Method for controlling an ignition timing

Abstract

A method for controlling an ignition timing for combustion in an internal combustion engine, wherein an ignition angle for combustion is determined based on a characteristic map and a knock limit offset, depending on an operating parameter of the internal combustion engine, characterized in that the knock limit offset for an operating point of the internal combustion engine is adapted using a learning method, wherein the knock limit offset is changed during the learning method until the knock limit is reached, and wherein the last value of the knock limit offset before reaching the knock limit for the current operating point is stored as the knock limit offset.

Description

[0001] The invention relates to a method for controlling an ignition timing according to the preamble of claim 1 and an engine control unit according to claim 9.

[0002] It is known in the art to monitor the ignition timing during combustion in an internal combustion engine with respect to knocking and, upon detection of knocking, to retard the ignition timing of the affected cylinder by an ignition timing offset during the next combustion cycle. Subsequently, the ignition timing offset is reduced again by a slow advance of the ignition timing. If knocking occurs again before the retardation of the ignition timing has completely subsided to the intended ignition timing, the ignition timing is immediately retarded again by the ignition timing offset. Due to the rapid retardation of the ignition timing during a knocking event and the subsequent slow re-advancement to the knock limit, the internal combustion engine can be operated with an optimized ignition timing close to the knock limit.

[0003] German patent DE 198 27 704 A1 discloses a method for cylinder-selective knock control of an internal combustion engine, wherein, when engine knock occurs in a specific cylinder, the ignition timing for that cylinder is retarded by a specific amount. This reduces the probability of knocking combustion occurring in that cylinder. During subsequent non-knocking engine operation, the ignition timing is slowly advanced again by a predetermined amount.

[0004] DE 195 39 171 A1 relates to a knock control system for a spark-ignition internal combustion engine with different knockback angles at various engine operating points, which are further adapted to current boundary conditions. The system is designed so that, given specific boundary conditions, a knock index that is essentially the same for all operating points is determined, from which the current knockback angle is derived depending on the operating point.

[0005] DE 100 51 974 A1 discloses a method for knock control of an internal combustion engine, in which values ​​for retarding an ignition timing are provided by means of an adaptable map, wherein the values ​​are assigned to at least one operating parameter, and wherein, when a dynamic change occurs in the at least one operating parameter, a map value is read from the map as a function of the current value of the at least one operating parameter. Furthermore, it is provided that a previous value for the ignition timing adjustment is only replaced by the map value if the magnitude of the difference between the previous value for the ignition timing adjustment and the map value is less than a predefinable ignition timing difference.

[0006] DE 196 05 407 A1 relates to a method for determining the ignition timing for an internal combustion engine with adaptive knock control, in which the occurrence of knocking combustion is reduced by controlled ignition timing retardation. The current values ​​for the retardation are stored in a map, dependent on operating parameters. Furthermore, an average retardation is determined from these map values, and from this, both a correction ignition timing and a control stroke limit for the knock control are determined. The method automatically detects fuel quality and environmental influences based on a learned RON (Reverse Oxide) level and uses this information to reduce the control effort of the knock control system.

[0007] A method of the type mentioned above for controlling the ignition timing for combustion in an internal combustion engine, in which an ignition angle for combustion is determined based on a characteristic map and a knock limit offset, depending on an operating parameter of the internal combustion engine, is known from DE 197 37 257 A1. Likewise, a generic method is known from the publication "Bosch Functional Framework EA888 2.0L ULEV MED17.5" (available at: https: / / files.s4wiki.com / docs / , page 2075).

[0008] The object of the invention is to provide an improved method for controlling an ignition timing for combustion in an internal combustion engine.

[0009] The object of the invention is achieved by the method according to claim 1 and the engine control unit according to claim 9.

[0010] Further advantageous embodiments are specified in the dependent claims.

[0011] One advantage of the described method is that it achieves precise and rapid control of the ignition timing close to the knock limit. This is achieved by determining the ignition angle for combustion in the internal combustion engine based on an operating parameter of the engine using a characteristic map and a knock limit offset. According to the invention, the knock limit offset for an operating point of the internal combustion engine is adjusted using a learning process. During this learning process, the knock limit offset is changed until the knock limit is reached, and the last value of the knock limit offset before reaching the knock limit is stored as the knock limit offset for the current operating point. Therefore, it is not necessary to modify the complex characteristic map for the base ignition angle or the characteristic map for the ignition angle difference value.It is sufficient if, during the operation of the internal combustion engine, for example on a test bench or in daily use of the motor vehicle, the knock limit offset is adjusted for different operating points and / or qualities of fuels, in particular the octane number.

[0012] By using the knock limit offset, it is possible to quickly provide a precise and actual knock limit even for areas that are rarely or never driven on.

[0013] In another version, the ignition angle is determined depending on a base ignition angle and a differential ignition angle value. This allows for a simple and precise determination of the ignition timing.

[0014] In another version, the ignition angle differential value is stored in a characteristic map as a function of an operating parameter of the internal combustion engine. This allows for rapid control.

[0015] In another version, an ignition angle field is used. This method offers the advantage that it is not necessary to specify ignition angle differential values.

[0016] In another version, the knock limit offset depends on an operating parameter of the internal combustion engine. This makes the control more precise.

[0017] In a further embodiment, a base ignition angle is determined based on an operating parameter of the internal combustion engine to control the ignition timing. This base ignition angle is then shifted by a correction angle towards a later ignition timing, calculated based on a characteristic map and a knock limit offset. This achieves a further refinement of the method.

[0018] In another embodiment, the correction angle is calculated using a virtual correction angle. This virtual correction angle is derived by adding the ignition timing difference value and the knock limit offset. The virtual correction angle is then compared to a predefined threshold. This threshold can, for example, be zero. If the virtual correction angle falls below the predefined threshold, it is used as the actual correction angle to correct the base ignition timing. This ensures that using the virtual correction angle does not shift the ignition timing into areas where such a shift is unnecessary. In particular, it prevents the ignition timing from being advanced compared to the base ignition timing.

[0019] In another embodiment, the knock limit offset is stored in the form of a characteristic curve or map, wherein the knock limit offset depends in particular on the quality of the fuel burned. Specifically, the knock limit offset can depend on the octane rating of the fuel burned. This eliminates the need to determine the characteristic map for the ignition timing difference value for each fuel quality.

[0020] In another embodiment, the characteristic map for a fuel of a predetermined octane rating is determined, and this map is then provided with an adjustment value for fuels with other octane ratings. This eliminates the need to experimentally or computationally determine a characteristic map for each fuel with a different octane rating. The differences in the knocking tendency of the various fuel qualities are accounted for by the knock limit offset.

[0021] In a further embodiment, the quality of the fuel, in particular the octane number of the fuel, is recorded and taken into account when selecting the knock limit offset and / or when choosing the ignition angle differential value from the map.

[0022] The invention will be explained in more detail below with reference to the figures. They show Fig. 1 a diagram for a first operating point with characteristic curves for a virtual knock limit, an ignition timing retard requirement and a knock limit offset, Fig. 2 a diagram for a second operating point, in which characteristic curves for the virtual knock limit, the ignition timing retard requirement and the knock limit offset, and Fig. 3 a schematic representation of the structure of an engine control unit for carrying out the procedure.

[0023] Fig. Figure 1 shows a diagram in which the ignition timing retard requirement is plotted on the y-axis and different fuel qualities are plotted on the x-axis, with the fuel quality decreasing in octane rating with increasing distance from the y-axis. Fig. Figure 1 shows a first measuring point 11 for a design fuel, i.e., a high octane fuel, a second measuring point 12 for a low-octane fuel, and a third measuring point 13 for a very low-octane fuel. A design fuel is, for example, a fuel with an octane rating of 98. A low-octane fuel is, for example, a fuel with an octane rating of 95. A very low-octane fuel is, for example, a fuel with an octane rating of 91. The fuel quality can be detected during the operation of the internal combustion engine using knock control. In addition, a sensor or measuring method for detecting the fuel quality, in particular the octane rating, can be provided, which the engine control unit uses to determine the fuel quality.

[0024] Furthermore, measured values ​​for the virtual knock limit 1, the ignition timing retard requirement 2, and the knock limit offset 44 are shown at the three measuring points 11, 12, and 13. The virtual knock limit of the three measuring points 11, 12, and 13 is connected to a first characteristic curve 21. The values ​​for the ignition timing retard requirement of the three measuring points 11, 12, and 13 are connected to a second characteristic curve 22. The knock limit offsets 44 for the three measuring points 11, 12, and 13 are connected to a third characteristic curve 23. The characteristic curves were created in the form of a linear approximation. In addition, in Fig. 1 In the form of a dashed line, an ignition angle differential value 42 is entered for the specified operating point and the design fuel, at which ignition occurs close to the limit of knocking combustion.

[0025] In the example shown, the internal combustion engine is at an operating point where the values ​​for the virtual knock limit 1, the ignition timing retard requirement 2 and the knock limit offset 44 for the three fuel qualities, i.e. for the three measuring points 11, 12, 13, are in a line.

[0026] The knock limit offset 44 has a value of 0 at the specified operating point for the design fuel. The knock limit offset 44 has a value of -3 at the specified operating point for a low-octane fuel. The knock limit offset 44 has a value of -6 at the specified operating point for a very low-octane fuel. Thus, the characteristic map 24 for the ignition angle difference values ​​can be easily adapted for different fuel qualities using the third characteristic curve 23 for the knock limit offset 44.

[0027] The third characteristic curve 23 for the knock limit offset values ​​44 can be determined experimentally on the engine test bench or during operation. In addition, a theoretical model can also be used to determine the knock limit offsets 44 for different fuel qualities, especially for different octane ratings.

[0028] Fig. Figure 2 shows a schematic diagram for a second operating point of the internal combustion engine, where the ignition timing retard requirement is plotted along the y-axis. Along the x-axis, first, second, and third measurement points 11, 12, and 13 are plotted, with measurement points 11, 12, and 13 being recorded for different qualities of the fuel burned. The first measurement point 11 corresponds to a design fuel, i.e., a fuel with a high octane rating. The second measurement point 12 corresponds to a low-octane fuel. The third measurement point 13 corresponds to a very low-octane fuel. The fuels were each measured at the same operating point of the internal combustion engine. The first characteristic curve 21 represents the measurement points of the virtual knock limit 1. The second characteristic curve 22 represents the measurement points of the ignition timing retard requirement. The third characteristic curve 23 represents the measurement points of the knock limit offset 44.At this operating point, the first characteristic curve 21 has different values ​​than the third characteristic curve 23.

[0029] To record the measured values ​​or characteristic curves, the internal combustion engine can, for example, be tested on an engine test bench at any number of operating points, depending on the respective ignition timing, to determine the knock limit for operation with design fuel. Determining the ignition timing for the knock limit, i.e., for the onset of knocking combustion, can be done in various ways. One possibility is to determine the knock limit with a low-octane fuel and then use a correction value to compensate for a high-octane or very low-octane fuel. The ignition timing for the determined knock limit can be stored either as an absolute value or as an ignition timing difference relative to a base ignition timing in a map within the engine control unit. Other reference systems for the stored ignition timing are also conceivable.The resulting ignition timing can also be too early and therefore unusable, i.e., in a virtual range. In the . Fig. 2. If the ignition angle withdrawal requirement values ​​>0 correspond to a range that is too early and are therefore not implemented.

[0030] If, during operation of the internal combustion engine, the knock limit is reached at a specific operating point after the engine map has been completed, the virtual knock limit 1 can be corrected to the actual knock limit, for example, by a learning knock limit offset. Reaching the actual knock limit can be detected, for example, by evaluating the signal from a structure-borne sound sensor by comparing it to a threshold or by the activation of the knock control system.

[0031] Thus, the true, expected knock limit is known across the entire operating range, even for non-mobile areas. This allows for the implementation of further knock control and knock detection measures.

[0032] For example, the ignition timing can be limited based on the virtual knock limit, thus advancing the ignition timing. Furthermore, measures are conceivable based on the known virtual knock limit, such as sensitive knock detection when operating close to the expected knock limit and a robust, insensitive detection system when operating farther from the knock limit.

[0033] A positive ignition timing retard requirement means adjusting the base ignition angle 41 towards an advanced ignition point. A negative ignition timing retard requirement means adjusting the base ignition angle 41 towards a retarded ignition point.

[0034] In Fig. Figure 2 shows the ignition angle differential value 42 with a magnitude of 44 as a dashed characteristic curve for the current operating point. The ignition angle differential value 42 is constant in the characteristic map 24 for different fuel types.

[0035] The characteristic map 24 was determined for a design fuel, whereby the ignition angle is selected at the present operating point such that knocking combustion does not occur. According to Fig. 2. The base ignition angle could be shifted 3° towards early without knocking combustion occurring.

[0036] For various operating points of the internal combustion engine, a characteristic curve for the knock limit offset is stored, depending on the fuel quality. Fig. The third characteristic curve 23 corresponds to the knock limit offset 44 for a defined operating point, depending on the quality of the fuel used. Thus, the characteristic curve for the knock limit offset 44 has a value of 0 at the defined operating point for the design fuel. The characteristic curve for the knock limit offset 44 has a value of -3 at the defined operating point for a low-octane fuel. The characteristic curve for the knock limit offset 44 has a value of -6 at the defined operating point for a very low-octane fuel. In this way, the characteristic map 24 can be easily adapted using the knock limit offsets for different fuel qualities.

[0037] Fig. Figure 3 shows a schematic representation of parts of an engine control unit 30, which is configured to execute the described procedure. In a first program block 31, the engine control unit 30 calculates a base ignition angle 41 based on an operating parameter of the internal combustion engine. Corresponding characteristic curves, maps, and programs are stored in the engine control unit 30 for this purpose. Furthermore, in a second program block 32, the engine control unit 30 determines an ignition angle differential value 42 based on a map 24, depending on the current operating point of the internal combustion engine, in particular on the engine speed and / or load. The ignition angle differential value 42 is fed to an adder 33. In a third program block 34, the engine control unit 30 also determines a knock limit offset 44. The knock limit offset is also fed to the adder 33.To determine the knock limit offset 44, the engine control unit 30 uses a characteristic curve, such as the one in . Fig. Figure 2 shows a characteristic curve where the value of the knock limit offset 44 is stored as a function of the fuel used and the current operating point of the internal combustion engine. Instead of a characteristic curve, a map for the knock limit offset 44 can also be used, which has a value for the knock limit offset 44 depending on the operating point and the quality of the fuel. Furthermore, the knock limit offset 44 can also be calculated as a function of an operating point of the internal combustion engine. An operating point of the internal combustion engine is also considered to be an operating parameter such as the quality, i.e., the octane rating, of the fuel used.

[0038] The adder 33 adds the knock limit offset 44 and the ignition angle difference value 33, thus determining a virtual knock limit 1. The virtual knock limit 1 is fed to a comparison block 35. The comparison block 35 compares the virtual knock limit 1 with a predefined comparison value 45. The comparison value 45 can, for example, be set to 0. The comparison block 35 represents a limiting function, whereby only the virtual knock limits 1 are passed on to a second adder 36 if they are below the comparison value 45. In the described example, only the virtual knock limits 1 that are less than 0, i.e., in the negative range, are passed on to the second adder 36. The second adder 36 adds the negative virtual knock limit 1 to the base ignition angle 41, thus determining the resulting ignition angle 46.The engine control unit 30 ignites the following combustion at the resulting ignition angle 46.

[0039] The characteristic map or curve for the knock limit offset values ​​44 can be determined, for example, by adding an increasing knock limit offset stepwise, starting from the ignition angle difference value 42, until knocking combustion begins. When knocking combustion occurs, the previous value of the knock limit offset 44, rather than the current value, is stored in the characteristic curve or map as the knock limit offset for the current operating point. In this way, the knock limit offset allows for precise adjustment to quickly set an ignition angle close to the knock limit.

[0040] In another embodiment, instead of the base ignition angle and the ignition angle difference map 24, an ignition angle field dependent on the operating points of the internal combustion engine can also be used. The ignition angle field is also determined experimentally for a defined fuel quality for various operating points. The ignition angle field is corrected with the knock limit offset 44, but a shift of the ignition angle towards an advanced ignition is prevented.

Claims

[1] Method for controlling an ignition timing for combustion of an internal combustion engine, wherein an ignition angle for combustion is determined based on a characteristic map and depending on a knock limit offset, depending on an operating parameter of the internal combustion engine, characterized by , that the knock limit offset for an operating point of the internal combustion engine is adjusted using a learning procedure, wherein the knock limit offset is changed during the learning procedure until the knock limit is reached, and wherein the last value of the knock limit offset before reaching the knock limit for the current operating point is stored as the knock limit offset. [2] Method according to claim 1, wherein the ignition angle is calculated depending on a base ignition angle and depending on an ignition angle difference value. [3] Method according to claim 2, wherein the ignition angle difference value is stored in a characteristic map depending on an operating parameter of the internal combustion engine. [4] Method according to claim 1, wherein the characteristic map represents an ignition angle field. [5] Method according to one of the preceding claims, wherein the knock limit offset depends on an operating parameter of the internal combustion engine. [6] Method according to any of the preceding claims, wherein the ignition angle difference value and the knock limit offset are added and a virtual correction angle is obtained, wherein the virtual correction angle is used as the correction angle by which the base ignition angle is shifted towards late when the virtual correction angle is less than a predetermined threshold, and wherein the threshold in particular corresponds to the value zero. [7] Method according to any of the preceding claims, wherein the knock limit offset depends on the quality of the fuel burned. [8] Method according to claim 7, wherein the characteristic map for the ignition angle difference value for a fuel of a predetermined octane number was determined. [9] Engine control unit configured to perform a method according to any of the preceding claims.

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