US3885115A - Switch-over contact - Google Patents

Abstract

A switch-over contact for relays or switches in which the contact forces can be easily, yet accurately adjusted without costly adjustment operations. According to the invention, the two contact arms of the switch-over contact have the form of an arc, i.e., they are elastically bent in the undeformed or unstressed state, but assume essentially the form of a straight line segment in the deformed or stressed state. The switch-over assembly comprises a pair of fixed contact members, and a pair of resilient contact arms, the fixed ends of the arms being mounted at substantially a common point in the device, the arms being bent to substantially a straight line positioning the free ends of the arms between the fixed contacts. An armature actuates to move the free ends of the arms into and out of contact with the fixed contact members.

Description

United States Patent 1 Schrotter SWITCH-OVER CONTACT [75] Inventor: Wolfgang Adalbert Schrotter,

Unterhaching, Germany [73] Assignee: Bunker Ramo Corporation, Oak

Brook, [11.

[22] Filed: Nov. 14, 1973 [21] Appl. No.: 415,652

[30] Foreign Application Priority Data Nov. 15, 1972 Germany 2256044 [52] US. Cl, 200/245; 200/247; 335/192; 335/200 [51] Int. Cl. H0111 1/50 [58] Field of Search 335/192, 193, 200, 185, 335/124, 187, 107; 200/245, 246, 247

[56] References Cited UNITED STATES PATENTS 2,812,406 11/1957 Egan 200/268 2,852,639 9/1958 Nelsen 335/124 3,020,365 2/1962 Neenan 200/245 3,146,327 8/1964 Ohki et a1. 200/246 3,165,607 1/1965 Hogan 335/187 1 May 20, 1975 Primary Examiner1-laro1d Broome Attorney, Agent, or Firm-D. A. Bair; F. M. Arbuckle 57 ABSTRACT A switch-over contact for relays or switches in which the contact forces can be easily, yet accurately adjusted without costly adjustment operations. According to the invention, the two contact arms of the switch-over contact have the form of an arc, i.e., they are elastically bent in the undeformed or unstressed state, but assume essentially the form of a straight line segment in the deformed or stressed state. The switchover assembly comprises a pair of fixed contact members, and a pair of resilient contact arms, the fixed ends of the arms being mounted at substantially a common point in the device, the arms being bent to substantially a straight line positioning the free ends of the arms between the fixed contacts. An armature actuates to move the free ends of the arms into and out of contact with the fixed contact members.

7 Claims, 4 Drawing Figures RUENTED 3 885,115

SHEET 2 [IF 2 Fig. 2

SWITCH-OVER CONTACT The present invention relates to a switchover contact for relays or manually operated switches with at least one fixed contact and at least one resilient contact arm cooperating with a second fixed contact.

Known switch-over contacts, for example those used in relays, have the form of a simple, flat spring, and are moved by an armature via an insulating member from the one position (rest position) to another position (closed position) and vice versa, with the springs undergoing certain uncontrollable elastic deformations in the final switched position, i.e., when contact is established. In these known devices, expensive adjustments to the contact force required for low contact resistance are necessary. Another disadvantage of prior art switch-over contacts results from the fact that in the switched position, the switch-over contact is constantly forced into locked position by the armature, so that vibrations or bouncing motions of the armature per se are transferred to closed contacts.

Apart from these type contacts, there have been used switch-over contacts comprising two spaced leaf springs. These models are free of the above-mentioned shortcoming of a transfer of armature vibrations and armature bouncing to the closed contact arm. However, even these switch-over contacts are not free of uncontrollable elastic deformations of the respective contact arm when contact is established under pressure from the armature, which means that adjustments must be made.

Another mechanical disadvantage of these two known types of switch-over contacts results from the conventional symmetric, more or less extensive, slitting of the contact arm, i.e., of the leaf springs. Slitting makes available two contact points on each contact side of a contact arm, which substantially increases the probability of establishing reliable contact. But it is a shortcoming of this configuration that the determination of exact spring characteristics (e.g. force-path diagram) is very difficult, because various spring cross sections must be considered over the free length of the spring. The two sections of a symmetrically slitted leaf spring do not have identical characteristics of vibrations and bouncing motions, so that no precise valuation of the performance characteristics can be readily obtained.

Particular difficulties are encountered in the design and adjustment of switch-over contacts in miniaturized relays of the type disclosed in German Pat. No. 1639 417. In this relay, the ends of the contact springs are bent and protrude as soldering terminals for attachment of the relay to printed circuit boards. Since for the sake of space reduction and for improved protection, the contacts are mounted inside the coil carrier, the contacts must extend beyond the two faces of the coil carrier to enable them to be bent after assembly of the relay. If the contacts are bent before assembly, they must be mounted on separate insulating members, so that they can be inserted into the coil carrier from both sides, which implies that the contacts cannot be arranged with the desired degree of accuracy.

If, on the other hand, the contacts are mounted on a single insulating member, the contact positions are well defined. but several contact ends must be bent after inserting the insulating member into the coil carrier. If, for the purpose of obtaining a certain terminal pattern,

the ends of a resilient contact must be bent, the elastic properties of the leaf springs cannot be optimized, since the material comprising the leaf ends would render the ends too hard for bending.

The problem of exactly predetermining the elastic deformations of resilient contacts, and hence the contact forces acting upon closed contacts, is particularly important in the case of miniaturized relays. This is evidenced by the fact that the gap width (measured in the direction of motion of the switch-over contact) between the fixed contacts amounts to typically 1.6 millimeters (about 0.06 inch). Proper functioning of a relay of this type necessitates certain minimum contact forces which must be surpassed in order to avoid excessive contact resistances.

The small dimensions of the contacts, the required contact forces, and the demand for high switch-over frequencies call for materials of maximum strength, which, after hardening or tempering, can no longer be sufficiently deformed as contacts.

Precise presetting of the elastics deformation is also hampered by the increasing influence of acceptable thickness tolerances (about 0.01 mm) and edge zones of increased strength, e.g., edges of cut or slotted pieces, when the spring cross section decreases. For example, a 0.01 mm tolerance of a nominal spring thickness of 0.1 mm implies contact force tolerances of about 30%.

It is the goal of the present invention to create a switch-over contact of the above-described kind, in which the contact forces can be easily, yet accurately adjusted without costly adjustment operations.

According to the invention, the two contact arms of the above-described switch-over contact have the form of an arc, i.e., they are elastically bent in the undeformed or unstressed state, but assume essentially the form of a straight line segment in the deformed or stressed state.

This switch-over contact configuration has the advantages that the spring characteristics, i.e., the forcepath diagram, is known and that therefore the contact forces can be precisely predicted. Elastic deformations can therefore be accurately controlled in the critical state of contact establishment so that laborious and, hence, costly adjustments need not be made. The contact forces can be determined by a single reference measurement and can be checked, after assembly of the contact set, with an optical test in which the contact arm is visually verified to be straight in the closed position of the contact set. Moreover, knowing the stress characteristics of the contact arm when in the straight position, determination of the point at which the armature becomes effective through an actuating member at the time of contact interruption can be made. This, in turn, allows optimization of the design of the armatureresetting spring and, hence, of both the magnetic flux pattern and the relay coil.

According to a preferred embodiment of the invention, in the undeformed state, two contact arms are preferably areed in opposite directions, but mounted in a position symmetric with respect to a common symmetry line. This arrangement results in a configuration in which each contact arm upon closing disengages from the armature at the instant contact is established with the fixed contact, so that armature motions no longer affect the closed contact.

When the two contact arms are in the form of blades or elongated leaves and mounted together at one end of each arm, the contact arms enclose an angle with the common symmetry line in the deformed straighf state. The spacing of the deformed contact arms can therefore be precisely predetermined; the spacing elim inates any interaction between the contact arms and, hence, any influence of the armature upon closed contacts, provided that the armature acts upon the contact which is open.

Moreover, it has proved advantageous to provide slits between the free end and the point at which each contact arm is mounted, so that individual tongue-like sections are formed on each contact arm. This con struction reduces the spring force to some extent but provides the essential advantage of an elastic deformation which can be accurately predicted for a constant cross section along the free spring length of individual tongue sections.

In an alternate embodiment of the invention the clamping points of the tongues of each contact arm are arranged in offset relationship with respect to the longitudinal direction of the contact arm. The tongues are then of different spring characteristics, and hence respond differently to vibrations and bouncing motions. This. in turn, increases the probability that the two tongues do not simultaneously interrupt the contact when contact bouncing occurs. The total time of the backward bouncing motion is therefore determined by the bouncing of the tongue which is less prone to bouncing. Naturally, when the elastic bending characteristics of the tongues are determined in the unstressed state, the different free lengths of the springs must be appropriately taken into account.

The advantage of different bouncing responses can also be obtained by providing tongues with different thicknesses and/or widths.

Particularly in the case of miniaturized switch-over contacts, it has proved advantageous to use contact arms which consist of one piece made of a resilient material (and which also include contact tongues if desired) and of another piece made of a relatively easily bending material and serving as soldering terminal. The two piece configuration provides the advantage that the contact-arm portion establishing contact consists of a material suitable for leaf springs which can given optimal spring characteristics by hardening, whereas the contact-arm portion serving as soldering terminal can be easily bent after hardening of the spring material and after assembly and adjustment of the individual contacts.

The contacts are preferably made of two-metal material for leaf springs; the resilient material is composed of beryllium bronze and the relatively easily bending material consists essentially of brass.

The following description of the invention is to be understood with reference to the appended drawings showing preferred embodiments. In the drawing:

FIG. 1 is a cross section side view of a miniaturized relay containing a switchover contact according to the invention.

FIG. 2 is a side view ofa switch-over contact in which the contact arms are shown in the unstressed state,

FIG. 3 is a top view of the switch-over contact shown in FIG. 2, with an additional clamping point provided for one of the tongues.

FIG. 4 is a top view of the switch-over contact of FIGS. 2 and 3 and shows the contact in the unfolded state.

FIG. 1 shows a relay which is generally denoted by 22 and comprises a coil 6 carrier with windings 15. Two pole shoes 23 and 24 are mounted inside coil 6 and extend in longitudinal direction of the coil body.

Resting contact (normally closed contact) 3, main contact (normally open contact) 4, and the actual switch-over contact, which is generally denoted by 20, are mounted along with holder 27 on a common insulator 7. Switch-over contact 20 consists of two contact arms 31, 32 in the form of elongated flat elements which carry contact ribs 25 and 26 on their opposite sides and on the ends facing the resting contact 3 and the main contact 4, respectively. Contact arms 31 and 32 are clamped at point 5, bent at a right angle with respect to the longitudinal axis of coil 6 at bend 37 opposite contact ribs 25 and 26, and formed as soldering terminals 8 and 9 protruding from the relay.

Relay 22 is shown in the rest state (no excitation) in which armature 16 has disengaged pole shoe 24. The armature is transferred into this position by armatureresetting spring 14. At the movable end 39 of armature 16, there is mounted an actuating member 13 provided with a U-shaped cut 28 shown in FIG. 1 with the legs 41 and 43 of the U facing out of the sheet. The opposite internal faces 29 and 30 of the U-shaped cut embrace contact arms 31 and 32.

Details of the switch-over contact and of contact arms 31 and 32 are shown in FIGS. 2 through 4. As can be inferred from FIG. 4, contact arms 31 and 32 are made of a split leaf, e.g., by slotting, and are joined along line of symmetry 33. Naturally, the contact arms can be produced as separate parts of different shapes, if desired. Contact arms 31 and 32 are bent along line of symmetry 33 so that apertures 34 and 35 are aligned and result in an attachment opening 10, as shown in FIG. 3.

Contact arms 31 and 32 can be made from a single material, e.g., of a material normally used for leaf springs. However, it it advantageous to use two-metal strips, one section of which consists of a resilient material such as beryllium bronze, whereas the other section is made of a material which can be easily bent, such as brass. The contact-arm configuration is such that the transition point between the two different metals is situated near attachment opening 10. The ends which carry contact ribs 25 and 26 are formed by leaf springs 1 and 2, whereas soldering terminals 8 and 9 consist of the material which can be easily bent. Two-metal components of this type are readily available on the market and need not be described in detail.

As can be inferred from FIG. 2, in the unstressed state, leaf springs 1 and 2 are arced toward opposite sides of line of symmetry X so that a continuous arc results between clamping point 5 and contact points defined by Contact ribs 25 or 26. This configuration has the advantage that the elastic deformation of the two leaf springs 1 and 2, and hence the contact forces exerted by these springs, can be exactly predetermined for the stressed state in which the springs assume the form of straightline segments.

When leaf spring 1 is transferred from the unstressed position shown in FIG. 2 into a stressed straight" position, the straight position is reached while leaf spring 1 includes an angle with the axis of symmetry X. When this angle is taken into account in the determination of the straight and stressed state of a leaf spring, a welldefmed distance between the two leaf springs is observed in the stressed state. Though this distance is smaller than the distance usually employed in contact devices, the resulting gap eliminates any interaction between leaf springs 1 and 2, and hence any influence of armature 16 upon the closed contacts via the open contact. The distance between the ends of the two leaf springs shown in the stressed state is denoted by A in FIG. 1. This small distance between leaf springs l and 2 facilitates a reduction of the distance between resting contact 3 and main contact 4, which is essential for miniaturization.

ln the device shown, switch-over contact is mounted in relay 22 by affixing contacts 3 and 4, along with switch- over contact arms 31, 32, on a common insulator 7, whereupon insulator 7 is inserted from the right side (FIG. 1) into coil 6. Since soldering terminals 8 and 9 are made of a relatively soft, flexible material, the soldering terminals can be easily bent without any damage to the assembled device or changes in the contact forces of the switch-over contact.

Relay 22 functions as follows:

Relay 22 is shown in the rest state (no excitation) in FIG. 1. In this position, lower leaf spring 1 bears against rest contact 3, leaf spring 1 being in the stressed, straight state and acting via contact rib 26. The upper inner face 29 of U-shaped cut 28 on actuating member 13 prevents upper leaf spring 2 from engaging main contact 4. When relay 22 is excited, armature 16 is drawn to pole shoe 24 and releases upper leaf spring 2 which, under the influence of its intinsic spring force, bears against main contact 4 in the stressed, straight state. Lower inner face 30 of U-shaped cut 28 bears against lower leaf spring 1 at point 12 and, hence, overcomes the spring force of leaf spring 1 and removes the same from resting contact 3. U-shaped cut 28 is preferably dimensioned, between the legs 41, 43 of the U, so that contact rib 26 is lifted from resting contact 3 before contact rib touches main contact 4 (switchover mode), or that the opposite function is obtained (sequence reversal mode). When the relay is deenergized, armature 16 is returned by armatureresetting spring 14 into the original position, whereupon lower leaf spring 1 and lower inner face of cut 28 on actuating member 13 move downward. Upper inner face 29 of actuating member 13 then contacts upper leaf spring 2 and pushes contact rib 25 away from main contact 4. Actuating member 13 continues downwardly (FIG. 1) until lower inner face 30 has completely disengaged from leaf spring 1 due to contact rib 26 engaging fixed contact 3. In this (resting) position, the leaf spring establishing contact, i.e., leaf spring 1, has disengaged from the armature. Complete disengagement of the armature means that no bouncing motions of the armature can be transferred to the leaf spring which establishes contact.

As can be inferred from FIG. 3, leaf springs 1 and 2 carry a slit 17 of a certain width between the free end 45 and clamping point 5. Slit 17 is conveniently arranged so that two tongues 18 and 19, which are symmetric with respect to symmetry line B, are obtained. The two tongues increase the reliability with which each contact arm establishes contact. However, the bouncing features of each contact arm can be improved by clamping one of the tongues (in the case considered, tongue 19) at point 21 which is off-set from the clamping point 47 of tongue 18 (off-set in longitudinal direction of symmetry line B). This measure increases the probability that both tongues 18 and 19 do not simultaneously break contact when bouncing motions occur.

Naturally, the advantage of different bouncing performance features of the two tongues 18 and 19 can also be obtained by using tongues of different thicknesses or varying width, e.g., tongues of trapezoidal shape.

From the foregoing, it can be readily realized that this invention can assume various embodiments. Thus, it is to be understood that the invention is not limited to the specific embodiments described herein, but is to be limited only the the appended claims.

I claim:

1. ln an electrical switching device, the combination of a first and a second fixed contact member in spaced oppositely facing relation to each other, a movable contact element for making contact alternatively to said first or to said second fixed contact member, said movable contact element comprising two contact arms, each arcuately curved when in free state, each having a contacting surface at one end thereof, the other ends of said contact arms being mounted to a fixed support so that their contacting surfaces are in the space between said first and second fixed contact members, and actuating means for moving said movable contact element, including a member engaging both contact arms, the improvement constituted by the sides of said contact arms which are concavely curved in free state facing outwardly from a common line a symmetry between said contact arms as mounted, and the location of said fixed contact members with respect to said contact arms being such that when the contacting surface of one of said contact arms engages one of said fixed contacts, said one of said contact arms has a curvature substantially less than that of its free state conformation.

2. An electrical switching device as claimed in claim 1, wherein when the contacting surface of one of said contact arms engages one of said fixed contacts, said one of said contact arms assumes essentially the form of a straight line segment.

3. An electrical switching device as claimed in claim 1, wherein said contact arms have the form of elongated flat leaf springs and are mounted with their fixed ends bearing against each other.

4. The electrical switching device as claimed in claim 1, wherein each contact arm has the form of a flat leaf and is slitted from its free end to a clamping point so that a plurality of individual tongues are formed for each arm.

5. The electrical switching device as claimed in claim 4, wherein the clamping points for the tongues of one contact arm are off-set with respect to each other in longitudinal direction of such contact arm.

6. The electrical switching device as claimed in claim 1, wherein each contact arm is formed of an integral piece consisting of a resilient material serving as a contact-tongue portion and of a material which can be relatively easily bent to serve as a soldering terminal portion.

7. The electrical switching device as claimed in claim 1, wherein said actuating means has a U-shaped member affixed thereto for confining said contact arms between the legs of said U-shaped member, said U-shaped member being affective upon actuation of said armature to move said contact arms into and out of contact with said fixed contact members.

i l i

Claims (7)

1. In an electrical switching device, the combination of a first and a second fixed contact member in spaced oppositely facing relation to each other, a movable contact element for making contact alternatively to said first or to said second fixed contact member, said movable contact element comprising two contact arms, each arcuately curved when in free state, each having a contacting surface at one end thereof, the other ends of said contact arms being mounted to a fixed support so that their contacting surfaces are in the space between said first and seCond fixed contact members, and actuating means for moving said movable contact element, including a member engaging both contact arms, the improvement constituted by the sides of said contact arms which are concavely curved in free state facing outwardly from a common line a symmetry between said contact arms as mounted, and the location of said fixed contact members with respect to said contact arms being such that when the contacting surface of one of said contact arms engages one of said fixed contacts, said one of said contact arms has a curvature substantially less than that of its free state conformation.

2. An electrical switching device as claimed in claim 1, wherein when the contacting surface of one of said contact arms engages one of said fixed contacts, said one of said contact arms assumes essentially the form of a straight line segment.

3. An electrical switching device as claimed in claim 1, wherein said contact arms have the form of elongated flat leaf springs and are mounted with their fixed ends bearing against each other.

4. The electrical switching device as claimed in claim 1, wherein each contact arm has the form of a flat leaf and is slitted from its free end to a clamping point so that a plurality of individual tongues are formed for each arm.

5. The electrical switching device as claimed in claim 4, wherein the clamping points for the tongues of one contact arm are off-set with respect to each other in longitudinal direction of such contact arm.

6. The electrical switching device as claimed in claim 1, wherein each contact arm is formed of an integral piece consisting of a resilient material serving as a contact-tongue portion and of a material which can be relatively easily bent to serve as a soldering terminal portion.

7. The electrical switching device as claimed in claim 1, wherein said actuating means has a U-shaped member affixed thereto for confining said contact arms between the legs of said U-shaped member, said U-shaped member being affective upon actuation of said armature to move said contact arms into and out of contact with said fixed contact members.

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