JP2023154274A - Gear cutting preform of resin gear for power transmission, and resin gear for power transmission - Google Patents

Abstract

To provide a gear cutting preform of a resin gear for power transmission in which a void in the injection molding can be prevented and a forming cycle can be shortened, and provide the resin gear for power transmission.SOLUTION: A preform 1 is provided before providing a gear tooth of a resin gear for power transmission. The preform comprises a cored bar 2 and an annular resin part 3 for covering up an outer circumference of the cored bar 2. The annular resin part 3 comprises an annular inside resin component 4, and an annular outside resin component 5 being the material different from the annular inside resin component 4. The annular inside resin component 4 covers up the outer circumference of the cored bar 2. The annular outside resin component 5 covers the outer circumference of the annular inside resin component 4. In the outer circumferential surface of the annular outside resin component 5, a recessed groove 6 providing a cutting margin is present in the position for providing the tooth groove of the gear tooth. In the axial side face B of the annular outside resin component 5, an axial thinned part 5A is present in the position between the tooth grooves adjacent in the circumferential direction of the resin gear for power transmission.SELECTED DRAWING: Figure 4

Description

The present invention relates to a power transmission resin gear comprising a metal core and an annular resin part.

In order to meet the needs for weight reduction and quietness, there is a power transmission resin gear made of a core metal and an annular resin part covering the outer periphery of the metal core (see, for example, paragraph [0003] of Patent Document 1).

The worm wheel of Patent Document 1 has a helical gear shape in order to avoid the appearance of voids on the tooth surface, and a preformed body with uniform tooth height and tooth thickness over the entire tooth width direction is molded. Shape. That is, first, a metal core bushing, which is a core metal, is placed in an injection mold as an insert work, and a blank of the shape described above is provided with a machining allowance for cutting so as not to become too thick. The feature 10 is injection molded. Next, a resin worm wheel finished in a predetermined worm wheel tooth surface shape is manufactured by cutting both the tooth portion 11 and tooth bottom 12 of the basic body 10 (see the figure in Patent Document 1). 3, see Figure 5).

On the other hand, there is a method in which the annular resin portion is molded in two stages (for example, see Patent Document 2). That is, in the worm wheel of Patent Document 2, after the connecting part 14 of thermoplastic resin is molded on the outer periphery of the inner part 12 which is a core metal, the outer part 16 of thermoplastic resin is molded around the outer periphery of the connecting part 14 ( (See FIG. 1 of Patent Document 3). The surface of the connecting portion 14 in the axial direction has thinning.

On the other hand, in a power transmission resin gear that does not have the core metal and is entirely made of synthetic resin, the ends of the helical teeth in the axial direction are recessed in order to transmit power accurately while suppressing noise generation. (For example, see Patent Document 3). That is, in the helical gear of Patent Document 3, by providing the concave portion 21 and the thin wall portion 22 at the end portion of the helical tooth 20, elastic deformation of the thin wall portion 22 reduces the impact when the ends of the helical tooth 20 collide with each other. (See FIG. 4 of Patent Document 3).

Patent No. 4423815 German Patent Application No. 102012102780 Japanese Patent Application Publication No. 2008-115886

Conventional resin gears for power transmission require gear cutting to create the teeth of the gear after molding, so it is necessary to increase the thickness of the resin in the area where the gear cutting is performed, resulting in a thick-walled molded product. . In the process of injection molding a thick-walled molded product, in order to suppress voids that become defects in the thick-walled molded product, it is necessary to increase the holding pressure in the pressure-holding process and lengthen the time of the pressure-holding process. Furthermore, since the solidification rate is slow, it is necessary to lengthen the cooling process time from the completion of the pressure holding process to the start of mold opening. Therefore, injection molding of thick-walled molded products requires a long molding cycle.

An object of the present invention is to provide a molded article of a resin gear for power transmission before gear cutting, which can suppress voids in injection molding and shorten the molding cycle, and a resin gear for power transmission.

The pre-gear cutting molded body of a resin gear for power transmission according to the first aspect of the present invention is a molded body before teeth of the resin gear for power transmission are provided, and is a molded body that covers a core metal and the outer periphery of the core metal. It consists of an annular resin part. The outer circumferential surface of the annular resin part has at least one concave groove provided with a cutting allowance at a position where a tooth groove of the tooth is provided. The axial end surface of the annular resin portion has an axial thinning at a position between circumferentially adjacent tooth grooves of the power transmission resin gear.

The pre-gear cutting molded article of the power transmission resin gear according to the second aspect of the present invention is the pre-gear cutting molded article of the power transmitting resin gear according to the first aspect, in which the annular resin part has an annular shape. It consists of an inner resin member and an annular outer resin member made of a different material from the annular inner resin member. The annular inner resin member covers the outer circumference of the core bar, and the annular outer resin member covers the outer circumference of the annular inner resin member. The groove is provided on the outer peripheral surface of the annular outer resin member, and the axial thinning is provided on the axial end surface of the annular outer resin member.

According to the molded article before gear cutting of a resin gear for power transmission according to the first aspect of the present invention and the molded article before gear cutting of a resin gear for power transmission according to the second aspect of the present invention, the resin for power transmission There is axial thinning between the tooth grooves adjacent in the circumferential direction of the gear. Therefore, the wall thickness of the resin at the part where the teeth are provided during gear cutting does not increase, so there is no need to increase the holding pressure in the holding pressure process to suppress voids that can cause defects in thick-walled molded products. There is no need to make the time longer. Furthermore, since the solidification rate is not as slow as that of thick-walled molded products, there is no need to increase the time required for the cooling process from the completion of the holding pressure process to the start of mold opening. Therefore, the molding cycle can be shortened. Furthermore, since there is the axial thickness loss, the weight of the molded body of the power transmission resin gear before gear cutting can be reduced.

In the pre-gear cutting molded article of the power transmission resin gear according to the third aspect of the present invention, in the pre-gear cutting molded article of the power transmitting resin gear according to the first aspect, the groove is formed between the teeth of the teeth. The grooves are located all around the circumference.

According to the pre-gear cutting molded article of the resin gear for power transmission according to the third aspect of the present invention, since the concave groove is provided over the entire circumference at the position where the tooth groove of the tooth of the resin gear for power transmission is provided, the molding Since the amount of resin used for this purpose is reduced, material costs can be reduced.

In the pre-gear cutting molded article of the power transmission resin gear according to the fourth aspect of the present invention, in the pre-gear cutting molded article of the power transmitting resin gear according to the first aspect, the axial thickness loss is Located on both axial end faces of the annular resin part.

According to the pre-gear cutting molded article of the power transmission resin gear according to the fourth aspect of the present invention, since the axial thickness loss is on both axial end surfaces of the annular resin part, it is difficult to deform due to molding shrinkage. Therefore, the shape accuracy of the molded body of the power transmission resin gear before gear cutting is not deteriorated.

The power transmission resin gear according to the fifth aspect of the present invention is the pre-gear cutting molded body of the power transmission resin gear according to the first aspect to the pre-gear cutting molded body of the power transmission resin gear according to the fourth aspect. The grooves of the teeth are provided around the entire circumference based on the position of the groove in any one of the teeth.

According to the power transmission resin gear according to the fifth aspect of the present invention, the molded article of the power transmission resin gear according to the first aspect before gear cutting or the power transmission resin gear according to the fourth aspect before gear cutting It has the same effect as a molded body.

As described above, according to the pre-cutting molded body of a resin gear for power transmission and the resin gear for power transmission according to the present invention, voids in injection molding can be suppressed and the molding cycle can be shortened.

FIG. 1 is a perspective view of a power transmission resin gear according to an embodiment of the present invention. It is a longitudinal cross-sectional side view of the said resin gear for power transmission. FIG. 3 is an enlarged front view of main parts of the power transmission resin gear. FIG. 2 is a perspective view of a molded body of a power transmission resin gear before gear cutting according to an embodiment of the present invention. FIG. 5 is a perspective view of the pre-gear cutting molded body of FIG. 4 viewed from the back side. FIG. 3 is a longitudinal cross-sectional side view of the molded body before gear cutting. It is an enlarged front view of the main part of the molded object before gear cutting. It is a perspective view which shows the modification of the said molded object before gear cutting.

Next, embodiments of the present invention will be described in detail based on the accompanying drawings.

In this specification, the direction of the rotating shaft of the power transmission resin gear A is referred to as the "axial direction", and the "radial direction" and "circumferential direction" are referred to as the axial center of the rotating shaft (symbol O in FIG. 2). Define. The front view is the view seen from the axial direction.

<Resin gear for power transmission>
As shown in the perspective view of FIG. 1 and the vertical cross-sectional side view of FIG. 2, the power transmission resin gear A includes a metal core 2 and an annular resin portion 3 covering the outer periphery thereof. Teeth T are formed on the outer circumferential surface of the annular resin portion 3 at equal intervals in the circumferential direction. The power transmission resin gear A is used, for example, as a worm wheel of a worm gear used in electric power steering.

(core metal)
The core metal 2 is, for example, an annular sleeve as shown in FIGS. 1 and 2, but may have a shaft portion instead of the annular sleeve.

(Circular resin part)
The annular resin portion 3 includes an annular inner resin member 4 and an annular outer resin member 5. The annular inner resin member 4 covers the outer periphery of the core bar 2 , and the annular outer resin member 5 covers the outer periphery of the annular inner resin member 4 . Incidentally, on one end surface of the annular inner resin member 4 in the axial direction, there are provided flesh gaps 4A arranged equally in the circumferential direction as shown in FIGS. 2, 5, and 6. Therefore, the annular outer resin member 5 narrowly covers the outer periphery of the annular inner resin member 4 on the one end surface side where the meat cutout 4A is located in a range up to the front of the meat cutout 4A, and The other end surface side of the inner resin member 4 in the axial direction is covered in a wider range radially inward than the one end surface side.

The annular inner resin member 4 is made of synthetic resin reinforced with a reinforcing material such as glass fiber, and the annular outer resin member 5 is made of synthetic resin that is not reinforced with the reinforcing material, for example. That is, the annular inner resin member 4 and the annular outer resin member 5 are made of different materials. "Different materials" includes not only cases where the polymers are different, but also cases where the polymers are the same but have different reinforcing material contents.

The annular resin portion 3 does not need to be composed of the annular inner resin member 4 and the annular outer resin member 5. That is, the annular resin part 3 may be an integral part made of synthetic resin that does not contain a reinforcing material such as glass fiber.

(Axial meat theft)
As shown in the vertical cross-sectional side view of FIG. 2, the axially opposite end surfaces B and C of the annular outer resin member 5 of the annular resin portion 3 have axial undercuts 5A and 5B. As shown in the enlarged front view of the main part in FIG. 3, the axial thinnings 5A and 5B are located between the circumferentially adjacent tooth grooves G and G of the power transmission resin gear A, and are spaced apart in the circumferential direction. They are arranged equally in the circumferential direction.

<Formed body of resin gear for power transmission before gear cutting>
The molded body 1 before gear cutting of the resin gear A for power transmission shown in the perspective views of FIGS. 4 and 5, the vertical cross-sectional side view of FIG. 6, and the enlarged front view of main parts of FIG. This is a molded article before teeth T (FIG. 1) are provided on the surface.

The outer peripheral surface of the annular outer resin member 5 of the annular resin part 3 has a recess provided with a cutting allowance over the entire circumference at the position where the tooth groove G (FIG. 1) of the tooth T is provided in the power transmission resin gear A. There is a groove 6.

(Axial meat theft)
In the annular outer resin member 5 of the annular resin portion 3, axial thinnings 5A and 5B are spaced apart in the circumferential direction and arranged equally in the circumferential direction. As shown in FIGS. 6 and 7, the axial thinning 5A, 5B is between the circumferentially adjacent concave grooves 6, 6, that is, between the circumferentially adjacent teeth of the power transmission resin gear A (FIG. 3). It is located between grooves G and G.

As shown in FIG. 6, the axial thinning 5A is caused by a shallow recess where the annular outer resin member 5 covers the surface of the annular inner resin member 4, and a deep recess located radially outward from the shallow recess. It is formed by a recess and a curved surface connecting the shallow recess and the deep recess. As shown in FIG. 6, the axial thinning 5B is formed by a deep recess located on the side opposite to the deep recess of the axial thinning 5A in the axial direction.

For example, with reference to FIG. 7, the radial position of the axial thinning 5A, 5B is 2 mm or more radially inward from the outer diameter of the annular outer resin member 5, and radially deeper than the innermost part of the groove 6. The direction is inward. In addition, in the resin gear A for power transmission, the bottom of the tooth T and its vicinity are the parts where strength is most required, so the root of the tooth in the part where the axial thinning 5A, 5B shown in FIGS. 2 and 6 is set is The width (Wa+Wb) is set to (W/4)≦(Wa+Wb)≦(W/3) with respect to the axial width W of the outer diameter portion of the annular outer resin member 5, and Wa and Wb are the width W. It is assumed that Wa≧(W/8) and Wb≧(W/8) are distributed at the center in the width direction (dotted chain line Wo in FIGS. 2 and 6). Thereby, both tooth root strength and moldability in injection molding, which is an object of the present invention, can be achieved.

The axial thinning may be formed on one end surface of the annular outer resin member 5 in the axial direction, but by molding on both end surfaces of the annular outer resin member 5 in the axial direction, deformation due to molding shrinkage can be avoided. Therefore, the shape accuracy of the molded body 1 before gear cutting is not deteriorated.

When forming an axial thinning on one end surface of the annular outer resin member 5 in the axial direction, Wa and Wb are set as follows with reference to FIGS. 2 and 6. That is, when there is no meat stealing 5a on the Wa side and there is meat stealing 5b on the Wb side, (W/8)≦Wb≦(W/6), and there is no meat stealing 5b on the Wb side and there is meat stealing 5a on the Wa side. If there is, (W/8)≦Wa≦(W/6). Thereby, both tooth root strength and moldability in injection molding, which is an object of the present invention, can be achieved.

As shown in Fig. 3, when the power transmission resin gear A is viewed from the front (one end or the other end in the axial direction), the wall thickness between the outer diameter side of the axial thickness reductions 5A and 5B and the tooth groove G is the minimum part. It is desirable that the distance be 2 mm or more and 3 mm or less. With this setting, while maintaining the strength of the teeth T in the substantially circumferential direction, moldability in injection molding, which is a problem of the present invention, can be ensured in relation to the groove 6 provided with a cutting allowance. .

(Injection molding of annular inner resin member)
As described above, the annular inner resin member 4 of the annular resin part 3 is made of synthetic resin reinforced with a reinforcing material such as glass fiber, and the synthetic resin as the binder is a thermoplastic resin or thermosetting resin. be.

As shown in the perspective view of FIG. 5, on one end surface of the annular inner resin member 4 in the axial direction, there are axial thinning holes 4A spaced apart in the circumferential direction and arranged equally in the circumferential direction. Injection molding of the annular inner resin member 4 is performed by setting the round shaft of a disc-shaped insert core (not shown) in an injection mold with the round shaft fitted into the inner diameter hole 2A of the core metal 2. The axially recessed portion 4A is formed by an axially protruding portion provided on the insert core that protrudes in the axial direction.

By providing the axial thickness reduction 4A in the annular inner resin member 4, the weight of the pre-gear cutting molded body 1 can be reduced. Moreover, the volume of the annular inner resin member 4 is reduced, and the solidification time is shortened, so that the molding cycle can be shortened.

(Injection molding of annular outer resin member)
As described above, the annular outer resin member 5 of the annular resin portion 3 is made of a synthetic resin that is not reinforced with a reinforcing material such as glass fiber, and the synthetic resin is a thermoplastic resin.

Injection molding of the annular outer resin member 5 is performed by setting the insert core, the core bar 2, and the annular inner resin member 4 in an injection mold. By injection molding the annular outer resin member 5, the axial thinning 5A and 5B on the axial end face and the groove 6 on the outer peripheral surface are formed.

According to the pre-gear cutting molded body 1 having the above configuration, there are axial thinnings 5A and 5B at positions between the circumferentially adjacent tooth grooves G and G of the power transmission resin gear A. Therefore, the wall thickness of the resin at the part where the teeth are provided during gear cutting does not increase, so there is no need to increase the holding pressure in the holding pressure process to suppress voids that can cause defects in thick-walled molded products. There is no need to make the time longer. Furthermore, since the solidification rate is not as slow as that of thick-walled molded products, there is no need to increase the time required for the cooling process from the completion of the holding pressure process to the start of mold opening. Therefore, the molding cycle can be shortened. Furthermore, since there are axial thickness reductions 5A and 5B, the weight of the molded body 1 before gear cutting can be reduced.

<Gear cutting process>
When gear cutting is performed on the molded body 1 before gear cutting shown in FIGS. 4 and 7 to complete the power transmission resin gear A provided with teeth T as shown in FIGS. 1 and 3, the gear cutting Tooth grooves G of tooth grooves T are provided around the entire circumference with reference to the position of the groove 6 on the outer peripheral surface of the preformed body 1. By cutting the tooth groove G based on the position of the concave groove 6, the axial thinning 5A, 5B and the tooth groove G do not interfere with each other.

The concave groove 6 provided on the outer peripheral surface of the annular outer resin member 5 of the annular resin part 3 only needs to be provided at one location as shown in the perspective view of FIG. In other words, the groove 6 may be provided at at least one location. However, if the concave groove 6 is provided all around the circumference as shown in FIG. 4, the amount of resin used for molding will be smaller, so the material cost can be reduced.

The above description of the embodiments is all illustrative, and the present invention is not limited thereto. Various improvements and changes can be made without departing from the scope of the invention.

1 Molded body of power transmission resin gear before gear cutting 2 Core metal 2A Inner diameter hole 3 Annular resin part 4 Annular inner resin member 4A Axial thickness loss 5 Annular outer resin member 5A, 5B Axial thickness loss 6 Concave Groove A Resin gears for power transmission B, C Axial end face G Tooth groove O Axial center T Teeth W Axial width of the outer diameter part of the annular outer resin member Wo Center in the width direction

Claims (5)

A molded body before teeth of a power transmission resin gear are provided,
Consisting of a core metal and an annular resin part covering the outer periphery of the core metal,
The outer peripheral surface of the annular resin part has at least one concave groove provided with a cutting allowance at a position where a tooth groove of the tooth is provided,
On the axial end surface of the annular resin portion, there is an axial thinning at a position between circumferentially adjacent tooth grooves of the power transmission resin gear.
Molded body of resin gear for power transmission before gear cutting. The annular resin part includes an annular inner resin member and an annular outer resin member made of a different material from the annular inner resin member,
The annular inner resin member covers the outer periphery of the core metal,
The annular outer resin member covers the outer periphery of the annular inner resin member,
The outer peripheral surface of the annular outer resin member has the groove,
The axial thickness loss is present on the axial end face of the annular outer resin member;
The molded article of the power transmission resin gear according to claim 1 before gear cutting. The groove is located all around the tooth at a position where a tooth groove is provided.
The molded article of the power transmission resin gear according to claim 1 before gear cutting. The axial thinning is on both end surfaces of the annular resin part in the axial direction,
The molded article of the power transmission resin gear according to claim 1 before gear cutting. For power transmission, the tooth grooves of the teeth are provided around the entire circumference based on the position of the concave groove in the pre-gear cutting molded product of the resin gear for power transmission according to any one of claims 1 to 4. resin gears.

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