DE102017204399B4 - Method and device for detecting knocking in an internal combustion engine - Google Patents

Abstract

Method for detecting knocking of an internal combustion engine, in which an actual signal is determined by evaluating the output signals of one or more knock sensors, the actual signal determined is compared with a plurality of knock detection threshold values of different magnitudes, the number of times the knock detection threshold values are exceeded is counted using one or more counters, and a Presence of knocking is then detected when the number of times the knock detection threshold values are exceeded is greater than or equal to a predetermined counter criterion for the number of times the number of times it has been exceeded, characterized in that the number of times the different levels of knock detection threshold values have been exceeded contributes to knock detection to different extents, and that with each violation the predetermined highest knock detection threshold value, a presence of knocking is detected.

Description

The invention relates to a method and a device for detecting knocking in an internal combustion engine.

Control devices of internal combustion engines are provided, among other things, to determine an optimal ignition point for the air/fuel mixture. This determination is made using characteristic diagrams stored in a memory of the internal combustion engine. Attempts are made to set the ignition point as early as possible when there are high loads and/or high speeds in order to ensure complete combustion and the best possible degree of efficiency. Advancing the ignition timing in this way can lead to undesired knocking or undesired knocking combustion. Since such knocking combustion is harmful to the internal combustion engine, it is necessary to recognize this knocking and to retard the ignition timing somewhat.

Knocking is usually detected using one or more knock sensors attached to the housing of the internal combustion engine, each of which detects vibrations occurring during the combustion processes, for example via a piezoceramic, and converts them into an electrical voltage, which is fed to the control unit of the internal combustion engine and evaluated there.

From the DE 101 38 110 A1 a method for detecting knocking in an internal combustion engine is known, which has a knocking sensor whose output signal is fed to an evaluation circuit. This contains at least one filter whose characteristics can be changed. The presence of knocking is detected when the detected and processed output signal of the knock sensor exceeds a reference value, which changes as a function of the noise of the internal combustion engine, in a predeterminable manner. During a phase during which the filter characteristic changes, a modified knock detection method is carried out, in which the knock detection threshold is switched to be less sensitive and/or the reference level tracking is modified.

From the DE 10 2005 057 987 A1 An engine knock detection device is known which is connected to a knock sensor which detects vibrations of an internal combustion engine for receiving a sensor signal therefrom. This device includes a bandpass filter device for filtering the sensor signal to select a knocking frequency component which is within a frequency range specific to the occurrence of knocking in the internal combustion engine. There is also provided a knock judging device, connected to the band-pass filter device, which judges whether or not knocking has occurred in the engine. The engine knock detection device includes a filter controller for successively adjusting a passband of the band-pass filter device to follow frequency changes occurring in the knock frequency component during a combustion stroke time interval of the internal combustion engine.

US 2010/0 242 909 A1 relates to a method in which ignition is delayed if continuously occurring knocking noises are detected, while ignition is not delayed if knocking occurring once is detected. By acquiring the number of occurrences of detection data from a knock sensor stored in a storage unit in a predetermined period of time, a distribution of the detection data is prepared. When a piece of detection data having a value not smaller than a knock determination value is inputted from the knock sensor, the distribution of the pieces of detection data is checked. For example, when the detection data is distributed in a wide range or the knock level voltage of the entire detection data is not less than a predetermined value, a deceleration command is issued.
If high engine speeds occur during operation of an internal combustion engine, then the noises caused by knocking are often increasingly superimposed by other engine noises. As a result, the signal-to-noise ratio decreases.

In order to do justice to this problem, an attempt has been made to find a suitable compromise between adequate detection of knocking and as few undesired false detections as possible. In this context, it should be prevented that a deterioration in engine efficiency and increased fuel consumption occur due to too many false detections due to the resulting late pull of the ignition. In known knock control algorithms, the knock threshold is raised to avoid such false detections. However, the consequence of this is that knocking events that should actually be recognized are not detected.

The object of the invention consists in demonstrating a way in which the reliability of the process of detecting knocking of an internal combustion engine can be improved.

This object is achieved by a method with the features specified in claim 1 and solved by a device having the features specified in claim 8.

Advantageous refinements and developments of the invention are specified in the dependent claims 2-7.

In the method specified in claim 1, an actual signal is determined by evaluating the output signals of one or more knock sensors. This is compared to a number of different knock detection threshold values. The number of times the knock detection thresholds are exceeded is counted. The presence of knocking is detected when the number of times the knock detection threshold values have been exceeded meets predetermined criteria.

The advantages of the invention are, in particular, that when knocking of an internal combustion engine is detected, the number of false detections is reduced. In particular, knocking events that are erroneously not detected using known methods are recognized. Accordingly, in these cases, the ignition timing can be retarded slightly in order to counteract knocking.

• 1 eine Blockdarstellung einer Vorrichtung zur Erkennung des Klopfens einer Brennkraftmaschine,
• 2 Skizzen zur Erläuterung eines klopffreien Betriebes,
• 3 Skizzen zur Erläuterung eines klopfenden Betriebes und
• 4 Skizzen zur Erläuterung eines Ausführungsbeispiels für ein erfindungsgemäßes Verfahren zur Erkennung des Klopfens einer Brennkraftmaschine.

Further advantageous properties of the invention result from their exemplary explanation based on the figures. It shows:

• 1 a block diagram of a device for detecting knocking of an internal combustion engine,
• 2 Sketches to explain knock-free operation,
• 3 Sketches to explain a knocking operation and
• 4 Sketches to explain an embodiment of a method according to the invention for detecting knocking of an internal combustion engine.

the 1 shows a block diagram of a device for detecting knocking of an internal combustion engine. This device has one or more knock sensors 1 , an evaluation unit 2 and a control unit 5 . The evaluation unit 2 can also be an integrated part of the control unit 5 . The evaluation unit 2 has a bandpass filter 3 and an integrator 4 . The control unit 5 contains a knock detection unit 6, a memory 7 and a control signal generator 8.

The output signals se of the knock sensor(s) 1 are fed to the evaluation unit 2 and evaluated in it. As part of this evaluation, bandpass filtering takes place in bandpass filter 3 and integration in integrator 4. The passband of bandpass filter 3 corresponds to the frequency range in which any knocking signals occur. The signals passing through the bandpass are integrated in the integrator 4 in order to obtain an averaged output signal which corresponds to a background noise. The mentioned integration of the knock detection signal takes place individually for each cylinder in a specific crank angle range.

The output signals of the integrator 4 are fed to the knock detection unit 6 in which, with known knock detection algorithms, a decision is made as to whether knocking is present or not by comparison with a predetermined knock detection threshold value taken from the memory 7 . This information is forwarded to the control signal generator 8 .

If the presence of knocking is detected, then the control signal generator 8 makes a control signal st3 available, by means of which a retardation of the ignition point is initiated. Furthermore, the control signal generator 8 provides a control signal st1, by means of which the passband of the bandpass filter 3 can be shifted if necessary. Furthermore, the control signal generator 8 provides a control signal st2, by means of which the integrator 4 is activated for the duration of said crank angle range.

In the method according to the invention, in contrast to the known knock detection algorithms described above, the output signals of the integrator 4 are compared with a number of predetermined different knock detection threshold values which are taken from the memory 7 in order to be able to distinguish whether knocking is present or not. In this case, using a counter in each case, it is counted how often the output signal of the integrator 4 exceeds the respective knock detection threshold value. The presence of knocking is detected when the number of times the respective knock detection threshold value is exceeded is greater than or equal to a respectively specified reference value for the number of times it is exceeded.

This is explained in more detail below with reference to the other figures.

the 2 shows sketches to explain knock-free operation.

Here is in the 2a a curve K1 is shown, which illustrates the percentage deviation of a currently observed cylinder compared to the other cylinders of an internal combustion engine with regard to the basic noise present in the period under consideration.

In the 2 B a curve G is shown, which illustrates the background noise of the currently considered cylinder. Furthermore, the 2 B a signal I, which corresponds to the result of the integration of the knock sensor output signal of the currently considered cylinder. Furthermore, in the 2 B Curves SW1, SW2 and SW3 are shown, which correspond to different levels of knock detection thresholds. With known knock detection algorithms, there is only one curve of this type, for example curve SW1. Consequently, there is only one knock detection threshold that is used for knock detection.

In the 2 B the signal I does not exceed the curve SW1 at any point, so that when using the known knock detection algorithm it is recognized that knock-free operation is present.

Furthermore, the signal I does not exceed one of the curves SW2 and SW3 at any point, so that when the knock detection algorithm according to the invention is used, it is also recognized that knock-free operation is present.

the 3 shows sketches to explain a knocking operation.

Here is in the 3a illustrates that when the presence of knocking is detected, an ignition angle retraction R of the cylinder under consideration is carried out if the 3c signal I shown exceeds curve SW 1, ie the highest of the three predetermined knock detection threshold values. This corresponds to the application of the well-known knock detection algorithm.

From the 3c it can be seen that the signal I already exceeds the curves SW2 and SW3, which correspond to the middle and the lowest of the three predetermined knock detection threshold values, at earlier points in time. These points in time are defined by the 3c illustrated arrows P illustrated.
When using the knock detection algorithm according to the invention, the number of times the respective knock detection threshold value is exceeded is counted using a counter in each case. The presence of knocking is detected when the number of times the respective knock detection threshold value is exceeded is greater than or equal to a respectively specified reference value for the number of times it is exceeded.

An example of a knock detection algorithm according to the invention is as follows:

• - das Signal I die Kurve SW1, d. h. den größten vorgegebenen Klopferkennungsschwellenwert, einmal übersteigt, d. h. bei jedem Übersteigen der Kurve SW1, oder
• - das Signal I die Kurve SW2 einmal übersteigt, wenn das Signal I vorher zu einem früheren Zeitpunkt die Kurve SW3 bereits mindestens dreimal überschritten hat, oder
• - das Signal I die Kurve SW2 zweimal übersteigt.

A presence of knocking is recognized when

• - the signal I exceeds the curve SW1, ie the largest predetermined knock detection threshold value, once, ie each time the curve SW1 is exceeded, or
• - signal I exceeds curve SW2 once, if signal I has previously exceeded curve SW3 at least three times, or
• - the signal I exceeds the curve SW2 twice.

With this procedure, the presence of knocking can be detected earlier than with known methods in which only a single knock detection threshold value is used to detect knocking.

In one advantageous embodiment, in addition to the above-described use of a plurality of knock detection threshold values for detecting knocking, an increase in the basic noise of the cylinder under consideration is taken into account. This is in the 3b and 3c shown, in which the arrow AN shows an increase in the basic noise and the arrow AB shows the decrease in the basic noise that has occurred after the ignition angle has been withdrawn.

Such an additional consideration of the increase in the background noise in the knock detection increases the reliability of the knock detection and reduces the probability of false detections.

the 4 shows sketches to explain an exemplary embodiment of a method according to the invention for detecting knocking of an internal combustion engine.

Here is in the 4a first illustrates that when the presence of knocking is detected, the ignition angle R of the cylinder under consideration is retracted. In this case, R denotes the ignition angle retraction, as is carried out in known methods. In the method according to the invention, the retraction can already be carried out at t1 or t5, as is shown in FIG 4d is illustrated.

In the 4b shows the percentage deviation of the cylinder under consideration compared to the other cylinders with regard to the background noise. It can be seen that this deviation is greater than a predetermined maximum value max1 during the duration of time intervals T1 and T2.

In the 4c are again the curve G describing the background noise of the considered cylinder, the signal I, which is the result of the Integration of the knock sensor output signal of the currently considered cylinder corresponds to the curves SW1, SW2 and SW3, which correspond to different high knock detection threshold values, and the time intervals T1 and T2, during which the percentage deviation of the considered cylinder compared to the remaining cylinders with regard to the basic noise exceeds the maximum value maxi, shown. It can be seen that the signal I exceeds the curves SW1, SW2 and SW3, which correspond to the differently high threshold values, at several points in each case.

From the 4d it can be seen that at a time t0 at which the signal I exceeds the threshold value SW3, a counter is started. It can also be seen that the count of this counter is increased at a subsequent point in time t1, at which the signal I exceeds the threshold values SW3 and SW2. Since at this subsequent point in time t1 a specified counter limit value max2 is exceeded due to the mentioned increase in the counter reading, it is recognized at this point in time t1 that knocking is present and a suitable anti-knock measure can be initiated at this point in time t1, for example a delay in the ignition point . At time t2, the counts are reset again.

Furthermore, from the 4d It can be seen that at a later point in time t3 the signal I again exceeds the threshold value SW3 and that at this point in time t3 the counter is started again. It can also be seen that the count of this counter is increased at a subsequent point in time t4, at which the signal I again exceeds the threshold value SW3. As a result of this increase in the counter reading at time t4, the specified counter limit value max2 is not yet exceeded. If, at a later point in time t5, the signal I again exceeds the threshold values SW3 and SW2, then the counter reading is increased further, as a result of which the specified counter limit value max2 is exceeded. At this point in time t5, it is recognized that knocking is present, and a suitable anti-knock measure can be initiated, for example a retarded ignition timing. At time t6 the counts are reset again.

In the 4e a time counter is illustrated, which is started at the point in time t0 or t3, at which the exceeding of the threshold value SW3 is detected, and has a maximum running time which ends at t _{max b} . This timer is reset either when knocking is detected and anti-knocking measures are initiated, or after the specified maximum running time t _{max b} has elapsed, if no knocking has been detected up to that point.

In the 4f a further timer is illustrated, which is started at the point in time t2 or t6, at which anti-knocking measures have been initiated, and is reset after a maximum running time t _{max c} has elapsed. As will be explained below, anti-knock measures can be carried out during this period of time, for example the already mentioned delay in the ignition timing and--as will be explained below--freezing of the detection threshold that is present in each case.

The invention has been explained above using exemplary embodiments in which a plurality of knock detection threshold values are used to detect knock, these knock detection threshold values being threshold values which are compared with the output signal of the integration of the knock sensor output signal of the cylinder currently under consideration.

As an alternative to this, there is also the possibility of using different knock energy values as knock detection threshold values, for example knock energy values of 1, 0.9 and 0.8. In this alternative embodiment, a knocking detection is already allowed at a knocking energy that is less than 1. In this alternative embodiment, too, the lower threshold values must be exceeded several times in order to start a suitable anti-knock measure. Such anti-knock measures here, as above, are a knock ignition pullback and an upward freezing of the knock threshold. For example, to detect knocking, the lowest threshold 0.8 must be exceeded three times, the middle threshold twice, or both thresholds once in each case in order to detect knocking. When the highest threshold value is exceeded, there is always an immediate ignition pullback.

After some time without a threshold value being exceeded or without a knocking event being detected, the counter readings are reset as above in order to ensure that only temporally related events can lead to a suitable anti-knock measure. This happens when the counter is off 4e the threshold t _{max b} is reached.

In a method according to the invention, either a plurality of knock detection threshold values are used to detect knocking of an internal combustion engine, or alternatively, knocking is detected even at a knock energy of less than 1. It will continuously exceed each Monitored thresholds, exceeding these thresholds contributes to different extents to a knock decision. The greater the distance between the threshold values and the background noise, the more the corresponding exceeding of this threshold value contributes to knock detection. If the largest threshold value is exceeded, the ignition is immediately pulled back, as in known methods. Furthermore, there is a time limit within which the recognition process must be completed. This ensures that only temporally related events can lead to a suitable anti-knock measure.

As explained above, such an anti-knock measure is an ignition retardation and/or an upper limit or freeze of the knock detection threshold for a specified time.

A detection in particular with the associated ignition retraction deletes all counters that control the time limit.

Furthermore, an evaluation was proposed that recognizes the above-described increasing background noise caused by non-detected knockers by comparing it with the background noise of the other cylinders and converting it into a percentage deviation or determining an increase and then initiates a suitable anti-knock measure.

A combination of both approaches promises the most robust distinction between actual knocking and false knock detection, since both events are unlikely to occur simultaneously in knock-free operation.

Claims (8)

Method for detecting knocking of an internal combustion engine, in which an actual signal is determined by evaluating the output signals of one or more knock sensors, the actual signal determined is compared with a plurality of knock detection threshold values of different magnitudes, the number of times the knock detection threshold values are exceeded is counted using one or more counters, and a Presence of knocking is detected when the number of times the knock detection threshold values are exceeded is greater than or equal to a predetermined counter criterion for the number of times the number of times it has been exceeded, characterized in that the number of times the different levels of knock detection threshold values have been exceeded contributes to knock detection to different extents, and that with each violation the predetermined highest knock detection threshold value, a presence of knocking is detected. procedure after claim 1 , characterized in that if the number of times the lowest knock detection threshold value is exceeded is equal to or greater than a predetermined number which is greater than 1, a presence of knocking is detected. procedure after claim 1 , characterized in that three or more knock detection threshold values are predetermined, and that if the number of times the lowest knock detection threshold is equal to or greater than a predetermined first number, which is greater than 1, and the number of times the next higher knock detection threshold is equal to or greater is a predetermined second number which is 1 or greater than 1, a presence of knocking is detected. Method according to one of the preceding claims, characterized in that when the presence of knocking is detected, the values of the counter or counters are reset. Method according to one of the preceding claims, characterized in that the values of the counter or counters are reset after a predetermined time interval has elapsed if the predetermined counter criterion has not been met by then. Method according to one of the preceding claims, characterized in that a basic noise determined using the output signals of the knock sensor or sensors is additionally evaluated in order to detect the presence of knocking. procedure after claim 6 , characterized in that an increase in the background noise is detected using the output signals of the knock sensor or sensors. Device for detecting knocking of an internal combustion engine, which has one or more knocking sensors and a control unit, characterized in that the control unit for controlling a method according to one of Claims 1 - 7 is trained.

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