Abstract:
Gliding board with a damping device for the vertical movements of the front or rear zone of the board said system including an arm whose first end is integral with an attaching point located in the front or rear zone of the board and whose second end is integral with the piston of a hydraulic device connected to the board near the attachment, said hydraulic device applying a retaining force during the movement of the second end of the arm in order to dissipate part of the kinetic energy from the front or rear zone of the board transmitted by said arm, wherein when the movement of the arm is consecutive to the movement of the attaching point downwards, the hydraulic device applies a retaining force which is less than the force applied when the movement of the arm is consecutive to a movement of the attaching point upwards.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of French patent Application No. FR 1456594, filed Jul. 9, 2014, and entitled “Gliding Board with a Damping Device,” which is hereby incorporated herein by reference in its entirety and for all purposes. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to the field of sports involving sliding. More specifically, it concerns special arrangements made to damp the movements of the tip of a gliding board. More particularly it concerns gliding boards with hydraulic damping devices. Although it is more specifically described for its application to an alpine ski, the present disclosure also describes other types of gliding boards, in particular snowboards. 
       BACKGROUND 
       [0003]    In general, it is known that the tip of a ski is exposed to many vibration phenomena. These vibrations are caused by the fact that the ski is moving over a surface containing obstacles which raise the end of the ski because of its relative flexibility. On the other hand, gravity tends to pull the tip of the ski down, causing chattering phenomena to occur. 
         [0004]    These chattering phenomena may extend for varying lengths of time depending on the mechanical properties of the ski and especially on its stiffness and damping. 
         [0005]    It is easily understood that these chattering phenomena are not propitious to good control of the gliding board and accordingly, many damping devices have been proposed to limit the amplitude and above all the duration of the vibration phenomena affecting the tip of the board. 
         [0006]    One interesting solution was proposed in document FR 1 407 710 which describes a ski with a damping system comprising an arm of which one end 
         [0007]    is integral with a fixed point in the front part of the ski. The rear part of this arm is integral with a hydraulic device comprising a piston and whose movement is ensured by the arm according to the deformation of the ski. 
         [0008]    Accordingly, the upward or downward movements of the front end of the ski are braked in the same way by the action of the hydraulic actuator. 
         [0009]    The symmetrical behaviour of this damping action, for upward or downward movements, is not entirely satisfactory. Indeed, if the damping becomes excessive, it tends to obstruct the downward movements of the tip of the ski thus delaying its recovery of a position in contact with the ground. Conversely, when damping is insufficient, the upward movements of the board are not braked sufficiently. 
         [0010]    In other words, it can be understood that a compromise must be found in choosing the damping value to obtain differentiated behaviour depending on whether the damping movements are upwards or downwards. 
         [0011]    A more fully integrated system is described in document U.S. Pat. No. 7,296,818 but it operates according to a similar principle, incorporating the same drawbacks, however. 
       SUMMARY OF THE DISCLOSURE 
       [0012]    Therefore, the presently described embodiments aim at optimizing the behaviour of the gliding board with respect to the damping of the tip movements, more particularly in such a way as to facilitate its control. 
         [0013]    Therefore, the presently described embodiments concern a gliding board with a damping system on the vertical movements of the front or rear zone of the board. This system has an arm the first end of which is integral with an attaching point integral with the front or rear zone of the board and a second end integral with a piston of a hydraulic device connected to the board near the attachment. 
         [0014]    This hydraulic device applies a retaining force during the moment of the second end of the arm, to dissipate part of the kinetic energy from the front or rear zone of the board, transmitted by the arm. 
         [0015]    In conformity with the presently described embodiments, this gliding board is characterized in that, when the movement of the arm is consecutive to a downward movement of the attaching point, the hydraulic device applies a retaining force which is less than the force applied when the arm movement is consecutive to an upward movement of the attaching point. 
         [0016]    In other words, the presently described embodiments consist in fitting the gliding board with a damping device whose performance is symmetrical and which thus damps more the upward movements of the board tip while, to the contrary, damping little its downward movements. In a conventional manner, the retaining force of a hydraulic damping device such as this is firstly proportional to the speed of movement of the arm. In other words, gliding board bending movements are damped more, when the board bends with the tip rising, compared to the counter-flexing movement when the board deflects in the opposite direction. Naturally, the same damping system can be installed at the tail of the board to limit the tail movements with the corresponding dimensional adaptations. 
         [0017]    Accordingly, a scheme conforming to the presently described embodiments offers improved behaviour because the upward movements of the tip are relatively limited whereas the inverse movements, designed to press the tip against the snow are damped less, thus ensuring the faster return of the board into contact with the snow. 
         [0018]    Advantageously, in actual practice, for a ski, the hydraulic device is placed at the front of the attachment stop which, on one hand, limits the addition of extra weight to the front tip of the ski, while increasing the length of the front end movement transmission arm. It is also possible for the hydraulic device to be arranged underneath the ski attachment, for instance, inside a suitable platform. To limit the overall dimensions of the hydraulic device, it could be considered to incorporate it, at least partially, inside the structure of the ski. In a preferential embodiment, the front end of the arm would be placed in a zone with considerable deflation amplitude and privilege will be given to the anti-nodes of the main vibration modes. The zone near the front contact line is privileged in benefiting from the greatest length of the arm. It is also possible to install the front end at the board. 
         [0019]    In one particular embodiment, the damper system can include a demultiplication mechanism based on connecting rods or a similar arrangement, to increase the stroke of the rear end of the arm, working together with the hydraulic device. Preferably, this type of mechanism will be added as far as possible from the end where the attaching point is located, so as not to generate extra weight at this end of the board. 
         [0020]    To limit the influence of the damping system on the flexing stiffness of the board, preference will be given to solutions in which the first end of the arm is connected to the forward zone of the board by a swiveling link as well as those in which the hydraulic devices connected to the upper face of the ski also include a swiveling link. In particular, this would make it possible to create solely a pure longitudinal translation movement, without any unwanted vertical or bending component. 
         [0021]    One particular solution concerning the hydraulic device consists in using a device having a main chamber inside which the piston can be moved with the piston dividing the main chamber into a compression chamber and a relief chamber. 
         [0022]    This device includes two independent hydraulic paths connecting the compression chamber and the relief chamber with two paths working in opposite directions and having different load losses. 
         [0023]    In other words, the flexing movement induces the circulation of fluid in the hydraulic device of the compression chamber to the relief chamber by a first hydraulic path while the counter-bending movement causes the fluid to move from the relief chamber to the compression chamber, by a second different hydraulic path, having different flow characteristics and therefore different damping capability. 
         [0024]    In practice, the selection of an active hydraulic power for each of the movements uses anti-return valves installed on each of the hydraulic paths, with the valves assembled in opposite directions. 
         [0025]    The damping difference between the two movements can be obtained by using flow reducers having different sections, installed on each of the hydraulic paths. 
         [0026]    These flow reducers can be obtained advantageously by grub screws, preferably adjustable, to allow optimal damping adjustment for the two characteristic movements. 
         [0027]    According to one variant of the hydraulic device, it can include:
       a main chamber inside which the piston can move, with the said piston dividing the said main chamber into a compression chamber and a relief chamber with said piston being pierced by a hydraulic channel connecting the compression and relief chambers together;   a complementary chamber having a variable volume, connected to the compression chamber by an anti-return valve and a hydraulic restriction.       
 
         [0030]    In this configuration, the movement of the piston inside the main chamber causes the fluid to flow between the compression chamber and the relief chamber on the one hand, but also between the compression chamber and the complementary chamber which is connected to it by a hydraulic arrangement. The hydraulic link between the compression chamber and the complementary chamber uses two separate paths, behaving differently according to the direction of fluid flow. Accordingly, the anti-return valve only opens in one direction of fluid flow whereas the hydraulic restriction is exposed to a similar flow in the opposite direction of fluid flow. 
         [0031]    In one particular embodiment, the hydraulic device includes a mechanism for adjusting the diameter of the hydraulic restriction. Under these conditions, the flow circulating in one direction or the other can be adjusted, between the complementary chamber and the compression chamber, so that the damping value generated by the movement of the piston is adjusted. 
         [0032]    According to one variant of the embodiment, the main chamber can be connected to a compensation chamber arranged to receive fluid from the main chamber under the effect of temperature. 
         [0033]    Because the board is designed to evolve in a wide range of temperature conditions, the fluid taking up the main chamber may be caused to expand and therefore be found in a compensation chamber forming an additional volume, not influencing the fluid flow movements. In parallel, the fluid moved by the piston can heat up when the system is under great solicitation and therefore expand. Similarly, the variations of altitude to which the ski is exposed can cause the expansion of gas fractions dissolved in the fluid, taken up by the compensation chamber. 
         [0034]    In practice, this compensation chamber can include a piston associated with return means applying force equivalent to the force applied by the expansion of the fluid. 
         [0035]    According to another characteristic of the presently described embodiments, the damping system can have means of limiting the stroke of the arm in the event of the fixed point moving downwards. In other words, the damping system can be connected so that the downward movement of the ski tip is locked when the ski tip which is an optimal position, corresponding approximately to the position in which it is in contact with the snow. 
         [0036]    In other words, movements of the ski tip downwards are prevented from continuing for too long, and maintaining the chatter which could disturb the control of the board. 
         [0037]    Various different embodiments can be considered to ensure this on travel limiting effect. Accordingly, in a first alternative, limitation is caused by the presence of a stop mounted on the arm and coming into contact with a fixed section of the hydraulic device when the arm moves. In other words, the movement of the arm is stopped in one direction by the presence of a device which abuts against the hydraulic device, and in particular the external case of the hydraulic device. 
         [0038]    It is also possible that the limitation is determined by a stop mounted inside the main chamber, confining the stroke of the piston in the event of the stationary point moving downwards. 
         [0039]    In other words, in this case, the piston acts as a stop by coming into contact with the bottom of the hydraulic device chamber. In another embodiment, this stop might not be hydraulic, to dampen more gently the end of the arm. This configuration generates additional retaining force which is proportional to the speed and movement of the arm. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0040]    The manner of implementing the presently described embodiments, and the resulting advantages will appear clearly in the description of the embodiment which follows, supported by the attached illustrations in which: 
           [0041]      FIG. 1  is a top view of a ski complying with the presently described embodiments. 
           [0042]      FIGS. 2 and 3  are side views of the ski of  FIG. 1 , shown in two different bending configurations. 
           [0043]      FIGS. 4 to 7  are sectional views in a horizontal plane of a first embodiment of the hydraulic device, shown in four different positions. 
           [0044]      FIG. 8  is a longitudinal sectional view on a vertical plane of the hydraulic device shown in  FIGS. 4 to 7 . 
           [0045]      FIG. 9  is a sectional view, similar to  FIGS. 4 to 7 , showing an alternative embodiment of the principle of arm movement limitation. 
           [0046]      FIG. 10  is a summary perspective view of a damping system with a hydraulic device according to a second embodiment. 
           [0047]      FIG. 11  is a longitudinal sectional view of the hydraulic device shown in  FIG. 10 , illustrating the flows of the fluid during a board bending movement. 
           [0048]      FIG. 11   a  is an identical view to  FIG. 11 , illustrating the flow of fluid during a counter-bending movement of the board. 
           [0049]      FIGS. 12 to 13  are transverse sectional views in the planes XII-XII′ and XIII-XIII′ of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0050]    As illustrated schematically in  FIG. 1 , a ski conforming to presently described embodiments  1  includes a zone  2  in which the attachment is located, materialised by a platform. 
         [0051]    This ski also has a front end  3  or tip liable to move up or down depending on the bending stiffness of the board and the obstacles encountered in its path. 
         [0052]    In conformity with the presently described embodiments, the ski  1  includes a damping device  4 . This device  4  consists essentially of an arm  5  extending longitudinally and whose front end  6  is connected to a plate  7  mounted permanently to the upper face of the ski, near the tip. In practice, the length of the arm can be approximately 500 to 700 mm long, inducing the movement of the rear end by approximately 2 to 5 mm. In the case of the use of a demultiplication mechanism, this movement can be greater, reaching approximately 10 mm. It will be seen that the longer the arm, the more the efficiency of the damper will be optimised. The transversal axis is placed preferably near the front contact line defined in standard ISO 6289 and typically between 20 and 60 mm from this point. 
         [0053]    The rear end  8  of arm  5  itself works together with a hydraulic device  10  which is made integral with the upper face of the ski by means of a plate  11 . More accurately, and as illustrated by  FIGS. 2 and 3 , the front end  6  of arm  5  is mounted to rotate about a swiveling axis  9 , placed transversely with respect to the ski on a clevis  8 , integral with a base  7 , itself attached to the upper face of the board. 
         [0054]    This enables the arm  5  to move more freely during the bending movements of the ski as illustrated in  FIG. 3 . As a complement to this, hydraulic device  10  is also assembled with a swiveling axis with respect to plate  11 , enabling it to lift off the upper face of the ski if the ski bends as shown in  FIG. 3 , allowing arm  5  to move inside hydraulic device  10 . 
         [0055]    One particular embodiment of hydraulic device  10  is shown in  FIG. 4 . 
         [0056]    In a simplified manner, this hydraulic device  10  includes a body  11  inside which a main chamber  20  is defined and within which a piston  23  is able to move. Main chamber  20  consists of two chambers separated by piston  23 , that is a compression chamber  21  and a relief chamber  22 . This piston  23  has a seal  24  ensuring sealing between compression chamber  21  and relief chamber  22 . The chamber is filled with a hydraulic fluid, in particular a low-temperature hydraulic oil whose viscosity properties are not excessively modified within the operating range of the ski. 
         [0057]    The main chamber  20  is blanked at the front by a plug mechanism  30  having an opening  31  at the centre, allowing the end of rear pin  8  of arm  5  to pass through it. 
         [0058]    The arm  5  passes longitudinally through the compression and relief chambers and the piston  23  is attached rigidly to the stem of arm  5 . Arm  5  and end  8  inside the hydraulic damper can be a monobloc structure or be connected by a rigid mechanical link, possibly adjustable for longitudinal translation, for instance of a screw and nut system type, to adjust the length of arm  5  and act on the lifting of the ski tip. 
         [0059]    Sealing means  26  are provided to enable the arm  5  to translate at plug  30 , and therefore piston  23  to move. 
         [0060]    At the rear, the main chamber is blanked by a similar plug system allowing the rear end  8  of arm  5  to pass so that the arm can possibly extend from the damper case at the rear towards the ski attachment  2 . 
         [0061]    This damper with its through rod offers the advantage of not needing to compensate for the volume of the rod. The pressure on the compensation volume is therefore not influenced by the rod. 
         [0062]    As shown in  FIG. 4 , the compression chamber  21  connects with a small intermediate chamber  42  by means of a channel  43 . This first intermediate chamber  42  connects through an anti-return device  45  with a flow reducer  46 . The anti-return device  45  consists of a ball  41  which blocks or does not block the hole  44 . It is arranged in such a way that the flow of fluid is allowed from the flow reducer  46  to chamber  42  only. 
         [0063]    The flow reduction device  46  has a channel  47  through which the flow of fluid can be reduced to a greater or lesser extent, adjusted by a grub screw  48 . The flow reduction device  46  is connected by a channel  49  to relief chamber  22 . 
         [0064]    In addition, compression chamber  21  connects via channel  53  to a second intermediate chamber  52 . This intermediate chamber  52  connects by an anti-return device  55  with a flow reducer  56 . Anti-return device  55  consists of a ball  51  which blocks or does not block the hole  54 . It is arranged so that the flow of fluid is allowed from chamber  52  to flow reducer  56  only. The flow reducing device  56  includes a channel  57  through which the passage of fluid can be reduced to a greater or lesser extent, adjustably by a grub screw  58 . 
         [0065]    The flow reduction device  56  connects through channel  59  to relief chamber  22 . 
         [0066]    In  FIG. 4 , piston  23  is shown in an intermediate position defining relief and compression chambers which have approximately the same volume. 
         [0067]      FIGS. 5 to 7  illustrate the operation of the device according to the deformations of the board and therefore the movement of arm  5 . Accordingly, in the configuration illustrated in  FIG. 5 , piston  23  moves towards the rear therefore pushing the fluid back in the second intermediate chamber  52 , anti-return valve  55  allows the fluid to pass as far as flow reducer  56  which is blanked off to some extent, generating relatively high load losses. Flow reducer  56  therefore enables the fluid to return to relief chamber  22  by means of channel  59 . 
         [0068]    In the configuration shown in  FIG. 5 , the piston abuts against plug  40  so that the upward movement of the ski tip is blocked. 
         [0069]    It will be seen that because of the orientation of the anti-return valve  45 , the fluid can no longer circulate through the first intermediate chamber  42  and the first flow reducer  46 .  FIG. 6  illustrates an opposite configuration in which the front end of the ski moves downward, causing arm  5  is to be pulled forward. In this case, piston  23  moves so as to compress the fluid contained in relief chamber  22 . The fluid then circulates through channel  49  as far as flow reducer  46 . The anti-return valve  45  is then open and the ball  41  is cleared from the hole  44 , allowing the fluid to pass through the first intermediate chamber  42  and return to compression chamber  21 . 
         [0070]    It is noteworthy that because of the configuration of the anti-return valve  55 , the second hydraulic path, passing through the second flow reducer  56 , is closed. 
         [0071]    It will also be seen that in the configuration of  FIG. 6 , piston  23  abuts against plug  30 , thus preventing the movements of arm  5  and the downward excursion of the ski tip. In particular, it is advantageous to position this stop so that the stroke of the arm is stopped when the ski tip is flat on the snow. 
         [0072]    The flow reducer  56  regulates the flow of fluid and therefore the damping of the ski in the bending direction during movements of the front end of the ski upwards. Conversely, the flow reducer  46  regulates the flow of fluid and therefore the damping of the ski in the counter-bending direction, during downward movements of the front tip of the ski. 
         [0073]    It will be observed that the flow reducer  46  is relatively slightly closed and in any case, less than flow reducer  56  so that the damping of the arm movement in this direction is smaller than in the configuration illustrated in  FIG. 5 . 
         [0074]    In particular, one advantageous configuration is to adjust the flow reducer is so that the bending ski damping action (corresponding to the action of the compression rod on the hydraulic damper) is between two and three times greater than the damping of the scheme during counter-bending (corresponding to the action of the rod relieving the hydraulic damper) for the same solicitation speed of the damper so that the ski performance is enhanced in that the tip remains locked to its path in the snow without breaking away from this curve under the effect of unwanted vibration. 
         [0075]    Subsequently, as shown in  FIG. 7 , arm  5  operates and thus moves piston  23  in the main chamber. The pressure in the compression chamber  21  becomes greater than the pressure prevailing in the relief chamber and the hydraulic path through the intermediate chamber, the anti-return valve  55  and the flow reducer  56  is active. 
         [0076]    In an alternative embodiment illustrated in  FIG. 9 , arm end  72  supporting the piston enters a housing  71  formed in plug  70 . This housing has a diameter slightly larger than that of the end  72  of the arm. In this way, the clearance  73  between the arm and the walls of the housing is reduced. Accordingly, when the arm moves towards the bottom of the housing, it expels the fluid through the small clearance  73 , with an increased retaining force, generating the effect of a hydraulic stop. 
         [0077]    Another characteristic of the presently described embodiments, illustrated in  FIG. 8  is that the relief chamber  22  is connected by a channel  62  to a compensation chamber  63 . This compensation chamber  63  has a variable volume because it is equipped with a piston  65  capable of moving upwards. Piston  65  is supported by a return spring  66  which is calibrated to allow the movement of piston  66  solely for very high pressure levels, corresponding to expansion or pressure phenomena due essentially to the altitude. Indeed, it is important for the volume of the compensation chamber to vary only for very high pressure levels and not for the variable pressure levels observed when the pressure increases in the relief chamber because of the movement of piston  23 . 
         [0078]    As far as the damping coefficients considered advantageous in the ski domain are concerned, with respect to the compression, the factor is included between 0.2 and 1 N/mm·s whereas at the relief level, it is included between 0.4 and 2 N/mm·s. 
         [0079]    Naturally, different geometrical configurations can be used and the presently described embodiments is not confined solely to the architecture illustrated in the figures. Accordingly, the grub screws  48 ,  58  are adjusted as shown in  FIGS. 4 to 7 , by a mechanism moving horizontally with adjustment of the grub screw position by a side screw but it could also be imagined that the flow reduction device be orientated on a vertical axis with the adjustment of the grub screw position by a screw accessible from the top. 
         [0080]    In this way, the compensation chamber shown in  FIG. 8  has been provided to connect with the relief chamber but it would also be possible to connect it to the compression chamber. 
         [0081]      FIGS. 10 to 13  illustrate a second embodiment in which the hydraulic device is constructed in a compact design, generally cylindrical in shape. More specifically, device  104  shown in  FIG. 10  includes essentially an arm  105  the front end  106  of which is equipped with an attaching system  107  forming a swiveling link designed for mounting on a plate similar to plate  7  of  FIG. 2 . The rear end  108  of arm  105  is connected to the hydraulic device  110  whose opposite end  111  has a swiveling link designed to allow it to be mounted to the upper face of the ski by means of a plate similar to plate  11  of  FIG. 2 . 
         [0082]    More accurately, and as illustrated in  FIG. 10 , hydraulic device  110  includes a first part  112  comprising a first cylinder receiving the end of arm  105 . Near the attaching point  111 , the hydraulic device  110  includes a second cylinder having a larger diameter,  113 , enclosing a complementary chamber. Between the two cylinders  100  and  113  there is a hollow rotating part  114  having a prominent area  115  which can be operated by hand and allowing the rotation of the device  114  about the main axis which is parallel to arm  105 . This rotating part  114  encloses the main chamber inside which piston  123  connected to end  108  of arm  105  moves. 
         [0083]    The internal composition of the hydraulic device is essentially illustrated in  FIG. 11 . More specifically, part  112  has an opening  130  containing a seal  131  allowing the end  108  of the arm  105  to be inserted into the damper  110 . More specifically, end  108  can be screwed onto the end of arm  105  in a tapped hole  109  provided for this purpose. Various devices are included inside part  112  to guide part  108  in its required translation, combined with optimal sealing. More accurately, part  112  screws onto end  150  of rotary part  114  by the outside threading of the latter. Part  112  covers part  140  which has a cylindrical hole  141  in which end  108  is able to slide thanks to a sliding bearing  142 , preferably of PTFE, to decrease friction, combined with a circular lip seal  143  ensuring tightness. 
         [0084]    The outer face of part  140  has threading working together with end  150  of rotary part  114 . More specifically, this part  114  has a central hole defining the main chamber  120  inside which piston  123  mounted to the end of part  108  is able to slide. This piston  123  is locked in its translation movement by a nut  152  on part  108  extending arm  105 . On its outer face, piston  123  has a shape providing good tightness by sliding on the inner surface  155  of the hollow forming the main chamber  120 . A circular seal can also be used for this purpose. 
         [0085]    In this way, the rotation of rotary part  114  causes the rotation of the parts integral with it, and more particularly the parts  140  and  112 . 
         [0086]    As illustrated in  FIG. 11 , piston  123  has an axial hole drilled into it forming channels  158  for bringing the two chambers with their variable volumes to connect, as defined from main chamber  120  either side of piston  123 . More specifically, a compression chamber  121  is defined as being the chamber in which the pressure increases when piston  123  is pushed into the hydraulic device towards the end  111 . The relief chamber  122 , is a chamber in which the pressure increases when the piston moves with the lengthening of arm  105  towards the end of arm  106 . 
         [0087]    The opposite end of main chamber  120  is blanked by part  170  mounted to the end  159  of part  114  having a central hollow  161  into which axial tube  171  of part  170  is inserted. This tube  171  is hollow, defining a passage channel  172  connecting compression chamber  121  to an anti-return valve device  175 . 
         [0088]    The anti-return valve includes, for instance, a ball  176  and a spherical bearing  177  working together with ball  176  so that fluid can pass from channel  178  formed on the outer face of part  170  towards channel  172  connected to compression chamber  121 . A locking nut  179  combined with a compressible washer serves to lock part  170  onto the end of rotary part  114 . Part  170  is attached to the ski and the rotary part  114  turns about part  117 . 
         [0089]    As a complement, end  159  of rotary part  114  has a hole  162  into which a calibrated hydraulic restriction is installed, forming a flow reducer. More accurately, and as shown in  FIG. 12 , end  159  of the rotary part includes three holes  162 ,  163 ,  164 , angularly offset with respect to the axis of rotation of part  114 . These three holes  162 ,  163 ,  164  are provided with hydraulic restrictions of different diameters, typically ranging between 0.25 and 0.55 mm. 
         [0090]    Part  170  covering the end of portion  159  also includes, as shown in  FIG. 13 , a hole in the form of a circle are  178  at the bottom of which there are three partially spherical housings  179 ,  180 ,  181 , in which an indexing device  182  is inserted, integral with rotary part  114 . In this way, during the angular movement of rotary part  114  with respect to the ski, and more specifically with respect to part  170 , the various hydraulic restrictions  162 ,  163 ,  164  in turn move in front of opening  174  connecting to the complementary chamber described below. The position of part  170  is indexed by cooperation between device  182  and the housings  179 ,  180 ,  181  in which the end of part  182  is inserted, under the effect of a return device (not shown). 
         [0091]    A bell  190  is placed over part  170 , inside which it is held in an angular position indexed by a shim  91 . The bell-shaped part  190  also contains a piston  192  and a return spring  193  operating by compression and opposing the moment of piston  192  towards the bottom of the bell-shaped part  190 . 
         [0092]    Inside the bell-shaped part  190 , and with the face opposite part  170 , piston  192  defines a complementary chamber  200 , hydraulically connected to compression chamber  121  by virtue of hydraulic restriction  162  and anti-return valve  175 . The bell-shaped part  190  is held in its swiveling link position with respect to the ski by means of the attaching portion  111 . 
         [0093]    In the normal operating mode, when arm  105  and therefore its end move according to the arrow C 0  towards the opposite attaching point  111 , under the effect of the bending of the ski, piston  113  moves, reducing the volume of compression chamber  121 . Part of the fluid contained in compression chamber  121  enters relief chamber  122  via the hydraulic channels  158  drilled through the piston in the direction of arrow C 1 . The volume displaced by piston  123  in compression chamber  121  is greater than the volume displaced in relief chamber  122  so that part of the volume from the compression chamber is pushed back into complementary chamber  200 , in the direction of arrow C 2  by means of the hydraulic restriction  162  while the ball  176  blocks the anti-return valve  175 . This compresses spring  193  and moves piston  192  towards the bottom of the bell-shaped part  190 . The load losses generated by the passage of fluid in hydraulic restriction  162  cause a loss of energy and therefore damp the bending moment of the ski. 
         [0094]    Conversely, when the ski bends in the opposite direction and when arm  105  moves (in the direction of arrow D 0 ), so that the piston decreases the volume in the relief chamber  122 , the fluid in the relief chamber moves towards compression chamber  121  through the hydraulic channels  158  according to arrow D 1  in  FIG. 12 . In parallel, fluid is drawn in from the complementary chamber  200  towards the compression chamber  121 , in the direction of arrow D 2 , for the greater part through the anti-return valve  175  which is no longer locked by ball  176  and very partially through restriction  162 . 
         [0095]    Accordingly, the generated load losses are less than in the opposite movement and damping is therefore more limited, depending on the load losses generated by hydraulic channels  158  drilled into piston  123 . Thus, the ski tends to be damped less by the counter-bending phenomena and more quickly recovers its position of contact with the snow. Accordingly, the hydraulic paths which are active during the bending movements (arrows C 1  and C 2 ) and counter-bending movements (arrows D 1 +D 2 ) are different with the first generating more load losses and therefore causing stronger damping. 
         [0096]    As already mentioned, rotary part  114  forming main chamber  120  can be moved angularly by manual action on fin  115  so that the hydraulic restriction opposite passage  174  is replaced by a larger or smaller diameter restriction, thus generating greater or lesser load losses and a different damping effect for the ski bending movements. Naturally, the number of positions and the respective load losses can be arranged according to the desired damping performance. 
         [0097]    Similarly, other mechanisms combining to hydraulic paths generating different load losses depending on the flow direction of the fluid could be considered. 
         [0098]    Naturally, the damping system described above could be installed behind the attachment to limit the ski tail movements. 
         [0099]    From the above, it is evident that the board conforming to the presently described embodiments offers advantageous behaviour because it brakes the upward movement of the ski tip because of considerable damping, to prevent the board from becoming more difficult to control. This is combined, on the contrary, with fast return of the ski tip to its low position near or in contact with the snow, with less damping. 
         [0100]    This means that the board offers better reaction and more accurate control. The board tends to keep to the path on which it is directed by the user so that the edge of the board remains anchored into the snow. This makes the board faster and offers better performance.