Abstract:
Responsive to a hydraulic piston advancing out of a piston housing in a second brake arm and contacting a piston cam surface of a first brake arm, the second brake arm pivots around a second pivot. As this is happening, a cam surface in the second brake arm lifts a contact surface of a first force transfer member of the first brake arm, imparting torque to the first brake arm which then pivots around a first pivot. The cam surface is shaped to impart synchronous motion to the first and second pad holders. Splitting one of the brake arms with a centering member permits a centering adjust feature.

Description:
BACKGROUND 
       [0001]    The present disclosure is directed to bicycle brakes and, more particularly, to bicycle rim brakes. 
         [0002]    In general, there are two types of rim brakes. One is referred to as a single pivot rim brake and the other is referred to as a two-post rim brake. The two-post rim brake usually includes a first brake arm pivotable about a first axis and a second brake arm pivotable about a second axis. The first and second brake arms include a link or connection therebetween for moving the brake pads at the same rate. A disadvantage of a two-post brake is the braked induced frame/fork post loads. There is a need to provide a two-post rim brake with reduced frame/fork post loads. 
       SUMMARY 
       [0003]    According to one aspect, a rim brake is provided that uses only one hydraulic piston assembly to actuate opposed angular motion of first and second brake arms. The first brake and has a first pivot adapted for pivotal attachment to the bicycle. A first brake pad holder of the first brake arm downwardly depends from the first pivot. The first brake pad holder is configured to move in a first arcuate direction around the first pivot. The second brake arm has a second pivot adapted for pivotal attachment to the bicycle. A second brake pad holder of the second brake arm downwardly depends from the second pivot. The second brake pad holder is configured to move in a second arcuate direction around the second pivot opposite the first arcuate direction. The second pivot is horizontally spaced from first pivot. The only one hydraulic piston assembly includes a piston slidably mounted in a piston housing of the second brake arm, the piston advancing along a piston axis responsive to hydraulic fluid pressure to cause a non-horizontal force to be exerted on the first brake arm to move the second brake pad bolder in the second arcuate direction around the second pivot. 
         [0004]    According to another aspect, a rim brake has first and second brake arms. The first brake arm has a first pivot from which downwardly extends a first pad holder. The second brake arm has a second pivot from which downwardly extends a second pad holder. Responsive to actuation of the brake, the first pad holder pivots in a first angular direction, and the second pad holder pivots in ail opposite, second angular direction. The second pivot is horizontally spaced from the first pivot. The second brake arm further includes a biasing member that upwardly extends from the second pivot. This biasing member pivots around the second pivot with the second pad holder as a unit. The second brake arm further has a force transfer member that upwardly extends from the second pivot. This force transfer member is operable to transmit torque in the second angular direction to the second pad holder upon actuation of the brake. A centering member, such a set screw, defines the angular position of the biasing member relative to the force transfer member. The centering member is adjustable to move the second pad holder without moving the first pad holder, thereby providing a center adjust function. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Further aspects and their advantages can be discerned in the following detailed description, in which like characters denote like parts and in which: 
           [0006]      FIG. 1  is an elevational view of a bicycle employing rim brakes according to the one embodiment; 
           [0007]      FIG. 2  is a perspective view of a rim brake according to one embodiment; 
           [0008]      FIG. 3  is a front view of the brake shown in  FIG. 2 ; 
           [0009]      FIG. 4  is a sectional view taken substantially along line  4 A- 4 A of  FIG. 3 ; 
           [0010]      FIG. 5  is part-sectional view of the brake shown in  FIG. 3 , diagramming certain spatial relationships; 
           [0011]      FIG. 6  is a back view of the brake shown in  FIG. 2 ; 
           [0012]      FIG. 7  is a transverse sectional view of the brake shown in  FIG. 3 , the section taken substantially orthogonally to a center plane; 
           [0013]      FIG. 8  is a detail of  FIG. 7  showing structure of a piston cam surface; 
           [0014]      FIG. 9  is a transverse sectional view of the brake shown in  FIG. 3 , the sectional plane being parallel to the sectional plane of  FIG. 7 ; 
           [0015]      FIGS. 10A and 10B  are force diagrams of different components of the brake shown in  FIG. 2 ; 
           [0016]      FIG. 11  is a right side view of the brake shown in  FIG. 2  and representative structure of a bicycle frame to which the brake is mounted; 
           [0017]      FIG. 12  is a part-sectional front view of the brake shown in  FIG. 3 , in a non-actuated condition; 
           [0018]      FIG. 13  is a part-sectional front view of the brake shown in  FIG. 3 , but shown in an actuated condition; 
           [0019]      FIG. 14  is a part-sectional view of the brake shown in  FIG. 3 , but shown in an open condition; 
           [0020]      FIGS. 15 and 16  are perspective and front views of an alternative embodiment in which a centering adjust is on a different brake arm; 
           [0021]      FIG. 17  is a perspective view of an alternative embodiment having no centering adjust; 
           [0022]      FIG. 18  is a perspective view of an alternative embodiment in which one end of a coil return spring is attached to a brake mount; 
           [0023]      FIG. 19  is a perspective view of an alternative embodiment in which the bias member is a torsion spring; 
           [0024]      FIG. 20  is a perspective view of an alternative embodiment including a torsion return spring wound around a brake mount; and 
           [0025]      FIG. 21  is a front view of a cable pull embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  is an elevational view of a bicycle indicated generally at  100 , which may be used to implement rim brakes disclosed herein. While the illustrated bicycle is a road bike, the brakes may be employed on any bicycle using one or more rim brakes, including touring bicycles, commuter bicycles, mountain bikes, cyclocross bikes and triathlon bikes. Bicycle  100  has a frame  102  that includes a head tube  104  and left and right seat stays (right seat stay  106  being shown). A fork  108  rotates within the head tube  104 . The fork  108  rotatably mounts a front wheel  110  to the rest of the bicycle  100 . Front wheel  110  has an axis  112  and a wheel rim  114 . The wheel rim  114  has a rim sidewall or other annular braking surface  116  against which a brake pad (described below) may be employed. The annular braking surface  116  is disposed at a predetermined radius from the wheel axis  112 . A front rim brake  118  may be hand-actuated by a user to apply fractional force to opposed annular braking surfaces  116 . The front rim brake  118  is mounted to the fork  108  on left and right axial mounts in a manner which will be described below. 
         [0027]    In the illustrated embodiment, a rear wheel  120  is rotatably mounted to the rest of the bicycle  100  at the junction of its seat stays and chain stays, right chain stay  121  being shown. The rear wheel  120  has a rear wheel axis  122  and a rim  124 . Sidewall or other opposed annular braking surfaces  126  of rim  124  are a predetermined radius away from the rear wheel axis  122 . The radii of wheels  120  and  110  typically are the same but don&#39;t have to be. Further, while a diamond frame  102  that includes both chain stays and seat stays is illustrated, some frame designs omit the seat stay or replace it with more elaborate shock-absorbing apparatus, and brake(s) disclosed herein may be used in conjunction with these other frame types. 
         [0028]    In the illustrated embodiment, a rear rim brake  128  is mounted on dual posts (not shown in the  FIG. 1 ) that are in turn formed on the left and right seat stays of the frame  102 . In other embodiments, the rear rim brake  128  may be mounted elsewhere on the frame  102  to be adjacent the rear annular braking surfaces  126 , such as on a seat tube  130  of frame  102 . The rim brake  200  described below may be employed as a front, rim brake  118 , a rear rim brake  128  or both. Unless it is being steered left or right, in use bicycle  100  occupies, and moves in, a vertical center plane P ( FIG. 5 ). 
         [0029]    A handlebar  132  rotates as a unit with fork  108 . In one conventional arrangement, mounted on the handlebar are two hand-operated brake levers (rear brake lever  134 , as typically mounted on the right side of handlebar  132 , being shown) that are operated by the user to actuate the brakes  118 ,  128 . In the embodiment illustrated in  FIGS. 2-14 , the brakes  118 ,  128  are hydraulic brakes, each of which incorporate a piston within a slave cylinder (described below) that moves responsive to the pressure of hydraulic fluid. As applied to hydraulic embodiments, brake lever  134  has a master piston and cylinder (not shown) incorporated within it and is connected by a hydraulic brake line  136  to rear brake  128 . Similarly, the left brake lever has a master piston and cylinder located within it, and is connected by a hydraulic brake line  138  to the front brake  118 . An increase in the fluid pressure of line  136  will cause the piston (described below) in the slave cylinder in brake  128  to move along the cylinder axis, causing brake  128  to clamp against annular braking surface  126 . An increase in the fluid pressure of line  138  will cause the piston in the slave cylinder in brake  118  to move along the cylinder axis, causing brake  118  to clamp against annular braking surfaces  116 . 
         [0030]    In another embodiment, the hydraulic brake lines or hoses  136 ,  138  are replaced by Bowden cables, which exert a rider-varied degree of tensile force on cable-actuated rim brakes to which they are connected. A cable-actuated embodiment will be described below. 
         [0031]      FIGS. 2-14  illustrate one hydraulic brake according to one embodiment. A brake indicated generally at  200  has a first brake arm  202  and a second brake arm  204 . In the view shown in  FIG. 3 , and as mounted on mounts of a pair of seat stays (not shown), the first brake arm  202  is the left brake arm and the second brake arm  204  is the right brake arm, although the entire structure can be easily reversed in mirror image. 
         [0032]    First brake arm  202  is pivotably attached to a first brake mount (not shown) on a first pivot or first axis  206  by suitable fasteners  207 . Second brake arm  204  is pivotably attached to a second brake mount (not shown) by suitable fasteners  209  on a second pivot or second axis  208 . Fasteners  207 ,  209  can each include a shaft and bushings. The first axis  206  is parallel to the center plane P and is a predetermined distance from plane P in a left outboard direction ( FIG. 5 ). The first axis  206  further is tangential to a vertical radius drawn from the bicycle wheel axis ( 112  or  122 ) with which it has been associated. The second axis  208  is likewise parallel to the center plane P and is spaced from it in a right outboard direction that that is equal to the spacing of first axis  206  from plane P ( FIG. 5 ). The first axis  206  is horizontally displaced from the second axis  208  such that a horizontal reference Line  205  extends therebetween ( FIG. 5 ). The axis  208  further is tangential to a vertical radius drawn from the bicycle wheel axis ( 112  or  122 ) with which it has been associated. 
         [0033]    First brake arm  202  has a “downwardly” depending first brake pad holder  210  having an end  212  that is displaced from first axis  206  toward wheel axis  112  or  122 . It should be understood that as used herein and as describing the structure of the different brake embodiments described herein, the words “downward”, “downwardly”, “lower”, “upward”, “upwardly” and “upper” all refer to a radial distance towards or away from wheel axis  112  or  122 , depending on where the brake is installed and which wheel  110 ,  120  the brake is meant to brake; as installed, the brake first and second axes  206 ,  208  will often be at a considerable angle to the horizontal. A brake pad  214  is affixed to the end  212  so as to reside within an arc (around first axis  206 ) that intersects an annular braking surface  126 A of rear wheel  120  (while the use of brake  200  as braking the rear wheel  120  is shown in particular in  FIGS. 2-13 , the description also applies to brake  200  being used as a front brake to brake wheel  110 ). Likewise, second brake arm  204  has a downwardly depending brake pad holder  215  with an end  216  that is displaced from axis  208  toward wheel axis  122 . A brake pad  218  is affixed to the end  216  so as to reside within an arc (around axis  208 ) that intersects the opposed annular braking surface  126 B of wheel  120 . 
         [0034]    The brake  200  includes a force transfer mechanism  201  between the first and second brake arms  202 ,  204  configured to move the first pad holder  210  in the first arcuate direction about the first pivot  206  as the piston advances. The force transfer mechanism  201  includes first and second force transfer members  220 ,  228 . The first brake arm  202  has the first force transfer member  220  which, in this embodiment, extends in an inboard and upward direction to an end  222 . In this illustrated embodiment, a contact surface such as a roller  224  is affixed to the transfer member end  222  along an axis which is parallel to first axis  206 . The first brake and  202  further has a piston cam surface  226  that is disposed in an inboard and upward direction from the first axis  206 . The piston cam surface  226  is convexly arcuate relative to first axis  206 . The piston cam surface  226  may be disposed forwardly from the transfer member end  222 ; in art alternative embodiment the transfer member end  222  may be disposed forwardly from the piston cam surface  226 . In the illustrated embodiment, the transfer member  220  and the piston earn surface  226  are integrally formed as by machining and/or molding and adjoin each other. Transfer member  220 , first brake pad holder  210  and piston cam surface  226  freely rotate around the first axis  206  as a unit. 
         [0035]    The second brake arm  204  has the second force transfer member  228  that extends upwardly and in an inboard direction from the second axis  208 . The second force transfer member  228  includes a piston housing or cylinder  230  formed along a piston axis  232 . In the illustrated embodiment the piston axis  232  rotates around second axis  208  as the brake  200  is being actuated. Nonetheless, throughout its range of motion, the piston axis  232  remains inboard from the first axis  206 . The piston housing  230  may be mostly or completely located on the other side of center plane P relative to second axis  208 . 
         [0036]    As particularly seen in  FIGS. 7 and 9 , a slave piston  234  slides within a cylinder  235  defined by the piston housing  230  along piston axis  232 . The piston  234  extends downwardly out of piston housing  230  responsive to an increase in fluid pressure in hydraulic hose or line  136 . An end of hose  136  is inserted into a chamber  231  and is fixed in place with the aid of a nut  233  and a compression fitting  237 . The fluid within hose  136  and chamber  231  is in fluid communication with hydraulic fluid within chamber  236  via passages  243  and  239 . The position of a piston stop  238  is set by a threaded barrel adjuster  240 . The piston stop  238  has an annular seal  242 , and the piston  234  has an annular seal  244 , both engaging cylindrical sidewall  235  and acting to contain the pressurized hydraulic fluid within hydraulic chamber  236 . A lower surface of the piston stop  238  defines the upper limit of slave piston  234 , as will obtain when the brake pad holders are in their open position ( FIG. 14 ). The cylinder  235  further is ported via passage  239  to a hydraulic fluid bleed port  241  ( FIG. 4 ). 
         [0037]    In the illustrated embodiment, the piston stop  238  may be advanced down or retracted up the piston axis  232  by one of two adjust mechanisms of a barrel adjuster  240 . A coarse adjust or “quick release” lever  246  rotates as a unit with a quick release stop  248 . Quick release stop  246  has relatively coarse threads which engage with a threaded upper bore  250  of the piston housing  230 . An inner bore  252  of the quick release stop  248  has relatively fine threads which threadedly engage with the shaft of a micro adjust rod  241 . When a user rotates the quick release lever  246 , the quick release stop and the micro adjust rod  241  will rotate with it as a unit, quickly advancing or retracting the piston  234  up or down the cylinder  235 , and quickly opening or closing the brake pads, as might be desired for removal and reinstallation of the wheel  120 . 
         [0038]    The brake pad gap relative to the wheel rim or annular braking surfaces  126  is set by twisting a barrel adjust housing  254  relative to the brake quick release lever  246 . Barrel adjust housing  254  turns as a unit with micro adjust rod  241 , and will advance or retract rod  241  relative to the quick release stop  248 . A helical spring  256  places tensile force between the inner bore  252  of the quick release stop  248  and the barrel adjust housing, reducing or preventing undesired relative movement of these components. 
         [0039]    As best seen in  FIG. 8 , piston  234  terminates at its lower end with a piston contact surface  258 . In the illustrated embodiment this contact surface  258  is a flat disk. Piston contact surface  258  meets the piston cam surface  226  at a line of contact  260  that stays in alignment with the piston axis  232 . The convexly arcuate shape of piston cam surface  226  is preselected so that the piston axis  232  goes through the line of contact  260  throughout the range of stroke of the piston  234 . In an alternative embodiment (not shown), the contact surface  258  or the piston cam surface  226  may be replaced with a roller. 
         [0040]    The second, force transfer member  228  of the second brake arm  204  further has, formed on or within it, a second contact surface, such as a transfer cam surface  262 . In the illustrated embodiment the transfer cam surface  262  is located in an upper and inboard direction from the second axis  208 , but is displaced somewhat downwardly from the piston housing  230  so as to be intermediate the piston housing  230  and the second axis  208 . In one embodiment, the position and shape of the transfer cam surface  262  are selected such that the speed with which brake pad  214  moves toward or away from rim  126 A equals the speed with which brake pad  218  moves toward or away from the opposed rim  126 B; the brake pads  214 ,  218 , and the arms  202 ,  204  to which they are attached, are then said to move synchronously. For synchronous movement, it has been discovered that the shape of transfer cam surface  262  can be nearly circularly cylindrical in the illustrated embodiment, the synchronizing transfer cam surface  262  has a radius  264  from a center  266  that is located inboard from first and second axes  206  and  208 . The center  266  is located downwardly from the transfer cam surface  262 . In an alternative embodiment, the roller  224  may be replaced with a cam surface (not shown) that slides on transfer cam surface  262 . In a still further embodiment (not shown), the first brake arm  202  may be fitted with a cam surface and the second brake arm with a roller, opposite the arrangement shown. 
         [0041]    In this Illustrated embodiment, the second brake and  204  is split into two parts; the second brake arm force transfer member  228 , and a biasing member or portion  268  that includes brake pad holder  215  and a centering adjust body  270  that extends upwardly from the second axis  208 . Both portions  228  and  268  are rotatably mounted to second axis  208 . A threaded bore  272  in the centering adjust body  270  is disposed upwardly from the axis  208  and accepts a centering member such as a set screw  274 . An end  276  of the set screw  274  abuts a surface  278  of the transferring member  228 . As set screw  274  is advanced into bore  272 , the centering adjust body  270  angularly displaces relative to transferring member surface  278 . As a result, brake pad holder  215  will move in an inboard direction, but brake pad holder  210  will not. Set screw  274  can be rotated in an opposite direction to open brake pad holder  215  relative to brake pad holder  210 . This provides an ability to center the brake pads  214 ,  218  around the wheel rims or annular braking surfaces  126 A, B. 
         [0042]    In this embodiment, the and  202  is biased against arm  204  by a helical return spring  280 . A first end  282  of the return spring is attached to a post  284  on the first brake arm  202 . A second end  286  of the return spring is attached to a post  288  on an end of the centering adjust body  270 . Spring  280  urges together posts  284  and  288 . Therefore, on the other side of the axes  206 ,  208 , the brake pad holders  210 ,  215  are biased to an open or retracted condition. The coil spring  280  also acts to urge the end  276  of the set screw  274  against surface  278  of the transferring member  228  of the second brake arm  204 , causing the second brake arm components  228  and  268  to rotate as a unit around second axis  208 . 
         [0043]    In operation and referring to  FIG. 5 , a rider squeezes a brake lever (such as rear brake lever  134 ) on the handlebar  132  (see  FIG. 1 ), causing a master cylinder therein (not shown) to put pressure on hydraulic fluid within hydraulic brake line  136 . This causes the slave piston  234  to downwardly extend from the piston housing  230  on the second brake arm  204 . The lower contact surface  258  of the piston  234  stays abutted against the piston cam surface  226  of the first brake arm  202 . Extension of the piston  234  causes second brake aim  204  to rotate around second axis  208 , and causes the second brake pad holder  215  to rotate in an inboard direction, eventually contacting an annular braking surface  126 B of the wheel. 
         [0044]    As this motion is occurring, the transfer cam surface  262  is lifting the roller  224  upward and leftward. This causes rotation of the first brake arm  202  around first axis  206 . In the illustrated embodiment, the shape of the transfer earn surface  262  ensures that the movement of brake pad holders  210 ,  215  are “synchronous”, that is, that they move at the same rotational speed around axes  206 ,  208  but in opposite angular directions. Since the brake pads  214 ,  218  are at the same radius from their respective axes  206 ,  208 , they will also move, in opposed directions, at the same tangential speed. 
         [0045]      FIGS. 10A-10B  show force vectors operating on the various components of the brake. F b  is the brake force, or the pad force operating on the annular braking surfaces  126 A,  126 B to generate stopping power. F f  is a frame force, acting on the frame or fork mounts and orthogonal to pivot axes  206 ,  208 . F p  is the non-horizontal force of the piston  234 ; an equal and opposite force between the piston  234  and the piston cam surface  226 . F r  is a roller force; an equal and opposite force between the roller  224  and transfer cam surface  262 . Φ is the angle relative to the horizontal at which forces F p  and F r  act (see  FIG. 5 ). The ratio of F f /F b  may be less than 2.5. Preferably, the ratio of F f /F b  may be less than 2.0. More preferably, the ratio of F f /F b  may be less than 1.5. One technical advantage is that the piston force F p  is spread among the roller force F r  and the frame forces F f  rather than just the frame forces F f  alone. This reduces loading on the brake mounts, creates a stiffer feel in actuating the brake, and lowers frame/fork mount strength requirements. 
         [0046]    An embodiment alternative to the one shown in  FIGS. 2-14  is shown at  1200  in  FIGS. 15 and 16 . In this embodiment, a first brake arm  1202  is rotatably mounted at axis  206  to a bicycle fork or frame member, and a second brake arm  1204  is rotatably mounted to a fork or frame member at axis  208 , as before. But the centering adjust mechanism has been moved from second brake arm  1204  to first brake arm  1202 . The first brake arm  1202  has a downwardly depending brake pad holder  1206 . An upwardly extending biasing member  1208  is integral with brake pad holder  1206  and rotates with holder  1206  around axis  206  as a unit. An upper end  1210  of the biasing member  1208  has a post  284  thereon that receives first end  282  of the coil return spring  280 . A force transfer member  1212  of the first brake arm  1202  is now split from the brake pad holder  1206  and may rotate around axis  206  independently of it. The transfer member  1212  continues to carry a contact surface such as cam roller  224  on its remote end  1214 . 
         [0047]    A centering adjust set screw  1216  is threadedly received into a bore  1218  in the biasing member  1208 . A front end  1220  of the set screw  1216  contacts a surface  1222  of the force transfer member  1212 . Rotating the set screw clockwise or counterclockwise will change the angular separation of the brake holder  1206  relative to the force transfer member  1212 , thus permitting a centering adjustment of the brake  1200 . 
         [0048]    The second brake arm  1204  is no longer split. A brake pad holder  1224  of the second brake arm  1204  is integral with a force transfer member  1226  thereof. The force transfer member  1226  contains the transfer cam surface  262  and the piston housing  230 . 
         [0049]    A further embodiment is shown in  FIG. 17 . This brake  1300  is similar to brake  200  ( FIGS. 2-14 ) but has no centering adjust mechanism at all. The first brake arm  1302  and the second brake arm  1304  are not split. 
         [0050]    The embodiment  1400  shown in  FIG. 18  is similar to the one shown in  FIGS. 15 and 16 , but the connections of a return spring  1402  are different. A first end  1404  of a helical return spring  1402  is connected to an end  1210  of the first brake arm  1202 . A second end  1406  of the return spring  1402  is affixed to a fastener  1408  that is coaxial with second axis  208 . In this position, the return spring  1402  continues to urge brake pad holders  1410 ,  1412  apart and continues to urge spit members  1212  and  1410  together. 
         [0051]      FIG. 19  illustrates another embodiment  1500  that generally is similar to brake  1200 . But in place of helical spring  1402  ( FIG. 18 ), a torsion spring  1502  is used. A first end  1504  of the torsion spring  1502  is affixed as by a fastener  1506  to biasing member end  1210 . A second end  1508  of torsion spring  1502  is affixed as by fastener  1408  to be coaxial with the second axis  208 . 
         [0052]      FIG. 20  shows an embodiment  1600  in which the spring member  1602  is constituted by a torsion spring that is wound around second axis  208 . A first end  1604  of the torsion spring  1602  is positioned to abut an interior surface  1605  of the brake holder  1606  of the second brake arm  204 . A second end  1608  of the torsion spring  1602  is joined to the first brake arm  202 . 
         [0053]    A cable pull embodiment  1700  is illustrated in  FIG. 21 . A first brake arm  1702  rotates as a unit around a first axis  206 . A second brake arm  1704  rotates as a unit around second axis  208 . The first brake arm has a first brake pad holder  1706  that downwardly depends from the axis  206 . A force transfer member  1708  is formed to be integral with the pad holder  1706  and extends inwardly, past center plane P, to an end  1710  that in the illustrated embodiment is positioned outboard and upward from second axis  208 . A contact surface, such as an arcuate roller cam surface  1712 , is formed by the force transfer member  1708 . 
         [0054]    The second brake arm  1704  has a second brake pad holder  1714  that downwardly depends from second axis  208 . A force transfer member  1716  upwardly and inwardly extends from the second axis  208  and is integrally formed with the second brake pad holder. In other embodiments, and in order to provide a centering adjust mechanism as has been described in conjunction with other embodiments, brake pad holder  1706  may be split from transfer member  1708 , or brake pad holder  1714  may be split from transfer member  1716 , and a set screw (not shown) or other centering member may be used to set the angular relationship between the split members. 
         [0055]    An end  1718  of the force transfer member  1716  has a contact surface such as a roller  1720  which engages with the roller cam surface  1712  of the force transfer member  1708 . Transfer member  1716  further has an upwardly extending lobe  1722  that is positioned to be on the same side of the center plane P as is end  1710  of the transferring member  1708 . A terminating fitting  1724  of a Bowden cable housing  1726  is pivotally affixed to the lobe  1722 . A brake cable  1728  that is threaded through the housing  1726  of the Bowden cable has an end  1730  that is pivotally attached to end  1710  by a suitable fastener  1732 . 
         [0056]    In the operation of this embodiment, the rider operates a hand lever located on the handlebar of the bicycle (not shown), creating tensile force on the cable  1728 . This will urge cable  1728  upward and into housing  1726 . Cable  1728  will draw transfer member end  1710  toward lobe  1722 . Tensile force on cable  1728  will also cause the arm  1702  to rotate as a unit around axis  206 , inwardly pivoting first brake pad holder  1706 . 
         [0057]    As this is happening, the roller cam surface  1712  lifts roller  1720  and therefore the end  1718  of the transfer member  1716 . This will cause the second brake arm  1704  to rotate, in an opposite direction, around axis  208 , pivoting second brake pad holder  1714  in an inboard direction. 
         [0058]    The motion of brake pad holders  1706 ,  1714  may be synchronized by correctly choosing the shape of the roller cam surface  1712 . In this illustrated embodiment, the synchronizing roller cam surface  1712  describes a circular arc around a center  1734  that is downward and inboard from the surface  1712 . 
         [0059]    The embodiments herein described have the technical advantage of producing linear actuation rates. 
         [0060]    Numerous modifications to the embodiments disclosed herein will be apparent to those skilled in the art in view of the foregoing description. For example, any of the embodiments disclosed herein may be modified to include any of the structures or/or methodologies disclosed in connection with different embodiments. Accordingly, this disclosure is to be construed as illustrative only and is presented for the purpose of enabling those skilled in the art to make and use the invention, and to teach the best mode of carrying out same. The exclusive rights to all modifications which come within the scope of the appended claims are reserved.