Inductor devices – With outer casing or housing
Reexamination Certificate
1999-12-08
2001-02-20
Gellner, Michael L. (Department: 2832)
Inductor devices
With outer casing or housing
C336S092000, C336S096000, C123S634000
Reexamination Certificate
active
06191674
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The present application is related to, and claims priority from, Japanese Patent Application No. Hei. 10-354084, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ignition coil for an internal combustion engine, and more specifically to a stick-type ignition coil directly mounted in an ignition plug hole.
2. Description of the Related Art
One type of conventional stick-type ignition coil for an internal combustion engine includes a center core part having an axially-disposed rod-like core body. A resin spool around which a primary coil and a secondary coil are wound is disposed around the center core part, and resin is filled within a coil housing to insulate the first coil from the second coil. The resin filled within the housing not only acts as an insulator but also prevents the coils from becoming loose, as the resin flows between adjacent wire rods of the coils before hardening.
Another type of conventional ignition coil includes a center core formed by disposing a permanent magnet having almost the same outer diameter as the core body outer diameter at both axial ends of the core body to increase the amount of voltage generated by the ignition coil. Alternatively, an ignition coil may include a rubber cushion member instead of the above-described permanent magnet to reduce axially-directed force acting on the core body due to different expansion coefficients of the respective members to prevent magnetostriction of the core body.
However, as shown for example in
FIG. 6
, because the core body and the permanent magnet or the cushion member are formed to have almost the same outer diameter, a bulge
82
is created at the interface
94
between the core body
93
and the permanent magnet
95
or the cushion member composing the center core part
92
unless the core body and the permanent magnet or the cushion member are co-axially assembled. Further, because cracks or voids in the insulation will occur where the center core part
92
expands and contacts, along with the resin insulating member and casing members having different expansion coefficients, due to temperature fluctuation, the center core part
92
is covered by a thermo-contractive tube
97
as a resin-made elastic cushion member, for example, to prevent the cracks from occurring.
However, because the thermo-contractive tube
97
also covers the outside of the bulge
82
, the thermo-contractive tube
97
also causes a bulge
97
a
. Therefore, assembly time is increased because the spool tends to catch on the bulge
97
a
during assembly of the center core part
92
into the spool of the secondary coil. Further, it is difficult to assure co-axial alignment of the primary coil, the secondary coil and the center core part
92
because the center core part
92
tends to tilt within the spool. As a result, voltage generated by the secondary coil is decreased, and desired high voltage cannot be applied to the ignition plug.
Further, because the thermo-contractive tube
97
is inhibited from shrinking uniformly due to the deformation in the vicinity of the bulge
97
a
, the end
97
b
of the thermo-contractive tube
97
comes off as shown in
FIG. 6
, the center core part
92
covered by the thermo-contractive tube
97
becomes larger than its predetermined size and the center core part
92
cannot be assembled at the predetermined position within the secondary spool, and the thermo-contractive tube
97
is damaged by a bulge
93
b
of the center core
93
opposite the bulge
97
a.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an ignition coil that can be easily assembled, that can assure co-axial alignment of a primary coil, a secondary coil and a center core part, and that can generate desired high voltage.
Another object of the invention is to provide an ignition coil that prevents cracks from occurring in the axial vicinity of both end corners of the center core and that generates desired high voltage.
Accordingly, the present invention provides a core body including an outer diameter larger than the outer diameter of a permanent magnet or a cushion member installed at an axial end of the core body, so that the permanent magnet or cushion member may be easily assembled to the core body within the range of the outer diameter of the core body. Consequently, it is possible to prevent the permanent magnet or cushion member from deviating and protruding radially away from the core body.
Further, it is possible to prevent the center core part from being caught within a secondary spool or from tilting within the secondary spool when the core body is assembled with the permanent magnet or cushion member in the secondary spool. Accordingly, the center core part may be readily inserted into the secondary spool. Also, the primary spool, the secondary spool and the center core part may be co-axially aligned, therefore making it possible for desired high voltage to be applied to the ignition plug.
More specifically, the center core part is preferably covered by an elastic cushion member at axial ends of the core body so that casing members surrounding the center core part and the resin insulating member are prevented from directly contacting both axial ends of the center core part.
Also, cracks in the resin insulating material and the casing member near the axial ends of the center core part are prevented, even when the resin insulating material and the casing member have expansion coefficients different from that of the center core part, and expand and contract repeatedly together with the center core part due to temperature changes. Cracks are prevented because the elastic cushion member absorbs the difference in the expansion coefficients of the center core part, the resin insulating material and the casing member. Therefore, voltage generated by the secondary coil is prevented from dropping, and desired high voltage can subsequently be applied to the ignition plug.
Further, the contraction temperature of the thermo-contractive casing member may be made higher than the ambient temperature to prevent expansion damage in the thermo-contractive casing member during coil operation.
The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings in which like numerals refer to like parts.
REFERENCES:
patent: 5703556 (1997-12-01), Kikuta et al.
patent: 5870012 (1999-02-01), Sakamaki et al.
patent: 8-93616 (1996-04-01), None
patent: 9-115749 (1997-05-01), None
patent: 9-246071 (1997-09-01), None
patent: 10-223464 (1998-08-01), None
patent: 11-74139 (1999-03-01), None
Adachi Norihiro
Kawai Kazuhide
Osuka Kazutoyo
Shimoide Yoshihiro
Denso Corporation
Gellner Michael L.
Mai Anh
Nixon & Vanderhye PC
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