DE102013218897A1 - Method for monitoring the quantity of a metering or injection system of an internal combustion engine, in particular of a motor vehicle - Google Patents

Abstract

The present invention relates to a method for monitoring the quantity of a metering or injection system of an internal combustion engine, in particular of a motor vehicle, wherein the metering or injection system comprises a fluid system containing piping, and wherein it is provided in particular that in the piping system, a fluidic pressure wave is generated (315) in that the pressure curve generated by the fluidic pressure wave is detected (320), that from the detected pressure curve a variable correlated with the propagation velocity of the fluidic pressure wave is determined (325), that the mechanical quantity correlated with the propagation velocity of the fluidic pressure wave or hydraulic rigidity of the line system is determined (330), and that the quantity monitoring takes place taking into account the determined rigidity of the line system.

Description

The invention relates to a method for monitoring the quantity of a metering or injection system of an internal combustion engine, in particular of a motor vehicle. The invention further relates to a computer program that carries out all steps of the method according to the invention when it runs on a computing device or a control device. and a computer program product with program code, which is stored on a machine-readable carrier, for carrying out the method according to the invention when the program is executed on a computing device or a control device.

State of the art

In the automotive field, injection systems or dosing systems for a liquid medium or fluid, e.g. Common rail injection systems for fuel or SCR catalyst systems for nitrogen oxide reduction by metering a urea solution (SCR fluid) known in which the deducted or metered in the respective piping system amount of fluid must be plausibility or monitored in the case of fuel or SCR To comply with fluid emissions legislation or, in the case of SCR fluid, to determine the amount of SCR fluid remaining in a reservoir.

In the field of SCR catalyst systems, such quantity monitoring is known by the term "consumption deviation monitoring" (CDM) and makes it possible to detect deviations in the delivery rate of the SCR fluid-conveying delivery pump, the detection of a leakage of the line system, or the detection of a malfunction a provided for injection or metering of the fluid injection or metering valve.

Quantity monitoring may e.g. be done by means of a mass flow sensor, but for cost reasons, such a sensor is saved in many cases, so that the quantity monitoring must be done otherwise. It is therefore already known to control the said injection or metering valve in a defined period of time for quantity monitoring at an effective zero output of said feed pump, to detect the resulting pressure profile in the line system and to calculate the mass flow through the valve from the detected pressure curve.

Disclosure of the invention

The invention is based on the finding that the accuracy of said, indirectly occurring quantity monitoring is essentially determined by the mechanical or hydraulic rigidity of the line system, since the rigidity, which significantly influences the pressure curve in the line system, is not constant. Thus, stiffness depends on a number of factors, e.g. the presence of trapped air in the fluid, e.g. determined by the modulus of elasticity of the lines, the temperature and the pressure of the fluid, as well as the aging and the manufacturing tolerances of the components used. However, the quantitative influence of these factors on the stiffness is usually not known or predictable or can only be determined with relatively high effort.

Furthermore, the finding is based on the fact that said stiffness can not be determined by a pressure change in the line system resulting from a given actuation of the valve, since this presupposes an exact knowledge of the relevant properties of the components actually to be monitored, which, however, precisely with the CDM mentioned above. Procedure should be checked.

The method according to the invention provides, in particular, to generate a pressure wave in the fluid in question in the respective fluid and to detect or determine the propagation velocity of the pressure wave in the conduit system. Since the propagation velocity thus determined is substantially equal to the effective velocity of sound in the fluid, the known relationship between the effective velocity of sound in the conduit system and the compression / modulus of the hydraulic system of conduits and fluid can be exploited to determine the rigidity of the system Close overall system. The above-mentioned relationship arises in particular from the dependence of the propagation velocity of pressure waves on the stiffness of the relevant line system.

The said pressure wave can be generated differently, by generating a short-term negative pressure or a short-term overpressure in the line system. Thus, when the feed pump is activated and the valve is closed, a short-term negative pressure or overpressure can occur due to pump movement be triggered or additionally activated valve by a short-term negative pressure generated by the pump first, a certain pressure in the piping system is constructed and this pressure is briefly reduced by subsequent brief opening of the valve. When the feed pump is not activated, a brief negative pressure or overpressure can be generated by briefly actuating at least one injection or metering valve, depending on how the relative pressure ratios are in front of and behind the valve.

All the above-mentioned methods for generating a pressure wave can advantageously be realized with relatively little effort in an existing metering or injection system of an internal combustion engine, in particular of a motor vehicle.

The method according to the invention can be implemented in the form of a separate functional module, e.g. an SCR catalyst system can be realized or integrated into an existing CDM function. In the latter case, the implementation costs can be minimized.

The invention makes it possible to determine the system rigidity of the line system containing the respective fluid at arbitrary times and in particular during the operation of the metering or injection system or the internal combustion engine, without requiring precise knowledge of the mass flows. The proposed method is also independent of the conveying behavior, i. the conveying mass or the conveying speed of the feed pump for the fluid and allows the determination of the rigidity even if not properly functioning components.

The invention therefore makes it possible to considerably improve the accuracy of said quantity monitoring (CDM).

The invention can in principle be used in any conduit system of a fluid in which a said pressure wave can be generated and the pressure can be measured with sufficient accuracy. The need for more accurate determination of system rigidity in the operation of a piping system involved herein will be apparent in those systems which include at least one component which can not be considered sufficiently rigid with respect to the static and dynamic mechanical or hydraulic performance of the overall system operated at different temperatures and / or pressures and which do not have a sufficiently accurate mass flow sensor.

In particular, the inventive method for quantity monitoring in an SCR catalyst system, a common rail injection system or the like of an internal combustion engine can be used with the advantages described herein.

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 schematically shows a metering device of an SCR catalyst system, according to the prior art.

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

3 shows a second embodiment of the method according to the invention with reference to a combined flow / block diagram.

4 shows a according to the second embodiment according to 3 resulting typical pressure curve.

Description of exemplary embodiments

The 1 schematically shows a known in the prior art metering device of an SCR catalyst system. In the exhaust system 10 an internal combustion engine 11 is an SCR catalyst 12 arranged, which selectively reduces nitrogen oxides in the exhaust gas by a selective catalytic reduction (SCR). For the reduction of urea water solution via a metering valve 13 in the exhaust system 10 upstream of the SCR catalyst 12 injected. The metering valve may also include one or more metering modules, which for example each comprise a plurality of injection valves.

The aqueous urea solution is stored in a storage tank 14 stored. To remove the urea solution is a suction line 15 intended. The reducing agent is via a feed pump 16 from the reducing agent tank 14 conveyed and under pressure in the pressure line 17 to the metering valve 13 directed. The urea solution is precisely and demand-dependent in the exhaust system 10 injected. This is the pressure of the reducing agent in the pressure line 17 prevail. This reducing agent pressure is regulated to a predefinable desired pressure. To detect the pressure in the pipe 17 is a pressure sensor 18 provided, the detected pressure signals to a control unit 19 forwards, so that the feed pump 16 via a signaling of the control unit 19 can adjust the predetermined target pressure.

The above-mentioned entire line system accordingly comprises the suction line in this embodiment 15 , the feed pump 16 , the pressure line 17 as well as the dosing valve 13 ,

The activation of the metering valve 13 also takes place via a signaling of the control unit 19 , The metering valve 13 is controlled with a so-called opening frequency, which is identical for different dosing amounts, but at the different dosing amounts in a differently long opening of the valve. The opening frequency is usually in the range of a few Hz, However, the metering valve 13 be controlled with a variable frequency even with a fixed opening time.

That in the 2 The first embodiment shown is preferably in one of the mentioned in 1 shown control unit 19 separate or functionally and spatially separated control unit implemented.

After the start 200 the in 2 shown routine is with the metering valve closed 13 by a short pump movement 205 the feed pump 16 a pressure wave of the SCR fluid in the conduit system 16 . 17 generated. The frequency of this pressure line passing through the line system is measured by means of a pressure sensor arranged in the line system 210 , From the measured frequency, the wave propagation velocity or effective sound velocity c_eff of the pressure wave is calculated 215 and in step 220 converted into a system stiffness.

The generation of the pressure wave can also without involvement of the pump 16 respectively. This alternative is particularly suitable for piping systems that have no return or a shut-off return. In the process, the metering valve becomes 13 briefly open to a pressure wave in the pipe system 16 . 17 to create. The determination of the system stiffness is as described herein.

The said pressure wave runs at the effective speed of sound c_eff through the pipe system 16 . 17 and will be on the side of the feed pump 16 and at the opposite end of the conduit system 16 . 17 reflected. The effective sound velocity c_eff is directly dependent on the modulus of elasticity of the components of the pipe system 16 . 17 and the SCR fluid as well as the density of the SCR fluid.

The change in the equilibrium pressure (steady-state pressure) in the system by the withdrawn or added mass corresponds to a mass flow dm / dt. To calculate this mass flow from a pressure curve, according to the prior art, the system stiffness is assumed to be a constant value, or a corresponding correction takes place via the temperature.

The actual system stiffness is unknown. This is defined by the bulk modulus B according to the known relationship B = -V · dp / dV, where p = pressure and V = volume. If a value for B is present, therefore, the mass flow (or the shortage in the system) can be calculated by measuring the pressure drop as follows. As described above, with a known basic volume V_0 of the system, known density of the fluid, measured pressure p1 before opening the metering valve, and measured pressure after briefly opening the metering valve at a pressure p2, the time difference Δt required for the pressure drop is measured.

mit

ṁ:

druckabhängiger Massenstrom durch das Ventil

V₀:

Grundvolumen des Systems(drucklos)

ρ:

Dichte des Fluids, näherungsweise gemittelt bei p1+p2 / 2

p₁, p₂:

Systemdruck vor bzw. nach dem Öffnen des Ventils

Δt:

Zeitintervall, in dem das Ventil offen ist

The following derivation for B yields the following derivation of the pressure-dependent mass flow ṁ (p) (hereinafter also: dm / dt (p)) through the metering valve:

With

m ':

pressure-dependent mass flow through the valve

V ₀ :

Basic volume of the system (without pressure)

ρ:

Density of the fluid, approximately averaged at p1 + p2 / 2

p ₁ , p ₂ :

System pressure before or after opening the valve

.delta.t:

Time interval in which the valve is open

für linear – elastische isotrope Materialien
mit E: E-Modul
und v: QuerkontraktionszahlSince the system stiffness is not known per se, this is determined as follows by measuring other variables independent of the metering mass flow. The relationship between the bulk modulus and the modulus of elasticity (strength theory) is exploited as follows:

for linear - elastic isotropic materials
with E: E module
and v: transverse contraction number

mit c: Schallgeschwindigkeit
und ρ: DichteThe modulus of elasticity of the present fluid is now calculated using the following relationship between density and velocity of sound, which is also known per se:

with c: speed of sound
and ρ: density

mit c_eff = effektive Schallgeschwindigkeit = Druckwellenausbreitungsgeschwindigkeit
und ρ: DichteThe stated equations are now transferred or applied according to the invention to the overall system rigidity of the line-fluid system. To determine the effective sound velocity c_eff, the definition of the modulus of elasticity for fluids is also transferred to the overall system as follows:

with c_eff = effective speed of sound = pressure wave propagation speed
and ρ: density

Based on these equations, the aforementioned compressibility (bulk modulus B) for the entire system can be calculated as:

r:

Innendurchmesser der Leitung

s:

Wandstärke

In practice, mostly only the density of the fluid is known, whereby the transverse contraction number ν and the effective sound velocity c_eff are mostly unknown. The effective speed of sound c_eff can, however, based on known correlations, eg according to Kottmann, A .; Schubert, W., "On the propagation speed of pressure waves in water pipes made of plastic pipes" in "3R International: Pipes, Pipeline Construction, Pipeline Transport", Issue 20/4 (1981), pages 184-193 , calculated as follows:

r:

Inner diameter of the pipe

s:

Wall thickness

r:

Innendurchmesser der Leitung

s:

Wandstärke

Another known correlation for calculating the eff. Sound velocity c_eff, results according to Korteweg, DJ, "On the Speed of Reproduction of Sound in Elastic Tubes," in "Annalen der Physik," Issue 241 (1878), No. 12, pp. 525-542 , to:

r:

Inner diameter of the pipe

s:

Wall thickness

The compressibility of the overall system can thus be calculated from the aforementioned equations. However, this requires, on the one hand, a measurement of the line properties (including the transverse contraction number ν for the entire system). In addition, the correlations mentioned are relatively inaccurate.

mit Δt: Zeitintervall zwischen zwei Druckpulsen
mit Δl: zurückgelegte Wegstrecke der DruckwelleAccording to the invention, it is therefore proposed to determine the effective speed of sound c_eff not by means of one of the above-mentioned correlations, but by measurement. The effective speed of sound c_eff or the pressure wave propagation speed corresponds to the speed with which a pressure pulse covers a certain distance in the line system. Therefore, the effective speed of sound c_eff can be determined by measuring the time interval of two pressure pulses and knowing the distance traveled between them as follows:

with Δt: time interval between two pressure pulses
with Δl: distance traveled by the pressure wave

The generation of the pressure pulse, as described above, either by stopping the feed pump, opening the metering valve and evaluation of the resulting pressure wave, or by closing the metering valve, performing a piston stroke of the feed pump and evaluation of the resulting pressure wave. Alternatively both methods can be executed and the value for c_eff can be plausibilized from both measurements.

If the pressure wave is measured with a single pressure sensor, the measurement result can be falsified by frequency shifts, which are caused by reflections at the valve and / or pump end. However, this measurement error can be prevented by measuring with two pressure sensors. As a result, pressure pulses are observed only on the path between the sensors. It should be emphasized that the calculation variants Ib) and II described below avoid this problem by already determining the correction factor with the same measurement error and thus compensating for possible frequency shifts.

When using the equations described above, all the necessary values are available to determine the mass flow dm / dt. To determine the mass flow dm / dt, the following procedures or variants exist.

Variant I: Explicit determination of compressibility and calculation of mass flow based on it

• a) The effective speed of sound c_eff is determined by means of one of the said correlations, e.g. according to Eq. (3a) or Eq. (3b). With the resulting value of c_eff, Eq. (2) calculates the compressibility "B_System", knowing the following quantities: the appropriate correlation (depending on conductivity type), the geometric dimension of the conduit, the transverse contraction number of the conduit, the transverse contraction number of the overall system, the density and the compressibility of the fluid ,
• b) Determination of the effective speed of sound c_eff over a pressure measurement according to Eq. (4). With the resulting value for c_eff, Eq. (2) Calculates the compressibility, knowing the length of the pipe or the distance of the pressure sensors, the transverse contraction number of the entire system and the density of the fluid.

The value of the compressibility determined according to variant Ia) or Ib) can e.g. once per drive cycle or at other intervals, e.g. depending on the outside temperature, checked or determined. This can be done with stored reference values for purposes of plausibility. The value of the compressibility is also stored or saved in the system.

Depending on the system concept, the actual CDM functionality (checking the mass flow through the dosing valve) is carried out regularly or only on request. As soon as the dosing quantity is to be checked, the effective delivery rate is reduced to zero and the valve is opened for a defined period of time. With the system pressure before and after opening the valve and the basic volume of the system, the mass flow dm / dt (p) through the valve according to Eq. (1) calculated.

Variant II: CDM with integrated stiffness determination

According to this variant, the compressibility is not determined at any time in advance and stored in the system to be used when needed to calculate the valve mass flow. Rather, a factor is determined by measuring the wave transit time, with the Eq. (1) is extended in a modified form so that the mass flow can be calculated directly from the pressure difference, corrected for the current system stiffness. In addition, the opening of the pressure difference valve for use of the Δp method is simultaneously used as the trigger for the pressure wave, which determines the system rigidity. Thus, the amount metered into the catalyst "wrongly" (since not required by dosing strategy) is minimized.

From the Gl. (2) results in:

und ist somit druckabhängig.The correction factor KF * or KF is defined as:

and is thus pressure-dependent.

A characteristic curve for the mentioned correction factor on the system pressure can either be learned during initial operation of the internal combustion engine (variant i), or determined and applied on the test bench (variant ii). For variant i) KF offers itself, because here no information about the system volume must be known. It is assumed that ṁ (p) corresponds to the nominal mass flow over pressure (valve characteristic curve) stored in the software, which can be assumed during initial operation. For the variant ii) KF * can be used. KF * corresponds to the physical expression 3 · (1 - 2ν_System) (see equation (5)) and can thus possibly also be calculated from material parameters, so that no further measurements are required.

• 1. Pumpe fördert nicht, Ventil geschlossen
• 2. Messen des Drucks p1
• 3. Öffnen des Ventils für Δt
• 4. Messen des Druckverlaufs p(t), Erkennen der Frequenz f
• 5. Berechnen der eff. Schallgeschwindigkeit nach Gl. (4)
• 6. Ermitteln des neuen stationären Drucks p2
• 7. Berechnen des Ventilmassenstroms nach Gl. (7),

und zwar gemäß der Beziehung

je nach Definition von KF oder KF*.Thus, the mass flow through the valve can be determined as follows:

• 1. Pump does not deliver, valve closed
• 2. Measuring the pressure p1
• 3. Opening the valve for Δt
• 4. Measuring the pressure curve p (t), detecting the frequency f
• 5. Calculate the eff. Speed of sound according to Eq. (4)
• 6. Determine the new steady state pressure p2
• 7. Calculate the valve mass flow according to Eq. (7)

according to the relationship

depending on the definition of KF or KF *.

The pressure-dependent correction factor KF * can be derived as follows:

That in the 3 shown second embodiment is preferably in an existing CDM function of a controller 19 integrated. It is believed that it is the feed pump 16 is a reciprocating pump.

After the start 300 the in 3 shown routine is first by means of the reciprocating pump a certain pressure level in the pipe system 15 . 16 . 17 generated 305 , After reaching this pressure level, the reciprocating pump is no longer activated 310 and the metering valve 13 open for a predetermined, short period of time 315 , In this case, the pressure curve over a predetermined period .DELTA.t _mess = t ₂ - t ₁ (see 4 ) in the pipe system 15 . 16 . 17 detected by a pressure sensor 320 , From the recorded pressure curve, the mass flow of SCR fluid is determined 325 and the system stiffness is calculated according to equations (1) and (2) 330 ,

In the 4 is a typical, by means of the pressure sensor 210 measured pressure curve p in the unit mbar over the time t shown, wherein the time axis shown corresponds only to the relative time course t _rel . This pressure curve represents one, from an upper pressure level 400 in the present embodiment emanating from about 7300 mbar, at the time 403 resulting pressure drop 405 which, by briefly opening the metering valve 13 is caused.

in der c_eff die Wellenausbreitungsgeschwindigkeit; p1, p2: den statischen Systemdruck vor und nach dem Öffnen des Dosierventils, Δt: die Öffnungsdauer des Dosierventils, KF(p): der genannte, druckabhängige Korrekturfaktor gemäß Gleichung 6 bedeuten.After reaching the lower pressure level 415 it comes to vibrations 410 with greatly decreasing amplitude. These pressure oscillations 410 are caused by the mentioned reflections of the pressure wave at the cable ends. According to the invention, an oscillation frequency is determined from these pressure oscillations which, as described above, is characteristic for the system rigidity and can therefore be converted into a value of the system rigidity by means of the equations (1) and (2) mentioned above. The thus determined system stiffness is finally taken into account in the quantity monitoring of a dosing or injection system concerned here, according to the following relationship, which determines the determination of the dosing valve 13 metered or injected mass on the basis of the pressure sensor 210 ascertainable pressure difference due to the pressure wave allows:

in c_eff the wave propagation velocity; p1, p2: the static system pressure before and after opening the metering valve, Δt: the opening time of the metering valve, KF (p): the named, pressure-dependent correction factor according to equation 6.

It should be noted that as an alternative to the above-described check of the valve mass flow and in particular in the in 2 shown embodiment, the pump mass flow can be checked. The evaluation of the generated pressure wave is carried out accordingly as described above.

The method described can be realized either in the form of a control program in an existing control unit for controlling an internal combustion engine or in the form of a corresponding control unit.

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 non-patent literature

• Kottmann, A .; Schubert, W., "On the propagation speed of pressure waves in water pipes made of plastic pipes" in "3R International: Pipes, Pipeline Construction, Pipeline Transport", Issue 20/4 (1981), pages 184-193 [0036]
• Korteweg, DJ, "The Speed of Reproduction of Sound in Elastic Tubes," in "Annalen der Physik," Issue 241 (1878), No. 12, pp. 525-542 [0037]

Claims (12)

Method for quantity monitoring of a dosing or injection system of an internal combustion engine, in particular of a motor vehicle, wherein the dosing or injection system comprises a fluid-containing line system, characterized in that in the line system, a fluidic pressure wave is generated ( 315 ) that the pressure curve generated by the fluidic pressure wave is detected ( 320 ) that a variable which correlates with the propagation velocity of the fluidic pressure wave is determined from the detected pressure curve ( 325 ) that the mechanical or hydraulic rigidity of the conduit system is determined from the determined variable correlated with the propagation velocity of the fluidic pressure wave ( 330 ), and that the quantity monitoring takes place taking into account the determined rigidity of the line system. Method according to Claim 1, characterized in that the quantity correlated with the propagation velocity of the fluidic pressure wave is based on the effective speed of sound (c_eff) in the line system, including the fluid contained in the line system. A method according to claim 2, characterized in that the effective sound velocity c_eff based on the equation c_eff = Δt / Δl with Δt: time interval between two pressure pulses with Δl: distance covered by the pressure wave is determined by measurement. A method according to claim 2 or 3, characterized in that the mechanical or hydraulic stiffness of the conduit system is determined on the basis of the relationship between the effective speed of sound in the conduit system and in the fluid and the compression modulus or modulus of the conduit system and the fluid. Method according to one of the preceding claims, characterized in that the pressure curve generated by the fluidic pressure wave is measured by at least two pressure sensors, wherein pressure pulses are detected substantially only in the arranged between the at least two sensors line region. Method according to one of the preceding claims, characterized in that the fluidic pressure wave is generated by a short-term negative pressure or a short-term overpressure in the line system. Method according to Claim 6 in a delivery pump ( 16 ) having line system ( 15 . 16 . 17 ), characterized in that the short-term negative pressure or overpressure by stopping the feed pump ( 16 ) is produced. Method according to Claim 6 in a delivery pump ( 16 ) and a metering valve or injection valve ( 13 ) having line system ( 15 . 16 . 17 ), characterized in that when the metering valve or injection valve is closed ( 13 ) by activation of the feed pump ( 16 ) a short-term fluidic negative pressure or overpressure in the line system ( 15 . 16 . 17 ) is produced. Method according to Claim 6 in a delivery pump ( 16 ) and a metering valve or injection valve ( 13 ) having line system ( 15 . 16 . 17 ), characterized in that by means of the feed pump ( 16 ) a certain fluidic pressure in the piping system ( 15 . 16 . 17 ) and that this built-up fluidic pressure at non-activated feed pump ( 16 ) by opening the metering valve or injection valve ( 13 ) is reduced for a short time. Method according to one or more of claims 7 to 9, characterized in that the effective sound velocity is determined by at least two different methods for generating the short-term negative pressure or the short-term overpressure in the line system and that in the at least two methods resulting values of the effective sound velocity be made plausible against each other. A computer program executing all the steps of a method according to any one of claims 1 to 10 when mounted on a computing device or controller ( 19 ) is performed. Computer program product with program code, which is stored on a machine-readable carrier, for performing a method according to one of claims 1 to 10, when the program is stored on a computing device or a control device ( 19 ) is performed.

Images