Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1997-09-08
2001-05-29
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S425000, C205S781000
Reexamination Certificate
active
06238536
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an arrangement for analyzing exhaust gases from a combustion process.
BACKGROUND OF THE INVENTION
In the field of motor vehicle combustion engines, there is a desire to have the ability to detect the concentration of different gaseous components in the exhaust gas stream from the engine. Such measurements can be used for controlling the operation of a combustion engine, with a view toward optimizing the amounts of injected fuel and air. If the engine can be provided with an optimal composition of the fuel/air mixture during all operating conditions, the fuel consumption and the harmful emissions from the combustion engine can be minimized.
In addition to engine control, such gas measurement should also provide the ability to be used in connection with a diagnosis of a vehicle's catalytic converter (catalyzer). In this context, the fuel and oxygen levels must lie within certain ranges in order that the vehicle's catalyzer should be able to operate optimally. A measure of the catalyzer's so-called “light-off” time, i.e. the time which elapses before the catalyzer purifies the exhaust gases optimally, can also be used during a diagnosis of the catalyzer's operation.
Different forms of gas sensors are known for achieving the above-mentioned objectives. One example of such a gas sensor, which is particularly for use in connection with motor vehicles, is the so-called lambda sensor, by means of which the oxygen content in the exhaust gases can be detected. The signal from a lambda sensor can be used in connection with optimizing the fuel and oxygen supply to the engine. In addition to the oxygen, it would be desirable to detect other components in the exhaust gases. Examples of known sensors (apart from lambda sensors) are thermistors, NO
x
sensors (i.e. sensors for nitrogen oxide compounds), oxygen sensors, carbon monoxide sensors and residual heat sensors.
An arrangement for detecting combustible gaseous hydrocarbons by means of a measurement bridge which has pellistors (pellet resistors) is known from British Patent No. 2,185,579. A pellistor is a resistor with a temperature-dependent resistance, as described in British Patent No. 2,044,937, for example. An application of pellistors in connection with the detection of exhaust gases in motor vehicles is described in Swedish Patent Application No. 9301715-0.
In connection with the measuring and detecting of different gas components in the exhaust gas stream from a combustion engine, a problem exists in that measurement signals from certain of the above-mentioned sensors can be influenced by other gases than those for which the sensor is intended. For example, the NO
x
sensor (apart from sensing the concentration of nitrogen oxide compounds) can also be sensitive to the concentration of oxygen and hydrocarbons. By using a plurality of different types of sensors at the same time, it should thus be possible to separate out each of the different gas components and, despite the cross-sensitivity of the different sensors, obtain a measurement of the composition of the measured gas. Using a plurality of different sensors in this way is, however, expensive and requires space. Each separate gas sensor requires a probe, a fixture, cabling, possibly an amplifier, an analyzer unit and a common analyzer unit which, from the signals of the different sensors, produces output signals giving the composition of the measured gas.
SUMMARY OF THE INVENTION
In accordance with the present invention, these and other objects have now been realized by the invention of apparatus for analyzing exhaust gases from a combustion process which comprises at least one sensor unit mounted for direct contact with the exhaust gases, the at least one sensor unit comprising a plurality of sensor elements mounted on a common substrate for detecting specific gases contained in the exhaust gases and generating signals based thereon, the substrate comprising an oxygen-ion-conductive ceramic material and the plurality of sensor elements comprising conductive patterns applied to the common substrate, and a common analyzer unit connected to the at least one sensor unit for analyzing the signals generated by the plurality of sensor elements. Preferably, the plurality of sensor elements include lambda sensors, NO
x
sensors, oxygen sensors, and residual heat sensors.
In accordance with one embodiment of the apparatus of the present invention, the common substrate comprises stabilized zirconium dioxide or titanium oxide. In one preferred embodiment, the NO
x
sensor includes oxygen-ion-transport means whereby the NO
x
sensor generates the signal based substantially only on the NO
x
content of the exhaust gases and substantially independent of the oxygen content of the exhaust gases. In a preferred embodiment, the oxygen-ion-transport means comprises the conductive pattern including a first conductive pattern comprising an anode, a second conductive pattern comprising a cathode, an external voltage source for driving a current comprising the oxygen ions, and current measuring means for measuring the current so as to provide the signal as a measure of the concentration of the NOx-compounds in the exhaust gases. Preferably, at least one of the anode and the cathode comprises gold.
In accordance with another embodiment of the apparatus of the present invention, the residual heat sensor comprises a first resistor including a surface exposed to the exhaust gases whereby the first resistor increases its temperature dependent resistance when heated in the presence of oxidizable gas components in the exhaust gases, and the second resistor, a measuring bridge connected to the residual heat sensor, and a voltage source for supplying a voltage to the measuring bridge. Preferably, the second resistor comprises a reference for comparison with the resistance of the first resistor.
In accordance with another embodiment of the apparatus of the present invention, the apparatus includes heating means for heating the common substrate. Preferably, the heating means comprises a heating wire mounted in the substrate, and including a voltage source connected to the heating wire.
In accordance with another embodiment of the apparatus of the present invention, the apparatus includes a protective cap substantially covering the at least one sensor unit.
In accordance with another embodiment of the apparatus of the present invention, at least one of the lambda sensors, NO
x
sensors and oxygen sensors comprises at least one of the plurality of sensor units, and the at least one of the lambda sensor, the NO
x
sensor and the oxygen sensor includes an associated air gap in the common substrate, a first electrode formed in the air gap, and a second electrode formed on the common substrate exposed to the exhaust gases.
In accordance with another embodiment of the apparatus of the present invention, the plurality of sensor units comprises a lambda sensor and a residual heat sensor, whereby the apparatus can be used for diagnosis of a catalyzer for purification of the exhaust gases. Preferably, the apparatus includes an associated air gap within the common substrate, and an electrode associated with the lambda sensor arranged in the air gap.
In accordance with another embodiment of the apparatus of the present invention, the plurality of sensor units includes at least one NO
x
sensor and a residual heat sensor whereby the apparatus can be used for analyzing the exhaust gases from a diesel engine. Preferably, the apparatus further comprises an oxygen sensor.
It has thereby been found that by placing a number of these sensors on one or more common substrates and by arranging the sensor elements in an integrated “multisensor” with a single attachment fixture, as well as common cabling, amplifier unit and analyzer unit, an analysis of the different gas components in the gas mixture present is possible.
REFERENCES:
patent: 3556950 (1971-01-01), Dahms
patent: 4452682 (1984-06-01), Takata et al.
patent: 4591422 (1986-05-01), Kato et al.
pa
Arlig Ulf
Hjortsberg Ove
Jobson Edward
Lundgren Staffan
Salomonsson Per
AB Volvo
Royston, Rayzor, Vickery, Novak & Druce, L.L.P.
Tung T.
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