DE102016205105A1 - A method for operating a metering system for the reducing agent solution of an SCR catalyst device in the exhaust line of an internal combustion engine - Google Patents

Abstract

In a method for operating a metering system for the reducing agent solution of an SCR catalytic converter device (11) in the exhaust line (10) of an internal combustion engine, the metering system comprises at least one coolable metering module (20) which is connected to a coolant circuit (30). Cooling of the metering module (20) takes place by requesting a cooling capacity of the coolant circuit (30). According to the invention, the temperature of the coolant is taken into account when requesting a cooling power, wherein the temperature of the coolant in the region of entry into the metering module (20) is determined on the basis of a model. At least information about the temperature of the coolant remote from the metering module (20) and at least information about the temperature in the area of the metering module (20) flow into the model.

Description

The present invention relates to a method for operating a metering system for the reducing agent solution of an SCR catalyst device in the exhaust system of an internal combustion engine, wherein the metering system comprises at least one coolable metering module, which is connected to a coolant circuit, in particular to a cooling water circuit.

State of the art

Methods and apparatuses for operating an internal combustion engine, in particular in motor vehicles, are known, in the exhaust gas region of which an SCR catalytic converter (selective catalytic reduction) is arranged, which reduces the nitrogen oxides (NO _x ) contained in the exhaust gas of the internal combustion engine to nitrogen in the presence of a reducing agent.

The basic principle of an SCR catalyst is that nitrogen oxide molecules are reduced on the catalyst surface in the presence of NH ₃ as a reducing agent to elemental nitrogen. The required reducing agent is usually metered into the exhaust gas line in the form of an aqueous urea solution. For this purpose, a metering device or a metering system with a metering module is provided, which meters the required reducing agent solution upstream of the SCR catalytic converter into the exhaust gas line.

Depending on the installation location in the exhaust gas line, the dosing module can be exposed to high temperatures which can damage the component or even lead to failure. In principle, two different cooling concepts for the metering module are known for reducing this thermal load. On the one hand, air-cooled dosing modules are used. On the other hand, dosing modules with water cooling are used, these dosing modules being connected to a cooling water circuit present in the motor vehicle. Based on a temperature model for the tip of the metering valve located in the metering module, the metering module can be additionally cooled under certain operating conditions by requesting minimum metering amounts of the liquid reducing agent. While in an air-cooled dosing an actively controlled cooling is possible only by this requirement of Mindestdosiermengen the reducing agent with the engine running, in a water-cooled metering the cooling can be actively influenced by requesting a specific cooling capacity of the cooling circuit. However, the temperature of the coolant (cooling water) entering the dosing module is generally not known exactly. As a substitute variables temperature measurements are used, which are detected far away from the dosing.

From the German patent application DE 10 2011 088 549 A1 For example, a dosing module for an SCR system is known, which has a heat sink in which a cooling water flow control is implemented. Depending on the temperature in the heat sink, there is a change in the cooling water flow rate, for which purpose a passive valve based on a temperature-dependent bimetallic strip is used.

From the German patent application DE 10 2014 103 986 A1 For example, a method for preventing dosing module heat damage is known. Here, a required coolant cooling amount for preventing the heat damage is calculated. A calculation is made of an engine coolant cooling amount that is changed depending on the operation of a clutch water pump. The operating condition of the clutch water pump is checked by comparing the required coolant cooling amount with the engine coolant cooling amount. When the clutch water pump is operated so that the required coolant cooling amount is greater than the engine coolant cooling amount, the clutch water pump is stopped. Here, the required coolant cooling amount is set by a temperature of the metering module in which a sum of the reducing agent cooling amount and the engine coolant cooling amount is balanced against a total exhaust heat energy.

Disclosure of the invention

Advantages of the invention

The inventive method is based on a method for operating a metering system for the reducing agent solution of an SCR catalyst device in the exhaust system of an internal combustion engine, wherein the metering comprises at least one coolable metering module which is connected to a coolant circuit, in particular to a cooling water circuit. A main function of this cooling water circuit may be, for example, the cooling of the internal combustion engine. The cooling of the dosing, which is required to prevent heat damage to the dosing, is done by requesting a cooling capacity of the coolant circuit. According to the invention, the temperature of the coolant is taken into account when requesting the cooling power, wherein the temperature of the coolant in the region of entry into the metering module is determined on the basis of a model. The invention is based on the assumption that there is no temperature measuring point for the coolant at this point, ie in the region of the dosing module. For a needs-based requirement of cooling capacity the temperature of the coolant in the region of entry into the metering module is determined on the basis of a model, wherein at least information about the temperature of the coolant remote from the metering module and at least information about the temperature in the area of the metering module are included in the model. This modeling is based on the fact that the temperature of the coolant when entering the metering module is between two limits. The one limit value is determined by a further measurable or otherwise detectable temperature value of the coolant, for example in the region of the coolant pump. The other limit value is determined by a temperature value at the dosing module. By a suitable calculation of the temperature between these two limit values, according to the invention, the temperature of the coolant when entering the metering module can be approximately determined and used for a demand-oriented request of a cooling capacity. In conventional methods, only one temperature measurement variable for the coolant, which is detected remotely from the dosing module, is taken into account, for example in the region of the coolant pump. A thermal influence of the coolant on the way from the temperature measuring point to the metering remains unconsidered here. Since the temperature of the coolant can change significantly in this way, a cooling power requirement on the basis of this measured only far away from the dosing module temperature value of the coolant is not appropriate. Due to the modeling according to the invention of the temperature value for the coolant in the area of the dosing module, it is therefore possible to demand a specific cooling capacity in a demand-oriented manner which is precisely adapted to the prevailing conditions.

In the method according to the invention, the information on the temperature of the coolant remote from the metering module is preferably derived from a measured value of a coolant temperature sensor located far away from the metering module or from a substitute value for such a coolant temperature sensor remote from the metering module. The temperature sensor can be located, for example, at the outlet of the cooler (eg water cooler) of the internal combustion engine, in the cooling circuit of which the dosing module is integrated. There are also cooling circuits without temperature sensor possible. In these cases, the temperature value can be replaced by the value of another sensor, which correlates with the temperature of the cooling circuit. For example, the metering module can be integrated into the cooling circuit of the intake air, wherein the measured ambient temperature can be used as a substitute variable for the temperature in the cooling circuit. The substitute value for a coolant temperature sensor value may, for example, also be a modeled value, which is calculated in a manner known per se as the temperature value of a coolant.

The information about the temperature in the region of the dosing module is preferably a temperature value on the dosing module itself. As a rule, the dosing module comprises an electrically controllable dosing valve so that, for example, the temperature value of a magnetic coil, ie the coil temperature value, can be used for this purpose. The coil temperature value can be determined in a manner known per se from the resistance and the current during active energization of the metering valve within the metering module.

Preferably, at least one piece of information about the current delivery rate of the coolant pump in the coolant circuit continues to flow into the model for calculating the coolant temperature in the region of the metering module.

In a particularly preferred embodiment, the model for modeling the cooling water temperature when entering the metering module is based on a linear interpolation between the information on the temperature of the coolant remote from the metering module and the information about the temperature in the region of the metering module. In particular, the linear interpolation can take place on the basis of an interpolation factor. In a particularly preferred manner, information about the current delivery rate of the coolant pump continues to flow into the calculation of this interpolation factor. Furthermore, filtering and / or smoothing can take place when determining the interpolation factor.

The invention also includes a computer program which is set up to carry out the described steps of the method according to the invention. Finally, the invention comprises a machine-readable storage medium, on which such a computer program is stored, as well as an electronic control device, which is set up to carry out the steps of the method according to the invention. The implementation of the method according to the invention as a computer program or as a machine-readable storage medium or as an electronic control unit has the particular advantage that the method according to the invention can thus also be used in existing motor vehicles in order to optimize the cooling of the metering module for the SCR system.

Further features and advantages of the method according to the invention will become apparent from the following description of exemplary embodiments in conjunction with the drawings. In this case, the individual features can be implemented individually or in combination with each other.

In the drawings show:

1 Schematic representation of components of the dosing with a coolable dosing module for the reducing agent solution of a SCR catalyst according to the prior art and

2 Schematic structure of the modeling of the temperature of the coolant at the entrance to the metering module according to a preferred embodiment of the method according to the invention.

Description of exemplary embodiments

1 shows a section of the exhaust system 10 an internal combustion engine, not shown, of a motor vehicle. The exhaust system 10 contains an SCR catalyst device 11 that flows from the exhaust of the internal combustion engine in the flow direction 12 is flowed through. Upstream of the SCR catalyst device 11 there is a dosing module 20 , via the demand-dependent manner for the SCR catalyst device 11 required reducing agent solution is sprayed. The dosing module 20 is supplied with a reducing agent solution which is in the tank 21 is stored. By means of a feed pump 22 becomes the reducing agent solution via the suction line 23 from the tank 21 taken and pressurized via the supply line 24 to the dosing module 20 promoted. To the dosing module 20 To be able to cool is the dosing module 20 to a coolant circuit 30 with a coolant inlet 31 and a coolant outlet 32 connected. In the coolant circuit 30 it is in particular a cooling water circuit, which is provided primarily for the cooling of the internal combustion engine of the motor vehicle. In the region of the coolant circuit, not shown here for the internal combustion engine, a temperature measurement of the cooling water or the coolant is provided. In the area of the dosing module 20 However, no direct temperature measurement of the coolant is possible. According to the invention, a modeling of the temperature at the coolant inlet into the metering module 20 , In this case, an interpolation is made between two limiting temperatures for the coolant, which are formed on the one side by a measured value or a replacement value for the coolant removed from the dosing module and on the other side by a temperature value at the dosing module itself.

2 illustrates a preferred modeling of the temperature of the coolant as it enters the dosing module, based on the described interpolation, taking into account the currently existing flow rate of a coolant pump (not shown) in the model. Initially, a temperature value flows into the model 110 for the coolant away from the dosing module. Furthermore, a temperature value flows 120 which is detected in the area of the dosing module. This may in particular be a coil temperature value of the magnetic coil of the electrically controllable metering valve of the metering module, which can be determined from the resistance and the current during an active energization of the metering valve. The temperature values 110 and 120 are considered taking into account an interpolation factor 130 linearly interpolated to a temperature value 150 for the coolant in the dosing module inlet area. In the calculation of the interpolation factor 130 flows the currently existing delivery rate 140 the coolant pump. Here, the interpolation factor 130 over a characteristic 141 depending on the delivery rate of the coolant pump and taking into account a filtering or smoothing 142 determined. In the filtering or smoothing 142 a characteristic curve flows 143 as the time constant for the smoothing. Taking into account these variables, the temperature value 150 determined for the coolant at the entrance to the dosing, which is based on a needs-based requirement of a specific cooling capacity for the dosing.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102011088549 A1 [0005]
• DE 102014103986 A1 [0006]

Claims (11)

Method for operating a dosing system for the reducing agent solution of an SCR catalytic converter device ( 11 ) in the exhaust gas line ( 10 ) of an internal combustion engine, wherein the dosing system comprises at least one coolable dosing module ( 20 ) connected to a coolant circuit ( 30 ), in particular to a cooling water circuit, is connected, and wherein a cooling of the dosing ( 20 ) by requesting a cooling capacity of the coolant circuit ( 30 ), characterized in that the temperature of the coolant is taken into account when requesting a cooling power, wherein the temperature of the coolant in the region of entry into the metering module ( 20 ) is determined on the basis of a model, wherein at least one piece of information ( 110 ) to the temperature of the coolant remote from the metering module ( 20 ) and at least one piece of information ( 120 ) to the temperature in the area of the dosing module ( 20 ). Method according to claim 1, characterized in that the information ( 110 ) to the temperature of the coolant remote from the metering module ( 20 ) from a measured value of a coolant temperature sensor far from the dosing module ( 20 ) or a substitute value for a coolant temperature value far from the dosing module ( 20 ). Method according to claim 1 or claim 2, characterized in that the information ( 120 ) to the temperature in the area of the dosing module ( 20 ) of a temperature value at the dosing module ( 20 ). Method according to claim 3, characterized in that the temperature value at the dosing module ( 20 ) is a temperature value of a solenoid coil of an electrically controllable metering valve within the metering module. Method according to one of the preceding claims, characterized in that at least one piece of information ( 140 ) flows to the current flow rate of a coolant pump of the coolant circuit. Method according to one of the preceding claims, characterized in that the model is based on a linear interpolation between the information ( 110 ) to the temperature of the coolant remote from the metering module ( 20 ) and the information ( 120 ) to the temperature in the area of the dosing module ( 20 ). Method according to Claim 6, characterized in that the linear interpolation is based on an interpolation factor ( 130 ), preferably containing information ( 140 ) to the current flow rate of a coolant pump of the coolant circuit ( 30 ). Method according to claim 7, characterized in that in determining the interpolation factor ( 130 ) filtering and / or smoothing takes place. Computer program adapted to perform the steps of a method according to one of claims 1 to 8. A machine-readable storage medium on which a computer program according to claim 9 is stored. An electronic control device adapted to perform the steps of a method according to any one of claims 1 to 8.

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