Method and device for monitoring an injection quantity of reducing agent into an exhaust tract of an engine system with an internal combustion engine

Abstract

The invention relates to a method for determining a quantity of injected reducing agent in a reducing agent injection system (1) for an exhaust tract (6) of an internal combustion engine, comprising the following steps: - Providing a predetermined reducing agent pressure in a pressure line (4) of the reducing agent injection system (1); - controlling (S2) a dosing unit (5) with at least one dosing valve corresponding to an opening time period for supplying reducing agent into the exhaust tract (6); - recording (S2) a pressure curve during the opening period of the dosing unit (5); - determining (S6, S7) a period duration indication to be determined of a pressure oscillation in the pressure line (4) resulting from the opening of the dosing unit (5); - Determining (S10) a quantity of injected reducing agent depending on the opening time, the specified reducing agent pressure and the period duration to be determined.

Description

Technical FieldThe invention relates to reductant injection systems for injecting reductant into an exhaust passage of an internal combustion engine, and more particularly to methods for monitoring and determining an amount of injected fuel.Background ArtTo reduce nitrogen oxides in the combustion exhaust gas of an internal combustion engine, a reducing agent is fed into an exhaust tract, which usually comprises an aqueous urea solution. The reducing agent is provided under pressure in a pressure line by means of a supply module and injected into the exhaust tract via a metering unit. The quantity of injected reducing agent is determined by adjusting the opening time duration of a metering valve of the metering unit.As is known, for example, from the publication DE 10 2008 001 789 A1, the amount of reducing agent injected is adjusted by the corresponding time control of the metering valve. In this case, the pressure of the reducing agent in the pressure line is taken into account for adjusting the reducing agent quantity.However, the effective pressure of the reducing agent at the dosing unit can deviate from the pressure of the reducing agent set in the pressure line due to dynamic properties of the pressure line, of the reducing agent and the speed of sound in the reducing agent. This applies in particular to short opening times of the dosing unit. Thus, in particular in the case of short opening times of the dosing unit, the injected reducing agent quantity can be determined only inaccurately.It is therefore an object of the present invention to provide an improved method for determining and monitoring the amount of reductant injected in a reductant injection system for an exhaust treatment device of an engine system having an internal combustion engine.Disclosure of the InventionThis object is achieved by the method for determining an amount of injected reducing agent in a reducing agent injection system for an exhaust tract of an internal combustion engine according to claim 1 as well as a corresponding device and a reducing agent injection system according to the subordinate claims.Further embodiments are given in the dependent claims.According to a first aspect, a method for determining an amount of injected reductant in a reductant injection system for an exhaust tract of an internal combustion engine is provided, comprising the following steps:providing a predetermined reductant pressure in a reductant injection system pressure line;activating a metering unit having at least one metering valve in accordance with an opening time duration for supplying reducing agent into the exhaust tract;recording a pressure curve during the opening time period of the dosing unit;determining a period duration indication to be determined of a pressure oscillation in the pressure line resulting from the opening of the metering unit;determining an amount of injected reducing agent as a function of the opening time duration, the predetermined reducing agent pressure and the period duration information to be determined.A reduction of nitrogen oxides in an exhaust tract of an internal combustion engine is achieved by controlled supply of reducing agent, such as an aqueous urea solution. This is achieved by means of a reducing agent injection system, through which reducing agent is injected into the exhaust tract.In order to achieve an optimum reduction in nitrogen oxide in the exhaust tract of the internal combustion engine, it is necessary to exactly adjust the metering of reducing agent. The reducing agent is atomized via a metering unit and thus injected into the exhaust gas flow in the exhaust tract, wherein the metering unit is controlled by a control signal which indicates the opening time of at least one metering valve of the metering unit. The injected quantity of reducing agent is determined from the reducing agent pressure with which the reducing agent is provided at the location of the metering valve and the opening time of the metering valve.The reductant pressure in the pressure line is provided by a supply module with a reductant pump. A pressure sensor is also provided in the supply module, so that the reducing agent pressure in the pressure line can be regulated.However, the arrangement of the pressure sensor in the supply module at a distance from the metering unit has the result that at the time of opening of the metering valve the pressure in the pressure line falls rapidly and then in the region of the metering valve the pressure of the reducing agent is lower than indicated by the pressure sensor. The pressure drop is determined by the dynamic properties of the injection system or the pressure line, such as, for example, the geometric properties of the pressure line, such as line length, line inner diameter and damping properties of the pressure line, a possibly provided pressure damper in the supply module, which provides the reducing agent under the desired pressure, and the delay of pressure oscillations between the metering unit and the supply module through the pressure line. Particularly in the case of short opening times of the metering valve, the pressure drop leads to an inaccurate determination of the injected reducing agent quantity. Furthermore, the direct pressure drop at the opening time of the metering valve causes the greatest deviations from the calculated metering quantity.At the opening time of the metering valve, an oscillation of the pressure distribution in the pressure line is triggered, which starts with a pressure drop, has a damped sinusoidal profile and decays rapidly.According to the above method, it is therefore provided that the injected quantity of reducing agent is determined, in addition to the set pressure of the reducing agent in the pressure line and the opening time duration of the metering valve, further as a function of the indication of the period duration of the pressure oscillations in the pressure line after an opening time.Furthermore, the period duration to be determined can be determined as a function of a first period duration indication which is determined according to a first measurement method on the basis of a time difference of a first pressure minimum and a subsequent pressure maximum after the opening time, wherein the first period duration indication corresponds to 1.9 to 2.1 times, in particular twice, the time difference between the pressure minimum and the pressure maximum.The period duration indication can thus be determined in the first measuring method on the basis of a time difference of a pressure minimum and a subsequent pressure maximum after the opening time, such that the time difference between the pressure minimum and the pressure maximum corresponds to approximately half a period duration indication of the pressure wave.This first measuring method enables an accurate determination of the period duration specification, but requires a precise measurement of the pressure profile after the opening of the metering valve and is therefore very susceptible to faults.Alternatively or additionally, it can be provided that the period duration indication to be determined is determined as a function of a second period duration indication which is determined according to a second measurement method as a function of a time difference between the time of opening of the at least one metering valve of the metering unit and the time of reaching a pressure drop or pressure change (delay time between opening of the metering unit and a change in the pressure signal) which is brought about by opening of the metering valve, wherein the second period duration indication corresponds to 3.9 to 4.1 times, in particular four times, the time difference.Thus, the period duration information of the pressure wave through the pressure line can be determined in a second measuring method by measuring the propagation delay between the time of opening the metering valve, which is predetermined by the activation time of the metering valve, and the time of reaching a first pressure minimum of the pressure drop, which is caused by the opening of the metering valve. This second measuring method for measuring the period duration indication is more robust with respect to disturbances, but less accurate in the determination of the period duration indication.It can be provided that the determination of the quantity of injected reducing agent is carried out by first determining an injection quantity depending on the opening time duration and the predefined reducing agent pressure and applying a correction value to the injection quantity, which correction value results according to an assignment function depending on the opening time duration, the predefined reducing agent pressure and the period duration indication to be determined.Thus, the quantity of injected reducing agent can be determined depending on the opening time duration, the pressure of the reducing agent in the pressure line and the period duration indication to be determined. In particular, the period duration information can be assigned to a correction value with the aid of an assignment table, with which the injected reducing agent quantity determined on a model basis from the opening period and the pressure is applied.Furthermore, the determination of the quantity of injected reducing agent can take place as a function of at least one release condition, wherein the release condition comprises that the pressure in the pressure line at the opening time is within a certain predefined range and / or that further systems which have an influence on the injection system, such as e.g. an adjusting system for the delivery stroke of the reducing agent pump, a second metering valve in a DI-SCR system, etc., are not activated.Both conditions ensure that no interference occurs with the reducing agent injection system, which leads to incorrect measurements of the period duration information.Furthermore, the quantity of injected reducing agent to be determined can be determined as a function of the first period duration indication as a period duration indication to be determined if the difference between the first period duration indication and the second period duration indication corresponds to less than a predefined threshold value, wherein otherwise the quantity of injected reducing agent to be determined is determined as a function of the second period duration indication as a period duration indication to be determined.It can be provided that both measuring methods are used simultaneously. In this case, it can be provided that the result of the first measuring method is not used if the result of the second measuring method deviates from the result of the second measuring method by more than a predetermined difference. In this case, the result of the second measurement method is used.Before the determination of the period duration information using the first and second measurement methods, the profile of the pressure signal of the pressure in the line can be filtered with the aid of a time-based filter in order to reduce interference, which can make the determination using the first measurement method inaccurate in particular.Further, the determined amount of injected reductant may be used to monitor, control, or regulate injection by the reductant injection system.According to a further aspect, a device, in particular a control device, is provided for carrying out the above method.According to a further aspect, a reducing agent injection system for an exhaust tract of an internal combustion engine is provided, comprising:a dosing unit for the controlled supply of reducing agent into the exhaust tract;a pressure line for supplying the reducing agent to the dosing unit;a reductant pump for providing reductant in the pressure line at a predetermined reductant pressure;a pressure sensor for detecting the reducing agent pressure in the pressure line;the above device.Brief Description of the DrawingsEmbodiments are explained in more detail below with reference to the attached drawings. The following are shown: FIG. 1 is a schematic illustration of a reductant injection system for injecting reductant into an exhaust passage of an internal combustion engine; FIG. 2 shows a method for determining an amount of injected reducing agent by measuring a period duration specification; and FIG. 3 shows a schematic illustration of a pressure profile in the pressure line when a metering valve is opened.DESCRIPTION OF EMBODIMENTSFIG. 1 shows a reducing agent injection system 1 having a reducing agent tank 2, from which reducing agent is conveyed into a pressure line 4 via a supply module 3. For this purpose, the supply module 3 has a reducing agent pump 31, which can provide reducing agent under a pressure in the pressure line 4. To control the pressure level in the pressure line 4, a pressure sensor 32 is provided in the supply module 3. Furthermore, the supply module 3 can have a pressure damper 33 in order to damp pressure fluctuations.The pressure line is connected to a dosing unit 5, through which reducing agent is injected into an exhaust tract 6 of an internal combustion engine or an exhaust gas aftertreatment device.The injection is controlled or regulated with the aid of a control unit 10 in a manner known per se for nitrogen oxide reduction.It is necessary to monitor the injected amount of reducing agent in order to always achieve an optimum nitrogen oxide reduction. Since the reducing agent quantity is not measured directly, modeling of the reducing agent quantity based on the measured variables is necessary.As described at the beginning, the influence of dynamic effects in the pressure line leads to the conventionally calculated quantity of reducing agent being inaccurate on the basis of the pressure in the pressure line 4 and the opening time duration of the metering valve of the metering unit 5. This reduces the quality of the nitrogen oxide reduction.The method described below enables a more accurate determination of the quantity of injected reducing agent based on a measurement of a period duration specification.The method is implemented in the controller 10 and may be applied at each injection cycle.In step S 1, it is checked whether an injection of reducing agent is to be carried out with the aid of the dosing unit 5.In step S 2, the metering valve of the metering unit 5 is controlled to open and at the same time a recording of the pressure profile is carried out by the pressure sensor 32. FIG. 3 shows a representation of the time pressure curve (curve K) after the opening of the metering valve. A damped sinusoidal oscillation is seen, which begins with a pressure drop.In step S 3 it is checked whether the dosing unit should be closed again after the predetermined time period has elapsed. If this is the case (alternative: yes), the method continues with step S 4; otherwise, the method jumps back to step S 3.In step S 4, it is checked whether release conditions for determining a period duration indication are fulfilled. These release conditions can specify a constant pressure before the beginning of the opening of the metering valve and a pressure in a specific predefined value range. Furthermore, the release conditions can provide that during the measurement of the pressure curve no further actuators which can influence the injection system have been activated. If the release conditions are fulfilled (alternative: yes), the method is continued with step S 5, otherwise the method is continued with step S 1 and the value determined last valid is used as the value for the amount of the injected reducing agent.In step S 5, the recorded pressure curve is now filtered with the aid of a time-based filter in order to eliminate disturbances and outliers in the measurement values. The filtered curve KF shown in FIG. 3 is obtainedIn step S 6, based on the filtered course curve according to a first measurement method, a time T 1 of a first pressure minimum is determined after the time T 0 of the opening of the metering valve and a time of a subsequent maximum T 2, and the corresponding time difference between the times is determined. The first period duration indication according to the first measuring method is then determined from the multiplication by 2 in order to obtain the period duration of the first sinusoidal half wave after the opening of the metering valve.In step S 7, the time duration between the time T 0 of the opening of the metering valve (time of the activation for opening) and the time T 3 of the reaching of the first pressure drop or pressure change after the opening of the metering valve is measured with the aid of a second measuring method, and the corresponding time difference is multiplied by the factor 4 in order to obtain the second period duration indication.In step S 8, it is determined which of the period duration information is to be taken into account for the subsequent correction of the determined quantity of injected reducing agent. Although the measurement of the first period duration indication is more accurate, it is not as robust as the second period duration indication which is obtained by the second measurement method. Therefore, the value of the first period duration indication is used as the period duration indication to be determined only if the value of the second period duration indication deviates from the value of the first period duration indication by not more than a predefined threshold value. Otherwise, the value of the second period duration indication is determined as a period duration indication to be determined.In step S 9, the period duration information to be ascertained and the pressure of the reducing agent in the pressure line 4 are assigned to a correction value according to an assignment table. The mapping table indicates a correction value.In step S 10, an injected reducing agent quantity, which is determined according to a model as a function of the pressure in the pressure line and the controlled opening time duration, is corrected, in particular additively or multiplicatively.The reducing agent quantity of injected reducing agent determined in this way can now be taken into account in step S 11 for monitoring and for determining a setpoint quantity of reducing agent to be injected for subsequent injection processes.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2008 001 789 A1

[0003]

Claims

Method for determining an amount of injected reducing agent in a reducing agent injection system (1) for an exhaust tract (6) of an internal combustion engine, having the following steps: - providing a predefined reducing agent pressure in a pressure line (4) of the reducing agent injection system (1); - actuating (S2) a metering unit (5) having at least one metering valve in accordance with an opening time duration for supplying reducing agent into the exhaust tract (6); - recording (S2) a pressure profile during the opening time duration of the metering unit (5); - determining (S6, S7) a period duration indication to be determined of a pressure oscillation resulting from the opening of the metering unit (5) in the pressure line (4); determining (S10) an amount of injected reducing agent as a function of the opening time duration, the predefined reducing agent pressure and the period duration indication to be determined.Method according to Claim 1, wherein the determination of the quantity of injected reducing agent is carried out by firstly determining an injection quantity as a function of the opening time duration and the predefined reducing agent pressure and applying a correction value to the injection quantity, which correction value results in accordance with an assignment function as a function of the opening time duration, the predefined reducing agent pressure and the period duration indication to be determined.Method according to Claim 1 or 2, wherein the period duration to be determined is determined as a function of a first period duration indication which is determined according to a first measurement method on the basis of a time difference of a first pressure minimum and a subsequent pressure maximum after the opening time, wherein the first period duration indication corresponds to twice the time difference between the pressure minimum and the pressure maximum.Method according to one of Claims 1 to 3, wherein the period duration indication to be determined is determined as a function of a second period duration indication which is determined according to a second measurement method as a function of a time difference between the time of opening of the at least one metering valve of the metering unit (5) and the time of reaching a pressure drop or a pressure change which is / is caused by the opening of the metering valve, wherein the second period duration indication corresponds to four times the time difference.Method according to Claim 4 in conjunction with Claim 3, wherein the quantity of injected reducing agent to be determined is determined (S8) as a function of the first period duration indication as a period duration indication to be determined if the difference between the first period duration indication and the second period duration indication corresponds to less than a predefined threshold value, wherein otherwise the quantity of injected reducing agent to be determined is determined as a function of the second period duration indication as a period duration indication to be determined.Method according to one of Claims 1 to 5, wherein the determination of the quantity of injected reducing agent takes place (S4) as a function of at least one release condition, wherein the release condition comprises the pressure in the pressure line (4) being within a specific predefined range at the opening time and / or further systems which have an influence on the injection system being not actuated.Method according to one of Claims 1 to 6, wherein the profile of the pressure signal is filtered (S5) using a time-based filter before the determination of the period duration indication to be determined.The method of any of claims 1 to 7, wherein the determined amount of injected reductant is used to monitor, control or regulate injection by the reductant injection system.Device, in particular control device (10), for carrying out the method according to one of Claims 1 to 8.Reducing agent injection system (1) for an exhaust tract (6) of an internal combustion engine comprising: - a dosing unit (5) for controlled supply of reducing agent into the exhaust tract (6); - a pressure line (5) for supplying the reducing agent to the dosing unit (5); - a reducing agent pump (31) for providing reducing agent in the pressure line (4) under a predetermined reducing agent pressure; - a pressure sensor (32) for detecting the reducing agent pressure in the pressure line (4); - a device (10) according to claim 9.

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