JP6653160B2 - Rack bar manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a rack bar.

  As a rack bar used in a steering device of a vehicle such as an automobile, a tooth portion including a plurality of rack teeth is formed at two places, one of the teeth meshes with a steering pinion of a steering shaft, and the other tooth portion assists. A dual pinion type rack bar that meshes with an auxiliary pinion of a mechanism is known. In a dual pinion type rack bar, a rotational angle difference around an axis may be set between two tooth portions in accordance with a positional relationship between a steering shaft and an assist mechanism in a vehicle.

  In the method of manufacturing a rack bar of a dual pinion type described in Patent Literature 1, the first bar member made of a hollow material having a tooth portion is the same as the first bar member arranged coaxially with the first bar member. And a second bar member made of a hollow material having an outer diameter of about 2 mm is relatively rotated about a central axis and frictionally pressed, and thereafter, a tooth portion is formed on the second bar member by cutting. Since both the first bar member and the second bar member are made of a hollow material, the weight of the rack bar can be reduced, and the tooth portion is formed on the second bar member after joining the first bar member and the second bar member. Is formed, the accuracy of the rotation angle difference between the teeth of the first bar member and the teeth of the second bar member is improved.

JP 2014-124767 A

  In the method of manufacturing a rack bar described in Patent Literature 1, the second bar member joined to the first bar member may be misaligned or fallen with respect to the first bar member. If the center is misaligned or falls down, the straightness of the rack bar decreases.

  Further, the rack teeth of the teeth formed on the second bar member by the cutting process are limited by the thickness of the second bar member made of a hollow material.

  The present invention improves the shape accuracy of a rack bar formed by joining a second bar member made of a hollow material to a first bar member made of a hollow material formed with a tooth portion made up of a plurality of rack teeth, and It is intended to increase the degree of freedom of the shape of the power transmission unit formed on the member.

The method of manufacturing a rack bar according to one aspect of the present invention includes a method of manufacturing a rack bar, in which the first bar member made of a hollow material having a plurality of rack teeth formed in a part thereof in the axial direction has a hollow. One end of a second bar member made of a material in the axial direction is joined, and at least a part of the second bar member joined to the first bar member in the axial direction is increased coaxially with the first bar member. By forming the meat , at least one of the misalignment and the inclination of the second bar member with respect to the first bar member, which is generated in the joining between the first bar member and the second bar member, is corrected . A power transmission part is formed in the thickened part of the two-bar member.

  ADVANTAGE OF THE INVENTION According to this invention, the shape accuracy of the rack bar which joins the 2nd bar member which consists of a hollow material to the 1st bar member which consists of a hollow material in which the tooth part which consists of several rack teeth was formed is improved, The degree of freedom of the shape of the power transmission unit formed on the two-bar member can be increased.

It is a front view of an example of a steering device for explaining an embodiment of the present invention. FIG. 2 is a front view of a rack bar incorporated in the steering device of FIG. 1. It is sectional drawing of the rack bar of FIG. FIG. 3 is a schematic view illustrating a manufacturing process of the rack bar of FIG. 2. FIG. 3 is a schematic view illustrating a manufacturing process of the rack bar of FIG. 2. FIG. 3 is a schematic view illustrating a manufacturing process of the rack bar of FIG. 2. FIG. 3 is a schematic view illustrating a manufacturing process of the rack bar of FIG. 2.

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

  The steering apparatus 1 shown in FIG. 1 includes a rack housing 2 and a rack bar 10 housed in the rack housing 2 so as to be slidable in the axial direction.

  The tie rods 3 are connected to both ends of the rack bar 10 via joints, respectively. When the rack bar 10 moves, the steering wheel of the vehicle is turned via a tie rod 3 and a steering mechanism to which the tie rod 3 is connected. You.

  A steering gear box 4 is provided at one axial end of the rack housing 2. The steering gear box 4 houses a steering pinion (not shown) formed on the input shaft 5 connected to the steering shaft. An auxiliary gear box 6 is provided at the other axial end of the rack housing 2. The auxiliary gearbox 6 houses an auxiliary pinion (not shown) driven by a motor 7 of the assist mechanism.

  The rack bar 10 is formed with a first tooth portion 20 including a plurality of rack teeth meshing with the steering pinion and a second tooth portion 21 including a plurality of rack teeth meshing with the auxiliary pinion.

  The steering pinion of the input shaft 5 is rotated by the rotation operation of the steering wheel, and the rack bar 10 meshing with the steering pinion is moved in the axial direction by the first tooth portion 20. Then, the driving force of the motor 7 of the assist mechanism, which is controlled in accordance with the steering force of the steering wheel, is transmitted to the rack bar 10 via the auxiliary pinion that meshes with the second tooth portion 21, and the rotation of the steering wheel is performed. The movement of the rack bar 10 is assisted.

  FIGS. 2 and 3 show the configuration of the rack bar 10.

  The rack bar 10 has a first bar member 11 formed with a plurality of rack teeth meshing with a steering pinion, and a second bar portion 21 formed with a plurality of rack teeth meshing with an auxiliary pinion. A second bar member 12 is provided, and one end of the first bar member 11 in the axial direction and one end of the second bar member 12 in the axial direction are joined to each other.

  The first bar member 11 is made of a hollow material having a circular cross section and formed of a metal material such as carbon steel such as JIS-S45C. The rack teeth of the first tooth portion 20 of the first bar member 11 made of a hollow material are formed, for example, as follows.

  First, a flat tooth forming surface is preliminarily formed on a portion (hereinafter, referred to as a tooth forming portion) that is to be a tooth portion in a part of the hollow material in the longitudinal direction. The tooth forming surface is formed by, for example, press working in which a tooth forming portion of the hollow material is crushed using a mold.

  Next, the hollow material is placed in a mold including a tooth mold pressed against the tooth forming surface and surrounding the tooth forming portion of the hollow material over the entire circumference, and the core metal is inserted through the hollow material. The flesh of the hollow material forming the tooth forming surface is squeezed from the inside by the inserted metal core and bites into the tooth mold pressed against the tooth forming surface. A plurality of rack teeth corresponding to the tooth form are formed in the hollow material by gradually increasing the thickness of the inserted core bar and repeating ironing.

  The second bar member 12 is also made of a hollow material having a circular cross section formed of a metal material such as carbon steel such as JIS-S45C. The rack teeth forming the second tooth portions 21 of the second bar member 12 are formed by, for example, cutting after the second bar member 12 is joined to the first bar member 11, as will be described later in detail.

  The tooth shape of the rack teeth of the first tooth portion 20 of the first bar member 11 and the second tooth portion 21 of the second bar member 12 may be the same or different, and a constant gear ratio (CGR). And VGR (Variable Gear Ratio).

  4 to 7 show a manufacturing process of the rack bar 10.

  As shown in FIG. 4, the first bar member 11 on which the first tooth portion 20 is formed in advance and the material of the second bar member 12 are coaxially arranged. In the illustrated example, the outer diameter of the material of the second bar member 12 is larger than the outer diameter of the first bar member 11, but may be the same as the outer diameter of the first bar member 11, or the outer diameter of the first bar member. It may be smaller than the diameter. The inner diameter of the material of the second bar member 12 is the same as the inner diameter of the first bar member 11, but may be different from the inner diameter of the first bar member 11.

  In the illustrated example, one end (joint end) 12a in the axial direction of the second bar member 12 disposed on the first bar member 11 side is connected to the joint end 12a by, for example, cutting. The first bar member 11 is formed in advance in an annular shape having the same inner diameter and outer diameter as one end (joint end) 11a in the axial direction of the first bar member 11 disposed opposite to the first bar member 11. When the outer diameter of the material of the second bar member 12 is smaller than the outer diameter of the first bar member 11, for example, upsetting is performed on the joint end portion 12a of the second bar member 12 in advance, and the outer end of the joint end portion 12a is formed. The diameter may be set to be equal to or larger than the outer diameter of the joining end portion 11a. If the inner diameter of the material of the second bar member 12 is larger than the inner diameter of the first bar member 11, for example, the joining end portion 12a of the second bar member 12 Drawing may be performed in advance, and the inner diameter of the joint end 12a may be set to be equal to or smaller than the inner diameter of the joint end 11a.

  As shown in FIG. 5, the second bar member 12 is moved toward the first bar member 11, and the respective end faces of the joint end portion 11a of the first bar member 11 and the joint end portion 12a of the second bar member 12 Butted against each other. Then, the first bar member 11 is rotated around the central axis.

  The metal structure of the joining end 11a and the joining end 12a changes due to frictional heat caused by the relative rotation of the respective end surfaces of the joining end 11a of the first bar member 11 and the joining end 12a of the second bar member 12 which are abutted to each other. Is generated, and the joining end 11a and the joining end 12a are pressed against each other by applying pressure.

  In the joining between the joining end 11a of the first bar member 11 and the joining end 12a of the second bar member 12 by the above friction welding, the joining end 12a has the same inner diameter and outer diameter as the joining end 11a. Is formed in advance, the plastic flow of each of the joining end portion 11a and the joining end portion 12a in the vicinity of the press contact surface becomes substantially equal, and the joining between the joining end portion 11a and the joining end portion 12a becomes more reliable. .

  In a state where the first bar member 11 and the second bar member 12 are joined, the second bar member 12 has a second bar member 12 due to, for example, an assembling error of a manufacturing apparatus or a pressure distribution on a pressure contact surface at the time of friction welding. There is a case where the center of the bar member 11 is misaligned or falls.

  Therefore, as shown in FIG. 6, the second bar member 12 is corrected coaxially with the first bar member 11. The correction of the second bar member 12 is performed by increasing the thickness of the second bar member 12. Assuming that the second bar member 12 is formed to have the same outer diameter as the first bar member 11, in the present example, the outer diameter of the material of the second bar member 12 is larger than the outer diameter of the first bar member 11. The diameter of the bar member 12 is reduced while the length in the axial direction is substantially unchanged, and the thickness is increased. Such thickening of the second bar member is performed, for example, by changing the cross-sectional shape of the second bar member 12 while hitting the second bar member 12 in the radial direction with a plurality of dies around the second bar member 12. It can be performed by processing (swaging). When the outer diameter of the material of the second bar member 12 is equal to or smaller than the outer diameter of the first bar member 11, the axial length of the second bar member 12 may be reduced to increase the thickness. In addition, the second bar member 12 may be formed to have a thickness increasing to an outer diameter different from that of the first bar member 11, and in the illustrated example, the second bar member 12 has a total length in the axial direction excluding the joining end 12 a. However, the thickness may be increased only in a part of the axial direction including a predetermined portion where the second tooth portion 21 is formed in a later step.

  Then, as shown in FIG. 7, a plurality of rack teeth constituting the second tooth portion 21 are formed at predetermined positions of the second bar member 12 by gear cutting using a broaching machine or the like. Heat treatment such as insertion is performed on the second teeth 21. Note that a surface finishing process such as a polishing process may be performed on the second bar member 12 between the thickening forming and the gear cutting.

  In the rack bar 10 manufactured as described above, the first bar member 11 and the second bar member 12 are both made of a hollow material, so that the weight of the rack bar 10 can be reduced.

  By increasing the thickness of the second bar member 12, the thickness of a predetermined portion of the second bar member 12 where the second tooth portion 21 is formed can be secured, and the shape of the rack teeth forming the second tooth portion 21 can be secured. The degree of freedom can be increased. Further, by increasing the thickness of the second bar member 12, the second bar member 12 can be corrected coaxially with the first bar member 11, and the straightness of the rack bar 10 can be increased.

  In the method of manufacturing the rack bar 10 described above, the second bar is formed between the thickening molding shown in FIG. 6 and the gear cutting shown in FIG. 7 with reference to the center axis of the first bar member 11. The member 12 may be subjected to outer diameter cutting. Thereby, the straightness of the rack bar 10 can be further increased, and the internal stress remaining on the surface layer of the material of the second bar member 12 can be removed.

  The hollow material which is the material of the second bar member 12 is generally manufactured by drawing, and a tensile internal stress remains on the surface layer side of this kind of hollow material, and a compressive internal stress remains on the deep layer side. The internal stress of tension is higher at the surface layer, the internal stress of compression is higher at the deeper layer, and the internal stress of tension or compression remaining in the intermediate layer between the surface layer and the deep layer is smaller than the internal stress of the surface layer and the deep layer. small.

  In the second bar member 12 subjected to the outer diameter cutting, the surface layer of the material is removed, and the intermediate layer of the material having a smaller internal stress than the surface layer is exposed. By forming the rack teeth constituting the second tooth portion 21 in this intermediate layer, even if internal stress is released by gear cutting or heat treatment, deformation of the second bar member 12 due to release of internal stress is prevented. Is suppressed. Thereby, the shape accuracy of the rack bar 10 can be further enhanced.

  The outer diameter of the material of the second bar member 12 and the allowance in the outer diameter cutting work are misaligned and fall of the second bar member 12 with respect to the first bar member 11, and remain in the material of the second bar member 12. It is appropriately set in consideration of the distribution of internal stress and the like, and preferably has a diameter of 1 mm or more and 2 mm or less.

  In the above-described example, the power transmission unit formed on the second bar member 12 is described as the second tooth unit 21 including a plurality of rack teeth. However, the power transmission unit is not limited to the tooth unit. It may be a thread groove of a ball screw.

DESCRIPTION OF SYMBOLS 1 Steering device 2 Rack housing 3 Tie rod 4 Steering gear box 5 Input shaft 6 Auxiliary gear box 7 Motor 10 Rack bar 11 First bar member 11a Joint end 12 Second bar member 12a Joint end 20 First tooth 21 Second Tooth

Claims (6)

One of the axial direction ends of the second bar member made of a hollow material is attached to one axial end of a first bar member made of a hollow material having a plurality of rack teeth formed in a part of the axial direction. Join the ends,
By forming at least a part of the second bar member joined to the first bar member in the axial direction coaxially with the first bar member, the first bar member and the second bar member are formed. Correcting at least one of misalignment and falling of the second bar member with respect to the first bar member, which occurred in joining ,
A method of manufacturing a rack bar, wherein a power transmission section is formed in a thickened portion of the second bar member. It is a manufacturing method of the rack bar of Claim 1, Comprising:
A method of manufacturing a rack bar, wherein at least a part of the second bar member joined to the first bar member in the axial direction is formed by drawing to increase the thickness coaxially with the first bar member. It is a manufacturing method of the rack bar of Claim 1 or 2, Comprising:
A method of manufacturing a rack bar, wherein the power transmission part is formed after the outer diameter cutting of the thickened portion of the second bar member is performed coaxially with the first bar member. The method for manufacturing a rack bar according to claim 3, wherein
A method of manufacturing a rack bar for heat-treating the power transmission unit formed on the second bar member. It is a manufacturing method of the rack bar as described in any one of Claims 1-4, Comprising:
A method of manufacturing a rack bar, wherein the second bar member is joined to the first bar member by friction welding that relatively rotates the first bar member and the second bar member around a central axis of the first bar member. It is a manufacturing method of the rack bar of Claim 5, Comprising:
The second bar member is friction-welded to the first bar member in a state where the joining end portion of the second bar member is preliminarily worked into an annular shape having the same inner diameter and outer diameter as the joining end portion of the first bar member. Rack bar manufacturing method.

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