Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Reexamination Certificate
1999-09-17
2001-10-23
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
C374S208000
Reexamination Certificate
active
06305841
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a temperature sensor incorporating a thermistor element that is used to detect temperature and, more particularly, to a temperature sensor required to have heat resistance up to a temperature of about 1000° C. which is suitable for use in, for example, an exhaust gas temperature sensor that is installed on a catalytic converter, and so forth, of an automobile exhaust system and detects abnormal temperatures or catalyst deterioration and so forth.
2. Description of the Related Art
This type of temperature sensor typically provides a thermistor element, having a certain temperature-resistance characteristic, at the end of a wiring member for the acquisition of thermistor signals. This end section is covered with a bottomed cylindrical metal case resulting in a composition in which the thermistor element is housed in the space formed by the metal case and the wiring member end section.
Normally, by filling insulating powder into a space between a metal outer cylinder and core wires, the composition of the wiring member is such that the core wires are insulated and retained in the outer cylinder, and these core wires are connected to electrode wires provided on the thermistor element.
Since a thermistor material composing the thermistor element is comprised of an oxide semiconductor, the resistance characteristics (temperature-resistance characteristics) of the thermistor section fluctuate according to the oxygen partial pressure of the ambient atmosphere of the thermistor element.
In this type of temperature sensor, since the thermistor element is housed in a metal case, oxidation of a heat-resistant metal occurs at high temperatures (e.g., 700° C. and above), and the oxygen partial pressure of the internal atmosphere decreases. In a harsh reducing atmosphere, a phenomenon occurs in which oxygen is temporarily taken from the oxide semiconductor of the thermistor section, resulting in a disturbance in the above resistance characteristics at high temperatures.
Therefore, it is necessary to provide the thermistor element housed in the metal case with suitable ventilation to stabilize the thermistor characteristics. Here, in the case of a temperature sensor employing a double tube structure in which the periphery of the wiring member is further covered with a metal cylinder, etc. (e.g., that described in
FIG. 8
of Japanese Patent No. 2621488), a ventilation pathway can be formed by using the gap between the wiring member and the metal cylinder.
More recent sensors, however, are required to accurately detect temperature over ranges of low temperature variation and perform on-off control for assessment of catalyst deterioration and so forth, thus requiring an even faster response. Consequently, there is a need to make the outer diameter of the temperature-sensitive section smaller to increase the speed of the sensor response. The above-mentioned double tube structure is structurally complex and unsuited for accommodating this need.
On the other hand, in the case of a single tube structure in which the end section of a wiring member provided with a thermistor element is covered only with a bottomed, cylindrical metal case, although it is advantageous to make the outer diameter of the temperature-sensitive section smaller, the ventilation pathway for the thermistor element must then be formed inside the wiring member.
However, as was mentioned above, since the wiring member employs a composition in which the core wires are insulated and held in a metal outer cylinder by insulating powder filled into the outer cylinder, it cannot be expected to provide good ventilation. In addition, when the outer diameter of the temperature-sensitive section is made smaller to increase the response speed, since this requires that the wiring member has a smaller diameter, it becomes difficult to secure ventilation. Therefore, the need arises to clarify the quantity of ventilation required to stabilize the thermistor characteristics.
Therefore, in consideration of the above points, the object of the present invention is to provide a temperature sensor incorporating a thermistor element housed in a metal case and a wiring member for acquisition of signals from said thermistor element, wherein the wiring member employs a ventilation composition that provides stable resistance characteristics of the thermistor element, and to provide a manufacturing process for a temperature sensor incorporating such wiring member composition.
SUMMARY OF THE INVENTION
As a result of earnest studies conducted by the inventors of the present invention and focusing on the quantity of ventilation of the wiring member, it was experimentally determined that, if the said quantity of ventilation was equal to or greater than a prescribed quantity, stable thermistor resistance characteristics are obtained, thereby leading to completion of the present invention.
The present invention provides a temperature sensor equipped with a thermistor element having a thermistor section comprised of a thermistor material, a wiring member comprising electrically conducting core wires coupled to said thermistor element, for acquiring thermistor signals from the thermistor element, insulated and held in a metal outer cylinder, and a cylindrical metal case that houses said thermistor element, has an opening in one end and is closed on the other end, and is joined to said outer cylinder at said opening; wherein said wiring member secures a ventilation quantity in said outer cylinder of at least 5×10
−4
ml/(MPa·sec) at normal temperature.
Accordingly, an amount of outside air based on the above-mentioned prescribed quantity of ventilation can be introduced through the inside of the wiring member into the space in which the thermistor element is housed, formed by the metal case and wiring member, thereby preventing the formation of a harsh reducing atmosphere around the thermistor element. Thus, according to the present invention, a ventilation composition can be realized that provides stable thermistor element resistance characteristics.
The thermistor element is preferably comprised of thermistor section comprised of a thermistor material and electrode wires extending from said thermistor section for acquisition of thermistor signals. In this case, the electrode wires are connected to the core wires.
According to experimental studies conducted by the inventors of the present invention, the above-mentioned prescribed ventilation quantity is preferably secured at 1×10
−3
ml/(MPa·sec) at normal temperature, and more preferably secured at 5×10
−3
ml/(MPa·sec) at normal temperature.
The inventors of the present invention have confirmed that the object of the present invention can be realized provided the above-mentioned ventilation quantity is secured even if the outer diameter of the outer cylinder, namely the outer diameter of the wiring member, is reduced to 3 mm or less and the outer diameter of the outer diameter of the outer cylinder is reduced to 2.5 mm or less.
As one specific wiring member means for achieving the above-mentioned prescribed ventilation quantity, the core wires of the wiring member can be insulated and held on the outer cylinder by filling insulating powder into the outer cylinder between said outer cylinder and core wires, and the outer cylinder can be made to have a coefficient of thermal expansion of 3×10
−6
(/°C.) or more larger than the insulating powder.
As a result, at high temperatures facilitating the formation of a reducing atmosphere, the insulating powder filled into the outer cylinder contracts relative to the outer cylinder, enabling the formation of a gap that allows the above-mentioned prescribed ventilation quantity to be secured between the outer cylinder and insulating powder. More specifically, magnesium oxide can be used for the insulating powder.
In a temperature sensor in which the above-mentioned outer cylinder has a coefficient of thermal expansion that is at least 3&tim
Fukaya Matsuo
Nagai Junichi
De Jesus Lydia M.
Denso Corporation
Gutierrez Diego
Pillsbury & Winthrop LLP
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