1. A drum brake, characterized in that the drum brake is provided with:

a cylindrical brake drum provided to a rotary member and rotatable integrally with the rotary member;

a brake shoe which is provided to the fixed member so as to be swingable, and which has a brake lining disposed along an inner circumferential surface of the brake drum;

an expansion device that presses the brake lining against an inner circumferential surface of the brake drum by swinging the brake shoe in accordance with a brake operation; and

a wear detection device that detects wear of the brake lining,

the expanding device has:

a pressing force generating member that causes a pressing force to act in an axial direction in accordance with a braking operation;

a transmission member provided to be rotatable about the axial direction with respect to the pressing force generation member;

a pressing member that is screwed in the axial direction with respect to the transmission member, is connected to the brake shoe so as to be non-rotatable in the axial direction, and presses the brake lining against the inner circumferential surface of the brake drum by swinging the brake shoe by the pressing force transmitted from the transmission member; and

a backlash adjustment mechanism that adjusts a backlash between the brake lining and an inner peripheral surface of the brake drum by rotating the transmission member in the axial direction and feeding out the pressing member in the axial direction to displace a relative position of the pressing member with respect to the transmission member in the axial direction,

the wear detection device is configured to include: a rotation detecting unit that detects a rotation amount of the transmission member in the axial direction; a rotation number calculation unit that accumulates and stores the rotation number of the transmission member based on the rotation amount detected by the rotation detection unit; and a wear determination unit that detects wear of the brake lining based on the number of rotations of the transmission member calculated by the rotation number calculation unit.

2. The drum brake according to claim 1, wherein the wear determination unit outputs an alarm signal when the number of rotations of the transmission member calculated by the number-of-rotations calculation unit exceeds a preset limit number of rotations.

3. A drum brake according to claim 1 or 2,

a first gear is formed on an outer peripheral surface of the transmission member,

the rotation detecting unit includes a second gear that rotates while meshing with the first gear, and a rotation sensor that is connected to the second gear and detects a rotation amount of the second gear, and detects a rotation amount of the transmission member via the rotation amount of the second gear.

4. A drum brake according to any one of claims 1 to 3,

the drum brake is provided with a reset switch that can be operated from the outside,

the rotation number information stored in the rotation number calculation unit is reset when the reset switch is operated.

Background

A drum brake is provided with: a cylindrical brake drum attached to be rotatable integrally with an axle; and a pair of brake shoes which are swingably held by the anchor bracket, are arranged along an inner peripheral surface of the brake drum, and brake the rotation of the brake drum (a wheel provided on the axle) by friction generated between the brake shoes provided on the brake shoes facing the brake drum by pressing the brake linings against the inner peripheral surface of the brake drum.

In such a drum brake, there is a structure as follows: an expansion device that performs an outward extending operation in response to a brake operation is attached to a front end of the brake shoe, and the brake shoe is swung by the extending operation of the expansion device to press the brake lining against the inner circumferential surface of the brake drum (see, for example, japanese patent application laid-open No. 2006-242238). The expanding device of the drum brake includes a tappet, a sleeve coaxially attached to the tappet, and a screw screwed to the sleeve and having an outer end connected to a brake shoe, and is configured by inserting the tappet into a housing space formed in a housing. Here, the tappet and the sleeve are connected via a circlip, so that the relative movement in the axial direction is restricted. Further, a one-way clutch is disposed between the tappet and the sleeve, and allows the sleeve to rotate in one direction about the axis with respect to the tappet, while restricting the sleeve from rotating in the other direction about the axis. The brake lining is worn by friction with the brake drum, but if the clearance between the brake lining and the brake drum (hereinafter also referred to as "shoe clearance") increases due to the wear, the braking effectiveness also deteriorates. Therefore, a drum brake is provided with a clearance adjustment mechanism that reduces a shoe clearance in accordance with wear of a brake lining and automatically adjusts the clearance so that the clearance between the brake lining and a brake drum is always constant. The clearance adjustment mechanism is configured to rotate the sleeve relative to the screw rod (in the one direction) independently, and to extend the screw rod screwed into the sleeve outward, thereby swinging the brake lining to reduce the shoe clearance.

In addition, in such a drum brake, there is known a brake lining wear detection device including: when the wear of the brake lining progresses and reaches a certain wear limit (use limit), the wear is detected and a warning is given to the driver (see, for example, japanese patent application laid-open No. 10-184748). The wear detection device is configured such that a wear detection piece is disposed from the back surface of the brake lining toward the brake drum side, and a wire connected to an alarm circuit is embedded in a loop shape in a front end portion of the wear detection piece. The wear detector is arranged such that when the wear of the brake lining progresses and reaches a wear limit, a tip end portion thereof comes into contact with the brake drum, the tip end portion is worn or broken by the contact with the brake drum, and the inner wire is cut. When the wire of the wear detector is cut, the alarm circuit detects the cut of the circuit based on a change in current or voltage, and notifies that the brake lining has reached the wear limit.

Disclosure of Invention

Problems to be solved by the invention

However, in the conventional wear detection device described above, when the brake lining reaches the wear limit and the brake shoe is replaced with a new one, the wear detector needs to be replaced with a new one in accordance with the wear limit. Therefore, there are problems as follows: when the brake shoe is replaced, the component cost becomes high, and a man-hour of reconnecting the harness occurs, so that the running cost increases. Further, the conventional wear detection device has the following problems: only the wear limit of the brake lining is detected, and the state of wear (amount of wear) cannot be detected until the brake lining reaches the wear limit.

The present invention has been made in view of the above-described problems, and an object thereof is to provide a drum brake capable of detecting a wear state of a brake lining with high accuracy while reducing running cost.

Means for solving the problems

In order to achieve the above object, a drum brake according to the present invention includes: a cylindrical brake drum provided to a rotary member and rotatable integrally with the rotary member; a brake shoe which is provided to the fixed member so as to be swingable, and which has a brake lining disposed along an inner circumferential surface of the brake drum; an expansion device that presses the brake lining against an inner circumferential surface of the brake drum by swinging the brake shoe in accordance with a brake operation; and a wear detection device that detects wear of the brake lining, characterized in that the expansion device includes: a pressing force generating member that causes a pressing force to act in an axial direction in accordance with a braking operation; a transmission member provided to be rotatable about the axial direction with respect to the pressing force generation member; a pressing member that is screwed in the axial direction with respect to the transmission member, is connected to the brake shoe so as to be non-rotatable in the axial direction, and presses the brake lining against the inner circumferential surface of the brake drum by swinging the brake shoe by the pressing force transmitted from the transmission member; and a clearance adjustment mechanism that adjusts a clearance between the brake lining and an inner circumferential surface of the brake drum by rotating the transmission member in the axial direction and sending out the pressing member in the axial direction, thereby displacing a relative position of the pressing member with respect to the transmission member in the axial direction, the wear detection device being configured to include: a rotation detecting unit that detects a rotation amount of the transmission member in the axial direction; a rotation number calculation unit that accumulates and stores the rotation number of the transmission member based on the rotation amount detected by the rotation detection unit; and a wear determination unit that detects wear of the brake lining based on the number of rotations of the transmission member calculated by the rotation number calculation unit.

In the drum brake according to the present invention, it is preferable that the wear determination unit outputs an alarm signal when the number of rotations of the transmission member calculated by the number-of-rotations calculation unit exceeds a preset limit number of rotations.

In the drum brake according to the present invention, it is preferable that a first gear is formed on an outer peripheral surface of the transmission member, the rotation detection unit includes a second gear that rotates while meshing with the first gear, and a rotation sensor that is connected to the second gear and detects a rotation amount of the second gear, and the rotation amount of the transmission member is detected via the rotation amount of the second gear.

Further, in the drum brake according to the present invention, it is preferable that a reset switch operable from the outside is provided, and the rotational speed information stored in the rotational speed calculation unit is reset when the reset switch is operated.

Effects of the invention

According to the drum brake of the present invention, the rotation amount of the transmission member is detected by the rotation detecting unit using the equivalent relationship between the rotation amount of the transmission member and the wear amount of the brake lining when the shoe clearance is adjusted, and the wear state of the brake lining is detected based on the rotation amount (integrated number of revolutions) of the transmission member, whereby the wear state of the brake lining can be detected with high accuracy even before the brake lining reaches the wear limit (for example, not limited to the inspection of the vehicle during running), and the wear detecting member does not need to be replaced as in the conventional art when the brake lining reaches the wear limit and the brake shoe is replaced, so that the component cost and the replacement man-hour can be reduced, and the running cost can be suppressed.

Drawings

Fig. 1 is a front view showing a drum brake according to the present embodiment.

Fig. 2 is a rear view of the drum brake.

Fig. 3 is a cross-sectional view taken along an arrow a-a in fig. 1, and shows a state where the drum brake is not operated.

Fig. 4 is a cross-sectional view taken along an arrow a-a in fig. 1, and shows operation of the drum brake.

Fig. 5 is a sectional view showing an exploded state of the sleeve assembly of the drum brake.

Fig. 6 is a schematic view showing the wear detection device of the drum brake.

Detailed Description

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. First, an overall structure of a drum brake according to an embodiment of the present invention will be described with reference to fig. 1 to 6. In fig. 3, 4, and the like, hatching of a part of the cross-sectional portion is omitted for ease of viewing the drawings.

As shown in fig. 1 and 2, the drum brake B is mainly configured by: an anchor bracket 2 fixed to the vehicle body together with the dust cover 29; a drum unit 3 provided on the axle 1 and provided with a brake drum 31 that rotates integrally with the axle 1; a brake shoe unit 4 provided swingably to the anchor bracket 2 and including a pair of brake shoes 40, 40 arranged along an inner circumferential surface of the brake drum 31; an expansion device 5 that swings the brake shoes 40, 40 in accordance with a braking operation and presses the brake shoes against the inner circumferential surface of the brake drum 31; and a wear detection device 7 that detects wear of the brake lining 43 of the brake shoe 40. In fig. 1, the drum unit 3 (brake drum 31) is indicated by a two-dot chain line, and detailed illustration thereof is omitted.

The anchor bracket 2 has a circular hole-shaped opening 21 at the center thereof, and is fixed to an axle housing (not shown) of a vehicle body via bolts (not shown) inserted into bolt holes 22 provided around the opening 21. Further, a brake shoe support 25 divided into two strands in a thickness direction (a direction orthogonal to the paper surface in fig. 1) is formed at a lower portion of the anchor bracket 2, and a pair of pin insertion holes 24 are opened in the brake shoe support 25 in parallel on the left and right sides in a front view.

A rim (not shown) is attached to a hub (not shown) rotatably attached to the axle 1 protruding outward from the opening 21 of the anchor bracket 2 via a bearing, and a brake drum 31 is coupled to the hub to constitute a drum unit 3. Further, a wheel is mounted on the rim, and the brake drum 31 and the wheel rotate integrally via the hub.

The brake shoe unit 4 is configured to have two brake shoes 40, 40 arranged on the left and right in front view with the anchor bracket 2 interposed therebetween. Each brake shoe 40 includes: a web portion 41 extending in an arc shape; a rim 42 attached to the outer peripheral end of the web 41; and a brake lining (hereinafter, referred to as "lining") 43 fixed to the rim 42 by a rivet or the like. The brake shoe 40 is disposed along the inner circumferential surface of the brake drum 31, and the lining 43 faces the inner circumferential surface of the brake drum 31.

The base end portion of the brake shoe 40 is pivotally connected to the anchor bracket 2 via an anchor pin 44 inserted into the pin insertion hole 24 of the brake shoe support portion 25, and is swingable about the anchor pin 44 in the left-right direction in fig. 1. A return spring 45 for connecting the front end portions of the pair of brake shoes 40 and 40 to each other is provided across the front end portions. When the brake operation is not performed (when the brake is not operated), each brake shoe 40 is biased by the return spring 45 and is held at a position where it swings inward (i.e., a position where it is separated from the brake drum 31).

Further, an expansion device 5 fixed to the anchor bracket 2 is disposed between the distal end portions of the pair of brake shoes 40, 40. As will be described in detail later, when the brake operation is performed (brake operation), the extension operation (feed operation) of each screw 57 presses the tip end portion of each brake shoe 40 outward against the biasing force of the return spring 45. The brake shoes 40 swing outward around the anchor pins 44, and the linings 43 are pressed against the inner circumferential surface of the brake drum 31, thereby braking the rotation of the brake drum 31 by the frictional force therebetween. This enables a predetermined braking action to be obtained with respect to the wheel that rotates integrally with the brake drum 31.

As shown in fig. 3 and 4, the expanding device 5 includes: a housing 51 having a wedge housing 51a formed in a central space thereof and a pair of cylinder portions 51b and 51b communicating with the wedge housing 51a from both side portions thereof; a wedge 52 that is attached to the wedge receiver 51a in a pluggable manner; a sleeve assembly 53 inserted into each cylinder 51b and slidably arranged in the direction of the axis X (hereinafter also referred to as the "axial direction"); and a screw 57 screwed with the sleeve assembly 53 in the axial direction and extending to the outside of the side of the housing 51. A shield 59 for preventing dust from being mixed into the cylinder 51b is detachably attached to the opening end of the cylinder 51b of the expansion device 5.

The expansion device 5 is configured to be bilaterally symmetrical in fig. 3 and 4, and hereinafter, with reference to the arrangement posture of the expansion device 5 shown in fig. 3 and 4, the inner side (the wedge housing portion 51a side) of the housing 51 in the axial direction is referred to as "one end side", and the outer side (the brake shoe 40 side) of the housing 51 in the axial direction is referred to as "the other end side". Fig. 3 shows a state of the expanding device 5 when the brake is not operated, and fig. 4 shows a state of the expanding device 5 when the brake is operated.

The wedge 52 is formed in a shaft shape, and is attached to the housing 51 in a direction orthogonal to the axial direction (hereinafter, also referred to as "axial orthogonal direction") so as to be insertable and removable by the action of the diaphragm in the chamber 9. As shown in fig. 3, the wedge 52 is pulled outward from the wedge housing 51a by the biasing force of the wedge spring 52a when the brake is not operated (when the brake is released). On the other hand, as shown in fig. 4, the wedge 52 is moved in the direction orthogonal to the axis (downward in fig. 4) in the wedge housing 51a against the biasing force of the wedge spring 52a during the operation of the brake, and is inserted into the wedge housing 51 a. The insertion end portion 52b, which is an end portion inserted into the wedge housing portion 51a, is formed in a wedge shape that tapers toward the tip, and has inclined surfaces 52c on both sides in the axial direction. Further, a roller holding body 52e that supports the pair of rollers 52f is provided on the front end side (insertion end portion 52b side) of the wedge 52. The pair of rollers 52f are provided rotatably with respect to the roller holder 52e and are movable in directions (axial directions) of approaching and separating from each other. The roller holding body 52e is provided to be reciprocatingly movable in the direction orthogonal to the axis, and is constantly biased toward the outside (upward in fig. 4) of the housing 51 by the wedge spring 52a together with the wedge 52. The roller holding body 52e converts linear motion in the direction orthogonal to the axis of the wedge 52 into linear motion in the axial direction of the sleeve assembly 53 in cooperation with the wedge 52.

As shown in fig. 3 to 5, the sleeve assembly 53 includes: a tappet 54 having a body portion 54a formed to have an outer diameter slightly smaller than the inner diameter of the cylinder portion 51b on one end side in the axial direction, and a cylinder portion 54b having an outer diameter smaller than the body portion 54a on the other end side in the axial direction; a sleeve 55 formed in a cylindrical shape having an outer diameter equal to that of the body portion 54a of the tappet 54 and fitted to the outside of the cylindrical portion 54b of the tappet 54 at one end side in the axial direction; a C-shaped circlip 56 that is provided on the fitting surfaces of the tappet 54 and the sleeve 55 to connect the two and restricts relative movement in the axial direction; and a torsion spring 61 supported between the tappet 54 and the sleeve 55.

The tappet 54 is formed in a stepped cylindrical shape by a body portion 54a and a cylindrical portion 54b having different outer diameters. An inclined surface 54c substantially parallel to the inclined surface 52a of the wedge 52 is formed on one end side of the body portion 54 a. A spring attachment hole 54s for supporting one end side of the torsion spring 61 is formed in the cylindrical portion 54 b. In addition, a ring attachment groove 54r is formed in the cylindrical portion 54b over the entire outer circumferential surface. The tappet 54 is fitted into the innermost side of the cylinder 51b, and the inclined surface 54c is brought into contact with the circumferential surface of the roller 52f, so that the tappet can slide in the axial direction in the cylinder 51b via the roller 52f by the insertion and extraction operation of the wedge 52.

The sleeve 55 is formed in a hollow substantially cylindrical shape having a through hole 55a extending in the axial direction. The through hole 55a is configured such that a cylindrical hole 55b into which the cylindrical portion 54b of the tappet 54 is fitted, a spring attachment hole 55s that supports the other end side of the torsion spring 61, and a female screw portion 55c into which the screw 57 is screwed are coaxially communicated in this order from one end side in the axial direction. A ring attachment groove 55r is formed in the cylindrical hole 55b of the sleeve 55 over the entire inner circumferential surface. Further, an output gear 55g for transmitting the rotation of the sleeve 55 to the detection gear 71 of the wear detection device 7 is integrally formed on the outer peripheral surface of the sleeve 55.

When the cylindrical portion 54b of the tappet 54 is fitted into the cylindrical hole 55b of the sleeve 55, the ring mounting groove 54r carved along the outer circumferential surface of the cylindrical portion 54b is aligned with the ring mounting groove 55r carved along the inner circumferential surface of the cylindrical hole 55b, and an integral gap for mounting the circlip 56 is formed between the fitting surfaces of the tappet 54 and the sleeve 55. When the cylindrical portion 54b of the tappet 54 is fitted into the cylindrical hole 55b of the sleeve 55, the spring attachment hole 54s, which is open on the other end side of the cylindrical portion 54b, is aligned with the spring attachment hole 55s, which is open on the one end side of the sleeve 55, and an integral clearance for arranging the torsion spring 61 is formed in the tappet 54 and the sleeve 55.

The spring ring 56 is formed of, for example, a steel wire rod subjected to heat treatment such as quenching, tempering, or austempering, and is formed into a C-shape (front ring shape) in which a part of a circular ring is cut out, and is formed so as to be elastically deformable in a diameter reduction direction. The spring ring 56 is disposed in ring mounting grooves 54r, 55r formed integrally with the tappet 54 and the sleeve 55 in alignment with each other, and thereby connects the tappet 54 and the sleeve 55 so as not to be disengaged in the axial direction.

The torsion spring 61 is, for example, a compression coil spring obtained by cutting a spring material wound with a wire rod having a circular cross section and processed into a coil shape into a predetermined length. The torsion spring 61 is attached in a state of being elastically compressed and deformed in the axial direction by having one end side outer peripheral surface thereof engaged with the inner peripheral surface of the spring attachment hole 54s of the tappet 54 and the other end side outer peripheral surface thereof engaged with the inner peripheral surface of the spring attachment hole 55 s. The torsion spring 61 has a one-way clutch function, and allows relative rotation of the sleeve 55 with respect to the tappet 54 around the axis line in a diameter reduction direction in which the outer diameter of the coil is reduced (for example, right rotation in the case where the winding direction of the coil is right winding), and the outer peripheral surface engages with and integrates the tappet 54 and the sleeve 55 in a diameter expansion direction in which the outer diameter of the coil is increased (for example, left rotation in the case where the winding direction of the coil is right winding), thereby preventing the relative rotation.

The screw 57 is formed in a rod shape extending in the axial direction, has an external thread portion 57 on the outer peripheral surface, and is provided so as to extend outward of the side portion of the housing 51 by screwing the external thread portion 57a into the internal thread portion 55c of the sleeve 55. An adjustment dial 57b is provided on the other end side of the screw 57 in the axial direction. A clip 58 rotatable about a screw axis of the screw 57 is locked to the adjustment dial 57 b. The clip 58 engages with the web 41 of the brake shoe 40. The screw 57 is connected to the brake shoe 40 via a clip 58 that clamps the adjustment dial 57 b.

A helical spline 55d is engraved on the outer peripheral surface of the sleeve 55, and the drive ring 62 is engaged with the helical spline 55d with a predetermined clearance (for example, 3 mm). The drive ring 62 has a conical surface 62a that abuts against an inclined surface 51c formed at the outer end of the cylinder portion 51b, and a predetermined frictional resistance is applied between the inclined surface 51c and the conical surface 62a by a drive spring 63 that biases the drive ring 62 toward one end side in the axial direction.

The expanding device 5 of this configuration includes a clearance adjusting mechanism 6 that automatically reduces the clearance (shoe clearance) between the lining 43 and the brake drum 31 to a predetermined clearance when the lining 43 is worn. The gap adjustment mechanism 6 includes a sleeve unit 53, a screw 57, a drive ring 62, a drive spring 63, and the like. The function of the gap adjustment mechanism 6 will be described later.

As shown in fig. 6, the wear detection device 7 includes: a rotation detection mechanism 70 that detects rotation of the sleeve 55; a control unit 75 that detects wear of the lining 43 based on the rotation information detected by the rotation detection mechanism 70; and a reset switch 79 which can be operated from the outside. In the present embodiment, the wear detection device 7 is mounted only on one of the pair of gap adjustment mechanisms 6, 6 (the right gap adjustment mechanism 6) in fig. 3 and 4, but the present invention is not limited to this configuration, and the wear detection device 7 may be mounted on each of the pair of gap adjustment mechanisms 6, 6.

The rotation detection mechanism 70 includes: a detection gear 71 that rotates while meshing with the output gear 55g of the sleeve 55; a rotation sensor 72 that detects the amount of rotation (rotation angle) of the detection gear 71; and a sensor holder 73 (see fig. 3 and 4) holding the rotation sensor 72.

The detection gear 71 is externally engaged with the output gear 55g of the sleeve 55, and is configured to be capable of meshing with the output gear 55g by the rotational force of the sleeve 55. An input shaft 72a of a rotation sensor 72 is directly connected to the axial center of the detection gear 71. In the present embodiment, the gear ratio of the output gear 55g to the detection gear 71 is set to 2: 1, and when the sleeve 55 rotates half a turn (rotates 180 degrees), the detection gear 71 rotates one turn (rotates 360 degrees). Therefore, the number of rotations (rotation angle) of the detection gear 71 is 2 times the number of rotations (rotation angle) of the sleeve 55.

The rotation sensor 72 is constituted by, for example, a ring-shaped rotary potentiometer incorporating a hall IC (hall element). The rotation sensor 72 detects the rotation (rotation angle) of the sleeve 55 through the rotation (rotation angle) of the detection gear 71 coupled to the input shaft 72 a. The rotation sensor 72 of the present embodiment can detect a rotation angle in a range of 0 degrees to 360 degrees and output a voltage proportional to the rotation angle (0 degrees to 360 degrees) of the input shaft 72a, that is, a voltage proportional to the rotation angle (0 degrees to 360 degrees) of the detection gear 71. That is, when the rotation angle of the detection gear 71 is 0 degrees, the output voltage is an initial voltage (0V), the output voltage increases in proportion to the rotation angle of the detection gear 71, and when the rotation angle of the detection gear 71 reaches 360 degrees, the output voltage becomes a maximum voltage (5V). Further, as described above, the number of rotations (rotation angle) of the sleeve 55 is half of the number of rotations (rotation angle) of the detection gear 71 detected by the rotation sensor 72.

The control unit 75 is mainly configured by a microcomputer mounted with a CPU, a ROM, a RAM, and the like, and detects wear of the lining 43 based on detection information input from the rotation sensor 72. In the present embodiment, the control unit 75 is configured as a control board on which various electronic and electric components are mounted. The control unit 75 is electrically connected to the rotation sensor 72 via a connector cable 78a (see fig. 2), and is electrically connected to an electronic control unit ECU of the vehicle via a connector cable 78b (see fig. 2).

As shown in fig. 6, the control unit 75 includes a rotation number calculation unit 76 and a wear determination unit 77.

The rotation number calculation unit 76 calculates an integrated rotation number obtained by integrating the rotation number of the sleeve 55 up to the present time based on the detection information from the rotation sensor 72, and temporarily stores the integrated rotation number in a memory (RAM). Specifically, the rotational speed calculation unit 76 detects that the sleeve 55 has rotated half a turn (rotated 180 degrees) each time the rotational angle input from the rotation sensor 72 reaches the maximum rotational angle (360 degrees) (each time the maximum output voltage (5V) is input from the rotation sensor 72), and adds "1/2" to the cumulative rotational speed of the sleeve 55. Further, the accumulated rotation number is reset to "0" when the reset switch 79 is operated. That is, the integrated number of revolutions is an accumulated number of revolutions (an accumulated value) accumulated during a period from the time when the zero reset is performed to the current time.

The wear determination unit 77 compares the integrated number of revolutions of the sleeve 55 stored in the memory with a preset limit number of revolutions, and determines whether or not the integrated number of revolutions of the sleeve 55 reaches the limit number of revolutions. Here, the feed amount of the screw 57 is in proportion to the wear amount of the lining 43. In the present embodiment, the amount of wear of the linings 43 and the amount of feed of the screw 57 are set to 1: in relation to 2, the feed amount of the screw 57 is designed to be 2 times the wear amount of the lining 43. Therefore, when the wear amount up to the limit of use of the lining 43 is 10mm, the feed amount of the screw 57 fed out in accordance with the wear amount is 20 mm. The feed amount of the screw 57 is obtained by integrating the number of revolutions (integrated number of revolutions) of the sleeve 55 and the pitch of the two threads 55c and 57 a. In the present embodiment, the pitch is set to 1mm, and the screw 57 is fed by one pitch amount (1mm) per 1 rotation of the sleeve 55. Therefore, in the present embodiment, the wear amount of the lining 43 reaches 10mm (use limit) when the sleeve 55 rotates 20 revolutions. Here, in the present embodiment, in order to issue an alarm before the wear amount of the lining 43 reaches the use limit, the limit rotation number of the sleeve 55 is set to 19 rotations (the rotation number corresponding to the wear amount of 9.5 mm).

The wear determination unit 77 outputs an alarm signal to the electronic control unit ECU of the vehicle when determining that the integrated number of rotations of the sleeve 55 has reached the limit number of rotations. The electronic control unit ECU executes a predetermined alarm operation upon receiving an alarm signal from the control unit 75. In the present embodiment, as the predetermined warning operation, for example, the proximity of the lining usage limit is notified to the driver by turning on a warning lamp disposed in the driver's seat of the vehicle, outputting a warning sound, turning on the warning lamp, or the like.

When it is determined that the integrated number of revolutions of the sleeve 55 has not reached the limit number of revolutions (or at predetermined fixed time intervals), the wear determination unit 77 outputs information on the integrated number of revolutions of the sleeve 55 or information on the amount of wear of the lining 43 converted from the integrated number of revolutions to the electronic control unit ECU. Thereby, the electronic control unit ECU can manage the wear amount of the lining 43 individually for each wheel. For example, when determining that the wear amounts of a plurality of wheels provided in a vehicle are not uniform, the electronic control unit ECU can adjust the operation of the brakes for each wheel by the control of the electronic control brake system (EBS) to make the wear amounts of the wheels nearly uniform. In particular, in the present embodiment, since the wear state (wear amount) of the lining 43 can be detected in units of the rotation angle of the sleeve 55, the operation of the brake can be finely controlled.

Next, the operation of the clearance adjustment mechanism 6 and the wear detection device 7 will be mainly described as the operation of the drum brake B configured as described above when the brake is operated or not operated.

First, when a brake operation is performed, compressed air is supplied into the chamber 9 in accordance with the brake operation, and the wedge 52 is pressed in the insertion direction (downward direction in fig. 3 and 4) into the wedge housing 51a against the biasing force of the wedge spring 52a by the operation of the diaphragm in the chamber 9. The pressing force is converted into a pressing force in the axial direction via the roller 52f by a wedge action between the inclined surface 52c of the wedge member 52 and the inclined surface 54c of the tappet 54 extending in parallel to each other, and is transmitted to the sleeve assembly 53. The tappet 54 and the sleeve 55 receive the pressing force and move in the cylinder portion 51b from one end side to the other end side in the axial direction in an integrated state.

The helical spline 55d of the sleeve 55 and the drive ring 62 are engaged with a predetermined gap in the axial direction. If the amount of movement of the sleeve 55 based on the brake operation is within the range of the clearance, the sleeve 55 does not rotate the drive ring 62 and moves linearly in the axial direction within the cylinder portion 51 b. At this time, the drive ring 62 is held in a state where the conical surface 62a abuts against the inclined surface 51c of the housing 51 by the urging force of the drive spring 63.

The screw 57 engaged with the sleeve 55 is locked to the brake shoe 40 by the clip 58, and linearly moves in the axial direction in cooperation with the sleeve 55 without relative rotation with respect to the sleeve 55 by the frictional resistance of the clip 58 and the frictional resistance on the thread surface. Further, the brake shoe 40 swings outward around the anchor pin 44 by the extension of the screw 57 in the axial direction, the lining 43 is pressed against the inner circumferential surface of the brake drum 31, and the rotation of the brake drum 31 is braked by the friction between the lining and the inner circumferential surface.

When the braking operation is released, the wedge 52 is moved in a direction (upward in fig. 3 and 4) to be pulled out from the wedge housing 51a by the biasing force of the wedge spring 52 a. The screw 57 and the sleeve unit 53 are moved from the other end side to the one end side in the axial direction in the cylinder portion 51b by the action of the return spring 45 provided astride between the two brake shoes 40, and are housed inward in the axial direction. If the amount of movement of the sleeve 55 is within the range of the clearance, the sleeve 55 linearly moves in the axial direction within the cylinder portion 51b without rotating as in the case of extension.

On the other hand, when the lining 43 is worn, the amount of movement in the axial direction of the screw 57 and the sleeve unit 53 is increased in order to obtain the same braking effect at the time of brake operation. At this time, when the amount of movement of the sleeve 55 during brake operation exceeds the amount of clearance, the meshing surface of the helical spline 55d abuts against the meshing surface of the drive ring 62, and the drive ring 62 receives a pressing force toward the other end side in the axial direction. By this pressing force, the frictional force between the inclined surface 51c and the conical surface 62a is reduced, and the drive ring 62 rotates along the meshing surface of the helical spline 55 d. Further, with the one-way clutch function of the torsion spring 61, the sleeve 55 is prevented from relative rotation with respect to the tappet 54, and thus moves linearly in the axial direction within the cylinder portion 51 b.

When the brake operation is released, the screw 57 and the sleeve assembly 53 are returned to one end side in the axial direction by the biasing force of the return spring 45, and the contact between the drive ring 62 and the helical spline 55d is released. Then, the drive ring 62 is pressed toward one end side in the axial direction by the urging force of the drive spring 63, and the conical surface 62a is brought into contact with the inclined surface 51c of the housing 51. Thereby, the drive ring 62 is restricted from rotating by frictional resistance at the abutment surfaces. In contrast, the sleeve 55 moves toward one end side in the axial direction within the cylinder portion 51b with a considerable amount of clearance between the helical spline 55d and the drive ring 62 without receiving resistance. On the other hand, if the amount of movement of the sleeve 55 exceeds the amount of play by a considerable amount, the helical spline 55d abuts against the meshing surface on the other end side of the drive ring 62 to prevent movement in the axial direction.

At this time, as described above, the drive ring 62 is restricted from rotating by the abutment with the inclined surface 51c of the housing 51, and cannot freely rotate. On the other hand, the torsion spring 61 incorporated in the sleeve unit 53 is formed so as to restrict rotation in a direction (e.g., left rotation) in which the sleeve 55 rotates along the meshing surface on one end side of the drive ring 62, and so as to allow rotation in a direction (e.g., right rotation) in which the sleeve 55 rotates along the meshing surface on the other end side of the drive ring 62. Therefore, this time, the sleeve 55 rotates along the engaging surface of the other end side of the drive ring 62. At this time, although a frictional resistance is applied to the relative rotation of the sleeve 55 with respect to the tappet 54 by the circlip 56, the return spring 45 exerts a biasing force to such an extent that the sleeve 55 is rotated against the frictional force.

Here, the screw 57 receives frictional resistance from the clip 58 locked to the brake shoe 40 and restricted from rotating. This frictional resistance is greater than the frictional resistance of the screw 57 and the thread surface of the sleeve 55, and therefore the screw 57 does not rotate integrally with the sleeve 55. Thus, the sleeve 55 rotates independently of the tappet 54 and the screw 57. Then, by the rotation of the sleeve 55, the screw 57 is fed out in the axial direction outward by a feed amount corresponding to the rotation amount (rotation angle) of the sleeve 55.

In this way, in the clearance adjustment mechanism 6, when the lining 43 is worn, the sleeve 55 moves by more than a predetermined amount (a clearance amount equivalent) when the brake is operated, and when the brake is released, the sleeve 55 rotates by a rotation amount (rotation angle) corresponding to the more than amount to feed the screw 57, thereby automatically adjusting the clearance between the lining 43 and the drum brake 31 to be always constant.

At this time, the control unit 75 constantly monitors the rotation amount (integrated rotation number) of the sleeve 55 based on the detection information input from the rotation sensor 72 in order to detect the wear amount of the lining 43 at the present time. That is, each time the detection information is input from the rotation sensor 72, the control unit 75 calculates the cumulative number of rotations of the sleeve 55 at the present time, compares the cumulative number of rotations with a predetermined limit number of rotations, and determines whether or not the cumulative number of rotations of the sleeve 55 reaches the limit number of rotations. When it is determined that the integrated number of revolutions of the sleeve 55 has reached the limit number of revolutions, the control unit 75 determines that the wear amount of the lining 43 is close to the usage limit, and outputs an alarm signal to the electronic control unit ECU of the vehicle.

When an alarm signal is input from the control unit 75, the electronic control unit ECU executes a predetermined alarm operation. As described above, the predetermined warning operation is a notification to the driver that the usage limit of the lining 43 is approaching, for example, by lighting a warning lamp disposed in the driver's seat of the vehicle, outputting a warning sound, lighting the warning lamp, or the like.

When such an alarm operation is performed, the brake braking force of the brake is reduced (safety of running is reduced) by further using the lining 43, and therefore, the replacement work of the brake shoe 40 (lining 43) is required. As a result, after the brake shoe 40 is replaced with a new one, the reset switch 79 is operated to reset the integrated number of revolutions (the integrated value of the number of revolutions) stored in the memory of the control unit 75 to zero.

As described above, according to the drum brake B of the present embodiment, the rotation amount of the sleeve 55 is detected by the rotation sensor 72 using the equivalent relationship between the rotation amount of the sleeve 55 and the wear amount of the lining 43 when the shoe clearance is adjusted, and the wear state of the lining 43 is detected based on the rotation amount (integrated number of revolutions) of the sleeve 55, whereby the wear state of the lining 43 can be detected with high accuracy even before the lining 43 reaches the use limit (for example, not limited to the inspection of the vehicle during running), and the wear detector does not need to be replaced as in the conventional art when the lining 43 reaches the use limit and the brake shoe 40 is replaced, so that the component cost and the replacement man-hours can be reduced, and the running cost can be suppressed.

The present invention is not limited to the above embodiments, and can be modified as appropriate within a range not departing from the gist of the present invention.

In the above embodiment, the potentiometer is exemplified as an example of the rotation sensor 72, but the present invention is not limited to this configuration, and other rotation sensors such as a rotary encoder and a laser sensor may be applied.

In the above embodiment, the limit rotation number of the sleeve 55 is set to 19 revolutions (the rotation number corresponding to the wear amount of 9.5 mm), but the present invention is not limited to this configuration, and the limit rotation number of the sleeve 55 may be appropriately set according to the required specifications of the vehicle, for example.

In the above embodiment, the shoe-type drum brake is exemplified as the drum brake B, but the present invention is not limited to this configuration, and for example, a one-way servo type, a two-way servo type, or a two-way type drum brake may be applied.