Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1998-10-07
2001-06-12
Chapman, Jeanette (Department: 3711)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S285000, C123S436000
Reexamination Certificate
active
06244042
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for monitoring the regulation of the smooth operation of an internal combustion engine in dependence on a measured value of the condition of the catalytic converter.
BACKGROUND AND PRIOR ART
For an internal combustion engine operating with a lean air/fuel mixture (lean burn engines), it is desirable to monitor operation thereof to ensure smooth operation. During lean burn operation, the formation of nitrogen oxides (NOx) can be decreased by operating the engine with as lean a mixture as possible. However, there are limits to the extent to which the strength of the air/fuel mixture can be a decreased, since if the mixture is too lean misfiring can occur which can lead to hunting, and in extreme cases, to stalling of the engine.
Efforts are therefore made in lean burn operation to operate the engine with as high an air/fuel ratio as possible (lean burn operation) while avoiding irregular running which may be perceptible to the driver. Thus to reduce nitrogen oxides emissions the engine has to be operated as close as possible to an irregular-running limit. The air/fuel ratio necessary to achieve this object can only be determined in advance very inexactly, since reaching the irregular-running limit depends on many parameters, some of which are subject to long-term or short-term drifting, for example the current engine operating parameters, the geometry of the combustion chambers, the quality of the mixture formation, the condition of the ignition system, etc. If a predetermined air/fuel ratio is used, the engine must be operated using a relatively large margin of safety from an air/fuel ratio corresponding to the irregular-running limit, and this has an unfavourable influence on the nitrogen oxides emissions.
It is basically known to measure the irregular running of an internal combustion engine. To obtain a measured value for the irregular running, it is preferred to evaluate the movement of the crankshaft. Increasing irregularity of running leads to more irregular running of the crankshaft, so that by means of statistical methods (e.g. comparison of the current angular velocity with an average value) a measured value can be determined which represents a measure of the irregular running.
OBJECT OF THE INVENTION
It is an object of the present invention to provide an improved method for monitoring the regulation of the smooth running of an internal combustion engine.
SUMMARY OF THE INVENTION
The present invention provides a method for monitoring the regulation of the smooth running of a multi-cylinder internal combustion engine in which the smooth running is regulated using at least one manipulated variable to influence the smooth running behavior, wherein measurement signals corresponding to at least one temperature at the catalyst are evaluated.
In lean burn operation the content of hydrocarbons (HC) and of oxygen in the “raw exhaust gas” increases at the limit of smooth running. The “raw exhaust gas” is defined as the composition of the exhaust gas before the catalytic converter. The hydrocarbons and the oxygen react in the catalytic converter with evolution of heat. With increased irregularity of running the HC content in the raw exhaust gas increases considerably. A greater quantity of heat is thereby liberated in the catalytic converter. This brings about increased heating up of the catalyst in the region of the outlet from the converter. By means of suitable sensors at the inlet and outlet of the converter the corresponding measurement signals, which represent a measure of the temperatures at the position of the sensors, are evaluated, in order to perform monitoring of the smooth running in dependence on a measured value generated from the measurement signals.
As the measured value for the monitoring of the smooth running, it is preferred to form the difference between the measurement signals at the inlet and outlet of the converter. The measurement signals can suitably be calibrated in advance.
The measured value for monitoring the smooth running is preferably formed from measurement signals at the HEGO (heated exhaust gas oxygen) sensors. These sensors have a temperature-dependent internal resistance which can be detected by means of a suitable measuring and evaluating device. With the increased evolution of heat on exceeding the irregular running limit the corresponding temperature change at the HEGO sensors can be read off through the change in their internal resistance. In order to obtain a measured value for the smooth running therefrom, the changes in the internal resistance of an HEGO sensor or its change with time can be used, but preferably both HEGO sensors or the changes in their internal resistance are invoked to form the measured value for monitoring irregular running. The difference can be compared with a reference value established by tests.
It can be provided, in accordance with the invention, that the threshold value for the monitoring of smooth running is varied in dependence on the speed and torque of the internal combustion engine by means of a functional connection (engine characteristic map). The characteristic map required is preferably determined by means of suitable series of tests.
It may also be provided that in the event that the reference value is exceeded the lean burn operation with smooth running control is abandoned and the engine is operated stoichiometrically.
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patent: 5365216 (1994-11-01), Kotwicki et al.
patent: 5964201 (1999-10-01), Dickers et al.
Dickers Guido
Grieser Klemens
Himmelsbach Johann
Phlips Patrick
Chapman Jeanette
Drouillard Jerome R.
Ford Global Technologies Inc.
Varma Sneh
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