How to polish the rack bar

Abstract

To provide a rack bar polishing method which enables reduction of friction resistance with a bearing member in a steering device.SOLUTION: The invention relates to a polishing method of a rack bar. The rack bar may slide relative to a bearing member supporting the rack bar when the rack bar is incorporated into a steering device, includes a shaft material, and has a rack part provided at the shaft material and formed with a rack which engages with a pinion, and a slide contact surface which slidably contacts with the bearing member. In the polishing method of the rack bar, the slide contact surface is polished by a polishing material so that a polishing direction is set along an axial direction of the rack bar.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a method for polishing a rack bar. [Background technology]

[0002] The rack bar is used as a component of a rack-and-pinion steering device mounted on, for example, an automobile, and includes a rack portion on which a rack having a plurality of teeth that mesh with a pinion is formed.

[0003] In manufacturing rack bars used in such rack-and-pinion steering devices, the rack is typically formed by pressing a die against a cylindrical or columnar steel material, and then heat treatment (hardening) is performed to increase the strength of the rack (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-66020 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the method described in Patent Document 1, when the rack is heat-treated (quenched), an oxide film is formed on the surface of the rack bar by the heat treatment, which causes unevenness on the surface of the rack bar.

[0006] Typically, in a steering device, the rack bar is supported by bearing members such as a support yoke that supports the opposite side in the thickness direction (described later) of the rack portion, and rack bushes that support both ends. When the pinion rotates by operating a steering shaft connected to the pinion, the rack bar moves along its axial direction. At this time, the rack bar moves while sliding against the bearing members (hereinafter, the surface of the rack bar that is supported by the bearing members is referred to as the "sliding surface").

[0007] Due to the drive mechanism of the steering device as described above, the bearing member may be worn due to sliding contact with the sliding surface of the rack bar, and therefore it is preferable that the friction resistance between the sliding surface of the rack bar and the bearing member is small.

[0008] In view of the above circumstances, an object of the present invention is to provide a rack bar polishing method for manufacturing a rack bar capable of reducing frictional resistance with a bearing member in a steering device. [Means for solving the problem]

[0009] In the method for polishing a rack bar according to the present invention, the rack bar is slidable relative to a bearing member that supports the rack bar when the rack bar is incorporated into the steering device, and includes a shaft member, the shaft member having a rack portion on which a rack that meshes with a pinion is formed, and a sliding contact surface that is in sliding contact with the bearing member, The sliding surface is polished with an abrasive so that the polishing direction is along the axial direction of the rack bar.

[0010] With this configuration, due to the grinding direction as described above, grinding marks are formed on the surface of the sliding surface along the axial direction of the rack bar. In other words, the direction of the grinding marks is along the direction of movement of the rack bar. Therefore, it is possible to reduce the friction resistance between the sliding surface of the rack bar and the bearing member.

[0011] In the method for grinding a rack bar according to the present invention, it is preferable to grind the sliding surfaces located on opposite sides facing each other in a thickness direction of the rack portion.

[0012] Here, in the steering device, the rack bar is supported by a bearing member called a support yoke at a sliding contact surface located on the opposite side facing the thickness direction of the rack part. This support yoke is usually biased toward the rack bar by a spring member or the like. For this reason, frictional resistance is relatively likely to occur between the support yoke and the sliding contact surface. In contrast, according to the above polishing method, the direction of the polishing marks formed on the surface of the sliding contact surface that slides against the support yoke is along the direction of movement of the rack bar, so that the frictional resistance can be reduced more effectively.

[0013] In addition, in the method for polishing a rack bar according to the present invention, As the abrasive material, a rotating grindstone that is disk-shaped and can rotate in a circumferential direction and has abrasive grains on the rotating outer peripheral surface is used, It is preferable to rotate the rotating grindstone so that the outer peripheral surface is aligned along the axial direction of the rack bar, and to grind the sliding surface with the outer peripheral surface while moving at least one of the rotating grindstone or the rack bar along the axial direction.

[0014] According to this configuration, the outer peripheral surface of the grinding wheel having abrasive grains (the grinding surface of the grinding wheel) is rotated along the axial direction of the rack bar, and the sliding surface is polished by the outer peripheral surface while moving at least one of the grinding wheel and the rack bar along the axial direction, so that both the rotation direction (the direction of polishing by rotating) of the outer peripheral surface (polishing surface) of the grinding wheel and the movement direction (the direction of polishing by moving) of the outer peripheral surface are along the movement direction of the rack bar. Therefore, polishing marks are more likely to be formed on the surface of the sliding surface along the axial direction of the rack bar. Therefore, the frictional resistance between the sliding surface of the rack bar and the bearing member can be further reduced. Effect of the Invention

[0015] As described above, according to the present invention, it is possible to provide a rack bar polishing method for manufacturing a rack bar that is capable of reducing frictional resistance with bearing members in a steering device. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram showing a steering device. [Diagram 2] FIG. 2 is a schematic side view of the rack bar. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] FIG. 5 is a diagram showing a surface to be polished that is located on the opposite side in the thickness direction of the rack portion. [Figure 6] FIG. 6 is a schematic diagram showing the outer circumferential surface of a grinding wheel. [Figure 7] FIG. 7 is a diagram showing the positional relationship between the rack bar and the abrasive in the rack bar abrasive grinding method of one embodiment, as viewed from a direction perpendicular to the axial direction of the rack bar. [Figure 8] FIG. 8 is a view of the rack bar in FIG. 7 as viewed from one axial side. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a method for grinding a rack bar according to one embodiment of the present invention will be described with reference to the drawings. Hereinafter, the axial direction of the rack bar may be referred to as the axial direction X (longitudinal direction). The horizontal direction perpendicular to the axial direction X may be referred to as the width direction Y (first short direction). The vertical direction perpendicular to each of the axial direction X and the width direction Y may be referred to as the thickness direction Z (second short direction). The cross section (YZ plane) of the rack bar perpendicular to the axial direction X may be referred to as the transverse section.

[0018] First, with reference to FIGS. 1 to 4, a rack bar 1 polished by the polishing method of the present embodiment will be described while showing a steering device 100 in which the rack bar 1 is used.

[0019] 1, the steering device 100 is a rack-and-pinion type steering device 100. The steering device 100 includes a pinion 2 connected to a steering shaft of a vehicle or the like, a rack bar 1 on which a rack 11a meshing with the pinion 2 is formed, and a bearing member 3 supporting the rack bar 1.

[0020] The rack bar 1 includes a shaft member 10. The shaft member 10 has a rack portion 11 in which a rack 11a is formed, and a sliding contact surface 13 which is the surface of the shaft member 10 and comes into sliding contact with the bearing member 3.

[0021] The rack bar 1 is manufactured from, for example, a solid (cylindrical) steel material or a hollow (cylindrical) steel material. Examples of such steel materials include carbon steel materials for machine structures as specified in JIS 4051:2016. Among these, S45C steel materials are preferred.

[0022] As shown in Figs. 1 and 2, the rack 11a is composed of a plurality of teeth 111 formed such that tooth tips 113 extend along the width direction Y (a direction perpendicular to the paper surface in Figs. 1 and 2). The teeth 111 are arranged, for example, at equal intervals along the axial direction X. The teeth 111 also form a plurality of grooves 112 between which the teeth of the pinion 2 can be inserted and removed. With this configuration, the rack bar 1 in the steering device 100 moves along the axial direction X in accordance with the rotation of the pinion 2 meshed with the rack 11a. At this time, the rack bar 1 moves so as to slide relative to the bearing member 3, and the sliding contact surface 13 comes into sliding contact with the bearing member 3.

[0023] The rack bar 1 has, as the sliding surface 13, a tooth back sliding surface 13a located on the opposite side facing the thickness direction Z of the rack portion 11, and both end sliding surfaces 13b located on both end portions where the rack 11a is not yet formed. As shown in Figures 3 and 4, in the cross section, the shape of the surface 131a of the tooth back sliding surface 13a is, for example, an arc shape. Also, in the cross section, the shape of the surface 131b of the both end sliding surfaces 13b is, for example, a circle shape.

[0024] In the steering device 100, the rack bar 1 is supported at its tooth back sliding surface 13a by a bearing member 31 called a support yoke, and at its both end sliding surfaces 13b by bearing members 32 called rack bushes. The bearing members 3 are usually made of a resin material.

[0025] In the steering device 100, the support yoke 31 is formed in a shape that covers the surface 131a of the tooth back sliding surface 13a from below. The support yoke 31 has a support surface on which the tooth back sliding surface 13a is placed, and supports the rack bar 1 with the support surface and the surface 131a in contact with each other.

[0026] Moreover, in the steering device 100, the rack bush 32 is formed in a shape that covers the surfaces 131b of the sliding contact surfaces 13b at both ends in the circumferential direction CY1 of the rack bar 1. The rack bush 32 has an inner circumferential surface that covers the sliding contact surfaces 13b at both ends in the circumferential direction CY1, and supports the rack bar 1 with the inner circumferential surface and the surface 131b in contact with each other.

[0027] 3 and 4, in the cross section, the diameter of the arc drawn by the surface 131a of the tooth back contact surface 13a and the diameter of the circle drawn by the surface 131b of the both end contact surfaces 13b are substantially the same. If these diameters are R1, the diameter R1 is, for example, 22 mm to 37 mm. The diameter R1 can be calculated by measuring the circumference at any five points on the both end contact surfaces 13b to calculate the average circumference C1, and then using the following formula (1). The value of pi is 3.14. R1=C1 / Pi...(1)

[0028] The tooth back contact surface 13a has a central angle θ1 of, for example, 170° in a cross section (YZ plane) of the arc described by the surface 131a. The central angle θ1 can be calculated by measuring the circumference at any five points on the tooth back contact surface 13a to calculate an average circumference C2, and then using the following formula (2). θ1=C2 / C1×360° (2)

[0029] The steering device 100 is configured such that the rack bar 1 moves along the axial direction X while sliding against the bearing member 3, and as a result, the sliding surface 13 comes into sliding contact with the mounting surface and the inner peripheral surface of the bearing member 3.

[0030] Next, a method for grinding the rack bar 1 of this embodiment will be described with reference to FIGS.

[0031] In the polishing method of this embodiment, an untreated rack bar 1a (a workpiece after heat treatment (hardening)) having an oxide film formed on its surface through a heat treatment such as high-frequency induction heating is polished with an abrasive 4 to obtain a treated rack bar 1b. At this time, as shown in Fig. 7, the sliding surface 13 is polished so that the polishing direction D is along the axial direction X (polishing direction D is approximately parallel to the axial direction X). By such a grinding direction D, grinding marks are formed on the surface of the sliding surface 13 so as to extend along the axial direction X. That is, the grinding marks are formed along the direction in which the sliding surface 13 and the bearing member 3 slide against each other. Therefore, the frictional resistance between the surface of the sliding surface 13 and the mounting surface or the inner peripheral surface of the bearing member 3 is suppressed. More specifically, for example, compared to a rack bar ground along the width direction Y, the frictional resistance between the rack bar 1 and the bearing member 3 in the axial direction X is suppressed. This also makes it possible to suppress wear of the bearing member 3. Note that the grinding direction D includes a direction inclined by ±5° from the axial direction X to the width direction Y or the thickness direction Z.

[0032] The polishing method of this embodiment may include a first polishing process for polishing the surface 131a of the tooth back contact surface 13a, and a second polishing process for polishing the surface 131b of the both end contact surfaces 13b. The first polishing process and the second polishing process may be performed simultaneously or separately. When performed separately, either the first polishing process or the second polishing process may be performed first, and the order may be changed as appropriate. Only one of the first polishing process and the second polishing process may be performed.

[0033] In the grinding method of this embodiment, it is preferable to grind the tooth back contact surface 13a located on the opposite side facing the thickness direction Z of the rack portion 11. As described above, in the steering device 100, the rack bar 1 is supported by a bearing member 31 called a support yoke 31 at a sliding surface (tooth back sliding surface 13a) located on the opposite side of the rack portion 11 facing the thickness direction Z. The support yoke 31 is usually biased toward the rack bar 1 by a spring member or the like. The tooth back sliding surface 13a is a sliding surface located on the opposite side of the rack portion 11 on which the rack 11a meshing with the pinion 2 is formed, and therefore is also a location to which stress is likely to be directly applied when meshing with the pinion. For this reason, frictional resistance is relatively likely to occur between the support yoke 31 and the sliding surface 13a. In contrast, according to the rack bar 1 obtained by the above grinding method, the grinding marks formed on the surface of the sliding surface 13a that slides against the support yoke 31 are formed along the moving direction of the rack bar 1, so that the frictional resistance can be reduced more effectively.

[0034] In the polishing method of the present embodiment, only the surface 131a of the tooth back sliding contact surface 13a that slides against the bearing member 31 may be polished. Here, depending on the steering device 100, a part of the surface 131a of the tooth back sliding contact surface 13a (particularly both end faces 133a, 133a (see FIG. 3) intersecting with the width direction Y) may not be in contact with the support yoke 31. In other words, in some steering devices 100, sliding contact with the support yoke 31 may occur concentratedly on a part of the surface 131a. For this reason, in order to polish the tooth back sliding contact surface 13a more efficiently, only a predetermined part of the surface 131a may be polished. In other words, a surface that needs to be polished (surface that needs to be polished) may be set on the surface 131a of the tooth back sliding contact surface 13a, and only the surface that needs to be polished may be polished.

[0035] The surface that needs to be ground may be set, for example, at a location (reference numeral 132a) as shown in FIG. 5. More specifically, in the cross section (YZ plane), an X-axis overlapping a line segment that defines the diameter R1 of the surface 131a (more specifically, a line segment that is parallel to the tooth tips 113 of the teeth 111 of the rack 11a and defines the diameter R1 of the surface 131a), a Y-axis perpendicular to the X-axis so as to bisect the rack bar 1, and an origin O of the X-axis and Y-axis are defined, the rack portion 11 is disposed on the negative side of the Y-axis, and the surface that needs to be ground 132a is set at a portion located on the positive side of the Y-axis. Then, the surface that needs to be ground 132a is set at a portion located on the positive side of the Y-axis via a pair of straight lines L1 that pass through the origin O and are inclined at ±65° with respect to the Y-axis. The surface that needs to be ground 132a is also set at a portion between the pair of straight lines L1 and a pair of straight lines L2 that pass through the origin O and are inclined at ±25° with respect to the Y-axis. That is, the contact surface between the surface 131a of the tooth back sliding surface 13a and the support yoke 31 is set to, for example, a portion of the surface 131a corresponding to 25 to 65° of the central angle θ1 and a portion corresponding to 115 to 155° of the central angle θ1, with the positive direction of the X-axis being 0° (FIG. 5). Also, as the wear of the support yoke 31 progresses, the contact surface becomes, for example, a portion of the surface 131a corresponding to 25 to 155° of the central angle θ1, with the positive side of the X-axis being 0°. Therefore, by setting the surface 132a to be ground to a portion corresponding to 25 to 155° in consideration of the wear of the bearing member as described above, the rack bar 1 can be made capable of sufficiently reducing the wear resistance.

[0036] As shown in FIG. 7, in the polishing method of this embodiment, a surface 131a of an untreated rack bar 1a fixed by a fixing member (not shown) is polished by an abrasive 4 configured to be movable along the axial direction X of the untreated rack bar 1a.

[0037] The untreated rack bar 1a is fixed, for example, so that the surface 131a faces upward in the vertical direction (thickness direction Z) and the tooth tip 113 of the tooth portion 111 of the rack 11a faces downward. The abrasive 4 is configured to be movable along the axial direction X of the untreated rack bar 1a, for example, in a state of contact with the surface 131a. Furthermore, the abrasive 4 may be configured to be movable along the vertical direction (thickness direction Z) so that it can be in both a contact state and a non-contact state with the surface 131a. Alternatively, the abrasive 4 may be fixed and the untreated rack bar 1a may be moved along the axial direction X. In order to reduce the occupied area of ​​the polishing device, it is preferable to move the abrasive 4 rather than moving the long untreated rack bar 1a.

[0038] 6 to 8, the abrasive material 4 in this embodiment is a rotary grindstone 4. The rotary grindstone 4 is formed in a disk shape and is rotatable around a rotation axis CY2. The rotary grindstone 4 has abrasive grains on a rotating outer peripheral surface 41. The rotary grindstone 4 is arranged so that its rotation direction B (movement direction of the outer peripheral surface 41) is aligned with the axial direction X of the untreated rack bar 1a.

[0039] The rotary grindstone 4 is composed of the abrasive grains and a resin serving as a binder for binding the abrasive grains. From the viewpoint of cost, alumina-based abrasive grains having a relatively low hardness, such as white alumina (WA), are used as the abrasive grains. Also, a ceramic-based binder, such as vitrified, is used as the binder. Note that a resin-based binder may also be used as the binder, taking into consideration the remaining parts during polishing of the curved surfaces 131a and 131b.

[0040] The grit size of the abrasive grains is #60 to #800, preferably #120 to #220. A grindstone with such a grit size can sufficiently remove the oxide film generated by quenching before the grinding process when grinding the untreated rack bar 1a, which requires a grinding allowance (for example, 10 to 30 μm), and can provide a surface roughness sufficient to reduce the above-mentioned wear resistance. When the rack bar 1 is assembled into the steering device 100, a lubricant such as grease is usually applied to the surface 131a and the surface 131b to improve the lubrication with the bearing member 3. Therefore, if the grindstone with the above grit size is used, it can also provide a surface roughness that allows the lubricant to be appropriately retained on the surface 131a and the surface 131b.

[0041] The outer diameter of the grinding wheel 4 is, for example, 200 mm or more and 360 mm or less. The contact pressure of the rotating outer circumferential surface 41 with respect to the sliding surface 13 during the grinding process of the grinding wheel 4 is, for example, 0.1 MPa or more and 1 MPa or less. The peripheral speed of the grinding wheel 4 during the grinding process is, for example, 25 m / s or more and 30 m / s or less.

[0042] 6, the rotary grindstone 4 has an outer peripheral surface 41 formed in a concave shape corresponding to the shape (arcuate shape) of the surface 131a of the tooth back sliding surface 13a. More specifically, the rotary grindstone 4 has an outer peripheral surface 41 having an arcuate portion 411 having a diameter the same as the diameter R1 of the surface 131a in a grindstone cross section overlapping with the rotation axis CY2.

[0043] In the grinding method of this embodiment, the grindstone 4 is rotated so that the outer peripheral surface 41 of the grindstone 4 as described above is aligned along the axial direction X of the untreated rack bar 1a, and the grindstone 4 or the untreated rack bar 1a (preferably the grindstone 4) is moved along the axial direction X to grind the sliding surface 13 with the outer peripheral surface 41. That is, grinding is performed so that both the rotation direction of the grindstone 4 and the movement direction of the outer peripheral surface 41 of the grindstone 4 are aligned along the axial direction X of the untreated rack bar 1a. This makes it easier to form polishing marks along the axial direction X of the untreated rack bar 1a on the surface of the sliding contact surface 13. This makes it possible to further reduce the friction resistance between the sliding contact surface 13 of the untreated rack bar 1a and the bearing member.

[0044] In the first grinding process, when a grindstone 4 having a concave outer peripheral surface 41 is used, it is preferable to perform a first single-sided grinding process for grinding a part of the surface 131a, and then a second single-sided grinding process for grinding another part of the surface 131a. More specifically, as shown in Fig. 8, when the positional relationship between the untreated rack bar 1a and the grindstone 4 is viewed from one side in the axial direction X of the untreated rack bar 1a, the rack bar 1 is rotated in one direction (e.g., counterclockwise) around the axial direction X so that the inclination angle θ2 of the tooth tip 113 of the tooth portion 111 with respect to the rotation axis CY2 of the grindstone 4 is 45±5° and fixed (state of Fig. 8(b)), the grindstone 4 is moved downward to contact the untreated rack bar 1a, and the grindstone 4 is rotated and moved along the axial direction X of the untreated rack bar 1a, thereby performing the first single-sided grinding process. After the first single-sided polishing process is completed, the grindstone 4 is moved upward so that the surface 131a and the grindstone 4 are not in contact with each other (for example, the state shown in FIG. 8(a)). Next, the rack bar 1 is rotated in the other direction around the axial direction (for example, the clockwise direction) so that the inclination angle θ2 is 45±5°, and fixed in this state (the state shown in FIG. 8(c)). The grindstone 4 is then moved downward to contact the untreated rack bar 1a, and the grindstone 4 is moved along the axial direction X of the untreated rack bar 1a, thereby carrying out the second single-sided polishing process.

[0045] The areas polished by the first single-sided polishing process and the areas polished by the second single-sided polishing process may overlap. This allows the polishing of the surface 132a that needs polishing to be focused. In other words, the areas where the surface 131a and the support yoke 31 are likely to come into sliding contact with each other can be polished relatively focused and efficiently.

[0046] The moving speed V of the grindstone 4 is set to, for example, 30 to 50 mm / sec (including a 10% error). More specifically, first, the amount of grinding (removal amount) is determined for each portion of the surface 131a corresponding to each tooth portion 111 of the untreated rack bar 1a. Then, for example, the moving speed V is set to 50±5 mm / sec in the portion where the removal amount is 10 to 20 μm, and the moving speed V is set to 30±3 mm / sec in the portion where the removal amount is 20 to 30 μm.

[0047] In the second polishing process, the entire surface 131b of the sliding contact surface 13b at both ends may be polished. On the other hand, in order to perform polishing more efficiently, it is preferable to focus on polishing a portion of the surface 131b where concentrated sliding contact with the inner peripheral surface of the rack bush 32 in the steering device may occur. In other words, it is preferable to set a polishing-required surface 132b that needs to be polished on the surface 131b.

[0048] The surface that needs to be ground 132b is set at a position corresponding to the position of the surface that needs to be ground 132a of the tooth back sliding surface 13a in the circumferential direction CY1 of the rack bar 1. This makes it possible to efficiently grind the surface that needs to be ground 132b following the grinding of the surface that needs to be ground 132a without changing the fixed state of the rack bar 1. Also, in the steering device 100, the load of the rack bar 1 tends to cause sliding contact with the sliding surfaces 13b at both ends to be concentrated at the bottom part of the inner peripheral surface of the rack bush 32. Therefore, by setting the position of the surface that needs to be ground 132b as described above, it is possible to focus on grinding the parts that tend to cause sliding contact with the rack bush 32.

[0049] In carrying out the polishing method of this embodiment, the untreated rack bar 1a has a predetermined polishing allowance, which is, for example, 10 to 30 μm.

[0050] In the polishing method of this embodiment, the moving direction D of the grindstone 4 relative to the rotation direction B of the grindstone 4 may be the same as or opposite to the axial direction X, as long as they are along the axial direction X.

[0051] In the polishing method of the present embodiment, a coolant liquid that suppresses heat generation during polishing may be used. The coolant liquid may be a water-soluble coolant liquid or an oil-based coolant liquid, but a water-soluble coolant liquid may be used from the viewpoint of cost.

[0052] According to the polishing method of this embodiment, the arithmetic mean roughness Ra of the sliding surface 13 in the axial direction X after polishing is 0.1 μm (measurement method: needle contact type measurement, evaluation length 4 mm, standard JIS2001), and the arithmetic mean roughness Ra in the circumferential direction CY1 is 0.4 μm (measurement method: needle contact type measurement, evaluation length 4 mm, standard JIS2001). That is, the rack bar polished by the polishing method of this embodiment has different roughness Ra in the axial direction X and the circumferential direction CY1. Specifically, the roughness Ra in the axial direction X is small, and the roughness Ra in the circumferential direction CY1 is large. Here, the bearing member 3 (particularly the rack bush 32) also has a function of preventing rotation of the rack bar 1 in the circumferential direction CY1 in the steering device 100. Therefore, the rack bar 1 having the sliding surface 13 with a relatively large arithmetic mean roughness Ra in the circumferential direction CY1 can enhance the above function of the bearing member 3, so that the rotation of the rack bar 1 in the circumferential direction CY1 in the steering device can be more effectively prevented.

[0053] As described above, one embodiment has been shown as an example, but the rack bar grinding method according to the present invention is not limited to the configuration of the above embodiment. Furthermore, the rack bar grinding method according to the present invention is not limited by the above-mentioned action and effect. The rack bar grinding method according to the present invention can be modified in various ways without departing from the gist of the present invention.

[0054] For example, in the above embodiment, the rotating grindstone 4 is used as the abrasive material, but the present invention is not limited to this, and the abrasive material 4 may be, for example, an abrasive cloth or a buff abrasive material.

[0055] In addition, in the above embodiment, the rack bar 1 or the abrasive material 4 is moved, but the present invention is not limited to this, and both the rack bar 1 and the abrasive material 4 may be moved. [Explanation of symbols]

[0056] 1: Rack bar, 10: shaft material, 11: rack portion, 11a: rack, 111: tooth portion, 112: groove, 113: tooth tip, 13: sliding surface, 13a: tooth back sliding surface, 131a: surface, 132a: surface to be polished, 13b: sliding surfaces at both ends, 131b: surface, 132b: surface to be polished, 133a: end face, 2: Pinion, 3: bearing member, 31: support yoke, 32: rack bush, 4: abrasive material, 41: outer peripheral surface, 411: arc-shaped portion, X: Axial direction, Y: Width direction, Z: Thickness direction, CY1: Circumferential direction, CY2: Rotation axis, θ1: central angle, θ2: tilt angle, B: Rotation direction, D: Grinding direction (direction of movement of the abrasive material), L1, L2: Straight line, R1: Diameter

Claims

1. A method for grinding a rack bar, comprising the steps of: the rack bar is slidable relative to a bearing member that supports the rack bar when the rack bar is incorporated into the steering device, and includes a shaft member, the shaft member having a rack portion on which a rack that meshes with a pinion is formed, and a sliding contact surface that is in sliding contact with the bearing member, A method for polishing a rack bar, comprising the steps of: using a rotating grindstone that is disk-shaped, rotatable along a circumferential direction, and has abrasive grains on its rotating outer peripheral surface as it rotates; rotating the rotating grindstone so that the rotation direction of the outer peripheral surface is along the axial direction of the rack bar; and polishing the sliding surface with the outer peripheral surface while moving at least one of the rotating grindstone or the rack bar along the axial direction.

2. The method for grinding a rack bar according to claim 1 , further comprising grinding the sliding surface located on an opposite side in the thickness direction to the rack portion.

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