DE102014222739B4 - Method for dosing quantity diagnosis of a reagent dosing system, device for carrying out the method, control unit program and ECU program product - Google Patents

Abstract

Method for dosing quantity diagnosis of a reagent dosing system (10), in which the rigidity (S) is determined as a measure of the dosing accuracy of the reagent dosing system (10), wherein the reagent dosing system (10) with an excitation pressure signal (AR ) is evaluated and the resulting reaction pressure signal (PR) is evaluated, characterized in that a periodic excitation pressure signal (AR) is provided, that the periodic excitation pressure signal (AR) has a constant, fixed predetermined frequency and that the phase shift (dPh) between the excitation pressure signal (AR) and a reaction pressure signal (PR) for determining the stiffness (S) are detected, wherein the phase shift (dPh) is inversely proportional to the stiffness (S).

Description

The invention relates to a method for dosing quantity diagnosis of a reagent dosing system, which doses, for example, a reagent in the exhaust gas region of an internal combustion engine, and a device for carrying out the method.

The invention further relates to a control unit program that performs all the steps of the method according to the invention when it runs on a control unit.

Moreover, the invention relates to a programmer program product with program code, which is stored on a machine-readable medium, for carrying out the method when the program is executed on a control unit.

State of the art

For the aftertreatment of the exhaust gas of an internal combustion engine, a selective catalytic reduction (SCR) with the aim of a reduction in NOx in the exhaust gas can be used. In this case, a defined amount of a selectively acting reagent is metered into the exhaust passage of an internal combustion engine. The reagent may for example be ammonia, which is obtained for example from a precursor in the form of a urea-water solution (HWL) in the exhaust gas channel by hydrolysis.

In current dosing systems, as they are known under the name DENOXTRONIC Applicant, a pump sucks the HWL from a reagent tank and compacts them to the required system for atomization system pressure of for example 3 to 9 bar. Taking into account, for example, current engine data and catalyst data, the metering rate of the HWL is tuned to the maximum possible NOx reduction.

The "California Air Resources Board" (CARB) calls for the detection of a dosing quantity deviation in the catalyst system, which can lead to exceeding a defined NOx emission limit of the exhaust system of an internal combustion engine. It must therefore be a recognition between requested and actually metered dosing mass or dosage of the reagent. In particular due to the presence of a reagent return in a delivery module of the reagent dosing system and due to the influence of the trapped air volume in the system on pressure gradients when dosing certain masses or quantities of the reagent is a detection of Dosiermengen deviations by evaluating the gradient of pressure curves in hydraulic system or, for example, based on an evaluation of a deviation of a pump speed from a target value difficult.

In the case of reagent dosing systems, such a dosing quantity diagnosis is known by the term "consumption deviation monitoring" (CDM) and makes it possible to detect deviations in the delivery rate of the pump delivering the reagent, the detection of a leakage of the conduit system or the detection of a malfunction of a reagent agent. Metering valve or a reagent injection valve.

The quantity monitoring can z. B. by means of a 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.

So is from the disclosure DE 10 2012 200 917 A1 a method for detecting a blockage of one or more injection ports of an injection valve of a reagent dosing system has become known, which comprises closing a metering valve, determining a first pressure curve in the hydraulic system in a delivery module and determining the rigidity of the reagent metering system from the first pressure curve , Subsequently, the injection valve is opened, a second pressure curve in the hydraulic system is determined and a blockage of one or more injection openings of the injection valve from the stiffness and the second pressure curve determined. In this way, the known method makes it possible to detect clogging of an injection valve without the need for a flow sensor in the hydraulic system.

In the non-prepublished publication DE 10 2013 218 897 A1 a procedure for the diagnosis of a reagent dosing system is described in which the dosing quantity diagnosis based on the determination of the mechanical or hydraulic rigidity of the reagent dosing. The stiffness, which significantly influences the pressure gradient in the piping system, is not constant. Thus, stiffness depends on a number of factors, such as: B. the presence of air bubbles in the reagent, the z. As determined by the modulus of elasticity of the lines, the temperature and pressure of the reagent and the aging and 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 known method provides for generating a pressure wave in the reagent dosing system and detecting or determining the propagation velocity of the pressure wave in the line system. Since the propagation velocity thus determined is substantially equal to the effective speed of sound in the reagent, the known relationship between the effective velocity of sound in the conduit system and the compression / modulus of the hydraulic system of conduits and reagent can be exploited to assess the stiffness of the system Close reagent metering 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 pump is activated and the valve is closed, a short-term negative pressure or overpressure can be triggered by pump movement, or if the valve is additionally activated, a short-term negative pressure is created by initially establishing a specific pressure in the piping system by means of the pump and this pressure by subsequent brief opening of the valve is briefly reduced. When the feed pump is not activated, a brief vacuum or overpressure may be generated by briefly actuating at least one injection valve, depending on how the relative pressure ratios are upstream and downstream of the valve.

The publication US 2013/0048096 A1 describes a method for dosing quantity diagnosis of a reagent dosing system in which the rigidity of the reagent dosing is determined as a measure of the dosing accuracy. A periodic excitation pressure signal is used, which has a constant, fixed predetermined frequency. To determine the stiffness, the amplitude of the resulting reaction pressure signal is detected, the amplitude being proportional to the rigidity of the reagent dosing system.

In the published patent application DE 10 2005 009 464 A1 A method of operating a reagent dosing system is described in which a diagnostic is provided to ensure diagnostic accuracy. For this purpose, the reagent pressure occurring upstream of a reagent metering valve is detected. Within the framework of a diagnosis, the specification of a time profile of the desired reagent pressure is provided, with an excitation diagnostic signal being superimposed on the normal dosing signal. The resulting pressure signal is detected and compared to a threshold.

The invention has for its object to provide a procedure for dosing quantity diagnosis of a reagent dosing, which is easy to implement and requires only a small amount of computation.

The object is achieved by the features specified in the independent method claim.

Disclosure of the invention

The procedure according to the invention is based on a metered dose diagnosis of a reagent metering system in which the rigidity of the hydraulic system is determined as a measure of the metering accuracy of the reagent metering system, wherein the reagent metering system is charged with an excitation pressure signal and the resulting reaction Pressure signal is evaluated. The procedure according to the invention is characterized in that a periodic excitation pressure signal is provided, that the periodic excitation pressure signal has a constant, fixed predetermined frequency and that the phase shift between the excitation pressure signal and a reaction pressure signal for determining the rigidity is detected , wherein the phase shift is inversely proportional to the stiffness. The stiffness is considered as a measure of the accuracy of the dosing. High rigidity results in higher accuracy than low rigidity.

The procedure according to the invention can be realized very simply. The excitation pressure signal has a constant, fixed predetermined frequency and is therefore relatively easy to implement. It is particularly advantageous that a normally existing pressure regulator for regulating the pressure of the reagent for default of the excitation pressure signal and the normally present measurement signal of the reagent pressure can be used to detect the resulting reaction pressure signal.

Advantageous developments and refinements of the procedure according to the invention are each objects of dependent method claims.

The device according to the invention for dosing quantity diagnosis of the reagent dosing system provides a specially prepared control unit for carrying out the method according to the invention.

The computer program according to the invention performs all the steps of the described method when it is executed on a control unit.

The computer program product according to the invention with program code carries out all the steps of the method according to the invention when the program is executed on a control unit.

The invention will be explained in more detail below with reference to an embodiment shown in FIGS.

Brief description of the figures

1 shows a block diagram of a reagent dosing system according to the invention and

2 Figure 4 shows waveforms versus time occurring within the reagent dosing system.

Detailed description of the embodiments

1 shows a reagent dosing system 10 which one in a tank 12 stored reagent 14 in the exhaust duct 16 an internal combustion engine 18 upstream of an SCR catalyst 20 dosed.

The reagent 14 is from a pump 22 in response to a pump signal 24 brought to a variable or preferably fixed predetermined reagent pressure, which from a pressure sensor 26 detected and as pressure p a control unit 28 is made available.

The metering rate of the reagent is determined by means of a metering valve 30 depending on a dosing signal 32 set.

One in the controller 28 existing dosing signal definition 34 determines the dosing signal 32 in response to at least one input signal 36 , which is at least one parameter of the internal combustion engine 18 and / or at least one characteristic of the SCR catalyst 20 and / or at least one characteristic of the exhaust gas channel 16 reflects existing exhaust gas.

The reagent 14 gets into the exhaust duct 16 upstream of the SCR catalyst 20 sprayed. The reagent 14 is in the SCR catalyst 20 especially needed for the conversion of NOx components of the exhaust gas. As a reagent 14 or as a precursor of a reagent, for example, a urea-water solution is provided, from which ammonia is split off by electrolysis in the warm exhaust gas, which in the SCR catalyst 20 acts as a reducing agent.

One in the control unit 28 existing pump signal definition 38 represents the pump signal 24 ready. The pump signal down 38 For example, regulates the pressure p of the reagent to a predetermined set point, which may for example be between 3 bar and 9 bar.

It should be noted at this point that, instead of the reagent dosing system, it is possible to provide any hydraulic system, such as a fuel injection system, which has a certain rigidity and whose dosing quantity is to be diagnosed as a function of the detected rigidity of the hydraulic system.

Due to legal requirements, a metered dose diagnosis of the reagent metering system 10 or in general a hydraulic system may be required. For this purpose leads a diagnosis control 40 a diagnosis by means of a diagnostic signal 42 is started.

For diagnosis, an excitation pressure signal AR is generated whose time course in 2 is shown. The excitation pressure signal AR may be, for example, the existing pump signal 24 be superimposed in a given operating point. The excitation pressure signal AR is designed as a periodic signal. Preferably, a sinusoidal signal is provided. Particularly advantageously, the excitation pressure signal AR is provided at a constant predetermined frequency. At the in 2 shown embodiment of the excitation pressure signal AR is the frequency, for example, 0.25 hertz.

In 2 the amplitude of the excitation pressure signal AR is shown in relative units. The amplitude of the excitation pressure signal AR preferably has a certain percentage of the pressure p during the normal metering operation. For example, a pressure fluctuations of +/- 1 bar or be provided when the operating pressure is for example 8 bar.

During dosing, the dosing signal setting 34 , which the diagnostic signal 42 is provided, the excitation pressure signal AR in the determination of the dosing signal 32 consider. Alternatively, the dosage can also be completely interrupted for the duration of the diagnosis.

Dose Rate Diagnosis is based on an assessment of a measure of the stiffness of the reagent dosing system hydraulic system 10 , In particular, if plastic lines are used for the guidance of the reagent, a temperature-dependent stiffness must be expected, which has an influence on the current metering rate.

The following relationship applies here: In the case of a high rigidity, only a small deviation between the prescribed metering rate and the actual metering rate has to be expected, whereas with a low rigidity, hearing deviations must be expected. For example, a limit value for the stiffness can be specified for the diagnosis, exceeding which an error message occurs. Alternatively or additionally, a correction of the dosing signal 32 from the dosing signal determination 34 depending on the stiffness, in order to take into account the rigidity in the dosage can.

According to the invention, the detection of a phase shift dPh between the excitation pressure signal AR and the resulting reaction pressure signal PR for determining the rigidity of the hydraulic part of the reagent dosing system 10 provided, which also in 2 is shown. The larger the phase shift dPh, the lower the rigidity of the hydraulic system. The determination of the phase shift dPh takes place in a phase shift determination 44 with an existing diagnostic signal 42 , Both signals AR, PR are in phase shift detection 44 processed so that the phase shift dPh can be determined. With sinusoidal excitation pressure signal AR, the phase shift dPh can be specified in degrees.

The phase shift dPh may be in a phase shift evaluation 46 already directly output as a measure of the stiffness SdPh on the basis of the determined phase shift.

According to one embodiment, in addition, a determination of a measure of the stiffness and therefrom of a measure of the accuracy of the dosing amount on the basis of the amplitude A of the resulting reaction pressure signal PR is provided. The detection of the amplitude A takes place in an amplitude determination 48 from the pressure p. The amplitude determination 48 provides amplitude A ready in an amplitude rating 50 is converted into a measure SA for stiffness based on the amplitude A. The stiffness SA based on the amplitude A is also a measure of the accuracy of the dosing amount, but in determining the stiffness, both the phase shift dPh and the amplitude A are taken into account. This is a stiffness determination 52 provided, which both the phase shift dPh and the amplitude A are provided. Furthermore, the stiffness determination 52 a weighting factor k is provided. The stiffness S is preferably determined according to the following relationship: S = k · dPh / dP_hmax + (1 - k) · A / A_max

So that the phase shift dPh and the amplitude A can be directly offset from one another, a normalization is required, which is achieved by referring the detected values dPh, A to the maximum possible value dPh_max, A_max. The maximum possible values dPh_max and A_max can be determined on the basis of experiments or calculated on the basis of models. The weighting factor k is numerically between 0 and 1 and is provided with a unit which corresponds to the stiffness S. A first weighting factor k and a second weighting factor 1-k are provided. The second weighting factor 1 - k corresponds to the first weighting factor k complementary to 1. The relationship shown takes account of the fact that the amplitude A is proportional to the stiffness S and the phase shift dPh is inversely proportional to the stiffness S.

The of the stiffness determination 52 determined stiffness can be re-evaluated directly as a measure of Dosiermengen accuracy, with a high stiffness S of higher accuracy and low stiffness S corresponds to a lower accuracy.

Claims (10)

Method for metering quantity diagnosis of a reagent metering system ( 10 ), in which the rigidity (S) as a measure of the metering accuracy of the reagent metering system ( 10 ), the reagent dosing system ( 10 ) is applied with an excitation pressure signal (AR) and the resulting reaction pressure signal (PR) is evaluated, characterized in that a periodic excitation pressure signal (AR) is provided, that the periodic excitation pressure signal (AR) has a constant, fixed predetermined frequency and that the phase shift (dPh) between the excitation pressure signal (AR) and a reaction pressure signal (PR) for determining the stiffness (S), wherein the phase shift (dPh) is inversely proportional to the stiffness (S). A method according to claim 1, characterized in that in determining the stiffness (S) both the amplitude (A) of a reaction pressure signal (AR) and the phase shift (dPh) are taken into account, wherein the amplitude (A) with a first weighting factor (k) and the phase shift are weighted by a second weighting factor (1-k). Method according to Claim 2, characterized in that the second weighting factor (1-k) is equal to the first weighting factor (k) complementary to 1. A method according to claim 2 or 3, characterized in that the phase shift (dPh) to a maximum possible phase shift (dPh_max) and the amplitude (A) to a maximum possible amplitude (A_max) are normalized. Method according to Claim 2, 3 and 4, characterized in that the sum of the weighted and normalized phase shift (dPh) and amplitude (A) is formed with the weighting factors (k, 1-k). Method according to one of the preceding claims, characterized in that the periodic excitation pressure signal (AR) is sinusoidal. Method according to one of the preceding claims, characterized in that the excitation pressure signal (AR) by driving a pump ( 22 ) is produced. Device for the diagnosis of a reagent dosing system, characterized in that a specially prepared control device ( 28 ) is provided for carrying out the method according to one of the preceding method claims. A computer program executing all the steps of a method according to any one of claims 1 to 7 when mounted on a control unit ( 28 ) is performed. Computer program product with program code, which is stored on a machine-readable carrier, for carrying out a method according to one of claims 1 to 7, when the program is stored on a control unit ( 28 ) is performed.

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