DEVICE FOR PREVENTING RADIO FREQUENCY INTERFERENCE FROM SPARK PLUG

DISPOSITIF POUR LA PREVENTION DES PARASITES RADIO ENGENDREES POUR LES BOUGIES D'ALLUMAGE

English Abstract

ABSTRACT OF THE DISCLOSURE:
A device for preventing radio frequency inter-
ference generated by spark plug of internal combustion
engines. The device includes a cover member adapted to
cover at least a part of the high-voltage portion of
the spark plug such as high-tension cord together with
the end of the plug connected to the cord. The cover
member is made of a highly soft, flexible and electrically
conductive rubber material (high molecular compound).
The cover member is grounded through a grounding line
to the body of the engine. This device is suitable for
use in machines having limited space for mounting the
radio frequency interference prevention device, such as
chain saw having an internal combustion engine.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A device for preventing radio frequency inter-
ference from spark plug including a high temperature base
portion and a high voltage portion remote from the base
portion for spark ignition type internal combustion engine,
comprising a cover member made of a soft, flexible and
electrically conductive rubbery high molecular compound,
wherein:
(a) said cover member fits tightly around at
least a part of the high voltage portion of the spark plug;
(b) said cover member is spaced from the
high temperature base portion;
(c) a grounding line is provided, said
grounding line being conductively connected to the engine
and to said cover member at a point remote from the spark
plug and disposed at a high tension connecting cord;
(d) said cover member fits tightly about
the spark plug and about the cord in watertight fashion.
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Description

1 BACKGROUND OF THE INVENTION
The present invention relates to a device for
preventing radio frequency interference from a spark plug
of spark ignition type internal combustion engine.
~arious devices have been proposed and used for
preventing radio frequency interference from spark plug
of internal combustion engines. In the case of engines
of automobiles, motorcycles and the llke, there are
comparatively large spaces for accomodating such devices,
so that the shape and size of the device have large freedom
of choîce. In the case of engines mounted on portable
working machines such as chain saws, the shape and size
of the device for preventing the radio frequency inter-
ference are impractically limited due to restriction in
the space and weight. In addition, there are various
problems such as contact with human body~ wetting by
water or moisture, and so on.
SUMMAR~ O~ THE IN~ENTI~N
Accordinly, an object of the invention is to
provide a device for preventing radio frequency interference
from spark plugs of spark ignition type internal combus-
tion engines, capable of eliminating the above-described
problems of the prior art.
To this end, according to the invention,

1 there is provided a device for preventing radio frequency
interference from spark plug of internal combustion
engines in which a cover member made from an electrically
conductive high molecular compound such as of rubbery
material is used in place of the conventional cover
member which is usually made of a metal gauze or the like
material having a high electric conductivity. Thls cover
member, due to its flexibility and elasticity, is quite
easy to attach and is never broken nor injure the human
body when it happens to come into contact with the human
body. This cover member is effective also in protecting
the protecting cap of the spark plug to prevent secular
change or deterioration of the latter. The flexibility
and elasticity also serve to closely fit the cover member
to the shape of the object or the shape of the space
therearound, while preventing water or moisture coming
to the inside thereof. Thus, the present invention
provides a highly practical and safe device for preventing
radio frequency interference from spark plugs of internal
combustion engines.
The above and other ob,jects, as well a~ a,dvantage-
ous ~eatures o~ the invention will become clear from
the following description of the preferred embodiments
taken in conjunction with the accompanying drawin~s.
BRIEF DESCRIPTION OF THE DRAWINGS:
The accompanying drawings show an embodiment
in which:

1 Fig. 1 is a side elevational view of a chain
S 2W; and
Fig. 2 is a sectional view of an essential part
of-a device for preventing radio frequency interference
in accordance with an embodiment of the inven~ion.
DESCRIPTION OF THE PREFERRED EMBODIMENT:
A preferred embodiment of the invention will be
described hereinunder with reference to the accompanying
drawings. This embodiment is applied to a spark ignition
type internal combustion engine mounted on a chain saw.
The engine has a substantially horizontally arranged
cylinder with a spark plug projecting rearwardly toward--
a rear handle of the chain saw. In this type of chain
saw, there is a :Large possibility of injury by contacting
the finger of the right hand of the operator with the spark
plug, though the latter is electrically insulated,-because
the operator grips the rear handle with his right hand
and manipulates a throttle lever of the engine with
suitable ~inger of his right hand. Similar problem is
experienced also in the chain saws having a vertical
cylinder. In this case, the accidental contact tends
to occur between the left hand flnger and the spark plug
positioned in the vicinity of the front handle.
It is highly desirable that the danger of
contact of fingers with the spark plug, as well as leak
of radio-frequency electric wave due to deterioration of
the plug cap or high-tension cord, be completely eliminated.
- 3 --

1 The chain saw 1 has the engine, front handle 3 3
rear handle 4 and a saw unit 5. The engine has a cylinder
2 disposed substantially horizontally to direct the
cylinder head rearwardly, so that the spark plug 6 is
projected into the space defined by the rear handle 4.
The spark plug 6 is electrically coupled to a high tension
cord (high voltage line3 8 extendi~g through a cap 7.
A throttle trigger 9 for controlling the engine
and other controlling parts are arranged in the vicinity
of the rear handle 4 which is adapted to be held by the
right hand of the operator. In consequence~ the fingers
of the right hand of the operator are positioned danger-
ously close ~o the spark plug 6. In
order to diminish as much as possible the amount of
projection of the spark plug 6 into the space, it is
possible to mount the spark plug 6 at an inclination to
the axis of the cylinder. This countermeasure, however,
cannot eliminate the leak of high-voltage current not
only through the fingers contacting the spark plug 6
but also directly to the body of the chain saw and, hence,
to the ground. This phenomenon is quite dangerous and
should be avoided by all means.
In the illustrated embodiment of the invention,
a cover member 10 is formed to have a size and shape
suitable for covering at least a part of the cap 7 of
the spark plug 6 and at least a part of the high-tension
cord 8 to cover and insulate the high-voltage circuit for
the sp rk plug 6 as much as possible. The cover member
-- 4 --
.,~

S,.3~
1 10 is made from a highly soft, flexible and electrically
conductive rubber material (high molecular compound).
As will be seen from Fig. 2, the spark
plug 6 has a cap 7 which in turn is protected by a cap
protecting cover 17 fitting thereon. The high-tension
cord 8 is extended through the cap 7. The most part of
the thus exposed high-voltage circuit is covered by the
cover member 10 made of the soft, flexible and electrical-
ly conductive rubber material (high molecular compound).
The cover member 10 has a grounding portion grounded to
the body of the chain saw 1 through a grounding line 11.
Since the soft and flexible material of the cover member
10 makes a tight fit around the parts covered by the
cover member 10, it effectively prevents ambient water
and mois-ture from penetrating inside the cover member 10.