JPWO2020166525A1 - Linear shaft and its manufacturing method - Google Patents

Abstract

A manufacturing method is realized in which the generation of frictional heat required for friction welding between the axial end portions of the first shaft portion and the second shaft portion is less likely to be hindered. A jig (37, 37a) is formed in a slit (33, 33a) which is an engaging portion formed at an axial end on the opposite side of the friction welding portion between the rack shaft portion (19) and the screw shaft portion (20). ) Is engaged with the rack shaft (19), and the screw shaft (20) and the jig (37, 37a) cannot rotate relative to each other. 20) is rotationally driven, and while the rotation of the rack shaft portion (19) is blocked by the jig (37), the axial ends of the rack shaft portion (19) and the screw shaft portion (20) are friction-welded to each other. ..

Description

The present invention relates to a linear motion shaft that is incorporated in, for example, a steering device for a vehicle and has a linear motion, and a method for manufacturing the same.

A steering device for a vehicle such as an automobile is provided with a linear motion shaft that makes a linear motion that is an axial motion in association with the operation of the steering wheel. The steering angles of the left and right steering wheels change with the linear motion of the linear motion axis.

Such a linear motion shaft has a large axial dimension, and has different shapes on one side portion in the axial direction and the other side portion in the axial direction. Therefore, from the viewpoint of improving the degree of freedom in designing the linear motion shaft and the ease of manufacturing, various methods have been proposed in which the linear motion shaft is divided into two shaft portions for manufacturing.

For example, Japanese Patent Application Laid-Open No. 2005-247163 describes a rack tooth portion on the outer peripheral portion of one side in the axial direction as a linear motion axis of an electric power steering device having a function of reducing a force for a driver to operate a steering wheel. A linear motion shaft having a ball screw portion on the outer peripheral portion of the other side portion in the axial direction is described. The rack tooth portion is an input portion into which the steering force transmitted from the steering wheel is input. Further, the ball screw portion is an input portion into which a steering assist force originating from an electric motor is input. Then, Japanese Patent Application Laid-Open No. 2005-247163 proposes a method of manufacturing such a linear motion shaft by dividing it into two shaft portions. Specifically, after separately manufacturing a rack shaft portion having a rack tooth portion on the outer peripheral portion and a screw shaft portion having a ball screw portion on the outer peripheral portion, the axial end portion of the rack shaft portion and the screw shaft portion A method of friction welding with each other has been proposed.

In the method for manufacturing a linear motion shaft described in Japanese Patent Application Laid-Open No. 2005-247163, in a step of friction welding between the axial end portions of the rack shaft portion and the screw shaft portion, the rack shaft portion and the screw shaft portion are included. By gripping the outer peripheral portion of one shaft portion with one gripping tool and gripping the outer peripheral portion of the other shaft portion of the rack shaft portion and the screw shaft portion with the other gripping tool, the rack shaft portion Centering with the screw shaft. In this state, one shaft is rotationally driven by one grip, and the other grip is holding the other shaft non-rotatingly while friction-welding the axial ends of both shafts. ..

Japanese Unexamined Patent Publication No. 2005-247163

In the conventional method for manufacturing a linear motion shaft described above, when the axial ends of the rack shaft and the screw shaft are friction-welded to each other, between the rack shaft and the screw shaft and the gripper that grips them. When slippage occurs in the rotational direction, the relative rotational speed between the rack shaft and the screw shaft decreases by that amount, and friction welding is performed between the axial ends of the rack shaft and the screw shaft. It may not be possible to generate the frictional heat required to do so.

An object of the present invention is to realize a manufacturing method in which the generation of frictional heat required for friction welding between the axial end portions of the first shaft portion and the second shaft portion is not easily hindered.

The linear motion shaft to be manufactured according to the present invention includes a first shaft portion, a second shaft portion, and a friction welding portion between the axial end portions of the first shaft portion and the second shaft portion.

In the method for manufacturing a linear motion shaft of the present invention, an engagement formed at an axial end portion of a target shaft portion, which is at least one of a first shaft portion and a second shaft portion, on the opposite side of the friction welding portion. By engaging the jig with the portion, the target shaft portion is rotationally driven by the jig in a state where the relative rotation between the target shaft portion and the jig is disabled, or the target shaft portion is rotationally driven by the jig. A step of friction welding the axial end portions of the first shaft portion and the second shaft portion with each other while preventing the rotation of the target shaft portion is provided.

In the method for manufacturing a linear motion shaft of the present invention, the engaging portion is extended in the radial direction of the axial end portion of the target shaft portion on the side opposite to the friction welding portion and on the side opposite to the friction welding portion. It can be an opening slit.

The slits are provided at one or more locations in the circumferential direction of the axial end portion of the target shaft portion on the side opposite to the friction welding portion. In this case, the slits are provided at two locations on the radial opposite side of the target shaft portion at the axial end portion opposite to the friction welding portion, or at four locations at equal intervals in the circumferential direction. be able to.

The axial end of the target shaft portion opposite to the friction welding portion is formed of a tubular portion having a screw hole that opens axially in the radial center portion, and the slit is formed in the tubular portion. The portions can be arranged so as to penetrate in the radial direction.

More specifically, the slit has a U-shaped inner surface shape viewed from the radial direction, is located on both sides in the width direction, and has a pair of inner surface surfaces formed of planes parallel to the axial direction. The jig has a short columnar base portion and an outer surface shape that protrudes from the axial side surface of the base portion and matches the inner surface shape of the slit, and has a width direction formed of a plane parallel to the axial direction of the base portion. It can consist of an engaging protrusion having both sides.

Alternatively, the slit has a wedge-shaped inner surface shape viewed from the radial direction, is located on both sides in the width direction, and is composed of a plane inclined in a direction away from each other toward the axial opening side of the slit. The jig has a pair of inner side surfaces, and the jig has an outer surface shape that protrudes from the axial side surface of the short columnar base portion and matches the inner surface shape of the slit, and approaches each other toward the tip side. It can consist of an engaging ridge having both sides in the width direction, which is a plane inclined in the direction.

Alternatively, the slit has a wedge-shaped axially-viewed inner surface shape, is located on both sides in the width direction, and is a pair of inner surfaces composed of planes that are inclined toward the outer side in the radial direction. Can be provided. In this case, the jig has an outer surface shape that matches the inner surface shape of the slit, has a wedge shape, and is composed of a plane that is inclined in a direction that approaches each other from the outer side in the radial direction to the inner side in the radial direction. It can consist of an engaging piece with both sides in the width direction. Alternatively, the jig has a cylindrical base portion, an outer surface shape that protrudes radially outward from the outer peripheral surface of the cylindrical base portion and matches the inner surface shape of the slit, has a wedge shape, and has a diameter. It can be provided with an engaging portion having both side surfaces in the width direction formed of planes inclined in a direction in which they approach each other from the outside in the direction toward the inside in the radial direction.

The target shaft portion may be provided with a hollow hole penetrating in the axial direction at the central portion in the radial direction.

A spline portion can be provided on the outer peripheral surface of the axial end portion of the target shaft portion on the side opposite to the friction welding portion.

In the method for manufacturing a linear motion shaft of the present invention, the position of the slit in the rotation direction is used to regulate the positional relationship between the first shaft portion and the second shaft portion in the rotation direction at the end of the friction welding. be able to.

In the method for manufacturing a linear motion shaft of the present invention, the jig can be engaged with the engaging portion at the same time as forming the engaging portion by plastic working using the jig as a tool. Alternatively, the engaging portion is formed at the time of casting the target shaft portion or by machining the target shaft portion, and then the jig and the engaging portion are engaged with each other. You can also do it.

In the method for manufacturing a linear motion shaft of the present invention, the linear motion shaft to be manufactured can be used for a steering device.

The linear motion shaft of the present invention includes a first shaft portion, a second shaft portion, and a friction welding portion between the axial end portions of the first shaft portion and the second shaft portion. Further, in the linear motion shaft of the present invention, the jig is rotated relative to the axial end portion of the target shaft portion, which is at least one of the first shaft portion and the second shaft portion, on the opposite side to the friction welding portion. It has an engaging portion that can be engaged in an impossible manner.

In the linear motion shaft of the present invention, the target shaft portion is composed of a screw shaft portion having a ball screw portion on the outer peripheral portion, and the axial end portion of the ball screw portion opposite to the friction welding portion is incomplete. A structure that is a threaded portion and a part of the incompletely threaded portion is cut out by the engaging portion can be adopted. Alternatively, the target shaft portion shall adopt a configuration including a rack shaft portion having rack teeth on the outer peripheral portion, a configuration having a structure other than the ball screw portion and the rack teeth, or a configuration having neither structure. You can also. The target shaft portion can be formed of either a solid or hollow shaft member.

In the linear motion shaft of the present invention, the engaging portion is a slit that extends in the radial direction of the axial end portion of the target shaft portion on the side opposite to the friction welding portion and opens on the opposite side of the friction welding portion. Can be.

The slits can be provided at one or more locations in the circumferential direction of the axial end portion of the target shaft portion on the side opposite to the friction welding portion. In this case, the slits are provided at two locations on the radial opposite side of the target shaft portion at the axial end portion opposite to the friction welding portion, or at four locations at equal intervals in the circumferential direction. be able to.

The axial end of the target shaft portion opposite to the friction welding portion is formed of a tubular portion having a screw hole that opens in the radial direction in the radial center portion, and the slit has the tubular portion in the tubular portion. It can be arranged so as to penetrate in the radial direction.

More specifically, the slit has a U-shaped inner surface shape viewed from the radial direction, is located on both sides in the width direction, and has a pair of inner surface surfaces formed of planes parallel to the axial direction. Can be done. Alternatively, the slit has a wedge-shaped inner surface shape viewed from the radial direction, is located on both sides in the width direction, and is composed of a plane inclined in a direction away from each other toward the axial opening side of the slit. It can have a pair of inner surfaces. Further, the slit has a wedge-shaped inner surface shape viewed from the axial direction, is located on both sides in the width direction, and has a pair of inner surfaces composed of planes inclined in a direction away from each other toward the outer side in the radial direction. be able to.

The target shaft portion may be provided with a hollow hole penetrating in the axial direction at the central portion in the radial direction.

A spline portion may be provided on the outer peripheral surface of the axial end portion of the target shaft portion on the side opposite to the friction welding portion.

In the linear motion shaft of the present invention, the linear motion shaft can be used for a steering device.

According to the present invention, when the axial ends of the first shaft portion and the second shaft portion are friction-welded to each other, the generation of frictional heat required for friction welding the axial ends is hindered. It can be made difficult.

FIG. 1 is a schematic view of an electric power steering device according to an embodiment of the present invention. FIG. 2 is a plan view of the linear motion shaft of the first example. FIG. 3A is a plan view of the rack shaft portion of the first example, and FIG. 3B is an end view of the rack shaft portion viewed from the left side of FIG. 3A. FIG. 4 is a perspective view of the rack shaft portion and the jig of the first example. 5 (a) is a plan view of the screw shaft portion of the first example, and FIG. 5 (b) is an end view of the screw shaft portion seen from the right side of FIG. 5 (a). FIG. 6 is a perspective view of the screw shaft portion and the jig of the first example. FIG. 7 is a plan view showing a start state of the work of friction welding the axial end portions of the rack shaft portion and the screw shaft portion in the first example. FIG. 8 (a) is a plan view showing an axial end portion of the screw shaft portion of the second example of the embodiment of the present invention on the opposite side to the frictional pressure contact portion, and FIG. 8 (b) is FIG. 8 (b). It is an end view of the screw shaft part seen from the right side of a). FIG. 9 is a perspective view of the screw shaft portion and the jig of the second example. FIG. 10 (a) is a plan view showing an axial end portion of the screw shaft portion of the third example of the embodiment of the present invention on the opposite side to the friction welding portion, and FIG. 10 (b) is FIG. 10 (b). It is an end view of the screw shaft part seen from the right side of a). FIG. 11 is a perspective view of the screw shaft portion and the jig of the third example. FIG. 12 (a) is a plan view showing an axial end portion of the screw shaft portion of the fourth example of the embodiment of the present invention opposite to the friction welding portion, and FIG. 12 (b) is FIG. 12 (b). It is an end view of the screw shaft part seen from the right side of a). FIG. 13 is a perspective view of the screw shaft portion and the jig of the fourth example. FIG. 14 (a) is a perspective view of the hollow screw shaft portion and the jig of the fifth example of the embodiment of the present invention, and FIG. 14 (b) is an end view of the screw shaft portion of the fifth example. Is. 15 (a) is a plan view of the rack shaft portion of the sixth example of the embodiment of the present invention, and FIG. 15 (b) is an end view of the rack shaft portion viewed from the left side of FIG. 15 (a). 15 (c) is a perspective view of the jig of the sixth example. 16 (a) is a plan view of the rack shaft portion of the seventh example of the embodiment of the present invention, and FIG. 16 (b) is an end view of the rack shaft portion viewed from the left side of FIG. 16 (a). Is. FIG. 17 is a plan view showing a start state of the work of frictionally pressing the end portions of the rack shaft portion and the screw shaft portion in the axial direction in the eighth example of the embodiment of the present invention. FIG. 18 (a) is a plan view showing an axial end portion of the screw shaft portion of the ninth example of the embodiment of the present invention opposite to the friction welding portion, and FIG. 18 (b) is FIG. 18 (b). It is an end view of the screw shaft part seen from the right side of a). 19 (a) is a plan view showing an axial end portion of the screw shaft portion opposite to the friction welding portion of the tenth example of the embodiment of the present invention, and FIG. 19 (b) is a plan view showing FIG. 19 (b). It is a cross-sectional view of AA of a). FIG. 20 is a schematic view of the electric power steering device of the eleventh example of the embodiment of the present invention. FIG. 21 is a plan view of the linear motion shaft of the eleventh example.

[First example]
A first example of the embodiment of the present invention will be described with reference to FIGS. 1 to 7. In the following description, the front-rear direction means the front-rear direction of the vehicle.

(Electric power steering device)
As shown in FIG. 1, the electric power steering device of this example includes a steering wheel 1 operated by a driver, a steering shaft 2, a pair of universal joints 3a and 3b, an intermediate shaft 4, and a rack and pinion type. The steering gear unit 5 and the electric assist device 6 are provided.

The steering wheel 1 is supported and fixed to the rear end portion of the steering shaft 2 that is rotatably supported with respect to the vehicle body. The front end portion of the steering shaft 2 is connected to the input shaft 7 of the steering gear unit 5 via the rear universal joint 3a, the intermediate shaft 4, and the front universal joint 3b. Therefore, the input shaft 7 can be rotated by rotating the steering wheel 1. The rotary motion of the input shaft 7 is converted into a linear motion of the linear motion shaft 9 of the steering gear unit 5. As a result, a pair of tie rods 11 connected to both ends of the linear motion shaft 9 in the axial direction via ball joints 10 are pushed and pulled, and the left and right steering wheels 12 have steering angles according to the amount of operation of the steering wheel 1. Granted. Further, at this time, the electric assist device 6 applies a steering assist force for the linear motion shaft 9 to make a linear motion to the linear motion shaft 9. As a result, the force required for the driver to operate the steering wheel 1 is reduced.

The steering gear unit 5 includes a housing 13 fixed to the vehicle body, an input shaft 7, a torsion bar (not shown), a pinion shaft 8, a linear motion shaft 9, and a pressing mechanism (not shown).

The pinion shaft 8 has a pinion tooth portion 14 on the tip side portion in the axial direction. The pinion shaft 8 is arranged coaxially with the input shaft 7 on the tip end side of the input shaft 7, and is connected to the input shaft 7 so as to be able to transmit torque via the torsion bar. The pinion shaft 8 is supported inside the housing 13 only by rotation by a rolling bearing (not shown).

The linear motion shaft 9 has a rack tooth portion 15 on a part in the circumferential direction of the outer peripheral portion of one side portion in the axial direction (left side portion in FIGS. 1 and 2), and the other side portion in the axial direction (FIG. 1). And a ball screw portion 16 is provided on the outer peripheral portion of (the right side portion in FIG. 2). The ball screw portion 16 constitutes a ball screw mechanism 17, which will be described later, and has a spiral male screw groove 18.

The linear motion shaft 9 has a rack shaft portion 19 having a rack tooth portion 15 on the outer peripheral portion, a screw shaft portion 20 having a ball screw portion 16 on the outer peripheral portion, and an axial end of the rack shaft portion 19 and the screw shaft portion 20. It is provided with a friction welding portion 21 which is a joint portion between the portions. That is, the linear motion shaft 9 is formed by friction welding the axial end portions of the rack shaft portion 19 and the screw shaft portion 20 manufactured separately. In this example, the screw shaft portion 20 corresponds to the first shaft portion, and the rack shaft portion 19 corresponds to the second shaft portion. Further, each of the rack shaft portion 19 and the screw shaft portion 20 is a solid shaft portion. When carrying out the present invention, at least one of the rack shaft portion 19 and the screw shaft portion 20 may be a hollow shaft portion.

As shown in FIGS. 3 (a), 3 (b), and 4, for example, the rack shaft portion 19 has a rack tooth portion 15 at one position in the circumferential direction of the axial intermediate portion. Further, the rack shaft portion 19 has a bottomed screw hole 31 that opens on one side in the axial direction at the radial center portion of the end portion on one side in the axial direction opposite to the friction welding portion 21. The peripheral portion of the screw hole 31 is a substantially cylindrical tubular portion 32. The screw hole 31 is for screwing a screw shaft for connection (not shown) provided in the ball joint 10 on the left side of FIG.

The rack shaft portion 19 has slits 33 extending in the radial direction, which are engaging portions, at two locations on the radial opposite sides of the tubular portion 32. The slit 33 is for engaging the jig 37 when performing friction welding between the axial end portions of the rack shaft portion 19 and the screw shaft portion 20. In this example, the slit 33 penetrates the tubular portion 32 so as to cross the one side portion in the axial direction in the radial direction, and is open on one side in the axial direction. The inner surface shape of the slit 33 seen from the radial direction is U-shaped. That is, of the inner surfaces of the slits 33, the pair of inner side surfaces 34 located on both sides in the width direction of the slits 33 are planes parallel to the axial direction of the rack shaft portion 19, and the back end surface in the axial direction is half. It is a cylindrical concave surface. In this example, one of the two slits 33 located on the radial opposite sides of the tubular portion 32 and the rack tooth portion 15 are arranged in the same phase in the circumferential direction. However, when the present invention is carried out, the phase of the arrangement can be made different from the case of this example. The size of the slit 33 can be arbitrarily determined. For example, the width dimension W of the slit 33 can be about 20% to 30% of the outer diameter dimension D of one side of the tubular portion 32 in the axial direction. Further, the axial dimension L of the pair of inner side surfaces 34 of the slit 33 can be about 5 mm to 10 mm.

The rack shaft portion 19 has a pressure welding side shaft portion 35 at an end portion on the other side in the axial direction, which is the friction welding portion 21 side. In this example, the pressure contact side shaft portion 35 is cylindrical, and the outer peripheral surface of the pressure contact side shaft portion 35 is a cylindrical surface. When carrying out the present invention, the pressure contact side shaft portion of the rack shaft portion may be formed in a cylindrical shape.

As shown in FIGS. 5 (a), 5 (b), and 6, for example, the screw shaft portion 20 is provided on the outer peripheral portion of the axial range excluding the end portion on one side in the axial direction, which is the friction welding portion 21 side. , Has a ball screw portion 16. Further, the screw shaft portion 20 has a bottomed screw hole 31a that opens on the other side in the axial direction at the radial center portion of the end portion on the other side in the axial direction opposite to the friction welding portion 21. The peripheral portion of the screw hole 31a is a substantially cylindrical tubular portion 32a having a part of the ball screw portion 16 on the outer peripheral portion. The screw hole 31a is for screwing a screw shaft for connection (not shown) included in the ball joint 10 on the right side of FIG.

The screw shaft portion 20 has slits 33a extending in the radial direction, which are engaging portions, at two locations on the radial opposite sides of the tubular portion 32a. The slit 33a is for engaging the jig 37a when performing friction welding between the axial end portions of the rack shaft portion 19 and the screw shaft portion 20. The slit 33a penetrates the tubular portion 32a so as to cross the other side portion in the axial direction in the radial direction, and is open to the other side in the axial direction. The inner surface shape of the slit 33a seen from the radial direction is U-shaped. That is, of the inner surfaces of the slits 33a, the pair of inner side surfaces 34a located on both sides in the width direction are planes parallel to the axial direction of the screw shaft portion 20, and the inner end surface in the axial direction is semi-cylindrical. It is a concave surface. Further, in this example, the circumferential direction of one of the two slits 33a located on the radially opposite sides of the tubular portion 32a and the end portion of the ball screw portion 16 on the other side in the axial direction of the screw thread. The phases of the arrangements with respect to are matched with each other. However, when the present invention is carried out, the phase of the arrangement in the circumferential direction may be different from that in the case of this example. In this example, the slit 33a of the screw shaft portion 20 and the slit 33 of the rack shaft portion 19 have the same shape and size. However, when the present invention is carried out, the slits 33 and 33a may have different shapes and sizes.

The screw shaft portion 20 has a pressure welding side shaft portion 35a at one end in the axial direction, which is the friction welding portion 21 side. In this example, the pressure contact side shaft portion 35a is cylindrical, and the outer peripheral surface of the pressure contact side shaft portion 35a is a cylindrical surface. When the present invention is carried out, the pressure contact side shaft portion of the screw shaft portion may be formed in a cylindrical shape.

In this example, in the completed state of the linear motion shaft 9, the positions (phases) of the two slits 33 of the rack shaft portion 19 and the two slits 33a of the screw shaft portion 20 in the rotational direction are matched with each other. .. When the present invention is carried out, the relationship between the positions in the rotational directions may be different from that in the case of this example.

The linear motion shaft 9 having the above-described configuration has its axial intermediate portion supported inside the housing 13 by a plurality of balls 27 constituting the ball screw mechanism 17 so as to enable linear motion. Further, in this state, the pinion tooth portion 14 of the pinion shaft 8 and the rack tooth portion 15 of the linear motion shaft 9 are in mesh with each other. As a result, the rotational motion of the pinion shaft 8 is converted into the linear motion of the linear motion shaft 9. Further, the rotation of the linear motion shaft 9 with respect to the housing 13 is blocked by the engagement between the rack tooth portion 15 and the pinion tooth portion 14.

The pressing mechanism is housed inside the housing 13 on the side opposite to the radial direction of the pinion shaft 8 with the linear motion shaft 9 interposed therebetween, and directs the linear motion shaft 9 toward the pinion shaft 8 based on the elasticity of the spring or the like. I'm urging. As a result, by keeping the meshing state of the pinion tooth portion 14 and the rack tooth portion 15 properly, it is possible to suppress the generation of abnormal noise at the meshing portion between the pinion tooth portion 14 and the rack tooth portion 15, and the steering wheel 1 The operation feeling of is improved.

The electric assist device 6 includes a torque sensor 22, an electric motor 23 as a power source, a ball screw mechanism 17, and a control unit (not shown).

The torque sensor 22 is housed inside the housing 13 and can detect the direction and magnitude of the torque transmitted from the steering wheel 1 to the input shaft 7. The electric motor 23 is supported by the housing 13, and its output shaft 24 is inserted inside the housing 13. The ball screw mechanism 17 is housed inside the housing 13, and has a ball nut 26 having a spiral female screw groove 25 on the inner peripheral surface, a plurality of balls 27, and a ball screw formed on the linear motion shaft 9. It is configured to include a part 16. The ball nut 26 is screwed into the ball screw portion 16 via a plurality of balls 27. In other words, the plurality of balls 27 are arranged between the female screw groove 25 of the ball nut 26 and the male screw groove 18 of the ball screw portion 16. The ball nut 26 is supported only by rotation with respect to the housing 13 by a rolling bearing (not shown). The rotational movement of the output shaft 24 of the electric motor 23 can be transmitted to the ball nut 26 via the drive pulley 28, the endless belt 29, and the driven pulley 30.

The electric assist device 6 detects the direction and magnitude of the torque transmitted from the steering wheel 1 to the input shaft 7 by the torque sensor 22. Then, the control unit rotationally drives the output shaft 24 of the electric motor 23 while controlling the amount of energization to the electric motor 23 according to the direction and magnitude of the torque detected in this way and the vehicle speed signal. The rotational movement of the output shaft 24 is transmitted to the ball nut 26 via the drive pulley 28, the endless belt 29, and the driven pulley 30. The rotational motion of the ball nut 26 is converted into a linear motion of the linear motion shaft 9 via the plurality of balls 27. As a result, the linear motion shaft 9 is linearly moved with a force larger than the operating force of the steering wheel 1 by the driver. As a result, the force required for the driver to operate the steering wheel 1 is reduced.

In the structure of this example, the ball screw portion 16 has an incompletely threaded portion at both ends in the axial direction and a completely threaded portion at the intermediate portion in the axial direction, which is the remaining portion. The completely threaded portion is a portion in which the shape of the lead groove is stable and has a predetermined thread height. On the other hand, the incompletely threaded portion is a portion in which the lead groove shape and the like are not stable and the thread height is insufficient as compared with the completely threaded portion. Therefore, in the ball screw portion 16, only the axial intermediate portion, which is a completely threaded portion, is used as a portion for engaging the ball 27, and the ends on both sides in the axial direction, which are incompletely threaded portions, engage the ball 27. It is not used as a part to be combined. That is, the axial movement range of the linear motion shaft 9 is restricted to the axial range in which the ball 27 can engage with the completely threaded portion which is the axial intermediate portion of the ball screw portion 16. On the other hand, in the structure of this example, in the screw shaft portion 20, as shown in FIG. 5A, the slit 33a is formed from the end edge of the screw shaft portion 20 on the other side in the axial direction to the other end in the axial direction of the ball screw portion 16. It extends axially to the axial position where the side end exists. In other words, a part of the incompletely threaded portion, which is the end portion of the ball screw portion 16 on the other side in the axial direction, is cut out by the slit 33a. In the structure of this example, a part of the incompletely threaded portion, which is the other end of the ball screw portion 16 in the axial direction, which is not used as the engaging portion of the ball 27, is effectively used as the forming range of the slit 33a. doing.

(Manufacturing method of linear motion shaft)
Next, a method of manufacturing the linear motion shaft 9 when manufacturing the electric power steering device of this example will be described.

The method of manufacturing the linear motion shaft 9 of this example includes a step of manufacturing the rack shaft portion 19 as shown in FIG. 4, a step of manufacturing the screw shaft portion 20 as shown in FIG. 6, and a rack shaft portion 19 and a screw. A step of friction welding the axial ends of the shaft portion 20 with each other is provided.

In the process of manufacturing the rack shaft portion 19, for example, a rod-shaped material such as a metal round bar is appropriately processed to provide a rack tooth portion 15, a screw hole 31 (cylinder portion 32), and a slit. A rack shaft portion 19 having a 33 and a pressure contact side shaft portion 35 is obtained. In this example, the processing method and processing order for forming the rack tooth portion 15, the screw hole 31 (cylinder portion 32), the slit 33, and the pressure contact side shaft portion 35 are not particularly limited. When the rod-shaped material is a round bar, the axial end portion of the round bar may be left unprocessed to form the pressure contact side shaft portion 35. If necessary, the rack tooth portion 15 is subjected to a heat treatment for improving mechanical performance at an appropriate timing.

In the process of manufacturing the screw shaft portion 20, for example, a rod-shaped material such as a metal round bar is appropriately processed to form a ball screw portion 16, a screw hole 31a (cylinder portion 32a), and a slit. A screw shaft portion 20 having a 33a and a pressure contact side shaft portion 35a is obtained. In this example, the processing method and processing order for forming the ball screw portion 16, the screw hole 31a (cylinder portion 32a), the slit 33a, and the pressure contact side shaft portion 35a are not particularly limited. When the rod-shaped material is a round bar, the axial end portion of the round bar may be left unprocessed to form the pressure contact side shaft portion 35a. If necessary, the ball screw portion 16 is subjected to a heat treatment for improving mechanical performance at an appropriate timing.

Next, a step of friction welding the axial ends of the rack shaft portion 19 and the screw shaft portion 20 will be described. Friction welding is a method of joining two metal members by abutting each other and rotating them relative to each other while applying pressure, and utilizing the frictional heat generated at the abutting portion.

When friction welding the axial ends of the rack shaft 19 and the screw shaft 20 with each other, first, the rack shaft 19 and the screw shaft 20 are centered to bring the rack shaft 19 and the screw into a screw. The shaft portion 20 is arranged coaxially, and the end face of the rack shaft portion 19 on the other side in the axial direction and the end face of the screw shaft portion 20 on the one side in the axial direction are abutted against each other to pressurize. At the same time, the rack shaft portion 19 and the screw shaft portion 20 are relatively rotated to generate frictional heat in the abutting portion. As a result, the butt portion is brought into a high temperature and high pressure state, and then the relative rotation is stopped. As a result, the linear motion shaft 9 which became the friction welding portion 21 as the butt portion was cooled is obtained.

More specifically, in this example, when performing the friction welding as described above, first, as shown in FIG. 7, the rack shaft portion 19 and the screw shaft portion 20 are set in the friction welding device. ..

That is, by gripping the outer peripheral surface of the pressure contact side shaft portion 35 of the rack shaft portion 19 with the gripping tool 36 and gripping the outer peripheral surface of the pressure contact side shaft portion 35a of the screw shaft portion 20 with the gripping tool 36a, the rack shaft portion Centering of 19 and the screw shaft portion 20 is performed. As the gripping tools 36 and 36a, various gripping tools such as a collet chuck and a hydraulic three-claw chuck can be adopted. Further, the jig 37 is engaged with the slit 33 of the rack shaft portion 19, and the jig 37a is engaged with the two slits 33a of the screw shaft portion 20.

The jig 37 has a short columnar base portion 38 and an engaging convex portion 39 protruding from the side surface of the base portion 38 on the other side in the axial direction. The engaging convex portion 39 is formed so as to extend in the radial direction of the side surface on the other side in the axial direction of the base portion 38. Both sides of the engaging convex portion 39 in the extending direction can be inserted into the inside of the two slits 33 of the rack shaft portion 19 from the axial direction, and have an outer surface shape that matches the inner surface shape of the two slits 33. That is, both side surfaces of the engaging convex portion 39 in the width direction are planes parallel to the axial direction of the base 38, and the tip surface of the engaging convex portion 39 is a semi-cylindrical convex surface. In this example, the jig 37 and the rack shaft portion 19 are engaged by inserting both sides of the engaging convex portion 39 of the jig 37 in the extension direction into the inside of the two slits 33 from the axial direction and engaging them. Relative rotation with and is disabled. In particular, in this example, since the pair of inner side surfaces 34 of the slits 33 are parallel to the axial direction, the effect of disabling relative rotation can be enhanced. In this state, the jig 37 is assembled to the friction welding device so that the relative rotation between the jig 37 and the gripping tool 36 becomes impossible. In the friction welding device, the gripping tool 36 and the jig 37 do not rotate when performing the friction welding operation.

The jig 37a has a short columnar base portion 38a and an engaging convex portion 39a protruding from a side surface of the base portion 38a on one side in the axial direction. The engaging convex portion 39 is formed so as to extend in the radial direction of the side surface of the base portion 38a on one side in the axial direction. Both sides of the engaging convex portion 39a in the extension direction can be inserted into the inside of the two slits 33a of the screw shaft portion 20 from the axial direction, and have an outer surface shape that matches the inner surface shape of the two slits 33a. That is, both side surfaces of the engaging convex portion 39a in the width direction are planes parallel to the axial direction of the base portion 38a, and the tip surface of the engaging convex portion 39a is a semi-cylindrical convex surface. In this example, the jig 37a and the screw shaft portion 20 are engaged by inserting both sides of the engaging convex portion 39a of the jig 37a in the extension direction into the inside of the two slits 33a from the axial direction. Relative rotation with and is disabled. In particular, in this example, since the pair of inner side surfaces 34a of the slits 33a are parallel to the axial direction, the effect of disabling relative rotation can be enhanced. In this state, the jig 37a is assembled to the friction welding device so that the jig 37a and the gripping tool 36a cannot rotate relative to each other. In the friction welding device, the gripping tool 36a and the jig 37a rotate and stop in synchronization with each other when performing the friction welding operation.

After the rack shaft portion 19 and the screw shaft portion 20 are set in the friction welding device as described above, then the rack shaft portion 19 (grip tool 36, jig 37) and the screw shaft portion 20 (grip tool 36a, By bringing the jig 37a) closer to the axial direction, the end surface of the rack shaft portion 19 on the other side in the axial direction and the end surface of the screw shaft portion 20 on the one side in the axial direction are abutted against each other to pressurize. At the same time, the gripping tool 36 and the jig 37 prevent the rack shaft portion 19 from rotating, and the gripping tool 36a and the jig 37a that rotate in synchronization with each other drive the screw shaft portion 20 to rotate. As a result, frictional heat is generated in the butt portion. As a result, after the butt portion is brought into a high temperature and high pressure state, the rotation of the screw shaft portion 20 is stopped by the gripping tool 36a and the jig 37a. As a result, the linear motion shaft 9 which became the friction welding portion 21 as the butt portion was cooled is obtained.

In this example, the rotational position management function of the gripping tool 36a and the jig 37a provided in the friction welding machine determines in advance the positional relationship between the rack shaft portion 19 and the screw shaft portion 20 in the rotational direction at the end of friction welding. It is regulated so that it has a predetermined positional relationship. In this example, the position of the slit 33 of the rack shaft portion 19 in the rotational direction can be used to accurately grasp the position of the rack tooth portion 15 in the friction welding machine in the rotational direction, and the screw shaft portion 20 of the screw shaft portion 20. By utilizing the position of the slit 33a in the rotation direction, the position of the ball screw portion 16 in the friction welding machine in the rotation direction can be accurately grasped. Therefore, the above-mentioned positional relationship can be easily regulated.

In the method of manufacturing the linear motion shaft 9 of this example, when the axial ends of the rack shaft portion 19 and the screw shaft portion 20 are friction-welded to each other, the jig 37 is engaged with the slit 33 of the rack shaft portion 19. By engaging the portions 39, the jig 37 prevents the rack shaft portion 19 from rotating in a state where the relative rotation between the rack shaft portion 19 and the jig 37 is disabled. Further, by engaging the engaging convex portion 39a of the jig 37a with the slit 33a of the screw shaft portion 20, the screw is screwed by the jig 37a in a state where the relative rotation between the screw shaft portion 20 and the jig 37a is disabled. The shaft portion 20 is rotationally driven. Therefore, during friction welding, slippage occurs between the jig 37 (and the gripping tool 36) and the rack shaft portion 19 in the rotational direction, and the rack shaft portion 19 is rotated around the screw shaft portion 20. Alternatively, slippage occurs between the jig 37a (and the gripping tool 36a) and the screw shaft portion 20 in the rotational direction, and the rotational speed of the screw shaft portion 20 is higher than the rotational speed of the jig 37a (and the gripping tool 36a). It can be prevented from becoming low. In other words, the relative rotation speed of the rack shaft portion 19 and the screw shaft portion 20 is lower than the relative rotation speed of the jig 37 (and the gripping tool 36) and the jig 37a (and the gripping tool 36a). Can be prevented. As a result, the frictional heat required for friction welding can be normally generated between the axial end portions of the rack shaft portion 19 and the screw shaft portion 20. In particular, as in this example, both the rack shaft portion 19 and the screw shaft portion 20 constituting the linear motion shaft 9 are provided with slits 33 and 33a as target shaft portions, so that, for example, two linear motion shafts are formed. It is possible to further improve the anti-slip effect at the time of friction welding as compared with the configuration in which only one of the shaft portions has a slit as the target shaft portion.

In this example, the positional relationship between the rack shaft portion 19 and the screw shaft portion 20 at the end of friction welding can be regulated so as to be a predetermined predetermined positional relationship. Therefore, in the assembly process of the steering gear unit 5, it is easy to automate the work of screwing the ball nut 26 into the ball screw portion 16 via the plurality of balls 27. Further, since the positional relationship in the rotational direction between the rack shaft portion 19 and the screw shaft portion 20 at the end of friction welding is determined to be a predetermined positional relationship, the bending direction of the linear motion shaft 9 caused by the heat treatment in the middle is substantially the same. Since it becomes constant, the work of correcting the bending can be efficiently performed.

In the first example, engaging portions (slits) are provided on both the rack shaft portion and the screw shaft portion, but in the case of carrying out the present invention, the rack shaft portion and the screw shaft portion are provided. An engaging portion may be provided only on one of the shaft portions. For example, with respect to the rack shaft portion, by gripping the rack tooth portion with the gripping tool at the time of friction welding instead of providing the engaging portion, slippage in the rotational direction occurs between the gripping tool and the rack shaft portion. It can also be prevented.

In the first example, a method is adopted in which the slits provided in the rack shaft portion and the screw shaft portion are formed in advance by machining such as casting or cutting before engaging the jig. However, when the present invention is carried out, the slits provided in the rack shaft portion and the screw shaft portion are formed by plastic working such as forging or pressing using a jig as a tool and using the joining pressure at the time of friction welding. You can also do it. In this case, the jig engages with the slit at the same time as the slit is formed. As described above, the slit can be formed by casting, machining, or plastic working.

In this example, the end portion on the side opposite to the friction welding portion of the rack shaft portion and the screw shaft portion, which are the target shaft portions, on the side where the slit is arranged is formed by the tubular portion, and the axial direction of the tubular portion is formed. A slit is formed on one side so as to cross the radial direction. When the present invention is carried out, when the target shaft portion is other than the rack shaft portion or the screw shaft portion, the end portion on the side opposite to the friction welding portion is composed of a solid portion, and the end face of the end portion is radially oriented. An extending slit can be directly formed. Further, in any case, in addition to the configuration in which the slit penetrates the tubular portion in the radial direction or penetrates the entire end portion in the radial direction, the slit is formed on one side of the tubular portion in the axial direction. In addition to being recessed from the inner peripheral surface to the outer diameter side, it can also be composed of a recess that opens on one side in the axial direction, or a recess that extends radially to the radial center of the end face of the end surface. Is.

In one embodiment of the present invention including the first example, slits 33, which are engaging portions, are provided at two locations on the radial opposite sides of the tubular portion 32 of the rack shaft portion 19, and slits 33 are provided at the base 38 of the jig 37. An engaging convex portion 39 that engages with is provided. Further, slits 33a, which are engaging portions, are provided at two locations on the radial opposite sides of the tubular portion 32a of the screw shaft portion 20, and engaging convex portions 39a that engage with the slit 33a are provided at the base portion 38a of the jig 37a. ing. However, in another embodiment of the present invention, engaging protrusions projecting axially from the axial end face of the tubular portion are provided at two locations on the radial opposite sides of the tubular portion of the rack shaft portion, and the jig is provided. An axially recessed recess is provided at least at a position corresponding to the engaging convex portion on the surface of the base portion facing the axial end surface of the rack shaft portion, or the jig base portion is radially penetrated and said. It is also possible to provide a slit that opens on the facing surface. Similarly, engaging protrusions protruding in the axial direction from the axial end face of the tubular portion are provided at two locations on the radial opposite sides of the tubular portion of the screw shaft portion, and the shaft of the screw shaft portion of the base of the jig is provided. An axially recessed recess is provided at least at a position corresponding to the engaging convex portion of the surfaces facing the end faces in the direction, or a slit penetrating the base of the jig in the radial direction and opening to the facing surface is provided. It can also be provided.

[Second example]
A second example of the embodiment of the present invention will be described with reference to FIGS. 8 (a), 8 (b), and 9. In this example, the shape of the slit 33b of the screw shaft portion 20a and the shape of the engaging convex portion 39b of the jig 37b that engages with the slit 33b are different from those of the first example.

In this example, the shape of the slit 33b seen from the radial direction is a wedge shape. That is, the width dimension of the slit 33b becomes larger toward the other side in the axial direction opposite to the friction welding portion, in other words, becomes larger toward the opening side of the slit 33b. That is, the inner surface of the slit 33b is a flat surface in which a pair of inner side surfaces 34b located on both sides in the width direction are inclined in a direction in which they are separated from each other toward the other side in the axial direction. Further, the engaging convex portion 39b of the jig 37b has an outer surface shape that matches the inner surface shape of the slit 33b. That is, both side surfaces of the engaging convex portion 39b in the width direction are flat surfaces that are inclined in a direction that approaches each other toward the tip end side.

In this example having such a configuration, the work efficiency when the engaging convex portion 39b is inserted into the slit 33b in the axial direction can be increased. Other configurations and operations of this example are the same as those of the first example.

[Third example]
A third example of the embodiment of the present invention will be described with reference to FIGS. 10 (a), 10 (b), and 11. In this example, the shape of the slit 33c of the screw shaft portion 20b and the shape of the jig 37c engaged with the slit 33c are different from those of the first example.

In this example, the inner surface shape of the slit 33c seen from the axial direction is a wedge shape. That is, the width dimension of the slit 33b increases from the inner side in the radial direction to the outer side in the radial direction, in other words, the width dimension increases from the inner peripheral surface to the outer peripheral surface of the tubular portion 32b. That is, the inner surface of the slit 33c is a flat surface in which a pair of inner side surfaces 34c located on both sides in the width direction are inclined in a direction in which they are separated from each other toward the outer side in the radial direction. Further, the jig 37c includes a pair of engaging pieces 40. Each of the pair of engaging pieces 40 has an outer surface shape that matches the inner surface shape of the slit 33c. That is, each of the pair of engaging pieces 40 has a wedge shape, and both side surfaces in the width direction are flat surfaces inclined in a direction in which they approach each other from the outer side in the radial direction to the inner side in the radial direction. ..

In this example, the pair of engaging pieces 40 constituting the jig 37c are placed in the slit 33c from the outside in the radial direction at two locations on the radial opposite sides of the tubular portion 32b, at positions that match the phase with the slit 33c. And engage with the slit 33c.

In this example having such a configuration, not only the relative rotation between the screw shaft portion 20b and the jig 37c becomes impossible due to the engagement between the screw shaft portion 20b, which is the target shaft portion, and the jig 37c, but also the screw. It is possible to restrain the shaft portion 20b from moving in the vertical direction or the horizontal direction, and it is possible to align the screw shaft portion 20b. It is also possible to apply the structure of this example to the rack shaft portion. Other configurations and operations of this example are the same as those of the first example.

[4th example]
A fourth example of the embodiment of the present invention will be described with reference to FIGS. 12 (a), 12 (b), and 13. In this example, the inner surface shape of the slit 33c of the screw shaft portion 20b is different from that of the first example, and the shape of the jig 37d that engages with the slit 33c is different from that of the first example and the third example.

The configuration of the screw shaft portion 20b, the tubular portion 32b, and the slit 33c in this example is the same as that in the third example. In this example, the jig 37d has a pair of a cylindrical base 41 having a central axis in the axial direction and a pair of cylinder bases 41 protruding outward in the radial direction from two locations on the opposite sides of the outer peripheral surface in the radial direction. A joint 42 is provided. Each of the pair of engaging portions 42 has an outer surface shape that matches the inner surface shape of the slit 33c. That is, each of the pair of engaging portions 42 has a wedge shape when viewed from the axial direction, and both side surfaces in the width direction are closer to each other from the outer side in the radial direction to the inner side in the radial direction. It is a sloping plane.

In this example, the jig 37d is inserted in the axial direction with respect to the tubular portion 32b of the screw shaft portion 20b. That is, with the end surface of the cylindrical base 41 of the jig 37d facing the screw hole 31a of the cylinder 32b and the end faces of the pair of engaging portions 42 facing the opening surface of the slit 33c, the jig 37d is placed. It is moved in the axial direction to engage the screw hole 31a and the slit 33c of the tubular portion 32b.

In this example having such a configuration, when the screw shaft portion 20b is attached to the friction welding machine, the screw shaft portion 20b and the jig 37c are engaged with each other by engaging the screw shaft portion 20b, which is the target shaft portion, with the jig 37c. Not only is it impossible to rotate relative to the screw shaft portion 20b, but it is also possible to restrain the screw shaft portion 20b from moving in the vertical direction or the horizontal direction, and the screw shaft portion 20b can be centered. It is also possible to apply the structure of this example to the rack shaft portion. Other configurations and operations of this example are the same as those of the first and third examples.

[Example 5]
A fifth example of the embodiment of the present invention will be described with reference to FIGS. 14 (a) and 14 (b). In this example, the structure of the screw shaft portion 20c, which is the target shaft portion, the arrangement of the slit 33a, and the shape of the jig 37e engaged with the slit 33a are different from those in the first example.

In this example, the screw shaft portion 20c is composed of a hollow pipe provided with a hollow hole 43 penetrating in the axial direction. In this example, the screw hole 31a that opens on the other side of the screw shaft portion 20c in the axial direction is coaxial with the hollow hole 43 and is continuous with the hollow hole 43. The inner peripheral surface of the screw hole 31a is formed by a female screw structure formed by cutting the inner peripheral surface of the hollow hole 43, and is directly continuous with the inner peripheral surface of the hollow hole 43, or has an inclined surface portion or a stepped portion. Continuous through. The screw shaft portion 20c is provided with a hollow hole 43 to reduce the weight thereof, and the friction welding area on one end surface in the axial direction on the friction welding portion 21 side is larger than that of the structure of the first example. It's getting smaller. As described above, the hollow structure screw shaft portion 20c does not apply a large torque during friction welding as compared with the solid structure screw shaft portion 20a. Therefore, in the screw shaft portion 20c of this example, the tubular portion 32c is provided with a slit 33a which is an engaging portion only at one position in the circumferential direction. The inner diameter of the hollow hole 43 can be made constant over the axial direction. Alternatively, the inner peripheral surface of the hollow hole may be formed of a surface whose inner diameter changes with respect to the axial direction, such as a stepped cylindrical surface or a conical surface.

The jig 37e has a short columnar base portion 38a and an engaging convex portion 39c protruding from a side surface of the base portion 38a on one side in the axial direction. However, the engaging convex portion 39c is formed so as to extend radially outward from the radial center portion at one location in the circumferential direction of the side surface, not the entire side surface on one side in the axial direction of the base portion 38a.

In this example having such a configuration, by engaging the engaging convex portion 39c of the jig 37e with the slit 33a of the screw shaft portion 20c which is the target shaft portion, the screw shaft portion 20c and the jig 37e are relative to each other. It is possible to disable the rotation. It is also possible to apply the structure of this example to the rack shaft portion and other shaft portions. Other configurations and operations of this example are the same as those of the first example.

[6th example]
A sixth example of the embodiment of the present invention will be described with reference to FIGS. 15 (a) to 15 (c). In this example, the structure of the rack shaft portion 19a, which is the target shaft portion, the arrangement of the slits 33, and the shape of the jig 37f engaged with the slits 33 are different from those in the first example.

In this example, the rack shaft portion 19a has slits 33, which are engaging portions, at four positions of the tubular portion 32 at equal intervals in the circumferential direction. Correspondingly, the jig 37f has a short columnar base portion 38 and an engaging convex portion 39d protruding from the side surface of the base portion 38 on the other side in the axial direction. The engaging convex portion 39d is formed on the side surface of the base portion 38 on the other side in the axial direction so as to extend in a cross shape from the radial center portion toward the radial outer side. The extension-direction outer portion of the engaging convex portion 39d can be inserted into the inside of the four slits 33 of the rack shaft portion 19a from the axial direction, and has an outer surface shape that matches the inner surface shape of the four slits 33. It is also possible to provide slits 33 at three locations at equal intervals in the circumferential direction of the tubular portion 32. The number of slits 33 is arbitrary, but is preferably 2 to 4 and more preferably 2 or 4. Further, the slits 33 are preferably arranged at equal intervals in the circumferential direction.

In this example having such a configuration, the rack shaft portion 19a and the jig 37f are relative to each other by engaging the engaging convex portion 39d of the jig 37f with the slit 33 of the rack shaft portion 19a which is the target shaft portion. Not only can the rotation be disabled, but the rack shaft 19a can also be restrained from moving in both the vertical and horizontal directions. Therefore, the effect of preventing the rack shaft portion 19a from falling is improved. It is also possible to apply the structure of this example to the screw shaft portion. Other configurations and operations of this example are the same as those of the first example.

[7th example]
A seventh example of the embodiment of the present invention will be described with reference to FIGS. 16 (a) and 16 (b). In this example, the structure of the rack shaft portion 19b, which is the target shaft portion, is different from that in the first example.

In this example, the rack shaft portion 19b is provided with a spline portion 44 on the outer peripheral surface of the tubular portion 32c. Specifically, of the outer peripheral surface of the tubular portion 32c, the tubular portion 32c protrudes radially from the outer peripheral surface of the tubular portion 32c at six positions in the radial direction, which are out of phase with the two locations provided with the slits 33. A spline portion 44 made of a male spline is formed by providing a convex portion extending in the entire axial direction of the outer peripheral surface.

In this example having such a configuration, a female spline corresponding to the male spline of the spline portion 44 is formed on the inner peripheral surface of the gripper that grips the tubular portion 32c of the rack shaft portion 19b of the friction welding machine from the outside in the radial direction. By providing a spline portion composed of the spline portion and engaging the spline portion 44 with the spline portion 44, the rack shaft portion 19b can receive a larger torque at the time of friction welding. Although not shown, the circumference of the female spline corresponding to the male spline of the spline portion 44 corresponds to the concave portion of the spline portion 44 on the other side surface of the base portion of the jig having the engaging convex portion in the axial direction. It can also be configured by a convex portion that protrudes in the axial direction from four positions in the direction and has an inner surface shape that matches the outer surface shape of the spline portion 44. It is also possible to apply the structure of this example to the screw shaft portion. Other configurations and operations of this example are the same as those of the first example.

[Example 8]
An eighth example of the embodiment of the present invention will be described with reference to FIG. In this example, in order to perform friction welding between the rack shaft portion 19 and the screw shaft portion 20, when the rack shaft portion 19 and the screw shaft portion 20 are set in the friction welding device, the rack shaft portion 19 and the screw shaft are set. Both portions 20 are fitted in the sleeve 45. The sleeve 45 is made of a metal tubular member, and the total length of the sleeve 45 is the axial length of the linear motion shaft 9, that is, the axial length of the rack shaft portion 19 and the axial length of the screw shaft portion 20. It is the same as or shorter than the total. The inner diameter of the inner peripheral surface of the sleeve 45 is the outer diameter of the outer peripheral surface of the rack shaft portion 19 other than the portion where the rack tooth portion 15 is provided, and the male screw thread of the ball screw portion 16 of the screw shaft portion 20. It is the same as or slightly larger than the diameter of the circumscribed circle. The sleeve 45 has a split type structure that can be divided into two in the circumferential direction, and the rack shaft portion 19 and the screw shaft portion 20 are sandwiched between the rack shaft portion 19 and the screw shaft portion 20 from opposite sides in the radial direction. It is preferable to fit it externally. Alternatively, with the sleeve 45 as an integrated structure, the rack shaft portion 19 and the screw shaft portion 20 in which the jigs 37 and 37a are fitted are respectively pressed from both sides in the axial direction of the sleeve 45 to the pressure contact side of the rack shaft portion 19. The end face of the shaft portion 35 and the end face of the pressure contact side shaft portion 35a of the screw shaft portion 20 can be inserted so as to be close to each other. In this example, the sleeve 45 is then gripped by the gripper of the friction welding machine.

In this example having such a configuration, the sleeve 45 can restrain the rack shaft portion 19 and the screw shaft portion 20, which are the target shaft portions, from moving in the radial direction during friction welding. Other configurations and operations of this example are the same as those of the first example.

[Example 9]
A ninth example of the embodiment of the present invention will be described with reference to FIGS. 18 (a) and 18 (b). In this example, at least the screw shaft portion 20d for friction welding has a knurled portion 46, which is an engaging portion, on the end surface on the other side in the axial direction. In this example, when performing friction welding, a jig (not shown) is engaged with the knurled portion 46 in an uneven manner so that the relative rotation between the screw shaft portion 20d and the jig is disabled. The screw shaft portion 20d is rotationally driven by a jig.

In this example, after the friction welding is completed, a screw hole 31a (see FIG. 5A) is formed as needed. That is, when the ball joint 10 on the right side of FIG. 1 is connected to the end of the screw shaft portion 20d on one side in the axial direction by using the screw hole 31a, the screw hole 31a is formed. On the other hand, when the ball joint 10 on the right side of FIG. 1 is connected by another method, the screw hole 31a is not formed. Other configurations and operations of this example are the same as those of the first example.

[Example 10]
A tenth example of the embodiment of the present invention will be described with reference to FIGS. 19 (a) and 19 (b). In this example, the screw shaft portion 20f does not have an engaging portion for engaging the jig so as not to rotate relative to each other when performing friction welding at the end on the other side in the axial direction. Instead, in this example, at least the screw shaft portion 20f for friction welding has a center hole 47 at the radial center of the end face on the other side in the axial direction. In this example, when performing friction welding, a center shaft for centering (not shown) is engaged with the center hole 47. Thereby, the centering accuracy of the screw shaft portion 20f can be improved. Further, in this example, when the steps of heat treatment and re-bending of the screw shaft portion 20f are performed before friction welding, the center hole 47 can also be used in this step. Therefore, when the center hole 47 is used in the step, the center hole 47 can be used as it is in the subsequent friction welding step, and no additional machining is required.

In this example, after the friction welding is completed, a screw hole 31a (see FIG. 5A) is formed as needed. Other configurations and operations of this example are the same as those of the first example.

[Example 11]
An eleventh example of the embodiment of the present invention will be described with reference to FIGS. 20 and 21. The linear motion shaft 9a constituting the electric power steering device of this example has rack teeth 15 and 15a on both sides in the axial direction. The pinion tooth portion 14 of the pinion shaft 8 meshes with one rack tooth portion 15, and the pinion tooth portion 14a of another pinion shaft 8a meshes with the other rack tooth portion 15a. The control unit of the electric assist device 6a controls the amount of energization to the electric motor 23a according to the direction and magnitude of the torque detected by the torque sensor 22 and the vehicle speed signal, and the electric motor 23a passes through the speed reducer 48. Another pinion shaft 8a is rotationally driven. Then, the meshing portion between the other rack tooth portion 15a and the pinion tooth portion 14a converts the rotational motion of another pinion shaft 8a into the linear motion of the linear motion shaft 9a, thereby applying a steering assist force to the linear motion shaft 9a. Give.

The linear motion shaft 9a includes one rack shaft portion 19 having one rack tooth portion 15 on the outer peripheral portion, the other rack shaft portion 19c having the other rack tooth portion 15a on the outer peripheral portion, and two rack shaft portions 19. , 19c is provided with a friction welding portion 21 which is a joint portion between the axial end portions.

In this example, the other rack shaft portion 19c has substantially the same shape and size as the one rack shaft portion 19, although the orientation in the axial direction is opposite to that of the one rack shaft portion 19. Further, in a state where the axial ends of one rack shaft portion 19 and the other rack shaft portion 19c are friction-welded to each other, the circumferential position of the rack tooth portion 15 of one rack shaft portion 19 and the other rack. The position of the rack tooth portion 15a of the shaft portion 19a in the circumferential direction is deviated by a predetermined angle.

In this example, when manufacturing such a linear motion shaft 9, the slit 33 of one rack shaft portion 19 and the slit 33 of the other rack shaft portion 19c are used in the same manner as in the first example. By the method, the axial end portions of one rack shaft portion 19 and the other rack shaft portion 19c are friction-welded to each other. In this way, when the linear motion shaft 9a is composed of a combination of the two rack shaft portions 19 and 19c, by providing the slits 33 in both rack shaft portions 19 and 19c, the rack shaft portions 19 and 19c are positioned. The phase difference can be easily set to a desired value by using the slit 33. Other configurations and operations of this example are the same as those of the first example.

The present invention can be implemented by appropriately combining the configurations of the above-described embodiments as long as there is no contradiction.

The present invention is, for example, a linear motion shaft constituting an electric power steering device of a type that applies a steering assist force to a portion other than the linear motion shaft or a steering device of a steer-by-wire system, and has a rack tooth portion on an outer peripheral portion. It can also be applied to a linear motion shaft provided with a rack shaft portion, an extension shaft portion that is a cylindrical or columnar round bar, and a frictional pressure contact portion between the axial end portions of the rack shaft portion and the extension shaft portion. can.

The present invention includes, for example, a linear motion shaft constituting a steering device of a steer-by-wire system, a screw shaft portion having a ball screw portion on the outer peripheral portion, and an extension shaft portion which is a cylindrical or columnar round bar. It can also be applied to a linear motion shaft provided with a friction welding portion between axial ends of a screw shaft portion and an extension shaft portion.

In the present invention, when friction welding is performed between the axial end portions of the first shaft portion and the second shaft portion, which of the first shaft portion and the second shaft portion is on the rotation side (or). Whether it is on the non-rotating side) can be arbitrarily determined.

When carrying out the present invention, the jig engages with the engaging portion of the target shaft portion when friction welding the axial ends of the first shaft portion and the second shaft portion with each other, thereby engaging the target shaft. As long as it has a function of rotationally driving the target shaft portion or preventing the rotation of the target shaft portion in a state where the relative rotation with the portion is disabled, the shape is not limited to the shape of each of the above-described embodiments. Any shape can be adopted.

When the steering device of the present invention is implemented, a non-rotating member existing in the periphery is engaged with an engaging portion formed on a target shaft portion which is at least one of a first shaft portion and a second shaft portion. By matching, it is possible to more reliably prevent the linear motion shaft from rotating. As a result, it is possible to more reliably prevent an unreasonable force from acting on a functional portion such as a rack tooth portion provided on the linear motion shaft, and it is possible to extend the life of the functional portion.

The present invention is applicable not only to a linear motion shaft for a steering device but also to a linear motion shaft for a device other than the steering device.

1 Steering wheel 2 Steering shaft 3a, 3b Swivel joint 4 Intermediate shaft 5 Steering gear unit 6, 6a Electric assist device 7 Input shaft 8, 8a Pinion shaft 9, 9a Linear shaft 10 Ball joint 11 Tie rod 12 Steering wheel 13 Housing 14, 14a Pinion tooth part 15, 15a Rack tooth part 16 Ball thread part 17 Ball screw mechanism 18 Male thread groove 19, 19a, 19b, 19c Rack shaft part 20, 20a, 20b, 20c, 20d, 20f Thread shaft part 21 Friction pressure welding part 22 Torque sensor 23, 23a Electric motor 24 Output shaft 25 Female thread groove 26 Ball nut 27 Ball 28 Drive pulley 29 Endless belt 30 Driven pulley 31, 31a Thread hole 32, 32a, 32b, 32c Cylinder 33, 33a, 33b, 33c Slit 34 , 34a, 34b, 34c Inner surface 35, 35a Pressure welding side shaft 36, 36a Grips 37, 37a, 37b, 37c, 37d, 37e, 37f Jigger 38, 38a Base 39, 39a, 39b, 39c, 39d Engagement Convex part 40 Engagement piece 41 Column base 42 Engagement part 43 Hollow hole 44 Spline part 45 Sleeve 46 Lauret processing part 47 Center hole 48 Reducer

Claims (29)

A method for manufacturing a linear motion shaft including a first shaft portion, a second shaft portion, and a friction welding portion between the axial end portions of the first shaft portion and the second shaft portion.
By engaging the jig with the engaging portion formed at the axial end on the side opposite to the friction welding portion of the target shaft portion, which is at least one of the first shaft portion and the second shaft portion, the jig is engaged. In a state where the relative rotation between the target shaft portion and the jig is disabled, the target shaft portion is rotationally driven by the jig, or the target shaft portion is prevented from rotating by the jig. A step of friction welding the axial ends of the 1st shaft and the 2nd shaft is provided.
Manufacturing method of linear motion shaft. The engaging portion is a slit that extends in the radial direction of the axial end portion of the target shaft portion opposite to the friction welding portion and opens on the opposite side of the friction welding portion.
The method for manufacturing a linear motion shaft according to claim 1. The method for manufacturing a linear motion shaft according to claim 2, wherein the slits are provided at one or more locations in the circumferential direction of the axial end portion of the target shaft portion opposite to the friction welding portion. The method for manufacturing a linear motion shaft according to claim 2, wherein the slits are provided at two locations on the opposite side in the radial direction at the axial end portion of the target shaft portion on the side opposite to the friction welding portion. The method for manufacturing a linear motion shaft according to claim 2, wherein the slits are provided at four locations at equal intervals in the circumferential direction at the axial end portion of the target shaft portion on the side opposite to the friction welding portion. The axial end of the target shaft portion opposite to the friction welding portion is formed of a tubular portion having a screw hole that opens in the radial direction in the radial center portion, and the slit has the tubular portion in the tubular portion. The method for manufacturing a linear motion shaft according to any one of claims 2 to 5, which is arranged so as to penetrate in the radial direction. The slit has a U-shaped inner surface shape viewed from the radial direction, is located on both sides in the width direction, and has a pair of inner surface surfaces formed of a plane parallel to the axial direction. Engagement with a columnar base, an outer surface shape that projects from the axial side of the base and matches the inner surface shape of the slit, and widthwise side surfaces made of a plane parallel to the axial direction of the base. The method for manufacturing a linear motion shaft according to claim 6, further comprising a convex portion. The slit has a wedge-shaped inner surface shape viewed from the radial direction, is located on both sides in the width direction, and is a pair of inner surfaces composed of planes inclined in a direction away from each other toward the axial opening side of the slit. The jig has a short columnar base portion and an outer surface shape that protrudes from the axial side surface of the base portion and matches the inner surface shape of the slit, and is inclined in a direction that approaches each other toward the tip end side. The method for manufacturing a linear motion shaft according to claim 6, further comprising an engaging convex portion having both side surfaces in the width direction formed of a flat surface. The slit has a wedge-shaped inner surface shape viewed from the axial direction, is located on both sides in the width direction, and has a pair of inner surface surfaces formed of planes that are inclined toward the outward side in the radial direction. The jig has an outer surface shape that matches the inner surface shape of the slit, has a wedge shape, and has both side surfaces in the width direction formed of planes that are inclined in a direction that approaches each other from the outer side in the radial direction to the inner surface in the radial direction. The method for manufacturing a linear motion shaft according to claim 6, further comprising an engaging piece. The slit has a wedge-shaped inner surface shape viewed from the axial direction, is located on both sides in the width direction, and has a pair of inner surface surfaces formed of planes inclined in a direction away from each other toward the outer side in the radial direction. The jig has a cylindrical base portion and an outer surface shape that protrudes radially outward from the outer peripheral surface of the cylindrical base portion and matches the inner surface shape of the slit, has a wedge shape, and is radially outward. The method for manufacturing a linear motion shaft according to claim 6, further comprising an engaging portion having both side surfaces in the width direction formed of planes inclined in a direction in which they approach each other toward the inside in the radial direction. The method for manufacturing a linear motion shaft according to any one of claims 1 to 10, wherein the target shaft portion is provided with a hollow hole penetrating in the axial direction at the center portion in the radial direction. The method for manufacturing a linear motion shaft according to any one of claims 1 to 11, wherein a spline portion is provided on an outer peripheral surface of an axial end portion of the target shaft portion opposite to the friction welding portion. Claim 2 and claims subordinate to claim 2, which regulate the positional relationship between the first shaft portion and the second shaft portion in the rotation direction at the end of the friction welding by utilizing the position of the slit in the rotation direction. Item 2. The method for manufacturing a linear motion shaft according to any one of Items 3 to 12. The linear motion shaft according to any one of claims 1 to 13, wherein the engaging portion is formed by plastic working using the jig as a tool, and at the same time, the jig is engaged with the engaging portion. Manufacturing method. Any one of claims 1 to 14, in which the first shaft portion and the second shaft portion are fitted into the sleeve in the step of friction welding the axial ends of the first shaft portion and the second shaft portion to each other. The method for manufacturing a linear motion shaft according to. The method for manufacturing a linear motion shaft according to any one of claims 1 to 15, wherein the linear motion shaft to be manufactured is for a steering device. It is a linear motion shaft provided with a first shaft portion, a second shaft portion, and a friction welding portion between the axial end portions of the first shaft portion and the second shaft portion.
A jig can be engaged with the axial end portion of the target shaft portion, which is at least one of the first shaft portion and the second shaft portion, on the side opposite to the friction welding portion so as not to rotate relative to each other. Have a joint
Linear axis. The target shaft portion is composed of a screw shaft portion having a ball screw portion on the outer peripheral portion.
The axial end of the ball screw portion opposite to the friction welding portion is an incomplete screw portion, and
A part of the incompletely threaded portion is cut out by the engaging portion.
The linear motion shaft according to claim 17. 17. The described linear motion axis. The linear motion shaft according to claim 19, wherein the slits are provided at one or more locations in the circumferential direction of the axial end portion of the target shaft portion opposite to the friction welding portion. The linear motion shaft according to claim 19, wherein the slits are provided at two locations on the radial end opposite to the friction welding portion of the target shaft portion on the opposite side in the radial direction. The linear motion shaft according to claim 19, wherein the slits are provided at four locations at equal intervals in the circumferential direction at the axial end portion of the target shaft portion on the side opposite to the friction welding portion. The axial end of the target shaft portion opposite to the friction welding portion is formed of a tubular portion having a screw hole that opens in the radial direction in the radial center portion, and the slit has the tubular portion in the tubular portion. The linear motion shaft according to any one of claims 19 to 22, which is arranged so as to penetrate in the radial direction. 23. Linear axis. The slit has a wedge-shaped inner surface shape viewed from the radial direction, is located on both sides in the width direction, and is a pair of inner surfaces composed of planes inclined in a direction away from each other toward the axial opening side of the slit. 23. The linear motion shaft according to claim 23. The slit has a wedge-shaped inner surface shape seen from the axial direction, is located on both sides in the width direction, and has a pair of inner surfaces composed of planes inclined in a direction away from each other toward the outer side in the radial direction. Item 23. The linear motion shaft. The linear motion shaft according to any one of claims 19 to 26, wherein the target shaft portion includes a hollow hole penetrating in the axial direction at the center portion in the radial direction. The linear motion shaft according to any one of claims 19 to 27, wherein a spline portion is provided on an outer peripheral surface of an axial end portion of the target shaft portion opposite to the friction welding portion. The linear motion shaft according to any one of claims 19 to 28, which is for a steering device.

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