Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1994-12-12
1996-04-09
Bell, Bruce F.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204426, 204427, 204429, 204408, G01N 2726
Patent
active
055058370
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is based on a sensor arrangement for determining gas components and/or gas concentrations in gas mixtures according to the preamble of the main claim.
2. Description of the Related Art
A generic sensor arrangement for determining CO concentrations in which a pump cell pumps oxygen to a measuring element is known from Sensors and Actuators B, 9 (1992), pp. 233-239. The measuring element in this instance is disposed in a measuring chamber without a defined reference to the pump cell and the gas mixture. It is only required that a sufficient oxygen concentration be present at the measuring element. It was determined that the resistance value of an SnO.sub.2 semiconductor gas sensor is three orders of magnitude greater in CO in air with 21% O.sub.2 than in CO in N.sub.2.
SUMMARY OF THE INVENTION
The present invention thus provides a sensor arrangement for determining gas components and/or gas concentrations of gas mixtures, particularly of CO, NO.sub.x and HC in exhaust gases of internal combustion engines, having a measuring element which has a sensitive region and having a pump cell that includes pump electrodes which are disposed on a solid electrolyte and which effect an oxygen transfer to the measuring element, characterized in that the pump cell and the measuring element are disposed so as to be spatially separated from one another such that they are located in different temperature zones during operation of the sensor arrangement.
The sensor arrangement according to the invention has the advantage of the provision of a good galvanic separation and thermal decoupling of the measuring element with respect to the pump cell. This is significant because considerably higher temperatures are necessary to operate the pump cell than the measuring element. Moreover, the object of the pump cell is to pump sufficient oxygen to the measuring element. Therefore, no feedback takes place between the pump cell and the measuring element. In this respect the galvanic separation of the pump cell and the measuring element is important. Relocating the measuring element in colder regions ultimately ensures that the measured gas is exposed to the least possible pre-catalysis. The integrated design of the sensor arrangement ultimately ensures that sufficient oxygen for eliminating the oxygen cross-sensitivity is present at the sensitive region of the measuring element.
Advantageous refinements and improvements of the sensor arrangement disclosed in the main claim are possible by means of the measures outlined in the dependent claims.
A sensor arrangement according to the invention may be characterized in that the pump cell and the measuring element are connected to one another by way of a diffusion segment via which the oxygen can diffuse from the pump cell to the measuring element. Such a sensor arrangement may be constructed as a layer system which includes at least one oxygen-ion-conducting, solid electrolyte ceramic for the pump cell, that the diffusion segment is integrated in the layer system, and that the diffusion segment employs a diffusion opening toward the measuring element, by way of which the oxygen pumped by the pump cell can be supplied to the measuring element. In such a sensor arrangement, the diffusion opening may be a recess cut into a cover film, in which opening the measuring element is disposed with its sensitive region. Such a sensor arrangement may be characterized in that the diffusion opening is cut into a cover layer surrounding the diffusion segment in a gas-tight manner, and that a porous insulating layer on which the measuring element is disposed with its sensitive region is located above the diffusion opening. The measuring element may be a semiconducting gas sensor.
Alternatively, the sensor arrangement may be characterized in that the diffusion opening is cut into a cover layer surrounding the diffusion segment in a gas-tight manner, and that the measuring element is an electrochemical measuring cell that is positioned with
REFERENCES:
patent: 4905652 (1990-03-01), Nakajima et al.
patent: 4927517 (1990-05-01), Mizutani et al.
Visser et al.: "Sensors for measuring combustibles in the absence of oxygen". In: Sensors and Actuators B., 9, 1992, Lausanne, CH, pp. 233-239. No month available.
Suzuki et al.: "Air-Fuel Ratio Sensor for Rich, Stoichiometric and Lean Ranges". In: SAE Technical Paper Series, Int. Congress and Exposition, Detroit, Michigan, Feb. 24-29, 1986.
Dietz Hermann
Friese Karl-Hermann
Gruenwald Werner
Hoetzel Gerhard
Neumann Harald
Bell Bruce F.
Robert & Bosch GmbH
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