Pneumatic reed switch

An invention is disclosed wherein one portion of conductor is fastened to a housing and another portion is movable. Fluid pressure applied through a passage forces the movable portion into contact with electrical terminals.

The invention relates to electrical switches and, more particularly, to 
switches of this type which utilize a reed conductor to complete a circuit 
between switching contacts. 
BACKGROUND OF THE INVENTION 
It is sometimes necessary to accomplish electrical switching in a remote, 
high temperature environment which is subject to high centrifugal forces. 
For example, in a gas turbine engine, temperatures can exceed 1000.degree. 
F. and rotating components can experience centrifugal forces of the order 
of 10,000 g's. In such an environment, ordinary remote switching means, 
such as transistors and relays, are found to be inadequate. Further, space 
limitations inside such engines dictate that any switches contained 
therein be of minimal size. 
OBJECTS OF THE INVENTION 
It is an object of the present invention to provide a new and improved 
electrical switch. 
It is a further object of the present invention to provide a new and 
improved remotely operated electrical switch which is tolerant of a high 
temperature environment. 
It is a further object of the present invention to provide a new and 
improved electrical switch which is operable in a high centrifugal force 
field. 
SUMMARY OF THE INVENTION 
One form of the switch of the present invention comprises a plurality of 
terminals supported near a movable conductor. Fluid pressure selectively 
applied to the conductor through a passage forces the movable conductor 
into contact with the terminals.

DETAILED DESCRIPTION OF THE INVENTION 
One form of the invention is shown in FIG. 1 wherein a housing 3 contains a 
V-shaped chamber 6. A first chamber wall 9 comprises a first leg of the 
"V" while a second chamber wall 12 comprises the second leg of the "V". A 
first electrical conductor 15 is extended along, and is fastened to, the 
first wall 9. This conductor is preferably a thin, elongated metallic 
foil, such as stainless steel or an alloy comprising nickel and chromium, 
and approximately 0.003 in. (0.0076 cm) thick. The foil may be plated with 
a low resistivity material such as gold. A second electrical conductor 18 
is fastened to the apex of the "V", namely at region 21. Both conductors 
15 and 18 extend away from the apex of the "V" through the housing, that 
is, through the region designated 24, and in this region are separated 
from each other by an electrical insulator 27 which is sandwiched between 
them. Insulator 27 may be constructed of a suitable high temperature 
material such as a glass, a ceramic, or asbestos. 
The second conductor 18 extends into the chamber 6 and extends along or 
near the second chamber wall 12. The second conductor 18 is preferably 
elongated, in that it extends away from the apex region 21 and 
substantially along the length 30 of chamber 6. The second conductor 18 is 
further reed-like in that it is elongated, wide, thin (approximately 0.003 
in. [0.0076 cm] thick), and flexible. The housing 3 contains an inlet air 
passage 33 which communicates with the chamber 6 through the second 
chamber wall 12. The housing 3 further contains an exhaust air passage 36 
which communicates with the chamber by penetrating the first chamber wall 
9 as well as the first conductor 15. The wide side, namely the side facing 
the first conductor 15, of the second conductor 18 is preferably of a 
shape identical to the second wall 12 but slightly smaller in size so that 
there is a clearance of, for example, 0.001 in. between itself and the 
housing 3 along edges 37, 39 and 42. Edges 37, 39, and 42 are more clearly 
shown in FIG. 3 and the clearance is indicated as spaces 37A, 39A, and 
42A. 
Being flexible, the second conductor 18 can be moved in the directions of 
arrows 48 and 51, but its natural tendency is to remain out of contact 
with the first conductor 15 either through the inherent resiliency of the 
second conductor 18 or through the centrifugal loading applied to it as 
explained below. 
The operation of the switch of FIG. 1 in the absence of centrifugal loading 
is as follows. Second conductor 18 serves to divide chamber 6 into two 
sub-chambers, namely 6A and 6B. A pressurized fluid such as air is applied 
to the inlet air passage 33, tending to expand sub-chamber 6B and to apply 
a force to the second conductor 18 in the direction of arrow 48 thereby 
moving the second conductor into contact with the first conductor 15. In 
so moving, the second conductor 18 reduces the size of sub-chamber 6B and 
the air which must be displaced by this reduction is exhausted through 
exhaust passage 36. If the air pressure is removed from inlet passage 33, 
the resiliency of the second conductor 18 (and, again, possibly 
centrifugal force) will cause it to move in the direction of arrow 51 
thereby displacing air contained in the sub-chamber 6B through the inlet 
passage 33. Of course, this latter motion may be assisted by the 
application of air pressure to exhaust passage 36. 
A second embodiment of the invention is shown in exploded form in FIG. 2. 
In that Figure, a rectangular first base 65, which is preferably a solid, 
heat-resistant ceramic such as sapphire or aluminum oxide sputtered to a 
stainless steel substrate is penetrated by and supports a pair of rod-like 
electrical terminals or contacts 68A-B. An exhaust passage 70 extends 
through the first base 65. A thin first rectangular layer or lamina 71, 
having a rectangular hole 72 cut in the center thereof is supported by the 
base 65. The rectangular hole 72 must be wide enough to allow the 
terminals 68A-B to pass therethrough so that the first rectangular layer 
can contact the first base 65. 
A thin second rectangular layer 73 is positioned adjacent the first 
rectangular layer 71. The second rectangular layer 73 includes a reed or 
contact member 74 which can be integrally formed into the second layer 73 
by cutting parallel slits 75 and 77 through the second layer 73 and 
connecting them with a slit 79 to provide a thin, elongated contact member 
74 supported at region 80. Since the second layer 73 is preferably 
composed of a thin material, the contact member 74 can be moved in the 
direction of arrows 83 and 86, that is, the contact member 74 is flexible 
and can pivot about the region of support 80 in the direction of arrows 83 
and 86. It is to be noted that the distance 68C, namely the distance which 
the terminals 68A-B extend above the surface of the rectangular base 65, 
must be less than the thickness of the first rectangular layer 71. 
Otherwise, the contact member 74 will at all times be in contact with the 
terminals 68A-B, thereby completing the circuit across them at all times. 
However, it is envisioned that it may be desirable in some cases to 
construct a switch in which the contact member 74 normally is in contact 
with the terminal 68-B. In such a case, the contact member will be 
disconnected from the terminals 68A-B by air pressure applied to the 
exhaust passage 70. 
A third rectangular layer 80, preferably identical in size and shape to the 
first layer 71, is positioned on top of the second layer 73. A second 
rectangular base 81, containing an inlet passage 84, lacking structures 
analogous to terminals 68A-B, but otherwise identical to rectangular base 
65 is positioned atop the third rectangular layer 80. The entire structure 
described forms a five-layered sandwich which can be clamped together by 
suitable means such as passing bolts (not shown) through holes 88, by 
diffusion bonding or welding. 
In a preferred form of the second embodiment, all of the rectangular 
components described have a length of 0.75 in. (1.95 cm) and a width of 
0.375 in. (0.953 cm), which dimensions correspond to, respectively, 
dimensions 92 and 93. The two rectangular bases 65 and 81 are preferably 
0.125 in. (0.318 cm) thick, which is the length of dimension 94. The three 
rectangular layers, namely 71, 73 and 80 in addition to having the lengths 
and widths just described, are preferably 0.004 inches thick and 
constructed of stainless steel. The reed or contact member 74 is 
preferably 0.5 in. (1.27 cm) long (dimension 95) and 0.125 in. (0.318 cm) 
wide (dimension 96). Reed 74 is preferably gold plated in the region near 
terminals 68A-B for better conductivity. 
The operation of the second embodiment of FIG. 2 is as follows. When air 
pressure is applied to the inlet passage 84, the pressure transmits a 
force to the reed 74 tending to push it in the direction indicated by 
arrow 86 and the force pushes the reed 74 into contact with the terminals 
68A-B. When contact is made between the reed 74 and terminals 68A-B the 
circuit is completed between these terminals. During this motion of reed 
74, the space contained within the rectangle 72 in the first rectangular 
layer 71 is decreased in volume and the air therein which is displaced is 
exhausted through the exhaust passage 70. When the air pressure is removed 
from the inlet passage 84, the reed 74 will tend to return to its original 
position due to its inherent resiliency, thus displacing air from the 
space containing within rectangle 98 in the third rectangular layer 80. 
This air flows out through the inlet passage 84. Of course, the return of 
reed 74 to its original position may be assisted by the application of air 
pressure to the exhaust passage 70. 
A third embodiment is contemplated in which the first and third rectangular 
layers are constructed of an insulating material such as asbestos and ony 
one of the terminals 68A-B is present. In this case, reed 74 itself serves 
as the other terminal. 
The use of any of the above embodiments in a high centrifugal force field 
such as in a gas turbine engine will now be described. FIG. 3 shows an 
axis 104 about which the housing 3 of FIG. 1 is rotated in the direction 
of arrow 105. The successive positions of housing 3 are indicated by 
phantom outlines 106A-C. (It is to be noted that the flat, wide surfaces 
of reed 18 are parallel to, and spin in, a radial plane, namely the plane 
of FIG. 3. The reed 18 moves in a path, indicated by curved arrows 48 and 
51, shown in FIG. 1, which path is actually arcuate, since the reed 18 
pivots about apex at region 21 in FIG. 1. However, the component of motion 
of the reed 18 in the radial direction (that is, in a direction against 
the centrifugal force) is viewed as small because the deflection of the 
reed 18 from its original position is small. Thus, the motion of the reed 
18 is viewed as being substantially parallel with the axis of rotation, 
that is, perpendicular to the plane of FIG. 3. 
During this rotation the switch experiences a radially directed force, 
commonly called centrifugal force, in the direction of arrows 108. At high 
rotational speeds, the centrifugal force can be extremely large. For 
example, at 10,000 rpm, an object 6 in. (0.5 foot) away from the axis of 
rotation experiences a centrifugal acceleration of 5.8.times.10.sup.5 
feet/sec.sup.2, which is approximately equivalent to 17,000 g's. Utilizing 
a switch under these conditions wherein a component is moved in a 
direction opposite to the centrifugal force, will require a similarly 
enormous force to move the component against the inhibiting centrifugal 
force. 
However, in the case of the switches of the first and second embodiments of 
the present invention, the centrifugal force is seen as assisting and not 
inhibiting the switching operation. The switching reeds 18 and 74 of FIGS. 
1 and 2 have been described as being 0.003 and 0.004 in. (0.0076 and 0.010 
cm) thick, respectively. That is, the reeds 18 and 74 are constructed of 
thin metallic foil. They can be thought of as flimsy for that reason. 
However, in the environment of the large, radial centrifugal force field, 
the otherwise flimsy foil, which extends in the radial direction, becomes 
rigid due to centrifugal stiffening. Viewed another way, a relatively 
large amount of strength and resiliency is imparted to a very lightweight 
and relatively weak material during rotation. Accordingly, the tendency of 
the switching reed 18 to return to its original position upon release of 
the air pressure from inlet passage 33 is increased, yet without the 
addition of springs or mass to the reed which would otherwise be needed in 
a static, nonrotating situation. The operation of the second embodiment 
during rotation is similar to that just described for the first 
embodiment. 
In a fourth embodiment of the invention, passages 115 and 118 (shown as 
dashed lines) are contained in rectangular bases 65 and 81 in FIG. 2, 
respectively, so that air pressure may be supplied to the passages 70 and 
84, respectively, from the end surfaces 119A and 119B. 
It has been found that the switching reed 18 or 74 sometimes flutters or 
vibrates during use. It is theorized that the vibration is caused by the 
blockage of the exhaust air passage 36 or 70 by the respective reed 18 or 
74. Such a blockage reduces airflow through the exhaust passage and, it is 
thought, reduces the force applied to the reed, thus allowing the reed to 
return to its original position. One method of alleviating this problem 
has been to provide a hole such as hole 120 in the reed 74. The hole 120 
allows continuity of some of the airflow through the exhaust passage 84. A 
similar hole 120A can be provided in the second conductor 18 in FIG. 1. 
A related patent application entitled, "Pneumatic Ball Contact Switch," by 
Danny L. Fenwick and Jon D. Hopkins, Ser. No. 06/443,826, which is 
concurrently filed herewith and assigned to a common assignee, is hereby 
incorporated by reference. The fluid pressure applied to the present 
invention can be provided by the invention described in the patent 
application entitled, "Pneumatic Signal Multiplexer," by Danny L. Fenwick 
and Charles M. Stanforth, Ser. No. 06/443,825, which is concurrently filed 
herewith, assigned to a common assignee, and hereby incorporated by 
reference herein. 
The switch of the present invention provides a remote electrical switching 
function which is tolerant to high temperatures and which can operate in a 
high centrifugal force field. Further, the centrifugal force field is 
utilized to provide a resiliency characteristic tending to push the 
switching member into a predetermined position and this characteristic is 
much greater than is obtained in the static case for the size and weight 
of the materials involved. 
While several embodiments of the invention have been described, it will be 
obvious to those skilled in the art that numerous modifications and 
substitutions can be undertaken without departing from the true spirit and 
scope of the present invention.