GB2137440A - Screwless terminal - Google Patents

Abstract

A screwless terminal has a spring (4) acting on a clamping cage (3) which clamps an inserted conductor (1) to a current bar (2). A lever mechanism (13) which acts to release the clamping cage (3) from its normally-open position has a force applied to one end (15) by the conductor being inserted and the force is amplified by its other end engaging a projecting lever (11) of the clamping cage (3), a significant distance from a retaining detent arrangement (5,6) which is then released causing the cage (3) to clamp the conductor. In another embodiment, the lever mechanism is in the form of a three-sided lever arrangement, one side being longitudinally displaceable by the conductor, to cause a rotational release movement of another side of the arrangement. <IMAGE>

Description

SPECIFICATION Screwless terminal This invention relates to a screwless terminal, in other words a terminal in which the force for retaining a conductor is derived from means other than a screw connection.

Many different types of such screwless terminals are known, wherein one or more springs secure the inserted conductor either directly or by means of a member which is engaged by the spring, for example by means of a clamping cage which is disposed around the spring in the closed position of the terminal. In the open position of the terminal, the springs or the member engaging same are releasably latched in the open position of the terminal, wherein release of the latching action is effected either by means of a tool which is passed through a closing opening provided in the housing of the terminal, or by virtue of the arrangement having release members which have already been disposed in the path of movement of the conductor to be inserted.The conductor, upon being inserted, impinges against the front of the release members causing the release members to act on the spring or the member engaged by the spring, in the direction of release of the latching action.

Reference is to be made, for example, to German patent specification No. DE-A-3 042 057 which describes such screwless terminals with or without a release member and with a spring-loaded clamping cage. Reference is also to be made to German patent specification No. DE-A-3 109 149 as an example of screwless terminals wherein the spring is latched directly to a release member.

Even in the case of screwless terminals which operate with a release member, in the constructions which have hitherto been known, there is no guarantee that the terminal will be reliably closed by virtue of the conductor being inserted therein, in particular when the conductor used is of relatively thin wire.

When such a thin wire conductor is inserted, the release force required for releasing the latching arrangement cannot be applied by the conductor and instead the conductor bends. In that respect, account must be taken of the fact that the terminal is produced in the open condition by the manufacturer, and the open position of the terminal must therefore be maintained even during transportation to the user. The consequence of this is that a really strong latching action needs to be provided which requires a correspondingly high release force. Otherwise, it very frequently happens that when the terminal finally reaches the user and is to be fitted by that person, the terminal is no longer in its open position so that the user firstly has to move it back into its open position.Having regard to the problems referred to above, terminals which operate with a release member are usually also provided with a closing opening for a tool so that, when using a thin wire conductor, the terminal can still be closed by means of the tool rather than by pressure from the conductor.

The present invention provides a screwless terminal having a spring operative to clamp an inserted conductor directly or by means of a member engaged by said spring, the spring or the member engaged thereby being releasably latched in an open position of the terminal, and having a release member disposed in the path of movement of the conductor to be inserted, wherein the release member comprises a lever mechanism disposed with one end in the path of movement of the conductor so as to amplify the release force applied thereto by the conductor and/or the moment thereof, the other end of said lever mechanism acting on the spring or the member engaged thereby to clamp the conductor in a closed position of the terminal.

Preferred embodiments of the invention provide screwless terminals which can be very reliably closed, even when using thin wire conductors, by insertion of the conductor itself.

The fact that the release member is in the form of a lever mechanism which amplifies the release force and/or the lever arm thereof provides that at any event, even the relatively small force which can be provided by a thin wire conductor and which can be applied to the lever mechanism without the risk of deforming the conductor, is sufficient to be able to cause the latching action to be released reliably, by the other end of the lever mechanism, whether a considerable release force can be applied by means of the output end of the lever mechanism or whether a considerable turning moment is formed in respect of the release force, by virtue of the spatial position of the output end of the lever mechanism.In that connection, it has surprisingly been found that the required transmission effect can be satisfactorily provided, in spite of the small size of the space available for this purpose in terminals of this kind.

Another advantage is that, as a result of the degree of reliability with which the release action can be produced even by means of a thin wire conductor, there is no longer any need for a closing opening for inserting a tool into the housing of the terminal, and the terminal housing can therefore be simplified in that respect.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a view in partial section through the connecting region of a screwless terminal according to one embodiment of the invention; and Figure 2 shows a corresponding partial section through part of a further screwless terminal according to another embodiment of the invention, but on an enlarged scale compared to Figure 1.

In the screwless terminal illustrated in Figure 1, in the clamping region which is of interest here, for the purposes of securing the conductor 1 which is to be inserted, the underside of a current bar 2 which is of a double-ply construction carries a clamping cage 3 through which the current bar 2 extends. Bearing against the top of the clamping cage 3 is a spring 4 which at its other end is supported against the top of the current bar 2. In the open position of the terminal, as shown in Figure 1, with the spring 4 in a compressed condition the clamping cage 3 is latched in an inclined tilted position by means of detent projections 5 provided thereon engaging into detent recesses 6 provided in a portion, that projects on both sides, of the upper layer or ply of the double-ply current bar 2.

The enclosing housing 7 of the terminal has one insertion opening 8 for inserting the conductor 1, and another insertion opening 9 on its top for inserting a tool in order to be able to move the clamping cage 3 into the open position as shown.

Also provided within the terminal housing 7 is a rounded guide cam portion 10 in order to facilitate the tilting movement of the clamping cage 3.

In addition, in this embodiment, secured to the clamping cage 3 on the underside thereof, on the side of the clamping cage which corresponds to the direction in which the conductor is withdrawn, is a lever 11 which projects downwardly and towards the above-mentioned side of the clamping cage 3.

Formed on the inside surface of the wall of the housing 7 of the terminal, in the path of movement of the lever 11, in a contact or abutment region 12.

Therefore, when the terminal is in the closed position and the conductor has been inserted therein, in the event of severe withdrawal force acting on the conductor, the lever 11 impinges against the region 12, the clamping cage 3 is caused to tilt and the conductor 1 is thus very securely pressed firmly in position.

A screwless terminal of this kind is supplied to the user by the manufacture in the open position as illustrated. The terminal is closed by inserting the conductor 1 itself. For that purpose, in the illustrated embodiment a release member is formed from a double-arm angle lever 13 which is mounted pivotalliy on a spindle or shaft 14 in the terminal housing.

One lever arm has a projection 15 projecting slightly within the clamping cage 3, in the path of movement of the conductor 1 to be inserted. The free end of the otherleverarmofthedouble-arm angle lever 13, that is to say, in practice, the output end of the lever mechanism, now acts on the lower free end of the lever 11 which is secured to the cage 3. Therefore, the lever action or moment with which the release force acts on the retaining connection of the clamping cage 3 is considerably amplified by way ofthe lever mechanism. The drawing shows that the moment of the force if applied directly by the conductor 1 with respect to the detent means would be clearly small.However, the lever mechanism provides a considerable step-up or amplifying transmission effect as the output end engages the cage 3 or the lever 11 secured thereto at the furtherest possible point from the detent region. In that way, a relatively small force which is applied by the conductor 1 to the lever mechanism 13 is sufficient to overcome a relatively high holding force in the detent latching means 5,6 applied by the spring 4.

Referring to Figure 2, with the screwless terminal illustrated therein being in other respects of similar construction to that of Figure 1, the embodiment shown in Figure 2 illustrates a different lever mechanism which itself provides for a step-up or amplifying transmission of the release force. For this purpose, a first lever part 17 is guided in the path of movement of the conductor 1 to be inserted, being longitudinally displaceable between the current bar 2 and a lug or projection 18 on the terminal housing.

At its end remote from the conductor 1, the lever part 17 is connected byway of an elastic region 19to a first one of two returning lever parts 20 and 21 which form a substantially triangular shape with the lever part 17 and which in turn are connected together by way of an elastic region 22. In that respect, the output lever part 21 is rotatably mounted on a shaft or spindle 23 in the vicinity of its output end, and is of a forked configuration at its operative end; the two forks 24 projecting to such a degree that, in the vicinity of the retaining detent connection 5,6, they can act on the two side walls of the clamping cage 3.

The conductor 1 is inserted between the two forks 24 and can be pressed against the end of the lever 17 which is facing the conductor. In this construction, when closing the screwless terminal, a relatively small force applied to the lever part 17 by the conductor 1 results, with deformation of the elastic regions 19 and 22, in a considerable movement of the lever part 17 and that, with a small displacement or pivotal movement of the output end about the shaft or spindle 23, results at the output end in a relatively high force being applied to the clamping cage 3, in the direction of releasing the retaining detent connection 5,6.

The embodiment of Figure 2 is particularly suitable for use in a very large number of different kinds of screwless terminal as it is clear that a lever mechanism 17,20,21 of that kind can also be arranged to act on a spring which is directly latched and arranged to clamp the conductor directly, even when the mechanism acts in the direct vicinity of its latching connection, using a high release force.

Claims (5)

1. A screwless terminal having a spring opera tire to clamp an inserted conductor directly or by means of a member engaged by said spring, the spring or the member engaged thereby being releasably latched in an open position of the terminal, and having a release member disposed in the path of movement of the conductor to be inserted, wherein the release member comprises a lever mechanism disposed with one end in the path of movement of the conductor so as to amplify the release force applied thereto by the conductor and/or the moment thereof, the other end of said lever mechanism acting on the spring or the member engaged thereby to clamp the conductor in a closed position of the terminal.

2. A terminal according to claim 1, wherein the lever mechanism comprises a first lever which is longitudinally displaceably guided in the path of movement of the conductor and which is connected by way of an elastic region to a second lever, which first and second levers together with a third lever form a triangle with the second and third levers also being connected together by way of an elastic region, the third lever being mounted rotatably in the vicinity of an output end thereof.

3. A terminal according to claim 1 or claim 2, wherein an output end of a releasing lever of the lever mechanism is turned back into the path of movement of the conductor to be inserted and is formed as a fork.

4. A terminal according to claim 1, having a displaceable and tiltable clamping cage which is subjected to the pressure of the spring and which is releasably latched in a tilted position in the open position of the terminal, a downwardly projecting lever being secured to the clamping cage on the side corresponding to the direction in which the conductor is withdrawn, wherein the lever mechanism is a rotatably mounted double arm angle lever, an output end of which acts on the end of the downwardly projecting lever secured to the clamping cage.

5. A screwless terminal substantially as hereinbefore described with reference to and as illustrated in Figure 1 or Figure 2 of the accompanying drawings.