Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-12-22
2001-08-21
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S277000, C060S284000
Reexamination Certificate
active
06276128
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for monitoring the conversion rate of an exhaust catalyst intended for an internal combustion engine.
2. Description of the Prior Art
DE German reference 44 33 988 A1 discloses a catalyst monitoring procedure which records exhaust-gas temperatures upstream and downstream of the catalyst. The rate of heat transfer from the exhaust gas to the catalyst material is continually calculated, and from this the catalyst temperature and the rate of change of this catalyst temperature are determined. The quotient from the rate of heat transfer and the rate of change of the temperature of the catalyst is determined for a specific period of time, this period of time being chosen from the cold start of the internal combustion engine to the reaching of the conversion temperature of the catalyst. On the basis of the variation over time of the quotient, a trend is continually determined for the time up until reaching the conversion temperature. The time elapsed up until reaching the conversion temperature is compared with a threshold value for this period of time and, if the threshold value is exceeded, an error signal is output.
One of the procedures disclosed in German reference DE 42 11 092 A1 is based on a temperature estimate for the catalyst on the basis of a temperature model. In the case of that procedure, it is assumed for the model that there is a still just usable catalyst after reaching the temperature at which conversion begins and for the heat produced in the conversion. For simulating the temperature behavior of the catalyst, in that procedure it is initially assumed that the heat capacity of the catalyst is known and, furthermore, the amount of heat supplied to the engine is estimated. This takes place by recording the amount of fuel fed to the engine and calculating the proportion of heat energy which is fed to the catalyst. In this case, the proportion of heat energy depends on the respective load state and the speed of the engine. Consequently, the amount of heat which is fed to the catalyst is recorded for comparatively small units of time from the amount of fuel, the load and the speed. These amounts of heat are summated, in order in this way to obtain a total amount of heat which the catalyst receives from the start of the procedure. In addition, the amount of heat dissipated from the catalyst to the surroundings is estimated. The temperature estimated with this amount of heat model is subsequently compared with its actual temperature. This procedure, which is also intended to be applicable in the driving mode of a vehicle, is only started if the catalyst is at approximately ambient temperature at the beginning of the procedure. From the start of the procedure, a catalyst temperature is estimated with the aid of a temperature model block, using signals of the load, speed, injection times, air temperature, air pressure and octane number of the fuel. This temperature is compared with a stored comparison temperature. It is subsequently further investigated whether the conversion temperature of the catalyst has already been reached.
SUMMARY OF THE INVENTION
The invention is based on the object of specifying an improved monitoring procedure for the conversion rate of an exhaust catalyst of an internal combustion engine which has increased diagnostic accuracy and independence from the catalyst coating and, in addition, is independent of the operating mode of the internal combustion engine after a cold start.
Pursuant to this object, and others which will become apparent hereafter, one aspect of the present invention resides in a method for monitoring a conversion rate of an exhaust catalyst for an internal combustion engine having an electronic control device, which method comprises the steps of cold starting the internal combustion engine, determining an exhaust-gas temperature value prevailing upstream of the exhaust catalyst, detecting current temperature values of exhaust gas present downstream and upstream of the exhaust catalyst with temperature sensors at least for a duration of a specific time window after the cold start, summating the temperature of values currently present downstream of the exhaust catalyst at least during the time window to give the sum value, comparing the sum value with a limit sum value, and triggering an air signal if the comparing step shows that a specific deviation value has been reached.
The procedure according to the invention provides that, after a cold start of the internal combustion engine, the temperature values currently present downstream of the exhaust catalyst are summated during a specific time window and this sum value is compared with a predetermined limit value.
This procedure is based on the recognition that a usable catalyst differs from an unusable catalyst during the specific time window in that the better catalyst reaches its conversion temperature at an earlier point in time and thus has a higher sum value during the duration of the time window than a poorer catalyst.
The procedure utilizes the recognition that the two said catalysts do not differ significantly from each other before reaching the time window and after elapse of the time window, and therefore the exact coordination with the time window is of extreme importance for the evaluation. Also important is the starting point for the time window, since the temperature values are accumulated from this point in time. After every cold start of the internal combustion engine, the beginning of the time window is fixed in dependence on the operating mode of the engine, i.e. it is considered whether the latter is being operated in a virtually steady state or comparatively dynamically. This operating mode has a considerable influence on the amount of heat introduced into the exhaust gas, which ultimately determines the point in time at which the conversion temperature is reached. As a result, the starting point of the time window and also the time duration of the time window are fixed mode-dependently.
In an advantageous development, the exhaust-gas temperature values upstream of the exhaust catalyst are either calculated with the aid of an exhaust-gas temperature model within the control device or, alternatively, are detected directly with the aid of a temperature sensor.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
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“Methods for monitoring and diagnosing the Efficiency of Catalytic Converters—A Patent oriented Survey” dated May 1998, published in Elsevier Science B.V., The Netherlands, pp. 260-263, M. Sideris.
Kammann Uwe
Loeck Harald
Cohen & Pontani, Lieberman & Pavane
Denion Thomas
Tran Binh
Volkswagen AG
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