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Патент USA US2405890

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A Aúg. v13, 1946.
w. H. KUNz
Filed May 5, 1944 ¿
Walden _ZZ £21112
i „from/Er
Patented Aug. 13, 1946
Walden H. Kunz, Jackson, Mich., assignor to P. R.
Mallory & Co., Inc., Indianapolis, Ind., a cor
poration of Delaware
Application May 5, 1944, Serial No. 534,216
2 Claims.
(Cl. YY1-242)
This invention relates to continuously variable
inductive tuning devices and has for its object to
provide a device of this type having novel and im
acteristic of the invention are set forth more in
proved details of construction and features of
detail in the claims appended hereto, the nature
and scope of the invention may be better under
stood by referring to the following description,
taken in connection with the accompanying
drawing forming a part thereof, in which a spe
Another object of the invention is to provide an
ciñc embodiment has been set forth for purposes
inductive tuner of the above type having a new
of illustration.
and improved rotary contact member and asso
In the drawing:
ciated control elements which are particularly
Fig. l is a side elevation of a continuously
adapted for use with inductance coils of small 10
variable inductive tuning device embodying the
Various other objects and advantages will be
apparent as the nature of the invention is more
fully disclosed.
Slide-wire variable inductance devices are used 15
Fig. 2 is a longitudinal section taken on the line
2--2 of Fig. l;
Fig. 3 is a transverse section taken on the line
for tuning radio receivers, oscillators and various
3-3 of Fig. 2; and
other electric and electronic instruments and de
vices. Generally, they comprise a bare wire coil
of Fig. 2.
trolley rod slides along the wire of the coil in
electrical contact therewith as the coil is rotated.
The mechanical and electrical requirements of
however, are to be interpreted in accordance with
the state of the art.
The variable inductive tuning device shown in
Fig. 4 is a transverse section taken on line ¿i-fl
In the following description certain specific
wound on a suitable insulating form which is
mounted on a shaft so as to rotate about its axis, 20 terms are used for convenience in referring to the
various details of the invention. These terms,
and a sliding Contact tracking on a stationary
such inductive tuning devices are severe, espe
cially since positive and constant contact must be
maintained for electrical reasons, while at the
same time lightness of contact is required for ease
of tuning and to keep down wear over long periods
of use.
The present invention provides a tuning device
of the foregoing type in which the Wire coil is sta
tionary and in which tuning is effected by rotat
ing the sliding contact member over the convolu
tions of the coil, The Contact itself comprises a
si r~le piece of light spring material having con
tacting nibs at its ends engaging the coil and a
A the drawing comprises a support or end plate Iii
carrying a coil form II of insulating material
such as resin impregnated über. The form is
shown as cylindrical but it is understood that it
may be made conical or frusto-conical if desired.
A bare wire coil I2 is wound on the surface of
form II with adjacent turns spaced from each
other. If desired, the form may be provided with
a shallow groove in which the wire I2 is wound.
ri‘he coil may suitably be made of hard drawn
copper wire plated with silver, and, if desired,
coated with a protective lubricant.
One end I3 of the coil I2 is soldered to a
central Contact portion in sliding engagement
terminal I4 mounted on an insulating block l5
with an axially extending trolley rod which is
adapted to be rotated around the coil. As the
trolîey rod is rotated about the coil, as by means
of a shaft extending axially through the coil, the
which is secured to the end plate I0 by stud iii.
The opposite end of the coil is soldered to a metal
disc I'I fixed to the outer end of the coil form I i.
spring contact slides along the convolutions of
the wire and at the same time slides longitudinally
on the trolley rod, insuring a positive and con
stant contact with a minimum of friction and
Another feature of the invention resides in the
provision of a novel stop mechanism for arresting
the movement of the spring contact at either end
of its travel without exerting any pressure on the
Contact itself, thus eliminating any possibility of
bending or otherwise damaging the contact or the
associated electrical connections.
Although the novel features which are char
The disc I'I carries a bearing sleeve I8 within the
bore I9 of the form II which is connected by a
wire 2B to a second terminal similar to the ter
minal I4. The wire 2€) extends through the bore
I9 and radially through the form II at a point
adjacent the second terminal.
A second bearing sleeve 2| is positioned within
the end of the bore I9 opposite the sleeve I8 and
a rotatable control shaft 22 of insulating mate
rial extends axially through both sleeves and
through the coil form II, one end of said shaft
projecting outwardly beyond end Plate Ill to re
ceive a suitable control knob, while the opposite
end of the shaft extends outwardly of the coil
form past the end disc Il.
A hub 23 is >secured to the inner end of the
shaft 22 by set screw 24; and an arm 25 secured
to hub 23 carries a trolley rod 26 which extends
axially along the side of coil form Il parallel to
the cylindrical surface thereof.
The arm 25 and
trolley rod 25 are composed of suitable conduct
ing material, and between them is secured a fork
posed between the rod 26 and the coil, and my im
proved construction enables this initial adjust
ment to be maintained indefinitely under all con
ditions of use.
While the present invention has been described
herein as carried out in a specific embodiment,
it is not to be limited thereto, but is only to be
restricted in accordance with the spirit and scope
of the appended claims.
What is claimed is:
tact brushes 28 which slide on the metal disc Il
1. A Variable. inductance device comprising in
on the inner end of coil form Il, thereby provid
combination a coil form of circular cross section.
ing a slip ring connection to the end of the coil
a bare helical conductive coil wound thereon, a
rotatable shaft extending axially through said
and to the contact to be desired.
A stop member 29 is slidably mounted on trolley
coil form, a trolley rod carried by said shaft ad
jacent and parallel to said coil form and mounted
rod 26. The stop member 23 is formed of Bake»
lite, ceramic or other suitable insulating material
to be rotated about said coil by said shaft, a con
tact element integrally formed of a single piece
and, in the embodiment illustrated, is of gener
of sheet metal in a substantially symmetrical and
ally tubularl shape with a substantially semi-cir
cular opening intermediate its ends exposing the 20 dynamically balanced shape, the ends of said ele
trolley rod 2t through said opening.
ment being bent into smooth-surfaced grooved
' contact nibs engaging the wire of said coil in the
A sliding contact member 3D, preferably
grooves therein and the mid-portion of said ele
stamped in a single piece from sheet spring metal,
has its central portion bent to form a semi-circu~
ment being bent into a smooth-surfaced trans
verse channel which is concave on the opposite
lar channel 3l which fits within the opening of
>:face of said element from said grooves and en
stop member 29 and engages the trolley rod 25,
gages the trolley rod, said contact element being
while the outer ends of the contact member are
biased to produce smoothly sliding and uniformly
formed to provide narrow channel-shaped nibs
distributed spring pressure against said coil at
32 conforming to and engaging the wire of coil l2.
The nibs 32 rest on the same turn of coil I 2 at 30 said nibs and against said rod at said channel for
movement along said rod when said shaft is ro
spaced points thereon and one nib is slightly
tated, a disc mounted on the inner end of said
twisted or skewed with respect to the other to
coil form, a spring contact arm attached to said
allow for the pitch angle of the helical coil.
trolley rod having sliding contact means with said
It will be evident that as the shaft 22 is ro
tated, «causing trolley rod 26 to rotate about'the 35 disc, and a terminal connected to said disc.
2; A variable inductance device comprising in
cylindrical surface of coil form ll, the nibs 32
combination a coil form of circular cross section,
of contact member 30 slide along the wire i2 and
a bare helical conductive coil wound thereon, an
move the member 3S and stop member 29 length
axially disposed bearing sleeve at each end of said
wise along the trolley rod. The contact member
30 is connected by the trolley rod 26, contact 40 coil form, a shaft extending axially through said
coil form and rotatable in said bearing sleeves, a
spring 2l', contacts 28, disc il and Wire 20 to the
trolley rod carried by said shaft adjacent and par
terminal I4.
allel to said coil formv and mounted to be rotated
In accordance with a feature of the invention,
about said coil by said shaft, a contact element
I provide stop members or lugs 34 and 35 on the
integrally formed of a single piece of sheet metal
cylindrical surface of coil form Il, adjacent op
in a substantially symmetrical and dynamically
posite ends thereof, for engagement with the slid
balanced shape, the ends of said element being
able stop member 29 whenever the trolley rod 25
bent into smooth-surfaced grooved contact nibs
is rotated suiñciently to bring the contact mem
engaging the wire of said coil in the grooves
ber 3l) near either end of the coil l2. The lugs
therein and the mid-portion of said element be
34 and 35 are so positioned that, when the »con
ing bent into a smooth-surfaced transverse chan
tact member 30 reaches a point adjacent the end
nel which is concave on the opposite face of said
of the coil, the leading side of stop member 29 will
element from said grooves and engages the trol
strike against the side of lug 34 or 35, as the case
ley rod, said contact element being biased to pro
may be, and thus prevent further rotation of the
shaped contact spring 2l' having silver alloy con
trolley rod.
duce smoothly sliding and uniformly distributed
A particular advantage of the foregoing con
struction is that the impact of stop member 29
against lugs 34 and 35 is completely isolated from
the delicate spring contact member 30 and there
fore cannot injure said contact member, noi- can
the nibs 32 of the contact member over-run the
ends of the coil or strike against the soldered ends
thereof. The contact member 353 is originally
spring pressure against said coils at said nibs and
against said rod at said channel for movement
along said rod when said shaft is rotated, a disc
integrally formed with the bearing sleeve at the
bent just enough to provide the proper spring
pressure on the nibs when the member is inter
inner end of said coil form, a spring contact arm
attached to said trolley rod having sliding con
tact means with said disc, and a terminal con
nected to said sleeve.
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