Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing liquid or solid sample
Reexamination Certificate
1998-06-01
2001-06-26
Warden, Jill (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing liquid or solid sample
C422S068100, C422S082050, C422S082060, C422S082080, C422S082110, C422S083000, C422S091000
Reexamination Certificate
active
06251342
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to an on-board gas composition sensor for monitoring oxygen content levels in the exhaust gas from an internal combustion engine. More particularly, the invention is related to an optic sensor element responsive to changing oxygen concentration and a process of making this element using sol-gel techniques whereby a fluorescent indicator is included in a metal oxide matrix.
2. Background of the Invention
Motor vehicle manufacturers use on-board gas sensors to measure exhaust gases for engine control purposes and for assessing the performance of a catalytic converter. Sensors of this type must be sufficiently robust to withstand the aggressive gases to which the sensor is exposed in an exhaust gas conduit and also the extreme conditions that exist there such as high temperatures (typically of about 500°-600° C.), temperature cycling, vibration, intermittent moisture, etc.
Exhaust gas sensors used to date are disadvantaged by the need for an electrical signal which varies in relation to the oxygen content level of the exhaust gas. The sensor output signal may be used as an input to an electronic engine control means, such as for an electronic engine control module controlling the air/fuel mixture which is fed at any given point in time to a combustion chamber of the engine. Maintaining the integrity of the electrical connections to the sensor presents a challenge in the field of motor vehicle engine control. In addition, a problem is presented in maintaining the correct functioning of the active sensor material exposed to the harsh environment of the exhaust conduit.
Recently issued U.S. Pat. No. 5,490,490 discloses a different type of oxygen sensor suitable for operation at exhaust gas temperatures of 400°-650° C. which is to overcome the disadvantages of such prior sensors. It employs a bead of porous inorganic oxide such as Cu-ZSM-5 zeolite fused to the end of a fiber-optic cable. The bead is exposed to exhaust gas and the cable is connected to a device consisting of a light source and fluorescence detector. Upon irradiation with ultraviolet or blue light (350-460 nm), the bead exhibits fluorescence whose intensity is related to either oxygen concentration or reductant to oxidant ratio of the exhaust gases. Attaching a bead to the end of the fiber, however, involves manufacturing complexity and using a bead provides an opportunity for it to be dislodged from the fiber during use. In addition, such a bead has high temperature durability issues, since a thermal expansion mismatch with the silica fiber might cause it to crack and fall off. It would be desirable to provide an optical fiber/fluorescent indicator element which has improved high temperature resistance, durability, and response time, which can be manufactured in a commercially desirable way.
The present invention provides such an element. These and other advantages of the invention will be understood from the following disclosure and detailed description of certain preferred embodiments.
SUMMARY OF THE INVENTION
A fluorescent oxygen sensor element useful at high temperatures is made using sol-gel techniques. The element comprises a gold-jacketed, optical fiber with a coating of, on at least a surface portion thereof, a substantially uniform mixture of metal oxide matrix material and ceramic fluorescent indicator material. The coating is deposited from a sol-solution mixture of (1) a metal oxide matrix forming material of at least one metal element selected from the group consisting of Si, Al, Ti, Zr or their mixture, and (2) ceramic fluorescent indicator material. Preferably the fiber is made of silica. The indicator is present in the coating in an amount of about 20 to 95%, by weight of the total coating, with higher concentration of this range being preferred. Preferably the forming material includes at least one metal alkoxide represented by the formula M(OR)
n
wherein R represents a lower alkyl group such as CH
3
or C
4
H
9
, M represents the metals disclosed above, and n is the valence of M.
The fluorescent indicator material may be any material that fluoresces when exposed to visible or ultraviolet light and whose fluorescence intensity changes when the gaseous environment around the material changes its oxygen or reductant concentrations. Examples of such material include, gamma-alumina, ceria, zirconia, titania, and copper ions incorporated in a matrix such as zeolite ZSM-5. The indicator material would be incorporated in the sol during processing prior to coating on the fiber.
Another aspect of the invention is the method of making the sensor element. The method includes first etching the silica cable surface to be coated with acid, and then coating the surface with a sol solution of the metal matrix material/indicator disclosed above, as by dipping the fiber into the sol. And then the sol coating is dried to form the element.
The current process advantageously provides a well adhering fluorescent indicator in a ceramic matrix onto an optic fiber. Further, it provides an extremely compact sensor element that can withstand the harsh and rugged environment of a vehicle exhaust system. And, the sensor element has improved response time over a “bead” sensor due to the intimate contact of the coating with the fiber surface.
REFERENCES:
patent: 4750806 (1988-06-01), Biswas
patent: 4816049 (1989-03-01), Hata et al.
patent: 5262192 (1993-11-01), Nelson et al.
patent: 5489988 (1996-02-01), Ackley et al.
patent: 5490490 (1996-02-01), Weber et al.
patent: 5589396 (1996-12-01), Frye et al.
patent: 5607644 (1997-03-01), Olstein et al.
patent: 5637507 (1997-06-01), Wicks et al.
patent: 5650311 (1997-07-01), Avnir et al.
patent: 5653777 (1997-08-01), Semerdjian
Fluorescence characteristics of Cu-ZSM-5 zeolites in reactive gas mixtures: mechanisms for a fiber-optic-based gas sensor, Applied Optics, Jun. 1, 1997, vol. 46, No. 16, p. 3699-3707.
Narula Chaitanya Kumar
Poindexter Bennie
Remillard Jeffrey Thomas
Weber Willes Henry
Ford Global Technologies Inc.
Handy Dwayne K
Melotik Lorraine S.
Warden Jill
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