Abstract:
A hydraulically actuated rim brake with a pair of brake arms. Both brake arms may rotate about a common axis, which is the axis of a single bolt that mounts the assembly to the bicycle. The system has one piston slidably disposed in a piston cylinder. The piston&#39;s cylinder may be formed in one of the two brake arms. Actuation of the piston in the cylinder causes movement of both brake arms.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to brake systems, and more particularly, to a hydraulic rim brake, preferably for a bicycle. 
         [0002]    While there are some examples of hydraulically actuated rim brakes for bicycles, hydraulic brake systems for bicycles have been more successful when used to actuate disc brakes with calipers. Hydraulic rim brakes marketed to date tend to be complex and heavy, but have found some success in the comfort bike and urban bike market, where light weight is not a primary concern. 
         [0003]    One reason why hydraulic rim brakes might be preferred over cable actuated brakes is the increase in braking. Power that can be generated and the numerous routing options of the hydraulic tubing. 
         [0004]    The invention provides a bicycle with a hydraulic rim brake that is not heavy or complex and has suitable performance characteristics. 
       SUMMARY OF THE INVENTION 
       [0005]    One aspect of the invention provides a hydraulic brake assembly for a bicycle the bicycle including a master cylinder operated by a brake lever, the hydraulic brake assembly including a first brake arm pivotally connected to a frame member of the bicycle. A second brake arm is configured to pivot relative to the first brake arm. One of the first and second brake arms includes a cylinder. The cylinder is non-rotatable relative to the one of the first and second brake arms. The cylinder is in fluid communication with the master cylinder and a piston is slidably disposed in the cylinder and configured such that movement of the piston in response to fluid displacement in the hydraulic brake assembly causes the first brake arm and the second brake arm to pivot. 
         [0006]    Other aspects of the invention provide wherein the cylinder is formed in one of the first and second brake arms. A link member may be configured to be responsive to movements of the piston such that movement of the piston is conveyed by the link member to the other of the first and second brake arms. The link member may be part of the other of the first and second brake arms. The hydraulic brake may further include an adjust mechanism configured to act upon the link member to adjust the spacing between the first and second brake arms. The hydraulic brake assembly may provide a link member having a first end in contact with the piston and a second end opposite the first end in contact with the other of the first and the second brake arms the second end having a head. The adjust mechanism may include an adjust knob engaged with and displacing the link member second end to adjust the spacing between the first and second brake arms. The adjust knob may have an internal configuration shaped to engage the head of the link member. The adjust mechanism may include a spring positioned between the adjust knob and the head of the link member. The adjust mechanism may include a detent block having an first (axial) through bore through which a cylindrical boss portion of the receiver is positioned and a second (transverse) hole through which the link member is received, the detent block having one or more projections positioned and shaped to cooperate with corresponding features on the adjust knob. 
         [0007]    The hydraulic brake assembly may include a receiver disposed in the other of the first and second brake arms wherein the link member is engaged with the receiver. The link member may be threadably engaged with the receiver. The adjust knob may cause the link member to displace the receiver through action of the threaded engagement. 
         [0008]    The hydraulic brake assembly may further comprise a quick-release mechanism configured to act upon the link member to adjust the spacing between the first and second brake arms. The quick-release mechanism may include a quick-release lever positioned on the other of the first and second brake arms, the quick-release lever operatively displacing the link member. The receiver may be displaceable by the quick-release mechanism, the receiver being disposed in the other of the first and second brake arms wherein the link member is engaged with the receiver. The receiver may be disposed in a lever bore formed off center through the quick-release lever such that the quick-release lever imparts a cam action to the receiver when the quick-release lever is rotated. 
         [0009]    The first brake arm and the second brake arm may share a common pivot. The hydraulic brake assembly may include a return spring positioned to bias the first brake arm and the second brake arm apart. The fluid communication between the cylinder and the master cylinder may, include a fluid passageway formed in the one of the first and second brake arms. One of the first and second brake arms may include a bleed port formed in communication with the fluid passageway to permit the release of fluid from the fluid passageway. The other of the first and second brake arms may include an upper end having a fork arrangement and wherein a combined adjust mechanism and a quick-release mechanism are disposed at the fork arrangement. 
         [0010]    Yet another aspect of the invention provides a hydraulic brake assembly for a bicycle, the bicycle including a master cylinder operated by a brake lever, the hydraulic brake assembly including a first brake arm and a second brake arm, wherein the first and second brake arms are pivotally connected to a frame member of the bicycle on a common pivot. A cylinder is provided in communication with the master cylinder. A piston is configured such that movement of the piston in response to a change in fluid pressure in the cylinder causes the first brake arm and the second brake arm to pivot. 
         [0011]    Other aspects of the invention provide a hydraulic brake assembly further including a cylinder formed in one of the first and second brake arms, the cylinder being in fluid communication with the master cylinder; and wherein the piston is slidably disposed in the cylinder. The hydraulic brake may further include a quick-release mechanism and an adjust mechanism configured on the other of the first and second brake arms to act between the first and second brake arms to adjust the spacing therebetween. The quick-release mechanism and the adjust mechanism may share a link member which extends between the first and second brake arms. The quick-release mechanism and the adjust mechanism may act upon the link member to adjust the spacing between the first and second brake arms. The link member may contact the piston and acts upon the piston to adjust the spacing between the first and second brake arms. 
         [0012]    These and other features and advantages of the present invention will be more fully understood from the following description of one or more embodiments of the invention, taken together with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    In the drawings: 
           [0014]      FIG. 1  is a front view of a brake assembly according to an embodiment of the invention; 
           [0015]      FIG. 2  is a side view:of the brake assembly of  FIG. 1 , showing its attachment to a bicycle frame member; 
           [0016]      FIG. 3  is the opposite side view of the brake assembly of  FIG. 2 ; 
           [0017]      FIG. 4  is a rear view of the brake assembly of  FIG. 1   
           [0018]      FIG. 5  is a cross-sectional view of section A-A shown in  FIG. 1 ; 
           [0019]      FIG. 6  is a cross-sectional view of section B-B shown in  FIG. 1 ; 
           [0020]      FIG. 7   a  and  FIG. 7   b  are two views of a quick-release lever of the brake assembly; 
           [0021]      FIG. 8   a ,  FIG. 8   b  and  FIG. 8   c  are three views of a detent block of the brake assembly; 
           [0022]      FIG. 9   a  and  FIG. 9   b  are two views of an adjust bolt of the brake assembly according to the invention; 
           [0023]      FIG. 10   a  and  FIG. 10   b  are two views of an adjust knob of the brake assembly according to the invention; 
           [0024]      FIG. 11  is a cross sectional view of section C-C shown in  FIG. 3   
           [0025]      FIG. 11   a  is a cross sectional view of the brake assembly according to another embodiment of the invention; 
           [0026]      FIGS. 12-15  are cross sectional views of section C-C shown in  FIG. 3 ; 
           [0027]      FIG. 16  is a cross sectional view of a brake lever body including a master cylinder assembly for operating the brake assembly of  FIG. 1-15 ; 
           [0028]      FIG. 17  is an isometric view of the brake assembly of  FIG. 1 ; 
           [0029]      FIG. 18  is an isometric view of a brake assembly according to a second embodiment of the invention; 
           [0030]      FIG. 19  is a top view of the brake assembly of  FIG. 18 ; 
           [0031]      FIG. 20  is an isometric view of the brake assembly of  FIG. 18 ; and 
           [0032]      FIG. 21  is a cross sectional view of the brake assembly of  FIG. 18 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Preferred embodiments of the invention will herein be described with reference to the drawings. It will be understood that the drawings and descriptions set out herein are provided for illustration only and do not limit the invention as defined by the claims appended hereto and any and all their equivalents. For example, the terms “first” and “second” or “left” and “right” are used for the sake of clarity and not as terms of limitation. 
         [0034]    Referring to  FIGS. 1-4 , the invention generally includes a brake assembly  50 , with a first brake pad assembly  4  and a second brake pad assembly  5  secured to first brake arm  2  and second brake arm  3 , respectively, in a manner that is well known in the art. A return spring  11  biases first brake pad assembly  4  and second brake pad assembly  5  apart from each other as shown in  FIG. 4  by acting on the first and second brake arms  2 ,  3 . Hydraulic fluid entering the brake assembly  50  from line  8  causes the first brake pad assembly  4  and second brake pad assembly  5  to draw together and conversely, permits the spring  11  to urge the first and second brake arms, and thus the brake pad assemblies  4 ,  5  apart when fluid leaves the brake assembly. 
         [0035]    Referring to  FIG. 2 , brake assembly  50  is attachable to a bicycle frame member  10 . The bicycle frame member  10  can be, for example, either a bicycle seat stay in the case of a rear brake, or a bicycle fork in the case of a front brake or an immobile part attached to the bicycle frame Pivot bolt  1  is insertable into a hole  1   a  in bicycle frame member  10 . Mounting nut  9  is inserted into this same hole  1   a  from the opposite side, and threadably engages pivot bolt  1 . Mounting nut  9  is tightened until the head of mounting nut  9  is fully seated in a counter bore  1   b  in the hole  1   a  in bicycle frame member  10  and serrated washer  14  is tightly pressed against the surface of bicycle frame member  10  as shown in  FIG. 2 . After tightening, pivot bolt  1  is non-rotatable relative to bicycle frame member  10 . It will be understood that other mounting arrangements are contemplated by the invention, for example a mounting arrangement with dual or multiple pivot points. 
         [0036]    Referring to  FIGS. 1-6 , brake assembly  50  may be constructed as follows. Referring to  FIGS. 1 and 5 , thrust washer  19  is rotatable relative to pivot bolt  1 . Bearing  21  is rotatably received in a hole  21   a  in first brake arm  2 , and is rotatable relative to pivot bolt  1 . Thrust washers  18  are rotatable relative to each other and relative to pivot bolt  1 . Bearing  20  is rotatably received in a hole  20   a  in second brake arm  3 , and is rotatable relative to pivot bolt  1 . Thrust washers  17  are rotatable relative to each other and relative to pivot bolt  1 . Nut  16  is threadably engaged with pivot bolt  1 , and is axially positioned such that there is little to no axial play between nut  16 , thrust washers  17 , second brake arm  3 , thrust washers  18 , first brake arm  2 , thrust washer  19 , and the head of pivot bolt  1 . Jam nut  15  is threadably engaged with pivot bolt  1 , and is tightened securely against nut  16 . After tightening jam nut  15 , nut  16  and pivot bolt  1  are fixed (i.e. non-rotatable) relative to each other. Serrated washer  14  is rotatable relative to pivot bolt  1 . 
         [0037]    Referring to  FIGS. 4 and 5 , the middle portion of return spring  11  engages a slot in nut  16 . This middle portion of return spring  11  cannot rotate relative to nut  16 , and therefore cannot rotate relative to pivot bolt  1  Since pivot bolt  1  is non-rotatable relative to bicycle frame member  10 , the middle portion of return spring  11  is also non-rotatable relative to bicycle frame member  10 . The two ends of return spring  11  are slidably engaged with spring leg holders  12  and  13 , respectively, and spring leg holders  12  and  13  are received in holes in second brake arm  3  and first brake arm  2 , respectively, in a manner that is well known in the art. Return spring  11  urges spring leg holder  12  and second brake arm  3  to rotate clockwise around pivot bolt  1  in  FIG. 4 , and return spring  11  urges spring leg holder  13  and first brake arm  2  to rotate counterclockwise around pivot bolt  1  as shown in  FIG. 4 . 
         [0038]      FIGS. 7   a  and  7   b  show a rear view and a side view of quick-release lever  6 , which forms part of and actuates a quick-release mechanism  94  ( FIG. 17 ) of the brake assembly  50 . Quick-release lever  6  has a cylindrical boss  6   a,  and a through bore  6   b,  which will also be referred to as a lever bore, that is not concentric with cylindrical boss  6   a.    FIG. 6  is a cross-sectional view of section B-B in  FIG. 1 . Referring to  FIG. 6 , cylindrical boss  6   a  of quick-release lever  6  is rotatably received in a hole  6   c  in first brake arm  2 . Receiver  23  is rotatably received in bore  6   b  of quick-release lever  6 . Referring to  FIGS. 6 ,  8   a - c  and  13 , distal end of receiver  23  is rotatably received in through bore or first hole  33   a  of detent block  33 . Adjust bolt  22  is rotatably and slidably received in through hole or second hole  33   b  of detent block  33  and is threadably engaged with a threaded hole  23   a  in adjust bolt receiver  23 . Adjust bolt  22  will also be referred to herein as a link member, rod or Piston rod. 
         [0039]    Referring to  FIGS. 9   a    9   b ,  10   a    10   b , and  13 , square head  22   a  of adjust bolt  22  is slidably and non-rotatably received in square hole  7   a  of adjust knob  7 . Detent spring  32  is received in square hole  7   a  of adjust knob  7 . A first end of detent spring  32  pushes against square head  22   a  of adjust bolt  22 , and a second end of detent spring  32  pushes against the bottom of square hole  7   a  of adjust knob  7 . Thus, detent spring  32  biases adjust knob  7  against detent block  33  in  FIG. 13 . 
         [0040]    Referring again to  FIG. 6 , a first end of a hydraulic brake line  8  is connected to a handlebar mounted actuator  80  (see  FIG. 16 ), and a second end of hydraulic brake line  8  is connected to brake assembly  50  in a manner that is well known in the art and is described as follows. Barbed fitting  30  has a barbed cylindrical portion that is received in the second end of hydraulic brake line  8 . One end of a compression ring  29  abuts a tapered section of a bore in second brake arm  3 . The top portion of the tapered bore is threaded, and threadably receives a compression nut  31 . Hydraulic brake line  8 , along with barbed fitting  30 , is also received in the bore in second brake arm  3 . Compression nut  31  is tightened to a specified torque, deforming compression ring  29  such that compression ring  29 , hydraulic brake line  8 , and barbed fitting  30  form a leak-proof seal. It will be understood that the connection of the hydraulic line can include any suitable connection. 
         [0041]    Referring to  FIGS. 6 and 11 , a piston  24  is received in a piston bore or cylinder  24   a  formed in second brake arm  3 . Piston  24  has a circumferential groove in which is located a seal, which may be in the form of an O-ring  26  and a back-up ring  25 . A first end of piston  24  preferably has a tapered bore with a spherically shaped bottom against which is abutted a corresponding spherically shaped end of adjust bolt  22 . Referring to  FIG. 6 , cross-drilled hole  3   a  of second brake arm  3  runs transversely across the bore that receives piston  24  and the bore that receives hydraulic brake line  8 . Connecting holes  34 ,  35  connect cross-drilled hole  3   a  to the cylinder  24   a  that receives piston  24  and the bore that receives hydraulic brake line  8 . Thus, hydraulic brake line  8  and the bore  24   a  that receives piston  24  are in fluid communication with each other. An open end of cross-drilled hole  3   a  is threaded and receives a small O-ring  28 . A bleed screw  27  is threadably received in the open end of cross-drilled hole  3   a,  and is tightened against O-ring  28  to form a leak-proof seal. In alternative embodiments the piston  24  and cylinder  24   a  may be disposed separate from the brake arms  2 ,  3  but configured to operate therebetween. 
         [0042]    A cycle of operation of brake assembly  50  is described as follows.  FIGS. 4 and 11  show brake assembly  50  in its unactuated state. Referring to  FIGS. 4 and 11 , return spring  11  urges first brake arm  2  in a counter-clockwise direction around pivot bolt  1 , and return spring  11  urges second brake arm  3  in a clockwise direction around pivot bolt  1 . But counter-clockwise rotation of first brake arm  2  and clockwise rotation of second brake arm  3  are prevented by the abutment of the bottom of piston  24  with the bottom of the bore  24   a  in second brake arm  3  that receives piston  24 . In other words, first brake arm  2  and second brake arm  3  are sprung against each other by spring  11 . However, at the same time it will be understood that the parts of the arms  2 ,  3  that hold respective brake pad assemblies are biased into an open or apart condition. 
         [0043]    Referring to  FIG. 6 , hydraulic brake line  8 , cross-drilled hole  3   a,  connecting holes  34 ,  35  and the handlebar-mounted actuator  80  ( FIG. 16 ) are filled with one continuous volume of any suitable hydraulic fluid. When the handlebar-mounted actuator  80  is actuated by manipulating lever  82 , advancing piston  84  within master cylinder  86  displaces a volume of fluid from reservoir  88  through fluid passageway  90  to flow through hydraulic brake line  8 , through cross-drilled hole  3   a,  and upwards into the bore  24   a  that receives piston  24 , pushing piston  24  upwards as shown in  FIG. 12 . The piston  84  preferably has seals  92 . This upwards force on piston  24  causes first brake arm  2  to rotate clockwise (in  FIG. 12 ) around pivot bolt  1  against the urging force of return spring  11 , since first brake arm  2  is operatively connected to piston  24 . Also, an equal and opposite downwards force causes second brake arm  3  to rotate counterclockwise (in  FIG. 12 ) around pivot bolt  1 . First brake arm  2  and second brake arm  3  continue to rotate about pivot bolt  1  until brake pad assemblies  4 ,  5  contact side walls of a bicycle rim  36 , providing a braking force to slow rotational motion of bicycle rim  36 . Further clockwise movement of first brake arm  2  and counter-clockwise movement of second brake arm  3  is prevented by the presence of bicycle rim  36 . When the handlebar-mounted actuator is released, first brake arm  2  rotates counter-clockwise and second brake arm  3  rotates clockwise due to the urging force of return spring  11 , and piston  24  pushes hydraulic fluid out of the bore  24   a  that receives piston  24  and back towards the handlebar-mounted actuator, until brake assembly  50  is again positioned in the unactuated state shown in  FIG. 11 . 
         [0044]    Because rims are available in different widths, and because brake pads wear down over time, it may be necessary to adjust the initial separation between first brake pad assembly  4  and second brake pad assembly  5 . The procedure for adjusting brake pad separation is described as follows. Referring to  FIG. 11 , first brake pad assembly  4  and second brake pad assembly  5  are separated by a distance D 1 . Referring to  FIGS. 8   a - c,    10   a,    10   b,  and  13 , when adjust knob  7 , which forms part of and actuates an adjust mechanism  96  (see also  FIG. 17 ) of the brake assembly  50 , is rotated in a first direction, recesses  7   b  of adjust knob  7  alternately engage and disengage projections  53   c  of detent block  53  due to the previously described urging force of detent spring  52 , producing a detenting action, as used on other mechanisms that are well known in the art. As adjust knob  7  rotates, adjust bolt  22  will rotate with it, since adjust knob  7  and adjust bolt  22  are non-rotatably coupled as previously described. As adjust bolt  22  rotates, its threaded engagement with adjust bolt receiver  23  causes it to move axially relative to adjust bolt receiver  23  and adjust knob  7  as shown in  FIG. 13 . As, adjust bolt  22  moves relative to adjust bolt receiver  23 , first brake arm  2  rotates counterclockwise (in  FIG. 13 ) about pivot bolt  1  and second brake arm  3  rotates clockwise about pivot bolt  1  under the urging force of return spring  11  until first brake pad assembly  4  and second brake pad assembly  5  are separated by a distance D 2  that is greater than D 1 . If, instead of increasing brake pad separation, it is desired to set the brake pad separation to a third distance D 3  that is less than D 1 , adjust knob  7  is simply rotated in a second direction opposite the first direction, causing adjust bolt  22  to move axially in the opposite direction, in turn causing first brake arm  2  to rotate clockwise (in  FIG. 13 ) and causing second brake arm  3  to rotate counter-clockwise against the urging force of return spring  11  until brake pad assemblies  4 ,  5  are separated by the desired third distance D 3  that is less than D 1 . 
         [0045]    Another feature of a preferred embodiment of the invention is the ability to quickly move brake pad assemblies  4 ,  5  apart to facilitate wheel removal. This feature is known as “quick-release”, and is described as follows, referring to parts of the brake assembly  50  that form the quick-release mechanism  94 . In  FIGS. 14 and 15 , detent block  53  is omitted so that other structure can be seen more clearly. Referring to  FIGS. 1 and 14 , brake assembly  50  is shown in the same non-actuated state as shown in  FIG. 11 , with quick-release lever  6  in the closed position. Referring to  FIGS. 7   a ,  7   b  and  14 , bore  6   b  of quick-release lever  6  and adjust bolt receiver  23  are oriented towards piston  24 . When quick-release lever  6  is rotated 180 degrees into the position shown in  FIG. 15 , bore  6   b  and adjust bolt receiver  23  are re-oriented away from piston  24  as shown. Since adjust bolt  22  is threaded into adjust bolt receiver  23  and moves with it, adjust bolt  22  moves to a new position relative to first brake arm  2 , allowing first brake arm  2  to rotate counter-clockwise (in  FIG. 15 ) about pivot bolt  1  under the urging force of return spring  11 , and allowing second brake arm  3  to rotate clockwise (in  FIG. 15 ) about Pivot bolt  1  under the urging force of return spring  11 , until brake pad assemblies  4 ,  5  are separated by a distance D 4  that is greater than D 1  with the objective of being wider than the bicycle tire. The bicycle tire and wheel can now be more easily removed from the bicycle. 
         [0046]    In order to reset the separation of brake pad assemblies  4 ,  5  back to the original separation distance D 1 , quick-release lever  6  is simply rotated back to the closed position shown in  FIG. 1 , which re-orients bore  6   b  and adjust bolt receiver  23  towards piston  24  as shown in  FIG. 14 , causing adjust bolt  22  to move relative to first brake arm  2  as shown in  FIG. 14 , forcing first brake arm  2  to rotate clockwise (in  FIG. 14 ) against the urging force of return spring  11 , and forcing second brake arm  3  to rotate counter-clockwise (in  FIG. 14 ) against the urging force of return spring  11 , until brake pad assemblies  4 ,  5  are once again separated by a distance D 1 . 
         [0047]      FIG. 11   a  shows a hydraulic brake assembly according to another embodiment of the invention. A first brake arm  202  and brake pad assembly  4  is pivotally connected to a bicycle at pivot element  1 . A second brake arm  203  and brake pad assembly  5  is configured to pivot relative to the first brake arm. A piston  224  is received in a piston bore or cylinder  224   a  formed in second brake arm  203 . Piston  224  has a circumferential groove in which is located a seal, which may be in the form of an O-ring  226  and a back-up ring  225 . Piston  224  has a bearing end  224   b  that extends from the cylinder  224   a  of the second arm  203  in the direction of the upper end  200   a  of the first arm  202 . The first arm  202  includes, at or near the upper end  200   a,  a surface  222 , preferably in the form of a curved surface that is shaped and positioned to contact the bearing end  224   b  of piston  224 . 
         [0048]    In use, fluid entering cylinder  224   a  displaces piston  224  in brake arm  203  in the direction of the upper end  200   a  of first arm  202 . The piston bearing end  224   b  pushes against surface  222 , and thus the upper end  200   a,  in order to cause the arms  202 ,  203  to pivot. The pivoting of arms  202 ,  204  cause the brake pad assemblies  4 ,  5  to be drawn towards each other when piston  224  is displaced outwardly from cylinder  224   a.    
         [0049]      FIGS. 18-21  shows yet another embodiment of the invention, wherein most of the components are the same as or are similar to those shown in  FIGS. 1-17  and described herein. The brake assembly  150  includes first brake arm  102  and second brake arm  103 , both may be pivotally connected to a frame member. Most of the components of a quick-release mechanism  194  and the adjust mechanism  196  are generally positioned at or within a fork arrangement  198  of an upper end  200  of arm  102 . Adjust mechanism  196  includes an adjust lever  107  that extends from the adjust mechanism on arm  102 . Operation of the adjust lever  107  causes the movement of the link member  122 . 
         [0050]    Quick-release mechanism  194  includes a quick-release lever  106  that extends from the quick-release mechanism on arm  102 . Operation of the quick-release lever  106  also causes movement of the link member  122 . 
         [0051]    Both quick-release mechanism  194  and adjust mechanism  196  act on link member  122 , which acts on piston  124  disposed in arm  103 . 
         [0052]    The hydraulic brake line  8  ( FIG. 18 ) is connected to arm  103  via fitting  31  in the same fashion as in the previous embodiment.  FIG. 19  shows the opening  204  in the arm  103 , into which the fitting  31  is fitted into the arm and through which hydraulic fluid passes to and from the cylinder  24   a  formed in the arm. 
         [0053]    In the embodiment depicted in  FIGS. 18-21  an embodiment of the adjust mechanism  196  is shown in detail. Adjust knob  107  has internal threads  107   a  that threadably connect the adjust knob to the link member  122 . A spring  32  biases the knob  107  and the head  22   a  apart. Both the adjust knob  107  and the link member  122  pass through receiver  123 , although receiver has a smooth walled interior  123   a.  For adjustment of the adjustment mechanism  196  to occur, when the knob  107  is turned, the link member  122  should be prevented from turning. 
         [0054]    Accordingly, there is an arrangement at the end of the link member head  22   a  that functions to prevent the link member from rotating when the adjust knob  107  is turned. The arrangement includes a piston  124  in cylinder  124   a  that is prevented by turning, for example, by providing the piston and seal  126  in a non-cylindrical shape, for example an oval shape, which is reciprocally disposed in a matching cylinder  124   a  (for example a corresponding oval shape). The piston  124  also has a socket  124   b  that is non-round and an end profile  122   a  on the link member  122  that non-rotatably fits within the socket. Thus, the piston  124  constrains the link member  122  from turning by virtue of the non-round configuration of the piston and cylinder  124   a  in combination with the locking socket  124   b  and end profile  122   a.    
         [0055]    While this invention has been described by reference to particular embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.