FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to a slack adjuster, and more particularly, to a slack adjuster with self-adjusting capability to maintain the position of the piston of the caliper within the predefined range in a hydraulic brake system of a bicycle.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is well known that a braking force generated from a friction pad of a rim brake system is used to halt a bicycle by clipping both wheel edges of the bicycle. However, the dust and moisture are easily accumulated on the surfaces of the wheel edges. Such a situation particularly occurs when the bicycle is ridden in a roadway covered with the mud or water. Therefore, operating circumstances of the friction pad go from bad to worse, resulting in many problems such as a brake performance reduction, or even the safety issues. Moreover, the cable is applied to transfer the braking force to the brake device at the wheel side. Since the cable will tend to be extended when the applied tension is too large when the braking lever is extremely pressed, the braking device will not give enough braking force in this situation.  
           [0003]    To solve the problems, a disc brake system  100  currently has been developed, as shown in FIG. 1. Braking fluid and pipelines are used as the medium to transmit the brake force in a braking system. When the rider pulls a drag bar of the braking system with a force  102 , a single piston  104  in the braking system pushes the braking fluid through a guide tube  106 . The braking fluid is injected into a brake member  108  of the braking system to pull out the friction pad  112  to impel a piston  110  against a disc  114  of the brake member  108 .  
           [0004]    To obtain an enough force ratio of disc brake system  100 , the cross-sectional area of the piston  110  of the disc brake system  100  is lower-than-normal. Therefore, the incoming and outgoing of the braking fluid is insufficient so that the friction pad  112  of the disc brake system  100  cannot be far away from the disc  114  after the braking process is finished. As a result, the friction pad  112  is incapable of completely separating from the disc  114 , consuming most of the applied force of the rider, making a loud noise and shock of the braking system  100  and making a abrasion of the friction pad  112  during a normal riding. Further, if the heat of the abrasion of the friction pad  112  is unable to be transmitted, a poor performance and danger of the bicycle occur.  
           [0005]    However, since the cross-sectional area of the piston  110  of the disc brake system  100  is lower-than-normal, the friction pad  112  cannot excessively separate from the disc  114  when the friction pad  112  in a balance position is idle. Due to the lack of the incoming and outgoing of the braking fluid, the friction pad excessively separated from the disc is incapable of moving toward the disc  114  and of contacting tightly the disc in a stroke.  
           [0006]    It is necessary to develop an adjustable abrasion clearance since the friction pad  112  cannot separate from the disc  114 . Traditionally, a screw  116  and a ratchet are applied to adjust the position of the piston  110  and the friction pad  112  corresponding to the disc  114 . However, the position adjustment must usually be adjusted. Further, a proper position of the friction pad  112  cannot be obtained, even resulting in danger during a riding.  
           [0007]    Consequently, after accomplishing the braking process, how to separate the brake disc and the friction pad for a proper clearance is an important problem. Moreover, as the friction pad is gradually worn down, how to make the braking system self-adjust the gap between the friction pad and the disc to maintain the clearance deviation of the friction pad for bicycle manufacturers to increase the rapid and precise brake effect of the brake system are also current significant issues.  
         SUMMARY OF THE INVENTION  
         [0008]    The primary object of the present invention is that a slack adjuster is used to self-adjust the piston of the braking system to an appropriate position after a braking process is completed to solve problems of noise, shock, abrasion and heat accumulation.  
           [0009]    Another object of the present invention is that the slack adjuster is used to self-adjust automatically a predetermined clearance between the piston and the friction pad after the friction pad is worn down to solve a problem of manual adjustment of the piston position.  
           [0010]    According to the above objects, the present invention sets forth an automatic slack adjuster with three embodiments to explain the spirit of the present invention.  
           [0011]    In first embodiment, the slack adjuster comprises a cylinder, a piston and a resilient body. The cylinder comprises a cavity which includes a rod along an axial center. The surface region of the cavity includes at least one protruding portion to control an elongation or compression deformation of the resilient body along the axial center. Additionally, the piston along the axial center has a friction pad to stop a disc of the braking system.  
           [0012]    The first end portion of the resilient body is mounted on the rod of the cylinder and the second end portion of the resilient body resists against the sidewall of the piston due to friction. The end portion of the rod has a flange opposed against the first end portion of the resilient body. A pin inserted into the end portion of the rod is also used to substitute for the flange. The resilient body contacts the protruding portion of the cylinder to control the elongation or compression along the axial center.  
           [0013]    When starting to brake, the fluid pressure within the cylinder is increased to move the piston toward the disc of the braking system so that the resilient body experiences a restoring force due to compression. When the braking process is finished, the piston moves away from the disc. If the thickness of the friction pad is constant, because a restoring force of the resilient body is smaller than the friction force between the second portion of the resilient body and the sidewall of the piston, the resilient body can move together with the piston. The resilient body is kept in the first balance position to ensure the clearance between the piston and the disc to be a predetermined value after the piston moves backward.  
           [0014]    If the friction pad has been worn down, the friction force between the second end portion of the resilient body cannot overcome the restoring force of the resilient body. Therefore, a relative movement between the resilient body and the piston occurs so that the resilient body slides from the first balance position to the second balance position. After the braking process is finished, the resilient body positioned in the second balance position removes away from the disc. Since the contact between the resilient body and the piston is changed such that a clearance between the piston and the disc is in a predetermined position.  
           [0015]    In second embodiment, the slack adjuster comprises a cylinder, a piston, an expansion ring, and a resilient body. The cylinder has a first cavity which includes a rod along an axial center. The piston has a first sidewall coupled with first cavity of cylinder so that the piston reciprocates in the first cavity, and the piston has a second cavity to receive the expansion ring.  
           [0016]    The expansion ring has a second sidewall coupled with the second cavity of piston by a friction force, and a flange is positioned at an end portion of expansion ring. The resilient body is coupled with the rod of cylinder. The resilient body has a first portion and a second portion wherein the first portion is mounted on the rod of the cylinder and the second portion resists the flange of expansion ring.  
           [0017]    If the friction pad has not been worn down, the friction force between the second sidewall of the expansion ring and the piston is overcome by the restoring force of the resilient body to move the resilient body together with the piston. The expansion ring is always kept in the first balance position. As a result, the clearance between the piston and the disc is same as the predetermined value after the piston moves backward.  
           [0018]    If the friction pad has worn down, the friction force between the second sidewall of the expansion ring and the piston cannot overcome the restoring force of the resilient body. Therefore, a relative movement between the resilient body and the piston occurs so that the expansion ring slides from the first balance position to the second balance position. After the braking process is finished, the resilient body positioned in the second balance position can remove the expansion ring and the piston from the disc. Since the contact between the expansion ring and the piston is changed such that a clearance between the piston and the disc is in a predetermined position.  
           [0019]    In third embodiment, the slack adjuster comprises a cylinder, a piston, an expansion ring, a shrinkage ring, and a resilient body. The cylinder has a first cavity which includes a rod along an axial center. The piston has a first sidewall coupled with the first cavity of the cylinder so that the piston reciprocates in the first cavity, and the piston has a second cavity to receive the expansion ring and to hold the shrinkage ring and the resilient body.  
           [0020]    The expansion ring has a second sidewall for mounting on the second cavity of the piston. A first flange is positioned at a first end portion of the expansion ring. The shrinkage ring has a third sidewall, the third sidewall slides on the rod of the cylinder, and a second flange is positioned at a second end portion of the shrinkage ring. The resilient body is coupled with the rod of the cylinder, and the resilient body is confined between the first flange of the expansion ring and the second flange of the shrinkage ring along the axial center.  
           [0021]    If the friction pad has not been worn down, the friction force between the shrinkage ring and the rod of the cylinder is overcome by the restoring force of the resilient body to move the resilient body together with the piston. The shrinkage ring always is kept in the first balance position. As a result, the clearance between the piston and the disc is same as the predetermined value after the piston moves backward.  
           [0022]    If the friction pad has worn down, the friction force between the second sidewall of the expansion ring and the piston cannot overcome the restoring force of the resilient body. Therefore, a relative movement between the shrinkage ring and the piston occurs so that the shrinkage ring slides from the first balance position to the second balance position. After the braking process is finished, the shrinkage ring positioned in the second balance position can remove the shrinkage ring and the rod from the disc. Since the contact between the shrinkage ring and the rod is changed such that a clearance between the piston and the disc is in a predetermined position.  
           [0023]    In summary, the slack adjuster uses a friction force among a piston, a resilient body, and a cylinder to self-adjust automatically the piston of the braking system to an appropriate position after a braking process is completed. The appropriate position between the friction pad and the disc is located in a predetermined range. More significantly, the slack adjuster is able to self-adjust a balance position of the piston to always acquire a predetermined clearance between a friction pad and a piston when the piston has been worn down due to a frictional motion.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0025]    [0025]FIG. 1 illustrates a slack adjuster of a bicycle according to the prior art;  
         [0026]    [0026]FIG. 2A illustrates a decomposed cross-sectional view of a slack adjuster of first embodiment according to the present invention;  
         [0027]    FIGS.  2 B- 2 E illustrate a schematic cross-sectional view of a slack adjuster of first embodiment operation according to the present invention;  
         [0028]    [0028]FIG. 3A illustrates a decomposed cross-sectional view of a slack adjuster of second embodiment according to the present invention;  
         [0029]    FIGS.  3 B- 3 E illustrate a schematic cross-sectional view of a slack adjuster of second embodiment operation according to the present invention;  
         [0030]    [0030]FIG. 4A illustrates a decomposed cross-sectional view of a slack adjuster of third embodiment according to the present invention; and  
         [0031]    FIGS.  4 B- 4 E illustrate a schematic cross-sectional view of a slack adjuster of third embodiment operation according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]    The present invention is directed to a slack adjuster for self-adjusting a position to improve the shortcomings of a braking system applied to bicycles in the prior art. A friction force between a piston, a resilient body, and a cylinder is used to control a braking system so that the piston is allowed to withdraw back to obtain an appropriate or a balance position after braking process is completed. More significantly, the slack adjuster is able to self-adjust a balance position of the piston to acquire a predetermined clearance between a friction pad and the piston when an end portion of the piston has been worn down due to a frictional motion. The slack adjuster of the present invention is also used in a variety of braking system of vehicles. Three embodiments of the present invention are shown as follows.  
         [0033]    First Embodiment  
         [0034]    [0034]FIG. 2A shows a decomposed cross-sectional view of a slack adjuster  200   a  of first embodiment according to the present invention. The slack adjuster  200   a  comprises a cylinder  202   a , a piston  204  and a resilient body  206   a . The cylinder  202   a  comprises a cavity  208  which includes a rod along an axial center  210   a . The surface region of the cavity  208  includes at least one protruding portion  214 , and preferably four protruding portions, to control an elongation or compression deformation of the resilient body  206   a  along the axial center  210   a . Additionally, the piston  204  along the axial center  210   a  has a friction pad  216  to clip a disc of the braking system.  
         [0035]    The first end portion  217  of the resilient body  206   a  is mounted on the rod  212   a  of the cylinder  204  and the second end portion  218  of the resilient body  206   a  resists the sidewall  221  of the piston  204  due to a friction. The end portion of the rod  212   a  has a flange  222  opposed to the first end portion  217  of the resilient body  206   a . A pin inserted into the end portion of the rod  212   a  is also used to substitute for the flange  222 .  
         [0036]    The resilient body  206   a  includes a conical spring or a compressible spring. The conical spring comprises a spiral coil including a first opening  224  and a second opening  226  located opposite the first opening. The cross-sectional area of the spiral coil includes a square, circular and the like cross-sections. The first opening  224  binds the rod of the cylinder and the second opening  226  expands outwardly on the sidewall of the piston  204  to create a frictional force between the outer edge of the spiral coil and the sidewall of the piston  204 .  
         [0037]    FIGS.  2 B- 2 E show a schematic cross-sectional view of a slack adjuster  200   a  of first embodiment operation according to the present invention. In FIG. 2B, if the friction pad  216  is not worn, the clearance between the piston  204  and the disc is constant and the resilient body  206   a  is located at a first balance position  228   a  within the piston  204 . In FIG. 2C, when starting to brake, the fluid pressure within the cylinder  202   a  is increased to move the piston  204  toward the disc of the braking system so that the resilient body  206   a  experiences a restoring force due to compression. When the braking process is finished, the fluid pressure of the cylinder  204  is decreased to move away from the disc of the braking system so that the restoring force of the resilient body  206   a  is used to pull back the piston, as shown in FIG. 2B.  
         [0038]    The restoring force of the resilient body  206   a  is smaller than or equal to the friction force between the second portion  218  of the resilient body  206   a  and the sidewall of the piston  204 . In other words, the friction force is overcome by the restoring force to move the resilient body  206   a  together with the piston  204  so that the resilient body  206   a  is always kept in the first balance position  228   a . As a result, the clearance between the piston  204  and the disc is invariable.  
         [0039]    In FIG. 2D, if the friction pad  216  has been worn down, the clearance between the piston  204  and the disc is increased. The resilient body  206   a  is positioned at the second balance position  230   a . In FIG. 2E, when starting to brake, the piston  204  moves toward the disc such that the resilient body  206   a  exerts a restoring force. When stopping braking, the piston  204  moves the friction pad away from the disc surface and is drawn back by the restoring force, as shown in FIG. 2D.  
         [0040]    The restoring force of the resilient body  206   a  is higher than the friction force between the second end portion of the resilient body  206   a  and the sidewall  221  of the piston  204 . In other words, the friction force cannot overcome the restoring force. Therefore, a relative movement between the resilient body  206   a  and the piston  204  occurs so that the resilient body  206   a  slides from the first balance position  228   a  to the second balance position  230   a . After the braking process is finished, the resilient body  206   a  positioned in the second balance position  230   a  removes away from the disc. Since the contact between the resilient body  206   a  and the piston  204  is changed such that a clearance between the piston  204  and the disc is in a predetermined position.  
         [0041]    Second Embodiment  
         [0042]    [0042]FIG. 3A shows a schematic cross-sectional view of a slack adjuster  200   b  of second embodiment according to the present invention. The slack adjuster  200   b  comprises a cylinder  202   b , a piston  204 , an expansion ring  208   a , and a resilient body  206   b . The cylinder  202   b  has a first cavity  232  which includes a rod  212   b  along an axial center. The piston  204  has a first sidewall  234  coupled with first cavity  232  of cylinder  202   b  so that piston  204  reciprocates in the first cavity  232 , and the piston  204  has a second cavity  238  to receive the expansion ring  208   a  and the resilient body  206   b.    
         [0043]    The expansion ring  208   a , hollow in shape, has a second sidewall  240  coupled with the second cavity  238  of piston  204  by a friction force, and a flange  242  is positioned at an end portion of expansion ring  208   a . The resilient body  206   a  coupled with the rod  212   b  of cylinder  202   b . The resilient body  206   b  has a first portion and a second portion wherein the first portion is mounted on the rod  212   b  of the cylinder  202   b  and the second portion resists the flange  242  of expansion ring  208   a  . Similarly, the piston  204  along the axial center  210   b  has a friction pad  216  to stop a disc of the braking system.  
         [0044]    In the preferred embodiment of the present invention, the second sidewall  240  of the expansion ring  208   a  includes a plurality of slots  244  and a plurality of protruding portions  246  to adjust the contact friction. Specifically, due to the protruding portions  246  and the slots  244  on the second sidewall  240  of the expansion ring  208   a , the expansion ring  208   a  is able to tightly or uniformly attach to the sidewall of the piston  204  to obtain a stable operation.  
         [0045]    The resilient body  206   b  comprises a disc spring having a first opening  248  and a second opening  250  along the axial center  210   b . A surface region positioned between first opening  248  and second opening  250  is used to generate a restoring force as the disc spring is applied to a force. The surface region further comprises a plurality of slots  252  to adjust the restoring force. Additionally, the first opening  248  of the disc spring has a hook portion along the surface region for mounting the disc spring on the cylinder  202   b.    
         [0046]    FIGS.  3 B- 3 E show a schematic cross-sectional view of a slack adjuster  200   b  of second embodiment operation according to the present invention. In FIG. 3B, if the friction pad  216  has not been worn away, the clearance between the piston  204  and the disc is constant and the expansion ring  208   a  is located at a first balance position  228   b  within the piston  204 . In FIG. 3C, when starting to brake, the fluid pressure within the cylinder  202   b  is increased to move the piston  204  toward the disc of the braking system so that the resilient body  206   b  experiences a restoring force due to compression. When the braking process is finished, the fluid pressure of the cylinder  202   b  is decreased to move away from the disc of the braking system so that the restoring force of the resilient body  206   b  is used to pull back the piston  204 , as shown in FIG. 3B. Besides, after a brake process is completed and the fluid pressure within the cylinder  202  is decreased, the piston  204  is attracted backward not only by a negative pressure but by the restoring force of the disc spring to induce the expansion ring  208   a.    
         [0047]    The restoring force of the resilient body  206   b  is smaller than or equal to the friction force between the second sidewall  240  of the expansion ring  208   a  and the piston  204 . In other words, the friction force is overcome by the restoring force to move the resilient body  206   b  together with the piston  204  so that the expansion ring  208   a  always is kept in the first balance position  228   b . As a result, the clearance between the piston  204  and the disc is invariable.  
         [0048]    In FIG. 3D, if the friction pad  216  has been worn down, the clearance between the piston  204  and the disc is increased. The expansion ring  208   a  is positioned at the second balance position  230   b . In FIG. 3E, when starting to brake, the piston  204  moves towards the disc such that the resilient body  206   b  exerts a restoring force. When braking is finished, the piston  204  moves away from the disc and is drawn back by the restoring force, as shown in FIG. 3D.  
         [0049]    The restoring force of the resilient body  206   b  is higher than the friction force between the second sidewall  240  of the expansion ring  208   a  and the piston  204 . In other words, the friction force cannot overcome the restoring force. Therefore, a relative movement between the expansion ring  208   a  and the piston  204  occurs so that the expansion ring  208   a  slides from the first balance position  228   b  to the second balance position  230   b . After the braking process is finished, the resilient body  206   b  positioned in the second balance position  230   b  can remove the expansion ring  208   a  and the piston  204  from the disc. Since the contact between the expansion ring  208   a  and the piston  204  is changed such that a clearance between the piston  204  and the disc is in a predetermined position.  
         [0050]    Third Embodiment  
         [0051]    [0051]FIG. 4A shows a decomposed cross-sectional view of a slack adjuster  200   c  of third embodiment according to the present invention. The slack adjuster  200   c  comprises a cylinder  202   c , a piston  204 , an expansion ring  208   b , a shrinkage ring  253 , and a resilient body  206   c . The cylinder  202   c  has a first cavity  254  which includes a rod  212   c  along an axial center  210   c . The piston  204  has a first sidewall  256  coupled with the first cavity  256  of the cylinder  202   c  so that the piston  204  reciprocates in the first cavity  256 , and the piston  204  has a second cavity  258  to receive the expansion ring  208   b , shrinkage ring  253  and the resilient body  206   c.    
         [0052]    The expansion ring  208   b , hollow in shape, has a second sidewall  260  to be mounted on the second cavity  258  of the piston  204 . A first flange  262  is positioned at a first end portion of the expansion ring  208   b . The shrinkage ring  253  has a third sidewall  264 , the third sidewall  264  slid with the rod  212   c  of the cylinder  202   c , and a second flange  259  is positioned at a second end portion of the shrinkage ring  253 . The resilient body  206   c  is coupled with the rod  212   c  of the cylinder  202   c . The resilient body  206   c  is confined between the first flange  262  of the expansion ring  208   b  and the second flange  259  of the shrinkage ring  253  along the axial center. Similarly, the piston  204  has a friction pad to stop a disc of the braking system.  
         [0053]    In the preferred embodiment of the present invention, the second sidewall  260  of the expansion ring  208   b  includes a plurality of slots  266  and a plurality of protruding portions  268  friction sufficient to mount the expansion ring  208   b  on the second cavity  258  of the piston  204 . The shrinkage ring  253  further comprises a plurality of slots and a plurality of protruding portions to adjust the friction force between the shrinkage ring  253  and the rod  212   c  of the cylinder  202   c.    
         [0054]    FIGS.  4 B- 4 E show a schematic cross-sectional view of a slack adjuster  200   c  of third embodiment operation according to the present invention. In FIG. 4B, if the friction pad  216  has not been worn down, the clearance between the piston  204  and the disc is constant and the shrinkage ring  253  is located at a first balance position  228   c  within the piston  204 . In FIG. 4C, when starting to brake, the fluid pressure within the cylinder  202   c  is increased to move the piston  204  toward the disc of the braking system so that the resilient body  206   c  gets a restoring force due to compression motion. When braking process is finished, the fluid pressure of the cylinder  202   c  is decreased to move away from the disc of the braking system so that the restoring force of the resilient body  206   c  is used to pull back the piston  204 , as shown in FIG. 4B.  
         [0055]    The restoring force of the resilient body  206   c  is smaller than or equal to the friction force between the third sidewall  264  of the shrinkage ring  253  and the rod  212   c  of the cylinder  202   c . In other words, the friction force is overcome by the restoring force to move the resilient body  206   c  together with the piston  204  so that the shrinkage ring  253  always is kept in the first balance position  228   c . As a result, the clearance between the piston and the disc is invariable.  
         [0056]    In FIG. 4D, if the friction pad  216  has worn down, the clearance between the piston  204  and the disc is increased. The shrinkage ring  253  is positioned at the second balance position  230   c . In FIG. 4E, when starting to brake, the piston  204  moves toward the disc so that the resilient body  206   c  acquires a restoring force. When stopping to brake, the piston  204  moves away from the disc and is drawn back by the restoring force, as shown in FIG. 4D.  
         [0057]    The restoring force of the resilient body  206   c  is higher than the friction force between the third sidewall  264  of the shrinkage ring  253  and the rod  212   c  of the cylinder  202   c . In other words, the friction force cannot overcome the restoring force. Therefore, a relative movement between the shrinkage ring  253  and the piston  204  occurs so that the shrinkage ring  253  slides from the first balance position  228   c  to the second balance position  230   c . After the braking process is finished, the shrinkage ring  253  positioned in the second balance position  230   c  can remove the shrinkage ring  253  and the rod  212   c  from the disc. Since the contact between the shrinkage ring  253  and the rod  212   c  is changed such that a clearance between the piston  204  and the disc is in a predetermined position.  
         [0058]    According to the above-mentioned, the slack adjuster uses a friction force among a piston, a resilient body and a cylinder, and a resilience of the resilient body. The piston automatically move backward in a predetermined position to ensure a proper clearance range between the friction pad and the disc. As a result, the contact between the friction pad and the disc is controllable to prevent wear, noise, shock and heat accumulation after a braking process is completed.  
         [0059]    More significantly, the slack adjuster is able to self-adjust a balance position of the piston to acquire a predetermined clearance between a friction pad and a piston when the piston has been worn down due to a frictional motion. Complex manual modification of position is effectively omitted. Moreover, since a clearance between the friction pad and the disc can be obtained from computation or experimentation, the next stroke of the piston is not affected when the friction pad is far away from the disc, thus solving the problem of insufficient withdrawal of the piston. In addition, the slack adjuster has many advantages such as good manufacturing, assembly, safety, and compatibility.  
         [0060]    As understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrations rather than limitations of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.
A slack adjuster with the capability of self-adjusting the position of the piston in the caliper within the predefined range is described. The slack adjuster has a cylinder, a piston and a resilient body. Due to the friction and resilience among the piston, the resilient body and shafts, the piston of the brake member can controllably drawn back into the cylinder according to a predetermined force to reduce vibration, noise and abrasion of a friction pad when the brake member is idle. The pull of the piston is allowed to be automatic adjusted into a balance position so that the distance between the friction pad and the disc is maintained in a predetermined range.