DE4208033C1 - Identifying and monitoring selected cylinders of IC engine - forming difference value between two RPM values of cylinders in ignition sequence - Google Patents

Abstract

The method involves determining a mean r.p.m. value for a selective cylinder during a working stroke of each cylinder across a mean crankshaft angle of rotation range. A difference value is formed between the mean r.p.m. values of two successive cylinders in the ignition sequence. This difference value as an identification parameter is compared with a predetermined threshold value. The predetermined threshold value is established depending on the load and the r.p.m. of the IC engine. With the overstepping of the threshold value, a fault indication is activated. The difference value (D2) for the actual working cycle in addition to the difference value (D2') for the preceding working cycle of the same cylinder (Z2) is used as the identification parameter (EP). USE/ADVANTAGE - For selective cylinder identification and monitoring of combustion misfires in multi-cylinder IC engine. In addition, high combustion interruption rates can be reliably identified.

Description

The invention relates to a method for cylinder-selective Detection and monitoring of combustion misfires a multi-cylinder internal combustion engine according to the preamble of claim 1 and an apparatus for performing this Method according to the preamble of claim 6.

For misfires, the cause can be an error liable fuel metering or ignition, in particular special misfires due to defects in an electronic Engine control device, the ignition coils and the spark plugs occurrence.

Modern motor vehicles are equipped with emission control systems equips that contain a catalytic converter. It is allqe my known that such a catalytic converter in case of overheating damaged and its effectiveness destroyed can. There is a particular risk from overheating Misfiring of the internal combustion engine if Nachreak ions of the unburned fuel-air mixture in the exhaust gas tract occur. A particular problem is that reduced in their effect by overheating or ineffective got rid of exhaust gas catalysts only with great effort are adjustable.  

It is already known to solve this problem (DE 40 09 285 A1), a multi-cylinder internal combustion engine on combustion monitoring misfires and to avoid a Damage to the catalyst due to afterburning the driver of a vehicle by lighting up an error lamp on the arm warning board and an error that has occurred for a Store customer service diagnostics.

This and goes to the detection of a misfire other known methods based on the consideration that the Combustion in each cylinder the resulting gas forces Generate torque on the crankshaft, which during the Dre hung around a crank angle range on the crankshaft work accomplishes. When the exile is suspended, this work not performed and the rotational energy decreases accordingly and thus the speed at the crankshaft in the assigned Crank angle range.

An easy way to detect such a rotation Decrease in the number of misfires is that during a working stroke of each cylinder via a be agreed crankshaft rotation angle range cylinder-select tive, averaged speed value is determined. Subsequently this speed value will precede the speed value of the the combustion or the preceding Zy in the firing order linders compared in such a way that a difference value det. This difference value is used as a detection parameter compared with a predetermined threshold. When over If the threshold value is exceeded, an error display is triggered.

The specification of a threshold value is necessary because not every slight deviation in the speed values between two Burns already indicates a misfire. Deviations are due to interference, for example cyclical fluctuations, manufacturing tolerances in the ring gear and retrospective bumps possible. The interference are dependent on the load and speed, so that they are known per se The predetermined threshold values in a characteristic  and are stored depending on the speed. A general, in itself known dependence of the interference is that these also become larger with greater load, so that the Threshold values for a larger load (or a larger load sig nal, such as a throttle valve position) larger are to be dimensioned.

The above procedure recognizes with good results individual misfires. At high dropout rates however, difficulties arise for the following reasons:

If a cylinder fails 100%, what z. B. a defective ignition corresponds to candle, so with a six-cylinder internal combustion engine machine at least 1/6 of the possible energy provided so that there is a corresponding reduction in performance results. This reduction in performance must be maintained constant driving condition (same vehicle speed) compared to the state before the cylinder was exposed higher load requirement (accelerate more) can be compensated.

This higher load requirement corresponds to a higher load sig nal, where the relation between load and torque is related to normal combustion that is not disturbed by misfires, no longer true. Because of the dropouts, only one higher load state via the larger load request signal feigned, with a high, from the threshold value map threshold value assigned to a high load state, read out becomes.

The state disturbed by a high dropout rate becomes a wrong, too high threshold value assigned, so the danger there is that this too high threshold of detection parameters not exceeded despite misfires and so that no misfire is recognized at all, although a very high dropout rate (in the present example a cylinder is 100%).

In contrast, the object of the invention is a Generic method for cylinder-selective detection and monitoring of misfires in a multi-cycle Linder internal combustion engine and correspondingly a device to carry out this method so that high misfire rates can also be reliably detected.

This task is marked with regard to the method nenden features of claim 1 and with respect to the Vorrich tion with the characterizing features of claim 6 ge solves.

According to claim 1, the difference is the detection parameter value for the current work cycle plus the difference value for the past working cycle of the same cylinder.

Now places a cylinder several times in succession or at 100% off, two (large) difference values, namely that for the current work cycle and that for past work play of the same cylinder added, which makes the detection parameter increases strongly and thus again over one of the Threshold value map output (at high misfire rates high) threshold. With individual dropouts (without that in the previous cycle of the same cylinder a ver misfiring has occurred) is the difference value for the current work cycle no difference or only a slight difference limit of the same cylinder for the previous work game added, so that such "single dropouts" in Connection to one corresponding to the actual load Threshold value can be recognized well.

In the above, a (ge middle) speed value within a certain crank shaft rotation angle range used. These speed values who by measuring the time when the particular crank passes shaft rotation angle range on a non-contact Sensor determined. The statements in connection with the Speed values and speed difference values are therefore the same  also with time values and time difference values adjustable.

As stated, in the event of a misfire, the Speed due to the Ver not provided in this work cycle combustion energy. The increases especially at low loads Speed only slow again after a misfire at. This can lead to incorrect double detection because then a large speed difference value to the previous ar beitstakt is registered, but only because of the slow Increase in speed after the misfire and not because another dropout occurs.

To avoid such false double detection proposed with claim 2 that the difference value for the current work cycle and the difference value for the past gene working cycle of the same cylinder each of the difference value of the cylinder preceding in the firing order or the previous combustion is deducted. If now in front was a dropout, so the double detection avoided. Was not in the previous work cycle Misfires are the difference values in the firing order preceding cylinder or previous burning Insignificantly small and practically ineffective.

For reliable detection of misfires even with a dynamic engine operation is a supplement the recognition parameter by a dynamic known per se compensation value proposed according to claim 3. At a dynamic engine operation is evident in acceleration fall a speed drop due to a misfire of an increase in speed due to acceleration superimposed where may not be recognized by a dropout. Ande on the other hand occurs when the internal combustion engine works correctly machine decelerates when decelerating, which leads to incorrect detection of a (non-existent) Ver misfire could result. The detection parameter is therefore according to claim 3 by a dynamic compensation value  added as the difference between the average speed values of two work cycles is formed, these two Ar beats at intervals of several burns lie to each other.

For an adaptation to the conditions of a specific distillery engine and to coordinate the process it is before partial, the components and sizes, especially the differences limit values from which the recognition parameter is formed, with assigned weighting factors depending on the load and / or weight the speed. For this purpose, claim 4 a corresponding map proposed in which this Ge weighting factors are stored.

The crankshaft rotation angle ranges for measuring their Transit time and the determination of the corresponding, average Ren speed values can each from top dead center (TDC) to at bottom dead center (UT). That closes one observation time immediately after the other every work cycle. If the size of these areas and / or whose position is changed within a work cycle, who the obviously different "averaged" speed values received for the assigned work cycle. this fact can be advantageous according to claim 5 for further adjustment and optimization of the process to specific circumstances be applied. It is suggested that values for the size ß and / or the position of the crankshaft rotation angle range as Measurement or observation window from a map load and / or depending on the speed.

A generic device for performing the procedure According to claim 6, rens consists of a first device for identification the crankshaft position. In a manner known per se in addition to an internal combustion engine using the four-stroke process works, a ring gear on a flywheel in verbin with a phase encoder on the camshaft the.  

The device further comprises a second device for Er averaging a cylinder-selective, averaged speed value over a certain crankshaft rotation angle range during of a working stroke of a cylinder.

The device further comprises a third device which a difference unit to form a difference value between between the averaged speed values of two, in the firing order contains successive cylinders.

A fourth device is also included in the device ten that a comparator unit and an associated Threshold value specification unit comprises, the difference value as Detection parameters from the third establishment of the comparison cher unit for comparison with the threshold value is supplied. This fourth facility is with a fifth facility connected as an error display, which over a threshold value is controlled.

According to the invention, the device is characterized in that that a memory is provided as a shift register, the determined difference values for a current work cycle and Differential values go back to a previous work game of the same cylinder temporarily saves. Next is in the third device also has a summing element, that is connected to the memory and that as a detection para meter the sum of the difference value for the current work game and the difference value read from the memory for the previous work cycle of the same cylinder bil det, the detection parameter determined in this way being the fourth Device for comparison with the threshold value is supplied.  

With such a device, misfires are high Misfire rates are reliably detected, even if caused by a "Wrong" load signal specified too high a threshold is how this in connection with the procedure according to An saying 1 has already been described.

To avoid double detection, the device further developed according to claim 7 in such a way that the third Device further comprises a differential element, which with the Memory is connected. To form the detection parameter is the difference value for the current work cycle and the Difference value for the past work cycle of the same Cylinder each the difference value in the firing order preceding cylinder or previous burning deducted.

For compensation of the speed change in a dynami The operation of the internal combustion engine is according to claim 8 third device equipped with a further summing element In the dynamic of the value for the recognition parameter compensation value is supplemented from the stored values as the speed difference value between averaged speed values two work cycles is formed, the at intervals of several burns.

With the features specified in claim 9, the Vorrich to the specific conditions of an internal combustion engine be adapted and optimized.

Using a drawing, the invention with further details units, features and advantages.

Show it

Fig. 1 is a schematic representation of an electronic control system with combustion misfire detection for a six-cylinder internal combustion engine,

FIG. 2 is a flow in the computer unit for He identification of misfires,

Fig. 3 is a diagram showing the speed profile over the crank shaft rotation angle of a six-cylinder Brennkraftma machine is, the second cylinder 100% exposed in each operating cycle,

Fig. 4 is a diagram corresponding to Fig. 3 with different positions of measuring windows and

Fig. 5 is a diagram corresponding to Fig. 3, with the second and fourth cylinders to 100%.

In Fig. 1, a gear 2 is placed on a crankshaft 1 , the teeth 3 or tooth flanks of which cooperate as a signal generator with a first sensor 4 . In an internal combustion engine that operates in four-stroke mode, each working cycle consists of two revolutions of the crankshaft. For a six-cylinder internal combustion engine, this results in three burnings per revolution. Each cylinder is assigned 1/3 of a circle, i.e. 120 °. With a number of 135 teeth on the gear 2 then corresponds to a crankshaft angle of 120 ° a number of teeth 45. The crankshaft 1 drives at half the crankshaft speed a camshaft 5 , which carries a phase mark 6 , which cooperates with a second sensor 7 . This phase marker enables a definite assignment of a specific cylinder to a crankshaft angle.

The signals from the two sensors 4 and 7 are fed to a digital control unit 8 , to which further parameter signals, in particular a load signal 9 , are fed. The Steuerge advises 8 determines the injection timing and the injection quantity and the ignition timing from the supplied signals for each cylinder and transmits corresponding signals to an electronic injection device 10 and an electronic ignition device 11 .

In addition, an arithmetic unit 12 is provided which, if the information about speed, position of the pistons of the internal combustion engine is supplied within a working cycle and load (arrow 13 ).

An error indicator 14 is connected to the arithmetic unit 12 (shown schematically as an error lamp), which is activated when a misfire occurs.

The structure and function of the computing unit 12 are explained in more detail with reference to the program sequence according to FIG. 2:

In a first step 15 , time measurements are carried out with the aid of the tooth signal (from the first sensor 4 ) and the phase signal (from the second sensor 7 ), the operation of a specific crankshaft rotation angle range (measuring window) being detected at the sensor 4 and via the phase signal is assigned to a certain cylinder. This time measurement takes place every working cycle of a cylinder. The measurement window can take the entire crankshaft angle (120 ° in the present example of a four-stroke six-cylinder internal combustion engine), but can also be selected as a measurement window, as will be explained in more detail in connection with FIG. 4.

In a further step 16 , the time measurement is used to calculate an average speed value within the measuring window. This averaged speed value is assigned to each work cycle in a cylinder-selective manner.

In a further program step 17 , a differential value is formed as the speed difference value between averaged speed values of two successive cylinders in the firing sequence or successive combustions or measurement windows.

In a further step 18 of the program, these difference values are stored in a shift register over two work cycles, so that the difference values are available for evaluation each time over two work cycles and can be read from the memory.

An essential step 19 of the program sequence relates to the formation of a recognition parameter EP, which is then compared with a threshold value:

The detection parameter is the sum of the difference value D2 for the current work cycle and the difference value D2 ′ for the past working cycle of the same cylinder det.

As an example, reference is made to FIG. 3 and the case of the formation of the detection parameter EP at the misfire of the cylinder Z2 (arrow 22 ) is shown.

In a simple embodiment, there is the orken nation parameter EP from the sum of the difference values D2 + D2 '.

In a further training, it is advantageous, in order to avoid double detections, to modify this detection parameter EP such that the difference value D6 or D6 'of the difference value D2 of the current work cycle and of the difference value D2' of the past work cycle of the same cylinder Z2 Ignition sequence preceding cylinder Z6 is subtracted, so that the following detection parameters result:
EP = (D2-D6) + (D2'-D6 ').

To take into account and compensate for dynamic states the recognition parameter EP is additionally determined by a Dyna Micro compensation value DK supplemented as the speed difference value between the average speed values of two work cycles is formed, but these work cycles in contrast to the speed difference values determined so far at a distance meh more burns, e.g. B. at intervals of 6 burns lie to each other.  

In addition, in program step 19 , an evaluation and weighting of the difference values used and the dynamic compensation value can be carried out in such a way that weighting factors X1 to X5 are stored in a map, depending on the load and / or speed, which depend on the individual components of the detection parameter for a weighting Load and speed status can be assigned. The overall result is a recognition parameter using the following formula:
EP = (X1D2-X2-D6) + (X3D2'-X4D6 ′) + X5DK.

A detection parameter EP formed in this way is compared in the program step 20 with a load- and speed-dependent threshold value, which is read from a corresponding map. If this threshold value is exceeded, an error display is triggered in program step 21 .

In the first program step 15 can be used for an adjustment and optimization Opti also the position of the measuring window for the time measurement within an operating cycle shifted, as will be on hand of Fig. 4 explained in more detail.

In Fig. 3, the speed curve over the crankshaft rotation angle is recorded for a six-cylinder internal combustion engine, the second cylinder Z2 being 100% suspended in each working game, for example if the associated spark plug is defective.

Referring to FIG. 3, the cylinder Z6, Z2 have a firing sequence Z5, Z1, Z4, Z3,. The entire work cycle is considered here as the measurement window, so that the averaged speed values shown are obtained. The difference value D2, which is assigned to the cylinder Z2, is thus calculated from the difference between the current, mean speed value 2 and the mean speed value 6 of the preceding cylinder Z6. It can also be seen from the diagram in FIG. 3 that with each misfire of the cylinder 2 the average speed drops and only gradually increases again during the combustion of the subsequent cylinders.

In Fig. 4 is a similar diagram as in Fig. 3 Darge presents, here a misfire occurs in the sixth cylinder Z6 and thereby the speed drops noticeably there within the assigned work cycle. With Fig. 4 is to be shown that the size and location sters substantially affect a Meßfen within a working stroke, the size of the average speed value and hence the position and size and, if applicable. A control-system change can be used for an adjustment and optimization.

For example, the measurement windows M3, M6 and M2 are in the middle of a respective work cycle and comprise 30 ° crankshaft revolution. This results in the average speed values 3, 6 and 2, as they are entered in Fig. 4.

Furthermore, in Fig. 4 towards the end of the respective work cycle shifted measuring windows M3 ', M6' and M2 'of the same size are shown. This clearly results in other, averaged speed values 3 ', 6' and 2 ', whereby the difference values formed from the averaged speed values are also changed depending on the position and size of the measurement window.

In Fig. 5, another diagram of the speed curve of a six-cylinder internal combustion engine is shown, in which the second cylinder Z2 and the fourth cylinder Z4 suspend 100%, as can be done, for example, in the event of failure of a double ignition coil. Obviously, the speed drops in each work cycle for cylinder 2 and cylinder 4 because of the misfires and then increases again. It is also indicated by brackets 23 that the difference value for the current work cycle is considered in each case to form the detection parameter and the difference value for the past work cycle of the same cylinder is added.

Claims (9)

1. A method for cylinder-selective detection and monitoring of misfires in a multi-cylinder internal combustion engine, wherein
a cylinder-selective, average speed value is determined during a work cycle of each cylinder over a specific crankshaft angle of rotation range,
in each case a difference value between the averaged speed values of two successive cylinders which are formed in the firing sequence
this difference value is compared as a detection parameter with a predetermined threshold value,
the predetermined threshold value is determined as a function of the load and the rotational speed of the internal combustion engine and
if the threshold value is exceeded, an error display is triggered, characterized in that
that the difference value (D2) for the current work cycle plus the difference value (D2 ′) for the previous work cycle of the same cylinder (Z2) is used as the detection parameter (EP). 2. The method according to claim 1, characterized in that from Difference value (D2) for the current work cycle and from Difference value (D2 ′) for the past work cycle of the same cylinder (Z2) the difference value (D6 or D6 ′) of the cylinder (Z6) preceding in the firing order or the previous combustion is subtracted. 3. The method according to claim 1 or 2, characterized in that the recognition parameter (EP) by one component as Dy namik compensation value (DK) is added, which as a rotation number difference value (D) between averaged speed values (n) two work cycles is formed, these two ar work cycles are at intervals of several burns. 4. The method according to any one of claims 1 to 3, characterized records that at least one of the difference values (D) with a weighting factor read from a map (X1 to X5) weighted depending on load and / or speed becomes. 5. The method according to any one of claims 1 to 4, characterized indicates that the size and / or location of the crankshaft Angle range (measuring window M) to determine the zy Lindelective, average speed value () from a Map is taken depending on the load and / or speed. 6. Device for performing the method according to claim 1,
with a first device ( 1 to 7 ) for identifying the crankshaft position,
with a second device for determining a cylinder-selective, averaged speed value over a specific crankshaft angle of rotation range during an operating stroke of a cylinder,
with a third device which contains a difference unit for forming a difference value between the averaged speed values of two cylinders which follow one another in the firing order
with a fourth device which includes a comparator unit and a threshold value presetting unit connected to it, the difference value being fed as a recognition parameter from the third device to the comparator unit for comparison with the threshold value and
with a fifth device as an error display, which is connected to the fourth device and which is activated when the threshold value is exceeded, characterized in that
that a memory is provided as a shift register, the determined difference values (D2) for a current working game and difference values (D2, D2 ') back up to a previous working game of the same cylinder (Z2) temporarily and
that in the third device also a summing element is seen before, which is connected to the memory and which, as a detection parameter, is the sum of the difference value (D2) for the current work cycle and the difference value (D2 ') read from the memory for the previous work cycle forms the same cylinder (Z2) and the detection parameter (EP) thus averaged is fed to the fourth device for comparison with the threshold value. 7. The device according to claim 6, characterized in that the third device further comprises a differential element, that is connected to the storage and to that for education of the detection parameter (EP) from the difference value (D2) for the current work cycle and the difference value (D2 ′) for the past working cycle of the same cylinder (Z2) each the difference value (D6 or D6 ') of the in Firing order of the preceding cylinder (Z6) or the pre- combustion is withdrawn. 8. The device according to claim 6 or 7, characterized net that the third device is another summing element contains a Dyna for the recognition parameter (EP) Mik compensation value (DK) is added, which from the Spei values as speed difference value between averaged Speed values () of two work cycles is formed, the at intervals of several burns lie. 9. Device according to one of claims 6 to 8, characterized ge indicates that maps with load and / or speed dependent map specifications are provided, over which the Difference values with read weighting factors (X1 up to X5) and / or by readout size Food and location values the size and location of the respective cure belwelle rotation angle range (measurement window M) set becomes.