Abstract:
A master cylinder apparatus is provided with a master cylinder and a booster. The booster comprises a booster shell whose interior is divided into a variable-pressure chamber and a constant-pressure chamber, a control valve to regulate the communication of the variable-pressure chamber with the constant-pressure chamber and the atmosphere. The master cylinder comprises a cylinder body provided with a cylinder and a master piston inserted in the cylinder. The cylinder body formed with an installation flange to which the booster shell is attached at the same end that the cylinder opens. Pull means connected to a brake pedal at one end and to the control valve at the other end. The installation flange is attached to a dashboard, so that the booster shell is disposed in one of a passenger room and an engine room and the cylinder body protrudes into the other room. When the brake pedal is stepped on, the pull means makes the control valve operate to communicate the atmosphere to the variable-pressure chamber, whereby the booster augments the stepping force exerted on the brake pedal. The master piston is moved by the output member of the booster to generate a fluid pressure in the master cylinder that is delivered to wheel cylinders. In this manner, the installation flange of the cylinder body is attached to a dashboard, so that the booster shell is disposed in one of a passenger room and an engine room and the cylinder body protrudes into the other room, whereby the flexibility in mounting the master cylinder apparatus with the booster on the vehicle can be increased tremendously. Moreover, as the stepping force exerted on the brake pedal is supported by the installation flange attached to the dashboard and does not act on the booster, the thickness of the booster shell can be made thin without deformation and vibration thereof.

Description:
INCORPORATION BY REFERENCE  
         [0001]    This application is based on and claims priority under 35 U.S.C. sctn. 119 with respect to Japanese Application No. 2002-326971 filed on Nov. 11, 2002, No. 2002-326984 filed on Nov. 11, 2002, No. 2002-350591 filed on Dec. 3, 2002, and No. 2003-353896 filed on Oct. 14, 2003 the entire content of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a master cylinder apparatus with a booster that augments the stepping force on a brake pedal of a vehicle.  
           [0004]    2. Discussion of the Related Art  
           [0005]    Heretofore, there has been known a so-called pull-type master cylinder apparatus with a booster that augments the stepping force on a brake pedal of a vehicle to generate boosted brake fluid pressure by pulling a pull rod connected between the brake pedal and a control valve for regulating air flow to and from the booster, as described in Japanese unexamined, published application No. 56-154357 (1981-154357) and No. 2001-294138. In the first known apparatus, the booster includes a booster shell comprising front and rear shells that sandwich a periphery of a diaphragm to divide the interior of the booster shell into constant-pressure chamber and a variable-pressure chamber. The control valve that regulates the communication of the variable-pressure chamber with the constant-pressure chamber and the atmosphere is provided in a piston that is attached to the diaphragm. The booster is attached to a master cylinder that comprises a cylinder body and a master piston. The cylinder body is provided with a cylinder that opens to a front surface of the cylinder body to which the booster shell is air-tightly fixed. The master piston is slidably inserted in the cylinder and has the rear end thereof entering a constant-pressure chamber of the booster to make abutting engagement with an output member of the booster. A reaction force generating device is interposed between the piston and the output member to make a reaction force act on the pull rod. The pull rod is connected to the brake pedal at the one end and is connected at the other end to a valve body of the control valve through holes made in the cylinder body, the master piston and the piston respectively. And the pull-type master cylinder apparatus with the booster is disposed in a engine room, and the rear end surface of the master cylinder is brought in abutment with a front surface of a dashboard of a vehicle to be attached thereto.  
           [0006]    However, in the first prior art pull-type master cylinder apparatus with the booster, as the pull rod connected to the brake pedal is connected to the valve body of the control valve through holes that are respectively made in the cylinder body, the master piston and the piston, it is disadvantageously required to use many seal members, which results in complication in configuration. In addition, the whole length of the master cylinder apparatus becomes long to worsen the flexibility in mounting the master cylinder apparatus on the vehicle, because the pull rod extends from the front end of the cylinder to the rear end of the booster through the holes made on the axis thereof. It also worsens th flexibility in mounting the master cylinder apparatus on the vehicle and makes the master cylinder apparatus to be prone to vibrate that the booster with a large diameter is fixed to the front end of the master cylinder which is attached to the dashboard at the rear end thereof in an engine room.  
           [0007]    In the second prior art pull-type master cylinder apparatus with the booster, the booster is attached at the rear end thereof to the dashboard in the engine room, and the master cylinder is fixed to the front and of the booster.  
           [0008]    In the second prior art pull-type master cylinder apparatus with the booster, as the rear end of the booster is attached to the dashboard to mount the master cylinder apparatus on the vehicle, the stepping force exerted on the brake pedal acts on the booster, therefore the booster shell of the booster is made thick to have enough strength to prevent the deformation thereof. This makes the booster or the master cylinder apparatus heavy and expensive.  
         SUMMARY OF THE INVENTION  
         [0009]    Accordingly, it is a primary object of the present invention to provide an improved master cylinder apparatus with a booster that is capable of increasing flexibility in mounting the master cylinder apparatus on a vehicle, and capable of reducing the weight thereof.  
           [0010]    Another object of the present invention is to provide an improved master cylinder apparatus with a booster that is capable of realizing easier assembling thereof and reduced manufacturing cost.  
           [0011]    Briefly, according to the present invention, there is provided a master cylinder apparatus with a booster, comprising a booster shell; a partition member dividing the interior of the booster shell into a variable-pressure chamber and a constant-pressure chamber; a piston attached to the partition member for transmitting the movement in a front-rear direction of the partition member responsive to the pressure difference between the variable-pressure chamber and the constant-pressure chamber, to an output member; a control valve disposed in the piston to regulate the communication of the variable-pressure chamber with the constant-pressure chamber and the atmosphere; a cylinder body provided with a cylinder that opens to an end thereof and an installation flange at the same end to which the booster shell is attached; a master piston slidably inserted in the cylinder and connected to the output member; a reaction force generating device interposed between the piston and the output member to make a reaction force act on a valve body of the control valve; pull means connected to a brake pedal at one end and to the valve body at the other end. The installation flange is attached to a dashboard, so that the booster shell is disposed in one of a passenger room and an engine room and the cylinder body protrudes into the other room through an installation hole made through the dashboard.  
           [0012]    With this configuration, when the brake pedal is stepped on, the pull means is pulled rearward to move the valve body relative to the piston. The control valve makes atmospheric air to be led to the variable-pressure chamber according to the movement of the valve body, whereby the pressure difference between the variable-pressure chamber and the constant-pressure chambers is brought about. The partition member and the piston are moved rearward in response to the pressure difference to move the output member through the reaction force generating device. The master piston is moved by the output member to generate a fluid pressure in the cylinder that is delivered to wheel cylinders of a brake system.  
           [0013]    The installation flange of the cylinder body is attached to a dashboard, so that the booster shell is disposed in one of a passenger room and an engine room and the cylinder body protrudes into the other room, whereby the flexibility in mounting the master cylinder apparatus with the booster on the vehicle can be increased tremendously. Moreover, as the stepping force exerted on the brake pedal is supported by the flange attached to the dashboard and does not act on the booster, the thickness of the booster shell can be made thin without deformation and vibration thereof. As a result, simpler construction, easier assembling and reduced manufacturing cost of the master cylinder apparatus can advantageously be realized. 
       
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS  
       [0014]    The foregoing and other objects and many of the attendant advantages of the present invention may readily be appreciated as the same becomes better understood by reference to the preferred embodiments of the present invention when considered in connection with the accompanying drawings, wherein like reference numerals designate the same or corresponding parts throughout several views, and in which:  
         [0015]    [0015]FIG. 1 is a longitudinal sectional view of a master cylinder apparatus with a booster according to the first embodiment of the present invention;  
         [0016]    [0016]FIG. 2 is a view shown from an arrow A in FIG. 1;  
         [0017]    [0017]FIG. 3 is a sectional view showing connection of a balancing member to an input portion of a valve body at the center and to a pair of pull rods at both ends in the first embodiment;  
         [0018]    [0018]FIG. 4 is a side view of the master cylinder apparatus attached to a dashboard of a vehicle in the first embodiment;  
         [0019]    [0019]FIG. 5 is a longitudinal sectional view of a master cylinder apparatus with a booster according to the second embodiment of the present invention;  
         [0020]    [0020]FIG. 6 is a side view of the master cylinder apparatus attached to a dashboard of a vehicle in the second embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    (First Embodiment)  
         [0022]    Hereinafter, an embodiment of a master cylinder apparatus with a booster according to the present invention will be described with reference to the drawings. As shown in FIG. 1, a booster shell  1  of a booster  1   a  is composed of a front shell  2  defining a front wall and a rear shell  3  defining a real wall. Between the shells  2  and  3 , a flexible diaphragm  4  is airtightly sandwiched at the peripheral bead and operates as a partition member which divides the interior of the booster shell  1  into a constant-pressure chamber  5  at the rear side and a variable-pressure chamber  6  at the front side.  
         [0023]    A disc-like plate  7  is overlapped over the diaphragm  4  within the constant-pressure chamber  5 . A piston  8  is air-tightly secured at an external surface of its rear end portion to center holes formed on the diaphragm  4  and the plate  7 . The rear end of the piston  8  is exposed within the constant-pressure chamber  5 . The front shell  2  is provided at the center thereof with a cylindrical projection  2   a  protruding forward which has an intake chamber  2   b  on its axis. The front portion of the piston  8  is accommodated in the intake chamber  2   b , and an air-tight seal member  9  is interposed between the internal surface of the intake chamber  2   b  and the external surface of the piston  8  to seal the variable-pressure chamber  6  from the intake chamber  2   b . An atmospheric air inlet pipe  10  is secured to the cylindrical projection  2   a  to introduce the atmospheric air into the intake chamber  2   b . A negative pressure inlet pipe  11  is secured to the rear shell  3 . The constant pressure chamber  5  is in communication with an intake manifold of an engine through the negative pressure inlet pipe  11  and is maintained at the negative pressure of a certain level.  
         [0024]    A cylinder body  20  of a master cylinder  12 , whose front end  12   a  passes through a center hole  3   a  formed on the rear shell  3  protrudes within the constant-pressure chamber  5  air-tightly. An installation flange  20   a  of the cylinder body  20  is in abutment with the rear surface of the rear shell  3  with a seal ring being interposed therebetween. Four flanged bolts  14  attached to the rear shell  3  protrude rearward into a passenger room  15 . The flanges  14   a  of the bolts  14  are in abutment with the internal surface of the rear shell  3 , and male screws  14   b  of bolts  14  extend rearward through rear shell  3 . The bolts  14  are air-tightly secured to the rear shell  3  by caulking the neck portions thereof to the rear shell  3 . The male screws  14   b  of the bolts  14  extend through bolt holes formed at the corners of the installation flange  20   a . By fastening up nuts  16  that engage the male screws  14   b  of the bolts  14 , the rear shell  3  is air-tightly fixed to the front surface of the cylinder body  20 . The master cylinder  12  enters the passenger room  15  through an installation hole  17   a  formed through a dashboard  17 . The rear surfaces of the nuts  16  are in abutment with the front surface of the dashboard  17  outside the passenger room  15 . By fastening up nuts  18  that engage male screws  14   b  of the bolts  14  that extend through the dashboard  17  with washers being interposed between the nuts  18  and the dashboard  17 , the installation flange  20   a  is attached to a dashboard  17 , so that the booster shell  1  is disposed in the engine room  66  and the cylinder body  20  protrudes into the passenger room  15  through an installation hole  17   a  made through the dashboard  17 .  
         [0025]    An elastic seal member  19  for fluid-tightly sealing the installation hole  17   a  is interposed between the rear shell  3  and the dashboard  17 . The seal member  19  is provided with peripheral loop portion  19   a  surrounding the installation flange  20   a , the nuts  16  and the installation hole  17   a . The opposite end surfaces of the peripheral loop portion  19   a  are in fluid-tight abutment with the rear surface of the rear shell  3  and the front surface of the dashboard  17  to prevent water from entering into the passenger room  15 . The seal member  19  is made of rubber, aluminum covered with rubber, resin or other elastic material.  
         [0026]    The cylinder body  20  is formed with a cylinder  21  that is in co-axial relation with the booster shell  1 . The cylinder  21  opens to the constant-pressure chamber  5  at the front end, and has a bottom at the rear end. First and second piston  22 ,  23  are slidably inserted in the cylinder  21  in line with the first piston  22  being positioned at the opening side of the cylinder  21 . The front portion of the first piston  22  enters into the constant-pressure chamber  5  by fluid-tightly passing through a seal member  39  secured to the front surface of the cylinder body  20  to which the cylinder  21  opens. A first cup seal  25  is mounted on a rear end portion of the first piston  22 , and a second cup seal  26  is mounted on a front end portion of the second piston  23  to partition the cylinder  21  as a first fluid pressure chamber  24  from which pressurized fluid is supplied to a first brake system (not shown). A third cup seal  27  is mounted on a rear end portion of the second piston  23  to partition the bottom portion of the cylinder  21  as a second fluid pressure chamber  28  from which pressurized fluid is supplied to a second brake system (not shown).  
         [0027]    In FIG. 1, the operating fluid pressurized within the first and second fluid pressure chamber  24  and  28  is supplied through the first and second ports  61 ,  62  to brake tubes that are laid in the passenger room  15  and are extended through the dashboard  17  to be connected to the wheel cylinders (not shown), so that the pressurized fluid is supplied to the wheel cylinders.  
         [0028]    It is possible to form passages in the cylinder body  20  that substitute for brake tubes laid in the passenger room  15  and open to the exterior of the cylinder body  20  in a space  65  between the rear shell  3  of the booster  1   a  and the dashboard  17  to make ports corresponding to the first and second ports  61 ,  62 , thereby to supply the pressurized fluid to the wheel cylinders. In this configuration, as the brake tubes are not laid in the passenger room  15 , it does not happen that the passenger room  15  is made dirty by the leakage of the operating fluid. And as the brake tubes do not extend through the dashboard  17 , seal members are not necessary for fluid-tightly sealing between brake tubes and dashboard  17 , and troublesome piping out of the passenger room  15  becomes unnecessary.  
         [0029]    From the rear end surface of the first piston  22 , there is protruded rearward a rod  29  which is provided with an engagement portion at the rear end thereof. A numeral  30  denotes a spring seat of a bell shape, which is guided by the rod  29  at a hole formed at the front end thereof and which is in engagement with the engagement portion of the rod  29 , so that the spring seat  30  is restrained from moving rearward. A numeral  31  denotes a first compression spring interposed between a flange which is expanded radially outwardly at the rear end of the spring seat  30  and the rear end surface of the first piston  22 . The first compression spring  31  urges the spring seat  30  rearward by a first set spring force until the spring seat  30  is engaged with the engagement portion of the rod  29 . A numeral  33  denotes a second compression spring interposed between the second piston  23  and the bottom surface of the cylinder  21 . The second compression spring  33  urges the second piston  23  forward by a second set spring force smaller than the first set spring force and brings the second piston  23  into engagement with the spring seat  30 . In this way, the first and second piston  22 ,  23 , the rod  29 , the spring seat  30 , the first compression spring  31  and the like constitute a master piston  40  which is slidably inserted in the cylinder  21  and protrudes into the constant-pressure chamber  5  at the front end portion thereof. The master cylinder  12  comprises the cylinder body  20 , the master piston  40 , the cup seals  25  through  27  and so forth.  
         [0030]    A reservoir  34  is mounted on the top of the cylinder body  20  and is secured thereto by means of a pin  63 . First and second output ports  35 ,  36  formed at the lower surface of the reservoir  34  are in fluid communication respectively with first and second supply ports  37 ,  38  which open to the top surface of the cylinder body  20  for replenishing the operating fluid to the first and second fluid pressure chambers  24 ,  28 . The first and second supply ports  37 ,  38  open to the first and second fluid pressure chamber  24 ,  28  when the first and second piston  22 ,  23  are positioned at the inoperative position. The front portion of the reservoir  34  to which a reservoir pipe  34   a  is secured extends into the space inside the peripheral loop portion  19   a  of the seal member  19  through the installation hole  17   a . The reservoir pipe  34   a  extends air-tightly to the atmosphere through the peripheral loop portion  19   a  of the seal member  19  that is interposed between the rear surface of the rear shell  3  and the front surface of the dashboard  17 .  
         [0031]    An output member  41  is interposed between the piston  8  and the first piston  22 . The piston  8  operates to transmit the rearward movement of the diaphragm  4  that is responsive to the pressure difference between the constant-pressure chamber  5  and the variable-pressure chamber  6 , to the first piston  16  through the output member  41 . Namely, a connection hole  22   a  is formed in the first piston  22  extending from the front end surface of the third piston  22  in the axial direction. The bottom of the connection hole  22   a  defines a conical space whose top is rounded. The output member  41  is formed with a rod portion  41   a  that is in pivotable abutment at the tip thereof with the rounded bottom surface of the connection hole  22   a , so that the rod portion  41   a  is automatically brought into alignment with the first piston  22 . An annular projection  41   b  formed at the front end of the output member  41  is axially movably fit in an annular recess  8   a  that is formed in the piston  8  to extend forward from the rear end surface thereof. A return spring  42  is interposed between the rear shell  3  and the rear end surface of the piston  8  to urge the piston  8  forward.  
         [0032]    A reaction force generating device  44  is interposed between the piston  8  and the output member  41  to make reaction force act on a valve body  48  of a control valve  46 . When the control valve  46  is operated upon the stepping-on of a brake pedal  43 , a pressure difference between the constant-pressure chamber  5  and the variable-pressure chamber  6  is generated to urge the diaphragm  4  or the piston  8  rearward, as will be described hereinafter. The reaction force generating device  44  has a disc-like reaction force member  45  made of an elastic material that is received in a reaction force chamber  41   c  surrounded by the annular projection  41   b  of the output member  41 . The reaction force member  45  is interposed between a reaction force end surface  8   b  surrounded by the annular recess  8   a  of the piston  8  and the bottom surface of the reaction force chamber  41   c . The reaction force member  45  is compressively deformable by the force that the piston  8  exerts on the output member  41  or the first piston  22 .  
         [0033]    The control valve  46  is disposed in the piston a and regulates the communication of the variable-pressure chamber  6  with the constant-pressure chamber  5  and the atmosphere. An annular valve seat member  47  is disposed in a valve hole  8   c  that is formed at the rear portion of the piston  8  in the axial direction. An annular valve seat member  47  is bodily connected at the front end thereof to a bellows  47   a  that permits the axial movement of the valve seat member  47 , and the circular portion  47   b  of the bellows  47   a  is air-tightly fit in the valve hole  8   c  and is urged by a compression spring  57  to the shoulder formed at the center portion of the valve hole  8   c.    
         [0034]    A negative pressure valve seat  47   d  is formed on the outer periphery of the rear end surface of the valve seat member  47 . The valve hole  8   c  is reduced in diameter to form a negative pressure valve portion  8   d  of an annular shape at the rear end portion of the valve hole  8   c . The negative pressure valve seat  47   d  is brought into abutment with a negative pressure valve portion  8   d  when the valve seat member  47  moves rearward relative to the piston  8 . A recess  8   g  that extends rearward from the inner periphery of the negative pressure valve portion  8   d  communicates to the variable-pressure chamber  6  through a hole  8   e  formed radially in the piston  8  to open to the exterior surface of the piston  8  at the position more rearward than the air-tight seal member  9 . The piston  8  is formed with a passage  8   f  that opens at one end to the space partitioned by the outer surface of the bellows  47   a  from the valve hole  8   c  and at the other end to the rear end surface of the piston  8  so that the negative pressure within the constant pressure chamber  5  is led to the variable-pressure chamber  6  via the passage  8   f  when the forward movement of the valve seat member  47  causes the negative pressure valve seat  47   d  to depart from the negative pressure valve portion  8   d.    
         [0035]    A valve body  48  is disposed on the axis of the piston  8  movably in the front-rear direction relative to the piston  8 . The middle portion of a large diameter of the valve body  48  is in the recess  8   g , and the front portion protrudes forward from the middle portion through the annular seat member  47  into the valve hole  8   c , and a rear portion protrudes rearward from the middle portion into the constant-pressure chamber  5 . An air valve portion  48   a  is formed in the form of a closed loop or an annulus at the front surface of the middle portion of the valve body  48 . A compression spring  49  interposed between the front surface of the valve seat member  47  and a shoulder formed on the front portion of the valve body  48 , urges the valve body  48  forward to bring the air valve portion  48   a  into abutment with a air valve seat  47   e  that is formed on the inner periphery of the rear end surface of the annular valve seat member  47 . When the air valve portion  48   a  departs from the air valve seat  47   e , the atmospheric air is led to the variable-pressure chamber  6  via an air filter  58 , the valve hole  8   c , the recess  8   g  and the hole  8   e . Retainers  67 ,  68  secured to the front portion of the valve body  48  at the front end thereof and the air filter  58  sandwiched between the retainers  67 ,  68  are fit in the front portion of the valve hole  8   c . The compression spring  57  is interposed between the retainer  67  and the circular portion  47   b  of the bellows  47   a.    
         [0036]    A numeral  50  denotes a stop member that is inserted radially in the hole  8   e  and is movable relative to the piston  8  by a predetermined amount in an axial direction. The stop member  50  protrudes radially outwardly from the exterior surface of the piston  8 , and is brought into abutting engagement with the inner shoulder portion of the cylindrical projection  2   a  formed on the front shell  2  to stop the forward movement of the piston  8  when the piston  8  is moved forward by resilient force of the return spring  42 . The stop member  50  is brought into abutting engagement with a flange  48   b  formed on the rear portion of the valve body  48  to stop the forward movement of the valve body  48  relative to the piston  8 . The booster  1   a  comprises the booster shell  1 , the diaphragm  4 , the piston  8 , the control valve  46 , the output member  41 , the reaction force generating device  44  and so forth.  
         [0037]    The rear portion of the valve body  48  is formed with the flange  48   b  and an input portion  48   c  which protrudes from the flange  48   b  into the constant-pressure chamber  5  through the reaction force member  45  and the front end of the output member  41 . Namely, an annular push member  51  that is slidably fit on the input portion  48   c  between the flange  48   b  and the reaction force member  45  is slidably fit in a hole formed on the bottom of the recess  8   g  and opening to a reaction surface  8   b  of the piston  8 . The annular push member  51  is brought into abutting engagement with the flange  48   b  at one end and with the reaction force member  45  elastically at the other end to make a reaction force act on the valve body  48  or the input portion  48   c  when the input portion  48   c  is pulled rearward. The output member  41  is formed with a wide portion  41   e  between the annular projection  41   b  and the rod portion  41   a , and an hole  41   d  elongated in the axial direction of the output member  41  is formed through the wide portion  41   e  in a diametrical direction of the booster shell  1 .  
         [0038]    The input portion  48   c  axially extends into the elongated hole  41   d  in the constant-pressure chamber  5  to be connect d to the center portion of a balancing member  52  which extends equally on both sides through the elongated hole  41   d  in a diametrical direction of the booster shell  1 . The balancing member  52  is formed with a through hole  52   a  on a center portion thereof in which the input portion  48   c  is loosely fit and a spherical concave seat  52   b  on the rear surface of the center portion thereof. A connecting member  54  which is formed with a spherical convex portion  54   a  engaging with the spherical concave seat  52   b  is attached to the rear end of the input portion  48   c  by a nut  55  screwed on the rear end of the input portion  48   c . The balancing member  52  is disposed close to the piston  8  to make a distance small between a rear surface of the piston  8  exposed to the constant-pressure chamber  5  and a front surface of the balancing member  52 . An annular spring member  59  is interposed between the return spring  42  and the rear surface of the piston B. The annular spring member  59  is in abutment with the balancing member  52  and urges the balancing member  52  rearward by the resilient force thereof to make the balancing member  52  normally contact with the spherical convex portion  54   a  of the connecting member  54  attached to the input portion  48   c . The balancing member  52  is well kept in a normal position by such a simple structure of interposing the annular spring member  59  between the return spring  42  and the rear surface of the piston  8 .  
         [0039]    Respective pull rods  53  that are disposed on both sides of the cylinder body  20  in parallel relation therewith are pivotally connected to the balancing member  52  at both ends thereof by spherical bearing  56 , and extend through the flange  20   a  of the cylinder body  20 , with keeping air-tight sealing between pull rods  53  and the flange  20   a  by seal members  60  interposed therebetween. As shown in FIG. 4, a brake pedal  43  is pivotably mounted on the dashboard  17  by a pin  64  at the middle portion thereof, and respective ends of a fork portion  43   a  formed at the upper end of the brake pedal  43  are pivotally connected to the pull rods  53 .  
         [0040]    (Operation of the First Embodiment)  
         [0041]    The operation of the master cylinder apparatus as constructed above will be described hereinafter. When the brake pedal  43  is stepped on forward, the brake pedal  43  is swiveled around the pin  64  to pull two pull rods  53  rearward. Two pull rods  53  pull the balancing member  52  rearward by the both ends thereof by means of the respective spherical bearings  56 . The spherical concave seat  52   b  pushes the spherical convex portion  54   a  to move the input portion  48   c  rearward. As positional errors of the input portion  48   c , the balancing member  52  and two pull rods  53  are absorbed by the self-adjustment movement of the spherical concave seat  52   b  relative to the convex spherical portion  54   a , the input portion  48   c  or the valve body  45  is smoothly moved rearward by the balancing member  52 .  
         [0042]    When the valve body  48  is moved rearward relative to the piston  8  against the resilient force of the compression spring  49  and  57 , the air valve portion  48   a  is forced to come off the air valve seat  47   e  of the valve seat member  47 , so that the atmospheric air that is introduced to the intake chamber  2   b  through the atmospheric air inlet pipe  10  and is filtered by the air filter  58  flows into the variable pressure chamber  6  through the hole  8   e . In response to the pressure difference between the variable-pressure chamber  6  and the constant-pressure chamber  5 , the diaphragm  4 , together with the plate  7  and the piston  8  fixed thereto, is moved rearward and the output member  41  is moved rearward by the piston  8  through the reaction force member  45  of the reaction force generating device  44 , so that the first piston  22  is pushed by the output member  41 .  
         [0043]    The first and second pistons  22 ,  23  are moved rearward with the rod  29 , the spring seat  30  and the first compression spring  31  being interposed therebetween, and the first and second supply ports  37 ,  38  are closed by the first and third cup seal member  25 ,  27 . After the first and second supply ports  37 ,  38  are closed, the first and second pistons  22 ,  23  are moved to increase the pressure of the operating fluid within the first and second fluid pressure chambers  24  and  28 , so that the increased fluid pressure is supplied from ports  61 ,  62  to the first and second brake systems.  
         [0044]    The piston  8  elastically deforms the reaction force member  45  with the force whose strength corresponds to the difference between the pressures acting on the both surfaces of the diaphragm  4 , and pushes the first piston  22  through the output member  41  while moving rearward relative to the valve body  48 . When the piston  8  pushes the output member  41  with the force that meets the stepping force exerted on the brake pedal  24 , the air valve seat  47   e  is brought into abutment with the air valve portion  48   a  thereby to block the fluid communication of the variable-pressure chamber  6  with the atmosphere, whereby the braking pressure is maintained at a value depending on the force exerted on the brake pedal  24 .  
         [0045]    At the same time with this, the force with which the brake pedal  24  is stepped on is transmitted to the reaction force member  45  from the input portion  48   c  through the flange  4   b  and the annular push member  51 . Since this causes the reaction force member  45  to be deformed in dependence on the pedal stepping force, the driver can feel the reaction force. Even if the connection between the balancing member  52  and one of two pull rods  53  is cut off by breakage of some parts, the other pull rod can pull the input portion  48   c  or the valve body  48  through the balancing member  52  that will be brought into abutment with the rear surface of the piston  8  because the distance between the rear surface of the piston  8  exposed to the constant-pressure chamber  5  and the front surface of the balancing member  52  is made small.  
         [0046]    When the brake pedal  43  is released, the valve body  48  is moved forward by the force of the compression spring  49 ,  57  relative to a piston  8  to bring the air valve portion  48   a  into abutment with the air valve seat  47   e  and to separate the negative pressure valve seat  47   d  from the negative pressure valve portion  8   d . This permits the negative pressure within the constant-pressure chamber  5  to be led to the variable-pressure chamber  6  via the passage  8   f  and the hole  8   e , whereby the pressure difference between the variable-pressure chamber  6  and the constant-pressure chambers  5  is lost. The piston  8 , the plate  7  and the diaphragm  4  are moved forward by the force of the return spring  42 , and the first and second piston  22 ,  23  are moved forward by the force of the first and second compression spring  31 ,  33  to depressurize the first and second fluid pressure chamber  24 . The valve body  48  is stopped from moving forward at the same time when the stop member  50  is brought into abutment with the inner shoulder portion of the cylindrical projection  2   a . The piston  8  is moved forward a little to be brought into abutment with the stop member  50 , and this brings the negative pressure valve portion  8   d  into abutment with the negative pressure valve seat  47   d , whereby the fluid communication between the constant-pressure chamber  5  and the variable pressure chamber  6  is shut off.  
         [0047]    In the master cylinder apparatus, a rear shell  3  of the booster shell  1  is in abutment with the front surface of the installation flange  20   a  and is air-tightly fixed to the installation flange  20   a  by the nuts  16  engaging with the bolts  14  fixed to the rear shell  3 . The master cylinder  12  is attached to the dashboard  17  by the nuts  18  engaging with th bolts  14 . The elastic seal member  19  provided with peripheral loop portion  19   a  surrounding the installation flange  20   a  and the installation hole  17   a  is interposed between the rear shell  3  and the dashboard  17  to fluid-tightly seal the installation hole  17   a , thereby to be able to make an enough space  65  between the booster  1   a  and the dashboard  17  to easily lay pipes such as brake tubes into and out of the passenger room  15 .  
         [0048]    Further, as the reservoir pipe  34   a  secured to a reservoir  34  of the master cylinder  12  extends air-tightly to the atmosphere through the peripheral loop portion  19   a  of the seal member  19 , it is capable to put operating fluid into the reservoir  34  outside of the passenger room  15 .  
         [0049]    The above-mentioned master cylinder apparatus with the booster  1   a  is made simple in configuration and short in length by disposing the pull rods  53  for connecting the brake pedal  43  to the valve body  48  of the control valve  46  in parallel to the cylinder body  20  to increase the flexibility in mounting the master cylinder apparatus on the vehicle. The seal members that are air-tightly mounted on the pull means are decreased in quantity, so that simpler construction for partitioning, easier assembling of the apparatus and reduced manufacturing cost can advantageously be realized.  
         [0050]    (Second Embodiment)  
         [0051]    Next, the second embodiment will be described with reference to FIGS. 5 and 6. As many parts and components in the second embodiment are identical or corresponding in configuration and function to those in the first embodiment, the parts and the components of the second embodiment are denoted in FIGS. 5 and 6 by the same reference numerals that denote the identical or corresponding parts and components of the first embodiment in FIGS. 1 and 4.  
         [0052]    The main different points of the second embodiment from the first embodiment is that an installation flange  20   a  which is formed on a cylinder body  20  at the rear end thereof is attached to a dashboard  17  in a passenger room  15 , so that a booster shell  1  is disposed in the passenger room  15  and the cylinder body  20  protrudes into an engine room  66 ; furthermore, in the second embodiment, a pull rod  53  is connected to a brake pedal  43  at one end and directly to a valve body  48  of a control valve  46  at the other end, and a master piston  40  of a master cylinder  12  is pulled by an output member  41  of a booster  1   a  to generate a fluid pressure in a cylinder  21  in which the master piston  40  is inserted.  
         [0053]    Front and rear shells  2  and  3  are joined to form a booster shell  1  by two tie-rods  70  that are air-tightly secured to the front shell  2  by caulking with flanges  70   a  formed on the tie-rods  70  being abutment with the internal surface of the front shell  2 . The respective tie-rods  70  extend forward through the front shell  2  and rearward air-tightly through a diaphragm  4  and rear shell  3 . By fastening up nuts  71  that engage male screws  70   c  formed on the rear and portions of the tie-rods  70 , the rear shell  3  is joined to the front shell  2  to form the booster shell  1 .  
         [0054]    The installation flange  20   a  is formed on the cylinder body  20  at the rear end thereof. The front surface of the front shell  2  is in air-tight abutment with the rear end surface of the installation flange  20   a . The male screws  70   b  formed on the front end portion of the tie-rods  70  extend through bolt holes formed at the corners of the installation flange  20   a . By fastening up nuts  72  that engage the male screws  70   b , the front shell  2  is air-tightly fixed to the rear end surface of the cylinder body  20 . The master cylinder  12  enters the engine room  66  through an installation hole  17   a  formed through a dashboard  17 . The front surface of the installation flange  20   a  is in abutment with the rear surface of the dashboard  17  inside the passenger room  15 . By fastening up nuts  73  that engage male screws  70   b  extending through the dashboard  17  into the engine room  66 , the installation flange  20   a  is attached to a dashboard  17 , so that the booster shell  1  is disposed in the passenger room  15  and the cylinder body  20  protrudes into the engine room  66  through an installation hole  17   a  made through the dashboard  17 .  
         [0055]    The cylinder body  20  is formed with a cylinder  21  that is in co-axial relation with the booster shell  1  and has a bottom at the front end. An end member  74  is fluid-tightly fixed to a rear hole  75  that is in co-axial relation with the cylinder  21  and has a larger diameter than the cylinder  21 , so that the end member  74  encloses the rear end of the cylinder  21 . The rear hole  75  communicates with the variable-pressure chamber  6  through a center hole  2   a  formed on the front shell  2 . First and second piston  22 ,  23  are slidably inserted in the cylinder  21  in line with the first piston  22  being positioned at the bottom side of the cylinder  21 . A piton rod  22   a  that protrudes from the rear end of the first piston  22  extends fluid-tightly through center holes formed in the second piston  23  and the end member  74  into the rear hole  75 . Compression springs  31  is interposed between the first and second pistons  22  and  23 , and compression springs  33  is interposed between the second piston  23  and the end member  74 , so that the second piston  23  is positioned at the inoperative position when the brake pedal  43  is released.  
         [0056]    A piston  8  is composed of a front portion  81  that is air-tightly secured to center holes formed on the diaphragm  4  and the plate  7  and a rear portion  82  that is fit on the front portion  81  and fixed thereto by caulking. The rear end of the rear portion  82  projects into the atmosphere through a cylindrical projection  3   a  formed on the rear shell  3  and an air-tight seal member  76  is interposed between the cylindrical projection  3   a  and the external surface of the rear portion  82  to seal the constant-pressure chamber  5  from the atmosphere.  
         [0057]    The control valve  46  is disposed in the piston  8  and regulates the communication of the variable-pressure chamber  6  with the constant-pressure chamber  5  and the atmosphere. An annular valve seat member  47  is disposed in a recess  89  that is formed in the front portion  81  of the piston  8  in the axial direction. An annular valve seat member  47  is bodily connected at the rear end thereof to a bellows  47   a , and the circular portion  47   b  of the bellows  47   a  is air-tightly fixed to a valve hole  8   c  made in the rear portion  82 . An air filter  58  is fixed to the rear portion of the valve hole  8   c . A negative pressure valve seat  47   d  is formed on the outer periphery of the rear end surface of the valve seat member  47 . The valve hole  8   c  of the rear portion  82  is reduced in diameter to form a negative pressure valve portion  8   d  of an annular shape at the contacting portion with the rear end of the front portion  81 . A recess  8   g  that extends forward from the negative pressure valve portion  8   d  communicates to the variable-pressure chamber  6  through a hole  8   e  formed axially in the front portion  81  to open to the front end surface thereof in the variable-pressure chamber  6 . The rear portion  82  is formed with a passage  8   f  that opens at one end to the space partitioned by the outer surface of the bellows  47   a  from the valve hole  8   c  and at the other end to the exterior surface of the rear portion  82  at the position more frontward than the air-tight seal member  76 .  
         [0058]    A valve body  48  is disposed on the axis of the piston  8  movably in the front-rear direction relative to the piston  8 . The middle portion of a large diameter of the valve body  48  is in the valve hole  8   c , and the front portion protrudes forward from the middle portion through the annular seat member  47  into the recess  8   g , and a rear portion protrudes rearward from the middle portion to be connected to a pull rod  53  by means of a ball joint. An air valve portion  48   a  is formed in the form of a closed loop or an annulus at the front surface of the middle portion of the valve body  48 . A compression spring  49  interposed between the front surface of the valve seat member  47  and a cup shape portion  48   d  bodily fixed to the front portion of the valve body  48 , urges the valve body  48  forward to bring the air valve portion  48   a  into abutment with an air valve seat  47   e  that is formed on the inner periphery of the rear end surface of the annular valve seat member  47 . The compression spring  57  is interposed between the rear surface of the middle portion of the valve body  48  and the circular portion  47   b  of the bellows  47   a . The cup shape portion  48   d  is bodily fixed to the front end of the front portion of the valve body  48  and is axially movably fit in the recess  8   g.    
         [0059]    The output member  41  is interposed between the piston  8  and the first piston  22 , so that the piston  8  transmits the rearward movement of the diaphragm  4  to the first piston  22  through the output member  41 . The output member  41  is formed at the rear end thereof with a flange  41   d  in the recess  8   g . A rod portion  41   a  of the output member  41  extends forward through the bottom of the recess  8   g  and is connected in the rear hole  75  to the rear end of the piston rod  22   a  by means of a universal joint  77 . The flange  41   d  has an annular projection  41   b  that projects forward at the periphery thereof, and is axially movably fit in the cup shape portion  48   d  of the valve body  48  in the recess  8   g . An annular push member  51  is axially movably fit in the annular projection  41   b  at the rear portion thereof and is fit in the cup shape portion  48   d  at the front portion thereof with the forward movement of the annular push member  51  relative to the cup shape portion  48   d  being restricted. The cup shape portion  48   d , the annular projection  41   b  and the annular push member  51  are axially movably fit in an annular recess  8   a  that is formed in the front portion  81  to extend forward from the bottom surface of the recess  8   g . A return spring  42  is interposed between the rear shell  3  and the flange formed on the front portion  81  so as to urge the piston  8  forward.  
         [0060]    A reaction force generating device  44  is interposed between the piston  8  and the output member  41  to make reaction force act on a valve body  48  of a control valve  46 . The reaction force generating device  44  has an annular reaction force member  45  made of an elastic material that is received in an annular reaction force chamber  41   c  formed between the rod portion  41   a  and the annular projection  41   b . The reaction force member  45  is interposed between a reaction force end surface  8   b  formed on the bottom of the recess  8   g  and the bottom surface of the reaction force chamber  41   c.    
         [0061]    (Operation of the Second Embodiment)  
         [0062]    The operation of the master cylinder apparatus as constructed above will be described hereinafter. When the brake pedal  43  is stepped on forward, the brake pedal  43  is swiveled around the pin  54  to pull the pull rod  53  whereby the valve body  48  is moved rearward relative to the piston  8  against the resilient force of the compression spring  49  and  57 . The air valve portion  48   a  is forced to come off the air valve seat  47   e  of the valve seat member  47 , so that the atmospheric air that is filtered by the air filter  58  flows into the variable pressure chamber  6  through the hole  8   e . In response to the pressure difference between the variable-pressure chamber  6  and the constant-pressure chamber  5 , the diaphragm  4  and the piston  8  is moved rearward. The output member  41  is moved rearward by the piston  8  through the reaction force generating device  44 , so that the first piston  22  is pulled by the output member  41 .  
         [0063]    The first and second pistons  22 ,  23  are moved rearward to increase the pressure of the operating fluid within the first and second fluid pressure chambers  24  and  28 , so that the increased fluid pressure is supplied from ports  61 ,  62  to the first and second brake systems.  
         [0064]    The piston  8  elastically deforms the reaction force member  45  with the force whose strength corresponds to the difference between the pressures acting on the both surfaces of the diaphragm  4 . When the piston  8  pulls the output member  41  with the force that meets the stepping force exerted on the brake pedal  24 , the air valve seat  47   e  is brought into abutment with the air valve portion  48   a  thereby to block the fluid communication of the variable-pressure chamber  6  with the atmosphere, whereby the braking pressure is maintained at a value depending on the force exerted on the brake pedal  24 .  
         [0065]    At the same time with this, the force with which the brake pedal  24  is stepped on is transmitted to the reaction force member  45  from the cup shape portion  48   d  and the annular push member  51 . Since this causes the reaction force member  45  to be deformed in dependence on the pedal stepping force, the driver can feel the reaction force.  
         [0066]    When the brake pedal  43  is released, the valve body  48  is moved forward by the force of the compression spring  49 ,  57  relative to a piston  8  to bring the air valve portion  48   a  into abutment with the air valve seat  47   e  and to separate the negative pressure valve seat  47   d  from the negative pressure valve portion  8   d . This permits the negative pressure within the constant-pressure chamber  5  to be led to the variable-pressure chamber  6  via the passage  8   f  and the hole  8   e , whereby the pressure difference between the variable-pressure chamber  6  and the constant-pressure chambers  5  is lost. The piston  8  and the diaphragm  4  are moved forward by the force of the return spring  42 , and the first and second pistons  22 ,  23  are moved forward by the force of the first and second compression spring  31 ,  33  to depressurize the first and second fluid pressure chambers  24 ,  28 .  
         [0067]    The valve body  48  is stopped from moving forward when the stop member  50  fixed to the pull rod  53  is brought into abutment with the rear surface of cylindrical projection  3   a  of the rear shell  3 , and this brings the negative pressure valve portion  8   d  into abutment with the negative pressure valve seat  47   d , whereby the fluid communication between the constant-pressure chamber  5  and the variable pressure chamber  6  is shut off.  
         [0068]    In the master cylinder apparatus, the front shell  2  of the booster shell  1  is in abutment with the rear surface of the installation flange  20   a  to be air-tightly secured thereto by nuts  72  engaging with male screws  70   b  formed on tie-rods  70  that is secured to the front shell  2  and join the front shell  2  and a rear shell  3  to form the booster shell  1 , and the installation flange  20   a  is attached to the dashboard  17  by nuts  73  engaging with the male screws  70   b , whereby by means of the plural tie-rods  70  that joins the front and rear shells  2 ,  3  into the booster shell  1 , the booster  1   a  is attached to the cylinder body  20 , and the master cylinder apparatus with the booster is mounted on the dashboard  17 .  
         [0069]    Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.