Method for controlling a dosing system with multiple dosing valves

Abstract

Method for controlling a dosing system (30) with a plurality of dosing valves (31, 32), wherein a first reduction factor is determined as a function of desired dosing quantity requirements for the dosing valves (31, 32) and a maximum possible total dosing quantity of all dosing valves (31, 32).

Description

[0001] The present invention relates to a method for controlling a dosing system with multiple dosing valves. Furthermore, the present invention relates to a computer program that executes each step of the method, as well as to a machine-readable storage medium that stores the computer program. Finally, the invention relates to an electronic control unit configured to execute the method. State of the art

[0002] Dosing systems for SCR catalyst systems with one or more dosing valves implement a desired quantity requested by the dosing strategy as promptly and precisely as possible by translating the desired quantity into a control of the dosing valves using known information about the potential flow rate of the respective dosing valves and the system pressure. However, if the desired quantity exceeds the physical capacity of the system—i.e., the maximum mass flow that can be metered by the respective dosing valve or the maximum mass flow that can be re-delivered by the delivery unit—this quantity must be limited to this physical upper limit. The quantity then implemented no longer corresponds to the requirement from the dosing strategy, which may then have to respond with increased readjustment.

[0003] In the case of two or more metering valves, however, the total mass flow metered by all valves at any one time must also be limited to the physical upper limit of the delivery unit. Current systems use a simple prioritization for this purpose; for example, in a system with two valves, the quantity request of the valve close to the motor is often first limited to the maximum possible pump mass flow, and only then is the quantity request of the underfloor metering valve limited to any remaining difference between the maximum pump mass flow and the metered quantity already requested for the first valve. Another prioritization option is to give priority to the metering point with the higher temperature; a third possibility is to give priority to the metering point with the higher quantity request. However, the quantity requests are often very unequal.For example, underfloor valves often receive a significantly lower flow rate requirement. With these simple prioritizations, the degree to which the catalysts fulfill their desired dosing requirements is unbalanced. This usually results in the dosing strategy's fill level controller oscillating, as the last valve experiences greater limitation. Disclosure of the invention

[0004] The method is based on the insight that all limitations of metered mass flows should be set such that the ratio of the metered mass flows of multiple metering valves in a metering system corresponds to the ratio of the original quantity requirement. This approach most closely corresponds to the requirements of the metering strategy. Unilateral limitation, however, would lead to an oscillation of the fill level controller, even with significantly unequal quantity requirements. To control a metering system with multiple metering valves, it is therefore planned to determine an initial reduction factor depending on the desired metering quantity requirements of the metering valves and the maximum possible total metering quantity of all metering valves.This reduction factor can subsequently be applied equally to the metered mass flows of all metering valves if the sum of the desired metering quantity requirements exceeds the possible total metering quantity of all metering valves.

[0005] The method can be used in particular for controlling the dosing system for an SCR catalyst system. Such dosing systems feature a feed pump that pumps the fluid to be pumped—in the case of an SCR catalyst system, a urea-water solution (HWL)—from a tank and transports it to the dosing valves. If such a feed pump is present, the maximum possible total dosing quantity is preferably determined from at least one parameter of the feed pump. This parameter is, in particular, a maximum mass flow rate that can be re-delivered by the feed pump.

[0006] In one embodiment of the method, each dosing valve doses a dosage amount corresponding to the product of the desired dosage amount requirement of the respective dosing valve and the first reduction factor. The first reduction factor has a maximum value of 1 and thus reduces the actual dosage amounts compared to the desired dosage amount requirements in such a way that the ratio of the metered mass flows to the ratio of the desired dosage amount requirements remains unchanged.

[0007] This embodiment of the method is preferably used when each dosing valve has separate output stages (fully independent parallel dosing is possible) or when an electronic control unit of the dosing system has a low side for each dosing system and a common high side for all dosing systems. This enables parallel dosing with multiple dosing valves because any number of dosing valves can be open simultaneously. Although the opening process may need to be slightly delayed or offset, this does not significantly impact the quantity limitation.

[0008] In another embodiment of the method, a dosing quantity is metered one after the other by means of the dosing valves within a dosing interval. The respective dosing quantity corresponds to the product of the desired dosing quantity requirement of the respective dosing valve, the first reduction factor, and a second reduction factor. This embodiment of the method, in which a second reduction factor is required in addition to the first reduction factor, is used in particular when an electronic control unit of the dosing system has a common output stage for all dosing valves. This has the advantage that temperature control can take place during heating of the dosing valve, that a saturation current of the dosing valve can be measured, and that the BIP (begin of injection point) and the EIP (end of injection point) can also be measured.These options are not available when using a separate low side for each dosing valve, but a shared high side, and operating the valves simultaneously. However, simultaneous dosing using multiple dosing valves is not possible in such a dosing system. Since switching between the dosing valves requires dosing pauses, the dosing valves cannot dose together over the entire length of the dosing interval.

[0009] The second reduction factor can preferably be determined by considering the desired dosing quantity requirements of all dosing valves, the maximum possible total dosing quantity, the maximum possible dosing quantities of the individual dosing valves, the first reduction factor, and a relatively available total dosing time within the dosing interval. The relatively available total dosing time is understood to be the percentage of the dosing interval that is not required for switching between the dosing valves and is therefore available for dosing.

[0010] The second reduction factor makes it possible to process all dosings within the dosing interval while still ensuring that the ratio of the dosed mass flows corresponds to the ratio of the desired dosing quantity requirements.

[0011] The different embodiments of the method can be implemented together in a computer program configured to perform each step of the method, particularly when running on a computer or electronic control unit. It enables the control of dosing systems with shared or separate output stages using the same strategy, i.e., within the framework of a unified architecture. For this purpose, it is stored on the machine-readable storage medium.

[0012] By loading the computer program onto a conventional electronic control unit, the electronic control unit is obtained, which is configured to control a dosing system with several dosing valves. Short description of the drawings

[0013] Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Fig. 1 schematically shows an SCR catalyst system whose dosing system can be controlled by means of embodiments of the method according to the invention. Fig. 2 shows the temporal sequence of several dosages in an embodiment of the method according to the invention. Embodiments of the invention

[0014] An internal combustion engine 10 has an SCR catalyst system 20 in its exhaust system 11, which Fig. 1. This has two SCR catalysts 21, 22, wherein the catalyst material of the first SCR catalyst 21 is arranged on a particulate filter (SCR on filter; SCRF). A metering system 30 is provided for metering a urea-water solution into the exhaust system 11. This has a first metering valve 31 upstream of the first SCR catalyst 21 and a second metering valve 32 between the two SCR catalysts 21, 22. A feed pump 33 feeds the urea-water solution from a reducing agent tank (not shown). It is transported through a reducing agent line that branches off downstream of the feed pump 33 to the two metering valves 31, 32. The first metering valve 31 has a structurally determined, first maximum metered quantity dm max,31 and the second dosing valve 32 has a structurally determined, second maximum dosing quantity dm max,32 The maximum possible total dosage dm max,gesof the two dosing valves 31, 32 does not correspond to the sum of their individual maximum dosing quantities dm max,31 , dm max,32 Rather, it is lower, as it is limited by the maximum mass flow of the urea-water solution that can be delivered by the feed pump 33. The two metering valves 31, 32 and the feed pump 33 are controlled by an electronic control unit 40.

[0015] In a first exemplary embodiment of the invention, the electronic control unit 40 has a separate low-side output stage for each metering valve 31, 32. However, a common high-side output stage is provided for both metering valves 31, 32. Unrestricted parallel metering is possible using the two metering valves 31, 32, for which purpose all driver levels in the electronic control unit 40 exist in duplicate and unrestricted. The quantity requests for both metering valves are received separately and independently and, in principle, are also processed independently. Only a pull-in phase is delayed for the second metering valve 32 compared to the first metering valve 31.

[0016] If in the electronic control unit 40 a total desired dosing quantity requirement dm Wunsch,ges , which is the sum of the desired dosage quantity requirement dm Wunsch,31 of the first dosing valve 31 and the desired dosing quantity requirement dm Wunsch,32of the second dosing valve 32, which is greater than the maximum possible total dosing quantity dm max,ges of all metering valves 31, 32, which in turn results from the delivery capacity of the feed pump 33, a first reduction factor f1 is calculated according to formula 1: f1=dmmax,gesdmDesire,ges=dmmax,gesdmDesire,31+dmDesire,32

[0017] The control of the dosing valves 31, 32 by means of the electronic control unit 40 is then not based on the respective desired dosing quantity requirements dm Wunsch,31 , dm Wunsch,32 Instead, according to formula 2, a limited dosage requirement dm Dos,31 calculated for the first dosing valve 31: dmDos,31=f1⋅dmWunsch,31

[0018] In an analogous manner, using the first reduction factor, a limited dosing quantity requirement dm Dos,32 for the second metering valve 32 according to formula 3: dmDos,32=f1⋅dmWunsch,32

[0019] In a second embodiment of the invention, the electronic control unit 40 has a common output stage for both metering valves 31, 32. First, the system waits until the first metering valve 31 has completed its metering. Then, a switching relay in the electronic control unit 40 switches the split output stage, and the quantity request from the second metering valve 32 is then implemented. This order, in which the metering requests to the two metering valves 31, 32 are processed, is predefined in the electronic control unit 40.

[0020] Fig. 2 shows three different dosages of urea water solutions in the exhaust line 11, each within a dosage interval Δt ges The dosing time Δt 31 of the first dosing valve 31 and the dosing time Δt 32of the second metering valve 32 have in the three shown metering intervals Δt ges each have different lengths, whereby the length of the dosing by means of the second dosing valve 32 in the third dosing interval shown Δt ges even 0. Between the dosings there are switching pauses Δt u , which always have the same length. The relative total available dosing time Δt rel within each dosing interval Δt ges This results in formula 4: Δtrel=(Δttot−2⋅Δtu)Δttot

[0021] If a total desired dosing quantity requirement dm Wunsch,ges which is greater than the maximum possible total dosage amount dm max,ges both metering valves 31, 32, the first reduction factor f1 is first calculated in the electronic control unit according to formula 1, as in the first embodiment.

[0022] Furthermore, a second reduction factor f2 is calculated according to formula 5: f2=Δtrel⋅dmmax,31⋅dmmax,32f1⋅dmDesire,31⋅dmmax,32+f1⋅dmDesire,32⋅dmmax,31

[0023] The limited dosage requirement dm Dos,31 , which is used as a basis for controlling the first metering valve 31, is then calculated using both reduction factors f1, f2 not according to formula 2, but according to formula 6: dmDos,31=f1⋅f2⋅dmWunsch,31

[0024] In an analogous manner, the limited dosing quantity requirement dm Dos,32 of the second metering valve 32 is not calculated according to formula 3, but according to formula 7: dmDos,32=f1⋅f2⋅dmWunsch,32

[0025] In yet another embodiment, it may be provided that the second reduction factor f2 is not set to the value resulting from formula 5, but to an even lower value.

Claims

[1] Method for controlling a dosing system (30) with a plurality of dosing valves (31, 32), wherein a first reduction factor is determined as a function of desired dosing quantity requirements for the dosing valves (31, 32) and a maximum possible total dosing quantity of all dosing valves (31, 32). [2] Method according to claim 1, characterized by that the maximum possible total dosing quantity is determined from at least one parameter of a feed pump (33) of the dosing system (30). [3] Method according to claim 1 or 2, characterized by that by means of each dosing valve (31, 32) a dosing quantity is dosed which corresponds to the product of the desired dosing quantity requirement of the respective dosing valve and the first reduction factor. [4] Method according to claim 3, characterized bythat each metering valve (31, 32) has separate output stages or an electronic control unit (40) of the metering system (30) has a low side per metering valve (31, 32) and a common high side for all metering valves (31, 32). [5] Method according to claim 1 or 2, characterized by that by means of the dosing valves (31, 32) within a dosing interval (Δt ges ) a dosing quantity is dosed one after the other, which corresponds to the product of the desired dosing quantity requirement of the respective dosing valve (31, 32), the first reduction factor and a second reduction factor. [6] Method according to claim 5, characterized by that an electronic control unit (40) of the dosing system (30) has a common output stage for all dosing valves (31, 32). [7] Method according to claim 5 or 6, characterized bythat the second reduction factor depends on the desired dosing quantity requirements, the maximum possible total dosing quantity, the maximum possible dosing quantities of the individual dosing valves (31, 32), the first reduction factor and a relatively available total dosing time within the dosing interval (Δt ges ) is determined. [8] A computer program arranged to carry out each step of the method according to any one of claims 1 to 7. [9] A machine-readable storage medium on which a computer program according to claim 8 is stored. [10] Electronic control device (40) which is arranged to control a dosing system (30) by means of a method according to one of claims 1 to 7.

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