It is known that electromagnetic relays of the magnetic-release type are used in low-voltage power switches in order to disengage the main contacts of the switch, for example during a short-circuit or an overvoltage. Said relays are constituted by one or more permanent magnets which retain a disengagement pin and by a solenoid which produces, when necessary, the demagnetization and therefore the release of the pin. However, electromagnetic relays of the magnetic-release type have the drawback that they are highly sensitive to magnetic fields, for example the fields induced by the short-circuit current that must be interrupted by opening the main contacts of the switch.

Another instance is when the short-circuit triggers the disengagement of the relay of a second switch which is adjacent to the first one and should not be disengaged in this situation.

In both cases, the disengagement of the relay can nonetheless be conditioned, and this leads to the need to shield said fields, making it complicated and expensive to manufacture the switch, especially in the case of a relatively large switch. The number of components of a disengagement actuator inside a switch can therefore be very large.

The aim of the present invention is to provide a low-voltage power switch which has a contact opening actuator which is fully insensitive to magnetic fields and is highly reliable.

Within the scope of this aim, an object of the present invention is to provide a low-voltage power switch which has a contact opening actuator which is constituted by a much smaller number of components than known actuators.

Another object of the present invention is to provide a low-voltage power switch

with contact opening actuator which requires less triggering energy for contact opening, making it also applicable in the field of low energies, and is therefore more sensitive and ultimately safer than known types of actuator.

Another object of the present invention is to provide a low-voltage power switch with contact opening actuator in which the electromagnetic relays used in known types of actuator are eliminated.

Another object of the present invention is to provide a low-voltage power switch with contact opening actuator which is highly reliable, relatively simple to manufacture and at competitive costs.

This aim, these objects and others which will become apparent hereinafter are achieved by a low-voltage power switch which comprises: -a moving contact and a fixed contact which can be mutually coupled/separated ; -an actuator for opening said contacts, which comprises: -actuation means which are suitable to act on an opening/closing kinematic mechanism which is operatively connected to said moving contact; -means for pre-loading said actuation means, characterized in that said actuation means comprise at least one dimorphic piezoelectric element whose deformation is suitable to allow the release of said actuation means.

Further characteristics and advantages of the invention will become apparent from the description of preferred but not exclusive embodiments of the switch according to the present invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein: Figure 1 is a perspective view of a first embodiment of the actuator used in the switch according to the present invention; Figure 2 is another perspective view of the actuator used in the switch according to the present invention shown in Figure 1; Figure 3 is a third perspective view of the actuator used in the switch according

to the invention shown in Figures 1 and 2; Figure 4 is a perspective view of a second embodiment of the actuator used in the switch according to the invention; Figure 5 is a view of a variation of the second embodiment of the actuator used in the switch according to the invention; and Figure 6 is a perspective view of a detail of the actuator of Figure 5.

With reference to the above figures, and initially to Figures 1 to 3, the low- voltage power switch comprises a moving contact and a fixed contact (both not shown) which can be mutually coupled/separated, an opening/closing kinematic mechanism (also not shown) which is operatively connected to the moving contact, and an actuator, generally designated by the reference numeral 1, which in a first embodiment comprises actuation means 2 which are suitable to act on the kinematic mechanism; the embodiment of the kinematic mechanism, as well as its functioning are well known in the art and therefore not illustrated herein.

The actuation means 2 conveniently comprise pre-loading means, for example a spring 200 which, in operating conditions, is kept pre-loaded as described in detail hereinafter.

The actuation means 2 comprise at least one dimorphic piezoelectric element 3 which is conveniently arranged so as to act as a triggering means for the actuation means 2. In particular, the piezoelectric element 3 acts on the spring 200 to disengage it and thus make it act on the kinematic mechanism of the switch in order to separate the moving contact from the corresponding fixed contact.

In the first illustrated embodiment, the piezoelectric element 3 is rigidly coupled at one end to a supporting element 11, for example the case of the switch, and acts indirectly on the spring 200.

The indirect connection between the piezoelectric element 3 and the spring 200 is provided by virtue of first lever means 4 which are conveniently inserted in

the spring 200 and are provided, in an upward region, with an engagement tooth 5 which is suitable to allow the engagement of the first lever means 4 in correspondence to a turn of the spring 200; in particular, as shown in figures 1-3, the engagement tooth 5 of the first lever means 4 acts on a circular element 15 which is arranged on the upper turn of the spring 200. Alternatively, the tooth 5 could be directly engaged with a turn of the spring 200.

The first lever means 4 are conveniently connected to second lever means 6 which are directly actuated by the piezoelectric element 3 and are suitable to act on second actuation means 7 which are conveniently constituted by a second spring whose disengagement, performed by the second lever means 6, determines the actuation of the first lever means 4 and accordingly determines the disengagement of the spring 200.

In detail, with reference to Figures 1 to 3, the operation of the first embodiment of the actuator according to the invention is as follows.

In operating conditions, the first spring 200 is pre-loaded and is kept in this condition by the engagement tooth 5 of the first lever means 4. In this condition, the second spring 7 also is pre-loaded and is kept pre-loaded by an engagement tooth 9 which is rigidly coupled to the spring 7 and is engaged by the second lever means 6, which in turn abut against the dimorphic piezoelectric element 3.

An electric actuation signal, sent for example by the control electronics of the piezoelectric element, induces a deformation of the dimorphic piezoelectric element 3, in particular, thanks to the dimorphic configuration, its flexing. Said flexing causes the piezoelectric element 3 to apply a force against the second lever means 6, which are pivoted at a pivot 10 on the supporting element 11 which is suitable to support the actuation means 2; in this way, the second lever means 6 rotate so as to disengage their tooth 12 from the engagement element 9 that is rigidly coupled to the second spring 7, and the pre-loading of the spring in this case is no longer maintained. The release energy of the spring 7 causes

said spring to impact against the first lever means 4, the engagement tooth 5 of said lever means disengaging from the spring 200, thus freeing said spring. The disengagement of the spring 200 acts on the kinematic mechanism of the switch in order to open its electric contacts.

Therefore, in this first embodiment the dimorphic piezoelectric element 3 acts indirectly on the first spring 200 by virtue of first and second lever means and by virtue of a second spring.

A second embodiment of the actuator according to the invention is shown in Figures 4 to 6.

In Figures 4 to 6, reference numerals identical to those used in Figures 1 to 3 respectively designate identical or technically equivalent elements.

In this embodiment, the action of the piezoelectric element for releasing the spring 200 is performed directly as it acts directly on the spring to be released.

In fact, with reference to Figure 4, the actuator, generally designated by the reference numeral 100, comprises a spring 200 which is kept pre-loaded by one or more dimorphic piezoelectric elements 3 which are arranged inside or outside the spring 200, are rigidly fixed to the supporting element 11, and are each provided, in an upward region, with a tooth 25 which allows to keep the spring 200 pre-loaded by engagement with notches formed in the upper circular element 15 which lies opposite the supporting element 11; in particular, in the embodiment shown in figure 4, the dimorphic piezoelectric elements are arranged substantially inside the actuation means 2, with their axis parallel thereto.

In this second embodiment, therefore, in operating conditions the spring 200 is pre-loaded and kept in this condition by the dimorphic piezoelectric elements 3 and in particular by the engagement teeth 25 of said piezoelectric elements.

When an electric disengagement signal is sent to the piezoelectric elements 3, for example by a control electronics, the elements 3 deform, in particular they

flex, thus causing the disengagement of the engagement teeth 25 from the notches formed in the element 15.

In a variation of this second embodiment, shown in Figures 5 and 6, each one of the piezoelectric 3 is connected, at its upper end which lies opposite the end rigidly coupled to the supporting element 11, to lever means 110 which are conveniently provided, in an upward region, with an engagement tooth, again designated by the reference numeral 25, which allows engagement with the element 15 arranged above the spring 2.

Figures 5 and 6 show four piezoelectric elements 3 which are arranged substantially along the axis of the spring 200; in this case, the piezoelectric elements 3 have their upper part positioned in correspondence of recesses formed in a cross-shaped part 20 which allows the passage of third lever elements 110 which rest against the respective piezoelectric elements 3.

In detail, the lever means 110 rotate about the pivots 21, which are suitable to abut against the lateral surface of the recesses 22 of the cross-shaped part 20.

In this case, during the flexing of the piezoelectric elements 3, said elements act on the lever means 110, which in turn release the spring 200. This solution, by acting on the lengths of the lever means 110, allows to extract from the piezoelectric element 3 more force or a larger movement if it is necessary to increase one of these two parameters with respect to the other.

In general, the number of piezoelectric elements 3 depends on the rigidity of the springs and on the materials used. This applies to both of the above described embodiments.

In practice, the switch according to the invention allows complete insensitivity to magnetic fields, by virtue of the absence of electromagnetic relays as actuators. Furthermore, the number of components required to provide the actuator is reduced considerably, leading to higher reliability of the switch.

Another advantage of the switch according to the invention is that the

piezoelectric elements 3 require less triggering energy than an electromagnetic relay, and this considerably broadens the range of application.

The use of piezoelectric elements, for example piezoceramic ones, instead of the expensive windings of electromagnetic relays entails a reduction in the manufacturing costs of the switch.

In practice it has been found that the low-voltage power switch according to the invention fully achieves the intended aim and objects, since it comprises an actuator which allows to perform disengagement of the contacts of a switch by acting both directly on the disengagement spring and indirectly by interposing suitable lever means.

The low-voltage power switch thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; all the details may furthermore be replaced with other technically equivalent elements.

In practice, the materials used, so long as they are compatible with the specific use, as well as the dimensions, may be any according to the requirements and the state of the art.