Method for avoiding incorrect combustion misfire fault detection in a motor vehicle

Abstract

A method is provided for avoiding incorrect combustion misfire fault detection in an internal combustion engine in a motor vehicle with a dual mass flywheel. In order to detect combustion misfiring, a characteristic variable, which is dependent on the acceleration of the internal combustion engine, is determined continuously during the ongoing operation of the internal combustion engine and compared with a predefined irregular running threshold value. When the irregular running threshold value is exceeded, a combustion misfire is detected, wherein the frequency of detected combustion misfiring, for example at a specific number of crank shaft revolutions, is detected. When a defined frequency threshold is exceeded, a combustion misfire fault detection is activated. When a dual mass flywheel bounce is detected with the simultaneous detection of combustion misfiring, the injection of at least one cylinder is reduced or switched off for a predefined frequency or for a predefined time.

Claims

1. A method for avoiding incorrect combustion misfire fault detection in an internal combustion engine of a motor vehicle having a dual mass flywheel, the method comprising the acts of: determining continuously a characteristic variable dependent on an acceleration of the internal combustion engine during operation of the internal combustion engine; comparing the characteristic variable with a predefined irregular running threshold value; detecting a combustion misfire when the characteristic variable exceeds the predefined irregular running threshold value; determining a frequency of detected combustion misfires; activating a combustion misfire fault detection when the frequency of the detected combustion misfires exceeds a defined frequency threshold; and reducing or switching-off a fuel injection of at least one cylinder of the internal combustion engine for a predefined frequency or for a predefined time when a dual mass flywheel bounce is detected simultaneously with the combustion misfires.

2. The method according to claim 1, wherein before carrying out the act of reducing or switching-off the injection, increasing an engine torque to provide a torque surge to counter the dual mass flywheel bounce.

3. The method according to claim 1, wherein the act of reducing or switching-off the injection is carried out by reducing or switching-off the injection of all cylinders of the internal combustion engine at least once.

4. The method according to claim 1, wherein the act of reducing or switching-off the injection is carried out by reducing or switching-off the injection of all cylinders of the internal combustion engine with a predefined frequency, the predefined frequency being variably defined as a function of engine speed and/or engine torque.

5. The method according to claim 1, wherein a start of the reduction of the injection is predefined for the defined frequency threshold when the combustion misfire fault detection is activated.

6. The method according to claim 1, wherein a start of the reduction of the injection is predefined when a pre-frequency threshold is reached, the pre-frequency threshold being formed by multiplying the defined frequency threshold by a factor between zero and one.

7. The method according to claim 6, wherein the factor between zero and one is variable as a function of at least one operating parameter of the internal combustion engine.

8. The method according to claim 1, wherein a start of the reduction of the injection is predefined when a pre-frequency threshold is reached, the pre-frequency threshold being formed by a parameterizable interval before the defined frequency threshold is reached.

9. The method according to claim 8, wherein the parameterizable interval is a fixed value.

10. A system for avoiding incorrect combustion misfire fault detection in an internal combustion engine of a motor vehicle having a dual mass flywheel, the system comprising: an electronic control unit configured to control the internal combustion engine, said electronic control unit being programmed to function as: a first monitoring module that detects combustion misfiring via an irregular running threshold value; a second monitoring module that performs combustion misfire fault detection via a frequency threshold; a third monitoring module that detects bounce of the dual mass flywheel; and a control module that reduces or switches-off a fuel injection of at least one cylinder of the internal combustion engine for a predefined frequency or for a predefined time when the bounce of the dual mass flywheel is detected simultaneously with the detection of combustion misfires.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graphical diagram in which the irregular running is plotted against time; and

(2) FIG. 2 is a schematic block logic diagram of the system according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(3) FIG. 1 illustrates a diagram in which the irregular running (IR) is plotted against the crank shaft angle (CA). Here, significantly increased irregular running (IR) is measured during a dual mass flywheel bounce (DMF B). The irregular running (IR) exceeds the irregular running threshold value (IT) repeatedly. In this context, a combustion misfire (CM) is detected every time. Each combustion misfire (CM) is counted by use of a predefined evaluation window (see hatched bar, for example over 200 crank shaft revolutions) and is preferably also weighted. This frequency of the combustion misfire (CM), which is acquired in this way, is compared with a defined frequency threshold value (FT). If this frequency threshold value (FT) were reached, a combustion misfire fault detection (CMFD) would therefore occur, resulting in a fault program.

(4) According to the invention, when a dual mass flywheel bounce (DMF B) is detected n times with the simultaneous detection of combustion misfires (CM), the injection INJ of preferably all the cylinders of the internal combustion engine is reduced (INJ=0). Here, for example, this is done in the form of a complete shut off. The predefined frequency n times can be predefined in a variable fashion by the engine speed and/or by the engine torque.

(5) The start (INJ=0) of the injection reduction can be predefined in every case before the frequency threshold (FT) for the combustion misfire fault detection (CMFD) is reached. The start (INJ=0) of the injection reduction is preferably predefined when a pre-frequency threshold (PFT) is reached, wherein the pre-frequency threshold (PFT) is formed, for example, by multiplying the frequency threshold (FT) by a defined factor which is between 0 and 1. This factor can be determined empirically and predefined permanently. However, it can also be predefined in a variable fashion as a function of operating parameters of the internal combustion engine.

(6) Components for carrying out the method described with respect to FIG. 1 are illustrated schematically in FIG. 2. An electronic control unit 1, which is present in any case in the motor vehicle and has the purpose of controlling the internal combustion engine, is expanded with functional modules that are connected to one another. The control unit 1 contains:

(7) (a) a first monitoring module 2 for detecting combustion misfires (CM) by way of the irregular running threshold value (IT),

(8) (b) a second monitoring module 3 for combustion misfire fault detection (CMFD) by use of the frequency threshold (FT),

(9) (c) a third monitoring module 4 for detecting the dual mass flywheel bounce (DMF B) and

(10) (d) a control module 5 for reducing or switching off the injection (INJ) of at least one cylinder for a predefined frequency or for a predefined time.

(11) Within the scope of the investigations other software based solutions have also been devised. On the one hand there is the possibility of avoiding (or prohibiting) the critical load range at which there is a risk of DMF bounce. However, this has proven unfeasible since it brings about unreproducible driving behavior on the part of the driver.

(12) On the other hand, load surges due to rapid successive raising and lowering of the load have been investigated. Load is understood to be, in particular, the engine torque. In order to raise and lower the load it is possible, as mentioned above, to increase the torque briefly before the frequency threshold for the combustion misfire fault detection is reached and before the injection reduction. However, in this context a maximum permissible increase in torque has to be defined in order to avoid undesired accelerations of the motor vehicle.

(13) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.