MEANS FOR ACTUATING A SNAP-ACTING M-BLADE

MOYEN D'ACTIONNEMENT D'UN DISPOSITIF A DECLIC

English Abstract

An electrical switch (10) incorporating
a snap-acting M-blade (12) is actuated
by a bridge (16) engaging a critical
region of the M-blade's (12) double-loop
end (20) to provide an extremely
low differential. Together, the means for
actuating cover a broad range of applications.
Additional features include a
snap-acting M-blade actuated by a second
snap-acting device and the lever
comprising an integral tab that serves as
a pivot point.

French Abstract

On actionne un commutateur électrique (10) comportant une lame en M (12) à déclic, à l'aide d'un pont (16) entrant en contact avec des zones critiques de l'extrémité à double boucle (20) de la lame en M (12), de façon à obtenir un différentiel extrêmement faible. Ensemble, ces moyens d'actionnement couvrent un large éventail d'applications. Selon une autre réalisation, une lame en M à déclic est actionnée par un second dispositif à déclic, un levier à patte intégrée servant de point de pivot.

Claims

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I claim:

CLAIMS


1. An auto-snap device, comprising:
a sheet metal spring member having a double-loop end opposite to a
closed end, said sheet metal spring member having a first outer leg, a second
outer leg, a
first inner leg, a second inner leg, and a cross member, said first outer leg
being coupled
to said second outer leg by way of said cross member at said closed end, said
first outer
leg coupled to said first inner leg by way of a first loop at said double-loop
end to define
a first slit between said first outer leg and said first inner leg and
longitudinally
extending from said cross member and terminating at a first termination point
at said
first loop, said second outer leg coupled to said second inner leg by way of a
second loop
at said double-loop end to define a second slit between said second outer leg
and said
second inner leg and longitudinally extending from said cross member and
terminating
at a second termination point at said second loop, said first loop including a
first sweet
spot situated such that said first termination point is between said first
sweet spot and
said cross member and said first termination point is further situated between
said first
sweet spot and said second loop, said second loop including a second sweet
spot situated
such that said second termination point is between said second sweet spot and
said cross
member and said second termination point is further situated between said
second sweet
spot and said first loop, said sheet metal spring member being distorted to
place said
inner legs out of coplanar alignment with said outer legs to provide said
sheet metal
spring member with a snap action;
an anchor point joining said first inner leg to said second inner leg at a
location between said double-loop end and said closed end;
a bridge engaging said first sweet spot and said second sweet spot;
and an actuator adapted to move said bridge relative to said anchor point
in a positive direction past a forward trip point and in a negative direction
past a return
trip point, whereby said sheet metal spring member experiences said snap
action at said
forward trip point and at said return trip point with the distance between
said forward
trip point and said return trip point being defined as a differential.

2. The auto-snap device of claim 1 further comprising a first electrical
contact on said cross member, a second electrical contact, and a stop, said
second
electrical contact being spaced apart from said stop with said first
electrical contact


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being free to travel a predetermined distance between said second electrical
contact and
said stop, said predetermined distance being at least five times greater than
said
differential.

3. The auto-snap device of claim 2 wherein said predetermined distance is at
least ten times greater than said differential.

4. The auto-snap device of claim 2 wherein said actuator includes
temperature responsive bimetallic material.

5. The auto-snap device of claim 4 further comprising an adjustment screw
acting upon said anchor point, and a spring attached to said anchor point and
opposing
said adjustment screw.

6. The auto-snap device of claim 5 further comprising a mounting post that
holds said screw, said spring, said stop, said second electrical contact, and
said actuator.

7. The auto-snap device of claim 1 wherein said actuator is a bimetallic disc
providing a second snap action in response to temperature.

8. The auto-snap device of claim 7 wherein said bridge is made of an
electrically insulated material.

9. The auto-snap device of claim 7 further comprising an electrical terminal
attached to said anchor point and said bridge straddles said electrical
terminal.

10. The auto-snap device of claim 7 further comprising a housing that
contains said sheet metal spring member, said housing having a protrusion that
extends
toward a central portion of said bimetallic disc.

11. An auto-snap device, comprising:
a sheet metal spring member having a double-loop end opposite to a
closed end, said sheet metal spring member having a first outer leg, a second
outer leg, a
first inner leg, a second inner leg, and a cross member, said first outer leg
being coupled
to said second outer leg by way of said cross member at said closed end, said
first outer
leg coupled to said first inner leg by way of a first loop at said double-loop
end to define


-8-


a first slit between said first outer leg and said first inner leg and
longitudinally
extending from said cross member and terminating at a first termination point
at such
first loop, said second outer leg coupled to said second inner leg by way of a
second loop
at said double-loop end to define a second slit between said second outer leg
and said
second inner leg and longitudinally extending from said cross member and
terminating
at a second termination point at said second loop, said first loop including a
first sweet
spot situated such that said first termination point is between said first
sweet spot and
said cross member and said first termination point is further situated between
said first
sweet spot and said second loop, said second loop including a second sweet
spot situated
such that said second termination point is between said second sweet spot and
said cross
member and said second termination point is further situated between said
second sweet
spot and said first loop, said sheet metal spring member being distorted to
place said
inner legs out of coplanar alignment with said outer legs to provide said
sheet metal
spring member with a snap action;
an anchor point joining said first inner leg to said second inner leg at a
location between said double-loop end and said closed end;
a bridge engaging said first sweet spot and said second sweet spot;
an actuator adapted to move said bridge relative to said anchor point in a
positive direction past a forward trip point and in a negative direction past
a return trip
point, whereby said sheet metal spring member experiences said snap action at
said
forward trip point and at said return trip point with the distance between
said forward
trip point and said return trip point being defined as a differential;
a first electrical contact on said cross member;
a second electrical contact; and
a stop spaced apart from said second electrical contact with said first
electrical contact being free to travel a predetermined distance between said
second
electrical contact and said stop, said predetermined distance being at least
ten times
greater than said differential.

12. The auto-snap device of claim 11, further comprising a temperature
responsive bimetallic material incorporated into said actuator; an adjustment
screw
acting upon said anchor point; a spring attached to said anchor point and
opposing said
adjustment screw; and a mounting post holding said screw, said spring, said
stop, said
second electrical contact, and said actuator.



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13. The auto-snap device of claim 11, wherein said actuator is a bimetallic
disc providing a second snap action in response to temperature, and wherein
said bridge
is made of an electrically insulated material.
14. The auto-snap device of claim 13 further comprising an electrical
terminal attached to said anchor point and said bridge straddles said
electrical terminal.
15. The auto-snap device of claim 13 further comprising a housing that
contains said sheet metal spring member, said housing having a protrusion that
extends
toward a central portion of said bimetallic disc.
16. A.n auto-snap device comprising:
a sheet metal spring member having a double-loop end opposite to a
closed end, said spring member having a first outer leg, a second outer leg, a
first inner
leg, a second inner leg, and a cross member, said first outer leg being
coupled to said
second outer leg by way of said cross member at said closed end, said first
outer leg
coupled to said first inner leg by way of a first loop at said double-loop end
to define a
first slit between said first outer leg and said first inner leg and
longitudinally extending
from said cross member and terminating at a first termination point at said
first loop,
said second outer leg coupled to said second inner leg by way of a second loop
at said
double-loop end to define a second slit between said second outer leg and said
second
inner leg and longitudinally extending from said cross member and terminating
at a
second termination point at said second loop, said sheet metal spring member
being
distorted to place said inner legs out of coplanar alignment with said outer
legs to
provide said sheet metal spring member with a snap action;
an anchor point joining said first inner leg to said second inner leg at a
location between said double-loop end and said closed end;
a lever having an actuation end opposite a reaction end with a pivot
situated therebetween, said reaction end being coupled to said anchor point;
and an actuator acting upon said actuation end to move said actuation end
relative to said pivot in a positive direction past a forward trip point and
in a negative
direction past a return trip point, whereby said sheet metal spring member
experiences
said snap action at said forward trip point and said return trip point with
the distance
between said forward trip point and said return trip point being defined as a
differential.


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17. The auto-snap device of claim 16 further comprising a housing coupled to
said pivot; a first electrical contact on said cross member; a first stop
attached to said
housing; and a second stop attached to said housing with one of said first
stop and said
second stop serving as a second electrical contact, said first electrical
contact moving
from said first stop to said second stop upon said actuator applying an
actuation force
against said actuation end, said actuation force being less than a contact
force with said
contact force being that force which is exerted by said first electrical
contact against said
second electrical contact when said first electrical contact is against said
second
electrical contact.
18. The auto-snap device of claim 17 whereby said first electrical contact
moves in substantially the same direction as said actuation end.
19. The auto-snap device of claim 18 further comprising a third electrical
contact wherein said first stop serves as said second electrical contact and
said second
stop serves as said third electrical contact.
20. The auto-snap device of claim 16 wherein said pivot enables said lever to
tilt by way of a bending action.
21. An auto-snap device comprising:
a sheet metal spring member having a double-loop end opposite to a
closed end, said spring member having a first outer leg, a second outer leg, a
first inner
leg, a second inner leg, and a cross member, said first outer leg being
coupled to said
second outer leg by way of said cross member at said closed end, said first
outer leg
coupled to said first inner leg by way of a first loop at said double-loop end
to define a
first slit between said first outer leg and said first inner leg and
longitudinally extending
from said cross member and terminating at a first termination point at said
first loop,
said second outer leg coupled to said second inner leg by way of a second loop
at said
double-loop end to define a second slit between said second outer leg and said
second
inner leg and longitudinally extending from said cross member and terminating
at a
second termination point at said second loop, said sheet metal spring member
being
distorted to place said inner legs out of coplanar alignment with said outer
legs to
provide said sheet metal spring member with a snap action;
an anchor point joining said first inner leg to said second inner leg at a
location between said double-loop end and said closed end;


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a lever having an actuation end opposite a reaction end with a pivot
situated therebetween, said reaction end being coupled to said anchor point;
an actuator acting upon said actuation end to move said actuation end
relative to said pivot in a positive direction past a forward trip point and
in a negative
direction past a return trip point, whereby said sheet metal spring member
experiences
said snap action at said forward trip point and said return trip point with
the distance
between said forward trip point and said return trip point being defined as a
differential;
a housing coupled to said pivot;
a first electrical contact on said cross member;
a first stop attached to said housing; and
a second stop attached to said housing with one of said first stop and said
second stop serving as a second electrical contact, said first electrical
contact moving
down from said first stop to said second stop when said actuation end moves
down upon
said actuator applying an actuation force downward against said actuation end,
said
actuation force being less than a contact force with said contact force being
that force
which is exerted by said first electrical contact against said second
electrical contact
when said first electrical contact is against said second stop.
22. The auto-snap device of claim 21 further comprising a third electrical
contact wherein said first stop serves as said second electrical contact and
said second
stop serves as said third electrical contact.
23. The auto-snap device of claim 21 wherein said pivot enables said lever to
tilt by way of a bending action.
24. An auto-snap device comprising:
a housing;
a first stop coupled to said housing;
a second stop coupled to said housing and spaced apart from said first
stop;
a first electrical contact moveable between said first stop and said second
stop;
a second electrical contact on one of said first stop and said second stop,
said first electrical contact selectively engaging and disengaging said second
electrical
contact as said first electrical contact moves between said first stop and
said second stop;


-12-


and an actuator having a rest position, a fully forward position, and an
intermediate position therebetween, said actuator being coupled to said first
electrical
contact such that said first electrical contact pushes with a first force
toward said first
stop when said actuator is at said rest position, said first electrical
contact pushes with a
second force toward said second stop when said actuator is at said fully
forward position,
and said first electrical contact pushes with a third force toward said first
stop when said
actuator is at said intermediate position, said third force being greater than
said first
force.
25. The auto-snap device of claim 24 further comprising:
a sheet metal spring member having a double-loop end opposite a closed
end, said spring member having a first outer leg, a second outer leg, a first
inner leg, a
second inner leg, and a cross member, said first outer leg being coupled to
said second
outer leg by way of said cross member at said closed end, said first outer leg
coupled to
said first inner leg by way of a first loop at said double-loop end to define
a first slit
between said first outer leg and said first inner leg and longitudinally
extending from
said cross member and terminating at a first termination point at said first
loop, said
second outer leg coupled to said second inner leg by way of a second loop at
said
double-loop end to define a second slit between said second outer leg and said
second
inner leg and longitudinally extending from said cross member and terminating
at a
second termination point at said second loop, said sheet metal spring member
being
distorted to place said inner legs out of coplanar alignment with said outer
legs to
provide said sheet metal spring member with a snap action, said first
electrical contact
being disposed on said cross member;
an anchor point joining said first inner leg to said second inner leg at a
location between said double-loop end and said closed end;
and a lever having an actuation end opposite a reaction end with a pivot
situated therebetween, said reaction end being coupled to said anchor point,
said
actuation end engaging said actuator, said actuator acting upon said actuation
end to
move said actuation end relative to said pivot in a positive direction past a
forward trip
point and in a negative direction past a return trip point, whereby said sheet
metal spring
member experiences said snap action at said forward trip point and said return
trip point
with the distance between said forward trip point and said return trip point
being defined
as a differential.

Description

CA 02341698 2004-07-13
MEANS FOR ACTUATING A SNAP-ACTING M-BLADE
Background of the Invention
Field of The Invention
The subject invention generally pertains to temperature and pressure
responsive
snap-acting switches and more specifically to novel means for actuating them.
Description of Related Art
Heretofore it has been well known to provide overcenter snap springs for
electrical control devices such as thermostats and switches. U.S. patents to
Burch, Nos.
3,213,228; 4,032,734; 4,424,506; 4,796,355 and Schwab Patent 5,555,972 (all of
which
may be referred to for further details) disclose how to stress a flat M-shaped
spring
member (M-blade) to become snap acting by spreading the inner legs of its U-
shaped
loops with an actuating member, thus side-stressing the planar spring member
thereby
causing it to become snap-acting and bistable.
The applicant of the present invention has designed, used and reduced to
practice
and commercialized numerous products using the M-blade for over 15 years and
has
become expert at Burch M-blade technology in the process. As a result of this
work, the
inventor of the present application has made numerous additional improvements,
discoveries and observations which greatly reduce the cost of producing snap-
switch
products and expand the usefulness and scope of application. In particular,
the present
invention relates to new methods for operating and actuating the M-blade
spring element
to cause it to snap overcenter and relates to means for constructing M-blade
snap- acting
switches with very low actuating forces ( 15 grams) and fewer moving parts.
These
improvements, discoveries and observations are the objects of this application
for patent.
One such observation is that typically conventional snap switches comprise two
moving parts to complete the electrical connections from a common terminal to
the other
switch terminals. A contact arm has a spring portion that urges an arm against
a hinge
member, wherein the hinge member engages the contact arm at one end and
engages the
switch common terminal at the other to complete the electrical circuit.
Other drawbacks of e,.isting snap-acting devices include inconsistent snap
action,
sluggish snap action; actuation forces that are relatively high compared tc
the contact
forces; excessively Large differentials, i.e. deadband distance the actuator
must travel
between two states of equilibrium and travel direction of actuator relative to
moving


CA 02341698 2002-O1-11
-2-
contact being incompatible with established electrical standards of normally
open and
normally closed terminal locations.
Summary of the Invention
To avoid the limitations and problems of existing snap-acting switches, the
S invention seeks to provide a bridge actuator that engages a critical region
of an M-blade to
provide extremely quick snap action at an extremely low differential of .001
inches or less.
Further the invention seeks to actuate an M-blade with a lever to provide a
contact force that is greater than the actuation force.
Further still the invention seeks to provide a lever that moves a common
electrical
contact in the same direction as the actuator in agreement with established
electrical
standards pertaining to the location of normally open and normally closed
terminals.
Still further the invention seeks to provide a temperature responsive switch
that is
consistently reliable by having a snap-acting disc act upon a snap-acting M-
blade.
Yet further the invention seeks to provide a temperature responsive switch
that is
extremely compact by virtue of a bridge straddling a terminal to engage the
critical region
of an M-blade.
Moreover the invention seeks to provide a lever having an integral tab that
bends
to serve as a pivot.
These and other aspects of the invention are provided by an M-blade being
actuated by at least one of a lever and a bridge. The bridge engages a
critical region in
the double-loop end of the M-blade to provide extremely quick snap actuation
at an
extremely low differential. The lever engages the center legs of an M-blade to
provide a
contact force greater than the force acting on the lever. The lever includes
an integral tab
that bends to allow the lever to tilt.
More particularly one aspect of~ the invention pertains to an auto-snap device
comprising a housing, a first stop coupled to the housing, a second stop
coupled to the
housing and spaced apart from the first stop, a first electrical contact
moveable between
the first stop and the second stop and a second electrical contact on one of
the first stop
and the second stop, the first electrical contact selectively engaging and
disengaging the
second electrical contact a5 the fast electrical contact moves between the
first stop and the
second stop. An actuator has a rest position, a fully forward position and an
intermediate
position therebetween, the actuator being coupled to the first electrical
contact such that


CA 02341698 2002-O1-11
._
the first electrical contact pushes with a first ford toward the first stop
when the actuator
is at the rest position, the first electrical contact pushes with a second
force toward the
second stop when the actuator is at the fully forward position and the first
electrical
contact pushes with a third force toward the first stop when the actuator is
at the
intermediate position, the third force being greater than the first force.
Another aspect of the invention provides an auto-snap device, comprising a
sheet
metal spring member having a double-loop end opposite to a closed end, the
sheet metal
spring member having a first outer leg, a second outer leg, a first inner leg,
a second inner
leg and a cross member. The first outer leg is coupled to the second outer leg
by way of
the cross member at the closed end. 'fhe first outer leg is coupled to the
first inner leg by
way of a first loop at the double-loop end to define a first slit between the
first outer leg
and the first inner leg and longitudinally extends from the cross member and
terminating
at a first termination point at the first loop. The second outer leg is
coupled to the second
inner leg by way of a second loop at the double-loop end to define a second
slit between
the second outer leg and the second inner leg and longitudinally extends from
the cross
member and terminates at a second termination point at the second loop. The
first loop
includes a first sweet spot situated such that the first termination point is
between the first
sweet spot and the cross member and the f:~rst termination point is further
situated between
the first sweet spot and the second loop. The second loop includes a second
sweet spot
situated such that the second termination point is between the second sweet
spot and the
cross member and the second termination point is further situated between the
second
sweet spot and the first loop. ~fhe sheet metal spring member is distorted to
place the
inner legs out of coplanar alignment with the outer legs to provide the sheet
metal spring
member with a snap action. An anchor point joins the first inner leg to the
second inner
leg at a location between the double-loop end and the closed end and a bridge
engages the
first sweet spot and the second sweet spot. An actuator is adapted to move the
bridge
relative to the anchor point in a positive direction past a forward trip point
and in a
negative direction past a return trip point, whereby the sheet metal spring
member
experiences the snap action at the forward trip point and at the return trip
point with the
distance between the forward trip point and the return trip point being
defined as a
differential.
Brief Description of the Drawings
Figure 1 is a schematic perspective of the invention.


CA 02341698 2002-O1-11
- 2B -
Figure 2 is the top view of an M-blade with its critical sweet spots being
cross-
hatched.
Figure 3 is a central cross-sectional view of a bridge actuated switch with
its
moving contact touching a normally closed terminal.
Figure 4 is the same view as figure 3, but with the moving contact touching a
normally open terminal.
Figure 5 shows where the bridge engages the M-blade of Figures 3 and 4.


CA 02341698 2001-02-26
WO 99/56294 PCT/US98/08342
-3-
Figure 6 is a cross-sectional side view of an adjustable, temperature
responsive
switch having a bridge actuated by a bimetallic arm.
Figure 7 is a cross-sectional view (taken along line 7-7 of Fig. 9) of a
compact
switch having two snap-acting elements.
Figure 8 is the switch of Figure 7 after being actuated.
Figure 9 is a cross-sectional view of Figure 7 taken along line 9-9.
Figure 10 is a perspective view of a lever actuated M-blade.
Figure 11 is a cut-away view of a lever actuated M-blade incorporated in an
electrical switch.
Figure 12 is the switch of Figure 11 after being actuated.
Figure 13 is the switch of Figure 11 showing the rest position of its
actuator.
Figure 14 is the switch of Figure 11 showing the intermediate position of its
actuator.
Figure 15 is the switch of Figure 11 showing the fully forward position of its
actuator.
Figure 16 is a graph showing how the contact force varies as a function of the
actuator's position.
Description Of The Preferred Embodiment
An auto-snap device 10 of Figure 1 includes a sheet metal spring member 12, an
anchor point 14 (e.g., rivet or weld spots), an electrically non-conductive
phenolic bridge
16, and an actuator 18. Spring member 12, also shown in Figure 2, includes a
double-
loop end 20 opposite a closed end 22, a first outer leg 24, a second outer leg
26, a first
inner leg 28, a second inner leg 30, a cross member 32, a first loop 34, and a
second loop
36. A first slit 38 extends from cross member 32 to a first termination point
40. A
second slit 42 extends to a second termination point 44. Termination points 40
and 44
are specifically defined as two points spaced as far away from each other as
possible
while remaining within slits 38 and 42, respectively, and being equidistant
from cross
member 32. To further define their location, points 40 and 44 are spaced as
far away as
possible from cross member 32 without compromising the aforementioned location
criteria.
A tab 46 near anchor point 14 spreads inner legs 28 and 30 apart to distort
spring
member 12 out of coplanar alignment with itself. This distortion provides
spring
member 12 with two positions of equilibrium as indicated by arrows 48 and S0.


CA 02341698 2001-02-26
WO 99/56294 PCT/US98/08342
-4-
An external force 52 can urge spring member 12 to snap over from one position
48 to the
other 50. This rapid snap-over movement from one position to the other is
referred to
herein and below as "snap action".
For auto-snap device 10 of Figure 1, external force 52 is provided by bridge
16
acting upon double-loop end 20 with a counteracting force provided at anchor
point 14.
Bridge 16 makes contact with spring member 12 at two regions each referred to
as a
"sweet spot". Referring to Figure 2, sweet spots 54 and 56 are defined as
those areas
that extend in two orthogonal directions beyond slits 38 and 92, i.e., above
and to the left
of termination point 44 for sweet spot 56 and below and to the left of
termination point
40 for sweet spot 54.
The results of applying an actuation force to sweet spots 54 and 56 is best
explained with reference to a switch 58 of Figures 3, 4 and 5. Switch 58
includes a first
electrical contact 60, a first stop 62 serving as a second electrical contact
64 and a
second stop 66 serving as a third electrical contact 68. Contact 60 snaps over
from
contact 68 (see Figure 3) to contact 64 (see Figure 4) as bridge 16 (traveling
in a positive
direction 70 from point 72) reaches a forward trip point 74. Contact 60 snaps
back to
contact 68 as bridge 16 returns in a negative direction 76 to return trip
point 78. The
distance between trip points 74 and 78 is referred to a differential 80. When
bridge 16
acts upon sweet spots 54 and 56 (as shown in Figure 5), differential 80 is
surprisingly no
more than 10 to 20 percent of a predetermined distance 82 that contact 60
travels.
Applying an actuation force outside sweet spots 54 and 56 results in
undesirably high
differentials and sluggish snap action.
An adjustable oven thermostat 84, shown in Figure 6, includes an inverted
bridge
16' acting upon sweet spots 54' and 56', and actuated by a temperature
responsive
bimetallic arm 86; spring member 12' with double-loop end 20'; an adjustment
screw 88
acting upon anchor point 14'; a leaf spring 90 attached to anchor point 14'
and urging its
center legs (one being item 30') toward screw 88; and a mounting post 92 that
holds
screw 88 spring 90, a stop 94, an electrical contact 60', and actuator arm 86.
A
temperature change causes arm 86 to move bridge 16', which in turn causes
spring
member 12' to experience a snap action that rapidly moves contact 60' between
stop 94
and a contact 98. Adjustment screw 88 determines a temperature threshold at
which the
snap action occurs.
Figures 7, 8 and 9 illustrate an over-temperature switch 100 that includes a
thermally conductive cover 101, and two snap action components. Switch 100
includes
a spring member 12", providing a first snap action; a bimetallic disc 102,
providing a
second snap action; an electrical terminal 104 attached to an anchor point
14'; a bridge


CA 02341698 2001-02-26
WO 99/56294 PCT/US98/08342
-$-
106 straddling terminal 104 and made of an electrically insulated material
such as a
phenolic; and a housing 107.
Disc 102 is a conventional bimetal disc that snaps overcenter upon reaching a
temperature limit. The disc serves as a protective device commonly found in a
variety of
small kitchen appliances. When switch 100 reaches a predetermined temperature
limit,
disc 102 snaps overcenter. As a result, disc 102 pushes against a protrusion
108 and
bridge 106. This causes spring member 12" to snap over to break electrical
continuity
between contacts 60" and 68, as shown in Figure 8. As switch 100 cools down,
disc 102
and spring member 12" snap back as shown in Figure 7.
In Figure 10, a lever 110 is coupled to spring member 12 at anchor point 14.
Lever 110 has an actuation end 112 opposite a reaction end 114 with a pivot
116
therebetween. In one embodiment of the invention, pivot 116 comprises a sheet
metal
tab 118 whose bending action allows lever 110 to tilt.
When incorporated into a switch 120 within housing 122 as shown in Figure 11,
lever 110 is actuated by an actuating plunger 124 Upon exerting an actuation
force 126
against actuation end 112, spring member 12 snaps over to push contact 60
against
contact 64 with a contact force 128 (see Figure 12). Lever 110 is such that
contact force
128 is greater than actuation force 126. Switch 120 snaps back, as shown in
Figure 11,
upon removing actuation force 126. Plunger 124 and contact 60 both move in
generally
the same direction, i.e., positive direction 70 and negative direction 76. The
timing of
the snap action between stops 62 and 66 (or contacts 64 and 68) is determined
by a
forward trip point 130, a return trip point 132, and differential 134.
Actuator plunger 124 moves from a rest position 140 (Figure 13), past an
intermediate position 142 (Figure 14), and to a fully forward position 144
(Figure 15).
As it does this, the force contact 60 exerts against contact 68 varies as
plotted in Figure
16. Force 146 at intermediate position 142 is greater than force 148 at rest
position 140.
The vertical line 150 of Figure 16 is where switch 120 snaps over to contact
64.
Although the invention is described with respect to a preferred embodiment,
modifications thereto will be apparent to those skilled in the art. Therefore,
the scope of
the invention is to be determined by reference to the claims which follow.

Representative Drawing