Condition responsive electrical switch having improved bridging contact means

An electrical switch actuatable upon the occurrence of a preselected level, includes a generally cup shaped, open ended housing which mounts therein a spaced pair of stationary contacts. The housing has two pairs of upwardly extending channels in its side walls, the two channels of the first pair aligned with the stationary contacts and the two channels of the second pair aligned with platform surfaces. An electrically conductive, flexible cruciform element is disposed in the housing with the distal end portions of two legs of the cruciform received respectively in the two channels of the first pair, and the distal end portions of the other two legs of the cruciform received respectively in the two channels of the second pair and resting on the platform surfaces. The stationary contacts may be disposed above or beneath the cruciform element for a normally open or normally closed switch as desired. The stationary contacts may lie in a plane parallel to the plane of the snap acting member or in planes which intersect each other and the plane of the snap acting member. A motion transfer pin extends between the snap acting member and the cruciform element and may be provided with a shoulder to prevent overtravel of the pin.

This invention relates generaly to condition responsive electrical switches 
and more specifically to pressure responsive electrical switches. Such 
switches are disclosed and claimed in coassigned U.S. Pat. No. 3,584,168 
which issued June 8, 1971. Generally, such switches include an open ended 
cup shaped housing in which a switch assembly is mounted comprising a pair 
of terminals extending through apertures in the housing walls, a 
stationary contact mounted on one of the terminals and a cantilever 
supported, flexible contact arm mounting at its distal end a movable 
contact which is adapted to move into portions of engagement and 
disengagement with the stationary contact. The contact arm is prebiased at 
its fixed end toward one of the above positions. A snap acting member is 
received at and closes the open end of the housing. A motion transfer pin 
is disposed between one side of the snap acting member and the contact arm 
while a port fitting is disposed at the opposite side of the snap acting 
member so that a pressure source can be communicated to the opposite side 
of the member. 
Such devices have proven to be very successful since they are relatively 
inexpensive yet are highly reliable in many applications. However with the 
ubiquitousness today of automotive air conditioning a new need has arisen 
which the above described switch cannot meet. In such air conditioning 
systems it is necessary to control evaporator temperature which can be 
accomplished by controlling the evaporator pressure due to the existing 
temperature-pressure relationship, an application requiring a life 
expectancy of 250,000 cycles or more. However in such an application, 
which also involves high pressure differentials, the impact forces on the 
contact arm occasioned by the snapping of the snap acting member are of 
such a magnitude that life expectancy of the switch is only in the order 
of 100,000 cycles at which time metal fatique in the cantilever mounted 
contact arm results in switch failure. 
Among the objects of the present invention, therefore, are the provisions 
of a pressure responsive electrical switch having improved life 
expectancy, a switch which is inexpensive yet reliable, a switch in which 
contact contamination is minimized and a switch which is particularly 
adapted to withstand high energy impact forces occasioned by high pressure 
differential switching. Other objects and features will be in part 
apparent and in part pointed out hereinafter. 
Briefly, a condition responsive electrical switch made in accordance with 
this invention comprises a housing mounting a pair of spaced stationary 
contacts and an electrically conductive, flexible cruciform element having 
the distal end portions of two of its legs aligned with and adapated to 
move into positions of engagement and disengagement with the stationary 
contacts and the distal end portions of its other two legs reacting 
against portions of the housing so that the first two legs are biased 
toward one of their two positions. A snap acting member is mounted on the 
housing and motion transfer pin is disposed between the snap acting member 
and the cruciform element so that snapping of the snap acting member upon 
occurrence of a predetermined condition will cause the motion transfer pin 
to move and force the first two legs of the cruciform element into their 
other position. The stationary contacts can be disposed beneath or above 
the cruciform for a normally opened, close on pressure rise switch or 
normally closed, open on pressure rise switch. The stationary contacts may 
lie in a plane parallel to the plane of the snap acting member or they may 
lie in planes which intersect each other and the plane of the snap acting 
member to optimize contact wiping. In several embodiments contact 
contamination is minimized by providing contact wiping by bending the 
cruciform element so that its legs are at an angle to its main body 
portion. The motion transfer pin may be provided with a shoulder to 
prevent overtravel. 
For the purpose of facilitating an understnading of the invention several 
preferred embodiments have been illustrated in the accompanying drawings, 
form an inspection of which, when considered in connection with the 
following description, the invention, its mode of construction, assembly 
and operation, and many of its advantages should be readily understood and 
appreciated.

Referring now to FIGS. 1 and 2 reference numeral 10 indicates a condition 
responsive electrical switch comprising a base housing 12, a snap acting 
member housing 14 and a port fitting 16. 
Base housing 12 is a generally cylindrical, cup shaped open ended housing 
with a bottom wall 18 and a side wall 20 extending upwardly therefrom. 
Housing 12 may be formed of any good electrically insulative material such 
as a resinous material. A spaced pair of apertures 22,24 are provided in 
bottom wall 18 which accomodate respective terminals 26,28 which extend 
into a switch cavity 30 formed in housing 12. One end of terminals 26,28 
are conveniently bayonet configured, however other terminal ending 
configurations could be employed if preferred. The opposite ends of 
terminals 26,28 disposed inside of switch cavity 30 are formed with 
respective tab portions 32,34 on which are mounted respective stationary 
electrical contacts 36,38 preferably formed of highly electrically 
conductive material such as a silver alloy. Tab portions 40,42 are bent 
from the main body portion of terminal 26 to maintain the terminal at a 
selected fixed position relative to housing 12. In like manner tabs 44 and 
46 are bent from the main body portion of terminal 28 to maintain it in a 
selected fixed location. A series of lands 48 and grooves 50 may be 
provided in the bottom wall of housing 12 to provide arc shadow and 
prevent tracking from one terminal to the other. 
As best seen in FIG. 2 side wall 20 is formed with first and second pairs 
of upwardly extending channels 50,52 and 54,56. Channels 50,52 of the 
first pair are diametrically opposed to each other and are respectively 
aligned with the stationary contact members 36,38. Channels 54,56 of the 
second pair are also diametrically opposed to each other and are aligned 
with respective platforms 58 and 60. 
An electrically conductive, flexible cruciform element 62 is received in 
housing 12 so that the distal end portions of first and second legs 64,66 
extend respectively into channels 50,52 and the distal end portions of 
third and fourth legs 68,70 extend respectively into channels 54,56 and 
rest respectively on platforms 58,60. It will be seen that channels 54,56 
cooperate with legs 68,70 of cruciform element 62 to maintain it in its 
desired alignment relative to the fixed contacts and the platforms. While 
the provision of channels is a convenient way to maintain the desired 
alignment since they can be included in the mold of the base member, it 
will be understood that equivalent location fixing means such as a cage 
receivable in the housing could be provided. 
A shoulder 72 is formed in the free distal wall portion 20 to facilitate 
reception of a generally disk shaped pin guide 74. Pin guide 74 has a 
centrally located bore 76 extending therethrough which bore slidably 
receives motion transfer pin 78. Pin 78 extends between cruciform element 
62 and snap acting member 80 disposed in housing 12. Snap acting member 80 
is attached at its periphery to annular support member 82 which is used to 
adjust the release pressure calibration of member 82 as set forth in the 
above referenced patent as well as to prevent deleterious effects of over 
pressure on member 82. Housing 14, of any suitable weldable material, snap 
acting member 80, support 82 and ring 84 are welded along their outer 
periphery at 86 to form a hermetic seal. Ring 84 is crimped onto housing 
12 as shown at 88 to fixedly mount housings 14 and 12 together. A 
conventional port fitting 16 having a central threaded bore 90 and 
communicating passage 92 is hermetically connected to housing 14 as be 
welding. 
Thus snap acting member 80 can be brought into communication with a 
pressure source by attaching port fitting 16 to a port in a pressure line. 
As shown in FIG. 1 snap acting member 80 is in a normal, at rest convex 
configuration. Upon occurrence of a preselected condition, for instance a 
particular pressure level, member 80 will snap to a concave cofiguration 
with the central portion thereof moving closer to the switch mechanism. 
This motion is transferred to cruciform element 62 causing the central 
portion of element 62 to be depressed and contacts 94,96 fixed on 
respective distal end portion of first and second legs 64,66 to move into 
engagement respectively with stationary contacts 36,38 as seen in dashed 
lines in FIG. 1, closing an electric current path therebetween. 
It will be seen that contacts 36,38 lie in a plane which is parallel to the 
plane in which the peripheral portion of member 80 lies. 
Upon decrease of the source pressure below the calibrated release pressure 
snap acting member 80 will snap back to its convex configuration and the 
reaction of the distal end portions of legs 68,70 against respective 
platform surfaces 58,60 will cause contacts 94,96 to move into 
disengagement with the stationary contacts. 
The device is easily assembled with identical terminals 26,28 inserted in 
their respective apertures 22,24 in molded base housing 12 and held in 
place by displacing tabs 40,42 and 44,46 or otherwise attaching by 
riveting, welding or the like. Cruciform element 62 is then dropped into 
place with legs 68,70 resting on their respective platform surfaces 58,60. 
Pin guide 74, which is preferably molded, is placed on shoulder 72 of wall 
20 and pin 76 is dropped into bore 76 of guide 74. Finally the snap acting 
member housing 14 and port fitting 16 are placed over base housing 12 and 
crimped thereon. 
The device shown in FIG. 1 is a normally open electrical switch which is 
adapted to close upon a preselected increase in pressure. In that 
structure the stationary contacts are disposed at a distance from the snap 
acting member greater than the distance that cruciform element 62 is 
spaced from the snap acting member. However if it is desired to provide a 
normally closed electrical switch which opens upon a preselected increase 
in pressure stationary contacts 36,38 may be disposed at a distance from 
the snap acting member which is less than the distance that cruciform 
element 62 is spaced from snap acting member 80, as shown in FIG. 3. Thus 
terminals 26' and 28' extend into switch cavity 30 with contacts 36', 38' 
disposed on the lower surface of tab portions 32' 34' in contradistinction 
to the upper surfaces of tabs 32,34 in the FIGS. 1, 2 embodiment. 
Cruciform element 62 is inverted so that contacts 94,96 are disposed on 
the side toward snap acting member 80. Thus upon a pressure rise of a 
preselected level snapping of member 80 will cause legs 64,66 to move into 
disengagement with the stationary contacts and a decrease of pressure to 
the release level will cause legs 64,66 to move into engagement with the 
stationary contacts due to the reaction of legs 68,70 against the platform 
surfaces. 
Also depicted in FIG. 3 is a modified motion transfer pin 78' which is 
formed with a shoulder 100 which has a diameter greater than the diameter 
of bore 76' which extends through motion transfer pin guide 74'. Guide 74' 
is provided with recessed area 102 which cooperates with shoulder 100 to 
prevent overtravel of pin 78'. Limiting travel of the motion transfer pin 
serves to mitigate over stress of cruciform member 62 by absorbing the 
metric energy in guide 74 rather than in cruciform element 62 and hence 
lengthens its useful life. 
Yet another embodiment is shown in FIG. 4 in which contact wiping is 
enhanced. As seen in the figure contacts 36 and 38 of respective terminals 
26" and 28" are disposed in planes which intersect each other and which 
form an actue angle with the plane in which the peripheral portion of the 
snap acting member lies. Terminals 26" and 28" are maintained in a desired 
fixed location by displacing respective tabs 42" and 46" away from the 
main body of their terminals. In this embodiment legs 64',66' are bent 
upwardly so that at their at rest configuration contacts 94,96 are 
disposed at angles conform generally to the stationary contacts. Thus as 
contacts 94 and 96 are brought into engagement and disengagement with 
stationary contacts 36 and 38 respectively the contact surfaces wipe 
against each other as indicated in FIG. 4 by arrows 104,106 with the solid 
line of cruciform element 62 indicating contact disengagement and dashed 
lines indicating contact engagement thereby maintaining the contact 
surface in a clean condition by wiping away arc contaminates which are 
deposited in the contact surfaces by the arcing which occurs on contact 
engagement and disengagement. 
In FIG. 5 an embodiment is depicted which is especially effective in 
minimizing contamination of the contacts which contamination tends to 
occur particularly when direct current is switched due to the depositing 
effect of arcing. The legs of cruciform element 62" are bent downwardly 
(only legs 64",66",68" are shown in the figure) so that contacts 94,96 lie 
in planes which intersect each other as well as the plane in which 
stationary contacts 36 and 38 lie. Cruciform element 62" is shown in FIG. 
5 in the contacts disengaged position. As motion transfer pin 78' is 
depressed it causes the lowermost surface portions of contacts 94,96 to 
engage with respective stationary contacts 36,38. Continued downward 
motion of pin 78' causes contacts 94,96 to rock and slide, as will be 
apparent in FIG. 5a, thereby wiping away any arc contamination which may 
have been deposited on the contact surfaces. Since pin 78' strikes the 
cruciform element with significant inertia the center of element 62" 
actually moves below the solid line position shown in FIG. 5a so the 
contacts slide beyond the position shown and then return to the at rest, 
contacts engages position shown in solid lines in the Figure. Thus upon 
contact engagement wiping of the contact surfaces occurs in two opposite 
directions as noted by arrows 108,110. 
The increase in cycle life of a switch made in accordance with the 
invention in the order of 2.5 times over the conventionally mounted 
cantilever contact arm is made possible because the stress concentration 
on the movable contact arm are greatly reduced. That is, the movable 
contact arm of the present invention, rather than having a fixed end, is 
mounted as a simple plate with four areas of support. 
Thus it will be seen that the invention provides a condition responsive 
electrical switch apparatus which has a markedly increased useful life 
expectancy while still being very simple, reliable and inexpensive to 
produce. 
Various changes and modifications in the above described embodiments such 
as a change in the number of the reaction legs or contact legs of element 
62 will be readily apparent to those skilled in the art and any of such 
changes or modifications are deemed to be within the spirit and scope of 
the present invention as set forth in the appended claims.