Patent Publication Number: US-2023135838-A1

Title: Brake assembly with active piston retraction

Description:
BACKGROUND 
     Various embodiments of the present disclosure generally relate to brake assemblies for a vehicle and more particularly to a brake assembly having an improved structure for retracting a brake piston during a release operation of an electric parking brake. 
     Generally, a brake assembly may include a service brake assembly and a parking brake assembly. The service brake assembly may have a rotor, a brake caliper, and brake pads on opposing sides of the rotor. The brake caliper is slidably supported on pins secured to an anchor bracket fixed to a non-rotatable component of a vehicle, and includes one or more piston bores, each of which houses a piston that is movable along a piston axis during a brake apply and release of the brake apply. The brake pads are connected to one or more hydraulically or pneumatically actuated pistons for movement between a non-braking position and a braking position where the brake pads are moved into frictional engagement with the opposed braking surfaces of the rotor. For example, when an operation of the vehicle depresses a brake pedal, brake fluid can move the piston into contact with one brake pad and then move one brake pad into contact with one side of the rotor, while another opposing brake pad is moved into contact with an opposing side of the rotor. 
     When a vehicle is stopped or parked, the parking brake assembly may be used to prevent movement of the vehicle. The parking brake assembly may be a discrete assembly, or may utilize one or more components of the service brake assembly. That is, the parking brake assembly may use the piston and the brake pads of the service brake assembly to create the brake apply. For example, the parking brake assembly may move the piston, which may move the brake pads into contact with the rotor to create and maintain a brake apply by clamping force applied to the rotor. 
     It is with respect to these and other general considerations that the following embodiments have been described. Also, although relatively specific problems have been discussed, it should be understood that the embodiments should not be limited to solving the specific problems identified in the background. 
     SUMMARY 
     The features and advantages of the present disclosure will be more readily understood and apparent from the following detailed description, which should be read in conjunction with the accompanying drawings, and from the claims which are appended to the end of the detailed description. 
     According to various embodiments of the present disclosure, a brake assembly may comprise: a brake piston configured to be movable for a brake apply or release, the brake piston having an inner wall forming a piston cavity; a linearly movable structure positioned within the piston cavity of the brake piston, the linearly movable structure configured to be linearly movable within the piston cavity in response to rotation of a rotatable structure operably coupled to the linearly movable structure; and a magnet disposed between the brake piston and the linearly movable structure so that the brake piston is movable toward the linearly movable structure in response to linear movement of the linearly movable structure by magnetic field generated by the magnet. 
     In some exemplary embodiments of the present disclosure, the magnet may be mounted to the linearly movable structure, and the brake piston may have magnetically-attractive material attractable by the magnet so that an attractive magnetic force can be generated between the brake piston and the magnet mounted to the linearly movable structure. 
     In certain exemplary embodiments of the present disclosure, the magnet may be positioned in an inner groove firmed on an inner circumferential surface at an end portion of the linearly movable structure. There may be a clearance between the magnet mounted to the linearly movable structure and the rotatable structure operably coupled to the linearly movable structure. The magnet may protrude outwardly from the inner groove of the linearly moveable structure toward the inner wall of the brake piston. The inner wall of the brake piston may have a groove in which the magnet mounted to the linearly movable structure is insertable when one or both of the linearly movable structure and the brake piston approaches another or each other. There may be a clearance between an outer circumferential surface of the magnet mounted to the linearly movable structure and an inner circumferential surface of the groove of the brake piston into which the magnet mounted to the linearly movable structure is insertable. A diameter of a groove of the inner wall of the brake piston into which the magnet is insertable may be greater than a diameter of the magnet positioned in an inner groove formed on an inner circumferential surface of the linearly movable structure. 
     In some exemplary embodiments of the present disclosure, the magnet may be positioned in an outer groove formed on an outer circumferential surface at an end portion of the linearly movable structure. The inner wall of the brake piston may have a groove into which the magnet is insertable when one or both of the linearly movable structure and the brake piston approach another or each other. The magnet mounted to the linearly movable structure may be configured to attract the brake piston having the magnetically-attractive material. 
     In certain exemplary embodiments of the present disclosure, the magnet may be mounted to the inner wall of the brake piston, and the linearly movable structure may have magnetically-attractive material attractable by the magnet so that an attractive magnetic force can be generated between the linearly movable structure and the magnet mounted to the brake piston. The inner wall of the brake piston may have a groove to which the magnet is mounted. 
     The magnet may have a bore through which the rotatable structure is allowed to pass. Alternatively, the magnet may have a concave surface configured to receive an end portion of the rotatable structure and/or the linearly movable structure. 
     According to various embodiments of the present disclosure, a brake assembly may comprise: a brake piston configured to be movable for a brake apply or release, the brake piston having an inner wall forming a piston cavity; and a linearly movable structure positioned within the piston cavity of the brake piston, the linearly movable structure configured to be linearly movable within the piston cavity in response to rotation of a rotatable structure operably coupled to the linearly movable structure, wherein the linearly movable structure is magnetized and the brake piston has magnetically-attractive material attractable by magnet field generated by the magnetized linearly movable structure so that the brake piston is movable in response to linear movement of the linearly movable structure by the magnet field generated by the magnetized linearly movable structure. 
     According to some embodiments of We present disclosure, a brake assembly ma comprise: a brake piston configured to be movable for a brake apply or release, the brake piston having an inner wall forming a piston cavity; and a linearly movable structure positioned within the piston cavity of the brake piston, the linearly movable structure configured to be linearly movable within the piston cavity in response to rotation of a rotatable structure operably coupled to the linearly movable structure, wherein the brake piston is magnetized and the linearly movable structure has magnetically-attractive material attractable by magnet field generated by the magnetized brake piston so that the magnetized brake piston is movable in response to linear movement of the linearly movable structure by an attractive magnetic force generated between the magnetized brake piston and the linearly movable structure having the magnetically-attractive material. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments in accordance with the present disclosure will be described with reference to the drawings, in which: 
         FIG.  1    illustrates a cross-sectional view of a brake assembly according to a first exemplary embodiment of the present disclosure. 
         FIG.  2 A  shows a cross-sectional view of a brake assembly taken at cross-section A-A of  FIG.  1    according to the first exemplary embodiment of the present disclosure. 
         FIG.  2 B  is an enlarged view of a square portion B shown in  FIG.  2 A  according to the first exemplary embodiment of the present disclosure. 
         FIG.  3 A  shows a cross-sectional view of a brake assembly in a disengaged condition according to the first exemplary embodiment of the present disclosure. 
         FIG.  3 B  is an enlarged view of a square portion C shown in  FIG.  3 A  according to the first exemplary embodiment of the present disclosure. 
         FIG.  4 A  shows a cross-sectional view of a brake assembly in an engaged condition according to the first exemplary embodiment of the present disclosure. 
         FIG.  4 B  is an enlarged view of a square portion D shown in  FIG.  4 A  according to the first exemplary embodiment of the present disclosure. 
         FIG.  5    is an exploded view of a brake assembly according to the first exemplary embodiment of the present disclosure. 
         FIG.  6    illustrates a cross-sectional view of a brake assembly according to a second exemplary embodiment of the present disclosure. 
         FIG.  7 A  shows a cross-sectional view of a brake assembly taken at cross-section E-E of  FIG.  6    according to the second exemplary embodiment of the present disclosure. 
         FIG.  7 B  is an enlarged view of a square portion F shown in  FIG.  7 A  according to the second exemplary embodiment of the present disclosure. 
         FIG.  8 A  shows a cross-sectional view of a brake assembly in a disengaged condition according to the second exemplary embodiment of the present disclosure. 
         FIG.  8 B  is an enlarged view of a square portion G shown in  FIG.  8 A  according to the second exemplary embodiment of the present disclosure. 
         FIG.  9 A  shows a cross-sectional view of a brake assembly in an engaged condition according to the second exemplary embodiment of the present disclosure. 
         FIG.  9 B  is an enlarged view of a square portion H shown in  FIG.  9 A  according to the second exemplary embodiment of the present disclosure. 
         FIG.  10    is an exploded view of a brake assembly according to the second exemplary embodiment of the present disclosure. 
         FIG.  11    illustrates a cross-sectional view of a brake assembly according to a third exemplary embodiment of the present disclosure. 
         FIG.  12 A  shows a cross-sectional view of a brake assembly taken at cross-section I-I of  FIG.  11    according to the third exemplary embodiment of the present disclosure. 
         FIG.  12 B  is an enlarged view of a square portion J shown in  FIG.  12 A  according to the third exemplary embodiment of the present disclosure. 
         FIG.  13 A  shows a cross-sectional view of a brake assembly in a disengaged condition according to the third exemplary embodiment of the present disclosure. 
         FIG.  13 B  is an enlarged view of a square portion K shown in  FIG.  13 A  according to the third exemplary embodiment of the present disclosure. 
         FIG.  14 A  shows a cross-sectional view of a brake assembly in an engaged condition according to the third exemplary embodiment of the present disclosure. 
         FIG.  14 B  is an enlarged view of a square portion L shown in  FIG.  14 A  according to the third exemplary embodiment of the present disclosure. 
         FIG.  15    is an exploded view of a brake assembly according to the third exemplary embodiment of the present disclosure. 
         FIG.  16    illustrates a cross-sectional view of a brake assembly according to a fourth exemplary embodiment of the present disclosure. 
         FIG.  17 A  shows a cross-sectional view of a brake assembly taken at cross-section M-M of  FIG.  16    according to the fourth exemplary embodiment of the present disclosure. 
         FIG.  17 B  is an enlarged view of a square portion N shown in  FIG.  17 A  according to the fourth exemplary embodiment of the present disclosure. 
         FIG.  18 A  shows a cross-sectional view of a brake assembly in a disengaged condition according to the fourth exemplary embodiment of the present disclosure. 
         FIG.  18 B  is an enlarged view of a square portion O shown in  FIG.  18 A  according to the fourth exemplary embodiment of the present disclosure. 
         FIG.  19 A  shows a cross-sectional view of a brake assembly in an engaged condition according to the fourth exemplary embodiment of the present disclosure. 
         FIG.  19 B  is an enlarged view of a square portion P shown in  FIG.  19 A  according to the fourth exemplary embodiment of the present disclosure. 
         FIG.  20    is an exploded view of a brake assembly according to the fourth exemplary embodiment of the present disclosure. 
         FIG.  21    illustrates a cross-sectional view of a brake assembly according to a fifth exemplary embodiment of the present disclosure. 
         FIG.  22 A  shows a cross-sectional view of a brake assembly taken at cross-section Q-Q of  FIG.  21    according to the fifth exemplary embodiment of the present disclosure. 
         FIG.  22 B  is an enlarged view of a square portion R shown in  FIG.  22 A  according to the fifth exemplary embodiment of the present disclosure. 
         FIG.  23 A  shows a cross-sectional view of a brake assembly in a disengaged condition according to the fifth exemplary embodiment of the present disclosure. 
         FIG.  23 B  is an enlarged view of a square portion S shown in  FIG.  23 A  according to the fifth exemplary embodiment of the present disclosure. 
         FIG.  24 A  shows a cross-sectional view of a brake assembly in an engaged condition according to the fifth exemplary embodiment of the present disclosure. 
         FIG.  24 B  is an enlarged view of a square portion T shown in  FIG.  24 A  according to the fifth exemplary embodiment of the present disclosure. 
         FIG.  25    is an exploded view of a brake assembly according to the fifth exemplary embodiment of the present disclosure. 
         FIG.  26    illustrates a cross-sectional view of a brake assembly according to a sixth exemplary embodiment of the present disclosure. 
         FIG.  27 A  shows a cross-sectional view of a brake assembly taken at cross-section U-U of  FIG.  26    according to the sixth exemplary embodiment of the present disclosure. 
         FIG.  27 B  is an enlarged view of a square portion V shown in  FIG.  27 A  according to the sixth exemplary embodiment of the present disclosure. 
         FIG.  28 A  shows a cross-sectional view of a brake assembly in a disengaged condition according to the sixth exemplary embodiment of the present disclosure. 
         FIG.  28 B  is an enlarged view of a square portion W shown in  FIG.  28 A  according to the sixth exemplary embodiment of the present disclosure. 
         FIG.  29 A  shows a cross-sectional view of a brake assembly in an engaged condition according to the sixth exemplary embodiment of the present disclosure. 
         FIG.  29 B  is an enlarged view of a square portion X shown in  FIG.  29 A  according to the sixth exemplary embodiment of the present disclosure. 
         FIG.  30    is an exploded view of a brake assembly according to the sixth exemplary embodiment of the present disclosure. 
         FIG.  31    illustrates a cross-sectional view of a brake assembly according to a seventh exemplary embodiment of the present disclosure. 
         FIG.  32 A  shows a cross-sectional view of a brake assembly taken at cross-section Y-Y of  FIG.  31    according to the seventh exemplary embodiment of the present disclosure. 
         FIG.  32 B  is an enlarged view of a square portion Z shown in  FIG.  32 A  according to the seventh exemplary embodiment of the present disclosure. 
         FIG.  33 A  shows a cross-sectional view of a brake assembly in a disengaged condition according to the seventh exemplary embodiment of the present disclosure. 
         FIG.  33 B  is an enlarged view of a square portion AA shown in  FIG.  33 A  according to the seventh exemplary embodiment of the present disclosure. 
         FIG.  34 A  shows a cross-sectional view of a brake assembly in an engaged condition according to the seventh exemplary embodiment of the present disclosure. 
         FIG.  34 B  is an enlarged view of a square portion BB shown in  FIG.  34 A  according to the seventh exemplary embodiment of the present disclosure. 
         FIG.  35    is an exploded view of a brake assembly according to the seventh exemplary embodiment of the present disclosure. 
         FIG.  36    illustrates a cross-sectional view of a brake assembly according to an eighth exemplary embodiment of the present disclosure. 
         FIG.  37 A  shows a cross-sectional view of a brake assembly taken at cross-section CC-CC of  FIG.  36    according to the eighth exemplary embodiment of the present disclosure. 
         FIG.  37 B  is an enlarged view of a square portion DD shown in  FIG.  37 A  according to the eighth exemplary embodiment of the present disclosure. 
         FIG.  38 A  shows a cross-sectional view of a brake assembly in a disengaged condition according to the eighth exemplary embodiment of the present disclosure. 
         FIG.  38 B  is an enlarged view of a square portion EE shown in  FIG.  38 A  according to the eighth exemplary embodiment of the present disclosure. 
         FIG.  39 A  shows a cross-sectional view of a brake assembly in an engaged condition according to the eighth exemplary embodiment of the present disclosure. 
         FIG.  39 B  is an enlarged view of a square portion FF shown in  FIG.  39 A  according to the eighth exemplary embodiment of the present disclosure. 
         FIG.  40    is an exploded view of a brake assembly according to the eighth exemplary embodiment of the present disclosure. 
     
    
    
     Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In the following detailed description, reference is made to the accompanying drawings which form a part of the present disclosure, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the spirit and scope of the invention. The following detailed description is therefore not to be taken in a limiting sense, and the scope of the invention is defined only by the appended claims and equivalents thereof. Like numbers in the figures refer to like components, which should be apparent from the context of use. 
     Referring to  FIGS.  1  to  5   , a brake assembly  10  may include a brake caliper  110 . The brake caliper  110  may be mounted in a floating manner by means of a brake carrier. A brake pad assembly or brake lining assembly  120  is provided in the brake caliper  110 , and includes a brake pad or lining  121  and a brake pad (or lining) carrier  122 . The brake caliper  110  may include a bridge with fingers, and the fingers of the brake caliper  110  may be in contact with the brake pad carrier  122 . The brake pad  121  is disposed with a small air clearance on a side of a brake rotor  125 , such as a brake disc, in a release position so that no significant residual drag moment occurs. The brake pad carrier  122  is disposed between the brake pad  121  and a brake piston  200 , the brake pad  121  and the brake pad carrier  122  move jointly together, and the movement of the brake pad carrier  122  causes the brake pad  121  to move with respect to the brake rotor  125 . When a vehicle is in motion, the brake rotor  125  may rotate with a wheel about an axle of a vehicle. The brake caliper  110  may be connected to any non-rotating or non-moving part of a vehicle. 
     The brake piston  200  is mounted in a movable manner in a caliper cavity or bore  115  defined in the brake caliper  110 . The caliper bore  115  can support the brake piston  200  therein. The brake piston  200  may be moved in a brake apply direction, which may function to move the brake pad  121 , towards the brake rotor  125  to create the clamping force. The brake piston  200  may be moved in a brake release direction, which may function to allow the brake pad  121  to move away from the brake rotor  125  to release the clamping force. 
     A linearly movable structure  300  may be received in the piston cavity  210  formed by the inner wall of the brake piston  200 . The linearly movable structure  300  may be configured to be linearly movable within the piston cavity  210  formed by the inner wall of the brake piston  200 . For example, the linearly movable structure  300  may be operable coupled with a rotatable structure  400 , and the linearly movable structure  300  is linearly movable in response to rotation of the rotatable structure  400 . The linearly movable structure  300  and the rotatable structure  400  may be configured to transfer a power output from an actuator assembly  800  into a linear or axial force to move the brake piston  200  along an axis of the caliper cavity  115 . The actuator assembly  800  may include, for example, but not limited to, one or more of a motor and one or more gears and/or belts for increasing a torque output of the motor. 
     In an exemplary embodiment of the present disclosure, the linearly movable structure  300  may include a spindle nut  305 , and the rotatable structure  400  may comprise a spindle  405 . The linearly movable structure  300  and the rotatable structure  400  may be operatable coupled by a threaded portion, a ball screw, a roller screw, a ball ramp, or any coupling structure or mechanism that can change the rotation movement to the linear movement. 
     The actuation of the actuator assembly  800  causes the spindle  405  to rotate and then the rotation of the spindle  405  causes the spindle nut  305  to be linearly moved. The motor of the actuator assembly  800  may be directly coupled to an end of the spindle  405 . Alternatively, the motor of the actuator assembly  800  may be indirectly and operably coupled to the spindle  405  via one or more torque transferring mechanisms, such as gears, gear trains, and belts. 
     The spindle nut  305  can move axially either towards or away from the brake rotor  125 . The direction that the spindle nut  305  is moved depends on the direction that the spindle  405  rotates. During a parking brake apply, the spindle  405  is rotated in an apply direction so that the spindle nut  305  is moved in a direction towards the brake rotor  125 . During a parking brake release, the spindle  405  is rotated in an opposing release direction so that the spindle nut  305  is moved in a direction away from the brake rotor  125 . 
     The spindle nut  305  has a head portion  310  which has a conical shape and can be brought into contact with a complementarily conical inner surface  205  of the brake piston  200 . In a release position, there is a clearance between the head portion  310  of the spindle nut  305  and the conical inner surface  205  of the brake piston  200 . The spindle nut  305  further comprises a body portion  320  extended from the head portion  310  of the spindle nut  305 . An outer diameter of the head portion  310  of the spindle nut  305  may be larger than an outer diameter of the body portion  320  of the spindle nut  305 . 
     The spindle nut  305  may threadably engage the spindle  405 . For example, an outer surface of the spindle  405  may have a threaded portion and an inner surface of the spindle nut  305  may have a threaded portion that is configured to threadably engage the threaded portion of the spindle  405 . Alternatively, the spindle nut  305  and the spindle  405  may be coupled to each other via a ball screw or nut, a roller screw, a ball ramp, or any rotary to linear mechanism configured to convert a rotary movement into a linear movement. 
     The rotation of the spindle  405  causes the spindle nut  305  to move linearly. The spindle nut  305  is restricted or prevented from rotating about an axis of the spindle  405 , or about the spindle itself. As illustrated in  FIG.  1   , the spindle nut  305  is keyed to the piston cavity  210  of the brake piston  200  to prevent the spindle nut  305  from rotating about the spindle  405  or spindle axis. 
     When service braking is performed, the brake assembly  10  is hydraulically actuated. For example, the brake assembly  10  may be hydraulically actuated by a driver via a brake pedal or via a drive assistance system. When the brake assembly  10  is hydraulically actuated, hydraulic fluid is pressurized in the piston cavity  210  such that the brake piston  200  is displaced in a direction toward the brake rotor  125 , and the brake pad  121  is pressed onto the brake rotor  125  by means of the brake caliper  110 . However, the spindle nut  300  remains unactuated, and therefore remains at an initial axial position. During the service braking application, the fluid may be pressurized, which may function to exert a fluid pressure force or a pressing force on the brake piston  200 . The fluid pressure force or the pressing force may move the brake piston  200  in the apply direction towards the brake pad  121 . The pressurized fluid pressure or the pressing force applied on the brake piston  200  in turn exerts a force onto the brake pad carrier  122 . 
     Operation of parking brake of the brake assembly  10  will now be described. It is understood that these operations or method steps can be performed in virtually any order, and one or more of the operations or steps described herein may be changed, combined, omitted or repeated. 
     For activating parking brake, a signal may be transmitted by an electronic control unit (ECU) or a controller to the actuator assembly  800  to apply the parking brake. In response to the signal of the ECU, the actuator assembly  800  provides torque to the spindle  405  in the brake apply direction so that the rotation force provided by the actuator assembly  800  can cause the spindle  405  to rotate in the apply direction and then the rotation of the spindle  405  can cause the spindle nut  305  to be advanced or linearly moved in a direction toward the brake rotor  125  and then the head portion  310  of the spindle nut  300  to contact and support the inner wall of the brake piston  200  (e.g. the conical inner surface  205 ) until the clearance between the brake pad  121  and the brake rotor  125  is removed. The continued rotation of the spindle  405  and thus linear movement of the spindle nut  305  to move the brake piston  200  and the brake pad  121  against the brake rotor  125  to generate the clamping force necessary to prevent movement of the vehicle. 
     Eventually, a forward or leading end of the spindle nut  305  may contact an end inner wall of the piston cavity  210 . After the contact is made between the forward or leading end of the spindle nut  305  and the end inner wall of the piston cavity  210 , continued rotation of the spindle  405  in the apply direction, and thus continued linear movement of the spindle nut  305  in the apply direction, causes the brake piston  200  to be pushed or moved in the apply direction towards the brake pad  121 . Continued movement of the brake piston in the apply direction eventually causes the brake piston  200  to move or push the brake pad  121  against the brake rotor  125  to create friction or a clamping force. 
     As a result, the position of the brake piston  200  is fixed in a parking brake state by the support of the spindle nut  305 . Once the brake piston  200  is supported by the spindle nut  305 , the hydraulic pressure in the piston cavity  210  may be removed. The parking brake state is maintained by the spindle nut  300  because of self-locking between the spindle nut  300  and the spindle  400 . The brake pad  121  pressing against the brake rotor  125  is supported via the spindle nut  300 . 
     To release the parking brake, the ECU or controller may transmit a signal for the parking brake release to the actuator assembly  800 . In response to the signal for the parking brake release, the actuator assembly  800  provides rotation force to the spindle  405  in an opposing direction or brake release direction, which is opposite to the direction that the spindle is rotated when the spindle is rotated in the apply direction, which causes the spindle  405  to rotate in the opposing direction or brake release direction and then the spindle nut  305  to move axially in the brake release direction or a direction away from the brake rotor  125 . The linear movement of the spindle nut  305  in the brake release direction may make the brake piston  200  free to relax and move away from the brake pad  121  so that the brake pad  121  can move away from the brake rotor  125  to release the clamping force. 
     When the parking brake state is released, pressurized hydraulic fluid is introduced into the brake cavity  210 . As a result, the brake piston  200  is displaced slightly toward the brake rotor  125  such that the spindle nut  305  can be relieved of axial load. Through the control of the actuator assembly  800 , the spindle nut  305  can be retracted in a direction away from the brake rotor  125  into the initial position. 
     The rotation of the spindle  405  in the release direction causes the spindle nut  305  to move linearly or axially in the release direction, or away from the end inner wall  205  of the brake piston  200 . The brake piston  200  can then move back into the caliper cavity  115  out of contact with the brake carrier  122 , thus allowing the brake pad  121  to move out of contact with the brake rotor  125  to release the clamping force. 
     A magnet  500  may be positioned between the brake piston  200  and the linearly movable structure  300  (e.g. the spindle nut  305 ) to retract the brake piston  200  in the brake release direction during the brake release operation. The magnet  500  can pull the brake piston  200  into the brake release position. The magnet  500  may be configured to generate magnetic field so that the brake piston  200  can be moved toward the linearly movable structure  300  (e.g. the spindle nut  305 ) by the magnetic field generated by the magnet  500 . The magnetic field strength generated by the magnet  500  may be sufficiently high for moving the brake piston  200 . The magnet  500  may provide a sufficient attraction force to move the brake piston  200  when the magnet  500  and the brake piston  200  are brought in sufficiently close proximity to each other. Accordingly, as the linearly movable structure  300  (e.g. the spindle nut  305 ) moves in the brake release direction, the magnet  500  positioned between the brake piston  200  and the linearly movable structure  300  (e.g. the spindle nut  305 ) can move the brake piston  200  toward the linearly movable structure  300  (e.g. the spindle nut  305 ), thereby retracting the brake piston  200  in the brake release direction. The magnet  500  may function to provide active retraction of the brake piston  200  when the linearly movable structure  300  (e.g. the spindle nut  305 ) moves in the brake release direction during the brake release operation. 
     The magnet  500  may include one or more of magnetic metallic elements (e.g., iron, cobalt, nickel, etc.), composite magnets (e.g., ceramic or ferrite magnets, alnico magnets, ticonal magnets, injection molded magnets, flexible magnets), rare earth magnets (e.g., samarium-cobalt magnets, neodymium-iron-boron magnets, etc.), Neodymium magnets, sets of any of these magnets, or any material or composition that produces a magnetic field. The magnet may be preferably a permanent magnet or the like. Alternatively, the magnet  500  can be an electro-magnet. Further, the magnet  500  may be replaced with a magnetized material, such as, but not limited to, a ferrous material including an iron, cobalt, nickel, steel, rare earth metal or their alloys, or the like. 
     The magnet  500  may be arranged in a location to magnetically interact with the brake piston  200  or the linearly movable structure  300  (e.g. the spindle nut  305 ) when the magnet  500  and the brake piston  200  (or the linearly movable structure  300  (e.g. the spindle nut  305 )) are in relative close proximity to each other. The magnet  500  may be mounted to various positions of the linearly movable structure  300  (e.g. the spindle nut  305 ) and/or the brake piston  200 . For example, as in the first exemplary embodiment illustrated in  FIGS.  1  to  5    and the second exemplary embodiment shown in  FIGS.  6  to  10   , the magnet  500  can be arranged in a fixed relation to the linearly movable structure  300  (e.g. the spindle nut  305 ), for example, by attaching the magnet  500  (e.g. magnet  500 - 1  of  FIG.  1  to  5  or  500 - 2    of  FIGS.  6  to  10   ) to a suitable location on a wall or on other structure of or in the linearly movable structure  300  (e.g. the spindle nut  305 ). Alternatively, as in the third exemplary embodiment illustrated in  FIGS.  11  to  15   , the magnet  500  can be arranged in a fixed relation to the brake piston  200 , for example, by attaching the magnet  500  (e.g. magnet  500 - 3  of  FIGS.  11  to  15   ) to a suitable location on a wall or on other structure of or in the brake piston  200 . Further, in another exemplary embodiment, the magnet  500  can be mounted to both the brake piston  200  and the linearly movable structure  300  to increase the strength of an attracting force moving the brake piston  200 . 
     First Exemplary Embodiment (FIGS.  1  to  5 ) 
     Referring to  FIGS.  1  to  5   , in the first exemplary embodiment, the magnet  500 - 1  may be fixed to the linearly movable structure  300  (e.g. the spindle nut  305 ) such that the magnet  500 - 1  can be moved together with the linearly movable structure  300  (e.g. the spindle nut  305 ), while the brake piston  200  may have magnetically-attractive material attractable by the magnet  500 - 1 , Accordingly, the attractive magnetic force can be generated between the magnet  500 - 1  mounted to the linearly movable structure  300  and the brake piston  200  having the magnetically-attractive material when the magnet  500 - 1  and the brake piston  200  are in relative close proximity to each other, and therefore the magnet  500 - 1  mounted to the linearly movable structure  300  may attract or pull the brake piston  200  having the magnetically-attractive material. The magnetically-attractive material of the brake piston  200  may include, for example, but not limited to, one or more of a ferromagnetic material, a paramagnetic material, or a magnetized material. The ferromagnetic material may include iron, nickel and cobalt and their alloys. For instance, the brake piston  200  is made of steel (e.g. low-carbon steel). However, the brake piston  200  can comprise, or be made of, any material which can be magnetically attracted by the magnet  500 - 1 . Further, the brake piston  200  may include an additional magnet to magnetically interact with the magnet  500 - 1 . 
     In the first exemplary embodiment, the magnet  500 - 1  may be positioned in an inner groove  510  formed on an inner circumferential surface of the linearly movable structure  300  (e.g. the spindle nut  305 ). For example, the inner groove  510  is formed at the head portion  310  of the spindle nut  305 , for instance, but not limited to, an end portion of the spindle nut  305  facing the end inner surface  205  of the brake piston  200 . The magnet  500 - 1  may be press-fitted in the inner groove  510  of the spindle nut  305 . Alternatively, the magnet  500 - 1  may be attached to the inner groove  510  of the spindle nut  305  using an adhesive, bolts, rivets, or other attachment mechanisms. 
     The magnet  500 - 1  may be formed in a hollow cylinder shape, a ring shape, or a disc shape. The outer or inner circumferential surface of the magnet  500 - 1  may have at least one of circular-shaped, square-shaped (such as square-cuts, lathe cuts, tabular cut or square rings), or polygon-shaped cross-section and a combination thereof. However, the magnet  500 - 1  may have any shape which can be fit in the inner groove  510  of the linearly movable structure  300  (e.g. the spindle nut  305 ), for instance, a shape of a nut. The magnet  500 - 1  may have a bore  511  at its center so that the spindle  405  is allowed to pass through the bore  511  of the magnet  500 - 1 . The clearance is provided between the inner surface  501  of the bore  511  of the magnet  500 - 1  and the outer circumferential surface of the spindle nut  305  so that the magnet  500 - 1  and the spindle nut  305  cannot be contacted with each other. 
     A groove  230  corresponding to the magnet  500 - 1  mounted on the inner circumferential surface of the spindle nut  305  may be formed on the end inner wall  205  of the brake piston  200 . The magnet  500 - 1  mounted to the linearly movable structure  300  (e.g. the spindle nut  305 ) is insertable into the groove  230  of the brake piston  200  when the linearly movable structure  300  (e.g. the spindle nut  305 ) and the brake piston  200  approach each oilier. There may be a gap or clearance between the outer surface  502  of the magnet  500 - 1  and an inner circumferential surface  231  of the groove  230  of the brake piston  200 . For example, a diameter of the groove  230  of the inner wall  210  of the brake piston  200  is greater than a diameter of the magnet  500 - 1  positioned in the inner groove  510  formed on an inner circumferential surface of the linearly movable structure  300  so that the magnet  500 - 1  mounted to the linearly movable structure  300  can be inserted into the groove  230  of the brake piston  200  when one of the brake piston  200  and the linearly movable structure  300  approaches the other of the brake piston  200  and the linearly movable structure  300 . The magnet  500 - 1  may protrude outwardly from the inner groove  510  of the linearly movable structure  300  toward the inner wall  205  of the brake piston  200 . An end side  503  of the magnet  500 - 1  may contact a part of the groove  230  of the brake piston  200  when the head portion  310  of the spindle nut  305  engages with the end inner surface  205  of the brake piston  200 . Alternatively, the magnet  500 - 1  may not contact the brake piston  200  even when the head portion  310  of the spindle nut  305  engages with the inner surface  205  of the brake piston  200  in order to reduce the noise caused by the contact between the magnet  500 - 1  and the brake piston  200 . 
     In operation, when the parking brake is in the brake apply position, the brake piston  200  is pushed by the linearly movable structure  300  (e.g. the spindle nut  305 ) and is in direct or indirect contact with the brake pad assembly  120  to maintain the clamping force of the brake pad assembly  120  against the brake rotor  125 . However, when the operation of releasing the parking brake is initiated, the spindle nut  305  is retracted in a brake release direction away from brake rotor  125  in response to the rotation of the spindle  405 , and then this linear movement of the spindle nut  305  in the brake release direction may make the inner surface  205  of the brake piston  200  disengaged from the head portion  310  of the spindle nut  305  as shown in  FIGS.  3 A and  3 B . Then, the brake piston  200  having the magnetically-attractive material is pulled toward the linearly movable structure  300  (e.g. the spindle nut  305 ) by the attractive magnetic force generated between the brake piston  200  and the magnet  500 - 1  mounted to the linearly movable structure  300  so that the retraction of the brake piston  200  can cause the inner surface  205  of the brake piston  200  to be engaged with the magnet  500 - 1  and/or the head portion  310  of the spindle nut  305  as illustrated in  FIGS.  4 A and  4 B , and therefore the brake piston  200  can be retracted together with the linearly movable structure  300  (e.g. the spindle nut  305 ). Accordingly, upon brake release, the brake piston  200  is forced back and retracted by the attractive magnetic force generated between the brake piston  200  having the magnetically-attractive material and the magnet  500 - 1  mounted to the linearly movable structure  300 . Thus, the magnet  500 - 1  advantageously assists in retracting the brake piston  200  having the magnetically-attractive material to pull the brake piston  200  to a pre-apply position and maintain a constant and repeatable air gap between the brake piston  200  and the brake rotor  125 . The magnet  500 - 1  attached to the linearly movable structure  300  can retract the brake piston  200  having the magnetically-attractive material actively when the spindle nut  305  moves in the brake release direction. The brake drag caused by contact forces between the brake pad assembly  120  and the brake rotor  125  due to insufficient retraction distance of the brake piston  200  during the brake release operation can be prevented, and therefore the brake piston retraction is improved. 
     Second Exemplary Embodiment (FIGS.  6  to  10 ) 
     In the first exemplary embodiment of  FIGS.  1  to  5    described above, the magnet  500 - 1  is disposed on the inner circumferential surface of the linearly movable structure  300  (e.g. the spindle nut  305 ). However, as illustrated in the second exemplary embodiment of  FIGS.  6  to  10   , a magnet  500 - 2  can be mounted on an outer circumferential surface of the linearly movable structure  300  (e.g. the spindle nut  305 ) instead of the inner circumferential surface of the linearly movable structure  300 . 
     Referring to  FIGS.  6  to  10   , in the second exemplary embodiment, the magnet  500 - 2  may be fixed to the linearly movable structure  300  (e.g. the spindle nut  305 ), while the brake piston  200  may have magnetically-attractive material attractable by the magnet  500 - 2 . Accordingly, the attractive magnetic force can be generated between the magnet  500 - 2  mounted to the linearly movable structure  300  and the brake piston  200  having the magnetically-attractive material when the magnet  500 - 2  and the brake piston  200  are in relative close proximity to each other, and therefore the magnet  500 - 2  mounted to the linearly movable structure  300  may attract or pull the brake piston  200  having the magnetically-attractive material. The magnetically-attractive material of the brake piston  200  may include, for example, but not limited to, one or more of a ferromagnetic material, a paramagnetic material, or a magnetized material. The ferromagnetic material may include iron, nickel and cobalt and their alloys. For instance, the brake piston  200  is made of steel (e.g. low-carbon steel). However, the brake piston  200  can comprise, or be made of, any material which can be magnetically attracted by the magnet  500 - 2 . Further, the brake piston  200  may include an additional magnet to magnetically interact with the magnet  500 - 1 . 
     The magnet  500 - 2  may be positioned in an outer groove  520  formed on the outer circumferential surface of the linearly movable structure  300  (e.g. the spindle nut  305 ). For example, the outer groove  520  is formed on an outer surface of the head portion  310  of the spindle nut  305 , for instance, but not limited to, an end portion of the spindle nut  305  facing the end inner surface  205  of the brake piston  200 . The magnet  500 - 2  may be press-fitted in the outer groove  520  of the spindle nut  305 . Alternatively, the magnet  500 - 2  may be attached to the outer groove  520  of the spindle nut  305  using an adhesive, bolts, rivets, or other attachment mechanisms. 
     The magnet  500 - 2  may be formed in a ring shape, a hollow cylinder shape or a disc shape. The outer or inner circumferential surface of the magnet  500 - 2  may have at least one of circular-shaped, square-shaped (such as square-cuts, lathe cuts, tabular cut or square rings), or polygon-shaped cross-section and a combination thereof. However, the magnet  500 - 2  may have any shape which can be fit in the outer groove  520  of the linearly movable structure  300  (e.g. the spindle nut  305 ), for instance, a shape of a nut (for example, a magnet  500 - 2  shown in  FIG.  30   ). 
     A groove  230  corresponding to the magnet  500 - 2  mounted on the outer surface of the spindle nut  305  may be formed on the end inner wall  205  of the brake piston  200 . A shape of the groove  230  of the brake piston  200  may be substantially mirrored to a part of the magnet  500 - 2  which is insertable into the groove  230 . The magnet  500 - 2  mounted to the linearly movable structure  300  (e.g. the spindle nut  305 ) is insertable into the groove  230 - 2  of the brake piston  200  when the linearly movable structure  300  (e.g. the spindle nut  305 ) and the brake piston  200  approach each other. There may be a gap or clearance between the outer surface  502  of the magnet  500 - 2  and an inner circumferential surface  231  of the groove  230  of the brake piston  200 . An end side  503  of the magnet  500 - 2  may contact a part of the groove  230  of the brake piston  200  when the head portion  310  of the spindle nut  305  engages with the inner surface  205  of the brake piston  200 . Alternatively, the magnet  500 - 2  may not contact the brake piston  200  even when the head portion  310  of the spindle nut  305  engages with the inner surface  205  of the brake piston  200  in order to reduce the noise caused by the contact between the magnet  500 - 2  and the brake piston  200 . 
     The operations of the second exemplary embodiment of  FIGS.  6  to  10    are substantially the same as or similar to those of the first exemplary embodiment of  FIGS.  1  to  5    described above, and therefore are not described herein in detail. It should be understood that operations, functions, structures, and features not described in relation to this second exemplary embodiment illustrated in  FIGS.  6  to  10    can be found in the descriptions of the first exemplary embodiment shown in  FIGS.  1  to  5    described above. 
     Third Exemplary Embodiment (FIGS.  11  to  15 ) 
     As described above in detail, both the magnet  500 - 1  of the first exemplary embodiment of  FIGS.  1  to  5    and the magnet  500 - 2  of the second exemplary embodiment of  FIGS.  6  to  10    are attached to the linearly movable structure  300  (e.g. the spindle nut  305 ). However, in a third exemplary embodiment, a magnet  500 - 3  is mounted to the brake piston  200  instead of the linearly movable structure  300 . 
     Referring to  FIGS.  11  to  15   , in the third exemplary embodiment, the magnet  500 - 3  may be fixed to the brake piston  200 , while the linearly movable structure  300  (e.g. the spindle nut  305 ) may have magnetically-attractive material attractable by the magnet  500 - 3 . Accordingly, the attractive magnetic force can be generated between the magnet  500 - 3  mounted to the brake piston  200  and the linearly movable structure  300  having the magnetically-attractive material when the magnet  500 - 3  and the linearly movable structure  300  are in relative close proximity to each other, and therefore the magnet  500 - 3  mounted to the brake piston  200  may attract the linearly movable structure  300  having the magnetically-attractive material. The magnetically-attractive material of the linearly movable structure  300  may include, for example, but not limited to, one or more of a ferromagnetic material, a paramagnetic material, or a magnetized material. The ferromagnetic material may include iron, nickel and cobalt and their alloys. For instance, the linearly movable structure  300  is made of steel (e.g. low-carbon steel). However, the linearly movable structure  300  can comprise, or be made of, any material which can be magnetically attracted by the magnet  500 - 3 . Further, the linearly movable structure  300  may include an additional magnet to magnetically interact with the magnet  500 - 3 . 
     The magnet  500 - 3  may be positioned in a groove  240  formed on the end inner wall  205  of the brake piston  200 . For example, the groove  240  of the brake piston  200 , in which the magnet  500 - 3  is disposed, is formed at the center of the end inner wall  205  of the brake piston  200  facing the head portion  310  of the spindle nut  305 . The magnet  500 - 3  may be press-fitted in the groove  240  of the brake piston  200 . Alternatively, the magnet  500 - 3  may be attached to the groove  240  of the brake piston  200  using an adhesive, bolts, rivets, or other attachment mechanisms. A shape of the groove  240  of the brake piston  200  may be substantially mirrored to a part of the magnet  500 - 3  which is inserted into the groove  240 . 
     The magnet  500 - 3  may be formed in a disc shape, a cylinder shape, or a ring shape. The outer or inner circumferential surface of the magnet  500 - 3  may have at least one of circular-shaped, square-shaped (such as square-oats; lathe cuts, tabular cut or square rings), or polygon-shaped cross-section and a combination thereof. However, the magnet  500 - 3  may have any shape which can be fit in the groove  240  of the brake piston  200 , for instance, a shape of a nut. As illustrated in  FIGS.  12  to  15   , the magnet  500 - 3  may have a bore  511  at its center so that the spindle  405  is allowed to pass through the bore  511  of the magnet  500 - 3 . Alternatively, as illustrated in  FIGS.  32  to  35   , instead of the bore  511 , the magnet  500 - 3  may have a concave surface or groove  512  which can receive an end portion of the rotatable structure  400  (e.g. the spindle  405 ) but does not contact the rotatable structure  400 . 
     A surface  504  of the magnet  500 - 3  contacting the head portion  310  of the spindle nut  305  may be angled or slanted depending on a curvature of the head portion  310  of the spindle nut  305 , although it is not required. 
     In operation, when the parking brake is in the brake apply position, the brake piston  200  is pushed by the linearly movable structure  300  (e.g. the spindle nut  305 ) and is in direct or indirect contact with the brake pad assembly  120  to maintain the clamping force of the brake pad assembly  120  against the brake rotor  125 . However, when the parking brake is released, the spindle nut  305  is retracted in a brake release direction away from brake rotor  125  in response to the rotation of the spindle  405 , and then this linear movement of the spindle nut  305  in the brake release direction may make the inner surface  205  of the brake piston  200  disengaged from the head portion  310  of the spindle nut  305  as shown in  FIGS.  13 A and  13 B . Then, the brake piston  200  having the magnet  500 - 3  is pulled toward the linearly movable structure  300  (e.g. the spindle nut  305 ) including the magnetically-attractive material by the attractive magnetic force generated between the linearly movable structure  300  and the magnet  500 - 3  mounted to the brake piston  200  so that the retraction of the brake piston  200  can cause the inner surface  205  of the brake piston  200  to be engaged with the magnet  500 - 3  and/or the head portion  310  of the spindle nut  305  as illustrated in  FIGS.  14 A and  14 B , and therefore the brake piston  200  can be retracted together with the linearly movable structure  300  (e.g. the spindle nut  305 ). Accordingly, upon brake release, the brake piston  200  is forced back and retracted by the attractive magnetic force generated between the magnet  500 - 3  mounted to the brake piston  200  and the linearly movable structure  300  having the magnetically-attractive material. Thus, the magnet  500 - 3  advantageously assists in retracting the brake piston  200  to pull the brake piston  200  to a pre-apply position and maintain a constant and repeatable air gap between the brake piston  200  and the brake pad assembly  120 . The magnet  500 - 3  can retract the brake piston  200  actively when the spindle nut  305  is retracted. The brake drag caused by contact forces between the brake pad assembly  120  and the brake rotor  125  due to insufficient retraction distance of the brake piston  200  during the brake release operation can be prevented, and therefore the brake piston retraction is improved. 
     Fourth Exemplary Embodiment (FIGS.  16  to  20 ) 
     In the first to third exemplary embodiments of  FIGS.  1  to  15   , the magnet  500  (e.g. magnet  500 - 1  to  500 - 3 ) is mounted to one of the brake piston  200  and the linearly movable structure  300  (e.g. the spindle nut  305 ). However, in the fourth exemplary embodiment of  FIGS.  16  to  20   , one of the brake piston  200  and the linearly movable structure  300  is magnetized instead of attaching the magnet  500  to one of the brake piston  200  and the linearly movable structure  300  (e.g. the spindle nut  305 ). 
     Referring to  FIGS.  16  to  20   , in the fourth exemplary embodiment, the linearly movable structure  300  is magnetized, and the brake piston  200  has magnetically-attractive material. Therefore, the attractive magnetic force can be generated between the magnetized linearly movable structure  300  and the brake piston  200  having the magnetically-attractive material when the magnetized linearly movable structure  300  and the brake piston  200  are in relative close proximity to each other, and therefore the magnetized linearly movable structure  300  can attract or pull the brake piston  200  having the magnetically-attractive material. The linearly movable structure  300  may include, or be made of, material which is magnetized and can create its own persistent magnetic field, such as ferromagnetic material. For instance, the ferromagnetic material may include one or more of iron, cobalt, nickel and most of their alloys, and some compounds of rare earth metals. Operations, functions, structures, and features of the fourth exemplary embodiment are the same as, or substantially similar to, the first and second exemplary embodiments shown in  FIGS.  1  to  10    described above except that the magnet  500 - 1  or  500 - 2  is omitted by having the magnetized linearly movable structure  300  (e.g. the magnetized spindle nut  305 ). 
     Alternatively, the brake piston  200  is magnetized, and the linearly movable structure  300  has magnetically-attractive material. Operations, functions, structures, and features of the alternative exemplary embodiment are the same as, or substantially similar to, the third exemplary embodiment shown in  FIGS.  11  to  15    described above except that the magnet  500 - 3  is omitted by having the magnetized brake piston  200 . 
     Any elements, operations, functions, structures, and features not described in relation to the fourth embodiment illustrated in  FIGS.  16  to  20    can be found in the descriptions of those embodiments shown in  FIGS.  1  to  15    described above. 
     Fifth to Eighth Exemplary Embodiments (FIGS.  21  to  40 ) 
     The first to fourth exemplary embodiments of  FIGS.  1  to  20    which are a metal piston type brake assembly may be implemented as a phenolic piston type brake assembly (for example, Phenolic MoC (Motor on Caliper) type brake assembly). Some exemplary embodiments applied to a phenolic piston type brake assembly are illustrated in  FIGS.  21  to  40   . For example, the first exemplary embodiment of  FIGS.  1  to  5    of the metal piston type brake assembly can be changed to a fifth exemplary embodiment of  FIGS.  21  to  25    of the phenolic piston type brake assembly, the second exemplary embodiment of  FIGS.  6  to  10    of the metal piston type brake assembly can be changed a sixth exemplary embodiment of  FIGS.  26  to  30    of the phenolic piston type brake assembly, the third exemplary embodiment of  FIGS.  11  to  15    of the metal piston type brake assembly can be changed a seventh exemplary embodiment of  FIGS.  31  to  35    of the phenolic piston type brake assembly, and the fourth exemplary embodiment of  FIGS.  16  to  20    of the metal piston type brake assembly can be changed an eighth exemplary embodiment of  FIGS.  36  to  40    of the phenolic piston type brake assembly. The phenolic piston type brake assembly may offer advantages such as relatively low specific gravities and relatively low thermal conductivities. 
     In the phenolic piston type embodiment of  FIGS.  21  to  40   , a phenolic outer layer  900  may be attached to the brake piston  200  (e.g. a steel core). The phenolic outer layer  900  may be positioned between the brake piston  200  (e.g. a steel core) and the brake caliper  110 . The phenolic outer layer  900  may be attached to the brake piston  200  in a process known as overmolding, although it is not required. The brake piston  200  (i.e. a core) may be formed substantially of metal and the outer layer  900  attached to the brake piston  200  may be formed substantially of phenolic material. The phenolic outer layer  900  may be slidably movable together with the brake piston  200  with respect to the brake caliper  110 . 
     The outer layer  900  may have a polymeric material, such as a thermosetting or thermoplastic polymer. Preferred polymeric material can include polymeric material made from a phenolic resin, or other appropriate polymeric material having suitable strength, rigidity, chemical resistance, low compressibility, and temperature capabilities for use in the environment of a disk brake piston. For example, a polymeric material having a temperature stability up to approximately 150° C., 200° C., 250° C. 300° C., 350° C. or higher can be favorably incorporated into the design. Suitable polymeric materials can be filled, such as glass fiber-filled, mineral-filled, metal-filled, and/or filled with other material appropriate for the strength temperature and durability requirements, or unfilled. Polymeric materials may be laminated and/or reinforced as desired. Suitable polymeric materials can include, but are not limited to, those made from phenolic resins such as novolacs and resols and include cross-linked forms of phenolic resins. 
     The magnets  500  (for example, magnets  500 - 1  to  500 - 3 ), the brake caliper  110 , the brake piston  200 , the linearly movable structure  300 , the rotatable structure  400 , the actuator assembly  800 , and their parts, components, and elements of the fifth to eighth exemplary embodiments of  FIGS.  21  to  40    can be constructed the same as or similar to those of the first to fourth exemplary embodiments of  FIGS.  1  to  20    described above. It should be understood that structures, features, materials, operations and functions not specifically discussed with respect to the fifth to eighth exemplary embodiments of  FIGS.  21  to  40    can be the same as or similar to the first to fourth exemplary embodiments of  FIGS.  1  to  20   . Any elements not described in relation to the fifth to eighth exemplary embodiments of  FIGS.  21  to  40    can be found in the descriptions of the first to fourth exemplary embodiments of  FIGS.  1  to  20    described above. For example, the descriptions for the fifth exemplary embodiment of  FIGS.  21  to  25    can be found in descriptions of the first exemplary embodiment of  FIGS.  1  to  5   , the descriptions for the sixth exemplary embodiment of  FIGS.  26  to  30    can be found in descriptions of the second exemplary embodiment of  FIGS.  6  to  10   , the descriptions for the seventh exemplary embodiment of  FIGS.  31  to  35    can be found in descriptions of the third exemplary embodiment of  FIGS.  11  to  15   , and the descriptions for the fifth exemplary embodiment of  FIGS.  36  to  40    can be found in descriptions of the fourth exemplary embodiment of  FIGS.  16  to  20   . 
     Although the example embodiments have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the present disclosure as defined by the appended claims. 
     Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the embodiments and alternative embodiments. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 
     The explanations and illustrations presented herein are intended to acquaint others skilled in the art with the invention, its principles, and its practical application. The above description is intended to be illustrative and not restrictive. Those skilled in the art may adapt and apply the invention in its numerous forms, as may be best suited to the requirements of a particular use. 
     Accordingly, the specific embodiments of the present invention as set forth are not intended as being exhaustive or limiting of the teachings. The scope of the teachings should, therefore, be determined not with reference to this description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The omission in the following claims of any aspect of subject matter that is disclosed herein is not a disclaimer of such subject matter, nor should it be regarded that the inventors did not consider such subject matter to be part of the disclosed inventive subject matter. 
     Plural elements or steps can be provided by a single integrated element or step. Alternatively, a single element or step might be divided into separate plural elements or steps. 
     The disclosure of “a” or “one” to describe an element or step is not intended to foreclose additional elements or steps. 
     While the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.