Abstract:
A braking mechanism for a skate, such as an in-line roller skate, has at least one braking wheel disposed transverse to the skate boot. The braking wheel operates a piston which displaces liquid from a piston housing when the piston is caused to travel within the piston housing by the rotation of the braking wheel. The piston and the piston housing are configured such that an increasing resistance is applied to the rotation of the braking wheel as the piston travels within the piston housing. Thus, when the skate boot is turned transverse to the direction of the skater and the angle of the boot is adjusted to cause the braking wheel to rotate, the increased resistance to the rotation of the braking wheel as the piston moves within the piston housing acts to slow the skater. When the piston fully traverses the piston housing, the rotation of the braking wheel is terminated and the skater comes to a stop.

Description:
FIELD OF THE INVENTION 
   This invention relates generally to skates and, more particularly, to braking mechanisms for skates, especially for in-line roller skates. 
   BACKGROUND OF THE INVENTION 
   In-line roller skates have become very popular. A problem persists with respect to in-line roller skates, however, regarding the inability of an in-line roller skate to stop efficiently as can an ice skate. In-line roller skates cannot stop quickly and efficiently like ice skates, because in-line roller skates cannot brake by turning one or, preferably, both of the skates transverse to the direction of travel. 
   Accordingly, there is a need for a braking mechanism for in-line roller skates which avoids this problem in the prior art. 
   SUMMARY OF THE INVENTION 
   The invention is a braking system for a skate, such as an in-line roller skate. Typically, such a skate has a base skating surface with a base skating surface longitudinal axis. The braking mechanism comprises (a) at least one braking wheel disposed above the base skating surface, the at least one braking wheel being rotatable about a braking wheel axis disposed in a vertical plane, the vertical plane intersecting the base skating surface longitudinal axis at an angle of between about −20° and about +20°; (b) a piston housing having piston housing side walls, a first piston housing section proximal to a first piston housing end and a second piston housing section distal to the first piston housing end, the first piston housing section defining a plurality of first piston housing section side wall apertures, the first piston housing section side wall apertures being disposed at a plurality of different distances from the piston housing first end, the second piston housing section comprising one or more second piston housing section side wall apertures; (c) a piston disposed within the piston housing, the piston having a first end and a second end, the first end comprising an internal piston flow channel and a slide valve disposed in the first end of the piston for controlling the flow of liquid from the piston flow channel to the first piston housing section, the piston further comprising one or more piston inlet channels for allowing the flow of liquid into the piston flow channel from the second piston housing section, the piston being mechanically connected to the at least one braking wheel such that the rotation of the at least one braking wheel moves the piston within the piston housing between (i) a first piston position wherein the piston is distal from the first piston housing end and wherein the piston is not adjacent to the first piston housing section side wall apertures, and (ii) a second piston position wherein the piston is proximal to the first piston housing end and the piston is adjacent to some or all of the first piston housing section side wall apertures, the slide valve being adapted to close when the piston is moved from the first piston position to the second piston position and to open when the piston is moved from the second piston position to the first piston position; (d) a first biasing mechanism for urging the piston towards the first piston position; (e) sealing means for sealing the piston within the piston housing such that (i) liquid disposed in the first piston housing section cannot leak around the piston to the second piston housing section, and (ii) when the piston is moved adjacent to one of the plurality of first piston housing section side wall apertures, liquid disposed in the first piston housing section cannot leak around the piston and out through that first piston housing section side wall aperture; and (f) an external flow channel having a first end a second end, the first end of the external flow channel being in fluid tight communication with the first piston housing section via the first piston housing section side wall apertures, the second end of the external flow channel being in fluid tight communication with the second piston housing section via the second piston housing section side wall apertures; whereby, (i) when a liquid is disposed within the first piston housing section, the application of an axial force to the braking wheel causes the rotation of the at least one braking wheel and its braking wheel axis to thereby move the piston from the first piston position towards the second piston position, the slide valve is closed and the piston pressurizes liquid out of the first piston housing section via the first piston housing section side wall apertures, and into the second piston housing section via the second piston housing section side wall apertures, and (ii) when the axial force on the at least one braking wheel is released, the first biasing means urges the piston from the second piston position towards the first piston position, the slide valve is opened and liquid returns to the first piston housing section from the second piston housing section via the piston flow channel. 
   Thus, when a liquid is disposed within the first piston housing section, the application of an axial force to the at least one braking wheel causes the rotation of the at least one braking wheel to thereby moves the piston from the first piston position towards the second piston position, the slide valve is closed and the piston pressurizes liquid out of the first piston housing section via the first piston housing section side wall apertures, and into the second piston housing section via the second piston housing section side wall apertures. Then, when the axial force on the at least one braking wheel is released, the first biasing means urges the piston from the second piston position towards the first piston position, the slide valve is opened and liquid returns to the first piston housing section from the second piston housing section via the piston flow channel. 

   
     DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description, appended claims and accompanying drawings where: 
       FIG. 1  is a side view of an in-line skate having a braking mechanism with features of the invention; 
       FIG. 2  is a front view of the in-line skate illustrated in  FIG. 1 , shown in a skating orientation; 
       FIG. 3  is a front view of the skate illustrated in  FIG. 1 , shown in a braking orientation; 
       FIG. 4  is a cross-sectional view of the braking mechanism portion of the skate illustrated in  FIG. 2 , taken along line  4 — 4 ; 
       FIG. 5  is a cross-sectional detail view of the first end of the braking mechanism illustrated in  FIG. 4 , showing the first piston housing end disposed in abutment with the first end of the elongate body and showing the piston as it begins to move from the first piston position; 
       FIG. 6  is a cross-sectional detail view of the first end of the braking mechanism illustrated in  FIG. 4 , showing the first piston housing end disposed proximal to, but not in abutment with, the first end of the elongate body and showing the piston as it begins to move from the first piston position. 
       FIG. 7  a cross-sectional detail view of the first end of the braking mechanism illustrated in  FIG. 4 , showing the piston as it begins to move from the second piston position; 
       FIG. 8  is a cross-sectional view of the braking mechanism illustrated in- FIG. 7 , taken along line  8 — 8 ; 
       FIG. 9  is a cross-sectional view of the braking mechanism illustrated in  FIG. 4 , taken along line  9 — 9 ; 
       FIG. 10  is a cross-sectional view of the braking mechanism illustrated in  FIG. 4 , taken along line  10 — 10 ; 
       FIG. 11  is a cross-sectional view of the braking mechanism illustrated in  FIG. 4 , taken along line  11 — 11 ; 
       FIG. 12  is a cross-sectional view of the braking mechanism illustrated in  FIG. 4 , taken along line  12 — 12 ; 
       FIG. 13  is a cross-sectional view of the braking mechanism illustrated in  FIG. 4 , taken along line  13 — 13 ; 
       FIG. 14  is a cross-sectional view of the braking mechanism illustrated in  FIG. 4 , taken along line  14 — 14 ; 
       FIG. 15  is a detail cross-sectional view of the braking mechanism illustrated in  FIG. 4 , showing the piston initially disposed in a first position; 
       FIG. 16  is a detail cross-sectional view of the braking mechanism illustrated in  FIG. 4 , showing the piston initially disposed in a second position; 
       FIG. 17  is a detail isometric view of a ball spline useable in the invention; 
       FIG. 18  is a detail isometric view of a ball screw useable in the invention; 
       FIG. 19  is a detail end view of the braking mechanism illustrated in  FIG. 4 , taken along line  19 — 19 ; 
       FIG. 20  is a detail cross-sectional side view of the forward end of the braking mechanism portion illustrated in  FIG. 4 ; 
       FIG. 21  is a detail exploded view of a portion of the braking mechanism illustrated in  FIG. 4 ; and 
       FIG. 22  is a side view of an ice skate having a braking mechanism with features of the invention. 
   

   DETAILED DESCRIPTION 
   The following discussion describes in detail one embodiment of the invention and several variations of that embodiment. This discussion should not be construed, however, as limiting the invention to those particular embodiments. Practitioners skilled in the art will recognize numerous other embodiments as well. 
   The invention is a braking mechanism  10  for a skate  12 , such as an in-line roller skate, a traditional roller skate or an ice skate. The invention is especially applicable as a braking mechanism for an in-line roller skate  12  as illustrated in  FIGS. 1–21 . 
     FIGS. 1 and 2  illustrate an in-line roller  12  skate having a boot  14  and four in-line skating wheels  16 . The skating wheels  16  are secured to a securing structure  18  which is attached to the boot  14 . The four in-line skating wheels  16  are aligned in a single line. The lowermost portion of each of the in-line skating wheels  16  provides a base skating surface  20  having a base skating surface longitudinal axis  22 . 
   The in-line skate  12  illustrated in  FIG. 1  further comprises the braking mechanism  10  of the invention, disposed below the boot  14 . 
   The braking mechanism  10  comprises at least one braking wheel  24 . In the embodiment illustrated in the drawings, the at least one braking wheel  24  is provided by a pair of braking wheels  24 . Each braking wheel  24  rotates about an axis  26 . The axis  26  is disposed within a vertical plane. Typically, the vertical plane is directly aligned with the base skating surface longitudinal axis  22 . However, this is not strictly necessary. Embodiments in which the vertical plane is “cocked” slightly with respect to the longitudinal axis  22  are also possible, such as embodiments in which the vertical plane intersects the base skating surface longitudinal axis  22  at an angle between about −20° and about +20°, most typically between about −5° and about +5°. 
   Each of the braking wheels  24  has an identical diameter, typically between about 65% of the diameter of the skating wheels  16  and about 85% of the diameter of the skating wheels  16 . Each of the braking wheels  24  is disposed an equal distance above the base skating surface  20 , typically between about 2 mm and about 20 mm above the base skating surface  20 , and most typically between about 3 mm and about 16 mm above the base skating surface  20 . The diameter of the braking wheels  24  and the distance at which the braking wheels  24  are disposed above the base skating surface  20  are chosen so that a skater can simultaneously engage the braking wheels  24  and disengage the skating wheels  16  by tilting the skate  12 , as illustrated in  FIG. 3 . 
   As illustrated in  FIG. 4 , the braking mechanism  10  further comprises a braking piston  28  having a first piston end  30  and a second piston end  32 . The first piston end  30  is secured within a piston housing  34  and the second piston end  32  is secured to one or more ball splines  94  (described below). The first piston end  30  is separated from the second piston end  32  by a thrust bearing, ball or ball bearing  35 . 
   The piston housing  34  is disposed within an elongate body  37  having an elongate body first end  38  and an elongate body second end  40 . The piston housing  34  is retained within the elongate body  37  by a retainer cylinder  41  and a retaining nut  55 . To allow for the convenient installation of the piston housing  34  within the elongate body  37 , the elongate body  37  is constructed from several assemblable elements as illustrated in  FIG. 21 . The elongate body  37  further comprises a fill port  43  for filling the piston housing  34  with a suitable brake fluid and a bleed port  45  for bleeding air from the elongate body  37  during the filling of brake fluid into the piston housing  34 . 
   The piston housing  34  has piston housing side walls  42 , a first piston housing end  44  and a second piston housing end  46 . The piston housing  34  further comprises a first piston housing section  48  disposed proximal to the first piston housing end  44  and a second piston housing section  49  disposed distal to the first piston housing end  44 . The first piston housing end  44  comprises a locator pin  51  sized and configured to be retained within a locator bore  53  within the first end  38  of the elongate body  37 . The piston housing  34  is firmly retained within the elongate body  37  by the retainer cylinder  41  and the retaining nut  55  which is threaded over the retainer cylinder  41 . 
   The piston housing  34  is disposed within the elongate body  37  such that the first piston housing end  44  is disposed proximal to the first end  38  of the elongate body  37 . The specific location of the piston housing  34  within the elongate body  37  can be axially adjusted by backing off on the retaining nut  55  and rotating the retainer cylinder  41  in one direction or the other. Adjusting the specific location of the piston housing  34  with respect to the elongate body  37  affects the clearance between the first piston housing end  44  and the first end  38  of the elongate body  37 .  FIG. 5  illustrates a setting wherein the first piston housing end  44  is disposed in abutment to the first end  38  of the elongate body  37 . In this setting, there is no clearance between the first piston housing end  44  and the first end  38  of the elongate body  37 .  FIG. 6  illustrates a setting wherein the first piston housing end  44  is disposed proximal to, but not in abutment with, the first end  38  of the elongate body  37 . In this setting, there is clearance between the first piston housing end  44  and the first end  38  of the elongate body  37 . Once the piston housing  34  is specifically located within the elongate body  37 , the retaining nut  55  is secured to the retainer cylinder  41  by tightening a set screw  57  disposed within the retaining nut  55 . 
   As best understood with reference to  FIGS. 5–8 , the first piston housing section  48  defines a plurality of first piston housing section side wall apertures  50 . The plurality of first piston housing section side wall apertures  50  are defined within the side walls  42  in the first piston housing section  48  at a variety of different distances from the first piston housing first end  44 . Typically, each first piston housing side wall aperture  50  is round and has a diameter between about 0.5 mm and about 0.95 mm. In a typical embodiment, the side walls  42  in the first piston housing section  48  have between about 12 and about 24 first piston housing section side wall apertures  50 . 
   The piston housing side walls  42  in the second piston housing section  49  comprise one or more second piston housing section side wall apertures  52 . Typically, each second piston housing section side wall aperture  52  is round and has a diameter between about 1.2 mm and about 2.2 mm. In a typical embodiment, the side walls  42  in the second piston housing section  49  have between about 4 and about 10 second piston housing section side wall apertures  52 . 
   Disposed within the piston housing  34  is the first end  30  of the piston  28 . In the embodiments illustrated in the drawings, the piston  28  is movable within the piston housing  34  as will be described below. 
   The first end  30  of the piston  28  comprises an internal piston flow channel  54  for allowing the flow of liquids through the first end  30  of the piston  28 . A slide valve  56  is disposed in the first end  30  of the piston  28  for controlling the flow of liquid from the piston flow channel  54  to the first piston housing section  48 . 
   The piston  28  further comprises one or more piston inlet channels  58  for allowing the flow of liquid into the piston flow channel  54  from the second piston housing section  49 . Typically, each of the piston inlet channels  58  is round and has a diameter between about 1.2 mm and about 2.2 mm. In a typical embodiment, between about 4 and about 8 piston inlet channels  58  are disposed within the piston  28 . 
   A first biasing mechanism  60  is disposed within the piston housing  34  for urging the piston  28  towards the first piston position. In the embodiment illustrated in the drawings, the first biasing mechanism  60  is a coil spring  62 . 
   The slide valve  56  is adapted to close when the piston  28  is moved from the first piston position to the second piston position and to open when the piston  28  is moved from the second piston position to the first piston position. In the embodiment illustrated in the drawings, the piston flow channel  54  has an open end  64  at the first end  30  of the piston  28 . The slide valve  56  comprises a slidable plug  66  which is slidably disposed and retained within the piston flow channel  54 . The slidable plug  66  comprises an elongate body  68  and an end cap  70 . The slidable plug  66  is slidable between a first plug position wherein the end cap  70  covers the open end  64  of the piston flow channel  54  and a second plug position wherein the end cap  70  does not cover the open end  64  of the piston flow channel  54 . In the embodiment illustrated in the drawings, a second biasing mechanism  72  is disposed within the piston flow channel  54  for urging the slidable plug  66  to the first plug position. The second biasing mechanism  72  is typically weaker than the first biasing mechanism  60 . In the embodiment illustrated in the drawings, the second biasing method is a coil spring  74 . 
   Sealing means  76  are provided in the braking mechanism  10  for sealing the piston  28  within the piston housing  34  such that liquid disposed in the first piston housing section  48  cannot leak around the piston  28  to the second piston housing section  49 . 
   The sealing means  76  further assure that, when the piston  28  is moved adjacent to one of the plurality of first piston housing section side wall apertures  50 , liquid disposed in the first piston housing section  48  cannot leak around the piston  28  and out through the first piston housing side wall section aperture  50 . 
   In the embodiment illustrated in the drawings, the sealing means  76  can be provided by O-rings  78 . One or more of the sealing means  76  may also be provided by close tolerances between adjoining surfaces. For example, an O-ring  78  can be replaced by close tolerances between the piston  28  and the piston housing  34 , such as by constructing the piston  28  and the piston housing  34  with tolerances between about 0.005 mm and about 0.010 mm. 
   The braking mechanism  10  further comprises an external flow channel  80  disposed externally of the interior of the first piston housing section  48  and the second piston housing section  49 . The external flow channel  80  has a first end  82  and a second end  84 . The first end  82  of the external flow channel  80  is disposed in fluid tight communication with the first piston housing section  48  via the first piston housing section side wall apertures  50 . The second end  84  of the external flow channel  80  is disposed in fluid tight communication with the second piston housing section  49  via the second piston housing section side wall apertures  52 . 
   In the embodiment illustrated in the drawings, the first piston housing section  48  further defines a piston housing end aperture  86 . In a typical embodiment, the piston housing end aperture  86  defines an open area between about 2 mm and about 4 mm. The piston housing end aperture  86  is capable of being disposed in fluid tight communication with the first end  82  of the external flow channel  80 . 
   In the embodiment illustrated in the drawings, the piston  28  further comprises a tapered projection  88  which is aligned with the piston housing end aperture  86  such that, when the piston  28  is disposed in the second piston position, the tapered projection  88  is disposed within the piston housing end aperture  86  to reduce the open area of the piston housing end aperture  86 . In one embodiment of the invention, the tapered projection  88  seals the piston housing end aperture  86  when the piston  28  is fully disposed in the second piston position. 
   The piston  28  is mechanically connected to each of the braking wheels  24  such that the rotation of the braking wheels  24  moves the piston  28  within the piston housing  34  between (i) a first piston housing position wherein the piston  28  is distal from the first piston housing end  44  and wherein the piston  28  is not adjacent to the first piston housing section side wall apertures  50 , and (ii) a second piston housing position wherein the piston  28  is proximal to the first piston housing end  44  and the piston  28  is adjacent to some or all of the first piston housing section side wall apertures  50 . 
   In the embodiment illustrated in the drawings, the piston  28  is mechanically connected to each of the braking wheels  24  in a way best understood from FIGS.  4  and  9 – 16 . Each braking wheel  24  has a built-in braking wheel gear  90  disposed coaxially with the braking wheel  24 . The braking wheel gear  90  meshes with a piston gear  92  which rotates about the piston  28 . The piston gear  92  is operatively connected to the second end  32  of the piston  28  so that the rotation of the piston gear  92  rotates the second end  32  of the piston  28 . 
   In the embodiment illustrated in the drawings, the piston gear  92  is operatively attached to the second end  32  of the piston  28  via a ball spline  94 . The ball spline  94  is shown in detail in  FIG. 17 . The ball spline  94  comprises an inner cylinder  96  having an interior surface  98  and an exterior surface  100 . The interior surface  98  of the inner cylinder  96  has three parallel longitudinal notches  102  which are sized and dimensioned to retain three parallel longitudinal ridges  104  disposed on the exterior surface of the second end  32  of the piston  28  in the vicinity of the ball spline  94 . The exterior surface  100  of the inner cylinder  96  of the ball spline  94  defines a plurality of ball bearing races  106  wherein are disposed a plurality of ball bearings  108 . The ball bearings  108  support the ball spline  94  on the second end  32  of the piston  28  and allow the piston  28  to freely travel in an axial direction while the ball spline  94  remains at a fixed location. The ball spline  94  also comprises an outer cylinder  110  which fully surrounds the ball bearing races  106 . The outer cylinder  110  is affixed to the inner cylinder  96 . The outer cylinder  110  defines a longitudinal key way  112 . Disposed within the key way  112  is a key  114 . The key  114  operatively connects the outer cylinder  110  of the ball spline  94  to the piston gear  92 . Ball splines are available from a variety of manufacturers, including from THK Company of Tokyo, Japan. Thus, it can be seen that the rotation of the braking wheels  24  rotates the piston gear  92  (because of the cooperation between the braking wheel gear  90  and the piston gear  92 ), the rotation of the piston gear  92  causes the rotation of the ball spline  94  rotates the second end (via the connection of the piston gear  92  to the ball spline  94  with the key  114 ) and the rotation of the ball spline  94  rotates the second end  32  of the piston  28  (due to the rotation of the longitudinal notches  102  disposed within the interior surface  98  of the inner cylinder  96  against the longitudinal ridges  104  disposed on the exterior surface of the piston  28 ). 
   When the rotation of the braking wheel  24  causes the rotation of the second end  32  of the piston  28  as described immediately above, the second end  32  of the piston  28  is caused to travel axially due to the rotation of the second end  32  within a ball screw  116  or similar device. A typical ball screw  116  is illustrated in  FIG. 18 . In the vicinity of the ball screw  116 , the second end  32  of the piston  28  is provided with a helical groove  118 . Within the ball screw  116 , a plurality of ball bearings  120  acts as screw teeth within the helical groove  118  to translate the rotation of the second end  32  of the piston  28  into axial motion. As can be seen from  FIG. 18 , in a typical ball screw  116 , the ball bearings  120  are caused to travel from one end of the ball screw  116  to the other, and are thereupon transferred to the opposite end of the ball screw  116  via an internal groove  122  disposed within the body of the ball screw  116 . Ball screws are available from a variety of manufacturers, including from THK Company of Tokyo, Japan. Because of the interaction of the second end  32  of the piston  28  with the ball spline  94  and the ball screw  116 , it can be seen that the rotation of the braking wheel  24  causes the piston  28  to travel towards the second piston position. 
   As can be understood from  FIGS. 15 and 16 , the first piston position can be adjusted relative to the piston housing  34 . This is accomplished by rotating an adjustment screw  124  disposed at the second end  32  of the piston  28 . Adjusting the location of the first piston position affects the length of travel between the first piston position and the second piston position. 
   In operation, the user initially opens the fill port  43  and the bleed port  45  and fills the piston housing  34  with a suitable brake fluid such as DOT 3, marketed by First Brands Corporation of Danbury, Conn. The user then adjusts the specific location of the piston housing  34  within the elongate body  37  by rotating the retainer cylinder  41  and loosening the set screw  57 , backing off the retaining nut  55  and sliding the piston housing  34  with respect to the elongate body  37 . Once the piston housing  34  is properly located within the elongate body  37 , the user tightens down on the retaining nut  55  and secures the retaining nut  55  with the set screw  57 . The user next adjusts the location of the first piston position by adjusting the adjustment screw  124  in one direction the other. Once these two adjustments are accomplished, the user then places the skates  12  on his or her feet and commences to skate. When the user wishes to stop his or her forward motion, the user tilts one of the skates  12  as illustrated in  FIG. 3 . When one of the skates  12  is tilted as is illustrated in  FIG. 3 , the skating wheels  16  are raised up above the base skating surface  20  while the braking wheels  24  are lowered to the brake skating surface  20 . By lowering the braking wheels  24  to the brake skating surface  20 , the contact of the braking wheels  24  with the brake skating surface  20  causes the braking wheels  24  to rotate. The rotation of the braking wheels  24  is translated to the linear motion of the piston  28  via the braking wheel gear  90 , the ball spline  94  and the ball screw  116 . The linear motion of the piston  28  is from the first piston position towards the second piston position. As the piston travels from the first piston position towards the second piston position as illustrated in  FIG. 5  or  FIG. 6 , braking fluid is displaced from the first piston housing section  48  to the external flow channel  80  via the first piston housing side wall apertures  50  ( FIG. 5 ) or via both the first piston housing section side wall apertures  50  and the piston housing end aperture  86  ( FIG. 6 ). The movement of the piston  28  towards the second piston position also displaces braking fluid from the external flow channel  80  into the second piston housing section  49  via the second piston housing section side wall apertures  52 . Braking fluid within the second piston housing section  49  is displaced into the piston flow channel  54  via the piston inlet channels  58 . As the piston  28  approaches the second piston position, the rate at which braking fluid is displaced from the first piston housing section  48  is markedly reduced because the piston  28  begins to seal off an increasing number of first piston housing section side wall apertures  50 . As the rate of displacement of the braking fluid is decreased, the linear travel of the piston  28  is resisted by a pressure which builds up within the first piston housing section  48 . This resistance to the travel of the piston  28  is translated to a resistance to the rotation of the braking wheels  24 . The resistance to the rotation of the braking wheels  24  acts to brake the forward momentum of the skater. Once the skater returns to a normal skating operation wherein the braking wheels  24  are raised up above the base skating surface  20 , the first biasing mechanism  60  urges the piston  28  to return to the first piston position. As this occurs (see  FIG. 7 ), fluid pressure in the second piston housing section  49  opens the end cap  70  so that braking fluid can quickly be displaced from the second piston housing section  49  back into the first piston housing section  48 . 
   As illustrated in  FIG. 22 , the braking mechanism of the invention can be used on an ice skate. 
   EXAMPLE 
   In one illustrative example of the invention, a boot  14  of a size 10 has skating wheels  16  with diameters of 72 mm. The diameters of the braking wheels  24  are 57 mm. The distance between the braking wheels  24  and the base skating surface  20  is 14.85 mm, the first piston housing section side wall apertures  50  have diameters of 0.79 mm and are 18 in number. The second piston housing section side wall apertures  52  have diameters of 1.6 mm and are 6 in number. The diameter of the piston housing end wall aperture  86  is 2.78 mm. The piston inlet channels  58  have a diameter of 1.6 mm and are 6 in number. 
   Having thus described the invention, it should be apparent that numerous structural modifications and adaptations may be resorted to without departing from the scope and fair meaning of the instant invention as set forth hereinabove and as described hereinbelow by the claims.