US1942147A - Contact finger for relays - Google Patents

Description

Jan. 2, 1934.

.1. F. MERKEL CONTACT FINGER FOR RELAYS Filed Aug. 9, 1928 %%RNEY OH riziza &

Patented Jan. 2, 1934 UNITED STATES PATENT; OFFICE General Railway Signal Company,

ter, N. Y.

Roches- Application August 9, 1928. Serial No. 298,449

Claims.

This invention relates in general to contact fingers for relays, and has more particular reference to an improved contact finger particularly useful in relays such as used in railway signaling 5 and train control, and arranged to withstand wear and deterioration unusually well.

In railway signaling systems, it is found in practice that the available energy for operating relays is comparatively small, especially in the case of track circuits. On account of this limitation in operating energy, a relay, made so that it will operate satisfactorily under these conditions, is capable of exerting only a comparatively small pressure between its contacts, and likewise, a

1i comparatively small force tending to separate the contacts. It is highly desirable, however, that the contact resistance be as low as possible, on account of the length of the circuits, the comparatively low voltages available, and the number of relay contacts often included in such circuits.

The desired low contact resistance can be obtained by the use of metal to metal contacts, but in the practical use of relays, it has been found that such metal to metal contacts have serious disadvantages. In the first place, the circuits opened and closed by the relay contacts are often highly inductive, and upon separation of the contacts by the de-energization of the relay, arcs are generally drawn. This repeated arcing between the contacts in time results in pitting and roughening the contact surfaces to such an extent that the contact resistance is materially increased, and frequent renewal of these contacts is required.

Also, it has been found in some cases that the metal to metal contacts have actually been fused together, due to excessive currents, occasioned by lightning or other heavy current discharges through the relay. On account of the comparatively small force available for separating the contacts, only a slight fusing or sticking together of the contacts is suflicient to prevent them from separating and breaking the circuit. This fusing of the contacts together is highly objectionable, since the entire safety of the signaling system depends upon the contacts separating and breaking the circuit when the relay is de-energized.

On account of these objections to the use of metal to metal contacts, it has been proposedto make either one or both'of the contacts of graphite, carbon or some other highly refractory material. In the contact construction for relays quite commonly used at the present time, a button of carbon or graphite is made the fixed contact, while the movable contact is made of some highly conductive metal, such as silver. Such a construction is found to obviate the disadvantages attendant upon the use of metal to metal contacts, but introduces the objection of high and variable contact resistance. Practical experience has demonstrated that there is great difficulty in obtaining low contact resistance with this construction, or a contact resistance which will remain constant, it having been found that for some reason the contacting surfaces of the carbon or metal are in some way caused to deteriorate and 5 increase the contact resistance after the relay has been operated for a time.

With the above and other objects in view, it is proposed, in accordance with this invention, to provide a contact construction for relays which afiords the desired requisite of low contact resistance and at the same time prevents rapid deterioration or fusing of the contact members.

Further objects are to improve the construction, decrease the cost of manufacturing, and prolong the useful life, of devices of the character in question.

Further objects, purposes and characteristic features of this invention will appear as the description progresses, reference being had to go the accompanying drawing, showing, merely by way of example, and in no manner'in a limiting sense, two forms which the inventioncan assume. In the drawing:-

Fig. 1 is a top plan view of a contact finger 5 constructed in accordance with this invention.

Fig. 2 is a side elevation of such finger with parts broken away.

Fig. 3 is a bottom plan finger of Fig. 1.

Fig. 4 is a sectional view, on line 4-4 of Fig. 2, viewed in the direction of the arrows.

Fig. .5 is a fragmentary side elevational view, with parts shown in section, of a second form of the invention.

Referring now to the drawing, and first to Figs. 1-4 inclusive, the contact finger comprises two main parts, a carrier member 1, and a pivoted member 2, pivoted to the member 1 by mounting it on an arm 3 consisting of a struck out portion of the member 1 bent upwardly at right angles thereto as shown. The arm 3 has a strip 4 cut from each edge thereof and bent downwardly and away from the body of arm 3, in a curved formation, as best shown in Fig. 2, to form a bearing for the pivoted'member 2, which. latter is slotted to pass over the upper end of arm 3. The arm 2 is held in position against the strips 4, by a wire 5 passing through a hole in the arm 3 above the pivoted member view of the contact 2, and bent in the general form of an S as best shown in Fig. 1.

The members 1 and 2, as shown, are formed of channel sections of thin material, as aluminum alloy for example, and preferably by stamping.

The carrier member is furnished with a plurality of apertures 6, variously spaced and formed to permit of fastening it to various operating means. In the particular form illustrated, the carrier member is shown bolted to a pivoted armature 7, of a DC relay, but it can, of course,

be used in connection with any desired type of relay.

The end of the carrier member 2 is furnished with an aperture 6 for connection to a lead-in wire, unless such connection be made at a different point, as described below.

The carrier member 1 has its free end bent slightly downwardly, as at 8, and then upwardly, as at 9, the part 9 being received in an aperture 10 formed in a downwardly projected end 11 on the member 2. The part 8 is received in an aperture 12 in a spring arm 13, riveted at 14 to the member 1, and having riveted to it a contact tip 15 of a highly conductive material, such as a metal, or more specifically, coin silver or the like.

To the outer end of pivoted member 2, support ears 16 are riveted, as at 16 for pivotally supporting a movable front contact member 17, having upwardly projecting contact surfaces 1' and 19 for cooperating, respectively, with fixed front contact parts C and 53 respectively, formed, respectively, of a refractory material, such as carbon, and of a relatively low resistance material, such as ooin silver. The members C and S are connected together, and to a post 21, by a bolt or the like 20, and the post 21 is connected, in any desired or usual manner, to the top plate or any other fixed part of the relay.

The movable contact member 17 is formed of a low resistance material, such as coin silver, for example, and in an alternative form, to be described below, the portion 18 thereof is formed of a refractory material, such as carbon or the like.

The fixed contact portion C, can be of carbon, or graphite, or carbon impregnated with a small percentage of copper.

The contact member 17 is normally biased to the position shown, with the contact surface 18 higher than contact surface 19 by means of a leaf spring 22, fixed at 23 to the arm 2, and passing through an opening 24 in, or connected to, one side of contact member 17, whereby to normally bias it in a clockwise direction as viewed in the drawing.

Connected to the contact member 17, is a fiexible wire 25, preferably of stranded copper, and fastened by a screw or the like 26, to the con tact. This wire 25 is then looped through the pivoted member 2, at 27, passes through a downwardly extending end 28 on spring arm 13, and has its other end soldered to a connecting ring 29, or the like, adapted to be clamped to a terminal post of the relay in which this contact finger is to be used.

The pivoted member 2, at its inner end, has adjustably connected to it a threaded bolt 30, by means of a nut, spring washer, and arm 31. The threaded bolt passing down through an opening 32 in member 1. About this bolt opening the material is cut back to form three arms 32 which are bent downwardly at right angles to the member to form a cup for receiving a washer 83. The bolt 30 has a head 34, and carries between the head and member 1, a tension spring 35, which operates to bias the pivoted member 2 and its front contact 17, away from the end of member 1, with the part 9 of member 1 bearing against the lower edge of aperture 10 therein, (Fig. a) while the spring arm 13 is formed to be normally biased away from member 1, with part 8 of member 1 bearing against the upper end of aperture 12.

It is thus clear that movement of the carrier member 1, about its fixed end, in an upwardly or downwardly direction, between the front contact, and the usual back contact (not shown) will operate to press the movable front and back con tacts 17 and 15, toward the member 1, until further motion is prevented by the apertures 10 or 12, against the tension of spring 35 and spring a in 13.

Referring now to the modified form shown in Fig. 5, th fixed front contact is exactly the same as that just described, except that it is rotated 18d from that in 2.

The movable front contact is very similar to that already described, the contact being biased, however, by means of a weight 36, instead of the leaf spring 22 of the form first described.

operation of the two forms of invention, substantially identical, and accordingly the following description applies equally well to each.

By reason of the constructions embodying this invention, upon picking up of the contact finger, electrical contact is first made between metal and a refractory material, and then between two metals of low resistance. Since the circuit is established between metal and carbon, any spark or are which may occur does not cause fusing, and by the time the metal to metal contact is made, the arc has disappeared. Furthermore, while the relay is energized, the electrical contact is between metal and metal, so that the contact resistance is low and remains substantially constant. Upon the de-energization of the relay,

the circuit is broken between metal and carbon,

and any arc or damage.

In short, the contact construction embodying this invention has the combined desirable advantages of a metal to metal contact, and a carbon to metal contact, without their disadvantages. Furthermore the construction is simple and inexpensive, is easy to adjust, and is not likely to work out of adjustment.

As referred to above, the movable front conspark which may occur does no tact 1'7, can, if desired, be made to have the con tact portion 18 formed of a refractory material, such as carbon, copper impregnated carbon or the like, with the contact portion 19 of a metal such as coin silver. With such a construction, electrical contact is first made between two members of refractory material, and then between two metals of low resistance, and when contact is broken, the circuit is broken between two members of refractory material. In this manner, the form just described safeguards the contacts to an even greater extent than when the movable contact 1'7 is entirely of silver or other low resistance metal.

The above rather specific description of two forms which applicants invention can assume, has been given solely by way of illustration, and is not intended, in any manner whatsoever, in a limiting sense. Obviously, the invention can assume various different physical forms, and is susceptible of numerous modifications, and all such forms and modifications, are intended to be covered by this application as come within the scope of the appended claims.

Having described my invention, I now claim:

1. In a relay, a contact post having two fixed continuous contact members, one of refractory material and the other of a relatively low resist ance metal, a movable contact finger having a pivoted biased contact piece having two projecting horns, said contact piece initially engaging said refractory fixed member with one horn as the finger is moved to its attracted position, and being rocked by such engagement to engage against said metallic fixed member with the other horn.

2. In a relay, a contact post having two fixed continuous contact members, one of refractory material and the other of a relatively low resistance metal, a movable contact finger having a pivoted contact piece, an ofiset weight fixed to the contact piece to gravity bias it to an initial position, said contact piece initially engaging said refractory fixed member as the finger is moved to its attracted position, and being rocked by such engagement to engage said metallic fixed member without breaking said first contact.

3. A contact post for relays, comprising, a metallic post, an angular block of metal con nected to said post, and a block of refractory material connected to said metal block and in the electrical contact therewith.

4. A contact post for relays, comprising, a metallic post, an angular block of metal connected to said post, and a block of refractory material connected to said metal block, said two blocks being positioned to form a plane face having separate zones of metal and refractory material.

5. In a relay, in combination, a contact post having two fixed continuous contact members, one of carbon and th other of low resistance metal, a contact finger on a fixed pivot, a contact piece on the finger and fastened thereto by a fixed pivot and biased to an initial position, two spaced projecting portions on the contact piece, one of the projecting portions initially engaging the carbon member as the finger is rocked on its pivot, the contact piece being rocked on its pivot, against its biasing means, to engage its other projecting portion with the metal contact member while wiping its first projecting portion over the carbon member.

JOSEPH F. MERKEL.

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