Method for operating a metering device and device for carrying out the method

Abstract

A method for operating a metering device (14) arranged at least partially in an exhaust gas section (12) of an internal combustion engine (10), in which fuel, which is also supplied to the internal combustion engine (10) as motive fuel, is metered as a reagent into the exhaust gas section (12) for operating an exhaust gas purification device (18), and in which a nominal metering operation is provided depending on a metering requirement (km, h, PM, dp), characterized in that outside the nominal metering operation an exchange metering operation is provided, in which the fuel present at least in those parts of the metering device (14) that are exposed to a temperature load is exchanged for incoming fuel, and that the exchange metering operation depends on a measure (km, te_Abg, te_Lu,te_Rea) for the aging of the fuel contained in the parts of the metering device (14) exposed to temperature stress.,

Description

[0001] The invention relates to a method for operating a metering device, at least parts of which are arranged in an exhaust gas area of ​​an internal combustion engine, and to a device for carrying out the method according to the preamble of the independent claims.

[0002] The present invention also relates to a control unit program and a control unit program product. State of the art

[0003] A method for operating an internal combustion engine is described in the prior art. An SCR (Selective Catalytic Reduction) catalyst is arranged in the exhaust system of this engine. The SCR catalyst reduces the nitrogen oxides contained in the exhaust gas to nitrogen using a reagent. The dosage of the reagent or a precursor to the reagent is preferably determined based on operating parameters of the internal combustion engine, such as the engine speed and the amount of fuel injected. Furthermore, the dosage is preferably determined based on exhaust gas parameters, such as the exhaust gas temperature or the operating temperature of the SCR catalyst. For example, ammonia, which can be obtained from a urea-water solution, is used as the reagent. The dosage of the reagent or of the precursors to the reagent must be carefully determined.Insufficient dosage results in nitrogen oxides not being completely reduced in the SCR catalyst. Excessive dosage leads to reagent slippage, which can result in unnecessarily high reagent consumption and, depending on the reagent's properties, unpleasant odors.

[0004] German patent application DE 10 2004 056 412 A1 describes a method for operating an internal combustion engine in which an exhaust gas treatment device is arranged in the exhaust gas section and in which a reagent is introduced into the exhaust gas section of the internal combustion engine. The reagent is fuel, which is intended to react exothermically on a catalytically active surface in order to increase the temperature of the catalytically active surface or, in particular, of the exhaust gas, for heating the exhaust gas treatment device.

[0005] In the described devices and methods, a reagent or a precursor of the reagent is metered into the exhaust gas duct of the internal combustion engine by a reagent metering device, whereby at least some parts of the reagent metering device may be exposed to increased temperature stress due to the exhaust gas temperature. Cooling may be necessary, particularly for reasons of the mechanical reliability of the affected parts. Such cooling is described in DE 44 36 397 A1, which provides a cooling jacket integrated into the cooling water circuit of an internal combustion engine, surrounding a metering valve of the reagent metering device. The metering valve is arranged in a common housing with a control valve. The control valve serves to control the introduction of compressed air, which is intended to assist the spraying process of the reagent.The compressed air prevents deposits and clumping of the sprayed reagent on the metering valve and, if applicable, on the control valve.

[0006] Furthermore, DE 103 22 155 A1 describes a method for operating an exhaust gas purification system in which a reagent is injected upstream of the exhaust gas purification system into the exhaust gas channel of an internal combustion engine by means of a metering valve. The reagent is metered according to a fixed time schedule to cool the metering valve.

[0007] German patent DE 10 2006 053 485 A1 describes a method for operating a metering valve located in the exhaust gas section of an internal combustion engine for dosing a reagent. To prevent overheating, cooling is provided, which is also achieved by dosing reagent as needed during pauses in the normal dosing process. In contrast to the previously described method, the amount of reagent used for cooling is specifically set to a minimum value.

[0008] FR 2 897 649 A1 discloses a method for cleaning an injector in a fuel injection system for use in the regeneration of a particulate filter. According to this method, the aging of the fuel is determined, compared with a fuel aging threshold, and a cleaning request for an injector is activated if this threshold is exceeded.

[0009] The invention is based on the objective of providing a method for operating a metering device, at least parts of which are arranged in the exhaust gas area of ​​an internal combustion engine and are thereby exposed to a temperature load, and a device for carrying out the method, which enables correct metering of the fuel used as a reagent within the framework of a nominal metering operation depending on a reagent requirement.

[0010] The problem is solved by the features specified in the independent claims. Disclosure of the invention

[0011] The inventive method for operating a metering device arranged at least partially in the exhaust gas section of an internal combustion engine, in which fuel, which is also supplied to the internal combustion engine as motive fuel, is metered into the exhaust gas section as a reagent for operating an exhaust gas purification device, is based on a nominal metering operation that is dependent on a metering requirement. According to the invention, an exchange metering operation is provided outside of the nominal metering operation, in which the fuel present at least in those parts of the metering device that are exposed to temperature stress is exchanged for incoming fuel. The exchange metering operation is carried out depending on a measure of the aging of the fuel contained in the parts of the metering device exposed to temperature stress.Temperature stress occurs particularly in components of the metering device that are located in the exhaust gas area.

[0012] The inventive method has the advantage that it takes into account the aging of the fuel contained at least in those parts of the metering device exposed to temperature stress. An aging problem arises particularly with biodiesel, for which, for example, a service life of only 6 hours at a temperature of 110°C must be assumed. At high temperatures, polymerization of the fuel and decomposition of the fuel additives occur, which would lead, on the one hand, to at least partial clogging of the metering device and, on the other hand, to corrosion.

[0013] Due to the aging processes of the fuel, precise metering of a predetermined amount of fuel according to the metering requirement would no longer be guaranteed. The inventive method avoids such malfunctions of the metering device by taking the aging of the fuel into account, whereby aged fuel is replaced by freshly flowing fuel.

[0014] Advantageous further developments and embodiments of the inventive method result from dependent claims.

[0015] One design uses the exhaust gas temperature as a measure of fuel aging. The exhaust gas temperature can be calculated based on parameters of the combustion engine or measured by a temperature sensor located in the exhaust manifold.

[0016] An additional or alternative embodiment provides that a measure of fuel temperature in those parts of the metering device exposed to thermal stress is considered as a measure of fuel aging. This measure reflects the aging of the fuel contained in the metering device with comparatively accurate accuracy. Preferably, the fuel temperature in the metering device is measured at least indirectly. For example, a measure of the fuel temperature can be calculated from the temperature of an electrically controlled solenoid valve contained in the metering device by evaluating the internal resistance of the solenoid coil, provided that the solenoid valve is located in the part of the metering device exposed to the increased thermal stress.

[0017] Another additional or alternative design considers the ambient temperature as a measure of fuel aging. The ambient temperature is generally already available in the combustion engine's control unit, so no additional effort is required to measure it.

[0018] The exchange dosing operation can be implemented if predefined temperature thresholds are exceeded.

[0019] Additionally or alternatively, it may be provided that the measure of fuel aging is determined based on the distance traveled by a motor vehicle in which the internal combustion engine is installed as the drive engine. In this case, an exchange metering operation is carried out upon reaching a mileage threshold. Additionally or alternatively, it may also be provided that the measure of fuel aging is determined based on the load of the internal combustion engine, which is preferably calculated from operating parameters of the internal combustion engine.

[0020] One design provides that the amount of fuel metered during exchange dosing operation corresponds at least to the amount of fuel present in those parts of the dosing device that are exposed to the temperature stress in the exhaust gas area of ​​the combustion engine. This ensures that at least the amount of fuel exposed to the highest temperature stress is exchanged.

[0021] The device according to the invention for carrying out the method initially relates to a specially designed control unit. The control unit includes, in particular, a nominal operation dosing control and an exchange operation dosing control as means for carrying out the method.

[0022] The control unit preferably contains at least one electrical memory in which the process steps are stored as a control unit program.

[0023] The control unit program according to the invention provides that all steps of the method according to the invention are executed when it runs in a control unit.

[0024] The control unit program product according to the invention, comprising a program code stored on a machine-readable carrier, executes the method according to the invention when the program runs in a control unit.

[0025] Exemplary embodiments of the invention are shown in the drawing and explained in more detail in the following description. Brief description of the characters

[0026] The figure shows a technical environment in which a method according to the invention for operating a metering device arranged at least partially in an exhaust gas area of ​​an internal combustion engine takes place, wherein at least parts of the metering device are exposed to a temperature load in the exhaust gas area. Detailed description of the exemplary implementations

[0027] The figure shows an internal combustion engine 10, in whose exhaust gas area 12 at least parts of a metering device 14, a temperature sensor 16 and an exhaust gas purification device 18 are arranged.

[0028] The temperature sensor 16 detects an exhaust gas temperature te_Abg that occurs in the exhaust gas section 12 of the combustion engine 10. In the illustrated embodiment, it is assumed that the temperature sensor 16 detects at least one measure of the exhaust gas temperature te_Abg upstream of the exhaust gas purification device 18. Alternatively or additionally, the further method can be based on an exhaust gas temperature te_Abg that occurs immediately downstream of the combustion engine 10.

[0029] The metering device 14 includes, for example, a metering valve 24, which is actuated by a control unit 30 with a metering signal s_Rea. The metering device 14 provides the control unit 30 with at least one measurement for the fuel temperature te_Rea, and the temperature sensor 16 provides at least one measurement 38 for the exhaust gas temperature te_Abg.

[0030] The exhaust gas purification device 18 preferably includes at least one catalyst 20 and / or, for example, a particulate filter 22. The catalyst 20 can be an oxidation catalyst and / or a NOx storage catalyst and / or an SCR catalyst. Depending on the specific design, the catalyst 20 and / or the particulate filter 22 may require an elevated exhaust gas temperature for regeneration. In the case of catalysts, particularly NOx storage catalysts, sulfur poisoning can occur, for example, which can be eliminated at a temperature of, for example, 850°C. Without further fuel additives, a particulate filter requires a temperature, for example, in the range of 550°C to 650°C, to ignite and subsequently burn off the stored particles.

[0031] To achieve a sufficiently high exhaust gas temperature te_Abg, the metering device 14 doses fuel into the exhaust gas area 12, which reacts exothermically with the support of the catalytically active area of ​​the catalyst 20, thereby heating the catalyst 20 and / or the particulate filter 22 directly or at least indirectly via the exhaust gas temperature te_Abg. The catalytically active area or the catalyst 20 can be contained within the particulate filter 22. The fuel used as a reagent is the same fuel that is also supplied to the internal combustion engine 10 as motive fuel.

[0032] Fuel metering occurs during a nominal metering operation depending on a metering request. This metering request can, for example, depend on the distance traveled by a motor vehicle (km), provided the internal combustion engine 10 is installed in a motor vehicle. Furthermore, the metering request can depend on the operating time (h) of the exhaust aftertreatment device 18. If the exhaust aftertreatment device 18 includes at least the particulate filter 22, the metering request can depend on the particle quantity (PM) measured by a particle sensor (not shown) located upstream of the exhaust aftertreatment device 18, or on an estimated value for the particle quantity (PM). Alternatively or additionally, the differential pressure (dp) occurring at the particulate filter 22 can be taken into account in the metering request.Furthermore, additional input variables, such as parameters of the combustion engine 10, like the rotational speed and / or the amount of fuel supplied to the combustion engine 10, can be taken into account. The metering request is converted by a nominal operation metering control 32 into a nominal metering signal s_Rea_Nenn, which is provided to the metering valve 24 as a metering signal s_Rea via an OR gate 34.

[0033] The fuel, in particular the fuel present in those parts of the metering device 14 that are exposed to increased temperature stress, especially in the exhaust gas area 12, may be subject to an accelerated aging process due to the elevated temperatures. Those parts of the metering device 14 that may be exposed to increased temperature stress, especially in the exhaust gas area 12 of the internal combustion engine 10, include, for example, the metering valve 24 or, for example, a simple check valve, as well as lines for conveying the fuel.

[0034] The aging process depends on the type of fuel. For example, regular diesel fuel has a service life of 60 hours at a temperature of 110°C, while biodiesel, for instance, has a service life of only 6 hours at 110°C. After exceeding either the service life or the specified maximum temperature, polymerization of the fuel and / or decomposition of any additives blended into the fuel must be expected. This alters the relationship between the actual metered fuel quantity and the metering signal s_Rea. Polymerization can lead to clumping, while decomposition, in particular, leads to corrosion of components of the metering device 14.

[0035] To ensure the most precise possible dosing depending on the nominal dosing signal s_Rea_Nenn, an exchange dosing operation is provided outside of the nominal dosing operation according to the present invention. In this operation, at least the fuel present in those parts of the dosing device 14 that are exposed to increased temperature stress is exchanged for incoming fuel. This measure ensures that no negative effects on the predetermined dosing quantity can occur in the event of increased temperature stress, which accelerates fuel aging.

[0036] The exchange dosing operation is carried out at least depending on at least one measure of the aging of the fuel contained in the dosing device 14, which is exposed to the increased temperature.

[0037] As a first measure of fuel aging, at least one measure of the exhaust gas temperature te_Abg can be considered. The exhaust gas temperature can be measured with the temperature sensor 16, which provides the control unit 30 with the value s_te_Abg for the exhaust gas temperature te_Abg. If necessary, the exhaust gas temperature te_Abg can be calculated, at least approximately, from operating parameters of the internal combustion engine 10. The rotational speed of the internal combustion engine 10 and, in particular, the amount of fuel supplied to the internal combustion engine 10 can be taken into account.

[0038] Alternatively or additionally, a measure of fuel temperature te_Rea can be considered as a measure of fuel aging. The fuel temperature te_Rea can be derived from a measured temperature in the metering device 14. For this purpose, a temperature sensor can be provided, for example, which directly detects the fuel temperature. A temperature sensor can be omitted if the temperature of the metering valve 24, which is designed as a solenoid valve controlled by the metering signal s_Rea, is used as the measure of fuel temperature te_Rea. The temperature of the metering valve 24 can be determined indirectly by evaluating the internal resistance of the solenoid coil.

[0039] Alternatively or additionally, the distance traveled by a motor vehicle (in km) can be considered as a measure of fuel aging, provided the internal combustion engine is intended as the drive system in a motor vehicle. The distance traveled is at least a rough measure of fuel aging. In this case, after exceeding a mileage threshold, for example 500 km, the exchange metering operation can be initiated, provided that no nominal metering operation has taken place.

[0040] As part of recording at least one measure for the exhaust gas temperature te_Abg and / or at least one measure for the fuel temperature te_Rea, an exchange dosing operation can be carried out if the exhaust gas temperature te_Abg or the fuel temperature te_Rea has exceeded temperature threshold values.

[0041] Another measure of fuel aging that can be considered is the ambient temperature te_Lu. The ambient temperature te_Lu is preferably used to shift the temperature thresholds, or in particular the mileage threshold, in the various previously described options for initiating the exchange metering operation. At lower ambient temperatures te_Lu, the threshold can be shifted to higher values ​​because the exchange metering operation can be delayed.

[0042] As a measure of fuel aging, at least one measure of the combustion engine load can be used, preferably calculated from at least one operating parameter of the combustion engine 10, such as the amount of fuel supplied. The relationship between the load and the measure of aging can be determined and defined within the scope of an application.

[0043] In the illustrated embodiment, the kilometers driven by a motor vehicle (km), the exhaust gas temperature (te_Abg), the ambient temperature (te_Lu), the fuel temperature (te_Rea), and other input variables not shown in detail, such as parameters of the combustion engine 10 and / or the metering device 14, are provided as input variables to an exchange-operation metering control 36, which provides an exchange metering signal (s_Rea_Austausch) that is provided to the OR gate 34, which provides the metering signal (s_Rea) to the metering valve 24.

[0044] The exchange operation dosing control 36 contains the nominal dosing signal s_Rea_Nenn as an additional input variable in order to be able to perform a reset of the exchange operation dosing control 36 in the event of a nominal dosing operation, since an exchange dosing operation is not required when a nominal dosing operation is requested.

Claims

[1] Method for operating a metering device (14) arranged at least partially in an exhaust gas section (12) of an internal combustion engine (10), in which fuel which is also supplied to the internal combustion engine (10) as motive fuel is metered as a reagent into the exhaust gas section (12) for operating an exhaust gas purification device (18), and in which a nominal metering operation is provided depending on a metering requirement (km, h, PM, dp), characterized by, that outside of the nominal metering operation an exchange metering operation is provided in which the fuel present at least in those parts of the metering device (14) that are exposed to a temperature load is exchanged for incoming fuel, and that the exchange metering operation is carried out depending on a measure (km, te_Abg, te_Lu, te_Rea) for the aging of the fuel contained in the parts of the metering device (14) exposed to the temperature load. [2] Method according to claim 1, characterized by , that a measure of the temperature (te_Abg) of the exhaust gas is taken into account as a measure of the aging of the fuel. [3] Method according to claim 1, characterized by , that a measure of the ambient temperature (te_Lu) is taken into account as a measure of the aging of the fuel. [4] Method according to claim 1, characterized by, that a measure of fuel temperature (te_Rea) is taken into account as a measure of fuel aging. [5] Method according to claim 4, characterized by , that the measure of fuel temperature (te_Rea) depends on a measured temperature in the metering device (14). [6] Method according to claim 1, characterized by , that the internal combustion engine (10) is arranged in a motor vehicle, and that the distance traveled (km) by the motor vehicle is taken into account as a measure of the aging of the fuel. [7] Method according to claim 1, characterized by , that a measure of the load of the internal combustion engine (10) is used as a measure of the aging of the fuel. [8] Method according to claim 7, characterized by , that the measure for the load of the internal combustion engine (10) is calculated from at least one operating parameter of the internal combustion engine (10). [9] Method according to claim 1, characterized by, that the amount of fuel metered in the exchange metering operation corresponds at least to the amount of fuel contained in those parts of the metering device (14) which are exposed to a temperature load in the exhaust gas area (12). [10] Device for operating a metering device (14) arranged at least partially in an exhaust gas area (12) of an internal combustion engine (10), characterized by , that at least one control unit (30) specially prepared for carrying out the method according to one of claims 1 to 9 is provided. [11] Device according to claim 10, characterized by , that the control unit (30) contains a nominal operation dosing control (32) and an exchange operation dosing control (36). [12] Control unit program that performs all steps of a method according to any one of claims 1 to 9 when the program runs in a control unit (30). [13] Control unit program product comprising a program code stored on a machine-readable carrier for carrying out the method according to any one of claims 1 to 9, when the program is executed in a control unit (30).

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