EP1884646A2 - Method for controlling a combustion machine - Google Patents

Abstract

The method involves computing a fuel mass from a measured fuel-pressure curve using a common-rail system, with which the mass is set as representation for controlling injection. A pressure curve (PE) of a single memory (7) is measured and a modeled pressure curve is reproduced to the curve by a hydraulic model, where the mass is computed from a hydraulic model. Deviations from the curve of the memory are computed for the modeled pressure curve and model parameters are adjusted until the deviations are smaller than a threshold value.

Description

The invention relates to a method for controlling an internal combustion engine with common rail system according to the preamble of claim one.

In an internal combustion engine, the start of injection, the injected fuel mass and the end of the injection decisively determine the quality of the combustion and the composition of the exhaust gas. To comply with the legal limits, the start of injection and the end of injection are usually controlled by an electronic control unit. There is a time offset between the start of energization of the injector, the needle stroke of the injector and the actual injection start, so that the actual injection start differs from the desired injection start. This causes unequal cylinder-specific operating values and exhaust gas values of the internal combustion engine for one and the same operating point. For the injection end this applies accordingly. Another uncertainty is that in practice the fuel mass is not measured directly but is calculated from other measured quantities.

From the DE 197 26 756 A1 a method for controlling an internal combustion engine with a common rail system is known in which the rail pressure as a direct measurement detected and the fuel mass is calculated via a mathematical function, such as a linear or root function, or via a map. According to the information in this reference, the method should be real-time capable by directly determining the fuel mass from the current rail pressure. However, due to the system, for example, the injection frequency and the delivery frequency of the high-pressure pump are superimposed as disturbance variables, so that the fuel mass calculated in real time is faulty or the rail pressure must first be filtered, as described in US Pat DE 31 18 425 A1 is shown.

That in the DE 197 26 756 A1 The method illustrated is intended for a conventional common rail system. The method is not directly applicable to a common rail system with individual memories. The common rail system with individual memories differs from a conventional common rail system in that the fuel to be injected is removed from the individual memory. The supply line from the rail to the individual memory is designed in practice so that a feedback of interference frequencies is damped in the rail. During the injection break, just enough fuel flows out of the rail that the individual accumulator is refilled at the beginning of the injection. The hydraulic resistance of the individual memory and the supply line are matched, ie the connection line from the rail to the individual memory has the highest possible hydraulic resistance. In a conventional common rail system without single memory, the hydraulic resistance between the rail and the injector should be as low as possible to achieve an unimpeded injection.

From the DE 195 16 923 A1 Also, a method for controlling an internal combustion engine is known, in which the pressure level in a line connecting the injection pump and the injection nozzle, is measured. The fuel mass is calculated by normalizing the pressure curve, forming the area integral and evaluating it by means of a proportionality constant. The method illustrated therein is not applicable in a common rail system with individual memories due to the structural differences. By way of example, an injection nozzle controlled by an injection pump is a passive element, while the injector can be actively activated in the case of a common rail system.

The invention is based on the object of designing a control system for a common rail system with individual memories in which the fuel mass is taken into account.

The object is solved by the features of the first claim. The embodiments are shown in the subclaims.

According to the fuel mass is calculated by the pressure curve of a single memory is measured, a modeled pressure curve over a hydraulic model is modeled on the measured pressure curve and then from the hydraulic model, the fuel mass is calculated.

To achieve the most accurate fuel calculation is provided that a deviation from the measured Pressure curve of the individual memory is calculated to the modeled pressure curve and the model parameters are adjusted until the deviation is smaller than a limit. In this case, the deviation is determined from the variables characterizing the injection. These are the start of injection, the end of injection, a pressure difference from start of injection pressure level to the end of injection pressure level and a spraying angle region alternatively an injection duration.

Since the hydraulic model represents a redundant system for setpoint specification of an injection, this can be used in the event of an error. The calculation uses the unfiltered single-store pressure, which makes the system robust. Of course, this also allows a more accurate injector evaluation.

In the drawings, a preferred embodiment is shown.

Figur 1

ein Systemschaubild;

Figur 2

ein Zeitdiagramm einer Einspritzung;

Figur 3

das Modell.

Show it:

FIG. 1

a system diagram;

FIG. 2

a timing diagram of an injection;

FIG. 3

the model.

1 shows a system diagram of an electronically controlled internal combustion engine 1. In this, the fuel is injected via a common rail system. This comprises the following components: a low-pressure pump 2 for fuel delivery from a fuel tank 3, a suction throttle 4 for determining a volume flow, a High-pressure pump 5 for conveying the fuel with pressure increase in a rail 6, individual memory 7 for temporarily storing the fuel and injectors 8 for injecting the fuel into the combustion chambers of the internal combustion engine. 1

The common rail system with individual memories differs from a conventional common rail system in that the fuel to be injected is removed from the individual memory 7. The supply line from the rail 6 to the individual memory 7 is designed in practice so that a feedback of interference frequencies in the rail 6 is attenuated. During the injection break just enough fuel flows from the rail 6 that the individual memory 7 is filled again at the beginning of the injection. The hydraulic resistance of the individual storage 7 and the supply line are matched, i. the connecting line from the rail 6 to the individual memory 7 has the highest possible hydraulic resistance. In a conventional common rail system without individual storage, the hydraulic resistance between the rail 6 and the injector 8 should be as low as possible in order to achieve unimpeded injection.

The operation of the internal combustion engine 1 is controlled by an electronic control unit (ADEC) 9. The electronic control unit 9 includes the usual components of a microcomputer system, such as a microprocessor, I / O devices, buffers and memory devices (EEPROM, RAM). In the memory modules relevant for the operation of the internal combustion engine 1 operating data in maps / curves are applied. About this calculates the electronic Control unit 9 from the input variables, the output variables. The following input variables are shown by way of example in FIG. 1: a rail pressure pCR which is measured by means of a rail pressure sensor 10, a speed signal nMOT of the internal combustion engine 1, pressure signals pE of the individual memory 7 and an input variable EIN. For example, the input quantity EIN subsumes the charge air pressure of a turbocharger and the temperatures of the coolant / lubricant and of the fuel.

In FIG. 1, the outputs of the electronic control unit 9 are a signal PWM for controlling the intake throttle 4, a power-determining signal ve, for example an injection quantity for displaying a desired torque in a torque-based control, and an output variable AUS. The output variable OFF is representative of the further control signals for controlling and regulating the internal combustion engine 1.

FIG. 2 shows a diagram of a measured pressure curve pE in a single memory and a modeled pressure curve pEMOD. The measured pressure curve pE is shown as a solid line. The modeled pressure curve pEMOD is shown as a dot-dash line. Here, the modeled pressure curve pEMOD after the first calculation pass is shown, d. H. the modeled pressure curve pEMOD differs significantly from the measured pressure curve pE.

On the abscissa, the crankshaft angle Phi is plotted. On the ordinate is the measured single memory pressure pE or the modeled Single memory pressure pEMOD applied. The pressure curve in the individual memory is measured and stored over a measuring interval. The measuring interval may correspond to a working cycle of the internal combustion engine, ie 720 degrees crankshaft angle. The measuring interval shown in FIG. 2 includes by way of example the range of 320 to 460 degrees crankshaft angle.

The procedure is as follows, wherein the steps described correspond to a program sequence of an executable program:

In a first step, the parameters of the injection are determined from the measured pressure curve pE. The characteristics are the injection start SB, the injection end SE, a pressure difference dp and a spray angle range dPhi. The pressure difference is calculated from the difference between injection start pressure level pE (SB) minus injection end pressure level pE (SE). The spray angle range dPhi is calculated from the difference of injection end angle Phi (SE) minus peak start angle Phi (SB). The injection start SB can also be determined from the injection end SE via a mathematical function. A corresponding method is from the DE 103 44 181 A1 known.

In a second step, the modeled pressure curve pEMOD is modeled on the measured pressure curve pE on the basis of the setpoint variables for the injection via the hydraulic model issued by the electronic control unit. The parameters characterizing the modeled pressure curve are preferably the modeled injection start SBMOD, the modeled injection end SEMOD, the modeled pressure difference dpMOD and the modeled angular range dPhiMOD.

In a third step, a difference of the parameters of the measured pressure curve pE to the modeled pressure curve pEMOD is then formed. The reference symbols dSB, dSE, ddp and ddPhi correspond to the respective difference. Here, ddp is calculated from the modeled pressure difference dpMOD minus the pressure difference dp. Accordingly, ddPhi is calculated from dSE minus dSB.

In a fourth step, the model parameters of the hydraulic model are then adjusted until the deviation becomes smaller than a limit value GW, for example GW <0.5 ° crankshaft angle. If this is the case, then the fuel mass calculated from the hydraulic model corresponds to the actual fuel mass. The fuel mass calculated from the model is then set as decisive for the further control of the internal combustion engine.

FIG. 2 shows the pressure curve pE and the modeled pressure curve pEMOD over the crankshaft angle Phi. Alternatively, the pressure curve can also be displayed over time. In this case, the references in the text are to be understood as references to the time.

In Figure 3, the hydraulic model is shown. The input variables are a first pressure p1, which corresponds to the pressure level provided by the high-pressure pump 5, and a first mass flow m1. The output quantities are a second pressure p2, a second mass flow m2, a third pressure p3 and a third mass flow m3. The second pressure p2 corresponds to the pressure level in the low pressure range. The second Mass flow m2 stands for the leakage of the system. The third pressure p3 corresponds to the cylinder pressure and is approximately constant. The third mass flow m3 stands for the injected fuel mass. Reference D1 stands for a first, D2 for a second and D3 for a third throttle. The latter corresponds to the Einspitzdüse. Reference numeral 11 denotes the single-storage volume. The hydraulic characteristics of the first throttle point D1 are known from test bench measurements and remain constant during operation. The hydraulic characteristics of the second throttle point D2 are variable, but can be determined from the pressure rise phase in the individual storage pressure and its deviation. The hydraulic characteristics of the third throttle point D3, so the injection nozzle, change with the needle stroke. Their temporal changes can be measured on a component test bench, for example by means of one of the DE 198 50 221 C1 known method.

• über die Modellierung des Einzelspeicherverlaufs kann die Kraftstoff-Masse genau bestimmt werden;
• der hydraulische Zustand des Injektors wird abgebildet;
• das hydraulische Modell stellt ein redundantes System dar und kann daher einen Weiterbetrieb im Fehlerfall gewährleisten.

From the above description, the method according to the invention offers the following advantages:

• the modeling of the individual storage history allows the fuel mass to be determined precisely;
• the hydraulic condition of the injector is displayed;
• the hydraulic model represents a redundant system and can therefore ensure continued operation in the event of a fault.

reference numeral

1

Internal combustion engine

2

Low pressure pump

3

Fuel tank

4

interphase

5

High pressure pump

6

Rail

7

Single memory

8th

injector

9

electronic control unit (ADEC)

10

Rail pressure sensor

11

Single storage volume

Claims (4)

Method for controlling an internal combustion engine (1) with a common rail system, in which a fuel mass is calculated from a measured fuel pressure curve and in which the fuel mass is set as decisive for the control of an injection,
characterized,
that the fuel mass is calculated by the pressure profile (PE) of a single memory (7) is measured, a modeled pressure curve (pEMOD) via a hydraulic model to the measured pressure variation (pE) is simulated, and calculates the fuel mass from the hydraulic model becomes. Method according to claim 1,
characterized,
that deviations from the measured pressure curve of the individual memory (pE) to the modeled pressure curve (pEMOD) are calculated and the model parameters are adjusted until the deviations become smaller than a limit value (GW). Method according to claim 2,
characterized,
that the deviations are determined for the variables characterizing the injection. Method according to claim 3,
characterized,
in that the variables correspond to an injection start (SB), an injection end (SE), a pressure difference (dp) from injection start pressure level (pSB) to injection end pressure level (pSE) and a spray angle range (dPhi) alternatively to an injection duration (dt).

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