US3740511A

US3740511A - Vacuum switch

Info

Publication number: US3740511A
Application number: US00140855A
Authority: US
Inventors: J Westmoreland
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-05-06
Filing date: 1971-05-06
Publication date: 1973-06-19
Anticipated expiration: 1990-06-19

Abstract

A sealed electrical switch is disclosed which includes a first conductive element and a second conductive element. The second conductive element is positioned with its first end in abutting relationship with the first end of the first conductive element, with the abutting surfaces of the conductive elements forming the contacts of the switch. Electrical terminals are connected to the other ends of the conductive elements, and an elastomer coating surrounds all of the switch except the electrical terminals.

Description

I United States Patent 1 Westmoreland 1 June 19, 1973 1 VACUUM SWITCH [76] Inventor: Julius C. Westmoreland, 6607 Avenida de La Pescas, La Jolla, Calif. 92037 22 Filed:' May'6, 1971 211 Appl.No.: 140,855

[52] US. Cl. 200/168 G, 200/144 B [51]. Int. Cl. 1101b 9/02 [58] Field of Search 200/144 B, 168 G [56] References Cited UNITED STATES PATENTS 1,836,654 12/1931 Dorn et al. 200/144 B 2,785,319 3/1957 Simpson et al.... 200/144 B 2,824,183" 2/1958- '--lVlarasco et al. 200/168 G 2,877,324 3/1959 Oshry 200/168 G Jennings 200/144 B 9/1965 Weissburg .1 200/168 6 X 3/1966 Clason 200/168 G X Primary Examiner-Robert S. Macon Attorney-Ronald W. Reagin and Ralph M. Braunstein [57] ABSTRACT A sealed electrical switch is disclosed which includes a first conductive element and a second conductive element. The second conductive element is positioned with its first end in abutting relationship with the first end of the first conductive element, with the abutting surfaces of the conductive elements forming the contacts of the switch. Electrical terminals are connected to the other ends of the conductive elements, and an elastomer coating surrounds all ofthe switch except the electrical terminals.

9 Claims, 5 Drawing Figures JUL /S C. WE 5 T MORE L A/VD INVENTOR Y am/ ATTORNEY VACUUM SWITCH This invention relates to electrical switches, and more particularly to a novel sealed electrical switch and a method for making the same in which tll'.S\YllCh I i can be manufactured at an extremely low cost.

where a spark between contacts might set off an explosion or the like. However, vacuum switches also have many advantages over conventional switchesin areas other than explosion hazard areas. For example, less arcing occurs between the contacts when there is no gaseous mediumto support an are when the contacts are broken while they are carrying current. Since the resultant pitting and erosion from such arcing is one of the major causes of contact wear and switch failure, vacuum switches typically exhibit a much longer life than. conventional switches. Also, it is known that in a vacuum switch it is not necessary toseparate the contacts by as great a distance to enable the switch to hold off a given voltage, since the absence of the gaseous medium between the contacts makes it less likely that arcing will occurat a time when the contacts are open.

However, to date the relatively high price of vacuum switcheshas limited their application to either explosion hazard areas,'where such-switches are absolutely 'required,"or to extremely high specification systems where the added cost of the vacuum switch can be justified. This added cost'is usually caused by the requirement that the switch have relatively expensive glass or ceramic "t'ometal seals in order to allow the electrical leads to be brought out in a suitably insulated manner while still maintaining the necessary hermetic seal of the container. v

It is accordingly an object of the present invention to provide an improved vacuum switch.

It is another object of the present invention to provide an improved vacuum switch which is simple and inexpensive to manufacture.

It is yet another object of the present invention to provide an improved method of making a vacuum switch.

" Briefly stated, and in accordance with the presently preferred embodiment of the invention, a vacuum switch is provided which includes a first electrically conductive element and a second electrically conductive element. Each of these conductive elements has a first end and a secondend,with the first end of each forming the contact surfaces of the switch. The first ends of the two conductive elements are complementary surfaces, and are preferably planar. These conductive elements are positioned with their first ends in abutting relationship so that the two contact surfaces normally mate with each other in intimate relation.- Suitable electrical terminals are connected to the second ends of the conductive elements. An elastomer coating is provided which surrounds all of the switch except the terminals, whereby a low resistance electrically conductive path normally exists between the contact surfaces of the two electrically conductive elements, and thus between the two terminals of the switch. However, if the switch is laterally deflected or elongated, a gap develops between the contact surfaces to form an open circuit between the electrical terminals. The elastomer coating allows the switch to elongate or to deform to enable this gap to'develop, but prevents any gaseous medium from getting between the contacts, and thus a self-contained and self-generated vacuum is developed between'the contacts.

In accordance with another, feature of the present invention, the vacuum switch is manufactured by forming the two conductive elements mentioned above from a single elongated body of electrically conductive mate rial. An electrical terminal is provided on each end thereof. The elongated body is then coated with an elastomer coating entirely along its length and over its shoulders, but leaving the terminals exposed for electrical connection. After the coating is applied, the elongated body is broken, for example by placing the switch under tension to break the elongated body into the two electrically conductive elements mentioned above. If desired, a notch may be provided in the side of the elongated body prior to the coating operation to assist this breaking step and' to assure that the break occurs at a desired location. By this method, the vacuum switch is formed in an extremely inexpensive manner while at the same time assuring that a good vacuum is employing the vacuum switch of FIG. 1', and

achieved between the contact surface when the switch is actuated. I

Fora complete understanding of the invention, and an appreciation of its other objects and advantages, please refer to the following detailed description of the attached drawings, in which: FIG. 1 shows a cross-section view of a vacuum switch in accordance with the present invention;

FIG. 2 shows a cross-sectional view of the vacuum switch of FIG. 1 and illustrates how the contacts of the switch are opened when the switch is elongated;

FIG. 3 shows a cross-sectional viewof the vacuum switch of FIG. 1 and illustrates how the contacts of the switch are opened when the switch is deflected laterally;

FIG. 4 is a cross-sectional view of a switch assembly FIG. 5 is a cross-sectional view of a second switch assembly employing two of the vacuum switches of FIG. 1.

FIG. 1 shows a cross-sectional view of a vacuum switch 10 in accordance with the present invention. As shown therein, the switch 10 is formed from a first conductive element 12 and a second conductive element 14. Each of the

conductive elements

12 and 14 contains a

first end

16 and 18 respectively and a second intimate contact to provide an extremely low resistance electrically conductive path between the two

conductive elements

12 and 14.

Electrical terminals

24 and 26 are directly connected to the

second ends

20 and 22 respectively of the

conductive elements

12 and 14. Thus, when the switch 10 is in the condition shown in FIG. 1,

essentially a short circuit exists between the

electrical terminals

24 and 26.

The switch is completed by an elastomer coating 28 which completely surrounds all of the switch 10 except the

electrical terminals

24 and 26. The elastomer coating 28 surrounds all of the side portions of the

conductive elements

12 and 14 and extends around the shoulder portion 30 of conductive element 12 and the shoulder portion 32 of conductive element 14 in order to prevent these elements from sliding out of the elastomer coating.

As shown in FIG. 1, the

conductive elements

12 and 14 are each substantially cylindrical elements along their length, but each has a tapered or frustro-conical portion at its first end adjacent the

contact surfaces

16 and 18. These tapered sections thus define a notch around the center of the conductive portion of the switchwhen it is in the condition shown in FIG. 1. The reason for this notch is explained in connection with the description below of the manufacturing process by which the vacuum switch is made.

FIG. 2 is a cross-sectional view similar to FIG. 1, but shows how an open circuit is developed between the

contact surfaces

16 and 18 of the vacuum switch 10 whenever the switch 10 is elongated, such as by applying tension between the

terminals

24 and 26. When this occurs, the elastomer coating 28 stretches slightly and allows the

conductive elements

12 and 14 to separate from each other, thereby causing a-gap 34 to develop between the

contact surfaces

16 and ,18. Since this gap 34is heremtically sealed from the outside atmosphere by the elastomer coating 28, if sufficient care is taken in the manufacturing process of switch 10 to assure that no gasses, are present within the elastomer coating 28 or the

conductive elements

12 and 14, the gap 34 is essentially a self-contained and self-generated vacuum, and thus switch 10 is a vacuum switch, with all the inherent advantages thereof. 1

FIG. 3 is again a' cross-sectional view similar to FIG. I, but illustrates what happens when a force, indicated by the arrow 36 is applied laterally against the center of switch 10 to cause'switch 10 to deflect laterally. As is shown in FIG. 3, a gap 34 again develops between

contact surface

16 and 18 to effect an open circuit between

terminals

24 and 26. Again, as in the case of FIG. 2, there are no gasses present in the gap 34 and it is thus essentially a vacuum. At this point is is appropriate to discuss the process by which the vacuum switch 10 just described is manufactured. In accordance with one of the features of the present invention, the two

conductive elements

12 and 14 are initially formed as a single unit. This unit is a cyleventually for'med. This notch may be either machined into the material or, ifthe cylinder is formed by a process such as die-casting or molding, it may be formed simultaneously with the conductive cylinder in the mold. The

electrical terminals

24 and 26 are next attached to the

ends

20 and 22 respectively.

It is important that the conductive cylinder be formed with as little gaseous material as possible within the conductive material. For many conductive materials, such as those mentioned above, it is sufficient if the material is machined or die-cast in a conventional man ner. For other materials which have a propensity to contain gas within their structure or to be porous mate rials, it may be necessary to do the casting in a vacuum to assure that no gasses are trapped within the material to be freed at the time the conductive cylinder is broken into two pieces, as is described below. If the conductive cylinder is formed from a particularly porous material, such as if it is sintered from a powdered metal, this forming in a vacuum may be quite important.

The switch 10 as thus processed is then coated with a coating of elastomer material 28 around all the portions shown in FIG. 1, including over the

shoulders

30 and 32. The elastomer material may be any synthetic or natural material which is capable of a hermetic seal and which has resilience or memory sufficient to return to its residual shape after major or minor distortion. Preferably, the elastomer material 28 is silicone, but it may also be any material exhibiting suitable elastomer characteristics, such as natural rubber, butyl, fluorosilicone, polyurethane, polyacrylate, nitrile or chloropene.

The final step in the manufacturing process is to break the central conductive core into the two

conductive elements

12 and 14. This may be easily effected by subjecting the coated switch 10 to a tensile pull sufficient to separate the

elements

12 and 14 at the notch while only slightly stretching the surrounding elastomer material 28. The contact surfaces 16 and 18 are thus produced within a self-contained vacuum. If the material is sufficiently brittle and exhibits a sufficiently low tensile to shear strength ratio as mentioned above, the

elements

12 and 14 will separate along a substantially planar break surface, thereby forming substantially planar contact surfaces 16 and 18 which will mate in intimate contact to provide good electrical conduction between the

terminals

24 and 26. In any event, even if the break occurs as other than a planar break, the contact surfaces 16 and 18 are inherently complementary and mate along their entire surface to provide good electrical contact.

Alternatively, the break may be effected by applying a lateral force to the switch 10 adjacent to the notch, much like a match stick might be broken. Again, this form of breaking results in complementary contact surfaces 16 and 18 within a self-contained vacuum.

FIG. 4 shows a cross-sectional view of a switch assembly 40 which incorporates the vacuum switch 10 described in FIGS. 1 and 3. above. As is shown in FIG. 4, the switch 10 is positioned in a cavity 42 within a housing 44. A leaf spring 46 is positioned behind the switch 10 and a cam element 48 is positioned in front of the switch 10. An actuating lever 50 is provided on cam 48, and if lever 50 is rotated clockwise as shown by arrow 52, cam 48 rotates in a clockwise manner to cause a section of cam 48 which has a larger radius to move against switch 10, causing it to deflect laterally back into cavity 42 against leaf spring 46. When this occurs an open circuit is created within switch 10 as is shown in FIG. 3 above, and this open circuit remains until the lever 52 is rotated back to the shown position of FIG, 4. At this time, leaf spring 46 deflects switch back into a straight position to cause a short circuit be- I tween its terminals, as is shown in FIG. 1 above.

switch 10 of FIGS. 1 through 3. The vacuum switches 62 and 64 are positioned within a cavity 66 in a housing 68. One terminal of each of the

switches

62 and 64 is pivotally connected to an electrically conductive lever '70, such as being mounted on a pin 72 which is secured to lever 70 The bottom end of lever 70 is pivotally mounted on a pin 74 which forms the common terminal of switch assembly 60. A leaf spring 76 is connected between the top end of lever 70 and the housing 68 to hold the lever 70 in the position shown in FIG. 5 whenever switch assembly 60 is not actuated.

As shown in FIG. 5, the other terminal of switch 62 is connected to a-pin 78, and the spacing between pin 78 and pin 72 is such that, when the assembly is in the position shown in FIGS, sufficient tension exists along switch 62 to cause its elastomer coating to stretch a sufficient amount to create an open circuit between its contact surfacesThis is shown in the hidden lines within switch 62. Thus,'pin 78 serves as a normally open contact relative to the common terminal at pin Conversely, pin 64 has its other terminal connected to a pin 80 which is spaced from pin 72 a sufficient distance that'the elastomer coating of switch 64 is in its relaxed state, whereby its contact surfaces mate intimately to provide a short'circuit between its terminals. Again, this is shown in the hidden lines in FIG. 5. Ac-

' cordingly, pin 80 is a normally closed contact relative to the common'terminal'at pin 74.

As is shownin FIG. 5, a push button actuator 82 is provided which is pivotally connected toa pin 84in the center of lever 70. In operation, whenever push button 82 is depressed, lever 70 pivots counter-clockwise on pin 74, deflects leaf spring 76 and causes pin 72 to move closer to pin 78 and further from pin 80. At this time, switch 62 is shortened and the contact surfaces therein are closed, thereby creating an electrical connection between the common terminal at pin 74 and the normally open contact at pin 78. Simultaneously switch 64 is elongated and its contact surfaces are opened, thereby creating an open circuit between the common terminal at pin 74 and the normally closed 'contact at pin 80. This condition remains until the is actuated and assures that the switches are opened and'closed only by elongation and shortening of the

switches

62 and 64.

While the invention is thus disclosed and'severalspecific embodiments described in detail, it is not intended that the invention be limited to these shown embodiments. Instead, many modifications will occur to those skilled in the art which lie within the spirit and scope of the invention. For example, in many applications it and 64 from laterally deflecting when push button82 will not be necessary to provide a notch all the way around the center of the conductive cylinder before it is coated with its elastomer coating. For some materials and applications it will be sufficient to provide a notch in only one side to assure a sufficiently clean break. For other materials or other breaking methods, it may not be necessary to provide a notch at all. It is thus in tended that the invention be limited in scope only by the appended claims.

What is claimed is:

1. A sealed switch, comprising:

a first conductive element having a first end and a second end, said first end of said first'conductive element forming a first contact surface and said second end of said first conductive element including a shoulder portion,

a second conductive element having a first end and a second end, said first end of said second conduc- I first terminal means connected to the second end of said first conductive element, 7

second terminal means connected to the second end of said second conductive element, and

an elastomer coating surrounding and being in intimate contact with all of said first and second conductive elements except said first and second terminal means and said first and second contact surfaces, said elastomer coating extending over said shoulder portions of said first and second conductive elements, whereby a low resistance electrically conductive path normally exists between said first and second terminal means and an open circuit between said first and second terminal means is formed by a resultant vacuum gap between said first and second contact surfaces whenever said vacuum switch is elongated or is laterally deflected.

2. The sealed switch of claim 1 in which said first and second surfaces are each substantially planar.

3. The sealed switch of claim 3 in which the area of said contact surfaces is less than the cross-sectional area of said conductive elements between said contact surfaces and said shoulder portions.

4. The sealed switch of claim 4 in which said elastomer material is selected from the group consisting of silicone, rubber, butyl, flourosilicone, polyurethane, polyacrylate, nitrile and chloropene.

5. A process for making a sealed switch which comprises the steps of:

forming an elongated body of electrical conductive material having a terminal at each end thereof, coating said body with an elastomer coating but leaving at least a portion of said terminals uncoated,

' and breaking said elongatedbody within said elastomer coating into first and second conductive elements, whereby the adjacent surfaces of said conductive elements, after breaking, form first and second contact surfaces, respectively, which are complementary and which are hermetically sealed by said formed entirely around the circumference of said body. elastomer coating. 8. The process of claim 7 in which said notch is ma- 6. The process of claim 5 which further includes the chined into said body after said body is formed. step of forming a notch in the side of said elongated 9. The process of claim 6 in which said body is body prior to the step of coating said body with an elas- 5 molded from a conductive material and said notch is tomer material. molded into said body at the time said body is formed.

7. The process of claim 6 in which said notch is

Claims

2. The sealed switch of claim 1 in which said first and second surfaces are each substantially planar.
3. The sealed switch of claim 3 in which the area of said contact surfaces is less than the cross-sectional area of said conductive elements between said contact surfaces and said shoulder portions.
4. The sealed switch of claim 4 in which said elastomer material is selected from the group consisting of silicone, rubber, butyl, flourosilicone, polyurethane, polyacrylate, nitrile and chloropene.
5. A process for making a sealed switch which comprises the steps of: forming an elongated body of electrical conductive material having a terminal at each end thereof, coating said body with an elastomer coating but leaving at least a portion of said terminals uncoated, and breaking said elongated body within said elastomer coating into first and second conductive elements, whereby the adjacent surfaces of said conductive elements, after breaking, form first and second contact surfaces, respectively, which are complementary and which are hermetically sealed by said elastomer coating.
6. The process of claim 5 which further includes the step of forming a notch in the side of said elongated body prior to the step of coating said body with an elastomer material.
7. The process of claim 6 in which said notch is formed entirely around the circumference of said body.
8. The process of claim 7 in which said notch is machined into said body after said body is formed.
9. The process of claim 6 in which said body is molded from a conductive material and said notch is molded into said body at the time said body is formed.