Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-12-03
2001-12-04
Warden, Sr., Robert J. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S426000, C204S427000, C205S787000
Reexamination Certificate
active
06325906
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a gas sensor for measuring the concentration of a combustible gas component. More particularly, the invention relates to a gas sensor for measuring the concentration of a combustible gas component contained in exhaust gas from an internal combustion engine, and to an apparatus for measuring combustible gas component concentration by use of the gas sensor.
Japanese Patent Application Laid-Open (kokai) No. 8-247995 discloses an apparatus for measuring combustible gas component concentration having the following structure. In this apparatus, a gas under measurement which contains combustible gas components is introduced into a first processing zone. By means of a first oxygen pump cell, the partial pressure of oxygen is reduced to a predetermined low value (10
−14
atm or less) at which combustible gas components remain substantially unburned. The thus-controlled atmosphere is introduced into a second processing zone. The combustible gas components contained in the atmosphere are burned with O
2
which is pumped into the second processing zone by means of a second oxygen pump cell. At this time, pump current flowing through the second oxygen pump cell or voltage developed between electrodes of the second oxygen pump cell is detected. The combustible gas component concentration of the gas under measurement is determined from the detected value.
In the above-described apparatus for measuring combustible gas component concentration proposed in Japanese Patent Application Laid-Open (kokai) No. 8-247995, when O
2
remains in the second processing zone, combustible gas components first burn through reaction with the residual O
2
. Accordingly, upon variation in the amount of O
2
remaining in the second processing zone, no proportional relationship is established between the amount of O
2
which is pumped into the second processing zone by means of the second oxygen pump cell and the amount of combustible gas components contained in the second processing zone. That is, this measuring apparatus suffers a measurement error, since, upon variation in the amount of O
2
remaining in the second processing zone, no proportional relationship is established between current flowing through the second oxygen pump cell and the combustible gas component concentration of the second processing zone.
To avoid the above-mentioned problem, the partial pressure of oxygen contained in gas introduced into the second processing zone from the first processing zone must be reduced to a significantly low, constant level (10
−14
atm or less). To fulfill this requirement, a driving force applied to the first oxygen pump cell must be increased, raising a new problem in that a burden imposed on the first oxygen pump cell increases. Additionally, if the partial pressure of oxygen is reduced excessively, dissociation of water will occur in the second processing zone, raising another problem in that a measurement error occurs.
Further, in this measuring apparatus, the operation of the second oxygen pump cell must be controlled such that the partial pressure of oxygen in the second processing zone becomes constant. To fulfill this requirement, in addition to the second oxygen pump cell, another element (e.g., oxygen concentration cell element) for measuring the partial pressure of oxygen in the second processing zone must be provided. Accordingly, the number of elements provided on the second processing zone side increases, causing complication of the sensor structure with a resultant increase in fabrication cost. Also, since the second oxygen pump cell is operated after detection of the partial pressure of oxygen in the second processing zone, responsiveness becomes poor.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a gas sensor having a simple structure and capable of measuring combustible gas components at high accuracy and over a wide range, as well as to provide a measuring apparatus using the gas sensor.
A gas sensor of the present invention includes the following means:
(1) Oxygen pump means (combustible-gas-component sensing element) for pumping out from a second processing chamber to the exterior thereof O
2
remaining in the second processing chamber; i.e., O
2
remaining unconsumed in burning of combustible gas components; and
(2) A third gas passage for stably introducing a predetermined amount of O
2
into the second processing chamber under diffusion resistance.
The gas sensor of the present invention also includes means for stabilizing the oxygen concentration of the second processing chamber to a possible extent through diffusion of O
2
into the second processing chamber in addition to introduction of O
2
into the second processing chamber through a second gas passage.
In the case where the gas sensor of the present invention is not provided with the third gas passage, the gas sensor can only measure combustible gas concentration over a range (a low-concentration range) corresponding to the amount of O
2
remaining in a first processing chamber. Through employment of the third gas passage, O
2
is introduced into the second processing chamber through the third gas passage in a predetermined amount required for substantially completely burning combustible gas components, thereby expanding a measurable concentration range.
Additionally, the gas sensor of the present invention eliminates the need to control to a significantly low, constant level the oxygen concentration of gas diffused from the first processing chamber to the second processing chamber. Also, it is not mandatory to detect the oxygen concentration of the second processing chamber and control the oxygen concentration of the second processing chamber to a significantly low, constant level according to the detected oxygen concentration. Thus, there is no need for providing respective oxygen-concentration sensing means which face the interiors of the first and second processing chambers. Particularly, it is not mandatory to detect the oxygen concentration of the second processing chamber. Accordingly, the present invention simplifies a gas sensor structure.
The operation of the gas sensor of the present invention will next be described. A gas under measurement which contains O
2
and combustible gas components diffuses from an atmosphere to be measured to the first processing chamber. O
2
is pumped out from or pumped into the first processing chamber to thereby control to a low level the oxygen concentration of the gas diffusing into the second processing chamber. As a result of this pumping-out or pumping-in operation, a first oxygen pump current flows through the oxygen-ion conductor of first oxygen pump means according to the oxygen concentration of the gas under measurement. The gas having oxygen concentration controlled to a low level diffuses into the second processing chamber. Additionally, sufficient O
2
is introduced into the second processing chamber through the third gas passage under diffusion resistance. A portion of O
2
introduced into the second processing chamber is consumed through reaction with combustible gas components; i.e., through burning of combustible gas components. O
2
which remains unconsumed in burning of combustible gas components is pumped out from the second processing chamber under a constant driving force provided by the second oxygen pump means. As a result of this pumping-out operation, a second oxygen pump current flows through the oxygen-ion conductor of the second oxygen pump means according to the amount of residual O
2
pumped-out from the second processing chamber. Through introduction of O
2
into the second processing chamber through the third gas passage, the oxygen concentration of the second processing chamber is stably maintained at a relatively high level. Thus, in principle, the second oxygen pump current is inversely proportional to the combustible gas component concentration of the second processing chamber. Therefore, information regarding the concentration of combustible gas componen
Fuma Tomohiro
Inoue Ryuji
Kato Kenji
Kitanoya Shoji
Oshima Takafumi
NGK Spark Plug Co. Ltd.
Olsen Kaj K.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Warden, Sr. Robert J.
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