Procedure to diagnose an exhaust gas treatment device and device to implement the procedure

Abstract

A procedure for the pressure diagnosis in a reagent substance metering system, which introduces a reagent substance into an exhaust gas area of an internal combustion engine upstream in front of at least one exhaust treatment device as well as a device to implement the procedure is proposed. The reagent substance pressure occurring between a metering valve and a security valve disposed downstream after the metering valve is measured during different operating conditions of the metering valve and/or the security valve and is compared with at least one threshold value. An error signal is provided when the threshold is exceeded. The procedural approach according to the invention allows for a leakage diagnosis of the reagent substance metering system. Furthermore, the procedural approach according to the invention allows for a diagnosis of metering valve and/or the security valve and/or the check valve. The procedural approach according to the invention contributes overall to the elevation of the security, especially if the reagent substance is combustible.

Description

STATE OF THE ART

The invention proceeds from a procedure to diagnose an exhaust gas treatment device and from a device to implement the procedure according to the class of the independent claims. The subject matter of the invention at hand is also a computer program as well as a computer program product.

In the German patent DE 10 2004 018 221 A1, a procedure and a device are described, in which a reagent substance standing under pressure is sprayed into the exhaust gas of an internal combustion engine in front of a SCR-catalytic converter. The reagent substance pressure is established as a function of a parameter to a specified set pressure of the reagent substance. As a parameter an operating parameter of the internal combustion engine and/or a parameter of the exhaust gas can be used. The specified set pressure of the reagent substance is controlled within the scope of a closed-loop control, in which the actual pressure of the reagent substance is acquired by a reagent substance pressure sensor. Compressed air can be mixed in with the reagent substance. The compressed air pressure can likewise be controlled within the scope of a closed-loop control as a function of a parameter to a specified compressed air pressure set point, whereby the actual value of the compressed air is acquired by a compressed air pressure sensor. A defect of at least one of the pressure sensors can lead to a reduced performance capability of the SCR-catalytic converter with the consequence of having toxic exhaust gas enter into the environment.

In the German patent DE 10 2004 044 506 A1 (not pre-published), a procedure according to class and a device according to class are described, in which likewise a reagent substance standing under pressure is sprayed into the exhaust gas of an internal combustion engine in front of a SCR-catalytic converter. The compressed air is carried across a check valve, which has an opening pressure. Provision is made for a diagnosis of the compressed air pressure, which begins at a starting time point with the closing of a compressed air control valve. A check is made at least at a second time point, if the compressed air pressure corresponds at least to a lower threshold value, which corresponds at least approximately to the opening pressure of the check valve added to the ambient air pressure. An error signal is provided, if this condition is not met.

In the German patent DE 10 2004 061 247 A1 (not pre-published), a procedure according to class and a device according to class are described, in which a reagent substance is introduced into the exhaust gas area upstream in front of an exhaust gas treatment device. The reagent substance pressure, which lies in a reagent substance path between a reagent substance safety valve and a reagent substance metering valve, is acquired during different conditions of the reagent substance safety valve and/or the reagent substance metering valve and compared in each case with at least one threshold value. When the threshold value is exceeded, an error signal is provided. The known procedural approach offers a high degree of security, which especially must be guaranteed if provision is made for fuel to be used as the reagent substance.

The task underlying the invention is to point out a procedure to operate an exhaust gas treatment device of an internal combustion engine, in whose exhaust gas area an exhaust gas treatment device is disposed, and in which a reagent substance is introduced in the exhaust gas area upstream in front of the exhaust gas treatment device. The task underlying the invention is also to point out a device to implement the procedure, which guarantees a high degree of security.

The task is solved in each case by the characteristics indicated in the independent claims.

DISCLOSURE OF THE INVENTION

The procedural approach according to the invention with the characteristics of the independent procedural claim has the advantage, in that the security of introducing the reagent substance into the exhaust gas area of an internal combustion engine is increased with the diagnosis implemented thereby. Especially the operating danger is greatly reduced, if provision is made for combustible material as the reagent substance, for example fuel.

Due to a specified activation of a metering valve and/or a security valve, not only is a leakage diagnosis possible, whereby in addition the place where the leak occurs can be enclosed, but also a diagnosis of the metering valve and/or the security valve and/or a check valve provided to introduce the reagent substance into the exhaust area of the internal combustion engine. For this reason, a diagnosis is possible to see if at least one of the valves is jammed in the open or closed state. Especially a measurement and/or diagnosis of a source pressure of a reagent substance is possible in addition to the other measurements and diagnoses with only one pressure sensor.

Advantageous configurations and embodiments of the procedural approach according to the invention result from the dependent procedural claims.

Provision is made in one embodiment for a check to see if the pressure of the reagent substance, when the metering valve and the security valve are closed, lies above the opening pressure of the check valve or below the source pressure of the reagent substance. A diagnosis is thereby possible to see whether the security valve or the metering valve is jamming in the open state.

Provision is made in another embodiment for a check to see after a subsequent opening of the metering valve, if the pressure of the reagent substance at least approximately corresponds to the source pressure of the reagent substance. In so doing, a diagnosis is possible to see if the security valve is jamming in the open state or the metering valve in the closed state.

Provision is made in an additional embodiment for a check to see after a subsequent closing of the metering valve if the pressure of the reagent substance still at least approximately corresponds to the source pressure of the reagent substance. In so doing, a diagnosis is possible to see if the security valve is jamming in the open state.

Provision is made in an embodiment to see after a subsequent opening of the metering valve, if the pressure of the reagent substance at least approximately corresponds to the opening pressure of the check valve. In so doing, a diagnosis is possible to see if the security valve is jamming in the closed state or the metering valve in the open state or the check valve in the closed state.

Provision is made in an embodiment to see when the metering valve and the security valve are simultaneously open, if the pressure of the reagent substance corresponds approximately to the opening pressure of the check valve. In so doing, a diagnosis is possible to see if the security valve or the metering valve or the check valve is jamming in the closed state. Furthermore, a leakage diagnosis of the connection between the security valve and the check valve are possible. It can especially be determined if the connection is interrupted.

Provision is made in an embodiment to check to see after a subsequent closing of the metering valve, if the reagent substance pressure corresponds still at least approximately to the opening pressure of the check valve. In so doing, a diagnosis is possible to see if the security valve is jamming in the open state, the metering valve in the open state or the check valve in the closed state. Furthermore a leakage diagnosis of the connection between the security valve and the check valve is possible. It can also here especially be determined if the connection is interrupted.

The device according to the invention to implement the procedure concerns initially a control device, which is specifically designed to implement the procedure.

The control device contains especially a diagnostic control, a threshold specification as well as a comparator to compare the pressure of the reagent substance with at least one threshold value.

The control device contains preferably at least one electrical memory, in which the procedural steps are deposited as a computer program.

Provision is made in the computer program according to the invention for all steps of the procedure according to the invention to be executed, if it is operating on a computer.

The computer program product according to the invention with a program code stored on a carrier, which is machine readable, executes the procedure according to the invention, if the program is executed on a computer or in a control unit.

Examples of embodiment of the invention are depicted in the drawing and are explained in more detail in the following description.

The following are shown:

FIG. 1 a technical layout, in which the procedure according to the invention is operating,

FIG. 2a a metering valve activation signal as a function of time,

FIG. 2b a security valve activation signal as a function of time and

FIG. 3a a measured pressure signal as a function of time.

FIG. 1 shows an internal combustion engine 10, in whose air intake area 11 an air acquisition 12 and in whose exhaust gas area 13 an exhaust gas temperature sensor 14, an exhaust gas pressure sensor 15, a check valve HCIV as well as a first and second exhaust gas treatment device 17, 18 are disposed.

In the exhaust gas area 13, an exhaust gas temperature te_Abg as well as an exhaust gas pressure p_Abg arise.

The air acquisition 12 provides an air signal ms_L to a control unit 20, the internal combustion engine 10 an engine rotational speed n, the exhaust gas temperature sensor 14 an exhaust gas temperature measurement signal te_Abg_Mess and the exhaust gas pressure sensor 14 an exhaust gas measurement signal p_Abg_Mess.

The control unit 20 provides a fuel signal m_K to a fuel metering device 21.

In a reagent substance metering system 30, a reagent substance is brought to a specified source pressure P_Q by a pump 31. The pump 31 is activated by a pump activation signal 32, which a metering control 33 disposed in the control unit 20 provides.

The reagent substance proceeds to a metering valve DDV, which is activated by a metering valve activation signal s_DDV, which is provided by the metering control 33. A security valve FCV is disposed downstream behind the metering valve DDV. The security valve FCV is activated by a security valve activation signal s_FCV, which likewise is provided by the metering control 33. The security valve FCV is connected with the check valve HCIV.

A reagent substance pressure sensor 40 is disposed between the metering valve DDV and the security valve FCV. This sensor acquires the reagent substance pressure p and provides it as a reagent substance pressure measurement signal p_Mess to a comparator 41.

A threshold value set point 42 is assigned to the comparator 41. The threshold value set point 42 is activated by a diagnostic control 43 with a threshold value selection signal 44.

Threshold values, which are available, include the ambient air pressure p_Lu, the exhaust gas pressure p_Abg, an opening pressure P_HCIV of the check valve HCIV as well as the source pressure P_Q.

The diagnostic control 43 provides a diagnostic signal 45 to the metering control 33. The metering control 33 is furthermore supplied with a metering signal 46.

The control unit 20 contains a fuel signal establishment 50, which is provided with the air signal ms_L, the engine rotational speed n as well as a torque-set point Md_Soll. The fuel signal establishment 50 provides the fuel signal m_K.

The control unit 20 contains additionally an exhaust gas model 51, which is provided with the fuel signal m_K, the engine rotational speed n as well as the exhaust gas temperature te_Abg and supplies a calculated exhaust gas pressure p_Abg_Mod.

The threshold value set point 42 provides the comparator 41 with a threshold value signal 60. The comparator 41 provides an error signal F.

FIG. 2a shows the metering valve activation signal s_DDV as a function of the time t. Between a first and a second time point ti1, ti2, between a third and fifth time point ti3, ti5 and from the sixth time point ti6 forward, the metering valve is closed. Between the second and third time point ti2, ti3 as well as between the fifth and the sixth time point ti5, ti6, the metering valve is at least partially open.

FIG. 2b shows the security valve activation signal s_FCV as a function of the time t. Between the first and the fourth time point ti1, ti4 and from the seventh time point ti7 forward, the security valve FCV is closed. Between the fourth time point ti4 and the seventh time point ti7, the security valve FCV is open.

FIG. 2c shows the reagent substance pressure p as a function of the time t. The ambient air pressure p_Lu, the exhaust gas pressure p_Abg, the opening pressure P_HCIV of the check valve HCIV as well as the source pressure P_Q are plotted.

The reagent substance pressure p lies between the first and second time point ti1, ti2 between the opening pressure P_HCIV and the source pressure P_Q. Between the second and fourth time point ti2, ti4 the source pressure P_Q is present. From the fourth time point ti4 forward, the opening pressure P_HCIV of the check valve HCIV occurs.

The procedure according to the invention proceeds in the following manner: The exhaust gas of the internal combustion engine 10 contains undesirable components, such as, for example, nitrogen oxides and particles. The exhaust gas treatment devices 17, 18 have the tasks of eliminating the undesirable exhaust gas components as much as possible.

The first exhaust gas treatment device 17 is, for example, is equipped as a catalytic converter and/or NO_x-storage catalytic converter and/or SCR-catalytic converter and/or oxidation catalytic converter.

The second exhaust gas treatment device 18 is, for example, equipped as a particle filter.

At least one exhaust gas treatment device 17, 18 can at least in certain operating circumstances require a minimum temperature. For example, a reaction takes place optimally on a catalytically active surface area within a certain temperature window. Furthermore, a minimum temperature can be required, in order to be able to implement a regeneration especially of a particle filter. For example, a particle filter requires a starting temperature, which can lie between 450-650° C., to start the particle flame cleaning. A NO_x-storage catalytic converter requires an elevated temperature during the regeneration. Especially for the regeneration of a sulfur contamination significantly elevated temperatures up to 800° C. are required. For the temperature elevation of the exhaust gas, the reagent substance can be introduced into the exhaust gas area, which reacts exothermally on a catalytically active surface area.

At least one of the exhaust gas treatment devices 17, 18 can require a reagent substance to support and/or to implement the emission control function. For example, a NO_x-storage catalytic converter requires an oxygen lean exhaust gas to implement the regeneration.

The check valve HCIV provided to introduce the reagent substance into the exhaust gas area 13 can, for example, be disposed upstream in front of the first exhaust gas treatment device 17. Alternatively the check valve HCIV can be disposed downstream behind the exhaust gas treatment device 17, in order to make the reagent substance available only to the second exhaust gas treatment device 18.

Fuel is the primary reagent substance, so that a separate transport of a reagent substance in a motor vehicle can be omitted. Due to the easy combustibility of fuel and especially fuel vapors, increased security demands are to be fulfilled.

The reagent substance is brought by the pump 31 to the specified source pressure P_Q. The pump 31 can be omitted if fuel is deployed as the reagent substance, which is drawn from a fuel circuit standing under pressure of the internal combustion engine 10. The fuel circuit contains, for example, a fuel pump disposed in a fuel tank.

For security reasons, provision is made for the security valve FCV in the reagent substance metering system 30, which is completely opened or closed by the security valve activation signal s_FCV.

The flow rate of the reagent substance can be adjusted with the metering valve DDV disposed upstream in front of the security valve FCV. The metering valve DDV is activated by the metering valve activation signal s_DDV. The metering valve is preferably continually shifted, whereby preferably provision is made for a clock timed operation, in which the metering valve DDV is charged with switching signals in quick chronological sequence. For reasons of clarity, the metering valve activation signal s_DDV shown in FIG. 2a between the second and third time point t2, t3 as well as between the fifth and sixth time point t5, t6 is depicted in a simplified manner.

The valve provided for introduction of the reagent substance into the exhaust gas area 13 is implemented preferably as a check valve HCIV for security reasons, which has the opening pressure P_HCIV. An additional advantage results from the fact that the check valve HCIV can be manufactured cost effectively with a high temperature performance, which is required, because the check valve HCIV at least partially can be exposed to the high exhaust gas temperatures occurring at least periodically.

The reagent substance pressure sensor 40 acquires the reagent substance pressure p between the metering valve DDV and the security valve FCV and provides with the reagent substance pressure measurement signal p_Mess at least a measurement for the reagent substance pressure p.

An evaluation of reagent substance pressure measurement signal p_Mess provided by the reagent substance pressure sensor 40 in regard to the absolute value and/or the changes allows initially a check to see if a leak exists in the reagent substance metering system 30. A leak, especially a leak, which occurs in the exhaust gas area 13, can be connected to an increased operational danger, especially if it deals with easily inflammable material as, for example, fuel. Furthermore, the pressure diagnosis allows for a statement about the functional capability of the metering valve DDV and/or the security valve FCV and/or the check valve HCIV by the evaluation of the reagent substance pressure measurement signal p_Mess. In an especially advantageous manner, the source pressure P_Q can be measured and/or checked.

The measurement of the source pressure P_Q allows for an intervention in the open-loop control of the metered amounts of the reagent substance, respectively the closed-loop control of the metered amounts of the reagent substance.

The evaluation of the reagent substance pressure measurement signal p_Mess occurs in the comparator 41 by means of a comparison of the reagent substance pressure measurement signal p_Mess with at least one specified threshold value p_Lu, p_Abg, P_HCIV, P_Q.

By a special diagnostic activation of the metering valve DDV and/or of the security valve FCV, a targeted diagnosis can be implemented. During the normal operation of exhaust gas treatment device 17, 18, of which there is at least one, and a required metering of the reagent substance, the metering is implemented as a function of the metering signal 46, which is provided to the metering control 33. The normal metering operation can be interrupted with the diagnostic signal 45, which the diagnostic control 43 provides. With the diagnostic signal 45, the pump activation signal 32 and/or the metering valve activation signal s_DDV and/or the security valve activation signal s_FCV can be affected.

According to the FIGS. 2a-2c, it is initially assumed at the first time point ti1 that no metering of the reagent substance results, whereby the metering valve DDV as well as the security valve FCV is closed. The exhaust gas pressure p_Abg lies during the operation of the internal combustion engine 10 generally above the ambient air pressure p_Lu, which is measured, for example, by an unspecified pressure sensor.

The exhaust gas pressure p_Abg can, for example, be measured by the exhaust gas pressure sensor 15, which provides the exhaust gas pressure measurement signal p_Abg_Mess as a measurement for the exhaust gas pressure p_Abg. Alternatively or additionally, the exhaust gas pressure p_Abg can, for example, for diagnostic purposes be calculated with the exhaust gas pressure-model 51, which provides the calculated exhaust gas pressure p_Abg_Mod. The calculated exhaust gas pressure p_Abg_Mod can be ascertained by a simple approximation from the engine rotational speed n and the fuel signal m_K.

If need be the exhaust gas temperature te_Abg is taken into account, which, for example, is provided by the exhaust gas temperature sensor 14 as the exhaust gas temperature measurement signal te_Abg_Mess or can be calculated using an exhaust gas temperature model. The exhaust gas pressure p_Abg lies at, for example, maximally 500 mbar. It is determined primarily by the backpressure of the exhaust gas treatment devices 17, 18. Provided an exhaust gas treatment device 17, 18 is implemented, particularly as a particle filter, the backpressure increases with the increasing degree of depletion.

Initially it is assumed, that the metering valve DDV as well as the security valve FCV are closed between the first and second time point ti1, ti2. The reagent substance pressure p occurring between the first and second time point ti1, ti2 depends upon the case history. In the example of embodiment shown, it is assumed that the reagent substance pressure p lies between the opening pressure P_HCIV of the check valve HCIV and the source pressure P_Q. In this case the reagent substance metering system 30 is in good working order. Provided the reagent substance pressure p lies beneath the opening pressure P_HCIV, it can be assumed that the security valve FCV is jammed in the open state. The opening pressure P_HCIV of the check valve HCIV lies at, for example, 4 bar. The reagent substance pressure p can sink beneath the opening pressure P_HCIV due to the dynamic effects in the reagent substance metering system 30. If, for example, a reagent substance wave runs through the reagent substance metering system 30, a negative pressure in the reagent substance metering system 30 with regard to the ambient air pressure p_Lu can even be determined under certain circumstances after the closing of the check valve HCIV. Provided the reagent substance pressure p at least approximately corresponds to the source pressure P_Q, which, for example, lies at 6 bar, the metering valve DDV jams in the open state.

The metering valve DDV is opened at the second time point ti2. The security valve remains closed. The reagent substance pressure p must thereby correspond to the source pressure P_Q. Provided the reagent substance pressure p at least approximately corresponds to the opening pressure P_HCIV of the check valve HCIV, the security valve FCV jams in the open state. The reagent substance pressure p, which appears, depends upon the volume flow of the undesirably metered reagent substance. Provided the reagent substance pressure p does not change, thus lies between the opening pressure P_HCIV and the source pressure P_Q, the metering valve DDV jams in the closed state.

From the third time point ti3 forward, the metering valve DDV is again closed. The security valve FCV remains further closed. Provided the reagent substance pressure p corresponds to the source pressure P_Q, the reagent substance metering system 30 is in good working order. Provided the reagent substance pressure corresponds to the opening pressure P_HCIV of the check valve HCIV, the security valve FCV jams in the open state.

At the fourth time point ti4 the security valve FCV is opened. The metering valve DDV remains further closed. Provided the reagent substance pressure p corresponds to the opening pressure P_HCIV of the check valve HCIV, the reagent substance metering system 30 is in good working order. Provided that the reagent substance pressure p corresponds to the source pressure P_Q, the security valve FCV jams in the closed state. Provided that the reagent substance pressure p corresponds to the opening pressure P_HCIV of the check valve HCIV, the metering valve DDV jams in the open state. Provided that the reagent substance pressure corresponds to the source pressure P_Q and provided that the reagent substance metering system 30 was previously filled, the check valve HCIV jams in the closed state. Provided that the reagent substance pressure p is smaller than the source pressure P_Q and provided that the reagent substance metering system 30 was previously emptied, the check valve jams likewise in the closed state.

At the fifth time point ti5 the metering valve DDV is opened in the chronological middle at least partially, and the security valve FCV is opened as well. This state corresponds to the normal metering operation. Provided the reagent substance pressure p at least approximately corresponds to the opening pressure P_HCIV, the reagent metering system 30 is in good working order. Provided the reagent substance pressure p corresponds to the source pressure P_Q, the security valve FCV jams in the closed state. Provided the reagent substance pressure p lies beneath the opening pressure P_HCIV of the check valve HCIV, the metering valve DDV jams in the closed state. A smaller pressure than the opening pressure P_HCIV can—as previously described—occur as a result of dynamic processes in the reagent metering system 30. Provided the reagent substance pressure p lies at least in the chronological middle between the exhaust gas pressure p_Abg and the ambient air pressure p_Lu, it can be assumed that the connection between the security valve FCV and the check valve HCIV has a leak or is even completely interrupted. Provided the reagent substance pressure p corresponds to the source pressure P_Q, the check valve jams in the closed state.

At the sixth time point ti6, the metering valve DDV is closed, while the security valve FCV continues to remain open. Provided the reagent substance pressure p corresponds to the opening pressure P_HCIV of the check valve HCIV, the reagent substance metering system 30 is in good working order. Provided the reagent substance pressure p corresponds to the source pressure P_Q, either the security valve FCV jams in the closed state or the check valve HCIV jams in the closed state. Provided the reagent substance pressure p corresponds at least approximately to the opening pressure P_HCIV of the check valve, the metering valve DDV jams in the open state. Provided the reagent substance pressure p at least approximately corresponds to the ambient air pressure p_Lu, it must be assumed, that a leak has occurred in the connection between the security valve FCV and the exhaust area 13 or that the connection is interrupted.

At the seventh time point ti7 the diagnosis is ended with the closing of the metering valve DDV as well the security valve FCV, whereby the reagent substance pressure p depends upon the case history, whereby the reagent substance pressure p in the example of embodiment depicted must therefore at least approximately have the opening pressure P_HCIV of the check valve HCIV.

Provided the comparator 41 establishes at least that the threshold has been exceeded, the error signal F is provided, which can be deposited in an error storage and/or brought to the indicator.

A clarification of the reagent substance measuring signal p_Mess provided by the reagent substance pressure sensor 40 can, for example, occur with the source pressure P_Q, the exhaust gas pressure p_Abg and/or the ambient air pressure p_Lu.

Claims

1. A method of diagnosing a pressure in a reagent substance metering system, which introduces a reagent substance into an exhaust gas area of an internal combustion engine upstream of at least one exhaust gas treatment device, the metering system including a continuous metering valve, a switchable security valve, and a check valve disposed in a direction of flow of the reagent substance that is brought to a specified source pressure, the method comprising:

measuring a reagent substance pressure between the metering valve and the security valve;

comparing the reagent substance pressure with at least one threshold value; and providing an error signal if the reagent substance pressure is greater than the threshold value.

2. A method according to claim 1, further comprising determining if the reagent substance pressure is greater than an opening pressure of the check valve and less than the source pressure when the metering valve and the security valve are closed.

3. A method according to claim 1, further comprising determining if the reagent substance pressure corresponds at least approximately to the source pressure when the metering valve is open and the security valve is closed.

4. A method according to claim 3, further comprising determining if the reagent substance pressure continues at least approximately to correspond to the source pressure after a subsequent closing of the metering valve.

5. A method according to claim 4, further comprising determining, after a subsequent closing of the metering valve, if the reagent substance pressure continues at least approximately to correspond to an opening pressure of the check valve.

6. A method according to claim 1, further comprising determining, after a subsequent closing of the metering valve, if the reagent substance pressure continues at least approximately to correspond to the opening pressure of the check valve.

7. A device that diagnoses a pressure in a reagent metering system, the device comprising a control unit for the implementation of a method of diagnosing a pressure in a reagent substance metering system, which introduced a reagent substance into an exhaust gas area of an internal combustion engine upstream of at least one exhaust gas treatment device, the metering system including a continuous metering valve, a switchable security valve, and a check valve disposed in a direction of flow of the reagent substance that is brought to a specified source pressure, the method comprising: measuring, a reagent substance pressure between the metering valve and the security valve; comparing the reagent substance pressure with at least one threshold value; and

providing an error signal if the reagent substance pressure is greater than the threshold value.

8. A device according to claim 7, wherein the control unit contains a diagnostic control, a threshold set point as well as a comparator to compare the reagent substance pressure with at least a threshold value.

9. A device according to claim 7, wherein the entire reagent substance metering system includes only one pressure sensor disposed between the metering valve and the security valve.

10. A computer program, operable on a computing system, which executes all steps of a method of diagnosing a pressure in a reagent substance metering system, which introduces a reagent substance into an exhaust gas area of an internal combustion engine upstream of at least one exhaust gas treatment device, the metering system including a continuous metering valve, a switchable security valve, and a check valve disposed in a direction of flow of the reagent substance that is brought to a specified source pressure, the method comprising: measuring a reagent substance pressure between the metering valve and the security valve; comparing the reagent substance pressure with at least one threshold value; and providing an error signal if the reagent substance pressure is greater than the threshold value.

11. A computer program product with a stored program code, executable on a computing system or in a control unit, on a machine readable carrier for the implementation of diagnosing a pressure in a reagent substance metering system, which introduces a reagent substance into an exhaust gas area of an internal combustion engine upstream of at least one exhaust gas treatment device, the metering system including a continuous metering valve, a switchable security valve, and a check valve disposed in a direction of flow of the reagent substance that is brought to a specified source pressure, the method comprising: measuring a reagent substance pressure between the metering valve and the security valve; comparing the reagent substance pressure with at least one threshold value; and providing an error signal if the reagent substance pressure is greater than the threshold value.