Misfire detection method for a piston combustion engine with...

Internal-combustion engines – Spark ignition timing control – Electronic control

Reexamination Certificate

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C123S406140

Reexamination Certificate

active

06336440

ABSTRACT:

In piston combustion engines having cylinder valves with completely-variable control and actuation via an electronic engine control, it is also possible to effect a load-dependent control of the piston combustion engine: Instead of reducing the fuel supply to all cylinders in partial-load operation, depending on the requirements, only the power of individual cylinders is reduced to “zero power” through the manipulation of the fuel supply and ignition, while the other cylinders are fired normally.
For the example of a six-cylinder engine, based on partial-load requirements, two cylinders are reduced to zero power through the reduction or cutoff of the fuel supply and ignition. In an advantageous measure, two cylinders are not reduced to zero-load power, that is, stopped, for the entire duration of the partial-load phase; instead, different cylinders are stopped, with respect to their fuel supply and ignition, successively in a cyclical exchange during this partial-load phase, so two different cylinders are stopped and four other cylinders are fired completely in sequence. The advantage of this procedure is that, instead of a reduction in the fuel supply to all six cylinders, only the stopped cylinders receive no more fuel in order to adapt to partial-load operation, while the fired cylinders are supplied with a quantity of fuel that corresponds to the quantity of fuel that would practically be necessary for full-load operation. As a result, optimum combustion can take place in the fired cylinders.
Periodically reducing the power of individual cylinders or stopping them forces a change in predetermined operating data, such as a reduction in the running smoothness. This also occurs when some of the cylinders are only supplied with less fuel. Because the operating anomaly of reduced running smoothness can also be used to detect a misfire, the fact that this reduction in smoothness is caused by individual cylinders would cause it to be perceived as a combustion misfire with the use of corresponding sensor equipment, although the relevant cylinder would have been stopped. If actual combustion misfires occur in this type of partial-load operation, they cannot be readily detected through a detection of, for example, fluctuations in rpm, because in this operating mode the piston combustion engine ordinarily operates with more severe rpm fluctuations than in “normal operation” because of the programmed change in the valve control.
The term “fuel supply” encompasses systems in which the fuel is metered separately to the individual cylinders, as is the case in fuel injection directly into the respective cylinder or its intake port.
The term “combustion misfire” refers to a failure of the supply of fuel and/or the ignition for one or more cylinders that is not caused by the engine control, but by a disturbance.
It is the object of the invention to provide a method that permits the detection of combustion misfires, also in the above-described operating mode of a partial-load control, by way of a reduction in power to zero power for only a few of the cylinders.
According to the invention, this object is accomplished in that, in the engine control, a cylinder-control program detects at least the cylinders that are reduced in power in the respective load situation with a cylinder-identification signal, and, in predetermined time intervals, detects the resulting deviations of predetermined operating characteristic data as “normal operation,” and deviations that exceed the predetermined operating data are recognized as having been caused by combustion misfires, and a control signal is generated. Over the sequence of cylinder-identification signals, at least for the cylinders operating at reduced power, the engine control detects a change in the predetermined operating characteristic data that was effected by a reduction in power of individual cylinders as “proper,” and therefore as “normal operation,” not only in full-load operation, but above all in partial-load operation.
If combustion misfires occur at cylinders that are fired completely or at reduced power during this type of operation, a change also occurs in the course over time of the detected operating characteristic data, which can be detected as “improper” through a deviation with respect to a predetermined threshold value of successive signals. Because the sequence of the cylinders that have been fired for the respective load situation has been predetermined by the cylinder-control program in the engine control, a precise allocation to the cylinder at which the combustion misfire occurred can be detected via the cylinder-identification signals. If combustion misfires occur, an “on-board diagnosis” can take place in, for example, the form of a control signal that is generated as a indicator, which compels the driver to seek the cause of the combustion misfire by taking the vehicle to a mechanic. It is also possible, however, to react directly via the engine control, and, at the cylinder for which a combustion misfire has been detected, to cut off the ignition and the fuel supply for one or more cylinders, or permanently, and perform the load distribution to the individual cylinders differently, via the engine control, corresponding to the load requirements predetermined by the driver.
An embodiment of the invention provides that the rpm fluctuations are detected as operating characteristic data to be predetermined.
An advantageous embodiment of the invention provides that the rpm fluctuations are detected as a periodic time signal, and time differences between successive time signals due to changing rpm fluctuations are detected as combustion misfires.
In another embodiment of the method of the invention, the indicated medium pressures of the individual cylinders are detected as predetermined operating characteristic data. The value for the indicated medium pressure, that is, the work generated per cycle, can be realized from the determination of the pressure course for each individual cylinder. In the process, the crankshaft position determined by corresponding sensors is converted into the instantaneous cylinder volume, and the work is determined through the creation of the contour integral ∫PdV, or the so-called indicated medium pressure Pmi is determined through division by the displacement. If the engine control operates one or more cylinders, or one cylinder successively in a cyclical exchange, at reduced power—which can also be zero power—specifically for partial-load operation, this is ascertained as a reduction in the indicated medium pressure Pmi. If this value lies below a predetermined threshold, the presence of a combustion misfire would be detected for the relevant cylinder. Because, however, the cylinder-control program in the engine control makes it known which cylinder is being operated at reduced power, the engine control only detects the presence of a combustion misfire if the reduced indicated medium pressure is detected at a cylinder that is operating properly at full power in accordance with the engine-control program, or is to be operated at reduced power. The threshold value of the indicated medium pressure of this programmed reduced power then represents the threshold that is detected as a combustion misfire when the value is not met for the relevant cylinder. As an alternative, the method can be modified such that the determined Pmi values for the cylinders that are known to be operating, i.e., are programmed to operate, at reduced power are multiplied by a corresponding factor, that is, “extrapolated,” before the threshold-value comparison. Thus, a detection of combustion misfires at cylinders that are operating properly at full load, or at reduced power, is also possible.
In another embodiment of the invention, it is provided that the exhaust-gas pressure in the exhaust train is detected as operating characteristic data to be predetermined. This pressure can be detected in the intake ports of the individual cylinders, so the association with individual cylinders can also be performed purely geometricall

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