EP3325799B1 - Method for implementation with the operation of an internal combustion engine - Google Patents

Description

The present invention relates to a method for carrying out the operation of an internal combustion engine according to claim 1.

Spark plugs in use with gasoline engines, especially gas engines, are subject to considerable fluctuations in terms of their service life. For example, in the variable-speed and load-variable engine, low combustion-accelerating combustion air ratios are used to meet transient times, which lead to high combustion chamber temperatures and high wear on the spark plug due to the additional heat flow in the wear element of the spark plug. This increased wear shows a high degree of variability in terms of tool life reliability, which can disadvantageously lead to an unforeseen failure. In the JP 2008-101585 A an electrode distance of a spark plug is determined based on a breakdown voltage and the cylinder pressure.

Based on this, the present invention is based on the object of specifying a method on the basis of which a failure can be predicted.

This object is achieved with a method having the features of claim 1. Advantageous further developments and embodiments of the invention are specified in the further claims.

According to the invention, a method is proposed for execution with the operation of an internal combustion engine which has a spark plug which is arranged on a combustion chamber of a cylinder of the internal combustion engine. The internal combustion engine is preferably, for example, a gas engine, generally preferably a gasoline engine, in the context of the present invention in particular a large engine, furthermore in particular a large engine running in lean operation, for example for a commercial vehicle such as a ship, a special vehicle, for example also for industrial applications.

The spark plug is preferably a prechamber spark plug which - in a manner known per se - can have a spark plug housing or a spark plug body, furthermore a prechamber cap which - together with the spark plug housing - defines a prechamber combustion chamber of the spark plug, i.e. an antechamber. The spark plug has an (ignition) electrode arrangement, particularly preferably accommodated in the prechamber combustion chamber, the ignition electrodes of which are spaced apart, i.e. an electrode gap (at the spark gap). The electrode arrangement comprises in particular a central electrode and at least one ground electrode, which define the distance between the electrodes (which varies with the burn-up of the electrodes over the life of the spark plug, in particular increases). The spark plug arranged on the combustion chamber is furthermore provided for spark ignition of the fuel mixture which has been introduced into the combustion chamber.

In the proposed method, which is preferably coordinated by a higher-level sequence control of the internal combustion engine, e.g. an ECU (ECU: Electronic Control Unit; central engine control unit) or generally a control unit, in a first step (during an ignition process) a cylinder pressure at the ignition point in the combustion chamber and a breakdown (ignition) voltage at the spark plug are recorded or determined (as the ignition point the time at which the ignition spark is triggered on the spark plug is designated in the context of the invention).

In this context, a cylinder pressure sensor is provided for the cylinder pressure detection, while the breakdown voltage can be detected by a suitable device. Such a device can e.g. comprise a temporally high-resolution measuring arrangement, e.g. delivering measurement signals in the gigahertz range, which e.g. taps voltage signals on an ignition voltage line (to the spark plug) to provide the breakdown voltage information or e.g. on a measuring line.

wobei mit "EA" der (aktuelle) Elektrodenabstand, mit "U_ZZP" die Durchbruchspannung (zum Zündzeitpunkt), mit "p_zzp " der Zylinderdruck (zum Zündzeitpunkt) und mit "K" die Proportionalitätskonstante bezeichnet ist.In a second step of the method, a current electrode spacing of the ignition electrodes, which represents a current ignition electrode wear state, is now determined based on the detected cylinder pressure, the detected breakdown voltage and a (proportionality) constant. Corresponding to the Paschen law, equation 1) can be used for this, according to which the following applies: $$\mathit{EA}=\frac{U_{\mathit{ZZP}}}{p_{\mathit{zzp}}K},$$

"EA" _denotes the (current) electrode spacing, "U _ZZP " _denotes the breakdown voltage (at the ignition point), " p _zzp " the cylinder pressure (at the ignition point) and "K" the proportionality constant.

Based on the determined current electrode spacing, a reliable failure prediction with regard to the spark plug is advantageously made possible, i.e. the determined electrode spacing advantageously serves as a wear indicator (since, as already mentioned, the electrode spacing varies with the operating time of the spark plug, in particular it generally increases over the running time of the spark plug, i.e. as a result of the spark electrodes burning off (melting)). With a precise prediction, the usual safety surcharges on the service life can subsequently be reduced, so that the wear-related costs can advantageously be reduced.

wobei mit "EA_bekannt" der vorbekannte Elektrodenabstand, mit "U_ZZP" die Durchbruchspannung (zum Zündzeitpunkt), mit "p_zzp " der Zylinderdruck (zum Zündzeitpunkt) und mit "K" die Proportionalitätskonstante bezeichnet ist. Die Proportionalitätskonstante hängt z.B. vom Gasgemisch an der Funkenstrecke (Elektrodenspalt), der Austrittsarbeit der Elektronen, dem Elektrodenwerkstoff und weiteren Parametern ab, so dass die Proportionalitätskonstante im Rahmen der Erfindung je systemindividuell (System aus Brennkraftmaschine und Zündkerze) ermittelt wird.The proportionality constant used in the second step is determined as a system-specific variable on the internal combustion engine, in particular once, and is based on a previously known electrode distance of the spark plug, a correspondingly determined cylinder pressure at the time of ignition and a breakdown voltage of the spark plug, which in turn is determined accordingly. The known electrode spacing is defined by the manufacturer, for example, that electrode spacing according to the delivery state of the spark plug. The proportionality constant is determined, for example, on a measurement setup comprising the internal combustion engine, ignition voltage and cylinder pressure measurement technology, the engine preferably being brought to a predetermined operating point. With the known electrode spacing, the proportionality constant or Paschen constant can then be determined: $$K=\frac{U_{\mathit{ZZP}}}{p_{\mathit{zzp}}{\mathit{EA}}_{\mathit{known}}}$$

"EA _known " means the known electrode spacing, "U _ZZP " the breakdown voltage (at the ignition point), " p _zzp " the cylinder pressure (at the ignition point) and " K " the proportionality constant. The proportionality constant depends, for example, on the gas mixture at the spark gap (electrode gap), the work function of the electrons, the electrode material and other parameters, so that the proportionality constant in the The scope of the invention is determined individually for each system (system of internal combustion engine and spark plug).

In a preferred development of the method, in a further step, which is based on the current electrode spacing of the ignition electrodes determined in the second step, a service life of the spark plug is now determined. The determined service life can be an elapsed service life, i.e. an age, alternatively or additionally, and preferably a remaining life. A characteristic curve can be used to determine the service life, with which the determined electrode spacing is correlated. The end of the service life is reached when the maximum electrode distance is reached, and therefore the maximum electrode wear.

wobei mit "EA_max" der maximale, das Lebensdauerende kennzeichnende Elektrodenabstand, mit "EA_min" der anfängliche, den Lebensdauerbeginn kennzeichnende minimale Elektrodenabstand und mit "d_{Verschleißkörper}" die Dicke des abbrandfähigen Elektrodenmaterials bezeichnet ist. Mit den bekannten Werten für EA_max und EA_min kann eine Lebensdauerkennlinie nunmehr auf einfache Weise generiert werden, z.B. empirisch ermittelt werden oder auch modellgestützt.The maximum electrode distance can be determined for the spark plug, for example: $${\mathit{EA}}_{\mathit{Max}}={\mathit{EA}}_{\mathit{min}}+d_{\mathit{Wear\; body}},$$

where "EA _max " denotes the maximum electrode distance which characterizes the end of the service life, "EA _min " the initial electrode distance which characterizes the start of the service life and "d _{wear body} " the thickness of the consumable electrode material. With the known values for EA _max and EA _min , a service life characteristic can now be generated in a simple manner, for example determined empirically or also model-based.

In a further development of the method, an information signal can be output to an operator based on the determined current electrode distance or the life span determined on the basis thereof, in particular prompted by the control unit, i.e. in particular with the aim of initiating user intervention as required, e.g. a spark plug change or cylinder deactivation.

Further developments of the method are preferably also provided in such a way that based on the electrode distance determined in the second step, in a further step, for example and preferably also in addition to determining the service life, at least one combustion parameter of the internal combustion engine is set or the current electrode distance is tracked, in particular a combustion air ratio (Lambda). By tracking one or more combustion parameters depending on the determined electrode distance, hence the spark plug age, the age-related influence of the spark plug on the combustion can now advantageously be compensated for - by the engine control - and consequently improved compliance with emission limit values can also be achieved. For example, the ignition energy can now also be made available on the spark plug as required (e.g. via ECU (and ignition system)), a burning time or blowing time adjusted (burning time or burning process controller) or other parameters depending on the determined electrode spacing can be set in a way that is favorable for combustion.

For such parameter influencing, the method can use a characteristic curve or a model which relates the determined electrode distance to a combustion parameter, in particular a conversion point, a combustion air ratio, a blowing time or a parameter different therefrom, i.e. for combustion-optimizing correction purposes.

In particular, the invention provides that the method is carried out iteratively and continuously, and consequently the distance between the ignition electrodes is continuously determined or monitored. Along with this, a continuous, electrode distance-dependent influencing of the combustion - as discussed above - is also provided, in addition e.g. also continuous lifespan determination and signaling.

The method also advantageously opens up the possibility of checking a spark plug for its originality or usability with the internal combustion engine. For this purpose, the method can be carried out with an unused spark plug (and known, system-specific proportionality constant), the determined electrode distance being compared with a new, target-electrode distance. If the determined electrode distance does not correspond to the target distance, it can be recognized that a spark plug other than the original one or the spark plug intended for use with the internal combustion engine has been arranged on the combustion chamber, e.g. can also be signaled to a user via suitable signaling.

Within the scope of the present invention, an internal combustion engine is also proposed, which is set up to carry out the method as discussed above. For this purpose, the internal combustion engine can have, in particular, a cylinder with a combustion chamber, a spark plug arranged on the combustion chamber, a cylinder pressure sensor and a device for detecting the breakdown voltage on the spark plug (tapping, for example, on the ignition line), in addition, a sequence control or control unit for controlling the method is preferred, in particular in the form of the ECU. Program code for carrying out the method can also be implemented in this and / or a data carrier, for example also characteristic curves or models that can be used with the method.

Further features and advantages of the invention result from the following description of exemplary embodiments of the invention, with reference to the figures of the drawings, which show details essential to the invention, and from the claims. The individual features can each be implemented individually or in several combinations in a variant of the invention.

Fig. 1

exemplarisch und schematisch stark vereinfacht eine Brennkraftmaschine, welche zur Durchführung des Verfahrens eingerichtet ist.

Fig. 2

exemplarisch und schematisch eine Kennlinie zur Ermittlung der Lebensdauer der Zündkerze.

Preferred embodiments of the invention are explained below with reference to the accompanying drawings. Show it:

Fig. 1

An internal combustion engine, which is set up to carry out the method, is greatly simplified by way of example and schematically.

Fig. 2

exemplary and schematic of a characteristic curve for determining the service life of the spark plug.

In the following description and the drawings, the same reference symbols correspond to elements of the same or comparable function.

Fig. 1 shows an example and schematically, particularly greatly simplified, an internal combustion engine 1, with the operation of which the inventive method can be carried out. The internal combustion engine 1, provided as a (lean-fueled) gas engine with fuel gas injection, for example fuel gas in the form of natural gas, biogas, special gas, landfill gas, hydrogen, has a cylinder 3 in which a combustion chamber 5 is defined, ie between a reciprocating piston 7 and one Combustion chamber deck 9. On the combustion chamber 5, in particular on the cylinder head or combustion chamber deck 9 of the cylinder 3, and in this respect projecting into the combustion chamber 5, there is a spark plug 11 for igniting the fuel gas / air mixture.

The spark plug 11 is provided as a prechamber spark plug and is connected via a plug connector 13 together with the ignition line 15 to an ignition system 17 of the internal combustion engine 1, which Receives ignition signals from a higher-level control unit 19, that is, from an engine control or ECU. Depending on the control of the ignition system by the ECU 19, the spark plug 11 is supplied with ignition voltage by the ignition system 17, so that ignition sparks are generated between the electrodes (not shown) of the spark plug 11. The current electrode spacing EA of the ignition electrodes, which comprise a center and a ground electrode, that is to say for the formation of the spark gap, is decisive for the ignition energy required to generate an ignition spark.

How Fig. 1 further illustrated, a cylinder pressure sensor 21, which supplies combustion chamber pressure information p _cyl to the engine control 19, is also arranged in operative connection with the combustion chamber 5. To detect a breakdown voltage at the spark plug 11, a measuring device 23 is also provided, which likewise provides the breakdown voltage information to the engine control 19. To detect the breakdown voltage, the measuring or scanning device 23, which in particular dissolves high frequencies and which scans in the GHz range, is coupled to the spark plug 11 via a measuring line 23a.

In active connection with the motor control 19 and controlled by it, there is also a combustion process or combustion duration controller 25, via which the combustion process is regulated and which can be influenced by the engine control 19 by target values.

A user interface 27 in the form of an operator information system is also provided on the internal combustion engine 1, which can be activated by the engine control unit 19 in a signaling manner. The user interface 27 can be permanently connected to the internal combustion engine 1, alternatively or additionally provide a remote interface module, for example in the form of a tablet PC or smartphone. Information can preferably be visualized or also represented acoustically via the user interface 27.

In the context of the present invention, the superordinate control unit 19 has program code, in addition characteristic curves are stored, in particular stored in a non-volatile memory, which enable the engine control 19 to control the sequence of the method according to the invention, which is described in more detail below.

und worin "K" die Proportionalitätskonstante, "U_ZZP" die Durchbruchspannung (zum Zündzeitpunkt), "EA_bekannt" einen vorbekannten Elektrodenabstand (an der Funkenstrecke) und "p_zzp" den Zylinderdruck zum Zündzeitpunkt bezeichnen.In the context of the proposed method, a (proportionality) constant or Paschen constant K is initially used as a system-specific variable for the implementation thereof Internal combustion engine determined, that is, within the framework of a measurement setup and using equation 2) mentioned at the beginning, according to which: $$K=\frac{U_{\mathit{ZZP}}}{p_{\mathit{zzp}}{\mathit{EA}}_{\mathit{known}}}$$

and in which "K" denotes the proportionality constant, "U _ZZP " the breakdown voltage (at the ignition point), "EA _known " a previously known electrode _distance (at the spark gap) and "p _zzp " the cylinder pressure at the ignition point.

The known electrode spacing EA is _known here as an electrode spacing of a new spark plug or the spark plug 11 when new, as specified by the manufacturer, and how this is used to determine the proportionality constant K once or initially. The other variables "U _ZZP " and "p _zzp " are determined by measurement using the new spark plug 11, that is to say by means of the cylinder _{pressure sensor} 21 and the device 23 for measuring the breakdown voltage. From this, the proportionality constant K is now determined for the method according to the invention that can be carried out with the internal combustion engine 1, in particular stored in the method-controlling control unit 19.

In the method - in particular continuously with the operation of the internal combustion engine 1 - a cylinder pressure at the ignition point (p _zzp ) at the combustion chamber 5 and a breakdown voltage (U _ZZP ) at the spark plug 11 are recorded in a first step. For this purpose, the cylinder pressure sensor 21 and the device 23 for determining the breakdown voltage each (continuously) supply suitable measurement signals to the ECU or the higher-level control unit 19.

wobei mit "EA" der (aktuelle) Elektrodenabstand, mit "U_ZZP" die Durchbruchspannung (zum Zündzeitpunkt), mit "p_zzp " der Zylinderdruck (zum Zündzeitpunkt) und mit "K" die Proportionalitätskonstante bezeichnet ist.In a second step - in particular again continuously with the operation of the internal combustion engine 1 - the current electrode distance EA of the ignition electrodes (at the spark gap), which represents a current state of wear of the ignition electrodes, is now based on the cylinder pressure p _zzp recorded in the first step, the detected breakdown voltage U _ZZP and the proportionality constant K determined as described above, ie determined by the ECU 19. The above-mentioned equation 1) is used in particular, according to which: $$\mathit{EA}=\frac{U_{\mathit{ZZP}}}{p_{\mathit{zzp}}K},$$

"EA" _denotes the (current) electrode spacing, "U _ZZP " _denotes the breakdown voltage (at the ignition point), " p _zzp " the cylinder pressure (at the ignition point) and "K" the proportionality constant.

From equation 1), the current electrode spacing EA is thus continuously known with continuous implementation of the method, which is preferably also used in the context of the invention for determining the service life, i.e. in a further step.

wobei mit "EA_max " der maximale, das Lebensdauerende kennzeichnende Elektrodenabstand bezeichnet ist, mit "EA_min " der anfängliche, den Lebensdauerbeginn kennzeichnende minimale Elektrodenabstand und mit "d_{Verschleißkörper} " die Dicke des abbrandfähigen Elektrodenmaterials. Fig. 2 shows an example of a characteristic curve for the spark plug 11 as it can be used for determining the service life, for example empirically determined. In the characteristic curve, which is also preferably stored in the ECU 19, the electrode distance EA is plotted over the operating hours Bh, and therefore the service life, the minimum (previously known) electrode distance corresponding to that at zero operating hours (EA (0Bh)), the maximum electrode distance that at the end of the service life (EA _max ), i.e. the maximum possible electrode spacing (with the maximum possible electrode erosion). The maximum possible electrode spacing EA _max can be determined based on equation 3) mentioned at the beginning in accordance with: $${\mathit{EA}}_{\mathit{Max}}={\mathit{EA}}_{\mathit{min}}+d_{\mathit{Wear\; body}}$$

where "EA _max " denotes the maximum electrode distance which characterizes the end of the service life, " EA _min " the initial electrode distance which characterizes the start of the service life and "d _{wear body} " the thickness of the consumable electrode material.

To determine the service life, preferably the remaining service life of the spark plug 11, the currently determined electrode distance EA is correlated with the characteristic curve. The distance that can thus be determined (by forming a difference) between the currently reached operating hours (corresponding to the current electrode distance) and the end of the service life (corresponding to the maximum electrode distance) now indicates the remaining service life, which is signaled by the ECU 19 via the user interface 27, that is to say with an information signal. As a result, a spark plug replacement is now advantageously possible as required.

In particular, parallel to the determination of the service life and signaling, in the method according to the invention, a combustion parameter of the internal combustion engine 1, in particular a combustion air ratio, is set in a step after the second step, in particular again continuously with the operation of the internal combustion engine.

The setting is based on the knowledge that the electrode spacing EA decisively determines the burning rate or the flow rate in the combustion chamber 5 - with otherwise unchanged conditions. For example, with a relatively small electrode spacing EA, for example when the spark plug 11 is new, the combustion would only be initiated slowly, in particular when only a small ignition spark jumps over the spark gap between the electrodes. As a result, the entire combustion would take place slowly, since the pressure drop between the prechamber and the combustion chamber 5 is disadvantageous, and consequently only a small depth of ignition beam penetration into the combustion chamber 5 is achieved, and the combustion in the combustion chamber 5 is subsequently carried over.

The invention now provides for the combustion air ratio λ to be adapted to the current electrode spacing EA, so that, for example, for a candle state as described above, an increased amount of fuel gas is blown into the combustion chamber 5, that is to say on the internal combustion engine (which is running in lean operation) 1, an enriched mixture is set so that the burning rate is increased, which means that faster combustion can be achieved at lower exhaust gas temperatures and improved emission values.

If the electrode distance EA becomes larger (due to wear), the enrichment can be reduced accordingly, e.g. the blowing time is shortened, so that the combustion and emission conditions which are always optimized with the invention can advantageously be easily achieved. In other words, provision is made to influence the course of the burn as a function of the current, determined electrode distance EA, i.e. by setting at least one firing parameter. For this purpose, suitable control signals are transmitted to the combustion process or combustion duration controller 25, i.e. on the part of the ECU 19.

Finally, it should also be mentioned that the invention also makes it possible to recognize pearl formation on the spark plug 11, which terminology means the formation of the smallest spheres on the surface referred to the electrodes, which can grow from a few micrometers to, for example, 100 µm. These beads form when the electrode melts and solidify after the spark is extinguished. From a certain size, the pearls can serve as a surface for further pearls, so that a kind of stalagmite is formed which can reduce the electrode spacing EA in such a way that the spark volume becomes too small for a mixture ignition, and mixture ignition can therefore no longer take place.

With the method or the currently determined electrode distance EA, an ignition energy control is advantageously also possible, in which the ignition energy supplied to the spark plug 11 is supplied to the spark plug 11 as a function of the determined, current electrode distance EA, i.e. advantageous according to need (so that pearl formation due to excessive temperature can be avoided, for example).

Such a method for regulating the ignition energy is, for example, from the publication DE 10 2013 010 685 A1 known.

Claims (9)

1. Method for implementation with the operation of an internal combustion engine (1) which has a spark plug (11) which is arranged on a combustion chamber (5) of a cylinder (3) of the internal combustion engine (1), wherein:

   - in a first step a cylinder pressure is measured at the combustion chamber (5) at the ignition time (p_zzp) and a breakdown voltage (U_ZZP) is measured at the spark plug (11),

   - in a second step a current electrode spacing (EA) of the ignition electrodes, which represents a current ignition electrode state of wear, is determined on the basis of the measured cylinder pressure (p_zzp), the measured breakdown voltage (U_ZZP) and a proportionality constant (K),
   characterized in that

   - the proportionality constant (K) is determined as a system-specific variable at the internal combustion engine (1), on the basis of a previously known electrode spacing (EA_known), a cylinder pressure at the ignition time (p_zzp) and a breakdown voltage (UZZP) of the spark plug (11).
2. Method according to Claim 1,
   characterized in that

   - in a further step, a service life of the spark plug (11) is determined on the basis of the current electrode spacing (EA) of the ignition electrodes, which is determined in the second step.
3. Method according to one of the preceding claims,
   characterized in that

   - in a further step, a combustion parameter of the internal combustion engine (1), in particular an air/fuel ratio (λ), is set on the basis of the current electrode spacing (EA), which is determined in the second step.
4. Method according to one of the preceding claims,
   characterized in that

   - the method is carried out iteratively.
5. Method according to one of the preceding claims, characterized in that

   - the method is carried out with an unused spark plug (11), wherein the determined current electrode spacing (EA) is compared with a new-state setpoint electrode spacing.
6. Method according to one of the preceding claims,
   characterized in that

   - an information signal for an operator of the internal combustion engine (1) is output on the basis of the determined electrode spacing (EA).
7. Method according to one of the preceding claims,
   characterized in that

   - a characteristic curve which relates the determined current electrode spacing (EA) to a service life is used with the method; and/or

   - a characteristic curve which relates the determined current electrode spacing (EA) to a combustion parameter, in particular to a conversion point or an air/fuel ratio (λ), is used with the method.
8. Method according to one of the preceding claims,
   characterized in that

   - the spark plug (11) is a prechamber spark plug; and/or

   - the internal combustion engine (1) is a gas engine.
9. Internal combustion engine (1) having a cylinder (3) with a combustion chamber (5), a spark plug (11) which is arranged on the combustion chamber (5), a cylinder pressure sensor (21) and a device (23) for measuring the breakdown voltage at the spark plug (11),
   characterized in that

   - the internal combustion engine (1) is configured to carry out the method according to one of the preceding claims.

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