Electric brake

Abstract

Provided is an electric brake of reduced size and weight and improved positive efficiency. In the present invention, a braking holding mechanism for a disk brake comprises: a planetary gear that is provided upstream of a rotating internal gear and that is caused to rotate by an electric motor; a planetary carrier that rotatably supports the planetary gear; a clutch mechanism that enables relative rotation between the planetary carrier and a small-diameter shaft part when a parking brake is applied, and disables relative rotation between the planetary carrier and the small-diameter shaft part when the parking brake is released; a roller bearing that enables relative rotation between the planetary gear and the planetary carrier when the parking brake is applied; and a rotating unit that enables relative rotation between the planetary gear and the planetary carrier when the parking brake is released. It is thereby possible to reduce size and weight while improving positive efficiency.

Description

Electric brake

[0001] The present invention relates to an electric brake used for braking a vehicle.

[0002] For example, the disc brake described in Patent Document 1 has a brake holding mechanism for holding a braking position, which includes a rotating member to which the rotational force of an electric motor is transmitted to one end side that penetrates the bottom wall of a cylinder; a linearly-acting member that engages with the other end side of the rotating member and moves linearly with the rotation of the rotating member to move the piston; a bottomed tubular member that is arranged between the rotating member and the bottom wall of the cylinder and has an annular plate portion that faces the bottom wall of the cylinder and a tubular portion that is integrally connected to the outer periphery of the annular plate portion and covers the rotating member; and a clutch mechanism that is arranged between the outer circumferential surface of the rotating member and the inner circumferential surface of the tubular portion and rotates the bottomed tubular member in one direction only when the rotating member rotates in the same direction. After the piston is pressed against the pair of pads by the rotational drive of the electric motor, the bottomed tubular member is clamped between the annular plate portion and the bottom wall of the cylinder so that it cannot rotate due to the reaction force applied to the rotating member, and the clutch mechanism is configured to restrict rotation of the rotating member in the return direction of the piston.

[0003] International Publication No. 2015 / 151618

[0004] In the disc brake described in the above-mentioned Patent Document 1, the brake holding mechanism is located downstream of the reduction mechanism in the rotation transmission path, and the rotational torque from the electric motor is amplified by the reduction mechanism and transmitted to the brake holding mechanism, which may result in the entire brake holding mechanism becoming larger, and ultimately the disc brake becoming larger.

[0005] Furthermore, in the disc brakes of the related art, braking force is self-maintained by a differential planetary gear reduction mechanism when the parking brake is applied, eliminating the need for a parking lock mechanism. However, in order to achieve a reverse efficiency (rotational efficiency in the release direction) of 0% or less, which is necessary for self-maintenance, the normal efficiency (rotational efficiency in the apply direction), which is approximately proportional to the reverse efficiency, must be kept to 50% or less, and currently it is difficult to improve the normal efficiency.

[0006] In view of the above-mentioned problems, an object of the present invention is to provide an electric brake that is small and lightweight while improving the braking efficiency.

[0007] As a means for solving the above problems, the electric brake according to the present invention comprises an electric motor, an input member to which rotation from the electric motor is input, and a reduction mechanism having an output member which reduces the rotation of the input member and outputs the reduced rotation, a brake mechanism which generates a braking force by pressing a braking member against a member to be braked by the rotation from the output member of the reduction mechanism, and a brake holding mechanism which holds the braking force generated by the brake mechanism, wherein, in a rotation transmission path from the electric motor, when the brake mechanism is defined as the downstream side and the electric motor is defined as the upstream side, the brake holding mechanism is provided upstream of the output member, The brake holding mechanism is characterized by comprising a rotating member rotated by the electric motor, a support member that rotatably supports the rotating member, a clutch mechanism that allows the braking member to rotate relative to the corresponding member when the electric motor rotates in a direction that presses the braking member against the braked member and prevents the braking member from rotating relative to the corresponding member when the electric motor rotates in a direction that moves the braking member away from the braked member, a bearing that allows the rotating member and the support member to rotate relative to each other when the clutch mechanism allows the rotating member to rotate relative to the corresponding member, and a rotating part that allows the rotating member and the support member to rotate relative to each other when the clutch mechanism prevents the rotating member from rotating relative to the corresponding member.

[0008] According to the electric brake according to one embodiment of the present invention, it is possible to improve the normal efficiency while realizing a small size and a lightweight design.

[0009] 1 is an external view of a disc brake according to a first embodiment; 2 is a cross-sectional view of the disc brake according to the first embodiment; 3 is an enlarged cross-sectional view of a main part of the disc brake according to FIG. 2; 4 is an enlarged cross-sectional view of a main part of the disc brake according to a second embodiment; 5 is an enlarged cross-sectional view of a main part of the disc brake according to a third embodiment; and 6 is an enlarged cross-sectional view of a main part of the disc brake according to a fourth embodiment.

[0010] This embodiment will be described in detail below with reference to Figures 1 to 6. The electric brake according to this embodiment, specifically the disc brake 1, generates a braking force by driving an electric motor 45 during normal driving. In the following description, the outer side of the vehicle (outer side) will be referred to as one end side (disc rotor D side) and the inner side of the vehicle (inner side) will be referred to as the other end side (cover member 38 side), as appropriate. That is, in Figures 2 to 6, the right side will be referred to as one end side and the left side will be referred to as the other end side, as appropriate.

[0011] First, a disc brake 1A according to a first embodiment will be described in detail with reference to FIGS. 1 to 3. Referring to FIGS. 1 and 2, the disc brake 1A according to the first embodiment is an electric brake including a pair of inner and outer brake pads 2, 3, and a caliper 4, which are arranged on either axial side of a disc rotor D attached to a rotating part (not shown) of a vehicle. The inner and outer brake pads 2, 3 correspond to braking members. The disc rotor D corresponds to a braked member. The disc brake 1A according to the first embodiment is configured as a floating caliper. The pair of inner and outer brake pads 2, 3, and the caliper 4 are supported by a carrier 5 so as to be movable in the axial direction of the disc rotor D. The carrier 5 is fixed to a non-rotating part (not shown), such as a knuckle, of the vehicle, and is disposed so as to straddle the outer periphery of the disc rotor D.

[0012] The carrier 5 includes a pair of pin connecting portions 9, 9 to which slide pins 7, 7 described below are respectively connected, and inner and outer support portions 11, 12 that are integrally connected to the pair of pin connecting portions 9, 9 and that independently support the inner and outer brake pads 2, 3, respectively. The pair of pin connecting portions 9, 9 are arranged at a distance from each other in the rotational direction of the disc rotor D. A pair of cylindrical, bottomed pin sliding portions 15, 15 that protrude radially outward on both sides of the disc rotor D are integrally formed in the cylinder portion 23 of the caliper body 30. The pair of pin sliding portions 15, 15 extend along the axial direction of the disc rotor D.

[0013] A pair of slide pins 7 are axially slidably inserted into the pair of pin sliding portions 15. Each pin sliding portion 15 is disposed on the inner side of the pair of pin connecting portions 9 of the carrier 5. The pair of slide pins 7 are axially slidably inserted into each pin sliding portion 15 from the outer side. Mounting bolts 17 are inserted into through holes 18 of the pin connecting portions 9 and fixed to the slide pins 7. As a result, the slide pins 7 are fixed to the pin connecting portions 9 by the mounting bolts 17. Reference numeral 19 denotes a pin boot having an expandable bellows portion that covers the slide pin 7.

[0014] The caliper body 22, which is the main body of the caliper 4, is arranged at the base end side facing the inner brake pad 2 and is equipped with a cylindrical cylinder portion 23 that opens facing the inner brake pad 2, a pair of claw portions 24, 24 that extend from the cylinder portion 23 to the outer side across the disc rotor D and are arranged at the tip side facing the outer brake pad 3 on the outer side, and a pair of pin sliding portions 15, 15 that protrude from the cylinder portion 23 radially outward on both sides of the disc rotor D.

[0015] A piston 30 is housed in the cylinder portion 23 of the caliper body 22, i.e., in the cylinder bore 26 of the cylinder portion 23, so as to be non-rotatable relative to the cylinder portion 23 but movable in the axial direction. The piston 30 presses against the inner brake pad 2 and is formed in a cup shape with a bottom. The piston 30 is housed in the cylinder bore 26 of the cylinder portion 23 so that its bottom faces the inner brake pad 2. A seal member (not shown) is arranged on the inner circumferential surface on the other end side of the cylinder bore 26 of the cylinder portion 23. The piston 30 is housed in the cylinder bore 26 so as to be movable in the axial direction while in contact with this seal member.

[0016] A dust boot 34 is interposed between the outer peripheral surface of the bottom side of the piston 30 and one end side of the cylinder portion 23. These sealing members and the dust boot 34 prevent foreign matter from entering the cylinder bore 26 of the cylinder portion 23. A housing 36 is attached to the bottom of the cylinder portion 23 of the caliper body 22. The open portion on the other end of the housing 36 is airtightly closed by a cover member 38. The interior of the housing 36 is kept airtight. The housing 36 includes a first housing portion 41 that covers the outer periphery of the bottom of the cylinder portion 23 and houses a reduction mechanism 46 (described later), and a second housing portion 42 that is integrally connected to and aligned with the first housing portion 41 and houses an electric motor 45 (described later).

[0017] 2 , the caliper body 22 is equipped with an electric motor 45, a reduction mechanism 46 having a pinion gear 71 to which rotation from the electric motor 45 is input and a rotary internal gear 85 that reduces the rotation of the pinion gear 71 and outputs the reduced rotation, a brake mechanism 47 that generates a braking force by pressing the piston 30 against the inner brake pad 2 using the rotation from the rotary internal gear 85 of the reduction mechanism 46, and a brake holding mechanism 48 that holds the braking force generated by the brake mechanism 47. The pinion gear 71 corresponds to the input member, while the rotary internal gear 85 corresponds to the output member. The electric motor 45 is a brushless DC motor including a rotor body 53 (permanent magnet), a stator 54, etc. However, other known motors, such as a brushed DC motor, may also be used as the electric motor 45.

[0018] As described above, the electric motor 45 is accommodated in the second housing portion 42 of the housing 36. The rotating shaft 50 extending from the rotor main body 53 of the electric motor 45 toward one end is rotatably supported in an accommodating recess 57 provided in the second housing portion 42 via a rolling bearing 58. Meanwhile, the rotating shaft 50 extending from the rotor main body 53 toward the other end is rotatably supported in a through hole 60 provided in the second housing portion 42 via the rolling bearing 58, and extends toward the other end. Referring to FIG. 1 , an electronic control unit (ECU) 63 for controlling the rotation of the electric motor 45 is electrically connected to the electric motor 45. During braking during normal driving, the electronic control unit (ECU) 63 controls the driving of the electric motor 45 based on detection signals from a detection sensor (not shown) corresponding to a driver's request, various detection sensors (not shown) that detect various situations requiring braking, and the like, as well as detection signals from a rotation angle detection means (not shown) for the electric motor 45 and a thrust sensor (not shown). A parking switch 64 that is operated to turn the parking brake on and off is electrically connected to the electronic control unit (ECU) 63. The electronic control unit 63 can also activate the parking brake based on a signal from the vehicle side, without operating the parking switch 64.

[0019] Referring to FIG. 2 , the reduction mechanism 46 is composed of a multi-stage gear reduction mechanism 67 composed of spur gears or helical gears, and a differential planetary gear reduction mechanism 68. The multi-stage gear reduction mechanism 67 is housed in the first housing portion 41 of the housing 36. The multi-stage gear reduction mechanism 67 includes a pinion gear 71 and a reduction gear 72. The pinion gear 71 is cylindrical and press-fitted onto the rotary shaft 50 of the electric motor 45. The pinion gear 71 and the reduction gear 72 are composed of, for example, a sintered or forged metal member, or a resin-molded member. The reduction gear 72 has a shaft hole 74 extending axially through its radial center. A gear shaft 77 is inserted into the shaft hole 74 of the reduction gear 72. One end of the gear shaft 77 is integrally fixed to a wall portion of the first housing portion 41 adjacent to the second housing portion 42. As a result, the reduction gear 72 is rotatably supported by the gear shaft 77. The reduction gear 72 is configured by integrally connecting a large-diameter gear 79 that meshes with the pinion gear 71 and a small-diameter shaft gear 80 that extends concentrically from the large gear 79 to the other end thereof. The small-diameter shaft gear 80 of the reduction gear 72 meshes with the differential planetary gear reduction mechanism 68.

[0020] The differential planetary gear reduction mechanism 68 has a reverse efficiency set to 0 or less so that it can maintain a braking state even when a reaction force against the pressing force from the disc rotor D acts via the piston 30 during braking. As a result, a parking lock mechanism for holding the piston 30 in the braking position is not required. With reference to FIGS. 2 and 3 , the differential planetary gear reduction mechanism 68 is housed in the first housing portion 41 of the housing 36. The differential planetary gear reduction mechanism 68 includes a sun gear 82, a plurality of planetary gears 83, a fixed internal gear 84, and a rotating internal gear 85. The sun gear 82, the plurality of planetary gears 83, the fixed internal gear 84, and the rotating internal gear 85 are made of, for example, sintered or forged metal members, or molded resin members.

[0021] The sun gear 82, the fixed internal gear 84, and the rotating internal gear 85 are arranged concentrically with one another. A support hole 88 penetrates the sun gear 82 at its radial center. The other end of a spindle 120 of the brake mechanism 47, which will be described later, is inserted into this support hole 88. The sun gear 82 is rotatably supported by the spindle 120. The sun gear 82 is composed of a large-diameter gear wheel 90 that meshes with the small-diameter gear wheel 80 of the reduction gear 72, and a small-diameter gear wheel 91 that extends axially and concentrically from the large gear wheel 90. The small-diameter gear wheel 91 extends toward one end. Each planetary gear 83 meshes with this small-diameter gear wheel 91.

[0022] The planetary gear 83 is formed in a cylindrical shape and includes a gear portion 93 that meshes with the small-diameter shaft gear 91 of the sun gear 82, the internal teeth 84A of the fixed internal gear 84, and the internal teeth 85A of the rotating internal gear 85, and a hole portion 94 through which the large-diameter shaft portion 112 of the support shaft 110, which will be described later, is inserted. A plurality of planetary gears 83 are arranged at equal intervals around the small-diameter shaft gear 91 of the sun gear 82. In this embodiment, four planetary gears 83 are arranged. The fixed internal gear 84 is supported in a non-rotatable manner relative to the first housing portion 41 of the housing 36. Internal teeth 84A are formed on one end of the fixed internal gear 84. An annular stopper portion 100 that protrudes inward is integrally formed on the other end of the fixed internal gear 84, spaced from the internal teeth 84A toward the other end. The other end of each planetary gear 83 meshes with the internal teeth 84A of the fixed internal gear 84. A rotating internal gear 85 is disposed on one end of the fixed internal gear 84.

[0023] The rotating internal gear 85 is rotatably supported by the first housing portion 41 of the housing 36. Internal teeth 85A are formed on the other end of the rotating internal gear 85. One end of each planetary gear 83 meshes with the internal teeth 85A of the rotating internal gear 85. An annular stopper portion 101 is formed integrally with one end of the rotating internal gear 85, protruding inward and spaced apart from the internal teeth 85A toward the one end. A cylindrical rotating portion 103 protruding toward the one end is integrally connected to the inside of the annular stopper portion 101. The inner circumferential surface of the cylindrical rotating portion 103 of the rotating internal gear 85 and the outer circumferential surface of a spindle 120 of the brake mechanism 47 (described later) are engaged, for example by spline engagement, so as to be unable to rotate relative to each other.

[0024] The number of teeth on the internal teeth 84A of the fixed internal gear 84 is different from the number of teeth on the internal teeth 85A of the rotating internal gear 85. For example, in this embodiment, the number of teeth on the internal teeth 84A of the fixed internal gear 84 is fewer than the number of teeth on the internal teeth 85A of the rotating internal gear 85, with the difference in the number of teeth being four. When the rotating shaft 50 of the electric motor 45 rotates, the sun gear 82 of the differential planetary gear reduction mechanism 68 rotates via the pinion gear 71 and reduction gear 72 of the multi-stage gear reduction mechanism 67. This rotation of the sun gear 82 causes each planetary gear 83 to rotate about its own axis while revolving around the axis of the sun gear 82, thereby rotating the rotating internal gear 85. In other words, because the number of teeth on the rotating internal gear 85 is slightly different from that of the fixed internal gear 84, the rotating internal gear 85 rotates slightly by the difference in the number of teeth, thereby achieving a large reduction ratio (paradox planetary gear reduction mechanism). The rotation from this rotating internal gear 85 is transmitted to the spindle 120. In this embodiment, the differential planetary gear reduction mechanism 68 is configured as a paradox planetary gear reduction mechanism, but the planetary gear 83 may be configured as a stepped gear with a variable number of teeth.

[0025] 2 and 3 , the brake holding mechanism 48 is provided in the differential planetary gear reduction mechanism 68. The brake holding mechanism 48 includes a plurality of planetary gears 83, a planetary carrier 106 that supports each planetary gear 83 rotatably about its own axis and rotatably about the axis of the sun gear 82, and a clutch mechanism 107 that allows relative rotation between the planetary carrier 106 and a small diameter shaft portion 113 (described later) when the electric motor 45 rotates in the apply direction, i.e., in the direction that presses the inner and outer brake pads 2, 3 against the disc rotor D, and prevents relative rotation between the planetary carrier 106 and the small diameter shaft portion 113 (described later) when the electric motor 45 rotates in the release direction, i.e., in the direction that separates the inner and outer brake pads 2, 3 from the disc rotor D. Note that each planetary gear 83 corresponds to a rotating member, and the planetary carrier 106 corresponds to a support member.

[0026] A pair of planetary carriers 106, 106 are disposed at both axial ends of each planetary gear 83, 83. The planetary carrier 106 is formed in the shape of an annular plate. The planetary carrier 106 has a plurality of holes 116 corresponding to each planetary gear 83. The holes 116 are formed at intervals in the circumferential direction to correspond to each planetary gear 83. In this embodiment, four holes 116 are formed, corresponding to the number of planetary gears 83. The small-diameter shaft gear portion 91 of the sun gear 82 is inserted inside the pair of planetary carriers 106, 106. The pair of planetary carriers 106, 106 are integrally connected by a plurality of bridges (not shown). A plurality of such bridges are disposed at intervals between each planetary gear 83, 83, i.e., along the circumferential direction of the planetary carrier 106. In this embodiment, four bridges are provided, corresponding to the number of spaces between the planetary gears 83, 83.

[0027] The planetary carrier 106 located at one end is disposed between each planetary gear 83 and the annular stopper portion 101 of the rotating internal gear 85, and its axial movement is restricted. On the other hand, the planetary carrier 106 located at the other end is disposed between each planetary gear 83 and the annular stopper portion 100 of the fixed internal gear 84, and its axial movement is restricted. Each planetary gear 83 is supported by a pair of planetary carriers 106, 106 via a respective support shaft 110 so as to be rotatable about its own axis and about the axis of the sun gear 82. The support shaft 110 is composed of a large-diameter shaft portion 112 located axially intermediate, and a pair of small-diameter shaft portions 113, 113 extending axially from both axial end faces of the large-diameter shaft portion 112.

[0028] The large diameter shaft portion 112 of the support shaft 110 is inserted into the hole 94 of the planetary gear 83. The outer peripheral surface of this large diameter shaft portion 112 and the inner peripheral surface of the hole 94 of the planetary gear 83 act as a rotating portion 97. In other words, when a clutch mechanism 107 (described later) disables relative rotation between the planetary carrier 106 located at the other end and the small diameter shaft portion 113 (at the time of release), this rotating portion 97 enables relative rotation between the planetary carrier 106 and the planetary gear 83 (about rotation around the axis of the planetary gear 83 itself). Note that, although the planetary gear 83 is directly supported by the large diameter shaft portion 112 in this embodiment, it may also be supported via a known bearing such as a bushing.

[0029] The pair of small diameter shaft portions 113, 113 are inserted into the hole portions 116, 116 of the pair of planetary carriers 106, 106, respectively. A clutch mechanism 107 is arranged between the inner peripheral surface of one end side of the hole portion 116 of the planetary carrier 106 located on the other end side and the outer peripheral surface of one end side of the small diameter shaft portion 113. In addition, a rolling bearing 118 is arranged between the inner peripheral surface of the other end side of the hole portion 116 of the planetary carrier 106 located on the other end side and the outer peripheral surface of the other end side of the small diameter shaft portion 113. In other words, between the hole portion 116 of the planetary carrier 106 located on the other end side and the small diameter shaft portion 113, the clutch mechanism 107 is arranged closer to the one end side than the rolling bearing 118. A rolling bearing 118 is also arranged between the inner peripheral surface of the planetary carrier 106 located on the one end side and the outer peripheral surface of the small diameter shaft portion 113.

[0030] The pair of planetary carriers 106, 106 and the pair of small diameter shaft portions 113, 113 are rotatable relative to each other via rolling bearings 118, 118, but any bearing element with sufficiently small rotational resistance may be used, and other known technologies such as journal bearings may be used. When the clutch mechanism 107, which will be described later, allows relative rotation with respect to the planetary carrier 106 located at the other end and the small diameter shaft portion 113 (when applied), these rolling bearings 118 allow the planetary carrier 106 and planetary gear 83 to rotate relative to each other (rotation about the axis of the planetary gear 83 itself).

[0031] The clutch mechanism 107 is a so-called one-way clutch that allows relative rotation between two corresponding members in one direction (i.e., when one member rotates, the other member rotates freely, allowing relative rotation between them), but restricts relative rotation in the other direction (i.e., the two corresponding members transmit rotational torque to each other, preventing relative rotation). A coil spring clutch, a cam clutch, or the like may be used as the clutch mechanism 107. In this embodiment, when the electric motor 45 rotates in the apply direction, i.e., in a direction that presses the inner and outer brake pads 2, 3 against the disc rotor D, the clutch mechanism 107 allows relative rotation between the planetary carrier 106 located at the other end and the small diameter shaft portion 113. On the other hand, when the electric motor 45 rotates in the release direction, i.e., in a direction that separates the inner and outer brake pads 2, 3 from the disc rotor D, the clutch mechanism 107 prohibits relative rotation between the planetary carrier 106 located at the other end and the small diameter shaft portion 113.

[0032] When the planetary gear 83 rotates in the apply direction (rotates in the apply direction around its own axis), the rotational resistance of the rotating part 97 between the outer circumferential surface of the large diameter shaft part 112 of the support shaft 110 and the inner circumferential surface of the hole 94 of the planetary gear 83 is greater than the sum of the rotational resistance when the clutch mechanism 107 runs idle and the rotational resistance of the small diameter shaft part 113 (outer circumferential surface) of the hole part 116 (inner circumferential surface) of the planetary carrier 106 via the rolling bearings 118. Therefore, when the planetary gear 83 rotates in the apply direction (rotates in the apply direction around its own axis), the clutch mechanism 107 causes the planetary carrier 106 and the small diameter shaft part 113, located at the other end, to rotate relatively, while the action of the rolling bearings 118 reduces the rotational resistance of the planetary gear 83 with respect to the planetary carrier 106.

[0033] On the other hand, with respect to rotation of the rotating internal gear 85 in the release direction (rotation in the release direction about the axis of the planetary gear 83 itself), the clutch mechanism 107 prevents the planetary carrier 106 located at the other end from rotating relatively to the small diameter shaft portion 113, and the rotational resistance of the rotating portion 97 between the hole portion 94 of the planetary gear 83 and the large diameter shaft portion 112 increases, so the rotational resistance of the planetary gear 83 relative to the planetary carrier 106 increases. Note that in this embodiment, the brake holding mechanism 48 is provided for all of the planetary gears 83 (four planetary gears), but it may be provided for one to three planetary gears 83.

[0034] The brake mechanism 47 is configured as a rotary-to-linear motion conversion mechanism having reverse operation capability that is activated by a reaction force from the brake mechanism 47. That is, referring to Fig. 2, the brake mechanism 47 converts the rotational motion from the electric motor 45 and the speed reduction mechanism 72 (the multi-stage gear reduction mechanism 67 and the differential planetary gear reduction mechanism 68), i.e., the rotational motion transmitted from the rotating internal gear 85 of the differential planetary gear reduction mechanism 68 to the spindle 120, into linear motion relative to the linearly moving member 121, and the movement of the linearly moving member 121 imparts thrust to the piston 30, thereby propelling the piston 30 (moving it toward one end). The spindle 120 is rotatably supported by the cylinder portion 23, and one end of the spindle 120 is disposed within the cylinder bore 26.

[0035] 2 , a portion of the spindle 120 that protrudes from the support hole 88 of the sun gear 82 of the differential planetary gear reduction mechanism 68 toward one end is engaged with the cylindrical rotating portion 103 of the rotating internal gear 85 so as to be unable to rotate relative to each other. This enables rotational torque to be transmitted between the rotating internal gear 85 and the spindle 120. A brake mechanism 47 including one end of the spindle 120 is disposed within the cylinder bore 26, between the bottom surface of the spindle 120 and the piston 30. When the spindle 120 rotates in conjunction with the rotation of the rotating internal gear 85 of the differential planetary gear reduction mechanism 68, the brake mechanism 47 acts to move the linearly acting member 121 forward toward the one end, thereby moving the piston 30 forward. The piston 30 presses the inner brake pad 2 against the disc rotor D, thereby generating a braking force for the vehicle.

[0036] Next, the operation of the disc brake 1A according to the first embodiment will be described. First, the operation of braking and brake release during normal driving will be described. During braking during normal driving, such as when the driver depresses the brake pedal, the electric motor 45 is rotated in the forward direction, i.e., the apply direction, by a command from the electronic control unit 63, and the sun gear 82 of the differential planetary gear reduction mechanism 68 is rotated via the multi-stage gear reduction mechanism 67. The rotation of the sun gear 82 causes each planetary gear 83 to rotate about its own axis while revolving around the axis of the sun gear 82, thereby rotating the rotating internal gear 85. The rotation from the rotating internal gear 85 is then transmitted to the spindle 120. When the spindle 120 rotates in response to the operation of the differential planetary gear reduction mechanism 68, the brake mechanism 47 acts to advance the linearly acting member 121, thereby advancing the piston 30. The advance of the piston 30 presses the inner brake pad 2 against the disc rotor D. Then, due to a reaction force against the pressing force of the piston 30 on the inner brake pad 2, the caliper body 22 moves inward (to the left in FIG. 2 ) relative to the carrier 5, and the claws 24, 24 press the outer brake pad 3 against the disc rotor D. As a result, the disc rotor D is sandwiched between the pair of inner and outer brake pads 2, 3, generating a frictional force, which in turn generates a braking force for the vehicle.

[0037] On the other hand, when the driver releases the brake pedal or the like to release the brake, the electric motor 45 rotates in the reverse direction, i.e., the release direction, in response to a command from the electronic control unit 63, and the rotation in the reverse direction is transmitted to the spindle 120 via the multi-stage gear reduction mechanism 67 and the differential planetary gear reduction mechanism 68. Then, as the spindle 120 rotates in the reverse direction, the brake mechanism 47 operates to move the linearly moving member 121 backward to return to its initial state, and the braking force applied to the disc rotor D by the pair of inner and outer brake pads 2, 3 is released.

[0038] Next, the parking brake function, which is one example of the function for maintaining the vehicle in a stopped state, will be described. First, when the parking switch 64 is operated to apply the parking brake from a released state, the electric motor 45 is rotated in the forward direction, i.e., the apply direction, by a command from the electronic control unit 63, and the sun gear 82 of the differential planetary gear reduction mechanism 68 is rotated via the multi-stage gear reduction mechanism 67. This rotation of the sun gear 82 causes each planetary gear 83 to rotate about its own axis while revolving about the axis of the sun gear 82, thereby rotating the rotating internal gear 85. The rotation from the rotating internal gear 85 is then transmitted to the spindle 120.

[0039] Therefore, when rotation in the apply direction from the electric motor 45 is transmitted to the differential planetary gear reduction mechanism 68 via the multi-stage gear reduction mechanism 67, the clutch mechanism 107 causes the planetary carrier 106 located on the other end side and the small diameter shaft portion 113 to rotate relative to each other, while the action of the rolling bearings 118, 118 reduces the rotational resistance of the planetary gear 83 (rotation about the axis of the planetary gear 83 itself) relative to the planetary carrier 106. As a result, even if a reaction force of the pressing force from the disc rotor D acts via the piston 30 during braking, the normal efficiency (rotational efficiency in the apply direction), which is approximately proportional to the reverse efficiency, can be improved to 50% or more.

[0040] Next, when the spindle 120 rotates in accordance with the operation of the differential planetary gear reduction mechanism 68, the brake mechanism 47 acts to move the linearly acting member 121 forward, thereby advancing the piston 30. As the piston 30 moves forward, it presses the inner brake pad 2 against the disc rotor D. Then, due to a reaction force against the pressing force of the piston 30 against the inner brake pad 2, the caliper body 22 moves inward relative to the carrier 5 (to the left in FIG. 2 ), and the claws 24 press the outer brake pad 3 against the disc rotor D.

[0041] As a result, the disc rotor D is sandwiched between the pair of inner and outer brake pads 2, 3, generating a frictional force, which in turn generates a braking force for the vehicle, thereby maintaining the braking state. The electronic control unit 63 drives the electric motor 45 until the pressing force from the pair of inner and outer brake pads 2, 3 onto the disc rotor D reaches a predetermined value, for example, until the current value of the electric motor 45 reaches a predetermined value. Thereafter, when the electronic control unit 63 detects that the pressing force onto the disc rotor D has reached the predetermined value by detecting that the current value of the electric motor 45 has reached the predetermined value, the electronic control unit 63 stops the supply of electricity to the electric motor 45. Alternatively, the brake mechanism 47 may be provided with a sensor that detects the pressing force onto the disc rotor D, and the supply of electricity to the electric motor 45 may be stopped based on the pressing force detected by the sensor.

[0042] In the differential planetary gear reduction mechanism 68, the reverse efficiency is set to 0 or less so that the braked state can be maintained even if a reaction force of the pressing force from the disc rotor D acts via the piston 30 during braking. Moreover, the brake holding mechanism 48 causes the reaction force of the pressing force from the disc rotor D to act via the piston 30, and even when the rotating internal gear 85 rotates in the release direction, the clutch mechanism 107 prevents the planetary carrier 106 located at the other end from rotating relatively to the small diameter shaft portion 113. This increases the rotational resistance of the rotating portion 97 between the hole 94 of the planetary gear 83 and the large diameter shaft portion 112, and therefore increases the rotational resistance of the planetary gear 83 (rotation about the axis of the planetary gear 83 itself) relative to the planetary carrier 106. As a result, the braked state can be reliably maintained.

[0043] On the other hand, when the brake is released, the electric motor 45 rotates in the reverse direction, i.e., the release direction, in response to a command from the electronic control unit 63, and the rotation in the reverse direction is transmitted to the spindle 120 via the multi-stage gear reduction mechanism 67 and the differential planetary gear reduction mechanism 68. That is, in the differential planetary gear reduction mechanism 68, the planetary gears 83 rotate in the reverse direction (spin in the reverse direction) while rotating relative to the large diameter shaft portions 112 of the support shafts 110, thereby transmitting the reverse rotation of the rotating internal gear 85 to the spindle 120. As a result, as the spindle 120 rotates in the reverse direction, the brake mechanism 47 acts to move the linearly moving member 121 backward to return to its initial state, and the braking force applied to the disc rotor D by the pair of inner and outer brake pads 2, 3 is released.

[0044] As described above, the disc brake 1A according to the first embodiment includes the brake holding mechanism 48 that holds the braking force generated by the brake mechanism 47, and the brake holding mechanism 48 includes the planetary gears 83 that are rotated by the electric motor 45, the planetary carrier 106 that rotatably supports the planetary gears 83, and the planetary carrier 106 that is rotatable relative to the corresponding members (the planetary carrier 106 and the small diameter shaft portion 113 in the first embodiment) when the electric motor 45 rotates in the apply direction, and the corresponding members (the planetary carrier 106 and the small diameter shaft portion 113 in the first embodiment) when the electric motor 45 rotates in the release direction. The planetary gear 83 is provided with a clutch mechanism 107 that prevents the planetary gear 83 from rotating relative to the corresponding member (planetary carrier 106 and small diameter shaft portion 113 in the first embodiment), a rolling bearing 118 that allows the planetary gear 83 and planetary carrier 106 to rotate relative to each other when the clutch mechanism 107 allows the planetary gear 83 to rotate relative to the corresponding member (planetary carrier 106 and small diameter shaft portion 113 in the first embodiment), and a rotating portion 97 that allows the planetary gear 83 and planetary carrier 106 to rotate relative to each other when the clutch mechanism 107 prevents the planetary gear 83 from rotating relative to the corresponding member (planetary carrier 106 and small diameter shaft portion 113 in the first embodiment), thereby achieving the above-mentioned effect.

[0045] This eliminates the need for a parking lock mechanism, enabling reductions in size, weight, and cost. Furthermore, in the disc brake 1A according to the first embodiment, the reverse efficiency is set to 0% or less so that the braked state can be maintained even when a reaction force from the pressing force of the disc rotor D acts via the piston 30 during braking. However, the forward efficiency, which is generally proportional to the reverse efficiency, can be improved to 50% or more. Furthermore, by locating the brake holding mechanism 48 upstream of the rotary internal gear 85 of the reduction mechanism 46 in the rotation transmission path, the load torque on the clutch mechanism 107 can be reduced compared to locating the brake holding mechanism 48 downstream of the rotary internal gear 85 (see Patent Document 1). This allows for the use of a compact clutch mechanism 107, thereby preventing the disc brake 1A itself from becoming larger. Furthermore, since the clutch mechanism 107 can be operated without being forcibly released when the parking brake is released, the generation of abnormal noise (such as stick-slip) during operation can also be suppressed.

[0046] Furthermore, in the disc brake 1A according to the first embodiment, the rolling bearing 118 reduces the rotational resistance of the planetary gears 83 relative to the planetary carrier 106 when the clutch mechanism 107 allows relative rotation with respect to the corresponding members (the planetary carrier 106 and the small diameter shaft portion 113 in the first embodiment) when the parking brake is applied. Furthermore, the rotating portion 97 increases the rotational resistance of the planetary gears 83 relative to the planetary carrier 106 when the clutch mechanism 107 prevents relative rotation with respect to the corresponding members (the planetary carrier 106 and the small diameter shaft portion 113 in the first embodiment) even when a reaction force of the pressing force from the disc rotor D acts via the piston 30 during braking. As a result, the rolling bearing 118 can further reduce the rotational resistance of the planetary gears 83 relative to the planetary carrier 106 when the parking brake is applied. On the other hand, when a reaction force against the pressing force from the disc rotor D acts during braking, the rotational resistance of the planetary gear 83 relative to the planetary carrier 106 can be increased by the rotating portion 97 .

[0047] Furthermore, in the disc brake 1A according to the first embodiment, the planetary gear 83 is supported by the planetary carrier 106 via the support shaft 110, the rolling bearing 118 and the clutch mechanism 107 are disposed between the inner circumferential surface of the hole 116 of the planetary carrier 106 and the outer circumferential surface of the small-diameter shaft portion 113 of the support shaft 110, and the rotating portion 97 is provided between the inner circumferential surface of the hole 94 of the planetary gear 83 and the outer circumferential surface of the large-diameter shaft portion 112 of the support shaft 110. That is, the rolling bearing 118 is provided around the axis of the small-diameter shaft portion 113, while the rotating portion 97 is provided around the axis of the large-diameter shaft portion 112. This can further reduce the rotational resistance of the rolling bearing 118 when the parking brake is applied. On the other hand, it can further increase the rotational resistance of the rotating portion 97 when a reaction force of the pressing force from the disc rotor D acts during braking.

[0048] Furthermore, in the disc brake 1A according to the first embodiment, the difference between forward and reverse efficiency during braking can be made larger by providing the brake holding mechanism 48 to the differential planetary gear reduction mechanism 68, which in principle is greatly affected by the rotational resistance between the planetary gear 83 and the large diameter shaft portion 112, and it is possible to achieve both improved reliability in maintaining braking force (reduced reverse efficiency) and improved forward efficiency during application.

[0049] Furthermore, when a cam-type clutch is used for the clutch mechanism 107 of the disc brake 1A according to the first embodiment, the idling torque of the clutch mechanism 107 generated when the braking force is increased when the parking brake is applied is small, and the normal efficiency can be further improved. Also, when a coil spring-type clutch is used for the clutch mechanism 107, costs can be reduced.

[0050] Next, a disc brake 1B according to a second embodiment will be described with reference to FIG. 4 . In this description, only the differences from the disc brake 1A according to the first embodiment will be described. To describe the brake holding mechanism 48 of the disc brake 1B according to the second embodiment in detail, each planetary gear 83 and the pair of planetary carriers 106 are rotatably supported by a support shaft 123. In other words, each planetary gear 83 is supported by the pair of planetary carriers 106 via the support shaft 123 so as to be rotatable about its own axis and about the axis of the sun gear 82. A clutch mechanism 107 and a pair of rolling bearings 118 are respectively provided between the inner circumferential surface of the hole 94 of the planetary gear 83 and the outer circumferential surface of the support shaft 123. The pair of rolling bearings 118 are respectively disposed on both axial sides of the clutch mechanism 107.

[0051] In the disc brake 1B according to the second embodiment, the inner circumferential surfaces of the holes 116, 116 of the pair of planetary carriers 106, 106 and the outer circumferential surface of the support shaft 123 act as rotating parts 97, 97, respectively. Note that, in the disc brake 1B according to the second embodiment, as in the disc brake 1A according to the first embodiment, the planetary gear 83 corresponds to the rotating member, and the planetary carrier 106 corresponds to the support member. In the disc brake 1B according to the second embodiment, the members corresponding to the clutch mechanism 107 are the planetary gear 83 and the support shaft 123. Note that in the disc brake 1B according to the second embodiment, the sun gear 82 is rotatably supported by a gear shaft 122. The other end of the gear shaft 122 is integrally fixed to the cover member 38.

[0052] When each planetary gear 83 rotates in the apply direction, the clutch mechanism 107 allows the planetary gear 83 and the support shaft 123 to rotate relative to each other, while the action of the rolling bearings 118 reduces the rotational resistance of the planetary gear 83 with respect to the planetary carrier 106. On the other hand, with respect to rotation of the rotatable internal gear 85 in the release direction, the clutch mechanism 107 prevents the planetary gear 83 and the support shaft 123 from rotating relative to each other, and the rotational resistance of the rotating parts 97 between the holes 116 of the pair of planetary carriers 106 and the support shaft 123 increases, so the rotational resistance of the planetary gear 83 with respect to the planetary carriers 106 increases.

[0053] As a result, the disc brake 1B according to the second embodiment can also achieve the same effects as the disc brake 1A according to the first embodiment. Moreover, in the disc brake 1B according to the second embodiment, the clutch mechanism 107 and the pair of rolling bearings 118, 118 are arranged inside the planetary gear 83, so that the disc rotor D can be made smaller in size along the axial direction.

[0054] Next, a disc brake 1C according to a third embodiment will be described with reference to FIG. 5 . This description will focus on differences from the disc brake 1A according to the first embodiment. In the disc brake 1C according to the third embodiment, a brake holding mechanism 48 is provided in the multi-stage gear reduction mechanism 67, upstream of the rotary internal gear 85 of the differential planetary gear reduction mechanism 68 in the rotation transmission path. Specifically, the brake holding mechanism 48 includes a clutch mechanism 107 and a pair of rolling bearings 118, 118, which are provided between the inner circumferential surface of the shaft hole 74 of the reduction gear 72, which is a component of the multi-stage gear reduction mechanism 67, and the outer circumferential surface of the gear shaft 77. The pair of rolling bearings 118, 118 are disposed on both axial sides of the clutch mechanism 107. In the disc brake 1C according to the third embodiment, the small-diameter shaft gear 80 of the reduction gear 72 extends from the large gear 79 toward one end. One end of the gear shaft 77 is rotatably supported in a support recess 125 provided in a wall portion of the first housing portion 41 adjacent to the second housing portion 42, while the other end of the gear shaft 77 is rotatably supported in a support recess 124 of the cover member 38.

[0055] In the disc brake 1C according to the third embodiment, the area between the outer peripheral surface of one end of the gear shaft 77 and the inner peripheral surface of the support recess 125 of the first housing part 41, and the area between the outer peripheral surface of the other end of the gear shaft 77 and the inner peripheral surface of the support recess 124 of the cover member 38, respectively, act as rotating parts 97, 97. In the disc brake 1C according to the third embodiment, the reduction gear 72 corresponds to the rotating member. Furthermore, the cover member 38 and the first housing part 41 correspond to the support members. The reduction gear 72 and the gear shaft 77 are the components that correspond to the clutch mechanism 107.

[0056] When the reduction gear 72 rotates in the apply direction, the clutch mechanism 107 allows the reduction gear 72 and the gear shaft 77 to rotate relative to each other, while the action of the rolling bearings 118, 118 reduces the rotational resistance of the reduction gear 72 with respect to the cover member 38 and the first housing part 41 (wall part). On the other hand, with respect to the rotation of the rotatable internal gear 85 in the release direction, the clutch mechanism 107 prevents the reduction gear 72 and the gear shaft 77 from rotating relative to each other, and the rotational resistance of the rotating parts 97, 97 between the gear shaft 77 and the support recesses 124, 125 of the cover member 38 and the first housing part 41 increases, so the rotational resistance of the reduction gear 72 with respect to the cover member 38 and the first housing part 41 increases.

[0057] It is to be noted that plain bearings may be provided between one end of the gear shaft 77 and the support recess 125 of the first housing part 41, and between the other end of the gear shaft 77 and the support recess 124 of the cover member 38. The rolling bearing 118 reduces the mutual rotational resistance more than the plain bearing. The disc brake 1C according to the third embodiment can also achieve the same effects as the disc brake 1A according to the first embodiment. Moreover, in the disc brake 1C according to the third embodiment, the clutch mechanism 107 and the pair of rolling bearings 118, 118 are provided inside the reduction gear 72, so that the disc rotor D can be made smaller in size along the axial direction.

[0058] Next, a disc brake 1D according to a fourth embodiment will be described with reference to FIG. 6 . This description will focus on only the differences from the disc brake 1A according to the first embodiment. In the disc brake 1D according to the fourth embodiment, a brake holding mechanism 48 is provided upstream of the rotating internal gear 85 of the differential planetary gear reduction mechanism 68, in the electric motor 45 and the second housing portion 42 of the housing 36 that accommodates the electric motor 45. To explain the brake holding mechanism 48 in more detail, a support recess 130 is formed in the rotor body 53 of the electric motor 45, with one end surface thereof open. A first rotating shaft 51 is rotatably accommodated and supported in the support recess 130. The first rotating shaft 51 is composed of a first large-diameter rotating shaft portion 133 rotatably supported in the support recess 130 and a first small-diameter rotating shaft portion 134 extending from the first large-diameter rotating shaft portion 133 toward one end.

[0059] The first small diameter rotating shaft portion 134 is rotatably supported in an accommodating recess 57 provided in the second housing portion 42. A clutch mechanism 107 and a rolling bearing 118 are provided between the outer peripheral surface of the first small diameter rotating shaft portion 134 and the inner peripheral surface of the accommodating recess 57. The rolling bearing 118 is disposed closer to one end than the clutch mechanism 107. A second rotating shaft 52 extends integrally with the electric motor 45 from the rotor main body portion 53 toward the other end. The second rotating shaft 52 is inserted through a through hole 60 provided in the second housing portion 42 via the rolling bearing 58. In the disc brake 1D according to the fourth embodiment, the space between the inner peripheral surface of the support recess 130 of the rotor main body portion 53 and the outer peripheral surface of the first large diameter rotating shaft portion 133 acts as a rotating portion 97. In the disc brake 1D according to the fourth embodiment, the rotor body 53 of the electric motor 45 corresponds to the rotating member, and the second housing portion 42 of the housing 36 corresponds to the support member. The members corresponding to the clutch mechanism 107 are the second housing portion 42 and the first small diameter rotating shaft portion 134.

[0060] When the rotor body 53 of the electric motor 45 rotates in the apply direction, the clutch mechanism 107 allows the second housing 42 and the first small diameter rotating shaft 134 to rotate relative to each other, while the action of the rolling bearing 118 reduces the rotational resistance of the rotor body 53 relative to the second housing 42. On the other hand, with respect to rotation of the rotating internal gear 85 in the release direction, the clutch mechanism 107 prevents the second housing 42 and the first small diameter rotating shaft 134 from rotating relative to each other, and the rotational resistance of the rotating part 97 between the rotor body 53 and the first large diameter rotating shaft 133 increases, resulting in an increase in the rotational resistance of the rotor body 53 relative to the second housing 42.

[0061] As a result, the disc brake 1D according to the fourth embodiment can also achieve the same effects as the disc brake 1A according to the first embodiment. Moreover, in the disc brake 1D according to the fourth embodiment, the clutch mechanism 107 is provided near the electric motor 45, which has the smallest rotational torque, so the clutch mechanism 107 can be made even smaller.

[0062] The brake holding mechanism 48 described above is applied to the disc brake 1 in this embodiment in which both the service brake and the parking brake are driven by the electric motor 45, but it may also be applied to other known electric brakes that require the maintenance of braking force, such as an electric parking brake in which the service brake is hydraulically operated.

[0063] This application claims priority to Japanese Patent Application No. 2024-004810, filed January 16, 2024. The entire disclosure of Japanese Patent Application No. 2024-004810, filed January 16, 2024, including the specification, claims, drawings, and abstract, is incorporated herein by reference in its entirety.

[0064] 1A, 1B, 1C, 1D Disc brake (corresponding to electric brake), 2 Inner brake pad (corresponding to braking member), 3 Outer brake pad (corresponding to braking member), 4 Caliper, 30 Piston, 38 Cover member (corresponding to support member in third embodiment), 41 First housing portion (corresponding to support member in third embodiment), 42 Second housing portion (corresponding to support member in fourth embodiment), 45 Electric motor, 46 Reduction mechanism, 47 Brake mechanism, 48 Brake holding mechanism, 53 Rotor main body portion (corresponding to rotating member in fourth embodiment), 67 Multi-stage gear reduction mechanism, 71 Pinion gear (input member), 72 Reduction gear (corresponding to rotating member in third embodiment), 85 Rotating internal gear (output member), 83 Planetary gear (corresponding to rotating member in first and second embodiments), 97 Rotating portion, 106 Planetary carrier (corresponding to the support member in the first and second embodiments), 107 clutch mechanism, 110 support shaft, 112 large diameter shaft portion, 113 small diameter shaft portion, 118 rolling bearing (corresponding to the bearing), 123 support shaft, D disc rotor (braked member)

Claims

1. An electric brake, comprising: an electric motor; an input member to which rotation from the electric motor is input, and a speed reduction mechanism having an output member that reduces and outputs the rotation of the input member; a brake mechanism that generates a braking force by pressing a braking member against a member to be braked by rotation from the output member of the speed reduction mechanism; and a braking force holding mechanism that holds the braking force generated by the brake mechanism, wherein the braking force holding mechanism is provided on the upstream side of the output member when the brake mechanism is on the downstream side and the electric motor is on the upstream side in the rotation transmission path from the electric motor, and the braking force holding mechanism includes a rotating member rotated by the electric motor, a supporting member that rotatably supports the rotating member, a clutch mechanism that is relatively rotatable with respect to a corresponding member when the electric motor rotates in a direction to press the braking member against the member to be braked, and is non-rotatable with respect to the corresponding member when the electric motor rotates in a direction to separate the braking member from the member to be braked, a bearing that allows relative rotation between the rotating member and the supporting member when the clutch mechanism is relatively rotatable with respect to the corresponding member, and a rotating portion that allows relative rotation between the rotating member and the supporting member when the clutch mechanism is non-rotatable with respect to the corresponding member.

2. The electric brake according to claim 1, wherein the bearing reduces the rotational resistance of the rotating member with respect to the supporting member when the clutch mechanism is relatively rotatable with respect to the corresponding member, and the rotating portion increases the rotational resistance of the rotating member with respect to the supporting member when the clutch mechanism is non-rotatable with respect to the corresponding member.

3. The electric brake according to claim 2, wherein the rotating member is supported by the supporting member via a support shaft, the support shaft has a stepped shape and includes a large-diameter shaft portion and a small-diameter shaft portion extending axially from the large-diameter shaft portion, the bearing and the clutch mechanism are disposed between the supporting member and the small-diameter shaft portion, and the rotating portion is provided between the rotating member and the large-diameter shaft portion.

4. In the electric brake according to claim 2, the rotating member is supported by the support member via a support shaft, the bearing and the clutch mechanism are disposed between the rotating member and the support shaft, and the rotating portion is provided between the support member and the support shaft. An electric brake characterized by this.

5. In the electric brake according to claim 1, the reduction mechanism has a differential planetary gear mechanism, and the braking holding mechanism is provided in the differential planetary gear mechanism. An electric brake characterized by this.

6. In the electric brake according to claim 1, the reduction mechanism has a multi-stage gear reduction mechanism, and the braking holding mechanism is provided in the multi-stage gear reduction mechanism. An electric brake characterized by this.

7. In the electric brake according to claim 1, the braking holding mechanism is provided in the electric motor and a housing that houses the electric motor. An electric brake characterized by this.

8. In the electric brake according to any one of claims 1 to 7, the clutch mechanism is a cam type clutch. An electric brake characterized by this.

9. In the electric brake according to any one of claims 1 to 7, the clutch mechanism is a coil spring type clutch. An electric brake characterized by this.

Images