Claims
- 1. A glow plug comprising a tubular casing having open ends provided wibh an external thread, an elongate tubular sleeve closed at one end and open at the other disposed in the tubular casing with the closed end protruding from one open end thereof and the open end within the tubular casing, an electrode rod disposed within the other open end of the casing and secured therein, said electrode rod extending axially into the tubular sleeve into abutting engagement with the closed end thereof and welded to said closed end of the tubular sleeve, said electrode rod being of two diameters and defining at the junction of the two diameters an annular shoulder located approximately mid-length of the tubular sleeve, a first electrically-conductive heating element in the form of a coil of predetermined positive resistance temperature coefficient disposed in the tubular sleeve about the electrode rod in concentric relation to the electrode rod and the tubular sleeve comprised of a helical coil of wire of open pitch and uniform diameter less than the inside diameter of the tubular sleeve, one end of which abuts the closed end of the tubular sleeve and is welded thereto, said coil being of a predetermined axial length, a second electrically-conductive heating element of predetermined positive resistance temperature coefficient higher than the first heating element disposed in the tubular sleeve about the electrode rod in concentric relation thereto and the tubular sleeve and axially spaced from the first heating element such that there is a gap between the adjacent ends of the heating elements, said heating elements collectively being of lesser axial length than the distance between the closed end of the tubular sleeve and the shoulder and said second heating element comprising a helical coil of wire of open pitch and uniform diameter corresponding in pitch and diameter to the first heating element and of an axial length greater than the axial length of the first coil with its distal end engaged with the shoulder and secured thereto and means connecting the coils at their adjacent ends comprising straight lengths of wire extending from the adjacent ends parallel to the longitudinal axis of the coils bridging the gap between the adjacent ends and welded to each other, an electrically-insulated, thermally-conductive particulate material filling the sleeve about the electrode rod and the spaces between the helices of the heating coils throughout the length of the tubular sleeve, characterized in that the gap between adjacent ends of the heating elements is of a length of 1.5 to 12 times the pitch of the helices of the coil of the first heating element, the ratio of the length of the first heating element to the diameter of the sleeve is less than 1.5, the resistance ratio at normal temperature of the first and second heating elements is 2.5 to 7.0 and the second heating element is comprised of nickel or low carbon steel.
Priority Claims (1)
Number |
Date |
Country |
Kind |
57-168738 |
Sep 1982 |
JPX |
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Parent Case Info
This application is a continuation-in-part of applicants' copending application Ser. No. 372,311, filed Apr. 27, 1982, now U.S. Pat. No. 4,476,378.
US Referenced Citations (2)
Number |
Name |
Date |
Kind |
4211204 |
Glauner et al. |
Jul 1980 |
|
4423309 |
Murphy et al. |
Dec 1983 |
|
Foreign Referenced Citations (5)
Number |
Date |
Country |
586327 |
Jul 1981 |
JPX |
57-26326 |
Feb 1982 |
JPX |
254482 |
Jul 1926 |
GBX |
1215013 |
Dec 1970 |
GBX |
2013277 |
Aug 1979 |
GBX |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
372311 |
Apr 1982 |
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