Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Reexamination Certificate
1999-07-22
2001-07-24
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
C338S025000, C338S028000, C374S208000
Reexamination Certificate
active
06264363
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a temperature sensor used for temperature detection and a method of manufacture thereof or, in particular, to a temperature sensor suitably used as an exhaust gas temperature sensor mounted on a catalyst converter or the like of an exhaust system of automobiles for detecting an abnormal temperature or detecting the deterioration of a catalyst.
2. Description of the Related Art
In the prior art, the temperature detecting apparatus described in Japanese Unexamined Patent Publication (Kokai) No. 9-126910 has been proposed as this type of temperature sensor. This conventional temperature sensor comprises a solid-cylindrical thermistor including a pair of electrodes (platinum) each in the shape of a cylindrical pipe. A pair of signal lines (wires for retrieving a thermistor signal) from a rear two-core pipe (sheath pin) are inserted into the hollow cylindrical electrodes. The electrodes and the signal lines are welded to each other. Further, a metal cap covering the thermistor is coupled to the outer cylinder of the two-core pipe.
This temperature detecting apparatus in which a pair of electrodes led out in one direction of a solid-cylindrical thermistor are connected to a pair of signal lines, respectively, arranged in the direction of extension of the electrodes is generally called a radial-type thermistor.
With the recent trend toward a higher responsiveness of sensors, the current demand is for a smaller diameter of a temperature detecting portion. For the temperature detecting portion to be reduced in diameter, a reduced diameter of the metal cap and hence the thermistor is naturally required. In the prior art described above, however, a platinum pipe embedded in the thermistor is used as a thermistor electrode, and the signal lines are inserted and joined in the pipe. Therefore, the pipe is larger in diameter than the signal lines by a size equivalent to the pipe thickness and the insertion gap.
On the other hand, the thermistor itself requires a volume sufficient for acquiring the desired resistance characteristic. Therefore, the portion embedded with the platinum pipe forms a dead space of the thermistor. An increased pipe diameter thus unavoidably increases the thermistor diameter. Also, as described above, once the diameter of the signal lines is determined, the pipe diameter and thickness are also determined. The reduction in thermistor diameter, therefore, has a limit.
For the thermistor to be reduced in diameter, the thermistor electrodes are required to be changed in shape from a pipe into a rod. A study conducted by the inventors shows, however, that a reduced diameter of the temperature detecting portion of a radial-type thermistor poses a problem depending on relative positions of a pair of rod-like electrode wires and a pair of signal lines. This problem will be described with reference to
FIGS. 5A
,
5
B.
FIGS. 5A
,
5
B show a working model of a radial-type thermistor fabricated by the inventor. A pair of rod-like electrode wires
2
led out in the same direction from a solid-cylindrical thermistor
1
are connected to a pair of signal lines, respectively, arranged in the same direction as the electrode wires (welded at points A in FIG.
5
A). Numeral
4
designates an outer cylinder of the two-core pipe.
FIG. 5B
is a sectional view taken in line C—C in FIG.
5
A.
As shown in
FIG. 5B
, each of the wires
2
and a corresponding one of the lines
3
are coupled to each other on the same side. The electrode wire pair
2
is normally arranged on lines on both sides of a cylinder axis
1
a
in order to minimize the body size while securing the required thickness of the thermistor
1
. The cylinder axis
1
a
of the thermistor
1
, therefore, is offset from a line connecting the signal lines
3
(by the distance indicated by numeral
5
in
FIG. 5
) and deviates from the center axis
4
a
of the outer cylinder of the two-core pipe. A cylindrical metal cap and an insulating member are arranged around the thermistor
1
. The eccentric structure of the thermistor
1
described above requires a large diameter of the metal cap and the insulating member, thereby substantially increasing the size of the temperature detecting portion.
Also, the axes
1
a
,
4
a
would coincide with each other if the electrode wires
2
and the signal lines
3
are welded at the ends thereof. welding ends to ends, however, makes it difficult to secure the reliability of the junction. Especially, this structure is not desirable for the exhaust gas temperature sensor or the like of automobiles exposed to vibrations and other external forces.
SUMMARY OF THE INVENTION
In view of the problem points described above, the object of the present invention is to provide a temperature sensor comprising a radial-type thermistor, a pair of rod-like electrode wires led out in the same direction from the thermistor and a pair of signal lines led out from the thermistor in the same direction and connected with the electrode wires, respectively, wherein the reliability of coupling between the electrode wires and the signal lines is secured while at the same time reducing the size of a temperature detecting portion.
The present inventors have found that the problem of decentering of the axis occurs for the thermistor in the shape of a parallelepiped solid cylinder or an elliptical solid cylinder as well as a round solid cylinder.
In view of this, a temperature sensor of the present invention comprises a pair of substantially parallel spaced electrode wires embedded along the axis of a solid-cylindrical thermistor and having an end portion thereof led out toward an end of the thermistor, and a pair of signal lines arranged in a substantially parallel spaced relation along the axis of the thermistor and connected to an end of the electrode wires respectively for retrieving the thermistor signal, wherein the electrode wires and the signal lines have a novel arrangement.
Specifically, according to a first aspect of the invention, there is provided a temperature sensor comprising a pair of electrode wires
22
, a pair of signal lines
31
, and a thermistor
21
, wherein the electrode wires
22
and the signal lines
31
are coupled to each other in such an overlapped position that the diagonal line K
1
connecting the electrode wires crosses the diagonal line K
2
connecting the signal lines
31
as viewed along the direction of the axis
21
a
of the thermistor
21
. The solid cylinder of the thermistor
21
includes a round, parallelepipedal or elliptical solid cylinder, of which the length may be longer or shorter than the width or thickness.
According to this invention, the wires
22
,
31
are coupled to each other in such a manner the diagonal lines K
1
, K
2
cross each other. Even in the case where external forces such as vibrations are applied to one overlapped portion of the electrode wires
22
and the signal lines
31
in such a direction as to separate them away from each other, therefore, the electrode wires
22
and the signal lines
31
attract each other at the other overlapped portion, thereby securing the coupling reliability.
With the working model shown in
FIG. 5
, the coupling reliability is low since external forces such as vibrations exerted on one overlapped portion in such a direction as to separate the wires
2
,
3
from each other also act on the other overlapped portion in the same direction.
According to this invention, in contrast, the wires
22
,
31
are coupled to each other while being overlapped in such a manner that the two diagonal lines K
1
, K
2
cross each other. Therefore, the crossing point of the diagonal lines K
1
, K
2
can be rendered to coincide with the axis
21
a
of the thermistor
21
. In this way, the increased diameter of the temperature detecting portion which otherwise might be caused by the decentering of the axis of the solid-cylindrical thermistor described above is prevented and the size of the temperature detecting portion can be reduced.
According to a second aspe
Nagai Junichi
Takahashi Sotoo
Denso Corporation
Gonzalez Madeline
Gutierrez Diego
Pillsbury & Winthrop LLP
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