Title: Center break switch with reduced opening force requirement
Abstract: A switch has respective open-assist bars fixed to switch blades near the switch contacts. The bars are arranged so that, as the blades are turned by rotation of their supports, the bars come together and serve as a fulcrum mechanism that provides a prying action helping reduce the required opening force. The action of the fulcrum mechanism overcomes friction between the contacts that may otherwise tend to cause bowing of the supports with appreciable increase in the required opening force.
Patent Number: 6,984,795 Issued on 01/10/2006 to Kowalik
| Inventors:
|
Kowalik; Peter M. (Trafford, PA)
|
| Assignee:
|
Cleaveland /Price Inc. (Trafford, PA)
|
| Appl. No.:
|
645068 |
| Filed:
|
August 21, 2003 |
| Current U.S. Class: |
200/48CB |
| Current Intern'l Class: |
H01H 31/00 (20060101) |
| Field of Search: |
200/48 R,48.P,48.KB,48.SB,48.CB,49
218/7,14-21
|
References Cited [Referenced By]
U.S. Patent Documents
Other References
Cleaveland/Price Inc., Bulletin DB-126A02, "Aluminum Center Break Switch", (published 2002).
Porter, Catalog 1-055, Issue No. 1, Nov. 1974, "LPC Center Side Break Disconnect Switch".
Johnson Manufacturing Company, "Type M Center Break Switch" (pub. date not shown).
Siemens-Allis, DS 1.3a, Jul., 1979, "Group Operated Switches".
Westinghouse, supplement to descriptive bulletin 36-250, "outdoor disconnecting
switches type CB center side break", Dec., 1962.
|
Primary Examiner: Fishman; Marina
Attorney, Agent or Firm: Telfer; Gordon H.
Claims
What is claimed is:
1. A center break switch comprising:
a base;
a pair of switch blades, each having a switch contact and each mounted on the
base by a rotatable support structure combined with an operating mechanism that
moves the switch blades and their contacts between closed and open positions upon
application of a motive force to the operating mechanism, each switch blade also
having a line terminal;
the support structure and operating mechanism being related for rotation of each
blade's support structure proximate the base with resulting movement of the blades
and contacts arcuately between the closed and open positions; and
a pair of pry bars, each of the pair being attached to one of the blades proximate
the contact with the bars arranged to have facing ends that work pivotally against
each other during at least part of a switch opening operation of the operating
mechanism to facilitate opening of the contacts.
2. The switch of claim 1 where:
the pry bars, at their facing ends, are located, relative to the contacts on
the blades, opposite the direction of movement of the contacts during switch opening.
3. The switch of claim 1 in a combination further comprising:
two additional center break switches each with a pair of switch blades and related
contacts, a pair of pry bars, each of the pair of pry bars being attached to one
of the blades proximate the contact with the bars arranged to have facing ends
that work pivotally against each other during at least part of a switch opening
operation of the operating mechanism to facilitate opening of the contacts, a pair
of line terminals and a pair of support structures, with each of the three pairs
of blades of the three switches being connectable at their line terminals to a
respective phase of a three-phase electrical system; and
the operating mechanism includes elements joined together for common operation
of all three switches by a single source of motive power.
4. The combination of claim 3 where:
the operating mechanism includes a manual operator or a motor operator.
5. The switch of claim 1 where:
the switch contacts engage each other with sliding friction during a period of
movement of the switch blades from the closed to open positions.
6. The switch of claim 5 further comprising:
a contact tightening mechanism that allows adjusting the pressure on the contacts
in the closed position to a desired amount.
7. The switch of claim 5 where:
the contacts, at least in part, have a configuration with mutual engagement in
a plane substantially the same as that in which the arcuate movement of the blades
occurs.
8. The switch of claim 5 where:
the support structure of each blade is insulative and extends a length from the
base with an axis of rotation running along the lengths.
9. The switch of claim 8 where:
the pry bars each comprise a rigid member secured to the respective blades so
extremities of the bars face each other in the fully closed position of the switch
contacts and mechanically engage as a pivot axis for a time during which the contacts
engage with sliding friction.
10. The switch of claim 9 where:
the bars are secured to the blades at locations for attachment of additional
elements for arc suppression.
11. The switch of claim 9 where:
the bars are of metal and are shaped and are attached to the blades with space
avoiding any direct contact to the switch contacts and with a small gap, in the
fully closed position, avoiding direct contact to each other.
12. The switch of claim 11 where:
the bars each have a flange-like portion at the extremities.
13. The switch of claim 9 where:
the bars, at least the extremities thereof, are insulative and are arranged with
either a small gap or no gap between them in the closed position.
14. The switch of claim 9 where:
the bars are plate-like members substantially parallel to the plane of arcuate
movement of the switch blade; and
the extremities of the plate-like members each have a corner edge, on the side
thereof away from the contacts, that engage to provide the pivot axis.
15. A switch comprising:
a pair of switch contacts;
a pair of supports that each support one of the switch contacts;
a switch operating mechanism related with the contacts and their supports for
relative motion of the contacts in an arcuate path including motion, in a switch
opening, from a fully closed position in which the contacts are stationary and
conductively engaged, through a partly open position in which the contacts have
relative motion while conductively engaged with sliding friction, to an open position
in which the contacts are separated; and
a fulcrum mechanism comprising elements, in addition to the switch contacts,
located proximate to and behind the contacts in relation to the path of relative
motion, that meet to provide a prying action increasing leverage to help overcome
the sliding friction between the contacts in movement through the partly open position.
16. The switch of claim 15 where:
the elements of the fulcrum mechanism form a pivot axis that is substantially
fixed in location while the contacts are engaged with sliding friction in the partly
open position.
17. The switch of claim 15 where:
the elements of the fulcrum mechanism comprise a pair of bars respectively attached
to a pair of contact blades and the bars engage each other and together form a
pivot axis to provide the prying action as the switch contacts slide against each
other in the partly open position.
18. The switch of claim 15 where:
the contacts have frictional engagement during switch opening in a first plane
in which the blades move during rotation of the supports or a second plane perpendicular
to the first plane, or in both planes.
19. The switch of claim 17 where:
the fulcrum mechanism comprises a pair of members respectively attached to each
of the pair of contact blades.
20. The switch of claim 17 where:
the fulcrum mechanism comprises a pair of elements respectively integral with
each of the pair of contact blades.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to center break switches, such as for electrical power
substations and transmission lines, and particularly to such a switch in an arrangement
facilitating opening of the switch.
2. Background Art
Center break switches have (in a single pole) two switch blades with mating
contacts that meet, and separate, between a pair of rotatable blade supports. In
a common type, the blade supports include ceramic or polymer insulators that are
generally cylindrical with lateral sheds. The supports are joined at one end (nominally,
the "bottom") to a quite rigid metal base with a bearing for rotation of each support
relative to the base and a mechanism for imparting rotational force to both supports,
hence moving the switch blades into or out of a closed contact position. The supports,
and their axes of rotation, are substantially parallel to each other in one switch
type or, in another type, are in a substantially V-shaped configuration. Switches
of interest include those described and illustrated in Cleaveland/Price Inc. descriptive
bulletin DB-126A02, "Aluminum Center Break Switch", published in 2002, that is
representative of prior art to the present invention.
Operation of such switches is in some cases manual (e.g., by a handcrank
or a swing handle) and in some cases by electric motor. Whether manually or motor
operated, it is desirable to operate the switch easily and quickly with only modest
requirements on the equipment and personnel. For example, some switches have a
handcrank operator for manual operation. The handcrank is connected to the rotatable
support apparatus through a gearbox with a gear ratio typically in a range from
about 10:1 to 40:1, as specified by a user. A higher gear ratio allows a switch
to be opened with less manual force but requires more time, which is generally undesirable.
Another factor in switch operation is that a typical installation has three
poles, substantially alike, one for each phase of a three phase electrical system,
and the operator must apply sufficient force to operate all three poles together.
A maximum operating force, for three-phase switches, is typically specified to
be in a range from about 35 to 70 pounds. Some installations have switches ganged
together in even larger numbers, such as six poles with two poles for each phase
of a three phase system.
Center break switches are now applied over a wide range of voltages, including
high voltage systems up to a nominal rating of at least about 230 kV. Required
switch size increases with increasing voltage (for contact clearance when the switch
is open and for sufficient distance across the insulative supports) so that the
rotatable supports and the contact blades reach up to several feet in length. This
makes for a relatively massive structure to be moved and the longer supports make
them more subject to bowing that can affect operation. In general, however, considerations
affecting the opening force requirements apply to some degree regardless of the
switch size or the number of switches operated together.
Switches operate in a variety of environments including those that can,
particularly with age, change the amount of required operating force. One type
of known switch has contacts with engaging surfaces that meet substantially in
a horizontal plane like that of the arcuate motion of the contacts resulting from
blade supports' rotation. This produces considerable wiping action between the
contacts during opening and closing that helps keep the contact zone free of debris
and oxides. In this respect, sliding friction between the contacts enhances switch
performance while also having an influence on the required opening force.
A variety of contact configurations are used in various center break switches.
For example, some have appreciable contact engagement in a vertical plane that
is substantially perpendicular to the plane in which the blades move. Still, in
any of the contact configurations, there is some degree of sliding friction that
can affect switch opening. Prior art has largely relied on a basic assumption that
the axes of rotation of the insulative supports are substantially fixed. While
prior center break switches have been generally successful, their design has not
addressed the fact that sliding friction between the contacts during a switch opening
can alter the location of the axes of rotation of the supports, particularly, but
not limited to, those of larger units. Altering the axes of rotation by contact
friction results in greater required force and time to separate the contacts than
if those axes were fixed.
SUMMARY OF THE INVENTION
The present invention takes into account the effects of friction, including possible
bowing movement of the support axes, and provides a simple arrangement for facilitating
switch opening despite such friction effects.
Without friction, a center break switch would open very easily with no forces
to distort the axes of rotation of the supports. With the switch blades at fixed
support axes, the blades would swing the contacts from a fully closed position
to a point of separation while only traversing a minimum distance. However, friction
between contacts can change that by introducing a drag effect altering the geometry.
Sliding friction between contacts can cause the points of rotation of the
blades, at the upper end of their supports, to move toward each other due to bowing
of the insulative supports. This is because the contacts generate forces to overcome
the sliding friction so that during the time contact motion has begun, but the
contacts are still not separated, the contacts are not moving in a perfect arc.
Their separation will only occur a distance beyond the minimum distance referred
to above. With that change, the required torque and operating force is increased.
Also, somewhat more time is required.
Now, in one embodiment of the present invention, a fulcrum mechanism is combined
with the switch elements that may be like the prior art in other respects. It can
include two additional members, such as bars (sometimes they may be referred to
by alternative expressions such as pry bars, pry-open bars, pry-out bars, pivot
bars, easy open bars, or open-assist bars) that are added in combination with a
typical center break switch of the prior art. The "bars" need not be very elongated
and can be any members that abut each other as described below during a switch
opening. The elements of the fulcrum mechanism can be members attached to the respective
blades or elements integral with the blades.
The bars are, in one example, relatively flat, stiff, metal plates, approximately
"L" (or backward "L") shaped. One bar is on each switch blade, e.g., with the bottom
of the "L" (or backward "L") bolted to the blade behind the contact on that blade
and the upper parts of the bars extending beside the contacts to face each other.
The facing portions abut and contact each other during a switch opening along with
initial contact movement and before full separation. That is, the upper parts of
an "L" on a right side blade and the upper part of a reverse "L" on a left side
blade are located behind the contacts (with respect to the direction the contacts
move) and the ends of the "L" and reverse "L" bars, which have some width and thickness,
possibly with a flange-like end, meet to produce the intended effect.
While the contacts are engaged in sliding friction, the bars provide a new
pivot point, or axis of rotation, during the opening motion that pries the contacts
apart and forces them to stay on a more perfect arc as they open. The bars reduce
bowing movement of the insulator supports and provide a contact parting at a point
substantially like one that would exist if there were no sliding friction, even
though the contacts do experience the same friction and wiping action.
The bars can be simply formed with the shape mentioned just as an example. Their
conductivity is not an issue as far as producing the effect described. They need
not touch in the fully closed position and need not have any direct contact with
the switch contacts. (If the bars are metal, it is generally preferred to avoid
any such contact.) They can be arranged to stay clear of any auxiliary switch elements
near the contacts, such as arc horns, and may be attached at any convenient location
along the blades, including at the same bolt locations arc horns are attached.
Fortunately, the bars assist appreciably in an opening operation without interfering
with a switch closing. They can be arranged to have little or no contact with each
other during a closing operation and not appreciably alter the closing force.
The earlier contact release point that is achieved appreciably reduces the required
operating force. A prototype test on a 230 kV, 3000 ampere switch showed a reduction
in operating force on a handcrank gearbox (having a gear ratio of 20:1) from about
40 pounds without the bars to about 15 pounds with them in place, with the same
contact pressure. Such switches have insulative supports over seven feet long and
switch blades with a radius of about five feet.
The arrangement can be economical, effective, and readily implemented on switches
already in service. It provides a convenient alternative, or a complement to other
approaches that could be taken, such as providing a higher ratio gearbox for a
handcrank operator.
Ancillary benefits include an opportunity to have higher contact pressure
because the pry bars alleviate concern that less pressure should be maintained
for easier opening. Also, flexibility of insulators can be less of a concern, so
they can possibly be made from a wider range of materials.
These and other aspects of the present invention will be further understood
from the following text and drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIGS. 1 and 2 are, respectively, side elevation and top plan views of a center
break switch showing an embodiment of the invention where FIG. 2 omits for clarity
elements of FIG. 1 below a top portion;
FIG. 3 is an enlarged plan view of part of the switch of FIGS. 1 and 2;
FIG. 4 is an elevation view of the parts shown in FIG. 3;
FIG. 5 is a plan view of the apparatus of FIGS. 3 and 4 during movement from
a fully closed position;
FIG. 6 is a schematic plan view of three mechanically interconnected switches;
FIGS. 7 and 8 are partial plan views of two alternative embodiments; and
FIGS. 9 and 10 are, respectively, partial plan and elevation views of a further embodiment.
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1,
2,
3,
4, and
5 are of the same apparatus
although some elements are shown only in FIG.
1. While each of FIGS. 1,
2,
3 and
4 show a fully closed switch position, FIG. 2 also
shows a position after contact separation.
FIG. 1 shows a switch (one-pole) with a rigid base
10, e.g., of hot-dip
galvanized steel, on which moveable elements of the switch are mounted. Rotatable
supports
12 and
13 are mounted at their bottom ends with bearings
(not shown) for their rotation relative to the base
10. In this example,
the supports
12 and
13 each include a respective stack of insulators
12a and
13a with intermediate metal couplings
12b
and
13b. The insulators
12a and
13a are
generally of a polymer (e.g., fiber reinforced plastic) or a ceramic material.
Even though they are not intended to flex, the insulators are subject to some inherent
flexing due to the described friction effects.
Contact blades
14 and
15 are respectively joined to the upper
ends of supports
12 and
13 (FIG.
1). Near the supported ends
of the contact blades
14 and
15 there is a respective one of a pair
of line terminals
20 and
21 for connection with a conductor of an
electrical system. Features for pivoting of the blades
14 and
15
in relation to the relatively fixed terminals
20 and
21 are included
but will not be detailed herein and may be the same as prior art. The blades
14
and
15 have ends away from the supports
12 and
13 with blade
ends, contacts and members to assist in switch opening (to be discussed later)
in an assembly identified collectively by reference numeral
50 in FIGS.
1 and 2 with more detailed identification of the elements in the subsequent enlarged views.
The blades
14 and
15 are, for example, each a single piece, aluminum,
square tube. Each blade
14 and
15 has one of a pair of switch contacts
16 and
17 at its end opposite its respective support
12 or
13.
In this example, as shown in FIGS. 3 and 4, the left side contact
16 includes
four pairs of conductive fingers: two upper pairs each having a top finger
16a
and a bottom finger
6b and two lower pairs each having a top
finger
16c and a bottom finger
16d, all of which are
conductively joined near their left ends to the blade
14.
The right side contact
17 includes a pair of conductive stabs
17a
and
17b, both conductively joined near their right ends to the
blade
15, that are respectively captured (in the closed position) within
a jaw formed by the upper pairs of contact fingers
16a and
16b
and within a jaw formed by the lower pairs of contact fingers
16c
and
16d. The elements of contacts
16 and
17 are
highly conductive, e.g., silver plated or silver overlaid copper.
In addition, there is a contact pressure adjusting mechanism
18, such
as
one supported from the blade
14 with bolts and adjusting nuts bearing on
spring plates that bear against the fingers of contact
16.
The figures omit for greater clarity corona or arc reducing spheres or horns,
and also an ice shield, that are conventionally arranged near contacts of such
a switch as that shown.
At the bottom of the switch (FIG. 1) a mechanism
30 is provided for operation
of the switch including a tie rod
31 mechanically coupled to both insulative
supports
12 and
13 at metal flange members not detailed here. Bearings
(not shown) for rotation of the supports
12 and
13 relative to the
rigid base
10 are located near the attachments of rod
31.
In this example, the mechanism
30 further includes a handcrank
32
schematically shown in a mechanically coupled relation through a gearbox
33
to the tie rod
31 that transmits rotational force to the supports
12
and
13, both together and also typically together with force transmitted
to two other switch poles of the same nature, as is later discussed in connection
with FIG.
6.
All of the elements discussed so far (not including any open-assist members
40
and
42 as described below) may be in accordance with known prior art switches
such as, but not limited to, that described in the above mentioned background publication
which is incorporated by reference herein for further description of examples of
the construction and use of such switches, including both those with substantially
parallel rotatable supports (as shown here) and those with substantially V-oriented
supports (not shown herein) with otherwise similar features.
While the invention is not so limited, the contacts
16 and
17
in this example have fingers and stabs that engage each other in one or more planes
parallel to the arcuate movement of the blades
14 and
15; a substantially
horizontal interface. (FIG. 2 gives a general picture of the blades and contacts
as they have been moved from a closed to a contact parted position by rotation
at their supports.) The contact fingers
16a-16d are
not totally planar, since (as shown in FIG. 4) they have a bend that makes the
principal direct contact with the stabs
17a and
17b along
a line
52 (in the closed switch position). Before the switch reaches a position
as shown in FIG. 2, those bends of the fingers move over the surfaces of the stabs
with a wiping action that is favorable for good conduction. The contact pressure
adjustment mechanism
18 allows a user to set the pressure to a desired level.
(For general reference, switches of the type described typically go to a fully
open position only after the blades have turned 90°. In views such as FIG.
2, the contacts have parted and have no more frictional engagement but the blades
have not yet reached the fully open position.)
FIGS. 3 to
5 show a contact assembly
50 that, in addition to
the elements that may be otherwise conventional, include a pair of plate-like bars
40 and
42 that are shown respectively attached (e.g., bolted) near
a first end
40a and
42a to the top of a switch blade
14 or
15 and shaped to extend in front of the contacts
16
and
17 to face each other at their ends
40b and
42b
that may have small flanges, as shown.
The bars
40 and
42 need not make physical contact to each other
in the fully closed position of the switch, so a gap may occur as shown in FIG.
3. (The "facing" relation is meant to include either with or without a gap).
The bars
40 and
42 assist in switch opening. When blade rotation
and contact movement has started, the bars
40 and
42 meet at at least
part of their facing ends
40b and
42b (e.g., edge corners
40c and
42c as shown in FIG. 5) and establish there
a new pivot or axis of rotation that facilitates switch opening. The line (or plane)
52 of principal contact engagement and wiping action shifts as the blades
move in the directions of the arrows in FIG.
5.
Now, instead of contact sliding friction causing bowing of the supports
12
and
13 so the switch opening is delayed due to extra travel of the contacts
16 and
17 and requires more force, the locus of the pivot comers
40c and
42c stays substantially fixed through the duration
of their contact to each other despite the contact friction.
By way of further example, the bars
40 and
42 are relatively stiff
metal plates that are relatively flat although FIG. 4 shows a small angular variation
and the abutting ends
40b and
42b have small vertical
flanges. These bars are, looking in the plane of FIG. 3, respectively substantially
L-shaped (bar
42) and reverse L-shaped (bar
40) with the bottom leg
of each "L" joined at
40a and
42a to the respective
blades and the ends of the top parts of the "L" configurations being the facing
ends
40b and
42b.
One factor making it convenient to attach the bars
40 and
42 to
the blades as shown is that the bar ends
40a and
42a can
be bolted to the blades at bolt locations as shown that are the same as those used
for attachment of arc horns (which are not shown in these views). This is particularly
convenient for putting the assembly together on switches already in the field.
A variety of other attachment locations and shapes for members performing the function
of bars
40 and
42 will be apparent.
FIG. 6 illustrates a three phase switch combination with respective switches
61,
62 and
63 that can each be like that previously described.
This schematically shows how a single mechanical arrangement
130 combining
tie rods and related parts of each of the three switches are joined together for
common operation from a single motive power source, e.g., a handcrank
132
and gearbox
133. This is a common situation and is shown to make the point
that the inventive combination has further benefit when practiced in multi-switch
gangs where opening force requirements are greater than with a single switch.
The described embodiment is also one that has the facing ends
40b and
42b that form the pivot point or axis, where corners
40c
and
42c meet per FIG. 5, off of the line
52 of the main
contact pressure. This is just one possible location. A general characteristic
of the inventive combination is that members comprising the fulcrum mechanism,
such as bars
40 and
42, meet and make a pivot point for the blades
14 and
16 at least some part of the time the contacts
16 and
17 are sliding together during a switch opening. Preferably, but not necessarily,
the fulcrum mechanism is such that its pivot action occurs substantially throughout
the sliding engagement of the contacts. Some benefit can be obtained even if it
occurs only part of that time, for example during early contact movement. After
the contacts have parted, the fulcrum mechanism need not operate.
FIG. 7 shows an alternative arrangement
150 for pivot members or bars
on a switch with other elements as previously described. In this embodiment, the
configuration of the blades
14 and
15 and the contacts
16
and
17 is the same as was previously described. The contacts
16 and
17 have a horizontal interface and move in the same direction as the contacts
of FIG.
5. However, now pivot members
140 and
142 are attached
to respective contact blades
14 and
16 on the side of the blades
toward the front of the switch (considering a view such as that of FIG. 1) near
their ends
140a and
142a. The members
140 and
142 are plate-like bars that, in this example, are shown just flat and their
ends
140b and
142b face each other, with a small gap
in the closed position. As shown, bars
140 and
142 are equal in length;
in general, they can have the same or different shape and size as long as their
locations cause the described pivot action. In FIG. 7, as the switch opens, with
blade movement as shown by the arrows, the pivot axis will occur at rear (or lower
in the drawing) corner edges
140c and
142c, substantially
as it does in the embodiment of FIG.
5. FIG. 7 represents just one alternative
form a fulcrum mechanism can take with contacts having horizontal engagement.
FIG. 8 shows a further alternative arrangement
150′. A fulcrum
mechanism comprises elements
140′ and
142′ that are
respectively integral with the blades
14′ and
15′.
For example, blades in the form of square tubes can have three sides partly cut
away leaving portions
140′ and
142′ extending from
the full square configuration. The extended material can be formed as desired,
such as to form the illustrated flange portions at
140b′ and
142b′ that face each other and whose back corners
140c′
and
142c′ initially engage to provide a pivot as the contacts open.
A variety of contact arrangements for center break switches are used in the art
other than that shown for contacts
16 and
17. Some have principal
contact engagement and a degree of wiping action that is not in a plane parallel
to the arcuate blade movement. For example, the contact faces may principally engage
in a substantially vertical interface plane. Even so, to the extent the contacts
engage with sliding friction in any of these alternative contact configurations,
the present invention can be beneficial to facilitate switch opening.
FIGS. 9 and 10 show an example of a combination
250 of pry bars with
a pair of contacts with a vertical interface. Blade
214 supports a first
contact
216 that has a loop forming a jaw within which a stab-like second
contact
217 on blade
215 is engaged. A closed switch is shown. The
arrows in FIG. 9 show the directions the blades
214 and
215 will
take during a switch opening. During that movement, front and back fingers of contact
116 slide against front and back ends of contact
217 and produce
sliding friction.
The combination
250 includes pry bars
240 and
242 that are
arranged and operate in substantially the same way as bars
40 and
42
previously described. Here the bars
240 and
242 are merely flat from
their secured ends
240a and
242a out to their facing
ends
240b and
242b at which a small vertical flange
occurs. Also, it will be noted the bars
240 and
242 will meet and
pivot, at the back comers
240c and
242c, along the
same line as that on which the contacts engage in the closed position.
It is, therefore, apparent that the invention applies either in the case in which
the contacts engage with sliding friction in a plane orientated the same as the
plane of the movement of the blades or the case in which the plane of contact engagement
is perpendicular to the blades' plane of motion. Also, it can be understood that
the contacts can be configured with elements such that they engage, and slide,
in both planes.
Among the considerations for members in the fulcrum, or open-assist, mechanism
is to make any gap between them in the closed position as small as reasonably attainable
so the pivot action can commence promptly upon contact movement. The gap can be
avoided entirely although it is not generally preferred to have any conduction
across the bars, if of metal, when closed. However, the bars need not be metal
but may instead be of an insulative material such as fiber reinforced plastic,
at least at the facing ends, so direct contact when closed would not be a concern.
The illustrated embodiments have a geometry for the open-assist elements with
a pivot axis centered in relation to the blades and the blade supports although
the contacts have a line of primary engagement, as shown in FIGS. 3,
7,
and
8, not quite centered between the ends of blades
14 and
15
or
14′ and
15′. Symmetrical elements
40 and
42,
140 and
142, and
140′ and
142′
are generally preferred for typical switches, such as those with equal length blades.
Variations can be implemented in which the abutting elements are not symmetrical;
in general, they can have the same or different shape and size, and the same or
different relative locations on the blades, as long as they meet to perform the
described pivot action during the sliding engagement of the contacts.
While the description sometimes refers to "upper", "lower", "top" or "bottom",
"horizontal" or "vertical" orientations (consistent with the Figures), it will
be understood the described switches can be mounted in essentially any orientation.
The specific embodiments disclosed are merely some examples of the various ways
in which the invention can be practiced.
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