DE102019208472B4 - Method for operating an internal combustion engine and internal combustion engine for carrying out such a method - Google Patents

Abstract

A method for operating an internal combustion engine (1), wherein - a prechamber (7) of each combustion chamber (3) of a plurality of combustion chambers (3) of the internal combustion engine (1) a fuel gas separately from a fuel gas supply (21) to a main combustion chamber (5) of the Combustion chamber (3) is supplied, wherein- the fuel gas is supplied to the prechamber (7) via a differential pressure controlled valve (15), wherein- at least one inlet valve (17) is assigned to each combustion chamber (3), wherein- a target closing point of the inlet valve (17) is determined for each combustion chamber (3) by means of a control system, a control variable being used which is selected from a group consisting of: a peak pressure or a temporal peak pressure position in the antechamber (7); a peak pressure or a temporal peak pressure position in the main combustion chamber (5); an intermediate pressure in the antechamber (7) or in the main combustion chamber (5); a combustion chamber-specific efficiency; a pressure curve over time in the antechamber (7) or in the main combustion chamber (5); and a combustion chamber-specific nitrogen oxide concentration in the exhaust gas, so that the fuel gas quantities supplied to the antechambers (7) of the combustion chambers (3) are matched to one another.

Description

The invention relates to a method for operating an internal combustion engine and an internal combustion engine for carrying out such a method.

An internal combustion engine of the type discussed here has a plurality of combustion chambers, each combustion chamber being assigned an antechamber. When the internal combustion engine is operating, each prechamber is supplied with a fuel gas separately from a fuel gas feed to a main combustion chamber of the combustion chamber assigned to the prechamber via a differential pressure-controlled valve. The antechambers are accordingly designed as so-called purged antechambers, which are supplied with fuel gas by a passive valve. In particular, due to minor, unavoidable structural differences and the specific arrangement of the various combustion chambers, in particular with reference to a fresh mass path through which combustion air or a combustion air-combustion gas mixture can be supplied to the combustion chambers, at least slightly different pressure conditions result in the various combustion chambers Combustion chambers of the internal combustion engine. It is therefore difficult to provide an exactly determined amount of fuel gas in the various antechambers and, in particular, the same amount of fuel gas for all antechambers. In principle, attempts can be made to compensate for the different conditions in the combustion chambers by means of static throttles; however, this only works satisfactorily - if at all - for one steady-state operating point. An unequal supply of fuel gas to the antechambers harbors the risk of misfiring or unintentionally high emissions of pollutants, in particular nitrogen oxides.

the end DE 10 2015 206 074 A1 discloses a method for operating an internal combustion engine, a combustion gas being supplied to a prechamber of each combustion chamber of a plurality of combustion chambers of the internal combustion engine separately from a fuel gas supply to a main combustion chamber of the combustion chamber. The fuel gas is fed to the antechamber via a differential pressure controlled valve. At least one inlet valve is assigned to each combustion chamber. As part of the method, a closing point of the at least one inlet valve is set separately for each combustion chamber.

The invention is based on the object of creating a method for operating an internal combustion engine and an internal combustion engine, the disadvantages mentioned not occurring.

The object is achieved in that the present technical teaching is provided, in particular the technical teaching of the independent claims and the embodiments disclosed in the dependent claims and the description.

The object is achieved in particular in that a closing point of at least one inlet valve assigned to the respective combustion chamber is set separately for each combustion chamber, so that the respective fuel gas quantities supplied to the antechambers of the combustion chambers are matched to one another. This is carried out in that a target closing point for the at least one inlet valve for each combustion chamber is determined by means of a control, using a controlled variable selected from a group consisting of: a peak pressure or a temporal peak pressure position in the prechamber; a peak pressure or a temporal peak pressure position in the main combustion chamber; an intermediate pressure in the antechamber or in the main combustion chamber; a combustion chamber-specific efficiency; a pressure curve over time in the antechamber or in the main combustion chamber; and a combustion chamber-specific nitrogen oxide concentration in the exhaust gas. Each combustion chamber is therefore assigned at least one inlet valve, the closing point of which is set separately, in particular independently of the setting of the closing points of the other inlet valves. By setting the closing point of the at least one inlet valve, the pressure in the combustion chamber can be influenced, which in turn influences the amount of fuel gas supplied to the prechamber via the differential pressure-controlled valve. It is thus possible in a simple, functionally reliable and dynamic manner - in particular not only in stationary operating points, but preferably even in transient operating ranges - to influence the fuel gas quantities supplied to the individual antechambers and, in particular, to adjust them to one another. For example, the pressure in the combustion chamber can be lowered during an intake stroke by moving the closing point of the intake valve to an early stage, whereby the amount of fuel gas supplied to the prechamber is increased due to the increased pressure difference between a fuel gas supply pressure upstream of the differential pressure-controlled valve and the combustion chamber pressure. In an analogous manner, by closing the inlet valve later, the combustion chamber pressure can be increased and thus the amount of fuel gas supplied to the prechamber can be reduced. By equalizing the fuel gas quantities supplied to the antechamber, the risk of misfiring or undesirably high pollutant emissions, in particular nitrogen oxide emissions, is effectively reduced significantly. At the same time, the individual combustion chambers are harmonized so that the efficiency of the internal combustion engine can be increased, for example, by enriching or advancing an ignition point. Simultaneously the smoothness of the internal combustion engine is increased and the load on the combustion chambers is harmonized.

The inlet valve is set up and arranged in particular to connect the combustion chamber assigned to it to the fresh mass path or to separate it from the fresh mass path in terms of flow. In particular, at least one inlet valve is assigned to each combustion chamber. It is possible for more than one intake valve, in particular two intake valves, to be assigned to a combustion chamber.

In a preferred embodiment, the closing point is set to adjust the fuel gas quantities supplied to the antechambers in a controlled manner, in particular by means of at least one regulator, preferably by means of one regulator per combustion chamber. According to another preferred embodiment, the closing point is set by means of predetermined data that are stored in a characteristic map. This refinement is technically simpler and more cost-effective to carry out than a regulation; however, a regulation is more flexible and, if necessary, more precise.

Each combustion chamber of the internal combustion engine is subdivided into a main combustion chamber and the prechamber assigned to the combustion chamber. The main combustion chamber and the antechamber are separated from one another by an antechamber wall and are fluidically connected to one another by at least one overflow bore formed in the antechamber wall.

The main combustion chamber is preferably supplied with fuel gas - separately from the antechamber - via a fuel gas supply, preferably via the fresh material path, in particular via the at least one inlet valve, in particular as a premixed, preferably compressed combustion air / fuel gas mixture. The fact that the prechamber fuel gas is fed separately from the fuel gas feed to the main combustion chamber means in particular that a prechamber fuel gas feed is set up in addition to the fuel gas feed, via which fuel gas is fed directly to the prechamber. In any case, fuel gas does not get into the antechamber exclusively via the main combustion chamber and the at least one overflow hole, but in any case also via an antechamber fuel gas path that exists in addition to the fuel gas supply. The antechamber is therefore supplied with fuel gas separately and in addition to the fuel gas supply to the main combustion chamber. In particular, fuel gas is fed to the antechamber separately and in addition to the fuel gas supply to the main combustion chamber of the same combustion chamber to which the antechamber is also assigned. Such an antechamber, which is assigned its own antechamber fuel gas supply, is also referred to as a purged antechamber.

A differential pressure-controlled valve is understood to mean a valve which is preloaded into a closed state and opens depending on a differential pressure dropping across the valve when the differential pressure dropping across the valve exerts a force on a valve member of the valve which acts in the closed functional position Exceeds preload. The valve opens in particular when the fuel gas supply pressure in the prechamber fuel gas supply is greater than the combustion chamber pressure in the main combustion chamber by a differential pressure predetermined by the design of the valve and its preload. The fuel gas supply pressure is preferably kept largely constant, but can also be adapted as a function of the operating point. By varying the combustion chamber pressure in the main combustion chamber, it is thus possible to influence the opening behavior of the differential pressure-controlled valve and thus the amount of fuel gas supplied to the antechamber. Such a differential pressure-controlled valve is also referred to as a passive valve.

A fuel gas is understood to mean, in particular, a combustible gas or combustible gas mixture which is gaseous under normal conditions, in particular at 1013 mbar and 25 ° C. The fuel gas can in particular be a methane-containing and / or hydrogen-containing fuel gas. In particular, the fuel gas can be selected from a group consisting of: natural gas, compressed natural gas (CNG), liquefied natural gas (LNG), biogas, landfill gas, sewage gas, special gas, flare gas, process gas from the chemical industry, the mining industry or metallurgical industry, associated raw material gas, lean gas, another suitable gas, and a mixture of at least two of the gases mentioned.

The internal combustion engine is preferably operated as a two-stroke or four-stroke engine. In particular, however, more than four cycles are also possible, for example six-cycle operation. A cyclically recurring sequence of cycles, for example four cycles in a four cycle operation and two cycles in a two cycle operation, is also referred to as a work cycle.

A closing point is understood to mean, in particular, a closing time and / or a closing crankshaft angle of the at least one inlet valve within a work cycle, thus a point in time or crankshaft angle within the work cycle at or at which the inlet valve closes.

A fuel gas quantity is understood to mean, in particular, a fuel gas mass or a fuel gas volume, thus a gravimetric or volumetric quantity, in a particularly preferred embodiment a fuel gas mass.

According to a further development of the invention, it is provided that a common, in particular middle, closing point is specified for all inlet valves, the individual closing points of the inlet valves being varied starting from the common closing point in order to equalize the respective fuel gas quantities supplied to the antechambers. It is thus possible in particular to use the specification of the closing point for various control objectives. In particular, the common closing point is preferably specified as a function of a global control target which is defined for the entire internal combustion engine and is therefore common to all combustion chambers, for example with regard to fuel gas consumption or global efficiency, the individual closing points for the inlet valves being individually different from the common , in particular the mean closing point, in order to meet combustion chamber-specific control goals, for example to optimize the efficiency for each combustion chamber individually, to align the peak pressures in the combustion chambers, to standardize the mean pressure, to increase the smoothness of the internal combustion engine, and to increase the pollutant emissions to harmonize, or something like that. In particular, starting from the common closing point, the individual closing points are preferably varied as a function of a control variable, in particular a control variable that is specific to the combustion chamber.

According to the invention, it is provided that a target closing point for the at least one inlet valve for each combustion chamber is determined by means of a control - in particular as a manipulated variable - using a - preferably combustion-chamber-individual - controlled variable that is selected from a group consisting of: A peak pressure or a temporal peak pressure position in the antechamber; a peak pressure or a temporal peak pressure position in the main combustion chamber; an intermediate pressure in the antechamber or in the main combustion chamber; a combustion chamber-specific efficiency; a pressure curve over time in the antechamber or in the main combustion chamber; and a combustion chamber-specific nitrogen oxide concentration in the exhaust gas. The control variables mentioned here are particularly suitable for use in a control system in which the fuel gas masses supplied to the antechambers are ultimately equalized by specifying the target closing points of the inlet valves as manipulated variables.

A peak pressure is understood to mean, in particular, a maximum pressure value reached in the antechamber or in the main combustion chamber during a work cycle, that is to say a combustion cycle.

A temporal peak pressure position is understood to mean, in particular, a point in time or a crankshaft angle during the work cycle at which the peak pressure in the prechamber or in the main combustion chamber is reached.

The peak pressure and / or the temporal peak pressure position can in particular be determined by time-dependent pressure detection in the antechamber or in the main combustion chamber. Such a time-dependent pressure detection can take place in particular by a pressure sensor, in particular a pressure measuring quartz. A time-dependent pressure measurement includes a pressure measurement that is dependent on the crankshaft angle. In this respect, the time on the one hand and the crankshaft angle on the other hand - which can be converted into one another via the current speed of the internal combustion engine - are to be regarded as equivalent. It is possible that a separate pressure measuring quartz or pressure transducer is assigned to each of the antechambers. However, it is also possible that, based on a pressure measurement in the main combustion chamber, conclusions can be drawn about the pressure in the respective prechamber. It is also possible for a pressure measuring device to be provided only in the antechamber, based on the measured values of which the pressure in the respective main combustion chamber can then be deduced. However, it is also possible for a pressure measuring device to be assigned separately to the main combustion chamber on the one hand and to the antechamber on the other. The peak pressure and / or the peak pressure position over time can in particular be obtained from a pressure curve over time.

In a preferred embodiment, a temporal gradient and / or a gradient of the pressure related to the crankshaft angle is determined as the temporal pressure curve, in particular a derivation of the pressure according to time and / or according to the crankshaft angle. A pressure increase in the work cycle is particularly preferably used as the pressure profile over time. The pressure increase has proven to be particularly meaningful with a view to the regulation proposed here.

A combustion chamber-specific nitrogen oxide concentration in the exhaust gas is preferably measured in separate exhaust gas flows assigned to the individual combustion chambers, or else time-resolved and / or crankshaft-resolved in an exhaust gas flow assigned to all combustion chambers or a subgroup of combustion chambers, with a time-resolved or crankshaft angle-resolved measurement being assigned to the individual combustion chambers based on an ignition sequence.

A combustion chamber-specific efficiency can in particular be determined from a pressure recorded as a function of time. As an alternative or in addition, a selective optimization of the efficiency of the individual combustion chambers can take place assuming a constant fuel gas calorific value and at a constant speed of the internal combustion engine. In this case, one combustion chamber after the other is preferably optimized for maximum efficiency by varying the fuel gas mass supplied to the respective prechamber. The fuel gas masses fed to the other antechambers are kept constant in the meantime. The maximization of the efficiency for the individual combustion chamber, the pre-chamber fuel gas mass of which is varied, can be recorded as an increase in efficiency on the output shaft of the internal combustion engine, in particular on its flywheel. This method can be carried out iteratively, even while the internal combustion engine is running, in particular at a stationary operating point, for all combustion chambers.

According to a further development of the invention, it is provided that a separate proportional-integral controller (PI controller) is used to determine the target closing point for each combustion chamber. In this way, the target closing points for the individual combustion chamber can be determined particularly precisely.

According to a further development of the invention, it is provided that the target closing point is determined for each combustion chamber by checking, starting from a starting closing point, whether the pressure increase in the combustion chamber during a work cycle is less than a predetermined minimum pressure increase or greater than a predetermined maximum Pressure increase is. The common closing point, in particular the common central closing point, is preferably used as the starting closing point. If the pressure increase when using the starting closing point is less than the predetermined minimum pressure increase, or is greater than the predetermined maximum pressure increase, the closing point is adjusted in a first, initial direction in a step a), in particular by a predetermined increment. The first, initial direction specifies in particular whether the closing point, in particular by the predetermined increment, is adjusted to early or late. In this context, “after early” means in particular towards a greater time interval from a bottom dead center of a piston that can be displaced in the main combustion chamber, the bottom dead center of the piston separating the intake stroke from a compression stroke; accordingly, “after late” means an adjustment closer to the bottom dead center. The adjustment of the closing point results in an adjusted closing point.

In a step b) the inlet valve is then activated with the adjusted closing point, and it is checked whether the pressure increase at the adjusted closing point compared to the previous closing point has approached the predetermined minimum pressure increase or the predetermined maximum pressure increase, or whether the pressure increase now lies within the interval between the predetermined minimum pressure increase and the predetermined maximum pressure increase. The wording "at the adjusted closing point" means in particular "when using the adjusted closing point in the same work cycle in which the test is carried out".

If c) the test in step b) shows that the pressure increase at the adjusted closing point has approached the predetermined minimum pressure increase or the predetermined maximum pressure increase compared to the previous closing point, the closing point is further adjusted in the same direction as immediately before, preferably again by the same predetermined step size.

The “previous closing point” referred to with regard to step b) is the starting closing point when step b) is carried out for the first time, and when step b) is carried out it is the last adjusted closing point.

If d) the test in step b) shows that the pressure increase at the adjusted closing point compared to the previous closing point has not approached the predetermined minimum pressure increase or the predetermined maximum pressure increase, in particular from the predetermined minimum pressure increase or from the predetermined maximum Has removed the pressure increase, i.e. in particular has become even smaller than the predetermined minimum pressure increase or has become even greater than the predetermined maximum pressure increase, and also does not lie in the interval in between, the closing point is in a direction opposite to the immediately preceding direction - preferably around the specified step size - adjusted.

Then e) steps b) to d) are carried out iteratively, i.e. repeated one after the other, until it is determined in step b) that the pressure increase at the adjusted closing point lies in the interval between the predetermined minimum pressure increase and the predetermined maximum pressure increase. If this is the case, the iteration is preferably aborted and the currently adjusted closing point is used as the target closing point.

Thus, within the scope of the iterative method proposed here, the target closing point is determined by varying the closing point starting from the starting closing point is determined by using the pressure increase in the combustion chamber, in particular in the antechamber or in the main combustion chamber, as a criterion, in particular as a control variable. By adjusting the closing point in the different directions, the combustion air-fuel mixture in the antechamber is gradually enriched or leaned, depending on the selected direction of the adjustment of the closing point, in order to keep the pressure increase in the permissible interval between the predetermined minimum pressure increase and the predetermined maximum pressure increase bring to.

According to a further development of the invention, it is provided that in step a) the first, initial direction is selected depending on whether the pressure increase in the combustion chamber during the working cycle is less than the predetermined minimum pressure increase or greater than the predetermined maximum pressure increase. The closing point is initially adjusted in the direction of an earlier closing point if the pressure increase is less than the predetermined minimum pressure increase. The early adjustment of the closing point has - as already explained above - an enrichment of the combustion air-fuel mixture, which is particularly suitable for accelerating the pressure increase. The closing point is adjusted in the direction of a later closing point if the pressure increase is greater than the predetermined maximum pressure increase. In any case, there is initially a leaning in order to reduce the pressure increase as far as possible. In this case, however, it is possible that with a combustion air-fuel mixture that is already significantly under-stoichiometric, i.e. a rich mixture with a lambda value of less than 1, leaning leads to an even higher pressure increase, since a stoichiometric mixture has a higher burning rate and thus a shows a greater increase in pressure. In this case, in particular, this is detected by the algorithm described above, and the sign of the adjustment of the closing time is changed, so that in the next step an advance adjustment and thus successively an additional enrichment of the mixture takes place in order to moderate the pressure increase and thus mechanically the components of the internal combustion engine to protect, in particular to avoid damage.

According to a further development of the invention it is provided that in step b) before the activation of the inlet valve with the adjusted closing point it is checked whether the adjusted closing point lies within a predetermined closing point range. The inlet valve is activated with the adjusted closing point when it is determined that the adjusted closing point is within the specified closing point range. If, on the other hand, it is determined that the adjusted closing point is not within the specified closing point range, the iteration is aborted and the immediately preceding closing point - before the last adjustment - is used as the target closing point. This measure ensures that the closing point is only adjusted if the adjustment is actually possible - in particular without damage to components or risk to the operation of the internal combustion engine. In particular, a predetermined adjustment range of a mechanism for the variable adjustment of the valve control times is maintained in this way.

If the iteration is ended and the previous closing point is used as the target closing point, at least one other measure is preferably initiated at the same time in order to bring the pressure increase into the predetermined interval between the predetermined minimum pressure increase and the predetermined maximum pressure increase. For this purpose, it is possible in particular to adjust an ignition point and / or to change the composition of the combustion air / fuel mixture supplied to the combustion chambers upstream of the inlet valve. Other suitable measures for influencing the rise in pressure are also conceivable.

According to a further development of the invention, it is provided that the target closing point for each combustion chamber is initially set to a maximum efficiency - in particular a maximum, combustion chamber-specific efficiency. Thereafter, in a preferred embodiment, a peak pressure for all combustion chambers is adjusted by further variations of the target closing points respectively assigned to the combustion chambers, in particular in order to protect components of the internal combustion engine from impermissibly high peak pressures. Furthermore, this measure makes it possible to operate the internal combustion engine as a whole closer to a knock limit and thus to further increase the efficiency. Because of the equalization of the peak pressures, there is no longer the risk that, when the knock limit is approached too closely, individual combustion chambers will start knocking due to peak pressure outliers. An otherwise necessary safety distance to the knock limit can therefore be reduced.

Preferably, after this measure, a mean pressure for all combustion chambers is adjusted by further variation of the target closing points. This increases the smoothness and smoothness of the operation of the internal combustion engine.

In particular, a hierarchy of measures is thus established in order to optimize the operation of the internal combustion engine. According to this hierarchy, the target closing points are first set to the respective maximum efficiency, then the peak pressures are adjusted, and then finally the mean pressures are harmonized.

The object is also achieved by creating an internal combustion engine which has a plurality of combustion chambers. Each combustion chamber has a main combustion chamber and an antechamber. Each prechamber is assigned a prechamber fuel gas supply with a differential pressure-controlled valve. The prechamber fuel gas supply is in particular assigned additionally and separately from a fuel gas supply to the respective main combustion chamber. In addition, the individual pre-chamber fuel gas feeds of the individual pre-chambers are preferably provided separately from one another, that is to say in particular can be influenced individually. Each combustion chamber - in particular each main combustion chamber - is assigned at least one inlet valve. The internal combustion engine also has a control device which is set up to specify a closing point for the respective at least one inlet valve for each combustion chamber. The control unit is set up to set the respective closing points for the inlet valves of the individual combustion chambers separately in such a way that the respective fuel gas quantities supplied to the antechambers are matched to one another. In particular, the control device is set up to carry out a method according to the invention or one of the previously described embodiments of the method for operating an internal combustion engine. In connection with the internal combustion engine, there are in particular the advantages that have already been explained in connection with the method.

The internal combustion engine is preferably designed as a gas engine, that is to say set up for operation with a combustion gas as fuel.

The internal combustion engine can be designed to operate in an Otto combustion process, in a diesel combustion process, in a dual-fuel operating process, in particular with pilot injection, or in another suitable manner, in particular for implementing another suitable combustion process.

The internal combustion engine is preferably designed as a two-stroke engine, as a four-stroke engine or as a multi-stroke engine with more than four strokes, for example as a six-stroke engine.

The internal combustion engine is designed in particular as a reciprocating piston engine.

• 1 eine schematische Darstellung eines Ausführungsbeispiels einer Brennkraftmaschine, und
• 2 eine schematische Darstellung einer Ausführungsform eines Verfahrens zum Betreiben der Brennkraftmaschine gemäß 1 in Form eines Flussdiagramms.

The invention is explained in more detail below with reference to the drawing. Show:

• 1 a schematic representation of an embodiment of an internal combustion engine, and
• 2 a schematic representation of an embodiment of a method for operating the internal combustion engine according to FIG 1 in the form of a flow chart.

1 shows a schematic representation of an embodiment of an internal combustion engine 1 , which have a plurality of preferably identically designed combustion chambers 3 has, of which here is an example of a combustion chamber 3 is shown. The combustion chamber 3 is divided into a main combustion chamber 5 and an antechamber 7th through an antechamber wall 9 are separated from each other. In the antechamber wall 9 are overflow holes 11 formed over which the antechamber 7th with the main combustion chamber 5 is in fluidic connection. Each antechamber 7th is a separate pre-chamber fuel gas supply 13th assigned, by means of which the antechamber 7th a fuel gas via a differential pressure controlled valve 15th is feedable. The differential pressure controlled valve 15th opens and closes depending on a differential pressure between a fuel gas supply pressure in the prechamber fuel gas supply 13th on the one hand and a combustion chamber pressure in the antechamber 7th .

Every combustion chamber 3 is also at least one inlet valve 17th assigned, via which a fresh matter path 19th alternately with the main combustion chamber 5 fluidically connected and from the main combustion chamber 5 Can be separated fluidically. The internal combustion engine 1 also has a fuel gas supply 21 on which the main combustion chamber 5 Fuel gas can be supplied, in particular via the fresh matter path 19th as well as via the inlet valve 17th , in particular in the form of a preferably premixed, preferably compressed, combustion air / fuel gas mixture. The pre-chamber fuel gas supply 13th is in particular additional and separate from the fuel gas supply 21 educated.

In 1 is also shown that the combustion chamber 3 an exhaust path 23 is assigned by at least one exhaust valve 25th optionally with the main combustion chamber in terms of flow 5 connected and from the main combustion chamber 5 Can be separated fluidically.

In addition, in 1 a piston 27 shown in the main combustion chamber 5 is movably displaceable. The internal combustion engine 1 is therefore designed in particular as a reciprocating piston engine.

The inlet valve 17th is variably controllable by a variable valve drive not explicitly shown. Preferably this applies to all of that Combustion chamber 3 associated inlet valves. This preferably applies to all of the combustion chamber 3 associated gas exchange valves, in particular also for the at least one outlet valve 25th .

The internal combustion engine 1 has a control unit 29 on the one with the variable valve train for the inlet valve 17th is operatively connected, which is symbolized schematically by a dashed line, which the control unit 29 with the inlet valve 17th connects. The control unit 29 is particularly so with all inlet valves 17th the combustion chambers 3 operatively connected to their control. The control unit 29 is set up for each combustion chamber 3 the combustion chambers 3 one closing point in each case, that is to say in particular closing time or closing crankshaft angle, for the respective inlet valve 17th pretend in the manner that the antechambers 7th the combustion chambers 3 each supplied fuel gas quantities are adjusted to each other. The variable control of the inlet valves makes it possible to control the pressures in the combustion chambers 3 and especially in the antechambers 7th to be coordinated so that in each case via the differential pressure controlled valves 15th equal amounts of fuel in the antechambers 7th be admitted. In this way, the risk of misfiring or undesirably high pollutant emissions, in particular nitrogen oxide emissions, is significantly reduced. The efficiency of the internal combustion engine 1 can be raised. At the same time, the internal combustion engine runs smoothly 1 increased, and loads on the combustion chambers 3 are harmonized.

In particular, in the context of one embodiment of a method for operating the internal combustion engine 1 the closing point for the various inlet valves 17th set separately so that the antechambers 7th the combustion chambers 3 each supplied fuel gas quantities are adjusted to one another.

A common, in particular middle, closing point is preferably used for all inlet valves 17th specified, in particular as a function of a global regulation target, the individual closing points of the inlet valves 17th starting from the common closing point - independently of one another - varied around the the antechambers 7th the combustion chambers 3 to adjust the fuel gas quantities supplied to each other.

A target closing point for the individual inlet valves is preferably established by means of a control system 17th the combustion chambers 3 determined using a controlled variable which is selected from a group consisting of a peak pressure or a temporal peak pressure position in the antechamber 7th , a peak pressure or a temporal syringe position in the main combustion chamber 5 , a medium pressure in the antechamber 7th or the main combustion chamber 5 , a combustion chamber-specific efficiency, a temporal pressure curve in the antechamber 7th or the main combustion chamber 5 , and a combustion chamber-specific nitrogen concentration in the exhaust gas.

It is particularly preferred to determine the target closing points for the individual combustion chambers 3 each per combustion chamber 3 a separate PI controller is used.

In a preferred embodiment of the method, the target closing point for each combustion chamber is initially set 3 adjusted to maximum efficiency, in particular for each combustion chamber 3 the efficiency is optimized individually. Thereafter, a peak pressure is preferably set for all combustion chambers 3 adjusted by varying the target closing points. A medium pressure is then preferably used for all combustion chambers 3 adjusted by varying the target closing points.

In 1 is shown that the internal combustion engine 1 one of the antechamber 7th assigned pressure sensor 31 , preferably has a pressure measuring quartz. Preferably each antechamber 7th such a pressure sensor 31 assigned. The control unit 29 is preferably with all pressure sensors 31 Operationally connected to a momentary pressure, a time-dependent pressure, or a pressure curve over time in the antechamber 7th for each individual antechamber 7th to be recorded and preferably to be evaluated. Alternatively or in addition, it is possible that such a pressure sensor 31 each of the main combustion chambers 5 assigned.

2 shows a schematic representation of an embodiment of a method for operating the internal combustion engine 1 in the form of a flow chart. First, the first step is S1 initially a starting closing point ES ₀ for one of the inlet valves 17th and applied in a subsequent work cycle. The common, preferably middle, closing point is preferably used as the starting closing point ES _0. In a second step S2 it is now checked whether a pressure increase dp / dt during a work cycle in the combustion chamber 3 when using the starting closing point ES _{0 is} less than a predetermined minimum pressure increase dp / dt _min or greater than a predetermined maximum pressure increase dp / dt _max. The time derivative dp / dt is used here as an example for the pressure increase; it is also possible that the crankshaft angle-dependent gradient of the combustion chamber pressure dp / dcp is used as the pressure increase.

Anyway, in the second step S2 checked whether the recorded pressure increase dp / dt is within the permissible limit values. If this is the case, a third step is used S3 the one previously chosen The closing point, that is to say the initial closing point ES ₀ during the first start run, and the corresponding previously set closing point during a later run, which ends the method.

If, on the other hand, the measured pressure increase dp / dt is less than the minimum limit value dp / dt _mm , compare the fourth step S4 , will be in a fifth step S5 an adjustment direction for adjusting the closing point is defined, here represented by the selection of a sign (VZ) for the calculation of a new closing point ES ₁ . Without loss of generality, the sign positive (+) is chosen initially in a first run.

In a sixth step S6 is done taking into account the previous in the fifth step S5 selected sign, the new closing point ES _{1 is} calculated as ES ₁ = ES ₀ - (VZ) ES _Δ , where ES _Δ denotes a predetermined increment for adjusting the closing point. The convention of choosing the prefix in the fifth step S5 in connection with the formulation of the equation in the sixth step S6 specifies here that the closing point is initially adjusted to early the first time the method is run. This is based on the idea that too little pressure increase due to too little, the antechamber 7th supplied amount of fuel gas is caused, so that the antechamber 7th The amount of fuel gas supplied is initially increased on a trial basis by advancing the closing point.

In a seventh step S7 it is checked whether the newly calculated closing point ES _{1 is} still within a closing point range specified _{by limits ES min} , ES _max.

If this is not the case, the procedure continues in the third step S3 continued by maintaining the previously selected closing point, i.e. the starting closing point ESo in the initial procedure. However, since it was determined at the same time that the pressure increase dp / dt is not within the predetermined limit values, other measures are now preferably initiated in order to influence the pressure increase, for example an ignition point is adjusted or a global one in the main combustion chamber 5 supplied combustion air-fuel mixture changed in its composition.

If, on the other hand, it is in the seventh step S7 newly calculated closing point ES ₁ within the specified closing point range is now in an eighth step S8 the new closing point ES _{1 is} applied, and in a ninth step S9 the pressure increase is then recorded again when the new closing point ES _{1 is used} .

In a tenth step S10 it is then checked whether the pressure increase at the new closing point ES ₁ compared to the previous closing point has approached the predetermined minimum pressure increase dp / dt _min or the predetermined maximum pressure increase dp / dt _max . In particular, it is now checked whether the pressure increase dp / dt has become smaller or larger due to the adjustment of the closing point.

If it is found that the pressure increase has become even smaller, that is, has moved further away from the permissible range, the method is carried out in the fifth step S5 continued, with the sign for the calculation of the next closing point being changed here. This is based on the idea that the adjustment of the closing point that was carried out previously was obviously carried out in the wrong direction, since the effect on the pressure increase that is contrary to the actually desired effect has occurred. Then the next steps S6 until S9 is repeated with the new sign, and the pressure increase is in the tenth step S10 again compared with the previous pressure increase.

Will be in the tenth step S10 found that the pressure increase dp / dt has become greater than the previous pressure increase, that is, in the case specifically present here, has approached the lower limit of the permissible limit value range, the method is now carried out in the second step S2 again continued, where it is checked again whether the measured pressure increase is within the permissible limit values.

The procedure is completely analogous if in the second step S2 it is established that the pressure increase dp / dt is greater than the predetermined maximum pressure increase dp / dt _max , compare the eleventh step S11 . In the twelfth step S12 an initial sign (VZ) is then selected for the calculation of the new closing point ES ₁ in a first pass, here too a positive sign (+) without restricting the generality. In a thirteenth step S13 the new closing point ES ₁ is then calculated according to the formula ES ₁ = ES ₀ + (VZ) ES _Δ , with the same closing point increment ES _Δ being particularly preferred, thus the same step size as in the sixth step S6 . The twelfth step S12 and the thirteenth step S13 show together that in this branch of the procedure, deviating from the fifth step S5 and the sixth step S6 , a retarded adjustment of the closing point is initially made during the initial run. This is because, due to the fact that the measured pressure increase is greater than the predetermined maximum pressure increase dp / dt _max , it is initially assumed that the antechamber 7th too much fuel gas is supplied, so that the closing point is adjusted to late and the amount of fuel gas is reduced.

In a fourteenth step S14 it is again checked whether the newly calculated closing point ES ₁ lies within the predetermined closing point range between the predetermined minimum closing point ES _min and the predetermined maximum closing point ES _max . If this is not the case, the third step is repeated S3 keep the last set closing point ES _0. At least one other measure is then preferably taken to bring the pressure increase into the permissible interval within the predetermined limit values, in particular adjusting the ignition point and / or changing the composition of the global combustion air-fuel mixture which is in the main combustion chamber 5 via the inlet valve 17th is fed.

If, on the other hand, the new closing point ES ₁ lies within the specified closing point range, then in a fifteenth step S15 the newly calculated closing point ES _{1 is} applied. In a sixteenth step S16 the pressure increase dp / dt when the new closing point ES ₁ is used is again measured. In a seventeenth step S17 the pressure increase dp / dt measured at the new closing point ES ₁ is now compared with the previous pressure increase dp / dt at the previously set closing point ES ₀ . If the pressure increase dp / dt at the new, adjusted closing point ES ₁ compared to the previous closing point ES _{0 has} approximated the predetermined minimum pressure increase dp / dt _min or the predetermined maximum pressure increase dp / dt _max , this is in particular the one specifically considered here If the newly measured pressure increase dp / dt branch is smaller than the previously measured pressure increase dp / dt, the method is again in the second step S2 continued.

However, it is also possible that the pressure increase dp / dt is greater than the previously measured pressure increase dp / dt, in particular when there is a reduction in the antechamber 7th supplied amount of fuel gas to a rather stoichiometric mixture in an ignition area within the prechamber 7th , especially in the area of an ignition source, so that the rate of combustion increases sharply. In this case, for reasons of component protection, it is necessary to reduce the pressure increase dp / dt by opening the antechamber 7th Even more fuel gas is supplied, the mixture in the antechamber 7th so is further enriched. In this case, therefore, in the twelfth step S12 changed the sign.

The method proposed here is preferably carried out iteratively until the measured pressure increase dp / dt at the last set closing point is within the permissible interval between the predetermined minimum pressure increase dp / dt _min and the predetermined maximum pressure increase dp / dt _max , the last one then Maintain the set closing point and terminate the process.

Alternatively, the method is also terminated when the closing point to be recalculated is no longer in the specified closing point range, as explained above.

The procedure can after the third step S3 also be restarted. In particular, it is possible for the method to be carried out continuously during operation of the internal combustion engine, with the program being able to be restarted in particular if it is in the third step S3 ended. A momentary, common, in particular a current middle, closing point can always be used as the initial starting closing point for each new program start.

Claims (8)

Method for operating an internal combustion engine (1), wherein - an antechamber (7) of each combustion chamber (3) of a plurality of combustion chambers (3) of the internal combustion engine (1), a fuel gas is supplied separately from a fuel gas supply (21) to a main combustion chamber (5) of the combustion chamber (3), wherein - The fuel gas is supplied to the prechamber (7) via a differential pressure-controlled valve (15), wherein - At least one inlet valve (17) is assigned to each combustion chamber (3), wherein - A target closing point of the inlet valve (17) for each combustion chamber (3) is determined by means of a control system, a control variable being used which is selected from a group consisting of: a peak pressure or a temporal peak pressure position in the antechamber (7) ; a peak pressure or a temporal peak pressure position in the main combustion chamber (5); an intermediate pressure in the antechamber (7) or in the main combustion chamber (5); a combustion chamber-specific efficiency; a pressure curve over time in the antechamber (7) or in the main combustion chamber (5); and a combustion chamber-specific nitrogen oxide concentration in the exhaust gas, so that - The antechambers (7) of the combustion chambers (3) each supplied fuel gas quantities are matched to each other. Procedure according to Claim 1 , characterized in that a common closing point is specified for all inlet valves (17), the individual closing points of the inlet valves (17) being varied starting from the common closing point around which the antechambers (7) of the Combustion chambers (3) to adjust the fuel gas quantities supplied to each other. Method according to one of the preceding claims, characterized in that a separate proportional-integral controller is used to determine the target closing point for each combustion chamber (3). Method according to one of the preceding claims, characterized in that the target closing point for each combustion chamber (3) is determined by - starting from a starting closing point, it is checked whether a pressure increase during a work cycle in the combustion chamber (3) is less than a predetermined minimum pressure increase or greater than a predetermined maximum pressure increase, wherein a) if the pressure increase is less than the predetermined minimum pressure increase or greater than the predetermined maximum pressure increase, the closing point is adjusted in a first, initial direction, wherein b) the inlet valve ( 17) is controlled with the adjusted closing point, whereby it is checked whether the pressure increase at the adjusted closing point compared to the previous closing point has approached the predetermined minimum pressure increase or the predetermined maximum pressure increase or in an interval between the predetermined minimum pressure increase and the predetermined mth maximum pressure increase, where c) if it is determined in step b) that the pressure increase has approached the predetermined minimum pressure increase or the predetermined maximum pressure increase, the closing point is adjusted in the same direction as in the immediately preceding adjustment of the closing point, wherein d) if it is determined in step b) that the pressure increase has neither approached the predetermined minimum pressure increase or the predetermined maximum pressure increase nor lies in the interval between the predetermined minimum pressure increase and the predetermined maximum pressure increase, the closing point in the direction of adjustment carried out immediately before is adjusted in the opposite direction, where e) steps b) to d) are repeated iteratively until it is determined in step b) that the pressure increase is within the interval between the predetermined minimum pressure increase and the past A certain maximum pressure increase lies, with the iteration being terminated if the pressure increase lies in this interval and the current adjusted closing point is used as the target closing point. Procedure according to Claim 4 , characterized in that in step a) the first, initial direction is selected depending on whether the pressure increase during the working cycle in the combustion chamber (3) is less than the predetermined minimum pressure increase or greater than the predetermined maximum pressure increase, wherein - the Closing point is adjusted in the direction of an earlier closing point if the pressure increase is smaller than the predetermined minimum pressure increase, and wherein - the closing point is adjusted in the direction of a later closing point if the pressure increase is greater than the predetermined maximum pressure increase. Method according to one of the Claims 4 and 5 , characterized in that in step b) before the control of the inlet valve (17) with the adjusted closing point it is checked whether the adjusted closing point is within a predetermined closing point range, wherein - if the closing point is within the predetermined closing point range, the Inlet valve (17) is controlled with the adjusted closing point, wherein - if the closing point is not within the specified closing point range, the immediately preceding closing point is used as the target closing point. Method according to one of the preceding claims, characterized in that i) first the target closing point for each combustion chamber (3) is set to maximum efficiency, after which preferably ii) a peak pressure for all combustion chambers (3) by varying the target closing points is adjusted, after which preferably iii) a mean pressure for all combustion chambers (3) is adjusted by varying the target closing points. Internal combustion engine (1), with - a plurality of combustion chambers (3), wherein - each combustion chamber (3) has a main combustion chamber (5) and a prechamber (7), wherein - each prechamber (7) has a prechamber fuel gas supply (13) a differential pressure-controlled valve (15) is assigned, wherein - at least one inlet valve (17) is assigned to each combustion chamber (3), and with - a control unit (29) which is set up to control a target for each combustion chamber (3) - to determine the closing point for the respective inlet valve (17), wherein - the control uses a control variable which is selected from a group consisting of: a peak pressure or a temporal peak pressure position in the antechamber (7); a peak pressure or a temporal peak pressure position in the main combustion chamber (5); an intermediate pressure in the antechamber (7) or in the main combustion chamber (5); one individual combustion chamber efficiency; a pressure curve over time in the antechamber (7) or in the main combustion chamber (5); and a combustion chamber-specific nitrogen oxide concentration in the exhaust gas, wherein - the control unit (29) is set up to set the target closing points for each combustion chamber (3) separately, so that the fuel gas quantities supplied to the antechambers (7) of the combustion chambers (3) correspond to each other be adjusted.

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