JP4203714B2 - Worm wheel manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a worm wheel having at least a tooth portion made of a synthetic resin material.
[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. Therefore, it has been proposed to finish the tooth profile by hobbing or polishing after forming the tooth profile of the worm wheel using a molding die (Japanese Patent Laid-Open No. 2000-84747).
[0004]
[Problems to be solved by the invention]
However, since the worm wheel has a tooth profile in which the tooth thickness at the central part in the tooth trace direction is thinner than the tooth thickness at both end parts, it cannot be removed from the mold in the tooth trace direction. Therefore, when trying to form a worm wheel tooth profile using a molding die, the molding die is composed of many members arranged in parallel in the rotational circumferential direction of the worm wheel, and it is necessary to perform die cutting along the radial direction of the worm wheel. become. If it does so, the structure of a shaping | molding die will become very complicated, and manufacturing cost will increase.
An object of this invention is to provide the manufacturing method of the worm wheel which can solve the said subject.
[0005]
[Means for Solving the Problems]
The present invention relates to a method of manufacturing a worm wheel having at least a tooth portion made of a synthetic resin material, a step of molding a preform having a tooth portion of the same tooth shape as a Hasuba gear, and the preform, The step of die cutting in the tooth trace direction of the gear and each tooth portion of the preform are hobbed so that the central part in the tooth trace direction has a tooth profile that is larger in tooth height and thinner than both end parts. And a step of forming a tooth portion of the worm wheel.
According to the present invention, a preform having a tooth portion having the same tooth shape as the helical gear is molded, and thereafter, the tooth portion of the preform has a tooth height at the central portion in the tooth trace direction than at both end portions. Hobbing is performed on the tooth portion of a worm wheel having a large tooth shape and a thin tooth thickness, so that the amount of burrs can be reduced by reducing the amount of hobbing. In addition, since the preformed molded body can be punched in the direction of the helical gear, there is no need to form the molding die from a large number of members arranged in parallel in the rotational circumferential direction of the worm wheel. The complexity of the structure can be prevented.
[0006]
Further, in the present invention, at each tooth portion of the preform, the tooth height is smaller at the front portion in the rotation direction of the hob cutter than at the rear portion in the rotation direction, and as the front portion in the rotation direction of the hob cutter is moved forward in the rotation direction. The machining allowance is molded integrally with the preform so that the tooth height is reduced, the machining allowance is hobbed together with each tooth of the preform, and the worm at the completion of the hobbing is processed. In the contact area between the wheel and the outer periphery of the hob cutter, the machining allowance before the tangent line between the edge located forward in the rotational direction of the hob cutter and the outer peripheral locus of the hob cutter is removed by hobbing as viewed from the rotational axis direction of the hob cutter. The angle formed with respect to the surface of the hob cutter is θa, and the tangent line between the edge located behind the hob cutter in the rotation direction and the outer locus of the hob cutter is used for hobbing. Ri angle as .theta.b which makes with the surface of the front of the preform to be removed, shall be the .theta.a <.theta.b.
As a result, the thickness of the portion removed by the hob cutter immediately before completion of the hob processing is near the edge located in the front of the hob cutter in the rotation direction in the contact area between the worm wheel and the outer periphery of the hob cutter when the hob processing is completed. It becomes thinner than the part located at the rear in the rotation direction. That is, by reducing the thickness of the part removed by the hob cutter in the vicinity of the position where burrs are likely to occur, the preform can be processed as if the thin skin is peeled off by the hob cutter. Occurrence is further suppressed.
[0007]
In a power steering apparatus that transmits the rotation of a steering assisting force generation motor to a wheel through a worm and a worm wheel meshing with the worm so that the rudder angle changes, the worm wheel of the present invention is used as the worm wheel. Is preferred.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The electric power steering device P of the comparative example 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 that the steering angle changes 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 comparative example , 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. The 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 rotation amount of the shafts 3 and 4 by the steering torque. A steering torque is detected from the output of the coil 7.
[0009]
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 integrated with the output shaft 4 via a metal sleeve 9. 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 through the worm 11, the worm wheel 10, and the steering shaft S so that the steering angle changes, whereby a steering assist force corresponding to the steering torque is applied.
[0010]
When the worm wheel 10 is manufactured, first, as shown in FIGS. 2 (1) and (2), a preform 13 having a tooth portion 13a having the same tooth shape as the helical gear is molded. The preform 9 is integrated with the sleeve 9 by inserting the sleeve 9 into the mold used for the molding. Each tooth portion 13a of the preform 13 has a uniform tooth thickness t and tooth height h in the tooth line direction (the direction of arrow A in FIG. 2 (1)). This molding is performed by, for example, injection molding.
[0011]
Next, the preform 13 is punched out from the molding die in the direction of the teeth of the helical gear. Thereafter, as shown in (1) and (2) of FIG. 3, each tooth portion 13a of the preform 13 has a tooth height ha at the central portion in the tooth line direction larger than the tooth height hb at both end portions, In addition, the tooth portion 10a of the worm wheel 10 is formed by hobbing using the hob cutter 15 so that the tooth thickness ta of the central portion is thinner than the tooth thickness tb of both end portions.
[0012]
FIG. 4 shows the positions of the outer peripheral locus of the worm wheel 10 and the hob cutter 15 when the hob processing of the comparative example is completed, as viewed from the direction of the rotation axis of the hob cutter 15 with a two-dot chain line. The part removed by the hob cutter 15 shown by is indicated by a broken line. The hob cutter 15 rotates in the direction of arrow B in the figure and is sent in the direction of arrow C. Thereby, the tooth bottom of each tooth 10a of the worm wheel 10 becomes a concave curved surface along the outer periphery locus of the hob cutter 15. In such hobbing, in the contact area between the worm wheel 10 and the outer periphery of the hob cutter 15 when the hobbing is completed, the edge located forward in the rotational direction of the hob cutter 15 as viewed from the rotational axis direction of the hob cutter 15 Burr is likely to occur in Ef ′. In this comparative example , as viewed from the direction of the rotation axis of the hob cutter 15, the preliminary forming before the tangent line 16 f between the edge Ef ′ positioned in the forward direction of the hob cutter 15 and the outer peripheral locus of the hob cutter 15 is removed by hobbing. An angle formed with respect to the surface 13 ′ of the body 13 is θa ′, and the preformed body 13 before the tangent 16 r between the edge Er positioned behind the hob cutter 15 in the rotation direction and the outer locus of the hob cutter 15 is removed by hobbing. Θa ′ = θb, where θb is the angle formed with respect to the surface 13 ′ of FIG.
[0013]
According to the comparative example , the preformed body 13 having the tooth portion 13a having the same tooth shape as the helical gear is molded, and then the tooth portion 13a of the preformed body 13 is formed so that the central portion has a tooth height higher than both end portions. Since hobbing is performed on the tooth portion 10a of the worm wheel 10 having a large tooth shape and a thin tooth thickness, the amount of hobbing can be reduced and the generation amount of burrs can be reduced. In addition, since the preformed body 13 that has been molded can be punched in the direction of the teeth of the helical gear, it is not necessary to form the molding die from a large number of members arranged in parallel in the rotational circumferential direction of the worm wheel 10. The complexity of the mold structure can be prevented.
[0014]
(1) in FIG. 5, (2), FIG. 6 shows the implementation form of the present invention. The difference from the comparative example is that, as shown in FIG. 5 (1), the machining allowance portion 13 b is molded integrally with the preform 13. Due to the machining allowance 13b, the tooth height of each tooth 13a of the preform 13 is smaller at the front part in the rotation direction of the hob cutter 15 than at the rear part in the rotation direction, and is rotated at the front part in the rotation direction of the hob cutter 15. The tooth height decreases as it goes forward. In the present embodiment, the tooth bottom of each tooth portion 13a of the preformed body 13 is inclined with respect to the rotation axis of the worm wheel 10 at a predetermined angle θm at the front portion in the rotation direction of the hob cutter 15 and is rearward in the rotation direction. It is made parallel in a part. The machining margin 13b is hobbed together with the teeth 13a of the preform 13 by the hob cutter 15 as shown in (2) of FIG.
[0015]
FIG. 6 shows the outer locus of the worm wheel 10 and the hob cutter 15 when the hob machining is completed, the position when viewed from the direction of the rotation axis of the hob cutter 15 by a two-dot chain line, and the hob cutter indicated by the one-dot chain line immediately before the hob machining is completed. The portion removed by 15 is indicated by a broken line. The hob cutter 15 rotates in the direction of arrow B in the figure and is sent in the direction of arrow C. In the contact area between the preform 13 and the outer periphery of the hob cutter 15 when the hobbing is completed, the edge Ef positioned in the forward direction of the hob cutter 15 and the outer locus of the hob cutter 15 as viewed from the rotational axis direction of the hob cutter 15 The angle formed with respect to the surface 13b 'in the machining allowance 13b before the tangent 16f of the hob cutter 15 is removed by hob machining is θa, and the tangent 16r between the edge Er positioned rearward in the rotation direction of the hob cutter 15 and the outer peripheral locus of the hob cutter 15 Θa <θb, where θb is an angle formed with respect to the surface 13 'of the preform 13 before being removed by hobbing. The other configuration is the same as that of the comparative example .
[0016]
According to the above you facilities embodiment can further reduce the generation of burr than that of the comparative example because there is a .theta.a <.theta.b. According to Sunawa Chi implementation embodiment, the thickness of the portion to be removed by the hob cutter 15 just prior to completion hobbing, the rotation of the hob cutter 15 in the contact area between the outer periphery of the worm wheel 10 and the hob cutter 15 during hobbing completion In the vicinity of the edge 10Ef located in the forward direction, the thickness is thinner than the portion located in the rearward direction of the hob cutter 15. That is, by reducing the thickness of the portion removed by the hob cutter 15 in the vicinity of the position where burrs are likely to occur, the pre-formed body can be processed as if the thin skin is peeled off by the hob cutter 15, so that the amount of hob processing is reduced. Therefore, the generation of burrs is further suppressed. Other effects can be obtained as in the comparative example .
[0017]
The present invention is not limited to the above embodiment. For example, instead of the whole of the worm wheel 10 as above you facilities form made of a synthetic resin material, metal core and may constitute a worm wheel in a synthetic resin material covering the metal core, The worm wheel only needs to have at least a tooth portion made of a synthetic resin material. Further, the worm wheel manufactured by the method of the present invention is not limited to that used in the power steering apparatus.
[0018]
【The invention's effect】
According to the method for manufacturing a worm wheel of the present invention, it is possible to reduce the number of processes and costs because the generation of burrs is reduced and a mold having a complicated configuration is not required.
[Brief description of the drawings]
[1] of the helical gear to be formed in the manufacturing process of the worm wheel of the comparative example of longitudinal section [2] The present invention of the electric power steering apparatus using the worm wheel of the comparative example of the present invention (1) tooth FIG. 3 is a partial vertical cross-sectional view. FIG. 3 is a diagram showing a tooth streak when the hobbing of the worm wheel of the comparative example of the present invention is completed. FIG. 3 is a partial vertical cross-sectional view. shows the (1) the tooth trace of the helical gear to be formed in the manufacturing process of the worm wheel of the implementation according to FIG. 5 shows the present invention showing a manufacturing step of the worm wheel of the comparative example of FIG. 4 of the present invention, (2) eXPLANATION oF REFERENCE nUMERALS diagram illustrating implementation form of the worm wheel of the manufacturing process of partial longitudinal sectional view the present invention; FIG
10 Worm wheel 10a Tooth part 13 Preliminary molded body 13a Tooth part 13b Processing allowance

Claims (1)

In a method of manufacturing a worm wheel having at least a tooth portion made of a synthetic resin material,
A step of molding a preform having a tooth portion of the same tooth shape as the helical gear;
A step of punching the preform in the direction of the teeth of the helical gear;
A step of forming each tooth portion of the preform into a tooth portion of a worm wheel by hobbing the tooth shape so that the tooth height is larger and the tooth thickness is thinner than the both end portions in the central portion in the tooth line direction; I have a,
At each tooth part of the preform, the tooth height is smaller at the front part in the rotation direction of the hob cutter than at the rear part in the rotation direction, and the tooth height is smaller toward the front in the rotation direction at the front part in the rotation direction of the hob cutter. In addition, the machining allowance is molded integrally with the preform, and the machining allowance is hobbed together with each tooth portion of the preform,
In the contact area between the worm wheel and the outer circumference of the hob cutter when the hobbing is completed, the tangent line between the edge located forward in the rotational direction of the hob cutter and the outer locus of the hob cutter is The angle formed with respect to the surface at the machining allowance before removal is θa, and the surface of the preform before the tangent line between the edge located at the rear in the rotation direction of the hob cutter and the outer peripheral locus of the hob cutter is removed by hobbing. A manufacturing method of a worm wheel, characterized in that θa <θb where θb is an angle formed with respect to .

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