Electric heating – Heating devices – Resistive element: igniter type
Reexamination Certificate
2002-05-28
2003-12-09
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Resistive element: igniter type
C361S266000, C123S14500A, C313S141000
Reexamination Certificate
active
06660971
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a heater for heating a heating object such as the gas or liquid, and a glow plug for the diesel engine.
BACKGROUND OF THE INVENTION
The conventional heater will be described below by way of example for a glow plug with reference to FIG.
5
. This glow plug
100
is roughly made up of a cylindrical metal shell
101
, a heating tube
102
that is cylindrical and has a uniform thickness with a top end cloned, the heating tube
102
fitted inside the metal shell
101
, and a center electrode
103
of round pole type. The center electrode
103
is passed through the center of the metal shell
101
to reach the heating tube
102
, in which the closed top end of the heating tube
102
and the top end of the center electrode
103
are electrically connected via a heating coil
104
. The metal shell
101
has an engagement portion
105
with an aperture (diameter) restricted (narrowed), and the heating tube
102
is fitted into the engagement portion
105
in interference fit. A rear end side of the heating tube
102
is passed through the engagement portion
105
of the metal shell
101
to protrude into the inside of the metal shell
101
.
One of the universal technical themes for the glow plug is a reduction in size and weight. For this purpose, it is indispensable that the outer diameter of the heating tube
102
is reduced. At present, the heating tube
102
having a diameter of 3.5 mm has been developed. The technical theme for reducing the size and weight generally applies to all the heaters.
SUMMARY OF THE INVENTION
If the heating tube
102
is made slender, the strength is lowered, resulting in a high risk that the heating tube
102
is bent when press fitted into the engagement portion
105
of the metal shell
101
. Also, in the case where the heating tube
102
having a uniform thickness is press fitted into the engagement portion
105
of the metal shell
101
, it is required that the heating tube
102
starts to be press fitted from the time when the rear end of the heating tube
102
enters the engagement portion
105
, and continues to be press fitted even after the rear end of the heating tube
102
gets out of the engagement portion
105
. Accordingly, the heating tube
102
is pushed into the inside of the metal shell
101
by a long distance, while being press fitted, whereby the press-fit load is likely to be great. Since there are many sections of the heating tube
102
contributing to (or involving) the press fitting, there is a great dispersion in press-fit load of the heating tube
102
, which is caused by variations in frictional force occurring with the engagement portion
105
of the metal shell
101
, resulting in poor controllability for the heating tube
102
. The magnitude of dispersion in press-fit load has been confirmed through the test of fitting the heating tube having a uniform thickness into the metal shell, as conducted by the present applicant. This dispersion in press-fit load makes it difficult to control the automatic fitting device for the heating tube
102
, developing a factor of aggravating the product accuracy.
In recent years, a glow plug is well known in which the heating tube has a two stage structure of a larger diameter portion on the base end side and a smaller diameter portion on the top end side to attain a temperature up performance at the early time, and the larger diameter portion of the heating tube is fitted into the engagement portion of the metal shell in interference fit. However, in the glow plug with this constitution, the press-fit load for the heating tube into the metal shell is likely to increase, because the outer diameter of the larger diameter portion is uniform in thickness. In fitting the heating tube having the two stage structure into the metal shell, in the case where it is designed to allow a part of the smaller diameter portion to be entered to a position of the engagement portion in the metal shell, the following problem arises, even though the heating tube is fitted into the metal shell. That is, since there is a section at the top end portion of the engagement face in the engagement portion not contributing to an interference fit with the heating tube (smaller diameter portion), if the glow plug drops in a process for manufacturing the glow plug or mounting it on the engine to exert a strong impact force toward the base end side of the heating tube from the outside, the heating tube is deviated toward the base end side of the metal shell, or gets rid of the metal shell by any chance.
The present invention has been achieved in the light of the above-mentioned problems, and it is an object of the invention to provide a heater and a glow plug that are highly reliable, in which the press-fit load for the heating tube into the metal shell is suppressed from increasing more than needed, without significant resistance in passage through the engagement portion at the early time of fitting the heating tube into the metal shell.
According to one embodiment of the present invention, there is provided a heater having a cylindrical metal shell formed with an engagement portion having a restricted aperture, and a cylindrical heating tube with a top end side closed to be fitted into the engagement portion in interference fit, in which a base end side of the heating tube is passed through the engagement portion to protrude into the inside of the metal shell, the heating tube comprising a fitting portion that is fitted into the engagement portion formed in the metal shell, a smaller diameter portion formed containing an end portion on the base end side protruding into the inside of the metal shell and having a smaller outer diameter than an inner diameter of the engagement portion, a large diameter portion on the base end side formed between the fitting portion and the smaller diameter portion and having an outer diameter larger than or equal to the inner diameter of the engagement portion, and a larger diameter portion on the top end side formed adjacent to a top end side of the fitting portion and having an outer diameter larger than or equal to the inner diameter of the engagement portion. Also, this invention provides a glow plug of the same structure in which the use of the heater is limited to starting aids of the diesel engine.
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patent: 4661686 (1987-04-01), Yokoi et al.
patent: 5039839 (1991-08-01), Masaka et al.
patent: 6046434 (2000-04-01), Locher et al.
patent: 6064039 (2000-05-01), Kumada
patent: 6215105 (2001-04-01), Simpkins et al.
patent: 6248980 (2001-06-01), Chiu et al.
patent: 6285007 (2001-09-01), Chiu et al.
patent: 6437493 (2002-08-01), Nasu et al.
patent: 6465759 (2002-10-01), Simpkins et al.
patent: 2762385 (1998-03-01), None
patent: 11-94253 (1999-04-01), None
patent: 2000-97434 (2000-04-01), None
Okuda Kouji
Terada Naoto
Dahbour Fadi H.
Morgan & Lewis & Bockius, LLP
NGK Spark Plug Co. Ltd.
Walberg Teresa
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