BACKGROUND OF THE INVENTION  
         [0001]    The present invention refers to a stop device usable in any application wherein it is necessary to arrange a deactivable stop device for avoiding the movement, at least in one direction, of a first moving structure with respect to a second structure.  
         SUMMARY OF THE INVENTION  
         [0002]    The object of the invention is to carry out a stop device which shows a simple structure, with reduced hindrance, economical to produce and at the same time is effective in the functioning.  
           [0003]    In view of attaining this purpose, the object of the invention is a stop device having the features defined in the enclosed claim  1 . Further advantageous features of the invention are defined in the remaining dependent claims. 
       
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       [0004]    The invention will be now described with reference to the enclosed drawings, which are given as not limitative example, wherein:  
         [0005]    [0005]FIG. 1 is a perspective view of a stop device according to the invention,  
         [0006]    [0006]FIG. 2 is a partially sectioned view of the device of FIG. 1, and  
         [0007]    [0007]FIG. 3 is a sectional view of the device of FIGS. 1, 2. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    With reference to the drawings, numeral  1  generally shows a fixed support structure comprising a box shaped body of a metal sheet  2  with two end flanges  3 ,  4  for allowing the mounting of the structure  1  on any structure which is designed to receive the same.  
         [0009]    Within the box shaped body  2 , two stop elements  5  are slidably mounted, which are movable between a mutual distant position, that can be seen in FIG. 3, and a mutual close position. In the aforesaid mutual distant position that can be seen in FIG. 3, the two stop elements  5  are designed to co-operate with a stop surface (not shown) arranged over a structure, at which respect the structure carrying the device according to the invention is movable, in order to determine a stop position of a structure with respect to the other. In the description and in the enclosed drawings, these structures mutually movable therebetween are not shown, as the device forming the object of the invention is of a general application.  
         [0010]    By mere way of example, the stop device-carrying structure can be a retractable bumper of a motor vehicle.  
         [0011]    At each of the stop elements  5  a first and a second coil springs  6  are associated (one of which is partially visible in FIG. 5), which are arranged according to the hole axes  6   a  of the stop element  5  that can be seen in FIG. 2. Coils  6  are arranged for operating under traction in order to tend to maintain the two stop elements  5  towards their mutual close position.  
         [0012]    As it is clearly evident in FIG. 3, the two stop elements  5  have two slanted surfaces  5   a  facing each other, substantially V-shaped, which co-operate with the two opposite slanted sides  7   a  of a wedge-shaped element  7 , acting as a cam, which is pushed by two coil springs  8  leftwards (with reference to FIG. 3) in order to hold the two stop elements  5  in their mutual distant position, against the action of the springs  6 . The wedge-shaped element  7  then acts as a cam which makes the two stop elements  5  coming out from the box body  2  due to the engagement of the opposite inclined planes  7   a ,  5   a.    
         [0013]    Still with reference to FIG. 3, the movement of the wedge-shaped element  7  is driven within two bushings  9  fixed to a bracket  10  belonging to the fixed support structure  1 , within which two cylindrical pins  11  are slidably mounted and fixed at one end to the wedge-shaped element  7 .  
         [0014]    In order to return the two stop elements  5  towards their mutual close position, a shape memory actuator, generally referred with the numeral  12 , is arranged, which in the illustrated example includes a shape memory wire  13  arranged according to a general U-shaped configuration, with two branches  14  substantially parallel, and an intermediate joining portion  13   a  engaged around a curved groove of a guide element  7   b  fixed to the wedge-shaped element  7  (see FIG. 2).  
         [0015]    The two opposite and adjacent ends of the shape memory wire  13  are rigidly connected with the fixed support structure  1 . This is obtained by using two metal rigid tubes  15 , each having one end fixed to the bracket  10  with the opposite end having a metal bushing  16  with a H-shaped section, within which a block  17 , fixed to the respective end of the flexible cable  13 , is mounted.  
         [0016]    The cable  13  is formed by extrusion of a shape memory metal alloy. By applying a co-extrusion method, along with the cable  13 , a synthetic material coating  18  is obtained, like the one which is the object of the previous patent application (still confidential) of the Applicant No. T02003A000045. The function of this coating will result apparent in the following. The whole of the wire  13  with its co-extruded sheath  18  is arranged through a sheath  19  (FIG. 2) which has one end fixed to the bracket  10  as well, and the opposite end ending against the cross sector of the bushing  16 .  
         [0017]    Means (not illustrated) for supplying an electric current through the wire  13  are also provided. As a result of the electric current passage, the wire  13  becomes warm and, due to the shape memory, it undergoes a length reduction. Since the two opposite ends of the wire are fixed to the bushings  16 , which are rigidly connected to the fixed support structure  1 , the shortening of the wire causes a displacement of the intermediate joining portion  13 a of the wire in the direction of the two adjacent ends of the wire, namely a displacement of the wedge-shaped element  7  (see FIG. 3) rightwards (always referring to FIG. 3), against the action of the springs  8 . This shifting of the wedge-shaped element  7  causes consequently a displacement of the two stop elements  5  towards their mutual close posistion due to the springs  6  action, which is no longer. opposed from the wedge-shaped element  7 . In this condition, the stop device is then deactivated. When the current supply ends, the wedge-shaped element  7  is brought back in its starting position, as illustrated in FIG. 3, through the springs  8 , whereby the wedge-shaped element  7  pushes the two stop elements  5  in their drawn active position. The advantage of using the coating  18  co-extruded with the shape memory wire  13  is, on one hand, to accelerate the wire cooling after the current interruption, and on the other hand to act as a kind of spring arranged throughout the wire length, in order to further increase the coming back of the wire to the quiescent condition when the current feed ends.  
         [0018]    Obviously, without prejudice for the principle of the invention, construction details and embodiments could widely vary with respect to what has been described and shown by mere way of example, however without leaving the scope of the present invention.  
         [0019]    For example, instead of one single U-shaped wire, two wires, e.g. in parallel, could be used, as well as one single wire corresponding to only one of the two wire branches illustrated herein. Moreover, the shape memory element could also be a rigid elengated element.
A stop device with a shape memory actuator includes two stop elements sliding within a fixed support structure and usually hold in their mutual distant position by cam means pushed through spring means. A shape memory actuator is started through an electric current passage for causing the displacement of the cam means in a position wherein they permit the backward movement of the two stop elements towards a mutual close position.