Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2002-02-27
2003-06-03
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S274000, C060S276000, C701S109000
Reexamination Certificate
active
06571550
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for adjusting the oxygen concentration in a three-way catalytic converter system, which includes a preliminary catalytic converter and a main catalytic converter, in an exhaust train of an internal combustion engine with lambda control.
Three-way catalytic converters are known to have the ability, when the engine is operating with excess oxygen (lean-burn operation), to store oxygen from the exhaust gas, and to release oxygen to the exhaust gas when the engine is operating with insufficient oxygen (rich-burn operation). The relative oxygen concentration in the catalytic converter may vary between extremes of 0% and 100%. However, a three-way catalytic converter only has optimum three-way conversion properties within a middle range of the oxygen concentration, for example, between 30% and 70%.
In the case of internal combustion engines with lambda control, the mean oxygen concentration of the catalytic converter system does not change as long as the internal combustion engine is operated with a stoichiometric mix (lambda=1). In the event of deviations from stoichiometric operation, for example, in the event of lean-burn operation in an overrun cutoff phase, the pollutant concentration in the catalytic converter system rises to values that lie outside the optimum range. When stoichiometric operation is restored, therefore, the oxygen concentration in the catalytic converter system has to be reset.
For such a purpose, after lean-burn operation and before transition to stoichiometric operation, the catalytic converter system is exposed to a rich mix, until a desired oxygen concentration has been produced in the catalytic converter system. In the case of a catalytic converter system with a preliminary catalytic converter and a main catalytic converter, the process may take place such that, after lean-burn operation, the oxygen concentration in both catalytic converters is respectively reduced in a controlled manner by an oxygen probe connected downstream of the corresponding catalytic converter. However, in combination with the oxygen sensor disposed upstream of the preliminary catalytic converter, the control requires a total of three oxygen sensors, which entails a correspondingly high manufacturing and control outlay. If the additional oxygen sensor downstream of the main catalytic converter is dispensed with, hitherto all that has been possible is purely controlled adjustment of the relative oxygen concentration of the main catalytic converter after lean-burn phases, a method that does not achieve any great adjustment accuracy.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for adjusting the oxygen concentration in a three-way catalytic converter system, including a preliminary catalytic converter and a main catalytic converter, in an exhaust train of an internal combustion engine with lambda control, that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that easily and with the highest possible accuracy allows the three-way conversion properties of the catalytic converter system to be optimized after the transition from operation with a lean or rich fuel/air mix to stoichiometric operation or during permanent stoichiometric operation.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for adjusting an oxygen concentration in a catalytic converter system with lambda control for optimizing three-way conversion properties of the catalytic converter system after the transition from lean-burn operation with a lean fuel/air mix to stoichiometric operation or during permanent stoichiometric operation, the method including the steps of providing a catalytic converter system in an exhaust train of an internal combustion engine, the catalytic converter system having a preliminary three-way catalytic converter, a main three-way catalytic converter disposed downstream of the preliminary catalytic converter with respect to an exhaust flow direction, a pre-cat oxygen sensor disposed upstream of the preliminary catalytic converter with respect to an exhaust flow direction and producing a measurement signal, an inter-cat oxygen sensor having a constant characteristic curve, the inter-cat oxygen sensor disposed between the preliminary catalytic converter and the main catalytic converter and producing a measurement signal, an air mass flow meter disposed in an intake section of the internal combustion engine and producing a measurement signal, and an operation control unit receiving measurement signals from the air mass flow meter, the pre-cat oxygen sensor, and the inter-cat oxygen sensor, switching operation to a predetermined rich fuel/air mix following one of a lean-burn operation and a permanent stoichiometric operation, determining a time at which the preliminary catalytic converter has been fully discharged through release of its stored oxygen to the exhaust gas utilizing the measurement signal from the inter-cat oxygen sensor, calculating on an ongoing basis a quantity of oxygen released to the exhaust gas from the main catalytic converter from the determined time onward utilizing the measurement signals from the inter-cat oxygen sensor and the air mass flow meter, and comparing the oxygen quantity with a desired predetermined value corresponding to a desired oxygen concentration in the main catalytic converter, ending operation with the rich air/fuel mix as soon as the quantity of oxygen released to the exhaust gas by the main catalytic converter has reached the desired predetermined value, and switching operation to stoichiometric mode.
With the objects of the invention in view, there is also provided a method for adjusting the oxygen concentration in a catalytic converter system with lambda control for optimizing the three-way conversion properties of the catalytic converter system after the transition from a rich-burn operation with a rich fuel/air mix to stoichiometric operation or during permanent stoichiometric operation, the method including the steps of providing a catalytic converter system in an exhaust train of an internal combustion engine, the catalytic converter system having a preliminary three-way catalytic converter, a main three-way catalytic converter disposed downstream of the preliminary catalytic converter with respect to an exhaust flow direction, a pre-cat oxygen sensor disposed upstream of the preliminary catalytic converter with respect to an exhaust flow direction and producing a measurement signal, an inter-cat oxygen sensor having a constant characteristic curve, the inter-cat oxygen sensor disposed between the preliminary catalytic converter and the main catalytic converter and producing a measurement signal, an air mass flow meter disposed in an intake section of the internal combustion engine and producing a measurement signal, and an operation control unit receiving measurement signals from the air mass flow meter, the pre-cat oxygen sensor, and the inter-cat oxygen sensor, switching operation to a predetermined lean fuel/air mix following one of a rich-burn operation and a permanent stoichiometric operation, determining a time at which the preliminary catalytic converter is fully laden as a result of taking up oxygen from the exhaust gas using the measurement signal from the inter-cat oxygen sensor, calculating on an ongoing basis a quantity of oxygen taken up from the exhaust gas by the main catalytic converter from the determined time onward utilizing the measurement signals from the inter-cat oxygen sensor and the air mass flow meter, and comparing the oxygen quantity with a desired predetermined value corresponding to a desired oxygen concentration in the main catalytic converter, ending the lean-burn operation as soon as the quantity of oxygen taken up from the exhaust gas by the main catalytic converter has reached the desired predetermined value, and switching operation to a stoichiometr
Rösel Gerd
Zhang Hong
Denion Thomas
Greenberg Laurence A.
Locher Ralph E.
Siemens Aktiengesellschaft
Stemer Werner H.
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