Shaft unit, method for manufacturing same, and electric assist device

Abstract

The present invention provides a shaft unit capable of suppressing deformation of a center hole caused by formation of a caulking portion, a method for manufacturing the same, and an electric assist device provided with the shaft unit. A shaft unit (56) is provided with: a shaft member (12) having a coupling shaft section (39) at an end on one side in the axial direction, and having a center hole (43a) that opens at an end surface on one side in the axial direction of the coupling shaft section (39); and a joint member (25) having a center hole (30) penetrating in the axial direction on the inside in the radial direction, the coupling shaft portion (39) being fitted into the center hole (30), the coupling shaft portion (39) having a caulking portion (41) formed by plastically deforming only a radially outer portion of an end edge portion on one side in the axial direction, the caulking portion (41) being in surface contact with an opening peripheral edge portion (77) on one side in the axial direction of the center hole (30) of the joint member (25).

Description

Technical Field

[0001] The present invention relates to a shaft unit formed by combining a shaft member and a joint member by a caulking portion, a manufacturing method thereof, and an electric assist device including the shaft unit. Background Art

[0002] In the field of steering devices, electric power steering devices configured to apply auxiliary power to steering force transmission components such as a steering shaft, a pinion shaft, and a rack shaft in order to reduce the force required to operate a steering wheel are becoming popular. The electric power steering device includes an electric assist device for applying auxiliary power.

[0003] The electric assist device includes an electric motor as a power source, a worm driven by the electric motor, and a worm wheel meshing with the worm. In the electric assist device, there is a structure including a coupling for connecting the output shaft of the electric motor and the worm in a manner that allows misalignment such as mutual tilt and axial center deviation and enables torque transmission (see U.S. Patent No. 11084522).

[0004] The coupling includes a joint component connected to the output shaft of the electric motor and a joint component connected to the end of one axial side of the worm. These joint components are connected directly or via an intermediate joint component in a manner that allows mutual misalignment and enables torque transmission.

[0005] The specification of U.S. Patent No. 11084522 describes the specific structure of an axis unit formed by combining an axis component composed of a worm gear and a joint component. In this axis unit, the axis component has a coupling shaft portion at the end on one axial side. The joint component has a center hole that penetrates along the axial direction on the radial inner side, and the coupling shaft portion of the axis component is embedded in the center hole. Moreover, the axis component has a center hole that is open in the radial central portion of the end face on one axial side of the coupling shaft portion. That is, the end on one axial side of the coupling shaft portion of the axis component is configured to be cylindrical.

[0006] The end edge of the connecting shaft portion is formed with an outward flange-shaped rivet portion formed by plastically deforming the entire end edge portion toward the radial outside. The rivet portion is used to press the opening peripheral edge of the central hole of the joint component on one axial side, thereby connecting the shaft component and the joint component.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: U.S. Patent No. 11084522 Summary of the invention

[0010] Technical problem that the invention aims to solve

[0011] In the above-mentioned conventional shaft unit, when forming the caulking portion, the entire axially one end edge portion of the coupling shaft portion of the shaft member is plastically deformed radially outward, so that the center hole of the coupling shaft portion is deformed.

[0012] The center hole is a part used when processing the outer peripheral surface of the shaft component, measuring the bending / rotational vibration of the shaft component, and assembling the shaft component with other components. Specifically, it is engaged with the center shaft for centering and / or rotation support. Therefore, if the center hole is deformed due to the formation of the riveted part, it may not be effectively used when performing the above-mentioned measurement and assembly.

[0013] Such a problem is not limited to the shaft unit composed of the worm and the joint member constituting the electric assist device, but also occurs similarly in shaft units constituting various mechanical devices.

[0014] An object of the present invention is to provide a shaft unit capable of suppressing deformation of a center hole caused by forming a caulking portion, a method for manufacturing the shaft unit, and an electric assist device including the shaft unit.

[0015] Technical solutions to the problem

[0016] A shaft unit according to one embodiment of the present invention comprises: a shaft component having a coupling shaft portion at an end portion on one axial side, and having a center hole opened at a radially central portion of an end face on one axial side of the coupling shaft portion; and a joint component having a center hole penetrating in the axial direction on the radial inner side, and the coupling shaft portion is embedded in the center hole. The joint component is a component for connecting the shaft component and a shaft component on the other side adjacent to the shaft component in a manner capable of transmitting torque.

[0017] In an axial unit of one embodiment of the present invention, the coupling shaft portion has a rivet portion formed by plastically deforming only the radially outer portion of the end edge portion on the axial side protruding from the center hole, and the rivet portion is in surface contact with the opening peripheral edge portion on the axial side of the center hole of the joint component.

[0018] In the shaft unit according to one embodiment of the present invention, at least a radially outer portion of a side surface on one axial side of the caulking portion is formed of an inclined surface portion that is inclined in a direction toward the other axial side as it goes radially outward.

[0019] In the shaft unit according to one embodiment of the present invention, the opening peripheral edge portion of the joint member is formed of a chamfered portion that is inclined in a direction that goes radially outward as it goes toward one side in the axial direction.

[0020] In the shaft unit according to one embodiment of the present invention, the shaft member is composed of a worm.

[0021] An electric assist device according to one embodiment of the present invention comprises: a worm wheel; a worm that meshes with the worm wheel; a coupling that includes a joint component that is coupled to a coupling shaft portion provided at an end portion on one axial side of the worm; and an electric motor that transmits torque to the worm via the coupling. A shaft unit including the worm and the joint component is constituted by the shaft unit according to one embodiment of the present invention.

[0022] In a manufacturing method of an axis unit according to one embodiment of the present invention, the axis unit to be manufactured comprises: an axis component, which has a connecting axis portion at an end portion on one axial side, and the axis component has a center hole opening at a radial central portion of an end face on one axial side of the connecting axis portion; and a joint component, which has a center hole penetrating along the axial direction on the radial inner side.

[0023] In a manufacturing method of an axis unit of one embodiment of the present invention, the following steps are provided: when the combining axis portion is embedded in the center hole of the joint component, the radial outer portion of the end edge portion of the combining axis portion protruding from the center hole on one axial side is pressed toward the other axial side using the pressing surface of a pressing punch, thereby flattening the radial outer portion in the axial direction to form a riveted portion, and making the riveted portion come into surface contact with the opening peripheral edge portion on the axial side of the center hole of the joint component.

[0024] In the manufacturing method of the shaft unit according to one aspect of the present invention, there is provided a step of press-fitting the joint member onto the outer peripheral surface of the coupling shaft portion from one axial side.

[0025] In the shaft unit,

[0026] The inner peripheral surface of the center hole is composed of a serration portion.

[0027] The entire outer diameter of the portion of the coupling shaft portion that protrudes from the center hole of the joint member to one side in the axial direction is less than the inner diameter of the serration portion.

[0028] In the step of press-fitting the joint component, the teeth of the serrations bite into the outer peripheral surface of the coupling shaft portion to complete the press-fitting of the joint component, thereby achieving a state in which the coupling shaft portion is fitted into the center hole of the joint component.

[0029] In the method for manufacturing a shaft unit according to one aspect of the present invention, in the step of forming the caulking portion, a side surface on one axial side of the caulking portion is pressed toward the other axial side and radially inward by a radially outer portion of the pressing surface.

[0030] In the method for manufacturing a shaft unit according to one aspect of the present invention, the shaft member is composed of a worm.

[0031] The present invention can be implemented by appropriately combining the structures of the above-mentioned embodiments within a range where no contradiction occurs.

[0032] Effects of the Invention

[0033] According to the present invention, it is possible to provide a shaft unit capable of suppressing deformation of a center hole caused by forming a caulking portion, a method for manufacturing the shaft unit, and an electric assist device including the shaft unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a partially cutaway side view showing an electric power steering device to which the electric assist device according to the first example of the embodiment of the present invention is applied.

[0035] Figure 2 The first example of the electric assist device is shown in FIG. Figure 1 AA section view.

[0036] Figure 3 The figure shows the connection part between the worm gear and the output shaft of the electric motor in the electric assist device of the first example. Figure 2 Enlarged view of part B.

[0037] Figure 4 The first example of the shaft unit includes a shaft member composed of a worm and a worm-side joint member.

[0038] Figure 5 It is a perspective view showing an end portion on one axial direction side of the shaft unit of the first example.

[0039] Figure 6 It is a cross-sectional view showing an end portion on one axial direction side of the shaft unit of the first example.

[0040] Figure 7 yes Figure 6 Enlarged view of part C.

[0041] Figure 8 This is a diagram showing an end portion on one axial side of the shaft member before the worm-side joint member is press-fitted onto the outer peripheral surface of the coupling shaft portion of the shaft member in the first example.

[0042] Fig. 9 This is a partial cross-sectional view showing a stage before the worm-side joint member is press-fitted onto the outer peripheral surface of the coupling shaft portion in the process of manufacturing the shaft unit of the first example.

[0043] Fig.10 This is a partial cross-sectional view showing a stage in which the worm-side joint member is press-fitted onto the outer peripheral surface of the coupling shaft portion in the process of manufacturing the shaft unit of the first example.

[0044] Fig.11 It is a cross-sectional view of a pressing punch used in the manufacturing method of the shaft unit of the first example.

[0045] Fig.12 yes Fig.11 Enlarged view of part D.

[0046] Fig.13 This is a partial cross-sectional view showing a stage immediately before forming a caulking portion in the process of manufacturing the shaft unit of the first example.

[0047] Fig.14 This is a partial cross-sectional view showing the initial stage of forming a caulking portion in the process of manufacturing the shaft unit of the first example.

[0048] Fig.15 yes Fig.14 Enlarged view of part E.

[0049] Fig.16 It is a partial cross-sectional view showing a stage in which the formation of the caulking portion is completed in the process of manufacturing the shaft unit of the first example.

[0050] Fig.17 yes Fig.16 Enlarged view of part F.

[0051] Fig.18 It is a half cross-sectional view of one axial side portion of a shaft member (worm) constituting a shaft unit according to a second example of an embodiment of the present invention.

[0052] Fig.19 (a) is a partial cross-sectional view showing a stage in which the worm-side joint member is press-fitted into the outer peripheral surface of the coupling shaft portion of the shaft member in the process of manufacturing the shaft unit of the second example, Fig.19 (b) is a partial cross-sectional view showing a completed stage of formation of the rivet portion. DETAILED DESCRIPTION

[0053] The present invention can be applied to various shaft units that are assembled as a part of various mechanical devices and are composed of shaft components and joint components. Examples of shaft components include torque transmission shafts such as worms, sliding screw shafts, ball screw shafts, motor shafts, steering shafts, rack shafts, pinion shafts, etc. Joint components are components used to connect shaft components and shaft components on the other side adjacent to the shaft components in a manner that can transmit torque. Examples of joint components include joint components that constitute various joint devices such as couplings, universal joints, and constant velocity joints.

[0054] [First example]

[0055] use Figure 1 to Figure 17A first example of an embodiment of the present invention will be described. In the first example, the present invention is applied to a shaft unit composed of a worm gear and a joint member thereof, which is assembled in an electric assist device of an electric power steering device.

[0056] (1) Shaft unit

[0057] The shaft unit 56 of the first example is particularly as follows Figure 1 to Figure 7 As shown. Figure 2 as well as Figure 3 As shown, the shaft unit 56 of this example comprises: a shaft component 12 having a coupling shaft portion 39 at an end portion on one axial side and a center hole 43a opened at a radially central portion of an end surface on one axial side of the coupling shaft portion 39; and a joint component 25 having a center hole 30 penetrating in the axial direction on the radial inner side and the coupling shaft portion 39 embedded in the center hole 30. The coupling shaft portion 39 has a rivet portion 41 formed by plastically deforming only the radially outer portion of the end edge portion on one axial side protruding from the center hole 30, and the rivet portion 41 is in surface contact with the opening peripheral edge portion 77 on one axial side of the center hole 30 of the joint component 25.

[0058] In addition, regarding the shaft unit 56, one axial side is Figure 2 and Figure 3 The right side of the axis is Figure 2 and Figure 3 on the left side of the .

[0059] In this example, the shaft member 12 is composed of a worm. In addition, the joint member 25 is composed of a worm-side joint member as one element of the coupling 13.

[0060] The shaft component (worm) 12 of this example is made of metal and has worm teeth 22 on the outer peripheral surface of the axial middle part. The constituent material and shape of the shaft component 12 can be arbitrarily determined according to the type and purpose of the shaft unit to which the present invention is applied. In the shaft component 12 of this example, the outer diameter of the coupling shaft portion 39 provided at the end on one axial side is smaller than the outer diameter of the portion adjacent to the other axial side. That is, the shaft component 12 of this example has a mating shaft portion 44 having a larger diameter than the coupling shaft portion 39 and a flange portion 45 protruding radially outward in the portion between the coupling shaft portion 39 and the worm teeth 22, in sequence from one axial side. The outer peripheral surface of the coupling shaft portion 39 and the outer peripheral surface of the mating shaft portion 44 are connected by a step surface 40 facing one axial side.

[0061] In this example, the center hole 43a opened in the radial center of the end face on the axial side of the coupling shaft portion 39 exists at the end on the axial side of the coupling shaft portion 39, and is arranged to overlap with the rivet portion 41 in the radial direction. At the end on the axial side of the coupling shaft portion 39, the portion around the center hole 43a is composed of a cylindrical portion 76. The center hole 43a is a portion used when processing the outer peripheral surface of the shaft member 12, measuring the bending / rotational vibration of the shaft member 12, and assembling the shaft member 12 with other components. Specifically, a center axis for centering and / or rotation support is engaged with the center hole 43a.

[0062] The shaft member 12 of this example also has a center hole 43 b opened in the radial center portion of the end surface on the other axial side at the end portion on the other axial side.

[0063] In this example, the portion of the outer peripheral surface of the coupling shaft portion 39 that is embedded in the center hole 30 of the coupling member (worm side coupling member) 25 is formed by a cylindrical surface. Figure 8 As shown in the figures, a relief groove 71 is provided over the entire circumference at the end portion of the outer circumferential surface of the coupling shaft portion 39, which is located closer to the axially opposite side than the portion embedded in the center hole 30 of the joint member 25. The relief groove 71 is a portion for retracting the blade of the cutting tool when manufacturing the worm 12. In the case of implementing the present invention, the relief groove 71 can be omitted if it is not necessary.

[0064] The joint member 25 of this example is made of metal. The constituent material and shape of the joint member 25 are arbitrarily determined according to the type and purpose of the shaft unit to which the present invention is applied. The center hole 30 of the joint member 25 is arranged radially inside the cylindrical portion 31 constituting the radial inner portion of the joint member 25. In this example, the inner peripheral surface of the center hole 30 is constituted by a serration portion 34.

[0065] like Figures 4 to 6 As shown in FIG. 1 , the joint member 25 of this example includes an annular flange portion 32 protruding radially outward from an axially intermediate portion of a cylindrical portion 31 and a tooth portion 33 protruding axially toward one side from a plurality of locations (four locations in this example) equally spaced in the circumferential direction of the radially outer portion of the flange portion 32. The radial thickness of the cylindrical portion 31 is greater at a portion located on the axially other side than the flange portion 32 than at a portion located on the axially one side than the flange portion 32.

[0066] In this example, the joint member 25 is formed by subjecting a metal material to necessary processing such as forging and cutting, and then heat-treated as a whole to be made harder than the worm 12. That is, the hardness of the serration portion 34 is greater than the hardness of the outer peripheral surface of the coupling shaft portion 39.

[0067] The joint member 25 is press-fitted from one axial side to the outer peripheral surface of the coupling shaft portion 39, and the end surface of the cylindrical portion 31 of the joint member 25 on the other axial side abuts against the step surface 40. In this example, as the joint member 25 is press-fitted, the teeth of the serration portion 34 (the tooth tops of the tooth portion 33) bite into the outer peripheral surface of the coupling shaft portion 39.

[0068] In this example, a large diameter portion 37 having an inner diameter larger than the inner peripheral surface of the center hole 30 is provided at the opening peripheral edge portion 78 on the other axial side of the center hole 30 of the joint member 25. The large diameter portion 37 is a portion that forms a space for accumulating the cutting slag generated during the above-mentioned press-in between the large diameter portion 37 and the outer peripheral surface of the coupling shaft portion 39. In addition, the large diameter portion 37 is composed of a conical surface such as a C chamfered portion that is inclined in a direction toward the radial outside as it moves toward the other axial side. However, in the case of implementing the present invention, the large diameter portion 37 can also be composed of a curved surface such as an R chamfered portion, a cylindrical surface having a larger diameter than the inner peripheral surface of the center hole, or the like.

[0069] In this example, if Figure 6 and Figure 7 As shown in the figure, the opening peripheral edge portion 77 of the center hole 30 of the joint member 25 on the axial side is composed of a chamfered portion 35 inclined in the direction toward the radial outer side as it moves toward the axial side. That is, the inner peripheral surface of the center hole 30 and the end surface 36 of the cylinder 31 on the axial side are connected via the chamfered portion 35. In this example, the chamfered portion 35 is composed of a C chamfered portion inclined linearly. However, in the case of implementing the present invention, the chamfered portion 35 can also be composed of an R chamfered portion inclined in a curved line, or a chamfered portion whose inclination angle increases stepwise as it moves toward the axial side, and the chamfered portion 35 constitutes the opening peripheral edge portion 77 of the joint member 25.

[0070] In this example, the outer diameter of the chamfered portion 35, that is, the inner diameter of the end surface 36 on the axial side of the cylinder portion 31, is larger than the groove bottom diameter of the serration portion 34. Therefore, the end of the groove on the axial side of the serration portion 34 is open only at the chamfered portion 35, and is not open at the end surface 36 on the axial side of the cylinder portion 31.

[0071] The engagement relationship between the shaft component 12 and the joint component 25 can be arbitrarily determined according to the type and purpose of the shaft unit to which the present invention is applied. For example, when the present invention is applied to a shaft unit composed of a worm and its joint component, the inner circumferential surface of the center hole of the joint component can be formed by a cylindrical surface, and the portion of the outer circumferential surface of the coupling shaft portion that is embedded in the center hole of the worm side joint component can be formed by a serrated portion, and the hardness of the worm side joint component can be reduced relative to the coupling shaft portion.

[0072] In addition, as the engagement relationship between the shaft component and the joint component, as long as the relative rotation between the shaft component and the joint component can be effectively prevented according to the constituent material, type and purpose of the shaft unit, press-fit engagement, knurled engagement, key engagement, spline engagement, serration engagement, etc. of the cylindrical surfaces can also be applied.

[0073] In this example, if Figure 6 and Figure 7 As shown, the rivet portion 41 formed by plastically deforming only the radially outer portion of the end edge portion on one axial side of the coupling shaft portion 39 is in surface contact with the chamfered portion 35 throughout the entire circumference. That is, the rivet portion 41 protrudes radially outward more than the portion of the outer peripheral surface of the coupling shaft portion 39 adjacent to the other axial side of the rivet portion 41. The side surface on the other axial side of the rivet portion 41 is composed of an annular surface that matches the chamfered portion 35 and is inclined in a direction toward the axial side as it moves toward the radial outside, and is in surface contact with the chamfered portion 35 in a manner throughout the entire circumference. In this example, the side surface on the other axial side of the rivet portion 41 is in surface contact with the chamfered portion 35 throughout the entire circumference and without a gap.

[0074] In this example, the entire opening of the groove of the serration portion 34 on one axial direction side is closed by the caulking portion 41 .

[0075] In this example, the joint member 25 is externally fitted and fixed to the coupling shaft portion 39 while being clamped by the step surface 40 and the rivet portion 41 of the shaft member 12 from both axial sides, and is prevented from falling off from the coupling shaft portion 39 to one axial side by the rivet portion 41.

[0076] In particular, in this example, the rivet portion 41 is in surface contact with the opening peripheral edge portion 77 (chamfered portion 35) of the joint member 25 throughout the entire circumference, so compared with the structure of the comparative example in which the rivet portion is in line contact with the opening peripheral edge portion (corner portion) of the center hole throughout the entire circumference, the joint member 25 can be firmly pressed from one axial side by the rivet portion 41. Therefore, the rivet portion 41 can effectively prevent the joint member 25 from falling off from the coupling shaft portion 39 to one axial side.

[0077] In this example, not only the locking force of the fitting portion between the serrated portion 34 of the joint component 25 and the outer peripheral surface of the connecting shaft portion 39 of the shaft component 12, and the friction force of the abutment portion between the end surface on the other axial side of the barrel portion 31 of the joint component 25 and the step surface 40 of the shaft component 12 are utilized, but also the larger friction force of the surface contact portion between the opening peripheral portion 77 of the joint component 25 and the riveted portion 41 of the shaft component 12 is utilized, so that the joint component 25 and the shaft component 12 can be effectively prevented from rotating relative to each other.

[0078] In particular, in the structure of this example, the contact area between the rivet portion 41 and the opening peripheral edge portion 77 (chamfered portion 35) can be increased compared to the structure of the above-mentioned comparative example in which the rivet portion makes line contact. Therefore, the friction force acting on the contact portion can be ensured to be large, and the relative rotation of the shaft member 12 and the joint member 25 can be effectively prevented.

[0079] In the present invention, the chamfered portion 35 of the opening peripheral edge 77 of the joint member 25 can be omitted. In this case, the opening peripheral edge in surface contact with the caulking portion 41 is the radially inner end of the end surface of the joint member 25 on one axial side.

[0080] In this example, if Figure 6 and Figure 7 As shown, at least the radially outer portion of the side surface on one axial side of the rivet portion 41 is formed by an inclined surface portion 42 that is inclined in a direction toward the other axial side as it moves toward the radially outer side. In this example, only the radially outer portion of the side surface on one axial side of the rivet portion 41 is formed by the inclined surface portion 42. However, in the case of implementing the present invention, the entire side surface on one axial side of the rivet portion 41 can also be formed by the inclined surface portion 42. The inclined surface portion 42 is formed by pressing the pressing punch 60 (see Fig.17 ) and the plastic working surface formed.

[0081] That is, in this example, when forming the rivet 41, the radially outer portion of the side surface on one axial side of the rivet 41, where at least the inclined surface portion 42 is formed, is pressed toward the other axial side and radially inward by the pressing punch 60, thereby applying compressive stress to the rivet 41. Therefore, compared with the case where the rivet is formed by pressing the entire side surface on one axial side of the rivet only toward the other axial side by a pressing punch, or the case where the rivet is formed by expanding the entire end edge portion on one axial side of the coupling shaft portion radially outward, cracks are less likely to occur in the rivet 41.

[0082] In this example, the generatrix shape (cross-sectional shape) of the inclined surface portion 42 is a straight line shape. The inclination angle θ of the inclined surface portion 42 relative to the imaginary plane orthogonal to the axial direction of the worm 12 can be arbitrarily set within a range greater than 0 degrees, but from the viewpoint of ensuring the crack suppression effect of the rivet portion 41, it is preferred to set the inclination angle θ to 15 degrees or more, and from the viewpoint of suppressing the processing force for forming the rivet portion 41, it is preferred to set the inclination angle θ to 45 degrees or less.

[0083] When the present invention is implemented, the generatrix shape (cross-sectional shape) of the inclined surface portion 42 constituting the side surface on one axial side of the caulking portion 41 can also be a curved shape.

[0084] When the present invention is implemented, the side surface on one axial direction of the caulking portion 41 may be formed by a plane perpendicular to the axial direction of the shaft member 12 .

[0085] (2) Manufacturing method of shaft unit

[0086] The manufacturing method of the shaft unit 56 of the first example is particularly Figure 8 to Figure 17 The manufacturing method of the shaft unit 56 of this example is characterized in that it comprises the following steps: when the coupling shaft portion 39 is embedded in the center hole 30 of the joint component 25, the radial outer side of the end edge portion of the coupling shaft portion 39 protruding from the center hole 30 is pressed toward the other side in the axial direction by the pressing surface 61 of the pressing punch 60, thereby flattening the radial outer side in the axial direction to form a rivet portion 41, and the rivet portion 41 is brought into surface contact with the opening peripheral edge portion 77 of the center hole 30 of the joint component 25 in the axial direction.

[0087] When manufacturing the shaft unit 56, as arbitrary preparation steps, a step of obtaining the intermediate shaft member 12a and the joint member 25 and a step of press-fitting the joint member 25 onto the outer peripheral surface of the coupling shaft portion 39a of the intermediate shaft member 12a from one axial side can be provided.

[0088] First, the intermediate shaft member 12a is obtained by any raw material and processing means before the coupling shaft portion 39a is fitted into the center hole 30 of the joint member 25 according to the constituent material and shape of the shaft member 12. In this example, the intermediate shaft member 12a is obtained by subjecting the metal raw material to necessary processing such as forging and cutting.

[0089] The intermediate shaft member 12a differs from the completed shaft member 12 only in the shape of the outer peripheral surface of the connecting shaft portion 39a. Specifically, the rivet portion 41 is not formed at the end portion on one axial side of the outer peripheral surface of the connecting shaft portion 39a. Figure 8 As shown, the outer peripheral surface of the coupling shaft portion 39a has a cylindrical surface portion 69 in the axial middle portion, a guide surface portion 70 at the end portion on one axial side adjacent to the cylindrical surface portion 69, and a tool withdrawal groove 71 extending throughout the entire circumference at the end portion on the other axial side adjacent to the cylindrical surface portion 69.

[0090] The cylindrical surface portion 69 is formed of a cylindrical surface whose outer diameter does not change in the axial direction. In this example, the axial range L of the cylindrical surface portion 69 is 69 The axial range L includes the portion of the shaft unit 56 that is fitted into the center hole 30 of the joint member 25 after completion. 30 ( ).

[0091] The outer diameter of the cylindrical surface portion 69 is larger than the inner diameter of the serration portion 34 of the joint member 25. More specifically, the outer diameter of the cylindrical surface portion 69 is larger than the tip diameter of the serration portion 34 and smaller than the root diameter of the serration portion 34.

[0092] The guide surface 70 is formed of a conical surface whose outer diameter decreases toward one side in the axial direction. The guide surface 70 functions as a guide when the joint member 25 is pressed into the outer peripheral surface of the coupling shaft portion 39a from one side in the axial direction. When the present invention is implemented, the guide surface 70 can also be omitted.

[0093] In addition, the joint component 25 can be obtained by using any raw material and processing means according to the constituent material and shape of the joint component 25. In this example, the joint component 25 is obtained by subjecting the metal raw material to necessary processing such as forging and cutting and heat treatment. Alternatively, if the required mechanical properties such as hardness can be ensured, the joint component 25 can also be obtained by sintering metal powder.

[0094] Next, the joint member 25 is press-fitted onto the outer peripheral surface of the coupling shaft portion 39a of the intermediate shaft member 12a from one axial side. In the process of press-fitting the joint member 25, first, Fig. 9 As shown, the intermediate shaft member 12a is supported by the support stand 57 in a state where the end portion on one axial side faces upward. Specifically, the outer peripheral surface of the intermediate shaft member 12a is fitted into the support hole 58 provided in the support stand, and the side surface on the other axial side of the flange portion 45 provided on the intermediate shaft member 12a is supported by the support surface 59 of the support stand 57, thereby preventing the intermediate shaft member 12a from being displaced in the radial direction and to the other axial side.

[0095] In this example, the worm gear 22 of the intermediate shaft component 12a is embedded in the support hole 58 of the support platform 57, and the conical convex side surface of the flange portion 45 of the intermediate shaft component 12a is supported by a conical concave support surface 59 provided on the opening peripheral edge portion of the support hole 58 on the axial side of the support platform 57.

[0096] Then, the joint member 25 is press-fitted onto the outer peripheral surface of the coupling shaft portion 39 a of the intermediate shaft member 12 a from one axial side using the cylindrical press-fit jig 72 .

[0097] In this example, the joint component 25 is press-fitted in a state in which a ball bearing 46 and a worm damper 53 on the other axial side are arranged around a portion of the intermediate shaft component 12a located above the support platform 57, and a worm damper 53 on one axial side is arranged around an end portion of the tubular portion 31 of the joint component 25 on the other axial side.

[0098] More specifically, first, Fig. 9 As shown, a cylindrical center shaft 65 is inserted without radial shake into a joint component 25 having a worm damper 53 on one axial side arranged around the end portion on the other axial side of the barrel 31, and a press-fit jig 72 arranged adjacent to the joint component 25, and a conical engaging portion 73 provided in the radial center portion of the lower end portion of the center shaft 65 is engaged with the center hole 43a on the axial side of the intermediate shaft component 12a.

[0099] Thus, above the intermediate shaft member 12 a , the worm damper 53 on the axial side, the joint member 25 , and the press-fit jig 72 are arranged coaxially with the intermediate shaft member 12 a .

[0100] Then, if Figures 9 and 10 As shown in the figure, the end face 36 on one axial side of the cylindrical portion 31 of the joint member 25 is pressed by the press-fitting jig 72, so that the joint member 25 is pressed from one axial side to the outer peripheral surface of the coupling shaft portion 39a, and the end face on the other axial side of the cylindrical portion 31 of the joint member 25 is brought into contact with the stepped surface 40 of the intermediate shaft member 12a. In this example, along with this press-fitting, the teeth of the serration portion 34 of the worm side joint member 25 (the tooth top of the tooth portion 33) are bitten into the cylindrical surface portion 69 provided in the axial middle portion of the outer peripheral surface of the coupling shaft portion 39a.

[0101] In this example, if cutting shavings are generated on the outer peripheral surface of the coupling shaft portion 39 a due to the press-fitting, the cutting shavings accumulate in the space between the outer peripheral surface of the coupling shaft portion 39 a and the large diameter portion 37 of the joint member 25 .

[0102] In this example, if Fig.10 As shown, when the joint component 25 is pressed into the outer peripheral surface of the connecting shaft portion 39a from one axial side, the end portion of the connecting shaft portion 39a on one axial side (including the end portion of the cylindrical surface portion 69 on one axial side) protrudes from the center hole 30 of the joint component 25 to one axial side.

[0103] Next, after the joint member 25 is pressed and fitted, the coupling shaft 39 is fitted into the center hole 30 of the joint member 25. Figure 11 to Figure 13 The pressing punch 60 shown in the figure is used to form the caulking portion 41. The pressing punch 60 is generally cylindrical and has a pressing surface 61 on the radially inner side of the lower end surface in the axial direction.

[0104] In this example, the radially inner portion of the pressing surface 61 is composed of a flat surface portion 62 that is at right angles to the axial direction of the pressing punch 60, and the radially outer portion of the pressing surface 61 is composed of an inclined surface portion 63 that is inclined in a direction that is downward as it goes radially outward. The radially outer end of the flat surface portion 62 is smoothly connected to the radially inner end of the inclined surface portion 63. The center hole of the pressing punch 60 has a guide hole portion 64 having a smaller diameter than the axially lower end portion in the portion from the axially middle portion to the axially upper end portion.

[0105] In the process of forming the rivet portion 41 using the pressing punch 60, first, Fig.13 As shown in FIG. 1 , the conical engagement portion 73a provided at the lower end of the center shaft 65a inserted into the guide hole 64 of the pressing punch 60 without play in the radial direction is engaged with the center hole 43a on the axial side of the intermediate shaft member 12a. Thus, the pressing punch 60 is coaxially arranged with the intermediate shaft member 12a above the intermediate shaft member 12a.

[0106] Next, from Fig.13 The status shown is Fig.14 and Fig.15 In the state shown, the pressing punch 60 is moved downward along the central axis 65a, and the flat surface portion 62 of the pressing surface 61 of the pressing punch 60 is brought into contact with the radially outer portion of the end surface on one axial side of the coupling shaft portion 39a.

[0107] Next, from Fig.14 and Fig.15 The status shown is Fig.16 and Fig.17 In the state shown, the pressing punch 60 is further moved downward along the central axis 65a, so that the radially outer side of the end edge of the coupling shaft portion 39a on one axial side is pressed toward the other axial side by the flat surface 62 of the pressing surface 61 of the pressing punch 60. Thus, the radially outer side is flattened in the axial direction to form the rivet portion 41.

[0108] Specifically, the radially outer portion is flattened in the axial direction, and the wall of the radially outer portion flows radially outward along the flat surface 62 and the inclined surface 63 of the pressing surface 61 of the pressing punch 60, thereby forming the rivet portion 41. Then, the rivet portion 41 is brought into surface contact with the chamfered portion 35 of the joint member 25 over the entire circumference.

[0109] In particular, in this example, when the rivet 41 is formed in this way, the radially outer portion of the side surface on one axial side of the rivet 41 is pressed toward the other axial side and radially inward by the inclined surface portion 63 of the pressing surface 61 of the pressing punch 60. Thus, compressive stress acts on the rivet 41. The side surface on one axial side of the rivet 41 becomes the inclined surface portion 42 as a plastically processed surface formed by pressing the inclined surface portion 63 of the pressing surface 61.

[0110] In this example, when forming the rivet portion 41, only the radially outer portion of the end edge portion on one axial side of the coupling shaft portion 39a is pressed by the pressing surface 61 of the pressing punch 60 to be plastically deformed, so that, unlike the case where the rivet portion is formed by expanding the entire end edge portion on one axial side of the coupling shaft portion radially outward, deformation of the center hole 43a can be substantially prevented. Therefore, after the rivet portion 41 is formed, the center hole 43a can be effectively used when measuring the bending / rotational vibration of the shaft member 12, assembling the shaft member 12 with other members, etc.

[0111] In this example, when forming the rivet 41, by pressing the radially outer portion of the side surface on one axial side of the rivet 41 toward the other axial side and the radially inner side, compressive stress can be applied to the rivet 41, so that cracks are not easily generated in the rivet 41. However, when implementing the present invention, when forming the rivet 41, the side surface on one axial side of the rivet 41 can also be pressed toward the other axial side using a flat surface portion perpendicular to the axial direction.

[0112] In addition, when the present invention is implemented, a structure can be adopted in which the rivet portion 41 contacts only a plurality of circumferentially separated locations of the opening peripheral edge portion 77 (e.g., the chamfered portion 35) on one axial side of the center hole 30 of the joint member 25. In this case, the processing load of the rivet portion can be suppressed, and manufacturing is easy.

[0113] When the present invention is implemented, the caulking portion 41 can be pressed in multiple times. In this case, the processing load per time can be suppressed, and manufacturing is easy.

[0114] (3) Electric power steering

[0115] like Figure 1 As shown, the electric power steering system 1 of this example includes a steering wheel 2, a steering shaft 3, a steering column 4, a pair of universal joints 5a, 5b, an intermediate shaft 6, a steering gear unit 7, and an electric assist device 8 to which the shaft unit 56 of this example is applied.

[0116] The steering wheel 2 is supported and fixed to the rear end of the steering shaft 3. The steering shaft 3 is rotatably supported inside a steering column 4, which is supported by the vehicle body. The front end of the steering shaft 3 is connected to the pinion shaft 9 of the steering gear unit 7 via a universal joint 5a on the rear side, an intermediate shaft 6, and a universal joint 5b on the front side.

[0117] Therefore, when the driver rotates the steering wheel 2, the rotation of the steering wheel 2 is transmitted to the pinion shaft 9 via the steering shaft 3, the pair of universal joints 5a, 5b and the intermediate shaft 6. The rotation of the pinion shaft 9 is converted into a linear motion of the rack shaft (not shown) of the steering gear unit 7 meshing with the pinion shaft 9. As a result, a steering angle corresponding to the rotation operation amount of the steering wheel 2 is given to the left and right steering wheels by pushing and pulling the pair of tie rods 10. The electric assist device 8 is a device that generates auxiliary power for reducing the force required for the driver to operate the steering wheel 2.

[0118] (4) Electric assist device

[0119] like Figure 2 as well as Figure 3 As shown, the electric assist device 8 of this example includes a worm wheel 11, a worm 12, a coupling 13, and an electric motor 14. In the electric assist device 8, the shaft member 12 constituting the shaft unit 56 of this example is applied as the worm 12.

[0120] The electric assist device 8 of this example transmits the rotational torque of the output shaft 23 of the electric motor 14 to the worm 12 via the coupling 13 , further increases the rotational torque by a worm reducer formed by meshing the worm 12 with the worm wheel 11 , and applies the torque to the steering shaft 3 .

[0121] The electric assist device 8 of this example further includes a housing 15, which is supported and fixed to the front end portion of the steering column 4. The housing 15 is a casting of an iron alloy, a die-casting molded product of a light alloy such as aluminum, or an injection molded product of a synthetic resin, and includes a worm wheel housing portion 16 and a worm housing portion 17, wherein the worm housing portion 17 is arranged at a position twisted relative to the worm wheel housing portion 16, and the axial middle portion is open to the worm wheel housing portion 16.

[0122] The worm wheel housing portion 16 is supported and fixed to the front end portion of the steering column 4 so that the central axis of the worm wheel housing portion 16 becomes coaxial with the central axis of the steering column 4 .

[0123] The worm housing portion 17 is formed in a cylindrical shape and has openings at both ends in the axial direction. In the following description, regarding the worm housing portion 17 and the components housed in the worm housing portion 17, one side in the axial direction is Figure 2 as well as Figure 3 The right side of the axis is Figure 2 as well as Figure 3 on the left side of the .

[0124] The opening on one side in the axial direction of the worm housing portion 17 is closed by the electric motor 14 supported and fixed to the housing 15 . The opening on the other side in the axial direction of the worm housing portion 17 is closed by a cover 18 .

[0125] The worm wheel 11 has gear teeth 19 on the outer peripheral surface and is rotatably supported inside the worm wheel housing portion 16. In this example, the worm wheel 11 is supported and fixed around the front end portion of the steering shaft 3 so as to rotate integrally with the steering shaft 3, and the steering shaft 3 is rotatably supported inside the worm wheel housing portion 16. The worm wheel 11 of this example is fixedly connected to a synthetic resin gear portion 21 having gear teeth 19 on the outer peripheral surface around a core portion 20 made of metal and in the shape of a circular wheel plate.

[0126] The worm 12 is rotatably supported by a pair of ball bearings 46 and 54 inside the worm housing 17. One axial end of the worm 12 is connected to a distal end of an output shaft 23 of an electric motor 14 via a coupling 13 so as to be torque-transmissible and oscillating.

[0127] An urging mechanism 55 is assembled between the outer peripheral surface of the ball bearing 54 supporting the other axial end of the worm 12 and the inner peripheral surface of the worm housing 17. The urging mechanism 55 is composed of an elastic body such as a coil spring and a leaf spring. The urging mechanism 55 elastically urges the worm teeth 22 of the worm 12 toward the gear teeth 19 of the worm wheel 11. According to such a structure, the generation of the tooth rattling sound is suppressed by suppressing the backlash between the worm teeth 22 and the gear teeth 19.

[0128] The electric assist device 8 of this example is disposed at a position where assist power is applied to the steering shaft 3. However, the present invention is also applicable to an electric assist device disposed at a position where assist power is applied to a pinion shaft or a rack shaft of a steering gear unit.

[0129] The coupling 13 includes: a worm-side joint component 25; a motor-side joint component 24, which is fixedly coupled to the terminal end of the output shaft 23 of the electric motor 14; and an intermediate joint component 26, which connects the motor-side joint component 24 and the worm-side joint component 25 in a manner that allows misalignment and transmits torque. The coupling 13 is entirely accommodated inside the worm accommodation portion 17. In the electric assist device 8 of this example, the joint component 25 of this example is applied to the worm-side joint component 25 constituting the coupling 13. Therefore, the shaft unit 56 of this example is constituted by the worm 12 and the worm-side joint component 25.

[0130] The motor-side joint member 24 is a metal member, and includes: a cylindrical barrel portion 27, which is externally fitted and fixed to the terminal end of the output shaft 23 of the electric motor 14; an annular flange portion 28, which protrudes radially outward from the axial middle portion of the barrel portion 27; and teeth 29, which protrude toward the other axial side from a plurality of locations (four locations in this example) equally spaced in the circumferential direction of the radial outer portion of the flange portion 28. The end portions (terminal ends) of the other axial side of these teeth 29 are arranged at a position closer to the other axial side than the barrel portion 27.

[0131] The intermediate joint component 26 is formed into an annular shape as a whole. The intermediate joint component 26 has an insertion hole 38a through which the tooth portion 29 of the motor side joint component 24 can be inserted at multiple locations (four locations in this example) equally spaced in the circumferential direction on one axial side, and has an insertion hole 38b through which the tooth portion 33 of the worm side joint component 25 can be inserted at multiple locations (four locations in this example) equally spaced in the circumferential direction on the other axial side. In this example, the intermediate joint component 26 is formed by combining a core material made of synthetic resin or metal material and an annular shape with a rubber buffer material. The portion of the inner circumferential surface of the insertion holes 38a, 38b that contacts the tooth portions 29, 33 when no torque is transmitted is formed of a buffer material.

[0132] The multiple teeth 29 of the motor-side joint member 24 are inserted from one axial side into the multiple insertion holes 38a of the intermediate joint member 26, and the multiple teeth 33 of the worm-side joint member 25 are inserted from the other axial side into the multiple insertion holes 38b of the intermediate joint member 26. Thus, the motor-side joint member 24 and the worm-side joint member 25 are connected via the intermediate joint member 26 in a manner that allows misalignment with each other and enables torque transmission.

[0133] In this example, the distal end of the output shaft 23 of the electric motor 14 is torque-transmittably connected to one axial end of the worm 12 via the coupling 13 , thereby enabling the worm 12 to swing relative to the output shaft 23 .

[0134] In addition, when implementing the present invention, the structure of the coupling is not limited to the structure of this example. For example, as a coupling, a structure can also be adopted in which the motor side joint component and the worm side joint component are directly connected without an intermediate joint component in a manner that allows misalignment between each other and can transmit torque.

[0135] In this example, the fitting shaft portion 44 of the worm 12 is supported by a ball bearing 46 so as to be rotatable relative to the worm housing portion 17 .

[0136] The ball bearing 46 includes an outer ring 47 , an inner ring 48 , and a plurality of balls 49 .

[0137] The outer ring 47 is fitted into a cylindrical surface portion 50 provided on the inner peripheral surface of the end portion on one axial side of the worm housing portion 17. In this state, the outer ring 47 is clamped from both axial sides by a step surface 51 facing one axial side at a portion adjacent to the other axial side of the cylindrical surface portion 50 in the worm housing portion 17 and a retaining ring 52 locked to the cylindrical surface portion 50.

[0138] The inner ring 48 is fitted to the fitting shaft portion 44 of the worm 12 in a clearance fit. In addition, the O-ring 67 is locked in the circumferential groove 66 formed on the outer peripheral surface of the axial middle portion of the fitting shaft portion 44, and the O-ring 67 is elastically clamped between the bottom surface of the circumferential groove 66 and the inner peripheral surface of the inner ring 48. That is, there is a small radial gap between the inner peripheral surface of the inner ring 48 and the outer peripheral surface of the fitting shaft portion 44, and the worm 12 and the worm-side joint member 25 are floatingly supported in the radial direction relative to the inner ring 48 by the O-ring 67.

[0139] The worm 12 and the worm-side joint member 25 are relatively displaceable in the radial direction with respect to the inner ring 48 by an amount corresponding to the above-mentioned small radial gap.

[0140] The inner ring 48 is arranged with a small axial gap between the side surface on the other axial side of the cylinder portion 31 of the worm-side joint member 25 and the stepped surface 68 facing the axial side provided on the outer peripheral surface of the fitting shaft portion 44. In addition, the inner ring 48 is clamped from both axial sides by the side surface on the one axial side of the flange portion 45 of the worm 12 and the side surface on the other axial side of the flange portion 32 of the worm-side joint member 25, respectively, via a pair of worm dampers 53 that can be elastically compressed in the axial direction.

[0141] Specifically, the side surface on the other axial side of the inner ring 48 abuts against the side surface on one axial side of the flange portion 45 via the worm damper 53 on the other axial side, and the side surface on one axial side of the inner ring 48 abuts against the side surface on the other axial side of the flange portion 32 via the worm damper 53 on the axial side.

[0142] That is, there are minute axial gaps between the side surface on one axial side of the inner ring 48 and the side surface on the other axial side of the tube portion 31 of the worm-side joint member 25, and between the side surface on the other axial side of the inner ring 48 and the stepped surface 68 of the worm 12, and the worm 12 and the worm-side joint member 25 are floatingly supported in the axial direction relative to the inner ring 48 by a pair of worm dampers 53. The worm 12 and the worm-side joint member 25 can be relatively displaced in the axial directions relative to the inner ring 48 by an amount corresponding to the minute axial gaps.

[0143] The plurality of balls 49 are arranged between an outer raceway provided on the inner peripheral surface of the outer race 47 and an inner raceway provided on the outer peripheral surface of the inner race 48 .

[0144] The ball bearing 46 has radial clearance between the outer ring 47 and the inner ring 48 and the balls 49 .

[0145] Therefore, the fitting shaft portion 44 of the worm 12 is supported by the worm accommodation portion 17 in a swingably displaceable manner based on the existence of the minute radial gap, the minute axial gap, and the radial gap.

[0146] When the electric assist device 8 of this example is in operation, an axial meshing reaction force acts on the meshing portion of the worm 12 that meshes with the worm wheel 11. The direction of the axial meshing reaction force is opposite to the direction of rotation of the worm 12.

[0147] The meshing reaction force acting on one side in the axial direction with respect to the worm 12 is supported by the retaining ring 52 via the worm damper 53 and the ball bearing 46 on the other side in the axial direction.

[0148] The meshing reaction force acting on the worm 12 toward the other axial side is supported by the step surface 51 of the worm housing portion 17 via the worm-side joint member 25, the worm damper 53 on the axial side, and the ball bearing 46. In particular, when the meshing reaction force acting on the worm 12 toward the other axial side becomes larger, the side surface on the axial side of the inner ring 48 contacts the side surface on the axial side of the cylinder 31 of the worm-side joint member 25, and a large force toward the axial side is applied from the inner ring 48 to the worm-side joint member 25.

[0149] In this case, in this example, the rivet portion 41 provided on the coupling shaft portion 39 of the worm 12 also makes surface contact with the chamfered portion 35 of the opening peripheral edge portion on the axial side of the center hole 30 constituting the worm-side joint member 25 over the entire circumference. Therefore, the rivet portion 41 can effectively prevent the worm-side joint member 25 from falling off from the coupling shaft portion 39 to the axial side.

[0150] [Second example]

[0151] use Fig.18 as well as Fig.19 A second example of the embodiment of the present invention will be described.

[0152] This example is the same as the first example. Fig.19 As shown in (a), in the shaft unit 56a, the inner circumferential surface of the center hole 30 of the joint component 25 is composed of a serration portion 34, and the teeth of the serration portion 34 (the top of the tooth portion 33) are bitten into the outer circumferential surface of the coupling shaft portion 39 embedded in the shaft component 12 by pressing the joint component 25 from one axial side into the outer circumferential surface of the coupling shaft portion 39.

[0153] In the manufacturing method of the shaft unit 56a of this example, as Fig.18 As shown, in the intermediate shaft member 12b before the joint member 25 is press-fitted from one axial side to the outer peripheral surface of the coupling shaft portion 39b, a portion of the coupling shaft portion 39b that protrudes from the radial inner side of the joint member 25 to the axial side after the joint member 25 is press-fitted (at the Fig.18 and Fig.19 The entire outer diameter of the portion (indicated by the axial range S in (a)) is set to be less than the inner diameter of the serration portion 34 provided on the inner peripheral surface of the center hole 30 of the joint member 25.

[0154] More specifically, in this case, Fig.18 As shown, the outer peripheral surface of the coupling shaft portion 39b of the intermediate shaft member 12b is provided with a small diameter portion 74 between the cylindrical surface portion 69 and the guide surface portion 70 in the axial direction. The small diameter portion 74 is composed of a cylindrical surface whose outer diameter does not change in the axial direction. The end of the small diameter portion 74 on one axial side is directly connected to the end of the guide surface portion 70 on the other axial side. The end of the small diameter portion 74 on the other axial side is connected to the end of the cylindrical surface portion 69 on one axial side via a connecting portion 75, and the connecting portion 75 is composed of a conical surface whose outer diameter increases as it goes to the other axial side.

[0155] In this example, if Fig.19 As shown in (a), when the process of press-fitting the external fitting joint component 25 is completed and the coupling shaft portion 39b is embedded in the center hole 30 of the joint component 25, only the end portion on the other axial side of the small diameter portion 74 is arranged radially inside the center hole 30 of the joint component 25. In other words, when the press-fitting operation is completed, the portion of the small diameter portion 74 other than the end portion on the other axial side and the guide surface portion 70 are arranged at a position protruding from the center hole 30 to one side in the axial direction.

[0156] In this example, the outer diameter of the small diameter portion 74 is equal to or smaller than the inner diameter of the serration portion 34 . Therefore, the outer diameter of the guide surface portion 70 is smaller than the inner diameter of the serration portion 34 .

[0157] In this example, by adopting the above-mentioned arrangement relationship and dimensional relationship, before the step of press-fitting the joint member 25 from one axial side to the outer peripheral surface of the coupling shaft portion 39b, the portion of the coupling shaft portion 39b that protrudes from the center hole 30 of the joint member 25 to one axial side after the press-fitting is completed (at the end of the coupling shaft portion 39b) is Fig.18 and Fig.19 The outer diameter of the entire portion (the portion represented by the axial range S in (a), that is, the portion of the small diameter portion 74 excluding the end portion on the other axial side and the entire guide surface portion 70 is set to be less than the inner diameter of the serration portion 34.

[0158] In this example, as the above-mentioned protruding part (in Fig.18 and Fig.19 The shape of the protruding portion (the portion indicated by the axial range S in (a)) is a shape formed by combining the small diameter portion 74 formed by a cylindrical surface and the guide surface portion 70 formed by a conical surface. However, in the case of implementing the present invention, the protruding portion can adopt any shape as long as its overall outer diameter is less than the inner diameter of the serration portion 34. For example, as the shape of the protruding portion, a shape in which the overall outer diameter is formed by a cylindrical surface and the outer diameter decreases continuously or stepwise as it moves toward one side in the axial direction can also be adopted.

[0159] In this case, as in the first case, Fig.19 As shown in (a), after the above-mentioned press-fitting is completed and the coupling shaft portion 39b is embedded in the center hole 30 of the joint member 25, as shown in Fig.19 (a) to Fig.19 As shown in (b), the radial outer portion of the end edge portion of the connecting shaft portion 39b protruding from the center hole 30 on one axial side is pressed toward the other axial side by the pressing surface of the pressing punch, thereby flattening the radial outer portion in the axial direction to form a rivet portion 41, so that the rivet portion 41 is in surface contact with the opening peripheral edge portion 77 (chamfered portion 35) on the axial side of the center hole 30 of the joint component 25.

[0160] In the manufacturing method of this example, the protruding portion (in Fig.18 and Fig.19 The entire outer diameter of the portion (indicated by the axial range S in (a)) is set to be less than the inner diameter of the serration portion 34. Therefore, compared with a structure in which the outer diameter of at least a part of the protruding portion is larger than the inner diameter of the serration portion 34 (such as the structure of the first example), the axial press-in stroke amount during the above-mentioned press-in can be suppressed to be smaller. Therefore, the energy required for the above-mentioned press-in can be suppressed accordingly.

[0161] In addition, a wider radial distance can be ensured between the outer peripheral surface of the protruding portion and the peripheral edge of the opening (in this example, the chamfered portion 35) on one axial side of the center hole 30. Therefore, when the radially outer portion of the protruding portion is axially flattened to form the rivet portion 41, the flattened material can easily flow to the outer diameter side, and the formability of the rivet portion 41 can be improved.

[0162] Moreover, it is possible to more effectively prevent the formation of axial passage marks (cutting marks) of the teeth of the serration portion 34 at multiple circumferential locations on the outer circumferential surface of the above-mentioned protruding portion. That is, in this example, even if axial passage marks of the teeth of the serration portion 34 are formed at multiple circumferential locations on the outer circumferential surface of the coupling shaft portion 39b, and grinding chips (burrs) are temporarily formed at the edges of the passage marks, the passage marks and grinding chips do not exist in the portion protruding from the center hole 30 of the joint member 25 to one axial side. The opening on one axial side of the inner side of the center hole 30, that is, the opening on one axial side of the groove of the serration portion 34, is blocked by the rivet portion 41. Therefore, it is possible to effectively prevent the grinding chips from falling off to the surroundings.

[0163] It should be noted that, in a structure in which the coupling shaft portion 39 is larger than the inner diameter of the serration portion 34 as a whole, the axial passing marks of the teeth of the serration portion 34 are formed at multiple circumferential positions on the outer peripheral surface of the above-mentioned protruding portion, and in the case where a grinding sheet is temporarily formed on the edge of the passing mark, after the riveting portion 41 is formed, before the completed shaft unit 56 is accommodated in the housing 15 of the worm reducer, a process of removing the grinding sheet is performed, thereby avoiding the problem that the grinding sheet falls off in the housing 15. In this example, such a process of removing the grinding sheet can be omitted. Other structures and effects are the same as those in the first example.

[0164] Description of Reference Numerals

[0165] 1 Electric power steering

[0166] 2 Steering wheel

[0167] 3 Steering axle

[0168] 4 Steering column

[0169] 5a, 5b universal joint

[0170] 6 Intermediate shaft

[0171] 7 Steering gear unit

[0172] 8 Electric assist device

[0173] 9 Pinion shaft

[0174] 10 Tie rod

[0175] 11 Worm gear

[0176] 12-axis components (worm gear)

[0177] 12a, 12b intermediate shaft components

[0178] 13 Coupling

[0179] 14 Electric Motor

[0180] 15 Housing

[0181] 16 Worm gear housing

[0182] 17 Worm housing

[0183] 18 Cover

[0184] 19 teeth

[0185] 20 Core

[0186] 21 Gear

[0187] 22 Worm teeth

[0188] 23 Output shaft

[0189] 24 Motor side connector parts

[0190] 25 Joint parts (Joint parts on the worm side)

[0191] 26 Intermediate joint parts

[0192] 27 barrel

[0193] 28 Flange

[0194] 29 teeth

[0195] 30 Center hole

[0196] 31 barrel

[0197] 32 Flange

[0198] 33 teeth

[0199] 34 Sawtooth

[0200] 35 Chamfer

[0201] 36 End face

[0202] 37 Large diameter part

[0203] 38a, 38b insertion holes

[0204] 39, 39a, 39b joint shaft

[0205] 40 Step surface

[0206] 41 Riveting Department

[0207] 42 Slanted Face

[0208] 43a, 43b center hole

[0209] 44 Fitting shaft

[0210] 45 flange

[0211] 46 Ball bearings

[0212] 47 outer ring

[0213] 48 Inner Circle

[0214] 49 Ball

[0215] 50 cylindrical face

[0216] 51 Step surface

[0217] 52 Retaining ring

[0218] 53 Worm gear damper

[0219] 54 Ball bearings

[0220] 55 Force applying mechanism

[0221] 56 axis unit

[0222] 57 Supporting platform

[0223] 58 Support hole

[0224] 59 Support surface

[0225] 60 Press Punch

[0226] 61 Pressing surface

[0227] 62 Flat Face

[0228] 63 Slanted Face

[0229] 64 Guide hole

[0230] 65, 65a center axis

[0231] 66 Circumferential groove

[0232] 67 O-ring

[0233] 68 Step surface

[0234] 69 cylindrical face

[0235] 70 Guide Facial

[0236] 71 Undercut groove

[0237] 72 Press-in jig

[0238] 73, 73a engagement portion

[0239] 74 Small Trail

[0240] 75 Connection

[0241] 76 cylindrical part

[0242] 77 Opening periphery

[0243] 78 Opening periphery

Claims

1. A shaft unit, characterized in that: have: A shaft component, wherein the shaft component has a coupling shaft portion at an end portion on one axial side, and the shaft component has a center hole opened at a radial center portion of an end surface on one axial side of the coupling shaft portion; and A joint component, wherein the joint component has a center hole extending axially inwardly in the radial direction, and the coupling shaft portion is embedded in the center hole. The coupling shaft portion has a caulking portion formed by plastically deforming only the radially outer portion of the end edge portion on one axial side protruding from the center hole, The caulking portion is in surface contact with an opening peripheral edge portion of the joint member on one axial side of the center hole.

2. The shaft unit according to claim 1, characterized in that At least a radially outer portion of a side surface on one axial side of the caulking portion is formed of an inclined surface portion that is inclined in a direction toward the other axial side as it goes toward the radially outer side.

3. The shaft unit according to claim 1, characterized in that The opening peripheral edge portion of the joint member is composed of a chamfered portion that is inclined in a direction that is directed radially outward as it is directed toward one side in the axial direction.

4. The shaft unit according to any one of claims 1 to 3, characterized in that The shaft member is formed by a worm.

5. An electric assist device, characterized in that: have: worm gear; a worm, the worm being meshed with the worm wheel; A coupling, the coupling comprising a joint component coupled to a coupling shaft portion provided at an end portion on one axial side of the worm; and an electric motor that transmits torque to the worm via the coupling, The shaft unit including the worm and the joint member is constituted by the shaft unit according to claim 4 .

6. A method for manufacturing a shaft unit, characterized in that: The shaft unit comprises: a shaft component, the shaft component having a coupling shaft portion at an end portion on one axial side, and the shaft component having a center hole opened at a radial central portion of an end surface on one axial side of the coupling shaft portion; and a joint component, the joint component having a center hole penetrating in the axial direction on a radial inner side, The manufacturing method of the shaft unit comprises the following steps: When the combining shaft portion is embedded in the center hole of the joint component, the radial outer portion of the end edge portion of the combining shaft portion protruding from the center hole on one axial side is pressed toward the other axial side using the pressing surface of the pressing punch, thereby axially flattening the radial outer portion to form a riveted portion, so that the riveted portion is in surface contact with the opening peripheral edge portion on the axial side of the center hole of the joint component.

7. The method for manufacturing a shaft unit according to claim 6, characterized in that: The method comprises the step of press-fitting the joint member onto the outer peripheral surface of the coupling shaft portion from one axial side. In the shaft unit, The inner peripheral surface of the center hole is composed of a serration portion. The entire outer diameter of the portion of the coupling shaft portion that protrudes from the center hole of the joint member to one side in the axial direction is less than the inner diameter of the serration portion. In the step of press-fitting the joint component, the teeth of the serrations bite into the outer peripheral surface of the coupling shaft portion to complete the press-fitting of the joint component, thereby achieving a state in which the coupling shaft portion is fitted into the center hole of the joint component.

8. The method for manufacturing a shaft unit according to claim 6, characterized in that: In the step of forming the caulking portion, a side surface on one axial side of the caulking portion is pressed toward the other axial side and radially inward by a radially outer portion of the pressing surface.

9. The method for manufacturing a shaft unit according to any one of claims 6 to 8, characterized in that: The shaft member is formed by a worm.

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