MAGNETIC SWITCH
United States Patent 3593236
A set of switch points are enclosed within a glass structure and include an armature that is magnetically movable to effect different connection arrangements of the switch points. A first magnet when acting alone attracts the armature to provide a first connective arrangement. A second magnet carried by a heat responsive bimetal is movable thereby to a position where its attractive influence on the armature overcomes that of the first magnet and transfers the points to a different connective arrangement. An alternative embodiment has the two magnets mounted for unitary movement, that is, as the one magnet is moved into attractive influence, the other magnet is moved away, and vice versa.
US Patent References:
Remotely controlled magnetic electric switch
Maxwell - June 1967 - 3325756
Ignition distributor contact-breaker for an internal combustion engine
Blaser - July 1967 - 3331928
Control device
Hewitt, Jr. - December 1962 - 3068333
Magnet operated switch
Chisholm - June 1951 - 2555571
Magnetic switch
Hildebrecht - May 1941 - 2240847
Remotely controlled magnetic electric switch
Maxwell - June 1967 - 3325756
Ignition distributor contact-breaker for an internal combustion engine
Blaser - July 1967 - 3331928
Control device
Hewitt, Jr. - December 1962 - 3068333
Magnet operated switch
Chisholm - June 1951 - 2555571
Magnetic switch
Hildebrecht - May 1941 - 2240847
Application Number:
05/021606
Publication Date:
07/13/1971
Filing Date:
03/23/1970
View Patent Images:
Export Citation:
Assignee:
International Telephone and Telegraph Corporation (New York, NY)
Primary Class:
Other Classes:
335/207
International Classes:
H01H36/00; H01H37/56; H01H37/00; H01H5/02; H01H1/66; H01H9/00
Field of Search:
200/19,166,34 335/90,93,134,145,153,154,205,206,207,151 337/90,341,344,351,366
US Patent References:
| 2121607 | Oscillator | June 1938 | McIlvaine |
Primary Examiner:
Gilheany, Bernard A.
Assistant Examiner:
Morgan, Dewitt M.
Parent Case Data:
BACKGROUND OF THE INVENTION
This application is a continuation-in-part of copending application Ser. No. 617,191 filed on Feb. 20, 1967, by Roland D. Beck for a "Magnetic switch, now abandoned." The benefit of the filing date of said application, therefore, is claimed for this application.
Claims:
What I claim is
1. A switch comprising:
2. The invention as defined in claim 1, wherein said magnetic means includes a support fixed to said base, said two permanent magnets being fixed to said support, said magnets being movable toward and away from respective opposite sides of said armature, said magnets being of equal polar strengths.
3. A switch magnetically actuable by magnetic flux externally applied along a predetermined path, comprising:
4. A switch magnetically actuable by magnetic flux externally applied along a predetermined path, comprising:
5. A switch comprising:
6. The invention as defined in claim 5, wherein said actuation means includes means to move said magnets simultaneously in the same direction simultaneously.
7. The invention as defined in claim 6, wherein said actuation means includes a substantially rigid member, said magnets being attached to said member.
8. The invention as defined in claim 6, wherein said actuation means includes means to support said magnets in a predetermined, spaced relation to each other.
9. The invention as defined in claim 8, wherein said actuation means includes a member, and first and second means to hold said magnets, respectively, in fixed positions relative to said member.
10. The invention as defined in claim 9, wherein said first means is releasable and engageable to permit adjustment of the position of at least one magnet.
11. The invention as defined in claim 10, wherein said second means is also releasable and engageable to permit adjustment of the position of the other magnet.
12. A switch magnetically actuable by magnetic flux externally applied along a predetermined path, comprising:
13. A switch comprising: a base; a sealed envelope fixed to said base; a moving contact arm located inside said envelope, said arm including a cantilever leaf spring having one movable end and one end fixed relative to said envelope; a magnetic armature fixed to said arm spring at a position spaced from said fixed end thereof; a first stop fixed relative to said envelope inside thereof; said arm spring movable end being movable back and forth in first and second directions, said arm spring being movable in said first direction into engagement with said first stop; a first permanent magnet fixed relative to said envelope outside thereof on one side thereof spaced in said first direction from said arm; an actuation device mounted on said base outside said envelope; and a second permanent magnet fixed to said device, said device being actuable to move said second magnet toward and away from said arm and said envelope in said first and second directions, respectively, said second magnet being adapted to produce a torque on said arm of a magnitude large enough to attract said armature away from under the influence of said first magnet and to pull said arm out of engagement with said stop when said second magnet is positioned sufficiently close to said armature by said device, said device being actuable to move said second magnet away from said armature a distance large enough that the influence of said first magnet on said armature pulls said arm into engagement with said first stop, said first magnet and said envelope being adjustable relative to each other at least during calibration to adjust the contact pressure between said arm and said first stop when said second magnet is moved away from said armature.
14. The invention as defined in claim 13, including a second stop fixed relative to said envelope inside thereof, said arm being movable in said second direction into engagement with said second stop when said device brings said second magnet toward said armature, at least one of said stops having a conductive portion, said arm also having at least one conductive portion spaced from the fixed end thereof and positioned to engage said one stop conductive portion when said arm engages said one stop.
15. The invention as defined in claim 14, wherein said first stop includes a cantilever leaf spring located inside said envelope, said first stop spring having a movable end and an end fixed relative to said envelope, said first stop being sufficiently flexible that it will move a substantial distance when engaged by said arm.
16. The invention as defined in claim 15, wherein the other of said stops also has a conductive portion, said arm also having another conductive portion to engage said other stop conductive portion when said arm engages said other stop, said second stop also including a cantilever leaf spring located inside said envelope, said second stop spring having a movable end and an end fixed relative to said envelope, said second stop being sufficiently flexible that it will move a substantial distance when engaged by said arm, said stop conductive portions being spaced from the fixed ends thereof, respectively.
17. The invention as defined in claim 13, wherein said stop includes a cantilever leaf spring located inside said envelope, said first stop spring having a movable end and an end fixed relative to said envelope, said first stop being sufficiently flexible that it will move a substantial distance when engaged by said arm.
18. The invention as defined in claim 17, wherein said first stop has a conductive portion spaced from the fixed end thereof; said arm having a conductive portion spaced from the fixed end thereof and positioned to engage said first stop conductive portion when said arm engages said first stop.
19. The invention as defined in claim 13, wherein said first stop has a conductive portion spaced from the fixed end thereof; said arm having a conductive portion spaced from the fixed end thereof and positioned to engage said first stop conductive portion when said arm engages said first stop.
1. A switch comprising:
2. The invention as defined in claim 1, wherein said magnetic means includes a support fixed to said base, said two permanent magnets being fixed to said support, said magnets being movable toward and away from respective opposite sides of said armature, said magnets being of equal polar strengths.
3. A switch magnetically actuable by magnetic flux externally applied along a predetermined path, comprising:
4. A switch magnetically actuable by magnetic flux externally applied along a predetermined path, comprising:
5. A switch comprising:
6. The invention as defined in claim 5, wherein said actuation means includes means to move said magnets simultaneously in the same direction simultaneously.
7. The invention as defined in claim 6, wherein said actuation means includes a substantially rigid member, said magnets being attached to said member.
8. The invention as defined in claim 6, wherein said actuation means includes means to support said magnets in a predetermined, spaced relation to each other.
9. The invention as defined in claim 8, wherein said actuation means includes a member, and first and second means to hold said magnets, respectively, in fixed positions relative to said member.
10. The invention as defined in claim 9, wherein said first means is releasable and engageable to permit adjustment of the position of at least one magnet.
11. The invention as defined in claim 10, wherein said second means is also releasable and engageable to permit adjustment of the position of the other magnet.
12. A switch magnetically actuable by magnetic flux externally applied along a predetermined path, comprising:
13. A switch comprising: a base; a sealed envelope fixed to said base; a moving contact arm located inside said envelope, said arm including a cantilever leaf spring having one movable end and one end fixed relative to said envelope; a magnetic armature fixed to said arm spring at a position spaced from said fixed end thereof; a first stop fixed relative to said envelope inside thereof; said arm spring movable end being movable back and forth in first and second directions, said arm spring being movable in said first direction into engagement with said first stop; a first permanent magnet fixed relative to said envelope outside thereof on one side thereof spaced in said first direction from said arm; an actuation device mounted on said base outside said envelope; and a second permanent magnet fixed to said device, said device being actuable to move said second magnet toward and away from said arm and said envelope in said first and second directions, respectively, said second magnet being adapted to produce a torque on said arm of a magnitude large enough to attract said armature away from under the influence of said first magnet and to pull said arm out of engagement with said stop when said second magnet is positioned sufficiently close to said armature by said device, said device being actuable to move said second magnet away from said armature a distance large enough that the influence of said first magnet on said armature pulls said arm into engagement with said first stop, said first magnet and said envelope being adjustable relative to each other at least during calibration to adjust the contact pressure between said arm and said first stop when said second magnet is moved away from said armature.
14. The invention as defined in claim 13, including a second stop fixed relative to said envelope inside thereof, said arm being movable in said second direction into engagement with said second stop when said device brings said second magnet toward said armature, at least one of said stops having a conductive portion, said arm also having at least one conductive portion spaced from the fixed end thereof and positioned to engage said one stop conductive portion when said arm engages said one stop.
15. The invention as defined in claim 14, wherein said first stop includes a cantilever leaf spring located inside said envelope, said first stop spring having a movable end and an end fixed relative to said envelope, said first stop being sufficiently flexible that it will move a substantial distance when engaged by said arm.
16. The invention as defined in claim 15, wherein the other of said stops also has a conductive portion, said arm also having another conductive portion to engage said other stop conductive portion when said arm engages said other stop, said second stop also including a cantilever leaf spring located inside said envelope, said second stop spring having a movable end and an end fixed relative to said envelope, said second stop being sufficiently flexible that it will move a substantial distance when engaged by said arm, said stop conductive portions being spaced from the fixed ends thereof, respectively.
17. The invention as defined in claim 13, wherein said stop includes a cantilever leaf spring located inside said envelope, said first stop spring having a movable end and an end fixed relative to said envelope, said first stop being sufficiently flexible that it will move a substantial distance when engaged by said arm.
18. The invention as defined in claim 17, wherein said first stop has a conductive portion spaced from the fixed end thereof; said arm having a conductive portion spaced from the fixed end thereof and positioned to engage said first stop conductive portion when said arm engages said first stop.
19. The invention as defined in claim 13, wherein said first stop has a conductive portion spaced from the fixed end thereof; said arm having a conductive portion spaced from the fixed end thereof and positioned to engage said first stop conductive portion when said arm engages said first stop.
Description:
This invention relates to highly reliable switches such as thermostat switches having a highly suitable differential and a low contact bounce.
In the past, a switch has been employed having a pole and a contact with a ferromagnetic armature fixed to the pole. A first permanent magnet is fixed and biases the pole in one direction. A second permanent magnet is movable toward and away from the armature on one side thereof opposite the side on which the fixed magnet is positioned. Thus, the pole is moved away from the fixed magnet when the movable magnet moves close enough, and vice versa. This prior art arrangement is disclosed in U.S. Pat. No. 2,555,571. Citations of references disclosing this prior art arrangement and other pertinent prior art will be found in the official file of said copending application. Attention is invited to said prior art citations including, but not limited to, the references cited by applicant in said file.
Said prior arrangement has not proven successful in the past because dirt and dust would accumulate on the switch contacts and insulate them. The switch would then become inoperative.
It was known for a number of years before the present invention that a single-pole, double-throw switch could be enclosed in a glass envelope to prevent foreign material from insulating the contacts. This is disclosed in U.S. Pat. No. 2,121,607. However, when a switch is so enclosed, it is impossible to adjust the contact pressure because once the switch is sealed inside the envelope, the switch arms cannot be bent to shape. That is, since the envelope is sealed, there is no practical way in which to get inside and bend a switch arm. As will be explained, in accordance with the present invention, it has been found that a certain contact pressure is extremely critical.
It is also an outstanding disadvantage of prior art switches that the switch points, i.e., contacts, "bounce" due to the bulk modulus of elasticity of the contacts and due to the resilience of whatever structures support them. When bounce occurs and/or is repetitive at high currents, contact pitting, spiking, and welding of two bouncing contacts occurs. This , then, causes switch deterioration and/or inoperativeness. The useful life of such a switch is also thereby shortened. Note will be taken that high currents may occur when switch contacts are opened while being connected to a large inductive load, although high currents may be otherwise produced.
SUMMARY OF THE INVENTION
In accordance with the device of the present invention, the above-described and other disadvantages of the prior art are overcome by providing an envelope for a switch having a pole to carry a magnetic armature and a fixed magnet and a movable magnet outside the envelope.
Thus, the fixed magnet may be adjusted in position to adjust contact pressure. Therefore, this overcomes the prior art problem where it was impossible to adjust contact pressure.
In accordance with the present invention, it has been found only through a great deal of effort that the quiescent pressure which is established between the switch pole and the contact spaced farthest way from the movable magnet is extremely critical. The pressure must fall within a narrow range to insure good electrical conductivity and a small differential when a bimetal carries the movable magnet. From the instant that the contact next to the fixed magnet opens the differential is the temperature change required to the instant the same contact closes. The use of the fixed magnet makes it possible to adjust contact pressure within the said narrow range because, although it is fixed, it can be adjusted to its correct, fixed position before use.
It is also an outstanding advantage of the present invention that a flexible leaf spring pole stop is employed to prevent contact bounce. The rubbing action of the contacts and the flexure losses act as a dashpot to absorb the kinetic energy of the moving pole over a greater length of time because the spring is relatively weak and allows energy exchange over a long period before any bounce can occur. That is, the kinetic energy absorption can take place as the leaf spring stop and pole rock back and forth without the contacts separating. Thus the stop and pole contacts may rub together instead of separating as the two leaf springs rock.
The above-described and other advantages of the invention will be better understood from the following description when considered in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, which are to be regarded as merely illustrative:
FIG. 1 is a perspective, diagrammatic, elevational view of the invention in one of its connective conditions;
FIG. 2 is a view similar to that of FIG. 1 with the switch shown in another connective condition;
FIG. 3 is an enlarged, sectional view of that portion of the invention included within the glass enclosure;
FIG. 4 is a sectional view taken along the line4-4 shown in FIG. 3;
FIG. 5 is a diagrammatic view of special magnetic actuating means;
FIGS. 6 and 7 depict a further embodiment of the invention;
FIG. 8 is a side elevational view of still another embodiment of the invention; and
FIG. 9 is a top plan view of a bracket shown in FIG. 8.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, a switch 10 of the present invention includes a spiral, heat responsive bimetal 11, a first magnet means 12 carried by member 11, an enclosed set of switch points 13, and a second magnet means 14 all mounted in a casing 15.
The enclosed set of switch points 13 includes first and second conducting blades 16 and 17 of a nonmagnetic, springlike material, which are provided adjacent an end thereof with respective contact points 18 and 19. The blades are mounted within a sealed glass envelope 20 so that the contact points are in a facing, directly opposed relation to one another. A somewhat longer armature blade 21 of flexible, springlike conductive material when assembled is disposed between blades 16 and 17 but insulated therefrom. A contact point 22 is provided on the armature and has opposite facing surfaces such that lateral movement of the armature produces contact with either of contact points 18 or 19, as the case may be. The end of the armature extending beyond the ends of blades 16 and 17 is provided with a body of magnetic material 23. Blades 16 and 17 and armature blade 21 are included within an hermetically sealed, elongated, tubular glass envelope 20 containing a nonreactive gas such as a hydrogen-nitrogen mixture, for example. External electrical connection to the switch points and armature is provided via leads 25, 26, and 27 extending from one end of the envelope. The armature and contact blades are so constructed that in the unactuated position, i.e., neither magnet in influential position, the armature will lie between the two blades; and contact point 22 will be free from contact with either of points 18 or 19.
A second magnet means 14 is mounted from casing 15 to have an extended surface in contact with the glass envelope and lies directly opposite the flat side of magnetic body 23 of the armature. The magnetic field set up by magnet 14 attracts the armature a sufficient amount to close the circuit between contact point 22 on the armature and point 19 on blade 17. The flexible, springlike quality of both blade 17 and the armature are chosen to provide a firm contacting relation and achieve "overtravel" of the armature about which further details will be given later.
The contact pressure in this biased direction may be easily adjusted by moving the fixed magnet relative to the envelope or vice versa.
As the environmental temperature increases, the bimetal spiral uncoils to move first magnet means 12 toward the glass envelope at the opposite side from that at which magnet 14 is disposed. Due to the greater polar strength of magnet means 12, there is a point (indicated by the dashed line) at which the mutual attraction between the first magnet means and the armature is sufficient to overcome the springlike forces within bimetal spiral 11 so that the magnet means is snapped against the glass envelope. At this same time, armature blade 21 is influenced sufficiently to overcome its attraction for magnet 14 and causing it to transfer, establishing contact between points 18 and 22. The device described to the point now resides in the condition shown in FIG. 2. It is emphasized that the release of the first connective condition and the production of the second connective condition is a rapid one in which the transfer from one to the other is rapid and sure.
With a subsequent reduction in environment temperature, spiral bimetal member 11 begins to coil producing a potential force therein which acts against the attractive influence of magnet means 12 for the armature blade 21. This coiling continues until a point is reached at which the restoring force of the bimetal spiral is great enough to overcome the magnetic attractive force, and the first magnet means is moved away from glass envelope 20 and beyond the critical limit of magnetic influence. Of course, with removal of the influence of magnet means 12, second magnet means 14 now acts solely on the armature blade and causes rapid transfer of the contacting condition to that shown in FIG. 1. Although the foregoing description is sufficient for general constructive aspects of the invention, certain, more detailed features of the invention will be explained at this time, a knowledge of which is necessary for a clear understanding of how the present invention can handle relatively large loads and yet only use low contact forces with correspondingly low actuation force requirements on the bimetal member.
With particular reference to FIG. 3, it is seen that the body of magnetic material 23 is unsymmetrically arranged at the end of armature blade 21. That is, a relatively longer portion 28 of magnetic material is on the side of the blade facing first magnet means 12 than the corresponding portion 29 facing second magnet means 14. This unsymmetrical character of magnetic body 23 has a remarkable and beneficial effect upon operation. In explanation and beginning with the device disposed as in FIG. 1, when magnet means 12 moves toward glass envelope 20, the mutual attractive influence between means 12 and magnetic portion 28 increases to the point where blade 21 begins to flex outwardly of point 22 toward means 12 while still maintaining electrical contact between points 22 and 19. As means 12 moves still further, the critical point is passed at which body 23 moves sufficiently to open contact points 22 and 19. Now, blade 21 begins to flex below point 22 and continues flexing until the points 22 and 18 are closed. However, in this latter connective state, blade 21 beyond point 22 does not flex as much as it did when in the other closed state due to the additional length of portion 28. Or, viewed from a different standpoint, the spacing of magnet means 12 and body 23 is less when points 18 and 22 are closed than is the spacing of the body and means 14 when contacts 22 and 19 are closed.
This differential spacing is reflected in requiring less bimetal force to move means 12 away from envelope 20 than would be the case if the blade had "overtraveled" as much as in the other connective aspect. It is also to be noted that the extra overtravel of body 23 on closing points 22 and 19 does not, by the same token, require additional force from the bimetal. This result is at variance with what had been previously considered the rule--namely, that higher contact pressures for accommodating higher electrical loads could only be achieved by increased bimetal work input. Whereas, in the present invention, the contact pressures have been able to be kept higher by controlling overtravel; and yet at the same time armature movement is held to a minimum, insuring that the bimetal work input is optimally small.
In FIGS. 3 and 4, there is shown the detailed aspects of contact blades 16 and 17 and armature blade 21 as they are assembled within the enclosure. Blades 16 and 17 are bent at their approximate midpoint so that when oriented with points 18 and 19 facing, the space between the blade portions is greater at this end than at the mounting end. Insulation sheets 30 and 31 are situated between blades 16, 21 and 17, 21, respectively. An alignment opening 32 is formed in each of the blades and the insulation sheets for receiving an insulating and alignment plug 33. As best shown in FIG. 4, insulating sheet 31 is protectively wrapped around the long edges of the blades to permit edge portions of blade 17 to engage securingly the edges of the assembly, making an integral structure.
Proper relative flexibility of blades 16, 17, and 21 is important to overall operation. If the blades are too rigid, the contacts will tend to bounce and produce welding. On the other hand, if the blades are too soft, sensitivity of transfer is adversely affected. It has been found, for example, that when the blades are constructed of the same material and of the same width, blades 16 and 17 should have a thickness that is at least twice that of the armature blade 21, but not exceed three times the armature thickness for best results. In actual constructions of phosphor-bronze, with the armature blade having a thickness of 0.004 inches, blades 16 and 17 of the same material were too flexible at 0.007 inches and too rigid at 0.015 inches in thickness.
FIG. 5 depicts a special magnet particularly advantageous for use as magnet means 12. The magnet includes a front magnetic layer 34 of polar arrangement as shown and a back magnetic layer 35 of polar arrangement opposite to that of 34. The back layer 35 is secured and in flush contacting relation to a plate 36 of magnetically influenceable material. Plate 36 is one plate of bimetal member 11. It has been found that the attractive force of the magnet means 12 is enhanced to a considerable degree by this structural arrangement.
Accordingly, there is provided in the practice of the invention a heat responsive magnetically actuable switch requiring a relatively small mass of bimetal to act as the prime mover and yet sufficient force is provided through magnetic means to exert sufficient pressure on the switch points so that substantial currents can be accommodated. As a result of the "latching" action achieved by the magnet means and the "overtravel" of the armature blade, undesirable contact bounce has been eliminated. Also, of equal importance is the fact that opening of the contact points is performed rapidly thereby eliminating the arcing erosion of points that results form incremental opening as in certain prior art devices.
An alternative form of the invention is depicted in FIGS. 6 and 7 in which a pair of magnet means are swung as a unit to produce switching action. The basic switch assembly comprising blades 16 and 17 and armature blade 21, enclosed within envelope 20, is identical to that already described; and for that same reason, the same reference numerals are used.
A magnet means 37 is secured to one extremity of bimetal 11 to face the envelope. A U-shaped support bracket 39 has the end of one leg secured to the bimetal on the side opposite where magnet means 37 is mounted and thereby disposing the other leg on the other side of envelope 20. Bracket 39 could be eliminated with its function being carried out by an extension of the bimetal. At the extremity of the other leg of member 39, there is secured a further magnet means 38 generally facing the envelope. The magnet means are so mounted and bracket 39 so dimensioned that when located at the extreme right position as in FIG. 6, magnet means 37 contacts the outer surface of the envelope; and magnet means 38 is disposed beyond its range of magnetic effectivity. Further, when the bracket is transferred to its extreme left position, magnet means 38 contacts the envelope; and magnet means 37 is spaced therefrom.
With magnet means 38 at its closest range as in FIG. 6, the armature is attracted thereto closing contacts points 19 and 22. As the temperature rises and bimetal 11 uncoils moving magnet means 37 toward the envelope and magnet means 38 away therefrom, a critical point is reached at which means 37 is snapped forward against the envelope. When this happens, contact points 19 and 22 are rapidly opened and points 18 and 22 are closed. At this time, the switch resides as is shown in FIG. 7.
A further possible modification would be to make body 23 symmetrical with both halves or parts of equal extent. This would result in a certain loss in sensitivity and perhaps an increase in bimetal volume. However, there would be a manufacturing advantage here since the armature, being of symmetrical construction, would be easier to fabricate.
Note will be taken that in FIGS. 6 and 7, it may be desirable to make the relative positions of magnets 37 and 38 adjustable. However, during operation, the magnets 37 and 38 would not change position relative to each other. Thus, as used herein and in the claims, the phrases "magnets...fixed in position relative to each other" and "magnets...fixed to said support" are hereby defined to include both, (1) magnets, the position of which cannot be adjusted relative to each other, and (2) magnets, the position of which can be adjusted relative to each other.
In FIG. 8, a somewhat different version of the embodiment of FIGS. 6 and 7 is shown. A rigid bar 39' is fixed to a bimetal strip 11'. Brackets B1 and B2 are fixed to bar 39'. Brackets B1 and B2 have slotted horizontal portions P1 and P2. Screws S1 and S2 are threaded into permanent magnets 37' and 38'. A slot L1 in bracket portion P1 is shown in FIG. 9. Note that screw S1 has a head H1 which is larger than the width of slot L1. Screws S1 and S2 may, thus, be tightened to hold magnets 37' and 38' rigid with brackets B1 and B2, respectively. When screws S1 and S2 are loosened, they may be moved longitudinally in the bracket slots and retightened. The positions of magnets 37' and 38', thus, are adjustable and movable relative to bar 39' for calibration, although they are both fixed relative to bar 39' during operation.
Note will be taken from FIGS. 2, 6, and 7 that when blade 21 moves from one extreme limit of its travel to the other, the center of contact 22 moves only about three times as far as the maximum deflection of blade 16 measured at the center of contact 18. Further, the maximum deflection of blade 17 measured at the center of contact 19 is about equal to the said maximum of blade 16. Thus, blades 16 and 17 have such flexibility that they themselves have a travel which is about equal to one-third that of blade 21.
From the foregoing, it will be appreciated that the fixed magnet 14 may, in calibration, be moved to adjust the pressure of contacts 19 and 22 to within an extremely small critical range for good electrical conductivity and small operating force.
Still further, the fact that blades 16 and 17 act as weak springs (see the large deflection of blade 16 in FIGS. 2 and 7, and the large deflection of blade 17 in FIG. 6) makes it possible to reduce bounce of contact 22 on contacts 18 and 19 to an extraordinary degree.
In the past, a switch has been employed having a pole and a contact with a ferromagnetic armature fixed to the pole. A first permanent magnet is fixed and biases the pole in one direction. A second permanent magnet is movable toward and away from the armature on one side thereof opposite the side on which the fixed magnet is positioned. Thus, the pole is moved away from the fixed magnet when the movable magnet moves close enough, and vice versa. This prior art arrangement is disclosed in U.S. Pat. No. 2,555,571. Citations of references disclosing this prior art arrangement and other pertinent prior art will be found in the official file of said copending application. Attention is invited to said prior art citations including, but not limited to, the references cited by applicant in said file.
Said prior arrangement has not proven successful in the past because dirt and dust would accumulate on the switch contacts and insulate them. The switch would then become inoperative.
It was known for a number of years before the present invention that a single-pole, double-throw switch could be enclosed in a glass envelope to prevent foreign material from insulating the contacts. This is disclosed in U.S. Pat. No. 2,121,607. However, when a switch is so enclosed, it is impossible to adjust the contact pressure because once the switch is sealed inside the envelope, the switch arms cannot be bent to shape. That is, since the envelope is sealed, there is no practical way in which to get inside and bend a switch arm. As will be explained, in accordance with the present invention, it has been found that a certain contact pressure is extremely critical.
It is also an outstanding disadvantage of prior art switches that the switch points, i.e., contacts, "bounce" due to the bulk modulus of elasticity of the contacts and due to the resilience of whatever structures support them. When bounce occurs and/or is repetitive at high currents, contact pitting, spiking, and welding of two bouncing contacts occurs. This , then, causes switch deterioration and/or inoperativeness. The useful life of such a switch is also thereby shortened. Note will be taken that high currents may occur when switch contacts are opened while being connected to a large inductive load, although high currents may be otherwise produced.
SUMMARY OF THE INVENTION
In accordance with the device of the present invention, the above-described and other disadvantages of the prior art are overcome by providing an envelope for a switch having a pole to carry a magnetic armature and a fixed magnet and a movable magnet outside the envelope.
Thus, the fixed magnet may be adjusted in position to adjust contact pressure. Therefore, this overcomes the prior art problem where it was impossible to adjust contact pressure.
In accordance with the present invention, it has been found only through a great deal of effort that the quiescent pressure which is established between the switch pole and the contact spaced farthest way from the movable magnet is extremely critical. The pressure must fall within a narrow range to insure good electrical conductivity and a small differential when a bimetal carries the movable magnet. From the instant that the contact next to the fixed magnet opens the differential is the temperature change required to the instant the same contact closes. The use of the fixed magnet makes it possible to adjust contact pressure within the said narrow range because, although it is fixed, it can be adjusted to its correct, fixed position before use.
It is also an outstanding advantage of the present invention that a flexible leaf spring pole stop is employed to prevent contact bounce. The rubbing action of the contacts and the flexure losses act as a dashpot to absorb the kinetic energy of the moving pole over a greater length of time because the spring is relatively weak and allows energy exchange over a long period before any bounce can occur. That is, the kinetic energy absorption can take place as the leaf spring stop and pole rock back and forth without the contacts separating. Thus the stop and pole contacts may rub together instead of separating as the two leaf springs rock.
The above-described and other advantages of the invention will be better understood from the following description when considered in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, which are to be regarded as merely illustrative:
FIG. 1 is a perspective, diagrammatic, elevational view of the invention in one of its connective conditions;
FIG. 2 is a view similar to that of FIG. 1 with the switch shown in another connective condition;
FIG. 3 is an enlarged, sectional view of that portion of the invention included within the glass enclosure;
FIG. 4 is a sectional view taken along the line4-4 shown in FIG. 3;
FIG. 5 is a diagrammatic view of special magnetic actuating means;
FIGS. 6 and 7 depict a further embodiment of the invention;
FIG. 8 is a side elevational view of still another embodiment of the invention; and
FIG. 9 is a top plan view of a bracket shown in FIG. 8.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, a switch 10 of the present invention includes a spiral, heat responsive bimetal 11, a first magnet means 12 carried by member 11, an enclosed set of switch points 13, and a second magnet means 14 all mounted in a casing 15.
The enclosed set of switch points 13 includes first and second conducting blades 16 and 17 of a nonmagnetic, springlike material, which are provided adjacent an end thereof with respective contact points 18 and 19. The blades are mounted within a sealed glass envelope 20 so that the contact points are in a facing, directly opposed relation to one another. A somewhat longer armature blade 21 of flexible, springlike conductive material when assembled is disposed between blades 16 and 17 but insulated therefrom. A contact point 22 is provided on the armature and has opposite facing surfaces such that lateral movement of the armature produces contact with either of contact points 18 or 19, as the case may be. The end of the armature extending beyond the ends of blades 16 and 17 is provided with a body of magnetic material 23. Blades 16 and 17 and armature blade 21 are included within an hermetically sealed, elongated, tubular glass envelope 20 containing a nonreactive gas such as a hydrogen-nitrogen mixture, for example. External electrical connection to the switch points and armature is provided via leads 25, 26, and 27 extending from one end of the envelope. The armature and contact blades are so constructed that in the unactuated position, i.e., neither magnet in influential position, the armature will lie between the two blades; and contact point 22 will be free from contact with either of points 18 or 19.
A second magnet means 14 is mounted from casing 15 to have an extended surface in contact with the glass envelope and lies directly opposite the flat side of magnetic body 23 of the armature. The magnetic field set up by magnet 14 attracts the armature a sufficient amount to close the circuit between contact point 22 on the armature and point 19 on blade 17. The flexible, springlike quality of both blade 17 and the armature are chosen to provide a firm contacting relation and achieve "overtravel" of the armature about which further details will be given later.
The contact pressure in this biased direction may be easily adjusted by moving the fixed magnet relative to the envelope or vice versa.
As the environmental temperature increases, the bimetal spiral uncoils to move first magnet means 12 toward the glass envelope at the opposite side from that at which magnet 14 is disposed. Due to the greater polar strength of magnet means 12, there is a point (indicated by the dashed line) at which the mutual attraction between the first magnet means and the armature is sufficient to overcome the springlike forces within bimetal spiral 11 so that the magnet means is snapped against the glass envelope. At this same time, armature blade 21 is influenced sufficiently to overcome its attraction for magnet 14 and causing it to transfer, establishing contact between points 18 and 22. The device described to the point now resides in the condition shown in FIG. 2. It is emphasized that the release of the first connective condition and the production of the second connective condition is a rapid one in which the transfer from one to the other is rapid and sure.
With a subsequent reduction in environment temperature, spiral bimetal member 11 begins to coil producing a potential force therein which acts against the attractive influence of magnet means 12 for the armature blade 21. This coiling continues until a point is reached at which the restoring force of the bimetal spiral is great enough to overcome the magnetic attractive force, and the first magnet means is moved away from glass envelope 20 and beyond the critical limit of magnetic influence. Of course, with removal of the influence of magnet means 12, second magnet means 14 now acts solely on the armature blade and causes rapid transfer of the contacting condition to that shown in FIG. 1. Although the foregoing description is sufficient for general constructive aspects of the invention, certain, more detailed features of the invention will be explained at this time, a knowledge of which is necessary for a clear understanding of how the present invention can handle relatively large loads and yet only use low contact forces with correspondingly low actuation force requirements on the bimetal member.
With particular reference to FIG. 3, it is seen that the body of magnetic material 23 is unsymmetrically arranged at the end of armature blade 21. That is, a relatively longer portion 28 of magnetic material is on the side of the blade facing first magnet means 12 than the corresponding portion 29 facing second magnet means 14. This unsymmetrical character of magnetic body 23 has a remarkable and beneficial effect upon operation. In explanation and beginning with the device disposed as in FIG. 1, when magnet means 12 moves toward glass envelope 20, the mutual attractive influence between means 12 and magnetic portion 28 increases to the point where blade 21 begins to flex outwardly of point 22 toward means 12 while still maintaining electrical contact between points 22 and 19. As means 12 moves still further, the critical point is passed at which body 23 moves sufficiently to open contact points 22 and 19. Now, blade 21 begins to flex below point 22 and continues flexing until the points 22 and 18 are closed. However, in this latter connective state, blade 21 beyond point 22 does not flex as much as it did when in the other closed state due to the additional length of portion 28. Or, viewed from a different standpoint, the spacing of magnet means 12 and body 23 is less when points 18 and 22 are closed than is the spacing of the body and means 14 when contacts 22 and 19 are closed.
This differential spacing is reflected in requiring less bimetal force to move means 12 away from envelope 20 than would be the case if the blade had "overtraveled" as much as in the other connective aspect. It is also to be noted that the extra overtravel of body 23 on closing points 22 and 19 does not, by the same token, require additional force from the bimetal. This result is at variance with what had been previously considered the rule--namely, that higher contact pressures for accommodating higher electrical loads could only be achieved by increased bimetal work input. Whereas, in the present invention, the contact pressures have been able to be kept higher by controlling overtravel; and yet at the same time armature movement is held to a minimum, insuring that the bimetal work input is optimally small.
In FIGS. 3 and 4, there is shown the detailed aspects of contact blades 16 and 17 and armature blade 21 as they are assembled within the enclosure. Blades 16 and 17 are bent at their approximate midpoint so that when oriented with points 18 and 19 facing, the space between the blade portions is greater at this end than at the mounting end. Insulation sheets 30 and 31 are situated between blades 16, 21 and 17, 21, respectively. An alignment opening 32 is formed in each of the blades and the insulation sheets for receiving an insulating and alignment plug 33. As best shown in FIG. 4, insulating sheet 31 is protectively wrapped around the long edges of the blades to permit edge portions of blade 17 to engage securingly the edges of the assembly, making an integral structure.
Proper relative flexibility of blades 16, 17, and 21 is important to overall operation. If the blades are too rigid, the contacts will tend to bounce and produce welding. On the other hand, if the blades are too soft, sensitivity of transfer is adversely affected. It has been found, for example, that when the blades are constructed of the same material and of the same width, blades 16 and 17 should have a thickness that is at least twice that of the armature blade 21, but not exceed three times the armature thickness for best results. In actual constructions of phosphor-bronze, with the armature blade having a thickness of 0.004 inches, blades 16 and 17 of the same material were too flexible at 0.007 inches and too rigid at 0.015 inches in thickness.
FIG. 5 depicts a special magnet particularly advantageous for use as magnet means 12. The magnet includes a front magnetic layer 34 of polar arrangement as shown and a back magnetic layer 35 of polar arrangement opposite to that of 34. The back layer 35 is secured and in flush contacting relation to a plate 36 of magnetically influenceable material. Plate 36 is one plate of bimetal member 11. It has been found that the attractive force of the magnet means 12 is enhanced to a considerable degree by this structural arrangement.
Accordingly, there is provided in the practice of the invention a heat responsive magnetically actuable switch requiring a relatively small mass of bimetal to act as the prime mover and yet sufficient force is provided through magnetic means to exert sufficient pressure on the switch points so that substantial currents can be accommodated. As a result of the "latching" action achieved by the magnet means and the "overtravel" of the armature blade, undesirable contact bounce has been eliminated. Also, of equal importance is the fact that opening of the contact points is performed rapidly thereby eliminating the arcing erosion of points that results form incremental opening as in certain prior art devices.
An alternative form of the invention is depicted in FIGS. 6 and 7 in which a pair of magnet means are swung as a unit to produce switching action. The basic switch assembly comprising blades 16 and 17 and armature blade 21, enclosed within envelope 20, is identical to that already described; and for that same reason, the same reference numerals are used.
A magnet means 37 is secured to one extremity of bimetal 11 to face the envelope. A U-shaped support bracket 39 has the end of one leg secured to the bimetal on the side opposite where magnet means 37 is mounted and thereby disposing the other leg on the other side of envelope 20. Bracket 39 could be eliminated with its function being carried out by an extension of the bimetal. At the extremity of the other leg of member 39, there is secured a further magnet means 38 generally facing the envelope. The magnet means are so mounted and bracket 39 so dimensioned that when located at the extreme right position as in FIG. 6, magnet means 37 contacts the outer surface of the envelope; and magnet means 38 is disposed beyond its range of magnetic effectivity. Further, when the bracket is transferred to its extreme left position, magnet means 38 contacts the envelope; and magnet means 37 is spaced therefrom.
With magnet means 38 at its closest range as in FIG. 6, the armature is attracted thereto closing contacts points 19 and 22. As the temperature rises and bimetal 11 uncoils moving magnet means 37 toward the envelope and magnet means 38 away therefrom, a critical point is reached at which means 37 is snapped forward against the envelope. When this happens, contact points 19 and 22 are rapidly opened and points 18 and 22 are closed. At this time, the switch resides as is shown in FIG. 7.
A further possible modification would be to make body 23 symmetrical with both halves or parts of equal extent. This would result in a certain loss in sensitivity and perhaps an increase in bimetal volume. However, there would be a manufacturing advantage here since the armature, being of symmetrical construction, would be easier to fabricate.
Note will be taken that in FIGS. 6 and 7, it may be desirable to make the relative positions of magnets 37 and 38 adjustable. However, during operation, the magnets 37 and 38 would not change position relative to each other. Thus, as used herein and in the claims, the phrases "magnets...fixed in position relative to each other" and "magnets...fixed to said support" are hereby defined to include both, (1) magnets, the position of which cannot be adjusted relative to each other, and (2) magnets, the position of which can be adjusted relative to each other.
In FIG. 8, a somewhat different version of the embodiment of FIGS. 6 and 7 is shown. A rigid bar 39' is fixed to a bimetal strip 11'. Brackets B1 and B2 are fixed to bar 39'. Brackets B1 and B2 have slotted horizontal portions P1 and P2. Screws S1 and S2 are threaded into permanent magnets 37' and 38'. A slot L1 in bracket portion P1 is shown in FIG. 9. Note that screw S1 has a head H1 which is larger than the width of slot L1. Screws S1 and S2 may, thus, be tightened to hold magnets 37' and 38' rigid with brackets B1 and B2, respectively. When screws S1 and S2 are loosened, they may be moved longitudinally in the bracket slots and retightened. The positions of magnets 37' and 38', thus, are adjustable and movable relative to bar 39' for calibration, although they are both fixed relative to bar 39' during operation.
Note will be taken from FIGS. 2, 6, and 7 that when blade 21 moves from one extreme limit of its travel to the other, the center of contact 22 moves only about three times as far as the maximum deflection of blade 16 measured at the center of contact 18. Further, the maximum deflection of blade 17 measured at the center of contact 19 is about equal to the said maximum of blade 16. Thus, blades 16 and 17 have such flexibility that they themselves have a travel which is about equal to one-third that of blade 21.
From the foregoing, it will be appreciated that the fixed magnet 14 may, in calibration, be moved to adjust the pressure of contacts 19 and 22 to within an extremely small critical range for good electrical conductivity and small operating force.
Still further, the fact that blades 16 and 17 act as weak springs (see the large deflection of blade 16 in FIGS. 2 and 7, and the large deflection of blade 17 in FIG. 6) makes it possible to reduce bounce of contact 22 on contacts 18 and 19 to an extraordinary degree.