FIELD OF THE INVENTION 
       [0001]    In general, the inventive arrangements relate to brakes and braking systems, and more specifically, to hydraulic brake master cylinders for bicycles or off-road vehicles. 
       BACKGROUND OF THE INVENTION 
       [0002]    The general operation of hydraulic brake master cylinders for bicycles or off-road vehicles is well known. The brake system includes a reservoir housing hydraulic fluid. The brake system operates by rotation of a lever which applies force to a piston. When force is applied, the piston slides in a longitudinal bore thereby producing an increase in hydraulic pressure in the bore which pressurizes the brake system. One or more fluid paths connect the piston bore to the reservoir. The reservoir contains a bladder that can expand and contract based on the needs of the system. 
         [0003]    When the lever is in its free state, also known as the “home” position, its distance from the handlebar is typically adjustable. Current adjusters are difficult to use and levers typically cannot be adjusted without the use of tools, such as an allen wrench. 
         [0004]    It is also critical to the bicycle industry to develop components that are smaller and lighter in weight. Reductions in the sizes, number of parts and weight of bike components, including the brake system, is advantageous since it reduces cost and overall weight. Reductions in weight enhance the appeal of the bike. 
         [0005]    Bicycle master cylinders are sometimes symmetric and are typically located in close proximity to the gear shifter. Each bike rider has his or her own individual preference for the location of the gear shifter relative to the master cylinder lever. However, the shape of the master cylinder typically limits where the gear shifter may be located. It therefore is advantageous to reduce the size of the master cylinder, specifically in the area of gear shifter actuation, to provide more placement options for the location of the gear shifter relative to the master cylinder lever. 
         [0006]    Another problem observed in the bike industry is the generation of high brake temperatures, especially during long descents. High brake temperatures expand the hydraulic fluid which requires compensation in the hydraulic fluid system. It is advantageous to make the reservoir expansion volume large enough to absorb all possible fluid expansion in the brake system. 
         [0007]    Another problem encountered by the bicycle manufacturing industry is to provide for the easy removal of air from the hydraulic system by bleeding. Bleeding air from the system can be difficult. Additionally, reorientation of the master cylinder is generally required. Some systems require removal of the reservoir cover and bladder to access the fluid. If a bleeder screw is used for bleeding purposes, it typically has an elastomeric seal that requires special geometry in the reservoir or bladder. It would therefore be advantageous to incorporate a bleeder screw that doesn&#39;t require an elastomeric seal or special reservoir and bladder geometry located in a position where reorientation of the master cylinder during bleeding is not required. 
         [0008]    As described, it is desirable to provide a substantially symmetric hydraulic brake master cylinder that is compact, light in weight, sculpted around the gear shifter, with reduced part numbers, sufficient fluid expansion capacity in the reservoir, and which provides for tool free adjustment of the lever, as well as a comfortable lever to use. Additionally, it is advantageous to improve the bleeding process by utilizing low cost bleeder screws located where reorientation of the master cylinder is not required. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to provide a master cylinder for a hydraulic brake master cylinder for a bicycle that is compact and light. 
         [0010]    It is also an object of the invention to provide a hydraulic brake master cylinder that has a reservoir shape which provides the necessary fluid volume as well as large expansion volume. 
         [0011]    It is a further object of the invention to provide a substantially symmetric hydraulic brake master cylinder that provides gear shifter operation clearance. 
         [0012]    It is also an object of the invention to provide a lever that has been sculpted to provide comfort throughout its stroke. 
         [0013]    It is a further object of the invention to provide an adjustment mechanism that allows for the modification of the lever home position without the use of tools. 
         [0014]    It is another object of the invention to provide defined increments of adjustment to the lever home position for further ease of use. 
         [0015]    It is an object of the invention to provide a lever having defined increments of adjustment through use of a pivot pin that is symmetric and utilizes low cost retention. 
         [0016]    It is a further object of the invention to provide a lever having a split end which allows for retention by a single, inexpensive clip. 
         [0017]    It is another object of the invention to provide a body having a single flange to which the split end of the lever is retained, allowing for reduced weight. 
         [0018]    It is also an object of the invention to provide for the removal of air from the brake system by bleeding without requiring reorientation of the master cylinder. 
         [0019]    Various other features, objects and advantages of the present invention will become apparent to one of ordinary skill in the art from the following detailed description taken together with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Preferred embodiments of the invention are described below with reference to the following drawings, which are provided for illustrative purposes only. The drawings illustrate a best mode contemplated for caring out the invention. In the drawings: 
           [0021]      FIG. 1  is an exploded view of the master cylinder; 
           [0022]      FIG. 2  is a front view of the master cylinder; 
           [0023]      FIG. 3  is a sectional view of the master cylinder taken along line  3 - 3  of  FIG. 2 ; 
           [0024]      FIG. 4  is a rear view of the master cylinder; 
           [0025]      FIG. 5  is a profile view of the master cylinder; 
           [0026]      FIG. 6  is a sectional view taken along line  6 - 6  of  FIG. 5 ; 
           [0027]      FIG. 7  is an exploded detail view of the adjuster; 
           [0028]      FIG. 8  is a side view of the master cylinder; 
           [0029]      FIG. 9  is a sectional view taken along line  9 - 9  of  FIG. 8 ; 
           [0030]      FIG. 10  is a detail area view taken along line  10 - 10  of  FIG. 9 ; 
           [0031]      FIG. 11  is a plan view of the lever; 
           [0032]      FIG. 12  is a sectional view taken along line  12 - 12  of  FIG. 11 ; 
           [0033]      FIG. 13  is a sectional view taken along line  13 - 13  of  FIG. 12 ; 
           [0034]      FIG. 14  is an exploded view of a second embodiment of the master cylinder; 
           [0035]      FIG. 15  is a front view of the second embodiment shown in  FIG. 14 ; 
           [0036]      FIG. 16  is a sectional view taken along line  16 - 16  of  FIG. 15 ; 
           [0037]      FIG. 17  is a plan view of the second embodiment shown in  FIG. 14 ; 
           [0038]      FIG. 18  is a detail view of the pin of the second embodiment shown in  FIG. 14 ; 
           [0039]      FIG. 19  is an end view of the pin of the second embodiment shown in  FIG. 14 ; 
           [0040]      FIG. 20  is a plan view of the lever in the second embodiment shown in  FIG. 14 ; 
           [0041]      FIG. 21  is a sectional view taken along line  21 - 21  of  FIG. 20 ; 
           [0042]      FIG. 22  is an exploded view of a portion of the third embodiment of the master cylinder; 
           [0043]      FIG. 23  is a front view of the third embodiment of the master cylinder; 
           [0044]      FIG. 24  is a sectional view taken along line  24 - 24  of  FIG. 23 ; 
           [0045]      FIG. 25  is a front view of the fourth embodiment of the master cylinder; 
           [0046]      FIG. 26  is a sectional view taken along line  26 - 26  of  FIG. 25 ; 
           [0047]      FIG. 27  is a plan view of the fourth embodiment of the master cylinder; 
           [0048]      FIG. 28  is a rear view of the body in a fifth embodiment of the master cylinder; and 
           [0049]      FIG. 29  is a profile view of the body in a fifth embodiment of the master cylinder as shown in  FIG. 28 . 
       
    
    
       [0050]    Before explaining embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0051]    In  FIGS. 1-13 , a first embodiment of a hydraulic brake master cylinder assembly  100  is shown. A body  50  is attached to a handlebar (not shown) on a bicycle or off-road vehicle by means of a clamp  51  and clamp screws  52 . A bladder  53  is fixed to the body  50  by a reservoir cap  54  and reservoir cap screws  55 . The space between the bladder  53  and the body  50  defines the reservoir fluid volume, while the space between the bladder  53  and the reservoir cap  54  defines the reservoir expansion volume. 
         [0052]    A lever  56  is pivotally attached to the body  50  by a pivot pin  57  and set screw  59 . The pivot pin  57  is necked down towards the center so that it cannot be removed when the set screw  59  is installed. The pivot pin  57  rotates relative to the body  50  on pivot pin bushings  58 . The pivot pin bushings  58  each have a flange  74  that keep them retained once the pivot pin  57  is installed and allow the lever  56  to rotate smoothly. 
         [0053]    A pushrod  63  is pivotally attached to the lever  56  by means of an adjuster nut  60 , adjuster bushings  61 , and spring washer  62 . One end of the pushrod  63  is a sphere and is engaged in a spherical pocket in the piston  67 . A retaining ring  64  fits within a groove in the body  50  and retains a washer  65  which contains a hole having a diameter smaller than that of the spherical end of the pushrod  63 . Once installed, the retaining ring  64  and washer  65  define an end stop for the pushrod  63 . 
         [0054]    The pushrod  63  is engaged with the adjuster nut  60  by threads. There are flat surfaces  63 A on the pushrod  63  and corresponding flat surfaces on the adjuster bushings  61 . The exterior of the adjuster bushings  61  are cylindrical and fit within a cylindrical pocket  75  in the lever  56 . As seen in  FIG. 7 , the adjuster nut  60  also contains cylindrical protrusions  60 A at each end coaxial to the threaded portion, the cylindrical protrusions  60 A being supported by corresponding pockets  61 B in the adjuster bushings  61 . The adjuster bushings  61  each contain a pocket  61 A which receives a detent spring  73  that reacts against surface interruptions in the cylindrical protrusions  60 A. As the adjuster nut  60  is rotated, the pushrod  63  is prevented from rotating by the flat surfaces  61 C and cylindrical exterior of the adjuster bushings  61  and therefore the adjuster nut  60  travels axially relative to the pushrod  63 . As the adjuster nut  60  is rotated, the detent spring  73  engages in the surface interruptions in the cylindrical protrusion  60 A of the adjuster nut  60 , providing distinct adjustment increments. As the adjuster nut  60  travels, it pivots within the lever  56 , forcing the lever  56  to rotate relative to the body  50  on the pivot pin  57 , and thus modifying the “home” position. 
         [0055]    An alternative embodiment for adjustment in defined increments to the mechanism of the detent spring  73  described herein is to place a detent ball  88  with the detent spring  73  into the cavity in the adjuster nut  60  where the detent ball  88  is forced by the detent spring  73  into surface interruptions in the adjuster bushings  61  to provide defined increments of adjustment. 
         [0056]    The piston  67  has an elastomeric primary seal  68  and secondary seal  66 . A spring  69  is fit at one end to the piston  67  and at the other end to the piston bore bottom  50 A in the body  50 . The volume of the piston bore  76  between the piston bore bottom  50 A and the primary seal  68  defines a first chamber and the area between the primary seal  68  and secondary seal  66  defines a second chamber. The primary seal  68  allows fluid to flow from the second chamber to the first chamber but no flow is allowed in the reverse direction. The secondary seal does not allow any fluid passage. 
         [0057]    When the lever  56  is released, the spring  69  pushes the piston  67  and pushrod  63  against the backstop of the washer  65  and retaining ring  64 . This is the initial position of the piston  67 . At this position, one or more port timing holes  79  are in the body  50  connecting the first chamber to the reservoir fluid volume. A compensating port  78  is located in the body  50  between the second chamber and the reservoir fluid volume throughout the piston  67  stroke range. A port on the body near the piston bore bottom  50 A communicates any pressure in the first chamber to the brake system. 
         [0058]    When the lever  56  is rotated relative to the body  50  (towards the handlebar), the pushrod  63  pushes the piston  67  towards the piston bore bottom  50 A which compresses the spring  69 . Once the primary seal  68  has passed the port timing hole  79 , pressure is generated in the first chamber and transmitted to the brake hose (not shown) which is connected to the body by a compression nut  71  and then covered by a nose cone  72  (see  FIG. 3 ). 
         [0059]    If the brake fluid expands due to heat generated during braking, in the initial position of the piston  67 , fluid will flow through the port timing holes  79  and into the reservoir fluid volume. The bladder  53  will deform into the reservoir expansion volume and thus increase the size of the reservoir fluid volume. 
         [0060]    In  FIG. 4 , the reservoir shape near the handlebar can be seen. By wrapping the reservoir cavity in the body  50 , the bladder  53 , and the reservoir cap  54  around the handlebar, a larger reservoir fluid volume and reservoir expansion volume is created in a compact package. In  FIG. 5 , the profile shape of the reservoir cap  54  can be seen. By adding the concave shape towards the center of the reservoir cap  54  for gear shifter operation clearance, a larger reservoir expansion volume is created near the ends of the reservoir cap  54 . 
         [0061]    In  FIG. 6 , a section of the reservoir is shown. By wrapping the reservoir fluid volume area more than 180 degrees (angle θ) around the exterior of the piston bore  76 , a larger reservoir fluid volume is created in a compact package. 
         [0062]    It has been found through testing that a reservoir expansion volume of at least 2.5 cc is preferred, although not necessary. By including the features described herein, an expansion of more than 2.5 cc is achieved without an undesirable effect on the gear shifter position relative to the hydraulic brake master cylinder  100 . Of course, other desirable effects can be achieved by obtaining a ratio of reservoir expansion volume to reservoir fluid volume in the system. Preferably, this ratio is at least 1.8 and this ratio is achieved through the invention. However, other ratios could be beneficial and are intended to be included herein. 
         [0063]    In  FIG. 10 , detail of the bleeder screw  70  installation can be seen. The bleeder screw  70  is engaged to a bleeder port in the body  50  by threads. The bleeder screw nose  77  is tapered and deforms the material in the bleeder port of the body  50  when installed, creating a low pressure fluid seal. The location of the bleeder port is on both sides of the body near the handlebar near the piston bore centerline in the reservoir fluid volume when viewed from the side (see bleeder screw  70  in  FIG. 5 ). This allows for simplified bleeding of the system without reorientation of the master cylinder  100 . 
         [0064]      FIGS. 11-13  show the detail of the finger contact area of the lever  56 . In  FIG. 11 , an hourglass shape of the finger contact area is described. In a preferred embodiment, the shape narrows in width from approximately 13.5 mm at the tip to approximately 11.5 mm near the first finger contact and then increases to approximately 15.5 mm near the inner end of the finger contact area. However, other sizes and tapering are possible and are intended to be included herein. 
         [0065]    As shown in  FIG. 12 , the finger contact area profile in a preferred embodiment has a fillet of approximately 8 mm near the tip and 12.5 mm near the inner end. The length between the fillet tangents is ideally approximately 25 mm. A flange at the tip is approximately 8.5 mm high in the preferred embodiment, thereby enhancing lever comfort for the user.  FIG. 13  shows a radius R that runs along the perimeter of the finger contact area. This radius tapers from approximately 6.5 mm at point P 1  ( FIG. 11 ) to approximately 2.5 mm at point P 2  ( FIG. 11 ). The shape of the finger contact area described above results in increased comfort for the user. However, the shape and amount of tapering can vary in degree and variations thereof are intended to be encompassed herein. 
         [0066]    A second embodiment of the hydraulic brake master cylinder  101  is shown in  FIGS. 14-21 . In this embodiment, the lever  80  is pivotally attached to the body  50  by a pivot pin  81 .  FIGS. 18-19  show details of the pivot pin  81 . The pivot pin  81  is symmetrical and has a concave pivot pin groove  87  around the circumference at each end to which a clip  82  is installed, thereby retaining the pivot pin  81  to the body  50 . Each end of the pivot pin  81  has a relief  81 A (shown in  FIG. 18 ) which allows for a tool such as a screwdriver to be inserted for easy removal of the clips  82 . The pushrod  84  is attached to an adjuster bushing  83  by threads. The adjuster bushing  83  pivots within the lever  80 . The remainder of the components of the hydraulic brake master cylinder  101  are as described in the first embodiment. 
         [0067]    To adjust the home position of the lever  80 , the pushrod  84  is rotated. The adjuster bushing  83  has a cylindrical exterior contained in a corresponding hole in the lever  80  which prevents it from rotating and thus the adjuster bushing  83  moves axially relative to the pushrod  84 . As the adjuster bushing  83  travels, it pivots within the lever  80 , thereby forcing the lever to rotate relative to the body  50  on the pivot pin  81  and thus modifying the home position. 
         [0068]    A preferred embodiment of the lever  80  is shown in  FIGS. 20-21 . The end of the lever  80  that accepts a pivot pin  81  and an adjuster bushing  83  is split into two legs  80 A. In a third embodiment, as shown in  FIGS. 22-24 , the end of the lever  80  is pivotally attached to the body  50  by a pivot pin  85  and clip  86 . The clip  86  is located between the lever legs  80 A. This arrangement allows for a reduced number of parts as well as reduced weight and improved appearance. 
         [0069]      FIGS. 25-27  show a fourth embodiment utilizing the split end of lever  80 . The body  90  has single flange  90 A that supports the pivot pin  91  and lever  80  between the lever legs  80 A. The pivot pin  91  is necked down towards the center so that it cannot be removed when the set screw  59  is installed. This arrangement allows for reduced weight, a reduced number of parts, and improved appearance. 
         [0070]    A fifth embodiment is shown in  FIGS. 28-29 . Here, the body  95  has alternate bleed port locations. The first bleed port  95 A is located on the back of the body  95  opposite the reservoir cap  54  near the handlebar in the reservoir fluid area. The second bleed port  95 B is located on the back of the body  95  opposite the reservoir cap  54  in the reservoir fluid area furthest from the handlebar. The third bleed port location  95 C is located on the side of the body  95  near the piston bore centerline (as shown) in the reservoir fluid area furthest from the handlebar. These alternate locations do not require special reservoir or bladder geometry. 
         [0071]    It is understood that the various preferred embodiments are shown and described above to illustrate different possible features in the invention and the varying ways these features may be combined. Apart from combining the different features of the above embodiments and varying ways, other modifications are also considered to be within the scope of the invention. 
         [0072]    The invention is not intended to be limited to the preferred embodiments described above, but rather is intended to be limited only by the claims setout below. Thus, the invention encompasses all alternate embodiments that fall literally or equivalently within the scope of these claims.
A hydraulic brake master cylinder is provided that is compact and light in weight. The master cylinder has a reservoir shape that provides increased reservoir expansion volume. The master cylinder also provides gear shifter operation clearance and a comfortable lever that allows easy adjustment without the use of tools. The lever has defined increments of adjustment which make it easy to use. The invention also includes a method of bleeding air from the system without requiring reorientation of the master cylinder. The retention methods for the various lever embodiments shown allow for easy and inexpensive retention of the lever and also provide for reduced overall weight and cost.