JP2021042839A - Worm wheel unit, its manufacturing method and worm reduction gear - Google Patents

Abstract

To obtain a manufacturing method of a worm wheel unit which can improve the coaxiality of a worm wheel tooth part with respect to a worm wheel shaft.SOLUTION: A worm wheel unit 48 comprises a pinion shaft 13 being a worm wheel shaft, and a worm wheel 24 externally fit to the pinion shaft 13. The worm wheel 24 comprises an inside wheel element 28 and a synthetic resin-made outside wheel element 29 having a worm wheel tooth part 27 at an external peripheral face. When manufacturing the worm wheel unit 48, metal molds 39, 40 are arranged at peripheries the pinion shaft 13 and the inside wheel element 28 in a state that the inside wheel element 28 is externally fit and fixed to the pinion shaft 13, and the outside wheel element 29 is formed by insert-molding for feeding a synthetic resin into a cavity 43 in a state that the pinion shaft 13 is held coaxially with the cavity 43 being a molding space of the outside wheel element 29.SELECTED DRAWING: Figure 8

Description

The present invention relates to a worm reducer, a worm wheel unit formed by combining a worm wheel and a worm wheel shaft constituting the worm reducer, and a method for manufacturing the worm wheel unit.

In an electric power steering device incorporated in an automobile, a worm reducer is widely used in order to increase the torque of an electric motor which is an auxiliary power source. The worm reducer includes a worm having a worm tooth portion on the outer peripheral surface of the intermediate portion in the axial direction, and a worm wheel having a worm wheel tooth portion that meshes with the worm tooth portion on the outer peripheral surface. The worm functions as a drive gear that is rotationally driven by an electric motor, and the worm wheel functions as a driven gear that rotates with the rotation of the worm. The rotational torque of the worm wheel is applied as auxiliary power to a steering member such as an output shaft connected to the front end of the steering shaft via a torsion bar and a pinion shaft or a rack shaft constituting the steering gear unit.

In such a worm reducer, for the purpose of suppressing the rattling noise generated at the meshing portion between the worm tooth portion and the worm wheel tooth portion when operating the steering wheel or running on a rough road, reducing the weight, and reducing the cost. Of the worm wheels, the portion that is externally fitted and fixed to the worm wheel shaft, which is the rotating shaft, may be made of metal, and the portion that meshes with the worm may be made of synthetic resin. More specifically, the worm wheel has an annular inner wheel element made of metal and a worm wheel tooth portion on the outer peripheral surface, and the radial outer portion of the inner wheel element is embedded over the entire circumference. It may be composed of an annular outer wheel element made of synthetic resin coupled to the inner wheel element (see, for example, Japanese Patent Application Laid-Open No. 2019-51764 (Patent Document 1)).

JP-A-2019-51764

The conventional structure as described above has room for improvement in terms of improving the coaxiality of the worm wheel tooth portion with respect to the worm wheel shaft.

That is, in the conventional structure as described above, the inner wheel element is used as an insert product and the outer wheel element is insert-molded (injection molded) to connect the outer wheel element to the inner wheel element and then to the worm wheel shaft. The inner wheel element is fitted and fixed. If the posture of the inner wheel element is tilted when the inner wheel element is fitted and fixed to the worm wheel shaft, the coaxiality of the worm wheel tooth portion with respect to the worm wheel shaft may decrease.

In view of the above circumstances, the present invention provides a manufacturing method and a structure capable of improving the coaxiality of the worm wheel tooth portion with respect to the worm wheel shaft with respect to the worm wheel unit formed by combining the worm wheel and the worm wheel shaft. The purpose is to realize it.

The worm wheel unit which is the object of the present invention includes a worm wheel shaft and a worm wheel which has worm wheel teeth on the outer peripheral surface and is externally fitted and fixed to the worm wheel shaft.
The worm wheel has an annular inner wheel element that is externally fitted and fixed to the worm wheel shaft, and the worm wheel tooth portion on the outer peripheral surface, and is coupled to the inner wheel element, and is made of a synthetic resin. It is equipped with a wheel element.

In the method for manufacturing a worm wheel unit of the present invention, a mold is arranged around the worm wheel shaft and the inner wheel element in a state where the inner wheel element is fitted and fixed to the worm wheel shaft, and the worm is manufactured. The outer wheel element is formed by insert molding in which a synthetic resin is fed into the cavity while the wheel shaft is held coaxially with the cavity which is the molding space of the outer wheel element formed inside the mold. ..

In one aspect of the manufacturing method of the present invention, the worm wheel shaft has pinion teeth on the outer peripheral surface.

In one aspect of the manufacturing method of the present invention, the worm wheel shaft has bearing support portions supported by bearings at one or a plurality of axial directions on the outer peripheral surface, and the bearing support portions are supported by the mold. By doing so, the worm wheel shaft is held coaxially with the cavity.

In one aspect of the manufacturing method of the present invention, the insert molding is performed with the inner wheel element fitted and fixed to one end of the worm wheel shaft on one side in the axial direction.

In one aspect of the manufacturing method of the present invention, the insert molding forms a disk portion covering a part of the outer wheel element on one side in the axial direction of the worm wheel shaft.

In one aspect of the manufacturing method of the present invention, the worm wheel shaft has a concave hole that opens on one end surface in the axial direction, and the concave hole is formed in a part of the outer wheel element by the insert molding. Form a resin engaging portion that engages with.

In one aspect of the manufacturing method of the present invention, the concave hole has an inner diameter side recess that is recessed outward in the radial direction on the inner peripheral surface, and is a part of the resin engaging portion by the insert molding. In addition, by engaging with the inner diameter side concave portion, an inner diameter side convex portion that prevents the axial displacement of the outer wheel element with respect to the worm wheel shaft is formed.

In one aspect of the manufacturing method of the present invention, the insert molding covers a part of the outer wheel element with a portion of the outer peripheral surface of the worm wheel shaft that is axially adjacent to the inner wheel element. Form a covering part.

In one aspect of the manufacturing method of the present invention, the worm wheel shaft has an outer diameter side recess that is radially inwardly recessed in a portion of the outer peripheral surface that is axially adjacent to the inner wheel element. By the insert molding, the outer diameter side convex portion is formed on a part of the shaft covering portion by engaging with the outer diameter side concave portion to prevent the axial displacement of the outer wheel element with respect to the worm wheel shaft. Form.

In one aspect of the manufacturing method of the present invention, a hot runner is used as a runner for feeding the synthetic resin into the cavity.

In the worm wheel unit of the present invention, the outer wheel element is an insert-molded product into which the inner wheel element is inserted, and is a portion that is insert-molded so as to cover a part of the surface of the worm wheel shaft. It has an insert cover.

In one aspect of the worm wheel unit of the present invention, the worm wheel shaft has pinion teeth on the outer peripheral surface.

In one aspect of the worm wheel unit of the present invention, the inner wheel element is externally fitted and fixed to one end of the worm wheel shaft on one side in the axial direction.

In one aspect of the worm wheel unit of the present invention, the insert covering portion includes a disc portion that covers an end face on one side in the axial direction of the worm wheel shaft.

In one aspect of the worm wheel unit of the present invention, the worm wheel shaft has a concave hole that opens on one end surface in the axial direction, and the insert covering portion is a resin engagement that engages with the concave hole. Including part.

In one aspect of the worm wheel unit of the present invention, the concave hole has an inner diameter side recess that is recessed outward in the radial direction on the inner peripheral surface, and the resin engaging portion is the inner diameter side recess. Includes an inner diameter side convex that prevents axial displacement of the outer wheel element with respect to the worm wheel shaft by engaging.

In one aspect of the worm wheel unit of the present invention, the insert covering portion includes a shaft covering portion that covers a portion of the outer peripheral surface of the worm wheel shaft that is axially adjacent to the inner wheel element.

In one aspect of the worm wheel unit of the present invention, the worm wheel shaft has an outer diameter side recess that is radially inwardly recessed in a portion of the outer peripheral surface that is axially adjacent to the inner wheel element. The shaft covering portion includes an outer diameter side convex portion that prevents the axial displacement of the outer wheel element with respect to the worm wheel shaft by engaging with the outer diameter side concave portion.

The worm reducer of the present invention has a worm wheel shaft, a worm wheel having worm wheel teeth on the outer peripheral surface, and a worm wheel externally fitted and fixed to the worm wheel shaft, and an axially intermediate worm wheel unit. A worm having a worm tooth portion that meshes with the worm wheel tooth portion is provided on the outer peripheral surface of the portion. The worm wheel unit is the worm wheel unit of the present invention.

According to the present invention, the coaxiality of the worm wheel tooth portion with respect to the worm wheel shaft can be improved.

FIG. 1 is a partially cut side view showing the electric power steering device of the first example of the embodiment. FIG. 2 is a cross-sectional view taken along the line AA of FIG. FIG. 3 is a cross-sectional view taken along the line BB of FIG. FIG. 4 is a view of the worm and the worm wheel as viewed from the worm side. FIG. 5 is a cross-sectional view of the worm wheel unit of the first example of the embodiment. FIG. 6 is an enlarged view of the upper right portion of FIG. FIG. 7 is a view seen from the right side of FIG. FIG. 8 is a cross-sectional view showing a step of injection molding (insert molding) the outer wheel element of the first example of the embodiment. FIG. 9 is an enlarged view of the right side portion of FIG. FIG. 10 is a diagram corresponding to FIG. 5, showing a second example of the embodiment. FIG. 11 is a view seen from the right side of FIG. FIG. 12 is a diagram corresponding to FIG. 8 showing a second example of the embodiment. FIG. 13 is a diagram corresponding to FIG. 5, showing a third example of the embodiment. FIG. 14 is a diagram corresponding to FIG. 8 showing a third example of the embodiment. FIG. 15 is a diagram corresponding to FIG. 5, showing a fourth example of the embodiment. FIG. 16 is a diagram corresponding to FIG. 8 showing a fourth example of the embodiment. FIG. 17 is a diagram corresponding to FIG. 5, showing a fifth example of the embodiment. FIG. 18 is a diagram corresponding to FIG. 8 showing a fifth example of the embodiment. FIG. 19 is a diagram corresponding to FIG. 5, showing the first example of the reference example. FIG. 20 is a diagram corresponding to FIG. 8 showing a first example of a reference example. FIG. 21 is a partially cut side view showing another example (first example) of the electric power steering device to which the present invention can be applied. FIG. 22 is a partially cut side view showing another example (second example) of the electric power steering device to which the present invention can be applied. FIG. 23 is a perspective view showing a steering device of a steer-by-wire system to which the present invention can be applied.

[First Example of Embodiment]
A first example of the embodiment of the present invention will be described with reference to FIGS. 1 to 9.

1 to 3 show a rack-assisted electric power steering device 1 incorporating the worm reducer of this example. The electric power steering device 1 of this example includes a steering wheel 2, a steering shaft 3, a steering column 4, a pair of universal joints 5a and 5b, an intermediate shaft 6, a steering gear unit 7, and an electric assist device 8. And.

The steering shaft 3 is rotatably supported inside the steering column 4 supported by the vehicle body. A steering wheel 2 is supported and fixed to the rear end portion of the steering shaft 3, and the front end portion of the steering shaft 3 is interposed via a rear universal joint 5a, an intermediate shaft 6, and a front universal joint 5b. , Is connected to the pinion shaft 9 of the steering gear unit 7. Therefore, when the driver rotates the steering wheel 2, the rotation of the steering wheel 2 is transmitted to the pinion shaft 9. The rotation of the pinion shaft 9 is converted into a linear motion of the rack shaft 10 of the steering gear unit 7 that meshes with the pinion shaft 9. As a result, the pair of steering wheels is provided with a steering angle corresponding to the amount of rotational operation of the steering wheel 2. The electric assist device 8 applies auxiliary power generated by using an electric motor as a power source to the rack shaft 10. As a result, the force required for the driver to rotate the steering wheel 2 is reduced.

The steering gear unit 7 includes a housing 11 supported by the vehicle body, a rack shaft 10 supported inside the housing 11 so as to be able to move only in the axial direction (vehicle width direction), and a rack shaft 10 inside the housing 11. A pinion shaft 9 supported only by rotation is provided in the vicinity of one side portion in the axial direction (right portion in FIG. 1). The pinion shaft 9 has pinion teeth on the outer peripheral surface of an axially intermediate portion (not shown) arranged inside the housing 11. The rack shaft 10 has a first rack tooth portion that meshes with the pinion tooth portion of the pinion shaft 9 at a part in the circumferential direction of the outer peripheral surface of one side portion in the axial direction arranged inside the housing 11, and the housing. A second portion of the outer peripheral surface of the other side portion in the axial direction (left portion in FIG. 1) arranged inside the 11 is engaged with the pinion tooth portion 20 of the pinion shaft 13 constituting the electric assist device 8. It has a rack tooth portion 12 (see FIG. 3).

The electric assist device 8 includes a pinion shaft 13 corresponding to a worm wheel shaft, a first bearing 14, and a second bearing 15, each of which is assembled in the vicinity of the other side of the rack shaft 10 in the axial direction of the housing 11. , The pressing block 16, the spring 17, the worm reducer 18, and the electric motor 19 are provided. The electric assist device 8 further includes a torque sensor (not shown).

The pinion shaft 13 is supported inside the housing 11 so as to be rotatable only in the vicinity of the other side portion in the axial direction of the rack shaft 10. In the following description, regarding the pinion shaft 13 and the worm wheel 24 described later, one side in the axial direction is the right side of FIGS. 3, 5, 6, 8 and 9, and the other side in the axial direction is shown in FIGS. It is on the left side of 6, 8 and 9.

The pinion shaft 13 has a pinion tooth portion 20 on the outer peripheral surface of the intermediate portion in the axial direction, and has a worm wheel fitting surface portion 21 on the outer peripheral surface of one end portion in the axial direction. The worm wheel fitting surface portion 21 is formed of a cylindrical surface centered on the central axis of the pinion shaft 13.

The pinion shaft 13 has a first bearing support portion 22 and a second bearing support portion 23 on the outer peripheral surface at two positions in the axial direction sandwiching the pinion tooth portions 20 from both sides in the axial direction. The first bearing support portion 22 located on one side in the axial direction from the pinion tooth portion 20 is formed of a cylindrical surface centered on the central axis of the pinion shaft 13, and its outer diameter D ₂₂ is the pinion tooth portion 20. The tooth tip diameter (diameter of the circumscribing circle) is the same as _{D 20 (D 22} = D ₂₀ ) or slightly larger than the diameter (D ₂₂ > D ₂₀ ). The second bearing support portion 23 located on the opposite side in the axial direction from the pinion tooth portion 20 is formed of a cylindrical surface centered on the central axis of the pinion shaft 13, and its outer diameter D ₂₃ is the pinion tooth portion 20. It is smaller than the tooth tip diameter D _{20 (D 22} <D ₂₀ ) (in the illustrated example, it is smaller than the tooth root diameter of the pinion tooth portion 20). The pinion shaft 13 is located at an axial position sandwiched between the worm wheel fitting surface portion 21 and the first bearing support portion 22, and is radially outward from the worm wheel fitting surface portion 21 and the first bearing support portion 22. It has an overhanging collar 82 over the entire circumference. Therefore, in this example, the outer diameter of the pinion shaft 13 is the outer diameter D ₈₂ of the flange portion 82, the outer diameter D 22 of the first bearing support portion ₂₂ , and the second from one side in the axial direction to the other side in the axial direction. The size of the bearing support portion 23 is configured to gradually decrease in the order of _{the outer diameter D 23 (D 23} <D ₂₂ <D ₈₂ ). In this example, when the pinion shaft 13 is manufactured, the cutting process for forming each of the first bearing support portion 22 and the second bearing support portion 23 is performed with one chuck (that is, for the machine tool). By doing this without re-grabbing the work), the coaxiality between the first bearing support portion 22 and the second bearing support portion 23 is increased.

In the pinion shaft 13, the first bearing support portion 22 is rotatably supported by the first bearing 14 with respect to the housing 11, and the second bearing support portion 23 is rotatably supported by the second bearing 15 with respect to the housing 11. It is supported as much as possible. In this example, the first bearing 14 is a ball bearing. The first bearing support portion 22 is used as a portion for externally fitting and fixing the inner ring constituting the first bearing 14. On the other hand, the second bearing 15 is a needle bearing. The second bearing support portion 23 is used as an inner ring track of a plurality of needles constituting the second bearing 15. When carrying out the present invention, each of the first bearing and the second bearing may be a different type of bearing from this example.

The pinion shaft 13 meshes the pinion tooth portion 20 with the second rack tooth portion 12 of the rack shaft 10. In this example, the backlash of the meshing portion between the pinion tooth portion 20 and the second rack tooth portion 12 is eliminated, and the meshing reaction force acting on the meshing portion between the pinion tooth portion 20 and the second rack tooth portion 12 is irrelevant. The rack shaft 10 is elastically urged toward the pinion shaft 13 in order to properly maintain the meshed state of the meshed portion. For this purpose, the pressing block 16 and the spring 17 are held inside the housing 11 at locations located on the opposite side of the rack shaft 10 from the pinion shaft 13. Then, by pressing the pressing block 16 against the rack shaft 10 by the elasticity of the spring 17, the rack shaft 10 is elastically urged toward the pinion shaft 13.

The worm reducer 18 includes a worm wheel 24 and a worm 25. The worm wheel 24 is externally fitted and fixed to the worm wheel fitting surface portion 21 of the pinion shaft 13 by press fitting. On the other hand, the worm 25 is connected to the output shaft of the electric motor 19 supported by the housing 11 so as to be able to transmit torque. Then, the worm tooth portion 26 provided on the outer peripheral surface of the axially intermediate portion of the worm 25 and the worm wheel tooth portion 27 provided on the outer peripheral surface of the worm wheel 24 are meshed with each other. As a result, auxiliary torque (auxiliary power) can be applied to the worm wheel 24 from the electric motor 19 via the worm 25.

In this example, the worm wheel tooth portion 27 has a shape like the tooth portion of a straight tooth spur gear as shown in FIG. That is, the tooth streaks of the worm wheel tooth portion 27 are parallel to _{the central axis X 24 of the worm wheel 24.} Accordingly, in the present embodiment, the intersection angle between the center axis X ₂₅ of the central axis X ₂₄ and the worm 25 of the worm wheel 24 and alpha, if the lead angle of the worm teeth 26 and the β, α = 90 ° - It is set to β (in FIGS. 1 to 3, for convenience of illustration, the intersection angle α is drawn to be 90 °, but in the case of this example, the intersection angle α is actually 90 ° −β). .. However, when the present invention is carried out, the worm wheel tooth portion may have a shape such as the tooth portion of a screw gear. That is, it is also possible to adopt a configuration in which the inclination angle of the tooth streaks of the worm wheel tooth portion with respect to the axial direction of the worm wheel is equal to the advance angle β of the worm tooth portion 26 and the intersection angle α is 90 °.

In this example, the worm wheel 24 is composed of an inner wheel element 28 and an outer wheel element 29.

The inner wheel element 28 is an annular member made of metal, and is formed in a ring shape as a whole. The inner wheel element 28 has a fitting hole 64 at the center in the radial direction for fitting with the worm wheel fitting surface portion 21 of the pinion shaft 13.

The inner wheel element 28 has an annular recess 65 recessed in the axial direction over the entire circumference on the radial outer portion of the side surface on one side in the axial direction. Of the outer diameter side peripheral surface 66, the inner diameter side peripheral surface 67, and the bottom surface 68 forming the inner surface of the annular recess 65, the outer diameter side peripheral surface 66 is the central axis of the inner wheel element 28 (= the central axis of the worm wheel 24). It is composed of a cylindrical surface centered on X _24). The inner diameter side peripheral surface 67 is formed of a curved surface (substantially conical surface) having a concave arc-shaped cross-sectional shape that is inclined inward in the radial direction toward one side in the axial direction. The bottom surface 68 is formed by a plane orthogonal to the central axis of the inner wheel element 28.

The inner wheel element 28 has an annular recess 69 recessed in the axial direction over the entire circumference in the radial intermediate portion of the side surface on the other side in the axial direction. Of the outer diameter side peripheral surface 70, the inner diameter side peripheral surface 71, and the bottom surface 72 that form the inner surface of the annular recess 69, the outer diameter side peripheral surface 70 has an engaging groove 33 and an uneven portion 34. The engaging groove 33 is formed at an end portion of the outer diameter side peripheral surface 70 on one side in the axial direction so as to be recessed outward in the radial direction over the entire circumference. The engaging groove 33 has a V-shaped cross-sectional shape in which the width dimension in the axial direction decreases from the opening on the inner diameter side toward the bottom on the outer diameter side. The concavo-convex portion 34 is formed over the entire circumference of the outer diameter side peripheral surface 70 in the remaining portion deviating from the engaging groove 33 on the other side in the axial direction. In other words, the engaging groove 33 is arranged adjacent to one side of the uneven portion 34 in the axial direction. The concavo-convex portion 34 is a concavo-convex portion (internal gear shape) related to the circumferential direction, in which concave portions and convex portions are alternately arranged in the circumferential direction. The radial depth of the engaging groove 33 is deeper than the radial depth of the plurality of recesses forming the concave-convex portion 34. In other words, the bottom portion of the engaging groove 33 is located radially outside the bottom portions of the plurality of recesses constituting the concave-convex portion 34. The inner diameter side peripheral surface 71 is formed of a cylindrical surface centered on the central axis of the inner wheel element 28. The bottom surface 72 is formed by a plane orthogonal to the central axis of the inner wheel element 28.

The outer peripheral surface 73 of the inner wheel element 28 is formed of a cylindrical surface centered on the central axis of the inner wheel element 28. Axial side surfaces 74 of the radial outer end of the inner wheel element 28, that is, side surfaces 74 on one side of the inner wheel element 28 on one axial direction adjacent to the radially outer side of the annular recess 65, and Of the side surfaces on the other side in the axial direction of the inner wheel element 28, each of the side surfaces 74 which are adjacent to the radial outer side of the annular recess 69 is formed by a plane orthogonal to the central axis of the inner wheel element 28. There is. In the illustrated example, the ends on both sides of the outer peripheral surface 73 in the axial direction and the end portions on the outer sides in the radial direction of the side surface 74 are connected by a chamfered portion having an arc-shaped cross-sectional shape.

In this example, in other words, the inner wheel element 28 has a cylindrical shape in which the inner diameter side annular portion 30 and the inner diameter side annular portion 30 are arranged coaxially with the inner diameter side annular portion 30. The radial inner end was coupled to the outer peripheral surface of the outer diameter side annular portion 31 and the inner diameter side annular portion 30, and the radial outer end was coupled to the inner peripheral surface of the outer diameter side annular portion 31. A ring-shaped connecting portion 32 is provided. The fitting hole 64 corresponds to the central hole of the inner diameter side annular portion 30. The outer diameter side peripheral surface 66 constituting the inner surface of the annular recess 65 corresponds to the inner peripheral surface of one side portion in the axial direction of the outer diameter side annular portion 31. The inner diameter side peripheral surface 67 and the bottom surface 68 forming the inner surface of the annular recess 65 correspond to the radial outer portion of the side surface on one side in the axial direction of the connecting portion 32. The outer diameter side peripheral surface 70 constituting the inner surface of the annular recess 69 corresponds to the inner peripheral surface of the other side portion in the axial direction of the outer diameter side annular portion 31. The inner diameter side peripheral surface 71 forming the inner surface of the annular recess 69 corresponds to the outer peripheral surface of the other side portion in the axial direction of the inner diameter side annular portion 30. The bottom surface 72 forming the inner surface of the annular recess 69 corresponds to the side surface of the connecting portion 32 on the other side in the axial direction. The outer peripheral surface 73 corresponds to the outer peripheral surface of the outer diameter side annular portion 31. The pair of side surfaces 74 correspond to the side surfaces on both sides in the axial direction of the outer diameter side annular portion 31.

In the illustrated example, the radial inner end of the connecting portion 32 is coupled to the axially one end of the outer peripheral surface of the inner diameter side annular portion 30, and the radial outer end of the connecting portion 32 is , It is coupled to the axial intermediate portion (specifically, the portion of the axial intermediate portion closer to one side in the axial direction) of the inner peripheral surface of the outer diameter side annular portion 31. However, when the present invention is carried out, the coupling position of the radial inner end portion of the connecting portion with respect to the outer peripheral surface of the inner diameter side annular portion and the radial outer end portion of the connecting portion with respect to the inner peripheral surface of the outer diameter side annular portion. The coupling position may be an axial position different from that of this example. The connecting portion is not limited to the circular ring shape, and may be composed of a plurality of spokes arranged in the radial direction.

As the metal constituting the inner wheel element 28, in addition to an iron alloy such as steel, various metals such as a copper alloy, an aluminum alloy, and a magnesium alloy can be adopted. As the processing for forming the inner wheel element 28, various cutting processing and plastic working can be adopted. However, in order to form with good yield and low cost, it is preferable to adopt plastic working (forging, pressing, flow forming, etc.). The engaging groove 33 can function as a relief for a mold (die) used when the uneven portion 34 is formed by plastic working.

The outer wheel element 29 is made of synthetic resin and is formed in an annular shape, and covers the outer diameter side annular portion 31 and the radial outer portion of the connecting portion 32, which are the radial outer portions of the inner wheel element 28, over the entire circumference. In the buried state, it is coupled to the inner wheel element 28.

The outer wheel element 29 has a worm wheel tooth portion 27 on the outer peripheral surface over the entire width in the axial direction. The worm wheel tooth portion 27 has a shape like the tooth portion of a straight tooth spur gear, and its tooth streaks are _{parallel to the central axis X 24} of the worm wheel 24 (see FIG. 4).

Each of the side surfaces 75 on both sides of the outer wheel element 29 in the axial direction is formed by a plane orthogonal to _{the central axis X 24 of the worm wheel 24.}

In the synthetic resin constituting the outer wheel element 29, the portion that has entered the radial outer portion inside the annular recess 65 constitutes the holding portion 35, and the portion that has entered the radial outer portion inside the annular recess 69 is formed. The holding portion 36 is configured. Then, based on the engagement between the outer diameter side peripheral surface 66 of the annular recess 65 and the holding portion 35, and the engagement between the outer diameter side peripheral surface 70 of the annular recess 69 and the holding portion 36, that is, the holding portion 35. By holding the outer diameter side annular portion 31 so as to be held by the 36, the holding force of the outer wheel element 29 with respect to the inner wheel element 28 in the moment direction is enhanced. Further, in this example, a part of the synthetic resin constituting the holding portion 36 enters the inside of the engaging groove 33 of the outer diameter side peripheral surface 70 to form the moment direction holding portion 76 that engages with the engaging groove 33. doing. Then, by engaging the engaging groove 33 with the moment direction holding portion 76, the holding force of the outer wheel element 29 with respect to the inner wheel element 28 in the moment direction is further increased.

Further, in this example, a part of the synthetic resin constituting the holding portion 36 enters the inside of a plurality of recesses constituting the concave-convex portion 34 of the outer diameter side peripheral surface 70, and holds the rotation direction to engage with the recesses. It constitutes a part 77. Then, by engaging the concave portion with the rotation direction holding portion 77, the holding force of the outer wheel element 29 in the rotation direction with respect to the inner wheel element 28 is increased. It should be noted that such a concavo-convex portion for increasing the holding force in the rotational direction can be formed at a portion different from this example on the surface of the inner wheel element embedded in the outer wheel element.

The inner peripheral surface 78 of one side portion in the axial direction of the outer wheel element 29 is composed of a conical surface (inclined portion) that is inclined inward in the radial direction toward the other side in the axial direction. The end on one side of the inner peripheral surface 78 in the axial direction is connected to the end on the inner side in the radial direction of the side surface 75 on one side in the axial direction of the outer wheel element 29. The end of the inner peripheral surface 78 on the other side in the axial direction is connected to the radial intermediate portion of the bottom surface 68 of the annular recess 65. The other side portion of the inner peripheral surface 78 in the axial direction corresponds to the inner peripheral surface of the holding portion 35, and enters the inside of the annular recess 65.

The inner peripheral surface 79 of the other side portion in the axial direction of the outer wheel element 29 includes a non-inclined portion 80 forming one side portion in the axial direction and an inclined portion 81 forming the other side portion in the axial direction. The non-inclined portion 80 is composed of a cylindrical surface centered on _{the central axis X 24 of the worm wheel 24.} The inclined portion 81 is formed of a conical surface that is inclined inward in the radial direction toward one side in the axial direction. One end of the non-inclined portion 80 in the axial direction is connected to the radial outer portion of the bottom surface 72 constituting the annular recess 69. The end of the non-tilted portion 80 on the other side in the axial direction is connected to the end of the inclined portion 81 on the other side in the axial direction. The end of the inclined portion 81 on the other side in the axial direction is connected to the end on the inner side in the radial direction of the side surface 75 on the other side in the axial direction of the outer wheel element 29. The non-inclined portion 80 and the end portion on one side in the axial direction of the inclined portion 81 correspond to the inner peripheral surface of the holding portion 36, and are arranged inside the annular recess 69. That is, in this example, the axial width W ₈₁ of the inclined portion 81 is larger than _{the axial width W a} between the side surface 74 and the side surface 75 on the other side of the worm wheel 24 in the axial direction _{(W 81} >. W _a ). In the case of carrying out the present invention, the inner peripheral surface of the outer peripheral surface of the outer wheel element 29 on the other side in the axial direction shall be an inclined portion that is inclined inward in the radial direction toward one side in the axial direction. You can also.

As the synthetic resin constituting the outer wheel element 29, in addition to polyamide 66 (PA66), polyamide 6 (PA6), polyamide 46 (PA46), polyamide 9T (PA9T), polyphenylene sulfide (PPS), polyethylene terephthalate (PET). ), Polyacetal (POM), phenol resin (PF) and other synthetic resins can be used. Various reinforcing fibers such as glass fiber, polyethylene fiber, carbon fiber, and aramid fiber can be mixed with these synthetic resins, if necessary.

In the electric power steering device 1 of this example, a torque sensor (not shown) constituting the electric assist device 8 detects the direction and magnitude of the torque applied from the steering wheel 2 to the steering shaft 3. The electric motor 19 rotates and drives the worm 25 based on the detection signal of the torque sensor, the vehicle speed signal output from the vehicle speed sensor incorporated in the transmission, and the like, and thereby racks the worm 25 via the worm wheel 24 and the pinion shaft 13. Auxiliary power is applied to the shaft 10. As a result, the force required for the driver to rotate the steering wheel 2 is reduced.

When manufacturing the worm wheel 24, the outer wheel element 29 is coupled to the inner wheel element 28 by using the inner wheel element 28 as an insert product and insert-molding the outer wheel element 29. In particular, in this example, such insert molding of the outer wheel element 29 is performed in a state where the inner wheel element 28 is externally fitted and fixed to the worm wheel fitting surface portion 21 of the pinion shaft 13.

That is, in this example, the inner wheel element 28 is externally fitted and fixed to the worm wheel fitting surface portion 21 of the pinion shaft 13 before the outer wheel element 29 is insert-molded. Specifically, the inner diameter side annular portion 30 of the inner wheel element 28 is press-fitted onto the worm wheel fitting surface portion 21, and the side surface of the inner diameter side annular portion 30 on the other side in the axial direction of the flange portion 82. It abuts against the stepped surface 37a, which is one side surface in the axial direction. As a result, the inner wheel element 28 is externally fitted and fixed to the worm wheel fitting surface portion 21 in a state of being positioned in the axial direction. In this example, in this state, the end face on one side in the axial direction of the pinion shaft 13 and the side surface on the one side in the axial direction of the inner diameter side annular portion 30 are in the same virtual plane orthogonal to the central axis of the pinion shaft 13. Exists. The outer diameter of the coupling body of the pinion shaft 13 and the inner wheel element 28, toward the one axial side to the other axial side, the outer diameter D ₂₈ of the inner wheel element 28, the outer diameter D ₈₂ of the flange portion 82 , the outer diameter D ₂₂ of the first bearing support portion 22, in the order of the outside diameter D ₂₃ of the second bearing support portion 23, its size is configured to be reduced stepwise (D ₂₃ <D ₂₂ <D ₈₂ <D ₂₈ ).

When the outer wheel element 29 is insert-molded, a mold device 38 as shown in FIGS. 8 and 9 is used. The mold device 38 includes a fixed mold 39 arranged on one side in the axial direction and a movable mold 40 arranged on the other side in the axial direction.

The movable mold 40 is capable of moving in the axial direction (horizontal direction in FIGS. 8 and 9) with respect to the fixed mold 39. The movable mold 40 has a holding hole 83 at the center of the movable mold 40 in which the pinion shaft 13 can be inserted from one side in the axial direction. The holding hole 83 has a first fitting portion 41 in which the first bearing support portion 22 of the pinion shaft 13 can be fitted inward without rattling in the radial direction, and a second bearing support portion 23 of the pinion shaft 13 in the radial direction. It has a second fitting portion 42 that can be fitted inward without rattling, and an inner diameter side holding surface 84 that can come into contact with a stepped surface 37b that is the side surface of the pinion shaft 13 on the other side in the axial direction. The movable mold 40 has an outer diameter side holding surface 85 that can come into contact with the radial intermediate portion of the bottom surface 72 of the annular recess 69 of the inner wheel element 28 on one end surface in the axial direction.

When the outer wheel element 29 is insert-molded, the movable mold 40 is moved axially away from the fixed mold 39 so that the mold device 38 is opened and the movable mold 40 is as shown in FIG. A coupling body of the pinion shaft 13 and the inner wheel element 28 is set on the mold 40. For this purpose, specifically, the pinion shaft 13 constituting the coupling is inserted from one side in the axial direction inside the holding hole 83 of the movable mold 40. As a result, the first bearing support portion 22 of the pinion shaft 13 is internally fitted into the first fitting portion 41 without radial rattling, and the second bearing support portion 23 of the pinion shaft 13 is fitted into the second fitting portion. It fits inside 42 without radial rattling, the stepped surface 37b of the pinion shaft 13 is brought into contact with the inner diameter side holding surface 84, and further, the radial intermediate portion of the bottom surface 72 of the annular recess 69 of the inner wheel element 28. Is in contact with the outer diameter side holding surface 85. In this example, the outer diameter of the combined body is configured to gradually decrease from one side in the axial direction to the other side in the axial direction (D ₂₃ <D ₂₂ <D ₈₂ <D _28). Therefore, as described above, the work of inserting the pinion shaft 13 constituting the coupling inside the holding hole 83 can be easily performed. Further, in this example, the first bearing support portion 22 and the second bearing support portion 23 arranged on both sides of the pinion tooth portion 20 (arranged largely apart in the axial direction) are referred to as the first fitting portion 41. By fitting the pinion shaft 13 inwardly with the second fitting portion 42, the holding rigidity of the pinion shaft 13 is increased so that the inclination of the inner wheel element 28 can be suppressed.

In this example, the bottom surface 72 of the annular recess 69 of the inner wheel element 28 and the outer diameter side holding surface 85 are brought into contact with each other to position the coupling in the axial direction with respect to the movable mold 40. With this contact alone, the inner wheel element 28 may be deformed due to the high pressure of the molten resin when the insert molding described later is performed. Therefore, in this example, in order to prevent such deformation, the stepped surface 37b of the pinion shaft 13 and the inner diameter side holding surface 84 are additionally brought into contact with each other. That is, in this example, the bottom surface 72 of the annular recess 69 of the inner wheel element 28 and the outer diameter side holding surface 85 are brought into contact with each other, and the stepped surface 37b of the pinion shaft 13 and the inner diameter side holding surface 84 are brought into contact with each other. As a result, the molten resin is evenly spread radially in that state under high injection pressure. As a result, the positions of the outer wheel element 29 and the pinion shaft 13 can be stabilized by positioning the coupling in the axial direction with respect to the movable mold 40, and variations between products can be suppressed.

After setting the coupling with respect to the movable mold 40 as described above, the movable mold 40 is then brought closer to the fixed mold 39 in the axial direction, as shown in FIGS. 8 and 9. The mold device 38 is closed by abutting the side surfaces 86 and 87 of the fixed mold 39 and the movable mold 40 facing each other. As a result, a cavity 43, which is a molding space for the outer wheel element 29, is formed between the inner wheel element 28 and the mold device 38. At the same time, a disc gate 44 is formed in a portion sandwiched between the inner wheel element 28 and the pinion shaft 13 and the fixed mold 39 in the axial direction.

The cavity 43 is arranged coaxially with the first fitting portion 41 and the second fitting portion 42 provided in the movable mold 40. That is, the cavity 43 is arranged coaxially with the pinion shaft 13. The downstream end portion P of the disc gate 44 is a portion of the cavity 43 adjacent to one side in the axial direction of the radial intermediate portion of the inner wheel element 28 (the inner peripheral surface 78 of the one side portion in the axial direction of the outer wheel element 29). Is open to the part where is formed). The fixed mold 39 includes a runner 45 extending in the axial direction inside the fixed mold 39, and the downstream end portion Q of the runner 45 is open to the central portion of the disc gate 44. The runner 45 is arranged coaxially with the first fitting portion 41 and the second fitting portion 42 provided in the movable mold 40. The runner 45 is a hot runner in which a heater (not shown) is arranged around the runner 45, and it is possible to hold the synthetic resin in a molten state inside the runner 45.

Then, in this state, the molten resin is sent into the cavity 43 through the runner 45 and the disc gate 44. The arrows in FIG. 9 indicate the flow direction of the molten resin in the runner 45, the disc gate 44, and the cavity 43. That is, the molten resin sent into the cavity 43 from the runner 45 and the disc gate 44 is adjacent to the radial outer side of the inner wheel element 28 from the portion adjacent to one axial side of the radial outer portion of the inner wheel element 28. The entire inside of the cavity 43 is filled by flowing toward a portion adjacent to the other side in the axial direction of the radial outer portion of the inner wheel element 28 via the portion to be formed.

Here, in this example, the worm wheel tooth portion 27 has a shape like the tooth portion of a straight tooth spur gear, and its tooth streaks are parallel to _{the central axis X 24 of the worm wheel 24.} Therefore, the molten resin passes straight (smoothly) in the axial direction through the portion of the cavity 43 where the worm wheel tooth portion 27 should be formed.

Further, in this example, the inner peripheral surface 79 of the other side portion in the axial direction of the outer wheel element 29 has an inclined portion 81 inclined inward in the radial direction toward the one side in the axial direction on the other side portion in the axial direction. The end portion of the inclined portion 81 on one side in the axial direction is arranged inside the annular recess 69. Therefore, on the inner surface of the cavity 43, an end portion on one side in the axial direction of the inclined portion forming portion 88, which is a portion having a shape matching the inclined portion 81, is also arranged inside the annular recess 69. Therefore, of the cavity 43, the molten resin that has passed through the portion of the inner wheel element 28 adjacent to the other side in the axial direction of the radial outer portion from the radial outer side to the radial inner side is passed along the inclined portion forming portion 88. , Can be smoothly guided to the inside of the annular recess 69.

Then, after the molten resin is cooled and solidified in the cavity 43 and the disc gate 44, the movable mold 40 is moved axially away from the fixed mold 39 to open the mold device 38. In this example, as the mold device 38 is opened in this way, the synthetic resin solidified in the cavity 43 and the disc gate 44 and the synthetic resin held in the molten state in the runner 45 which is a hot runner are formed. , It is separated at the portion corresponding to the downstream end portion Q of the runner 45. After that, the composite resin solidified in the cavity 43 and the disc gate 44 and the pinion shaft 13 are pushed out to one side in the axial direction by a plurality of ejector pins 89 installed in the movable mold 40. The coupling is removed from the movable mold 40. Then, the synthetic resin solidified in the cavity 43 and the synthetic resin solidified in the disc gate 44 are combined with the downstream end portion P of the disc gate 44 (inner peripheral surface 78 on one side in the axial direction of the outer wheel element 29). The synthetic resin solidified in the disc gate 44 is removed by separating at the portion corresponding to. Then, if necessary, the surface and corners of the outer wheel element 29, which is a synthetic resin solidified in the cavity 43, are finished to complete the worm wheel 24. In other words, the worm wheel unit 48, which is a combination of the worm wheel 24 and the pinion shaft 13, is completed.

In this example, during the finishing process described above, no additional gear cutting process is performed on the tooth surface 47, which is the circumferential side surface of the plurality of teeth 46 constituting the worm wheel tooth portion 27. That is, in this example, the tooth surface 47 of the worm wheel tooth portion 27 is left as an injection-molded surface, which is a surface formed by injection molding. Further, in this example, in the completed worm wheel 24, a gate separating portion (a synthetic resin cooled and solidified in the disc gate 44) is applied to the inner peripheral surface 78 of one side portion in the axial direction of the outer wheel element 29. It is a separated portion, and there is, for example, a cut portion or a broken portion).

According to the structure of this example as described above, the coaxiality of the worm wheel tooth portion 27 with respect to the pinion shaft 13 can be improved (increased). That is, in this example, when the worm wheel 24 is manufactured, the inner wheel element 28 is used as an insert product, and the outer wheel element 29 is insert-molded to connect the outer wheel element 29 to the inner wheel element 28. Is performed in a state where the inner wheel element 28 is externally fitted and fixed to the worm wheel fitting surface portion 21 of the pinion shaft 13. More specifically, when the outer wheel element 29 is insert-molded in such a state, the pinion shaft 13 is provided by the first fitting portion 41 and the second fitting portion 42 provided in the movable mold 40. The first bearing support portion 22 and the second bearing support portion 23 are fitted inward without rattling in the radial direction. As a result, the pinion shaft 13 and the cavity 43, which is the molding space of the outer wheel element 29 including the worm wheel tooth portion 27, are coaxially arranged. Therefore, even if the posture of the inner wheel element 28 is tilted when the inner wheel element 28 is externally fitted and fixed to the pinion shaft 13, the coaxiality of the worm wheel tooth portion 27 with respect to the pinion shaft 13 is increased. can do.

Therefore, in this example, it is possible to reduce vibration, fluctuation, sound, and the like when the worm wheel tooth portion 27 and the worm tooth portion 26 are engaged with each other. As a result, it is possible to improve the feeling of operation of the steering wheel by the driver, the controllability of the electric assist device 8, and the quietness.

Further, in this example, the runner 45 is arranged coaxially with the first fitting portion 41 and the second fitting portion 42 provided in the movable mold 40. Therefore, the flow of the molten resin sent into the cavity 43 through the runner 45 and the disc gate 44 in the cavity 43 can be made uniform over the entire circumference. Therefore, the moldability of the outer wheel element 29 is improved, and the strength of the outer wheel element 29 is stabilized.

Further, in this example, since the worm wheel tooth portion 27 has a shape like the tooth portion of a straight tooth spur gear, when the outer wheel element 29 is insert-molded, the molten resin is used as the worm wheel tooth in the cavity 43. The portion 27 can be passed straight (smoothly) in the axial direction through the portion to be formed. Therefore, the moldability of the worm wheel tooth portion 27 can be improved. Therefore, from such a viewpoint as well, it is possible to make it difficult for vibration, fluctuation, sound, etc. to occur when the worm wheel tooth portion 27 and the worm tooth portion 26 are engaged with each other.

Further, in this example, the molten resin can be smoothly guided to the inside of the annular recess 69 along the inclined portion forming portion 88 on the inner surface of the cavity 43. Therefore, the molten resin is easily distributed inside the annular recess 69. Therefore, in this respect as well, the moldability of the outer wheel element 29 can be improved.

Further, in this example, since the coaxiality of the worm wheel tooth portion 27 with respect to the pinion shaft 13 can be improved only by injection molding, additional gear cutting is not required. Further, in this example, since the moldability of the worm wheel tooth portion 27 by injection molding can be improved, additional gear cutting is not required from this point as well. Therefore, the manufacturing cost of the worm wheel 24 can be suppressed.

Although it is different from this example, it is also possible to use a method in which the pinion shaft and the inner wheel element are integrally manufactured as a single component, and this single component is set in a mold device to manufacture the outer wheel element by injection molding. , The coaxiality of the worm wheel tooth portion with respect to the pinion shaft can be improved. However, when such a method is adopted, the shape of the single part becomes complicated, and it is necessary to perform complicated processing when manufacturing the single part, so that the manufacturing cost tends to increase. On the other hand, in this example, the pinion shaft 13 and the inner wheel element 28 are separate parts. That is, the shapes of the pinion shaft 13 and the inner wheel element 28 are not complicated, and it is not necessary to perform complicated processing when manufacturing the pinion shaft 13 and the inner wheel element 28, so that the manufacturing cost can be easily suppressed.

Further, in this example, the inner wheel element 28 is externally fitted and fixed to one end of the pinion shaft 13 in the axial direction. Therefore, although the pinion shaft 13 protrudes greatly from the inner diameter side of the inner wheel element 28 to the other side in the axial direction, it does not protrude greatly from the inner diameter side of the inner wheel element 28 to one side in the axial direction (in this example). Not protruding at all). Therefore, in this example, the inner wheel element is externally fitted and fixed to the axial middle portion of the pinion shaft, and the pinion shaft protrudes significantly from the inner diameter side of the inner wheel element to both sides in the axial direction. The structure of the molten resin passage (runner 45 and disc gate 44) provided in the mold device 38 can be simplified. Therefore, the manufacturing cost of the mold device 38 can be suppressed by that amount, and the manufacturing cost of the worm wheel unit 48, which is a combination of the pinion shaft 13 and the worm wheel 24, can be suppressed.

[Second Example of Embodiment]
A second example of the embodiment of the present invention will be described with reference to FIGS. 10 to 12.

In this example, as shown in FIG. 12, when the outer wheel element 29a constituting the worm wheel 24a of the worm wheel unit 48a is insert-molded, the portion used as the disc gate 44 in the first example of the embodiment (FIG. 8). And FIG. 9) is a part of the cavity 43a, which is the molding space of the outer wheel element 29a. As a result, the worm wheel unit 48a of this example uses the synthetic resin solidified inside the portion that was used as the disc gate 44 in the first example of the embodiment as a disc-shaped disc portion 49 that corresponds to the insert covering portion. I have. In this example, one axial side portion (including the disc portion 49) of the outer wheel element 29a covers the entire side surface of the inner wheel element 28 on one axial direction (including the entire inner surface of the annular recess 65). .. The disk portion 49 covers the end surface of the pinion shaft 13 on one side in the axial direction.

In such a structure of this example, the work of removing the disc portion 49 can be omitted when the outer wheel element 29a is insert-molded. Therefore, the manufacturing cost of the worm wheel unit 48a can be suppressed accordingly. Further, based on the presence of the disc portion 49, the coupling strength of the outer wheel element 29a with respect to the inner wheel element 28 and the rigidity of the entire worm wheel 24a can be improved.
Other configurations and effects are the same as in the first example of the embodiment.

[Third example of the embodiment]
A third example of the embodiment of the present invention will be described with reference to FIGS. 13 and 14.

In this example, the pinion shaft 13a constituting the worm wheel unit 48b is provided with a concave hole 50 that opens only on one side in the axial direction at the center portion in the radial direction of the end portion on one side in the axial direction. The concave hole 50 has an annular groove 51 that is recessed outward in the radial direction at one to a plurality of locations (two locations in the illustrated example) on the inner peripheral surface in the axial direction. A part of the synthetic resin constituting the outer wheel element 29b of the worm wheel unit 48b enters the entire inside of the concave hole 50 (including the annular groove 51) at the time of insert molding, so that it is axially oriented from the central portion of the disc portion 49. It constitutes a resin engaging portion 52 corresponding to an insert covering portion that protrudes to the other side and engages with the concave hole 50. In particular, the resin engaging portion 52 has an annular convex portion 53 protruding outward in the radial direction at a portion of the outer peripheral surface that matches each of the annular grooves 51. Then, by engaging the annular convex portion 53 with the annular groove 51, the axial displacement of the outer wheel element 29b with respect to the pinion shaft 13a is prevented. In this example, the annular groove 51 corresponds to the inner diameter side concave portion, and the annular convex portion 53 corresponds to the inner diameter side convex portion.

In such a structure of this example, a holding force for preventing the worm wheel 24b from falling off to one side in the axial direction with respect to the pinion shaft 13a is provided based on the engagement between the annular groove 51 and the annular convex portion 53. Can be improved.
Other configurations and effects are the same as in the second example of the embodiment.

[Fourth Example of Embodiment]
A fourth example of the embodiment of the present invention will be described with reference to FIGS. 15 and 16.

In this example, the concave hole 50a of the pinion shaft 13b constituting the worm wheel unit 48c has a spiral groove 54 such as a female thread groove on the inner peripheral surface. The resin engaging portion 52a that engages with the concave hole 50a has a spiral convex portion 55 that protrudes outward in the radial direction at a portion of the outer peripheral surface that matches the spiral groove 54. Then, by engaging the spiral convex portion 55 with the spiral groove 54, the axial displacement of the outer wheel element 29c with respect to the pinion shaft 13b is hindered. In this example, the spiral groove 54 corresponds to the inner diameter side concave portion, and the spiral convex portion 55 corresponds to the inner diameter side convex portion.

In such a structure of this example, a holding force for preventing the worm wheel 24c from falling off to one side in the axial direction with respect to the pinion shaft 13b based on the engagement between the spiral groove 54 and the spiral convex portion 55. Can be improved.

In this example, when the outer wheel element 29c is manufactured by injection molding, the molten resin enters the inside of the spiral groove 54 without interruption along the forming direction of the spiral groove 54, so that the molten resin bites air. It is possible to suppress the intrusion and make it difficult for the spiral convex portion 55 to be poorly formed.
Other configurations and effects are the same as in the third example of the embodiment.

[Fifth Example of Embodiment]
A fifth example of the embodiment of the present invention will be described with reference to FIGS. 17 and 18.

In this example, the outer wheel element 29d of the worm wheel unit 48d further includes a portion of the surface of the inner wheel element 28 that covers the radial inner portion on the other side in the axial direction. Specifically, the other side portion of the outer wheel element 29d in the axial direction is the entire side surface of the inner wheel element 28 on the other side in the axial direction, excluding the portion abutting on the stepped surface 37a (the entire inner surface of the annular recess 69). Includes). In other words, in this example, the outer wheel element 29d covers the entire surface of the inner wheel element 28 that is not in contact with the pinion shaft 13c.

The outer wheel element 29d is a cylindrical shaft cover corresponding to an insert cover portion extending from the radial inner end portion of the other side portion in the axial direction to the other side in the axial direction in the portion covering the surface of the inner wheel element 28. A portion 56 is further provided. Then, the shaft covering portion 56 covers the outer peripheral surface of the flange portion 82a of the outer peripheral surface of the pinion shaft 13c. In this example, the flange portion 82a has an annular groove 57 that is recessed inward in the radial direction at one or a plurality of axial directions (one location in the illustrated example) on the outer peripheral surface. The shaft covering portion 56 of the outer wheel element 29d has an annular convex portion 58 protruding inward in the radial direction at a portion of the inner peripheral surface that matches the annular groove 57. Then, by engaging the annular convex portion 58 with the annular groove 57, the axial displacement of the outer wheel element 29d with respect to the pinion shaft 13c is hindered. In this example, the annular groove 57 corresponds to the outer diameter side concave portion, and the annular convex portion 58 corresponds to the outer diameter side convex portion.

In such a structure of this example, since the outer wheel element 29d covers the entire surface of the inner wheel element 28 that is not in contact with the pinion shaft 13c, the outer wheel element 29d with respect to the inner wheel element 28 The bond strength of the worm wheel 24d and the rigidity of the entire worm wheel 24d can be improved.

In the structure of this example, the holding force for preventing the worm wheel 24d from falling off to one side in the axial direction with respect to the pinion shaft 13c is improved based on the engagement between the annular groove 57 and the annular convex portion 58. Can be done.
Other configurations and effects are the same as in the second example of the embodiment.

[First example of reference example]
A first example of a reference example related to the present invention will be described with reference to FIGS. 19 and 20.

In this reference example, the worm wheel unit 48z is configured as a single component in which the pinion shaft 13z and the worm wheel 24z are integrally formed of synthetic resin.

In this example, as shown in FIG. 20, the fixed mold 39z and the movable mold 40z are abutted against each other in the axial direction, so that the mold device 38z is closed and the mold device 38z is closed. Inside, a cavity 43z, which is a molding space for the worm wheel unit 48z, is formed.
Other configurations and effects are the same as in the second example of the embodiment.

The worm reducer of the present invention is not limited to the rack-assisted electric power steering device, and can be incorporated into an electric power steering device having various structures.
For example, in the pinion assist type electric power steering device 1a as shown in FIG. 21, the electric assist device 8a provided with the worm reducer 18a is assembled to the pinion shaft 9a of the steering gear unit 7a.
In the column assist type electric power steering device 1b as shown in FIG. 22, the electric assist device 8b provided with the worm reducer 18b is assembled to the front end portion of the steering shaft 3.

The worm reducer of the present invention can also be incorporated into, for example, a steer-by-wire type steering device 59 as shown in FIG. 23. The steering device 59 of the steer-by-wire system includes a steering device 60 having a steering wheel 2 and a steering device 61 for imparting a steering angle to a pair of steering wheels electrically connected to the steering device 60. .. When driving an automobile, the amount of rotational operation of the steering wheel 2 is detected by a sensor of the steering device 60, and the electric actuator 62 of the steering device 61 is driven based on the output signal of the sensor to form a pair. A steering angle is given to the steering wheel. The electric actuator 62 includes a worm reducer 18c for increasing the output torque of the electric motor 63 as a drive source, and the worm reducer of the present invention can be used as the worm reducer 18c.

The structures of the above-described embodiments can be appropriately combined and implemented as long as there is no contradiction.

The worm reducer of the present invention can be incorporated not only in a steering device but also in various mechanical devices.

1, 1a, 1b Electric power steering device 2 Steering wheel 3 Steering shaft 4 Steering column 5a, 5b Flexible joint 6 Intermediate shaft 7, 7a Steering gear unit 8, 8a, 8b Electric assist device 9, 9a Pinion shaft 10 Rack shaft 11 Housing 12 2nd rack teeth 13, 13a, 13b, 13c, 13z Pinion shaft 14 1st bearing 15 2nd bearing 16 Pressing block 17 Spring 18, 18a, 18b, 18c Warm reducer 19 Electric motor 20 Pinion teeth 21 Warm wheel Fitting surface 22 1st bearing support 23 2nd bearing support 24, 24a, 24b, 24c, 24z Warm wheel 25 Warm 26 Warm tooth part 27 Warm wheel tooth part 28 Inner wheel element 29, 29a, 29b, 29c, 29d Outer wheel element 30 Inner diameter side annular part 31 Outer diameter side annular part 32 Connecting part 33 Engagement groove 34 Concavo-convex part 35 Holding part 36 Holding part 37a, 37b Step surface 38, 38z Mold device 39, 39z Fixed mold 40, 40z Movable mold 41 1st fitting part 42 2nd fitting part 43, 43a, 43z Cavity 44 Disc gate 45 Runner 46 Tooth 47 Tooth surface 48, 48a, 48b, 48c, 48d, 48z Warm wheel unit 49 Disc part 50, 50a concave hole 51 annular groove 52, 52a resin engaging part 53 annular convex part 54 spiral groove 55 spiral convex part 56 shaft covering part 57 annular groove 58 annular convex part 59 steer-by-wire type steering device 60 steering device 61 steering device 62 Electric actuator 63 Electric motor 64 Fitting hole 65 Annular recess 66 Outer diameter side peripheral surface 67 Inner diameter side peripheral surface 68 Bottom surface 69 Ring recess 70 Outer diameter side peripheral surface 71 Inner diameter side peripheral surface 72 Bottom surface 73 Outer surface surface 74 Side surface 75 Side surface 76 Moment direction holding part 77 Rotation direction holding part 78 Inner peripheral surface 79 Inner peripheral surface 80 Non-tilted part 81 Inclined part 82, 82a Bearing part 83 Holding hole 84 Inner diameter side holding surface 85 Outer diameter side holding surface 86 Side surface 87 Side surface 88 Inclined part Bearing 89 Ejector pin

Claims (19)

With the worm wheel shaft,
A worm wheel having worm wheel teeth on the outer peripheral surface and externally fitted and fixed to the worm wheel shaft is provided.
The worm wheel has an annular inner wheel element that is externally fitted and fixed to the worm wheel shaft, and the worm wheel tooth portion on the outer peripheral surface, and is coupled to the inner wheel element, and is made of a synthetic resin. With a wheel element,
It is a manufacturing method of the worm wheel unit.
With the inner wheel element fitted and fixed to the worm wheel shaft, a mold is arranged around the worm wheel shaft and the inner wheel element, and the worm wheel shaft is formed inside the mold. The outer wheel element is formed by insert molding in which a synthetic resin is fed into the cavity while being held coaxially with the cavity which is the molding space of the outer wheel element.
How to manufacture a worm wheel unit. The worm wheel shaft has pinion teeth on the outer peripheral surface.
The method for manufacturing a worm wheel unit according to claim 1. The worm wheel shaft has bearing support portions supported by bearings at one or a plurality of axial directions on the outer peripheral surface.
By supporting the bearing support portion with the mold, the worm wheel shaft is held coaxially with the cavity.
The method for manufacturing a worm wheel unit according to claim 1 or 2. The insert molding is performed with the inner wheel element fitted and fixed to one end of the worm wheel shaft on one side in the axial direction.
The method for manufacturing a worm wheel unit according to any one of claims 1 to 3. By the insert molding, a disc portion covering the end face on one side in the axial direction of the worm wheel shaft is formed on a part of the outer wheel element.
The method for manufacturing a worm wheel unit according to claim 4. The worm wheel shaft has a concave hole that opens on one end surface in the axial direction.
By the insert molding, a resin engaging portion that engages with the concave hole is formed in a part of the outer wheel element.
The method for manufacturing a worm wheel unit according to claim 5. The concave hole has an inner diameter side recess that is recessed outward in the radial direction on the inner peripheral surface.
By the insert molding, an inner diameter side convex portion is formed in a part of the resin engaging portion by engaging with the inner diameter side concave portion to prevent the axial displacement of the outer wheel element with respect to the worm wheel shaft.
The method for manufacturing a worm wheel unit according to claim 6. By the insert molding, a shaft covering portion is formed on a part of the outer wheel element so as to cover the portion of the outer peripheral surface of the worm wheel shaft that is axially adjacent to the inner wheel element.
The method for manufacturing a worm wheel unit according to any one of claims 1 to 7. The worm wheel shaft has an outer diameter side recess that is recessed inward in the radial direction in a portion of the outer peripheral surface that is axially adjacent to the inner wheel element.
By the insert molding, an outer diameter side convex portion is formed in a part of the shaft covering portion by engaging with the outer diameter side concave portion to prevent the axial displacement of the outer wheel element with respect to the worm wheel shaft.
The method for manufacturing a worm wheel unit according to claim 8. A hot runner is used as a runner for feeding the synthetic resin into the cavity.
The method for manufacturing a worm wheel unit according to any one of claims 1 to 9. With the worm wheel shaft,
A worm wheel having worm wheel teeth on the outer peripheral surface and externally fitted and fixed to the worm wheel shaft is provided.
The worm wheel has an annular inner wheel element that is externally fitted and fixed to the worm wheel shaft, and the worm wheel tooth portion on the outer peripheral surface, and is coupled to the inner wheel element, and is made of a synthetic resin. With a wheel element,
The outer wheel element is an insert-molded product into which the inner wheel element is inserted, and has an insert covering portion that is a portion that is insert-molded so as to cover a part of the surface of the worm wheel shaft.
Warm wheel unit. The worm wheel shaft has pinion teeth on the outer peripheral surface.
The worm wheel unit according to claim 11. The inner wheel element is externally fitted and fixed to one end of the worm wheel shaft on one side in the axial direction.
The worm wheel unit according to claim 11 or 12. The insert covering portion includes a disc portion that covers an end face on one side in the axial direction of the worm wheel shaft.
The worm wheel unit according to claim 13. The worm wheel shaft has a concave hole that opens on one end surface in the axial direction.
The insert covering portion includes a resin engaging portion that engages with the concave hole.
The worm wheel unit according to claim 14. The concave hole has an inner diameter side recess that is recessed outward in the radial direction on the inner peripheral surface.
The resin engaging portion includes an inner diameter side convex portion that prevents axial displacement of the outer wheel element with respect to the worm wheel shaft by engaging with the inner diameter side concave portion.
The worm wheel unit according to claim 15. The insert covering portion includes a shaft covering portion that covers a portion of the outer peripheral surface of the worm wheel shaft that is axially adjacent to the inner wheel element.
The worm wheel unit according to any one of claims 11 to 16. The worm wheel shaft has an outer diameter side recess that is recessed inward in the radial direction in a portion of the outer peripheral surface that is axially adjacent to the inner wheel element.
The shaft covering portion includes an outer diameter side convex portion that hinders axial displacement of the outer wheel element with respect to the worm wheel shaft by engaging with the outer diameter side concave portion.
The worm wheel unit according to claim 17. A worm wheel unit having a worm wheel shaft, a worm wheel tooth portion on the outer peripheral surface, and a worm wheel externally fitted and fixed to the worm wheel shaft.
A worm having a worm tooth portion that meshes with the worm wheel tooth portion is provided on the outer peripheral surface of the intermediate portion in the axial direction.
The worm wheel unit is the worm wheel unit according to any one of claims 11 to 18.
Warm reducer.

Images