Patent Publication Number: US-4367447-A

Title: Electromagnetic relay having a pivoted armature fitted with a permanent magnet

Description:
This invention relates to a bistable electromagnetic relay with a pivoted armature fitted with a permanent magnet. 
     A relay of this type is essentially composed of a U-shaped yoke fixed on a base and provided with one or two excitation coils. Said yoke cooperates with an H-shaped armature formed by a permanent magnet which constitutes the crossbar of the H and on which are fixed two projecting plates forming pole-pieces and constituting the arms of the H. The ends of the yoke are positioned with a substantial clearance between said arms and, depending on the respective polarities applied to the yoke ends, the projecting plates close against the arms in an oblique position of the armature, either in one direction or in the other. 
     The pivoted armature is covered externally with an insulating material and adapted to carry flexible strips. Said strips are in turn adapted to carry movable contacts and extend along the arms of the H in order to cooperate with stationary contacts carried by the base. 
     Known relays of this type suffer from a certain number of disadvantages. On the one hand, they entail the need for a flexible electrical connection between the output terminals and the movable flexible strips attached to the armature. On the other hand, this construction involves a current flow path of substantial length within the relay. Finally, since relays of this type are of the single-break type, they result in high stray capacitance between the open contacts. 
     The aim of the present invention is to provide a pivoted-armature relay which is free from the disadvantages mentioned above. 
     In accordance with the invention, the electro-magnetic relay with a pivoted armature is designed in the manner described in the foregoing and is distinguished by the fact that the free end of each flexible strip carries two electrically coupled movable contacts adapted to cooperate with stationary contacts for connecting said contacts to each other. 
     In order to carry out the contact-closing operation, a very short bridging of the stationary contacts is provided by an electrical connection between the movable contacts, this connection being established only over a very small portion of the flexible strip. In consequence, said strip does not need to be permanently coupled to a fixed terminal by means of any connection and a very short path is provided for the flow of current within the relay. Moreover, this double-break action reduces the stray capacitance between open contacts. 
     In a preferred embodiment of the invention, the axis of rotation of the armature is located between the stationary contacts and the point of attachment of the flexible strip to the armature. 
     This arrangement has the effect of increasing lateral friction between the movable contacts and the stationary contacts as well as the self-cleaning action at the time of closing of the contacts. 
     In a preferred embodiment of the invention, the two movable contacts of one and the same strip remain located in the same plane parallel to the axis of the yoke and the corresponding stationary contacts are located in the same plane parallel to the plane of the yoke; that face of the base which carries said stationary contacts is perpendicular to the plane of the yoke and parallel to the axis of said yoke. 
     In consequence, no curved portion is necessary between the stationary contacts and the output terminals corresponding to said contacts. 
     In a first alternative embodiment of the invention, the relay comprises two stationary flexible strips on each side of the armature. Said strips are intended to cooperate with two respective pairs of stationary contacts in order to constitute a double-break changeover contact circuit without common point. 
     In a second alternative embodiment, the relay comprises three equidistant stationary contacts spaced at predetermined intervals and a flexible strip curved in such a manner as to ensure that a movable contact is located within each interval between the stationary contacts, the movable contacts being relatively displaced by the value of the interval aforesaid. 
     There is thus obtained a double-break changeover contact circuit with common point. 
     In an improved embodiment of the invention, each arm of the yoke is fitted with a coil and the end portions of said arms are provided with flat surfaces in order to cooperate in juxtaposed planes with the projecting plates of the pivoted armature in its angular end-positions. 
     Preferably, the assembly formed by the yoke and its coils is encapsulated in an insulating material so as to form a parallelepipedal block. A first face of the block is adapted to carry coil connection terminals and stationary contacts. The end portions of the yoke arms are adapted to project from a second block face which is perpendicular to the first, said second face being provided with means for pivotally mounting and centering the armature in coaxial relation to the yoke. 
     A perfectly protected block is thus formed and only the ends of the yoke and the terminals to be connected emerge from said block. In consequence, the coil is not liable to pollute the contacts. 
     In a first form of construction, the aforementioned second face of the block is surrounded by a skirt which forms an extension of said block and encloses the end portions of the yoke arms. Said skirt is intended to be fitted with a lid which comprises part of the means for pivotal mounting and centering of the armature. 
     The operation of the relay can thus be inspected prior to fitting of the lid. Furthermore, said lid is easier to manufacture than a housing. 
     In a second form of construction, the relay comprises a removable trough which can be fitted on the aforementioned second face of the block. The means for pivotal mounting and centering of the armature are mounted on the bottom wall of the trough and stationary contacts are mounted on one of the side walls of said trough. 
     This form of construction permits the use of two different insulating materials for encapsulation and for the trough. The trough insulating material may be adapted, for example, to high-frequency insulation. 
     In an advantageous embodiment of the invention, the yoke has two additional arms opposite to the first arms. Said additional arms are arranged symmetrically and encapsulated together with said first arms within one and the same block so as to cooperate with a second armature which is symmetrical with the first and provided with similar contact circuits. 
    
    
     These and other features of the invention will be more apparent upon consideration of the following description and accompanying drawings, wherein: 
     FIG. 1 is a sectional view of a relay in accordance with the invention, this view being taken along line I--I of FIG. 2; 
     FIG. 2 is a side view taken along line II--II of FIG. 1; 
     FIG. 3 is a view which is similar to FIG. 1, in one alternative embodiment; 
     FIG. 4 is an exploded side view of a relay in a particular embodiment, in which it is assumed that the armature has been removed; 
     FIG. 5 is a fragmentary exploded view in another embodiment, in which it is assumed that the armature has been removed. 
    
    
     Referring now to FIGS. 1 and 2, a relay in accordance with the invention comprises a U-shaped yoke 1 fixed on a plate 2 of a base 3, said yoke being provided with two arms 4 on which are wound coils 5. The two arms 4 project from the plate 2 and are placed with a substantial clearance between the arms of an H-shaped pivoted armature 6, the axis of pivotal displacement being intended to coincide with the axis of the yoke 1. 
     Said armature is essentially constituted by a permanent magnet 7 forming the crossbar of the H and by two projecting plates 8a and 8b which form pole-pieces. Said plates are provided externally with an insulating covering 9 completed by two insulating plates 11a, 11b which cover the magnet 7. Recesses are formed in said plates for accommodating pivots 12a, 12b which are rigidly fixed to a base 3. Said pivots permit centering and pivotal displacement of the armature 6. The ends of the yoke arms 4 are provided with flat surfaces 13 so arranged as to permit cooperation of the projecting plates 8a, 8b with said arms in juxtaposed planes. 
     Two flexible strips 14 of conductive material are each fixed at one end on the insulating covering 9 so as to extend along each projecting plate 8a, 8b. Two movable contacts 15a, 15b are fixed at the other end of each strip in order to cooperate with stationary contacts 16a, 16b. The point of attachment 17 of each strip is located in a position such that the axis of the pivots 12a, 12b is located between the movable contacts and said point of attachment. 
     The stationary contacts 16a and 16b corresponding to one and the same strip are located in one and the same plane parallel to the plane of the yoke 1 and are connected directly and without bending to respective terminals 18a, 18b which project from one face 19 of the base which carries said contacts, namely the face which is perpendicular to the plane of the yoke and parallel to the axis of the yoke. Said face 19 is also adapted to carry the output terminals 21 of the coils 5 (this connection is not shown in the drawings). 
     It is observed that, during the movement of rotation of the armature 6, the movable contacts remain located in the same plane parallel to the axis of the yoke. 
     During operation, when a given polarity is applied to the arms 4 of the yoke 1, the armature 6 undergoes a pivotal displacement in such a manner as to ensure, for example (referring to FIG. 1), that the plate 8a is applied against the left-hand arm 4 and that the plate 8b is applied against the right-hand arm. The movement of the lower strip 14 then has the effect of applying the movable contacts 15a, 15b against the stationary contacts 16a, 16b (as shown in FIG. 2). Said stationary contacts are then connected electrically by a very short portion of the strip 14 which has negligible resistance. 
     If the polarities of the yoke arms are reversed, the armature 6 undergoes a pivotal displacement in the opposite direction, the lower contacts (shown in FIG. 1) open and the upper contacts close. The operation is therefore of the bistable type and the rotary armature provides good impact resistance. 
     The location of the point 17 of attachment of each movable strip produces a substantial lagging action which results in lateral friction between the movable contacts and the stationary contacts at the time of closing, thus having a self-cleaning effect on the contacts. 
     It will be noted that, apart from their contact-carrying ends, the strips 14 do not perform any conducting function and do not need to be attached to an output terminal by means of a connection which would have to be flexible. 
     Furthermore, the double-break operation endows the relay with a considerably higher breaking capacity and has the effect of reducing stray capacitance. 
     The relay described in the foregoing constitutes a double-break changeover circuit without a common point. 
     Referring to FIG. 3, there will now be described a relay which forms a double-break changeover-contact circuit with a common point. 
     This embodiment is somewhat similar to the preceding embodiment and will therefore be described only in regard to its distinguishing features. 
     A U-shaped yoke provided with two coils 105 has two arms 104 located between the arms 108a, 108b of a pivotally mounted H-shaped armature 106 comprising a permanent magnet 107. On one face of its insulating covering 109, said armature is adapted to carry a flexible strip 114 which has two arms 114a, 114b. Each arm is adapted to carry a movable contact 115a, 115b respectively, each contact being intended to operate on both faces of the strip. 
     Three stationary contacts 116a, 116b, 116c are arranged on the face 119 of the base 103 so as to ensure that they are uniformly spaced at predetermined intervals. These contacts have extensions in the form of terminals 118a, 118b, 118c. 
     The distance between the arms 114a and 114b of the strip 114 is equal to each interval mentioned above, with the result that, in one end position of the armature 6, the movable contact 115a comes against the contact 116a and the movable contact 115b comes against the contact 116b whereas, in the other end position, the movable contact 115a comes against the contact 116b and the movable contact 115b comes against the contact 116c. 
     A connection is therefore established either between the contacts 116a and 116b or between the contacts 116b and 116c, thus effectively providing a changeover-contact circuit with a common point. 
     In a practical embodiment of the invention (as shown in FIG. 4), the assembly formed by the yoke and the coils is encapsulated in a block 222 of insulating material. In FIG. 4, there is shown an alternative embodiment in which the yoke 201 has two additional arms 204a at the end remote from the arms 204 and disposed symmetrically in order to cooperate with a second armature (not shown) corresponding to two other pairs of stationary contacts 223a, 223b. 
     The block 222 is extended on each side of the relay by a skirt which is designated respectively by the references 224a, 224b and in which are fixed the stationary contacts. 
     The pivots 212a of the armature are rigidly fixed to the block 222 whereas the pivots 212b are rigidly fixed to removable lids 225a, 225b which are intended respectively to close the skirts 224a, 224b. Before the lids are fitted in position, the skirts are designed to protect the moving parts of the relay. 
     During normal service, the only elements which project from the block on the face 219 are the terminals which serve to connect the contacts 218a, 218b, 226a, 226b, and the coil connection terminals 221. 
     In an alternative embodiment (shown in FIG. 5), the skirts are dispensed with; a trough 327 which is adapted to cooperate with the block 322 performs the functions both of skirt and lid. A pivot 312b for the armature (not shown) is fixed on the bottom wall of the trough. The stationary contacts 316a, 316b which form extensions of the terminals 318a, 318b are fixed on one of the side walls of the trough. 
     By virtue of this arrangement, a different insulating material can be provided for the block 222 and for the trough 327 which carries the contacts. In particular, a material which is well suited to encapsulation can be chosen for the block and a material which affords good insulation at high frequencies can be chosen for the trough. 
     As will readily be apparent, the invention is not limited to the examples hereinabove described and a number of minor alternative forms of construction may accordingly be contemplated without thereby departing either from the scope or the spirit of the invention.