Note: Descriptions are shown in the official language in which they were submitted.
* * * * * * *
The subject invention is directed to an ignition
distributor rotor and, more specifically, to a radio frequency
interference suppressing ignition distributor rotor.
Various studies have shown that one of the sources of
motor vehicle radio frequency interference radiation is the
breakdown of the distributor gap between the distributor rotor
segment output tip surface and each of the circumferentially
disposed distributor output terminals. Laboratory observations
indicate that the radio frequency interference generated across
this distributor gap is substantially reduced with a reduction
of distributor gap breakdown voltage. These laboratory observa-
tions further indicate that excessive radio frequency interference
radiation is produced when the distributor gap breakdown voltage
exceeds approximately 12 kilovolts. Therefore, an ignition dis-
tributor rotor including an arrangement which substantially re-
duces the distributor gap breakdown voltage is desirable.
- ,................... .
~.
.""'1"' . :' ' ' ' '~ "'' ' ' " ':- ~ ' ." .' " ' '' ~ ' ' :: ' ' ' ' ' ' . ' ' : . . . '
10~ S6
It is, therefore, an object of this invention to .
provide an improved ignition distributor rotor. .- :
It is another object of this invention to provide : ~.
an improved ignition distributor rotor that substantially reduces
distributor gap radio frequency interference radiation. . :
It is a further object of this invention to provide an ~ ~
improved ignition distributor rotor having a layer of dielectric .
material secured to at least a portion of the longitudinal ..
surface area of the rotor segment in close proximity to the rotor . :
10 segment output tip surface. .:
In accordance with this invention, a radio fre~uency
interference suppressing ignition dis~ributor rotor is provided :
wherein a layer of silicone rubber dielectric material is secured
to at least a portion of the longitudinal surface area of the
rotor segment in close proximity to the rotor segment output tip
surface~
For a better understanding of the present invention,
together with additional objects, advantages and features there- :
of, reference is made to the following description and accompany-
ing drawing in which:
FIGURE 1 is a vertical section view of a portion of an
ignition distributor showing the distributor rotor of this in-
vention mounted therein. ;
FIGURE 2 is a top view of the distributor rotor of ;-.
this invention showing, in addition, the relationship between .-.
the rotor segment output tip surface and one of the distr~lbutor ~.
output terminals;
FIGURE 3 is a section view of FIGURE 2 taken along .;
line 3-3 and looking in the direction of the arrows; and
FIGURE 4 is a perspective view of a portion of the
distributor rotor of this invention. .
~080~5G
In the several FIGURES of the drawing, like elements
have been assigned like numerals of reference.
As is well known in the automotive art, the ignition
distributor rotor 10, FIGURE 1, is rotated by a driving shaft 11,
usually gear-coupled to the camshaft of the associated internal ~-
combustion engine, within a distributor cap 12 having a center
input terminal 13, to which is connected one end of the associ-
ated ignition coil secondary winding and a plurality of output
terminals, one of which is shown at 15, circumferentially dis-
posed about the rotor 10 axis of rotation to which the engine
spark plugs are connected through respective spark plug leads in
a manner well known in the automotive art. Although only one
distributor output terminal is shown in FIGURE 1, in which the
distributor cap 12 is illustrated in cross-section, it is to be
specifically understood that an output terminal is provided for
each of the engine spark plugs and that they are circumferenti-
ally disposed about the center input terminal in a manner well
known in the automotive art.
The ignition distributor rotor of this invention com-
prises a body member 20 of an electrical insulating material
,,: . . .
adapted to engage and be rotated about an axis of rotation bydriving shaft 11 and a rotor segment 21 of an electrically con-
ductive material such as copper supported by body member 20.
Rotor segment 21 extends in a direction toward and terminates
radially inwardly from the circumferentially disposed distributor
output terminals. The cross-section surface area of rotor segment
21 at the extremity thereof nearest the circumferentially disposed ~
distributor output terminals defines an output tip surface 21a ~ ;
that extends substantially parallel to the axis of rotation of
30 body member 20 and which, while ro-tor segment 21 is rotated with -~
body member 20, traces a circular path radially inwardly from the
'" ' ' ' 1 '
3 -
-- ~0~0~56
circumferentially disposed distributor output terminals by a
predetermined arc gap 22. In the automotive art, the arc gap
corresponding to arc gap 22 is usually called the "distributor
gap" and will hereinafter be so referred toO Without intention
or inference of a limitation thereto, rotor segment 21 is illus-
trated in the drawing as being of a rectangular cross-section
having opposite top and bottom flat face surfaces 21b and 21c,
FIGURE 3, and opposite edge surfaces 21d and 21e, FIGURE 4. With
this embodiment, the top and bottom flat face surfaces 21b and
21c define, at the extremities thereof nearest the circumferen-
tially disposed distributor output terminals, the top and bottom
edge boundaries of output tip surface 21a that extends sub- `
stantially parallel to the axis of rotation of body member 20. `
Rotor segment 21 may he placed in electrical circuit
contact with center electrode 13 through a contact member 30 of
an electrically conductive material such as copper or stainless
steel. Contact member 30 is an intimate electrical contact with
rotor segment 21 along adjacent surfaces of both located beneath -
a retaining member 31 and is arranged to be also in electrical
20 contact with center input terminal 13 of distributor cap 12. ;
Alternatively, rotor segment 21 may be of a sufficient length to
electrically contact center input terminal 13. In a practical
application, the electrical insulating material of which body
member 20 is made is a 30% glass-reinforced thermoplastic poly-
ester molding material. Body member 20 may be secured to the
distributor centrifugal weight base, not shown, by screws, one
of which is illustrated in FIGURE 1 and referenced by the numeral ~;
32. As the distributor centrifugal weight base is rotated by
shaft 11 in a manner weIl known in the automotive art, body member
20 is rotated therewith about a vertical axis of rotation as
viewing FIGURE 1. One ex~mple of an ignition distributor with
~8~056
which the distributor rotor of this invention may be used is
described in United States patent No. 3,923,028, Campbell et al,
which issued December 2, 1975 and is assigned to the same assignee
as is this application. It is to be specifically understood,
however, that any other arrangement through which body member 20
is adapted to engage and be rotated by driving shaft 11 may be
employed without departing from the spirit of this invention.
In the actual embodiment illustrated in the drawing,
contact member 3~ is shown to be an elongated member of an elec-
trically conductive material such as copper or stainless steel
in intimate electrical contact with rotor segment 21 and having
one end thereof in electrical contact with center input terminal
13 of distributor cap 12. With this arrangement, the ignition
spark potential produced by the secondary winding of the associ-
ated ignition coil may be delivered to successive ones of the
circumferentially disposed distributor ou-tput terminals as rotor
body member 20 is rotated by shaft 11 in timed relationship with -~
an associated internal combustion engine, in a manner well known
in the automotive art. This circuit may be traced through input
terminal 13, contact member 30, rotor segment 21 and the distri-
butor gap 22 between the rotor segment 21 output tip surface 21a
and each of the distributor output terminals. The distributor
gap 22 is best seen in FIG~RES 1, 2 and 3 of the drawing. ~;
As has been previously brought out, the higher the
: . . :,
voltage required to break down the distributor gap, the higher
is the radio frequency interference radiation. Consequently, ~;
one way of reducing the distributor gap radio frequency inter-
. : .:- .
ference radiation is to reduce the magnitude of the voltage re-
quired to break down the distributor gap.
As it is necessary that free electrons be provided to
initiate an arc across the distributor gap and since the number
, '~':'' '
...: , .'
.. ~.. ..... .
~L08~56
of free electrons provided is determined by the available charge
or the electric field intensity, one way of reducing the distri-
butor gap breakdown voltage is to provide a higher electric field
intensity in the vicinity of the distributor gap. In this regard,
actual observations show that the distributor gap breakdown
voltage is inversely proportional to the electric field intensity,
the greater the electrical field intensity the lower the breakdown
voltage. To increase the electric field intensity at the dis-
tributor gap, a layer of silicone rubber dielectric material 40
is secured to at least a portion of the longitudinal surface area
of rotor segment 21 and located in close proximity to the rotor
segment 21 output tip surface 21a. The interface between the
layer o~ silicone rubber dielectric material 40 and the metal of
rotor segment 21 intensifies the electric field in the vicinity
of the distributor gap 22. This localized intensified electric ~
field at the silicone rubber dielectric layer-rotor segment metal -
interface enhances electron discharge from the metal of rotor
segment 21 for the reason that this intensified electric field
produces a local corona discharge. The radiation resulting from
this local corona discharge causes electrons to be emitted into
the distributor gap. Upon the initiation of emission of elec-
krons into the distributor gap, the effect avalanches, a con-
dition which results in a significantly reduced distributor gap
breakdown voltage. It may be noted that, since the emission of
electrons from the metal of the rotor segment 21 is required to
initiate the distributor gap discharge, rotor segment 21 must be
negatively polarized. Furthermore, the field intensification at
the interface between the layer of silicone rubber dielectric
material 40 and the metal of the rotor segment 21 is directly
proportional to the dielectric constant of the silicone rubber
dielectric material employed. Actual observations indicate that `i~
- - :
056
the silicone rubber dielectric material should have a minimum
dielectric constant of the order of 4. Further, actual obser-
vations indicate that the terminating edge of the layer of sili- -
cone rubber dielectric material nearest the rotor segment 21
output tip surface 21a should be within a range of 0" to .040"
radially inwardly from output tip surface 21a. In an actual
embodiment, the silicone rubber dielectric material employed is
a commercially available silicone rubber dielectric material
marketed by the General Electric Company under the designation
10 RTV 102, White. This material has a dielectric constant of -
approximately 4.7. In this actual embodiment with a distributor
rotor of the type illustrated in the drawing, the breakdown volt-
age across a 3 millimeter distributor gap is reduced from 20 kilo-
volts to 8 kilovolts. Actual observations also indicate that it
is extremely important that the layer of silicone rubber dielectric
material not extend over any portion of the rotor segment 21 out-
put tip surface 21a and, further, that the silicone rubber di-
electric material not extend beyond the edge of the rotor segment
21 output tip surface 21a as both of these conditions result in
intolerable "in car" FM radio receiver noise.
Although the layer of silicone rubber dielectric
material 40 is shown in the drawing to be secured to the top flat
face surface 21b of rotor segment 21, it is to be specifically ;
understood that this layer of silicone rubber dielectric material -
may be secured to the bottom flat face surface 21c or both of ~ -
these surfaces so long that it does not extend beyond nor cover
any portion of output tip surface 21a. Further, the layer of
silicone rubber may be employed with rotor segments having cross-
sections other than rectangular.
While a preferred embodiment of the present invention
has been shown and described, it will be obvious to those qkilled
... , ,. . . , , , :
., ,, . : . . .
5~
in the art that various modifications and substitutions may be ~ :
made without departing from the spirit of the invention which is
to be limited only within the scope of the appended claims. ~
' ' .' . .
"...~
~,. . ''
''' ~ ' ;''
"~ ~, ' ''"
:', ,; ', :' ' '
~ '
.~.,. ;~; ~. .
,
:":, ::'
'`''.,'`'
' - :
: ~ ' :':
"',' '' '."
., . ,, ",
8 ~.
