JP7407064B2 - drum brake - Google Patents

Description

The present invention relates to a drum brake, and more particularly to a drum brake equipped with a gap adjustment mechanism.

A drum brake has a cylindrical brake drum that is rotatably attached to an axle, and a pair of brake shoes that are swingably held by an anchor bracket and arranged along the inner circumferential surface of the brake drum. By pressing the brake lining provided on the brake shoe facing the brake drum against the inner peripheral surface of the brake drum, the rotation of the brake drum (wheel mounted on the axle) is braked using the friction generated between the two. It is something to do.

In such drum brakes, an expander is attached to the tip of the brake shoe that extends outward in response to brake operation, and the expansion of the expander causes the brake shoe to swing and move the brake lining onto the brake drum. There is one that is configured to be pressed against the inner peripheral surface. This drum brake expander has a tappet, a sleeve that is coaxially attached to the tappet, and a screw that is screwed into the sleeve and whose outer end connects to the brake shoe. It is constructed by being inserted into the space. Here, the tappet and the sleeve are connected via a circlip to restrict relative movement in the axial direction. Additionally, a one-way clutch is disposed between the tappet and the sleeve, allowing rotation of the sleeve in one direction around the axis relative to the tappet, and restricting rotation in the other direction around the axis. ing. The brake lining wears out due to friction with the brake drum, and when the gap between the brake lining and the brake drum (hereinafter also referred to as shoe clearance) increases due to this wear, it also causes deterioration in brake effectiveness. Therefore, drum brakes are equipped with a gap adjustment mechanism that automatically adjusts the shoe clearance according to the wear of the brake lining to maintain a constant gap between the brake lining and the brake drum (for example, , see Patent Document 1). The gap adjustment mechanism rotates the sleeve independently relative to the screw (rotating in one direction), causing the screw that is engaged with the sleeve to extend outward, thereby swinging the brake lining and adjusting the shoe clearance. It is configured to pack.

JP2006-242238A

However, in the above-mentioned conventional drum brake, if the shoe clearance is adjusted even after the wear of the brake lining progresses and reaches a certain wear limit (usage limit), the screw is extended outwards excessively, causing the brake There was a problem in that the gap adjustment mechanism and brake drum could be damaged due to interference with the drum (biting into the brake drum).

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a drum brake that can prevent damage to the gap adjustment mechanism and the brake drum due to over-adjustment of shoe clearance. shall be.

In order to achieve the above object, the drum brake according to the present invention includes a cylindrical brake drum that is provided on a rotating member and is rotatable integrally with the rotating member, and a cylindrical brake drum that is provided on a fixed member so as to be swingable. A brake shoe having a brake lining disposed along the inner circumferential surface of the brake drum; and an expander that swings the brake shoe in response to a brake operation and presses the brake lining against the inner circumferential surface of the brake drum. The expander is provided with a pressing force generating member that applies a pressing force in the axial direction in response to a brake operation, and a pressing force generating member that is rotatable around the axial direction with respect to the pressing force generating member. a transmission member; the transmission member is screwed into the transmission member in the axial direction and is connected to the brake shoe so as not to rotate around the axial direction; a pressing member that presses the brake lining against the inner circumferential surface of the brake drum by swinging the brake lining, and rotating the transmission member around the axial direction to extend the pressing member in the axial direction, A gap adjustment mechanism is provided that adjusts a gap between the brake lining and the inner peripheral surface of the brake drum by displacing the relative position of the pressing member in the axial direction with respect to the transmission member, and the pressing member , further comprising a stopper that prevents the pressing member from being extended beyond a prescribed amount in the axial direction with respect to the transmission member.

In the drum brake according to the present invention, the transmission member has a receiving part that receives the pressing member along the axial direction, and the receiving part is provided with a stopper receiving part, and the pressing member It is preferable that when the pressing member is paid out in the axial direction by the specified amount, the stopper comes into contact with the stopper receiving portion, so that the pressing member is prevented from being paid out in the axial direction by more than the specified amount. .

Further, in the drum brake according to the present invention, the pressing member includes a first pressing member that is screwed to the transmission member and received in the receiving portion, and a first pressing member that is provided on a distal end side of the first pressing member and that is attached to the brake member. and a second pressing member connected to the shoe, and preferably the first pressing member and the second pressing member are separably coupled to each other.

Furthermore, in the drum brake according to the present invention, the transmission member and the pressing force generating member are arranged such that relative rotation of the transmitting member with respect to the pressing force generating member in one direction around the axial direction is allowed. A wrap spring is disposed to restrict relative rotation in other directions around the axial direction, and the outer diameter of the stopper is formed to be smaller than the inner diameter of the wrap spring, so that the stopper It is preferable to be configured so that it can be inserted in the axial direction.

According to the drum brake according to the present invention, the stopper function is activated when the amount of extension of the pressing member reaches a specified amount, thereby preventing the pressing member from being extended excessively, thereby limiting the use of the brake lining. Even if the drum brake is used continuously for a period exceeding This enables effective suppression.

Further, in the drum brake according to the present invention, the pressing member is divided into two parts, the first pressing member and the second pressing member, and the first pressing member and the second pressing member are separably connected. When installing a dustproof boot across the brake housing and the brake housing, the boot can be attached to the brake housing with the first pressing member and the second pressing member separated, making it easy to replace the boot. It becomes possible to convert into

Furthermore, in the drum brake according to the present invention, the outer diameter of the stopper is formed to be smaller than the inner diameter of the wrap spring, and the stopper is configured to be able to be inserted into the wrap spring in the axial direction. Although it is made compact, it is possible to ensure a large stroke in the feeding direction (axial direction) of the pressing member.

It is a front view showing the drum brake of this embodiment. FIG. 2 is a sectional view taken along the arrow AA in FIG. 1, and shows the drum brake when it is not in operation. FIG. 2 is a cross-sectional view taken along arrow AA in FIG. 1, showing the drum brake when it is in operation. FIG. 3 is a sectional view showing an exploded state of the sleeve assembly of the drum brake. It is a sectional view showing the assembled state of the screw of the above-mentioned drum brake. FIG. 3 is a sectional view showing a disassembled state of the screw of the drum brake.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, the overall configuration of a drum brake according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6. In addition, in FIGS. 2, 3, etc., hatching of some cross-sectional parts is omitted to make the figures easier to see.

As shown in FIG. 1, the drum brake B includes an anchor bracket 2 that is fixed to the vehicle body together with a dust cover 29, and a drum unit 3 that includes a brake drum 31 that is provided on the axle 1 and rotates integrally with the axle 1. A brake shoe unit 4 includes a pair of brake shoes 40, 40 that are swingably provided on the anchor bracket 2 and arranged along the inner circumferential surface of the brake drum 31, and It is mainly composed of an expander 5 that swings 40, 40 and presses it against the inner circumferential surface of the brake drum 31. In addition, in FIG. 1, the drum unit 3 (brake drum 31) is shown by a two-dot chain line, and detailed illustration is omitted.

The anchor bracket 2 has a circular hole-shaped opening 21 in the center, and is connected to an axle housing (not shown) of the vehicle body through a bolt (not shown) inserted into a bolt hole 22 provided around the opening 21. Fixed. Further, a brake shoe support portion 25 is formed at the bottom of the anchor bracket 2, and the brake shoe support portion 25 is bifurcated in the thickness direction (direction perpendicular to the plane of FIG. 1). They are lined up on the left and right when viewed from the front.

The drum unit 3 has a wheel rim (not shown) attached to a wheel hub (not shown) rotatably attached via a bearing to the axle 1 that projects outward from the opening 21 of the anchor bracket 2. , brake drum 31 are combined. Note that a wheel is attached to the wheel rim, and the brake drum 31 and the wheel rotate together through the wheel hub.

The brake shoe unit 4 includes two brake shoes 40 and 40 disposed on the left and right sides in a front view with the anchor bracket 2 in between. Each brake shoe 40 includes a web part 41 extending in an arc shape, a rim part 42 attached to the outer peripheral end of the web part 41, and a brake lining (hereinafter referred to as "lining") fixed to the rim part 42 with rivets or the like. 43. The brake shoe 40 is disposed along the inner circumferential surface of the brake drum 30, and has a lining 43 facing the inner circumferential surface of the brake drum 31.

The brake shoe 40 has its base end 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 swings around the anchor pin 44 as shown in FIG. It is possible to swing from side to side. A return spring 45 is provided between the tip ends of the pair of brake shoes 40, 40 to connect them to each other. When the brakes are not operated (brake non-operation), each brake shoe 40 is at a position where it is swung inward under the urging force of the return spring 45 (i.e., at a position away from the brake drum 31). ) is held.

Furthermore, an expander 5 fixed to the anchor bracket 2 is disposed between the tip ends of the pair of brake shoes 40, 40. As will be described in detail later, when the brake is operated (brake operation), the expander 5 causes the tip of each brake shoe 40 to attach to the return spring 45 by the extension operation (feeding operation) of each screw 57. Push outward against the force. Each brake shoe 40 swings outward around each anchor pin 44, and each lining 43 is pressed against the inner peripheral surface of the brake drum 31, and the rotation of the brake drum 31 is braked by the frictional force between the two. be done. Thereby, a predetermined braking effect can be obtained on the wheels that rotate integrally with the brake drum 31.

As shown in FIGS. 2 and 3, the expander 5 includes a housing 51 having a wedge accommodating portion 51a formed in the center and a pair of cylinder portions 51b, 51b communicating with the wedge accommodating portion 51a from both sides. , a wedge 52 that is removably attached to the wedge accommodating portion 51a, and a sleeve that is inserted into each cylinder portion 51b so as to be slidable in the direction of the axis X (hereinafter also referred to as the “axial direction”). The housing 51 is configured to include an assembly 53 and a screw 57 that is threadedly engaged with the sleeve assembly 53 in the axial direction and extends outward from the side of the housing 51. A boot 59 is removably attached to the open end of the cylinder portion 51b of the housing 51 to prevent dust from entering the cylinder portion 51b.

The expander 5 is configured symmetrically in FIGS. 2 and 3, and hereinafter, the inner side of the housing 51 in the axial direction ( The wedge accommodating portion 51a side) will be referred to as "one end side," and the outer side of the housing 51 in the axial direction (brake shoe 40 side) will be referred to as the "other end side." Note that FIG. 2 shows the state of the expander 5 when the brake is not applied, and FIG. 3 shows the state of the expander 5 when the brake is applied.

The wedge 52 is formed into a shaft shape and is attached to the housing 51 so that it can be inserted into and removed from the housing 51 in a direction perpendicular to the axial direction (hereinafter also referred to as an "orthogonal direction to the axis") by the operation of a diaphragm in the chamber 9. When the brake is not activated (when the brake is released), the wedge 52 is pulled out to the outside of the wedge accommodating portion 51a by the biasing force of the wedge spring 52a, as shown in FIG. Ru. On the other hand, when the brake is activated, the wedge 52 moves in the direction perpendicular to the axis (downward in FIG. 3) within the wedge housing portion 51a against the biasing force of the wedge spring 52a, as shown in FIG. It is in a state where it is inserted into the accommodating portion 51a. The insertion end 52b, which is the end inserted into the wedge accommodating portion 51a, is formed into a wedge shape that tapers toward the tip, and has inclined surfaces 52c on both sides in the axial direction. Furthermore, a roller holder 52e that supports a pair of rollers 52f is provided on the tip side (insertion end 52b side) of the wedge 52. The pair of rollers 52f are provided rotatably relative to the roller holder 52e and movable in directions toward and away from each other (axial direction). Further, the roller holder 52e is provided so as to be able to reciprocate along the direction orthogonal to the axis, and is always urged toward the outside of the housing 51 (upward in FIG. 3) together with the wedge 52 by the wedge spring 52a. . The roller holder 52e cooperates with the wedge 52 to convert the linear motion of the wedge 52 in the direction orthogonal to the axis into the linear motion of the sleeve assembly 53 in the axial direction.

As shown in FIG. 4, the sleeve assembly 53 has a main body part 54a formed at one end in the axial direction, the outer diameter of which is slightly smaller than the inner diameter of the cylinder part 51b, and a main body part 54a at the other end in the axial direction. A tappet 54 having an outer diameter 54b smaller than that of the tappet 54a, and a tappet 54 formed into a cylindrical shape having the same outer diameter as the main body 54a of the tappet 54 and fitted outwardly to the cylindrical portion 54b of the tappet 54 at one end in the axial direction. A C-shaped circlip 56 is provided on the fitting surfaces of the tappet 54 and the sleeve 55 to connect them and restrict their relative movement in the axial direction, and the tappet 54 and the sleeve 55. The wrap spring 61 is supported by a wrap spring 61.

The tappet 54 is formed into a stepped cylindrical shape including a main body portion 54a and a cylindrical portion 54b having different outer diameters. An inclined surface 54c that is substantially parallel to the inclined surface 52a of the wedge 52 is formed on one end side of the main body portion 54a. A spring attachment hole 54s that supports one end of the wrap spring 61 is formed in the cylindrical portion 54b. Further, a ring attachment groove 54r is formed in the cylindrical portion 54b over the entire circumference of the outer peripheral surface. The tappet 54 is fitted into the innermost part of the cylinder part 51b, and has an inclined surface 54c in contact with the circumferential surface of the roller 52f, and when the wedge 52 is inserted and removed, the inside of the cylinder part 51b is moved along the axis through the roller 52f. It is possible to slide in the direction.

The sleeve 55 is formed into a hollow, substantially cylindrical shape having a through hole 55a extending along the axial direction. The through hole 55a includes, in order from one end in the axial direction, a cylindrical hole 55b into which the cylindrical portion 54b of the tappet 54 is fitted, a spring mounting hole 55s that supports the other end in the axial direction of the wrap spring 61, and a screw 57. A stopper insertion hole 55c, into which a stopper 57d formed at one end in the axial direction is inserted, and a female threaded part 55d, into which the male threaded part 57c of the screw 57 is screwed, are coaxially communicated with each other. . In the cylindrical hole 55b of the sleeve 55, an annular ring attachment groove 55r is formed over the entire circumference of the inner peripheral surface. Further, the inner diameter of the stopper insertion hole 55c is larger than the outer diameter of the stopper 57d. An annular stopper receiving portion 55e extending in a direction orthogonal to the axial direction is formed in a stepped portion between the stopper insertion hole 55c and the female screw portion 55d.

When the cylindrical portion 54b of the tappet 54 and the cylindrical hole 55b of the sleeve 55 are fitted together, a ring mounting groove 54r carved along the outer peripheral surface of the cylindrical portion 54b and a groove 54r carved along the inner peripheral surface of the cylindrical hole 55b are formed. The provided ring attachment grooves 55r align with each other, and an integral gap is formed between the fitting surfaces of the tappet 54 and the sleeve 55 for mounting the circlip 56 thereon. Furthermore, when the cylindrical portion 54b of the tappet 54 and the cylindrical hole 55b of the sleeve 55 are fitted together, a spring mounting hole 54s opens at the other end of the cylindrical portion 54b and a spring mounting hole 54s opens at one end of the sleeve 55. The holes 55s are aligned to form an integral gap inside the tappet 54 and the sleeve 55 in which the wrap spring 61 is disposed.

The circlip 56 is made of a steel wire that has been heat-treated, such as quenching, tempering, or austempering, and has a C shape (front ring shape) with a part of the ring cut out, and can be elastically deformed in the radial direction. is formed. The circlip 56 is arranged in ring mounting grooves 54r and 55r that are aligned and integrated with each other between the fitting surfaces of the tappet 54 and the sleeve 55, so that the tappet 54 and the sleeve 55 can be connected in the axial direction. is irremovably connected to.

The wrap spring 61 is a compression coil spring obtained by cutting a spring material into a predetermined length into a predetermined length, for example, by winding a wire having a circular cross section and processing the spring material into a coil shape. The wrap spring 61 has an outer circumferential surface on one end side engaged with an inner circumferential surface of the spring mounting hole 54s of the tappet 54, and an outer circumferential surface on the other end side engaged with the inner circumferential surface of the spring mounting groove 55s, so that the axis It is attached in a state where it is elastically compressed and deformed in the direction. This wrap spring 61 has a one-way clutch function, and rotates around the axis of the sleeve 55 with respect to the tappet 54 in the diameter reduction direction in which the outer diameter of the coil is reduced (for example, clockwise rotation when the coil winding direction is clockwise). In the diameter expansion direction in which the outer diameter of the coil is expanded (for example, counterclockwise rotation when the coil winding direction is clockwise), the outer circumferential surface bites into the tappet 54 and the sleeve 55 and are integrated to prevent this relative rotation. As shown in FIG. 2, the inner diameter of the wrap spring 61 is larger than the outer diameter of the stopper 57d, and the stopper 57d can be inserted through the wrap spring 61 in the axial direction. Thereby, while the drum brake B as a whole is made smaller and more compact, a large stroke in the feeding direction (axial direction) of the screw 57 can be ensured.

As shown in FIGS. 5 and 6, the screw 57 includes a threaded shaft portion 57a received in the through hole 55a of the sleeve 55, and an adjustment dial separably fastened to the threaded shaft portion 57a with a countersunk bolt 57j. 57b.

The threaded shaft portion 57a is formed into a rod shape extending in the axial direction, and has a male threaded portion 57c on its outer peripheral surface. This male threaded portion 57c is screwed into the female threaded portion 55c of the sleeve 55. Further, a flange-shaped stopper 57d having an outer diameter larger than that of the male threaded portion 57c is integrally formed at one end of the threaded shaft portion 57a in the axial direction. This stopper 57d is inserted into the through hole 55a of the sleeve 55 and is formed so as to be able to come into contact with the stopper receiving portion 55e. Thereby, the screw 57 is attached to the through hole 55a of the sleeve 55 in a manner that prevents it from coming off. Further, a fitting portion 57e that is convex toward the adjustment dial portion 57b is formed on the other end of the screw shaft portion 57a in the axial direction. A screw hole 57f into which a countersunk bolt 57j is screwed is bored in the axial direction of the fitting portion 57e.

The adjustment dial portion 57b is detachably attached to the other end of the screw shaft portion 57a in the axial direction. A clip 58 is locked to the adjustment dial portion 57b so as to be rotatable around the screw shaft of the screw 57. Clip 58 engages web portion 41 of brake shoe 40 . The screw 57 is connected to the brake shoe 40 via a clip 58 that is provided while holding the adjustment dial portion 57b. Further, a center hole 57g through which a countersunk bolt 57j is inserted is formed through the adjustment dial portion 57b in the axial direction. Further, the adjustment dial portion 57b is provided with a fitting hole 57h that is formed to be able to fit into the fitting portion 57e of the screw shaft portion 57a. Further, a boot mounting groove 57i is formed along the circumferential direction on the outer peripheral portion of the adjustment dial portion 57b.

In the screw 57 having such a configuration, after fitting the fitting portion 57e of the screw shaft portion 57a into the fitting hole 57h of the adjustment dial portion 57b, the countersunk bolt 57j is inserted into the screw shaft through the center hole 57g of the adjustment dial portion 57b. It is assembled integrally by screwing into the screw hole 57f of the portion 57a. Further, the screw 57 is attached to the sleeve 55 by screwing the male threaded portion 57c of the screw shaft portion 57a into the female threaded portion 55d of the sleeve 55. A boot 59 is removably attached between the screw 57 and the housing 51 to prevent dust from entering the cylinder portion 51b. To attach the boot 59, first, the screw shaft portion 57a is attached to the through hole 51a of the housing 51 in a manner that it cannot be removed, and then one end side of the boot 59 is press-fitted into the boot attachment hole 51d of the housing 51. Then, by fastening the adjustment dial portion 57b to the screw shaft portion 57a with the countersunk bolt 57j and engaging the other end side of the boot 59 with the boot mounting groove 57j of the adjustment dial portion 57b, the boot 59 is connected to the screw 57. It will be attached so as to straddle between the housing 51 and the housing 51. By dividing the screw 57 into two parts, the screw shaft part 57a and the adjustment dial part 57b, the boot 59 can be attached to the housing 51 with the screw shaft part 57a and the adjustment dial part 57b separated. Therefore, the work of replacing the boots 59 can be facilitated. Note that other fastening members (fastening means) such as a knock pin or a retaining ring may be used as the fastening member (fastening means) between the screw shaft portion 57a and the adjustment dial 57b.

A spiral helical spline 55f is carved on the outer peripheral surface of the sleeve 55, and the drive ring 62 meshes with the helical spline 55f with a predetermined play (for example, 3 mm). The drive ring 62 has a conical surface 62a that comes into contact with an inclined surface 51c formed at the outer end of the cylinder portion 51b, and a drive spring 63 that biases the drive ring 62 toward one end in the axial direction It is configured to provide a predetermined frictional resistance between the conical surface 51c and the conical surface 62a.

The expander 5 having such a configuration has a gap adjustment mechanism 6 that automatically closes the gap (shoe clearance) between the lining 43 and the brake drum 31 to a predetermined gap when the lining 43 wears out. It is equipped. The gap adjustment mechanism 6 includes a sleeve assembly 53, a screw 57, a drive ring 62, a drive spring 63, and the like.

Next, the operation of the drum brake B having the above configuration when the brake is activated and when it is not activated will be explained.

First, when the brake is operated, compressed air is supplied into the chamber 9 in response to the brake operation, and due to the operation of the diaphragm in the chamber 9, the wedge 52 is pushed into the wedge housing part against the biasing force of the wedge spring 52a. It is pressed in the direction of insertion into 51a (downward in FIGS. 2 and 3). This pressing force is converted into a pressing force in the axial direction via the roller 52f due to the wedge action between the inclined surface 52c of the wedge 52 and the inclined surface 54c of the tappet 54, which extend parallel to each other, and is transmitted to the sleeve assembly 53. In response to this pressing force, the tappet 54 and the sleeve 55 move in an integrated state within the cylinder portion 51b from one end to the other end in the axial direction.

The helical spline 55f of the sleeve 55 and the drive ring 62 are engaged with each other with a predetermined play in the axial direction. If the amount of movement of the sleeve 55 due to the brake operation is within the range of play, the sleeve 55 moves linearly within the cylinder portion 51b along the axial direction without rotating the drive ring 62. At this time, the drive ring 62 is held with the conical surface 62a in contact with the inclined surface 51c of the housing 51 by the biasing force of the drive spring 63.

The screw 57 that is engaged with the sleeve 55 is locked to the brake shoe 40 by a clip 58, and cooperates with the sleeve 55 without rotating relative to the sleeve 55 due to the frictional resistance of the clip 58 and the frictional resistance on the threaded surface. It moves directly in the axial direction. Then, due to the extension of the screw 57 in the axial direction, the brake shoe 40 swings outward around the anchor pin 44, and the lining 43 is pressed against the inner peripheral surface of the brake drum 31, and the friction between the two causes the brake shoe 40 to swing outward about the anchor pin 44. The rotation of the drum 31 is braked.

When the brake operation is released, the wedge 52 moves in the direction of removal from the wedge accommodating portion 51a (upward in FIGS. 2 and 3) due to the biasing force of the wedge spring 52a. The screw 57 and the sleeve assembly 53 move within the cylinder portion 51b from the other end in the axial direction to the one end due to the action of the return spring 45 installed between both the brake shoes 40, 40, and move inside the cylinder portion 51b in the axial direction. It is stored in the opposite direction. If the amount of movement of the sleeve 55 is within the range of play, the sleeve 55 moves linearly along the axial direction within the cylinder portion 51b without rotating, similarly to when it is extended.

On the other hand, as the lining 43 becomes worn, the amount of movement of the screw 57 and sleeve assembly 53 in the axial direction increases in order to obtain the same braking effect during brake operation. At this time, if the amount of movement of the sleeve 55 during brake operation exceeds an amount equivalent to the backlash, the engagement surface of the helical spline 55f comes into contact with the engagement surface of the drive ring 62, and the drive ring 62
receives a pressing force toward the other end in the axial direction. This pressing force reduces the frictional force between the inclined surface 51c and the conical surface 62a, and the drive ring 62 rotates along the engagement surface of the helical spline 55f. Note that the sleeve 55 is prevented from rotating relative to the tappet 54 by the one-way clutch function of the wrap spring 61, and moves linearly within the cylinder portion 51b along the axial direction.

Further, 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 urging force of the return spring 45, so that the contact between the drive ring 62 and the helical spline 55f is released. Then, the drive ring 62 is pressed toward one end in the axial direction by the biasing force of the drive spring 63, and the conical surface 62a is brought into contact with the inclined surface 51c of the housing 51. As a result, rotation of the drive ring 62 is restricted by frictional resistance on the contact surface. On the other hand, the sleeve 55 moves toward one end in the axial direction within the cylinder portion 51b without receiving resistance by an amount equivalent to the play between the helical spline 55f and the drive ring 62. On the other hand, when the amount of movement of the sleeve 56 exceeds an amount equivalent to the backlash, the helical spline 55f comes into contact with the engagement surface on the other end side of the drive ring 62, preventing movement in the axial direction.

At this time, as described above, the rotation of the drive ring 62 is restricted by contact with the inclined surface 51c of the housing 51, and cannot rotate freely. On the other hand, the wrap spring 61 built into the sleeve assembly 53 restricts rotation in the direction in which the sleeve 55 is rotated along the engagement surface on one end side of the drive ring 62 (for example, counterclockwise rotation). The sleeve 55 is formed to allow rotation in the direction in which the sleeve 55 is rotated along the engagement surface on the other end side of the drive ring 62 (for example, clockwise rotation). Therefore, the sleeve 55 is now rotated along the engagement surface on the other end side of the drive ring 62. At this time, the circlip 56 applies frictional resistance to the relative rotation of the sleeve 55 with respect to the tappet 54, but the return spring 45 exerts a biasing force sufficient to rotate the sleeve 55 against this frictional force. do.

Here, the screw 57 receives frictional resistance from a clip 58 that is locked to the brake shoe 40 and whose rotation is restricted. Since this frictional resistance is greater than the frictional resistance between the threaded surfaces of the screw 57 and the sleeve 55, the screw 57 does not rotate together with the sleeve 55. Therefore, the sleeve 55 rotates independently with respect to the tappet 54 and the screw 57. As the sleeve 55 rotates, the screw 57 is extended outward in the axial direction by an amount corresponding to the amount of rotation of the sleeve 55.

In this way, in the gap adjustment mechanism 6, when the lining 43 is worn, the sleeve 55 moves by an amount exceeding a predetermined amount (an amount corresponding to backlash) when the brake is applied, while the sleeve 55 moves by this excess amount when the brake is released. The gap (shoe clearance) between the lining 43 and the drum brake 31 is always constant by rotating the screw 57 by an amount corresponding to the amount of rotation and letting the screw 57 extend outward in the axial direction by an amount corresponding to the amount of rotation. Automatically adjust so that

Here, the amount of feed of the screw 57 is proportional to the amount of wear of the lining 43. In this embodiment, the amount of wear of the lining 43 and the amount of payout of the screw 57 are in a 1:2 relationship, and the amount of payout of the screw 57 is designed to be twice the amount of wear of the lining 43. Therefore, if the amount of wear of the lining 43 up to the limit of use is 10 mm, the amount of payout of the screw 57 corresponding to this amount of wear (limit of use) will be 20 mm. Further, the feeding amount of the screw 57 can be obtained by integrating the number of rotations (cumulative number of rotations) of the sleeve 55 and the thread pitch of both screws 55c and 57a. In this embodiment, the screw pitch is set to 1 mm, and each time the sleeve 55 rotates once, the screw 57 moves by the screw pitch (
1mm). Therefore, in this embodiment, when the sleeve 55 rotates 20 times, the amount of feed of the screw 57 becomes 20 mm, and the wear amount of the lining 43 reaches 10 mm (usage limit).

In this embodiment, in order to prevent excessive feeding of the screw 57, the stopper 57d of the screw 57 comes into contact with the stopper receiving portion 55e of the sleeve 55 when the wear amount of the lining 43 reaches the usable limit (10 mm). The stopper function is activated. Specifically, when the drum brake B is used for a long period of time and the amount of the screw 57 is fed out reaches a predetermined amount (20 mm), the stopper 57d comes into contact with the stopper receiving portion 55e, and the screw is stopped. 57 in the axial direction is restricted. By preventing the screw 57 from being extended excessively beyond the specified amount (by preventing over-adjustment of the shoe clearance), the screw 57 can be prevented from interfering with the brake drum 31 during brake operation ( (biting into the brake drum 31) can be prevented.

As described above, according to the drum brake B according to the present embodiment, the stopper function is activated when the amount of the screw 57 that is fed out reaches the specified amount, and the screw 57 is prevented from being fed out excessively. Even if the drum brake B is continued to be used beyond the usage limit of the lining 43, the screw 57 is prevented from interfering with the brake drum 31 when the brake is activated, resulting in damage to the gap adjustment mechanism 6 and the brake drum 31. , and the occurrence of wheel locking can be effectively prevented.

In addition, in the drum brake B according to the present embodiment, the screw 57 is divided into two parts, the screw shaft part 57a and the adjustment dial part 57b, and the screw shaft part 57a and the adjustment dial part 57b are separably fastened with a countersunk bolt 57j. As a result, when the dustproof boot 59 is attached across the screw 57a and the housing 51, the boot 59 can be attached to the housing 51 with the screw shaft portion 57a and the adjustment dial portion 57b separated. Therefore, the work of replacing the boots 59 can be facilitated.

Furthermore, in the drum brake B according to the present embodiment, the outer diameter of the stopper 57d is formed to be smaller than the inner diameter of the wrap spring 61, and the stopper 57d is configured to be able to be inserted into the wrap spring 61 in the axial direction. Therefore, it is possible to ensure a large stroke in the feeding direction (axial direction) of the screw 57 while making the drum brake B as a whole smaller and more compact.

Note that the present invention is not limited to the above embodiments, and can be modified as appropriate without departing from the gist of the present invention.

In the above embodiment, the specified feeding amount of the screw 57 is set to 20 mm, which corresponds to the usage limit (limit wear amount) of the lining 43, but the configuration is not limited to this, and the specified feeding amount of the screw 57 is It can be set appropriately according to the required specifications of the vehicle, etc., for example, by setting the specified feeding amount of the screw 57 to less than 20 mm, the stopper function is activated before the amount of wear on the lining 43 reaches its usage limit. It may be configured as follows.

In the above embodiment, the screw 57 is divided into two parts, the screw shaft part 57a and the adjustment dial part 57b, but the structure is not limited to this. For example, the stopper 57d is divided from the other part of the screw 57 The stopper may be configured to be detachable.

In the above embodiment, the screw shaft portion 57a and the adjustment dial portion 57b are configured to be removable by the screw fastening structure, but the configuration is not limited to this, and the screw shaft portion 57a and the adjustment dial portion 57b are It may be configured to be removable by a fitting structure (concave-convex fitting structure) having a detent that restricts relative rotation. To prevent rotation between the screw shaft portion 57a and the adjustment dial portion 57b, for example, width across flat fitting, D-cut fitting, spline fitting, key fitting, etc. can be adopted.

In the above embodiment, the drum brake B is a leading-trailing type drum brake. Brakes may be applied.

B Drum brake 1 Axle (rotating member)
2 Anchor bracket (fixing member)
3 Drum unit 4 Brake shoe unit 5 Expander 6 Gap adjustment mechanism 31 Brake drum 40 Brake shoe 43 Brake lining 53 Sleeve assembly 54 Tappet (pressing force generating member)
55 Sleeve (transmission member)
55a Through hole (receiving part)
55e Stopper receiving part 57 Screw (pressing member)
57a Screw shaft portion (first pressing member)
57b Adjustment dial part (second pressing member)
57d Stopper 57j Flathead bolt 59 Boot 61 Wrap spring

Claims (4)

a cylindrical brake drum that is provided on a rotating member and is rotatable integrally with the rotating member;
A brake shoe that is swingably provided on a fixed member and has a brake lining that is disposed along the inner circumferential surface of the brake drum;
A drum brake comprising an expander that swings the brake shoe in response to a brake operation and presses the brake lining against the inner peripheral surface of the brake drum,
The expander includes a pressing force generation member that applies a pressing force in the axial direction in response to a brake operation, a transmission member that is rotatably provided around the axial direction with respect to the pressing force generation member, and a transmission member that is rotatable around the axial direction with respect to the pressing force generation member. The brake lining is threadedly engaged with the brake shoe in the axial direction and is unrotatably connected to the brake shoe in the axial direction, so that the brake shoe is oscillated by the pressing force transmitted from the transmission member. a pressing member that presses the inner circumferential surface of the brake drum, and by rotating the transmission member around the axial direction to extend the pressing member in the axial direction, the pressing member is pressed against the transmission member. a gap adjustment mechanism that adjusts the gap between the brake lining and the inner peripheral surface of the brake drum by displacing the relative position in the axial direction;
The drum brake is characterized in that the pressing member is provided with a stopper that prevents the pressing member from being extended beyond a specified amount in the axial direction relative to the transmission member. The transmission member has a receiving portion that receives the pressing member along the axial direction,
The receiving portion is provided with a stopper receiving portion,
When the pressing member is paid out in the axial direction by the prescribed amount, the stopper comes into contact with the stopper receiving portion, thereby preventing the pressing member from being paid out in the axial direction by more than the prescribed amount. The drum brake according to claim 1, characterized in that: The pressing member includes a first pressing member that is screwed to the transmission member and received in the receiving portion, and a second pressing member that is provided on the distal end side of the first pressing member and connected to the brake shoe. has
The drum brake according to claim 2, wherein the first pressing member and the second pressing member are separably coupled to each other. A space between the transmission member and the pressing force generating member is arranged such that relative rotation of the transmission member in one direction around the axial direction with respect to the pressing force generating member is allowed and relative rotation in the other direction around the axial direction is allowed. A wrap spring is installed to regulate the
The outer diameter of the stopper is smaller than the inner diameter of the wrap spring, and the stopper is configured to be able to be inserted into the wrap spring in the axial direction. Drum brake mentioned in either.

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