Method for operating a hydraulic conveying and dosing system

Abstract

Method for operating a hydraulic conveying and metering system, in particular a conveying and metering system for the reaction agent solution of an SCR catalyst, wherein the conveying and metering system comprises a conveying path (60) and a return path (70), characterized in that during and / or after a flushing of the return path (70) with the metering unit (50) closed, an evaluation of the pressure in the system is carried out to verify the plausibility of the return path (70), where the pressure is evaluated to check whether an applicable pressure threshold is exceeded and, if the pressure threshold is exceeded, a fault in the return path (70) is inferred, wherein in case of error a defrost cycle is requested and subsequently preferably a further plausibility check of the return path (70) is carried out, If a defrost cycle is required multiple times, the defrosting time is extended by the system control.

Description

[0001] The present invention relates to a method for operating a hydraulic delivery and metering system, in particular a delivery and metering system for the reactant solution of an SCR catalyst. Furthermore, the invention relates to a computer program and a computer program product with program code suitable for implementing the method. State of the art

[0002] Methods and devices for operating an internal combustion engine, particularly in motor vehicles, are known. An SCR (Selective Catalytic Reduction) catalyst is installed in the exhaust gas area of ​​the internal combustion engine. This catalyst reduces the nitrogen oxides (NOx) contained in the exhaust gas of the internal combustion engine to nitrogen in the presence of a reducing agent. This can significantly reduce the proportion of nitrogen oxides in the exhaust gas. Ammonia (NH3) is required for the reaction to proceed, and is added to the exhaust gas. NH3 or NH3-releasing reagents are used as the reactant. Typically, an aqueous urea solution is used for this purpose, which is injected into the exhaust system upstream of the SCR catalyst.

[0003] DE 10 2004 061 259 A1 discloses that in a method and a device for thawing detection in a metering device of an SCR catalyst for reducing nitrogen oxides in an exhaust gas stream, in particular of an internal combustion engine, wherein a reagent is metered into the exhaust gas stream by means of the metering device, it is provided that the metering device is heated in at least one thawing phase and, following the at least one thawing phase, plausibility checks are carried out on the basis of which it is indirectly determined whether the metering device has actually been thawed.

[0004] DE 10 2011 003 499 A1 discloses that in a method for monitoring a dosing system, in particular for an SCR catalyst (12), with a tank (14) for a liquid medium, a pressure-controlled feed pump (16) and at least one dosing valve (13), the control value of the feed pump (16) is compared with predeterminable reference values ​​and if the reference values ​​are exceeded and / or undershot, a fault in the dosing system is concluded.

[0005] The urea solution is typically stored in a urea solution tank in the vehicle. A delivery and dosing system is generally provided to deliver the urea solution. This system includes, in addition to the urea solution tank, a delivery unit, a pressure line, a dosing unit, the necessary sensors, and an electronic control unit. Furthermore, one or more heating devices are provided to heat the delivery and dosing system at low ambient temperatures and, if necessary, thaw frozen medium, so that the system can be ready for dosing. For demand-based dosing, the delivery pump delivers the desired and required amount of urea solution from the tank.

[0006] The urea solution is fed into the pressure line in a system pressure range and sprayed into the exhaust system via the dosing unit, which may comprise one or more dosing valves.

[0007] To prevent damage to the sensitive components of this system, especially the metering valve(s), due to ice pressure at low temperatures, it is often provided that after the engine or vehicle is shut down, the urea solution is sucked back from the metering unit into the pressure line or tank. For this purpose, a feed pump with a switching unit, such as a 4 / 2-way valve, can be provided. In other systems, a separate return channel with a switching valve or a separate return pump is provided, which allows the medium to be sucked back from the metering unit.

[0008] If the system needs to be heated at low ambient temperatures and the medium in the system is partially or completely thawed, this so-called "defrost" process or thawing cycle may result in undefined starting conditions and potentially significantly different localized medium conditions. To avoid the associated inaccuracies in dosing, a flushing process can be performed that includes the return path. The medium is pumped from the tank by the feed pump with the dosing unit closed and then returned to the tank via the return path.

[0009] The invention is based on the object of providing an improved method for operating a hydraulic conveying and dosing system in which errors, in particular blockages, can be detected and, if necessary, rectified. This object is achieved by a method for operating a hydraulic conveying and dosing system as set forth in claim 1. Preferred embodiments of this method, as well as a corresponding computer program and a corresponding computer program product, are the subject of the further claims. Disclosure of the inventionAdvantages of the invention

[0010] The method according to the invention is based on a hydraulic delivery and metering system in which a liquid medium is delivered, for example, from a storage container and metered under pressure via a metering unit, for example, into the exhaust system of an internal combustion engine. This can, in particular, be the delivery and metering system for the reactant solution (urea solution) of an SCR catalyst. The system comprises a delivery path with at least one delivery pump and a return path or return feed path for sucking the medium back out of the metering unit. The return path can, for example, be activated via a switchable valve in the return line. It can also be provided that a separate return pump is provided in the return path.The medium can thus be sucked back from the pressure-side area of ​​the conveying system into a tank in order to be able to remove the liquid medium from the dosing unit and, if necessary, also from the remaining pressure-side area of ​​the system, for example after a suitably equipped motor vehicle has been parked. This prevents damage to the components, in particular to the dosing valves, caused by the ice pressure caused by the frozen medium at low temperatures. Heating devices can also be provided in order to be able to thaw the liquid medium, for example the urea solution, after it has frozen. Such a conveying and dosing system allows a flushing process via the return path, whereby medium is pumped out of the tank by means of the feed pump and, with the dosing unit closed, is returned to the tank via the return path. Such flushing can be useful, for example, after the medium has thawed.According to the invention, the pressure in the system is recorded and evaluated during and / or after such a flushing process in order to carry out a plausibility check of the return path. The method according to the invention can be carried out in particular during a system start or during a system reset or a system restart. According to the invention, it can be determined whether there is an error in the system and in particular in the return path. In particular, it can be determined in this way whether the return is blocked. A blockage can be caused, for example, by frozen medium not having completely thawed. Furthermore, blockages can occur, in particular in the return, due to contamination or the like, for example in the changeover valve. Furthermore, there can also be a blockage of the return pump, if present, for example.the cause of the error can be further narrowed down in the course of the method according to the invention, as will be explained later.

[0011] If no fault is detected, it can be assumed that the return line is open and that the return pump, if present, is functioning, so that system operation can continue. In this case, for example, the system can be started up again until dosing readiness is reached. In the event of a fault, it can be assumed that the return line is blocked or has not thawed, or possibly that the return pump is blocked. Traditionally, the functionality of the return path is not checked, since the conveying and dosing system can be made ready for dosing regardless of a functioning return line. However, this poses the problem that if the return path is blocked or has not yet thawed, the system cannot be properly relieved and emptied or partially emptied after the vehicle is turned off. This can lead to component damage if the medium in the system freezes.Furthermore, a system reset by flushing is not possible, which means that air bubbles, for example, can remain in the feed pump. With the help of the plausibility check method according to the invention, it is possible to check the functionality of the return path without great effort and to identify and, if necessary, rectify existing errors, in particular blockages. In this way, system operation with a defective return can be avoided, thus ruling out any subsequent errors that may occur. The method according to the invention can detect whether the return has not completely thawed. This can prevent component damage due to renewed or increased freezing after a system shutdown. Furthermore, the plausibility check method according to the invention can detect whether the thawing of frozen medium in the system is taking place satisfactorily.Particularly in systems where the return pump is operated purely in a controlled manner, the heating output during thawing may be too low, as the temperature information from the pump coil may be insufficient. This can lead to thawing occurring too slowly. The resulting blockages in the return path caused by incompletely thawed medium are detected by the invention, allowing the conditions for the thawing process to be adjusted more effectively.

[0012] The inventive evaluation of the pressure in the system takes place during and / or after the flushing process of the return path. For flushing, the dosing valve or generally the dosing unit is closed and the feed pump can be controlled at an applicable frequency. During this time, the return path is opened. For this purpose, the corresponding switching valve in the return can be opened or, if a return pump is present in the return path (return path), the return pump can be controlled at an applicable frequency so that the pump function is active. On the other hand, it is also possible for the return pump, if present, to be controlled at 100% without cycling, so that its valve function is active and the return path is completely open without active back pumping taking place. During this operating state, the pressure signal is monitored and evaluated according to the invention.The required pressure signal can be obtained, for example, via a pressure sensor installed in the system in such a way that the pressure in the flushing circuit can be measured. However, the method can also be used in systems without a pressure sensor, where a pressure interpretation is derived, for example, from the current signal of the feed pump. During the pressure evaluation, a particular check is made to determine whether an applicable pressure threshold (plimit) is being or has been exceeded. If a certain pressure builds up, it can be assumed that there is a blockage in the return path. If the pressure threshold is exceeded, it is therefore concluded that there is a fault in the return path.

[0013] To evaluate the pressure signals, it can be provided, for example, that the pressure threshold is exceeded within a certain applicable time. Alternatively or additionally, it can be checked whether the pressure threshold is exceeded below an applicable delivery rate or delivery mass and / or below an applicable number of strokes of the feed pump and / or, if applicable, the return pump. Pressure signals that are recorded during the flushing process can be used for this evaluation. Alternatively, it is also possible to record and evaluate the pressure signals after the flushing process has been completed and to compare them with suitable reference values, for example. In this way, a significant and sustained pressure build-up can be detected, which can be interpreted as an indication of a partial or complete blockage of the return channel. From this, it can be concluded, for example, that the return channel orthe medium contained therein has not been completely thawed, if the plausibility check was carried out, for example, after a thawing cycle.

[0014] Preferably, debouncing is provided during the plausibility check during the evaluation so that temporary pressure peaks cannot lead to false detection of errors.

[0015] In a preferred embodiment of the method according to the invention, the dosing unit is not opened in the event of a fault. This has the advantage that any gas present in the pressure-side system remains in the line system. This gas volume in the system provides protection for the dosing valve if the medium freezes (again). The gas remaining in the system can also provide component protection for other components in the system.

[0016] It is advisable to allow sufficient time for the purging to account for any gas volume present in the system, particularly on the pressure side. Pressure buildup takes longer if gas volumes are present in the system, so a sufficiently long application time ensures that pressure buildup can actually occur in the event of a fault.

[0017] The method according to the invention can, in principle, be used for all sufficiently long flushing processes. However, it can also be provided that further release conditions are specified for the inventive plausibility check of the return path. For example, the implementation of the inventive plausibility check can be made dependent on whether a thawing cycle was previously carried out. In particular, when thawing frozen medium, the problem of a blockage of the return path can arise, especially if the medium has not been completely thawed. In order to detect such a case in good time and avoid the associated problems, the method according to the invention is therefore, in a particularly preferred embodiment, carried out after a thawing cycle has been carried out and / or after a warm start following a driving cycle in which a thawing cycle was carried out.If a fault is detected in the return path, especially in these cases, a new thawing cycle can be requested to completely thaw any media that may not have fully thawed yet. A subsequent plausibility check can be performed to determine whether the blockage has been cleared, allowing normal system operation to resume if necessary.

[0018] Further release conditions may include the absence of a fault in the relevant actuator and / or sensor system. Furthermore, other application-specific release conditions can be specified alternatively or additionally, for example, specific temperature values, specifications regarding the vehicle's shutdown times, etc. By setting suitable release conditions, the method according to the invention can be adapted and optimized for specific applications.

[0019] The method according to the invention makes it possible to differentiate between different causes of errors in the event of a blocked return line. A distinction can be made here between errors that can be rectified by an appropriate system control (on-board) (F1 error) and errors that must be rectified externally (off-board), i.e. in particular in a workshop (F2 error). The cause of an F1 error can primarily be incompletely thawed medium in the return line. The medium in the return line that is still frozen can generally be liquefied by a further thawing cycle, so that this error can be rectified by an appropriate system control. According to the invention, it can initially be assumed that an F1 error is present in the event of an error and that the return line is most likely still frozen. In this case, the method according to the invention provides that a further thawing cycle is requested by the system control.This renewed thawing cycle can be specified to be shorter than the previous thawing cycle. Subsequently, the return flow can be rechecked during a subsequent rinsing process. The number of possible repetitions can be limited by the application.

[0020] If the return line remains blocked despite repeated requests for a defrost cycle and the error is therefore not rectified, it can be assumed with a high degree of probability that an F2 error is present. In these cases, it can be concluded that an error that can be rectified externally is present, so that a corresponding warning message or error entry can be generated. Causes in this case could be, for example, a defective return pump or a filter in the return line blocked by dirt. In these cases, the plausibility check according to the invention can serve as a helpful "pinpointing" tool for the workshop, providing a targeted indication of the cause and / or location of the error.

[0021] If it frequently occurs that the return line must be thawed with multiple thawing cycles, i.e., if an additional thawing cycle is requested multiple times, the system control can be configured to extend the thawing time as an adaptation. This is based on the fact that the thawing time in the first thawing cycle is most likely not sufficient to completely thaw the frozen medium. This can be detected by the invention, so that the thawing time can be extended accordingly. Through this learning (adaptation), the frequency of a necessary additional thawing cycle can be significantly reduced.

[0022] The invention further comprises a computer program that executes all steps of the described method when executed on a computing device or a control unit. Furthermore, the invention comprises a computer program product with program code stored on a machine-readable medium for carrying out the method according to the invention when the program is executed on a computing device or a control unit. Implementing the method according to the invention as a computer program or as a computer program product has the advantage that this program can also be readily used in existing motor vehicles, thus enabling the advantages of the plausibility check method according to the invention to be utilized.

[0023] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments in conjunction with the drawings. The individual features can be implemented individually or in combination with one another. Short description of the drawings

[0024] The drawings show: Fig. 1 a schematic representation of the components of a conventional system for the conveying and dosing of a liquid medium with a return pump; Fig. 2 a schematic representation of the components of a conventional system for the conveying and dosing of a liquid medium with a non-return valve in the return line and Fig. 3 schematic flow diagram to illustrate a preferred embodiment of the method according to the invention. Description of implementation examples

[0025] The Fig. 1 and Fig. 2 illustrate two current hydraulic delivery and metering systems in which the method according to the invention can be used. However, the invention is not limited to such systems. Rather, the plausibility check method according to the invention can also be used for other hydraulic delivery and metering systems that have a separate return path or return feed path.

[0026] Fig. 1 schematically shows a delivery and metering system, for example, for the reactant solution of an SCR catalyst. The reactant solution (urea solution) is stored in a reactant tank 10. A delivery module 20 with a delivery pump 21 is provided for the removal and delivery of the reactant. The reactant required for exhaust gas aftertreatment is taken from the tank 10 and fed into a pressure line 40 by the delivery pump 21. The reactant is sprayed under pressure into the exhaust system (not shown) upstream of the SCR catalyst (not shown) via the metering unit or metering valve 50. The pressure in the metering unit 50 is crucial for the precise injection of the reactant solution into the exhaust system. The pressure can be detected or derived via a pressure sensor (not shown) or, for example, from a pressure interpretation of the current signal of the delivery pump 21.

[0027] If the reactant solution freezes at low outside temperatures, damage to the sensitive components of the system, particularly the metering valve 50, can occur due to ice pressure. To prevent this, the medium is sucked back from the metering valve 50 and, if necessary, from the pressure line 40 after the vehicle has been parked. Fig. In the embodiment of the system illustrated in Figure 1, a separate return module 30 with a return pump 31 is provided for this purpose. The delivery and metering system can be subdivided into a delivery path 60 and a return path (return path) 70. The return module 30 further comprises an intake valve 32 and an outlet valve 33. Correspondingly, an intake valve 22 and an outlet valve 23 are also provided in the delivery module 20. The delivery pump 21 and the return pump 31 can, for example, be reciprocating piston pumps, each comprising a lifting magnet, a spring, a diaphragm, and a reciprocating piston. However, the application of the method according to the invention is not limited to such lifting magnet pump systems. The plausibility check method according to the invention can, for example, also be used in pump systems with other pump drives, such as rotary motors or stepper motors.

[0028] Fig. Figure 2 illustrates another feed and metering system that can also be used for the feed and metering of the reactant for an SCR catalyst. In contrast to the system shown in Fig. 1, the return path in this embodiment is equipped with a switching valve 300 instead of a return pump. The other components essentially correspond to the components of the system from Fig. 1 and are provided with the corresponding reference numerals. In the system in Fig. 2, the return channel or return path can be opened by appropriately switching the switching valve 300, allowing the medium to be pushed back into the tank 10. However, it is not possible to actively pump the medium in the return path. This system only allows for pulsed recirculation for small recirculation volumes.

[0029] The method according to the invention for verifying the plausibility of the return path is carried out during and / or after a flushing process in which the metering valve 50 is closed and the feed pump 21 is actively controlled. At the same time, the return path is opened, for example, by opening the switching valve 300 ( Fig. 2) or by controlling an open valve function of the return pump 31 or by actively pumping the return pump 31 ( Fig. 1). During this flushing process, the medium should be pumped in a circuit from the tank and back into the tank via the return path. During this operating phase, the pressure in the system is recorded according to the invention, in particular the pressure downstream of the feed pump 21 and upstream of the return pump 31 or the switching valve 300 in the return line. Pressure signals from any pressure sensors present can be used for this purpose. On the other hand, it is also possible to derive a pressure interpretation, for example, from the current signal of the feed pump 21, so that the method according to the invention can also be used in systems without a pressure sensor with indirect pressure detection. If an applicable pressure threshold is sustained and exceeded, it is concluded that there is a fault in the return line. In this case, the return channel is completely or partially blocked.The reason for this could be, for example, that the medium has not yet completely thawed after a thawing cycle. Even in the event of a fault, the dosing valve 50 should preferably remain closed so that any gas pockets present in the system do not escape and are available to protect the components in the event of the medium freezing. If no significant pressure buildup is detected during the plausibility check process according to the invention, it can be assumed that the return channel is sufficiently open so that regular system operation can continue.

[0030] Fig.3 shows a flow chart to illustrate an exemplary implementation of the method according to the invention, wherein in this embodiment of the method, plausibility check is used to check, particularly after a thawing cycle, whether the return channel is error-free. After the start 100, a check is first made in step 110 to determine whether the operating state of flushing the conveying system, and in particular the return, is present. This flushing of the system with a closed metering valve, active feed pump, and open return path, optionally with pumping operation of the return pump, can be regularly provided, for example, after each thawing cycle. If this operating state is not present, the program jumps from step 110 back to the start 100. If the operating state "flushing" is present, the program checks in the subsequent step 120 to determine whether a thawing cycle has previously occurred in the conveying and dosing system. If this is not the case, the program jumps back to the start 100.If a thawing cycle has preceded the cycle, possibly also in a previous driving cycle that occurred before a warm start, pressure values ​​that can be detected during and / or after the flushing process are recorded in step 130. The pressure values ​​can, for example, originate from pressure sensors at a suitable point in the delivery and dosing system. However, the pressure values ​​can also be determined indirectly, for example by interpreting the pressure from the current signal of the delivery pump. The pressure values ​​are evaluated in step 140 to determine whether they exceed an applicable threshold (p > plimit). In this case, it can be checked, for example, whether the applicable threshold plimit is exceeded within a certain applicable time and / or below an applicable delivery quantity or delivery mass and / or below an applicable number of strokes of the delivery pump and / or, if applicable, the return pump.If this is not the case, it is assumed that the system is error-free and regular system operation 150 can continue. For example, the system start can continue until dosing readiness is reached. If the predeterminable limit plimit is reached or exceeded, it is initially assumed that an error F1 has occurred. In this context, “error F1” means that the error can be rectified by an appropriate system control. In particular, it is assumed that the error is due to a return line that is still frozen or to the medium in the return line that has not completely thawed. A thawing cycle is therefore requested in step 160. Subsequently, pressure values ​​are recorded or evaluated again in step 170 during or after a subsequent flushing process with the dosing valve closed. When the pressure values ​​are evaluated in step 180, a check is carried out to determine whether the applicable threshold plimit is exceeded for the pressure values.A check is therefore carried out to determine whether a significant and sustained pressure build-up occurs again. If the pressure threshold is not exceeded, it can be assumed that the blockage has been cleared. The assumption that error F1 existed was therefore correct. Regular system operation 190 can be resumed. However, if it is determined in step 180 that the pressure threshold plimit has been exceeded, it may be possible to return to step 160 and request a new thawing cycle. If it cannot be assumed that the error can be rectified by further thawing in the system, error output 200 is generated after the pressure limit plimit is exceeded in check step 180, indicating that an error that can only be rectified externally, i.e. error F2, has occurred.In this case, the blockage in the return path is not due to insufficiently thawed medium in the system, but to another cause, such as a clogged strainer or a blocked or defective return pump.

[0031] If the error could be corrected by one (or more) subsequent defrost cycles (step 190), an adaptation or learning process can optionally be provided in step 195, whereby the heating times are adjusted and increased in the system control during a defrost cycle. This is particularly advantageous in cases where the system could be "cured" systematically, i.e., repeatedly, through multiple defrost requests. In these cases, it can be assumed that the originally planned defrost times were insufficient.

Claims

[1] Method for operating a hydraulic conveying and dosing system, in particular a conveying and dosing system for the reactant solution of an SCR catalyst, wherein the conveying and dosing system comprises a conveying path (60) and a return path (70), characterized by that during and / or after a flushing of the return path (70) with the dosing unit (50) closed, an evaluation of the pressure in the system is carried out to check the plausibility of the return path (70), wherein, when evaluating the pressure, it is checked whether an applicable pressure threshold is exceeded and, if the pressure threshold is exceeded, a fault in the return path (70) is concluded, wherein in the event of an error, a thawing cycle is requested and then preferably a further plausibility check of the return path (70) is carried out, If a defrost cycle is requested multiple times, the defrosting time is extended by the system control. [2] Method according to claim 1, characterized by that exceeding the pressure threshold - within an applicable time and / or - below an applicable flow rate or flow mass and / or - is checked below an applicable number of strokes of a feed pump (21) and / or a return pump (31). [3] Method according to one of the preceding claims, characterized by that debouncing is provided for during the plausibility check. [4] Method according to one of the preceding claims, characterized by that in the event of a fault the dosing unit (50) is not opened. [5] Method according to one of the preceding claims, characterized by that release conditions are specified for the plausibility of the return path (70). [6] Method according to claim 5, characterized by that the release condition is: - a thawing cycle was previously carried out and / or - after a warm start, a defrost cycle was carried out during the previous driving cycle and / or - there is no fault in the relevant actuators and / or sensors and / or - there are application-specific release conditions. [7] Method according to one of the preceding claims, characterized by that a distinction is made between an error that can be corrected by a control panel and an error that must be corrected externally. [8] Method according to claim 1, characterized by that if a defrost cycle is requested multiple times and the error is not rectified, it is concluded that the error is an external error that needs to be rectified. [9] A computer program which carries out all the steps of a method according to any one of claims 1 to 8 when executed on a computing device or a control device. [10] Computer program product with program code stored on a machine-readable carrier for carrying out a method according to one of claims 1 to 8 when the program is executed on a computing device or a control device.

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