Gravity switch and method of making same

This invention relates to improvements in a gravity operated electrical switch and to a method for its manufacture.

Sealed gravity actuated switches are known which comprise a conducting shell arranged coaxially within an insulating shell as illustrated, for example, in US-A-2,206,094; US-A--2,228,456 and US-A-4,042,796.

One object of the present invention is to provide an improved switch of the above type which is of simplified low cost design and construction, is light in weight, compact, highly reliable, and is capable of economical manufacture by automated mass production procedures.

Another object of the present invention is to provide such a switch in which the possibility of shorting to ground is minimized and the electrical contacts are effectively sealed from the atmosphere and corrosion.

A further object of the present invention is to provide such a switch having improved contact elements,

A still further object of the present invention is to provide an improved economical and automated method of manufacturing such a switch wherein dimensional tolerances between the external electrical contacts are closely maintained without recourse to precise and expensively maintained dimensions for the component parts.

In accordance with one aspect of the present invention there is provided a gravity switch for opening or closing an electrical circuit in accordance with the inclination of the axis of the switch from a horizontal position, characterized in that said switch comprises a cup-shaped dielectric member having axially extending side walls forming an enclosure, a base closing one axial end of said enclosure, and a mouth opening axially endwise at the opposite axial end of said enclosure; first contact means of electrical conducting material comprising an interior electrical contact within said enclosure adjacent to said base, an exterior electrical -^pontart externally of said enclosure, and means extending through said member and electrically connecting said interior and exterior contacts; second contact means of electrical conducting material spaced from the first contact means and fixed with respect to said enclosure, said second contact means having guide portions extending axially along said sidewalls in the direction from said base toward said mouth and effecting an interference fit with said sidewalls, said guide portions terminating in said direction and closing said mouth and defining a second exterior contact; and means for selectively completing an electrical connection between said guide portions and interior contact comprising gravity actuated contact means movable axially along said guide portions in electrical contact therewith to and from position of electrical contact with said interior contact in accordance with the inclination of said axis.

In accordance with another aspect of the present invention there is provided a method of manufacturing a gravity actuated switch which comprises a moulded first cup-shaped housing member of dielectric material having a base and cylindrical sidewalls, first contact means of electrical conducting material having interior and exterior contacts adjacent axially opposite sides of said base and a connecting portion extending axially through said base, a second cup-shaped housing member of electrical conducting material having a base and cylindrical sidewalls, first contact means of electrical conducting the sidewalls of said first and second housing members telescoping coaxially one within the other in fluid seating-engagement with the mouth of said second cup-shaped housing member contact opening toward said base of said member, and gravity actuated contact means freely movable axially within the cylindrical walls of said second cup-shaped housing member in electrical contact therewith for selectively making or breaking an electrical connection between the latter sidewalls and said interior contact in accordance with tilting of the axis of the coaxial sidewalls, in which method said first cup-shaped housing member is formed by injection moulding at elevated temperature and pressure with said first contact means moulded within said base as an insert, one of said cup-shaped housing members is arranged with its cylindrical axis vertical and its mouth opening upwardly, and while the plastic of said housing is still warm from the moulding operation, dropping said gravity-actuated contact means into the upwardly opening mouth of said one cup-shaped housing member and the cylindrical sidewalls of the other cup-shaped housing member are forced for a predetermined distance in coaxial telescoping relationship with the cylindrical sidewalls of said one cup-shaped housing member with the mouth of said other cup-shaped member confronting the base of said housing.

In accordance with a further aspect of the present invention there is provided a method of manufacturing a gravity actuated electrical switch, characterised by providing first contact means of electrical conducting material having axially spaced interior and exterior contacts connected by an axial connecting portion; providing a one-piece cup-shaped second contact means of electrical conducting material having cylindrical sidewalls of predetermined axial length defining an enclosure, an integral base closing one axial end of said enclosure, and a mouth opening axially at the opposite end of the enclosure; providing a gravity actuated contact member dimensioned to move freely axially within the enclosure defined by said second contact means and in electrical contact with the sidewalls of the latter; forming by injection moulding a one-piece cup-shaped means of dielectric material having axially extending cylindrical sidewalls defining a second enclosure, an integral second base closing one axial end of said second enclosure, a second mouth opening axially at the opposite end of said second enclosure, and having said first contact member moulded as an insert in said dielectric material with said interior and exterior contacts snugly engaging the interior and exterior of said second base respectively and with said connecting portion extending axially through said second base in fluid sealing engagement therewith; dimensioning the cylindrical sidewalls of said conducting and dielectric cup-shaped means for telescoping coaxially together at a fluid sealing interference fit, and while said dielectric material is still warm from the moulding operation, arranging one of said cup-shaped means in an upright position with its mouth opening upwardly, dropping said gravity actuated contact into the latter mouth, forcing said sidewalls of said cup-shaped means coaxially into said telescoping fluid sealing fit with the mouth of said second contact means confronting said second base, and terminating said forcing when said second contact means is spaced from said first contact means but sufficiently close thereto that, when said gravity actuated contact is in electrical contact with said interior contact, it is also in electrical contact with the sidewalls of said second contact means, said predetermined axial length of said second contact means being such that said gravity actuated contact is enabled to move axially within the enclosure of said second contact means to a position out of electrical contact with said interior contact.

In a preferred embodiment the gravity actuated contact means comprises a spherical contact member or metallic ball movable by gravity so that the operation of the switch is assured regardless of the rotational position of the housing axis.

Among the problems involved in the substitution of such a gravity switch for a mercury switch are ball sticking or a welding effect and high millivolt drop across the electrical contacts. Ball sticking orwelding of the ball to the contacts atthe "on" or a closed circuit position impairs gravity induced movement of the ball to the "off" or open circuit condition. Also a comparatively high voltage drop between the ball and the switch contacts at the closed circuit condition results in loss of electrical power, or luminous intensity when the switch is employed with an electric light.

The above problems are overcome by providing means for significantly increasing the contact pressure between the ball and the switch contact elements. Inasmuch as the overall switch dimensions are severely limited by the requirement of maintaining interchangeability with customarily employed mercury switches, the design of the ball switch is critical.

Advantageously there is provided an improved switch design which, without increasing the external dimensions of the switch enables use of a larger diameter ball contact element of correspondingly greater weight, which in turn has been found to reduce the voltage drop across the ball contacts materially when the switch is tilted to the "on" position. In consequence, a comparatively costly lead ball, which has been heretofore preferred in small switches because of its high specific gravity, can be replaced by a larger, heavier, and less costly brass ball which reduces voltage loss across the contacts and likewise the welding effect and enables efficient operation of the switch with larger current flow than heretofore. By suitably plating the ball element, as for example with zinc, tin, or cadmium, and by sonic cleaning of the contact elements immediately prior to their assembly, the welding effect and consequent ball sticking are further reduced and optimum electrical conductivity through the switch is achieved.

The prior art does not include the construction of a cup-shaped dielectric member and a cup-shaped conductor pressed together in axially telescoping relationship at an interference fit, whereby the two cup-shaped members are fixed with respect to each other to comprise an integrated dimensionally stable sealed housing for a contact element movable axially within the members and adapted for selectively making or breaking an electrical connection between the cup-shaped conductor and a second conductor extending axially through the base of the cup-shaped dielectric member, whereby the axially outer surfaces of the electrical contacts for the switch, comprising the base of the cup-shaped conductor and the second conductor, are available for making electrical contact with a pair of axially spaced contacts within a container for the switch.

It is an advantage that the overall axial dimension between the axially outer surfaces of the switch contacts may be readily preselected and maintained in production without recourse to closely maintained and costly axial tolerances in the fabrication of the cup-shaped members.

Advantageously the dielectric cup-shaped member has a cylindrical portion of reduced outer diameter with respect to its base and extending therefrom for a comparatively short axial extent to its open end, and wherein the conducting member is sleeved or telescoped over the reduced outer diameter portion in tightly fitting sealing engagement, thereby to reduce the costly dielectric plastic material to a minimum and achieve the maximum internal diameter for the conducting member without increasing the overall outer diameter of the switch.

The invention will now be described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:-

• Figure 1 is a side elevational view, partly broken away to show details of construction of a housing for an electric lamp and gravity operated switch embodying the present invention.
• Figure 2 is a sectional view along the longitudinal axis of the switch, taken in the direction of the arrows substantially along the line 2-2 of Figure 1.
• Figure 3 is a schematic plan view illustrating multiple stations in the automated manufacture of the switch of Figure 2.
• Figure 4 is a schematic plan view of one of the stations illustrated in Figure 3.
• Figures 5, 6, 7 and 8 are schematic views illustrating processes in the automated manufacture of the switch at four successive stations, and
• Figures 9 and 10 are sectional views similar to Figure 2, showing modifications of the invention.

Referring to the drawings, a plastic housing 10 is illustrated in Figure 1 having a conventional socket for a small electric light bulb, such as a conventional wedge base bulb 11 adapted for operation at approximately one ampere in a twelve volt D.C. circuit, and a cavity 12 for removably receiving 'a conventional gravity-operated mercury switch, or a switch 13 described in detail below.

The housing 10 is provided with a pair of electrical leads 14 and 15 adapted, for example, to be connected respectively with the positive terminal of a battery and to ground. The lead 14 extends through base 16 of the housing 10 and is electrically connected with a conventional resilient or spring contactor 17 at one axial end of the cavity 12. A second contactor 18, which may also be resilient, is confined within the housing 10 at the opposite axial end of the cavity 12 and is arranged for electrically contacting one contact element of the bulb 11.

The lead 15 extends through the body of the housing 10 and is arranged for contacting a second electrical contact of the bulb 11 to complete an electrical circuit through the bulb 11 when the switch 13 is electrically closed, as described below. Except for the switch 13, the details of the housing 10 and its electrical contacts may be conventional.

Referring to Figure 2, details of the switch 13 are illustrated comprising a one-piece injection moulded cup-shaped plastic housing 19, which may comprise a thermoplastic, such as glass fibre filled polyester resin, capable of expanding slightly and softening when heated and of shrinking slightly and hardening when cooled to room temperature, or a nylon 103 and preferably for dimensional stability a Noryl resin (Noryl is a Trade Mark). The housing 19 is cylindrical in cross section to define an enclosure 20 open at one end 20a and closed at its opposite end or base 21.

Suitably secured within the base 21 and effecting a fluid tight seal therewith is a one-piece brass rivet-shaped contact means or electrical conductor 22 of circular section having an enlarged head or interior contact 23 adjacent the interior of the base 21, a connecting portion 24 extending coaxially through the base 21, and an exterior contact 25 which may be slightly swaged if desired to clamp the base 21 firmly between the contacts 23 and 25 and to assure a fluid sealing engagement between the material of the base 21 and portion 24 entirely around its circumference in the event the conductor 22 is not moulded as an insert within the base 21, as described below.

If desired, the conductor 22 may be assembled with the housing 19 by forcing the small end of the conductor 22 through the opening in the base 21, as for example in some instances which the housing 19 and base 21 are warm, as for example between about 37.78° and 82.22°C (100° and 180°F), depending upon the plastic, or the base 21 may be warmed around its opening by first heating the conductor 22 and forcing it through the base opening. In any event, when the base 21 cools and shrinks around the connecting portion 24, a fluid tight bond and seal is effected between the portion 24 and the adjacent plastic of the base 21. Thereafter if desired, the exterior contact portion 25 may be swaged to effect the aforesaid clamping and enhance the seal.

A brass cup-shaped second electrical conductor or contact means 26 of cylindrical cross section defines an enclosure 26a open at its inner end 26b and closed at its axially opposite base 27 or exterior contact. A spherical lead conductor or ball 28 rolls freely within the enclosure 26a, which is dimensioned so that when the ball 28 is in contact with the interior contact 23, it will also be in contact with the cylindrical interior sidewall of the conductor 26. The interior surface of the cylindrical enclosure 26a thus serves as a guide for the ball 28 in electrical contact therewith at all times.

Upon tilting of the longitudinal axis of the switch 13 clockwise or counterclockwise from the horizontal position shown, the ball 28 will roll to an open switch or closed switch position. Also the lead ball 28 preferably comprises an alloy containing 2% antimony which increases the hardness and durability of the ball 28 without significantly decreasing its essential weight. The conductor 22 is preferably zinc-coated to facilitate identification of the switch polarity. Also preferably, the conductor 26 is dimensioned to effect a fluid sealing interference fit between its cylindrical sidewalls and the cylindrical sidewalls of the plastic housing 19. Thus the interfitting cylindrical walls of the members 19 and 26 may be telescoped together coaxially with moderate force to assure dimensional stability for the switch 13 and a fluid-tight seal between the cylindrical sidewalls of the members 19 and 26. Similarly to the heating of the base 21 by first heating the conductor 22, the housing sidewalls may be heated by first heating the conductor 26 and pressing the latter coaxially into the enclosure 20 to complete the assembly of the members 19 and 26. On the other hand, the nylon 103 and preferred Noryl are non-galling and sufficiently resistant to abrasion so that the housing 26 may be readily assembled with the conductors 25 and 26 by the pressing operations at room temperature.

It is believed to be apparent from the foregoing that the axially outer or exterior surfaces of the contact 25 and base 27 comprise electrical contact surfaces adapted to be frictionally confined tightly between the contacts 17 and 18, at least one of which may be resilient, thereby to enable selective completion of an electric circuit through the lamp 11 upon appropriate tilting of the housing 10. By virtue of the cylindrical sidewalls of the cup-shaped conductor 26, the ball 28 is guided axially within the switch 13 in electrical contact with the conductor 26 regardless of the rotational position of the cylindrical axis of the switch 13 within housing 10.

The housing 19 may be formed by conventional injection moulding processes. The conductor 22 and the cup-shaped conductor 26 may be formed by conventional stamping or drawing operations. By virtue of the coaxial arrangement of these parts and the location of the base contact 27 as shown, the conductor 26 may be forced coaxially into the housing 19 until a desired preselected overall axial length for the switch 13 is obtained, without particular regard to the axial length of either the housing 19 or conductor 26. It is only essential that the members 19 and 26 be dimensioned axially with regard to the eventual overall desired axial length of the switch 13 so that, in the final assembled position, the external contact base 27 will project slightly endwise from the open end 20a of the housing 19. The arrangement described thus reduces the necessity for maintaining close production tolerances for the axial length of the members 19 and 26, with resulting production economies.

Figures 3 to 8 illustrate the apparatus and a preferred method for manufacturing the switch 13 at four progressive work stations located 90° apart around a rotating conveyor 29. The upper parts of a multiple-part injection moulding die 49, Figure 6, at each station above a partition or datum plane 30 may be non-rotatable. The die parts below the datum plane 30 are pregressively indexed through the Stations 1, 2, 3 and 4 by rotation of the carrier 29.

Station No. 1 is a conductor feeding station whereat the conductors 22 are fed one at a time from a hopper, (not shown), along a feed track 31 to the position illustrated in Figure 5 by operation of a horizontally reciprocating plunger 32. In Figures 5 to 8, the connection 24 between the contacts 23 and 25 has the same diameter as the contact 25. In other words, the contact 25 is not swaged or enlarged, which is optional and immaterial to the method described below.

When the rotating conveyor 29 indexes the lower parts of the die 49 to the No. 1 Station, a single conductor 22 is fed to a position in advance of the plunger 32, which is initially retracted to the phantom position shown. The plunger 32 is then activated to move to the right in Figure 5 and locate the conductor 22 as shown against a vertical semi-circular cylindrical wall 33 of the die 49. The latter comprises vertically movable parts 35, 36, 37 and 38 carried by conveyor 29 and located initially as illustrated in solid lines, Figure 5, at Station No. 1.

The aforesaid rightward movement of plunger 32 slides the conductor 22 in the upright position shown along a horizontal portion of track 31 flush with the top of die part 38, thence along the latter top and into position with the right half of the contact 25 seated on a mating upper horizontal semi-circular surface of cylindrical die part 37 and against the vertical wall 33 of the die part 36. The left half of the contact 25 will then overlie a mating semi-circular cylindrical cavity 39 in the upper interior portion of die part 38, see also Figure 4. The conductor 22 is thus supported and clamped radially between the wall 33 of die part 36 and plunger 32.

A vertically movable locating plunger 40 having a lower cavity 41 shaped to closely confine the upper or interior surface of the contact 23 of conductor 22 now moves downwardly from the phantom position, Figure 5, to the solid line position, thereby to secure the conductor 22 against inadvertent movement upon the subsequent retraction of plunger 32 to the phantom position of Figure 5 and the movement of the die parts 36 and 38 to their solid line. positions illustrated in Figure 6. At such positions, the contact 25 of conductor 22 is secured between mating half cylindrical surfaces 33 and 34 of mould portions 36 and 38 respectively, Figure 5. The surface 34 defines a vertical wall of recess 39.

After the contact 25 is secured between surfaces 33 and 34, plunger 40 is retracted to the phantom position of Figure 5 and the die conveyor 29 indexes the lower die parts 35 to 38 to the No. 2 Station, Figure 6, whereat a vertically movable upper die part 41 is moved downwardly and the die part 35 is moved upwardly to meet at the partition surface 30, Figure 6.

The die parts 35 to 38 and 41 at the Figure 6 position co-operate to provide a mould cavity 42 having the shape of the desired housing 19. Also as illustrated in Figures 6 and 7, the lower die parts 35 to 38 co-operated to define the cavity for the housing base 21 and support the latter after the moulding operation. The plastic that eventually hardens to provide the housing 19 is then injected in a fluid condition at elevated temperature and pressure into the cavity 42 by conventional means to form the housing 19 with its base 21 around the connecting portion 24 and bonded thereto in fluid sealing engagement. Formation of the housing 19 with the insert 22 by injection moulding assures rapid and complete filling of the cavity 42 and sealing around the brass insert portion 24. Depending upon the plastic, typical moulding temperatures and pressures of 260° to 282.22°C (500° to 540°F) and 34.48 to 103.43 bar (500 to 1500 psi), may be employed. Preferably a plastic is selected that can be moulded satisfactorily at about 68.96 bar (1000 psi).

Upon completion of the injection moulding, the upper die part 41 is retracted vertically to expose the housing 19 in an upright position as illustrated in Figure 7. The rotating carrier 29 is then indexed with the housing still confined at its base 21 within the lower die parts 35 to 38 to the No. 3 Station, Figure 7, whereat the upper opening 20a is aligned with a ball feeder 43. The latter comprises a chute and a detent mechanism 44, 45 which is then moved to the right to centre an opening 46 in the lower detent 44 with the chute 43 to enable release of one of the balls 28 into the housing 19. Simultaneously, the upper detent 45 moves into the chute to prevent release of a second ball 28. Thereafter the detent mechanism 44, 45 returns to its solid line position illustrated in Figure 7 and the die conveyor 29 indexes the lower die parts with the housing 19 and ball 28 to the Figure 8 position of the No. 4 Station.

At Station No. 4, the brass conductor 26 is fed with its open end 26b down into a position between a pair of diametrically spaced gripping members 47, phantom position Figure 4. Thereafter the gripping members 47 are activated to move to the solid line position, Figure 4, and grip the conductor 26 at diametrically opposite sides adjacent its lower open end and move the conductor 26 into coaxial alignment with the upwardly opening housing 19 as illustrated in phantom Figure 8. A vertically movable plunger 48 is then moved downwardly from the phantom position in coaxial alignment with the conductor 26, Figure 8, to force the latter downwardly and coaxially into the upper open end 20a until the overall preselected axial dimension for the assembled switch 13 is obtained.

The cylindrical sidewalls of the conductor 26 are dimensioned to effect an interference fit with the interior of the housing 19, as for example, at the region of the cylindrical enlargement or offset 19a that may be provided optionally to accommodate the cylindrical sidewall of conductor 26. Also to avoid reheating, the insertion of the conductor 26 into the housing 19 may be done while the latter is still warm from the moulding operation, as, for example, between about 37.78° and 82.22°C (100° and 180°F), and the plastic of the housing 19 is still sufficiently flexible to enable insertion of the conductor 26 without excessive force. When the housing 19 cools and shrinks around the conductor 26, a fluid sealing bond between the members 19 and 26 and a unitary dimensional stable switch 13 results. By reason of the light weight of the conductor 26, comparatively little force is required by the gripper 47 to hold and locate the conductor 26 in coaxial alignment with the housing 19. Accordingly, when the plunger 48 moves downwardly, the conductor 26 readily slides downwardly relative to the grippers 47.

Upom completion of the downward movement of plunger 48, the latter and the grippers 47 are retracted to their phantom positions illustrated in Figures 4 and 8, in preparation for the next successive conductor 26 upon the next successive action at Station No. 4. Also the die parts 36, 37 and 38 are then moved upwardly to eject the assembled switch 13 from the die. The switch 13 is then blown into a retaining basket, examined for defects, tested for performance, and shipped to the customer.

Referring to Figure 9, a preferred production version of the present invention is illustrated wherein the various parts are identified by numerals corresponding to the identifying numerals for the parts previously described but multiplied by a factor of ten. Likewise the various parts operate and may be manufactured the same as described above, with differences noted below. For example, the brass cup-shaped conductor 260 is provided with a slightly chamfered outer edge 260c that tapers toward the inner end 260b, and the latter is provided with an annular rounded inner edge 260d. The chamfer 260c serves as a guide and leading edge to facilitate the initial insertion of the conductor 260 into the open end 200a of the plastic housing 190 and avoids cutting of the plastic material during the assembly operation, Figure 8. The rounded edge 260d prevents interference with movement of the ball 180, particularly in the event that the plane of the inner end 260b is adjacent the centre of the ball 180 at the contact position when the switch 13 is finally assembled.

The conductor 220 is provided with an enlarged exterior contact base 250 and is forced into an opening in the housing base 210 that provides an interference fit with the circular cylindrical connector 240, so that, when the parts are assembled as described above by forcing the contact surface 230 through the aforesaid opening, a fluid tight seal will be effected between the plastic base 210 and the cylindrical portion 240 entirely around the latter. The inner contact end 230 of the conductor 220 is rounded spherically with a radius comparable to the radius of the ball 180 and serves as a rounded guide upon its insertion coaxially to the assembled position shown, Figure 9. Also preferably the brass conductor 220 is zinc or cadmium coated to facilitate electrical conductivity and identification of polarity.

The spherical contact surface 230 assures an essentially point contact with the ball 180 and maximum gravity induced pressure loading therebetween when in electrical contact. Such maximum pressure contact is particularly important in a small light weight gravity-operated switch of the type described capable of replacing a mercury switch, as for example, in the housing 10, Figure 1. Accordingly the ball 180 is preferably a heavy material, such as lead or the lead-antimony alloy described, which is also a good electrical conductor. For a low amperage light bulb of the type illustrated in Figure 1 for use with an automobile under-the-hood or rear deck illumination in a typical twelve volt DC circuit, the ball 180 will usually be less than 6.25 mm (a quarter of an inch) in diameter and preferably less than 5.08 mm (two tenths of an inch) for the sake of economy of material.

In the preferred construction illustrated in Figure 9, the lead-antimony ball 180 weighs 0.61 grams, has a diameter of 4.826 mm (0.19 inch) and is sonic cleaned prior to being confined within the cavity 260a of the assembled switch 13 to remove any accumulated dirt or oxides and to assure good electrical contact with the surface 230. The internal diameter of the cup-shaped conductor 260 is between 4.953 and 5.08 mm (0.195 and 0.200 inch), enabling the ball 182 to roll freely therein. The diameter of the spherical surface 230 is 4.445±0.025 mm (0.175±0.001 inch). The diameter of the cylindrical connector portion 240 is the same as the diameter of the spherical portion 230. The cylindrical opening in the base 210 for the portion 240 is formed during the injection moulding of the housing 190 to effect a cylindrical interference diameter of 2.794 mm (0.173 inch) within a tolerance of plus 0.000 and minus 0.076 mm (plus 0.000 and minus 0.003 inch), thereby to effect the aforesaid fluid tight seal.

The housing 190 is moulded from the aforesaid resin separately from the conductors 220 and 260 to provide an outer diameter for the switch 13 of approximately 9.398 mm (0.37 inch). The internal diameter of the enlarged or radially offset cylindrical inner surface 190a is dimensioned to effect a diametrical interference of 0.127 mm (0.005 inch) with the outer diameter of the cylindrical wall of the cup-shaped conductor 260. The radial shoulder at the inner end of the offset enlargement 190a provides a movement limiting stop for the conductor 260 in the event the latter should be inadvertently forced axially too far into the housing 190. In such an event, although the overall axial dimension of the resulting switch 13 might be less than preferred, the spring contactor 17 of Figure 1 will be adequate to compensate for the shorter axial length and effect the necessary electrical contact with the base 250.

The aforesaid interference dimensions in conjunction with the moulded resin housing assure the necessary fluid seals between the housing 190 and conductors 220 and 260. Also by virtue of the nylon or Noryl housing 190, its assembly with the conductors 220 and 260 by forcing the latter coaxially thereinto as described may be accomplished at room temperatures.

The foregoing describes several important aspects of the present invention that enable the production of an improved ball or gravity switch wherein it is important to confine a major portion of the brass shell 26 or 260 within the dielectric housing 19 or 190, as for example where the possibility of inadvertent electrical grounding or shorting of the shell 26, 260 is a problem. Where exposure of the major portion of the conducting cup-shaped shell is not a problem, additional significant improvements in a ball or gravity switch are illustrated in Figure 10 wherein similar parts function in the manner of those already described and are identified by the same reference numerals, distinguished by a prime mark.

Thus, in Figure 10, a cup-shaped cylindrical brass shell 26', 27' enclosing space 26a' for a conducting ball 28' is telescoped or sleeved over the outer cylindrical surface of a diametrically reduced portion 19a' of a cup-shaped dielectric housing member 19'. The inner edge 26c' of the annular end 26b' is chamfered to facilitate initiation of the telescoping assembly. The portion 19a' extends axially from the base 21' to its open end 20a', which terminates at approximately the level of the innermost portion of the spherical surface of the brass contact 23', or extends for an axial distance approximately equal to or less than the radius of the ball 28'. The axial extent of the reduced diameter portion 19a' is preferably no more than is required to effect a fluid tight seal with the inner cylindrical surface of the shell 26' pressed thereon at an interference fit. In consequence, a minimum of the dielectric material is required.

In the Figure 10 structure, the dielectric from which the housing part 19' is moulded preferably comprises the above-mentioned Noryl because of its dimensional stability and its capability of being formed within close tolerances by conventional moulding processes. In other respects the part 19' co-operates with the brass contact 22' in the manner of the aforesaid parts 19, 190 co-operating with the contacts 22, 220.

The annular shoulder 21a' comprising the portion of the base 21' around the reduced diameter portion 19a' serves as an abutment to stop axial movement of the shell 26' during assembly. By virtue of the dimensional stability of the Noryl material of the part 19' and the feasibility of forming the brass shell 26' within close tolerances, it is usually unnecessary to provide an adjustment gap between the shoulder 21a' and the open end 26b' of the shell 26'. Furthermore the close tolerance to which the Noryl can be moulded facilitates sealing between the housing portions 19a' and 26'.

In the event that adjustability of the overall axial length of the switch is desired, suitable clearance between shoulder 21a' and end 26b' may be provided. The housing members 19' and 26' may then be assembled by selective telescoping as described above in regard to Figure 8. The contact 22', with or without an enlarged exterior contact 25', may be moulded in position within the base 21', or the contact surface 23' may be forced axially into position through the opening in the base 21' around the connector portion 24', as described above in regard to the contacts 22, 220.

It is to be observed that by virtue of the construction shown in Figure 10, without increasing the overall outer diameter of the switch, the diameter of the ball 18' may be increased significantly. Thus the 4.763 mm (3/16"), 0.61 gram lead ball 18 can feasibly be replaced by a less costly 7.938 mm (5/16") 2.17 gram brass ball 18' that significantly reduces the voltage drop across the ball contacts and enables increased current flow through the closed switch without increasing ball sticking or welding. Furthermore, the assembled switch is readily received within the cavity 12, Figure 1.

Although the greater weight of a lead ball 18' would reduce ball-contact voltage loss even more than the brass ball 18' and could be used where the additional cost is warranted, the more economical brass ball 18' performs adequately in the typical installation. Zinc or cadmium plating of the ball 18' and contact 22' further reduces power loss and the welding effect by eliminating the corrosion tendency of the unplated brass contacts. No appreciable welding effect between the interior of shell 26' and ball 18' occurs because these elements are in electrical contact at all times and make or break of the electric circuit does not take place therebetween. Finally, to eliminate dust, flashing, and other foreign contamination of the switch contact elements, these are preferably cleaned by known sonic processes immediately before assembly of the switch to assure optimum operating efficiency.