Rack bar and steering device

Abstract

In the rack bar (2) and steering device using the same according to the present invention, an endmost tooth bottom (225) for reducing stress exerted on a first forging die during die forging of a rack tooth molding part (22) is formed on the endmost side of a plurality of tooth bottoms. Specifically, in the present embodiment, the endmost tooth bottom (225) is formed so that the depth (D2) thereof is less than the depth (D1) of an ordinary tooth bottom (224) by a difference (Dx). The amount of flow of material during formation of the endmost tooth bottom (225) can thereby be reduced by an amount commensurate with the difference (Dx). As a result, stress exerted on the first forging die can be reduced, and the occurrence of heat checking in the first forging die can be suppressed.

Description

[Technical field]

[0001] The present invention relates to a rack bar and a steering device. [Background technology]

[0002] A conventional rack bar is known, for example, from Patent Document 1 below.

[0003] The rack bar described in Patent Document 1 is formed by so-called die forging, in which a solid round bar-shaped material is sandwiched between upper and lower dies and the material is subjected to plastic flow, and has a rack tooth molding portion within a specified axial range of the rack body. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-192681 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the die forging, which is performed by plastically flowing the raw material, when the tooth bottom on the extreme end side of the rack teeth molding portion, which is the end of the plastic flow, is formed, there is a risk that a so-called heat check, such as a crack, may occur in the upper die that forms the rack teeth molding portion. However, in the conventional rack bar, no consideration is given to the heat check.

[0006] The present invention has been devised in view of the above technical problems, and provides a rack bar and a steering device that can suppress heat checking that occurs in a forging die during die forging of the rack bar. [Means for solving the problem]

[0007] In one embodiment of the present invention, an endmost tooth bottom is formed on the endmost side of a plurality of tooth bottoms, which reduces the stress acting on the forging die during die forging. Effect of the Invention

[0008] According to the present invention, it is possible to suppress heat checking that occurs in a forging die during die forging of a rack bar. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of a steering device according to the present invention; [Diagram 2] FIG. 2 is a perspective view of the rack bar shown in FIG. [Diagram 3] 3 is an enlarged view of a main portion of the rack bar shown in FIG. 2 taken along line AA. [Figure 4] 3 is a view seen from the arrow, illustrating a meshing state between the rack bar and the pinion shaft shown in FIG. 2. [Diagram 5] 5A shows a manufacturing method (manufacturing process) of a rack bar according to the present invention, in which (a) shows the state in which a material is set in a forging die, (b) shows the forging process, (c) shows the state in which a forged product has been released from the die, and (d) shows the burr removal process. [Figure 6] 1A and 1B are diagrams showing the results of an analysis of the stress acting on an upper die during die forging of a rack bar, where (a) is a cross-sectional view of a main part of the rack bar according to the present invention, and (b) is a cross-sectional view of a main part of a conventional rack bar. [Figure 7] FIG. 5 is a view corresponding to FIG. 3 and showing a rack bar according to a second embodiment of the present invention. [Figure 8] FIG. 5 is a view corresponding to FIG. 3 and showing a rack bar according to a third embodiment of the present invention. [Figure 9] FIG. 5 is a view corresponding to FIG. 3 and showing a rack bar according to a fourth embodiment of the present invention. [Figure 10] FIG. 10 is a view corresponding to FIG. 3 and illustrating a rack bar according to a fifth embodiment of the present invention. [Figure 11] FIG. 11 is a cross-sectional view of the rack bar shown in FIG. 3 along line BB, showing a sixth embodiment of the rack bar according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of a rack bar and a steering device according to the present invention will be described in detail with reference to the drawings. In each of the following embodiments, the rack bar is applied to a steering device of an automobile, as in the conventional case.

[0011] [First embodiment] (Streering device configuration) FIG. 1 shows an embodiment of a steering device equipped with a rack bar according to the present invention, and is a schematic diagram of the steering device according to the present invention.

[0012] The steering device shown in FIG. 1 includes a steering shaft 1 rotatably connected to a steering wheel SW, and a rack bar 2 connected to the steering shaft 1 via a well-known rack and pinion mechanism and transmitting steering operation to the steered wheels WL, WR by converting the rotational motion of the steering shaft 1 into axial motion.

[0013] The steering shaft 1 includes an input shaft 11 having one end connected to the steering wheel SW so as to be rotatable together with the steering wheel SW, and a pinion shaft 12 as an output shaft having one end connected to the other end of the input shaft 11 via a torsion bar (not shown) so as to be rotatable relative to the input shaft 11 and having the other end connected to a rack bar 2 in meshing engagement. The input shaft 11 is directly connected to the steering wheel SW via a shaft coupling or the like. The pinion shaft 12 has pinion teeth 120 that mesh with rack teeth 20 formed on the rack bar 2 on the outer periphery of the other end side connected to the rack bar 2. In addition, a torque sensor TS is provided between the input shaft 11 and the pinion shaft 12 to detect steering torque, for example, by detecting a change in magnetic flux accompanying the relative rotation of the input shaft 11 and the pinion shaft 12.

[0014] The rack bar 2 has a round bar shape extending linearly along the axis Z direction, and has rack teeth 20 that can mesh with pinion teeth 120 formed in a predetermined region that meshes with the pinion shaft 12 in the axis Z direction. One end and the other end of the rack bar 2 are linked to the left and right steered wheels WR, WL via tie rods 3 and knuckle arms (not shown), respectively. That is, the steering device is configured so that the directions of the left and right steered wheels WR, WL are changed by pulling the knuckle arms (not shown) via tie rods 3 as the rack bar 2 moves in the axial direction.

[0015] The steering device also has a steering assist mechanism that applies a steering assist torque to the rack bar 2 according to the steering torque of the driver based on the detection results of the torque sensor TS and a vehicle speed sensor (not shown) provided on the steering shaft 1. This steering assist mechanism includes a motor unit 4, which is a power source, and a transmission mechanism 5 that transmits the rotation of the motor unit 4 to the rack bar 2. The motor unit 4 is integrally formed with an electric motor 41 and a control device 42 that drives and controls the electric motor 41. The electric motor 41 has a drive shaft 410 that rotates about an axis Zx parallel to the axis Z of the rack bar 2, and the drive shaft 410 is connected to the rack bar 2 via the transmission mechanism 5. The control device 42 is attached to the opposite side of the drive shaft 410 of the electric motor 41, and drives and controls the electric motor 41 based on various detection signals input from the torque sensor TS and the vehicle speed sensor (not shown) and the like.

[0016] The transmission mechanism 5 includes an input pulley 51, an output pulley 52, a ball screw mechanism (not shown), and a belt 53. The input pulley 51 is provided on the outer periphery of the drive shaft 410 of the electric motor 41, and rotates integrally with the drive shaft 410 around the axis Zx. The output pulley 52 is provided on the outer periphery of the rack bar 2 so as to be relatively rotatable, and rotates around the axis Z of the rack bar 2. The ball screw mechanism (not shown) is provided between the output pulley 52 and the rack bar 2, and reduces the speed of the rotation of the output pulley 52 and converts it into axial motion of the rack bar 2. The belt 53 is wound around the input pulley 51 and the output pulley 52, and transmits the rotation of the input pulley 51 to the output pulley 52, thereby rotating the input pulley 51 and the output pulley 52 in synchronization with each other.

[0017] In the steering device according to this embodiment, a rack-assist type electric power steering device that performs steering assist by applying the rotational force of the electric motor 31 to the rack bar 2 is exemplified, but the steering device according to the present invention is not limited to this type. In other words, the steering device according to the present invention may be an electric power steering device having another assist type, such as a pinion assist type that performs steering assist by applying the rotational force of the electric motor 31 to the pinion shaft 12, in addition to the rack assist type.

[0018] The steering device according to the present invention may be an electric power steering device that performs steering assist using the rotational force of the electric motor 31, or may be a power steering device that uses another power source, such as a hydraulic power steering device that performs steering assist using hydraulic pressure. Furthermore, the steering device according to the present invention may be a mode in which the steering shaft 1 (input shaft 11) is directly connected to the steering wheel SW, as exemplified in this embodiment, or may be a mode in which the steering shaft 1 (input shaft 11) is separated from the steering wheel SW (including a mode in which the steering shaft 1 (input shaft 11) can be connected by a clutch not shown), such as steer-by-wire. In addition, the steering device according to the present invention may be a steering device for manual driving in which the driver inputs steering force via the steering wheel SW, or may be a steering device for automatic driving in which the steering force is input from a power source such as an electric motor not shown without the driver's steering operation.

[0019] (Rack bar configuration) Fig. 2 shows a perspective view of the rack bar 2 shown in Fig. 1. In the following description, for convenience, the direction along the axis Z of the rack bar 2 is defined as the "axial direction", the direction perpendicular to the axis Z of the rack bar 2 is defined as the "radial direction", and the direction around the axis Z of the rack bar 2 is defined as the "circumferential direction".

[0020] 2, the rack bar 2 is integrally formed from a metal material (such as S45C, S48C, or an iron-based material). The rack bar 2 has a rack body 21 formed in a generally round bar shape, and a rack tooth molding portion 22 in which rack teeth 20 are formed by die forging in a partial circumferential range of the rack body 21 along the axial direction.

[0021] The rack body 21 corresponds to a portion of the entire rack bar 2 where the rack tooth molding portion 22 is not formed. That is, the rack body 21 has a generally circular cross section in the axial direction in the region where the rack tooth molding portion 22 is not formed, and has a generally D-shaped cross section in the region where the rack tooth molding portion 22 is formed.

[0022] The rack tooth molding portion 22 is formed in a part of the rack body 21 by plastically flowing the metal material through a forging die (not shown) used for die forging, and has a plurality of rack teeth 20 each extending in a direction intersecting the axis Z of the rack bar 2 with a predetermined twist angle and formed in parallel in the axial direction. Specifically, the rack tooth molding portion 22 (the plurality of rack teeth 20) has a plurality of tooth bottoms 221 formed in a concave shape from the outer periphery of the rack body 21 toward the inside in the radial direction, and a plurality of protruding teeth 222 formed between each of the tooth bottoms 221 adjacent to each other in the axial direction.

[0023] The tooth bottoms 221 each have a tooth width W extending in a direction intersecting the axis Z of the rack bar 2 (rack body 21), are arranged in parallel, and have tooth surfaces 223 formed on both axial sides. The protruding teeth 222 are each formed to protrude in a tapered shape toward the radially outer side of the rack body 21.

[0024] Fig. 3 is a cross-sectional view of the rack bar 2 shown in Fig. 2 taken along line AA, and shows an enlarged view of the extreme end of the rack tooth molding portion 22. Fig. 4 shows an arrow view illustrating the meshing state between the rack teeth 20 and the pinion teeth 120 at the axial extreme end of the rack tooth molding portion 22.

[0025] As shown in Fig. 3, the tooth bottoms 221 include a general tooth bottom 224 formed on the axial center side (closer to the center) of each tooth bottom 221 except for the axial end side, and an endmost tooth bottom 225 formed on the axial end side of each tooth bottom 221, in which the stress acting on a forging die (not shown) during die forging is smaller than that of the general tooth bottom 224. Each of the general tooth bottoms 224 is set to a predetermined depth D1 and has a predetermined width W1. The endmost tooth bottom 225 is set to a depth D2 smaller than the general tooth bottom 224 by a difference Dx, has a width W2 equal to the width W1 of the general tooth bottom 224, and is provided at each of the end portions on both axial sides of the rack tooth molding section 22. In addition, this embodiment illustrates an example in which one end-side tooth bottom 225 is provided on each axial side of the rack tooth molding portion 22, but this is not limited to this example, and multiple end-side tooth bottoms 225 may be provided on both axial ends of the rack tooth molding portion 22.

[0026] The tooth flanks 223 are inclined at a predetermined pressure angle θ, and include general tooth flanks 223a formed on both axial sides of the general tooth root 224 and an endmost tooth flank 223b formed on the axial end side of the endmost tooth root 225. As shown in Fig. 4, the general tooth flank 223a meshes with the pinion teeth 120 of the pinion shaft 12, while the endmost tooth flank 223b does not come into contact with the pinion shaft 12. In other words, the endmost tooth root 225 is used to form a so-called dummy tooth portion that does not basically mesh with the pinion teeth 120, and at least the endmost tooth flank 223b does not mesh with the pinion teeth 120.

[0027] 4, grease G is applied to the surfaces of the rack teeth 20 and the pinion teeth 120, and this grease G lubricates the meshing between the rack teeth 20 and the pinion teeth 120. Note that as the rack teeth 20 and the pinion teeth 120 mesh and the pinion shaft 12 moves to the axial end of the rack tooth molding portion 22, this grease G moves from a general tooth bottom 224, which is on the axial center side, to a tooth bottom 225 on the axial end side and is held at the tooth bottom 225 on the axial end side.

[0028] (Manufacturing method of rack bar) FIG. 5 is a cross-sectional view of the rack bar 2 showing the manufacturing method (manufacturing process) of the rack bar 2, where (a) shows the state in which the raw material M1 is set in the forging die, (b) shows the forging process, (c) shows the state in which the forged product M2 has been released from the die, and (d) shows the burr removal process.

[0029] First, the forging die used in manufacturing (die forging) the rack bar 2 will be described with reference to Fig. 5(a). This forging die includes a first forging die FD1, which is a movable die arranged on one side in the circumferential direction of the rack body 21 (material), and a second forging die FD2, which is a fixed die arranged on the opposite side of the first forging die FD1. The first forging die FD1 has a rack forming part 61 used to form the rack tooth forming part 22, and a pair of burr forming parts 62 provided on both sides of the rack forming part 61 and used to form burrs B described later. The second forging die FD2 has a material supporting part 63 having a cross section of a substantially concave semicircular shape corresponding to the outer shape of the material M1, and this material supporting part 63 is used to support the material M1 during die forging.

[0030] To manufacture the rack bar 2 using a forging die consisting of a first forging die FD1 and a second forging die FD2, first, as shown in FIG. 5(a), the first forging die FD1 is raised to set a raw material M1 on the raw material support portion 63 of the second forging die FD2 which has been opened.

[0031] 5(b), the first forging die FD1 is lowered, and the material M1 is pressed and deformed by being sandwiched between the first forging die FD1 and the second forging die FD2, thereby transferring the rack forming portion 61 and performing die forging (forging process). That is, the material M1 is pressed by the rack forming portion 61 of the first forging die FD1, whereby the upper end portion of the material M1 is crushed, and the crushed material plastically flows into the burr forming portions 62 on both axial sides. As a result, the rack forming portion 61 is transferred to form the rack tooth molding portion 22 (rack teeth 20), and a pair of burrs B are formed by the pair of burr forming portions 62.

[0032] Thereafter, as shown in Fig. 5(c), the first forging die FD1 is raised to open the die, and the die-forged forged product M2 is taken out. Finally, as shown in Fig. 5(d), the tip sides of a pair of burrs B formed by the die forging are cut off to form a pair of burr removal portions 226 (burr removal process), and the manufacture of the rack bar 2 is completed.

[0033] (Effects of this embodiment) FIG. 6 shows the analysis results of the stress acting on the first forging die FD1 during die forging of the rack bar 2, where (a) is a cross-sectional view of a main part of the rack bar 2 according to this embodiment, and (b) is a cross-sectional view of a main part of a conventional rack bar 2'.

[0034] According to the die forging of the conventional rack bar 2', as shown in FIG. 6(b), when forming the general tooth bottom 224 on the most end side of the rack tooth forming part 22, which is the end of the plastic flow of the material M1, a relatively large stress acts on the first forging die FD1. Specifically, among the tooth bottom forming parts 611 protrudingly formed on the rack forming part 61 of the first forging die FD1, a relatively large stress acts on the first tooth surface forming part 611a which is used to form the tooth surface (general tooth surface 223a) on the opposite end side of the general tooth bottom 224 on the most end side (see the dark color part P in FIG. 6(b)). As a result, there is a risk that a so-called heat check, such as a crack, may occur in the first tooth surface forming part 611a of the first forging die FD1. However, in the conventional rack bar 2', the heat check is not taken into consideration at all.

[0035] In contrast, the rack bar 2 according to this embodiment is a rack bar that is formed by die forging and that transmits steering operation to the steered wheels WR, WL by converting the rotational motion of the pinion shaft 12, which rotates in conjunction with the steering wheel SW, into axial motion, and includes a rack body 21 formed in a rod shape from a metallic material, and a rack tooth molding portion 22 formed in the rack body 21 by plastically flowing the metallic material through forging dies (first forging die FD1 and second forging die FD2) used for the die forging, the rack tooth molding portion 22 having a tooth bottom 221, a protruding tooth 222, and a tooth surface 223, the tooth bottom 221 including a plurality of tooth bottoms formed in a concave shape from the outer periphery of the rack body 21 toward the radially inward side, and the plurality of tooth bottoms each having a concave shape extending from the outer periphery of the rack body 21 toward the radially inward side. The protruding teeth 222 are formed between the plurality of tooth bottoms adjacent to each other in the axial direction and protrude in a tapered shape toward the radial outside of the rack body 21. The tooth surfaces 223 are formed on both sides of the plurality of tooth bottoms in the axial direction, and the tooth surface (the endmost tooth surface 223b) of the rack body 21 at the end of the axial direction does not come into contact with the pinion shaft 12.

[0036] In other words, the steering device according to this embodiment is a steering device including a pinion shaft 12 that rotates in conjunction with a steering wheel SW, and a rack bar 2 that is formed by die forging and that transmits a steering operation to the steered wheels WR, WL by converting the rotational motion of the pinion shaft 12 into axial motion, and the rack bar 2 includes a rack body 21 that is formed in a rod shape from a metal material, and a rack tooth molding portion 22 that is formed on the rack body 21 by plastically flowing the metal material through a forging die (a first forging die FD1 and a second forging die FD2) used for the die forging, and the rack tooth molding portion 22 has a tooth bottom 221, a protruding tooth 222, and a tooth surface 223, and the tooth bottom 221 includes a plurality of tooth bottoms that are formed in a concave shape from the outer periphery of the rack body 21 toward the inside in the radial direction, and The multiple tooth bottoms each have a tooth width W extending in a direction intersecting the axis Z of the rack body 21 and are formed in parallel to each other. Among the multiple tooth bottoms, there is a general tooth bottom 224 formed at the center side of the axial direction of the rack body 21, and an end-side tooth bottom 225 formed at the end-most side of the multiple tooth bottoms in the axial direction, and the stress acting on the forging die during the die forging is smaller than that of the general tooth bottom 224. The protruding tooth 222 is formed between the multiple tooth bottoms adjacent to each other in the axial direction and is formed to protrude in a tapered shape toward the radial outside of the rack body 21. The tooth surfaces 223 are formed on both sides of the multiple tooth bottoms in the axial direction, and the tooth surface at the end-most side of the rack body 21 in the axial direction (end-most tooth surface 223b) does not abut against the pinion shaft 12.

[0037] In this way, in the rack bar 2 according to this embodiment and the steering device using the same, an end-side tooth bottom 225 is formed on the end-most side of the multiple tooth bottoms, which reduces the stress acting on the first forging die FD1 when die-forging the rack tooth molding portion 22. Specifically, in this embodiment, the depth D2 of the end-side tooth bottom 225 is formed shallower than the depth D1 of the general tooth bottom 224.

[0038] In this manner, in this embodiment, the depth D2 of the endmost tooth bottom 225 is formed shallower than the depth D1 of the general tooth bottom 224 by the difference Dx. This makes it possible to reduce the amount of material flow when forming the endmost tooth bottom 225 by the difference Dx. As a result, as shown in Fig. 6(a), the stress acting on the first tooth surface forming portion 611a of the first forging die FD1 can be reduced, and the occurrence of the heat check in the first tooth surface forming portion 611a of the first forging die FD1 can be suppressed.

[0039] Furthermore, in this embodiment, the rack tooth molding portion 22 has one end-side tooth bottom 225 shallower than the depth D1 of the general tooth bottom 224 at each end in the axial direction.

[0040] In this manner, in this embodiment, one end-side tooth bottom 225 is provided on each of both axial ends of the rack tooth molding portion 22. This makes it possible to reduce the size of the rack tooth molding portion 22 compared to a case in which a plurality of end-side tooth bottoms 225 are provided, and thus makes it possible to miniaturize the rack bar 2.

[0041] In this embodiment, grease G is held at the end-most tooth bottom 225 .

[0042] In this manner, the grease G is held at the end-most tooth bottom 225 that is not used for meshing with the pinion teeth 120. This allows the oil content of the grease G held at the end-most tooth bottom 225 to flow (seep out) to the general tooth bottom 224, thereby enabling lubrication between the general tooth surface 223a connected to the general tooth bottom 224 and the pinion teeth 120.

[0043] [Second embodiment] 7 shows a second embodiment of the rack bar and steering device according to the present invention. Note that this embodiment is obtained by changing the configuration of the end-most tooth bottom 225 in the first embodiment, and other configurations are the same as those in the first embodiment. Therefore, the same reference numerals are used to denote the same configurations as in the first embodiment, and description thereof will be omitted.

[0044] (Rack bar configuration) As shown in Figure 7, in the rack bar and steering device of this embodiment, the endmost tooth bottom 225 and the general tooth surface 223a connected to one axial side (opposite end side) of the endmost tooth bottom 225, and the endmost tooth surface 223b connected to the other axial side (end side) of the endmost tooth bottom 225 are connected by a chamfered portion, a radius portion 226a having an arc-shaped longitudinal section.

[0045] That is, in this embodiment, the amount of material removed in forming the endmost tooth bottom 225, i.e., the amount of flow of the material M1 in forming the endmost tooth bottom 225, is formed to be less than the general tooth bottom 224 by the amount of the rounded portion 226a. In other words, the rounded portion 226a forms the remaining material portion M remaining on both axial sides of the endmost tooth bottom 225 to be greater than the general tooth bottom 224 (see the virtual line in FIG. 7).

[0046] The R portion 226a illustrated in this embodiment shows a preferred embodiment of the chamfered portion formed between the endmost tooth bottom 225 and the general tooth bottom 224, and between the endmost tooth bottom 225 and the endmost tooth surface 223b. In other words, the chamfered portion formed between the endmost tooth bottom 225 and the general tooth bottom 224, and between the endmost tooth bottom 225 and the endmost tooth surface 223b is not limited to the R portion 226a illustrated in this embodiment, and may be formed by a chamfered portion 226b consisting of a flat inclined surface, such as a so-called C-chamfer.

[0047] (Effects of this embodiment) As described above, in the rack bar and steering device of this embodiment, a radius portion 226a (or a chamfered portion 226b) is formed between the end-most tooth bottom 225 and the tooth surface (general tooth surface 223a) connected to one axial side of the end-most tooth bottom 225, and between the end-most tooth bottom 225 and the tooth surface (end-most tooth surface 223b) connected to the other axial side of the end-most tooth bottom 225.

[0048] In this manner, in this embodiment, the rounded portion 226a (or the chamfered portion 226b) is formed between the endmost tooth bottom 225 and the general tooth surface 223a and the endmost tooth surface 223b, which are tooth surfaces connected to the endmost tooth bottom 225. As a result, the amount of material removed for forming the endmost tooth bottom 225, that is, the flow amount of the material M1 for forming the endmost tooth bottom 225, is smaller than that of the general tooth bottom 224 by the amount of the rounded portion 226a. As a result, during die forging of the rack tooth forming portion 22, the surface pressure acting on the corner portion 611b (see FIG. 6(a)) of the tooth bottom forming portion 611 of the first forging die FD1 can be reduced. This makes it possible to suppress the action of local stress on the first forging die FD1 (the corner portion 611b of the tooth bottom forming portion 611) during the formation of the endmost tooth bottom 225, and the occurrence of the heat check in the first forging die FD1 can be suppressed.

[0049] [Third embodiment] 8 shows a rack bar and a steering device according to a third embodiment of the present invention. Note that this embodiment is obtained by changing the configuration of the end-most tooth bottom 225 in the first embodiment, and other configurations are the same as those in the first embodiment. Therefore, the same reference numerals are used to denote the same configurations as those in the first embodiment, and description thereof will be omitted.

[0050] (Rack bar configuration) As shown in FIG. 8, in the rack bar and steering device according to this embodiment, the width W2, which is the length of the end-most tooth bottom 225, is formed larger than the width W1, which is the length of the general tooth bottom 224, in the axial direction.

[0051] In this embodiment, the depth D2 of the endmost tooth bottom 225 is set to be greater than the depth D1 of the general tooth bottom 224, but is not limited to this embodiment. In other words, according to the present invention, it is sufficient that the width W2 of the endmost tooth bottom 225 is greater than the width W1 of the general tooth bottom 224, and the depth D2 of the endmost tooth bottom 225 may be the same as the depth D1 of the general tooth bottom 224, or may be smaller than the depth D1 of the general tooth bottom 224.

[0052] (Effects of this embodiment) As described above, in the rack bar and steering device according to this embodiment, the length (width W2) of the end-most tooth bottom 225 is formed to be greater than the length (width W1) of the general tooth bottom 224 in the axial direction.

[0053] In this manner, by setting the width W2 of the endmost tooth bottom 225 larger than the width W1 of the general tooth bottom 224, it is possible to reduce the surface pressure acting on the tooth tip 611b (see FIG. 6(a)) of the tooth bottom forming portion 611 of the first forging die FD1 during die forging of the rack tooth forming portion 22. This makes it possible to suppress the action of local stress on the first forging die FD1 (corner portion 611b of the tooth bottom forming portion 611) during formation of the endmost tooth bottom 225, and thus suppress the occurrence of the heat check in the first forging die FD1.

[0054] In addition, in this embodiment, the general tooth surface 223a and the endmost tooth surface 223b are connected to the endmost tooth bottom 225 by the corner portion 225a, but the present invention is not limited to this. In other words, in the present invention, it is sufficient that the width W2 of the endmost tooth bottom 225 is set larger than the width W1 of the general tooth bottom 224, and for example, as shown in Fig. 9, the general tooth surface 223a and the endmost tooth surface 223b are connected to the endmost tooth bottom 225 by the radius portion 226a as disclosed in the second embodiment.

[0055] [Fourth embodiment] 10 shows a fourth embodiment of the rack bar and steering device according to the present invention. Note that this embodiment is obtained by modifying the configuration of the end-most tooth bottom 225 in the first embodiment, and other configurations are the same as those in the first embodiment. Therefore, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0056] (Rack bar configuration) As shown in Fig. 10, in the rack bar and steering device according to this embodiment, the angle θ2 between the most end side tooth bottom 225 and the general tooth surface 223a connected to one axial side (opposite the most end side) of the most end side tooth bottom 225, and the angle θ2 between the most end side tooth bottom 225 and the most end side tooth surface 223b connected to the other axial side (the most end side) of the most end side tooth bottom 225 are formed larger than the angle θ1 between the general tooth bottom 224 and the general tooth surface 223a (see the imaginary line in Fig. 10) connected to the general tooth bottom 224. In other words, in this embodiment, the length L2 of the general tooth surface 223a and the most end side tooth surface 223b connected to the most end side tooth bottom 225 is configured to be longer than the length L1 of the general tooth surface 223a connected to the general tooth bottom 224.

[0057] In this embodiment, the depth D2 of the endmost tooth bottom 225 is set to be greater than the depth D1 of the general tooth bottom 224, and the depth W2 of the endmost tooth bottom 225 is set to be greater than the depth W1 of the general tooth bottom 224, but this is not limited to this embodiment. In other words, according to the present invention, the angle θ2 between the general tooth surface 223a and the endmost tooth surface 223b connected to the endmost tooth bottom 225 is formed to be greater than the angle θ1 between the general tooth surface 223a connected to the general tooth bottom 224, and the depth D2 and width W2 of the endmost tooth bottom 225 may be the same as the depth D1 and width W1 of the general tooth bottom 224, or may be smaller than the depth D1 and width W1 of the general tooth bottom 224.

[0058] (Effects of this embodiment) As described above, in the rack bar and steering device of this embodiment, the angle θ2 between the end-most tooth bottom 225 and the tooth surface (general tooth surface 223a) connected to one axial side (opposite end-most side) of the end-most tooth bottom 225, and the angle θ2 between the end-most tooth bottom 225 and the tooth surface (general tooth surface 223b) connected to the other axial side (end-most side) of the end-most tooth bottom 225 are formed larger than the angle θ1 between the general tooth bottom 224 and the tooth surface (general tooth surface 223a) connected to the general tooth bottom 224.

[0059] In this manner, in this embodiment, the angle θ2 between the endmost tooth bottom 225 and the general tooth surface 223a and the endmost tooth surface 223b, which are tooth surfaces connected to the endmost tooth bottom 225, is formed to be larger than the angle θ1 between the general tooth bottom 224 and the general tooth surface 223a, which is a tooth surface connected to the general tooth bottom 224. This makes it possible to form the length L2 of the general tooth surface 223a and the endmost tooth surface 223b connected to the endmost tooth bottom 225 to be longer than the length L1 of the general tooth surface 223a connected to the general tooth bottom 224. As a result, during die forging of the rack tooth forming portion 22, the surface pressure acting on the tooth surface 611c (see FIG. 6(a)) of the tooth bottom forming portion 611 of the first forging die FD1 can be reduced. This makes it possible to suppress the action of local stress on the first forging die FD1 (tooth surface 611c of the bottom forming portion 611) when forming the endmost tooth bottom 225, thereby suppressing the occurrence of heat checking in the first forging die FD1.

[0060] [Fifth embodiment] 11 shows a fifth embodiment of the rack bar and steering device according to the present invention. Note that this embodiment is obtained by modifying the configuration of the end-most tooth bottom 225 in the first embodiment, and other configurations are the same as those in the first embodiment. Therefore, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0061] (Rack bar configuration) As shown in FIG. 11, in the rack bar and steering device according to this embodiment, the depth D2 of the most end tooth bottom 225 of the rack tooth molding portion 22 is formed to be variable in a direction intersecting the axis Z of the rack body 21. Specifically, at one end in the width direction (right side in FIG. 11) that meshes with the pinion teeth (not shown), the depth of the most end tooth bottom 225 is formed to be relatively large in order to ensure meshing with the pinion teeth. On the other hand, at the other end in the width direction (left side in FIG. 11) that does not mesh with the pinion teeth (not shown), the depth of the most end tooth bottom 225 is formed to be relatively small. As a result, the depth D2 of the most end tooth bottom 225 is configured to be upwardly inclined from one end to the other end in the width direction, that is, the distance S to the tooth tip 222a of the protruding tooth 222 gradually becomes smaller.

[0062] (Effects of this embodiment) As described above, in the rack bar and steering device according to this embodiment, the depth D2 of the end-most tooth bottom 225 is formed to be variable in the direction intersecting the axis Z of the rack body 21.

[0063] In this manner, in this embodiment, the depth D2 of the most end tooth bottom 225 is changed between the region meshing with the pinion shaft 12 (pinion teeth 120) and the region not meshing with the pinion shaft 12 (pinion teeth 120). Specifically, the depth D2 of the most end tooth bottom 225 is relatively large at one end in the width direction where the pinion teeth 120 are meshed, and the depth D2 of the most end tooth bottom 225 is relatively small at the other end in the width direction where the pinion teeth 120 are not meshed. For this reason, it is possible to suppress the flow amount of the material M1 at the most end tooth bottom 225 when the rack bar 2 is die forged to the minimum necessary. As a result, the heat check occurring in the first forging die FD1 during die forging of the rack bar 2 can be suppressed.

[0064] The present invention is not limited to the configurations of the above-described embodiments, and can be freely modified according to the specifications of the rack bar 2 and the steering device to which the rack bar 2 is applied.

Claims

1. A rack bar formed by die forging, which transmits steering operation to steered wheels by converting the rotational motion of a pinion shaft that rotates in conjunction with a steering wheel into axial motion, A rack body formed into a rod shape from a metal material; a rack tooth forming portion formed on the rack body by plastically flowing the metal material through a forging die used in the die forging; Equipped with The rack tooth molding portion has a tooth bottom, a protruding tooth, and a tooth surface, The tooth bottom includes a plurality of tooth bottoms formed in a concave shape from an outer periphery of the rack body toward a radially inward direction, The plurality of tooth bottoms each have a tooth width extending in a direction intersecting the axis of the rack body, and are formed in parallel to each other. The plurality of tooth bottoms include a general tooth bottom formed on the central side of the axial direction of the rack body, and an end-most tooth bottom formed on the end-most side of the axial direction of the rack body, and the stress acting on the forging die during the die forging is smaller than that of the general tooth bottom. The protruding teeth are formed between the plurality of tooth bottoms adjacent to each other in the axial direction, and are formed to protrude in a tapered shape toward a radially outer side of the rack body, the tooth surfaces are formed on both sides of the plurality of tooth bottoms in the axial direction, and the tooth surfaces on the axial end side of the rack body do not come into contact with the pinion shaft, The depth of the tooth bottom on the end side is variable in a direction intersecting with the axis of the rack body. A rack bar characterized by:

2. 2. The rack bar according to claim 1, The depth of the tooth bottom on the end side is formed to be shallower than the depth of the general tooth bottom. A rack bar characterized by:

3. 3. The rack bar according to claim 2, The end-most tooth bottoms, which are shallower than the depth of the general tooth bottoms, are provided on both ends of the rack tooth molding portion in the axial direction. A rack bar characterized by:

4. 2. The rack bar according to claim 1, Grease is held at the tooth bottom on the end side. A rack bar characterized by:

5. 2. The rack bar according to claim 1, In the axial direction, the length of the tooth bottom on the end side is formed to be larger than the length of the general tooth bottom. A rack bar characterized by:

6. 2. The rack bar according to claim 1, A radiused portion or a chamfered portion is formed between the endmost tooth bottom and the tooth surface connected to one axial side of the endmost tooth bottom, and between the endmost tooth bottom and the tooth surface connected to the other axial side of the endmost tooth bottom. A rack bar characterized by:

7. 2. The rack bar according to claim 1, The angle between the endmost tooth bottom and the tooth surface connected to one axial side of the endmost tooth bottom, and the angle between the endmost tooth bottom and the tooth surface connected to the other axial side of the endmost tooth bottom are formed larger than the angle between the general tooth bottom and the tooth surface connected to the general tooth bottom. A rack bar characterized by:

8. A pinion shaft that rotates in conjunction with the steering wheel; a rack bar formed by die forging and configured to convert the rotational motion of the pinion shaft into axial motion to transmit steering operation to the steered wheels; A steering device comprising: The rack bar is A rack body formed into a rod shape from a metal material; a rack tooth forming portion formed on the rack body by plastically flowing the metal material through a forging die used in the die forging; Equipped with The rack tooth molding portion has a tooth bottom, a protruding tooth, and a tooth surface, The tooth bottom includes a plurality of tooth bottoms formed in a concave shape from an outer periphery of the rack body toward a radially inward direction, The plurality of tooth bottoms each have a tooth width extending in a direction intersecting the axis of the rack body, and are formed in parallel to each other. The plurality of tooth bottoms include a general tooth bottom formed on the central side of the axial direction of the rack body, and an end-most tooth bottom formed on the end-most side of the axial direction of the rack body, and the stress acting on the forging die during the die forging is smaller than that of the general tooth bottom. The protruding teeth are formed between the plurality of tooth bottoms adjacent to each other in the axial direction, and are formed to protrude in a tapered shape toward a radially outer side of the rack body, the tooth surfaces are formed on both sides of the plurality of tooth bottoms in the axial direction, and the tooth surfaces on the axial end side of the rack body do not come into contact with the pinion shaft, The depth of the tooth bottom on the end side is variable in a direction intersecting with the axis of the rack body. A steering device characterized by:

9. 9. The steering device according to claim 8, The depth of the tooth bottom on the end side is formed to be shallower than the depth of the general tooth bottom. A steering device characterized by:

10. 10. The steering device according to claim 9, The end-most tooth bottoms, which are shallower than the depth of the general tooth bottoms, are provided on both ends of the rack tooth molding portion in the axial direction. A steering device characterized by:

11. 9. The steering device according to claim 8, Grease is held at the tooth bottom on the end side. A steering device characterized by:

12. 9. The steering device according to claim 8, In the axial direction, the length of the tooth bottom on the end side is formed to be larger than the length of the general tooth bottom. A steering device characterized by:

13. 9. The steering device according to claim 8, A radiused portion or a chamfered portion is formed between the endmost tooth bottom and the tooth surface connected to one axial side of the endmost tooth bottom, and between the endmost tooth bottom and the tooth surface connected to the other axial side of the endmost tooth bottom. A steering device characterized by:

14. 9. The steering device according to claim 8, The angle between the endmost tooth bottom and the tooth surface connected to one axial side of the endmost tooth bottom, and the angle between the endmost tooth bottom and the tooth surface connected to the other axial side of the endmost tooth bottom are formed larger than the angle between the general tooth bottom and the tooth surface connected to the general tooth bottom. A steering device characterized by:

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