Patent Application
20110269333
The invention relates to a screw terminal for connecting at least one electrical conductor to a conducting strip of an electrical equipment unit. The object of the invention is more precisely to guarantee effective clamping of a terminal with creep compensation. In particular, the invention relates to a terminal comprising a device for indicating the tightening torque of the screw.
Cable connection terminals can have a tendency to come loose after a long period of service and this loosening gives rise to large heat rises in electrical equipment units. To monitor this phenomenon in order to be able to perform any necessary retightening, document EP 1 531 519 thus proposes to add a system indicating the quality of tightening, in particular a lever taking two positions.
To prevent loosening itself, terminals in which means compensating creep have been developed. The document EP 1 271 697 thus presents a screw terminal comprising a connection tunnel equipped with a tapped hole, a screw collaborating with the tapped hole and a flexible pressure part which presses on the electrical conductor. The pressure part comprises a head strip and a pressure strip connected to one another by a flexible wing designed to store a clamping energy, the head strip being able to be solicited by the screw head and the pressure strip being able to be applied against one of the conductors to be connected. Due to the pressure exerted under the screw head, this application of pressure prevents the terminal from coming loose and/or enables the creep of the conductor clamped by the terminal to be compensated. To improve balancing of the terminal, the pressure part comprises two flexible wings symmetrical with respect to an axial plane of the screw and of concave shape.
By means of this system, the installation time can be very short while at the same time ensuring the quality of the wiring and guaranteeing continuity of service. However, the operator has no practical indication on the actual position of the screw, at all times, and remains sole judge as to the clamping force applied on the electrical conductor and therefore of the contact pressure. This lack of information may lead to a certain hesitation to the detriment of the time required to perform the operations. Moreover, due to the fact that no indication of the actual tightening torque is available, for fear of creep occurring, the operator may be led to check the tightness of the terminal clampings regularly, even though any creep has been compensated.
Among other advantages, the object of the invention is to palliate this shortcoming of the prior art terminal and to propose a system enabling the tightening torque of a terminal with creep compensation to be indicated.
In particular, the invention relates to detection means for detecting a tightening torque of a screw terminal equipped with a pressure device and located between walls, said means comprising an element securedly affixed to the pressure device and an element securedly affixed to a wall cooperating with one another to actuate indicating means when the tightening torque reaches a threshold.
According to the invention, the detection means form part of a connection system comprising a housing with insulating walls with which a terminal is associated that comprises a connection tunnel provided with a screw and with a pressure device of annular shape preferably captively coupled with the screw so as to be driven by the latter. The pressure device comprises a head strip secured to the screw and located opposite a pressure strip that is movable in the tunnel, as well as two symmetric concave wings that join the latter, the central part of the wings moving towards the walls of the terminal housing when the device is compressed between its head strip and its pressure strip, i.e. in particular when the screw is tightened onto a conductor and/or a connecting strip located in the tunnel. The pressure device is preferably conducting and provided with an insulating flap moving with the latter so as to blank off a hole for passage of a conductor of the housing.
A first detection element is located on a wall of the housing and a second element is fitted on the adjacent wing, preferably at the level of the central part which deforms the most and/or on the insulating flap. Means enable a minimum threshold of the distance separating the two elements to be determined, said threshold corresponding to a predetermined tightening torque of the screw, i.e. a compressive force of the device, said means actuating indicating means, for example a light-emitting diode, depending on whether the threshold is reached or not. The two elements preferably come up against a stop when the predetermined tightening torque is reached, and contact between the two elements advantageously closes a power supply circuit of the indicating means. The first element can then comprise two conducting tracks extending parallel to the axis of the screw over a length covering at least the maximum displacement of the tunnel, and the second element a strip joining the two tracks or not.
The invention also relates to a connection system with the above-mentioned terminal, the housing and the detection means, the housing being able to form part of an electrical equipment unit at the level of one of its connection strips or be comprised in an independent case. The invention then relates to a terminal block that can accommodate several terminals and in particular comprise three housings and three tunnel terminals advantageously forming three integral connection systems.
More generally, the system for connecting an electrical equipment unit according to the invention comprises a housing delineated by insulating walls, a terminal comprising a connection tunnel and a cooperating screw for relative movement of the screw with respect to the tunnel, and a pressure device comprising two flexible wings joined to one another at one end by a head strip affixed to the screw and at the other end by a pressure strip located in the connection tunnel. The wings are symmetrical with respect to an axial plane of the screw and comprise a central part, such that the separation between the central parts of the wings increases when compression of the pressure device takes place between its head strip and its pressure strip so that said pressure device is able to store a clamping energy. The system according to the invention further comprises means for detecting a predetermined tightening torque of the screw comprising a first element securedly affixed to a wall and a second element securedly affixed to a wing, said wing and said wall being adjacent to one another when the terminal is fitted in place in the housing, means for determining the distance separating the first and second elements, indicating means coupled to the means for determining and indicating when said distance is smaller than or equal to a threshold distance.
According to a preferred embodiment, the first and second elements come into contact when the predetermined tightening torque is reached, said threshold distance being zero. The first and second elements can be conductive and form part of a power supply circuit of the indicating means so that the indicating means are supplied when the predetermined tightening torque is reached. For example the first element comprises two conducting tracks and the second element comprises a conducting strip. The second element is preferably located at the level of the central part of the wing and the first element extends in a direction parallel to the axis of relative movement of the terminal over a sufficient length to be facing the second element in all the relative positions of the terminal with respect to the housing. The second element can be fitted on an insulating flap fixed to a wing of the pressure device.
Other advantages and features will become more clearly apparent from the following description of particular embodiments of the invention given for illustrative and in no way restrictive example purposes only, represented in the appended drawings.
For an electric equipment unit (not illustrated), a fixed connecting strip 1 is accessible via an opening 2 of the case so as to be able to associate one or more conductors 4 therewith by direct clamping. As illustrated in
A pressure device 24 is coupled to the screw 16, preferably in captive manner, so as to move with the latter and to be solicited by the clamping. The device 24 is a flexible unitary part, usually made from metal, substantially closed on itself in the form of a ring and symmetrical with respect to an axial plane of the screw 16. A head strip 26 surrounds the neck 20 of the screw 16, under the head 18 of the latter, so as to ensure balanced clamping, and a pressure strip 28 can be applied on one of the conductors 1, 4 to be placed in contact, acting as interface with the seat 22 of the screw 16. On each side of the axis of the screw 16, a wing 30 joins the strips 26, 28 of the device 24 via a connection area determining a salient angle. The wings 30 are concave, with a central part 32 closer to the axis of the screw 16.
The pressure strip 28 can be curved to give the end part of the device 24 opposite the head strip 26 a general convex shape and/or to present embossments 28A collaborating with a withdrawn part 1A of the conducting 1 strip. The combination of the concaveness of the wings 30 and of the sloping or convex shape of the strips 26, 28 is designed for the pressure device 24 to be deformed by compression with a decreasing curvature when the pressure increases. The central parts 32 move away from one another.
In particular, in the illustrated embodiment, cooperation of the screw thread with the tapped hole 14 means that rotation of the screw 16 results in translation of the tunnel 12 with respect to the housing 8 until its comes up against the stop formed by a surface of the fixed connection strip 1. In parallel, the screw 16 moves with respect to the tunnel 12 and housing 8 until the pressure strip 28 comes up against the stop formed by the opposite surface of the fixed strip 1. Continued rotation of the screw 16 then results in compression stressing of the pressure device 24, which leads to the concaveness of the wings 30 decreasing and the seat 22 of the screw 16 being applied against the surface of the pressure strip 28 opposite the fixed strip 1—
Preferably, at rest, a small distance is provided between the bearing seat 22 of the screw 16 and the surface facing the pressure strip 28. The distance is determined so that compensation of the latter produces the desired level of stress of the pressure device 24. Advantageously, the head of the screw 16 presses on the head strip 20 in a region situated at a small distance from the axis of the screw 16 so as to create a leverage force which accentuates the torque exerted on the device 24.
An insulating flap 34 is advantageously fixed onto a wing 30 facing the insertion opening 2 of the cable 4. The flap 34 moves together with the pressure device 24 so as to partly mask the insertion opening 2 and thereby reduce the risks of nuisance contact.
The distance e between the internal surfaces of the central parts 32 of the wings 30 is minimal at rest; it is at least equal to and preferably slightly greater than the width of the tunnel 12 so that the tunnel 12 can slide freely within the pressure device 24. Preferably, in the clamped position, the distance e between the internal surfaces of the central parts 34 increases until the wings 30 take a shape having a nil or inversed concaveness.
According to the invention, when the recommended tightening torque is reached, the distance e between the internal surfaces of the wings 30 is maximal: means are provided to detect and indicate the predetermined minimum of the residual distance d between the central part 32 of one of the wings 30 and the adjacent wall 6 of the housing 8. When the distance d corresponding to this position is detected, an indication, which can be audible or preferably visual, enables the operator to know that his tightening is sufficient. This sole criterion suffices for connection to be made in reliable and rapid manner. Moreover, so long as the above-mentioned clamped position is indicated, the operator can recognize the reality of clamping of the screw 16 so as not to perform an operation involving retightening a screw 16 for a terminal 10 which is in fact correctly connected.
Detection of the minimum of distance d is preferably performed by fitting a stop system cooperating between the wall 6 and the wing 30, which, in addition to simplicity of detection, avoids too great stressing of the pressure device 24 and a too high tightening torque. The detection means thus comprise a first stop 38 on a wall 6 cooperating with a second stop element 40 on the adjacent wing 30. The detection means are of dry switch type and the two stop elements 38, 40 are conductors closing a supply circuit of the indicating means 42, for example a light-emitting diode, a controller input, safety circuit, etc.
The second element 40 located on the wing 30 can comprise a protuberance of said metal wing. The second element 40 is advantageously a conductor fitted on an insulating support so as to prevent any accidental contact between the wing 30 itself and the first element 38. In particular the second element 40 comprises a conducting strip fitted on the flap 34. For enhanced precision, it is preferred for the second element 40 to be located at the level of the central part 32 of the wing 30, which is subjected to the greatest strain when clamping is performed.
The first element 38, located on the adjacent wall 6, advantageously comprises two conducting tracks 44 insulated from one another, each track 44 being connected to the supply circuit of the indicating means 42. The distance separating the two tracks 44 is smaller than or equal to the width of the strip 40 in the same direction. The tracks 44 advantageously extend parallel to the axis of the screw 16 over a length corresponding at least to the possible movement of the second element 40, i.e. wing 30/flap 34 with respect to wall 6. Other embodiments are possible.
In a preferred embodiment illustrated in
Although the invention has been described with reference to a terminal 10 in which the tunnel 12 and screw 16 are movable with respect to the housing 8, 48 in which the terminal 10 is placed, it is by no means limited thereto. In particular it is possible with the system and/or terminal block 50 according to the invention to have a tunnel 12 or a screw 16 fitted in fixed manner with respect to the walls 6. The terminal 10 can enable a conductor 4 to be clamped between the bearing seat 22 and the fixed strip 1 or on the other side of the strip 1, or one conductor to be fixed on each side. It is further possible to achieve the switch circuit of the indicating means 42 using the pressure device 24 as a bridge connecting two first elements 38 located on the opposite two walls 48 of a terminal block 50, or any other alternative. Other means for determining the distance between the two elements 38, 40 can be envisaged. In particular it is possible to use means enabling two threshold distances to be identified so as to inform the user that clamping is desirable or compulsory.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 01843 | Apr 2010 | FR | national |
