DE112012007121B4 - Adaptation of a knock control - Google Patents

Abstract

The invention relates to a method with an associated device for adapting a knock control for an externally ignited internal combustion engine for determining an internal combustion engine-specific and operating point-specific knock level setpoint for the knock control. When the internal combustion engine is operating, an ignition angle variation is carried out for at least one cylinder of the internal combustion engine in order to determine a position of a knock limit as a function of a knock level. Structure-borne sound waves from the internal combustion engine are detected by at least one knock sensor and output as a knock level. The measured values determined during the ignition angle variation for knock levels as a function of the ignition angle are used to determine knock level gradients as a function of the ignition angle. An internal combustion engine-specific knock level setpoint is set equal to the knock level of a specific ignition angle at which the knock level gradient corresponds to a limit knock level gradient.

Description

Technical area

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

State of the art

With a gasoline engine combustion under normal conditions, the mixture is specifically ignited by an external ignition. During the combustion, the flame front moves three-dimensionally through the combustion chamber from the ignition point until the mixture is burned. In the event of a knocking combustion, part of the mixture ignites automatically at hot points in the combustion chamber due to the increased combustion pressure and the increased combustion chamber temperature during the combustion, even before the flame front reaches these areas. An explosive combustion occurs, which increases the combustion speed and a correspondingly high combustion pressure results. The resulting pressure waves and pressure vibrations 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. On the other hand, there is the associated increased tendency to knock burns. The knocking burns increase the thermal and mechanical loads on the internal combustion engine and thus also the risk of the internal combustion engine being destroyed. However, even with persistent knocking burns, low knock levels do not necessarily lead to damage, so that the knock level must always be considered in connection with the frequency of the knocking burns. The ignition timing is primarily adjusted to quickly suppress dangerous knocking burns. Other methods are also possible to counteract knocking burns.

Knock sensors are generally used to detect knocking burns, which are arranged, for example, on the crankcase of the internal combustion engine and which determine the residual structure-borne noise of the knocking combustion that is present there. The knock sensors or structure-borne sound sensors convert the structure-borne sound vibrations resulting from the knocking combustion into alternating voltage signals. The structure-borne noise signals of the knock sensor recorded in this way are fed to an evaluation unit, for example an engine control unit, and processed accordingly by filters so that dangerous knocking burns can be detected.

In order to be able to operate the internal combustion engine as close as possible to the knock limit to optimize efficiency, knock controls are provided. With these knock controls, knocking combustion is permitted up to a predetermined knock intensity or knock intensity, which does not lead to damage to the internal combustion engine. Conventional knock control methods form a structure-borne sound vibration signal averaged from several combustion cycles, which 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 purpose, a distance or a ratio between the currently determined structure-borne noise signal and the reference signal is evaluated. If the reference signal is named as noise and the currently determined structure-borne noise signal is named as a signal, a signal-to-noise ratio or a signal-to-noise ratio to be assessed can be assumed. Assuming that the signal of knocking combustion always clearly differs from that of non-knocking combustion, i.e. the signal is clearly greater than the noise, the detection value of the signal-to-noise ratio, from which a knocking combustion occurs, is determined by the cylinder and speed and load are stored in a map and are therefore firmly specified.

Since the ignition point, which is specified as the ignition angle at a distance from the top dead center of the internal combustion engine between the compression and power cycle, significantly influences the combustion and the knocking tendency, it is set later when a knocking combustion is detected. A knocking combustion is detected when the current signal-to-noise ratio exceeds a corresponding detection value. The signal-to-noise ratio, in which there is a change between non-dangerous knocking combustion and dangerous knocking combustion, is also referred to as the knock limit.

From these conventional knock control methods, such as those in DE 195 49 175 A1 or EP 0 166 033 B1 and a large number of other documents are described, some disadvantages are derived, among other things. For example, a lot of effort is required to optimize the signal-to-noise ratio. The knock sensor is to be arranged on the internal combustion engine in such a way that mainly combustion noises can be detected compared to interfering noises. The noise has a direct effect on the signal-to-noise ratio. The structure-borne noise signal detected by the knock sensor, which represents a knock level, must be carried out in a complex signal processing process in order to minimize the interference component be subjected. The knock control method must be adapted in such a way that variations that are to be expected in series production of internal combustion engines are also included.

In the conventional knock control methods, measures to prevent knocking burns are taken after the dangerous knocking burns take place. Since the reference level is formed from the combustion noise of the internal combustion engine itself, every increase in the noise of the internal combustion engine leads to an increase in the reference level. With a fixed signal-to-noise ratio, the minimally recognizable actual level rises, so that knocking burns are not recognized as such and the destructive burns cannot be counteracted. These knocking noises in turn lead to a further increase in the reference level, whereby a process of automatic deactivation of the knock control can be started. In contrast to this, a reduction in the noise level leads to a reduction in the minimum recognizable actual level, so that dangerous knocking burns are detected although no destructive combustion has taken place. The ignition angle would be set unnecessarily late, which would result in an increased loss of efficiency. In the case of internal combustion engines with low combustion noises, poor structure-borne noise transmission or unfavorable knock sensor positioning, knock control cannot be carried out adequately.

Due to the relative evaluation of the structure-borne noise vibrations, changes in the noise level of the internal combustion engine due to aging or running time are insufficiently taken into account. A trend evaluation is not possible. Stochastic malfunctions due to worn or defective engine components cause increased noise levels, which are incorrectly recognized as knocking combustion.

According to the DE 102 19 659 A1 a method for determining the ignition angle for electronic controls of internal combustion engines is known, with a basic ignition angle and for this a steady-state speed / load operating point being set in the dynamic test bench to determine the ignition angle for a speed / load operating point and operating state the internal combustion engine is operated in this operating state for a specified period of time. Then a starting ignition angle is set for a period of time and the ignition angle is adjusted in increments in the retarded direction until a component limit temperature is reached at a final ignition angle and / or misfires are detected. The ignition angle is adjusted from the final ignition angle in decrements in the early direction until knocking and / or combustion misfires are detected. The actuating time for the ignition angle adjustment is determined as a function of the load and the measured values are scanned at each measuring point for a period of time.

According to the DE 102 25 937 A1 a method for optimizing the efficiency of a catalytic converter of an automobile is known. Accordingly, an air / fuel ratio supplied to the cylinders of an internal combustion engine is adjusted in such a way that a desired oxidant level is maintained in the catalytic converter. For this purpose, the actual amount of oxidants stored in the catalytic converter is determined at different times. The actual amount of oxidant is compared to a target amount of oxidant to be stored in the catalyst. The air / fuel ratio delivered to the cylinder is adjusted based on the size of the difference between the actual amount of oxidant and the target amount of oxidant to prevent NOx or hydrocarbon breakthrough.

According to the DE 38 79 514 T2 an adaptive control system for an internal combustion engine is known, a control strategy being designed in such a way that it can be used for corrections of a base value up to a maximum value depending on the difference between a desired slope and an actual slope and then for corrections of another base value according to the difference to Reduce the same is available.

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, the internal combustion engine being operated at the knock limit with optimum efficiency.

Solution of the task

The object is achieved by a method for adaptation according to the features of patent claim 1 and claim 7 and by a device for adaptation according to the features of patent claim 9.

Description of the invention

The invention provides an improved method for adapting a knock control and an improved device for adapting a knock control compared to the prior art, an improved adaptation of a knock limit taking place and the internal combustion engine being operated at the knock limit with optimum efficiency. Through the According to an advantageous invention, an adaptable knock control system is provided that, starting from an internal combustion engine, independently adapts to further model lines of an engine family and to individual differences of the respective internal combustion engine from a series production without additional effort. The process steps required for the method are divided into a development phase and a use phase of the internal combustion engine. During the development phase, engine control device data is carried out using an exemplary internal combustion engine, which is 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 brought to an engine test bench and an ignition angle variation is carried out for each operating point and each cylinder. The operating point is determined by an engine speed and an engine load. The engine load can be described, for example, by an engine torque or by a combustion medium pressure. The support points of the operating points for the engine speed and engine load are predefined according to a suitable resolution of a characteristic map. The ignition angle variation is carried out for each operating point and each cylinder by adjusting the ignition angle starting from a current ignition angle in the retarded direction and then in predefinable steps back in the early direction until the knock limit is briefly and significantly exceeded. The ignition angle is then adjusted again in the retarded direction.

A limit knock intensity, which is predefined by means of a cylinder pressure measurement and describes a knock limit, is used as a termination criterion for adjusting the ignition angle. Exceeding the knock limit during the ignition angle adjustment serves to be able to determine the exact position of the knock limit as a function of the ignition angle. During the operation of the internal combustion engine on the engine test bench, the combustion pressure inside the cylinder is recorded by a pressure sensor and evaluated accordingly as knock intensity. The knock intensity is a measure of the extent to which the pressure curve of a dangerous knocking combustion differs from a normal combustion. The limit knock intensity is defined, which describes the knock limit. The knock strength is given as pressure. During the adjustment of the ignition angle, in addition to measuring the pressure, the structure-borne noise vibrations of the internal combustion engine are recorded by at least one knock sensor and output as a knock level in the form of a voltage. For the knock limit, a limit knock level is then also available in addition to the limit knock intensity.

In an advantageous manner according to the invention, the adjustment of the ignition angle in the late and early direction is carried out in a predefined ignition angle sequence with specific ignition angle steps, which can also be specified as a function of the operating point. As a result, for operating points at which the risk of knocking combustion is increased, an adapted ignition angle sequence can be specified, at which the ignition angle is changed, for example, in smaller steps.

The measured values determined from this for knock intensity and knock level as a function of the ignition angle can be described or approximated by means of compensation functions. In the simplest version, the compensation function can take place through the simple linear connection of the measured values as support points. Alternatively, suitable mathematical functions can be approximated to the measured course of the measured values, the measured values serving as support points. A gradient curve, that is to say the change in the knock level as a function of the ignition angle, can be determined from the determined measured values of the knock level ignition angle curve. For this purpose, for example, a polynomial function of at least the second degree can be used as a compensation function. The gradient profile is then determined in a simple manner by a mathematical derivation of the compensation function created for the description of the knock level ignition angle profile, that is, the differentiation according to the ignition angle.

The knock limit can thus be described by the limit knock intensity, the limit knock level and additionally by a limit knock level gradient. The limit knock level gradient is set equal to the knock level gradient of a certain ignition angle at which a knock intensity corresponds to the limit knock intensity, the course of the knock intensity being determined as a function of the ignition angle by measuring the cylinder pressure during the ignition angle variation. The nonlinear relationship between knock intensity or knock level and ignition angle adjustment is used to describe the knock limit using the limit knock level gradient. The knock intensity or the knock level increases disproportionately with an increasingly earlier ignition angle. The knock level gradient thus also rises with an increasingly earlier ignition angle. The limit knock level gradient can thus be used to describe the knock limit.

The limit knock level, together with the limit knock level gradient, is advantageously additionally individual to the operating point stored individually for each cylinder in an engine control unit for the internal combustion engine. The advantage of the method according to the invention is that the limit knock level gradient is used to adapt the knock control 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 basic data.

In a further step in the development phase, an average value of an operating point-specific limit knock level representative of a series spread can be determined from a sufficient sample of internal combustion engines, compared and stored in each individual engine control unit of an internal combustion engine. At the end of the development work on the test bench, the limit knock level gradient for the adaptation of the knock control during the use phase and the limit knock level as basic data for a knock level setpoint for the knock control are advantageously stored in the engine control unit of the internal combustion engine.

In the usage phase of the individual internal combustion engine built into a vehicle, for example, an adaptation is carried out based on the values for the knock level gradient already stored in the engine control unit in order to determine an internal combustion engine-specific knock limit for optimal operation at the knock limit. The adaptation is necessary because each individual internal combustion engine has an individual signal transmission of the knocking combustion via the engine structure and the sensors to the evaluation unit and the individual internal combustion engine is therefore subject to certain tolerances and changes that affect the function and ultimately the combustion. These tolerances result from the series spread that occurs in the manufacture of internal combustion engines. Series variances can result, for example, from manufacturing tolerances of mechanical elements or from differences in signal acquisition and transmission. In addition to the series distribution of a model series of an internal combustion engine, the internal combustion engines can also be equipped with different units and modules. Aging and wear and tear also result in a change in the operation of the internal combustion engine. Adaptation can react to these influences. The adaptation is carried out during the operation of the internal combustion engine over the entire period of use under predetermined conditions and use intervals.

The method for adaptation, in particular for determining an internal combustion engine-specific and operating point-specific knock level setpoint for knock control includes the ignition angle variation for at least one cylinder during operation of the internal combustion engine in order to determine a position of the knock limit as a function of the knock level. The structure-borne noise vibrations of the internal combustion engine are detected by at least one knock sensor and output as a knock level. The measured values determined during the ignition angle variation for knock levels as a function of the ignition angle are mapped by a knock level compensation function. Using this knock level compensation function, a knock level gradient is determined as a function of the ignition angle and an internal combustion engine-specific knock level setpoint is set equal to the knock level of a specific ignition angle at which the knock level gradient corresponds to a limit knock level gradient.

In other words, the knock level setpoint value for the individual internal combustion engine that is valid for the individual internal combustion engine is determined on the basis of the generally applicable knock level gradient ignition angle curve and the limit knock level gradient, which are stored in the engine control unit. The ignition angle variation is carried out and the internal combustion engine-specific knock level setpoint is determined by determining that 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.

According to the invention, the adaptation advantageously takes place during a quasi-stable operating state of the internal combustion engine, in which only slight changes in speed and load occur. If such an operating point is recognized, the adaptation is carried out for the respective operating point. The adaptation can also be carried out individually for each cylinder. For the detection of a quasi-stable operating point, among other things, a predefined threshold value of a load and speed change rate can be used. Furthermore, predictions about impending signal or operational changes of the internal combustion engine can be used for the decision to adapt.

The operating point-specific and, if necessary, cylinder-specific adaptation takes place by varying the ignition angle. The ignition angle is adjusted using an ignition angle sequence which corresponds to the ignition angle sequence during the application. Alternatively, a simplified ignition angle sequence or an ignition angle sequence adapted to the operating point can also be used. During the adjustment of the ignition angle, the knock level that occurs is detected by the knock sensor installed on the internal combustion engine. As a result, several measured values of the knock level are available for the respective operating point, which are sufficient for an approximation, depending on the ignition angle, so that a course of the knock level is obtained results over the ignition angle. The course is in turn described or approximated by a compensation function. The first mathematical derivation of the compensation function according to the ignition angle generates an operating point-specific and, if necessary, cylinder-specific curve of the knock level gradient for the individual internal combustion engine. For the ignition angle at which the course of the knock level gradient corresponds to the limit knock level gradient stored in the engine control unit during the development phase, the corresponding knock level is determined using the compensation function and used as the internal combustion engine-specific limit knock level. In other words, a knock level is recalculated based on the operating point and, if applicable, cylinder-specific curve of the knock level gradient, for whose ignition angle the limit knock level gradient corresponds to the value of the operating point and, if applicable, cylinder-specific curve of the knock level gradient. The operating point and, if applicable, cylinder-specific and internal-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, in particular for determining an internal combustion engine-specific and operating point-specific knock level setpoint, comprises the ignition angle variation for at least one cylinder during operation of the internal combustion engine in order to determine a position of the knock limit as a function of 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 determined during the ignition angle variation for knock levels as a function of the ignition angle are mapped by a knock level compensation function. Using this knock level compensation function, a knock level gradient is determined as a function of the ignition angle and an internal combustion engine-specific knock level setpoint is set equal to the knock level of a specific ignition angle at which the knock level gradient corresponds to a limit knock level gradient.

The adaptive component results from the difference between the predefined limit knock level already stored in the engine control unit and the limit knock level specific to the internal combustion engine. In other words, the predefined limit knock level is corrected based on the internal combustion engine-specific limit knock level. The knock level setpoint required for knock control results according to the invention as the sum of the predefined limit knock level and the adaptive component. In principle, it is also possible to use the currently determined internal combustion engine-specific knock level limit without deleting the predefined knock limit limit. The predefined limit knock level is therefore always available as a fall-back level. Using a freely selectable weighting, the first adaptations to the further operating points can be interpolated or extrapolated without successful adaptation. Thus, the first successful adaptation already 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 clear operating point assignment. For the adaptation of the knock control, at least two storage cells are assigned in the device for an operating point of the internal combustion engine. 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. A further memory cell can be provided in the device for each operating point, in which the adapted internal combustion engine-specific knock level setpoint or the correction of the predefined knock level setpoint to the internal combustion engine-specific knock level setpoint can be stored as an adaptive component.

After each successful adaptation, an operating point and, if applicable, cylinder-specific status counter is increased by a predefined counter value and stored accordingly in a status map. The support points are the same as those of the adaptation map so that each adaptation value is assigned its status value exactly. 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 is reduced in order to enable a new adaptation under the appropriate conditions. The reliability of the adaptation value is guaranteed when the status counter has reached or exceeded a threshold value provided for it. If the signal is significantly influenced during the first part of the adaptation sequence, that is to say during the ignition angle advance, the adaptation is ended and restarted. If this is the case in the second part of the adaptation sequence, the result is stored in the adaptation map, as described above. The status counter is increased by a count value that is reduced compared to the count value of a successful adaptation.

If a safety threshold value of a knock level is reached in relation to the predefined limit knock level prior to the desired limit knock level gradient in the ignition angle advance, then it can be assumed that the noise level is outside a permissible range. The adaptation is then canceled.

The start values are retained unchanged. The behavior is repeated with others Adaptation attempts, 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 knock level setpoint also required for knock control, which represents a current and stable knock level as a voltage signal during operation of the internal combustion engine, is determined as a moving average over a defined number of cyclically successive knock sensor signals. The number of signals used for averaging is predetermined by parameters that influence the signal. Such parameters can be, for example, speed, load and combustion center position and their rate of change in dynamic operation of the internal combustion engine. Changes in the signal processing, such as when switching the signal evaluation, or the connection or disconnection of engine components, such as charging units or charge movement flaps, can also be taken into account.

A controller is used for knock control in which the actual knock level value is compared with the adapted limit knock level specific to the internal combustion engine. The ignition angle is used as the control variable. In an advantageous manner according to the invention, a PID controller is used for the controller.

The method described 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 compared to conventional knock control methods. This increases the efficiency of the internal combustion engine significantly compared to conventional internal combustion engines, which is evident, for example, from fuel savings.

The inventive method for knock control also enables diagnostic functions. During the operation of the internal combustion engine, a stochastic noise can be recognized by storing a standard deviation of the knock level in a characteristic map for each operating point and cylinder. If the mean value calculated from the characteristic diagram exceeds a predefined threshold value, a presumed stochastic background noise is concluded. Trend recognition of the noise level of the internal combustion engine by analyzing the D component of the controller is possible. During the adaptation, the standard deviation of the knock level can also be determined via the ignition angle. If the gradient of the course of the standard deviation of the knock level determined in this way over the ignition angle exceeds a predetermined limit value in a defined range, a stochastic noise is recognized. Depending on the result of this diagnosis, the parameters for the adaptation and control can be adjusted. A predefined gradient of the standard deviation can also be used as a termination criterion for adjusting the ignition angle of the adaptation.

For optimal knock control, the knock sensor signal is recorded, filtered and evaluated in the representative time and frequency range. For this, a time window or a crankshaft angle window is defined depending on the load and speed. The frequency is filtered by a filter with a passband bandwidth from the first to the third natural frequency of the combustion chamber. The pass bandwidth is defined using a high and low pass frequency. In contrast to conventional knock controls, the window is opened before the top dead center, which is assigned to the ignition point, in order to be able to reliably detect the actual knock level during the adaptation. Furthermore, pre-ignition can also be detected by comparing the actual knock level with a corresponding threshold value and if it is exceeded, an extremely strong knocking combustion is deduced. All information that emerges 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 effort for optimal sensor placement. The adaptation of the engine-specific knock level limit enables stable knock control with high control quality, which adapts to series variances 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 differently loud background noises. In order to avoid the loss of efficiency resulting from the interference, it is proposed to observe the change in noise during an ignition angle intervention. If the noise changes caused by the ignition angle intervention do not follow the stored relationship between the ignition angle and the noise level within a deviation described by a threshold value, these are recognized as a fault. If this threshold value is exceeded for a predetermined number of combustion cycles, the ignition angle intervention is set back to the initial value. It can also be provided that the knock control is set for a predetermined number of combustion cycles. Alternatively, a new adaptation of the knock control can also be initiated.

As a result, incorrect identifications of dangerous knocking burns can be significantly reduced and the efficiency of the internal combustion engine can be increased. Furthermore, even small deviations between the engine-specific knock level limit as the knock level setpoint and the knock level actual value can be evaluated and responded to with slight changes in the ignition angle, so that the engine can be operated more stable and closer to the knock limit. Since the combustion noise changes depending on the mixture, engine temperature and other parameters, correction values can be stored for this in order to allow the dependency to flow into the calculation of the setpoint.

When the operating point of the internal combustion engine changes, the internal combustion engine-specific limit knock level is adapted. The adaptation can be accelerated or delayed depending on the operating point or a dynamic requirement.

Sporadically occurring knocking events, which are caused, for example, by increased oil entry into the combustion chamber or sooting in the combustion chamber, can be included by means of a safety function, in particular by considering individual values instead of considering average values. The frequency of the sporadically occurring knock events can be determined by counting. If the frequency of the sporadically occurring knock events in relation to an observation period exceeds a predefined threshold value, it is recognized that the sporadically occurring knock events do not follow the stored relationship between the ignition angle and the noise level. The engine-specific limit knock level is lowered. The amount of the reduction can be stored, for example, as a function of the number of sporadically occurring knocking events within the observation period.

Embodiment

• 1: eine schematische Darstellung zur Ermittlung eines vordefinierten Sollklopfpegels und Schwellenwertes eines Klopfpegelgradienten, und
• 2: eine schematische Darstellung einer Rückrechnung vom Grenzklopfpegelgradienten zu einem brennkraftmaschinenindividuellen Klopfpegelsollwert.

A possible embodiment of the method according to the invention for adapting a knock control is shown here as an example. In the accompanying figures show:

• 1 : a schematic representation for determining a predefined setpoint knock level and threshold value of a knock level gradient, and
• 2 : a schematic representation of a back calculation from the limit knock level gradient to an internal combustion engine-specific knock level setpoint.

The method according to the invention for adapting a knock control includes several method steps which are divided into a development phase and a use phase of the internal combustion engine. During the development phase, engine control device data is carried out using an exemplary internal combustion engine, which is 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 internal combustion engine from this series production. Within this exemplary embodiment, the procedure of the method is described at a specific operating point and a specific cylinder of an internal combustion engine.

During the development phase, a voltage curve of a knock level ( 1 ) by means of a knock sensor depending on the ignition angle ( 2 ) certainly. In 1 a diagram for an application is shown, which among other things shows a knock level curve ( 3 ) depending on the ignition angle ( 2 ) shows. The ignition angle ( 2 ) is on an abscissa axis ( 4th ) and the knock level ( 1 ) on an ordinate axis ( 5 ) applied. To determine the voltage curve, an adjustment of the ignition angle ( 2 ) and the corresponding knock level ( 1 ) measured as a voltage signal from the knock sensor. The resulting knock level curve ( 3 ) is then compensated for by a knock level function ( 6 ), which is executed here as an example of a polynomial of the fourth degree. For the exact determination of the knock level compensation function ( 6 ) must 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. Simultaneously to the determination of the knock level curve ( 3 ) becomes a knock strength ( 7th ), which is recorded by means of a cylinder pressure sensor, depending on the ignition angle ( 2 ) to a knock strength curve ( 8th ) detected. This can be used to check whether the course of the knock level measured by the knock sensor ( 3 ) representative of the measured knock intensity curve ( 8th ) is. Using an assigned knock intensity compensation function ( 9 ), which is analogous to the knock level compensation function ( 6 ) is determined, a predetermined knock limit can be determined by a limit knock intensity ( 10 ) so that a limit knock level ( 11 ) results.

A mathematical derivation of the knock level compensation function ( 6 ) after the ignition angle, a gradient curve ( 12th ) of the knock level curve ( 3 ) calculated. This means that the knock limit is next to the limit knock level ( 11 ) a knock level gradient of the knock limit is also available, which is used as a limit knock level gradient ( 13th ) is stored in an engine control unit of each internal combustion engine in series production.

A correction of the limit knock level ( 11 ) as the knock level setpoint for the knock control is determined during the use phase of an individual internal combustion engine in the vehicle as soon as the conditions for it are met. For this purpose, a knock level profile for the individual internal combustion engine ( 14th ) via ignition angle ( 2 ) determined. 2 shows a diagram for an adaptation analogous to the diagram in 1 . The internal combustion engine-specific knock level curve ( 14th ) is controlled by an internal combustion engine-specific knock level compensation function ( 15th ), the derivation of which is an internal combustion engine-specific gradient curve ( 16 ) of the internal combustion engine-specific knock level curve ( 14th ) represents. The internal combustion engine-specific gradient curve ( 16 ) deviates from the gradient curve due to series variations and signs of wear and tear as well as differences in signal processing ( 12th ), which was determined during the development of the internal combustion engine. For a limit ignition angle ( 17th ), for which the gradient of the engine-specific knock level curve ( 14th ) equal to the limit knock level gradient ( 13th ), or is within a certain tolerance, is based on the internal combustion engine-specific knock level curve ( 14th ) an internal combustion engine-specific knock level limit ( 18th ) determines which engine-specific limit knock strength ( 19th ) and thus represents the engine-specific knock limit. Despite different knock levels ( 3 ) and internal combustion engine-specific knock level curve ( 14th ) the internal combustion engine-specific limit knock strength ( 19th ) equal to the limit knock strength ( 10 ) be. The functionality of the method according to the invention is thus shown.

The difference from the limit knock level ( 11 ), which was advantageously determined from a sufficient sample of internal combustion engines in series production, and the internal combustion engine-specific knock level limit ( 18th ) represents the correction of the limit knock level ( 11 ) to the engine-specific limit knock level ( 18th ) for knock control and is stored in the engine control unit. On the basis of the adaptation determined in this way, the knock control is carried out by means of a PID controller.

Alternatively, the engine-specific knock level limit ( 18th ) redundant to the limit knock level ( 11 ) can be stored in the engine control unit. The general limit knock level ( 11 ) is not deleted in order to always provide a safe fallback level in the event of malfunctions.

The method described in this exemplary embodiment for a certain operating point and a certain cylinder is carried out several times for an application and adaptation of the knock control in order to obtain at least enough setpoint values within the operating range and for all cylinders of the internal combustion engine to enable improved operation of the internal combustion engine .

List of reference symbols

1

Knock level

2

Ignition angle

3

Knock level curve

4th

Abscissa axis

5

Ordinate axis

6

Knock level compensation function

6a, 6b, 6c, 6d, 6e

Readings

7th

Knock strength

8th

Knock strength curve

9

Knock intensity compensation function

10

Limit knock strength

11

Limit knock level

12th

Gradient curve

13th

Limit knock level gradient

14th

Internal combustion engine-specific knock level curve

15th

Internal combustion engine-specific knock level compensation function

16

Internal combustion engine-specific gradient course

17th

Limit ignition angle

18th

Internal combustion engine-specific limit knock level

19th

Internal combustion engine-specific limit knock strength

Claims (9)

Method for adapting a knock control for an externally ignited internal combustion engine for Determination of an internal combustion engine-specific and operating point-specific knock level setpoint for knock control, - by performing an ignition angle variation for at least one cylinder of the internal combustion engine during operation of the internal combustion engine in order to determine a position of a knock limit as a function of a knock level, with structure-borne sound waves of the internal combustion engine being detected and are output as knock level, - the measured values determined during the ignition angle variation for knock levels depending on the ignition angle are used to determine knock level gradients depending on the ignition angle, - and the internal combustion engine-specific and operating point-specific knock level setpoint is equated to the knock level of a specific ignition angle, at which level the knock level gradient is a limit knocking level corresponds. Method for adapting a knock control for an externally 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 by a knock level compensation function and the knock level gradient is determined as a function of the ignition angle using the knock level compensation function. Method for adapting a knock control for an externally ignited internal combustion engine according to one of the preceding claims, characterized in that a predefined knock level setpoint is corrected on the basis of the internal combustion engine-specific knock level setpoint. Method for adapting a knock control for an externally ignited internal combustion engine, according to one of the preceding claims, characterized in that the limit knock level gradient is set equal to the knock level gradient of a certain ignition angle at which a knock intensity corresponds to a limit knock intensity, the course of the knock intensity depending on the ignition angle by a cylinder pressure measurement is determined during the ignition angle variation. Method for adapting a knock control for an externally 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. Method for adapting a knock control for an externally ignited internal combustion engine, according to one of the preceding claims, characterized in that the ignition angle variation is carried out on the basis of a predefined ignition angle sequence, wherein the ignition angle sequence can be specified individually for each operating point. Method for adapting a knock control for an externally ignited internal combustion engine, according to one of the preceding claims, characterized in that the internal combustion engine-specific knock level setpoint is stored in an engine control unit and used as a setpoint specification of a PID controller for knock control. Method for adapting a knock control for a spark-ignition internal combustion engine, the process steps necessary for the method being divided into a development phase and a use phase of the internal combustion engine, with at least one predefined knock level setpoint and at least one operating point-specific knock level gradient being determined on the basis of an exemplary internal combustion engine for a complete series production of the corresponding internal combustion engines are valid and are stored as basic data in an engine control unit, and in the usage phase of the respective individual internal combustion engine from this series production, the predefined knock level setpoint is corrected using an internal combustion engine-specific knock level setpoint that was determined during operation of the internal combustion engine. Device that is set up, one of the methods according to Claim 1 to 8th execute.

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