DE112014002374T5 - Method for detecting a blockage - Google Patents

Abstract

A method of detecting a flow obstruction (205) in a fluid system (201) wherein the flow obstruction is between a first fluid conduit (203) and a second fluid conduit (204) connected to the first fluid conduit via the flow obstruction (205) , The method includes controlling a flow source (202) connected to the first fluid line (203) such that at least one inflow (208) is created in the first fluid line (203) and controlling a metering device (206). which is connected to the second fluid line (204), such that at least one outflow (209, 219) is generated from the second fluid line. The method comprises generating one of said flows (209) as a time dependent flow of known magnitude and having a time constant τ and said at least one remaining flow (208, 219) as a substantially constant flow during the time constant τ, such that at least one of said fluid lines (203, 204) pressure fluctuations arise so that the amplitude of the pressure fluctuations can be measured and on the basis of the measured amplitude, the blockage (205) can be detected.

Description

Field of the invention

The present invention is a method for detecting a blockage. More particularly, but not exclusively, the invention relates to the realization of such a method for detecting the degree of blockage of a filter in an SCR system (SCR = Selective Catalytic Reduction) for exhaust gas purification. Another object of the invention is a computer program product comprising program code for carrying out a method according to the invention, and an electronic control device.

Technical background

In order to meet the current requirements for exhaust gas purification, today's motor vehicles are usually equipped with a catalyst in the exhaust pipe to achieve a catalytic conversion of environmentally harmful exhaust gas constituents into less environmentally harmful substances. One method used to achieve effective catalytic conversion is based on injecting a reductant into the exhaust gases before the catalyst. A reduction substance contained in or generated by the reducing agent enters the catalyst with the exhaust gases where it is absorbed at active sites in the catalyst, resulting in accumulation of the reducing agent in the catalyst. The accumulated reducing agent can either desorb, that is, dissolve from the active sites, or react with an exhaust gas substance, wherein such an exhaust gas substance is converted into a harmless substance. Such a reduction catalyst may be, for example, an SCR catalyst (SCR = Selective Catalytic Reduction). This type of catalyst is referred to below as the SCR catalyst. An SCR catalyst selectively reduces NO _x in the exhaust gases but not the oxygen in the exhaust gases. In an SCR catalyst is usually a reducing agent based on urea or ammonia, z. B. AdBlue injected into the exhaust gases in front of the catalyst. When urea is injected into the exhaust gases, ammonia forms and this ammonia is the reductant that contributes to the catalytic conversion in the SCR catalyst.

The documents SE 1150862 and WO 2011/142708 describe SCR systems for injecting a reducing agent into an exhaust system upstream of an SCR catalyst. Such an SCR system comprises a container for the reducing agent. The SCR system also includes a pump that can pump said reducing agent from the container through a suction hose and through a pressurized hose to a metering device placed on an exhaust system in the vehicle, such as an exhaust pipe of the exhaust system , The metering device may, according to operating procedures stored in a control device of the vehicle, inject a required amount of the reducing agent into the exhaust gas line upstream of the SCR catalytic converter. In order to more easily control the pressure at a low or no dosage level, the system may also have a return hose routed from one pressure side of the system back to the reservoir. According to this configuration, it is possible to cool the metering device with the reducing agent which, when cooled, flows from the reservoir through the pump and the metering device back to the reservoir. In this way, an active cooling of the metering device is achieved. The return from the metering device to the container is substantially constant. The SCR system further includes a filter for filtering the reductant prior to metering with the metering device. The filter may protect the dosing device from particle clogging, such as soil particles, dirt, etc. The filter may be a paper filter, but of course other types of filters may be used.

One problem with such filters is that they can clog easily, resulting in flow blockage, so that the reductant can not be dosed as desired. Such a blockage must be detected and remedied, otherwise the emission of NO _x gases increases. In the patent WO 2011/142708 this problem is solved by continuously measuring the accumulated amount of liquid provided by a metering device. Based on these measurements, it is determined if the filter needs to be replaced. This method is based on assumptions about a certain amount of the provided reducing agent, which leads to a certain degree of clogging of the filter. In order to avoid the unnecessary replacement of filters and the deterioration of the exhaust gas purification, it is desirable to have a possibility of detecting whether the filter is clogged.

One way to detect a clogging, such as a filter, is to measure the pressure drop across the fully or partially clogged filter. If the flow rate of the filter is known, the degree of clogging can be determined. However, the pressures in the fluid lines on the filter on both sides of the filter as well as the flow rate of the blockage must be known. Therefore, pressure sensors are required for both fluid lines. Alternatively, at least the fluid line must be on a Side consist of a closed space with a known elasticity. An example of this is a pressurized container of known size containing a pressurized medium. This container is emptied by a blockage, for example in the form of a throttle. Based on the knowledge of the medium, the degree of constipation can be estimated. Unfortunately, this technology can not be used on a fluid system where there are unknown inflows and outflows at the same time as the net flow into or out of the reservoir is critical to the pressure drop.

Summary of the invention

It is an object of the present invention to provide a method for detecting clogging in a fluid system at an early stage and by simple means without compromising the normal function of the fluid system.

According to one aspect of the invention, this object is achieved by a method for detecting a blockage in a fluid system. The blockage is located between a first fluid line and a second fluid line, which is connected by the blockage with the first fluid line. By the method, a flow source connected to the first fluid line can be controlled so that at least one inflow into the first fluid line is generated, and a metering device connected to the second fluid line can be controlled so that at least one outflow from the first fluid line second fluid line is generated. The method also includes generating one of said flows as a time-dependent flow of known magnitude and with a time constant τ and the remainder of said at least one flow as a constant or substantially constant flow during the time constant τ such that pressure fluctuations occur in at least one of said fluid lines in order to be able to measure the extent of the pressure fluctuations in one of the said fluid lines, in which the pressure fluctuations occur, and on the basis of the measured circumference the blockage can be determined.

Since the amount of pressure fluctuation depends on the degree of clogging, it is possible to detect if clogging is present by measuring the circumference. If there is no obstruction, the amount of pressure fluctuations is smaller. The extent of the pressure fluctuations increases with increasing blockage, since the two fluid lines are increasingly delimited by the blockage. By means of the method according to the invention, a blockage can be detected at an early stage before it reaches a critical state and leads to serious consequences. The same can be achieved by measuring only the pressure in one of the fluid lines delimited by the blockage. Thus, a pressure sensor is sufficient to measure the pressure drop at the blockage, which reduces the equipment requirement compared to the known technique described above. In addition, when the method is performed in an SCR system described above, it also does not interfere with the normal operation of the system since the method can be performed independently of constant or substantially constant inflows and outflows of the two fluid lines and a time dependent flow source already exists is. The blockage can thus be detected while at the same time fluid is flowing through the system as usual.

In one embodiment, the clogging is detected based on the measured perimeter, the magnitude of the time dependent flow, and the volume V and elasticity E of the fluid system. By knowing these characteristics, a more reliable detection of the clogging is achieved.

In one embodiment, the measured amount is used as a test size t ₁ that is tested against an alarm criterion, and when the alarm criterion is met, an error code is generated. As a result, a control device, which is used for automatically carrying out the method, can generate an alarm if the blockage has to be rectified. By directly using the measured perimeter, no calculations of the actual degree of clogging must be made by the controller.

According to another embodiment, the degree of clogging is calculated based on the measured perimeter, the time dependent flow magnitude, the volume V ₁ and the elasticity E _{1 of} the first fluid conduit and the volume V ₂ and the elasticity E _{2 of} the second fluid conduit. By knowing the stated properties, the degree of blockage can be calculated, which is useful when the blockage reaches critical levels only when it exceeds a certain degree. Then measures can be taken at the right time and it can be an exchange z. As a filter can be avoided because the filter is only slightly clogged and the fluid system still works satisfactorily.

According to one embodiment, the calculated degree is used as a test variable t ₁ which is tested against an alarm criterion, and when the alarm criterion is met, an error code is generated generated. As a result, a control device, which is used for automatically carrying out the method, can generate an alarm if the blockage has to be rectified.

According to one embodiment, the alarm criterion is fulfilled if the test variable t ₁ exceeds a predetermined threshold value. It is an easy way to determine if a blockage needs to be corrected. Regardless of whether the calculated degree of clogging or the measured amount of pressure fluctuations is used as the test variable t ₁ , the threshold value may advantageously be chosen to suit the given fluid system, ie, the feed volumes, elasticity, characteristics of the fluid Fluids, the environmental parameters such as pressure and temperature, the time-dependent flow rate, etc. of the fluid system is optimized.

According to a further embodiment, the method is carried out for a system in which the said fluid lines differ in volume. Preferably, the volume of one of said fluid lines is at least ten times as large as the volume of the other of said fluid lines. The pressure fluctuations may be more pronounced in such a system in the smaller of the two fluid lines, which facilitates the detection of the blockage.

According to another embodiment, the time-dependent flow is generated in that of the said fluid lines which has the smaller volume. This usually results in the most pronounced pressure fluctuations.

According to another embodiment, the amount of pressure fluctuations is measured in that of the said fluid lines which has the least volume. According to another embodiment, the extent of the pressure fluctuations in that of said fluid lines is measured, in which the time-dependent flow is generated. This makes it very easy to detect the pressure fluctuations, as they are usually very pronounced in both cases. Of course, the one of the said fluid lines having the least volume may at the same time be the said fluid line in which the time-dependent flow is generated.

According to another embodiment, at least one said inflow into the first fluid conduit is created by controlling a flow source in the form of a pump to pump the fluid from a container into said first fluid conduit. By using a pump, said inflow can be generated either as a time dependent or as a constant or substantially constant flow.

According to a variant of this embodiment, the fluid from the second fluid conduit to said container flows back in a said outflow in the form of a return flow, and fluid is discharged from the fluid system in a said outflow in the form of a consumption flow. As a result, a flow of fluid is generated in the system, which is advantageous if a part of the fluid system depends on that the flow cools. In a system such as injecting a reductant upstream of an SCR catalyst, a portion of the reductant is often used for metering in the exhaust system by the metering device effluent and the portion of the reductant that is not used returns to the tank in a return flow , This part of the reducing agent is advantageously used as a coolant in order to avoid overheating of the metering device. The reductant in the recycle stream is filtered, and the SCR system thus becomes self-cleaning to some extent. The returned, filtered reducing agent thereby does not contribute to a further blockage of the filter.

According to one embodiment, the metering device is controlled so that said time-dependent flow is generated. This is advantageous in applications where it is desired for the fluid to leave the fluid system in the form of intermittent dosages rather than continuous outflow. This is often the case in systems for injecting a reductant upstream of an SCR catalyst.

According to another embodiment, the time-dependent flow is generated in the form of a regular flow. Preferably, the regular flow is generated approximately in the form of a rectangular wave. Such a flow can be easily by z. B. achieve the opening and closing of a valve, whereby a flow is generated approximately in the form of a square wave with a certain time constant. Preferably, the regular flow is generated at regular intervals of 0.1 to 10 seconds. More advantageously, 0.2-5 seconds and more preferably 0.25-1 seconds.

In one embodiment, the method is performed for a fluid system that includes flow blocking through a filter that is clogged to some extent, thereby detecting the degree of clogging of the filter.

According to a further embodiment, the method is for a system for injecting a reducing agent, such as a Urea- or ammonia-based reducing agent, performed before an SCR catalyst in an exhaust pipe of an internal combustion engine. The method is well suited for use with such a system, since the system typically includes a time dependent flow source, such as a metering device, which supplies the reductant in intermittent metering to the flue, and the clogging of a filter in such a system may need to be independent of be measured substantially constant flows, which are also present in the system. The method is also advantageous, since no additional pressure transducer is required, but the blockage can be detected with the existing equipment in the system.

According to a further aspect of the invention, the object is solved by a computer program which can be downloaded into an internal memory of a computer and which comprises software for controlling the steps according to the above-mentioned method when said program is executed by a computer.

According to another aspect of the invention, the object is solved by a computer program product comprising a computer readable data storage medium storing the computer program code of a computer program as indicated above.

According to a further aspect of the invention, the object is achieved by an electronic control device comprising an execution means, a memory connected to the execution means and a data storage medium connected to the execution means. The computer program code in a computer program is stored on said data storage medium as indicated above.

According to a further aspect of the invention, the object is achieved by a motor vehicle comprising an electronic control device as indicated above.

Further advantageous features and advantages of the invention will become apparent from the following description.

Drawing Summary

The invention will be described below with reference to embodiments with reference to the accompanying drawings.

Fig. 10 is a schematic diagram of a system in which the method according to the invention can be carried out.

FIG. 12 is a schematic diagram of a system for injecting reductant upstream of an SCR catalyst. FIG.

is a schematic diagram of a control device for carrying out a method according to the invention.

Detailed description of embodiments of the invention

The term "blockage" here refers to the degree of blockage, d. H. also on a partial constipation. The partial blockage may be on a filter or in other locations in the fluid system, e.g. B. on a throttle or the like.

Fluid system refers to a liquid or gas system. Preferably, but not necessarily, a system is designed to flow through a liquid. Preferably, but not necessarily, this is a fluid system in a vehicle. The fluid system may be, for example, a system for injecting a reductant upstream of an SCR catalyst into an exhaust pipe of an internal combustion engine, a fuel system for supplying an internal combustion engine with fuel, a hydraulic brake system in a vehicle, a hydraulic system, a pneumatic system, etc.

The term "fluid conduit" refers to a conduit for guiding and transporting a fluid, such as a reducing agent in liquid form. The cable can be of any size. The conduit may be made of any suitable material, such as plastic, rubber or metal.

The term metering device refers to a device that includes a valve device that can be controlled to produce a constant or time-dependent flow of known magnitude.

By a constant or substantially constant flow is meant a flow whose time constant is considerably greater than the time constant of the time-dependent flow, so that the constant or substantially constant flow fluctuations over time are much slower than the time-dependent flow fluctuations over time.

A first fluid system 101 in which the method according to the invention can be carried out is schematically shown in FIG shown. The fluid system includes a flow source in the form of a pressurized fluid container 102 With a volume V _B. a first fluid line 103 with a volume V ₁ , a second fluid line 104 with a second volume V ₂ and flow blocking 105 between the first and second fluid lines. A metering device 106 is with the second fluid line and with a pressure sensor 107 connected.

To calculate the degree of flow blocking 105 becomes an inflow 108 from the pressurized container 102 in the first fluid line 103 generated. Using the dosing device 106 becomes a time-dependent outflow 109 of a known magnitude and with a time constant τ (ie, the time it takes for the flow to increase / decrease to around 63% of its maximum strength) from the second fluid line 104 generated. Then arise pressure fluctuations in the fluid system 101 , Using the pressure sensor 107 becomes the pressure in the second fluid line 104 measured and the extent of pressure fluctuations detected. Since the amplitude of the pressure fluctuations is a function of the degree of clogging, clogging can be detected, for example, by observing how the amplitude changes over time. The higher the degree of clogging, the more the amplitude of the pressure fluctuations increases. Based on the knowledge of the input volume V _B , V ₁ and V _{2 of} the fluid system and the elasticity E _{B of} the container 102 and the respective elasticity E ₁ and E _{2 of} the fluid lines and the magnitude of the outflow, the degree of clogging can be estimated. If restrictions of at least the size of the flow blocking 105 between the pressurized container 102 and the first fluid line 103 in the fluid system 101 can be present, the volume and elasticity of the container 102 be ignored.

In a fluid system comparable to the system described above, instead of a pressurized container, a pump connected to a fluid container may be used as the flow source. The pump may be controlled to produce a time-dependent inflow, and the metering device may then generate a constant outflow, or generate an outflow that is substantially constant during the time constant τ of the inflow. The pressure sensor may be connected to one of the two fluid lines, but suitably the fluid system is designed so that the pressure sensor is connected to the fluid line, which has the smaller volume, since the pressure fluctuations are most pronounced in this fluid line. Preferably, but not necessarily, this fluid line is the fluid line in which the time-dependent flow is generated, which can lead to even more pronounced pressure fluctuations.

A fluid system 201 for injecting a reducing agent before an SCR catalyst (not shown) in an exhaust pipe of an internal combustion engine is schematically in shown. The system includes a flow source in the form of a pump 202 , the reducing agent via a fluid line 211 from a container 212 in a fluid line 203 inflated. In direct connection to the fluid line 203 there is a main filter 205 and behind it is a fluid line 204 placed. Associated with this is a metering device 206 , which can be electrically controlled by a control device (not shown) and the reducing agent in the said, not shown exhaust pipe via a metering valve 210 can inject. The metering device 206 includes an electronic control board (not shown) for handling communication with the controller. The metering device 206 may also include plastic or rubber components that may melt or otherwise be adversely affected by excessive temperatures. A pressure sensor 207 serves to measure the pressure in the second fluid line 204 , To the metering device 206 is a return line 213 connected by a choke 214 to the container 212 returns. Except for the main filter 205 are several filters 215 . 216 . 217 placed in the fluid system. In this case, the filter is 217 considerably larger than the main filter 205 ,

When used, a substantially constant inflow 208 of reducing agent in the fluid line 203 using the pump 202 generated. The reducing agent is in the main filter 205 filtered and flows into the fluid line 204 , Behind the fluid line 204 the reducing agent is using the metering device 206 dosed fed to the exhaust pipe. In this case, the metering device 206 by opening and closing the dosing valve 210 so controlled that an outflow 209 a known thickness of the second fluid line 204 is generated in the form of approximately a square wave. About the metering device 206 also will not metered reducing agent in a substantially constant return flow 219 over the throttle 214 to the container 212 recycled. Thanks to the return flow 219 can the metering device 206 be continuously cooled using the reducing agent. When the metering valve 210 is closed, pressure is in the direction of the throttle 214 in the fluid line 204 using the pump 202 built up. When the metering valve 210 is opened, the pressure decreases, since the reducing agent then through both the metering valve and through the throttle 214 flows. The pressure fluctuations are caused by the pressure sensor 207 measured. The controller calculates the amplitude of the pressure fluctuations, and based on this calculation, the degree of blockage of the main filter 205 be determined. Based on the measured amplitude, the strength of the time-dependent flow, the volume V ₁ and the elasticity E _{1 of} the fluid line 203 and the volume V ₂ and the elasticity E _{2 of} the fluid line 204 is the degree of blockage of the main filter 205 calculated.

In this embodiment of the method according to the invention, the fluid system is 201 with a first fluid line 203 executed, whose volume V _{1 is} about ten times as large as the volume V _{2 of} the second fluid line 204 , The time-dependent flow 209 is in the form of a square wave in the second fluid line 204 generated, in which also the pressure is measured. This allows the pressure fluctuations with the pressure sensor 207 be easily measured. The degree of blockage of the main filter 205 can be independent of the essentially constant inflows and outflows 208 . 219 of the reducing agent in the fluid lines 203 . 204 be determined. The fact that the flows are essentially constant in this case results in the time constant of the time-dependent flow 209 , which in this case has the shape of a square wave, is considerably smaller than potential time constants of the other currents 208 . 219 is. This may, for example, result in the time constant τ for the time-dependent flow being in the region of tenths of a second, while the other flows vary over a considerably longer time, such as with a time constant in the interval 5-30 s.

The calculated degree of clogging may conveniently be used as a test variable t ₁ which is tested by the controller using an alarm criterion. If the alarm criterion is met, an error code is generated. The alarm criterion can be selected, for example, such that it is fulfilled if the test variable t ₁ exceeds a predetermined threshold value.

Instead of calculating the degree of blockage, it may be expedient to use the measured amplitude of the pressure fluctuations as test variable t ₁ . In this case, the threshold may be chosen to take into account the properties of the fluid system, such as the volumes and elasticity of the fluid lines, so that an actual value for the degree of clogging need not be calculated. Suitable thresholds may e.g. B. be determined empirically or by means of a simulation. For certain applications, however, the properties of the fluid system may vary depending on temperature and pressure, for example. For example, in a fuel system, the pressure may vary between about 500 and 2000 bar, and the elasticity of the system will be highly dependent on the pressure. In such cases, it may be advantageous to either calculate the degree of clogging and use it as a test variable t ₁ or to use a threshold value that is, for example, pressure-dependent.

A computer program code for carrying out a method according to the invention is expediently contained in a computer program which can be loaded into the internal memory of a computer, for example into the internal memory of an electronic control device of a motor vehicle. Such a computer program is expediently provided by a computer program product comprising a data storage medium, readable by an electronic control device, in which the computer program is stored. Said data storage medium is, for example, an optical data storage medium in the form of a CD-ROM, a DVD, etc., a magnetic data storage medium in the form of a hard disk, a floppy disk, a cassette, etc. or a flash memory or a memory in the form of ROM, PROM, EPROM or EEPROM.

schematically shows an electronic control device 40 that is an execution agent 41 includes, for example, a central processing unit (CPU) for executing computer software. The execution agent 41 communicates with a memory 42 in RAM, for example, over a data bus 43 , The control device 40 also includes a data storage medium 44 , for example in the form of a flash memory, or a memory in the form of ROM, PROM, EPROM or EEPROM. The execution agent 41 communicates with the data storage medium 44 over the data bus 43 , A computer program comprising computer program code for carrying out a method according to the invention is located on the data storage medium m 44 saved.

The invention is in no way limited to the embodiments described above. For an expert in the field of the invention, many possible modifications of the invention should be readily apparent, without departing from the scope of the invention, which is defined by the appended claims.

Claims (21)

Method for detecting a flow blockage ( 105 . 205 ) in a fluid system ( 101 . 201 ) between a first fluid line ( 103 . 203 ) and a second fluid line ( 104 . 204 ) caused by flow blocking ( 105 . 205 ) is connected to the first fluid line, the method for controlling a flow source ( 102 . 202 ), which is connected to the first fluid line ( 103 . 203 ), so that at least one inflow ( 108 . 208 ) in the first fluid line ( 103 . 203 ) generated and controlling a metering device ( 106 . 206 ) connected to the second fluid line ( 104 . 204 ) is connected, so that at least one outflow ( 109 . 209 . 219 ) is generated from the second fluid line, characterized in that: the method comprises generating one of said flows ( 109 . 209 ) as a time-dependent flow of known magnitude and with a time constant τ and said at least one remaining flow ( 108 . 208 . 219 ) as a constant or substantially constant flow during the time constant τ, so that in at least one of said fluid lines ( 103 . 104 . 203 . 204 ) Pressure fluctuations occur, so that the amplitude of the pressure fluctuations in one of said fluid lines ( 104 . 204 ) can be measured, in which the pressure fluctuations arise, and based on the measured amplitude, the blockage ( 105 . 205 ) can be recognized. Method according to claim 1, characterized in that the blockage ( 105 . 205 ) on the basis of the measured amplitude, the strength of the time-dependent flow ( 109 . 209 ) and the volume V and the elasticity E of the fluid system is detected. A method according to claim 1 or 2, characterized in that the measured amplitude is used as a test variable t ₁ , which is tested on the basis of an alarm criterion, and that, if the alarm criterion is met, an error code is generated. Method according to claim 1, characterized in that the degree of blockage ( 105 . 205 ) on the basis of the measured amplitude, the strength of the time-dependent flow ( 109 . 209 ), the volume V ₁ and the elasticity E _{1 of} the first fluid line and the volume V ₂ and the elasticity E _{2 of} the second fluid line is calculated. A method according to claim 4, characterized in that the calculated degree is used as a test variable t ₁ , which is tested on the basis of an alarm criterion, and that, when the alarm criterion is met, an error code is generated. A method according to claim 3 or 5, characterized in that the alarm criterion is met when the test quantity t ₁ exceeds a predetermined threshold. Method according to one of the above-mentioned claims, characterized in that it is carried out for a system in which said fluid lines ( 103 . 104 . 203 . 204 ) vary in volume. Method according to claim 7, characterized in that it is carried out for a system in which the volume of one of said fluid lines ( 203 ) is at least ten times as large as the volume of the other of said fluid lines ( 204 ). Method according to claim 7 or 8, characterized in that the time-dependent flow in that of said fluid lines ( 104 . 204 ), which has the least volume. Method according to one of the above-mentioned claims 7 to 9, characterized in that the amplitude of the pressure fluctuations in those of said fluid lines ( 104 . 204 ), which has the smallest volume. Method according to one of the above-mentioned claims, characterized in that the amplitude of the druch fluctuations in that of said fluid lines ( 104 . 204 ), in which the time-dependent flow ( 109 . 209 ) is produced. Method according to one of the above-mentioned claims, characterized in that at least one said inflow ( 208 ) in the first fluid line ( 203 ) is generated by a flow source in the form of a pump ( 202 ) is controlled so that the fluid from a container ( 212 ) into said first fluid line ( 203 ) is pumped. Method according to claim 12, characterized in that fluid from the second fluid line ( 204 ) to said container ( 212 ) in a said outflow in the form of a return flow ( 219 ) and that fluid from the fluid system ( 201 ) in a said outflow in the form of a consumption flow ( 209 ) is discharged. Method according to one of the above-mentioned claims, characterized in that the metering device ( 106 . 206 ) is controlled so that said time-dependent flow ( 109 . 209 ) arises. Method according to one of the above-mentioned claims, characterized in that the time-dependent flow ( 109 . 209 ) is generated in the form of a regular flow. Method according to one of the above-mentioned claims, characterized in that it is carried out for a fluid system which has flow blocking ( 105 . 205 ) through a clogged filter, the degree of clogging of the filter ( 105 . 205 ) is recognized. Method according to one of the above-mentioned claims, characterized in that the method for a system ( 201 ) is performed for injecting a reducing agent in front of an SCR catalyst in an exhaust pipe of an internal combustion engine. A computer program comprising computer program code for causing a computer to perform a method according to any one of claims 1-17 when the computer program is executed by the computer. A computer program product comprising a computer readable data storage medium storing the computer program code of a computer program according to claim 18. Electronic control device ( 40 ), which is an execution means ( 41 ), a memory ( 42 ), which is connected to the execution means, and a data storage medium ( 44 ) connected to the execution means, the computer program code in a computer program according to claim 18 being stored on said data storage medium ( 44 ) is stored. Motor vehicle having an electronic control device ( 40 ) according to claim 20.

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