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Патент USA US2108635

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Feb. 15, 1938.
Filed May 14, 1929
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j 2,108,635
Patented Feb. 15, 1938
Charles B. Aiken, New'York, n.1, and Thomas
Durfce, East Orange, N. J., assl‘gnors to Bell
Telephone Laboratories, Incorporated, New
, York, N. Y., a corporation of New York
Application may 14, 1929, Serial No. 362,940
2 Claims.
The present: invention relates to reduction of
interference in signaling'appal‘atus arising from
the ignition system of a gas engine or similar
source. - More speci?cally the invention relates
5 to a ‘means for suitably electrically shielding the
ignition system, including the spark plug to re
duce disturbances in adjacently located signaling
apparatus suchas a radio transmitter or receiver.
The invention has particular application to
10 airplane motor ignition systems, but is applicable
also to similar uses where practically complete
. shielding is to be obtained.
_ An object of the present invention~ is to pro
(01. 123-189)
In‘ the drawing Fig. 1 shows in simple, diagram
matic form the ‘essentials of a typical ignition,
wiring system, Fig. 2 shows a part sectional view
of a shielded cable and spark plug according to
this invention, Fig. 3 is a similar view of a modi- 5
?ed construction according - to the invention,
and Fig. 4 is a perspective view showing the con
struction of the clamping member of Fig. 3.
In Fig. 1 only so much of the ignition system
isshown as is necessary to an undertsanding of 10
the shielding requirements. The high-tension
magneto l supplies, the requisite high voltage cur_
rent to the several ignition leads 2, 3, 4 etc., in
vide shielding which is adequate from the stand
15 point of protecting signaling apparatus from dis
turbances and which will stand up for inde?nitely
long periods .of time under any and all service
succession, of which there may be any number de
pending on the type of motor. One side of all 15,
of the ignition circuits in common is formedby
the ground connection 5 which may be the en
gine frame or chassis. Each lead 2, 3, 4 etc. ex
Shielding which'is adequate to suppress dis
tends to a motor cylinder, only one of which is
20 turbances. inthe radio sets must extend to the indicated, at 6. The spark plug 1 'in each cylin- 20
entire ignition system including the spark plugs der of the motor may be a commercial type of
themselves. It is ,a comparatively'simple matter .. plug ofany suitable make or design. The lead 4
.to shield the ignition system from the magneto is shown as extending to the plug 1' and both the
to the spark plug since this may be done by-com— _ lead and the plug are covered over with a cop
25 pletely covering the high tension circuit with - per braid sheath which is kepth at ground poten- 25
a grounded'metal shield in the form of a metal tial by contact with the magneto casing and the
tube or .a screen composed, for example, of
braided copper wire.
‘cylinder of the motor as well as ground con
nections at several other points (not shown)
The problem which has presented great diffi
30 culty in the past has been the provision of
along the sheath.
The leads 2, 3, 4 etc. each consists of a rubber- 30
shielding for the spark plugs which would be
covered cable having a single, usually stranded,
adequate for reducing disturbances and at the
copper conductor at the center. Between this
same time would not in any way impair the
operation of the motor even after long periods
35 of use and under adverse weather conditions.
While it has been recognized for years that
radio interference on an airplane could be re
conductor and the grounded sheath a high poten
tial exists, which must be carried to and ap
plied across the spark terminais within the motor 35
‘cylinder. . To accomplish this successfully, the
‘insulation resistance between the copper cable
duced by shielding the ignition system attempts - and the grounded sheath should be maintained
to apply such shielding (have resulted in ignition at all times at a high value.
A description of the shielded plug construc- 40
40 failures in so'"many instances that appreheni
sions have‘ been raised in the minds of aviators tion of the invention will now be'given in con
and manufacturers of engines and airplanes as nection with Fig. 2. The plug itself is shown as
to the reliability of this method oft-reducing in
vcomprising a threaded base Ill, an apron ll,
Applicants have devised a shielded spark plug
. construction which has proved successful and de
pendable in service under extremely adverse
weather conditions both in long, continuous ?y
ing and what is even more trying, in short ?ights
I50"in wet weather ‘with alternate heating and‘cool
ing of the motor.
The construction constituting the present in-,
hexagonal assembly nut i2, insulator l3, and ter
minal it. 'As stated, the plug itself "may be a 45
commercial type of any suitable design.
“A hollow insulating cylinder l5, open at the
lower end, is placed over the terminal l4 and ex
tends well down over the insulator I3. The lower
edge of the cylinder l5 may be beveled, as shown. 50
This cylinder is preferably made ,of a ceramic
productv similar to porcelain, known as “iso
vention will now be described indetail in con
lantite", a commercial insulating product of the
nection with the attached drawing forming part ‘ lsolantite Company of America, located at Belle
55 of this speci?cation.
ville, N‘. J. This material is preferred because 55
or its high ‘insulation resistance, mechanical
the high tension core at this point keeps the insu-l
' strength and the fact that it can be easily ma‘
lation resistance high. Also a ?lm of moisture
chined before ?ring. Any other suitable insula
that might form over the surface of the rubber I‘
tion such as porcelain,‘ a phenolic condensation or the outside of insulator I5 is rendered harmless
product such as bakellte, or the like may be used, . by the spacing between any exposed high tension 5
. part (I!) and the shield. Protection against con-
The cylinder l5'has an aperture atthe top to
admit the rubber-covered cable l6 of the shielded
connecting cable 4. The rubber insulation is
10 shown in section at I‘! and the copper core at’ l8. .
The latter is secured to the spring clip I9 as by
passing through an aperture in the clip and be
ing soldered to the metal of the clip. The clip
engages the terminal H or the plug and makes
15 good electrical contact therewith.
The internal
diameter of cylinder I5 is such that clip I! can
not be spread far enough to disengage terminal
duction along the'path 34 may be further guarded
against by ?lling the space between cable l6 and
aperture wall in insulator II with rubber cement.
These facts; particularly the fact that no ground
ed metal close to the outer surface of the rubber
insulation becomes hot, make for ‘long life and
reliable service.
' '
Instead of securing the braided. shield' to‘ the »
base or the plug by wrapping wire around the
shield as shown in Fig.1 a clamp of any suitable
design such as a “hose" clamp may be employed.
A special design of combined clamp and shield
I 4 when the cylinder i5 is once in place. '
The copper braid covering 2| over the cable member is illustrated in Figs. 3 and 4.
20 4 is spread as it approaches the plug and is drawn
The construction shown in Fig. 3 may be iden
over the cylinder I5 and brought down-into con ' tical-with that in Fig. i so far as concerns the
tact with the base of the plug. It is there se
spark plug III, II,_ l2, l2 and M, the isolantite
cured in place. in any suitable manner as by pass— cylinder- l5 and the disposition of the high ten
ing a few turns of wire‘!!! around it. A clamp sion cable I6 and spring clip l9. _ _
25 4’ holds theshield 2| securely around the cable
After the cable I‘, clip I! and cylinder Ii have
It at the point where the shield begins to spread. ' been placed in position as shown in Fig. 3, how
To assemble the plug and shield, the braided
covering 2| is drawn back over the cable l8
which is then cut to the proper length and se
30 cured to spring clip l9 after ?rst being passed
through" the aperture in the insulator IS. The
latter is‘ pushed upward on the cable l6 far
enough to enable clip l9'to be placed on terminal
14. Then cylinder I5 is dropped over the plug
35 until its lower edge engages the plug. ' The braid
ed shielding is now- brought over the whole and
secured'in the position shown, by wire 20.
ever, the cylinder is engaged and held ?rmly in
‘place by the split sleeve 24 which is provided with‘ :
screw clamping means indicated at 25 and 26 for
tightening down the sleeve on the cylinder II and 30
the hexagonal portiongéihe spark plug base. In ’
assembling, the split
ve 24 will have ‘been
placed loosely in position before ‘the clip I 8 and
cylinder ii are moved into place. After these
parts'have been positioned, the sleeve is made to
grasp ?rmly the cylinder II" and the plug base by
tightening down on screws 25 and 26. The con
struction of the split sleeve is shown more fully
structure is that the top of the struc'urevwhere in Fig. 4.
40 the high tension lead is brought in ‘remains cool
Aiter these parts. have been secured in place‘
due to the heat radiation from the copper braid. ' the braided sheathv 2| is drawn down over the
Another important point is that the lead It outside of the sleeve 24 and is served with wire
passes through an insulator (l5) instead 01 29 to hold‘the braiding in place. To facilitate
through a vgrounded metal shield. A contribut
45 ing factor also is the good contact- between the ' this a bulge is made at ‘I. in the sleeve 24. In
stead of using a sheathing or“ wire 29 ronthis
cable .core and the terminal II, a feature often Purpose any suitable clamping means such as a
overlooked in prior art constructions. All of split ring may be used. The sleeve 24 is made
thesefeatures cooperate to ‘give reliable opera
approximately hexagonal at ‘the base in order to
tion. Heat soon deteriorates rubberdinsulation.
50 Where the cable passes through a tight ?tting conform to the plug base and also‘projects under 50
the edge 01' the hexagonal base portion. -Instead
metal which becomes hot applicants haveob
of- brlngipg thebralded sheath over the outside -
An important effect present in applicants’
served complete failure or at least a great reduc
tion'in insulation resistance. The presence of a
55 spark causes rapid deterioration of rubber in
sulation, probably due to the production of ozone
which attacks the rubber.
tated by the cooling, the spring temper being
retained inde?nitely.
in place by tightening screws 2' and 26.
It will be understood that the construction may
This is overcome vin , be varied widely within the scope of the append- . -
applicants’ device by the soldered connection and
spring clip. The use of the s ring clip is facili
or. the sleeve 24, it may be placed inside between '
sleeve 24 and insulator II and securely clamped
Too great cooling is not advantageous; The,
sparking terminals and the lower end of the plug .
generally must be hot in order to prevent ‘ac
65 cumulation of soot or carbon which would par
tiallyshunt the gap. The construction must be
such as to keep the sparking end hot and the
opposite or top end ,su?lciently cool for reasons
above given. In applicants’ structure, the top
70 portion through which the cable passes never be
comes too hot to be grasped by the bare .hand,
even after hours of ?ying.
The spreading of the shielding braid to pass
over cylinder I515 advantageous in two ways. It
< promotes cooling. am1 the greatenspacing from
ed claims without. departing from the spirit of the
invention, the forms above described being illus
trative rather than‘ limiting.
'Whatls claimed is:
1. In a shield construction for a spark plug, a
ceramic housing over the Plus terminal and sur-“
roimding the upper portion 01' said plug insulator
having an aperture in its wall for admitting the
‘high-tension lead wire, means inside the housihg
tor'electrlcally cunnectinglthe lead wire to the '
plug terminal, and a metal shield extending over '
theoutslde oi the lead wire and‘ the housing and
contacting with the base of the plug. said ceram 70'
ic housing serving to hold the metal shield away
from ‘the plug terminal and from the high‘ ten-.
sion lead wire and its rubber insulation where the
latter-‘approaches and enters the said aperture.
2. A shield construction for a spark plug com- . 75
2,108,635? .
prising a hollow insulator surrounding the upper
portion of the plug insulator and enclosing the
plug terminal and having an aperture through
sulator, being less than'the expansion width of
said spring clip, and a metallic covering over said
insulator, high tension lead, and the exposed in
sulator portion of the spark plug.
which the high'tension lead extends, and an ex
pansible spring clip carried by the end of said .
high tension lead adapted to engage said plug
terminal, the internal diameter of said hollow in-v
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