Patent Publication Number: US-2023150468-A1

Title: Brake apparatus for vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from and the benefit of Korean Patent Application No. 10-2021-0158534, filed on Nov. 17, 2021, which is hereby incorporated by reference for all purposes as if set forth herein. 
     BACKGROUND 
     1. Technical Field 
     Exemplary embodiments of the present disclosure relate to a brake apparatus for a vehicle, and more particularly, to a brake apparatus for a vehicle that generates a braking force by converting an operating force applied to a pedal by a driver into an electrical signal. 
     2. Discussion of Related Art 
     In general, a brake apparatus for a vehicle refers to an apparatus for braking a vehicle by using a frictional force between a pad and a disc which is generated when the pad and the disc come into close contact with each other as a piston is pushed by driving power. 
     Among the brake apparatuses, an electromechanical brake (EMB) refers to an apparatus that has a motor-driven actuator mounted directly on a caliper and generates a braking force by pressing a piston through a mechanism such as a gear or a screw without using a hydraulic pressure. The EMB is advantageous in that the EMB may perform implement additional functions such as ABS, ESC, TCS, and AEB as well as general main braking because the EMP may perform active braking and independent braking for each wheel, and implement higher performance because there is no delay in transmitting a hydraulic pressure. 
     The EMB in the related art ensures quick responsiveness and high efficiency of the piston by means of a ball screw. However, because the ball screw cannot perform self-locking capable of restricting a rotation of the ball screw because of the structural nature of the ball screw, there is a problem in that a braking force is arbitrarily eliminated by a repulsive force between the pad and the piston when a supply of power to a motor is cut off. 
     The background technology of the present disclosure is disclosed in Korean Patent Application Laid-Open No. 10-2010-0098846 (published on Sep. 10, 2010 and entitled ‘Disc Brake Having Parking Function’). 
     SUMMARY 
     Various embodiments are directed to a brake apparatus for a vehicle, which is capable of stably maintaining a parking braked state. 
     In an embodiment, a brake apparatus for a vehicle includes: a drive unit configured to generate a driving power; a transmission gear configured to be rotated by the driving power transmitted from the drive unit; a piston configured to (1) move along a first axis in response to a rotation of the transmission gear and (2) press or release a pad depending on a movement direction of the piston; a parking gear engaged with the transmission gear, and configured to be rotated in response to the rotation of the transmission gear; and a restriction unit configured to move toward and engage with the parking gear to restrict a rotation of the parking gear. 
     In addition, the transmission gear may include: a first transmission gear configured to be rotated with an output shaft of the drive unit; a second transmission gear engaged with the first transmission gear, and configured to be rotated in response to a rotation of the first transmission gear; and a third transmission gear engaged with the second transmission gear, and configured to be rotated in response to a rotation of the second transmission gear and transmit a rotational force to the piston. 
     In addition, the parking gear may engage with the second transmission gear. 
     In addition, a diameter of the parking gear may be smaller than a diameter of the second transmission gear. 
     In addition, a diameter of the parking gear may correspond to a diameter of the first transmission gear. 
     In addition, the parking gear may include: a body unit; a toothed unit protruding from an outer peripheral surface of the body unit and engaged with the second transmission gear; and an insertion structure concavely recessed into the body unit, wherein the restriction unit is inserted into the insertion structure. 
     In addition, the restriction unit may include: a parking drive unit configured to generate an electromagnetic force; a rod slidably movable in the parking drive unit, and configured to move to a first direction when the electromagnetic force is supplied thereto; a restoration unit positioned between the rod and the parking drive unit, and configured to move the rod to a second direction when a supply of the electromagnetic force is discontinued; and a stopper configured to be inserted into the parking gear when the rod moves to the second direction. parking gear 
     In addition, the restriction unit may further include a rotation prevention unit configured to prevent a rotation of the rod relative to the parking drive unit. 
     In addition, the rotation prevention unit may have a polygonal cross-section and surrounds an outer surface of the rod. 
     In addition, the stopper may have a polygonal cross-sectional shape. 
     In addition, the restriction unit may further include an insertion guide unit configured to guide the insertion of the stopper unit into the parking gear. 
     In addition, the insertion guide unit may be positioned at an edge of an end portion of the stopper and inclined at a predetermined angle. 
     In addition, the restoration unit may be elastically deformable in a longitudinal direction thereof. 
     In addition, the piston may include: a ball screw connected to the transmission gear configured to rotate; a ball nut configured to rectilinearly reciprocate in a longitudinal direction of the ball screw in response to a rotation of the ball screw; and a rolling element positioned between and being in rollable contact with the ball screw and the ball nut. 
     According to the brake apparatus for a vehicle according to the present disclosure, the restriction unit may prevent the piston from being arbitrarily separated from the pad part and thus inhibit a loss of braking force even though the operation of the drive unit is released during the parking braking. 
     In addition, according to the brake apparatus for a vehicle according to the present disclosure, the parking gear may engage with the second transmission gear and thus be prevented from interfering with an adjacent component such as an ECU installed at the periphery of a driving shaft of the drive unit. 
     In addition, according to the brake apparatus for a vehicle according to the present disclosure, the diameter of the parking gear may be smaller than the diameter of the second transmission gear, which makes it possible to reduce a magnitude of a load applied to the restriction unit when the restriction unit restricts the rotation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view schematically illustrating a configuration of a brake apparatus for a vehicle according to an embodiment of the present disclosure. 
         FIG.  2    is a perspective view illustrating the configuration of the brake apparatus for a vehicle according to the embodiment of the present disclosure when viewed at a point in time different a point in time illustrated in  FIG.  1   . 
         FIG.  3    is a cross-sectional view schematically illustrating the configuration of the brake apparatus for a vehicle according to the embodiment of the present disclosure. 
         FIG.  4    is an enlarged view schematically illustrating the configuration of the brake apparatus for a vehicle according to the embodiment of the present disclosure. 
         FIG.  5    is an enlarged view schematically illustrating configurations of a parking gear and a restriction unit according to the embodiment of the present disclosure. 
         FIG.  6    is a perspective view schematically illustrating the configuration of the parking gear according to the embodiment of the present disclosure. 
         FIG.  7    is a perspective view schematically illustrating the configuration of the restriction unit according to the embodiment of the present disclosure. 
         FIG.  8    is a cross-sectional view schematically illustrating the configuration of the restriction unit according to the embodiment of the present disclosure. 
         FIG.  9    is an enlarged view schematically illustrating a configuration of an insertion guide unit according to the embodiment of the present disclosure. 
         FIGS.  10  to  12    are operational views schematically illustrating an operating process of the brake apparatus for a vehicle according to the embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a brake apparatus for a vehicle will be described with reference to the accompanying drawings through various embodiments. 
     Here, thicknesses of lines, sizes of constituent elements, or the like illustrated in the drawings, may be exaggerated for clarity and convenience of description. In addition, the terms used below are defined in consideration of the functions thereof in the present disclosure and may vary depending on the intention of a user or an operator or a usual practice. Therefore, such terms should be defined based on the entire contents of the present specification. 
     In addition, in the present specification, when one constituent element is referred to as being “connected to (or coupled to)” another constituent element, the constituent elements can be “directly connected to (coupled to)” each other, and can also be “indirectly connected to (coupled to)” each other with other elements interposed therebetween. Unless explicitly described to the contrary, the word “comprise (or include)” and variations such as “comprises (or includes)” or “comprising (or including)” will be understood to imply the further inclusion of stated elements, not the exclusion of the stated elements. 
     In addition, throughout the specification, the same reference numerals denote the same constituent elements. Even though the same or similar reference numerals are not mentioned or described with reference to specific drawings, the same or similar reference numerals may be described with reference to the other drawings. In addition, even though there are parts denoted by no reference numeral in specific drawings, the parts may be described with reference to the other drawings. In addition, the numbers, shapes, sizes, relative differences in sizes, and the like of the detailed constituent elements illustrated in the drawings of the present application are set for convenience of understanding, do not limit the embodiments, and may be variously implemented. 
       FIG.  1    is a perspective view schematically illustrating a configuration of a brake apparatus for a vehicle according to an embodiment of the present disclosure,  FIG.  2    is a perspective view illustrating the configuration of the brake apparatus for a vehicle according to the embodiment of the present disclosure when viewed at a point in time different a point in time illustrated in  FIG.  1   ,  FIG.  3    is a cross-sectional view schematically illustrating the configuration of the brake apparatus for a vehicle according to the embodiment of the present disclosure, and  FIG.  4    is an enlarged view schematically illustrating the configuration of the brake apparatus for a vehicle according to the embodiment of the present disclosure. 
     Referring to  FIGS.  1  to  4   , a brake apparatus  1  for a vehicle according to an embodiment of the present disclosure includes a caliper body part  100 , pad parts  200 , a housing  300 , a drive unit  400 , a transmission gear  500 , a piston  600 , a parking gear  700 , and a restriction unit  800 . 
     The caliper body part  100  is fixed to a vehicle body by means of a torque member  10  and supports the pad parts  200 , the housing  300 , and the piston  600  which will be described below. The caliper body part  100  is coupled to the torque member  10  by means of guide pins connected to two opposite sides thereof so as to be slidable in a direction parallel to an axial direction of a brake disc. The caliper body part  100  is slidably supported on the torque member  10  by means of the guide pins connected to the two opposite sides thereof. The caliper body part  100  is slid in the direction parallel to the axial direction of the brake disc (not illustrated) by a reaction force generated when the piston  600  to be described below presses the pad parts  200 . 
     The caliper body part  100  according to the embodiment of the present disclosure includes a bridge unit  110 , a finger unit  120 , and a cylinder unit  130 . 
     The bridge unit  110  defines an upper external appearance of the caliper body part  100 . The bridge unit  110  according to the embodiment of the present disclosure may be provided in the form of a plate disposed such that an inner surface thereof is spaced apart from an outer peripheral surface of the brake disc at a predetermined interval and faces the outer peripheral surface of the brake disc. The specific shape and area of the bridge unit  110  may be variously changed in design depending on the size or the like of the brake disc. 
     The finger unit  120  defines a front external appearance of the caliper body part  100  and presses or releases the pad parts  200  to be described below in conjunction with the sliding of the caliper body part  100 . The finger unit  120  according to the embodiment of the present disclosure perpendicularly extends downward from a front end of the bridge unit  110 . The finger unit  120  is disposed such that an inner surface thereof faces one of the pair of pad parts  200  disposed at an outer side based on the brake disc in a width direction of the vehicle. 
     The cylinder unit  130  defines a rear external appearance of the caliper body part  100  and supports the piston  600  to be described below so that the piston  600  is movable. The cylinder unit  130  according to the embodiment of the present disclosure perpendicularly extends downward from a rear end of the bridge unit  110 . The cylinder unit  130  has a hollow cylindrical shape opened at one side thereof. The cylinder unit  130  is disposed such that the opened side faces one of the pair of pad parts  200  disposed at an inner side based on the brake disc in the width direction of the vehicle. 
     The pad parts  200  are disposed to face the brake disc that rotates together with a wheel of the vehicle. The pair of pad parts  200  is disposed to face two opposite surfaces of the brake, respectively, disc with the brake disc interposed therebetween. The pad parts  200  are supported on the caliper body part  100  so as to be slidable in the direction parallel to a central axis of the brake disc. The pad parts  200  are brought into contact with the brake disc by a pressing force applied by the caliper body part  100  and the piston  600  to be described below or separated from the brake disc, thereby generating or eliminating the braking force for braking the vehicle. A friction pad made of a material such as rubber with a high frictional coefficient may be attached to one surface of the pad part  200  facing the brake disc. The specific shape of the pad part  200  is not limited to the shape illustrated in  FIGS.  1  to  4    and may be variously changed in design within the technical spirit of the brake pad that applies the braking force to the vehicle by coming into contact with the brake disc. 
     The housing  300  is coupled to the caliper body part  100  and entirely supports the drive unit  400 , the transmission gear  500 , the parking gear  700 , and the restriction unit  800 , which will be described below. The housing  300  according to the embodiment of the present disclosure is coupled to a rear surface of the caliper body part  100 , more specifically, a rear surface of the cylinder unit  130 . The housing  300  may be detachably coupled to the cylinder unit  130  by bolting or the like or integrally coupled to the cylinder unit  130  by welding or the like. The housing  300  has therein a vacant space in which the drive unit  400 , the transmission gear  500 , the parking gear  700 , and the restriction unit  800  may be installed. The housing  300  may be openable and closable so that the components installed in the housing  300  may be easily installed and managed. 
     The drive unit  400  is installed at one side of the housing  300  and generates the driving power by being supplied with power from the outside. The drive unit  400  may be electrically connected to a battery or the like of the vehicle and supplied with power. The examples of the drive unit  400  according to the embodiment of the present disclosure may include various types of electric motors that generate a rotational force by being supplied with power. 
     The transmission gear  500  is rotated by the driving power transmitted from the drive unit  400  and transmits the driving power, generated by the drive unit  400 , to the piston  600  to be described below. 
     The transmission gear  500  according to the embodiment of the present disclosure includes a first transmission gear  510 , a second transmission gear  520 , and a third transmission gear  530 . 
     The first transmission gear  510  is connected to an output shaft of the drive unit  400  and rotated together with the output shaft of the drive unit  400 . The first transmission gear  510  according to the embodiment of the present disclosure may be provided in the form of a hollow helical or spur gear having teeth formed on an outer peripheral surface thereof. The first transmission gear  510  is supported in a state in which the output shaft of the drive unit  400  is inserted into a central portion of the first transmission gear  510 . A central axis of the first transmission gear  510  is disposed coaxially with the output shaft of the drive unit  400 . When the drive unit  400  operates, the first transmission gear  510  rotates at the same angular velocity as the output shaft of the drive unit  400 . 
     The second transmission gear  520  engages with the first transmission gear  510  and rotates in response to the rotation of the first transmission gear  510 . The second transmission gear  520  according to the embodiment of the present disclosure may be provided in the form of a hollow helical or spur gear having teeth formed on an outer peripheral surface thereof. The second transmission gear  520  engages with the first transmission gear  510 . In this case, the outer peripheral surface of the second transmission gear  520  may engage directly with the outer peripheral surface of the first transmission gear  510  or engage with the first transmission gear  510  by means of a separate small-diameter gear. A central axis of the second transmission gear  520  is disposed in parallel with the central axis of the first transmission gear  510 . When the first transmission gear  510  rotates, the second transmission gear  520  transmits a rotational force while rotating in a direction opposite to the rotation direction of the first transmission gear  510 . A diameter of the second transmission gear  520  is larger than a diameter of the first transmission gear  510 . Therefore, when the first transmission gear  510  rotates, the second transmission gear  520  may rotate at a lower angular velocity than the first transmission gear  510 , thereby increasing a magnitude of the rotational force transmitted from the first transmission gear  510 . 
     The third transmission gear  530  engages with the second transmission gear  520 . The third transmission gear  530  transmits the rotational force to the piston  600  to be described below while rotating in response to the rotation of the second transmission gear  520 . The third transmission gear  530  according to the embodiment of the present disclosure may be provided in the form of a hollow helical or spur gear having teeth formed on an outer peripheral surface thereof. The third transmission gear  530  engages with the second transmission gear  520 . In this case, the outer peripheral surface of the third transmission gear  530  may engage directly with the outer peripheral surface of the second transmission gear  520  or engage with the second transmission gear  520  by means of a separate small-diameter gear. A central axis of the third transmission gear  530  is disposed in parallel with the central axis of the second transmission gear  520 . When the second transmission gear  520  rotates, the third transmission gear  530  transmits the rotational force while rotating in a direction opposite to the rotation direction of the second transmission gear  520  or rotating in a direction identical to the rotation direction of the first transmission gear  510 . A central shaft of the third transmission gear  530  is connected to the piston  600  to be described below and may transmit the rotational force to the piston  600  while rotating about the central shaft. A diameter of the third transmission gear  530  is larger than the diameter of the second transmission gear  520 . Therefore, when the second transmission gear  520  rotates, the third transmission gear  530  may rotate at a lower angular velocity than the second transmission gear  520 , thereby increasing the magnitude of the rotational force to be transmitted to the piston  600 . 
     The piston  600  is installed in the caliper body part  100  so as to be movable along an axis. The piston  600  moves forward or rearward in response to the rotation of the transmission gear  500 . The piston  600  applies or releases the braking force by pressing the pad parts  200  against the brake disc or releasing the pad parts  200  in the direction in which the piston  600  moves forward or rearward. 
     The piston  600  according to the embodiment of the present disclosure includes a ball screw  610 , a ball nut  620 , rolling elements  630 , and a piston member  640 . 
     The ball screw  610  is connected to the transmission gear  500  and rotated. The ball screw  610  according to the embodiment of the present disclosure has an approximately rod shape and is rotatably installed in the cylinder unit  130 . A longitudinal direction of the ball screw  610  is disposed in parallel with a longitudinal direction of the cylinder unit  130 . A rear end of the ball screw  610  is connected to the third transmission gear  530 , such that the ball screw  610  axially rotates about a central axis thereof when the third transmission gear  530  rotates. A groove is formed in an outer peripheral surface of the ball screw  610 , and one peripheral portion of each of the rolling elements  630  to be described below is seated in the groove. The groove extends in a spiral shape in the longitudinal direction of the ball screw  610  and defines a circulation route for the rolling elements  630 . 
     The ball nut  620  rectilinearly reciprocates in the longitudinal direction of the ball screw  610  in response to the rotation of the ball screw  610 . The ball nut  620  according to the embodiment of the present disclosure may have a hollow cylindrical shape that surrounds the outer peripheral surface of the ball screw  610 . An inner peripheral surface of the ball nut  620  faces an outer peripheral surface of the ball screw  610  and is spaced apart from the outer peripheral surface of the ball screw  610  at a predetermined interval. When the ball screw  610  rotates, the ball nut  620  rectilinearly reciprocates forward or rearward in the longitudinal direction of the ball screw  610  by means of the circulation of the rolling elements  630  to be described below. A groove may be formed in the inner peripheral surface of the ball nut  620 , and the other peripheral portion of each of the rolling elements  630  may be seated in the groove. The groove extends in a spiral shape in the longitudinal direction of the ball nut  620  and defines a circulation route for the rolling elements  630 . 
     The rolling element  630  is disposed between the ball screw  610  and the ball nut  620  and has two opposite sides in rollable contact with the ball screw  610  and the ball nut  620 . The rolling element  630  according to the embodiment of the present disclosure has an approximately spherical shape and is installed between the ball screw  610  and the ball nut  620 . The peripheral portions of the two opposite sides of the rolling element  630  are respectively in rollable contact with the groove formed in the outer peripheral surface of the ball screw  610  and the groove formed in the inner peripheral surface of the ball nut  620 . When the ball screw  610  rotates, the rolling elements  630  convert the rotational motion of the ball screw  610  into the rectilinear reciprocating motion of the ball nut  620  while circulating along the grooves. 
     The piston member  640  presses or releases the pad parts  200  in the movement direction while rectilinearly reciprocating together with the ball nut  620 . The piston member  640  according to the embodiment of the present disclosure is slidably installed in the cylinder unit  130 . A rear end of the piston member  640  is integrally coupled to a front end of the ball nut  620 , such that the piston member  640  rectilinearly reciprocates together with the ball nut  620  in the longitudinal direction of the cylinder unit  130 . When the ball nut  620  moves forward, a front end of the piston member  640  comes into contact with the pad part  200  and presses the pad part  200  against the brake disc. When the ball nut  620  moves rearward, the piston member  640  separates from the pad parts  200  and releases the pad part  200 . 
     The parking gear  700  engages with the transmission gear  500  and rotates in response to the rotation of the transmission gear  500 . The parking gear  700  according to the embodiment of the present disclosure may engage with the second transmission gear  520 . Therefore, the parking gear  700  may be prevented from interfering with an adjacent component such as an ECU installed at the periphery of a driving shaft of the drive unit  400 . In this case, a diameter of the parking gear  700  is smaller than the diameter of the second transmission gear  520 . More specifically, the parking gear  700  may have a size corresponding to the diameter of the first transmission gear  510  and rotate at the same angular velocity as the first transmission gear  510 . Therefore, the parking gear  700  may rotate and decrease the magnitude of the rotational force increased by the second transmission gear  520 , thereby reducing a magnitude of a load applied to the restriction unit  800  to be described below when the restriction unit  800  restricts a rotation of the parking gear  700 . 
       FIG.  5    is an enlarged view schematically illustrating configurations of the parking gear and the restriction unit according to the embodiment of the present disclosure, and  FIG.  6    is a perspective view schematically illustrating the configuration of the parking gear according to the embodiment of the present disclosure. 
     Referring to  FIGS.  5  and  6   , the parking gear  700  according to the embodiment of the present disclosure includes a body unit  710 , a toothed unit  720 , and an insertion structure  730 . 
     The body unit  710  defines a schematic external appearance of the parking gear  700  and provides a space in which the toothed unit  720  and the insertion structure  730 , which will be described below, may be formed. The body unit  710  according to the embodiment of the present disclosure may have an approximately cylindrical shape. An outer peripheral surface of the body unit  710  may face the outer peripheral surface of the second transmission gear  520  and is spaced apart from the outer peripheral surface of the second transmission gear  520  at a predetermined interval. A central axis of the body unit  710  is disposed in parallel with the central axis of the second transmission gear  520 . A shaft or the like extending from the housing  300  may be inserted into a front portion of the body unit  710 , such that the body unit  710  may be rotatably supported on the second transmission gear  520 . 
     The toothed unit  720  protrudes from the body unit  710  and engages with the second transmission gear  520 . The toothed unit  720  according to the embodiment of the present disclosure may protrude perpendicularly from the outer peripheral surface of the body unit  710  in a radial direction of the body unit  710  and have gear teeth extending in a circumferential direction of the body unit  710 . The toothed unit  720  engages with the second transmission gear  520  and rotates the body unit  710  in a direction opposite to the rotation direction of the second transmission gear  520  when the second transmission gear  520  rotates. The specific shape of the toothed unit  720  may be changed in design to various shapes such as helical gear teeth or spur gear teeth depending on the shape of the second transmission gear  520 . 
     The insertion structure  730  is concavely recessed into the body unit  710 , and the restriction unit  800  to be described below is inserted into the insertion structure  730 . The insertion structure  730  according to the embodiment of the present disclosure may be provided in the form of a groove concavely recessed from a rear portion of the body unit  710  in an axial direction of the body unit  710 . The insertion structure  730  may have a polygonal cross-sectional shape. Therefore, when the restriction unit  800  to be described below is inserted into the insertion structure  730 , it is possible to prevent the rotation of the insertion structure  730  relative to the restriction unit  800 .  FIG.  7    illustrates an example in which the insertion structure  730  has an octagonal cross-sectional shape, but the shape of the insertion structure  730  is not limited to the above-mentioned shape and may be changed in design to various shapes such as a quadrangular or hexagonal shape. The insertion structure  730  may have a width that decreases toward the inside of the body unit  710  so that the restriction unit  800  may be smoothly inserted into the insertion structure  730 . 
     The restriction unit  800  is installed in the housing  300  so as to be reciprocatingly movable toward the parking gear  700 . During the parking braking, the restriction unit  800  is inserted into the parking gear  700  and restricts the rotation of the parking gear  700 . Therefore, the restriction unit  800  may prevent the piston  600  from being arbitrarily separated from the pad part  200  and thus inhibit a loss of braking force even though an operation of the drive unit  400  is released during the parking braking. 
       FIG.  7    is a perspective view schematically illustrating the configuration of the restriction unit according to the embodiment of the present disclosure, and  FIG.  8    is a cross-sectional view schematically illustrating the configuration of the restriction unit according to the embodiment of the present disclosure. 
     Referring to  FIGS.  7  and  8   , the restriction unit  800  according to the embodiment of the present disclosure includes a parking drive unit  810 , a rod  820 , a restoration unit  830 , a stopper unit  840 , a rotation prevention unit  850 , and an insertion guide unit  860 . 
     The parking drive unit  810  generates an electromagnetic force by power applied from the outside. The parking drive unit  810  according to the embodiment of the present disclosure may have a hollow cylindrical shape. A longitudinal direction of the parking drive unit  810  is disposed in parallel with an axial direction of the parking gear  700 , and a central axis of the parking drive unit  810  is disposed coaxially with a central axis of the parking gear  700 . The parking drive unit  810  may be installed in the housing  300  or penetrate the housing  300 . A front portion of the parking drive unit  810  faces the insertion structure  730  and is spaced apart from the insertion structure  730  at a predetermined interval. A spiral coil made of an electrically conductive material such as copper is wound in a longitudinal direction of the parking drive unit  810  and disposed between an outer peripheral surface and an inner peripheral surface of the parking drive unit  810 . When the power is applied to the coil, the parking drive unit  810  generates the electromagnetic force therein in a direction parallel to the longitudinal direction. 
     The rod  820  is slidably installed in the parking drive unit  810 . The rod  820  is moves to a first direction by the electromagnetic force generated by the parking drive unit  810 . Hereinafter, the first direction will be described in which the rod  820  moves in a direction away from the parking gear  700  in response to the electromagnetic force generated by the parking drive unit  810 . However, the rod  820  is not limited thereto and may move in a direction toward the parking gear  700  in response to the electromagnetic force generated by the parking drive unit  810 . 
     The rod  820  according to the embodiment of the present disclosure may have an approximately rod shape. A longitudinal direction of the rod  820  is disposed in parallel with the longitudinal direction of the parking drive unit  810 . A rear end of the rod  820  is inserted into the parking drive unit  810  and slidably supported by adjoining the inner peripheral surface of the parking drive unit  810 . A front end of the rod  820  penetrates the front portion of the parking drive unit  810  and protrudes toward the parking gear  700 . The rod  820  may be made of a ferromagnetic material such as iron so as to be movable in response to the electromagnetic force generated by the parking drive unit  810 . When the parking drive unit  810  generates the electromagnetic force, the front end of the rod  820  moves in the direction away from the parking gear  700 . 
     The restoration unit  830  is disposed between the rod  820  and the parking drive unit  810  and moves the rod  820  to a second direction when the electromagnetic force from the parking drive unit  810  is eliminated. The restoration unit  830  according to the embodiment of the present disclosure may be provided in the form of a coil spring elastically deformable in the longitudinal direction thereof. Two opposite sides of the restoration unit  830  are respectively fixed and supported by the rear end of the rod  820  and a bottom surface of the parking drive unit  810 . When the rod  820  moves to one side, the restoration unit  830  accumulates an elastic restoring force while being compressed in the longitudinal direction. When the electromagnetic force from the parking drive unit  810  is eliminated, the restoration unit  830  applies the accumulated elastic restoring force to move the rod  820  to the second direction, i.e., in the direction toward the parking gear  700 . 
     The stopper unit  840  is inserted into the parking gear  700  when the rod  820  moves to the second direction  700  by a predetermined distance or more. The stopper unit  840  according to the embodiment of the present disclosure is fixed to the front end of the rod  820  and faces the parking gear  700 . A central axis of the stopper unit  840  is disposed coaxially with the central axis of the parking gear  700 . When the rod  820  moves, the stopper unit  840  moves forward or rearward together with the rod  820  in the direction parallel to the axial direction of the parking gear  700 . The stopper  840  may have a polygonal cross-sectional shape. Therefore, when the stopper  840  is inserted into the insertion structure  730 , the stopper  840  may be coupled to and caught by the inner peripheral surface of the insertion structure  730  and stably restrict the rotation of the parking gear  700 . 
     The rotation prevention unit  850  prevents the rotation of the rod  820  relative to the parking drive unit  810 . The rotation prevention unit  850  according to the embodiment of the present disclosure has a polygonal cross-section and surrounds a front peripheral surface of the rod  820 . The rotation prevention unit  850  may be integrated with an outer peripheral surface of the rod  820  or manufactured separately from the rod  820  and then coupled to the outer peripheral surface of the rod  820 . The rotation prevention unit  850  is supported by adjoining the inner peripheral surface of the front portion of the parking drive unit  810  into which the front portion of the rod  820  is penetratively inserted. Therefore, when the stopper  840  is inserted into the insertion structure  730 , the rotation prevention unit  850  may prevent the relative rotation of the rod  820  in the parking drive unit  810  due to the rotational force transmitted from the parking gear  700 . 
     The insertion guide unit  860  guides the insertion of the stopper  840  into the parking gear  700 . 
       FIG.  9    is an enlarged view schematically illustrating a configuration of the insertion guide unit according to the embodiment of the present disclosure. 
     Referring to  FIG.  9   , the insertion guide unit  860  according to the embodiment of the present disclosure is disposed at an edge of an end of the stopper  840  and inclined at a predetermined angle. That is, the insertion guide unit  860  may be provided in the form of an inclined surface inclinedly extending from an edge of a front end of the stopper  840  toward a rear side of the stopper  840 . The insertion guide unit  860  defines a closed curve by extending in a circumferential direction of the stopper  840 . The insertion guide unit  860  has a width that increases toward the rear side of the stopper  840 . 
     Hereinafter, an operating process of the brake apparatus  1  for a vehicle according to the embodiment of the present disclosure will be described in detail. 
       FIGS.  10  to  12    are operational views schematically illustrating an operating process of the brake apparatus for a vehicle according to the embodiment of the present disclosure. 
     Referring to  FIGS.  1  to  12   , the drive unit  400  generates the driving power and rotates the transmission gear  500  during parking braking of the vehicle. 
     The driving power generated by the drive unit  400  is transmitted to the ball screw  610  of the piston  600  sequentially through the first transmission gear  510 , the second transmission gear  520 , and the third transmission gear  530 . 
     As the ball screw  610  rotates about the central axis thereof, the ball nut  620  moves forward by means of the circulation of the rolling element  630 . 
     The piston member  640  moves forward together with the ball nut  620 , comes into contact with the pad part  200 , and presses the pad part  200  against the brake disc, thereby generating the parking braking force. 
     In this process, the rod  820  is moved in the first direction, the direction away from the parking gear  700  by the electromagnetic force generated by the parking drive unit  810 , and the stopper  840  is kept separated from the parking gear  700 . 
     Thereafter, when a sufficient parking braking force is generated, the parking drive unit  810  eliminates the electromagnetic force. 
     When the electromagnetic force generated by the parking drive unit  810  is eliminated, the restoration unit  830  applies the accumulated elastic restoring force and presses the rod  820  in the second direction, the direction toward the parking gear  700 . 
     As the rod  820  moves toward the parking gear  700  by a predetermined distance or more, the stopper  840  is inserted into the insertion structure  730 . In this case, the smooth insertion of the stopper  840  into the insertion structure  730  may be guided by the insertion guide unit  860 . 
     Since the stopper  840  and the insertion structure  730  each have a polygonal cross-sectional shape, the outer peripheral surface of the stopper  840  and the inner peripheral surface of the insertion structure  730  are caught by and coupled to each other. 
     Thereafter, the drive unit  400  stops generating the driving power, and the rotational force, which is applied in a direction opposite to the direction of the rotational force transmitted during the parking braking, is transmitted to the parking gear  700  by the reaction force generated between the piston member  640  and the pad parts  200 . 
     The catching/coupling force between the stopper  840  and the insertion structure  730  is offset against the rotational force and restricts the rotation of the parking gear  700 . 
     Since the rotation of the parking gear  700  is restricted, the rotation of the transmission gear  500  engaging with the parking gear  700  is also restricted, which makes it possible to maintain the parking braked state. 
     While the present disclosure has been described with reference to the exemplary embodiment depicted in the drawings, the exemplary embodiment is described just for illustration, and those skilled in the art to the present technology pertains will understand that various modifications of the exemplary embodiment and any other exemplary embodiment equivalent thereto are available. 
     Thus, the true technical scope of the present disclosure should be defined by the following claims.