Electrical resistors – Resistance value responsive to a condition – Ambient temperature
Reexamination Certificate
1999-05-19
2002-12-31
Easthom, Karl D. (Department: 2832)
Electrical resistors
Resistance value responsive to a condition
Ambient temperature
C338S028000, C374S185000
Reexamination Certificate
active
06501366
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 in various locations, and which is suited for use as a high-temperature thermistor-type temperature sensor that detects catalyst temperature and exhaust system temperature in diesel engines and gasoline engines.
2. Description of the Related Art
In high-temperature thermistor-type temperature sensors that detect catalyst temperature and exhaust system temperature in diesel engines and gasoline engines of the prior art, a thermistor element equipped with a thermistor section and electrode wires (normally platinum wires) for acquisition of thermistor signals is housed in a cylindrical case. In order to prevent breakage of the platinum wires by absorbing mechanical stress due to engine vibrations and the temperature fluctuating from nearly −40° C. to nearly 1000° C., an opening in one end of the cylindrical case is filled with an insulating cushioning material such as alumina powder around the thermistor element to form a unit structure.
Moreover, in order to prevent entry of exhaust gas from the above opening in the cylindrical case as well as preventing the insulating cushioning material from spilling outside the case, the above-mentioned cylindrical case is inserted, from the end containing the above-mentioned opening, into a bottomed cylindrical metal tube. As a result, a double cylinder structure is formed that houses the above-mentioned unit, employing a form in which the above-mentioned opening is covered with the bottom of the metal tube.
However, accompanying higher engine speeds resulting from enhanced engine performance in recent years, due to the sensor holding structure at the site where the sensor is attached (catalyst or exhaust pipe, etc.) being reinforced, vibrations of greater magnitude are applied to the sensor at higher frequencies (e.g., 1 kHz or higher). Consequently, problems relating to the breakage of the platinum wires are becoming increasingly common, as indicated below, due to these intense, high-frequency vibrations.
The first problem is caused by the insulating cushioning material. In the above-mentioned structure of the prior art, spilling of insulating cushioning material to the outside is prevented by covering the opening in the cylindrical case with a metal tube, since the case is inserted into a metal tube. However, an extremely narrow gap (on the order of several tenths of a millimeter) neccessarily exists between the case and metal tube.
Here, when intense, high-frequency vibrations are applied to the sensor, the insulating cushioning material housed inside the case causes vibrations at the granular level due to the high frequency. These granules gradually break up and form tiny fragments that are able to enter the above-mentioned gap. Consequently, these tiny fragments spill out into the above-mentioned gap from the above-mentioned opening resulting in a loss of the thermistor element holding function and eventually leading to the risk of breakage of the electrode wires by vibration.
Another problem is caused by the material structure of the electrode wires themselves. Namely, although platinum wires are normally used for the electrode wires, according to a study conducted by the inventors of the present invention, during the course of manufacturing thermistor elements, the crystal grains of the platinum material become increasingly coarse in the firing process during which the platinum wires are molded by being embedded in a thermistor material (normally a semiconductor material) and firing (shrink-fitting) at 1300-1600° C. Intense, high-frequency vibrations induce shifting at the grain boundary of the coarse crystals, thereby leading to the risk of grain boundary breakage of the platinum wires.
In this manner, the potential for breakage of electrode wires of thermistor elements will become even greater in the future due to the high-frequency vibrations accompanying higher engine speeds.
Therefore, in consideration of the above-mentioned problems of the prior art, the object of the present invention is to prevent breakage of the electrode wires caused by high-frequency vibrations in a thermistor-type temperature sensor equipped with a thermistor element having a thermistor section and electrode wires for acquiring thermistor signals.
SUMMARY OF THE INVENTION
The present invention was achieved by focusing on the two points consisting of (1) providing the thermistor element with a holding structure function so that insulating cushioning material does not come out of the case even if it breaks up, and (2) providing the platinum material used for the electrode wires with a structure so that the crystal grains do not become coarse even if exposed to high temperatures.
Namely, a first aspect of the present invention is characterized by being a thermistor-type temperature sensor equipped with a thermistor element equipped with a thermistor section and electrode wires extending from the thermistor section, a cylindrical electrically conducting first case having an opening in one end that houses the thermistor element, an insulating cushioning material of coagulated powder that is housed in the first case from the opening and insulates and holds the thermistor element in the first case, and a second case having a bottomed, or closed-ended, shape that houses and holds the first case so that the bottom covers the opening; wherein, a heat-resistant adhesive is juxtaposed between the first case and second case so as to at least seal the opening.
The above-mentioned “coagulated powder” means a state of powder which is not sintered but can be shaved by a finger nail, and usually attained by heating a powder or slurry of an inorganic oxide to a temperature of 700° C. to 1000° C., preferably 800° C. to 1000° C.
This aspect of the present invention is based on the above-mentioned point (1). As a result of juxtaposing a heat-resistance adhesive between the above-mentioned first case and above-mentioned second case so as to at least seal the above-mentioned opening, even if the insulating cushioning material housed inside the first case is broken up and forms tiny fragments due to high-frequency vibrations, it can be prevented from spilling out from the opening into the gap between the first case and second case. Consequently, the thermistor element holding function can be maintained, and breakage of the electrode wires due to high-frequency vibrations can be. prevented. Furthermore, the heat resistance of the adhesive is preferably that which can withstand temperatures of, for example, 1000° C. in consideration of exhaust temperature sensors and so forth.
The above-mentioned adhesive is preferably also disposed at the portion corresponding to the portion in which the insulating cushioning material of the first case is housed between the first and second case.
Although an insulating cushioning material of coagulated powder is normally filled into the first case from the opening in one end and contained in the form of a powder or slurry, in order to improve the ease of filling, a hole for venting air may also be provided in the portion of the first case in which the insulating cushioning material is contained in addition to the opening. Thereafter, the powder or slurry is heated to be coagulated. Thus, in this case, if the above-mentioned adhesive is disposed at the portion corresponding to the portion at which the insulating cushioning material of the first case is contained, the insulating cushioning material can be prevented from spilling out since the hole other than the opening can be sealed, thereby making it possible to prevent breakage of the electrode wires.
The temperature sensor of the above-mentioned first aspect includes a temperature sensor which has a so-called axial type of thermistor element. This temperature sensor is equipped with a wiring member for acquiring thermistor signals from the above-mentioned electrode wires to the outside which member comprises an el
Fukaya Matsuo
Takahashi Sotoo
Denso Corporation
Easthom Karl D.
Nixon & Vanderhye PC
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