JP2014040881A - Brake drum for vehicle and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brake drum for a vehicle, in which durability can be improved by reducing a stress generated during braking event without increasing manufacturing cost.SOLUTION: A plurality of bolt holes 7 are pierced serially in a circumferential direction in a flange part 6 of a brake drum 5 so as to be fastened to a side of a wheel hub 2 by a hub bolt 9, and a casted surface 5a of an inner circumference is cut while remaining a location in the vicinity of the flange part 6 as cutting stock, thereby forming a slide-contact face 16 with which a brake shoe 11 is brought into slide-contact. Around each of the bolt holes 7 on a right side face of the flange part 6, a circular counter-bored part 17 is formed to which a head 9a of the hub bolt 9 is abutted, respectively, and by forming the circular counter-bored part 17, the casted surface 5a remained as the cutting stock in the vicinity of the flange part 6 is cut off in an arcuate shape in an outer circumferential direction. Thus, thickness of a corner 14 in the circumferential direction of the brake drum 5 is reduced only in an area of the circular counter-bored part 17 (an area of a fastening outer circumferential end 13), thereby suppressing stress generation.

Description

  The present invention relates to a vehicle brake drum and a method for manufacturing the same, and more particularly to a brake drum capable of reducing stress generated by a force in the outer peripheral direction from a brake shoe during braking and a method for manufacturing the same.

  As is well known, drum brakes are widely used in large vehicles such as trucks and buses because they have the characteristic of obtaining a strong braking force by self-boosting action. For example, a drum brake is configured such that a pair of brake shoes are provided on the axle side of the vehicle, the brake drum is bolted to the wheel hub side to which the wheel is fixed, and the brake drum is rotated together with the wheel on the outer peripheral side of the brake shoe. Has been. Both brake shoes are actuated in the expansion direction by a hydraulic wheel cylinder, and the braking force is applied to the wheel side by sliding the brake lining attached to the outer peripheral surface of the brake shoe against the inner peripheral surface of the brake drum. Yes.

Due to the extension of the brake shoe, a large force acts on the brake drum during braking. In particular, a large stress is generated at the head portion of each hub bolt that fastens the brake drum to the wheel hub side, and durability that can withstand the stress is required for the brake drum. As a countermeasure, it is possible to increase the thickness of the entire brake drum to improve durability, but the unsprung weight of the vehicle increases with the weight of the brake drum, which causes adverse effects such as deterioration of riding comfort. It will occur.
Therefore, for example, in the technique described in Patent Document 1, shot peening is applied to the inner peripheral surface of the brake drum to give a compressive residual stress, thereby reducing the stress generated in the brake drum due to the force from the brake shoe. We are trying to improve the performance.

Japanese Patent Laid-Open No. 6-200966

The application of compressive residual stress by shot peening according to the technique of Patent Document 1 has a property of uniformly reducing the stress in the entire area subjected to shot peening. However, as described above, each brake drum during braking is Since the stress is rapidly increased locally at the head of the hub bolt, the countermeasure by shot peening cannot sufficiently reduce the stress at the head of the bolt head, and it must be said that the countermeasure is insufficient. In addition to the existing process for manufacturing the brake drum, it is necessary to newly provide a process for performing shot peening, which causes another problem of increasing the manufacturing cost.
The present invention has been made to solve such problems, and the object of the present invention is to reduce the stress generated during braking and improve the durability without increasing the manufacturing cost. An object of the present invention is to provide a vehicle brake drum and a method for manufacturing the same.

  In order to achieve the above-mentioned object, the invention of claim 1 is formed by respectively drilling a plurality of bolt holes in a circumferential direction in a flange portion integrally formed at one side end in an annular shape, It is configured so that it can be fastened to the wheel hub side by a hub bolt through a bolt hole, and a smooth sliding contact surface is formed by cutting the inner peripheral surface while leaving a portion near the flange portion as a cutting allowance. In the brake drum of a vehicle in which a brake shoe is slidably contacted to generate a braking force, a circular counterbore portion with which the head of the hub bolt abuts is formed around each bolt hole on the other side surface of the flange portion. By forming the circular counterbore portion, the inner peripheral surface left as a cutting allowance in the vicinity of the flange portion is cut in an arc shape toward the outer peripheral direction.

According to a second aspect of the present invention, in the first aspect, each circular counterbore part is formed with the same axial center with respect to each corresponding bolt hole.
According to a third aspect of the present invention, in the first aspect, the circular counterbore portions are formed eccentrically in the outer peripheral direction of the brake drum with respect to the corresponding bolt holes.

  According to a fourth aspect of the present invention, there is provided a material manufacturing process for manufacturing a material for a brake drum having a flange portion integrally formed on one side end thereof, and an inner peripheral surface of the material for the brake drum manufactured by the material manufacturing process is turned to form a flange. Hub bolts are inserted into the flange portion of the brake drum after forming the sliding contact surface by the sliding contact surface forming step of forming a smooth sliding contact surface while leaving the portion in the vicinity of the portion as a cutting allowance A plurality of bolt holes are respectively drilled so as to be arranged in the circumferential direction, and a circular counterbore part with which the head of the hub bolt abuts is formed around each bolt hole on the inner side surface of the flange part. A bolt hole / counterbore forming step is provided in which the inner peripheral surface of the brake drum left as a cutting allowance in the vicinity of the flange portion is formed in an arc shape toward the outer peripheral direction.

  As described above, according to the vehicle brake drum of the first aspect of the present invention, a plurality of bolt holes are formed in the flange portion at one end so as to be arranged in the circumferential direction, and the hub bolts are provided on the wheel hub side. It is possible to fasten and form a sliding contact surface for cutting the inner peripheral surface and sliding the brake shoe while leaving a portion near the flange portion as a cutting allowance, and around each bolt hole on the other side surface of the flange portion. A circular counterbore portion with which the head portion of the hub bolt abuts is recessed, and by forming this circular counterbore portion, the inner peripheral surface left in the vicinity of the flange portion is cut into an arc shape in the outer peripheral direction.

  Therefore, due to the formation of the circular counterbore, the thickness of the corner (corresponding to the outermost periphery of the flange) in the circumferential direction of the brake drum is reduced only in the area of the circular counterbore, in other words, the area corresponding to the fastening outer peripheral edge. Will do. And since the flange part of the brake drum is fastened to the wheel hub side by each hub bolt, the outer peripheral side of the head part of each hub bolt of the flange part, that is, the fastening outer peripheral end, by the force in the outer peripheral direction received from the brake shoe during braking The stress generated in the region increases rapidly.

At this time, since the thickness of the corner of the brake drum is sufficiently secured in the region other than the circular counterbore, the brake drum at the time of braking is rigidly opposed to the force from the brake shoe, and large deformation is suppressed, The original braking function can be exhibited without any problems. On the other hand, since the thickness of the corner portion of the brake drum is reduced in the region of each fastening outer peripheral end in the circumferential direction, it is possible to reliably reduce stress and improve durability.
In addition, because of the simple structure in which the inner peripheral surface of the brake drum is scraped off by the circular counterbore portion functioning as the contact surface of the hub bolt in this way, the manufacturing process of the brake drum can be prevented from becoming complicated and the cost increase can be suppressed. Can do.

According to the brake drum of the vehicle of the invention of claim 2, in addition to claim 1, a circular counterbore portion is formed with the same axis as each bolt hole.
Therefore, the drilling of the bolt hole and the recess of the circular counterbore can be simultaneously processed, and the manufacturing cost can be further reduced.

According to the brake drum of the vehicle of the invention of claim 3, in addition to claim 1, the circular counterbore portion is formed by decentering in the outer peripheral direction of the brake drum with respect to each bolt hole.
Therefore, even when the bolt holes are spaced apart from the inner peripheral surface of the brake drum on the inner peripheral side, the rigidity of the brake drum is increased without unnecessarily increasing the radius of the circular counterbore. After securing, the inner peripheral surface can be cut into an arc shape by each circular counterbore.

According to the vehicle brake drum manufacturing method of the invention of claim 4, the brake drum material including the flange portion is manufactured, and the inner peripheral surface of the manufactured brake drum material is turned so that a portion near the flange portion is formed. A sliding contact surface is formed while remaining as a machining allowance, and a plurality of bolt holes are formed in the flange portion so as to be arranged in the circumferential direction, and a circular counterbore portion is provided around each bolt hole on the inner surface of the flange portion. By providing the recess, the inner peripheral surface of the brake drum left in the vicinity of the flange portion is scraped off in an arc shape in the outer peripheral direction.
Therefore, the brake drum having the function and effect described in claim 1 can be manufactured by a simple process.

It is sectional drawing which shows the structure of the drum brake provided with the brake drum of the truck of embodiment. It is the front view which looked at the brake drum from the vehicle body inner side. It is a perspective view which shows the cross-sectional shape of the corner | angular part periphery of a brake drum similarly. It is sectional drawing which similarly shows the cross-sectional shape around a corner | angular part. FIG. 3 is a detailed view of a portion A in FIG. 2 showing a bolt hole and a fastening outer peripheral end of a flange portion. It is a perspective view which shows the cross-sectional shape of the corner | angular part periphery of a prior art brake drum. It is sectional drawing which similarly shows the cross-sectional shape around a corner | angular part. It is detail drawing which shows the bolt hole and fastening outer periphery end of a flange part.

Hereinafter, an embodiment in which the present invention is embodied in a brake drum of a truck will be described.
FIG. 1 is a cross-sectional view showing a structure of a drum brake provided with a brake drum according to the present embodiment. In the figure, the drum brake on the left side of the rear axle of the vehicle is shown as viewed from the rear, with the right side in the figure corresponding to the inside of the vehicle body (final drive device side) and the left side corresponding to the outside of the vehicle body (wheel side). . The right drum brake also has the same symmetrical configuration.

An axle tube 1 constituting a rear axle of the vehicle extends in the left-right direction, and an annular wheel hub 2 is disposed at the left end so as to surround the axle tube 1 and is rotatably supported by a pair of bearings 3. Yes. An axle shaft 4 is disposed in the axle tube 1, and the left end of the axle shaft 4 is formed in a hook shape and is fastened to the left end of the wheel hub 2 by a bolt (not shown).
The right end of the axle shaft 4 is connected to a differential mechanism of a final drive device (not shown), and driving force from the engine is distributed to the left and right axle shafts 4 via the differential mechanism so that the wheel hub 2 rotates together with the axle shaft 4. It has become.

  FIG. 2 is a front view of the brake drum as seen from the inside of the vehicle body. An annular brake drum 5 is disposed on the right side of the wheel hub 2 so as to surround the axle tube 1, and a flange portion 6 is integrally formed at the left end (one side end) so as to be bent inward. . The flange portion 6 of the brake drum 5 is in contact with a flange portion 2a integrally formed on the outer periphery of the wheel hub 2 in a state in which the rotation axis is made coincident by an inlay. Bolt holes 7 are formed in 10 locations so as to be arranged in the circumferential direction in the flange portion 6 of the brake drum 5, and screw holes 8 are formed in the flange portion 2 a of the wheel hub 2 so as to correspond to these bolt holes 7. Are penetrating each other.

Hub bolts 9 are inserted into the bolt holes 7 of the brake drum 5 from the right, and the hub bolts 9 are screwed into the screw holes 8 of the wheel hub 2 to fasten the brake drum 5 to the wheel hub 2. The tip of each hub bolt 9 protrudes leftward from the screw hole 8, although not shown, the wheel is attached to the wheel hub 2 using these hub bolts 9.
A brake mechanism 10 is disposed on the axle tube 1 so as to be positioned inside the brake drum 5. A pair of brake shoes 11 of the brake mechanism 10 are arranged in a direction orthogonal to the paper surface of FIG. 1, and the outer peripheral surface of each brake shoe 11 forms an arc shape corresponding to the inner peripheral surface of the brake drum 5 and the lining is attached. Has been.
A wheel cylinder 12 is disposed between the upper parts of the brake shoes 11, and the wheel cylinder 12 operates the brake shoes 11 in the extending direction by hydraulic pressure in accordance with a driver's brake operation. As a result, the linings of both brake shoes 11 are brought into sliding contact with the inner peripheral surface of the brake drum 5 to generate a braking force.

  By the way, as described in [Problems to be Solved by the Invention], the brake drum 5 at the time of braking generates a stress by receiving a force in the outer peripheral direction by the expanded brake shoe 11, in order to reduce the stress. Increasing the thickness of the entire brake drum 5 causes an increase in the weight of the brake drum 5 and thus an increase in the unsprung weight of the vehicle. In addition, the technique of Patent Document 1 using shot peening causes another problem that the stress cannot be sufficiently reduced and the manufacturing cost increases.

In order to deal with such problems, the present inventor considered the force acting on the brake drum 5 during braking, and consequently the stress generated on the brake drum 5 accordingly.
As described above, the brake drum 5 at the time of braking receives a force in the outer peripheral direction by the expanded brake shoe 11. Since the flange portion 6 side of the brake drum 5 is fixed to the wheel hub 2 by the hub bolt 9, a position on the outer peripheral side of the head 9a of each hub bolt 9 (hereinafter referred to as a fastening outer peripheral end 13) is used as a starting point. As shown by the two-dot difference line, the brake drum 5 is deformed so that the opened right side is displaced to the outer peripheral side. As a result, in addition to the fastening force of the hub bolt 9, a force from the brake shoe 11 acts on each fastening outer peripheral end 13 of the flange portion 6 to locally generate a high stress.

  The deformation of the brake drum 5 occurs in two regions corresponding to (slidably contacting with) the pair of brake shoes 11 that receive a force in the outer peripheral direction, but is not deformed by being released from the force in other regions. , Continuously receiving only the bolt fastening force. Accordingly, each part of the entire circumference of the brake drum 5 repeats the undeformed state indicated by the solid line and the deformed state indicated by the two-dot chain line in FIG. Thus, the stress generated at each fastening outer peripheral end 13 varies periodically, and durability that can withstand this stress is required of the brake drum 5.

  In view of the stress generation situation as described above, it is not always necessary to reduce the stress of the brake drum 5 as a whole. If the stress rapidly increasing locally at each fastening outer peripheral end 13 is reduced, the durability of the brake drum 5 is improved. You can see that they are connected. And each fastening outer periphery end 13 is located in the outermost periphery of the flange part 6, is sufficiently close to the corner | angular part 14 with which the outermost periphery of the flange part 6 and the left end of the brake drum 5 couple | bond, It can be regarded as the same position.

In order to reduce the stress, it is effective to reduce the thickness of the portion where the stress is generated. In this case, the stress of each fastening outer peripheral end 13 can be reduced by reducing the thickness of the corner portion 14. However, if the thickness of the corner portion 14 is reduced over the entire circumference, the rigidity of the entire brake drum 5 is lowered. Therefore, in order to reduce the local stress at each fastening outer peripheral end 13 while ensuring rigidity, it is necessary to reduce the wall thickness only in a region corresponding to each fastening outer peripheral end 13 in the circumferential direction of the corner portion 14. There is.
In order to satisfy such a demand for the brake drum 5 shape, a complicated manufacturing process is required. In the present embodiment, the desired brake drum 5 shape can be obtained with a minimum number of processes by devising the manufacturing process. Realized. Hereinafter, the shape of the brake drum 5 according to the present embodiment, particularly the cross-sectional shape around the corner 14 will be described along with the manufacturing process.

3 is a perspective view showing a cross-sectional shape around the corner portion 14 of the brake drum 5, FIG. 4 is a cross-sectional view showing the cross-sectional shape around the corner portion 14, and FIG. 5 shows a bolt hole 7 and a fastening outer peripheral end 13 of the flange portion 6. FIG. 3 is a detailed view of a portion A in FIG.
The material of the brake drum 5 is made of cast iron and is integrally formed by casting including the flange portion 6. The entire surface of the brake drum 5 before processing is covered with a casting surface, and a chamfered portion 15 is formed at a corner portion 14 of the brake drum 5. However, the chamfered portion 15 is not necessarily formed, and the chamfered portion 15 may be omitted and the corner portion 14 may be formed in a right-angle cross section.

The inner peripheral surface of the brake drum 5 is formed by cutting a cast surface 5a indicated by a broken line in FIG. 4 with a lathe to form a smooth sliding contact surface 16, and the brake shoe 11 is in sliding contact with the sliding contact surface 16 during braking. . In the width direction (left-right direction) of the brake drum 5, a portion in the vicinity of the flange portion 6 is not cut and a cast surface 5 a (inner peripheral surface) remains as a cutting allowance.
Bolt holes 7 are respectively drilled in the flange portion 6 at predetermined positions in the circumferential direction, and hub bolts 9 are inserted into these bolt holes 7 from the right side and fastened to the wheel hub 2 side. The cast surface 5b (other side surface) on the right side of the flange portion 6 is counterbored by an end mill with each bolt hole 7 as a center, so that each bolt hole 7 has a circular shape having an annular shape around the same axis. The counterbore part 17 is recessed at a predetermined depth.

The head portion 9a of the hub bolt 9 abuts against the bottom surface 17a of the circular counterbore portion 17, and the outer peripheral side portion (the outer peripheral side portion of the bolt head portion 9a) in the bottom surface 17a acts as the fastening outer peripheral end 13 for braking. Sometimes local stress is generated.
As shown in FIG. 4, the radius (that is, the radius of the end mill) R of the circular counterbore portion 17 is set to be larger than the distance L from the center of the bolt hole 7 to the casting surface 5a of the inner periphery of the brake drum 5. . Therefore, the casting surface 5a of the inner periphery of the brake drum 5 left as a cutting allowance in the vicinity of the flange portion 6 as described above is the outer periphery of the brake drum 5 as each circular counterbore portion 17 is formed as shown in FIG. Each is cut into an arc shape in the direction. In the present embodiment, the outermost periphery (the portion where the cast surface 5a is scraped off) of each circular counterbore portion 17 is located on the inner peripheral side of the sliding contact surface 16 of the brake drum 5, but the present invention is not limited thereto. The outermost periphery of each circular counterbore part 17 may be made to correspond with the slidable contact surface 16.

By forming each circular counterbore portion 17 as described above, the thickness of the corner portion 14 of the brake drum 5 is reduced only in a region corresponding to each fastening outer peripheral end 13 in the circumferential direction of the brake drum 5.
That is, in this embodiment, since the chamfered portion 15 is formed on the outer periphery of the corner portion 14 of the brake drum 5, the shortest distance from the chamfered portion 15 to the inner peripheral side of the brake drum 5 is defined as the thickness of the corner portion 14. it can. As shown in FIG. 4, in a region other than the circular counterbore portion 17, the shortest distance t <b> 1 from the chamfered portion 15 to the cast skin surface 5 a on the inner periphery of the brake drum 5 can be regarded as the thickness of the corner portion 14. On the other hand, in the area of the circular counterbore part 17, the casting surface 5 a is scraped, so the shortest distance t2 (<t1) from the chamfering part 15 to the outermost periphery of the circular counterbore part 17 is the thickness of the corner part 14. It can be seen that the wall thickness is reduced compared to other areas.

As described above, since the fastening outer peripheral end 13 of each hub bolt 9 exists in the bottom surface 17a of each circular counterbore part 17, as a result, the brake drum 5 is limited to a region corresponding to the fastening outer peripheral end 13 in the circumferential direction of the brake drum 5. The thickness of the corner portion 14 is reduced, and a sufficient thickness t1 is secured in the corner portion 14 in most other regions.
As described above, since a sufficient thickness t1 is ensured in most of the circumferential direction of the brake drum 5, the brake drum 5 is rigidly opposed even when receiving a force in the outer circumferential direction from the brake shoe 11 during braking. Thus, large deformation is suppressed and the original braking function can be exhibited without any problems. On the other hand, since the wall thickness t2 of the corner portion 14 of the brake drum 5 is reduced in the region corresponding to each fastening outer peripheral end 13 in the circumferential direction, the stress generated in the corner portion 14 and eventually the fastening outer periphery at substantially the same position. The stress generated at the end 13 can be reliably reduced, and as a result, the durability of the brake drum 5 can be improved.

Next, the manufacturing procedure of the brake drum 5 configured as described above will be described.
First, the material of the brake drum 5 is molded by casting with the flange portion 6 integrated (material manufacturing process). Next, the material of the brake drum 5 after casting is set on a lathe, and the inner peripheral surface is cut except for the portion near the flange portion 6 (sliding contact surface forming step). As a result, the casting surface 5a indicated by a broken line in FIG. 4 is cut off to form the sliding contact surface 16 on the inner periphery of the brake drum 5, and the casting surface 5a remains on the flange portion 6 side of the sliding contact surface 16. It is.

After that, each bolt hole 7 is drilled in the flange portion 6 using a multi-axis drilling machine or the like, and each circular counterbore portion 17 is counterbored by an end mill (bolt hole / bore portion forming step). Along with the formation of the circular counterbore portions 17, the inner peripheral casting surface 5a of the brake drum 5 is scraped off into an arc shape, and the manufacture of the brake drum 5 is thus completed.
Since the bolt hole 7 and the circular counterbore part 17 have the same axis, both processes are simultaneously performed in this embodiment. However, the present invention is not limited to this, and both processes may be performed in separate steps.

The important point here is that the bolt hole 7 for inserting the hub bolt 9 is indispensable, and the circular counterbore portion 17 also functions as a contact surface of the head 9 a of the hub bolt 9. It can be regarded as an indispensable processing step. In the present embodiment, the radius of the circular counterbore 17 is appropriately set (specifically, radius R> distance L), and the casting surface 5a of the inner periphery of the brake drum 5 is formed at the outermost periphery of the circular counterbore 17. By cutting off into an arc shape, the thickness of the corner portion 14 of the brake drum 5 is reduced only in the region corresponding to the fastening outer peripheral end 13 to obtain the above-described effect.
For this reason, the manufacturing process of the brake drum 5 is never complicated for the implementation of the present invention, and the manufacturing process of the brake drum 5 can be suppressed in advance because it can be manufactured in the same process as before. .

Next, in order to clarify the characteristics of the brake drum 5 of the present embodiment, it will be further described in comparison with the brake drum shape of the prior art and its manufacturing process.
6 is a perspective view showing a cross-sectional shape around the corner of a brake drum according to the prior art, FIG. 7 is a cross-sectional view showing the cross-sectional shape around the corner, and FIG. 8 is a bolt hole and a fastening outer peripheral end of the flange. FIG.
In the brake drum 101 of the prior art, base portions 104 corresponding to the respective bolt holes 103 are integrally projected on the right side surface of the flange portion 102 during casting so as to be continuous in the circumferential direction. The contact surface 106 of the head portion 105a of the hub bolt is formed by cutting the cast surface 101a of 104 with a lathe. Cutting of the sliding contact surface 107 with other lathes and drilling of the bolt holes 103 with a drill are the same as those in the above-described embodiment.

  The thickness t3 of the corner portion 109 of the manufactured brake drum 101 is uniform in all regions in the circumferential direction. Therefore, if the thickness t3 of the corner portion 109 is increased (e.g., equivalent to the above-mentioned t1), the stress at the fastening outer peripheral end 110 is rapidly increased and the durability is lowered, and conversely, the thickness t3 is reduced (e.g., equivalent to the above-described t2). If so, the rigidity of the brake drum 101 is insufficient. Unlike the prior art, in this embodiment, the thickness of the corner portion 14 is reduced only in the region corresponding to the fastening outer peripheral end 13 in the circumferential direction of the brake drum 5. It can be seen that

On the other hand, regarding the manufacturing procedure of the brake drums 5 and 101, instead of the counterbore processing of the circular counterbore portion 17 performed in the present embodiment, the base portion 104 needs to be turned in the prior art. Therefore, in this embodiment, the number of processes does not increase as compared with the prior art. Rather, if the circular counterbore portion 17 is processed simultaneously with the drilling of the bolt holes 7, the number of processes and the processing time are reduced compared to the conventional technique. It can be seen that the manufacturing cost can be reduced by shortening.
This conventional drum brake 101 and the drum brake 5 of the present embodiment are analyzed by CAE (Computer Aided Engineering), and are applied to respective fastening outer peripheral ends 13 and 110 (areas indicated by hatching in FIGS. 5 and 8) during braking. The generated stress was verified. In order to approximate the analysis conditions, the thickness t1 of the brake drum 5 of the present embodiment is set equal to the thickness t3 of the brake drum 101 of the prior art, and the thickness 2 is set to a smaller value. While the stress generated at the fastening outer peripheral end 110 of the brake drum 101 of the prior art was 42.9 MPa, it was confirmed that the stress at the fastening outer peripheral end 13 can be reduced to 35 MPa in the brake drum 5 of the present embodiment.

  This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the embodiment described above, the brake drum 5 provided on the rear shaft of the truck is embodied, but the present invention is not limited to this. For example, it may be embodied in the brake drum 5 provided on the front shaft, or may be applied to other vehicles such as a bus. In addition, the structure of the drum brake is not limited to the above embodiment and can be arbitrarily changed. For example, the connection relationship of the brake drum 5 to the wheel hub 2 is changed, or the number of hub bolts 9 for fastening is changed. You may do it.

Further, in the above embodiment, the bolt hole 7 and the circular counterbore part 17 have the same axial core so that the drilling of the bolt hole 7 and the concave part of the circular counterbore part 17 can be simultaneously processed. It is not limited to. For example, when the bolt holes 7 are arranged away from the inner peripheral surface of the brake drum 5 toward the inner peripheral side (when the distance L is large), the radius R of the circular counterbore portion 17 is set accordingly. There is a need to increase it. Inevitably, the area of the circular counterbore part 17 is expanded beyond the contact surface required for the hub bolt 9, and it becomes difficult to ensure the rigidity of the brake drum 5.
In such a case, the circular counterbore 17 may be eccentric with respect to each bolt hole 7 in the outer peripheral direction of the brake drum 5. With this configuration, the cast skin surface 5a on the inner periphery of the brake drum 5 can be scraped off by each circular counterbore portion 17 without increasing the radius R of the circular counterbore portion 17 more than necessary, and as a result, the rigidity of the brake drum 5 is increased. After securing, the effects such as stress reduction of the fastening outer peripheral end 13 can be achieved.

2 Wheel hub 5 Brake drum 5a Cast surface (inner peripheral surface)
6 Flange 9 Hub bolt 9a Head 11 Brake shoe 16 Sliding surface 17 Round counterbore

Claims (4)

A plurality of bolt holes are drilled in the flange part that is formed in an annular shape as a whole and integrally formed on one side end, and can be fastened to the wheel hub side by hub bolts through each bolt hole. In addition, the inner peripheral surface is cut to leave a portion near the flange portion as a cutting allowance to form a smooth sliding contact surface, and a brake shoe is slid on the sliding contact surface to generate a braking force. In the vehicle brake drum,
A circular counterbore part with which the head of the hub bolt abuts is formed around each bolt hole on the other side surface of the flange part, and the formation of the circular counterbore part leaves a shaving margin in the vicinity of the flange part. A brake drum for a vehicle, wherein the inner peripheral surface is scraped off in an arc shape toward the outer peripheral direction.   2. The vehicle brake drum according to claim 1, wherein each of the circular counterbore portions is formed with the same axial center with respect to each of the corresponding bolt holes.   2. The vehicle brake drum according to claim 1, wherein each of the circular counterbore portions is formed eccentrically with respect to the corresponding bolt hole in the outer peripheral direction of the brake drum. A material manufacturing process for manufacturing a brake drum material integrally formed with a flange on one side end;
A slidable contact surface forming step of turning the inner peripheral surface of the material of the brake drum manufactured by the raw material manufacturing step to form a smooth slidable contact surface while leaving a portion in the vicinity of the flange portion as a cutting allowance;
A plurality of bolt holes into which hub bolts are inserted are formed in the flange portion of the brake drum after the sliding contact surface is formed in the sliding contact surface forming step so as to be arranged in the circumferential direction. A circular counterbore part with which the head of the hub bolt abuts is formed around each bolt hole on the inner side surface, and the formation of the circular counterbore part allows the inner part of the brake drum left as a cutting allowance in the vicinity of the flange part. A method of manufacturing a brake drum for a vehicle, comprising: a bolt hole and counterbore forming step for scraping the peripheral surface in an arc shape toward the outer peripheral direction.

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