Abstract:
A brake caliper ( 10 ) includes a first caliper arm ( 12 ) that opposes a first frictional surface ( 6   a ) of a vehicle wheel ( 5 ) and a second caliper arm ( 14 ) that opposes a second frictional surface ( 6   b ) of the same. A movable brake pad ( 7 ) is supported by the first caliper arm ( 12 ) and applies a braking force to the first frictional surface ( 6   a ). A plurality of pistons ( 55 ) which drive the movable brake pad ( 7 ) in accordance with expansion of a diaphragm ( 75 ) provided in the brake caliper ( 10 ), and a guide member ( 65 ) that guides displacement of the plurality of pistons ( 55 ) in a right-angle direction relative to the first frictional surface ( 6   a ) are provided, and therefore the movable brake pad ( 7 ) applies an even braking force to the vehicle wheel ( 5 ) in cooperation with a fixed brake pad ( 700 ) fixed to the second caliper arm ( 14 ).

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a caliper brake device for a vehicle, which applies a brake to a rotary body by sandwiching two frictional surfaces formed on either side face of the rotary body. 
       BACKGROUND OF THE INVENTION 
       [0002]    A railway vehicle is typically installed with a pneumatic-hydraulic converter that converts air pressure supplied from an air pressure source into oil pressure such that a hydraulic brake is activated by the oil pressure, which is supplied thereto from the pneumatic-hydraulic converter via a hydraulic pipe. 
         [0003]    In relation to this point, JPH08-226469 and JPH08-226471, published by the Japan Patent Office in 1996, disclose a hydraulic brake device for a railway vehicle in which a hydraulic cylinder presses a brake pad against a frictional surface of a rotary body such as a brake rotor in accordance with a supplied oil pressure. 
         [0004]    Meanwhile, by installing a pneumatic brake that is activated by air pressure supplied from an air pressure source in the railway vehicle, it may be possible to omit the pneumatic-hydraulic converter and the hydraulic pipe. 
         [0005]    In relation to this point, JPH11-193835, published by the Japan Patent Office in 1999, discloses an air brake device for a railway vehicle in which a pneumatic actuator presses a brake pad against a frictional surface of a rotary body when compressed air is supplied to an air chamber of the pneumatic actuator.  FIG. 6  of this conventional technique further discloses an air brake device employing a lever. 
       SUMMARY OF THE INVENTION 
       [0006]    In these railway vehicle brake devices, the hydraulic cylinder or the actuator presses a part of the brake pad rather than pressing the entire brake pad. As a result, a brake caliper may be bent by a reaction force corresponding to the pressing force, causing the frictional surface to deform. Further, when a local temperature increase occurs in the brake pad, a frictional coefficient of the brake pad decreases, and as a result, it may be impossible for the brake pad to exhibit its original braking force. Moreover, partial wear is likely to occur on the brake pad. 
         [0007]    In the case of an air brake employing a lever, it is difficult to cause the brake pad to press the frictional surface evenly due to the effect of frictional force acting on a bearing portion of the lever, and therefore partial wear is particularly likely to occur on the brake pad. 
         [0008]    It is therefore an object of this invention to make a pressing force with which a brake pad presses a rotary body even. 
         [0009]    To achieve the object described above, this invention provides a caliper brake device for a vehicle, which applies a brake to rotation of a rotary body by sandwiching a first frictional surface and a second frictional surface formed on either side face of the rotary body, comprising a brake caliper having a first caliper arm that faces the first frictional surface and a second caliper arm that faces the second frictional surface, a movable brake pad that is supported by the first caliper arm and applies a braking force to the first frictional surface by displacing toward the first frictional surface, a pressure chamber formed in the brake caliper, a diaphragm that expands in accordance with a pressure of the pressure chamber, a plurality of pistons that drive the movable brake pad in a rotary axis direction of the rotary body in accordance with the expansion of the diaphragm, and a guide member that guides a displacement of the plurality of pistons in a right-angle direction relative to the first frictional surface. 
         [0010]    The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a plan view of a caliper brake device according to this invention. 
           [0012]      FIG. 2  is a side view of the caliper brake device. 
           [0013]      FIG. 3  is a longitudinal sectional view of the caliper brake device taken along a III-III line in  FIG. 2 . 
           [0014]      FIGS. 4A and 4B  are longitudinal sectional views of a support structure for an upper slide pin and a lower slide pin according to this invention. 
           [0015]      FIGS. 5A and 5B  are a plan view of a movable brake pad of a conventional hydraulic piston type caliper brake device and a plan view of a movable brake pad of the caliper brake device according to this invention. 
           [0016]      FIG. 6  is similar to  FIG. 3 , but shows a variation relating to the structure of a diaphragm. 
           [0017]      FIG. 7  is a side view of a caliper brake device according to a second embodiment of this invention. 
           [0018]      FIG. 8  is a longitudinal sectional view of the caliper brake device according to the second embodiment of this invention, taken along a VIII-VIII line in  FIG. 7 . 
           [0019]      FIG. 9  is a side view of a caliper brake device according to a third embodiment of this invention. 
           [0020]      FIG. 10  is a longitudinal sectional view of the caliper brake device according to the third embodiment of this invention, taken along a X-X line in  FIG. 9 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Referring to  FIG. 1  of the drawings, a caliper brake device  1  for a railway vehicle applies a brake to the rotation of a vehicle wheel  5  using a movable brake pad  7  and a fixed brake pad  700  that oppose each other. An X axis, a Y axis, and a Z axis in the figure correspond to an axle direction of the vehicle wheel  5 , a vertical direction, and a front-rear direction, respectively. A first frictional surface  6   a  and a second frictional surface  6   b  are formed in advance on the respective side faces of the vehicle wheel  5  so as to face the movable brake pad  7  and the fixed brake pad  700 , respectively. 
         [0022]    The movable brake pad  7  is supported on a tip end of a first caliper arm  12 . The fixed brake pad  700  is supported on a tip end of a second caliper arm  14 . The first caliper arm  12  and second caliper arm  14  form a part of a brake caliper  10  disposed so as to straddle the vehicle wheel  5 . 
         [0023]    Referring to  FIG. 2 , the brake caliper  10  is latched to a support frame  20  by an upper slide pin  30  and a lower slide pin  32 . The support frame  20  is fixed to a bogie of the railway vehicle or a vehicle body. 
         [0024]    Referring to  FIGS. 4A and 4B , the upper slide pin  30  and the lower slide pin  32  respectively penetrate two-pronged brackets  15  and  16  formed on the brake caliper  10 . The respective ends of the upper slide pin  30  and the lower slide pin  32  are latched to the brackets  15  and  16 . 
         [0025]    The upper slide pin  30  penetrates the support frame  20  between the brackets  15  and  16  via a pair of rubber bushes  33  and a radial bearing  35  disposed between the pair of rubber bushes  33 . The radial bearing  35  allows the upper slide pin  30  to displace in the X axis direction and oscillate about the X axis, and also to oscillate within a fixed range about the Z axis centering on the radial bearing  35 . On the other hand, parallel movement of the upper slide pin  30  in the Y axis direction and the Z axis direction of the figure is restricted. 
         [0026]    The lower slide pin  32  penetrates the support frame  20  between the brackets  15  and  16  via a rubber bush  36 . The rubber bush  36  allows the lower slide pin  32  to displace in the X axis direction and oscillate about the X axis, and to oscillate within a fixed range about the Z axis, similarly to the upper slide pin  30 . Furthermore, elastic deformation of the rubber bush  36  allows the lower slide pin  32  to perform a slight parallel movement in the Y axis direction and the Z axis direction of the figure. 
         [0027]    A gap between the brackets  15  and  16  is set to be considerably wider than a width of the support frame  20 , and the upper slide pin  30  is covered by a rubber boot  34  between the support frame  20  and each of the brackets  15 ,  16  so as not to be exposed to the outside. Similarly to the upper slide pin  30 , the lower slide pin  32  is covered by the rubber boot  34  between the support frame  20  and each of the brackets  15 ,  16 . 
         [0028]    By forming the upper slide pin  30  and lower slide pin  32  in the manner described above, the brake caliper  10  can displace in the X axis direction between the bogie or the vehicle body and the vehicle wheel  5 , or in other words in the X axis direction following relative displacement in a vehicle transverse direction. Further, the movable brake pad  7  and the fixed brake pad  700  are held parallel to a first frictional surface  6   a  of the vehicle wheel  5  and a second frictional surface  6   b  of the vehicle wheel  5 , respectively. 
         [0029]    Returning to  FIG. 1 , the brake caliper  10  comprises a yoke  13  that joins the first caliper arm  12  to the second caliper arm  14 . 
         [0030]    The fixed brake pad  700 , which is disposed on an opposite side of the vehicle wheel  5  to the movable brake pad  7 , is fixed directly to the second caliper arm  14 . The fixed brake pad  700  comprises a lining  9  that is configured to contact the second frictional surface  6   b  while the vehicle wheel  5  rotates. 
         [0031]    A diaphragm actuator  60  that drives the movable brake pad  7  is built into the first caliper arm  12  supporting the movable brake pad  7 . The movable brake pad  7  is constituted by a lining  9  that is configured to contact the first frictional surface  6   a  while the vehicle wheel  5  rotates, a body  7   a  to which the lining  9  is fixed, and an engaging portion  7   b  formed on a rear surface of the body  7   a . The engaging portion  7   b  is inserted into a holder  8  to be free to displace in the Y axis direction. The holder  8  comprises guide rails  8   a  that oppose one another in the Y axis direction, for accommodating and holding the engaging portion  7   b.    
         [0032]    Referring to  FIG. 3 , an upper end and a lower end of the holder  8  are respectively fitted into engaging grooves  98  formed in an outer periphery of anchor pins  43  disposed above and below the holder  8 . The anchor pins  43  project toward the vehicle wheel  5  from adjustors  41  that are respectively fixed to an upper end and a lower end of the first caliper arm  12  by anchor bolts  42 . By fitting the upper end and lower end of the holder  8  into the engaging grooves  98 , an upper end and a lower end of the engaging portion  7   b  of the movable brake pad  7  abut against the tip ends of the anchor pins  43  such that displacement of the movable brake pad  7  in the Y axis direction is restricted. 
         [0033]    To attach the movable brake pad  7  to the first caliper arm  12 , the engaging portion  7   b  of the movable brake pad  7  is inserted into an inner side of the guide rails  8   a  of the holder  8  from below in a state where the adjustor  41  and the anchor pin  43  are detached from the lower end of the first caliper arm  12 . When the engaging portion  7   b  has reached a predetermined position of the holder  8 , the adjustor  41  and the anchor pin  43  are fixed to the lower end of the first caliper arm  12  by the anchor bolt  42 . Thus, the upper end and lower end of the holder  8  are respectively fitted into the engaging grooves  98  of the anchor pins  43  such that displacement of the movable brake pad  7  in the Y axis direction is restricted. 
         [0034]    The adjustor  41  comprises a return spring  44  that biases the movable brake pad  7  in a separating direction from the first frictional surface  6   a , and a gap adjustment mechanism  45  that adjusts a gap between the movable brake pad  7  and the first frictional surface  6   a  to a substantially fixed value when a force other than the spring force of the return spring  44  does not act on the movable brake pad  7 . When the brake is released, the movable brake pad  7  is removed from the first frictional surface  6   a  by the return spring  44  and opposes the first frictional surface  6   a  at the gap prescribed by the gap adjustment mechanism  45 . 
         [0035]    The adjustor  41  is a well-known mechanism disclosed in JPH06-288417, published by the Japan Patent Office in 1994. The content thereof is incorporated herein by reference, and therefore a detailed description has been omitted. 
         [0036]    By means of the support structure described above, the movable brake pad  7  is supported by the first caliper arm  12  to be capable of displacing in the X axis direction while remaining parallel to the first frictional surface  6   a.    
         [0037]    Returning to  FIG. 2 , arc-shaped adjustor attachment recess portions  12   a  and  12   b  for attaching the adjustors  41  are formed on the upper end and the lower end of the first caliper arm  12 , respectively. The diaphragm actuator  60  is attached to the first caliper arm  12  between the upper and lower adjustors  41  so as to face the movable brake pad  7 . 
         [0038]    Returning to  FIG. 3 , the diaphragm actuator  60  comprises a closed-end cylinder  70  formed in the first caliper arm  12 , a diaphragm  75  housed in the cylinder  70 , a pressure chamber  63  defined between a bottom portion  72  of the cylinder  70  and the diaphragm  75 , a plurality of pistons  55  interposed between the diaphragm  75  and the movable brake pad  7 , and a guide frame  65  that supports the pistons  55  so that the pistons  55  slide in the X axis direction. During braking of the railway vehicle, the diaphragm  75  drives the plurality of pistons  55  in accordance with an air pressure introduced into the pressure chamber  63  such that the holder  8  is pressed in the X axis direction, and as a result, the movable brake pad  7  is pressed against the first frictional surface  6   a . For this purpose, the holder  8  is formed in advance with a larger planar form than a region of the diaphragm  75  in which the pistons  55  are disposed. 
         [0039]    The cylinder  70  comprises a cylinder inner wall  71  that has a substantially kidney-shaped cross-section and extends in the X axis direction, the bottom portion  72 , which is formed integrally with the cylinder inner wall  71  on a plane defined by the Y axis and the Z axis and closes one end of the cylinder  70 , and a ring-shaped attachment seat  73  formed on another end of the cylinder inner wall  71  to latch a peripheral edge portion  76  of the diaphragm  75 . 
         [0040]    Returning to  FIG. 2 , the lining  9  of the movable brake pad  7  takes an overall curved shape in a rotation direction of the vehicle wheel  5 , and is divided into a plurality of segments relative to the rotation direction of the vehicle wheel  5 , as shown by broken lines in the figure. Each segment is fixed to the body  7   a.    
         [0041]    When seen from the X axis direction, the cylinder inner wall  71  is constituted by curved wall portions  71   c  and  71   d  formed around an outer periphery of the lining  9  of the movable brake pad  7  so as to face the Z axis direction, or in other words the front-rear direction of the railway vehicle, and upper and lower arc-shaped wall portions  71   a  and  71   b  connected to the curved wall portions  71   c  and  71   d . The arc of the curved wall portions  71   c  and  71   d  when seen from the X axis direction corresponds to a concentric circle centering on the axle of the vehicle wheel  5 . 
         [0042]    The cylinder  70  and the movable brake pad  7  are vertically symmetrical to a parallel center line Oz to the Z axis of the brake caliper  10 . The adjustor attachment recess portions  12   a  and  12   b  are disposed in vertically symmetrical positions relative to the center line Oz. The arc-shaped wall portions  71   a  and  71   b  of the cylinder inner wall  71  form arcs that are oppositely oriented to the adjustor attachment recess portions  12   a  and  12   b.    
         [0043]    Returning to  FIG. 3 , the ring-shaped attachment seat  73  is formed on one end of the cylinder inner wall  71  on a plane defined by the Y axis and the Z axis. A peripheral edge portion of the guide frame  65  is fixed to the attachment seat  73  by a plurality of bolts  66 . Further, the peripheral edge portion  76  of the diaphragm  75  is sandwiched between the peripheral edge portion of the guide frame  65  and the attachment seat  73 . 
         [0044]    The diaphragm  75  is constituted by the peripheral edge portion  76 , a bellows portion  77  that expands from the peripheral edge portion  76  toward the bottom portion  72  along the cylinder inner wall  71  and then curves back substantially 180 degrees inward, and a piston pressing portion  79  that forms a parallel plane to the movable brake pad  7  on the inside of the bellows portion  77 . The peripheral edge portion  76 , bellows portion  77 , and piston pressing portion  79  are formed integrally from rubber. The piston pressing portion  79  has a substantially kidney-shaped planar form which is slightly smaller than, but similar to, a transverse section of the cylinder  70  defined by the cylinder inner wall  71 . 
         [0045]    The guide frame  65  is disposed between the diaphragm  75  and the holder  8 . Guide holes  65   a  are formed in the guide frame  65  in the X axis direction in an identical number to the pistons  55 , and the pistons  55  are fitted into the respective guide holes  65   a  so as to be free to slide in the X axis direction. 
         [0046]    Returning to  FIG. 2 , the guide holes  65   a  are formed at equal angular intervals in three concentric circles centering on the axle of the vehicle wheel  5 . The guide holes  65   a  arranged in a central circle of the three concentric circles are disposed at equal intervals facing a central portion of the movable brake pad  7 . The guide holes  65   a  arranged in an outside circle of the three concentric circles are disposed at equal intervals along the curved wall portion  71   c  so as to face an outer peripheral portion of the movable brake pad  7 . The guide holes  65   a  arranged in an inside circle of the three concentric circles are disposed at equal intervals along the curved wall portion  71   d  so as to face an inner peripheral portion of the movable brake pad  7 . 
         [0047]    An outer diameter of each piston  55  is set at 22 millimeters (mm), for example. The pistons  55  are disposed at a substantially equal density over the entire region of the movable brake pad  7 . 
         [0048]    In  FIG. 2 , the pistons  55  are disposed in three columns, but the arrangement of the pistons  55  is not limited thereto. By varying the outer diameter and axial direction length of the pistons  55 , a distribution of the pressing force applied to the movable brake pad  7  can be controlled. 
         [0049]    Returning to  FIG. 3 , a disc-shaped adiabatic plate  61  formed from an adiabatic material is attached to a tip end of each piston  55 . The adiabatic plate  61  prevents heat generated in the lining  9  from being transmitted to the diaphragm  75 . 
         [0050]    A back surface plate  62  is attached to a back surface of the piston pressing portion  79  of the diaphragm  75 . The back surface plate  62  is fixed to the piston pressing portion  79  by a plurality of bolts  67 . The back surface plate  62  is formed from a plate material having a substantially identical shape to the piston pressing portion  79 . The bolts  67  are disposed at substantially equal intervals around the peripheral edge portion of the back surface plate  62 . 
         [0051]    Returning to  FIG. 2 , a through hole  69  for supplying compressed air to the pressure chamber  63  from an air pressure source installed in the railway vehicle is formed in the brake caliper  10 . The through hole  69  is formed on the center line Oz of the brake caliper  10  by machine processing. The supply of compressed air into the pressure chamber  63  through the through hole  69  is controlled via a switching valve that operates in accordance with a command signal from a controller. When braking is not underway, the pressure chamber  63  is open to the atmosphere. 
         [0052]    When braking is not underway in the caliper brake device  1  constituted in the manner described above, the movable brake pad  7  is separated from the first frictional surface  6   a  of the vehicle wheel  5  by an elastic force of the return springs  44  of the pair of adjustors  41 . Furthermore, the pressure in the pressure chamber  63  is low, and therefore the diaphragm  75  contracts such that the pistons  55  are held in a withdrawn position. 
         [0053]    During braking, the diaphragm  75  expands in accordance with the supply of compressed air to the pressure chamber  63 , and therefore the return springs  44  of the adjustors  41  are deformed such that the movable brake pad  7  is pressed toward the first frictional surface  6   a  via the pistons  55 , the adiabatic plate  61 , and the holder  8 . As a result, the lining  9  of the movable brake pad  7  contacts the first frictional surface  6   a  of the vehicle wheel  5  such that a brake is applied to the rotation of the vehicle wheel  5  by means of frictional force. 
         [0054]      FIG. 5A  shows a conventional hydraulic piston type caliper brake device. This conventional device performs braking by having a pair of pistons press the movable brake pad  7  against a rotor using working oil pressure introduced into an oil pressure chamber  48 . In this conventional device, the dimensions of a cylinder  47  housing the pistons and a required oil pressure introduced into the oil pressure chamber  48  are set as follows. A hatched portion of the figure indicates a pressure receiving surface area of the piston. 
         [0055]    Diameter of cylinder  47 : φ 38 (mm)×2 
         [0056]    Sectional area of cylinder  47  (pressure receiving surface area of piston): 2,268 square millimeters (mm 2 ) 
         [0057]    Required oil pressure: 9 megapascals (MPa) 
         [0058]    Pressing force=2268×9=approx. 20 kilonewtons (kN) 
         [0059]      FIG. 5B  shows the air pressure diaphragm type caliper brake device  1  according to this invention. Here, the sectional area of the cylinder  70  and the required air pressure introduced into the pressure chamber  63  are set as follows. 
         [0060]    Sectional area of cylinder  70  (=pressure receiving surface area of diaphragm  75 ):  27 , 697  (mm 2 ) 
         [0061]    Required air pressure: 0.75 (MPa) 
         [0062]    Pressing force=27697×0.75=approx. 20 (kN) 
         [0063]    The movable brake pad pressing force of the caliper brake device  1  according to this invention is approximately 20 kN, i.e. identical to that of the conventional hydraulic piston type caliper brake device. 
         [0064]    Hence, a sufficiently large pressure receiving surface area can be secured on the diaphragm  75  within the limited space of the brake caliper  10 , and therefore the diaphragm actuator  60  of the caliper brake device  1  can apply the required pressing force to the movable brake pad  7  using air pressure that is much lower than the required oil pressure. 
         [0065]    The caliper brake device  1  according to this invention presses the movable brake pad  7  against the first frictional surface  6   a  via the plurality of pistons  55  by causing the diaphragm  75  to expand. Even when the brake caliper  10  bends or deformation occurs on a rotation surface of the first frictional surface  6   a  due to a reaction force to the pressing force, the movable brake pad  7  is pressed against the first frictional surface  6   a  with an even contact pressure. Therefore, a frictional coefficient of the movable brake pad  7  can be kept high at all times, and as a result, the original braking force of the movable brake pad  7  can be exhibited. Furthermore, since the contact pressure is even, local temperature increases are unlikely to occur in the movable brake pad  7  and the first frictional surface  6   a , and therefore partial wear is unlikely to occur on the movable brake pad  7  and the first frictional surface  6   a.    
         [0066]    When the first caliper arm  12  of the brake caliper  10  bends in a separating direction from the first frictional surface  6   a  of the vehicle wheel  5  during braking, the movable brake pad  7  is held parallel to the first frictional surface  6   a . Hence, partial wear of the lining  9  in a radial direction can be prevented. 
         [0067]    In the caliper brake device  1 , the pistons  55  and the guide frame  65  are interposed between the diaphragm  75  and the movable brake pad  7 , and therefore heat generated by the movable brake pad  7  is prevented from being transmitted to the diaphragm  75  by these members. Hence, the diaphragm  75  is unlikely to suffer heat-related damage. 
         [0068]    The diaphragm actuator  60  drives the movable brake pad  7  directly using air pressure supplied from the air pressure source installed in the railway vehicle, and therefore, there is no need to install a pneumatic-hydraulic converter, an oil pressure source, and hydraulic piping in the railway vehicle. Hence, by employing the caliper brake device  1  according to this invention, a reduction in the weight of the railway vehicle can be achieved. 
         [0069]    Instead of supplying air pressure to the pressure chamber  63  of the caliper brake device  1 , oil pressure may be supplied. In this case also, a large number of pistons are used in comparison with a conventional hydraulic piston type caliper brake device, and therefore the movable brake pad  7  can be pressed evenly. Moreover, by employing a large number of pistons, the pressure receiving surface area increases, and as a result, the required pressing force can be secured at a low oil pressure. Hence, the size of the pneumatic-hydraulic converter can be reduced. 
         [0070]    The brake caliper  10  is supported in a floating state via the upper slide pin  30  and the lower slide pin  32  so as to be capable of displacing in the X axis direction relative to the support frame  20 , and therefore, by driving the diaphragm actuator  60  provided in the first caliper arm  12 , of the first caliper arm  12  and second caliper arm  14  which extend so as to straddle the two frictional surfaces  6   a  and  6   b , the movable brake pad  7  can be pressed against the opposing first frictional surface  6   a  and the fixed brake pad  700  can be pressed against the second frictional surface  6   b  with equal force. Hence, the number of constitutional components of the diaphragm actuator  60  can be reduced, enabling a reduction in the size of the caliper brake device  1 . 
         [0071]    In the caliper brake device  1 , the movable brake pad  7  is supported by the brake caliper  10  via the pair of anchor pins  43 , and the pressure chamber  63  is formed between the anchor pins  43 . Therefore, when the anchor pins  43  expand and contract in accordance with expansion of the diaphragm  75 , the movable brake pad  7  can advance toward and retreat from the first frictional surface  6   a  smoothly. Furthermore, the pressure receiving surface area of the diaphragm  75  can be secured sufficiently in a space located between the anchor pins  43 , and therefore the required pressing force can be applied over a wide range of the movable brake pad  7 . Moreover, the diaphragm  75  and the guide frame  65  are disposed so as to overlap in the X axis direction, and therefore these members can all be disposed within the limited space of the brake caliper  10 . Hence, an increase in the size of the brake caliper  10  can be avoided. 
         [0072]    The lining  9  of the movable brake pad  7  takes a curved shape corresponding to the first frictional surface  6   a , and the cylinder inner wall  71  is constituted by the front and rear curved wall portions  71   c ,  71   d  shaped in alignment with the lining  9  and the upper and lower arc-shaped wall portions  71   a ,  71   b  linking the front and rear curved wall portions  71   c ,  71   d . Therefore, the pressure receiving surface area of the diaphragm  75  can be secured sufficiently within the limited space of the brake caliper  10 . Moreover, bending of the peripheral edge portion  76  of the diaphragm  75  can be avoided, and therefore favorable durability can be obtained in the diaphragm  75 . 
         [0073]    In the caliper brake device  1 , the holder  8 , the adiabatic plate  61 , and the pistons  55  are interposed between the movable brake pad  7  and the piston pressing portion  79  of the diaphragm  75 , and therefore heat transmission from the movable brake pad  7  to the diaphragm  75  can be blocked reliably. Hence, the rubber diaphragm  75  can be prevented from suffering heat-related damage. 
         [0074]    In the caliper brake device  1 , the back surface plate  62  is fixed to the piston pressing portion  79 , and therefore the rigidity of a contact portion between the piston pressing portion  79  and the adiabatic plate  61  is improved, leading to an improvement in the strength of the piston pressing portion  79 . However, the back surface plate  62  may be omitted, as shown in  FIG. 6 . 
         [0075]    Referring to  FIGS. 7 and 8 , a second embodiment of this invention will be described. 
         [0076]    Referring to  FIG. 8 , the caliper brake device  1  according to this embodiment comprises a cylinder  80  formed in the first caliper arm  12  with two open ends, which takes the place of the cylinder  70  according to the first embodiment, and a cover  92  that closes one end of the cylinder  80  to form a bottom portion. The diaphragm  75  is housed in the cylinder  80 . 
         [0077]    The cylinder  80  comprises a cylinder inner wall  82  that has a substantially elliptical cross-section and extends in the X axis direction, and a ring-shaped attachment seat  81  that is formed on a plane defined by the Y axis and the Z axis to latch the peripheral edge portion  76  of the diaphragm  75 . 
         [0078]    Referring to  FIG. 7 , the cylinder  80 , the movable brake pad  7 , the cover  92 , and the attachment seat  81  are formed to be vertically symmetrical about the center line Oz of the brake caliper  10 , which is parallel to the Z axis. 
         [0079]    A plurality of bolt holes are formed in the attachment seat  81  at predetermined intervals, and the cover  92  is fixed to the attachment seat  81  via bolts  84  screwed into the bolt holes. 
         [0080]    The cylinder inner wall  82  is constituted by front and rear curved wall portions  82   c  and  82   d  that curve around the lining  9  of the movable brake pad  7 , and upper and lower arc-shaped wall portions  82   a  and  82   b  that connect the front and rear curved wall portions  82   c  and  82   d.    
         [0081]    Returning to  FIG. 8 , the peripheral edge portion  76  of the diaphragm  75  is sandwiched between the attachment seat  81  and the cover  92 . 
         [0082]    A chamfered portion  83  is formed between the attachment seat  81  and the cylinder inner wall  82  of the cylinder  80 . The chamfered portion  83  serves to ensure that the diaphragm  75  curves gently, rather than sharply, from the peripheral edge portion  76  to the bellows portion  77 . 
         [0083]    The bellows portion  77  curves by substantially 90 degrees around the chamfered portion  83  from the peripheral edge portion  76 , expands in the direction of the guide frame  65  along the cylinder inner wall  82 , and then curves substantially 180 degrees inward to reach the piston pressing portion  79 . By forming the diaphragm  75  in this manner, the cylinder inner wall  82  is positioned on the outside of the pressure chamber  63 , in contrast to the cylinder inner wall  71  of the first embodiment. 
         [0084]    A ring-shaped attachment seat  95  opposing the vehicle wheel  5  is formed on an opposite end portion of the cylinder  80  to the cover  92 . The guide frame  65  is fixed to the attachment seat  95  by a plurality of bolts  96 . 
         [0085]    All other constitutions are identical to the first embodiment. 
         [0086]    Similar favorable effects to those of the first embodiment are obtained in this embodiment. 
         [0087]    Referring to  FIGS. 9 and 10 , a third embodiment of this invention will be described. 
         [0088]    This embodiment is similar to the second embodiment, but the holder  8  is omitted and the movable brake pad  7  is supported by the respective anchor pins  43  directly. 
         [0089]    The movable brake pad  7  is constituted by the lining  9 , which is configured to contact the first frictional surface  6   a , which is rotating, the body  7   a  to which the lining  9  is fixed, and the engaging portion  7   b  formed on the rear surface of the body  7   a.    
         [0090]    A ring-shaped engaging groove  86  is formed in the outer periphery of each anchor pin  43 . Edges  85  that engage with the engaging grooves  86  in the upper and lower anchor pins  43  are formed respectively on the upper end and the lower end of the engaging portion  7   b.    
         [0091]    By engaging the edges  85  with the engaging grooves  86  in the upper and lower anchor pins  43 , the movable brake pad  7  is latched to the first caliper arm  12 . The anchor pins  43  are supported by the adjustors  41  to be capable of advancing and retreating relative to the first frictional surface  6   a . The movable brake pad  7  approaches the first frictional surface  6   a  or separates from the first frictional surface  6   a  in accordance with the expansion/contraction operation of the diaphragm  75 . 
         [0092]    Similar favorable effects to those of the second embodiment are obtained in this embodiment. 
         [0093]    Furthermore, in this embodiment, the edges  85  on the upper end and lower end of the engaging portion  7   b  of the movable brake pad  7  are supported directly by the anchor pins  43  such that during braking, the diaphragm  75  presses the movable brake pad  7  directly via the pistons  55 . Therefore, the holder  8  can be omitted, enabling simplification of the structure of the caliper brake device  1  and a reduction in the X axis direction dimension of the brake caliper  10 . 
         [0094]    The contents of Tokugan 2007-265597, with a filing date of Oct. 11, 2007 in Japan, are hereby incorporated by reference. 
         [0095]    Although the invention has been described above with reference to certain embodiments, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, within the scope of the claims. 
         [0096]    For example, in the above embodiments, the frictional surfaces  6   a  and  6   b  formed on either side of the vehicle wheel  5  are sandwiched between the brake pads  7  and  700 . However, this invention may be applied to a caliper brake device in which the frictional surfaces  6   a  and  6   b  are formed on the respective surfaces of a rotor that rotates integrally with the vehicle wheel  5  such that the frictional surfaces  6   a  and  6   b  are sandwiched between the brake pads  7  and  700 . 
       INDUSTRIAL APPLICABILITY 
       [0097]    As described above, with the caliper brake device according to this invention, a pressing force for pressing a brake pad against a rotary body can be made even. Hence, when the caliper brake device according to this invention is applied to a vehicle wheel braking device for a railway vehicle, in which a large brake pad pressing force is required, a particularly favorable effect is obtained. 
         [0098]    The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows: