Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For nitrogen or nitrogen containing compound
Reexamination Certificate
2001-03-27
2002-09-24
Tung, T. (Department: 1743)
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For nitrogen or nitrogen containing compound
C204S425000, C204S426000, C205S784000, C205S784500, C205S788000
Reexamination Certificate
active
06454931
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to sensors for use in detecting gaseous components and more particularly to ceramic sensors for use in analyzing combustion emission components.
BACKGROUND OF THE INVENTION
A variety of sensors have been developed for detecting different gaseous combustion emission components. Examples of the different gaseous components which these sensors can detect include, but are not limited to oxygen (O
2
), carbon monoxide (CO), carbon dioxide (CO
2
), hydrocarbons (HC), and nitrogen oxides (NO
x
). These sensors can be used in a variety of devices including, for example, automotive engines, diesel engines, gas turbine engines, jet engines, power plants, furnaces, and barbeques. Many of these gaseous components are hazardous.
Information derived from these sensors can be used for a variety of purposes. Data from the sensors can be used for feedback control of different aspects of a device which is producing a gaseous emission. Alternatively, these sensors can simply be used to monitor the content of the emission. For example, these sensors can be used as a component of an on-board, OEM emissions control system for an automotive engine or as an off-board emissions measuring device used for inspection and maintenance, for example as a tool for an automotive mechanic.
A need exists for sensors which can detect a wide array of gaseous components. For example, a need exists for a sensor which can determine the concentrations of oxygen, carbon monoxide, carbon dioxide, hydrocarbons, and nitrogen oxides in a sample. The sensors should have a high signal-to-noise ratio and thus be able to accurately determine the concentrations of various components of a gaseous sample. The sensors should be simple, reliable, and inexpensive to manufacture. These and other objectives are provided by the sensors, devices, and methods of the present invention.
SUMMARY OF THE INVENTION
The present invention relates to a modified universal exhaust gas oxygen sensor, referred to herein as a CEGA sensor, which can be used to measure the concentration of a variety of components of a gaseous emission including CO, CO
2
, O
2
, H
2
, and H
2
O. The CEGA sensor employs at least one additional electrode on a ceramic substrate which possess a different catalytic activity relative to the electrodes that are normally found on a UEGO sensor. The ceramic substrate may be made of any suitable ceramic and is preferably made of zirconia.
The difference in catalytic activity between the additional electrode(s) and the electrodes native to the UEGO sensor create an oxygen gradient which enables a measure of combustion completeness to be calculated. Combustion completeness is a parameter quantifying the degree to which the gaseous emissions of combustion are in chemical equilibrium. In combination with an air/fuel ratio measured by the sensor, the concentrations of different components in the emission can be calculated.
A method is also provided for measuring concentrations of components of a gaseous emission by measuring an air/fuel ratio using a ceramic sensor, measuring combustion completeness using the ceramic sensor and determining concentrations of components of a gaseous emission based on the measured air/fuel ratio and measured combustion completeness. The CEGA sensor of the present invention enable these functions of the method to be performed by a single sensor.
In one regard, the CEGA sensor is an improved universal exhaust gas oxygen sensor (UEGO) for measuring properties of a gaseous emission which includes at least one oxygen pumping cell and a sensing cell in contact with a detection cavity, the sensing cell including a ceramic in gas communication inside the detection cavity, a first electrode in contact with ceramic positioned inside the detection cavity, and a second electrode in contact with the other side of the ceramic, a first voltage potential externally applied between the first and second electrodes for pumping oxygen across the ceramic into and out of the detection cavity, the first voltage potential controlled by a second voltage potential formed across a third and fourth electrode of the sensing cell, an air/fuel ratio measurement of the gaseous emission being obtainable from the current passing between the first and second electrodes, the improvement comprising the addition of a fifth electrode which has a different catalytic activity than the first electrode positioned inside the detection cavity in contact with the pumping cell ceramic, a third voltage potential externally applied between the fifth electrode and either the second electrode or a sixth electrode located on the same side of the pumping cell ceramic as the second electrode, the third voltage potential controlled by a fourth voltage potential formed between the first and fifth electrodes, a measure of combustion completeness being obtainable from the current passing between the first and sixth electrodes.
In one particular embodiment of a CEGA sensor, the sensor includes
a detection cavity;
a diffusion passage across which the gaseous emission enters the detection cavity; an oxygen pumping cell defining a portion of the detection cavity formed of a ceramic substrate and a first electrode in the detection cavity and a second electrode outside the detection cavity for pumping oxygen into and out of the detection cavity across the ceramic substrate to maintain a target oxygen level concentration in the detection cavity, an air/fuel ratio measurement of the gaseous emission being obtainable from current passing between the first and second electrodes; and
a sensing cell defining a portion of the detection cavity formed of a ceramic substrate, the sensing cell including
a third electrode within the detection cavity,
a fourth electrode outside the detection cavity, a second voltage potential being formed between the third and fourth electrodes due to a difference in oxygen concentration across the third and fourth electrodes, and
a fifth electrode in contact with the ceramic within the detection cavity which has a different catalytic activity than the first electrode, a forth voltage potential being formed between the fifth electrode and the first electrode, a measure of combustion completeness being obtainable from a current passing between the fifth and sixth electrodes.
The present invention also relates to several methods, devices and systems which can be used with various types of ceramic sensors including the CEGA sensor of the present invention in order to improve their performance.
In one regard, the invention relates to a method for calibrating a ceramic sensor which, as one of its functions, determines an air/fuel ratio. This method can be used in combination with any sensor which calculates an air/fuel ratio including, but not limited to UEGO, NO
x
and CEGA sensors.
According to the method, a ceramic sensor is operated at a constant, known air/fuel ratio. While being operated at a constant, known air/fuel ratio, the pumping current (I
pm
) of the sensor is measured. A basic relationship which correlates the air/fuel ratio to the pumping current for the family of sensors to which the specific ceramic sensor belongs is then used to calibrate the sensor by comparing the measured pumping current (I
pm
) to the expected pumping current from the basic relationship for that air/fuel ratio (I
p
). A transformation between the measured pumping current (I
pm
) and the current that the basic relationship gives for a known air/fuel ratio is created. During subsequent sensor usage, this transformation is used to modify the measured pumping current to create a value which is used with the basic relationship to obtain an air/fuel ratio that is accurate for the specific sensor.
In one particular embodiment, the method for calibrating a ceramic sensor which, as one of its functions, determines an air/fuel ratio includes the steps of:
operating the ceramic sensor at a constant, known air/fuel ratio;
measuring a pumping current of the sensor;
comparing the measured pumping current to an expected pump
DeAmicis Fabio
Patrick Ronald S.
ECM Engine Control and Monitoring
Suzue Kenta
Tung T.
Wilson Sonsini Goodrich & Rosati
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