EP1265262A1

EP1265262A1 - Switch with thermal circuit breaker

Info

Publication number: EP1265262A1
Application number: EP02011327A
Authority: EP
Inventors: Antonio Coppola; Giancarlo Lupoli
Original assignee: Signal Lux MDS Srl
Current assignee: Signal Lux MDS Srl
Priority date: 2001-06-07
Filing date: 2002-05-23
Publication date: 2002-12-11
Also published as: ITMI20011203A0; ITMI20011203A1

Abstract

A switch with thermal circuit breaker of bimetallic strip (14) type, with a rocker (2), at least one rocking contact member (9) operated by the rocker and provided with a contact (9B) arranged to cooperate with a fixed counter-contact (9C), said contact (9B) and said fixed counter-contact (9C) defining a first contactor, and with a second contactor (13A, 14A) operated by the rocker (2), the second contactor (13A, 14A) comprising a fixed contact (13A) and a counter-contact (14A) rigid with the bimetallic strip (14).

Description

The present invention relates to a switch with thermal circuit breaker in accordance with the introduction to claim 1.
Switches incorporating a thermal circuit breaker are known. Such a switch with thermal circuit breaker is described for example in US-A- 4,167,720. This known switch comprises a bimetallic strip (as its thermal circuit breaker), an angle lever, a latching lever and a switching rocker. If overcurrent arises, the bimetallic strip moves the angle lever, which separates from the latching lever to enable this latter to rotate (by the effect of springs). This rotation enables a contactor (against which the latching lever acts to maintain it closed) to open, with simultaneous rotation of the rocker to the "off' position (circuit open). The known switch has the drawback of requiring a plurality of components, some of which are complicated and possibly wearing out after only a relatively small number of cycles.
Moreover, the fact that the rocker automatically returns to the "off" position in the case of unacceptable overcurrent, even though this may appear to be an advantageous aspect, constitutes in reality a point of weakness of the switch, on the one hand because the connection linkage between the latching lever and the rocker is subject to considerable wear and on the other hand because it does not provide the user with any visual information regarding the state of the circuit into which the switch is connected.
The main object of the present invention is to provide a switch with thermal circuit breaker which is of simplified construction and hence economical and of increased life.
A further object of the present invention is to provide a switch with thermal circuit breaker, of simplified bipolar type, able to provide the user with a visual indication of the conditions of the circuit in which it is mounted.
A further object of the invention is to provide a switch with thermal circuit breaker which is compact, is of high current interruption power, and has a useful life comprising a large number of cycles, enabling it to be advantageously used in the electric motor field, where a considerable number of interventions is involved.
These and further objects which will be more apparent from the ensuing detailed description, are attained by a switch with thermal circuit breaker in accordance with the technical teachings stated in the accompanying claims.
The invention will be better understood from the detailed description of preferred embodiments thereof given hereinafter by way of non- limiting example and illustrated in the accompanying drawings, in which:
Figure 1 is a perspective view of the switch (with its casing removed) and shown only by dashed lines) with its components in the ON position in which the circuit into which it is inserted is closed;
Figure 2 is a further perspective of the switch in the same position (i.e. ON) taken from a different angle, namely obliquely from below with reference to Figure 1;
Figure 3 is a perspective view substantially analogous to that of Figure 1, but with the switch in its open (i.e. OFF) position;
Figure 4 is a perspective view of the switch from below, shown in its open (i.e. OFF) position;
Figure 5 shows the switch, seen from a different angle, in its OFF position;
Figure 6 shows the switch, seen from another angle, in its OFF position;
Figure 7 is a schematic view of the switch of the preceding figures connected into a user circuit;
Figure 8 is a vertical section through the switch of Figures 1-6 in its closed (ON) position, the view being taken substantially on the plane F-F of Figure 2;
Figure 9 is a detailed partial vertical section through that switch region comprising the bimetallic strip and the contactor associated with it, said partial section being taken on a vertical plane perpendicular to the plane F-F, with the switch in its closed (ON) position;
Figure 10 is a schematic view in the direction of the arrow A of Figure 9.
The switch provided with thermal protection, shown in the drawings by way of example only, is a double-pole switch, even though the invention can be extended to "n" poles, where "n" is a whole number greater than 1.
The switch comprises a box casing 1 (Figures 1 and 8) of plastic material which rotatably supports a rocker 2 provided for rocking purposes with lateral pins 3 received in corresponding seats, not shown, in the box casing 1.
The rocker 2 (also of plastic) presents three parallel guide cheeks 4, 5, 6. The cheeks 4, 5 are joined together by an intermediate transverse baffle 7 comprising a downwardly projecting protuberance 7A acting as a spring guide for a compression spring 8 (Figures 1 and 8). This spring 8 (see Figure 8 in particular) acts with its free end against a substantially inverted omega-shaped rocking contact member 9 of electrically conductive metal centrally pivoted, at 10, on the upper edge of a conductive strip 11 mounted in the casing 1 and emerging from it to enable the necessary electrical connections to be made to the circuit in which the switch is located. One of the arms 9A of the rocking contact member 9 carries a contact 9B cooperating with a counter-contact 9C present on one side of an inverted L-shaped conductive strip 12 mounted in the casing 1 and emerging from it to enable the electrical connection to be made to said circuit. The contact B and counter-contact 9C together form a first contactor.
On one of the two arms 9A of the rocking contact member 9 there is provided a projecting fin 9D on which the transverse baffle 7 acts (as explained hereinafter) to obtain (during opening of the switch) the forced rocking of the rocking contact member 9 during a first part of the angular excursion of the rocker 2.
The switch also comprises a further conductive strip 13, mounted in the casing 1 and emerging therefrom to enable the electrical connection to be made to said circuit. The conductive strip 13 carries a contact 13A arranged to cooperate electrically with a counter-contact 14A of a bimetallic strip 14 fixed on one side (opposite that of the counter-contact 14A - see Figure 10 in particular) to a conductive strip 15 so that it projects therefrom. The conductive strip 15 is mounted in the casing 1 and projects therefrom to enable the electrical connection to be made to said circuit. The contact 13A and the counter-contact 14A form a second contactor.
In the casing 1 there is slidingly mounted a piston 16 on which there operates a compression spring 16 which tends to move the piston upwards, i.e. towards the overlying bimetallic strip (see Figure 9 in particular). As will be more apparent hereinafter, depending on the operating conditions of the switch the piston 16 can either bear against the lower edge of the bimetallic strip 14 and casing strip 13 (as can be seen for example in Figure 6) or be spaced from the bimetallic strip 14 (as can be seen for example in Figure 3).
In its interior the rocker 2 comprises a first cam 18 associated with a wall or baffle 19 (see Figure 9 in particular). When the rocker 2 is in a given position (during switch opening) the cam 18 cooperates with a suitably bent upper end 14B of the bimetallic strip 14 so as to flex this latter and distance the counter-contact 14A from the contact 13A, and enable this baffle 19 to interpose itself between the contact 13A and counter-contact 14A, so increasing the discharge path when the two are separated.
The rocker 2 also comprises a second cam or finger 20 intended to withdraw the piston 16, against the action of the spring 17, from the position in which, when in a certain operative condition (that of Figure 6), it becomes interposed between the bimetallic strip 14 and the casing strip 13.
As can be seen from the electrical schematic of Figure 7, in which the load C (for example a motor) is powered via the described switch and in which the same reference numerals are used to indicate parts corresponding to those of the preceding figures, the two phases (F and N) powering the load C are controlled respectively by the first contactor (formed by the contact members 9B and 9C) and by the second contactor (formed by the contact members 13A and 14A, these latter relative to the thermal circuit breaker of which the bimetallic strip 14 constitutes the active part).
It will be assumed that by acting on the rocker 2 the user has put the switch in the "ON" position to power the load C (this situation is reflected in particular in Figures 1, 2, 6 and 9). In this position the first contactor 9B and 9C is closed and the second contactor 13A and 14A is also closed. The piston 16 (see Figure 9 in particular) acts on the lower edge of the bimetallic strip 14. The load C is powered. When the user wishes to interrupt power to the load C he acts on the rocker 2. During a first part of its angular excursion the rocker 2 interferes via its baffle 7 with the projecting fin 9A-9D to cause the switch 1 to open by the forced rocking of the contact member 9 into the open position (aided by intervention of the spring 8), so that the first contactor 9B and 9C opens. During this first part of its angular excursion the rocker has not yet caused the second contactor 13A, 14A (of which the bimetallic strip 14 forms part) to open, for the reason that the members provided for this opening (represented by the first cam 18 and the baffle 19) are out of phase so as to operate only during the second part of the angular excursion of the rocker 2. During this second part of the angular excursion the cam 18 cooperates with the bent end of the bimetallic strip 14 to flex this latter and open the second contactor 13A, 14A, and then interposes the baffle 19 between the two contacts 13A, 14A of the second contactor, so lengthening the discharge path between the two contacts. At the same time the second cam 20 urges the piston 16 downwards to withdraw it from the bimetallic strip 14 (this situation is represented in Figures 3 and 4).
With the opening firstly of the first contactor 9B, 9C and then of the second contactor 13A, 14A the advantage is obtained of eliminating those sparking phenomena which prejudice the life of the contacts 13A, 14A.
It will now be assumed that with the switch closed (i.e. ON), for accidental reasons the current passing through circuit of the load C (for example an electric motor) reaches a value such that the thermal circuit breaker, i.e. the bimetallic strip 14, intervenes. In this event the bimetallic strip 14 flexes, the second contactor 13A, 14A opens and the piston 16 interposes itself between the conductive strip 13 and the bimetallic strip 14 to prevent closure of the contactor 13A, 14A even when the bimetallic strip 14 has cooled, given that the power circuit to the load has been interrupted (such a situation is expressed by Figures 5 and 6).
If power to the load is to be restored, the rocker 2 has firstly to be returned to its "OFF" position. The contact member 9 then rocks into the position in which the first contactor 9B, 9C is open, and the second cam 20 moves the piston 16 downwards, to withdraw it from its position interposed between the bimetallic strip 14 and the contact strip 13. However the second contactor 13A, 14A does not close because the first cam 18 has acted to maintain the bimetallic strip 14 diverged.
Only with the next passage of the rocker into the "ON" position is power restored to the load C. In this respect, the rocker member 9 rocks to close the first contactor 9B and 9C, the first cam 18 (with the relative baffle 19) withdraws from the bimetallic strip 14, to close the second contactor 13A, 14A, and the second cam 20 releases the piston 16 which halts against the lower edge of the bimetallic strip 14.

Claims

A switch with thermal circuit breaker of bimetallic strip (14) type, with a rocker (2), at least one rocking contact member (9) operated by the rocker and provided with a contact (9B) arranged to cooperate with a fixed counter-contact (9C), said contact (9B) and said fixed counter-contact (9C) defining a first contactor, and with a second contactor (13A, 14A) operated by the rocker (2), characterised in that the second contactor (13A, 14A) comprises a fixed contact (13A) and a counter-contact (14A) rigid with the bimetallic strip (14).
A switch as claimed in claim 1, wherein the rocker (2) presents a first cam (18) arranged to cooperate with the bimetallic strip (14) to cause it to flex and hence open the second contactor (13A, 14A).
A switch as claimed in claim 1 or in claims 1 and 2, wherein the rocker (2) presents a baffle (19) arranged to interpose itself between the contact (13A) and counter-contact (14A) of the second contactor (13A, 14A) to lengthen the discharge path between them.
A switch as claimed in at least one of the preceding claims, comprising an elastically loaded (17) piston element (16) which in the case of unacceptable overcurrent becomes interposed between the bimetallic strip (14) and a fixed strip (13) carrying the contact (13A) of the second contactor (13A, 14A).
A switch as claimed in claim 4, wherein, when the second contactor (13A, 14A) is closed, the piston element (16) presses against the lower edge of the bimetallic strip (14).
A switch as claimed in at least one of the preceding claims 4 and 5, wherein the rocker (2) presents a second cam (20) arranged to urge the piston element (16) against the action of the elastic load (17).
A switch as claimed in claim 1 and at least one of claims from 2 to 6, wherein the rocking contact member (9) and the rocker (2) present means (7 and 9D) which cooperate to produce the forced rocking of the first contactor (9B, 9C) into its open position in advance of the opening of the second contactor (13A, 14A).
A switch as claimed in at least one of the preceding claims, wherein the bimetallic strip (14) presents a bent appendix (14B) arranged to cooperate with the first cam (18) in order to open the second contactor (13A, 14A).
A switch as claimed in at least one of the preceding claims, wherein the rocker (2) controls several rocking contact members (9) positioned side by side.