EP2142785B1 - Method and device for controlling injection in an internal combustion engine - Google Patents

Description

State of the art

Due to increasing requirements of emission legislation, for example in Europe and the US, it is becoming increasingly important in common rail fuel injection systems to achieve a high accuracy of the injected fuel quantity. On the other hand, steadily growing demands are placed on the maximum rail pressure of future CR systems.

In order to meet the desire for high rail pressures, the leakage losses must be reduced. This can be achieved, inter alia, by shortening the funding phase. The shortened delivery phases lead in particular at high speeds to high flow rates and thus to steep pressure gradients in the rail, which complicates the exact metering of the desired injection quantity.

In order to realize the desired injection quantity for each injector as accurately as possible, the pressure in the rail is measured by a pressure sensor shortly before the actuation of the injectors and with this pressure value, the control duration from a map - the so-called flow-control duration map - determined.

Through various low-pass filters in the pressure sensor and in the control unit required for noise reduction, the real rail pressure signal in the control unit is applied with a time delay. In addition, the reading of the print must already be in the dynamic Interrupt before the actual energization of the injector done in order to hold sufficient time in the control unit for calculating the required control period. In total, this results in a time delay Δt between the measurement of the pressure value and the availability of this pressure value in the control unit, where it can be used to determine the activation duration of the injector.

In some operating points at high speed and thus steep rail pressure gradients resulting from the above delay Δt pressure differences of up to 80bar between the measured rail pressure used in the control unit and the actual rail pressure applied at the time of injection. Since the injection quantity depends inter alia on the pressure applied to the rail, this pressure deviation leads to significant injection quantity errors.

From the DE 198 57 971 A1 a method is known in which is determined by a linear interpolation of the pressure value at the time of injection start. However, this method is only conditionally usable if the pressure gradients are very steep and, moreover, are subject to considerable fluctuations.

Disclosure of the invention

The invention is based on the object to provide a method which allows a more accurate metering of the injection quantity and which can be realized as inexpensively as possible.

This object is achieved in a method for operating a fuel injection system for internal combustion engines with a high-pressure pump, with a common rail, with a pressure sensor, with at least one injection valve, and with a control device for controlling the injection valves, wherein a first rail pressure p _{Rail- 1 of} the common rail for each injection at a first time is detected and evaluated, wherein the first time is a time interval .DELTA.T before the injection of the injector, achieved in that at a second time, a second rail pressure p _{Rail-2 of} the common Rails for each injection is detected that the second Time later than the first time is and that of the first time for injection j detected first rail pressure p _Rail-1 (j) in response to the second time t ₂ (jr) a time earlier injection (j - r) detected second rail pressure p _Rail-2 (jr) is corrected.

The method according to the invention makes use of the fact that the error resulting from the time delay between the detection of the first rail pressure p _Rail-1 at the first time t ₁ and the second rail pressure p _Rail-2 at the first time t _{2 has} a certain regularity having. This makes it possible to use this systematic error, which is known relatively accurately from past injections jr, to correct the first rail pressure p _Rail-1 in the next injection j. As a result, the error with respect to the rail pressure can be significantly reduced and, as a result, the injection quantity can be dosed more accurately. Additional hardware is not required.

Another important advantage of the method according to the invention is that no additional hardware is needed, since only an additional pressure measurement has to be performed by the already existing pressure sensor. The method according to the invention can thus also be realized by means of a software update even for fuel injection systems already in series.

In a further advantageous embodiment of the method according to the invention, it is provided that the correction of the first rail pressure at the first time t ₁ , the injection j, and the first rail pressure p _Rail-1 (j - r) of a time earlier injection j - r is used. Thereby, the correction of the rail pressure can be further improved and the accuracy of the injected fuel amount can be further improved.

A particularly advantageous embodiment of the method according to the invention provides that the correction of the first rail pressure p _rail-1 according to the equation shown in claim 3.

• Unter einem Arbeitsspiel wird bei einer nach dem Viertaktverfahren arbeitenden Brennkraftmaschine zwei Umdrehungen der Kurbelwelle, entsprechend 720° Kurbelwellenwinkel verstanden. Innerhalb eines solchen Arbeitsspiels durchläuft jeder der m Zylinder der Brennkraftmaschine alle vier Takte (Ansaugen, Verdichten, Arbeiten und Ausschieben) eines 4-Takt-Motors. Danach wiederholt sich der Ablauf in dem nächsten Arbeitsspiel, so dass die Vorgänge innerhalb einer Brennkraftmaschine periodisch bezüglich eines Arbeitsspiels sind. Der Laufindex j wird benutzt, um die m Zylinder der Brennkraftmaschine zu nummerieren.

To explain this equation, the following terms are introduced:

• Under a working cycle is understood in an operating according to the four-stroke cycle engine two revolutions of the crankshaft, corresponding to 720 ° crankshaft angle. Within such a cycle, each of the m cylinder of the engine undergoes all four strokes (suction, compression, working and pushing out) of a 4-stroke engine. Thereafter, the process repeats in the next cycle so that the processes within an internal combustion engine are periodic with respect to a work cycle. The running index j is used to number the m cylinders of the internal combustion engine.

For the purposes of the invention, the injection j means that fuel is injected into the cylinder with the number j. Within a working cycle, fuel is injected once into each of the m cylinders of the internal combustion engine, with no distinction being made between main injection, pilot injection and post-injection in the context of the invention, since the method according to the invention is applied to a main injection and / or a pre-injection and / or a post-injection can be.

Since the high-pressure fuel pump is rigidly coupled to the crankshaft of the internal combustion engine, the delivery strokes of the high-pressure fuel pump also follow a certain periodicity, the periodicity of the delivery strokes preferably being usually whole multiples of the working cycles. The number of delivery strokes within a working cycle depends on the number of pump elements of the high-pressure fuel pump and the transmission ratio between the high-pressure fuel pump and the crankshaft of the internal combustion engine. As a rule, the number of delivery strokes within a work cycle is an integer. For example, in the case of a 4-cylinder internal combustion engine, two delivery strokes may be performed by the high-pressure fuel pump within one operating cycle.

If, for example, four injections and two delivery strokes of the high-pressure fuel pump take place in a four-cylinder internal combustion engine within a working cycle, a delivery stroke is eliminated for every second injection. This also means that two injections j-2 have prevailed before the current injection j very similar pressure conditions in the rail. This effect makes use of the method according to the invention in order to correct the current injection pressure p _{Rail-1 of} the next injection j. By the method according to the invention, it is possible to significantly reduce the injection quantity error caused by incorrect pressure values.

In the example presented, the offset between the current injection j and the comparable earlier injection is equal to 2. This offset is denoted by the letter r below.

In connection with the equation according to claim 3, therefore, r = 2 applies to the example of a 4-cylinder internal combustion engine described above.

It should be noted that only in the case of a series cylinder system with injection-synchronous promotion and sufficient Gleichfördereigenschaften the pump can be used on the cylinder in the firing order ahead. In the case of non-injection-synchronous gear ratios and / or the use of V-systems, the rail pressure curve deviates in the environment of the injection between the individual cylinders. It must therefore be system dependent. in the firing order by one or more cylinders, corresponding to the offset r, are returned to the past in order to determine the first rail pressure p _Rail-1 (jr) and the second rail pressure p _Rail-2 (jr) known from the injection jr in the cylinder jr ( jr) for correcting the currently available first rail pressure p _Rail-1 (j) to use. The following table shows the offset r for the common engine concepts and transmission ratios between the engine and the high-pressure fuel pump. Table 1: Warpage r as a function of the delivery strokes per working cycle for different engine types. engine Conveying strokes per work cycle Offset r comment Row, m = 4 4 1 Row, m = 5 5 1 Row, m = 6 6 1 V, m = 6 6 2 Regular ignition changes between the cylinder banks leads to the same printed images in injections on a bench. V, m = 8 8th 8th Irregular ignition changes only lead to a repetition of the printed image after a complete working cycle Row, M = 4 2 2

In a further advantageous embodiment of the invention, it is provided that for correcting the first rail pressure p _Rail-1 (j) of the injection j, the second rail pressure p _Rail-2 and / or the measured first rail pressure p _{Rail-1 of} the cylinder j - r is used , wherein in the cylinders j and j - r similar pressure conditions prevail immediately before and / or during the injection.

The object of the invention is also achieved by a control unit which operates according to one of the methods of the invention.

Further advantages and advantageous embodiments of the invention are the following drawings, the description and the claims removable. All in the drawing, the description and in the claims mentioned features may be essential to the invention both individually and in any combination.

Brief description of the drawings

Figur 1

eine schematische Darstellung eines Common-Rail-Kraftstoff-Einspritzsystems und

Figur 2

den Druckverlauf innerhalb eines Arbeitsspiels bei einer Vierzylinder-Brennkraftmaschine mit zwei Förderhüben je Arbeitsspiel.

Show it:

FIG. 1

a schematic representation of a common rail fuel injection system and

FIG. 2

the pressure curve within a working cycle in a four-cylinder internal combustion engine with two delivery strokes per working cycle.

Embodiments of the invention

In Fig. 1 a fuel injection system for internal combustion engines is schematically illustrated, by means of which the inventive method will be explained below.

With 100 injectors are designated, via which the fuel is metered to the individual combustion chambers of the internal combustion engine, not shown. Each injector 100 is associated with a cylinder of the internal combustion engine, not shown. In the embodiment according to Fig. 1 three injectors 100-1 to 100-4 of a 4-cylinder internal combustion engine are shown. In the case of another number of cylinders m of the internal combustion engine, the number of injectors 100-1 to 100-m changes accordingly.

The injectors are fueled by a pressure accumulator, hereinafter referred to as "common rail" 200. The common rail 200 is connected via a high pressure line 210 with a high pressure pump 220 in connection. The high-pressure pump 220, in turn, is connected via a low-pressure line 240 to a low-pressure pump 250, which is usually designed as an electric fuel pump. The low pressure pump 250 is preferably disposed in a fuel tank 255.

At the pressure accumulator 200, a pressure sensor 205 is arranged. Between the low-pressure pump 250 and the high-pressure pump 220, a quantity control valve 230 is arranged. Alternatively, the quantity control valve 230 may be disposed between the high-pressure pump 220 and the common rail 200 (not shown). The quantity control valve 230 and the injectors 100 are energized by an output stage 160. The output stage 160 is preferably integrated in a control unit 260 which processes the output signals of the pressure sensor 205 and various other sensors 270.

The fuel injection system now operates as follows: The low pressure pump 250 delivers the fuel, which is in the tank 255, via the low pressure line 240 to the high pressure pump 220. This compresses the fuel and delivers it via the high pressure line 210 into the pressure accumulator. By driving the injector 100-j, the start and the end of the injection j of fuel into the j-th cylinder can be controlled. This control takes place as a function of the operating characteristics of the internal combustion engine recorded with the sensors 270.

By means of the pressure sensor 205, the fuel pressure p _rail (t) prevailing in the pressure accumulator 200 is detected and preferably evaluated in the control unit 260.

The quantity control valve 230 is controlled as a function of the measured pressure value p _{rail in} such a way that the desired pressure value p _Soll in the common rail 200 is established. By means of the quantity control valve 230, the amount of fuel delivered by the high-pressure pump 220 can be controlled and thus the pressure build-up in the pressure accumulator 200 can be controlled. For this purpose, it is necessary that the quantity control valve 230 is activated at a specific first time and the activation is withdrawn at a second time. In order to achieve accurate pressure control, it is necessary that the mass control valve 230 opens and / or closes at the exact pre-calculated time. It is advantageous if the delay time between the activation of the quantity control valve 230 and the actual reaction, ie the opening and / or closing of the quantity control valve 230, is as small as possible.

In demand control, the high pressure pump 220 delivers the fuel mass needed to maintain or a desired change in pressure P _Rail in the pressure accumulator 200 is necessary.

In FIG. 2 is the course of the rail pressure p _Rail over more than one cycle, corresponding to a crankshaft angle of 720 °, shown in diagram form. The rail pressure p _Rail (t) represented by a line 280 follows a periodic pattern. Within a working cycle, corresponding to a crankshaft angle of 0 ° to 720 °, two delivery strokes take place. These delivery strokes can be recognized at the maxima of the rail pressure p _Rail (t) at 180 ° and 540 ° crankshaft angle.

The two delivery strokes are immediately before the injections in the cylinders 2 and 4 of the internal combustion engine. The injections j of the total four cylinders of the internal combustion engine are identified by numbered markers j = 1, j = 2, j = 3 and j = 4. During the injection of the cylinders 1 and 3, corresponding to the markers j = 1 and j = 3, there is no promotion of the high-pressure fuel pump.

Since the fuel quantity in the common rail 200 is reduced by the injection of fuel into the combustion chamber, the pressure p _rail in the common rail 200 decreases during the injections 1 and 3. This too can be clearly seen from the first line 280.

Since, as already mentioned, from the detection of the rail pressure p _Rail to the injection a certain time delay is unavoidable, the control unit, which calculates, for example, the injection period for the injection j = 1 of fuel in the first cylinder at a crankshaft angle of 0 °, to a fall at the time t ₁ (j = 1) measured first rail pressure p _Rail-1 (j = 1). Since between the time t ₁ (j = 1) and the first injection j = 1 at a crankshaft angle of 0 ° no promotion of fuel through the high-pressure fuel pump, the rail pressure p _rail remains almost constant within this time interval .DELTA.T.

The situation is different with the injection j = 2 into the second cylinder, represented by the marker j = 2. Again, the time interval ΔT is entered here again. In this injection changes due to the promotion by the high-pressure fuel pump the pressure p _Rail in the time interval .DELTA.T, which begins at the time points (j = 2) and ends with the injection at a crankshaft angle of 180 °, considerably. Now, as is conventional with conventional methods of controlling the injection quantity of an internal combustion engine, only the first rail pressure p _Rail-1 (j = 2) at the time point (j = 2) for the second injection j = 2 is used to determine the injection duration , the actually injected fuel quantity will be greater than desired, since at the beginning of the second injection j = 2, the actual prevailing pressure p _Rail in the common rail 200 is significantly higher than the pressure p _Rail-1 on which the determination of the activation duration is based. In the in FIG. 2 shown diagram, the pressure difference in the second injection j = 2 between the second rail pressure P _Rail-2 and the first rail pressure P _{Rail-1 is} about 80 bar!

According to the invention, it is now provided to detect the rail pressure before each injection j at a second time t ₂ (j). This second time t ₂ (j) is immediately before or simultaneously with the injection. The pressure difference between the second rail pressure p _Rail-2 and the first rail pressure p _Rail-1 is in the present case about 80 bar. This systematic "mistake" is repeated, as is the case FIG. 2 it can be seen, at the fourth injection j = 4, which by the marker j =. 4 and takes place at a crankshaft angle of 540 °, in a nearly identical manner.

This periodicity makes the inventive method is utilized by the front of the fourth injection j = 4 at time t ₁ (j = 4) measured first rail pressure p _{rail 1} (j = 4) by the second injection j = 2 determined pressure difference (p _Rail-2 (j = 2) -p _Rail-1 (j) = 2)) is corrected. This makes it possible to significantly reduce the error in the injection quantity due to a faulty pressure value.

Claims (8)

1. Method for operating a fuel injection system for internal combustion engines having a high-pressure pump (220), having a common rail (200), having a pressure sensor (205), having at least one injection valve (100-j, where j = 1 to m) and having a control unit (160) for actuating the injection valves (100), wherein a first rail pressure (p_Rail-1 (j)) of the common rail (200) is measured and evaluated for an injection (j) at a first time t₁ (j), wherein the first time (t₁ (j) is before the injection (j) of the injector (100-j) by a time interval (ΔT), characterized in that at a second time (t₂(j)) a second rail pressure (p_Rail-2 (t₂(j)) of the common rail (200) is measured for each injection (j), in that the second time (t₂(j) is later than the first time (t₁(j)), and in that the rail pressure (p_Rail-1(j)) which is measured at the first time (t₁ (j)) for the injection (j) is corrected as a function of the second rail pressure (p_Rail-2 (t₂ (j-r) ) which is measured at the second time (t₂(j-r)) of a chronologically earlier injection (j-r).
2. Method according to Claim 1, characterized in that the first rail pressure (p_Rail-1 (t₁(j-r)) of a chronologically earlier injection (j-r) is also used to correct the first rail pressure (p_Rail-1 (t₁(j)).
3. Method according to Claim 1 or 2, characterized in that the correction of the first rail pressure (p_Rail-1 (t₁(j)) is carried out according to the following equation: $${\mathrm{p}}_{\mathrm{Rail}-\mathrm{1},\mathrm{corr}}\left({\mathrm{t}}_{\mathrm{1}}\left(\mathrm{j}\right)\right)={\mathrm{p}}_{\mathrm{Rail}-\mathrm{1}}\left({\mathrm{t}}_{\mathrm{1}}\left(\mathrm{j}\right)\right)+\left[{\mathrm{p}}_{\mathrm{Rail}-2}({\mathrm{t}}_2\left(\mathrm{j}-\mathrm{r}\right)-{\mathrm{p}}_{\mathrm{Rail}-\mathrm{1}}({\mathrm{t}}_{\mathrm{1}}\left(\mathrm{j}-\mathrm{r}\right)\right]$$

   

   where: P_Rail-1, corr (t₁ (j)): corrected first rail pressure of the injection j p_Rail-1 (t₁ (j)): measured first rail pressure of the injection j p_Rail-2 (t₂ (j-r): measured second rail pressure of an injection j-r which occurs chronologically before the injection j p_Rail-1 (t₁ (j-r): measured first rail pressure of an injection j-r which occurs chronologically before the injection j j: running index (j = 1 to m, wherein m corresponds to the number of cylinders of the internal combustion engine) r: r) ≤ j, offset
4. Method according to one of the preceding claims, characterized in that the time interval (ΔT) is longer than or equal to a delay between measurement of a signal and determination of an injection duration and a start of injection.
5. Method according to one of the preceding claims, characterized in that the time interval (ΔT) is longer than or equal to a duration of an interrupt and a start of injection.
6. Method according to one of the preceding claims, characterized in that the second rail pressure p_Rail-2 (t₂, j-r) and/or the measured first rail pressure p_Rail-1 (t₁(j-r)) of a cylinder (j-r) is used to correct the first rail pressure p_Rail-1 (t₁(j)) of the injection j, and in that similar pressure conditions are present at the cylinders j-r and j directly before and/or during the injection.
7. Computer program, characterized in that it executes all the steps of a method according to one or more of Claims 1 to 6 when it is run.
8. Control unit for an internal combustion engine, characterized in that it executes all the steps of a method according to one or more of Claims 1 to 6 when it is in operation.

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