JP2002155975A - Shoe expansion device of drum brake - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shoe expansion device of a drum brake having sufficient durability and stable braking performance in a long term, and not generating an abnormal sound, wherein an immovable member for mounting a brake lever of a crank mechanism as the shoe expansion device does not wear out. SOLUTION: The crank mechanism 22 is mounted on an upper surface of attaching bolts 20, 21 for attaching an anchor block 16 as the immovable member. A bottom of a notched groove 24a of the brake lever 24 is formed in a flat inclining surface 24g or a arc-shaped surface 24h so that the bottom of the notched groove 24a of the brake lever 24 and a shoe web 13a are contact at an angle part on a side of an opposite direction to a towing direction of a remoter force transmitting member 26 when a free end part 24c of the brake lever 24 for structuring the crank mechanism 22 is towed in a direction parallel to a brake shaft direction, and the brake lever 24 and a strut 23 pivoted and supported by the brake lever 24 relatively rotate to expand and operate a pair of the brake shoes 12, 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drum brake shoe expansion device for expanding a pair of brake shoes, and more particularly, to a structure for slidingly contacting a stationary member of a crank mechanism as the shoe expansion device. It is.

[0002]

2. Description of the Related Art A mechanical shoe expanding apparatus having a crank mechanism for expanding a pair of brake shoes has been previously filed by the applicant as Japanese Patent Application Laid-Open No. Hei 6-337027. The drum brake provided with this shoe expansion device will be outlined with reference to FIGS. Note that "left" and "right" used in the description are those in FIGS.

The shoe rims 12b and 13b of a pair of brake shoes 12 and 13 having a T-shaped cross section are movably mounted by shoe hold mechanisms 14 and 15 on a back plate 11 fixed to a stationary portion 10 of the vehicle body. Have been. 3, the lower adjacent ends of the shoe webs 12a, 13a in FIG. 3 are supported by the upright portions 16a of the substantially L-shaped anchor blocks 16, and the upper adjacent ends are connected by adjusters 17. The abutment state is maintained by a pair of upper and lower shoe return springs 18 and 19 stretched between the brake shoes 12 and 13.

[0004] The anchor block 16 in this embodiment has its seat 16b attached to the stationary part 10 of the vehicle body with mounting bolts 20 and 21 across the back plate 11, and these constitute a stationary member. However, the fixing structure of the anchor block 16 may be directly fastened to the back plate 11 in some cases.

A crank mechanism 22 for extending one of the two brake shoes 12 and 13 on the opposite side includes a strut 23,
It comprises a brake lever 24 and a lever pin 25. The crank mechanism 22 is disposed adjacent to the upright portion 16a of the anchor block 16 with a slight gap between the shoe webs 12a, 13a of the brake shoes 12, 13.

The strut 23 is formed of a single plate, and is provided with a bridging portion 23a at the middle portion in the longitudinal direction in FIG.
Is formed. The opposing pieces 23b, 23b form a wide gap 23c at an intermediate portion in the longitudinal direction, and a narrow gap 23d continuous with the wide gap 23c at a right end. I have. Further, the left end portion is closely attached by projection welding or the like, and a notch groove 23e operatively engaged with the shoe web 12a of the left brake shoe 12 is formed therein. However, the close contact and integration of the two pieces 23b, 23b at the left end aim at the function of preventing the opening of the two pieces 23b, but are not an essential element.

The brake lever 24 is composed of two superposed plates, and the gap 23 between the struts 23
c, 23d. The right half sides of the two plate members are tightly integrated by projection welding or the like, and the shoe web 1 of the right brake shoe 13
A cutout groove 24a operatively engaged with 3a is formed, and a projection (base) 24b on the upper side of the shoe web 13a forming the cutout groove 24a is formed on the right end of the strut 23. It is pivotally supported by a lever pin 25. Also, the left half free ends 24c of both plate members
A gap 24d is formed so that a cable end 27a main body fixed to an end of an inner cable 27 constituting a brake cable 26 to be described later can be inserted so as to be inserted;
Semicircular grooves 24e, 24e are formed on the side opposite to the traction direction of the brake cable 26 to connect the both ears 27b, 27b of the cable end 27a. As shown in FIG. 4, the groove bottom of the cutout groove 24a is formed in parallel with the inner surface of the shoe web 13a so as to press substantially the center of the thickness of the shoe web 13a. or,
It is also known that the flat surface of the groove bottom of the notch groove 24a is instead formed as an arc-shaped surface protruding from the center in the groove width direction.

The strut 23 and the brake lever 24 of the crank mechanism 22 have their ends 23f, 24f on the brake cable 26 pulling direction side slide on the heads of the mounting bolts 20, 21. It is freely placed. And the edge 23f of the strut 23 is
A flat surface is formed so as to translate on the head of the left mounting bolt 20, and an edge 24 f of the brake lever 24.
Is the lever pin 25 on the head of the right mounting bolt 21.
Is formed on the arc surface so as to translate while rotating around the fulcrum.

Brake cable 2 as remote force transmitting member
Reference numeral 6 denotes an inner cable 27, an outer casing 28, and the like. One end of these drum brakes is disposed in a direction parallel to the brake axis direction, and passes through an intermediate portion disposed along a chassis (not shown) to protect an inner cable 27 from outside air. Is fixed to an undercarriage, and the other end of the inner cable 27 slidably fitted therein is fixed to an operation lever in the vehicle compartment.

Thus, one end of the brake cable 26 is arranged as follows. The anchor block 1
6, one end of a guide pipe 29 is forged, and the other end extends vertically through the back plate 11 and the stationary part 10 of the vehicle body (in a direction parallel to the brake axis direction). One end of the outer casing 28 is fixed to the outer end of the guide pipe 29, and one end of the inner cable 27 extending and protruding in the guide pipe 29 is substantially fixed to the end. The lugs 27b, 27b of the cross-shaped cable end 27a are connected to the semicircular grooves 24e, 24e of the brake lever 24.

Next, the operation of the brake in the above-described configuration will be described. Now, when the free end 24c of the brake lever 24 is pulled through the inner cable 27, the brake lever 24 rotates counterclockwise in FIG. 4 with the lever pin 25 as a fulcrum, and expands the right brake shoe 13. A friction engagement is made with a brake drum (not shown). At the same time, the reaction force acts on the strut 23 via the lever pin 25 while slightly moving the lever pin 25 upward, thereby expanding the left brake shoe 12 to frictionally engage the brake drum. . Thus, the frictional force of the primary side brake shoe 12 or 13 with respect to the rotation direction of the brake drum is transmitted to the secondary side brake shoe 13 or 12 via the adjuster 17, and this is supported by the anchor block 16 and the braking force is applied. And acts as a duo-servo type drum brake.

[0012]

In the above-described crank mechanism during the operation of the brake, one of the brake shoes is supported by the anchor block from the time when both brake shoes are frictionally engaged with the brake drum, and a braking force is generated. While rotating, it rotates integrally with both brake shoes and brake drums. At this time, the crank mechanism translates while sliding under the state of being strongly pressed on the head of the mounting bolt by the pulling force of the inner cable. Thus, in the conventional crank mechanism, particularly, the end of the brake lever that comes into contact with the head of the mounting bolt is in line contact, and the length of the line is the same as the plate thickness. Therefore, every time the brake is actuated, the brake lever slides while a large pressing force always acts locally on the head of the mounting bolt,
There is a problem that the wear of the head of the mounting bolt is easily promoted, which hinders the smooth sliding of the brake lever for a long time. Further, if the head of the mounting bolt becomes rough, an abnormal sound (sliding sound or scratching sound) is generated, which may cause discomfort to the occupant. In order to solve the above-mentioned problem, conventionally, grease has been applied to the head of the mounting bolt or a relatively hard surface treatment such as hard chrome plating has been applied to the mounting bolt. The long-term reliability was poor and the cost was high. In particular, for the structure where the crank mechanism slides on the back plate,
As a solution, it is common to apply grease, and it has been troublesome to apply the grease frequently.

According to the present invention, even if the brake is repeatedly operated,
It is an object of the present invention to provide a drum brake shoe expansion device that has a high durability without abrasion of the upper portion of the mounting bolt and the like, and provides stable braking performance over a long period of time. It is still another object of the present invention to provide a drum brake shoe expansion device that does not generate an unusual sound and does not cause discomfort to an occupant.

[0014]

In order to achieve the above-mentioned object, in a shoe expansion device for a drum brake according to the present invention, a contact between a notch groove bottom of a brake lever and a shoe web at the time of a brake operation is determined. This is a corner formed on the side opposite to the traction direction of the remote force transmitting member. In order to make the above-mentioned contact between the brake lever and the shoe web on the anti-traction direction side of the remote force transmission member, the notch groove bottom of the brake lever is moved toward the shoe web as it goes toward the anti-traction direction side of the remote force transmission member. It is good to make it a flat slope approaching, or to make the notch groove bottom of the brake lever an arc surface whose fulcrum is on the anti-traction direction side of the remote force transmitting member.

According to the drum brake shoe expanding device constructed as described above, during normal braking operation, the bottom of the notch groove of the brake lever is caught by the corner of the inner surface of the shoe web, and this corner is Due to the tendency to bite into the notch groove bottom, the pressing force acting on the head of the mounting bolt is greatly reduced or not exerted on the traction of the remote force transmitting member. Accordingly, since the braking operation in which a large pressing force acts on the head of the mounting bolt is limited only to the emergency braking which is used very rarely, the local wear on the head can be greatly reduced. Stable braking performance can be maintained for a long period of time, and furthermore, severe roughening of the sliding surface can be eliminated and generation of abnormal noise can be suppressed. The above-described processing of the flat inclined surface or the arcuate surface at the bottom of the notch groove of the brake lever can be integrally formed at the same time as the punching-out molding by the press, so that the processing is simple.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A drum brake shoe expanding device according to the present invention will be described below. In the description, the only difference from the conventional example is the groove bottom shape of the notch groove 24a of the brake lever 24.
This will be mainly described.

First, FIG. 1 shows Embodiment 1 of the present invention.
This will be described with reference to an enlarged view of the notch groove 24a shown in FIG. In this embodiment, the bottom of the notch groove 24a of the brake lever 24 at the time of the brake operation is
The bottom surface of the cutout groove 24a of the brake lever 24 is shifted toward the anti-traction direction side of the brake cable so that the bottom surface of the notch groove 24a is brought into contact with the corner portion of the brake cable, which is the remote force transmission member on the inner surface of FIG. It is formed on a flat slope 24g approaching the inner surface of the web 13a.

When the brake is operated in the above-described configuration, the brake lever 24 rotates counterclockwise about the lever pin 25 as a fulcrum. 13a is brought into contact with a corner of the inner surface, and this corner has a phenomenon of cutting into a flat slope 24g. When the brake cable is subsequently towed, the brake lever 24 starts rotating about the two contact points O and presses the shoe web 13a as shown by the phantom line from this point, and presses the shoe web 13a. The strut 23 is pressed through the same, but the subsequent brake operation is the same as in the above-described conventional example, and the description thereof is omitted.

As is apparent from the above description, the distance from the contact point O of the brake lever 24 to the edge 24f on the head of the mounting bolt 21 is greater than the distance from the axis of the lever pin 25 to the edge 24f. Therefore, under the condition indicated by the imaginary line of the brake lever 24, the edge 24f moves while slightly rising from the head of the mounting bolt 21. Therefore, unless an extremely large traction force is applied to the brake cable, for example, in the case of an emergency brake that is used very rarely, the edge 2
4f does not abut on the head of the mounting bolt 21, and as a result, stable braking performance can be obtained over a long period of time and no noise is generated. However, in this case, even if the edge 24f of the brake lever 24 abuts on the head of the mounting bolt 21, the contact point O at the bottom of the notch groove 24a is easily shifted upward. In this example, the case where the angle of the flat slope 24g is large is described. However, even if the angle is slightly smaller than this, the phenomenon that the slope 24g is caught on the corner of the shoe web 13a occurs. The pressing force from the edge 24f of the brake lever 24 acting on the head of 21 is greatly reduced. Therefore, the wear of the sliding portion can be reduced, and stable braking performance can be maintained for a long period of time, and furthermore, severe roughening of the sliding surface can be eliminated and generation of abnormal noise can be suppressed.

Next, a second embodiment according to the present invention will be described.
This will be described with reference to an enlarged view of the cutout groove 24a shown in FIG. Thus, also in this example, the bottom of the notch groove 24a of the brake lever 24 at the time of braking operation is
The brake lever 2 is positioned so as to come into contact with the corner on the anti-traction direction side of the brake cable, which is a remote force transmitting member on the inner surface of 3a.
No. 4 cutout groove 24a is formed in a circular arc surface 24h with the fulcrum on the side opposite to the traction direction of the brake cable. In other words, the bottom surface of the notch groove 24a is an arc surface 24h whose fulcrum is above the extension of the upper surface of the shoe web 13a. Since it is clear that the operation and effect of this embodiment is equivalent to that of the first embodiment, the description is omitted.

Although the crank mechanism 22 of the first and second embodiments is mounted on the heads of the mounting bolts 20 and 21 of the anchor block 16 in the duo-servo type drum brake, the present invention is not limited to this. However, the present invention is not limited to this. For example, when the anchor block 16 has a pin-like anchor pin shape, the crank mechanism 22 is placed on the back plate 11. Further, in place of the adjuster 17 in the conventional example, a so-called leading / trailing type drum brake in which a fixed anchor having the same function as the anchor block 16 is disposed can be applied.
Also in this case, the crank mechanism 22 is mounted on the back plate 11. Furthermore, although the brake lever 24 is exemplified by a combination of two plates, this may be formed from a single plate and replaced with a cable end connectable thereto.

[0022]

Since the present invention is configured as described above, it has the following effects. That is, at the time of the brake operation, the contact between the notch groove bottom of the brake lever constituting the crank mechanism and the inner surface of the shoe web is set at the corner of the remote force transmitting member (brake cable) in the anti-traction direction side. During normal operation, when most of the brake operation is performed, the bottom of the notch groove of the brake lever catches on the corner of the inner surface of the shoe web, and this corner tends to bite into the bottom of the notch groove, and the edge of the brake lever becomes It tends to move away from the contacted member. Therefore, the pressing force acting on the head of the mounting bolt (immobile member) is greatly reduced or not exerted on the traction force of the remote force transmitting member. As a result, local wear, particularly on the heads of the mounting bolts, can be greatly reduced, stable braking performance can be maintained for a long period of time, and severe roughness of the sliding surface can be eliminated. The generation of noises (sounds of movement and scratching) can be suppressed, and the occupants do not feel uncomfortable.

Further, in order to make the contact between the brake lever and the shoe web with the corner of the remote force transmitting member on the side opposite to the traction direction, the bottom of the notch groove of the brake lever is provided with the opposite traction of the remote force transmitting member. It may be a flat slope approaching the inner surface of the shoe web as it goes to the direction side, or it may be an arc surface with the fulcrum direction side of the remote force transmitting member as a fulcrum.
Since it can be integrally formed at the same time as the outside punching by press working, the working is extremely simple and suitable for mass production.

Further, the brake lever may be a combination of two plates, or may be a single plate. In addition, the immovable member on which the brake lever and the strut are slidably mounted may be a mounting bolt or a back plate for attaching an anchor block, and can be applied to a duo servo type or a leading / trailing type drum brake. Its scope is extensive.

[Brief description of the drawings]

FIG. 1 is an enlarged explanatory view showing a notched groove portion of a brake lever according to a first embodiment of the present invention.

FIG. 2 is an enlarged explanatory view showing a notched groove portion of a brake lever according to a second embodiment of the present invention.

FIG. 3 is a plan view of a drum brake on which the present invention is based.

FIG. 4 is a sectional view taken along line IV-IV of FIG.

FIG. 5 is a sectional view taken along line VV of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Unmovable part of vehicle body 11 Back plate (immovable member) 12, 13 Brake shoe 12a, 13a Shoe web 16 Anchor block 17 Adjuster 20, 21 Mounting bolt (immovable member) 22 Crank mechanism 23 Strut 23c Wide gap 23d Narrow gap 23e Notch groove 24 Brake lever 24a Notch groove 24b Projection (base) 24c Free end 24e Semicircular groove 24f End edge 24g Flat slope 24h Arc surface 26 Brake cable (remote force transmitting member)

Claims (3)

[Claims] 1. A strut for operatively engaging a notch groove at one end with a shoe web of one brake shoe and a middle portion between the struts. The strut is housed in a gap formed over the other end so as to pivotally support the base to the other end of the strut and operatively engage the notch groove in the shoe web of the other brake shoe. A brake lever that engages and connects a remote force transmitting member to a free end thereof, wherein the remote force transmitting member is pulled in a direction parallel to a brake axis direction to perform a brake operation. A contact between the notch groove bottom of the brake lever and the shoe web at the time of braking operation is formed at a corner of the remote force transmitting member on the side opposite to the traction direction. Shoe expansion unit of the brake. 2. The drum according to claim 1, wherein the bottom of the notch groove of the brake lever is formed as a flat slope approaching the shoe web as it goes in the anti-traction direction side of the remote force transmitting member. Brake shoe expansion device. 3. The shoe expansion of a drum brake according to claim 1, wherein the bottom of the notch groove of the brake lever is formed as an arcuate surface with the fulcrum of the remote force transmitting member as a fulcrum. apparatus.