US20210180676A1 - Worm wheel, worm decelerator, and method for producing worm wheel - Google Patents
Worm wheel, worm decelerator, and method for producing worm wheel Download PDFInfo
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- US20210180676A1 US20210180676A1 US16/074,363 US201716074363A US2021180676A1 US 20210180676 A1 US20210180676 A1 US 20210180676A1 US 201716074363 A US201716074363 A US 201716074363A US 2021180676 A1 US2021180676 A1 US 2021180676A1
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- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/14—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles
- B29C45/14311—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles using means for bonding the coating to the articles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/17—Component parts, details or accessories; Auxiliary operations
- B29C45/26—Moulds
- B29C45/27—Sprue channels ; Runner channels or runner nozzles
- B29C45/2701—Details not specific to hot or cold runner channels
- B29C45/2708—Gates
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C19/00—Bearings with rolling contact, for exclusively rotary movement
- F16C19/22—Bearings with rolling contact, for exclusively rotary movement with bearing rollers essentially of the same size in one or more circular rows, e.g. needle bearings
- F16C19/34—Bearings with rolling contact, for exclusively rotary movement with bearing rollers essentially of the same size in one or more circular rows, e.g. needle bearings for both radial and axial load
- F16C19/36—Bearings with rolling contact, for exclusively rotary movement with bearing rollers essentially of the same size in one or more circular rows, e.g. needle bearings for both radial and axial load with a single row of rollers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16H—GEARING
- F16H1/00—Toothed gearings for conveying rotary motion
- F16H1/02—Toothed gearings for conveying rotary motion without gears having orbital motion
- F16H1/04—Toothed gearings for conveying rotary motion without gears having orbital motion involving only two intermeshing members
- F16H1/12—Toothed gearings for conveying rotary motion without gears having orbital motion involving only two intermeshing members with non-parallel axes
- F16H1/16—Toothed gearings for conveying rotary motion without gears having orbital motion involving only two intermeshing members with non-parallel axes comprising worm and worm-wheel
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
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- F16H55/00—Elements with teeth or friction surfaces for conveying motion; Worms, pulleys or sheaves for gearing mechanisms
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- F16H55/06—Use of materials; Use of treatments of toothed members or worms to affect their intrinsic material properties
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16H—GEARING
- F16H55/00—Elements with teeth or friction surfaces for conveying motion; Worms, pulleys or sheaves for gearing mechanisms
- F16H55/02—Toothed members; Worms
- F16H55/22—Toothed members; Worms for transmissions with crossing shafts, especially worms, worm-gears
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/17—Component parts, details or accessories; Auxiliary operations
- B29C45/26—Moulds
- B29C45/27—Sprue channels ; Runner channels or runner nozzles
- B29C45/2701—Details not specific to hot or cold runner channels
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- B29C2045/2714—Gates elongated, e.g. film-like, annular
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
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- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/14—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles
- B29C45/1459—Coating annular articles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2705/00—Use of metals, their alloys or their compounds, for preformed parts, e.g. for inserts
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
- B29L2015/00—Gear wheels or similar articles with grooves or projections, e.g. control knobs
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D5/00—Power-assisted or power-driven steering
- B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
- B62D5/0403—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear characterised by constructional features, e.g. common housing for motor and gear box
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D5/00—Power-assisted or power-driven steering
- B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
- B62D5/0409—Electric motor acting on the steering column
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2361/00—Apparatus or articles in engineering in general
- F16C2361/61—Toothed gear systems, e.g. support of pinion shafts
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16H—GEARING
- F16H55/00—Elements with teeth or friction surfaces for conveying motion; Worms, pulleys or sheaves for gearing mechanisms
- F16H55/02—Toothed members; Worms
- F16H55/06—Use of materials; Use of treatments of toothed members or worms to affect their intrinsic material properties
- F16H2055/065—Moulded gears, e.g. inserts therefor
Definitions
- the present invention relates to a worm wheel which includes an inner wheel element which serves as a core material and a synthetic resin outer wheel element having a tooth part, a worm reduction gear including the worm wheel, and a manufacturing method of the worm wheel.
- FIGS. 12 to 17 illustrate one example of an electric power steering device which is described in Patent Document 1 and the like and is known from the past.
- a front end part of a steering shaft 2 in which a steering wheel 1 is attached to a rear end part is rotatably supported in a housing 3 .
- a worm wheel 4 is fixed to a portion driven rotationally by the steering shaft 2 .
- a worm shaft 6 is connected to an output shaft of an electric motor 5 .
- a worm tooth part 18 provided in an outer circumferential surface of an axial intermediate portion of the worm shaft 6 is engaged with a worm wheel tooth part 19 provided in the outer circumferential surface of the worm wheel 4 , so that a predetermined magnitude of the auxiliary torque (auxiliary power) can be applied with respect to the worm wheel 4 from the electric motor 5 in a predetermined direction.
- the worm wheel 4 is externally fitted and fixed to an axial intermediate portion of the output shaft 7 which serves as an output part of the auxiliary torque, and is rotated together with the output shaft 7 .
- the output shaft 7 is coupled with the front end part of the steering shaft 2 through a torsion bar 9 in the housing 3 in a state where a portion near both ends of the axial intermediate portion is supported to be rotatable only by one pair of rolling bearings 8 a and 8 b.
- the electric motor 5 rotationally drives the worm shaft 6 according to a direction and a magnitude of a steering torque which is detected by a torque sensor 10 and is applied from the steering wheel 1 to the steering shaft 2 , and the auxiliary torque is applied to the output shaft 7 .
- the rotation of the output shaft 7 is transmitted to a pinion shaft 14 which serves as an input part of a steering gear unit 13 through one pair of universal joints 11 a and 11 b and an intermediate shaft 12 , and a desired steering angle is given to a steering wheel.
- the worm wheel 4 is formed by combining a metal inner wheel element 15 and a synthetic resin outer wheel element 16 . That is, in the worm wheel 4 , the portion which is externally fitted and fixed to the output shaft 7 serves as the metal inner wheel element 15 having a circular ring shape, and the portion including the worm wheel tooth part 19 serves as the synthetic resin outer wheel element 16 .
- the outer wheel element 16 is made of a synthetic resin, so as to facilitate an operation (cost reduction) that forms the worm wheel tooth part 19 in the outer circumferential surface of the worm wheel 4 , and to reduce a tooth hitting noise generated in the engaging portion between the worm tooth part 18 of the worm shaft 6 and the worm wheel tooth part 19 of the worm wheel 4 .
- the outer wheel element 16 is made of a synthetic resin, and a radially outer end part of the inner wheel element 15 is embedded therein over the entire circumference through an injection molding (insertion molding).
- a (gear-shaped) concave-convex part 17 in a circumferential direction is provided, and a portion of a synthetic resin constituting the outer wheel element 16 enters into a plurality of concave parts constituting the concave-convex part 17 , so as to improve a holding power of the outer wheel element 16 in a rotation direction with respect to the inner wheel element 15 .
- the concave-convex part 17 in the circumferential direction is provided in the outer circumferential surface of the inner wheel element 15 , and the portion of a synthetic resin constituting the outer wheel element 16 enter into the plurality of concave parts constituting the concave-convex part 17 .
- the portion which is superimposed on the radially outer side with respect to the concave-convex part 17 may have different the radial thickness for each of portions in which a plurality of teeth 20 and 20 constituting the worm wheel tooth part 19 are positioned (see FIGS. 16 and 17 ).
- the molding shrinkage amount during the injection molding is different (is large in a portion (for example, ⁇ portion of FIG. 17 ) having a large radial thickness, and is small in a portion (for example, ⁇ portion of FIG. 17 ) having a small radial thickness) for each of portions where the plurality of teeth 20 and 20 are positioned.
- a difference occurs in sizes of the plurality of teeth 20 and 20 after molding, so that a manufacturing error such as a pitch error may occur in the worm wheel tooth part 19 .
- Patent Document 1 JP-T-2013-084613
- the invention is made in consideration of the above-described situation, and an object thereof is to implement a structure and a manufacturing method which can improve a holding power of a synthetic resin outer wheel element with respect to an inner wheel element and suppress the manufacturing error in the worm wheel tooth part provided in the outer circumferential surface of the outer wheel.
- a worm wheel of the present invention includes an inner wheel element and an outer wheel element.
- the inner wheel element includes a first annular concave part provided to be recessed in an axial direction at a position of an axial one-side surface located closer to a radial inside than an outer circumferential edge, a second annular concave part provided to be recessed in the axial direction at a position of an axial other-side surface located closer to a radial inside than an outer circumferential edge, a first concave-convex part provided in an outer diameter side circumferential surface constituting an inner surface of the first annular concave part in a circumferential direction, and a second concave-convex part provided in at least a part of an inner surface ⁇ outer diameter side circumferential surface, inner diameter side circumferential surface, and bottom surface (axial other-side surface) ⁇ of the second annular concave part in a circumferential direction, and an outer circumferential surface thereof is formed to be a cylindrical surface part in which a diameter in the axial direction is not changed; and an outer circumferential surface thereof is
- the outer wheel element is made of a synthetic resin, has a worm wheel tooth part in an outer circumferential surface, and embeds the inner wheel element so as to cover a continuous range from a radial intermediate portion of a bottom surface constituting the inner surface of the first annular concave part, through an outer circumferential surface of the inner wheel element, to an inner diameter side circumferential surface constituting at least the inner surface of the second annular concave part in a surface of the inner wheel element over an entire circumference, and the synthetic resin partially enters into a concave part constituting the first concave-convex part and a concave part constituting the second concave-convex part.
- the tooth tip circle diameter and the tooth bottom circle diameter in a portion of the worm wheel tooth part overlapping at least the cylindrical surface part, which is the outer circumferential surface of the inner wheel element, are not changed in the axial direction, respectively.
- metal may be adopted as a material of the inner wheel element.
- a synthetic resin may be adopted which is excellent in the thermal resistance compared to the material of the outer wheel element and hardly receives heat effect when the outer wheel element is injection-molded (for example, thermoplastic resin is adopted as the synthetic resin constituting the outer wheel element, and a thermosetting resin is adopted as the synthetic resin constituting the inner wheel element).
- the inner wheel element may be embedded in the outer wheel element, such that a continuous range from the inner diameter side circumferential surface constituting the inner surface of the first annular concave part through the outer circumferential surface of the inner wheel element to an inner diameter side circumferential surface constituting an inner surface of the second annular concave part in the surface of the inner wheel element is covered over an entire circumference.
- a tilted surface part which is tilted in a direction in which a width dimension in a radial direction of the second annular concave part becomes larger toward an axial other side with respect to a central axis of the inner wheel element may be provided in at least one circumferential surface among an outer diameter side circumferential surface and the inner diameter side circumferential surface constituting the inner surface of the second annular concave part.
- the tilted surface part and a non-tilted surface part which is not tilted with respect to the central axis of the inner wheel element may be provided in the outer diameter side circumferential surface constituting the inner surface of the second annular concave part.
- the tilted surface part and the non-tilted surface part which is not tilted with respect to the central axis of the inner wheel element may be provided in the inner diameter side circumferential surface constituting the inner surface of the second annular concave part.
- a projecting part which projects on the axial other side from a portion adjacent to the radially outer side may be provided in a radially inner end part (for example, the same radial position as the radially inner end part of the second annular concave part in the axial other-side surface of the outer wheel element) of an axial other-side surface of the outer wheel element.
- the first concave-convex part may be provided over the entire axial length of the outer diameter side circumferential surface configuring the inner surface of the first annular concave part, and the synthetic resin may partially enter into the entire concave part configuring the first concave-convex part.
- the second concave-convex part may be provided over the entire axial length of the outer diameter side circumferential surface configuring the inner surface of the second annular concave part, and the synthetic resin may partially enter into the entire concave part configuring the second concave-convex part.
- the radially outer end parts of both axial surfaces of the inner wheel element which are continuous (directly or through the chamfered portion) with respect to both axial end edges of the cylindrical surface part which is the outer circumferential surface of the inner wheel element each may serve as flat surface parts orthogonal to the central axis of the inner wheel element. Accordingly, the both axial end edges of the cylindrical surface part which is the outer circumferential surface of the inner wheel element each can be formed to have a circular shape in which the axial position is not changed in the circumferential direction.
- a plurality of concave parts and a plurality of convex parts configuring the first concave-convex part may be formed in parallel to the axial direction of the worm wheel.
- a plurality of concave parts and a plurality of convex parts configuring the second concave-convex part may be formed in parallel to the axial direction of the worm wheel.
- the plurality of teeth configuring the worm wheel tooth part may be formed in the direction which is tilted in a predetermined direction with respect to the axial direction of the worm wheel
- the plurality of concave parts and the plurality of convex parts configuring the first concave-convex part may be formed in the direction which is tilted in the opposite direction to the predetermined direction with respect to the axial direction of the worm wheel.
- the plurality of concave parts and the plurality of convex parts configuring the second concave-convex part may be formed in the direction which is tilted in the opposite direction to the predetermined direction with respect to the axial direction of the worm wheel.
- a sub concave part may be provided to be recessed radially outward in a portion which is positioned on an axial deep side from an axial opening-side end edges of the first annular concave part in the outer diameter side circumferential surface configuring the inner surface of the first annular concave part, and a portion of the synthetic resin configuring the outer wheel element may enter into the sub concave part.
- a cross section of the sub concave part with respect to a virtual plane including the central axis of the inner wheel element may have a V shape such that a width dimension in the axial direction becomes smaller from an opening part on an inner diameter side toward a bottom part on an outer diameter side.
- a worm reduction gear of the invention includes a housing, a rotation shaft, a worm wheel, and a worm shaft.
- the rotation shaft is supported to be rotatable with respect to the housing.
- the worm wheel has a worm wheel tooth part in an outer circumferential surface and is externally fitted and fixed to the rotation shaft.
- the worm shaft has a worm tooth part in an axial intermediate portion of an outer circumferential surface and is supported to be rotatable with respect to the housing in a state where the worm tooth part is engaged with the worm wheel tooth part.
- the worm wheel is the worm wheel of the invention.
- a rolling bearing which includes an inner ring, an outer ring, and a plurality of rolling bodies provided between an outer circumferential surface of the inner ring and an inner circumferential surface of the outer ring, and supports the rotation shaft to be rotatable with respect to the housing may be provided in a portion adjacent to an axial other side of the worm wheel.
- an axial other-side surface of the outer wheel element constituting the worm wheel may face an axial one-side surface of the inner ring and an axial one-side surface of the outer ring in the axial direction.
- an axial distance between the axial other-side surface of the outer wheel element and the axial one-side surface of the inner ring may be smaller than an axial distance between the axial other-side surface of the outer wheel element and the axial one-side surface of the outer ring.
- a projecting part which projects on the axial other side from a portion adjacent to the radially outer side may be provided in a radially inner end part of the axial other-side surface of the outer wheel element constituting the worm wheel, and an axial other-side surface of the projecting part may face the axial one-side surface of the inner ring in the axial direction.
- the projecting part which projects on the axial other side from the portion which faces the axial one-side surface of the outer ring in the axial direction may be provided in the portion which faces the axial one-side surface of the inner ring in the axial direction.
- a manufacturing method of the worm wheel of the invention is a manufacturing method for the worm wheel of the invention.
- a radially outer end part of a disc gate may be positioned in the radially inner end part of the axial other side of the outer wheel element when an insertion molding is performed in which the outer wheel element is coupled with the inner wheel element at the same time when the outer wheel element is manufactured by the injection molding.
- the worm wheel, the worm reduction gear, and the manufacturing method of the worm wheel according to the above-described invention it is possible to improve the holding power of the synthetic resin outer wheel element with respect to the inner wheel element and to suppress the manufacturing error in the worm wheel tooth part provided in the outer circumferential surface of the outer wheel.
- FIG. 1 is a sectional view similar with FIG. 14 according to a first embodiment of the invention.
- FIG. 2 is a sectional view of a worm wheel according to the first embodiment.
- FIG. 3 is a half-sectional view of the worm wheel according to the first embodiment when partially cut away.
- FIG. 4 is a sectional view taken along line A-A of FIG. 2 according to the first embodiment.
- FIG. 5 is a sectional view taken along line B-B of FIG. 2 according to the first embodiment.
- FIG. 6 is an enlarged view of C portion of FIG. 4 according to the first embodiment.
- FIG. 7 is a sectional view of a worm wheel according to a second embodiment of the invention.
- FIG. 8 is a sectional view illustrating a state where an outer wheel element is injection-molded according to the second embodiment.
- FIG. 9 is a half-sectional view of a worm wheel according to a third embodiment of the invention when partially cut away.
- FIG. 10 is a sectional view of a worm wheel according to a fourth embodiment of the invention.
- FIG. 11 is a sectional view illustrating a state where an outer wheel element is injection-molded according to the fourth embodiment.
- FIG. 12 is a side view illustrating one example of a structure of the electric power steering device in the related art partially cut away.
- FIG. 13 is an enlarged sectional view taken along line D-D of FIG. 12 .
- FIG. 14 is an enlarged sectional view taken along line E-E of FIG. 12 .
- FIG. 15 is a sectional view of the worm wheel.
- FIG. 16 is a sectional view taken along line F-F of FIG. 15 .
- FIG. 17 is an enlarged view of G portion of FIG. 16 .
- FIGS. 1 to 6 A first embodiment of the invention will be described with reference to FIGS. 1 to 6 .
- FIG. 1 illustrates an electric power steering device in which a worm reduction gear of this embodiment is assembled.
- a front end part of a steering shaft 2 in which a steering wheel 1 (see FIG. 12 ) is attached to a rear end part is supported to be rotatable in a housing 3 .
- a worm wheel 4 a is fixed to a portion rotationally driven by the steering shaft 2 .
- a worm shaft 6 (see FIG. 13 ) is connected to an output shaft of an electric motor 5 .
- a worm tooth part 18 provided in the outer circumferential surface of the axial intermediate portion of the worm shaft 6 is engaged with a worm wheel tooth part 19 a provided in the outer circumferential surface of the worm wheel 4 a, so that a predetermined magnitude of auxiliary torque (auxiliary power) can be applied from the electric motor 5 with respect to the worm wheel 4 a in the predetermined direction.
- the worm wheel 4 a is externally fitted and fixed to an axial intermediate portion of an output shaft 7 which corresponds to a rotation shaft described in appended claims and serves as an output part of the auxiliary torque, and rotates together with the output shaft 7 .
- the output shaft 7 is coupled with the front end part of the steering shaft 2 through a torsion bar 9 in the housing 3 in a state where a portion near both ends of the axial intermediate portion is supported to be rotatable by one pair of rolling bearings 8 a and 8 b.
- the electric motor 5 rotationally drives the worm shaft 6 according to a direction and a magnitude of a steering torque which is detected by a torque sensor 10 and is applied from the steering wheel 1 to the steering shaft 2 , and the auxiliary torque is applied to the output shaft 7 .
- the rotation of the output shaft 7 is transmitted to a pinion shaft 14 (see FIG. 12 ) which serves as an input part of a steering gear unit 13 through one pair of universal joints 11 a and 11 b and an intermediate shaft 12 , and a desired steering angle is given to a steering wheel.
- one pair of the rolling bearings 8 a and 8 b are ball bearings which include inner rings 33 a and 33 b which are externally fitted to and supported by the output shaft 7 , outer rings 34 a and 34 b internally fitted to and supported by the housing 3 , and a plurality of balls 35 a and 35 b which each are a rolling body and are provided to be rollable between an inner ring raceway provided in the outer circumferential surface of the inner rings 33 a and 33 b and an outer ring raceway provided in the inner circumferential surface of the outer rings 34 a and 34 b, respectively.
- another kind of rolling bearing such as a cylindrical roller bearing or a tapered roller bearing also may be adopted as one pair of rolling bearings 8 a and 8 b.
- the worm wheel 4 a is formed by combining an inner wheel element 15 a and an outer wheel element 16 a.
- the inner wheel element 15 a is formed of metal in an annular shape (substantially circular ring shape), and a fitting hole 21 for internally fitting and fixing the axial intermediate portion of the output shaft 7 in a torque-transmittable manner is included in a radial intermediate portion.
- a first annular concave part 22 is provided to be recessed in an axial direction over the entire circumference of a radial intermediate portion of an axial one-side surface (the left surface in FIGS. 1 to 3 and 6 ) of the inner wheel element 15 a.
- the outer diameter side circumferential surface is provided with a first (gear-shaped) concave-convex part 23 in the circumferential direction which is formed in such a manner that a concave part 26 and a convex part 27 are arranged alternately (to have constant pitch in the illustrated example) in the circumferential direction in the entire length and the entire circumference of the outer diameter side circumferential surface in an axial direction.
- a broken line hidden line
- a plurality of the concave parts 26 and a plurality of the convex parts 27 constituting the first concave-convex part 23 are formed in parallel to the axial direction (a right and left direction in FIGS. 1 to 3 ) of the inner wheel element 15 a (worm wheel 4 a ).
- the first concave-convex part 23 is formed such that the plurality of the convex parts 27 and 27 each extending in the axial direction are arranged to be spaced apart from each other in the circumferential direction (at equal intervals in the circumferential direction in the illustrated example) in the entire length and the entire circumference of the outer diameter side circumferential surface configuring the inner surface of the first annular concave part 22 in the axial direction, and the portions between the convex portions 27 and 27 adjacent in the circumferential direction are formed as concave portions 26 and 26 , respectively.
- the inner diameter side circumferential surface which configures the inner surface of the first annular concave part 22 serves as a cylindrical surface part 36 having a simple cylindrical surface shape.
- the bottom surface which configures the inner surface of the first annular concave part 22 serves as a flat surface part 37 which is orthogonal to a central axis of the inner wheel element 15 a and has a circular ring shape.
- the axial other end portions of the plurality of the convex parts 27 and 27 configuring the first concave-convex part 23 are connected to the flat surface part 37 .
- a second annular concave part 38 is provided to be recessed in the axial direction over the entire circumference of the radial intermediate portion of the axial other-side surface (the right surface in FIGS. 1 to 3 ) of the inner wheel element 15 a.
- the bottom surface (the axial other-side surface) configuring the inner surface of the second annular concave part 38 is provided with a (face spline shaped) second concave-convex part 49 in the circumferential direction.
- the second concave-convex part 49 is formed such that a plurality of convex parts 50 and 50 each extending in a radial direction are arranged to be spaced apart from each other in the circumferential direction (at equal intervals in the circumferential direction in the illustrated example) in the entire length and the entire circumference of the bottom surface configuring the second annular concave part 38 in the radial direction, and the portions between the convex portions 50 and 50 adjacent in the circumferential direction are formed as concave portions 51 and 51 , respectively.
- the outer diameter side circumferential surface serves as an outer diameter side cylindrical surface part 40 formed in a simple cylindrical surface shape
- the inner diameter side circumferential surface serves as an inner diameter side cylindrical surface part 48 formed in a simple cylindrical surface shape.
- Both end parts in the radial direction of the plurality of convex parts 50 and 50 configuring the second concave-convex part 49 are connected to the outer diameter side cylindrical surface part 40 and the inner diameter side cylindrical surface part 48 , respectively.
- the outer circumferential surface (excluding chamfered portions thereof in a case where the chamfered portions are provided in both axial end edge parts) serves as a cylindrical surface part 24 formed in a simple cylindrical surface shape which has a bus line parallel to the central axis of the inner wheel element 15 a (worm wheel 4 a ) and has a diameter which is not changed in the axial direction.
- the radially outer end part (the portion positioned on the radially outer side from the first annular concave part 22 ) of the axial one-side surface of the inner wheel element 15 a and the radially outer end part (the portion positioned on the radially outer side from the second annular concave part 38 ) of the axial other-side surface of the inner wheel element 15 a are continuous (directly or through the chamfered portion) with respect to both axial end edges of the cylindrical surface part 24 and serve as flat surface parts 25 a and 25 b which have a circular ring shape and are orthogonal to the central axis of the inner wheel element 15 a, respectively.
- the inner wheel element 15 a includes an inner diameter side annular part 28 and an outer diameter side annular part 29 which are arranged coaxially with each other, and a connection part 30 which has a circular ring shape and connects the axial intermediate portions of the outer circumferential surface of the inner diameter side annular part 28 and the inner circumferential surface of the outer diameter side annular part 29 .
- the outer circumferential surface of the outer diameter side annular part 29 serves as the cylindrical surface part 24
- both axial surfaces of the outer diameter side annular part 29 serve as the flat surface parts 25 a and 25 b.
- the portion surrounded by three sides of the axial one end portion of the outer circumferential surface of the inner diameter side annular part 28 , the axial one end portion of the inner circumferential surface of the outer diameter side annular part 29 , and the axial one-side surface of the connection part 30 serves as the first annular concave part 22 .
- the portion surrounded by three sides of the axial other end portion of the outer circumferential surface of the inner diameter side annular part 28 , the axial other end portion of the inner circumferential surface of the outer diameter side annular part 29 , and the axial other-side surface of the connection part 30 serves as the second annular concave part 38 .
- the axial one end portion serves as the first concave-convex part 23
- the axial other end portion serves as the outer diameter side cylindrical surface part 40
- the axial one end portion serves as the cylindrical surface part 36
- the axial other end portion serves as the inner diameter side cylindrical surface part 48
- the axial one-side surface serves as the flat surface part 37
- the axial other-side surface serves as the second concave-convex part 49 .
- various kinds of metals such as copper alloy, aluminum alloy, and magnesium alloy in addition to ferrous metal such as iron and steel may be adopted as a metal constituting the inner wheel element 15 a.
- various kinds of cutting processes or plastic processes can be adopted as a process to mold the inner wheel element 15 a.
- the plastic process forging, pressing, flow forming, and the like is preferably adopted when molded in a high yield at low cost.
- the outer wheel element 16 a is manufactured by injection-molding a synthetic resin, a portion of the inner wheel element 15 a is embedded over the entire circumference through the injection molding (insertion molding). Specifically, one portion (the radially outer end part and the intermediate portion) of the inner wheel element 15 a is embedded in the outer wheel element 16 a, such that the continuous range from the radial intermediate portion of the bottom surface (flat surface part 37 ) constituting the inner surface of the first annular concave part 22 , through the outer circumferential surface (cylindrical surface part 24 ) of the inner wheel element 15 a, to the inner diameter side circumferential surface (inner diameter side cylindrical surface part 48 ) constituting the inner surface of the second annular concave part 38 in the surface of the inner wheel element 15 a is covered over the entire circumference.
- a portion of the synthetic resin enters into the first annular concave part 22 and the second annular concave part 38 .
- the portion entering into the first annular concave part 22 configures a first suppression part 31 having an annular shape and the portion entering into the second annular concave part 38 configures a second suppression part 42 having an annular shape.
- a portion of the synthetic resin constituting the first suppression part 31 enters into the entire portion of the plurality of concave parts 26 and 26 constituting the first concave-convex part 23 (the portion between the convex parts 27 and 27 adjacent in the circumferential direction), so as to cover the entire surface of the first concave-convex part 23 .
- a first rotation holding part 32 is configured to be engaged with the first concave-convex part 23 (have a shape coinciding with the first concave-convex part 23 ).
- a portion of the synthetic resin constituting the second suppression part 42 enters into the entire portion of the plurality of concave parts 51 and 51 constituting the second concave-convex part 49 (the portion between the convex parts 50 and 50 adjacent in the circumferential direction), so as to cover the entire surface of the second concave-convex part 49 .
- a second rotation holding part 52 is configured to be engaged with the second concave-convex part 49 (have a shape coinciding with the second concave-convex part 49 ).
- the worm wheel tooth part 19 a is formed in the outer circumferential surface of the outer wheel element 16 a.
- the axial intermediate portion of the worm wheel tooth part 19 a is radially superimposed with the cylindrical surface part 24 .
- the direction of forming the plurality of teeth 20 a and 20 a constituting the worm wheel tooth part 19 a is tilted with respect to the axial direction of the worm wheel 4 a.
- a tooth tip circle diameter and a tooth bottom circle diameter of the worm wheel tooth part 19 a are not changed with respect to the axial direction, respectively.
- the radially outer end part (outer circumferential part) of the disc gate 47 is positioned in a portion in which the radially inner end part of the axial other side of the outer wheel element 16 a.
- the runner 46 is provided to extend from the central portion of the disc gate 47 to the axial other side. The molten resin fed into the cavity 45 from the runner 46 and the disc gate 47 flows from the inner diameter side to the outer diameter side along the axial other-side surface of the inner wheel element 15 a, and part thereof enters into the second annular concave part 38 .
- the molten resin fed into the cavity 45 reaches a portion corresponding to the first suppression part 31 and stops after entering into the portion where the radially outer end part of the outer wheel element 16 a in the cavity 45 is formed.
- the portion does not abut on the molten resin having flowed from the other direction. As a result, it can be prevented that weld or the like which is weak in strength occurs in the outer wheel element 16 a obtained by the injection molding.
- the molding device 44 is opened and the plurality of dies are separated from each other.
- the synthetic resin which is cooled and solidified in the cavity 45 is cut over the entire circumference in the portion corresponding to the radially inner end part of the axial other side of the outer wheel element 16 a, and the worm wheel 4 a is obtained by performing a finishing process as needed.
- various kinds of synthetic resins such as the polyamide 46 (PA46), a polyamide 9T (PA9T), a polyphenylene sulfide (PPS), a polyethylene terephthalate (PET), and a polyacetal (POM) may be adopted as a synthetic resin constituting the outer wheel element 16 a.
- various kinds of reinforced fibers such as a glass fiber, a polyethylene fiber, a carbon fiber, and an aramid fiber may be mixed in the synthetic resin.
- the entire engaging portion of the worm tooth part 18 and the worm wheel tooth part 19 a is radially superimposed with the cylindrical surface part 24 provided in the outer circumferential surface of the inner wheel element 15 a.
- the holding power of the synthetic resin outer wheel element 16 a can be secured from the metal inner wheel element 15 a, and the manufacturing error can be suppressed in the worm wheel tooth part 19 a provided in the outer circumferential surface of the outer wheel element 16 a.
- the description will be given below about these points.
- the first annular concave part 22 and the second annular concave part 38 are provided over the entire circumferences in both axial surfaces of the inner wheel element 15 a, respectively. Further, a portion of the inner wheel element 15 a is embedded in the outer wheel element 16 a, such that the continuous range from the radial intermediate portion of the bottom surface (flat surface part 37 ) constituting the inner surface of the first annular concave part 22 , through the outer circumferential surface (cylindrical surface part 24 ) of the inner wheel element 15 a, to the inner diameter side circumferential surface (inner diameter side cylindrical surface part 48 ) constituting the inner surface of the second annular concave part 38 in the surface of the inner wheel element 15 a is covered over the entire circumference.
- the radial intermediate portion in the inner wheel element 15 a as well as the radially outer end part is embedded in the outer wheel element 16 a.
- the holding power of the outer wheel element 16 a in the direction of the moment M with respect to the inner wheel element 15 a can be larger compared to a case where only the radially outer end part is embedded.
- a portion of the synthetic resin constituting the outer wheel element 16 a enters into the first annular concave part 22 to configure the first suppression part 31 having an annular shape, and enters into the second annular concave part 38 to configure the second suppression part 42 having an annular shape.
- the holding power of the outer wheel element 16 a in the direction of the moment M with respect to the inner wheel element 15 a can be enlarged on the basis of the engagement of the first annular concave part 22 and the first suppression part 31 and the engagement of the second annular concave part 38 and the second suppression part 42 .
- the first concave-convex part 23 in the circumferential direction is provided in the outer diameter side circumferential surface configuring the inner surface of the first annular concave part 22 , and a portion of the synthetic resin configuring the first suppression part 31 enters into the entire plurality of the concave parts 26 and 26 configuring the first concave-convex part 23 , thereby configuring the first rotation holding part 32 which is engaged with the first concave-convex part 23 .
- the second concave-convex part 49 in the circumferential direction is provided in the bottom surface configuring the inner surface of the second annular concave part 38 , and a portion of the synthetic resin configuring the second suppression part 42 enters into the entire plurality of the concave parts 51 and 51 configuring the second concave-convex part 49 , thereby configuring the second rotation holding part 52 which is engaged with the second concave-convex part 49 .
- the first concave-convex part 23 is provided over the entire axial length of the outer diameter side circumferential surface configuring the inner surface of the first annular concave part 22
- the second concave-convex part 49 is provided over the entire radial length of the bottom surface configuring the inner surface of the second annular concave part 38 , and thus the holding power in the rotation direction can be large.
- the outer circumferential surface of the inner wheel element 15 a serves as the cylindrical surface part 24 in which the diameter in the axial direction is not changed.
- the portion which is superimposed on the radially outer side with respect to the cylindrical surface part 24 which is the outer circumferential surface of the inner wheel element 15 a has the (substantially) same radial thickness in the portions where the plurality of teeth 20 a and 20 a constituting the worm wheel tooth part 19 a are positioned.
- the tooth tip circle diameter and the tooth bottom circle diameter of the worm wheel tooth part 19 a provided in the outer circumferential surface of the outer wheel element 16 a is not changed in the axial direction, respectively.
- the radially outer end parts of the both axial surfaces of the inner wheel element 15 a which are continuous with respect to the both axial end edges of the cylindrical surface part 24 which is the outer circumferential surface of the inner wheel element 15 a serve as the flat surface parts 25 a and 25 b which have the circular ring shape and are orthogonal to the central axis of the inner wheel element 15 a, respectively.
- the both axial end edges of the cylindrical surface part 24 which is the outer circumferential surface of the inner wheel element 15 a each have a circular shape in which the axial position is not changed in the circumferential direction.
- the portion which is superimposed on the radially outer side with respect to the outer circumferential surface of the inner wheel element 15 a has almost the same radial thickness over the entire axial length including both axial end edge parts in the portions in which the plurality of teeth 20 a and 20 a constituting the worm wheel tooth part 19 a are positioned.
- the portion which is superimposed on the radially outer side with respect to at least the outer circumferential surface of the inner wheel element 15 a can be set such that the amount of the molding shrinkage, which occurs during the injection molding, of the portions in which the plurality of teeth 20 a and 20 a are positioned is almost the same.
- the plurality of teeth 20 a and 20 a after molding can be set to have almost the same magnitude (radial thickness), so as to suppress the manufacturing error such as the pitch error with respect to the worm wheel tooth part 19 a.
- the plurality of concave parts 26 and the plurality of the convex parts 27 constituting the first concave-convex part 23 are formed in parallel to the axial direction. For this reason, it is suppressed that the first concave-convex part 23 causes the deformation of the outer wheel element 16 a associated with the molding shrinkage of the synthetic resin, and the outer wheel element 16 a can be molded accurately.
- the entire engaging portion 50 of the worm tooth part 18 and the worm wheel tooth part 19 a is radially superimposed with the cylindrical surface part 24 in a state where the worm reduction gear is assembled.
- the worm tooth part 19 a the worm tooth part 18 is engaged with the portion which suppresses the manufacturing error such as the pitch error as described above. For this reason, it is possible to make the engaged state of the engaging portion 50 excellent.
- FIGS. 7 and 8 A second embodiment of the invention will be described with reference to FIGS. 7 and 8 .
- the outer diameter side circumferential surface is formed such that respective axial end edges of an outer diameter side tilted surface part 39 provided in one side (an one end portion and an intermediate portion) and an outer diameter side cylindrical surface part 40 provided in the other side (other end portion) are continuous to each other in the axial direction.
- the outer diameter side tilted surface part 39 corresponds to a tilted surface part described in appended claims, and is formed in a partially tapered surface shape that is tilted in a direction (the direction toward the radially outer side) in which a radial width dimension of the second annular concave part 38 a is larger toward the axial other side with respect to the central axis of the inner wheel element 15 b.
- the outer diameter side cylindrical surface part 40 corresponds to a non-tilted surface part described in appended claims, and is formed in a simple cylindrical surface shape not to be tilted with respect to the central axis of the inner wheel element 15 b.
- the inner diameter side circumferential surface constituting the inner surface of the second annular concave part 38 is configured only by an inner diameter side tilted surface part 41 .
- the inner diameter side tilted surface part 41 corresponds to the tilted surface part described in appended claims, and is formed in a partially tapered surface shape that is tilted in a direction (the direction toward the radially inner side) in which the radial width dimension of the second annular concave part 38 a is larger toward the axial other side with respect to the central axis of the inner wheel element 15 b.
- the inner wheel element 15 a is embedded in an outer wheel element 16 b configuring the worm wheel 4 b such that a continuous range from the inner diameter side circumferential surface (cylindrical surface part 36 ) configuring the inner surface of the first annular concave part 20 through the outer circumferential surface (cylindrical surface part 24 ) of the inner wheel element 15 b to an inner diameter side circumferential surface (inner diameter side tilted surface part 41 ) configuring an inner surface of the second annular concave part 38 a in the surface of the inner wheel element 15 b is covered over an entire circumference.
- the projecting part 43 is provided over the entire circumference in a radial position which is the same as the radially inner end part of the second annular concave part 38 a in the state of projecting from the inside (the axial other-side surface of the second suppression part 42 a ) of the second annular concave part 38 to the axial other side.
- the insertion molding is performed in which the outer wheel element 16 b is coupled with respect to the inner wheel element 15 b.
- the radially outer end part (outer circumferential part) of the disc gate 47 is positioned in a portion in which the radially inner end part of the axial other side of the outer wheel element 16 a is formed as illustrated in FIG. 8 similarly to the case of the above-described first embodiment.
- the molten resin fed into the cavity 45 from the runner 46 and the disc gate 47 flows from the inner diameter side to the outer diameter side along the axial other-side surface of the inner wheel element 15 b, and part thereof enters into the second annular concave part 38 a.
- the inner diameter side tilted surface part 41 and the outer diameter side tilted surface part 39 are provided in the inner diameter side circumferential surface and the outer diameter side circumferential surface configuring the inner surface of the second annular concave part 38 a, the molten resin enters into the portion where the radially outer end part of the outer wheel element 16 b in the cavity 45 is formed without greatly disturbing the flow.
- the molding device 44 is opened and the plurality of dies are separated from each other, and the synthetic resin which is cooled and solidified in the cavity 45 is cut over the entire circumference in the portion corresponding to the radially inner end part of the axial other side of the outer wheel element 16 b, and the worm wheel 4 b is obtained by performing a finishing process as needed.
- a portion (the portion to be removed originally) of the synthetic resin positioned in the radially outer end part of the disc gate 47 remains without removal to form the projecting part 43 . Accordingly, a yield is excellent, and the projecting part 43 can be formed at low cost.
- the axial other-side surface of the outer wheel element 16 b and the axial one-side surface of the inner ring 33 a and the axial one-side surface of the outer ring 34 a which are provided in the portion adjacent to the axial other side of the worm wheel 4 b and configure the rolling bearing 8 a, face each other in the axial direction through a gap.
- the portion corresponding to the projecting part 43 faces the axial one-side surface of the inner ring 33 a in the axial direction
- the portion corresponding to the radial intermediate portion of the second suppression part 42 a faces the axial one-side surface of the outer ring 34 a in the axial direction.
- the axial one-side surface of the inner ring 33 a and the axial one-side surface of the outer ring 34 a are provided in almost the same position in the axial direction while in the axial other-side surface of the outer wheel element 16 a, the portion (the axial other-side surface of the projecting part 43 ) corresponding to the projecting part 43 is positioned on the axial other side (by at least an axial dimension of the projecting part 43 ) from the portion (the axial other-side surface of the radial intermediate portion of the second suppression part 42 a ) corresponding to the radial intermediate portion of the second suppression part 42 .
- an axial distance X between the axial other-side surface (the axial other-side surface of the projecting part 43 ) of the outer wheel element 16 a and the axial one-side surface of the inner ring 33 a is smaller than the axial distance Y between the axial other-side surface (the axial other-side surface of the radial intermediate portion of the second suppression part 42 a ) of the outer wheel element 16 a and the axial one-side surface of the outer ring 34 a (X ⁇ Y).
- a range covering the axial one-side surface of the inner wheel element 15 b by the synthetic resin configuring the outer wheel element 16 b is enlarged to the inner diameter side circumferential surface (the cylindrical surface part 36 ) configuring the inner surface of the first annular concave part 22 (the radial length of the first suppression part 31 a is increased), as compared to the case of the above-described first embodiment. Therefore, the holding power in the direction of the moment M of the outer wheel element 16 b with respect to the inner wheel element 15 b can be increased by the extent.
- the outer diameter side cylindrical surface part 40 is provided in the outer diameter side circumferential surface configuring the inner surface of the second annular concave part 38 a. For this reason, the engaging power of the second annular concave part 38 a and the second suppression part 42 a with respect to the moment M can be enlarged compared to a case where the entire outer diameter side circumferential surface serves as the outer diameter side tilted surface part 39 . As a result, it is possible to enlarge the holding power of the outer wheel element 16 b in the direction of the moment M with respect to the inner wheel element 15 b.
- the inner diameter side tilted surface part 41 and a non-tilted surface part such as the inner diameter side cylindrical surface part can be provided together in the inner diameter side circumferential surface configuring the inner surface of the second annular concave part 38 a.
- the axial distance X between the axial other-side surface (the axial other-side surface of the projecting part 43 ) of the outer wheel element 16 b and the axial one-side surface of the inner ring 33 a becomes smaller than the axial distance Y between the axial other-side surface (the axial other-side surface of the radial intermediate portion of the second suppression part 42 a ) of the outer wheel element 16 b and the axial one-side surface of the outer ring 34 a (X ⁇ Y).
- a third embodiment of the invention will be described with reference to FIG. 9 .
- a first annular concave part 22 a provided in an axial one-side surface of an inner wheel element 15 c constituting a worm wheel 4 c is configured to be different from the case of the above-described first embodiment.
- a plurality of concave parts 26 a and a plurality of convex parts 27 a constituting the first concave-convex part 23 a provided in the outer diameter side circumferential surface are formed to be tilted in an inverse direction to the tilted direction of the plurality of teeth 20 a and 20 a constituting the worm wheel tooth part 19 a provided in the outer circumferential surface of the outer wheel element 16 c with respect to the central axis of the worm wheel 4 c.
- the tilted direction of the plurality of teeth 20 a and 20 a constituting the worm wheel tooth part 19 a and the tilted direction of the plurality of concave parts 26 a and the plurality of convex parts 27 a constituting the first concave-convex part 23 a are set to be opposite to each other with respect to the central axis of the worm wheel 4 c.
- FIGS. 10 to 11 A fourth embodiment of the invention will be described with reference to FIGS. 10 to 11 .
- This embodiment is a modification of the above-described second embodiment illustrated in FIGS. 7 and 8 .
- a sub concave part 53 is provided to be recessed radially outward over the entire circumference in an axial deep end part (which is an axial other end portion and a right end part in FIGS. 10 and 11 ) of the first annular concave part 22 .
- the cross section of the sub concave part 53 with respect to a virtual plane including the central axis of the inner wheel element 15 d has a V shape such that the width dimension in the axial direction becomes smaller from an opening part on the inner diameter side toward the bottom part on the outer diameter side.
- the first concave-convex part 23 is provided in the entire portion deviated from the sub concave part 53 in the outer diameter side circumferential surface constituting the inner surface of the first annular concave part 22 . Further, the axial deep end parts of the concave parts 26 constituting the first concave-convex part 23 are opened to the inner surfaces of the sub concave parts 53 , respectively. Incidentally, in the case of this embodiment, the radial depth of the sub concave part 53 is slightly larger than the radial depth of the concave part 26 constituting the first concave-convex part 23 .
- the radial depth of the sub concave part 53 may be configured to be the same as the radial depth of the concave part 26 or be configured to be less than the radial depth of the concave part 26 .
- a portion of the portion (the suppression part 31 a having an annular shape) having entered into the first annular concave part 22 enters into the entire sub concave part 53 to cover the entire inner surface of the sub concave part 53 , so as to configure a sub suppression part 54 (which has a shape coinciding with the sub concave part 53 ) engaged with the sub concave part 53 .
- the holding power of the outer wheel element 16 d in the direction of the moment M with respect to the inner wheel element 15 d can be improved on the basis of the engagement of the sub concave part 53 and the sub suppression part 54 .
- the sub suppression part 54 (sub concave part 53 ) can prevent that the flow of the molten resin into the cavity 45 is hindered.
- the cross section of the sub concave part 53 has a V shape such that the width dimension in the axial direction becomes smaller from the opening part on the inner diameter side toward the bottom part on the outer diameter side. The molten resin can smoothly enter from the opening part of the sub concave part 53 toward the bottom part. Accordingly, it can be prevented that the flow of the molten resin into the cavity 45 is hindered, and the moldability of the sub suppression part 54 can be made excellent.
- the sub concave part 53 when the inner wheel element 15 d is manufactured, after the sub concave part 53 is molded with respect to the outer diameter side circumferential surface constituting the inner surface of the first annular concave part 22 , in a case where the first concave-convex part 23 is molded by the plastic process such as cold forging, the sub concave part 53 may be used as an escape part of a molding die of the first concave-convex part 23 or an escape part of a metal material deformed according to the molding of the first concave-convex part 23 .
- the molding load of the first concave-convex part 23 is suppressed to be low, so as to reduce the molding facility capacity of the first concave-convex part 23 and to improve the lifetime of the molding die.
- the sub concave part 53 may be molded by the cutting process or the like.
- the invention may be implemented by appropriately combining the configurations of the above-described embodiments.
- the inner wheel element is formed of metal.
- the inner wheel element may be formed of a synthetic resin which is excellent in the thermal resistance compared to the synthetic resin constituting the outer wheel element. Also in this case, it is possible to obtain the effect similar with the case of the above-described embodiments.
- the surface of the inner wheel element if at least one portion (for example, the cylindrical surface part) in the portions which are covered with the synthetic resin constituting the outer wheel element serves as a minute concave-convex surface formed by various kinds of processes such as a knurling process, an emboss process, and a shot blast, a portion of the synthetic resin constituting the outer wheel element enters into the concave part constituting the minute concave-convex surface.
- a portion of the synthetic resin constituting the outer wheel element enters into the concave part constituting the minute concave-convex surface.
- the depth of the concave part constituting the minute concave-convex surface is set to be equal to or less than one tenth (for example, equal to or less than one twentieth or equal to or less than one thirtieth) of the radial height of the teeth constituting the worm wheel tooth part, so as to hardly make an effect on the volume of the synthetic resin constituting the outer wheel element, it can be suppressed that the manufacturing error occurs in the portion engaged with the worm tooth part in the worm wheel tooth part.
- the worm wheel and the worm reduction gear of the invention are not limited to the electric power steering device, but may be used in various kinds of mechanical devices such as a wiper device in an assembled state.
- 34 a, 34 b outer ring
Abstract
A first concave-convex part is formed in an outer diameter side circumferential surface of a first annular concave part provided in an axial one-side surface of an inner wheel element, and a second concave-convex part is formed in a bottom surface of a second annular concave part provided in the axial other-side surface of the inner wheel element. An outer circumferential part of the inner wheel element is embedded in an outer wheel element, and synthetic resin forming the outer wheel element partially enters into a plurality of concave parts constituting the first concave-convex part and the second concave-convex part. Thus, a configuration is achieved in which the holding power of a synthetic resin outer wheel can be secured from the metal inner wheel element, and the manufacturing error can be suppressed in the worm wheel tooth part provided in the outer circumferential surface of the outer wheel.
Description
- The present invention relates to a worm wheel which includes an inner wheel element which serves as a core material and a synthetic resin outer wheel element having a tooth part, a worm reduction gear including the worm wheel, and a manufacturing method of the worm wheel.
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FIGS. 12 to 17 illustrate one example of an electric power steering device which is described in Patent Document 1 and the like and is known from the past. A front end part of asteering shaft 2 in which a steering wheel 1 is attached to a rear end part is rotatably supported in ahousing 3. Aworm wheel 4 is fixed to a portion driven rotationally by thesteering shaft 2. On the other hand, aworm shaft 6 is connected to an output shaft of anelectric motor 5. Further, aworm tooth part 18 provided in an outer circumferential surface of an axial intermediate portion of theworm shaft 6 is engaged with a wormwheel tooth part 19 provided in the outer circumferential surface of theworm wheel 4, so that a predetermined magnitude of the auxiliary torque (auxiliary power) can be applied with respect to theworm wheel 4 from theelectric motor 5 in a predetermined direction. - The
worm wheel 4 is externally fitted and fixed to an axial intermediate portion of theoutput shaft 7 which serves as an output part of the auxiliary torque, and is rotated together with theoutput shaft 7. Theoutput shaft 7 is coupled with the front end part of thesteering shaft 2 through atorsion bar 9 in thehousing 3 in a state where a portion near both ends of the axial intermediate portion is supported to be rotatable only by one pair ofrolling bearings electric motor 5 rotationally drives theworm shaft 6 according to a direction and a magnitude of a steering torque which is detected by atorque sensor 10 and is applied from the steering wheel 1 to thesteering shaft 2, and the auxiliary torque is applied to theoutput shaft 7. The rotation of theoutput shaft 7 is transmitted to apinion shaft 14 which serves as an input part of asteering gear unit 13 through one pair ofuniversal joints intermediate shaft 12, and a desired steering angle is given to a steering wheel. - In the case of the illustrated example, the
worm wheel 4 is formed by combining a metalinner wheel element 15 and a synthetic resinouter wheel element 16. That is, in theworm wheel 4, the portion which is externally fitted and fixed to theoutput shaft 7 serves as the metalinner wheel element 15 having a circular ring shape, and the portion including the wormwheel tooth part 19 serves as the synthetic resinouter wheel element 16. Further, as described above, theouter wheel element 16 is made of a synthetic resin, so as to facilitate an operation (cost reduction) that forms the wormwheel tooth part 19 in the outer circumferential surface of theworm wheel 4, and to reduce a tooth hitting noise generated in the engaging portion between theworm tooth part 18 of theworm shaft 6 and the wormwheel tooth part 19 of theworm wheel 4. - The
outer wheel element 16 is made of a synthetic resin, and a radially outer end part of theinner wheel element 15 is embedded therein over the entire circumference through an injection molding (insertion molding). In the outer circumferential surface of theinner wheel element 15, a (gear-shaped) concave-convex part 17 in a circumferential direction is provided, and a portion of a synthetic resin constituting theouter wheel element 16 enters into a plurality of concave parts constituting the concave-convex part 17, so as to improve a holding power of theouter wheel element 16 in a rotation direction with respect to theinner wheel element 15. - In the case of the above-described structure in the related art, there is room for improvement from the viewpoint of reducing the manufacturing error of the worm
wheel tooth part 19 provided on the outer circumferential surface of theouter wheel element 16. That is, in the case of the above-described structure in the related art, the concave-convex part 17 in the circumferential direction is provided in the outer circumferential surface of theinner wheel element 15, and the portion of a synthetic resin constituting theouter wheel element 16 enter into the plurality of concave parts constituting the concave-convex part 17. For this reason, in theouter wheel element 16, the portion which is superimposed on the radially outer side with respect to the concave-convex part 17 may have different the radial thickness for each of portions in which a plurality ofteeth wheel tooth part 19 are positioned (seeFIGS. 16 and 17 ). In this case, the molding shrinkage amount during the injection molding is different (is large in a portion (for example, α portion ofFIG. 17 ) having a large radial thickness, and is small in a portion (for example, β portion ofFIG. 17 ) having a small radial thickness) for each of portions where the plurality ofteeth teeth wheel tooth part 19. - Patent Document 1: JP-T-2013-084613
- The invention is made in consideration of the above-described situation, and an object thereof is to implement a structure and a manufacturing method which can improve a holding power of a synthetic resin outer wheel element with respect to an inner wheel element and suppress the manufacturing error in the worm wheel tooth part provided in the outer circumferential surface of the outer wheel.
- A worm wheel of the present invention includes an inner wheel element and an outer wheel element.
- The inner wheel element includes a first annular concave part provided to be recessed in an axial direction at a position of an axial one-side surface located closer to a radial inside than an outer circumferential edge, a second annular concave part provided to be recessed in the axial direction at a position of an axial other-side surface located closer to a radial inside than an outer circumferential edge, a first concave-convex part provided in an outer diameter side circumferential surface constituting an inner surface of the first annular concave part in a circumferential direction, and a second concave-convex part provided in at least a part of an inner surface {outer diameter side circumferential surface, inner diameter side circumferential surface, and bottom surface (axial other-side surface)} of the second annular concave part in a circumferential direction, and an outer circumferential surface thereof is formed to be a cylindrical surface part in which a diameter in the axial direction is not changed; and an outer circumferential surface thereof is formed to be a cylindrical surface part in which a diameter in the axial direction is not changed. The outer wheel element is made of a synthetic resin, has a worm wheel tooth part in an outer circumferential surface, and embeds the inner wheel element so as to cover a continuous range from a radial intermediate portion of a bottom surface constituting the inner surface of the first annular concave part, through an outer circumferential surface of the inner wheel element, to an inner diameter side circumferential surface constituting at least the inner surface of the second annular concave part in a surface of the inner wheel element over an entire circumference, and the synthetic resin partially enters into a concave part constituting the first concave-convex part and a concave part constituting the second concave-convex part.
- In a case where the worm wheel of the invention is implemented, the tooth tip circle diameter and the tooth bottom circle diameter in a portion of the worm wheel tooth part overlapping at least the cylindrical surface part, which is the outer circumferential surface of the inner wheel element, are not changed in the axial direction, respectively.
- In a case where the invention is implemented, metal may be adopted as a material of the inner wheel element. However, for example, a synthetic resin may be adopted which is excellent in the thermal resistance compared to the material of the outer wheel element and hardly receives heat effect when the outer wheel element is injection-molded (for example, thermoplastic resin is adopted as the synthetic resin constituting the outer wheel element, and a thermosetting resin is adopted as the synthetic resin constituting the inner wheel element).
- In a case where the worm wheel of the invention is implemented, for example, the inner wheel element may be embedded in the outer wheel element, such that a continuous range from the inner diameter side circumferential surface constituting the inner surface of the first annular concave part through the outer circumferential surface of the inner wheel element to an inner diameter side circumferential surface constituting an inner surface of the second annular concave part in the surface of the inner wheel element is covered over an entire circumference.
- In a case where the worm wheel of the invention is implemented, for example, a tilted surface part which is tilted in a direction in which a width dimension in a radial direction of the second annular concave part becomes larger toward an axial other side with respect to a central axis of the inner wheel element may be provided in at least one circumferential surface among an outer diameter side circumferential surface and the inner diameter side circumferential surface constituting the inner surface of the second annular concave part.
- In a case where the worm wheel of the invention is implemented, for example, the tilted surface part and a non-tilted surface part which is not tilted with respect to the central axis of the inner wheel element may be provided in the outer diameter side circumferential surface constituting the inner surface of the second annular concave part.
- In a case where the worm wheel of the invention is implemented, for example, the tilted surface part and the non-tilted surface part which is not tilted with respect to the central axis of the inner wheel element may be provided in the inner diameter side circumferential surface constituting the inner surface of the second annular concave part.
- In a case where the worm wheel of the invention is implemented, for example, a projecting part which projects on the axial other side from a portion adjacent to the radially outer side may be provided in a radially inner end part (for example, the same radial position as the radially inner end part of the second annular concave part in the axial other-side surface of the outer wheel element) of an axial other-side surface of the outer wheel element.
- In a case where the worm wheel of the invention is implemented, for example, the first concave-convex part may be provided over the entire axial length of the outer diameter side circumferential surface configuring the inner surface of the first annular concave part, and the synthetic resin may partially enter into the entire concave part configuring the first concave-convex part.
- For example, the second concave-convex part may be provided over the entire axial length of the outer diameter side circumferential surface configuring the inner surface of the second annular concave part, and the synthetic resin may partially enter into the entire concave part configuring the second concave-convex part.
- In a case where the worm wheel of the invention is implemented, for example, the radially outer end parts of both axial surfaces of the inner wheel element, which are continuous (directly or through the chamfered portion) with respect to both axial end edges of the cylindrical surface part which is the outer circumferential surface of the inner wheel element each may serve as flat surface parts orthogonal to the central axis of the inner wheel element. Accordingly, the both axial end edges of the cylindrical surface part which is the outer circumferential surface of the inner wheel element each can be formed to have a circular shape in which the axial position is not changed in the circumferential direction.
- In a case where the worm wheel of the invention is implemented, for example, a plurality of concave parts and a plurality of convex parts configuring the first concave-convex part may be formed in parallel to the axial direction of the worm wheel.
- When the second concave-convex part is provided in the outer diameter side circumferential surface constituting the inner surface of the second annular concave part, a plurality of concave parts and a plurality of convex parts configuring the second concave-convex part may be formed in parallel to the axial direction of the worm wheel.
- Further, the plurality of teeth configuring the worm wheel tooth part may be formed in the direction which is tilted in a predetermined direction with respect to the axial direction of the worm wheel, and the plurality of concave parts and the plurality of convex parts configuring the first concave-convex part may be formed in the direction which is tilted in the opposite direction to the predetermined direction with respect to the axial direction of the worm wheel.
- When the second concave-convex part is provided in the outer diameter side circumferential surface constituting the inner surface of the second annular concave part, the plurality of concave parts and the plurality of convex parts configuring the second concave-convex part may be formed in the direction which is tilted in the opposite direction to the predetermined direction with respect to the axial direction of the worm wheel.
- In a case where the worm wheel of the invention is implemented, for example, a sub concave part may be provided to be recessed radially outward in a portion which is positioned on an axial deep side from an axial opening-side end edges of the first annular concave part in the outer diameter side circumferential surface configuring the inner surface of the first annular concave part, and a portion of the synthetic resin configuring the outer wheel element may enter into the sub concave part.
- In this case, for example, a cross section of the sub concave part with respect to a virtual plane including the central axis of the inner wheel element may have a V shape such that a width dimension in the axial direction becomes smaller from an opening part on an inner diameter side toward a bottom part on an outer diameter side.
- A worm reduction gear of the invention includes a housing, a rotation shaft, a worm wheel, and a worm shaft.
- The rotation shaft is supported to be rotatable with respect to the housing.
- Further, the worm wheel has a worm wheel tooth part in an outer circumferential surface and is externally fitted and fixed to the rotation shaft.
- Further, the worm shaft has a worm tooth part in an axial intermediate portion of an outer circumferential surface and is supported to be rotatable with respect to the housing in a state where the worm tooth part is engaged with the worm wheel tooth part.
- Particularly, in the case of the worm reduction gear of the invention, the worm wheel is the worm wheel of the invention.
- In a case where the worm reduction gear of the invention is implemented, for example, a rolling bearing which includes an inner ring, an outer ring, and a plurality of rolling bodies provided between an outer circumferential surface of the inner ring and an inner circumferential surface of the outer ring, and supports the rotation shaft to be rotatable with respect to the housing may be provided in a portion adjacent to an axial other side of the worm wheel.
- Further, an axial other-side surface of the outer wheel element constituting the worm wheel may face an axial one-side surface of the inner ring and an axial one-side surface of the outer ring in the axial direction.
- Further, an axial distance between the axial other-side surface of the outer wheel element and the axial one-side surface of the inner ring may be smaller than an axial distance between the axial other-side surface of the outer wheel element and the axial one-side surface of the outer ring.
- In a case where the worm reduction gear of the invention is implemented, for example, a projecting part which projects on the axial other side from a portion adjacent to the radially outer side may be provided in a radially inner end part of the axial other-side surface of the outer wheel element constituting the worm wheel, and an axial other-side surface of the projecting part may face the axial one-side surface of the inner ring in the axial direction.
- To put this in another manner, in the axial other-side surface of the outer wheel element, the projecting part which projects on the axial other side from the portion which faces the axial one-side surface of the outer ring in the axial direction may be provided in the portion which faces the axial one-side surface of the inner ring in the axial direction.
- A manufacturing method of the worm wheel of the invention is a manufacturing method for the worm wheel of the invention.
- In the manufacturing method of the worm wheel of the invention, a radially outer end part of a disc gate may be positioned in the radially inner end part of the axial other side of the outer wheel element when an insertion molding is performed in which the outer wheel element is coupled with the inner wheel element at the same time when the outer wheel element is manufactured by the injection molding.
- According to the worm wheel, the worm reduction gear, and the manufacturing method of the worm wheel according to the above-described invention, it is possible to improve the holding power of the synthetic resin outer wheel element with respect to the inner wheel element and to suppress the manufacturing error in the worm wheel tooth part provided in the outer circumferential surface of the outer wheel.
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FIG. 1 is a sectional view similar withFIG. 14 according to a first embodiment of the invention. -
FIG. 2 is a sectional view of a worm wheel according to the first embodiment. -
FIG. 3 is a half-sectional view of the worm wheel according to the first embodiment when partially cut away. -
FIG. 4 is a sectional view taken along line A-A ofFIG. 2 according to the first embodiment. -
FIG. 5 is a sectional view taken along line B-B ofFIG. 2 according to the first embodiment. -
FIG. 6 is an enlarged view of C portion ofFIG. 4 according to the first embodiment. -
FIG. 7 is a sectional view of a worm wheel according to a second embodiment of the invention. -
FIG. 8 is a sectional view illustrating a state where an outer wheel element is injection-molded according to the second embodiment. -
FIG. 9 is a half-sectional view of a worm wheel according to a third embodiment of the invention when partially cut away. -
FIG. 10 is a sectional view of a worm wheel according to a fourth embodiment of the invention. -
FIG. 11 is a sectional view illustrating a state where an outer wheel element is injection-molded according to the fourth embodiment. -
FIG. 12 is a side view illustrating one example of a structure of the electric power steering device in the related art partially cut away. -
FIG. 13 is an enlarged sectional view taken along line D-D ofFIG. 12 . -
FIG. 14 is an enlarged sectional view taken along line E-E ofFIG. 12 . -
FIG. 15 is a sectional view of the worm wheel. -
FIG. 16 is a sectional view taken along line F-F ofFIG. 15 . -
FIG. 17 is an enlarged view of G portion ofFIG. 16 . - A first embodiment of the invention will be described with reference to
FIGS. 1 to 6 . -
FIG. 1 illustrates an electric power steering device in which a worm reduction gear of this embodiment is assembled. A front end part of asteering shaft 2 in which a steering wheel 1 (seeFIG. 12 ) is attached to a rear end part is supported to be rotatable in ahousing 3. Aworm wheel 4 a is fixed to a portion rotationally driven by the steeringshaft 2. On the other hand, a worm shaft 6 (seeFIG. 13 ) is connected to an output shaft of anelectric motor 5. Further, aworm tooth part 18 provided in the outer circumferential surface of the axial intermediate portion of theworm shaft 6 is engaged with a wormwheel tooth part 19 a provided in the outer circumferential surface of theworm wheel 4 a, so that a predetermined magnitude of auxiliary torque (auxiliary power) can be applied from theelectric motor 5 with respect to theworm wheel 4 a in the predetermined direction. - The
worm wheel 4 a is externally fitted and fixed to an axial intermediate portion of anoutput shaft 7 which corresponds to a rotation shaft described in appended claims and serves as an output part of the auxiliary torque, and rotates together with theoutput shaft 7. Theoutput shaft 7 is coupled with the front end part of thesteering shaft 2 through atorsion bar 9 in thehousing 3 in a state where a portion near both ends of the axial intermediate portion is supported to be rotatable by one pair of rollingbearings electric motor 5 rotationally drives theworm shaft 6 according to a direction and a magnitude of a steering torque which is detected by atorque sensor 10 and is applied from the steering wheel 1 to thesteering shaft 2, and the auxiliary torque is applied to theoutput shaft 7. The rotation of theoutput shaft 7 is transmitted to a pinion shaft 14 (seeFIG. 12 ) which serves as an input part of asteering gear unit 13 through one pair ofuniversal joints intermediate shaft 12, and a desired steering angle is given to a steering wheel. - Incidentally, in the case of the illustrated example, one pair of the rolling
bearings inner rings output shaft 7,outer rings housing 3, and a plurality ofballs inner rings outer rings bearings - The
worm wheel 4 a is formed by combining aninner wheel element 15 a and anouter wheel element 16 a. - The
inner wheel element 15 a is formed of metal in an annular shape (substantially circular ring shape), and afitting hole 21 for internally fitting and fixing the axial intermediate portion of theoutput shaft 7 in a torque-transmittable manner is included in a radial intermediate portion. - A first annular
concave part 22 is provided to be recessed in an axial direction over the entire circumference of a radial intermediate portion of an axial one-side surface (the left surface inFIGS. 1 to 3 and 6 ) of theinner wheel element 15 a. - In an inner diameter side circumferential surface, an outer diameter side circumferential surface, and a bottom surface (axial one-side surface) constituting the inner surface of the first annular
concave part 22, the outer diameter side circumferential surface is provided with a first (gear-shaped) concave-convex part 23 in the circumferential direction which is formed in such a manner that aconcave part 26 and aconvex part 27 are arranged alternately (to have constant pitch in the illustrated example) in the circumferential direction in the entire length and the entire circumference of the outer diameter side circumferential surface in an axial direction. In the case of this embodiment, as illustrated by a broken line (hidden line) in an upper half portion inFIG. 3 , a plurality of theconcave parts 26 and a plurality of theconvex parts 27 constituting the first concave-convex part 23 are formed in parallel to the axial direction (a right and left direction inFIGS. 1 to 3 ) of theinner wheel element 15 a (worm wheel 4 a). To put this in another manner, the first concave-convex part 23 is formed such that the plurality of theconvex parts concave part 22 in the axial direction, and the portions between theconvex portions concave portions - Further, the inner diameter side circumferential surface which configures the inner surface of the first annular
concave part 22 serves as acylindrical surface part 36 having a simple cylindrical surface shape. - Further, the bottom surface which configures the inner surface of the first annular
concave part 22 serves as aflat surface part 37 which is orthogonal to a central axis of theinner wheel element 15 a and has a circular ring shape. The axial other end portions of the plurality of theconvex parts convex part 23 are connected to theflat surface part 37. - A second annular
concave part 38 is provided to be recessed in the axial direction over the entire circumference of the radial intermediate portion of the axial other-side surface (the right surface inFIGS. 1 to 3 ) of theinner wheel element 15 a. - The bottom surface (the axial other-side surface) configuring the inner surface of the second annular
concave part 38 is provided with a (face spline shaped) second concave-convex part 49 in the circumferential direction. The second concave-convex part 49 is formed such that a plurality ofconvex parts concave part 38 in the radial direction, and the portions between theconvex portions concave portions - In the inner surface of the second annular
concave part 38, the outer diameter side circumferential surface serves as an outer diameter sidecylindrical surface part 40 formed in a simple cylindrical surface shape, and the inner diameter side circumferential surface serves as an inner diameter sidecylindrical surface part 48 formed in a simple cylindrical surface shape. Both end parts in the radial direction of the plurality ofconvex parts convex part 49 are connected to the outer diameter sidecylindrical surface part 40 and the inner diameter sidecylindrical surface part 48, respectively. - In the
inner wheel element 15 a, the outer circumferential surface (excluding chamfered portions thereof in a case where the chamfered portions are provided in both axial end edge parts) serves as acylindrical surface part 24 formed in a simple cylindrical surface shape which has a bus line parallel to the central axis of theinner wheel element 15 a (worm wheel 4 a) and has a diameter which is not changed in the axial direction. Further, the radially outer end part (the portion positioned on the radially outer side from the first annular concave part 22) of the axial one-side surface of theinner wheel element 15 a and the radially outer end part (the portion positioned on the radially outer side from the second annular concave part 38) of the axial other-side surface of theinner wheel element 15 a are continuous (directly or through the chamfered portion) with respect to both axial end edges of thecylindrical surface part 24 and serve asflat surface parts inner wheel element 15 a, respectively. - To put this in another manner, in the case of this embodiment, the
inner wheel element 15 a includes an inner diameter sideannular part 28 and an outer diameter sideannular part 29 which are arranged coaxially with each other, and aconnection part 30 which has a circular ring shape and connects the axial intermediate portions of the outer circumferential surface of the inner diameter sideannular part 28 and the inner circumferential surface of the outer diameter sideannular part 29. Further, the outer circumferential surface of the outer diameter sideannular part 29 serves as thecylindrical surface part 24, and both axial surfaces of the outer diameter sideannular part 29 serve as theflat surface parts annular part 28, the axial one end portion of the inner circumferential surface of the outer diameter sideannular part 29, and the axial one-side surface of theconnection part 30 serves as the first annularconcave part 22. The portion surrounded by three sides of the axial other end portion of the outer circumferential surface of the inner diameter sideannular part 28, the axial other end portion of the inner circumferential surface of the outer diameter sideannular part 29, and the axial other-side surface of theconnection part 30 serves as the second annularconcave part 38. Further, in the inner circumferential surface of the outer diameter sideannular part 29, the axial one end portion serves as the first concave-convex part 23, and the axial other end portion serves as the outer diameter sidecylindrical surface part 40. Further, in the outer circumferential surface of the inner diameter sideannular part 28, the axial one end portion serves as thecylindrical surface part 36, and the axial other end portion serves as the inner diameter sidecylindrical surface part 48. In addition, in theconnection part 30, the axial one-side surface serves as theflat surface part 37, and the axial other-side surface serves as the second concave-convex part 49. - Incidentally, various kinds of metals such as copper alloy, aluminum alloy, and magnesium alloy in addition to ferrous metal such as iron and steel may be adopted as a metal constituting the
inner wheel element 15 a. Further, various kinds of cutting processes or plastic processes can be adopted as a process to mold theinner wheel element 15 a. Herein, the plastic process (forging, pressing, flow forming, and the like) is preferably adopted when molded in a high yield at low cost. - On the other hand, since the
outer wheel element 16 a is manufactured by injection-molding a synthetic resin, a portion of theinner wheel element 15 a is embedded over the entire circumference through the injection molding (insertion molding). Specifically, one portion (the radially outer end part and the intermediate portion) of theinner wheel element 15 a is embedded in theouter wheel element 16 a, such that the continuous range from the radial intermediate portion of the bottom surface (flat surface part 37) constituting the inner surface of the first annularconcave part 22, through the outer circumferential surface (cylindrical surface part 24) of theinner wheel element 15 a, to the inner diameter side circumferential surface (inner diameter side cylindrical surface part 48) constituting the inner surface of the second annularconcave part 38 in the surface of theinner wheel element 15 a is covered over the entire circumference. - In this state, a portion of the synthetic resin enters into the first annular
concave part 22 and the second annularconcave part 38. Thus, the portion entering into the first annularconcave part 22 configures afirst suppression part 31 having an annular shape and the portion entering into the second annularconcave part 38 configures asecond suppression part 42 having an annular shape. - Further, in this state, a portion of the synthetic resin constituting the
first suppression part 31 enters into the entire portion of the plurality ofconcave parts convex parts convex part 23. Thus, a firstrotation holding part 32 is configured to be engaged with the first concave-convex part 23 (have a shape coinciding with the first concave-convex part 23). Along with this, a portion of the synthetic resin constituting thesecond suppression part 42 enters into the entire portion of the plurality ofconcave parts convex parts convex part 49. Thus, a secondrotation holding part 52 is configured to be engaged with the second concave-convex part 49 (have a shape coinciding with the second concave-convex part 49). - The worm
wheel tooth part 19 a is formed in the outer circumferential surface of theouter wheel element 16 a. The axial intermediate portion of the wormwheel tooth part 19 a is radially superimposed with thecylindrical surface part 24. Further, as illustrated in the upper half portion ofFIG. 3 , the direction of forming the plurality ofteeth wheel tooth part 19 a is tilted with respect to the axial direction of theworm wheel 4 a. Further, in the case of this embodiment, a tooth tip circle diameter and a tooth bottom circle diameter of the wormwheel tooth part 19 a are not changed with respect to the axial direction, respectively. - In the case of this embodiment, at the same time when the
outer wheel element 16 a is manufactured by the injection molding, when the insertion molding is performed in which theouter wheel element 16 a is coupled with respect to theinner wheel element 15 a, in a state where theinner wheel element 15 a is set in a molding device 44 (seeFIG. 8 relating to a second embodiment to be described below) formed by combining a plurality of dies, molten resin is fed into an annular cavity 45 (seeFIG. 8 ) which is defined between theinner wheel element 15 a and themolding device 44 from arunner 46 and a disc gate 47 (seeFIG. 8 ) which are provided in the axial other-side surface side of theinner wheel element 15 a. In thecavity 45, the radially outer end part (outer circumferential part) of thedisc gate 47 is positioned in a portion in which the radially inner end part of the axial other side of theouter wheel element 16 a. Further, therunner 46 is provided to extend from the central portion of thedisc gate 47 to the axial other side. The molten resin fed into thecavity 45 from therunner 46 and thedisc gate 47 flows from the inner diameter side to the outer diameter side along the axial other-side surface of theinner wheel element 15 a, and part thereof enters into the second annularconcave part 38. Further, the molten resin fed into thecavity 45 reaches a portion corresponding to thefirst suppression part 31 and stops after entering into the portion where the radially outer end part of theouter wheel element 16 a in thecavity 45 is formed. The portion does not abut on the molten resin having flowed from the other direction. As a result, it can be prevented that weld or the like which is weak in strength occurs in theouter wheel element 16 a obtained by the injection molding. Themolding device 44 is opened and the plurality of dies are separated from each other. Then, the synthetic resin which is cooled and solidified in thecavity 45 is cut over the entire circumference in the portion corresponding to the radially inner end part of the axial other side of theouter wheel element 16 a, and theworm wheel 4 a is obtained by performing a finishing process as needed. - Incidentally, in addition to a polyamide 66 (PA66), various kinds of synthetic resins such as the polyamide 46 (PA46), a polyamide 9T (PA9T), a polyphenylene sulfide (PPS), a polyethylene terephthalate (PET), and a polyacetal (POM) may be adopted as a synthetic resin constituting the
outer wheel element 16 a. Further, as needed, various kinds of reinforced fibers such as a glass fiber, a polyethylene fiber, a carbon fiber, and an aramid fiber may be mixed in the synthetic resin. - Further, in a state where the electric power steering device of this embodiment is assembled, the entire engaging portion of the
worm tooth part 18 and the wormwheel tooth part 19 a is radially superimposed with thecylindrical surface part 24 provided in the outer circumferential surface of theinner wheel element 15 a. - In the
worm wheel 4 a and the worm reduction gear of this embodiment configured as above, the holding power of the synthetic resinouter wheel element 16 a can be secured from the metalinner wheel element 15 a, and the manufacturing error can be suppressed in the wormwheel tooth part 19 a provided in the outer circumferential surface of theouter wheel element 16 a. The description will be given below about these points. - When the auxiliary torque is applied to the
output shaft 7 through theworm wheel 4 a, the moment M in a tilted direction is applied to theworm wheel 4 a as illustrated by an arrow inFIG. 2 on the basis of an axial component of an engaging counterforce which acts on the engaging portion of the wormwheel tooth part 19 a of theworm wheel 4 a and theworm tooth part 18 of theworm shaft 6. - With respect thereto, in the case of this embodiment, the first annular
concave part 22 and the second annularconcave part 38 are provided over the entire circumferences in both axial surfaces of theinner wheel element 15 a, respectively. Further, a portion of theinner wheel element 15 a is embedded in theouter wheel element 16 a, such that the continuous range from the radial intermediate portion of the bottom surface (flat surface part 37) constituting the inner surface of the first annularconcave part 22, through the outer circumferential surface (cylindrical surface part 24) of theinner wheel element 15 a, to the inner diameter side circumferential surface (inner diameter side cylindrical surface part 48) constituting the inner surface of the second annularconcave part 38 in the surface of theinner wheel element 15 a is covered over the entire circumference. That is, in the case of this embodiment, the radial intermediate portion in theinner wheel element 15 a as well as the radially outer end part is embedded in theouter wheel element 16 a. For this reason, the holding power of theouter wheel element 16 a in the direction of the moment M with respect to theinner wheel element 15 a can be larger compared to a case where only the radially outer end part is embedded. - Further, in the case of this embodiment, a portion of the synthetic resin constituting the
outer wheel element 16 a enters into the first annularconcave part 22 to configure thefirst suppression part 31 having an annular shape, and enters into the second annularconcave part 38 to configure thesecond suppression part 42 having an annular shape. For this reason, the holding power of theouter wheel element 16 a in the direction of the moment M with respect to theinner wheel element 15 a can be enlarged on the basis of the engagement of the first annularconcave part 22 and thefirst suppression part 31 and the engagement of the second annularconcave part 38 and thesecond suppression part 42. - In the case of this embodiment, the first concave-
convex part 23 in the circumferential direction is provided in the outer diameter side circumferential surface configuring the inner surface of the first annularconcave part 22, and a portion of the synthetic resin configuring thefirst suppression part 31 enters into the entire plurality of theconcave parts convex part 23, thereby configuring the firstrotation holding part 32 which is engaged with the first concave-convex part 23. In addition, the second concave-convex part 49 in the circumferential direction is provided in the bottom surface configuring the inner surface of the second annularconcave part 38, and a portion of the synthetic resin configuring thesecond suppression part 42 enters into the entire plurality of theconcave parts convex part 49, thereby configuring the secondrotation holding part 52 which is engaged with the second concave-convex part 49. For this reason, in the case of this embodiment, it is possible to secure the holding power of theouter wheel element 16 a in the rotation direction with respect to theinner wheel element 15 a. Particularly, in the case of this embodiment, the first concave-convex part 23 is provided over the entire axial length of the outer diameter side circumferential surface configuring the inner surface of the first annularconcave part 22, the second concave-convex part 49 is provided over the entire radial length of the bottom surface configuring the inner surface of the second annularconcave part 38, and thus the holding power in the rotation direction can be large. - Further, in the case of this embodiment, the outer circumferential surface of the
inner wheel element 15 a serves as thecylindrical surface part 24 in which the diameter in the axial direction is not changed. For this reason, in theouter wheel element 16 a, the portion which is superimposed on the radially outer side with respect to thecylindrical surface part 24 which is the outer circumferential surface of theinner wheel element 15 a has the (substantially) same radial thickness in the portions where the plurality ofteeth wheel tooth part 19 a are positioned. - In the case of this embodiment, the tooth tip circle diameter and the tooth bottom circle diameter of the worm
wheel tooth part 19 a provided in the outer circumferential surface of theouter wheel element 16 a is not changed in the axial direction, respectively. Together with this, the radially outer end parts of the both axial surfaces of theinner wheel element 15 a which are continuous with respect to the both axial end edges of thecylindrical surface part 24 which is the outer circumferential surface of theinner wheel element 15 a serve as theflat surface parts inner wheel element 15 a, respectively. In other words, the both axial end edges of thecylindrical surface part 24 which is the outer circumferential surface of theinner wheel element 15 a each have a circular shape in which the axial position is not changed in the circumferential direction. For this reason, in the case of this embodiment, in theouter wheel element 16 a, the portion which is superimposed on the radially outer side with respect to the outer circumferential surface of theinner wheel element 15 a has almost the same radial thickness over the entire axial length including both axial end edge parts in the portions in which the plurality ofteeth wheel tooth part 19 a are positioned. - Therefore, according to this embodiment, in the
outer wheel element 16 a, as illustrated inFIG. 6 , the portion which is superimposed on the radially outer side with respect to at least the outer circumferential surface of theinner wheel element 15 a can be set such that the amount of the molding shrinkage, which occurs during the injection molding, of the portions in which the plurality ofteeth teeth wheel tooth part 19 a. - In the case of this embodiment, the plurality of
concave parts 26 and the plurality of theconvex parts 27 constituting the first concave-convex part 23 are formed in parallel to the axial direction. For this reason, it is suppressed that the first concave-convex part 23 causes the deformation of theouter wheel element 16 a associated with the molding shrinkage of the synthetic resin, and theouter wheel element 16 a can be molded accurately. - In the case of this embodiment, the entire engaging
portion 50 of theworm tooth part 18 and the wormwheel tooth part 19 a is radially superimposed with thecylindrical surface part 24 in a state where the worm reduction gear is assembled. In other words, in the wormwheel tooth part 19 a, theworm tooth part 18 is engaged with the portion which suppresses the manufacturing error such as the pitch error as described above. For this reason, it is possible to make the engaged state of the engagingportion 50 excellent. - A second embodiment of the invention will be described with reference to
FIGS. 7 and 8 . - In a case of this embodiment, regarding a second annular
concave part 38 a provided in an axial other-side surface of aninner wheel element 15 b configuring aworm wheel 4 b, in an inner diameter side circumferential surface, an outer diameter side circumferential surface, and a bottom surface (axial other-side surface) configuring an inner surface of the second annularconcave part 38 a, the outer diameter side circumferential surface is formed such that respective axial end edges of an outer diameter side tiltedsurface part 39 provided in one side (an one end portion and an intermediate portion) and an outer diameter sidecylindrical surface part 40 provided in the other side (other end portion) are continuous to each other in the axial direction. The outer diameter side tiltedsurface part 39 corresponds to a tilted surface part described in appended claims, and is formed in a partially tapered surface shape that is tilted in a direction (the direction toward the radially outer side) in which a radial width dimension of the second annularconcave part 38 a is larger toward the axial other side with respect to the central axis of theinner wheel element 15 b. With respect thereto, the outer diameter sidecylindrical surface part 40 corresponds to a non-tilted surface part described in appended claims, and is formed in a simple cylindrical surface shape not to be tilted with respect to the central axis of theinner wheel element 15 b. - Further, the inner diameter side circumferential surface constituting the inner surface of the second annular
concave part 38 is configured only by an inner diameter side tiltedsurface part 41. The inner diameter side tiltedsurface part 41 corresponds to the tilted surface part described in appended claims, and is formed in a partially tapered surface shape that is tilted in a direction (the direction toward the radially inner side) in which the radial width dimension of the second annularconcave part 38 a is larger toward the axial other side with respect to the central axis of theinner wheel element 15 b. - Further, in the case of this embodiment, the
inner wheel element 15 a is embedded in anouter wheel element 16 b configuring theworm wheel 4 b such that a continuous range from the inner diameter side circumferential surface (cylindrical surface part 36) configuring the inner surface of the first annularconcave part 20 through the outer circumferential surface (cylindrical surface part 24) of theinner wheel element 15 b to an inner diameter side circumferential surface (inner diameter side tilted surface part 41) configuring an inner surface of the second annularconcave part 38 a in the surface of theinner wheel element 15 b is covered over an entire circumference. - In the case of this embodiment, on the axial other-side surface of the
outer wheel element 16 b, the projectingpart 43 is provided over the entire circumference in a radial position which is the same as the radially inner end part of the second annularconcave part 38 a in the state of projecting from the inside (the axial other-side surface of thesecond suppression part 42 a) of the second annularconcave part 38 to the axial other side. - In the case of this embodiment, at the same time when the
outer wheel element 16 b is manufactured by the injection molding, the insertion molding is performed in which theouter wheel element 16 b is coupled with respect to theinner wheel element 15 b. At this time, in thecavity 45, the radially outer end part (outer circumferential part) of thedisc gate 47 is positioned in a portion in which the radially inner end part of the axial other side of theouter wheel element 16 a is formed as illustrated inFIG. 8 similarly to the case of the above-described first embodiment. Also in the case of this embodiment, the molten resin fed into thecavity 45 from therunner 46 and thedisc gate 47 flows from the inner diameter side to the outer diameter side along the axial other-side surface of theinner wheel element 15 b, and part thereof enters into the second annularconcave part 38 a. At this time, in the case of this embodiment, since the inner diameter side tiltedsurface part 41 and the outer diameter side tiltedsurface part 39 are provided in the inner diameter side circumferential surface and the outer diameter side circumferential surface configuring the inner surface of the second annularconcave part 38 a, the molten resin enters into the portion where the radially outer end part of theouter wheel element 16 b in thecavity 45 is formed without greatly disturbing the flow. As a result, it is possible to manufacture theouter wheel element 16 b with much higher quality. Even in the embodiment, after the molten resin is fed into theentire cavity 45, themolding device 44 is opened and the plurality of dies are separated from each other, and the synthetic resin which is cooled and solidified in thecavity 45 is cut over the entire circumference in the portion corresponding to the radially inner end part of the axial other side of theouter wheel element 16 b, and theworm wheel 4 b is obtained by performing a finishing process as needed. At that time, in the case of this embodiment, a portion (the portion to be removed originally) of the synthetic resin positioned in the radially outer end part of thedisc gate 47 remains without removal to form the projectingpart 43. Accordingly, a yield is excellent, and the projectingpart 43 can be formed at low cost. - In a state where the electric power steering device of this embodiment is assembled, the axial other-side surface of the
outer wheel element 16 b and the axial one-side surface of theinner ring 33 a and the axial one-side surface of theouter ring 34 a which are provided in the portion adjacent to the axial other side of theworm wheel 4 b and configure the rolling bearing 8 a, face each other in the axial direction through a gap. Specifically, in the axial other-side surface of theouter wheel element 16 b, the portion corresponding to the projectingpart 43 faces the axial one-side surface of theinner ring 33 a in the axial direction, and the portion corresponding to the radial intermediate portion of thesecond suppression part 42 a faces the axial one-side surface of theouter ring 34 a in the axial direction. Herein, in the case of this embodiment, the axial one-side surface of theinner ring 33 a and the axial one-side surface of theouter ring 34 a are provided in almost the same position in the axial direction while in the axial other-side surface of theouter wheel element 16 a, the portion (the axial other-side surface of the projecting part 43) corresponding to the projectingpart 43 is positioned on the axial other side (by at least an axial dimension of the projecting part 43) from the portion (the axial other-side surface of the radial intermediate portion of thesecond suppression part 42 a) corresponding to the radial intermediate portion of thesecond suppression part 42. For this reason, an axial distance X between the axial other-side surface (the axial other-side surface of the projecting part 43) of theouter wheel element 16 a and the axial one-side surface of theinner ring 33 a is smaller than the axial distance Y between the axial other-side surface (the axial other-side surface of the radial intermediate portion of thesecond suppression part 42 a) of theouter wheel element 16 a and the axial one-side surface of theouter ring 34 a (X<Y). - In the embodiment having the above-described configuration, a range covering the axial one-side surface of the
inner wheel element 15 b by the synthetic resin configuring theouter wheel element 16 b is enlarged to the inner diameter side circumferential surface (the cylindrical surface part 36) configuring the inner surface of the first annular concave part 22 (the radial length of thefirst suppression part 31 a is increased), as compared to the case of the above-described first embodiment. Therefore, the holding power in the direction of the moment M of theouter wheel element 16 b with respect to theinner wheel element 15 b can be increased by the extent. - In the case of this embodiment, in addition to the outer diameter side tilted
surface part 39, the outer diameter sidecylindrical surface part 40 is provided in the outer diameter side circumferential surface configuring the inner surface of the second annularconcave part 38 a. For this reason, the engaging power of the second annularconcave part 38 a and thesecond suppression part 42 a with respect to the moment M can be enlarged compared to a case where the entire outer diameter side circumferential surface serves as the outer diameter side tiltedsurface part 39. As a result, it is possible to enlarge the holding power of theouter wheel element 16 b in the direction of the moment M with respect to theinner wheel element 15 b. - In a case where the invention is implemented, the inner diameter side tilted
surface part 41 and a non-tilted surface part such as the inner diameter side cylindrical surface part can be provided together in the inner diameter side circumferential surface configuring the inner surface of the second annularconcave part 38 a. With this configuration, it is possible to enlarge the holding power of theouter wheel element 16 b in the direction of the moment M with respect to theinner wheel element 15 b by the extent of providing the non-tilted surface part. - The axial distance X between the axial other-side surface (the axial other-side surface of the projecting part 43) of the
outer wheel element 16 b and the axial one-side surface of theinner ring 33 a becomes smaller than the axial distance Y between the axial other-side surface (the axial other-side surface of the radial intermediate portion of thesecond suppression part 42 a) of theouter wheel element 16 b and the axial one-side surface of theouter ring 34 a (X<Y). For this reason, for example, although a portion which regulates the axial position of theoutput shaft 7 with respect to the housing 3 (seeFIG. 1 ) is broken so that theoutput shaft 7 and theworm wheel 4 b are displaced to the axial other side, the axial other-side surface of theouter wheel element 16 b contacts only the axial one-side surface (the axial other-side surface of the projecting part 43) of theinner ring 33 a among the axial one-side surface of theinner ring 33 a and the axial one-side surface of theouter ring 34 a, and does not contact the axial one-side surface (the axial other-side surface of the radial intermediate portion of the second suppression part 42) of theouter ring 34 a. Thus, it can be prevented that the rotation of theworm wheel 4 b is locked. - The other configuration and effect are similar with the case of the above-described first embodiment.
- A third embodiment of the invention will be described with reference to
FIG. 9 . - In the case of this embodiment, a first annular
concave part 22 a provided in an axial one-side surface of aninner wheel element 15 c constituting aworm wheel 4 c is configured to be different from the case of the above-described first embodiment. In the case of this embodiment, in the inner surface of the first annularconcave part 22 a, a plurality ofconcave parts 26 a and a plurality ofconvex parts 27 a constituting the first concave-convex part 23 a provided in the outer diameter side circumferential surface are formed to be tilted in an inverse direction to the tilted direction of the plurality ofteeth wheel tooth part 19 a provided in the outer circumferential surface of theouter wheel element 16 c with respect to the central axis of theworm wheel 4 c. - In the case of this embodiment, the tilted direction of the plurality of
teeth wheel tooth part 19 a and the tilted direction of the plurality ofconcave parts 26 a and the plurality ofconvex parts 27 a constituting the first concave-convex part 23 a are set to be opposite to each other with respect to the central axis of theworm wheel 4 c. Thus, when the torque is transmitted from the worm shaft 6 (seeFIG. 13 ) to theworm wheel 4 c, a force is applied in a direction in which the synthetic resin constituting theouter wheel element 16 c does not come out from the plurality ofconcave parts convex part 23 a toward the axial one side. The other configuration and effect are similar with the case of the above-described first embodiment. - A fourth embodiment of the invention will be described with reference to
FIGS. 10 to 11 . - This embodiment is a modification of the above-described second embodiment illustrated in
FIGS. 7 and 8 . - In the case of this embodiment, in the outer diameter side circumferential surface constituting the inner surface of the first annular
concave part 22 provided in an axial one-side surface of aninner wheel element 15 d constituting aworm wheel 4 d, a subconcave part 53 is provided to be recessed radially outward over the entire circumference in an axial deep end part (which is an axial other end portion and a right end part inFIGS. 10 and 11 ) of the first annularconcave part 22. Further, the cross section of the subconcave part 53 with respect to a virtual plane including the central axis of theinner wheel element 15 d has a V shape such that the width dimension in the axial direction becomes smaller from an opening part on the inner diameter side toward the bottom part on the outer diameter side. - In the case of this embodiment, the first concave-
convex part 23 is provided in the entire portion deviated from the subconcave part 53 in the outer diameter side circumferential surface constituting the inner surface of the first annularconcave part 22. Further, the axial deep end parts of theconcave parts 26 constituting the first concave-convex part 23 are opened to the inner surfaces of the subconcave parts 53, respectively. Incidentally, in the case of this embodiment, the radial depth of the subconcave part 53 is slightly larger than the radial depth of theconcave part 26 constituting the first concave-convex part 23. Herein, in a case where the invention is implemented, the radial depth of the subconcave part 53 may be configured to be the same as the radial depth of theconcave part 26 or be configured to be less than the radial depth of theconcave part 26. - In the case of this embodiment, in a synthetic resin constituting an
outer wheel element 16 d, a portion of the portion (thesuppression part 31 a having an annular shape) having entered into the first annularconcave part 22 enters into the entire subconcave part 53 to cover the entire inner surface of the subconcave part 53, so as to configure a sub suppression part 54 (which has a shape coinciding with the sub concave part 53) engaged with the subconcave part 53. - In the case of this embodiment having the above-described configuration, the holding power of the
outer wheel element 16 d in the direction of the moment M with respect to theinner wheel element 15 d can be improved on the basis of the engagement of the subconcave part 53 and thesub suppression part 54. - In the case of this embodiment, as illustrated in
FIG. 11 , when theouter wheel element 16 d is injection-molded, the molten resin fed into thecavity 45 through therunner 46 and thedisc gate 47 reaches the portion corresponding to thesuppression part 31 a (sub suppression part 54) and stops. For this reason, the sub suppression part 54 (sub concave part 53) can prevent that the flow of the molten resin into thecavity 45 is hindered. Particularly, in the case of this embodiment, the cross section of the subconcave part 53 has a V shape such that the width dimension in the axial direction becomes smaller from the opening part on the inner diameter side toward the bottom part on the outer diameter side. The molten resin can smoothly enter from the opening part of the subconcave part 53 toward the bottom part. Accordingly, it can be prevented that the flow of the molten resin into thecavity 45 is hindered, and the moldability of thesub suppression part 54 can be made excellent. - In the case of this embodiment, when the
inner wheel element 15 d is manufactured, after the subconcave part 53 is molded with respect to the outer diameter side circumferential surface constituting the inner surface of the first annularconcave part 22, in a case where the first concave-convex part 23 is molded by the plastic process such as cold forging, the subconcave part 53 may be used as an escape part of a molding die of the first concave-convex part 23 or an escape part of a metal material deformed according to the molding of the first concave-convex part 23. As a result, the molding load of the first concave-convex part 23 is suppressed to be low, so as to reduce the molding facility capacity of the first concave-convex part 23 and to improve the lifetime of the molding die. Herein, in a case where the invention is implemented, after the first concave-convex part 23 is molded, the subconcave part 53 may be molded by the cutting process or the like. - The other configuration and effect are similar with the case of the above-described second embodiment.
- Incidentally, in a case where the invention is implemented, the invention may be implemented by appropriately combining the configurations of the above-described embodiments.
- In the above-described embodiment, the inner wheel element is formed of metal. However, in a case where the invention is implemented, for example, the inner wheel element may be formed of a synthetic resin which is excellent in the thermal resistance compared to the synthetic resin constituting the outer wheel element. Also in this case, it is possible to obtain the effect similar with the case of the above-described embodiments.
- In the structure of the above-described embodiment, in the surface of the inner wheel element, if at least one portion (for example, the cylindrical surface part) in the portions which are covered with the synthetic resin constituting the outer wheel element serves as a minute concave-convex surface formed by various kinds of processes such as a knurling process, an emboss process, and a shot blast, a portion of the synthetic resin constituting the outer wheel element enters into the concave part constituting the minute concave-convex surface. Thus, it is possible to improve the holding power (adhesiveness) of the outer wheel element with respect to the inner wheel element. Incidentally, also in a case where such a configuration is adopted, if the depth of the concave part constituting the minute concave-convex surface is set to be equal to or less than one tenth (for example, equal to or less than one twentieth or equal to or less than one thirtieth) of the radial height of the teeth constituting the worm wheel tooth part, so as to hardly make an effect on the volume of the synthetic resin constituting the outer wheel element, it can be suppressed that the manufacturing error occurs in the portion engaged with the worm tooth part in the worm wheel tooth part.
- The worm wheel and the worm reduction gear of the invention are not limited to the electric power steering device, but may be used in various kinds of mechanical devices such as a wiper device in an assembled state.
- The present application is based on Japanese Patent Application (No. 2016-018234) filed on Feb. 2, 2016 and Japanese Patent Application (No. 2016-249615) filed on Dec. 22, 2016. The contents thereof are incorporated hereinto by reference.
- 1: steering wheel
- 2: steering shaft
- 3: housing
- 4, 4 a to 4 d: worm wheel
- 5: electric motor
- 6: worm shaft
- 7: output shaft
- 8 a, 8 b: rolling bearing
- 9: torsion bar
- 10: torque sensor
- 11 a, 11 b: universal joint
- 12: intermediate shaft
- 13: steering gear unit
- 14: pinion shaft
- 15, 15 a to 15 d: inner wheel element
- 16, 16 a to 16 d: outer wheel element
- 17: concave-convex part
- 18: worm tooth part
- 19, 19 a: worm wheel tooth part
- 20, 20 a: teeth
- 21: fitting hole
- 22, 22 a: first annular concave part
- 23, 23 a: first concave-convex part
- 24: cylindrical surface part
- 25 a, 25 b: flat surface part
- 26, 26 a: concave part
- 27, 27 a: convex part
- 28: inner diameter side annular part
- 29: outer diameter side annular part
- 30: connection part
- 31, 31 a: first suppression part
- 32: rotation holding part
- 33 a, 33 b: inner ring
- 34 a, 34 b: outer ring
- 35 a, 35 b: ball
- 36: cylindrical surface part
- 37: intermediate flat surface part
- 38: second annular concave part
- 39: outer diameter side tilted surface part
- 40: outer diameter side cylindrical surface part
- 41: inner diameter side tilted surface part
- 42, 42 a: second suppression part
- 43: projecting part
- 44: molding device
- 45: cavity
- 46: runner
- 47: disc gate
- 48: inner diameter side cylindrical surface part
- 49: second concave-convex part
- 50: convex part
- 51: concave part
- 52: second rotation holding part
- 53: sub concave part
- 54: sub suppression part
Claims (12)
1. A worm wheel comprising:
an inner wheel element; and
an outer wheel element, wherein:
the inner wheel element includes a first annular concave part provided to be recessed in an axial direction in an axial one-side surface, a second annular concave part provided to be recessed in the axial direction in an axial other-side surface, a first concave-convex part provided in an outer diameter side circumferential surface constituting an inner surface of the first annular concave part in a circumferential direction, and a second concave-convex part provided in an inner surface of the second annular concave part in a circumferential direction, and an outer circumferential surface thereof is formed to be a cylindrical surface part in which a diameter in the axial direction is not changed; and
the outer wheel element is made of a synthetic resin, has a worm wheel tooth part in an outer circumferential surface, and embeds the inner wheel element so as to cover a continuous range from a radial intermediate portion of a bottom surface constituting the inner surface of the first annular concave part, through an outer circumferential surface of the inner wheel element, to an inner diameter side circumferential surface constituting at least the inner surface of the second annular concave part in a surface of the inner wheel element over an entire circumference, the synthetic resin partially enters into a concave part constituting the first concave-convex part and a concave part constituting the second concave-convex part.
2. The worm wheel according to claim 1 , wherein
a tilted surface part which is tilted in a direction in which a width dimension in a radial direction of the second annular concave part becomes larger toward an axial other side with respect to a central axis of the inner wheel element is provided in at least one circumferential surface among an outer diameter side circumferential surface and the inner diameter side circumferential surface constituting the inner surface of the second annular concave part.
3. The worm wheel according to claim 2 , wherein
the tilted surface part and a non-tilted surface part which is not tilted with respect to the central axis of the inner wheel element are provided in the outer diameter side circumferential surface constituting the inner surface of the second annular concave part.
4. The worm wheel according to claim 2 , wherein
the tilted surface part and the non-tilted surface part which is not tilted with respect to the central axis of the inner wheel element are provided in the inner diameter side circumferential surface constituting the inner surface of the second annular concave part.
5. The worm wheel according to claim 1 , wherein
a projecting part which projects on the axial other side from a portion adjacent to the radially outer side is provided in a radially inner end part of the axial other-side surface of the outer wheel element.
6. The worm wheel according to claim 1 , wherein:
a sub concave part is provided to be recessed radially outward in a portion which is positioned on an axial deep side from an axial opening-side end edge of the first annular concave part in the outer diameter side circumferential surface constituting the inner surface of the first annular concave part; and
a portion of the synthetic resin constituting the outer wheel element enters into the sub concave part.
7. The worm wheel according to claim 6 , wherein
a cross section of the sub concave part with respect to a virtual plane including the central axis of the inner wheel element has a V shape such that a width dimension in the axial direction becomes smaller from an opening part on an inner diameter side toward a bottom part on an outer diameter side.
8. The worm wheel according to claim 1 , wherein
a plurality of teeth constituting the worm wheel tooth part are formed in a direction inclined in a predetermined direction with respect to the axial direction of the worm wheel, and a plurality of concave parts and convex part constituting the first concave-convex part are formed in a direction inclined in a direction opposite to the predetermined direction with respect to the axial direction of the worm wheel.
9. A worm reduction gear comprising:
a housing;
a rotation shaft which is supported to be rotatable with respect to the housing;
a worm wheel which has a worm wheel tooth part in an outer circumferential surface and is externally fitted and fixed to the rotation shaft; and
a worm shaft which has a worm tooth part in an axial intermediate portion of an outer circumferential surface and is supported to be rotatable with respect to the housing in a state where the worm tooth part is engaged with the worm wheel tooth part, wherein the worm wheel is the worm wheel according to claim 1 .
10. The worm reduction gear according to claim 9 , wherein:
a rolling bearing which includes an inner ring, an outer ring, and a plurality of rolling bodies provided between an outer circumferential surface of the inner ring and an inner circumferential surface of the outer ring, and supports the rotation shaft to be rotatable with respect to the housing is provided in a portion adjacent to an axial other side of the worm wheel;
an axial other-side surface of the outer wheel element constituting the worm wheel faces an axial one-side surface of the inner ring and an axial one-side surface of the outer ring in the axial direction; and
an axial distance between the axial other-side surface of the outer wheel element and the axial one-side surface of the inner ring is smaller than an axial distance between the axial other-side surface of the outer wheel element and the axial one-side surface of the outer ring.
11. The worm reduction gear according to claim 10 , wherein:
a projecting part which projects on the axial other side from a portion adjacent to the radially outer side is provided in a radially inner end part of the axial other-side surface of the outer wheel element; and
an axial other-side surface of the projecting part faces the axial one-side surface of the inner ring in the axial direction.
12. A manufacturing method of the worm wheel according to claim 1 , the method comprising:
positioning a radially outer end part of a disc gate in the radially inner end part of the axial other side of the outer wheel element when an insertion molding is performed in which the outer wheel element is coupled with the inner wheel element at the same time when the outer wheel element is manufactured by an injection molding.
Applications Claiming Priority (7)
Application Number | Priority Date | Filing Date | Title |
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JPJP2016-018234 | 2016-02-02 | ||
JP2016018234 | 2016-02-02 | ||
JP2016-018234 | 2016-02-02 | ||
JP2016-249615 | 2016-12-22 | ||
JPJP2016-249615 | 2016-12-22 | ||
JP2016249615 | 2016-12-22 | ||
PCT/JP2017/002669 WO2017135135A1 (en) | 2016-02-02 | 2017-01-26 | Worm wheel, worm decelerator, and method for producing worm wheel |
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US20210180676A1 true US20210180676A1 (en) | 2021-06-17 |
US11047466B1 US11047466B1 (en) | 2021-06-29 |
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US16/074,363 Active 2038-07-10 US11047466B1 (en) | 2016-02-02 | 2017-01-26 | Worm wheel, worm decelerator, and method for producing worm wheel |
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US (1) | US11047466B1 (en) |
EP (1) | EP3396207B1 (en) |
JP (1) | JP6547854B2 (en) |
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DE102019211451A1 (en) * | 2019-07-31 | 2021-02-04 | Rolls-Royce Deutschland Ltd & Co Kg | Web gear |
KR20210027798A (en) * | 2019-09-03 | 2021-03-11 | 주식회사 만도 | Worm Wheel of Reducer for Steering Apparatus and Manufacturing Method of The Same |
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US3610066A (en) * | 1969-11-03 | 1971-10-05 | Frank J Rychlik | Reinforced plastic gear |
JP4331863B2 (en) * | 2000-05-09 | 2009-09-16 | 株式会社ショーワ | Manufacturing method of resin gear |
JP4868220B2 (en) * | 2006-01-11 | 2012-02-01 | 株式会社ジェイテクト | Electric power steering device |
DE102006030097B3 (en) * | 2006-06-28 | 2008-02-14 | Zf Friedrichshafen Ag | screw gear |
JP5181483B2 (en) | 2007-01-26 | 2013-04-10 | 株式会社ジェイテクト | Gear and electric power steering device |
JP4997488B2 (en) * | 2007-03-30 | 2012-08-08 | 株式会社ジェイテクト | Compound gear and electric power steering device |
US8431432B2 (en) | 2007-04-27 | 2013-04-30 | Semiconductor Energy Laboratory Co., Ltd. | Manufacturing method of light-emitting device |
JP2010139041A (en) | 2008-12-15 | 2010-06-24 | Tigers Polymer Corp | Synthetic resin gear |
JP2011202682A (en) * | 2010-03-24 | 2011-10-13 | Jtekt Corp | Gear |
EP2735771B1 (en) | 2011-12-07 | 2023-12-06 | NSK Ltd. | Worm wheel and electric power steering device |
US20150298725A1 (en) * | 2012-11-15 | 2015-10-22 | Nsk Ltd. | Electric power steering system |
WO2014129629A1 (en) * | 2013-02-25 | 2014-08-28 | 日本精工株式会社 | Worm wheel, and electric power steering device |
JP2016018234A (en) | 2014-07-04 | 2016-02-01 | 三菱電機株式会社 | Communication environment determination system, communication environment determination method, and program |
JP2016023698A (en) * | 2014-07-18 | 2016-02-08 | キヤノン株式会社 | Composite gear and method of manufacturing the same |
WO2017135141A1 (en) * | 2016-02-02 | 2017-08-10 | 日本精工株式会社 | Worm wheel, worm reduction gear, and method for producing worm wheel |
WO2017141965A1 (en) * | 2016-02-16 | 2017-08-24 | 日本精工株式会社 | Worm wheel and worm reducer |
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2017
- 2017-01-26 EP EP17747293.3A patent/EP3396207B1/en active Active
- 2017-01-26 JP JP2017565506A patent/JP6547854B2/en active Active
- 2017-01-26 US US16/074,363 patent/US11047466B1/en active Active
- 2017-01-26 WO PCT/JP2017/002669 patent/WO2017135135A1/en active Application Filing
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JPWO2017135135A1 (en) | 2018-11-22 |
EP3396207A1 (en) | 2018-10-31 |
CN108603581A (en) | 2018-09-28 |
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CN108603581B (en) | 2021-04-06 |
US11047466B1 (en) | 2021-06-29 |
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