Method and device for monitoring injection amount of reducing agent into exhaust gas line section of motor system having internal combustion engine

Abstract

The invention relates to a method for determining an amount of injected reducing agent in a reducing agent injection system (1) for an exhaust gas line section (6) of an internal combustion engine, comprising the following steps: providing a predefined reducing agent pressure in a pressure line (4) of the reducing agent injection system (1); actuating (S2) the dosing unit (5) by means of at least one dosing valve as a function of an opening duration for feeding the reducing agent into the exhaust gas line section (6); recording (S2) a pressure profile during an opening duration of the dispensing unit (5); determining (S6, S7) cycle duration data to be ascertained of the pressure oscillations in the pressure line (4) obtained by opening the dosing unit (5); determining (S10) the amount of the injected reducing agent as a function of the opening duration, the predefined reducing agent pressure and the cycle duration data to be ascertained.

Description

Field of the Invention

[0001] The invention relates to a reducing agent injection system for injecting a reducing agent into an exhaust gas line section of an internal combustion engine, and in particular to a method for monitoring and determining the amount of injected fuel. Background Art

[0002] In order to reduce nitrogen oxides in the combustion exhaust gas of an internal combustion engine, a reducing agent is conveyed into the exhaust gas line section, and the reducing agent usually comprises an aqueous urea solution. The reducing agent is provided under the pressure in a pressure line by means of a supply module and is injected into the exhaust gas line section by a metering unit. The amount of the injected reducing agent is determined by setting the opening duration of a metering valve of the metering unit.

[0003] As is known, for example, from the published document DE 102008001789 A1, the amount of the injected reducing agent is set by corresponding time control of the metering valve. Herein, the pressure of the reducing agent in the pressure line is taken into account for setting the amount of the reducing agent.

[0004] However, the effective pressure of the reducing agent at the metering unit can differ from the pressure of the reducing agent set in the pressure line due to the dynamic characteristics of the pressure line, the reducing agent, and the speed of sound in the reducing agent. This applies in particular to short opening times of the metering unit. Therefore, in particular in the case of short opening times of the metering unit, the amount of the injected reducing agent can only be determined imprecisely.

[0005] Therefore, the object of the invention is to provide an improved method for determining and monitoring the amount of the injected reducing agent in a reducing agent injection system for an exhaust gas treatment device of a motor system having an internal combustion engine. Summary of the Invention

[0006] The object is achieved by a method for determining the amount of the injected reducing agent in a reducing agent injection system for an exhaust gas line section of an internal combustion engine according to claim 1, and corresponding devices and reducing agent injection systems according to the parallel claims.

[0007] Further design options are set forth in the dependent claims.

[0008] According to a first aspect, there is provided a method for determining the amount of the injected reducing agent in a reducing agent injection system for an exhaust gas line section of an internal combustion engine, the method comprising the following steps:

[0009] - Providing a pre-given reducing agent pressure in a pressure line of the reducing agent injection system;

[0010] - Controlling the metering unit with at least one metering valve according to an opening duration for conveying the reducing agent into the exhaust gas line section;

[0011] - Record the pressure trend during the opening duration of the metering unit;

[0012] - Determine the period duration data to be determined of the pressure oscillation in the pressure line obtained by opening the metering unit;

[0013] - Determine the amount of reductant injected depending on the opening duration, a pre-given reductant pressure, and the period duration data to be determined.

[0014] The reduction of nitrogen oxides in the exhaust gas section of an internal combustion engine is achieved by controlled delivery of a reductant, such as an aqueous urea solution for example. This is achieved by means of a reductant injection system through which the reductant is injected into the exhaust gas section.

[0015] In order to achieve optimal reduction of nitrogen oxides in the exhaust gas section of an internal combustion engine, precise metering of the reductant is required. The reductant is atomized by a metering unit and is then injected into the exhaust gas flow in the exhaust gas section, where the metering unit is controlled by a control signal that specifies the opening time of at least one metering valve of the metering unit. Here, the amount of reductant injected is determined by the reductant pressure and the opening time of the metering valve, at which reductant pressure the reductant is provided at the position of the metering valve.

[0016] The reductant pressure in the pressure line is provided by a supply module with a reductant pump. In addition, a pressure sensor is provided in the supply module such that the reductant pressure in the pressure line can be adjusted.

[0017] However, the arrangement of the pressure sensor spaced apart from the metering unit in the supply module causes the pressure in the pressure line to drop rapidly at the time point of opening the metering valve, and then the pressure of the reductant in the region of the metering valve is less than the pressure given by the pressure sensor. The pressure drop is determined by the dynamic characteristics of the injection system or the pressure line, such as the geometric characteristics of the pressure line (such as the line length, inner diameter, and attenuation characteristics of the pressure line), a pressure attenuator that may be provided in the supply module (which provides the reductant under the desired pressure), and the delay of the pressure oscillation through the pressure line between the metering unit and the supply module. In particular, in the case of a short opening time of the metering valve, the pressure drop leads to an inaccurate determination of the amount of reductant injected. In addition, the immediate pressure drop at the time point of opening the metering valve causes the largest deviation from the calculated metering amount.

[0018] At the time point of opening the metering valve, an oscillation of the pressure distribution in the pressure line occurs, which starts with a pressure drop, has a damped sine trend, and decays rapidly.

[0019] Thus, as specified by the above method, in addition to the set pressure of the reducing agent in the pressure line and the opening duration of the metering valve, the amount of the reducing agent injection is determined based on the data of the cycle duration of the pressure vibration in the pressure line after the opening time point.

[0020] Furthermore, the cycle duration to be determined can be obtained based on the first cycle duration data. The first cycle duration data is determined according to the first measurement method based on the time difference between the first pressure minimum value and the immediately following pressure maximum value after the opening time point. The first cycle duration data corresponds to 1.9 to 2.1 times, especially twice, the time difference between the pressure minimum value and the pressure maximum value.

[0021] Therefore, in the first measurement method, the cycle duration data can be determined based on the time difference between the pressure minimum value and the next pressure maximum value after the opening time point, such that the time difference between the pressure minimum value and the pressure maximum value approximately corresponds to half of the cycle duration data of the pressure wave.

[0022] This first measurement method can accurately determine the cycle duration data. However, it requires accurate measurement of the pressure trend after the metering valve is opened and is thus very susceptible to interference.

[0023] As an alternative or additional option, it can be specified that the cycle duration data to be determined is obtained based on the second cycle duration data. The second cycle duration data is determined according to the second measurement method based on the time difference between the time point of opening at least one metering valve of the metering unit and the time point of achieving the pressure drop or pressure change caused by the opening of the metering valve (the delay time between the opening of the metering unit and the change in the pressure signal). The second cycle duration data corresponds to 3.9 to 4.1 times, especially four times, the time difference.

[0024] Therefore, in the second measurement method, the cycle duration data of the pressure wave passing through the pressure line can be determined by measuring the propagation delay between the time point of opening the metering valve (predetermined by the control time point of the metering valve) and the time point of the first pressure minimum value of the achieved pressure drop (caused by the opening of the metering valve). This second measurement method for measuring the cycle duration data is more robust against interference, but is less accurate in determining the cycle duration data.

[0025] It can be specified that the determination of the amount of the injected reducing agent is performed in such a way that first, the injection amount is determined based on the opening duration and the predetermined reducing agent pressure, and a correction value is applied to the injection amount. The correction value is obtained according to the distribution function based on the opening duration, the predetermined reducing agent pressure, and the cycle duration data to be determined.

[0026] Therefore, it is possible to determine the amount of the injected reducing agent depending on the opening duration, the pressure of the reducing agent in the pressure line, and the cycle duration data to be determined. In particular, the cycle duration data can be assigned to a correction value by means of a distribution table, and the correction value is applied to the amount of the injected reducing agent determined in a model-based manner from the opening duration and the pressure.

[0027] Furthermore, it is possible to determine the amount of the injected reducing agent depending on at least one release condition, wherein the release condition includes: the pressure in the pressure line is within a determined predefined range at the opening time point, and / or no other system that affects the injection system is actuated, such as, for example, an adjustment system for the delivery stroke of the reducing agent pump, a second metering valve in a DI-SCR system, etc.

[0028] The two conditions ensure that no interference affects the reducing agent injection system, which would lead to an incorrect measurement of the cycle duration data.

[0029] Furthermore, when the difference between the first cycle duration data and the second cycle duration data is less than a predefined threshold, the amount of the injected reducing agent to be determined, which depends on the first cycle duration data, can be determined as the cycle duration data to be determined, wherein, otherwise, the amount of the injected reducing agent to be determined, which depends on the second cycle duration data, is determined as the cycle duration data to be determined.

[0030] It can be provided that two measuring methods are used simultaneously. Here, it can be provided that when the result of the second measuring method differs from the result of the second measuring method by more than a predefined difference, the result of the first measuring method is not used. In this case, the result of the second measuring method is used.

[0031] Before determining the cycle duration data by the first and second measuring methods, the trend of the pressure signal of the pressure in the line can be filtered by means of a time-based filter in order to reduce interference, which can in particular make the determination by the first measuring method inaccurate.

[0032] Furthermore, the determined amount of the injected reducing agent can be used to monitor, control, or regulate the injection carried out by the reducing agent injection system.

[0033] According to a further aspect, there is provided a device, in particular a controller, for performing the above method.

[0034] According to a further aspect, there is provided a reducing agent injection system for an exhaust gas section of an internal combustion engine, comprising:

[0035] - a metering unit for controllably delivering a reducing agent into the exhaust gas section;

[0036] - A pressure pipeline for delivering a reducing agent to a dosing unit;

[0037] - A reducing agent pump for providing a reducing agent in the pressure pipeline under a predetermined reducing agent pressure;

[0038] - A pressure sensor for detecting the reducing agent pressure in the pressure pipeline;

[0039] - The above devices. Description of the Drawings

[0040] Next, the embodiments will be explained in more detail with reference to the drawings. Among them:

[0041] Figure 1 A schematic diagram of a reducing agent injection system for injecting a reducing agent into an exhaust gas pipe section of an internal combustion engine is shown;

[0042] Figure 2 A method for determining the amount of injected reducing agent by measuring the cycle duration data is shown; and

[0043] Figure 3 A schematic diagram of the pressure trend in the pressure pipeline when the dosing valve is opened is shown. Detailed Embodiments

[0044] Figure 1 A reducing agent injection system 1 with a reducing agent storage tank 2 is shown. The reducing agent is delivered from the reducing agent storage tank to the pressure pipeline 4 through a supply module 3. For this purpose, the supply module 3 has a reducing agent pump 31, which can provide a reducing agent under the pressure in the pressure pipeline 4. In order to adjust the pressure level in the pressure pipeline 4, a pressure sensor 32 is provided in the supply module 3. In addition, the supply module 3 can have a pressure attenuator 33 to attenuate pressure fluctuations.

[0045] The pressure pipeline is connected to a dosing unit 5, through which the reducing agent is injected into the exhaust gas pipe section 6 of an internal combustion engine or an exhaust gas aftertreatment device.

[0046] The control or regulation of the injection is achieved in a manner known per se for nitrogen oxide reduction by means of a controller 10.

[0047] It is necessary to monitor the amount of injected reducing agent in order to always achieve optimal nitrogen oxide reduction. Since the amount of reducing agent is not directly measured, the modeling of the amount of reducing agent must be based on measurement parameters.

[0048] As described at the beginning, the influence of the dynamic effects in the pressure line causes the reduction dose calculated conventionally based on the pressure in the pressure line 4 and the opening duration of the metering valve of the metering unit 5 to be inaccurate. Thereby, the quality of nitrogen oxide reduction is reduced.

[0049] The method described next enables a more precise determination of the amount of reductant injected based on the measurement of cycle duration data.

[0050] The method is executed in the controller 10 and can be applied in each injection cycle.

[0051] In step S1, it is detected whether the injection of the reductant should be carried out by means of the metering unit 5.

[0052] In step S2, the metering valve of the metering unit 5 is controlled to open, and at the same time the recording of the pressure trend is carried out by means of the pressure sensor 32. Figure 3 The diagram of the pressure trend (curve K) over time after opening the metering valve is shown. The damped sine vibration starting with the pressure drop is identified.

[0053] In step S3, it is detected whether the metering unit should be closed again after a predefined duration. If this is the case (or: yes), then the method continues with step S4, otherwise it jumps back to step S3.

[0054] In step S4, it is detected whether the release condition for determining the cycle duration data is met. The release condition can be predefined as a constant pressure before starting to open the metering valve and a pressure within a certain predefined value range. In addition, the release condition can stipulate that no other actuator that can affect the injection system is activated during the measurement of the pressure trend. If the release condition is met (or: yes), then the method continues with step S5, otherwise the method continues with step S1, and the last effectively determined value is used as the value for the amount of reductant injected.

[0055] In step S5, the recorded pressure trend is now filtered by means of a time-based filter in order to eliminate interference and outliers in the measured values. The filtered curve KF shown in Figure 3 is obtained.

[0056] In step S6, based on the filtered trend curve, according to the first measurement method, the time point T1 of the first pressure minimum and the time point T2 of the maximum value following it after the time point T0 of opening the metering valve are determined, and the corresponding time difference between these time points is determined. According to the first measurement method, the first cycle duration data is then obtained by multiplying by 2 in order to obtain the cycle duration of the first sine half-wave after opening the metering valve.

[0057] In step S7, the duration between the time point T0 (time point for the opening actuation) at which the metering valve is opened and the time point T3 at which a first pressure drop or pressure change is achieved after the metering valve is opened is measured by means of a second measuring method, and the corresponding time difference is multiplied by the factor 4 in order to obtain second cycle duration data.

[0058] In step S8, it is determined which of the cycle duration data in the cycle duration data should be taken into account for the subsequent determination of the metered amount of reducing agent. Although the measurement of the first cycle duration data is more precise, it is less robust than the second cycle duration data obtained by the second measuring method. Therefore, the value of the first cycle duration data is used as the cycle duration data to be determined only if the value of the second cycle duration data deviates from the value of the first cycle duration data by no more than a pre-given threshold. Otherwise, the value of the second cycle duration data is determined as the cycle duration data to be determined.

[0059] In step S9, the cycle duration data to be determined and the pressure of the reducing agent in the pressure line 4 are assigned to correction values according to an assignment table. The assignment table gives the correction values.

[0060] In step S10, the metered amount of reducing agent determined according to a model that depends on the pressure in the pressure line and the opening duration of the actuation is corrected, in particular in an additive or multiplicative manner.

[0061] Now, in step S11, the thus determined amount of reducing agent of the metered reducing agent can be taken into account for the subsequent injection process in order to monitor and to determine the target amount of reducing agent to be injected.

Claims

1. A method for determining the amount of injected reducing agent in a reducing agent injection system (1) for an exhaust gas line section (6) of an internal combustion engine, the method comprising the following steps: - providing a predetermined reducing agent pressure in the pressure line (4) of the reducing agent injection system (1); - controlling (S2) the metering unit (5) with at least one metering valve depending on the opening duration for supplying the reducing agent into the exhaust gas line section (6); - recording (S2) the pressure trend during the opening period of the dosing unit (5); - determining (S6, S7) period duration data to be determined of the pressure oscillations in the pressure line (4) resulting from opening the metering unit (5); - Determining ( S10 ) the quantity of reducing agent injected as a function of the opening period, the predefined reducing agent pressure and the cycle duration data to be ascertained.

2. The method according to claim 1, wherein: The amount of injected reducing agent is determined in that the injected amount is first determined as a function of the opening period and a predefined reducing agent pressure, and a correction value is applied to the injected amount, which is obtained according to a distribution function as a function of the opening period, the predefined reducing agent pressure and the cycle duration data to be determined.

3. The method according to claim 1 or 2, wherein: The cycle duration to be determined is determined relying on first cycle duration data, which are determined according to a first measuring method based on a time difference between a first pressure minimum and a subsequent pressure maximum after the opening time point, wherein the first cycle duration data corresponds to twice the time difference between the pressure minimum and the pressure maximum.

4. The method according to any one of claims 1 to 3, wherein: The cycle duration data to be determined are determined based on second cycle duration data, which are determined according to a second measuring method based on the time difference between the time point when at least one dosing valve of the dosing unit (5) is opened and the time point when the pressure drop or pressure change caused by opening the dosing valve is realized, wherein the second cycle duration data corresponds to four times the time difference.

5. The method according to claim 4 in combination with claim 3, wherein: When the difference between the first cycle duration data and the second cycle duration data is smaller than a predetermined threshold value, the amount of reducing agent injected to be determined depending on the first cycle duration data is determined (S8) as the cycle duration data to be determined, wherein otherwise, the amount of reducing agent injected to be determined depending on the second cycle duration data is determined as the cycle duration data to be determined.

6. The method according to any one of claims 1 to 5, wherein: The amount of injected reducing agent is determined (S4) as a function of at least one release condition, wherein the release condition comprises that the pressure in the pressure line (4) is within a certain predetermined range at the opening time and / or no other systems are being manipulated which have an influence on the injection system.

7. The method according to any one of claims 1 to 6, wherein: Before the period duration data to be ascertained are determined, the profile of the pressure signal is filtered ( S5 ) by means of a time-based filter.

8. The method according to any one of claims 1 to 7, wherein: The determined amount of injected reducing agent is used to monitor, control or regulate the injection by the reducing agent injection system.

9. A device, in particular a control unit (10), for carrying out the method according to any one of claims 1 to 8.

10. A reducing agent injection system (1) for an exhaust gas line section (6) of an internal combustion engine, comprising: a metering unit (5) for the controlled delivery of reducing agent into the exhaust gas line section (6); - a pressure line (5) for conveying the reducing agent to the dosing unit (5); a reducing agent pump (31) for providing reducing agent in the pressure line (4) at a predetermined reducing agent pressure; - a pressure sensor (32) for detecting the reducing agent pressure in the pressure line (4); - Device (10) according to claim 9.

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