Abstract:
One of brake pads  5  is pressed against the disc rotor D by a piston of a caliper  3  which is floatably supported on the carrier  2,  and in reaction thereto, the other brake pad  5  is pressed against the disc rotor D by a claw portion  14  on the caliper  3,  thereby producing a braking force. During brake release, the spring force of a return spring  22  separates the brake pad  5  from the disc rotor D. A positioning convex portion  27  is provided on the carrier  2  in a standing position adjacent to the return spring  22,  and serves to restrict the sideward movement of the distal end portion of the return spring  22.  Thus displacement and deformation of the return spring can be prevented, and its functions can be maintained.

Description:
RELATED APPLICATION  
       [0001]     This application is a divisional application of Ser. No. 10/209,836 filed Jul. 30, 2002, the entire content of which is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to an electric braking apparatus for producing braking force by torque of a motor, and particularly to an electric braking apparatus added with a parking brake function.  
         [0003]     There are currently electric braking apparatuses with a caliper comprising a piston, a motor and a rotation-linear movement conversion mechanism for converting rotation of the motor into linear movement. In such an electric braking apparatus, the piston is moved in accordance with rotation of a rotor of the motor to thereby press a brake pad against a disk rotor and produce braking force. Further, such an electric braking apparatus normally has a sensor for detecting pressing force or a stroke distance of a brake pedal depressed by an operator and controls the amount of the rotation (a rotational angle) of the electric motor in accordance with the detection results detected by the above sensor to thereby achieve the desired braking force.  
         [0004]     However, in recent times, there have been various attempts made to enhance the functionality of an electric braking apparatus of this kind by adding the parking brake function. For example, U.S. Pat. No. 5,348,123 and corresponding German Patent Laid-open No. (Offenlegungsschrift) DE4229042A1 have proposed a mechanical brake operating mechanism in which a rotating shaft is connected to a pivoting member of the rotation-linear movement conversion mechanism described above via a clutch mechanism and a ball ramp mechanism. A rotational force is exerted on the rotational shaft from the outside by an operation of, for example, a lever, to engage the clutch via the ball ramp mechanism, thereby placing the rotation-linear movement conversion mechanism in operation to produce braking force.  
         [0005]     However, in the mechanical brake operating mechanism described in the above publications, when the brake pedal is depressed while the parking brake is made effective by the operation from the outside, the problem arises that since the rotation-linear movement conversion mechanism is operationally connected to the outside operating portion via the clutch mechanism, the electric brake does not operate. Further, it is also a problem that since the rotating shaft is connected in series to the pivoting member of the rotation-linear movement conversion mechanism via the clutch mechanism and the ball ramp mechanism, the caliper is elongated in the axial direction. Therefore, the mechanical brake operating mechanism may not be suited for all vehicles due to possible interference with the wheel.  
         [0006]     The invention has been made in view of the above-described technical background. It is a purpose thereof to provide an electric braking apparatus equipped with a parking brake function that does not interfere with the normal braking operation of the braking apparatus. It is still another purpose thereof to provide an electric braking apparatus that can be mounted on any vehicles.  
       SUMMARY OF THE INVENTION  
       [0007]     In order to resolve the above-described problem, according to an aspect of the invention, there is provided an electric braking apparatus with a caliper comprising a piston, a motor and a rotation-linear movement conversion mechanism for converting rotation of the motor into linear movement and transmitting the linear movement to the piston, so that the piston is moved in accordance with the rotation of a rotor of the motor to press a brake pad against a disk rotor to generate braking force, wherein a parking brake locking mechanism is arranged around the rotor, which functions to restrict rotation of the rotor in the brake releasing direction when no electricity is supplied to the motor and to release the restriction on the rotor in accordance with the amount of electricity supplied to the motor.  
         [0008]     In the electric braking apparatus according to such constitution, when electricity supplied to the motor is cut after braking force caused by rotation of the rotor of the motor has been generated, the parking brake locking mechanism operates to restrict rotation of the rotor, the braking force is maintained and the parking brake thus carries out its function. Under this condition, when a supply of electricity to the motor begins, the rotor begins to rotate, so that the parking brake locking mechanism unlocks and the parking brake is automatically released. Further, the parking brake locking mechanism is arranged around the rotor and therefore, the length of the caliper in the axial direction is not enlarged. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a sectional view showing the structure of an electric braking apparatus according to the invention;  
         [0010]      FIG. 2  is an enlarged sectional view showing a portion of the electric braking apparatus;  
         [0011]      FIG. 3  is a schematic view showing the structure of a parking brake locking mechanism according to a first embodiment of the invention;  
         [0012]      FIG. 4  is a schematic view showing the parking brake locking mechanism in operation according to the first embodiment;  
         [0013]      FIG. 5  is another schematic view showing the parking brake locking mechanism in operation according to the first embodiment;  
         [0014]      FIG. 6  is a schematic view showing the structure of a parking brake locking mechanism according to a second embodiment of the invention;  
         [0015]      FIG. 7  is a schematic view showing the parking brake locking mechanism in operation according to the second embodiment;  
         [0016]      FIG. 8  is another schematic view showing the parking brake locking mechanism in operation according to the second embodiment;  
         [0017]      FIG. 9  is a schematic view showing the structure of a parking brake locking mechanism according to a third embodiment of the invention;  
         [0018]      FIG. 10  is a schematic view showing the parking brake locking mechanism in operation according to the third embodiment;  
         [0019]      FIG. 11  is a schematic view showing the structure of a parking brake locking mechanism according to a fourth embodiment of the invention;  
         [0020]      FIG. 12  is a schematic view showing the parking brake locking mechanism in operation according to the fourth embodiment;  
         [0021]      FIG. 13  is another schematic view showing the parking brake locking mechanism in operation according to the fourth embodiment;  
         [0022]      FIG. 14  is a sectional view showing the structure of a self-holding type solenoid used in the fourth embodiment; and  
         [0023]      FIG. 15 ,  FIG. 16 ,  FIG. 17  and  FIG. 18  are time charts showing operational timings of an electric brake and a parking brake in an electric braking apparatus according to the fourth embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     A detailed explanation will be given of embodiments of the invention in reference to the attached drawings.  
         [0025]      FIGS. 1 through 3  show an electric braking apparatus according to a first embodiment of the invention. In these drawings, numeral  1  designates a carrier fixed to a nonrotational portion (a knuckle or the like) of a vehicle, which carrier is disposed further inside the vehicle than a disk rotor D; numeral  2  designates a caliper floatably supported by the carrier  1  in the axial direction of the disk rotor D; numerals  3  and  4  designate a pair of brake pads arranged on both sides of the disk rotor D. The brake pads  3  and  4  are supported by the carrier  1  so that they can move in the axial direction of the disk rotor D. The caliper  2  includes a caliper main body  10  having a claw member  5  with a claw portion  5   a  at the front end, an annular base member  6  coupled to the base of the claw member  5  by means of bolts (not illustrated), an annular support plate  8  coupled to the base member  6  by means of bolts  7 , and a motor case  9 . The claw portion  5   a  of the claw member  5  is arranged proximately to the back face of the brake pad  4 , which is located outward of the vehicle.  
         [0026]     According to the embodiment, inside the caliper  2 , there are arranged a piston  11  capable of abutting against the back face of the brake pad  3  facing the interior of the vehicle; a motor  12 ; a ball ramp mechanism (a rotation-linear movement conversion mechanism)  13  for converting rotational movement outputted from the motor  12  into linear movement and transmitting the linear movement to the piston  11 ; a differential speed reducing mechanism  14  for reducing the rotation speed of the motor  12  and transmitting the rotation to the ball ramp mechanism  13 ; a pad wear compensating mechanism  15  ( FIG. 2 ) which adjusts the position of the piston  11  in accordance with wear of the brake pads  3  and  4 ; and a parking brake locking mechanism  16  ( FIGS. 1 and 3 ) which serves as a parking brake.  
         [0027]     As shown by  FIG. 2 , the piston  11  includes a main body portion  20  with a large diameter and a shaft portion  21  with a small diameter. The main body portion  20  is arranged proximately to the brake pad  3  toward the interior of the vehicle. The shaft portion  21  of the piston  11  is formed with a shaft hole  21   a  having a square cross-section. The piston  11  is axially slidably but nonrotatably supported by a support rod  23  in such a manner that the shaft hole  21   a  is inserted with the front end portion of the support rod  23 , which is extended from the end plate  22  of the motor case  9 . Further, a cover  24  made of rubber for sealing the inside of the caliper main body  10  from the outside is provided between the main body portion  20  of the piston  11  and the caliper main body  10 .  
         [0028]     The motor  12  is provided with a stator  25  fixedly fitted in the motor case  9 . A hollow rotor  26  is arranged inside the stator  25 . The rotor  26  is pivotally supported by the motor case  9  and the support plate  8  through bearings  27  and  28 . With the instruction from a controller (not illustrated), the motor  12  is operated to rotate the rotor  26  with desired torque and over desired angle. The rotational angle of the rotor  26  is detected by a rotation detector, not illustrated, arranged inside the rotor  26 . Further, the caliper main body  10  is attached with a connector  29  for dealing with a signal line that connects the stator  25  and the rotation detector and the controller.  
         [0029]     The ball ramp mechanism  13  is provided with a ring-shaped first disk (a pivoting member)  31  pivotally supported by the inner periphery of the annular base member  6  of the caliper main body  10  via a cross roller bearing  30 , a ring-shaped second disk (a linearly moving member)  32  coupled to the shaft portion  21  of the piston  11  via screw portion S, and three balls  33  interposed between the two disks  31  and  32 . The second disk  32  is arranged to abut against the rear face of the main body portion  20  of the piston  11  and is normally restricted from rotating by friction force of a wave washer  34  interposed between the second disk  32  and the caliper main body  10 .  
         [0030]     The three balls  33  are respectively disposed between three ball grooves  35  and  36  respectively formed on respective faces of the first disk  31  and the second disk  32  facing each other along the circumference. The three ball grooves  35  and  36  are inclined in the same direction and arranged to shift axially by the same interval in the range of the same center angle (for example, 90 degrees). When the first disk  31  is rotated in the counterclockwise direction as viewed from the right in  FIGS. 1 and 2 , the second disk  32  is pressed to the left. At this time, rotation of the second disk  32  is restricted from rotating by the wave washer  34  and therefore moves straight forward. As a result, the piston  11  is moved forward and presses the brake pad  3  facing the interior of the vehicle to the disk rotor D.  
         [0031]     Meanwhile, on the portion of the second disk  32  screwed to the shaft portion  21  of the piston  11  (screw portion S) is continuously provided with the extended cylindrical portion  37  greatly extended toward the end plate  22  of the motor case  9 . Inside of the extended cylindrical portion  37  there is arranged disk springs  38  one of which is fixed to the support rod  23  and which normally urge the second disk  32  toward the first disk  31  via the extended cylindrical portion  37 . Thereby, the balls  33  of the ball ramp mechanism  13  are strongly pressed between the two disks  31  and  32 , and when the first disk  31  is rotated clockwise as viewed from the right in  FIGS. 1 and 2 , the second disk  32  is moved backward to the right in the drawings, which thereby separates the piston  11  from the brake pad  3 .  
         [0032]     As is well shown in  FIG. 2 , the differential speed reducing mechanism  14  is constituted with an eccentric shaft  39  formed at one end of the rotor  26  of the motor  12  extended toward the disk rotor D; an eccentric plate  41  mounted to fit to the eccentric shaft  39  pivotally via a bearing  40 ; an Oldham mechanism  42  interposed between the eccentric plate  41  and the support plate  8  of the caliper main body  10 ; and a cycloid ball speed reducing mechanism  43  interposed between the eccentric plate  41  and the first disk  31  of the ball ramp mechanism  13 . The eccentric plate  41  dose not rotate but revolves in accordance with rotation of the eccentric shaft  39  by operation of the Oldham mechanism  42 . Meanwhile, in accordance with revolving of the eccentric plate  41 , the cycloid ball speed reducing mechanism  43  is operated and the first disk  31  is rotated in a direction reverse to that of the rotor  26  at a speed that is in a constant ratio to that of rotor  26 . Further, in  FIG. 1 , notation O 1  designates the rotational center of the rotor  26 ; notation O 2  designates the rotational center of the eccentric shaft  39 ; and notation  6  designates the amount of eccentricity.  
         [0033]     The rotation ratio N of the first disk  31  to the rotor  26 , becomes N=(D−d)/D, where d is the diameter of a reference circle of a cycloid groove on the side of eccentric plate  41  in the cycloid ball speed reducing mechanism  43  and D is the diameter of a reference circle of a cycloid groove on the side of the first disk  31 . In this case, the number of rotations of the rotor  26  when the first disk  31  is rotated by one rotation is the speed reduction ratio α (=1/N). Further, the second disk  32  is moved forward by S=(L/360)×(θ/α) where the rotor  26  is rotated by a certain angle θ; the rotational angle θA of the first disk  31  is θ/α; and L is the inclination (lead) of the ball grooves  35  and  36  of the ball ramp mechanism  13 .  
         [0034]     As is well shown in  FIG. 2 , the pad wear compensating mechanism  15  comprises a limiter  44  pivotally fitted to the extended cylindrical portion  37  of the second disk  32  of the ball ramp mechanism  13  and connected to the first disk  31  during operation with a clearance in the rotational direction, a spring holder  46  which is fitted to the extended tubular portion  37  of the second disk  32  and whose position is fixed relative to the second disk  32  by a pin  45 , and a coil spring  47  which is arranged around the spring holder  46 , one end of which is connected to the limiter  44  and other end of which is connected to the spring holder  46 .  
         [0035]     The pad wear compensating mechanism  15  functions in such a manner that, when the brake pads  3  and  4  are worn, the limiter  44  rotates in accordance with rotation of the first disk  31  of the ball ramp mechanism  13 , and that that rotation is then transmitted to the second disk  32  via the coil spring  47 , the spring holder  46  and the pin  45 , and that the piston  11 , restricted in rotation by the support pin  23 , moves forward along the support pin  23  until the brake pad  3  is pressed to the disk rotor D, i.e., until the braking force is generated, so that the gap caused by the pad wear is eliminated. Meanwhile, after producing the braking force, the large friction resistance produced at the screw portion S between the piston  11  and the second disk  32  hampers rotation of the second disk  32 . Therefore, rotational misalignment between the second disk  32  and the first disk  31 , that is, rotational misalignment between the spring holder  46  and the limiter  44  is absorbed by twisting of the coil spring  47 .  
         [0036]     As is well shown by  FIG. 3 , the parking brake locking mechanism  16  includes a claw wheel  50  formed integrally with the outer peripheral face of the rotor  26  of the motor  12 ; a arm lever  52  which is arranged beside the claw wheel  50  and pivotally attached at its base end to the caliper main body  10  by using a pin  51 ; an engaging claw  54  the base end of which is pivotally attached midway along the length of the arm lever  52  by using a pin  53 ; a tensile spring (urging means)  55  interposed between a front end of the arm lever  52  and the caliper main body  10  for normally urging the arm lever  52  close to the claw wheel  50 ; and a stopper portion  56  provided on the caliper main body  10  which abuts against a side face of the arm lever  52  urged by the tensile spring  55  so that the arm lever  52  is substantially orthogonal to one of the lines through the center of the rotor  26 .  
         [0037]     Each of the tooth portions  57  of the claw wheel  50  is given a tooth shape in which a steep tooth engaging face  57   a  faces in direction L that the rotor  26  rotates when braking is being released (the counterclockwise direction when viewed from the right in  FIG. 1 ), and an inclined escape face  57   b  faces in direction R that the rotor  26  rotates when braking is being applied (the clockwise direction when viewed from the right in  FIG. 1 ). Further, the arm lever  52  is provided with a torsion spring  58  that normally urges the engaging claw  54  in the counterclockwise direction as viewed in  FIG. 3 ; and a projection  59  that restricts rotation of the engaging claw  54  in the counterclockwise direction and keeps the engaging claw  54  in a direction substantially orthogonal to the arm lever  52 . That is, through the combined positioning control functions provided by the arm lever  52  urged by the tensile spring  55  and the engaging claw  54  per se urged by the torsion spring  58 , the end portion of the engaging claw  54  is normally positioned so as to engage with the teeth  57  of the claw wheel  50 .  
         [0038]     An explanation will be given of operation of the electric braking apparatus according to the first embodiment also in reference to  FIG. 4  and  FIG. 5 .  
         [0039]     (In Operating Electric Brake)  
         [0040]     When the apparatus is operated as a normal electric brake, the rotor  26  of the motor  12  rotates in the clockwise direction as viewed from the right in  FIGS. 1 and 2  upon input of a braking signal from the driver. Then, the eccentric plate  41 , since attached via the bearing  40  to the eccentric shaft  39  formed integrally with the rotor  26 , revolves, not rotate, by the Oldham mechanism  42 . By the revolution of the eccentric plate  41 , the cycloid ball speed reducing mechanism  43  is operated and the first disk  31  of the ball ramp mechanism  13  is rotated in the reverse direction (counterclockwise) at a speed in a constant ratio N to that of the rotor  26  as described above. Meanwhile, the rotation of the second disk  32  of the ball ramp mechanism  13  is restricted due to the resistance force by the wave washer  34 . Accordingly, the second disk  32  moves forward toward the disk rotor D in accordance with rotation of the first disk  31 . The piston  11  thereby moves and presses the brake pad  3  facing the interior of the vehicle to the disk rotor D. Then, by the reactive force thereon, the caliper  2  moves relative to the carrier  1 . The claw portion  5   a  of the claw member  5  presses the brake pad  4  facing the outside of the vehicle to the outer face of the disk rotor D to thereby produce braking force in accordance with torque of the motor  12 . At this time, if the brake pads  3  and  4  have been worn, the pad wear compensating mechanism  15  is operated to eliminate the gap formed by pad wear as described above.  
         [0041]     Further, when the electric brake is operated, the claw wheel  50  of the parking brake locking mechanism  16  rotates in the clockwise direction R, along with the rotor  26 . As a result, the engaging claw  54  slides along the inclined escape face  57   b  of a tooth portion  57  while abutting against the projection  59 . Since the rotational torque of the rotor  26  is sufficiently larger than the urging force of the tensile spring  55 , the arm lever  52 , as shown in  FIG. 4 , rotates around the pin  51  counterclockwise to move away from the claw wheel  50  over the urging force of the tensile spring  55 , so that the engaging claw  54  smoothly climbs over the tooth portions  57  of the claw wheel  50 . That is, the rotor  26  smoothly rotates in the clockwise direction (the braking direction) R to thereby assure the functioning of the electric brake.  
         [0042]     (In Releasing Electric Brake)  
         [0043]     When the river releases the operation of electric brake, the rotor  26  of the motor  12  rotates counterclockwise as viewed from the right in  FIGS. 1 and 2 . Urged by the disk springs  38 , the second disk  32  and the piston  11  move backward together to remove the pressing force on the disk rotor D and thereby release the braking force.  
         [0044]     At the same time, the claw wheel  50  of the parking brake locking mechanism  16  rotates in the counterclockwise direction L integrally, along with the rotor  26 , so that as shown in  FIG. 5 , the engaging claw  54  is pressed down against the force of the torsion spring  58  by the tooth faces  57   a  of the tooth portions  57 . As a result, the rotor  26  smoothly rotates in the counterclockwise direction (brake releasing direction) L to assure the releasing of the electric brake. That is, the parking brake locking mechanism  16  is automatically unlocked (detached) by the rotational torque produced when electricity is supplied to the motor  12 . Thus, sophisticated control of rotation of the motor  12  is not required.  
         [0045]     (In Operating Parking Brake)  
         [0046]     When the driver activate the parking brake, the rotor  26  of the motor  12  rotates in the clockwise direction R. The piston  11  then moves to produce the braking force as is the above case where the electric brake is turned on. Further, according to the first embodiment, control is made on supply of electricity to the motor  12  to cut it off simultaneously with the production of the braking force. When electricity is cut off, a rotational torque appears in the counterclockwise direction L on the rotor  26  of the motor  12  by influence of rigidity of the caliper or the like. This rotational torque exerts downward force on the engaging claw  54  of the parking brake locking mechanism  16  is pushed down. However, since the rotational torque from the rotor  26  is significantly smaller than that from it when the electric motor is operated, the engaging claw  54  is held, due to the urging force of the torsion spring  58 , in the projecting position shown in  FIG. 3  in which it is in contact with the projection  59 . As a result, engagement of the engaging claw  54  and the claw wheel  50  restricts the rotor  26  from rotating in the counterclockwise direction L, whereby the parking brake becomes effective.  
         [0047]     (In Releasing Parking Brake)  
         [0048]     When the driver releases the parking brake, electricity begins to flow through the motor  12 . As is the case where the electric brake is turned off, the rotor  26  rotates in the counterclockwise direction (brake releasing direction) L, and the claw wheel  50  of the parking brake locking mechanism  16  also rotates in the same direction L integrally, along with the rotor  26 . Since the rotational torque of the rotor  26  at this time is considerably larger than the urging force of the torsion spring  58  trying to hold the engaging claw  54  in the projecting position, as shown in  FIG. 5 , the engaging claw  54  is pressed down by the rotation of the steep tooth engaging face  57   a  of the tooth portion  57  of the claw wheel  50 . That is, the rotor  26  becomes free in rotation in the direction in which the brake is released. As the rotor so rotates, the piston  11  is moved rearward, and the pressure on the disk rotor D is removed and the parking brake is thereby released.  
         [0049]      FIGS. 6 through 8  show an electric braking apparatus according to a second embodiment of the invention. Since the other parts of the electric braking apparatus are the same as those shown in  FIGS. 1 and 2 , an illustration thereof is omitted here. Further, the basic structure of the parking brake locking mechanism  16  is the same as that of the first embodiment. Therefore, the same parts and portions are given the same numbers and description thereof is omitted here. The second embodiment is characterized in that a solenoid mechanism  60  is used in place of the tensile spring  55  in the above-described parking brake locking mechanism  16 . The solenoid mechanism  60  includes: a solenoid (actuator)  62  which is fixed to the caliper main body  10 ; a plunger  61  the front end portion  61  of which is pivotally attached to the arm lever  52 ; and a compressing spring (urging means)  63  which normally pulls the plunger  61  of the solenoid  62  rearward. The arm lever  52  is normally held upright in contact with the stopper portion  56  by the function of the compressing spring  63  ( FIG. 6 ). With supply of electricity, the solenoid  62  operates to move the plunger  61  forward, which then hold the arm lever  52  inclined in the direction away from the claw wheel  50  ( FIG. 7 ).  
         [0050]     An explanation will be given of operation of the electric braking apparatus according to the second embodiment.  
         [0051]     (Actuating the Electric Brake)  
         [0052]     In the normal operation of the electric braking apparatus, the rotor  26  of the motor  12  rotates clockwise as seen from the right in  FIGS. 1 and 2 . When the driver inputs the brake operating signal, as happens in the first embodiment, the piston  11  moves to generate braking force proportional to the torque of the motor  12 . Further, when the electric brake is operated, simultaneously with supply of electricity to the motor  12 , electricity is also supplied to the solenoid  62  of the brake locking mechanism  16 . As a result, the plunger  61  of the solenoid  62  extends as shown in  FIG. 7 . The arm lever  52  is thus held inclined away from the claw wheel  50 . When the arm lever  52  is inclined, the engaging claw  54  is held in a position where it is slightly away from the tooth portion  57  of the claw wheel  50 , so that the rotor  26  becomes free in rotation in the clockwise direction (braking direction) R to assure the proper functioning of the electric brake. Since the rotor  26  rotates while the engaging claw  54  and the claw wheel  50  are not in contact with each other, noise from contact of these members and wear on these members are prevented. Furthermore, due to no contact resistance between these members, the motor  12  can work efficiently.  
         [0053]     (Deactivating the Electric Brake)  
         [0054]     When the driver releases the electric brake, the rotor  26  of the motor  12  rotates counterclockwise as viewed from the right in  FIGS. 1 and 2 . The piston  11  then moves rearward to thereby release braking. However, electricity to the solenoid  62  of the brake locking mechanism  16  is kept on, so that the engaging claw  54  of the brake locking mechanism  16  is held slightly away from the tooth portion  57  of the claw wheel  50  as shown in  FIG. 7 . The claw wheel  50  of the parking brake locking mechanism  16  thus becomes free in rotation in the counterclockwise direction (brake releasing direction) L, together with the rotor  26 , without contact with the engaging claw  54 , whereby release of the electric brake is assured.  
         [0055]     (Activating the Parking Brake)  
         [0056]     When the driver operates the parking brake, the rotor  26  of the motor  12  rotates in the clockwise direction R. Similarly to the normal operation of the electric brake, the piston  11  moves to generate the braking force. Further, according to the second embodiment, control is made on the electricity supplied to the solenoid  62  of the parking brake locking mechanism  16  and the motor  12  so as to cut it off simultaneously with generation of the braking force. As supply of electricity to the solenoid  62  is cut off, as shown in  FIG. 6 , the plunger  61  moves rearward due to the urging force of the compressing spring  63 . The arm lever  52  then returns to its initial upright position, whereby the engaging claw  54  is positioned so as to engage with the claw wheel  50 . Further, as electricity to the motor  12  is cut off, a rotational torque appears on the rotor  62  of the motor  12  in the counterclockwise direction L by influence of rigidity of the caliper or the like. This rotational torque exerts downward force on the engaging claw  54  of the parking brake locking mechanism  16 . However, since the rotational torque of the rotor  26  is significantly smaller than that when the electric motor is operating, as shown in  FIG. 6 , the engaging claw  54  is held, due to the urging force of the torsion spring  58 , in the projecting position in which it is in contact with the projection  59 . Engagement of the engaging claw  54  and the claw wheel  50  restricts the rotor  26  from rotating in the counterclockwise direction (brake releasing direction) L. As a result, the parking brake performs its function.  
         [0057]     (Releasing the Parking Brake)  
         [0058]     When the driver releases the parking brake, electricity begins to flow though the solenoid  62  of the parking brake locking mechanism  16  to extend the plunger  61  of the solenoid  62 . The engaging claw  54  of the brake locking mechanism  16  is held slightly away from the tooth portion  57  of the claw wheel  50  as shown in  FIG. 7 . Simultaneously with supply of electricity to the solenoid  62 , electricity is also supplied to the motor  12 , and, as happened in the release operation of the electric brake, the rotor  26  rotates in the counterclockwise direction (brake releasing direction) L. The claw wheel  50  of the parking brake locking mechanism  16  then rotates smoothly in the counterclockwise direction L, along with the rotor  26 , without contact with the engaging claw  54  ( FIG. 7 ), so that the parking brake is released.  
         [0059]     Further, according to the second embodiment, if the solenoid  62  becomes inoperative, as shown in  FIG. 8 , the plunger  62  remains retracted rearward. However, the compressing spring  63  works to pull the plunger  62  rearward as the tensile spring  55  does ( FIGS. 3 through 5 ) in the first embodiment. Therefore, the parking brake can be operated.  
         [0060]      FIGS. 9 and 10  show an electric braking apparatus according to a third embodiment of the invention. The other parts of the electric braking apparatus are the same as those shown in  FIGS. 1 and 2  and therefore, an illustration thereof is omitted. This third embodiment is characterized in that there is no member corresponding to the arm lever  52  of the parking brake locking mechanism  16  in the first and the second embodiments. Instead, a relatively large and long engaging claw  54 ′ engages with the claw wheel  50 . The engaging claw  54 ′ is pivotally attached in its middle to the caliper main body  10  by using a pin  70 . Further, the caliper main body  10  has a tensile spring (urging means)  71  for urging the engaging claw  54 ′ away from the claw wheel  50  and a solenoid  72  for rotating the engaging claw  54 ′ to a position where it engages with the claw wheel  50 . Further, with supply of electricity, the solenoid  72  operates to extend a plunger  73  thereof.  
         [0061]     An explanation will be given of operation of the electric braking apparatus according to the third embodiment.  
         [0062]     (Activating the Electric Brake)  
         [0063]     When the apparatus performs the normal braking operation, with a brake operating signal from the driver, the rotor  26  of the motor  12  rotates clockwise as viewed from the right in  FIGS. 1 and 2 . The piston  11  then moves, as it does in the first and the second embodiments, to generate braking force proportional to the torque of the motor  12 . Further, when the electric brake is in operation, supply of electricity to the solenoid  62  of the brake locking mechanism  16  is cut off. Thus, as shown in  FIG. 9 , the engaging claw  54 ′ is placed slightly away from the tooth portion  57  of the claw wheel  50  by the urging force of the tensile spring  71 . As a result, the rotor  26  becomes free in rotation in the clockwise direction R, whereby the function as the electric brake is assured. Also, since the rotor  26  rotates while the engaging claw  54 ′ is away from the claw wheel  50 , as happens in the second embodiment, both noise and wear are prevented. Furthermore, the motor  12  can work efficiently.  
         [0064]     (Releasing the Electric Brake)  
         [0065]     When the driver release the electric brake, the rotor  26  of the motor  12  rotates counterclockwise as viewed from the right in  FIGS. 1 and 2 . The piston  11  moves rearward to thereby release the braking. Since at that time, electricity to the solenoid  72  of the parking brake locking mechanism  16  is cut off, the engaging claw  54 ′ of the brake locking mechanism  16  remains slightly away from the tooth portion  57  of the claw wheel  50  as shown in  FIG. 9 . The claw wheel  50  of the parking brake locking mechanism  16  thus smoothly rotates in the counterclockwise direction L, along with the rotor  26 , without contacting the engaging claw  54 ′, whereby release of the electric brake is reliably carried out.  
         [0066]     (Activating the Parking Brake)  
         [0067]     When the driver operates the parking brake, the rotor  26  of the motor  12  rotates in the clockwise direction R. The piston  11  thereby moves as it does in the normal operation of the electric brake to generate the braking force. Further, according to the third embodiment, control is made in such manner that electricity begins flowing through the solenoid  72  of the brake locking mechanism  16  simultaneously with generation of the braking force while electricity to the motor  12  is cut off. With supply of electricity to the solenoid  62 , the plunger  73  extends. The engaging claw  54 ′ is thereby positioned so that it engages with the claw wheel  50  against the urging force of the tensile spring  71 , as shown in  FIG. 10 . Further, after cutting off electricity to the motor  12 , a rotational force appears on the rotor  26  of the motor  12  in the counterclockwise direction L due to the influence of the caliper rigidity or the like. This rotational force pushes downward the engaging claw  54 ′ of the parking brake locking mechanism  16 , whereby rotation of the rotor  26  in the counterclockwise direction L is restricted. As a result, the parking brake properly functions. With a tensile spring  71  having urging force smaller than the rotational force of the rotor  26 , the force of the claw wheel  50  pushing the engaging claw  54 ′ overcomes the urging force of the tensile spring  71 . Thus, electricity to the solenoid  72  may be cut off at an appropriate timing.  
         [0068]     (Releasing the Parking Brake)  
         [0069]     When the driver releases the parking brake, supply of electricity begins to the motor  12 . The rotor  26  then rotates slightly in the clockwise direction (braking direction) R. By the urging force of the tensile spring  71 , the engaging claw  54 ′ rotates counterclockwise away from the tooth portion  57  of the claw wheel  50 . When the rotor  26  of the motor  12  is thereafter rotated in the counterclockwise direction (brake releasing direction) L thereafter at an appropriate timing, the claw wheel  50  of the parking brake locking mechanism  16  smoothly rotates in the counterclockwise direction L, along with the rotor  26 , without contacting the engaging claws  54  ( FIG. 9 ), and thereby the parking brake is released.  
         [0070]     According to the third embodiment, when the parking brake is operated, electricity is supplied only temporarily to the solenoid  72 . Thus, heat generation from the solenoid  72  is suppressed.  
         [0071]      FIGS. 11 through 14  show an electric braking apparatus according to a fourth embodiment of the invention. The other parts of the electric braking apparatus are the same as those shown in  FIGS. 1 and 2  and therefore, an illustration of these parts is omitted. According to the fourth embodiment, the coil spring  47  is set to have a torque larger than residual torque that comes from the differential speed reducing mechanism  14  when the motor is not rotated. Thus, the coil spring  47  functions as a piston returning mechanism for returning the piston  11  to a reference position when the motor is not in operation.  
         [0072]     As is well shown in  FIGS. 11 through 13 , the parking brake locking mechanism  116  according to the fourth embodiment includes a locking mechanism  150  capable of locking the rotor  26  of the motor  12  against rotating in the brake releasing direction L and releasing the lock, and a solenoid (actuator)  151  for causing this locking mechanism  150  to perform the locking and unlocking functions.  
         [0073]     The locking mechanism  150  is provided with: a claw wheel  152  integrally formed around the outer peripheral of the rotor  26 ; an arm lever  154 , arranged near the claw wheel  152 , the base end portion of which is pivotally attached to the caliper main body  10  by using a pin  153 ; an engaging claw  156 , the base end portion of which is pivotally attached to the mid portion of the arm lever  154  by using a pin  155 ; a stopper portion  157  provided at the caliper main body  10  against which the arm lever  154  abuts along its side and is held thereby in the direction tangential to the rotor  26 ; a torsion spring (urging means)  158  for normally urging the engaging claw  156  counterclockwise as viewed in  FIG. 11 ; and a projection  159  for acting with the torsion spring  158 , stopping and holding the engaging claw  156  in an position where the engaging claw  156  engages with the claw wheel  152 . Here, each tooth portion  160  of the claw wheel  152  is provided with a steep tooth engaging face  160   a  facing front when the rotor  26  rotates in the direction L for releasing the brake (the counterclockwise direction in  FIGS. 1 and 2 ) and an inclined escape face  160   b  facing front when the rotor  26  rotates in the direction R for applying the brake (the clockwise direction in  FIGS. 1 and 2 ).  
         [0074]     The solenoid  151 , serving as an actuator, is of a two direction self-holding type. As shown in  FIG. 14 , the solenoid  151  of a two direction self-holding type is comprised of a housing  162  containing a plunger  161  for sliding therein, and two coils  164  and  165  arranged in series and sandwiching a permanent magnet  163  therebetween. A rod  166  is supported by the plunger  161 . By supplying electricity alternately to the coil  164  or  165 , the plunger  161  moves in either direction A or B to either the forward extension point or the rear extension point where it is held by the pulling force of the permanent magnet  163 .  
         [0075]     As shown by  FIGS. 11 through 13 , the parking brake locking mechanism  116  includes the solenoid  151  of a self-holding type provided on the caliper main body  10 , where one end portion of the rod  166 , being supported by the plunger  161 , is pivotally attached to the end of the arm lever  154  of the locking mechanism  150 .  
         [0076]     In the parking brake locking mechanism  116  of such a structure, when electricity is supplied to the coil  164  of the solenoid  151 , the rod  166 , being supported by the plunger  161 , moves left A (the forward moving direction) in  FIG. 12 . The arm lever  154  then rotates away from the rotor  26 , whereby the front end of the engaging claw  156  leaves a tooth portion  160  of the claw wheel  152 . That is, the locking mechanism  150  performs the unlock operation. The rotor  26  thereby becomes free in rotation in the brake releasing direction L and the braking direction R. Since the plunger  161  is held in the forward extension position even after the supply of electricity is cut off, a supply of electricity to the coil  164  may be temporary. Further, when electricity is supplied to the other coil  165  from this state, the rod  166  moves, along with the plunger  161 , to the right (the rearward direction B) in  FIG. 11 . The arm lever  154  rotates towards the rotor  26 . The front end of the engaging claw  156  engages with a tooth portion  160  of the claw wheel  152 . That is, the locking mechanism  150  performs its locking operation. As a result, rotation of the rotor  26  in the brake releasing direction L is restricted. Also, since the plunger  161  is held ion the rear extension position even after supply of electricity is stopped, a supply of electricity to the coil  165  may be temporary. Suppose that while the locking mechanism  150  is in the locking position, electricity is supplied to the motor  12  to forcibly rotate the rotor  26  in the brake releasing direction L. Since the motor torque is larger than the urging force of the torsion spring  158 , the rotor  26  will rotate in the brake releasing direction L while the steep tooth engaging faces  160   a  of the tooth portions  160  of the claw wheel  152  are pushing down the engaging claw  156 .  
         [0077]     Operation of the electric braking apparatus according to the fourth embodiment will here be explained, referring again to  FIG. 15  through  FIG. 18 .  
         [0078]     (Normal Braking Operation)  
         [0079]     When the drive initiates the normal braking of the electric brake, the rotor  26  of the motor  12  rotates clockwise as viewed from the right in  FIGS. 1 and 2 . At this time, as shown in  FIG. 12 , the solenoid  151  of the parking brake locking mechanism  116  moves the rod  166 , along with the plunger  161 , to the forward extension position, where the locking mechanism  150  is held in the unlock position due to the self-holding capability of the solenoid  151 . Therefore, when the rotor  26  rotates clockwise as described above, the eccentric plate  41  attached to the eccentric shaft  39  via the bearing  40  revolves, not rotate, by the function of the Oldham mechanism  42 . Revolution of the eccentric plate  41  causes the cycloid ball speed reducing mechanism  43  to operate. The first disk  31  of the ball ramp mechanism  13  thereby rotates in the opposite direction than the rotor  26  (the counterclockwise direction) at a speed with a ratio N to the rotor speed, as described above. Since the second disk  32  of the ball ramp mechanism  13  is restricted in rotation by the resistance force of the wave washer  34 , the second disk  32  moves forward towards the disk rotor D as the first disk  31  rotates. Thus, the piston  11  moves, and the brake pad  3  facing the interior of the vehicle is pressed against the disk rotor D. Then, in reaction thereto, the caliper  2  moves relative to the carrier  1 , whereby the claw portion  5   a  of the claw member  5  presses the brake pad  4  facing the outside of the vehicle against the outer side face of the disk rotor D. As shown by  FIG. 15 , braking force of a magnitude proportional to the rotational angle and the torque (current) of the motor  12  is generated. Further, when the brake pads  3  and  4  are worn, the gap caused by the pad wear is eliminated by the operation of the pad wear compensating mechanism  15  as described above. Further, while braking is effective, electricity to the self-holding type solenoid  151  is cut off, but the locking mechanism  150  is held in its unlocking position.  
         [0080]     (Releasing the Normal Braking)  
         [0081]     When the driver releases the electric brake, the rotor  26  of the motor  12  rotates counterclockwise as viewed from the right in  FIGS. 1 and 2 . The urging force of the disk springs  38  moves the second disk  32  rearward, along with the piston  11 . The force pressing the disk rotor D is thereby released, and the electric brake is thus released. At this time, electricity to the self-holding type solenoid  151  is cut off, and the locking mechanism  150  of the parking brake locking mechanism  116  is held in the unlocking position. Accordingly, the rotor  26  can smoothly rotates in the brake releasing direction L ( FIG. 12 ).  
         [0082]     (Occurrence of Failure During the Normal Braking Operation)  
         [0083]     If a failure occurs in the electric circuit of the motor  12  for some reason during the above-described normal braking operation, the torque (current) of the motor  12  drops as shown in  FIG. 16 . The piston returning mechanism (coil spring  47 ) or reactive force from the brake pads causes the piston  11  to move rearward. The second disk  32  then moves rearward. The rotor  26  of the motor  12  thereby rotates counterclockwise as viewed from the right in  FIGS. 1 and 2  to the original angle position, whereby the electric brake is released. Since the locking mechanism  150  of the parking brake locking mechanism  116  is held in the unlocking position as it is in the normal braking operation, the electric brake is smoothly released.  
         [0084]     (Operation of the Parking Brake (PKB))  
         [0085]     When the driver operates the parking brake, the rotor  26  of the motor  12  rotates clockwise as viewed from the right in  FIGS. 1 and 2 , as it does in the above-described normal braking operation. The piston  11  thereby moves, so that as shown in  FIG. 17 , braking force proportional to the rotational angle and the torque (current) of the motor  12  is generated. Further, simultaneously with the generation of the braking force, electricity is supplied temporarily to the coil  165  ( FIG. 14 ) in the self-holding type solenoid  151  of the parking brake locking mechanism  116 . Thereby, the rod  166  moves in the rearward direction B, along with the plunger  161  in the solenoid  151 , and the locking mechanism  150  is brought into the locking position. Thus, as shown in  FIG. 11 , the rotor  26  is restricted in rotation in the brake releasing direction L. Further, at about the same time electric current is supplied to the self-holding type solenoid  151 , supply of electricity to the motor  12  is cut ff. As a result, the locking mechanism  150  of the parking brake locking mechanism  116  is held in the locking position by the self-holding capability of the solenoid  151 . Thus, as shown in  FIG. 17 , the parking brake is kept effective.  
         [0086]     (Releasing the Parking Brake (PKB))  
         [0087]     When the driver releases the parking brake, electricity is supplied temporarily to the coil  164  ( FIG. 14 ) of the self-holding type solenoid  151  of the parking brake locking mechanism  116 . Thereby, the rod  166 , along with the plunger  161  in the solenoid  151 , moves in the forward direction A. The locking mechanism  150  is thus brought into the unlocking position in which as shown by  FIG. 12 , the rotor  26  becomes free in rotation in the brake releasing direction L. At this time, since the supply of electricity to the motor  12  is stopped, the piston  11  moves rearward by reactive force from the brake pads. The second disk  32  in turn moves rearward, and the rotor  26  of the motor  12  rotates counterclockwise as viewed from the right in  FIGS. 1 and 2 . As a result, as shown in  FIG. 18 , the motor  12  returns to its original angle position, whereby the parking brake is released.  
         [0088]     (Occurrence of Failure During the Parking Brake Operation)  
         [0089]     Suppose that the solenoid  151  fails or becomes inoperable for some reason while the parking brake is in operation. When the driver releases the parking brake, electricity is supplied to the motor  12  as happens when the electric brake is released. The rotor  26  then rotates counterclockwise as viewed from the right in  FIGS. 1 and 2 . The claw wheel  152  of the parking brake locking mechanism  116  thereby rotates in the brake releasing direction L, along with the rotor  26 . Since the rotational torque of the rotor  26  at this time is considerably larger than the urging force of the torsion spring  158  holding the engaging claw  156  upright, the engaging claw  156 , as shown in  FIG. 13 , kept pushed down by the steep tooth engaging faces  160   a  of the tooth portions  160  of the claw wheel  152 . That is, the rotor  26  can be rotated in the brake releasing direction L. Along the rotation of the rotor, the piston  11  moves rearward, and the force pressing the disk rotor D is released, whereby the parking brake is released.  
         [0090]     As has been described in detail, according to the electric braking apparatus of the invention, the parking brake is operated by utilizing rotation of the motor. Therefore, the parking brake function can sufficiently be achieved without sacrificing the basic braking function of the apparatus as an electric brake. Thus, the reliability of the apparatus is significantly improved.  
         [0091]     Further, the parking brake locking mechanism is arranged around the rotor. Therefore, the axial length of the caliper can be made short, whereby the mountability of the apparatus to the vehicle is improved. Particularly, when the parking brake locking mechanism is arranged inside the caliper, the mountability to the vehicle is further improved.  
         [0092]     Further, if the parking brake locking mechanism functions in such a manner that it releases the lock by operation of the rotational torque generated when electricity is supplied to the motor, since the parking brake locking mechanism can be unlocked by merely rotating the rotor in the brake releasing direction, control of the motor is simplified.  
         [0093]     Further, if the parking brake locking mechanism functions in such a manner that an actuator having self-holding capability locks and unlocks the locking mechanism, the parking brake function can be sufficiently achieved without sacrificing the basic electric brake function. Further, even if the motor fails, the parking brake can be released with certainty. Thus, the reliability of the apparatus is significantly improved.  
         [0094]     Further, when the self-holding type solenoid is used as the actuator, the structure of the actuator becomes simple and compact. Therefore, the caliper can be made small. Further, since electricity does not have to be constantly supplied, the apparatus contributes to power saving.  
         [0095]     Further, when there is provided a piston returning mechanism for returning the piston to the reference position when there is no current supplied to the motor, even in case of failure in the motor and the actuator, by the function of the piston returning mechanism, the parking brake can reliably be released.