JP2002310267A - Resin-made worm wheel, manufacturing device thereof, and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a resin-made and highly precise worm wheel having tooth parts 1, 1,... in a resin-made outer peripheral part and a tooth groove bottom part 2 between the tooth parts 1 and 1 in a recessed shape recessed in the direction of length of a tooth groove. SOLUTION: This resin-made worm wheel W consists of two half-split bodies W1, W1 obtained by dividing in a substantially central part in the axial direction, and both half-split bodies W1, W1 are joined and integrated mutually at a tooth bottom position of each tooth part 1a on small diameter side faces 4, 4 where a diameter of each half-split body becomes small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to a technical field related to a resin worm wheel, and an apparatus and method for manufacturing the same.

[0002]

2. Description of the Related Art Generally, this kind of worm wheel is
A plurality of teeth extending spirally (obliquely) with respect to the axial direction are formed on the outer peripheral portion. When power is transmitted between the worm wheel and the worm, the worm is disposed on the outer peripheral portion of the worm wheel. Is disposed so that its axis intersects with the axis of the worm wheel so as to be substantially orthogonal to the axis of the worm wheel. To be transmitted to. And the bottom of the tooth space between the teeth of the worm wheel normally meshes with the teeth of the worm, so that the central portion in the tooth groove length direction is recessed corresponding to the outer peripheral shape of the teeth of the worm. It is formed in a concave shape.

[0003] When such a worm wheel is manufactured from a resin, it is common practice to cut the outer peripheral portion of the blank with a hob to form teeth like a metal worm wheel. . However, with this method, a resin worm wheel having high strength and dimensional accuracy can be manufactured, but there is a problem in that the cost is increased because cutting is required.

Therefore, the worm wheel may be formed by injecting the resin into the cavity in the mold by utilizing the moldability of the resin, but as described above, the bottom of the tooth space between the outer peripheral teeth is formed. Even if an attempt is made to form a concave shape, the bottom of the tooth space is undercut, and the worm wheel cannot be released from the mold after molding.

[0005] For this reason, as a resin worm wheel manufactured by molding, a helical gear in which the tooth groove bottom of each tooth portion is flat (linear) is conventionally used (conventional example 1). ).

On the other hand, as shown in, for example, Japanese Utility Model Laid-Open No. 4-49254 (conventional example 2), one half in the longitudinal direction of a tooth groove bottom between teeth of a worm wheel has a concave half. The halves are formed in an arc shape so that the other half has a flat shape parallel to the axis, eliminating the undercut at the bottom of the tooth space and injecting the worm wheel with resin in the mold cavity. There has been proposed one that can be molded and released.

Further, as shown in Japanese Patent Application Laid-Open No. 11-286032 (conventional example 3), core molds are provided on both sides of a mold having teeth forming portions for forming teeth of a worm wheel on the inner peripheral surface. After forming a cavity between these molds and injecting resin into the cavity to form a worm wheel, the worm wheel is turned along the twist angle of the teeth and the worm wheel is elastically deformed. It has been proposed that the resin is extracted from the mold by using the shrinkage of the resin while the resin is contracted.

[0008]

However, the prior art described above has the following problems. That is, in Conventional Example 1 in which a helical gear is used as the worm wheel, since the bottom of the tooth space between the teeth of the helical gear is flat, the contact area between the worm and the teeth decreases, and a large load is applied. However, there is a disadvantage that it cannot be transmitted.

Further, in the conventional example 2, the contact area with the worm is larger than in the case of using the helical gear, but the worm is still in contact with the worm in comparison with a normal worm wheel in which the entire bottom of the tooth space is depressed. The contact area is small, and is not suitable for a case where high strength is required in a gear transmission mechanism or the like provided in an electric power steering device for an automobile, for example.

Further, in the conventional example 3, it is necessary to deform the teeth when the worm wheel after molding is released from the mold, which is inappropriate when high precision is required for the dimensional accuracy of the teeth. It is.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to improve a molding die and a molding method for molding a worm wheel by molding a resin to thereby improve a tooth groove bottom portion. An object of the present invention is to provide a worm wheel having a normal shape, which is entirely depressed, inexpensively and with high precision by molding.

[0012]

In order to achieve the above object, according to the present invention, the worm wheel is moved in the axial direction by 2 mm.
It was composed of divided halves, and both halves were joined and integrated.

More specifically, according to the first aspect of the present invention, a resin worm has a toothed portion on an outer peripheral portion made of resin, and a tooth groove bottom between the toothed portions is recessed in a tooth groove length direction. As a wheel, this resin worm wheel is composed of two halves divided at a substantially central portion in the axial direction, and both halves are located at the root positions of the tooth portions of the side surfaces on both sides in the axial direction. , And are joined and integrated on a small-diameter side surface (joining surface) on the small-diameter side.

According to the above configuration, the resin worm wheel is formed by joining and integrating two axially divided halves, so that the entire bottom of the tooth space between the teeth of the worm wheel is toothed. Even if the shape is concave in the groove length direction, the teeth on the outer periphery of the half body are aligned with the teeth of the worm wheel and the tooth groove bottom in the length direction (axial direction of the worm wheel).
When the outer diameters at the root positions of the tooth portions on both sides in the axial direction of each half are compared, one of them becomes a small-diameter side surface having a smaller diameter than the other, and the other is a large-diameter side surface. Become. For this reason, when forming each half with a molding die, it is only necessary to extract the formed half from the large-diameter side surface, and no undercut occurs, so that the half can be molded with the molding die. The small-diameter side surface of each half body is used as a joining surface, and a pair of half bodies may be aligned so that the respective outer peripheral teeth are continuous with each other, and the small-diameter side surfaces may be joined and integrated. As a result, a resin worm wheel in which the entire tooth groove bottom is formed in a concave shape in the tooth groove length direction is obtained.

In this resin worm wheel, the entire bottom of the tooth space between the teeth is recessed in the length direction of the tooth space. It is capable of transmitting a large load, and is also suitable for a case where high strength is required in a gear transmission mechanism or the like provided in an electric power steering device for an automobile.

Further, as described above, since only the half body is formed by the molding die and is extracted from the large-diameter side surface after the molding, the half body does not need to be removed while being elastically deformed from the molding die. The tooth portion of the split body can be formed with high precision, and the dimensional accuracy of the worm wheel can be improved.

Further, since the halves are formed by a molding die and the formed halves are joined to form a worm wheel, the cost is reduced and the cost is reduced as compared with the case where the teeth are formed by cutting. A resin worm wheel is obtained.

In the second aspect of the present invention, the two halves are the same, and are joined symmetrically with respect to the axis. This makes it possible to form a resin worm wheel by molding one type of half body with a molding die and joining a pair of the halves, further reducing the cost.

According to the third aspect of the present invention, at least a small diameter side surface of each half is provided with a positioning portion for positioning the half in the circumferential direction with respect to the other half. In this case, the positions in the circumferential direction can be easily positioned by the positioning portions in the joining step of the two halves, and workability in the joining step can be improved.

According to the fourth aspect of the present invention, the chamfered portion or the arc surface is formed at the end of the tooth portion of the half body on the side of the small diameter side. Thus, when the two halves are joined and integrated, the corresponding tooth portions are connected via the chamfered portion or the arc surface, so that a step is less likely to occur at the joint portion between the tooth portions. ,
By distributing the load transmitted to and from the worm to the teeth of the two halves (entire teeth of the worm wheel), smooth transmission and transmission of a larger load can be performed.

According to a fifth aspect of the present invention, the resin worm wheel constitutes a part of a gear transmission mechanism of an electric power steering device of an automobile. This provides the optimum use of the resin worm wheel.

In the invention according to claim 6, the resin in the resin worm wheel is a thermoplastic resin. In this way, a resin worm wheel having tough (elastic) teeth is obtained.

According to a seventh aspect of the present invention, the outer peripheral portion made of resin has a tooth portion, the bottom of the tooth space between the tooth portions is recessed in the length direction of the tooth groove, and a substantially central portion in the axial direction is formed. A resin worm wheel composed of two divided bodies, wherein the two halves are joined and integrated on a small-diameter side surface which is a small-diameter side at a root position of a tooth portion among both side surfaces in the axial direction. Manufacturing apparatus. This apparatus for manufacturing a resin worm wheel is provided with a first molding die having an inner peripheral surface provided with a tooth molding portion for molding the outer teeth of the half body, and disposed on one side of the first molding die. A second molding die having a molding surface for molding the small diameter side surface of the half body, and a third molding die arranged on the other side of the first molding die and having a molding surface for molding the large diameter side surface of the half body. It is characterized by having. In the invention of claim 8, the first and second molds are integrated. According to these inventions, the resin worm wheel can be easily manufactured.

According to a ninth aspect of the present invention, the outer peripheral portion made of resin has a tooth portion, and a tooth groove bottom portion between the tooth portions is recessed in the tooth groove length direction. A resin worm wheel composed of two divided bodies, wherein the two halves are joined and integrated on a small-diameter side surface which is a small-diameter side at a root position of a tooth portion among both side surfaces in the axial direction. It is a manufacturing method of. In this manufacturing method, a mold having a tooth forming portion formed on an inner peripheral surface for molding an outer tooth portion of the half body is prepared, and a resin is filled in a cavity of the mold to form a half. The method is characterized in that a body is formed, and a pair of half bodies are joined and integrated on each small diameter side surface. Thus, the resin worm wheel can be easily manufactured.

According to the tenth aspect, the tooth forming portion of the forming die is formed by electric discharge machining. This makes it possible to easily form the tooth molding of the molding die.

[0026]

(Embodiment 1) FIGS. 1 and 2 show a resin worm wheel W according to Embodiment 1 of the present invention.
It constitutes a part of a gear transmission mechanism of an electric power steering device of an automobile. That is, the electric power steering device is disposed on a path for transmitting a steering motion of a steering wheel (handle) to a rack and pinion mechanism, and the gear transmission mechanism includes a worm wheel that is drivingly connected to the rack and pinion mechanism and a worm wheel. A worm engaged with the wheel. And this worm wheel is attached to the output shaft of the electric motor,
The electric motor detects the steering direction and the steering speed of the steering wheel, and is controlled by an ECU (control unit) in accordance with the detected direction and the steering speed. The resin worm wheel W of this embodiment includes the gear transmission mechanism described above. Used as a worm wheel.

The outer peripheral portion of the worm wheel W is made of, for example, a thermoplastic resin (which may be a thermosetting resin), and the outer periphery of the resin portion has a direction along the axis O (see FIG. 1). A plurality (even number) of tooth portions 1, 1,... Extending spirally (obliquely) with respect to the worm and engaging with the worm are formed. Corresponding to the outer peripheral shape of the tooth portion, the central portion in the tooth groove length direction has a middle concave shape in which it is concave in an arc shape.

The worm wheel W of this embodiment has two half-pieces W1, divided at the center in the axial direction.
W1. The two halves W1 and W1 are the same as each other. As shown in FIG. 3, one of the two halves W1 on the both sides in the axial direction (the left side surface in FIG. 3) is located at the root position of each tooth 1a. The small-diameter side surface 4 which is the small-diameter side, and the other side surface are each tooth portion 1a
Are formed on the large-diameter side surface 5 which is the large-diameter side at the bottom of the tooth, and the pair of half bodies W1 and W1 are connected to each other with the small-diameter side surfaces 4 as joining surfaces. They are joined and integrated symmetrically with respect to the axis O in the butted state.

Specifically, a center hole 6 is formed at the center of each half body W1 so as to penetrate therethrough, and a ring-shaped insert 8 is inserted through the center hole 6 to be integrally joined (integrated) with the resin portion. ) Has been. In this insert metal fitting 8, a positioning pin hole 9 as a positioning portion for performing positioning in the circumferential direction with respect to the half body W1 on the other side is formed so as to penetrate so as to extend in the axial direction. As shown, the two halves W1, W1 are arranged concentrically with their small diameter side surfaces 4, 4 abutting and the positioning pin holes 9, 9 aligned with each other. (Not shown)
A cylindrical center pin 12 having an axial hole 11 for inserting the same, and positioning pins 13 in positioning pin holes 9, 9.
Respectively, the two half-pieces W1, W1 are joined and integrated, and the corresponding tooth portions 1a, 1 of the two half-pieces W1, W1.
a continuously form one tooth portion 1 of the worm wheel W. The two half-pieces W1 and W1 may be joined and integrated by bonding the small diameter side surfaces 4 and 4 to each other with an adhesive or welding a resin portion.

Next, a manufacturing apparatus and a manufacturing method for manufacturing the resin worm wheel W of the above embodiment will be described. First, as shown in FIG.
The third mold 16 to 18 (molding mold), and the first mold 16 called a nest is a disk-shaped member having the same thickness as the half body W1. A circular hole 21 having a penetrating shape is formed, and a tooth forming portion 22 for forming the outer teeth 1, 1,... Of W1 is provided on the inner peripheral surface of the circular hole 21.

The second mold 17 is also disc-shaped, and has on one side (the right side in FIG. 6) a molding surface 23 for molding the small diameter side surface 4 of the half body W1, and an insert. A fitting holding portion 24 for fitting and holding the fitting 8 and a pin hole insertion portion 25 inserted into the positioning pin hole 9 of the insert fitting 8 to prevent resin from entering the positioning pin hole 9. Is formed.

Further, the third mold 18 is also a disk-shaped one,
A molding surface 26 for molding the large diameter side surface 5 of the half body W1 is formed on one side surface (the left side surface in FIG. 6).

In the first mold 16, the tooth forming section 22
The method of forming the hole will be described. As shown in FIG. 4, a hole 16a 'is formed in a plate-like body 16' serving as the first mold 16, and a tooth is formed in the hole 16a 'on the outer periphery. Part 2
, And a master electrode 28 for electric discharge machining, in which a part of each tooth portion 28a in the longitudinal direction is formed in the same shape as each tooth portion 1a of the half body W1, is inserted. The master electrode 28 is advanced while rotating along the tooth portion 28a, and the tooth portion forming portion 22 is formed on the inner peripheral surface of the hole 16a 'of the plate-like body 16' by electric discharge machining. As a result, as shown in FIG. 5, the first mold 16 having the tooth forming portion 22 on the inner peripheral surface is formed.
To manufacture. As described above, the tooth molding 2 of the first mold 16 is formed.
2 is formed by electric discharge machining, the formation of the tooth forming portion 22 of the first mold 16 is easily performed.

Then, the first to third molds 16 having the above configuration
As shown in FIG. 7, as a manufacturing method of manufacturing the resin worm wheel W by using the manufacturing apparatus 18 to 18, the insert metal fitting 8 is inserted into the metal fitting holding portion 24 of the second die 17, and the positioning pin hole 9 is formed. The first to third molds 16 to 18 are fitted and held in a state where the pin hole insertion portion 25 is inserted into the
Are placed on both sides of the first mold 16 in the second and third molds 17 and 18.
(The first mold is located between the second and third molds 17 and 18).
The cavity C is sectioned by assembling with the mold 16 interposed), and the cavity C is filled with a molten resin and cured to form one half body W1. After the resin is cured, the second and third molds 17 and 18 are separated from the first mold 16 and opened, and the half body W1 is taken out from the first mold 16. One pair of the half bodies W1 thus formed is combined, and the small-diameter side surfaces 4, 4 of the pair of half bodies W1, W1 are combined.
Are brought into contact with each other so that the insert metal fittings 8 and 8 and the positioning pin holes 9 and 9 respectively correspond to each other, and the center pin 12 is inserted between the two insert metal fittings 8 and 8.
Also, by pressing the positioning pins 13 over the positioning pin holes 9, 9, the two halves W 1, W 1 are joined and integrated at the small diameter side surfaces 4, 4. As a result, FIG.
And the resin worm wheel W shown in FIG. 2 is obtained.

At this time, since the positioning pin holes 9 are formed in the insert fitting 8 integrally formed with each half body W1, only the positioning pins 13 are pressed in with the positioning pin holes 9, 9 aligned with each other. Thus, the position in the circumferential direction between the two halves W1 and W1 can be easily positioned so that the teeth 1a and 1a thereof are continuous, and the two halves W1 and W1 can be easily positioned.
Workability in the joining process of W1 and W1 can be improved.

It is to be noted that an insert fitting 8 is attached to each of the half bodies W1.
In the case where is not integrally molded, as shown in FIG. 8, the same molding as described above may be performed in a state where the insert fitting 8 is not inserted and held in the fitting holding portion 24 of the second mold. The manufactured worm wheel W can be manufactured. In this case, in the resin worm wheel W, the center hole 6 of each half body W1 is formed by the shaft hole 11 of the worm wheel W.
Is configured. The two halves W1 and W1 are joined and integrated by bonding the small diameter side surfaces 4 and 4 to each other with an adhesive or welding a resin.

Therefore, in this embodiment, the resin worm wheel W is formed by joining and integrating two axially divided halves W1 and W1. Even if the whole tooth space bottom 2 between the two is in a concave shape recessed in the tooth groove length direction, each half body W1
The outer peripheral tooth portion 1a is obtained by dividing the tooth portion 1 and the tooth groove bottom 2 of the worm wheel W into two in the longitudinal direction (the axial direction of the worm wheel W). When the outer diameters of the tooth portions 1a of the side surfaces 4 and 5 at the tooth bottom position are compared, one becomes the small diameter side surface 4 having a smaller diameter than the other, and the other becomes the large diameter side surface 5. For this reason, each half body W1 is placed in the cavity C in the first to third molds 16 to 18.
When the mold is opened, the mold half is opened after the molding, and then the half body W1 in the first mold 16 is relatively moved in the direction from the small-diameter side surface 4 to the large-diameter side surface 5 (rightward in FIG. 6). What is necessary is just to pull out while rotating along the direction of the part 1a,
Undercut does not occur, and the half body W1 can be smoothly extracted from the first mold 16. That is, the half body W
1 can be molded by the molds 16 to 18, and these 1
The pair of halves W1, W1 may be aligned such that the outer peripheral teeth portions 1a, 1a are continuous with each other, and joined and integrated with the small diameter side surfaces 4, 4, whereby the tooth portion made of resin is formed. A worm wheel W made of resin and having a concave shape in which the entire tooth groove bottom portion 2 between the tooth portions 1 and 1 has a concave shape in the tooth groove length direction is obtained.

Then, the resin worm wheel W
Since the entire tooth groove bottom 2 between the teeth 1 and 1 has a concave shape, a large contact area with the teeth of the worm can be ensured, and a large load can be transmitted between the worm and the worm. It is also suitable when high strength is required for a gear transmission mechanism provided in an electric power steering device for an automobile.

Further, as described above, only the half body W1 is formed by the molds 16 to 18 and is withdrawn from the large-diameter side surface 5 after the molding, so that the half body W1 is withdrawn from the mold while being elastically deformed. The hollowing is unnecessary, and the tooth portion 1a of the half body W1 can be formed with high accuracy, and the dimensional accuracy of the worm wheel W can be increased.

Further, the half body W1 is formed by the molds 16 to 18, and the pair of formed half bodies W1 and W1 are joined and integrated to form the worm wheel W. The cost can be reduced as compared with the case of forming the worm wheel, and the resin worm wheel W can be manufactured at low cost.

The resin worm wheel W is formed by joining the same half-pieces W1 and W1 in a point-symmetric manner with respect to the axis O, so that one kind of half-pieces W1 is
8 and joining a pair of them, a worm wheel W made of resin can be made, and the cost can be further reduced.

Since the resin in the resin worm wheel W is a thermoplastic resin, the resin worm wheel W having tough (elastic) teeth 1, 1,...
Is obtained. In particular, the toughness of the tooth portions 1, 1,... Makes the resin worm wheel W suitable as a part of a gear transmission mechanism of an electric power steering device for an automobile.

(Embodiment 2) FIGS. 9 and 10 show Embodiment 2 of the present invention (in the following embodiments, FIGS.
The same parts as those in FIG. 8 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, the tooth width and the tooth height of the tooth portion 1 are reduced toward the small-diameter side surface 4 side at the edge portion on the small-diameter side surface 4 side of each tooth portion 1 of each half body W1. The chamfered portion 3 is formed so that
Alternatively, an arc surface may be formed).

Therefore, this embodiment can also provide the same functions and effects as those of the first embodiment. Particularly, in this embodiment, when the halves W1 and W1 are joined and integrated to form the worm wheel W, each of the halves W1 and W1 is formed.
1, the corresponding tooth portions 1a, 1a of W1 are connected via the chamfered portions 3, 3 (or an arc surface), so that a step is less likely to occur at the joint between the tooth portions 1a, 1a.
The load transmitted between the worm and both halves W1, W1
Teeth 1a, 1a (entire teeth 1 of worm wheel W)
And smooth transmission and transmission of a larger load can be performed.

(Embodiment 3) FIGS. 11 and 12 show Embodiment 3 of the first and second dies 16 to 18 for forming the half body W1. , 17 are integrated into a fourth mold 19. That is, a circular concave portion 31 is formed on one side surface of the fourth mold 19, and an outer peripheral tooth portion 1, 1,. A molding surface 23 for molding the small-diameter side surface 4 of the half body W1 is formed on the tooth portion molding portion 22 and on the bottom surface of the concave portion 31, respectively. In addition, on the bottom surface of the concave portion 31, a metal fitting holding portion 24 for fitting and holding the insert metal fitting 8, and resin entering the positioning pin hole 9 by being inserted into the positioning pin hole 9 of the insert metal fitting 8. Is not provided with the pin hole insertion portion 25 for preventing the above.

Therefore, this embodiment can also provide the same functions and effects as those of the above embodiments. Further, the tooth forming portion 22 is formed on the inner peripheral surface of the concave portion 31 of the fourth mold 19.
12, a tooth portion 28a having the same shape as the tooth portion 1a of the half body W1 is provided on the outer peripheral portion in a concave portion 31 'of a plate-shaped body 19' serving as the fourth mold 19, as shown in FIG. The master electrode 28 for electric discharge machining is inserted, and the master electrode 28 is advanced while rotating along the tooth portion 28a to form the tooth portion forming portion 22 on the inner peripheral surface of the concave portion 31 by electric discharge machining. The tooth molding 22 of the fourth mold 19 can be easily formed.

(Embodiment 4) FIGS. 13 to 15 show Embodiment 4 in which positioning portions formed on the small diameter side surface 4 of each half body W1 are changed. That is, in this embodiment, as shown in FIG. 14 and FIG. 15, a substantially semicircular fitting recess 33 is formed in one half of the small diameter side surface 4 of each half body W1.
The other half has a fitting recess 33 having the same shape as the fitting recess 33.
Are formed respectively, which can be fitted to
As shown in FIG. 13, when a pair of half-pieces W1 and W1 are joined at the small diameter side surfaces 4 and 4, the fitting half 33 of one half-piece W1 fits into the fitting recess 33 of the other half-piece W1. By fitting the projections 34, the two halves W1, W1 are positioned and joined.

In this embodiment, the insert fitting 8
Are not provided, and the center holes 6, 6 of the half-pieces W1, W1 are not provided.
The shaft itself is the shaft hole 11 of the worm wheel W. The two halves W1 and W1 are joined and integrated by bonding the small-diameter side surfaces 4 and 4 with an adhesive or by welding a resin portion.

Therefore, in this embodiment, the same operation and effect as those of the above embodiments can be obtained. Further, since the fitting concave portion 33 and the fitting convex portion 34 as the positioning portions are formed in advance, the fitting concave portion 33 is formed when the two half-pieces W1 and W1 are joined.
And only by fitting the fitting projections 34, the respective teeth 1a, 1
The position a can be matched, and the work of inserting the positioning pin 13 at the time of joining the two halves W1 and W1 as in each of the above embodiments is not required, so that the number of work steps can be reduced and the cost can be reduced. it can.

(Embodiment 5) FIG. 16 shows Embodiment 5, in which Embodiments 1-4 are applied to a resin worm wheel W having an even number of teeth 1, 1,. , The number of teeth is odd.

That is, in this embodiment, each half W
One half of the small-diameter side surface 4 has, for example, a predetermined outer peripheral tooth portion 1.
a small-diameter circular (pin-shaped) fitting convex portion 34 at a position corresponding to a and a tooth adjacent to the fitting convex portion 34 in the other half at a position substantially diametrically opposed to the fitting convex portion 34, for example. Part 1a,
1a, a pair of fitting recesses 33, 33, into which the fitting projections 34 can be fitted, are formed at positions corresponding to the small diameter side surfaces 4, 4, respectively. 4
In the case of joining and integrating with each other, the fitting protrusion 34 of the other half body W1 is fitted into one of the two fitting recesses 33, 33 of one half body W1, thereby forming the two half bodies. W1 and W1 are positioned and joined. Other configurations are the same as those of the fourth embodiment.

Therefore, in this embodiment, even if the resin worm wheel W has an odd number of teeth 1, 1,..., The half body W1 is formed and the two half bodies W1, W1 are positioned. Embodiment 4 can be joined and integrated.
The same operation and effect as described above can be obtained.

[0054]

As described above, according to the first aspect of the present invention, the outer peripheral portion made of resin has teeth and the bottom of the tooth space between the teeth is recessed in the length direction of the tooth space. Resin worm wheel is composed of two half-pieces divided at the approximate center in the axial direction, and both half-pieces are joined and integrated on the small-diameter side surface that becomes the small-diameter side at the root position of each tooth. As a result, the resin worm wheel is manufactured by molding to reduce its cost, and the bottom of the tooth space between the teeth of the resin worm wheel is depressed to secure a large contact area with the teeth of the worm. However, a large load can be transmitted between the worm and the worm, and the dimensional accuracy of the worm wheel can be improved by accurately forming the teeth of the half body.

According to the second aspect of the present invention, the two halves are made identical to each other and joined in a point-symmetric manner with respect to the axis, so that one kind of halves is formed by a molding die, thereby further reducing the cost. Can be planned.

According to the third aspect of the present invention, at least the small-diameter side surface of each half is provided with a positioning portion for positioning the half in the circumferential direction with respect to the other half. Workability in the process can be improved.

According to the fourth aspect of the present invention, since the chamfered portion or the arc surface is formed at the small-diameter side edge of each tooth portion of the half body, the joint between the corresponding tooth portions of the two half bodies is formed. It is possible to disperse the transmission load to the teeth of both halves by making it difficult to generate a step in the part,
Smooth transmission and transmission of a larger load can be performed.

According to the fifth aspect of the present invention, since the resin worm wheel constitutes a part of the gear transmission mechanism of the electric power steering device of an automobile, the optimum use of the resin worm wheel is improved. can get.

According to the sixth aspect of the present invention, a resin worm wheel having a tough tooth portion can be obtained by using a thermoplastic resin for the resin in the resin worm wheel.

According to a seventh aspect of the present invention, there is provided an apparatus for manufacturing a resin worm wheel, comprising: a first molding die having an inner peripheral surface provided with a tooth molding portion for molding an outer tooth portion of a half body; A second molding die disposed on one side of the first molding die and having a molding surface for molding the small-diameter side surface of the half body, and a large-diameter side surface of the half molding body arranged on the other side of the first molding die. And a third molding die having a molding surface to be formed. In the invention of claim 8, the first and second molds are integrated.
According to these inventions, the resin worm wheel can be easily manufactured.

According to the ninth aspect of the present invention, as a method of manufacturing a resin worm wheel, a tooth forming portion for forming an outer tooth portion of a half body is formed in a cavity of a molding die formed on an inner peripheral surface. A resin worm wheel can be easily manufactured by filling a resin to form a half body, and joining and integrating a pair of half bodies at respective small diameter side surfaces.

According to the tenth aspect of the present invention, since the tooth forming portion of the mold is formed by electric discharge machining, the tooth forming portion of the mold can be easily formed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a resin worm wheel according to Embodiment 1 of the present invention.

FIG. 2 is a front view of a resin worm wheel.

FIG. 3 is a sectional view showing a half body of a resin worm wheel.

FIG. 4 is a cross-sectional view showing a state where a molding surface of a first mold is formed by electric discharge machining.

FIG. 5 is a sectional view of a first mold.

FIG. 6 is a cross-sectional view showing a state before the first to third molds are matched.

FIG. 7 is a cross-sectional view showing a state in which first to third molds are matched.

FIG. 8 is a view corresponding to FIG. 7, showing a state where an insert fitting is not inserted.

FIG. 9 is an enlarged sectional view showing a tooth portion of a half body of a resin worm wheel according to a second embodiment of the present invention.

FIG. 10 is a view in the direction of the arrow X in FIG. 9;

FIG. 11 is a sectional view of a fourth mold according to the third embodiment of the present invention.

FIG. 12 is a view corresponding to FIG. 4, showing a state in which a molding surface of a fourth mold is formed by electric discharge machining.

FIG. 13 is a view corresponding to FIG. 1 showing a resin worm wheel according to a fourth embodiment of the present invention.

FIG. 14 is a view showing a half body of a resin worm wheel.
FIG.

FIG. 15 is a front view of a half body of a resin worm wheel as viewed from a small diameter side surface.

FIG. 16 is a view corresponding to FIG. 15, showing a half body of a resin worm wheel according to Embodiment 5 of the present invention.

[Explanation of symbols]

 W Resin worm wheel W1 Half body 1 Tooth 1a Tooth 2 Tooth groove bottom 3 Chamfer 4 Small diameter side 5 Large diameter side 8 Insert fitting 9 Positioning pin hole 13 Positioning pin 16 First die 17 Second die 18 Third mold 19 Fourth mold 22 Tooth forming part 28 Master electrode 33 Fitting concave part 34 Fitting convex part

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3J030 BA03 BB02 BC01 BC08 CA10 4F213 AD03 AH12 AH17 AJ02 AJ08 AP06 AP12 AR07 AR13 WA05 WA33 WA39 WB01 WB11 WC01 WE16 WF05 WK01 WK03 WW01 WW06 WW15

Claims (10)

[Claims] 1. A resin worm wheel having an outer peripheral portion made of resin and having a tooth portion formed between the tooth portions and having a tooth groove bottom recessed in the tooth groove length direction, wherein the resin worm wheel has a substantially central portion in the axial direction. Consists of two halves divided by
A resin worm wheel characterized in that the two halves are joined and integrated on a small-diameter side surface which is a small-diameter side at a tooth root position of a tooth portion of both side surfaces in the axial direction. 2. The resin worm wheel according to claim 1, wherein the two halves are identical to each other and are joined symmetrically with respect to an axis. 3. The resin worm wheel according to claim 1, wherein at least a small-diameter side surface of each half body is provided with a positioning portion for circumferential positioning with respect to a counterpart half body. Worm wheel made of resin. 4. The resin worm wheel according to any one of claims 1 to 3, wherein a chamfer or an arc surface is formed at an end portion on a small diameter side surface side of each tooth portion of the half body. Worm wheel made of resin. 5. The resin worm wheel according to claim 1, which forms a part of a gear transmission mechanism of an electric power steering device of an automobile. 6. The resin worm wheel according to claim 1, wherein the resin is a thermoplastic resin. 7. A toothed portion having an outer peripheral portion made of a resin, having a tooth groove bottom portion between the toothed portions recessed in the tooth groove length direction, and being divided at a substantially central portion in the axial direction. An apparatus for manufacturing a resin worm wheel, comprising a split body, wherein the two halves are joined and integrated on a small-diameter side surface which is a small-diameter side at a root position of a tooth portion among both axial side surfaces. A first forming die provided on an inner peripheral surface with a tooth forming portion for forming an outer tooth portion of the half body; and a small-diameter side surface of the half body disposed on one side of the first forming die. A second molding die having a molding surface to be molded; and a third molding die disposed on the other side of the first molding die and having a molding surface for molding a large-diameter side surface of the half body. For manufacturing resin worm wheels. 8. The manufacturing apparatus for a resin worm wheel according to claim 7, wherein the first and second molds are integrated. 9. A toothed portion having an outer peripheral portion made of a resin, wherein a tooth groove bottom portion between the toothed portions is recessed in a tooth groove length direction, and is divided at a substantially central portion in an axial direction. A method for manufacturing a resin worm wheel, comprising a divided body, wherein the two halves are joined and integrated on a small-diameter side surface which is a small-diameter side at a root position of a tooth portion among both axial side surfaces. Preparing a molding die having a tooth forming portion formed on the inner peripheral surface for molding the outer teeth of the half body, and filling the cavity of the molding die with a resin to form the half body A method of manufacturing a resin worm wheel, wherein a pair of halves are joined and integrated at respective small diameter side surfaces. 10. The method for manufacturing a resin worm wheel according to claim 9, wherein the tooth forming portion of the mold is formed by electric discharge machining.