Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1998-05-19
2001-08-07
Warden, Sr., Robert J. (Department: 1744)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S406000, C219S486000, C219S501000
Reexamination Certificate
active
06270638
ABSTRACT:
The present invention relates to a pyro-sensor such as oxygen and NOx sensors, a heater therefor and a pyro-control circuit.
BACKGROUND OF THE INVENTION
In a pyro-sensor such as oxygen and NOx sensors in which a sensing portion is heated by the heater, the characteristics of the pyro-sensor will be changed depending on a heater's itself temperature variation or a temperature variation of the heater due to the temperature variation around the environment. For example, a platinum thin film heater changes its resistance in response to temperature as shown in T (temperature)-R (resistor) characteristics of FIG.
1
.
As a conventional heater temperature control method, for example, JP-A-60-114758 official gazette has been proposed to maintain temperature of the pyro-sensor to high temperature value. This method measures an environmental temperature by disposing a temperature sensor such as thermocouples or a thermistor adjacent to the sensor, and a load voltage to the heater is controlled as the result to maintain a sensor temperature to a predetermined value. In this case, the temperature sensor that ambient air temperature is only measured should be necessary, and a sensor's structure becomes much more complex, and it results in an expensive cost.
FIGS. 2 and 3
show another heater for the pyrosensor and its pyro-control circuit disclosed in Japanese Patent Application No. 8-298267 that is filed by the inventor on Oct. 22, 1996. In
FIG. 2
, a main heater
30
of platinum thin film is mounted on an insulator substrate
2
in alignment with a detective or sensing area, and an auxiliary heater
32
of platinum thin film is also arranged inside the main heater
30
.
In
FIG. 3
, a collector of a transistor
20
is connected to the positive line voltage +Vc line, and its emitter is grounded through a bridge circuit
18
and the main heater
30
. A first resistor
12
of the bridge circuit
18
is serially connected to the auxiliary heater
32
at a node
13
, and its second resistor
14
is serially connected to its third resistor
16
and a variable resistor
34
through a node
17
.
These nodes
13
and
17
are respectively connected to inputs of an operational amplifier
24
. An output of the amplifier
24
is connected to the base of the transistor
20
through a protection resistor
22
. The resistor
36
for supplying an early voltage to the bridge circuit
18
upon triggering is connected between the collector and emitter of the transistor
20
.
In
FIG. 3
, the transistor
20
is so controlled by the amplifier
24
that the electric potential e
1
of the node
13
is identical to that e
2
of node
17
to maintain the temperature of the auxiliary heater
32
to a fixed or predetermined value.
For example, when the temperature of the auxiliary heater
32
is lower than the predetermined temperature value or e
1
<e
2
, the output voltage of the amplifier
24
is raised, and the main heater
30
and the auxiliary heater
32
are further heated to maintain the predetermined temperature condition.
In
FIG. 2
, the leakage current may flow to the auxiliary heater by the potential difference induced between the main and auxiliary heaters when the insulation of the insulator substrate arranged on the main and auxiliary heaters is deteriorated by, for example, aging. Therefore, though a configuration of the conventional pyro-control circuit is simple, the electric potential e
1
will be increased by the leakage current, and the temperature of the auxiliary heater
32
has a problem to decrease less than the predetermined value.
FIG. 4
shows a block diagram of another conventional pyro-sensor. In
FIG. 4
, a common power supply
46
is provided to heat a heater
42
in a sensor
40
through first power supply
43
, and to supply an applied voltage to a cell
44
in the sensor
40
through second power supply
45
.
FIG. 5
is a cross-sectional top view to show an example of the sensor
40
. In this drawing, a platinum thin film heater
42
is mounted or affixed on, for example, one surface of an insulator substrate
50
, and its entire surface is covered with an insulating material
51
having the heat proof and corrosion tolerant characteristics. A cell substrate
55
for supporting the cell
44
is mounted on other side of the insulator substrate
50
through an insulation spacer
53
.
When the above common power supply
46
drives the sensor
40
having, for example, a structure of
FIG. 5
, the deterioration or contact of the insulation characteristics between the heater
42
and the cell
44
may be generated by aging, and it is afraid that an unusual leakage current flows therebetween. This leakage current degrades the characteristics of the fresh sensor, and it is one of the causes which make reliability decline.
In other words, in the limit current type oxygen sensor having the structure like
FIG. 5
, the insulation characteristics between the heater
42
and the cell
44
is supposed to be degraded, because first power supply
43
and second power supply
45
are directly connected to the common power supply
46
, a leakage current is generated regardless of more or less therebetween, one current loop (see
FIG. 6
) is generated through common ground both of power supplies. Then, the output of the sensor go wrong or the deterioration and reliability of the sensor is degraded.
Accordingly, it is an object of the invention to provide a high-reliable heater for the pyro-sensor and its pyro control circuit in which any leakage current doesn't occur even if the electric insulation of the insulator substrate deteriorates by aging, and then the main heater can maintain a predetermined temperature value as well as the auxiliary heater that serves as a temperature sensor.
It is another object of the invention to provide a method for driving a high-reliable sensor in which any leakage current from the heater is not generated, even if insulation characteristics between the heater and cell is degraded.
It is still another object of the invention to provide a driving method of the high reliable pyro-sensor that a current loop doesn't appear between the heater and the cell.
A main heater
30
consisting of first fever area
30
a
and second fever area
30
b
, and an auxiliary heater
32
are arranged on an insulator substrate to maintain a sensing portion, for example, 400° C. A grounded first fever area
30
a
is contiguously arranged between second fever area
30
b
and grounded auxiliary heater
32
. An amplifier
24
controls a load voltage to a bridge circuit
18
containing the auxiliary heater
32
, first, second and third resistors
12
,
14
,
16
and the main heater
30
based on the output of the bridge circuit
18
. An inverting input of an amplifier
23
is connected to a node
13
, and a non-inverting input thereof is connected to a node
17
of second and third resistors
14
and
16
, and an output terminal is connected to the base or gate of the transistor
20
supplying the load voltage to the main heater
30
. The resistance ratio of first fever area
30
a
and second fever area
30
b
is determined to be identical to that of third resistor
16
and second resistor
14
. Pyro-sensor or limit current type oxygen sensor comprises a cell
44
capable of maintaining a high temperature, for example, 400° C. and a heater
42
for heating the cell
44
to the predetermined temperature. It firther comprises a DC-DC converter
48
isolating a first power supply
43
supplying electric power to the heater
42
from second power supply
45
applied a voltage to the cell
44
.
A leakage current by deterioration of the insulator substrate is not generated, and temperature of a sensing portion is constantly maintained by the main heater to a high temperature. The sensor cell is protected from a leakage current from the heater from occurring.
A heater for the pyro-sensor according to the present invention is characterized in that a main heater consisting of first and second fever areas, and an auxiliary heater are arranged respectively on an insulator subs
Hopgood, Calimafde, Judlowe & Mondolino LLP
Kabushiki Kaisha Riken
Olsen Kaj K.
Warden, Sr. Robert J.
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