JP2021105441A - Rack bar and steering device and rack bar manufacturing method - Google Patents

Abstract

To achieve reduction of the number of components of a steering device and downsizing of the steering device.SOLUTION: A rack bar 10 includes: a flat first flat crushed part 14 provided at a first area A1 of an outer periphery of a hollow shafting 13; a first rack 11 formed at the first flat crushed part 14; a second flat crushed part 15 provided at a second area A2 of the outer periphery of the shafting 13; and a second rack 12 formed at the second flat crushed part 15. At least a part as seen in an axial direction of the first rack 11 and at least a part as seen in the axial direction of the second rack are overlapped with each other while sandwiching a plane P which divides the outer periphery of the shafting 13 into two parts, the first area A1 and the second area A2. A first pinion 3 coupled to a steering shaft 2 is engaged with the first rack 11 and a second pinion 5 which is driven by a first assist motor 4 is engaged with the second rack 12.SELECTED DRAWING: Figure 1

Description

The present invention relates to a rack bar, a steering device, and a method for manufacturing the rack bar.

As a rack bar used for the steering device of vehicles such as automobiles, it has two racks, one rack meshes with the steering pinion of the steering shaft, and the other rack meshes with the auxiliary pinion of the assist motor. Rack bars are known.

Further, as a dual pinion type rack bar, a rack bar in which a hollow first shaft member and a solid second shaft member are joined is also known (see, for example, Patent Document 3). The first shaft member and the second shaft member on which the rack is formed in advance are coaxially arranged with their end faces abutting against each other, and the first shaft member and the second shaft member are subjected to friction welding by relative rotation.

The hollow first shaft member rack is manufactured, for example, as follows. First, a flat crushed portion is formed on the outer peripheral surface of the shaft material by press working. Next, the core metal is press-fitted into the shaft member in a state where the rack tooth mold is pressed against the flattened portion. By repeatedly press-fitting the core metal, the material of the flattened portion plastically flows toward the rack tooth mold, and a rack is formed in the flattened portion. The rack of the solid second shaft member is formed by, for example, cutting.

Japanese Unexamined Patent Publication No. 2006-160113 Japanese Unexamined Patent Publication No. 2013-193704 Japanese Unexamined Patent Publication No. 2014-124767

When the pinion rotates, a force that separates the pinion and the rack from each other acts, and by pressing the rack against the pinion against this separating force, the clearance of meshing is maintained. In the rack bar described in Patent Document 1-3, two racks are separated from each other in the axial direction of the shaft member, and a mechanism for pressing the rack against the pinion is required for each rack.

The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the number of parts of the steering device and to reduce the size.

The rack bar according to one aspect of the present invention is provided in the first region when the outer circumference of the shaft member is divided into a first region and a second region by a plane including the central axis of the shaft member. A first rack composed of a plurality of first rack teeth arranged in the axial direction of the shaft member, and a second rack provided in the second region and composed of a plurality of second rack teeth arranged in the axial direction of the shaft member. , And at least a part of the first rack in the axial direction and at least a part of the second rack in the axial direction overlap with each other with the central axis in between.

Further, the steering device according to one aspect of the present invention includes the rack bar, a first pinion connected to the steering shaft, and a second pinion driven by a first assist motor.

Further, in the method for manufacturing a rack bar according to one aspect of the present invention, the outer periphery of the shaft member is divided into a first region and a second region by a plane including the central axis of the hollow shaft member. A flat first flattening portion extending in the axial direction of the shaft member is provided, and a flat second flattening portion extending in the axial direction of the shaft member is provided in the second region, and the shaft of the shaft member is provided. A first rack tooth mold provided with a plurality of first rack tooth grooves arranged in the direction is pressed against the first flattening portion, and a plurality of second rack tooth grooves provided in the axial direction of the shaft member are provided. By press-fitting the core metal into the shaft member while the two-rack tooth mold is pressed against the second flat-crushed portion, the material of the first flat-crushed portion is plastically directed toward the first rack tooth mold. The first rack is formed in the first flattening portion by flowing, and the material of the second flattening portion is plastically flowed toward the second rack tooth mold to form a second rack in the second flattening portion. The rack is formed, and the first rack tooth mold and the second rack tooth mold are pressed against the first flat crushed portion and the second flat crushed portion, and the first rack tooth groove is arranged. At least a part in the axial direction and at least a part in the axial direction of the arrangement of the second rack tooth grooves overlap each other with the central axis in between.

According to the present invention, the number of parts of the steering device can be reduced and the size can be reduced.

It is a schematic diagram of an example of a steering device for demonstrating the embodiment of this invention. It is a vertical sectional view of the rack bar of the steering apparatus of FIG. It is a cross-sectional view of the rack bar of FIG. It is a vertical cross-sectional view of the modification of the rack bar of FIG. It is a vertical cross-sectional view of another modification of the rack bar of FIG. It is a cross-sectional view of another modification of the rack bar of FIG. It is a schematic diagram of an example of the manufacturing method of the rack bar of FIG. It is a schematic diagram of an example of the manufacturing method of the rack bar of FIG. It is a schematic diagram of an example of the manufacturing method of the rack bar of FIG. It is a schematic diagram of an example of the manufacturing method of the rack bar of FIG. It is a schematic diagram of an example of the arrangement of the 1st pinion and the 2nd pinion which mesh with the 1st rack and the 2nd rack of the rack bar of FIG. It is a schematic diagram of another example of the arrangement of the 1st pinion and the 2nd pinion which mesh with the 1st rack and the 2nd rack of the rack bar of FIG. It is a schematic diagram of another example of a steering apparatus for demonstrating the embodiment of this invention.

FIG. 1 shows an example of a steering device for explaining an embodiment of the present invention.

The vehicle steering device 1 shown in FIG. 1 has a first pinion 3 connected to a vehicle steering shaft 2, a second pinion 5 driven by a first assist motor 4, and a first rack that meshes with the first pinion 3. It includes a rack bar 10 provided with a second rack 12 that meshes with the 11 and the second pinion 5. The ends of the rack bar 10 on both sides in the axial direction are connected to the wheels via ball joints, tie rods, knuckles, and the like.

The rotation operation of the steering handle 7 is transmitted to the first pinion 3 via the steering shaft 2, and the rack bar 10 is moved in the axial direction according to the rotation of the first pinion 3. Further, the steering torque input to the steering shaft 2 is detected by the torque detection unit 6, and the first assist motor 4 drives the second pinion 5 according to the detected steering torque. According to the rotation of the second pinion 5, the movement of the rack bar 10 based on the rotation of the first pinion 3 is assisted.

2 and 3 show the rack bar 10.

The rack bar 10 is a so-called hollow rack bar made of a hollow shaft member 13. Assuming that the outer circumference of the shaft member is divided into a first region A1 and a second region A2 by a plane P including the central axis X of the shaft member 13, the rack bar 10 is a flat first flat extending in the axial direction of the shaft member 13. The crushed portion 14 is provided in the first region A1, and the flat second flat crushed portion 15 extending in the axial direction of the shaft member 13 is provided in the second region A2.

The first rack 11 that meshes with the first pinion 3 is provided in the first flattening portion 14, and has a plurality of first rack teeth 16 formed in the first flattening portion 14. These first rack teeth 16 are arranged in the axial direction of the shaft member 13. The first rack 11 may be a CGR (Constant Gear Ratio) in which the pitch of the first rack teeth 16 is constant, or a VGR (Variable Gear Ratio) in which the pitch changes. Further, the tooth width direction of the first rack tooth 16 may be a direction perpendicular to the axis of the shaft member 13, or a direction in which the tooth width direction is inclined with respect to the axis of the shaft member 13.

The second rack 12 that meshes with the second pinion 5 is provided in the second flattening portion 15, and has a plurality of second rack teeth 17 formed in the second flattening portion 15. These second rack teeth 17 are arranged in the axial direction of the shaft member 13. The second rack 12 may also be a CGR in which the pitch of the second rack teeth 17 is constant, or a VGR in which the pitch changes. Further, the tooth width direction of the second rack tooth 17 may be a direction perpendicular to the axis of the shaft member 13, or a direction in which the tooth width direction is inclined with respect to the axis of the shaft member 13.

At least a part of the first rack 11 in the axial direction and at least a part of the second rack 12 in the axial direction are formed so as to overlap each other with the central axis X in between, and therefore, the axial direction of the first flattening portion 14 is formed. At least a part of the above and at least a part of the second flattening portion 15 in the axial direction are also formed so as to overlap each other with the central axis X in between. In the examples shown in FIGS. 2 and 3, the first flattening portion 14 and the second flattening portion 15 overlap over the entire length in the axial direction, while the partial OP1 in the axial direction of the first rack 11 And a part of OP2 in the axial direction of the second rack 12 overlap. Further, the first flattening portion 14 and the second flattening portion 15 are parallel to each other.

As shown in FIG. 4, the first flattening portion 14 and the second flattening portion 15 overlap each other over the entire length in the axial direction, and the first rack 11 and the second rack 12 have the overall length in the axial direction. It may overlap over. Further, as shown in FIG. 5, a part of the first flattening portion 14 in the axial direction and a part of the second flattening portion 15 in the axial direction overlap each other, and similarly, one part of the first rack 11 in the axial direction. The portion and a part of the second rack 12 in the axial direction may overlap with each other. Further, the first flattening portion 14 and the second flattening portion 15 are not limited to being parallel to each other, and may be inclined to each other as shown in FIG.

7A to 7D show an outline of the manufacturing process of the rack bar 10.

As shown in FIG. 7A, the shaft member 13 as a material is a hollow shaft member having a circular cross section made of steel such as JIS-S45C and JIS-SMn433, and both ends of the shaft member 13 in the axial direction are open. ing. The shaft member 13 is typically subjected to a zinc phosphate film treatment or the like that enhances moldability and corrosion resistance.

<Preliminary molding process>
As shown in FIG. 7B, the first flattening portion 14 is formed in the first region A1 on the outer periphery of the shaft member 13, and the second flattening portion 15 is formed in the second region A2. In the first flattening portion 14, a part of the first flattening portion A1 is flattened by the first flattening punch 20, and a part of the second flattening portion 15 and the second flattening portion A2 is the second flattening portion. It is crushed flat by the crushing punch 21. The first region A1 is crushed to the vicinity of the tooth bottom height of the first rack tooth 16 formed in the next tooth forming step, and the second region A2 is formed in the next tooth forming step. The rack teeth 17 are crushed to the vicinity of the tooth bottom height.

Preferably, the first flattening portion 14 and the second flattening portion 15 are formed so as to overlap each other over the entire length in the axial direction. Further, preferably, the first flattening portion 14 and the second flattening portion 15 are formed in parallel with each other. The stress acting on the shaft member 13 becomes equal with the plane P that divides the outer circumference of the shaft member 13 into the first region A1 and the second region A2, and the molding accuracy of the shaft member 13 in the preforming is improved.

<Tooth molding process>
Next, the first rack 11 is formed in the first flattening portion 14, and the second rack 12 is formed in the second flattening portion 15. First, as shown in FIG. 7C, the first rack tooth mold 22 is pressed against the flat surface of the first flattened portion 14, and the second rack tooth mold 23 is pressed against the flat surface of the second flattened portion 15. The first rack tooth mold 22 has a plurality of first rack tooth grooves 24 arranged in the axial direction of the shaft member 13, and the second rack tooth mold 23 has a plurality of second rack teeth arranged in the axial direction of the shaft member 13. It has a groove 25.

As shown in FIG. 7D, the core metal 26 is press-fitted into the shaft member 13 in a state where the first rack tooth mold 22 and the second rack tooth mold 23 are pressed against the shaft member 13. Then, the core metal 26 to be press-fitted is gradually made larger, and the press-fitting of the core metal 26 is repeated. By repeatedly press-fitting the core metal 26, the material of the first flattening portion 14 plastically flows and enters the plurality of first rack tooth grooves 24 of the first rack tooth mold 22, and the plurality of first rack teeth 16 are formed. It is formed. At the same time, the material of the second flattening portion 15 plastically flows and enters the plurality of second rack tooth grooves 25 of the second rack tooth mold 23 to form the plurality of second rack teeth 17.

As shown in FIG. 2, at least a part of the first rack 11 in the axial direction and at least a part of the second rack 12 in the axial direction overlap each other with the central axis X in between. Therefore, with the first rack tooth mold 22 and the second rack tooth mold 23 pressed against the shaft member 13, at least a part of the arrangement of the plurality of first rack tooth grooves 24 in the axial direction and the plurality of second rack teeth. It overlaps with at least a part of the arrangement of the rack tooth grooves 25 in the axial direction with the central axis X in between.

According to the manufacturing process of the rack bar 10 described above, the first rack teeth 16 and the second rack teeth 17 are formed at the same time, so that the production efficiency is excellent. Since the relative angle between the first rack tooth 16 and the second rack tooth 17 around the central axis X is determined by the mold, the angle accuracy is higher than when the first rack tooth 16 and the second rack tooth 17 are processed in order. Excellent for.

Preferably, the total volume of the first rack teeth 16 included in the overlapping portion OP1 (see FIG. 2) of the first rack 11 and the second rack teeth included in the overlapping portion OP2 (see FIG. 2) of the second rack 12 The difference from the total volume of 17 is −20% to + 20% of the total volume of the first rack teeth 16. By press-fitting the core metal 26, the loads applied to the first flat crushing portion 14 and the second flat crushing portion 15 become substantially equal, and the molding accuracy of the first rack teeth 16 and the second rack teeth 17 is improved. More preferably, the total volume of the first rack teeth 16 included in the overlapping portion OP1 (see FIG. 2) of the first rack 11 and the second rack included in the overlapping portion OP2 (see FIG. 2) of the second rack 12 It is equal to the total volume of the teeth 17. In other words, the total volume of the first rack tooth groove 24 for forming the first rack tooth 16 included in the overlapping portion OP1 and the second for forming the second rack tooth 17 included in the overlapping portion OP2. It is equal to the total volume of the rack tooth grooves 25.

After that, heat treatment for increasing the strength of the first rack 11 and the second rack 12, the first flattening portion 14 and the second flattening portion 15, and the shaft member 13 accompanying the formation of the first rack 11 and the second rack 12 The rack bar 10 is manufactured by appropriately performing processing such as straightening the bending of the rack bar 10 and threading the inner diameter portions of both ends of the rack bar 10.

FIG. 8 shows an arrangement example of the first pinion 3 and the second pinion 5 that mesh with the first rack 11 and the second rack 12.

The first pinion 3 connected to the steering shaft 2 meshes with the first rack 11, and the second pinion 5 driven by the first assist motor 4 meshes with the second rack 12. Then, in response to the rotation operation of the steering handle 7, the first pinion 3 rotates, and at the same time, the second pinion 5 also rotates. Based on the rotation of the first pinion 3, a force that separates the first pinion 3 and the first rack 11 from each other acts, and based on the rotation of the second pinion 5, the second pinion 5 and the second rack 12 separate from each other. Power works.

However, the first pinion 3 and the second pinion 5 are arranged on opposite sides of the rack bar 10 with the rack bar 10 in between. Then, the axial distance between the first pinion 3 and the second pinion 5 is shortened as compared with the case where the first rack 11 and the second rack 12 are separated in the axial direction without overlapping. Therefore, the force that the first pinion 3 and the first rack 11 separate from each other and the force that the second pinion 5 and the second rack 12 separate from each other are effectively offset. As a result, the mechanism for pressing the first rack 11 against the first pinion 3 and the mechanism for pressing the second rack 12 against the second pinion 5 can be omitted.

From the viewpoint of canceling the force that the first pinion 3 and the first rack 11 separate from each other and the force that the second pinion 5 and the second rack 12 separate from each other, the first pinion 3 and the second pinion 5 are , It is preferable that the rack bars 10 are arranged so as to face each other with the rack bar 10 in between.

Here, the rotation axis C1 of the first pinion 3 is parallel to the flat surface of the first flattening portion 14, and is inclined with respect to the central axis X of the shaft member 13. Then, in the example shown in FIG. 8, the rotation axis C2 of the second pinion 5 is parallel to the flat surface of the second flattening portion 15, and the rotation of the first pinion 3 with respect to the central axis X of the shaft member 13. It is inclined in the same direction as the axis C1. In this case, the rolling of the rack bar 10 rotating around the central axis X is suppressed, the tooth meshing is maintained, and the steering feeling is improved.

As shown in FIG. 9, the rotation axis C2 of the second pinion 5 is parallel to the flat surface of the second flattening portion 15, and the rotation of the first pinion 3 with respect to the central axis X of the shaft member 13. It may be inclined in the direction opposite to the axis C1. In this case, it becomes easy to secure a space for installing the first assist motor 4 that drives the second pinion 5.

FIG. 10 shows another example of a steering device for explaining an embodiment of the present invention.

The example shown in FIG. 10 further includes a third pinion 9 driven by a second assist motor 8. The second rack 12 is longer than the first rack 11 and has a non-overlapping portion NOP extending axially beyond the end of the first rack 11, and the third pinion 9 has a third pinion 9 in the non-overlapping portion NOP. 2 It meshes with the rack 12. When the first rack 11 extends in the axial direction beyond the length required for meshing with the first pinion 3, the third pinion 9 is the second rack 12 at the overlapping portion with the first rack 11. May mesh with.

The rack bar 10 is supported at three different locations by meshing with the first pinion 3, meshing with the second pinion 5, and meshing with the third pinion 9. Then, in the axial direction of the shaft member 13, the first pinion 3 that meshes with the first rack 11 is arranged between the second pinion 5 and the third pinion 9 that mesh with the second rack 12. As a result, yawing in which the rack bar 10 rotates around the z-axis is suppressed, and the steering feeling is further improved.

The second assist motor 8 drives the third pinion 9 according to the steering torque input to the steering shaft 2, and assists the movement of the rack bar 10 based on the rotation of the first pinion 3. For example, if the required assist force is obtained by the two motors of the first assist motor 4 and the second assist motor 8, a small motor having excellent responsiveness can be used for the first assist motor 4 and the second assist motor 8. And the response when starting to turn the steering handle 7 can be improved.

Further, the second assist motor 8 can be used as a backup for the first assist motor 4, and when a problem occurs in the first assist motor 4, the second assist motor 8 continues to assist and the steering handle 7 is operated. Can be avoided from suddenly becoming heavy.

Up to this point, the rack bar 10 has been described as being made of a hollow shaft member 13, but a solid shaft member may be used. When the rack bar 10 is made of a solid shaft material, the plurality of first rack teeth constituting the first rack 11 and the plurality of second rack teeth constituting the second rack 12 are formed by, for example, forging, cutting, or the like. Can be formed.

As described above, the rack bar disclosed in the present specification is the first region when the outer circumference of the shaft member is divided into a first region and a second region by a plane including the central axis of the shaft member. A first rack composed of a plurality of first rack teeth arranged in the axial direction of the shaft member, and a plurality of second racks provided in the second region and arranged in the axial direction of the shaft member. A second rack composed of teeth is provided, and at least a part of the first rack in the axial direction and at least a part of the second rack in the axial direction overlap each other with the central axis interposed therebetween.

Further, the rack bar disclosed in the present specification is a combination of the total volume of the first rack teeth included in the overlapping portion of the first rack with the second rack and the first rack in the second rack. It is equal to the total volume of the second rack teeth contained in the overlapping portion.

Further, in the rack bar disclosed in the present specification, the shaft member is a hollow shaft member, and in the first region, a flat first flattened portion extending in the axial direction of the shaft member and the second region. A flat second flattening portion extending in the axial direction of the shaft member is provided, the first rack is formed in the first flattening portion, and the second rack is the second flattening portion. At least a part of the first rack in the axial direction and at least a part of the second rack in the axial direction overlap each other with the central axis in between.

Further, in the rack bar disclosed in the present specification, the first flattening portion and the second flattening portion overlap with each other over the entire length in the axial direction with the plane in between.

Further, the steering device disclosed in the present specification includes the rack bar, a first pinion connected to a steering shaft, and a second pinion driven by a first assist motor.

Further, in the steering device disclosed in the present specification, the first pinion and the second pinion are arranged so as to face each other with the rack bar interposed therebetween.

Further, in the steering device disclosed in the present specification, the rotation axis of the first pinion is tilted with respect to the central axis of the rack bar, and the rotation axis of the second pinion is the central axis of the rack bar. On the other hand, it is tilted to the same side as the rotation axis of the first pinion.

Further, in the steering device disclosed in the present specification, the rotation axis of the first pinion is tilted with respect to the central axis of the rack bar, and the rotation axis of the second pinion is the central axis of the rack bar. On the other hand, it is tilted to the opposite side of the rotation axis of the first pinion.

Further, the steering device disclosed in the present specification includes a third pinion that is driven by a second assist motor and meshes with the second rack of the rack bar.

Further, the method for manufacturing a rack bar disclosed in the present specification is the first region when the outer periphery of the shaft material is divided into a first region and a second region by a plane including the central axis of the hollow shaft material. A flat first flattening portion extending in the axial direction of the shaft member is provided in the second region, and a flat second flattening portion extending in the axial direction of the shaft member is provided in the second region of the shaft member. A first rack tooth mold provided with a plurality of first rack tooth grooves arranged in the axial direction was pressed against the first flattening portion, and a plurality of second rack tooth grooves arranged in the axial direction of the shaft member were provided. With the second rack tooth mold pressed against the second flat tooth mold, the core metal is press-fitted into the shaft material so that the material of the first flat tooth mold is directed toward the first rack tooth mold. The first rack is formed in the first flattening portion by plastic flow, and the material of the second flattening portion is plastically flowed toward the second rack tooth mold to form a second rack in the second flattening portion. Two racks are formed, and in a state where the first rack tooth mold and the second rack tooth mold are pressed against the first flat crushing portion and the second flat crushing portion, the arrangement of the first rack tooth grooves is arranged. At least a part of the axial direction and at least a part of the arrangement of the second rack tooth grooves in the axial direction overlap each other with the central axis in between.

1 Steering device 2 Steering shaft 3 1st pinion 4 1st assist motor 5 2nd pinion 6 Torque detector 7 Steering handle 8 2nd assist motor 9 3rd pinion 10 Rack bar 11 1st rack 12 2nd rack 13 Shaft material 14 1st flat crushing part 15 2nd flat crushing part 16 1st rack tooth 17 2nd rack tooth 20 1st flat crushing punch 21 2nd flat crushing punch 22 1st rack tooth mold 23 2nd rack tooth mold 24 1st rack tooth Groove 25 2nd rack Tooth groove 26 Core metal A1 1st region A2 2nd region C1 Rotation axis of 1st pinion C2 Rotation axis of 2nd pinion OP1 Overlap part of 1st rack OP2 Overlap part of 2nd rack P plane X axis Central axis of material

Claims (10)

When the outer circumference of the shaft member is divided into a first region and a second region by a plane including the central axis of the shaft member,
A first rack provided in the first region and composed of a plurality of first rack teeth arranged in the axial direction of the shaft member,
A second rack provided in the second region and composed of a plurality of second rack teeth arranged in the axial direction of the shaft member, and
With
A rack bar in which at least a part of the first rack in the axial direction and at least a part of the second rack in the axial direction overlap each other with the central axis in between. The rack bar according to claim 1.
The total volume of the first rack teeth included in the overlapping portion with the second rack in the first rack and the total volume of the second rack teeth included in the overlapping portion with the first rack in the second rack. Is equal to a rack bar. The rack bar according to claim 1 or 2.
The shaft material is a hollow shaft material, and the shaft material is a hollow shaft material.
In the first region, a flat first flattening portion extending in the axial direction of the shaft member,
In the second region, a flat second flattened portion extending in the axial direction of the shaft member,
With
The first rack is formed in the first flattened portion, the second rack is formed in the second flattened portion, and at least a part of the first rack in the axial direction and the first rack. A rack bar that overlaps with at least a part of the two racks in the axial direction with the central axis in between. The rack bar according to claim 3.
The first flattening portion and the second flattening portion are rack bars that are overlapped with each other across the central axis over the entire length in the axial direction. The rack bar according to any one of claims 1 to 3 and
The first pinion connected to the steering shaft and
The second pinion driven by the first assist motor,
Steering device equipped with. The steering device according to claim 5.
The first pinion and the second pinion are steering devices arranged so as to face each other with the rack bar interposed therebetween. The steering device according to claim 5 or 6.
The rotation axis of the first pinion is tilted with respect to the central axis of the rack bar.
A steering device in which the rotation axis of the second pinion is inclined to the same side as the rotation axis of the first pinion with respect to the central axis of the rack bar. The steering device according to claim 5 or 6.
The rotation axis of the first pinion is tilted with respect to the central axis of the rack bar.
A steering device in which the rotation axis of the second pinion is inclined to the side opposite to the rotation axis of the first pinion with respect to the central axis of the rack bar. The steering device according to any one of claims 5 to 8.
A steering device including a third pinion that is driven by a second assist motor and meshes with the second rack of the rack bar. When the outer circumference of the shaft member is divided into a first region and a second region by a plane including the central axis of the shaft member, a flat first flattened portion extending in the axial direction of the shaft member is formed in the first region. In addition, a flat second flattening portion extending in the axial direction of the shaft member is provided in the second region.
A plurality of second rack tooth grooves provided with a plurality of first rack tooth grooves arranged in the axial direction of the shaft member are pressed against the first flattening portion, and a plurality of second rack tooth grooves arranged in the axial direction of the shaft member. The material of the first flattening portion is pressed into the inside of the shaft material in a state where the second rack tooth mold provided with the above is pressed against the second flattening portion, so that the material of the first flattening portion is pressed against the first rack tooth. The first rack is formed in the first flattened portion by plastically flowing toward the mold, and the material of the second flattened portion is plastically flowed toward the second rack tooth mold to form the second flat. A second rack is formed on the crushed part,
In a state where the first rack tooth mold and the second rack tooth mold are pressed against the first flattening portion and the second flattening portion, at least one of the arrangement of the first rack tooth grooves in the axial direction. A method for manufacturing a rack bar in which a portion and at least a part of the arrangement of the second rack tooth grooves in the axial direction overlap each other with the central axis interposed therebetween.

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