiating ignition center 18 is present. The temperature and pressure increase sharply upon combustion in the knock. The externally ignited combustion 16 initiated by the ignition mechanism 11 and the combustion from the self-initiated ignition center 18 meet at the speed of sound. In the process, pressure peaks occur, which can damage several different cylinder components, in particular the ignition mechanism 11. Audible and measurable high-frequency vibrations occur in the cylinder pressure curve due to the reflections.

Fig. 2 shows a plot of the pressure change in the combustion chamber 13 of the cylinder 14 for two different combustions.

Fig. 2 (a) shows a first graph 20, which shows a pressure curve in the combustion chamber 13 of the internal combustion engine cylinder 14 during the externally ignited combustion, in which case acoustic vibrations occur. Acoustic vibrations may lead to rapid combustion. A first cylinder pressure curve 24a is shown in the upper region of the first graph 20. The first cylinder pressure curve 24a describes the pressure prevailing in the combustion chamber 13 of the combustion engine cylinder 14 as a function of the crankshaft angle. Ignition is caused with an ignition angle 22 corresponding to a crankshaft angle of-15 °. The pressure present in the combustion chamber 13 of the cylinder 14 increases with a first slope up to a crankshaft angle of about +3°. The first cylinder pressure curve 24a then increases with a second slope up to a crankshaft angle of approximately +10°. The second slope is greater than the first slope. The first cylinder pressure curve 24a includes a low frequency base signal 25 and a high frequency superimposed signal 27a. The low-frequency base signal 25 and the high-frequency superimposed signal 27a are each shown on top of one another only in fig. 2 (a) and are marked with reference numerals at positions where the corresponding components are clearly visible. The low frequency base signal 25 and the high frequency superimposed signal 28 together form a first cylinder pressure curve 24a. At a crankshaft angle of about +11°, the base signal 25 reaches a maximum 26 in this example.

In the case of the externally ignited combustion, the low-frequency base signal 25 starts at a crankshaft angle of approximately 5 ° and is therefore superimposed with a first high-frequency superimposed signal 27a in the vicinity of the maximum 26 of the base signal 25. Such a superimposed signal 27a can be separated from the cylinder pressure curve 24a, for example, using a high-pass filter and is shown in the lower region of the first graph 20. The scale is adjusted for better visibility than the plot of the upper cylinder pressure curve 24a in fig. 2 (a). From a crank angle of about 5 °, the pressure in the combustion chamber 13 fluctuates in correspondence with the magnitude of the high-frequency superimposed signal 27a. The shown fluctuations correspond to their magnitude after acoustic vibrations. Such acoustic vibrations may occur at different crank angles. If the acoustic vibrations begin at a smaller crank angle than shown in this example, they may result in a gain 34 that causes the cylinder pressure curve 24a to rise more steeply than if the acoustic vibrations were not initiated. Combustion with the steeper slope of the cylinder pressure curve 24a is generally referred to as rapid combustion.

The superimposed signal derivative 28a is shown centrally in fig. 2 (a). In this plot, the envelope 36a of the derivative 28a of the separated superimposed signal is shown together. The envelope 36a of the superimposed signal derivative 28a may be approximately described as "drop-shaped".

Fig. 2 (b) shows a second graph 32 of the pressure change in the combustion chamber 13 of the cylinder 14 at the time of the knock combustion. A second cylinder pressure curve 24b is shown in the upper region of the second graph 32. The second cylinder pressure curve 24b also shows the pressure prevailing in the combustion chamber 13 of the engine cylinder 14 with respect to the crankshaft angle.

Up to a crankshaft angle of about +10 deg., the second cylinder pressure curve 24b is dominated by the low frequency base signal 25. From a crankshaft angle of about +10°, it can be seen that the base signal 25 is superimposed with a superimposed signal 27b of a higher frequency with respect to the base signal 25.

A high frequency superimposed signal 27b separated from the low frequency base signal 25 is shown below in fig. 2 (b). The derivative 28b of the separated superimposed signal is shown centrally in fig. 2 (b). The envelope 36b here represents the form of the superimposed signal derivative 28b. It can be seen that the envelope 36b of the superimposed signal derivative 28b increases sharply at a crankshaft angle of approximately 10 ° and then decreases again immediately after an approximately exponential curve. The maximum 29 of the superimposed signal derivative 28 reaches a value of about 100bar/° KW here and is therefore significantly smaller in terms of value than the minimum 31 of-150 bar/° KW measured at a slightly smaller crankshaft angle. The joint evaluation of the maximum and minimum values of the superimposed signal derivative 28 is achieved in the method according to the invention in that the superimposed signal derivative 28b is adjusted in such a way that its negative value is reversed. This is described in detail with respect to fig. 3.

In order to be able to compare the graph in fig. 2 (a) with the graph in fig. 2 (b), the scales thereof are correspondingly chosen to be identical to each other. If the superimposed signal derivative 28a is compared to the superimposed signal derivative 28b, it appears that the knock combustion in fig. 2 (b) results in a significantly steeper curve slope compared to the combustion with acoustic vibrations in fig. 2 (a). It appears that the amplitude of the superimposed signal derivative 28a tends to be smaller in the case of acoustic vibrations than the superimposed signal 27a itself on a selected scale. In contrast, in the case of the knock combustion, a further increase in the amplitude of the derivative 28b of the superimposed signal can be observed compared to the superimposed signal 27b itself. The acoustic vibration signal (which also includes rapid combustion) occurring at similar frequencies can be distinguished from knock combustion.

In fig. 3 and 4, a plot of the pressure change in the combustion chamber 13 of the cylinder 14 and the parameters derived therefrom and the steps of the method 400 according to a particular embodiment of the invention associated therewith are shown.

Fig. 4 shows the individual steps of a method 400 for knock detection in a combustion chamber 13 of a cylinder 14 of an internal combustion engine having a crankshaft according to a specific embodiment of the invention.

In a first step 402 of the method 400, a cylinder pressure curve 24 is measured with respect to the crankshaft angle parameter, wherein the cylinder pressure curve 24 contains the high-frequency superimposed signal 27 and the low-frequency base signal 25. The low frequency base signal 25 is drawn separately in dashed form in fig. 3. The crank angle parameter is the crank angle in the example shown in fig. 3.

In a second step 404, the derivative of the cylinder pressure curve is calculated. Because the cylinder pressure curve has a high frequency signal with a higher maximum slope and a low frequency signal with a smaller maximum slope, the derivative of the cylinder pressure curve 24 allows the base signal 25 to be separated from the superimposed signal 27.

In a third step 406, it is involved to separate the derivative 28a,28b of the superimposed signal from the derivative of the base signal with at least one filter. The filter may comprise a high pass filter and/or a low pass filter. As filters, in principle, analog filters and digital filters can be used.

The derivatives 28a,28b of the superimposed signal are adjusted in a fourth step 408 by reversing the negative values of the derivatives 28a,28b of the superimposed signal. The result of this intermediate evaluation is an adjusted superimposed signal derivative 312.

The fourth step 408 is particularly for obtaining a higher density of positive amplitudes of the derivative of the superimposed signal. As discussed above, the knock signal is distinguished from rapid combustion by the particularly steep slope of the superimposed signal derivatives 28a,28 b. A negative amplitude and a positive amplitude may indicate a knock signal. By reversing the negative values, the density of the estimated values of the superimposed signal derivatives 28a,28b is increased, and thus the identification of knocking in the cylinder pressure curve 24 is improved. In particular, it can be provided in a fourth step 408 that the superimposed signal derivative 28a,28b is adjusted by reversing the total negative value of the superimposed signal derivative 28a,28 b.

In a fifth step 410, a first value 310 of the crankshaft angle parameter is determined, at which point the adjusted derivative 312 of the superimposed signal reaches a maximum 314. In the example shown in FIG. 3, the first value 310 of the crank angle parameter is a crank angle of approximately 8.1.

In a sixth step 412, a second value 316 of the crankshaft angle parameter is determined, at which the base signal 25 reaches a maximum value 26. In the example shown in FIG. 3, the second value 316 of the crankshaft angle parameter is approximately 8.4.

The integration curve 318 of the adjusted superimposed signal derivative 312 is calculated in a seventh step 414. The integral curve 318 is calculated here only as a function of the crankshaft angle up to the first value 310 of the crankshaft angle parameter, i.e. up to 8.1 ° in this example. Calculation up to the first value 310 is sufficient for determining combustion strength without data loss and reduces calculation costs.

In an eighth step 416, a combustion intensity value is determined from the integral curve 318. The combustion intensity value is determined as the maximum slope of the integration curve 318 at the first value 310 of the crankshaft angle parameter. The maximum slope of the integration curve 318 at the first value 310 of the crankshaft angle parameter is determined from two measurement points of the integration curve 318. The first measurement point is located directly at the first value 310 of the crankshaft angle parameter and the second measurement point is the point of the integration curve immediately preceding it. The skilled person is aware of other possibilities in addition to the slope of the integration curve 318 at the first value 310 for calculating the crankshaft angle parameter.

In a ninth step 418 of the method 400, a value of the relative combustion angle is determined as a difference between the first value of the crankshaft angle parameter and the second value of the crankshaft angle parameter. The relative combustion angle thus indicates the angular difference between the crankshaft angle at which the maximum base signal 25 is located and the crankshaft angle at which the maximum adjusted superimposed signal derivative 312 is located.

Fig. 5 shows a graph 500 of the correspondence between a plurality of signals 502 and acoustic vibrations and a plurality of different knock signal strengths. The signal has been generated using the method 400 of the present invention as explained for example with respect to fig. 4. Signal 502 is characterized by combustion intensity and relative combustion angle, respectively, and is shown as a black dot in graph 500. The exemplary measured signal 502 has a combustion intensity between about 0.3 bar and 8.6 bar. The relative firing angle of signal 502 is approximately between-2 deg. and +4.5 deg.. The significant concentration of signal 502 is located at a relative firing angle of around 0 deg. and about 1 bar lower region of intensityThe high combustion strength does not occur simultaneously with the high relative combustion angle in this example.

A negative relative combustion angle means that the maximum intensity of the high frequency superimposed signal has occurred at a time instant or at a crank angle before the base signal reaches the maximum intensity. The positive relative combustion angle means, in each case, that the maximum intensity of the high-frequency superimposed signal occurs at a point in time or at a crank angle after the base signal reaches the maximum intensity.

The graph 500 is divided into four different regions in which the signal 502 is located. Depending on which of the four zones the signal is in, it is assigned to a certain type of combustion. The region boundary is selected in correspondence with the internal combustion engine being examined in this example. For other internal combustion engines, the region boundaries of the combustion intensity are to be set in particular.

In this example, the first region 504 extends between 0 and 1.2 bar combustion intensity and between-2 ° and +6.8° relative combustion angle. If signals 502 in this region are measured, they are assigned to a set of acoustic vibrations, in particular because of their low combustion strength. Signals 502 having a combustion intensity of more than 1.2 bar are in this example correspondingly assigned to a set of knock signals. But in this case a more accurate corresponding allocation can also be achieved as explained in relation to the areas 506, 508 and 510.

The second region 506 is located between a high relative firing angle of +1.8° to +6.8° and a firing strength of 1.2 bar to 2.5 bar. The signal 502 in the second area 506 is identified as a low intensity knock signal and is therefore correspondingly assigned to a set of low intensity knock signals.

The third region 508 extends from a relative combustion angle that is within the order of magnitude of the second region 506 to a relative combustion angle of 0 deg. and extends between combustion intensities from 1.2 bar to 5 bar. The signal 502 in the third region 508 is indirectly assigned to a set of medium intensity knock signals in terms of intensity and position.

The fourth zone 510 extends between relative combustion angles of 0 deg. to-2 deg. and combustion intensities of 1.2 bar to 10 bar. The signal 502, which should be assigned to the fourth region 510, is assigned to a set of high-intensity knock signals in terms of intensity and position. The knock signal can be identified according to the method as a high and medium intensity signal. A more accurate distribution as low, medium and high intensity knock signals can be achieved by an additional analysis of the relative combustion angle.

Thus, the two parameters, namely the relative combustion angle and the combustion intensity, allow to distinguish between combustion cycles with and without a knock signal. The method of the invention allows particularly error-free recognition of the knock signal.

The above explanation of the embodiments describes the present invention only in the scope of examples.

List of reference numerals

10. First cross section

11. Ignition mechanism

12. Second cross section

13. Combustion chamber

14. Cylinder

16. Exogenous ignition combustion

18. Self-initiating ignition center

20. First graph of

22. Ignition angle

24,24a,24b cylinder pressure curve

25. Base signal

26. Maximum value of base signal

27,27a,27b superimposed signal

28a,28b of the superimposed signal

29. Maximum value of superimposed signal derivative

31. Minimum value of superimposed signal derivative

32. Second graph

34. Gain of

Envelope of 36a,36b

310. First value of crankshaft angle parameter

312. Adjusted superimposed signal derivative

314. Maximum value of modified derivative of superimposed signal

316. Second value of crankshaft angle parameter

318. Integral curve

400. Knock recognition method

402. First step of the method

404. Second step of the method

406. Third step of the method

408. Fourth step of the method

410. Fifth step of the method

412. Sixth step of the method

414. Seventh step of the method

416. Eighth step of the method

418. Ninth step of the method

500. Drawing of the figure

502. Signal signal

504. First region

506. Second region

508. Third region

510. Fourth region

Claims

1. A method (400) for identifying knocking in a combustion chamber (13) of a cylinder (14) of an internal combustion engine having a crankshaft, comprising the steps of:

a) Measuring a cylinder pressure curve (24, 24a,24 b) with respect to a crankshaft angle parameter, wherein the cylinder pressure curve (24, 24a,24 b) comprises a high-frequency superimposed signal (27) and a low-frequency base signal (25);

b) Determining a derivative (28 a,28 b) of the superimposed signal;

c) Adjusting the derivative (28 a,28 b) of the superimposed signal by reversing the negative value of the derivative (28 a,28 b) of the superimposed signal;

d) Determining a first value (310) of a crank angle parameter at which the adjusted superimposed signal derivative (312) reaches a maximum value (314);

e) Determining a second value (316) of the crankshaft angle parameter, at which the base signal (25) reaches a maximum value;

f) Determining an integral curve (318) of the adjusted superimposed signal derivative (312);

g) Determining a combustion intensity value from the integral curve (318); and is also provided with

h) A relative combustion angle value is determined as a difference between a first value (310) of the crank angle parameter and a second value of the crank angle parameter.

2. The method (400) of claim 1, further comprising the step of:

i) The superimposed signal (27) is assigned to a set of knock signals or a set of acoustic vibrations in dependence on the combustion intensity value and/or the relative combustion angle value.

3. The method (400) according to claim 1 or 2, wherein step b) further comprises the steps of:

b1.1 Determining a derivative of the cylinder pressure curve (24, 24a,24 b); and is also provided with

b1.2 -separating the derivative (28 a,28 b) of the superimposed signal from the derivative of the base signal with at least one filter; or alternatively

b2.1 -separating the superimposed signal (27) from the base signal (25) with at least one filter; and is also provided with

b2.2 Deriving the separated superimposed signal.

4. The method (400) according to claim 1 or 2, wherein the integration curve (318) is calculated only up to the first value (310) of the crank angle parameter.

5. The method (400) according to claim 1 or 2, wherein the combustion intensity value is determined as a maximum slope of the integration curve (318) at the first value (310) of the crank angle parameter.

6. The method (400) according to claim 1 or 2, wherein the filter comprises a high pass filter and/or a low pass filter.

7. The method (400) of claim 1 or 2, wherein the filter has a filtering frequency between 3kHz and 5 kHz.

8. The method (400) of claim 7, the filter having a filtering frequency of 4kHz.

9. The method (400) of claim 2, further comprising the step of:

j) The superimposed signals (27) which are assigned to a group of knock signals are assigned to a knock signal group with low intensity, a knock signal group with medium intensity or a knock signal group with high intensity depending on the combustion intensity value and/or the relative combustion angle value.

10. Measuring device set up for employing a method (400) according to one of the preceding claims.

11. An internal combustion engine comprising a sensor for measuring a cylinder pressure curve (24, 24a,24 b) and a measuring device according to claim 10 connected to the sensor in terms of signal technology.