EP2698520A1 - Method for operating a combustion engine - Google Patents

Abstract

The method involves detecting a cylinder-specific signal of each cylinder, such as of cylinder internal pressure, cylinder exhaust gas temperature, nitrogen oxide emissions or combustion-air ratio, and forming a set value from the signals of the cylinder. A combustion parameter of the corresponding cylinder is adjusted in dependence on the deviation of a signal from the set value. The signal is tracked to the target value, where the median of the signals is formed as the set value.

Description

The invention relates to a method for operating an internal combustion engine, in particular a gas engine, having at least three cylinders, wherein a cylinder-individual signal is detected by each cylinder, wherein from the signals of the cylinder, a desired value is formed, wherein in dependence on the deviation of a signal from the desired value at least one combustion parameter of the corresponding cylinder is set, wherein the signal is tracked to the desired value.

The cylinders of an internal combustion engine usually have combustion-technical differences, that is, with global control of combustion parameters, such as fuel quantity or ignition timing, the individual contributions of the cylinders to the total performed work of the internal combustion engine are different. In the context of the invention, global or engine-global regulation of combustion parameters means that all cylinders of an internal combustion engine are operated with the same values for the corresponding manipulated variables, that is, for example, that in a global control with respect to fuel quantity, each cylinder is acted upon with the same opening duration of the gas injection valve or that in a global control with respect to ignition timing, the ignition of the cylinder in each case at the same piston position of the respective piston in the cylinder - usually expressed in degrees crank angle before TDC (top dead center of the piston in the cylinder) - are activated.

In a reciprocating engine, the work of a cylinder is transmitted to an operating shaft of the internal combustion engine via a crankshaft connected to a piston connecting rod of the cylinder, wherein often an electric generator is connected to the working shaft in order to convert the mechanical energy of the working shaft into electrical energy. Among the various possibilities of cylinder equalization is the one in focus, to match the peak pressures in the individual cylinders in order to achieve the most uniform mechanical peak load on the components. Alternative gender equality options see, for example, the optimization of engine efficiency or the minimization of pollutant emissions in the foreground.

Regarding a cylinder equalization scheme is in the US Pat. No. 7,957,889 82 described that the fuel delivery for each cylinder of an internal combustion engine is adjusted so that the maximum cylinder internal pressure or cylinder peak pressure of each cylinder is set to a common target value with tolerance band. This target value results from the arithmetic mean of all cylinder peak pressures.

By equalizing the cylinder tip pressures, each cylinder provides substantially the same power contribution, and thermo-mechanical overloading of individual cylinders can be avoided. In addition, a knocking combustion can be taken into account in the fuel metering. Thus, e.g. It may be provided that cylinders which exceed a certain knock intensity do not receive an increased fuel supply in order to avoid stronger knocking and possibly mechanical damage.

The systems described so far use the arithmetic mean of cylinder-individual signals such as e.g. the peak cylinder pressure as a target for a cylinder equalization scheme. However, the use of the arithmetic mean has the disadvantage that strong outliers have a significant effect on the arithmetic mean. Thus, for example, cylinders which have unfavorable combustion or whose cylinder pressure signal is inaccurate or falsified - for example, due to defective sensors or due to aging effects of sensors or due to electromagnetic interference in signal transmission and / or signal processing - a significant and above all undesirable influence to the target value for all cylinder tip pressures.

The object of the invention is therefore to avoid the disadvantages described above and to provide a comparison with the prior art improved method for operating an internal combustion engine. In particular, the target value or target value for the cylinder equalization control should be more robust than in previously known methods.

This object is achieved by the features of claim 1. Advantageous embodiments of the invention are specified in the dependent claims.

According to the invention, it is thus provided that the median of the signals is formed as the desired value.

The median, which is often also referred to as the central value or as the 0.5-quantile, is a positional parameter of a sampling distribution, wherein in the context of the invention the distribution of the detected cylinder-individual signals is a sampling distribution. In the known control or regulation systems on which a control or regulation of an internal combustion engine can be based, the determination or output of the median is usually not provided and is therefore not performed in the known method.

In contrast to the arithmetic mean, in which all values of a sample distribution are added together and divided by the number of individual values, the median divides the sample distribution into two halves of the same size. The median can be determined by first arranging the signals in ascending order according to their signal values. If the number of signals is odd - e.g. with an odd number of cylinders - then the signal value of the middle signal is the median. If the number of signals is even - e.g. with an even number of cylinders - then the median can be determined by taking the arithmetic mean of the two mean signal values of the ordered sample distribution.

An important feature of the median is that, compared to the arithmetic mean, which is often simply referred to as the mean or average, it is much more robust against outliers or extremely deviant values within the sampling distribution.

Thus, according to the proposed solution, the arithmetic mean of the signal values is expressly not formed and used as the desired value, but the median of the signal values is formed and used as the desired value.

Preferably, it may be provided that at least one of the following individual signals of each cylinder is detected: cylinder internal pressure, cylinder exhaust gas temperature, nitrogen oxide emissions, combustion air ratio. A particular embodiment provides that a maximum internal cylinder pressure of a combustion cycle is detected as a signal.

In order to obtain a better signal quality and thus a higher quality of control, it can preferably be provided that the detected signal is temporally filtered over 10 to 1000 combustion cycles, preferably 40 to 100 combustion cycles, as the signal of a cylinder.

In a preferred embodiment of the invention, it may be provided that the combustion parameter of a cylinder is set if the deviation of the signal of the cylinder from the desired value exceeds a predefinable tolerance value. This allows a quieter control dynamics can be achieved.

According to a particularly preferred embodiment it can be provided that a fuel quantity for the corresponding cylinder is set as the combustion parameter. In the case of an internal combustion chamber engine ignited by an internal combustion chamber, this can be the fuel quantity for the respective main combustion chamber of a cylinder. The amount of fuel for a cylinder may be increased if the signal of the cylinder is less than the desired value and the fuel quantity for a cylinder may be reduced if the signal of the cylinder is greater than the desired value. Preferably, a fuel metering valve may be provided for each cylinder, wherein the opening duration of the corresponding Brennstoffdosierventils is set to adjust the amount of fuel for a cylinder. Such a fuel metering valve may preferably be a port injection valve which is arranged in the region of the inlet tract of a cylinder. It can also port injection valves are used, for example, allow only a fully open or a fully closed position. Here, the opening period may be defined as the period in which the valve is in its fully open position. In general, however, can also stroke-controlled Valves are used, in which for adjusting the amount of fuel for a cylinder, the opening duration and / or the opening stroke of a valve can be adjusted.

A regulation with respect to the combustion parameter fuel quantity can be carried out in accordance with Table 1 below, depending on the individual cylinder signal used. In this case, column 1 of Table 1 lists the respective cylinder-specific signal and a suitable possibility for detecting the respective signal. According to column 2 of Table 1, an increase in the amount of fuel for a cylinder takes place if the respective signal of the cylinder is smaller than the desired value. According to column 3 of Table 1, a reduction in the amount of fuel for a cylinder takes place if the respective signal of the cylinder is greater than the desired value. The setpoint is in each case the median of the respective signal of all cylinders of the internal combustion engine. The amount of fuel can be increased for a cylinder, for example, by increasing the opening time of the cylinder associated Brennstoffdosierventils. Accordingly, the amount of fuel for a cylinder can be reduced by reducing the opening time of the fuel metering valve associated with the cylinder. Table 1: Control measures regarding the fuel quantity Cylinder-individual signal Increase the amount of fuel for a cylinder, if Reducing the amount of fuel for a cylinder, if Cylinder tip pressure, detected by cylinder pressure sensor in the combustion chamber low cusp tip pressure high cylinder tip pressure Cylinder exhaust temperature detected by thermocouple after exhaust valve low cylinder exhaust temperature high cylinder exhaust temperature Nitrogen oxide emissions detected by NOx sensor low nitrogen oxide emissions high nitrogen oxide emissions Inverse of combustion air ratio detected by broadband lambda probe or oxygen sensor low inverse of the combustion air ratio high inverse of the combustion air ratio

In a further preferred embodiment it can be provided that an ignition point for the corresponding cylinder is set as the combustion parameter. Preferably, an ignition device may be provided for each cylinder, wherein the ignition timing of the ignition device in degrees crank angle before TDC (top dead center of the piston in the cylinder) is set.

The ignition timing is usually expressed in degrees crank angle before TDC (top dead center of the piston in the cylinder) and thus indicates when a corresponding ignition device for igniting a fuel or fuel-air mixture in the cylinder or combustion chamber is triggered. The ignition device may be a spark plug (e.g., spark plug or laser spark plug) or a pilot injector for performing a pilot injection of e.g. Diesel fuel act. As an ignition device, an antechamber can also be used. Usually, the ignition timing for each cylinder of an internal combustion engine is set at the same globally given value (global default value) expressed in degrees crank angle before TDC. For example, this value is 20 to 30 degrees crank angle before TDC, the value depending on the speed of the internal combustion engine and / or can be determined depending on the ignition device used. This global default value can be derived from an ignition timing map in which suitable values for the ignition point are stored as a function of the power and / or the charge air pressure and / or the charge air temperature and / or the engine speed of the internal combustion engine.

In a preferred embodiment of the invention, it may be provided that the spark timing for a cylinder is set earlier (compared to the global default value) if the signal of the cylinder is less than the target value and the spark timing for a cylinder is set later (compared to the global default value) if the signal of the cylinder is greater than the setpoint.

A control with respect to the combustion parameter ignition time can be carried out in accordance with Table 2 below, depending on the individual cylinder signal used. In this case, column 1 of Table 2 lists the respective cylinder-specific signal and a suitable possibility for detecting the respective signal. According to column 2 of Table 2, a previous ignition timing is set for a cylinder if the respective signal of the cylinder is smaller than the desired value. According to column 3 of Table 2, a later ignition timing is set for a cylinder if the respective signal of the cylinder is greater than the desired value. The setpoint is in each case the median of the respective signal of all cylinders of the internal combustion engine. Table 2: Control Interventions Regarding Ignition Timing Cylinder-individual signal Set spark timing earlier for one cylinder if Set the spark timing for a cylinder later, if Cylinder tip pressure detected by cylinder pressure sensor in the combustion chamber low cusp tip pressure high cylinder tip pressure Nitrogen oxide emissions detected by NOx sensor low nitrogen oxide emissions high nitrogen oxide emissions

According to a particularly preferred embodiment, provision can be made for a parameter value to be determined for setting the at least one combustion parameter, the parameter value preferably comprising a predefinable global engine target value and a cylinder-specific differential value.

The cylinder-specific difference value may, for example, be in a range of +/- 4 degrees crank angle before TDC, preferably in a range of +/- 2 degrees crank angle before TDC with respect to setting the combustion parameter ignition timing.

The predefinable target value may be a global value that applies to all cylinders of the internal combustion engine.

The predetermined target value with respect to the setting of the ignition timing as the combustion parameter may be the global target value for the ignition timing in the cylinders of a stationary gas engine. The predefinable target value can be derived from a Zündzeitpunktkennfeld. In the Zündzeitpunktkennfeld suitable values for the ignition timing in dependence be stored by the power and / or the charge air pressure and / or the charge air temperature and / or the engine speed of the internal combustion engine. The values stored in the ignition timing map can be determined on a test bench.

The predetermined target value with respect to the setting of the fuel quantity as the combustion parameter may be an engine global basic value for the opening times of fuel metering valves or gas injection valves for the cylinders of a stationary gas engine.

In principle, it is possible to distinguish between air-guided and fuel-guided combustion processes in the case of combustion processes used in internal combustion engines. In the case of an air-guided combustion method, for example, a quantity of fuel to be metered is determined as a function of the operating point of the internal combustion engine and a predefinable target value for the fuel-air ratio in order to obtain a specific emission quantity or a specific charge air pressure. The engine controls used usually include an emission regulator. In a fuel-guided or gas-fired combustion process, a quantity of fuel to be metered is determined as a function of the operating point of the internal combustion engine and a predefinable target value for the power and / or the rotational speed of the internal combustion engine. Fuel-guided combustion processes have their application in particular in variable-speed operation of an internal combustion engine, in an internal combustion engine in isolated operation, at engine start or during idling of the internal combustion engine. The motor controls used in this case usually include a power controller and / or a speed controller.

For air-driven combustion processes in which, for example, an emission regulator is used, it can preferably be provided that the predefinable target value is determined from a predefinable fuel-air ratio, wherein preferably the predefinable fuel-air ratio from a power equivalent of the output power of the internal combustion engine , Preferably an electrical power of a generator connected to the internal combustion engine, and / or is determined from a charge air pressure and / or from an engine speed of the internal combustion engine.

In the context of this invention, a power equivalent is understood to be the actual mechanical power of the internal combustion engine or a substitute variable corresponding to the mechanical power. This may be, for example, an electric power of a generator connected to the internal combustion engine, which is measured from the power output of the generator. It may also be a calculated mechanical power of the internal combustion engine, which is calculated from the engine speed and torque or from the electrical power of the generator and the efficiency of the generator. It may also be only about the engine speed, if the power consumption of the consumer is known exactly about the speed. Furthermore, the power equivalent may also be the indicated mean pressure, which can be determined in known manner from the in-cylinder pressure curve, or the effective mean pressure, which can be calculated in known manner from the torque output or from the electrical or mechanical power. In this case, a power equivalent of the internal combustion engine can be determined from the known relationship between effective mean pressure, the displacement of a cylinder and the work performed at a power stroke.

The predefinable fuel-air ratio can be determined in a conventional manner from the charge air pressure and the power of the internal combustion engine. Thus, the predefinable fuel-air ratio for an engine designed as a gas engine, for example, according to EP 0 259 382 B1 be determined.

The predefinable target value for the gas injection duration can be determined from the flow behavior of the gas injection valves and the boundary conditions prevailing at the gas injection valves (such as pressure and temperature of the fuel gas, intake manifold pressure or charge air pressure, respectively). From the conditions in the intake manifold of the gas engine, in particular from charge air pressure and charge air temperature, the air mass equivalent (a value corresponding to the air mass) of the gas engine can be determined. With the predeterminable fuel-air ratio can be determined from the setpoint for the fuel gas mass. With the flow behavior of the gas injection valves and the boundary conditions at the Gaseinblaseventilen then the required global opening duration or Gas Einblasedauer be determined for the gas injection valves to introduce the previously determined fuel gas mass in the gas engine. This global gas injection duration corresponds in this example to the predefinable target value.

For gas-fired combustion processes in which, for example, a power controller and / or a speed controller is used, it can be preferably provided that the predefinable target value as a function of the deviation of a power equivalent of the output power of the internal combustion engine from a predetermined target power equivalent and / or in dependence Deviation of an engine speed of the internal combustion engine is determined by a predetermined target speed of the internal combustion engine.

In this case, a power regulator can be provided which, depending on the deviation of a current power equivalent of the output power (actual power) of the internal combustion engine (eg a measured electric power of a generator connected to the internal combustion engine) from the predetermined target power equivalent (target power) of the internal combustion engine, a global motor default value for the fuel mass flow determined. Alternatively or additionally, a speed controller may be provided which determines a motor global default value for the fuel mass flow as a function of the deviation of a current engine speed (actual speed) of the internal combustion engine from the predefinable target speed (target speed) of the internal combustion engine. From the determined target value for the fuel mass flow, the predefinable target value - e.g. for the engine-global opening duration of fuel metering valves or for the engine global default value for the ignition timing of ignition devices.

A particular embodiment variant provides that the cylinder-specific difference value contains a cylinder-specific precontrol value, the cylinder-specific pilot control value preferably being determined from a charge air pressure and preferably additionally from a charge air temperature of the internal combustion engine. The cylinder-specific precontrol values can thereby originate from measurements during the commissioning of the internal combustion engine and, for example, can also be used as fallback values in the event that a sensor for detecting the cylinder-specific signal fails or is disturbed.

The cylinder-individual precontrol values can take into account, for example, the gas dynamics in the intake manifold and / or in the gas rail of a gas engine as well as corresponding component tolerances, wherein the gas dynamics can be determined by simulations or measurements. The gas dynamics and the effects of component tolerances are influenced inter alia by the charge air pressure, the engine speed and the charge air temperature. It is therefore advantageous to derive suitable cylinder-specific precontrol values from a characteristic map which contains corresponding values for different charge air pressures and charge air temperatures. Thus, upon commissioning of the gas engine corresponding measurement data can be detected or corresponding maps are determined by experiments or simulations. It is also possible that an adaptive map is generated by online measurements during operation of the gas engine.

It has proved to be particularly advantageous when the cylinder-specific difference value is subjected to a compensation value, the compensation value corresponding to the arithmetic mean value of the cylinder-specific difference values. This is particularly advantageous in order to install or retrofit the proposed solution in internal combustion engines, which were previously operated without cylinder equalization or only with a global controller. By means of such a correction of the cylinder-specific difference values, it can be achieved, in particular, that a globally metered quantity of fuel is not influenced by the proposed solution and that an optionally existing global emission control of the internal combustion engine does not have to be adapted. Since the values for the respective ignition times can also be incorporated into a global engine control system, by correcting the cylinder-specific difference values, also with respect to the setting of the ignition timing, an undesirable effect on the global engine control can be avoided.

In a preferred embodiment of the invention, it may be provided that a combustion state is monitored for each cylinder and evaluated as normal or abnormal with respect to a predeterminable desired state, the combustion parameter of a cylinder being adjusted only if the combustion state of the cylinder is judged to be normal. It can as Combustion state knocking and / or glow ignition and / or exposure to be monitored in the combustion, wherein the combustion state of a cylinder is judged normal, if no knocking and / or no ignition and / or no exposure to the combustion are detected.

Fig. 1a

Zylinderinnendruckverläufe von mehreren Zylindern einer Brennkraftmaschine über mehrere Verbrennungszyklen und die jeweils daraus ermittelten arithmetischen Mittelwerte und Mediane,

Fig. 1b

eine Darstellung gemäß Fig. 1a mit einem gestörten Zylinderdrucksignal eines Zylinderinnendrucksensors eines Zylinders,

Fig. 2

eine Brennkraftmaschine mit mehreren Zylindern und einer Regelungsvorrichtung zum Betreiben der Brennkraftmaschine gemäß einer Ausführungsvariante des vorgeschlagenen Verfahrens,

Fig. 3

eine schematische Darstellung von 3 Zylindern einer Brennkraftmaschine und eine Regelungsvorrichtung zum Betreiben der Brennkraftmaschine gemäß einer Ausführungsvariante des vorgeschlagenen Verfahrens,

Fig. 4

eine schematische Darstellung gemäß Fig. 3 mit einer Brennkraftmaschine mit einem brennstoffgeführten Brennverfahren,

Fig. 5

eine schematische Detaildarstellung einer vorgeschlagenen Regelungsvorrichtung,

Fig. 6

eine schematische Darstellung gemäß Fig. 3 einer weiteren Ausführungsvariante des vorgeschlagenen Verfahrens und

Fig. 7

eine schematische Detaildarstellung einer Regelungsvorrichtung einer weiteren Ausführungsvariante des vorgeschlagenen Verfahrens.

Further details and advantages of the present invention will be explained with reference to the following description of the figures. Showing:

Fig. 1a

Cylinder internal pressure curves of several cylinders of an internal combustion engine over several combustion cycles and the respectively determined therefrom arithmetic mean values and medians,

Fig. 1b

a representation according to Fig. 1a with a faulty cylinder pressure signal of a cylinder internal pressure sensor of a cylinder,

Fig. 2

an internal combustion engine having a plurality of cylinders and a control device for operating the internal combustion engine according to an embodiment of the proposed method,

Fig. 3

3 a schematic representation of three cylinders of an internal combustion engine and a control device for operating the internal combustion engine according to an embodiment variant of the proposed method,

Fig. 4

a schematic representation according to Fig. 3 with an internal combustion engine with a fuel-fired combustion process,

Fig. 5

a schematic detail of a proposed control device,

Fig. 6

a schematic representation according to Fig. 3 a further embodiment of the proposed method and

Fig. 7

a schematic detail of a control device of another embodiment of the proposed method.

Fig. 1a shows by way of example the respective course of the cylinder-specific signal maximum cylinder internal pressure or peak pressure p _max over several combustion cycles c of several cylinders 2 of an internal combustion engine 1. In previously known methods for cylinder equalization for each combustion cycle c each of the arithmetic mean p _{mean of} the detected Cylinder-individual signals p _max formed and used as a reference variable for the control. As a result, outliers have a significant effect on the reference variable and thus on the overall cylinder equalization control.

In contrast, the proposed method does not form the arithmetic mean of the cylinder-specific signals p _max, but instead the median or central value as the desired value p _median . This setpoint p _median then forms the reference variable for the cylinder equalization control. The use of the median of all cylinder-specific signals p _max results in a more stable target value for setting a combustion parameter, for example the fuel quantity or gas metering of each individual cylinder 2. The influence of individual cylinder tip pressures with disturbance variables can thereby be minimized. Thus, a more stable and accurate cylinder equalization can be achieved because the setpoint p _median is subject to less fluctuation. In addition, a better equality of the cylinder 2 can be achieved by using the median, especially in transient engine operation (eg load jumps). This is the case in particular if a signal of the detected signal p _max filtered over a number of combustion cycles c is used as the respective individual signal for each cylinder. Due to the higher stability of the median compared to the arithmetic mean, the filtering times over several combustion cycles c can be shortened.

Fig. 1b shows a representation similar to the Fig. 1a in which the signal p _max * of a cylinder 2 of the internal combustion engine 1 has falsified values as a result of a faulty internal cylinder pressure sensor 4. In a control to the arithmetic mean of the prior art which relied on this command variable p _maen is strongly influenced by the disturbance of individual sensor signals. In such a control on the arithmetic mean p _mean would in the case shown - at least in the falsified combustion cycle range c ₁ - for each cylinder with plausiblem Zylinderspitzdruck p _max reduces the fuel metering and for the cylinder 2 with disturbed signal p _max * would increase the fuel metering. In the case of a control with respect to the arithmetic mean value p _{mean of} the cylinder _peak pressures p _max, individual faulty signals p _max * thus cause a clear inequality of all cylinders 2.

However, according to the proposed method, if the median of the cylinder peak pressures p _{max is used} as the target variable or setpoint p _median , then the desired value p _median is influenced only slightly, if at all, by a disturbed signal p _max *. Only with the cylinder 2 with the disturbed signal p _max * could result in control deviations. The equality of all other cylinders 2 could, however, be respected.

Overall, with a proposed median-based cylinder equalization, a more robust motor control can be achieved with higher accuracy with simultaneously improved transient engine operation.

Fig. 2 shows an internal combustion engine 1 with three cylinders 2. At each cylinder 2, a cylinder pressure sensor 4 is arranged to detect a cylinder-individual signal. The cylinder- _specific signal may be the time profile of the cylinder _internal pressure p _cyl or the maximum cylinder internal pressure p _max over a combustion cycle c. The cylinder-specific signal may also be a time-filtered signal of the maximum in-cylinder pressure p _max over a plurality of combustion cycles c, for example over 10 to 1000 combustion cycles c, preferably 40 to 100 combustion cycles c. The detected individual cylinder signal of a cylinder 2 is supplied via a signal line 14 of a control device 7, wherein the determination of the maximum cylinder pressure p _max over a combustion cycle c or the temporal filtering of the maximum cylinder pressure p _max over several combustion cycles c can also be done by the control device 7. As described below, in each case a cylinder-specific fuel quantity Q to be metered is determined by the control device 7 according to the proposed method as a combustion parameter for the cylinders 2 and reported to corresponding fuel metering valves 3 by means of control lines 15. Through the fuel metering valves 3, the corresponding cylinder-specific fuel quantities Q are metered into the cylinders 2 and thus the cylinder-specific signals according to the proposed method tracked by the control device 7 setpoint - the median of the cylinder-specific signals.

Fig. 3 shows a schematic block diagram of three cylinders 2 of an internal combustion engine 1 with an air-driven combustion process. Each cylinder 2 is a Fuel metering valve 3 assigned, which can be adjusted by the respective Brennstoffdosierventil 3, the corresponding cylinder 2 supplied amount of fuel Q. In this case, a control device 7 controls the fuel _{metering valves} 3 by the control _{device 7} outputting a respective cylinder-specific opening duration of the fuel _{metering valve} 3 in the form of a cylinder- _specific parameter value t _cyl .

The Brennstoffdosierventile 3 are executed in this example as a port injection valves, which know only a fully open and a fully closed position. When the fuel metering valve 3 is fully open, a fuel in the form of a propellant gas is injected into the inlet tract of the cylinder 2 assigned to the fuel metering valve 3. As a result of the opening duration of the fuel metering valve 3, the fuel quantity Q for the respective cylinder 2 can thus be established.

From each cylinder 2, a cylinder-specific signal p _{max is} detected and fed to the control device 7. A cylinder-specific signal p _max corresponds to the maximum cylinder internal pressure of the corresponding cylinder 2 during a combustion cycle c. In the example shown, the cylinder-specific signals p _{max are} supplied to a difference value calculation 8 of the control device 7. The difference-value calculating 8 determines a difference value .DELTA.t _cyl, the t are each at a predeterminable target value _g is added for each cylinder 2, and for each fuel metering valve 3, whereby for each fuel metering valve 3 as the parameter value t _cyl a cylinder-specific opening period is obtained.

The specifiable engine global target value t _g is determined in the example shown from a predeterminable fuel-air ratio λ, wherein the predetermined fuel-air ratio λ by an emission controller 5a from a power equivalent P of the output power of the internal combustion engine 1 (eg, a measured electric power a generator connected to the internal combustion engine 1) and / or from a charge air pressure p _A and / or from an engine speed n of the internal combustion engine 1 is determined. In addition to the fuel-air ratio λ can in a target value calculation 6 additionally the pressure p _A and the temperature T _{A of} the charge air, the pressure p _G and the temperature T _{G of} the fuel supply and the engine speed n the internal combustion engine 1 flow. In addition, a flow characteristic of the fuel metering valves 3 (eg effective flow diameter according to the polytropic outflow equation or a Kv value) and parameters of the fuel or fuel gas (eg the gas density, the polytropic exponent or the calorific value) can also be included in the target value calculation 6. From this, the target value calculation 6 determines the predefinable target value t _g , which corresponds to an engine-global opening duration basic value for the opening durations of all fuel metering valves 3.

The difference _value calculation 8 is used to determine a cylinder- _specific opening duration offset or differential _value Δt _cyl for each individual fuel _{metering valve 3} . These cylinder- _specific difference _values Δt _cyl depend on the deviation of the cylinder _peak pressure p _{max of} the respective cylinder 2 from the median p _{median of} the cylinder peak pressures p _{max of} all cylinders 2. The respective sum of motorglobal opening duration basic value t _g and cylinder- _specific opening duration offset Δt _{cyl indicates} the the driver electronics of the respective Brennstoffdosierventils 3 commanded target opening time t _cyl .

As an alternative or in addition to the use of the maximum cylinder internal pressure p _max as a cylinder-specific signal, the use of the respective cylinder-specific cylinder exhaust gas temperature T _E is also indicated by dashed lines. Again, from the deviations of the cylinder- _{specific cylinder exhaust temperatures} T _E to the median of the cylinder _{exhaust temperatures} T _E corresponding cylinder- _specific opening duration offsets Δt _{cyl can be} calculated over all cylinders 2. The cylinder-specific cylinder exhaust temperatures T _E can be used, for example, as an alternative if no cylinder internal pressure sensors 4 are installed or as a fallback solution when cylinder pressure signals fail to increase the availability of the internal combustion engine 1 in the event of a cylinder pressure sensor failure.

Fig. 4 shows a block diagram according to Fig. 3 In this case, the internal combustion engine 1 is operated with a gas-guided combustion process. The predefinable global motor target value t _g is determined in the example shown by a controller 5b, which may include a power controller and / or a speed controller. For In addition to a power equivalent P of the output power of the internal combustion engine 1 (actual power), the power controller can serve as a predefinable target power equivalent P _S (setpoint power) of the internal combustion engine 1 and for the speed controller can be preset in addition to a respective current engine speed n (actual speed) of the internal combustion engine 1 Target speed n _S (target speed) of the internal combustion engine 1 serve as input. In the controller 5b, a global engine default value for the fuel mass flow m is determined from the subsequently determined in a target value calculation 6 the predetermined target global engine value t _g - eg for the motor global opening duration of Brennstoffdosierventilen or for the engine global default value for the ignition of ignition devices - is determined.

Fig. 5 shows a block diagram according to Fig. 3 , wherein the control device 7 and the difference value calculation 8 are shown in more detail. This illustration shows the control sequence for only one cylinder 2 of the internal combustion engine 1 in detail. Further cylinders 2 of the internal combustion engine 1 are indicated by dashed lines.

In each cylinder 2, a cylinder internal pressure sensor 4 is arranged. A cylinder internal _{pressure sensor} 4 can detect the course of the cylinder internal pressure p _cyl via a combustion cycle c. A maximum value detection 9 can determine the maximum in-cylinder pressure p _max or peak pressure of the respective cylinder 2 in the preceding combustion cycle c.

The peak pressures of all cylinders 2 are supplied as cylinder-specific signals p _{max to} a setpoint calculation 10. This setpoint calculation 10 forms the median from the cylinder-specific signals p _max and outputs this as a setpoint p _median . In a setpoint controller 11, the deviation of the signal p _{max of} a cylinder 2 from the setpoint p _{median is} determined and subsequently a difference _value .DELTA.t _cyl for the fuel _{metering valve} 3, which is assigned to the cylinder 2, determined. The respective difference _value .DELTA.t _cyl is added to a motor global, predetermined target value t _g , resulting in an opening period for the Brennstoffdosierventil 3 as a parameter value t _cyl . The predefinable target value t _g is thereby, as in Fig. 3 described, determined from an emission regulator of the internal combustion engine 1. He can basically also off a power controller and / or a speed controller (as in Fig. 4 described) of the internal combustion engine 1 are determined.

In the example shown, the respective difference value .DELTA.t _cyl comprises a cylinder-specific pilot value t _p, defined by a pre-control value calculation 12 from the charge air pressure p _A and / or the charge air temperature T _A and / or the engine speed n of the internal combustion engine is determined. 1 This respective precontrol value t _p can be determined, for example, by measurements during startup of the internal combustion engine 1 and stored in a map.

In general, the setpoint controller 11 can be executed, for example, as a P, PI or PID controller. However, other controller concepts and controller types can also be used, such as LQ controllers, robust controllers or fuzzy controllers.

In order to avoid unwanted effects on the global engine control, and in particular to the emission controller 5a, the difference values .DELTA.t _cyl be with a compensation value t ₀ each acted upon addition of a compensation value calculation. 13 This equalization value t ₀ , which is the same for all difference _values Δt _cyl, corresponds to the arithmetic mean of the difference _values Δt _{cyl of} all cylinders 2 and may be positive or negative. Overall, it is thus possible to retrofit the proposed method even with internal combustion engines 1, which were previously operated without cylinder equalization or only with a global controller, without this additional regulation has an effect on the global engine control.

Fig. 6 shows a schematic block diagram similar to the Fig. 3 However, with the illustrated embodiment of the invention, not the fuel quantities Q are set for the cylinder 2 but the ignition Z of arranged on or in the cylinders 2 igniters 18. The global predeterminable target value t _g (global default) for the ignition timing Z is determined from a Zündzeitpunktkennfeld 16, wherein in Zündzeitpunktkennfeld 16 suitable values for the global default value t _g depending on the performance or the performance equivalent P and / or the charge air pressure p _A and / or the charge air temperature T _A and / or the engine speed n of the internal combustion engine 1 are stored. The respective parameter value t _cyl determined by the control _device 7 expressed as degrees Crank angle before TDC - is reported to an ignition controller 17. Ignition control 17 activates the respective ignition device 18 for the respective ignition point Z indicated. In this example, ignition timing Z of a cylinder 2 is set earlier than global default value t _g if cylinder peak pressure p _max of cylinder 2 is smaller than setpoint value p _median and Ignition timing Z of a cylinder 2 later adjusted to the global default value t _g , if the cylinder peak pressure p _{max of} the cylinder 2 is greater than the setpoint p _median .

Fig. 7 shows a schematic block diagram of another embodiment of the invention similar to the Fig. 5 , However, not the fuel quantities Q for the cylinder 2 but the ignition timing Z are arranged on or in the cylinders 2 arranged ignition devices 18. In this example, in each case the nitrogen oxide emissions E _{cyl of} a cylinder 2 are detected by a NOx _{sensor 19} via a combustion cycle c and supplied to an evaluation unit 20. The evaluation unit 20 determines from the time profile of the nitrogen oxide emissions E _cyl via a combustion cycle c a filtered emission value, which is supplied as a cylinder- _specific signal E of the setpoint calculation 10. From the cylinder-specific signals E of all cylinders 2, the setpoint calculation 10 forms the median and outputs this as the setpoint value E _median to the setpoint value controller 11. In the setpoint controller 11, the deviation of the cylinder-specific signal E from the setpoint value E _{median is} determined and a difference _value .DELTA.t.sub.Cyl is _determined for the ignition time Z of an ignition device 18 assigned to the corresponding cylinder 2. The respective difference _value .DELTA.t _cyl is added to a motor global, predetermined target value t _g , resulting in an ignition Z in degrees crank angle before TDC as a parameter value t _cyl , which is reported to an ignition control 17, wherein the ignition control 17 for the specified ignition Z the Ignition 18 (eg a spark plug) activated. The predefinable target value t _g is thereby, as in Fig. 6 described, from a Zündzeitpunktkennfeld 16 determined.

Claims (15)

Method for operating an internal combustion engine (1), in particular a gas engine, with at least three cylinders (2), wherein a cylinder-individual signal (p _max , E) is detected by each cylinder (2), whereby from the signals (p _max , E) the cylinder (2) a setpoint (p _median , E _median ) is formed, wherein depending on the deviation of a signal (p _max , E) from the setpoint (p _median , E _median ) at least one combustion parameter (Q, Z) of the corresponding Cylinder (2) is set, wherein the signal (P _max , E) is tracked to the setpoint (p _median , E _median ), characterized in that as a setpoint (p _median , E _median ) the median of the signals (p _max , E ) is formed. A method according to claim 1, characterized in that from each cylinder (2) at least one of the following _individual cylinder signals is detected: in-cylinder pressure (p _cyl ), cylinder _{exhaust temperature} (T _E ), nitrogen oxide emissions (E), combustion air _ratio , preferably as a signal maximum cylinder internal pressure (P _max ) of a combustion cycle (c) is detected. A method according to claim 1 or 2, characterized in that as a signal of a cylinder, the detected signal (p _max , E) over 10 to 1000 combustion cycles (c), preferably 40 to 100 combustion cycles (c), time filtered. Method according to one of Claims 1 to 3, characterized in that the combustion parameter (Q, Z) of a cylinder (2) is set if the deviation of the signal (p _max , E) of the cylinder (2) from the desired value (p _median , E _median ) exceeds a predefinable tolerance value. Method according to one of claims 1 to 4, characterized in that a fuel quantity (Q) for the corresponding cylinder (2) is set as the combustion parameter, wherein preferably the fuel quantity (Q) for a cylinder (2) is increased if the signal ( p _max , E) of the cylinder (2) is smaller than the desired value (p _median , E _median ) and / or the fuel quantity (Q) for one Cylinder (2) is reduced if the signal (p _max , E) of the cylinder (2) is greater than the setpoint (p _median , E _median ). A method according to claim 5, characterized in that for each cylinder (2) a Brennstoffdosierventil (3) is provided, wherein for adjusting the _amount of fuel (Q) for a cylinder (2) the opening duration (t _cyl ) of the corresponding Brennstoffdosierventils (3) set becomes. Method according to one of Claims 1 to 6, characterized in that an ignition point (Z) for the corresponding cylinder (2) is set as the combustion parameter, the ignition point (Z) preferably being set earlier for a cylinder (2) if the signal (p _max , E) of the cylinder (2) is smaller than the desired value (p _median , E _median ) and / or the ignition timing (Z) for a cylinder (2) is set later if the signal (p _max , E) of the Cylinder (2) is greater than the setpoint (p _median , E _median ). A method according to claim 7, characterized in that for each cylinder (2) an ignition device (18) is provided, wherein the ignition timing (Z) of the ignition device (18) in degrees crank angle before TDC (t _cyl ) is set. Method according to one of claims 1 to 8, characterized in that for setting the at least one combustion parameter (Q, Z), a parameter value (t _cyl ) is determined, wherein preferably the parameter value (t _cyl ) a predetermined motor global target value (t _g ) and a cylinder- _specific difference _value (Δt _cyl ) includes. A method according to claim 9, characterized in that the predetermined target value (t _g ) from a predetermined fuel-air ratio (λ) is determined, wherein preferably the predetermined fuel-air ratio (λ) of a power equivalent (P) of the votes Power of the internal combustion engine (1), preferably an electrical power of a generator connected to the internal combustion engine (1), and / or from a charge air pressure (p _A ) and / or from an engine speed (n) of the internal combustion engine (1) is determined. A method according to claim 9, characterized in that the predetermined target value (t _g ) in dependence on the deviation of a power equivalent (P) of the output power of the internal combustion engine (1) of a predetermined target power equivalent (P _S ) and / or in dependence on the deviation an engine speed (n) of the internal combustion engine (1) from a predetermined target speed (n _S ) of the internal combustion engine (1) is determined. Method according to one of Claims 9 to 11, characterized in that the cylinder- _specific differential _value (Δt _cyl ) contains a cylinder- _{specific precontrol value} (t _p ), wherein preferably the cylinder- _specific pilot control _value (t _p ) consists of a charge air pressure (p _A ) and preferably additionally of a Charge air temperature (T _A ) of the internal combustion engine (1) is determined. Method according to one of Claims 9 to 12, characterized in that the cylinder- _specific difference _value (Δt _cyl ) is subjected to a compensation _value (t ₀ ), the compensation value (t ₀ ) corresponding to the arithmetic mean value of the cylinder- _specific difference _values (Δt _cyl ). Method according to one of Claims 1 to 13, characterized in that a combustion state is monitored for each cylinder (2) and assessed as normal or abnormal with respect to a predefinable desired state, the combustion parameter (Q, Z) of a cylinder (2) being only is set if the combustion state of the cylinder (2) is judged normal. A method according to claim 14, characterized in that is monitored as a combustion state knocking and / or Glühzünden and / or exposure to combustion, wherein the combustion state of a cylinder (2) is judged normal, if no knocking and / or no Glühzünden and / or no exposure to combustion can be detected.

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