WO2013167242A1

WO2013167242A1 - Method for operating an internal combustion engine

Info

Publication number: WO2013167242A1
Application number: PCT/EP2013/001262
Authority: WO
Inventors: Simon Binder; Yuriy Bogachik; Thomas Liebscher; Rüdiger Pfaff
Original assignee: Daimler Ag
Priority date: 2012-05-05
Filing date: 2013-04-26
Publication date: 2013-11-14
Also published as: DE102012009008A1

Abstract

The invention relates to a method for operating an internal combustion engine (1), in particular of a motor vehicle, wherein said internal combustion engine (1) comprises a fuel injection system (4) having at least one injector (5) for each combustion chamber (3) of the internal combustion engine (1). Improved combustion properties can be attained during the service life of the internal combustion engine (1), if during a predetermined operational state of the internal combustion engine (1) for at least one combustion chamber (3), an actual conversion rate of the fuel injected into said combustion chamber (3) by the respective injector (5) is determined during a combustion process, if the actual conversion rate is compared to a desired conversion rate for the predetermined operational state of the internal combustion engine (1), and if, subject to a determined desired-actual deviation, at least one injection parameter of the fuel injection system (4) is adapted to reduce the desired-actual deviation.

Description

Method for operating an internal combustion engine

The present invention relates to a method for operating an internal combustion engine, in particular a motor vehicle. The invention also relates to an associated internal combustion engine.

Modern internal combustion engines have a fuel injection system with at least one injector per combustion chamber of the internal combustion engine. The respective injector is usually a needle valve, which is characterized by a needle-shaped valve member for controlling injection holes. By selecting the number of injection holes per injector as well as selecting the geometry of the injection holes, such as hole cross section and hole length, the fuel injection can be influenced. Small hole cross sections are advantageous, since this improves the atomization effect during the injection process and produces smaller, faster evaporating fuel droplets. However, the smaller the hole cross-sections, the greater the risk of coking the injection holes. Due to the coking of the injectors in the region of the injection holes, the flow-through cross section of the injection holes decreases, which influences the amount of injected fuel per injection process, namely reduced. As a result, the combustion process changes, which affects the operating state of the internal combustion engine. On the one hand, the internal combustion engine, in particular in the idling range, can run restlessly. On the other hand, the energy efficiency changes

Fuel consumption and pollutant emissions.

DE 10 2005 034 449 A1 discloses a method and a device for detecting coking at injection nozzles in combustion chambers of internal combustion engines. In this case, it is provided that, at a prescribable operating point of the injection of fuel into an unpolluted injection nozzle, at least one cylinder pressure gradient criterion or at least one thermodynamic criterion in an origin is measured at a predeterminable time (original time of origin) and in the same Operating point, the at least one measured criterion of the cylinder pressure curve or the thermodynamic profile of the same injector to a predetermined

Time is measured for diagnostic purposes (diagnosis time point), wherein the value measured at the time of diagnosis for the detection of coking with the in

Origin measured value.

A suitable cylinder pressure gradient criterion is, for example, a maximum

Cylinder pressure increase per cycle at the time of origin and at the time of diagnosis. Another cylinder pressure gradient criterion is, for example, an average pressure that can be calculated per working cycle from the cylinder pressure curve. A suitable thermodynamic criterion is, for example, a level of a plateau of an integral heating course per working cycle between the combustion of a pre-injection and main injection. Another thermodynamic criterion is, for example, an angular position of the 5% energy conversion point per working cycle or alternatively an angular position of a minimum of the heating profile per working cycle. The

Detection of coking should be carried out as part of an on-board diagnosis and generate a corresponding error signal in the case of a detected coking and possibly be signaled via a warning device. This makes it possible, for example, to allow the injectors to be cleaned in the event of coking in order to enable proper operation for the internal combustion engine.

The present invention is concerned with the problem of providing an improved embodiment for a method or for an internal combustion engine of the aforementioned type, which is characterized in particular by the fact that the effects of coking of the respective injector on the operating behavior of the internal combustion engine are reduced.

This problem is in the present invention in particular by the

Objects of the independent claims solved. Advantageous embodiments are the subject of the dependent claims.

The invention is based on the general idea, the presence of a

To recognize coking in order to adapt in case of coking the fuel injection system so that an influence of the coking on the combustion process in the respective combustion chamber is reduced or eliminated. In other words, the coking of

Injectors are monitored and the fuel injection system is adapted depending on the determined coking so that the adverse consequences of coking are eliminated or at least reduced. In particular, the invention proposes this in particular during a

predetermined operating state of the internal combustion engine for at least one

Combustion chamber to determine an actual conversion rate of injected with the respective injector in this combustion chamber fuel during a combustion process.

Subsequently, this actual conversion rate can be compared with a target conversion rate, which is predetermined for the predetermined operating state of the internal combustion engine. If a setpoint-actual deviation occurs, at least one injection parameter of the fuel injection system can now be adapted to reduce the actual-to-actual deviation as a function of this setpoint-actual deviation. This means that the adaptation of the

Fuel injection system with the objective that takes place in an earlier

Combustion process occurring target-actual deviation of the conversion rate is reduced at a later combustion process and at best eliminated, that is within tolerable limits. This process can be realized, for example, in the manner of a closed-loop control or in the manner of a closed loop.

The target conversion rate, which is used for the target / actual comparison, can be determined, for example, in the context of a reference measurement with new injectors.

In this case, the invention utilizes the knowledge that the conversion rate of the fuel converted in the combustion chamber during a combustion process at least in the

predetermined operating state, a significant correlation with the injected

Has fuel quantity or the mass flow curve of the injected Krafftstoffs. However, the injected fuel quantity is specified comparatively exactly for the predetermined operating state, namely by the relevant for this

Injection parameters, such. B. hole cross-section, number of holes, injection pressure and

Opening time during the injection process. By way of a desired-actual deviation of the conversion rate, it is thus possible to conclude comparatively accurately a deviation of the injected fuel quantity. The invention now also makes use of the consideration that by coking at the respective injector essentially only the effective hole cross section, that is to say the cross section present for the throughflow, can change, while the other injection parameters are essentially unaffected by coking. Consequently, a reduced amount of fuel suggests a coking of the injection holes.

By the solution according to the invention, it is possible in particular via a

extended period in the life of the engine almost constant Combustion characteristics, since the fuel injection system automatically adapts to the degree of coking of the injectors. This does not just apply to one

increasing coking. Rather, a decreasing coking can be adapted by the target-actual comparison of the conversion rate and adaptation of the respective injection parameter. A decreasing coking can occur, for example, when coking residues detach from the injection holes, for example due to thermal expansion effects, vibrations and the like. Since the coking of

Injection holes can be compensated due to the procedure according to the invention, even very small and smallest nozzle hole geometries can be used. As a result, for example, the raw emission of the internal combustion engine can be improved. Furthermore, an exhaust gas aftertreatment can thereby be improved. Also, it comes then to a reduced oil dilution by lower fuel accumulation on combustion chamber walls.

According to an advantageous embodiment, a full-load operation of the internal combustion engine can be used as the predetermined operating state of the internal combustion engine. This embodiment is based on the consideration that, especially in full load operation, there is a direct correlation between the conversion rate and the fuel quantity per combustion process. For example. are in full load disturbing influences, such. As a high exhaust gas recirculation rate and / or a stoichiometric air supply, reduced. Of course, an operating point in the partial load can be used as a predetermined operating condition.

According to another advantageous embodiment, the actual conversion rate can be determined during a predetermined crankshaft angle range. These

Embodiment is based on the consideration that it is not absolutely necessary to determine the conversion rate, the entire crankshaft angle range of the

To monitor the combustion process associated cycle of the cylinder containing the combustion chamber. As a result, the determination of the actual conversion rate can be carried out faster, which improves the evaluation and the adaptation of the fuel injection system.

According to another advantageous embodiment, the actual conversion rate can be determined on the basis of a pressure curve which is present in the respective combustion chamber during the course of the combustion process

Combustion process is measured. It is clear that for this purpose the internal combustion engine can be equipped with a corresponding, suitable pressure-measuring sensor, with which it is possible, in particular, to measure the pressure within the respective combustion chamber. The pressure curve in the combustion chamber correlates with the chemical energy released during the combustion process, ie the conversion or the conversion rate of the injected fuel. This in turn correlates with the injected one

Fuel quantity. Thus, the injected fuel quantity can be determined via the time-resolved pressure curve.

An embodiment in which an injection pressure provided to the respective injector is adapted as an injection parameter is particularly expedient. These

Embodiment is based on the finding that the injected amount of fuel substantially the product of the available, permeable

Cross section of the injection holes, the injection period and the available injection pressure. At a reduced actual sales rate, the one reduced

Fuel quantity corresponds to reduce the effect of coking, thus increasing the injection pressure. In this way, the reduced through the coking flow-through cross section of the injection holes can be compensated. Suitably, the injection duration remains constant. To compensate for the coking is

According to the invention thus only a single parameter, namely the injection pressure varies, so that the adaptation of the fuel injection system is particularly easy to implement.

In a fuel injection system with at least one common

Pressure supply line, so-called "common rail" operates, to which a plurality of injectors are connected, the injection pressure can be varied by varying the fuel pressure in this pressure supply line, in other words, at a

Common rail system, the rail pressure is varied to achieve the desired adaptation of the fuel injection system. The rail pressure, that is to say the fuel pressure in the respective common pressure supply line, can, for example, be preceded by a corresponding activation of one of the respective pressure supply lines

High-pressure fuel pump can be realized.

In contrast, in a fuel injection system that with a

Fuel pump per injector works, so-called. "Pump-nozzle system", the injection pressure can be varied by varying a pump pressure generated by the respective fuel pump.

According to another advantageous embodiment, a splash duration map, which assigns injection durations to all operating states of the internal combustion engine, can be adapted depending on the changed injection pressure. Such a splash duration map assigns all the operating conditions of the internal combustion engine the respectively required

Amount of fuel, by at constant injection pressure to achieve the assigns required injection quantity required injection time. By the proposed here adaptation of the injection pressure depending on the coking or

Depending on the target / actual comparison of the turnover rate, a substantial change is made

Parameters for the calculation or design of the splash duration map, namely the injection pressure.

By a suitable adaptation of the splash duration map to the changed

Injection pressure, for example, by taking into account a dependent of the changed injection pressure correction factor, it is possible for all operating conditions of the

Internal combustion engine to adapt the injection periods, although the target-actual deviation of the turnover rate preferably only for a single predetermined

Operating state of the internal combustion engine has been determined. This results in a huge advantage for the adaptation of the control of the internal combustion engine.

In another advantageous embodiment, a plurality of actual conversion rates can be detected during the predetermined operating state, wherein for determining the target-actual deviation then a mean actual conversion rate is compared with the predetermined target conversion rate. This can either for all injectors

average actual turnover rate can be determined or for each individual injector an average actual turnover rate can be determined. The determined actual turnover rates then have a higher reliability.

According to another embodiment, the adaptation of the at least one

Injection parameters are performed globally for all injectors of the internal combustion engine. In this embodiment, coking is considered to occur substantially equally with all injectors. The realization of such an embodiment is comparatively simple. In this case, the actual conversion rate can also be averaged for all injectors.

In an alternative embodiment, the adaptation of the at least one

Injection parameters locally for the respective injector, so be performed individually. In this case, individual coking per injector is taken into account. In this case, the actual sales rate is also recorded individually for the respective injector.

An internal combustion engine according to the invention, which is used, for example, in a motor vehicle, comprises a fuel injection system which has at least one injector for each combustion chamber of the internal combustion engine. Furthermore, the Internal combustion engine equipped with a control device that is configured or programmed so that they can perform the method described above for operating the internal combustion engine. For this purpose, the control device can be suitably coupled to the injectors or with suitable pressure sensors or with at least one fuel pump.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawing and from the associated description of the figures with reference to the drawing.

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

Preferred embodiments of the invention are illustrated in the drawings and will be explained in more detail in the following description.

The sole FIGURE 1 shows a greatly simplified schematic diagram of an internal combustion engine.

According to FIG. 1, an internal combustion engine 1, which, for example, can be arranged in a motor vehicle, comprises a plurality of cylinders 2, each of which encloses a combustion chamber 3. In the respective cylinder 2, a piston, not recognizable here, is arranged such that it can be adjusted in terms of stroke. The internal combustion engine 1 is equipped with a fuel injection system 4, which is configured in the illustrated preferred example as a common rail system. The fuel injection system 4 has, for each combustion chamber 3, an injector 5, which projects into the respective associated combustion chamber 3 with an injector end 6 which has a plurality of injection holes (not shown here). All injectors 5 are connected to a common pressure supply line 7, so-called "rail" or "common rail". A high-pressure fuel pump 8 is the pressure side connected to the pressure supply line 7 and generates a fuel pressure in the pressure supply line 7, which may correspond to the injection pressure of the injectors 5. In individual embodiments, the individual injectors 5 can also contain so-called pressure translators which convert the fuel pressure provided via the pressure supply line 7 into a significantly higher input. can translate injection pressure. Since the pressure booster act only a relative pressure gain, a variation of the fuel pressure in the pressure supply line 7 to a proportional variation of the injection pressure at the respective injector 5. For simplicity, injectors 5 are considered without such pressure booster, so that the fuel pressure in the pressure supply line 7 the injection pressure of the injector 5 corresponds.

Fuel not required by the injectors 5 is supplied via a throttle 9 and a return line 10 to a fuel tank 11, from which, in the example, a feed line 12 leads to the high-pressure pump 8. In other configurations, additional pumps, valve means, and the like may be present.

The internal combustion engine 1 is equipped with a plurality of cylinder pressure sensors 13, wherein each cylinder 2, such a cylinder pressure sensor 13 is provided, with the aid of which the pressure in the combustion chamber 3 of the respective cylinder 2 can be measured. In the example, a line pressure sensor 14 is also provided, by means of which the pressure in the pressure supply line 7 can be measured.

The internal combustion engine 1 is also equipped with a control device 15. This is electrically connected via control lines 16 to the injectors 5, via a control line 17 to the high-pressure pump 8, via signal lines 18 to the cylinder pressure sensors 13 and via a signal line 19 to the line pressure sensor 14. The control device 15 can thus control the injectors 5 and the high-pressure pump 8. Furthermore, it receives the pressure measurement signals of the cylinder pressure sensors 13 and of the line pressure sensor 14. Furthermore, the controller 15 knows the current operating state of the internal combustion engine 1. For example, the control device 15 can be coupled to a corresponding engine control unit. Likewise, it is possible to integrate the control device 15 at least partially in terms of hardware in the engine control unit and / or at least partially implement software in the engine control unit.

The internal combustion engine 1 presented here can be operated with the aid of the control device 15 as follows:

During a predetermined operating state of the internal combustion engine 1, preferably at full load operation of the internal combustion engine 1, with the aid of the cylinder pressure sensors 13 the temporal pressure curve within the combustion chambers 3 are determined during the respective combustion process. From the pressure curve in the respective combustion chamber 3 during a predetermined crankshaft angle range, an actual conversion rate of the fuel injected with the respective injector 5 into the respective combustion chamber 3 during the combustion process can be determined. The actual conversion rate determined in this way can now be compared with a desired conversion rate, which is predetermined or known for the predetermined operating state of the internal combustion engine 1. This desired conversion rate can be determined, for example, during the predetermined operating state in the context of a reference measurement, which is expediently carried out with new injectors 5.

By a target-actual comparison of the conversion rate, a desired-actual deviation can now be determined. Depending on this target / actual deviation, at least one injection parameter of the fuel injection system 4 can now be adapted such that a reduction of the nominal / actual deviation occurs. For example. For example, the controller 15 may adapt the injection pressure available to the injectors 5 for performing the fuel injection. In detail, the control device 15 can for this purpose control the high-pressure pump 8 to generate an increased fuel pressure. In this way, the desired-actual deviation of the conversion rate can be minimized, so that in the best case over the entire life of the internal combustion engine 1 almost constant combustion properties can be ensured.

The control device 15 expediently has access to a spray duration characteristic map 20 which assigns injection periods to all operating states of the internal combustion engine 1. If the control device 15 now due to a target-actual comparison of the conversion rate a

Adaption of the injection pressure performs, the controller 15 may additionally perform a corresponding adaptation of the injection duration map 20 to the changed injection pressure. As a result, the adapted injection duration characteristic map 20 can be used as before in all operating states of the internal combustion engine 1, although the target actual deviation of the conversion rate has been determined only for a single, predetermined operating state, namely preferably full load operation.

Claims

claims

1. A method for operating an internal combustion engine (1), in particular a

Motor vehicle,

- wherein the internal combustion engine (1) with a fuel injection system (4)

has at least one injector (5) per combustion chamber (3) of the internal combustion engine (1),

wherein during a predetermined operating condition the

Internal combustion engine (1) for at least one combustion chamber (3) an actual conversion rate of the injected with the respective injector (5) in this combustion chamber (3) fuel is determined during a combustion process,

in which the actual conversion rate is compared with a target conversion rate which is predetermined for the predetermined operating state of the internal combustion engine (1), in which at least one injection parameter of the fuel injection system (4) for reducing the desired value depends on a determined desired-actual deviation - Actual deviation is adapted and

as a predetermined operating state of the internal combustion engine (1)

Full load operation of the internal combustion engine (1) is used.

2. The method according to claim 1,

characterized in that

the actual turnover rate is determined during a predetermined crankshaft angle range.

3. The method according to claim 1 or 2,

characterized in that the actual rate is determined by reference to a pressure curve which is measured in the respective combustion chamber (3) during the combustion process.

4. The method according to any one of claims 1 to 3,

characterized in that

as an injection parameter, an injection pressure provided to the respective injector (5) is adapted.

5. The method according to claim 4,

characterized,

that in a fuel injection system (4) with at least one

common to the pressure supply line (7) to which a plurality of injectors (5) are connected, the injection pressure by varying the fuel pressure in the pressure supply line (7) is varied, or that in a fuel injection system (4) with a fuel pump per injector (5) operates, the injection pressure is varied by varying a pump pressure generated by the respective fuel pump.

6. The method according to claim 4 or 5,

characterized in that

a Spritzdauerkennfeld (20), which assigns all operating conditions of the internal combustion engine (1) injection periods, depending on the changed injection pressure is adapted.

7. The method according to any one of claims 1 to 6,

characterized in that

During the predetermined operating state, a plurality of actual conversion rates are detected, wherein an average actual conversion rate is compared with the target conversion rate for determining the target / actual deviation.

8. The method according to any one of claims 1 to 7,

characterized,

that the adaptation of the at least one injection parameter is carried out globally for all injectors (5) of the internal combustion engine (1), or the adaptation of the at least one injection parameter is performed locally for the respective injector (5) individually.

9. internal combustion engine, in particular a motor vehicle,

- With a fuel injection system (4), for each combustion chamber (3) of the

Internal combustion engine (1) has at least one injector (5),

- With a control device (15) for carrying out the method according to one of claims 1 to 9.