Pressure actuated snap switch

First and second contact bars are spaced apart in fixed positions. A pressure responsive ram has first and second positions of penetration into a casing which contains the bars and other elements. A bolt is disposed between the ram and a first element which is pivotable about the second bar between a first position and a second position. A second elemtn is coupled to the first element. When the ram is in its first position, the bolt places the first element in the first position causing the second element to establish a current carrying path between the bars. When the ram is in its second position, the bolt places the first element in the second position, causing the second element to break the current path. A device disposed between the belt and the ram exerts a biasing pressure on one end of the ram which maintains the ram in its first position. When a larger pressure is exerted on the other end of the ram, the ram is moved into the second position.

BACKGROUND OF THE INVENTION 
The present invention relates to a pressure-actuated snap switch with a 
casing, wherein a connecting link is supported by spring tension in a 
bearing. The switching operation is under control of a bolt guided in the 
switch casing. The bolt itself is controlled by a ram passing through the 
casing wall and bearing upon the longer lever arm of a lever pivotably 
mounted in the casing. 
In order to initiate a switching action in such a snap switch, it is 
necessary for a force acting upon the operating ram, to be sufficiently 
high to force a snap spring over the dead-center position and, optionally, 
to tension an additional restoring spring. The force which has to be 
applied is several times greater than that producing the contact pressure. 
Thus, if a minimum contact pressure is required, this presupposes the 
action of a correspondingly higher force on the operating ram. In 
applications where only limited forces are available for operating the 
switch, as for example when the switch is to be tripped by shock waves in 
the medium surrounding it, the attainable contact pressure is normally 
limited. 
It has been known to use a compression spring to actuate the ram by 
pretensioning the spring to such an extent that the force or tension 
stored therein is lower than that necessary for initiating the switching 
operation. Thus, in this embodiment only a small additional force acting 
on the operating ram is necessary for initiating the switching operation. 
In order to be able to better adapt such a snap switch to the operating 
conditions, it has also been proposed in connection with this embodiment 
to operate the operating ram via a lever and not directly. An auxilliary 
ram acts upon the lever, and a pretensioned opposing spring adjustable 
counter to the operation of the auxiliary ram acts on the lever. This 
embodiment suffers from the disadvantage that there are two springs, which 
partly reciprocally compensate one another and consequently make the 
construction more complicated and expensive. Moreover, during operation, 
the length of the opposing spring and consequently the force stored 
therein is significantly changed. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to further develop a snap switch 
of the aforementioned type so that only one spring is required, whose 
force value only changes insignificantly during operation. 
In accordance with the principles of the invention, a snap switch mounted 
in a casing is provided with first and second contact bars which are 
spaced apart in fixed positions. A first electrically conductive element 
is pivotable about the second bar between first and second positions. A 
second electrically conductive element is mechanically and electrically 
coupled to the first means. The second element, when the first element is 
in the first position, is moved to a corresponding first position at which 
a current carrying path is established between the first and second bars, 
and when the first element is in the second position, is moved to a 
corresponding second position at which said path is broken. 
A pressure responsive ram has one end extending into the casing, which is 
disposed adjacent but spaced from said first element and has an opposite 
end disposed outside the casing. The one end of the ram has first and 
second positions of penetration into the casing, the depth of penetration 
being greater in the second position then that in the first position. The 
first element is in its first position when the one end of the ram is in 
the first penetration position and is in its second position when the one 
end of the ram is in the second penetration position. 
A bolt is disposed between the one end of the ram and the first element to 
place the first element in the first position when the one end of the ram 
is in the first penetration position and to place the first element in the 
second position when the one end of the ram is in the second position. 
A biasing device is disposed between the bolt and the one end of the ram to 
exert a biasing pressure on the one end of the ram which in the absence of 
a larger and oppositely directed pressure on the other end of the ram 
maintains the one end of the ram in the first penetration position whereby 
the current carrying path is established, said path being opened when said 
larger and oppositely directed pressure is applied to the other end of the 
ram and causes the one end of the ram to be moved into the second position 
of penetration. 
A tension spring may be provided which is pretensioned against the casing, 
which acts under a small acute angle on a lever arm whereby the component 
of the force stored in the tension spring acting on the lever is lower 
than the force necessary to initiate the switching operation. Only one 
tension spring is required for starting the switching operation. As a 
result of its geometrical arrangement with respect to the lever, the 
reduction of its force value is kept small. This permits switching with 
constant pressures of the medium. The foregoing as well as additional 
objects and advantages of the invention will either be explained or will 
become apparent to those skilled in the art when this specification is 
read in conjunction with the brief description of the drawings and the 
detailed description of preferred embodiments which follow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The FIGURE shows the switch in one position wherein a current path is 
established between fixed contact bars 27 and 26 via a contact 10 provided 
on a link 5, and a bow shaped member 3. The member 3 which conducts 
current together with a bearing 28 is pivotable about bar 26 in a casing 2 
under the control of a bolt 1. Link 5 has knife edges 6 and is movably 
mounted in a bearing 28 having a knife-edge support 4. A snap spring 7 is 
movably fixed at its one end 8 to a bolt 25 supported in casing 2 and at 
its other end 9 to the connecting link 5. Thus, snap spring 7 holds 
together under pretension the snap-action system which comprises 
bow-shaped member 3, bearing 28 and connecting link 5. This pretension 
builds up a first contact pressure, for example of x.cN at a contact point 
of contact 10 of the contact bar 27. The first contact pressure of x.cN 
leads to establishment of a second force of 8x.cN in the direction of 
arrow A at a support point 11 of bolt 1. In turn, this force requires an 
operating force of 8x.cN in the direction of arrow C. 
In order to reduce the operating force in the direction of arrow C from 
8x.cN to a lower amount, as for example 2x.cN, a two-arm bent lever 13 
movably mounted on a fulcrum 12 in casing 2 is applied in support point 
11. A tension spring 14, has one end 14' applied to an angle tip 15 of the 
two-arm lever 13 and the other end 14" applied to an application point 16 
on a bearing bolt 17 displaceable in the direction of arrow B and reduces 
the operating force in the direction of arrow C. As a result of the 
leverage of lever arms 13' and 13", a force in the direction of arrow E is 
obtained on a bead 18 made in the longer lever arm 13'. This force can be 
overcome by the sought operating force from the outside via a ram 19 with 
a force of 2x.cN applied in the direction of arrow E. The direction of 
movement of ram 19 can coincide with or differ from that of bolt 1. 
In order to maintain variable the necessary operating pressures via ram 19 
on bead 18 in the direction of arrow E, the adjustment of the pretension 
of tension spring 14 can be adjusted. This is brought about by displacing 
bearing bolt 17 in a guide groove 20 running in the direction of arrow B. 
A set screw 21 can be rotated as for example by a screwdriver engaging a 
screw slot 22. An adjustment part 23 screwed on set screw 21 can be moved 
by the latter in the direction of arrow F. Bearing bolt 17 engaging on the 
edge of adjustment part 23 consequently modifies the pretension of tension 
spring 14. Edge 24 appropriately engages bolt 17 under an angle differing 
from 90.degree. to the direction of guide groove 20, so that bearing bolt 
17 rests in clearance-free manner on one side of guide groove 20. 
When the force acting on ram 19 along direction E exceeds the force acting 
in direction D, the bolt 1 is moved against the bearing 28, causing member 
3 to pivot about bar 26. This action causes link 5 to swing contact 10 out 
of engagement with contact bar 27 to interrupt the current path between 
the contact bars 26 and 27. 
While the invention has been described with detailed reference to the 
drawing, it will be obvious to those skilled in the art that many 
modifications and changes can be made within the scope and sphere of the 
invention as defined in the claims which follow.