JPH11269507A - Sintered gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintered gear, in which the tooth part has particularly high strength and the high dimensional precision at a prescribed position can be obtd. in a few processes at low cost. SOLUTION: In the sintered gear, in which the tooth part 30C formed at the outer periphery, the outer peripheral part 32 near the tooth part and the inner peripheral part 33 on the inside thereof are compacted with different forming dies and, thereafter, the sintering treatment is executed, a step part 31 at the boundary caused by the raised core of each of the forming dies of the outer peripheral part 32 and the inner peripheral part 33, is formed near the tooth part. It is desirable to be a helical gear having spiral tooth line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered gear that is formed by compacting a metal powder and then performing a sintering process.

[0002]

2. Description of the Related Art In a gear, a portion of a gear to which power is transmitted by meshing is a portion where strength is particularly required, and an outer peripheral portion including a tooth portion is made of a material having excellent strength such as carbon steel. However, there is an example in which the inner peripheral portion is made of a material having a small specific gravity such as an aluminum alloy, and both are solid-phase bonded by pressure welding or welding (Japanese Utility Model Laid-Open No. 1-67370).

However, the number of manufacturing steps is large and the manufacturing cost is high. After the point compacting, the sintering process is performed by dividing the molding die and compacting the outer and inner peripheral portions including the tooth portion with another mold to change the powder density. The sintered gear having a particularly high strength can be provided at low cost with a small number of man-hours.

[0004]

In the compacting and sintering method, high dimensional accuracy can usually be ensured. However, when the molding die is divided, a step is formed at the boundary generated by the mold division, and the high dimensional accuracy is high. It is difficult to maintain dimensional accuracy. Further, correction by sizing (re-pressing) increases the manufacturing cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sintered gear which can maintain teeth at particularly high strength and maintain high dimensional accuracy at a required portion with a small number of steps and at low cost. Is to offer.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a method of forming a mold by forming a tooth on an outer periphery, an outer peripheral portion in the vicinity thereof, and an inner peripheral portion inside the molding die. A sintered gear that is powder-formed and then subjected to a sintering process, and a stepped portion formed by mold splitting of each of the outer peripheral portion and the inner peripheral portion is formed near the teeth. .

By compacting the outer peripheral portion and the inner peripheral portion including the teeth with different molding dies, the powder density of the outer peripheral portion can be particularly increased to increase the strength of the teeth, and each molding die can be compacted. Is formed near the teeth, so that the teeth and the inner peripheral portion other than the vicinity of the teeth, which generally require dimensional accuracy, can be maintained at high dimensional accuracy over a wide range. In addition, a sintered gear can be provided inexpensively with a small number of steps for sintering after compacting.

According to a second aspect of the present invention, in the sintered gear according to the first aspect, the sintered gear is a helical gear having a spiral-shaped tooth.

The helical gear can be easily formed by compressing while rotating the forming die on the outer peripheral side along the helical gear teeth, and the helical gear allows power to be transmitted more smoothly and efficiently. Will be

According to a third aspect of the present invention, in the sintered gear according to the first or second aspect, the sintered gear comprises:
It is a primary driven gear attached to a clutch outer of a small vehicle.

[0011] Since the step portion of the boundary generated by the mold splitting of each molding die is formed near the teeth, the inner peripheral portion of the primary driven gear with which the clutch outer comes into contact can be secured with high dimensional accuracy, and the primary driven gear can be connected to the shaft. It is possible to position accurately in the direction.

According to a fourth aspect of the present invention, in the sintered gear according to the third aspect, the step portion is formed on an outer periphery of the primary driven gear from a contact surface with the clutch outer. I do.

The contact surface of the primary driven gear with the clutch outer can ensure sufficient dimensional accuracy.
The primary driven gear can be accurately positioned in the axial direction to avoid collision with a side plate or the like, thereby preventing occurrence of a tapping sound.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment according to the present invention will be described with reference to FIGS. The sintered gear according to the present embodiment is used as a primary driven gear 30 used in a clutch portion of a motorcycle. FIG. 1 is a cross-sectional view of an internal combustion engine and a power transmission system of the motorcycle.

The internal combustion engine 1 is a one-cylinder two-cycle engine in which a reciprocating motion of a piston 3 in a cylinder 2 is changed to a rotating motion of a crankshaft 5 by a connecting rod 4.
And a primary drive gear 7 is fitted to the other end.

A main shaft 8 and a counter shaft 9 are provided in parallel with the crankshaft 5.
A transmission gear group 10 selectively meshing with each other intervenes between the gears 9 to transmit power, and the rear wheels are driven via a chain hung on a sprocket 11 fitted to the end of the counter shaft 9.

A friction clutch 20 is connected to one end of the main shaft 8.
Are provided, and the clutch outer 21 of the friction clutch 20 is provided.
A primary driven gear 30 attached to the primary drive gear 7 fitted to the crankshaft 5
Is engaged. The primary drive gear 7 and the primary driven gear 30 are helical gears having meshing teeth with helical teeth.

Referring to FIG. 2, the clutch outer 21 of the friction clutch 20 has a cylindrical portion 21b with a hollow disk portion 21a as a bottom wall.
A hub 22 is spline-fitted to the main shaft 8 protruding into the cylinder and fixed with a nut 23. The hub 22 has a central cylindrical portion 24 of a clutch center 24.
a is fitted.

In the clutch center 24, an annular disk portion 24b extends radially from the central cylindrical portion 24a and forms a cylindrical portion 24c so as to be folded back.
d is formed and rotates integrally with the main shaft 8 via the hub 22.

A pressure plate 25 is slidably supported at the center of the hub 22 inside the clutch center 24 inside the cylinder of the clutch outer 21. Pressure plate 25
An annular disk portion 25a faces the clutch center 24, and a cylindrical portion 25b extending from near the outer peripheral portion of the disk portion 25a is formed along the outer peripheral surface of the cylindrical portion 24c of the clutch center 24.

In a space between the outer peripheral surface of the cylindrical portion 25b of the pressure plate 25 and the inner peripheral surface of the cylinder of the clutch outer 21, a plurality of clutch desks 26 on the clutch outer 21 side and a plurality of clutch plates 27 on the pressure plate 25 side are provided. They are arranged alternately. The plurality of clutch desks 26 and clutch plates 27 are sandwiched between a flange portion 24d of the clutch center 24 and a disk portion 25a of the pressure plate 25.

Therefore, when the pressure plate 25 approaches the clutch center 24 to reduce the interval, the clutch desk 26
And the clutch plate 27 approach each other to strengthen the frictional engagement to easily transmit the rotation of the clutch outer 21 to the clutch center 24 and the main shaft 8. Conversely, when the pressure plate 25 moves away from the clutch center 24, the power transmission is reduced. Will be shut off. Thus, the engagement and disengagement of the friction clutch 20 is performed.

The primary drive gear 7 and the primary driven gear 30 for transmitting the rotation of the crankshaft 5 to the clutch outer 21 are sintered helical gears, and the primary driven gear 30 has a shape as shown in FIGS. You are. Specifically, referring to FIG. 4 in particular, an annular disk portion 30b extends in the radial direction from the central cylindrical portion 30a, and has a helical tooth in a spiral shape on the outer peripheral edge thereof.
30c is formed.

A step portion 31 is formed in a circular shape at a boundary between an outer peripheral portion 32 including the helical teeth 30c and an inner peripheral portion 33 inside the outer peripheral portion 32. The step 31 is located near the helical tooth 30c.
The clutch outer 21 abuts on the inner peripheral portion 33 inside the 31.

In the inner peripheral portion 33, six large-diameter large holes 34 are formed at equal intervals around the cylindrical portion 30a.
Three small-diameter small holes 35 are formed at regular intervals along the step 31. The small circular hole 35 is provided with a step having a reduced inner diameter on the inner peripheral surface.

The primary driven gear 30 is shown in FIG.
As shown in the figure, the cylindrical portion 30a is rotatably fitted to the main shaft 8 via the outer collar 40, and is sandwiched between the washers 41 and 42 on both sides thereof to perform positioning in the axial direction together with the outer collar 40.

The primary driven gear 30 has an inner peripheral portion 33 with which the disk portion 21a of the clutch outer 21 abuts, and a cushion rubber fitted into six large circular holes 34 of the inner peripheral portion 33.
Six bosses 21c protruding from the disk portion 21a of the clutch outer 21 are inserted into the 36, and the clutch outer 21 is locked in a floating state via the buffer rubber 36.

The inner peripheral portion 33-3 of the primary driven gear 30
Elastic rubber 37 is fitted into each of the small circular holes 35, and the elastic rubber 37
Protrudes from the side surface of the inner peripheral portion 33 when no external force is applied. When the disk portion 21a of the clutch outer 21 comes into contact with the primary driven gear 30, the end surface of the boss 21c penetrating the cushion rubber 36 fitted in the large circular hole 34 slightly protrudes from the side surface of the primary driven gear 30.

Clutch side plate having a hollow disk shape
The clutch outer plate 21 abuts on the end surface of the boss 21c of the clutch outer 21 so as to face the side surface of the inner peripheral portion 33, and is fixed to the boss 21c by a rivet 29 to integrally attach the clutch side plate 28 to the clutch outer 21.

Three small circular holes of the primary driven gear 30
The elastic rubber 37 fitted on the 35 is the clutch side plate 28
The restoring force acts on the primary driven gear 30 in a direction to separate the clutch side plate 28 to the left in FIG.
The clutch outer 21 integrated with the primary driven gear 30
To maintain the contact state.

In this state, a required gap C is formed between the primary driven gear 30 and the clutch side plate 28 as shown in FIG. As described above, the clutch outer 21 is mounted on the primary driven gear 30 via the cushion rubber 36 in a floating state.

When the crankshaft 5 rotates when the internal combustion engine 1 is driven, the rotation is transmitted to the primary driven gear 30 meshing with the primary drive gear 7 integrated with the crankshaft 5, but the two gears 7, 30 are helical gears. Power transmission is performed smoothly and efficiently.

Since the rotation of the primary driven gear 30 is transmitted to the clutch outer 21 via the cushion rubber 36, the fluctuation of the rotational load due to the start of the internal combustion engine 1 or the engagement / disengagement of the friction clutch 30 is buffered by the cushion rubber 36. And smooth power transmission can be maintained.

Here, the clearance C between the primary driven gear 30 and the clutch side plate 28 is ensured, so that the relative rotation of the primary driven gear 30 and the clutch outer 21 becomes free. As a result, when the rotational load fluctuates, the cushioning rubber 36 works effectively and the power transmission can be performed smoothly.

Further, since the primary drive gear 7 and the primary driven gear 30 are helical gears and the helical teeth are meshed with each other, when the rotational load fluctuates, the primary driven gear 30 rotates relative to the clutch outer 21 as described above. A phase difference is generated and a force is applied in the axial direction.

Therefore, if the gap C formed between the primary driven gear 30 and the clutch side plate 28 is not secured to the necessary minimum, the primary driven gear
There is a possibility that the striking sound may occur due to the 30 abutting against the clutch side plate 28.

In order to prevent the occurrence of the tapping sound, the gap C
Must be secured to the minimum necessary, and for that purpose, the primary driven gear 30 needs to be manufactured with high dimensional accuracy. Especially the inner periphery of the primary driven gear 30
33 width length with high dimensional accuracy is required.

The primary driven gear 30 is a sintered helical gear which has been subjected to a sintering process after being compacted. The outer peripheral portion 32 including the helical teeth 30c is required to have particularly high strength as compared with the inner peripheral portion 33. In order to compact the helical teeth 30c of the portion 32, the molding die must be rotated, and the inner peripheral portion 33 has a large circular hole 34 and the like. 33 is compacted with a different mold.

This compacting method will be described with reference to the schematic diagrams of FIGS. 6 and 7. The compacting machine is a pair of upper and lower parts inside a die 50 having an annular shape and helical teeth formed on the inner peripheral surface. The punch is fitted and the metal powder filled between the upper and lower punches is compressed to form a green compact.

A primary driven gear is mounted on the center axis of the die 50.
A rod 51 that forms the cylindrical portion 30a of 30 penetrates, and a rod that forms the large circular hole 34 and the small circular hole 35 (not shown)
Penetrates at predetermined locations.

A pair of upper and lower upper boss punches 52a and 52b are fitted to the outer periphery of the center rod 51 so as to be vertically movable.
An upper inner punch 53a and a lower inner punch 53b are fitted around the upper and lower boss punches 52a and 52b, respectively, so as to be vertically movable.
An upper outer punch 54a and a lower outer punch 54b are fitted between the upper and lower inner punches 53a and 53b and the die 50, respectively.

Helical teeth are formed on the outer peripheral surfaces of the upper and lower outer punches 54a and 54b, and the upper and lower outer punches 54a and 54b spirally engage with the helical teeth of the die 50 and move up and down while rotating relatively. Therefore, the inner upper and lower boss punches 52a and 52b and the upper and lower inner punches 53a and 53b move only in the vertical direction, and the outer upper and lower outer punches 54a and 54b rotate and move in the vertical direction.

As described above, the molding die is divided into an inner side and an outer side. The inner peripheral portion 33 of the primary driven gear 30 is formed by the inner upper and lower boss punches 52a and 52b and the upper and lower inner punches 53a and 53b, and the outer upper and lower outer punches 54a are formed. , 54b to form the outer peripheral portion 32.

In the initial stage of molding, as shown in FIG. 6, the filled metal powder 55 is compressed by the inner upper and lower boss punches 52a, 52b and the upper and lower inner punches 53a, 53b. It is pushed to the periphery.

Later, the upper and lower outer punches 54a, 54b are delayed.
While rotating, the outer peripheral portion of the metal powder 55 is compressed to form an outer peripheral portion together with the helical teeth.
As shown in FIG. 7, a compression molded body is formed substantially on the same plane as 53b.

In the compression-molded body thus formed, the outer peripheral portion including the helical teeth compressed at a later timing has a high density of the metal powder, and when the green compact is sintered, the helical teeth of the outer peripheral portion 32 are formed. The strength of 30a can be increased.

In the compacting stage, the upper and lower outer punches 54a,
54b and the upper and lower inner punches 53a and 53b are formed so as to be substantially flush with each other, but it is difficult to completely form the same surface. The step 31 is formed at the boundary due to the misalignment of the mold division.

As shown in FIG. 5, the primary driven gear
30 has a step portion 31 with a mold deviation amount D near the outer periphery near the helical tooth 30c, so that the step portion 31 is located on the outer periphery from the portion where the clutch outer 21 contacts, and as described above, the primary driven gear 30 The width of the inner peripheral portion 33 between the clutch outer 21 and the clutch side plate 28 which requires particularly high dimensional accuracy can secure necessary dimensional accuracy.

Accordingly, the necessary minimum gap C between the primary driven gear 30 and the clutch side plate 28 is ensured, and it is possible to prevent the primary driven gear 30 from abutting against the clutch side plate 28 and generating a tapping sound.

As shown in FIG. 11, if the stepped portion 031 is located not in the vicinity of the helical teeth 030 c but in the center side in contact with the clutch outer 021 as shown in FIG. The clearance C between the clutch side plate 028 and the clutch side plate 028 cannot be secured to a necessary minimum, and it is impossible to prevent the occurrence of a tapping sound.

As described above, the primary driven gear 30
Can be manufactured inexpensively with a small number of steps by compacting and sintering, and the required dimensional accuracy of the inner peripheral portion 33 can be kept high.

The primary driven gear 30 shown in FIG.
The outer peripheral portion 32 is shifted from the inner peripheral portion 33 toward the clutch outer 21 to form the step portion 31. However, as shown in FIG. 8 (the same members are denoted by the same reference numerals), the primary driven gear 60 The outer peripheral portion 62 has a clutch outer
Although the step 61 is formed on the side of the clutch side plate 28 opposite to that of the step 21, there is a step 61 on the outer periphery from a portion where the clutch outer 21 contacts, and the required width of the inner peripheral portion 63 is required. Has high dimensional accuracy and is a primary driven gear
A minimum gap C between the clutch side plate 60 and the clutch side plate 28 can be ensured, and the occurrence of a tapping sound can be prevented.

If higher dimensional accuracy is required than the dimensional accuracy obtained by the above compacting and sintering process, FIGS. 9 and 10 (the same members are denoted by the same reference numerals).
A cutting allowance 76 is formed near the step 71 on the side surface of the inner peripheral portion 73 on the clutch side plate 28 side like the primary driven gear 70 shown in FIG.

By cutting the convex portion 77 protruding from the cutting allowance 76 on the side surface of the inner peripheral portion 63, the width of the inner peripheral portion 63 can be easily formed with higher dimensional accuracy, and the And the gap C between the primary driven gear 70 and the clutch side plate 28 can be set to a required gap length with high accuracy.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an internal combustion engine and a power transmission system of a motorcycle to which a sintered gear according to an embodiment of the present invention is applied.

FIG. 2 is a cross-sectional view showing a clutch and the vicinity of the clutch.

FIG. 3 is a front view of a primary driven gear unit without a clutch side plate.

FIG. 4 is a front view of a primary driven gear.

FIG. 5 is an enlarged cross-sectional view of a main part of FIG. 2;

FIG. 6 is a sectional view showing a main part of the powder compacting machine.

FIG. 7 is a sectional view of another state.

FIG. 8 is a sectional view of a main part according to another embodiment.

FIG. 9 is a cross-sectional view of main parts when a primary driven gear according to another embodiment is used.

FIG. 10 is a front view of the primary driven gear portion in the embodiment with the clutch side plate omitted.

FIG. 11 is an explanatory diagram showing an example different from the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Cylinder, 3 ... Piston, 4 ... Connecting rod, 5 ... Crankshaft, 6 ... AC generator, 7 ... Primary drive gear, 8 ... Main shaft, 9 ... Counter shaft, 10 ... Transmission gear Flock, 11
… Sprocket, 20… friction clutch, 21… clutch outer, 22… hub, 23… nut, 24… clutch center, 25…
Pressure plate, 26 ... Clutch desk, 27 ... Clutch plate, 28 ... Clutch side plate, 29 ... Rivet, 30 ... Primary driven gear, 31 ... Step, 32 ... Outer periphery, 33 ... Inner periphery, 34 ... Large hole, 35: small circular hole, 36: cushion rubber, 37: elastic rubber, 40: outer collar, 41, 42: washer, 50: die, 51: rod, 52a: upper boss punch, 52b
... lower boss punch, 53a ... upper inner punch, 53b ... lower inner punch, 54a ... upper outer punch, 54b ... lower outer punch, 55 ... metal powder, 60 ... primary driven gear, 61 ... stepped portion, 62 ... outer peripheral portion, 63 ... inner periphery Part, 70: primary driven gear, 71: stepped part, 72: outer peripheral part, 73: inner peripheral part, 76: cutting allowance, 77: convex part.

Claims (4)

[Claims] 1. A sintered gear in which teeth formed on an outer periphery and an outer peripheral portion in the vicinity of the teeth and an inner peripheral portion thereof are compacted by different molding dies and then subjected to a sintering process. A sintered gear characterized in that a step formed at the boundary generated by the mold splitting of the forming part and the inner peripheral part is formed near the teeth. 2. The sintered gear according to claim 1, wherein the sintered gear is a helical gear having a spiral helical gear. 3. The sintered gear according to claim 1, wherein the sintered gear is a primary driven gear attached to a clutch outer of a small vehicle. 4. The sintered gear according to claim 3, wherein the step portion is formed on an outer periphery of the primary driven gear from a contact surface with the clutch outer.