Abstract:
A variable ratio of force-enlargement master cylinder for a braking system is described. The variable ratio of force-enlargement master cylinder has a cylinder, an outer piston, and an inner piston, in which comprise a plurality of cavities and openings therein. When a force is uniformly applied to the variable ratio of force-enlargement master cylinder, the flow rate of the fluid is preferably changed into a predetermined value by incorporating the cavities and openings located on the cylinder, the outer piston, and the inner piston in a suitable time.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to a braking device, and more particularly, to a variable ratio of force-enlargement master cylinder for a braking device 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 above problems, a disc brake system  100  has been developed, as shown in FIG. 1. Braking fluid and the pipelines are used as the medium of transmitting the brake force to the braking devices. When the rider pulls the lever of the braking device with a force  102 , the piston  104  in the braking device pushes the braking fluid through a guide tube  106 . The braking fluid is pressed into a brake member  108  of the braking device to pull out the friction pad  112  to impel a piston  110  against a disc  114  of the brake member  108 . The braking fluid, the single piston  104  and the piston  1   10  serve as transmission interface of the braking force in the disc brake system  100 . A ratio of force-enlargement is defined as magnifying rate of a force between the single piston  104  and the piston  110 . There is a need to increase the ratio of force-enlargement master cylinder.  
           [0004]    If the cross-sectional area of the piston  104  and the piston  110  is reduced, the ratio of the force-enlargement is increased, which results in a reduction of braking force applied on the rider&#39;s hand. However, such a situation of cross-sectional area decrement of the piston  104  diminishes the flow rate of braking fluid in the piston  104  and the displacement of the piston  110  is decreased and thus leaded into the following drawbacks: (a) The piston  110  has an insufficient forward displacement. Even if the piston  104  is entirely pushed down, the piston  110  still cannot propel the friction pad  112  onto the brake disc  114 , which leads to an inadequate force imposed on the braking system. (b) The piston  110  has an insufficient backward displacement. Even if the piston  104  is totally released, the piston  110  with the friction pad  112  still cannot be separated from the brake disc  114 , which leads to abrasion, vibration, noise and human power dispersion.  
           [0005]    Consequently, how to control the brake speed and the braking force of the braking device and how to increase the braking force and the high ratio of force-enlargement are important problems and are currently main issues for braking device manufacturers of the bicycles.  
         SUMMARY OF THE INVENTION  
         [0006]    The primary object of the present invention is that a friction pad of a variable ratio of force-enlargement master cylinder rapidly attaches to the disc of the brake member to increase the manipulation of the bicycle when a lever is dragged down in the beginning.  
           [0007]    Another object of the present invention is that the friction pad of the variable ratio of force-enlargement master cylinder is imposed at a higher normal force to increase the braking effect of vehicles.  
           [0008]    According to the above objects, the present invention sets forth a variable ratio of force-enlargement master cylinder. The variable ratio of force-enlargement master cylinder comprises a cylinder, an outer piston and an inner piston. The cylinder comprises a first cavity which includes a first opening, second opening and third opening on the periphery of the first cavity. The first cavity is filled with fluid stored in a fluid supply device.  
           [0009]    The first channel located inside a sidewall of the cylinder is connected to the second opening with the third opening. The fluid in the first cavity is transmitted into the brake member by the first channel of the cylinder to apply pressure to the friction pad serving as an imposition on the disc of the brake member.  
           [0010]    The outer piston, hollow and cylindrical in shape, is coupled to the first cavity of the cylinder by a first resilient body to reciprocate along the first cavity. The outer piston has a second cavity and a second channel inside a sidewall. The second cavity is connected to the first cavity of cylinder via the second channel to fill the second cavity with the fluid. Moreover, the outer piston includes a fourth opening and a fifth opening on the surface region of the outer piston to drain the fluid outwardly. An annular recess is preferably positioned on a surface region adjacent to the fourth opening of the outer piston to drain the fluid passing through the annular recess via the first channel.  
           [0011]    The inner piston coupled to the second cavity of the outer piston is allowed to reciprocate with a second resilient body between the outer piston and the inner piston along the second cavity. More significantly, the cross-section area of the inner piston is smaller than that of the outer piston along the axial center. When the rider applies force to the inner piston, the fluid stored in the first cavity of the cylinder is quickly exhausted at a higher speed to push the brake forward and then the friction pad is pressed onto the disc at a larger-than-normal force. In addition, the inner piston has a third channel therein to circulate the fluid around the variable ratio of force-enlargement master cylinder.  
           [0012]    In the use of the variable ratio of force-enlargement master cylinder, if a lever of the braking device is pulled, the outer piston compresses the fluid within the first cavity of the cylinder. Both sides of the third channel are aligned with the second channel and the fourth opening of the outer piston, respectively. Also, the fifth opening is shielded with the sidewall of the cylinder so that the fluid passes sequentially through the first cavity, the second channel, the third channel and the fourth opening. Finally, the fluid exhausts from the first channel to transfer hydraulic pressure to the friction pad of the brake member.  
           [0013]    The friction pad of the braking member is propelled by the fluid with a higher speed to serve as the step of “fast approaching”. Therefore, the friction pad rapidly contacts the disc to increase the manipulation of the bicycle.  
           [0014]    If the rider continuously presses the lever, the outer piston propels the fluid within the first cavity until the bottom of the outer piston contacts the bottom of the first cavity. Also, the third opening of the cylinder aligns with the fifth opening of the outer piston. Meanwhile, the fluid in the second cavity of the outer piston flows through the fifth opening of the outer piston and the third opening of the cylinder. Afterward, the fluid later is drained away from the first channel of the cylinder.  
           [0015]    In contrast with the step of fasting approaching, because the effective cross-area of the inner piston is smaller than that of the outer piston, the fluid within the second cavity moves at a lower speed and at a higher pressure. Consequently, a higher pressure is transmitted into the friction pad to increase the normal force applied to the disc, which is a step of “high pressure” to increase the variable ratio of force-enlargement.  
           [0016]    In summary, the variable ratio of force-enlargement master cylinder makes the friction pad rapidly attach to the disc to reduce the braking time. After the friction pad contacts the disc, the friction pad continuously presses the disc at a higher-than-normal force to increase the variable ratio of force-enlargement. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    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:  
         [0018]    [0018]FIG. 1 illustrates a brake disc of a bicycle device according to the prior art;  
         [0019]    [0019]FIG. 2 illustrates a cross-sectional view of a variable ratio of force-enlargement master cylinder according to the present invention;  
         [0020]    [0020]FIG. 3 illustrates a cross-sectional view of a variable ratio of force-enlargement master cylinder whose fluid is transmitted at a higher speed according to the present invention; and  
         [0021]    [0021]FIG. 4 illustrates a cross-sectional view of a variable ratio of force-enlargement master cylinder whose fluid is transmitted at a higher pressure according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    The present invention is directed to a variable ratio of force-enlargement master cylinder to improve the shortcomings of a braking device applied to bicycles in the prior art. A fluid filled within the variable ratio of force-enlargement master cylinder is transmitted into a brake member of the braking device to push a friction pad so that the bicycle is effectively halted. The variable ratio of force-enlargement master cylinder in the present invention is also preferably used to a variety of braking devices of vehicles.  
         [0023]    The main theory of the variable ratio of force-enlargement master cylinder in the present invention is based on some factors including a brake torque (T), a brake force between the friction pad and a disc, and the equivalent brake radius of the friction pad on the disc, as shown in the following equation:  
           T=Fr= (μ N ) r= μ( PA ) r    
         [0024]    where  
         [0025]    T is the brake torque;  
         [0026]    F is the brake force between the friction pad and the disc;  
         [0027]    r is the equivalent friction radius of the friction pad opposed against the disc;  
         [0028]    μ is the friction coefficient;  
         [0029]    N is the normal force which the friction pad opposes against the disc;  
         [0030]    P is the fluid pressure imposed on pistons of the braking device; and  
         [0031]    A are the effective area of the pistons.  
         [0032]    In view of the above-mentioned, if the brake torque need to be enlarged, the value of these items including P, A, r, or μ must be increased. However, μ is concerned with the material of the friction pad and the disc and r is concerned with the size of the braking components. As a result, in the present invention, the A area of the pistons is allowed to be changed to vary the P pressure so that the pistons in the variable ratio of force-enlargement master cylinder are sequentially propelled at a higher speed or variable ratio of force-enlargement. In the preferred embodiment of the present invention, two or more pistons are used to improve the single piston of the prior art.  
         [0033]    [0033]FIG. 2 shows a cross-sectional view of a variable ratio of force-enlargement master cylinder according to the present invention. The variable ratio of force-enlargement master cylinder  200  comprises a cylinder  202 , an outer piston  204  and an inner piston  206 . The cylinder  202 , a hollow column in shape, comprises a first cavity  208  which includes a first opening  210 , second opening  212  and third opening  214  on the periphery of the first cavity. The first cavity  208  is filled with fluid stored in a fluid supply device  216 , such as an oil bowl or a chamber via the first opening.  
         [0034]    A first channel  218  located inside a sidewall of the cylinder  202  connects the second opening  212  with the third opening  214 . The fluid in the first cavity  208  is transmitted into a brake member by the first channel  218  of the cylinder  202  to apply pressure to the friction pad serving as an imposition on the disc of the brake member.  
         [0035]    The outer piston  204 , hollow and cylindrical in shape, is coupled to the first cavity  208  of the cylinder  202  by a first resilient body  224  to reciprocate along the first cavity  208 . The first resilient body  224 , such as a compressible spring, preferably connects the bottom of the cylinder  202  with the bottom of the outer piston  204 . The outer piston  204  also has a second cavity  228  and a second channel  230  inside a sidewall of the outer piston  204 . The second cavity  228  is connected to the first cavity  208  of the cylinder  202  via the second channel  230  to fill the second cavity  228  with the fluid. Moreover, the outer piston  204  includes a fourth opening  232  and a fifth opening  234  on the surface region of the outer piston  204  to drain the fluid outwardly. In the preferred embodiment of the present invention, an annular recess  220  is positioned on a surface region adjacent to the fourth opening  232  of the outer piston  204  to drain the fluid passing through the annular recess  220  via the first channel  218  of the cylinder  202 .  
         [0036]    The inner piston  206 , columnar, square, or the like in shape, which is coupled to the second cavity  228  of the outer piston  204 , is allowed to reciprocate with a second resilient body  226  between the outer piston  204  and the inner piston  206  along the second cavity  228 . The second resilient body  226 , such as a compressible spring, preferably connects the bottom of the outer piston  204  with the bottom of the inner piston  206 . More importantly, the cross-section area  238  of the inner piston  206  is smaller than cross-section area  240  of the outer piston  204  along an axial center  236 . When the rider applies a force to the inner piston  206 , the fluid stored in the first cavity  208  of the cylinder  204  is quickly exhausted at a higher speed to push the friction pad forward and then the friction pad is pressed onto the disc at a larger-than-normal force. In addition, the inner piston  206  has a third channel  242  therein to circulate the fluid around the variable ratio of force-enlargement master cylinder  200 .  
         [0037]    Furthermore, when the variable ratio of force-enlargement master cylinder  200  is in an idle status, inactive brake, the fluid stored in the fluid supply device  216  is injected into the first cavity  208  and flows the outer piston  204  and the third channel  242  of the inner piston  206 . Finally, the fluid is drained away from the first channel  218  of the outer piston  204 . In other words, the fluid passes through the first direction  246  to communicate the fluid between the fluid supply device  216  and the brake member to recover the stroke of the piston due to the abrasion of the friction pad.  
         [0038]    [0038]FIG. 3 shows a cross-sectional view of the variable ratio of force-enlargement master cylinder whose fluid is transmitted at a higher speed according to the present invention. If a lever of the braking device is pulled, the outer piston  204  compresses the fluid within the first cavity  208  of the cylinder  202 . Both sides of the third channel  242  are aligned with the second channel  230  and the fourth opening  232  of the outer piston  204 , respectively. Also, the fifth opening  234  is shielded with the sidewall of the cylinder  202  so that the fluid passes sequentially through the first cavity  208 , the second channel  230 , the third channel  242  and the fourth opening  232 . Finally, the fluid exhausts from the first channel  218  to transfer hydraulic pressure to the friction pad of the brake member.  
         [0039]    Specifically, when the rider slightly pulls the lever, the first cavity  208  is pressed by the cross-section area  240  of the outer piston to increase the flow rate of the fluid passing through the first channel  218 . As a result, due to the higher fluid rate, the friction pad rapidly comes near the disc to serve as a step of “fast approaching”. For the same stroke of the lever, the friction pad is allowed to approach the disc since the fluid exhausts at a high speed. Therefore, the friction pad rapidly contacts the disc in the beginning to reduce greatly the movement of the lever, which increases the manipulation of the bicycle.  
         [0040]    In the preferred embodiment of the present invention, a distance of the annular recess  220  of the outer piston  204  along the axial center  236  is equal to or more than that between the third opening  214  of the cylinder and the fifth opening  234  of the outer piston  204 . In the “fast approaching” step, the fluid passed through the fourth opening always exhausts from the first channel  218  of the cylinder  202 .  
         [0041]    Additionally, in the preferred embodiment of the present invention, the fluid sequentially flows into the first cavity  208  and second cavity  228  to conserve sufficient fluid when the lever is pressed. Specifically, the fluid flows along the second direction  248 .  
         [0042]    [0042]FIG. 4 shows a cross-sectional view of a variable ratio of force-enlargement master cylinder whose fluid is transmitted at a higher pressure according to the present invention. If the rider continuously pulls the lever of the braking device, the outer piston  204  propels the fluid within the first cavity  208  until the bottom of the outer piston  204  contacts the bottom of the first cavity  208 . Also, the third opening  214  of the cylinder  202  aligns with the fifth opening  234  of the outer piston  204 . Meanwhile, the fluid in the second cavity  228  of the outer piston  204  flows through the fifth opening  234  of the outer piston  204  and the third opening  214  of the cylinder  202 . The fluid later is drained away from the first channel  218  of the cylinder  202 . In other words, the fluid flows along the third direction  250 .  
         [0043]    Therefore, after the friction pad attaches to the disc, the inner piston  206  moves along the first cavity  208  of the outer piston  204  if the rider continuously imposes a force on the inner piston  206 . In contrast with the step of “fasting approaching”, the fluid within the second cavity  228  moves at a lower speed and at a higher pressure because the effective cross-area  238  of the inner piston  206  is smaller than that  240  of the outer piston  206 . Consequently, a higher pressure is transmitted into the friction pad to increase the normal force applied to the disc, which is a step of “high pressure” to increase the variable ratio of force-enlargement.  
         [0044]    According to the above-mentioned, when an rider pulls the lever of the bicycle, the outer piston of the variable ratio of force-enlargement master cylinder is able to move rapidly so that the stroke of lever completes much early to reduce the brake time. After the friction pad contacts the disc, the friction pad presses the disc at a higher-than-normal force to increase the variable ratio of force-enlargement. As a result, the present invention solves the problem of a long brake stroke and insufficient brake force.  
         [0045]    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 that they 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.