Inductor devices – With outer casing or housing
Reexamination Certificate
2003-01-29
2004-10-26
Mai, Anh (Department: 2832)
Inductor devices
With outer casing or housing
C336S092000, C336S096000, C029S602100
Reexamination Certificate
active
06809621
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ignition coil for generating a high voltage that is applied to spark plugs of an internal combustion engine and a method for fabricating the same ignition coil.
BACKGROUND OF THE INVENTION
An internal combustion engine ignition coil (hereinafter, simply referred to as an “ignition coil”) is a device for generating a spark across a gap of a spark plug by producing a high voltage through mutual induction actions of coils. There are several types of ignition coils. For example, there is a stick-type ignition coil adapted to be installed in a plug hole and this stick-type ignition coil has a rod-like core, a cylindrical secondary spool disposed around the outer circumference of the core, a secondary coil wound around the secondary spool, a cylindrical primary spool disposed around the outer circumference of the secondary coil and a primary coil wound around the primary spool. Namely, the core, secondary spool, secondary coil, primary spool and primary coil are disposed coaxially in that order from the inner circumference of the ignition coil. These members are accommodated in a hollow cylindrical case. In addition, in order to secure electric insulation between the respective members and to allow the members to adhere to each other in the case, a resin insulating material is filled in the case.
In this respect, a base resin constituting, in particular, the spool of the primary and secondary spools which is disposed between the primary coil and the secondary coil (the primary spool in the aforesaid conventional example) has conventionally been required to have high electric insulation. This is because, in the case where a failure of insulation occurs to allow the secondary coil side, that is, the high-tension side and the primary coil side, that is, the low-tension side to electrically communicate with each other, there is a risk that a desired voltage cannot be secured on the secondary coil side.
In addition, the base resin constituting, in particular, the spool of the primary and secondary spools which is disposed between the primary coil and the secondary coil has conventionally been required to have a high adhesion to the resin insulating material. This is because the coefficient of linear expansion of the base resin of the spool is different from that of a wire constituting the coil which is wound around the spool, and, due to this, if the adhesion between the resin insulating material filled between the spool and the wire and the base resin of the spool is low, there is a risk that the spool and the resin insulating material may separate from each due to thermal stress. If the spool separates from the resin insulating material, a corona discharge is produced within a space formed by the separation, leading to a risk that electric insulation between the primary coil and the secondary coil cannot be secured.
Thus, the base resin constituting the spool has conventionally been required to be highly insulating and to have high adhesion to the resin insulating material.
In order to satisfy the aforesaid requirements, conventionally used for the base resin of the spool have been polyphenylene ether (PPE), polybutylene terephthalate (PBT), polyethylene terephthalate and the like which are highly insulating and have high adhesion to the resin insulating material.
However, when the spool is formed of a base resin which has a high adhesion to the resin insulating material, the following problems occur. Namely, as the coefficient of linear expansion of the base resin is different from that of the wire constituting the coil, if the ignition coil is used under a thermal cycling environment where the temperature is raised and lowered repeatedly, thermal stress is produced repeatedly in the spool due to the difference in coefficient of linear expansion. This thermal stress so produced can be relaxed only if the spool separates from the resin insulating material. However, the adhesion between the spool and the resin insulating material is made high in order to restrain the separation. Due to this, the thermal stress cannot be relaxed as desired, and there may be incurred the risk that cracks are produced in the spool. Then, if cracks are produced in the spool, the high-tension side and the low-tension side are allowed to electrically communicate with each other, leading to a risk that the desired voltage cannot be secured.
To cope with this, for example, with a conventional ignition coil disclosed in Japanese Unexamined Patent Publication (Kokai) No. 11-111545, as shown in
FIGS. 9A
,
9
B, a separation tape
203
was wound between a spool
200
and a resin insulating material
202
filled on a wire
201
side. The generation of thermal stress attributed to the difference in coefficient of linear expansion between the spool
200
and the resin insulating material
202
in FIG.
9
A and between the spools
200
and
206
and the wire
201
and resin insulating materials
202
,
204
in
FIG. 9B
was restrained by separating the spool
200
from the resin insulating material
202
with the separation tape
203
, whereby the generation of cracks in the spools
200
and
206
was restrained.
In addition, with the conventional ignition coil, in order to restrain the generation of cracks in the spools, a rubber component such as styrene ethylene butene styrene (SEBS) was added to a base resin for the spools. Then, the toughness of the spools was enhanced by the rubber component so added to thereby restrain the generation of cracks in the spools.
Thus, with the conventional ignition coil, in order to suppress the generation of cracks in the spool, a separation tape was wound around the spool or the rubber component was added in the spool, which served not only to increase the production costs of the ignition coil but also to complicate the production process.
Incidentally, the aforesaid problems are attributed to the high adhesion between the base resin constituting the spool and the resin insulating material. To cope with this, if a resin such as polyphenylene sulfide (PPS) introduced in Japanese Unexamined Patent Publication (Kokai) No. 8-339928, which has a low adhesion to the resin insulating material, is used as the base resin, the risk that cracks are produced in the spool will be reduced.
However, when compared with PPE, PBT, and PET, PPS has lower electric insulating properties. Due to this, if PPS is used as the base resin, due to the low adhesion inherent in PPS, there may be a risk that the resin insulating material separates from the spool, and if this occurs, there may be a risk that the insulation breakdown between the high-voltage side and the low-voltage side can be facilitated.
Namely, a slight gap existing between the resin insulating material and the spool may damage the insulation therebetween. Due to this, in the prior art, it was arranged for ignition coils to use, as a base resin for constituting a spool, a resin having a high adhesion to the resin insulating material so that, if unavoidable, there is formed, between the resin insulating material and the spool, as small a gap as possible.
As has been described heretofore, base resins for constituting the spool have conventionally been required to have the high electric insulation and high adhesion to the insulating resin. However, with the high adhesion, cracks are produced in the spool. In contrast, with the low adhesion, the spool and the resin insulating material are made to separate from each other easily.
The inventor of the invention studied the relationship between the combination of the adhesion of the base resin constituting the spool to the resin insulating material and the electric insulation of the base resin and the failure of insulation. As a result, the inventor determined that the failure of insulation can be prevented, without using the separation tape, by using as the base resin for the spool, a resin having a low adhesion to the resin insulating material and high electric insulation.
DISCLOSURE OF THE INVENTION
An ignition coil of the invention was complet
Kawai Kazuhide
Konishi Atsuyuki
Nagata Takashi
Osuka Kazutoyo
Wada Jun-ichi
Denso Corporation
Mai Anh
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