Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For nitrogen or nitrogen containing compound
Patent
1996-07-24
1998-04-07
Tung, T.
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For nitrogen or nitrogen containing compound
204424, 204425, 204426, 204428, 2057835, 2057845, G01N 27407
Patent
active
057360286
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a sensor for detection of oxides of nitrogen in accordance with the preamble of appended claim 1. The invention also relates to a use of a sensor in accordance with claim 9 and a method for detection of oxides of nitrogen in accordance with appended claim 10.
In connection with combustion processes, particularly in environments having high concentrations of oxygen, it would be advantageous to use a sensor for detection of oxides of nitrogen ("NO.sub.x compounds") in the combustion exhaust gases.
In particular, such a sensor ("NO.sub.x sensor") may be utilized in motor vehicles and may preferably be arranged in connection with a catalytic converter in the motor vehicle. Such a NO.sub.x sensor could be adapted to emit an output signal which indicates the concentration of NO.sub.x compounds in the exhaust gases. If the NO.sub.x sensor is arranged upstream of the catalytic converter, this output signal can be used to minimize the emission of NO.sub.x compounds by controlling the operation of the engine.
A device for detection of NO.sub.x compounds is previously known from U.S. Pat. No. 4,816,749, which device comprises a substrate 1 which may be a ceramic material. The device also comprises a cathode 2 which may have a section 7 consisting of porous gold serving as a "diffusion barrier", and an anode 3. Furthermore, the device comprises a solid electrolyte 4. The NO.sub.x compounds contained in the surrounding gases may diffuse through the cathode 2 and be transported through the electrolyte 4 towards the anode 3. The electric current thus produced may be recorded by means of a measuring instrument 6.
A disadvantage with the device according to U.S. Pat. No. 4,816,749 is that it cannot produce a precise measurement of the concentration of NO.sub.x compounds in the surrounding gases, but only an indication, e.g. an alarm signal, when a certain concentration (corresponding to a certain predetermined limit level) of NO.sub.x compounds is present.
The object of the invention is to provide an improved sensor for detection of oxides of nitrogen, in particular in connection with exhaust gas systems in vehicles. This is accomplished by means of a device of the above-mentioned kind, the features of which will be apparent from claim 1.
The device in accordance with the invention allows an accurate measurement of the concentration of NO.sub.x compounds. This is carried out with a short response time and a high selectivity for NO.sub.x compounds when measuring in gases with high levels of oxygen. The device allows a continuous measurement of the NO.sub.x concentration, in contrast to the device according to the above-mentioned US document which may only give an indication when a certain level has been reached.
By means of its construction, the device according to the invention is thermally and mechanically stable and thereby suitable for use in both mobile and fixed combustion apparatus. Furthermore, it is cheap and allows simple mass production, which makes it possible to mount it on mass produced motor vehicles and to arrange it for emitting a signal containing a measure of the concentration of NO.sub.x compounds in the exhaust gases, to a control unit arranged in the vehicle.
In accordance with a preferred embodiment, the invention comprises means for heating thereof to a suitable working temperature. This provides a stable and uniform operation in connection with detection of NO.sub.x compounds.
In accordance with a further embodiment, the device may he provided with a heat stabilizing protective cover, which to a high degree renders the signal from the sensor independent of fluctuations in the temperature of the surrounding gas.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in the following with reference to a preferred embodiment and the annexed drawings, in which FIGS. 1 and 2 show the front and the rear faces, respectively, of a device in accordance with the present invention, FIGS. 3, 4, 5 and 6 show how the device can be arranged in a vehicle, and FIG. 7 is
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Orbit Search Service, File WPAT, Accession No. 93-031766/04, Mitsubishi Motor Corp., JP04359144-A, 91.12.11 (9304) 4p, abstract.
Arlig Ulf
Hjortsberg Ove
Lundgren Staffan
AB Volvo
Tung T.
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