Method for flushing a pressure line of a delivery device

Abstract

The invention relates to a method for operating a device (1) for delivering an aqueous urea solution in a motor vehicle, comprising a delivery device (9) which has a pump (2) for delivering the aqueous urea solution, said aqueous urea solution being pumped by the delivery device (9) from a tank (3) via a suction line (7) and to an injector (4, 5) arranged outside of the delivery device (9) via a pressure line (6). The injector (4, 5) is arranged on an exhaust gas line and is designed to inject the aqueous urea solution into the exhaust gas line, and a bypass (8) leads from the pressure line (6), at a location upstream of the injector (4, 5), to the tank (3). The pump (2) is operated in a first pumping direction in a first pumping process in order to deliver the aqueous urea solution to the injector (4, 5), and after the first pumping process in the first pumping direction of the pump (2) has ended, the injector (4, 5) is closed, and the pump (2) is operated in a second pumping direction opposite the first pumping direction in a second pumping process, wherein the injector (4, 5) is opened for a specified duration T1, and air is suctioned into the pressure line (6) through the injector (4, 5). The air suctioned through the injector (4, 5) is suctioned into the delivery device (9). The pump (2) is then once again operated in the first pumping direction in a third pumping process while the injector (4, 5) is closed, and the air suctioned into the delivery device (9) is pushed along the bypass (8) to the tank (3).

Description

[0001] Description

[0002] Method for flushing a pressure line of a conveying device

[0003] Technical area

[0004] The invention relates to a method for operating a device for conveying an aqueous urea solution in a motor vehicle, comprising a conveying device which has a pump for conveying the aqueous urea solution, wherein the aqueous urea solution is conveyed via a suction line from a tank through the conveying device via a pressure line to an injector arranged outside the conveying device, wherein the injector is arranged on an exhaust line and is designed to inject the aqueous urea solution into the exhaust line, wherein a bypass leads from the pressure line from a point upstream of the injector to the tank, wherein the pump is operated in a first conveying process in a first conveying direction in order to convey aqueous urea solution to the injector,After the first delivery process in the first delivery direction of the pump has ended, the injector is closed, and the pump is operated in a second delivery process in a second delivery direction opposite to the first delivery direction, wherein the injector is opened for a predetermined period of time T1 and air is sucked through the injector into the pressure line. Furthermore, the invention relates to an apparatus for carrying out the method.

[0005] State of the art

[0006] Many countries around the world have enacted legal regulations that set upper limits for the content of certain substances in the exhaust gases of internal combustion engines. These are usually substances whose release into the environment is undesirable. One of these substances is nitrogen oxide (NOx), the proportion of which in the exhaust gas must not exceed legally stipulated limits. Due to the framework conditions, for example the design of internal combustion engines with a view to low fuel consumption or similar, internal engine-based prevention of nitrogen oxide emissions is only of limited use in reducing the proportion of nitrogen oxides in the exhaust gas, so that exhaust gas aftertreatment is required to comply with relatively low limits.

[0007] It has been shown that selective catalytic reduction (SCR) of nitrogen oxides is advantageous. This SCR method requires a reducing agent that contains nitrogen. In particular, the use of ammonia (NH3) as a reducing agent has emerged as a possible alternative. Due to its chemical properties and legal regulations in many countries, ammonia is not usually stored in pure form, as this can lead to problems, particularly in motor vehicles or other mobile applications. Instead of storing the reducing agents themselves, reducing agent precursors are often stored and carried along. A reducing agent precursor is understood to be a substance that splits off the reducing agent or can be chemically converted into the reducing agent.For example, urea is a reducing agent precursor for the reducing agent ammonia.

[0008] The aqueous ammonia solution, the urea, is carried in a tank and pumped into the exhaust line in precisely measured quantities using a suitable pumping device. The pumping device typically includes, among other things, a pump for pumping the fluid, one or more filters for cleaning the fluid, optionally heating devices for thawing the fluid, and a control device for processing internal and external data and controlling the pump, the heating devices, and other controllable components, such as one or more injectors.

[0009] The conveying devices used to deliver the aqueous ammonia solution, and in particular the injectors, must be designed to prevent freezing of the aqueous ammonia solution, particularly to prevent damage to the injectors. Therefore, processes are used to remove the aqueous urea solution from the injectors after the conveying device has been shut down. At the same time, these processes must ensure that the components of the conveying device remain pressurized with aqueous ammonia solution to prevent crystallization of the aqueous ammonia solution on these components. For this purpose, a flushing process is performed in which the conveying pump is operated in the opposite direction while the injectors are closed.The injectors are finally opened for a defined period of time, whereby air is sucked through the injectors towards the conveying device and the aqueous ammonia solution is sucked out of the lines and the injectors.

[0010] A particular disadvantage of the prior art solutions is that it is very difficult to scale the generated negative pressure and the backflow generated by the negative pressure in such a way that the injectors and the lines leading to the injectors are emptied, but not the remaining components of the delivery device. This leads to generally low negative pressures being built up, and thus the backflow is also low. This can lead to residues of the aqueous ammonia solution remaining in the injectors or lines, where they form deposits.

[0011] If the negative pressure and thus the backflow are scaled too high, this can lead to air being sucked into the delivery device, causing crystallization on the pump, filter, or other components of the delivery device. This is particularly due to the fact that all installed components have certain component tolerances, which causes the actual delivery capacity of the pump to vary unpredictably from pump to pump, resulting in an unknown amount of aqueous ammonia solution being sucked in. The unpredictability of the amount of aqueous ammonia solution sucked in leads to an unsafe flushing process, which cannot reliably prevent damage to the injectors or the delivery device.

[0012] Description of the invention, task, solution, advantages

[0013] Therefore, the object of the present invention is to provide a method for operating an exhaust gas aftertreatment device that ensures a reliable flushing process of the lines to the injectors and the injectors themselves, preventing damage to the injectors and the delivery device itself. Furthermore, the object of the present invention is to provide a device.

[0014] The problem with regard to the method is solved by a method having the features of claim 1.

[0015] An embodiment of the invention relates to a method for operating a device for conveying an aqueous urea solution in a motor vehicle, comprising a conveying device which has a pump for conveying the aqueous urea solution, wherein the aqueous urea solution is conveyed via a suction line from a tank through the conveying device via a pressure line to an injector arranged outside the conveying device, wherein the injector is arranged on an exhaust line and is designed to inject the aqueous urea solution into the exhaust line, wherein a bypass leads from the pressure line from a point upstream of the injector to the tank, wherein the pump is operated in a first conveying process in a first conveying direction in order to convey aqueous urea solution to the injector,wherein, after the end of the first delivery process in the first delivery direction of the pump, the injector is closed and the pump is operated in a second delivery process in a second delivery direction opposite to the first delivery direction, wherein the injector is opened for a predetermined period of time T1 and air is sucked through the injector into the pressure line, wherein the air sucked through the injector is sucked into the delivery device, wherein the pump is subsequently operated in the first delivery direction in a third delivery process while the injector is closed, wherein the air sucked into the delivery device is pressed along the bypass towards the tank.

[0016] The method is specifically designed to generate a negative pressure in the pressure line and parts of the delivery device during the second delivery process, which is significantly higher than the method known from the prior art. This results in the aqueous urea solution in the pressure line being drawn back into the delivery device significantly further than usual when the injector(s) are opened. This ensures that no aqueous urea solution remains at the injectors and, preferably, in the entire pressure line, and, in particular, that no deposits form in the pressure line.

[0017] By providing a third delivery process, in which the pump again delivers aqueous urea solution from the tank toward the pressure line or toward the injector(s), the air contained in the delivery device is pumped through the bypass branching off from the pressure line into the tank, where the air can be removed from the system via a tank vent. Since the injector(s) are completely closed during the third delivery process, the air is preferentially conveyed along the bypass.Since the section of the pressure line downstream of the bypass branch and upstream of the injector(s) is also filled with air before the third delivery process, this air is displaced toward the closed injector(s) by the aqueous urea solution subsequently delivered during the third delivery process, where it is compressed by the inherently incompressible aqueous urea solution. This compressed air volume ensures that the injector(s) are not pressurized with aqueous urea solution after the third delivery process has been completed.

[0018] After the third delivery cycle is complete, the air compressed upstream of the injector(s) expands again slightly, as the pump's compressive delivery pressure is removed. This increases the length of the pressure line filled with air.

[0019] It is particularly advantageous if a portion of air remaining in the pressure line remains in the section of the pressure line that ends at the injector. This ensures that the injector(s) are not exposed to the aqueous urea solution when the device is not in operation. This ensures that the injector(s) are not damaged.

[0020] It is also advantageous if the air remaining in the pressure line at the injector expands after the pump is shut down, with the air volume being small enough that no air enters the delivery device via the pressure line. This further ensures that no aqueous urea solution remains at the injector(s). Furthermore, the expansion of the air volume remaining in the pressure line prevents air from re-entering the delivery device and thus potentially entering the pump, filter, or other components that are preferably fully exposed to the aqueous urea solution outside of operation.

[0021] A preferred embodiment is characterized in that the pressure built up during the third delivery process is low enough to prevent the delivery of aqueous urea solution to the injector. This is intended to prevent aqueous urea solution from being delivered to the injector(s).

[0022] It is also preferable if two injectors are provided which are fluidically connected in parallel to each other and are arranged in the pressure line downstream of the bypass.

[0023] Furthermore, it is advantageous if the negative pressure generated by the pump during the second delivery process is selected such that the entire aqueous urea solution present in the pressure line is sucked back into the delivery device. This is advantageous to ensure that the pressure line is completely emptied, no aqueous urea solution remains at the injector(s), and no deposits or residues of the aqueous urea solution remain in the pressure line.

[0024] Furthermore, it is advantageous if, during the third delivery process, the air in the delivery device and the pressure line is forced into the tank via the bypass, whereby a portion of the air remains compressed in front of the closed injectors, the air forming a cushion between the aqueous urea solution and the injectors. The air forced into the tank can be easily removed from the tank via a tank vent, as is known from the prior art. Because the injector or injectors are completely closed during the third delivery process, the air located directly in front of the injector or injectors before the third delivery process has no opportunity to escape. As a compressible medium, it is compressed by the incompressible aqueous urea solution in front of the closed injector or injectors.

[0025] The object with regard to the device is achieved by a device having the features of claim 8.

[0026] An embodiment of the 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, wherein the conveying device has a pump which is designed to suck the aqueous urea solution out of the tank along an intake line and to convey it along a pressure line to the injector, wherein a bypass runs from the pressure line upstream of the injector to the tank, wherein the pump is designed to be operated in a first conveying direction and in a second conveying direction which is opposite to the first conveying direction.

[0027] Such an invention can be advantageously operated by means of the method described above.

[0028] It is also expedient to provide two fluidically parallel injectors outside the conveying device, which are connected to the pressure line downstream of the bypass branch. Advantageous further developments of the present invention are described in the dependent claims and in the following description of the figures.

[0029] Short description of the drawings

[0030] The invention is explained in detail below using an exemplary embodiment with reference to the drawing. The drawing shows:

[0031] Fig. 1 is a schematic representation of a device according to the invention, which is operated with a method according to the invention, wherein

[0032] Preferred embodiment of the invention

[0033] Figure 1 shows three images of a device 1, wherein different operating states of the device 1 are shown in the three images from left to right.

[0034] The left-hand figure shows the state of device 1 in which pump 2 has completed its regular operation, in which it pumps the aqueous urea solution from tank 3 to the two injectors 4, 5 along the pressure line 6. It can be seen that the intake line 7 from tank 3 to pump 2, the bypass 8, which runs from the pressure line 6 to tank 3, and the pressure line 6 to the injectors 4, 5 are completely filled with the aqueous urea solution.

[0035] The actual conveying device 9 consists in particular of the pump 2, the bypass 8 and, if appropriate, a filter for the aqueous urea solution. The conveying device is preferably arranged in its own housing, which has connections for the suction line from the tank 3 and the pressure line 6, which is connected to the conveying device. The second conveying process is shown in the middle figure. The pump 2 is operated opposite to the conveying direction of the normal conveying operation, so that the aqueous urea solution is conveyed from the injectors 4, 5 along the pressure line 6 to the tank 3. Because the injectors 4, 5 are open during this process, a negative pressure is created in the pressure line 6 by the back conveyance and air is conveyed through the open injectors 4, 5 into the pressure line 6 and finally into the pump 2 and the bypass 8, while at the same time displacing the aqueous urea solution previously located there in the direction of the tank 3.At the end of the second delivery process, injectors 4, 5 are closed and pump 2 is switched off.

[0036] The right-hand figure shows the third delivery cycle following the second delivery cycle. During this cycle, pump 2 is again operated in the delivery direction 9 intended for regular delivery operation, with the injectors 4 and 5 still closed. This again pumps aqueous urea solution from tank 3 into the pressure line 6. The bypass 8, which is fluidly connected to tank 3, is also filled with aqueous urea solution by the third delivery cycle.

[0037] As can be seen in the right-hand figure, a certain amount of air remains directly in front of the closed injectors 4, 5, where it is compressed by the subsequently delivered aqueous urea solution. This ensures that the injectors 4, 5 are not in direct contact with the aqueous urea solution and, at the same time, that the delivery device 9 or the individual components of the delivery device 9 are completely supplied with aqueous urea solution.

[0038] After the third delivery process has ended, the air previously compressed by the aqueous urea solution expands in front of the injectors 4, 5 and pushes the aqueous urea solution slightly back into the pressure line 6.

[0039] The state shown in the right-hand figure represents the final state of device 1 after the end of normal operation. In this state, the injectors 4, 5 are protected against freezing, and the delivery device 9 is fully supplied with the aqueous urea solution, so that no crystallization can occur on its components, which could lead to damage to the components. The embodiment of Figure 1 is not limiting in nature and serves to clarify the inventive concept.

[0040] List of reference symbols

[0041] 1 . Device

[0042] 2. Pump

[0043] 3. Tank

[0044] 4. Injector

[0045] 5. Injector

[0046] 6. Pressure line

[0047] 7. Intake line

[0048] 8. Bypass

[0049] 9. Conveyor device

Claims

Patent claims 1. A method for operating a device (1) for conveying an aqueous urea solution in a motor vehicle, comprising a conveying device (9) which has a pump (2) for conveying the aqueous urea solution, wherein the aqueous urea solution is conveyed via a suction line (7) from a tank (3) through the conveying device (9) via a pressure line (6) to an injector (4, 5) arranged outside the conveying device (9), wherein the injector (4, 5) is arranged on an exhaust line and is designed to inject the aqueous urea solution into the exhaust line, wherein a bypass (8) leads from the pressure line (6) from a point upstream of the injector (4, 5) to the tank (3), wherein the pump (2) is operated in a first conveying process in a first conveying direction in order to convey aqueous urea solution to the injector (4, 5), wherein after the end of the first conveying process in the first conveying direction of the pump (2), the Injector (4,5) is closed and the pump (2) is operated in a second conveying process in a second conveying direction opposite to the first conveying direction, wherein the injector (4, 5) is opened for a predetermined time period T1 and air is sucked through the injector (4, 5) into the pressure line (6), characterized in that the air sucked through the injector (4, 5) is sucked into the conveying device (9), wherein the pump (2) is then operated again in the first conveying direction in a third conveying process while the injector (4, 5) is closed, wherein the air sucked into the conveying device (9) is pressed along the bypass (8) towards the tank (3).

2. Method according to claim 1, characterized in that a portion of air remaining in the pressure line (6) remains at the section of the pressure line (6) ending in the injector (4, 5).

3. Method according to claim 2, characterized in that the air remaining in the pressure line (6) at the injector (4, 5) expands in the pressure line (6) after the pump (2) has been switched off, the air quantity is small enough that no air enters the conveying device via the pressure line (6).

4. Method according to one of the preceding claims, characterized in that the pressure which is built up during the third conveying process is low enough to exclude the conveyance of aqueous urea solution to the injector (4, 5).

5. Method according to one of the preceding claims, characterized in that 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. Method according to one of the preceding claims, characterized in that the negative pressure generated by the pump (2) during the second conveying process is selected such that the entire aqueous urea solution present in the pressure line (6) is sucked back into the conveying device (9).

7. Method according to one of the preceding claims, characterized in that during the third conveying process, the air in the conveying device (9) and the pressure line (6) is pressed into the tank (3) via the bypass (8), a portion of the air remaining compressed in front of the closed injectors (4, 5), the air forming a cushion between the aqueous urea solution and the injectors (4, 5).

8. Device for conveying an aqueous urea solution in a motor vehicle, wherein the device comprises a conveying device (9) which is designed to convey the aqueous urea solution from a tank (3) to at least one injector (4, 5) arranged outside the conveying device (9), wherein the at least one injector (4, 5) is designed to inject the aqueous urea solution into an exhaust line, wherein the conveying device (9) has a pump (2) which is designed to convey the aqueous urea solution along an intake line (7) from the tank (3) and to convey this along a pressure line (6) to the injector (4, 5), wherein a bypass (8) runs from the pressure line (6) upstream of the injector (4, 5) to the tank (3), wherein the pump (2) is designed to be operated in a first conveying direction and in a second conveying direction which is opposite to the first conveying direction. Device (1) according to claim 8, characterized in that two injectors (4, 5) arranged in fluid parallel are provided outside the conveying device (9), which are connected to the pressure line (6) downstream of the branch of the bypass (8).

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