As is known, circuit breakers are electrical devices the main function of which is to protect the power supply circuit in which they are used, as well as the loads and users supplied by said circuit, against any electrical faults and malfunctions, for example against short-circuits, overloads, etcetera ; this function is performed by separating suitable fixed and moving contacts and consequently interrupting the flow of current that circulates in the circuit.

In particular, the separation of the contacts and the consequent interruption of the flow of current, as well as the reclosing of said contacts and the restoring of normal operating conditions, occur by using an appropriate kinematic mechanism that facilitates the transmission of movement and forces between the actuation components of the circuit breaker and the moving contacts, thus allowing to move said moving contacts.

For this purpose, the kinematic mechanisms are composed of a certain number of levers and springs that are suitably mutually associated and are conceived so as to first of all assist in meeting certain requirements that are fundamental for the correct operation of circuit breakers and of the circuit they protect. In particular, on the one hand they must ensure that when an electrical fault occurs the separation of the contacts occurs as rapidly as possible; on the other hand, they must ensure that when the circuit breaker is closed, i. e., when the fixed contacts and the moving contacts are mutually coupled, the pressure generated between the surfaces in contact is high enough and such as to ensure adequate

electrical coupling between the parts throughout the useful life of the circuit breaker, even in the presence of eroded contacts.

These requirements become even more important and convincing, especially as regards contact separation speed, when the current levels involved are high and therefore the dimensions of the circuit breaker to be used are large, for example with circuit breakers of the type to which the present invention relates, for nominal currents above 100 A.

The constructive solutions currently used in known circuit breakers, particularly as regards their kinematic mechanisms, despite allowing to meet these requirements, have some drawbacks and critical aspects.

In particular, one conventional solution uses, in addition to the necessary levers with corresponding coupling springs, two additional springs: a first spring, which contributes specifically to reaching the necessary coupling pressure between the contacts in the closed position of the circuit breaker, and a second spring, which instead provides the energy required to increase the movement speed of the kinematic mechanism and therefore increase the contact separation speed in case of electrical fault.

The presence of these two additional springs entails an increase in the manufacturing times and costs of the circuit breaker and increases the complexity of its assembly; moreover, said springs, which are generally of the flexural type, do not lend themselves easily to achieving high loads and in any case entail problems in terms of setting and balancing.

A second solution that is known in the art instead uses a single spring that contributes both to achieving an adequate coupling pressure between the contacts when the circuit breaker is closed and to providing the energy useful for increasing contact separation speed during opening.

Although this solution is more convenient than the preceding one, since there is a single additional spring instead of two, it too has critical aspects, especially as

regards the constructive execution of the various levers and the assembly of the circuit breaker. Known embodiments in fact use multiple levers that are arranged so that they rotate about different pivots of the case of the circuit breaker and are operatively connected to an actuating knob by means of a linkage or U-shaped member. At least some of these levers have particular notches and slots, so as to provide couplings that allow specific relative movements between the parts; in turn, the additional spring is anchored, at its ends, to one of the levers and to the linkage, or to two levers, and the entire assembly is designed so that as a whole there is an imbalance of the forces applied by the two ends of the spring to the respective anchoring points.

With this solution, neither of the two engagement points of the spring is fixed and both have mobility characteristics, albeit limited ones constrained to a few positions, and this entails that in this case also the setting and calibration operations are delicate. Moreover, mounting the various levers arranged on different pivots, and most of all the adoption of the various notches and slots, in addition to increasing manufacturing costs, makes it particularly labor-intensive and complicated to assemble the circuit breaker and causes the corresponding couplings to be very delicate and extremely sensitive to clearance, vibration and wear, which are inevitably present during the useful life of the circuit breaker.

This entails risks of imbalance of the setting of the spring and of variation of its position and has a negative effect on the overall reliability of the circuit breaker and on the constancy of its performance.

The aim of the present invention is to obviate the above cited drawbacks and in particular to provide a circuit breaker for a low-voltage electric circuit in which a high opening speed in case of electrical fault and an adequate coupling pressure of the contacts when the circuit breaker is closed can be achieved in a simplified manner with respect to known types of circuit breaker.

Within the scope of this aim, an object of the present invention is to provide a

circuit breaker for a low-voltage electric circuit in which the number of components used, specifically the ones required to achieve the necessary performance in terms of contact coupling pressure and contact separation speed, is optimized as regards both their number and their embodiment.

Another object of the present invention is to provide a circuit breaker for a low- voltage electric circuit in which the operations for assembling, setting and calibrating the various components, particularly the ones required to achieve the required performance in terms of contact coupling pressure and contact separation speed, are considerably simplified with respect to the background art even for particularly high levels of required mechanical and electrical performance.

Another object of the present invention is to provide a circuit breaker for a low- voltage electric circuit that is highly reliable and relatively easy to manufacture at competitive costs.

This aim, these objects and others that will become apparent hereinafter are achieved by a circuit breaker for a low-voltage electric circuit, comprising: --a containment case; -- terminals for the input and output connection of the circuit breaker to said electric circuit; -- separable contact means, which comprise at least one fixed contact and a corresponding moving contact; -- an actuating knob, which rotates about a first pivot that is rigidly coupled to the case between a closed position, in which said fixed contact and said moving contact are coupled, and an open position, in which they are mutually separated, a first spring for return to the open position being associated with said knob; -- electric arc quenching means, which comprise at least one arc quenching chamber and two arc guiding conductors associated with said chamber; -- protection means, which are suitable to facilitate the separation of the

contacts when an electrical fault occurs; -- a kinematic mechanism, which comprises a first supporting lever, on which said moving contact is arranged, said supporting lever being operatively connected to said actuating knob by virtue of a connecting element, and a second release lever, which is operatively associated with said protection means, said first and second levers being mounted coaxially so that they rotate about a second pivot that is rigidly coupled to the case, a second spring being associated with said first and second levers; characterized in that said kinematic mechanism comprises a third actuation lever, which is operatively coupled to said moving contact and is mounted on the first supporting lever, said third lever being able to rotate about an axis that is parallel to the coaxial mounting axis of said first and second levers, and in that a third actuation spring is associated with said third actuation lever and has a first end, which is connected to a third pivot rigidly coupled to the case, and a second end, which is anchored to the actuation lever itself, said third spring applying to the actuation lever a force that is suitable to facilitate an adequate coupling pressure between the contacts in the closed position and to cause the rotation thereof together with the moving contact when said protection means intervene.

Further characteristics and advantages of the invention will become apparent from the description of a preferred but not exclusive embodiment of the circuit breaker according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein: Figure 1 is a side view of the circuit breaker according to the invention, in the closed position and with the contacts coupled; Figure 2 is a side view of the circuit breaker according to the invention, in the open position and with the contacts separated; Figure 3 is an exploded perspective view of some of the components of the kinematic mechanism used in the circuit breaker according to the invention.

With reference to the cited figures, the circuit breaker according to the invention comprises a containment case 1, which is shown partially in Figures 1 and 2 and on which there are two terminals 2 and 3 for the input and output connection of said circuit breaker to a low-voltage electric power supply circuit.

The case 1 contains: separable contact means, which comprise at least one fixed contact 4 and a corresponding moving contact 5 that can be coupled thereto; means for quenching the electric arcs generated during the opening and closing of the circuit breaker; protection means suitable to facilitate the separation of the contacts and the automatic opening of the circuit breaker when an electrical fault occurs; and a kinematic mechanism, generally designated by the reference numeral 20, which is suitable to move the moving contact 5, for the purposes and in the manners that will become apparent in detail from the description that follows.

Furthermore, an actuating knob 6 is used which is arranged so that it rotates about a first pivot 7 that is rigidly coupled to the case 1 and protrudes outside said case; said actuating knob 6, which is available to the intervention of an operator, can be operated between a closure position, shown in Figure 1, in which the fixed contact 4 and the moving contact 5 are coupled, and an open position, shown in Figure 2, in which the contacts are mutually separated. A first spring 8 for return to the open position is associated with the actuating knob 6 and is also arranged around the first pivot 7.

As shown in Figures 1 and 2, the fixed contact 4 is electrically connected to the terminal 2 by virtue of an appropriate conductor 9 and is connected to a first arc guiding conductor 10 that is extended toward an end of an arc quenching chamber 11; the opposite end of the arc quenching chamber 11 is delimited by a second arc guiding conductor 12, which is electrically connected to the second terminal 3. Furthermore, the fixed contact is configured so that when the circuit breaker is closed the directions of the current that circulates in the fixed contact

and in the moving contact are mutually opposite; accordingly, with particularly high overcurrents a repulsion force is generated between the contacts that tends to separate them, contributing to the fast opening of the circuit breaker. These repulsion effects can be increased by using a suitable metallic plate which is for example U-shaped and is arranged around the moving contact and helps to increase the repulsion effect between the contacts, thus increasing the speed of contact separation, and to guide the electric arc more rapidly toward the arc quenching chamber 11.

The protection means comprise an electromagnetic device for protection against overcurrents and a thermal protection device against overloads. According to embodiments that are widely known in the art and are therefore not described in detail, the electromagnetic device comprises a coil 13, which is wound on a suitable supporting frame, and a release element 14, which is actuated in case of an overcurrent condition, for example a short circuit, so as to interact with the kinematic mechanism 20; in turn, the thermal protection device comprises a bimetallic lamina 15, to which the moving contact 5 is electrically connected by means of a flexible braid 16, and an actuation element 17, which also acts on the kinematic mechanism 20 when an overload condition occurs.

As shown in greater detail in Figure 3, the kinematic mechanism 20 comprises a first supporting lever 21, on which the moving contact 5 is arranged, and a second release lever 22, which is suitable to interact operatively with the release element 14 and with the actuation element 17, said two levers 21 and 22 being mounted coaxially with respect to each other and rotating about a second pivot 19 that is rigidly coupled to the case 1. The supporting lever 21 is operatively connected to the knob 6 by means of a connecting element 18, generally a U- shaped member or a linkage, in which a first end is fixed to the actuating knob 6 and a second end is inserted in a seat formed on said lever 21; furthermore, a second spring 23 of the flexural type is associated with the supporting lever 21

and the release lever 22 and pushes the two levers toward each other, coupling their movement and so that in normal operating conditions one end 40 of the lever 22 engages and retains in position the U-shaped member 18.

Advantageously, in the circuit breaker according to the present invention, the kinematic mechanism 20 comprises a third actuation lever 24, which is operatively coupled to the moving contact 5 and is mounted on a first pivot 28 formed on the body of the first supporting lever 21 and therefore rotates about an axis that is parallel to the rotation axis of the levers 21 and 22; furthermore, a third spring 25 for actuating the mechanism 20 is associated with the third actuation lever 24 and has a first end, which is connected to a third pivot 26 rigidly coupled to the case 1, and a second end, which is anchored to said actuation lever 24. Said third spring 25, as detailed in the description that follows, applies to the actuation lever 24 a force that is suitable to facilitate the reaching of an adequate coupling pressure between the contacts 4 and 5 in the closed position and is suitable to cause the rotation of said actuation lever together with the moving contact 5 following an intervention of the protection means, so as to provide faster circuit breaker opening.

In particular, as shown in detail in Figure 3, the first supporting lever 21 has a contoured body that is pivoted to the pivot 19 and comprises, in addition to the first pivot 28 on which the lever 24 is mounted, a second pivot 27, on which the moving contact 5 and the release lever 22 are mounted, said pivot being arranged along the axis of the pivot 19 and therefore along the coaxial rotational axis of said levers 21 and 22, parallel to the pivot 28 ; and a containment seat 46 for the second spring 23; in the illustrated embodiment, the pivot 27 has a hollow cylindrical body so as to be crossed by the pivot 19. The release lever 22 has a contoured body on which there are means for operative coupling, respectively, to the kinematic mechanism of an accessory device that can be associated with the circuit breaker, and to an additional auxiliary lever

31 that can be used in the kinematic mechanism 20 for the purposes that will become apparent from the description that follows; in the illustrated embodiment, said coupling means comprise a slot 42, in which it is possible to insert a pivot of the kinematic mechanism of the accessory device, and a tooth 43, which protrudes on the opposite side with respect to the slot 42 and interacts with the body of the auxiliary lever 31.

During assembly, the release lever 22 is arranged on the pivot 27 so as to be directly laterally adjacent to the body of said lever 21, with the second spring 23 interposed between them; in turn, the third actuation lever 24 is arranged on the pivot 28 adjacent to the second release lever 22, with the moving contact 5 interposed between them.

Advantageously, in the embodiment of the circuit breaker according to the invention, the third actuation lever 24 has a contoured body with an arm 44 on which there are means for coupling with clearance to the body of the moving contact 5; in particular, said coupling means comprise a pivot 29 that enters with clearance a slot 30 formed in the body of the moving contact 5, so that a relative movement occurs between the two components. Furthermore, on the lever 24 there is a contoured protrusion 33, which is arranged opposite the pivot 29 and interacts operatively with the auxiliary lever 31, a seat (not shown in the figure), which accommodates the pivot 28, and a hole (also not shown in the figure), which freely accommodates the pivot 19.

As mentioned, the kinematic mechanism 20 can also comprise a fourth auxiliary lever 31, which is conveniently provided with coupling means suitable to be operatively connected to the kinematic mechanism of an additional accessory device that can be associated with the circuit breaker; in particular, said coupling means comprise a slot 32 whose shape is similar to the slot 42 and in which it is possible to insert a pivot of the kinematic mechanism of the associated circuit breaker. In this manner, by virtue of the adoption of the

coupling means on the release lever 22 and the auxiliary lever 31, the circuit breaker can be provided with accessories on both sides. Said fourth lever 31 is also arranged coaxially to the moving contact 5 and to the levers 21 and 22, and is mounted at a cylindrical end 45 thereof that rotates about the pivot 19 by arranging it adjacent to the third lever 24, with a part of the tooth 43 acting as a resting surface for it; in this manner, the lever 31 moves substantially solidly with the release lever 22, by virtue of the interaction with the tooth 43 and so that part of its body can instead interact with the contoured protrusion 33 of the lever 24.

Finally, the circuit breaker according to the invention uses a fifth retention lever 34, which is mounted so that it can rotate about a fourth pivot 35 that is rigidly coupled to the case 1 and with which an additional spring 41 is associated; said lever 34, in cooperation with the spring 41, is suitable to interact operatively with the knob 6 and with the moving contact 5 so as to lock it at a predefined distance from the fixed contact 4 during closure performed by acting on said actuating knob. For this purpose, as shown in Figures 1 and 2, the retention lever 34 has a hollow 36, in which a protrusion 37 of the moving contact 5 engages, and a contoured head 38, which is suitable to interact with a cam-like surface 39 provided on the knob 6.

The functional operation of the circuit breaker is now described starting from the position shown in Figure 1 in which the circuit breaker is closed and the contacts are coupled.

In this position, the actuation spring 25 is loaded and applies to the actuation lever 24 a return force toward the third pivot 26; said force is contrasted and overcome by the thrust applied by the U-shaped member 18 against the supporting lever 21, which is locked in this position by the end 40 of the release lever 22 and helps to keep the entire mechanism in the stable equilibrium position shown in the figure. In case of an electrical fault, for example an

overcurrent, the electromagnetic protection device trips, the release element 14 striking the release lever 22, triggering its movement. In a fully similar manner, if an electrical fault due to an overload is occurring, the thermal protection device trips, the actuation element 17 acting on the release lever 22 so as to trigger its movement.

In particular, the release element 14, after striking the release ever 22, briefly continues its stroke, striking also against the moving contact 5 and thus providing an amount of energy that is useful to separate it from the fixed contact 4. The release lever 22, following the impact of the release element 14, overcomes the contrast of the spring 23 and rotates slightly with respect to the supporting lever 21; in this manner, an initial uncoupling occurs between the two levers 21 and 22 and the end 40 frees the U-shaped member 18. In this situation, the thrust applied by the U-shaped member 18 against the supporting lever 21 is eliminated and no longer contrasts the actuation spring 25, which pulls the actuation lever 24 and facilitates its rotation together with the moving contact 5 and the supporting lever 21, the release lever 22, and the auxiliary lever 31. In this manner, the spring 24 releases an amount of pre-stored energy, which is expended to achieve an adequate contact separation speed, thus contributing significantly to a faster opening of the circuit breaker.

At the end of the switching action, the lever 22 reengages the U-shaped member 18, forcing it to resume the initial position, the contacts are mutually separated, and the knob 6 is in the position of Figure 2.

If the opening of the circuit breaker is caused by the intervention of an accessory device associated therewith and coupled on the side of the release lever 22 or of the auxiliary lever 31, the kinematic mechanism of said accessory device transmits the movement to the release lever 22 or to the auxiliary lever 31 ; accordingly, the lever coupled to the accessory device starts to rotate and, by virtue of the operative couplings between the various elements, entrains the

other levers and the moving contact 5, ultimately facilitating its separation from the fixed contact, in a manner fully similar to what has been described above.

In the presence of a very high overcurrent, the initial separation of the moving contact from the fixed contact occurs by virtue of the repulsion effect caused by the currents with opposite orientations that circulate in said contacts and by virtue of the metallic plate, if provided; in this case, the moving contact 5, by virtue of the coupling between the pivot 29 and the slot 30, entrains the actuation lever 24, which by means of the contoured protrusion 33 pulls the auxiliary lever 31, triggering in practice the movement that allows to disengage the U-shaped member 18 and therefore to actuate the spring 25, as described above.

Once the fault has been extinguished, the circuit breaker can be reclosed and the flow of current can be restored by operating the actuating knob 6. In particular, starting from the position of Figure 2, the knob 6 is turned in the direction of the arrow 50, so that the U-shaped member 18 connected thereto pushes the supporting lever 21, together with the other levers and the moving contact 5, making them rotate and reloading the actuation spring 25. At a certain point of the rotation, the hollow 36 of the retention lever 34 engages the protrusion 37 and retains the moving contact at a preset distance from the fixed contact 4. As the rotation of the knob 6 continues, the cam-like surface 39 acts on the contoured head 38, overcoming the action of the spring 41 and disengaging the protrusion 37 from the hollow 36, so that the moving contact can thus continue its stroke toward the fixed contact independently of the movement of the actuating knob 6.

As the switching action continues, the assembly is conceived so that before the actuating knob reaches the end of its stroke in the position shown in Figure 1 the moving contact 5 is already in abutment against the fixed contact 4; in this condition, in the last part of the rotation of the knob 6 the actuation lever 24, by

virtue of the coupling with clearance between its pivot 29 and the slot 30, can continue to rotate with respect to the moving contact 5. By virtue of this additional stroke, the actuation lever 24 pulls the corresponding spring 25 further, increasing its preloading. In this manner, the spring 25 applies a greater force to the entire mechanism and forces the thrust applied by the U-shaped member 18 to be increased correspondingly. In this manner, in normal conditions the coupling pressure between the contacts reaches adequately high values. Furthermore, the pre-stored energy to be released during opening is higher.

Furthermore, the coupling with clearance and the corresponding additional stroke of the actuation lever 24 with respect to the moving contact 5 allows to obtain a satisfactory coupling pressure throughout the useful life of the circuit breaker, since it allows to compensate effectively for any variations with respect to an intended nominal behavior, particularly as regards contact erosion.

In practice it has been found that the circuit breaker according to the invention fully achieves the intended aim and objects, providing a significant series of advantages with respect to the known art. In the circuit breaker according to the invention there is in fact a single spring, which on the one hand helps to attain a contact coupling pressure that is necessary to ensure adequate electrical coupling and on the other hand applies a force that is useful in speeding up the separation of the contacts during opening; moreover, this result is achieved with a solution that is extremely effective from the functional point of view and is structurally simplified with respect to the known art. The use of a traction spring in which one end is anchored and fixed to a pivot of the case in fact facilitates considerably the operations for assembling, setting and calibrating said spring and allows to achieve easily even very high stress levels.

Furthermore, the mounting of the actuation lever directly on the supporting lever and the arrangement of said lever together with the release lever, the

auxiliary lever and the moving contact about a same pivot facilitates considerably the steps for the assembly of the circuit breaker, allows to reduce the effects of any clearance and vibration, and allows to simplify both the constructive structure of said levers, for which the adoption of particular notches, openings and slots and the corresponding couplings becomes unnecessary. Finally, the entire system is assembled in a case having optimized dimensions.

The circuit breaker thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; for example, the shape of the levers and the provision thereon of the various operative coupling means can be changed appropriately according to the specific requirements or needs of the application; all the details may furthermore be replaced with other technically equivalent elements.

In practice, the materials employed, as well as the dimensions and the contingent shapes, may be any according to the requirements and the state of the art.