EP3026245B1 - Method for controlling a combustion machine - Google Patents

Description

The invention relates to a method for controlling an internal combustion engine having the features of the preamble of claim 1 and to an internal combustion engine having the features of the preamble of claim 8.

It is known that by the torsion of the crankshaft of internal combustion engines crank angle-dependent signals such. B. timing for the ignition, the fuel injection o. Ä. Are occupied with an error that affects the performance and / or efficiency of the engine. There are therefore in the prior art proposals for compensation or to take into account the caused by the torsion of the crankshaft deviations from the desired timing. For example, from the DE 19 722 316 a method for controlling an internal combustion engine, wherein starting from a signal which characterizes a preferred position of a shaft (top dead center of the cylinder), control variables are predetermined, wherein cylinder-specific corrections of this signal are provided. These corrections are stored in a map of correction values. The control variables may be the injection of fuel, in particular the injection time. Due to torsional vibrations of the crankshaft and / or the camshaft, there is a deviation between the position of the reference pulse R and the actual top dead center of the crankshaft. According to this document, it is provided that correction values are determined, stored in a memory and taken into account in the calculation of the control signals. These correction values are stored in a memory depending on operating conditions for each cylinder. A similar procedure goes out of the DE 10 2007 019279 A1 out.

The DE 69 410 911 describes an apparatus and method for compensating crankshaft torsional distortions. The method described therein relates to the detection of misfire in internal combustion engines and a system for compensating for systematic irregularities in the measured engine speed caused by torsional bending of the crankshaft. For this purpose, cylinder-specific correction factors for ignition pulses, which are generated offline and stored in a memory device, are used to compensate for irregularities in the synchronization of profile ignition measurement intervals. This map of correction factors is determined during the calibration of a motor type by a test motor or by a simulation.

The DE 112 005 002 642 describes a motor control system based on a rotational position sensor. Here, the engine control system includes two angular position sensors for a rotating engine component to determine the torsional deflection of the component. The engine controller responds to torsional deflections by changing the operation of the engine. It is provided that the crankshaft each having a sensor at the front and at the rear end of the crankshaft to determine the angular positions of the front and the rear end relative to each other. A similar procedure goes out of the JP 2001-003793 A but the torsional deflection is determined by means of two sensors crank angle resolved.

A disadvantage of the solutions known from the prior art is that only a local rotation with respect to individual cylinders or a global rotation of the crankshaft with respect to the crankshaft angle is determined or calculated.

A further disadvantage of the solutions known from the prior art is that the crankshaft angle information is determined only for a single selected crankshaft angle position, usually at the top or bottom Dead center. This is particularly disadvantageous because not all sensor and / or actuator events necessarily have to be correlated with top dead center.

It is therefore an object of this invention to provide a method and an internal combustion engine, by which or by which individual cylinder and crank angle resolved determines the crank angle deviation for individual or all cylinders and thus a corresponding crank angle-dependent sensor and / or crank angle-dependent actuator signal can be corrected.

This object is achieved by a method according to claim 1 and an internal combustion engine according to claim 8. Advantageous embodiments are defined in the subclaims.

This is achieved in the method according to the invention in that a cylinder-individual and crank angle-resolved value of the angular deviation is determined for at least two of the cylinders and the crank angle-dependent actuator or sensor signals are corrected as a function of the determined angular deviation, whereby the cylinder-individual and crank angle-resolved value of the angular deviation is calculated. wherein the calculation of the cylinder-individual and crank angle-resolved value of the angular deviation takes into account the geometric distance of the individual cylinders from the output side of the crankshaft assumed to be firmly clamped and the firing interval of the cylinders.

In other words, this means that at least two of the cylinders are assigned a cylinder-individual crank angle-resolved value of the angular deviation and, depending on the angular deviation, crank angle-dependent sensor and / or crank angle-dependent actuator signals are corrected.

Cylinder-individual determination of the crank angle position means that for each position of the crankshaft to which a cylinder is assigned, the crank angle position is determined or determinable.

Crank angle resolved means that the crank angle information is present not only, as described in the prior art, for a single selected crankshaft angular position, but for each crank angle of a working cycle (720 ° in a 4-stroke engine).

The cylinder-individual value thus indicates, for a single cylinder of the plurality of cylinders, that angular deviation in degrees which the respective cylinder has with respect to its angular position with the crankshaft unloaded, thus not affected by torsion.

It has been shown in experiments and calculations of the applicant that the torsional angle deviation of individual cylinders does not correspond to the interpolated from a global torsional rotation angle deviation. Rather, there are significant deviations from this idealized consideration, which are caused on the one hand by additional, the torsion superimposed torsional vibrations. This may, for example, lead to the angle deviation having a different sign compared to the value calculated by interpolation of the global rotation, that is, H. The expected passage time of the corresponding crankshaft position can take place earlier instead of earlier or vice versa.

The particular advantage of the method according to the invention is also that the information about the actual crank angle is present not only for each individual cylinder, ie, for each cylinder position along the longitudinal axis of the crankshaft, but also for crankshaft angle resolution. This is particularly interesting because not all sensor and / or actuator events necessarily have to be correlated with top dead center. Examples of crank angle-dependent interventions that are not at top dead center take place, are about the ignition, the injection, pilot injection and the evaluation of crank angle-based parameters, such as the cylinder pressure. Therefore, it is relevant to know the real crank angle offset also for a different angular position of the crankshaft than the top dead center.

According to the invention, it is provided that the cylinder-specific value of the angular deviation is calculated.

It is thus provided that for at least one of the n cylinders the value of the angular deviation is determined by computational methods. One possibility for this are analytical solutions for the deformation of the crankshaft as a function of the currently prevailing operating conditions, such as power and / or torque.

According to one embodiment, a replacement function is formed, which outputs, based on existing input values, the torsion of the crankshaft from all existing interpolation points of the propagating torsional vibration over the engine cycle.

• Zündreihenfolge
• Zündabstand
• Distanz zwischen Zylinderposition zur Messposition an der Kurbelwelle
• Materialeigenschaften und Geometrie der Kurbelwelle
• Maximale Amplitude der Torsion bei einem definiertem Lastpunkt (ermittelt entweder aus einer Modellrechnung der Verformung der Kurbelwelle bei gegebenem Drehmoment oder aus Referenzmessung am gegenüberliegen dem Ende der Kurbelwelle)
• Motorlast (zur Skalierung der Amplitude im Betrieb)

The following quantities are used as input variables of the equivalent function of the crankshaft torsion according to this example:

• firing order
• firing interval
• Distance between cylinder position and the measuring position on the crankshaft
• Material properties and geometry of the crankshaft
• Maximum amplitude of torsion at a defined load point (determined either from a model calculation of the crankshaft deformation for a given torque or from a reference measurement at the opposite end of the crankshaft)
• Motor load (to scale the amplitude during operation)

In the calculation, a cylinder-specific weighting factor is first determined for all cylinders. This weighting factor takes into account the firing intervals of successive firing cylinders. The firing interval is the angular difference in the ignition timing of two successive firing cylinders.

Thereafter, a torsion index can be determined for each cylinder. The torsion index results from multiplying the spark gap to the previous cylinder (according to the firing order) with the distance to the reference point of the shaft and the weighting factor.

The torsion index is scaled over the maximum amplitude of the torsion. That is, the amount of the calculated torsion index is calibrated with the amount of torsion determined by measurement for a selected position. Conveniently, the calibration is done with the maximum value of the torsion.

The torsion index can now be scaled by considering the engine load for different load points.

Subsequently, a weighting factor of the vertices is defined on the basis of the ratio of the firing intervals of successive firing cylinders. Based on the angular distance between two successive firing cylinders, the distance to the reference point of the shaft and the calculated weighting factor of the vertices, a torsion index is calculated for each cylinder. This measure is scaled with the measured, modeled or calculated maximum amplitude of the torsion.

Now the next cylinder in the firing order is chosen. This cylinder is assigned a factor which is proportional to the geometric distance, ie the distance of the corresponding crankshaft crankshaft of this cylinder to the output cylinder. This factor is representative of the degree Rotation with respect to a reference point, such as the ring gear on which a rotation can be easily measured, because the rotation of two cylinders to each other is the same torsional moment, the greater the further the two cylinders are apart.

In the next step, the cylinder next in the firing order is selected again and the geometric distance to the last fired cylinder is used as a factor.

This factor is determined in the same way for all remaining cylinders. Then the magnitude of the factor with the second measured value on the crankshaft is calibrated such that the correct value for the angular deviation results at this second measuring position by application of the multiplication factor. In other words, by multiplying the angular deviation of the first cylinder by the factor of the last cylinder, the angular deviation for the last cylinder must result. Via the relation of these two positions, accessible by measurement, the multiplication factors of all cylinders can be calibrated.

The effect of the replacement function is explained by means of an example:
the firing order is a chronological sequence of the firing times of the individual cylinders predetermined by the crankshaft crankshafts, ie mechanically and for a given engine.

If this factor is then plotted for all cylinders according to the firing order, the angular deviation caused by the torsion is seen for each cylinder.

For the replacement function, an amplitude value (amount of rotation) is determined for at least one cylinder with which the calculation result can be scaled. The amount of twist is a measure of the elastic characteristics and stiffness of the crankshaft.

The amount is the larger, the farther its predecessor is removed.

In order to map the torsional behavior of the crankshaft correctly, the ignition sequence and ignition intervals are considered next. For example, in a V engine, the spark gaps may be at 60 ° and 30 ° crank angles, so all cylinders are split into a 720 ° crank angle cycle. The firing interval is a measure of the unevenness with which torsional or torsional vibration is introduced into the crankshaft.

In the next step, the cylinder following the reference cylinder is considered: its contribution to the rotation is determined by multiplying the value determined for the reference cylinder by the geometric longitudinal distance.

It can preferably be provided that the cylinder-specific value of the angular deviation, Δφ _i , is calculated by a model function. This concerns the case in which a model function is created for the deformations of the crankshaft, from which the value Δφ _{i of} the angular deviation can be determined for the position of the crankshaft associated with the cylinder i. On the one hand, the geometrical and elastic parameters of the crankshaft are included in the model function, on the other hand, the currently prevailing operating conditions, such as the power and / or the torque. The model function, which contains all relevant geometric and elastic parameters of the crankshaft, can now be easily calibrated using the previously determined correction function. As a boundary condition, the rotation must be zero even for zero load.

According to a preferred embodiment, it is provided that the cylinder-specific value Δφ _{i of} the angular deviation is calculated in real time based on engine output signals. Thus, the case is detected in which the calculation of the angular deviation happens in real time, that is, not is resorted to a ready-made solution for the angular deviation, but the calculation instantaneous, ie directly, in the current engine cycle, takes place. The particular advantage of this embodiment is that quickly changing parameters, such as a fluctuating engine load, can be taken into account in the evaluation.

It can preferably be provided that at least one motor control variable is changed as a function of at least one cylinder-specific value of the angular deviation Δφ _i . This describes the case that at least one motor control variable receives the determined angular deviation Δφ _i as a further input variable, and thus the angular deviation of the at least one cylinder can be compensated. The engine control variable may be, for example, the ignition timing or the injection timing of a fuel or the opening time of a fuel introduction device. For example, when determining a positive angular deviation Δφ _i for a cylinder Z i (that is, the cylinder Z with index i reaches its position earlier than intended), the ignition timing for this cylinder can be advanced.

According to a further preferred embodiment, it is provided that at least one engine measurement signal is corrected via at least one cylinder-specific value Δφ _{i of} the angular deviation. By this is meant that measurement signals from the engine, for example the signals of a cylinder pressure detection, are corrected with the aid of the determined value of the angular deviation Δφ _i . To be corrected means that by taking into account the angular deviation, the measurement signals can be assigned much more accurately to the actual position of the piston of the considered piston-cylinder unit. This is particularly interesting for cylinder pressure detection, because the crank angle determines the spatial position of the piston in the cylinder. In the case of an angular deviation, therefore, the detected cylinder pressure is assigned to a wrong spatial position of the piston. Therefore, a correction is particularly advantageous for engine diagnostics in general, since sensor signals can now always be assigned to the correct crankshaft position.

Fig. 1a und 1b

eine schematische Darstellung einer Brennkraftmaschine

Fig. 2

eine Darstellung der torsionsbedingten Kurbelwellenwinkelabweichung für 90° Zündabstand

Fig. 3

eine Darstellung der torsionsbedingten Kurbelwellenwinkelabweichung für 120°/60° Zündabstand

The advantages of the invention will be explained in more detail with reference to FIGS. Showing:

Fig. 1a and 1b

a schematic representation of an internal combustion engine

Fig. 2

a representation of the torsional crankshaft angle deviation for 90 ° Zündabstand

Fig. 3

a representation of the torsional crankshaft angle deviation for 120 ° / 60 ° Zündabstand

The following is the detailed description of the figures.

FIG. 1a schematically shows an internal combustion engine with 8 cylinders, wherein the output side (in this case marked by the generator G) is started to count on the left cylinder bank. For the V engine, cylinders Z1 - Z4 are located on the left cylinder bank and cylinders Z5 - Z8 on the right cylinder bank. Also indicated is the crankshaft K, with which the cylinders Z1 to Z8 are connected via connecting rods. The cylinder Z1, that is to say the location of the introduction of force through the connecting rod of cylinder Z1, is very close to the output side assumed to be clamped.

FIG. 1b shows an internal combustion engine with eight cylinders in a series arrangement. In the in-line engine is counted from Z1 to Z8.

The firing order in these examples is Z1 → Z6 → Z3 → Z5 → Z4 → Z7 → Z2 → Z8.

In FIG. 1b is the firing interval, expressed as the crank angle difference, 90 °. After ignition of the cylinder Z8 you start again with cylinder Z1. For this example, the ignition distance with respect to the crank angle is therefore the same Distributed intervals on the cylinders. Every 90 ° crank angle, a firing event takes place.

FIG. 2 shows a diagram in which the ordinate the torsional angular deviation of the crankshaft at the position of cylinder Z8, Δφ ₈ , over a total cycle, ie 720 ° crank angle is plotted.

If the firing order explained above is run through, the resulting angular deviation Δφ ₈ results, which will be discussed below. For a better understanding, those cylinders that ignite at the respective crankshaft position were entered in a parallel-shifted auxiliary axis. First cylinder Z1 ignites at 0 ° crank angle. Since cylinder Z1 is located very close to the output side assumed to be rigid, the ignition event of cylinder Z1 with respect to the crankshaft position of cylinder Z8 can cause virtually no twisting of the crankshaft.

The next ignition event, 90 ° crankshaft angle later, takes place at the cylinder Z6. This causes due to the distance to the output side, the greater contribution to the rotation of the crankshaft.

Expressed in words, the peak of the curve Δφ ₆ at the crankshaft position 90 ° corresponds to the contribution of the angular deviation of the crankshaft caused by cylinder Z6 to the position of the cylinder Z6.

The next firing event, this is cylinder Z3, takes place at 180 ° crankshaft angle. This cylinder (more precisely: the point of engagement of the associated connecting rod on the crankshaft) is located less far from the output side than Z8 and can thus only make a smaller contribution to the rotation of the crankshaft at the position of cylinder Z8. The next ignition event (cylinder Z5) takes place at 270 ° crankshaft angle and delivers a much lower contribution to the rotation at the crankshaft position of cylinder Z8 because of the still closer position to the output for example, the cylinders Z8 and Z3. Next, cylinder Z4 fires and causes a greater twist (comparable to cylinder Z8) as it is similarly far from the output as cylinder Z8. The next firing event is the ignition of cylinder Z7 at 450 ° crankshaft angle. The next ignition event is cylinder Z2 at 540 ° and Z8 at 630 °. The 720 ° correspond again to the beginning of the scale at 0 °, ie ignition of cylinder Z1.

If one plots torsional angular deviation for other cylinders in the diagram, then the maxima lie below the curve plotted for cylinder Z8, scaled by their respective distance from the output side assumed to be firmly clamped.

It can therefore be seen that the cylinders, due to their different distance from the output side, produce very different amounts for the rotation of the crankshaft at the cylinder position Z8. The resulting curve thus describes crankshaft angle resolution and cylinder-specific (shown here for the crankshaft position of cylinder Z8) the torsion-related twisting of the crankshaft. This characteristic of the angular deviation Δφ _i (with i as a counter of the respective cylinder) can now be extrapolated to any cylinder or to any axial position of the crankshaft, since as a further boundary condition the torsion-induced angular deviation for the cylinder Z1 is "zero "is known.

Due to the equidistant selection of the firing intervals (every 90 °), the same time interval results with respect to the propagation of a torsional vibration for all cylinders, which means that the torsional vibration has the same time for all cylinders to propagate. The height of the angular deviation Δφ _i is thus given purely by the axial position of the cylinders on the crankshaft.

FIG. 3 shows in a diagram analogous to FIG. 2 the angular deviation Δφ ₈ for the cylinder Z8 of in FIG. 1a 8-cylinder engine shown, but with different firing intervals. The firing order was maintained with Z1 → Z6 → Z3 → Z5 → Z4 → Z7 → Z2 → Z8, but the ignition distances expressed in crank angles are 120 °, 60 °, 120 °, 60 °, 120 °, 60 °, 120 ° etc. It is therefore, as based on FIG. 2 explains, again 180 ° crank angle between the firing events of the cylinders Z1, Z3, Z4 and Z2, but only 60 ° between the firing events between cylinders Z6 → Z3, Z4 → Z7, and Z8 → Z1. The changed firing intervals affect the pattern of the angular deviation, which is plotted here for the crankshaft position at cylinder Z8. The ignition of the cylinder Z1 at 0 ° crankshaft angle again has no significant effect on the rotation of the crankshaft at the position of the cylinder Z8. The contributions to the rotation behave in proportion to the firing intervals, because a firing interval of 120 ° causes an initiated torsional vibration to propagate longer than is the case with a firing interval of 60 °.

While in the example of ignition intervals after FIG. 2 , where all cylinders are ignited at the same firing intervals, and so the resulting torsional vibration each has the same time to propagate, resulting in the example of the firing intervals 120 ° / 60 ° in FIG. 3 another picture of the angle deviation. The contributions to the torsional vibration of those cylinders which are ignited at 120 ° Zündabstand behave to those cylinders which are ignited at 60 ° Zündabstand, such as 2: 1, the ratio of the contributions, expressed as a weighting factor, is thus at 2/3 3.1.

The weighting factor takes into account how much later the next force is applied.

Again, the resulting pattern of angular deviation Δφ _{i can} now be transferred to any axial position of the crankshaft, as Edge condition is again established that with cylinder Z1 on the output side no rotation takes place.

According to the method, it is thus possible, without measurement and only from knowledge of the firing intervals and the firing order, and the distance of the cylinders to each other, crankshaft angle resolved for each cylinder to determine the amount of the angular deviation caused by the torsion or torsional vibration. The invention thus makes use of the knowledge that a standing wave of the torsion or of the torsional oscillation prevails over a period of 720 ° crankshaft angle.

The weighting factor takes into account whether the firing order is harmonious (same firing interval across all cylinders), or whether the firing intervals occur at unequal intervals, expressed as crank angle. The crank angle, which is between two firing events, is equal to the time the vibration has to stamp out. When interpreted as waves means a uniform firing interval that all ignition events occur in phase, with unequal firing intervals there are several waves (two waves at two different firing intervals), which are in shifted phase relation to each other.

Motor diagnostics can be operated particularly advantageously with the method according to the invention since sensor signals can now always be assigned to the correct crankshaft position. For example, sensor signals of cylinder pressure monitoring with respect to the torsional angle deviation can be corrected. In sum, higher quality combustion control can be achieved, resulting in higher efficiency and higher power density. Particularly favorable, the method by the improved accuracy of the ignition timing and measurements in the cylinder, such. B. a cylinder pressure detection.

Claims (9)

1. A method of controlling an internal combustion engine (1) having a plurality of cylinders (Z), wherein actuators of the internal combustion engine (1) are actuable in crank angle-dependent relationship and/or sensor signals of the internal combustion engine (1) can be ascertained in crank angle-dependent relationship,
   for compensation of a torsion of a crankshaft (K), by which torsion deviations in the crank angle occur between a twisted and an untwisted condition of the crankshaft (K),
   wherein for at least two of the cylinders (Z) a cylinder-individual and crank angle-resolved value of the angle deviation (Δϕ_i) is ascertained and the crank angle-dependent actuator or sensor signals are corrected in dependence on the detected angle deviation (Δϕ_i), characterised in that the cylinder individual and crank angle-resolved value of the angle deviation (Δϕ_i) is calculated, wherein for calculation of the cylinder individual and crank angle-resolved value of the angle deviation (Δϕ_i) the geometrical spacing of the individual cylinders (Z) from the drive output side of the crankshaft (K), which is assumed to be fixedly clamped, and the firing spacing of the cylinders (Z) is taken into consideration.
2. A method as set forth in claim 1 characterised in that a stationary internal combustion engine e is used.
3. A method as set forth in one of claims 1 or 2 characterised in that the cylinder-individual and crank angle-resolved value of the angle deviation (Δϕ_i) is calculated by a model function.
4. A method as set forth in one of claims 1 through 3 characterised in that the cylinder-individual and crank angle-resolved value of the angle deviation (Δϕ_i) is calculated in real time based on engine output signals.
5. A method as set forth in one of the preceding claims characterised in that at least one engine management parameter is varied in dependence on at least one cylinder-individual and crank angle-resolved value of the angle deviation (Δϕ_i).
6. A method as set forth in one of the preceding claims characterised in that at least one engine measurement signal is corrected by way of at least one cylinder-individual and crank angle-resolved value of the angle deviation (Δϕ_i).
7. A method as set forth in claim 6 characterised in that the engine measurement signal is the result of a cylinder pressure measurement operation.
8. An internal combustion engine (1) having a plurality of cylinders (Z), adapted for carrying out the method as set forth in at least one of claims 1 through 7.
9. An internal combustion engine (1) as set forth in claim 8 characterised in that the internal combustion engine is a stationary internal combustion engine.

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