Method for testing a moisture sensor of a diesel engine

Abstract

A method for testing a moisture sensor of a diesel engine includes: measuring, by an NOx sensor, an untreated NOx emissions content in exhaust gas of the diesel engine upstream of a Selective Catalytic Reduction (SCR) catalytic converter at particular steady-state operating points in a defined window, to obtain an actual concentration value of NOx emissions; determining an oxygen concentration in intake air from an intake pipe of the diesel engine, and converting the result obtained from the determination, by a characteristic curve, into an NOx concentration to obtain a model value of NOx concentration; comparing the actual value with the model value; and identifying a faulty condition of the moisture sensor if a deviation that exceeds a set value (R) is detected between the actual and model values.

Claims

1. A method for testing a moisture sensor (6) of a diesel engine, the method comprising: measuring, by an NOx sensor (5), an untreated NOx emissions content in exhaust gas of the diesel engine upstream of a Selective Catalytic Reduction (SCR) catalytic converter (4) at particular steady-state operating points in a defined window, to obtain an actual concentration value of NOx emissions; determining an oxygen concentration in intake air from an intake pipe (2) of the diesel engine, and converting the result obtained from the determination, by a characteristic curve, into an NOx concentration to obtain a model value of NOx concentration; comparing the actual value with the model value; and identifying a faulty condition of the moisture sensor (6) if a deviation that exceeds a set value (R) is detected between the actual and model values, wherein the oxygen concentration in the intake air is determined by measuring the air mass, exhaust gas recirculation (EGR) mass, if available, and moisture in the intake pipe (2) of the diesel engine.

2. The method as claimed in claim 1, wherein the moisture sensor (6) is identified as faulty if the deviation that exceeds a set value (R) is detected at a high ambient temperature.

3. The method as claimed in claim 2, wherein the high ambient temperature corresponds to a value of over 35 C.

4. A method for testing a moisture sensor (6) of a diesel engine, the method comprising: measuring, by an NOx sensor (5), an untreated NOx emissions content in exhaust gas of the diesel engine upstream of a Selective Catalytic Reduction (SCR) catalytic converter (4) at particular steady-state operating points in a defined window, to obtain an actual concentration value of NOx emissions; determining an oxygen concentration in intake air from an intake pipe (2) of the diesel engine, and converting the result obtained from the determination, by a characteristic curve, into an NOx concentration to obtain a model value of NOx concentration; comparing the actual value with the model value; and identifying a faulty condition of the moisture sensor (6) if a deviation that exceeds a set value (R) is detected between the actual and model values, wherein the model value is adapted with the actual value at the particular steady-state operating points and at a low ambient temperature.

5. The method as claimed in claim 4, wherein the steady-state operating points comprise operating points of engine speed and load.

6. A method for testing a moisture sensor (6) of a diesel engine, the method comprising: measuring, by an NOx sensor (5), an untreated NOx emissions content in exhaust gas of the diesel engine upstream of a Selective Catalytic Reduction (SCR) catalytic converter (4) at particular steady-state operating points in a defined window, to obtain an actual concentration value of NOx emissions; determining an oxygen concentration in intake air from an intake pipe (2) of the diesel engine, and converting the result obtained from the determination, by a characteristic curve, into an NOx concentration to obtain a model value of NOx concentration; comparing the actual value with the model value; and identifying a faulty condition of the moisture sensor (6) if a deviation that exceeds a set value (R) is detected between the actual and model values.

7. The method as claimed in claim 6, further comprising, in a case in which a faulty moisture sensor (6) is detected: providing an indication that the moisture sensor (6) requires replacement; and initiating replacement of the moisture sensor (6).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in detail below with reference to an exemplary embodiment in connection with the drawings. In the drawings:

(2) FIG. 1 shows a schematic illustration of a diesel engine having a control unit; and

(3) FIG. 2 shows a flowchart of the individual method steps.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

(4) The diesel engine, which is shown only schematically in FIG. 1, has an engine block 1 with an air intake tract that has an air intake pipe 2. Furthermore, the diesel engine has an exhaust tract with an exhaust pipe 3, in which an SCR catalytic converter 4 (SCR=selective catalytic reduction) is arranged. Upstream of the SCR catalytic converter 4 there is an NO.sub.x sensor 5, by which the untreated NO.sub.x emissions content in the exhaust gas is measured.

(5) A schematically illustrated exhaust gas recirculation system (EGR=exhaust gas recirculation) is indicated at 7. Thus, some of the exhaust gas is recirculated into the air intake pipe 2 and is mixed there with the air drawn in.

(6) In the method according to one aspect of the invention, the NO.sub.x content in the exhaust gas of the diesel engine upstream of the SCR catalytic converter 4 is, on the one hand, now measured at particular steady-state operating points (engine speed, load) by the NO.sub.x sensor. The corresponding signal is fed to a controller illustrated schematically at 9.

(7) On the other hand, two sensors 8 are used to measure the air mass in the intake pipe 2 and the EGR mass (mass of recirculated exhaust gas). Moreover, the air humidity in the intake pipe 2 is measured by a moisture sensor 6. The signals of the three sensors are like-wise fed to the controller 9.

(8) From the signals of the sensors 8 and 6, the controller 9 determines an NO.sub.x concentration by a characteristic curve stored in the controller in storage, this concentration being introduced into the method as a model value. This model value is compared by the controller 9 with the NO.sub.x content measured by sensor 5 as the ACTUAL value. If the controller 9 detects a deviation between these values that exceeds a set value, a faulty moisture sensor 6 is identified, and this is indicated by a suitable indicator, for example. Otherwise, the moisture sensor 6 is classified as operating correctly.

(9) More specifically, if a large deviation between the values is detected at a high ambient temperature, e.g. 40 C., a faulty moisture sensor is identified during this process. By the indicator provided, the person controlling the associated vehicle, for example, receives an indication that the moisture sensor needs to be replaced, and can initiate said replacement.

(10) FIG. 2 shows the individual steps of the method in a block diagram. In step 10, the NO.sub.x content in the exhaust gas of the diesel engine is measured by the NO.sub.x sensor, more specifically at a steady-state operating point in respect of the engine speed and load. The corresponding signal is fed to a controller and made available there as an ACTUAL value (step 12).

(11) Furthermore, the EGR mass and the air mass in the intake pipe as well as the moisture content in the intake pipe are measured (step 11). The corresponding signals are fed to the controller. From these, the oxygen concentration in the intake pipe is determined in step 13, and, from this, the NO.sub.x concentration is calculated as a model value using a stored characteristic curve (step 13).

(12) At step 14, the two values are compared with one another. At step 15, it is determined whether or not the deviation is greater than a set value (R), wherein a high ambient temperature is taken as a basis. The corresponding moisture sensor is then classified as faulty or not faulty.

(13) Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.