Method for Diagnosing a Measurement of a Pressure Difference

Abstract

A method for diagnosing a measurement of a pressure difference. The measurement is carried out with a measuring arrangement for a component of an exhaust gas device, the input of which is connected to a first exhaust gas pipe and the output of which is connected to a second exhaust gas. The measuring arrangement is provided with a pressure difference measuring device and with a first and second pressure measurement point, which are connected to the pressure difference measuring device for measuring the pressure difference between a pressure measured at the first pressure measurement point and at the second pressure measured at the second pressure measurement point. The pressure difference between the two pressure measurement points is measured with a pressure difference between measuring device.

Claims

1-9. (canceled)

10. A method for diagnosing a measurement of a pressure difference, comprising: the measurement is carried out with a measuring arrangement for a component of an exhaust gas system, the input of which is connected to a first exhaust gas pipe and the output of which is connected to a second exhaust gas pipe, wherein the measuring arrangement is provided with a pressure difference measuring device and with a first and a second pressure measurement point, which are connected to a pressure difference measuring device for measurement of the pressure difference between a pressure measured at the first pressure measurement point and a pressure that is measured at the second pressure measurement point, wherein the first pressure measurement point is arranged at the first exhaust gas pipe and the second pressure measurement point is arranged at the second exhaust gas pipe, wherein the pressure difference between the two pressure measurement points is measured with the pressure difference measuring device, wherein a first, maximum value p1 is measured for an exhaust gas pressure wave at a first point in time t1, and a second, minimum value p2 of the pressure difference is measured at a second point in time p2, wherein a diagnostic value is calculated as:
d=(p1|p2|)/(p1+|p2|) wherein in the case when d is approximately equal to 1, an interruption of a connection to the first pressure measurement point is diagnosed by the pressure difference measuring device, and wherein in the case when d is approximately equal to 1, an interruption of a connection of the second pressure measurement point to the pressure measuring device is diagnosed.

11. The method according to claim 10, which is carried out by the measuring arrangement, wherein the component is a catalytic converter.

12. The method according to claim 10, wherein in the case when d is approximately equal to 0, a connection is diagnosed of both pressure measurement points to the pressure difference measuring device.

13. The method according to claim 16, wherein an amount of a maximum of an amplitude of the pressure difference is measured as the first value p1, and an amount of a minimum of the amplitude of the pressure difference is measured as the second value p2.

14. The method according to claim 10, wherein the first value p1 of the pressure difference is determined with a first, maximum drag indicator max_Sz, and the second value p2 of the pressure difference is determined with a second, minimum drag indicator min_Sz.

15. The method according to claim 14, wherein the first drag indicator max_Sz is determined with an asymmetric filter of a falling edge of a course of the pressure difference, and the second drag indicator min_Sz is determined with an asymmetric filter of a rising edge of the course of the pressure difference.

16. The method according to claim 10, which is carried out with the measuring arrangement (14), wherein the pressure difference measuring device (20) is connected via a first hose (22) to the first pressure measurement point (16) and via a second hose (24) to the second pressure measurement point (18).

17. The method according to claim 11, wherein the second point p2 adjusts the pressure difference as a function of the first value p1 minus a pressure drop in the catalyst (4).

18. A system for diagnosing a measurement of a pressure difference, comprising: a measuring arrangement for a component of an exhaust gas system, of which the input is connected to a first exhaust gas pipe and the output of which is connected to a second exhaust gas pipe, wherein the measuring arrangement is provided with a pressure difference measuring device and a first as well as a second pressure measurement point, which are connected to the pressure difference measuring device for measurement of the pressure difference between the pressure measured at a first pressure measurement point and the pressure measured at the second pressure measurement point, wherein the first pressure measurement point is arranged at the first exhaust gas pipe and the second pressure measurement point is arranged at the second exhaust gas pipe, wherein a first, maximum value p1 of the pressure difference is measured for an exhaust gas pressure wave at the first pressure measurement point at a first point in time t1, and a second, minimum value p2 of the pressure difference is measured at a second point in time t2, wherein the system is provided with a control device, which is connected to the pressure difference measuring device and which is adapted to calculate a diagnostic value:
d=(p1|p2|)/(p1+|p2|) wherein the control device is adapted to generate in the case when d approximately equal to 1 information about the fact that a connection of the first pressure measurement point or pressure measurement point to the pressure measurement measuring device is interrupted, and in the case when d approximately equal to 1 to generate information about the fact that a connection of the second pressure measurement point to the pressure measuring device is interrupted.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0037] The invention will now be explained based on the embodiments that are schematically indicated in the figure and it will be described in detail with reference to the figures.

[0038] FIG. 1 shows in a schematic representation an example of a measuring arrangement for an exhaust gas system and an embodiment of the system according to the invention.

[0039] FIG. 2 shows a first diagram and a second diagram of an operating parameter which are taken into account in an embodiment of the method according to the invention.

[0040] The figures are described in a coherent and comprehensive manner and the same components are labeled with the same reference numerals.

DETAILED DESCRIPTION OF DRAWINGS

[0041] The exhaust system 2 shown by way of an example in FIG. 1 comprises as components a first catalytic converter 4, which is here designed as a four-way catalytic converter and provided with at least one filter. In this case, the catalytic converter 4 is arranged between a first exhaust gas pipe 6 and a second exhaust gas pipe 8. Further, the exhaust system 2 comprises a second catalytic converter 10, here a three-way converter, which is arranged between another exhaust gas pipe 12 and the first exhaust gas pipe 6

[0042] The exhaust system 2 is here connected downstream of an internal combustion engine of a motor vehicle by which gasoline or diesel fuel is combusted as fuel here. Exhaust gas which is generated by combusting the fuel in the combustion chamber, usually in cylinders, by the internal combustion engine, flows successively through the exhaust gas pipe 12, the second catalytic converter 10, the first exhaust gas pipe 6, the first catalytic converter 4 and the second exhaust gas pipe 8, wherein the exhaust gas is purified in each of the catalytic converters 4, 10.

[0043] FIG. 1 also shows an example of the measuring arrangement 14 which is provided with a pressure measurement point 16, which is arranged at the first exhaust gas pipe 6 in front of the catalytic converter 4, and a second pressure measurement point 18, which is arranged at the second exhaust gas pipe behind the first catalytic converter 4. In addition, the measuring arrangement 14 comprises a pressure difference measuring device 20, which is designed as a differential pressure measuring device 20 and which is connected via a first hose 22 with the first pressure difference measuring point 16 and via a second hose 24 that is used as a connecting element to the second pressure measuring point 18.

[0044] The components of the measuring arrangement 14 listed above can be also designed as components of the exhaust gas system 2. FIG. 1 shows in addition a control device 26, which is designed as a component of the system 28 according to the invention, wherein the control device 26 is adapted to control at least one step of the method according to the invention. The control device 26 can be designed and/or referred to depending on the definition as a component of the measuring arrangement 14 and/or of the exhaust gas system 2.

[0045] Further, FIG. 1 shows a linear lambda probe 30 arranged on the other exhaust gas pipe 12, a binary lambda probe 32 arranged on the first exhaust gas pipe 6, and an additional binary lambda probe 34 which is arranged on the second exhaust gas pipe 8.

[0046] Both diagrams 36, 38 of FIG. 2 include a horizontal axis on which are plotted the values of time t, wherein both horizontal axes are here synchronous with one another and have the same origin. Along the vertical axes of the first diagrams 36 are plotted in the graph the values of the pressure p. It can be seen from this that the exhaust gas pressure wave is present or can be found at a first point in time t1 in front of the catalytic converter 4 and at a second point in time after the catalytic converter.

[0047] The value of the pressure difference results from the position of the first pressure measuring point 16 in front of the catalytic converter 4 minus the pressure of the position of the second pressure measuring point after the catalyst 4 and it is plotted along the vertical axis of the second diagram 38.

[0048] After each discharge of the exhaust gas from a combustion chamber of the internal combustion engine, a pressure wave of the exhaust gas flows from the internal combustion engine through the exhaust system 2 and passes successively through the exhaust gas pipe 6, the first catalytic converter 4 and the second exhaust gas pipe 8.

[0049] For this purpose, the first diagram 36 shows a first course 40 of the pressure of the exhaust gas pressure wave, which is prevalent inside the first exhaust gas pipe 6 and which is detected at the first gas pressure measuring point 16. The first diagram 36 further shows a second course 42 of the pressure of the exhaust gas pressure wave which is prevalent inside the second exhaust gas pipe 8 and which is detected via the pressure measurement point 18. At the same time, a maximum amplitude of the first course 40 of the pressure is detected via the first pressure measurement point 16 at the first point in time t1. A maximum or a maximum amplitude of the second course 42 of the pressure is detected via the second pressure measurement point 18 at a second point in time t2 after the first point in time t1. A difference t between the two points t1 and t2 depends on the distance between the two pressure measurement points 16, 18 and a velocity of the exhaust gas pressure wave, which in turn depend on at least one operating parameter of the internal combustion engine, for example a rotational speed of the internal combustion engine, a density and/or a temperature of the exhaust gas.

[0050] The second diagram 38 includes a course 44 of the pressure difference, which is measured with the pressure difference measuring device 20 between the two pressure measurement points 16, 18. In this case, the second diagram 38 shows that the pressure difference of the pressure difference wave displays a maximum positive value p1 or a maximum positive amplitude at the first point in time p1, and a minimum is displayed at a second point t2 with a maximum negative value p2 or a maximum negative amplitude.

[0051] In this case, the maximum positive value p1 of the pressure difference is determined via a first, maximum drag indicator 46, and the minimum value p2 of the pressure difference is determined via a second, minimum drag indicator 48. In this case it is provided that the first drag indicator 46 is generated with an asymmetric filter via a falling edge of the course 44 of the pressure difference, and the second drag indicator 48 is generated with an asymmetric filter via a rising edge of the course 48 of the pressure difference.

[0052] A diagnostic value is calculated with the first, maximum value p1 of the pressure difference, and with the second, wherein a minimum value p2 of the pressure difference is calculated as:

d=(p1|p2|)/(p1+|p2|)

[0053] As is schematically indicated in FIG. 1, both pressure measurement points 16, 18 are connected via hoses 22, 24 as connecting elements with the pressure difference measuring device 20 when the measuring arrangement 14 is correctly arranged and/or installed. If the result during the operation of the measuring arrangement 14 is that d-1, a connection of the first pressure measurement point 15 to the pressure difference measuring device 20 is interrupted, which may be due to the fact that the first hose 22 has been loosened. In this case, p10. If the result is that d1, a connection of the second pressure measurement point 16 with the pressure measuring device 20 has been interrupted, which may be due to the fact that the second hose 24 has been loosened. In this case, p20. If d0, both pressure measurement points 22, 24 are correctly connected to the pressure difference measuring device 20. In this case, 1|p2|. Usually, p1 is slightly larger than |p2|.

[0054] A difference between p1 and |p2| is dependent on a pressure drop of the exhaust gas pressure wave when it passes through the catalytic converter 4, while such a pressure drop can be also generated when the pressure difference measuring device 20 is connected to both pressure measurement point 16, 18. The pressure drop is as a rule a few percent, for example 10%. If both hoses 22, 24 are correctly connected to both exhaust gas pipes 6, 8 and the diagnostic value is approximately 0, this means that xdx, wherein 0<x<1. If the connection to the first pressure measurement point 16 is interrupted, then d<x and if the connection to the second pressure measurement point is interrupted, then d>x. In this case, x can be for example 0.5 depending on the pressure drop of the exhaust gas wave in the catalytic converter.