EP0540878A2 - Method for evaluating ignition pulses - Google Patents

Abstract

Methods for evaluating ignition pulses (51, 52, 53, 54) of an internal combustion engine with spark ignition are proposed, in which methods in each case the amplitude of the detected pulses (51, 52, 53, 54) are compared with a predetermined variable threshold (57, 58) and those pulses (51, 52, 53, 54) which exceed the threshold (57, 58) are evaluated. According to a first embodiment, there is provision for the threshold (57, 58) to be fixed at a value at which the time intervals (62, 63, 64) of at least two successive pulses (52, 51; 53, 52; 54, 53) lie within a predetermined ratio. According to a different embodiment in which the ignition pulses (51) of a reference cylinder are additionally detected, there is provision for the threshold (57, 58) to be fixed at a value at which the number of detected ignition pulses (51, 52, 53, 54) within an interval which is given by the interval between two successive pulses (51) of the reference cylinder corresponds to an expected number. <IMAGE>

Description

State of the art

The invention is based on methods for evaluating ignition pulses of a spark-ignited internal combustion engine according to the category of claims 1 or 2. From the specialist book by P. PAULSEN, "Electronic engine test equipment", 1977, Franzis-Verlag (Munich), p. 207 and Figure 9.35 a circuit of an ignition voltage oscilloscope is known which has a trigger device which triggers a horizontal beam deflection when a trigger pulse occurs. The trigger pulse is derived from an ignition pulse of a reference cylinder. The trigger threshold can be adjusted with a trim potentiometer. The trim potentiometer is adjusted when the ignition voltage oscilloscope is adjusted. It is not intended to change the trigger threshold in later operation.

The specification of a fixed threshold is sufficient if only trigger pulses are derived from a reference cylinder, a temporal reference to pulses from other cylinders initially not being important. A quantitative analysis of ignition pulses, especially in ignition systems that contain several independent ignition circuits, requires careful setting of the trigger threshold so that unwanted interference pulses are suppressed and all ignition pulses are detected.

The invention has for its object to provide a method for evaluating ignition pulses of a spark ignition internal combustion engine, which has a high level of operational reliability.

The object is achieved by the features specified in claims 1 or 2.

Advantages of the invention

According to a first embodiment of the method according to the invention, it is provided that the threshold is variable and that the threshold is set to a value at which the time intervals of at least two successive ignition pulses lie within a predetermined ratio.

According to a second embodiment of the method according to the invention, it is provided that the threshold is variable and that the threshold is set to a value at which the number of detected ignition pulses within an interval, which is given by the distance between two successive pulses of a reference cylinder, with a expected number matches.

Both methods have the advantage that an adaptive determination of the threshold above which the ignition pulses are evaluated results in a high level of operational safety in different ignition systems. The increasingly used distributorless ignition systems, some of which contain several independent ignition circuits, can have deviations in the amplitudes of the ignition pulses between the individual ignition circuits. Reliable evaluation of ignition pulses by the variable threshold is also provided in ignition systems of this type.

The method according to the invention enables the threshold to be determined in such a way that the relevant ignition pulses are being detected and interference pulses whose amplitude is lower are suppressed. Interference pulses, the amplitude of which is in the amount of the expected ignition pulses or above, are recognized by the method according to the invention and a corresponding message can be issued.

The evaluation of the time intervals of at least two successive pulses to determine the threshold assumes that the time intervals of the expected ignition pulses are within a predetermined ratio. At constant engine speed, the time intervals are the same, corresponding to a ratio of 1: 1. Specifying a range of the ratio, for example from 1: 0.7 to 1: 1.1, allows acceleration processes to be taken into account. One area limit of the ratio of 1: 0.7 corresponds to a positive acceleration and the other area zone of 1: 1.1 corresponds to a negative acceleration. The information given so far only applies to symmetrical engines in which the top dead centers of the cylinders are evenly distributed in relation to a crankshaft rotation. In the case of asymmetrical engines, an offset of the top dead centers, which corresponds to a time offset of the ignition points of successive cylinders, must be taken into account when determining the ratio. With a normalization of the time intervals between successive ignition processes, a ratio of 1: 1 at constant speed can also be used as a basis for asymmetrical engines. Instead of standardization, the actual ratio at constant speed can of course also be selected from the starting point, which then deviates from 1: 1, the range of the predetermined ratio then also correspondingly changing.

The other criterion for determining the threshold, in which the number of detected ignition pulses within an interval, which is given by the distance between two successive pulses of a reference cylinder, must match an expected number, assumes that an ignition pulse of a reference cylinder is detected separately. An engine cycle is completely defined on the basis of the known number of cylinders of the internal combustion engine. The threshold can be reliably determined on the basis of the expected number of ignition pulses compared to the actually detected ignition pulses.

Advantageous developments of the method according to the invention result from subclaims.

A combination of the first and second versions is particularly advantageous. According to a first exemplary embodiment, the relationship between the time intervals of at least two successive pulses is checked, and the result is then checked by evaluating the number of ignition pulses within an engine cycle. According to a second exemplary embodiment, the number of ignition pulses is first determined within the interval given by the ignition pulses of the reference cylinder, the result then being checked by evaluating the time intervals of successive pulses.

In both exemplary embodiments, there is a further increase in operational reliability through an expansion of the plausibility checks.

An advantageous embodiment of the method according to the invention provides for the threshold to be specified as discrete steps. A particularly simple implementation of the method according to the invention is possible by specifying two stages, only a switchover between the two stages being necessary.

A further development of the method according to the invention provides that a separate threshold is in each case assigned to each sensor signal which is derived from different sensors.

Another development provides that the signals detected by different sensors are first combined and that a separate threshold is assigned in chronological order to the pulses expected one after the other in time.

An embodiment of the method according to the invention in accordance with the first embodiment provides that the shortest detected distances between successive pulses are used as the basis for determining the threshold. This measure ensures that the ignition pulses are completely detected even if periodically recurring ignition pulses occur, the amplitude of which is increased compared to the other ignition pulses.

Advantageous further developments and improvements of the method according to the invention result from further subclaims in connection with the following description.

drawing

FIG. 1 shows a block diagram of a measuring device which is connected to an ignition system, FIG. 2 shows a time course of ignition pulses in an ignition system and FIG. 3 shows a block diagram of a measuring device.

In Figure 1, an ignition system 10 is shown, which is connected to a measuring device 11. Ignition system 10 and measuring device 11 are drawn separated from one another by dashed lines.

The ignition system 10 contains two ignition coils 12, 13, which each have first primary connections 14, 15, second primary connections 16, 17, first secondary connections 18, 19 and second secondary connections 20, 21. The secondary connections 18, 19, 20, 21 of the ignition coils 12, 13 are each connected to spark plugs 23, 24, 25, 26 connected to a ground 22. The first primary connections 14, 15 of the ignition coils 12, 13 are each connected to a switch 27, 28, which are arranged in an ignition switching device 29. The second primary connections 16, 17 of the ignition coils 12, 13 lead to an ignition switch 30, which connects the ignition system 10 to a battery 31 connected to ground 22. The two switches 27, 28 in the ignition switching device 29 are also each connected to ground 22.

The points entered in the outline of the ignition switching device 29 mean that the ignition switching device 29 can contain further such switches in addition to the two switches 27, 28 shown. Likewise, the points in the connecting line of the second primary connections 16, 17 of the ignition coils 12, 13 mean that this line can lead to further ignition coils.

On the connecting lines between the switch 27 and the first primary connection 14 of the ignition coil 12 and the switch 28 and the first primary connection 15 of the ignition coil 13, contacts 32, 33 are provided, to which measuring lines 34, 35 are connected, which lead to the measuring device 11.

The measuring lines 34, 35 are connected to an evaluation arrangement 36 and each with comparators 37, 38. The comparators 37, 38 each output signals 39, 40 to a signal processing arrangement 41. The arrangement 41 in turn outputs an output signal 42 to the evaluation arrangement 36. The signal processing arrangement 41 also receives input signals from a cylinder number generator 43 and from a reference signal generator 44. The reference signal generator 44 is connected via a further measuring line 45 and via a further contact 46 to a line which leads to the spark plug 26.

FIG. 2 shows a signal curve as a function of the time T that occurs in the ignition system 10. The voltage U that occurs at the contacts 32, 33 is indicated. The signal curve can initially occur either at one contact 32 or at the other contact 33. Furthermore, it is possible to combine the signals at the contacts 32, 33, so that the signal curve shown in FIG. 2 arises from the superimposition of two or more signals. The signal is referred to as the primary ignition signal.

When the ignition switch 30 is closed and the switch 27, 28 is also closed, a current flows in the primary winding of the ignition coil 12, 13 and increases over time. During this time, the voltage U which can be tapped at the contacts 32, 33 has a potential which, apart from a saturation voltage of the switches 27, 28 which may be present, is at ground potential. This period of time, which is shown in FIG. 2 with the reference symbol 50, is the closing phase. Subsequent to the closing phase 50, the switch 27, 28 opens, so that the current flowing through the primary winding 12, 13 switches over to a capacitor (not shown in FIG. 1). A rapid change in current results in a high induced voltage, which occurs as an ignition voltage on the secondary side of the ignition coil 12, 13. An ignition pulse likewise occurs on the primary side of the ignition coil, the amplitude of which reaches a value which is mainly given by the transmission ratio of the ignition coil between the primary and secondary windings. The four The successive ignition pulses shown in FIG. 2 bear the reference symbols 51, 52, 53, 54. The ignition phase 51, 52, 53, 54 is followed in each case by the burning phase 55, during which there is a gas discharge on the spark plug 23, 24, 25, 26 . The burning phase 55 is followed by an opening phase 56 during which the switch 27, 28 is open. At the beginning of the closing phase 50, another ignition process is initiated.

A first and a second threshold 57, 58 are entered in FIG. 2, the first threshold 57 being exceeded by the first, third and fourth ignition pulses 51, 53, 54 and the second threshold 58 being exceeded by all ignition pulses 51, 52, 53, 54. The time intervals between the individual ignition pulses 51, 52, 53, 54 are also entered. An interval begins where the amplitude of the ignition pulses 51, 52, 53, 54 either reaches the first threshold 57 or the second threshold 58 and ends at the corresponding point of the subsequent pulse. A rising edge 59 of the ignition pulses 51, 52, 53, 54 is provided as the intersection points of the ignition pulses 51, 52, 53, 54 with the thresholds 57, 58. A first time interval 60 lies between the first and third ignition pulses 53, based on the first threshold 57. A second time interval 61 lies between the third and fourth ignition pulses 53, 54, also based on the first threshold 57. Third, fourth and fifth time intervals 62, 63, 64 each lie between two successive firing pulses 51, 52; 52, 53; 53, 54, based in each case on the second threshold 58.

Another block diagram of the measuring device 11 is shown in FIG. Corresponding parts in Figures 1 and 3 have the same reference numerals. The measuring lines 34, 35 are fed to a signal combining arrangement 70, which outputs an output signal to a comparator 71, the output signal 72 of which is fed to a signal processing arrangement 73.

The methods according to the invention are explained in more detail using the block diagrams shown in FIGS. 1 and 3 in conjunction with the signal curve shown in FIG. 2:
The ignition pulses 51, 52, 53, 54 occurring in the ignition system 10 are tapped at the contacts 32, 33. Instead of the galvanic connection of the measuring lines 34, 35 shown in FIG. 1 to the first primary connections 14, 15 of the ignition coils 12, 13, a capacitive or an inductive coupling is also possible. The ignition pulses 51, 52, 53, 54 can also be tapped at another point in the ignition system 10, for example on the secondary side of the ignition coils 12, 13. Instead of the primary-side ignition signal curve shown in FIG. 2, there is then, for example, a secondary-side ignition signal curve, although the characteristic ignition pulses 51, 52, 53, 54 are present.

The measuring lines 34, 35 leading to the measuring device 11 are usually first prepared for further signal processing in a signal conditioning circuit, which is not shown in FIG. 1. For example, such a signal conditioning circuit can contain a voltage divider, an impedance converter or an amplifier circuit. The signals are then fed to the evaluation arrangement 36, which carries out a qualitative or quantitative analysis of the signals. Some of these evaluations depend on the time. Such evaluations are, for example, the determination of the ignition times of the individual cylinders in chronological order during an engine cycle. When evaluating as a function of time, a digital signal is used instead of the analog signal shown in FIG. 2, which starts or stops devices for determining times by a defined level or a defined edge. The output signal 42 of the signal processing arrangement 42 is such a signal with which the evaluation arrangement 36 carries out the time-related evaluations. The signal 42 contains, for example, pulses which are resolved every time an ignition pulse 51, 52, 53, 54 occurs. In order that reliable pulses can be derived from the signal shown in FIG. 2, a careful determination of the threshold 57, 58 is necessary, and when the threshold pulses 57, 52, 53, 54 are exceeded, a pulse is triggered in each case. According to the invention it is initially provided that the threshold 57, 58 is variable. It is considered equivalent to this measure that the threshold 57, 58 is fixed and that the amplitude of the signal is changed in accordance with the arrangement of the prior art mentioned at the beginning. The signals on the measuring lines 34, 35 are fed to the comparators 37, 38, respectively. The signal processing arrangement 41 initially sets the threshold 57, 58 to a high value, which is reduced as a function of determined time intervals and / or as a function of counting results.

According to the first embodiment of the method according to the invention, it is provided that the time intervals of at least two successive ignition pulses 51, 52; 52, 53; 53, 54 lie within a predeterminable ratio. At an initially comparatively high threshold, which corresponds, for example, to the first threshold 57 shown in FIG. 2, the first time interval 60 between the first and third ignition pulses 51, 53 and then the second time interval 61 between the third and fourth ignition pulses 53, 54 determined. The ratio of the time intervals 60, 61 is then approximately 2: 1. The signal processing arrangement 41 detects a faulty operating state by suitably specifying a ratio within which the time intervals 60, 61 must lie. Knowledge can be used as the basis for determining a suitable range for the relationship be that an internal combustion engine can achieve a maximum acceleration between successive ignition pulses. An experimentally determined value is currently around 30%. It follows that the ratio can preferably be specified in a range from approximately 1: 0.7 to 1: 1.1. Braking of the internal combustion engine has already been taken into account in this specification, a maximum change of approximately 10% between successive ignition pulses being taken as a basis.

After the signal processing arrangement 41 has determined that the time intervals 60, 61 of at least two successive ignition pulses 51, 53; 53, 54 is outside the predetermined ratio, the threshold 57, 58 is lowered. As soon as the threshold has reached a value which, for example, corresponds to the second threshold 58 entered in FIG. 2, the signal processing arrangement 41 determines the time intervals 62, 63, 64 between successive firing pulses 51, 52; 52, 53; 53, 54. Since these distances 62, 63, 64 lie within the predetermined ratio, the corresponding pulses are output as an output signal 42 to the evaluation arrangement 36.

A development of this method according to the invention provides that the shortest detected distances 62, 63, 64 are used as a basis when determining the threshold 57, 58. This measure precludes a faulty operating state, which could occur, for example, in the case of a signal according to FIG. 2, if periodically occurring pulses occur with an amplitude that is above the amplitude of the other pulses. This would be the case in FIG. 2, for example, if the fourth firing pulse 54 has an amplitude comparable to the second firing pulse 52 would. If the variable threshold is set to a value that corresponds to the first threshold 57, the signal processing arrangement 41 would be evaluated by evaluating the ratio of the time interval 60 between the first and third firing pulses 51, 53 and a further distance, not shown in FIG third firing pulse 53 and an unregistered fifth firing pulse determine that the distances are within the predetermined ratio, even though there is a faulty operating state. This case is excluded with the advantageous further training.

An embodiment of the method according to the invention provides that the variable threshold can be specified in stages. Two stages, corresponding to the first and second thresholds 57, 58, are preferably provided, with a particularly simple implementation in terms of circuitry or software being possible.

According to another embodiment of the method according to the invention it is provided that the threshold 57, 58 is set to a value at which the number of the detected ignition pulses 51, 52, 53, 54 within an interval given by the distance between two successive pulses of the reference cylinder matches an expected number. The prerequisite for this procedure is the detection of ignition pulses from a reference cylinder. In Figure 1 it is assumed that the spark plug 26 is provided to ignite the reference cylinder. The measuring line 45 is therefore connected to the further contact 46 on the line leading to the spark plug 26. Instead of the galvanic connection shown, both capacitive and inductive coupling is possible. The further measuring line 45 feeds the tapped signal to the reference signal generator 44, which outputs an output signal to the signal processing arrangement 41. The reference signal generator contains, for example, a voltage divider, an impedance converter and / or an amplifier and a comparator. The reference signal generator 44 is also intended to emit a pulse-shaped signal, such as the comparators 37, 38, which is produced by comparing the input signal with a threshold. However, it is much easier to specify a threshold here because the input signal can be clearly identified. Usually, the reference signal is detected by a trigger gun that detects the spark plug current flowing in the secondary circuit or at least its changes.

The reference signal generator 44 emits a signal to the signal processing arrangement 41 each time the first ignition pulse 51 occurs, for example. So that the arrangement 41 can determine the ignition pulses occurring within an engine cycle, the number of cylinders must be communicated to it. For this purpose, the cylinder counter 43 is provided, which is controlled, for example, by an input. The variable threshold 57, 58 is set during operation such that the signal processing arrangement 41, starting from the first ignition pulse 51, counts four ignition pulses until the first ignition pulse occurs again, which corresponds to the ignition pulse for the reference cylinder. In the example, a four-cylinder internal combustion engine has been assumed.

A combination of the first and the second method is particularly advantageous. A further increase in operational safety is thereby achieved, with one method representing a plausibility check of the other method. So it is possible to first use the first method and then to check the result with the second method and vice versa.

In the example shown in FIG. 1, it is assumed that two or more independent ignition circuits with the ignition coils 12, 13 are present are, each with different measuring lines 34, 35 lead to separate comparators 37, 38. The threshold for each comparator 37, 38 can be specified individually. Instead of the separate comparators 37, 38, a single comparator 71 can be provided according to FIG. 3, to which a combined signal is fed. For the signal merging of the signals lying on the measuring lines 34, 35, the signal merging arrangement 70 is provided which superimposes the signals, which can be implemented, for example, as an analog OR combination.

The signal processing arrangement 73 differs from the arrangement 41 shown in FIG. 1 with regard to the specification of the threshold for the comparator 71. Instead of the specification of a uniform threshold, provision is preferably made for the specification of a threshold which changes over time, the threshold being able to be defined either for individual expected ignition pulses or groups of ignition pulses. From previous ignition pulses, the threshold can be specified in advance at a time after which the next ignition pulse is expected.

The methods according to the invention can be implemented in analog circuit technology as well as run in a microprocessor system. In the case of a digital implementation in a microprocessor system, the detected signals are first subjected to an analog / digital conversion and then the comparison operations and evaluation processes are carried out in the number range.

Claims (9)

Method for evaluating ignition pulses of a spark-ignited internal combustion engine, in which the amplitude of the detected pulses is compared with a predetermined threshold and only those pulses are evaluated which exceed the threshold, characterized in that the threshold (57, 58) is variable and that the threshold (57, 58) is set to a value at which the time intervals (62, 63, 64) of at least two successive ignition pulses (52, 51; 53, 52; 54, 53) lie within a predetermined ratio. Method for evaluating ignition pulses of a spark-ignited internal combustion engine, in which the amplitude of the detected pulses is compared with a predetermined threshold and only those pulses are evaluated which exceed the threshold and are detected at the ignition pulses of a reference cylinder, characterized in that the threshold (57, 58) is variable and that the threshold (57, 58) is set to a value at which the number of detected ignition pulses (51, 52, 53, 54) within an interval determined by the distance between two successive ignition pulses (51) Reference cylinder is given, matches an expected number. Method for evaluating ignition pulses, consisting of a combination of the subjects of claims 1 and 2. Method according to one of the preceding claims, characterized in that the threshold (57, 58) can be predetermined in stages. Method according to claim 4, characterized in that two stages (57, 58) are provided. Method according to one of the preceding claims, characterized in that the ignition pulses (51, 52, 53, 54) are detected by separate devices (32, 34; 33, 35) and in that each of these devices (32, 34; 33, 35) a separate threshold (57, 58) is assigned. Method according to Claim 6, characterized in that the pulses emitted by a plurality of devices (32, 34; 33, 35) are combined and in that the threshold (57, 58) before the expected ignition pulse (51, 52, 53, 54) is timed Episode is switched. Method according to claim 1 and according to one of claims 3 to 7, characterized in that the ratio is determined in a range from 1: 0.7 to 1: 1.1. Method according to Claim 1 and one of Claims 3 to 8, characterized in that the shortest detected distances (62, 63, 64) between successive ignition pulses (52, 51; 53, 52; 54, 53) when determining the threshold ( 57, 58) are used as a basis.

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