Electrical connector

Abstract

An electrical connector assembly in the form of a tubular element having a generally cylindrical cross section formed from a strap-like member with overlapped curvilinear end portions. The overlapped end portions are tapped and threaded while the tubular element is in a clamped, compressed condition and while so compressed clamping screws are threaded into the openings. The tubular element is formed of a high strength material, such as stainless steel, and encloses a sleeve member formed of a conducting material, such as copper, in which the bared end of a conductor is inserted and securely clamped therein by tightening the screws.

Parent Case Text

This is a continuation of application Ser. No. 273,691, filed July 21, 1972, now abandoned.

Description

This invention relates to an electrical connector of the screw actuated pressure type for use as a terminal, a splice or a tap. As distinguished from electrical connectors of the compression type where the connector is swaged over a stranded conductor through the use of precision dies that exert as much as forty tons of pressure, the present invention involves an electrical connector wherein the compression pressure between the stranded conductor and the connector is obtained by tightening a screw.

More specifically, the present invention is an improvement over electrical connectors of the type employing in their assembly overlapping straps or castings or forgings through which one or more screws are driven for clamping the conductor to the connector assembly.

It is an object of this invention to provide an electrical connector of the screw actuated type designed to exert tremendous clamping pressure between the connector and the stranded conductor while eliminating the tendency for the threads in the tapped hole in the connector to strip.

More specifically, the present invention has for its object the provision of an electrical connector capable of producing a permanently high strength connection with a stranded conductor which involves the use of simple stampings utilizing a minimum of material.

Another object of the present invention resides in the provision of a connector in the form of a spirally wound connector member having overlapped ends through which one or more tapped openings are provided for receiving clamping screws designed to exert pressure against the end of a stranded conductor inserted into the spirally wound member.

In connection with the preferred form of the present invention, another object is to provide an electrical connector assembly employing materials which are good electrical conductors for contact with the stranded conductor and employing other materials (such as stainless steel) which have substantially higher strength characteristics and lower ductility than electrical conductors for those components of the connector assembly which are subjected to considerable stress in establishing the high pressure, high strength connection between the connector assembly and the stranded conductor.

Generally speaking, the preferred form of electrical connector of the present invention includes an assembly of an outer tubular element of circular spiral shape having overlapping end portions provided with tapped holes for receiving clamping screws. A sleeve of a conductive material (such as copper) is enclosed within the spirally wound element. The sleeve is provided with openings registering with the clamping screws. Within the sleeve there is arranged a saddle underlying the inner ends of the screws and adapted to overlie the conductor strands adjacent the inner ends of the screws for applying clamping pressure to the conductor strands without crushing or breaking them.

Other features of the present invention will become apparent from the accompanying description and drawings, in which:

FIG. 1 is a perspective view of a stranded conductor cable having the connector of the present invention attached thereto;

FIG. 2 is a sectional view along line 2--2 in FIG. 1;

FIG. 3 is a sectional view along line 3--3 in FIG. 2 and showing one of the clamping screws in the tightened position and the other in the initially assembled condition;

FIG. 4 is a diagrammatic view illustrating one advantage obtained by using curvilinear overlapping end portions in the connector assembly of the present invention;

FIG. 5 is an end view of a four conductor cable utilizing the electrical connector of the present invention;

FIGS. 6 and 7 are perspective views illustrating modified forms of electrical connectors according to the present invention;

FIG. 8 is a perspective view of one component of an electrical connector of the present invention for joining three stranded conductors;

FIG. 9 is an exploded perspective view showing the electrical connector of the present invention employed for connecting a conductor to an electrical storage battery;

FIG. 10 is a sectional view along line 10--10 in FIG. 9;

FIG. 11 is a fragmentary view showing a modified form of the battery connector illustrated in FIG. 9.

Referring first to FIGS. 1 through 3, there is illustrated a cable 10 which comprises a stranded conductor 12 enclosed within an insulating sheath 14. One end of cable 10 has sheath 14 stripped therefrom with the bared ends of the conductor inserted within and clamped to one form of connector assembly 16 of the present invention. Connector assembly 16 includes an outer tubular element 18 in the form of a strap which is spirally wound in circular fashion with overlapping ends 20,22. The inner periphery of tubular element 18 is preferably shaped to present a generally circular cylinder by providing a bend therein as at 24 so that the inner overlapped end portion 22 is formed to the radius of the tubular element 18 and the abrupt bend 24 offsets the outer overlapping end portion 20 radially outwardly. With this arrangement there results only a slight gap 26 in the inner periphery of the generally cylindrical socket 28 defined by member 18. Within socket 28 there is arranged a sleeve 30 formed of a good electrically conducting material (such as copper). The outer diameter of sleeve 30 has a close fit with cylindrical socket 28 and the inner diameter of sleeve 30 is adapted to receive the bared end 32 of cable 10. One end of sleeve 30 is flattened as at 34 to form a terminal lug for connecting cable 10 to another conductor, such as a bus bar or a terminal stud (not illustrated).

As shown in FIG. 2, the extent of overlap of the ends 20,22 is preferably at least about 120.degree.. These overlapping end portions are provided with two tapped openings 36,38 for receiving clamping screws 40,42, respectively. Screws 40,42 preferably have a relatively large diameter in relation to the inner diameter of copper sleeve 30. As shown in FIGS. 2 and 3, sleeve 30 is provided with a pair of openings 44,46 for accommodating the inner ends of screws 40,42.

In the preferred embodiment of the invention tubular element 18 is formed of a high strength, acid resistant material (such as stainless steel) having some degree of resilience. As originally formed and in the free state of element 18 the end portions 20,22 of member 18 are overlapped to a lesser extent than shown in FIG. 2. Thereafter, element 18 is clamped in suitable manner to increase the overlap to the extent shown in FIG. 2. In the clamped condition openings 36,38 are drilled and tapped and screws 40,42 are threaded thereinto. The clamping pressure is then removed from element 18 so that the overlapping end portions 20,22 tend to spring or shift circumferentially apart to the positions they assumed prior to clamping. End portion 20 has a tendency to shift circumferentially in a clockwise direction and end portion 22 has a tendency to shift in a counterclockwise direction as viewed in FIG. 2. Thus, the tension exerted by the overlapping portions 20,22 against diametrically opposite sides of screws 40,42 result in the screws being tightly gripped in the threaded openings. This not only serves to retain the screws within the threaded openings so that they do not become loosened and lost during shipment, but also results in a lock washer effect without requiring a separate lock washer. The radial pressure exerted by the overlapping portions 20,22 against diametrically opposite sides of the screws can be varied from zero or a very slight amount to a very high value, depending upon the clamping pressure exerted against the lateral sides of member 18 when the holes therein are drilled and tapped.

In some instances, particularly in the case of fine wire strands, it is inadvisable to have the inner ends of socket head screws 40,42 bear directly upon the wire strands because of the possibility of shearing or crushing of the wire strands. Accordingly, it is preferred to employ a saddle 48 within sleeve 30 to prevent such shearing, cutting or crushing of the stranded wire. As shown in FIG. 6, saddle 48 has a longitudinally extending strap portion 50 which preferably is of slightly arcuate cross section in a generally transverse direction to conform to the inner diameter of sleeve 30. At one end strap 50 is flared radially outwardly as at 52 and at the opposite end strap 50 is formed with an end portion 54 which extends transversely across sleeve 30 with a return bent end portion 56 adapted to frictionally engage the portion of sleeve 30 diametrically opposite the portion engaged with strap 50. The outwardly flared end 52 of saddle 48 forms a stop for limiting the extent to which the saddle can be inserted into sleeve 30 and the transversely bent portion 54 forms a stop against which the free end of the bared portion 32 of the cable is adapted to abut. Saddle 48 is dimensioned to have a rather tight fit in sleeve 30 so that once it is inserted therein it will be retained by friction, thus enabling the entire assembly to be shaped intact without the probability of individual components becoming loosened and lost.

When it is desired to connect cable 10 to connector 16 the bared end 32 of the cable is inserted within sleeve 30 with the strap portion 50 of the saddle overlying the wire strands circumferentially adjacent the inner ends of screws 40,42. After the bared end of the wire is fully inserted within sleeve 30 to the position shown in FIG. 3, screws 40,42 may be tightened as by a conventional Allen wrench 58. In FIG. 3 screw 40 is shown in the tightened clamping position while screw 42 is shown in the free condition. The section of FIG. 2 is taken through screw 42 and, thus, FIG. 2 illustrates the condition of the connector before the screw is tightened. When screw 42 is tightened so as to advance it to the broken line position 60, the strap portion 50 of saddle 48 will have a depression formed therein similar to the distorted depression 62 formed in the strap portion under the inner end of clamping screw 40. Between these two depressions the strap will remain generally flat as indicated at 63. As can be seen in FIG. 3, tightening of screws 40,42 exerts tremendous pressure against the bared end of the stranded conductor -- particularly those portions thereof radially aligned with the inner ends of screws 40,42. While saddle 48 prevents the wire strands from being crushed or sheared by the ends of the screws, nevertheless the wire strands (particularly those adjacent the inner ends of the screws) are substantially distorted in an axial direction so as to substantially increase the resistance against pulling the cable out of the connector by tensioning the cable. Saddle 48 provides an additional function as illustrated in FIG. 3; namely, that of confining the wire strands within the sleeve 30 so that all of the wire strands are effectively compressed together within the connector when the screws are tightened.

It will be appreciated in the embodiment illustrated in FIGS. 1 through 3, since the tubular element 18, screws 40,42, and preferably saddle 48 are formed of a ferrous material (such as stainless steel) which is substantially stronger than copper or other good electrically conductive materials and since the conductor strands 12 are compressed into intimate contact with sleeve 30 which is formed of copper or the like, the connector assembly provides a low resistance connection between the cable and sleeve 30 while utilizing the high strength characteristics of those components (namely, screws 40,42, saddle 48 and element 18) which are subjected to high mechanical stresses. When screws 40,42 are tightened strap portion 50 would have to fail in tension to pull the cable out of the connector.

The tight spiral design of element 18 possesses several distinct advantages over electrical connectors of the type, for example, shown in U.S. Pat. No. 2,907,978 which shows a generally rectangularly shaped connector with flat overlapping strap portions through which a clamping screw is threaded. One of these advantages is illustrated in FIG. 4 and resides in the fact that when the overlapped portions through which the screws extend are of curvilinear shape a substantially greater amount of thread area results than is the case where the overlapping portions are simply flat strap ends. For example, as shown in FIG. 4, the portions of the threaded openings displaced circumferentially from the axes of screws 40,42 have an axial extent corresponding to the length a. The axial extent of these threads gradually diminishes to a minimum value at each side of the screw aligned with the axis of the connector, which length is designated in FIG. 4 as b. The length b corresponds to the double thickness of the strap from which element 18 is formed. Thus, if the overlapping portions of the connector were formed as flat straps the maximum thread depth would correspond to the dimension b which, as shown diagrammatically in FIG. 4, is substantially less than the maximum axial extent a when the overlapped ends are of curvilinear shape.

For example, in a connector of the present invention where the strap from which element 18 is formed is fourteen gauge metal having a nominal thickness of 0.075 inch and the screws 40,42 have a half inch diameter, if the inner diameter d of element 18 is about three-fourths inch, then the axial extent a of the thread of the curvilinear overlapped portions is over 20 percent greater than the axial extent b, which would be the case if the overlapped portions were simply flat straps. In addition, it will be noted that since threaded openings 36,38 are formed in curvilinear surfaces they are actually of oval shape and, therefore, have a slightly greater circumference than a circular opening formed in a flat surface. Thus, by forming the overlapped end portions 20,22 of curvilinear shape the engaging thread area between the screws and the threaded openings is very substantially increased over similar openings formed in flat overlapping straps. Obviously when the amount of engaged thread area is substantially increased and the overlapping ferrous end portions 20,22 are under spring tension, the tendency for the threads to strip is eliminated.

In addition, since the overlapping end portions 20,22 were coiled and clamped when tapped, they exert a radial pressure on the screw resulting from the coil or spiral attempting to unwind in proportion to the clamping pressure employed when the holes are drilled and tapped. Furthermore, when the strands of the cable end 32 are fully compressed so that the screws "bottom", continued rotation of the screws results in the application of substantial pressure at the section C of the inner overlapped portion 22 and the section D of the outer overlapped portion 20. These are exactly the sections where the threads have their maximum axial extent. If continued force is applied to the screws the inner member 22 cannot rise away from the saddle 48 because it underlies the outer member 20. Therefore very substantial energy is stored within the threads of the inner member 22. Since the free end of the outer member 20 is permitted to rise slightly, continued rotation of the screws after they have bottomed will cause the free end of the outer member 20 to rise slightly, thus resulting in the action of a split lock nut and thereby effectively locking this stored up energy in the connector. Furthermore, the tight circular coil of element 18 has a relatively close fit with sleeve 30 which in turn closely embraces the bared end of the conductor. Thus there is very little slack in the connector which would result in distortion of the connector rather than clamping the conductor when the screws are tightened.

This extremely effective locking action is of great importance in electrical connectors. All electrical conductors physically expand when electrical energy flows through their resistance. This mechanical expansion and contraction through heat and cooling cycles of varying loads is one of the primary causes for connector failure due to bolts, screws or nuts working loose after a period of operation. This problem of loosening of the connectors is aggravated in the case of portable power equipment, such as lift trucks, electric trains and other heavy moving equipment, because of the mechanical vibration involved in the use of such equipment.

Another advantage of the present invention is shown somewhat diagrammatically in FIG. 5 which illustrates a four conductor cable 64 wherein each stranded conductor 66 is provided with a connector such as shown at 16 in FIGS. 1 through 3. When the connectors 16 are arranged as illustrated with their overlapping ends facing radially outwardly, it will be noted that a maximum spacing s between each of the conductors 66 is obtained and that the adjacent portions of the connectors 16 are of single metal thickness. This arrangement is important in connection with three-phase current where it is important to maintain maximum spacing between the conductors. With the conductor of the present arrangement this maximum spacing is obtained within a minimum of all cross sectional area of cable 64 while still retaining the advantages of the tubular curvilinear double thickness of material for the tapped screw holes. In addition, the screws are located around the outer periphery of the cable and are thus radially accessible.

The embodiment illustrated in FIG. 6 is very similar to that illustrated in FIGS. 1 through 3 with the exception that sleeve 68 is a strap of semi-circular configuration as distinguished from the completely circular configuration of sleeve 30 and is stamped from flat stock so as to provide a flat attaching lug 70 integral with one end thereof. In other respects the connector shown in FIG. 6 is similar in construction and function to that shown in FIGS. 1 through 3.

In the embodiment illustrated in FIG. 7 the connector element 72 is shaped similarly to the connector element 18. However, connector element 72 is formed of a conductive material (such as copper) rather than a ferrous material (such as stainless steel). Thus connector element 72 can be formed from flat stock integrally with an attachment lug 74. With the arrangement shown in FIG. 7 the need for an inner sleeve, such as sleeve 68 or sleeve 30, is eliminated but the advantages of the increased thread area because of the curvilinear shape of the overlapped end portions of element 72 are retained.

FIG. 8 illustrates a T-shaped sleeve member 76 having three legs 78. Sleeve member 76 is formed of a good electrically conductive material (such as copper) and is employed with three connectors of the type illustrated in FIGS. 1 through 3 and 6 for electrically interconnecting three cables.

FIGS. 9 through 11 illustrate the connector of the present invention used for connecting a battery cable 80 to a storage battery strap 82. Strap 82 is a lead casting having sockets which are permanently attached to the battery posts 84 by burning them into place so as to puddle the lead. In the arrangement shown in FIGS. 9 and 10, at one end strap 82 has an integrally cast cylindrical socket member 86. In the process of casting strap 82 a copper sleeve 88 (which has the same function as sleeve 30 in FIGS. 1 through 3) is lead coated to resist corrosion and is cast in place within socket member 86. Sleeve 88 is received within a stainless steel tubular element 18 and the battery cable 80 is connected therewith utilizing a saddle 48 in the same manner as described previously in connection with FIGS. 1 through 3. As a matter of convenience sleeve 88 can be formed with diametrically opposed openings 90 so that strap 82 can be inverted from the position shown in FIG. 9 depending upon the post arrangement of the battery and, thus, enable the screw 92 on element 18 to be accessible from the top face of the battery regardless of the orientation of strap 82.

The arrangement shown in FIG. 11 is substantially identical to that shown in FIGS. 9 and 10 except that the socket member 94 is cast on the battery strap 82 so that the axis of socket 94 is inclined at an angle of about 45.degree. to the axis of strap 82. The arrangement shown in FIG. 11 is utilized in connection with batteries of particular design where accessibility to the battery cable connection is facilitated by this angular disposition of the connector.

The connector arrangements illustrated in FIGS. 9 through 11 can be made entirely acid resistant by enclosing the entire connector assembly in an acid resistant, heat shrinkable sleeve (not illustrated).

Claims

I claim:

1. An electrical connector comprising a tubular element formed as a metal strap having overlapped end portions, said overlapped end portions defining generally concentric, circular segments which are disposed in face-to-face contacting relation through an arcuate extent at least about 120.degree., the center of curvature of said circular segments corresponding generally to the central axis of the tubular member, said overlapped portions being provided with a radially extending opening therethrough disposed centrally between the ends thereof, said opening having a thread extending continuously through said overlapped portions, a metal clamping screw threaded through said opening and adapted when tightened to clamp a stranded electrical conductor within the tubular element, said threaded opening having a diameter at least as large as the radius of curvature of the contacting faces of said overlapped end portions so that the axial extent of the threads on diametrically opposite sides of the threaded opening in a direction circumferentially of said overlapped ends is substantially greater than the radial thickness of said overlapped end portions whereby, when a stranded conductor sized to substantially completely fill said tubular element is inserted therein and the screw is tightened, said two overlapped end portions are tensioned circumferentially in opposite directions along the arcuate path of said circular segments when the leading end of the screw bottoms on the conductor and thereby tightly interengage said diametrically opposite sides of said threaded opening substantially throughout their axial extent with the juxtaposed threads of the screw.

2. An electrical connector as called for in claim 1 wherein said tubular element is formed of a resilient metal and is prestressed by circumferential contraction prior to forming the threaded opening therein such that the outer overlapping end portion exerts radial pressure in one circumferential direction against the thread at one side of the screw and the inner overlapping end portion exerts radial pressure in the opposite circumferential direction against the thread at the circumferentially opposite side of the screw.

3. An electrical connector as called for in claim 2 wherein the outer overlapping end portion has a radially outwardly bent portion adjacent the free end of the inner overlapping end portion, the free end of the inner overlapped portion being disposed directly adjacent said radially outwardly bent portion and serving to limit the extent to which the tubular element can be circumferentially contracted and thereby control said radial pressures exerted by said overlapping portions against opposite sides of the screw thread.

4. An electrical connector as called for in claim 3 wherein the inner overlapped end portion cooperates with the inner periphery of the remaining portion of said strap to define a generally cylindrical socket for the end of the stranded electrical conductor.

5. An electrical connector as called for in claim 1 including an axially extending sleeve having a close fit in said tubular element, said sleeve being formed of a highly electrically conductive material and having an opening therein registering with the inner end of said screw and through which the screw is adapted to extend, and a separate metal saddle member removably disposed within said sleeve and being formed of a readily deformable metal, said saddle extending axially within said sleeve and registering axially and circumferentially with the inner end of said screw.

6. An electrical connector as called for in claim 5 wherein said metal saddle comprises a sheet metal strip having one end disposed within said tubular element adjacent one end thereof and its opposite end projecting outwardly from the opposite end of the tubular element, the inner end of said saddle defining an end wall in the tubular element for limiting the extent to which a conductor can be inserted therein and the outer end engaging said opposite end of said tubular member to limit the extent to which the saddle can be inserted into said tubular element.

7. An electrical connector as called for in claim 6 wherein said saddle is sized to be frictionally retained within the tubular element.