JPH1163167A - Transmission gear for motorcycle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the tilting of a catch for a dog clutch during hot forging by unevenly providing a side face continuing from the outer peripheral surface of a cylindrical boss in the catch for the dog clutch in the center side of a diameter direction with a level difference from the outer peripheral surface. SOLUTION: A transmission gear 1 for a motorcycle is composed of a large diameter part 3 having a tooth 2, a cylindrical boss 4 on the same axis in one end of the large diameter part 3 in an axial direction, a dog clutch first catch 5 projectingly provided in the other end of the large diameter part 3 in the axial direction and a dog clutch second catch 6 projectingly provided in the end surface of the boss in the axial direction. Pluralities of first and second catches 5 and 6, for example four each, are provided at equal intervals in the circumferential direction of the transmission gear 1. The side face 6a of the second catch 6 continuous from the outer peripheral surface 4a of the boss 4 is unevenly located in the center side of a diameter direction with a level difference from the outer peripheral surface 4a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission gear for a motorcycle having a dog clutch pawl.

[0002]

2. Description of the Related Art Conventionally, as a transmission gear of this type, a cylindrical boss is integrally formed on an end face of a large diameter portion forming teeth, and a dog having a prismatic projection is formed on an end face in the axial direction of the boss. Some clutch pawls are integrally formed so as to protrude in the axial direction of the transmission gear.
In this transmission gear, the large-diameter portion, the boss, and the claw are integrally formed by subjecting a transmission gear material to hot forging, and further, by machining the molded product, the teeth and the shaft center portion are formed. Shaft hole and a groove for engaging a shift fork.

[0003]

However, the conventional transmission gear constructed as described above has a disadvantage that the meshing with the meshed gear is not smooth when used. This is because the nail formed by hot forging rarely has a shape transferred from the cavity of the mold. That is, despite the fact that the claw is formed so that the claw extends linearly along the axial direction,
The tip of the pawl was displaced inward in the radial direction of the transmission gear, and the pawl was slightly inclined, resulting in the dimensions not being within the designed but within tolerance.

[0004] For this reason, in the conventional transmission gear, after the hot forging is finished, the inner surface in the radial direction of the claw is subjected to finish processing by a lathe or the like despite the increase in cost.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is an object of the present invention to prevent a dog clutch pawl from inclining during a hot forging process, thereby reducing the cost by eliminating post-processing. With the goal.

[0006]

In order to achieve this object, a transmission gear for a motorcycle according to the present invention comprises a dog clutch pawl having a side surface connected to an outer peripheral surface of a cylindrical boss, and a step formed from the outer peripheral surface. Are located at the center in the radial direction. The inventors have clarified that the cause of the inclination of the claws in the hot forging process is the contact between the claws and the mold that recovers from the elastic deformation state at the time of mold release.

When a transmission gear having a large-diameter portion for forming a gear and a boss and a pawl for a dog clutch is manufactured by hot forging, the large-diameter portion is generally formed by an upper die and the boss and the pawl are lowered. Mold with a mold. The cavity of the lower mold is formed in a shape in which the portion for forming the nail is relatively deeply dug. The concave portion for forming the claw is opened at a portion where the boss is formed in the cavity, that is, at the bottom of the outer peripheral portion of the circular concave portion. At the time of molding, the material plastically deformed by molding pressure is filled in the concave portion for forming the claw and the circular concave portion for forming the boss.

In this molding, the peripheral wall of the circular recess for forming the boss is elastically deformed so as to be displaced radially outward by the molding pressure transmitted through the material. At this time, the resilience of the peripheral wall itself and the pressure applied to the wall by the material are balanced. That is, an internal stress is generated in the peripheral wall in which the direction of the force is directed to the center in the radial direction, and the internal stress causes the peripheral wall to urge the outer peripheral surface of the boss.

After the molding is completed, the upper mold is separated upward from the lower mold and the molded product (raw material), and then the molded product is extruded upward from the lower mold. At the time of releasing, while the boss is in contact with the peripheral wall, the above-mentioned two forces are maintained in a balanced state, but the molded product moves further upward and the boss separates upward from the peripheral wall. Then, the two forces cannot be balanced. That is, when the claws face the peripheral wall, the peripheral wall is restored from the elastically deformed state to the initial state by the internal stress. In other words, at this time, the inner diameter of the peripheral wall becomes smaller.

In the transmission gear according to the present invention, the side surface of the claw facing the peripheral wall is unevenly distributed radially inward from the outer peripheral surface of the boss. Therefore, when the inner diameter of the peripheral wall is reduced, the peripheral wall is clawed. Never touch. Therefore, the claw is not pressed or inclined or bent by the peripheral wall.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a transmission gear for a motorcycle according to the present invention will be described below in detail with reference to FIGS. FIG. 1 is a longitudinal sectional view of a transmission gear for a motorcycle according to the present invention. FIG. 2 is a bottom view of the transmission gear for a motorcycle according to the present invention as viewed from the boss side. is there. 3A and 3B are cross-sectional views showing a state at the time of molding. FIG. 3A is a longitudinal sectional view of a mold and a molded product, and FIG. 3B is an enlarged sectional view showing a state of a wall of a mold for forming a boss. It is. 4A and 4B are cross-sectional views showing a state at the time of mold release. FIG. 4A is a vertical cross-sectional view of a mold and a molded product, and FIG. 4B is an enlarged cross-section showing a state of a wall of a mold for forming a boss. FIG.

In these figures, reference numeral 1 denotes a transmission gear for a motorcycle according to this embodiment. The transmission gear 1 has a large-diameter portion 3 having teeth 2, a cylindrical boss 4 provided on one axial end of the large-diameter portion 3 on the same axis, It comprises a first dog clutch pawl 5 projecting from the end and a dog clutch second pawl 6 projecting from the axial end surface of the boss 4.

The boss 4 is formed with a series of concave grooves 7 in the outer peripheral portion without interruption in the circumferential direction. A shift fork (not shown) is engaged with the concave groove 7. Also, this boss 4
A shaft hole 8 into which a support shaft (not shown) for supporting the transmission gear 1 movably in the axial direction is spline-fitted is formed in the axial center portion of the large diameter portion 3.

A plurality of the first claws 5 and the second claws 6 are provided at equal intervals in the circumferential direction of the transmission gear 1. In this embodiment, four claws 5 and 6 are provided four by four. The side surface 6a of the second claw 6 which is continuous with the outer peripheral surface 4a of the boss 4 is unevenly distributed toward the center in the radial direction with a step from the outer peripheral surface 4a.

Next, a procedure for manufacturing the transmission gear 1 will be described. First, a preheated material is loaded into a hot forging die. This mold is indicated by reference numeral 9 in FIGS. The mold 9 used in this embodiment includes an upper mold 11 having a cavity 10 for molding the large-diameter portion 3 and the first claw 5 and a boss 4 and a second claw 6. A lower mold 13 having a cavity 12 to be formed and a knockout pin 14 for extruding a molded product from the lower mold 13 at the time of release from the mold.

The lower mold 13 is provided at the center of the first mold 1.
3a, a cylindrical second mold 13b fitted to the outer periphery of the first mold 13a, and a third mold 13c fitted to the outer peripheral surface of the second mold 13b And are formed separately. In the cavity 12 of the lower mold 13, the second
A boss-forming circular recess 12a located inside a peripheral wall 13d formed by an upper part of a mold 13b, and the circular recess 12a.
Claw forming recess 1 that opens to the inner bottom surface and extends downward
2b are formed in series.

After the material is loaded into the upper and lower molds 11 and 13, it is compressed by the upper and lower molds 11 and 13 and plastically deformed in the cavities 10 and 12. Upper and lower dies 11, 13
By performing the above-described compression until the mating surfaces contact each other, the material is formed so as to follow the shape of the cavities 10 and 12 as shown in FIG. This molded product is indicated by the symbol W. At this time, as shown in FIG. 3B, a molding pressure indicated by an arrow P1 in FIG. 3 is applied to the peripheral wall 13d of the lower mold 13 so that the peripheral wall 13d is displaced radially outward by the molding pressure P1. Elastically deform. The position of the wall 13d before elastic deformation is indicated by a two-dot chain line in FIG. In this state, the molding pressure P1 is balanced with the elastic force P2 of the peripheral wall 13d itself. That is, the peripheral wall 13
An internal stress in which the direction of the force is directed to the center in the radial direction is generated in d, and the peripheral wall 13d urges the outer peripheral surface 4a of the boss 4 due to the internal stress.

After the molding process is completed, the upper mold 11 is separated from the lower mold 13 upward in FIG.
Further, the knockout pin 14 is moved upward to
The molded product W is extruded upward as shown in FIG. At the time of this release, while the boss 4 is in contact with the peripheral wall 13d as shown by a two-dot chain line in FIG.
The state where 1 and P2 are balanced is maintained. However, FIG.
As shown by the solid line in FIG. 7B, when the boss 4 is separated upward from the peripheral wall 13d, the two forces P1 and P
2 cannot be balanced. That is, the claw 6 is
The peripheral wall 13d is restored from the elastically deformed state to the initial state by the internal stress in a state opposed to the state d. In other words, at this time, the inner diameter of the peripheral wall 13d becomes smaller.

In the transmission gear 1, the side surface 6a of the claw 6 facing the peripheral wall 13d is formed by the outer peripheral surface 4a of the boss 4.
The inner wall of the front peripheral wall 13d is unevenly distributed inward in the radial direction, so that when the inner diameter of the peripheral wall 13d is reduced as described above, the peripheral wall 13d does not contact the claw 6.
The conventional transmission gear employs a structure in which the peripheral wall comes into contact with the pawl at the time of release from the mold. Therefore, the pawl is pushed by the peripheral wall and is inclined or bent.
As described above, since the wall 13d does not contact the claws 6, the claws 6 are not inclined or curved, but are formed in a straight line.

The phenomenon in which the peripheral wall is elastically deformed in the molding step and returns to the original state when the mold is released, becomes remarkable when the lower mold 13 is divided into a plurality of parts as shown in this embodiment. This is because the rigidity of each of the dies 13a to 13c is lower than when the dies 13a to 13c of the lower die 13 are integrally formed.

After the release, the molded product W is machined,
By forming the teeth 2, the shaft hole 8, the concave groove 7, and the like, the manufacturing process of the transmission gear 1 is completed. Nail 6
Is formed in a straight line in the hot forging step, and therefore does not need to be machined.

In this embodiment, an example is shown in which the lower mold 13 is divided into a plurality of parts. However, the present invention is not limited to such a limitation, and the first to third molds 13a to 13a are not limited thereto.
3c can be formed integrally. In the case of adopting this configuration, the concave portion 12b for claw molding of the cavity 12 is formed by electric discharge machining. When the transmission gear 1 is formed by this integrated lower mold, the corners of the pawl 6 are curved as shown by the two-dot chain line in FIG.

[0023]

As described above, according to the present invention, when the mold is released in the hot forging step, the claw is kept separated from the wall for forming the boss in the mold, so that the claw is pressed by the wall. It does not tilt or bend.
Therefore, the transmission gear for a motorcycle according to the present invention can smoothly mesh with the gear to be meshed even if the dog clutch pawl is not subjected to a finishing process by machining, so that it is inexpensive and has a smooth gear shift. Can be done.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a transmission gear for a motorcycle according to the present invention.

FIG. 2 is a bottom view of the transmission gear for a motorcycle according to the present invention as viewed from the boss side.

FIG. 3 is a cross-sectional view showing a state during molding.

FIG. 4 is a cross-sectional view showing a state at the time of mold release.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transmission gear, 3 ... Large diameter part, 4 ... Boss, 4a ... Outer peripheral surface, 6 ... Second claw, 6a ... Side surface, 13 ... Lower mold, 13
d ... peripheral wall.

Claims (1)

[Claims] 1. A motorcycle transmission gear in which a dog clutch pawl protrudes in an axial direction from an axial end face of a cylindrical boss, wherein a side surface of the pawl connected to an outer peripheral surface of the cylindrical boss is formed on the side surface of the pawl. A transmission gear for a motorcycle, wherein the transmission gear is unevenly distributed toward a center in a radial direction with a step from an outer peripheral surface.