Methods for knock detection in a combustion chamber of a cylinder

Abstract

Method (400) for knock detection in a combustion chamber (13) of a cylinder (14) of an internal combustion engine with a crankshaft, comprising the steps: a) Measuring a cylinder pressure curve (24, 24a, 24b) as a function of a crankshaft angle parameter, wherein the cylinder pressure curve (24, 24a, 24b) comprises a higher frequency superposition signal (27) and a low frequency base signal (25); b) Determining the derivative of the superposition signal (28a, 28b); c) Adjusting the derivative of the superposition signal (28a, 28b) by inverting negative values ​​of the derivative of the superposition signal (28a, 28b); d) Determining a first value (310) of the crankshaft angle parameter at which the adapted derivative of the superposition signal (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 integration curve (318) of the fitted derivative of the superposition signal (312); g) Determining a value of a combustion intensity from the integration curve (318); and h) Determining a value of a relative combustion angle as the difference between the first value (310) of the crankshaft angle parameter and the second value of the crankshaft angle parameter.

Description

[0001] The present invention relates to a method for knock detection in a combustion chamber of a cylinder of an internal combustion engine with a crankshaft, as well as a measuring device and an internal combustion engine based on the method.

[0002] In the technical field of internal combustion engines, it is known that uncontrolled combustion of fuel in a cylinder's combustion chamber can cause a characteristic knocking noise. The uncontrolled combustion associated with knocking is detrimental to the combustion process and the service life of internal combustion engine components and can be prevented by adapting the engine control system. A first step toward adapting the engine control system is detecting the knock signals.

[0003] Methods for knock detection are known from the prior art, for example from EP 0 722 562 A1. This method uses a knock sensor for knock detection, which measures the engine noise and adjusts a threshold to the engine noise in order to detect knock even when the engine is very loud.

[0004] DE 10 2013 109 742 A1 discloses a method for knock detection in an internal combustion engine of a motor vehicle. In the method, a combustion noise of the internal combustion engine is recorded over a plurality of combustion cycles, and a reference value is determined based on the combustion noise over the plurality of combustion cycles. A threshold value for a current combustion noise is then determined and adjusted based on the reference value, and knock detection is performed based on this threshold value.

[0005] These known methods enable knock detection in simple internal combustion engines. However, new, advanced internal combustion engines exhibit special characteristics regarding knock behavior. In modern and developing internal combustion engines, however, not only knock signals but also rapid combustion processes occur alongside the desired combustion process. During a rapid combustion process, the pressure in the cylinder is rich in harmonics that cause pressure fluctuations during flame front propagation. These oscillations degrade the signal-to-noise ratio because the level of background noise increases significantly. This behavior interferes with known methods of knock detection. Furthermore, rapid combustion processes also frequently occur in newer internal combustion engines.Rapid combustion processes are also associated with oscillations, but they are not as detrimental to the internal combustion engine and the combustion process as knocking. Even in modern internal combustion engines, knocking must be avoided, although rapid combustion processes can be tolerated. Distinguishing between these two processes is therefore advantageous.

[0006] The problem underlying the invention is therefore to improve knock detection in internal combustion engines.

[0007] The problem is solved by a method according to claim 1.

[0008] The proposed invention is based on identifying how flame front propagation affects cylinder pressure oscillations during a rapid combustion process. According to the invention, the envelope of the high-frequency cylinder pressure curve is extracted cycle by cycle under knock conditions. From this envelope, the knock intensity and knock position relative to the angle of the peak firing pressure can be identified with much lower background noise compared to the current state of the art.

[0009] According to a first aspect, the invention provides a method for knock detection in a combustion chamber of a cylinder of an internal combustion engine having a crankshaft, comprising the steps: a) measuring a cylinder pressure curve as a function of a crankshaft angle parameter, wherein the cylinder pressure curve comprises a higher-frequency superimposed signal and a low-frequency base signal; b) determining the derivative of the beat signal; c) adjusting the derivative of the beat signal by inverting negative values ​​of the derivative of the beat signal; d) determining a first value of the crankshaft angle parameter at which the adjusted derivative of the overlay signal reaches a maximum value; e) determining a second value of the crankshaft angle parameter at which the base signal reaches a maximum value; f) determining an integration curve of the adjusted derivative of the beat signal; g) determining a value of a combustion intensity from the integration curve; and h) determining a value of a relative combustion angle as the difference between the first value of the crankshaft angle parameter and the second value of the crankshaft angle parameter.

[0010] The internal combustion engine can, in particular, be a spark-ignition internal combustion engine. The higher-frequency superimposed signal has a higher frequency than the base signal. Similarly, the low-frequency base signal has a lower frequency than the superimposed signal. The signals are thus higher-frequency and lower-frequency, respectively, relative to each other.

[0011] A crankshaft angle parameter is a parameter that has an assignable relationship to the crankshaft angle, in particular a parameter from which the crankshaft angle can be determined. The crankshaft angle parameter can preferably be the crankshaft angle itself. Alternatively, the crankshaft angle parameter can also be, for example, a relative point in time with which the crankshaft angle can be determined for later points in time with the aid of the engine speed and a crankshaft start angle or a cylinder position. Depending on the specific choice of the crankshaft angle parameter, a derivative is formed according to the variable on which the cylinder pressure curve depends. According to the invention, a crankshaft angle would thus be derived with respect to time. According to the invention, a relative point in time could thus be derived from the crankshaft angle.An acceleration signal measured on the engine housing can also be used as a crankshaft angle parameter, from which the crankshaft angle can be derived. Alternatively or additionally, an acoustic signal can also be used as a crankshaft angle parameter, provided the crankshaft angle can be derived from it.

[0012] The cylinder pressure curve includes signals from which the cylinder pressure can be derived. These are at least signals correlated with the cylinder pressure. The base signal is generally of higher intensity than the superimposed signal.

[0013] Inverting negative values ​​of the derivative of the overlay signal can be achieved mathematically by squaring all values ​​and then extracting the square root of the squared values. This process step corresponds to applying the magnitude function to all values ​​of the overlay signal.

[0014] A first value of the crankshaft angle parameter at which the derivative of the superposition signal reaches a maximum value may be a value at which the crankshaft angle parameter reaches an absolute maximum.

[0015] The combustion intensity is preferably a maximum pressure generated during a combustion process. Based on the values ​​of the combustion intensity and / or the relative combustion angle, a signal can be identified as a knock signal or a non-knock signal.

[0016] Preferably, the method may further comprise the step: i) Assigning the superposition signal to a group of knock signals or to a group of acoustic oscillations depending on the value of the combustion intensity and / or the value of the relative combustion angle.

[0017] By determining a value for the combustion angle and a value for the combustion intensity, it is generally possible to identify knock signals. Distinguishing between knock signals and acoustic oscillations, and thus assigning them to one of these groups, enables a more precise analysis of the combustion processes in the engine. For some of the recorded signals, examining just a value for the combustion intensity or the value of the relative combustion angle is sufficient for this differentiation. Particularly low combustion intensities are an indication of acoustic oscillations. Particularly high combustion intensities or even small relative combustion angles can be an indication that a knock signal is present. However, for a particularly reliable assignment, it is advantageous to analyze both values, the value of the combustion intensity and the value of the relative combustion angle.Acoustic oscillations are defined as all higher-frequency superimposed signals in the cylinder pressure curve that are not attributable to knock signals. Acoustic oscillations can have various causes and generally exhibit a lower signal intensity than knock signals.

[0018] Preferably, step b) may further comprise the steps: b1.1) Determine the derivative of the cylinder pressure curve; and b1.2) separating the derivative of the beat signal from the derivative of the base signal with at least one filter; or b2.1) separating the beat signal from the base signal with at least one filter; and b2.2) Deriving the separated heterodyne signal.

[0019] Both alternatives, b1) and b2), allow step b) of the procedure to be carried out with little computational effort.

[0020] Further advantages are achieved if the integration curve is calculated only up to the first value of the crankshaft angle parameter.

[0021] The computational effort for determining the value of the combustion intensity and the value of the combustion angle is significantly reduced by limiting the calculation of the integration curve without reducing the accuracy of the knock detection.

[0022] It is particularly advantageous if the value of the combustion intensity is defined as a maximum slope of the integration curve at the first value of the crankshaft angle parameter.

[0023] This allows a value for the combustion intensity to be determined with high accuracy and little computational effort. In particular, it can be provided that the slope of the integration curve is calculated from two measuring points, with one of the measuring points being at the first value of the crankshaft angle parameter determined in step d) and the second measuring point being the measuring point immediately before the first value of the crankshaft angle parameter. The distance between the points is thus dependent on a measuring frequency. The superposition signal is at its maximum at the first value of the crankshaft angle parameter. The slope of the superposition signal also increases with increasing proximity to the maximum slope. For a sufficiently accurate determination of the slope, it is sufficient to select these two measuring points.These two measuring points can in particular have a time interval of less than 1 ms, preferably less than 0.1 ms and particularly preferably less than 0.05 ms from each other.

[0024] Further advantages can be achieved if the filter is provided to include a high-pass filter and / or a low-pass filter.

[0025] A high-pass filter or a low-pass filter can be used to easily separate the base signal from the overlay signal. The filter can be configured as a digital or analog filter.

[0026] Further advantages can be achieved if the method provides that a filter frequency of the filter is between 3 kHz and 5 kHz, preferably 4 kHz.

[0027] For example, if a high-pass filter filters all signals with a frequency below a value between 3 kHz and 5 kHz, preferably 4 kHz, the method is particularly well suited for knock detection in a variety of internal combustion engines with a wide range of applications, such as those used in passenger cars. For many operating modes of such engines, signal filtering and thus knock detection at these frequencies is particularly effective.

[0028] Further advantages are achieved if the method provides for the use of a pressure sensor in the combustion chamber to measure the cylinder pressure curve.

[0029] A pressure sensor in the combustion chamber allows for particularly high measurement accuracy. Alternative methods, such as the use of an acceleration sensor, for example, on the outer casing of the combustion engine, also allow for conclusions about the pressure present in the combustion chamber, but may be subject to greater measurement errors. The lower measurement errors of this particular embodiment of the invention result in a further reduction in the proportion of false-positive and / or false-negative knock signals.

[0030] Further advantages can be achieved if the method further comprises the step of: i) Assigning the superposition signal associated with a group of knock signals to a subgroup of low-intensity knock signals, a subgroup of medium-intensity knock signals, or a subgroup of high-intensity knock signals depending on the value of the combustion intensity and / or the value of the relative combustion angle.

[0031] The precise assignment of the superposition signal identified as a knock signal enables a more precise analysis of the combustion processes in the engine.

[0032] According to a second aspect, the invention provides a measuring device adapted to apply a method according to any one of claims 1-8.

[0033] 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 connected to the sensor by signal technology.

[0034] The sensor can in particular be a pressure sensor in the combustion chamber of the cylinder.

[0035] Further advantages and features of the invention are apparent from the following figures. Herein, schematically: Fig. 1 Sections through a cylinder of an internal combustion engine during a normal combustion process ( Fig. 1a) and during knocking combustion ( Fig. 1b); Fig. 2 a plot of pressure development in a combustion chamber of a cylinder during knocking combustion ( Fig. 2a) and during rapid combustion ( Fig. 2b); Fig. 3 a plot of pressure development in a combustion chamber of a cylinder and derived quantities; Fig. 4 steps of a method for knock detection according to a particular embodiment of the invention; and Fig. 5 a map with an assignment of a variety of signals to acoustic oscillations and different intensities of a knock signal.

[0036] Fig. 1 shows sections 10, 12 through a cylinder 14 of an internal combustion engine during a combustion process. Fig. 1a) shows a first section 10 during a spark-ignited braking process, in which only the spark-ignited combustion 16 triggered by an ignition device 11 takes place in the combustion chamber 13. Fig. 1b shows a second section 12 during a spark-ignited combustion process, in which, in addition to the spark-ignited combustion 16 triggered by an ignition device 11, another self-triggered ignition core 18 is created in the combustion chamber 13. Knocking combustion refers to the uncontrolled combustion of the fuel in which such additional self-triggered ignition cores 18 are created. Temperature and pressure rise suddenly during knocking combustion. The spark-ignited combustion 16 triggered by the ignition device 11 and the combustion originating from the self-triggered ignition core 18 collide at the speed of sound. During this process, pressure peaks occur that can damage various cylinder elements, in particular the ignition device 11. Reflection causes a high-frequency oscillation in the cylinder pressure curve, which is audible and measurable.

[0037] Fig. 2 shows plots of pressure development in a combustion chamber 13 of a cylinder 14 for two different types of combustion.

[0038] Fig. 2a shows a first diagram 20, which illustrates the pressure curve in a combustion chamber 13 of a cylinder 14 of an internal combustion engine during spark-ignition combustion, during which acoustic oscillations occur. These acoustic oscillations can lead to rapid combustion. The upper area of ​​the first diagram 20 shows a first cylinder pressure curve 24a. The first cylinder pressure curve 24a describes the pressure present in the combustion chamber 13 of a cylinder 14 of an internal combustion engine as a function of the crankshaft angle. At an ignition angle 22, which corresponds to a crankshaft angle of -15°, ignition is triggered. The pressure present in the combustion chamber 13 of the cylinder 14 rises with a first gradient up to a crankshaft angle of approximately +3°. Following this, the first cylinder pressure curve 24a rises with a second gradient up to a crankshaft angle of approximately +10°. The second gradient is greater than the first gradient.The first cylinder pressure curve 24a comprises a low-frequency base signal 25 and a higher-frequency superimposed signal 27a. The low-frequency base signal 25 and the higher-frequency superimposed signal 27a are shown in . Fig. 2a above, each is shown only superimposed on one another and is provided with reference symbols at the points where the respective components are clearly visible. Together, the low-frequency base signal 25 and the higher-frequency superimposed signal 28 form the first cylinder pressure curve 24a. At a crankshaft angle of approximately +11°, the base signal 25 reaches a maximum value 26 in this example.

[0039] During spark-ignition combustion, the low-frequency base signal 25 is superimposed by a first higher-frequency superimposed signal 27a starting at a crankshaft angle of approximately 5° and thus around the maximum value 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 area of ​​the first diagram 20. The scale has been enlarged for better visibility compared to the plot of the cylinder pressure curve 24a in Fig. 2a above. Starting at a crankshaft angle of approximately 5°, the pressure in the combustion chamber 13 fluctuates according to the magnitude of the higher-frequency superimposed signal 27a. The fluctuation shown corresponds in magnitude to acoustic oscillations. Such acoustic oscillations can occur at different crankshaft angles. If the acoustic oscillations begin at lower crankshaft angles than those shown in this example, they can lead to an amplification 34, which results in a steeper rise in the cylinder pressure curve 24a than would be the case without the onset of acoustic oscillations. Combustions with a steeper rise in the cylinder pressure curve 24a are generally referred to as rapid combustion.

[0040] A derivative of the beat signal 28a is shown in Fig. 2a is shown in the center. This plot also shows an envelope 36a of the separated, derived overlay signal 28a. The envelope 36a of this derivative of the overlay signal 28a can be approximately described as "droplet-shaped."

[0041] Fig. Figure 2b shows a second diagram 32 of a pressure development in a combustion chamber 13 of a cylinder 14 during knocking combustion. A second cylinder pressure curve 24b is shown in the upper area of ​​the first diagram 20. The second cylinder pressure curve 24a also shows the pressure present in the combustion chamber 13 of a cylinder 14 of an internal combustion engine as a function of the crankshaft angle.

[0042] Up to a crankshaft angle of approximately +10°, the second cylinder pressure curve 24b is dominated by the low-frequency base signal 25. From a crankshaft angle of approximately +10°, it can be seen that this base signal 25 is superimposed by the superposition signal 27b, which has a higher frequency relative to the base signal 25.

[0043] The higher frequency superposition signal 27b separated from the low frequency base signal 25 is in Fig. 2b shown below. In Fig. 2b, a separated derivative of the superposition signal 28b is shown in the center. An envelope 36b shows the shape of the derivative of the superposition signal 28b. It can be seen that the envelope 36b of the derivative of the superposition signal 28b rises steeply at a crankshaft angle of approximately 10° and shortly thereafter falls again with an approximately exponential curve. The maximum value 29 of the derivative of the superposition signal 28 reaches a value of approximately 100 bar / °CA and is thus significantly smaller in magnitude than a minimum value 31 of -150 bar / °CA measured at a somewhat lower crankshaft angle. A joint evaluation of the maximum values ​​and the minimum values ​​of the derivative of the superposition signal 28 is made possible in the method according to the invention by adapting the derivative of the superposition signal 28b in such a way that its negative values ​​are inverted. This is explained in connection with Fig. 3 in more detail.

[0044] To view the diagrams of the Fig. 2a with those of Fig. 2b, their scaling has been chosen to be the same. When comparing the derivative of the superposition signal 28a with the derivative of the superposition signal 28b, it is noticeable that knocking combustion in Fig. 2b a significantly steeper rise of this curve compared to combustion with acoustic oscillations in Fig. 2a. Furthermore, it is noticeable that, with acoustic oscillations, the deflections of the derivative of the overlay signal 28a tend to become smaller compared to the overlay signal 27a itself, at the selected scale. In contrast, with knocking combustion, it can be observed that the deflections of the derivative of the overlay signal 28b tend to increase even further compared to the overlay signal 27b itself. This leads to a distinction between the signals of the acoustic oscillations (which also include rapid combustion) occurring at similar frequencies and those of knocking combustion.

[0045] In the Fig. 3 and Fig. 4 shows a plot of a pressure development in a combustion chamber 13 of a cylinder 14, as well as variables derived therefrom in connection with steps of a method 400 according to a particular embodiment of the invention.

[0046] 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 with a crankshaft according to a particular embodiment of the invention.

[0047] In a first step 402 of the method 400, a cylinder pressure curve 24 is measured as a function of a crankshaft angle parameter, wherein the cylinder pressure curve 24 comprises a higher-frequency superimposed signal 27 and a low-frequency base signal 25. The low-frequency base signal 25 is shown as a broken line in Fig. 3 is shown separately. The crankshaft angle parameter is shown in Fig. Example of the crankshaft angle shown in Figure 3.

[0048] In a second step 404, the derivative of the cylinder pressure curve is calculated. Since the cylinder pressure curve is a higher frequency signal with higher

[0049] maximum gradients and a low-frequency signal with lower maximum gradients, the derivation of the cylinder pressure curve 24 enables a separation of the base signal 25 from the superposition signal 27.

[0050] A third step 406 involves separating the derivative of the beat signal 28a, 28b from the derivative of the base signal using at least one filter. The filter may comprise a high-pass filter and / or a low-pass filter. In principle, an analog or a digital filter can be used as the filter.

[0051] In a fourth step 408, the derivative of the overlay signal 28a, 28b is adjusted by inverting negative values ​​of the derivative of the overlay signal 28a, 28b. The result of this intermediate evaluation is an adjusted derivative of the overlay signal 312.

[0052] This fourth step 408 serves, among other things, to achieve a higher density of positive deflections in the derivative of the superposition signal. As discussed above, knock signals can be distinguished from rapid combustion by a particularly steep rise in the derivative of the superposition signal 28a, 28b. Both negative and positive deflections can provide indications of a knock signal. By inverting negative values, the density of evaluable values ​​in the derivative of the superposition signal 28a, 28b is increased, thus improving the detection of knocking in a cylinder pressure curve 24. In particular, the fourth step 408 can provide for the derivative of the superposition signal 28a, 28b to be adjusted by inverting all negative values ​​in the derivative of the superposition signal 28a, 28b.

[0053] In a fifth step 410, a first value 310 of the crankshaft angle parameter is determined at which the adjusted derivative of the superposition signal 312 reaches a maximum value 314. In Fig. In the example shown in Figure 3, the first value 310 of the crankshaft angle parameter is at a crankshaft angle of approximately 8.1°.

[0054] 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 Fig. In the example shown in Figure 3, the second value 316 of the crankshaft angle parameter is approximately 8.4°.

[0055] In a seventh step 414, an integration curve 318 of the adjusted derivative of the superposition signal 312 is calculated. The integration curve 318 is calculated only up to the first value 310 of the crankshaft angle parameter, i.e., in this example, up to a crankshaft angle of 8.1°. A calculation up to this first value 310 is sufficient for a data-loss-free determination of the combustion intensity and reduces the computational effort.

[0056] In an eighth step 416, a value of a combustion intensity is determined from the integration curve 318. The value of the combustion intensity is defined as a 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 on the integration curve 318. The first measurement point is directly at the first value 310 of the crankshaft angle parameter, and the second measurement point is the point on the integration curve immediately preceding it. In addition to this method, those skilled in the art will be aware of other possibilities for calculating the slope of the integration curve 318 at the first value 310 of the crankshaft angle parameter.

[0057] In a ninth step 418 of method 400, a value of a relative combustion angle is determined as the 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 difference angle between a crankshaft angle at which the base signal 25 is at its maximum and a crankshaft angle at which the adjusted derivative of the superposition signal 312 is at its maximum.

[0058] Fig. Figure 5 shows a map 500 with a mapping of a plurality of signals 502 to acoustic oscillations and different intensities of a knock signal. The signals were generated using a method 400 according to the invention, as described, for example, in connection with Fig.4. The signals 502 are each characterized by a combustion intensity and a relative combustion angle and are represented as black dots in the map 500. The signals 502 of an exemplary measurement have combustion intensities between approximately 0.3 bar and 8.6 bar. The relative combustion angles of the signals 502 are approximately between -2° and +4.5°. A particular clustering of the signals 502 occurs at a relative combustion angle of around 0° and a south intensity of approximately 1 bar. In this example, high combustion intensities do not occur simultaneously with high relative combustion angles.

[0059] A negative relative combustion angle means that the maximum intensity of the higher-frequency superimposed signal has already occurred at a time or crankshaft angle that precedes a time or crankshaft angle at which the base signal has reached its maximum intensity. A positive relative combustion angle means that the maximum intensity of the higher-frequency superimposed signal has already occurred at a time or crankshaft angle that precedes a time or crankshaft angle at which the base signal has reached its maximum intensity.

[0060] Map 500 is divided into four different ranges containing signals 502. Depending on which of the four ranges a signal falls into, it is assigned to a specific combustion type. The range boundaries were selected according to the internal combustion engine tested in this example. For other internal combustion engines, the range boundaries, in particular, must be adapted to the combustion intensity.

[0061] In this example, a first range 504 extends from combustion intensities between 0 and 1.2 bar and relative combustion angles between -2° and +6.8°. If signals 502 are measured that fall within this range, they are assigned to a group of acoustic oscillations, particularly due to their low combustion intensity. Signals 502 with a combustion intensity higher than 1.2 bar are assigned to a group of knock signals in this example. However, a more precise assignment is also possible, as explained with reference to ranges 506, 508, and 510.

[0062] A second range 506 lies between high relative combustion angles between +1.8° and +6.8° and combustion intensities between 1.2 bar and 2.5 bar. Signals 502 that fall within the second range 506 are identified as low-intensity knock signals and thus assigned to a group of low-intensity knock signals.

[0063] A third range 508 extends from relative combustion angles of the order of magnitude of the second range 506 to relative combustion angles of 0° and combustion intensities between 1.2 bar and 5 bar. Signals 502 whose intensity and position fall within the third range 508 are assigned to a group of medium-intensity knock signals.

[0064] A fourth range 510 extends from relative combustion angles between 0° and -2° and combustion intensities between 1.2 bar and 10 bar. Signals 502 whose intensity and position can be assigned to the fourth range 510 are assigned to a group of high-intensity knock signals. Knock signals can be identified using this method as high- and medium-intensity signals. A more precise assignment as low-, medium-, and high-intensity knock signals is possible through additional analysis of the relative combustion angle.

[0065] The two parameters of relative combustion angle and combustion intensity thus enable a distinction between combustion cycles with and without knock signals. The method according to the invention enables particularly accurate detection of knock signals.

[0066] The above explanations of the embodiments describe the present invention exclusively by way of examples. List of reference symbols 10 first cut 11 Ignition device 12 second cut 13 Combustion chamber 14 cylinders 16 spark-ignited combustion 18 self-triggered ignition core 20 first diagram 22 ignition angle 24, 24a, 24b Cylinder pressure curve 25 Base signal 26 Maximum value of the base signal 27, 27a, 27b Overlay signal 28a, 28b Derivation of the superposition signal 29 Maximum value of the derivative of the beat signal 31 Minimum value of the derivative of the beat signal 32 second diagram 34 reinforcements 36a, 36b Envelope 310 first value of the crankshaft angle parameter 312 Adjusted derivative of the beat signal 314 Maximum value of the adjusted derivative of the beat signal 316 second value of the crankshaft angle parameter 318 Integration curve 400 methods for knock detection 402 first step of the procedure 404 second step of the procedure 406 third step of the procedure 408 fourth step of the procedure 410 fifth step of the procedure 412 sixth step of the procedure 414 seventh step of the procedure 416 eighth step of the procedure 418 ninth step of the procedure 500 card 502 signals 504 first area 506 second area 508 third area 510 fourth area

Claims

[1] Method (400) for knock detection in a combustion chamber (13) of a cylinder (14) of an internal combustion engine with a crankshaft, comprising the steps: a) measuring a cylinder pressure curve (24, 24a, 24b) as a function of a crankshaft angle parameter, wherein the cylinder pressure curve (24, 24a, 24b) comprises a higher-frequency superposition signal (27) and a low-frequency base signal (25); b) determining the derivative of the beat signal (28a, 28b); c) adjusting the derivative of the beat signal (28a, 28b) by inverting negative values ​​of the derivative of the beat signal (28a, 28b); d) determining a first value (310) of the crankshaft angle parameter at which the adjusted derivative of the overlay signal (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 integration curve (318) of the adjusted derivative of the beat signal (312); g) determining a value of a combustion intensity from the integration curve (318); and h) determining a value of a relative combustion angle as the difference between the first value (310) of the crankshaft angle parameter and the second value of the crankshaft angle parameter. [2] The method (400) of claim 1, further comprising the step: i) Assigning the superposition signal (27) to a group of knock signals or to a group of acoustic oscillations depending on the value of the combustion intensity and / or the value of the relative combustion angle. [3] Method (400) according to one of the preceding claims, wherein step b) further comprises the steps of: b1.1) Determining the derivative of the cylinder pressure curve (24, 24a, 24b); and b1.2) separating the derivative of the beat signal (28a, 28b) from the derivative of the base signal with at least one filter; or b2.1) separating the superposition signal (27) from the base signal (25) with at least one filter; and b2.2) Deriving the separated heterodyne signal. [4] Method (400) according to one of the preceding claims, wherein the integration curve (318) is calculated only up to the first value (310) of the crankshaft angle parameter. [5] Method (400) according to one of the preceding claims, wherein the value of the combustion intensity is determined as a maximum slope of the integration curve (318) at the first value (310) of the crankshaft angle parameter. [6] Method (400) according to one of the preceding claims, wherein the filter comprises a high-pass filter and / or a low-pass filter. [7] Method (400) according to one of the preceding claims, wherein a filter frequency of the filter is between 3 kHz and 5 kHz, preferably 4 kHz. [8] Method (400) according to one of claims 2 to 7, further comprising the step: j) Assigning the superposition signal (27) assigned to a group of knock signals to a subgroup of knock signals with low intensity, a subgroup of knock signals with medium intensity or a subgroup of knock signals with high intensity depending on the value of the combustion intensity and / or the value of the relative combustion angle. [9] Measuring device adapted to apply a method (400) according to any one of the preceding claims. [10] Internal combustion engine, comprising a sensor for measuring a cylinder pressure curve (24, 24a, 24b) and a measuring device according to claim 9 which is connected to the sensor by signal technology.

Images