POLYMER TYPE PTC ASSEMBLY

Abstract: A PTC polymer assembly in which a sheet of PTC polymer (2) is sandwiched between two electrodes (3, 4), and electric terminations (5, 6) are mechanically and electrically connected to the electrodes, at least one of the terminations is a looped spring connected at one end (15) to one of the electrodes and at another end (17) to a mounting element, with a loop between the electrode and the mounting element to which it is mechanically connected.

Description: The invention concerns a PTC assembly including a PTC polymer device having opposite side faces and being sandwiched between two electrodes connected with said side faces, a pair of terminal members for connecting said PTC device in an electrical circuit, each said terminal member having first end portions defined by said electrodes and having remote second end portions defining connecting means for connection in an electrical circuit, said terminal members having sufficient stiffness for suspending said PTC device therebetween when said connecting means are connected in an electrical circuit. In certain applications of PTC polymer materials, a sheet of PTC polymer with faces on opposite sides is sandwiched between two electrodes in the form of sheets of electrically conductive material, and electric terminals are mechanically and electrically connected to the electrodes and to mounting elements in an electric circuit. The terminals or terminations are attached to the electrodes with solder or welded. They are likely to be themselves rigid and to be rigidly attached to the mounting elements. For example, in a door lock motor, such a PTC device is snapped into the end cap of a motor on one end and riveted in place at its opposite end. Stresses placed on the PTC element and its electrodes as a result of attachment in its application and particularly in the elongation of the terminations with temperature when the element is rigidly connected and is cycled in use, can, by placing the polymeric element in shear or tension, cause a permanent change in PTC characteristics. At the same time, it is desirable that the terminations be dimensionally fixed at the time that they are attached to the mounting element. EP-A-0201171 discloses polymer-based PTC devices having a PTC element fixed to electrodes that are prevented from moving by a rigid wall through which they extend. The electrodes are weakened or otherwise shaped on the PTC side of the rigid wall to allow lateral bending thereof in the plane of the PTC element. The object of this invention is to provide a simple, economically acceptable, and dependable polymeric PTC element construction that will obviate or minimize changes in PTC characteristics as a result of the mounting of the element. This object is achieved according to the invention in that said terminal members are completely free and unrestrained between said first and second end portions thereof and at least one of said terminal members has a spring loop between its electrode and its connecting means for providing play between said PTC device and such connecting means during thermal and mechanical relative movement between said PTC device and said connecting means on said one terminal member. Advantageous embodiments of the invention are described in the dependent claims. In accordance with this invention, generally stated, in a PTC polymer assembly in which a sheet of PTC polymer with faces on opposite sides is sandwiched between two electrodes in the form of sheets of electrically conductive material electrically connected to and substantially coextensive with the opposite faces of the polymer sheet and electrically connected to one another by and through the PTC polymer, and electric terminations mechanically and electrically connected to the electrodes and to mounting elements in an electric circuit, at least one of the terminations is a self-supporting spring loop connected at one end to one of the electrodes and at another to the mounting element, formed to maintain its location during assembly but to provide play between the electrode and the mounting element to which it is mechanically connected during thermal and mechanical relative movement between the PTC element and the mounting element. The spring loop may take the form of a U or V loop, and that termination is made of beryllium copper (BeCu). Preferrably the termination is made with a flat metal loop, but it may be in the form of a spring wire with an open loop in it. In either case, the dimensions and positions of the terminations are fixed when they are not forcibly deflected. Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawing, wherein: Figure 1 is a view in perspective of one embodiment of PTC element assembly of this invention; Figure 2 is a view in perspective of another embodiment of PTC element assembly of this invention; and Figure 3 still another embodiment of PTC element assembly of this invention. Referring now to the drawing and particularly to Figure 1, for a preferred embodiment of this invention, reference numeral 1 indicates a complete assembly, ready for mounting to mounting elements of an electrical circuit, not here shown. The assembly includes a sheet of PTC material 2 sandwiched between a lower electrode 3 and an upper electrode 4. A lower termination 5, is, in this embodiment, integral with the lower electrode 3. An upper termination 6 is, in this embodiment, integral with the upper electrode 4. As will be seen from the drawing, the upper and lower electrodes are substantially coextensive with upper and lower broad faces of the sheet of PTC material 2. The lower termination is provided with a plug-in prong 7, projecting at right angles to the plane of the lower electrode 3. The upper termination 6 includes a loop 14 with a depending leg 16 and a riser leg 15, and a connector plate 17. The connector plate 17 has a rivet hole 18 in it to receive a rivet connecting it to a mounting element. In this, illustrative, embodiment, the polymer sheet is approximately 0,0254 cm (.010 inch) thick. The lower electrode 3 is 0,08128 cm (.032 inch) thick brass. The upper electrode 4 is 0,03048 cm (.012 inch) BeCu. For some applications, a 0,0508 cm (.020 inch) thick brass plate can be welded or otherwise secured to the underside of the connector plate 17. As is customary, both broad surfaces of the polymeric sheet are initially covered by 0,00254 cm (.001 inch) thick nickle foil, and the upper and lower electrodes 4 and 3 are soldered to the outer surface of the foil. This is conventional. In mounting, the prong 7 is snapped into the endcap of a motor, for example, and the connector plate 18 is riveted to a fixed mounting terminal. It can be seen that, absent a deforming force, the relative positions of the prong 7 and the hole 18 will remain fixed, so that the installation of the assembly is easily accomplished, and may be automated. Referring now to Figure 2 for another embodiment of this invention, reference numeral 201 indicates the complete assembly, which includes a sheet of polymeric PTC material 202, a lower electrode 203, an upper electrode 204, a lower termination 205, and an upper termination 206. In this embodiment, as in the embodiment shown in Figure 1, the lower termination 205 is integral with the lower electrode 203, and the upper electrode 204 is integral with the upper termination 206. In this embodiment, a prong 207, of different configuration but same function as the prong 7, extends substantially perpendicularly to the plane of the lower electrode 203, and is provided with a slot 208, extending through a portion of the prong 207 and through a connecting reach of the termination. The upper termination 206 of this embodiment has a more nearly V-shaped loop 214 than the loop 14, with a depending leg 215 and a riser leg 216, and a connector plate 217. In this embodiment, the connector plate 217 is shown as having a rivet 219 connected to it. The function and operation of this embodiment of PTC assembly 201 are the same as those of the assembly 1. Referring now to Figure 3 for still another embodiment of this invention, reference numeral 301 represents the completed assembly, which, like the assemblies of the devices shown in Figures 1 and 2, has a sheet of PTC material 302, a lower electrode 303, an upper electrode 304, and a lower termination 305, with a plug-in prong 307 corresponding exactly to the electrode 3 and the prong 7 of the embodiment shown in Figure 1. An upper termination 306 of this embodiment is in the form of a BeCu wire, circular in cross section and about 0,05588 cm (.022 inch) in diameter. The termination 306 is stiffly resilient. It has an electrode connecting end 308 which is soldered or welded to the upper electrode 304, a loop 314 which, in this embodiment, lies in a plane parallel to the plane of the upper electrode 304, and a connector section 311. The loop 314 is U-shaped, with an outward leg 309 and a return leg 310. The connector section 311 has at its outer end an eye 312 formed by a bend in the wire. The dimensions of the PTC element, hence the electrodes, and the shapes and dimensions of the terminations will be varied as the requirements of their application vary. In any event, however, the provision of the spring loop reduces the stresses on the PTC element resulting from expansion of the terminations during the heating cycle sufficiently to prevent unacceptable changes in the resistance characteristics of the element, which when the spring is not provided may be as much as fifty percent. Numerous variations in the construction of the assembly of this invention, within the scope of the appended claims, will occur to those skilled in the art in the light of the foregoing disclosure. The terminations can both be provided with looped springs. They can be formed of materials different from the brass and BeCu given as examples, so long as the termination with the loop is stiffly springy and both are electrically conductive. The type of termination that is broad relative to its thickness can be welded or otherwise secured to the electrode, but making it integral with the electrode has clear advantages. The loop can be a helix or spiral, or of different configuration or construction, as long as it is self-supporting under conditions of installation, and provides play between the PTC element and the mounting element during thermal or mechanical relative movement between them. These variations are merely illustrative.

Claims: A PTC assembly including a PTC polymer device (2,202 or 302) having opposite side faces and being sandwiched between two electrodes (3,4 or 203,204 or 303,304) connected with said side faces, a pair of terminal members (5,6 or 205,206 or 305, 306) for connecting said PTC device (2,202 or 302) in on electrical circuit, each said terminal member having first end portions (3,4 or 203,204 or 303,304) defined by said electrodes (3,4 or 203,204 or 303,304) and having remote second end portions (7,17 or 207,217 or 307,312) defining connecting means for connection in an electrical circuit, said terminal members having sufficient stiffness for suspending said PTC device therebetween when said connecting means are connected in an electrical circuit, characterized in that said terminal members are completely free and unrestrained between said first and second end portions thereof and at least one of said terminal members (6,206,306) has a spring loop (14,214,314) between its electrode (4,204 or 304) and its connecting means (17,217 or 312) for providing play between said PTC device and such connecting means during thermal and mechanical relative movement between said PTC device and said connecting means on said one terminal member. The PTC assembly of claim 1 wherein said connecting means (17) on said one terminal member (6) comprises a connector plate (17,217) having a rivet receiving hole (18) therein. The PTC assembly of claim 2 wherein said connector plate (17) extends substantially parallel to said side faces of said PTC device. The PTC assembly of claim 2 wherein said connecting means (7) on the other (5) of said terminal members comprises a plug-in prong (7). The PTC assembly of claim 1 wherein said terminal members extend outwardly from said PTC device in opposite directions when said PTC device is positioned with said side faces thereof extending horizontally. The PTC assembly of claim 5 wherein said connecting means (7,207,307) on the other of said terminal members (5,205,305) comprises a plug-in prong (7,207,307) extending substantially perpendicular to the plane of said side faces.

Inventors: YAGHER, CHARLES, JR.
Applicants: EMERSON ELECTRIC CO.
Application year: 1988
Main classification: H01C7
IPC codes: H01R4, H01C7, H01C1