DE10256240A1 - Method for controlling a fuel metering system of an internal combustion engine - Google Patents

Abstract

A method for controlling a fuel metering system of an internal combustion engine, in which a control period of at least one electrically operated injector determines the amount of fuel to be injected, is characterized in that a drift in the amount of fuel to be injected over the running time of the at least one injector is compensated for by lengthening the injection period and in addition in order to extend the injection period, the start of injection of the injection is postponed earlier.

Description

State of technology

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

A method for controlling a fuel metering system of an internal combustion engine is based, for example, on DE 199 45 618 A1 out. With this method, the minimum activation period during which fuel is being injected is determined in certain operating states. Starting from a start value, the activation duration is increased or decreased for this. The activation period at which a change in a signal characterizing the injection occurs is stored as the minimum activation period.

From the unpublished DE 102 15 610 results in a system and a method for correcting the injection behavior of injectors, in which, in order to increase the yield, an injector quantity comparison is carried out in several test points, preferably in four test points, namely in the pre-injection at idle mode, at the emission point and at full load.

This injector quantity comparison is required because such injectors due to their mechanical Manufacturing tolerances have different quantity maps. Under a quantity map is the relationship between the injection quantity and rail pressure and control time to understand. As a result, despite electrically defined control of each individual injector the combustion chamber fills with different amounts of fuel.

To make one possible low fuel consumption in compliance with strict emission standards to achieve the injectors in operation only have very small tolerances on the injection quantity. These required small tolerances can due to the mechanical manufacturing tolerances become. In order to achieve a defined injection quantity for the injectors ensure the injectors are characteristic after manufacture Working points or test points measured for their injection quantity and classified into classes. The respective class must be in Operation of the internal combustion engine known to the engine control unit be so that the Control to the special characteristics of the class, injector-specific customized can be. The class information is stored on the injector, for example by different coding, such as barcode resistors on the injector or by plain text on the injector.

In addition, it is possible that in the Electronic injectors are provided, in which, for example, the class information is stored. The control unit can over these values Read an interface from the injector and in subsequent operation use.

With the injectors affected here, Especially in the case of common rail injectors, there is now a drift in quantity over the service life to be observed individually with each injector pronounced and depends for example on the load profile or the injector type. This Quantity drift has an adverse effect on low fuel consumption, compliance with strict emissions standards as well as disadvantageous in relation on, for example, the noise level the internal combustion engine.

Through the measures described above Correcting the injection quantities of the injectors is already becoming a clear one Improvement of the noise level the internal combustion engine, the exhaust gas values as well as the fuel consumption achieved. Extensive series of tests have shown, however, that the here affected injectors, for example common rail injectors Injection behavior change over time and compliance with in the future required even stricter emission limits through such activities to compensate for the influence of volume drifts is not possible.

Object of the invention

The object of the invention is therefore a method for controlling a fuel metering system of an internal combustion engine of the type described at the outset in such a way that also changes related to the duration the injection behavior, e.g. Injection quantity drift taken into account and future ones tighter emission limits can be met.

Presentation of the invention

This task is accomplished through a process for controlling a fuel metering system of an internal combustion engine solved with the features of claim 1.

The basic idea of the invention is additionally to vary the duration of the injection also the start of injection to vary. Extensive tests by the applicant have shown that that not only an increasing decrease in the injection quantity at a given one Trigger time of the injectors occurs. Rather, it occurs over their Service life also postpones the start of injection later. It has been shown that the Reduction of the injection quantity and the shift in the start of injection are related to each other. Show this behavior especially common rail injectors.

The invention is based on this finding out and extended not only the injection duration, but also shifts the start of injection earlier.

The times are preferably at which the start of injection is postponed earlier, ie the start of injection correction, as a function of the values of the extension of the injection duration, ie as a function of the control correction.

This determination is made on the Basis of construction-specific data of the injectors.

In an advantageous embodiment it is provided that the Time by which the start of injection is postponed earlier, the start of injection correction, is chosen to be essentially half the size like the control duration correction, i.e. the time by which the injection duration extended becomes. This value carries the relationship the size of the flow restrictor to the size of the inlet throttle more common today Injectors for Internal combustion engine bill.

To the values of the extension the injection duration or the shift in the start of injection over the Determining the life of the injectors looks advantageous Design of the method before that the trigger duration correction and the start of spray correction determined in continuous runs of the injectors become.

Preferably, the drive duration architecture and the spray start correction is stored in at least one map. You are so late easily accessible during operation.

drawing

Other advantages and features of Invention are the subject of the following description and the graphic representation of some embodiments.

The drawing shows:

1 a schematic representation of part of a known from the prior art common rail system, in which the inventive method is used;

2 schematically the main injection quantity over the activation period of an injector and

3 the control voltage, the line pressure and the injection curve of an injector over time.

Description of the embodiments

In 1 The high-pressure part of a common rail accumulator injection system is shown, only the main components and those components which are essential for understanding the present invention being explained in more detail below.

The arrangement comprises a high pressure pump 10 which via a high pressure line 12 with the high pressure accumulator ("Rail") 14 communicates. The high pressure accumulator 14 is about further high pressure lines with injectors 18 connected. In the present illustration there is a high pressure line 16 and an injector 18 shown. The injector 18 is installed in an internal combustion engine of a motor vehicle. The system shown is from an engine control unit 20 controlled. By the engine control unit 20 in particular, the injector is controlled 18 ,

On the injector 18 is a facility 22 to store information that is specific to the injector 18 Respectively. The information in the facility 22 can be stored by the engine control unit 20 are taken into account, so that an individual control of each injector 18 can be done. The information is preferably correction values for the quantity map of the injector 18 , The facility 22 The information can be stored, for example, as a data store or as one or more electrical resistors, as a bar code, by means of alphanumeric encryption or the like, or by means of one on the injector 18 arranged integrated, semiconductor circuit can be realized. The engine control unit 20 can also have an integrated semiconductor circuit for evaluating the in the device 22 have stored information.

That of every injector 18 The metered injection quantity depends on the rail pressure in one in the engine control unit 20 stored map, the map is determined based on several test points (pre-injection, idling, emission point, full load), which correspond to different operating conditions of the internal combustion engine. At these checkpoints, a quantity comparison is made with known and from the DE 102 15 610 outlined manner. The injection quantity is determined by the injection duration of the injector 18 determined, that is, the time that elapses between the start of injection and the end of injection.

To measure the amount of fuel in the entire operating range of the internal combustion engine and the injector 18 to enable the adjustment values to be interpolated between the support points defined by the test points.

Over the life of the injectors 18 a quantity drift can now be observed in that over the life of the injectors 18 the injection quantity originally determined by determining the start of injection and the injection duration changed.

The injection quantity injected at a predetermined actuation duration changes. Like for example 2 , in which the main injection quantity is shown over the actuation period of an injector over its service life, the main injection quantity decreases with increasing life of the injector. compensation now takes place, for example, with a control duration of 0.5 ms in that the control duration t is extended by approximately Δt = 80 μs. This extension makes the same for an injector that has a running time of 100 or 450 operating hours Main injection volume achieved as with an injector that has 0 operating hours.

With the reduction in the main injection quantity, which is compensated for by an increase in the actuation duration, a shift in the start of injection at later times can also be observed with increasing duration. In 3 the control voltage, the line pressure and the injection curve are shown over time. The in 3 The curve shown above shows the opening and closing of the injector. The injector opens at about 0.1 ms and closes again at 0.6 ms. This results in an injection curve shown in the bottom curve, which in turn leads to a line pressure which is shown in the middle curve. As the life of the injector increases, the start of injection of the injectors shifts to later times. Compensation takes place in that the injection begins by the control unit 20 is moved to earlier times. As in 3 shown, the start of injection is shifted approximately 40 μs earlier (Δt = 40 μs). This value corresponds essentially to half the value of the extension of the injection period. The ratio of the prolongation of the injection duration (control duration correction) to the shifting of the start of injection earlier (injection start correction) is essentially determined by the design of the injector. In the 2 and 3 Curves shown were measured on known common rail injectors for diesel engines.

Through a systematic evaluation of endurance runs a correction map can be created with such measurements, with its help based on the determined actuation duration correction the spray start correction can be determined.

In principle, the correction map can also can be determined in that the aforementioned four checkpoints Idling, pre-injection, emission point and full load of the injector volume comparison the control duration correction and the start of injection correction are determined and due to interpolations and extrapolations the entire map is closed.

Claims (7)

Method for controlling a fuel metering system of an internal combustion engine, in which a control period of at least one electrically operated injector defines the amount of fuel to be injected, characterized in that a drift in the amount of fuel to be injected over the running time of the at least one injector is compensated for by extending the injection period and in addition to extending it the injection duration, the start of injection of the injection is postponed earlier. A method according to claim 1, characterized in that the Time by which the start of injection is postponed earlier (start of injection correction), in dependence from the time of extension the injection duration (control duration correction) is determined. A method according to claim 2, characterized in that the Spray start correction based on building-specific data from the at least one injector is determined. A method according to claim 2 or 3, characterized in that the Spray start correction is selected to be essentially half as large like the control duration correction. Method according to one of the preceding claims, characterized characterized that the Control correction and the spray start correction in continuous runs of Injectors can be determined. Method according to one of the preceding claims, characterized characterized that the Driving time correction and the start of injection correction in at least a map can be saved. Method according to claims 1 to 7, characterized in that as Injectors common rail injectors are used.