US2789178A - Relay - Google Patents

Description

April 16, 1957 F. H. SHEPARD, JR 2,789,178

RELAY Filed Oct. 2'7, 1953 74 53 68 as M F 3 INVENTOR.

5244/05 H. Sue-meek United States Patent Ofiice RELAY Francis 11. Shepard, In, Summit, N. J.

Application October 27, 1953, Serial No. 388,535

3 Claims. (Cl. 200-113) My invention relates to relays and more particularly to an improved relay which is simple in construction, economical to manufacture, reliable in operation and which has a long life.

The useful life expectancy of relays of the prior art is limited in the number of make-and-breaks and it has long been a problem in the relay art to provide a relay having a relatively longer life. When relays of the prior art have been in use for a period of time, the contacts deteriorate, and as a result, the relay will not function properly. The contacts may weld together due to metal transfer between them with the result that the circuit completed by the relay will not be broken when the relay is tie-energized. On the other hand, the contacts may become pitted, again due to metal transfer, or the contact material may oxidize. Both these latter defects result in a poor contact and an increase in the resistance through the contact which affects the operation of the external circuit associated with the relay.

All the above-mentioned dilliculties may be traced to arcing between the contacts on the make or break. The arcing on the make is not so great a cause of difficulty since the cross-sectional area of the arc is always increasing as the contact is made, and the arc will not start soon enough to be as extended as is the are on the break. The are on thebreak on the other hand, is extended and attenuated before being completely broken so that it is concentrated on a small area of the contacts. The deleterious efiects of arcing would not so seriously affect the relay if there were only One make and one break on each operation of the relay. I have discovered, however, that in relays of the prior art contact is made and broken a number of times on each operation of the relay, thus creating and extinguishing a number of arcs. The multiplicity of arcs is caused by the moving contact bouncing away from the stationary contact a number of times, after having first engaged it. As a result of this rapid make and break the life of the relay is shortened considerably. I have invented an improved relay which ensures that the contact will be made sufiiciently gently in order to eliminate bounce, and I have provided damping means to damp vibrations which might be incident to making the contact.

One object of my invention is to provide an improved relay which is simple in construction, economical to manufacture, reliable in operation and which has a long life.

Another object of my invention is to provide an improved relay including means for preventing relative motion between the contacts during the operation of the relay once contact has initially been established.

Still another object of my invention is to provide an improved relay including damping means to absorb the impact of one contact on the other and reduce the tendency to bounce.

A further object of my invention is to provide an improved relay including means for ensuring that the engagement of one contact with the other is very gentle.

2,789,178 Patented Apr. 16, 1957 Other and further objects of my invention will appear from the following description.

In general my invention contemplates the provision of an improved relay including a base, a first contact element, shock-absorbing means mounting the first contact element on the base, a second contact element, spring means normally urging the second contact element in a direction to make contact with the first contact element and control means acting against the spring means to control the relative motion between the contact elements when the relay has been energized. In addition, I provide means for adjusting the control means so as to regulate its operation in governing the velocity of making contact.

In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

Figure l is a top plan view of my improved relay with the cover removed.

Figure 2 is a bottom plan view of my improved relay with the cover in place.

Figure 3 is a sectional view of my improved relay taken generally along the line 3-3 of Figure l with the cover in place and showing the relay associated with an external circuit to be controlled.

More particularly referring now to the drawings, I provide a base 10 made of a suitable insulating material such as Bakelite or the like. On top of the base, adjacent one end thereof, I mount a block of suitable insulating material 12 fixed to the base by means of screws 14 and formed with a V-shaped groove 16 in its upper surface. The block 12 is formed of insulating material which also provides a mechanical damping means which absorbs impact. Such a material, for example, is cellu lose nitrate plastic, such as Viscoloid, or the like.

A first contact element 18, which may be a short length of conductor, is imbedded in the plastic block 12 so as to extend across the V-shaped groove 16. The conductor 18 extends out through one side of the block 12 and runs to a binding post 20 having a nut 22 thereon. Binding post 20 extends downwardly through the base and has a nut 24 at its lower end to provide means on the base of the relay by which an external conductor may be attached.

The second contact element 28 is made of an appropriate conducting material such as silver, silver-plated copper or the like, and is fixed at one end by suitable means such as soldering to a leaf spring 30 held between a pair of washers 32 and 34 on a bolt 36 running through the base 10. I form the spring 30 of beryllium copper or the like, and the bolt 36 of appropriate conducting material to provide an electrical path between contact 28 and the bottom of bolt 36. Bolt 36 extends below the bottom of base 10 and is fixed in position on the base by a nut 38. A suitable knurled nut 39 is also threaded on the end of bolt 36 to provide a means for attaching an external conductor thereto. It is to be noted that instead of forming spring 30 and bolt 36 of conducting material I could provide a separate conductor running from contact element 28 to the external circuit, but preferably I employ the arrangement illustrated for convenience.

A milled head screw 40 is threaded into an internallythreaded opening 42 provided in base 10 so that it may be moved up or down therein. I insert one end of a length 44 of soft iron wire in a hole 46 near the head of screw 40 and wind a few turns of the wire 44 around the shank of screw 40. I fix the other end of wire 44 to spring 30 at a point adjacent the point to which contact 28 is fixed by suitable means such as a rivet 48. The end of screw 40 extends below the bottom of base and is threaded through a plate 50 carried by a stud 52 screwed into the base 10. Screw 40 may be threaded up or down in the opening 42 withoutrotating plate 50. A lock nut 54 is threaded on screw 40 over the plate 50 to hold screw 40 in the position to which it has been moved. Stud 52 extends below plate 50 and has a knurled nut 56 thereon by means of which an external conductor can be, connected to the stud 52. It is to be noted that I have selected the length of wire 44 to be made of soft iron which has a relatively high resistivity and a relatively large coeflicient of thermal expansion. I may, of course, select other suitable materials which have a relatively high resistivity and large coeflicient of thermal expansion. That is, the product of the resistivity and coeflicient of thermal expansion of the material selected should be high as compared with other materials.

I provide a cover 58 for my improved relay which is secured to the base 10 by any suitable means such as screws 60 threaded into the base.

An example of a circuit to be controlled by my improved relay is illustrated in Fig. 3. A conductor 62 is fixed to a lug 64 secured to binding post 20 by nut 24 on base 10. The other end of conductor 62 is attached to the device 66 to be controlled which may be, for .example, a motor. A conductor 68 is fixed to 8. lug 70 which is held in contact with bolt 36 by the nut 39. The other end of conductor 68 is connected to a source of energy for the relay such as a battery 72. A switch 74 of any suitable design is connected to stud 52 by a lead 76 fixed to a lug 78 held on stud 52 by nut 56. A common conductor 80 connects the device 66, the battery 72 and the switch 74 in parallel. It is to be understood, of course, one source of potential may control the heating of the wire 44 and another source of potential may be controlled by contacts 18 and 28.

It is to be noted that spring 30 normally tends to urge contact 28 to the position indicated by the broken lines in Figure 3 where it engages the contact 18. However, I adjust screw 40 to a position where the length of wire 44 holds spring 30 and the associated contact 28 to the full line position shown in Figure 3 where movable contact 28 will not engage stationary contact 18.

In use, the operator closes the switch 74. As a result current will flow from battery 72 through conductor 68, through bolt 36, the spring 30, the wire 44, down through screw 40, across strip 50, through stud 52, conductor 76, through the switch 74 and back to the other side of battery 72. Owing to the fact that the resistance of wire 44 is relatively high, the temperature of wire 44 will be raised by the current flow. Since it has a relatively large coefficient of thermal expansion, it will lengthen, permitting contact 28, which is biased downwardly by spring 30, to engage contact 18, thus completing the circuit to the device 66. Current to the device will flow through conductor 68, bolt 36, spring 30, contacts 28 and 18, down through binding post 20, through conductor 62, through device 66 and back to the battery. It will be appreciated that I may adjust the position of screw 40 so that the action of spring 30 is controlled to any degree and the engagement between contacts 28 and 18 will be made with a very small relative momentum. This will largely eliminate the bounce found in relays of the prior art.

It will be observed that if the angle subtended by spring 39 and wire 44 adjacent rivet 48 is small, a very slight change in the length of wire 44 will produce a comparatively large motion of the contact 28. Increasing the angle embraced between wire 44 and spring 30 reduces the motion resulting from a change in the length of the wire 44. Stated differently, the angle lying between wire 44 and spring 30 is a measure of the sensitivity of the relay, the smaller this angle is, the greater the sensitivity.

In order to set the operating point of the relay, it is necessary to adjust the initial P tion o the Contact 2 with respect to contact 18. The screw 40, as pointed out above, enables this adjustment to be made. If the screw is threaded downwardly into the base, the distance between the point where the wire 44 leaves the shank of the screw and rivet 48 will tend to decrease. I desire to maintain sensitivity once it is adjusted. In order to accomplish this, therefore, I continue the threads of the screw 40 so that as the distance decreases between the head of the screw and the base 10, the wire 44 will be wrapped around the screw and raised an equal amount. In this manner the angle between wire 44 and spring 30 will be maintained at a constant, thus maintaining the sensitivity of my relay while permitting the adjustment of the initial separation between contact 28 and contact 18.

As mentioned hereinbefore, the block 12 carrying contact 18 is formed of some material such as a cellulose nitrate plastic. One of the properties of such materials is good shock absorption. Accordingly, the energy of momentum of contact 28 and spring 30, which is kept low through low velocity of movement, will tend to be absorbed by block 12 through contact 18 without bounce when the contacts engage.

I may also provide increased sensitivity for my relay by chrome plating and highly polishing the length of wire 44. As a result of this treatment, radiation of heat from the wire will be reduced. The heat generated by a given current flow through the wire will heat the material to a higher degree and cause a greater elongation of the wire. Thus the relay will be fixed to close with less current in the wire or more rapidly with a given current. Similarly the heat will be retained for a longer time and the relay will be slower to open when the contact made by switch 74 is broken. 0n the other hand, I may blacken wire 44 to increase radiation and make my relay close more slowly and open faster.

The current drawn by the' iron wire circuit when switch 74 is closed will not affect the current through the device 66 to be controlled to an appreciable extent, because the switch 74 and the device 76 are connected in parallel across a voltage source having negligible resistance. Since this is so, the two circuits may be considered independent and the current through the device to be controlled determined within close limits.

Thus it will be seen that I have accomplished the objects of my invention. I have provided an improved relay which is simple in construction, economical to manufacture, reliable in operation and which has a long life. My improved relay eliminates the disadvantages of the prior art relays in that bouncing between the contacts of the relay is reduced to a I have provided means by which the relative motion between the contacts prior to closing is closely controlled so that the energy momentum of the moving contact will be a minimum at the time of contact. In addition, I have provided shock absorbing means which will absorb any energy due to momentum which might be present when the contacts engage. Differential adjustment is provided whereby very close control is possible and means are provided for regulating the sensitivity of the relay. Since the bounce found in relays of the prior art has been minimized, welding, pitting and oxidation of the contacts will be a minimum, thus ensuring an extremely long life for my improved relay.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made within the scope of my claims without departing from the spirit of my invention. It is therefore to be understood that my invention is not to be limited to the specific details shown and described. 7

Having thus described my invention, what I claim is:

l. A relay for controlling the operation of an external circuit including in combination a base, a first contact carried by said base, a second contact normally out of engagement with the first contact, biasing means normally urging said second contact in a direction to engage the first contact with the second contact to establish said external circuit and control means acting against said biasing means to control the velocity of relative movement between the contacts in a direction toward each other to establish said external circuit when the relay is energized, said control means including a length of wire connected at one end to said resilient means and an adjusting screw carried by said base, the other end of said wire being connected to said screw to be disposed at a particular angle with respect to said base, said wire being wrapped around said screw when said screw is screwed into said base to adjust said length whereby said angle remains substantially constant.

2. A relay as in claim 10 in which said length of wire is formed of a material whose product of its resistivity and coeflicient of thermal expansion is large.

3. A relay as in claim 1 including shock absorbing means for mounting said first contact on said base.

References Cited in the file of this patent UNITED STATES PATENTS Brown July 6, Phelps May 11, Shoenberg Jan. 21, Wilkins Oct. 25, Schmidinger Mar. 23, Schmidinger Oct. 18, Lacey July 18, Schramm Dec. 17, Hottenroth May 27, Schmidinger Oct. 27, Leuthold May 18, Schmidinger June 8, Oleson Nov. 8, Schenck Oct. 31, Sitzer June 9, Boddy Mar. 16,

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