Plug cap

Details Plug cap Plug cap

1999-09-09

2001-05-01

Paumen, Gary F. (Department: 2833)

Electrical connectors

Having spark or glow plug cover

Reexamination Certificate

active

06224400

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plug cap for connecting to a spark plug of an internal combustion engine, and more particularly relates to a plug cap configuration which induces less wear of a threaded terminal on the spark plug, and has elements which are resistant to wear.
2. Background Art
Utility Model Laid-Open Publication No. Sho. 63-60288 “Plug Cap” and Utility Model Laid-Open Publication No. Sho. 63-87277 “Attaching Structure for Plug Cap with Integrated Ignition Coil of an Internal Combustion Engine” show conventional plug cap configurations. In FIG. 5 of publication No. 63-60288, a cylindrical member 15 is fixed to a terminal 4a by a pin member 17 meshing with the terminal 4a. A threaded terminal is shown in FIG. 4. In FIG. 3 of publication No. 63-87277 a plug cap is shown which has an integrated ignition coil IC built into a plug cap C. The plug cap C is therefore heavy and the load is borne by a shroud 4 via a seal bar S.
FIGS.
15
(
a
) to (
c
) are views describing the operation of a conventional pin member. FIG.
15
(
a
) shows a configuration having a straight section
103
of a spring pin housed in a groove
102
of a cylindrical member
101
. Member
101
meshes with a screw thread
105
on the terminal side. FIG.
15
(
b
) is a view showing the operation when beginning extraction of the cylindrical member
101
. When the cylindrical member
101
is moved upwards, a force in the direction of arrow A acts on the straight section
103
. This force is orthogonal to an inclined surface of the screw thread
105
, and when the force changes direction to that of direction of arrow B, a horizontal component of this force is generated in the direction of arrow C. The straight section
103
then pushes out towards the left due to the horizontal component of the force in the direction of arrow C. As a result, as shown in FIG.
15
(
c
), the straight section
103
moves as far as the top of the screw thread
105
, and the cylindrical member
101
is withdrawn in the direction of the vertically extending arrow.
FIGS.
16
(
a
) to
16
(
c
) are views showing difficulties arising in the use of conventional plug caps. FIG.
16
(
a
) shows depressions
106
that are generated by the hard straight section
103
wearing upon the relatively soft screw thread
105
during long periods of use. As shown in FIG.
16
(
b
), when it is intended to withdraw the cylindrical member
101
upwards, the straight section
103
cannot be moved horizontally (in the direction X in the drawings) by applying force to the straight section
103
in the direction of arrow A, due to the depth of the wear-induced depressions
106
.
FIG.
16
(
c
) is an enlarged view of FIG.
16
(
b
). In this figure it can be seen that when the center of the straight section
103
reaches, for example, a point P
2
which is further inward than point P
1
, the straight section
103
cannot now be pushed horizontally. Conversely, if the center of the straight section
103
is further left of or outward from point P
1
, lateral movement is still possible. However, after long periods of use, it is possible that the center of the straight section
103
will reach the point P
2
inward from the point P
1
. Regarding this point, in the case of a plug cap integrally fitted with an ignition coil as in Publication No. Sho. 63-87277, in order to fix the plug cap to the terminal in a reliable manner, it is necessary to make the spring force of the pin member large. When the spring force is large, the wear of the screw threads occurs after a relatively short period of time.
In the above, a description is given of wear on the side of the threaded terminal of the spark plug, but the same also occurs on the side of the cylindrical member of the plug cap.
FIGS.
17
(
a
) and
17
(
b
) are views showing examples of deficiencies in conventional cylindrical members. FIG.
17
(
a
) shows that the width of the groove
102
is substantially the same as the diameter of the straight section
103
. This straight section
103
moves up and down so as to knock against an upper sidewall
107
and a lower sidewall
108
during vibration. As a result, as shown in FIG.
17
(
b
), the sides of the relatively soft sidewalls
107
and
108
are deformed and a so-called tadpole shape is formed. The straight section
103
meshes as a result of movement to the right in the drawings and is released as a result of movement to the left. Movement to the left is therefore indispensable if the cylindrical member
101
is to be detached.
In FIG.
17
(
b
), as the straight section
103
is inserted into a concave part
109
, it is necessary to apply quite a large force in order to cause movement in the direction of the arrow
3
. The operability of the configuration of FIG.
17
(
a
) is therefore low and this configuration is not preferred. As shown by these illustrations, conventional configurations are seen to develop a considerable reduction in operability after extended use.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to prevent the occurrence of depressions at the screw threads on the terminal side.
It is further an object of the present invention to prevent the occurrence of depressions in a groove on the side of a cylindrical section.
It is an additional object of the present invention to prevent a reduction in operability in detaching the plug cap.
In order to achieve the aforementioned objects, a plug cap attachment method is disclosed utilizing a plug cap having a conductive section covering the threaded terminal, a groove cut to a fixed depth from the outer surface of a cylindrical section towards the center thereof, and an alignment section of an attachment element installed at the groove. The attachment element may be a spring pin having a substantially straight section serving as the alignment section. The straight portion of the spring pin meshes with the threaded terminal, with the threaded terminal located on a spark plug installed in an internal combustion engine. The spark plug is typically installed in a manner substantially parallel to the cylinder axis of an ignition chamber. When the plug cap is connected to the spark plug, the straight section of the spring pin lies in a plane orthogonal to the axis of a crankshaft of the internal combustion engine.
Vibrations of the internal combustion engine mainly occur in a plane orthogonal to the axis of the crankshaft. Therefore, when the straight section of the spring pin is arranged in this plane, the threaded terminal is arranged in parallel with this surface. External force therefore operates in each direction in this plane but external forces do not generally operate in directions orthogonal to this plane. Because the external force does not operate in a direction orthogonal to this plane, there is no knocking of the screw thread and no danger of depressions being created at the screw thread.
The internal combustion engine can be mounted on a vehicle in such a manner that the crankshaft extends across the width of the vehicle and the cylinders are above the axis of the crankshaft. A main direction of vibration of the internal combustion engine is therefore substantially orthogonal with the cylinder axis and the axis of the crankshaft, and the straight section of the spring pin extends in parallel with the main direction of vibration. Because the straight section is parallel to the direction of vibration, external force does not operate in a direction orthogonal to the pin axis, and there is no danger of knocking at the screw thread or at sidewall grooves. There is accordingly no danger of depressions occurring at the screw thread or groove sidewalls.
The main direction of vibration of the internal combustion engine is typically in a direction from the front to the back of the vehicle, the cylinder axis of this internal combustion engine being substantially vertical and the straight section of the spring pin extending substantially in a direction from the front to the back of the vehicle.
In addition to ther

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