Method for monitoring the function of a pressure sensor in an exhaust aftertreatment system

Abstract

The invention relates to a method for monitoring the function of a pressure sensor (22) in an exhaust aftertreatment system (2), which comprises: - a conveying device (8) for conveying a reaction agent for a selective catalytic reduction, - a supply line (14) for supplying the reaction agent to an exhaust gas stream, wherein the supply line (14) is fluidically connected to the conveying device (8), - the pressure sensor (22) which is designed to detect the pressure of the reaction agent in the supply line (14) as the first pressure value, - a metering device (16) with an actuator (18), wherein the metering device (16) is configured to meter the reaction agent supplied via the supply line (14) into the exhaust gas stream, the method comprising the following steps: - Detecting a pressure-dependent property of the actuator (18) that depends on the pressure of the reaction medium in the supply line (14), - Converting the pressure-dependent property of the actuator (18) using a conversion model that models the relationship between the pressure-dependent property and the pressure of the reaction medium in the supply line (14) into a second pressure value for the reaction medium in the supply line (14), - Monitoring the functionality of the pressure sensor (22) by comparing the first and second pressure values.

Description

Technical field

[0001] The invention relates to a method for monitoring the function of a pressure sensor in an exhaust aftertreatment system, as well as to an exhaust aftertreatment system. Furthermore, the invention relates to an exhaust system of a motor vehicle. The invention also relates to a motor vehicle. Technical background

[0002] An exhaust aftertreatment system for selective catalytic reduction (SCR) typically includes a tank containing a reagent, such as a urea solution. A pumping and metering system is generally provided to transfer the reagent from the tank. This system comprises a pumping unit and a feed line leading to a metering unit. The metering unit injects the reagent under pressure into the exhaust stream. This is a pressure-controlled system, with regulation and monitoring primarily based on signals from a pressure sensor designed to detect the reagent pressure in the feed line. The injection of the reagent via the metering unit occurs at a predefined system pressure.

[0003] Since the delivery and metering system is an emissions-relevant component of the vehicle, its function must be monitored. In current systems, the pressure sensor signal is only monitored for minimum and maximum limits at a pressure of 0 bar. This static monitoring is generally performed by comparing the signal to the ambient pressure of the vehicle. During metering operation, the system typically only checks whether the pressure is within the expected range. Therefore, if, for example, an overpressure error occurs, it is not possible to determine precisely whether a line is blocked or whether a pressure sensor is defective. Furthermore, it is impossible to determine whether the pressure is actually within the expected range or whether a faulty pressure sensor is causing an erroneous reading. Since there is usually no second pressure sensor in the system, dynamic monitoring of the pressure sensor is not possible.

[0004] It is therefore an object of the invention to provide a method for monitoring the function of a pressure sensor in an exhaust aftertreatment system and an exhaust aftertreatment system which enable improved dynamic monitoring of the pressure sensor with minimal effort. Disclosure of the invention

[0005] The invention relates to a method for monitoring the function of a pressure sensor in an exhaust aftertreatment system, which comprises: - a conveying device for conveying a reaction agent for a selective catalytic reduction, - a feed line for supplying the reaction agent to an exhaust gas stream, wherein the feed line is fluidically connected to the conveying device, - the pressure sensor, which is designed to detect the pressure of the reactant in the feed line as the first pressure value, - a metering device with an actuator, wherein the metering device is configured to meter the reaction agent supplied via the supply line into the exhaust gas stream, the procedure comprises the following steps: - Capturing a pressure-dependent property of the actuator that depends on the pressure of the reactant in the supply line, - Converting the pressure-dependent property of the actuator into a second pressure value for the reaction medium in the supply line using a conversion model that models the relationship between the pressure-dependent property and the pressure of the reaction medium in the supply line. - Monitoring the functionality of the pressure sensor by comparing the first and second pressure values.

[0006] The method according to the embodiments of the invention enables the dynamic monitoring of the pressure sensor within its operating range. Since the method is based on components already present in the exhaust aftertreatment system, it is not necessary to integrate additional components to monitor the pressure sensor in its operating range. Instead, existing components, in particular the actuator of the metering device, are used to detect a pressure-dependent characteristic. This pressure-dependent characteristic is converted into a second pressure value using the conversion model. This second pressure value is used to validate the first pressure value supplied by the pressure sensor. This enables monitoring of the pressure sensor within its operating range. By using existing components, the design complexity and thus the costs are reduced.

[0007] Furthermore, the invention relates to an exhaust aftertreatment system for exhaust aftertreatment in an exhaust stream, wherein the exhaust aftertreatment system comprises: - a conveying device for conveying a reaction agent for a selective catalytic reduction, - a supply line for supplying the reaction agent to the exhaust gas stream, wherein the supply line is fluidically connected to the conveying device, - the pressure sensor, which is designed to detect the pressure of the reactant in the feed line as the first pressure value, - a metering device with an actuator, wherein the metering device is configured to meter the reaction agent supplied via the supply line into the exhaust gas stream, - a monitoring device designed to to detect a pressure-dependent property of the actuator that depends on the pressure of the reaction medium in the supply line, to convert the pressure-dependent property of the actuator into a second pressure value for the reaction medium in the supply line using a conversion model that models the relationship between the pressure-dependent property and the pressure of the reaction medium in the supply line, and to monitor the functionality of the pressure sensor by comparing the first and second pressure values.

[0008] Furthermore, the invention relates to an exhaust system of a motor vehicle, which includes an exhaust aftertreatment system as described above.

[0009] The invention also relates to a motor vehicle comprising an exhaust system with an exhaust aftertreatment system as described above.

[0010] It is advantageous if the actuator is a solenoid valve and if the pressure-dependent characteristic corresponds to or depends on an electrical current flowing through the solenoid valve when it opens. The relationship between the electrical current flowing when the solenoid valve opens and the pressure in the supply line can usually be determined with sufficient accuracy and converted into a model to validate or monitor the measured values ​​provided by the pressure sensor within the operating range.

[0011] Preferably, the time at which the solenoid valve opens is determined depending on the second derivative of the electric current through the solenoid valve and in particular by recognizing a characteristic curve for the opening of the solenoid valve.

[0012] According to a preferred embodiment, the method further comprises: - Detecting the electrical voltage applied to the solenoid valve, - Taking the measured electrical voltage into account when determining the second pressure value using the conversion model.

[0013] Preferably the method further comprises: - Determining the temperature of the solenoid valve, - Taking the temperature of the solenoid valve into account when determining the second pressure value using the conversion model.

[0014] According to a preferred embodiment, the temperature of the solenoid valve is determined by the following steps: - Determining the resistance of the solenoid valve based on the voltage applied to the solenoid valve and the saturation current flowing through the solenoid valve, and - Deriving the temperature of the solenoid valve from the resistance of the solenoid valve using a resistance-temperature relationship of the solenoid valve.

[0015] It is advantageous if the procedure includes performing a reference measurement in which the current is recorded when the solenoid valve is opened at a time when the reagent in the supply line is not under overpressure.

[0016] Preferably, the conversion model is created using modeling software based on a large number of data sets.

[0017] According to a preferred embodiment, the conversion model is a machine learning model trained to convert the pressure-dependent property of the actuator into a second pressure value of the reaction agent in the supply line.

[0018] Preferably, each time the actuator is activated, it is determined whether a deviation between the first pressure value and the second pressure value exceeds a predetermined limit value, whereby if one or more successive exceedances of the limit value occur, a malfunction of the pressure sensor is detected and a specific reaction is triggered.

[0019] According to a preferred embodiment, the solenoid valve has: - a magnetic coil, - a movable anchor, - a valve needle for opening and closing the solenoid valve, which is connected to the movable armature.

[0020] Preferably, the solenoid valve has a spring element designed to push the valve needle into the closed position of the solenoid valve. Brief description of the drawings

[0021] The embodiments are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 an exhaust aftertreatment system for carrying out selective catalytic reduction; Fig. 2 a solenoid valve designed to meter the reagent into the exhaust stream; Fig. 3 a representation of the forces acting on the movable armature and the valve needle of the solenoid valve; Fig. 4 the current through the magnetic coil as a function of time; Fig. 5 A representation of different data sets that indicate the relationship between pressure and required opening current under different conditions. Description of embodiments

[0022] Fig. Figure 1 shows an exhaust aftertreatment system 2 designed to reduce the proportion of pollutants in the engine's exhaust gases by means of selective catalytic reduction (SCR). To carry out selective catalytic reduction, a reagent, for example an aqueous urea solution known as "AdBlue", is added to the exhaust gas stream. The aqueous urea solution acts as a reducing agent to reduce the nitrogen oxides contained in the exhaust gas.

[0023] The in Fig. The exhaust aftertreatment system 2 shown in Figure 1 comprises a tank 4 in which the reagent is stored. The exhaust aftertreatment system 2 includes a pumping device 8 with a pump 10, which is designed to draw the reagent from the tank 4 via a suction line 12 and deliver it via a feed line 14 to a metering device 16. The metering device 16 includes an actuator 18, for example a solenoid valve, through which the reagent is metered into the exhaust stream 20 at a predetermined system pressure.

[0024] The system's pressure control is based on signals from a pressure sensor 22, which is designed to detect the pressure in the supply line 14. The initial pressure value detected by the pressure sensor 22 is forwarded to a control unit 24 and compared with a setpoint. Pressure control can then be achieved by appropriately controlling the actuators in the system. In particular, the control unit 24 can be configured to generate a control signal 26 for the pumping device 8. Using the control signal 26, the speed of the pump 10 can, for example, be adjusted so that the pressure of the reaction medium in the supply line 14 is brought to the specified system pressure.

[0025] The reaction agent is metered into the exhaust stream 20 by the metering device 16 at a defined metering point, which is arranged so that the metered reaction agent is available for the selective catalytic reaction at the catalyst 28 installed in the exhaust stream 20.

[0026] Since pressure sensor 22 is an emissions-related component of the vehicle, monitoring of pressure sensor 22 is required in accordance with OBD requirements (OBD stands for On-Board Diagnostics). This monitoring should be designed to detect any malfunction of pressure sensor 22 within its operating range.

[0027] To monitor the pressure sensor 22, it is proposed to evaluate a pressure-dependent property of the actuator 18 of the dosing device 16 on the pressure side of the system and to convert it into a second pressure value using a conversion model. The first pressure value supplied by the pressure sensor 22 can then be compared with this second pressure value. The result of this comparison allows a conclusion to be drawn about the plausibility of the first pressure value detected by the pressure sensor 22.

[0028] To carry out this monitoring, the following is included in Fig. 1. Exhaust aftertreatment system 2 shown includes a monitoring device 30. This monitoring device 30 is designed to evaluate a pressure-dependent value transmitted to it by the actuator 18 and to derive the second pressure value from this pressure-dependent value using the conversion model. Furthermore, the monitoring device 30 is designed to compare the first pressure value supplied by the pressure sensor 22 with the second pressure value and thus check the plausibility of the first pressure value. If the first pressure value detected by the pressure sensor 22 proves to be inconsistent, it can be concluded that a malfunction of the pressure sensor 22 exists. The monitoring device 30 can be implemented as a standalone device or, for example, as part of the control unit 24.

[0029] According to a preferred embodiment, the actuator 18 can be a solenoid valve. Fig. Figure 2 shows the construction of such a solenoid valve 32, which can be used to meter the reaction agent into the exhaust stream 20. The solenoid valve 32 comprises a solenoid coil 34 and a movable armature 36, which is connected to a valve needle 38. The solenoid valve 32 also includes a spring 40. When the solenoid valve is closed, the spring 40 presses the movable armature 36 together with the valve needle 38 against the outlet 42 of the solenoid valve 32. To open the solenoid valve 32, an electric current is passed through the solenoid coil 34, which attracts the armature 36 against the acting forces such as spring force, frictional force, and pressure force, and opens the outlet 42 of the solenoid valve 32 through the valve needle 38. The solenoid coil 34 and the armature 36 form a magnetic circuit. The movement of the armature 36 results in a changing air gap in the magnetic circuit, which significantly influences the inductance of the magnetic circuit and thus the current flow through the magnetic coil.

[0030] The solenoid valve's pressure-dependent property is the current required through the solenoid coil 34 to open the solenoid valve 32. This required opening current is a measure of the magnetic force needed to open the solenoid valve 32. The magnetic force depends on the prevailing pressure in the supply line 14, as the pressure of the reactant opposes the opening of the solenoid valve 32.

[0031] In Fig. Figure 3 shows the forces acting on the movable armature 36 and the valve needle 38 of the solenoid valve 32 when the solenoid valve 32 opens. The magnetic force 44 acting on the movable armature 36 is visible, pulling the armature 36 and the valve needle 38 away from the outlet 42 of the solenoid valve 32. Opposing the magnetic force 44 is the spring force 46 exerted on the movable armature 36 by the spring 40. The pressure force 48 exerted by the pressurized reagent also acts on the valve needle 38 and the movable armature 36, pressing the valve needle 38 against the outlet 42 of the solenoid valve 32. Furthermore, in Fig. Figure 3 shows the frictional force 50, which opposes the movement of the armature 36. To open the solenoid valve 32, the magnetic force 44 must therefore overcome the three opposing forces: the spring force 46, the pressure force 48, and the frictional force 50. The solenoid valve 32 opens as soon as the magnetic force 44 is equal to or greater than the three forces opposing the opening of the solenoid valve 32.

[0032] The required opening current is a measure of the magnetic force 44 needed to open the solenoid valve 32. Since the magnetic force 44 depends on the pressure, the opening current is a pressure-dependent property of the solenoid valve 32. The opening current detected at the time the solenoid valve 32 opens therefore allows conclusions to be drawn about the pressure at which the reactant is located in the supply line 14 and the metering device 16. From the opening current detected at the time the solenoid valve 32 opens, the pressure of the reactant can be derived using a suitable conversion model and provided as a second pressure value.

[0033] It is advantageous to determine the opening current required to open the solenoid valve 32 as part of a reference measurement, also for the case where the reactant in the supply line 14 is not under pressure. For example, at the beginning of each operating cycle, the solenoid valve 32 can be activated in a pressureless state and the required opening current determined. The opening current describes the required magnetic force 44 and can be equated in the pressureless system with the sum of the spring force 46 and the frictional force 50. Since the frictional force 50 is significantly lower than the spring force 46, the opening current can, as a first approximation, be equated with the spring force 46. With the aid of such a reference measurement, the respective spring force 46 of the metering device 16 used can therefore be determined under the currently prevailing conditions and taken into account in the conversion model.

[0034] In Fig. Figure 4 illustrates how the current required to open the solenoid valve 32 is determined. For this purpose, see in Fig. 4 The current through the solenoid coil 34 of the solenoid valve 32 is plotted as a function of time. With regard to the solenoid valve 32, it is intended to monitor its correct function as part of the on-board diagnostics (OBD). The functional test is performed during the opening (BIP: Beginning of Injection Period) of the solenoid valve 32, whereby the opening of the solenoid valve 32 within the period specified in Fig. The measurement takes place in the first measurement window 52 shown in Figure 4. The monitoring algorithm used to monitor the solenoid valve 32 is based on the second derivative 54 of the measured current through the solenoid coil 34, with the second derivative 54 of the current in window 56 in Fig. Figure 4 is shown. Using the second derivative 54 of the measured current through the solenoid coil 34, the opening time 58 can be determined as the maximum of the second derivative 54. The current flowing through the solenoid coil 34 at the opening time 58 determined in this way is the opening current of the solenoid valve 32. Thus, the monitoring algorithm provides both the opening time 58 and the current required to open the solenoid valve 32. Furthermore, in Fig. Figure 4 shows a second measuring window 60, which is used to determine the saturation current through the solenoid coil 34. This saturation current is required, for example, as described below, to determine the temperature of the solenoid valve 32.

[0035] To refine the conversion model used and thus achieve a more accurate conversion of the opening current into the pressure of the reaction medium, it is advantageous to consider additional parameters in the conversion model besides the opening current of the solenoid coil 34. In particular, it is advantageous to consider the temperature of the solenoid valve 32, which is determined at the solenoid coil 34 of the solenoid valve 32, in the conversion model. Furthermore, it is advantageous to consider the voltage applied to the solenoid coil 34 when the solenoid valve 32 is actuated in the conversion model.

[0036] The temperature T Coil The magnetic coil 34 of the solenoid valve 32 can be measured using the measured resistance R. Coil (T) can be calculated according to the following relationship: TCoil=RCoil(T)R20−1α+20°

[0037] In this formula, R denotes 20The nominal coil resistance of the solenoid 34 at 20°C, whereas a denotes the specific temperature coefficient of copper, the material of the solenoid 34. Both values ​​are stored in the control unit and can therefore be used for calculations. The resistance R Coil (T) of the magnetic coil 34 can be determined using the relationship R Coil (T) = U / I Sättigung from the voltage U applied to the magnetic coil 34 and the measured saturation current I Sättigung can be derived.

[0038] To create the conversion model, the relationship between pressure and required opening current is recorded under various conditions such as pressure, voltage, temperature, and spring force. Fig.Figure 5 shows the pressure as a function of the opening current for three different data sets, recorded under varying conditions, such as different temperatures, voltages, spring forces, etc. Based on this data, a conversion model can be created using modeling software to convert the respective pressure-dependent quantity into the corresponding pressure. For example, a mathematical formula or algorithm can be derived from this data using suitable modeling software, representing this relationship between opening current and pressure for different conditions such as temperature, voltage, spring force, etc. If further values ​​are known on the control unit side, these can also be used in the conversion model.The algorithm derived in this way can be stored in the control unit and, with the help of the measured input information, a corresponding pressure can be output for each activation of the solenoid valve 32 under the various conditions.

[0039] Alternatively to this embodiment, the conversion model can also be implemented in the form of a machine learning model that is trained to convert a pressure-dependent property of the actuator 18, in particular the opening current of the solenoid valve 32, into a second pressure value.

[0040] To validate the signals from pressure sensor 22, the second pressure value determined using the conversion model is compared with the first pressure value supplied by pressure sensor 22 each time the solenoid valve 32 is activated during operation of the dosing unit 16. If a significant deviation between the two pressure values ​​is observed over a longer period or across multiple dosing cycles, it is assumed that pressure sensor 22 is outputting an erroneous value within its operating range. In the event of a fault, a specific system response can then be triggered. For example, the fault can be logged in the fault memory.

[0041] The features disclosed in the foregoing description, the claims and the drawings can be important for the realization of the invention in its various embodiments, both individually and in any combination.

Claims

[1] Method for monitoring the function of a pressure sensor (22) in an exhaust aftertreatment system (2) which comprises: - a conveying device (8) for conveying a reaction agent for a selective catalytic reduction, - a supply line (14) for supplying the reaction agent to an exhaust gas stream, wherein the supply line (14) is fluidically connected to the conveying device (8), - the pressure sensor (22) which is designed to detect the pressure of the reaction agent in the supply line (14) as the first pressure value, - a metering device (16) with an actuator (18), wherein the metering device (16) is configured to meter the reaction agent supplied via the supply line (14) into the exhaust gas stream, the method comprising the following steps: - Detecting a pressure-dependent property of the actuator (18) that depends on the pressure of the reaction medium in the supply line (14), - Converting the pressure-dependent property of the actuator (18) using a conversion model that models the relationship between the pressure-dependent property and the pressure of the reaction medium in the supply line (14) into a second pressure value for the reaction medium in the supply line (14), - Monitoring the functionality of the pressure sensor (22) by comparing the first and second pressure values. [2] Method according to claim 1, characterized by , that the actuator (18) is a solenoid valve (32) and that the pressure-dependent property corresponds to or depends on an electric current flowing through the solenoid valve (32) when the solenoid valve (32) is opened. [3] Method according to claim 2, characterized by, that the time at which the solenoid valve (32) opens is determined depending on the second derivative (54) of the electric current through the solenoid valve (32) and in particular by recognizing a characteristic curve for the opening of the solenoid valve (32). [4] Method according to claim 2 or claim 3, characterized by , that the procedure further shows: - Detecting the electrical voltage applied to the solenoid valve (32), - Taking the measured electrical voltage into account when determining the second pressure value using the conversion model. [5] Method according to any one of claims 2 to 4, characterized by , that the procedure further shows: - Determining the temperature of the solenoid valve (32), - Taking into account the temperature of the solenoid valve (32) when determining the second pressure value by the conversion model. [6] Method according to claim 5, characterized by, that the temperature of the solenoid valve (32) is determined by the following steps: - Determining the resistance of the solenoid valve (32) based on the voltage applied to the solenoid valve (32) and the saturation current flowing through the solenoid valve (32), and - Deriving the temperature of the solenoid valve (32) from the resistance of the solenoid valve (32) using a resistance-temperature relationship of the solenoid valve (32). [7] Method according to any one of claims 2 to 6, characterized by , that the method includes performing a reference measurement in which the current is recorded when the solenoid valve (32) is opened at a time when the reaction agent in the supply line (14) is not under overpressure. [8] Method according to any one of claims 1 to 7, characterized by that the conversion model is created using modeling software based on a large number of data sets. [9] Method according to any one of claims 1 to 7, characterized by , that the conversion model is a machine learning model that is trained to convert the pressure-dependent property of the actuator (18) into a second pressure value of the reaction agent in the supply line (14). [10] Method according to any one of claims 1 to 9, characterized by , that each time the actuator (18) is activated, it is determined whether a deviation between the first pressure value and the second pressure value exceeds a predetermined limit value, whereby if one or more successive exceedances of the limit value occur, a malfunction of the pressure sensor (22) is detected and a specific reaction is triggered. [11] Exhaust aftertreatment system (2) for exhaust aftertreatment in an exhaust stream, wherein the exhaust aftertreatment system (2) comprises: - a conveying device (8) for conveying a reaction agent for a selective catalytic reduction, - a supply line (14) for supplying the reaction agent to the exhaust gas stream, wherein the supply line (14) is fluidically connected to the conveying device (8), - the pressure sensor (22) which is designed to detect the pressure of the reaction agent in the supply line (14) as the first pressure value, - a metering device (16) with an actuator (18), wherein the metering device (16) is designed to meter the reaction agent supplied via the supply line (14) into the exhaust gas stream, - a monitoring device (30) designed to to detect a pressure-dependent property of the actuator (18) which depends on the pressure of the reaction medium in the supply line (14), to convert the pressure-dependent property of the actuator (18) into a second pressure value for the reaction medium in the supply line (14) using a conversion model that models the relationship between the pressure-dependent property and the pressure of the reaction medium in the supply line (14), and to monitor the functionality of the pressure sensor (22) by comparing the first and second pressure values. [12] Exhaust aftertreatment system (2) according to claim 11, characterized by , that the actuator (18) is a solenoid valve (32) and that the pressure-dependent property corresponds to or depends on an electric current flowing through the solenoid valve (32) when the solenoid valve (32) is opened. [13] Exhaust aftertreatment system (2) according to claim 12, characterized by , that the solenoid valve (32) has: - a magnetic coil (34), - a movable anchor (36), - a valve needle (38) for opening and closing the solenoid valve (32), which is connected to the movable armature (36). [14] Exhaust aftertreatment system (2) according to claim 13, characterized by , that the solenoid valve (32) has a spring element (40) designed to push the valve needle (38) into the closed position of the solenoid valve (32). [15] An exhaust system of a motor vehicle comprising an exhaust aftertreatment system (2) according to any one of claims 11 to 14.

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