EP3069014B1 - Method for operating an ignition system - Google Patents

Description

State of the art

The present invention relates to an ignition system for an internal combustion engine and a method for operating an ignition system. In particular, an ignition spark discharge at a spark gap is to be suppressed at an unsuitable point in time. Ignition systems for spark-igniting internal combustion engines are known in the prior art in which, for example, a current flow through the primary side of an inductive system is interrupted, which causes a spark on the secondary side via a spark gap specially provided for this purpose in the combustion chamber of the internal combustion engine. If the spark breaks through an ignitable mixture at the time of ignition, the mixture burns and drives the engine. Due to various circumstances, however, it can happen that the ignition spark goes out prematurely or does not even come about. In this case, residual energy can remain in the capacitances of the ignition system, which can also be, for example, parasitic capacitances of the secondary winding or parasitic capacitances of other discrete components such as EFU diodes (switch-on spark suppression). There is thus still a voltage across the spark gap. This can lead to an undesired discharge and thus ignition sparks occurring in the combustion chamber at a later, unsuitable point in time, since, for example, at this point in time there is a lower mixture pressure and / or less turbulence in the mixture in the combustion chamber. If the spark generated by the residual charge leads to a burn, serious damage to the unit can result. DE 102 50 736 A1 describes that in an externally ignited internal combustion engine, in which an ignitable fuel-air mixture is ignited by an ignition process by triggering a discharge of a previously charged ignition device, depending on the engine operating point, when a full load or supercharged operating state is present, at least one additional ignition process by charging and subsequent discharge of the ignition device is carried out in a work cycle range of the internal combustion engine in which there is no ignitable mixture.

It is therefore an object of the present invention to suppress or prevent an ignition spark discharge at a spark gap at an unsuitable point in time, with energy being saved and the load on the components of the ignition system being reduced.

Disclosure of the invention

The aforementioned object is achieved according to the invention by a method according to one of the independent claims 1-3.

The method comprises generating a conductive path by means of an ignition spark at the spark path at a point in time that is before the fictitious unsuitable point in time. At least when an ignition spark discharge is to be suppressed at an unsuitable point in time, the timely generation of an ignition spark will reduce the remaining charge by creating a conductive path in the combustion chamber at the spark gap. The point in time is chosen in such a way that the internal combustion engine cannot be damaged.

The subclaims show preferred developments of the invention.

The point in time for generating the conductive path is preferably selected such that there is comparatively little turbulence in a mixture around the spark path. This prevents the controlled discharge ignition for suppressing the ignition spark discharge from being unsuccessful due to fluid movements in the combustion chamber.

More preferably, the point in time for generating the conductive path is in a work cycle in which work and / or fluid is ejected from a combustion chamber containing the spark path. Since the working cycles of working and ejecting take place before the working cycles of suction and compression (i.e. the more critical working cycles with regard to uncontrolled ignition of the mixture), an uncontrolled ignition which may damage the unit can be avoided. Alternatively or additionally, the point in time for generating the conductive path can be selected so that the discharge ignition occurs at a suitable point in time in the "suction" and "compression" work cycles when the energy stored in one or more electrical energy stores of the ignition system Residual energy is below a predetermined threshold. The discharge ignition must therefore only have a residual amount of energy which is not sufficient to ignite the fuel mixture in the combustion chamber. In this way, subsequent uncontrolled ignition can be prevented by additional ignition and the internal combustion engine can be protected as a result.

The ignition spark discharge to be suppressed is more preferably caused by a spark break. In other words, ignition initially leads to the risk of an ignition spark discharge that is to be suppressed. According to the invention, the conductive path for discharging the ignition system is then produced at a suitable time. In this way, reliable avoidance of ignition spark discharges at unsuitable times is ensured.

The methods according to the invention each include a detection of a spark break and / or a detection of a misfire. In response to this, a conductive path is created by the ignition spark at the ignition spark gap. The spark voltages or currents can be evaluated to implement these process steps. The measurement of ignition spark currents can take place, for example, on the secondary side of the ignition system and by means of an electronic evaluation which is assigned in particular to a respective ignition spark gap (spark plug). In this way, if the spark does not break, standard discharge ignition at a suitable point in time is unnecessary, which saves energy and reduces the load on the components of the ignition system.

It is very advantageous if it is determined before the creation of the conductive path whether there is residual energy in an electrical capacitance of the ignition system is present, since in this way it can be recognized whether an undesired spark discharge is imminent.

In addition, according to the invention, before the conductive path is generated, a check is carried out to determine whether there is no ignitable mixture in a combustion chamber of an internal combustion engine. In this way it is ensured that the defined discharge of the residual energy that has remained in the capacitance after a spark break does not lead to ignition in the combustion chamber of the internal combustion engine. To discharge the residual energy, only an electrically conductive spark gap is generated in a non-ignitable environment.

It is advantageous if the generation of an ignition spark according to a first alternative is triggered internally in the ignition system, for example in an internal control unit or in internal electronic components, since in this way the ignition system detects independently whether a defined discharge is necessary and thus the communication effort with a external control device can be reduced. It is also advantageous if, according to a second alternative, the generation of an ignition spark is also triggered by an external control device, for example an engine control device, since this can reduce the effort within the ignition system and, depending on the operating states of the combustion chamber conditions recorded in the control device, the defined discharge can be controlled.

The ignition system for an internal combustion engine, with which the method according to the invention is carried out, comprises a first electrode and a second electrode of a spark gap, at which an ignition spark is generated and which is used to ignite a combustible mixture in a combustion chamber of the internal combustion engine. The ignition system further comprises a voltage generator for generating an ignition spark. The voltage generator can be configured inductively, for example, by means of which a secondary-side ignition voltage is generated when a primary-side current is switched off. In principle, the first voltage generator can also be supported by further voltage generators during the ignition or the maintenance of an existing ignition spark. In addition, the ignition system comprises a control unit or regulating unit for controlling the voltage generator. By way of example, the control unit determines an ignition point or a generation of an ignition spark at a suitable one Time (see above) controlled and initiated. The activation of the extinguishing spark can be implemented internally by the ignition system or externally by the control unit (parameterization of the ignition map), whereby activation depending on other operating parameters is also possible (e.g. extinguishing spark only if A) full load or B) high load EGR) .

The ignition system preferably comprises a voltage sensor, which is set up to detect an electrical voltage remaining in the ignition system after a regular ignition point for mixture ignition and, in response to a predefined threshold value of the voltage being exceeded, to cause the conductive path to be generated by the ignition spark at the spark gap. In other words, sensors are used to identify and initiate a requirement for discharging the ignition system according to the invention. In this way, there is no need for a standard discharge of the ignition system, for example after a predefined time window which follows each regular ignition time.

In the context of the present invention, ignition is regarded as successful if a sparkover occurs and the electrically stored energy is reduced to a value below a predefined threshold value.

In the event of an unsuccessful ignition, a distinction must be made between two cases. In the first case, the spark does not cause the mixture to ignite, which is known as a misfire. The remaining energy in the ignition system can lead to malfunctions in the further course. In a second case, the spark does lead to a mixture ignition, which does not correspond to a classic misfire and can be described as a spark break-off, since the spark breaks off prematurely, which means that residual electrical energy remains in the ignition system. Ignition that is unsuccessful in the context of the present invention is therefore the case when the remaining electrical energy in the ignition system exceeds a predefined threshold value.

An ignition system with which the method according to the invention is carried out comprises a (discrete or parasitic) capacitance which, in the event of an unsuccessful ignition with excessively high residual energy content due to spark breakdown, stores a voltage, which in turn is generated by an ignition spark at the spark gap at least at a suitable time is proportionally discharged. The capacitance can for example be contained in a secondary-side mesh of the ignition system together with the spark gap in order to store energy which is used to maintain the ignition spark after ignition. Since this capacity holds energy ready in the event of an unsuccessful ignition, which could cause problematic, uncontrolled and undesired ignition in the combustion chamber at an unsuitable ignition time, a remedy can be provided according to the invention.

More preferably, the conductive path is generated by the ignition spark, in other words the discharge ignition, at the spark gap by the same voltage generator that prepared the ignition spark discharge to be suppressed. In other words, only an additional control of the voltage generator is required in order to implement the above invention in a known ignition system. There is therefore no need for additional hardware.

Brief description of the drawings

Figur 1

ein schematisches Schaltbild eines Teils eines Zündsystems;

Figur 2

ein schematisches Schaltbild eines Teils eines alternativen Zündsystems;

Figur 3

ein Druck-Kurbelwellenwinkel-Diagramm veranschaulichend prinzipielle Druckverhältnisse während unterschiedlicher Arbeitstakte einer Brennkraftmaschine; und

Figur 4

ein Flussdiagramm veranschaulichend Schritte eines Ausführungsbeispiels eines erfindungsgemäßen Verfahrens.

Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawings is:

Figure 1

a schematic diagram of part of an ignition system;

Figure 2

a schematic diagram of part of an alternative ignition system;

Figure 3

a pressure / crankshaft angle diagram illustrating basic pressure conditions during different work cycles of an internal combustion engine; and

Figure 4

a flow chart illustrating steps of an exemplary embodiment of a method according to the invention.

Embodiments of the invention

Figure 1 shows an ignition system 1 which has a transformer 2 with a primary side 3 and a secondary side 4 as a voltage generator. The primary side 3 and the secondary side 4 are magnetically coupled. Both a capacitance C and a spark gap F lie parallel to the secondary side 4. The secondary side 4 is grounded by an electrical contact with the electrical ground 5.

Figure 2 shows an alternative embodiment of an ignition system 1 according to the invention. In contrast to FIG Figure 1 The arrangement shown, the capacitance C is arranged in series with the secondary side 4 of the transformer 2. The secondary side 4, the capacitance C and the spark gap F are thus in a single common mesh.

Figure 3 shows an exemplary schematic pressure profile in the combustion chamber of an internal combustion engine over the crank angle (measured in “degrees crank angle”). It shows the four work cycles of a gasoline engine intake I, compression II, combustion III and exhaust IV. The work cycles of suction I and compression II represent a critical area X for the discharge of an uncontrolled spark. While a controlled ignition takes place in the transition from the second work cycle of compression II to the third work cycle of combustion III, a discharge according to the invention of the ignition system according to the invention should be in the areas of combustion III and ejection IV (as the appropriate time according to the claims). In this way, a discharge takes place before the critical area marked with X enables damaging, uncontrolled combustion in a next working cycle due to the remaining charge. An extinguishing spark can also be provoked in areas I and II, whereby care must be taken that the discharge does not release enough energy to ignite the mixture. Figure 4 FIG. 3 shows a flow chart illustrating steps of an exemplary embodiment of a method according to the invention.

In step 100 an attempt to ignite a mixture in the combustion chamber is undertaken. The ignition attempt can fail, which corresponds to a misfire, a critical spark current interruption or a remaining, excessively high capacitively stored residual energy. This is recognized in step 200 by determining and evaluating a secondary-side voltage and / or a secondary-side current. In the case of the evaluation of the secondary-side current, a check is carried out to determine whether this exceeds a predetermined threshold value. If this threshold value is exceeded, a check is made as to whether there is a suitable point in time for reducing the residual energy by determining whether there is no ignitable mixture in a combustion chamber of an internal combustion engine. If there is no ignitable mixture in the combustion chamber, a second ignition takes place in step 300, that is to say at a suitable point in time, which preferably occurs in work cycles III, IV (see FIG Figure 3 ) he follows.

It is a core idea of the present invention that after the combustion process, in a non-critical state, a discharge spark is generated on the spark plug electrodes in the combustion chamber, as can be done, for example, by the corresponding energization and switching off the primary coil of the ignition coil. The resulting discharge sparks create a conductive path through which the remaining energy of the capacities on the secondary side of the ignition system can be discharged. This process is preferably carried out with little turbulence in the combustion chamber. Due to the low turbulence, the spark breaks off at an uncritically low voltage or current value. This means that the stored energy is almost completely converted into the spark. The residual energy corresponding to the low value of the spark current is below the energy required for uncontrolled ignition. The method according to the invention can optionally be triggered with every ignition, after a detected spark breakage or in the event of a detected misfire (eg due to failure of a main ignition in the area of top dead center or a spark breakout).
The generation of an ignition spark in step 300 can, according to a first alternative, be triggered internally in the ignition system, for example in an internal control device or in internal electronic components. According to a second Alternatively, the generation of an ignition spark can also be triggered by an external control device, for example an engine control device.
In the embodiments according to Fig.1 and Fig.2 The steps 200, 300 can include the following steps: The secondary-side current is determined and a spark break and / or a misfire is detected from a sudden change in the secondary-side current. This is done by checking whether the amount of change in the secondary-side current exceeds a predetermined first threshold value. If this is the case, an exceeding condition is met.
Instead of the secondary-side current, a secondary-side voltage can also be detected, which is preferably determined only after a predetermined time delay after a start time of the method in order to have a steady state in the ignition system. The time delay is, for example, a function of the speed and / or a function of a crankshaft angle. A spark separation and / or a misfire is recognized when the detected secondary-side voltage exceeds a predetermined second threshold value. If this is the case, the exceeding condition is fulfilled.
It is then determined whether an ignition condition is met by checking whether there is no ignitable mixture in a combustion chamber of an internal combustion engine. If the exceedance condition and the ignition condition are met, a conductive path is created in step 300 by an ignition spark.
In a further exemplary embodiment, the ignition system additionally includes a step-up converter for maintaining an ignition spark. Such an ignition system with a step-up converter is for example in the DE 10 2013 218227 A1 disclosed, the content of which is expressly intended to be part of the disclosure content of this application.

The step-up converter comprises as in the DE 10 2013 218227 A1 an inductor, a switch, a capacitance C and a diode. The inductance of the step-up converter is designed in the form of a transformer with a primary side and a secondary side. The inductance serves as an energy store to charge the capacitor. The capacitance C of the step-up converter is as in Fig. 2 in series to the secondary side 4 of the transformer 2 arranged. The output power of the boost converter is related to Fig. 2 is fed into the secondary side 4 of the ignition system 1 via a node located between the secondary side 4 of the transformer 2 and the capacitance C and is made available to the spark gap F. The output voltage of the step-up converter is correspondingly applied to the mentioned node.

According to the invention, it is also recognized in the further exemplary embodiment that residual energy is present in an electrical capacitance C of the ignition system. An ignition spark is then generated at a suitable time. The electrical capacitance C can be a capacitor of the step-up converter or a parasitic capacitance in the ignition system.

In the exemplary embodiment with the step-up converter, step 200 comprises the following steps: It is first determined whether the step-up converter of the ignition system is switched off. If this is the case, an output voltage of the step-up converter is measured, in particular after a predetermined time has elapsed after the step-up converter has been switched off, in order to have a steady state in the ignition system. It is then determined whether the measured output voltage exceeds a predetermined second threshold value. If the second threshold value is exceeded, one can conclude that the ignition was unsuccessful, since too much residual energy is stored in the capacity of the step-up converter and there is a risk of unintentional ignition at an unsuitable time. It is then checked whether there is a suitable point in time for reducing the residual energy by determining whether there is no ignitable mixture in a combustion chamber of an internal combustion engine. If there is no ignitable mixture in the combustion chamber, a suitable point in time is present and ignition is initiated according to step 300.

Alternatively, in the further exemplary embodiment, the unsuccessful ignition can be determined by measuring an ignition spark current. In this case, step 200 comprises the following steps: First, the ignition spark current is measured. It is then determined whether the measured ignition spark current falls below a predetermined third threshold value. If the third threshold value is not reached, it can be concluded that the ignition was not successful. By continuing to operate the Step-up converter after the unsuccessful ignition, the voltage across the output capacitance of the step-up converter continues to rise, which increases the risk of an unwanted spark discharge. It is therefore determined whether the unsuccessful ignition takes place with the boost converter switched on or switched off. If the step-up converter is switched on, it is additionally determined whether a time difference between the point in time when the second threshold value was first undershot and a known end of the step-up converter operation exceeds a predetermined fourth threshold value. If the fourth threshold value is exceeded, too much residual energy is stored in the capacity of the step-up converter, so that there is a risk of unintentional ignition. It is then checked whether there is a suitable point in time for reducing the residual energy by determining whether there is no ignitable mixture in a combustion chamber of the internal combustion engine. If there is no ignitable mixture in the combustion chamber and the above conditions are met, the ignition is initiated according to step 300.

Even if the inventive aspects and advantageous embodiments have been described in detail with reference to the embodiments explained in connection with the accompanying drawing figures, modifications and combinations of features of the embodiments shown are possible for the person skilled in the art without departing from the scope of the present invention, the scope of which is covered by the appended claims are defined.

Claims (3)

1. Method for operating an ignition system for an internal combustion engine, comprising a voltage generator and a spark gap (F) for generating an ignition spark, characterized by the steps of:

   - identifying (200) a spark break and/or a misfire by the steps of

   - ascertaining a secondary-side current or a secondary-side voltage,

   - ascertaining whether an overshooting condition is satisfied, wherein the overshooting condition is satisfied when a change in the secondary-side current overshoots a predetermined first threshold value, or when the secondary-side voltage overshoots a predetermined second threshold value,

   - ascertaining whether an ignition condition is satisfied by way of ascertaining whether there is no ignitable mixture in a combustion space of an internal combustion engine, wherein the ignition condition is satisfied when there is no ignitable mixture in the combustion chamber of the internal combustion engine,

   - in response to this generating (300) a conductive path by an ignition spark at the spark gap (F) in a suitable working cycle of the internal combustion engine when the overshooting condition and the ignition condition are satisfied, wherein the suitable working cycle is a working cycle (I, II, III, IV),

   - in which working (III) and/or expulsion (IV) of liquid from a combustion chamber which contains the spark gap (F) take/takes place, and/or

   - in which intake (I) and/or compression (II) take/takes place and in which the residual energy which is stored in one or more electrical energy stores of the ignition system lies below a predetermined threshold value.
2. Method for operating an ignition system for an internal combustion engine, comprising a voltage generator and a spark gap (F) for generating an ignition spark, wherein the ignition system additionally has a step-up converter for maintaining an ignition spark, which step-up converter comprises an electrical capacitor (C) for temporarily storing ignition energy, characterized by the steps of:

   - identifying (200) a spark break and/or a misfire by the steps of

   - ascertaining whether a state condition is satisfied by way of ascertaining whether the step-up converter of the ignition system is switched off,

   - measuring an output voltage of the step-up converter when the step-up converter is switched off,

   - ascertaining whether an overshooting condition is satisfied, wherein the overshooting condition is satisfied when the measured output voltage overshoots a predetermined second threshold value,

   - ascertaining whether an ignition condition is satisfied by way of ascertaining whether there is no ignitable mixture in a combustion space of an internal combustion engine,

   - in response to this generating (300) a conductive path by an ignition spark at the spark gap (F) in a suitable working cycle of the internal combustion engine when the state condition, the overshooting condition and the ignition condition are satisfied, wherein the suitable working cycle is a working cycle (I, II, III, IV)

   - in which working (III) and/or expulsion (IV) of fluid from a combustion chamber which contains the spark gap (F) take/takes place, and/or

   - in which intake (I) and/or compression (II) take/takes place and in which the residual energy which is stored in one or more electrical energy stores of the ignition system lies below a predetermined threshold value.
3. Method for operating an ignition system for an internal combustion engine, comprising a voltage generator and a spark gap (F) for generating an ignition spark, wherein the ignition system additionally has a step-up converter for maintaining an ignition spark, which step-up converter comprises an electrical capacitor (C) for temporarily storing ignition energy, characterized by the steps of:

   - identifying (200) a spark break and/or a misfire by the steps of

   - ascertaining whether a state condition is satisfied by way of ascertaining whether the step-up converter of the ignition system is switched on,

   - measuring an ignition spark current,

   - ascertaining whether an undershooting condition is satisfied, wherein the undershooting condition is satisfied when the measured ignition spark current undershoots a predetermined third threshold value,

   - when the step-up converter is switched on, ascertaining whether an overshooting condition is satisfied, wherein the overshooting condition is satisfied when a time difference between the time of first undershooting of the third threshold value and an end of operation of the step-up converter overshoots a predetermined fourth threshold value,

   - ascertaining whether an ignition condition is satisfied by way of ascertaining whether there is no ignitable mixture in a combustion space of an internal combustion engine,

   - in response to this generating (300) a conductive path by an ignition spark at the spark gap (F) in a suitable working cycle of the internal combustion engine when the undershooting condition, the state condition, the overshooting condition and the ignition condition are satisfied, wherein the suitable working cycle is a working cycle (I, II, III, IV)

   - in which working (III) and/or expulsion (IV) of fluid from a combustion chamber which contains the spark gap (F) take/takes place, and/or

   - in which intake (I) and/or compression (II) take/takes place and in which the residual energy which is stored in one or more electrical energy stores of the ignition system lies below a predetermined threshold value.

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