JP2017087819A - Manufacturing method for rack bar - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance shape accuracy of a rack bar made by joining a second bar member to a first bar member having a tooth part constituted of a plurality of rack teeth formed therein.SOLUTION: One end part in a shaft direction of a second bar member 12 with a larger diameter than a diameter of a first bar member 11 is joined to one end part in a shaft direction of the first bar member 11 having a first tooth part 20 constituted of a plurality of rack teeth formed at one part in the shaft direction thereof. At least part in the shaft direction of the second bar member 12 joined to the first bar member 11 is formed concentrically with the first bar member 11 by outer diameter cutting processing, and at the part subjected to the outer diameter cutting processing of the second bar member 12 is formed a second tooth part 21 constituted of a plurality of rack teeth.SELECTED DRAWING: Figure 2

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 composed of a plurality of rack teeth is formed at two locations, and meshes with a steering pinion of a steering shaft at one tooth portion and assists at the other tooth portion. A dual pinion type rack bar that meshes with an auxiliary pinion of a mechanism is known. In a dual pinion type rack bar, there may be a case where a rotational angle difference around an axis is set at two tooth portions in accordance with the positional relationship between a steering shaft and an assist mechanism in a vehicle.

  In the method of manufacturing a dual pinion type rack bar described in Patent Document 1, a first bar member in which teeth are formed and a second bar member arranged coaxially with the first bar member are arranged around the central axis. It is relatively rotated and friction welded, and then teeth are formed on the second bar member by cutting. By forming the tooth portion on the second bar member after joining the first bar member and the second bar member, the accuracy of the rotation angle difference between the tooth portion of the first bar member and the tooth portion of the second bar member is improved. Has been enhanced.

JP 2014-124767 A

  In the method of manufacturing a rack bar described in Patent Document 1, the second bar member joined to the first bar member may have a misalignment or a tilt with respect to the first bar member. If misalignment or collapse occurs, the straightness of the rack bar decreases.

  Further, the internal stress remaining in the second bar member is released by the formation of the tooth portion of the second bar member and the quenching of the tooth portion of the second bar member, and the second bar member is twisted. In some cases, an error may occur in the difference in rotation angle between the teeth of the first bar member and the teeth of the second bar member due to twisting.

  An object of the present invention is to improve the shape accuracy of a rack bar in which a second bar member is joined to a first bar member in which tooth portions including a plurality of rack teeth are formed.

  In the rack bar manufacturing method of one aspect of the present invention, the first bar member is formed at one axial end portion of the first bar member in which a tooth portion including a plurality of rack teeth is formed in a part in the axial direction. One end in the axial direction of the second bar member having a larger diameter is joined, and at least a part of the second bar member joined to the first bar member in the axial direction is cut by outer diameter cutting. It is formed coaxially with the bar member, and a power transmission portion is formed at the outer diameter cutting portion of the second bar member.

  According to the present invention, it is possible to improve the shape accuracy of the rack bar formed by joining the second bar member to the first bar member in which the tooth portion including a plurality of rack teeth is formed.

It is a front view of an example of a steering device for describing 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. It is a schematic diagram which shows the manufacturing process of the rack bar of FIG. It is a schematic diagram which shows the manufacturing process of the rack bar of FIG. It is a schematic diagram which shows the manufacturing process of the rack bar of FIG. It is a schematic diagram which shows the manufacturing process of the rack bar of FIG. It is a perspective view which shows an example of the deformation | transformation which arises in a rack bar. It is sectional drawing of the modification of the rack bar of FIG.

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

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

  Tie rods 3 are connected to both ends of the rack bar 10 via joints, and the steering wheel of the vehicle is rotated by the movement of the rack bar 10 via the steering mechanism to which the tie rod 3 and the tie rod 3 are connected. The

  A steering gear box 4 is provided at one end of the rack housing 2 in the axial direction. 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. In the auxiliary gear box 6, an auxiliary pinion (not shown) driven by the motor 7 of the assist mechanism is accommodated.

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

  The steering pinion of the input shaft 5 is rotated by the turning operation of the steering wheel, and the rack bar 10 that meshes 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 that is controlled according to 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 steering wheel is turned. The movement of the rack bar 10 is assisted.

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

  The rack bar 10 has a first bar member 11 formed with a first tooth portion 20 made of a plurality of rack teeth meshing with the steering pinion, and a second tooth portion 21 made of a plurality of rack teeth meshed with the auxiliary pinion. The second bar member 12 is provided, and one end portion in the axial direction of the first bar member 11 and one end portion in the axial direction of the second bar member 12 are joined to each other.

  In the illustrated example, the first bar member 11 is 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 of the first tooth portion 20 of the first bar member 11 made of a hollow material are formed as follows, for example.

  First, a flat tooth forming surface is preformed at a portion (hereinafter, referred to as a tooth portion forming portion) which is a tooth portion in a part of the longitudinal direction of the hollow material. The tooth forming surface is formed, for example, by pressing to crush the tooth portion forming portion of the hollow material using a mold.

  Next, the hollow material is placed in a molding die that includes a tooth mold that is pressed against the tooth forming surface and surrounds the tooth portion forming portion of the hollow material over the entire circumference, and the core metal is inserted into the hollow material. The meat of the hollow material constituting 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. The thickness of the cored bar to be inserted is gradually increased, and the ironing process is repeated, whereby a plurality of rack teeth corresponding to the tooth shape are formed in the hollow material.

  The second bar member 12 is made of a solid material having a circular cross section formed of a metal material such as carbon steel such as JIS-S45C. The rack teeth of the second tooth portion 21 of the second bar member 12 made of a solid material are formed by cutting, for example.

  The first bar member 11 may also be made of a solid material, and the rack teeth of the first tooth portion 20 of the first bar member 11 made of a solid material are formed by cutting, for example.

  The first tooth portion 20 of the first bar member 11 and the second tooth portion 21 of the second bar member 12 may have the same or different tooth shapes, and CGR (Constant Gear Ratio). And an appropriate combination of VGR (Variable Gear Ratio).

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

  As shown in FIG. 4, the 1st bar member 11 in which the 1st tooth | gear part 20 was formed previously, and the raw material of the 2nd bar member 12 are arrange | positioned coaxially. The outer diameter of the material of the second bar member 12 is larger than the outer diameter of the first bar member 11.

  In the illustrated example, one end portion (joint end portion) 12a in the axial direction of the second bar member 12 disposed on the first bar member 11 side is opposed to the join end portion 12a by, for example, cutting. The first bar member 11 is arranged in advance in an annular shape having the same shape as the one end (joining end) 11a in the axial direction, that is, the same inner diameter and outer diameter. In addition, when the 1st bar member 11 consists of solid materials, the joining end part 12a of the 2nd bar member 12 is the column shape which has the same shape as the joining end part 11a of the 1st bar member, ie, the same outer diameter. Is previously formed.

  As shown in FIG. 5, the second bar member 12 is moved toward the first bar member 11, and the end surfaces of the joining end 11a of the first bar member 11 and the joining end 12a of the second bar member 12 are mutually opposite. Faced. Then, the first bar member 11 is rotated around the central axis.

  Changes in the metal structures of the joining end portion 11a and the joining end portion 12a are caused by frictional heat due to relative rotation of the end surfaces of the joining end portion 11a of the first bar member 11 and the joining end portion 12a of the second bar member 12 which are abutted with each other. The joint end 11a and the joint end 12a are brought into pressure contact by being generated and further applied with pressure.

  In the joining of the joining end portion 11a of the first bar member 11 and the joining end portion 12a of the second bar member 12 by the friction welding described above, the joining end portion 12a is previously formed in the same shape as the joining end portion 11a. As a result, the plastic flow of each of the joining end portion 11a and the joining end portion 12a in the vicinity of the pressure contact surface becomes substantially equal, and the joining between the joining end portion 11a and the joining end portion 12a becomes more reliable.

  In the state where the first bar member 11 and the second bar member 12 are joined, the second bar member 12 has a first distribution due to, for example, an assembly error of the manufacturing apparatus or a pressure distribution on the pressure contact surface during friction welding. There is a case where a core misalignment or a collapse occurs with respect to the 1 bar member 11.

  Therefore, as shown in FIG. 6, the second bar member 12 is corrected coaxially with the first bar member 11 by outer diameter cutting. In the illustrated example, the second bar member 12 is subjected to outer diameter cutting over the entire length in the axial direction, and the second bar member 12 is coaxial and identical to the first bar member 11 over the entire length in the axial direction. Although it is formed in the outer diameter, it may be formed in an outer diameter different from that of the first bar member 11, and only in a part in the axial direction including a predetermined portion where the second tooth portion 21 is formed in a subsequent process. Only a part in the axial direction including a predetermined portion where the outer diameter cutting process is performed and the second tooth portion 21 is formed may be formed coaxially with the first bar member 11.

  Then, as shown in FIG. 7, a plurality of rack teeth constituting the second tooth portion 21 are formed at a predetermined portion of the second bar member 12 by gear cutting using a broaching machine or the like. Heat treatment such as insertion is applied to the second tooth portion 21. In addition, for example, surface finishing such as polishing may be performed on the second bar member 12 between the outer diameter cutting and the gear cutting.

  In the rack bar 10 manufactured as described above, the second bar member 12 is formed coaxially with the first bar member 11 by the external cutting shown in FIG. 6, so that the straightness of the rack bar 10 is increased.

  Furthermore, the internal stress remaining on the surface layer of the material of the second bar member 12 is removed by the outer diameter cutting shown in FIG.

  The solid material that is the material of the second bar member 12 is generally manufactured by drawing, and internal tensile stress remains on the surface layer side of this type of solid material, and compressive internal stress remains on the deep layer side. The tensile internal stress is greater in the surface layer, the compressive internal stress is greater in the deep layer, and the tensile or compressive internal stress remaining in the intermediate layer between the surface layer and the deep layer is the internal stress of the surface layer or the deep layer. Smaller than that.

  In the second bar member 12 subjected to the outer diameter cutting process, the surface layer of the material is removed, and the intermediate layer of the material whose internal stress is smaller than that of the surface layer is exposed. By forming the rack teeth constituting the second tooth portion 21 in the intermediate layer, even if the internal stress is released by gear cutting or heat treatment, the deformation of the second bar member 12 accompanying the release of the internal stress is prevented. It is suppressed.

  As the deformation of the second bar member 12 due to the release of the internal stress, as shown in FIG. 8, a twist around the central axis can be exemplified, and when the second bar member 12 is twisted, the second tooth portion There is a possibility that the pitch of the rack teeth 21 is changed, the meshing with the pinion is deteriorated and the transmission efficiency is lowered. The removal of the internal stress remaining on the surface layer of the material of the second bar member 12 by the outer diameter cutting is particularly effective for suppressing the twisting of the second bar member 12 that causes a reduction in transmission efficiency.

  The machining allowance in the outer diameter cutting of the material of the second bar member 12 is the displacement of the core of the second bar member 12 with respect to the first bar member 11 or the collapse, and the internal stress remaining in the material of the second bar member 12 Although it sets suitably considering distribution etc., 1 mm or more and 2 mm or less are suitable at a diameter.

  In this way, the second bar member 12 joined to the first bar member 11 is formed coaxially with the first bar member 11 by the outer diameter cutting process, and then the outer diameter cutting part of the second bar member 12 is formed. By forming the plurality of rack teeth constituting the second tooth portion 21, the straightness of the rack bar 10 can be increased, the deformation of the second bar member 12 can be suppressed, and the shape accuracy of the rack bar 10 can be increased.

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

  In the above-described example, the second bar member 12 is described as being made of a solid material having a diameter larger than that of the first bar member 11. However, as shown in FIG. 9, the second bar member 12 is the first bar member 11. It may be made of a hollow material having a larger diameter.

  Even when the second bar member 12 is made of a hollow material, at least a part of the second bar member 12 joined to the first bar member 11 in the axial direction has an outer diameter, as in the method of manufacturing the rack bar 10 described above. A rack bar can be manufactured by forming it coaxially with the first bar member 11 by cutting and forming a power transmission portion made up of rack teeth, screw grooves, etc. in the outer diameter cutting portion of the second bar member 12.

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 1st bar member 11a Joining end part 12 2nd bar member 12a Joining end part 20 1st tooth part 21 2nd Tooth part (power transmission part)

Claims (4)

One axial end of the second bar member having a diameter larger than that of the first bar member is formed at one end in the axial direction of the first bar member having a plurality of rack teeth formed in a part in the axial direction. Join the ends of
Forming at least part of the axial direction of the second bar member joined to the first bar member coaxially with the first bar member by outer diameter cutting;
A method for manufacturing a rack bar, wherein a power transmission portion is formed in an outer diameter cutting portion of the second bar member. A manufacturing method of a rack bar according to claim 1,
A method for manufacturing a rack bar, wherein the power transmission unit formed on the second bar member is heat-treated. It is a manufacturing method of the rack bar according to claim 1 or 2,
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. A manufacturing method of a rack bar according to claim 3,
A method of manufacturing a rack bar, wherein the second bar member is friction-welded to the first bar member in a state in which the joint end of the second bar member is previously processed into the same shape as the joint end of the first bar member.

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