WO2014071900A1

WO2014071900A1 - Adaptation of a knock control

Info

Publication number: WO2014071900A1
Application number: PCT/DE2012/001099
Authority: WO
Inventors: Michael Günther; Matthias Kratzsch; Alexander Stahr
Original assignee: Iav Gmbh
Priority date: 2012-11-12
Filing date: 2012-11-12
Publication date: 2014-05-15
Also published as: DE112012007121B4; DE112012007121A5

Abstract

The invention relates to a method and a corresponding device for adapting a knock control for an externally-ignited internal combustion engine for determining a knock level reference value for controlling knock, which value is individual to an internal combustion engine and operating point. When operating the internal combustion engine, an ignition angle is varied for at least one cylinder of the internal combustion engine, in order to determine a position of a knock limit depending on a knock level. Structure-borne sound waves of the internal combustion engine are detected by at least one knock sensor and emitted as the knock level. The measurement values for knock levels depending on the ignition angle, ascertained when varying the ignition angle, are used to determine the knock level gradients depending on the ignition angle. A knock level reference value individual to an internal combustion engine is equated to the knock level of a specific ignition angle, at which the knock level gradient corresponds to a limit knock level gradient.

Description

Adaptation of a knock control Technical area

The present invention relates to a method and a device for adapting a knock control of a spark-ignited internal combustion engine.

State of the art

In an Otto engine combustion under normal conditions, the mixture is specifically ignited by a spark ignition. During combustion, the flame front moves from the ignition location three-dimensionally through the combustion chamber until the mixture is burnt. In a knocking combustion, a part of the mixture ignites at hot spots of the combustion chamber by the increased

Combustion pressure and the increased combustion chamber temperature during the

Burning independently, even before the flame front reaches these areas. It comes to an explosive combustion, causing the

Burning rate increases and a correspondingly higher

Combustion pressure results. The resulting pressure waves and pressure oscillations propagate through the components of the internal combustion engine as structure-borne noise and are perceived as knocking.

To increase the efficiency of spark-ignition internal combustion engines high compression ratios are sought. In contrast, however, stands the associated increased tendency to knocking burns. The knocking burns the thermal and mechanical loads of

Internal combustion engine and thus the risk of destruction of the internal combustion engine increases. However, low knock levels also result in ongoing knocking

Burns do not necessarily cause damage, so the knock level must always be considered in conjunction with the frequency of knocking burns. For rapid suppression of dangerous beating burns, the ignition timing is adjusted as a priority. Furthermore, other methods are possible to

to counteract knocking burns. To detect knocking burns, knock sensors are generally used, which are arranged, for example, on the crankcase of the internal combustion engine and determine the residual body sound of the knocking combustion present there. The knock sensors or structure-borne noise sensors convert the structure-borne sound vibrations resulting from the knocking combustion into alternating-current signals. The thus detected structure-borne sound signals of the knock sensor become one

Evaluation unit, for example, supplied to an engine control unit and processed accordingly by filters so that dangerous knocking burns can be detected.

In order to operate the engine as efficiently as possible at the knock limit for optimizing efficiency, knock controls are provided. In these knocking controls, beating burns are up to a predetermined one

Knock strength or knock intensity allowed that do not lead to damage to the internal combustion engine. Conventional knock control methods form a signal of the structure-borne sound oscillation which is averaged over several combustion cycles and represents a reference signal. To assess the combustion, a currently determined structure-borne noise signal is then compared with the previously determined reference signal. For this, a distance or a relationship between currently determined

Structural sound signal and reference signal evaluated. If the reference signal is called noise and the currently determined structure-borne noise signal is a signal, the signal-to-noise ratio to be evaluated or a signal-to-noise ratio can be evaluated

be assumed. Assuming that the signal is knocking

Burns always stands out clearly from the non-knocking burns, the signal is therefore appreciably greater than the noise, the detection value of the signal-to-noise ratio, from which a knocking combustion occurs over

Cylinder, speed and load stored in a map and thus fixed.

Since the ignition, as the ignition angle at a distance to the top dead center of the

Internal combustion engine is specified between the compression and power stroke, the combustion and the tendency to knock decisively influenced, this is set later in time when detected knocking combustion. A knocking combustion is detected when a current signal-to-noise ratio is a corresponding one

Detection value exceeds. The signal-to-noise ratio at which a change between not dangerous knocking combustion and dangerously knocking combustion occurs, also referred to as knock limit.

From these conventional knock control methods, as described, for example, in US Pat

DE 195 49 175 A1 or EP 0 166 033 B1 and a multiplicity of further publications are described, among others some disadvantages are derived. For example, it takes a lot of effort to optimize the signal-to-noise ratio. The knock sensor is to be arranged on the internal combustion engine so that mainly

Combustion noise can be detected in comparison to noise. The

Noise directly affects the signal-to-noise ratio. The structure-borne sound signal detected by the knock sensor, which represents a knocking level, must be used for

Minimizing the noise component of a complex signal processing are subjected. The knock control procedures must be adapted so that also scatters that are to be expected in mass production of internal combustion engines are included.

In the conventional knock control methods, measures are taken to prevent knocking combustion after the dangerously beating burns have taken place. Since the reference level is formed from the combustion noise of the internal combustion engine itself, any increase in the noise of the internal combustion engine leads to an increase in the reference level. At a fixed signal-to-noise ratio thus increases the minimum detectable actual level, so that knocking burns are not recognized as such and the destructive burns can not be counteracted. These knocking sounds in turn lead to a further increase of the reference level, whereby a process of automatic deactivation of the knock control can be set in motion. In contrast, a reduction in the noise level results in a reduction in the minimum detectable actual level, so that dangerously knocking burns are detected although no destructive combustion has occurred. The ignition angle would be unnecessarily late, which increased

Loss of efficiency would result. In internal combustion engines with low

Combustion noise, poor transmission of structure-borne sound or unfavorable knock sensor positioning, knock control is insufficiently feasible.

Due to the relative evaluation of the structure-borne sound vibrations aging or maturity-related changes in the noise level of Internal combustion engine insufficiently taken into account. A trend evaluation is not possible. Stochastic disturbances due to worn or defective

Engine components cause increased noise levels, which are falsely recognized as knocking combustion.

Object of the invention

The object of the invention is to provide an improved method for adapting a knock control and an improved device for adapting a knock control, wherein the internal combustion engine is operated at optimal efficiency at the knock limit.

Solution of the task

The object is achieved by a method for adaptation according to the characteristics of

Claim 1 and of claim 7 and solved by a device for adaptation according to the features of claim 9.

Description of the invention

The invention provides a comparison with the prior art improved method for adapting a knock control and an improved device for adapting a knock control, wherein an improved adaptation of a knock limit occurs and the internal combustion engine is operated optimal efficiency at the knock limit. The advantageous invention provides an adaptable knock control system that independently adapts itself from an internal combustion engine to further model lines of an engine family as well as to individual differences of the respective internal combustion engine from a series production without additional effort. The process steps necessary for the method are divided into a development phase and a use phase of the internal combustion engine. During the development phase are based on an exemplary internal combustion engine

Engine ECU accomplished that are valid for a complete series production of the corresponding internal combustion engines. The adaptation of the knock control is then carried out in the use phase of the respective individual internal combustion engine from this series production. During the development phase, an exemplary internal combustion engine is placed on an engine test bench and an ignition angle variation is performed for each operating point and each cylinder. The operating point is determined by an engine speed and an engine load. The engine load can, for example by a

Engine torque or by a combustion medium pressure will be described. The interpolation points of the operating points for the engine speed and engine load are predefined according to a suitable resolution of a characteristic field. The Zündwinkelvariation is performed for each operating point and each cylinder by the ignition angle is adjusted starting from a current ignition angle in the late direction and then in predefinable steps back towards early until the knock limit has been briefly and significantly exceeded. Subsequently, the ignition angle is adjusted again in the direction of late.

As a termination criterion for the adjustment of the ignition angle, a predefined limit knock intensity is used, for example, by means of a cylinder pressure measurement, which describes a knock limit. Exceeding the knock limit during the

Ignition angle adjustment serves to be able to determine the position of the knock limit as a function of the ignition angle exactly. During operation of the

Internal combustion engine on the engine test bench, the combustion pressure in the interior of the cylinder is detected by a pressure sensor and evaluated accordingly as knock strength. The knock intensity is a measure of the extent to which a pressure curve of a dangerously knocking combustion compared to a normal combustion

different. The limit knock strength is defined, which is the knock limit

describes. The knock strength is given as pressure. During the adjustment of the ignition angle, in addition to the pressure measurement, the structure-borne sound vibrations of the internal combustion engine are detected by at least one knock sensor and output as a knock level in the form of a voltage. For knock limit is then in addition to the Grenzklopfstärke also a Grenzklopfpegel available.

In accordance with the invention advantageously, the adjustment of the ignition angle in

Direction late and early in a predefined Zündwinkelsequenz performed with certain Zündwinkelschritten, which can also be specified operating point dependent. As a result, for operating points in which the risk of knocking combustion is increased, an adapted firing angle sequence can be specified in which the firing angle is changed, for example, in smaller steps. The measured values for knock strength and knock level as a function of the ignition angle can be described or approximated by compensation functions. In the simplest version, the compensation function can be carried out by the simple linear connection of the measured values as interpolation points. Alternatively, suitable mathematical functions can be approximated to the measured course of the measured values, the measured values serving as reference points. From the determined measured values of the knock level ignition angle curve, a gradient curve, that is to say the change in the knock level as a function of the ignition angle, can be determined. For this purpose, for example, a polynomial function of at least second degree as

Compensation function can be used. Then the determination of the

Gradient curve in a simple manner by a mathematical derivation of the created for the description of the knock level Zündwinkelverlaufs compensation function, ie the differentiation of the ignition angle.

The knock limit can thus be described by the limit knock level, the limit knock level, and additionally by a limit knock level gradient. Of the

Grenzklopfpegelgradient is set equal to the Klopfpegelgradienten a certain ignition angle at which a knock strength of the Grenzkloppfstärke corresponds, the course of the knock strength depending on the firing angle by a

Cylinder pressure measurement is determined during the Zündwinkelvariation. For the

Description of the knock limit over the limit knock level gradient will be the

Non-linear relationship between knock strength or knock level and Zündwinkelverstellung exploited. The knock intensity or the knock level increases disproportionately with an increasingly earlier ignition angle. Thus, the Klopfpegelgradient increases with increasingly earlier ignition angle. This can be the

Limit knock gradient can be used to describe the knock limit.

The limit knock level becomes coincident with the limit knock level gradient

Operating point individually in an advantageous manner cylinder individually stored in an engine control unit for the internal combustion engine. The advantage of the method according to the invention lies in the fact that the limit knocking gradient for adapting the

Knocking control is used during the use phase, which is valid regardless of the background noise of the internal combustion engine. The predefined limit knock level is used as the basic condition. In a further step in the development phase, from a sufficient sample of internal combustion engines, a mean value of an operating point-specific limit knocking level representative of a series deviation can be determined, adjusted and stored in each individual engine control unit of an internal combustion engine. At the end of the development work on the test bench are in the engine control unit

Internal combustion engine advantageously for each operating point and each cylinder of Grenzklopfpegelgradient for the adaptation of the knock control during the

Use phase and the limit knocking level as a basic condition of a

Knock level setpoint stored for knock control.

In the use phase of the individual internal combustion engine installed, for example, in a vehicle, an adaptation is carried out on the basis of the values already stored in the engine control unit for the limit knock gradient gradient in order to determine an engine-specific limit knocking level for optimum operation at the knock limit. Adaptation is necessary as each individual

Internal combustion engine has an individual signal transmission of the knocking combustion on the engine structure and the sensor to the evaluation and thus the individual internal combustion engine subject to certain tolerances and changes that affect the function and ultimately the combustion. These tolerances result from the series production, which in the production of

Internal combustion engine occurs. Series deliveries can be made for example

Manufacturing tolerances of mechanical elements or from differences in the signal detection and transmission result. In addition to the series production of a model series of an internal combustion engine, the internal combustion engines can also be equipped with different units and modules. Also aging and wear phenomena pull a change of the operation of the

Internal combustion engine after itself. These influences can be responded to by the adaptation. The adaptation is performed during the operation of the internal combustion engine over the entire service life under predetermined conditions and use intervals.

The method of adaptation, in particular for the determination of a

Internal combustion engine individual and operating point individual knock level setpoint for a knock control comprises the Zündwinkelvariation for at least one cylinder during operation of the internal combustion engine to a position of the knock limit in To determine the dependence on the knock level. Here are the

Structure-borne sound vibrations of the internal combustion engine detected by at least one knock sensor and output as a knock level. The measured values for knock levels as a function of the ignition angle, determined during the ignition angle variation, are mapped by a knock level compensation function. Based on this

Knock level equalization function becomes a knock level gradient depending on

Ignition angle determined and an internal combustion engine individual Klopfpegelsollwert equated to the knock level of a specific ignition angle at which the

Tap level gradient corresponds to a Grenzklopfpegelgradienten.

In other words, the valid for the individual internal combustion engine

Operating point-specific knock level setpoint based on the generally valid

Knock level gradient Zündwinkverlaufverlaufs and the Grenzklopfpegelgradienten determines which are stored in the engine control unit. It will be the

Zündwinkelvariation performed and the engine individual

Knock level setpoint determined by determining the knock level for which the knock level gradient corresponds to the limit knock level gradient. The knock level setpoint is then set equal to this knock level.

Advantageously according to the invention, the adaptation takes place during a quasi-stable

Operating state of the internal combustion engine, in which only low speed and

Load changes occur. If such an operating point is detected, the adaptation is carried out for the respective operating point. The adaptation can additionally

be carried out individually for each cylinder. For the detection of a quasi-stable

Operating point, among other things, a predefined threshold of a load and speed change speed can be used. Furthermore, for the decision to adapt to forecasts of impending signal or

Changes in the operation of the internal combustion engine.

The operating point-specific and possibly cylinder-individual adaptation is effected by a Zündwinkelvariation. The ignition angle is based on a

Ignition sequence adjusted, which corresponds to the ignition angle sequence during the application. Alternatively, a simplified ignition angle sequence or a firing angle sequence adapted to the operating point can also be used. During the adjustment of the ignition angle of the self-adjusting knock level on the at the Internal combustion engine installed knock sensor detected. As a result, a plurality of measured values of the knocking level as a function of the firing angle are available for the respective operating point, so that a profile of the knocking level over the firing angle results. The course is again described or approximated by a compensation function. By the first mathematical derivation of the compensation function according to the ignition angle for the individual engine operating point and possibly cylinder-individual course of the Klopfpegelgradienten is generated. For the firing angle at which the course of the knock level gradient coincides with the limit knock gradient gradients stored in the engine control unit during the development phase, the corresponding one becomes

Knock level determined using the compensation function and as

internal combustion engine individual limit knock level used. In other words, there is a recalculation to a knocking level on the basis of the operating point and, if appropriate, cylinder-specific course of the knocking level gradient, for the firing angle of which the limit-knocking gradient coincides with the value of the operating point and possibly cylinder-individual course of the knocking level gradient. The operating point and possibly cylinder-individual as well as individual combustion engine-specific limit knock level determined in this way represents the knock limit at which the internal combustion engine is to be operated.

In other words, the method for adaptation comprises, in particular, for the determination of an individual engine-internal and operating-point-specific one

Knock level set point, the ignition angle variation for at least one cylinder during operation of the internal combustion engine to determine a position of the knock limit depending on the knock level. The structure-borne sound waves of the internal combustion engine are detected by at least one knock sensor and output as a knock level. The measured values for knock levels as a function of the ignition angle, determined during the ignition angle variation, are mapped by a knock level compensation function. On the basis of this knock level compensation function, a knock level gradient as a function of the ignition angle is determined, and an engine-specific knock level setpoint is set equal to the knock level of a specific ignition angle at which the

Tap level gradient corresponds to a Grenzklopfpegelgradienten.

From the difference between the predefined values already stored in the engine control unit

Grenzklopfpegels and internal combustion engine individual Grenzklopfpegels arises the adaptive component. In other words, the predefined limit knock level is corrected based on the engine knock limit level. The one for the

Knocking level required Knockpegelsollwert results according to the invention as a sum of the predefined Grenzklopfpegel and the adaptive share. In principle, it is also possible to use the currently determined engine-specific limit knocking level without deleting the predefined limit knocking level. Thus, the predefined limit knock level is always present as a fallback level. By means of a freely selectable weighting, first adaptations to the other operating points without successful adaptation can already be interpolated or extrapolated. Thus already the first successful adaptation corrects the knock level setpoint of the

Knock control in the entire control range.

For this purpose, a device for adapting a knock control is provided, in which a plurality of memory cells are provided which have a unique operating point assignment. For the adaptation of the knock control are for an operating point of

Internal combustion engine associated with at least two memory cells in the device. A predefined knock level setpoint is stored in a first memory cell and a limit knock level gradient is stored in a second memory cell. For each operating point, a further memory cell may be provided in the device, in which the adapted engine-specific knocking level nominal value or the correction of the

predefined knock level setpoint for the engine-individual

Knock level setpoint can be stored as an adaptive component.

After each successful adaptation, an operating point and possibly cylinder-individual status counter is increased by a predefined count value and

stored accordingly in a status map. The interpolation points are identical to those of the adaptation parameter field, so that each adaptation value is assigned exactly its status value. The current adaptation result is averaged with the stored value. If the difference between the two values is outside a tolerance to be defined, the

Status counter reduced to allow re-adaptation under appropriate conditions. The reliability of the adaptation value is guaranteed if the status counter has reached or exceeded a threshold intended for this purpose. Occurs during the first part of the adaptation sequence, ie at the

Ignition angle early adjustment, a significant signal interference on, the adaptation is terminated and restarted. If this is the case in the second part of the adaptation sequence, the result, as described above, stored in the adaptation map. The status counter is increased by a count which is reduced compared to the count value of a successful adaptation.

If a safety threshold value of a knocking level in relative advance of the predefined limit knocking level before the desired limit knocking gradient gradient is reached in the ignition angle early adjustment, then it can be assumed that the noise level is outside a permissible range. Then the adaptation is aborted.

The start values are kept unchanged. If the behavior is repeated in further adaptation experiments, the relevant cylinder-specific adaptation point is marked as not adaptable in order to avoid further unnecessary adaptation attempts. A corresponding entry can be made in the diagnostic system.

The Knockpegelsollwert also necessary for the knock control, the current and stable knock level during operation of the internal combustion engine as

Voltage signal is determined as a moving average over a defined number of cyclically consecutive knock sensor signals. The number of signals used for the averaging is predetermined by signal-influencing parameters. Such parameters can be, for example, speed, load and

Combustion center position and its rate of change in

be dynamic operation of the internal combustion engine. You can also continue

Changes in the signal processing, such as when switching the signal evaluation, or the connection or disconnection of engine components, such as superchargers or cargo flaps, are included in the consideration.

For knock control, a controller is used in which the knock level actual value is compared with the adapted engine-specific limit knock level. The control variable used is the ignition angle. In accordance with the invention advantageously a PID controller is used for the controller.

The described method provides a knock control with which the individual internal combustion engine can be operated significantly closer to the knock limit and thus significantly closer to the thermodynamic optimum than conventional knock control methods. This increases the efficiency of the Internal combustion engine compared to conventional internal combustion engines significantly, which is made clear for example by a fuel economy.

The inventive method for knock control allows further

Diagnostic functions. Thus, during operation of the internal combustion engine, a stochastic noise can be detected by a standard deviation of the knock level operating point and cylinder selectively stored in a map.

If the mean calculated from the map exceeds a predefined value

Threshold, it is concluded that a probable stochastic noise. A trend detection of the noise level of the internal combustion engine through the analysis of the D component of the controller is possible. During the adaptation can also the

Standard deviation of the knock level can be determined via ignition angle. If the gradient of the thus determined curve of the standard deviation of the knock level via ignition angle in a defined range exceeds a predetermined limit value, a stochastic noise is detected. Depending on the result of this

Diagnosis can be adapted to the parameters for adaptation and control. A predefined gradient of the standard deviation can also be used as a termination criterion for the ignition angle adjustment of the adaptation.

For optimum knock control, the knock sensor signal is detected, filtered and evaluated in the representative time and frequency domain. For a time window or a crankshaft angle window is defined as a function of load and speed. The frequency filtering is performed by a filter having a passband width from the first to the third combustion chamber natural frequency. The passband bandwidth is defined by a high and lowpass frequency. In contrast to conventional knock control, the window is already before top dead center, the

Ignition timing is assigned, opened to the actual knock level during adaptation can safely capture. Furthermore, pre-ignition can also be detected by comparing the actual knocking level with a corresponding threshold value and, when it is exceeded, concluding an extremely strongly knocking combustion. All information resulting from the diagnostic functions can be further processed in the engine control unit in order to further optimize the operation of the internal combustion engine. The knock control method according to the invention reduces the outlay for optimum sensor placement. The adaptation of the internal combustion engine individual Grenzklopfpegels allows a stable knock control with high control quality, based on series variations between different internal combustion engines, to

Deviations in the measuring chain, to the aging of the internal combustion engine, to

different fuel qualities and to different loud noise adapts. In order to avoid the loss of efficiency resulting from the noise, it is proposed to change the noise at a Zündwinkeleingriff

observe. Follow the caused by the Zündwinkeleingriff

Noise changes that are not related to the relationship between firing angle and noise level within a deviation described by a threshold, these are recognized as a fault. If this threshold is exceeded for a predetermined number of combustion cycles, the Zündwinkeleingriff is reset to the initial value. Furthermore, it can be provided that the knock control is set for a predetermined number of combustion cycles. Alternatively, a renewed adaptation of the knock control can be initiated.

As a result, error detection of dangerous beating burns can be significantly reduced and the efficiency of the internal combustion engine can be increased. Furthermore, even small deviations between the engine-specific limit knocking level can be evaluated as Knopfpegelsollwert and Klopfpegelistwert and reacted to it with small Zündwinkeländerungen, causing the

Internal combustion engine can be operated according to stable and closer to the knock limit. Since the combustion noise changes as a function of mixture, engine temperature and other parameters, correction values can be stored for this in order to incorporate the dependency in the calculation of the setpoint.

At an operating point change of the internal combustion engine is the

Internal combustion engine customized Grenzklopfpegel adapted. It can the

Adaptation as a function of the operating point or a desired dynamics accelerated or delayed.

Sporadic occurring knock events, which, for example, increased by

Oil entry into the combustion chamber or sooting caused in the combustion chamber, can by means of a security function, in particular by a

Individual value analysis instead of a mean value analysis. The frequency of sporadic knock events can be determined by counting. If the frequency of sporadically occurring knocking events exceeds a predefined threshold value with respect to an observation period, it is recognized that the sporadically occurring knocking events are not reflected

Relationship between ignition angle and noise level follows. It will be one

Reduction of the internal combustion engine individual Grenzklopfpegels made. The amount of the reduction can be stored, for example, as a function of the number of sporadically occurring knock events within the observation period.

embodiment

By way of example, a possible embodiment of the method according to the invention for adapting knock control is shown here. In the accompanying figures show:

FIG. 1: a schematic representation for determining a predefined

Target knock level and threshold of a knock level gradient, and

FIG. 2: a schematic representation of a recalculation of

Grenzklopfpegelgradienten to an internal combustion engine individual

Knocking level setpoint.

The method according to the invention for adapting a knock control involves a plurality of method steps, which relate to a development phase and to a development phase

Split use phase of the internal combustion engine. During the development phase are based on an exemplary internal combustion engine

Engine ECU accomplished that are valid for a complete series production of the corresponding internal combustion engines. The adaptation of the knock control is then in the use phase of the respective internal combustion engine from this

Serial production carried out. Within this embodiment, the

Procedure of the method at a certain operating point and a specific cylinder of an internal combustion engine described.

During the development phase the selected operating point of the

Internal combustion engine, a voltage curve of a knocking level (1) by means of a Knock sensor determined depending on the ignition angle (2). In Fig. 1, a diagram for an application is shown, which among other things a

Knock level profile (3) in dependence of the ignition angle (2) shows. The ignition angle (2) is plotted on an abscissa axis (4) and the knock level (1) on an ordinate axis (5). For the determination of the voltage curve an adjustment of the ignition angle (2) is made and the corresponding knock level (1) as

Voltage signal of the knock sensor measured. The resulting

The knock level history (3) is then described by a knock level equalization function (6), here exemplified as a fourth degree polynomial. For the exact determination of the knock level compensation function (6) at least as many

Measured values (6a, 6b, 6c, 6d, 6e) are available, as are necessary for the determination of the parameters of the compensation function. At the same time for determining the knock level curve (3), a knock magnitude (7), which is recorded by means of a cylinder pressure sensor, becomes a function of the ignition angle (2)

Knocking strength course (8) recorded. This can be checked if the by the

Knock sensor measured knock level profile (3) is representative of the measured Klopfstärkeverlauf (8). On the basis of an associated knocking strength compensation function (9), which is determined analogously to the knock level compensation function (6), a

predetermined knock limit be set by a Grenzklopfstärke (10), so that there is also a Grenzklopfpegel (11).

By a mathematical derivation of the knock level compensation function (6) according to the ignition angle, a gradient profile (12) of the knock level profile (3) is additionally produced.

calculated. As a result, a knock level gradient of the knock limit is available for the knock limit in addition to the limit knock level (11)

Grenzklopfpegelgradient (13) is stored in an engine control unit of each internal combustion engine series production.

A correction of the Grenzklopfpegels (11) as Klopfpegelsollwert for the knock control is determined during the use phase of an individual internal combustion engine in the vehicle, as soon as the conditions are met. This will be for the individual

Internal combustion engine an internal combustion engine individual Klopfpegelverlauf (14) via ignition angle (2) determined. FIG. 2 shows a diagram for an adaptation analogous to the diagram in FIG. 1. The internal combustion engine-specific knock level profile (14) is determined by an internal combustion engine-specific knock level compensation function (15). described, the derivative of an internal combustion engine individual

Gradient curve (16) of the engine-individual Kloptpegelverlaufs (14). The engine gradient gradient (16) deviates from the gradient curve (12), which was determined during the development of the internal combustion engine, due to series deviations and signs of wear as well as differences in the signal processing. For a Grenzzündwinkel (17), for which the gradient of the engine-individual knock level erlaufs (14) is equal to the Grenzklopfpegelgradienten (13), or is within a certain tolerance, based on the internal combustion engine individual Klopfpegelverlaufs (14) an engine-specific Grenzklopfpegel (18) is determined which the

Internal combustion engine individual Grenzklopfstärke (19) and thus the

combustion engine-specific knock limit represents. Despite different

Knock level course (3) and internal combustion engine individual Klopfpegelverlauf (14), the internal combustion engine individual Grenzklopfstärke (19) equal to the

Grenzklopfstärke (10) be. Thus, the functionality of the method according to the invention is shown.

The difference between the limit knock level (11), which was advantageously determined from a sufficient sample of internal combustion engines of series production, and the engine-specific limit knock level (18) represents the correction of the limit knock level (11) to the engine-individual

Limit knock level (18) for a knock control and is stored in the engine control unit. Based on the adaptation thus determined, the knock control is performed by means of a PID controller.

Alternatively, the internal combustion engine-specific limit knock level (18) can be stored redundantly to the limit knock level (11) in the engine control unit. Of the

Generally valid limit knock levels (11) are not cleared to always provide a safe fallback level in case of malfunction.

The method described in this exemplary embodiment for a specific operating point and a specific cylinder is repeatedly performed for application and adaptation of the knock control, in order to obtain at least sufficiently many setpoint values within the operating range and for all cylinders of the internal combustion engine in order to enable improved operation of the internal combustion engine , List of used reference numbers

1 knock level

2 ignition angle

3 Knock level course

4 abscissa axis

5 ordinate axis

6 Knock level compensation function

6a, 6b, 6c, 6d, 6e measured values

7 Knock strength

8 Knock strength course

9 knocking strength compensation function

10 border knock strength

11 limit knock level

12 gradient course

13 Boundary level gradient

14 internal combustion engine individual Klopfpegelverlauf

15 internal combustion engine individual knock level compensation function

16 combustion engine-individual gradient curve

17 limit ignition angle

18 individual engine limit knocking levels

19 internal combustion engine individual Grenzklopfstärke

Claims

claims

1. A method for adapting a knock control for a spark-ignited

Internal combustion engine for determining an engine-specific and operating-point-specific knocking level set point for the knock control,

in that during the operation of the internal combustion engine for at least one cylinder of the internal combustion engine an ignition angle variation is carried out in order to determine a position of a knock limit as a function of a knock level, wherein structure sound waves of the internal combustion engine are detected by at least one knock sensor and output as knock level,

the measured values for knock levels as a function of the firing angle determined during the ignition angle variation are used to determine knock gradient gradients as a function of the firing angle,

- And the engine individual and operating point individual

Knock level setpoint is set equal to the knock level of a particular firing angle at which the knock level gradient corresponds to a tap limit level gradient.

2. Method for adapting a knock control for a spark-ignited

Internal combustion engine according to claim 1, characterized in that the measured values for knock levels determined during the ignition angle variation are mapped as a function of the ignition angle by a knock level compensation function and based on the knock level compensation function of the

Knöpfpegelgradient is determined in dependence on the ignition angle.

3. Method for adapting a knock control for a spark-ignited

Internal combustion engine according to one of the preceding claims, characterized in that a predefined knock level setpoint value is corrected on the basis of the engine-specific knocking level setpoint value.

4. Method for adapting a knock control for a spark-ignited

Internal combustion engine according to one of the preceding claims, characterized in that the limit knocking gradient is set equal to the knocking level gradient of a specific ignition angle at which a knocking strength corresponds to a limiting knocking force, the course of the knocking force in Dependence on the ignition angle is determined by a cylinder pressure measurement during Zündwinkelvariation.

5. Method for adapting a knock control for a spark-ignited

Internal combustion engine according to one of the preceding claims, characterized in that a polynomial function of at least the second degree is used as the knock level compensation function.

6. Method for adapting a knock control for a spark-ignited

Internal combustion engine, according to one of the preceding claims, characterized in that the Zündwinkelvariation is performed on the basis of a predefined Zündwinkelsequenz, the ignition angle sequence can be specified operating point individual.

7. Method for adapting a knock control for a spark-ignited

Internal combustion engine, according to one of the preceding claims, characterized in that the engine-individual knock level setpoint stored in an engine control unit and is used as setpoint input of a PID controller for a knock control.

8. Method for adapting a knock control for a spark-ignited

Internal combustion engine, which are necessary for the process

Divide process steps on a development phase and a use phase of the internal combustion engine, wherein during the development phase based on an exemplary internal combustion engine at least one predefined operating point individual Klopfpegelsollwert and at least one

Betriebsspunktindividueller Grenzklopfpegelgradient is determined, which are valid for a complete series production of the corresponding internal combustion engines and are stored as a basic condition in an engine control unit, and in the use phase of the respective individual

Internal combustion engine from this series production of the predefined

Knock level setpoint based on an individual combustion engine

Knock level setpoint is corrected, which during operation of the

Internal combustion engine was determined.

9. A device for adapting a knock control, in which a plurality of memory cells are provided, which have a unique operating point assignment, wherein for an adaptation of a knock control an operating point of

Internal combustion engine are assigned at least two memory cells in the device and in a first memory cell, a predefined

Knock level setpoint and in a second memory cell

Grenzklopfpegelgradient is stored.