Method and Device for Identifying and Distinguishing a Cause of at Least One Misfire of an Internal Combustion Engine

Abstract

The present disclosure relates to a method for detecting and distinguishing a cause of at least one combustion misfire of an internal combustion engine. The internal combustion engine has several cylinders, at least one exhaust gas tract, and an exhaust gas sensor which is arranged in the exhaust gas tract. The method includes the following steps: acquisition of a measurement signal with the exhaust gas sensor over a certain first period of time gas tract; subdivision of the measurement signal into measurement signal sections; assignment of the measurement signal sections to the corresponding cylinders, whereby cylinder-selective measurement signal profiles are produced that are characteristic of the respective oxygen content downstream of the respective cylinders over the determined first period of time of time; and evaluation of the cylinder-selective measurement signal profiles to detect at least one combustion misfire of the internal combustion engine.

Claims

1. A method for detecting and distinguishing a cause of at least one combustion misfire of an internal combustion engine, the internal combustion engine having several cylinders, at least one exhaust gas tract, and an exhaust gas sensor arranged in the exhaust gas tract, the method comprising the following steps: acquisition of a measurement signal with the exhaust gas sensor over a first period of time, the measurement signal is characteristic of oxygen content in the exhaust gas tract; subdivision of the measurement signal into measurement signal sections; assignment of the measurement signal sections to corresponding cylinders, whereby cylinder-selective measurement signal profiles are produced that are characteristic of the respective oxygen content downstream of the respective cylinders over the first period of time; and evaluation of the cylinder-selective measurement signal profiles to detect at least one combustion misfire of the internal combustion engine; wherein, when the at least one combustion misfire is detected, an evaluation of the cylinder-selective measurement signal profiles takes place in order to distinguish the cause of the at least one combustion misfire.

2. The method of claim 1, wherein, during the evaluation of the cylinder-selective measurement signal profiles in order to identify that cylinder in which the combustion failed, the cylinder-selective measurement signal profiles can be compared with each other.

3. The method of claim 2, wherein the combustion failed in that cylinder whose cylinder-selective measurement signal profile has the largest signal deflection compared with the other cylinder-selective measurement signal profiles.

4. The method of claim 1, wherein at least one of the combustion misfires is detected as soon as at least one of the cylinder-selective measurement signal profiles exceeds a first threshold value.

5. The method of claim 4, wherein, in order to distinguish the cause of the at least one combustion misfire, at least one of the cylinder-selective measurement signal profiles is compared with a second threshold value.

6. The method of claim 5, wherein, when the at least one combustion misfire is detected, the one combustion misfire is detected as an ignition misfire if at least one of the cylinder-selective measurement signal profiles only exceeds the first threshold value of the threshold values.

7. The method of claim 5, wherein, when the at least one combustion misfire is detected, the combustion misfire is detected as an injection misfire if at least one of the cylinder-selective measurement signal profiles exceeds the first threshold value and exceeds the second threshold value.

8. The method of claim 1, wherein a cylinder-specific characteristic diagram which takes into account a rotational speed of the internal combustion engine is used to assign the measurement signal sections.

9. The method of claim 1, wherein, in order to detect at least one combustion misfire, the cylinder-selective measurement signal profiles are compared with a comparison value which is characteristic of a mean value of the corresponding cylinder-selective measurement signal profiles, wherein the mean value is determined over a second period of time which is longer than the first period of time.

10. A device for detecting and distinguishing a cause of at least one combustion misfire of an internal combustion engine, the internal combustion engine having several cylinders, at least one exhaust gas tract, and an exhaust gas sensor arranged in the exhaust gas tract, the device comprising: a control unit configured to execute a method, the method comprising: acquisition of a measurement signal with the exhaust gas sensor over a first period of time, the measurement signal is characteristic of oxygen content in the exhaust gas tract; subdivision of the measurement signal into measurement signal sections; assignment of the measurement signal sections to corresponding cylinders, whereby cylinder-selective measurement signal profiles are produced that are characteristic of the respective oxygen content downstream of the respective cylinders over the first period of time; and evaluation of the cylinder-selective measurement signal profiles to detect at least one combustion misfire of the internal combustion engine; wherein, when the at least one combustion misfire is detected, an evaluation of the cylinder-selective measurement signal profiles takes place in order to distinguish the cause of the at least one combustion misfire.

11. The device of claim 10, wherein, during the evaluation of the cylinder-selective measurement signal profiles in order to identify that cylinder in which the combustion failed, the cylinder-selective measurement signal profiles can be compared with each other.

12. The device of claim 11, wherein the combustion failed in that cylinder whose cylinder-selective measurement signal profile has the largest signal deflection compared with the other cylinder-selective measurement signal profiles.

13. The device of claim 10, wherein at least one of the combustion misfires is detected as soon as at least one of the cylinder-selective measurement signal profiles exceeds a first threshold value.

14. The device of claim 13, wherein, in order to distinguish the cause of the at least one combustion misfire, at least one of the cylinder-selective measurement signal profiles is compared with a second threshold value.

15. The device of claim 14, wherein, when the at least one combustion misfire is detected, the one combustion misfire is detected as an ignition misfire if at least one of the cylinder-selective measurement signal profiles only exceeds the first threshold value of the threshold values.

16. The device of claim 14, wherein, when the at least one combustion misfire is detected, the combustion misfire is detected as an injection misfire if at least one of the cylinder-selective measurement signal profiles exceeds the first threshold value and exceeds the second threshold value.

17. The device of claim 10, wherein a cylinder-specific characteristic diagram which takes into account a rotational speed of the internal combustion engine is used to assign the measurement signal sections.

18. The device of claim 10, wherein, in order to detect at least one combustion misfire, the cylinder-selective measurement signal profiles are compared with a comparison value which is characteristic of a mean value of the corresponding cylinder-selective measurement signal profiles, wherein the mean value is determined over a second period of time which is longer than the first period of time.

Description

DESCRIPTION OF DRAWINGS

[0035] FIG. 1 shows a schematic block diagram of a multi-cylinder internal combustion engine,

[0036] FIG. 2 shows a schematic representation of a control unit of an internal combustion engine,

[0037] FIG. 3 shows a first diagram of the detection of combustion misfires in an internal combustion engine,

[0038] FIG. 4 shows a second diagram of the detection of combustion misfires in an internal combustion engine, and

[0039] FIG. 5 shows a third diagram of the detection of combustion misfires in an internal combustion engine.

[0040] Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0041] FIG. 1 shows a schematic representation of an internal combustion engine 10 with six cylinders CYL(0)-CYL(5), where the internal combustion engine 10 may be configured to drive a vehicle, for example. The internal combustion engine 10 has a first cylinder bank CYLB1 and a second cylinder bank CYLB2, which are arranged parallel to one another. The cylinders CYL(0), CYL(2), CYL(4) are arranged in the first cylinder bank CYLB1, and the cylinders CYL(1), CYL(3), CYL(5) are arranged in the second cylinder bank CYLB2. The internal combustion engine 10 also has an intake tract 11 which is configured to supply air to the internal combustion engine 10. In this regard, the intake tract 11 has a throttle valve 16 which is configured to control the air supply. In addition, the internal combustion engine 10 has a fuel supply device 12 which is configured to supply the internal combustion engine 10 with fuel. The internal combustion engine 10 additionally has an exhaust gas tract 13A, 13B which is arranged immediately downstream of the cylinders CYL(0)-CYL(5) in the direction of flow through the internal combustion engine 10. The exhaust gas tract 13A, 13B may be divided into a first exhaust gas tract 13A and a second exhaust gas tract 13B. The first exhaust gas tract 13A is arranged downstream of the first cylinder block CYLB1 and the second exhaust gas tract 13B is arranged downstream of the second cylinder block CYLB2.

[0042] As shown in FIG. 1, a first exhaust gas sensor 15A is arranged in the first exhaust gas tract 13A, and a second exhaust gas sensor 15B is arranged in the second exhaust gas tract 13B. The exhaust gas sensors 15A, 15B are arranged downstream of the cylinders CYL(0)-CYL(5). A first exhaust gas catalytic converter 14A is additionally arranged in the first exhaust gas tract 13A and a second exhaust gas catalytic converter 14B is additionally arranged in the second exhaust gas tract 13B. The exhaust gas catalytic converters 14A, 14B are arranged downstream of the respective exhaust gas sensors 15A, 15B.

[0043] FIG. 2 shows a control unit 20 in a schematic representation. The control unit 20 has a computing unit 21, a program memory 22, a memory 23, an air/fuel control device 24 and a fault memory 25. The control unit 20 is configured to output corresponding output signals AS from input signals ES and to control an internal combustion engine 10 accordingly. The control unit 20 can additionally be configured to actuate a fault display device 27, which is configured to display a fault, such as a combustion misfire V (not shown in FIG. 2), to a driver or to someone else. For example, a characteristic diagram KF, a first threshold value S1 and/or a second threshold value S2 can be stored in the memory 23. The characteristic diagram KF can be, for example, a gas flow characteristic diagram that is used to assign measurement signal sections MS_CYL_AB.

[0044] The control unit 20 can, for example, be an engine control unit which is configured to process a large number of data items and to actuate a wide variety of components of the internal combustion engine 10. The control unit 20 can accordingly also be configured to detect combustion misfires V of the internal combustion engine 10 and to distinguish their cause.

[0045] FIGS. 3 and 4 show a first diagram 100 and a second diagram 200 for detecting combustion misfires V in an internal combustion engine 10. According to these figures, a measurement signal MS_CYL of an exhaust gas sensor 15A, 15B is evaluated over a specific period of time Δt1. The measurement signal MS_CYL is characteristic of the oxygen content in an exhaust gas tract 13A, 13B of an internal combustion engine 10 downstream of cylinders CYL(0)-CYL(5). The measurement signal MS_CYL is then evaluated, for example, by the control unit 20 as shown in FIG. 2, in order to identify and subdivide combustion misfires V. For this purpose, the measurement signal MS_CYL is subdivided into measurement signal sections MS_CYL_AB. The measurement signal sections MS_CYL_AB are then assigned to the corresponding cylinders CYL(0)-CYL(5) so that cylinder-selective measurement signal profiles MS_CYL_SEL(0-5) are produced. The cylinder-selective measurement signal profiles MS_CYL_SEL(0-5) are consequently characteristic of the respective oxygen content in the exhaust gas tract 13A, 13B downstream of the respective cylinders CYL(0)-CYL(5). The cylinder-selective measurement signal profiles MS_CYL_SEL(0), MS_CYL_SEL (2), MS_CYL_SEL (4) of the cylinders CYL(0), CYL(2), CYL(4) are illustrated in FIGS. 1 and 2. It is conceivable that other cylinders CYL(0)-CYL(5) or all the cylinders CYL(0)-CYL(5) are also evaluated.

[0046] To detect at least one combustion misfire V, the cylinder-selective measurement signal profiles MS_CYL_SEL(0-5) are evaluated. In some examples, at least one of the combustion misfires V is detected as soon as at least one of the cylinder-selective measurement signal profiles MS_CYL_SEL(0-5) exceeds a first threshold value S1. The first threshold value S1 can, for example, be stored in the memory 23 of the control unit 20 and continuously compared with the cylinder-selective measurement signal profiles MS_CYL_SEL(0-5) by the control unit 20. In the diagrams 100, 200 in FIGS. 3 and 4, the cylinder-selective measurement signal profiles MS_CYL_SEL(0), MS_CYL_SEL (2), MS_CYL_SEL (4) are plotted over time t. The cylinder-selective measurement signal profiles MS_CYL_SEL(0), MS_CYL_SEL (2), MS_CYL_SEL (4) show signal deflections that begin at the time t1. For example, if at least one of the signal deflections exceeds the first threshold value S1, it is possible to infer a combustion misfire V that occurred a short time previously in one of the cylinders CYL(0)-CYL(5) arranged upstream. In the diagrams 100, 200 in FIGS. 3 and 4, the lower area in each case shows the time t at which the combustion misfire V occurred. Correspondingly, the combustion misfire V can be seen offset in time in the cylinder-selective measurement signal profiles MS_CYL_SEL(0), MS_CYL_SEL (2), MS_CYL_SEL (4).

[0047] To distinguish the cause of the combustion misfire V, the cylinder-selective measurement signal profiles MS_CYL_SEL(0-5) can be compared with a second threshold value S2. If the signal deflection of the cylinder-selective measurement signal profiles MS_CYL_SEL(0-5) exceeds the second threshold value S2, the combustion misfire V can be identified as an injection misfire, and if the signal profile of the cylinder-selective measurement signal profiles MS_CYL_SEL(0-5) does not exceed the second threshold value S2, the combustion misfire V can be identified as an ignition misfire. Diagram 100 in FIG. 3 shows the signal deflections which exceed the second threshold value S2, and consequently the combustion misfire V can be identified as an injection misfire according to this example. The diagram 200 in FIG. 4 shows the signal deflections which do not exceed the second threshold value S2, and consequently the combustion misfire V can be identified as an ignition misfire according to this example.

[0048] FIG. 5 shows a third diagram 300 which differs from the second diagram 200 and the first diagram 100 in that several combustion misfires V follow one another in a short time. Accordingly, the signal deflections of the cylinder-selective measurement signal profiles MS_CYL_SEL(0), MS_CYL_SEL (2), MS_CYL_SEL (4) shown deviate from one another to a relatively large extent. For the purpose of precise detection of the combustion misfires V, it may be appropriate to compare the cylinder-selective measurement signal profiles MS_CYL_SEL(0), MS_CYL_SEL (2), MS_CYL_SEL (4) with a comparison value that is characteristic of a mean value of the corresponding cylinder-selective measurement signal profiles MS_CYL_SEL(0), MS_CYL_SEL (2), MS_CYL_SEL (4), where the mean value is determined over a second period of time Δt2, which is longer than the first period of time Δt1.

[0049] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.