Abstract:
A master cylinder having at least one piston that pressurizes a hydraulic fluid when a stepping force on a brake pedal is transmitted thereto and sends the pressurized hydraulic fluid to at least a wheel cylinder. The piston includes a large diameter passage and a small diameter passage having a diameter smaller than that of the large diameter passage, and a valve body is fastened to the large diameter passage to control fluid communication between the large diameter passage and the small diameter passage, the valve body including a plunger coupling hole and a channel through which the hydraulic fluid communicates between the large diameter passage and the small diameter passage, wherein a plunger slidably passes the valve body through the plunger coupling hole and closes the channel of the valve body when the stepping force on the brake pedal is transmitted to the piston.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to Korean Patent Application Number 2008-0066033 filed on Jul. 8, 2008, the entire contents of which are incorporated herein for all purposes by this reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a master cylinder, and more particularly, to a brake master cylinder for vehicles, in which channel and sealing structures are improved. 
         [0004]    2. Description of Related Art 
         [0005]    In general, a hydraulic brake system generates a braking force by transmitting hydraulic pressure, which is generated by stepping on a brake pedal, to hydraulic brakes installed on front and rear wheels. This hydraulic brake system includes a booster increasing force when the brake pedal is applied, a hydraulic fluid reservoir storing a hydraulic fluid for forming hydraulic pressure, and a master cylinder transferring the hydraulic pressure to wheel cylinders in cooperation with the booster. 
         [0006]      FIG. 1  is a cross-sectional view illustrating a conventional master cylinder before braking.  FIG. 2  is a cross-sectional view illustrating a conventional master cylinder during braking.  FIG. 3  is an enlarged cross-sectional view illustrating an important part of  FIG. 2 . 
         [0007]    As illustrated in  FIGS. 1 and 2 , the conventional master cylinder includes a cylinder  10  having a blind end and first and second pistons  20  and  30  housed in the cylinder  10 . The first and second pistons  20  and  30  are spaced apart from each other so as to be able to make relative motion. 
         [0008]    A first boosting force transmission member  18  is interposed between an output shaft of the booster and the first piston  20 . A second boosting force transmission member  19  is interposed between the first piston  20  and the second piston  30 . 
         [0009]    At this time, a space between the first piston  20  and the second piston  30  and a space between the second piston  30  and the blind end of the cylinder  10  serve as a first hydraulic chamber  21  and a second hydraulic chamber  31 , respectively. The first and second hydraulic chambers  21  and  31  are provided with respective return springs  40  for returning the first and second pistons  20  and  30 . 
         [0010]    Further, the cylinder  10  is provided with first and second inlets  22  and  32  feeding a fluid into the master cylinder, and first and second outlets  23  and  33  transferring the fluid pressurized at the first and second hydraulic chambers  21  and  31  to the wheel cylinders. The first and second inlets  22  and  32  are connected with an oil tank. 
         [0011]    Meanwhile, the first and second pistons  20  and  30  are equipped with first and second inflow chambers  24  and  34  in intermediate portions thereof in which the fluid introduced into the cylinder  10  through the first and second inlets  22  and  32  is stored before it is sent to the first and second hydraulic chambers  21  and  31 . The first and second pistons  20  and  30  are provided with communication holes  50  in leading ends thereof which connect the first and second inflow chambers  24  and  34  with the first and second hydraulic chambers  21  and  31 . 
         [0012]    The communication holes  50  have center valves  60  installed therein so as to interrupt or allow the fluid that flows through the communication holes  50  to thereby close or open the first and second hydraulic chambers  21  and  31 . 
         [0013]    Each center valve  60  includes a valve body  62  and a sealing member  61  fitted around a leading end of the valve body  62 . Each of the communication holes  50 , which hold the respective center valves  60 , includes a large diameter passage  51  holding the sealing member  61 , and a small diameter passage  52  holding the remaining valve body  62  other than the sealing member  61 . 
         [0014]    The fluid flows through each communication hole  50 , particularly a gap between the center valve  60  and the communication hole  50 . In contrast, when the sealing member  61  comes into contact with a valve seat  53  formed by transition from the large diameter passage  51  to the small diameter passage  52 , the fluid does not flow through each communication hole  50 . To this end, the sealing member  61  held in the large diameter passage  51  is formed so as to have an outer diameter that is smaller than an inner diameter of the large diameter passage  51  and is greater than an inner diameter of the small diameter passage  52 . Further, the inner diameter of the small diameter passage  52  is formed so as to be greater than an outer diameter of the valve body  62  held in the small diameter passage  52 . 
         [0015]    Meanwhile, in the rear of the respective center valves  60 , cylinder pins  70  pass through the first and second inflow chambers  24  and  34  and are fixed to the cylinder  10 . An elastic member  64  is installed in the large diameter passage  51  of each communication hole  50  so as to elastically support the corresponding center valve  60  toward the corresponding cylinder pin  70 . The center valves  60  allow or block the flow of fluid through the communication holes  50  by interaction of the cylinder pins  70  and the elastic members  64  and by forward or backward movement of the first and second pistons  20  and  30 . 
         [0016]    Now, the operation of the conventional master cylinder will be described in detail. 
         [0017]    When the brake pedal is applied for breakage, the first boosting force transmission member  18  is pushed by the output shaft of the booster, and thus the first piston  20  moves forwards. Then, the second boosting force transmission member  19  is pushed in cooperation with the first piston  20 , and thus the second piston  30  also moves toward the blind end of the cylinder  10 . 
         [0018]    As the first and second pistons  20  and  30  move forwards, the center valves  60  moves along with the first and second pistons  20  and  30 . As a result, as in  FIG. 2 , the valve bodies  62  of the center valves  60  are separated from the respective cylinder pins  70 . 
         [0019]    Further, when the valve bodies  62  of the center valves  60  are separated from the respective cylinder pins  70 , i.e. are not supported on the respective cylinder pins  70 , the elastic members  64  extend. Due to the extension of the elastic members  64 , the center valves  60  are pushed in the communication holes  50  in a backward direction, so that the sealing members  61  come into close contact with the respective valve seats  53 . 
         [0020]    As a result, the flow of fluid through each communication hole  50  is interrupted, and thus the first and second hydraulic chambers  21  and  31  are closed. Afterwards, due to the continued movement of the first and second pistons  20  and  30 , the fluid of each of the first and second hydraulic chambers  21  and  31  is pressed to move to the wheel cylinders. 
         [0021]    When the breakage is released, the first and second pistons  20  and  30  are returned to their original positions by the return springs  40 , and thereby the valve bodies  62  of the center valves  60  are supported on the cylinder pins  70  again as in  FIG. 1 . 
         [0022]    In this state, the center valves  60  press the respective elastic members  64  in the front thereof, so that the elastic members  64  move forwards in the communication holes  50 . Thereby, the sealing members  61  are separated from the respective valve seats  53 , and thus the first and second hydraulic chambers  21  and  31  become open. 
         [0023]    Meanwhile, this conventional master cylinder is used for applying the braking force to the wheels although the brake is not operated in a brake hydraulic control system, which is equipped with an anti-lock brake system (ABS) for preventing the wheels from locking during braking, a traction control system (TCS) for preventing the drive wheels from excessively slipping when abruptly starting off or accelerating, and an electronic stability program (ESP) for regulating a traveling direction of the vehicle in which a driver wants to go when the traveling direction of the vehicle is not identical to an actual traveling direction of the vehicle as a result of analyzing the state of the steering wheel. 
         [0024]    In this manner, when the wheels slip regardless of the operation of the brake pedal, a hydraulic pump draws the fluid of the master cylinder through the first and second outlets  23  and  33 , and then pressurizes the drawn fluid again so as to brake the wheels. 
         [0025]    However, this conventional master cylinder has a problem in that, because a space where the fluid flows through the communication holes  50  is narrow, the fluid does not smoothly flow from the first and second inflow chambers  24  and  34  to the first and second outlets  23  and  33  through the communication holes  50  when the hydraulic pump draws the fluid of the master cylinder through the first and second outlets  23  and  33 . 
         [0026]    Further, as illustrated in  FIG. 3 , an edge  61   a  of the sealing member  61  made of rubber is squeezed between the first piston  20  and the valve body  62  of the center valve  60 , and thus the sealing member  61  is reduced in durability and sealing efficiency. 
         [0027]    The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
       SUMMARY OF THE INVENTION 
       [0028]    Various aspects of the present invention are directed to provide a master cylinder capable of sufficiently securing a channel through which a hydraulic fluid flows and increasing durability of a sealing member. 
         [0029]    In an aspect of the present invention, in a master cylinder having at least one piston that pressurizes a hydraulic fluid when a stepping force on a brake pedal is transmitted thereto and sends the pressurized hydraulic fluid to at least a wheel cylinder, the piston includes a large diameter passage and a small diameter passage having a diameter smaller than that of the large diameter passage, and a valve body is fastened to the large diameter passage to control fluid communication between the large diameter passage and the small diameter passage, the valve body including a plunger coupling hole and a channel through which the hydraulic fluid communicates between the large diameter passage and the small diameter passage, wherein a plunger slidably passes the valve body through the plunger coupling hole and closes the channel of the valve body when the stepping force on the brake pedal is transmitted to the piston. 
         [0030]    The channel may be formed by at least a spoke extending from the plunger-coupling hole in a radial direction thereof. 
         [0031]    The valve body may include a first sealing member disposed around outer surface of the valve body and configured to selectively seal the channel of the valve body and the plunger in the large diameter passage of the piston. 
         [0032]    The valve body may further include a second sealing member protruding from the first sealing member to the large diameter passage and configured to seal the first sealing member and the large diameter passage of the piston. 
         [0033]    The valve body may include a second sealing member protruding from outer surface of the valve body to the large diameter passage and configured to seal the valve body and the large diameter passage of the piston. 
         [0034]    One end portion of the plunger slidably passing through the plunger coupling hole of the valve body and disposed in the small diameter passage may be coupled with an elastic member, which returns the plunger to close the channel of the valve body when the force stepping on the brake pedal disappears wherein the plunger includes a plunger body slidably passing through the plunger-coupling hole and coupled to the elastic member in the small diameter passage, and a channel open plate disposed in the large diameter passage to selectively close or open the channel of the valve body according to restoring force of the elastic member or the force stepping on the brake pedal. 
         [0035]    The valve body may include a first sealing member disposed around outer surface of the valve body and configured to selectively seal the channel of the valve body and the channel open plate of the plunger in the large diameter passage of the piston, wherein the valve body further includes a second sealing member protruding from the first sealing member to the large diameter passage and configured to seal the first sealing member and the large diameter passage of the piston. 
         [0036]    The valve body may include a second sealing member protruding from outer surface of the valve body to the large diameter passage and configured to seal the valve body and the large diameter passage of the piston. 
         [0037]    The one end portion of the plunger may be coupled to the elastic member by an elastic member guide configured to extend integrally from rear end of the valve body in a longitudinal direction thereof in the small diameter passage so as to receive the elastic member thereon, the plunger coupling hole being formed through the valve body and the elastic member guide, wherein the plunger includes a plunger body movably passing through the plunger-coupling hole and coupled to the elastic member guide in the small diameter passage, and a channel open plate disposed in the large diameter passage to selectively close or open the channel of the valve body according to restoring force of the elastic member or the force stepping on the brake pedal. 
         [0038]    The valve body may include a first sealing member disposed around outer surface of the valve body and configured to selectively seal the channel of the valve body and the channel open plate of the plunger in the large diameter passage of the piston, wherein the valve body further includes a second sealing member protruding from the first sealing member to the large diameter passage and configured to seal the first sealing member and the large diameter passage of the piston. 
         [0039]    The valve body may include a second sealing member protruding from outer surface of the valve body to the large diameter passage and configured to seal the valve body and the large diameter passage of the piston. 
         [0040]    The plunger body may include a guide coupler at an end portion thereof to receive an end of the elastic member guide therein. 
         [0041]    The elastic member guide may have a protrusion protruding outwards from outer surface of the elastic member guide to retain the elastic member between the valve body and the protrusion and a catch coupled to the guide coupler of the plunger body. 
         [0042]    The valve body may be elastic. 
         [0043]    The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]      FIG. 1  is a cross-sectional view illustrating a conventional master cylinder before braking. 
           [0045]      FIG. 2  is a cross-sectional view illustrating a conventional master cylinder during braking. 
           [0046]      FIG. 3  is an enlarged cross-sectional view illustrating an important part of  FIG. 2 . 
           [0047]      FIG. 4  is a cross-sectional view illustrating an exemplary master cylinder according to the present invention. 
           [0048]      FIG. 5  is an enlarged perspective view illustrating a valve body of  FIG. 4 . 
           [0049]      FIG. 6  is a cross-sectional view illustrating the state in which a braking force is generated from the master cylinder of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0050]    Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0051]      FIG. 4  is a cross-sectional view illustrating a master cylinder according to an exemplary embodiment of the present invention.  FIG. 5  is an enlarged perspective view illustrating a valve body of  FIG. 4 .  FIG. 6  is a cross-sectional view illustrating the state in which a braking force is generated from the master cylinder of  FIG. 4 . 
         [0052]    As illustrated in  FIGS. 4 and 5 , according to various embodiments of the present invention, the master cylinder includes a cylinder  100  having a blind end and first and second pistons  200  and  300  housed in the cylinder  100 . The first and second pistons  200  and  300  are spaced apart from each other so as to be able to make relative motion. 
         [0053]    A first boosting force transmission member  180  is interposed between an output shaft of the booster connected with a brake pedal and the first piston  200 . A second boosting force transmission member  190  is interposed between the first piston  200  and the second piston  300 . 
         [0054]    At this time, a space between the first piston  200  and the second piston  300  and a space between the second piston  300  and the blind end of the cylinder  100  serve as a first hydraulic chamber  210  and a second hydraulic chamber  310 , respectively. The first and second hydraulic chambers  210  and  310  are provided therein with respective return springs  400  for returning the first and second pistons  200  and  300  when breakage is released. 
         [0055]    Further, the cylinder  100  is provided with first and second inlets  220  and  320 , which feed a fluid into the cylinder  100 , and first and second outlets  230  and  330 , which transfer the fluid pressurized at the first and second hydraulic chambers  210  and  310  to wheel cylinders. The first and second inlets  220  and  320  are coupled with an oil tank. 
         [0056]    Meanwhile, the first and second pistons  200  and  300  are equipped with first and second inflow chambers  240  and  340  in intermediate portions thereof in which the fluid introduced into the cylinder  100  through the first and second inlets  220  and  320  is stored before it is sent to the first and second hydraulic chambers  210  and  310 . The first and second pistons  200  and  300  are provided with communication holes  500  which connect the first and second inflow chambers  240  and  340  with the first and second hydraulic chambers  210  and  310 . 
         [0057]    Hereinafter, a structure of the first piston  200  will be described, which is equally applied to a structure of the second piston  300 . 
         [0058]    The first piston  200  includes a stepped transition  530  in the inner circumference thereof. The communication hole  500  includes a large diameter passage  510  located in front of the transition  530 , and a small diameter passage  520  located in the rear of the transition. The diameter of the small diameter passage  52  is smaller than that of the large diameter passage  51 . 
         [0059]    The large diameter passage  510  is equipped with a valve body  620  contacting the transition  530 , a plunger  630  moving through the valve body  620  when hydraulic pressure is generated, a sealing member  640  installed on the outer circumference of the valve body  620 , and an elastic member  650  installed on one end of the plunger  630  and returning the plunger  630  to a standby position when force stepping on the brake pedal disappears. The valve body  620  is fastened to the large diameter passage  510  of the first piston  200  so that the valve body  620  functions as a stationary member for the plunger  630  reciprocates therethrough. 
         [0060]    Herein, the standby position refers to the state in which the hydraulic pressure is not formed in the first piston  200 . A braking position refers to the state in which the hydraulic pressure is formed in the first piston  200 , and thus a braking force is applied to the wheel cylinders. 
         [0061]    As illustrated in  FIGS. 4 and 5 , the valve body  620  is provided therein a channel  621  through which a hydraulic fluid flows. In various embodiments of the present invention, the channel  621  may be formed by a plurality of spokes  646 . The channel  621  is radially formed around a plunger-coupling hole  623  as the spokes  646  extends in radial direction from the plunger-coupling hole  623 , thereby securing a maximum space through which the hydraulic fluid is to flow. 
         [0062]    In various embodiments of the present invention, the plunger-coupling hole  623  may be formed in a central region of the valve body  620  so as to movably hold the plunger  630 . The plunger-coupling hole  623  guides the plunger  630  such that the plunger  630  can stably move without fluctuation. 
         [0063]    Further, the plunger  630  includes a plunger body  631  movably passing through the plunger-coupling hole  623  of the valve body  620 , a guide coupler  633  installed on one end of the plunger body  631 , and a channel open plate  635  installed on the other end of the plunger body  631  so as to open or close the channel  621  of the valve body  620 . 
         [0064]    The guide coupler  633  is coupled with an elastic member guide  660  guiding the elastic member  650 . The guide coupler  633  is provided so as to correspond to a shape of the elastic member guide  660 . According to various embodiments of the present invention, the guide coupler  633  is recessed such that the elastic member guide  660  is caught thereon. 
         [0065]    The elastic member  650  is coupled to the elastic member guide  660  at one end thereof, and is supported by the valve body  620  at the other end thereof. This elastic member  650  is not limited to its shape as long as elastic force is produced, and can be configured in a variety of shapes such as a coil spring, a leaf spring, and so on. 
         [0066]    The elastic member guide  660  is interposed between the plunger body  631  and the elastic member  650  so as to prevent the elastic member  650  from separating outwards. This elastic member guide  660  includes a catch  661  coupled to the guide coupler  633 . Preferably, the catch  661  is forcibly coupled to the guide coupler  633  so as to be able to prevent separation of the elastic member  650 . Furthermore the elastic member guide  660  includes a protrusion  664  so as to receive the elastic member  650  to prevent separation of the elastic member  650 . 
         [0067]    Meanwhile, the sealing member  640  enclosing the outer circumference of the valve body  620  includes a first sealing member  641  that slightly protrudes from the valve body  620  in a radial direction to selectively seal the channel open plate  635  and the valve body  620  and a plurality of second sealing members  643  that protrudes outwards from the first sealing member  641  in an annular shape in a radial direction to seal a gap between the first sealing member  641  and the large diameter passage  510 . 
         [0068]    Here, preferably, the outer diameter of each second sealing member  643  is somewhat greater than the inner diameter of the first piston  200  so as to improve sealing efficiency. 
         [0069]    Since the channel open plate  635  is formed so as to correspond to the first sealing member  641 , the channel  621  is open at a standby position where the channel open plate  635  is separated from the first sealing member  641 , and thus the hydraulic fluid flows through the channel  621 . In contrast, the channel  621  is closed at a braking position where the channel open plate  635  is in close contact with the first sealing member  641 , and thus a sealed stated in which the hydraulic fluid does not flow through the channel  621  is maintained. 
         [0070]    Various embodiments of the present invention may not include a sealing member  640  if the valve body  620  is elastic and sufficiently large enough to seal the large diameter passage  510  and thus the channel  621  can be further enlarged. 
         [0071]    Other exemplary embodiments of the present invention may include one of the first and second sealing member  641  and  643  in case that the valve body  620  is elastic. 
         [0072]    Now, the operation of the master cylinder as described above will be described below. 
         [0073]    When the brake pedal is applied for breakage, the first boosting force transmission member  180  is pushed by the output shaft of the booster, and thus the first piston  200  moves forwards. Then, the second boosting force transmission member  190  is pushed in cooperation with the first piston  200 , and thus the second piston  300  also moves toward the blind end of the cylinder  100 . 
         [0074]    The operation of the first piston  200  will be described below, which is equally applied to the operation of the second piston  300 . 
         [0075]    As the first piston  200  moves, the valve body  620  moves along with the first piston  200 . As a result, the elastic member  650  compressed between the valve body  620  and the elastic member guide  660  extends, and thus the channel open plate  635  of the plunger  630  comes into close contact with the first sealing member  641  of the sealing member  640  as illustrated in  FIG. 6 . As the first piston  200  continues to move, the plunger body  631  is separated from the cylinder pin  700  and moves along with the first piston  200 . 
         [0076]    In this process, the flow of fluid through the communication hole  500  is interrupted, and thus the first hydraulic chamber  210  is closed. Afterwards, due to the continued movement of the first piston  200 , the fluid of the first hydraulic chamber  210  is pressed to move to the wheel cylinders. 
         [0077]    When the breakage is released, the first piston  200  is returned to its original position by the return spring  400 . In this process, the plunger body  631  of the plunger  630  moving along the first piston  200  comes into contact with the cylinder pin  700 . Then, the valve body  620 , which moves in combination with the first piston  200 , compresses the elastic member  650 . Thereby, the elastic member  650  is compressed, so that the plunger body  631  is separated from the first sealing member  641  and the valve body  620 , and thus the first hydraulic chamber  210  is open. 
         [0078]    Meanwhile, this master cylinder according to various embodiments of the present invention may be used for applying the braking force to the wheels although the brake is not operated in a brake hydraulic control system, which is equipped with an anti-lock brake system (ABS) for preventing the wheels from locking during braking, a traction control system (TCS) for preventing the drive wheels from excessively slipping when abruptly starting off or accelerating, and an electronic stability program (ESP) for regulating a traveling direction of the vehicle in which a driver wants to go when the traveling direction of the vehicle is not identical to an actual traveling direction of the vehicle as a result of analyzing the state of the steering wheel. 
         [0079]    In this manner, when the wheels slip regardless of the operation of the brake pedal, a hydraulic pump draws the fluid of the master cylinder through the first and second outlets  230  and  330 , and then pressurizes the drawn fluid again so as to brake the wheels. 
         [0080]    As described above, according to various embodiments of the present invention, the channel  621  are formed in the valve body  620 , so that the channel  621  through which the hydraulic fluid flows can be sufficiently secured, and so that the sealing member  640  avoids being installed in the channel  621 , and thus is increased in durability. 
         [0081]    For convenience in explanation and accurate definition in the appended claims, the terms “forwards” and “backwards” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
         [0082]    The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.