Method for operating a hydraulic conveying and dosing system

Abstract

Method for operating a hydraulic conveying and dosing system, in particular a conveying and dosing system for the reactant solution of an SCR catalyst, characterized in that during a pressure build-up in the system, the pressure curve (110, 120, 130, 140) is continuously checked for plausibility and in the process it is checked whether a substantially continuous pressure increase can be detected, wherein during operation of the conveying and dosing system, a back-suction of the reactant solution from the pressure-side part of the system is provided, wherein the use of the plausibility check is dependent on a back-suction strategy and / or a back-suction quantity.

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] The urea solution is typically stored in a urea solution tank in the motor vehicle. To deliver the urea solution, a delivery and dosing system is generally provided. 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. For on-demand dosing, the delivery pump delivers the desired and required amount of urea solution from the tank. The urea solution is fed into the pressure line at a system pressure range and sprayed into the exhaust system via the dosing unit, which may include one or more dosing valves.

[0004] 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.

[0005] Before the delivery and dosing system can enter dosing readiness, pressure must be built up to reach the required system pressure or a system pressure range. If the system pressure is incorrect, sufficient spraying of the reactant in the exhaust tract cannot be guaranteed, which may result in insufficient chemical conversion and deposits forming. Furthermore, if the system pressure is incorrect, an accurate dosing quantity may not be guaranteed. Therefore, various approaches already exist to monitor the system pressure or the reagent pressure. For example, the German patent application DE 10 2010 013 695 A1 describes a method in which the pressure build-up is determined from a characteristic current curve at the delivery pump.In a process described in German patent application DE 10 2007 028 487 A1, the reagent pressure in the system is calculated and validated using a calculable pressure model. A failed pressure buildup is typically detected when the required pressure is not reached within a specified time tmax. The system cannot then enter dosing readiness, meaning exhaust gas aftertreatment cannot be performed as intended.

[0006] DE 10 2010 013 602 A1 discloses a method for detecting a malfunction in an electronically controlled fuel injection system of an internal combustion engine, by means of which the cause of the fault in a fuel injection system can be effectively isolated. In particular, it can be determined whether the cause of the fault lies in the low-pressure system or the high-pressure system of the fuel injection system.

[0007] DE 10 2010 027 675 B4 relates to a method for detecting faulty components or faulty subsystems of an electronically controlled fuel injection system of an internal combustion engine having a high-pressure pump, comprising the following steps: - carrying out a test routine in which the pressure of the fuel in the fuel injection system is increased and then reduced, various parameters of the fuel injection system being determined and stored as part of the test routine, - in a subsequent evaluation process the stored parameters are evaluated to detect malfunctions, and - individual pump strokes of the high-pressure pump are evaluated as part of the evaluation process.

[0008] DE 10 2013 212 734 A1 discloses 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, wherein a relationship between a pressure build-up in the system and a delivery rate is evaluated to check the plausibility of the delivery path.

[0009] The invention is based on the object of providing an improved method for operating a delivery and metering system, in particular a delivery and metering system for the reactant solution of an SCR catalyst, in which the monitoring of the pressure buildup is optimized. This object is achieved by a method for operating a hydraulic delivery and metering 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 tank 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 generally a return path or a return path for sucking the medium back out of the metering unit. The return path can be activated, for example, via a switchable valve in the return line or via a separate return pump in the return path. The reactant pressure at the metering valve is crucial for precise and demand-based metering of the reactant.The system must therefore be operated at a predeterminable system pressure or a predeterminable system pressure range. In order to achieve the system pressure or system pressure range required for dosing readiness, pressure must be built up after the system has started up. According to the invention, the pressure curve is continuously checked for plausibility even while the pressure is being built up in the system, and it is checked whether an essentially continuous pressure increase can be detected. The pressure build-up is therefore continuously monitored and evaluated so that an error in the system can be detected very quickly. It is therefore particularly advantageous if an implausible pressure curve is detected, the pressure build-up can be immediately aborted or interrupted and / or an alternative reaction or other error handling can be carried out.Therefore, if the pressure curve becomes implausible during pressure build-up, it can be recognized at a very early stage that the pressure build-up will fail, so that appropriate measures can be taken.

[0011] The method according to the invention offers major advantages in terms of time optimization. A fault in the system is detected more quickly than with conventional methods, so that the fault can be rectified quickly if necessary by initiating a substitute reaction and system readiness can be achieved more quickly than with conventional methods. This is particularly important during a warm start, where dosing readiness should be achieved very quickly due to the rapidly accumulating NOx emissions. Even during certification, any faults that occur should be rectified as quickly as possible in order to reliably comply with legal limit values. The inventive ongoing plausibility check already during pressure build-up can therefore significantly shorten the time until system readiness is reached, since any necessary measures to rectify the fault can be initiated immediately.In addition, the method according to the invention has the great advantage of achieving load optimization. Due to the earlier detection of a possible fault, the feed pump no longer has to be operated until a certain threshold is reached, for example the aforementioned timeout threshold tmax. This allows the operating load to be reduced and the components to be protected. A further advantage of the method according to the invention is that the effect of any leaks that may be present is minimized. In particular, in the case of leaks in the system that only become significant above a certain pressure due to the expansion of the leak or rupture point, the method according to the invention has the advantage that the total leak quantity that escapes until the system is shut down can be kept to a minimum, since the time until the system can be shut down, if necessary, is reduced by the early detection of the fault.This applies both to leaks where reducing agent escapes to the outside and to leaks where reactant unintentionally enters the exhaust tract.

[0012] The core of the method according to the invention is that, during the pressure buildup, a check is carried out to determine whether a substantially continuous pressure increase, i.e., an approximately continuously rising pressure curve, can be detected. The term "substantially" refers to the fact that, under certain circumstances, a temporarily constant pressure can still be considered plausible.

[0013] It is advisable to close the metering valve and, if applicable, the return line during pressure build-up so that the feed pump delivers into a closed volume during pressure build-up. Due to the system compressibility of the hydraulically closed system, if an additional fluid mass or volume is introduced by the actively pumping feed pump, it can be assumed that the pressure will increase or, in the limiting case of a very soft system, remain at approximately the same pressure level for a certain period of time. This results in a more or less significant increase in pressure, although in very soft systems the pressure can in principle remain constant over a certain period of time. In the correct case, however, a reduction in pressure cannot occur in a short period of time. This property of a hydraulically closed system is used according to the invention to continuously monitor and plausibility check the pressure build-up process.If the pressure in the system drops or remains the same for too long despite the feed pump being actively pumping, the system is not behaving correctly, so it can be concluded that the pressure build-up is implausible.

[0014] Incorrect system behavior can be caused, for example, by air in the system. If an air bubble gets into the feed pump through the suction channel, for example from the filter or the tank, the feed pump can no longer pump this air into the pressure area above a certain system pressure because the opening pressure at the pressure outlet valve is no longer reached. In this case, the pressure drops or remains the same. According to the invention, this is detected immediately and appropriate measures can be taken. Even in the event of a leak, the pressure build-up does not occur correctly, in particular if the leak becomes significantly large above a certain pressure due to a gap widening. Furthermore, the pressure build-up cannot occur as intended if the feed pump can no longer perform a sufficient full stroke above a certain pressure, for example because the flow rate is set too low.All of these error cases can be detected very quickly with the invention. They can be quickly corrected if necessary, so that dosing readiness is achieved in a short time, despite the initial error.

[0015] According to the invention, various mathematical evaluations are possible in order to verify an approximately continuously increasing pressure build-up. In a particularly preferred embodiment of the method according to the invention, the plausibility of the pressure curve is checked based on an evaluation of pressure differences, in particular calculable pressure differences. In particular, pressure differences between the current pressure value and a pressure value at the beginning of the pressure build-up are used. During the evaluation, it is checked whether these pressure differences are increasing approximately continuously. This embodiment is particularly advantageous because it requires only a small amount of storage space in the electronic control unit, since it does not have to save and evaluate a complete graph of the pressure curve, but only a few individual values.Furthermore, this method is very robust, and an assessment can easily be performed during the ongoing process. In another embodiment of the method according to the invention, a plausibility check can be performed, for example, based on an evaluation of pressure gradients. This embodiment may require more storage space. Nevertheless, this embodiment can also offer particular advantages, for example, with regard to a more differentiated evaluation.

[0016] The pressure values ​​used to monitor the pressure curve in the course of the method according to the invention can be based on sensor signals and / or model data. For example, existing pressure sensors in the system can be used for this purpose, or the pressure values ​​can be derived indirectly, for example, based on the current flow of the feed pump, or conventional pressure models can be used to generate values ​​for the pressure in the system.

[0017] Both filtered and unfiltered pressure values ​​can be used. Filtering the pressure signals has the advantage that it often allows for a more robust implementation. In general, filtering the pressure signals also prevents false statements. If the pressure signals are not filtered, this can offer the advantage that the inventive plausibility check can be performed even faster.

[0018] In a further embodiment of the method according to the invention, the plausibility check is only initiated after the pressure in the system exceeds a predefined threshold (plimPlausi). This is based on the fact that evaluation may be less robust at very low pressures. For example, the system is very soft if there is a lot of air in the system. In these cases, it is particularly advantageous if the plausibility check is only activated above a certain pressure in order to improve the reliability of the plausibility check.

[0019] In a further embodiment of the method, it can be provided that, as a further criterion for aborting (or interrupting) the pressure build-up, it is checked whether the threshold plimPlausi is reached within a predeterminable time tplimPlausi and / or before reaching a predeterminable number of pump strokes nplimPlausi and / or before reaching a predeterminable delivery volume or mass VplimPlausi. This represents a supplementary test that can be carried out in addition to monitoring the continuous pressure increase. The advantage here is that additional or supplementary monitoring is possible even at very low pressures, at which the actual plausibility check method according to the invention is not yet activated or is only slightly robust.

[0020] A further possible embodiment of the method according to the invention relates to systems in which the reactant solution is sucked back, particularly from the pressure-side part of the system. In these systems, the use or retrieval of the plausibility check according to the invention can be made dependent on the suck-back strategy and / or the suck-back quantity, whereby, for example, the software or the application values ​​of the plausibility check method are configured accordingly. If, for example, no suck-back has taken place beforehand, it can be assumed that there is no air or only a small amount of air in the system. It can then be assumed that the pressure build-up will occur more quickly, so that the plausibility check according to the invention can be parameterized accordingly. This can further increase the robustness as well as the accuracy and informative value of the plausibility check according to the invention.

[0021] During the regular pressure buildup, it may be provided that the pressure buildup is interrupted by briefly opening the metering valve in order to dispose of any air present in the pressure-side part of the system into the exhaust tract. Since this ventilation can be associated with a drop in pressure, particularly in the case of metered air, it may advantageously be provided in the course of the method according to the invention to subsequently reset or reinitialize the values ​​to be evaluated for the method according to the invention. In the case of other interruptions or aborts of the pressure buildup, a reset is also advisable before continuing or repeating the pressure buildup.

[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 during pressure buildup.

[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 switching valve in the return line and Fig. 3 a graphical representation of the pressure build-up process in relation to the pressure in the system. 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 method according to the invention can also be used in other hydraulic delivery and metering systems to monitor the pressure build-up process.

[0026] Fig. 1 schematically shows a delivery and metering system, for example, for the reactant solution of an SCR catalyst in the exhaust system of a motor vehicle. 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 delivery pump 21 is assigned an inlet valve 22 and an outlet valve 23. The reactant required for exhaust gas aftertreatment is withdrawn from the tank 10 by the delivery pump 21 and fed into a pressure line 40. 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 in the pressure-side part of the system can be detected or derived, for example, via a pressure sensor (not shown) or from a pressure interpretation of the current flow at the feed 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, a back-suction of the medium from the metering valve 50 and, if necessary, from the pressure line 40 is provided 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 return module 30 further comprises an intake valve 32 and an outlet valve 33. The feed 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 method according to the invention for verifying the plausibility of the pressure build-up can also be used, for example, in pump systems with other pump drives, such as rotary motors or stepper motors.

[0028] In the comparable system in Fig. 2, the return channel or return path can be opened by appropriately switching the switching valve 35, 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 in this system. Only pulsed recirculation for small recirculation volumes is possible.

[0029] Before precise dosing can occur via the dosing valve 50, a specific system pressure or a specific system pressure range must be reached in the system. According to the invention, the process of the pressure build-up required for this is continuously monitored and checked for plausibility. This check is carried out to determine whether the pressure curve increases approximately continuously. Since in borderline cases, particularly in very soft systems, the pressure can remain the same over a certain period of time, it can still be plausible in these cases if no increase in the pressure curve is detectable, but merely a temporary, constant level. However, it is important that this constant level only exists for a specific period of time and not for too long. The mathematical evaluation during the plausibility check according to the invention can be carried out in different ways. An evaluation based on pressure differences is explained in more detail below.This design is particularly advantageous because it requires very little memory space in the engine control unit. Nevertheless, this method is very robust.

[0030] For evaluation using pressure differences, the pressure difference DP between the current pressure value (pCurrent), i.e., a pressure value during the pressure build-up process, and the pressure at the beginning of the pressure build-up (pStart) is used. The starting value pStart is advantageously stored temporarily. Thus, the pressure difference DP is calculated as follows: DP=pCurrent−pStart

[0031] The pressure values ​​used for this calculation can be filtered or unfiltered. The use of filtered pressure signals has the advantage that it allows for even more robust behavior of the plausibility check according to the invention. The pressure values ​​can, for example, originate from a pressure sensor present in the system or be derived from a model, for example from an evaluation of the current curve at the feed pump. The pressure difference DP is continuously calculated during the pressure build-up and is initially initialized to zero. If a state change occurs during the pressure build-up, for example after ventilation, the calculation of the pressure difference should be suspended in a suitable manner and then restarted. In particular, pStart is reinitialized with the value after the state change. The pressure difference DP is initialized to zero.

[0032] At the beginning of the procedure, the DP value should be approximately zero. During a plausible pressure buildup, the DP value should increase approximately steadily. Under certain circumstances, particularly in a very soft system state, the DP value may remain constant for a certain period of time. However, after a short time, the DP value should increase again. It is advisable to save the current, maximum DP value (DPmax) so that it can be used for a subsequent assessment of the subsequent pressure buildup. If the state changes during the pressure buildup, DPmax is preferably reset to zero.

[0033] The procedure of the method according to the invention is described below with reference to Fig. 3 is explained in more detail. The course of the pressure build-up process is shown on the x-axis. This can, for example, be the time course or the x-axis can represent the number of strokes performed by the feed pump or alternatively the pumped volume or mass. The y-axis represents the pressure in the system. The dash-dotted line 100 indicates the end of the pressure build-up process. The end 100 of the pressure build-up process can, for example, be specified in time by a maximum value tMax or as the maximum number of pump strokes nMax or as the maximum amount of pumped mass or volume VSysMax. The values ​​for tMax, nMax or VSysMax must be applied accordingly large for large system volumes, so that the time frame provided for a regular, conventional pressure build-up is relatively long.Since the invention allows the successful pressure build-up to be determined during the pressure build-up process, any necessary measures can be taken at an early stage to ensure dosing readiness as quickly as possible, even in the event of a fault. Overall, this results in time optimization, which also results in load optimization, because the feed pump does not have to operate for the entire duration of the pressure build-up in the event of a fault.

[0034] The Fig.The pressure thresholds pDosMin and pDosMax shown in Figure 3 limit the intended system pressure range for dosing operation (pDosing range). As soon as pDosMin is reached, dosing operation can begin. However, the pressure can continue even after the pDosMin threshold has been reached up to a further threshold, not shown here, in order to ensure a safety margin in the event of pressure drops. This further threshold can, for example, be located halfway between pDosMin and pDosMax or at a different position between pDosMin and pDosMax. Various pressure curves 110, 120, 130, and 140 are shown during pressure build-up. The pressure curve is continuously monitored and continuously checked for plausibility. Curve 110 represents correct system behavior, in which a steadily increasing pressure build-up curve can be observed.As soon as the detectable pressure exceeds the threshold pDosMin, which represents the lower threshold of the permissible system pressure range, the system goes into dosing readiness and the pressure build-up can be assessed as correct.

[0035] The pressure curves 120, 130, and 140 represent cases in which the system behavior during pressure buildup is incorrect. According to the plausibility check method according to the invention, in these cases it can be determined already during the pressure buildup process that there is no approximately continuous pressure increase, so that the pressure buildup is to be assessed as implausible and appropriate measures can be taken. In particular, the pressure buildup is terminated prematurely. In curve 120, the pressure initially rises and then drops steeply after a maximum. Based on the no longer existing continuous pressure increase, it can be determined at a very early point in time that the pressure buildup 120 will fail. According to the invention, this can be determined long before the time period for the complete runthrough of the pressure buildup process has elapsed.Curve 130 represents another curve that does not lead to correct pressure buildup. After an initial increase in the pressure curve, the pressure remains at a constant level, but below the threshold pDosMin. Since the pressure remains constant over a longer period of time, it is concluded from this curve according to the invention that the pressure buildup will not be successful. The pressure buildup process is terminated prematurely. Curve 140 shows another case of incorrect system behavior. After the pressure initially increases continuously up to DPmax, a pressure drop subsequently occurs, so that it can be concluded according to the invention that the pressure buildup will fail and the pressure buildup process can be terminated prematurely.

[0036] Since the method may be less robust at very low pressures, a lower limit plimPlausi can be specified. As long as the pressure remains below this threshold, the plausibility check according to the invention is not activated. The plausibility check according to the invention only starts once plimPlausi has been exceeded. The curve 150 represents a case in which no evaluation of the pressure takes place in the manner according to the invention because the detectable pressure values ​​are below plimPlausi. The plimPlausi threshold can be used optionally. For example, the plimPlausi threshold can be used depending on the backflow strategy or the backflow quantity. If, for example, no medium has been backflowed and it can therefore be assumed that there is little or no air in the system, the plimPlausi threshold can be disregarded.If the plimPlausi threshold is taken into account and is not reached within a certain time (tplimPlausi) or, alternatively, not with a specified number of pump strokes (nplimPlausi) or a specified delivery volume or mass (VplimPlausi), the pressure build-up process can also be aborted. This represents a supplementary check to the continuous pressure increase check. The values ​​tplimPlausi or, if applicable, nplimPlausi or VplimPlausi can still be optionally used by the suction-back strategy or the suction-back quantity.

[0037] For the evaluation during the plausibility check according to the invention, the pressure differences DP are calculated from the difference between the current pressure value (pCurrent) and the pressure at the start of the pressure build-up (pStart). If the determined DP values ​​for an applicable time (tPlaus) or an applicable number of feed pump strokes (nPlaus) or for an applicable delivery volume or an applicable delivery mass (VPlaus) are less than or equal to the previously reached maximum value DPmax, this is considered an implausible pressure build-up. The pressure build-up process can be aborted immediately and / or an alternative reaction, for example flushing the system, can be carried out. A new pressure build-up attempt can then be started. If a subsequent pressure build-up attempt also fails, this process can be repeated, whereby the number of pressure build-up attempts can be limited to an applicable value.If failed pressure build-up attempts occur in conjunction with a very low tank level for the reactant, it can be assumed that the cause of the error is most likely gas or air drawn into the feed pump. To correct this error, the reactant should be refilled. Using the method according to the invention, the incorrect system behavior can be correctly interpreted, and in this case, an error entry can be avoided that is attributed to the pump because the cause is an excessively low tank level.

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, characterized by that during a pressure build-up in the system the pressure curve (110, 120, 130, 140) is continuously checked for plausibility and in the process it is checked whether an essentially continuous pressure increase can be detected, wherein during operation of the conveying and dosing system a back-suction of the reactant solution from the pressure-side part of the system is provided, wherein the use of the plausibility check is dependent on a back-suction strategy and / or a back-suction quantity. [2] Method according to claim 1, characterized by that if an implausible pressure curve (120, 130, 140) is detected, the pressure build-up is aborted. [3] Method according to claim 1 or claim 2, characterized bythat in the event of an ascertainable implausible pressure curve (120, 130, 140), at least one substitute reaction and / or error treatment is carried out. [4] Method according to one of the preceding claims, characterized by that a plausibility check of the pressure curve is carried out on the basis of an evaluation of pressure differences, in particular of calculable pressure differences, whereby pressure differences between current pressure values ​​and pressure values ​​at the beginning of the pressure build-up are preferably used. [5] Method according to claim 4, characterized by that it is checked whether the pressure differences increase approximately continuously. [6] Method according to one of claims 1 to 3, characterized by that the pressure curve is checked for plausibility by evaluating pressure gradients. [7] Method according to one of the preceding claims, characterized bythat the pressure curve is monitored using pressure values ​​based on sensor signals and / or model data. [8] Method according to claim 7, characterized by that the pressure values ​​are filtered. [9] Method according to one of the preceding claims, characterized by that the start of the plausibility check depends on the pressure in the system exceeding a predefined threshold plimPlausi. [10] Method according to claim 9, characterized by that as a criterion for terminating the pressure build-up, it is checked whether the threshold plimPlausi is reached within a predeterminable time tplimPlausi and / or before reaching a predeterminable number of pump strokes nplimPlausi and / or before reaching a predeterminable delivery volume or mass VplimPlausi. [11] Method according to one of the preceding claims, characterized bythat after an interruption in the pressure build-up, in particular after venting the system, the values ​​used for the process are reset. [12] A computer program which carries out all the steps of a method according to any one of claims 1 to 11 when executed on a computing device or a control device. [13] Computer program product with program code stored on a machine-readable carrier for carrying out a method according to one of claims 1 to 11 when the program is executed on a computing device or a control device.

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