BACKGROUND OF THE INVENTION 
     The present invention relates to a device for braking the movement of a movable member with respect to a support structure. 
     A device of this type is known for example from German Utility Model DE 296 04 260 U1, which describes a tilting handle provided with a handgrip articulated on a mounting wall of a vehicle. The handgrip is rotatable against the action of resilient means from a rest position, close to the mounting wall, to an operating position. The handgrip is brought automatically from the operating position to the rest position after being released by the user. The return movement to the rest position is made softer by a braking device which acts on the axis of rotation of the handgrip. 
     The braking device is produced as a rotary damper, comprising a cylindrical casing, which defines within it an annular chamber filled with a viscous medium, a rotor mounted in a sealed manner on the casing and rotatable in the annular chamber, and a central through-opening, which is provided in the casing, and within which the axis of rotation of the handgrip is arranged. 
     The conventional rotary dampers normally used in the above-mentioned application do not, in reality, make it possible to obtain very high braking torques (customarily not more than a few N·cm), which limits their range of use. Moreover, the braking action on the rotor is developed not only by the viscous fluid contained in the device, but also to a large extent by the sealing O-rings interposed between the rotor and the casing, which makes the performance of the device substantially dependent on the operating temperature and percentage of humidity. 
     It is an aim of the present invention to provide a braking device of compact dimensions which makes it possible to obtain substantially higher braking torques than the prior art, without exhibiting the problems of reliability described above. 
     SUMMARY OF THE INVENTION 
     This aim is achieved according to the invention by a device for braking the movement of a movable member with respect to a support structure. 
     In such a device, the braking action on the device derives from the effect of the resistance which the viscous fluid offers to the rotational movement of a piston-like member or portion. This causes the O-rings arranged in the device predominantly to perform a sealing function, without having a substantial influence on the braking performance. 
     Advantageously, the type of movement provided for in the device according to the invention makes it possible to predetermine an end stop incorporated in the device, which is not possible in the rotational devices of known type. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the device according to the invention will become clearer from the following detailed description of an embodiment of the invention which is given with reference to the appended drawings which are provided purely by way of non-limiting example and in which: 
         FIG. 1  is a diagrammatic view of a handle provided with a braking device; 
         FIG. 2  is a plan view of a braking device according to the invention; 
         FIG. 3  is a view in side elevation of the device of  FIG. 2 ; 
         FIG. 4  is a view in longitudinal section of the device of  FIG. 2 , along the line IV-IV of that figure; 
         FIG. 5  is a view in longitudinal section of the device of  FIG. 2 , along the line V-V of that figure; 
         FIG. 6  is a plan view of a casing of the device of  FIG. 2 , before the assembly of the device; 
         FIG. 7  is a view in side elevation of a rotor of the device of  FIG. 2 ; 
         FIG. 8  is a plan view from below of the rotor of  FIG. 7 ; 
         FIG. 9  is another view in side elevation of the rotor of  FIG. 7 ; 
         FIG. 10  is a plan view of a casing of a first variant of the device of  FIG. 2 , before assembly; 
         FIG. 11  is a view in longitudinal section of the casing of  FIG. 10 , along the line XI-XI of that figure; 
         FIG. 12  is a view in longitudinal section of the casing of  FIG. 10 , along the line XII-XII of that figure; 
         FIG. 13  is a plan view of a casing of a second variant of the device of  FIG. 2 , before assembly; 
         FIG. 14  is an exposed view of a casing of a third variant of the device of  FIG. 2 , before assembly; and 
         FIG. 15  is a view in longitudinal section of the casing of  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The drawings illustrate a braking device  10 , produced as a rotary damper, adapted to being fitted for example to a tilting handle M (illustrated in  FIG. 1 ), mounted on a wall W inside the passenger compartment of a vehicle. The handgrip of the handle is rotatable against the action of resilient means E from a rest position to a use position. After being released by the user, the handgrip is then brought automatically from the use position to the rest position. The device  10  serves to slow down the return movement of the handle. In particular, as will be explained hereinafter, the device illustrated in the drawings is adapted to be mounted at the axis of rotation or hinge axis x of the aforesaid handle. 
     s can be seen from  FIGS. 2 to 6 , the device  10  comprises a casing  12  on which a rotor  14  is mounted. The casing  12  is substantially cylindrical and has a central through-opening  15  (illustrated in  FIGS. 4 to 6 ), which allows the device to be mounted on the axis of rotation x of the handle M, in a manner similar to that illustrated in Utility Model DE 296 04 260 U1. 
     As can be seen in  FIGS. 4 to 6 , the casing  12  defines an annular chamber  16  coaxial with the central opening  15  and containing a viscous fluid, for example silicone oil. The annular chamber  16  is bounded laterally by a radially inner wall  17  and by a radially outer wall  18 , and is closed at one end by an end wall  19 . The annular chamber  16  is in the shape of an open ring, and is therefore bounded, in the circumferential direction of the ring, by a meridian partition  19   a , visible in  FIGS. 5 and 6 , extending in a meridian plane passing through the axis of rotation x. In this embodiment, the meridian partition  19   a  is formed by a rigid wall, produced in one piece with the radially inner wall  17 , the radially outer wall  18  and the bottom wall  19  of the casing  12 . 
     The end of the annular chamber  16  opposed to the end wall  19  is open, and from that end the radially outer wall  18  has an edge with a mouth  18   a  in which the radially outer wall  18  is folded towards the inside of the chamber  16 , for example by hot or ultrasound riveting. In a position adjacent to the mouth  18   a , a shoulder  18   b  is provided on the inner surface of the radially outer wall  18 . 
     With such an arrangement, the casing  12  holds the rotor  14  axially, so that this is capable of closing the annular chamber  16 . The rotor  14  in fact has a flange  14   a  provided on its radially outer surface, intended to be engaged axially between the shoulder  18   b  and the folded-back mouth  18   a  of the casing  18 . The type of mounting of the rotor  14  on the casing  18  is not, of course, essential to the purposes of the invention, provided that it allows relative rotation between them. 
     The leaktight seal of the closure of the annular chamber  16  is guaranteed by a pair of O-rings  21 ,  22 . One O-ring  21  is housed in a corresponding seat  23  provided on the radially inner wall  17  of the casing  12 , and is interposed between the radially inner wall  17  and a radially inner surface of the rotor  14 , so as to provide a radial seal. The other O-ring  22  is housed in a corresponding seat  24  provided on the radially outer surface of the rotor  14 , and is interposed between the radially outer surface and the radially outer wall  18  of the casing  12 , so as to provide a radial seal. 
     The alignment and centring of the rotor  14  with respect to the chamber  16  of the casing  12  is guaranteed by the lateral walls  17  and  18  of the casing  12 . In particular, the radially inner wall  17  of the casing  12  defines the rotation shaft of the rotor  14 . In the rotor  14  a through hole  25  is provided, intended to receive the axis of rotation x of the movable member to which the device  10  is connected. The through hole  25  has a cross-section  26  of enlarged diameter, intended to receive the radially inner wall  17  of the casing  12  acting as a rotation shaft. In the drawings, the arrows A indicate the directions of rotation of the rotor  14  with respect to the casing  12 . 
     Referring also to  FIGS. 7 to 9 , the rotor  14  further has an elongate portion  31  produced in one piece with the rotor  14 , extending in the direction of the axis x and arranged so as to be received within the annular chamber  16  when the rotor  14  is assembled to the casing  12 . In an alternative embodiment, not illustrated, the elongate portion  31  may be substituted by an elongate member rigidly connected to the rotor  14 . 
     The elongate portion  31  is connected by one of its ends to the remainder of the body of the rotor  14 , and at the other has a fin  32  having a tapered plate-like shape, this also extending in the direction of the axis x. The length of the elongate portion  31 , including the fin  32 , is such that, in the assembled state of the braking device  10 , the free end of the fin  32  reaches a predetermined distance from the inner surface of the bottom wall  19  of the casing  12 , so as to define therewith a passage opening  33 . 
     The elongate portion  31  has in general, in a plane passing through the axis of rotation x, a longitudinal section shaped so as to block, except for sizing tolerances, the meridian section of the annular chamber  16 , except for the passage opening  33  defined by the end fin  32  in co-operation with the radially outer wall  18 , the radially inner wall  17  and the bottom wall  19  of the casing  12 . 
     In addition, the elongate portion  31  has a cross-section substantially in the shape of a sector of a circular crown (visible in particular in  FIG. 8 ). 
     Because of the arrangement described herein, rotation of the rotor  14  with respect to the casing  12  brings about the rotatory displacement of the elongate portion  31  along the annular chamber  16  and within the latter. 
     As stated above, the elongate portion  31  of the rotor  14  is of such dimensions that it does not completely block the meridian section of the chamber  16  of the casing  12 , and at the end fin  32 , leaves the passage opening  33  for the transfer of fluid. In this way, the elongate portion  31  of the rotor  14  separates the annular chamber  16  into two end regions  16   a  and  16   b  arranged on circumferentially opposed sides of the elongate portion  31  of the rotor  14 , which are in mutual fluid communication via the passage opening  33 . For greater clarity, the end regions  16   a  and  16   b  are shown by dashed lines in  FIG. 6 , together with the elongate portion  31  of the rotor  14 , this also being shown by dashed lines. The sliding of the elongate portion  31  of the rotor  14  in the chamber  16  therefore urges the viscous fluid contained in the chamber  16  to transfer forcibly from the chamber  16   a  to the chamber  16   b  or vice versa, via the passage opening  33 . The elongate portion  31  of the rotor  14  then acts as a piston inside the annular chamber  16 . The meridian partition  19   a  thus defines the end-of-stroke positions of the piston portion  31 . 
     The elongate portion  31  of the rotor  14  is consequently braked by the viscous medium present in the chamber  16 , and the braking effect depends both on the viscosity of the viscous fluid and on the dimensions of the passage opening  33 , and therefore on the resistance offered by the passage opening  33  to the transfer of the fluid from one region  16   a  to the other  16   b  at the sides of the elongate protuberance  31  of the rotor  14 . In this way it is possible definitively to regulate the braking torque of the device  10 , since said torque, which opposes the rotation of the rotor  14  with respect to the casing  12 , obviously depends on the movement of the elongate portion  31  of the rotor  14  in the chamber  16 . The Applicant has, for example, produced a device of the type described above, having an overall diameter of around 1.3 cm and an overall height of around 1.6 cm., capable of exerting a braking torque of up to several tens of N·cm. 
     The device according to the invention is preferably produced from plastics material. It may be without the central through hole  15 , utilising external coupling systems and/or shaped blind holes; this permits smaller overall radial dimensions. 
     As may be appreciated, the O-rings  21  and  22  exert almost solely a sealing action, while they have no braking action relating to the movement of the device. This means that the physical characteristics of the O-rings, sensitive to temperatures and humidity, cannot alter the braking performance of the device. 
     The type of connection of the device to the bodies between which braking of the relative movement is desired may be of any type known to an expert in the field, according to the different requirements for application. In the examples illustrated in the drawings, in which the device is intended to be applied to a tiltable handle mounted in an automotive vehicle, the characteristics intended for connection are produced in a similar manner to that described in German Utility Model DE 296 04 260 U1. Namely, the front end of the rotor  14 , emerging from the casing  12 , has two tongues  64  extending in diametrically opposed radial directions, while the radially outer wall  18  of the casing  12  has a tongue  65  extending in the axial direction of the casing  12 . The tongues  64  and  65  are intended to engage corresponding mounting seats (not shown) provided respectively in the tiltable handle M and in the support wall W for the handle. The device in the form described above is intended to be arranged at the axis of rotation x of the handle. However, it is possible to envisage other arrangements of the device, depending on the type of application: for example, an arrangement in which a gearwheel is integral with the rotor, and the gearwheel engages a rack integral with a movable member the movement of which is to be slowed down, according to a configuration of the type normally used for example in doors or drawers of audio and/or video reproducing/recording equipment or instrument panels of automotive vehicles. 
     In the device described above, the braking action exerted by the viscous fluid is substantially identical in both directions of displacement of the elongate portion  31  of the rotor  14 , and therefore in both directions of rotation of the rotor. In applications in which a different braking action for the two directions is required, it is possible to adopt the variant illustrated in  FIGS. 10 ,  11  and  12 . The characteristics of the device of  FIGS. 10 to 12  identical to those of the device described previously have been indicated by the same reference numbers. The device differs in that the meridian partition  19   a  is formed by a flexible tongue  19   a ′ of resilient material. The flexible tongue  19   a ′ is mounted, on radially opposed sides, between a pair of strip-like portions  71 ,  72  provided integrally on the radially inner wall  17  of the casing  12 , and between a pair of strip-like portions  73 ,  74  provided integrally on the radially outer wall  18  of the casing  12 .  FIG. 11  shows in section the pair of strip-like portions  73 ,  74  provided integrally on the radially outer wall  18  of the casing  12 . The arrangement of the pair of strip-like portions  71 ,  72  provided integrally on the radially inner wall  17  of the casing  12  is identical to that illustrated in  FIG. 11 . As can be seen, on one side (with respect to the circumferential direction of the chamber  16 ) of the flexible tongue  19   a ′ the strip-like portions  71  and  73  extend for the entire height of the annular chamber  16 , while on the other side (with respect to the circumferential direction of the chamber  16 ) of the flexible tongue  19   a ′ the strip-like portions  72  and  74  extend for only a part of the height of the annular chamber  16 , namely that nearest to the rotor  14 . In this way, the flexible tongue  19   a ′ is able to flex in its end portion nearest to the bottom wall  19  of the casing  12 , as indicated by a dash-dotted line in  FIG. 11 , and on only one side with respect to the circumferential direction of the chamber  16 . 
     The braking action of the device therefore differs according to the direction of rotation of the elongate portion  31  of the rotor  14 . 
     In the clockwise direction of rotation (according to the arrangement of  FIG. 10 ) of the rotor  14 , the flexible tongue  19   a ′, being urged by the action of the fluid compressed by the elongate portion  31  of the rotor  14 , is pressed against the long strip-like portions  73  and  71  of the radially outer wall  18  and of the radially inner wall  17  of the casing  12 , maintaining a substantially rigid behaviour. 
     In the anticlockwise direction of rotation of the rotor  14 , the flexible tongue  19   a ′ flexes at the end through the action of the fluid compressed by the elongate portion  31  of the rotor  14 , moving away, therefore, from the long strip-like portions  71  and  73 , since the short strip-like portions  72  and  74  provide a support surface only for a part of the flexible tongue  19   a ′. In this movement, the movable end of the flexible tongue  19   a ′ creates a passage for the fluid between it and the bottom wall  19  of the casing  12 . This reduces the resistance opposed by the compressed fluid to the anticlockwise movement of the elongate portion  31  of the rotor  14 , which will consequently be slowed down in an attenuated manner with respect to its clockwise movement. Obviously, by reversing in the casing  12  the arrangement of the long strip-like portions  71  and  73  and of the short strip-like portions  72  and  74  it is possible to reverse the unidirectional effect in the opposite direction. 
       FIG. 13  shows a second variant of the device of  FIG. 2 . The characteristics of the device of  FIG. 13  identical to those of the preceding device of  FIG. 2  have been indicated by the same reference numbers. The device differs from the preceding solution in that it defines an annular chamber  16 ″ which, compared to the annular chamber  16  of the device of  FIG. 2 , has a width in the radial direction which varies in the circumferential direction of the annular chamber  16 ″. In the example illustrated, this is obtained by the fact that the casing  12  has a radially outer wall  18 ″ having a thickness which varies in the circumferential direction of the annular chamber  16 ″, while the thickness of the radially outer wall  18  of the casing  12  of the solution in  FIG. 2  was constant in the circumferential direction of the annular chamber  16 . More particularly, the radially outer wall  18 ″ has a radially inner surface  18   a ″ the profile of which, in the transverse plane of  FIG. 13 , substantially follows the course of one turn of a spiral. Thus, the annular chamber  16 ″ has a minimum width at one side  19   b  of the meridian partition  19   a , and a maximum width at the opposite side  19   c  of the meridian partition  19   a . The difference d between the maximum width and the minimum width is equal to a predetermined value, and is indicated in  FIG. 13 . 
     The rotor intended to be coupled to the casing  12  illustrated in  FIG. 13  is the same as that illustrated with reference to  FIGS. 2 to 9 .  FIG. 13  shows diagrammatically by a dashed line the elongate portion  31  of the rotor, intended to rotate in the chamber  16 ″. In a direction of rotation A 1 , which is anticlockwise in the drawing, the elongate portion  31  of the rotor slides inside the chamber  16 ″, the overall meridian section of which increases progressively. Therefore, the braking action exerted by the viscous fluid decreases progressively, since in addition to the passage  33  at the end of the elongate portion  31  there is also a lateral passage of increasing width between the elongate portion  31  and the radially inner surface  18 ″ of the radially outer wall  18 ″. In a direction of rotation A 2 , which is clockwise in the drawing, the elongate portion  31  of the rotor slides inside the chamber  16 ″, the overall meridian section of which decreases progressively. Therefore, the braking action exerted by the viscous fluid increases progressively, since the lateral passage between the elongate portion  31  and the radially inner surface  18   a ″ of the radially outer wall  18 ″, has a width decreasing until it is substantially zero. 
     The device described with reference to  FIG. 13  makes it possible to compensate at least in part for the variation of the resilient force applied to the part in motion which is to be slowed down, for example the handle M of  FIG. 1 . In particular, the device is particularly adapted to compensate for a resilient force which is maximum at one end-of-stroke position, and is minimum in the other end-of-stroke position of the part in motion. 
     The resilient force may also be compensated with the third variant of the device illustrated in  FIGS. 14 and 15 . The characteristics of the device of  FIGS. 14 and 15  identical to those of the preceding device of  FIG. 2  have been indicated by the same reference numbers. The device differs from the preceding solution in that it defines an annular chamber  16 ″′ which, compared to the annular chamber  16  of the device of  FIG. 2 , has an amplitude in the axial direction which varies in the circumferential direction of the annular chamber  16 ″′. In the example illustrated, this is obtained by the fact that the casing  12  has a bottom wall  19 ″′ having a thickness which varies in the circumferential direction of the annular chamber  16 ″′, while the thickness of the bottom wall  19  of the casing  12  of the solution in  FIG. 2  was constant in the circumferential direction of the annular chamber  16 . More particularly, the bottom wall  19 ″′ has an axially inner surface  19   b ″′ which is defined by a plane inclined with respect to the state orthogonal to the axis x. Thus, the annular chamber  16 ″′ has a minimum meridian section at the highest point of the axially inner surface  19   b ″′, and a maximum meridian section at the lowest point of the axially inner surface  19   b″′.    
     The rotor intended to be coupled to the casing  12  illustrated in  FIGS. 14 and 15  is the same as that illustrated with reference to  FIGS. 2 to 9 . In a direction of rotation which brings the elongate portion  31  of the rotor, sliding inside the chamber  16 ″′, to lie above the lowest point of the axially inner surface  19   b ″′, the overall meridian section exhibited by the chamber  16 ″′ increases progressively. Therefore, the braking action exerted by the viscous fluid decreases progressively, since the passage  33  at the end of the elongate portion  31  between the elongate portion  31  and the axially inner surface  19   b ″′ of the bottom wall  19 ″′ tends to widen out axially. In a direction of rotation which brings the elongate portion  31  of the rotor to lie above the highest point of the axially inner surface  19   b ″′, the overall meridian section exhibited by the chamber  16 ″′ decreases progressively. Therefore, the braking action exerted by the viscous fluid increases progressively, since the passage  33  at the end of the elongate portion  31  between the elongate portion  31  and the axially inner surface  19   b ″′ of the bottom wall  19 ″′ tends to narrow axially. By suitably arranging the axially inner surface  19   b ″′ of the bottom wall  19 ″′ with respect to the meridian partition  19   a , this configuration is particularly suitable for compensating a resilient force which has a maximum or a minimum at an intermediate position between the two end-of-stroke positions of the part in motion. 
     It is to be understood that the invention is not limited to the embodiments described and illustrated herein, but is capable of modifications relating to shape and arrangements of parts, constructional and functional details. Although in the embodiments illustrated the opening  33  for the passage of fluid through the elongate portion  31  of the rotor  14  is arranged at the free end of the elongate portion  31 , it is possible to envisage different passage arrangements. The Applicant has however found that the arrangement illustrated herein appears to be optimal from the point of view of reliability and of the performance of the braking device  10 .
A device for braking the movement of a movable member with respect to a support structure includes a casing fixable to the movable member or to the structure and defining a chamber containing a viscous braking fluid, and a rotor, operationally associable with the movable member or with the structure, and which is rotatably connected to the casing and is mounted thereon so as to close the chamber. The rotor includes a piston-like member or portion, mounted so as to slide within the chamber in such a way as to separate the chamber into separate regions in mutual fluid communication. The piston-like member or portion is movable integrally with the rotor, such that rotation of the rotor brings about a rotatory displacement of the piston-lie member or portion, braked by the resistance to the passage of the fluid from one region to the other of the chamber caused by the displacement of the piston-like member or portion.