Electric heating – Heating devices – Resistive element: igniter type
Reexamination Certificate
2002-06-10
2003-09-30
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Resistive element: igniter type
C123S14500A, C313S141000, C313S143000
Reexamination Certificate
active
06627854
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heater for heating an object material, such as a gas, a liquid and the like, and to a glow plug for a diesel engine.
2. Description of the Related Art
A related art heater will be described on the basis of
FIG. 6
of the accompanying drawings taking as an example the glow plug disclosed in Japanese Patent Laid-Open No. 10-2557. This glow plug
100
roughly includes a main metal member constituting a tubular member
101
, a cap type sheath tube
102
fixed to a front end of the tubular member
101
, and a central electrode constituting a shaft-like member
103
. The shaft-like member
103
extends through the center of the tubular member
101
to reach the sheath tube
102
, and a front end of the sheath tube
102
and that of the shaft-like member
103
are electrically connected to each other via a control coil
104
and a heating coil
105
. A stepped bore
106
is formed in a rear end (upper portion of the drawing) of the tubular member
101
, and an upper portion of the shaft-like member
103
is fixed in the center of the tubular member
101
by a bush type insulating ring
107
fitted in the stepped bore
106
.
Thus, the glow plug
100
employs a seal structure having a clearance
108
between the surface of the tubular member
101
which defines the stepped bore
106
and the shaft-like member
103
, an O-ring
109
being fitted in the clearance
108
and crushed by a stepped portion of the stepped bore
106
and the insulating ring
107
, the clearance
108
being thereby closed.
3. Problem Solved by the Invention
When the O-ring
109
is inserted into the stepped bore
106
of the glow plug
100
, there is the possibility that the O-ring
109
be broken or cracked, i.e., damaged. Especially, in recent years, the miniaturization of the glow plug
100
has progressed, and a glow plug in which a nominal diameter (diameter of a ridge) of a male thread
110
to be engaged with a diesel engine is not larger than 10 mm is being manufactured. In such a glow plug, a stepped bore
106
has a small diameter, and an O-ring
109
is extremely small, so that the O-ring is in great danger of being damaged. Needless to say, the damage to the O-ring
109
causes an imperfect sealing of the glow plug
100
and exerts a bad influence upon the performance thereof. Therefore, it becomes essential to visually inspect the O-ring after the O-ring is inserted into the stepped bore, and this renders it difficult to automate the O-ring setting operation.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned circumstances, and has as an object to provide a heater and a glow plug which have a seal structure adapted to seal with an O-ring a clearance between an inner surface of a stepped bore in a tubular member and an outer surface of a shaft-like member inserted into the stepped bore, and which are capable of reducing a rate of occurrence of damage to the O-ring during an O-ring setting operation.
The present invention (1) provides a heater having a seal structure formed by inserting a shaft-like member into a stepped bore made in a tubular member, and providing an O-ring on a stepped portion of the stepped bore so as to close a clearance between the shaft-like member and tubular member, wherein a seal region is formed on a stepped portion of the stepped bore, a conical introduction port portion extending divergently in the rearward direction from the seal region toward an opening of the stepped bore is formed, and a cone angle &agr; of the introduction port portion with respect to the axis of the tubular member being set not larger than 35°.
When the introduction port portion of a cone angle of not larger than &agr;=35° is formed in the stepped bore as mentioned above, the O-ring is forced into the seal region as the O-ring is deformed slowly, so that the breakage and cracking of the O-ring rarely occur. When the cone angle &agr; is set in the range of 10° to 20°, which structure will hereinafter be referred to as preferred aspect of the invention (2), a substantial rate of occurrence of damage to the O-ring of 0% can be attained. Preferably, the axial length of the introduction port portion is set to a level which permits the O-ring set in the introduction port portion, and not yet forced down, to be sunk by at least a half portion thereof into the introduction port portion, which structure will hereinafter be referred to as preferred aspect of the invention (3). This enables the O-ring to be smoothly forced into the stepped bore.
REFERENCES:
patent: 4633064 (1986-12-01), Atsumi et al.
patent: 5059768 (1991-10-01), Hatanaka et al.
patent: 5118921 (1992-06-01), Aota
patent: 5218183 (1993-06-01), Kimata
patent: 5521356 (1996-05-01), Bauer
patent: 5767485 (1998-06-01), Kumada
patent: 6064039 (2000-05-01), Kumada
patent: 6236148 (2001-05-01), Nasu et al.
patent: 6420683 (2002-07-01), Chiba et al.
patent: 6437493 (2002-08-01), Nasu et al.
patent: 10-2557 (1998-01-01), None
patent: 3039819 (2000-03-01), None
Goto Shunsuke
Kumada Chiaki
Terada Naoto
Dahbour Fadi H.
NGK Spark Plug Co. Ltd.
Sughrue & Mion, PLLC
Walberg Teresa
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