JP2021046888A - Worm wheel, manufacturing method thereof and worm reduction gear - Google Patents

Abstract

To realize structure of a worm wheel which can improve productivity and quality.SOLUTION: A worm wheel 18 comprises an inside wheel element 22, and a synthetic resin-made outside wheel element 23 having a worm wheel tooth part 21, and embedding a radial-direction outside part of the inside wheel element 22 over an entire periphery. The inside wheel element 22 has an annular recess 56 at a side face at one side in an axial direction. The outside wheel element 23 has a pressing part 33 having a first inclined face part 31 which is inclined in a direction toward a center side in the axial direction as progressing toward the outside in the radial direction at the radial-direction outside part of side faces 29 at both sides in the axial direction, and engaged with an outside diameter side peripheral face 57 of the annular recess 56 while intruding into the annular recess 56. An internal peripheral face of the outside wheel element 23 at one side part in the axial direction has a second inclined face part 66 which is inclined in a direction progressing toward the inside in the radial direction as progressing toward the other side in the axial direction, and an end part of the second inclined face part 66 at the other side in the axial direction is located inside the annular recess 56.SELECTED DRAWING: Figure 7

Description

The present invention relates to a worm reducer, a worm wheel constituting the worm reducer, and a method for manufacturing the same.

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 the output shaft connected to the front end of the steering shaft via the torsion bar and the steering members such as the pinion shaft or the 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. In some cases, the part of the worm wheel that is externally fitted and fixed to the rotating shaft is made of metal, and the part that meshes with the worm is made of synthetic resin.

FIG. 16 shows an example of a worm wheel having such a configuration, which is described in International Publication No. 2017/135140 (Patent Document 1). In the following description, with respect to the worm wheel 100, one side in the axial direction is the left side in FIGS. 16 and 17, and the other side in the axial direction is the right side in FIGS. 16 and 17.

The worm wheel 100 is made of synthetic resin and is annular in a state in which a metal annular inner wheel element 101 and a radial outer portion of the inner wheel element 101 are embedded over the entire circumference and coupled to the inner wheel element 101. The outer wheel element 102 of the above is provided. The outer wheel element 102 has a worm wheel tooth portion 103 on the outer peripheral surface over the entire width in the axial direction. The side surfaces 104 on both sides of the outer wheel element 102 in the axial direction, including the side surfaces on both sides in the axial direction of the worm wheel tooth portion 103, are formed by a plane orthogonal to _{the central axis X 100 of the worm wheel 100.}

When manufacturing the worm wheel 100, the outer wheel element 102 is manufactured by injection molding, and at the same time, the outer wheel element 102 is coupled to the inner wheel element 101.

When the outer wheel element 102 is manufactured by injection molding, as shown in FIG. 17, the inner wheel element 101 is set inside the mold device 105 formed by combining a plurality of molds, and the inner wheel element 101 is set. The molten resin is fed from the runner 107 and the disk gate 108 provided on the other side in the axial direction of the mold device 105 into the annular cavity 106 defined between the mold device 105 and the mold device 105. The downstream end of the disc gate 108 is formed by a portion of the cavity 106 adjacent to the other side in the axial direction of the radial intermediate portion of the inner wheel element 101 (the inner peripheral surface of the other side in the axial direction of the outer wheel element 102 is formed. It is open to the part to be used). The runner 107 extends from the center of the disc gate 108 to the other side in the axial direction. The arrows in FIG. 17 indicate the flow direction of the molten resin in the runner 107, the disc gate 108, and the cavity 106.

The synthetic resin cooled and solidified in the cavity 106 opens the mold device 105 to separate the plurality of molds from each other, and then separates the synthetic resin cooled and solidified in the runner 107 and the disk gate 108. Then, if necessary, the surface and corners of the outer wheel element 102 are finished to complete the worm wheel 100.

International Publication No. 2017/135140

The conventional worm wheel 100 described above has room for improvement in terms of improving productivity and quality. This point will be described below.

When the outer wheel element 102 is manufactured by injection molding, the molten resin sent into the cavity 106 from the runner 107 and the disc gate 108 is a radial outer portion of the inner wheel element 101 as shown by an arrow in FIG. It flows from the portion adjacent to the other side in the axial direction, via the portion adjacent to the radially outer side of the inner wheel element 101, and toward the portion adjacent to the axial one side of the radially outer portion of the inner wheel element 101. The direction of the flow of the molten resin at this time changes along the mold.

On the other hand, each of the side surfaces 104 on both sides of the outer wheel element 102 in the axial direction is formed by a plane orthogonal to _{the central axis X 100 (see FIG. 16) of the worm wheel 100.} That is, the axial side surface of the worm wheel tooth portion 103 and the radial outer end surface (tooth tip surface) of the worm wheel tooth portion 103 are arranged at right angles. Therefore, the direction of the flow of the molten resin changes abruptly at the axial end portion (P portion in FIG. 17) of the worm wheel tooth portion 103. Therefore, if the injection speed is increased, the molten resin may entrain air at the axial end portion (P portion in FIG. 17) of the worm wheel tooth portion 103 to form a nest (vacancy). Therefore, it is necessary to reduce the injection rate in order to prevent the formation of such a nest.

However, when the injection speed is reduced, the molding time is lengthened accordingly, and the productivity of the worm wheel 100 is lowered (the production cost per piece is increased). Therefore, from the viewpoint of improving the productivity of the worm wheel 100, it is desired to increase the injection speed while preventing the formation of nests.

Further, in general, in injection molding, the higher the injection speed, the better the transferability to the mold, and the dimensional accuracy of the worm wheel tooth portion 103 and the surface roughness of the tooth surface can be ensured better. In particular, when the synthetic resin contains reinforcing fibers, the amount of the reinforcing fibers exposed on the surface can be suppressed, and the surface roughness of the tooth surface tends to be small. If the dimensional accuracy of the worm wheel tooth 103 and the surface roughness of the tooth surface can be improved in this way, vibration, fluctuation, sound, etc., occur when the worm wheel tooth 103 and the worm tooth mesh with each other. Can be less likely to occur. As a result, it is possible to improve the feeling of operation of the steering wheel by the driver, the controllability of the electric power steering device, the quietness, and the like. Therefore, from such a viewpoint, it is desired to be able to increase the injection speed.

Even when the injection speed is reduced, the gear accuracy of the worm wheel tooth portion 103 can be improved or the tooth surface roughness can be reduced by performing additional gear cutting after injection molding. .. However, there is a problem that the productivity becomes lower when the additional gear cutting process is performed.

In view of the above circumstances, it is an object of the present invention to realize a structure of a worm wheel that can improve productivity and quality.

The worm wheel of the present invention has an annular inner wheel element and a worm wheel tooth portion on the outer peripheral surface, and the inner wheel element is embedded in the radial outer portion of the inner wheel element over the entire circumference. It comprises a coupled, synthetic resin, annular outer wheel element.
The inner wheel element has an annular recess recessed in the axial direction on one side surface in the axial direction over the entire circumference.
The outer wheel element has a first inclined surface portion inclined in a direction toward the central side in the axial direction toward the outer side in the radial direction on the outer side portion in the radial direction of at least one of the side surfaces on both sides in the axial direction. In addition, it has a holding portion that enters the inside of the annular recess and engages with the outer diameter side peripheral surface that constitutes the inner surface of the annular recess.
The inner peripheral surface of the axial one-sided portion of the outer wheel element, including the inner peripheral surface of the holding portion, is inclined in at least one axial direction and inward in the radial direction toward the other axial direction. It has a second inclined surface portion, and an end portion of the second inclined surface portion on the other side in the axial direction is arranged inside the annular recess.

In one aspect of the worm wheel of the present invention, a gate separating portion exists on the inner peripheral surface of the other side portion in the axial direction of the outer wheel element.

In one aspect of the worm wheel of the present invention, the inner diameter of the first inclined surface portion is equal to or smaller than the tooth bottom diameter of the worm wheel tooth portion.

In one aspect of the worm wheel of the present invention, the inner diameter of the first inclined surface portion is larger than the tooth bottom diameter of the worm wheel tooth portion.

In one aspect of the worm wheel of the present invention, the inner diameter of the first inclined surface portion is larger than the outer diameter of the inner wheel element.

In one aspect of the worm wheel of the present invention, on the side of the worm wheel where the first inclined surface portion exists in the axial direction, the side surface of the outer wheel element is adjacent to the inside of the first inclined surface portion in the radial direction. partial axial width between the side surface of the radially outer end of the inner wheel element (e.g., W _a in FIGS. 7 and 8), the first inclined surface portion of the axial width (e.g., FIGS. 7 and It is larger than _{W b} ) in FIG.

In one aspect of the worm wheel of the present invention, reinforcing fibers are mixed in the synthetic resin.

In one aspect of the worm wheel of the present invention, the tooth surface of the worm wheel tooth portion is an injection molded surface.

In one aspect of the worm wheel of the present invention, the tooth streaks of the worm wheel teeth are parallel to the central axis of the worm wheel.

In one aspect of the worm wheel of the present invention, the inner wheel element has a concavo-convex portion in the circumferential direction on the outer diameter side peripheral surface forming the inner surface of the annular recess, and the restraining portion has the concavo-convex portion. It has a rotation direction holding portion that enters the inside of the concave portion constituting the portion and engages with the concave portion.

In one aspect of the worm wheel of the present invention, the inner wheel element has an engaging groove recessed outward in the radial direction on the outer diameter side peripheral surface forming the inner surface of the annular recess over the entire circumference. The holding portion has a moment direction holding portion that enters the inside of the engaging groove and engages with the engaging groove.

In one aspect of the worm wheel of the present invention, the engaging groove is arranged adjacent to one side in the axial direction of the uneven portion.

The method for manufacturing a worm wheel of the present invention is a method for manufacturing a worm wheel of the present invention.
In such a method for manufacturing a worm wheel of the present invention, a mold is arranged around a radial outer portion of the inner wheel element, and the outer side is defined between the inner wheel element and the mold. The outer wheel element is formed by injection molding in which a synthetic resin is fed into a cavity which is a molding space for the wheel element.

In one aspect of the method for manufacturing a worm wheel of the present invention, when the injection molding is performed, a disc gate is formed in a portion of the cavity where an inner peripheral surface of the other side in the axial direction of the outer wheel element is formed. Open the downstream end of a gate such as a ring gate.

The worm reducer of the present invention includes a worm wheel having a worm wheel tooth portion on the outer peripheral surface, and a worm having a worm tooth portion that meshes with the worm wheel tooth portion on the outer peripheral surface of the intermediate portion in the axial direction.
In particular, in the worm reducer of the present invention, the worm wheel is the worm wheel of the present invention.

According to the present invention, the productivity and quality of the worm wheel 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 perspective view of the worm wheel of the first example of the embodiment. FIG. 6 is a view of the worm wheel of the first example of the embodiment as viewed from the axial direction. FIG. 7 is a cross-sectional view taken along the line CC of FIG. FIG. 8 is an enlarged view of the upper part of FIG. 7. FIG. 9 is a cross-sectional view showing a process of injection molding the outer wheel element. FIG. 10 is a perspective view of the worm wheel of the second example of the embodiment. FIG. 11 is a view of the worm wheel of the second example of the embodiment as viewed from the axial direction. FIG. 12 is a cross-sectional view taken along the line DD of FIG. FIG. 13 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. 14 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. 15 is a perspective view showing a steering device of a steer-by-wire system to which the present invention can be applied. FIG. 16 is a cross-sectional view of a conventional worm wheel. FIG. 17 is a cross-sectional view showing a process of injection molding an outer wheel element constituting a conventional worm wheel.

[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 column assist type electric power steering device 1 incorporating the worm reducer 16 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, an electric assist device 5, a pair of universal joints 6a and 6b, an intermediate shaft 7, and a steering gear unit 8. And a pair of tie rods 9.

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 includes an electric assist device 5, a universal joint 6a on the rear side, an intermediate shaft 7, and a universal joint on the front side. It is connected to the pinion shaft 10 of the steering gear unit 8 via the joint 6b. Therefore, when the driver rotates the steering wheel 2, the rotation of the steering wheel 2 is transmitted to the pinion shaft 10. The rotation of the pinion shaft 10 is converted into a linear motion of a rack shaft (not shown) of the steering gear unit 8 that meshes with the pinion shaft 10 and pushes and pulls a pair of tie rods 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 5 includes a housing 11, an electric motor 12, a torsion bar 13, an output shaft 14, a pair of ball bearings 15a and 15b, a worm reducer 16, and a torque sensor 17.

The housing 11 is coupled and fixed to the front end portion of the steering column 4. The electric motor 12 is supported and fixed to the housing 11. The front end portion of the steering shaft 3 is inserted inside the housing 11. An output shaft 14 is connected to the front end of the steering shaft 3 via a torsion bar 13. The front end portion of the output shaft 14 projects forward from the front end surface of the housing 11, and the rear universal joint 6a is coupled to the front end portion. The output shaft 14 is supported only in rotation by a pair of ball bearings 15a and 15b with respect to the housing 11 at the intermediate portion in the axial direction.

The worm reducer 16 includes a worm wheel 18 and a worm 19. The worm wheel 18 is externally fitted and fixed to a portion of the output shaft 14 located between the pair of ball bearings 15a and 15b in the axial direction. On the other hand, the worm 19 is connected to the output shaft of the electric motor 12 so as to be able to transmit torque. Then, the worm tooth portion 20 provided on the outer peripheral surface of the axially intermediate portion of the worm 19 and the worm wheel tooth portion 21 provided on the outer peripheral surface of the worm wheel 18 are meshed with each other. As a result, auxiliary torque (auxiliary power) can be applied to the worm wheel 18 from the electric motor 12 via the worm 19.

In this example, the worm wheel tooth portion 21 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 21 are parallel to _{the central axis X 18 of the worm wheel 18.} Accordingly, in the present embodiment, the intersection angle between the center axis X ₁₉ of the central axis X ₁₈ and the worm 19 of the worm wheel 18 and alpha, if the lead angle of the worm teeth 20 was 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 20 and the intersection angle α is 90 °.

The torque sensor 17 is arranged around the rear end portion of the output shaft 14. The torque sensor 17 detects the direction and magnitude of the torque applied to the steering shaft 3 from the steering wheel 2. The electric motor 12 assists the output shaft 14 via the worm wheel 18 by rotationally driving the worm 19 based on the detection signal of the torque sensor 17 and the vehicle speed signal output from the vehicle speed sensor incorporated in the transmission. Apply torque. As a result, the force required for the driver to rotate the steering wheel 2 is reduced.

In this example, the worm wheel 18 is composed of an inner wheel element 22 and an outer wheel element 23. In the following description, with respect to the worm wheel 18, one side in the axial direction is the left side of FIGS. 3 to 5 and 7 to 9, and the other side in the axial direction is shown in FIGS. 3 to 5 and 7 to 7. It is on the right side of 9.

The inner wheel element 22 is a metal annular member, and is formed in a ring shape as a whole. The inner wheel element 22 has a fitting hole 51 that fits with the axial intermediate portion of the output shaft 14 at the central portion in the radial direction.

The inner wheel element 22 has an annular recess 52 recessed in the axial direction over the entire circumference on the outer side in the radial direction of the side surface on the other side in the axial direction. Of the outer diameter side peripheral surface 53, the inner diameter side peripheral surface 54, and the bottom surface 55 that form the inner surface of the annular recess 52, the outer diameter side peripheral surface 53 is the central axis of the inner wheel element 22 (= the central axis of the worm wheel 18). It is composed of a cylindrical surface centered on X _{18 (see FIG. 7).} The inner diameter side peripheral surface 54 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 the other side in the axial direction. The bottom surface 55 is formed by a plane orthogonal to the central axis of the inner wheel element 22.

The inner wheel element 22 has an annular recess 56 recessed in the axial direction over the entire circumference in the radial intermediate portion of the side surface on one side in the axial direction. Of the outer diameter side peripheral surface 57, the inner diameter side peripheral surface 58, and the bottom surface 59 that form the inner surface of the annular recess 56, the outer diameter side peripheral surface 57 has an engaging groove 27 and an uneven portion 28. The engaging groove 27 is formed at the end of the outer diameter side peripheral surface 57 on the other side in the axial direction so as to be recessed outward in the radial direction over the entire circumference. The engaging groove 27 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 28 is formed over the entire circumference of the outer diameter side peripheral surface 57 in the remaining portion deviating from the engaging groove 27 on one side in the axial direction. In other words, the engaging groove 27 is arranged adjacent to the other side of the uneven portion 28 in the axial direction. The concavo-convex portion 28 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 27 is deeper than the radial depth of the plurality of recesses constituting the uneven portion 28. In other words, the bottom portion of the engaging groove 27 is located radially outside the bottom portions of the plurality of recesses constituting the uneven portion 28. The inner diameter side peripheral surface 58 is formed of a cylindrical surface centered on the central axis of the inner wheel element 22. The bottom surface 59 is formed by a plane orthogonal to the central axis of the inner wheel element 22.

The outer peripheral surface 60 of the inner wheel element 22 is formed of a cylindrical surface centered on the central axis of the inner wheel element 22. Axial side surfaces 50 of the radial outer end of the inner wheel element 22, that is, side surfaces 50 of the other side of the inner wheel element 22 in the axial direction, which are adjacent to the radial outer side of the annular recess 52, and Of the side surfaces on one side in the axial direction of the inner wheel element 22, each of the side surfaces 50, which are adjacent to the radial outer side of the annular recess 56, is formed by a plane orthogonal to the central axis of the inner wheel element 22. There is. In the illustrated example, the ends on both sides of the outer peripheral surface 60 in the axial direction and the end portions on the outer sides in the radial direction of the side surface 50 are connected by chamfered portions having an arcuate cross-sectional shape.

In this example, in other words, the inner wheel element 22 has a cylindrical shape in which the inner diameter side annular portion 24 and the inner diameter side annular portion 24 are arranged coaxially with the inner diameter side annular portion 24. The radial inner end was coupled to the outer peripheral surface of the outer diameter side annular portion 25 and the inner diameter side annular portion 24, and the radial outer end was coupled to the inner peripheral surface of the outer diameter side annular portion 25. A ring-shaped connecting portion 26 is provided. The fitting hole 51 corresponds to the central hole of the inner diameter side annular portion 24. The outer diameter side peripheral surface 53 constituting the inner surface of the annular recess 52 corresponds to the inner peripheral surface of the other side portion in the axial direction of the outer diameter side annular portion 25. The inner diameter side peripheral surface 54 and the bottom surface 55 constituting the inner surface of the annular recess 52 correspond to the radial outer portion of the side surface on the other side in the axial direction of the connecting portion 26. The outer diameter side peripheral surface 57 constituting the inner surface of the annular recess 56 corresponds to the inner peripheral surface of one side in the axial direction of the outer diameter side annular portion 25. The inner diameter side peripheral surface 58 constituting the inner surface of the annular recess 56 corresponds to the outer peripheral surface of one side in the axial direction of the inner diameter side annular portion 24. The bottom surface 59 constituting the inner surface of the annular recess 56 corresponds to the side surface of the connecting portion 26 on one side in the axial direction. The outer peripheral surface 60 corresponds to the outer peripheral surface of the outer diameter side annular portion 25. The pair of side surfaces 50 correspond to the side surfaces on both sides in the axial direction of the outer diameter side annular portion 25.

In the illustrated example, the radial inner end of the connecting portion 26 is coupled to the axially opposite end of the outer peripheral surface of the inner diameter side annular portion 24, and the radial outer end of the connecting portion 26 is , It is coupled to the axial intermediate portion (specifically, the portion of the axial intermediate portion closer to the other side in the axial direction) of the inner peripheral surface of the outer diameter side annular portion 25. 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.

As the metal constituting the inner wheel element 22, various metals such as a copper alloy, an aluminum alloy, and a magnesium alloy can be adopted in addition to an iron alloy such as steel. As the processing for forming the inner wheel element 22, 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 27 can function as a relief for a mold (die) used when the uneven portion 28 is formed by plastic working.

The outer wheel element 23 is made of synthetic resin and is formed in an annular shape, and encloses the outer diameter side annular portion 25 and the radial outer portion of the connecting portion 26, which are the radial outer portions of the inner wheel element 22, over the entire circumference. In the buried state, it is coupled to the inner wheel element 22.

The outer wheel element 23 has a worm wheel tooth portion 21 on the outer peripheral surface over the entire width in the axial direction. The worm wheel tooth portion 21 has a shape like the tooth portion of a straight tooth spur gear, and its tooth streaks are _{parallel to the central axis X 18} of the worm wheel 18 (see FIG. 4).

Each of the side surfaces 29 on both sides of the outer wheel element 23 in the axial direction includes a flat surface portion 30 forming a radial inner portion and a first inclined surface portion 31 forming a radial outer portion. That is, the radial outer end of the flat surface portion 30 is connected to the radial inner end of the first inclined surface portion 31. The flat surface portion 30 is formed by a flat surface orthogonal to _{the central axis X 18 of the worm wheel 18.} The first inclined surface portion 31 is formed of a conical surface that is inclined toward the center side in the axial direction of the worm wheel 18 toward the outer side in the radial direction.

In this example, the inner diameter (= outer diameter of the flat surface portion 30) D ₃₁ of the first inclined surface portion 31 is regulated to be equal to or less than _{the tooth bottom diameter D 21} of the worm wheel tooth portion 21 _{(D 31} ≤ D ₂₁ ). In the example of, it is smaller than _{the tooth bottom diameter d 21 of the worm wheel tooth portion 21 (D 31} <D ₂₁ ). That is, each of the side surfaces of the worm wheel tooth portions 21 on both sides in the axial direction is composed of the first inclined surface portions 31 as a whole.

In this example, on each side of the one axial side and the other side in the axial direction of the worm wheel 18, the axial width W _a between the flat portion 30 and the side surface 50 of the inner wheel element 22 of the outer wheel element 23 _{, The width in the axial direction W b} of the first inclined surface portion 31 of the outer wheel element 23 is made larger (W _a > W _b ). Further, the inner diameter D ₃₁ of the first inclined surface portion 31 is made larger than the outer diameter D ₂₂ of the inner wheel element _{22 (D 31> D 22)} . However, when the present invention is carried out _{, a configuration in which W a} ≤ W _b or a configuration in which D ₃₁ ≤ D ₂₂ can be adopted can also be adopted.

In the synthetic resin constituting the outer wheel element 23, the portion that has entered the radial outer portion inside the annular recess 52 constitutes the holding portion 32, and the portion that has entered the radial outer portion inside the annular recess 56 is formed. The holding portion 33 is configured. Then, based on the engagement between the outer diameter side peripheral surface 53 of the annular recess 52 and the holding portion 32, and the engagement between the outer diameter side peripheral surface 57 of the annular recess 56 and the holding portion 33, that is, the holding portion 32. By holding the outer diameter side annular portion 25 so as to be held by the 33, the holding force of the outer wheel element 23 with respect to the inner wheel element 22 in the moment direction is enhanced. Further, in this example, a part of the synthetic resin constituting the holding portion 33 enters the inside of the engaging groove 27 of the outer diameter side peripheral surface 57 to form the moment direction holding portion 61 that engages with the engaging groove 27. are doing. Then, by engaging the engaging groove 27 with the moment direction holding portion 61, the holding force of the outer wheel element 23 with respect to the inner wheel element 22 in the moment direction is further increased.

Further, in this example, a part of the synthetic resin constituting the holding portion 33 enters the inside of a plurality of recesses constituting the uneven portion 28 of the outer diameter side peripheral surface 57, and holds the rotation direction to engage with the recesses. It constitutes a part 62. Then, by engaging the concave portion with the rotation direction holding portion 62, the holding force of the outer wheel element 23 in the rotation direction with respect to the inner wheel element 22 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 63 of the other side portion in the axial direction of the outer wheel element 23 is formed of a conical surface (inclined surface portion) that is inclined inward in the radial direction toward one side in the axial direction. The end of the inner peripheral surface 63 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 29 (plane portion 30) on the other side in the axial direction of the outer wheel element 23. One end of the inner peripheral surface 63 in the axial direction is connected to the radial intermediate portion of the bottom surface 55 of the annular recess 52. One side of the inner peripheral surface 63 in the axial direction corresponds to the inner peripheral surface of the holding portion 32, and enters the inside of the annular recess 52.

The inner peripheral surface 64 of one side portion in the axial direction of the outer wheel element 23 includes a cylindrical surface portion 65 forming the other side portion in the axial direction and a second inclined surface portion 66 forming one side portion in the axial direction. The cylindrical surface portion 65 is composed of a cylindrical surface centered on _{the central axis X 18 of the worm wheel 18.} The second inclined surface portion 66 is formed of a conical surface that is inclined inward in the radial direction toward the other side in the axial direction. The end of the cylindrical surface portion 65 on the other side in the axial direction is connected to the radial outer portion of the bottom surface 59 constituting the annular recess 56. The end portion of the cylindrical surface portion 65 on one side in the axial direction is connected to the end portion of the second inclined surface portion 66 on the other side in the axial direction. The end portion on one side in the axial direction of the second inclined surface portion 66 is connected to the end portion on the inner side in the radial direction of the side surface 29 (plane portion 30) on one side in the axial direction of the outer wheel element 23. The ends of the cylindrical surface portion 65 and the second inclined surface portion 66 on the other side in the axial direction correspond to the inner peripheral surface of the holding portion 33, and are arranged inside the annular recess 56. That is, in this embodiment, the axial width W ₆₆ of the second inclined surface 66 is larger than the axial width W _a between the flat portion 30 and the side surface 50 in the one axial side of the worm wheel 18 ( W _66> W _a). In the case of carrying out the present invention, the inner peripheral surface of one side portion in the axial direction of the outer wheel element 23 is a second inclined surface portion that is inclined inward in the radial direction toward the other side in the axial direction. You can also do it.

As the synthetic resin constituting the outer wheel element 23, 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.

When manufacturing the worm wheel 18, the outer wheel element 23 is manufactured by injection molding, and at the same time, the outer wheel element 23 is coupled to the inner wheel element 22.

When the outer wheel element 23 is manufactured by injection molding, as shown in FIG. 9, the inner wheel element 22 is set in the mold device 34 formed by combining a plurality of molds, that is, the diameter of the inner wheel element 22. In the annular cavity 35, which is the molding space of the outer wheel element 23, defined between the inner wheel element 22 and the mold device 34 with a plurality of molds arranged around the outer portion in the direction. The molten resin is fed from the runner 36 and the disc gate 37 provided on the other side of the mold device 34 in the axial direction.

Here, the inner surface 40 of the mold device 34 constituting the cavity 35 has a shape that matches the outer surface of the outer wheel element 23. In particular, in this example, the first inclined surface forming portion 41, which is a portion of the inner surface 40 having a shape matching the first inclined surface portion 31, and the inner surface 40, the radial outer end surface of the worm wheel tooth portion 21. The tooth tip surface forming portion 42, which is a portion having a shape matching the (tooth tip surface), is arranged so as to form an obtuse angle. The downstream end E of the disc gate 37 is a portion of the cavity 35 adjacent to the other side in the axial direction of the radial intermediate portion of the inner wheel element 22 (inner peripheral surface 63 of the other side in the axial direction of the outer wheel element 23). Is open to the part where is formed). The runner 36 extends from the center of the disc gate 37 to the other side in the axial direction.

The arrows in FIG. 9 indicate the flow direction of the molten resin in the runner 36, the disc gate 37, and the cavity 35. That is, the molten resin sent into the cavity 35 from the runner 36 and the disc gate 37 is sent from a portion of the inner wheel element 22 adjacent to the other side in the axial direction of the radial outer portion of the inner wheel element 22, as shown by an arrow in FIG. It flows through a portion adjacent to the radial outer side of the inner wheel element 22 and toward a portion adjacent to one axial side of the radial outer portion of the inner wheel element 22. The direction of the flow of the molten resin at this time changes along the inner surface 40 of the mold device 34. In particular, in this example, of the inner surface 40 of the mold device 34, the first inclined surface forming portion 41 and the tooth tip surface forming portion 42 are arranged so as to form an obtuse angle. Therefore, the direction of the flow of the molten resin gradually changes at the axial end portion (Q portion in FIG. 9) of the cavity 35 where the worm wheel tooth portion 21 should be formed.

Further, in this example, the worm wheel tooth portion 21 has a shape like the tooth portion of a straight tooth spur gear, and its tooth streak is parallel to _{the central axis X 18 of the worm wheel 18.} Therefore, the molten resin passes straight (smoothly) in the axial direction through the portion of the cavity 35 where the worm wheel tooth portion 21 should be formed.

Further, in this example, the axial width W between the flat surface portion 30 of the outer wheel element 23 and the side surface 50 of the inner wheel element 22 on each side of the worm wheel 18 in the axial direction and the other side in the axial direction. _The configuration in which a is made larger than _{the axial width W b} of the first inclined surface portion 31 of the outer wheel element 23 _{(W a} > W _{b ) and the inner diameter D 31} of the first inclined surface portion 31 are set outside the inner wheel element 22. At least one of the configurations (D ₃₁ > D _{22 ) having a diameter larger than D 22} (both configurations in this example) is adopted. Therefore, in the cavity 35, a portion of the inner wheel element 22 adjacent to the other side in the axial direction of the radial outer portion and a portion of the inner wheel element 22 adjacent to the other side of the radial outer portion in the axial direction, respectively. It is possible to prevent the flow path of the molten resin from being sharply narrowed in the above portion. Therefore, the molten resin can easily pass through these portions.

Further, in this example, the inner peripheral surface 64 of one side portion in the axial direction of the outer wheel element 23 is a second inclined surface portion inclined in the direction toward the inner side in the radial direction toward the other side in the axial direction toward the one side portion in the axial direction. The end of the second inclined surface portion 66 on the other side in the axial direction is arranged inside the annular recess 56. Therefore, of the inner surface 40 of the cavity 35, the end portion on the other side in the axial direction of the second inclined surface forming portion 67, which is a portion having a shape matching the second inclined surface portion 66, is also arranged inside the annular recess 56. ing. Therefore, of the cavity 35, the molten resin that has passed through the portion of the inner wheel element 22 adjacent to one side in the axial direction of the radial outer portion from the radial outer side to the radial inner side is passed to the second inclined surface forming portion 67. Along the route, it can be smoothly guided to the inside of the annular recess 56.

The synthetic resin cooled and solidified in the cavity 35 opens the mold device 34 to separate the plurality of molds from each other, and then separates the synthetic resin cooled and solidified in the runner 36 and the disk gate 37. Then, if necessary, the surface and corners of the outer wheel element 23 are finished to complete the worm wheel 18. However, in this example, during this finishing process, no additional gear cutting process is performed on the tooth surface 39, which is the circumferential side surface of the plurality of teeth 38 constituting the worm wheel tooth portion 21. That is, in this example, the tooth surface 39 of the worm wheel tooth portion 21 remains as an injection-molded surface, which is a surface formed by injection molding. Further, in this example, in the completed worm wheel 18, a gate separating portion (a synthetic resin cooled and solidified in the disc gate 37) is applied to the inner peripheral surface 63 of the other side portion in the axial direction of the outer wheel element 23. 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 productivity and quality of the worm wheel 18 can be improved. This point will be described below.

In this example, when the outer wheel element 23 constituting the worm wheel 18 is manufactured by injection molding, the axial end portion of the cavity 35 where the worm wheel tooth portion 21 should be formed (Q portion in FIG. 9). In, the direction of the flow of the molten resin can be changed gently. Therefore, when the outer wheel element 23 is manufactured by injection molding, even if the injection speed is increased, air is less likely to be entrained by the molten resin in the portion of the cavity 35 where the worm wheel tooth portion 21 should be formed. Nests due to the entrainment are unlikely to be formed. Therefore, in this example, since the injection speed can be increased while preventing the formation of such a nest, the molding time of the outer wheel element 23 can be shortened accordingly, and the productivity of the worm wheel 18 is improved. (The production cost per piece can be suppressed).

Further, in this example, the molten resin can pass straight (smoothly) in the axial direction through the portion of the cavity 35 where the worm wheel tooth portion 21 should be formed. Therefore, from this aspect as well, the injection speed can be increased while preventing the formation of nests.

Further, in this example, the molten resin is applied to the portion of the cavity 35 adjacent to the other side in the axial direction of the radial outer portion of the inner wheel element 22 and the axial outer portion of the inner wheel element 22 to one side in the axial direction. It can easily pass through the adjacent portion. Therefore, the moldability of the outer wheel element 23 can be improved.

Further, in this example, the molten resin can be smoothly guided to the inside of the annular recess 56 along the second inclined surface forming portion 67 of the inner surface 40 of the cavity 35. Therefore, the molten resin is easily distributed inside the annular recess 56. Therefore, in this respect as well, the moldability of the outer wheel element 23 can be improved. That is, in this example, at the time of injection molding, the temperature of the molten resin tends to decrease in the vicinity of the engaging groove 27 and the uneven portion 28, which are farthest from the disc gate 37, and the injection speed of the molten resin tends to decrease. Therefore, by providing the second inclined surface forming portion 67 which is a slope toward the engaging groove 27 and the uneven portion 28, the distance between the engaging groove 27 and the uneven portion 28 and the second inclined surface forming portion 67 is narrowed. By doing so, Bernoulli's theorem suppresses the decrease in injection speed. This prevents the formation of welds due to uneven injection speed, and prevents the engagement strength between the engagement groove 27 and the moment direction holding portion 61 and the coupling strength between the uneven portion 28 and the rotation direction holding portion 62 from decreasing. ing.

Further, in this example, since the injection speed can be increased, the transferability to the mold can be improved, and the dimensional accuracy of the worm wheel tooth portion 21 and the surface roughness of the tooth surface 39 can be ensured satisfactorily. it can. In particular, when the synthetic resin contains reinforcing fibers, the amount of the reinforcing fibers exposed on the surface can be suppressed, and the surface roughness of the tooth surface 39 can be reduced. Thereby, when the worm wheel tooth portion 21 and the worm tooth portion 20 are engaged with each other, vibration, fluctuation, sound and the like can be made less likely to occur. 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 5, the quietness, and the like. Further, the amount of wear of the worm tooth portion 20 due to the reinforcing fibers exposed on the tooth surface 39 of the worm wheel tooth portion 21 can be suppressed. Further, since the surface roughness of the tooth surface 39 can be reduced only by injection molding, additional gear cutting is not required. Therefore, the productivity of the worm wheel 18 can be improved in this respect as well.

[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, in the outer wheel element 23a constituting the worm wheel 18a, the inner diameter D 31} of the first inclined surface portion 31a of the flat surface portion 30a and the first inclined surface portion 31a forming the side surfaces 29a on both sides in the axial direction is the worm wheel. It is larger than the tooth bottom diameter D _{21 of the tooth portion 21a (D 31} > D ₂₁ ). That is, in this example, each of the side surfaces of the worm wheel tooth portions 21a on both sides in the axial direction is composed of the first inclined surface portion 31a in the radial direction and the flat surface portion 30a in the radial inner portion. .. Therefore, in this example, as compared with the case of the first example of the embodiment, the axial width dimension of the tooth root of the worm wheel tooth portion 21a can be increased, and the strength of the tooth root can be improved. ..
Other configurations and effects are the same as in the first example of the embodiment.

The worm reducer of the present invention is not limited to the column assist type 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. 13, the worm wheel of the worm reducer 16a constituting the electric assist device 5a is supported and fixed to the pinion shaft 10a of the steering gear unit 8a.
In the rack-assisted electric power steering device 1b as shown in FIG. 14, the worm wheel of the worm reducer 16b constituting the electric assist device 5b is located at a portion of the steering gear unit 8b deviating from the pinion shaft 10 in the width direction of the vehicle. The pinion shaft 43 is arranged so as to be fitted and fixed to the outside, and the pinion shaft 43 is meshed with the rack shaft 44 of the steering gear unit 8b.

The worm reducer of the present invention can also be incorporated into, for example, a steer-by-wire type steering device 45 as shown in FIG. The steering device 45 of the steer-by-wire system includes a steering device 46 having a steering wheel 2 and a steering device 47 electrically connected to the steering device 46 for imparting a steering angle to a pair of steering wheels. .. When driving an automobile, the amount of rotational operation of the steering wheel 2 is detected by a sensor of the steering device 46, and the electric actuator 48 of the steering device 47 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 48 includes a worm reducer 16c for increasing the output torque of the electric motor 49 as a drive source, and the worm reducer of the present invention can be used as the worm reducer 16c.

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

In the case of carrying out the present invention, the first inclined surface portion may be provided only on one of the side surfaces of the outer wheel elements constituting the worm wheel in the axial direction. The first inclined surface portion may be provided over the entire radial width of the axial side surface of the outer wheel element.

1, 1a, 1b Electric power steering device 2 Steering wheel 3 Steering shaft 4 Steering column 5, 5a, 5b Electric assist device 6a, 6b Flexible joint 7 Intermediate shaft 8, 8a, 8b Steering gear unit 9 Tie rod 10, 10a Pinion shaft 11 Housing 12 Electric motor 13 Torsion bar 14 Output shaft 15a, 15b Ball bearing 16, 16a, 16b, 16c Warm reducer 17 Torque sensor 18, 18a Warm wheel 19 Warm 20 Warm tooth part 21, 21a Warm wheel tooth part 22 Inner wheel element 23, 23a Outer wheel element 24 Inner diameter side annular part 25 Outer diameter side annular part 26 Connecting part 27 Engagement groove 28 Concavo-convex part 29, 29a Side surface 30, 30a Flat part 31, 31a First inclined surface part 32 Holding part 33 Holding part 34 Mold device 35 Cavity 36 Runner 37 Disc gate 38 Tooth 39 Tooth surface 40 Inner surface 41 First inclined surface forming part 42 Tooth tip surface forming part 43 Pinion axis 44 Rack axis 45 Steering by wire type steering device 46 Steering device 47 Steering device 48 Electric actuator 49 Electric motor 50 Side surface 51 Fitting hole 52 Annular recess 53 Outer diameter side peripheral surface 54 Inner diameter side peripheral surface 55 Bottom surface 56 Circular recess 57 Outer diameter side peripheral surface 58 Inner diameter side peripheral surface 59 Bottom surface 60 Outer surface surface 61 Moment direction Holding part 62 Rotating direction holding part 63 Inner peripheral surface 64 Inner peripheral surface 65 Cylindrical surface part 66 Second inclined surface part 67 Second inclined surface forming part 100 Worm wheel 101 Inner wheel element 102 Outer wheel element 103 Warm wheel tooth part 104 Side surface 105 Gold Mold device 106 Cavity 107 Runner 108 Disc gate

Claims (15)

An annular inner wheel element and
An annular outer wheel element made of synthetic resin, which has a worm wheel tooth portion on the outer peripheral surface and is coupled to the inner wheel element in a state where the radial outer portion of the inner wheel element is embedded over the entire circumference. , With
The inner wheel element has an annular recess recessed in the axial direction on one side surface in the axial direction over the entire circumference.
The outer wheel element has a first inclined surface portion inclined in a direction toward the central side in the axial direction toward the outer side in the radial direction on the outer side portion in the radial direction of at least one of the side surfaces on both sides in the axial direction. In addition, it has a holding portion that enters the inside of the annular recess and engages with the outer diameter side peripheral surface that constitutes the inner surface of the annular recess.
The inner peripheral surface of the axial one-sided portion of the outer wheel element, including the inner peripheral surface of the holding portion, is inclined in at least one axial direction and inward in the radial direction toward the other axial direction. It has a second inclined surface portion, and the end portion on the other side in the axial direction of the second inclined surface portion is arranged inside the annular recess.
Warm wheel. A gate disconnection portion exists on the inner peripheral surface of the other side portion in the axial direction of the outer wheel element.
The worm wheel according to claim 1. The inner diameter of the first inclined surface portion is equal to or less than the tooth bottom diameter of the worm wheel tooth portion.
The worm wheel according to claim 1 or 2. The inner diameter of the first inclined surface portion is larger than the tooth bottom diameter of the worm wheel tooth portion.
The worm wheel according to claim 1 or 2. The inner diameter of the first inclined surface portion is larger than the outer diameter of the inner wheel element.
The worm wheel according to any one of claims 1 to 4. On the side of the worm wheel where the first inclined surface portion exists in the axial direction, a portion of the side surface of the outer wheel element adjacent to the inside of the first inclined surface portion in the radial direction and a portion outside the radial direction of the inner wheel element. The axial width between the side surface of the end portion is larger than the axial width of the first inclined surface portion.
The worm wheel according to any one of claims 1 to 5. Reinforcing fibers are mixed in the synthetic resin.
The worm wheel according to any one of claims 1 to 6. The tooth surface of the worm wheel tooth portion is an injection molded surface.
The worm wheel according to any one of claims 1 to 7. The tooth streaks of the worm wheel teeth are parallel to the central axis of the worm wheel.
The worm wheel according to any one of claims 1 to 8. The inner wheel element has an uneven portion in the circumferential direction on the outer diameter side peripheral surface forming the inner surface of the annular recess.
The holding portion has a rotation direction holding portion that enters the inside of the concave portion constituting the concave-convex portion and engages with the concave portion.
The worm wheel according to any one of claims 1 to 9. The inner wheel element has an engaging groove recessed outward in the radial direction over the entire circumference on the outer diameter side peripheral surface forming the inner surface of the annular recess.
The holding portion has a moment direction holding portion that enters the inside of the engaging groove and engages with the engaging groove.
The worm wheel according to any one of claims 1 to 10. The engaging groove is arranged adjacent to one side in the axial direction of the uneven portion.
The worm wheel according to claim 11, which cites claim 10. The method for manufacturing a worm wheel according to any one of claims 1 to 12.
A mold is arranged around the radial outer portion of the inner wheel element, and a synthetic resin is placed in a cavity which is a molding space of the outer wheel element, which is defined between the inner wheel element and the mold. The outer wheel element is formed by injection molding by feeding.
How to make a worm wheel. When the injection molding is performed, the downstream end portion of the gate is opened in the portion of the cavity where the inner peripheral surface of the other side portion in the axial direction of the outer wheel element is formed.
The method for manufacturing a worm wheel according to claim 13. A worm wheel with worm wheel teeth on the outer peripheral surface,
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 is the worm wheel according to any one of claims 1 to 12.
Warm reducer.

Images