U.S. patent number 3,918,020 [Application Number 05/517,490] was granted by the patent office on 1975-11-04 for multi-stage switching apparatus.
This patent grant is currently assigned to Essex International, Inc.. Invention is credited to Gideon A. DuRocher.
United States Patent |
3,918,020 |
DuRocher |
November 4, 1975 |
Multi-stage switching apparatus
Abstract
A multi-stage switching apparatus adapted to make and break an
electrical circuit comprises a first compressible body having a
resistance which varies inversely according to its state of
compression and a second compressible body having a substantially
uniform resistance lower than that of the first body, the two
bodies being so arranged that the first body is compressed prior to
compression of the second body in response to making of the circuit
and is decompressed following decompression of the first body in
response to breaking of the circuit.
Inventors: |
DuRocher; Gideon A. (Mount
Clemens, MI) |
Assignee: |
Essex International, Inc. (Fort
Wayne, IN)
|
Family
ID: |
24060030 |
Appl.
No.: |
05/517,490 |
Filed: |
October 24, 1974 |
Current U.S.
Class: |
338/114; 200/16R;
200/533; 338/100; 338/198; 200/511; 252/511; 338/99; 338/110;
439/810 |
Current CPC
Class: |
H01H
13/12 (20130101); H01H 1/029 (20130101) |
Current International
Class: |
H01H
1/029 (20060101); H01H 1/02 (20060101); H01H
13/12 (20060101); H01c 013/00 () |
Field of
Search: |
;338/99,100,101,110,114,198,217,223,225 ;117/215,216,217,226,227
;335/280 ;252/502,511,518 ;337/382,394 ;339/272R,278C
;200/16R,86R,153LA,159R,264,266 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mayewsky; Volodymyr Y.
Attorney, Agent or Firm: Learman & McCulloch
Claims
I claim:
1. An electrical switch comprising a pair of spaced apart
electrical conductors; switching means; means mounting said
switching means in a position to bridge said conductors; operating
means; and means mounting said operating means for movements
relatively to said switching means for applying and releasing
compressive force to and from said switching means, said switching
means comprising a compressible first body having an electrical
resistance which varies inversely in accordance with the
compressive force applied thereto by said operating means and a
compressible second body having an electrical resistance lower than
that of said first body when both of said bodies are compressed by
said operating means.
2. A switch according to claim 1 wherein said switching means is
interposed between said conductors.
3. A switch according to claim 1 wherein said first and second
bodies occupy positions in which movement of said operating means
in a direction to apply compressive force to said switching means
effects sequential compression of said first and second bodies.
4. A switch according to claim 3 wherein one of said bodies has an
opening extending therethrough and in which the other of said
bodies is accommodated, said one of said bodies being thicker than
the other of said bodies.
5. A switch according to claim 4 wherein said one of said bodies is
said first body.
6. A switch according to claim 4 wherein said one of said bodies is
said second body.
7. A switch according to claim 1 wherein said first and second
bodies are side-by-side.
8. A switch according to claim 7 wherein said first and second
bodies are of substantially uniform thickness.
9. A switch according to claim 7 wherein said first and second
bodies are of different thickness.
10. A switch according to claim 1 wherein one of said bodies has an
opening therein in which the other of said bodies is
accommodated.
11. A switch according to claim 10 wherein said first and second
bodies are of different thicknesses.
12. A switch according to claim 1 wherein said first body has an
opening therein in which said second body is accommodated, said
first body being thicker than said second body.
13. A switch according to claim 1 wherein said second body has an
opening therein in which said first body is accommodated, said
first body being thicker than said second body.
14. A switch according to claim 1 wherein said first body is
non-conductive in the absence of compressive force being applied
thereto.
15. A switch according to claim 14 wherein said second body is
non-conductive in the absence of conductive force being applied
thereto.
16. A switch according to claim 14 wherein said second body is
conductive in the absence of conductive force being applied
thereto.
17. A switch according to claim 1 wherein one of said bodies is
non-conductive in the absence of conductive force being applied
thereto and the other of said bodies is conductive in the absence
of compressive force being applied thereto.
18. A switch according to claim 1 wherein neither of said bodies is
conductive in the absence of compressive force being applied
thereto.
Description
This invention relates to electrical switching apparatus and more
particularly to a switch having at least two compressible,
electrically conductive members which are compressible and
decompressible sequentially. The first member to be compressed has
an electrical resistance which varies inversely according to its
state of compression, whereas the second body has a substantially
uniform resistance which is less than that of the first body.
Sequential compression of the two members, therefore, establishes a
first electrically conductive path through the first body of
diminishing resistance, followed by the establishment of a second
electrically conductive path through the second member and
bypassing of the first member. Upon decompression of the members,
the electrical path through the lower resistance member is broken
first and an electrical path of increasing resistance is
reestablished through the variable resistance member.
In a resistive circuit such as that having incandescent lamps
controlled by a switch, closing of the switch to complete a circuit
to the lamps results in a momentary high inrush current of
extremely high peak value. In a circuit of the kind having an
inductive load controlled by a switch, opening of the switch
results in a momentary, extremely high voltage peak. These
characteristics of resistive and inductive circuits are
objectionable for many well-known reasons. Although these
objectionable characteristics can be minimized by the utilization
of rheostatic switches, such switches have disadvantages. For
example, the resistance of a rheostatic switch depends upon a
particular setting thereof. Unless considerable care is exercised
to assure precise setting of the switch in its operating mode, then
the resistance of the circuit may be either too little or too
great. Another disadvantage of rheostatic switches is that they
generate substantial heat in operation. Provision must be made to
dissipate such heat, and the problems associated with heat
dissipation are magnified in those instances in which precise
adjustment of the switch is not assured.
An object of this invention is to provide switching apparatus which
is highly effective in suppressing current and voltage peaks
attendant the making and breaking of resistive and inductive
circuits, respectively.
Another object of the invention is to provide switching apparatus
of the character described and which comprises at least a pair of
conductive members, one of which has variable resistance
characteristics and the other of which has substantially constant
resistance characteristics, the two members being so arranged that
the variable resistance member is the first to become electrically
conductive and the last to become non-conductive.
A further object of the invention is to provide a multi-stage
switching apparatus which has the advantages of a rheostatic
switch, but none of its disadvantages.
Other objects and advantages of the invention will be pointed out
specifically or will become apparent from the following description
when it is considered in conjunction with the appended claims and
the accompanying drawings, in which:
FIG. 1 is a plan view of a switch incorporating apparatus
constructed in accordance with one embodiment of the invention;
FIG. 2 is a sectional view taken on the line 2--2 of FIG. 1 and
illustrating the parts in circuit closing condition;
FIG. 3 is a view similar to FIG. 2, but illustrating the parts in
open-circuit condition;
FIG. 4 is a sectional view taken on the line 4--4 of FIG. 2;
FIG. 5 is a plan view of the switching member illustrated in FIGS.
2 and 3;
FIG. 6 is a sectional view taken on the line 6--6 of FIG. 5;
FIG. 7 is a view similar to FIG. 6, but illustrating the switching
member interposed between a pair of conductors and subjected to
compressive force;
FIG. 8 is a view similar to FIG. 6, but illustrating a modification
of the switching member; and
FIG. 9 is a side elevational view of switching apparatus
incorporating switch members according to another embodiment of the
invention.
Apparatus constructed in accordance with the embodiment of the
invention shown in FIGS. 1-7 comprises a switch casing 1 having a
base 2, a pair of upstanding, spaced apart side walls 3, and front
and rear walls 4 and 5, respectively. The casing also includes a
cover 6 fixed to the side, front, and rear walls in any suitable
manner. Slidably accommodated within the casing 1 is an actuator 7
having a blind bore 8 extending inwardly from its rearward end. At
the forward end of the actuator 7 is an elongate operating stem 9
that extends through a tubular guide 10 which projects forwardly
from the front wall 4 of the casing. Fitted into the bore 8 is a
compression spring 11, one end of which seats on the base of the
bore and the opposite end of which bears against an abutment 12
that is fixed to the bottom wall 2 of the casing. The spring 11
normally biases the actuator to the position shown in FIG. 2 in
which it abuts the front wall 4 of the casing and in which position
the free end of the operating stem 9 extends beyond the guide
10.
Within the casing 1 is a pair of electrical conductors 13 and 14
the forward ends of which are fitted into notches 15 and 16,
respectively, formed in the front wall 4 of the casing. The rear
ends of the conductors 13 and 14 extend through openings formed in
the rear wall 5 of the casing to form terminals 18 and 19 which are
provided with reinforcing ribs 20 and 21, respectively. The
terminal 18 may be connected to a source of energy, such as a
battery B, and the terminal 19 may be connected to a load L.
The conductor 14 bears against the top wall 6 of the casing to
prevent upward deflection of the conductor. The conductor 13 has a
section 22 thereof which is spaced below the conductor 14 and
terminates at its rearward end in a downwardly turned leg 23 which
is joined to the terminal 18 so as to provide spacing between the
terminals 18 and 19 and permit reciprocation of the actuator 7
without unwanted interference with the conductor 13.
The section 22 of the conductor 13 is provided along its opposite
edges with a pair of downwardly extending, V-shaped projections 24
which lie in the path of movement of cams 25 carried by the body 7
at that side of the latter which confronts the conductor section
22. The forward ends of the cams 25 terminate in upwardly and
rearwardly inclined surfaces 26.
At substantially the center of the conductor 14 is a pair of
downwardly struck mounting ears 27, 28 by means of which a
switching member 30 is supported on the conductor 14 and between
the latter and the conductor 13.
The switching member 30 comprises two resiliently compressible
bodies 31 and 32, the body 31 being annular in configuration and
having a peripheral flange 33. The body 32 is disc-like and has a
peripheral flange 34. The body 31 encircles the body 32 and is
thicker than the latter for a purpose presently to be explained.
The body 32 may be retained frictionally within the body 31 or it
may be bonded to the latter.
The switching member 30 is secured to the conductor 14 by fitting
the flange 33 of the body 31 between the ears 27, 28 and the main
body portion of the conductor 14. Alternatively, the ears 27, 28
may be dispensed with and the switching member 30 secured to the
conductor 14 by any one of a number of known conductive
cements.
In the operation of the apparatus thus far described, movement of
the actuator 7 by means of the operating stem 9 from the position
shown in FIG. 2 to the position shown in FIG. 3 moves the cams 25
out of engagement with the projections 24 so as to enable the
section 22 of the conductor 13 to assume a substantially horizontal
position in which the conductor 13 is out of engagement with the
switching member 30. Upon return movement of the actuator to the
position shown in FIG. 2, however, the cams 25 will engage the
projections 24 and deflect the section 22 of the conductor 13
upwardly or toward the conductor 14. As the conductor 13 is
deflected upwardly, it will engage the body 31 and compress the
latter. When the body 31 has been compressed an amount
corresponding to the difference in thickness between the bodies 31
and 32, further deflection of the conductor 13 toward the conductor
14 will effect compression of both of the bodies 31 and 32, as is
shown in FIG. 7. Compression of the body 31, therefore, precedes
compression of the body 32.
Upon movement of the actuator 7 from the position shown in FIG. 2
to the position shown in FIG. 3, the projections 24 will slide down
the inclined surfaces 26 of the cams 25 so as to enable the section
22 of the conductor 23 to move away from the conductor 14. During
such movement of the section 22, both of the bodies 31 and 32 will
be decompressed. Eventually, the body 32 will be fully
decompressed, and full decompression of the body 32 precedes full
decompression of the body 31.
When the switching member 30 is utilized in the manner described,
the annular body 31 is the first to be compressed and the last to
be decompressed. Accordingly, the body 31 should be so constructed
as to have an electrical resistance which varies inversely
according to the state of its compression. Preferably, the body 31
comprises a molded member of resiliently compressible,
non-conductive material, such as silicone rubber, containing a
quantity of electrically resistive, conductive particles of such
size as to accommodate the currents and heat to be encountered in
normal usage. The body 31 may be molded from either a thermosetting
or room temperature vulcanization silicone resin containing the
appropriate catalyst and a quantity of fine particulate material
such as carbon, tungsten, nickel-chromium, and the like. Excellent
results have been obtained when a body 31 intended for use with a
14 volt, d.c. battery contained A.M.I. nichrome of 140-200 mesh
size and in a weight ratio of about 7 parts nichrome to 1 part of
silicone rubber. Although the body 31 may be normally conductive
even when it is not subjected to compressive force, the resistance
of the body 31 preferably approaches infinity in its normal,
uncompressed state, and diminishes generally linearly as the body
is compressed.
The body 32 also comprises a molded member of resiliently
compressible, non-conductive material, such as silicone rubber,
throughout which is dispersed a quantity of electrically conductive
particles of a size appropriate to the voltage and current of the
circuit in which it is to be used. As compared to the particles
contained in the body 31, the particles contained in the body 32
are of considerably less resistance. Stated differently, the body
32 is considerably more conductive than the body 31. This
relationship can be obtained by utilizing silver or silver- coated
copper particles in the body 32. Excellent results have been
obtained with a body 32 for use with the aforementioned d.c.
battery and containing silver-coated copper particles of 25-50 mesh
size in a weight ratio of about 10 parts of particles to 1 part of
silicone rubber.
If desired, the body 32 may be molded under pressure so as to be
conductive even in the absence of the application of compressive
force thereto. Alternatively, the body 32 may be molded at
atmospheric pressure so as to be non-conductive until compressed.
In either event, the electrical resistance of the body 32, when
conductive, corresponds substantially to the resistance of silver
and is substantially less than the resistance of the body 31 when
the latter is in its compressed state and conductive.
It is desirable that both of the bodies 31 and 32 be compressible.
Such a construction makes it possible for the member 30 to
accommodate overtravel of the conductor 13 toward the conductor 14,
thereby assuring sufficient movement of the conductor 13 to ensure
compression of the body 32 without risking damage to the other
parts of the switch mechanism.
It also is desirable that the body 31 be more easily compressible
than the body 32 so as to avoid the necessity of having to use
excessive force in the operation of the switching member 30.
Excellent results may be obtained if the body 31 has a durometer
rating of about half that of the body 32.
When the switching member 30 is interposed between the conductors
13 and 14 and the actuator 7 moves from the position shown in FIG.
3 toward the position shown in FIG. 2, deflection of the conductor
section 22 toward the conductor 14 will cause the body 31 to be
subjected to compression, thereby enabling current to flow from the
battery B through the terminal 20 to the conductor 13, thence
through the body 31 to the conductor 14, and from the latter
through the terminal 19 to the load L which, in the illustrative
case, comprises a filament f of an incandescent lamp, thereby
providing a resistive load, but it will be understood that the load
could be either resistive or inductive.
If the battery B has a voltage of 14 volts, the voltage drop across
the conductors 13 and 14 will diminish substantially linearly as
the body 31 is compressed inasmuch as the particles contained in
the body are subjected to the compressive force. When the body 31
has been compressed an amount corresponding to the difference in
thickness between the body 31 and 32 further movement of the
conductor 13 toward the conductor 14 will effect compression of
both of the bodies 31 and 32. Since the resistance of the body 32
is substantially less than that of the body 31, the establishment
of a conductive path between the conductors 13 and 14 via the body
32 will cause the body 31 to be short circuited or by-passed. The
voltage drop between the conductors 13 and 14 thus will correspond
to the voltage drop across the conductive body 32. If the
conductive particles of the body 32 are silver, or silver-coated
particles, the resistance of the body 32 will be substantially
constant and will correspond substantially to the resistance of a
silver or silver-coated conductor.
The utilization of the two-part switching member 30 enables full
voltage to be applied to the load L in two stages, the first of
which has a variable resistance and the second of which has a
substantially constant resistance. As a consequence, the inrush
current to which the load L is subjected is substantially
suppressed.
When the actuator 7 moves from the position shown in FIG. 2 toward
the position shown in FIG. 3, the conductor 13 moves away from the
conductor 14, thereby relieving the compressive force on the member
30. Due to the difference in thickness between the bodies 31 and
32, the body 32 is fully decompressed while the body 31 still is
subjected to compression. As a consequence, the conductive path
through the body 30 is transferred from the body 32 to the body 31
and the resistance of the body 31 increases as it is decompressed.
In this manner the peak voltage transient associated with the
opening of an inductive load circuit is substantially
suppressed.
The rapidity of compression and decompression of the member 30
depends upon the speed of movement of the actuator 7 and upon the
length and inclination of the surfaces 26 of the cams 25. The rate
at which the member 30 is compressed and decompressed may vary
within wide limits, but care should be taken to avoid maintaining
the current path through the resistive body 31 to such an extent
that heat generated by the electrical resistance is detrimental to
the silicone rubber.
To assist in the dissipation of whatever heat may be generated in
the body 31, the latter preferably encircles the more conductive
body 32. Such an arrangement is not essential, however. If desired,
a switching member 30a (see FIG. 8) may be constructed in such
manner that a variable resistance body 31a is encircled by a more
conductive body 32a, the bodies 31a and 32a corresponding in
construction to the bodies 31 and 32, respectively, with the
exception that the body 31a is thicker than the body 32a so as to
be compressed prior to the body 32a and to be decompressed
following decompression of the body 32a.
Although the disclosed switching members 30 and 30a incorporate
only two discrete bodies, it will be understood that a greater
number of discrete bodies may be included in a single switching
member. In such a construction each body would contain particles
having conductive properties different from those of the other
bodies and the thickness of each more resistive body would be
greater than that of a less resistive body.
It is not essential that the discrete bodies of a multi-stage
switching member be concentric. As is indicated in FIG. 9, an
insulating base 40 supports a pair of spaced conductors 41 and 42
adapted to be bridged by a blade 43 swingable about a pivot 44.
Mounted side by side on the conductor 41 is a pair of bodies 31b
and 32b corresponding in construction to the bodies 31 and 32,
respectively, except for their configuration. The variable
resistance body 31b is located in a position such that movement of
the blade in the direction of the arrow a from the full line
position to the dotted line position b effects compression of the
body 31b and establishment of a variable resistance path between
the conductors 41 and 42 via the blade 43 and the body 31b. Further
movement of the blade in the direction of the arrow a to the dotted
line position c will effect compression of the more conductive body
32b, whereupon the conductive path between the conductors 41 and 42
is via the blade 43 and the body 32b. The effect of this
arrangement is the same as that which has been described
earlier.
Tests of switching members constructed in accordance with the
invention have demonstrated remarkable uniformity of the electrical
characteristics of such switching members. For example, a
construction corresponding to the member 30 was subjected to
several hundred thousand on-off cycles with virtually no variation
in the voltage drop across the member when the more conductive body
32 was conductive.
The disclosed embodiments are representative of presently preferred
forms of the invention but are intended to be illustrative rather
than definitive thereof. The invention is defined in the
claims.
* * * * *