US3004127A

US3004127A - Contacts for electric switches

Info

Publication number: US3004127A
Application number: US759987A
Authority: US
Inventors: Carding Joseph Thom; Jelley Gordon Albert
Original assignee: JA Crabtree and Co Ltd
Current assignee: JA Crabtree and Co Ltd
Priority date: 1957-09-16
Filing date: 1958-09-09
Publication date: 1961-10-10
Anticipated expiration: 1978-10-10
Also published as: DE1149437B; BE571173A; GB856058A; GB856059A; FR1211643A; US2993967A

Description

Oct. 10, 1961 J. T. CARDING ETAL 3,004,127

CONTACTS FOR ELECTRIC SWITCHES Filed Sept. 9, 1958 2 Sheets-Sheet 1 Oct. 10, 1961 CARDING r 3,004,127

CONTACTS FDR ELECTRIC swI'rcHEs Filed Sept. 9, 1958 2 Sheets-Sheet 2 v I 50 I 24 g 23 i: 4 '22 El 6-\:!N /0 "5 i/ l 1 Y5 A9 a- I 24 JO 3,004,127 t CONTACTS FOR ELECTRIC SWlTCHES Joseph Thom Carding, Wolverhampton, and Gordon Al bert Jelley, Walsall, England, assignors to J. A. Crabtree "8: Co. Limited, Walsall, England, a British com- Filed Sept. 9, 1958, Ser. No. 759,987 Claims priority, application Great Britain Sept. 16,1957

, 13 Claims. (Cl. 200-166) This invention relates to improvements in contacts for electric switches and is particularly concerned with contacts for contactor-operated motor starters, the object of the invention being to provide an improved arrange ment for eliminating or minimising bounce ofthe rapidly moving contact when making engagement with its fixed contact, thereby reducing the possibility of the contacts welding and ensuring long life. d I

Contact Wear is a very important consideration for contactor-operated motor starting switches which are called upon to operate with great frequency over long periods. At the same time spaceconsiderations require such switches to be of minimum size. I

Cntact bounce is a well-known cause of wear which necessitates undesirable breakdowns of equipment in order to replace new contacts. Extremely strong springs might considerably reduce such bounce, but springs of this nature are quite impractical for a number of reasons in cluding the necessity for an operating magnet structure which would have to be so powerful as to be excessively large and hence result in an exceptionally large size of switch. t

Most known means for reducing the bounce of electric contacts involve the use of a mechanical spring. Such springs absorb the initial shock and by virtue of their elastic character a succession of shocks follow which are of gradually diminishing value.

The arrangement of the present invention enables the employment of the minimum size of spring and consequently necessitating only a small magnet. The moving contact plate is mounted on a sleeve-like piston disposed in an actuating cylinder and a small quantity of viscous material is introduced between the end or" the piston and the cylinder. The spring being located between the contact plate and the piston enables the latter to impose retardation in movement of the'contact when it engages its' fixed contact to eliminate bounce thereof. 7 i

The closed end of the piston is a fluid-tight seal in the cylinder and is movable therein against the action of a spring disposed within the piston, the seal being obtained by the aid of a viscous material such as grease. The contact may be carried on the free end of a piston rod, comprising a pair of fiatplates around which the spring is coiled. The spring also provides a sealing by compressing a washer within the closed end of the cylinder. The plates constituting the piston rod extend through openings in this washer andthe closed end of the piston and are bent over for their retention rearwardly of the latter.

The improved arrangement provides a lightweight construction, in which the viscous material around the circumferential wall of the piston and in the space behind it is distorted upon the rapid engagement of the contacts. Air'behind the piston acts as an extensible high rate spring operated in a sealed space for a fraction (about onernillisecond or one thousandth) of a second during which the bounce of themoving contact plate is restrained by the resulting vacuous condition set up during the instantaneous expansion of such space as the piston is rapidly repulsed against the action of the spring by the impingement of the moving contact on the fixed contacts. i

Thus the shearing effect on the grease, the hydraulic action and the vacuous condition momentarily set up exert an instantaneous damping action which effectively acts as a shock absorbing means to exclude bounce of the, moving contact on its engagement with the fixed con tact. The provision of a spring disposed within the piston ensures a compact construction of this type of switch. In order to enable the invention to be readily understood referencewill now. be made to the accompanying drawings illustrating a contactor-operated, motor starting switch embodying moving contacts in accordance with the invention, in which drawings:

FIGURE 1 is a perspective view of a moving contact.

FIGURE 2 is a section, to a larger scale, on the line 11-11 of FIGURE 1.

FIGURE 3 is a section on the line III-III of FIG- URE 2.

FIGURE 4 is a front elevation with parts in section of part of a motor starter incorporating moving contacts as shown in FIGURES 1-3, and i FIGURE Sis a section on the line V--V of FIGURE 4.

Referring to the drawings, a body 1, which may be moulded from insulating material, is of rectangular shape in external section and is formed with a bore 2 constitut-j ing a cylinder for the introduction of an aluminium piston 3 through its open end 1. A small quantity of a grease, such as silicone grease provides a fluid-tight seal ofthe piston. The temperature co-efiicient ofsilicone ensures reasonable viscosity at high operating temperatures. I

The closed end of the cylinder is formed with a transverse hole 4 through which passes a transmission rod 5 for actuating the contact through linkage 5 The piston 3 is hollow, and extending through it are a pair of fiat arms 6. having bent-over ends 6? which engage the bottom of the piston. The, arms extend through a slot like opening 7 in the closed end and this opening is sealed by a washer 8 which is tightly seated by a helical compression spring 9 coiled around the arms. The

other end of the spring is seated against a transverse plate 10 extending through aligning slots 11 in the armsv and having its ends disposed in openings 12 in opposed" walls of the insulating body. The arms are of extended, length so as to protrude through a central hole 13 in a contact plate 14 disposed transversely across the mouth of the body. The plate isseated in position on this open end of the body between guiding ribs 15 on the open end of the latter by a'short pin 16 extending through aligned slots 17 in the outer ends of the arms. H

. The cylinder 1 being connected with the actuating means 5 carries the moving contact plate 14 into engage.

ment with the fixed contacts 24. Upon such engagement the plate is arrested and the cylinder continues movement for a short distance. It will be seen that during this period which amounts to only a few milliseconds, the space below the piston, in which thegrease constitutes a fluid-tight seal is slightly enlarged. Hence a vacuous condition is set up in such momentarily enlarged space which resultsin great resistance to virtually eliminate bounce of the plate 14. This shock absorbing actionis due to the high speed of engagement of the con-- tact, for if the contact, plate and cylinder are moved slowly in relation to each other, there is an equalization of pressure effected between the enlarged space and the open end of the cylinder. It is, therefore, impossible to create a vacuous condition with consequent retarda- 4 tion of resistance to the movement of the contact plate weight construction and it may be formed with strengthening side flanges 14 between which may be disposed a thin flat plate 19, made of steel for example, having pointed ends 19 projecting beyond the silver buttons in order to constitute arcing horns. The are plates 19, and if'necessary the contacts, are readily replaceable.

For a motor starting switch there are mounted on a back plate 20 three insulating blocks 21 each formed with a tunnel-shaped opening 22 at the rear and a central bore 23 in which is guidingly slidable a contact carrier actuated by the transmission rod extending transversely through the tunnels. I The front of each block is formed with recesses 21*, above and below the central bore, each adapted for the mounting of a fixed contact 24 and terminal. Each terminal comprises a bent strap 25 having a channel-shaped cable clamp 27 secured to one end, its other end being located and secured in a recess by a pair of

screws

28, 29 passing freely through openings in the strap, into tapped inserts Si? in the block. One screw 29 secures the strap 25 to the block and the fixed contact plate 24 is laid flat on the strap, a recess 24 therein receiving the head of the screw. The second screw 28 is then passed through the contact 24 and the strap 25 for securing the former in position, the head of this screw being disposed in a recess 24 in the contact plate. The inner ends of each plate are formed with a flat slit or saw cut parallel to its wider face in order to impart limited resiliency for the silver button 24 mounted thereon.

A removable are shield 33 having partitions 31 and de-ion grids 32 is disposed over the contacts. On' the back plate 20 is mounted an auxiliary contact device 34 constructed in accordance with copending applica tion Serial No. 759,969 for Contactor-Operated Motor Starter.

The forms of the invention here described and illustrated are presented merely as examples of how the invention may be embodied and applied. Other forms, embodiments and applications of the invention, coming within the proper scope of the appended claims, will of course suggest themselves to those skilled in the art.

Having thus described our invention, we claim:

1. In an electric switch including a pair of fixed contacts, a movable contact member comprising an actuating cylinder, a contact plate carried by said cylinder, a sleeve-like piston mounted within the bore of said cylinder, a helical compression spring housed within said piston, viscous material forming a fluid-tight seal disposed between said piston and the closed end of said bore, said piston adapted to slide against the action of said spring and cause said seal to retard the movement of said plate upon engagement of said plate with said fixed contacts, an insulated block provided with a tunnelshaped opening disposed at the rear thereof, an extending portion projecting beyond the front face of said block forming a central bore for guiding said cylinder mounted for sliding movement therein, recesses disposed in the front face of said block to separately mount said pair of fixed contacts above and below said extending portion, a bent strap terminal provided for each of said fixed contacts, recesses disposed in said front face to seat said terminals, a first means to secure each of said terminals to said front face and a second means entering said front face to secure said fixed contacts to said terminals.

2. A moving contact device for use in an electric switch, said device comprising an actuating body member having a cylindrical bore therein, viscous material disposed within said here, a spring, a piston slidably mounted against said spring within said bore, said piston cooperating with said material to form a fluid tight seal therein, an arm disposed on said piston extending from said body, means for actuating said body, a contact plate transversely mounted in said arm, said spring disposed within said body adapted to press said arm-carried plate toward fixed contacts in said switch whensaid body is actuated.

3. A moving contact device according to claim 2 wherein a thin plate having arcing horns at its ends is disposed between side flanges on said contact plate.

4. A moving contact device according to claim 2 wherein said arm extends from said piston, said spring is coiled around said arm within said piston and said transversely carried moving contact plate is disposed on the free extending end of said arm.

5. A moving contact device according to claim 4 wherein said piston comprises a cylindrical sleeve provided with a pair of flat arms disposed centrally thereof, and the other end of said arms being bent over to engage the bottom of said sleeve.

6. A moving contact device according to claim 3 wherein said spring provides a sealing washer in the closed end of said actuating member. 7. Moving contact devices according to claim 6 for use in a multipole electric switch in which each of said cylinders is provided with a hole disposed through the closed end thereof, a rod connected to transmission linlo age adapted to pass through the hole in each of said cylinders wherein said multipole devices are actuated by a common actuating means.

8. In an electric switch having a fixed contact, a movable contact and rapid means for actuating said movable contact into impinging engagement with said fixed contact, a shock absorbing device for eliminating movable contact bounce resulting from such engagement, said device comprising a moving contact actuating cylinder having a closed end, a piston having a closed end disposed within said cylinder and movable relative thereto, highly viscous material disposed between said two juxtaposed closed ends providing a fluid-tight seal therebetween, the rapid withdrawal of said piston within said cylinder upon impinging engagement of said contacts effecting a vacuous condition between said closed sealed ends to cushion the return of said piston after such impingement and thus prevent bounce of said moving contact relative to said fixed contact.

9. For use in an electric switch having a pair of fixed contacts therein, a shock absorbing movable contact member for eliminating bounce resulting from rapid engagement of said fixed and movable contacts, said member comprising an insulated cylinder having a bore extending between an open end and a closed end therein, a piston having a closed end slidably mounted within said bore, a plate carried by said piston and extending transversely across the open end of said bore, a movable contact disposed on each end of said plate for engagement with said fixed contacts, a greasy material disposed between the closed ends of said bore and of said piston to provide a fluid-tight seal of said piston within said bore, and means for actuating said cylinder to impinge said movable contacts on said fixed contacts, said cylinder being actuated beyond said piston upon such impingcment expanding the space between said sealed ends and setting up a vacuous condition therein which absorbs the shock of said plate and eliminates bounce of said movable contacts thereon.

10. A movable contact member according to claim 9 wherein said piston is open. at its other end and is provided with a compression spring mounted therein to urge said closed end toward said closed bore end.

11. A movable contact member according to claim 9 wherein said piston comprises a close-fitting sleeve slidably mounted within said bore, a helical compression spring housed within said sleeve, said sleeve being adapted to be snapped forward against the action of said spring when said contacts impinge on engagement, such instantaneous action of said sleeve distorting greasy material disposed between said sleeve and said bore to cause a momentary damping action on said plate.

12. A device according to claim 8 wherein both said piston and said cylinder have an open end, a movable contact plate rigidly connected to said piston is disposed transversely of said cylinder, a recess is disposed at the open end of said cylinder extending between two lateral guides for said plate, a first and second stop for said piston, said first stop disposed in said cylinder to limit theforward motion of said piston by engagement therewith and said recess forming said second stop to limit the rearward motion of said piston by seating engagement with said plate.

13. A device according to claim 12 wherein a corm pression spring is mounted between the closed end of said piston and said first stop, said first stop extending through a slotted member connecting said contact plate to said piston, and said plate is urged by said spring to bear against said second stop to force said piston toward the closed end of said cylinder.

References Cited in the file of this patent UNITED STATES PATENTS Bea-rss et a1 May 23, Heller July 25, Besag et a1. Dec. 2, Hairy July 3, Aldasoro Dec. 18, Davidson Mar. 25, Parstorfer Apr. 29, Brauneck Dec. 29,

FOREIGN PATENTS Great Britain June 30,