DE102015105220B3 - Method of performing a knock control - Google Patents

Abstract

The invention relates to a method for performing a knock control in an operation of an internal combustion engine, wherein a volume of combustion for at least one cylinder of the internal combustion engine is detected, wherein the detected volume is compared with a predetermined limit value to detect a knocking combustion, wherein when detected a knocking combustion, at least one parameter for a subsequent combustion of a cylinder is changed to at least reduce a knocking combustion, and wherein the limit value is adjusted depending on the change of the parameter, and wherein for at least one subsequent combustion of a cylinder, the adjusted limit value for the detection of a knocking combustion is used.

Description

The invention relates to a method for performing a knock control according to claim 1, such as from DE 10 2004 024 161 B4 is known.

In the prior art it is known to monitor combustion of an internal combustion engine with respect to a knocking combustion. If a knocking combustion is detected, as a measure in the next combustion, for example, the ignition angle of the affected cylinder is retarded by an ignition angle offset. Subsequently, the ignition angle offset is reduced again by a slow ignition angle advance. If a knocking combustion occurs again before the retardation of the retard angle retardation to the intended target ignition angle has been completely reduced, an immediate retardation of the ignition angle by the ignition angle offset is again carried out.

The object of the invention is to provide an improved method of performing a knock control to reduce knocking burns.

The object of the invention is achieved by the method according to claim 1. Further advantageous embodiments are specified in the dependent claims.

An advantage of the method described is that a more precise control for reducing knocking burns is achieved. This is achieved by detecting a combustion volume to detect a knocking combustion and comparing it with a limit value. Depending on the comparison, at least one parameter of the combustion is changed in order to at least reduce, in particular completely avoid, the occurrence of knocking burns.

Experiments have shown that it is advantageous to set the threshold depending on a change in the parameter being changed for a reduction in knocking burns. In this way it is achieved that the limit value used to detect a knocking combustion simultaneously depends on the change of the parameter. This makes it possible to adapt the limit value to changed combustion conditions. Thus, a more precise determination of the limit value for the respective combustion is achieved.

In one embodiment, the limit value is determined as a function of a reference volume, the reference volume being determined as a function of the measured volume of the combustion. The reference volume is an essential feature with which knocking combustion can be checked.

In one embodiment, the change in the parameter for reducing combustion for at least one additional cylinder is taken into account in order to determine the limit value. In this way a kind of averaging can be achieved. Experiments have shown that this approach causes an improvement in the smoothness of the internal combustion engine.

In a further embodiment, the parameter consists in an adjustment of the ignition timing of the combustion with respect to a predetermined Sollzündzeitpunkt, which is determined, for example, depending on load and speed. By adjusting the ignition timing, effective knock control can be achieved.

In a further embodiment, the threshold is determined as a function of an average of changes in the parameter for reducing knocking burns for at least two cylinders. In this case, a positive or a negative deviation of the parameter for reducing the knocking combustion of the cylinder relative to the mean value can be taken into account in order to determine the limit value. Thus, a further improvement in the smoothness of the internal combustion engine is achieved.

In a further embodiment, a deviation of the ignition angle retreat of the current cylinder from the mean value of the ignition angle retractions of at least two cylinders in the direction of a later ignition leads to an increase of the correction factor or the knock detection threshold.

In a further embodiment, a deviation of the ignition angle retreat of the current cylinder from the mean value of the ignition angle retractions of at least two cylinders in the direction of an earlier ignition leads to a lowering of the correction factor or the knock detection threshold.

In a further embodiment, a simple implementation of the control is achieved in that the change in the combustion parameter is taken into account as a factor with which the limit value is evaluated, in particular multiplied. Thus, improved limit can be calculated with simple means.

Show it

1 a schematic representation of a knock control via a Zündwinkeleingriff,

2 Diagrams for a schematic representation of a knock control,

3 a schematic representation of a method for a knock control,

4 Diagrams for a schematic representation of another knock control,

5 a schematic representation of another method for a knock control, and

6 a schematic representation of a control device for carrying out the method.

1 shows a schematic representation of a diagram in which over the time t a detected combustion volume 1 an internal combustion engine is applied. The combustion volume is detected, for example, with a knock sensor, ie a structure-borne noise sensor, and forwarded to a control unit. To determine a current combustion volume, a structure-borne sound signal of the internal combustion engine is detected. For an efficient determination and separation of the useful signal from noise sources, the structure-borne noise signal can first be band-pass filtered, then rectified and then integrated over a time range (knocking window) aligned with the respective combustion of the cylinder. The final integration value thus obtained represents the current combustion volume of a cylinder of combustion.

There is also a reference volume 2 shown, from a temporal averaging of the combustion volume 1 is calculated by the controller. Furthermore, a knock detection threshold 3 which uses a threshold for detecting a knocking combustion. The knock detection threshold 3 is determined by the control unit eg based on the reference volume and a knock detection factor. In a simple embodiment, the knock detection factor is stored, for example, in a memory with which the control unit is connected. The controller determines the knock detection threshold 3 is by multiplying the reference volume 2 with the knock detection factor.

In addition, a firing angle retreat 4 represented opposite to a Sollzündwinkel. The Sollzündwinkel is determined by the control unit, for example, depending on the load and the speed of the engine based on formulas, curves and / or tables that are stored in memory. The ignition angle retraction 4 is shown in angular units. The negative values represent a shift in the direction of a later ignition point relative to the Sollzündzeitpunkt or Sollzündwinkel. The ignition angle retreat 4 is determined by the control unit upon detection of a knocking combustion, for example as a function of the load and the speed of the internal combustion engine using formulas, tables and / or maps stored in the memory. With the aid of the ignition angle retraction, upon detection of a knocking combustion, the ignition angle is shifted in such a way that the occurrence of a knocking combustion is reduced, in particular avoided.

A knocking combustion is detected, for example, when the combustion volume 1 above the knock detection threshold 3 lies. This is the case, for example, for the first time t1 = 2.5 ms. As a result, the ignition angle retreat becomes 4 shifted by a set value towards a late ignition. This can be determined by the stage of the ignition angle retraction 4 t1 = 2.5 ms are detected at the first time. Subsequently, the ignition angle retreat 4 gradually shifted back towards the Sollzündwinkel early. The displacement is carried out until either the Sollzündwinkel is reached, or again a knocking combustion is detected. In the illustrated example, a knocking combustion is again detected at 7.5 ms at the second time t2. Thus, a shift of the ignition angle in the direction of a late ignition takes place again at this second time t2 again. Subsequently, the ignition angle retraction is again 4 reduced in the direction of the Sollzündwinkel until again a knocking combustion at the third time t3 is detected. Thus, also at the third time t3 again a shift of the ignition angle in the direction of a late ignition. Subsequently, the ignition angle retraction is again 4 degraded in the direction of the Sollzündwinkel. By means of this method it is attempted to reduce the occurrence of a knocking combustion, in particular to avoid it, since the knocking combustion can result in an increased load on the internal combustion engine, in particular damage to the internal combustion engine.

Experiments have shown that by the ignition angle retreat 4 also the combustion volume is lower. Thus decreases with a Zündwinkelrückzug 4 opposite the Sollzündwinkel the reference volume 2 from. Because the knock detection threshold 3 depending on the reference volume 2 is determined, also decreases the knock detection threshold 3 from. By lowering the knock detection threshold 3 There is a risk that already burns are considered knocking, which have a relatively low combustion noise. In extreme cases, the knock detection threshold 3 sink so far that already burns with whole normal combustion volume can be recognized as knocking. As a result of these false identifications of knocking burns, the ignition angle of the affected cylinder of the internal combustion engine is continuously adjusted in the direction of a late ignition and can no longer be regulated back to the starting level of the nominal ignition angle with suitable input threshold. As a result, the smoothness of the engine may decrease, but the consumption and the exhaust gas increase.

Experiments have shown that it is advantageous to set the limit value for detecting a knocking combustion in response to a change in the target ignition angle, i. to determine depending on the ignition angle retraction. To reduce or avoid knocking combustion, various parameters such as the ignition angle, a reduction of the load, ie the effective mean pressure, an enrichment of the mixture with fuel for internal cooling of the combustion chamber of the cylinder, a reduction of the compression ratio, an injection of cooling, detonation-preventing substances such as Water-ethanol, propane, etc. are changed. If at least one of these parameters is changed in order to reduce or avoid a knocking combustion, a change of the at least one parameter for calculating the limit value can also be taken into account.

A quick and effective intervention in the combustion is achieved by means of the ignition angle, that is the ignition timing. By a shift of the ignition timing relative to a Sollzündzeitpunkt in the direction of a late combustion a knocking combustion is reduced, in particular avoided. The Sollzündzeitpunkt is determined as a function of the load and the speed of the internal combustion engine by appropriate procedures, curves and diagrams. If now a knocking combustion is detected by a control unit, at least one parameter of the combustion is changed with respect to the desired value, in particular the ignition timing is shifted in the direction of late in order to reduce or avoid the knocking combustion. In addition, the changed parameter of the combustion is subsequently shifted stepwise or continuously in the direction of the setpoint.

2 shows a first diagram 5 in which the ignition angle retreat 4 and a correction factor 6 over time, that is represented over combustion cycles of a cylinder. Under the first diagram 5 is a second diagram 7 shown for the same combustion cycles of the cylinder as the first diagram 5 the current combustion volume 1 , the reference volume 2 , the knock detection threshold 3 and the knock detection threshold used in the prior art 8th are shown.

There is also a third diagram 9 over the same combustion cycles of the cylinder as the first and second diagrams 5 . 7 shown, the third diagram 9 a relative combustion volume 10 and a knock detection factor 11 represents. The current combustion volume divided by the reference volume represents the relative combustion volume 10 From the measured current combustion volumes of a fixed number of previous burns such as the number 5 , For a cylinder based on a flowing averaging the reference volume of the cylinder is formed.

The knock detection factor 11 is determined from a predetermined value and the correction factor. For example, the knock detection factor becomes 11 from a multiplication of the predetermined value with the correction factor 6 calculated. At a zeroth time start point t0 is the ignition angle retreat 4 the value 0. The value of the correction factor is the same 6 the value 1. The combustion volume 1 is smaller than the knock detection threshold until a first time t1 3 , At the first time t1 exceeds the combustion volume 1 the knock detection threshold 3 , Thus, then at a second time t2, the ignition angle retreat 4 set in the direction of late. At the same time, it depends on the ignition angle retraction 4 the correction factor 6 elevated. Depending on the chosen embodiment, the correction factor 6 proportional to the increase of the ignition angle retraction 4 also the correction factor 6 increase. The dependence between the ignition angle retraction 4 and the correction factor 6 is stored in the memory eg as a formula or as a characteristic. Based on the third diagram 9 can be seen that at the first time t1 and the relative combustion volume 10 increases and the knock detection factor 11 exceeds.

By introducing a correction factor dependent on the ignition angle retraction and determining the knock detection threshold 3 depending on the correction factor 6 the knock detection threshold can be kept at an initial level (diagram 7 ). Thus, false detections of knocking events are avoided by a decrease in the reference noise and the resulting knock knock threshold by the ignition angle retreat.

The ignition angle is controlled independently of the ignition angle retraction and depending on the combustion noise in the direction of the Sollzündwinkel again early. Thus, an optimum ignition angle can be maintained for each cylinder. 2 shows the corresponding values for only one Cylinder. This procedure is performed for each cylinder of the internal combustion engine.

On the basis of the second diagram can be seen how, according to the prior art, the previous knock detection threshold 8th has changed. After the previous procedure, the previous Knockferkennungsschwelle 8th reduces, so for example, a combustion volume at a third time t3, which is less than the original knock detection threshold 3 is, was also recognized as knocking combustion. This misrecognition is avoided using the new method described.

3 shows a schematic representation of a program flow for a method for knock control according to the embodiment of 2 , At the start of the method, initial values for the limit value, the correction factor and the knock recognition factor are read from a memory by the control unit. Subsequently, the control unit detects at program point 110 the current combustion volume for combustion of a cylinder. Then at a program point 120 calculates a reference volume depending on the detected combustion volume. The reference volume is calculated, for example, by averaging a predetermined number of previous measured actual combustion volumes. In addition, the current combustion volume is divided by the reference volume and a relative combustion volume 10 determined.

At a following program point 130 becomes the relative combustion volume 10 with a knock detection factor 11 compared. The knock detection factor is calculated from the predetermined value for the knock detection factor and the correction factor 6 determined. In the simplest case, the knock detection factor is multiplied by the correction factor to obtain the weighted knock detection factor. However, other dependencies may also be used, such as experimentally determined.

Returns the comparison at program point 130 that the relative combustion volume 10 is greater than the rated knock detection factor, knocking combustion is detected and becomes a program point 140 branched.

Returns the comparison at program point 130 that there is no knocking combustion, so becomes program point 110 branches back.

At program point 140 At least one parameter of the following combustion is changed for the cylinder in such a way that the probability for a knocking combustion is reduced, in particular a knocking combustion is prevented. This can be done, for example, that the ignition is shifted in the direction of a late ignition. To change the parameter, appropriate tables, characteristics or formulas are stored. At a following program point 150 the change in the parameter for a subsequent combustion is taken into account to calculate a new limit, in particular by a new knock detection factor. For this purpose, appropriate tables, formulas or characteristic curves are stored which define a new knock detection factor as a function of the change of the parameter. For example, a correction factor may be used to determine the new knock detection factor. The correction factor may, for example, depend directly on the parameter, in particular on the change of the parameter. For this purpose, for example, a characteristic can be stored, as in diagram 5 is shown. The newly calculated correction factor becomes when the program is executed again at program point 130 taken into account to calculate the knock detection factor.

In the example of 2 the value of the correction factor increases proportionally with the increase of the ignition angle retraction. Depending on the selected embodiment, other dependencies between the change of the parameter, in particular the change of the ignition angle and the limit value, in particular the correction factor can be stored. The evaluated knock detection factor is calculated, for example, by multiplying the predetermined knock detection factor by the correction factor.

After execution of program point 150 becomes program point 110 branches back. This method is performed for each of the cylinders of the internal combustion engine.

4 shows a fourth, a fifth and a sixth diagram 12 . 13 . 14 , which are plotted over time, ie combustion cycles of a cylinder. In the fourth diagram 12 is the ignition angle retraction 4 , the correction factor 6 , and represents an average of the retractions of at least two, in particular all cylinders of the internal combustion engine. In the fifth diagram 13 is the current combustion volume 1 , the reference volume 2 , the previous knock detection threshold 8th in the prior art and the knock detection threshold 3 presented the new method. In the sixth diagram 14 are the knock detection factor 6 and the relative combustion volume 10 shown.

An average 15 the Zündwinkelrückzuge at least two cylinders, in particular the Zündwinkelrückzüge all cylinders is replaced by a Averaging of the ignition angle retractions formed. The correction factor 6 A cylinder becomes dependent on a positive or a negative deviation of the ignition angle retreat of the cylinder from the mean value 15 determined. For this purpose, corresponding formulas or characteristic curves are stored, which depend on the positive or negative difference between the mean value 15 and the ignition angle retraction of the respective cylinder the correction factor 6 set for the next combustion. This allows the firing angles of all cylinders to be kept close to their mean. This increases the smoothness of the engine. Thus, a change in the reference volume by the Zündwinkelverstellung not be compensated exactly.

For cylinders with retard angle retardation deviating too late from the mean value, the correction factor and thus also the knock detection threshold are raised. For cylinders with ignition angle retardation deviating early with respect to the mean value, the correction factor and thus also the knock detection threshold are lowered. Thus, as the firing angle deviates, the sensitivity of the knock detection is lowered, i.e., delayed. the firing angle can more easily return to the average of all firing angles of the cylinders. If the ignition angle deviates toward early, the sensitivity is increased. This increases the probability of detecting a knocking combustion with the ignition angle retardation, which brings the ignition angle of the cylinder back toward the average of all cylinders. By infinitely raising the knock detection threshold with ignition angle deviations to late, knocking burns can always be reliably detected and corrected.

That on the basis of 4 described knock control method allows an adjustment of the limit to both higher and lower values. In the fourth diagram 12 It can be seen that with an increase of the ignition angle retraction, ie with larger negative values, the correction factor 6 above the value 1 increases. When the ignition angle retraction is reduced to smaller negative values, the correction factor decreases 6 again and falls below even the value 1. In the fifth diagram 13 it can be seen that the current combustion volume 1 at the first, second and third time t1, t2, t3, the knock detection threshold 3 exceeds. The knock detection threshold increases again by a predetermined value each time the knock detection threshold is exceeded. Even at a fourth time t4, the combustion volume exceeds 1 the knock detection threshold 3 , Will not exceed the knock detection threshold 3 by the combustion volume 1 If more is detected, the knock detection threshold drops 3 gradually back off. At a fifth time t5, the correction factor corresponds 6 the value 1 and cuts in the illustrated embodiment, the average 15 , The knock detection threshold 3 continues to decrease so long until a sixth time t6 again the combustion volume 1 the knock detection threshold 3 exceeds. As a result, the knock detection threshold becomes 3 increases and also the ignition angle retraction 4 enlarged again. The sixth diagram is analogous to the fifth diagram 14 the course of the knock detection factor 6 compared to the relative combustion volume 10 ,

5 shows a schematic program flow for performing the method according to the 4 , At program point 200 the procedure is started. At the start of the method, initial values for the limit value, the correction factor and the knock recognition factor are read from a memory by the control unit. At a following program point 210 the controller detects the current combustion volume. The controller then calculates at a following program point 220 a reference volume. The reference volume is calculated, for example, by averaging a predetermined number of previous measured actual combustion volumes. In addition, the current combustion volume is divided by the reference volume and a relative combustion volume 10 determined.

At a following program point 230 will check if the relative combustion volume 10 is greater than a knock detection factor 11 , The knock detection factor 11 is determined from the predetermined value for the knock detection factor and the correction factor. In the simplest case, the knock detection factor is multiplied by the correction factor to obtain the weighted knock detection factor. However, other dependencies may also be used, such as experimentally determined.

Returns the comparison at program point 230 in that the relative combustion volume is smaller than the knock detection factor, then becomes program point 210 branches back. Returns the comparison at program point 230 that the relative combustion volume is greater than the knock detection factor, becomes a program point 240 branched.

When starting at program point 200 Also, an average value for the change of the parameter for influencing the combustion to avoid a knocking combustion is set.

At program point 240 an average value for the change of the parameter of the combustion of at least two, in particular all cylinders of the internal combustion engine for avoiding the knocking combustion is formed. The parameter may be, for example, the ignition angle adjustment with respect to the Sollzündwinkel. The Sollzündwinkel is determined depending on the load and the speed of the engine.

In addition, a correction factor for the considered cylinder is formed depending on a positive or negative deviation from the mean value. For this purpose, characteristics, tables or formulas can be stored that determine or correct the correction factor depending on the ignition angle retraction of the cylinder and the deviation of the ignition angle retraction of the cylinder from the mean value 15 set the ignition angle retractions. Subsequently, the newly calculated correction factor is stored. Then becomes program point 210 branches back. On a subsequent run of the program, the new correction factor for determining the knock detection factor for program point 230 used. In this way, an adjustment of the correction factor in both directions can take place.

6 shows a schematic representation of a possible structure of a function of a control unit 16 , The control unit 16 has a first, a second and a third input 17 . 18 . 19 on. About the first entrance 17 For example, the load of the internal combustion engine, via the second input 18 the speed of the internal combustion engine and the third input 19 the ignition angle of the current cylinder is read. Depending on the load, the speed and the ignition angle of the current cylinder is from a map 25 a correction factor is read out.

If the ignition angle retraction of the current cylinder has a positive distance to the mean value, then the determined value for the ignition angle retraction of the cylinder is additionally reduced by a negative value. If the ignition angle retraction of the current cylinder has a negative distance to the mean value of the ignition angle retractions, then the determined ignition retraction is increased by a positive value.

It also has a fourth entrance 20 recorded a cylinder angle retraction for the current cylinder. In addition, an average value for ignition-angle retractions of at least two cylinders, in particular all cylinders, is determined. Furthermore, via a fifth input 21 an average value of at least two firing angle retractions of two cylinders, in particular an average of all firing angle retractions of all cylinders is detected.

Based on the cylinder retraction of the current cylinder and the mean value is at a first program block 22 determines a deviation from the mean.

If the ignition angle retraction of the current cylinder has a positive distance to the mean value, then the determined value for the ignition angle retraction of the cylinder is additionally reduced by a negative value.

Based on the deviation from the mean and on the basis of the correction factor from the map 25 is determined by a rating, in particular a multiplication in a second program block 23 a new correction factor is determined. The correction factor becomes a third program block 24 fed.

In addition, the fourth program block 24 a predetermined knock detection threshold 3 fed. The third program block 24 performs a multiplication of the knock detection threshold 3 with the correction factor and thus determines the current knock detection threshold, which also represents a corrected knock detection threshold. The current knock detection threshold is used to check a knocking combustion of at least one cylinder of the internal combustion engine in a subsequent combustion.

The same method can also be used to replace the knock detection threshold with the knock detection factor in the fourth program block 24 to be fed and adapted depending on the correction factor.

Claims (7)

A method of performing a knock control in an internal combustion engine operation, wherein a volume of combustion is detected for at least one cylinder of the internal combustion engine, wherein the detected volume is compared to a predetermined threshold to detect knocking combustion, wherein upon detecting a knocking combustion at least a parameter for a subsequent combustion of a cylinder is changed to at least reduce knocking combustion, and wherein the limit value is adjusted in response to the change in the parameter, and wherein for at least one subsequent combustion of a cylinder, the adjusted limit value for knocking combustion detection wherein the internal combustion engine comprises a plurality of cylinders, wherein the limit value for the detection of a knocking combustion in a first cylinder depends on a change of a parameter of the combustion to avoid a knocking verb tion for at least one further cylinder of the internal combustion engine is determined, characterized in that the limit value for the review of a knocking combustion is determined in the first cylinder depending on an average of the changes in the parameters for avoiding a knocking combustion for burns of at least two cylinders of the internal combustion engine.  The method of claim 1, wherein the parameter represents an adjustment of an ignition timing of the combustion with respect to a predetermined Sollzündzeitpunkt.  Method according to one of the preceding claims, wherein the limit value depends on a reference volume, and wherein the reference volume is determined depending on the detected volume.  Method according to one of the preceding claims, wherein a positive and / or a negative deviation of the change of the parameter of the cylinder from the mean value of the changes of the parameters of the at least two cylinders are taken into account.  The method of claim 4, wherein a deviation of the ignition angle retraction of the current cylinder from the mean of the Zündwinkelrückzüge least two cylinders towards a later ignition leads to an increase of the correction factor and the knock detection threshold.  A method according to claim 4 or 5, wherein a deviation of the ignition angle retreat of the current cylinder from the mean value of the ignition angle retractions of at least two cylinders in the direction of a previous ignition leads to a reduction of the correction factor or the knock detection threshold.  Method according to one of the preceding claims, wherein the change of the parameter for the combustion is taken into account as a factor with which the limit value is evaluated.

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