DIFFERENTIATING A FLOW RATE ERROR AND A DYNAMIC ERROR OF AN EXHAUST GAS RECIRCULATION SYSTEM

Abstract

A method and a computer program for recognizing and differentiating a flow rate error and a dynamic error of an exhaust gas recirculation system (EGR) of an internal combustion engine. Measured and modeled EGR mass flow signals are each subjected to bandpass filtering using time constants optimized for determining flow rate errors and bandpass filtering using time constants optimized for determining dynamic errors. The energy is determined for each of the filtered signals and an energy quotient is computed between the energies of the signals filtered for dynamic errors and the signals filtered for flow rate errors. A dynamic error and a flow rate error of the exhaust gas recirculation may be recognized and differentiated from one another on the basis of the energy quotients.

Claims

1. A method for recognizing and differentiating a flow rate error and a dynamic error of an exhaust gas recirculation system (EGR) in an air charge system of an internal combustion engine, at least one of a high-pressure gas recirculation valve and a low-pressure gas recirculation valve being associated with the air charge system, the method comprising: measuring indirectly or directly, an EGR mass flow to provide a measured EGR mass flow signal; modeling the EGR mass flow to provide a modeled EGR mass flow signal; supplying each of the measured EGR mass flow signal and the modeled EGR mass flow signal to two respective bandpass filters, a first one of the bandpass filters having a time constant adapted for a recognition of flow rate errors, and a second one of the bandpass filtering having a time constant adapted for a recognition of dynamic errors; determining, for each of the measured EGR mass flow signal filtered for flow rate errors and dynamic errors, respectively, and for each of the modeled EGR mass flow signals filtered for flow rate errors and dynamic errors, respectively, an energy; forming a first energy quotient based on the energy of measured EGR mass flow signal filtered for flow rate errors and the energy of the modeled EGR mass flow signal filtered for flow rate errors; forming a second energy quotient based on the energy of the measured EGR mass flow signal filtered for dynamic errors and the energy of the modeled EGR mass flow signal filtered for dynamic errors; recognizing a flow rate error if the first energy quotient is in a predefined flow rate error range; and recognizing a dynamic error if the second energy quotient is in a predefined dynamic error range.

2. The method as recited in claim 1, wherein the first and second energy quotients are determined via a predefined number of diagnostic events and associated with energy quotient ranges, the flow rate error is deduced if the focal point of the distribution thus obtained of the energy quotients is in the predefined flow rate error range, and the dynamic error is deduced if the focal point of the distribution of the energy quotients is in the predefined dynamic error range.

3. The method as recited in claim 1, wherein the flow rate error range is at comparatively lower energy quotients and the dynamic error range is at comparatively higher energy quotients.

4. The method as recited in claim 1, wherein a scaling of the particular energy components is carried out.

5. The method as recited in claim 1, wherein, to determine each of the energies, the associated filtered EGR mass flow signal is squared and subsequently integrated, wherein one of: (i) the integration is carried out with the aid of an integration duration which is specific to signals, and (ii) a point in time for a start of the integration of the two signals being triggered both in the event of a rising signal flank of the output signal and in the event of a falling signal flank.

6. The method as recited in claim 1, wherein the determination of the energies and the formation of the energy quotients are restricted to at least one of positive and negative components of the filtered EGR mass flow signals.

7. The method as recited in claim 1, wherein one of a low-pressure exhaust gas recirculation mass flow via the low-pressure exhaust gas recirculation valve or a high-pressure exhaust gas recirculation mass flow via the high-pressure exhaust gas recirculation valve of the internal combustion engine is monitored, at least one of the low-pressure exhaust gas recirculation mass flow and the high-pressure exhaust gas recirculation mass flow being determined by modeling, on the one hand, and being directly measured or computed from measured values for an air mass flow in the supply air area of the internal combustion engine, from at least one of a speed of the internal combustion engine, and an inlet or boost pressure, on the other hand, and a function of at least one of the low-pressure exhaust gas recirculation valve and the high-pressure exhaust gas recirculation valve being monitored.

8. The method as recited in claim 1, wherein the first energy quotient and the second energy quotient are determined separately for two or more EGR valve position ranges of at least one of the low-pressure exhaust gas recirculation valve, and the high-pressure exhaust gas recirculation valve, the flow rate error being associated with a particular EGR valve position range of the at least one of the flow-pressure exhaust gas recirculation valve and the high-pressure exhaust gas recirculation valve if the first energy quotient is in a predefined flow rate error range, and the dynamic error being associated with a particular EGR valve position range if the second energy quotient is in a predefined dynamic error range.

9. A non-transitory computer-readable storage medium on which is stored a computer program product, which may be loaded directly into the internal memory of a digital computer and includes software code sections, the computer product, when executed by a computer, causing the computer to perform: receiving data from which a measured EGR mass flow signal can be determined; receiving data from which a modeled EGR mass flow signal can be determined; supplying each of the measured EGR mass flow signal and the modeled EGR mass flow signal to two respective bandpass filters, a first one of the bandpass filters having a time constant adapted for a recognition of flow rate errors, and a second one of the bandpass filtering having a time constant adapted for a recognition of dynamic errors; determining, for each of the measured EGR mass flow signal filtered for flow rate errors and dynamic errors, respectively, and for each of the modeled EGR mass flow signals filtered for flow rate errors and dynamic errors, respectively, an energy; forming a first energy quotient based on the energy of measured EGR mass flow signal filtered for flow rate errors and the energy of the modeled EGR mass flow signal filtered for flow rate errors; forming a second energy quotient based on the energy of the measured EGR mass flow signal filtered for dynamic errors and the energy of the modeled EGR mass flow signal filtered for dynamic errors; recognizing a flow rate error if the first energy quotient is in a predefined flow rate error range; and recognizing a dynamic error if the second energy quotient is in a predefined dynamic error range.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 shows a schematic view of the technical environment in which the method according to the present invention may be applied.

[0025] FIG. 2 shows a block diagram of a method for recognizing a dynamic error and a flow rate error.

[0026] FIG. 3 shows a distribution diagram of diagnostic events.

[0027] FIG. 4 shows a distribution of the number of diagnostic events, which are associated with various energy quotient ranges and EGR valve actuator position ranges.

[0028] FIG. 5 shows a diagram of the evaluation of the error severity in the case of a low-flow error.

[0029] FIG. 6 shows the diagram shown in FIG. 5 for the evaluation of the error severity in the case of a high-flow error.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0030] FIG. 1 shows a schematic view of the technical environment in which the method according to the present invention may be applied. An internal combustion engine 10 designed as a diesel engine having an air supply line 30 and an exhaust gas discharge line 20 is shown by way of example. The illustration is restricted to the parts needed for the description of the present invention. Fresh air 31 is supplied along a supply duct 36 of air supply line 30 via a hot-film air mass sensor 32, a compressor 12 of a turbocharger 11, and a fresh air throttle 34 to internal combustion engine 10. Air supply line 30 is divided into a supply air low-pressure area 14 upstream from compressor 12 and a supply air high-pressure area 15 in the flow direction downstream from compressor 12.

[0031] Exhaust gas 26 of internal combustion engine 10 is discharged via exhaust gas discharge line 20 from internal combustion engine 10 along an exhaust gas duct 21 via an exhaust gas turbine 13 of turbocharger 11, a particle filter 22, an exhaust flap 24, and a muffler 25 to the surroundings. Exhaust gas discharge line 20 is divided into an exhaust gas high-pressure area 17 and an exhaust gas low-pressure area 16, exhaust gas low-pressure area 16 beginning downstream from exhaust gas turbine 13 in the flow direction.

[0032] In the example shown, a low-pressure exhaust gas recirculation system 40 connects exhaust gas low-pressure area 16 downstream from particle filter 22 to supply air low-pressure area 14 downstream from hot-film air mass sensor 32. Low-pressure exhaust gas recirculation system 40 contains an exhaust gas filter 41, a first exhaust gas recirculation cooler 42, and a low-pressure exhaust gas recirculation valve 43 including a differential pressure sensor 44, via which a low-pressure exhaust gas recirculation mass flow 49 is guided. The pressure of exhaust gas 26 upstream from exhaust flap 24 is determined with the aid of a first pressure sensor 23 and is determined in the exhaust gas high-pressure area with the aid of a fourth pressure sensor 27. The pressure of fresh air 31 is determined with the aid of a second pressure sensor 33 upstream from fresh air throttle 34 and is determined with the aid of a third pressure sensor 35 downstream from the throttle. Pressure sensors 23, 27, 33, 35 may also be designed in another specific embodiment as modeled and converted back via differential pressure sensor.

[0033] A high-pressure exhaust gas recirculation system 45 (EGR) connects exhaust gas high-pressure area 17 upstream from exhaust gas turbine 13 via a second exhaust gas recirculation cooler 46 and a high-pressure exhaust gas recirculation valve 47 to supply air high-pressure area 15 downstream from fresh air throttle 34, so that a high-pressure exhaust gas recirculation mass flow 48 may be recirculated.

[0034] During operation, the mass of fresh air 31 supplied to internal combustion engine 10 is determined using hot-film air mass sensor 32. A partial flow of exhaust gas 26 is admixed to fresh air 31 via low-pressure exhaust gas recirculation system 40. The air mixture thus resulting is compressed by compressor 12 of turbocharger 11, subsequently a further partial flow of exhaust gas 26 is admixed thereto via high-pressure exhaust gas recirculation system 45. The mixture thus resulting is supplied to internal combustion engine 10. Resulting exhaust gas 26 drives turbocharger 11 via exhaust gas turbine 13 and is depressurized to a lower pressure level. Subsequently, particles are filtered out of exhaust gas 26 using particle filter 22.

[0035] In the method according to the present invention, high-pressure exhaust gas recirculation mass flow 48 and/or low-pressure exhaust gas recirculation mass flow 49 is/are directly measured or derived indirectly from measured values. Thus, for example, high-pressure exhaust gas recirculation mass flow 48 may be determined from the measured values of air mass flow via throttle valve (fresh air throttle valve 34), speed, and inlet pressure (boost pressure), for example, in supply air high-pressure area 15. High-pressure exhaust gas recirculation mass flow 48 and/or low-pressure exhaust gas recirculation mass flow 49 is/are continued to be modeled.

[0036] FIG. 2 shows a block diagram of a method for recognizing a dynamic error and a flow rate error in low-pressure exhaust gas recirculation system 40 and/or high-pressure exhaust gas recirculation system 45 of internal combustion engine 10.

[0037] A measured EGR mass flow signal 50 is supplied to a first and a second bandpass filter 51.1, 51.2. A modeled EGR mass flow signal 60 is supplied to a third and a fourth bandpass filter 61.1, 61.2. First and third bandpass filters 51.1, 61.1 each have time constants, which are suitable for recognizing flow rate errors. The time constants of second and fourth bandpass filters 51.2, 61.2 are optimized for the recognition of dynamic errors. Flow rate errors are static EGR high/low-flow errors, while dynamic errors represent EGR slow response errors, as are described above in the possible causes thereof.

[0038] Thus, a measured EGR mass flow signal 52.1 filtered for flow rate errors, a measured EGR mass flow signal 52.2 filtered for dynamic errors, a modeled EGR mass flow signal 62.1 filtered for flow rate errors, and a modeled EGR mass flow signal 62.2 filtered for dynamic errors are obtained. Filtered EGR mass flow signals 52.1, 52.2, 62.1, 62.2 are each supplied to a squaring unit 53.1, 53.2, 63.1, 63.2 and subsequently to an integrating unit 54.1, 54.2, 64.1, 64.2. An energy E.sub.meas, flow 55.1 of measured EGR mass flow signal 52.1 filtered for flow rate errors, an energy E.sub.meas, dyn 55.2 of measured EGR mass flow signal 52.2 filtered for dynamic errors, an energy E.sub.mod, flow 65.1 of modeled EGR mass flow signal 62.1 filtered for flow rate errors, and an energy E.sub.mod, dyn 65.2 of modeled EGR mass flow signal 62.2 filtered for dynamic errors are thus obtained over an integration period of time. In a first divider 56, an energy quotient r.sub.flow 57 is determined as the ratio between energy E.sub.meas, flow 55.1 and energy E.sub.mod, flow 65.1. In a second divider 66, an energy quotient r.sub.dyn 57 is ascertained as the ratio between energy E.sub.meas, dyn 55.2 and energy E.sub.mod, dyn 65.1.

[0039] FIG. 3 shows a distribution diagram of diagnostic events. To determine the distribution diagram, energy quotients r 57, 58 ascertained according to the block diagram shown in FIG. 2 are associated with particular energy quotient ranges, in the present case in steps of 0.1, and the frequency at which diagnostic events are associated with a particular energy quotient range is plotted in relation to an energy quotient axis 70 and a frequency axis 71. A flow error distribution 74 shows a typical distribution of determined energy quotients r.sub.flow 57, as is obtained in the event of a flow rate error, in the present case a low-flow error, for example, at a high-pressure exhaust gas recirculation system 45. A slow response error distribution 75 is obtained for energy quotients r.sub.dyn 67, if a dynamic error of exhaust gas recirculation system (40, 45) exists. As error distributions 74, 75 show, in the case of flow rate errors, statistically smaller energy quotients r.sub.flow 57 are obtained, and in the case of dynamic errors, statistically larger energy quotients r.sub.dyn 57 are obtained. Therefore, the individual flow rate errors (high-flow errors, low-flow errors) and the asymmetrical slow response errors may be recognized and differentiated from one another by an appropriate evaluation. A flow rate error is deduced if, for example, the statistical mean of energy quotients r.sub.flow 57 is in a flow rate error range 72. A dynamic error is recognized if the statistical mean of energy quotient r.sub.dyn 67 is within a dynamic error range 73.

[0040] FIG. 4 shows a distribution of the number of diagnostic events, which are associated with various energy quotient ranges 77.1, 77.2, 77.3 and EGR valve actuator position ranges 76. The distribution is accordingly plotted in relation to a frequency axis 71.

[0041] FIG. 5 shows a diagram for the evaluation of the error severity in the case of a low-flow error. For this purpose, a valve characteristic curve 83 is plotted in relation to an effective EGR valve area axis 80 and an EGR valve actuator position 81. A first effective EGR valve area a.sub.1 82.1, a second effective EGR valve area a.sub.2 82.2, and a third effective EGR valve area a.sub.3 82.3 are marked in relation to valve area axis 80. An energy quotient axis 70 forms a second ordinate. An energy quotient r=0 70.1, a first energy quotient threshold 70.2, and an energy quotient r=1 70.3 are marked along energy quotient axis 70. Valve characteristic curve 83 characterizes the effective area of an exhaust gas recirculation valve 43, 47 at various EGR valve actuator positions.

[0042] In the present case, EGR valve actuator position ranges 76 are divided into 20% steps of the maximum value in FIG. 4. In the exemplary embodiment shown, the focal point of the error distribution is in an EGR valve actuator position range 76 of 41% to 60%. A maximum of the diagnostic events was associated with first energy quotient range 77.1 within EGR valve actuator position range 76. First energy quotient range 77.1 includes in the present case energy quotients r.sub.flow 57 of 0.1-0.2 and is therefore below first energy quotient threshold 70.2 shown in FIG. 5. Transferred to the diagram shown in FIG. 5, this indicates that, for example, due to sooting, the effective EGR valve area in the range between second effective EGR valve area a.sub.2 82.2 and third effective EGR valve area a.sub.3 82.3, corresponding to an EGR valve actuator position of 60% to 100%, is no longer usable. This results in a lower exhaust gas recirculation rate than expected. It may be ascertained by emission tests whether such a reduction of the exhaust gas recirculation rate results in exceedance of the OBD emission limiting values. If this is the case, the diagnosis thus has to recognize a low-flow error as a flow rate error in the present case.

[0043] FIG. 6 shows the diagram shown in FIG. 5 for the evaluation of the error severity in the case of a high-flow error. The maximum of the diagnostic events is also associated here with an energy quotient range 77.1, 77.2, 77.3, which is below a second energy quotient threshold 70.4. Such an error case may occur, for example, if a leak occurs at the mixing point between an EGR mass flow and fresh air. This may again be associated with an effective EGR valve area, which in the present case is smaller than first effective EGR valve area a.sub.1. The effective EGR valve area may be associated with an EGR valve actuator position x.sub.1.

[0044] Below this EGR valve actuator position x.sub.1, exhaust gas recirculation valve 43, 47 is no longer effectively usable. The EGR rate is elevated accordingly. Diagnostic events below EGR valve actuator position x.sub.1 therefore result in low energy quotients r (57, 67). It may be ascertained by emission tests whether such an increase of the exhaust gas recirculation rate results in exceedance of the OBD emission limiting values.