Insulation-Cutting Connectors and Method of Making Connections

The present invention relates to paired-prong terminals, to methods by which the terminals make connections to insulated wire, and to resilient paired-prong terminal members and their method of manufacture.

It has long been known that insulated wire can be forced into the gap of a divided terminal without first stripping the insulation. In some cases the terminal edges at the gap are rigid while in others the terminal has stiff yet resilient prongs. The insulation is generally crushed by opposite edges of the terminal as the wire is forced into the gap, to bare areas of the wire for contact. In some instances, there are sharp corners on the terminal at the entrance to the gap. The sharp corners are intended to make short incisions in the insulation extending parallel to the length of the wire, thus facilitating further rupture of the insulation where the conductor of the insulated wire is to make contact with the terminal. Sharpness at those corners may rupture protective oxide-inhibiting plating on the metal conductor and, in the case of stranded conductor wire, it may shear some of the strands.

Special tools are sometimes used to forcibly assemble the wire to the terminal. In other cases, the terminal structure includes a removable cover which is formed to serve as a driver. In general, more-or-less brute force of the terminal acting against the wire driven against it is relied on to crush and part the area of insulation that must be removed in making wire-to-terminal contact. Where stranded wire is used, the crushing action often drives some insulation between the strands, making the prongs bear against insulation, creating unreliable connection. The construction often imposes critical parameters on the design and manufacture of the terminals. Thus, a terminal having a slot bounded by rigid sides or excessively stiff prongs may well be very effective in tearing through wire insulation, but it may fail to make dependable long-term contact with wire's conductors or it may slice conductor strands, depending on the wire size. In a rigid structure, a wire which is disturbed after insertion, as by handling, may loosen and provide intermittent contact. Excessively supple resilient prongs of a terminal may not be consistently effective in stripping insulation as intended.

A widely known form of insulation-rupturing wire terminal involves a strip of metal having an end portion divided lengthwise into a pair of prongs. That terminal characteristically includes three zones: (1) an end zone having a wire-receiving gap; (2) an intermediate zone where edges of the prongs are pre-biased against each other; and (3) an elongated slot with separated edges, terminating where the prongs join the rest of the terminal strip. The slot evidently was considered a manufacturing requirement, and because it adds length to the prongs, the prongs have been stiffly pre-biased toward each other to meet the basic insulation-crushing and wire-contacting functions.

It is known from my U.S. Pat. No. 3,609,642 issued Sept. 28, 1971, that certain materials, especially certain grades of polymeric materials, can be used to cut through polymeric insulation without risking incision into the copper conductor of the insulated wire. Evidently, that principle has not been put to use in wire-stripping connectors.

The disclosed connector includes terminals each comprising a pair of resilient prongs having opposed elongated contact edges separated by a gap, and a driver having paired edges for cutting wire insulation but not the metal conductor of the wire. Where the driver is part of the connector, it is normally formed of electrical insulation. Indeed, the driver can be a separate tool. The driver is particularly effective in making the present incisions in wire insulation without harming the copper or other relatively soft conductor, where it is made of "medium-hard" material, i.e. harder than wire insulating material, but softer than the conductor material. For vinyl-insulated copper-conductor wire, the driver may be of relatively soft metal such as aluminum or it may be of "medium-hard" insulation such as a suitably hard polymeric material. In the illustrative embodiment of the invention, the driver's cutting edges are in planes spaced apart a little more than the thickness of the prongs. The driver disposes a wire across the ends of the prongs. As the wire is driven laterally toward and along the prongs, initially pairs of incisions are formed in the wire insulation. The insulation between the pairs of incisions is ruptured to expose areas of the wire's conductor for contact and the locally exposed conductor is driven between the contact edges of the pair of prongs. More generally, areas of the wire are bared by the contact-making prongs at incisions first made by the driver.

The disclosed terminals are formed of a metal strip. An end portion of the strip is slit initially, forming a pair of prongs. While the prongs are constrained against moving apart by more than a prescribed gap, a depression is coined into the strip at opposed edges of the slit at a point partway along the slit. The resulting resilient prongs are separated by a wire-receiving gap that extends along some or all of the prong length. The entire length of the prongs contributes to their resilience. The terminals are heat-treated for relieving internal stresses so that no dependence is placed on pre-biasing the prongs toward each other.

The contribution of the driver and its cutting edges in preparing the insulation for final rupture by the pair of prongs of the terminal may reduce drastically the stresses imposed on the prongs, simplifying the design criteria heretofore involved in producting such terminals. In using stranded wire, a very critical balance was previously required, on one hand between prongs stiff enough to reliably force off all insulation, leaving none between the strands and the prongs, and on the other hand, prongs not yielding enough, and thus shearing some of the strands. With the novel terminals, once the geometry and material of the prongs are determined, since the wire insulation is pre-cut by the driver, there is nothing critical about both providing optimum contact of the terminal to the wire, and providing assurance that the terminal will serve adequately in its role of completing the removal of insulation from the contact areas as discussed above.

The nature of the invention in its various aspects, including further novel features and advantages, will be recognized and appreciated more fully from the following detailed description of an illustrative embodiment that is shown in the accompanying drawings.

FIG. 1 is an end view of a novel electrical connector including a base and head;

FIG. 2 is a side view of the connector;

FIG. 3 is a top plan view of the connector;

FIG. 4 shows the head of FIGS. 1-3 including four drivers for four wires, the head being viewed as in the case of FIG. 1;

FIG. 5 is a side view of the head;

FIG. 6 is a bottom plan view of the head, FIGS. 1-6 all being shown enlarged;

FIG. 7 is a greatly enlarged fragmentary view of the driver at the right end of FIG. 4;

FIG. 8 is a fragmentary longitudinal cross-section of the driver as seen from the plane 8--8 in FIG. 7;

FIGS. 9 and 10 are cross-sections of the driver as seen from the planes 9--9 and 10--10, respectively, toward plane X--X in FIG. 8;

FIG. 11 is an enlarged lateral view of one of four terminals of the novel electrical connector;

FIG. 12 is a fragmentary cross-section of the terminal of FIG. 11 at a vertical medial plane;

FIG. 13 shows the terminal as viewed from the right in FIG. 11;

FIG. 14 is a greatly enlarged fragmentary cross-section of portions of the electrical connector, including a driver as seen in FIG. 8 and a terminal, plus a wire in its initial position, just before initial movement of the driver into engagement with the wire;

FIGS. 15 and 16 are fragmentary cross-sections of the structure in FIG. 14 viewed at the planes 15--15 and 16--16 in FIG. 14;

FIG. 17 is a greatly enlarged lateral perspective view of a wire after initial cuts in the insulation are made;

FIG. 17A is a fragmentary view of the insulated wire looking down on FIG. 17;

FIG. 18 is a crosss-section of the wire at plane 18--18 in FIG. 17;

FIG. 19 is a view like FIG. 17A just before the wire is driven between prongs of a terminal; and

FIG. 20 is a cross-section of the wire at plane 18--18 after connection is completed.

In FIGS. 1-3, head 10 includes a cover portion 12 and four drivers 14 of generally rectangular cross-section that slide loosely in like-shaped passages 31' in portion 31 of base member 18. Head 10 and base member 18 are of molded nylon in a practical example, such as heat-stabilized Nylon 6.

Four strips of metal 20, of tin-plated copper alloy in an example, constitute terminals that are appropriately fixed in position in base member 18. Strips 20 are of different lengths to extend into respective wire-clamping collars 22 at staggered positions (FIG. 3). Screws 24 are threaded in the top walls of collars 22. The ends of the screws bear against the top surfaces of their respective strips 20. A wire (not shown) inserted into a collar 22 (from the right in FIG. 2) below its strip 20 is drawn against strip 20 as the screw is tightened. Base member 18 is one of a series of like base members of electrical connectors having bottom formations 26 adapting them to lock onto a mounting rail (not shown). My U.S. Pat. No. 3,253,251, issued May 24, 1966, shows this rail, and the details of collar 22.

As seen in FIGS. 11-13, each terminal 20 includes an upstanding portion 20a that is formed to grip an inserted wire. Its opposite end 20b is received in a collar 22 that clamps a wire against the lower surface of the strip terminal.

The method of manufacture of portion 20a represents a departure from previous methods used for manufacturing wire-stripping terminals. In fabrication, the strip is subjected to a shearing operation that develops a medial slit along the strip, defining a pair of prongs. This lancing operation causes one of the prongs to curve out of its original plane. The slit strip is then flattened. At this point the lanced prong tends to curve divergently from the center line, because parent metal was stretched at the base of lance. The strip is then placed in a confining die section, the walls of which are spaced apart a distance slightly larger than the initial width of the strip up to point A (FIG. 13), and above point A the walls of the die section are spaced by a distance equal to the initial width of the strip plus the width of gap 28. A coining tool then forms depression 30, while the outer edges of prongs 32 are confined between the walls of the die. A shearing tool then cuts the end of the strip to form surfaces 26, which diverge at an angle of 30.degree. in an example. Prongs 32 and their wire-engaging edges at gap 28 become parallel and spaced apart by a controlled uniform dimension less than the nominal diameter of the wire to be forced into the gap. Advantageously, the part is heat-treated to relieve stresses, largely or entirely eliminating any pre-tensioning of the prongs toward each other. By virtue of slit 34 below the coined depression 30, flexibility of the prongs is increased so that they can spread apart elastically and grip tightly but resiliently wires of a limited range of different diameters when forced into gap 28.

The drivers 14 of the head are shaped as shown in FIGS. 4 through 10. As noted above, drivers 14 slide loosely in portion 31 of base member 18. The outermost drivers 14 have outward projecting detents 36 (FIG. 4) that cooperate with complementary cavities 37 and 38 (FIG. 1) in base member 18 to hold head 10 alternatively in its elevated (solid-line) position and in its fully depressed (dotted-line) position. Driver 14 has a slot 39 that is only slightly wider (e.g. 0.055 inch) than the thickness of terminal 20 (e.g. 0.047 inch). Driver 14 also has a slot 40 (FIG. 4) which, with slot 39, divides the lower end portion of driver 14 into four legs 42 (FIG. 6), namely legs 42a, 42b, 42c and 42d (FIG. 9). The surfaces of slot 39 are parallel to the broad faces of strip portion 20a. Strip portion 20a is received in slot 39 when the head is depressed. The legs of driver 14 have recesses defined in part by surfaces a and b (FIGS. 8 and 14) which lie in planes parallel to the plane of those views. Each slot 40 has chamfers 48 that meet the faces of slot 39 at dull insulation-cutting edges 47 (e.g. 0.005 inch wide). (Even if these cutting edges were sharp, they would become deformed in the cutting operation and then they would behave as dull edges). Tiny triangular areas 44 diverge from their apices at cutting edges 47 and span the insulated wire. Edges 47 merge into shearing edge 46 over the wire. The included angle between the surfaces that form cutting and shearing edges 47 and 46 may vary widely in dependence on the hardness of the driver and the hardness of the wire insulation, for example 30.degree. to 60.degree.. The material of drivers 14, in an example, is a tough grade of nylon, e.g. heat-stabilized Nylon 6. This has proved highly effective for making incisions into and through the insulation of vinyl-insulated wire without damaging solid or stranded copper wire. For this purpose, the material of driver 14 in an example may have a hardness of Rockwell Scale R110 to 118. Gap 28 is narrower than the space between the opposed cutting edges 47 as seen in FIG. 15.

In use, a wire W is inserted in slot 40 above diverging edges 26 (FIG. 15) of terminal 20, as shown in FIGS. 1-3. Upward-diverging edges 26 of terminal 20 and downward-diverging areas 44 act initially to center the wire above gap 28, the narrowed top portions 14' permitting drivers 14 to deflect sideways, as needed to ensure centering. The wire is centered by the action of a couple which comprises the wire-engaging areas of the driver and of the prongs. These areas in pairs diverge downward and upward, respectively, in the illustrated example, yielding the benefit already noted of causing the wire to center each driver over the respective pairs of prongs.

As head 10 is driven downward farther, areas 44 are driven into the insulation. At this time, prongs 32 support the wire against the driver's thrust. In an example, strip 20 is resilient copper alloy 0.047.times.0.135 inch so that the ends of the prongs provide supporting areas for the wire against the thrust of the driver. Areas 44 start to make incisions in the wire insulation, these areas being defined by the surfaces of slot 39 and surfaces 48 extending at an angle to each other, and in addition slanting about 30.degree. to the vertical. Areas 44 and edges 47 thus progressively form two pairs of incisions I (FIGS. 17 and 17A) in the wire insulation at opposite sides of the wire, each transverse pair being separated along the axis of the wire by a distance slightly greater than the thickness of portion 20a of terminal 20. These four incisions divide two bands M of insulation from the remainder of the wire insulation. Bands M are connected to the wire insulation at necks N and N' (FIGS. 17 and 18). After incisions I have been made, formations 46 and their adjacent chamfered surfaces drive downward and form incisions I' (FIG. 19), into or through the insulation on the top surface of the wire, thus forming an inverted "U"-shaped strip of insulation U (FIG. 19) attached to the rest of the wire insulation only at neck N. Further downward movement of head 10 forces conductor C toward gap 28 of terminal portion 20a, shearing the strip U from the neck N. The stiffness required of prongs 32 is, therefore, only that required to shear insulation at the neck N. Continuation of downward movement forces conductor C into the gap 28, both compressing the stranded wire and spreading the prongs 32 elastically. The end result is shown in FIG. 20. A U-shaped piece of insulation has been removed from the wire. Neck N of insulation has entered gap 28 of the terminal. Notably, three steps occur: (1) the driver first forms U-shaped incisions; (2) the driver forces the wire toward the terminal slot 28, causing the ends of the U-shaped strip of insulation to be ruptured so as to part the U-shaped strip completely from the rest of the insulation; and (3) the bared conductor is forced into the gap 28 between the prongs of the metal terminal.

It is understood that the sequence of cutting actions may vary, depending on the geometry of the cooperating parts and on their relative hardnesses. Thus, the parting of neck N' from the insulation along the wire, resulting from the action of the driver, might be less than complete before the wire is driven downward between the prongs. In that event, complete rupture of neck N' would take place while the wire is moving downward between the prongs of the terminal. Correspondingly, the slots I may penetrate incompletely through the insulation in some cases, making it easy for the prongs of the terminal to complete the removal of the wire insulation where the conductor is to be bared.

Conductor C often is of stranded copper. Chamfered or rounded transitions 50 are provided between diverging end surfaces 26 and the edges of slot 28, thereby avoiding damage to the conductor, as by tearing some of the strands of the conductor C. At the same time, prongs 32 are elastically spread a little in receiving the conductor C and thus grip conductor C resiliently. This resilience is controlled by the extended length of the cut 34 below gap 28 that divides the terminal prongs, and by the modulus of elasticity of the metal. The collective cross-section of the stranded conductor C is distorted by the grip of terminal portion 20a, but a secure connection is realized. Prongs 32 do not require any initial pre-bias. However, after the conductor is forced into gap 28, prongs 32 apply firm bias and make dependable contact to conductor C. Within limits, various wire sizes can be accommodated, and multiple wires having respective stranded conductors can be forced into gap 28 in successive driving operations of head 14.

Referring once again to FIGS. 1-3, drivers 14 extend into a space below guide portion 31 of the base member 18. In this region, the four legs 42 of the driver operate between and slide along walls 18' forming outside walls and inter-phase barriers providing external insulation for the terminals 20 and insulating terminals 20 from each other. Between walls 18' and below portion 31 of the base member, there are large openings 50 for each circuit, to admit a wire W and to facilitate assembly of terminals 20 into base member 18.

The illustrative embodiment of the invention described in detail above and shown in the accompanying drawings is readily modified by those skilled in the art without departing from the spirit of the invention and, accordingly, the invention should be broadly construed.