US3418608A

US3418608A - Magnetically actuated miniature relay

Info

Publication number: US3418608A
Application number: US624497A
Authority: US
Inventors: Henry R Angel; Morgan A Henry
Original assignee: Electronic Controls Inc
Current assignee: Electronic Controls Inc
Priority date: 1966-03-20
Filing date: 1967-03-20
Publication date: 1968-12-24
Anticipated expiration: 1985-12-24
Also published as: FR1559362A; DE1639232B1; GB1220999A

Description

Dec. 24, 1968 H. R. ANGEL ET AL 3,418,608

MAGNETICALLY ACTUATED MINIATURE RELAY Filed March 20, 1967 FIG. I.-

3 Sheets-Sheet l INVENTORS: HENRY R. ANGEL A. HENRY MORGAN BY W4? ATTYS.

Dec. 24, 1968 H. R. ANGEL. ET AL MAGNETICALLY ACTUATED MINIATURE RELAY 3 Sheets-Sheet 2 Filed March 20, 1967 INVENTORS HENRY R. ANGEL A. HENRY MORGAN ATTYS.

H. R. ANGEL ET AL 3,418,668

I MAGNETICALLY ACTUATED MINIATURE RELAY Filed March 20. 1967 """HIHHMWH 3 Sheets-Sheet 5 /Z64 //a F I613 w HENRY R. ANGEL A.HENRY MORGAN ATTYS INVENTORSI Uited States Patent M 3,418,608 MAGNETICALLY ACTUATED MINIATURE RELAY Henry R. Angel, Trumbull, and A. Henry Morgan, Norwalk, ComL, assignors to Electronic (Iontrols, Inc., Wilton, Conn., a corporation of Maryland Filed Mar. 20, 1967, Ser. No. 624,497 19 Claims. (Cl. 335131) ABSTRACT OF THE DISCLOSURE This invention relates to switches and relays and more particularly relates to an improved multi-contact switch of the type of US. Patent 3,226,508 in a special improved relay configuration.

The present invention provides a quick acting relay having multiple switch elements in a small package capable of inclusion on a printed circuit board in electronics equipment wherein space requirements are quite limited. Each switch is capable of carrying relatively high amounts of power through its respective contacts for an extended period of time. The switches, and the relay as a whole, are capable of long life and operation over more than 100,000,000 cycles of operation.

In the prior art the reed relay has been a preferred means of rapid response switching. However, reed relays suffer from the fact that their contacts are normally of the same material as a reed, which is designed for its reed action and not contact properties and the contact areas are also, of necessity, relatively small. Since factors which make for good positive switch contact connections are missing from reed relays, such relays become less and less satisfactory as power and current requirements rise. On the other hand, conventional switches having contacts and other characteristics making them useful in high power and/or current applications are usually slow in response and/or too bulky for inclusion in electronics equipment employing printed circuit boards.

The present invention provides a structure in which heavy duty switch contacts and structure providing for positive switch contact may be employed together with conductors and terminals capable of carrying relatively high levels of power and current. The present invention preferably employs a switch actuator bar enabling control of a compact array of movable contact supporting elements and the advantageous geometry and multiple pole switch configuration described in US. Patent 3,226,508. The actuator bar heretofore has been actuated by means generally orthogonally arranged to the general plane of the bar and movable switch blades. The present invention reduces the actuator to a relatively small, compact volume and provides magnetic circuitry arranged side-by-side, which makes is possible to put the actuator even in the same general plane with the switches and actuator. The switches are preferably double throw and in any event have two stable positions. In one position the magnetic circuit is de-energized and mechanical spring means holds the movable contacts in one position, preferably against one set of fixed contacts. In the other position the magnetic circuit is energized and effectively 3,418,608 Patented Dec. 24, 1968 opposes the spring means and moves the movable contacts to their other position, preferably against a second set of fixed contacts, The arrangement permits the switch housing or wafer to be completely enclosed if desirable, for example, in explosion-proof units.

More specifically, the relay of the present invention comprises switch contacts, including at least one movable contact and associated current carrying support elements supported on a support structure. Actuator means is provided for moving the at least one movable contact to change the switch condition. The actuator means includes a magnetic element movable with and capable of moving the rest of the actuator means. Reciprocating movement of the actuator means moves the switch from one position to the other. At least one air gap is included between the bar and the rest of the magnetic circuit. The size of the air gap is changed by movement of the actuator means as the result of the eifect of the flux on the magnetic element of the actuator means. The means for generating magnetic flux in the magnetic circuit is arranged side-by-side in a generally parallel arrangement with the support structure and in different embodiments may be along side of or above the support structure. In preferred embodiments the support structure may be a closed housing containing the actuator means.

For a better understanding of the present invention, reference is made to drawings of which:

FIG. 1 is an enlarged plan view from above of a preferred embodiment of relay in accordance with the present invention with the top cover removed showing certain areas of the structure broken away and in section;

FIG. 2 is a side elevational view of the same structure with its side-wall partially removed;

FIG. 3 is an end view of the structure of FIGS. 1 and 2 on the same scale;

FIG. 4 is a further enlarged sectional view taken along lines 44 of FIG. 1;

FIG. 5 is a view on the same general scale as FIG. 4 taken along lines 5-5 of FIG. 2;

FIG. 6 is a perspective view of the magnetic circuit and associated parts removed from the rest of the structure of FIGS. 1-5;

FIG. 7 is a schematic showing similar to FIG. 2 but more highly enlarged of a modified version of the magnetic structure in accordance with the present invention;

FIG. 8 is a side elevation view partially in section, showing an enlarged, modified structure similar to that of FIGS. l6;

FIG. 9 is a sectional view taken along line 99 of FIG. 8;

FIG. 10 is an enlarged plan view from above similar to FIG. 1 showing a relay in accordance with the present invention having a modified type of magnetic actuator;

FIG. 11 is a side elevational view of the structure of FIG. 10;

FIG. 12 is an end view of the structure ofFIGS. 10 and 11;

FIG. 13 is a further enlarged sectional view taken along line 13-13 of FIG. 10; and

FIG. 14 is a sectional view taken along line 1414 of FIG. 13.

All embodiments shown in the drawings employ a pair of double pole switches on each side of an actuator means thereby providing a four pole double throw relay. This configuration is meant to be by way of example rather than limitation and any number of poles of single or double throw switches may be substituted. The arrays illustrated are somewhat narrower than the switch structures shown and described in US. Patent 3,226,508 but of the same general type and construction. In the embodiment of FIGS. 1-6, as in all illustrated embodiments,

there is employed a long narrow housing, generally designated 11, preferably camposed of rigid resinous material which may assume one of the structural forms discussed in connection with US. Patent 3,226,508 but may also depart from those structures and even consist merely of a suitable contact support frame. More specifically, the housing preferably consists, as is most easily seen in FIG. 4 of an integrally molded bottom and inside side wall structure 12, top wall pieces 14 and end walls 16. Side wall 13 is preferably composed of transparent rigid resinous material and is held to wall structure 12 by cooperation with grooves 15 which are provided in columns 12a at the opposite end of the housing parallel to the inside side wall and at the edge of the bottom Wall of housing wall structure 12. Other side wall enclosures may be used. The top wall pieces 14 are separated by a gap in the center of the housing above a rigid actuator bar 10, of the type described above.

End walls 16 advantageously may be composed of laminar pieces of the same resinous material as housing 12. Supported by each end wall are a pair of essentially parallel, resilient conductive contact support blades 18. Within the end walls these blades overlap and are held in good electrical contact with terminals 180. In other embodiments blades and terminals may be made intergal structures. These support blades are characteristically side-by-side within, through and, in their terminal extensions, outside of the housing end walls. All of the support blades extend through the housing wall and into the housing in essentially co-planar relationship with one another and their support by the housing is such that they remain insulated from one another. The rivets 20 hold together the end walls, including all contact support blades and their associated terminals, and connect the end walls to the top walls 14 and housing wall structure 12. The pieces of the end walls are'contrived to insulate the rivets 20 from the blades 18 and terminals 18a and the blades and terminals from one another. The two pair of resilient support blades extend into the housing from the opposite end walls toward one another and terminate short of the center. The unsupported ends of the blades 18 are received in notches which constitute blade retaining slots in the rigid insulator actuator bar 10, which is arranged within the housing transverse to the blades. Movement of an actuator bar in a direction tending to move it out of the plane of the blades, i.e., perpendicular to the plane of blades 18 tends to deflect the blades 18 and the movable contacts carried thereon. A prebent deflection of the blades 18 causes them to serve as flat springs thereby acting to contain themselves within the open topped notches of actuator bar 10. The same spring action urges the actuator bar into stop 12b on the bottom wall. Each blade 18 has a pair of contacts located directly opposite one another near that end engaged by the actuator bar 10. Each lower contact 22 is caused by the actuator bar in its lower position to bear against and displace fixed contact 24 supported on a blade 26 which is similar to blade 18. The blades 26 extend through the end walls parallel to blades 18 and are similarly extended outside of the end walls by terminals 26a. The upper contact on each movable support blade 18 is contact 28 which is caused by the actuator bar in its upper position to bear against and displace an opposed fixed contact 30 on flexible support blade 32. Support blades 32 for contacts 30 are similar to support

blades

18 and 26 and parallel to those blades and extended through housing end wall by terminals 32a. All of the blades 32 are in the same plane, parallel to the plane in which all of the blades 18 and all of the blades 26 are respectively located.

As seen in the drawings, the de-energized position for the relays is with contacts 22 closed against contacts 24 and

contacts

28 and 30 open. Urging the actuator bar 10 into the position shown in FIGS. 2 and 4 are the prebent spring blades 18, but which in other embodiments may be any other suitable type of spring means. Spring blades 18 urge the bar 10 downwardly against a stop 12b formed integrally with housing 12 which prevents further motion of the actuator bar toward the bottom of housing wall structure 12. In this position of the actuator bar, each of the blades 18 is deflected, as shown, so that its contact 22 does not merely touch contact 24 but actually slightly displaces the contact due to the resilience .of its support blade 26.

Contacts

22 and 24 are opened by upward movement of the actuator bar 10 and when this occurs the backstop bar 2612 restrains each blade 26 from further upward movement and prevents contact 24 from following contact 22 indefinitely. A similar backstop bar 32b restrains blades 32 and contacts 30 from following contact 28 as those contacts open in the other switch position. Clearances are designed so that as the actuator bar 10 moves upwardly it will ultimately be stopped by the

magnetic frame pieces

42 and 44. In that position contact 22 will be completely separated from contact 24 and contact 28 will be moved against contact 30 sufliciently positively to displace it slightly against the resilience of its support blade 32 in order to assure positive switch contact. A non-magnetic shim 36a secured to magnetic member 36 ailixed to actuator bar 10 causes a slight magnetic gap to exist between

frame pieces

42 and 44 and magnetic member 36, even when member 36 is attracted to

pieces

42 and 44. This gap facilitates return of the actuator bar to its normal position when power is discon nected from winding 48 even if some residual magnetism remains in the magnetic circuit because of the hysteresis properties of the magnetic materials.

Most of the structure thus far described is essentially like that shown and described in U.S. Patent 3,226,508 with the notable exception of differences in the actuator bar 10, spring blades 18 and

frame pieces

42 and 44. It is significant that the actuator bar is mechanically integral with magnetic element 36. Element 36, is a strip which provides a part of a magnetic circuit used in moving the actuator bar against the action of the spring blades 18. Cover 35 serves to enclose the contact assembly against contaminants such as dust. Other means of enclosing the contact assembly may be used, as for example, to allow for hermetically sealing for severe environmental applications (see for example FIGS. 4 and 5 As can best be seen in FIG. 6 the magnetic circuit is an array of magnetic material arranged side-by-side with switch housing 11 along the inner side wall of housing structure 12 and having a portion extending over the switch housing 12 at least in the area of the actuator bar 10. As a practical matter the magnetic circuit consists of two similar but symmetrically

opposite pieces

42 and 44 of formed sheet soft iron, or other suitable magnetic material, which are separated by a gap. A core 46 for a winding 48, best seen in FIGS. 5 and 6, complete the magnetic circuit or loop except for the gap at the member 36. However, instead of passing directly through the gap between

frame members

42 and 44 in the magnetic circuit, the flux has a lower reluctance path through magnetic element 36 affixed to the actuator bar and separated from the

magnetic members

42 and 44 by air gaps which are cumulatively smaller than the gap between the edges of

members

42 and 44. The winding is provided with a pair of terminals 50 through which current may be applied to energize the winding and developed the magnetic flux needed for the magnetic circuit. Upon this occurrence the magnetic strip 36, acting like an armature, is drawn to- ,

ward plates

42 and 44, against the urging of the spring stop provided by

frame pieces

42 and 44 and shim 36a. When the winding is de-energized spring blades 18 urge the actuator bar 10, blade 18 and their supported contacts quickly from the pole of contacts 30 back to the pole of contacts 24. The magnetic circuit is held to the switch housing preferably by the same rivets 20 which place the magnetic structure in proper position relative to the switch housing. For this reason

magnetic members

42 and 44 lie over the top of the switch housing in each direction from the gap to the ends. These members become progressively wider as the distance from the gap increases and, some place before the ends, achieve their full width which is determined by the cumulative width of housing and winding. From above the shape of

pieces

42 and 44 leaves a generally trapezoidal open area above the winding.

Sidewalls of the switch housing may provide sufiicient structure to retain the actuator bar 10, but where these sidewalls are omitted some other expedient is necessary. This is accomplished by providing notches in actuator bar in which prebent spring blades 18 are seated. Barrier sections formed into actuator bar 10 prevent motion of actuator bar 10 transverse to the long axis of blades 18 and by this means avoid any contact between the actuator bar 10 and the side walls of the contact assembly.

FIG. 7 shows an alternative arrangement for a magnetic circuit wherein corresponding parts are given corresponding numbers with the addition of primes thereto. As can be seen in FIG. 7, frame piece 44' is abbreviated while frame piece 42' is extended to the same general position as the embodiment of FIGS. 1-6. However, in this case a spring member of magnetic material 58 is employed to provide a complete continuous magnetic circuit at all times between the member 44 and the magnetic element 36' on the actuator bar. As a consequence only one small gap is necessary instead of the two employed in the embodiment of FIGS. 1-6. Obviously, the bar itself need not be the spring and an additional auxiliary spring member could be employed.

Referring to FIGURES 8 and 9 a structure similar to the structure of FIGS. 1-6 is shown and corresponding parts are given corres-ponding numbers with the addition thereto of double primes. In this case, however, the housing is completely enclosed in order to maintain the contacts in a completely dustfree environment, or even to provide an explosion-free enclosure. For example, the housing may be wrapped and essentially enclosed in a non-magnetic wrapper 60 of brass, Mylar, or other suitable material. As shown in FIG. 9, wrapper 60 preferably extends completely around the housing in the direction of width and thickness and may be made to overlap itself for sealing using suitable adhesives. The ends of this wrapping are preferably allowed to extend beyond the ends of the housing and the bounding walls formed thereby and ends of the housing are filled with suitable resinous material 62, such as an epoxy resin. If it is desired to have a completely explosion-proof structure this can be accomplished by providing flush temporary means for holding the end walls and bottom and top walls of the housing together until it is wrapped, then replacing these with rivets punching holes in the wrapper for the purpose or passing through holes which are previously intentionally left in the wrapper for that purpose. Then, before the

magnetic members

42 and 44 are put in place, suitable resinous material may be used to seal the wrapper and housing top wall to the rivet 20". In fact, the magnetic pieces may be put in place and riveted together before the resinous material has set, thereby causing them to become part of an integral structure. Finally, suitable resinous material is used to fill in the hole in the wrapper below the bottom end of the rivet 20" in the area designated 64. For added protection, it is possible to pot or suitably coat the whole structure by dipping or other known process, which might, for example, provide a .75

coating of waterproofing, as well as sealing the housing, by use of a coating material like latex.

Many other techniques for suitably sealing the housing will occur to those skilled in the art and the technique shown and described is intended to be only by way of example, and not by way of limitation.

Reference is now made to FIGS. 10-14. These figures have been included primarily to show a modified magnetic actuator structure. They also show a modified type of terminal which is particularly useful in this and the other embodiments shown for attachment of the structure to printed circuit boards.

In the embodiment of FIGS. 10-14 the internal structure of the relay, including the switch housing, contact supports, contacts, actuator bar and magnetic strip, is similar to that shown in the FIGS. l-6 embodiment and corresponding parts are numbered the same with addition of to the number designator so that the same designator has a 1 applied in the 100s digit place before the number. As can be seen in these figures, instead of arranging the winding 148 at one side of the housing 111 it is placed above the housing as best seen in FIGS. 11 and 13, and 12 and 14. In this arrangement the

magnetic members

142 and 144 are essentially uniform in width throughout their length. The length of each magnetic member extends between the point of closest approach to the other magnetic member at the gap above the actuator bar (and its associated magnetic strip 13). Each magnetic member extends along the top of -the housing to and just beyond the end of the housing at which point it is bent upward away from the housing at approximately a right-angle. The core 146 is fixed to extend between these upward extending portions of the

magnetic members

142 and 144 and the winding is wound on this core. The magnetic structure outside the housing is held in place exactly as it is in the previously described embodiment by the rivets 120, which also tend to hold together the housing structure at its ends.

Operation of the FIGS. 10-14 structure is essentially the same as the FIGS. 1-6 structure with magnetic strip 136 on actuator 110 completing the magnetic circuit through a pair of air gaps to

magnetic members

142 and 144. The structure in its de-energize d condition is shown in FIG. 13 wherein contacts 122 are brought to bear against contacts 124 due to the inherent resiliency of contact support arms 118, which also urge actuator 110 downward into the position shown. Upon energization of the coil 148, magnetic strip 136 is attracted by

magnetic members

142 and 144 to reduce the air gap between the strip and these members and in opposition to the effect of spring arms 118. As long as the coil 148 is energized the switch contacts 128 will remain closed against contacts 130. When the coil is de-energized, however, the spring arm 118 will urge the relay back into the condition in which contacts 122 are closed against contacts 124 and

contacts

128 and 130 are open.

FIGURES 11 and 13, in particular, also show a modified type of terminal structure which is preferred. As can be seen in FIGURES l1 and 13, these terminals 118a, 126a, and 132a are all bent at right angles. Terminal 132a extends out further from the end of the housing to its bend and thereafter extends a distance well below the bottom of the housing. Terminal 118a extends a distance from the housing somewhat less than terminal 1320, but somewhat more than terminal 126a, before bending downwardly. Downward portions of all terminals terminate at approximately the same level.

The terminals 118a, 126a, and 132a are all bent and made to extend below the bottom of the housing so that they can be inserted through preformed holes in a printed circuit board and soldered into its circuitry. In a similar manner the terminals from the winding 148 are made to extend downwardly from the winding past the back side of the housing and beyond bottom of the housing, so that they may be similarly soldered into a printed circuit board. In other embodiment the coil terminals 150 may be shorter and connected to conventional leads rather than to a printed circuit board. Various other possibilities for connections will, of course, occur to those skilled in the art. It will be clear that the structure of FIGS. 16 may have its terminals modified in this manner as well.

The terminals 150 in this particular embodiment are shown brought out through non-conductive end blocks 160, which are formed to provide a tortuous course for the terminal in order to prevent the terminal from being readily pulled loose from the end of the winding to which it is soldered or, otherwise appropriately secured.

In each of the embodiments illustrated four circuits can be switched at one time, as opposed to the usual single switch of a reed relay. In each the contacts make positive contact because of use of good contact material so that poweron the order of 150 watts in each circuit is practical. Current in reed relays is normally limited to something on the order of A ampere whereas current in the switch of the present invention depending upon the design of the switch may be many amperes. A breakdown voltage of 1500 volts RMS is easily within the capability of this invention and enables high voltage applications of the invention to be employed. Overall power capabilities exceed 150 watts at each switch pole. At the same time the switch size is extremely small and has been made with overall dimensions exclusive of terminals of .820 inch width, .340 inch height and 1.750 inch length. The switches are capable of 100 million to 1 billion cycles of life, or even higher.

Certain modifications have been suggested and described. Other modifications and variations will occur to those skilled in the art. All such modifications and variations within the scope of the claims are intended to be within the scope and spirit of the present invention.

We claim:

1. A magnetically actuated relay comprising:

a support structure,

switch contacts, including at least one movable contact and associated current carrying support elements supported on the support structure,

actuator means movable relative to the support for moving the at least one movable contact to change the switch condition and including a magnetic element movable with the actuator means and whose movement moves the actuator means, an energizing Winding, and

a magnetic circuit including the magnetic element of the actuator means and an essentially closed loop of magnetic material with one or more small air gaps of a size on the order of the movement of the at least one movable contact between the magnetic element of the actuator means and the essentially closed magnetic circuit, the size of the at least one air gap being changed by movement of the actuator means and its magnetic element, said essentially closed loop of magentic material being arranged so that part of the magnetic material provides a core for said energizing winding, at least part of which winding lies between planes normal to the contact movement and defined by the upper and lower limits of switch contact positions.

2. The magnetically actuated relay of claim 1 in which the switch structure and the actuator means are enclosed within a housing which provides the support structure.

3. The magnetically actuated relay of claim 2 in which the housing is entirely closed and sealed.

4. The magnetically actuated relay of claim 3 in which the magnetic parts of the magnetic circuit except for the magnetic element movable with the actuator means are outside the sealed housing.

5. The magnetically actuated relay of claim 1 in which a plurality of switches are employed in generally parallel side-by-side relationship and enclosed within a housing.

6. The magnetically actuated relay of claim 5 in which the means for generating magnetic flux is a winding on a core forming a part of the magnetic circuit generally parallel to the length of the housing and arranged side-by-side therewith.

7. The magnetically actuated relay of claim 6 in which the winding is generally in the plane of the switches.

8. The magnetically actuated relay of claim 7 in which the winding is generally parallel to the plane of the switches.

9. The magnetically actuated relay of claim 5 in which flexible switch contact support-ing elements are supported at one end by the housing and at the other end are engaged by the actuator means all enclosed within the housing.

10. In combination with a switch comprising a housing:

a plurality of essentially parallel resilient, switch contact support blades side-by-side within and supported by the housing and extending through the wall and into the housing in essentially co-planar relationship at one end of the housing so that they are electrically insulated from one another,

a rigid actuator bar within the housing transverse to the blades within the general plane of the blades and having slot means receiving the other unsupported ends of the blades and movable out of the common plane of the blades to deflect the movable contacts, and

a plurality of fixed contacts opposed to individual contacts on the blades so that movement of the blades by the actuator will cause the movable contacts to move in unison between opened and closed position with their opposed fixed contacts,

said housing closely enclosing the switch contacts,

blades and actuator bar,

the improvement consisting of magnetic material made mechanically part of the bar to move with the bar,

an energizing winding, and

a magnetic circuit including the magnetic portion of the actuator bar and an essentially closed loop of magnetic material with one or more small air gaps of a size on the order of the movement of the at least one movable contact between the actuator bar and the closed loop of magnetic material, the size of which at least one air gap is changed by movement of the actuator bar, said essentially closed loop of magnetic material being arranged so that part of the magnetic material provides a core for said energizing winding, at least part of which winding lies between planes normal to the contact movement and defined by the upper and lower limits of switch contact positions.

11. The structure of claim 10 in which the means for generating magnetic flux is an electrical Winding and the magnetic circuit consists of a core of magnetic material in the magnetic circuit for the winding positioned sideby-side with the switch housing in the general plane of the switch blades and actuator bar such that the switch housing and necessary thickness of overlying parts of the magnetic circuit deter-mine the thickness of the switch.

12. The structure of claim 11 in which the core for the winding extends along one edge of the switch housing and is terminated at opposite ends in magnetic members which are brought around the ends of the winding and toward one another with the parts extending toward one another also extending at least in part above the switch housing and terminating above the actuator bar to provide the gap.

13. The structure of claim 12 in which the portions of the magnetic circuit above the switch housing are connected to the housing thereby connecting together the housing and the structure of the magnetic circuit.

14. The structure of claim 10 in which the means for generating magnetic flux is an electrical winding and the magnetic circuit consists of a core of magnetic material in the magnetic circuit for the winding positioned above the switch housing such that the number and width of switches arrayed side-by-side, their intermediate spacing, and housing sidewall thickness determine the width of the switch.

15. The structure of claim 14 in which the core for the winding extend over the top of the switch housing and is terminated at opposite ends in magnetic members which are brought around the ends of the Winding and toward one another immediately above the switch housing and between the housing and the winding and terminate above the actuator bar to provide the gap.

16. The structure of claim 15 in which the portions of the magnetic circuit immediately above the switch housing are connected to the housing thereby connecting together the housing and the structure of the magnetic circuit.

17. The structure of claim 10 in which at least one of the magnetic members of the magnetic circuit overlaps and is closely adjacent the actuator bar so that the gap between the magnetic member and the magnetic portion of the actuator bar -is essentially in the direction of movement of the actuator bar.

18. The structure of claim 17 in which both members of the magnetic circuit overlap edges of the magnetic 10 member afiixed to the actuator bar and provide two separate parallel air gaps between their edges and the magnetic portion of the actuator bar.

19. The structure of claim 18 in which one portion of the magnetic circuit is terminated along the length of the switch housing well before the actuator bar and is connected by magnetic material to the magnetic portion of the actuator bar so that but a single air gap exists between the magnetic material of the actuator bar and the magnetic circuit.

References Cited UNITED STATES PATENTS 1,665,640 4/1928 Randle 335187 2,036,295 4/1936 Piffath 335-188 2,514,947 7/1950 Gray 335188 2,916,585 12/1959 Moyer 335187 2,972,070 2/1961 Loverde 335-237 3,138,678 6/1964 Ra-ab 335203 3,158,712 11/1964 Fligue 335203 3,236,965 2/1966 Bianco 335-188 BERNARD A. GILHEANY, Primary Examiner. HAROLD BROOME, Assistant Examiner.

US. Cl. X.R.