Abstract:
A caliper for a disk brake consists of a housing having first and second brake pads mounted therein to receive a brake disk therebetween. At least one of the brake pads is advanced along an advancement axis towards the other brake pads by an actuator within the housing. During actuation the brake pads impart a compression force on a brake disk disposed therebetween which results in a tensile force in the housing parallel to the advancement axis. A reinforcing member operatively engages the housing to oppose the tensile force on the housing. A method of making a caliper housing as described above consists of forming the housing as a single piece of metal and preloading the housing with a compression force parallel to the advancement axis to oppose the tensile force. Preloading may be accomplished by forming a pair of bores in the housing radially space from the advancement axis with the bores having an internally threaded portion at one end. A screw is threadably engaged with each internally threaded portion with a screw head abutting the housing about the periphery of the bore opposite the internally threaded portion.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims priority from United States Provisional Patent Application Ser. No. 60/195,560, filed Apr. 6, 2000, entitled “Mechanical Disc Brake Caliper”, the contents of which are incorporated herein in their entirety. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention is directed to bicycle disc brakes, and more particularly to a reinforced single piece caliper housing for resisting tensile forces on the housing during caliper actuation.  
         BACKGROUND ART  
         [0003]    Disc brakes are being included on more and more by bicycles as consumers are increasingly demonstrating a preference for disc brakes over conventional rim brakes such as caliper brakes, cantilever brakes and side pull cantilever brakes. While both mechanical and hydraulic disc brakes have been available for bicycles for many years, one of the greatest objections to disc brakes is that a disc brake systems weighs more than conventional rim brakes. As a result, manufacturers of disc brakes strive to minimize weight wherever possible.  
           [0004]    One way to minimize weight is to minimize the amount of material which makes up the disc brake caliper housing and to use relatively light weight material. For example, early prior art single piece caliper housings were made of steel whereas aluminum, having a significantly lesser weight, is preferred. However, one problem with an aluminum housing, particularly a single piece housing, is that it is less resistant to tensile forces than a steel housing. Tensile forces are applied to the caliper housing when brake pads within the housing are actuated to compress a disc therebetween. One way of resisting these tensile forces is to increase the amount of material used in the single piece caliper housing. However, this is directly contradictory to the goal of minimizing housing weight, and further leads to a bulkier appearing housing. Furthermore, use of lightweight and relatively soft materials such as aluminum in the housing allows for flexure of the housing that can dissipate braking power and fatigue the housing. Thus, there is a need for a single piece caliper housing structure that is durable, strong, has a good stiffness to weight ratio and is inexpensive. Known two piece caliper housings provide screws to hold the cam halves together, but a two piece housing is considerably more expensive than a single piece housing to manufacture.  
           [0005]    The present invention is directed to overcoming one or more of the problems discussed above.  
         SUMMARY OF THE INVENTION  
         [0006]    The first aspect of the invention is a caliper for a disc brake. The caliper consists of a single piece housing containing first and second brake pads mounted therein to receive a brake disc therebetween. At least one of the brake pads is advanced along at an advancement axis toward the other brake pad by an actuator. During actuation the brake pads impart a compression force on a brake disc disposed therebetween, which results in a tensile force in the single piece housing parallel to the advancement axis. A reinforcing member operatively engages the housing to oppose the tensile force on the housing. The reinforcing member is preferably a screw received in a bore in the housing. The bore has an internally threaded portion at one and the screw has a head abutting the housing about the periphery of the bore at a side of the bore opposite the threaded portion. The portion of the screw opposite the head threadably engages the threaded portion of the bore. Preferably a pair of screws engage identical bores spaced radially relative to the advancement axis. The screws are preferably tightened to preload the housing by imparting a compression force on the housing before the actuator advances the brake pads to impart a compression force on the brake disc. The preloaded compression force is preferably between about 1,000-1,400 pounds per screw. The caliper is preferably made from metal, for example aluminum, in a single piece.  
           [0007]    A second aspect of the invention is a method of making a single piece caliper housing for a disc brake assembly. The single piece caliper housing defines a pair of opposing recesses for receiving brake pads on opposite sides of a disc and a cylinder for receiving an actuator advancing at least one of the brake pads along an advancement axis to exert a compression force on a disc disposed between the brake pads. Application of the compression force imparts a tensile force to the housing parallel to the advancement axis. The method consists of forming the housing as a single piece of metal and preloading the housing with a compression force parallel to the advancement axis to oppose the tensile force. The step of preloading the housing may consist of forming a pair of bores in the housing radially spaced from the advancement axis, the bores having an internally threaded portion at one end. A screw is threadably engaged with each internally threaded portion with a screw head abutting the housing about the periphery of the bore opposite the internally threaded portion. The screw is preferably tightened to apply a preloaded compression force of about 1,000-1,400 pounds to the housing.  
           [0008]    The present invention provides a reinforced single piece housing for opposing tension forces on the housing resulting from actuation of the caliper. Reinforced or preloading the caliper housing in accordance with the present invention allows the housing itself to be made of a relatively lightweight material, thereby minimizing the weight of the caliper. The reinforcing members themselves are preferably steel screws which are sufficiently axially rigid to bear the tensile forces otherwise applied to the housing without significantly stressing the housing. Not only does this prevent cracking or failure of the housing, it virtually eliminates any flexure of the housing that could dissipate braking power or fatigue the housing. This is accomplished while minimizing housing weight. Use of steel screws in accordance with the present invention also provides a low cost and highly reliable single piece housing. The structure has a significant cost advantage over a two piece housing held together by screws because it minimizes machining costs of the housing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a perspective view showing the ball bearing mechanical disc brake caliper of the present invention mounted to a fork of a bicycle in operative engagement with a brake disc;  
         [0010]    [0010]FIG. 2 is the ball bearing mechanical disc brake caliper of FIG. 1 including an adaptor for mounting to a frame with different mounts;  
         [0011]    [0011]FIG. 3A is a front elevation view of the ball bearing mechanical disc brake caliper of FIG. 1 including a floating cable stop;  
         [0012]    [0012]FIG. 3B is identical to FIG. 3A except it further includes an alternate embodiment of the floating cable stop;  
         [0013]    [0013]FIG. 3C is a cross-section of the floating cable stop taken along line  3 C- 3 C of FIG. 3A;  
         [0014]    [0014]FIG. 4A is an exploded perspective view of the ball bearing mechanical disc brake caliper of FIG. 1;  
         [0015]    [0015]FIG. 4B is an exploded perspective view from a perspective rotated 180° from that of FIG. 4A;  
         [0016]    [0016]FIG. 4C is a bottom perspective view of a clamp plate in accordance with the present invention;  
         [0017]    [0017]FIG. 5 is a cross-section of the ball bearing mechanical disc brake caliper taken along line  5 - 5  of FIG. 3A with the brake pads retracted;  
         [0018]    [0018]FIG. 6 is the same as FIG. 5 only with the brake pads extended using the pad wear compensation apparatus;  
         [0019]    [0019]FIG. 7 is the same as FIG. 5 only it illustrates the brake pads advanced by the drive mechanism into contact with a disc;  
         [0020]    [0020]FIG. 8 is a cross-section of the ball bearing mechanical disc brake caliper taken along line  8 - 8  of FIG. 3A;  
         [0021]    [0021]FIG. 9 is a cross-section of the ball bearing mechanical disc brake caliper taken along line  9 - 9  of FIG. 8;  
         [0022]    [0022]FIG. 10 is a right side view of the ball bearing mechanical disc brake caliper with the lever arm in an at rest position;  
         [0023]    [0023]FIG. 11 is a right side elevation view of the ball bearing mechanical disc brake caliper with the lever arm actuated to the braking position;  
         [0024]    [0024]FIG. 12 is a cross-section of the cable feed taken along line  12 - 12  of FIG. 10;  
         [0025]    [0025]FIG. 13 is a front exploded view of the cable feed;  
         [0026]    [0026]FIG. 14 is an exploded view of the outer indexing knob assembly;  
         [0027]    [0027]FIG. 15 is an exploded view of the inner indexing knob assembly;  
         [0028]    [0028]FIG. 16A is a perspective view of the ball bearing mechanical disc brake caliper with a portion of the housing cut away to reveal the pad receiving cavity;  
         [0029]    [0029]FIG. 16B is a sectional view of the ball bearing mechanical disc brake caliper taken along line  16 B- 16 B of FIG. 10;  
         [0030]    [0030]FIG. 17A-C are alternate embodiments of the backing plates of the brake pad assemblies;  
         [0031]    [0031]FIG. 18 is identical to FIG. 16, only showing the pad assembly installed with the pad assembly recess;  
         [0032]    [0032]FIG. 19 is a perspective view of the outer knob;  
         [0033]    [0033]FIG. 20 is a perspective view of the outer knob from a perspective rotated  180 ° from that of FIG. 19;  
         [0034]    [0034]FIG. 21 is a perspective view of the inner knob;  
         [0035]    [0035]FIG. 22 is a perspective view of the inner knob taken from a perspective rotated 180° from that of FIG. 21;  
         [0036]    [0036]FIG. 23 is a front view of the lever arm illustrating the progressive, eccentric shape of the cable guide surface;  
         [0037]    [0037]FIG. 24 is a front view of the lever arm illustrating the constant, concentric shape of the cable guide surface;  
         [0038]    [0038]FIG. 25 is a perspective view of a ball retainer;  
         [0039]    [0039]FIG. 26 is a sectional view of a ball retainer taken along line  26 - 26  of FIG. 25 with a ball engaged therein;  
         [0040]    [0040]FIG. 27 is a perspective view of an alternate embodiment of a ball retainer;  
         [0041]    [0041]FIG. 28 is a sectional view taken along line  28 - 28  of FIG. 27 with a ball engaged by the retainer; and  
         [0042]    [0042]FIG. 29 is a plan view of an alternate embodiment of ramped grooves in a fixed cam.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0043]    A ball bearing mechanical disc brake caliper  10  in accordance with the present invention is shown in FIG. 1 mounted to a frame or, more particularly, a front fork  12  of a bicycle in operative engagement with a disc  14 . As shown in FIGS.  1 - 3 , the caliper  10  is mounted to a front fork  12  for use with a front wheel. For use with the rear wheel, the caliper is typically mounted to the seat stay, chain stay, drop out plate, after market adapter or the like. The disc  14  in turn is rigidly mounted to the hub of a wheel assembly by the bolts  16 . For the sake of clarity, the bicycle wheel and hub are not shown.  
         [0044]    The ball bearing mechanical disc brake caliper consists of a caliper housing  18  having a pair of mounting feet  20 ,  22  extending therefrom for attachment to a corresponding pair of internally threaded attachment bosses  24 ,  26  which extend from the front fork  12 . A pair of mounting bolts  28  secure the mounting feet  20 ,  22  to the attachment bosses  24 ,  26 . The mounting feet preferably include elongate slots  27  (see FIG. 5) receiving the mounting bolts  28  and complimentary pairs of concave/convex washers  30  to provide for adjustable attachment of the ball bearing mechanical disc brake caliper to a bicycle frame. Such an attachment structure is described in detail in applicant Wayne Lumpkin&#39;s, co-pending patent application Ser. No. 09/383,121, the disclosure of which is hereby incorporated in its entirety herein.  
         [0045]    As seen in FIG. 1, a lever arm  32  is pivotably attached at a first end  34  to the caliper housing  18 . A second end of the lever arm  36  has a cable clamp  38  which secures an end of the cable  40 . The cable  40  is directed through a cable feed  42  attached to the caliper housing  18  with a cable housing  44  abutting the cable feed  42 . While the operation of the ball bearing mechanical disc brake will be described in considerably greater detail below, it is useful at the outset to understand that the ball bearing mechanical disc brake caliper is actuated by tension being applied to an opposite end of the cable  40  by a cable actuator such as a conventional cable brake lever (not shown) and this tension causes the lever arm  32  to pivot about pivot axis  46  in the direction of arrow  48  so that the second end of the lever arm  36  is drawn toward the cable guide  42  to advance a brake pad into contact with the disc  14  by a rotary to linear linkage between the first end  34  of the lever arm  32  and the brake pad.  
         [0046]    [0046]FIG. 2 shows the ball bearing mechanical disc brake caliper  10  mounted to a front fork  12 ′ having internally threaded attachment bosses  24 ′ and  26 ′ with an axis parallel to the axis of rotation of the disc  14 . The ball bearing mechanical disc brake caliper  10 ′ is in all manner identical to the ball bearing mechanical disc brake  10  described above with regard to FIG. 1. For simplicity, all unnecessary corresponding reference numbers have been omitted. An adapter bracket  60  is fastened by a pair of bolts  62  to the attachment bosses  24 ′,  26 ′ and includes a pair of internally threaded receptor bores  64  that enable the caliper housing  18  to be attached to the front fork  12 ′ in an identical position relative to the disc  14  described above with respect to FIG. 1. Thus, the adapter bracket provides an equivalent mounting surface to that provided by the attachment bases  24 ,  26 , as shown in FIG. 1.  
         [0047]    [0047]FIG. 3A is a front elevation view of the ball bearing mechanical disc brake caliper  10  mounted to a bicycle frame  12  as illustrated in FIG. 1. FIG. 3 differs from FIG. 1 by the inclusion of the floating cable stop  70 , which will be described in greater detail below.  
         [0048]    The ball bearing mechanical disc brake caliper  10  is shown in an exploded perspective view in FIG. 4A. FIG. 4B is identical to FIG. 4A, only the perspective is rotated 180°. First and second brake pad assemblies  72 ,  74  consist of mirror image backing plates  76 ,  78  each having a trailing surface  80  including a post receiving receptacle  81  and a leading surface  82  to which a brake pad  84  is permanently adhered. When the ball bearing mechanical disc brake caliper is operatively associated with a disc  14 , the disc  14  resides between the pads  84  of the first and second brake pad assembly  72 ,  74  which are held in place in part by a pad retention clip  85  in a manner which will be described in greater detail below.  
         [0049]    As oriented in FIG. 4A, the second brake pad assembly  74  is also known as the back or inboard brake pad assembly. A pad wear compensator  73  for the inboard pad assembly includes inboard pressure foot  86 , which as discussed below, functions as an indicator. The inboard brake pad assembly  74  is attached to the inboard pressure foot  86  by means of a washer-shaped magnet  88  which is adhered to a cooperatively shaped receptacle  90  in the leading surface  92  of the inboard pressure foot  86 . An axial post  94  extends through the hole in the washer-shaped magnet  88  and protrudes beyond the leading surface  92  to engage the post receiving receptacle  81  in the trailing surface of the backing plate. A trailing portion or indicator dog  96  having a rectangular cross-section extends from a trailing surface of the inboard pressure foot  86  along the same axis of the axial post  94 . The edge of the inboard pressure foot  86  is threaded as indicated at  100  between the leading surface  92  and the trailing surface  98 . The threads  100  are sized to threadably engage complimentary threads  102  in the inner diameter of an inside cylinder  104  of the caliper housing  18  (see FIGS. 4B and 5). This threaded engagement allows for linear advancement of the pressure foot as it is rotated. An inboard pad advancement adjustment knob  106  has knurled edge  108 , an axial orifice or hole  110 . The axile hole is configured snugly, axially, slidably receive the indicator dog  96  of the inboard pressure foot  86  but to prevent rotation between the pressure foot and the adjustment knob. A plurality of axially inward extending legs  112  having radially outwardly extending barbs  114  at their distal ends. An inside indexing spring clip  116  has a plurality of radially extending legs  118  sized to be received between the axially inwardly extending legs  112  of the inner knob  106 . The inside indexing spring clip  116  further includes axially inwardly extending bars  122  having radially outward extending detents  123  at their distal ends. As best seen in FIG. 5, the dog  96  extends through the hole  126  in the inside indexing spring clip  116  and into the axial hole  110  in the inner knob  106 . The barbs  114  engage an inner edge of an inward extending annular flange  125  to lock the inner knob  106  against axial movement. The detents  123  in turn engage equally circumferentially spaced indexing knurls  127  in the inner surface of the flange  125 . As will be described below, the complimentary detents and indexing knurls provide a tactile indication of pad adjustment as the inboard knob  106  is rotated.  
         [0050]    With continued reference to FIGS. 4A, 4B and  5 , the caliper housing  18  also includes an outboard cylinder  128  which is coaxial with the inboard cylinder  104 . The bulk of the remaining components of the ball bearing mechanical disc brake caliper  10  reside within the outboard cylinder  128 . The outboard cylinder  128  has an annular groove  130  (see FIG. 4B) in its inner diameter sized to receive the hoop-shaped polymer dust seal  132 . Outboard pressure foot  134  has an identical leading surface to the leading surface  92  of the inboard pressure foot  86  and identical reference numbers are used in FIG. 4B. Washer-shaped magnet  88 ′, which is identical to washer-shaped magnet  88 , is adhered within the cooperative shaped receptacle  90  of the leading surface  92  of the outer pressure foot  134 . The outside or first brake pad assembly  72  is attached by the washer-shaped magnet  88 ′ to the leading surface of the outer pressure foot  134 . The trailing surface  136  has an axially extending post  138  having an annular groove  140  in its sidewall near the distal end. In the distal end is an axial cup  142 . Split ring  144  is sized to be received in the annular groove  140 . Ball bearing  146  is sized to be received in and to extend axially from the axial cup  142 .  
         [0051]    An indicator foot screw  148  has a head  149  with a leading surface  150  which abuts the ball bearing  146 . Behind the head  149  is a shaft  152  which is threaded adjacent to the head  149  as indicated at  154 . The trailing end of the shaft  152  has a pair of flats  156  (one shown in FIG. 4A) on opposite sides. The indicator foot screw  148  is an integral part of a pad wear compensator  153  for the outboard brake pad assembly.  
         [0052]    Drive cam  158  has an enlarged diameter base  160  having a plurality of equally spaced curved, ramped grooves  162  in its trailing surface. The preferred embodiment has three ramped grooves  162  spaced at 120°. A cylindrical shaft  164  extends rearward of the enlarged diameter base  160  and has an axial bore  166  which extends axially through the drive cam  158 . As best viewed in FIG. 5, the axial bore includes a threaded inner diameter portion  168  which threadably engages the threaded portion  154  of the foot screw  148  with the shaft  152  extending rearwardly from the axial bore  166 . Further referring to FIG. 5, an inwardly extending flange  170  acts as a stop against a rearward portion of the head  149 . The distal end of the outside cylindrical shaft  164  is threaded at  172  and adjacent the treaded portion  172  is a hex portion  174 . One of three ball bearings  176  resides in each ramped groove  162 . The outer diameter of the enlarged diameter base  160  is sized to fit snugly within the inner diameter of the outside cylinder  128  and have a sealing relationship with the dust seal  132  as best seen in FIGS. 5 and 7.  
         [0053]    Fixed cam  178  has a generally cylindrical body  180  with a constant inner diameter orifice  182 . An intermediate step  184  has a spring tension limiting boss  186  which extends axially onto the cylindrical body  180 . A leading step  188  has an outer diameter greater than that of the intermediate step  184  and an enlarged outside diameter annular flange  190  rises from the leading step  188  adjacent the intermediate step  184 . A locking boss  192  extends toward the leading surface  193  collinearly with the spring tension limiting boss  186  at a height matching that of the enlarged outer diameter annular flange  190 . The locking boss  192  is sized to key into a receiving slot  194  in the inner diameter of the outside cylinder  128  to lock the fixed cam  178  against axial rotation (see FIG. 4A). In addition, the leading surface of the enlarged outer diameter annular flange  190  abuts a step  196  in the inner diameter of the outside cylinder  128  to halt axial insertion of the fixed cam  178  into the outside cylinder  128  from the opened end as viewed in FIG. 4A. The engaged relationship can best be seen in FIG. 5. The leading surface  193  of the fixed cam  178  is best viewed in FIG. 4B. The leading surface has a plurality of equally circumferentially spaced ramped grooves corresponding to the ramped grooves of the drive cam  158 . FIG. 4B shows three ramped grooves  200  spaced at 120° which correspond to the ramped grooves  162  of the drive cam  158 , only with the ramps extending circumferentially in opposite directions when aligned as shown in FIGS. 4A, 4B and  5 - 7 . A ball bearing  176  resides between each ramped groove pair  162 ,  200  as best viewed in FIGS.  5 - 7 . Referring to FIG. 5, with balls residing in the grooves  162 ,  200 , the grooves and ball bearings act as an angular contact bearing which is able to accommodate axial loads on the drive cam exerted by the lever arm  32 . In addition, the ramped grooves self-center the drive cam shaft  164  within the inner diameter  182  of the fixed cam  178  with the drive cam under an axial load. This feature eliminates the need for an optional split bushing (not shown) being press fit in the inner diameter  182  of the fixed cam  178 . It further eliminates friction between the drive cam shaft  164  and fixed cam  178 . It further reduces needs for tight tolerances between the drive cam shaft  164  and fixed cam  178 , thus eliminating the need for costly centerless grinding of the drive cam shaft and reaming of the fixed cam bore  182 . These combined advantages significantly improve performance and minimize parts cost and assembly complexity and attendant cost.  
         [0054]    When the fixed cam is seated within the outside cylinder  128  as described above and as viewed in FIG. 5, it is locked against axial movement by locking ring  204  which has a threaded outer diameter  206  and evenly spaced engagement slots  208  in the inner diameter  210 . The inner diameter is sized to snugly receive the intermediate step  184  of the fixed cam  178  and the engagement slots  208  allow for engagement by a special turning tool (not shown) so that the threaded outer diameter  206  can be brought into threaded engagement with corresponding threads  212  in the inner diameter of the outside cylinder  128 .  
         [0055]    A generally washer-shaped spring tension biasing plate  220  has an inner diameter which snugly axially receives the intermediate step  184  of the fixed cam  178  and includes a spring tension limiting slot  222  which receives the spring tension limiting boss  186 . A cut in the outer diameter of the spring tension biasing plate forms a stop surface  224 . Near the stop surface  224  is a hole  226 . Return spring  228  has a pair of axially extending ends  230 ,  232 . The inner diameter of the return spring  228  is large enough to axially receive the fixed cam  178  and the shaft  164  of the drive cam  158  as best viewed in FIG. 5. The axially extending end  230  is received in the hole  226  of the spring tension biasing plate  220  (see FIG. 5). A dust seal  234  defines an annular cover  236  for the return spring  228  as seen in FIGS.  4 B and FIGS.  5 - 7 . The inner diameter of the trailing orifice  238  is sized to receive and have a sealing relationship with the outer diameter of a leading flange  240  of the lever arm  32 . A hole  242  in the trailing surface of the cover  236  receives the axially extending rod  232 . The axially extending rod  232  in turn is received in the hole  244  near the first end  34  of the lever arm  32 .  
         [0056]    A hex orifice  246  near the first end  34  of the lever  32  axially receives the hex portion  174  of the cylindrical shaft  164  of the drive cam  158  with a hex inner diameter washer  248  therebetween to radially fix the lever arm  32  to the drive cam  158 . Washer  252  abuts the trailing surface  254  and is sandwiched by a larger outer diameter washer  256 . The larger outer diameter washer  256  has a number of equally circumferentially spaced indexing knurls  258  in its outer diameter. The washers  252 ,  256  and the lever arm  32  are axially secured to the cylindrical shaft  164  of the drive cam  158  by nut  260  which threadably engages the threaded portion  172  of the cylindrical shaft  164 .  
         [0057]    An outboard knob  264  has a knurled edge  266  and an orifice or axial hole  268  sized and dimensioned to snugly receive the flats  156  of the trailing end of the foot screw  148  therein, as illustrated in FIG. 5. Referring to FIG. 4B, a plurality of axially inwardly extending legs  270  are equally circumferentially spaced in an inside surface of the outer knob  264 . At the distal end of each axially inwardly extending leg  270  is an inwardly protruding barb  272 . An outside indexing spring clip  274  has a plurality of axially extending bars  276  each having an inwardly extending detent  278  near its distal end. The axially extending bars  276  are sized to snugly fit between the axially inwardly extending legs  270  of the outboard knob (see FIG. 4A). With the outside indexing spring clip axially engaged with the outer knob  264  in the orientation illustrated in FIG. 4A, the outer knob  264  is axially advanced over the nut  260  and the inwardly protruding barbs  272  lockingly engage the outer diameter edge of the large outer diameter washer  256  to lock the outer knob  264  against axial movement. When attached in this manner, the inwardly extending detents  278  of the outside indexing spring clip engage the indexing knurls  258  of the larger outer diameter washer  256 . This can be best seen in detail with reference to FIGS. 14 and 5. As will be described further below, the complimentary detents and indexing knurls provide a tactile indication of pad advancement as the outboard knob  264  is rotated.  
         [0058]    With reference to FIGS. 4A, 12 and  13 , the cable feed  42  consists of a mount  284  which is preferably integrally cast with the housing  18 . The mount  284  includes an orifice  286  centered along a guide axis  288 . A cylindrical housing stop ferrule  290  has a cylindrical main body  292  having an outer diameter dimensioned to fit freely yet snugly within the orifice  286 . A minor boot retention barb  294  extends axially from a leading end of the housing stop ferrule. A major boot retention barb  296  extends axially from a trailing end of the housing stop ferrule  290 . An annular retention flange  298  extends radially from the main body  292  adjacent to the major boot retention barb  296  and forms a stop which halts axial insertion of the housing stop ferrule  290  into the orifice  286 , as best seen in FIG. 12. Further referring to FIG. 12, the inside of the housing stop ferrule  290  has a trailing portion having an inner diameter slightly larger than that of a standard cable housing to axially receive the cable housing  44  therein. An annular flange  302  extends inwardly to define a cable guide orifice  304 . The inner diameter of the minor boot retention barb  306  is of a size between that of the trailing inner diameter  300  and the cable guide orifice  304 .  
         [0059]    A hollow minor retention boot  310  is molded of an elastimeric material and at its trailing edge has an inwardly extending annular flange  312  configured to lockingly engage with the minor boot retention barb  294  of the housing stop ferrule  290 . With the housing stop ferrule  290  inserted in the orifice  286  as illustrated in FIG. 12 and the minor retention boot mounted with the inwardly extending annular flange  312  engaging the minor boot retention barb  294 , the housing stop ferrule is secured against removal from the orifice  286 . The minor retention boot has a leading nipple  314  having a leading hole  316  with an inner diameter slightly less than the outer diameter of the standard bicycle brake cable  40 . In this manner, the leading nipple forms a wipe seal with the brake cable  40  as seen in FIG. 12.  
         [0060]    A hollow major retention boot  320  molded of an elastomeric material has an inwardly extending annular flange  322  sized to lockingly engage with the major boot retention barb  296  on the trailing end of the housing stop ferrule  290  as best viewed FIG. 12. The trailing end  324  has a tapered inner diameter, which at the extreme trailing end is slightly smaller than the outer diameter of the standard cable housing to form a sealing relationship therewith.  
         [0061]    With the lever arm  32  pivotably attached to the housing as illustrated in FIGS.  1 - 3 B,  10  and  11 , a curved horn  330  defining an axially flat, circumferentially curved cable guide surface  332  extends from a trailing end of the second end  36  of the lever  32 . The curved horn  330  curves about the axis of rotation  46  of the lever arm  32 . In the preferred embodiment, the curved horn is eccentric about the axis as illustrated schematically in FIG. 23 to provide for progressive increase in power as the lever is actuated by a cable  40 . Alternatively, the curved horn can be concentric as shown in FIG. 24 or eccentric and regressive, which though not illustrated, would require the curved horn to have an increasing radius as it extends toward its free end, essentially the opposite of the progressive horn illustrated in FIG. 23.  
         [0062]    The cable clamp  38  consists of a screw  334  having a threaded shaft  336  sized to threadably engage an internally threaded bore in the lever arm  32  having an axis normal to the axis of rotation  46 . In the preferred embodiment, a clamp plate  338  is secured between the head of the screw  334  and the second end  36  of the lever arm  32 . The clamp plate has a tab  340  which is received in a notch  342  defined in the distal end of the lever arm  32  to fix the clamp plate against rotation. A groove  344  is formed in the underside of the clamp plate adjacent to the notch  342  to receive the cable  40  and has a number of protrusions  345  extending therein to improve the grip of the cable, as illustrated in FIG. 4B.  
         [0063]    The curved horn  330  is configured so that with the ball bearing mechanical disc brake caliper installed on a bike frame as illustrated in FIGS.  1 - 3 B, the guide axis  288  is essentially tangent to the free end of the curved horn  330 . Essentially tangent means a cable  40  does not have a significant bend when it contacts the cable guide surface  332 , but instead has a very gradual transition to the cable guide surface  332  as viewed in FIG. 3. When tension is applied to the cable  40  by a tension actuator such as a conventional bicycle brake lever, the lever arm  32  is drawn toward the cable feed  42 . Because of the circumferentially curved cable guide surface  332 , the fixed cable clamp and the fixed cable feed  42 , no sharp bends are introduced to the cable  40  which might fatigue the cable and lead to premature failure of the cable, which could have disastrous results for a user.  
         [0064]    In the embodiment illustrated in FIG. 1, the conventional cable housing extends from the trailing end of the major retention boot  320 . An improvement to this conventional brake setup is to provide a floating cable stop  70  mating with the trailing inner diameter  300  of the housing stop ferrule  290  as illustrated in FIG. 3A as part of a bicycle cable guide system. The floating cable stop  70  consists of a axially and radially rigid tube  348  made of a suitable material such as a metal like aluminum or stainless steel or an exceptionally rigid thermoplastic. As used herein, axially and radially rigid means the tube  348  has sufficient rigidity that it will not radially buckle about its lengthwise axis upon application of tension within the normal range of operating tensions applied to the cable  40  which runs within the tube  348 . In the preferred embodiment, the tube  348  has a standard cylindrical cross-section (see FIG. 3C), although other cross-sections may be useful or desired. The outer diameter is preferably essentially the same to that of a standard cable housing  44  so that it can fit into a trailing end of the housing stop ferrule  290  in the same manner as the housing  44  as illustrated in FIG. 12. This forms an axially fixed connector for the tube  348 . A connector ferrule  350  connects the tube  348  to a conventional cable housing  44 . This combination forms another axially fixed connector for the tube  348 . The conventional cable housing allows the cable to be radially deflected as may be required to attach the cable to a brake lever. A significant advantage of the floating cable stop  70  is that when it replaces conventional cable housings, it provides a straight path for the cable inside with minimal or no contact with the inner diameter of the tube. Over all but the shortest of lengths, the axially flexible cable housing will radially buckle about the lengthwise axis under application of even minor tension to the cable within and the resultant compression to the cable housing. Elimination of this buckling further reduces contact of the cable with the inner diameter of the tube and serves to further minimize friction on the cable. The floating cable stop can be deployed wherever there is a straight length of cable, independent of fixed housing stops on the bicycle frame. It also provides a protective barrier for the cable, much like conventional cable housing, but at a lesser weight.  
         [0065]    In a preferred embodiment illustrated in FIG. 3B, a small length of conventional housing  352  is disposed between the tube  348  and the housing stop ferrule  290  and is joined to the tube  348  by connector ferrule  354  to form an axially fixed connector. The transition housing  352  is advantageous because it will radially flex in the event of a lateral blow to the tube  348  and thereby minimize the risk of bending of the tube  348  which would detract somewhat from its performance and could even result in undesired radial buckling of the tube  348 . Preferably, the transition housing  352  is of a length that will not radially buckle under application of operating tensions to the cable  40  but will still provide sufficient radial flexibility to protect the tube  348 . Alternatively, if required, the transition housing  352  could be long enough to bend the cable as required to properly direct the cable to the cable feed. Or, an apparatus such as the ROLLAMAJIG, manufactured to Avid, L.L.C., of Englewood, Colo., U.S. Pat. No. 5,624,334, the disclosure of which is hereby incorporated by reference, could be substituted for the transition housing to minimize friction where a bend is required to direct the cable.  
         [0066]    It should be apparent to those skilled in the art that floating cable stop  70  could be deployed on any cable actuated bicycle component, including cantilevered brakes, caliper brakes, side pull caliper brakes and derailuers.  
         [0067]    The first and second brake pad assemblies  72 ,  74  are made to be removable from the caliper housing when a rotor is not operatively associated with the caliper housing between the brake pad assemblies. Referring to FIG. 16A, a retention structure for the first and second brake pad assembly  72 ,  74  is illustrated. The caliper housing has a cavity  360  configured to receive the disc or rotor  14 . The cavity  360  has a mouth  362  at a leading end and includes a pair of opposing recesses  364  (one shown in FIG. 16A). The recesses  364  are configured to nest the backing plates  76 ,  78  of the brake pad assemblies  72 ,  74  on opposite sides of the disc so that the friction pads  84  can be brought into and out of engagement with the disc by an actuating or drive apparatus along an advancement axis  366  in a manner that will be described in greater detail below. At a leading end  368  of pad assembly  72  is a retention tab  370  formed from a pair of extending posts  372 ,  374  having oppositely extending protrusions  376 . Referring to FIG. 16B, within the cavity  360  opposite the mouth  362  is a retention clip cavity  378  opening into the cavity  360 . Engagement flanges  380  extend from opposite sidewalls of the retention clip cavity. Pad retention clip  85  is shown in FIG. 16A installed within the retention clip cavity  378 . The pad retention clip  85  has a base  382  with a pair of extending sidewalls or legs  384 ,  386  with a retention detent  388  near the far end of each leg protruding inwardly. Near the base  282  a plurality of retention barbs  390  extend laterally from the sidewalls or legs  384 ,  386 . As illustrated in FIG. 16B, these retention barbs  390  are configured to snap fit with the engagement flanges  380  to lock the pad retention clip  85  within the retention clip cavity  378 .  
         [0068]    Referring back to FIG. 16A, the pad assembly  72  is installed by grasping the handle  392  and advancing the leading edge  368  into the mouth  362  along the engagement axis  394  and aligning the retention tab  370  with the pad retention clip  85  and further advancing the pad assembly so that the protrusions  370  mate within the retention detents  388 . The pad can then be slid into the recess  364  along the advancement axis  366  to seat the pad assembly within the recess  364 , as viewed in FIG. 18. When seated in this manner, the walls of the recess  364  secure the pad assembly against movement transverse the advancement axis  366  as a rotating disc is engaged. As best viewed in FIG. 5, it should be appreciated that the axial post  94  of the respective inboard or outside pressure foot  86 ,  134  is received within the receptacle  81  and the trailing surface  80  of the backing plates to thereby prevent withdrawal of the pad assembly from the mouth  362  of the cavity  360  with the brake pad seated as illustrated in FIG. 18. This connection is also the primary support against withdrawal along the engagement axis as the pad assembly is advanced and withdrawn by the actuation mechanism. The magnet  88  or  88 ′ holds the backing plate in abutment with the respective pressure foot  86 ,  134  to maintain engagement between the axial post  94  and the receptacle  81 . As the brake pads are advanced along the advancement axis, the cooperating engagement flanges  380  of the pad retention clip and the protrusions  376  of the pad retention tab define a rail facilitating movement forward and backward along the advancement axis. The pad clips can be easily removed from the orifice simply by manually advancing them inward along the advancement axis to bring the receptacle  81  out of engagement with the axial post  94  whereupon the engagement flanges  380  can be snapped out of engagement with the protrusions  376 . As shown in FIGS. 16A and 16B, the handle  392  has straight edges. To facilitate gripping, the handle may be modified as shown in FIGS.  17 A-C. In FIG. 17A, the handle has a distal enlargement  395 . In FIG. 17B, the handle has grooves  396 . In FIG. 17C, the handle has knurls or bumps  397 . Other grip enhancing structures will also be apparent to those skilled in the art.  
         [0069]    The operation of the ball bearing mechanical disc brake caliper  10  drive mechanism is best understood with reference to FIGS. 1, 5,  6 , and  7 . Upon actuation of the lever arm  32  by tension applied to the cable  40 , the lever arm rotates about the pivot axis  46  in the direction of arrow  48 . This in turn causes rotation of the drive cam  158  about this same axis. As the drive cam  158  is rotated, the ball bearings  176  cause the drive cam to advance within the outside cylinder  128  which in turn advances the foot screw  148  which is threadably engaged with the drive cam. The leading surface  150  of the foot screw  148  in turn advances the ball bearing  146  and the outside pressure foot  134  to urge the pad  84  of the outside brake pad assembly  72  into contact with the disc. Further advancement will deflect the disc  14  into contact with pad  84  of the outside brake pad assembly  74 , as illustrated in FIG. 7. Upon release of the tension in the cable, the lever arm is biased back to its at rest position by the return spring  228  and the pads are retracted out of contact with the disc to reassume the position illustrated in FIG. 5.  
         [0070]    [0070]FIG. 10 illustrates that with the lever arm  32  in an at rest position, the cable extends between the cable clamp  38  and the cable feed  42  at a slight angle. With the lever arm  32  rotated about the pivot axis in the direction of arrow  48  so as to bring the pads into engagement with the disc, the lever arm advances axially along the advancement axis with the outer brake pad assembly  72  so that this slight angle is eliminated, as seen in FIG. 11. Thus, it is desirable that the axially flat, circumferentially curved cable guide surface  332  be wide enough in the axial direction to accommodate the axial movement of the lever arm  32 . As the pads wear, it may be necessary or desirable to advance the pressure feet within the inboard and outboard cylinders to maintain the original spacing between the pads and the disc. The present invention provides a pad wear compensating apparatus that allows for such advancement (or retraction) by rotary to linear linkages between the knobs  106 ,  264  and the respective pressure feet  86 ,  134  and associated pads.  
         [0071]    As described above, the pad wear compensator includes inboard pressure foot or inboard indicator  86  which is threadably engaged with the sidewall of the inside cylinder. Rotation of the inner knob  106  in a clockwise direction advances the pressure foot within the cylinder and therefore the pad assembly along the advancement axis as illustrated in FIG. 6. As the pressure foot is advanced, the trailing end or indicator dog  96  received in the axial hole  110  of the inside knob  106  advances, to provide both a visual and tactile indication of the amount the pressure foot has advanced within the inside cylinder. In addition, the radially outwardly extending detents  124  of the inside indexing spring clip  116  engage with equally circumferentially spaced knurls  126  in the inner diameter of the flange  125  to provide a tactile indication of movement of the knob. The knurls  126  and radially outwardly extending detents  124  are spaced so that each engagement between the detents and sockets indicates a uniform linear distance of advancement of the pad toward the disc. For example, in the preferred embodiment, each tactile click equates to {fraction (1/16)} of a full rotation and {fraction (1/16)} of a millimeter of pad advancement. The inboard pad assembly is retracted by rotating the inside knob counter-clockwise.  
         [0072]    The outboard pad wear compensation apparatus  153  relies on a similar rotary to linear linkage as the inboard pad compensator  73 , but it is slightly more complicated. Rotation of the outside knob  264  in a clockwise direction in turn causes rotation of the indicator foot screw  148  in a clockwise direction. This rotation threadably advances the indicator foot screw  148  relative to the drive cam  158  which in turn advances the ball bearing  146 , the outside pressure foot  134  and the corresponding first brake pad assembly  72 . The outside pressure foot in its advanced position is illustrated in FIG. 6. It should be noted that the split washer  141  received in the annular groove  140  causes friction between the outside pressure foot and the fixed cam to prevent the outside pressure foot from simply sliding out of the outside cylinder. As with the inside knob, the outside knob also provides a tactile indication of rotation corresponding to a select linear advancement. This is provided by the inwardly extending detents  278 , which engage with the indexing knurls  258  of the larger outer diameter washer  256 . In addition, as described above, advancement of the indicator foot screw  148  and therefore the outside pressure foot  134  can be monitored visually and by feel by noting how far the trailing end  156  of the indicator foot screw  148  advances relative to the outer surface of the outer knob  264  within the axial hole  268 . To retract the pad, the outside knob is rotated counter-clockwise to retract the indicator foot screw  148  and the drive mechanism is actuated to squeeze the disc, which in turn retracts the outside pad assembly  72  and the outside pressure foot  134  by forcing them into abutment with the retracted foot screw  148 .  
         [0073]    The pad wear compensating apparatus not only allows for convenient advancement of the brake pad assemblies as the brake pads wear, but the structure also provides a quick and convenient way to properly align the caliper housing  18  relative to a disc  14 . This can be done by loosening the mounting bolts  28  and then advancing the pad assemblies into contact with the disc using the inboard and outboard pad wear compensators  73 ,  153 . With the disc squeezed between the pads, the mounting structure including the slotted mounting feet  20 ,  22  and the concave and convex washers  30  enables precise alignment of the caliper housing to maintain the leading pad surfaces parallel to the disc. Tightening the mounting bolts  28 ,  30  then secures the precise alignment. For example, because the inner pad assembly is stationary, it is generally preferred to provide a very small clearance between the inner pad and the disc and a greater clearance between the moveable outer pad and the disc. This set up can be achieved by starting with the pads fully withdrawn along the advancement axis into the cavity  360  as shown in FIG. 5 and then advancing the inner pad assembly using the inner knob a short distance while advancing the pad associated with the outer knob a greater distance into contact with the disc. The mounting bolts are then tightened and the knobs are turned to retract the pad assemblies to provide a desired operative gap with the disc.  
         [0074]    While this greatly simplifies the process of properly aligning the caliper housing and brake pads during initial set up, the pad advancement structure in combination with the caliper housing mounting system also provide for simplified field repair. For example, if a user crashes and one of the attachment bosses is bent, the user can detach the mounting bolts  28 , bend the bent attachment boss back in position as well as possible by eye-balling it and then reposition the caliper housing with the brake pads properly aligned parallel to the disc simply by repeating the procedure described in the preceding paragraph.  
         [0075]    Referring to FIG. 6, in operation, as the brake pads are caused to compress the disc therebetween, a high tensile force represented by the arrow  398  is applied to the housing in the vicinity of the inside and outside cylinders. This can put tremendous stress on the housing, and can even cause the housing to split apart. This problem is all the more acute where the housing is cast from a lightweight, relatively low tensile strength metal such as aluminum. To address this problem, the ball bearing mechanical disc brake housing has a pair of threaded bores  400 ,  402 , which extend the width of the housing on opposite sides of and radially spaced from the pivot or advancement axis  46 . Referring to FIG. 8, a steel screw  404  threadably engages each threaded bore  400 ,  402  and is tightened to pre-stress or preload the caliper housing to reinforce the housing. Preferably only a portion of the bore opposite the screw head is threaded, with the reminder of the bore being a clearance bore. The compression force is illustrated by arrows  399 . The screws are preferably tightened to apply a compression force of about 1,000-1,400 lbs. This not only prevents cracking and failure of the housing, it virtually eliminates any flexure of the housing that could dissipate braking power or fatigue the housing.  
         [0076]    The ball bearing mechanical disc brake caliper  10  also includes a mechanism for adjusting the return force on the lever arm  32  applied by the return spring  228 . Referring to FIG. 9, adjustment screw  410  is threadably received in a threaded bore  412  in the housing which breaches the outer cylinder with the axis of the bore  412  aligned with the stop surface  224  of the spring tension biasing plate  220 . As the adjustment screw  410  is advanced within the treaded bore  412 , the spring tension biasing plate  220  rotates about the cylindrical body  180  of the fixed cam  178  to increase the tension on the spring. Turning the adjustment screw  410  to retract it from the bore causes rotation of the spring tension biasing plate  220  which decreases the tension on the spring  228 . As seen in FIG. 9, the spring tension limiting slot  222  cooperates with the spring tension limiting boss  186  of the fixed cam  178  to limit rotation of the spring tension biasing plate  220  and therefore the range of return force applied to the lever arm  32 .  
         [0077]    It may be useful or desirable to provide a ball spacer between the drive cam  158  and the fixed cam  178  to maintain the ball bearings  176  equally spaced within the elongated ramped grooves  162 ,  200 . If such a ball spacer is to be used, one embodiment of a design for such a ball spacer is illustrated in FIGS. 25 and 26. The ball spacer  420  could be made of a simple sheet metal stamping consisting of a ring body  422  with inwardly extending radial leg pairs  424  spaced to correspond to the desired spacing of the ball bearings. The radial legs  424  can be curled as illustrated in FIG. 25 to define a ball receiving socket  426 . The legs  424  of each pair are circumferentially spaced so that a ball bearing  176  can be snap fit therebetween as illustrated in FIG. 26. FIGS. 27 and 28 depict another embodiment of a ball spacer molded of plastic. Notches  427  in a ring  428  are sized to snap fit with the ball bearings  176 . The ring is thick enough and the insides of the notch are slightly concave (see  429  in FIG. 27) to secure the ball bearing about an axis as illustrated in FIG. 28. Either ball spacer embodiment secures the ball bearings  176  about an axis and thus ensures that the ball bearings  176  will maintain an equal radial spacing and further ensures that the ball bearings will be the same distance between the face of the drive cam and the fixed cam.  
         [0078]    The ramped groove structure of the fixed cam and drive cam illustrated in FIGS. 4A and 4B is useful for most applications, but it limits the amount the lever arm can be rotated to, at most, slightly under 120°. An alternate ramp structure is depicted in FIG. 29. As illustrated in FIG. 29, the ramps  430  spiral inward as they ramp upward toward the leading surface  432 . With such corresponding structures provided in the leading surface of the fixed cam and the drive cam, the ramped grooves  430  can be much greater in length and have a much more gradual incline. This will enable the associated lever arm  32  to rotate much greater than 120° and for the inboard brake pad to be advanced linearly at a slower rate as the lever arm  32  is pivoted.  
         [0079]    The outer knob is shown in a perspective view in FIG. 19. The outer knob has an elongate slot  440  corresponding to each axially inwardly extending leg  270 . Referring to FIG. 20, each elongate slot  440  overlies a corresponding barb  272 . The holes  440  are formed during molding of the outer knob  264  by a mandrel which occupies the space that defines the hole  440 , with the distal end of the mandrel contributing to the forming of the undercut of the barb. In this manner, the undercuts are introduced to the knob while still enabling the knob to be injection molded in a single step. Referring to FIGS. 21 and 22, the inner knob  106  likewise has elongate slots  442  corresponding to each inward axially extending leg  112 . As with the outer knob described above, the slots overly the barbs  114  and enable formation of the undercut on the barbs by means of mandrels as described above with regard to the inner knob.