JP5392388B2 - Worm wheel manufacturing method and worm reducer - Google Patents

Description

  The present invention relates to, for example, a worm speed reducer incorporated in an electric power steering apparatus and a method for manufacturing a worm wheel constituting the worm speed reducer.

  As a device for reducing the force required for the driver to operate the steering wheel when giving a steering angle to the steering wheel of a vehicle (usually the front wheel, excluding special vehicles such as forklifts), a power steering device is used. Widely used. In addition, an electric power steering apparatus that uses an electric motor as an auxiliary power source in such a power steering apparatus has begun to spread in recent years. In addition, a reduction gear is incorporated in such an electric power steering apparatus, but as this reduction gear, a worm reduction gear having a large lead angle and reversibility with respect to the transmission direction of power is generally used. Has been.

5 to 6 show a structure described in Patent Document 1 as an example of a conventional structure of a worm speed reducer incorporated in such an electric power steering apparatus. This worm speed reducer is provided inside a speed reducer housing 2 fixed to the electric motor 1, and a worm shaft 4 having a worm 3 formed in the middle in the axial direction and a worm meshed with the worm 3. A wheel 5. Of these, the worm shaft 4 is rotatably supported inside the housing 2 by a pair of ball bearings 6, 6 fitted on both ends in the axial direction. At the same time, one end portion (left end portion in FIG. 5 ) of the worm shaft 4 is connected to the output shaft 7 of the electric motor 1 so that the worm shaft 4 can be driven to rotate.

The worm wheel 5 is rotatably provided inside the housing 2, and its own rotation center axis is disposed at a twisted position with respect to the worm shaft 4. Then, the tooth portion 8 formed on the outer peripheral edge portion of the worm wheel 5 is engaged with the worm 3 so that the rotational force can be transmitted between the worm wheel 5 and the worm shaft 4. In the case of the illustrated example, the worm wheel 5 has a radially inner end portion and an intermediate portion made of metal, and a radially outer end portion including the tooth portion 8 (a diagonal lattice is shown in FIGS. 5 to 6 ) . The part shown) is made of synthetic resin 9. As a result, the hitting sound and sliding sound generated at the meshing part during operation are reduced and the weight is reduced. Further, such a worm wheel 5 is fitted and fixed to an intermediate portion of the steering shaft 10. As a result, the rotational driving force generated by the electric motor 1 can be transmitted to the steering shaft 10 via the worm speed reducer including the worm shaft 4 and the worm wheel 5.

  The electric power steering apparatus including the worm reduction gear as described above operates as follows. In order to give a steering angle to the steered wheels, when the driver operates the steering wheel and the steering shaft 10 rotates, a torque sensor (not shown) detects the rotation direction and torque of the steering shaft 10, A signal representing the detected value is sent to a controller (not shown). Then, the controller energizes the electric motor 1 and rotates the steering shaft 10 in the same direction as the rotation direction based on the operation of the steering wheel via the worm speed reducer. As a result, the steering shaft 10 rotates in response to assist torque (auxiliary power) generated by the electric motor 1 based on energization in addition to torque generated based on the operation of the steering wheel. Therefore, the force required for the driver to operate the steering wheel can be reduced by this auxiliary power. On the other hand, for example, when the electric motor 1 to which the worm shaft 4 is connected fails, the worm speed reducer is reversely operated based on the operation of the steering wheel. This prevents the steering wheel from being unable to be operated.

  By the way, in the case of the worm wheel 5 constituting the worm speed reducer as described above, for example, as described in Patent Documents 1 and 2, etc., the hob cutter having a plurality of slits formed on the outer peripheral surface allows the synthetic resin 9 portion to be formed. The formation of the tooth portion 8 is generally performed. Also, among these, Patent Document 2 discloses that a portion of the worm wheel 5 that is to become the tooth portion 8 is preliminarily molded with a helical gear (helical gear) to form an intermediate material. A technique is described in which a tooth portion (portion where a helical gear is formed) is subjected to hobbing (cutting with a hob cutter) to form the tooth portion 8 of the worm wheel 5. If such a technique is adopted, a die (molding die) for molding (injection molding) can be simply configured, and burrs can be generated and processing cost can be reduced, thereby reducing processing costs.

On the other hand, in Patent Document 1, instead of the hob cutter as described above, as shown in FIG. 7 , the processing of the tooth portion 8 of the worm wheel 5 is performed by a processing worm 11 formed by electrodepositing abrasive grains on the surface. Techniques for performing are described. That is, this working worm 11 has the same shape and the same size as the worm 3 (see FIGS. 5 and 6 ) that meshes with the tooth portion 8 during use (or the tooth pitch in the axial direction is the same, and the tooth A large number of abrasive grains are electrodeposited on the surface of the worm (the portion shown with a slanted lattice) whose tip and root diameter are slightly larger. Then, as shown in FIGS. 7A and 7B, the intermediate material 12 having a cylindrical outer peripheral surface and the processing worm 11 are respectively in a speed relationship corresponding to the reduction ratio of the worm reducer. The rotating worm 11 is pressed against the outer peripheral surface of the intermediate material 12 in the rotated state. By this machining worm 11 by grinding the outer peripheral surface of the intermediate material 12 (or cutting), as shown in FIG. 7 (c), to form the tooth portion 8 in the outer peripheral surface of the intermediate material 12. In this way, if the worm wheel 5 is processed (the tooth portion 8 is formed) using the machining worm 11 having substantially the same shape as the worm 3 to be meshed when used, the worm wheel 5 and the worm are compared with the case where the hob cutter is used. The contact area of the meshing part with 3 can be secured in a high dimension.

  By the way, when the tooth portion 8 is formed using the machining worm 11 as described above, for example, the machining cost is reduced, the machining time is shortened, the tool life is ensured, and the cost is reduced (the manufacturing cost is reduced). For example, prior to processing (formation of the tooth portion 8) by the processing worm 11, the portion to be the tooth portion 8 of the worm wheel 5 in advance as described in Patent Document 2 described above. It is conceivable to form a helical gear. However, in such a case, it may not be possible to sufficiently achieve both the durability of the tooth portion 8 and the reduction of processing cost (cost reduction) simply by forming a helical gear. There is. That is, when the worm reduction gear is configured by combining the worm wheel 5 having the synthetic resin tooth portion 8 and the metal worm 3, in order to ensure the durability of the tooth portion 8 of the worm wheel 5, It is necessary to increase (thicken) the tooth thickness of each tooth constituting the tooth portion 8. On the other hand, in order to increase the tooth thickness of each tooth constituting the tooth portion 8 in this way, the tooth thickness of a helical gear (helical gear) formed in advance in a portion to be the tooth portion 8 of the worm wheel 5 is also increased. It is necessary to keep it. However, in this case, simply increasing the tooth thickness of the helical gear also increases the root diameter of the helical gear, and the machining allowance for the tooth bottom (tooth gap bottom) part is correspondingly increased. growing. In particular, when machining using the machining worm 11 as described above, the machining amount (cutting amount per unit time) is smaller than machining with a hob cutter, so that the machining cost as described above is increased. Is not preferred.

JP 2006-142400 A JP 2003-334724 A

  In view of the circumstances as described above, the present invention provides a method for manufacturing a worm wheel and a worm speed reducer capable of achieving a high degree of compatibility between ensuring the durability of the tooth portion of the worm wheel and reducing the machining cost (lowering the cost). Invented to realize the above.

Of the worm wheel manufacturing method and worm speed reducer according to the present invention, the worm wheel manufacturing method according to claim 1 is such that at least the surface layer portion of the tooth portion {the tooth surface (surface contacting the worm)} is made of a synthetic resin. The present invention relates to a method of manufacturing a manufactured worm wheel.
Such a method of manufacturing a worm wheel according to the present invention is such that the portion to be the tooth portion of the worm wheel is equal to or less than the pressure angle of the tooth portion after completion (the pressure angle of the tooth portion after completion). A helical gear having a small pressure angle is formed, and a tooth root groove (relief) is formed on the tooth bottom of the helical gear to reduce the machining allowance for the tooth tip of the machining worm used in the later machining process. Groove) to form an intermediate material. The tooth bottom groove has a shape having side surfaces parallel to each other. Such an intermediate material is formed by injection molding of a synthetic resin, that is, a shape of a portion corresponding to a portion to be a tooth portion in an inner surface of a cavity (internal tooth type) such as a helical gear. It can be made by injection molding using a shaped mold.

  If the intermediate material is formed in this way (by injection molding), the tooth portion (portion where the helical gear is formed) of the intermediate material is compared with the worm that meshes in use, and the axial direction is related. The tooth pitch is the same, and the diameters of the tooth tip and the bottom of the tooth are the same or larger. Is about 1 to 3%) large} is processed by a working worm in which abrasive grains (for example, diamond abrasive grains) are fixed to the surface of the worm by electrodeposition, adhesion or the like. The worm meshing with the worm wheel at the time of use may be either a cylindrical worm or a drum worm. The machining worm is a cylindrical worm or a drum-shaped worm according to the worm meshed with the worm wheel during use.

According to a second aspect of the present invention , a worm speed reducer is formed by meshing a worm and a worm wheel.
In particular, in the worm speed reducer according to claim 2 , the worm wheel is manufactured by the manufacturing method according to claim 1 described above.

As described above, in the worm wheel manufacturing method of the present invention, a tooth bottom groove (relief groove) for reducing the machining allowance for the tooth tip of the working worm is formed on the tooth bottom of the helical gear. Form an intermediate material. For this reason, even if the tooth thickness is increased, it is necessary to grind (or cut) with the above processing worm, reducing the processing cost of the root part, and ensuring both durability and reduction of the processing cost. It can be planned in a high dimension.
In the case of the worm speed reducer of the present invention incorporating the worm wheel manufactured by the manufacturing method as described above, the contact area of the meshing portion between the worm wheel and the worm can be secured at a high level, and the durability It is possible to achieve a balance between ensuring safety and reducing costs.

It is the elements on larger scale which show the state which processes the helical gear formed in the intermediate material with the process worm, (a) is one example of the reference example regarding this invention , (b) is the structure of (a). The case where the pressure angle of the helical gear is larger than that of FIG. The elements on larger scale similar to FIG. 1 which show the helical gear formed in the intermediate material. The partial cut perspective view which shows an intermediate material typically. The elements on larger scale of the intermediate material which show an example of embodiment of this invention . Sectional drawing of the part which incorporated the worm reduction gear among power steering devices. FIG. It is a figure which shows the process process of the conventional worm wheel, (a) is a state before grinding (or cutting) a worm wheel with a process worm, (b) is a roll cross section of (a), (C) shows the state after grinding (or cutting) with a working worm.

[ Example of Reference Example of the Present Invention ]
1-3 (a) has shown one example of the reference example regarding this invention . The feature of the present reference example is the method of manufacturing the worm wheel 5a and the structure of the worm speed reducer that includes the worm wheel 5a. Structure and function of the other parts, for example because it is the same as in the conventional construction shown in Figures 5-6 described above, illustration and description overlapping is omitted or simplified below, the central characteristic portions of the present embodiment Explained.

Also in this reference example, the machining worm 11 as shown in FIG. 7 is used as a tool for machining the tooth portion 8a of the worm wheel 5a. That is, also in the case of this reference example, the tooth pitch in the axial direction is the same, and the diameter dimensions of the tooth tip and the tooth bottom are equal to or greater than those of the worm 3 (see FIGS. 5 and 6 ) meshed during use . A certain {for example, the tooth tip and the tooth base are each slightly larger (about 1 to 10%, more preferably about 1 to 3% with respect to the worm 3 meshed during use)} The tooth portion 8a is machined by a machining worm 11 formed by electrodeposition of grains). In particular, in the case of the present reference example , prior to the processing of the tooth portion 8a using such a working worm 11, a portion of the worm wheel 5a that is to become the tooth portion 8a in advance is a helical gear. The intermediate material 12a on which the (helical gear) 13 is formed is formed.

For this reason, in the case of this reference example , for example, a mold (molding die) having a helical gear 13 having a shape corresponding to a portion to be the tooth portion 8a in the inner surface of the cavity is used. An intermediate material 12a as shown in FIGS. 2 and 3 (a) is manufactured by injection molding a synthetic resin. Furthermore, in the case of this reference example , the pressure angle θ ₁ of each tooth of the helical gear 13 formed on the outer peripheral surface of such an intermediate material 12a (the tooth pattern at an arbitrary point A on the tooth surface). The angle θ ₁ ) between the tangent plane α to the cylinder P ₁ and the normal β of the tangent plane to the cylinder P ₁ that is coaxial with the reference pitch cylinder P and passes through the arbitrary point A, and the tooth portion of the worm wheel 5a after completion The pressure angle θ _{2 of} 8a (the method of the tangent plane γ to the tooth mold at an arbitrary point B on the tooth surface and the tangent plane to the cylinder P ₁ coaxial with the reference pitch cylinder P and passing through the arbitrary point B) It is smaller (θ ₁ <θ ₂ ) than the angle θ ₂ formed with the line δ. Then, after such an intermediate material 12a is formed, the helical gear 13 formed on the outer peripheral surface of the intermediate material 12a is processed (ground or cut) by the processing worm 11 as shown in FIG. The tooth portion 8a of the worm wheel 5a is formed. Since the processing performed using such a processing worm 11 is described in detail in the above-mentioned Patent Document 1, the description thereof is omitted.

According to the manufacturing method of the worm wheel 5 of the present reference example as described above, the machining allowance of the tooth bottom (tooth gap bottom) portion can be reduced while sufficiently securing the tooth thickness of the tooth portion 8a after completion, It is possible to achieve a high level of compatibility between ensuring durability and reducing machining costs.
That is, as described above, in the case of this reference example , the pressure angle θ ₁ of each tooth of the helical gear (helical gear) 13 formed on the intermediate material 12a before being processed by the processing worm 11 is completed. The pressure angle θ ₂ of the rear tooth portion 8a is smaller (θ ₁ <θ ₂ ). For this reason, even if the tooth thickness of each helical gear 13 formed on the intermediate material 12a is increased in order to increase (thicken) the tooth thickness of the tooth portion 8a after completion, Since the pressure angle θ ₁ of each tooth of the gear 13 is reduced, the extent to which the root diameter is increased (the root groove becomes shallow) can be reduced.

That is, in order to increase (thicken) the tooth thickness of the tooth portion 8a after completion, as shown in FIG. 2, the tooth thickness of the helical gear 13 formed on the intermediate material 12a is increased from the state indicated by the chain line. Consider the case. In this case, as shown by the solid line in FIG. 2 (b), without changing the size of the pressure angle theta ₁ (in a state set to as the magnitude of the pressure angle theta ₁₎ when the large tooth thickness In addition to an increase in tooth thickness, the diameter of the root circle increases as indicated by t in FIG. 2B (the depth of the root groove becomes shallower). When the helical gear 13a represented by a solid line in FIG. 2B is subjected to grinding or cutting by the working worm 11 as shown in FIG. 1B, The portion represented by the oblique lattice in each of FIGS. 1 and 3B is a portion (machining allowance) that must be scraped off by the working worm 11.

On the other hand, when the tooth thickness of the helical gear 13 is increased and the pressure angle θ ₁ is reduced, the tooth thickness is as shown by the solid line in FIG. Even if the thickness is increased, the diameter of the root circle diameter can be kept as it is (the depth of the root groove can be kept as it is). When the helical gear 13 represented by a solid line in FIG. 2A is subjected to grinding or cutting by the working worm 11 as shown in FIG. 1A, The portions represented by the oblique grids in FIGS. 1 and 3A are portions (machining allowances) that must be cut off by the working worm 11. As is apparent from FIGS. 1 and 3, if the pressure angle θ ₁ of each tooth of the helical gear 13 formed on the intermediate material 12 a is reduced, the tooth thickness of the completed tooth portion 8 a is increased. However, the machining allowance of the tooth bottom (tooth gap bottom) portion can be reduced. Therefore, in the case of the present reference example, the magnitude of the pressure angle theta ₁ of the helical gear 13 formed on the intermediate material 12a, and regulated by the relationship between the pressure angle theta ₂ of the tooth portion 8a of the completed ing.

That is, the pressure angle θ ₁ of the helical gear 13 formed on the intermediate material 12 a is smaller than the pressure angle θ ₂ of the tooth portion 8 a after completion (θ ₁ <θ ₂ ). In this way, by reducing the pressure angle θ ₁ of the helical gear 13, the diameter of the root circle is reduced (the root groove is deepened), and the tooth thickness of the completed tooth portion 8 a is sufficiently increased. While ensuring, the machining allowance of the tooth bottom (tooth gap bottom) portion is made small so that both the ensuring of durability and the reduction of machining allowance can be achieved at a high level. In the case of this reference example in which such a worm wheel 5a is incorporated in a worm speed reducer, the worm wheel 5a processed by the processing worm 11 and the worm 3 (see FIGS. 5 and 6 ) are meshed as described above . Therefore, the contact area of the meshing portion between the worm wheel 5a and the worm 3 can be secured in a high dimension. In addition, since the worm wheel 5a manufactured as described above is incorporated, it is possible to achieve both high durability and low cost.

[ Example of Embodiment ]
FIG. 4 shows an example of an embodiment of the present invention . In the case of this example, the pressure angle θ ₁ of each tooth of a helical gear (helical gear) 13b formed on the intermediate material 12b before being processed by the processing worm 11 (see FIGS. 1 and 7 ) It is the same as the pressure angle θ ₂ (see FIG. 1) of the tooth portion 8a (θ ₁ = θ ₂ ). However, in the case of this example, the tooth bottom groove 14 for reducing the machining allowance for the tooth tip of the machining worm 11 on the tooth bottom of the helical gear 13b, that is, teeth having side surfaces parallel to each other. A bottom groove 14 is provided as the intermediate material 12b. For this purpose, for example, the shape of the inner surface of a mold (molding die) for injection molding the intermediate material 12b is formed to be a cavity corresponding to the helical gear 13b as shown in FIG. . In the case of this example as well, as in the above-described reference example , even if the tooth thickness is increased, the machining allowance for the tooth bottom portion that must be ground (or cut) by the machining worm 11 is reduced. Therefore, it is possible to achieve a high level of compatibility between ensuring durability and reducing processing costs.
Since the configuration and operation of other parts are the same as those of the reference example described above, overlapping illustrations and descriptions are omitted.

In addition, although illustration is abbreviate | omitted, in one example of embodiment mentioned above, the helical gear (helical gear) 13b formed in the intermediate raw material 12b before processing with the processing worm 11 (refer FIG. 1, 7 ) is shown. The pressure angle θ ₁ of each tooth can be made smaller (θ ₁ <θ ₂ ) than the pressure angle θ ₂ of the tooth portion 8a after completion. That is, the pressure angle θ ₁ of each tooth of the helical gear 13b formed in the intermediate material 12b in this way is made smaller than the pressure angle θ ₂ of the tooth portion 8a after completion (θ ₁ <θ ₂ ), A tooth bottom groove 14 for reducing the machining allowance for the tooth tip of the working worm 11 can be provided on the tooth bottom of the helical gear 13b as shown in the example of the above-described embodiment. .

DESCRIPTION OF SYMBOLS 1 Electric motor 2 Housing 3 Worm 4 Worm shaft 5, 5a Worm wheel 6 Ball bearing 7 Output shaft 8 Tooth part 9 Synthetic resin 10 Steering shaft 11 Worm for processing 12, 12a, 12b Intermediate material 13, 13a, 13b Helical gear
14 tooth bottom groove

Claims (2)

A method for producing a worm wheel in which at least a surface layer portion of a tooth portion is made of a synthetic resin,
A helical gear having a pressure angle equal to or less than the pressure angle of the completed tooth portion is formed in a portion to be a tooth portion of the worm wheel, and the helical gear tooth bottom is formed in a later processing step. In order to reduce the machining allowance for the tooth tip of the working worm used, after forming a root groove having side surfaces parallel to each other and making it an intermediate material,
Compared with the worm to be meshed during use, the above-mentioned machining worm is formed by adhering abrasive grains to the surface of the worm having the same tooth pitch in the axial direction and the diameters of the tooth tip and the tooth bottom being equal or larger. , Process the teeth of the intermediate material,
Worm wheel manufacturing method. A worm reducer comprising a worm and a worm wheel meshed with each other, wherein the worm wheel is produced by the method for manufacturing a worm wheel according to claim 1 .

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