Method for draining fluid supply systems

Abstract

The present invention relates to a method for purging a fluid supply system (100), the fluid supply system having a delivery unit (110), a delivery pipe (130), a pressure pipe (132), and a return pipe (134) with a check valve (154). The delivery unit (110) is connected to a fluid tank (120) via the delivery pipe, the delivery unit (110) is connected to a metering module (136) via the pressure pipe, and the delivery unit (110) is connected to the fluid tank (120) via the return pipe. The delivery unit (110) can operate in a conventional delivery direction such that fluid (121) is drawn through the delivery pipe (130) and delivered to the pressure pipe (132) and the return pipe (134). The delivery unit can also operate in the opposite direction of delivery, wherein the delivery unit (110) operates in a first purging process (200) followed by a second purging process in which the metering module (136) is closed and in the delivery direction at a first power level (L1) until a predetermined standard is reached.

Description

Technical Field

[0001] The present invention relates to a method for venting a fluid supply system, such as an SCR supply system, as well as a computing unit and a computer program for performing the method. Background Technology

[0002] DE 10 2016 210 262 A1 describes a method for purging a fluid supply system, referred to therein as a reducing agent delivery system. Purging is necessary to prevent the fluid or reducing agent from freezing in the pipes or delivery unit when the associated transport vehicle is stopped or not in operation (in the case of a typical reducing agent such as urea, the freezing point may be, for example, -11°C). Summary of the Invention

[0003] According to the present invention, a method for venting a fluid supply system, a computing unit, and a computer program product for performing the method are provided. Advantageous designs are the subject of the following description.

[0004] In the after-treatment of exhaust gases in motor vehicles, the so-called SCR method (Selective Catalytic Reduction) can be used, especially for the reduction of nitrogen oxides (NOx). x Here, an aqueous urea solution (HWL) is introduced as a reducing agent into the typically oxygen-rich waste gas.

[0005] For this purpose, a metering module or metering valve can be used as part of the fluid supply system. This module or valve includes nozzles to inject or carry the urea aqueous solution into or into the exhaust gas stream. Upstream of the SCR catalyst, the urea aqueous solution reacts to form ammonia, which then combines with nitrogen oxides on the SCR catalyst to produce water and nitrogen.

[0006] Typically, the metering valve is connected to the delivery unit via a pressure line. A pump or transfer pump in the delivery unit pumps the urea solution from the reducing agent tank to the metering valve or metering module. Additionally, in most cases, a reflux device is connected to the reducing agent tank, through which excess urea solution can be returned. A baffle or throttle valve in the reflux device controls the reflux.

[0007] This invention investigates a method for emptying a fluid supply system, particularly an SCR supply system. The fluid supply system based on this invention comprises a delivery unit, a delivery pipeline, a pressure pipeline, and a return pipeline with a check valve. The delivery unit is connected to a fluid tank or reducing agent tank via the delivery pipeline, the delivery unit is connected to a metering module via the pressure pipeline, and the delivery unit is connected to the fluid tank via the return pipeline. The return pipeline can, in particular, branch off from the pressure pipeline.

[0008] The delivery unit can operate in the conventional delivery direction, allowing fluid to be drawn from the fluid tank via a delivery pipe and delivered into a pressure pipe (and then to the metering module via the pressure pipe). Alternatively, it can operate in the opposite direction, allowing fluid to be returned to the fluid tank via the delivery pipe. For this purpose, the delivery unit typically has a pump, such as a diaphragm pump or a piston pump, to which the delivery and pressure pipes are connected by one or more suitable valves. For example, a suitable directional valve can be provided to switch the pump between the delivery and pressure pipes, allowing fluid to be delivered in both the conventional and opposite directions, while the pump itself only provides one delivery direction. However, an actively controllable valve that can reverse the delivery direction may also be considered.

[0009] The present invention further proceeds from this point, namely, to empty the fluid supply system, for example, after the vehicle or its internal combustion engine has stopped, a first purging process is performed in which the delivery pipes, pressure pipes, and return pipes are emptied at least as well as possible. For this purpose, in simple cases, the delivery unit can be operated against the conventional delivery direction. However, the method described in DE10 2016 210 262 A1 is also suitable, and explicit reference is made to that document. Specifically, here the metering module or metering valve is first closed, and then the delivery unit is operated against the conventional delivery direction, thereby returning fluid from the delivery pipes and the delivery unit itself to the fluid tank. The metering module is then opened, allowing fluid to also reach the fluid tank from the metering module, pressure pipes, and return pipes. The metering module is then closed again, and the delivery unit can be stopped or shut off.

[0010] While this method effectively empties the fluid supply system to a large extent, some fluid may still remain in the pressure sensor or its cavity, typically located in the delivery unit, especially when the pressure sensor is located in the return line. The check valve in the return line has been shown to play a significant role in this process, as it remains closed during the aforementioned (first) evacuation process.

[0011] In this context, now within the framework of the proposed invention, a second purging process is performed after the aforementioned first purging process. In this case, after the conveying unit is turned on again where possible, the second purging process is carried out with the metering module closed and along the conveying direction at or with a first power level until a predetermined standard is reached. The first power level has a power of, in particular, between 2% and 40% of the maximum power of the conveying unit, preferably between 5% and 30%, and more preferably between 5% and 15%. Particularly suitable, for example, is 10% of the maximum power. Such a (relatively) small power level also means a relatively small conveying flow provided by the conveying unit, which carries air from the conveying unit to the return pipe (where the fluid has been removed from the pipe and the conveying unit during the first purging process, leaving only air). The return pipe up to the check valve can also be referred to as the return channel, on which, for example, a pressure sensor is then arranged.

[0012] The pre-defined standard is specifically chosen such that, upon reaching this standard, the check valve has been opened by overpressure in the return pipe. That is, the pressure is increased by operating the delivery unit until the check valve opens (the metering valve is closed). Thus, any fluid that may still be present in the return pipe is delivered through the return pipe to the fluid tank, and, in particular, any fluid that may be present in the pressure sensor is removed from it, as shown.

[0013] In this process, particular care should be taken to ensure that, although the pressure is increased to the point that the check valve opens, no fluid is drawn from the fluid tank into the delivery unit as much as possible. This can be achieved, for example, by monitoring the aforementioned criteria in a suitable manner. The pre-defined criteria preferably include the pressure drop in the fluid supply system. The pressure drop (the pressure being known, for example, using the pressure sensor already mentioned) means that the opening pressure of the check valve has been reached or exceeded, allowing air, along with any possible fluid, to escape, thus causing the pressure to drop particularly quickly. At this point, it is possible to consider, for example, determining a pressure gradient, at which a significant pressure drop is identified.

[0014] However, equally appropriate, the pre-defined criteria include the end of a pre-defined duration. This duration can then be pre-defined, in particular, based on the volume of the fluid supply system and the first power stage. If the volumetric flow rate provided by the delivery unit and the volume present in the delivery unit and the important piping (in which air may be compressed) are known, it can be determined how long the delivery unit must operate until a sufficiently high pressure is generated for the check valve to open.

[0015] Using the proposed approach, not only can the pipes and delivery units themselves be better emptied, but fluid that may be present in the pressure sensor or its cavity can also be removed. As a result, damage caused by cryogenic fluid freezing can be reduced and thus the lifespan of the components can be increased.

[0016] After a predetermined standard is reached, or from the point onwards, the conveying unit is preferably operated in the reverse conveying direction, and particularly with or using a second power level higher than the first power level. Suitably, the second power level has a power between 2% and 60% of the maximum power of the conveying unit, preferably between 5% and 40%, and more preferably between 25% and 35%. Particularly suitable is, for example, 30% of the maximum power. In this way, fluid that might have been drawn into the conveying pipe while the conveying unit is operating at the first power level can be removed from the conveying pipe and returned to the fluid tank.

[0017] Subsequently, for example, when the pressure reaches the value before or at the start of the second venting process, the power of the conveying unit can be reset to zero, and it can be (e.g., by switching the appropriate directional valve) adjusted back to the normal conveying direction—as preparation for the next normal conveying operation—before the conveying unit can be completely disconnected. It is also possible to consider performing the second venting process multiple times, if it proves suitable.

[0018] In particular, the computing unit according to the invention is set up in a programming manner, such as a motor control device or an exhaust aftertreatment control device for a motor vehicle, for executing the method according to the invention.

[0019] It is also advantageous to implement the method according to the invention in the form of a computer program or a computer program product (which has program code for performing all method steps), as this results in particularly low costs, especially if the implemented control equipment is also used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memory, EEPROMs, DVDs, and so on. The program can also be downloaded via computer networks (the Internet, intranets, etc.).

[0020] Other advantages and designs of the present invention will become apparent from the description and drawings. Attached Figure Description

[0021] The invention is illustrated schematically with the aid of the embodiments in the accompanying drawings, and the invention is described below with reference to the accompanying drawings.

[0022] Figure 1 A fluid supply system is schematically illustrated, in which the method according to the invention can be performed;

[0023] Figure 2The process of the method according to the invention is schematically illustrated in a preferred embodiment;

[0024] Figure 3 In a preferred embodiment, the pressure and control trends of the conveying unit utilizing the method according to the invention are schematically shown. Detailed Implementation

[0025] exist Figure 1 The diagram schematically illustrates a fluid supply system 100, which enables the execution of the method according to the invention. The fluid supply system 100 is specifically configured as an SCR system and includes a delivery unit 110 having a pump or delivery pump 140 and a directional valve 142. This delivery unit is configured to draw the reducing agent 121 (or a reducing agent solution) as the fluid to be delivered along a conventional delivery direction via a delivery conduit 130 from the fluid tank or reducing agent tank 120 and deliver it via a filter 150 and a pressure conduit 132 to a metering module or metering valve 136. The reducing agent 121 is then injected into the exhaust gas line 170 of the internal combustion engine.

[0026] In addition, the fluid supply system 100 includes a return pipe 134 branching from the pressure pipe 132, through which the reducing agent can be returned from the system to the reducing agent tank 120. In addition to a baffle or throttle valve 152 providing local flow resistance, the return pipe 134 also includes a check valve 154 with a specific opening pressure.

[0027] In addition, a pressure sensor 144 is provided, which is configured to measure the pressure in the return pipe, specifically in the section before the check valve 154 (also referred to as the return channel). For example, a computing unit 160, configured as an exhaust gas aftertreatment control device, is connected to the pressure sensor 140 and obtains information about the pressure in the corresponding pipe from the pressure sensor. Furthermore, the exhaust gas aftertreatment control device 160 is connected to the delivery unit 110, particularly the pump 140, and to the metering module 136 so that the metering module can be controlled.

[0028] By operating the reversing valve 142, the conveying direction of the conveying unit 110 can be reversed, so that the fluid can be conveyed to the reducing agent tank 120 via the conveying pipe 130 in the opposite direction to the normal conveying direction.

[0029] exist Figure 2 The preferred embodiment schematically illustrates the flow of the method according to the invention. Figure 3In a preferred embodiment, the pressure and control trends of a delivery unit utilizing the method according to the invention are schematically illustrated, where p gives (exemplary) pressure in mbar, L gives (exemplary) power of the delivery unit or pump, and S gives the position of the directional valve; the trends are plotted over time t. A general description will follow. Figure 2 and Figure 3 .

[0030] First, for example, after the internal combustion engine is stopped, a first purging process 200 is performed in the fluid supply system. As already mentioned, this first purging process can be performed, for example, as described in DE 10 2016 210 262 A1. The first purging process typically ends with the disconnection of the delivery unit and the shutdown of the metering module.

[0031] The second purging process is then carried out, which includes, for example, subsequent steps 210, 220, 230 and 240.

[0032] First, according to step 210, at time t1, the delivery unit operates at, for example, 10% of its first power level (or "duty cycle") L1, and along the normal delivery direction, meaning the reversing valve's position S is 0, and the metering module remains closed. If this is not already the case, then the metering module is closed accordingly. Subsequently, air in the delivery pipe is pumped into the return pipe—but also into the pressure sensor or its cavity. However, fluid is deliberately avoided here, and in any case, it is not pumped into the pressure pipe or the return pipe.

[0033] This process continues until a pre-defined standard is reached. As mentioned, this standard may include, for example, voltage drop or duration. This is in... Figure 3 As can be seen, the pressure p rises from time point t1 because the metering module is off and the check valve is initially closed anyway. However, once the check valve's opening pressure is reached (approximately 70 mbar in the example shown), the check valve opens, air escapes along with any fluid that may be in the pressure sensor or its cavity, and the pressure p drops rapidly. A specific gradient G of pressure p can be plotted exemplarily; for example, reaching this gradient can be considered as a criterion being met or achieved. This is the case at time point t2.

[0034] However, the duration from time point t1 to time point t2 can also be calculated, taking into account the volumetric flow rate of the delivery unit at power level L1 and the volume of air to be pumped or transported. For this purpose, knowledge of the fluid supply system volume is necessary; however, for a specific fluid supply system or a particular type, this can be obtained, for example, through simple measurement or otherwise.

[0035] According to step 220, at time point t2, the conveying direction of the conveying unit is reversed by switching the reversing valve and setting the pose S to 1. Simultaneously, or possibly shortly thereafter, the conveying unit is then operated at, for example, a higher power level L2 of 30%. In this way, fluid that may be present in the conveying pipe and previously pumped out is conveyed back into the fluid tank, further reducing the pressure.

[0036] According to step 230, at time point t3, when the pressure, for example, reaches the initial value before or at time point t1 again, the power of the conveying unit is reset to zero, L=0. Then, according to step 240, at time point t4, the entire conveying unit is disconnected and the reversing valve 142 is switched back to the normal conveying direction in preparation for subsequent use, S=0.

[0037] Depending on the situation, after the standard is reached, at time point t2, the power of the conveying unit (which is then adjusted to the normal conveying direction, that is, the pose S has a value of 0) can be reset to zero according to step 231, and then the process can continue as before according to step 240.

[0038] The proposed method can therefore be used to evacuate the fluid supply system particularly effectively, and in particular, to evacuate the pressure sensor or its cavity, thereby preventing potential damage caused by frost.

Claims

1. Method for emptying a fluid supply system (100) having a delivery unit (110), a delivery line (130), a pressure line (132) and a return line (134) with a non-return valve (154), the delivery unit (110) being connected via the delivery line with a fluid tank (120), the delivery unit (110) being connected via the pressure line with a metering module (136), the delivery unit (110) being connected via the return line with the fluid tank (120), the delivery unit (110) being operable along a regular delivery direction, so that fluid (121) is sucked and delivered via the delivery line (130) into the pressure line (132) and into the return line (134), and the delivery unit being operable against the delivery direction, wherein the delivery unit (110) is operated in a second emptying process after a preceding first emptying process (200) in a state with closed metering module (136) and along the delivery direction at a first power level (LI) until a predefined criterion is reached, wherein the predefined criterion is chosen so that the non-return valve (154) is opened by an overpressure in the return line (134) when the predefined criterion is reached. the delivery unit (110) is operated in the second emptying process against the delivery direction since the predefined criterion is reached. the delivery unit (110) is operated in the second emptying process against the delivery direction at a second power level (L2) higher than the first power level (LI) since the predefined criterion is reached. the second power level (L2) is a power between 2% and 60% of a maximum power of the delivery unit (110). the second power level (L2) is a power between 5% and 40% of a maximum power of the delivery unit (110). the second power level (L2) is a power between 25% and 35% of a maximum power of the delivery unit (110). the first power level (LI) is a power between 2% and 40% of a maximum power of the delivery unit (110). the first power level (LI) is a power between 5% and 30% of a maximum power of the delivery unit (110). the first power level (LI) is a power between 5% and 15% of a maximum power of the delivery unit (110). the predefined criterion comprises a pressure drop in the fluid supply system (100). the predefined criterion comprises an end of a predefined time duration. the time duration is predefined depending on a volume of the fluid supply system (100) and the first power level (LI). wherein 13. Computing unit (150) which is set up to perform all method steps of the method according to any one of claims 1 to 12.

14. Computer program product which is set up to perform all method steps of the method according to any one of claims 1 to 12. ​ 2. The method of claim 1, wherein, ​ 3. The method of claim 2, wherein, ​ 4. The method of claim 3, wherein, ​ 5. The method of claim 4, wherein, ​ 6. The method of claim 5, wherein, ​ 7. The method of any one of claims 1 to 6, wherein, ​ 8. The method of claim 7, wherein, ​ 9. The method of claim 8, wherein, ​ 10. The method of any one of claims 1 to 6, wherein, ​ 11. The method of any one of claims 1 to 6, wherein, ​ 12. The method of claim 11, wherein, ​ ​ ​ 15. Machine-readable storage medium having stored thereon a computer program, the computer program being configured to perform all the steps of the method according to any one of claims 1 to 12.

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