DE102008001180B4 - Method for controlling an internal combustion engine - Google Patents

Abstract

Method for controlling an internal combustion engine, the fuel injection being divided into at least a first and a second partial injection of at least one injector (131) and a signal determining the fuel quantity being correctable with a correction value, characterized in that the correction value is formed from the sum of a base correction value adapted to an operating point of the internal combustion engine, a mechanical influence of the at least one injector (131) on an injector-specific correction value (qm) that takes into account a residual quantity wave and an injector-specific correction value (qL) determined during operation of the internal combustion engine.

Description

The invention relates to a method for controlling an internal combustion engine according to the preamble of independent claim 1.

The present invention also relates to a computer program and a computer program product for carrying out the method when the program is executed on a computer or a control device.

State of the art

The increasing demands on direct-injection internal combustion engines, in particular diesel engines with regard to noise and pollutant emissions, require very high precision of the fuel quantity injected by the injection system over the entire service life and in all operating conditions of the internal combustion engine. Due to manufacturing tolerances, signs of wear and aging of the internal combustion engine or the injection system of the internal combustion engine and the mutual influence in the case of multiple injections, namely pre-injection, main injection and post-injection, the actual injection quantities and injection times can deviate greatly from the applied target values. For example, disturbances are caused by pressure waves which are triggered by a first injection and which have not yet subsided in the injection system during the time of the second injection immediately following the first injection.

The injection quantity, which changes in waves over the time interval of individual partial injections, is briefly referred to below as the “quantity wave”. Various correction methods are known from the prior art for their correction.

For example, the EP 1303 693 B1 a method and a device for controlling an internal combustion engine, in which, for pressure wave correction, the fuel quantity injected during a second partial injection is corrected as a function of a pressure quantity that characterizes the fuel pressure, the fuel quantity quantity and a further quantity. The further variable can be, for example, a variable that characterizes the fuel temperature.

From the DE 197 12 143 A1 A method and a device for controlling an internal combustion engine have become known, in which the fuel injection is divided into at least a first and a second partial injection. A signal determining the amount of fuel injected can be corrected with a correction value. This correction value is formed multiplicatively from a first value and a second value. The first value can be specified as a function of at least the measured fuel pressure value and / or the distance between the first and the second partial injection, and the second value can be specified as a function of at least one injection quantity that is metered in the first partial injection or on the duration of the first partial injection , Fluctuations in the fuel pressure between a measurement of the fuel pressure value and the second partial injection are taken into account by the correction value. A corrected fuel pressure value is formed on the basis of the correction value and a measured fuel pressure value.

In the publication ROBERT BOSCH GmbH: Diesel engine management. 4th edition. Wiesbaden: Vieweg, 2004. p.372f. - ISBN 3-322-80332-0 different correction procedures are described to compensate for different influences on the injection accuracy.

Also the DE 10 2005 036 192 A1 describes a method for controlling an injection system. The influence of a first partial injection on a second partial injection is corrected.

The DE 103 31 241 A1 describes a method for adjusting the injector quantity in the pre-injection.

The EP 1 172 541 A1 shows a method for operating a piezoelectric actuator of an injection valve.

The DE 10 2007 043 879 A1 shows a method for operating an injection valve. A second partial injection is shortened depending on the pause time between a first and a second injection.

For reasons of principle, however, these compensation methods only achieve a finite correction quality. The remaining deviation of the actual quantity from the target value, which is referred to as the residual quantity wave, cannot be easily compensated in this way.

The invention is therefore based on the object of developing a method for pressure wave correction of the generic type in such a way that a residual wave of this type can also be compensated for.

Disclosure of the invention

Advantages of the invention

This object is achieved by a method with the features of independent claim 1.

Characterized in that the correction value, with which the signal determining the fuel quantity is corrected, from the sum of a basic correction value adapted to an operating point of the internal combustion engine, an injector-specific correction value taking mechanical influences of the at least one injector on a residual quantity wave into account, and an individual injector determined during operation of the internal combustion engine Correction value is formed, errors that are caused by the above-mentioned residual quantity waves can also be compensated for in a very advantageous manner. In this way, a residual quantity deviation in multiple injections can be further reduced in time following an optionally used pressure wave correction method. An essential idea of the method is a grouping of residual quantity waves to describe the relationship between higher-frequency pressure fluctuations, mechanical influencing variables and the injection quantity error during operation. In addition to the reduction of higher-frequency vibrations, this method also very advantageously creates an intervention option for mechanical parameters, for example based on information about setting parameters and tolerances and the like. In this way, injector-specific and therefore also cylinder-selective corrections can be made. This is particularly advantageous, especially when there are short intervals between two partial injections. Finally, a correction during the operation of the internal combustion engine and thus a correction of injection quantity errors due to signs of aging is also possible.

The measures listed in the dependent claims allow advantageous developments and improvements of the method specified in the independent claim.

An advantageous embodiment of the method provides for the base correction value to be taken from a previously determined reference map and to be multiplied by a scaling factor which characterizes the adaptation to the operating point. In the basic map there are reference curves that were determined and stored for each pressure when grouped into pressure levels. A base correction value is calculated from this map, which is then multiplied by the scaling factor. The scaling factor is preferably also taken from a previously determined scaling map. This scaling map contains factors for the optimized adaptation of the reference curve to the respective measuring point, that is to say to the respective operating point.

Alternatively, in order to reduce the memory space requirement of the characteristic diagrams, the basic correction value including the information about the scaling factor can be achieved by a model-based approach, i.e. a suitable model can be determined on the basis of several superimposed exponentially damped sine vibrations and a function term for the description of the non-hydraulic vibration components.

Both the reference map and the scaling map or the model-based approach are determined on the basis of at least the following variables: the quantity injected during a first injection, the rail pressure, the time difference between the first and the second injection and the injection quantity of the post-injection.

The injector-specific correction value that takes into account the mechanical influences of the injector is advantageously determined in each case as a function of the operating point during the manufacture of the injector and is stored in a data carrier assigned to the injector. This injector-specific correction value takes mechanical parameters into account, for example.

In this way, injector-specific and thus also cylinder-selective corrections can be made compared to the prior art. This is particularly helpful when there are short intervals between two partial injections. The data carrier, on which the injector-specific correction values are stored, is, for example, a data matrix code assigned to the injector, as it is known to the engine control unit when a so-called injector quantity adjustment method (IMA) is carried out when installing the injector. communicated ”.

Another very advantageous embodiment of the method provides for “starting up” and teaching in individual injection patterns of the internal combustion engine. These values form the injector-specific correction values. They also make a correction possible over the life of the injectors.

The method can be implemented as a computer program and stored on a computer program product, for example on a machine-readable data carrier. In this way, it can be “read” into existing control devices for internal combustion engines and, to a certain extent, “retrofitted”.

list of figures

Embodiments of the invention are shown in the drawings and explained in more detail in the following description.

• 1 eine schematische Darstellung eines aus dem Stand der Technik bekannten Common-Rail-Einspritzsystems;
• 2a schematisch ein Blockdiagramm zur Erläuterung einer Ausgestaltung des erfindungsgemäßen Verfahrens;
• 2b schematisch ein Blockdiagramm zur Erläuterung einer weiteren Ausgestaltung des erfindungsgemäßen Verfahrens und
• 3 schematisch die eingespritzte Menge über der Zeitdifferenz zweier benachbarter Einspritzungen jeweils mit und ohne Anwendung des erfindungsgemäßen Verfahrens.

Show it:

• 1 a schematic representation of a known from the prior art common rail injection system;
• 2a schematically a block diagram for explaining an embodiment of the method according to the invention;
• 2 B schematically a block diagram to explain a further embodiment of the method according to the invention and
• 3 schematically the amount injected over the time difference between two adjacent injections, each with and without using the method according to the invention.

Embodiments of the invention

In the 1 Components of a high-pressure fuel injection system required for understanding the invention are shown using the example of a common rail system. With 100 is called a fuel tank. The fuel tank 100 stands for the delivery of fuel through a first filter 105 as well as a pre-feed pump 110 with a second filter 115 in connection. From the second filter 115 the fuel reaches a high-pressure pump via a line 125 , The connecting line between the second filter 115 and the high pressure pump 125 is also a low pressure relief valve 145 having connecting line with the reservoir 100 in connection. The high pressure pump 125 stands with a rail 130 in connection. The rail 130 is also referred to as a (high pressure) accumulator and is in turn located above fuel lines with various injectors 131 in a pressure-conducting connection. Via a pressure relief valve 135 is the rail 130 with the fuel tank 100 connectable. The pressure relief valve 135 is by means of a coil 136 controllable.

The lines between the outlet of the high pressure pump 125 and the inlet of the pressure relief valve 135 are referred to as the "high pressure area". In this area the fuel is under high pressure. The pressure in the high pressure area is measured by a sensor 140 detected. The line between the fuel tank 100 and the high pressure pump 125 are, however, referred to as the "low pressure range".

One control 160 acts on the high pressure pump 125 with a control signal AP, the injectors 131 each with a control signal A and / or the pressure relief valve 135 with a control signal AV. The control 160 processes various signals from different sensors 165 which characterize the operating state of the internal combustion engine (not shown) and / or the motor vehicle which is driven by this internal combustion engine. Such an operating state is, for example, the speed N of the internal combustion engine.

This in 1 The injection system shown works as follows: The fuel that is in the fuel tank 100 is using the pre-feed pump 110 through the first filter 105 and the second filter 115 promoted through. If the pressure in the specified low pressure range rises to impermissibly high values, the low pressure relief valve opens 145 and gives the connection between the output of the pre-feed pump 110 and the reservoir 100 free. The high pressure pump 125 promotes the amount of fuel Q1 from the low pressure area to the high pressure area. The high pressure pump 125 builds in the rail 130 a very high pressure. Usually, maximum pressure values of approximately 30 to 100 bar are achieved in injection systems for spark-ignited internal combustion engines and maximum pressure values of approximately 1000 to 2000 bar in the case of self-igniting internal combustion engines (diesel internal combustion engines). By means of the injectors 131 the fuel can thus be metered to the individual combustion chambers (cylinders) of the internal combustion engine under high pressure.

By means of the sensor 140 the pressure P in the rail or in the entire high pressure range is recorded. By means of the controllable high pressure pump 125 and / or the pressure relief valve 135 the pressure in the high pressure area is regulated.

As a pre-feed pump 110 electric fuel pumps are usually used. For higher flow rates, which are particularly necessary for commercial vehicles, several parallel feed pumps can be used.

Injections in such internal combustion engines are divided into several partial injections during a metering cycle. As a rule, at least one or two pre-injections, a main injection and at least one post-injection are provided. The intervals of the individual partial injections can be applied variably, they can be predefined depending on the system or they can be predefined depending on the operating state of the internal combustion engine.

Each injection in such multiple injections triggers vibrations, so-called pressure waves, in the line system of the common rail high-pressure circuit. These pressure waves systematically influence the quantities of subsequent injections. The injection quantity which is wave-shaped over the time interval of individual partial injections is shown schematically in FIG 3 based on the curve 310 shown. Such a disturbance, hereinafter referred to briefly as “quantity wave”, is compensated for by methods known per se for pressure wave correction in a control device of the internal combustion engine, in particular in the engine control unit. For reasons of principle, however, such compensation only achieves a finite correction quality. In addition to higher-frequency vibrations, the volume waves are also superimposed by mechanical influences, for example by armature bouncing in common rail injectors. For reasons of principle, these cannot be compensated for by pressure wave correction methods known per se and remain as the “residual wave” referred to below. Accordingly, there remains a deviation of the actual quantity from the target value in the form of these residual quantity waves. The basic idea of the invention is now to also compensate for these residual quantity waves and thus to further improve the measuring accuracy.

In order to also compensate for such residual quantity waves and thus to further improve the tensile measurement accuracy in the case of multiple injections, a first embodiment of the invention and in connection with 2a schematically explained method first in a first step 210 , which can be referred to as a basic correction, quantity qRoh injected from the input variables, rail pressure pRail, time difference between two neighboring injections t _diff and influenced subsequent partial injection quantity qE2 211 stored reference curves, which were previously determined, in particular calculated, and stored in a grouping in pressure stages for each pressure, a basic correction value is determined or calculated, which is then carried out in one step 215 with a scaling factor that is a scaling map 214 is taken, multiplied. The scaling map 214 contains factors for the optimized adaptation of the reference curve of the basic map 211 to the respective operating point of the internal combustion engine, i.e. to the current measuring point.

An alternative embodiment of the method is described below in connection with 2 B in which the same elements are denoted by the same reference numerals as in 2a , to whose description reference is made. As an alternative to the previously described determination of the basic correction by means of the basic map 211 and scaling using the scaling map 214 the basic correction can also be carried out using a mathematical model, in 2 B through a function 212 : q = f (x) on the basis of several superimposed exponentially damped sine waves and a function term for the description of the non-hydraulic vibration components. This mathematical model describes the basic map 211 , the scaling map 214 and the step 215 analytically.

Then follow the steps 223 . 233 two additions of the quantities qm and qL explained below to the correction value determined in this way. A first addition 223 takes into account the superimposed injector-specific mechanical component. This square meter portion will be in one step 220 determines and is based on injector-specific parameters, for example in a data matrix code assigned to the injector 221 are stored and communicated to an engine control unit when installing the injector. “Communicated” means something like taking into account the relevant data.

Another addition 233 takes into account lem points during the operation of the internal combustion engine. These values are also injector-specific. They are determined, for example, by learning points being “approached” while the internal combustion engine is operating. The correction value qL is in one step 230 calculated. The advantage of this consideration is that a better adaptation between measurement and driving operation can be achieved in this way and that in particular a consideration can be realized during the operation of the internal combustion engine, ie over its lifetime. This enables compensation for errors caused by aging effects, for example of the injectors.

The result of this calculation is a corrected injection quantity q _corr . In 3 is schematic based on the curve 320 an example of a correction of a signal generated in this way 310 shown. As can be seen from this figure, the residual quantity wave is largely compensated for, the positive and negative quantity deviations are significantly reduced.

The method described above can be implemented, for example, as a computer program on a computing device, in particular a control device of an internal combustion engine, and run there. The program code can be stored on a machine-readable medium that the control unit can read. In this way, the process can be "retrofitted" to a certain extent even with existing control units.

Claims (9)

Method for controlling an internal combustion engine, the fuel injection being divided into at least a first and a second partial injection of at least one injector (131) and a signal determining the fuel quantity being correctable with a correction value, characterized in that the correction value is formed from the sum of a base correction value adapted to an operating point of the internal combustion engine, a mechanical influence of the at least one injector (131) on an injector-specific correction value (qm) that takes into account a residual quantity wave, and an injector-specific correction value (qL) determined during operation of the internal combustion engine. Procedure according to Claim 1 , characterized in that the base correction value is taken from a previously determined reference map (211) and multiplied by a scaling factor which characterizes the adaptation to the operating point. Procedure according to Claim 2 , characterized in that the scaling factor is taken from a previously determined scaling map (214). Procedure according to Claim 2 or 3 , characterized in that the reference map (211) and the scaling map (214) show the relationship between the quantity injected during a first partial injection (qRoh), the rail pressure (pRail), the time difference between the first and the second partial injection (t _diff ) and represent the injection quantity of the second partial injection (qE2). Procedure according to Claim 1 , characterized in that the base correction value is determined by a mathematical model (212) on the basis of a number of predeterminable, superimposed and exponentially damped sine oscillations and a predefinable function term which describes the non-hydraulic oscillation components. Procedure according to Claim 1 , characterized in that the injector-specific correction value (qm) which takes into account the mechanical influences of the injector (131) is determined in each case as a function of the operating point when the injector (131) is manufactured and is stored in a data carrier (221) assigned to the injector (131). Procedure according to Claim 1 , characterized in that the injector-specific correction value (qL) determined during the operation of the internal combustion engine is determined by specifically approaching predeterminable operating points of the internal combustion engine and is stored in a memory of a control device of the internal combustion engine, in particular a control unit. Computer program that covers all steps of a method according to one of the Claims 1 to 7 executes when it runs on a computing device, in particular a control device of an internal combustion engine. Computer program product with program code, which is stored on a machine-readable carrier, for carrying out the method according to one of the Claims 1 to 7 , if the program is executed on a computer or a control device of the internal combustion engine.

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