Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Patent
1997-05-21
1999-02-23
Dombroske, George
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
73116, 731173, 123419, 123436, G01M 1500
Patent
active
058754113
DESCRIPTION:
BRIEF SUMMARY
IN THE DISCLOSURE
The invention relates to a method for detecting combustion misfires in internal combustion engines.
BACKGROUND OF THE INVENTION
Combustion misfires lead to an increase of toxic substances emitted during operation of the engine and can, in addition, lead to damage of a catalytic converter in the exhaust-gas system of the engine. A detection of combustion misfires in the entire rpm and load ranges is necessary to satisfy statutory requirements as to onboard monitoring of exhaust-gas relevant functions. In this context, it is known that, during operation with combustion misfires, characteristic changes occur in the rpm curve of the engine compared to normal operation without misfires. Normal operation without misfires and operation with misfires can be distinguished from a comparison of these rpm curves.
A method operating on this basis is already known from German patent publication 4,138,765.
In this known method, a crankshaft angular region which is characterized as a segment is assigned to each cylinder. The segments are realized, for example, by markings on a transducer wheel coupled to the crankshaft. The segment time in which the crankshaft passes through this angular region is dependent, inter alia, upon the energy converted in the combustion stroke. Misfires lead to an increase of the segment times detected in synchronism with the ignition. According to the known method, a criterion for the rough running of the engine is computed from the differences of the segment times. In addition, slow dynamic operations such as the increase of the engine rpm for a vehicle acceleration are mathematically compensated. A rough-running value which is computed in this way for each ignition, is likewise compared ignition-synchronously to a predetermined threshold value. Exceeding this threshold value is evaluated as a misfire. The threshold value is dependent, as may be required, from operating parameters such as load and engine speed (rpm).
The reliability with which misfires can be detected with this method drops naturally to a greater extent the less individual misfires operate on the rpm of the crankshaft. The reliability of the misfire detection therefore drops with increasing number of the cylinders of the engine and with increasing rpm as well as decreasing load.
SUMMARY OF THE INVENTION
In view of this background, the object of the invention is to provide a method which further improves the reliability of the misfire detection in internal combustion engines having a high number of cylinders even at high rpm and low loads.
The invention is based upon the realization that the segment time increase as a consequence of a misfire at high rpm is no longer distributed to one segment time but instead to several segment times.
An element of the invention comprises undertaking an evaluation including a greater crankshaft angle. This takes place, for example, by considering additional segment times before and after a possible misfire. Various computation rules have been shown to be advantageous for the computation of a rough-running quantity while considering further segment times. It is common for these rules that they are defined by discrete convolution in the signal processing stage and feature extraction stage by means of a digital filter and predetermined filter coefficients.
These various rules can be expressed without dynamic corrections with the following formula: ##EQU1## wherein: b(n) are filter coefficients, Ma, Me are filter start and filter end, respectively, and M=Ma-Me+1 is the filter length and * is the convolution operator.
Multiplication by the reciprocal value of ts(n).sup.3 as a proportionality factor operates to eliminate the dependency upon rpm.
In lieu of the segment times, the speeds .omega., which are allocated to the segments, can be used: ##EQU2##
It is an essential feature of the invention that the methods for detecting misfires can be supplemented by methods for dynamic compensation. The object is to eliminate the influence of misfire-like rpm changes.
BRIEF DESCRIP
REFERENCES:
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patent: 5687082 (1997-11-01), Rizzoni
"Engine Misfire Detection" HAVANT GB, No. 324, Apr. 1991, p. 253.
Forster Jurgen
Hafner Sigrid
Lohmann Andrea
Ries-Muller Klaus
Volkart Asmus
Dombroske George
Ottesen Walter
Robert & Bosch GmbH
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