Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For oxygen or oxygen containing compound
Reexamination Certificate
1999-09-03
2001-09-18
Warden, Sr., Robert J. (Department: 1744)
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For oxygen or oxygen containing compound
C205S781000, C204S425000, C204S426000
Reexamination Certificate
active
06290840
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas sensor for measuring gas components such as NO, NO
2
, SO
2
, CO
2
, and H
2
O contained in, for example, atmospheric air and exhaust gas discharged from vehicles or automobiles. The present invention also relates to a method for controlling the gas sensor.
2. Description of the Related Art
Recently, a gas sensor
10
A as shown in
FIG. 8
has been known, which is based on the use of an oxygen ion conductor (for example, see Japanese Laid-Open Patent Publication No. 8-271476).
The gas sensor
10
A is operated as follows. That is, a measurement gas existing in the external space is introduced into a first hollow space
14
via a first diffusion rate-determining means
12
. A first oxygen pumping means
22
, which comprises an inner pumping electrode
16
, an oxygen ion conductor
18
, and an outer pumping electrode
20
, is used to pump in or pump out oxygen contained in the measurement gas in the first hollow space
14
to such a degree that the nitrogen oxide as a measurement objective is not decomposed.
Subsequently, the measurement gas in the first hollow space
14
is introduced into a second hollow space
26
via a second diffusion rate-determining means
24
. A second oxygen pumping means
36
, which is disposed for the second hollow space
26
and which comprises a measurement gas-decomposing electrode
28
, an oxygen ion conductor
30
, and a reference electrode
34
disposed in a reference air section
32
, is used to pump out oxygen produced by decomposition effected by the catalytic action of the measurement gas-decomposing electrode
28
or the electrolysis caused by voltage application. A current value, which is required to pump out oxygen by using the second oxygen pumping means
36
, is measured to indirectly measure the nitrogen oxide.
Examples of practical use of the gas sensor
10
A include, for example, NOx sensors, H
2
O sensors, and CO
2
sensors for measuring measurement gases containing those having bound oxygen.
When the conventional gas sensor
10
A is applied as an NOx sensor, for example, Rh or Pt is used for the measurement gas-decomposing electrode
28
to catalytically decompose NOx. The oxygen, which is produced during the decomposition, is detected as a pumping current, or the oxygen is detected as a change in voltage.
When the conventional gas sensor
10
A is applied as an H
2
O sensor or a CO
2
sensor, it is difficult to perform catalytic decomposition. Therefore, a voltage, at which each of the gases is decomposable, is applied to the second oxygen pumping means
36
. The oxygen, which is produced by electrolysis caused by the voltage application, is detected as a pumping current.
By the way, in the case of the conventional gas sensor
10
A described above, a GND line of a DC power source
38
for controlling the first oxygen pumping means
22
cannot be used in common with that of a DC power source
40
for controlling the second oxygen pumping means
36
, because of the following reason. That is, the leak current flows from the outer pumping electrode
20
to the measurement gas-decomposing electrode
28
, or the leak current flows from the measurement gas-decomposing electrode
28
to the inner pumping electrode
16
.
When the current flows through the oxygen ion conductor, the movement of oxygen occurs, in accordance with which the control operation may become unstable, and the pumping current for measurement may be affected. Consequently, it is feared that the measurement cannot be performed.
Therefore, the conventional gas sensor
10
A requires two DC power sources which are insulated from each other, for driving the first and second oxygen pumping means
22
,
36
.
On the other hand, a gas sensor
10
B shown in
FIG. 9
has been suggested. The gas sensor
10
B includes an auxiliary pumping electrode
42
provided in the second hollow space
26
to construct a third oxygen pumping means (i.e., auxiliary pumping means)
46
by the auxiliary pumping electrode
42
, oxygen ion conductors (
18
,
44
,
30
), and the reference electrode
34
. Accordingly, the oxygen, which diffuses to cause invasion in an minute amount from the first hollow space
14
, is pumped out again to greatly improve the measurement accuracy (especially, the dependency on oxygen concentration) (Japanese Laid-Open Patent Publication No. 9-
113484).
The illustrative suggested gas sensor
10
B requires as much as three DC power sources which are insulated and independent from each other, due to the addition of the auxiliary pumping means
46
.
FIG. 10
shows a control circuit system of the illustrative suggested gas sensor
10
B shown in FIG.
9
. In this case, the three DC power sources (first DC power source
50
A, second DC power source
50
B, and third DC power source
50
C), which are insulated and independent from each other, are used to control the first, second, and third oxygen pumping means
22
,
36
,
46
.
The first DC power source
50
A is used as a power source for a pumping control circuit
52
for controlling the first oxygen pumping means
22
. In the pumping control circuit
52
, an electromotive force between a measuring electrode
54
and the reference electrode
34
is detected by a first comparator
56
. Subsequently, a difference with respect to a target voltage (for example, 300 mV) is determined by a second comparator
58
, and the differential voltage is amplified by an amplifier
60
. The amplified voltage is applied, as a control voltage E
0
, between the outer pumping electrode
20
and the inner pumping electrode
16
of the first oxygen pumping means
22
. Thus, the first oxygen pumping means
22
is controlled.
The second DC power source
50
B is used as a power source for supplying a voltage E
1
to the auxiliary pumping means (third oxygen pumping means)
46
. Specifically, a constant voltage is obtained by using a Zener diode
62
. After that, a voltage E
1
to be applied to the auxiliary pumping means
46
is generated by using a voltage-dividing circuit
64
, which is applied to the auxiliary pumping means
46
.
The third DC power source
50
C is used as a power source for supplying a voltage E
2
to the second oxygen pumping means
36
. The voltage E
2
to be supplied to the second oxygen pumping means
36
is generated in accordance with a method similar to that used in the second DC power source
50
B, which is supplied to the second oxygen pumping means
36
.
As shown in
FIG. 11
, each of the mutually insulated and independent three DC power sources (hereinafter referred to as “insulated type power source”, while a power source, which does not require the insulated and independent arrangement, is hereinafter referred to as “non-insulated type power source”)
50
A,
50
B,
50
B is basically constructed by an oscillation circuit
72
, an insulated type transformer
74
, and a rectifier circuit
76
connected to downstream positions of a battery
70
(for example, 12 V in the case of a car battery). In such an arrangement, the non-insulated type power source can be constructed by using only semiconductor parts such as transistors and operational amplifiers, while the insulated type power source as described above requires the transformer
74
. Therefore, it is difficult for the insulated type power source to miniaturize the control circuit system of the gas sensor
10
A,
10
B and reduce the weight thereof, and an inconvenience is feared in that the production cost becomes expensive.
SUMMARY OF THE INVENTION
The present invention has been made considering the problems as described above, an object of which is to provide a gas sensor and a method for controlling the gas sensor in which it is possible to use a common reference electric potential line (for example, GND line) for a plurality of DC power sources, it is possible to minimize the number of insulated and independent DC power sources (insulated type power sources), and it is possible to miniaturize a control circuit system of the gas sensor and reduce the weight thereof.
According
Hamada Yasuhiko
Kato Nobuhide
NGK Insulators Ltd.
Olsen Kaj K.
Parkhurst & Wendel L.L.P.
Warden, Sr. Robert J.
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