Abstract:
A brake assembly for a hydraulic brake system of a handlebar-steered vehicle, the brake assembly including a housing mountable to a handlebar of the vehicle and having a chamber formed therein. The brake assembly is provided with a variable rate linkage. A piston assembly is received and axially guided within the chamber and is provided with a piston adjustment mechanism that does not affect the function of the variable rate linkage.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    A hydraulic brake system for a bicycle typically includes a hydraulic brake actuation device, a rotor attached to a wheel of the bicycle and a brake caliper operatively connected to the brake actuation device. The caliper is responsive to changes in hydraulic pressure generated by the brake actuation device to urge brake pads into contact with the rotor and effect braking. 
         [0002]    When the brake actuation device is initially actuated, no braking forces are generated because a gap must be closed between the brake pads and the rotor. Typical hydraulic brake systems that have a linear rate of travel of the piston relative to the travel of the lever blade require an undesirable amount of lever travel before braking occurs, i.e., a significant amount of “dead band.” Most hydraulic brake systems do not address dead band and changes in dead band from pad wear, and except for set-up procedures, there have been few efforts to develop mechanisms that are adjustable to provide a minimal gap and without affecting the rate of travel of the piston relative to the brake lever. Furthermore, especially in systems with a variable rate of travel of the brake system piston relative to the lever travel, it would be desirable to adjust the dead band without affecting the performance of the system related to the variable rate of the brake system. 
         [0003]    There is a demand, therefore, to minimize dead band without the number of parts, weight and the expense of a complicated mechanism, and without degrading brake performance. The invention satisfies the demand with the additional benefits of lighter weight and reduced manufacturing cost. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention provides linkages for a brake system, for example, in a hydraulic brake system for a bicycle. The invention relates to an assembly for brake actuation systems for bicycles and includes a variable rate linkage brake arrangement and lever preferably providing one or more of the following objects: 1) increased pad/brake surface gap, 2) increased end of stroke brake force, and 3) improved modulation and control, and 4) adjustability of the gap without affecting the selected variable rate of action of the linkage. 
         [0005]    The movement of the linkage according to an aspect of the invention creates a changing, i.e., variable lever blade stroke per piston actuation rate. This rate can be tuned to allow for greater initial fluid movement and subsequently increased pad/rotor clearance for the same lever blade stroke. The rate can also be tuned to have increased brake force at the end of the lever blade stroke. Modulation and brake control can be tuned to a desired brake force in the beginning, middle, and ending ranges of the lever blade stroke with the advantage of increased brake performance. Tuning the linkage also preferably provides a reduction in eccentric piston loading. 
         [0006]    Among other features, the invention may provide a variable lever pull/master piston actuation rate for increased end-of-stroke power, variable lever pull/master piston actuation rate for reduced initial brake force, variable lever pull/master piston actuation rate for greater fluid capacity for increasing pad/rotor clearance for the same lever stroke, variable lever pull/master piston actuation rate tuned to a desired brake force in the beginning, middle, and ending ranges of the lever blade stroke with the advantage of increased brake performance. The invention provides reduced complexity and part count over the prior art for reduced brake system weight and reduced complexity and part count over prior art for reduced manufacturing cost. Moreover, the invention provides a mechanism for adjusting the dead band of the lever without affecting the desired variable lever piston actuation rate by changing the rest position of the piston. 
         [0007]    The invention provides a brake assembly for a hydraulic brake system of a handlebar-steered vehicle, the brake assembly including a housing mountable to a handlebar of the vehicle and having a fluid chamber formed therein. A piston assembly is received and axially guided within the fluid chamber. A lever is pivotally attached to the housing. A cam link is provided on the lever. A follower link is pivotally attached to the housing, wherein movement of the lever moves the cam link and the follower link, wherein the cam and follower links interact to produce a variable rate of travel of the piston assembly relative to the travel of the lever and a pushrod is disposed between the follower link and the piston assembly. 
         [0008]    Other aspects of the invention provide a brake assembly wherein the lever and cam link may both pivot on a common pivot. The follower link may have a first end that is pivotally disposed about a housing pivot and the pushrod is threadably attached to the follower link on a second end. The cam link may include a cam surface. The follower link may include a roller positioned to contact the cam surface. The follower link may have a first end that is pivotally disposed about a housing pivot and the pushrod is threadably attached to the follower link on a second end. The roller may be positioned between the first and second ends of the follower link. The piston assembly may include a piston disposed in a bore of the housing. The fluid chamber may be defined by the wall of the bore and the piston. The piston assembly may include a cap member positioned between the pushrod and the piston. The cap member may include an interior into which the pushrod keys, the pushrod rotationally fixed to the cap member. The cap member may abut the piston at an end portion thereof, the cap member end portion including a flange. The assembly may further include a piston adjustment mechanism disposed in the housing, the piston adjustment mechanism including a manually movable member positioned about and keyed to the piston assembly, wherein the movable member moves axially to adjust a rest position of the piston assembly in the bore without affecting the variable rate of travel of the piston. The manually movable member may be manually rotatable and moves axially when rotated. The piston assembly may include a cap member that abuts a piston at an end portion thereof, the cap member end portion including a flange. The movable member of the position adjustment mechanism may contact the flange of the cap member and wherein adjustment of the position of the movable member in the housing causes adjustment of the rest position of the piston assembly. The movable member may be threadably engaged with the housing. The pushrod may be threadably engaged to the follower link. The pushrod may be keyed to the piston assembly wherein a thread pitch of the movable member to the housing matches a thread pitch of the pushrod in the follower link such that when the piston assembly position is adjusted by rotation and axial movement of the position adjustment mechanism the pushrod is moved an equal amount in the same direction to retain contact with the piston assembly. The piston adjustment mechanism may include a detent mechanism disposed in the housing that acts on the movable member of the piston adjustment mechanism. The detent mechanism may be a ball detent. The piston adjustment mechanism may include a manually operated dial keyed to the rotatable member and the ball detent acts upon a non-round exterior of the dial of the piston adjustment mechanism. The cam link may be formed as a single piece with the lever or may be pivotally attached to the lever. 
         [0009]    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 
         [0010]    In the drawings: 
           [0011]      FIG. 1  is an assembled brake assembly according to the invention; 
           [0012]      FIG. 2  is an exploded view of a brake assembly according to the invention; 
           [0013]      FIG. 3  is a sectional view of a brake assembly in a rest or home position; 
           [0014]      FIG. 4  is a sectional view of a brake assembly in a pulled or actuated position; 
           [0015]      FIG. 5  is a sectional view of a brake assembly with a reach adjust mechanism adjusted to be in an inward orientation; 
           [0016]      FIG. 6  is a sectional view of a brake assembly with the reach adjust mechanism adjusted to be in an outward orientation; 
           [0017]      FIG. 7  is a sectional view of a brake assembly with a piston adjustment assembly adjusted to provide a larger amount of dead band; 
           [0018]      FIG. 8  is a sectional view of a brake assembly with a piston adjustment assembly adjusted to provide a smaller amount of dead band; and 
           [0019]      FIG. 9  is a sectional view of a brake assembly with a variable rate linkage including a cam link and a follower link. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    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 are not for the purpose of limiting the invention as defined by the claims appended hereto and any and all their equivalents. 
         [0021]    In the following, the construction of a brake assembly is described, which according to an embodiment may be constructed or arranged to operate an otherwise conventional hydraulic brake system (not shown). In the described embodiment, in its most general form, the invention provides a brake assembly and system constructed to produce a desired variable lever ratio, i.e., one that is non-linear, which will be described in detail hereinbelow. Also, the invention contemplates the provision of a mechanism to adjust the dead band in the assembly without affecting the desired non-linear nature of the brake assembly. The inventive brake assembly may be used on any type of hand operated brake for bicycles, motorcycles, three and four-wheelers, for example. For bicycles, variations are possible for road style brake levers, different styles of mountain bike brake levers, or BMX brake levers. Other applications could include hydraulic clutch systems. 
         [0022]    Turning to  FIGS. 1-8 , the brake assembly  18  includes a housing  20 . The brake assembly  18  includes a lever  22  pivotally attached to the housing  20 . The lever  22  may include a lever adjustment mechanism  38 . The housing  20  includes a bore  24 . A piston assembly  28  is reciprocally disposed within the bore  24 . The bore  24  includes a fluid chamber  26 . A linkage  21  operates between the lever  22  and the piston assembly  28  to produce a variable rate of travel of the piston assembly. An optional piston adjustment mechanism  40  operates between the linkage  21  and the piston assembly  28  to adjust the amount of dead band in the system without affecting the operation of the linkage  21 . A clamp device  25  or any suitable fastening means may be part of or attached to the housing  20  for attaching the housing to a handlebar of a bicycle (not shown), for example.  FIG. 9  shows the brake assembly of  FIGS. 1-8  and is an embodiment that omits the piston adjustment mechanism. 
         [0023]    The lever  22  may be in the form of a blade pivotally attached to the housing  20  of the brake assembly  18  by a first pin or pivot  34 . A cam or cam-shaped link  42 , which is part of one embodiment of the linkage  21 , is either formed as part of the lever  22  or pivotally disposed on the first pin  34 . The cam  42  has a cam-shaped surface  44  along one portion  46 . 
         [0024]    A lever adjusting mechanism  38  may be adustably attached to the lever  22  on a second pin or pivot  36 , with the second pin attached to the lever. The second pin  36  may be generally outboard from the first pin  34 . 
         [0025]    The lever adjusting mechanism  38  may include a threaded shaft  47  threadably engaged with the second pin  36 . One end of the lever adjusting mechanism  38  includes a grasping part  48  that is accessible and manipulatable by a user and the other end of the lever adjusting mechanism  38  includes a flared end or stop  50 . The stop  50  abuts the cam  42  at the end  52  generally opposite the cam surface  44 . Twisting the grasping part  48  causes the shaft  47  to either be inserted farther or removed from its engagement with the second pin  36 , and as a result change the distance between the second pin  36  and the adjustment end of the cam  52 . In this manner, the orientation of the cam  42  on the lever  22  can be changed, and the position of the lever is altered relative to a handlebar (not shown) when mounted thereon or the housing  20 . 
         [0026]    The linkage  21  also includes a follower  54 . The follower  54  is pivotally disposed on the housing  20 . The follower  54  may be disposed on a third pin or pivot  56  attached to the housing  20 . The follower  54  includes a fourth pin  60 , which is located opposite the third pin  56 . The fourth pin  60  may include a threaded bore  62 . The follower  54  may include a roller  56 , which is rotatably disposed between the third pin  56  and the fourth pin  60 . The roller  56  engages the cam surface  44  of the cam link. The interaction of the follower  54  and the cam  42  when the lever  22  is moved causes the piston assembly  28  to travel according to the profile of the cam surface  44 . The position of the roller  58  on the cam surface  44  determines the part of the profile of the cam surface actuating the piston assembly  28  in response to movement of the lever  22 . The follower  54  may be secured to the third pin  56  with a locknut  68 . 
         [0027]    The housing  20  may be any suitable shape that can define a hollow interior including a bore  24 , and accommodates the mounting of and operation of the linkage  21 . The housing  20  may be made of any suitable material, for example, metal, plastic, composite materials or combinations thereof. The bore  24  includes a fluid chamber  26 . The fluid chamber  26  includes brake fluid as is known. 
         [0028]    The illustrated brake assembly  18  is known as an “open” type of fluid system. The assembly  18  includes a “backpack” reservoir  100 . The backpack reservoir  100  includes a reservoir chamber  102  defined in a portion of the housing  20  in communication with the fluid chamber  26 . Extending through the bore wall  33  between the reservoir chamber  102  is a timing port  104  and a compensating port  106 . A diaphragm or seal  70  made of an elastomeric material such as silicon rubber is made to cover the reservoir chamber  102 . 
         [0029]    The basic operation of the brake assembly  18  is well understood by those skilled in the art. Pivoting the lever  22  from a rest position causes the piston assembly  28  to drive the piston into the bore  24 . As the piston inwardly, the cup or umbrella seal  31  covers the timing port  104  which pressurizes the fluid within the hydraulic line  110  at the end of the fluid chamber  26  and which in turn actuates a slave cylinder within a hydraulically coupled brake caliper (not shown). When the lever  22  is released, the compression spring  64  biases the piston  30  toward the first end of the fluid chamber  26  to reassume the rest or home position. The distance between the cup seal  31  and the timing port  104  is referred to as the “dead-band.” During the part of lever actuation where the cup seal  31  is between the timing port  104  and the first end of the fluid chamber  26 , fluid in the reservoir  102  between the seal  31  and the timing port  104  returns to the reservoir  102 , perhaps causing expansion of the diaphragm  70 . During this part of lever actuation, the second end of the fluid chamber  26  cannot be pressurized. It is highly desirable to be able to adjust the length of the dead-band in accordance with user preferences. 
         [0030]    A piston assembly  28  is disposed in the bore  24  and fluid chamber  26 . The piston assembly  28  may include a piston  30  positioned at one end thereof, e.g., at or near a distal end  27  of the assembly, which piston may be provided with one or more seal  31 . The seal  31  sealingly engages the wall  33  of the bore  24  at predetermined positions within the fluid chamber  26  and reciprocates therein. The seal  31  may be one or more O-rings, for example, or umbrella seals, for example. Where two seals  31  are used, the rearmost  31 A of the two seals ( 31 A,  31 B) may be considered to define with the piston  30  and the wall  33  of the bore  24  the fluid chamber  26 , i.e., the volume of the bore that includes fluid. 
         [0031]    The piston assembly  28  is constructed and positioned within the bore  24  to reciprocate along a piston assembly axis  32 . The piston assembly  28  is preferably biased in a rest or home position by a piston assembly biasing element  64 , which may be a spring, such as a coil spring as shown. The action of the biasing element  64  may also return the lever  22  to a rest or home position. 
         [0032]    The piston assembly  28  may include a separate cap member  74 . The cap member  74  may be a barrel shaped piece that fits within the bore  24  and abuts the proximal end of the piston  30 . The cap member  74  includes a flange  76  or the like at or near the end abutting the piston. The cap member  74  may also include a non-round interior  78  that may in the form of a key hole or the like. 
         [0033]    A pushrod  80  is connected to the follower  54  at one end and contacts the piston assembly  28  at the other end. The pushrod  80  includes a head  82 . The head  82  includes a ball surface received in a corresponding interior  78  of the cap member  74  of the piston assembly  28  in a keyed relationship. The pushrod  80  may be threaded engaged with a threaded bore  62  of the fourth pin  60  at an end opposite the head  82 . 
         [0034]    The piston assembly  28  can be a single-piece as shown or formed as multiple pieces. In one example contemplated by the invention, the piston  30  may be a separate part of the assembly  28 . Alternatively, the piston  30  may be formed as a single-piece construction with the cap member  74 . 
         [0035]    The linkage  21  is operated by movement of the lever  22 , which in turn causes the piston assembly  28  to move and generate fluid pressure within the fluid chamber  26 . In the illustrated example, the linkage  21  includes a cam link member  42  attached to the lever  22  and a follower link member  54  attached to the housing  20 . 
         [0036]    In a hydraulic system, the fluid chamber  26  will be connected to a remote slave cylinder (not shown) which operates the hydraulic brake system through a hydraulic line to effect the application of fluid pressure on a brake component such as a disc brake or the like in a known manner. 
         [0037]    The brake assembly may include a piston adjustment mechanism  40  that is disposed in the housing  20 . The piston adjustment mechanism  40  includes a sleeve member  86  that is disposed about and keyed to the cap member  74 . The sleeve member  86  is also threadably engaged in the bore  24  of the housing  20 . The sleeve member  84  may be turned by a manually movable member  84  that is keyed to the sleeve member. The movable member  84 , when rotated, causes axial movement of the sleeve member  86  and movement of the sleeve member causes axial movement of the cap member  74  through interaction of the sleeve member with the flange  76  of the cap member. At the same time that the sleeve member  86  is moved axially, the pushrod  80  is translated axially the same amount and in the same direction as the cap member  74  by the threaded engagement of the pushrod in the fourth pin  60 . In this way, no slack or lash is created by adjustment of the dead band with the piston adjustment mechanism  40 . Also, the positions of the elements of the linkage  21  are unaffected. 
         [0038]    A biasing spring  120  ( FIG. 2 ) is positioned between the lever blade  22  and the lever body housing  20 . This spring  120  applies a torsional load between the lever  22  and the housing  20 . The purpose is to maintain the components of the brake and adjustment mechanisms in contact with each other. Without spring  120 , the components would be loose inside the lever and housing  20 . 
         [0039]    A ball detent mechanism  88  disposed in the housing  20  may be used to retain the dial  84  in position. The ball detent mechanism  88  includes a ball  92  urged against the dial  84  by a spring  94 . The ball detent mechanism  88  is held in the housing  20  by a screw  96  or the like. The dial  84  may have exterior features  90  formed on the outside thereof that interacts with the ball  92  to resist unintended rotation thereof. 
         [0040]    As a result of the arrangement of link members and the shape of the cam surface  44 , the elements of the linkage  21  creates a variable or changing lever blade stroke relative to the piston actuation rate. Beneficially, by altering the positional interaction of the links, this rate can be tuned to be initially higher than a conventional linear brake system and then, near the end of the lever blade stroke tuned to be at or lower than the rate of a conventional brake system. The variable rate linkage of the invention thus yields increased brake performance in accordance with a number of braking aspects. A benefit to the changing or variable rate system according to embodiments of the invention is a decreased initial brake/surface force that increases as the lever is further actuated. A brake system can thus be tuned to have less initial “bite” upon first contact of the pads to the brake surface, have moderate brake force through the mid-stroke, and then have the maximum brake force at higher user hand forces. This allows for greater control and predictability by the user. Also, the dead band of the system can be adjusted by the user without affecting the operation, performance and feel of the brake rate provided by the linkage according to the invention. 
         [0041]    While this invention has been described by reference to a particular embodiment, 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 embodiment, but that it have the full scope permitted by the language of the following claims.