US3825781A

US3825781A - Magnetically driven timer

Info

Publication number: US3825781A
Application number: US00323729A
Authority: US
Inventors: L Woods
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1973-01-15
Filing date: 1973-01-15
Publication date: 1974-07-23
Anticipated expiration: 1991-07-23
Also published as: CA999443A

Abstract

A magnetically driven timer is disclosed comprising electric switch means, a generally disc shaped rotatable magnetic follower, and means for dampening hunting action by the magnetic follower when rotatably driven by extrinsic magnetic drive means. Rotational speed reduction means are coupled with the magnetic follower. Switch actuation means are coupled with the rotational speed reduction means for actuating the switch means.

Description

United States Patent 11 1 Woods July 23, 1974 [54] MAGNETICALLY DRIVEN TIMER 3,420,184 1/1969 Englesberg et al. 310/104 X 7 3,609,268 9/1971 Sanchez 200 107 A [75] Inventorwoods Mormon 3,649,781 3/1972 Johnsen et al. 200/38 B x 3 Assignee; General Electric Company, Fort 3,699,278 10/1972 Jones et al. 200/38 R Wayne Ind 3,742,160 6/1973 Murray et a1, 200/38 R v 3,743,872 7/1973 Dochterman 310/90 [22] Filed: Jan. 15, 1973' [2 1] App], .No 323,729 Primary Examiner-James R. Scott [52] US. Cl. 310/90, 310/99, 310/103, [57] 1 ABSTRACT a v A magnetically driven t1mer 1s d1sclosed compnslng 7 2 electric switch means, a generally disc shaped rotat. 1 O/ 2 R able magnetic follower, and means for dampening u 5 l 104 hunting action by the magnetic follower when rotat- 5 1 r g ably drivenby extrinsic magnetic drive means. Rotai 1 a tional speed reduction means are coupledwith the [56]- a J -Rgierencesc v magneticvfollower. Switch actuation means are cou- EN pled with the rotational speed reduction means for ac- 2,611,051 9/1952 Kloff'..',...,'. ZOO/81.9 M X mating the switch means. 2,915,606 12/1959, Knauth. ZOO/81.9 M X I 3,295,370 :1 1/1967 Marat. 310 104 x 2 Claims, 6.1)1-awing Figures 1 I 4 V O I- Y 45 0 1 I I l @L 1' 1 1 1 1 a .z2- -44 [b 4 v 22 6 1 \i I )K i i I ELECTRIC l8 E H '35 'oToR," /T w v 1 2O 24 2a; 33 I t 1 PATENTEB 3.825.781 A SHEEI 1 BF 3 FIG] I PATENTEUJULZBIBH 3.825.781

.snm m3 FIG MAGNETICALLY DRIVEN TIMER BACKGROUND OF THE INVENTION tially controlling cyclicv operations of appliances such as refrigerators, ovens and the like-.Some of these timers have been coupled to .the rotatable output shaft of drive motors by means'of dynamic magnetic fields. Such fields may, for example, be created by means of 'a permanent-magnet secured to the'end-ofthe motor output shaft or to the timer gear train.'A rotatable ferromagnetic memberis secured'to theother drive component within the field. Quite often this other ferro- 'magnetic member is itself also permanently magnetized.

The use of such magnetic motor-to-timer"couplings has negated the'practical necessity of having to assernble the motor and timer together prior to assembly within the. appliance, as may be required in those cases where coupling is achieved through mechanical linkage directly connecting-the motor output shaft to the timer. In addition, where the: motor drives other appliance loads, more complex mechanical linkage is requiredl Though thisf'complexity may be alleviated by use of double output motors, such motors usually havegreater oil leakage and tighter tolerance requirements necessitatingthe use of more costly forms of motors. Magnetic couplings thushave also provided a practical solution to this dilemma. I Thus, for the applications just described, it is seen that themagnetic couples employed have typically comprised a permanent magnet securedto the end of the motor shaft, or to a member of the timer. gear train, or to both. The magnet is usually in the form of a disc or disc segment coaxially secured tothe end of the motor output shaft or to one of the timer gears. Al-

though radial interfacing configurations are sometimes employed, typically an end or interface is adopted by means of a mating disc. or disc segmentshaped magnet coaxially secured tov the other shaftor gear coupling tween ferromagnetic componentsof the magnetic coupling. Another troublesome area has been the degree of difficulty heretofore associated with examining the condition of the timer components during trouble shooting and maintenance once the timer is mounted with the appliance it controls.'Yet another technical problem has been in mechanically coupling the timer switch actuator with the timer gear train in an efficient manner. v 1

Accordingly, it is a general object of the present inventionto provide an improved magnetically driven timer.. I

More specifically, it is an object of the invention to provide a magnetically driven .timer with improved magnetic coupling means.

Another object of the invention is to provide amagnetically driven timer with means covering'and supporting and yet permitting observation of the condition of selectedtimer-components.

.Yet another object of the invention is to provide a magnetically driven timer having improved means for is used, the other coupling member may not be permanently magnetizedbut instead comprise an annular set of pole pieces.

Upon rotation of the motor shaft, the magnet or fer;-

romagnetic pole pieces secured thereto rotate relative to the mating or driven magnet or set of pole pieces. The resultant cutting of magnetic flux lines imparts a torque to the coupling member secured to a timer gear to control various appliance operations at the conclusion of a substantial period of time. Frequently, the specific reduction ratio is. quite large such as several hunvdred thousand to one.

Magneticallydriven timers of the type just described have met with an encouraging degree of acceptance in the industry. I-Iowevenseveral quite significanttechnig 1 U cal problems have eluded solution. Perhaps foremost among'these, although not necessarily recognized, has been that of timing error occasioned by slippage be- SUMMARY OF THE INVENTION In one form of the invention a magnetically driven timer is provided comprising electric switch means, a generally disc shaped rotatable magnetic follower, and means'for dampening hunting action by the magnetic follower-when rotatably driven by extrinsic magnetic drive means. Rotational speed reduction means are coupled with the magnetic follower. Switch actuation means are coupled with the rotational speed reduction means for actuating the switch means. 7

Another feature of the invention is theinclusion-in a magnetically driven timer of a .train of gears with a magnetic follower mounted to a driving gear and with a driven gear having a bearing disposed about the driven gear axis. An electric switch and a cam for actuating the electric switch are provided with the cam having ashaft extension journalled in the driven gear bearing. Clutch means may couple the cam with the driven gear-[to limit relative .-unidirectional-rotary motion between the cam; and driven gear. v l

- Another feature of the'invention is'the provision of a transparent cover in a magnetically driven timer through which the condition of a gear'train, switch actuating and electric switch means may-be observed, and

through which cover the switch actuating means are ro-- tatably journalled.

BRIEF DESCRIPTION OF THE DRAWING also shown in FIG. 3, in magnetic coupling relation with a driving magnet of a motive means embodied, in one form of the'prese'rit invention; and

FIG. 6 is a schematic view showing a multiple disc .type magnet as illustrative of the driving and driven magnets of FIG. 5.

Referring now in detail to the drawings and in particular to FIGS. 1 and 3, there is shown a magnetically driven timer embodying principles of the invention, having two mounting plates 10 and 11 spaced apart'by three cylindrical posts 12 and secured together by nuts run up flush with plate 10 upon threaded extensions of the posts passing through and beyond the plate. A train of gears is disposed within the compartment partially bounded by mounting plates l0, 11 with each end of each member gear shaft rotatably journalled within an individual bearing 14 within one of the plates. A driving pinion member 16 of the gear train is mounted for rotation about a stationary shaft 18. One end of shaft 18 is journalled through a hole in a member of nonmagnetic material, such as an aluminum cup 20, an annular lip of which cup issecured to mounting plate 10 by tabs, unshown, which pass through and are bent over the edge of slots in the plate. Referring now also to FIGS. 5 and 6, driven means, such as a disc shaped permanent magnet 22, is press fitted about an annularportion of pinion l6 closely adjacent the planar portion of cup 20. Preferably, magnet 22 is disposed less than one-eighth of an inch from the cup. A flux concentrating washer 24 is held flush against the magnet by a spring washer 26.

A driven gear member 28, which is the output member of the train, has a hollow, cylindrical extension 28 which is rotatably journalled through a bushing 26 within mounting plate 11. A shaft extension 29 of a cam 30 is rotatably journalled within a bearing 32 formed within gear extension 28' coaxially about the gear axis. A clutch spring 34 is fitted about the periphery of gear extension 28' with a spring terminus 35 in pressure contact with an annular knurled, inner surface switch blade 45

couples switch blades

44 and 46 whereby one blade follows the other when the other is forced more than a definitive distance therefrom.

Dielectric mounting board 40, with

switch blades

44, 45 and 46 secured thereto, is press fitted into slots within a transparent cover 60, which cover is preferably formed of a moldable clear plastic material. When board 40 is so press fitted, terminals 44', and 46' extend to the exterior of the cover through a plurality of complementary cover slots 62. The cover and switch assembly is secured to the gear train and cam assembly by means of three screws 64, as shown in FIG. 1, which pass'through mounting plate 10 and are screwed into threaded holes 66 within cover 60. In performing the assembly two'tabs 41'formed unitarily with board 40 are fitted with two slots 42 in plate 10. With the. cover' thusly secured to mounting late 10, an annular portion 68 of cover is disposed about the periphery of the gear-trainthereby, together with board 40, providing'a peripheral portion of the gear train compartment structure. Annular extension 33 of cam 30 is journalled in a unitary bearing within cover 60 itself.

For operation, the timer is mounted to an electric motor by screw or bolt means passing through mounts with the planar, exterior portion or surface of cup 20 preferably disposed adjacent the planar outboard surface of a rotatable magnetic driving means, such as disc shaped permanent magnet, affixed to the end of the motor output shaft, and with the cup surface and drive magnet also disposed mutually coaxial and substantially parallel FIG. 5. Upon energization, the motor output shaft and drive magnet affixed thereto rotates. The magnet field created by the drive magnet in turn rotates and drives magnetic follower 22 generally in synchronous with the drive magnet. Rotation of follower 22 causes pinion l6 and the other members of the gear train in turn to rotate including output gear 28. Clutch spring 34 mounted to gear 28 couples cam 30 with the gear.

, With reference to FIG. 2, it may be seen that in the position depicted switch contacts 50 and 48 are closed and switch contacts 48 and 52 are open. Clockwise rotation of cam 30 from the depicted position will enable the free end of resilient switch blade 44 to snap to the left to thecam surface of smaller radius adjacent cam lip 51. Thus, movement of switch blade 44 enables switch blade 45 also to move to the left due to its spring biasHowever, it is stopped by the cam lip 51 causing contacts 50 and 48 to snap open. Simultaneously, dielectric link 55 engaged by the movement of switch blade 44 to the left pulls switch blade 52 also to the left snapping contacts 52 and 48 closed. Continued clockwise rotation of the cam causes switch blade 45 to snal to the left thereby reclosing contacts 48 and 50 and reopening contacts 48 and 52 preparatory to commencement of a new cycle.

Timers of the type just described have been found to exhibit minimal hunting action. This is believed to be primarily attributable to the presence of the stationary highly conductive plate provided by cup 20 overlaying in very close proximity thereto the planar surface of the disc shaped magnet 22. One sixteenth of an inch is a preferred spacial separation between the cup and magnetic follower, but other spacial separations may be employed depending on the use and construction of various timers. In theory, it is believed that the eddy currents generated in the disc shaped portion of conductive cup 20 produce magnetic fields of sufficient flux density to dampen nonsynchronous hunting action by the follower. As eddy current magnitudes vary directly with flux linkages, disc magnetic followers having a number of polesare preferred, as illustrated in FIG. 6. For example, a bar or segmented disc magnet having but two poles, while operative, is less preferred to a disc magnet having four poles. A disc shaped magnetic follower having eight or even sixteen poles would be even more preferred to that of the four pole magnet were it not for the difficulty ordinarily encountered in efficiently magnetizing such. Thus, as a balance between efficiency of manufacture and performance the four pole follower of FIG. 6 may be preferred. Of course, a set of pole pieces having coplanar annularly arranged terminals could be substituted for the permanently magnetized follower or driver, and the eddy currents generated solely by amagnetized drive or 00 lower relied up for dampening.,but such would require.

the use of a relatively large permanent magnet unsuited for many appliance uses. f

I Whethera hunting action dampening effect may be achieved by interbb ng an annular eddy current conductor between a radial interfacing magnetic drive and follower is not known. However, the difficulty in practice of efficiently achieving close member'proximity with such configuration in addition to the packaging problems created by that configuration render suchunpreferred. 1

In addition to the improved accuracy in timing provided by the just described hunting damper, timers depicted in the drawing also include significantly improved features over timers of the prior art. One such feature, for example, is embodied in the cam to output gear coupling exemplified in FIG. 3. Assembling of the cam to output gear facilitated by the provision of hearing 32 carried by gear 28 into which bearing shaft extension 29 carried by the cam is journalled. With continued reference to FIG. 3, it may be seen that assembly may be achieved by merely sliding clutch spring 34 over extension 28', then sliding shaft extension 29 of cam 30 into bearing 32, and finally securing cover 60 with cam extension 33 journalled in a unitary bearing in the cover. With cover 30 being transparent the position and condition of the cam and switches may subsequently be observed without disassembly.

It should, of course, be understood that the just described embodiment merely illustrates principles of the correcting nonsynchronous hunting action of the driven means relative to the driving means upon the magnetic coupling rotation thereof comprising a relatively' thin nonmagnetic member having a relatively great electrical conductive capacity for disposition between the driving means and the driven means and spaced closely adjacent the driven means, the member being effective to conduct eddy currents generated upon the establishment of the magnetic field and the eddy currents themselves also establishing another magnetic field in opposition to thefirstnamed magnetic field and acting on the driven means for correct-,

ing the nonsynchronous hunting action thereof relative to the rotation ofthe driving means.

2. In a timer for controlling operations of an appliance or the like, a casing for mounting adjacent a rotat able magnetic driving means, means in the casing for driven magnetic coupling rotation with the driving means, electrical switch means mounted to the casing, means coupled with the driven means for-actuating the electrical switch means upon the magnetic coupling rotation of the driving means and the driven means; at least a portion of the casing including a relatively thin nonmagnetic material having a relatively great electrical conductive capacity generally spaced closely adjacent the driven means and adapted to be disposed adjacent the driving means, and the nonmagnetic electrical conductive material being generally effective to conduct eddy currents generated in response to the magnetic coupling rotation of the driving means and the driven means and the generated eddy currents themselves also establishing a magnetic field of sufficient flux density generally in opposition to the magnetic field effected upon the magnetic coupling rotation of the driving means and the driven means for damping hunting action of the driven means relative to the driving means.

C01. Col.

1, line 42, 2, line 6,

UNITED STATES PATENT OFFiQE CERTIFICATE OF CORRECTION PATENT NO. 3,825,781 DATED July 23, 1974 INVENTOMS): Lee 0. Woods Hiscmflfiedmatamrammaminmeamwe-memfimdpamntmdfimtsmdLefimsPamm amhawymnwmdasmwnmmw lines 27-51, delete in their entirety and insert the delete "or" and insert on-. delete "with" and insert within-;

following:

In general and in one form of the inven tion, a timer is adapted to be mounted adjacent a rotatable magnetic driving means. Means is responsive to a magnetic field established upon rotation of the driving means for driven magnetic coupling rotation generally in synchronous with the driving means. Means for correcting nonsynchronous hunting action of the driven means relative to the driving means upon the magnetic coupling rotation thereof includes a nonmagnetic member having a relatively great electrical conductive capacity for disposition between the driving means and the driven means. This member is effective to conduct eddy currents generated upon the establishment of the magnetic field, and the eddy currents themselves also establish another magnetic field in opposition to the first named magnetic field and acting on the driven means for correcting the nonsynchronous hunting action thereof relative to the rotation of the driving means.

Further in general and in one exemplification, the timer of the present invention may include rotational-- UNITED STATES PATENT OFFICE Page 2 CERTIFICATE OF CORRECTION PATENT NO. I 3,825,781

DATED 1 July 23, 1974 INVENTOR(S) Lee 0. Woods It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col, 2, line 62, delete "of";

line 63, delete "FIG. 3";

Col. 3, line 4, insert -Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

The following examples illustrate the invention and are not to be construed as limiting.-;

line 24, after "6," insert -a-; line 63, before "threaded insert -a plurality of complementary.

Col. 4, line 12, after "parallel" insert line 34, delete "snal" and insert -snap--; line 67, delete "foo" and insert -fol- Col. 5, line 17, after "gear" insert -is-.

Signed and Sealed this twenty-ninth Day of July 1975 [SEAL] A ttest:

RUTH C. MASON C. MARSHALL DANN Arresting ()jfr'rer (mnmr'ssr'mrcr nj'lurcnrs and Trademarks

Claims

1. In a timer adapted to be mounted adjacent a rotatable magnetic driving means, means responsive to a magnetic field established upon rotation of the driving means for driven magnetic coupling rotation generally in synchronous with the driving means; and means for correcting nonsynchronous hunting action of the driven means relative to the driving means upon the magnetic coupling rotation thereof comprising a relatively thin nonmagnetic member having a relatively great electrical conductive capacity for disposition between the driving means and the driven means and spaced closely adjacent the driven means, the member being effective to conduct eddy currents generated upon the establishment of the magnetic field and the eddy currents themselves also establishing another magnetic field in opposition to the first named magnetic field and acting on the driven means for correcting the nonsynchronous hunting action thereof relative to the rotation of the driving means.

2. In a timer for controlling operations of an appliance or the like, a casing for mounting adjacent a rotatable magnetic driving means, means in the casing for driven magnetic coupling rotation with the driving means, electrical switch means mounted to the casing, means coupled with the driven means for actuating the electrical switch means upon the magnetic coupling rotation of the driving means and the driven means; at least a portion of the casing including a relatively thin nonmagnetic material having a relatively great electrical conductive capacity generally spaced closely adjacent the driven means and adapted to be disposed adjacent the driving means, and the nonmagnetic electrical conductive material being generally effective to conduct eddy currents generated in response to the magnetic coupling rotation of the driving means and the driven means and the generated eddy currents themselves also establishing a magnetic field of sufficient flux density generally in opposition to the magnetic field effected upon the magnetic coupling rotation of the driving means and the driven means for damping hunting action of the driven means relative to the driving means.