Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2000-01-07
2001-03-27
Denion, Thomas (Department: 3747)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S274000, C123S406260, C123S435000, C073S118040, C073S035080
Reexamination Certificate
active
06205774
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
Priority is claimed with respect to german application no. 199 01 066.8-13 filed in Germany on Jan. 14, 1999, the disclosure of which is incorporated herein by reference:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a method for detecting flow-reducing changes in an exhaust-gas catalyst body of an exhaust-gas purification system during the operation of an associated internal combustion engine with at least one engine cylinder, the exhaust gas from which impinges upon the exhaust-gas catalyst body and to which an ion-current measuring probe is assigned.
2. Discussion
Generally, if exhaust-gas catalytic converters become too hot, they can lose not only their property of chemical conversion but can also suffer mechanical damage or even destruction. Fragments formed during this process can pass via the exhaust valves into an upstream engine cylinder and lead to engine damage. There is therefore a requirement to be able to detect those types of mechanical damage to the catalyst body which typically result in disintegration of its mechanical honeycomb structure and, associated with this, a reduction in the cross section of passage available for the exhaust gas flowing through.
One method that may be considered for detecting such mechanical changes in the exhaust-gas catalyst body which reduce the cross section of passage is to determine the exhaust-gas backpressure, which increases upstream of the catalyst body due to the said reduction in the cross section of passage of the latter. Due to the high temperatures prevailing, however, this procedure requires a relatively high outlay. Another possibility of detecting the mechanical state of the catalyst body is temperature measurement, but this necessitates a corresponding temperature sensor.
It is known practice to use an ion-current measuring probe in an engine cylinder, i.e. in its combustion chamber, to carry out ion-current measurement during a respective operating cycle of the engine cylinder, it being possible for a spark plug to act as the ion-current measuring probe. The ion-current signal supplied by the ion-current measuring probe is customarily used particularly for knock detection, see Patent Specification DE 196 14 288 C1, which also mentions that ion-current measurement can also be used to detect spark failures, which can cause damage to a connected exhaust-gas catalytic converter. This and further applications of ion-current measurement, such as ignition-point feedback, transient lambda-value control, injection control and exhaust-gas recirculation control, are mentioned in a magazine article with the title “Ion-gap sensing for engine control” in Automotive Engineering, September 1995, page 65.
The technical problem underlying the invention is to provide a method of the type stated at the outset by means of which flow-reducing changes in an exhaust-gas catalyst body, particularly those due to destruction of its mechanical structure by excessive temperatures, can be detected reliably with a relatively low outlay.
SUMMARY OF THE INVENTION
The method of the present invention is based on the realization that a flow-reducing change in the catalyst body leads to an increased exhaust-gas backpressure upstream of the catalyst body and, as a result, to an increased residual-gas rate in those engine cylinders which are connected on the exhaust side to this exhaust-gas catalyst body. With the ion-current measuring probe active, an increased residual-gas rate in the engine cylinder leads to lower ionization and hence to a lower ion-current signal from the latter, given otherwise identical conditions, in particular given the same engine operating point.
According to the invention, the ion-current signal of the ion-current measuring probe is then monitored to determine whether its signal strength for a particular operating cycle of the associated cylinder continuously falls below a minimum strength which can be specified as a function of the engine operating state.
It is self-evident that the minimum strength value concerned is chosen so that it is exceeded by the ion-current signal when the engine is operating correctly and the catalyst body is undamaged. If undershooting of the minimum strength value is detected, therefore, this is an indication that a flow-reducing change in the catalyst body may have taken place, in particular degradation of its mechanical honeycomb structure by overheating. In this case, warning information to this effect is generated.
It is self-evident that this warning information represents a condition which is necessary but not always sufficient to prove that there is a flow-reducing change in the catalyst body. This means that, in systems in which the reduction concerned in the ion-current signal strength cannot have any other cause, it is possible to infer the presence of a flow-reducing change in the catalyst body directly from the generation of the warning information. If, on the other hand, other causes for such a reduction in the ion-current signal strength are possible, it may be necessary to carry out a supplementary check to determine whether the generation of the warning information has actually been caused by a flow-reducing change in the catalyst body or whether there is some other reason for it. For safety's sake, provision can be made for the warning information to trigger engine cut-off or at least an interruption to injection to the engine cylinders concerned. In either case, it is possible to infer that the exhaust-gas catalyst body is intact as long as no warning information is generated.
The signal strength of the ion-current signal in a particular engine-cylinder operating cycle, which signal strength is used for evaluation, can be implemented in various ways. One embodiment of the present invention implements a specific provision a peak-value amplitude or the time integral of the ion-current signal for the particular operating cycle as the signal strength to be evaluated and to specify suitable minimum values dependent on the engine operating state for this purpose. To avoid incorrect generation of warning information due to “maverick events” or cycle fluctuations of the ion-current signal, which result in fluctuations of the ion-current amplitude even in the case of a constant engine operating point, the signal strength determined from the ion-current signal measured is smoothed or averaged over a number of operating cycles.
In an alternate embodiment of the present invention, the method includes a step where the minimum strength is specified on the basis of a reference-strength characteristic map as a function of the speed and load of the internal combustion engine, thereby allowing for the fact that the ion-current signal amplitude changes as a function of the engine speed and engine load. Specifying such a characteristic map makes it possible to evaluate the ion-current signal for any flow-reducing changes in the catalyst body at every engine operating point in the characteristic map.
As an additional alternative embodiment of the invention, the minimum strength is specified only for a selected desired engine operating state for evaluation, it being possible for this desired state to represent one or more engine operating points or part of the overall range of the engine operating point. The evaluation of the ion-current signal strength as regards detection of flow-reducing changes in the catalyst body is then limited to actual engine operating states which correspond to this desired engine operating state for evaluation. This eliminates the need to specify a characteristic map for the entire engine operating range.
A further aspect of the present is that the method developed is suitable specifically for systems with a plurality of parallel exhaust-gas catalyst converters. In this case, flow-reducing deterioration in one catalytic converter can be detected by comparing the ion-current signal strength for the cylinders connected to this catalytic converter with the ion-current signal strength of the remaining cyli
Hohner Peter
Miroll Jörg
Wilstermann Hartung
Daimler-Chrysler AG
Denion Thomas
Lorelli Marc
Tran Diem
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