Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
2000-10-30
2002-04-30
Denion, Thomas (Department: 3747)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S276000, C060S277000, C204S421000, C204S424000
Reexamination Certificate
active
06378295
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method of cleaning the exhaust gas of an internal combustion engine.
In order to clean the exhaust gas of an internal combustion engine, a three-way catalytic converter is usually disposed in the exhaust tract of the engine. A lambda probe is provided upstream of the catalytic converter. An emitted voltage signal of the lambda probe is, as in the case of all lambda probes, dependent on residual oxygen contained in the exhaust gas. The residual oxygen component is dependent, in turn, onf a mixture that has been fed to the internal combustion engine. The residual oxygen component in the raw exhaust is lower for fuel excess (rich mixture), and higher for air excess (lean mixture). In the case of a lean mixture (lambda>1), the output voltage of the lambda probe is usually below 100 mV. The output voltage of the lambda probe changes virtually discontinuously in the region where lambda=1. Finally, the output voltage of the lambda probe reaches more than 0.8 V in the case of a rich mixture (lambda<1). Such output voltage range is denoted as two-step action. The internal combustion engine operates such that the output signal, reproducing the lambda value of the raw exhaust gas, of the lambda probe fluctuates about a predetermined mean value. Because a three-way catalytic converter exhibits optimum catalytic properties for a raw exhaust gas with lambda=1, the predetermined mean value should correspond to lambda=1.
However, the dynamic and static properties of the lambda probe upstream of the three-way catalytic converter undergo change through aging and poisoning. As a result, the mean value corresponding to the lambda=1 shifts its position. The prior art discloses locating a further lambda probe likewise exhibiting two-step action downstream of the three-way catalytic converter. The further lambda probe is used as a monitor probe to monitor the catalytic conversion and permits fine control of the mixture by correcting the predetermined mean value such that the lambda value most favorable for the conversion can always be observed. This method is denoted as guiding control or trimming control.
In addition to the three-way catalytic converter, a NO
x
catalytic converter is provided for further reducing the pollutant emissions of modern internal combustion engines. A NO
x
-sensitive measuring sensor is present for optimally operating such a catalytic converter, which can, for example, be a storage catalytic converter that stores NO
x
in one operating state of the internal combustion engine and converts the stored NO, in another operating state.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method of cleaning the exhaust gas of an internal combustion engine that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that makes it possible to dispense with a separate lambda probe disposed downstream of the catalytic converter while still retaining the ability of trimming control.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of cleaning an exhaust gas of an internal combustion engine having a three-way catalytic converter disposed in an exhaust tract and a lambda probe disposed upstream of the three-way catalytic converter and exhibiting two-step action, including the steps of controlling operation of the internal combustion engine to fluctuate a lambda value of a raw exhaust gas at the lambda probe about a predetermined mean value, measuring, in a trimming controller, a concentration of an exhaust gas component downstream of the three-way catalytic converter with an amperometric measuring sensor made from a solid-state electrolyte and having a first measuring cell connected to a second measuring cell, a first electrode, a second electrode, an outer electrode, and a reference electrode exposed to ambient air, measuring, in the first measuring cell, an oxygen concentration through a first Nernst voltage between the first electrode and the reference electrode exposed to ambient air, and controlling, in the first measuring cell, the oxygen concentration by a first oxygen-ion pumping current between the first electrode and the outer electrode, measuring, in the second measuring cell, the oxygen concentration through a second Nernst voltage between the second electrode and the reference electrode, tapping a voltage between the outer electrode and the reference electrode in conjunction with a series connection of the first and second measuring cells, and using the voltage as a signal, dependent on the oxygen concentration and indicating two-step action, for trimming control and correcting predetermined mean values dependent on the measured concentration of the exhaust gas component downstream of the three-way catalytic converter.
According to the invention, there is provided, downstream of the three-way catalytic converter, an amperometric-measuring sensor, preferably, a NO
x
measuring sensor, for controlling a NO
x
-reducing catalytic converter, and having two measuring cells. In conjunction with a series connection of the two measuring cells, the voltage between the outer electrode and the reference electrode of the amperometric measuring sensor is tapped, and a signal dependent on the oxygen concentration and indicating two-step action is obtained thereby. The signal indicating two-step action is used in a conventional way for trimming control. As a result, the operation of the prior art trimming control no longer requires a separate lambda probe, indicating two-step action, downstream of the catalytic converter.
In accordance with another mode of the invention, the amperometric-measuring sensor is a NO
x
-measuring sensor and there is provided the step of controlling, in the second measuring cell of the NO
x
-measuring sensor, the oxygen concentration in the second measuring cell through a second oxygen-ion pumping current.
In accordance with a further mode of the invention, there is provided the step of correcting the signal indicating two-step action dependent on the first oxygen-ion pumping current to compensate for a fault voltage caused by a contact resistance over which the first oxygen-ion pumping current flows.
In accordance with a concomitant mode of the invention, there is provided the step of correcting the signal depending on the oxygen concentration and indicating two-step action dependent on a temperature of the amperometric-measuring sensor.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of cleaning exhaust gas with trimming control, it is, nevertheless, not intended to be limited to the details shown since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
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“Performanc
Denion Thomas
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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