Method for diagnosing an exhaust gas system of an internal combustion engine

Abstract

The present invention relates to a method for diagnosing an exhaust gas system of an internal combustion engine with at least one three-way catalytic converter, at least one four-way catalytic converter and at least one binary lambda sensor, wherein during the testing of the functional operability of the at least one binary lambda sensor and/or of at least one four-way catalytic converter on the basis of a lambda change with a changeover of the internal combustion engine from a lean operation to a rich operation following a thrust operation clearing out at least one three-way catalytic converter occurs.

Claims

1. A method for diagnosing an exhaust gas system of an internal combustion engine provided with at least one three-way catalytic converter, at least one four way catalytic converter and at least one binary lambda sensor comprising: testing a functional operability of the at least one binary lambda sensor and the at least one four-way catalytic converter on the basis of a lambda change, wherein during the testing, a changeover of the internal combustion engine from a lean operation to a rich operation occurs following a thrust operation for clearing out the at least one three-way catalytic converter, classifying a first binary lambda sensor that is arranged in a flow direction of the exhaust generated by the internal combustion engine after the at least one four-way catalytic converter as faulty when a function of lambda values are determined by the first binary lambda sensor over time, such that during the changeover of the internal combustion engine from the lean operation taking place during the thrust operation to the rich operation following the lean operation of the internal combustion engine to clear out the at least one three-way catalytic converter, an increase of the function of lambda values is displayed which is below a predetermined first threshold value, classifying the at least one four-way catalytic converter as faulty, when the first binary lambda sensor generates, after the input of a predetermined rich gas amount in the at least one four-way catalytic converter, a Nernst voltage above a second threshold value, and determining a signal delay by the first binary lambda sensor during a changeover from the rich operation to the lean operation, wherein a time interval is determined between an occurrence of a maximum of measured values of the first binary lambda sensor and a point in time at which the changeover of the internal combustion engine occurs from the rich operation to the lean operation, wherein the rich operation is selected following the thrust operation for clearing out the at least one three-way catalytic converter.

2. The method according to claim 1, wherein an additional input of a rich gas amount in the at least one three-way catalytic converter occurs when a second binary lambda sensor that is arranged after the at least one three-way catalytic converter and before the at least one four-way catalytic converter generates a Nernst voltage which is above a predetermined threshold value.

3. The method according to claim 1, wherein the second threshold value is a Nernst voltage of 0.8 Volts.

4. The method according to claim 1, wherein the signal delay of the first binary lambda sensor is detected during the changeover from the rich operation to the lean operation, wherein a time interval occurs between the occurrence of a minimum of measured values of the first binary lambda sensor and a point in time at which the changeover of the internal combustion engine from the lean operation to the rich operation occurs, so that the rich operation is selected following the thrust operation for clearing out at least one three-way catalytic converter.

5. An exhaust gas system for an internal combustion engine, comprising: at least one three-way catalytic converter, at least one four-way catalytic converter, at least one binary lambda sensor arranged after the at least one four-way catalytic converter in the flow direction of at least one internal combustion engine and a control device, wherein the control device is configured to classify the at least one binary lambda sensor as faulty when a function of the values determined over time by the least one binary lambda sensor during a changeover of the internal combustion engine to a rich operation following a thrust operation for clearing out the at least one three-way catalytic converter displays a gradient that is below a predetermined threshold value, and wherein the control device is further configured to classify the at least one four-way catalytic converter as faulty when the at least one binary lambda sensor after the input of a predetermined amount of rich gas in the at least one four-way catalytic converter generates a Nernst voltage above a second threshold value.

6. The exhaust gas system according to claim 5, wherein the internal combustion engine is a gasoline engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is schematically illustrated based on embodiments in the figures and schematically described in detail with reference to the figures.

(2) FIG. 1 shows a schematic representation of a possible embodiment of a gas exhaust gas system according to the invention.

(3) FIG. 2 shows a schematic representation of the progress in a possible embodiment of the method according to the invention.

(4) FIG. 3 is another schematic representation of the progress in a possible embodiment of the method according to the invention.

(5) The figures are described in a contiguous and general manner. The same reference symbols are used for the designation of the same features.

DETAILED DESCRIPTION OF THE DRAWINGS

(6) FIG. 1 illustrates a gas exhaust gas system 1, which is connected to an internal combustion engine. The internal combustion engine, not shown, generate exhaust gas which flows through the gas tract 3 in the flow direction as indicated by the arrow 5. During its passage through the gas exhaust 3, the gas exhaust first flows to a linear gas exhaust sensor 7 which detects a composition of the gas exhaust or a fuel content in the gas exhaust. After the linear gas exhaust sensor 7, the gas exhaust flows through a three-way catalytic converter 9 and after that through a binary lambda sensor 11, wherein the binary lambda sensor 11 can also be integrated in the three-way catalytic converter 9.

(7) During its passage in the direction toward the exhaust, the exhaust gas passes through a four-way catalytic converter 13, i.e. a particle filter which is provided with a catalytically active layer made of a noble metal. Before the gas exhaust leaves the gas exhaust tract 3, the composition of the gas exhaust is determined by a binary lambda sensor 15 that can be optionally also provided.

(8) In order to test the three-way catalytic converter 9, the four-way catalytic converter 13 and the lambda sensors 11 and 15, it is provided that respective values determined by the lambda sensor 7, 11 and 15 are interpreted by means of a control device 17 with respect to their relation to respective operational phases of the internal combustion engine.

(9) FIG. 2 shows a diagram 20, which is plotted over time on the horizontal axis 21 with a lambda value before the catalytic converter indicated on the vertical axis 23, which is to say a lambda value determined as shown in the FIG. 1. Starting from the drive phase of an internal combustion engine, which is indicated by the line 25, the internal combustion engine is switched on at the point t1 as indicated by arrow 27, in which the internal combustion engine does not generate any or any significant input of fuel in the respective gas exhaust. At the point of the thrust operation which is indicated by arrow 27, the internal combustion engine is switched to a rich operation at the point t3 as indicated by arrow 29 in order to clear out a catalytic converter, such as the three-way catalytic converter 9 illustrated in FIG. 1, which is to say in order to empty an oxygen storage device of the three way catalytic converter 9. Accordingly, the lambda value is increased at the beginning of the clearing out operation, only to stagnate during the clearing out operation when a plateau is reached at point T4 so that after that, it is increased again at point t5 as indicated by line 26.

(10) During the operating phase indicated by the arrow 28, the internal combustion engine is left in the rich operating mode so as to generate a predetermined amount of rich exhaust gas by means of which the four-way catalytic converter is to be tested as explained below.

(11) Furthermore, FIG. 2 shows a diagram 30 in which Nernst voltage is plotted in Volts on the vertical axis 33 over time indicated on the horizontal axis 31 (in seconds). Line 35 represents the course of a Nernst voltage of a lambda sensor 11 which is arranged before the four-way catalytic converter 13 and after the three-way catalytic converter 9.

(12) Line 37 represents the course of a Nernst voltage of the lambda sensor 15 which is arranged after the four-way catalytic converter 13. In order to test the lambda sensor 15 for a filter inclination, the gradient 39 of the Nernst voltage can be evaluated according to the line 37 after a transition from a rich operation to a lean operation. Such a transition from a rich operation to a lean operation can be occur for example during a transition from a driven operation phase to a thrust operation as shown between the points t1 and t3. Due to a latency of the lambda sensor 15, the progress level 37 of the Nernst voltage is decreased first at point t2 and not already at point t1. If the gradient 39 of the progress level 37 of the Nernst voltage of the lambda sensor 15 is greater than a predetermined threshold value, the lambda sensor 15 indicates a good step response and the can be classified as good or as being in working condition. If the gradient is below the threshold value, this indicates a filter inclination of the lambda sensor 15 so that it will be classified as poor or unable to operate.

(13) It is noticeable that the changeover to the thrust operation at point t1 is detected by the lambda sensor 11 earlier than by the lambda sensor 15 which is further away from the internal combustion engine in the flow direction, as shown in a comparison of the corresponding lines 35 and 37. At point t3, the internal combustion engine is switched to a rich operating mode in order to clear out the three-way catalytic converter 9, which is to say to empty the oxygen storage device of the three-way catalytic converter 9. Accordingly, the Nernst voltage levels generated by the lambda sensors 11 and 15 are increased at point t3, wherein the Nernst voltage of the lambda sensor 11 is steeper as shown by line 35 and it rises higher than the Nernst voltage of the lambda sensor 15 shown by line 37.

(14) At point t4, the Nernst voltage of the lambda sensor 11 exceeds the value of 0.8 volts. Accordingly, it can be assumed from this that at this point in time, an oxygen storage device of the three-way catalytic converter 9 has been emptied. Up until the point t5, the internal combustion engine operates in a rich operating mode, which is to say in an operating mode that generates a rich exhaust gas as indicated by the arrow 28 in the diagram 20. The internal combustion engine is operated in the rich operating mode for as long until a predetermined amount of exhaust gas is provided and introduced into the four-way catalytic converter 13. When after the introduction of the predetermined amount of exhaust gas the Nernst voltage no longer exceeds a threshold value of the lambda sensor 15 of for example 0.8 Volts, it can be assumed that the four-way catalytic converter 13 has an oxygen storage device that is greater than what is required from the oxygen storage device for converting the predetermined amount of rich gas. Accordingly, the four-way catalytic converter is to be classified as good or as being in operating condition. In this case, the predetermined amount of generated exhaust gas or the duration of the rich operating phase is selected for example as a function of respective requirements on the exhaust gas.

(15) FIG. 3 shows a possible method for determining signal delays of the lambda sensors 11 and 15. In diagram 40 are plotted on the horizontal axis 41 indicating the time (in seconds) and on the vertical axis 43 indicating a lambda value three lines 44, 45, 46, wherein line 44 shows the course of a combustion air ratio in front of a three-way catalytic converter 9, line 45 shows the course of a combustion air ratio after the three-way catalytic converter 9, and line 46 represents the course of a combustion air ratio after the four-way catalytic converter 9.

(16) It can be seen from the diagram 40 that the internal combustion engine is switched on approximately at the second 92 to a lean operation so that a combustion air ratio, i.e. , is increased in front of the three-way catalytic converter 9 and, with a delay, after the four-way catalytic converter 13. Approximately at the second 100, the internal combustion engine is operated in a rich operating mode for as long until the lambda sensor 15 generates after the four-way catalytic converter a Nernst voltage of approximately 0.8 Volts.

(17) Further, FIG. 3 shows a diagram 50 which plots on the vertical axis 47 the Nernst voltage over the horizontal axis 49 indicating the time (in seconds).

(18) Line 53 shows a course of the Nernst voltage of the lambda sensor 15 after the four-way catalytic converter 13 and line 51 shows a course of the Nernst voltage of the lambda sensor 11 after the three-way catalytic converter 9 or before the four-way catalytic converter 13.

(19) When the operating phase of the internal combustion engine is changed at the second 92 to a lean operation, the Nernst voltages of the lambda sensors 11 and 15 are also lowered so that by means of a gradient 55 of for example the line 53, a filter tendency of the lambda sensor 15 can be discontinued. For this purpose, the gradient 55 can be adjusted for example with a predetermined threshold value. If an amount of the gradient 55 is greater than the threshold value, a good step response of the lambda sensor 15 is to be assumed, so that the lambda sensor 15 should be classified as good or as being in good operating order.

(20) In order to determine the signal delay of the lambda sensor 11 and 15, the internal combustion engine is switched on at the minute 111 to a lean operating mode until the catalytic converter 9 is filled up to approximately 50% to 70%. By means of a time offset of the occurrence of the respective maxima 57 of the line 51 and 53 to the point in time when the internal combustion engine is switched to the lean operation, which is to say approximately at the second 111, the reaction time and accordingly also the signal delay 59 or the inertia of the lambda sensor 11 and 15 can be determined with a lambda changeover from a rich to a lean operation.

(21) A signal delay 61 of the lambda sensor 11 and 15 with a lambda changeover from a lean to a rich can be determined during a transition of the internal combustion engine from the lean operation to the rich operation via a time shift of the occurrence of the respective minima 63 of the lines 51 and 53 to the point in time when the internal combustion engine is switched on in the rich operation approximately at the second 100.

(22) A filter tendency of the lambda sensor 15 during a changeover of an operating state of the internal combustion engine from the lean to the rich operation can be determined for example on the basis of the gradient 65. If the gradient 65, i.e. in particular an amount of the gradient 65, is below a predetermined threshold value so that the line 53 is particularly flat, the lambda sensor 15 is sluggish and it should therefore be classified as poor or as unable to operate.