EP0732499A2 - Method for evaluating ignition pulses - Google Patents

Abstract

The switched prim. windings of two ignition coils are wired to an evaluation circuit and two comparators. Pulses (51-54) which exceed predetermined variable thresholds (57,58) are evaluated. The thresholds are adjusted in one embodiment to obtain a predetermined ratio of intervals (62-64) between successive pulses. Another embodiment detects the pulse (51) of a reference cylinder and sets the thresholds for a required number of pulses during the interval between reference pulses.

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 is adjustable 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, makes a careful one Setting the trigger threshold beforehand so that unwanted interference pulses are suppressed and all ignition pulses are recorded.

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 an 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 an expected Number matches.

The method has the advantage that a high level of operational safety is achieved in different ignition systems by adaptively determining the threshold above which the ignition pulses are evaluated. 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 given in such ignition systems.

The method according to the invention enables the threshold to be defined 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 equal to or higher than the expected ignition pulses, are recognized by the method according to the invention and a corresponding message can be issued.

The criterion for determining the threshold at which the number of firing pulses detected must match an expected number within an interval given by the distance between two successive pulses of a reference cylinder assumes that a firing 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 in comparison to the actually detected ignition pulses.

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

A combination of the design with a further criterion is particularly advantageous. According to a first exemplary embodiment, the ratio of 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 firing pulses is first determined within the interval given by the number of firing pulses within the interval given by the firing pulses of the reference cylinder, the result subsequently being determined by the Evaluation of the time intervals of successive pulses is checked.

In the exemplary embodiment 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 that the threshold is 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 assigned to each sensor signal that is derived from different sensors.

Another development provides that the signals detected by different sensors are first combined and that the pulses that are expected successively in time are each assigned a separate threshold in chronological order.

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

drawing

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

Description of exemplary embodiments

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 coil 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 transmitter 43 and from a reference signal transmitter 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 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 time period, which is entered 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 swings 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 successive ignition pulses shown in FIG. 2 have the reference numerals 51, 52, 53, 54. The ignition phase 51, 52, 53, 54 is followed in each case by the burning phase 55, while the one on the spark plug 23, 24, 25, 26 There is a gas discharge. The burning phase 55 is followed by an opening phase 56 during which the switch 27, 28 is open. When the closing phase 50 begins, a new 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 the third ignition pulse 53, based on the first threshold 57 second time interval 61 lies between the third and fourth ignition pulses 53, 54, likewise with respect to the first threshold 57. Third, fourth and fifth time intervals 62, 63, 64 each lie between two successive ignition 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 emits 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 on the basis of 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 initially in a signal conditioning circuit, which is not entered in Figure 1, prepared for further signal processing. 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 through 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 if 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 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 detected ignition pulses 51, 52, 53, 54 is within an interval which is 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, a capacitive as well as an inductive coupling is possible. The further measuring line 45 feeds the tapped signal to the reference signal generator 44, which emits 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-like 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 will. For this purpose, the cylinder counter 43 is provided, which is controlled, for example, by an input. The variable threshold 57, 58 is determined 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 cylinders. In the example, a four-cylinder internal combustion engine has been assumed.

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

In the example shown in FIG. 1, it is assumed that there are two or more independent ignition circuits with the ignition coils 12, 13, each of which leads to separate comparators 37, 38 with different measuring lines 34, 35. 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 default A uniform threshold is preferably provided for a threshold that 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 point in 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 numerical range.

Claims (6)

Method for evaluating ignition pulses of an externally 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 according to Claim 1, characterized in that a second threshold (57, 58) is variable and in that the second threshold (57, 58) is set to a value at which the time intervals (62, 63, 64) of at least two successive ones Ignition pulses (52, 51; 53, 52; 54, 53) are within a predetermined ratio. Method according to one of the preceding claims, characterized in that the threshold (57, 58) can be predetermined in steps. Method according to claim 3, 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 5, 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.

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