Improved intermediate support relay for use particularly in motor vehicles

Abstract: The invention concerns a relay for use particularly in motor-vehicles, comprising a stable ferromagnetic core (1), an excitation coil (2) wound around said core, a movable assembly composed from at least one movable ferromagnetic armature (3), a flexion foil (4) fixed in a determined point (5) of said movable armature and an exchange contact (6), said relay also includes a return spring (7) to maintain in a position of maximum air gap such armature with respect to said core when the device is in a release condition and at least one (8a, 8c) closure and/or opening contact that is activated by the movable armature (3), through its exchange contact (6), when this is drawn or released by the core (1). The main characteristic of the invention consists in the fact that it has an intermediate support element (9) for said flexion foil (4) obtained on one of the elements of the movable assembly, and that said support (9) is of such a height and is to be found at a distance from the fixing point (5) so as to produce a sensitive pre-charge of said foil (4), even before the closure.

Description: The invention concerns a relay for use particularly in motor-vehicles, comprising a stable ferromagnetic core, an excitation coil wound around said core, a movable assembly composed from at least one movable ferromagnetic armature, a flexion foil fixed in a determined point of said movable armature and an exchange contact, said relay also includes a return spring to maintain in a position of maximum air gap such armature with respect to said core when the device is in a release condition and at least one closure and/or opening contact that is activated by the movable armature, through its exchange contact, when this is drawn or released by the core. Relays of the type described are known. Such relays have the drawback that, particularly in certain applications, such as capacitive charges, the wear of the contacts is relatively high, which causes the useful life of the relay to be relatively short; the problem is increased by the mechanical working tolerances that determine a spread of the pressure characteristics with which the contacts become closed. Another drawback concerns the way with which the flexion foil is united with the movable armature. As shown in figure 1 this is normally united through riveting, that creates only one binding point. This generates an imperfect joint that produces inconstancies on the real value of geometry in play. In the European patent application N. 0 326 116 a relay is described in which the flexion foil has a pre-charge crease that in closure reduces the bouncing of the contacts; however such disposition requires on opening a greater energy; in other words the closure results in being facilitated, but hinders the opening. In the European patent application N. 0 484 592, which is considered to be the closest prior art, a relay is described in which the flexion foil terminates in the form of a T and has two contacts; furthermore each branch of the T has a support tab that rests on the movable armature, with the aim of facilitating the aperture of the contacts utilising the impact energy of the armature. With such aim, and for conserving constant as much as possible the flexibility characteristics of the foil, the application instructs the positioning of the support between the foil and armature in the immediate vicinity of the contacts (column 2, lines 21-27). The aim of the present invention is that of eliminating the drawbacks of the known art and in particular to indicate an improved relay that has a wear of the contacts being lesser than that of the traditional relays and therefore a longer useful life. In view of reaching such aims, the invention has as its object a relay for use particularly in motor-vehicles, comprising a stable ferromagnetic core, an excitation coil wound around said core, a movable assembly constituted of at least one movable ferromagnetic armature, a flexion foil fixed in a determined point of said movable armature and an exchange contact , said relay also includes a return spring to maintain in a position of maximum air gap such armature with respect to said core when the device is in a release condition and at least one closure and/or opening contact that is activated by the movable armature, through its exchange contact, when this is drawn or released by the core, characterised in that it has an intermediate support element for said flexion foil obtained on one of the elements of the movable assembly, and that said support (9) is of such a height and is to be found at a distance from the fixing point (5) so as to produce a sensitive pre-charge of said foil (4), even before the closure. Further aims and advantages of the present invention will result in being clear from the specified description that follows with reference to the annexed drawings, supplied as a pure and non-limiting example, in which: figure 1 schematically represents a relay of the known type; figure 2 represents a family of curves forces of attraction/air gap at constant magnetomotive force, relative to relays with geometric characteristics of the type being object of the invention; figure 3 contains one of the curves of figure 2 and a segmented line that schematically represents the reaction movement of the mechanical system (proportional to the forces on the contacts) depending on the movement carried out under the action of the electromagnetic force of the relay in fig. 1, detected on the axis of the bobbin; the figures 4, 4A, 4B, 4C, and 4E, show the positions of the movable assembly with reference to the segmented line of figure 3; figure 5 schematically represents a relay according to invention; the figures 6, 6 C, 6 D, and 6E represent, in the case of the relay of figure 5, the segmented line equivalent to that of figure 4 and the positions C, D and E of the movable assembly with reference to the segmented line of figure 3; figure 7A schematically represents the flow of the current in the case in which the charge for the relay is represented by a halogen lamp, while figure 7B represents in an enlarged scale the peak of the initial current of figure 7A; figure 8 schematically represents the movement of the reaction force of the mechanical system and of the magnetomotive force, both for the relay of fig. 1 and for the relay of Fig. 5, taking into consideration the relative manufacturing tolerances of a case being of equal value of additional movement; figure 9 indicates the overlapped situations that are verified in the relays of figure 1 and figure 5 due to wear; figure 10 indicates schematically the difference between the forces that manifest in the relays of figure 1 and figure 5 in the part of additional movement; figure 11 schematically indicates the difference of the free flexion length of the foil having contact in the return to the stable position, between a relay of the type shown in figure 1 and one of the type shown in figure 5. Normally relays of the type described in the following description are used in motor vehicles. All such relays have substantially a structure having a ferromagnetic core, an excitation coil and at least one movable armature. In figure 1 a traditional relay of the used type in motor vehicles is schematically represented. The reference number 1 indicates a stable ferromagnetic core; the reference number 2 indicates an excitation coil wound around said core; the reference number 3 indicates a movable ferromagnetic armature; the reference number 4 indicates a flexion foil, for example being of an approximate triangular form, fixed in a determined point of said movable armature, indicated in turn with the reference number 5; the reference number 6 indicates an electric exchange contact; the reference number 7 indicates a return spring for maintaining such armature in a position of maximum air gap with respects said core when the device is in a rest condition; finally the reference number 8a indicates an electric opening contact and the reference number 8c indicates an electric closure contact that are activated by the movable armature 3, through its exchange contact 6, when this is respectively released or drawn by the core 1. In such devices the interaction between a force that is created by the excitation of a variable reluctance magnetic circuit and the corresponding reaction of the mechanical system is verified; the task of such force is to attract said movable armature towards the core of the device. To obtain such aims an electromagnetic attraction force is generated, which is represented by an expression of the type: F = k 1 I 2 / (k 2 + x) 2 where I is the excitation current of the magnetic circuit which is supposed as being constant, k1 and k2 are constant that express geometric and magnetic parameters of the device, X is the variable of the air gap valued in reference to the axis of the excitation bobbin. The above mentioned formula forms, on a Cartesian plane, a hyperbole family, to each of which corresponds a current value, as represented in fig. 2. The significant part of such curves is obviously that which goes from an air gap being equal to zero ( x=O ) to an air gap being equal to the maximum value t, (x=t). The corresponding reaction of the mechanical system can be represented, for traditional relays, being on the same previously indicated Cartesian plane, with a segmented line formed from three segments, as represented in figure 3. The corresponding reaction of the mechanical system is the result of the combination of the return force of the spring 7 and of the deformation force of the foil 4 that varies depending on the position of the movable assembly as will be clearly seen in the following. The segmented line, represented in figure 3, is the simple result of the analysis of an extremely simple mechanical model, formed by a movable assembly hinged to an extremity, subjected in the central part to the action of a force and stopped in movement by the appropriately positioned support points. In such model in absence of the attraction force (rest condition) corresponds the maximum closure force on contact 8a, due to the action of the return spring 7 in equilibrium with the reaction due to the elastic deformation of a small portion of foil 4. Point A of the segment A-B (see fig. 4A). Subjecting the movable armature to the attraction force, that will be indicated with FB (necessary force for reaching point B of the graphic of figure 4), the elastic deformation of the foil is cancelled and with a minimum air gap reduction the sole reaction of the return spring is balanced. Point B of the segment A-B (see Fig. 4 B). Increasing the attraction force to a value FC (necessary force for reaching point C of the graphic of figure 4), the air gap is reduced due to the effect of the rotation of the movable armature on the hinge with minimum force increments due to the characteristic of the return spring, while the exchange contact 6 passes from the contact position with the stable contact 8a to the contact position with the stable contact 8c. Point C of the segment B-C (see fig. 4C). At this moment the exchange contact 6 of the flexion foil rests on the contact 8c with an initially zero force, (point C). In such a situation the movable armature is separated from the core by an air gap entity conventionally defined as additional movement. Increasing furthermore the acting force up to a value FE (necessary force for reaching point E of the graphic of figure 4), the segment C-E is covered, to which strong force increments correspond, due to the reaction of elastic deformation of the foil 4 that in point E reveal their maximum value, when the movable armature 3 comes to rest on the core 1, as shown in figure 4E. The elastic deformation of the foil 4 during the additional movement determines the closure force of the contacts and as a result determines their capacity in supplying current, in point E the armature has carried-out its complete movement and the foil is retracted respects the former, after having rested on the contact 8c. Until the complete closure of the contacts of the device is reached, it is evident that the minimum current admissible for a given relay is that for which the curve of the attraction force remains above the segmented line curve of the mechanical reaction of the actual relay as indicated in figure 3, that represents the hyperbole limit. According to invention the movable armature 3 is furnished, at its extremity, with a relief 9 (fig. 5), obtained making an indentation on such armature; due to the effect of such relief 9, the foil 4 results in being furnished with an intermediate point of support appropriately positioned, situated for example approximately midway respect its length. Such relief 9 will be advantageously positioned, if compared to the work length of the foil 4, or appropriately dimensioned concerning the height, in a such a way to confer to the gradient of the exercised force on the contact, immediately after its closure, the suitable value according to the type of use of the relay. Furthermore the foil 4 is fixed, through a small fixation plate 5, that transversely extends to the foil 4 for all its width thus realising a perfect joint condition. In a preferred form of realisation a hole (10) is provided in the flexion foil 4 so as to allow access to the movable armature of a measuring element of the functional characteristics. Up to point C of the graphic, in figure 6, the behaviours of the relay of known type of figure 1 and of the new relay of figure 5 are similar. During a first phase of the additional movement in which the foil 4 is not yet detached from the point of support 9 the elastic deformation of the foil is limited only to the section L2 (see fig. 6 point D); in the second phase of the additional movement, after the detachment of the foil from the point of support 9, the elastic deformation occurs along the whole length of the foil L1 + L2 (Fig. 6 E); in such a way that a four segments diagram of stress is obtained (see Fig. 6). The third segment (C-D) is of a relatively high slope (due to the reduced flexion length L2), while the fourth segment (D-E) is of a minor slope (due to the flexion length L1 + L2). The relay according to the invention has the following advantages if compared to traditional relays: In every productive process the manufacturing tolerances that determine maximum and minimum admissible values exist; the most influencing variable is the mechanical tolerance on the additional movement that determines two segmented lines of limit forces, inside of which all the segmented lines of force relative to produced devices are found; in particular for the lower force segmented lines the verified situation in the case of foil with intermediate support is significantly more favourable than in the case of conventional foil. See confrontation in figure 8, where in the left part of the figure the situation of the tolerances for a relay of known type is represented, while in the right part of the figure the behaviour of the tolerances for a relay according to invention is represented; both the representations of the procedures have been indicated with dot/dash lines for the minimum values of the tolerances, while with dotted lines for indicating the maximum values of the tolerances. The two parts, left and right, of figure 8 have been indicated under parity of conditions. The substantial advantage of the relay according to invention resides in the fact that point E that indicates the closure force of the contacts is in case B significantly greater than in case A. The realisation of a perfect joint condition of the flexible foil with the movable armature assures reproducible fixation conditions with a constant functional guaranty. The wear of the closure contacts of the relay, brings about a reduction of the additional movement, and therefore in the diagram of the forces to a displacement of the origin of the axis towards the right; it can be noted how the relay with intermediate support determines in the whole field of the tolerances a greater closure force; the maximum benefit is produced in the field where the tolerances are of major influence, as demonstrated in the comparison in figure 9 where the segmented line of 4 segments refers to the relay according to the invention, while the segmented line of 3 segments refers to a relay of the known type. In figure 9 the vertical dotted line U represents the position assumed by the axis of the ordinates in a wear condition of the contacts. As already mentioned, the current that two contacts are able to commute without drawbacks is directly proportional to the force with which they are maintained closed; in the case of so-called capacitive currents, having a transitory similar to the charge current of a capacitor (note for example figure 7), a closure force is required that immediately manifests high values; it can be noted from figure 10 that the segmented line T of four segments of the relay according to the invention manifests in the first section of the additional movement force increments being much greater if compared to the S shape of three segments of a traditional relay. This determines a closure of the contacts with sufficient force to commute currents of a powerful initial start, which is obtained in the closure on very low initial resistance charges. One of the fundamental variants that determine the life of a relay, is the speed with which the transitories are accomplished, i.e. the time between the beginning and the end of a manoeuvre; experimentally it has been proved that, under a parity of conditions, with relays with intermediate support, inferior duration is always obtained; or transitories of equal duration with lower excitation voltages, for the same reasons it has been noted experimentally the same benefits, united to a lower number of bounces, in passing from one contact to another during the deviation manoeuvre, mainly in the return to the stable equilibrium position for the greater length of flexion ( L2 ) with which the foil of the relay of figure 5 absorbs the impact energy as demonstrated in figure 11. In fact in traditional relays the flexion length in the opening position L3 is minor, with consequent minor capacity to absorb the bounces. From the executed description the advantages of the present invention become clear. Of course numerous variants are possible to the relay object of the present invention. For example the relief 9 that realises the intermediate support could be obtained on the foil 4 rather than on the armature 3. Other variants could be realised by replacing the constructive elements shown in the figures with simple technical equivalents.

Claims: Relay for the use particularly in motor-vehicles, comprising a stable ferromagnetic core (1), an excitation coil (2) wound around said core, a movable assembly composed from at least one movable ferromagnetic armature (3), a flexion foil (4) fixed in a determined point (5) of said movable armature (3) and an exchange contact (6), said relay also including a return spring (7) to maintain in a position of maximum air gap such armature with respect to said core when the device is in a release condition and at least one (8a, 8c) closure and/or opening contact that is activated by the movable armature (3), through its exchange contact (6), when this is drawn or released by the core (1), said relay also including an intermediate support element (9) for said flexion foil (4) obtained on one of elements of the movable assembly, characterized in that said support (9) is of such a height and is to be found at a distance from the fixing point (5) so as to produce a sensitive pre-charge of said foil (4), even before the closure, and in that the armature fixing point (5), the intermediate support (9), the foil (4) and the contacts (8c) are realised so as that during a phase of additional movement, initially there is a flexion of only a part (L2) of the foil (4) and after there is a flexion of all (L1 + L2) the foil (4). Relay according to claim 1, characterised in that said element of intermediate support (9) for the foil (4) of said exchange contact (6) is obtained on the movable armature (3). Relay according to claim 1, characterised in that said element of intermediate support (9) for the foil (4) of said exchange contact (6) is obtained on the foil (4). Relay according to any one of claims 1 to 3, characterised in that said element of Intermediate support (9) is placed in a position, respects the work length of the foil (4), such to confer to the gradient of the exercised force on the contact, immediately after its closure, the appropriate value to the type of relay usage. Relay according to any one of claims 1 to 4, characterised in that said element of intermediate support (9) is placed about midway as to the length of said foil (4). Relay according to any one of claims 1 to 5, characterised in that said element of intermediate support (9) has a thickness of such to confer to the gradient of the exercised force on the contact, immediately after its closure, the appropriate value to the type of relay usage. Relay according to claim 3, characterised in that said element of intermediate support (9) is obtained making a relief on the foil (4). Relay according to any one of claims 1 to 7, characterised in the fact that the foil (4) is pre-charged only in closure, while in opening the pre-charging means eventually act in a manner so as to favour the opening. Relay according to any one of claims 1 to 8, characterised in that a fixing element is provided between the flexion foil (4) and the movable armature that produces a perfect joint condition of the foil for all its width. Relay according to claim 9, characterised in that said perfect joint is realised through a fixing plate (5) that is substantially extended along the whole width of the flexion foil (4). Relay according to any one of claims 1 to 10, characterised in that the foil (4) has a hole (10) that allows for the access to the movable armature of a measuring element of the functional characteristics. Relay according to any one of claims 1 to 11, characterised in that the armature (3), the fixing point (5), the foil (4) and the stable contact (8a) are realised in order that in rest position the flexion length (L2) of the foil (4) is such to assure a substantial dampening of the bounces. Relay according to any one of claims 8 to 12, characterised in that means (9) are provided that, in the return position to the rest position, produce an increase of the path being subject to flexion of the foil (4) without increasing its projection respect to the maximum longitudinal size of the plan of the movable armature (3).

Inventors: GUIDI GUIDO, PETRONE ALBERTO, GUIDI, GUIDO, PETRONE, ALBERTO
Applicants: BITRON SPA, BITRON S.P.A.
Application year: 1993
Main classification: H01H50
IPC codes: H01H50