Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-03-30
2004-10-19
Olsen, Kaj K. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S425000, C204S427000
Reexamination Certificate
active
06805782
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a compound layered type of sensing device used for multiple measurement, and in particular, to such a sensing device which can be disposed in the exhaust gas system of an automobile internal combustion engine in order to detect the concentration of NOx contained in its exhaust gas, an air fuel ratio and other characteristics.
There has been known a gas sensor disposed in the exhaust system of an automobile internal combustion engine and configured to detect not only the concentration of NOx contained in its exhaust gas but also the concentration of oxygen contained in the exhaust gas in the form of a &lgr;-characteristic. This gas sensor is very effective, because physical quantities, such as the concentration of NOx, an A/F (air fuel ratio), and a &lgr;-characteristic can be detected by the same single sensor.
As a compound layered type of sensing device used for such a gas sensor, a four-sell type of device has been known conventionally, of which sectional configuration is shown in FIG.
1
. As shown therein, this device
9
has a porous substrate
91
, solid electrolyte plate
92
, spacer
93
, substrate
94
, spacer
95
, solid electrolyte plate
96
, spacer
97
, and layered type of heater
99
, which are stacked in turn.
The sensing device
9
has a first chamber
81
and a second chamber
82
, in addition to a reference gas chamber
89
in which a reference gas is charged. The first chamber
81
communicates with the outer space of the device
9
through a first diffusive resistance passage
810
, while the second chamber
82
communicates with the first chamber
81
through a second diffusive resistance passage
820
.
Additionally, the sensing device
9
has a first electrochemical cell
83
, located therein so as to be exposed to the first chamber
81
, that is capable of pumping oxygen from the outer space depending on an applied voltage thereto. The sensing device
9
also has a second electrochemical cell
85
, located therein so as to be exposed to the second chamber
82
, that is capable of outputting current corresponding to the concentration of NOx contained in an exhaust gas in response to a specified voltage applied thereto.
The sensing device
9
has also a third electrochemical cell
84
formed so that it is able to measure the concentration of an exhaust gas exhausted outside the device. Also, in the sending device
9
is provided a fourth electrochemical cell
86
that is exposed to the second chamber
82
and has the function of monitoring the concentration of oxygen present in the second chamber
82
.
An electromotive force provided by the fourth electrochemical cell
86
is used to control voltage to be applied to the first electrochemical cell
83
.
This type of sensing device makes it possible to measure the concentration of oxygen contained in an exhaust gas together with the concentration of NOx contained in an exhaust gas, so that a &lgr;-characteristic and air fuel ratio can be obtained. Since the single sensor enables parallel measurement of both concentration of NOx and &lgr;-characteristic (or air fuel ratio), providing the device with saved space and reducing a fitting cost of the device.
However, the foregoing compound layered type of sensing device has a drawback of being fairly low in accuracy of measurement of oxygen concentration, whereby being also low in accuracy of measurement of the &lgr;-characteristic.
This drawback is mainly results because the first and third electrochemical cells
83
and
84
are located on the same solid electrolyte plate. The voltage applied to the first electrochemical cell
83
fluctuates and its output is fairly larger in amount than that of the third electrochemical cell
84
, which largely influences the output of the third electrochemical cell
84
.
As understood from
FIG. 1
, a total of five plates ranging from the first solid electrolyte plate
92
to the second one
96
are present between two electrodes of the second electrochemical cell
85
. This presence gives rise to a larger amount of inner resistance to the second electrochemical cell, making the second electrochemical cell liable to influences of surrounding conditions such as temperature.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to solve the foregoing drawback owned by the conventional sensing device, and to provide a compound layered type of sensing device capable of measuring the &lgr;-characteristic with precision.
Another object of the present invention is to provide a compound layered type of sensing device capable of measuring the &lgr;-characteristic with precision by detecting oxygen concentration more accurately.
Still another object of the present invention is to provide a compound layered type of sensing device, which is directed to multiple detection purposes, capable of concurrently detecting various physical parameters relating to a gas to be measured, with influences of surrounding conditions suppressed.
In order to realize the object, as one aspect of the present invention, there is provided a compound layered type of sensing device, comprising: a plurality of solid electrolyte plates; and first to third electrochemical cells each having a single pair of electrodes disposed on the solid electrolyte plates, in which a concentration of a gas specified from a gas to be measured pre-processed based on oxygen pumping by the first electrochemical cell is detected by the second electrochemical cell and a difference in electromotive force between the gas to be measured and a reference gas is detected by the third electrochemical cell; wherein the single pair of electrodes of the third electrochemical cell is disposed on a same surface of one of the solid electrolyte plates, and both of the first and third electrochemical cells are located with different ones of the solid electrolyte plates.
In this configuration, the single pair of electrodes of the third electrochemical cell is placed on the same surface of the same solid electrolyte plate with the electrodes close to each other. Thus the inner resistance of the third electrochemical cell becomes smaller, thereby resisting influence of sensor output measuring devices and/or outer circuits. Further, the smaller inner resistance reduces influence of outside atmospheric temperature.
Further, disposing the one pair of electrodes of the third electrochemical cell in that way makes it possible that voltage applied to this cell is fixed at a constant magnitude, without changes over time. Outputs of the third electrochemical cell are therefore reluctant to fluctuations over time.
Because each of the first and third electrochemical cells is disposed with different solid electrolyte plates, the third electrochemical cell shows resistance to influence of temporal changes in voltage applied to the first electrochemical cell.
Hence, accuracy of detecting differences in electromotive force between the gas to be measured and the reference gas by the third electrochemical cell can be raised. The difference in electromotive force is proportional to the concentration of oxygen contained in the gas to be measured. When the compound layered type of seasoning device according to the present invention is disposed in the combustion exhaust system of an internal combustion engine, a &lgr;-characteristic of the engine can be measure with precision the third electrochemical cell.
Additionally, the applied voltage to the first electrochemical cell may be controlled in such a manner that a map is produced in advance based on amounts of current obtained from the concentration of oxygen contained in a gas to be measured, and the applied voltage is controlled using the map. Higher accuracy is therefore secured in controlling the concentration of oxygen present in the chambers into a predetermined constant.
Thus a compound layered type of sensing device with higher accuracy of measurement of the &lgr;-characteristic can be provided.
In the foregoing one aspect of the present invention, it is preferred that the device fu
Miyashita Akira
Mizutani Keigo
Saito Toshitaka
Tanaka Akio
Denso Corporation
Nixon & Vanderhye PC
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