Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2000-03-27
2001-11-13
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S274000, C060S276000, C123S184550
Reexamination Certificate
active
06314723
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention concerns a method of checking the functional capability of a catalytic converter.
In lambda-controlled internal-combustion engines, a catalytic converter, usually a three-way catalytic converter, is used in the exhaust system for emission control, wherein the efficiency of the catalytic converter is essential for the quality of the emission control. However, aging and contamination reduce the converting capability of the catalytic converter and consequently its efficiency. It is known that the oxygen storage capability of a catalytic converter decreases with its efficiency. The oxygen storage capability of a three-way catalytic converter is, however, strongly temperature-dependent.
To ensure that given limit values are met during the operation of the internal-combustion engine, the efficiency of the catalytic converter is checked on the basis of the oxygen storage capability. If the efficiency of the catalytic converter falls below a predetermined threshold, which may for example have the consequence that the exhaust gas emitted does not meet legal regulations, a signal indicating a defective catalytic converter is generated.
Published Non-Prosecuted European Patent Application EP 0 444 783 A1 discloses a method of monitoring the efficiency of a catalytic converter in which an oxygen sensor which measures the oxygen concentration in the exhaust gas is provided at the outlet of the catalytic converter. Since in conventional lambda control the air/fuel ratio fed to the internal-combustion engine is set such that it oscillates about the lambda value one, the oxygen sensor downstream of the catalytic converter measures an oscillating oxygen concentration. According to Published Non-Prosecuted European Patent Application EP 0 444 783 A1, the difference between the maximum value and the minimum value of this oscillating oxygen concentration is used as a measure of the oxygen storage capability and consequently of the efficiency and converting capability of the catalytic converter, in particular, the smaller the difference between the maximum value and the minimum value, the higher the efficiency of the catalytic converter.
Published Non-Prosecuted German Patent Application DE 196 30 940 A1 and the corresponding U.S. Pat. No. 5,862,661 disclose a further method of monitoring the functional capability of a catalytic converter, in which the mean value of the oxygen concentration downstream of the catalytic converter is determined from the signal of an oxygen sensor. The area bounded by the oscillation of the oxygen sensor signal about this mean value is used as a measure of the oxygen storage capability of the catalytic converter.
Both methods work in a continuous manner in a certain time pattern and consequently utilize the fact that the signal of the oxygen sensor downstream of the catalytic converter allows to ascertain the oxygen storage capability of the catalytic converter.
Both methods, in particular the method according to DE 196 30 940 A1, allow a relatively accurate ascertainment of the efficiency of the catalytic converter, but require essentially steady-state operating conditions of the internal-combustion engine, since the temperature of the exhaust gas of a lambda-controlled internal-combustion engine, and consequently the temperature of the catalytic converter, depends strongly on the operating condition of the internal-combustion engine. The non-isothermal behavior of the catalytic converter after non-steady-state operating conditions is particularly pronounced if the catalytic converter exhibits strong temperature fluctuations on account of the installation conditions. This is the case, for example, with a metal catalytic converter, which has a high thermal conductivity due to its physical properties. Catalytic converters which are provided close to the exhaust manifold and have a small volume are also subjected to strong temperature fluctuations. Such catalytic converters are increasingly used in internal-combustion engines, since they can be installed advantageously on account of the close proximity to the internal-combustion engine and, what is more, respond rapidly when the internal-combustion engine is started.
With the requirement for steady-state operating conditions, it is attempted to ensure that the catalytic converter is isothermally at the temperature of the exhaust gas. Then the temperature of the exhaust gas is taken into account when determining the efficiency of the catalytic converter.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method of checking the functional capability of a catalytic converter, in particular a three-way catalytic converter, which overcomes the above-mentioned disadvantages of the heretofore-known methods of this general type and which does not require to impose such strict requirements with regard to steady-state operating conditions.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of checking a functional capability of a catalytic converter in an exhaust system of a lambda-controlled internal-combustion engine. The method includes the steps of:
determining an efficiency value of an efficiency of the catalytic converter by determining an oxygen storage capability of the catalytic converter;
calculating a substitute value for a temperature in the catalytic converter;
adjusting the efficiency value for temperature influences with the substitute value for providing an adjusted efficiency value; and
subsequently obtaining a measure of a functional capability of the catalytic converter from the adjusted efficiency value.
In other words, according to the invention, a substitute value for the temperature in the catalytic converter is calculated and the value for the efficiency of the catalytic converter, which is determined in a conventional manner, is adjusted for temperature changes. In this way, the requirements for the steady state of the operating conditions can be relaxed.
A measure of the functional capability is then obtained from the efficiency of the catalytic converter, for example by calculating a normalized value averaged over various test cycles. If a threshold value is exceeded, the catalytic converter is identified as defective, which is displayed in a suitable manner.
The invention is based on the realization that, even after non-steady-state operating conditions, i.e. when the internal-combustion engine is again running in a largely steady-state operating phase, the temperature changes in the catalytic converter have not yet been completed. The value for the efficiency of the catalytic converter, which has been determined by conventional methods, is therefore corrected through the use of the substitute value, which takes into account these temperature influences in the not yet isothermal catalytic converter after non-steady-state operating conditions.
For this purpose, this substitute value is calculated in the same time frame or time pattern as the efficiency of the catalytic converter.
For calculating the substitute value, preferably the heat supplied by the exhaust gas is added up. This addition of heat can be gathered from a characteristic map, dependent on the speed and load of the internal-combustion engine. In order in this case to take into account only short-term temperature changes and not to allow the substitute value to be falsified by long-term, almost isothermal trends, which after all are already included in the determination of the efficiency of the catalytic converter according to one of the known methods by taking the temperature of the exhaust gas into account, the substitute value can be subjected to low-pass filtering, and this low-pass-filtered value can be deducted from the substitute value, so that only short-term temperature changes are reflected in the substitute value.
In accordance with another mode of the invention, the substitute value is subjected to a smoothing function, which may for example cause a PT1 smoothing.
In ac
Ketterer Alexander
Pfleger Hartmut
Denion Thomas
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellshaft
Stemer Werner H.
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