Actuator for a parking brake

Abstract

An actuator for a parking brake is disclosed. According to one aspect of the disclosure, an actuator for a parking brake comprises a motor that generates a force; a reduction gear section configured to transmit the force of the motor to a locking section that implements a parking brake application of a vehicle; a housing in which the motor and the reduction gear section are accommodated; a housing cover by which the housing is closed; and a locking section configured to limit the rotation of the reduction gear section.wherein the locking section is formed by a locking element provided in such a way that it is movable in an axial direction of the reduction gear section and is in close contact with or spaced apart from the reduction gear section, an elastic element that elastically supports the locking element towards the reduction gear section, and an electromagnetic element designed to separate the locking element from the reduction gear section by generating an electromagnetic force when current is applied.

Description

[Technical field]

[0001] The disclosure relates to an actuator for a parking brake, and more precisely, an actuator for a parking brake that is capable of stably maintaining a parking brake state when the parking brake is applied. [General state of the art]

[0002] Generally, a vehicle is equipped with a braking system to perform braking. Such a braking system requires a service brake function, which provides braking force when the vehicle is in motion, and a parking brake function, which keeps the vehicle stationary when parked.

[0003] A conventional parking brake primarily uses a foot brake, operated by pressing a pedal with one foot, and a handbrake, operated by pulling a lever with one hand. Regarding the handbrake, a user pulls the lever upwards with considerable force to engage the parking brake lever, which can lead to back injuries or arm strain for drivers who frequently stop or park a vehicle. Furthermore, the parking brake lever is located in the center of a console, restricting the use of the vehicle's interior space.

[0004] Therefore, a method is now being developed to implement an electromechanical parking brake by using an actuator that generates a braking force through a motor when it receives an electrical signal from the driver indicating their intention to apply a parking brake, such as by pressing a button.

[0005] During a vehicle's parking brake application, a parking component, such as a piston and threaded spindle in a caliper brake or a parking brake shoe in a drum brake, maintains the braking force. However, even if the parking component maintains the parking brake force, the vehicle's parking brake state can be released if a variable prevents it from being maintained, such as an external impact or if the vehicle needs to be parked on a slope. In such cases, the vehicle can move. Accordingly, blocks or struts are often placed between the wheels or at the rear of the wheels to prevent the vehicle from moving despite the parking brake being applied.

[0006] To maintain the parking brake state when a parking brake function of the vehicle is operated as described above, various locking methods have been developed, such as a separate locking gear provided in a gearbox section of the actuator to maintain the fixed state of the actuator.

[0007] EP 3 263 414 A1 discloses an electromagnetic parking brake for a vehicle, wherein a locking element is moved away from a motor shaft by means of an electromagnet and blocks rotation of the motor shaft when the electromagnet is not energized.

[0008] DE 602 06 416 T2 discloses an electromagnetic parking brake for a vehicle, wherein a drive gear is blocked by a locking element which engages with the gear when an electromagnet is not energized. [Revelation][Technical Problem]

[0009] One aspect of the disclosure is the provision of an actuator for a parking brake that is capable of suppressing a vehicle rolling backward during a parking brake application.

[0010] Another aspect of the disclosure is the provision of an actuator for a parking brake that is capable of improving responsiveness and stability during parking braking.

[0011] Another aspect of the disclosure is the provision of an actuator for a parking brake, which is able to improve the ease of assembly of a product and enhance the design freedom of the vehicle.

[0012] Another aspect of the disclosure is the provision of an actuator for a parking brake that maintains a locked state when no current is applied in order to reduce the vehicle's power consumption and has a failsafe function. [Technical solution]

[0013] According to one aspect of the present disclosure, an actuator for a parking brake comprises a motor that generates a force; a reduction gear section configured to transmit the force of the motor to a locking section that implements a parking brake application of a vehicle; a housing in which the motor and the reduction gear section are accommodated; a housing cover by which the housing is closed; and a locking section configured to limit the rotation of the reduction gear section;wherein the locking section is formed by a locking element provided in such a way that it is movable in an axial direction of the reduction gear section and is in close contact with or spaced apart from the reduction gear section, an elastic element that elastically supports the locking element towards the reduction gear section, and an electromagnetic element designed to separate the locking element from the reduction gear section by generating an electromagnetic force when current is applied.

[0014] According to the invention, the locking element comprises a plate. Furthermore, the locking element can have a first friction element which is provided on a surface of the plate facing the reduction gear section and is provided to be brought into close contact with the reduction gear section.

[0015] According to the invention, the locking element has at least one pin, one side of which is coupled to the plate and the other side is inserted into the housing cover to prevent rotation of the plate.

[0016] The elastic element can be provided as at least one coil spring inserted between the housing cover and the plate.

[0017] At least one pin can be arranged radially with respect to a central axis of the plate.

[0018] The housing can have at least one projection that protrudes at a position corresponding to the at least one pin and has a recessed hole for receiving the at least one pin.

[0019] The electromagnetic element can have a core, one side of which is coupled to the housing cover and the other side protrudes towards the locking element, and a coil wound on an outer circumferential surface of the core to generate an electromagnetic force.

[0020] The reduction gear section may further comprise a second friction element provided on a surface facing the first friction element.

[0021] The plate, the first friction element, the second friction element and the reduction gear section can be provided side by side.

[0022] In the reduction gear section, a surface facing the first friction element can be friction-coated.

[0023] The plate can be arranged coaxially with the reduction gear section and can be provided in a round shape.

[0024] The at least one pin can be coupled to at least one extension section that extends radially from an edge of the plate.

[0025] The reduction gear section may include a drive gear linked to a drive shaft of the motor, a sun gear coupled to the drive gear for common rotation, several planet gears toothed with the sun gear, and an external gear toothed with the several planet gears and having a connecting section connected to the locking section.

[0026] According to another aspect of the present disclosure, an actuator for a parking brake comprises a motor that generates a force; a reduction gear section comprising a drive gear that receives the force from a drive shaft of the motor and transmits the force to a locking section that applies a parking brake to the vehicle; and a locking section that is provided to be movable up and down from a top of the drive gear and is provided to be brought into close contact with the drive gear in order to limit rotation of the drive gear.

[0027] The locking section may include a locking element provided in close contact with the drive gear to limit rotation of the drive gear by means of a frictional force; an elastic element that elastically supports the locking element towards the reduction gear section; and an electromagnetic element configured to separate the locking element from the reduction gear section by generating an electromagnetic force when current is applied. [Beneficial effects]

[0028] One embodiment of the disclosure can provide an actuator for a parking brake that is capable of suppressing a vehicle rolling backward during a parking brake application.

[0029] Furthermore, an embodiment of the disclosure may provide an actuator for a parking brake that is able to improve the responsiveness and stability during parking braking.

[0030] Furthermore, one embodiment of the disclosure can provide an actuator for a parking brake which is able to improve the ease of assembly of a product and enhance the design freedom of the vehicle.

[0031] Furthermore, an embodiment of the disclosure may provide an actuator for a parking brake which maintains a locked state when no current is applied in order to reduce the vehicle's power consumption and has a failsafe function. [Description of the drawings] Fig. Figure 1 is a cutaway perspective view schematically representing a cross-section of an actuator for a parking brake according to an embodiment of the disclosure. Fig. Figure 2 is an expanded perspective view showing an actuator for a parking brake according to one embodiment of the disclosure. Fig. Figure 3 is a perspective view showing a state in which a reduction gear section of an actuator for a parking brake is mounted on a housing, according to an embodiment of the disclosure. Fig. Figure 4 is a perspective view showing a state in which a reduction gear section and a locking element of an actuator for a parking brake are mounted on a housing according to an embodiment of the disclosure. Fig. Figure 5 is a perspective view showing a state in which a locking section of an actuator for a parking brake is mounted on a housing cover, according to an embodiment of the disclosure. Fig. Figure 6 is a sectional view showing the operation of the actuator for a parking brake in a locking mode according to an embodiment of the disclosure. Fig. Figure 7 is a sectional view showing the operation of the actuator for a parking brake when the locking mode is released, according to one embodiment of the disclosure. [Embodiments of the invention]

[0032] With reference to the accompanying drawings, embodiments of the present disclosure will be described in detail below. It should be understood that the terms used in the description and the accompanying claims are not to be interpreted as being limited to their general and lexical meanings, but rather, based on the principle that the inventor may define terms appropriately for the best explanation, they are to be interpreted on the basis of the meanings and concepts that correspond to the technical aspects of the disclosure. Therefore, the description proposed in this application merely represents a preferred example, serving only for illustrative purposes and not intended to limit the scope of the disclosure. It should therefore be understood that other correspondences and modifications could be made to it without departing from the spirit and scope of the disclosure.

[0033] Fig. Figure 1 is a cutaway perspective view showing a cross-section of an actuator for a parking brake according to an embodiment of the disclosure. Fig. Figure 2 is an expanded perspective view depicting an actuator for a parking brake according to one embodiment of the disclosure; Fig. 3 and Fig. Figure 4 are perspective views showing a state in which a reduction gear section and a locking element of an actuator for a parking brake are mounted on a housing according to an embodiment of the disclosure, and Fig. Figure 5 is a perspective view showing a state in which a locking section of an actuator for a parking brake is mounted on a housing cover, according to an embodiment of the disclosure.

[0034] With reference to Fig. According to one embodiment of the disclosure, an actuator 1 for a parking brake can have a motor 10 generating a force, a reduction gear section 20 to transmit the force of the motor 10 to a locking section (not shown) implementing a parking brake application of the vehicle, a housing 30 in which the motor 10 and the reduction gear section 20 are housed, a housing cover 40 closing the housing 30, and a locking section 100 to restrict the rotation of the reduction gear section 20.

[0035] The motor 10 generates power by receiving an electrical signal. The motor 10 can be housed in an interior of the casing 30, which is coupled to a vehicle body (not shown) or a brake caliper (not shown).

[0036] Furthermore, a rotating gear 12 is coupled to one end of a drive shaft 11 of the motor 10 in order to be linked to a drive gear 21 of the reduction gear section 20 described later. For example, the rotating gear 12 of the motor 10 transmits the power via a belt coupled to the drive gear 21, or via at least one connecting gear (not shown) that meshes with the drive gear 21.

[0037] The housing 30 can be configured to accommodate the motor 10, the reduction gear section 20, the locking section 100, and the like. In particular, the housing 30 can accommodate and support the motor 10 on one side, accommodate the reduction gear section 20 on the other side, and be coupled to the housing cover 40 to seal its interior.

[0038] The housing cover 40 can be provided to close the inside of the housing 30.

[0039] Furthermore, the housing cover 40 is designed to project towards the locking section 100 at a position corresponding to a pin 113 described later, and has several projections 41 for receiving the pins 113, each with a recessed hole in the center. Each projection 41 can also be provided with a stepped section 41a formed on the inside to receive the pins 113 and also to support an elastic element 130.

[0040] The reduction gear section 20 can transfer the power of the motor 10 to the locking section (not shown) and adjust the reduction ratio to decrease the speed while increasing the torque.

[0041] The reduction gear section 20 can include the drive gear 21 linked to the rotating gear 12, a sun gear 23 located at a lower end of the drive gear 21 and coupled to the same rotating shaft as the drive gear 21 for common rotation, several planet gears 24 externally meshed with the sun gear 23, and an external gear 25 externally meshed with the several planet gears 24 so that it rotates and transmits the power to the locking section (not shown).

[0042] The rotary shaft of the reduction gear section 20 can be provided parallel to the drive shaft 11 of the motor 10, and the drive gear 21 and the sun gear 23 can be coupled to the same rotary shaft so that they can rotate together.

[0043] The drive gear 21 can be provided on one side with a cavity for receiving the sun gear 23, the planet gears 24, and the outer gear 25. As a result, the drive gear 21 can receive power from the motor 10 and transmit the power sequentially via the sun gear 23, the planet gears 24, and a connecting section 25a of the outer gear 25 to the locking section (not shown).

[0044] An upper surface of the drive gear 21 can be configured to rub against a first friction element 112 of the locking section 100 described later. More precisely, a surface of the drive gear 21 facing the locking section 100 can be provided with a friction coating to improve the frictional force, thereby increasing the frictional force of the locking section 100. Alternatively, instead of the friction coating, a second friction element 22 can be provided on the surface of the drive gear 21 facing the locking section 100, such that it is frictionally engaged with the first friction element 112. The second friction element 22 can be provided in a shape corresponding to that of the first friction element 112. In this case, the second friction element 22 can be made of the same material as the first friction element 112 and be formed from a synthetic resin with a high coefficient of friction.

[0045] The sun gear 23 can be connected to the same rotating shaft as the drive gear 21 so that it can rotate together with it, and transmits the power to the outer gear 25 via at least one planet gear 24, which is externally toothed with the sun gear 23. The planet gears 24 can rotate in place of each other.

[0046] The outer gear 25 is externally meshed with the planet gears 24 on one side, and the connecting section 25a provided on the other side of the outer gear 25, which is connected to the locking section (not shown), can transmit the force from the planet gears 25 to the locking section (not shown). Furthermore, the outer gear 25 can be supported at its lower end by a support guide 26.

[0047] The connecting section 25a can be provided in the form of a groove in which gear teeth are provided and can be connected to the locking section (not shown). For example, in a caliper brake system, the locking section (not shown) can comprise a threaded spindle, a piston, a brake pad, and the like, and the spindle is coupled to the connecting section to transmit the force so that the brake pad is pressed against a disc. Since the specific process of applying the parking brake is a well-known technique, a detailed description of it will be omitted. Moreover, the parking brake actuator of the disclosure is not limited to the caliper brake system but can also be applied to the locking section (not shown) of a drum brake system.Accordingly, it should be understood in the same way even if the connecting section 25a of the reduction gear section 20 is connected to the locking section (not shown) which implements the parking brake of the drum brake system.

[0048] The locking section 100 can be arranged on the housing cover 40 and selectively positioned so that it is in close contact with the reduction gear section 20 to restrict the rotation of the reduction gear section 20. In other words, to prevent the locking section from being released in the parking brake state, the locking section 100 can be positioned so that it is in close contact with the reduction gear section 20 to restrict the rotation of the reduction gear section 20 by means of friction.

[0049] The locking section 100 can be provided such that it is movable in one axial direction of the reduction gear section 20. The locking section 100 can be inserted between the reduction gear section 20 and an electromagnetic element 120 such that it is in close contact with the side of the reduction gear section 20 and is separated from it by the electromagnetic force of the electromagnetic element 120.

[0050] The locking section 100 can include a locking element 110, which is in close contact with or spaced apart from the reduction gear 20, and the elastic element 130, which elastically supports the locking element 110 so that the locking element 110 is brought into close contact with the side of the reduction gear 20, and the electromagnetic element 120, which moves the locking element 110 away from the reduction gear section 20 by generating an electromagnetic force when current is applied.

[0051] The locking element 110 can comprise a plate 111 provided in a round shape, the first friction element 112 provided on a surface of the plate 111 facing the reduction gear section 20 in such a way that it is in close contact with the reduction gear section 20, and at least one pin 113, one side of which is coupled to the plate 111 and the other side is bound to the housing cover 40 to prevent rotation of the plate 111.

[0052] The plate 111 can be made of a material that can be moved by the electromagnetic force of the electromagnetic element 120, and can, for example, be made of a metal such as steel. Furthermore, the plate 111 can be in a round shape and can have at least one radial extension section 111a at one edge of it. The extension section 111a can be arranged radially, and one end of the pin 113 can be coupled to the extension section 111a.

[0053] One surface of the first friction element 112 is attached to the plate 111, while its other surface is positioned so that it is in close contact with the reduction gear section 20. More precisely, the first friction element 112 can be in close contact with the drive gear 21 or the second friction element 22 when the plate 111 moves, thus limiting the rotation of the reduction gear section 20.

[0054] One end of the pin 113 is fixed to the extension section 111a of the plate 111, and its other end is inserted into the projection 41 provided on the housing cover 40 to prevent the plate 111 from rotating circumferentially. In other words, the pin 113 is fixed to the housing cover 40 in such a way that axial movement of the plate 111 is permitted, but rotational movement of the plate 111 in the circumferential direction is restricted.

[0055] Furthermore, at least one pin 113 can be provided, and each pin 113 can pass through a center point of the elastic element 130 and be inserted into the socket 41. The pin 113 and the elastic element 130 are inserted together into the socket 41, and the elastic element 130 can be supported by the step section 41a of the socket 41.

[0056] The elastic element 130 can elastically support the locking element 110 such that the locking element 110 is brought into close contact with the side of the reduction gear section 20. More precisely, the elastic element 130 can be provided as a helical spring inserted between the housing cover 40 and the locking element 110, through which the pin 113 passes. As a result, one side of the elastic element 130 is supported by the housing cover 40 and its other side by the plate 111, so that the elastic element can elastically support the locking element 111 towards the reduction gear section 20. Accordingly, the locking element 111 and the reduction gear section 20 are in close contact with each other.

[0057] The electromagnetic element 120 can be provided to generate an electromagnetic force when current is applied, thereby separating the locking element 110 from the reduction gear section 20.

[0058] The electromagnetic element 120 can have a core 121, one end of which is fixed to the housing cover 40, while its other side protrudes towards the locking element 111, and a coil 122, which surrounds an outer circumferential surface of the core 121 and generates an electromagnetic force.

[0059] The core 121 is provided in a cylindrical shape, and one end of the core, on the side of the housing cover 40, is designed to expand in a radial direction, thereby fixing it in place so that it does not come loose while inserted into the housing cover 40. The coil 122 can be wound at least several times around an outer circumferential surface of the core 121 and fixed to it.

[0060] The coil 122 can be connected to a power source to generate an electromagnetic force when an electrical signal is applied. The attractive force exerted by this electromagnetic force acts on the plate 111 of the locking element 110, thereby separating the locking element 110 from the reduction gear section 20. In other words, the magnitude of the electromagnetic force generated by the coil 122 when current is applied is greater than that of the elastic force of the elastic element 130, and this electromagnetic force can maintain a constant distance between the locking element 110 and the reduction gear section 20 while the vehicle is in motion.

[0061] The operation of actuator 1 for a parking brake according to one embodiment of the disclosure will be described below.

[0062] Fig. Figure 6 is a sectional view showing the operation of actuator 1 for a parking brake in a locking mode according to one embodiment of the disclosure, and Fig. Figure 7 is a sectional view showing the operation of the actuator for a parking brake when the locking mode is released, according to one embodiment of the disclosure.

[0063] With reference to Fig. 6 and Fig. 7. According to one embodiment of the disclosure, the actuator 1 for a parking brake can operate in a locking mode in which the parking brake state of the vehicle is maintained, and in a locking release mode as a result of the release of the parking brake of the vehicle.

[0064] First, the parking brake actuator 1, in locking mode, receives an electrical signal from an electronic control unit (ECU, not shown). This generates a force through the motor 10, which then transmits the force through the reduction gear section 20 to the locking section (not shown), thus applying the parking brake. Once the parking brake is fully applied, the locking section 100 prevents the reduction gear section 20 from rotating in the direction in which the brake is released, thereby maintaining the braking state.More precisely, when braking is complete, the current applied to the electromagnetic element 120 is removed and the electromagnetic force acting on the locking element 110 is extinguished. At this time, the locking element 110 is elastically supported by the elastic element 130 towards the reduction gear section 20 and is thus in close contact with the reduction gear section 20, preventing it from rotating. When the locking element 110 and the reduction gear section 20 are in close contact, the first friction element 112 provided on the plate 111 is in close contact with the second friction element 22 provided on the drive gear 21 (or the friction coating section of the drive gear), so that rotation of the reduction gear section is prevented by a frictional force.

[0065] When the locking mode is released, the parking brake actuator 1 disconnects the locking section 100 from the reduction gear section 20 to release the parking brake, allowing the reduction gear section 20 to rotate in the brake release direction. More precisely, the ECU applies current to the electromagnetic element 120 to generate an electromagnetic force, and the locking element 110 is therefore separated from the reduction gear section 20 by this electromagnetic force. At this time, the electromagnetic force is greater than the elastic force of the elastic element 130, which elastically supports the locking element 110 towards the reduction gear section 20, thus separating the locking element 110 from the reduction gear section 20. Specifically, the electromagnetic force generated by the coil 122 acts on the plate 111, causing the plate to move towards the housing cover 40.As a result, a gap is created between the first friction element 112 and the second friction element 22, so that no frictional force is generated, thus allowing the rotation of the reduction gear section 20.

[0066] When the locking section 100 is moved to a distance, the motor 10, which receives an electrical signal from the ECU (not shown), generates a force in such a direction as to release the parking brake and transmits the force through the reduction gear section 20, thereby implementing the release of the brake.

[0067] As described above, according to one embodiment of the disclosure, the actuator 1 for a parking brake can prevent the brake from being released while the parking brake is engaged. Furthermore, it is possible to quickly and stably maintain the vehicle's position in the parked state without additional power consumption, since no current is applied to the locking section 100 in the parking mode.

[0068] And since the locking section 100 is set up on the housing cover 40, it is possible to replace only the housing cover 40 when replacing parts or changing the design by removing the housing cover 40, thus improving assembly and design freedom.

[0069] Although, as described above, only a few embodiments of the disclosure have been shown and described, those skilled in the art will understand that modifications can be made to these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.

Claims

[1] Actuator (1) for a parking brake, comprising a motor (10) that generates a force; a reduction gear section (20) designed to transmit the power of the motor (10) to a locking section that implements a parking brake of a vehicle; a housing (30) in which the motor (10) and the reduction gear section (20) are housed; a housing cover (40) having a plurality of holes, thereby closing the housing (30); and a locking section (100) designed to limit the rotation of the reduction gear section (20); the blocking section (100) is further executed by: a locking element (110) which is provided in such a way that it is movable in an axial direction of the reduction gear section (20) and is in close contact with or spaced apart from the reduction gear section (20), an elastic element (130) that elastically supports the locking element (110) towards the reduction gear section (20), and an electromagnetic element (120) designed to separate the locking element (110) from the reduction gear section (20) by generating an electromagnetic force when current is applied, wherein the locking element (110) has a plate (111) which faces the reduction gear section 20, and wherein the locking element (110) has several pins (113), one side of which is coupled to the plate (111) and the other side is received in the respective holes of the housing cover to prevent rotation of the plate (111). [2] Actuator according to claim 1, wherein the locking element a first friction element which is provided on a surface of the plate which faces the reduction gear section and is provided to be brought into close contact with the reduction gear section, exhibits. [3] Actuator (1) according to claim 2, wherein the elastic element (130) is provided as at least one helical spring which is inserted between the housing cover (40) and the plate. [4] Actuator (1) according to claim 1, wherein the at least one pin is arranged radially with respect to a central axis of the plate. [5] Actuator (1) according to claim 1, wherein the housing (30) has at least one projection which protrudes at a position corresponding to the at least one pin and has a recessed hole therein for receiving the at least one pin. [6] Actuator (1) according to claim 1, wherein the electromagnetic element (120) a core, one side of which is coupled to the housing cover (40) and the other side protrudes towards the locking element (110), and a coil wound on an outer circumferential surface of the core to generate an electromagnetic force, exhibits. [7] Actuator (1) according to claim 2, wherein the reduction gear section (20) further comprises a second friction element which is provided on a surface which faces the first friction element. [8] Actuator (1) according to claim 7, wherein the plate, the first friction element, the second friction element and the reduction gear section (20) are provided side by side. [9] Actuator (1) according to claim 2, wherein in the reduction gear section (20) a surface which is facing the first friction element is friction-coated. [10] Actuator (1) according to claim 1, wherein the plate is arranged coaxially with the reduction gear section (20) and is provided in a round shape. [11] Actuator (1) according to claim 10, wherein the at least one pin is coupled to at least one extension section extending radially from an edge of the plate. [12] Actuator (1) according to claim 1, wherein the reduction gear section (20) a drive gear that is linked to a drive shaft of the motor, a sun gear coupled to the drive gear for common rotation, several planet gears meshed with the sun gear, and an external gear that is meshed with the several planetary gears and has a connecting section linked to the locking section, exhibits. [13] Actuator (1) for a parking brake, comprising a motor (10) that generates a force; a reduction gear section (20) coupled to a rotating gear (12) with one end of a drive shaft (11) of the motor (10), which has a drive gear that receives the power from a drive shaft of the motor and transmits the power to a locking section that implements a parking brake of the vehicle; a locking section (100) which is provided such that it is movable up and down from a top of the drive gear, and is provided such that it is brought into close contact with the drive gear in order to restrict rotation of the drive gear, and a housing (30) in which the motor (10) and the reduction gear section (20) are housed; a housing cover (40) with a plurality of holes, thereby closing the housing (30); where the restricted section (100) has: a locking element (110) which is provided in such a way that it is in close contact with the drive gear in order to limit rotation of the drive gear by using a frictional force; an elastic element (130) that elastically supports the locking element (110) towards the reduction gear section (20); and an electromagnetic element (120) configured to separate the locking element (110) from the reduction gear section (20) by generating an electromagnetic force when current is applied, wherein the locking element (110) a record, and a first friction element which is provided on a surface of the plate which is facing the reduction gear section (20) and is provided to be brought into close contact with the reduction gear section (20), exhibits wherein the locking element (110) has a plate (111) which faces the reduction gear section 20, and wherein the locking element (110) has several pins (113), one side of which is coupled to the plate (111) and the other side is received in the respective holes of the housing cover to prevent rotation of the plate (111).

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