Patent Publication Number: US-9835214-B2

Title: Electronic disc brake

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 2015-0133890, filed on Sep. 22, 2015 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The present disclosure relates to an electronic disc brake, and more particularly, to an electronic brake system capable of realizing a parking function by an operation of an electric motor. 
     2. Description of the Related Art 
     Generally, a brake device is a device for stopping a vehicle to prevent the vehicle from moving when the vehicle is braked or parked and serves to hold wheels of the vehicle to prevent the wheels from rotating. 
     An electronic parking brake (EPB) system that electronically controls an operation of a parking brake is widely used nowadays and is mounted on a typical disk brake to perform a function of the parking brake. Types of electronic disc brakes include a cable puller type, a motor-on-caliper (MOC) type, and a hydraulic parking brake type. 
     RELATED ART DOCUMENT 
     Korean Patent Publication No. 10-2011-0072877 (Jun. 29, 2011) 
     The above document relates to an MOC type EPB actuator structure in which a motor generating power is connected to an actuator, and the power generated by the motor is transmitted to the actuator and a caliper by increasing torque while decelerating using a plurality of gear devices to perform a braking operation. 
     However, the plurality of gear devices installed for transmitting power has an adverse effect in terms of operating noise when braking. For example, an imprecise control of a coupling (an engagement) between gears may cause noise and vibration to be generated when the actuator operates and may degrade a durability of the actuator in more serious cases. 
     SUMMARY 
     Therefore, it is an aspect of the present disclosure to provide an electronic disc brake in which a connection structure between elements such as a connection unit that transmits a driving force of a motor and a deceleration unit that decreases a rotational force is improved. 
     Additional aspects of the disclosure 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 disclosure. 
     In accordance with one aspect of the present disclosure, an electronic disc brake includes a disc, a caliper, and an actuator. The disc may be configured to rotate with vehicle wheels. The caliper housing may be configured to operate pad plates installed at both sides of the disc. The actuator may have a piston provided inside the caliper housing to press the pad plates to adhere the pad plates to the disc, a spindle rotatably installed at the caliper housing to reciprocate the piston, an electric motor configured to rotate the spindle, and a decelerator configured to transmit a rotational force of the electric motor to the spindle. The decelerator may include a power connection unit connected to the electric motor, planetary gear units configured to connect the power connection unit to the spindle, and a center pin configured to pass through the power connection unit and the planetary gear units. The power connection unit may include a driving gear provided at a shaft of the electric motor and a driven gear connected to the planetary gear units. The planetary gear units each may include a sun gear, a plurality of planetary gears engaged to an outer portion of the sun gear, a ring gear which is an internal gear configured to accommodate the planetary gears, a carrier installed to rotatably support the planetary gears and coaxially rotate with the sun gear and configured to and to output a rotational power, and an output shaft provided on the carrier and coupled to the spindle. The center pin may have one end thereof press-fitted and fixed to the output shaft. 
     The center pin may be spaced apart from and slidably and rotatably provided at a central hole provided at central portions of the driven gear of the power connection unit and the sun gear and the carrier of each of the planetary gear units. 
     The decelerator may further include a housing cap configured to surround the power connection unit and the planetary gear units, and the center pin may have the other end thereof rotatably supported by the housing cap. 
     A grease is applied between the center pin and the decelerator through which the center pin passes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the disclosure 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 cross-sectional view illustrating an electronic disc brake according to an embodiment of the present disclosure; 
         FIG. 2  is an exploded perspective view of a part of the electronic disk brake according to the embodiment; and 
         FIG. 3  is an enlarged cross-sectional view of a part of the electronic disc brake according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Embodiments to be introduced below are provided as examples to sufficiently convey the spirit of the present disclosure to those of ordinary skill in the art to which the present disclosure pertains. The present disclosure is not limited to the embodiments to be described below and may also be embodied in other forms. To clearly describe the present disclosure, parts unrelated to the description have been omitted from the drawings, and widths, lengths, thicknesses, and the like of elements in the drawings may be exaggerated for convenience. Like reference numerals refer to like elements throughout. 
       FIG. 1  is a cross-sectional view illustrating an electronic disc brake according to an embodiment of the present disclosure, and the electronic disc brake illustrated in the drawing is a motor-on-caliper (MOC) type.  FIG. 2  is an exploded perspective view of a part of the electronic disk brake according to the embodiment, and  FIG. 3  is an enlarged cross-sectional view of a part of the electronic disc brake according to the embodiment. 
     Referring to the drawings, an electronic disc brake  10  of the embodiment includes a disc  11  configured to rotate with vehicle wheels, a carrier (not illustrated) on which a pair of pad plates  12  and  13  to which disc pads  14  and  15  are respectively attached are installed by being spaced apart from each other at a predetermined interval, a caliper housing  20  slidably installed at the carrier to operate the pad plates  12  and  13 , and an actuator  30  having a piston  31  installed to be movable back and forth inside the caliper housing  20 . 
     The caliper housing  20  is slidably installed at the carrier by a pair of guide rods (not illustrated), and the caliper housing  20  includes a cylinder unit  21  in which the piston  31  is inserted, a finger unit  23  configured to operate an outer pad plate  12  to be described below, and a connection unit  25  configured to connect the finger unit  23  to the cylinder unit  21 . 
     The carrier is mounted on a knuckle of a vehicle body by a mounting bolt, and the caliper housing  20  is slidably coupled to both end portions of the carrier by the guide rods. 
     The disc pads  14  and  15  are attached to inner surfaces of the pair of pad plates  12  and  13 , respectively. The pad plates  12  and  13  include an inner pad plate  13  disposed so that an outer surface thereof is in contact with a front end of the piston  31  and the outer pad plate  12  disposed so that an outer surface thereof is in contact with the finger unit  23 . 
     The actuator  30  includes the piston  31  slidably inserted into the cylinder unit  21  of the caliper housing  20 , a spindle  33  rotatably installed inside the cylinder unit  21  of the caliper housing  20 , a nut spindle  36  installed inside the piston  31  to press the piston  31  or release the pressing of the piston  31  while moving back and forth by a rotation of the spindle  33 , an electric motor  41  configured to rotate the spindle  33 , and a decelerator  45  configured to transmit a rotational force of the electric motor  41  to the spindle  33 . 
     The piston  31  is slidably inserted into the cylinder unit  21  as described above, and the piston  31  is provided in a cylindrical shape in which the inside thereof is recessed in a cup shape. 
     The spindle  33  has a support part  34  rotatably supported at a rear end side of the cylinder unit  21  and a male screw part  35  configured to extend a predetermined length into an inner central portion of the piston  31  from the support part  34 . 
     The nut spindle  36  is formed in a cylindrical shape and includes a female screw portion  37 , which is fastened to the male screw portion  35  of the spindle  33 , formed at an inner surface thereof to move back and forth in an axial direction by the rotation of the spindle  33 . Consequently, when the spindle  33  rotates in a forward direction or a reverse direction, the nut spindle  36  moves back and forth and presses the piston  31  such that braking occurs. 
     The electric motor  41  receives power by manipulation of a switch (not illustrated) provided at a driver seat of the vehicle and converts electrical energy into mechanical rotational kinetic energy. A braking operation according to an operation signal of the switch is controlled by an electronic control unit (ECU) of the vehicle which is not illustrated. 
     The decelerator  45  includes a power connection unit  50  and a plurality of planetary gear units  60 . 
     The power connection unit  50  connects a shaft of the electric motor  41  to the planetary gear units  60 . The power connection unit  50  may include a driving gear  51  provided at the electric motor  41 , a driven gear  53  connected to the planetary gear units  60 , and an intermediate gear  52  that connects the driving gear  51  to the driven gear  53  between the driving gear  51  and the driven gear  53 . 
     In addition, the power connection unit  50  may further include a frame  54  configured to maintain distances between shafts of the driving gear  51 , the intermediate gear  52 , and the driven gear  53  and configured to support the shaft of the intermediate  52 . 
     Here, the number of teeth of the gears preferably increases from the driving gear  51  toward the driven gear  53  in the power connection unit  50  so that a rotation of the electric motor  41  may be decelerated and transmitted to the planetary gear units  60 . 
     In addition, the electric motor  41  is installed to a side of the planetary gear units  60  and is disposed so that a central axis line thereof is parallel to a central axis line of the planetary gear units  60 . When the electric motor  41  is disposed to the side of the decelerator  45  so that the central axis line of the electric motor  41  is parallel to the central axis line of the planetary gear units  60  as described above, an overall length of the electronic disc brake may be shortened. An undescribed reference numeral  56  refers to a housing cap configured to cover the decelerator  45  and the electric motor  41 . 
     To obtain a large reduction gear ratio by multi-stage deceleration, the planetary gear units  60  include first and second planetary gear units  61  and  62  continuously connected from the power connection unit  50  connected to the electric motor  41  to the spindle  33 . 
     The first and second planetary gear units  61  and  62  respectively include sun gears  61   a  and  62   a,  a plurality of planetary gears  61   b  and  62   b  engaged to outer portions of the sun gears  61   a  and  62   a,  ring gears  61   c  and  62   c  which are internal gears configured to accommodate the planetary gears  61   b  and  62   b,  and carriers  61   d  and  62   d  installed to rotatably support the planetary gears  61   b  and  62   b  and to coaxially rotate with the sun gears  61   a  and  62   a  and configured to output rotational power. 
     Although it is illustrated that the sun gear  61   a  of the first planetary gear unit  61  is integrally provided with the driven gear  53  of the power connection unit  50  and that the sun gear  62   a  of the second planetary gear unit  62  is integrally provided with the carrier  61   d  of the first planetary gear unit  61  in the embodiment, this may be properly modified and changed by an ordinary technician by bonding or coupling. In addition, the ring gears  61   c  and  62   c  may be provided by forming a gear at an inner surface of a housing body  64  in a cylindrical shape. 
     Here, the decelerator  45  will be briefly described again. The sun gear  61   a  of the first planetary gear unit  61  is connected to the driven gear  53  of the power connection unit  50  connected to the electric motor  41  by a gear, and the sun gear  62   a  of the second planetary gear unit  62  is connected to a central shaft of the carrier  61   d  which is an output side of the first planetary gear unit  61 . That is, the plurality of planetary gear units  61  and  62  are continuously coupled in the above manner, and finally, the carrier  62   d  of the second planetary gear unit  62  is connected to the spindle  33  of the actuator by using an output shaft  65 . 
     Consequently, according to the embodiment, the decelerator  45  may miniaturize the electric motor  41  which is a driving source and still rotate the spindle  33  with great force. Thus, when, for example, an operation of the electric motor  41  is stopped while braking is performed, the rotation of the spindle  33  is limited by the large reduction gear ratio of the decelerator  45  such that a braking state may be remained. 
     Meanwhile, the gears of the decelerator  45  described above, e.g., the driven gear  53  of the power connection unit  50  and the sun gears of the first and second planetary gear units  61  and  62 , and central shafts of the carriers may be aligned on the same axis by using a center pin  70 . 
     As illustrated in  FIG. 3 , one end of the center pin  70  is rotatably coupled to the housing cap  56  and the other end thereof is fixed to the output shaft  65  by passing through the planetary gear units  60 . The housing cap  56  has a pin hole in the form of a through-hole so that the center pin  70  is slidably and rotatably fitted thereinto, and the output shaft  65  also has a shaft hole  65   a  recessed in a predetermined depth so that the center pin  70  is forcedly press-fitted to the shaft hole  65   a.  In this case, the center pin  70  is slidably and rotatably inserted into a central hole  67  provided at central portions of the sun gear  61   a  and the carrier  61   d  of the first planetary gear unit  61  and the sun gear  62   a  and the carrier  62   d  of the second planetary gear unit  62  through which the center pin  70  passes to be slidably rotatable. 
     Since the center of the decelerator  45  is centered by the center pin  70  which is spaced a predetermined distance apart from and slidably and rotatably coupled to the central hole  67  provided in the driven gear  53  and the sun gears and the carriers of the first and second planetary gear units  61  and  62 , the decelerator  45  may effectively reduce power loss and noise caused by torsion of a gear when power is transmitted using a plurality of gears. Furthermore, assembling the decelerator is facilitated. 
     In addition, the center pin  70  having one end press-fitted and fixed to the output shaft  65  is unlikely to have eccentric rotation during rotation of the spindle  33  since the output shaft is directly connected to the spindle  33 , so that misalignment of gears in the decelerator caused by the center pin  70  being bent may be effectively prevented. 
     Although not illustrated in detail, a lubricating material such as grease may be applied between the central hole  67  of the driven gear  53 , the sun gears  61   a  and  62   a,  and the carriers  61   d  and  62   d  of the decelerator and the center pin  70  which are spaced apart from each other to prevent the introduction of foreign substances and to facilitate smooth rotation. 
     A braking operation of an electronic disc brake having the above structure is performed as below. 
     When a driver manipulates a parking switch provided near a driver seat of a vehicle for braking (including parking), the electric motor  41  rotates. The rotation of the electric motor  41  is decelerated through the decelerator  45  and rotates the spindle  33  with a great force. 
     The nut spindle  36  moves in the axial direction when the spindle  33  rotates, and braking is performed as the nut spindle  36  presses the piston  31 . 
     After braking is performed, the electric motor  41  stops operating, and the rotation of the spindle  33  is prevented since the decelerator  45  has a large reduction gear ratio. Accordingly, the braking state is maintained without change as long as the electric motor  1  does not operate again. 
     When the driver releases braking, the driver manipulates the parking switch near the driver seat to release the braking. Here, since the electric motor  41  rotates in a reverse direction of braking and the spindle  33  rotates in the reverse direction of braking, the nut spindle  36  releases the pressing of the piston  31  and thus the braking is released. 
     According to an embodiment of the present disclosure, by centering gears of a power connection unit and planetary gear units of a decelerator on the same axis using a center pin, power loss and noise caused by a misalignment of the gears can be reduced. 
     In addition, according to an embodiment of the present disclosure, an electronic disc brake includes a center pin press-fitted and fixed to an output shaft to which a spindle is directly connected such that convenience of assembling is high. In addition, as the output shaft is unlikely to have eccentric rotation during rotation of the spindle, misalignment of gears caused by the center pin being bent can be effectively prevented. 
     The disclosed embodiments have been described above with reference to the accompanying drawings. Those of ordinary skill in the art to which the present disclosure pertains should understand that the present disclosure may be practiced in forms different from the disclosed embodiments without changing the technical spirit or essential features of the present disclosure. The disclosed embodiments are merely illustrative and are not to be construed as limiting.