DE102015220405A1 - Method and device for controlling a fuel injection system of an internal combustion engine - Google Patents

Abstract

The present invention relates to a method and an apparatus for controlling a fuel injection system of an internal combustion engine having a high-pressure fuel accumulator and at least one injector, wherein multiple injections are carried out with at least two temporally successive partial injections, characterized in that an injection quantity-based pressure wave compensation (210 -220) of quantity errors in the case of said multiple injections is additionally carried out taking into account at least one time variable (214) characteristic of at least one partial injection (235).

Description

The invention relates to a method and a device for controlling a fuel injection system of an internal combustion engine according to the preambles of the respective independent claims. The present invention also relates to a computer program, a machine-readable data carrier for storing the computer program and an electronic control unit, by means of which the method according to the invention can be carried out.

State of the art

In today, eg in the DE 100 02 270 C1 described in common rail fuel injection systems (CR injection system), in particular in auto-ignition internal combustion engines, the entire, injected by an injection actuator or injector into the respective combustion chamber injection quantity to improve the mixture preparation is divided into an increasing number of partial injections, often in one very close temporal distance to each other. These partial injections usually consist of one or more subsequent injections in time before an actual main injection and / or on this main injection.

In the case of the partial injections mentioned, the precision of the particular injection quantity is of great importance. However, it is also known at the same time that each injection by means of an injector of said CR injection system causes a brief drop in the fuel pressure in a supply line from a high-pressure accumulator (rail) to the relevant injector. In addition, the closing of an injector or a corresponding nozzle needle leads to an increase in pressure. The combination of pressure drop and pressure increase then leads to a fuel pressure wave preferably occurring between the rail and the injector. This pressure wave leads in particular to undesirable fluctuations in the injected fuel quantity, with this pressure wave effect even increasing with increasing needle speed of the nozzle needle of the injector, so that its attention especially in future injection systems where high-speed piezo actuator as injection actuators for nozzle needle control in the respective Injector are used, even an even greater importance.

Due to the fluidic damping effect, said pressure wave influence decreases with increasing time interval between the respectively adjacent injections. As a result, the influence on the injection quantity of a respective subsequent injection decreases with increasing time interval and approaches the undisturbed quantity that would be obtained with a time-isolated injection for sufficiently large time intervals.

Since the described pressure wave effects are of a strictly systematic nature, namely essentially dependent on the time interval of the injections involved, the injected fuel quantity, the hydraulic fuel pressure and the fuel temperature in the hydraulically relevant pipe system, they can be corrected by a suitable control function in the engine control unit. One from the DE 10 2010 062 609 A1 A known approach for minimizing the pressure wave influence mentioned is therefore to measure this influence on the injection quantities of the respective injectors and to take into account the results of this measurement, for example when presetting the control data of the injection system, wherein the respective injection periods are determined in a so-called quantity path. Corresponding correction of the aforementioned drive data is based on a number of pre-empirically or experimentally determined fuel quantity waves as a function of the time interval between two or possibly even several partial injections. An appropriately performed pressure wave compensation (DWK) sets the measured at a reference system quantity influence on a subsequent injection in maps and compensates for the amount of influence during runtime of the internal combustion engine by corresponding change in the energization of the respective subsequent injection.

Disclosure of the invention

The invention is based on the idea of a here affected, preferably in a common rail (CR) injection system and based on injection quantities pressure wave compensation (DWK) of quantity errors in the aforementioned multiple injections in addition, taking into account the characteristic temporal quantities or of the Perform time behavior of the CR system characteristic sensor signals in the CR system and thereby correct not only the amount, but also the timing of multiple injections. In contrast to the prior art, instead of injection quantities or quantity errors, in particular temporal operating quantities of an injection, e.g. the start of injection, the end of injection and the duration of injection corrected.

The invention is based on the finding that the pressure waves mentioned not only the injection quantity of an injector affected here, but also the temporal injection behavior, eg a hydraulically effective injection duration and / or a hydraulically effective injection start and / or a hydraulically effective injection end and / or a hydraulically effective time delay of the start of injection, significantly influence. It has been recognized that a correction that corrects these temporal changes provides better results than a pure set correction.

The invention is also based on the finding that the pressure waves mentioned can be better characterized on the basis of hydraulic time variables such as the injection duration and the hydraulic distance than on the basis of injection quantities and electrical distances, as is the case in the prior art in the case of the DWK is.

Such temporal quantities can also be determined in a manner known per se by means of a corresponding sensor system, e.g. Pressure sensors, switching sensors, or the like, are detected and corrected. If this is the case, then a high degree of correctness can also be achieved in quantity errors occurring over the lifetime, e.g. due to coking of fuel injectors. Said sensor system can be arranged as part of the injection system or separated from it. However, the temporal quantities can also be provided by means of a controller or by means of a previously-fed map structure.

The temporal pressure wave effects mentioned are considered according to the invention by means of a suitable data processing structure preferably implemented in a control unit of the internal combustion engine. Such a data processing structure goes beyond an initially mentioned quantity path and also takes into account the variables which concern the temporal injection behavior.

The procedure according to the invention also makes possible a clear separation between individual or different quantity-influencing effects occurring in the case of multiple injections. The respective individual quantities are determined on the basis of previously determined measurement or simulation data. This, in turn, allows for multiple injections to carry out individual partial injections with an injection duration that is ideal only for single injections, as a result of which the metering accuracy in such multiple injections can be significantly improved. As a result, this leads to a more stable temporal injection behavior as well as to reduced injection quantity tolerances over the life of the injection system, e.g. a said CR injection system.

The cited consideration of characteristic time variables also includes, in particular, a changeover of electrical pause times between partial injections to actually present hydraulic pause times or injection intervals located in time between two partial injections. Thus, the consideration of the temporal injection distance in a coked or otherwise contaminated injector to a significant improvement in the imaging quality of a bulk wave over the lifetime of the CR injection system. As a result, in particular smaller injection distances can be stably realized. Such a stable injection timing or correspondingly time-stable injection intervals in turn allow the generation of new injection patterns, which can additionally contribute to reducing emissions.

• – Berechnen einer unkorrigierten Einspritzmenge einer ersten Teileinspritzung sowie wenigstens einer der ersten Teileinspritzung zeitlich vorausgehenden zweiten Teileinspritzung anhand einer Mengenvorgabe für einen vorliegenden Injektor;
• – Berechnen einer elektrischen Pausenzeit zwischen den beiden Teileinspritzungen;
• – Ermitteln von hydraulischen Werten (z.B. der hydraulisch wirksamen Pausenzeit und den hydraulisch wirksamen Einspritzdauern) auf der Basis von elektrischen Pausenzeiten und von unkorrigierten Mengenvorgaben;
• – Ermitteln einer Korrekturkurve für den vorliegenden Injektor;
• – Berechnen von Korrekturwerten für den Einspritzbeginn, das Einspritzende und die Einspritzddauer für die erste Teileinspritzung anhand der genannten ermittelten Korrekturkurve sowie anhand von weiteren, den Betriebszustand der Brennkraftmaschine charakterisierenden Größen, z.B. anhand des Raildrucks;
• – Umwandeln des unkorrigierten Mengenwertes in einen korrigierten Ansteuerdauerwert und Ansteuerbeginn anhand der injektorspezifischen Kennlinie und den genannten Korrekturwerten für den Einspritzbeginn, das Einspritzende und die Einspritzdauer;
• – Bereitstellen des korrigierten Ansteuerdauerwertes und des Ansteuerbeginns als Sollwert für eine nachfolgende Ansteuerung des vorliegenden Injektors.

According to one embodiment, the method according to the invention comprises the following steps:

• - calculating an uncorrected injection quantity of a first partial injection and at least one of the first partial injection temporally preceding second partial injection based on a quantity specification for a present injector;
• Calculating an electrical pause time between the two partial injections;
• - Determining hydraulic values (eg the hydraulically effective dead time and the hydraulically effective injection periods) on the basis of electrical dead times and uncorrected quantity specifications;
• - determining a correction curve for the present injector;
• Calculating correction values for the start of injection, the end of injection and the duration of injection for the first partial injection based on the determined correction curve and on the basis of further variables characterizing the operating state of the internal combustion engine, for example based on the rail pressure;
• Converting the uncorrected quantity value into a corrected activation duration value and activation start on the basis of the injector-specific characteristic curve and the correction values for the start of injection, the end of injection and the duration of injection;
• - Providing the corrected Ansteuerdauerwertes and the Ansteuerbeginns as setpoint for a subsequent control of the present injector.

Such a method can advantageously be integrated particularly simply and therefore cost-effectively into a known existing injection quantity-based pressure wave compensation.

The invention can be used in all CR injection systems in which pressure waves have an influence on the metering accuracy of injection quantities described here. Since in a CR injection system existing hydraulic time intervals of already existing injection applications can be relatively easily transferred to an injection timing according to the invention, In addition, this advantageously results in a reduction of the complexity of the data. Because the transmission of hydraulic injection intervals, instead of electrical injection pauses, allows a parameterization of injection patterns, which can be better transferred from one CR system to another CR system, even if the causal relationship between electrical control and hydraulic response change should.

In addition, an existing DWK implementation can be relatively easily extended to a functionality according to the invention, without having to change an existing data processing structure with great effort. Because with such an extension, the input and output signals can be combined via a simple mathematical function and transferred to an existing DWK.

The computer program according to the invention is set up to carry out each step of the method, in particular if it runs on a computing device or a control device. It allows the implementation of the method according to the invention on an electronic control unit, without having to make structural changes to this. For this purpose, the machine-readable data carrier is provided on which the computer program according to the invention is stored. By applying the computer program according to the invention to an electronic control unit, the electronic control unit according to the invention is obtained, which is set up to preferably control a CR injection system by means of the method according to the invention.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

Brief description of the drawings

1 shows a known in the prior art method and a corresponding device for pressure wave compensating control of temporally successive partial injections in a CR injection system of an internal combustion engine, using a combined block / flow diagram.

2 shows an embodiment of the method and the device according to the invention with reference to a combined block / flow diagram.

3 shows a possible integration of the method according to the invention into an existing DWK data processing structure.

Description of exemplary embodiments

The 1 shows in block or flowchart form a known in the prior art method and apparatus for pressure wave compensating (DWK) control of an internal combustion engine, wherein final injection periods are determined substantially in a so-called quantity path. In the present example, an injection situation consisting of two partial injections is assumed, namely consisting of a main injection 'HE' and one of these temporally preceding pilot injection 'VE'. It is further assumed that a pressure wave originating from the VE influences the HE in the manner described above.

Initially, a quantity specification is used 100 for determining a desired driver quantity m_FW, for example on the basis of a current accelerator pedal position. Because of this quantity value m_FW, an uncorrected main injection quantity m_HE_uncorr and a pre-injection quantity m_VE and a suitable pause time t_diff between these two partial injections are calculated by the engine control in a manner known per se 105 , Already in advance, the already mentioned correction curve, ie the wave-shaped activation duration as a function of the pause time t_diff, is determined experimentally or by means of a model calculation for the respective injector 110 ,

On the basis of a characteristic curve AD = f (m) which is preferably also present for each injector 130 becomes the drive Dauerwelle a correction quantity wave 115 calculated for the main injection quantity. By means of the quantity wave 115 Now, the uncorrected quantity value m_HE_unkorr is converted into a (pressure wave) corrected quantity value m_HE_korr on the basis of the present pause value t_diff (HE, VE) 120 , The corrected quantity value m_HE_korr is then based on the characteristic curve 130 in a corrected Ansteuerdauerwert AD_HE_korr converted, which is finally used as the basis for the electrical control of the affected HE of the present injector 135 ,

The 2 shows an embodiment of the method and the device according to the invention with reference to a combined block / flow diagram, in which the injection data are determined both in a specified quantity path and in a time path. Also in this example, as in 1 , a main injection 'HE' and one of these temporally preceding pilot injection 'VE' assumed.

Again, based on a set quantity 200 First, an uncorrected main injection quantity m_HE_unkorr and a pre-injection quantity m_VE and a suitable electrical pause time t_diff between these two partial injections are calculated 205 , In the following step 213 there is a hydraulic correction of said electrical pause time t_diff, on the basis of supplied sensor data 214 concerning the current injection timing.

It should be noted that with an existing sensor in step 213 On the basis of the correspondingly available sensor data, a correction of the electrical drive signals is performed. Without such a sensor, this correction can also be controlled, on the basis of previously determined on a test bench or by numerical simulation data, which are preferably stored in an engine control unit. These two options can also be combined.

As sensor data 214 serve in the embodiment of the injection system or at a arranged there injector metrologically detected hydraulic or hydraulic effective temporal events of VE and HE (eg, an injection start, an end of injection, or the like).

The said hydraulic correction 213 In the present exemplary embodiment, correction values t_diff_korr, t_open_korr_VE and t_open_korr_HE are provided in the subsequent steps 210 and 220 be based on. Based on these correction values, a correction curve is determined for the respective injector as a function of the so-corrected pause times t_diff_korr, t_open_korr_VE and t_open_korr_HE, namely on the basis of a model calculation 210 , Furthermore, on the basis of injector-specific maps 230 from the correction curve thus determined 210 corresponding wavy correction curves 215 for the start of injection, the end of injection and / or the injection duration calculated for the HE, based on which the electrical control start and the electrical control AD_HE_unkorr an uncorrected quantity m_HE_unkorr be converted into a (pressure wave) corrected drive time AD_HE_korr and in a (pressure wave) corrected start of control . 220 , These two (pressure wave) corrected variables are finally used as the setpoint value in a control-based electrical activation of the HE of the present injector which is known per se. 235 ,

The 3 shows an exemplary integration of the method according to the invention in an existing DWK data processing structure and the corresponding execution of the method after integration. In step 300 First, a conversion of input signals 320 , eg the injection duration t_open, by means of mathematical functions, eg the function linear: signal_out = signal_in * a + offset, so as to be able to be used in the existing DWK ( 305 ) to be able to use hydraulic input signals (distance, injection duration). In this case, said characteristic sensor signals can enter from the CR system. On the basis of the thus converted input signals, in step 305 an already existing pressure wave compensation (DWK) performed in a conventional manner. On the basis of information that has been adequately provided, this function provides volume waves for the entire operating range of an (assumed) ideal injection system. The step 310 provides a completely corrected quantity wave as the output signal of the DWK and converts this quantity wave into a corresponding signal size on the basis of mathematical functions (see eg the function just mentioned "linear"). In step 315 there is a division 325 the calculated signal size into individual, volume-influencing effects 330 . 335 . 340 with respect to the injection timing of existing multiple injections.

The method described can be implemented in the form of a control program for an electronic control unit for controlling an internal combustion engine or in the form of one or more corresponding electronic control units (ECUs).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10002270 C1 [0002]
• DE 102010062609 A1 [0005]

Claims (9)

Method for controlling a fuel injection system of an internal combustion engine having a fuel high-pressure accumulator and at least one injector, wherein multiple injections are carried out with at least two temporally successive partial injections, characterized in that a compensation ( 305 ) of quantity errors caused by pressure waves in the multiple injections, taking into account at least one time variable characteristic for at least one partial injection ( 214 ) is carried out ( 235 ). A method according to claim 1, characterized in that the at least one characteristic time size of at least one sensor or by means of a pre-fed map is provided ( 214 ). A method according to claim 2, characterized in that the at least one characteristic time variable comprises a hydraulically effective injection duration and / or a hydraulically effective injection start and / or a hydraulically effective injection end and / or a hydraulically effective time delay of the injection start. Method according to one of the preceding claims, characterized in that the compensation ( 305 ) of quantity errors caused by pressure waves in the multiple injections, provides a correction value for the control of the at least one partial injection by means of a model ( 235 ). Method according to one of claims 2 to 4, characterized by the following steps: - calculating an uncorrected injection quantity of a first partial injection and at least one of the first partial injection temporally preceding second partial injection based on a quantity specification ( 200 ) for a given injector; - To calculate ( 205 ) an electrical pause time between the two partial injections; - Carry out ( 213 ) a hydraulic correction of the electrical break time ( 205 ) and control on the basis of sensor data ( 214 ) or model data to provide a hydraulic correction value for the pause time; - Determine ( 210 ) a correction model for the present injector as a function of the corrected pause time and the corrected drive; - To calculate ( 215 ) of correction values for the start of injection, the end of injection and / or the injection duration for the first partial injection on the basis of injector-specific characteristic diagrams ( 230 ) and based on the ( 210 ) Correction model (); - Convert ( 220 ) of an uncorrected quantity based on the calculated ( 215 ) Correction values for the beginning of injection, the end of injection and / or the duration of injection into a pressure-wave-corrected actuation start and into a pressure wave-corrected actuation duration; - Provide ( 235 ) of the corrected drive start and the corrected drive time as a setpoint for a subsequent control of the present injector. A method according to claim 5, characterized in that in the last method step, the corrected control duration value is used as the setpoint value for a control-based electrical control of the present injector ( 235 ). A computer program configured to perform each step of a method according to any one of claims 1 to 6. Machine-readable data carrier on which a computer program according to claim 7 is stored. Electronic control unit, which is set up, a fuel high-pressure accumulator and at least one injector having fuel injection system of an internal combustion engine, in which multiple injections are carried out with at least two temporally successive partial injections, by means of a method according to one of claims 1 to 6 in the multiple injections compensating for mass errors caused by pressure waves ( 305 ) to control.

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