Abstract:
A switch includes two interacting contacts ( 1, 2 ) and a closing spring ( 5, 11, 15, 21 ) for moving the contacts into the closed position, an operating button which can be used to initiate a prestressing phase of the closing spring ( 5, 11, 15, 21 ), and a locking device ( 6 ) for locking the contacts ( 1, 2 ) until a predetermined moment at which the influence of the prestressed closing spring ( 5, 11, 15, 21 ) is to be released onto the contacts. The locking device ( 6 ) is designated to lock the interacting contacts ( 1, 2 ), during the prestressing phase, at a contact distance. The contact distance to be locked being less than the contact distance in the open position of the contacts ( 1, 2 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a switch comprising at least two interacting contacts, a closing spring for moving the contacts into the closed position, an operating button which can be used to initiate a prestressing phase of the closing spring, and a locking device for locking the contacts, in closing the switch, until a predetermined moment at which the influence of the prestressed closing spring is to be released onto the contacts. 
     A switch of this nature is known from international patent application WO 96/17368. 
     This known switch has two interacting contacts, namely a fixed contact and a movable contact which is attached to a switch shaft by means of a contact arm. This switch shaft is rotated by means of a prestressed closing spring in order to move the said contacts into the closed position. To this end, the closing spring is firstly prestressed by rotating the actuating button. In this process, a catch is used, comprising the movement of a knee device beyond the dead centre. The result is a snap action in which the spring is fully prestressed before the contacts are released. The closing spring also takes care of the contact force. In switches of this nature, the aim is to design them in such a manner that the switch can be closed in an operator-independent manner, i.e. that the contact pressure and the closing speed are as far as possible independent of the person operating the switch. This characteristic is important since it is necessary to prevent the contacts in a switch being damaged, on the one hand by being closed too quickly, in which event the contacts may be burnt away as a result of bouncing, and on the other hand by being closed too slowly, in which case the contact pressure is built up too slowly, so that contacts may become welded in place. 
     The known switch is also provided with a locking device for locking the contacts, beyond the theoretical turn-over point of the catch, in order to ensure that the closing spring is sufficiently prestressed. However, the problem remains that, particularly when using butt contacts, the risk of the contacts bouncing remains high, and consequently the contacts are burnt away and welded in place when a short circuit is closed. 
     In U.S. Pat. No. 4,687,891 as with of the above kind is described, in which the locking device is designed to lock the interacting contacts, during the prestressing phase, at a contact distance, the contact distance to be locked being less than the contact distance in the open position of the contacts. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a switch of the type mentioned in the preamble in which the abovementioned problems are avoided. 
     According to a first aspect of the invention, this object is achieved by the fact that on that side of the contact arm of the movable contact which is remote from the fixed contact there is a control lever which can pivot at a point between its ends and, at one end, adjoins the contact arm, the profile of this end being such that, by rotating this lever under the influence of the prestressed closing spring, the movable contacts can be moved into contact with the fixed contact, and in that the locking device comprises a releasable securing element which, in the prestressing phase of the closing spring, secures the control lever in a position in which the movable contact lies at the contact distance which is to be locked from the fixed contact. 
     According to a second aspect of the invention the above object is achieved by the fact that on that side of the contact arm ( 3 ) of the movable contact ( 2 ) which is remote from the fixed contact, there is a first lever ( 16 ) which can pivot about a point ( 17 ) between its ends and one end of which is directed towards the contact arm ( 3 ) and is pivotably ( 19 ) connected to an end of a second lever ( 18 ), the other end of which is pivotably connected to the contact arm ( 3 ), and in that the locking device comprises a releasable securing element ( 20 ) which, in the prestressing phase of the closing spring ( 5 ,  21 ), secures the first lever ( 16 ) in a position in which the movable contact lies at the contact distance which is to be locked from the fixed contact ( 1 ). 
     As a result, the contacts are moved towards one another during the stressing of the closing/contact-force spring as far as a distance which is selected to be such that there is no possibility of any spark-over between the contacts. After the closing/contact-force spring has been sufficiently prestressed, the effect of the closing/contact-force spring is released onto the contacts. Compared to the conventional way of closing the switch, only a small fraction of the spring energy which is built up will be converted into kinetic energy from the closing/contact-force spring system to the contacts. Using the invention considerably reduces the risk of bouncing and also of the contacts experiencing welding phenomena. 
     It should be noted that a blocking device for preventing the switch shaft from bouncing back out of the open position, i.e. towards the closed position, of the contacts is known per se from international patent application WO 95/29499. However, this device is used to suppress bouncing phenomena when the switch is opened. 
     The locking device of the switch of U.S. Pat. No. 4,687,891 is provided between prestressing spring and contact arm. In contrast the locking device of the switch of present invention is located separately. Thereby a higher power can be switched, which is not possible with the switch known from U.S. Pat. No. 4,687,891. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a first embodiment of the present invention; 
     FIG. 2 is a schematic illustration of a second embodiment of the present invention; 
     FIG. 3 is a schematic illustration of a third embodiment of the present invention; 
     FIG. 4 is a schematic illustration of a fourth embodiment of the present invention; 
     FIG. 5 is a schematic illustration of a fifth embodiment of the present invention; and 
     FIG. 6 is a schematic illustration of a sixth embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will be explained in more detail below with reference to the drawings, in which FIGS. 1-6 diagrammatically depict embodiments of the invention. 
     The switch comprises a set of contacts, of which only two interacting contacts, comprising the fixed contact  1  and the movable contact  2 , are shown in the embodiments illustrated in FIGS. 1-6. The movable contact  2  is attached to a contact arm  3 . The closing drive for the movable contact  2  is formed by a knee, which comprises the lever  4  and the closing/contact-force spring  5 . Said knee acts on the contact arm  3  of the movable contact  2 . The switch furthermore comprises a locking device  6  for locking the contacts so that they cannot readily close from the open position. 
     The switch shown in the figures is depicted in the open position. The opening spring is not shown in FIG.  1 . 
     When the switch is to be closed, an actuating button  4 ′ is used to exert a force F in the direction of the arrow on the knee of the knee device comprising the knee lever  4  and the closing spring  5 . The actuating button and the link between the actuating button and the knee of the knee device is not shown for the sake of clarity, but is obviously easy for a person skilled in the art to design. When the force F is exerted on the knee of the knee device  4 ,  5 , the free end of the contact arm  3 , and therefore the contact  2 , is moved to the right towards the fixed contact  1 . The closing force F initiates and continues a prestressing phase of the closing/contact-force spring. In this prestressing phase, after an initial period, the movable contact  2  is locked by means of the locking device  6 . At the end of this initial period, the movable contact  2  has been moved to a distance from the fixed contact  1  which is such that there is no possibility of spark-over between the contacts. The movable contact  2  is held at this contact distance which is to be locked, which distance is less than the contact distance in the open position of the contacts. After this initial period, the closing/contact-force spring is prestressed further until it has reached a level of prestress which is sufficient to close the two contacts  1 ,  2 . As soon as this level is reached, the locking device  6  is released. 
     It should be noted that in the initial period of the prestressing phase the movable contact is moved to the said shorter contact distance, which is to be locked, from the associated fixed contact by the closing spring being stressed by means of the force F while the movable contact  2  is not yet locked. However, it is quite conceivable for this shorter contact distance to be brought about in some other, for example mechanical, way. 
     In the embodiment shown in FIG. 1, the locking device  6  comprises a securing element  7  which, in the prestressing phase of the closing spring  5 , secures the movable contact  2  after the said shorter contact distance which is to be locked has been reached. Obviously, various securing elements are possible, and it is conceivable, for example, for a pawl device to be present on the other side of the contact arm  3 , which device locks the movable contact, for example by the contact arm  3  butting against a pawl (not shown) which, when it is rotated away, can release the contact arm  3 . 
     The securing element shown in FIG. 1 is in the form of a grip lever which is pivotably attached at one end. By means of a prestressing spring (not shown), this grip lever  7  is prestressed in the position shown. The free end of the grip lever  7  is provided with a hook  8  which, in the open position of the contacts  1 ,  2 , engages behind a hook  9  which is attached to the contact arm  3  of the movable contact  2 . In the open position of the switch shown in FIG. 1, the mutually facing grip faces of the hooks  8 ,  9  lie at a distance from one another which is equal to the contact distance in the open position less the contact distance which is to be locked. 
     When, after the initial period of the prestressing phase of the closing/contact-force spring  5 , the said spring has been sufficiently prestressed, the grip lever  7  is pivoted in the direction of the arrow A, counter to the force of its prestressing spring, with the result that the hook  8  and, with it, the contact arm  3  and the associated movable contact  2  are released. The released contact  2  will make contact with the fixed contact  1  in an operator-independent manner and with the minimum possible risk of bouncing. 
     It should be noted that the rotation of the grip lever  7  in the direction A can be produced, in a manner not shown, by the actuating button (likewise not shown) of the switch. 
     Furthermore, it is clear that the grip lever and/or the fixed hook  8  are attached in such a manner that, when the contact arm  3  moves from the closed position into the open position of the contacts, they automatically slide over one another until the position shown in FIG. 1 is reached. 
     The switch in the embodiment shown in FIG. 2 comprises the fixed contact  1 , the movable contact  2  with the contact arm  3 , and the locking device  7 ,  8 ,  9 , as in the embodiment shown in FIG.  1 . For this reason, these components will not be described. 
     This figure also shows the opening spring  10 . 
     In the embodiment shown in FIG. 2, the movable contact  2  is driven, via the contact arm  3 , by a coil spring  11 . The coil spring  11  is prestressed by a moment M which can be derived, in a simple manner which will be standard procedure for a person skilled in the art, from the actuating button (not shown) of the switch. 
     The said moment will move the movable contact  2  towards the fixed contact  1 , so that this movement is locked by grip lever  7 . After the closing spring has been sufficiently prestressed, the movable contact  2  is released by grip lever  7  being rotated in the direction of the arrow A, and the contacts will close in an operator-independent, bounce-free manner. 
     In the switch shown in FIG. 3, the movable contact  2  is driven by means of a control lever  12  which is pivotable at a point  13 . One end of the control lever  12  interacts with the contact arm  3 . This particular end has a profile which is such that, through the rotation of this control lever  12 , the contact arm  3 , and therefore the contact  2 , is moved towards the fixed contact  2 . Here too, a prestressed closing spring  5  is present. The control lever  12  is locked by means of the locking device  6  which, in this embodiment, comprises a releasable securing element  14 . In the prestressing phase of the closing spring  5 , this securing element  14  secures the control lever  12  in a position in which the movable contact  2  lies at the contact distance which is to be locked from the fixed contact  1 . 
     To close the switch, the closing spring  5  is prestressed by means of a force F which is derived from the movement of the actuating button of the switch. In the initial period of the prestressing phase of the closing spring  5 , the control lever  12  is rotated in the direction of the arrow B and, by means of the profile of that end of the control lever  12  which bears against the contact arm  3 , the movable contact  2  is moved a short distance to the right, until the contact distance is equal to the abovementioned contact distance which is to be locked. As soon as this contact distance is reached, the control lever  12  is secured by means of the securing element  14 , which in this embodiment is designed as a pivotable pawl  14 . In the remaining part of the prestressing phase, the closing spring  5  is prestressed further until it has reached a predetermined level of prestress, after which the securing element  14  is rotated in the direction of the arrow A. This rotation can be derived from the movement of the actuating button (not shown) of the switch. It should furthermore be noted that the securing element  14  is prestressed in the position shown in FIG.  3 . 
     In the open position of the switch, the distance between the free end of the securing element  14  and the opposite face of the control lever  12  is equal to the contact distance in the open position less the contact distance which is to be locked. 
     It should be noted that the pawl  14  of the locking device can also interact with the top face of the right-hand section of the control lever  12 . 
     In the embodiment of the switch according to the invention shown in FIG. 4, the opening spring  10  is also illustrated. In this embodiment, the control lever  12  is driven by the coil spring  15 . By means of a moment M, which can be derived from the actuating button, acting on the closing spring  3 , the control lever  12  is rotated in the direction of the arrow B, with the result that the contacts  1 ,  2  are moved towards one another. The movement of the contact arm  3  is terminated temporarily by the securing element  14  or pawl securing the control lever  12 . The position of the contact arm  3 , and therefore of the movable contact  2 , is maintained, while the coil spring  15  is prestressed further. At the moment when the coil spring  15  has been sufficiently prestressed, the securing element  14  is rotated in the direction of the arrow A, which rotation may, if appropriate, be derived from the movement of the actuating button of the switch. As a result, the control lever  12  is released and, under the influence of the prestressed coil spring  15 , the contacts  1 ,  2  will close in an operator-independent manner and with the minimum possible risk of bouncing. 
     In the embodiments shown in FIGS. 5 and 6, the movable contact  2 , in particular contact arm  3 , is driven by a set of levers which comprises a first lever  16  which can pivot about a point  17 . The right-hand end of the first lever  16  is pivotably connected to one end of a second lever  18 . The other end of the second lever  18  is pivotably connected to the contact arm  3 . The locking device  6  in this case comprises the releasable securing element  20 , which is in the form of a pivotable pawl. 
     In the embodiment shown in FIG. 5, the two contacts, comprising the fixed contact  1  and the movable contact  2 , are driven by the closing spring  5  which has been prestressed by means of a force F. The closing spring  5  acts on the knee between the two levers  16  and  18 . Obviously, the spring may act on a different location on the set of levers, provided that the prestressing force acts in the correct direction. 
     By exerting the force F, the first lever  16  will be rotated in such a manner that, by means of the second lever  18 , the contact arm  3 , and therefore the movable contact  2 , will move towards the fixed contact  1 , until this movement is temporarily interrupted by the securing element  20 . As soon as the closing spring  5  has been sufficiently prestressed, the securing element  20  is rotated in the direction of the arrow A, so that the first lever  16  is released and the prestressed spring  5 , via the system of levers  16 ,  18 , will drive the contact arm  3 , and therefore the contact  2 , towards the fixed contact, and the contacts will close in an operator-independent manner and with the minimum possible risk of bouncing. 
     In the embodiment shown in FIG. 6, the coil spring  21  is used as the closing spring. This closing spring  21  is prestressed by a moment M which can be derived from the actuating button. By means of the moment M, the first lever  16 , via the closing spring  21 , will be rotated in such a manner that, by means of the second lever  18 , the contact arm  3 , and therefore the movable contact  2 , are moved towards the fixed contact  7  until this movement is again terminated temporarily by the securing element  20 . As soon as the coil spring  21  is sufficiently prestressed, the first lever  16  is released, by the securing element  20  being rotated in the direction of the arrow A. As a result of this first lever  16  being released, the contacts  1 ,  2  will, under the influence of the prestress in the coil spring  21 , via the second lever  18  and the contact arm  3 , close in an operator-independent manner and with the minimum possible risk of bouncing. 
     It should further be noted that the securing element or the pawl  21  can also interact, to the right of the pivot point  12 , with the first or second lever, or even at the location of the connection. In the latter case, the pawl has to be pulled away in order to release the set of levers.