US3890477A

US3890477A - Control device

Info

Publication number: US3890477A
Application number: US361561A
Authority: US
Inventors: James F Saunders
Original assignee: Maytag Corp
Current assignee: Maytag Corp
Priority date: 1973-05-18
Filing date: 1973-05-18
Publication date: 1975-06-17
Anticipated expiration: 1992-06-17
Also published as: CA994841A

Abstract

A leaf spring actuator is fixed at one end to a frame and is pivotally supported thereby at the other end to subject the spring actuator to longitudinal compression to in turn form the actuator in an arcuate shape. The actuator is responsive to an input loading applied to its face for snap action from the arcuate shape to an S-shape to provide a mechanical output signal. The device is particularly useful in pressure responsive switches and in such devices serves to isolate the input signal from the output signal and particularly isolates the currentcarrying contacts from the spring actuator.

Description

United States Patent Saunders 1 1 June 17, 1975 1 1 CONTROL DEVICE 3,573,410 4/1971 Budzich 200/83 P [75] Inventor: James F. Saunders, Clarksville, FOREIGN PATENTS OR APPLICATIONS Term- 962,745 7/l964 United Kingdom ZOO/153 T t 6 [73] Ass1gnee: 'llhe Maytag Company, Newton gti/ iiz rl iiid Owa [22] Filed: May 18, 1973 Primary Examiner-Robert K. Schaefer 7 Assistant Examinerwilliarn J. Smith [21] Appl' 361561 Attorney, Agent, or FirmRichard L. Ward [52] US. Cl 200/83 P; ZOO/67 DB, ZOO/153 T [57] ABSTRACT [51] hit. Cl "01]! /20; "01h 35/34 A |eaf spring actuator i fi at one end to a frame [58] Fmld Search 200,67 153 83 and is pivotally supported thereby at the other end to ZOO/67 67 DA subject the spring actuator to longitudinal compression to in turn form the actuator in an arcuate shape. [56] References C'ted The actuator is responsive to an input loading applied UNITED STATES PATENTS to its face for snap action from the arcuate shape to an 1,215,665 2/1917 Landis 200/67 DB p t pr id a m hani al output signal. The 1,622,721 3/1927 Hook 200/67 DB X device is particularly useful in pressure responsive 2,133,309 /1938 dinge 200/67 B X switches and in such devices serves to isolate the input gl a 28x56: signal from the output signal and particularly isolates 1 rams 3,050,599 8/1962 Brevick 200/67 DB the canymg contacts from the spnng actuator 3,366,756 1/1968 Watson 200/67 DB 3 Claims, 6 Drawing Figures CONTROL DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to control devices and more particularly to a spring actuator for a control device such as a pressure responsive switch.

2. Description of the Prior Art In prior art snap action devices, the snap action spring member or actuator is a current-carrying component operable from a first position to a second position for making and breaking electrical circuits. The typical prior art device is operable by snap action between the first and second positions and is commonly stable in each of the positions.

One problem of prior art devices is that of burning or arcing of the contacts because of the decrease in contact pressure as the actuator approaches the snap action condition. When an actuating force is applied to the actuator of the prior art devices for initiating snap action operation, there is a decrease in contact pressure which is in turn the common cause of contact burning. More specifically, just before and just at the beginning of the snap action operation of the actuator, the movable contact is momentarily subjected to very low pressure as it moves from the stationary contact.

At least in part because of the current-carrying characteristics of the actuator, prior art devices show the actuator supported by a plastic housing. A plastic support, however, is subject to variations in dimensional characteristics under adverse environmental conditions and under long-term aging.

SUMMARY OF THE INVENTION It is an object of the instant invention to provide an improved snap actuator for a control device.

It is a further object of the instant invention to provide a control device having a snap action actuator isolated from the electrical current-carrying components of an electrical control device.

It is a further object of the instant invention to provide an improved pressure responsive switch device including an electrical switch operated by and effectively isolated from a snap action spring actuator.

The instant invention achieves these objects in a control device including an elongated leaf spring actuator fixed at one end and pivotally supported at the other end for longitudinal loading of the actuator and forming it in a generally arcuate stable condition. The actuator is responsive to an input force applied to the face thereof for transformation to an S-shape by snap action to effect a mechanical output signal. In a preferred embodiment the invention is applied to a pressure responsive switch operable for receiving a pressure input and providing a mechanical output signal to in turn control an electrical circuit.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings illustrate a preferred embodiment of the invention with similar numerals referring to similar parts throughout the several views wherein:

FIG. 1 is a plan view of a pressure responsive switch assembly embodying the instant invention;

FIG. 2 is a sectional view of the device of FIG. 1 as taken generally along lines 2-2;

FIG. 3 is an enlarged view of the control device of FIGS. and 2 with substantial portions removed for clarity in describing the instant invention;

FIG. 4 is a fragmentary portion of a control device such as shown in FIGS. 1 and 2 and showing the stable unactuated condition thereof;

FIG. 5 is a view similar to that of FIG. 4 showing the control device at an intermediate step of actuation; and

FIG. 6 is a view similar to FIGS. 4 and 5 showing the device in the actuated condition.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, there is shown a pressure switch assembly 10 useful in a washing apparatus for controlling some phase of apparatus operation responsive to a condition of fluid level. Generally, the assembly 10 includes a disc-like plate 13, a resilient diaphragm 14, an annular clamp ring 15, a force transmitting input member 16, a mounting bracket 17, a leaf spring actuator 18 supported by the bracket 17, and a control switch 20 also mounted on the bracket 17. The peripheral flange 23 of the disc-like plate 13 and the annular clamp ring l5 receive the outer flange 24 ofthe diaphragm l4 therebetween and are joined by staked rivets 25 to connect the three elements as a subassembly.

The diaphragm 14 is formed of a resilient elastomer and includes a thin, flexible. imperforate central portion 26 depending, as shown in FIG. 2, from the outer flange 24. The central portion 26 is movable responsive to an applied force which is transmitted from the diaphragm 14 through the input member 16. The input member 16 includes a disc-like portion 29 attached to the central portion 26 of the diaphragm l4 and further includes a protruding pin 30 engageable with the spring actuator 18. The outermost periphery 24 of the diaphragm member 14 defines a lip 31 engageable with the flange of a mounting wall to provide a watertight seal as will be shown.

The mounting bracket 17 as best shown in FIGS. 2 and 3, includes a base 33 and a flange 34 extending at substantially a right angle from the base 33. The base 33, in turn, comprises a first portion 35 that is welded to the disc-like plate 13 and a second portion 36 separated from the fixed first portion 35 by a cutout 39, as best shown in FIG. 3, but is connected to the fixed portion 35 through the upstanding flange 34. The flange 34 is reduced at the point 40 adjacent to the cutout 39 to establish a deflectable connection between the fixed and

movable base portions

35 and 36. The fixed and movable portions of the bracket base 33 are also connected by a threaded member 41 extending through an upturned tab 43 of the movable portion 36 and threadingly connected with an upturned tab 44 of the fixed portion 35. The threaded member 41 is adjustable to change the relative spacing between the

upturned tabs

43 and 44 with the movable base portion 36 effectively pivoting at the deflectable connection 40.

The fixed base portion 35 of the bracket 17 includes an inclined portion 45 to which is fixed one end of the leaf spring actuator 18 by a rivet 46. The movable base portion 36 includes an upturned tab 49 having a notch 50, as in FIGS. 4, 5, and 6, for pivotally receiving the other end of the spring actuator 18 as will be more fully described hereinafter. The base 33 of the supporting bracket 17 defines a hole 51 aligned with a similar hole 3 52 in the disc-like plate 13 and receives the input plunger 30 of input member 16 for operative engagement with the actuator 18.

The electrical switch 20 is a conventional device including a pair of current-carrying contacts 54, 55 and operable between open and closed position by a snap actuatable spring member 56 disposed within the switch body and responsive to a plunger 60 depending from the switch 20 as in FIG. 2. The switch 20 is assem bled to the upstanding flange 34 of the supporting bracket 17 by a pair of threaded members 61.

The assembly I may be mounted on a bottom wall (not shown) of a dishwasher chamber. for example. by inverting the assembly and dropping the switch end of the assembly through an opening in the wall so that the depending portion 26 of the diaphragm 14 in FIG. 2 faces upwardly into the chamber to respond to a pressure head therein. Inversion of the assembly 10 will position the annular peripheral lip 31 for engagement with a flange (not shown) surrounding the opening in the chamber wall. The assembly 10 will be fixed to the wall with threaded members extending through the openings 63 defined in the disc-like plate 13 adjacent the periphery thereof as best shown in FIG. 1.

Referring to FIG. 3 the snap actuator I8 is shown in plan view and includes one end 64 having a mounting hole to receive rivet 46 and a pair of outwardly extending ears 65. The elongated actuator 18 tapes down to a generally middle portion that is engageable by the input plunger as will be further shown and then extends longitudinally to a bifurcated end portion 66 engageable with the notch 50 of upturned tab 49. In this preferred embodiment the actuator member 18 is formed of a stainless steel spring material having a thickness of 0.005 inch.

The one end 64 of the spring actuator 18 is connected by the rivet 46 to the fixed bracket inclined portion 45 with the outwardly extending ears 65 abutting upwardly lanced shoulders 69 of the bracket 17. The other bifurcated end 66 of the spring actuator 18 bears against the notch 50 formed in the upturned tab 49 of the movable bracket portion 36 to pivotally support the end 66 of the leaf spring actuator 18. The spacing between the fixed end 64 of the leaf spring actuator and the pivot notch 50 of the upturned tab 49 is less than the actual length of the actuator 18 between these two points, and during operation remains a constant, so that there is a longitudinal compression loading on the actuator 18 to cause a buckling thereof for forming the actuator 18 into an arcuate shape. as shown in FIGS. 2 and 4, having an effective length between the ends of less than the actual length. The input plunger 30, effectively attached to and movable with the flexible portion 26 of diaphragm 14 as shown in FIG 2, is engageable with the actuator 18 in this arcuate shape and is operable for applying a transverse force to the leaf spring actuator 18 to effect a snap action operation therof as will be shown hereinbelow. The input plunger 30 is shown schematically in FIGS. 4, 5. and 6.

The threaded connection between the movable and fixed portions 36 and of the mounting bracket 17 provides adjustment of the spacing between the fixed end 64 of the actuator 18 and the pivoted end 66. More specifically, turning of the screw 41 effects deflection of the bracket flange 34 at the connection so that a pivoting action of the movable portion 36 relative to the fixed portion 35 alters the spacing between the ends of the actuator. Stated differently, turning of the screw changes the chord of the are formed by the actuator and thus changes the effective length of the actuator 18 so that a predetermined design length may be maintaincd to insure proper snap action of the spring actua tor l8. This adjustment compensates for fabrication and assembly tolerances of the various components and may be considered as providing an operationally constant spacing between the fixed point and the pivoted point. Turning the screw 41 in" is effective for reducing the spacing between the

tabs

43 and 44 and in the absence of deformation at 40 the tabs will separate when the screw 41 is backed out A nut could. however, be provided on screw 41 between the

tabs

43 and 44 and engageable with tab 43 to separate the tabs if deformation should occur at 40.

The operation of the device is best described by considering the fragmentary schematic views of FIGS. 4, 5, and 6. These views depict the invention in its simplest form and include the supporting bracket 17, means for transmitting an input force such as including the input plunger 30, the actuator 18, and output signal means such as including the switch plunger 60.

In FIGS. 4, 5, and 6 the actuator 18 corresponds, respectively. to the stable arcuate position, the actuating or momentary intermediate position, and the unstable actuated position. Referring more specifically to FIG. 4, the spring actuator 18 is shown in a stable arcuate condition under the urging of a longitudinally applied compression load. The plunger 30 extends through bracket base 33 into engagement with the actuator 18 but the input force on the actuator 18 is below that required to cause movement or deformation of the actuator 18 from the stable arcuate condition.

As pressure builds on the diaphragm 14, as in FIG. 2, for example. and transmits increased force through the input plunger 30, the spring actuator 18 is deformed and forced upwardly at the point of engagement by the plunger 30 until a configuration corresponding generally to that shown in FIG. 5 is achieved. This condition is unstable and if the force of the plunger 30 is removed the spring actuator 18 will return to the position shown in FIG. 4. In normal operation. however, the pressure will be maintained on the diaphragm 14 and at a predetermined applied force the actuator 18 will operate by a snap action from the intermediate shape shown in FIG. 5 to S-shape shown in FIG. 6.

In the actuated position of FIG. 6, the right-hand portion of the elongated spring actuator 18 has reversed so that it engages and applies a force to the output plunger in a direction as indicated by the arrow 70. It must be remembered that the left-hand end of the spring actuator 18 is fixed to the bracket 17 so that reversal of the entire actuator is prevented. It is noted that this movement of the right-hand portion of the spring actuator 18 is by snap action and thus occurs dynamically so that the output plunger 60 is moved rapidly from its normal position to its depressed condition. Dynamic movement of the right-hand portion of the spring actuator 18 thus effects, through snap action member 56 of switch 20. for example, substantially instantaneous opening of the contacts 54, 55.

If the actuating force applied to the spring actuator 18 through the input plunger 30 is decreased to a predetermined lower level the actuator 18 will return to the condition of FIG. 4 without the application of other returning forces. The device may thus be considered as monostable.

Referring again to FIGS. 2 and 3 the adjustable feature will be more specifically explained. In the construction of the preferred embodiment. it is desired that the spring actuator 18 operate by snap action from the arcuate shape of FIG. 4 to the S-shape of FIG. 6 upon the application of a predetermined force through the input plunger 30 and to reset to the arcuate shape responsive to a predetermined lower applied force corresponding to a lower pressure acting on the diaphragm 14. If the spacing between the fixed end 64 and the pivoted end 66 of the actuator 18 is too small, the actuator 18 will be subjected to an excessive amount of curva ture and will require a higher actuating force but in addition can become bistable and not return from the S- shape condition to the arcuate shape even when all transversely applied force is removed. 0n the other hand, if the spacing is too great the actuator 18 will require a smaller actuating force but will not operate by a snap action to the S-shape as the actuator 18 approaches and reaches the configuration shown in FIG. 5. Thus in the preferred embodiment the operation of the spring actuator 18 may be used as a visual indication of the presence of the proper or predetermined spacing, which in operation will effectively remain a constant for providing the desired snap action characteristics. The operation and reset range of the actuator 18 as provided in the preferred embodiment provides the desired range of fluid level control for a dishwasher apparatus.

As previously indicated, the prior art devices have been subject to a problem of decreasing and insufficient contact pressure at the electrical contacts as the snap action device approaches the switching position. More specifically. just before the actuator, of prior art devices, snaps over center there is a period of reduced contact pressure. In the present invention, however, the actuator 18 is effectively isolated from the electrical contacts 54, 55 and there is no decrease in the contact pressure or movement of the contacts 54, 55 except during the actual snap action portion of movement of the actuator 18 from the arcuate position to the S-shape position. Since the actuation is dynamic, the period of time during which the contact pressure is decreasing to zero is so fast as to be substantially instantaneous and thus there is little or no chance of the burning or frying of the contacts 54, 55. Thus it is noted that the contact pressure is independent of the actuator 18 until actual snap action occurs.

Other advantages of the construction of the instant invention include reduced fabrication cost ofthe actuator 18 since the isolation of the contacts from the actuator 18 make fabrication and operational requirements of the actuator somewhat simplified. The construction also permits the use of a unitary metal frame, such as 17, for supporting the actuator 18 so that the frame has greater stability and resistance to dimensional change during exposure to adverse operating environments. Long-term deterioration has been shown to be a prob lem in prior art devices having an actuator supported at least in part by a plastic member. Such plastic members are subject to dimensional instability when exposed to long-term usage or adverse operating environments.

Other alternative embodiments that may be considered as arising from the instant invention would include devices in which the input and output plungers are both positioned on the same side of the actuator. Furthermore, the improved actuator is shown as used in a pressure switch 10 but could also be used in other control devices wherein an input signal is transmitted to an actuator, such as 18, for in turn effecting a mechanical output signal isolated from the input signal.

Still further it is recognized that an alternate embodiment may be useful wherein the spacing between the fixed and pivoted points of the actuator are decreased to the dimension where the device is bistable and requires an overt action to reset the actuator to the original arcuate position.

It is thus seen that the instant invention provides an actuator for a control device for achieving improved operational characteristics, both immediate and long term. The assembly is simple and relatively inexpensive and especially reliable for providing accurate control when used with a pressure switch.

In the drawings and specification there is set forth a preferred embodiment of the invention and although specific terms are employed these are used in a generic and descriptive sense only and not for purposes of limitation. Changes in form and the proportion of parts as well as the substitution of equivalents are contemplated as circumstances may suggest or render expedient with out departing from the spirit or scope of this invention as defined in the following claims.

I claim:

1. A double snap-action pressure-responsive switch comprising: a supporting base defining an opening; bracket means fixed to said base defining first and second spaced-apart supports; an elongated snap-action actuator fixed at one end to a first of said supports for preventing movement of said one end of the actuator and pivotally supported at the other end to the second support at a distance from said first support of less than the actual length of said actuator to subject said actuator to longitudinal compression and deformation for forming said actuator in a first position comprising a stable arcuate condition; input signal means including a movable plunger extending through the opening in said supporting base and a resilient diaphragm fixed along its periphery to said supporting base and operable on said plunger, said plunger being engageable with said actuator in said first position and operable responsive to a predetermined pressure on said diaphragm for moving said actuator from said first arcuate position to an unstable intermediate second position from which said actuator is movable by snap action to a third position comprising an unstable S-shape condition; and output signal means engageable by said actuator and including snap-action switch means responsive to snap action movement of said actuator into said S-shape condition for operating from a first electrical posture to a second electrical posture, said actuator being movable from said unstable S-shape condition to said stable arcuate condition responsive to a predetermined lower pressure acting on said diaphragm.

2. A double snap-action pressure-responsive switch as defined in claim 1 wherein said bracket means is in the form of a unitary metallic member for maintaining the effective length of said actuator as an operational constant and includes an integral pivot portion for adjusting the spacing between said first and second spaced apart supports to condition said actuator to assume said stable arcuate position and to operate to said carrying contacts operated by said actuator through an intermediate electrically insulating member whereby the current-carrying contacts of said switch means are electrically isolated from said actuator

Claims

2. A double snap-action pressure-responsive switch as defined in claim 1 wherein said bracket means is in the form of a unitary metallic member for maintaining the effective length of said actuator as an operational constant and includes an integral pivot portion for adjusting the spacing between said first and second spaced apart supports to condition said actuator to assume said stable arcuate position and to operate to said S-shape position responsive to a predetermined force thereon.

3. A double snap-action pressure-responsive switch as defined in claim 1 wherein said snap-action switch means includes a pair of relatively movable current-carrying contacts operated by said actuator through an intermediate electrically insulating member whereby the current-carrying contacts of said switch means are electrically isolated from said actuator.