Abstract:
A brake device includes: a braking element which comes into contact with a disc rotating with a wheel and imparts a frictional force to brake the wheel; a pressing piston which presses the disc with the braking element; a pressing part which presses the pressing piston toward the braking element; a driving shaft which moves the pressing piston to a side to which the pressing piston retracts from the braking element; an electric motor which rotates the driving shaft about an axis thereof; a releasing mechanism which rotates the driving shaft to the side to which the pressing piston retracts from the braking element; a switching mechanism which switches between connection and separation of the releasing mechanism and the driving shaft; and a stopper mechanism which restricts rotation of the driving shaft to a side to which the pressing piston advances toward the braking element.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a brake device, which brings a braking element into contact with a disc rotating together with a wheel to thereby obtain a braking force, and in particular, to a brake device which has a release device for retracting the braking element from the disc. 
     The present application claims priority from Japanese Patent Application No. 2011-231885, filed Oct. 21, 2011, the entirety of which is hereby incorporated by reference. 
     2. Description of Related Art 
     In recent years, disc brakes are increasingly employed as brakes for railway vehicles because they do not require wear of the wheel to be considered, compared to a brake device of the type which presses a brake shoe directly against a wheel to obtain a braking force, and also they are capable of obtaining a stable braking force regardless of the state of the wheel. As a disc brake for a railway vehicle, there is known a type of disc brake in which a braking element is pressed in a direction toward the disc with the force of a mechanical spring, and it is moved in a direction to separate the two from each other by, for example, an actuator which uses hydraulic fluid pressure. 
     This type of a disc brake device is provided with a so-called fail safe function such that the braking force still functions with the pressing force of the mechanical spring even in a case where problems with fluid pressure supply occur. 
     Incidentally, a hydraulic disc brake device requires periodic oil maintenance due to oil leakage and so forth, and has problems with its serviceability. Consequently, it has been considered to use electricity rather than fluid pressure as the power source for disc brake devices for railway vehicles (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2010-25313). 
     However, in a state where fail safe is functioning, the braking force remains being applied to the wheel and it becomes difficult to move the vehicle. In particular, in comparison with a brake device that uses fluid pressure, in the case of a brake device that uses electricity, a transmission mechanism such as a decelerating mechanism intervenes between the output shaft of the electric motor and the shaft of the pressing piston that presses the braking element, and therefore, a conventional releasing mechanism cannot be simply used. 
     SUMMARY OF THE INVENTION 
     The present invention takes into consideration the above circumstances, with an object of providing a brake device provided with a release device capable of, with a simpler configuration, restricting movement of a pressing piston that is being released. 
     The brake device of the present invention is a brake device which imparts a frictional force to a disc rotating together with a wheel to thereby brake the wheel, the brake device comprising: a braking element which comes in contact with the disc and imparts a frictional force thereto; a pressing piston which advances and retracts in a direction of pressing the braking element against the disc so as to be able to press the disc with the braking element; an pressing part which presses the pressing piston toward the braking element; a driving shaft which has a driving side screw part threadably engaged with a piston side screw part formed in the pressing piston, and which is capable, by rotating about its axis, of moving the pressing piston to a side to which the pressing piston retracts from the braking element; an electric motor which is connected to the driving shaft and is capable of rotating the driving shaft about its axis; a releasing mechanism which rotates the driving shaft to a side, to which the pressing piston retracts from the braking element; a switching mechanism which is capable of switching between a connected state where the release mechanism and the driving shaft are connected and a separated state where they are separated; and a stopper mechanism which, in the connected state, restricts rotation of the driving shaft to a side to which the pressing piston advances toward the braking element. 
     According to the above configuration, even in a case where, due to defects in the electric motor, the pressing piston cannot retract from the braking element using the rotation of the driving shaft, the pressing piston can still retract from the braking element using the releasing mechanism. 
     Moreover, since the stopper mechanism restricts movement of the pressing piston, there is no need for using a separate device for maintaining the separated state, and as a result, the release mechanism can be provided in a simpler configuration. 
     Furthermore, the releasing mechanism may be restrained from operating in a direction corresponding to a direction of the driving shaft rotating to the side to which the pressing piston advances toward the braking element, and the stopper mechanism may be constituted by the release mechanism. 
     According to the above configuration, since the stopper mechanism is constituted by the releasing mechanism, a release mechanism having a stopper mechanism can be realized with a simpler configuration. 
     Moreover, the releasing mechanism may be provided with a driven gear which is capable of rotating according to the rotation of the driving shaft, and a worm gear which engages with the driven gear. 
     According to the above configuration, by configuring the release mechanism with a worm gear and a driven gear, it is possible to rotate the driven gear by rotating the worm gear. Furthermore, with the tangential force of the driven gear acting in the axial direction of the worm gear, rotation of the driven gear can be restricted. As a result, a releasing mechanism having a stopper mechanism can be realized with a simple configuration. 
     Moreover, the release mechanism may be provided with a first gear provided on the driving shaft, a second gear which is connected to and separated from the first gear by the switching mechanism, and a third gear provided coaxially with the second gear, and the third gear may serve as a driven gear engaging with the worm gear. 
     According to the above configuration, by connecting and separating the second gear to and from the first gear, the connected state and the separated state can be easily switched. 
     Moreover, the configuration may be provided such that the driven gear is a gear provided coaxially with the driving shaft, and the worm gear and the driven gear are connected and separated by the switching mechanism. 
     According to the above configuration, the releasing mechanism can be provided with a minimum configuration. 
     According to the present invention, even in a case where, due to defects in the electric motor, the pressing piston cannot retract from the braking element using the rotation of the driving shaft, the pressing piston can still retract from the braking element using the release mechanism. Moreover, since the stopper mechanism restricts movement of the pressing piston, there is no need for maintaining, for example, the function of the releasing mechanism using a separate device, and as a result, the release mechanism can be provided in a simpler configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side sectional view of a brake device according to a first embodiment of the present invention. 
         FIG. 2  is an enlarged view of the main parts of a manual releasing mechanism of the brake device according to the first embodiment of the present invention. 
         FIG. 3  is an A-A sectional view of  FIG. 2 . 
         FIG. 4  is a side sectional view of a manual release mechanism of the brake device according to the second embodiment of the present invention. 
         FIG. 5  is a B-B sectional view of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     Hereunder, embodiments of the present invention are described in detail, with reference to the drawings. 
     As shown in  FIG. 1 ,  FIG. 2 , and  FIG. 3 , a brake device  1  of the present embodiment is a disc brake type device which presses a pad  3  against a disc  2  rotating together with a wheel (not shown in the figure), to thereby apply a frictional force and brake the wheel. 
     The brake device  1  is provided with: an electric motor  4 ; an electromagnetic brake  5  provided so as to brake rotation of an output shaft  4   a  of the electric motor  4 ; a ball speed reducer  6  which decelerates rotation of the electric motor  4 ; a screw shaft  7  which is rotated by decelerated rotation; a pressing piston  8  which transmits a pressing force to the pad  3 ; a mechanical spring  9  which presses the pressing piston  8  toward the pad  3 ; a caliper  10  which has the disc  2  and the pad  3  built in; and a manual releasing mechanism  11  for forcing the pad  3  to retract. 
     In the following description, the output shaft  4   a  which is rotated by driving of the electric motor  4 , a transmission shaft  13  connected to the output shaft  4   a  (described later), and a screw shaft  7  are collectively referred to as a driving shaft S. Moreover, the direction along the driving shaft S is referred to as an axial direction X, the direction of the pressing piston  8  projecting to press the pad  3  is referred to as a first axial direction X 1 , and the direction opposite thereof is referred to as a second axial direction X 2 . 
     The caliper  10  is provided with a caliper casing  41 , the disc-shaped disc  2  which rotates together with the wheel, the pad  3  to be pressed against the disc  2 , and a plurality of pins (not shown in the figure) which slidably support the pad  3 . 
     On the output shaft  4   a  of the electric motor  4 , the transmission shaft  13  is attached. The transmission shaft  13  is a shaft member attached to the output shaft  4   a  in a state where rotation with respect to the rotation shaft  4   a  is restrained, so as to extend the output shaft  4   a  of the electric motor  4 , and it is constituted by a main body shaft  13   a  and a connection part  13   b . On the connection part  13   b  a first gear  21  is attached. The first gear  21  is a gear which constitutes the manual release mechanism  11 . 
     The electromagnetic brake  5  is attached to the transmission shaft  13 , and it is a part which brakes and maintains rotational movement of the electric motor  4  transmitted to the transmission shaft  13  via the output shaft  4   a . The transmission shaft  13  is provided so that the main body shaft  13   a  projects to the one axial side from the electromagnetic brake  5 . 
     The ball speed reducer  6  is a speed reducer which is attached on one axial side of the electromagnetic brake, for decelerating the rotational speed of the electric motor  4 . Specifically, the screw shaft  7  described later is connected to the one end of the ball speed reducer  6  (that is, the first axial direction X 1  side), and the main body shaft  13   a  of the transmission shaft  13  is connected to the other end of the ball speed reducer  6  (that is, the second axial direction X 2  side). 
     The ball speed reducer  6  described above is fixed to the other end (that is, the second axial direction X 2  side) of a casing  15  that is fixed to the caliper  10 . Specifically, the ball speed reducer  6  is fixed to the casing  15  via a bracket  16  which is fixed to the other end of the casing  15 . Furthermore, the electromagnetic brake  5  is fixed directly to the other end (that is, the second axial direction X 2  side) of the ball speed reducer  6  with a fastening member such as a bolt, and the electric motor  4  is arranged on the other end (that is, the second axial direction X 2  side) of the electromagnetic brake  5 . That is to say, the ball speed reducer  6 , the electromagnetic brake  5 , and the electric motor  4  are arranged so as to be connected in series in the axial direction. 
     The screw shaft  7  is fixed within the case  15  in a state of being able to rotate about its axis, and the pressing piston  8  is configured so as to move axially with rotation of the screw shaft  7 . The other end (that is, the second axial direction X 2  side) of the screw shaft  7  is, as described above, connected to the one end (that is the first axial direction X 1  side) of the ball speed reducer  6 . That is to say, the screw shaft  7  is connected to the electric motor  4  via the ball speed reducer  6  and the transmission shaft  13 , and is configured so as to be able to rotate with driving of the electric motor  4 . 
     The pressing piston  8  includes; a moving nut part  18  which is threadably engaged with a driving side screw part  7   a  formed on the outer circumference of the screw shaft  7 , a piston main body  20 , and a moving bracket  19  which connects the moving nut part  18  and the piston main body  20 . 
     In the moving nut part  18 , there is formed a piston side screw part  8   a  threadably engaged with the driving side screw part  7   a  via a plurality of balls. With this configuration, as a result of rotation of the screw shaft  7 , the moving nut part  18  (pressing piston  8 ) reciprocates in the axial direction X with a so-called ball screw mechanism. In the following description, the rotational direction of the driving shaft S (screw shaft  7 ) in which the moving nut part  18  moves in the second axial direction X 2  is referred to as one direction (forward direction). That is to say, with the output shaft  4   a  of the electric motor  4  rotating in the one direction, the pressing piston  8  moves in the second axial direction X 2 . 
     Moreover, on the moving nut part  18 , there is formed a flange  18   a.    
     The moving bracket  19  is fixed to the one end (that is, the first axial direction X 1  side) of the moving nut part  18 , and moves in the axial direction in response to the movement of the moving bracket  19 . On the one end (that is, the first axial direction X 1  side) of the moving bracket  19 , the piston main body  20  is fixed. 
     The mechanical spring  9  is arranged to the ball speed reducer  6  side (that is, the second axial direction X 2  side) from the flange  18   a  of the moving nut part  18 . Specifically, the mechanical spring  9  is constituted by a disc spring, and it is arranged between the flange  18   a  and a shaft end wall  15   a  of the casing  15 . Thereby, the moving nut part  18  (pressing piston  8 ) is always pressed in the first axial direction X 1 . 
     Next, the manual releasing mechanism  11  is described. The manual release mechanism  11  has: the first gear  21  provided on the transmission shaft  13 ; a moving unit  22 ; and a frame  23  which movably supports the moving unit  22 . The moving unit  22  can be in a connected state, in which the manual releasing mechanism  11  moves toward and engages to the first gear  21 , and a separated state, in which the manual release mechanism  11  is separated from the first gear  21 . 
     The first gear  21  is a spur gear provided integrally with the transmission shaft  13 , and rotates in response to driving of the electric motor  4 . 
     The frame  23  is in a box shape with one open face, and it is attached on the upper face of the electromagnetic brake  5  via a flange  23   a  provided on the one face. Specifically, the frame  23  includes; an upper wall  25  on the opposite side to the open one face, a pair of first side walls  26  orthogonal to the axial direction, and a pair of second side walls  27  orthogonal to the upper wall  25  and the first side walls  26 . 
     The moving unit  22  has: a cube-shaped moving housing  29 ; a second gear  30  which is set to engage with the first gear  21  by placing the moving unit  22  in the connected state; a rotation shaft  31  on which the second gear  30  is fixed; a worm wheel  32  (helical gear) fixed to the rotation shaft  31 ; and a worm gear  33  arranged so as to engate with the worm wheel  32 . 
     The moving housing  29  includes: a moving upper wall  35  provided parallel with the upper wall  25  of the frame  23 ; a pair of shaft fixation walls  36  provided parallel with the first side walls  26  of the frame  23 ; and a pair of worm fixation walls  37  provided parallel with the second side walls  27  of the frame  23 . 
     The upper wall  25  of the frame  23  and the moving upper wall  35  of the moving housing  29  are connected via a moving bolt  38 . The moving bolt  38  includes a head part  38   a  and a thread part  38   b , and the head part  38   a  is attached to the upper wall  25  so as to be able to rotate about the axis of the thread part  38   b . Moreover, in the head part  38   a , there is formed a hexagonal socket  38   c . In the moving upper wall  35 , there is formed a threaded hole  35   a  corresponding to the thread part  38   b  of the moving bolt  38 . 
     The rotation shaft  31  is fixed between the pair of shaft fixation walls  36  of the moving housing  29  so as to be able to rotate freely and be parallel with the driving shaft. 
     The second gear  30  is fixed on the rotation shaft  31  at a position where it engages with the first gear  21  when the moving housing  29  has moved into the connected state. 
     The worm wheel  32  is fixed on the rotation shaft  31  in the vicinity of the end part on the opposite side to the second gear  30 . 
     The worm gear  33  is rotatably fixed between the pair of the worm fixation walls  37  of the moving housing  29 , at a position where it engages with the worm wheel  32 . In the one end face of the worm gear  33 , a hexagonal socket  32   a  is formed. 
     Here, a moving operation of the moving unit  22  is described. In order to move the moving unit, the moving bolt  38  is rotated using a hexagonal wrench or the like. By rotating the moving bolt  38 , the moving housing  29  moves in the axial direction of the moving bolt  38  due to the screw action between the moving bolt  38  and the threaded hole  35   a  which is formed in the moving upper wall  35  of the moving housing  29  and is threadably engaged with the thread part  38   b  of the moving bolt  38 . 
     In the moving housing  29 , rotation of the shaft fixation walls  36  and the worm fixation walls  37  about the axis of the moving bolt  38  is restricted by the first side walls  26  and the second side walls  27 . Therefore, the moving housing  29  will not be rotated by rotation of the moving bolt  38 . 
     Next, an operation of the manual releasing mechanism  11  is described. 
     When making the manual release mechanism  11  to function, the moving unit  22  is moved by the method described above to bring the manual releasing mechanism  11  into a state of being connected with the driving shaft. In this state, the worm gear  33  is rotated, using a tool such as a hexagonal wrench. With the rotation of the worm gear  33 , the worm wheel  32  is rotated, and in response to this, the rotation shaft  31  and the second gear  30  rotate. 
     Since the manual release mechanism  11  is in the connected state, the first gear  21  is rotated with the rotation of the second gear  30 , and as a result, the transmission shaft  13  which constitutes the driving shaft, rotates in the one direction. With the rotation of the transmission shaft  13  in the one direction, the driving shaft rotates via the ball speed reducer  6  in the one direction, and the ball screw mechanism moves the moving nut part  8  in the second axial direction X 2  to thereby separate the pressing piston from the pad  3 . As a result, the brake device is brought to a released state. 
     According to the embodiment above, even in a case where, due to defects in the electric motor  4 , the pressing piston  8  cannot retract from the pad  3  using the rotation of the driving shaft S, the pressing piston  8  can still retract from the pad  3  using the manual releasing mechanism  11 . 
     Moreover, since a worm gear  33  is used as an input gear for operating the manual release mechanism  11 , the tangential force of the worm wheel  32  is placed in the axial direction of the worm gear  33 . As a result, shifting of the pressing piston  8  in the first axial direction X 1  by unintended rotation of the first gear  21 , which is connected to the worm gear  33  through the worm wheel  32 , the rotation shaft  31 , and the second gear  30 , can be prevented. That is to say, the worm gear  33  functions as a stopper mechanism to restrict the shifting of the pressing piston  8 . Therefore for example, there is no need for maintaining the function of the releasing mechanism using a separate device, and as a result, the release mechanism can be provided in a simpler configuration. 
     Moreover, by connecting and separating the second gear  30  to and from the first gear  21 , the connected state and the separated state can be easily switched. 
     Second Embodiment 
     Next, a brake device  1 B according to the second embodiment of the present invention is described. 
     As shown in  FIG. 4  and  FIG. 5 , a manual releasing mechanism  11 B of a brake device  1 B of the present embodiment includes a worm wheel  50  and a moving worm gear mechanism  51 . 
     The worm wheel  50  is a helical gear which engages with a worm gear main body  53  described later, and it is fixed to the transmission shaft  13  as with the first gear  21  of the first embodiment. 
     The moving worm gear mechanism  51  includes: a casing  52 ; a worm gear main body  53  which cooperates with the worm wheel  50  to function; and a moving shaft  54  which is a rotation shaft of the worm gear main body  53 . 
     The moving shaft  54  is attached to the casing  52  so as to be able to freely rotate and freely move in the direction orthogonal to the driving shaft S (the rotation shaft of the worm wheel  50 ). Specifically, both ends of the moving shaft  54  are slidably supported on a pair of bushes  55  that are fixed to the casing  52 . Moreover, in one end face of the moving shaft  54 , there is formed a hexagonal socket  56 , and the one end of the moving shaft  54  extends out to the outside of the casing  52 . 
     The worm gear main body  53  is fixed substantially at the center of the moving shaft  54 , and it can be connected to the worm wheel  50  upon sliding movement of the moving shaft  54 . Moreover, the worm gear main body  53  can be separated from the worm wheel  50  upon sliding movement of the moving shaft  54 . 
     Hereunder, an operation of the manual release mechanism  11 B according to the present embodiment is described. 
     In the normal state of the brake device  1 B, the worm gear main body  53  and the worm wheel  50  are in a separated state. 
     When making the manual releasing mechanism  11 B to function, the moving shaft  54  is moved to thereby bring the worm gear main body  53  and the worm wheel  50  into a connected state where they are connected. In this state, the moving shaft  54  is rotated using a hexagonal nut or the like to rotate the worm gear main body  53 . Upon rotation of the worm gear main body  53 , the worm wheel  50  rotates and the transmission shaft  13  rotates in the one direction. As a result of the rotation of the transmission shaft  13  in the one direction, the brake device  1  is brought to a released state with the action similar to that of the first embodiment. 
     According to the embodiment above, even in a case where, due to defects in the electric motor  4 , the pressing piston  8  cannot retract from the pad  3  using the rotation of the driving shaft S, the pressing piston  8  can still retract from the pad  3  using the manual release mechanism  11 B. 
     Moreover, since a worm gear main body  53  is used as an input gear for operating the manual releasing mechanism  11 B, shifting of the pressing piston  8  in the first axial direction X 1  by unintended rotation of the worm wheel  50  can be prevented. That is to say, the worm gear main body  53  functions as a stopper mechanism to restrict the shifting of the pressing piston  8 . Therefore for example, there is no need for maintaining the function of the release mechanism using a separate device, and as a result, the releasing mechanism can be provided in a simpler configuration. 
     Furthermore, by slide-moving the moving shaft  54 , the connected state and the separated state can be easily switched. 
     Moreover, it is possible to provide a release mechanism with fewer constituents in comparison with the first embodiment. 
     The technical scope of the present invention is not limited by the above embodiments, and various modifications may be made without departing from the scope of the invention. 
     In each embodiment described above, a worm gear is used as a stopper mechanism to restrict the driving shaft S from rotating to the side where the pressing piston  8  shifts toward the pad  3 . However for example, the stopper mechanism may be provided with use of a spur gear substituted for the worm gear, with a plate spring arranged so as to be always in contact with the teeth of the spur gear in order to restrict rotation of the spur gear. 
     DESCRIPTION OF REFERENCE SYMBOLS 
     
         
           1  Brake device 
           2  Disc 
           3  Pad (braking element) 
           4  Electric motor 
           7  Screw shaft 
           7   a  Driving side screw part 
           8  Pressing piston 
           8   a  Piston side screw part 
           9  Mechanical spring (pressing part) 
           11  Manual releasing mechanism (release mechanism) 
           13  Transmission shaft 
           18  Moving nut part 
           21  First gear 
           22  Moving unit (switching mechanism) 
           30  Second gear 
           32  Worm wheel (third gear) 
           33  Worm gear (stopper mechanism) 
           50  Worm wheel 
           51  Moving worm gear 
           53  Worm gear main body 
         S Driving shaft