Electric lamp and discharge devices – Spark plugs – Plural parallel gaps
Reexamination Certificate
2000-03-20
2002-12-03
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Spark plugs
Plural parallel gaps
C313S137000, C313S135000, C313S141000, C313S142000
Reexamination Certificate
active
06489709
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to spark plugs for internal combustion engines and more particularly to captive spark plug gaskets.
2. Description of the Related Art
A spark plug has a metal shell. The metal shell has a threaded portion for securing the spark plug to a cylinder head of an engine. The spark plug is generally provided with an annular gasket which is so-called a captive spark plug gasket. The gasket is generally formed from an annular metal sheet by bending the metal sheet radially thereof. The gasket is mounted on the metal shell at a location adjacent an inner end of the threaded portion. At a location adjacent the inner end of the threaded portion, the metal shell has a flanged, seat portion. When the threaded portion is screwed into a threaded hole of the cylinder head to cause the gasket to be compressed between the seat portion and the outer surface of the cylinder head around the threaded hole, the gasket provides a seal between the outer surface of the cylinder head around the threaded hole and the seat portion of the metal shell for thereby providing a seal between the threaded portion of the metal shell and the threaded hole.
In this connection, to attain a seal by means of the gasket, it is important to control the tightening torque for screwing the treaded portion into the threaded hole so that a proper compressive force is applied to the gasket. To this end, for each type of spark plug, a recommended tightening torque range for attaining a good seal is fixed.
FIG. 14
shows a relation between tightening torque and compressive deformation &agr; of gasket due to advance or axial movement of the threaded portion, which is exhibited by a prior art gasket. The prior art gasket heretofore used causes, at the initial state of deformation, the compressive force to concentrate at a bent portion or portions thereof and is thus compressed and deformed considerably even when the compressive force is still within a relatively low range and tightening of the spark plug is still at the initial stage. In such a low range, a tightening force necessary for attaining a desired seal can be hardly obtained.
However, when the deformation proceeds further to make smaller the space for allowing further deformation, a larger compressive force is necessitated for further compressive deformation, thus causing the tightening torque to increase abruptly. As shown in
FIG. 14
, in case of the prior art gasket, the recommended tightening torque range for the spark plug, which is indicated by the hatched area, is located on a sharply sloped line portion of the graph where the tightening torque increases sharply or abruptly with increase of deformation. From this, it will be understood that the gasket deformation &agr; range capable of attaining the recommended tightening torque range is quite narrow.
SUMMARY OF THE INVENTION
In recent automotive engines, the lean air-fuel mixture is used increasingly as the restriction on the exhaust emission control becomes severer (i.e., so-called lean-burn engines are used increasingly). As shown in
FIG. 13
, since the lean mixture is low in the ratio of fuel mixed, misfire may possibly be caused in case the mixture is introduced into the combustion chamber K in a certain direction (or in case the intake valve is disposed in a certain position) to cause the flow of the mixture into the spark gap g between the center electrode
203
and the ground electrode
204
to be obstructed by the ground electrode
204
. For this reason, this kind of engine generally takes instructions that the threaded portion
201
a
of the metal shell
201
of the spark plug
200
is screwed into the threaded hole S
1
of the cylinder head SH so as to orient the ground electrode
204
to optimize ignition.
However, when the threaded portion
201
a
is screwed into the threaded hole S
1
to such an extend as to attain a desired seal, the ground electrode
204
is not always oriented to optimize ignition. In this connection, if the threaded portion
201
a
is tightened further or loosened so as to adjust the orientation of the ground electrode
204
, the tightening torque changes to be out of the above described recommended limits since the gasket deformation &agr; range capable of attaining the recommended tightening torque is so narrow. For example, when further tightening causes the tightening torque to become larger beyond the upper limit of the recommended tightening torque range, there is a possibility that the gasket
206
and/or the threaded portion
201
a
of the metal shell
201
is damaged to deteriorate the seal, and in the worst case, part of the metal shell is twisted off from the remaining section. On the contrary, when the threaded portion
201
a
is loosened to cause the tightening torque to become smaller than the lower limit of the recommended range, a desired seal cannot be obtained, thus leading to a trouble of leakage of gas or the like. In the meantime, indicated by reference numeral
202
is an insulator.
It has been proposed, as for example disclosed in Japanese Patent Provisional Publication No. 11-13613, to enable the ground electrode
204
to be oriented to optimize ignition, even if the recommended torque range is so narrow, by making the positional relation between a starting end of the thread of the threaded portion
201
a
and the ground electrode
204
constant. However, this method requires positioning of the ground electrode
204
with respect to the starting end of the thread of the threaded portion
201
a,
thus requiring much labor and longer working time and therefore causing lowered manufacturing efficiency and increased cost.
It is accordingly an object of the present invention to provide a gasket for a threaded element such as a spark plug, which enables to adjust the orientation or circumferential location of a certain reference part of a threaded portion of the threaded element within wide limits, under the condition where a suitable tightening torque is maintained, and accordingly which enables to adjust the orientation of a ground electrode of a spark plug relative to a cylinder head with ease and without causing any problem.
It is a further object of the present invention to provide a spark plug or the like threaded element with a captive gasket of the foregoing character.
To accomplish the above objects, there is provided according to an aspect of the present invention a gasket for a threaded element to be screwed into a threaded hole of a support. The threaded element has a threaded portion and an annular seat portion. The gasket is adapted to be installed on the threaded element and compressed between the seat portion and an outer surface of the support around the threaded hole, when the threaded element is screwed into the threaded hole, to provide a seal between the threaded hole and the seat portion. The gasket is formed from an annular sheet material and in the form of an annular strip of a cross section including a plurality of bent portions. The cross section is made by a plane including a center axis of the gasket and of a such a bent shape as to enable an imaginary reference line which is located on the plane and parallel with the center axis, to cross at least three portions of the cross section. An initial axial size of the gasket is at least 2.5 mm.
The structure for enabling the reference line parallel to the center axis to cross at least two portions of the cross section, means that, when a gasket
70
shown in
FIG. 2
is taken as an example and reference is also made to
FIG. 12A
, the cross section is so shaped as to extend from a portion Sg
1
crossed by the reference line PB to another portion Sg
2
crossed by the reference line PB by way of a turnaround portion DC
1
. When the gasket
70
is deformed yieldingly or plastically in the direction of the center axis O, its deformation is mainly caused by buckling of the above described turnaround portion DC
1
. The structure for enabling the reference line PB to cross at least three portions of
Matsutani Wataru
Teramura Hideki
Berck Kenneth A
NGK Spark Plug Co. Ltd.
Patel Vip
LandOfFree
Captive spark plug gasket does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Captive spark plug gasket, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Captive spark plug gasket will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2949694