Patent Publication Number: US-2022235839-A1

Title: Electromechanical brake

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0010117, filed on Jan. 25, 2021 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The disclosure relates to an electromechanical brake, and more particularly, to an electromechanical brake for realizing braking of a vehicle using rotational driving force of a motor. 
     BACKGROUND 
     Vehicles are essentially equipped with a brake system for performing braking, and various types of brake systems have been proposed for a safety of drivers and passengers. 
     In a conventional brake system, a method of supplying a hydraulic pressure required for braking to wheel cylinders using a mechanically connected booster when a driver depresses a brake pedal has been mainly used. However, as a next-generation brake system, an electromechanical brake system that receives a driver&#39;s intention to brake as an electric signal and operates an electronic device such as a motor based on the electronic signal to provide braking force for a vehicle is being been developed. 
     Such an electromechanical brake system converts rotational force of a motor into linear motion through the motor and a speed reducer to provide a clamping pressure of a brake disc, thereby performing a service brake and a parking brake of a vehicle. 
     On the other hand, a friction pad of a pad plate that directly contacts and presses a brake disc of a vehicle is gradually abraded according to the repeated braking operations of the vehicle. To maintain braking performance of a vehicle despite wear of a friction pad, compensation for the wear of the friction pad wear is required. However, the compensation for the wear of the friction pad causes that the size or axial length of a brake system is increased, so that applicability of the vehicle is deteriorated. 
     SUMMARY 
     An aspect of the disclosure is to provide an electromechanical brake capable of maintaining and improving braking performance of a vehicle despite wear of a friction pad attached to a pad plate. 
     Another aspect of the disclosure is to provide an electromechanical brake capable of improving applicability of a vehicle by reducing size and weight, and promoting space utilization of the vehicle. 
     Another aspect of the disclosure is to provide an electromechanical brake capable of easily compensating for wear of a friction pad with a simple structure. 
     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 an aspect of the disclosure, an electromechanical brake includes a power converter including a nut provided in a cylinder portion of a caliper housing slidably coupled to a carrier and configured to rotate by receiving a driving force from an actuator, and a spindle connected to the nut and configured to move forward or backward by rotation of the nut in a first direction or a second direction; a pressing member coupled to a front side of the spindle and configured to press a pad plate; and a position adjuster screwed into the cylinder portion so that the power converter is mounted and configured to adjust a relative position of the caliper housing in response to an operation of the power converter. 
     The position adjuster may include a transfer portion provided between the power converter and the cylinder portion; a first screw thread formed on an outer circumferential surface of the transfer portion; a second screw thread formed on an inner circumferential surface of the cylinder portion and meshing with the first screw thread; and an adjuster configured to rotate the transfer portion in the first direction or the second direction by rotation of the nut to move backward or forward a relative position of the caliper housing with respect to the transfer portion. 
     The transfer portion may be provided in a hollow cylindrical shape to surround an outer side of the nut to be spaced apart from the nut by a predetermined interval. 
     The adjuster may include a first protrusion protruding from the nut; and a second protrusion formed to protrude from the transfer portion and configured to move the relative position of the caliper housing backward when the nut rotates in the first direction by being caught by the first protrusion to induce the first direction rotation of the nut and the transfer portion. 
     A first angle between the first protrusion and the second protrusion in a braking release state of a vehicle may be greater than a second angle at which the first protrusion rotates from the braking release state of the vehicle to a braking state of a vehicle. 
     The first protrusion may be formed to protrude from an outer circumferential surface of the nut to be spaced apart from an inner circumferential surface of the transfer portion, and the second protrusion is formed to protrude from the inner circumferential surface of the transfer portion to be spaced apart from the outer circumferential surface of the nut. 
     The electromechanical brake may further include an electronic control unit (ECU) configured to control an operation of the actuator; and a detector configured to measure fastening force between the pad plate and the disk rotating together with a wheel of a vehicle. 
     The pressing member may be press-fitted or bolted to the front side of the spindle in order to move together with the spindle. 
     The pressing member may be provided with an anti-rotation means so that rotation thereof is restricted, the anti-rotation means may include an anti-rotation groove or protrusion formed in a front of the pressing member facing the pad plate; and a rotation prevention protrusion or groove formed on a rear side of the pad plate facing the pressing member, the rotation prevention protrusion or groove matching the anti-rotation groove or protrusion. 
     The electromechanical brake may further include a boot provided to prevent an inflow of foreign substances into the cylinder portion of the caliper housing. 
    
    
     
       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 perspective view illustrating an electromechanical brake according to an embodiment of the disclosure. 
         FIG. 2  is a side cross-sectional view illustrating an electromechanical brake according to an embodiment of the disclosure. 
         FIG. 3  is an enlarged side cross-sectional view illustrating a main part of an electromechanical brake according to an embodiment of the disclosure. 
         FIG. 4  is an exploded perspective view illustrating a main part of an electromechanical brake according to an embodiment of the disclosure. 
         FIG. 5  is a cross-sectional view taken along A-A′ direction of  FIG. 3  and illustrating positions of first and second protrusions in a pre-braking state of the vehicle or in a braking release state of the vehicle. 
         FIG. 6  is a side cross-sectional view illustrating an operation of an electromechanical brake according to an embodiment of the disclosure in a braking state of a vehicle. 
         FIG. 7  is a cross-sectional view taken along B-B′ direction of  FIG. 6  and illustrating positions of the first and second protrusions in a braking state of the vehicle. 
         FIG. 8  is a side cross-sectional view illustrating an operation of an electromechanical brake according to an embodiment of the disclosure in order to compensate for wear of a friction pad. 
         FIG. 9  is a cross-sectional view taken along C-C′ direction of  FIG. 8  and illustrating positions of the first and second protrusions. 
         FIG. 10  is a side cross-sectional view illustrating an operation of an electromechanical brake according to an embodiment of the disclosure in a braking release state of a vehicle after wear compensation of a friction pad. 
         FIG. 11  is a cross-sectional view taken along D-D′ direction of  FIG. 10  and illustrating positions of the first and second protrusions in a braking release state of a vehicle after compensating for wear of a friction pad. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the embodiments of the disclosure will be described in detail with reference to accompanying drawings. It should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the disclosure on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the disclosure, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the disclosure. 
       FIG. 1  is a perspective view illustrating an electromechanical brake according to an embodiment of the disclosure, and  FIG. 2  is a side cross-sectional view illustrating an electromechanical brake according to an embodiment of the disclosure. 
     Referring to  FIGS. 1 and 2 , an electromechanical brake  100  according to an embodiment of the disclosure may include a carrier  10  in which a pair of pad plates  11  and  12  are installed to press a disk (not shown) rotating together with wheels of the vehicle, a caliper housing  20  slidably installed on the carrier  10  to operate the pair of pad plates  11  and  12 , an actuator  130  that generates and provides driving force for moving the pair of pad plates  11  and  12 , a power converter  110  that receives a rotational driving force provided from the actuator  130  and converts the rotational driving force into a linear motion to implement forward and backward movement of the pair of pad plates  11  and  12 , a pressing member  120  coupled to a spindle  115  of the power converter  110  to press the pad plate  11 , a position adjuster  140  that compensates for wear of friction pads  13  attached to the pair of pad plates  11  and  12  by adjusting a position of the caliper housing  20  with respect to the power converter  110 , a detector  150  that measures adhesive force between the disk and the pair of pad plates  11  and  12  or fastening force of the pair of pad plates  11  and  12 , and an electronic control unit (ECU) (not shown) that controls an operation of the actuator based on information provided from the detector  150 . 
     The pair of pad plates  11  and  12  is provided with the friction pad  13  attached to an inner surface thereof, respectively. The pair of pad plates  11  and  12  includes the inner pad plate  11  arranged to contact the pressing member  120  and the outer pad plate  12  arranged to contact a finger portion  22  of the caliper housing  20 , which will be described later, and is slidably installed on the carrier  10 . In other words, the pair of pad plates  11  and  12  are installed on the carrier  10  fixed to a vehicle body and move forward and backward toward both sides of the disk to perform a braking operation. 
     The caliper housing  20  includes the finger portion  22  bent downwardly on a front side (left side with reference to  FIG. 2 ) to operate the outer pad plate  12 , and a cylinder portion  25  including the power converter  110  and the position adjuster  140 . The caliper housing  20  is slidably fastened to the carrier  10  through the guide rod  21 . The cylinder portion  25  and the finger portion  22  are integrally formed. The caliper housing  20  slides from the carrier  10  and moves toward the disk side by reaction force caused by pressing of the inner pad plate  11  when the vehicle is braked. In addition, the outer pad plate  12  by the finger portion  22  according to the movement of the caliper housing  20  may approach the disk side, thereby pressing the disk. 
     On the other hand, the cylinder portion  25  is provided in a hollow shape through which front and rear thereof are penetrated. On an inner circumferential surface of the cylinder portion  25  may be formed a second screw thread  142  that meshes with a first screw thread  141  formed in a transfer portion  143  of the position adjuster  140  to be described later. The structure in which the transfer portion  143  is screwed with the cylinder portion  25  will be described again below. 
       FIGS. 3 and 4  are an enlarged lateral cross-sectional view and an exploded perspective view illustrating a main part of the electromechanical brake  100  according to an embodiment of the disclosure. Referring to  FIGS. 1 to 4 , the power converter  110  is provided inside the cylinder portion and may be mounted on the transfer portion  143  of the position adjuster  140  to be described later. Furthermore, the power converter  110  may receive power through the actuator  130  to press the inner pad plate  11  toward the disk. The power converter  110  may operate the position adjuster  140  to adjust a relative position of the caliper housing  20  with respect to the transfer portion  143 , and the operation thereof will be described again below. 
     The power converter  110  may include a nut  111  rotating by receiving driving force from the actuator  130 , a spindle  115  that is arranged inside the position adjuster  140  screw-coupled to the cylinder portion  25  to be described later and is screwed to the nut  111  to move forward by rotation of the nut  111  in a first direction or move backward by the rotation of the nut  111  in a second direction, and a plurality of balls (not shown) interposed between the nut  111  and the spindle  115 . The power converter  110  may be provided as a ball-screw type conversion device for converting a rotational motion of the nut  111  into a linear motion. 
     The rotation in the first direction of the nut  111  to be described below refers to a rotational direction in which the spindle  115  is advanced (left side with reference to  FIG. 2 ) by the rotation of the nut  111 , and the rotation in the second direction of the nut  111  refers to a rotational direction in which the spindle  115  is retreated (right side with reference to  FIG. 2 ) by rotation of the nut  111  as a rotation in the opposite direction to the first direction. 
     The nut  111  may be formed in a cylindrical shape in which one side thereof is opened so that the spindle  115  is inserted therein and an accommodation space is formed therein. Furthermore, an internal thread  112  may be formed on an inner circumferential surface of the nut  111  for coupling with the spindle  115 . The spindle  115  is inserted into one side (a front side, which is the left side with reference to the drawings) of the nut  111 , and the other side (a rear side, which is the right side with reference to the drawings) of the nut  111  is connected to the actuator  130  to receive the driving force. For example, the other side of the nut  111  may be coupled to an output shaft  135  output from the actuator  130  in a spline manner. 
     The spindle  115  has a predetermined length, and an external thread  116  that meshes with the internal thread  112  of the nut  111  via balls (not shown) may be formed on the outer circumferential surface thereof. Accordingly, the spindle  115  may move forward or backward according to the rotation of the nut  111  in the first direction or the second direction. At this time, the spindle  115  is provided in a state in which rotation is restricted in order to perform a linear motion according to the rotation in the first direction or in the second direction of the nut  111 . The rotation of the spindle  115  may be prevented through the pressing member  120 . 
     The pressing member  120  is coupled to the front side of the spindle  115 . As shown in drawings, the pressing member  120  may have a press-fitting protrusion  127  protruding to be press-fitted to a press-fitting groove  117  formed in the front side of the spindle  115 . In the front of the pressing member  120 , a rotation prevention groove  124 , which matches an anti-rotation protrusion  14 , is formed so that the anti-rotation protrusion  14  protruding from the inner pad plate  11  is inserted and caught. Accordingly, as the rotation of the pressing member  120  is restricted by the inner pad plate  11 , the rotation of the spindle  115  is restricted. 
     On the other hand, as described above, the pressing member  120  is shown and described as being press-fitted to the spindle  115 , but is not limited thereto. The pressing member  120  and the spindle  115  are coupled in a spline manner, or the pressing member  120  may be coupled to the front side of the spindle  115  in a fastening manner such as bolting. 
     Furthermore, as an example of anti-rotation structure, the structure that the rotation prevention groove  124  is formed in the front of the pressing member  120  and the anti-rotation protrusion  14  is formed in the inner pad plate  11  has been shown and described, but is not limited thereto. Alternatively, the rotation prevention groove  124  may be formed in the inner pad plate  11 , and the anti-rotation protrusion  14  may be formed in the front of the pressing member  120 . 
     The actuator  130  may include a motor  132  and a reduction device  134  having a plurality of reduction gears, and may receive power from a power supply device installed in the vehicle to generate and provide driving force. The actuator  130  may be connected to the other end of the nut  111  to transmit the generated driving force to the nut  111  through the output shaft  135  of the reduction device  134  as a rotational movement. The actuator  130  may be installed outside the caliper housing  20  or in the vehicle, and the reduction device  134  may reduce power of the motor  132  to be provided the nut  111  by applying various structures such as a planetary gear assembly or a worm structure. 
     The position adjuster  140  compensates for wear of the friction pad  13  by adjusting the relative position of the caliper housing  20  with respect to the transfer portion  143 , and is provided in the cylinder portion so that the power converter  110  is mounted. 
     The position adjuster  140  may include the transfer portion  143  provided between the power converter  110  and the cylinder portion  25 , the first screw thread  141  formed on the outer circumferential surface of the transfer portion  143 , the second screw thread  142  formed on the inner surface of the cylinder portion  25  and meshing with the first screw thread  141 , and an adjuster  145  for moving the transfer portion  143  forward or backward by rotating the transfer portion  143  in the first direction or the second direction by the rotation of the nut  111 . At this time, the forward or backward movement of the transfer portion  143  represents the movement of the caliper housing  20  as the cylinder portion  25  screwed with the transfer portion moves linearly when the transfer portion  143  is rotated by the nut  111 . In other words, because the caliper housing  20  is provided slidably on the carrier  10  in a state in which the rotation thereof is restricted, the cylinder portion  25  integrally formed with the caliper housing  20  may linearly move, leading to the relative position of the caliper housing  20  being adjusted. 
     A first direction rotation of the transfer portion  143  will be described below is the same rotational direction as the first direction rotation of the nut  111  described above, and refers to a rotational direction in which the transfer portion  143  advances from the cylinder portion, but substantially the caliper housing  20  is retreated. 
     Furthermore, a second direction rotation of the transfer portion  143  is the same rotational direction as the second direction rotation of the nut  111  described above as a rotation opposite to the first direction, and refers to a rotational direction in which the transfer portion  143  moves backward from the cylinder portion, but substantially the caliper housing  20  is moved forward. 
     The transfer portion  143  is provided in a hollow cylindrical shape to surround an outer side of the nut  111  by a predetermined interval, and the first screw thread  141  is formed on the outer circumferential surface thereof. The transfer portion  143  may rotate together with the nut  111  when the nut  111  is rotated by the adjuster  145  to be described later. In other words, the first screw thread  141  of the transfer portion  143  is screwed with the second screw thread  142  of the cylinder portion  25  and the caliper housing  20  forming the cylinder portion  25  is coupled to the carrier  10  fixed to the vehicle body, so that rotation thereof is restricted. Accordingly, the caliper housing  20  moves linearly from the transfer portion  143  when the transfer portion  143  rotates. 
     The adjuster  145  may generate rotation of the transfer portion  143  through the nut  111  to advance or retreat the relative position of the caliper housing  20  with respect to the transfer portion  143 . The adjuster  145  may include a first protrusion  146  protruding from the nut  111 , and a second protrusion  147  protruding from the transfer portion  143 . During the first direction rotation of the nut  111 , the second protrusion  147  is caught by the first protrusion  146  to induce the first direction rotation of the nut  111  and the transfer portion  143 , so that the relative position of the caliper housing  20  is retreats. 
     More specifically, referring to  FIGS. 2 to 5 , the first protrusion  146  may be formed on an outer circumferential surface of the nut  111 . Furthermore, the first protrusion  146  may be formed to protrude from the outer circumferential surface of the nut  111  and spaced apart from an inner circumferential surface of the transfer portion  143 . 
     The second protrusion  147  may be formed on the inner circumferential surface of the transfer portion  143 . Furthermore, the second protrusion  147  may be formed to protrude from the inner circumferential surface of the transfer portion  143  and spaced apart from the outer circumferential surface of the nut  111 . 
     The first and second protrusions  146  and  147  are formed at positions corresponding to each other, so that the first and second protrusions  146  and  147  may be provided to be caught each other when the nut  111  rotates in the first direction or the second direction. 
     The first and second protrusions  146  and  147  may be formed to protrude at an angle spaced apart from each other in a pre-braking state of the vehicle or in a braking release state of the vehicle. 
     Specifically, an angle between the first and second protrusions  146  and  147  (hereinafter referred to as first angle θ 1 ) in the pre-braking state of the vehicle or in the braking release state of the vehicle is provided to be greater than a rotational angle of the first protrusion  146  (refer to  FIG. 7 , hereinafter referred to as second angle θ 2 ) from in the braking release state to in a braking state of the vehicle. If the second angle θ 2  is greater than the first angle θ 1 , the second protrusion  147  is caught by the first protrusion  146  to generate the first direction rotation of the nut  111  and the transfer portion  143  during a general vehicle braking. As a result, the caliper housing  20  moves backward from the transfer portion  143  and the finger portion  22  moves toward the outer pad plate  12 . At this time, the power converter  110  also operates together, so fastening force between the pressing member  120  and the inner pad plate  11  is rapidly increased, so that braking force of the vehicle is greater than a braking amount required by the driver. Furthermore, a drag phenomenon may occur, which may decrease driving stability of the vehicle and fuel efficiency of the vehicle. Accordingly, by providing the first angle θ 1  larger than the second angle θ 2 , the first and second protrusions  146  and  147  may be prevented from contacting each other during general vehicle braking, and thus the relative position of the caliper housing  20  with respect to the transfer portion  143  may be constantly maintained, and the driver&#39;s braking operability and driving stability may be promoted. 
     Referring to  FIGS. 2 and 3  again, the detector  150  is provided to measure adhesion force or fastening force between the disk and the friction pad  13 . The detector  150  may be provided as a force sensor that detects a load of the spindle  115  or the actuator  130  to measure the fastening force between the disk and the friction pad  13 , but it is not limited thereto. The detector  150  may transmit the measured fastening force information of the friction pad  13  to the ECU, and the ECU may determine a wear or a drag of the friction pad  13  based on the measured fastening force information by the detector  150 . Herein, the detector  150  is illustrated as being provided inside the front side of the pressing member  120  but it is not limited thereto. For example, the detector may be provided in the power converter  110  or the actuator  130  that receives reaction force when the pad plates  11  and  12  are pressed. 
     On the other hand, an unexplained reference numeral  30  refers to a boot. The boot  30  prevents foreign substances from being introduced into the cylinder portion  25  of the caliper housing  20 . As shown in the drawings, the boot  30  may have one end thereof installed on the rear side of the cylinder portion  25  and the other end thereof installed on the actuator  130 . The boot  30  has a corrugated shape to be stretchable and may be made of a rubber material to have elasticity. Accordingly, when the relative position of the caliper housing  20  is adjusted, the boot  30  expands or contracts and the function of preventing the inflow of foreign substances may be smoothly performed. 
     Although the boot  30  is shown to be installed to block only foreign substances between the cylinder portion  25  and the actuator  130 , but it is not limited thereto, and a boot may be installed additionally so that one end thereof is installed on the pressing member  120  and the other end thereof is installed on the front side of the cylinder portion  25 . 
     Hereinafter, operating states during the braking and the braking release using the electromechanical brake  100  as described above and a mode for compensating for wear of the friction pad  13  will be described. 
       FIG. 6  is a side cross-sectional view illustrating the operation of the electromechanical brake according to an embodiment of the disclosure in the braking state of the vehicle, and  FIG. 7  is a cross-sectional view taken along B-B′ direction of  FIG. 2  and illustrating the positions of the first and second protrusions in the braking state of the vehicle. 
       FIGS. 2, 3, and 5 to 7 , when the driver applies a pedal effort to a brake pedal (not shown) to brake the vehicle, a pedal displacement sensor (not shown) converts the driver&#39;s intention to brake into an electrical signal and transmits the signal to the ECU. The ECU controls the operation of the actuator  130  so that the disc and the pair of pad plates  11  and  12  are in close contact to implement the braking of the vehicle. In other words, the electromechanical brake according to the embodiment of the disclosure may operate to in the braking state shown in  FIGS. 6 and 7  from the braking release state (or the pre-braking state) shown in  FIGS. 2, 3 and 5 . 
     Specifically, during the braking of the vehicle, the nut  111  rotates in the first direction by the operation of the actuator  130  and while the spindle  115  moves forward in response to the rotation of the nut  111  in the first direction, the pressing member  120  also advances toward the inner pad plate  11 . As the friction pad  13  mounted on the inner pad plate  11  approaches and closely adheres to the disk, fastening force is generated. In addition, by reaction force generated by pressing of the inner pad plate  11 , as the caliper housing  20  is slid from the carrier  10  to move toward the disk side, the outer pad plate  12  approaches the disk by the finger portion  22  and presses the disk, thereby occurring the braking of the vehicle. 
     At this time, the first protrusion  146  provided on the nut  111  rotates by the second angle θ from the braking release state of the vehicle to the braking state of the vehicle according to the first direction rotation of the nut  111 . However, because the first angle θ 1  between the first and second protrusions  146  and  147  of the transfer portion  143  in the braking release state of the vehicle is greater than the second angle θ, the first and second protrusions  146  and  147  do not contact each other in a general braking situation. As a result, the relative position of the caliper housing  20  with respect to the transfer portion  143  may be constantly maintained. 
     Furthermore, when the caliper housing  20  slides by the reaction force according to the braking operation, the transfer portion  143  screwed with the cylinder portion  25  and the actuator  130  may move together. At this time, because the power converter  110  is provided in a state spaced apart from the transfer portion  143 , the power converter  110  is not affected by the movement of the transfer portion  143 , thereby maintaining a state connected to the actuator  130 . 
     During the braking release of the vehicle, the vehicle may operate from the braking state shown in  FIGS. 6 and 7  to the braking release state shown in  FIGS. 2, 3  and  5 . Specifically, the nut  111  rotates in the second direction by the operation of the actuator  130  and as the spindle  115  is retreated by the second direction rotation of the nut  111 , the pressing member  120  is also spaced apart and retreated from the inner pad plate  11  together. Furthermore, as the caliper housing  20  is also returned to its original position, the friction pads  13  mounted on the pair of pad plates  11  and  12  are spaced apart from the disc, thereby the braking of the vehicle may be released. The first protrusion  146  provided on the nut  111  returns to its original position according to the second direction rotation of the nut  111 . 
     Hereinafter, to maintain braking performance of the vehicle despite wear of the friction pad  13 , a mode in which the electromechanical brake  100  according to the embodiment of the disclosure compensates for the wear of the friction pad  13  will be described. 
       FIG. 8  is a side cross-sectional view illustrating the operation of an electromechanical brake according to an embodiment of the disclosure in order to compensate for wear of the friction pad, and  FIG. 9  is a cross-sectional view taken along C-C′ direction of  FIG. 8  and illustrating the locations of the first and second protrusions. 
     Referring to  FIGS. 8 and 9 , in response to that the adhesion force or fastening force between the disk and the pad plates  11  and  12  measured by the detector  150  in a general braking operation state is smaller than a predetermined value in a normal range, the ECU (not shown) determines that wear is present in the friction pad  13  to enter a mode for compensating for the wear. 
     For example, in response to determining that the friction pad  13  is worn, the ECU rotates the nut  111  in the first direction by controlling the operation of the actuator  130  in order to enter a wear compensation mode. At this time, the ECU generates an additional first direction rotation (more than the first angle θ 1  in  FIG. 5 ) greater than the first direction rotation of nut  111  in the general braking state (refer to the second angle θ 2  in  FIG. 7 ). As a result, the first protrusion  146  provided on the nut  111  rotates in contact with the second protrusion  147  provided on the transfer portion  143 . Because the second protrusion  147  is caught by the first protrusion  146  to rotate together in the first direction, the nut  111  and the transfer portion  143  also rotate in the first direction. The relative position of the cylinder portion  25  with respect to the transfer portion  143  may be retreated by the first direction rotation of the nut  111  and the transfer portion  143 . In other words, as the relative position of the caliper housing  20  with respect to the transfer portion  143  moves backward, the outer pad plate  12  moves together toward the disk side, thereby compensating for the wear of the friction pad  13 . 
     After the completion of the mode for compensating for the wear of the friction pad  13 , the electromechanical brake  100  according to the embodiment of the disclosure returns to the braking release state of the vehicle or the pre-braking state of the vehicle. 
       FIG. 10  is a cross-sectional side view illustrating the operation of the electromechanical brake according to an embodiment of the disclosure in the braking release state of the vehicle after compensating for wear of the friction pads, and  FIG. 11  is a cross-sectional view taken along D-D′ direction of  FIG. 10  and illustrating the locations of the first and second protrusions in the braking release state of the vehicle after compensating for the wear of the friction pad. 
     Referring to  FIGS. 10 and 11 , after compensating for the wear of the friction pad  13 , the ECU generates the second direction rotation of the nut  111  by controlling the operation of the actuator  130 . Specifically, the actuator  130  rotates the nut  111  in the second direction to return the braking release state of the vehicle. In other words, the ECU may rotate the nut  111  in the second direction so that the first protrusion  146  of the nut  111  may maintain the first angle θ 1  with the second protrusion  147 . 
     Accordingly, the spindle  115 , which is returned to its original position after performing the wear compensation mode of the friction pad  13 , may perform the braking when the braking of the vehicle is operated again according to the first protrusion  146  of the nut  111  rotates by the second angle θ 2 . At this time, the braking operation is performed while compensating for the wear of the friction pad  13 , so that the braking of the vehicle may stably performed. 
     On the other hand, after the wear compensation, the nut  111  may be returned to the pre-braking state of the vehicle. In other words, the additional first direction rotation of the nut  111  occurs in the wear compensation mode, but the ECU may return the spindle  115  to its original position by rotating the nut  111  in the second direction by an amount corresponding to that of the additional first direction rotation generated in the wear compensation mode. 
     As is apparent from the above, the electromechanical brake according to the embodiments of the disclosure may maintain and improve braking performance of the vehicle despite the wear of the friction pad attached to the pad plate. 
     Furthermore, the electromechanical brake according to the embodiments of the disclosure may improve applicability of the vehicle by reducing size and weight, and promote space utilization of the vehicle. 
     Furthermore, the electromechanical brake according to the embodiments of the disclosure may easily compensate for wear of the friction pad with a simple structure. 
     As described above, the exemplary embodiments of the present disclosure have thus far been described with reference to accompanying drawings. It will be obvious to those of ordinary skill in the art that the present disclosure may be practiced in other forms than the exemplary embodiments as described above without changing the technical idea or essential features of the present disclosure. The above exemplary embodiments are only by way of example, and should not be interpreted in a limited sense.