Electro-mechanical brake apparatus

Abstract

The present disclosure relates to an electro-mechanical brake apparatus including a ball-screw actuator assembly including a spindle, a ball nut, a plurality of first rolling elements, an angular contact ball bearing, a spindle head, and a piston member.

Description

ELECTRO-MECHANICAL BRAKE APPARATUS

[0001] This application is based on and claims priority from Korean Patent Application No. 10- 2024-0180897, filed on December 6, 2024, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

[0002] The present disclosure relates to an electro-mechanical brake apparatus for a vehicle, in which miniaturization is achieved by applying a ball-screw actuator assembly.

[0003] A vehicle brake apparatus is an essential device for ensuring safe driving of a vehicle and serves to reduce the speed of the vehicle or bring the vehicle to a stop. The apparatus is configured to generate a braking force through hydraulic pressure or pneumatic pressure when the driver depresses the brake pedal and to cause brake pads installed on the vehicle's wheels to apply frictional force to discs, thereby reducing the vehicle's speed.

[0004] Brake systems widely used in current vehicles include hydraulic disc brakes and drum brakes, and each system has advantages and disadvantages depending on its structural characteristics and operating principles. Recently, electronic control brake systems (e.g., ABS or ESC) have been introduced to improve braking performance of vehicles and to more precisely control the braking force. As described above, because brake systems are directly associated with vehicle safety, various technologies have been developed to enhance braking performance.

[0005] The electro-mechanical brake (EMB) system is an advanced braking device that generates a braking force through electrical signals, unlike conventional hydraulic or pneumatic brake systems. When a driver depresses a brake pedal in the EMB system, an electrical signal is generated through an electronic control device rather than hydraulic or pneumatic pressure, and this signal operates a brake motor or an actuator to directly apply frictional force to the vehicle's wheels. Due to reduced mechanical components, the EMB system is reduced in weight compared to conventional brake systems, and by electronically controlling the braking force, the EMB system offers advantages such as a faster braking response time and precise distribution of braking force.

[0006] In addition, this technology enables automation and integrated control of braking performance, and allows active braking and wheel-independent braking, making it possible to implement not only general main braking but also various additional functions such as ABS, ESC, TCS, and AEB. Furthermore, by eliminating hydraulic transmission delays, the technology is attracting attention as being suitable for next-generation vehicles such as electric vehicles and autonomous vehicles. The EMB system also has the potential to improve energy efficiency by integrating functions such as regenerative braking in addition to physical frictional braking.

[0007] Recently, in response to the demands of the automotive market, research on miniaturization of actuators applied to EMB systems is being actively conducted from various perspectives, and one of the proposed approaches is a technology that employs a ball screw. A ball screw is a component that converts rotational motion into linear motion. In an EMB system, the ball screw receives rotational torque generated by a drive unit such as a motor and moves linearly to generate braking pressure. During this process, a large axial load of about 65 kN or greater and a radial load are generated. However, when the ball-screw actuator is miniaturized, such loads may not be sufficiently supported by general wheel bearings or ball bearings.

[0008] [Prior Art Documents]

[0009] [Patent Documents]

[0010] (Patent Document 1) Korean Laid-open Patent Publication No. 2023-0078028

[0011] According to an embodiment of the present disclosure, there is provided an electro-mechanical brake apparatus including a drive unit configured to generate a rotational force, and a ball-screw actuator assembly operatively driven by the rotational force generated by the drive unit.

[0012] The ball-screw actuator assembly comprises a spindle having a first spiral groove formed on its outer surface, a ball nut having a second spiral groove formed on its inner surface, the spindle being movable inside the ball nut, a plurality of first rolling elements inserted into a space formed between the first spiral groove of the spindle and the second spiral groove of the ball nut, an angular contact ball bearing configured to support the ball nut, a spindle head coupled to a front end of the spindle, and a piston member coupled to the spindle head and configured to push a brake pad.

[0013] The angular contact ball bearing comprises an inner race integrally formed with the ball nut and having a raceway surface on its outer surface, a ring-shaped outer race spaced apart radially from the raceway surface of the inner race and having a raceway surface on its inner surface, a plurality of second rolling elements provided between the inner and outer races, and a cage configured to maintain circumferential spacing among the plurality of second rolling elements.

[0014] The cage comprises a first ring, a second ring having a larger diameter than the first ring, a plurality of bridges each having one end connected to the first ring and the other end connected to the second ring and arranged at uniform intervals in a circumferential direction, and a plurality of holes each formed by the first ring, the second ring, and two adjacent bridges, each hole configured to accommodate one of the second rolling elements.

[0015] The first ring of the cage may comprise at least one protrusion that extends radially inward and rearward from a body portion of the first ring on an inner surface thereof, and the inner race may comprise at least one undercut at a position corresponding to that of the protrusion.

[0016] A free end of the protrusion may be positioned within the undercut.

[0017] The first ring of the cage may comprise a hinge portion disposed between the protrusion and the body portion of the first ring, and the hinge portion may be configured to be elastically deformable during assembly of the angular contact ball bearing to permit pivotal movement of the protrusion about the hinge portion.

[0018] Each protrusion may be formed at a position on the inner surface of the first ring corresponding to each of the plurality of holes, and the undercut may be formed on the outer surface of the inner race along the entire circumference.

[0019] The outer race may comprise an annular retaining shoulder that protrudes from an inner surface of the outer race at an axial position between the second ring and the second rolling element.

[0020] A diameter of an imaginary circle defined by the innermost edge of the retaining shoulder may be determined by adding a diameter of the second rolling element to a pitch circle diameter defined by centers of the second rolling elements and then subtracting 3% to 10% of the diameter of the second rolling element therefrom.

[0021] The retaining shoulder may be asymmetric with respect to a plane perpendicular to an axial direction and including the innermost edge of the retaining shoulder.

[0022] At least a portion of the piston member may extend rearward, so that, when viewed in a radial direction of the angular contact ball bearing, at least the portion of the piston member and at least a portion of the angular contact ball bearing overlap each other.

[0023] The piston member may comprise a recess on at least a portion of the rear side surface thereof, and at least a portion of an outer peripheral portion of the spindle head may be inserted into the recess.

[0024] The outer race may further comprise a concave portion on at least a portion of the inner surface located forward of the raceway surface of the outer race.

[0025] The electro-mechanical brake apparatus may further comprise a transmission gear unit disposed between the drive unit and the ball-screw actuator assembly, and the transmission gear unit may be configured to receive the rotational force from the drive unit and transmit the rotational force to the ball nut of the ball-screw actuator assembly.

[0026] According to an embodiment of the present disclosure, there is provided an electro-mechanical brake that can achieve a highly compact EMB system.

[0027] In addition, the electro-mechanical brake may comprise an accidental separation-prevention structure inside the angular contact ball bearing serving as the support bearing that supports the ball-screw actuator, thereby preventing the inner race, the ball set, and the outer race of the angular contact ball bearing from being easily separated during transportation or assembly. This may significantly improve productivity and efficiency in assembly operations of the actuator and the brake apparatus.

[0028] According to another embodiment of the present disclosure, there is provided an EMB system that can achieve miniaturization while ensuring load-bearing capability of an actuator by applying an angular contact ball bearing as a support bearing for a ball-screw actuator assembly.

[0029] In addition, the EMB system can improve productivity and efficiency in assembly operations of an electro-mechanical brake apparatus including a ball-screw actuator by applying the angular contact ball bearing structure having high assembly compatibility.

[0030] The problems to be solved by the present disclosure are not limited to those described above, and other problems not mentioned herein will be clearly understood by those ordinarily skilled in the art from the descriptions below.

[0031] The effects obtainable from embodiments of the present disclosure are not limited to those described above, and other effects not mentioned herein will be clearly understood by those of ordinary skill in the art from the descriptions below.

[0032] Features and advantages of embodiments of the present disclosure will become more apparent from the following description, which is to be read together with the accompanying drawings.

[0033] FIG. 1 is a cross-sectional view schematically illustrating an electro-mechanical brake apparatus according to an embodiment of the present disclosure, in which an enlarged view of a portion of a ball-screw actuator assembly is separately illustrated.

[0034] FIG. 2 is an enlarged cross-sectional view schematically illustrating a portion of an angular contact ball bearing, which is a support bearing of the ball-screw actuator assembly of the electro-mechanical brake apparatus according to an embodiment of the present disclosure.

[0035] FIG. 3 is a view schematically illustrating a cage provided in the angular contact ball bearing comprised in the electro-mechanical brake apparatus according to an embodiment of the present disclosure, in which FIG. 3A is a perspective view illustrating the entire cage, and FIG. 3B is a cross-sectional view of the cage.

[0036] Embodiments of the present disclosure are exemplified for describing the technical spirit of the present disclosure. The scope of the present disclosure is not limited to the embodiments presented below or the detailed descriptions of such embodiments.

[0037] In describing embodiments of the present disclosure, detailed descriptions of well-known technologies related to the present disclosure will be omitted when it is determined that such descriptions may unnecessarily obscure the gist of the present disclosure. Unless otherwise defined, all technical and scientific terms used in the present disclosure have meanings commonly understood by those ordinarily skilled in the technical field to which the present disclosure pertains. All of the terms used herein are selected for the purpose of describing the present disclosure more clearly, and are not selected to limit the scope of rights according to the present disclosure.

[0038] As used herein, expressions such as "comprising," and "having," are to be understood as open-ended terms having the possibility of encompassing other embodiments, unless otherwise mentioned in the phrase or sentence including such expressions.

[0039] Herein, when a portion such as a layer, a film, a region, or a plate is described as being located "on" or "over" another portion, this includes not only cases in which the portion is directly on the other portion but also a case in which another portion is interposed therebetween. Conversely, when a portion is described as being "directly above" another portion, this means there is no other portion therebetween. In addition, describing that a portion is located "on" or "over" a reference portion means that the portion is positioned above or below the reference portion, and does not necessarily mean that the portion is positioned in a direction opposite to the direction of gravity. This is similarly to the expressions "beneath" or "under."

[0040] As used herein, the expression "in a plan view" refers to when a subject of the present disclosure is viewed from above, and the expression "in a cross-sectional view" refers to when a cross-section obtained by cutting the subject vertically with respect to the ground or installation surface is viewed from the side.

[0041] As used herein, the expressions "the same" and "identical" not only indicate a strictly identical state but also encompass states in which variations such as tolerances or differences that allow substantially the same function to be obtained are present.

[0042] As used herein, expressions indicating relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "in parallel," "perpendicular," "toward a center," "concentric," or "coaxial," not only indicate strictly such arrangements, but also encompass states in which variations in angles or distances, such as tolerances or differences that allow substantially the same function to be obtained, are present.

[0043] As used herein, the term "front" refers to a direction in which the vehicle's wheel becomes closer with respect to the ball-screw actuator assembly, and the term "rear" refers to a direction in which the vehicle's wheel becomes farther away with respect to the ball-screw actuator assembly.

[0044] As used herein, the term "inner surface" refers to a surface facing in a direction approximately toward the center of the ball-screw actuator assembly, and the term "outer surface" refers to a surface opposite to the "inner surface." In addition, the term "inner side" refers to a side facing in a direction approximately the center of the ball-screw actuator assembly, and the term "outer side" refers to a side opposite thereto.

[0045] Singular expressions described herein may include the meaning of the plural unless otherwise specified, and this similarly applies to singular expressions described in the claims.

[0046] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In this process, the thickness of lines or the size of components illustrated in the drawings may be exaggerated for clarity and convenience of description. In the following descriptions of embodiments, descriptions of components that are identical or correspond to each other may be omitted to avoid redundancy. However, even if the description of a component is omitted, it is not intended that such a component is excluded from a certain embodiment.

[0047] Furthermore, the embodiments described below are merely illustrative examples of the components presented in the claims of the present disclosure and are not intended to limit the scope of rights of the present disclosure. Embodiments that fall within the technical spirit described throughout the specification of the present disclosure and include components that may be substituted as equivalents for the components recited in the claims may be included in the scope of rights of the present disclosure.

[0048] Electro-Mechanical Brake Apparatus (EMB)

[0049] FIG. 1 is a cross-sectional view schematically illustrating an electro-mechanical brake apparatus 1 according to an embodiment of the present disclosure, in which a ball-screw actuator assembly 10 is illustrated in an enlarged manner. The electro-mechanical brake apparatus 1 according to the embodiment of FIG. 1 comprises a caliper body portion including a bridge portion 2, a finger portion 3, and a cylinder portion 4, and a pair of brake pads 6 that provide frictional force to a brake disc. The cylinder portion 4 comprises a drive unit (not illustrated) configured to generate a rotational force, a ball-screw actuator assembly 10 operatively driven by the rotational force generated by the drive unit, and a cylinder body 5 configured to support these components. In addition, the cylinder portion 4 may further comprise a transmission gear unit configured to transmit the rotational force generated from the drive unit to the ball-screw actuator assembly 10, as needed.

[0050] The caliper body portion is fixed to a vehicle body and supports the brake pads 6 and the cylinder portion 4. The bridge portion 2 and / or the finger portion 3 of the caliper body portion may be coupled to slide with respect to the vehicle body in a direction parallel to an axial direction of the brake disc by means of guide pins connected to opposite sides thereof. The bridge portion 2 and / or the finger portion 3 of the caliper body portion may slide in a direction parallel to the axial direction of the brake disc (not illustrated) by a reaction force generated when the piston member 15 presses the brake disc.

[0051] The bridge portion 2 of the caliper body portion forms an upper exterior of the caliper body portion. The bridge portion 2 may have a shape of a relatively thick plate such that the inner side surface thereof is disposed to face an outer peripheral edge of the brake disc while being spaced apart by a predetermined interval. Since specific shape, size, and area of the bridge portion 2 may be variously modified in design depending on, for example, a size of the EMB system and a size of the brake disc, the present disclosure does not particularly limit these.

[0052] The finger portion 3 forms a front exterior of the caliper body portion and presses or releases the brake pads 6 in association with sliding movement of the bridge portion 2. The finger portion 3 vertically extends downward from a front end of the bridge portion 2, and the inner side surface of the finger portion 3 on the side facing the brake disc may face one of the brake pads 6.

[0053] The cylinder portion 4 comprises a drive unit, the ball-screw actuator assembly 10, and a cylinder body 5 that supports them with at least a portion thereof fixed to the vehicle body, and a spindle 11, a spindle head 14, and a piston member 15 of the ball-screw actuator assembly 10 are movably provided within the cylinder portion 4.

[0054] The drive unit is fixed to at least a portion of the cylinder body 5 and generates a rotational force or rotational torque by receiving power from an external source. The drive unit may receive power by being electrically connected to, for example, a battery of the vehicle. The drive unit may be a device that generates the rotational force using the received power. For example, the drive unit may be an electric motor.

[0055] The cylinder portion 4 of the electro-mechanical brake apparatus 1 may further comprise a transmission gear unit disposed between the drive unit and the ball-screw actuator assembly 10. The transmission gear unit may comprise a plurality of gears rotated by receiving the rotational force from the drive unit and transmits the rotational force generated from the drive unit to the ball nut 12 of the ball-screw actuator assembly 10.

[0056] Ball-Screw Actuator Assembly

[0057] An electro-mechanical brake apparatus 1 according to an embodiment of the present disclosure comprises a ball-screw actuator assembly 10 configured to apply or release braking force to or from a brake disc. The ball-screw actuator assembly 10 comprises a spindle 11 having a first spiral groove formed on its outer surface, a ball nut 12 having a second spiral groove formed on its inner surface, the spindle 11 being movable inside the ball nut, a plurality of first rolling elements 13 inserted into a space formed between the first spiral groove of the spindle 11 and the second spiral groove of the ball nut 12, an angular contact ball bearing 20 mounted on the cylinder body 5 and configured to support the ball nut 12, a spindle head 14 coupled to a front end of the spindle 11, and a piston member 15 coupled to the spindle head 14 and configured to push a brake pad 6.

[0058] The spindle 11 may be provided as a member having a generally rod-like shape with the first spiral groove formed on its outer surface. In this case, the first spiral groove is continuously formed along a length direction of the spindle 11. The first spiral groove may be formed along the entire length of the spindle 11 or may be formed only on at least a portion of the outer surface of the spindle 11. As the ball nut 12 rotates about the central axis, the spindle 11 can be moved forward or moved rearward inside the ball nut 12 through the rolling of the first rolling elements 13. In addition, the spindle head 14, which provides a connection between the piston member 15 and the spindle 11, may be coupled to a front end of the spindle 11, and a rear end of the spindle 11 may remain as a free end.

[0059] The ball nut 12, which has the second spiral groove formed on its inner surface, is provided as a generally cylindrical member having a through-hole into which the spindle 11 is inserted. The ball nut 12 rotates by receiving a rotational force directly from the drive unit or, when necessary, through the transmission gear unit. When the ball nut 12 rotates, the spindle 11 can move forward or rearward by the rolling motion of the plurality of first rolling elements 13 caused by the second spiral groove.

[0060] The spindle 11 and the ball nut 12 may constitute a general ball screw that converts rotational motion into linear motion through the rolling of the plurality of first rolling elements 13 inserted into the space formed between the first spiral groove and the second spiral groove.

[0061] The plurality of first rolling elements 13 are inserted into the space formed between the first spiral groove of the spindle 11 and the second spiral groove of the ball nut 12. An inner side circumference of each first rolling element 13 is in rolling contact with the first spiral groove of the spindle 11, and an outer side circumference of each first rolling element 13 is in rolling contact with the second spiral groove of the ball nut 12. Each first rolling element 13 may have a generally spherical shape. The first rolling elements 13 roll along the first and second spiral grooves during the rotation of the ball nut 12 and convert the rotational motion of the ball nut 12 into linear reciprocating motion of the spindle 11.

[0062] One or more first springs may be disposed between the plurality of first rolling elements 13. In addition, at least one second spring may be disposed at one or more of both ends of the plurality of first rolling elements 13. In this case, each first spring may have a shorter length than each second spring.

[0063] The first spring may be additionally provided to reduce frictional loss between the first rolling elements 13 during the rotation of the ball nut 12. As the ball nut 12 rotates and each first rolling element 13 rolls along the first spiral groove and the second spiral groove, two adjacent first rolling elements 13 rotate in opposite directions. As a result, considerable frictional loss occurs between the two adjacent first rolling elements 13, and inserting the first spring between the two adjacent first rolling elements 13 may significantly reduce the frictional loss.

[0064] The first spring may be disposed regularly or irregularly between every N first rolling elements 13 (where N is an integer of 1 or more). The frictional resistance attenuating effect may increase as the number of first springs increases and each first spring may be disposed between every adjacent ones of the plurality of first rolling elements 13.

[0065] The at least one second spring is provided in the form of a long spring disposed at one or more of both ends of the plurality of first rolling elements 13. The role of the second spring varies depending on its position.

[0066] The second spring disposed at the front end of both ends of the plurality of first rolling elements 13 is compressed by the plurality of first rolling elements 13 when the spindle 11 moves forward during braking. When the spindle 11 moves rearward due to release of braking, the second spring is restored and pushes the plurality of first rolling elements 13 rearward. More specifically, during braking operation of the EMB system, the ball nut 12 rotates within an angle of 180° or less, and typically within an angle of 120°. That is, the ball nut 12 does not make a complete rotation by one full turn. As the ball nut 12 rotates during braking, the plurality of first rolling elements 13 move forward along the first spiral groove and the second spiral groove, and by this movement, the second spring disposed at the front end is compressed. When braking is released in the EMB system, the second spring disposed at the front end is restored, and due to this tensile restoring force, the plurality of first rolling elements 13 are pushed rearward to move along the first and second spiral grooves. Through this, a significant portion of the energy required for the rearward movement of the spindle 11 can be saved, and because the restoring force of the spring is immediately applied when the driver releases the brake pedal, a rapid response time for braking release can be assured. The first rolling elements 13 can be returned only by the restoring force of the second spring disposed at the front end, without reverse rotation of the ball nut 12 by the drive unit.

[0067] The second spring disposed at the rear end of the both ends of the plurality of first rolling elements 13 serves to push the first rolling elements 13 forward with a predetermined force in a no-load state (that is, in a state in which braking has been released and the spindle 11 has returned to its original position) so as to align the first rolling elements 13 in their proper positions.

[0068] The piston member 15 is mounted on the front end side of the spindle 11 through the spindle head 14 and linearly reciprocates together with the spindle 11. The piston member 15 is installed to be slidable inside the cylinder portion 4. A brake pad 6 is interposed between the brake disc and at least one surface of the piston member 15 that faces the brake disc. The piston member 15 comrpises a generally cylindrical shape with its front portion closed, and at least a portion of a rear-opened portion of the piston member 15 may be formed to extend rearward. Accordingly, when viewed in a radial direction of the angular contact ball bearing, at least a portion of the piston member 15 and at least a portion of the angular contact ball bearing 20 may overlap each other. The piston member 15 is coupled to the spindle 11 through the spindle head 14, and as the spindle 11 moves forward in a direction toward the brake disc (i.e., to the front), the piston member 15 also moves forward to press the brake pad 6 against the brake disc. Conversely, as the spindle 11 moves rearward in a direction away from the brake disc (i.e., to the rear), the piston member 15 moves rearward together with the spindle 11 to release the pressing force from the brake pad 6 with respect to the brake disc.

[0069] The piston member 15 may comprise a recess provided on at least a portion of its rear side surface so as to allow a portion of the spindle head 14 to be inserted therein. The recess may be formed in a ring shape. When at least a portion of an outer peripheral portion of the spindle head 14 is inserted into the recess of the piston member 15, they are engaged with each other to form an interlocking structure, through which a simple, intuitive, and robust coupling can be achieved. In addition, by virtue of the engagement structure, when the spindle 11 moves rearward in a direction away from the brake disc, the piston member 15 may also move rearward together and return to its original position.

[0070] Angular Contact Ball Bearing

[0071] An electro-mechanical brake apparatus 1 according to an embodiment of the present disclosure comprises an angular contact ball bearing 20 as a support bearing configured to support the ball-screw actuator assembly 10 with respect to the cylinder body 5.

[0072] The angular contact ball bearing 20 is a bearing that supports loads between rotating components and has a structure capable of simultaneously withstanding an axial load and a radial load. This bearing is configured such that raceway surfaces of an inner race 21 and an outer race 22 are inclined at a predetermined angle with respect to a rotational axis, allowing for stable rotation when a load is applied in the axial direction. In addition, because the angular contact ball bearing 20 is open on both the front and rear sides of the rolling elements without raceway shoulders, a sufficient internal space is secured, allowing the rolling elements to be maximized in size. Accordingly, a large supporting load can be secured while miniaturizing the support bearing. Conversely, due to the absence of the raceway shoulders, the angular contact ball bearing 20 may be unintentionally disassembled during transportation or assembly and may hence reduce productivity and efficiency of actuator assembly operations. The angular contact ball bearing 20 comprised in the electro-mechanical brake apparatus 1 according to the embodiment of the present disclosure comprises an accidental separation-prevention structure.

[0073] The angular contact ball bearing 20 comprises an inner race 21 that is integrally formed with the ball nut 12 and has a raceway surface on its outer surface, a ring-shaped outer race 22 that is radially spaced apart from the raceway surface of the inner race 21 and has a raceway surface on its inner surface, a plurality of second rolling elements 23 disposed between the inner race 21 and the outer race 22, and a cage 24 configured to maintain circumferential spacing among the plurality of second rolling elements 23. As illustrated in FIG. 1, the angular contact ball bearing 20 functions as a support bearing that supports the ball-screw actuator assembly 10 with respect to the cylinder body 5 by including a structure in which the inner race 21 is integrally formed with the ball nut 12 and the outer race 22 is coupled to the cylinder body 5.

[0074] FIG. 2 is an enlarged cross-sectional view schematically illustrating a cross-sectional structure of the angular contact ball bearing 20 comprised in the electro-mechanical brake apparatus 1 according to an embodiment of the present disclosure. Referring to FIG. 2, the angular contact ball bearing 20 comprises the inner race 21, the outer race 22, the plurality of second rolling elements 23, and the cage 24. In the assembled state, the inner race 21, the outer race 22, and the cage 24 are disposed concentrically, and their central axes coincide with a rotational axis of the angular contact ball bearing 20 and a rotational axis of the ball nut 12.

[0075] As illustrated in FIG. 2, the inner race 21 may be formed integrally with at least a portion of the outer surface of the ball nut 12. The inner race 21 may be manufactured as a separate component from the ball nut 12 and then coupled to the ball nut 12 through, for example, press-fitting. The inner race 21 may comprise at least one raceway surface configured to form at least one row of raceways together with the outer race 22 on its radially outer surface. The raceway surface of the inner race 21 is in rolling contact with the plurality of second rolling elements 23. Through this, the raceway surface of the inner race 21 can be supported axially and radially by the plurality of second rolling elements 23. A plurality of inner races 21 may be provided, in which case each inner race 21 may comprise a raceway surface forming a separate row of raceways.

[0076] At least a portion of the outer surface of the inner race 21 located forward of the raceway surface may be formed in a flat shape parallel to the central axis. At least a portion of the outer surface of the inner race 21 located rearward of the raceway surface may comprise an undercut 211 configured to receive a protrusion 245, which is formed on an inner surface of the first ring 241 of the cage 24 described later, at a position corresponding to the protrusion 245. Since the undercut 211 may be variously modified in design within the technical concept of limiting the axial movement of the protrusion 245, the present disclosure does not particularly limit, for example, the size or shape of the undercut 211.

[0077] The remaining portion of at least the portion of the outer surface of the inner race 21 located rearward of the raceway surface, excluding the undercut 211, may be formed in a flat shape parallel to the central axis. This flat portion may cooperate with a flat portion of a inner surface of the outer race 22 located rearward of the raceway surface of the outer race 22, described later, to form a mounting portion for assembling a shield member or a sealing member 25 that is provided as a separate component. The shield member and the sealing member 25 used in the present disclosure may employ components that are generally used in the technical field to which the present disclosure pertains, and therefore, the present disclosure does not particularly limit these components.

[0078] The outer race 22 may be provided as a ring-shaped component that is radially spaced apart from the raceway surface of the inner race 21 and has a raceway surface on its radially inner surface. At least a portion of the outer race 22 is coupled to the cylinder body 5 to provide supporting force. The outer race 22 may comprise at least one raceway surface configured to form at least one row of raceways together with the inner race 21 on its radially inner surface. The raceway surface of the outer race 22 is in rolling contact with the plurality of second rolling elements 23. Through this, the raceway surface of the outer race 22 can support the plurality of second rolling elements 23 axially and radially.

[0079] In a case where a plurality of inner races 21 are provided, the outer race 22 may comprise a number of raceway surfaces corresponding to the number of the inner races 21.

[0080] A portion of the inner surface of the outer race 22 located forward of the raceway surface may define an insertion opening into which the second rolling elements 23 are inserted. The outer race 22 may comprise a retaining shoulder 221 having a predetermined height on at least a portion of inner surface of the outer race 22 located forward of the raceway surface adjacent to the second rolling elements 23. As illustrated in FIG. 2, the retaining shoulder 221 protrudes radially inward at an axial position between the second ring 242 of the cage 24 and centers of the second rolling elements 23.

[0081] The height of the retaining shoulder 221 may be dimensioned to allow the second rolling elements 23 to easily ride over the retaining shoulder during assembly, and to prevent the second rolling elements from easily escaping after the assembly. A diameter of a virtual circle defined by the innermost edge of the retaining shoulder 221 may be determined as a value obtained by adding a diameter of the second rolling element 23 to a pitch circle diameter (PCD) defined by centers of the second rolling elements 23, and then subtracting 3% to 10% of the diameter of the second rolling element 23. The retaining shoulder 221 may be formed in an asymmetrical shape with respect to a plane perpendicular to an axial direction and including the innermost edge of the retaining shoulder 221.

[0082] The remaining portion of at least the portion of the inner surface of the outer race 22 located forward of the raceway surface, excluding the retaining shoulder 221, may be formed in a flat shape parallel to the central axis. The remaining portion of the outer race 22 may cooperate with the flat portion of the inner race 21 on the opposite side to form a mounting portion for assembling a shield member or a sealing member 25 provided as a separate component.

[0083] The outer race 22 may further comprise a recess 222 on at least of the portion of the inner surface of the outer race 22 located forward of the raceway surface, in which the thickness of the outer race 22 is locally reduced. A front edge of the recess 222 may be connected to the flat portion, and a rear edge of the recess 222 may be continuously connected to the retaining shoulder 221 without foming a non-continuous step. By forming the recess 222, a clearance may be provided between a radially outer edge of the second ring 242 of the cage 24 and the outer race 22, thereby preventing the second ring 242 of the cage 24 and the outer race 22 from contacting each other during rotation. In addition, since additional machining such as polishing of the outer surface of the inner race 21 and the inner surface of the outer race 22 is required for mounting the shield member or the sealing member 25, the recess 222 may allow such additional machining to be omitted, thereby achieving an incidental effect of reducing the area to be polished.

[0084] A portion of the inner surface of the outer race 22 located rearward of the raceway surface may be formed in a flat shape parallel to the central axis. The flat portion on the rear side of the outer race 22 may cooperate with the flat portion on the rear side of the inner race 21 to form a mounting portion for assembling the shield member or the sealing member 25 that is provided as a separate component.

[0085] The plurality of second rolling elements 23 are inserted between the inner race 21 and the outer race 22, more specifically, between the raceway surface of the inner race 21 and the raceway surface of the outer race 22. At least a portion of each second rolling element 23 is in rolling contact with the raceway surface of the inner race 21, and at least another portion of each second rolling element 23 is in rolling contact with the raceway surface of the outer race 22. Each second rolling element 23 may have a generally spherical shape.

[0086] The angular contact ball bearing 20 comprises a cage 24 configured to maintain a constant circumferential spacing between the second rolling elements 23 by being engaged with the second rolling elements 23 arranged in a row of raceways between the inner race 21 and the outer race 22. FIG. 3 schematically illustrates a cage 24 of the angular contact ball bearing 20 comprised in the electro-mechanical brake apparatus 1 according to an embodiment of the present disclosure. FIG. 3A is a perspective view of the cage 24, and FIG. 3B is a partially enlarged cross-sectional view of the cage 24. In FIGs. 3A and 3B, the cage 24 comprises a first ring 241, a second ring 242 formed to have a larger diameter than the first ring 241, a plurality of bridges 243 each having one end connected to the first ring 241 and the other end connected to the second ring 242 and arranged at regular intervals in a circumferential direction, and a plurality of holes 244 each formed by the first ring 241, the second ring 242, and two adjacent bridges 243, and configured to receive the second rolling elements 23. The cage 24 may be made of an elastic material, and the cage 24 may be made of a synthetic resin such as plastic.

[0087] Each second rolling element 23 is supported in the circumferential direction on both sides by two adjacent bridges 243, and is supported axially and radially by at least one surface of the first ring 241 and at least one surface of the second ring 242. Each of circumferentially opposite side surfaces of each bridge 243 may comprise a pocket surface that matches an outer contour of a second rolling element 23, and at least one surface of each of the first ring 241 and the second ring 242 may also comprise pocket surfaces that match the outer contours of the second rolling elements 23.

[0088] In FIG. 3A, each bridge 243 may be formed in a shape bent at the intermediate portion. The bridge 243 comprises a first bridge 2431 extending in an axial direction from at least a portion of the first ring 241, and a second bridge 2432 bent radially outward from the first bridge 2431 at a predetermined inclination angle with respect to the axial direction and extending to the second ring 242. Since the inclination angle with respect to the axial direction is a design variable, the range of which is determined depending on a contact angle of the angular contact ball bearing 20, the present disclosure does not particularly limit this inclination angle.

[0089] At least a portion of the first ring 241 including a pocket surface, at least a portion of the second ring 242 including a pocket surface, and the two adjacent bridges 243 may form a hole 244 configured to receive a second rolling element 23. A plurality of holes 244 may be provided to correspond to the number of second rolling elements 23, and the plurality of holes 244 may be arranged at equal intervals in the circumferential direction around the central axis. Since dimensions of individual holes 244 are design variables determined depending on the size of the second rolling elements 23, the present disclosure does not particularly limit the dimensions of the holes 244.

[0090] The first ring 241 of the cage 24 may comprise a main body portion and a protrusion 245 extending from the main body portion and protruding rearward while being inclined radially inward. A plurality of protrusions 245 may be provided to correspond to the number of holes 244, and may be formed at positions on an inner surface of the first ring 241 corresponding to the plurality of holes 244. The protrusions 245 may be provided in a number greater or smaller than the number of holes 244.

[0091] The protrusion 245 may be configured to cooperate with an undercut 211 of the inner race 21. Referring to FIG. 2, the protrusion 245 comprises a coupling portion 2451 connected to a body portion of the first ring 241, an extension portion 2452 extending from the coupling portion 2451 toward the inner race 21, and a terminal end 2453 forming a free end of the protrusion 245. The extension portion 2452 may extend in an inclined manner such that it becomes closer to the central axis as it becomes farther from the first ring 241. The terminal end 2453 may be positioned within the undercut 211 of the inner race 21. As a result, the terminal end 2453 can be contacted with a rear side wall of the undercut 211 so that a range of relative axial movement of the cage 24 can be limited. That is, through the contact structure formed by the protrusion 245 and the undercut 211, accidental separation between the inner race 21 and a ball set comprising the cage 24 and the second rolling elements 23 may be prevented.

[0092] A hinge portion 246 may be formed between the coupling portion 2451 and the body portion of the first ring 241. The hinge portion 246 may be configured to permit pivotal movement of the protrusion about the hinge portion. The hinge portion 246 may have a reduced thickness. During the assembly process of the ball set and the inner race 21, when the ball set is externally fitted to the inner race 21 along the axial direction, the outer surface of the inner race 21 presses the protrusion 245 radially outward, and at this time, force is concentrated on the hinge portion 246, causing the hinge portion 246 to elastically deform. When the external fitting of the ball set is completed, the pressing by the outer surface of the inner race 21 is released, and as the elastic deformation of the hinge portion 246 is restored, the terminal end 2453 of the protrusion 245 is positioned within a space defined by the undercut 211.

[0093] The first ring 241, the second ring 242, and the plurality of bridges may be manufactured as an integral component.

[0094] The above description is merely illustrative of the technical spirit of the present disclosure, and those ordinarily skilled in the art to which the present disclosure pertains will appreciate that various modifications and changes may be made without departing from the essential characteristics of the present disclosure. Therefore, the embodiments disclosed herein are provided for illustrative purposes rather than for limiting the technical spirit of the present disclosure, and the scope of the technical spirit of the present disclosure should not be construed as being limited by such embodiments. The scope of protection of the present disclosure should be interpreted based on the claims below, and all technical ideas falling within equivalent scopes should be interpreted as being included within the scope of rights of the present disclosure.

Claims

1.An electro-mechanical brake apparatus comprising:a drive unit configured to generate a rotational force; anda ball-screw actuator assembly operatively driven by the rotational force generated by the drive unit;wherein the ball-screw actuator assembly comprises:a spindle having a first spiral groove formed on its outer surface;a ball nut having a second spiral groove formed on its inner surface, wherein the spindle is movable inside the ball nut;a plurality of first rolling elements inserted into a space formed between the first spiral groove of the spindle and the second spiral groove of the ball nut;an angular contact ball bearing configured to support the ball nut, the angular contact ball bearing comprising:an inner race integrally formed with the ball nut and having a raceway surface on its outer surface,a ring-shaped outer race spaced apart radially from the raceway surface of the inner race and having a raceway surface on its inner surface,a plurality of second rolling elements provided between the inner and outer races, anda cage configured to maintain circumferential spacing among the plurality of second rolling elements;a spindle head coupled to a front end of the spindle; anda piston member coupled to the spindle head and configured to push a brake pad,wherein the cage comprises a first ring, a second ring having a larger diameter than the first ring, a plurality of bridges each having one end connected to the first ring and the other end connected to the second ring and arranged at uniform intervals in a circumferential direction, and a plurality of holes each formed by the first ring, the second ring, and two adjacent bridges, each hole configured to accommodate one of the second rolling elements.2.The electro-mechanical brake apparatus according to claim 1,wherein the first ring of the cage comprises at least one protrusion that extends radially inward and rearward from a body portion of the first ring on an inner surface thereof, andwherein the inner race comprises at least one undercut at a position corresponding to that of the protrusion.3.The electro-mechanical brake apparatus according to claim 2,wherein a free end of the protrusion is positioned within the undercut.4.The electro-mechanical brake apparatus according to claim 2,wherein the first ring of the cage comprises a hinge portion disposed between the protrusion and the body portion of the first ring, andwherein the hinge portion is configured to be elastically deformable during assembly of the angular contact ball bearing to permit pivotal movement of the protrusion about the hinge portion.5.The electro-mechanical brake apparatus according to claim 2,wherein each protrusion is formed at a position on the inner surface of the first ring corresponding to each of the plurality of holes, andwherein the undercut is formed on the outer surface of the inner race along the entire circumference.6.The electro-mechanical brake apparatus according to claim 1,wherein the outer race comprises an annular retaining shoulder that protrudes radially inward from the inner surface of the outer race at an axial position between the second ring and a center of the second rolling element.7.The electro-mechanical brake apparatus according to claim 6,wherein a diameter of an imaginary circle defined by the innermost edge of the retaining shoulder is determined by adding a diameter of the second rolling element to a pitch circle diameter defined by centers of the second rolling elements and then subtracting 3% to 10% of the diameter of the second rolling element therefrom.8.The electro-mechanical brake apparatus according to claim 1,wherein the retaining shoulder is asymmetric with respect to a plane perpendicular to an axial direction and including the innermost edge of the retaining shoulder.9.The electro-mechanical brake apparatus according to claim 1,wherein at least a portion of the piston member extends rearward so that when viewed in a radial direction of the angular contact ball bearing, at least the portion of the piston member and at least a portion of the angular contact ball bearing overlap each other.10.The electro-mechanical brake apparatus according to claim 1,wherein the piston member comprises a recess on at least a portion of the rear side surface thereof, andwherein at least a portion of an outer peripheral portion of the spindle head is inserted into the recess.11.The electro-mechanical brake apparatus according to claim 1,wherein the outer race further comprises a concave portion on at least a portion of the inner surface located forward of the raceway surface of the outer race.12.The electro-mechanical brake apparatus according to claim 1, further comprising:a transmission gear unit disposed between the drive unit and the ball-screw actuator assembly,wherein the transmission gear unit is configured to receive the rotational force from the drive unit and transmit the rotational force to the ball nut of the ball-screw actuator assembly.

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