GB2124040A - Further improvements in electric fittings - Google Patents

Abstract

An electric fitting, particularly a plug connector, has two relatively movable body parts (1, 2) which clamp the conductors of an electric lead between them. The main body part has three individual valleys (25, 26, 27) housing metal contact strips each provided with a clamping element (12, 14, 16) of toothed configuration. The second body part (2) of plastics material carries three blocks (28, 29, 30) integral therewith in positions corresponding to the metal clamping elements. Each of the blocks has a flat clamping surface (78) and enters a respective valley (25, 26, 27) as the two body parts are closed. A preferred configuration of the metal clamping elements is described in which a parallel sided trough 68 is present between a pair of teeth (66, 67). The electric fitting also has a cord grip having a head unit (80) which is resilient and which is held in guides (91) so that it adopts a transverse position relative to the cord. It is urged against the cord by a screw (31) having an axial bore, in which a stud on the head unit is rotatably engaged. <IMAGE>

Description

SPECIFICATION Further improvements in electric fittings This invention relates to electric fittings and is an improvement in or modification of the invention of British Patents Nos. 1 600 066 and 1600067.

British Patent No. 1 600 066 describes an electric plug connector comprising a body having a bottom surface from which contact pins project, conductive tracks within the body leading from the contact pins to individual contact positions, and securing means for securing two or more individual conductors of an electric lead in said contact positions, said body comprising a main body part and a clamping part which is movable relative thereto, wherein the bottom surface of the body has a recess which receives the clamping part, and the said contact positions are located in the said recess so that a single clamping movement of the clamping part relative to the main body part operates the securing means for all of the contact positions.

British Patent No. 1 600 067 describes an electric fitting comprising a body having first and second relatively movable body parts and securing means for securing two or more individual conductors of an electric lead in individual contact positions in the body, each of said contact positions being located in an individual valley on said first body part, a first clamping element of saw-tooth configuration in each of said valleys with the teeth lying across the valley, and second clamping elements of complementary saw-tooth configuration in corresponding positions on said second body part, such that conductors of an electric lead may be laid in the valleys over the first saw-tooth clamping elements and a single clamping movement of one body part relative to the other body part operates the securing means for all of the contact positions by gripping the conductors between the complementary clamping elements.

In relation to the electric fittings of British Patent No. 1 600 067 it has been found that the use of two clamping elements of complementary saw-tooth configuration is unsatisfactory in some situations, particularly if the cord has a relatively thick insulating covering.

According to one aspect, the present invention provides an electric fitting comprising a body having first and second relatively movable body parts and securing means for securing two or more individual conductors of an electric lead in individual contact positions in the body, each of said contact positions being located in an individual valley on said first body part, a first clamping element of toothed configuration in each of said valleys with the teeth lying across the valley and second clamping elements of non-toothed configuration in corresponding positions on said second body part, each of said second clamping elements comprising a block carried on said second body part in a position corresponding to a respective one of said contact positions in a valley, each of said blocks having a flat clamping surface and being adapted to seat down onto a first clamping element in the respective valley such that conductors of an electric lead may be laid in the valleys over the first toothed clamping element and a single clamping movement of one body part relative to the other body part operates the securing means for all of the contact positions by gripping the conductors between the respective clamping elements.

Preferably each of the first clamping elements comprises two spaced-apart teeth in the form of parallel ridges in which the opposed inward faces of the two ridges are in planes which are substantially parallel to each other and to the general direction of clamping movement, whereas the outward faces of the ridges are each inclined at an acute angle to the respective inward face.

The plug connector as described in British Patent No. 1 600 066 is provided with a cord grip in the form of a screw which extends through the clamping part. The inner end of the screw is broadened out into a head having a textured surface. When the clamping part is closed against the main body part, the screw can be tightened from outside the plug to press the electric cord against the main body part.

It has been found that the cord grip as described above may be too severe in its effect on the cord and in very rigorous testing the cord grip has been found to damage the cord in a small percentage of cases.

It is an object of the present invention to provide a cord grip which does not have this disadvantage. The cord grip of the invention is useful in plug connectors and other electric fittings which are not necessarily in accordance with British Patent No. 1 600 066 or 1 600 067.

According to a second aspect of the present invention, a cord grip for electric fittings comprises a screw having an axial bore therein, and a head unit of plastics material which has the following features: a) it is provided with a stud which is rotatably engageable in the bore in the screw b) it is shaped so that it can be held against rotation in the electric fitting c) it has a pressing surface perpendicular to the axis of the stud for acting against a cord to grip it in the electric fitting d) it is hollow behind the pressing surface so that it has a limited resilience in the direction of the axis of the stud.

Preferably the head unit is a hexahedron with at least four generally rectangular faces, one of which is the pressing surface. In this case, the head unit is adapted to be held in the electric fitting with the long edges of the pressing surface transverse to the cord. The hollow in the head unit is preferably provided by an elongated slot through the head unit in a direction parallel to the pressing surface.

According to a third aspect, the present invention provides an electric fitting comprising a body having first and second relatively movable body parts and a channel which gives access for a cord into said body, said fitting having a cord grip comprising a screw which is movable in threaded engagement in the second body part in a direction perpendicular to said channel, and a head unit which is urged by said screw towards said first body part to grip the cord in said channel, the head unit being held in guides so that it lies transversely across said channel.

When the screw of this improved cord grip is tightened in an internally-threaded aperture in the electric fitting, the head unit does not turn but remains in a transverse position across the cord. Nevertheless the action of tightening the screw presses the head unit onto the cord and thus presses the cord against the main body part of the fitting. The limited resilience in the head unit enables the pressing surface of the head unit to adopt a somewhat arcuate shape which assists in locating and gripping the cord.

Various aspects of the invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view from the rear of the bottom of one embodiment of a plug in accordance with the invention having a flat clamping means, the flap being shown in the open position; Fig. 1 is comparable to Fig. 1 of British Patents Nos. 1 600066/7; Figure 2 shows a top view of the flap of Fig. 1 (omitting the cord grip); Fig. 2 is comparable to Fig. 6 of British Patents Nos.

1 600066/7; Figure 3 is similar to Fig. 2 but showing the cord grip in position; Figure 4 is an exploded perspective view of the cord grip; Figure 5 is an exploded side view of the cord grip, with the screw shown in section; Figure 6 is an enlarged side view of the toothed configuration of a clamping claw of the main body part together with a clamping element of the flap; Figure 7 is a further enlarged side view of one of the teeth; Figure 8a, b and c are respectively a side view, a bottom view and an end view of an earth contact strip and claw; Figure 9a, b and c are a top view and two side views of a live contact strip and claw; Figure 1 ova, b and c are respectively a top view and two side views of a neutral contact strip;; Figure 11 is a cross section through a pair of clamping elements on the line A-A in Fig.

12; Figure 12 is a cross section on the line B-B in Fig. 11.

The plug shown in Fig. 1 is similar to that in Figs. 1-7 of British Patents Nos.

1 600 066/7 and the same reference numerals are used for equivalent parts. The clamping movement of the flap 2 relative to the main body part 1 is the same as in the said Patents. The bottom surface 18 of the main body part, from which earth pin 3, neutral pin 4 and live pin 5 extend, has a recess 51 which receives the flap 2. The flap is hinged on stub axles 62 which project from a neck portion 63 of the flap. The neck portion is slidably received in a bay portion 64 of the recess 51 defined by the base 40 between contact pins 4 and 5, and the stub axles rotate and slide up and down in channels 65 which face each other across the bay portion 64. The stub axles are inserted from above into the channels 65 before the base 40 is assembled with the cover 41.

Platform 1 7 in the recess 51 is formed by the cover 41. Three valleys or lead channels 25, 26, 27 are provided in the platform 1 7 and contact positions 12, 14, 16 are located in the valleys. Live contact strip 11 lies in valley 25, neutral contact strip 1 3 lies in valley 26, and earth contact strip 1 5 lies in valley 27. The contact strips are of brass.

The end portion of each of the contact strips is a claw formed with a toothed configuration. The teeth 66, 67 extend across each of the respective valleys.

The toothed configuration for the claw on each of the contact strips is shown in more detail in Figs. 6 and 7. Each claw consists of two ridge-shaped teeth 66, 67 separated by a trough 68 having a width dwhich is suitably about 2 mm. The teeth have a height h which is suitably about 1.7 mm. The height of the teeth is exaggerated in Fig. 1 for purposes of clarity and explanation.

The opposed inward faces 69, 70 of the teeth 66, 67 respectively are parallel to one another and perpendicular to the contact strip 11 (or 13 or 15). The inward faces 69, 70 therefore lie in planes which are parallel to each other and to the direction of clamping movement, furthermore, the sides of the trough 68, formed by the faces 69, 70 are also parallel. The outward faces 71, 72 of the teeth are inclined at an acute angle (suitably about 30 ) to the inward faces. The peak 73 of each tooth is flattened, as shown in Fig. 7, so as to form a somewhat blunted cutting edge 79.

The teeth project from a block 74 which itself projects from the free end of the respective contact strips 11, 13, 15. The other end portion 75 of the live contact strip 11 is secured to a fuse holder (not shown), while the other ends 76, 77 of the neutral contact strip 1 3 and the earth contact strip 1 5 are secured at the top of the neutral pin 4 and earth pin 3 respectively. The contact strips are received in grooves in the cover 41 which are generally similar to those shown in Fig. 4 of British Patents Nos. 1 600 066/7, although it will be seen from Figs. 9a and 1 Oa of the present application that the shapes of the live and neutral contact strips are somewhat different from those of the said Patents.

The flap 2 carries three clamping members 28, 29, 30 in locations which correspond to the three contact positions 12, 14, 16. Each of the clamping members 28, 29, 30 comprises a block of truncated triangular cross section with a flat clamping surface 78 which is of slightly greater area than the area bounded by the cutting edges 79 of the teeth 66, 67, i.e. the clamping surface 78 has a width substantially equal to the ridge-length of the teeth, and a length in the direction d which is slightly greater than the separation d between the teeth, as shown in Fig. 6. The blocks are formed of the plastics material of the flap and are dimensioned to fit into the respective valleys.

When the flap is closed, each of the clamping members 28, 29, 30 seats down onto a respective set of teeth in one of the contact positions 12, 14, 1 6. The upper face of the flap 2 comes flush or substantially flush against the platform 1 7 and the blocks 28, 29, 30 enter the respective valleys, 25, 26, 27; the extent of penetration of the blocks into the valleys is greater than would be evident from Fig. 1, due to the exaggerated height of the teeth in that Figure, as already explained. If a conductor with its insulating covering intact has been laid into each of the valleys 27, the conductor is clamped between the cutting edges 79 of the teeth 66, 67 on the one hand and the respective clamping member on the other hand. The cutting edges 79 cut through the insulating covering until they contact the conductor wire.Surplus insulating material can be accommodated in the trough 68 between the teeth. The clamping surface 78 presses against the insulating covering but does not cut into it.

Figs. 11 and 1 2 show the closed position of a pair of clamping elements 14 and 29; (the other pairs of clamping elements are similar). The contact strip 14 lies in a valley 26 defined by side walls 96, 97. At the end where the conductor is to be introduced the valley is partly closed by a transverse wall 98 having a notch 99 to accommodate the conductor. One side wall 97 has a bevelled edge 100 to permit the block 29 to enter the valley as the flap 2 is swivelled into the clamping position; (this bevelled edge is not necessary in valley 27). The flap 2 has been closed down until it is almost flush with the surface of platform 17. The block 29 has entered the valley 26 to clamp the conductor (not shown) between clamping surface 78 and the cutting edges of teeth 66, 67.

Flap 2 is provided with a cord grip as shown in inverted position in Figs. 4 and 5 (although in the correct disposition for consideration in relation to Fig. 1). The cord grip comprises a screw 31 and a head unit 80.

The screw 31 is an externally threaded cylinder, suitably of plastics material, (e.g. nylon 66) with a slot 95 to receive a screw-driver at its lower end and an axial bore 81 extending into the cylinder at its upper end. The bore has an entry portion 93 of restricted diameter and broadens into the interior of the cylinder.

The screw 31 is drivable in an internally threaded aperture 82 in flap 2.

The head unit or "saddle" 80 comprises a 6-sided polyhedron of plastics material, e.g.

an acetal resin, with 4 rectangular faces. One face 83 is the pressing surface which acts against the cord. A cylindrical stud 84 projects from the face 85 which is opposed to the pressing surface 83. The stud 84 is a loose rotatable fit in the bore 81 of the head unit. A rib 86 extends around the stud just above its median line. This rib is a push fit in the entry portion 93 of the bore. After it has been pushed home, the entry portion of the bore is freely rotatable on the portion of the stud between rib 86 and face 85, the top surface 87 of the screw abutting face 85 of the head unit.

The head unit is penetrated by a moulded slot 88 which extends parallel to the pressing surface 83. A bridge 89 of plastics material remains between the slot 88 and the pressing surface 83. The slot is longer than the diameter of any cord which is likely to be used in this plug and it permits the bridge 89 to flex inwardly so as to form an arcuate portion when it is engaged against the surface of a cord. In Fig. 5, a cord 94 is indicated in dotted outline and the flexed position of the bridge 89 is also shown in dotted outline. The head unit suitably is about 20 mm long, about 5 mm broad, and about 6 mm deep, while the slot is about 1 2 mm long and about 2 mm deep.

The head unit slides up and down in a rectangular recess 90 on both sides of opening channel 24 in the flap 2, the guide surfaces being provided by two pairs of opposed pillars 91 formed in the material of the flap. When it is tightened against the main body portion, the head unit is received in a rectangular recess 92 extending across the platform 1 7 on both sides of the opening channel 23.

The screw 31 is inserted into aperture 82 from below and head unit 80 is then placed into position in recess 90, the stud 84 being slid into bore 81 until rib 86 engages behind entry portion 93. Head unit 80 is thus retained in position in the flap.

After a cord 94 has been laid in opening channel 23 with the three conductor ends in contact positions 12, 14, 16, the flap 2 is closed and fixing screws 20 are tightened to clamp the flap 2 firmly against the main body part 1 and to clamp the conductors between the teeth 66, 67 and clamping elements 28, 29, 30.

When the screw 31 is tightened, it urges pressing surface 83 against the cord 94, head unit 80 being held against rotation by pillars 91. Thus the head unit remains transverse to the cord as it is tightened and grips the cord against the main body part 1.

This cord grip is capable of gripping a variety of different kinds of cord such as 3 X 1.5 mm2 PVC cord, 2 x 0.5 mm2 flat twin PVC cord and 3 x 1.5 mm2 rubber cord.

Because the head of the cord grip does not rotate relative to the cord, it has a relatively gentle action on the cord and does not damage the cord. Nevertheless it has been found in tests to exert a very satisfactory grip on cords as mentioned above.

Claims (9)

1. An electric fitting comprising a body having first and second relatively movable body parts and securing means for securing two or more individual conductors of an electric lead in individual contact positions in the body, each of said contact positions being located in an individual valley on said first body part, a first clamping element of toothed configuration in each of said valleys with the teeth lying across the valley and second clamping elements of non-toothed configuration in corresponding positions on said second body part, each of said second clamping elements comprising a block carried on said second body part in a position corresponding to a respective one of said contact positions in a valley, each of said blocks having a flat clamping surface and being adapted to seat down onto a first clamping element in the respective valley such that conductors of an electric lead may be laid in the valleys over the first toothed clamping element and a single clamping movement of one body part relative to the other body part operates the securing means for all of the contact positions by gripping the conductors between the respective clamping elements.

2. An electric fitting according to claim 1, wherein each of the first clamping elements comprises two spaced-apart teeth in the form of parallel ridges in which the opposed inward faces of the two ridges are in planes which are substantially parallel to each other and to the general direction of clamping movement, whereas the outward faces of the ridges are each inclined at an acute angle to the respective inward face.

3. An electric fitting according to either of the preceding claims, wherein the peak of each tooth is adapted to cut through an insulating covering on a conductor.

4. An electric fitting according to claim 3, wherein a parallel-sided trough is provided between the teeth to accommodate insulating material.

5. An electric fitting having a cord grip comprising a screw having an axial bore therein, and a head unit of plastics material which has the following features: a) it is provided with a stud which is rotatably engageable in the bore in the screw b) it is shaped so that it can be held against rotation in the electric fitting c) it has a pressing surface perpendicular to the axis of the stud for acting against a cord to grip it in the electric fitting d) it is hollow behind the pressing surface so that it has a limited resilience in the direction of the axis of the stud.

6. An electric fitting according to claim 5, wherein the head unit is a hexahedron with at least four generally rectangular faces, one of which is the pressing surface.

7. An electric fitting according to claim 5 or 6, wherein the hollow in the head unit is provided by an elongated slot through the head unit in a direction parallel to the pressing surface.

8. An electric fitting comprising a body having first and second relatively movable body parts and a channel which gives access for a cord into said body, said fitting having a cord grip comprising a screw which is movable in threaded engagement in the second body part in a direction perpendicular to said channel, and a head unit which is urged by said screw towards said first body part to grip the cord in said channel, the head unit being held in guides so that it lies transversely across said channel.

9. An electric fitting substantially as described herein with reference to the accompanying drawings.