Method for flushing pressure line of delivery device

Abstract

The invention relates to a method for operating a device (1) for conveying an aqueous urea solution in a motor vehicle, comprising a conveying device (9) having a pump (2) for conveying the aqueous urea solution, the aqueous urea solution is conveyed by a conveying device (9) from the tank (3) via a suction line (7) and then via a pressure line (6) to injectors (4, 5) arranged outside the conveying device (9), the injectors (4, 5) being arranged on the exhaust line and being designed to inject the aqueous urea solution into the exhaust line, and a bypass (8) leading from the pressure line (6) to the tank (3) from a position upstream of the injectors (4, 5), the pump (2) is operated in a first conveying direction in a first conveying process in order to convey the aqueous urea solution to the injector (4, 5), after the first conveying process of the pump (2) in the first conveying direction ends, the injector (4, 5) is closed and the pump (2) is operated in a second conveying direction opposite the first conveying direction in a second conveying process, the injector (4, 5) is opened for a predetermined period of time T1, according to the invention, air is sucked into the pressure line (6) by the injectors (4, 5), the air sucked in by the injectors (4, 5) is sucked into the delivery device (9), then the pump (2) is again operated in the first delivery direction in a third delivery process while the injectors (4, 5) are closed, and the air sucked into the delivery device (9) is pressed into the tank (3) along the bypass (8).

Description

Technical Field

[0001] The present invention relates to a method for operating a device for conveying a urea-water solution in a motor vehicle. The device includes a conveying device having a pump for conveying the urea-water solution. The conveying device conveys the urea-water solution from a tank via a suction line and then via a pressure line to an injector arranged outside the conveying device. The injector is arranged in an exhaust line and is configured to inject the urea-water solution into the exhaust line. A bypass leads from the pressure line to the tank at a point upstream of the injector. The pump operates in a first conveying direction during a first conveying operation to convey the urea-water solution to the injector. After the first conveying operation in the first conveying direction is completed, the injector is closed and the pump operates in a second conveying direction, opposite to the first conveying direction, during a second conveying operation. The injector is open for a predetermined time period T1, and air is drawn into the pressure line by the injector. The present invention also relates to a device for implementing the method. Background Art

[0002] Many countries around the world have laws and regulations that set upper limits for certain substances in the exhaust gases of internal combustion engines. These substances are often undesirable for release into the environment. One such substance is nitrogen oxides (NOx), the proportion of which in the exhaust gases must not exceed legally mandated limits. Due to limiting conditions, such as the design of internal combustion engines for low fuel consumption, avoiding NOx emissions within the engine has limited effectiveness in reducing the NOx content in the exhaust gases. Therefore, exhaust aftertreatment is necessary to achieve relatively low limits.

[0003] It has been shown that selective catalytic reduction (SCR) of nitrogen oxides is advantageous. This SCR method requires a nitrogen-containing reducing agent. In particular, the use of ammonia (NH3) as a reducing agent has proven to be a viable alternative. Due to its chemical properties and the legal regulations in many countries, ammonia is usually not stored in pure form, as this could cause problems, especially in motor vehicles or other mobile applications. The reducing agent itself is usually not stored and carried, but rather a reducing agent precursor. A reducing agent precursor is understood to be a substance that can split into a reducing agent or can be chemically converted into a reducing agent. For example, urea is a reducing agent precursor for the reducing agent ammonia.

[0004] An aqueous ammonia solution (urea) is carried in a tank and fed into the exhaust line in precisely metered quantities using a suitable delivery system. For this purpose, the delivery system typically includes a pump for conveying the fluid, one or more filters for purifying the fluid, a heating device for thawing the fluid, and a control system for processing internal and external data and for controlling the pump, the heating device, and other controllable components, such as one or more injectors.

[0005] The delivery system, particularly the injectors, used to transport the aqueous ammonia solution must be designed to prevent freezing of the aqueous ammonia solution, particularly to prevent damage to the injectors. Therefore, after the delivery system is shut down, appropriate methods are required to remove the aqueous urea solution from the injectors. These methods must also ensure that the components of the delivery system remain coated with the aqueous ammonia solution to prevent crystallization of the aqueous ammonia solution on these components. To achieve this, a flushing process is performed, during which the delivery pump is operated in the reverse direction while the injectors are closed. Finally, the injectors are opened for a specified period, drawing air through the injectors into the delivery system and removing the aqueous ammonia solution from the pipeline and the injectors.

[0006] A particular disadvantage of prior art solutions is the difficulty in regulating the generated negative pressure and the resulting backflow so that the ejector and the line leading to it are emptied without emptying the remaining components of the conveying system. This often results in a low negative pressure and, therefore, a low backflow. This can lead to the aqueous ammonia solution remaining in the ejector or line and forming deposits.

[0007] If the negative pressure and return flow are set too high, air can be sucked into the conveying system, causing crystallization on the pump, filter, or other components of the conveying system. This is particularly due to the fact that all installed components have certain component tolerances, resulting in unpredictable variations in the actual pump output from one pump to another, and therefore an unknown amount of ammonia solution drawn in. This unpredictable amount of ammonia solution drawn in makes the flushing process unreliable and makes it impossible to reliably prevent damage to the injector or the conveying system. Summary of the Invention

[0008] The object of the present invention is therefore to provide a method for operating an exhaust gas aftertreatment device which ensures a reliable flushing process of the injector line and the injector itself in order to prevent damage to the injector and the delivery device itself. Furthermore, the object of the present invention is to provide a device.

[0009] With regard to the method, the object is achieved by a method having the features of claim 1 .

[0010] One embodiment of the present invention relates to a method for operating a device for conveying a urea-water solution in a motor vehicle.

[0011] The device includes a delivery device having a pump for delivering a urea-water solution, the delivery device delivering the urea-water solution from a tank via a suction line and then via a pressure line to an injector arranged outside the delivery device, the injector being arranged in an exhaust line and configured to inject the urea-water solution into the exhaust line, wherein a bypass leads from the pressure line to the tank at a position upstream of the injector, wherein the pump is operated in a first delivery direction in a first delivery process to deliver the urea-water solution to the injector, wherein after completion of the first delivery process of the pump in the first delivery direction, the injector is closed, and the pump is operated in a second delivery direction opposite to the first delivery direction in a second delivery process, wherein the injector is opened for a predetermined time period T1, air is drawn into the pressure line through the injector, and the air drawn in through the injector is drawn into the delivery device, and then the pump is operated again in the first delivery direction in a third delivery process with the injector closed, and the air drawn into the delivery device is forced along the bypass into the tank.

[0012] The method is particularly aimed at generating a significantly higher negative pressure in the pressure line and in parts of the delivery device during the second delivery process than in methods known from the prior art. As a result, when the injector is open, the urea-water solution in the pressure line is drawn back into the delivery device significantly further than usual. This ensures that no more urea-water solution remains in the injector and preferably also in the entire pressure line, and in particular ensures that no deposits form in the pressure line.

[0013] By providing a third delivery process, during which the pump again delivers urea-water solution from the tank toward the pressure line or toward the injector, any air present in the delivery system is pumped into the tank via a bypass branching off the pressure line. This air can then be expelled from the system via the tank vent. Since the injector is completely closed during the third delivery process, air is preferentially delivered via the bypass. Since the section of the pressure line downstream of the bypass branch and upstream of the injector is also filled with air before the third delivery process, this air is forced toward the closed injector by the urea-water solution subsequently delivered during the third delivery process, where it is compressed by the inherently incompressible urea-water solution. This compressed air volume ensures that the injector is free of urea-water solution after the third delivery process.

[0014] After the third delivery process is completed, the compressed air in front of the ejector expands slightly again due to the disappearance of the delivery pressure of the pump for compression, thereby increasing the length of the pressure line filled with air.

[0015] It is particularly advantageous if some of the air remaining in the pressure line remains at the section of the pressure line that ends at the injector. This ensures that the injector is not filled with urea-water solution when the system is not in operation, thus preventing damage to the injector.

[0016] It is also advantageous that, after the pump is stopped, any air remaining in the pressure line at the injector expands in the pressure line, wherein the amount of air is sufficiently small that no air can enter the delivery device through the pressure line. This further ensures that no urea-water solution remains at the injector. Furthermore, the expansion of the air remaining in the pressure line prevents air from re-entering the delivery device and thus possibly entering the pump, filter, or other components that are preferably completely filled with urea-water solution during the shutdown.

[0017] A preferred embodiment is characterized in that the pressure built up during the third delivery process is sufficiently low to prevent the delivery of urea-water solution to the injector, thereby preventing the delivery of urea-water solution to the injector.

[0018] It is also preferred to provide two injectors which are fluidically connected in parallel to one another and are arranged downstream of the bypass in the pressure line.

[0019] Furthermore, it is advantageous to select the negative pressure generated by the pump during the second delivery process so that all the urea-water solution present in the pressure line is sucked back into the delivery device. This helps ensure that the pressure line is completely emptied, with no urea-water solution remaining at the injector and no urea-water solution deposits or residues in the pressure line.

[0020] Furthermore, during the third delivery process, air in the delivery device and pressure line is compressed into the tank via a bypass. Simultaneously, some of the air remains compressed in front of the closed injector, thereby forming a buffer between the urea-water solution and the injector. As is known in the art, the air compressed into the tank can be easily discharged from the tank through the tank vent. Because the injector is completely closed during the third delivery process, the air immediately in front of the injector prior to the third delivery process cannot escape. This air, acting as a compressible medium, is compressed by the incompressible urea-water solution in front of the closed injector.

[0021] With regard to the device, the object is achieved by a device having the features of claim 8 .

[0022] One embodiment of the present invention relates to a device for conveying an aqueous urea solution in a motor vehicle, wherein the device comprises a conveying device, which is designed to convey the aqueous urea solution from a tank to at least one injector arranged outside the conveying device, wherein the at least one injector is designed to inject the aqueous urea solution into an exhaust line, the conveying device having a pump, which is designed to draw the aqueous urea solution from the tank along a suction line and convey the aqueous urea solution to the injector along a pressure line, a bypass extending from the pressure line to the tank upstream of the injector, and the pump being designed to operate in a first conveying direction and in a second conveying direction opposite to the first conveying direction.

[0023] Such an invention may advantageously be operated by the method described above.

[0024] It is also expedient to provide two injectors arranged fluidically in parallel outside the delivery device, which are connected to the pressure line downstream of the branching point of the bypass.

[0025] Advantageous developments of the invention are described in the dependent claims and in the subsequent description of the figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be described in detail below based on the embodiments with reference to the accompanying drawings.

[0027] Figure 1 A schematic diagram of a device according to the invention is shown, which is operated using the method according to the invention. DETAILED DESCRIPTION

[0028] Figure 1 Three figures of the device 1 are shown, which illustrate different operating states of the device 1 from top to bottom.

[0029] The upper figure shows the following state of the device 1, in which the pump 2 has completed its normal operation, in which it conveys the urea-water solution from the tank 3 along the pressure line 6 to the two injectors 4 and 5. It can be seen that the suction line 7 from the tank 3 to the pump 2, the bypass 8 from the pressure line 6 to the tank 3, and the pressure line 6 leading to the injectors 4 and 5 are completely filled with the urea-water solution.

[0030] The actual delivery device 9 comprises in particular the pump 2, the bypass 8 and possibly a urea / water filter. The delivery device is preferably arranged in a separate housing having a connection for the suction line from the tank 3 and a connection for the pressure line 6 connected to the delivery device.

[0031] The middle diagram shows the second delivery process. Pump 2 delivers in the opposite direction to that of normal delivery operation, delivering urea-water solution from injectors 4 and 5 along pressure line 6 to tank 3. Because injectors 4 and 5 are open at this point, this return delivery generates a negative pressure in pressure line 6. Air enters pressure line 6 through the open injectors 4 and 5, ultimately entering pump 2 and bypass 8. Simultaneously, the urea-water solution previously located there is pushed toward tank 3. At the end of the second delivery process, injectors 4 and 5 close, and pump 2 stops.

[0032] The figure below shows the third delivery process following the second delivery process. During the third delivery process, with the injectors 4 and 5 still closed, the pump 2 is again operated in the delivery direction 9 provided for normal delivery operation. As a result, urea-water solution is again delivered from the tank 3 into the pressure line 6. The bypass 8, which is fluidically connected to the tank 3, is also filled with urea-water solution by the third delivery process.

[0033] As shown in the figure below, a certain amount of air remains immediately in front of the closed injectors 4, 5 and is compressed there by the subsequently delivered urea-water solution. This ensures that the injectors 4, 5 do not come into direct contact with the urea-water solution and that the delivery device 9 or its individual components are completely filled with urea-water solution.

[0034] After the third delivery process is completed, the air previously compressed by the urea-water solution expands upstream of the injectors 4 , 5 and slightly presses the urea-water solution back into the pressure line 6 .

[0035] The state shown in the figure below represents the final state of the system 1 after normal operation. In this state, the protective injectors 4 and 5 are protected against freezing, and the delivery device 9 is always filled with urea-water solution, so that crystals that could cause damage to the components cannot form on the delivery device 9.

[0036] Figure 1 The exemplary embodiments are particularly not to be regarded as limiting and are merely intended to illustrate the inventive concept.

[0037] Reference Signs List

[0038] 1. Equipment

[0039] 2. Pump

[0040] 3. Storage tank

[0041] 4. Injector

[0042] 5. Injector

[0043] 6. Pressure pipeline

[0044] 7. Suction line

[0045] 8. Bypass

[0046] 9. Conveying device

Claims

1. A method for operating a device (1) for conveying a urea-water solution in a motor vehicle, the device comprising a conveying device (9) having a pump (2) for conveying the urea-water solution, the conveying device (9) conveying the urea-water solution from a tank (3) via a suction line (7) and then via a pressure line (6) to injectors (4, 5) arranged outside the conveying device (9), wherein: The injectors (4, 5) are arranged on an exhaust line and are configured to inject a urea-water solution into the exhaust line, wherein a bypass (8) leads from a pressure line (6) to a tank (3) at a position upstream of the injectors (4, 5), wherein the pump (2) operates in a first delivery direction in a first delivery process to deliver the urea-water solution to the injectors (4, 5), wherein after the first delivery process of the pump (2) in the first delivery direction is completed, the injectors (4, 5) are closed and the pump (2) operates in a second delivery direction opposite to the first delivery direction in a second delivery process, wherein the injectors (4, 5) are opened for a predetermined time period T1 and air is sucked into the pressure line (6) through the injectors (4, 5), characterized in that the air sucked in through the injectors (4, 5) is sucked into a delivery device (9), and then the pump (2) operates in the first delivery direction again in a third delivery process, while the injectors (4, 5) are closed and the air sucked into the delivery device (9) is pressed into the tank (3) along the bypass (8).

2. The method according to claim 1, characterized in that Part of the air remaining in the pressure line (6) remains in the section of the pressure line (6) that ends in the ejector (4, 5).

3. The method according to claim 2, characterized in that After the pump (2) stops, the air remaining in the pressure line (6) at the ejectors (4, 5) expands in the pressure line (6), wherein the air amount is sufficiently small that no air enters the delivery device through the pressure line (6).

4. The method according to claim 1, wherein The pressure built up during the third delivery process is low enough to avoid delivery of urea-water solution toward the injectors (4, 5).

5. The method according to claim 1, wherein Two injectors (4, 5) are provided, which are fluidically connected in parallel to one another and are arranged in the pressure line (6) downstream of the bypass (8).

6. The method according to claim 1, wherein The negative pressure generated by the pump (2) during the second delivery process is selected such that the entire urea-water solution present in the pressure line (6) is sucked back into the delivery device (9).

7. The method according to any one of the preceding claims, characterized in that During the third delivery process, the air in the delivery device (9) and the pressure pipeline (6) is pressed into the tank (3) through the bypass (8), and a portion of the air remains in a compressed state in front of the closed injectors (4, 5), forming a buffer between the urea aqueous solution and the injectors (4, 5).

8. A device for conveying urea-water solution in a motor vehicle, the device comprising a conveying device (9) for conveying urea-water solution from a tank (3) to at least one injector (4, 5) arranged outside the conveying device (9), the at least one injector (4, 5) being configured to inject the urea-water solution into an exhaust line, the conveying device (9) comprising a pump (2) configured to draw urea-water solution from the tank (3) along a suction line (7) and convey the urea-water solution to the injectors (4, 5) along a pressure line (6), a bypass (8) extending from the pressure line (6) to the tank (3) upstream of the injectors (4, 5), the pump (2) being configured to operate in a first conveying direction and in a second conveying direction opposite to the first conveying direction.

9. The device (1) according to claim 8, characterized in that Two fluidically parallel-arranged injectors (4, 5) are provided outside the delivery device (9) and are connected to the pressure line (6) downstream of the branching point of the bypass (8).

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