JP4273296B2 - Worm wheel and its mold - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a worm wheel suitable for being molded and a mold for manufacturing the worm wheel.
[0002]
[Prior art]
For example, in an electric power steering device that transmits the rotation of a steering assist force generation motor to a wheel through a worm and a worm wheel meshing with the worm so that the steering angle changes, the worm wheel is made of a synthetic resin material. Therefore, weight reduction and noise reduction are achieved.
[0003]
Conventionally, the worm wheel has been formed by hobbing a synthetic resin material. However, since a large amount of burrs are generated when the hobbing is performed, a huge amount of man-hours are required for removing the burrs.
[0004]
Therefore, it is conceivable to mold the worm wheel. However, the teeth of a normal worm wheel have a thinner tooth thickness and a longer tooth length at the center position in the tooth trace direction than at both end positions, so the molded worm wheel cannot be punched from the mold in the tooth trace direction. . Therefore, when trying to mold the worm wheel, it is necessary to form the mold from a large number of members arranged in parallel in the rotational circumferential direction of the worm wheel, and to perform die cutting along the radial direction of the worm wheel. If it does so, the structure of a shaping | molding die will become very complicated, manufacturing cost will increase, and a shaping | molding precision will fall.
[0005]
Therefore, as shown in FIG. 8, the tooth surface 101a on one side and the tooth surface 101b on the other side in the rotational direction of each tooth 101 of the worm wheel 100 are replaced with helical surface portions 101a 'and 101b' having the same shape as the tooth surface of the helical gear. And a concave curved surface portion 101a ″, 101b ″ along a convex curved tooth surface of a worm (not shown). (Japanese Patent Laid-Open No. 2001-280428). In this conventional example, on each tooth surface 101a, 101b, helical surface portions 101a ', 101b' are arranged on one side in the rotation axis direction, and concave curved surface portions 101a ", 101b" are arranged on the other side. As a result, in each of the tooth surfaces 101a and 101b, the distance between the tooth surfaces in the concave curved surface portions 101a ″ and 101b ″ opposite to the tooth height direction dimension increases toward the boundary with the helical surface portions 101a ′ and 101b ′. . In the helical surface portions 101a 'and 101b', the distance between the tooth surfaces opposite to the tooth height direction dimension is constant in the tooth line direction. Therefore, when the worm wheel 100 is molded, the molded worm wheel 100 can be punched from the molding die in the direction of the helical surface portions 101a ′ and 101b ′ (arrow direction H in the drawing).
[0006]
[Problems to be solved by the invention]
In the conventional worm wheel 100, the helical surface portions 101a 'and 101b' are arranged on one side in the rotation axis direction on all the tooth surfaces 101a and 101b, and the concave curved surface portions 101a "and 101b" are arranged on the other side. ing. Further, as indicated by a two-dot chain line in FIG. 8, since the tooth surface 102 of the worm is a convex curved surface, the contact region with the concave curved surface portions 101a ″ and 101b ″ rather than the contact region with the helical surface portions 101a ′ and 101b ′. Becomes larger. Therefore, when the rotational force is transmitted from the worm to the worm wheel 100, the force is biased to the other side in the rotational axis direction where the concave curved surface portions 101a "and 101b" are arranged. As a result, smooth rotation transmission is hindered, and there is a problem that the life is shortened due to uneven wear and breakage of the tooth surfaces of the worm and the worm wheel 100.
An object of this invention is to provide the worm wheel which can solve the said subject, and the shaping | molding die for its manufacture.
[0007]
[Means for Solving the Problems]
The worm wheel of the present invention includes a plurality of teeth that mesh with the teeth of the worm, and a tooth surface on one side and a tooth surface on the other side in the rotational direction of each tooth include a helical surface portion having the same shape as the tooth surface of the helical gear. And a concave curved surface portion along the convex curved tooth surface of the worm. Each tooth surface includes a plurality of first tooth surfaces in which a helical surface portion is disposed on one side in the rotational axis direction of the worm wheel and a concave curved surface portion is disposed on the other side, and concave in one side in the rotational axis direction. It is classified into a plurality of second tooth surfaces in which the curved surface portion is disposed and the helical surface portion is disposed on the other side, and each first tooth surface is disposed so as to face the first tooth surface, and each second tooth surface is disposed. The tooth surface is arranged so as to face the second tooth surface, and in the concave curved surface portion of each of the first and second tooth surfaces, the tooth height direction dimension increases toward the boundary with the helical surface portion, and the teeth facing each other. The distance between the surfaces increases as it goes to the boundary with the helical surface portion. In the helical surface portions of the first and second tooth surfaces, the tooth height direction dimension is constant in the tooth trace direction and the distance between the tooth surfaces facing each other. The distance is constant in the tooth trace direction. To.
According to the present invention, on the first tooth surface, the helical surface portion is disposed on one side in the rotation axis direction and the concave curved surface portion is disposed on the other side, and on the second tooth surface, the helical surface portion is disposed on one side in the rotation axis direction. A concave curved surface portion is disposed and a helical surface portion is disposed on the other side. Thereby, the bias direction of the force acting on the worm wheel from the worm is reversed between the position where the tooth surface of the worm contacts the first tooth surface and the position where the tooth surface contacts the second tooth surface. Therefore, it is possible to suppress the bias of the force acting on the worm wheel from the worm. In addition, each first tooth surface is disposed so as to face the first tooth surface, each second tooth surface is disposed so as to face the second tooth surface, and the concave curved surface portion is relative to the tooth height direction dimension. The distance between the facing tooth surfaces increases as it goes toward the boundary with the helical surface portion. In the helical surface portion, the distance between the tooth height direction dimensions and the opposite tooth surface is constant in the tooth line direction. The molded worm wheel can be punched in the direction of the teeth on the helical surface.
[0008]
The parallel order of the first tooth surface and the second tooth surface is determined so that any first tooth surface and any second tooth surface simultaneously contact the tooth surface of the worm. preferable. Thereby, the bias | biasing of the force which acts on a worm wheel from a worm | warm can be suppressed more.
[0009]
The number of worms is preferably plural. As a result, the difference between the area where the tooth surface of the worm simultaneously contacts the first tooth surface of the worm wheel and the area where the tooth surface contacts the second tooth surface becomes smaller, and a biased force is applied to the worm wheel from the worm. It can be prevented more reliably.
[0010]
When the number of teeth in the worm wheel of the present invention is an even number, it is preferable that pairs of first tooth surfaces facing each other and pairs of second tooth surfaces facing each other are alternately arranged in the rotation direction. When the number of teeth in the worm wheel of the present invention is an odd number, a pair of first tooth faces facing each other is continuously arranged at one place in the rotational direction, and a pair of first tooth faces facing each other at other places. And pairs of second tooth surfaces facing each other are preferably alternately arranged in the rotation direction.
A pair of first tooth surfaces facing each other and a pair of second tooth surfaces facing each other are alternately arranged in the rotational direction, so that the region where the tooth surface of the worm simultaneously contacts the first tooth surface of the worm wheel; The difference from the region in contact with the second tooth surface becomes smaller, and it is possible to more reliably prevent the biased force from acting on the worm wheel from the worm.
[0011]
The molding die of the present invention is used for molding the worm wheel of the present invention in which at least the teeth are made of a synthetic resin, and the first mold and the other side for molding one side in the rotational axis direction of the worm wheel. And a split surface between the first mold and the second mold overlaps each tooth when viewed in the radial direction of the worm wheel, and a portion of the helical surface portion along the tooth trace direction is mutually connected. A portion located on one side in the rotational axis direction of the worm wheel with respect to the portion between the second tooth surfaces facing each other, and on the other side in the rotational axis direction of the worm wheel with respect to a portion between the first tooth surfaces facing each other. It is preferable to have the part located.
According to the molding die of the present invention, the molded worm wheel of the present invention can be punched in the direction of the tooth trace of the helical surface portion.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The electric power steering device P shown in FIG. 1 transmits the rotation of the steering shaft S due to the steering of the steering wheel H to the wheels so as to change the steering angle via a steering gear outside the figure. The type of the steering gear is not limited as long as the rotation of the steering shaft S can be transmitted to the wheels so that the steering angle changes. Rack and pinion type steering gear that transmits to the wheels can be adopted. A torque sensor 1 for detecting a steering torque transmitted by the steering shaft S is provided. The torque sensor 1 has a known configuration in this embodiment, and is connected to the sensor housing 2, the input shaft 3, and the input shaft 3 via a torsion bar 8 so as to be coaxially and elastically relatively rotatable. An output shaft 4 and a magnetic flux generating coil 7 constituting a magnetic circuit are provided, and the magnetic resistance in the magnetic circuit changes according to the elastic relative rotational amount of the shafts 3 and 4 by the steering torque. The steering torque is detected from the output.
[0013]
Both shafts 3 and 4 constitute part of the steering shaft S and are supported by the sensor housing 2 via bearings 6a and 6b. A steering assist force generating motor M is attached to the sensor housing 2. A worm wheel 10 made of a synthetic resin material is provided on the output shaft 4 via a metal sleeve 9 so as to rotate together. A worm 11 meshing with the worm wheel 10 is driven by a steering assist force generating motor M. The motor M is controlled by a non-illustrated control device in accordance with the steering torque detected by the torque sensor 1. The rotation of the motor M is transmitted to the wheels via the worm 11, the worm wheel 10, and the steering shaft S so that the steering angle changes, whereby a steering assist force according to the steering torque is applied.
[0014]
As shown in FIGS. 2 and 3, the worm wheel 10 has an annular wheel body 10B and a plurality of teeth 10A arranged in parallel on the outer periphery of the wheel body 10B. Each tooth 10A is a tooth 11A of the worm 11. Engage with.
[0015]
As shown in FIGS. 4 and 5 (1) to (4), the tooth surface 10a on one side (lower side in FIG. 4) and the other side (upper side in FIG. 4) of each tooth 10A of the worm wheel 10 in the rotational direction. The tooth surface 10b has helical surface portions 10a 'and 10b' having the same shape as the tooth surface of the helical gear, and concave curved surface portions 10a "and 10b" along the convex curved tooth surfaces of the teeth 11A of the worm 11.
[0016]
Each of the tooth surfaces 10a and 10b has helical surface portions 10a 'and 10b' arranged on one side (left side in FIG. 4) in the rotational axis direction of the worm wheel 10 and a concave curved surface portion on the other side (right side in FIG. 4). A plurality of first tooth surfaces A on which 10a ″ and 10b ″ are arranged, concave curved surface portions 10a ″ and 10b ″ are arranged on one side in the rotational axis direction, and helical surface portions 10a ′ and 10b ′ are arranged on the other side. Are classified into a plurality of second tooth surfaces B in which are arranged. Each first tooth surface A is disposed so as to face the first tooth surface A, and each second tooth surface B is disposed so as to face the second tooth surface B.
[0017]
In the concave curved surface portions 10a "and 10b" in the first and second tooth surfaces A and B, the distance D "between the tooth surfaces opposite to the tooth height direction dimension H" is equal to the helical surface portions 10a 'and 10b'. Increases toward the boundary. In the helical surface portions 10a ′ and 10b ′, the distance D ′ between the tooth surfaces facing the tooth height direction dimension H ′ is constant in the tooth line direction. The concave curved surface portions 10a ″ and 10b ″ and the helical surface portions 10a ′ and 10b ′ are connected smoothly at the boundary of the central position in the tooth line direction. The boundary position may be determined so that the molded worm wheel 10 can be removed from the mold, and in the present embodiment, the center position of each tooth surface in the streak direction is set. For smooth die cutting, the area of the helical surface portions 10a ′ and 10b ′ may be made larger than the area of the concave curved surface portions 10a ″ and 10b ″.
[0018]
The first tooth surface A and the second tooth surface B are arranged in parallel so that any first tooth surface A and any second tooth surface B are in contact with the tooth surface of the tooth 11A of the worm 11 at the same time. It is preferable that Furthermore, in order to further increase the area of the first tooth surface A and the area of the second tooth surface B that simultaneously contact the tooth surface of the tooth 11A of the worm 11, when the number of teeth of the worm wheel 10 is an even number, As shown in FIG. 4, it is preferable that pairs of first tooth surfaces A facing each other and pairs of second tooth surfaces B facing each other are alternately arranged in the rotation direction. Further, when the number of teeth of the worm wheel 10 is an odd number, the pair of first tooth surfaces A facing each other is continuously arranged at one place in the rotation direction as shown in the modification of FIG. In the place, it is preferable that the pair of first tooth surfaces A facing each other and the pair of second tooth surfaces B facing each other are alternately arranged in the rotation direction. The worm and the worm wheel do not mesh two or more teeth at the same time depending on the specifications, but generally two or more teeth mesh at the same time. Preferably, the teeth are engaged.
[0019]
The worm wheel 10 is molded, for example, injection molded. The worm wheel 10 and the sleeve 9 can be integrated by inserting the sleeve 9 into the mold used for the mold forming. As shown by a two-dot chain line in FIG. 7, the molding die 30 has a first die 31 that molds one side in the rotation axis direction of the worm wheel 10 and a second die 32 that molds the other side. The split surface PL between the first mold 31 and the second mold 32 overlaps with each tooth 10A in the radial direction of the worm wheel 10 and a portion PL1 along the tooth trace direction of the helical surface portions 10a ′ and 10b ′. The portion PL2 located on one side in the rotation axis direction of the worm wheel 10 with respect to the portion between the second tooth surfaces B facing each other, and the rotation shaft of the worm wheel 10 with respect to the portion between the first tooth surfaces A facing each other. And a portion PL3 located on the other side in the direction. Thus, the first tooth surface A is formed by the first mold 31, the second tooth surface B is formed by the second mold 32, and the first mold 31 and the second mold 32 are connected to the helical surface portions 10a ', 10b'. The molded worm wheel 10 can be punched out of the mold 30 by separating it by relative movement along the tooth trace direction (arrow direction H in the figure).
[0020]
According to the worm wheel 10, on the first tooth surface A, the helical surface portions 10a 'and 10b' are disposed on one side in the rotation axis direction, and the concave curved surface portions 10a "and 10b" are disposed on the other side. In the second tooth surface B, concave curved surface portions 10a "and 10b" are arranged on one side in the rotation axis direction, and helical surface portions 10a 'and 10b' are arranged on the other side. Thereby, the bias direction of the force acting on the worm wheel 10 from the worm 11 is reversed between the position where the tooth surface 11A of the worm 11 is in contact with the first tooth surface A and the position where it is in contact with the second tooth surface B. Therefore, the bias of the force acting on the worm wheel 10 from the worm 11 can be suppressed. In addition, each first tooth surface A is disposed so as to face the first tooth surface A, and each second tooth surface B is disposed so as to face the second tooth surface B, and the concave curved surface portion 10a ″, In 10b ″, the distance between the tooth surfaces opposite to the tooth height direction dimension increases toward the boundary with the helical surface portions 10a ′ and 10b ′, and the helical surface portions 10a ′ and 10b ′ face each other in the tooth height direction dimension. Since the distance between the tooth surfaces to be fixed is constant in the tooth trace direction, the molded worm wheel 10 can be punched in the tooth trace direction of the helical surface portions 10a ′ and 10b ′. It is suitable to use the molding die 30 of the above embodiment for the molding.
Also, any of the first tooth surfaces A and any of the second tooth surfaces B are simultaneously in contact with the tooth surfaces of the teeth 11A of the worm 11, so that the bias of the force acting on the worm wheel 10 from the worm 11 is reduced. It can be suppressed more. Further, when the number of teeth of the worm wheel 10 is an even number, the pair of first tooth surfaces A that face each other is opposed to each other except for one place in the direction of rotation when the number of teeth is an odd number. The pair of second tooth surfaces B to be alternately arranged in the rotation direction makes it possible for the tooth surface 11A of the worm 11 to simultaneously contact the first tooth surface A and the region contacting the second tooth surface B. A difference becomes smaller and it can prevent more reliably that the force biased from the worm 11 to the worm wheel 10 acts. Furthermore, it is preferable that the number of the worms 11 is plural, for example, two or three. Thereby, the difference between the region of the first tooth surface A and the region of the second tooth surface B simultaneously contacting the tooth surface of the tooth 11A of the worm 11 is reduced, and a biased force is applied from the worm 11 to the worm wheel 10. Can be more reliably prevented.
[0021]
The present invention is not limited to the above embodiment. For example, instead of making the entire worm wheel 10 made of a synthetic resin material as in the above embodiments, the worm wheel may be constituted by a core metal and a synthetic resin material covering the core metal. Further, the worm wheel may be sintered. Further, a pair of first tooth surfaces facing each other or a pair of second tooth surfaces facing each other may be continuously arranged at a plurality of locations in the rotation direction.
[0022]
【The invention's effect】
According to the present invention, it is possible to provide a worm wheel that can be molded at low cost without requiring a complicated mold, and that can transmit rotation smoothly with a long life, and a mold for manufacturing the worm wheel.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an electric power steering apparatus using a worm wheel according to an embodiment of the present invention. FIG. 2 is a partial perspective view of a worm wheel according to an embodiment of the present invention. FIG. 4 is a partially developed view of a worm wheel according to an embodiment of the present invention. FIG. 5 shows a first tooth surface on one side in the rotational direction of the worm wheel according to the embodiment of the present invention. (2) is a diagram showing a first tooth surface on the other side in the rotational direction, (3) is a diagram showing a second tooth surface on one side in the rotational direction, and (4) is a second tooth surface on the other side in the rotational direction. FIG. 6 is a partial development view of a worm wheel according to a modification of the present invention. FIG. 7 is an explanatory diagram of a configuration of a mold according to an embodiment of the present invention. FIG. 8 is a partial development view of a conventional worm wheel. Explanation】
10 Worm wheel 10A Tooth 10a, 10b Tooth surface 10a ', 10b' Helical surface portion 10a ", 10b" Concave surface portion A First tooth surface B Second tooth surface 11 Worm 11A Tooth 30 Mold PL Split surface

Claims (5)

It has a plurality of teeth that mesh with the teeth of the worm, and the tooth surface on one side and the tooth surface on the other side in the rotational direction of each tooth are a helical surface portion that is the same shape as the tooth surface of the helical gear, and the convex curved teeth of the worm. In the worm wheel having a concave curved surface portion along the surface,
Each tooth surface includes a plurality of first tooth surfaces in which a helical surface portion is disposed on one side in the rotational axis direction of the worm wheel and a concave curved surface portion is disposed on the other side, and concave in one side in the rotational axis direction. The curved surface portion is arranged and classified into a plurality of second tooth surfaces on which the helical surface portion is arranged on the other side,
Each first tooth surface is disposed to face the first tooth surface,
Each second tooth surface is arranged to face the second tooth surface,
In the concave curved surface portions of the first and second tooth surfaces, the dimension in the tooth height direction increases as it goes toward the boundary with the helical surface portion, and the distance between the tooth surfaces facing each other increases as it goes toward the boundary with the helical surface portion. In the helical surface portions of the first and second tooth surfaces, the tooth height direction dimension is constant in the tooth line direction, and the distance between the tooth surfaces facing each other is constant in the tooth line direction. Worm wheel to be. The parallel order of a 1st tooth surface and a 2nd tooth surface is defined so that any 1st tooth surface and any 2nd tooth surface may contact simultaneously with the tooth surface of the worm | warm. The worm wheel according to 1. The number of teeth is even,
The worm wheel according to claim 1 or 2, wherein a pair of first tooth surfaces facing each other and a pair of second tooth surfaces facing each other are alternately arranged in a rotation direction. The number of teeth is odd,
A pair of first tooth surfaces facing each other is continuously arranged at one place in the rotation direction, and a pair of first tooth faces facing each other and a pair of second tooth faces facing each other are rotated at other positions. The worm wheel according to claim 1, wherein the worm wheel is alternately arranged in a direction. A molding die used for molding a worm wheel according to claim 1, wherein at least the teeth are made of synthetic resin,
A first mold for molding one side in the rotation axis direction of the worm wheel and a second mold for molding the other side;
The dividing surface of the first mold and the second mold overlaps with each tooth in the radial direction view of the worm wheel and is a portion between the portion along the tooth streak direction of the helical surface portion and the second tooth surface facing each other. And a portion located on one side in the rotational axis direction of the worm wheel, and a portion located on the other side in the rotational axis direction of the worm wheel rather than a portion between the first tooth surfaces facing each other. Molds for manufacturing worm wheels.

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