JP6491543B2 - Duo servo type drum brake - Google Patents

Description

  The present invention relates to a duo-servo type drum brake, and more particularly to a technique for improving the braking force of a drum brake as compared with the conventional one.

  One type of duo servo type drum brake includes: (a) an arcuate primary shoe and secondary shoe arranged to be expandable on a backing plate; and (b) one end portion of the primary shoe and one end portion of the secondary shoe. (C) a spring that biases one end of the primary shoe and one end of the secondary shoe toward each other; and (d) the primary shoe. A connecting device for connecting the other end of the secondary shoe to the other end of the secondary shoe, and (e) a brake having a base end connected to one end of the secondary shoe by a mounting shaft so as to be relatively rotatable about the mounting shaft. A lever; and (f) a first engagement portion provided on the inner peripheral edge of the brake lever at a predetermined distance from the mounting shaft, and a shoe of the primary shoe There is provided a longitudinal-shaped struts which spans between the second engagement portion provided on the drive. For example, a duo-servo type drum brake as shown in Patent Document 1 is this.

  In the duo-servo type drum brake as described above, an operating force is generated at the tip of the brake lever at the time of braking, so that the brake lever rotates around the mounting shaft, thereby achieving a lever ratio of the brake lever. A force larger than the operating force is applied to the second engagement portion of the primary shoe via the strut to expand one end portion of the primary shoe, and the reaction of the force applied to the strut Thus, one end of the secondary shoe is expanded through the mounting shaft.

JP 2014-145378 A

  By the way, in the duo-servo type drum brake as described above, in order to improve the braking force of the drum brake, for example, the distance between the mounting shaft provided on the brake lever and the tip of the brake lever is A, and the brake lever If the distance between the mounting shaft provided on the first engagement portion of the brake lever and the first engagement portion of the brake lever is B, it is conceivable to increase the lever ratio A / B of the brake lever. If the distance A is increased in order to increase the lever ratio A / B of the brake lever, the tip end portion of the brake lever interferes with the coupling device, so that the lever ratio of the brake lever is easily improved. There was a problem that I could not.

  The present invention has been made against the background described above, and an object of the present invention is to provide a duo-servo type drum brake in which the braking force of the drum brake can be improved as compared with the prior art.

  In order to achieve such an object, the gist of the present invention is that: (a) a primary shoe and a secondary shoe having an arc shape disposed in a backing plate so as to be expandable; one end portion of the primary shoe; An anchor member disposed in a fixed position between one end portion of the secondary shoe, a spring that biases the one end portion of the primary shoe and the one end portion of the secondary shoe toward each other, and A connecting device for connecting the other end and the other end of the secondary shoe, a brake lever having a base end connected to one end of the secondary shoe by a mounting shaft so as to be relatively rotatable around the mounting shaft; A first engagement portion provided at a predetermined distance from the mounting shaft at an inner peripheral edge of the brake lever and a shoe of the primary shoe A duo-servo type drum brake including a strut spanned between a second engagement portion provided on the web, wherein (b) the primary shoe includes the anchor member and the center of the drum brake; And (c) the tip of the brake lever is arranged on the straight line.

  According to the duo-servo type drum brake configured as described above, since the tip end portion of the brake lever is arranged on the straight line, the distance A between the mounting shaft and the tip end portion of the brake lever in the linear direction is become longer. As a result, the distance A between the mounting shaft provided on the brake lever in the linear direction and the tip of the brake lever is longer than before, and the lever ratio A / B of the brake lever is increased. The braking force of the drum brake is improved as compared with the prior art.

  Here, preferably, the one end portion and the other end portion of the coupling device are an intermediate position between the inner peripheral edge and the outer peripheral edge of the other end portion of the primary shoe and the inner peripheral edge and the outer peripheral edge of the other end portion of the secondary shoe. Are engaged at intermediate positions. Accordingly, one end and the other end of the coupling device can be arranged on the center side of the drum brake as compared to the conventional duo servo type drum brake. The distance to the output point to the connecting device can be shortened compared to the conventional case. For this reason, when the operating force is applied to the second engagement portion of the primary shoe from the brake lever via the strut during braking, the amount of rotation by which one end portion of the primary shoe rotates about the output point is increased. Since it becomes larger than a conventional duo-servo type drum brake, the amount of biting into the inner peripheral surface of the rotary drum by the primary shoe is increased, and the braking force of the drum brake is further improved.

  Preferably, (a) an electric actuator for pulling a brake cable connected to the tip of the brake lever is provided, and (b) an output shaft of an electric motor provided in the electric actuator is rotated. As a result, the brake cable is pulled, and the operating force is generated at the tip of the brake lever. For this reason, the braking force of the drum brake is improved in the duo-servo type drum brake as compared with the conventional one. Therefore, if the braking force equivalent to that of the conventional duo-servo type drum brake is generated, the electric actuator is provided. The output of the electric motor can be reduced.

It is a front view which shows the duo servo type drum brake of one Example of this invention. It is the enlarged view to which the duo servo type drum brake of FIG. 1 was expanded. FIG. 3 is a sectional view taken along line III-III in FIG. 1. It is a front view which shows the conventional duo servo type drum brake.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiments, the drawings are appropriately simplified or modified for easy understanding, and the dimensional ratios, shapes, and the like of the respective parts are not necessarily drawn accurately.

  FIG. 1 is a front view of a drum-in disc brake 12 in which a parking brake drum brake (electric drum brake) 10 is provided at the center, with a hat-type disc and calipers removed. As shown in FIG. 1, the drum brake 10 is provided with a substantially disc-shaped backing plate 14 and an outer peripheral portion of the backing plate 14 that can be moved toward and away from each other, that is, can be expanded. A pair of first brake shoe (primary shoe) 16 and second brake shoe (secondary shoe) 18, and between one end portion 16 a of first brake shoe 16 and one end portion 18 a of second brake shoe 18. 1 between the anchor member 20 and the one end portion 16a of the first brake shoe 16, and between the anchor member 20 and one end portion 18a of the second brake shoe 18. The one end 16a of the first brake shoe 16 and the one end 1 of the second brake shoe 18 are respectively stretched. A is stretched between a pair of return springs (springs) 22 and 24 that always urges a toward each other, and one end 16a of the first brake shoe 16 and one end 18a of the second brake shoe 18. The longitudinal strut 26 is interposed between the other end portion 16b of the first brake shoe 16 and the other end portion 18b of the second brake shoe 18, and the total length is changed with the rotation of the adjusting wheel 28a. Accordingly, a longitudinal gap adjusting device (connecting device) 28 for adjusting a gap between the brake drum (rotating drum) 30 and the pair of first brake shoes 16 and the second brake shoes 18, that is, the shoe gap is provided. ing. The gap adjusting device 28 is stretched between the other end portion 16b of the first brake shoe 16 and the other end portion 18b of the second brake shoe 18 so that the other end portions 16b and 18b approach each other. A coil-like spring 28b is provided at an intermediate portion for always energizing and clamping the gap adjusting device 28 in the longitudinal direction. The gap adjusting device 28 is connected to the other end 16b of the first brake shoe 16 and the It functions as a connecting device that connects the other end 18b of the two brake shoes 18 so as to be relatively rotatable. The strut 26 is provided with a coiled spring 32 that constantly urges the strut 26 toward the second brake shoe 18 side. In the drum brake 10, when the brake drum 30, that is, the wheel attempts to rotate in the forward direction, that is, the direction of the arrow F <b> 1 during the drum brake braking in which the first brake shoe 16 and the second brake shoe 18 are expanded, This is a duo-servo type drum brake in which the pressing force by which the shoe 16 bites into the inner peripheral surface 30a of the brake drum 30 and the second brake shoe 18 is pressed against the inner peripheral surface 30a of the brake drum 30 is increased.

  Each of the pair of first brake shoes 16 and second brake shoes 18 has a flat plate shape substantially parallel to the plate surface of the backing plate 14 and is entirely curved in an arc shape in the front view shown in FIG. 34 and 36, belt-plate-like shoe rims 38 and 40 integrally fixed so that the cross-section is substantially T-shaped along the outer peripheral side edge forming the arc shape thereof, and the shoe rims 38 and 40 Linings 42 and 44 made of a friction material that are integrally fixed to the outer peripheral surface with an adhesive or the like.

  As shown in FIGS. 1 and 2, the second brake shoe 18 is provided with an elongated flat plate-like brake lever 48 having a substantially cylindrical mounting shaft 46, and one end portion of the second brake shoe 18. 18a and the base end portion 48a of the brake lever 48 are connected by a mounting shaft 46 so as to be relatively rotatable around the axis C1 of the mounting shaft 50. The brake lever 48 is formed with a first engaging portion 48b that engages with one end portion 26a of the strut 26 that is spaced a predetermined distance from the mounting shaft 46 at the inner peripheral edge of the base end portion 48a. Further, the first brake shoe 16 is formed with a second engagement portion 34 a that engages with the other end portion 26 b of the strut 26 at the inner peripheral edge of the end portion of the shoe web 34 on the strut 26 side.

  As shown in FIGS. 1 to 3, a cable insertion hole 14 a provided through the backing plate 14 is provided in the backing plate 14 so as to pass the brake cable 50 having a circular cross section into the inside and outside of the backing plate 14. Is provided. One end 50a of the brake cable 50 is hooked and connected to the tip 48c of the brake lever 48.

  As shown in FIG. 3, on the outside of the backing plate 14, the electric force F <b> 2 is generated at the tip 48 c of the brake lever 48 by pulling the other end 50 b of the brake cable 50 from the outside of the backing plate 14. An actuator 52 is provided.

  As shown in FIG. 3, the electric actuator 52 includes an electric motor 54 that rotates the output shaft 54 a by a driving current output from an electronic control device (not shown), and rotation of the output shaft 54 a of the electric motor 54. A reduction gear device 60 having a first gear 56 that is transmitted via a gear 54 b fixed to the output shaft 54 a and a second gear 58 that meshes with the first gear 56, and a second gear 58 of the reduction gear device 60. A cylindrical female screw hole 58a drilled along the first rotational axis D1 of the two gear 58 and a male screw 62a screwed with the female screw 58b formed on the inner peripheral surface of the female screw hole 58a of the second gear 58 A shaft-shaped screw shaft member 62 formed on the surface and having the other end 50b of the brake cable 50 connected to the tip 62b, the screw shaft member 62, the reduction gear device 60, the electric motor A housing case 64 that houses the motor 54 is provided.

  In the electric actuator 52, when the output shaft 54a of the electric motor 54 is rotationally driven around the output shaft 54a in the predetermined rotational direction E, that is, rotated in the normal rotation, the gear 54b and the first gear 56 are used to drive the reduction gear device 60. The second gear 58 rotates about the first rotation axis D1, and the front end 62b of the screw shaft member 62 has a male screw 62a formed on the outer peripheral surface of the screw shaft member 62 and a female screw in the female screw hole 58a of the second gear 58. It moves in the direction approaching the second gear 58 by the action of the screw 58b.

  As shown in FIG. 2, the housing case 64 includes a cable support 64 a that protrudes from the cable insertion hole 14 a of the backing plate 14 to the inside of the backing plate 14 to support the brake cable 50, and the housing case 64 by fastening bolts 66. A case attaching portion 64b attached to the backing plate 14 and an accommodating portion 64c for accommodating, for example, the screw shaft member 62, the reduction gear device 60, the electric motor 54, and the like are provided. The first gear 56 is rotatably supported around the second rotation axis D2 by a pair of bearings 68 and 68 provided in the housing portion 64c of the housing case 64. The second gear 58 is rotatably supported around the first rotation axis D1 by a pair of thrust bearings 70, 70 provided in the housing portion 64c of the housing case 64.

  According to the electric actuator 52 configured as described above, for example, when a parking lever or a parking pedal (not shown) is operated and a drive current is output from the electronic control device to the electric motor 54, the output shaft 54a of the electric motor 54 is output. Is driven to rotate in the rotation direction E, and the brake cable 50 is pulled, so that the operating force F2 is generated at the tip 48c of the brake lever 48 via the brake cable 54, and the tip 48c of the brake lever 48 is attached to the mounting shaft. The drum brake 10 rotates about 50 axis C1 toward the center C2 of the drum brake 10, that is, the center C2 side of the backing plate 14.

  FIG. 4 is a front view showing a conventional drum brake (duo servo type drum brake) 100. In the conventional drum brake 100, the first brake shoe (primary shoe) 102 connects the axis C3 of the columnar anchor portion 20a of the anchor member 20 and the center C2 of the drum brake 100, that is, the center C2 of the backing plate 14. It differs from the drum brake 10 of the present embodiment in that it is symmetrical with the second brake shoe (secondary shoe) 104 with respect to the straight line L1 and the shape of the brake lever 106 is different from the shape of the brake lever 48. The rest is substantially the same as the drum brake 10. The size of the conventional drum brake 100 and the drum brake 10 of the present embodiment are the same. In the description of the conventional drum brake 100, parts common to the drum brake 10 of the present embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 4, in the conventional drum brake 100, the first brake shoe 102 is symmetrical with the second brake shoe 104 with respect to the straight line L1, so that the other end portion 102a of the first brake shoe 102 and A gap adjusting device 28, which is a connecting device connected to the other end 104a of the second brake shoe 104, is disposed on the straight line L1. Therefore, in the conventional drum brake 100, an attempt is made to increase the lever ratio R1 calculated based on the positions of the tip end portion 106a, the mounting shaft 50, and the first engagement portion 106b of the brake lever 106, that is, the brake lever in the direction of the straight line L1. In order to increase the distance A1 between the axial center C1 of the mounting shaft 46 provided at 106 and the tip end portion 106a of the brake lever 106, the tip end portion 106a of the brake lever 106 is arranged on the straight line L1. 28, so that the brake lever 106 does not come into contact with the gap adjusting device 28 even when the brake lever 106 rotates around the axis C1 of the mounting shaft 50 during braking or non-braking. The position of the front end portion 106a is determined.

  Further, in the conventional drum brake 100, in order to avoid interference with the brake lever 106, the one end portion 28c and the other end portion 28d of the longitudinal gap adjusting device 28 are within the other end portion 102a of the first brake shoe 102. A position as far as possible from the intermediate position between the peripheral edge and the outer peripheral edge, and a position as close as possible to the intermediate position between the inner peripheral edge and the outer peripheral edge of the other end 104a of the second brake shoe 104. Since they are engaged with the positions on the outer peripheral edge side, for example, the dimension CR1 which is the distance between the one end portion 28c of the gap adjusting device 28 and the center C2 of the drum brake 100 becomes a relatively large value.

  The lever ratio R1 is the distance A1 from the axis C1 of the mounting shaft 50 to the tip end portion 106a of the brake lever 106 in the direction of the straight line L1, and the first relationship of the brake lever 106 from the axis C1 of the mounting shaft 50 in the direction of the straight line L1. It is a value (A1 / B1) divided by the distance B1 to the joint portion 106b. The dimension CR1 is a distance from the center C2 of the backing plate 14 to the output point C4 to the gap adjusting device 28 of the first brake shoe 102 in a direction orthogonal to the longitudinal direction of the longitudinal gap adjusting device 28. is there. The output point C4 is a contact point between the one end portion 28c of the longitudinal gap adjusting device 28 and the other end portion 102a of the first brake shoe 102.

  As shown in FIGS. 1 and 2, in the drum brake 10 of the present embodiment, the arc-shaped first brake shoe 16 is asymmetric with the arc-shaped second brake shoe 18 with respect to the straight line L1. Since the arc lengths at both ends of the second brake shoe 18 are longer than the arc lengths at both ends of the arc-shaped first brake shoe 16, the other end portion 16b of the first brake shoe 16 and the second brake The gap adjusting device 28 connected to the other end 18b of the shoe 18 is not disposed on the straight line L1 unlike the conventional drum brake 100. The gap adjusting device 28 is not located on the straight line L1, for example, at a position around the cable insertion hole 14a of the backing plate 14. For this reason, in the drum brake 10, the lever ratio R2 calculated based on the positions of the tip 48c, the mounting shaft 46, and the first engaging portion 48b of the brake lever 48 is increased, that is, the mounting shaft 46 and the brake in the direction of the straight line L1. The distance A2 from the tip 48c of the lever 48 is increased, and the tip 48c of the brake lever 48 is arranged on the straight line L1.

  As shown in FIGS. 2 and 4, in the conventional drum brake 100, the gap adjusting device 28 is disposed on the straight line L1, and the tip end portion 106a of the brake lever 106 cannot be disposed on the straight line L1. The distance A2 is longer than the distance A1, and the lever ratio R2 of the brake lever 48 is higher than the lever ratio R1 of the brake lever 106. The lever ratio R2 is the distance A2 from the axis C1 of the mounting shaft 46 to the tip 48c of the brake lever 48 in the direction of the straight line L1, and the first relationship of the brake lever 48 from the axis C1 of the mounting shaft 46 in the direction of the straight line L1. It is a value (A2 / B2) divided by the distance B2 to the joint portion 48b. The distance B2 of the drum brake 10 of the present embodiment is the same as the distance B1 of the conventional drum brake 100.

  As shown in FIGS. 2 and 4, in the drum brake 10 of this embodiment, the one end 28 c and the other end 28 d of the gap adjusting device 28 are connected to the inner peripheral edge of the other end 16 b of the first brake shoe 16. The intermediate position of the second brake shoe 18 and the intermediate position of the inner peripheral edge and the outer peripheral edge of the other end 18b of the second brake shoe 18 are respectively engaged, and one end 28c of the gap adjusting device 28 is compared with the conventional drum brake 100. Since the drum brake 10 is disposed on the center C2 side, the dimension CR2 is smaller than the dimension CR1. The dimension CR2 is from the center C2 of the backing plate 14 in the direction orthogonal to the longitudinal direction of the longitudinal gap adjusting device 28 to the output point C4 to the one end 28c of the gap adjusting device 28 of the first brake shoe 16. Distance. The output point C4 is a contact point between the one end portion 28c of the longitudinal gap adjusting device 28 and the other end portion 16b of the first brake shoe 16. In the drum brake 10 of the present embodiment, the gap adjusting device 28 is not disposed on the straight line L1, and the other end 16b of the first brake shoe 16 and the second brake shoe 18 are separated by the tip 48c of the brake lever 48. Since the position of the gap adjusting device 28 between the end portion 18b is no longer restricted, the one end portion 28c and the other end portion 28d of the gap adjusting device 28 are connected to the inner peripheral edge and the outer edge of the other end portion 16b of the first brake shoe 16. It can be engaged with an intermediate position between the peripheral edge and an intermediate position between the inner peripheral edge and the outer peripheral edge of the other end 18b of the second brake shoe 18, respectively.

  According to the drum brake 10 configured as described above, when a parking lever or a parking pedal (not shown) is operated, an operating force F2 is generated by the electric actuator 52 at the distal end portion 48c of the brake lever 48, and the brake is applied. The lever 48 rotates around the axis C1 of the mounting shaft 46. As a result, the force that is greater than the operating force F2 based on the lever ratio R2 calculated based on the positions of the tip end portion 48c of the brake lever 48, the axis C1 of the mounting shaft 46, and the first engaging portion 48b is strut 26. Acting on the second engaging portion 34a of the first brake shoe 16 via the first end 16a of the first brake shoe 16 and the other end portion 16b of the first brake shoe 16 and one end portion 28c of the gap adjusting device 28. While rotating around the contact position, that is, the contact point C4, the one end portion 18a of the second brake shoe 18 is expanded through the mounting shaft 46 by the reaction of the force acting on the strut 26. Therefore, for example, when the brake drum 30, that is, the wheel tries to rotate in the forward direction, that is, in the direction of the arrow F 1, the first brake shoe 16 bites into the inner peripheral surface 30 a of the brake drum 30, and the second brake shoe 18 The pressing force pressed against the peripheral surface 30a is increased, and a braking force is generated in the drum brake 10.

  As described above, according to the drum brake 10 of the present embodiment, the first brake shoe 16 is asymmetric with the second brake shoe 18 with respect to the straight line L1 connecting the anchor member 20 and the center C2 of the drum brake 10. Therefore, the gap adjusting device 28 disposed between the other end 16b of the first brake shoe 16 and the other end 18b of the second brake shoe 18 is on a straight line L1 as in the conventional drum brake 100. Since they are not arranged, the tip end portion 48c of the brake lever 48 is arranged on the straight line L1 so that the distance A2 between the mounting shaft 46 and the tip end portion 48c of the brake lever 48 in the direction of the straight line L1 becomes long. As a result, the distance A2 between the mounting shaft 48 provided on the brake lever 48 and the tip 48c of the brake lever 48 in the direction of the straight line L1 is longer than the distance A1 of the conventional drum brake 100, and the lever ratio of the brake lever 48 is increased. Since R2 becomes high, the braking force of the drum brake 10 is improved as compared with the conventional art.

  Further, according to the drum brake 10 of the present embodiment, the one end portion 28c and the other end portion 28d of the gap adjusting device 28 are located at an intermediate position between the inner peripheral edge and the outer peripheral edge of the other end portion 16b of the first brake shoe 16. The two brake shoes 18 are respectively engaged at intermediate positions between the inner peripheral edge and the outer peripheral edge of the other end 18b. As a result, the one end portion 28c and the other end portion 28d of the gap adjusting device 28 can be arranged closer to the center C2 side of the drum brake than the conventional drum brake 100, so that the first brake is started from the center C2 of the drum brake 10. The distance to the output point C4 of the shoe 16 to the gap adjusting device 28, that is, the dimension CR2 can be made shorter than the dimension CR1 of the conventional drum brake 100. Therefore, when the operating force F2 acts on the second engagement portion 34a of the first brake shoe 16 from the brake lever 48 during braking via the strut 26, the one end portion 16a of the first brake shoe 16 rotates around the output point C4. Since the amount of rotation to move is larger than that of the conventional drum brake 100, the amount of biting into the inner peripheral surface 30a of the brake drum 30 by the first brake shoe 16 is increased, and the braking force of the drum brake 10 is improved.

  Further, according to the drum brake 10 of the present embodiment, the electric actuator 52 that pulls the brake cable 50 connected to the distal end portion 48 c of the brake lever 48 is provided, and the output of the electric motor 54 provided in the electric actuator 52 is provided. When the shaft 54a is rotated, the brake cable 50 is pulled, and an operating force F2 is generated at the tip 48c of the brake lever 48. For this reason, since the braking force of the drum brake 10 is improved in the drum brake 10 as compared with the conventional drum brake 100, the electric actuator 52 is provided if a braking force equivalent to that of the conventional drum brake 10 is generated. Further, the output of the electric motor 54 can be reduced.

  As mentioned above, although the Example of this invention was described in detail based on drawing, this invention is applied also in another aspect.

  In the drum brake 10 of the present embodiment, an operating force F2 is generated at the distal end portion 48c of the brake lever 48 via the brake cable 50 when the output shaft 54a of the electric motor 54 provided in the electric actuator 52 is rotationally driven. Although it was an electric drum brake, for example, a manual drum brake that applies an operation force for operating a parking lever or a parking pedal by a driver to the tip 48c of the brake lever 48 via the brake cable 50 is applied. May be.

  Moreover, although the drum brake 10 of the present embodiment is a drum brake dedicated to a parking brake, it may be used as a service brake (ordinary brake) used while the vehicle is running.

  Further, in the drum brake 10 of the present embodiment, the one end portion 28c and the other end portion 28d of the gap adjusting device 28 are located at an intermediate position between the inner peripheral edge and the outer peripheral edge of the other end portion 16b of the first brake shoe 16 and the second brake. The other end portion 18b of the shoe 18 is engaged with an intermediate position between the inner peripheral edge and the outer peripheral edge, but the intermediate position is the exact distance between the inner peripheral edge and the outer peripheral edge of the other end portions 16b, 18b. It is not limited to the position divided in half, but includes the peripheral portion of the position.

  The above description is only an embodiment, and the present invention can be implemented in variously modified and improved forms based on the knowledge of those skilled in the art.

10: Drum brake (Duo servo type drum brake)
14: Backing plate 16: First brake shoe (primary shoe)
16a: one end 16b: the other end 18: second brake shoe (secondary shoe)
18a: one end 18b: the other end 20: anchor member 22, 24: return spring (spring)
26: Strut 26a: One end portion 26b: Other end portion 28: Gap adjusting device (connecting device)
28c: one end 28d: the other end 30: brake drum (rotary drum)
30a: inner peripheral surface 34: shoe web 34a: second engaging portion 46: mounting shaft 48: brake lever 48a: base end portion 48b: first engaging portion 48c: tip end portion 50: brake cable 52: electric actuator 54: Electric motor 54a: output shaft C2: center F2: operating force L1: straight line

Claims (3)

An arcuate primary shoe and a secondary shoe arranged to be expandable on the backing plate; an anchor member arranged to be fixed between one end of the primary shoe and one end of the secondary shoe; A spring that biases one end of the primary shoe and one end of the secondary shoe in a direction approaching each other, a connecting device that connects the other end of the primary shoe and the other end of the secondary shoe, A brake lever having a base end connected to one end of the secondary shoe by a mounting shaft so as to be relatively rotatable around the mounting shaft, and a first provided at a predetermined distance from the mounting shaft at an inner peripheral edge of the brake lever. A strut spanned between the engaging portion and the second engaging portion provided on the shoe web of the primary shoe. A obtain duo-servo type drum brake,
The primary shoe is asymmetric with the secondary shoe with respect to a straight line connecting the anchor member and the center of the drum brake,
A duo-servo type drum brake, wherein a tip end portion of the brake lever is arranged on the straight line.   One end and the other end of the coupling device are respectively associated with an intermediate position between the inner peripheral edge and the outer peripheral edge of the other end of the primary shoe and an intermediate position between the inner peripheral edge and the outer peripheral edge of the other end of the secondary shoe. The duo-servo type drum brake of Claim 1 combined. An electric actuator for pulling a brake cable connected to the tip of the brake lever;
The duo-servo type drum brake according to claim 1 or 2, wherein the operating force is generated at a distal end portion of the brake lever by pulling the brake cable by rotating an output shaft of an electric motor provided in the electric actuator.

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