Threaded shaft and method for manufacturing the same and electric position adjustment device for a steering wheel and method for manufacturing the same

Abstract

Threaded shaft (21) comprising: a large diameter shaft section (23) and a small diameter shaft section (24); wherein the large diameter shaft portion (23) has an external thread portion (19) over the entire length of its outer peripheral surface; and the small-diameter shaft portion (24) is arranged in an axial direction adjacent to the large-diameter shaft portion (23) and has an outer diameter which is smaller than an outer diameter of the large-diameter shaft portion (23), characterized by the fact that the small-diameter shaft portion (24) has a spiral rolling mark (27) on its outer peripheral surface which is in phase with an extension line of a spiral curve which is a root circle line of the external thread portion (19), and the external thread portion (19) comprises a fully threaded portion having a predetermined thread height and incompletely threaded portions arranged at edge portions at both ends of the external thread portion (19) in the axial direction, which do not reach the predetermined thread height, and the entire external threaded portion (19) functions as a normal threaded portion and only the roll mark corresponds to a non-threaded portion which does not function as the normal threaded portion.

Description

[Technical Area]

[0001] The present invention relates to a threaded shaft of a feed worm mechanism incorporated in various mechanical devices and a manufacturing method thereof, as well as to a threaded shaft mechanism and an electric position adjusting device for a steering wheel having an electric motor and a feed worm mechanism and a manufacturing method thereof. [Technical background]

[0002] Various electric position adjusting devices for a steering wheel are known which are suitable for adjusting the forward and backward position and the height position of a steering wheel by using an electric motor as a drive source (see, for example, JP 2005-199760A, JP 2006-321484A, JP 2015-227166A).

[0003] A feed screw mechanism is widely used as a mechanism for converting the rotary motion of a drive source into linear motion, and is incorporated into various mechanical devices, including devices such as an electric position adjusting device for a steering wheel. A feed screw mechanism includes a threaded shaft with an externally threaded portion on the outer peripheral surface and a nut with an internally threaded portion on the inner peripheral surface.

[0004] Feed worm mechanisms include sliding-thread type feed worm mechanisms and ball-screw type feed worm mechanisms. In a sliding-thread type feed worm mechanism, the male thread portion of the threaded shaft and the female thread portion of the nut are engaged with each other. In a ball-screw type feed worm mechanism, the male thread portion of the threaded shaft forms an external thread groove, the female thread portion of the nut forms an internal thread groove, and a plurality of balls are arranged between the external thread groove and the internal thread groove.

[0005] In each of these screw-feed mechanisms, the external thread portion of the threaded shaft can be formed by rolling. In the process of rolling the external thread portion, the workpiece, which is an intermediate blank of the threaded shaft, is rolled between multiple thread rolling dies, and the outer peripheral surface of the workpiece is plastically deformed by these thread rolling dies to form the external thread portion.

[0006] Regarding the process of rolling the external thread portion, there exists a method in which running occurs, which is a phenomenon in which the workpiece moves in the axial direction with respect to the thread rolling forms (see, for example, JP 2003-033841A, JP 2008-281142A).

[0007] Document WO 2019 / 176334 A1 further describes a method for manufacturing a steering shaft of a steering device. The method includes a step of forming a diameter-reducing part for forming a second state element by forming a diameter-reducing part in a first state element. Furthermore, the method includes a step of forming a ball screw groove for forming a third state element by forming a ball screw groove in the second state element by rolling. [List of citations][Patent literature] [Patent Literature 1] JP 2005-199760A [Patent Literature 2] JP 2006-321484A [Patent Literature 3] JP 2015-227166A [Patent Literature 4] JP 2003-033841A [Patent Literature 5] JP 2008-281142A [Summary of the invention][Technical problem]

[0008] In the process of rolling the external thread portion according to the method described in JP 2003-033841A, JP 2008-281142A and the like, in which running occurs, there is room for improvement in the machining accuracy of the external thread portion. This will be described below with reference to Fig. 10 described.

[0009] Fig. Fig. 10 shows a part of a step of forming the external thread portion 3 on the outer peripheral surface of the large-diameter portion of the workpiece 1 by means of this type of rolling process. Note that the number of thread rolling dies 2 used at this time is two or more (plural); in Fig. However, only one of them is shown in Figure 10. More precisely, as in the Fig. 10A and Fig. 10B, when rolling the workpiece 1 between the plurality of thread rolling dies 2, running, which is a movement of the workpiece 1 in the axial direction, is allowed to occur, and the external thread portion 3 is formed by plastically deforming the outer peripheral surface of the large-diameter portion of the workpiece 1 by means of a plurality of thread rolling dies 2. Fig. 10B shows a state in which, in order to form the external thread portion 3, up to the edge of the end portion of the large-diameter portion of the workpiece 1 on one side in the axial direction (according to the Fig. 10A to 10C of the right side) allows the workpiece 1 to run to a position where the end portion on one side of the thread rolling dies 2 deviates in the axial direction from the outer peripheral surface of the large diameter portion of the workpiece 1.

[0010] If the positional relationship between the workpiece 1 and the thread rolling dies 2 changes, as shown in the Fig. 10A and Fig. 10B, the rolling load, which is in the Fig. 10A, between the end portion of the thread rolling die 2 on one side in the axial direction and the large diameter portion in which Fig. 10B, causing a large change in the distribution of the rolling load acting between the thread rolling die 2 and the workpiece 1. As shown in Fig. 10C, due to the change in the degree of elastic deformation of the rolling machine that holds the thread rolling dies 2 and the workpiece 1, there is a tendency for a relative displacement such as an inclination or the like to occur between the thread rolling dies 2 and the workpiece 1 by an amount corresponding to this change. This lowers the machining accuracy at the end portion on one side in the axial direction of the external thread portion 3 formed on the large-diameter portion of the workpiece 1. Such a problem similarly occurs at the Fig. 10A to 10C not shown) on the other side of the external thread portion 3 in the axial direction.

[0011] When the machining accuracy decreases in this way, it becomes difficult to make both end portions of the external thread portion 3 in the axial direction function as a normal external thread portion, and there occurs a problem that the working stroke of the feed screw mechanism is shortened accordingly.

[0012] It is an object of the present invention to provide an electric position adjusting device for a steering wheel, which comprises a threaded shaft having good machining accuracy at both end portions of the external thread portion in the axial direction, an electric motor, and a feed screw mechanism, wherein the working stroke of the feed screw mechanism is sufficiently maintained. [Solution to the problem]

[0013] The claimed invention is defined by the subject matter of the independent claims. Further embodiments form the subject matter of the dependent claims.

[0014] The threaded shaft according to the present invention comprises a large diameter shaft portion and a small diameter shaft portion.

[0015] The large diameter shaft section has an external thread section along the entire length of its outer peripheral surface.

[0016] The small-diameter shaft portion is arranged adjacent to the large-diameter shaft portion in an axial direction, has an outer diameter smaller than an outer diameter of the large-diameter shaft portion, and has a spiral roll mark on its outer peripheral surface in phase with an extension line of a spiral curve that is a root circle line of the external thread portion.

[0017] Preferably, in the threaded shaft according to the present invention, the outer diameter of the small diameter shaft portion is not smaller than 0.9 times and not larger than 1.1 times the root circle diameter of the external thread portion.

[0018] The threaded shaft according to the present invention may include an adjacent shaft portion disposed adjacent to the small diameter shaft portion on a side opposite to the large diameter shaft portion in the axial direction and having a larger outer diameter than the outer diameter of the small diameter shaft portion.

[0019] In the threaded shaft according to the present invention, the small-diameter shaft portion may include a first small-diameter shaft portion disposed on one side of the large-diameter shaft portion in the axial direction; and a second small-diameter shaft portion disposed on the other side of the large-diameter shaft portion in the axial direction.More specifically, in this case, the first small-diameter shaft portion is disposed adjacent to one side of the large-diameter shaft portion in the axial direction, has an outer diameter smaller than the outer diameter of the large-diameter shaft portion, and has a spiral first rolling mark on its outer peripheral surface in phase with an extension line of a spiral curve that is the root circle of the external thread portion; and the second small-diameter shaft portion is disposed adjacent to the other side of the large-diameter shaft portion in the axial direction, has an outer diameter smaller than the outer diameter of the large-diameter shaft portion, and has a spiral second rolling mark on its outer peripheral surface in phase with an extension line of the spiral curve.

[0020] Preferably, in the threaded shaft according to the present invention, both the outer diameter of the first small diameter shaft portion and the outer diameter of the second small diameter shaft portion are not less than 0.9 times and not more than 1.1 times the root circle diameter of the external thread portion.

[0021] The threaded shaft according to the present invention can be incorporated into an electric position adjusting device for a steering wheel.

[0022] A method for manufacturing the threaded shaft according to the present invention includes a step of performing a rolling process on a workpiece having a large-diameter rolling shaft portion and a small-diameter rolling shaft portion disposed adjacent to the large-diameter rolling shaft portion in an axial direction and having an outer diameter smaller than an outer diameter of the large-diameter rolling shaft portion; wherein, in the rolling process, the workpiece is caused to run in the axial direction by using a plurality of thread rolling dies to form an externally threaded portion over an entire length of an outer peripheral surface of the large-diameter rolling shaft portion.

[0023] More specifically, in the method for manufacturing the threaded shaft according to the present invention, in the step of performing the rolling process on the workpiece using the thread rolling dies, a spiral roll mark is formed on an outer peripheral surface of the small diameter shaft portion for rolling, while simultaneously performing the rolling process for forming the external thread portion on the outer peripheral surface of the large diameter shaft portion for rolling.

[0024] Preferably, in the method for manufacturing the threaded shaft according to the present invention, an outer diameter of the small diameter shaft portion for rolling is not less than 0.9 times and not more than 1.1 times a root circle diameter of the external thread portion to be formed on the outer peripheral surface of the large diameter shaft portion for rolling.

[0025] In the method for manufacturing the threaded shaft according to the present invention, the workpiece may have an adjacent shaft portion disposed adjacent to the small diameter shaft portion for rolling on the side opposite to the large diameter shaft portion for rolling in the axial direction and having a larger outer diameter than the outer diameter of the small diameter shaft portion for rolling.

[0026] In the method for manufacturing the threaded shaft according to the present invention, the workpiece may be configured such that its second small-diameter rolling shaft portion includes a first small-diameter rolling shaft portion disposed on one side of the large-diameter rolling shaft portion in the axial direction, and a second small-diameter rolling shaft portion disposed on the other side of the large-diameter rolling shaft portion in the axial direction.In this case, in the step of performing the rolling process on the workpiece using the thread rolling forms while simultaneously performing the rolling process for forming the external thread portion on the outer peripheral surface of the large-diameter shaft portion for rolling, a spiral first roll mark is formed on the outer peripheral surface of the first small-diameter shaft portion for rolling, and a spiral second roll mark is formed on the outer peripheral surface of the second small-diameter shaft portion for rolling. Preferably, both an outer diameter of the first small-diameter shaft portion and an outer diameter of the second small-diameter shaft portion are not less than 0.9 times and not more than 1.1 times the root diameter of the external thread portion.

[0027] In the method for manufacturing the threaded shaft according to the present invention, a threaded shaft incorporated in an electric position adjusting device for a steering wheel can be used as the threaded shaft to be manufactured.

[0028] The electric position adjusting device for a steering wheel according to the present invention comprises an electric motor, a feed screw mechanism and a steering component.

[0029] The feed screw mechanism includes a threaded shaft having an external thread portion on its outer peripheral surface, and a nut having an internal thread portion on an inner peripheral surface that engages with the external thread portion; and is configured so that the threaded shaft and the nut can be moved with respect to each other in an axial direction in accordance with relative rotation of the threaded shaft and the nut due to rotational force transmitted from the electric motor.

[0030] It is possible to use either a sliding screw-type feed worm mechanism or a ball screw-type feed worm mechanism as the feed worm mechanism. In the sliding screw-type feed worm mechanism, the male thread portion and the female thread portion are directly engaged or meshed with each other. In the ball screw-type feed worm mechanism, the male thread portion and the female thread portion are engaged with each other via multiple balls.

[0031] The steering component is provided such that, in a state where it is used, a steering wheel is attached thereto, and the steering component can be displaced in a position adjusting direction of the steering wheel upon displacement of the threaded shaft and the nut with respect to each other in the axial direction.

[0032] In the electric position adjusting device for a steering wheel according to the present invention, the threaded shaft is formed by the threaded shaft according to the present invention.

[0033] In the electric position adjusting device for a steering wheel according to the present invention, in a state where the steering wheel is shifted to an end portion of a position adjusting range, a part of the internally threaded portion in the axial direction may be arranged at a position in the axial direction shifted from the externally threaded portion.

[0034] In a method for manufacturing an electric adjustment device for a steering wheel according to the present invention, the electric position adjustment device for a steering wheel comprises an electric motor, a feed worm mechanism, and a steering component; wherein the feed worm mechanism comprises a threaded shaft having an externally threaded portion on its outer peripheral surface and a nut having an internally threaded portion on an inner peripheral surface that engages with the externally threaded portion; and is configured such that the threaded shaft and the nut can be moved with respect to each other in an axial direction in accordance with relative rotation of the threaded shaft and the nut due to rotational force transmitted from the electric motor; and the method includes a step of manufacturing the threaded shaft by performing a rolling process on a workpiece having: a large-diameter rolling shaft portion; a first small-diameter rolling shaft portion disposed on one side of the large-diameter rolling shaft portion in the axial direction and having an outer diameter smaller than the outer diameter of the large-diameter rolling shaft portion; and a second small-diameter rolling shaft portion disposed on the other side of the large-diameter rolling shaft portion in the axial direction and having an outer diameter smaller than the outer diameter of the large-diameter rolling shaft portion;wherein the rolling process using a plurality of thread rolling dies to form the external thread portion over an entire length of an outer peripheral surface of the large diameter shaft portion for rolling causes the workpiece to run in the axial direction;

[0035] In particular, in the method for manufacturing an electric adjusting device for a steering wheel according to the present invention, the method for manufacturing a threaded shaft according to the present invention is applied to the process of manufacturing the threaded shaft. [Advantageous results of the invention]

[0036] The present invention provides an electric position adjusting device for a steering wheel, the electric position adjusting device for a steering wheel comprising a threaded shaft having good machining accuracy at both end portions of an externally threaded portion in the axial direction, an electric motor, and a feed screw mechanism, wherein the working stroke of the feed screw mechanism is sufficiently maintained. [Brief description of the drawings] Fig. 1 is a partial sectional view illustrating an electric position adjusting device for a steering wheel according to an example of an embodiment of the present invention. Fig. 2A is a view that Fig. 1 and shows a state in which the steering wheel is arranged forward and backward at the rear end portion of the position adjusting range, and Fig. 2B is a view that Fig. 1 and shows a state in which the steering wheel is arranged at the front end portion of the position adjusting range forward and backward. Fig. 3 is a side view of a threaded shaft according to an example embodiment of the present invention. Fig. 4 is a side view of a workpiece which is an intermediate blank of a threaded shaft according to an example embodiment of the present invention. Fig. 5 is a diagram of an example of an embodiment of the present invention, showing a state in which a workpiece is placed in a rolling machine. Fig. 6 is a diagram of an example of an embodiment of the present invention, showing a state in which the distance between the two thread rolling dies rotating in the forward rotation direction is reduced, and the thread rolling dies are pressed against the large-diameter shaft portion of the workpiece to be rolled to initiate the rolling process. Fig. 7A is a diagram of an example of an embodiment of the present invention, showing a state in an intermediate stage of the rolling process in which the workpiece has run to the end on one side in the axial direction upon rotation of the thread rolling dies in the forward rotation direction; and Fig. 7B is a diagram showing a state in which the workpiece has passed to the end on the other side in the axial direction when the thread rolling dies rotate in the reverse rotation direction. Fig. 8A is a diagram of an example of an embodiment of the present invention, showing a state in the final stage of the rolling process in which the workpiece runs to the end on one side when the thread rolling dies are rotated in the forward rotation direction in the axial direction, and the roll marks are formed on the outer peripheral surface of the small-diameter shaft portion to be rolled on the other side of the workpiece in the axial direction; and Fig. 8B is a diagram illustrating a state in the final stage of the rolling process in which the workpiece travels to the end on the other side in the axial direction when the thread rolling dies rotate in the reverse rotation direction, and the rolling marks are generated on the outer peripheral surface of the small-diameter shaft portion to be rolled on the one side in the axial direction of the workpiece. Fig. 9 is an enlarged view of part A in Fig. 8A. The Fig. Figures 10A to 10C are diagrams describing problems that occur in a conventional thread rolling process. [Description of the embodiments][Example]

[0037] An example of an embodiment of the present invention will be described with reference to the Fig. 1 to 9 described. (Electric position adjustment device for a steering wheel and threaded shaft)

[0038] Fig. 1 and Fig. 2 show an electric position adjustment device for a steering wheel, in which the threaded shaft 21 ( Fig. 3) is used according to this example. It should be noted that, with regard to the electric position adjusting device for a steering wheel, the front and rear direction refers to the front and rear direction with respect to the vehicle in which the device is mounted, with the front being in the Fig. 1 to 3 is the left side and the back is in the Fig. 1 to 3 is the right side. Furthermore, the electric position adjusting device for a steering wheel according to this example enables adjustment of the position of the steering wheel 12 forward and backward by using an electric motor (not shown) as a drive source. Fig. 1 shows a state in which the steering wheel 12 is arranged in a central portion of the front-and-rear position adjustment range; Fig. 2A shows a state in which the steering wheel 12 is arranged at the rear end portion of the position adjustment range forward and backward; and Fig. 2B shows a state in which the steering wheel 12 is arranged at the front end portion of the position adjustment range forward and backward.

[0039] The electric position adjusting device for a steering wheel according to the present invention may be constituted by a steering column 4, a steering shaft 5, and an electric actuator 6. The electric position adjusting device for a steering wheel according to the present invention includes at least one electric motor (not shown) and a feed screw mechanism 14 constituting the electric actuator 6, and an outer tube 10 constituting a steering shaft 5 and corresponding to a steering component.

[0040] The steering column 4 includes a front outer column 7 and a rear inner column 8, which are telescopically assembled. Displacement of the outer column 7 in the axial direction relative to the vehicle body is prevented. The front portion of the inner column 8 is slidably inserted into the inner diameter side of the rear portion of the outer column 7.

[0041] The steering shaft 5 includes an inner shaft 9 on the front side and an outer tube 10 on the rear side. The inner shaft 9 and the outer tube 10 are connected by spline engagement or the like so that torque can be transmitted and they can be extended or contracted. The inner shaft 9 is rotatably supported on the inner diameter side of the outer column 7 via a bearing (not shown). The outer tube 10 is rotatably supported on the inner diameter side of the inner column 8 via a bearing 11. With this type of configuration, the steering shaft 5 is rotatably supported on the inner diameter side of the steering column 4. Together with this, the inner column 8 and the outer tube 10 can be displaced relative to each other in the axial direction with respect to the outer column 7 and the inner shaft 9.The steering wheel 12 is held by and fixed to the rear end portion of the outer tube 10, which is a steering component.

[0042] The electric actuator 6 includes a housing 13, a feed screw mechanism 14, and an electric motor (not shown). The housing 13 is supported by and secured to the underside of the outer column 7.

[0043] The feed screw mechanism 14 comprises a nut 15 and a rod 16. The central axis of the feed screw mechanism 14 is arranged parallel to the central axes of the steering shaft 5 and the steering column 4.

[0044] The nut 15 has an internally threaded portion 17 on its inner peripheral surface. The nut 15 is rotatably held in the housing 13 so that it cannot be displaced in the axial direction and can be rotatably driven by an electric motor via a worm gear 18.

[0045] The rod 16 is formed by connecting a threaded shaft 21 arranged on the front side and an extension shaft 22 arranged on the rear side. The rear end portion of the extension shaft 22 of the rod 16 is connected to the rear portion of the inner column 8 via an arm portion 20.

[0046] The threaded shaft 21 includes a large-diameter shaft portion 23, a first small-diameter shaft portion 24 and a second small-diameter shaft portion 25 corresponding to a small-diameter shaft portion, and a base-end shaft portion 26 corresponding to an adjacent shaft portion.

[0047] The large-diameter shaft portion 23 has an external thread portion 19 on the outer peripheral surface over the entire length in the axial direction, which engages with the internal thread portion 17. The external thread portion 19 is formed by a rolling process. The axially central portion of the external thread portion 19, excluding the edge portions at both ends in the axial direction, is formed by a fully threaded portion having a predetermined thread pitch. Each of the edge portions at both ends of the external thread portion 19 in the axial direction is formed by an incompletely threaded portion that does not reach a predetermined thread pitch.According to this example, the entire external thread portion 19, including not only the fully threaded portion but also the incompletely threaded portion, is precisely finished to function like a normally threaded portion. In other words, the side surface of the external thread portion 19 is precisely finished not only at the axially central portion, which is a fully threaded portion, but also at the edge portions at both ends in the axial direction, which are incompletely threaded portions. Therefore, according to this example, the length of the entire external thread portion 19 in the axial direction corresponds to the effective thread length. Note that the side surface is the side surface of the thread, or in other words, the serrated surface.According to this example, the lead angle θ of the male thread portion 19 is less than 4°. However, in the case of implementing the present invention, the lead angle θ of the male thread portion 19 may be set to 4° or more.

[0048] The first small-diameter shaft portion 24 is disposed adjacent to a side in the axial direction, which is the front side of the large-diameter shaft portion 23. The first small-diameter shaft portion 24 is a columnar portion having a smaller outer diameter than the outer diameter of the large-diameter shaft portion 23 and a spiral first roll mark 27 on the outer peripheral surface. The first roll mark 27 is formed in the rolling process by thread rolling 35 for forming the external thread portion 19. The first roll mark 27 is in phase with the extension line of the spiral curve, which is the root circle line of the external thread portion 19.

[0049] The second small-diameter shaft portion 25 is disposed adjacent to the other side in the axial direction, which is the rear side of the large-diameter shaft portion 23. The second small-diameter shaft portion 25 is a columnar portion having a smaller outer diameter than the outer diameter of the large-diameter shaft portion 23 and a spiral second roll mark 28 on the outer peripheral surface. The second roll mark 28 is formed in the rolling process by thread rolling 35 for forming the external thread portion 19. The second roll mark 28 is in phase with the extension line of the spiral curve, which is the root circle line of the external thread portion 19.

[0050] According to this example, the outer diameter d1 of the first small-diameter shaft portion 24 and the outer diameter d2 of the second small-diameter shaft portion 25 are the same (d1 = d2). However, in the case of implementing the present invention, the outer diameter d1 of the first small-diameter shaft portion 24 and the outer diameter d2 of the second small-diameter shaft portion 25 may be set different from each other.

[0051] According to this example, both the outer diameter d1 of the first small-diameter shaft portion 24 and the outer diameter d2 of the second small-diameter shaft portion 25 are set to not less than 0.9 times and not more than 1.1 times the root diameter D of the external thread portion 19 (within a range of ±10% of the root diameter) (1.1D≧d1≧0.9D, 1.1D≧d2≧0.9D). However, in the case of implementing the present invention, the range of the outer diameters d1 and d2 may be set to a range different from the range according to this example.

[0052] According to this example, the outer diameter d1 of the first small-diameter shaft portion 24 and the outer diameter d2 of the second small-diameter shaft portion 25 are each smaller than the inner diameter of the internal thread portion 17 of the nut 15 (the inscribed diameter of the thread). Therefore, neither the first rolling mark 27 nor the second rolling mark 28 engages with the internal thread portion 17 of the nut 15. In other words, both the first rolling mark 27 and the second rolling mark 28 correspond to a non-threaded portion that does not function as an external thread portion that engages with the internal thread portion 17 of the nut 15.

[0053] The base-end shaft portion 26 is located on the opposite side in the axial direction from the large-diameter shaft portion 23 with respect to the second small-diameter shaft portion 25, or in other words, is arranged adjacent to the other side in the axial direction, which is the rear side of the second small-diameter shaft portion 25. The base-end shaft portion 26 is a stepped columnar portion having an outer diameter larger than the outer diameter of the second small-diameter shaft portion 25 as a whole. The base-end shaft portion 26 has a flange portion 29 projecting outward in the radial direction at a central portion in the axial direction. Furthermore, the portion of the base-end shaft portion 26 located further to the rear than the flange portion 29 is formed by a columnar insert portion 30.

[0054] The extension shaft 22 is a hollow shaft having a circular tubular shape. The insertion portion 30 of the threaded shaft 21 is fitted and fixed inside the front end portion of the extension shaft 22. The rear end surface of the flange portion 29 of the threaded shaft 21 contacts the front end surface of the extension shaft 22, thereby positioning the threaded shaft 21 with respect to the extension shaft 22 in the axial direction.

[0055] When adjusting the forward and backward position of the steering wheel 12, the rod 16 is displaced in the axial direction relative to the nut 15 by rotating the nut 15 by an electric motor via the worm gear 18. When the rod 16 is displaced in the axial direction, the inner column 8 connected to the rod 16 via the arm portion 20 and the outer tube 10 held on the inner diameter side of the inner column 8 are displaced in the same direction (the position adjustment direction of the steering wheel 12) as the rod 16, and the forward and backward position of the steering wheel 12 is adjusted. According to this example, the lead angle θ of the external thread portion 19 is less than 4°, so rotating the nut 15 is difficult even in a case where an axial force acts as a counter-input from the rod 16 to the nut 15.

[0056] According to this example, the entire male thread portion 19 of the screw shaft 21 of the feed screw mechanism 14 is finished with good precision to function like a normal thread portion. Therefore, when adjusting the position of the steering wheel 12, the rod 16 can be displaced back and forth with respect to the nut 15 in the axial direction up to the position where the edge portion of the end of the male thread portion 19 engages with the female thread portion 17 in the axial direction. Furthermore, the rod 16 can be displaced in the axial direction with respect to the nut 15 until a part of the female thread portion 17 in the axial direction reaches a position in the axial direction away from the male thread portion 19.

[0057] According to this example, the steering wheel 12, as shown in Fig. 2A, until the front portion in the axial direction of the female thread portion 17 reaches the edge of the first small-diameter shaft portion 24 (a position covering at least the entire first rolling mark 27). According to this example, the steering wheel 12, as shown in Fig. 2B, until the rear portion in the axial direction of the female thread portion 17 reaches the edge of the second small-diameter shaft portion 25 (a position covering at least the entire second rolling mark 28).

[0058] According to this example, in a case where the external thread portion 19 is set to a fixed length, the working stroke of the feed screw mechanism 14 can be extended, or in other words, the front-and-rear position adjustment range of the steering wheel 12 can be increased, compared to conventional products in which the end portions of the external thread portion in the axial direction cannot function as a normal thread portion. On the other hand, in a case where the working stroke of the feed screw mechanism 14 is set to a certain length, the dimensions of the feed screw mechanism 14 in the axial direction can be made smaller, compared to the conventional product in which the two end portions of the external thread portion in the axial direction cannot function as a normal thread portion.Specifically, according to this example, the rod 16 can be displaced in the axial direction with respect to the nut 15 until a part of the internal thread portion 17 in the axial direction reaches a position in the axial direction remote from the external thread portion 19. To this extent, the result of being able to increase the adjustment range of the position of the steering wheel 12 forward and backward and the result of being able to reduce the dimensions of the feed screw mechanism 14 in the axial direction can be further improved.

[0059] In the case of implementing the present invention, in a state where a configuration is used in which, in a state where the steering wheel is shifted to the end portion of the position adjustment range, a part of the internal thread portion in the axial direction is arranged at a position in the axial direction away from the external thread portion, the length La of the part in the axial direction in this state in the axial direction of the internal thread portion can be set to at most about 70% of the length Lb of the engaging portion of the internal thread portion and the external thread portion in the axial direction (La ≈ 0.7 Lb).

[0060] According to this example, it is possible to move a part of the internal thread portion 17 of the nut 15 in the axial direction to the edge of the first rolling mark 27 and the second rolling mark 28, therefore, the first rolling mark 27 and the second rolling mark 28 can function as a lubricant reservoir for lubricating the feed screw mechanism 14.

[0061] According to this example, the configuration is as in Fig. 2B, the rear surface of an annular contact member 37, which is fixed to the rear end portion of the housing 13 and arranged around the threaded shaft 21, comes into contact with the front surface of the flange portion 29 of the base-end shaft portion 26 when the steering wheel 12 is moved to the front end portion of the position adjustment range. This prevents the steering wheel 12 from moving further to the front. In other words, the flange portion 29 functions as a stopper that defines the front end portion of the position adjustment range of the steering wheel 12. (Manufacturing method for the electric position adjusting device for a steering wheel and manufacturing method for the threaded shaft)

[0062] The manufacturing method for an electric position adjusting device for a steering wheel according to the present invention relates to a method for manufacturing an electric position adjusting device for a steering wheel, which includes an electric motor (not shown), a feed screw mechanism 14, and an outer tube 10, which is a steering component; wherein the feed screw mechanism 14 includes a threaded shaft 21 having an externally threaded portion 19 on the outer peripheral surface, and a nut 15 having an internally threaded portion 17 on the inner peripheral surface that engages with the externally threaded portion 19; and the threaded shaft 21 and the nut 15 are configured to be displaceable with respect to each other in the axial direction according to the relative rotation of the threaded shaft 21 and the nut 15 by the rotational force transmitted from the electric motor;and thereby the outer tube 10 can be moved in the position adjustment direction of the steering wheel 12.;

[0063] The method for manufacturing the electric position adjusting device for a steering wheel according to the present invention includes a step of manufacturing a threaded shaft 21 by performing a rolling process on a workpiece 31 including a large-diameter rolling shaft portion 32 and a first small-diameter rolling shaft portion 33 and a second small-diameter rolling shaft portion 34 arranged adjacent to the large-diameter rolling shaft portion 32 in the axial direction and having an outer diameter smaller than the outer diameter of the large-diameter rolling shaft portion 32, to form an externally threaded portion 19 over the entire length of the outer peripheral surface of the large-diameter rolling shaft portion 32, using a plurality of thread rolling dies 35 and causing running of the workpiece 31.

[0064] The method for manufacturing the threaded shaft 21 according to the present invention will be described with reference to Fig. 4 to 9. In the following description, unless otherwise stated, the axial direction refers to the axial direction of the workpiece 31, which is an intermediate blank of the threaded shaft 21, wherein the one side in the axial direction is in the Fig. 4 to 9 is the left side, and the other side in the axial direction in the Fig. 4 to 9 is the right side.

[0065] Fig. 4 shows the workpiece 31. The workpiece 31 has a different shape than the external thread portion 19, the first roll mark 27 and the second roll mark 28 of the threaded shaft 21 (see Fig. 3). In other words, the workpiece 31 includes a large-diameter rolling shaft portion 32 on which an external thread portion 19 is formed on the outer peripheral surface, a first small-diameter rolling shaft portion 33 on which a first rolling mark 27 is formed on the outer peripheral surface, a second small-diameter rolling shaft portion 34 on which a second rolling mark 28 is formed on the outer peripheral surface, and a base-end shaft portion 26.

[0066] The outer peripheral surface of the large-diameter rolling shaft portion 32 is a cylindrical surface whose outer diameter does not change with respect to the axial direction except for chamfered portions formed at the edge portions at both ends in the axial direction. The first small-diameter rolling shaft portion 33 is arranged adjacent to one side of the large-diameter rolling shaft portion 32 in the axial direction and has an outer diameter smaller than the outer diameter of the large-diameter rolling shaft portion 32. The second small-diameter rolling shaft portion 34 is arranged adjacent to the other side of the large-diameter rolling shaft portion 32 in the axial direction and has an outer diameter smaller than the outer diameter of the large-diameter rolling shaft portion 32.In addition, the outer diameter of the first small diameter shaft portion 33 for rolling is d1 and coincides with the outer diameter of the first small diameter shaft portion 24 (see . Fig. 3), and the outer diameter of the second small diameter rolling shaft portion 34 is d2 and is the same as the outer diameter of the second small diameter rolling shaft portion 25 (see Fig. 3).

[0067] In a case where a rolling process is carried out on the workpiece 31 to produce the threaded shaft 21, the workpiece 31 is first arranged in the rolling machine as shown in Fig. 5. The rolling machine comprises two thread rolling dies 35. Each of the thread rolling dies 35 is a round die having a short cylindrical shape and arranged parallel to the other with the outer peripheral surfaces facing each other. Each of the thread rolling dies 35 has spiral rolling teeth 36 on the outer peripheral surface for rolling the external thread portion 19 (see Fig. 9, where the form in the Fig. 5 to 8 is not shown). Furthermore, according to this example, the dimensions of the thread rolling dies 35 in the axial direction substantially coincide with the dimensions of the large-diameter shaft portion 32 for rolling the workpiece 31 in the axial direction. However, in the case of implementing the present invention, the dimensions of the thread rolling dies 35 in the axial direction may be set larger or smaller than the dimensions of the large-diameter shaft portion 32 for rolling in the axial direction.

[0068] As in Fig. 5, the distance between the outer peripheral surfaces of the two thread rolling dies 35 at the stage where the workpiece 31 is placed in the rolling machine is sufficiently larger than the outer diameter of the large-diameter shaft portion 32 for rolling the workpiece 31. In a state where the workpiece 31 is placed in the rolling machine, the workpiece 31 is arranged parallel to the two thread rolling dies 35 at an intermediate position between the outer peripheral surfaces of the two thread rolling dies 35. Each of the outer peripheral surfaces of the thread rolling dies 35 faces the outer peripheral surface of the large-diameter shaft portion 32 for rolling the workpiece 31. Moreover, the workpiece 31 is held in the axial direction on both sides by a pair of bosses provided on a workpiece holding device (not shown) of the rolling machine.In this state, the workpiece 31 is rotatably held by the workpiece holding device and moved in the axial direction with respect to the two thread rolling dies 35. Even in a case where the workpiece 31 is stretched due to the process of rolling the workpiece 31, the workpiece holding device allows the stretching by increasing the distance between the two bosses.

[0069] In a state where the workpiece 31 is placed in the rolling machine, a holding force in the axial direction is applied to the workpiece 31 by the two hubs. In the case of this example, the portion of the workpiece 31 located further than the large-diameter rolling shaft portion 32 on the other side in the axial direction is constituted by the second small-diameter rolling shaft portion 34 and the base-end shaft portion 26. The outer diameter of the base-end shaft portion 26 is larger than the outer diameter of the second small-diameter rolling shaft portion 34.Therefore, in the case of the workpiece 31 according to this example, the strength of the portion located further than the large-diameter rolling shaft portion 32 on the other side in the axial direction becomes higher compared to a case where the outer diameter of the portion corresponding to the base-end shaft portion 26 matches the outer diameter of the second small-diameter rolling shaft portion 34. Therefore, when a holding force is applied in the axial direction from the two bosses, it is possible to effectively prevent warpage of the portion located further than the large-diameter rolling shaft portion 32 on the other side in the axial direction.

[0070] Next, when the two thread rolling dies 35 are rotated in the same direction, the distance between the two thread rolling dies 35 is reduced. As shown in Fig. 6, valley cutting is initiated, which is a step in which the outer peripheral surface (the rolling teeth 36) of two thread rolling dies 35 are caused to cut into the outer peripheral surface of the large-diameter rolling shaft portion 32 for rolling the workpiece 31. When valley cutting is initiated, a rotating force is applied to the workpiece 31 from the two thread rolling dies 35, and the workpiece 31 rotates in the opposite direction to the two thread rolling dies 35. As a result, the entire circumference of the outer peripheral surface of the large-diameter rolling shaft portion 32 is rolled for rolling the workpiece 31, and the external thread portion 19 is gradually formed.

[0071] In the rolling process according to this example, according to the lead angle error that occurs in the course of valley cutting between the rolling teeth 36 of the two thread rolling dies 35 and the large-diameter shaft portion 32 for rolling the workpiece 31, running occurs, which is a phenomenon in which the workpiece 31 moves in the axial direction with respect to the two thread rolling dies 35.

[0072] According to this example, the two thread rolling dies 35 are rotated alternately in a forward rotation direction, which is the rotation direction at the beginning of valley cutting, and in a reverse rotation direction, which is the opposite direction, by NC control. Therefore, the workpiece 31 undergoes a rolling process, reciprocating in the axial direction between the outer peripheral surfaces of the two thread rolling dies 35. More specifically, in a case where the two thread rolling dies 35 rotate in the forward rotation direction, the workpiece 31 moves to the other side in the axial direction, as shown in Fig. 7A, and in a case where the two thread rolling dies 35 rotate in the reverse direction, the workpiece 31 moves to one side in the axial direction as shown in Fig. 7B. The rolling of the workpiece 31 is performed while the workpiece 31 repeatedly and alternately moves to one side in the axial direction and to the other side in the axial direction.

[0073] According to this example, the configuration is such that the movement of the workpiece 31 to the other side in the axial direction due to the NC control at a position shown in Fig. 7A shown position in the axial direction. The Fig. The position in the axial direction shown in Fig. 7A is a position in the axial direction at which the entry of the entire first small-diameter shaft portion 33 for rolling the workpiece 31 between the outer peripheral surfaces of the two thread rolling dies 35 is completed. Similarly, the movement of the workpiece 31 to the one side in the axial direction is Fig. 7B shown position in the axial direction. The Fig. The position in the axial direction shown in FIG. 7B is a position in the axial direction where the entry of a small-diameter portion of the second shaft portion 34 for rolling the workpiece 31, except for the end portion on the other side in the axial direction, between the outer peripheral surfaces of the two thread rolling dies 35 is completed. Therefore, according to this example, the rolling process is performed without each of the two thread rolling dies 35 colliding with the base-end shaft portion 26 of the workpiece 31.

[0074] According to this example, the valley cutting process, as shown in the Fig. 8A and Fig. 9, by means of a pair of thread rolling dies 35, a rolling process for forming the external thread portion 19 on the outer circumference of the large diameter rolling shaft portion 32 is carried out, while simultaneously forming a spiral first rolling mark 27 on the outer circumferential surface of the small diameter rolling shaft portion 33, and as shown in Fig. 8B, a rolling process for forming the external thread portion 19 is performed by two thread rolling dies 35 on the outer peripheral surface of the large-diameter rolling shaft portion 32, and simultaneously, a spiral second rolling mark 28 is formed on the outer peripheral surface of the small-diameter rolling shaft portion 34. According to this example, the first rolling mark 27 and the second rolling mark 28 are formed in this way; therefore, both the first rolling mark 27 and the second rolling mark 28 are spiral marks with the same phase as the extension line of the spiral curve, which is the root circle line of the external thread portion 19.

[0075] When the outer diameter d1 of the first small-diameter rolling shaft portion 33 and the outer diameter d2 of the second small-diameter rolling shaft portion 34 are equal to or larger than the root diameter D of the external thread portion 19, each of the first rolling mark 27 and the second rolling mark 28 is a spiral mark generated in association with the external thread portion 19. On the other hand, when the outer diameter d1 of the first small-diameter rolling shaft portion 33 and the outer diameter d2 of the second small-diameter rolling shaft portion 34 are smaller than the root diameter D of the external thread portion 19 to some extent, each of the first rolling mark 27 and the second rolling mark 28 and the external thread portion 19 may be non-continuous.

[0076] After completion of the valley cutting process, the distance between the two thread rolling dies 35 is increased and the finished threaded shaft 21 is removed from the rolling machine.

[0077] By the manufacturing method for the threaded shaft 21 according to this example, the side surface of the externally threaded portion 19 can be precisely finished not only at the central portion in the axial direction, which is a fully threaded portion, but also at the edge portions at both ends in the axial direction, which are incompletely threaded portions.

[0078] According to this example, after the valley cutting process has started, as shown in the Fig. 7A and Fig. 7B, in a state where the outer peripheral surfaces of the two thread rolling dies 35 are in contact only with the outer peripheral surface of the large-diameter shaft portion 32 for rolling the workpiece 31, a rolling process for forming the external thread portion 19 is carried out. At this time, as shown in Fig. 7A, in a case where the end portion on the one side in the axial direction of the outer peripheral surface of the two thread rolling dies 35 deviates from the outer peripheral surface of the large diameter shaft portion 32 for rolling due to running in the axial direction caused to the workpiece 31; or as shown in Fig. 7B, in a case where the end portion on the other side in the axial direction of the outer peripheral surface of the two thread rolling dies 35 deviates from the outer peripheral surface of the large-diameter shaft portion 32 for rolling due to axial running caused by the workpiece 31, a large change occurs in the distribution of the rolling load acting between the two thread rolling dies 35 and the workpiece 31. The amount of elastic deformation of the rolling machine that holds the two thread rolling dies 35 and the workpiece 31 changes by the amount corresponding to this change, and therefore, relative displacement such as inclination or the like tends to occur between the two thread rolling dies 35 and the workpiece 31. As a result, the machining accuracy of the two end portions of the external thread portion 19 in the axial direction during machining becomes low.

[0079] However, in the final stage of the valley cutting process, as shown in the Fig. 8A and Fig. 8B, the outer peripheral surfaces of the two thread rolling dies 35 not only contact the outer peripheral surface of the large-diameter rolling shaft portion 32, but also contact the outer peripheral surface of the first small-diameter rolling shaft portion 33 and the second small-diameter rolling shaft portion 34. At this time, the end portion on one side in the axial direction of the outer peripheral surface of the two thread rolling dies 35, as shown in Fig. 8A, in a case where the end portion on one side of the outer peripheral surface of the two thread rolling dies 35 in the axial direction deviates from the outer peripheral surface of the large-diameter rolling shaft portion 32 due to axial running occurring in the workpiece 31, the end portion contacts and is held by the first small-diameter rolling shaft portion 33; therefore, it is possible to prevent a large change in the distribution of the rolling load acting between the two thread rolling dies 35 and the workpiece 31. At this time, the end portion on the other side of the outer peripheral surface of the two thread rolling dies 35 in the axial direction, as shown in Fig. 8B, in a case where the end portion on the other side in the axial direction of the outer peripheral surface of the two thread rolling dies 35 deviates from the outer peripheral surface of the large-diameter rolling shaft portion 32 due to axial running occurring in the workpiece 31, the end portion contacts and is held by the second small-diameter rolling shaft portion 34, therefore, it is possible to prevent a large change in the distribution of the rolling load acting between the two thread rolling dies 35 and the workpiece 31. Therefore, it is possible to suppress the change in the amount of elastic deformation of the rolling machine that holds the two thread rolling dies 35 and the workpiece 31 in the final stage of the valley cutting process. Therefore, it is possible to make it difficult for displacement such as inclination or the like to occur between the two thread rolling dies 35 and the workpiece 31.

[0080] According to this example, the external thread section 19 is a so-called triangular thread of a metric coarse worm; and the contact area between the two thread rolling dies 35 and the workpiece 31 increases, as shown in the Fig. 8 and Fig. 9, in the final stage of the valley cutting process, by increasing the valley cutting size to the extent that the material of the workpiece 31 (the top surface of the external thread portion 19) comes into contact with the root portion of the rolling teeth 36 of the two thread rolling dies 35. Therefore, it also becomes possible to make it difficult for a relative displacement such as inclination or the like to occur in the final stage of the valley cutting process. This can improve the machining accuracy of both end portions of the external thread portion 19 in the axial direction in the final stage of the valley cutting process. In other words, the side surface of the external thread portion 19 is precisely finished not only at the central portion in the axial direction, which is a fully threaded portion, but also at the edge portions at both ends in the axial direction, which are incompletely threaded portions.

[0081] In the case of implementing the present invention, it is also possible to employ a double rolling (double rotation rolling) method, which is a method of performing rolling on the workpiece 31 in two steps. In this case, it is possible to make it more difficult for a relative displacement such as an inclination or the like to occur in the final stage of the valley cutting process by making the thread of the external thread portion 19 higher in the second rolling process.

[0082] In the case of implementing the present invention, when the outer diameter d1 of the first small-diameter rolling shaft portion 33 and the outer diameter d2 of the second small-diameter rolling shaft portion 34 are kept larger than the root circle diameter D of the external thread portion 19, the resistance force becomes larger when the end portions of the rolling teeth 36 of the thread rolling dies 35 in the axial direction from the large-diameter rolling shaft portion 32 abut on the first small-diameter rolling shaft portion 33 or the second small-diameter rolling shaft portion 34 because these outer diameters d1 and d2 become larger in the final stage of the valley cutting process.

[0083] In other words, a chamfered portion (not shown) such as a C-chamfered portion, an R-chamfered portion, or the like is provided at the edge portion of the end of the rolling teeth 36 in the axial direction. When the end portion of the rolling teeth 36 in the axial direction from the large-diameter rolling shaft portion 32 abuts against the first small-diameter rolling shaft portion 33 or the second small-diameter rolling shaft portion 34, the chamfered portion presses the material of the first small-diameter rolling shaft portion 33 or the second small-diameter rolling shaft portion 34 in the axial direction, respectively. However, the chamfered portion has no teeth (cutting edges), so the resistance force against pressing the material in the axial direction is large.Furthermore, as the outer diameters d1 and d2 increase, the degree to which the chamfered portion presses the material in the axial direction increases. Therefore, the resisting force becomes larger as the outer diameters d1 and d2 increase. If the resisting force becomes excessive, excessive stretching or twisting of the workpiece 31 occurs, which adversely affects the machining accuracy of the external thread portion 19.

[0084] In order to prevent such a problem from occurring, according to this example, in a case where the outer diameter d1 of the first small-diameter shaft portion 33 for rolling and the outer diameter d2 of the second small-diameter shaft portion 34 for rolling are made larger than the root diameter D of the external thread portion 19, these outer diameters d1 and d2 are set to 1.1 times or less of the root diameter D (+10% or less of the root diameter D) of the external thread portion 19 (1.1D ≥ d1 > D, 1.1D ≥ d2 > D).

[0085] On the other hand, in a case where the outer diameter d1 of the first small diameter shaft portion 33 for rolling and the outer diameter d2 of the second small diameter shaft portion 34 for rolling are kept smaller than the root circle diameter D of the external thread portion 19, a relative displacement such as an inclination or the like caused between the two thread rolling dies 35 and the workpiece 31 can be reduced in the Fig. 8A and Fig. 8B cannot be sufficiently prevented if these diameters d1, d2 are too small.

[0086] In order to prevent such a problem from occurring, according to this example, in a case where the outer diameter d1 of the first small-diameter shaft portion 33 for rolling and the outer diameter d2 of the second small-diameter shaft portion 34 for rolling are made smaller than the root diameter D of the external thread portion 19, these outer diameters d1 and d2 are set to 0.9 times or more of the root diameter D (-10% or more of the root diameter D) of the external thread portion 19 (D > d1) ≥ 0.9D, D > d2 ≥ 0.9D).

[0087] In the case of implementing the present invention, there are no particular restrictions on the number of threads of the external thread portion 19 of the threaded shaft 21 to be manufactured. In addition to a single-start thread as shown in the figures, the external thread portion 19 may, for example, be a double-start thread. When the external thread portion 19 is formed by a double-start thread, the load balance during rolling is improved compared to a case where the external thread portion 19 is a single-start thread.

[0088] In the case of implementing the present invention, the area for forming the first roll mark 27 and the second roll mark 28 in the axial direction, the lengths of the first roll marks 27 and the second roll marks 28 in the circumferential direction, and the like can be set to arbitrary values. The length of the area for forming the first roll mark 27 and the second roll mark 28 in the axial direction can be, for example, approximately 0.02 to 2.5 times (for example, approximately 1.0 to 1.5 times) the pitch of the external thread portion 19.

[0089] According to this example, in order to prevent interference between the thread rolling dies 35 and the base-end shaft portion 26 during the rolling process, a small-diameter portion of the second shaft portion 25 is provided at which the second roll mark 28 is not formed at the end portion on the other side in the axial direction. However, in the case of implementing the present invention, the entire portion located on the other side in the axial direction with respect to the portion on which the second roll mark 28 is formed may be the base-end shaft portion 26.

[0090] In the case of implementing the present invention, as a modified example of an embodiment, a method may be employed in which, from the beginning to the end of the valley cutting process, the rotation direction of the two thread rolling dies is maintained in a certain direction without reversing the rotation direction. In this case, the valley cutting process may be performed, for example, from the Fig. 8B shown position in the axial direction and at the position shown in Fig. 8A shown position in the axial direction.

[0091] For example, as long as the method for rolling the threaded shaft according to the present invention is a rolling method in which running of the workpiece occurs during the rolling process, it is possible to employ methods such as a continuous rolling method described in JP 2003-033841A, a flat die rolling method, or the like.

[0092] In the continuous rolling method, two thread rolling dies (round dies) are used to cause the workpiece to roll, for example, with their center axes inclined relative to each other. The workpiece is conveyed between the two thread rolling dies while the thread rolling dies rotate in the same direction in the axial direction, while the distance between the two thread rolling dies is kept constant. A rolling process is performed on the workpiece, with the workpiece being passed between the two thread rolling dies by running between them in the axial direction.According to the present invention, in this process, a pair of thread rolling dies are used to perform a rolling process for forming an externally threaded portion on the outer peripheral surface of a large-diameter rolling shaft portion, while simultaneously forming a spiral first roll mark on the outer peripheral surface of a first small-diameter rolling shaft portion; and the pair of thread rolling dies are used to perform a rolling process for forming the externally threaded portion on the outer peripheral surface of the large-diameter rolling shaft portion, while simultaneously forming a spiral second roll mark on the outer peripheral surface of a second small-diameter rolling shaft portion.

[0093] In the through-rolling method, the workpiece is passed between two thread rolling dies in the axial direction, therefore, it is preferable to use a workpiece which does not have a portion having a larger outer diameter than that of the first small-diameter rolling shaft portion on one side in the axial direction further than the first small-diameter rolling shaft portion, and which does not have a portion having a larger outer diameter than that of the second small-diameter rolling shaft portion on the other side in the axial direction further than the second small-diameter rolling shaft portion.However, as in the case of the workpiece 31 according to an example of an embodiment of the present invention, for example, even if the base-end side shaft portion 26 having a larger outer diameter than the second small-diameter shaft portion 34 for rolling is provided further than the second small-diameter shaft portion 34 for rolling on the other side in the axial direction, in a case where the dimensions L of the second small-diameter shaft portion 34 for rolling in the axial direction are sufficiently larger than the dimensions of each of the two thread rolling dies in the axial direction, by inserting the workpiece 31 between the two thread rolling dies from one side in the axial direction, it is possible to form the external thread portion while avoiding mutual interference by the two thread rolling dies and the base-end side shaft portion 26 by pass-through rolling.

[0094] For example, the flat die rolling method uses a pair of thread rolling dies, each having a flat plate shape. The side surfaces of the two thread rolling dies face each other, and the side surfaces have rolling teeth. The workpiece is inserted between the side surfaces, and the two thread rolling dies are moved relative to each other in directions parallel to the facing side surfaces. By rolling the workpiece between the side surfaces, a rolling process is performed on the workpiece, causing the workpiece to run.According to the present invention, in this process, a pair of thread rolling dies are used to perform a rolling process for forming an externally threaded portion on the outer peripheral surface of a large-diameter rolling shaft portion, while simultaneously forming a spiral first roll mark on the outer peripheral surface of a first small-diameter rolling shaft portion; and the two thread rolling dies are used to perform a rolling process for forming the externally threaded portion on the outer peripheral surface of the large-diameter rolling shaft portion, while simultaneously forming a spiral second roll mark on the outer peripheral surface of a second small-diameter rolling shaft portion.

[0095] In a case where rolling is carried out using the flat die rolling method on the workpiece 1 according to an example of an embodiment of the present invention, the rolling process can be carried out, for example, from the Fig. 8B shown positional relationship between the workpiece 31 and the two thread rolling dies, and the rolling process can be initiated in the Fig. 8A shown positional relationship between the workpiece 31 and the two thread rolling dies can be terminated.

[0096] In a case of implementing the method for manufacturing a threaded shaft according to the present invention, the number of thread rolling dies used for rolling may also be three or more.

[0097] The present invention can be applied not only to a screw shaft of a slide screw type feed screw mechanism, but also to a screw shaft of a ball screw type feed screw mechanism. In this case, the external thread portion of the screw shaft becomes an external thread groove. Note that in a case where the present invention is applied to a screw shaft of a ball screw type feed screw mechanism, neither the first rolling mark nor the second rolling mark of the screw shaft is used as the external thread portion for multi-ball meshing.

[0098] The electric position adjusting device for a steering wheel according to the present invention can be applied to various conventionally known devices (devices by which at least one of the front and rear position of the steering wheel and the up and down position can be adjusted) having a different structure, such as those described in JP 2005-199760A, JP 2006-321484A, JP 2015-227166A, and the like.

[0099] The feed screw mechanism provided with the threaded shaft according to the present invention is not limited to being incorporated into an electric position adjusting device for a steering wheel, but can also be incorporated into various mechanical devices such as the steering wheel of an automobile, the electric bearing device of a headlight, a table moving device of a machine tool, and the like. [List of reference symbols] 1 workpiece 2 thread rolling die 3 external thread section 4 Steering column 5 Steering shaft 6 electric actuator 7 outer column 8 inner column 9 inner shaft 10 outer tube 11 camps 12 Steering wheel 13 housings 14 Feed screw mechanism 15 Mother 16 bars 17 Internal thread section 18 worm gears 19 Internal thread section 20 arm section 21 Threaded shaft 22 Extension shaft 23 Large diameter shaft section 24 first shaft section with small diameter 25 second shaft section with small diameter 26 base end shaft section 27 first rolling mark 28 second roll mark 29 Flange section 30 insertion section 31 Workpiece 32 large diameter shaft section 33 first shaft section with small diameter for rolling 34 second shaft section with small diameter for rolling 35 thread rolling die 36 rolling teeth 37 Contact element

Claims

[1] Threaded shaft (21) comprising: a large diameter shaft section (23) and a small diameter shaft section (24); wherein the large diameter shaft portion (23) has an external thread portion (19) over the entire length of its outer peripheral surface; and the small-diameter shaft portion (24) is arranged in an axial direction adjacent to the large-diameter shaft portion (23) and has an outer diameter which is smaller than an outer diameter of the large-diameter shaft portion (23), characterized by the fact that the small-diameter shaft portion (24) has a spiral rolling mark (27) on its outer peripheral surface which is in phase with an extension line of a spiral curve which is a root circle line of the external thread portion (19), and the external thread portion (19) comprises a fully threaded portion having a predetermined thread height and incompletely threaded portions arranged at edge portions at both ends of the external thread portion (19) in the axial direction, which do not reach the predetermined thread height, and the entire external threaded portion (19) functions as a normal threaded portion and only the roll mark corresponds to a non-threaded portion which does not function as the normal threaded portion. [2] The threaded shaft (21) according to claim 1, wherein the outer diameter of the small diameter shaft portion (24) is not smaller than 0.9 times and not larger than 1.1 times the root circle diameter of the external thread portion. [3] Threaded shaft (21) according to one of claims 1 or 2, comprising: an adjacent shaft portion disposed adjacent to the small diameter shaft portion (24) on a side opposite to the large diameter shaft portion (23) in the axial direction and having a larger outer diameter than the outer diameter of the small diameter shaft portion (24). [4] The threaded shaft (21) according to any one of claims 1 to 3, wherein the small-diameter shaft portion (24) comprises: a first small-diameter shaft portion (24) disposed on one side of the large-diameter shaft portion (23) in the axial direction; and a second small-diameter shaft portion (24) disposed on the other side of the large-diameter shaft portion (23) in the axial direction. [5] . A threaded shaft (21) according to claim 4, wherein both an outer diameter of the first small-diameter shaft portion (24) and an outer diameter of the second small-diameter shaft portion (24) are not less than 0.9 times and not more than 1.1 times the root diameter of the externally threaded portion. [6] A threaded shaft (21) according to claim 4 or claim 5, wherein the threaded shaft (21) can be incorporated into an electric position adjusting device for a steering wheel. [7] A method for manufacturing the threaded shaft (21) according to claim 1, comprising: a step of performing a rolling process on a workpiece comprising a large-diameter rolling shaft portion (23) and a small-diameter rolling shaft portion (24) disposed adjacent to the large-diameter rolling shaft portion (23) in an axial direction and having an outer diameter smaller than an outer diameter of the large-diameter rolling shaft portion (23); wherein, in the rolling process, the workpiece is caused to roll by using a plurality of thread rolling dies to form the externally threaded portion (19) over an entire length of an outer peripheral surface of the large-diameter rolling shaft portion (23) in the axial direction; and in the course of performing the rolling process on the workpiece using the thread rolling forms, the spiral rolling mark (27) is produced on an outer peripheral surface of the small diameter shaft portion (24) for rolling, while at the same time the rolling process for producing the external thread portion is carried out on the outer peripheral surface of the large diameter shaft portion (23) for rolling. [8] Method according to claim 7, wherein the external thread portion (19) comprises a fully threaded portion having a predetermined thread height and incompletely threaded portions arranged at edge portions at both ends of the external thread portion in the axial direction, which do not reach the predetermined thread height, and the entire external threaded portion (19) functions as a normal threaded portion and only the roll mark corresponds to a non-threaded portion which does not function as the normal threaded portion. [9] The method according to claim 7 or 8, wherein an outer diameter of the small diameter shaft portion (24) for rolling is not less than 0.9 times and not more than 1.1 times a root circle diameter of an external thread portion to be formed on an outer peripheral surface of the large diameter shaft portion (23) for rolling. [10] The method according to any one of claims 7 to 9, wherein the workpiece comprises an adjacent shaft portion disposed adjacent to the small diameter rolling shaft portion (24) on the side opposite to the large diameter rolling shaft portion (23) in the axial direction and having a larger outer diameter than an outer diameter of the small diameter rolling shaft portion (24). [11] The method according to any one of claims 7 to 10, wherein the workpiece is configured such that its small diameter rolling shaft portion (24) comprises a first small diameter rolling shaft portion (24) disposed on one side of the large diameter rolling shaft portion (23) in the axial direction, and a second small diameter rolling shaft portion (24) disposed on the other side of the large diameter rolling shaft portion (23) in the axial direction. [12] The method according to claim 11, wherein both an outer diameter of the first small diameter shaft portion (24) and an outer diameter of the second small diameter shaft portion (24) are not less than 0.9 times and not more than 1.1 times the root circle diameter of the external thread portion. [13] A method according to claim 11 or claim 12, wherein a threaded shaft (21) to be incorporated into an electric position adjusting device for a steering wheel is used as the threaded shaft (21). [14] Threaded shaft mechanism comprising: a threaded shaft (21) comprising: a large diameter shaft section (23), and a small diameter shaft section (24); wherein the large diameter shaft portion (23) has an external thread portion (19) over the entire length of its outer peripheral surface; and the small-diameter shaft portion (24) is arranged in an axial direction adjacent to the large-diameter shaft portion (23), has an outer diameter smaller than an outer diameter of the large-diameter shaft portion (23), and has a spiral roll mark (27) on its outer peripheral surface that is in phase with an extension line of a spiral curve that is a root circle of the external thread portion, wherein the external thread portion (19) comprises a fully threaded portion having a predetermined thread height and incompletely threaded portions that do not reach the predetermined thread height and are arranged at edge portions at both ends of the external thread portion (19) in the axial direction, and wherein the entire external threaded portion (19) functions as a normal threaded portion and only the rolling mark corresponds to a non-threaded portion which does not function as the normal threaded portion; and a nut having an internal thread portion on an inner peripheral surface engaging with the external thread portion (19), wherein a part of the internal thread portion in the axial direction can be arranged at a position in the axial direction which deviates from the external thread portion (19). [15] A threaded shaft mechanism according to claim 14, wherein the rolling mark does not engage with the internal thread portion of the nut. [16] Electric position adjustment device for a steering wheel, comprising: an electric motor, a feed screw mechanism and a steering component; wherein the feed screw mechanism comprises a threaded shaft (21) having an externally threaded portion (19) on its outer peripheral surface, and a nut having an internally threaded portion on an inner peripheral surface that engages with the externally threaded portion (19); and is configured such that the threaded shaft (21) and the nut can be moved with respect to each other in an axial direction in accordance with relative rotation of the threaded shaft (21) and the nut due to a rotational force transmitted from the electric motor; the steering component is provided such that, in use, a steering wheel is attached thereto and such that the steering component can be displaced in a position adjustment direction of the steering wheel upon displacement of the threaded shaft (21) and the nut with respect to each other in the axial direction; and the threaded shaft (21) is formed by the threaded shaft (21) according to claim 6. [17] The electric position adjusting device for a steering wheel according to claim 16, wherein a part of the internally threaded portion in the axial direction can be arranged at a position in the axial direction shifted from the externally threaded portion (19) in a state in which the steering wheel is shifted to an end portion of a position adjusting range. [18] A method of manufacturing an electric position adjusting device for a steering wheel, the electric position adjusting device for a steering wheel comprising an electric motor, a feed worm mechanism, and a steering component; the feed worm mechanism comprising a threaded shaft (21) having an externally threaded portion (19) on its outer peripheral surface and a nut having an internally threaded portion on an inner peripheral surface that engages with the externally threaded portion (19); and configured so that the threaded shaft (21) and the nut can be moved with respect to each other in an axial direction in accordance with relative rotation of the threaded shaft (21) and the nut due to rotational force transmitted from the electric motor; the method comprises a step of manufacturing the threaded shaft (21) by performing a rolling process on a workpiece, comprising: a large-diameter shaft portion (23) for rolling; a first small-diameter shaft portion (24) for rolling, which is arranged on one side of the large-diameter shaft portion (23) for rolling in the axial direction and has an outer diameter smaller than the outer diameter of the large-diameter shaft portion (23) for rolling; and a second small-diameter shaft portion (24) for rolling, which is arranged on the other side of the large-diameter shaft portion (23) for rolling in the axial direction and has an outer diameter smaller than the outer diameter of the large-diameter shaft portion (23) for rolling;wherein the rolling process using a plurality of thread rolling dies to form an external thread portion over an entire length of an outer peripheral surface of the large-diameter shaft portion (23) causes the workpiece to run for rolling in the axial direction; wherein in the step of manufacturing the threaded shaft (21) the method for manufacturing a threaded shaft (21) described in claim 13 is applied.

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