Patent Application
20140113507
The invention relates to a flexible tunnel for connection terminal, said tunnel being made by cutting and bending a metal strip to form a flexible frame delimiting an opening of quadrangular cross section for the insertion of a cable that is to be connected. Said opening is delimited by a first and a second lateral branch extending parallel to one another from a bottom. The first branch is extended by an upper branch closing the one-piece structure of the tunnel, the latter two branches being separated from the second branch by at least one first axial clearance running in the direction of travel of the screw.
The invention also relates to a connection terminal comprising a flexible tunnel.
Tunnel-type terminals of the type mentioned generate significant pressure forces when the cable that is to be connected is clamped. These forces in the terminal may be as high as 600 daN, even though one tenth of that value is sufficient to ensure adequate electrical contact pressure to enable current to pass. A high initial force has the advantage of causing the formation of the conductors of the cable, but this force can decrease as the metal of the conductors creeps and deforms over time. This results in an effect whereby the terminals become loose, leading to risks of overheating in the region of the contact zone.
Terminals with a certain degree of flexibility to compensate for any loosening of the screws have already been proposed. Documents FR-A-2696584 and DE-A-19513281 relate to tunnel-type terminals equipped with a compression spring intended to store up a reserve of elastic energy to ensure that the conductor that is to be connected is still correctly retained in the event of a slight unscrewing of the clamping screw.
Document EP 336251 describes a screw terminal having a clamping frame and a fixing yoke which are arranged perpendicular to one another and allow double connection of a contact land and of a wire or cable. A gap is provided between the ends of the open frame.
Document EP1085601 describes a connection terminal able to undergo controlled deformation during the clamping of a cable to a connection land of a switching device, this elastic deformation having the benefit of ensuring a certain clamping compensation in the event of cable creep. However, this deformation of the terminal during the course of clamping gives rise to a certain axial misalignment of the clamping screw. The result of this drawback is that the clamping becomes less effective.
The object of the invention is to create a clamping terminal with a flexible tunnel that permanently guarantees good electrical contact with the cable without using an additional spring inside the tunnel.
According to one embodiment of the tunnel according to the invention, when the tunnel is in an untightened state, the upper branch through which the clamping screw is intended to pass in a perpendicular manner forms a first angle of deformation with a longitudinal axis of the tunnel parallel to the first and second lateral branches. Furthermore, the bottom forms a second angle of deformation with the longitudinal axis of the tunnel.
According to one particular embodiment of the tunnel, the first angle of deformation is greater than 90° and the second angle is preferably less than 90°.
For preference, when the tunnel is in a tightened state, the two angles of deformation are substantially equal to 90°.
According to one particular embodiment of the tunnel, the second lateral branch has an end which projects from the upper branch supporting the screw, and comprises a rectangular orifice into which an extension of said upper branch engages.
Advantageously, the terminal extension bears against the lower edge of the rectangular orifice, being separated from the upper edge by the first axial clearance when the terminal is in the untightened state.
For preference, the second transverse clearance is provided between the internal face of the second lateral branch and the base of the extension.
For preference, the terminal extension of the upper branch takes the form of a tenon having an end extending substantially parallel to the second lateral branch.
For preference, the end of the branch has a deformation running as close as possible to the clamping screw, said deformation making it possible to prevent the end from slipping on an external radius of the extension at the end of tightening.
The connection terminal according to the invention comprises a clamping screw housed in a tapped hole formed in the upper branch of the flexible tunnel, said screw has a longitudinal axis perpendicular to said branch and is intended to clamp a cable between a clamping pad secured to said screw and a connection land.
According to one development, the clamping pad secured to one end of the clamping screw is secured to a mobile screen, a mobile assembly formed by said pad and said screen tending to move closer to the bottom of the tunnel at the time of the tightening phase.
For preference, the mobile screen is positioned parallel to one of the two faces for accessing the tunnel and is able to close off, in part, the opening of the tunnel.
Other advantages and features will become more clearly apparent from the following description of one embodiment of the invention which is given by way of nonlimiting example and depicted in the attached drawings in which:
With reference to
The tunnel 12 has a one-piece structure produced by cutting and folding a conducting metal strip, so as to form a frame of substantially quadrangular cross section. The inside of the tunnel 12 is provided with an opening 18 opening onto two faces via which said tunnel can be accessed. The opening is delimited by a bottom 20. Extending from the bottom 20 are two lateral branches 22, 24 running parallel to one another. Moreover, the two branches run substantially parallel to a longitudinal axis Y of the tunnel 12.
A first branch 24 is extended by an upper branch 26 through which the clamping screw 14 passes. The clamping screw 14 extends perpendicular to the upper branch 26. The clamping screw 14 has a longitudinal axis Z.
A branch 26 positioned at the opposite end to the bottom 20 tends to close up the one-piece structure of the tunnel 12.
The second lateral branch 22 is provided at the upper part with an orifice 28 in which a terminal extension 30 of the upper branch 26 engages. The orifice is preferably rectangular. The terminal extension 30 of the upper branch 26 takes the form of a tenon. According to one particular embodiment, said tenon has the particular feature of having an end 37 which extends substantially parallel to the lateral branch 22.
The screw 14 is housed in a tapped hole 32 formed in a collar 34 of the upper branch 26. The clamping screw 14 has a first end positioned outside the tunnel and having a socket 17 intended to collaborate with a tightening tool. The clamping screw 14 has a second end positioned inside the tunnel 12. A clamping pad 16 is fixed to the second end of the clamping screw 14. The connection land 46 is positioned against the bottom 20 of the flexible tunnel 12.
The metal clamping pad 16 is housed in the opening 18 of the tunnel 12 while running parallel to the branch 26, and is intended to clamp the cable 36 against the connection land 46 when the screw 14 is tightened. The clamping pad 16 is made of copper or, preferably, of steel.
Because the tunnel 12 is fixed relative to the casing of a switching device, the clamping pad 16 secured to the end of the threaded shank of the screw 14 moves translationally in the opening 18 as the screw 14 is turned. If the screw 14 is tightened, the clamping pad 16 moves closer to the fixed connection land 46 and to the bottom 20, causing the cable 36 to be clamped against this land.
According to a preferred development of the invention, the tunnel 12 has two extreme operating positions.
As depicted in
As depicted in
The flexible tunnel 12 has the particular feature of deforming elastically between these two operating positions.
In the first operating position (the untightened state), the longitudinal axis Z of the clamping screw 14 is not aligned with the longitudinal axis Y of the tunnel 12 defined by the first and second parallel lateral branches 22, 24. In other words, the upper branch 26 is not perpendicular to the first and second lateral branches 22, 24. What happens is that the upper branch 26 forms a first angle of deformation α1 with the longitudinal axis of the tunnel 12. Furthermore, the bottom 20 forms a second angle of deformation α2 with the longitudinal axis of the tunnel 12.
According to one particular embodiment, the first angle of deformation α1 is preferably greater than 90° and the second angle α2 is preferably less than 90°.
In the second operating position (tightened state), the longitudinal axis Z of the clamping screw 14 is aligned with the longitudinal axis Y of the tunnel 12 defined by the first and second parallel lateral branches 22, 24. In other words, the upper branch 26 is perpendicular to the lateral branches 22, 24. What happens is that the first angle of deformation α1 is then equal to 90°. Further, the bottom 20 is also perpendicular to the first and second lateral branches 22, 24. The second angle of deformation α2 is also equal to 90°.
According to the invention, the end of the second lateral branch 22 has an end 23 which projects with respect to the upper branch 26. The terminal extension 30 of the upper branch 26 rests on the lower edge of the rectangular orifice 28, being separated from the upper edge by a first axial clearance J1 when the terminal 10 is in the untightened state (
According to one particular embodiment as depicted in
During the phase of connecting up a cable 36, which phase is illustrated in
When the tightening of the screw 14 is continued after the extension 30 has come into abutment, the tunnel 12 becomes more rigid, and the axial tensile force in the terminal 10 increases rapidly. Depending on the torque exerted on the screw 14, an intermediate degree of clamping somewhere between the first threshold S1 and a second max threshold S2 of 600 daN is then obtained.
The deformation of the tunnel 12 during this second phase of tightening is less than the elastic deformation caused during the take-up of the first clearance J1. According to this embodiment, the deformation is very little, or even non-existent.
Furthermore, as soon as the first clearance J1 has been taken up, the tunnel deforms in such a way that the longitudinal axis Z of the clamping screw 14 coincides with the longitudinal axis Y of the tunnel 12. An axial deformation angle β between the two longitudinal axes Y and Z tends to disappear. Regions of connection between the bottom 20 and the first and second lateral branches 22, 24 deform in such a way that the bottom 20 ultimately becomes perpendicular to the two branches. The conducting connection land 46 sandwiched between the bottom 20 and the electric cable 36 thus finds itself lying on a flat surface. This laying flat allows good exchange of heat between the cable 36 and the connection land 46 positioned against the bottom 20 of the tunnel 12. This laying flat thus makes it possible to reduce the heating caused by the passage of current. Further, the tunnel 12 also experiences deformation at the connection points between the upper branch 26 and the two lateral branches 22, 24. Said upper branch 26 is ultimately perpendicular to the two branches. The tunnel thus has a substantially rectangular profile.
The deformation of the tunnel 12 during the screwing-in of the screw 14 results in a double-gradient spring function. In the event of loosening following the compaction and creep of the conductors of the cable 36, the axial force in the tunnel 12 decreases and is returned toward the first threshold S1. This elastic reserve nonetheless remains sufficient to maintain correct contact between the land 46 and the cable 36.
In both of the embodiments of
According to an alternative form of embodiment as depicted in
| Number | Date | Country | Kind |
|---|---|---|---|
| 12 60074 | Oct 2012 | FR | national |
