US2666108A - Fixed differential adjusting means for pressure sensitive electrical control devices - Google Patents

Description

Jan. 12, 1954 W. E. BROWN FIXED DIFFERENTIAL ADJUSTING MEANS FOR PRESSURE SENSITIVE ELECTRICAL CONTROL DEVICES iled Nov. 25, 1949 hl Mn 1 c EQUAL. TO WEAR ALLOWANCE PLUS ARC GAP PLUS LEVER THICKNESS.

AME-m @(ibxww Patented Jan. 12, 1954 FIXED DIFFERENTIAL ADJUSTING MEANS FOR PRESSURE SENSITIVE ELECTRICAL CONTROL DEVICES William E. Brown,

Cutler-Hammer,

Pewaukee, Wis., assignor to Inc., Milwaukee, Wis., a corporation of Delaware Application November 25, 1949, Serial N 0. 129,468

8 Claims.

This invention relates to pressure sensitive electrical control devices and more particularly to a fixed differential adjusting means therefor.

As is well known, control devices of the aforementioned character are designed to open an electrical circuit at a predetermined pressure (or temperature) and to reclose the circuit at a different predetermined pressure (or temperature), the difference between the aforementioned pressures (or temperatures) being the differential of the control device.

In the known arts of manufacturing pressure sensitive electrical control devices, the cumulation of manufacturing tolerances in the electrical control assemblies renders it impractical to obtain a predetermined fixed operating differential by means of close adherence to actual contact spacing, contact pressure, and confined arc gap. Hence the desired operating differential is usually obtained by fixing the arc gap to an approximat dimension and setting the differential by varying the wear allowance, or fixing the wear allowance and setting the differential by varying the arc gap. This necessitates pneumatic or thermostatic equipment for setting the differential. Moreover the differential is secured without providing for simultaneous control of both the amount of wear allowance and the size of the arc gap.

A primary objective of the present invention is to eliminate th aforementioned undesirable characteristics of prior devices of the type under consideration, and more particularly to provide in pressure (or temperature) responsive electrical control devices means affording accurate and simultaneous predetermination of contact are gap, wear allowance, and differential.

'Another object is to achieve the aforementioned simultaneous predetermination of all three factors through the medium of a single adjusting member, which member may be extremely accurately and yet inexpensively and practically produced.

Another object is to provide in a control device of the aforementioned character means for varying the ratio of contact are gap to contact wear allowance without changing the sum of those two factors and hence without affecting the differential of the device, thus permitting reestablishment of a desired contact wear allowance when the contacts have worn down without affecting the difierential of the device.

Another object is to provide means of the aforementioned character affording accurate simultaneous predetermination of differential, conmodifications may be made in the embodiment illustrated without departing from the spirit and scope of the appended claims.

In the drawings,

Figure l is a somewhat schematic view of a control device embodying the invention, and

Fig. 2 is a side elevation of a fixed differential screw utilized in the control device.

Referring first to Fig. 1, the reference numeral 5 denotes a pair of spaced stationary contacts within a circuit (not shown) to be con trolled, which contacts 5 are adapted to be.

bridged by a contactor 6 biased sition by a spring 1.

To effect movement of contactor 6 out of bridging engagement with contacts 5 a snap acting system comprising pivoted levers or flippers 8 and 9, and an over-center spring I!) connected therebetween is provided. Movement of said snap acting mechanism is in turn controlled by a conventional pressure (or temperature) responsive means shown as comprising a bellows assembly ll, loading spring l2, and range adjusting means [3 comprising a screw [3 and a nonrotatable nut I3 As will be apparent, increased pressure in the bellows II will effect upward movement of the outer end of the flipper 9 connected thereto until spring [0 goes through cen ter, thus effecting snap movement of lever 8 to the dotted line position shown in Fig. 1, thus providing for corresponding movement of contactor 6 into bridging engagement with contacts 5, through the medium of spring I.

As previously pointed out, one of the objects of the present invention i the provision of means for effecting an accurately predetermined fixed differential in electrical control devices of the character described. In the embodiment illustrated, the aforementioned means takes the form to the closed D0- of a fixed differential screw I4 which, as shown in Fig. 2, has a peripheral groove 14 formed therein, by machining or otherwise, to provide spaced parallel surfaces M and 14.

Screw I4 is adapted for threading into the mounting plate l5 of the control device in such relation to the aforementioned snap acting mechanism as to permit the free end of flipper 8 to oscillate upwardly and downwardly within the limited space afforded by groove M of screw it. As best illustrated in Fig. 2, the spacing of surfaces 14* and {.4 affording the limits to travel of the free end of lever B is calculated to equal the desired contact wear allowance and are gap plus the thickness of lever B, such spacing being ac,- curately and inexpensively provided in screw Id, as by machining or otherwise, and with tolerances of .001 inch or less.

For example, if it were desired to have .032 inch wear allowance, .025 inch arc gap, and the thickness of lever B were .030 inch, it would be necessary to machine or otherwise form groove M to .087 inch.

In assembling the control the threaded portion W of fixed differential screw it may be threaded into mounting plate i5 until lever 8 is forced to just open the contacts. Screw it is then backed off enough to provide the desired predetermined wear allowance, for example, for a #8-32 screw thread, one full turn would give a desi ed wear allowance of .032 inch. Screw it may then be retained in this position by conventional retaining means, such as a non-rotatably supported frictional spring wire clip it. Since the total travel of lever Bis limited by groove f l to an exact maximum adjusting the control for a predetermined wear allowance provides a definite'arc gap and simultaneously an accurately controlled and uniformly close predetermined differential for each control device produced.

Moreover, the aforedescribed desired relation ship of screw 14 and flipper 8 having once been established, an enclosing casing of conventional form (not shown) affording no access to screw I4, visual or otherwise, may be assembled to the control since no further adjustment is necessary, the control having already been set with a known predetermined fixed differential and accurately predetermined contact wearallowance and arc gap. Thus utilization of pneumatic or thermostatic means is notnecessary to effect initial setting of the control device, nor are further adjust ments necessary to achieve such initial setting.

However, at such time as the contacts have worn down-to a point where'the predetermined wear allowancehas been dissipated, the screw it maybe-readjusted to reestablish the desired contact wear allowance without changing the dif-' ferential of the devi e, since the parallel surfaces limiting travel of lever B will be moved siinultaneously inthe same direction and to the same degree, their relationship being fixed.

Lclaim:

.1. A- pressureresponsive electrical control de vice comprisinga setof contacts, a pressure responsive operating element therefor, and means affording simultaneously a predetermined fixed operating differential for said device a contact arc gap andwear allowance the ratio of which-maybe varied while the sum thereof remains constant, said means affording adjustability to reestablish a contact wear allowance to compensate'for contact wear without affecting said-operating differential and comprising integrally formed fixedly spaced, surfaces to limit.

travel of said operating element, and the spacing of-said surfaces being equal to the sum of the desired wearallowance and are gap of said contacts plus the thickness of said operating element.-

:2. A pressure responsive electrical control device comprising a set of electrical contacts, a pressure responsive operating element therefor, and means affording simultaneously a predetermined fixed operating differential for said device and predetermined total contact are gap and wear allowance, said means affording adjustability to reestablish a contact wearallowance to compensate for contact wear without affecting said operating differential and comprising a screw having a peripheral groove of predetermined width forming a pair of integrally formed fixedly spaced parallel surfaces between which said operating element'is adapted to oscillate, said surfaces limiting the travel of said operating element, and the spacing of said surfaces being equal to the sum of the desired wear allowance and are gap of said contacts plus the thickness of said operating element.

3. in a pressure responsive electrical control device, a single means affording said device a predetermined fixedoperating differential and simultaneously a predetermined total contact are gap and wear allowance, said means affording adjustability to reestablish a contact wear allowance .to

compensate for contact wear without affecting said operating differential and comprising integrally formed fixedly spaced surfaces limiting travel of an operating element of said device, the

spacing of said surfaces being equal to the sum of the desired contact wear allowance and arc gap plus the thickness of saidoperating element.

l. A pressure responsive electrical control device including an operating element, and means affording said device adjustability to reestablish a desired contact wear allowance to compensate for contact wear without affecting a predetermined fixed operating differential for the device,-

said means comprising integrally formed fixedly spaced parallel surfaces to limit travel ofsaid operating element and said surfaces being adjust able jointly while maintainingsaid fixedly spaced relation therebetween, thereby affording variation of the ratio between contact are gap and wear allowance but maintaining the sumthereof constant.

5. A wholly enclosed pressure responsive electrical control device comprising a set of contacts, a pressure responsiveoperating element therefor,

an enclosing casing for said device, and means aftegrally formed fixedly spaced parallel surfaces between which said operating element-isadapted to oscillate, said surfaces limiting travel of .said' element, and the spacingof said surfaces being equal to the sum of said predetermined contact wear allowance and are gap plus the thickness of said operating element.

6. A pressure responsive electrical control -de-' which may be varied whilethe'sum thereof re-" mains constant, said means comprising fixedly spaced surfaces to limit travel of the said 'opr ating element, and the spacing of said surfaces vice comprising a set of contacts, a pressure rebeing equal to the sum of the desired wear allowance and are gap of said contacts, plus the thickness of said operating element.

7. A pressure responsive electrical control device comprising, a contact biased for movement to a first position, an operating element for said contact having connection therewith to move said contact to a second position, and to release said contact for movement to said first position, and means affording simultaneously a predetermined fixed operating differential for said device and a contact are gap and wear allowance, the ratio of which may 'be varied while the sum thereof remains constant, said means comprising fixedly spaced surfaces to limit travel of said operating element, and the spacing of said surfaces being equal to the sum of the desired wear allowance and are gap of said contacts, plus the thickness of said operating element.

8. A pressure responsive electrical control device comprising, snap acting mechanism including a pressure responsive operating element and a snap acting element operated thereby, a contact connected for operation by said snap acting element and movable relative thereto, and means affording simultaneously a, predetermined fixed operating differential for said device and a contact arc gap and wear allowance, the ratio of which may be varied while the sum thereof remains constant, said means comprising fixedly spaced surfaces to limit travel of said snap acting element, and the spacing of said surfaces being equal to the sum of the desired wear allowance and are gap of said contact plus the thickness of said snap acting element.

WILLIAM E. BROWN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,092,559 Runaldue Sept. 7, 1937 2,193,127 Furnas et al Mar. 12, 1940 2,194,533 Van Dyke Mar. 26, 1940 2,393,455 Beeman Jan. 22, 1946 2,437,846 Yeida Mar. 16, 1948 2,459,522 Grooms Jan. 18, 1949 2,548,877 Dillman Apr. 17, 1951

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