Patent Publication Number: US-2010122877-A1

Title: Electric disc brake

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of Korean Patent Application No. 2008-0115153 and No. 2008-0115152, filed on Nov. 19, 2008 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Embodiments of the present invention relate to an electric disc brake capable of achieving a great braking force. 
     2. Description of the Related Art 
     Differently from general hydraulic disc brakes, electric disc brakes employ an electric motor as a power source of a driving device to press a friction pad. 
     Such an electric disc brake is disclosed in KR Patent Publication No. 2003-93691. The electric disc brake includes a motor rotating forward and backward to brake and release wheels, a screw gear unit connected to a rotational shaft of the motor, and a piston pressing a friction pad by moving back and forth according to rotation of the screw gear unit. 
     However, in the conventional electric disc brake, the screw gear unit that drives the piston back and forth is in direct connection with the rotational shaft of the motor. Therefore, it is difficult to generate a great driving force. 
     SUMMARY 
     Therefore, it is an aspect of the present invention to provide an electric disc brake capable of generating a great braking force. 
     Additional aspects of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     In accordance with one aspect of the present invention, an electric disc brake includes friction pads to press a disc, a carrier to support the friction pads, a caliper housing supported by the carrier to be movable back and forth so as to press the friction pads, and a pressing device to press the friction pads, wherein the pressing device includes a pressing member mounted to the caliper housing and moved back and forth to thereby press and release any one of the friction pads, a screw axis connected to the pressing member, a drive shaft mounted across the screw axis, a motor rotating the drive shaft forward and backward, and a worm gear including a worm wheel connected to the screw axis and a worm formed at the drive shaft and engaged with the worm wheel, so as to transmit rotation of the drive shaft to the screw axis, and the screw axis and the worm wheel of the worm gear are disposed in the center of an inner space of the caliper housing while the motor is disposed at the outside of the caliper housing eccentrically from the center according to a mounting position of the worm gear. 
     The pressing device may further include a motor shaft and a reduction gear device mounted to the drive shaft, so that rotation of the motor is reduced and transmitted to the drive shaft. 
     The reduction gear device may include a drive gear mounted to the motor shaft, and a driven gear having a greater number of teeth than the drive gear, being mounted to the drive shaft to be meshed with the drive gear. 
     The reduction gear device may include a sun gear mounted to the motor shaft, a plurality of planet gears arranged around the sun gear and meshed with the sun gear, an inscribing gear fixed to outsides of the planet gears to be meshed with the planet gears, and a carrier connecting axes of the planet gears with the drive shaft. 
     In accordance with another aspect of the present invention, in an electric disc brake including friction pads to press a disc, a carrier to support the friction pads, a caliper housing supported by the carrier to be movable back and forth so as to press the friction pads, and a pressing device to press the friction pads, the pressing device may include a pressing member mounted to the caliper housing and moved back and forth to thereby press and release any one of the friction pads, a screw axis connected to the pressing member, a drive shaft mounted across the screw axis, a motor rotating the drive shaft forward and backward, and a worm gear including a worm wheel connected to the screw axis and a worm formed at the drive shaft and engaged with the worm wheel, so as to transmit rotation of the drive shaft to the screw axis, and the motor may be disposed in the center of the caliper housing at the outside of the caliper housing while the screw axis and the worm gear are disposed in the caliper housing eccentrically from the center by as much as the size of the drive shaft and a radius of the worm wheel. 
     The pressing member may have an extended end extended toward the center of the friction pad. 
     In accordance with a further aspect of the present invention, in an electric disc brake comprising friction pads to press a disc, a carrier to support the friction pads, a caliper housing supported by the carrier to be movable back and forth so as to press the friction pads, and a pressing device to press the friction pads, the pressing device may include a pressing member mounted to the caliper housing and moved back and forth to thereby press and release any one of the friction pads, a screw axis connected to the pressing member, a drive shaft mounted across the screw axis, a motor rotating the drive shaft forward and backward, a worm gear including a worm wheel connected to the screw axis and a worm formed at the drive shaft and engaged with the worm wheel, so as to transmit rotation of the drive shaft to the screw axis, and a reduction gear device mounted to the motor shaft and the drive shaft so as to reduce rotation of the motor and transmit the reduced rotation to the drive shaft. 
     The reduction gear device may include a drive gear mounted to the motor shaft, and a driven gear having a greater number of teeth than the drive gear, being mounted to the drive shaft to be meshed with the drive gear. 
     The reduction gear device may include a sun gear mounted to the motor shaft, a plurality of planet gears arranged around the sun gear and meshed with the sun gear, an inscribing gear fixed to outsides of the planet gears to be meshed with the planet gears, and a carrier connecting axes of the planet gears with the drive shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a sectional view showing an electric disc brake according to an embodiment of the present invention; 
         FIG. 2  is a view schematically showing a pressing device of the electric disc brake shown in  FIG. 1 ; 
         FIG. 3  is a sectional view of an electric disc brake according to another embodiment of the present invention; 
         FIG. 4  is a sectional view of an electric disc brake according to still another embodiment of the present invention; 
         FIG. 5  is a sectional view of an electric disc brake according to a further embodiment of the present invention; 
         FIG. 6  is a sectional view of  FIG. 5  cut along a line A-A′; and 
         FIG. 7  is a view of an electric disc brake according to a further embodiment of the present invention, showing another version of a reduction gear device. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
       FIG. 1  is a sectional view showing an electric disc brake according to an embodiment of the present invention, and  FIG. 2  is a view schematically showing a pressing device of the electric disc brake shown in  FIG. 1 . 
     As shown in  FIG. 1 , the electric disc brake includes a disc  10  rotated with wheels of a vehicle, first and second friction pads  11  and  12  disposed at both sides of the disc  10 , respectively, a caliper housing  20  pressing the first and the second friction pads  11  and  12 , and a pressing device  40  mounted to the caliper housing  20  to perform the braking operation. 
     The first and the second friction pads  11  and  12  are supported by a carrier  30  fixed to a vehicle body, to be movable back and forth with respect to both sides of the disc  10 . The caliper housing  20  is also supported by the carrier  30  to be movable back and forth in a direction to press the friction pads  11  and  12 . 
     The caliper housing  20  includes a hollow housing body  21 , an extension part  22  extended from the housing body  21  toward the second friction pad  12 , and a finger part  23  connected to the extension part  22  to support a rear side of the second friction pad  12 . The pressing device  40  is mounted to the housing body  21  of the caliper housing  20  so as to press the first friction pad  11 . 
     As shown in  FIGS. 1 and 2 , the pressing device  40  includes a pressing member  41  mounted in the housing body  21  to be movable back and forth so as to apply and release pressure to and from the first friction pad  11 , a screw axis  42  connected to the pressing member  41 , a drive shaft  44  mounted across the screw axis  42 , a motor  46  rotating the drive shaft  44  forward and backward, and a worm gear  45  transmitting rotation of the drive shaft  44  to the screw axis  42 . 
     The pressing member  41  is mounted inside the housing body  21  to be moved back and forth in a state of being restricted in rotation. The pressing member  41  includes a female screw part  41   a  connected to the screw axis  42 . Here, restriction in rotation of the pressing member  41  may be achieved by forming an outer surface of the pressing member  41  and an inner surface of the housing body  21  into polygonal shapes correspondingly connected to each other. Alternatively, guide units (not shown) in the form of a key and a key recess may be formed at the outer surface of the pressing member  41  and the inner surface of the housing body  21 , respectively, to restrict the rotation. 
     The screw axis  42  includes a male screw part  42   a  formed at one side to be engaged with the female screw part  41   a.  The screw axis  42  is rotatably mounted in the housing body  21 , being parallel with the moving direction of the pressing member  41 . A first bearing  47  and a second bearing  48  are mounted in the housing body  21 , separately by a predetermined interval, so as to support the screw axis  42 . 
     The worm gear  45  includes a worm wheel  45   a  connected to an outer surface of the screw axis  42  to rotate in a vacant space  27  in the housing body  21 , and a worm  45   b  formed at the drive shaft  44  mounted across the screw axis  42 . The worm  45   b  is engaged with the worm wheel  45   a.    
     The drive shaft  44  is rotatably supported by the housing body  21 . A part of the drive shaft  44  where the worm  45   b  is mounted is inserted in the housing body  21 . One end of the drive shaft  44  is extended to the outside of the housing body  21 , penetrating a lower part of the housing body  21 . 
     The motor  46  is fixed to the lower part of the housing body  21  of the caliper housing  20  by fixing screws  49 . 
     As shown in  FIG. 2 , the screw axis  42  of the pressing device  40  and the worm wheel  45   a  of the worm gear  45  are disposed in the center of the inside of the housing body  21 . On the other hand, the motor  46  is disposed eccentrically from the center of the housing body  21  according to the eccentric position of the worm  45   b.    
     Hereinafter, the operation of the electric disc brake will be described. 
     When an operator orders a braking operation, the motor  46  is rotated in a direction to perform braking. When the operator releases the braking operation, the motor  46  is rotated in a reverse direction with respect to the braking direction so as to release the braking. 
     As the motor  46  rotates for the braking, the drive shaft  44  is rotated. 
     When the worm  45   b  is rotated by rotation of the drive shaft  44 , the worm wheel  45   a  engaged with the worm  45   b  is rotated. When the worm wheel  45   a  is rotated, the screw axis  42  is accordingly rotated. Here, speed reduction is achieved by a great reduction gear ratio between the worm  45   b  and the worm wheel  45   a.  Therefore, a rotational force transmitted to the screw axis  42  is further increased in direct proportion to the reduction of the rotation of the screw axis  42 . 
     When the screw axis  42  is rotated, the pressing member  41  moves toward the first friction pad  11 , thereby pressing the first friction pad  11 . As a reaction to this, the caliper housing  20  is moved in the opposite direction to a moving direction of the pressing member  40 , such that the finger part  34  presses the second friction pad  12  toward the disc  10 . Thus, the braking is performed. On the other hand, when the motor  46  is rotated in the reverse direction, the pressing member  41  is moved in a direction for releasing pressure from the first friction pad  11 , thereby releasing the braking operation. 
       FIG. 3  is a sectional view of an electric disc brake according to another embodiment of the present invention. In the following description, the same elements as in one embodiment described above will not be repeatedly explained. 
     Referring to  FIG. 3 , the electric disc brake of this embodiment includes a pressing member  141 , a screw axis  142  connected to a female screw part  141   a  of the pressing member  141 , and a worm gear  145  constituted by a worm wheel  145   a  connected to the screw axis  142  and a worm  145   b  engaged with the worm wheel  145   a.  While the pressing member  141 , the screw axis  142  and the worm gear  145  are disposed eccentrically from the center of the inside of the housing body  21 , a motor  146  is mounted in the center in the housing body  21 . 
     More specifically, since the motor  146  is mounted in the central position, the screw axis  142  and the worm gear  145  are mounted eccentrically from the center by as much as the size of a drive shaft  144  and a radius of the worm wheel  145   a.    
       FIG. 4  is a sectional view of an electric disc brake according to still another embodiment of the present invention. In the following description, the same elements as in one embodiment described above will not be repeatedly explained. 
     According to this embodiment as shown in  FIG. 4 , a pressing member  241 , a screw axis  242  connected to a female screw part  241   a  of the pressing member  241 , and a worm gear  245  constituted by a worm wheel  245   a  connected to the screw axis  242  and a worm  245   b  engaged with the worm wheel  245   a  are disposed eccentrically from the center of the inside of the housing body  21 . However, a motor  246  is disposed in the center in the housing body  21 . 
     Here, the center of the pressing member  241 , which is connected with the screw axis  242 , is disposed eccentrically from the first friction pad  11 . The pressing member  241  has an extended end  241  b extended toward the center of the first friction pad  11  so that a pressing force is efficiently transmitted to the center of the first friction pad  11 . 
     More specifically, a pressing device  240  may be disposed in a manner that the center of the pressing member  241  is eccentrically disposed due to the worm gear  245 . However, since the pressing force is transmitted through the extended end  241  b of the pressing member  241  extended to the center of the first friction pad  11 , transmission of the pressing force to the first friction pad  11  may be favorably performed. 
       FIG. 5  is a sectional view of an electric disc brake according to a further embodiment of the present invention.  FIG. 6  is a sectional view of  FIG. 5  cut along a line A-A′. The same elements as in the previous embodiments will not be repeatedly explained. 
     As shown in  FIG. 5  and  FIG. 6 , the pressing device  40  further includes a reduction gear device  50  mounted to a motor shaft  46   a  and the drive shaft  44  so that rotation of the motor shaft  46   a  is reduced and transmitted to the drive shaft  44 . 
     The reduction gear device  50  includes a drive gear  51  mounted to the motor shaft  46   a,  and a driven gear  52  mounted to the drive shaft  44  and meshed with the drive gear  51 . The reduction gear device  50  is structured in a manner that the driven gear  52  has a larger number of teeth than the drive gear  51 , accordingly achieving speed reduction. The arrangement of the drive gear  51  and the driven gear  52  may be adjusted according to the mounting position of the motor  46 . Also, sizes of the gears  51  and  52  may be varied in order to adjust the reduction gear ratio. 
     The above-structured electric disc brake is operated in the following manner. First, rotation of the motor  46  is primarily reduced by the reduction gear device  50  while being transmitted to the drive shaft  44 . Whereas the rotation speed of the drive shaft  44  is reduced according to the primary reduction by the reduction gear device  50 , a rotational force transmitted to the drive shaft  44  is increased. 
     As the worm  45   b  is rotated by rotation of the driving shaft  44 , the worm wheel  45   a  engaged with the worm  45   b  is rotated. As the worm wheel  45   a  rotates, the screw axis  42  is rotated. Here, speed reduction is secondarily performed by a great reduction gear ratio of the worm gear  45 . Accordingly, the rotational force transmitted to the screw axis  42  is increased in direct proportion to the reduction in rotation of the screw axis  42 . 
     Specifically, according to the electric disc brake, rotation of the motor  46  is reduced primarily by the reduction gear device  50  and secondarily by the worm gear  45 , thereby increasing the rotational force transmitted to the screw axis  42  corresponding to the reduction gear ratio. Accordingly, the pressing member  41  is capable of pressing the first friction pad  11  with a great force. As a consequence, a great braking force is achieved. 
     In addition, although the worm gear  45  is provided in the embodiment shown in  FIGS. 5 and 6 , the screw axis  42  and the worm gear  45  are disposed in the center of the housing body  21  and the motor  46  is also disposed in the center because of the presence of the reduction gear device  50 . 
       FIG. 7  is a sectional view of an electric disc brake according to a further embodiment of the present invention. In the following description, the same elements as in one embodiment described above will not be repeatedly explained. 
     The present embodiment suggests another reduction gear device  60  that connects a motor shaft with a drive shaft. 
     The reduction gear device  60  includes a sun gear  61  mounted to the motor shaft  46   a,  a plurality of planet gears  62  arranged around the sun gear  61  and meshed with the sun gear  61 , an inscribing gear  63  fixed to outsides of the planet gears  62  to be meshed with the planet gears  62 , and a carrier  65  connecting axes  64  of the planet gears  62  with the drive shaft  44 . The reduction gear device  60  operates in the following manner. When the sun gear  61  rotates by the operation of the motor  46 , the planet gears  62  are rotated, transmitting the rotation to the drive shaft  44  through the carrier  65 . As a result, the drive shaft  44  performs reduction rotation. 
     More specifically, rotation of the motor  46  is primarily reduced by the reduction gear device  60  and secondarily by the worm gear  45 , accordingly increasing the rotational force transmitted to the screw axis  42  corresponding to the reduction gear ratio. Therefore, the pressing member  41  is capable of pressing the first friction pad  11  with a great force. As a consequence, a great braking force is achieved. 
     As is apparent from the above description, in accordance with an electric disc brake according to the embodiments of the present invention, rotation of a motor is reduced by a worm gear. Therefore, a pressing member is able to pressing a first friction pad by a great force, accordingly achieving a great brake force. 
     Since the reduction is performed during transmission of rotation of the motor to a screw axis, a sufficient braking force may be obtained even with a small-size and small-output motor. As a result, the volume of the device may be accordingly reduced. 
     In addition, according to the embodiments of the present invention, the screw axis and a motor shaft may be mounted in different directions from each other. Therefore, the motor may be mounted at a lower part of a caliper housing body, accordingly reducing the length of the device in the screw axis direction. 
     Furthermore, in the electric disc brake according to the embodiments, since rotation of the motor is primarily reduced by the reduction gear device before being transmitted to the worm gear, the pressing member is able to press the first friction pad by a great force. Consequently, a great braking force may be generated. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.