Electric heating – Heating devices – Resistive element: igniter type
Reexamination Certificate
2002-05-31
2004-06-01
Look, Edward K. (Department: 3742)
Electric heating
Heating devices
Resistive element: igniter type
C219S270000
Reexamination Certificate
active
06744015
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a heater capable of raising the temperature of a heating element portion thereof through supply of electricity to the portion, such as a glow plug used in an internal combustion engine for improving start-up of the engine, and to a method for manufacturing the same.
BACKGROUND OF THE INVENTION
In order to improve the start-up of a diesel engine at low temperature, the heating element of a glow plug is disposed within the combustion chamber. Applying electricity to the glow plug heats the heating element and accelerates ignition of fuel, thereby enhancing start-up.
In some cases, in order to heat a liquid such as cooling water or a gas such as air in an engine, a glow plug may be used as a heater. Similarly, a heater having a similar configuration may be used as a heat source for igniting kerosene or a gas.
A glow plug is generally configured in the following manner: a heating element is disposed in a cylindrical metallic shell in such a manner as to project from the front end of the metallic shell. One electrode of the heating element is electrically connected to the metallic shell while the other electrode is electrically led to an external terminal, which is disposed in the vicinity of the rear end of the metallic shell while being electrically insulated from the metallic shell, by use of a rod-like axial member, a lead wire, or other electrically conductive member.
However, in an engine, since the heating element of a glow plug is disposed within a combustion chamber or a prechamber, which is exposed to high pressure, the glow plug must be gas-tight such that a gas within the combustion chamber does not leak through the glow plug (through the metallic shell) to the exterior of the glow plug.
When a heating element is configured such that a heating resistor, formed of a high-melting-point metal wire, together with a ceramic powder heat resistant insulation, such as MgO, is disposed within a closed-bottomed cylindrical metal sheath, the glow plug must also be gas-tight. This prevents the ceramic powder insulation from absorbing moisture and deteriorating in insulating performance, from entry of water, water vapor, or oil from the side toward the external terminal (the side toward the rear end of the metallic shell).
Also, a heater that serves as an ignition heat source for heating water or the like must be gas-tight so as to prevent leakage of water, water vapor, or the like to the exterior of the heater or entry of the same into the heater, through the metallic shell.
In order to establish such gas-tightness, a glow plug or a like heater employs a seal mechanism, such as a glass seal or an O-ring, provided in the vicinity of the rear end portion of the metallic shell. However, employment of a seal mechanism such as a glass seal or an O-ring involves various problems such as an increased number of manufacturing steps, resulting in increased cost.
The present invention has been accomplished in view of the above-mentioned problems, and an object of the invention is to provide an inexpensive heater with good gas-tightness, as well as a method for manufacturing the same.
SUMMARY OF THE INVENTION
The present invention is a heater comprising a cylindrical metallic shell having a front end, a rear end, and a through-hole extending therein between the front end and the rear end. A heating element is disposed in the through-hole of the metallic shell such that a portion thereof projects from the front end of the metallic shell. The heating element is adapted to generate heat upon application of electricity thereto. A lead member extends through the through-hole at least from the rear end of the metallic shell while being electrically insulated from the metallic shell, and electrically connected to the heating element. A gas-tight seal member, formed of an insulating polymeric material, is interposed between the lead member and an inner wall surface of the through-hole of the metallic shell in such a manner as to surround at least a longitudinal portion of the lead member. The metallic shell includes a crimped portion at which the metallic shell is crimped from an outer surface thereof to bring the gas-tight seal member into close contact with the lead member and the inner wall surface of the through-hole. This maintains gas-tightness within the through-hole between the side toward the front end and the side toward the rear end with respect to the gas-tight seal member.
In the heater of the present invention, the metallic shell includes a crimped portion at which the gas-tight seal member is in close contact with the lead member and the inner wall surface of the through-hole, to thereby maintain gas-tightness between the side toward the front end and the side toward the rear end with respect to the gas-tight seal member.
Thus, when this heater is used as a glow plug, leakage of high-pressure gas within the combustion chamber of an engine from the side toward the front end to the side toward the rear end can be prevented. Also, entry of water, such as water vapor, or oil from the side toward the rear end to the side toward the front end can be prevented, thereby preventing deterioration of the heat resistant insulation powder within the heating element.
The heater of the invention can establish gas-tightness without provision of a seal mechanism, such as a glass seal or an O-ring, at a rear end portion of the metallic shell, and is therefore inexpensive.
Examples of a heater to which the present invention is applicable include a glow plug used in a diesel engine for assisting start-up, and a heater used as a heat source for heating a liquid such as water or a gas such as air, or for igniting kerosene or the like.
Preferably, the present invention is applied to a heater to be used as a glow plug. That is, preferably, a glow plug comprises a cylindrical metallic shell having a front end, a rear end, and a through-hole extending therein between the front end and the rear end. A heating element is disposed in the through-hole of the metallic shell such that a portion thereof projects from the front end of the metallic shell. The heater portion is adapted to generate heat upon application of electricity thereto. A lead member extends through the through-hole, at least from the rear end of the metallic shell, while being electrically insulated from the metallic shell. The lead member is electrically connected to the heating element. A gas-tight seal member, formed of an insulating polymeric material is interposed between the lead member and an inner wall surface of the through-hole of the metallic shell in such a manner as to surround at least a longitudinal portion of the lead member. In the glow plug, the metallic shell includes a crimped portion at which the metallic shell is crimped from an outer surface thereof so as to bring the gas-tight seal member into close contact with the lead member and the inner wall surface of the through-hole, to maintain gas-tightness within the through-hole between the side toward the front end and the side toward the rear end with respect to the gas-tight seal member.
Preferably, the heater of the present is gas-tight such that no leakage arises in the course of a gas-tightness test conducted through application of a gas pressure of 1.5 MPa to the gas-tight seal member from the side toward the front end.
The heater of the present invention has high gas-tightness such that no leakage arises even when high gas pressure is imposed thereon. Thus, gas-tightness can be reliably maintained between the side toward the front end and the side toward the rear end with respect to the gas-tight seal member.
Having such high gas-tightness, the heater used as a glow plug exhibits high reliability.
Preferably, the above-described heater is configured such that a total contact area S between the gas-tight seal member and the inner wall surface of the through-hole as measured in a region located radially inward of the crimped portion is not less than 45 mm
2
.
In this heater, the gas-tight seal member has a predetermin
Nagasawa Masakazu
Tanaka Katsuhiko
Finnegan Henderson Farabow Garrett & Dunner LLP
Look Edward K.
NGK Spark Plug Co. Ltd.
Patol Vinod D.
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