AT517534B1 - Method for operating an internal combustion engine - Google Patents

Abstract

Method for operating an internal combustion engine (1), in particular a gas engine, with at least two cylinders (2) of which a cylinder-individual signal can be detected by sensors (4) which is characteristic of a reference pressure (Pref i) present in the respective cylinder (2) , wherein either a common reference pressure setpoint (Pref desired global) for the at least two cylinders (2) or individual reference pressure setpoints (Pref desired i) for the at least two cylinders (2) are stored in a control device (5), wherein deviations between the cylinder-specific reference pressures (Pref i) and the common setpoint (Pref set global) or between the cylinder-specific reference pressures (Pref i) and the individual setpoint values (Pref setpoint i) and based on the determined deviation (s) on the respective reference pressure -Setpoint (Pref global, Pref desired i) is regulated, the rules on the respective reference pressure Sollwer t (Pref global, Pref target i) by adjusting the at least two cylinders (2) supplied amount of fuel-air mixture or air by means of a variable valve train (3).

Description

Description [0001] The present invention relates to a method for operating an internal combustion engine having the features of the preamble of claim 1.

The cylinders of an internal combustion engine usually have combustion differences: this means that in global control of combustion parameters such as a fuel quantity or the ignition timing, the contributions of the individual cylinders to the total performed work of the internal combustion engine are different.

In the context of the invention, global regulation of combustion parameters means that all cylinders of an internal combustion engine are operated with the same values for the corresponding combustion parameters, that is, for example, that in a global control with respect to the ignition timing, each cylinder is operated with the same ignition timing.

The work of a cylinder is transmitted in a trained as a reciprocating engine engine via the connecting rod of the cylinder to the crankshaft of the internal combustion engine. With the internal combustion engine, an electric generator is often connected to convert the mechanical power of the crankshaft into electrical power. In order to achieve a uniform component load of each cylinder, it is an effort to bring about a so-called cylinder equalization. In a cylinder equalization makes each cylinder of an internal combustion engine essentially the same proportion of the total work done.

With respect to a cylinder equalization control, it is described in US Pat. No. 7,957,889 B2 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. The manipulated variable is a cylinder-specific fuel injection via a port-injection valve.

With regard to the manner of introducing fuel into the piston-cylinder units, internal combustion engines can be divided into two types: [0007] The first type are so-called air-charged internal combustion engines with cylinder-individual fuel supply (for example, using port injection technology). Valves or diesel injectors).

The second type are mixed supercharged internal combustion engines in which a fuel-air mixture is compressed with a predetermined fuel-air ratio and fed to the combustion chambers. The fuel input is thus not cylinder-individual.

While the cylinder-individual fuel supply allows a very effective cylinder equalization in air-charged internal combustion engines, it is only possible in the prior art mixed-charged internal combustion engines to vary by varying the ignition timing, the respective peak cylinder pressure within certain limits. These limits are given for example by cylinder-specific emission differences, cylinder-specific occurrence of knocking or misfire (misfires). This is also known from WO 2012/057761 A1 or EP 1188916 A2.

The object of the present invention is to provide a method for compensating for variations between individual cylinders of an internal combustion engine, which method is also applicable flexibly for mixed-charged internal combustion engines.

This object is achieved by a method for operating an internal combustion engine with the features of claim 1. Advantageous embodiments are specified in the dependent claims. According to the invention, it is thus provided that the regulation takes place to the respective reference pressure set value by adapting an amount of fuel / air mixture or air fed to the at least two cylinders by means of a variable valve drive.

The reference pressure in a combustion chamber or cylinder before ignition is representative of an air mass or cylinder filling in this cylinder. By determining the reference pressure, it is therefore possible to deduce the air mass present in the combustion chamber. It is provided according to the invention that a pressure occurring during combustion of the fuel-air mixture present in the cylinder is measured as the reference pressure.

In accordance with the invention, adjusting the amount of fuel-air mixture or air supplied to the at least two cylinders by means of a variable valve train provides the possibility of influencing the cylinder charge participating in the combustion.

The invention is applicable to supercharged and supercharged internal combustion engines. In the case of supercharged internal combustion engines, it is additionally possible to influence the ratio of air to fuel (lambda value) compared to supercharged internal combustion engines.

A particular advantage of the invention is that it is no longer subject to the limits of influencing the cylinder pressure via variation of the ignition timing. In this respect, the method is therefore more flexible applicable.

As for a present in the respective cylinder reference pressure signal, for example, the signal of a cylinder pressure sensor can be used. Cylinder pressure sensors are often designed as piezoelectric elements such as quartz. Alternatively, to output a signal characteristic of the reference pressure, an ion current sensor which detects an ion current variable by the course of the combustion could also be used.

The reference pressure of the cylinder pressure may be, for example, peak firing pressure (PFP), indicated mean effective pressure (IMEP), or another characteristic value of the cylinder pressure. Thus, as a reference pressure of the cylinder pressure, a single value from the compression line before ignition to a certain position (e.g., 50 degrees crank angle before top dead center (TDC) of a combustion chamber bounding piston) can be determined. Also, a plurality of values may be averaged (e.g., 21 values from a range of 50 degrees crank angle to 48 degrees crank angle before top dead center of the piston with a resolution of 0.1 degrees crank angle).

Since cylinder pressure measurements in the range of substantially 49 degrees crank angle before the top dead center of the piston are often performed for the monitoring of combustion processes, can be provided according to a preferred embodiment, to use these cylinder pressure measurements for determining the reference pressure of the cylinder pressure.

In order to increase the accuracy, the reference value for the cylinder pressure over several cycles of the internal combustion engine can be averaged over time.

The control can be done on a common reference pressure setpoint of at least two cylinders or individual reference pressure setpoints for the at least two cylinders.

In other words, either a cylinder equalization to a common reference pressure set point or a targeted unequal position of the cylinder can be done.

By a targeted unequal position of the cylinder with respect to their reference pressure cylinder individual differences - for example, in relation to the cylinder parameters air filling, deposits and wear, combustion focus position or mechanical tolerances - are taken into account. As a result, it can be achieved, for example, that the cylinders of the internal combustion engine have similar emissions and / or similar efficiencies, despite different reference pressures.

If the control is based on a common reference pressure setpoint value, then this can be determined as a median or as the arithmetic mean value of the cylinder-specific signals.

Median control has been found to be particularly advantageous as the median is more robust against outliers (excessive signal excursions) or failure of sensors.

Preferably, the application of the method to stationary internal combustion engines, in particular stationary gas engines, particularly preferred for gensets.

The invention will be explained in more detail by the figures. 1 a, 1 b show schematic diagrams of an internal combustion engine; FIG. 2 shows a graph of the course of the cylinder pressure when the method according to the invention is used. [0027] FIG.

Figure 1a shows a cylinder 2 of an internal combustion engine 1 in detail, while in Figure 1b, the individual cylinders are shown only schematically. In reality, internal combustion engines 1 have a plurality of cylinders 2. A cylinder 2 has an inlet valve 8 and an outlet valve 9 in this example. The intake valve 8 can be actuated in a cylinder-specific manner via a variable valve drive 3. A signal characteristic of a reference pressure present in the respective cylinder 2 is detected by a sensor 4 and transmitted to a control device 5.

Figure 1b shows schematically an internal combustion engine 1 with, for example, three cylinders 2. At each cylinder 2, a sensor 4 is arranged, through which a cylinder-individual signal can be detected, which is characteristic for a reference pressure occurring in the combustion pref i i in the respective cylinder 2 (FIG. As already stated, reference pressure pref i can be a peaking pressure (PFP), an indicated mean effective pressure (IMEP) The reference pressure may also be subjected to temporal filtering, for example over 10 to 1000 combustion cycles.

The cylinder-specific signals are transmitted via signal lines 6 to the control device 5.

First, deviations between the cylinder-specific reference pressures pref i and the common desired value pref soii are determined globally or between the cylinder-specific reference pressures pref i and the individual desired values (pref Soii i). Based on the determined deviation (s) is now on the respective reference pressure setpoint (pref Son global, Pref soii i) regulated.

By the control device 5 is a cylinder for adjusting to the setpoint necessary amount of fuel-air mixture for the cylinder 2 is determined and reported by means of control lines 7 to the variable valve train 3.

On the position of the variable valve train 3, the degree of filling of the cylinder 2 is influenced.

In the case of supercharged internal combustion engines, the position of the variable valve drive 3 influences the quantity of fuel-air mixture metered to a cylinder 2. In a change in the direction of larger amount of fuel-air mixture thereby passes more chemical energy in the form of fuel in the cylinder 2. By the variable valve train 3, the cylinders 2 supplied amounts of fuel-air mixture cylinder-individually changed and thus the cylinder-specific reference pressures pref to the respective reference pressure setpoint (prefsoii global, Prefsoiii) are regulated.

In the case of supercharged internal combustion engines, only the amount of air admitted to a cylinder 2 is influenced by the position of the variable valve train 3.

Assuming a constant fuel addition in this case, the amount of fuel remains unchanged.

The invention allows by using a variable valve train 3, a cylinder equalization in mixed-supercharged internal combustion engines, as it was previously only possible for luftaufgela-dene internal combustion engines.

FIG. 2 shows a graph of the course of the cylinder pressure when using the method according to the invention. The cylinder pressure is plotted in bar over time.

By way of example, the reference pressures pref, occurring during combustion, are shown for three cylinders (Z1, Z2 and Z3). In the present example, the reference pressure is the peak cylinder pressure. It can be seen that at the beginning of the observation period (time t = 0) the reference pressures pref, the cylinders Z1, Z2 and Z3 differ significantly.

Also shown is the median of the reference pressures pref, the cylinder Z1, Z2 and Z3. By the exemplary choice of three cylinders, the median of the three reference pressures corresponds to the value of the cylinder Z2.

Also entered is the mean value of the reference pressures pref, the cylinders Z1, Z2 and Z3.

The engine limit is a pressure value specific to each engine 1, which sets a mechanical load upper limit. So it should be the reference pressures of all cylinders 2 below this limit.

It can be seen that by operating the method according to the invention, the reference pressures pref i of the cylinders Z1, Z2 and Z3 are guided into a narrower band and closer to the limit value. The duration of the procedure is marked by the dotted folder. Typically, the controlled state is reached after about 100 combustion cycles.

By the method is thus achieved on the one hand, that individual cylinder 2 with too high reference pressures pref, be brought back to a tolerable for the internal combustion engine 1 measure, and on the other hand, the reference pressures pref, a plurality of cylinders 2 are guided in a narrower band , Due to the more uniform component loads and the more similar operating points, the power density of the internal combustion engine can be increased without exceeding limit values for the individual cylinders 2. LIST OF REFERENCE SIGNS USED: 1 Internal combustion engine 2 Cylinders 3 Variable valve train 4 Sensor 5 Control device 6 Signal line 7 Control line 8 Inlet valve 9 Outlet valve

Claims (3)

claims 1. A method for operating an internal combustion engine (1), in particular a gas engine, with at least two cylinders (2) of which by sensors (4) a cylinder-individual signal can be detected, which characteristic of a respective cylinder (2) present reference pressure (prefi) is, wherein either a common reference pressure setpoint (pref soii global) for the at least two cylinders (2) or individual reference pressure setpoints (Pref soii i) for the at least two cylinders (2) in a control device (5) are deposited, Deviations between the cylinder-specific reference pressures (pref) and the common setpoint (pref soii global) or between the cylinder-specific reference pressures (pref i) and the individual setpoints (pref Son i) are determined and based on the determined deviation (s) on the respective Reference pressure setpoint (pref Soii global, Pref soii i) is regulated, wherein the rules on the respective reference pressure Sollwer t (pref summer global, Pref soii i) by adjusting the at least two cylinders (2) supplied amount of fuel-air mixture or air by means of a variable valve train (3), characterized in that as a reference pressure (prefi) in a combustion the pressure occurring in the cylinder (2) present in the fuel-air mixture is measured. 2. The method of claim 1, wherein as the reference pressure (pref,) in the respective cylinder (2) occurring peak cylinder pressure is determined. 3. The method of claim 1, wherein the reference pressure (pref,) of the respective cylinder (2) occurring indicated mean pressure is determined. For this 2 sheets of drawings