JP2002155976A - 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 crank mechanism as a shoe expansion device does not wear out. SOLUTION: The drum brake included a crank mechanism 22 mounted on an upper surface of attaching bolts 20, 21 for attaching an anchor block 16 as the immovable member, and expands and operates a pair of brake shoes 12, 13 by towing a free end pat 24c of the brake lever 24 for structuring the crank mechanism 22 in a direction parallel to a brake shaft direction, and relatively rotating the brake lever 24 and a strut 23 pivoted and supported by the lever 24. At least an angle part of a sliding and contacting part of the brake lever 24 is formed in a chamfer 24g or 24h to remove a scratching phenomenon in operating a brake.

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 FIG. 7 and FIG.

A pair of brake shoes 12 and 13 are movably mounted by shoe hold mechanisms 14 and 15 on a back plate 11 fixed to a stationary part 10 of a vehicle body. The two brake shoes 12, 13 are shown in FIG.
An anchor block 16 whose lower adjacent end is substantially L-shaped
Of the brake shoes 12, 13 are connected by an adjuster 17 at the upper adjacent end.
A pair of upper and lower shoe return springs stretched between them
8, 19, these contact states are maintained.

[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 between the brake shoes 12 and 13 adjacent to the upright portion 16a of the anchor block 16.

The strut 23 is formed of a single plate, and is provided with a bridging portion 23a at an intermediate portion in the longitudinal direction in FIG. 7, and is bent into a U-shape with a downward opening to form opposing pieces 23b, 23b. . 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 is closely contacted by projection welding or the like, and a shoe engaging groove 23e operatively engaged with the left brake shoe 12 is formed here. However, the two pieces 23b, 2 at the left end are
The closeness and integration of 3b aims at the function of preventing the mouth from opening, but is 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 closely integrated by projection welding or the like, and a shoe engagement groove 24a operatively engaged with the right brake shoe 13 is formed therein. A projection (base) 24b on the upper side of the shoe web 13a forming the shoe engagement groove 24a is pivotally supported by a right end of the strut 23 with a lever pin 25. Further, a free end 24c on the left half side of both plates is connected to an inner cable 27 constituting a brake cable 26 described later.
A gap 24d is formed so that the cable end 27a body fixed to the end of the cable end 27a can be inserted so as to be insertable, and the two ends 27b, 27b of the cable end 27a can be connected to the brake cable 26 in the anti-traction direction side. Arc-shaped grooves 24e, 2
4e are formed respectively.

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
One end of the guide pipe 29 is fixed to the seat 16b of the sixth, and the other end extends vertically (in a direction parallel to the brake axis direction) through the back plate 11 and the stationary part 10 of the vehicle body. One end of the outer casing 28 is fixed to the outer end of the guide pipe 29, and the inner cable 2 extending inside the guide pipe 29.
At one end of the bracket 7, ears 27b, 27b of a substantially cross-shaped cable end 27a fixed to the end are connected to 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. 8 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 is applied to the strut 23 via the lever pin 25.
This causes the left brake shoe 12 to expand and 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. However, in the conventional crank mechanism, particularly, the end of the brake lever that slides on the head of the mounting bolt is in line contact, and the length of the line is the same as the plate thickness. Therefore, when the brake lever rotates integrally with the brake drum or the like with the brake axis as a fulcrum and translates in parallel on the head of the mounting bolt, the sliding contact portion may be scratched by a sharp corner in the plate thickness direction. State. The repetition of the brake operation in such a state tends to promote the wear of the head of the mounting bolt, which hinders the smooth sliding of the brake lever. 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 problems, conventionally, grease is applied on the head of the mounting bolt or a relatively high surface treatment such as hard chrome plating is applied to the mounting bolt. However, long-term reliability was poor and the cost was high. In particular, with respect to the structure in which the crank mechanism slides on the back plate, it is common practice to apply grease as a solution, and the application work is often forced, which is cumbersome.

[0014] In the strut, the sliding portion that slides on the head of the mounting bolt has a flat surface in favorable conditions.
This sliding contact surface is a fractured surface by press working to the last. Therefore, if the crank mechanism is operated even in a state in which the crank mechanism is slightly inclined in the brake radial direction, the struts of the struts also have sharp edges in the plate thickness direction. Occurs.

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.

[0016]

In order to achieve the above-mentioned object, a drum brake shoe expanding device according to the present invention comprises a brake lever constituting the shoe expanding device or a stationary member of both the brake lever and the strut. The corner portion in the thickness direction of the sliding contact portion that slides upward is chamfered. Alternatively, the sliding contact side sliding on the immovable member of the above-mentioned brake lever or both the brake lever and the strut is forged, and the forged surplus is bulged out of the plate surface, and the bulged portion is slid. The contact portion has a chamfered corner in the thickness direction. The brake lever described above,
Alternatively, the shape of the corner of the strut in the thickness direction may be a C-chamfer shape or an R-chamfer shape. Further, the above-mentioned brake lever may be a combined body in which two plate bodies are overlapped and integrated, or may be formed from one plate body. Further, the immovable member on which the brake lever and the strut are mounted may be a mounting plate of an anchor block for supporting the brake shoe or a back plate on which the brake shoe is movably mounted.

According to the shoe expansion device for a drum brake configured as described above, when the crank mechanism rotates integrally with the brake drum or the like, the surfaces of the immovable member are not rubbed by the sharp corners of the brake lever and the strut. . or,
If the sliding contact portion sliding on the immovable member is forged and widened in the plate thickness direction, the posture of the crank mechanism sitting on the immovable member is improved. Therefore, since the local wear of the stationary member can be reduced and the crank mechanism slides smoothly, stable braking performance can be maintained for a long period of time, and further, the rough surface of the sliding surface is eliminated and the abnormal noise is eliminated. Can be suppressed. The C-chamfered and R-chamfered shapes formed at the corners in the thickness direction of the brake lever and strut can be formed by press working, so that the working is simple and suitable for mass production. Further, the brake lever may be composed of a combined body in which two plates are overlapped and integrated, or a single plate, and the immovable member may be a fixing bolt or a back plate of an anchor block. Therefore, the present invention can be applied to various drum brakes, so that the applicable range is wide.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A drum brake shoe expanding device according to the present invention will be described below. In the description, except for the crank mechanism and the cable end of the inner cable, the same components as those of the conventional example described above are denoted by the same reference numerals, and the description of the structure and brake operation is omitted.

First, a first embodiment of the present invention will be described with reference to FIGS. However, in this example, only the shape of one part of the brake lever 24 and the strut 23 is different from that of the above-described conventional example, and therefore, the description will be made focusing on the difference. Thus, the brake lever 24 in this example is
Both corners of the sliding contact portion sliding on the mounting bolt 21 in the plate thickness direction, that is, the arc surface (corresponding to the edge 24f of the conventional example) having the axis center of the lever pin 25 as a fulcrum. In both corners, C chamfers 24g, 24g as clearly shown in FIG.
It has been subjected to. Thereby, the brake lever 24 at the time of the brake operation slides smoothly without the corner of the sliding contact portion rubbing on the head of the mounting bolt 21.
The wear can be reduced, stable braking performance can be maintained for a long time, and generation of abnormal noise can be suppressed. The processing of the C chamfers 24g and 24g described above may be performed by pressing the individual plate members by pressing, or may be performed after the two plate members are integrated. It is possible.

Further, as clearly shown in FIG. 3, similarly to the brake lever 24, C-chamfers 23g, 23g are provided at both corners in the plate surface direction on the sliding contact portion which slides on the mounting bolt 20 of the strut 23. It is good to apply. Conventional strut 23
Although the edge 23f has a substantially flat surface under favorable conditions, it is a broken surface formed by press working, and therefore, when the crank mechanism 22 is operated even in a state where the crank mechanism 22 is slightly tilted in the brake radial direction, the sharpness is increased. At some corners, the head of the mounting bolt 20 could be scratched. Therefore, the C chamfer 2 described above
If the sharp corners are removed by 3g and 23g, so that the mounting bolt 20 always slides smoothly on the head, the braking performance can be further improved and the generation of abnormal noise can be suppressed. It is clear that. Also, this C chamfer 23
g and 23 g can be easily formed by press working.

The shapes of the chamfers of the brake lever 24 and the struts 23 are not limited to those described above. For example, the chamfered shape of the brake lever 24 shown in FIG. Is the code 24
h, 24h, and the chamfer of the strut 23 is denoted by reference numeral 23.
h, 23h). The point is that the fixing bolts 20 and 21 of the anchor block 16 which are immovable members
The chamfered shape of the sliding contact portion of the crank mechanism 22 that slides on the head may be any shape that removes both sharp corners.

Next, a second embodiment according to the present invention will be described.
This will be described with reference to FIG. This embodiment differs from the first embodiment only in the shapes of the sliding portions of the brake lever 24 and the strut 23 that slide on the heads of the mounting bolts 21 and 20. Therefore, only this shape will be described. I do. That is, the sliding contact side of the two 24, 23 is forged and the excess thickness bulges out from both plate surfaces, and the bulges 24j, 24j and 23j, 23j (also in this example, for simplicity of the drawing, a common diagram is used. Is formed in a chamfered shape. Therefore, since the sliding portions of the two 24 and 23 are widened in the plate thickness direction, they can be seated on the heads of the mounting bolts 21 and 20 in a correct posture, and the operation and effect of the first embodiment can be further improved. it can.

The brake levers 24 of the first and second embodiments have been described as being composed of a combined body in which two plates are superposed and integrated, but the invention is not limited to this. is not. The brake lever shown in FIG. 6 is composed of a single plate, and the cable ends are different accordingly. Therefore, the brake lever 24 and the cable end 2 shown in the first and second embodiments described above.
Only the portion 7a will be described by replacing the twentieth digit with the thirty digit. That is, since the brake lever 34 is formed of a single plate, the cable end 37a fixed to the end of the inner cable 37 has a hollow rectangular frame, and this hollow portion is connected to the free end 34c of the brake lever 34. It is configured to be fitted and connected to the semicircular groove 34e. Although not shown, substantially the same operation and effect can be obtained by forming both corners of the sliding contact portion of the brake lever 34 sliding on the immovable member in the same manner as in the first or second embodiment described above. It is clear that the description will be omitted.

The crank mechanism 22 according to the present invention described above.
Has been described as an example in which the anchor block 16 is mounted on the heads of the mounting bolts 20 and 21 of the anchor block 16 in the duo servo type drum brake. However, the present invention is not limited to this. In the case of the pin type, the crank mechanism 22 is mounted on the back plate 11. Further, instead 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 arranged can be applied. Chamfers 23g, 23g, 24g, 24g placed on top and formed at the sliding contact portion
Etc. may be only the corners on the inner side of the brake.

[0025]

Since the present invention is configured as described above, it has the following effects. That is, since the sharp corners of the sliding contact portions of the line contact that slide on the immovable member of the brake lever are formed in a chamfered shape, wear of the sliding portion due to repetition of the brake operation can be greatly reduced, and smoothness can be achieved at all times. You can expect smooth sliding. Thus, stable braking performance can be obtained over a long period of time. Further, since the rough surface of the sliding portion can be eliminated, it is possible to suppress the generation of abnormal noise (sliding sound and scratching sound) that gives an occupant an uncomfortable feeling. or,
If the corner of the sliding contact portion of the strut that comes into surface contact with the immovable member is also formed in a chamfered shape, even if the crank mechanism is slightly tilted in the radial direction of the brake, the immovable member is formed with a sharp corner. Since the surface slides smoothly without rubbing, the above effect is further improved. Also, if the brake lever and the strut are forged at the sliding contact side with the immovable member, and this forged surplus is bulged in the plate surface direction to form a chamfered corner, the crank mechanism for the immovable member can be used. Since the user is seated in a correct posture, the above-described effect is further improved. The above chamfers and bulges can be processed by press molding, so that the processing is relatively simple and suitable for mass production. Further, the brake lever may be a combination of two plates or 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 a vertical sectional view of a crank mechanism according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a sectional view taken along the line III-III of FIG. 1;

FIG. 4 is an enlarged view showing a modified example of a chamfered shape of a brake lever and a strut.

FIG. 5 is an enlarged view showing a modification of the sliding portion of the brake lever and the strut according to the second embodiment of the present invention.

6A and 6B are explanatory views of a modification of the crank mechanism according to the present invention, wherein FIG. 6A is a plan view showing a state where a cable end is connected, FIG. 6B is a side view of the cable end, and FIG. -C sectional view

FIG. 7 is a plan view of a drum brake on which the present invention is based.

FIG. 8 is a VIII-VIII view of FIG. 7;

9 is a sectional view taken along line IX-IX of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Unmovable part of vehicle body 11 Back plate 12, 13 Brake shoe 16 Anchor block 17 Adjuster 20, 21 Mounting bolt 22 Crank mechanism 23 Strut 23c Wide gap 23d Narrow gap 23e Shoe engaging groove 23g C chamfer 23h R chamfer 23j Expansion Protruding part 24 Brake lever 24a Shoe engaging groove 24b Projection (base) 24c Free end 24g C chamfer 24h R chamfer 24j Swelling part 26 Brake cable 27a Cable end 34 Brake lever 37a Cable end

Claims (8)

[Claims] 1. A crank mechanism for extending one side of a pair of brake shoes, a strut having one end operatively engaged with one brake shoe, and a strut extending from an intermediate portion to the other end of the strut. Housed in the formed gap,
A plate-shaped brake lever rotatably pivoting the base to the other end of the strut, operatively engaging the other brake shoe, and connecting a remote force transmitting member to the free end. When the remote force transmitting member is pulled in a direction parallel to a brake axis direction, the brake lever relatively rotates about a pivot portion with a strut as a fulcrum, and both of them slide on an immovable member to perform a brake operation. A shoe expansion device for a drum brake, wherein a corner portion of a sliding contact portion that slides on the immovable member of the brake lever or both of the brake lever and the strut is chamfered. apparatus. 2. A strut having one end operatively engaged with one brake shoe and a strut extending from one end to the other end of the pair of brake shoes. Housed in the formed gap,
A plate-shaped brake lever rotatably pivoting the base to the other end of the strut, operatively engaging the other brake shoe, and connecting a remote force transmitting member to the free end. When the remote force transmitting member is pulled in a direction parallel to a brake axis direction, the brake lever relatively rotates about a pivot portion with a strut as a fulcrum, and both of them slide on an immovable member to perform a brake operation. In the shoe expanding device, the brake lever, or both the brake lever and the strut, are forged at a sliding contact side that slides on the immovable member, and the forged surplus bulges from a plate surface, and the bulging is performed. A shoe expanding device for a drum brake, wherein a corner portion of a sliding contact portion of a protrusion is formed in a chamfered shape. 3. The shoe expansion device for a drum brake according to claim 1, wherein a corner portion of the sliding contact portion of the brake lever or the strut is formed in a C-chamfered shape. 4. The shoe expansion device for a drum brake according to claim 1, wherein a corner portion of the sliding contact portion of the brake lever or the strut is formed in an R-chamfered shape. 5. The shoe expansion device for a drum brake according to claim 1, wherein the brake lever comprises a combined body in which two plate bodies are overlapped and integrated. . 6. The shoe expansion device for a drum brake according to claim 1, wherein the brake lever comprises a single plate. 7. An anchor block according to claim 1, wherein an anchor block is provided adjacent to said crank mechanism and supports one adjacent end of said pair of brake shoes, and said anchor block is connected to said stationary member. A shoe expansion device for a drum brake, wherein a sliding contact portion of the brake lever and the strut is slidably mounted on a fastening member attached to the shoe. 8. The sliding contact portion of the brake lever and the strut according to claim 1, wherein the sliding portion of the brake lever and the strut is slidably mounted on a stationary back plate that movably supports the pair of brake shoes. A drum expansion shoe expansion device, which is mounted.