Ball screw nut, rotating unit and method for manufacturing ball screw nut

Abstract

The present invention relates to a ball screw nut, which includes a nut component (110) and a pulley component (120), wherein the pulley component (120) is integrally molded with the nut component (110) on the outer peripheral side of the nut component (110) and has external teeth (121). The pulley component (120) includes: a cylindrical portion (122) extending in the axial direction and facing the nut component (110) in the radial direction; and an extension portion (123) extending radially inward from the cylindrical portion (122) and facing the nut component (110) in the axial direction. A limiting component (130) for limiting the relative rotation of the nut component (110) and the pulley component (120) is provided between a facing surface (125) of the extension portion (123) facing the nut component (110) and a facing surface (115) of the nut component (110) facing the extension portion (123). The invention also relates to a rotary unit and a method for producing a ball screw nut.

Description

Technical Field

[0001] The invention relates to a ball screw nut, a rotating unit, and a method for manufacturing a ball screw nut. Background Art

[0002] Japanese Patent Application Publication No. 2018-90081 discloses a steering device in which a driven pulley is integrally molded on the outer peripheral surface of a ball screw nut. An uneven portion, such as a sawtooth, is provided on the outer peripheral surface of the ball screw nut to limit the relative rotation of the ball screw nut and the driven pulley in the circumferential direction. An uneven portion to be fitted to the uneven portion formed on the outer peripheral surface of the ball screw nut is formed on the inner peripheral surface of the driven pulley integrally molded on the outer peripheral surface of the ball screw nut. Summary of the invention

[0003] In a driven pulley integrally molded on the outer peripheral surface of a ball screw nut, since an uneven portion corresponding to the uneven portion formed on the outer peripheral surface of the ball screw nut is formed on the inner peripheral surface of the driven pulley, there are thicker parts and thinner parts. In the thicker part of the driven pulley, the thermal contraction during the molding of the driven pulley is relatively large, while in the thinner part of the driven pulley, the thermal contraction during the molding of the driven pulley is relatively small. Therefore, the amount of thermal contraction of the driven pulley varies according to the thickness of the driven pulley. This may affect the accuracy of the tooth tip of the external teeth formed on the outer periphery of the driven pulley.

[0004] The ball screw nut according to the first aspect of the present invention includes: a cylindrical nut component having a ball rolling groove in a spiral shape on the inner peripheral surface; and a cylindrical pulley component, which is integrally molded with the nut component on the outer peripheral side of the nut component and has external teeth. The pulley component includes: a cylindrical portion extending in the axial direction and facing the nut component in the radial direction; and an extension portion extending radially inward from the cylindrical portion and facing the nut component in the axial direction. A limiting component for limiting the relative rotation of the nut component and the pulley component is provided between the surface of the extension portion facing the nut component and the surface of the nut component facing the extension portion.

[0005] In the above aspect, by arranging the limiting member at a position where the nut member and the pulley member face each other in the axial direction, the variation in the thickness of the pulley member can be easily reduced, compared with, for example, a case where the limiting member is arranged at a position where the nut member and the pulley member face each other in the radial direction. Therefore, the variation in the amount of heat shrinkage on the outer peripheral surface of the pulley member is reduced.

[0006] In the ball screw nut, the outer peripheral surface of the nut component and the inner peripheral surface of the cylindrical portion may be circumferential surfaces over the entire axial range where the external teeth are formed. By the above configuration, the variation in the thickness of the pulley component can be reduced compared to the case where the outer peripheral surface of the nut component and the inner peripheral surface of the cylindrical portion are not circumferential surfaces over the entire axial range where the external teeth are formed. Therefore, the variation in the amount of thermal shrinkage on the outer peripheral surface of the pulley component over the entire axial region where the external teeth are formed can be reduced.

[0007] In the ball screw nut, the pulley component can be formed on the outer periphery of the nut component by insert molding using only resin material as the molding material. Through the above configuration, the pulley component is formed by insert molding using resin material as the molding material, so that the weight of the pulley component is reduced more than the case where the pulley component is molded using a metal material.

[0008] In a ball screw nut, a pulley component may be formed on the periphery of a nut component by insert molding using a resin material containing metal powder as a molding material. When the pulley component is formed on the periphery of the nut component by insert molding, heat shrinkage occurs in the pulley component during the insert molding of the pulley component. In the case where the pulley component is formed by insert molding using a molding material containing only a resin material, the amount of heat shrinkage of the pulley component during the insert molding may be reduced, compared to the case where the pulley component is formed by insert molding using a molding material containing metal powder. Therefore, the variation in the amount of heat shrinkage on the outer peripheral surface of the pulley component is further reduced.

[0009] In a ball screw nut, one of the facing surfaces of the nut component and the pulley component may have a protrusion, the other of the facing surfaces of the nut component and the pulley component may have a recess into which the protrusion is fitted, and the limiting component may be constructed to include the protrusion and the recess.

[0010] Through the above configuration, the relative rotation of the nut component and the pulley component can be limited by fitting the protrusion into the recess. The rotating unit according to the second aspect of the present invention includes a motor and a transmission mechanism. The transmission mechanism includes: a ball screw nut; a ball screw shaft having a ball rolling groove spirally formed on the outer peripheral surface; a plurality of balls, wherein the plurality of balls are arranged between the ball rolling groove of the ball screw shaft and the ball rolling groove of the ball screw nut; a drive pulley connected to the rotating shaft of the motor and having external teeth on the outer peripheral surface; and a toothed belt having internal teeth meshing with the external teeth of the drive pulley and the external teeth of the pulley component, and the toothed belt stretches between the drive pulley and the pulley component.

[0011] Through the above configuration, the rotational force of the motor is transmitted from the driving pulley connected to the rotating shaft of the motor to the pulley component via the toothed belt. The nut component rotates integrally with the pulley component. The rotational force of the nut component is converted into the axial movement of the ball screw shaft by rolling the balls between the ball rolling grooves of the nut component and the ball rolling grooves of the ball screw shaft. In the ball screw nut, the reduction of the tooth tip accuracy of the external teeth on the pulley component is prevented, and therefore, the deterioration of the meshing of the external teeth on the pulley component with the internal teeth of the toothed belt can be prevented. Thereby, the reduction of the transmission efficiency for transmitting the rotational force of the motor to the nut component can be prevented.

[0012] In the method of manufacturing a ball screw nut according to the third aspect of the present invention, the pulley component is molded integrally with the nut component by insert molding using the nut component as an insert.

[0013] According to the ball screw nut, the rotating unit, and the method for manufacturing the ball screw nut of the present invention, it is possible to prevent the reduction in the accuracy of the tooth tips of the external teeth on the pulley member. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0015] Figure 1 is a schematic configuration diagram of an electric power steering device;

[0016] Figure 2 is a cross-sectional view taken in the axial direction near the transmission mechanism of the electric power steering device;

[0017] Figure 3 It is along Figure 2 The cross-sectional view is taken along the line III-III in the figure and is perpendicular to the axial direction of the ball screw nut. Figure 3 The external teeth are not shown in the figure;

[0018] Figure 4 is a cross-sectional view taken along the axial direction in a state where molten resin is not injected into the cavity while a mold for molding the pulley component is assembled to the outer periphery of the nut component;

[0019] Figure 5 is a cross-sectional view taken along the axial direction in a state after the molten resin is solidified while a mold for molding the pulley component is assembled to the outer periphery of the nut component;

[0020] Figure 6 is a cross-sectional view along the axial direction of a ball screw nut according to another embodiment; and

[0021] Figure 7is a cross-sectional view along the axial direction of a ball screw nut according to another embodiment. DETAILED DESCRIPTION

[0022] An embodiment of an electric power steering device (hereinafter referred to as "EPS") provided with a ball screw nut will be described with reference to the accompanying drawings. Figure 1 As illustrated in FIG. 1 , the EPS 1 is provided with a steering shaft 3 to which a steering wheel 2 is connected, and a rotating unit 4 for rotating a rotating wheel 5 connected to each end of a rack shaft 51 as a ball screw shaft.

[0023] The steering shaft 3 is constructed by connecting a column shaft 31, an intermediate shaft 32, and a pinion shaft 33 in order from the steering wheel 2 side. The pinion shaft 33 has pinion teeth 33a formed over the entire circumference on the outer peripheral surface of the end portion opposite to the steering wheel 2.

[0024] The rotating unit 4 includes a motor 41, a transmission mechanism 42, and a housing 43, through which a rack shaft 51 is inserted to be reciprocally movable, and the housing 43 accommodates the transmission mechanism 42. Rack teeth 51a are formed on the rack shaft 51 within a predetermined axial range. The housing 43 is formed by axially connecting a first housing 44 and a second housing 45 each formed in a cylindrical shape. The pinion shaft 33 and the rack shaft 51 are arranged in the first housing 44 at a predetermined intersection angle. The rack teeth 51a formed on the rack shaft 51 and the pinion teeth 33a formed on the pinion shaft 33 are meshed with each other to form a rack and pinion mechanism 6. A tie rod 7 is connected to each end of the rack shaft 51. The tip of the tie rod 7 is connected to a steering knuckle (not shown), and the rotating wheel 5 is assembled to the steering knuckle. Therefore, in EPS1, the rotation of the steering shaft 3 accompanying the steering operation is converted into axial movement of the rack shaft 51 by the rack and pinion mechanism 6, and the axial movement is transmitted to the steering knuckle via the tie rod 7, thereby changing the rotation angle of the turning wheel 5, that is, the driving direction of the vehicle.

[0025] The rotating unit 4 will be described in detail. In the following description, for the convenience of description, the side of the rack shaft 51 opposite to the rack and pinion mechanism 6, i.e. Figure 2 The left side of the rack shaft 51 is defined as an axial end side. Figure 2 The right side is defined as the other axial end side.

[0026] like Figure 2As shown in the figure, the first housing 44 has a first cylindrical portion 44a and a first accommodation portion 44b formed on one axial end side of the first cylindrical portion 44a. The first accommodation portion 44b is formed in a cylindrical shape having a diameter larger than the diameter of the first cylindrical portion 44a. The first accommodation portion 44b is formed with a projection 44c having a shape in which a portion of the circumferential wall of the projection 44c projects to the side where the motor 41 is provided. An insertion hole 44d that penetrates the rack shaft 51 in the axial direction is formed in the end wall of the projection 44c.

[0027] The second housing 45 has a second cylindrical portion 45a and a second accommodating portion 45b formed on the other axial end side of the second cylindrical portion 45a. The second accommodating portion 45b is formed in a cylindrical shape having a diameter larger than the diameter of the second cylindrical portion 45a. A covering member 45c is formed in the second accommodating portion 45b to cover the opening of the protrusion 44c of the first housing 44.

[0028] The rotating shaft 41a of the motor 41 is inserted into the boss 44c via an insertion hole 44d formed in the boss 44c. The motor 41 is attached to the first housing 44 by a bolt 41b in such a manner that the rotating shaft 41a is parallel to the rack shaft 51.

[0029] The transmission mechanism 42 includes: a rack shaft 51, which serves as a ball screw shaft; a ball screw nut 100, which is coaxially arranged on the outer periphery of the rack shaft 51; a plurality of balls 52, which are arranged between the rack shaft 51 and the ball screw nut 100; a drive pulley 53, which is connected to the rotating shaft 41a of the motor 41; and a toothed belt 54.

[0030] The ball screw nut 100 is provided with a cylindrical nut component 110 having a ball rolling groove 111 spirally formed on an inner peripheral surface, and a cylindrical pulley component 120 having external teeth 121. The pulley component 120 is integrally molded with the nut component 110 on the outer peripheral side of the nut component 110. The pulley component 120 is formed on the outer periphery of the nut component 110 by insert molding using only a resin material as a molding material.

[0031] The nut component 110 is formed into a stepped cylindrical shape with different outer diameters. The nut component 110 has a large diameter cylindrical portion 112 and a small diameter cylindrical portion 113 arranged on one axial end side of the large diameter cylindrical portion 112. The outer diameter of the large diameter cylindrical portion 112 is set to be larger than the outer diameter of the small diameter cylindrical portion 113. An annular support 114 extending radially outward from the large diameter cylindrical portion 112 and the small diameter cylindrical portion 113 is formed between the large diameter cylindrical portion 112 and the small diameter cylindrical portion 113. The outer peripheral surface of the large diameter cylindrical portion 112 forms a circumferential surface having a constant distance from the central axis to the outer peripheral surface. The nut component 110 is made of a metal material such as iron.

[0032] On the outer periphery of the small diameter cylindrical portion 113, the end face on one axial end side of the adjacent support 114 is fitted with a bearing 60, and the end face on one axial end side of the inner ring of the adjacent bearing 60 is fitted with a retainer 61. In a portion on the outer periphery of the small diameter cylindrical portion 113 close to one axial end side, an annular fixing groove 113a extending over the entire circumference of the portion is formed. A portion of the retainer 61 is embedded and pressed into close contact with the fixing groove 113a, whereby the bearing 60 is fixed in a state where the end face on the other axial end side of the inner ring of the bearing 60 is pressed against the support 114. Therefore, the ball screw nut 100 is rotatably supported in the first accommodating portion 44b and the second accommodating portion 45b. For the bearing 60, a double row angular contact ball bearing is used. The bearing 60 is pressurized by the retainer 61 so that the internal clearance of the bearing 60 becomes a set clearance.

[0033] A retaining member 62 is provided on each side portion of the outer ring of the bearing 60 adjacent to the axial direction. An elastic body such as rubber or a metal spring is used for the retaining member 62. The retaining member 62 is provided in a compressed state between the first housing 44 and the end surface on the other axial end side of the outer ring of the bearing 60 and between the second housing 45 and the end surface on one axial end side of the outer ring of the bearing 60. Therefore, the outer ring of the bearing 60 is elastically supported relative to the first housing 44 and the second housing 45.

[0034] The ball rolling groove 111 is spirally formed on the inner peripheral surface of the nut component 110. The ball rolling groove 51b corresponding to the ball rolling groove 111 is spirally formed on the outer peripheral surface of the rack shaft 51. The ball rolling groove 111 formed in the nut component 110 and the ball rolling groove 51b formed in the rack shaft 51 face each other. By the ball rolling groove 111 and the ball rolling groove 51b facing each other, a spiral rolling path R is formed. The plurality of balls 52 are arranged in the rolling path R while being sandwiched between the ball rolling groove 111 and the ball rolling groove 51b. That is, the nut component 110 is screwed to the outer periphery of the rack shaft 51 via the plurality of balls 52. Therefore, each ball 52 rolls in the rolling path R while receiving a load caused by the relative rotation of the rack shaft 51 and the nut component 110. The relative axial position of the rack shaft 51 and the nut member 110 is displaced by the rolling of each ball 52, so that the torque of the motor 41 is applied as an auxiliary force to the rack shaft 51. Although not shown, the nut member 110 is provided with a circulation path that opens at two points of the rolling path R and short-circuits the opening portions at the two points. The plurality of balls 52 can circulate endlessly in the rolling path R via the circulation path.

[0035] like Figure 3 As shown in the figure, a plurality of recesses 116 are formed in the end face on the other axial end side of the nut component 110. The end face on the other axial end side of the nut component 110 is a surface 115 facing the pulley component 120 in the axial direction, as described later. The plurality of recesses 116 are arranged at equal intervals in the circumferential direction. In the present embodiment, four recesses 116 are formed in the facing surface 115. Each recess 116 is formed at a radially intermediate position between the outer peripheral edge and the inner peripheral edge in the facing surface 115 of the nut component 110. Each recess 116 is a circular hole. Each recess 116 is pre-formed before the pulley component 120 is integrally molded with the nut component 110.

[0036] like Figure 2 As shown in the figure, the pulley component 120 is formed in a stepped cylindrical shape with a belt bottom having different inner diameters. The pulley component 120 has: a cylindrical portion 122; an extension portion 123, which is formed on the other axial end side of the cylindrical portion 122; and a flange 124, which is formed on one axial end side of the cylindrical portion 122. The inner diameter of the cylindrical portion 122 is set to be larger than the inner diameter of the extension portion 123. The pulley component 120 is made of a resin material.

[0037] The cylindrical portion 122 has a cylindrical shape extending in the axial direction. The cylindrical portion 122 is integrally molded on the outer peripheral surface of the large diameter cylindrical portion 112 of the nut component 110. The inner peripheral surface of the cylindrical portion 122 forms a circumferential surface having a constant distance from the central axis to the inner peripheral surface. By integrally molding the pulley component 120 with the nut component 110, the inner peripheral surface of the cylindrical portion 122 and the outer peripheral surface of the large diameter cylindrical portion 112 are in close contact with each other in the radial direction. External teeth 121 are formed on the outer peripheral surface of the cylindrical portion 122. The tooth lines of the external teeth 121 are formed at equal intervals in the circumferential direction. The external teeth 121 are formed as inclined teeth whose tooth lines are inclined relative to the axial direction. The external teeth 121 are formed on the entire circumferential area and the entire axial area on the outer peripheral surface of the cylindrical portion 122.

[0038] The extension portion 123 has a cylindrical shape whose inner diameter is smaller than that of the cylindrical portion 122. The extension portion 123 extends radially inward from the surface on the other axial end side of the cylindrical portion 122. The inner diameter of the extension portion 123 is set to be larger than the inner diameter of the nut member 110 and the outer diameter of the rack shaft 51. That is, the extension portion 123 is positioned radially outward from the inner peripheral surface of the nut member 110 and the outer peripheral surface of the rack shaft 51. The facing surface 125 on one axial end side of the extension portion 123 and the facing surface 115 on the other axial end side of the nut member 110 face each other in the axial direction. By integrally molding the pulley member 120 with the nut member 110, the facing surface 115 and the facing surface 125 are in close contact with each other in the axial direction.

[0039] The flange 124 has a cylindrical shape whose outer diameter is larger than that of the cylindrical portion 122. The flange 124 extends radially outward from a surface on one axial end side of the cylindrical portion 122. The flange 124 is formed on one axial end side of the external teeth 121.

[0040] like Figure 3 As shown in the figure, a plurality of protrusions 126 are formed on a facing surface 125 on one axial end side of the extension portion 123. The plurality of protrusions 126 are formed to be the same in number as the plurality of recesses 116, and the plurality of protrusions 126 are arranged at equal intervals in the circumferential direction in the same manner as the recesses 116. That is, in the present embodiment, four protrusions 126 are formed in the facing surface 125. Each protrusion 126 has a cylindrical shape. Each protrusion 126 is formed when the pulley component 120 is integrally molded with the nut component 110. When the pulley component 120 is integrally molded with the nut component 110, each protrusion 126 is fitted into each recess 116 in a convex-concave manner, thereby forming a limiting component 130, which limits the relative rotation of the nut component 110 and the pulley component 120 in the circumferential direction.

[0041] like Figure 2 As shown in the figure, the driving pulley 53 has a cylindrical shape. The driving pulley 53 is integrally mounted on the outer peripheral surface of the rotating shaft 41a of the motor 41 in a rotatable manner. External teeth 53a are formed on the outer peripheral surface of the driving pulley 53. The external teeth 53a correspond to the external teeth 121 of the pulley component 120. The tooth lines of the external teeth 53a are formed in the circumferential direction at equal intervals. The external teeth 53a are formed as inclined teeth whose tooth lines are inclined relative to the axial direction. The external teeth 53a are formed on the entire circumference of the outer peripheral surface of the driving pulley 53. The external teeth 53a are formed in an axial range except for the end portion on one axial end side of the outer peripheral surface of the driving pulley 53 and the end portion on the other axial end side. The external teeth 53a are inclined teeth inclined in the axial direction.

[0042] The toothed belt 54 is wound between the driving pulley 53 and the pulley component 120 of the ball screw nut 100 to generate a predetermined tension. An internal tooth 54a corresponding to the external tooth 53a of the driving pulley 53 and the external tooth 121 of the pulley component 120 is formed on the inner circumferential surface of the toothed belt 54. The tooth line of the internal tooth 54a is formed in the circumferential direction at equal intervals. The internal tooth 54a is formed as an inclined tooth whose tooth line is inclined relative to the axial direction, corresponding to the external tooth 53a and the external tooth 121 as the inclined tooth. The internal tooth 54a meshes with the external tooth 53a and the external tooth 121 in the circumferential direction. The toothed belt 54 is made of a resin material. The torque of the motor 41 is sequentially transmitted to the driving pulley 53 and the toothed belt 54-the driving pulley 53 and the toothed belt 54 are attached to the rotating shaft 41a-and the pulley component 120 of the ball screw nut 100, so that the ball screw nut 100 rotates around the axis m.

[0043] The belt reducer for transmitting the rotation of the motor 41 to the ball screw nut 100 is composed of a pulley component 120 of the integrally molded ball screw nut 100, a drive pulley 53, and a toothed belt 54. The nut component 110 of the integrally molded ball screw nut 100, the rack shaft 51, and the balls 52 constitute a ball screw device for converting the rotation of the motor 41 transmitted via the belt reducer into the axial movement of the rack shaft 51.

[0044] The formation range of the external teeth 121 in the axial direction is formed on the entire axial area on the outer peripheral surface of the cylindrical portion 122. In the present embodiment, the external teeth 121 are not formed on the outer peripheral surface of the extension portion 123. The limiting member 130 is provided only in a range other than the inner peripheral portion of the pulley member 120 and the outer peripheral portion of the nut member 110 corresponding to the formation range of the external teeth 121. That is, the limiting member 130 is provided at a portion of the pulley member 120 that is unlikely to cause a decrease in the tooth tip accuracy of the external teeth 121.

[0045] A method for manufacturing the ball screw nut 100 will be described. Figure 4 As illustrated in FIG. 1 , the nut member 110 is first manufactured before the pulley member 120 is integrally molded on the outer periphery of the nut member 110. The nut member 110 having the above-mentioned shape is manufactured by subjecting a cylindrical metal material to plastic working such as cold forging. In the manufacturing, the ball rolling groove 111 is molded on the inner peripheral surface of the nut member 110, and the concave portion 116 serving as the restricting member 130 is molded on the facing surface 115 of the nut member 110.

[0046] After the molding of the nut component 110, the pulley component 120 is integrally molded on the outer periphery of the nut component 110. First, the annular first mold 200 and the bottomed cylindrical second mold 201 are assembled to cover the outer periphery of the molded nut component 110. The inner diameter of the first mold 200 is set to be equal to the outer diameter of the large diameter cylindrical portion 112 of the nut component 110. The first mold 200 is attached to the outer peripheral surface of the large diameter cylindrical portion 112 of the nut component 110 in a state adjacent to the other axial end side of the support 114 of the nut component 110. The first mold 200 is constructed by combining mold pieces 200a and 200b formed by dividing into two pieces in the radial direction. The mold pieces 200a and 200b have the same shape. The second mold 201 is set on the outer peripheral side of the large diameter cylindrical portion 112 with a gap formed on the radial outside of the large diameter cylindrical portion 112, and the second mold 201 is adjacent to the other axial end side of the first mold 200. The second mold 201 has an inner shaft part 202 that abuts on an end portion of the other axial end side of the inner peripheral surface of the nut part 110. The second mold 201 has an outer tooth molding part 203 on the inner peripheral surface for molding the outer teeth 121 of the pulley part 120. In the outer tooth molding part 203, tooth lines corresponding to the outer teeth 121 as inclined teeth are formed at equal intervals. A resin injection port 205 penetrating in the axial direction is formed in the bottom 204 of the second mold 201. The nut part 110, the first mold 200, and the second mold 201 serve as molds for molding the pulley part 120, which is a resin molded product. A space surrounded by the outer peripheral surface of the large-diameter cylindrical portion 112 of the nut member 110, the facing surface 115 on the other axial end side of the nut member 110, the surface on the other axial end side of the first mold 200, the inner peripheral surface of the second mold 201, the bottom 204 of the second mold 201, and the outer peripheral surface of the inner shaft member 202 of the second mold 201 is a cavity CV for molding the pulley member 120. The cavity CV is shaped for forming the pulley member 120 by insert molding.

[0047] After assembling the first mold 200 and the second mold 201 to the periphery of the nut component 110, the nozzle of the resin injection device for injecting molten resin is inserted into the resin injection port. The resin injection device starts injecting molten resin at a predetermined time. The molten resin injected from the resin injection device passes through the resin injection port 205 and then fills the cavity CV. The resin injection device fills the cavity CV with molten resin so that the pressure of the molten resin in the cavity CV remains constant. Then, the molten resin filling the cavity CV is cooled and solidified.

[0048] like Figure 5 As shown in the figure, when the solidification of the molten resin is completed, the first mold 200 and the second mold 201 are removed from the nut component 110 and the molded pulley component 120. At this time, the second mold 201 is removed toward the other axial end side while rotating along the tooth line of the inclined teeth of the external teeth 121 on the pulley component 120. This makes it possible to reduce the influence of the external tooth molded component 203 on the external teeth 121 when the second mold 201 is removed. The first mold 200 is removed in the radial direction in a state where it is divided into mold pieces 200a, 200b. Thus, the manufacture of the ball screw nut 100 is completed, in which the pulley component 120 is integrally molded on the outer periphery of the nut component 110.

[0049] The effect of the present embodiment will be described. The limiting member 130 for limiting the relative rotation between the nut member 110 and the pulley member 120 in the circumferential direction is not provided at a position where the large-diameter cylindrical portion 112 and the cylindrical portion 122 of the pulley member 120 formed with the external teeth 121 face each other, but is provided at a position between the facing surface 115 and the facing surface 125, which is a position where the nut member 110 and the pulley member 120 face each other in the axial direction. Therefore, compared with, for example, the case where the limiting member is provided at a position where the nut member 110 and the pulley member 120 face each other in the radial direction, the variation in the radial thickness of the cylindrical portion 122 formed with the external teeth 121 can be easily reduced. In the present embodiment, since the inner peripheral surface of the cylindrical portion 122 is formed as a circumferential surface, the radial thickness of the cylindrical portion 122 is constant except for the thickness difference between the tooth tip and the tooth root of the external teeth 121. In the thicker portion of the pulley member 120, the amount of heat shrinkage during molding is relatively large, while in the thinner portion of the pulley member 120, the amount of heat shrinkage during molding is relatively small. Since the radial thickness of the cylindrical portion 122 is constant except for the thickness difference between the tooth tip and the tooth root of the external teeth 121, the variation in the amount of heat shrinkage on the outer peripheral surface of the pulley member 120 is reduced.

[0050] The effect of the present embodiment will be described. In the ball screw nut 100 in which the pulley part 120 is integrally molded on the outer periphery of the nut part 110, the radial thickness of the cylindrical part 122 is constant except for the thickness difference between the tooth tip and the tooth root of the external tooth 121, thereby preventing the reduction of the accuracy of the tooth tip of the external tooth 121 formed on the outer peripheral surface of the cylindrical part 122.

[0051] Compared with the case where the outer circumferential surface of the nut part 110 or the inner circumferential surface of the cylindrical part 122 is not a circular surface over the entire axial range where the external teeth 121 are formed, since each of the outer circumferential surface of the nut part 110 and the inner circumferential surface of the cylindrical part 122 is formed as a circular surface, the change in the amount of thermal shrinkage on the outer circumferential surface of the pulley part 120 can be reduced.

[0052] The pulley member 120 is formed by insert molding using a resin material as a molding material, and therefore, the weight of the pulley member 120 can be reduced more than in the case where the pulley member 120 is molded using a metal material.

[0053] The pulley component 120 is integrally molded on the outer periphery of the nut component 110 so that the recess 116 formed in the facing surface 115 of the nut component 110 is fitted to the protrusion 126 formed on the facing surface 125 of the pulley component 120. Therefore, when the nut component 110 and the pulley component 120 are relatively rotated in the circumferential direction, the recess 116 and the protrusion 126 abut against each other, so that the relative rotation of the nut component 110 and the pulley component 120 in the circumferential direction can be restricted. In addition, since there is no need to use a separate member such as a bolt to restrict the relative rotation of the nut component 110 and the pulley component 120, the number of components of the transmission mechanism 42 can be reduced.

[0054] The rotational force of the motor 41 is transmitted from the driving pulley 53 connected to the rotating shaft 41a of the motor 41 to the pulley component 120 of the ball screw nut 100 via the toothed belt 54. Since the relative rotation between the nut component 110 and the pulley component 120 in the circumferential direction is limited by the limiting component 130, the nut component 110 rotates integrally with the pulley component 120 in the circumferential direction. The rotational force of the nut component 110 is converted into the axial movement of the rack shaft 51 by rolling the balls 52 between the ball rolling grooves 111 of the nut component 110 and the ball rolling grooves 51b of the rack shaft 51. In the ball screw nut 100 of the present embodiment, the reduction in the accuracy of the tooth tips of the external teeth 121 on the pulley component 120 is prevented, and therefore, the deterioration of the meshing of the external teeth 121 on the pulley component 120 with the internal teeth 54a of the toothed belt 54 can be prevented. This can prevent a decrease in the transmission efficiency for transmitting the rotational force of the motor 41 to the nut member 110 .

[0055] When the nut component and the pulley component are not integrally molded but are separate bodies, it is necessary to form a gap between the outer peripheral surface of the nut component and the inner peripheral surface of the pulley component so that the pulley component can be assembled to the outer periphery of the nut component. In particular, when the pulley component is molded using a resin material, it is difficult to press the pulley component onto the outer periphery of the nut component, and therefore, there is no choice but to form a gap. Therefore, when the gap is formed as described, the pulley component may be eccentrically assembled to the outer periphery of the nut component, so that the concentricity between the axial center of the nut component and the axial center of the pulley component is reduced. In the present embodiment, by integrally molding the pulley component 120 on the outer periphery of the nut component 110, the outer peripheral surface of the nut component 110 and the inner peripheral surface of the pulley component 120 can be brought into close contact with each other. This can improve the concentricity between the axial center of the nut component 110 and the axial center of the pulley component 120.

[0056] The above-mentioned embodiment can be modified as follows. In addition, the following other embodiments can be combined with each other to the extent that there is no technical contradiction. The external teeth 121 formed on the pulley component 120 are not limited to inclined teeth, but can be, for example, flat teeth in which the tooth line is formed along the axial direction. The external teeth 53a formed on the driving pulley 53 and the internal teeth 54a formed on the toothed belt 54 are not limited to inclined teeth, but can be, for example, flat teeth in which the tooth line is formed along the axial direction.

[0057] In the present embodiment, four recesses 116 are formed in the facing surface 115, but the present invention is not limited thereto. In the facing surface 115, one to three recesses 116 may be formed, or five or more recesses 116 may be formed. Four protrusions 126 are formed on the facing surface 125, but the present invention is not limited thereto. On the facing surface 125, one to three protrusions 126 may be formed, or five or more protrusions 126 may be formed.

[0058] In the present embodiment, the recesses 116 are arranged at equal intervals in the circumferential direction in the facing surface 115, but the recesses 116 may not be arranged at equal intervals. The protrusions 126 are provided at equal intervals in the circumferential direction on the facing surface 125, but the protrusions 126 may not be arranged at equal intervals.

[0059] In the present embodiment, the recess 116 is formed in the facing surface 115 of the nut member 110, and the protrusion 126 is formed in the facing surface 125 of the pulley member 120, but the present invention is not limited thereto. Figure 6, for example, the protrusion 116a may be formed on the facing surface 115 of the nut member 110, and the recess 126a to be fitted to the protrusion 116a may be formed in the facing surface 125 of the pulley member 120. In this case, the restricting member 130 is composed of the protrusion 116a formed on the facing surface 115 and the recess 126a formed on the facing surface 125.

[0060] like Figure 7 As illustrated in FIG. 1 , for example, a recess 116b may be formed in the facing surface 115 of the nut member 110, a recess 126b facing the recess 116b in the axial direction may be formed in the facing surface 125 of the pulley member 120, and a pin 140 as a separate member may be fitted into each of the recesses 116b, 126b. In this case, the restricting member 130 is composed of the recess 116b formed in the facing surface 115, the recess 126b formed in the facing surface 125, and the pin 140 as a separate member to be fitted into each of the recess 116b and the recess 126b. In the case where the limiting part 130 is formed using the pin 140 as a separate component, when the first mold 200 and the second mold 201 are assembled to the outer periphery of the nut part 110, the ball screw nut 100 is manufactured by injecting molten resin into the cavity CV in a state where the pin 140 as a separate component is fitted into the recess 116b formed in the relative surface 115.

[0061] The limiting member 130 limits the relative rotation of the nut member 110 and the pulley member 120 in the circumferential direction by engaging the recess 116 formed in the facing surface 115 of the nut member 110 with the protrusion 126 formed on the facing surface 125 of the pulley member 120 in a convex-concave manner, but the present invention is not limited thereto. For example, the surface of the facing surface 115 of the nut member 110 may be roughened to increase the friction between the surface of the facing surface 125 of the pulley member 120 and the facing surface 115. In this case, since a tiny uneven portion for increasing friction is formed on the surface of the facing surface 115, and a tiny uneven portion for increasing friction is also formed on the surface of the facing surface 125, a concave-convex fit is formed.

[0062] The pulley component 120 is formed on the periphery of the nut component 110 by insert molding using only a resin material as a molding material, but the present invention is not limited thereto. For example, the pulley component 120 can be formed on the periphery of the nut component 110 by insert molding using a resin material containing metal powder as a molding material. That is, the pulley component 120 is not limited to being molded by resin molding, but can be molded by metal powder injection molding. Compared with the case where the pulley component 120 is formed by insert molding using a molding material containing only a resin material, in the case where the pulley component 120 is formed by insert molding using a molding material containing metal powder, the amount of heat shrinkage of the pulley component 120 during insert molding can be reduced. Therefore, the change in the amount of heat shrinkage on the outer peripheral surface of the pulley component 120 can be further reduced.

[0063] In the pulley member 120 , the flange 124 is formed on one axial end side of the cylindrical portion 122 , but the flange 124 may be formed on the other axial end side of the cylindrical portion 122 . The flange 124 may not be formed on the pulley member 120 .

[0064] In addition to the outer circumferential surface of the cylindrical portion 122, the outer teeth 121 may be formed on the outer circumferential surface of the extension portion 123. The outer circumferential surface of the large diameter cylindrical portion 112 of the nut member 110 is formed as a circumferential surface, and the inner circumferential surface of the pulley member 120 is formed as a circumferential surface, but the present invention is not limited thereto. The outer circumferential surface of the large diameter cylindrical portion 112 and the inner circumferential surface of the pulley member 120 may each be formed as a circumferential surface that is not an ideal circumferential surface, such as a slightly elliptical circumferential surface.

[0065] The first mold 200 and the second mold 201 are used as molds for molding the pulley component 120, but the present invention is not limited thereto, and the shape and number of the molds can be appropriately changed. For example, although the first mold 200 is composed of mold pieces 200a, 200b, the first mold 200 can be composed of three or more mold pieces. When the support member 114 is not formed in the nut component 110, the first mold 200 can be composed of one mold piece. The second mold 201 can also be composed of a plurality of mold pieces.

[0066] The ball screw nut 100 is not limited to being implemented in the rotating unit 4, but may also be implemented in other devices such as machine tools. In the present embodiment, it has been shown that the ball screw nut 100 is implemented in the EPS 1 provided with the rotating unit 4, but the present invention is not limited to this. For example, the device may be configured as a steer-by-wire type steering device in which the power transmission between the steering unit steered by the driver and the rotating unit 4 for steering the rotating wheel 5 according to the steering of the driver is separated. In the case where the ball screw nut 100 is implemented as a steer-by-wire type steering device, the embodiment may be used not only as a front-wheel steering device but also as a rear-wheel steering device or a four-wheel steering device.

Claims

1. A ball screw nut (100), characterized in that: The ball screw nut (100) comprises: a cylindrical nut part (110) having a ball rolling groove (111) in a spiral shape on an inner peripheral surface; and A cylindrical pulley component (120) is integrally molded with the cylindrical nut component (110) on the outer peripheral side of the cylindrical nut component (110), and the cylindrical pulley component (120) has external teeth (121), wherein: The cylindrical pulley component (120) includes: a cylindrical portion (122) extending in the axial direction and facing the cylindrical nut component (110) in the radial direction; and an extension portion (123) extending radially inward from the cylindrical portion (122) and facing the cylindrical nut component (110) in the axial direction, and A limiting component (130) for limiting relative rotation between the cylindrical nut component (110) and the cylindrical pulley component (120) is provided between a facing surface (125) of the extending portion (123) facing the cylindrical nut component (110) and a facing surface (115) of the cylindrical nut component (110) facing the extending portion (123). The external teeth (121) are formed in the axial range of the outer peripheral surface of the cylindrical pulley component (120) where the cylindrical portion (122) is provided, except for the axial range where the extended portion (123) is provided. The outer peripheral surface of the cylindrical nut member (110) and the inner peripheral surface of the cylindrical portion (122) are circumferential surfaces over the entire axial range in which the external teeth (121) are formed. The cylindrical pulley component (120) is formed on the outer periphery of the cylindrical nut component (110) by insert molding using only a resin material as a molding material.

2. The ball screw nut (100) according to claim 1, characterized in that: One of the facing surface (115) of the cylindrical nut component (110) and the facing surface (125) of the cylindrical pulley component (120) has a protrusion (116a, 126), The other of the facing surface (115) of the cylindrical nut component (110) and the facing surface (125) of the cylindrical pulley component (120) has a recess (116, 126a, 116b, 126b), the protrusion (116a, 126) being fitted into the recess (116, 126a, 116b, 126b), and The restricting member (130) is configured to include the protruding portion (116a, 126) and the recessed portion (116, 126a, 116b, 126b).

3. A rotating unit (4), characterized in that: The rotating unit (4) comprises: a motor (41); and A transmission mechanism (42), wherein: The transmission mechanism (42) comprises: a ball screw nut (100) according to claim 1 or 2; a ball screw shaft (51), the ball screw shaft (51) having a ball rolling groove (51b) spirally formed on the outer peripheral surface; a plurality of balls (52), the plurality of balls (52) being arranged between the ball rolling groove (51b) of the ball screw shaft (51) and the ball rolling groove (111) of the ball screw nut (100); a driving pulley ( 53), the driving pulley (53) is connected to the rotating shaft (41a) of the motor (41) and has external teeth (53a) on the outer peripheral surface; and a toothed belt (54), the toothed belt (54) has internal teeth (54a) meshing with the external teeth (53a) of the driving pulley (53) and the external teeth (121) of the cylindrical pulley component (120), and the toothed belt (54) extends between the driving pulley (53) and the cylindrical pulley component (120).

4. A method for manufacturing a ball screw nut (100) according to claim 1 or 2, characterized in that: The cylindrical pulley component (120) is molded integrally with the cylindrical nut component (110) by insert molding using the cylindrical nut component (110) as an insert.

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