US2924684A - Contact device - Google Patents

Description

Feb. 9, 1960 P. H. E. CLAESSON 2,924,684

CONTACT DEVICE Filed March 8, 1956 F1 7. .5 INVENTOR PER HARRY ELIAS CLAESJON ATTORNEYS United States Patent CONTACT DEVICE Per Harry Elias Claesson, Danderyd, Sweden Application March 8, 1956, Serial No. 570,331

Claims priority, application Sweden March 11, 1955 9 Claims. (Cl. 200-104) The present invention relates to contact devices of the kind comprising contact springs and being adapted for so called indirect operation. Contact devices of this kind have found wide use in electromagnetic relays, even in realys of the polarized type, and a relay may comprise a plurality of such contact devices, the contact springs being arranged in one or more groups.

By indirect operation I mean a mode of operation according to which a contact closure is effected by two contacts being moved into engagement due to the action of the spring tension in at least one of the contact springs which is released e.g. by the energization or release of a relay. Thus no external forces are acting upon the contact springs during the closing process, whereas external means are used to keep the springs out of engagement when in non-operated position. In practice one (called the movable spring) of the springs of a contact device for indirect operation is pre-tensioned or biased sothat it strives to move its contact end towards the contact end of the other spring (called the fixed spring), and in non-operated condition the movable contact spring is kept separated from the fixed contact spring by means of a lifting stud which may be operated e.g. by the armature of a relay.

Hitherto contacts with indirect operation have been used for the purpose of suppressing contact vibrations when two contacts strike against each other (are closed). The springs to which the contacts are attached, have been made relatively long with a low natural frequency of vibration whereby the contacts have approached each other relatively slowly so that the contact vibration at the first moment has been suppressed. Furthermore, the energy from detrimental vibrations of the movable contact springs has been dissipated due to friction between the contacts and/or between the contact springs of a spring set so that it has been possible to eliminate even slow contact vibrations due to the low natural frequency of vibration of the contact springs. However, the abovementioned design of the contacts also involves certain drawbacks. Thus the contact devices become very susceptible to accelerations and retardations and to shakings within the resonant frequency range of the device, and consume large space and material and require considerable forces in order to yield rapid make and break functions when the contacts are removed from each other.

It is an object of the present invention to provide a contact device of the kind defined above which has no or little susceptibility to accelerations and retardations and in which contact vibrations and bouncing are effectively suppressed.

The contact device according to the invention is foremost characterized by the contact springs being pre-tensioned to such extent that they yield a force at the contact points amounting to at least 30 times, for example 50 times, the weight of the free end of the spring inelusive the contacts.

It will be easily understood that a contact device having this characteristic will have little susceptibility to accelerations and retardations, but it is by no means obvious that it will also be free from contact vibrations and bouncing on closure, for there is no simple relation between liability to contact vibrations and the ratio of the contact pressure to the weight of the free ends of the contact springs. However, I have found that a contact device having the abovementioned characteristic shows a surprisingly high freedom from contact vibrations. The movements performed by the contacts during a closing operation from the moment the contacts first touch each other till they have come to a state of rest or equilibrium, depend on a large number of factors, and therefore it has not been possible to explain theoretically the freedom from contact vibrations which is characteristic of the contact device according to the invention.

When the contact on the movable contact spring strikes the contact on the fixed contact spring, an elastic deformation of the contacts occurs, and thereby forces arise which strive to separate the contacts again. The movements of the contacts after the impact will not however be determined solely by the elasticity of the contacts but also to a high degree by the properties of the springs to which they are attached. On the contact closure the fixed contact spring will be deflected from its normal position and thereby exert a force on the contact on the movable spring which force has a direction opposite to the initial direction of movement of said contact. Furthermore, that part of the movable contact spring which is situated between the fixed end of the spring and the contact, will continue its movement after the contacts have first come into engagement, so that the movable spring will have a deflection between the fixed end and the contact. This deflection produces a force which also acts upon the contacts and may be considered as an addition to the contact pressure which exists between the contacts when they have reached the state of rest. The continued movements of the contacts after their elastic deformation has reached its maximum, will depend on these forces, and the mutual relations of these forces probably determine whether the contacts will reach the state of rest with or Without repeated interruptions and closures. There are indications that the contacts will reach the state of rest without interruptions on the condition that the pressure existing between the contacts when their elastic deformation has reached its maximum, does not exceed the sum of the force causm by the abovementioned deflection of the movable contact spring and the contact pressure existing between the contacts when they have come to rest, but it has not been established to a certainty that the fulfilment of this condition is necessary or suflicient in order that contact vibrations shall be avoided. The movements of the contacts with respect to each other will of course also be dependent in a high degree on the natural frequencies of vibration of the contact springs and the phase angles of the vibrations occurring during the closure period. It has proved that the liability to contact bouncing is reduced if the natural frequency of vibration of the fixed contact spring is equal to or somewhat higher than that of the movable spring.

The contact pressure existing between the contacts when they have come to rest in engagement with each other, is determined by the dimensions and the material of the contacts and the contact springs, the initial tension of the springs and the distance between their fixed ends. These factors also determine the movements of the contacts during the closing process, and it is obvious that if a contact device is designed with a view to have a certain ratio of the contact pressure to the weight of the free ends of the contact springs, the movements of the contacts during the closing process will also be determined thereby, although the relation between the closing process and the said ratio is extremely complicated and difiicult to establish theoretically. However it has been shown experimentally that if the contact device is designed in accordance with the present invention, it will have a great freedom from contact vibrations during the closing period.

In practical embodiments of the invention the contact springs have a small length and thickness and are made of a material allowing a pre-tensioning of the springs to such extent that the contact pressure will be at least 30 times, e.g. 50 times, the weight of the contacts plus the weight of the free end of the movable contact spring. In contact devices the contact springs of which are liable to fatigue a spring material is required which allows comparatively high bending stress e.g. steel or beryllium copper.

In an embodiment of the invention the contact springs are made of beryllium copper, steel or other material allowing a high bending stress and having small liability to fatigue. The springs have a free length of to 25 millimetres and a diameter of 0.2 to 0.6 millimetre in the case that they have a circular cross section or a corre sponding cross sectional area in the case that they have rectangular cross section. The contact pressure is 10 to 20 grams. It is obvious that a contact device according to the invention will require less material and space than previously known contact devices of similar type.

The invention is illustrated in the accompanying drawing in which Figure 1 is a side elevation of a relay embodying the invention.

Figure 2 is a front view of a contact spring assembly of another relay embodying the invention.

Figure 3 is a section taken along line 33 in Figure 2.

Figures 4 and 5 show in top plan view and side view respectively another embodiment of the contact spring assembly in a switching device embodying the invention.

In Figure 1 the magnetic circuit 1 of a relay and its armature 2 which is preferably balanced with respect to its fulcrum 40, is shown schematically.

The contact springs are designated 3--7, the springs 3-5 forming a change-over contact and 6-7 a make contact. Contact springs 3-7 may be in the form of wires (see Figures 45) and are secured to a holder 8 in some known manner. The movable contact springs 3, 5 and 6 are actuated by means of a stud 9 attached to armature 2. Contact springs 3 and 5 are pre-tensioned towards contact spring 4. In the same manner spring 6 is pre-tensioned towards spring 7. Spring 10 acts upwardly on stud 9 so that the contacts on springs 3 -4 and 6-7 are normally kept separated. The armature has a stop 11 which determines its maximum rotation. When the relay is energised, the force exerted by springs 10 and 5 is overcome so that the make contacts on springs 3-4 and 6-7 are closed and the contact between springs 4-5 is broken. The fixed contact springs 4 and 7 should be more rigid than the movable springs which can be attained in known manner either by adequate dimensioning or by means of supporting studs.

Since the actuating stud 9 is attached to the armature, the tension of spring 10 is utilized not only for the actuation of the contacts as described above but also to keep the armature in the home position for the event that the armature is not wholly balanced and the relay is subjected to heavy accelerations or retardations in the case that it is mounted in vehicles or movable objects. The downwardly projecting part 41 of stop 11 balances the stud 9.

Figures 2 and 3 illustrate how the invention can be applied to such types of relays wherein the contact springs are attached to a holder of the tube socket type. Figure 2 shows a relay of this type in front view, and Figure 3 shows a section taken along line 3--3 in Figure 2. Only those parts of the relay which are necessary for the understanding of the invention, have been shown on these figures. Thus th armature and the ne g z ng coil h v been omitted. The contact springs can be fastened to the socket in known manner either by moulding orinserting them in holes or soldering or welding them to pins which in turn are fastened to the socket 12. In Figures 2-3 contact springs 13-24 are shown forming four change-over contacts. The movable springs are running through holes in a disc. 25 which is rotated in known manner about its centre when the relay is energised. The tension correspondin to. that obt f Spring 10 in Figure 1 can be attained in the embodiment according to Figures 2-3 by means of one or more springs (not shown in Figure 3).

In Figures 4-5 an embodiment of the invention is shown having contacts formed by wires. Onlyone change-over contact having springs 26--28 is shown. The movable stud 9, the holder 8 and spring 10 have the same designations as in Figure 1 and are analogous to the corresponding parts in Figure l.

The contact springs formed by wires are U-shaped and fixed as shown in the figure so that the greatest possible rigidity is obtained in a direction at right angles to. their direction of travel when actuated. The fixed springs have preferably a width difiering from that of the movable springs. Thus in the figure the fixed and comparatively rigid spring 27 is shown having a larger width than the movable springs 26 and 28. Hereby contact points 29 and 30 are obtained between springs 27 and 28.

A suitable contact material is, attached in known mannor to the contact points. Alternatively a material can be chosen which is suitable both as spring material and contact material which results in great simplicity of design as will be seen from Figures 4 and 5. An alloy which can be used both as spring material and contact material is described in Swedish Patent No. 125,889 and consists of at least 50% silver or other noble metal, at least 0.10% and at most 10% beryllium, the rest being metals belonging to the first and/or eighth group, of the periodic system, e.g. copper, nickel, cobalt or iron,

The abovementioned U-shaped, Contact springs of wires are very suitable for any types of relays and other con-. tact devices. The fastening of the wires te the holder 8 is preferably effected either by moulding or by clamping the wires between plates having grooves for guiding the wires. The wires may be provided with loops at the soldering terminals in order to facilitate soldering Having now particularly described and ascertained the nature of my invention and in what manner the same is to be performed, I declare that what I claim is;

1. A switching device comprising in combinationan energizing coil, a magnet core, an armature, fixed contact springs, movable contact springs, said movable contact springs being pre-tensioned so that their free ends are biased towards fixed contact springs and to yield at the contact points a force amounting to at least 50 times the weight of the movable part of the contact spring inclusive the contacts; a pre-tensioning spring; and contact actuating means operable to move the free ends of the movable contact springs away from the fixed contact springs, said actuating means being operatively associated with said armature and said preetensioning spring and the pre-tensioning spring being tensioned to exert a force upon the contact actuating means which force is eppositely directed to the force exerted upon the contact actuating means by the armature when attracted.

2. A switching device as claimed in claim 1 wherein said armature is balanced with respect to its. fulcrum.

A s i g d ic co pri n t least one fi ed contact spring, and at least one cooperating movable contact spring, said contact springs consisting of l. .I,-.shaped wires with portions thereof engageable to' form contact p in idm ab t t p in bein pre-tsn nss so that its free end is biased towards said fixed contact p n to Yi d atthc cn c po n s a forc amm t us to at least 50 times the weight of the movable of the contact.

t A switching devi e as. c aimed in. 3, wh re said fixed contact spring has a width differing from that of the movable contact spring.

5. A switching device as claimed in claim 3, wherein the fixed contact spring has a length difiering from that of the movable contact spring.

6. A switching device as defined in claim 3, further comprising a pre-tensioning spring, and contact actuating means operable to move the free end of the movable con tact spring in a direction away from the fixed contact spring; said pre-tensioning spring being tensioned to exert a force upon the contact actuating means oppositely directed to the operating movement of said contact actuating means.

7. A switching device as defined in claim 3, wherein the natural frequency of vibration of the fixed contact spring is somewhat higher than the natural frequency of vibration of the movable contact spring.

8. A switching device having fixed contact springs and movable contact springs arranged for indirect operation, wherein said contact springs are pre-tensioned so as to yield at the contact points a force amounting to at least 50 times the weight of the movable part of the contact spring inclusive contacts, and wherein the natural frequency of vibration of the fixed contact springs inclusive their contacts is somewhat higher than the natural frequency of vibration of the movable contact springs inclusive their contacts.

9. A switching device comprising fixed contact springs and movable contact springs arranged for indirect operation, wherein said contact springs consist of U-shaped wires made of an alloy consisting of at least 50 percent silver, at least 0.1 and at most 10 percent beryllium, the rest consisting of metals belonging to the first and eighth group of the periodic system, and wherein the contact springs are pre-tensioned to yield at the points of contacts a force amounting to at least 50 times the weight of the movable part of the contact spring.

References Cited in the file of this patent UNITED STATES PATENTS Johnson Ian. 8, 1929 2,178,656 Swenson Nov. 7, 1939 2,282,687 Vigren et al May 12, 1942 2,290,725 Bartels et al. July 21, 1942 2,339,610 Baker Jan. 18, 1944 2,368,201 Clare Jan, 30, 1945 2,393,901 Haigh et al Jan. 29, 1946 2,562,091 Harrison July 24, 1951 2,577,468 Knos Dec. 4, 1951 2,587,458 Fritts Feb. 26, 1952 2,590,996 Miloche Apr. 1, 1952 2,612,367 Blomqvist Sept. 30, 1952 2,616,993 Koehler Nov. 4, 1952 FOREIGN PATENTS 125,889 Sweden Aug. 30, 1949 730,125 Great Britain May 18, 1955

Images