US3867594A

US3867594A - Pressure sensitive switch with diaphragm and dish contact means

Info

Publication number: US3867594A
Application number: US420024A
Authority: US
Inventors: Paul E Graf; Daniel R Pimentel
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1973-11-29
Filing date: 1973-11-29
Publication date: 1975-02-18
Anticipated expiration: 1992-02-18

Abstract

A pressure sensitive switch including a resilient diaphragm deformable in response to a difference in pressures on its opposite surfaces. The switch further includes an insulative base, a first electrode carried by said base and a second electrode. The second electrode comprises a resilient deformable dish-shaped conductive element positioned adjacent the first electrode and movable in response to increased force applied thereto to abruptly change its shape from a first curvature wherein it is bowed away from the first electrode to a second curvature wherein it is bowed toward the first electrode and movable in response to a decrease in the force applied thereto to abruptly change from its second curvature and return toward its first curvature. Means linking the diaphragm and the second electrode apply to the second electrode a force which is a function of the degree of deformation of the diaphragm. The switch also includes means which adjustably bias the linking means to resist the application of force to the second electrode by said linking means whereby the second electrode is actuated to its second curvature at a predetermined diaphragm pressure differential.

Description

United States Patent Graf et a1.

[451 Feb. 18, 1975 1 PRESSURE SENSITIVE SWITCH WITH DIAPHRAGM AND DISH CONTACT MEANS [75] Inventors: Paul E. Graf, Foxboro; Daniel R. Pimentel, Seekonk, both of Mass.

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex,

[22] Filed: Nov. 29, 1973 [2]] Appl. No.: 420,024

(52] U.S. Cl. 200/83 P, 200/83 S, 200/275, 200/76 [51] Int. Cl. H0lh 35/34 [58] Field of Search.. ZOO/DIG. l, 181, 76, 83 WM, 200/83 P. 83 S, 83 SA, 83 A, 159 B, 239, 249, 275, 83 R, 83 N [5 6] References Cited UNITED STATES PATENTS 2,453,861 11/1948 Rothwell 200/83 SA 2,773,147 12/1956 Judson 200/83 S 3,549,838 12/1970 Waskowskym. 200/83 WM 3,653,038 3/1972 Webb ZOO/DIG. 1 3,725,907 4/1973 Boulanger 240/365 A Primary Examiner-Robert K. Schaefer Assistant Examiner-Gerald P. Tolin Attorney, Agent, or Firm1larold Levine; John A. Haug; James P. McAndrews III/Z7111 [57] ABSTRACT A pressure sensitive switch including a resilient diaphragm deformable in response to a difference in pressures on its opposite surfaces. The switch further includes an insulative base, a first electrode carried by said base and a second electrode. The second electrode comprises a resilient deformable dish-shaped conductive element positioned adjacent the first electrode and movable in response to increased force applied thereto to abruptly change its shape from a first curvature wherein it is bowed away from the first electrode to a second curvature wherein it is bowed toward the first electrode and movable in response to a decrease in the force applied thereto to abruptly change from its second curvature and return toward its first curvature. Means linking the diaphragm and the second electrode apply to the second electrode a force which is a function of the degree of deformation of the diaphragm. The switch also includes means which adjustably bias the linking means to resist the application of force to the second electrode by said linking means whereby the second electrode is actuated to its second curvature at a predetermined diaphragm pressure differential.

5 Claims, 4 Drawing Figures PRESSURE SENSITIVE SWITCH WITH DIAPHRAGM AND DISH CONTACT MEANS BACKGROUND OF THE INVENTION This invention relates to switches and more particularly to pressure sensitive switches.

Such switches are widely used in the appliance field particularly for sensing water levels in automatic washing machines so that the tub will be filled to a desired level commensurate with the washing load. Prior pressure sensitive switches for washing machines and the like typically included a diaphragm-operated conventional overcentering switch mechanism and a coil spring for biasing the mechanism to an open circuit position. Such switches were relatively bulky and expensive to manufacture, and tended to be heavier than necessary for use with solid state and integrated circuitry proposed for use in performing control functions in such appliances.

SUMMARY OF THE INVENTION Among the several objects of this invention may be noted the provision of an improved pressure sensitive switch of high reliability and sensitivity; the provision of such a switch which is particularly suited for use with the low power levels associated with integrated circuits and their loads and low pressure differentials between preselected water levels in an automatic washing machine; the provision of such a switch which has an inherent operating differential in that the switch actuates in response to one pressure level and returns to its normal position in response to a second, but lower, pressure level; the provision of such a switch in which the pressure level at which the switch operates is easily adjusted; the provision of such a switch which is of low profile and compact size; and the provision of such a switch which has long life and is simple and economical to manufacture. Other objects and features will be in part apparent and in part pointed out hereinafter.

Briefly, a pressure sensitive switch includes a resilient diaphragm deformable in response to a difference in pressures on the opposite surfaces thereof, an insulative base, and a first electrode carried by the base. The switch further includes a second electrode comprising a resilient deformable dish-shaped conductive element positioned adjacent the first electrode and movable in response to increased force applied thereto to abruptly change its shape from a first curvature wherein it is bowed away from the first electrode to a second curvature wherein it is bowed toward the first electrode and movable in response to a decrease in the force applied thereto abruptly to change from its second curvature and return toward its first curvature. Means linking the diaphragm and the second electrode apply to the second electrode a force which is a function of the degree of deformation of the diaphragm. Means adjustably bias the linking means to resist the application of force to the second electrode by the linking means whereby the second electrode is actuated to its second curvature at a predetermined diaphragm pressure differential.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross section of a pressure sensitive switch of the present invention showing the components thereof in a deactuated mode;

FIG. 2 shows the components of the FIG. 1 switch in an actuated mode;

LII

FIG. 3 is a perspective showing certain internal components of the switch of FIG. 1; and

FIG. 4 is a section on line 4-4 of FIG. 1.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, a pressure sensitive switch of this invention is indicated generally by reference numeral 1. Switch 1 comprises a generally circular base 3 made of a rigid electrically insulating material such as Micarta or the like. Base 3 has a central aperture 5, a pair of parallel slots 7, 9 spaced on opposite sides of aperture 5, and a second aperture 11 equidistant from slots 7, 9 and intermediate aperture 5 and the edge of base 3. Slots 7, 9 receive tangs l3, l5, respectively, which extend perpendicularly from the body of a support or bracket 17 made of an electrically conductive material such as steel or the like with a coating of gold or tin or the like.

Tangs

13, 15 are sized for a compression fit into respective slots 7, 9 whereby support 17 is secured to base 3. The lower portion of tang l3 constitutes a spade terminal.

A generally circular diaphragm 19 is supported around its periphery and spaced above base 3 by a cylindrical spacer 20 so that diaphragm l9 and base 3 are in substantial registration Spacer 20, like base 3, is preferably made of thermosetting synthetic resin material. Diaphragm 19 is formed of a resilient deformable electrically insulating material such as neoprene or rubber. The base, spacer and diaphragm are secured within and held assembled by a generally cup-shaped housing 21 of aluminum or the like which is so formed that it will peripherally seal the outer margin of the diaphragm and which has its lower edge swaged or rolled over to positively grip the underside of the base 3. Housing 21 is provided with a central nipple 22 which communicates with a chamber 23 formed between the upper surface of the diaphragm and upper portion of the housing.

Support 17 has a central recess 24 with the top end 25 thereof enlarged to form a counterbore, the ledge of which lossely supports the periphery of a dished metallic disc 27 which is nested therein. This recess is coaxial with aperture 5 in which a rivet 28 is secured substantially aligned along the central axis of the disc. The upper head of rivet 28 constitutes a stationary electrode or contact 29 which is of smaller diameter than recess 24 so that contact 29 and support 17 are electrically isolated. A second spade terminal 30 is secured to the underside of the switch base 3 by the lower head of rivet 29.

Disc 27 is a resilient deformable dish-shaped monometallic electrically conductive element and constitutes a second electrode or contact of switch 1. Such a disc is fully described in US. Pat. No. 3,725,907. Suffice it to say that disc 27 is movable in response to increased force applied centrally to its top surface to abruptly change its shape from a first curvature wherein it is bowed away (concave) from contact 29 to a second curvature wherein it is bowed toward (convex) and engages contact 29, as shown in FIG. 2. Disc 27 is also movable in response to a decrease in the force applied thereto abruptly to change from its second curvature and return to its first curvature.

As shown in the drawings, the right end of support 17 comprises a tang 31 extending perpendicularly from base 3 toward diaphragm 19, while the opposite end of support 17 has a threaded aperture 33 which is coaxial with, but of a smaller radius than, aperture 11. Aperture 33 receives a screw 35, the shank end of which terminates a pin 37. The end of tang 31 is bifurcated and serves as a seat to support one end of an elongate flat resilient beam 39 the other end of which includes an aperture 41 which receives pin 37. Beam 39 comprises a spring element which is preferably formed of a thin strip (e.g., mils in thickness) of springy stainless steel (e.g., 18-8) or beryllium-copper or the like and which is preferably positioned in a plane generally parallel to but spaced from that of the disc. Turning screw 35 in one direction causes the left end of beam 39 to move toward diaphragm 19 while rotation of the screw in the opposite direction permits the left end to move away from diaphragm 19. As will be explained hereafter, beam 39 and screw 35 comprise-adjustable biasing means.

Diaphragm l9 and disc 27 are linked by a back-up plate 42 having a generally circular base thereof engaging the underside of diaphragm 19 and a stem 43 struck from a central portion thereof and extending perpendicularly from plate 42 through a slot 45 in beam 39. The distal end of stem 43 engages the top surface of disc 27 at the central axis of the disc. Stem 43 has abutment means or shoulders 47 which bear on the surface of beam 39 facing away from disc 27 and toward diaphragm l9.

Nipple 22 is connected by tubing (not shown) to an opening in the bottom of a washing machine tub or the like. The tubing provides pressure communication between chamber 23 and the level of water in the appliance. As the waterlevel in the appliance rises or falls, air trapped in chamber 51 and the tubing exerts an increasing or decreasing pressure against the upper surface of diaphragm 19, the undersurface of which is at ambient atmospheric pressures. Thus, the diaphragm will deform as a function of the pressure differential across the diaphragm.

As the water level rises the air pressure in chamber 23 will increase. Although switch l is compact in size (e.g., 2 V2 inches in diameter) a small pressure differential applied across the surface area of the diaphragm will cause it to deform and apply to disc 27 via stem 43 substantial forces which are a function of the degree of deformation of diaphragm 19. As increased pressure is applied to the diaphragm, the central portion of disc 27 will be depressed and the disc flattened. until it abruptly changes its curvature and snaps into electrical contact with electrode 29. Beam 39 biases stem 43 to resist application of force to disc 27 and by raising and lowering the left end of beam 39 via adjustment of screw 35, the biasing resistance can be varied to effect closure of contacts 27- and 29 at various predetermined diaphragm pressure differentials. As the diaphragm pressure differential is decreased, disc 27 will abruptly change from its second curvature and return toward its first curvature. However, this reversal in curvature does not occur until the pressure differential decreases significantly below the predetermined level at which disc 27 changed its curvature in response to an increase in pressure. Thus switch I has a differential between its actuation and deactuation pressures.

Switch 1 is thus useful in performing control functions in appliances such as sensing when a water level rises or falls to preselected levels and controlling the operation of water fill and drain circuits and solenoids. In a typical automatic washing machine switch 1 serves to terminate the flow of water into the tub when a particular level is reached, but because of the differential noted above the reversal of curvature of disc 27 at a substantially lower pressure differential is also useful in certain permanent press cycles to terminate the draining of hot water from the tub when the level has dropped to some percentage (e.g., 25 50 percent of filled level) and initiate the flow of cold water to effect a gradual cooling of the laundry load and to avoid a disadvantageous thermal shock to permanent press clothes resulting from sudden cooling.

Switch 1 is particularly useful in conjunction with solid state and integrated circuit controls but may also be used with other types of control circuits. lf high current loads are to be directly energized and deenergized, a button of silver-bearing contact material, for example, may be secured centrally to the undersurface of disc 27 and contact material can be used in conjunction with the upper head of rivet 28. Alternately, as shown in phantom at 49, a coating of a dielectric constituted by any conventional electric insulation material may be applied to the surface of the upper half of rivet 28 so that there is no actual electrical contact of the lower electrode 29 by the disc electrode 27 as the latter abruptly moves into its second curvature. The substantial change in capacitance between the electrodes as the spacing therebetween is changed may be used to initiate or terminate desired control functions.

Switch 1 is quite sensitive to minor pressure differentials over a wide range of adjustment. For example, switch 1 is sufficiently sensitive to detect A inch changes of the water level in an appliance and can be adjusted to actuate at any preselected level over a '10 l 6 inch range, all with excellent repeatability. As inexpensive stampings rather than machined components are utilized and because of the simplicity and minimal number of components, the switch of this invention may be economically fabricated.

in view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A pressure sensitive switch comprising:

a resilient diaphragm deformable in response to a difference in pressures on the opposite surfaces thereof;

an insulative base;

a first electrical contact carried by said base;

an electrically conductive support with an opening therein, said support being secured to said base with said first contact centrally located in one end of said support opening, said support having said opening enlarged at its other endforming a generally circular recess in said support;

a second electrical contact comprising a resilient deformable generally circular dish-shaped conductive disc element nested and loosely supported around its periphery in said support recess adjacent said first Contact with the central axis of said disc sub stantially aligned with said first contact, said disc element being movable in response to increased force applied thereto to abruptly change its shape from a first curvature wherein it is bowed away from said first contact to a second curvature wherein it is bowed into contact with said first electrical contact and is movable in response to a decrease in the force applied thereto abruptly to change from its second curvature and return toward its first curvature;

means linking said diaphragm and said second electrical contact for applying a force to said second contact which is a function of the degree of deformation of the diaphragm, said linking means comprising a stem extending from said diaphragm to contact the surface of said second electrical contact disc, said stem having a shoulder thereon facing away from said diaphragm; and

means adjustably biasing the linking means to resist the application of force to said second contact by said linking means whereby the second contact is actuated to its second curvature at a predetermined diaphragm pressure differential, said biasing means comprising an elongated beam supported at its opposite ends on the base and positioned between the diaphragm and the disc in a plane generally parallel to but spaced from that of the disc and having means for moving one end of said beam toward and away from the diaphragm, said beam having a slot therein aligned generally with the axis of the disc, having said linking means stem projecting through said slot to contact the disc and having said stem shoulder bearing on the surface of the beam which faces away from said disc toward the diaphragm.

2. A switch as set forth in claim 1 which includes a housing enclosing all of the aforesaid components and having a chamber a surface of which is constituted by one surface of the diaphragm, and means for providing pressure communication between said chamber and the level of water in an appliance whereby when water supplied to said appliance attains a predetermined level the switch will be actuated to terminate further supply of water thereto.

3. A pressure sensitive switch comprising:

an insulative base;

a first electrical contact carried by said base;

a second electrical contact comprising a resilient deformable dish-shaped conductive elemet movable in response to selected force applied thereto to abruptly change its shape from a first curvature to a second curvature wherein it is movable in response to a selected decrease in said force applied thereto to abruptly change from its second curvature and return to its first curvature;

an electrically conductive support secured at one surface of said base, said support having a recess therein receiving and loosely holding the dishshaped second contact element around its periphery normally supporting the element in its first curvature disposition bowed away from said first contact to be moved into electrical engagement with said first contact when said dish-shaped element is moved to its second curvature disposition in response to said selected force being applied thereto;

a resilient diaphragm deformable in response to a difference in pressures on the opposite surfaces thereof, said diaphragm being mounted with one surface thereof in spaced facing relation to said one base surface for exposing the other surface of said diaphragm to varying fluid pressures; and

a rigid stem fixedly secured to said diaphragm for coextensive movement with said diaphragm and extending from said one diaphragm surface into engagement with said dish-shaped second contact element to directly apply force to said second contact element in response to deformation of said diaphragm, whereby selected deformation of said diaphragm in response to a predetermined pressure differential appliedto opposite surfaces of said diaphragm applies said selected force to said second contact and is effective to move said second contact to its second curvature disposition to engage said first contact.

4. A pressure sensitive switch as set forth in claim 3 having means mounted on said base biasing said diaphragm away from said base, and means moving a portion of said biasing means toward and away from said diaphragm for determining the pressure differential applied to said diaphragm which is effective to move said second contact to its second curvature disposition.

5. A switch as set forth in claim 4 wherein said first contact has a dielectric coating thereon and said second contact is moved to engage said coating when said second contact is moved to its second curvature disposition.

Claims

1. A pressure sensitive switch comprising: a resilient diaphragm deformable in response to a difference in pressures on the opposite surfaces thereof; an insulative base; a first electrical contact carried by said base; an electrically conductive support with an opening therein, said support being secured to said base with said first contact centrally located in one end of said support opening, said support having said opening enlarged at its other end forming a generally circular recess in said support; a second electrical contact comprising a resilient deformable generally circular dish-shaped conductive disc element nested and loosely supported around its periphery in said support recess adjacent said first contact with the central axis of said disc substantially aligned with said first contact, said disc element being movable in response to increased force applied thereto to abruptly change its shape from a first curvature wherein it is bowed away from said first contact to a second curvature wherein it is bowed into contact with said first electrical contact and is movable in response to a decrease in the force applied thereto abruptly to change from its second curvature and return toward its first curvature; means linking said diaphragm anD said second electrical contact for applying a force to said second contact which is a function of the degree of deformation of the diaphragm, said linking means comprising a stem extending from said diaphragm to contact the surface of said second electrical contact disc, said stem having a shoulder thereon facing away from said diaphragm; and means adjustably biasing the linking means to resist the application of force to said second contact by said linking means whereby the second contact is actuated to its second curvature at a predetermined diaphragm pressure differential, said biasing means comprising an elongated beam supported at its opposite ends on the base and positioned between the diaphragm and the disc in a plane generally parallel to but spaced from that of the disc and having means for moving one end of said beam toward and away from the diaphragm, said beam having a slot therein aligned generally with the axis of the disc, having said linking means stem projecting through said slot to contact the disc and having said stem shoulder bearing on the surface of the beam which faces away from said disc toward the diaphragm.

3. A pressure sensitive switch comprising: an insulative base; a first electrical contact carried by said base; a second electrical contact comprising a resilient deformable dish-shaped conductive elemet movable in response to selected force applied thereto to abruptly change its shape from a first curvature to a second curvature wherein it is movable in response to a selected decrease in said force applied thereto to abruptly change from its second curvature and return to its first curvature; an electrically conductive support secured at one surface of said base, said support having a recess therein receiving and loosely holding the dish-shaped second contact element around its periphery normally supporting the element in its first curvature disposition bowed away from said first contact to be moved into electrical engagement with said first contact when said dish-shaped element is moved to its second curvature disposition in response to said selected force being applied thereto; a resilient diaphragm deformable in response to a difference in pressures on the opposite surfaces thereof, said diaphragm being mounted with one surface thereof in spaced facing relation to said one base surface for exposing the other surface of said diaphragm to varying fluid pressures; and a rigid stem fixedly secured to said diaphragm for coextensive movement with said diaphragm and extending from said one diaphragm surface into engagement with said dish-shaped second contact element to directly apply force to said second contact element in response to deformation of said diaphragm, whereby selected deformation of said diaphragm in response to a predetermined pressure differential applied to opposite surfaces of said diaphragm applies said selected force to said second contact and is effective to move said second contact to its second curvature disposition to engage said first contact.