Method for monitoring a tank of reducing agent

Abstract

The invention relates to a method for monitoring a reducing agent tank of a delivery module of an SCR catalytic converter system. The method comprises: determining a first system pressure (p1) of the delivery module when a return valve is activated; deactivating the return valve; determining a second system pressure (p2) of the delivery module after the return valve has been deactivated for a predefinable period of time (t); and determining from the first system pressure (p1) and the second system pressure (p2) whether a return line of the delivery module is immersed in a reducing agent solution in the reducing agent tank.

Description

Technical Field

[0001] This invention relates to a method for monitoring the reductant tank of a delivery module in an SCR catalyst system. Furthermore, this invention relates to a computer program for implementing each step of the method and a machine-readable storage medium for storing the computer program. Finally, this invention relates to an electronic controller configured to implement the method. Background Technology

[0002] Nitrogen oxides in the exhaust gases of internal combustion engines, especially diesel engines, can be reduced by selective catalytic reduction (SCR) using ammonia. Here, nitric oxide molecules are reduced to elemental nitrogen by ammonia, which acts as a reducing agent, on the catalyst surface. Urea, as an ammonia decomposition agent, is added to the exhaust pipe of the internal combustion engine upstream of the SCR catalyst in the form of a reducing agent solution (Harnstoff-Wasserlösung; HWL (urea aqueous solution)). For this purpose, the reducing agent solution is supplied from a reducing agent reservoir to a metering valve via a delivery module. The absorption of the reducing agent solution is carried out via a delivery line immersed in the reducing agent solution.

[0003] When the internal combustion engine is shut off, the reducing agent solution still in the metering valve and delivery module is returned to the reducing agent tank via a return line. For this purpose, a return valve reverses the delivery direction of the delivery pump located in the delivery module. The return line should not be immersed in the reducing agent solution. If the return line is immersed in the reducing agent solution due to an excessively high fill level in the reducing agent tank or due to the vehicle's tilted parking position, there is a risk that the reducing agent solution will flow back into the delivery module via the return line, provided a check valve is not installed at the delivery module. Summary of the Invention

[0004] A method for monitoring the reductant tank of the delivery module in an SCR catalyst system includes determining a first system pressure of the delivery module when the reflux valve is activated. The activation (ON state) of the reflux valve causes the delivery direction of the delivery pump in the delivery module to be reversed, thereby allowing the reductant solution to be returned from the delivery module to the reductant tank. Specifically, the system pressure measured in the pressure line between the reflux pump and the metering valve of the SCR catalyst system can typically drop below ambient pressure when the reflux valve is activated because a negative pressure is created within the delivery module and its piping system by evacuating it.

[0005] The reflux valve is then deactivated (OFF state). Therefore, the delivery direction of the delivery pump is switched back to deliver the reducing agent solution to the delivery module. This deactivation also occurs in the normal operating strategy of the delivery module to prepare for shutting it down, ensuring that the delivery pump is already set to the correct delivery direction for delivering the reducing agent solution upon restarting. To prevent the reducing agent solution from being delivered back to the delivery module before shutdown during reflux valve deactivation, the delivery pump is shut off before reflux valve deactivation. If the reflux line is not immersed in the reducing agent solution, pressure balance can now be achieved between the air volume in the reducing agent tank and the air volume in the delivery module that is below negative pressure.

[0006] After the reflux valve is deactivated for a pre-defined time period, the second system pressure of the delivery module is calculated. Subsequently, it is determined whether the reflux line of the delivery module is immersed in the reducing agent solution located in the reducing agent tank by analyzing the first and second system pressures. If the reflux line is actually immersed in the reducing agent solution, then no pressure balance occurs between the exhaust gas volumes; instead, the reducing agent solution is drawn into the delivery module through the reflux line. Here, other pressure change curves are obtained in the delivery module, which can be analyzed to determine whether the reflux line is immersed in the reducing agent solution.

[0007] Preferably, the first system pressure is determined immediately before the reflux valve is deactivated, so that the difference between the two determined system pressures is based solely on the possible pressure balance between the reducing agent tank and the delivery module.

[0008] Preferably, the reflux line is identified as being immersed in the reducing agent solution when the difference between the second system pressure and the first system pressure exceeds a threshold. If the reflux line is not immersed in the reducing agent solution, the system pressure can be made as compatible as possible with the pressure in the reducing agent tank after the delivery pump is shut down and the reflux valve is activated. Therefore, pressure changes may be expected after the reflux valve is deactivated. Conversely, if the reflux line is immersed in the reducing agent solution, this pressure balance cannot be achieved. Pressure balance is only achieved after the reflux valve is deactivated by drawing the reducing agent solution into the delivery module through the reflux line. This creates a large difference between the first system pressure and the second system pressure, which can be used as a feature to identify the immersion of the reflux line.

[0009] Furthermore, preferably, the reflux line is identified as being immersed in the reducing agent solution when the first system pressure is greater than the second system pressure and, moreover, the first system pressure and / or the second system pressure are outside a predetermined pressure range. In this case, an undesirably high negative pressure has already been created when the reflux valve is activated, and the removal of the reflux valve does not, for example, release the negative pressure, but rather results in a further decrease in pressure in the delivery module. This similarly indicates the immersion of the reflux line. If the reducing agent tank is severely contaminated and the reflux line is immersed in the reducing agent solution, then both the delivery line and the reflux line will be completely blocked. In this case, a negative pressure is initially maintained in the delivery module. In a cold environment, the air in the delivery module will be cooled. Therefore, the pressure in the delivery module will decrease further.

[0010] Different measures can be initiated when the reflux line is detected to be immersed in the reducing agent solution:

[0011] One measure involves activating the malfunction indicator light (MIL) when it is detected that the return line has become submerged in the reducing agent solution. This informs the driver of a vehicle equipped with an SCR catalytic converter system about the malfunction and urges the driver to seek a repair shop. If the submersion is caused, for example, by an excessively high level of the reducing agent solution, a portion of the reducing agent solution can be pumped out of the reducing agent reservoir in the repair shop.

[0012] Another approach could be to generate a fault record in a cloud database when the return line is detected to be immersed in the reducing agent solution. A cloud database capable of collecting fault reports from numerous vehicles would enable automakers or OEMs (original equipment manufacturers) to identify cumulative occurrences of the return line being immersed in the reducing agent solution for a specific vehicle model, and either implement structural adaptations while the vehicle is under development, or consider this awareness at least for subsequent models only if the fault occurs after the vehicle has entered the market.

[0013] The computer program is configured to execute each step of the method, particularly when running on a computing device or electronic controller. This enables different implementations of the method on an electronic controller without requiring structural changes. For this purpose, the computer program is stored on a machine-readable storage medium. An electronic controller is obtained by loading the computer program onto a conventional electronic controller configured to monitor the reductant tank of the delivery module of the SCR catalyst system using the method. Attached Figure Description

[0014] Embodiments of the present invention are shown in the accompanying drawings and explained in more detail in the following description. Wherein:

[0015] Figure 1 This illustrates a prior art reducing agent storage tank and delivery module;

[0016] Figure 2 It shows that in accordance with Figure 1 Pressure balance between the reducing agent storage tank and the delivery module;

[0017] Figure 3 A reducing agent tank and delivery module according to the prior art are shown, wherein the reducing agent tank can be monitored by means of a method according to an embodiment of the present invention;

[0018] Figure 4 It shows that in accordance with Figure 3 Pressure balance between the reducing agent storage tank and the delivery module;

[0019] Figure 5 A flowchart of a method according to an embodiment of the present invention is shown;

[0020] Figure 6 The figure shows a time-varying curve of system pressure in one embodiment of the present invention;

[0021] Figure 7 The figure shows the time-varying curve of system pressure in another embodiment of the invention;

[0022] Figure 8 The curve showing the change of system pressure over time in another embodiment of the invention is shown. Detailed Implementation

[0023] Figure 1The components of the DENOX2.2 SCR catalytic converter system from Robert Bosch GmbH are shown. This catalytic converter system has a reductant tank 10 containing an aqueous urea solution (HWL) as a reductant solution 11. A delivery module 20, having a delivery pump (not shown) and a return valve (not shown), is used to deliver the reductant solution 11. The delivery module is connected to the reductant tank 10 via a delivery line 30 immersed in the reductant solution 11 and a return line 40 not immersed in the reductant solution 11. A check valve 41 is arranged at the return line 40 such that even if the return line 40 is undesirably immersed in the reductant solution 11, the reductant solution 11 is prevented from flowing from the reductant tank 10 into the delivery module 20 through the return line 40. The reducing agent solution 11 delivered from the delivery module 20 is conveyed to the metering module via the pressure line 50, by means of which the reducing agent solution can be added to the exhaust pipe of the motor vehicle (not shown). The delivery module 20 and the metering valve 51 are controlled by the electronic controller 60.

[0024] If the reflux valve is activated, a negative pressure will form in the delivery module 20 when the reducing agent solution 11 is returned from the delivery module 20 to the reducing agent tank 10 through the reflux line 40. To prevent this, the metering valve 51 is opened during the return process. However, if the metering valve is blocked, a negative pressure will form. When the reflux valve is deactivated again, the reducing agent solution 11 is then returned to the tank 10. Figure 2 The solution then flows back into the delivery module 20 in the manner shown to compensate for the pressure difference between the reducing agent tank 10 and the delivery module 20. If the ambient temperature now drops below the freezing point of the reducing agent solution, ice pressure failure will occur in the delivery module 20.

[0025] Therefore, in Robert Bosch GmbH's Denoxtronic SCR catalytic converter system DENOX6-HD, in Figure 3 The method shown abandons the check valve 41. If a negative pressure is created in the delivery module 20, this negative pressure can be compensated by the return line 40, which is not immersed in the reducing agent solution 11, so that the reducing agent solution 11 does not flow into the delivery module 20. However, if the return line 40 is undesirably immersed in the reducing agent solution 11, once the return valve is deactivated, the reducing agent solution 11 will flow into the delivery module 20 due to the lack of the check valve 41 in the presence of negative pressure. Figure 4As shown, the solution is drawn into the delivery module 20 via the return line 40. Here, in addition to the risk of ice pressure damage, particles present in the reducing agent tank 10 can also enter the delivery module because the return line 40, unlike the delivery line 30, does not have a particle filter, unlike the return line 40 used for drawing the reducing agent solution 11.

[0026] In one embodiment of the method according to the invention, monitoring is performed to determine whether the reducing agent solution 11 enters the delivery module 20 through the reflux line 40. For example, in Figure 5 As shown, this is first checked 70 to see if all the enabling conditions of the method are met. These enabling conditions include: the vehicle is stopped, the internal combustion engine is off, the delivery module 20 is in inertial operation, and a negative pressure has been built into the delivery module. Then, while the return valve is still active, but immediately before its deactivation during inertial operation, the first system pressure p1 of the delivery module 20 is first determined 71. At this point, the delivery pump has been shut down. This determination 71 is performed in the delivery module 20 using a pressure sensor (not shown). After the return valve 72 is deactivated, a period of time is waited at time t1. Until time point t2, and then the second system pressure p2 in the delivery module 20 is calculated 73. Subsequently, the first system pressure p1 and the second system pressure p2 are used to determine whether the return line 40 is immersed in the reducing agent solution 11 74. This is in Figures 6 to 8 The text illustrates three different scenarios.

[0027] exist Figure 6 The diagram shows the case where the reflux line 40 is not immersed in the reducing agent solution 11, and the graph shows the change of system pressure p over time t. Here, the system pressure p is explained relative to ambient pressure, where a value of 0 corresponds to ambient pressure. Furthermore, the on / off state S of the reflux valve is shown, where a value of 0 corresponds to deactivating the reflux valve, and a value of 1 corresponds to activating the reflux valve. When the reflux valve is activated, a negative pressure is initially built up, which is rapidly released again at time t0 when the delivery pump is shut down. At time t1, the first system pressure p1 is almost equal to the ambient pressure, and only small pressure changes occur until time t2. Therefore, it can be inferred that pressure balance can still be achieved through the return line 40 before the time point t1, which indicates that the return line is not immersed in the reducing agent solution 11.

[0028] exist Figure 7The diagram shows the reflux line 40 immersed in the reducing agent solution 11. Here, pressure balance cannot be achieved through the reflux line 40 between the time point t0 when the delivery pump is shut down and the time point t1 when the reflux valve is deactivated. Only during this time period... The pressure balance begins only after the reducing agent solution 11 flows through the return pipe 40. This causes a large pressure difference between the two time points t1 and t2. This indicates that the return pipe 40 is immersed in the reducing agent solution 11.

[0029] exist Figure 8 The diagram illustrates another scenario where the return line 40 is immersed in the reducing agent solution 11. Here, the reducing agent tank 10 is severely contaminated, resulting in not only the return line 40 being blocked by the reducing agent solution, but also the delivery line 30 being blocked by dirt particles. After the delivery pump is shut down at time t0, a further pressure decrease occurs in the delivery module 20. The low absolute value of the first system pressure p1 at time t1 provides a first indication that the return line 40 is immersed in the reducing agent solution 11 and that a negative pressure is maintained in the delivery module 20. This is verified by the following method, at time point... The system pressure p further decreases, so that the second system pressure p2 is less than the first system pressure p1. This is based on the air cooling in the delivery module 20, and the pressure in the delivery module 20 thus decreases further in the absence of the possibility of pressure equalization.

[0030] If the method described above is used to identify according to Figure 7 Or according to Figure 8 If a fault occurs, the driver is notified by activating the motor indicator light. Furthermore, fault records are generated in a cloud database via a wireless communication connection, allowing automakers and the manufacturer of the SCR catalytic converter system to access these records and thus identify the cumulative occurrence of the fault in a specific vehicle model.

Claims

1. A method for monitoring the reductant tank (10) of the delivery module (20) of an SCR catalyst system, the method comprising the following steps: - When the reflux valve is activated, the first system pressure (p1) of the delivery module (20) is determined (71). - Deactivate the reflux valve (72). - The reflux valve is designed for a pre-defined time period ( After deactivation, the second system pressure (p2) of the delivery module (20) is calculated (73), and - The first system pressure (p1) and the second system pressure (p2) are used to determine whether the return line (40) of the delivery module (20) is immersed in the reducing agent solution (11) located in the reducing agent tank (10) (74).

2. The method according to claim 1, characterized in that, The first system pressure (p1) is determined immediately before the reflux valve is deactivated (72).

3. The method according to claim 1, characterized in that, When the difference between the second system pressure (p2) and the first system pressure (p1) is ( When the threshold is exceeded, it is identified that the return pipe (40) is immersed in the reducing agent solution (11).

4. The method according to any one of claims 1 to 3, characterized in that, When the first system pressure (p1) is greater than the second system pressure (p2) and the first system pressure (p1) and / or the second system pressure (p2) are outside a pre-defined pressure range, it is identified that the return line (40) is immersed in the reducing agent solution (11).

5. The method according to any one of claims 1 to 3, characterized in that, The motor indicator light is activated when the return line (40) is detected to be immersed in the reducing agent solution (11).

6. The method according to any one of claims 1 to 3, characterized in that, When the return line (40) is detected to be immersed in the reducing agent solution (11), a fault record is generated in the cloud database.

7. A computer program configured to perform each step of the method according to any one of claims 1 to 6.

8. A machine-readable storage medium on which the computer program according to claim 7 is stored.

9. An electronic controller (60) configured to monitor the reductant tank (10) of the delivery module (20) of the SCR catalyst system by means of any one of claims 1 to 6.

Images