WO2019235239A1 - Rack bar in preliminary form before quenching and rack bar manufacturing method - Google Patents

Rack bar in preliminary form before quenching and rack bar manufacturing method Download PDF

Info

Publication number
WO2019235239A1
WO2019235239A1 PCT/JP2019/020489 JP2019020489W WO2019235239A1 WO 2019235239 A1 WO2019235239 A1 WO 2019235239A1 JP 2019020489 W JP2019020489 W JP 2019020489W WO 2019235239 A1 WO2019235239 A1 WO 2019235239A1
Authority
WO
WIPO (PCT)
Prior art keywords
shaft member
rack
rack bar
rack teeth
teeth
Prior art date
Application number
PCT/JP2019/020489
Other languages
French (fr)
Inventor
Makoto Nomura
Wataru Matsumoto
Koji Koyama
Original Assignee
Neturen Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Neturen Co., Ltd. filed Critical Neturen Co., Ltd.
Publication of WO2019235239A1 publication Critical patent/WO2019235239A1/en

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
    • B21K1/00—Making machine elements
    • B21K1/76—Making machine elements elements not mentioned in one of the preceding groups
    • B21K1/767—Toothed racks
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
    • B21K1/00—Making machine elements
    • B21K1/76—Making machine elements elements not mentioned in one of the preceding groups
    • B21K1/767—Toothed racks
    • B21K1/768—Toothed racks hollow
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D3/00—Steering gears
    • B62D3/02—Steering gears mechanical
    • B62D3/12—Steering gears mechanical of rack-and-pinion type
    • B62D3/126—Steering gears mechanical of rack-and-pinion type characterised by the rack
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/06—Surface hardening
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H55/00—Elements with teeth or friction surfaces for conveying motion; Worms, pulleys or sheaves for gearing mechanisms
    • F16H55/02—Toothed members; Worms
    • F16H55/26—Racks
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/673—Quenching devices for die quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/32—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for gear wheels, worm wheels, or the like

Definitions

  • Illustrative aspects of the present invention relate to a rack bar in a preliminary form before quenching and a method for manufacturing a rack bar.
  • a rack bar used for a rack-and-pinion type steering device of a car is quenched.
  • the rack bar is quenched in a restrained state (see, for example, JP2001-011536A and JP2014-133924A).
  • a rack bar manufacturing method disclosed in JP2014-133924A a rack bar is quenched in a state in which a torsional torque is applied to the rack bar, so that the rack bar is prevented from being torsionally deformed during quenching.
  • the torsional deformation of the rack bar may cause deterioration of meshing between a rack and a pinion and may reduce transmission efficiency. This may particularly be a problem with a dual pinion type rack bar having two rack portions, one being configured to mesh with a steering pinion of a steering shaft and the other being configured to mesh with an assist pinion of an assist mechanism, since the torsional deformation of the rack bar may reduce accuracy of a difference in an angular position around a central axis given to the two rack portions.
  • the method of JP2014-133924A can prevent the torsional deformation of the rack bar by applying torsional torque to the rack bar when quenching the rack bar. However, this requires an additional equipment for applying the torsional torque.
  • Illustrative aspects of present invention provide a technique for easily reducing a torsion of a rack bar (the word “torsion” is intended to mean a torsional deviation from a desired shape).
  • a preliminary rack bar served for quenching includes a shaft member having a plurality of rack teeth arranged side by side in an axial direction of the shaft member, and the pitch surface of the plurality of rack teeth is twisted around a central axis of the shaft member.
  • a method for manufacturing a rack bar includes forming a plurality of rack teeth in a shaft member side by side in an axial direction of the shaft member such that the pitch surface of the rack teeth is twisted around a central axis of the shaft member, and quenching the shaft member having the rack teeth such that the pitch surface is twisted back by the quenching.
  • Fig. 1 is a plan view of a rack bar according to an embodiment of the present invention.
  • Fig. 2 is a sectional view of the rack bar of Fig. 1.
  • Fig. 3 is a plan view of the rack bar of Fig. 1 before being quenched.
  • Fig. 4 is a schematic view illustrating a rack bar manufacturing method according to an embodiment of the present invention.
  • Fig. 5 is another schematic view illustrating the rack bar manufacturing method.
  • Fig. 6 is a schematic view of an example of rack teeth forming die shown in Fig. 5.
  • Fig. 7 is a plan view of a rack bar according to another embodiment of the present invention.
  • Fig. 8 is a sectional view of the rack bar of Fig. 7.
  • Fig. 9 is a plan view of rack bar of Fig. 7 before being quenched.
  • Fig. 1 and Fig. 2 illustrate a rack bar 10 according to an embodiment of the present invention.
  • Fig. 3 illustrates the rack bar illustrated in Fig. 1 and Fig. 2 before it is being quenched, i.e., rack bar in a preliminary form before quenching (hereinafter referred to as preliminary rack bar 16).
  • the rack bar 10 has a hollow cylindrical shaft member 11.
  • the shaft member 11 is made of metal such as steel.
  • the shaft member 11 has a rack portion 12 having a plurality of rack teeth 13 configured to mesh with a pinion of a steering device.
  • the rack portion 12 is provided on one side of the shaft member 11 having an end portion 11a.
  • the shaft member 11 has a hollow cylindrical shaft portion 14 configured to be supported movably on a housing of the steering device.
  • the shaft portion 14 is provided on the other side of the shaft member 11 having the other end portion 11b.
  • the rack portion 12 has a flattened portion 15 extending in an axial direction of the shaft member 11.
  • the plurality of rack teeth 13 is formed on an outer surface of the flattened portion 15 such that the rack teeth 13 are arranged side by side in the axial direction of the shaft member 11.
  • a pitch surface PS of the rack teeth 13 is a plane parallel to a central axis of the shaft member 11.
  • the pitch surface PS is an imaginary surface that makes a rolling contact with a pitch circle of the pinion.
  • each of tooth traces TT of the rack teeth 13 is inclined with respect to a direction perpendicular to the axial direction of the shaft member 11, and a pitch p1 between adjacent ones of the rack teeth 13 is fixed.
  • the tooth trace TT is a line of intersection between a tooth surface of the rack tooth 13 and the pitch surface PS.
  • the tooth trace of the rack tooth 13 may be perpendicular to the axial direction of the shaft member 11.
  • the pitch between the adjacent ones of the rack teeth 13 may be variable, for example, to be relatively narrow at an axially central portion of the rack portion 12 and relatively wide at axial end portions of the rack portion 12.
  • the rack portion 12 and the shaft portion 14 are quenched.
  • the preliminary rack bar 16 illustrated in Fig. 3 is, in other words, the rack bar 10 with the rack portion 12 and the shaft portion 14 being not quenched yet.
  • the preliminary rack bar 16 is configured in a similar manner as the rack bar 10.
  • the pitch surface PS of the rack teeth 13 of the preliminary rack bar 16 is twisted around the central axis of the shaft member 11.
  • the pitch surface PS of the preliminary rack bar 16 is twisted in a direction A of widening the pitch p2 of the rack teeth 13 (p1 ⁇ p2).
  • top lands 13a of the rack teeth 13 of the preliminary rack bar 16 are arranged within the same plane parallel to the axial direction of the shaft member 11.
  • Bottom lands 13b of the rack teeth 13 are also arranged within the same plane parallel to the axial direction of the shaft member 11.
  • the side of an end portion 11a of a shaft member 11 is squashed into a flat shape by press working so that a flattened portion 15 extending in an axial direction of the shaft member 11 is formed. If necessary, chemical conversion coating for forming a phosphate film may be then applied to a surface of the shaft member 11. After that a plurality of rack teeth 13 can be formed on the flatly squashed portion 15.
  • a part of the shaft member 11 in the axial direction including the flattened portion 15 is held by a metal mold 20.
  • the metal mold 20 is provided with an upper mold 21 and a lower mold 22.
  • the upper mold 21 and the lower mold 22 are opened/closed by a mold clamping mechanism (not shown) to interpose the shaft member 11 from above and below to thereby hold an outer circumference of the shaft member 11.
  • a tooth forming die 23 is detachably mounted in the upper mold 21.
  • the tooth forming die 23 is fixed in contact with an outer surface of the flattened portion 15.
  • a plurality of tooth grooves 25 for forming the rack teeth 13 are provided in a molding surface 24 of the tooth forming die 23 brought into contact with the flattened portion 15.
  • a mandrel 30 is inserted into the shaft member 11 through an opening formed in the side of the end portion 11a of the shaft member 11 to be press-fitted into an inside of the flattened portion 15 by a push bar 31.
  • the press-fitted mandrel 30 is pushed back by a push bar 32 inserted from an opening formed in the side of the end portion 11b of the shaft member 11 so that the mandrel 30 can be discharged from the shaft member 11.
  • the material of the flattened portion 15 is forged by the mandrel 30 to thereby plastically deform toward the tooth forming die 23.
  • the mandrel 30 is replaced with one which is gradually larger, and the press-fitting of the mandrel 30 is repeated. In this manner, the material of the flattened portion 15 gradually enters into the tooth grooves 25 of the tooth forming die 23. The shape of the molding surface 24 of the tooth forming die 23 is transferred to the flattened portion 15. As a result, a plurality of rack teeth 13 are formed on the flattened portion 15.
  • the preliminary rack bar 16 is manufactured via the aforementioned methods.
  • the rack portion 12 and the shaft portion 14 are quenched in order to increase harness of the rack portion 12 and increase hardness of the shaft portion 14.
  • the preliminary rack bar 16 including the rack portion 12 and the shaft portion 14 may be entirely quenched. Heating during the quenching can be applied, for example, by high frequency induction heating but is not limited to the high frequency induction heating.
  • Torsional deformation is generated in the rack portion 12 caused by the quenching.
  • a heat distribution in the rack teeth during the quenching is considered as a cause of the torsional deformation.
  • the torsional deformation caused by the heat distribution is generated in a fixed direction.
  • transformation stress during the quenching is considered as another cause of the torsional deformation.
  • the torsional deformation caused by the transformation stress is determined by the shape of the rack teeth 13. When tooth traces TT of the rack teeth 13 are set to be inclined with respect to a direction perpendicular to the axial direction of the shaft member 11, the torsional deformation caused by the transformation stress is generated in a direction to narrow the pitch of the rack teeth 13.
  • the pitch surface PS of the preliminary rack bar 16 is twisted in a direction A (see Fig. 3) of widening the pitch of the rack teeth 13. Due to quenching applied to the preliminary rack bar 16, the torsional deformation is caused to the rack portion 12 in a direction (an opposite direction to the direction A) to narrow the pitch of the rack teeth 13. Thus, the pitch surface PS is twisted back to a plane parallel to the axial direction of the shaft member 11.
  • a torsional deformation amount (a torsion angle) generated in the rack portion 12 due to the quenching and a torsion angle of the pitch surface PS of the preliminary rack bar 16 cancelling the deformation amount are experimentally predetermined to be, for example, about 0.05°to 0.1°in the rack portion 12 having a standard length.
  • the pitch surface PS of the rack teeth 13 of the preliminary rack bar 16 is twisted around a central axis of the shaft member 11.
  • the pitch surface PS is twisted back to a planar shape caused by the quenching applied to the preliminary rack bar 16. Accordingly, it is possible to easily reduce torsion of the rack bar 10 which is formed by quenching the preliminary rack bar 16.
  • Fig. 6 illustrates an example of the tooth forming die 23 used for manufacturing the rack bar 10.
  • a tangential line TL between each of side surfaces of the tooth grooves 25 and a corresponding one of the pins 26 is inclined gradually in a direction in which the tooth grooves 25 arrange from one end side toward the other end side.
  • Rack teeth 13 are molded by the tooth grooves 25.
  • the tangential lines TL between the side surfaces of the tooth grooves 25 and the pins 26 correspond to tooth traces TT of the rack teeth 13 respectively. Since the tangential lines TL between the side surfaces of the tooth grooves 25 and the pins 26 are inclined gradually, the tooth traces TT of the molded rack teeth 13 thus are also inclined gradually.
  • the pitch surface PS where the tooth traces TT of the rack teeth 13 of the preliminary rack bar 16 exist is twisted around the central axis of the shaft member 11.
  • Each of bottom surfaces 25a of the tooth grooves 25 can be formed so as to be parallel to a central axis of the pin 26 disposed in the tooth groove 25.
  • the bottom surfaces 25a are inclined gradually in the direction in which the tooth grooves 25 arrange from one end side toward the other end side.
  • the bottom surfaces 25a are formed within the same plane.
  • manufacturing of the tooth forming die 23 becomes easy.
  • top lands 13a of the rack teeth 13 of the preliminary rack bar 16 are provided within the same plane parallel to the axial direction of the shaft member 11 respectively.
  • a top face 25b of a protrusion between adjacent two of the tooth groves 25 can be formed so as to be parallel to the central axis of the pin 26 disposed in one of the two tooth grooves 25.
  • the top faces 25b are gradually inclined in the direction in which the tooth grooves 25 from one end side toward the other end side.
  • the top faces25b are formed on the same plane respectively.
  • the manufacturing of the tooth forming die 23 becomes easy.
  • Fig. 7 and Fig. 8 illustrate a rack bar 110 according to another embodiment of the present invention.
  • Fig. 9 shows illustrates the rack bar of Fig. 7 and Fig. 8 before it is being quenched, i.e., preliminary rack bar 116.
  • Elements that are same as or similar to those of the rack bar 10 and the preliminary rack bar 16 described above will be denoted by the same reference signs, and description thereof will be omitted or simplified.
  • the rack bar 110 has a solid cylindrical shaft member 111.
  • the shaft member 111 has a rack portion 112 having a plurality of rack teeth 113.
  • the rack portion 112 is provided on one side of the shaft member 111 having an end portion 111a of.
  • the shaft member 111 has a solid cylindrical shaft portion 114.
  • the solid cylindrical shaft portion 114 is provided on the other side of the shaft member 111 having the other end portion 111b.
  • tooth traces TT of the rack teeth 113 are perpendicular to an axial direction of the shaft member 111.
  • the preliminary rack bar 116 illustrated in Fig. 9 is, in other words, the rack bar 100 with the rack portion 112 and the shaft portion 114 being not quenched yet.
  • the preliminary rack bar 116 is configured in a similar manner as the rack bar 110.
  • the pitch surface PS of the rack teeth 113 of the preliminary rack bar 116 is twisted around a central axis of the shaft member 111.
  • the preliminary rack bar 116 is formed by, for example, forging using a metal mold including a tooth forming die.
  • the rack bar 110 is manufactured by quenching the preliminary rack bar 116. Torsional deformation is generated in the rack portion 112 caused by the quenching. A heat distribution in the rack teeth during the quenching is considered as a cause of the torsional deformation. The torsional deformation caused by the heat distribution is generated in a fixed direction. The torsion angle can be experimentally predetermined.
  • the pitch surface PS of the preliminary rack bar 116 is twisted in an opposite direction to the twist direction caused by the heat distribution of the rack teeth. Thus, the pitch surface PS is twisted back so as to be parallel to the axial direction of the shaft member 111 during the quenching.
  • an preliminary rack bar includes a shaft member having a plurality of rack teeth arranged side by side in an axial direction of the shaft member, and the pitch surface of the rack teeth is twisted around a central axis of the shaft member.
  • the top lands of the rack teeth may be provided within the same plane parallel to the central axis of the shaft member.
  • the bottom lands may be provided within another plane parallel to the central axis of the shaft member.
  • Tooth traces of the rack teeth may be inclined with respect to a direction perpendicular to the axial direction, and the pitch surface may be twisted in a direction of widening the pitch of the rack teeth.
  • the shaft member may be a hollow shaft member.
  • a method for manufacturing a rack bar includes forming a plurality of rack teeth in a shaft member side by side in an axial direction of the shaft member such that the pitch surface of the rack teeth is twisted around a central axis of the shaft member, and quenching the shaft member having the rack teeth such that the pitch surface is twisted back by the quenching.
  • the rack teeth may be formed such that the top lands of the rack teeth are provided within the same plane parallel to the central axis of the shaft member.
  • the rack teeth may be formed such that the bottom lands of the rack teeth are provided within another plane parallel to the central axis of the shaft member.
  • the rack teeth may be formed such that the pitch surface is twisted in a direction of widening the pitch of the rack teeth.
  • the shaft member may be a hollow shaft member.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • General Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Transportation (AREA)
  • Gears, Cams (AREA)
  • Heat Treatment Of Articles (AREA)

Abstract

An rack bar includes a shaft member having a plurality of rack teeth arranged side by side in an axial direction of the shaft member. In a preliminary form before quenching, the pitch surface of the plurality of rack teeth is twisted around a central axis of the shaft member. This rack bar is then quenched such that the pitch surface is twisted back by the quenching.

Description

RACK BAR IN PRELIMINARY FORM BEFORE QUENCHING AND RACK BAR MANUFACTURING METHOD Technical Filed
Illustrative aspects of the present invention relate to a rack bar in a preliminary form before quenching and a method for manufacturing a rack bar.
Generally, a rack bar used for a rack-and-pinion type steering device of a car is quenched. From a viewpoint of suppressing the rack bar from being deformed during the quenching, the rack bar is quenched in a restrained state (see, for example, JP2001-011536A and JP2014-133924A). In a rack bar manufacturing method disclosed in JP2014-133924A, a rack bar is quenched in a state in which a torsional torque is applied to the rack bar, so that the rack bar is prevented from being torsionally deformed during quenching.
The torsional deformation of the rack bar may cause deterioration of meshing between a rack and a pinion and may reduce transmission efficiency. This may particularly be a problem with a dual pinion type rack bar having two rack portions, one being configured to mesh with a steering pinion of a steering shaft and the other being configured to mesh with an assist pinion of an assist mechanism, since the torsional deformation of the rack bar may reduce accuracy of a difference in an angular position around a central axis given to the two rack portions. The method of JP2014-133924A can prevent the torsional deformation of the rack bar by applying torsional torque to the rack bar when quenching the rack bar. However, this requires an additional equipment for applying the torsional torque.
Summary
Illustrative aspects of present invention provide a technique for easily reducing a torsion of a rack bar (the word “torsion” is intended to mean a torsional deviation from a desired shape).
According to an illustrative aspect of the present invention, a preliminary rack bar served for quenching is provided. The preliminary rack bar includes a shaft member having a plurality of rack teeth arranged side by side in an axial direction of the shaft member, and the pitch surface of the plurality of rack teeth is twisted around a central axis of the shaft member.
According to another illustrative aspect of the present invention, a method for manufacturing a rack bar is provided. The method includes forming a plurality of rack teeth in a shaft member side by side in an axial direction of the shaft member such that the pitch surface of the rack teeth is twisted around a central axis of the shaft member, and quenching the shaft member having the rack teeth such that the pitch surface is twisted back by the quenching.
Other aspects and advantages of the invention will be apparent from the following description, the drawings and the claims.
Fig. 1 is a plan view of a rack bar according to an embodiment of the present invention. Fig. 2 is a sectional view of the rack bar of Fig. 1. Fig. 3 is a plan view of the rack bar of Fig. 1 before being quenched. Fig. 4 is a schematic view illustrating a rack bar manufacturing method according to an embodiment of the present invention. Fig. 5 is another schematic view illustrating the rack bar manufacturing method. Fig. 6 is a schematic view of an example of rack teeth forming die shown in Fig. 5. Fig. 7 is a plan view of a rack bar according to another embodiment of the present invention. Fig. 8 is a sectional view of the rack bar of Fig. 7. Fig. 9 is a plan view of rack bar of Fig. 7 before being quenched.
Fig. 1 and Fig. 2 illustrate a rack bar 10 according to an embodiment of the present invention. Fig. 3 illustrates the rack bar illustrated in Fig. 1 and Fig. 2 before it is being quenched, i.e., rack bar in a preliminary form before quenching (hereinafter referred to as preliminary rack bar 16).
The rack bar 10 has a hollow cylindrical shaft member 11. The shaft member 11 is made of metal such as steel. The shaft member 11 has a rack portion 12 having a plurality of rack teeth 13 configured to mesh with a pinion of a steering device. The rack portion 12 is provided on one side of the shaft member 11 having an end portion 11a. The shaft member 11 has a hollow cylindrical shaft portion 14 configured to be supported movably on a housing of the steering device. The shaft portion 14 is provided on the other side of the shaft member 11 having the other end portion 11b.
The rack portion 12 has a flattened portion 15 extending in an axial direction of the shaft member 11. The plurality of rack teeth 13 is formed on an outer surface of the flattened portion 15 such that the rack teeth 13 are arranged side by side in the axial direction of the shaft member 11. A pitch surface PS of the rack teeth 13 is a plane parallel to a central axis of the shaft member 11. Here, the pitch surface PS is an imaginary surface that makes a rolling contact with a pitch circle of the pinion.
In the present example, each of tooth traces TT of the rack teeth 13 is inclined with respect to a direction perpendicular to the axial direction of the shaft member 11, and a pitch p1 between adjacent ones of the rack teeth 13 is fixed. Here, the tooth trace TT is a line of intersection between a tooth surface of the rack tooth 13 and the pitch surface PS. The tooth trace of the rack tooth 13 may be perpendicular to the axial direction of the shaft member 11. The pitch between the adjacent ones of the rack teeth 13 may be variable, for example, to be relatively narrow at an axially central portion of the rack portion 12 and relatively wide at axial end portions of the rack portion 12.
In order to increase hardness of the rack portion 12 meshing with the pinion of the steering device and increase hardness of the shaft portion 14 supported on the housing of the steering device, the rack portion 12 and the shaft portion 14 are quenched.
The preliminary rack bar 16 illustrated in Fig. 3 is, in other words, the rack bar 10 with the rack portion 12 and the shaft portion 14 being not quenched yet. The preliminary rack bar 16 is configured in a similar manner as the rack bar 10. However, the pitch surface PS of the rack teeth 13 of the preliminary rack bar 16 is twisted around the central axis of the shaft member 11. In the present example in which each of the tooth traces TT of the rack teeth 13 is inclined with respect to the direction perpendicular to the axial direction of the shaft member 11, the pitch surface PS of the preliminary rack bar 16 is twisted in a direction A of widening the pitch p2 of the rack teeth 13 (p1<p2).
In the present example, top lands 13a of the rack teeth 13 of the preliminary rack bar 16 are arranged within the same plane parallel to the axial direction of the shaft member 11. Bottom lands 13b of the rack teeth 13 are also arranged within the same plane parallel to the axial direction of the shaft member 11.
A method for manufacturing the rack bar 10 will be described with reference to Fig. 4 and Fig. 5.
First, as shown in Fig. 4, the side of an end portion 11a of a shaft member 11 is squashed into a flat shape by press working so that a flattened portion 15 extending in an axial direction of the shaft member 11 is formed. If necessary, chemical conversion coating for forming a phosphate film may be then applied to a surface of the shaft member 11. After that a plurality of rack teeth 13 can be formed on the flatly squashed portion 15.
As shown in Fig. 5, at least a part of the shaft member 11 in the axial direction including the flattened portion 15 is held by a metal mold 20. The metal mold 20 is provided with an upper mold 21 and a lower mold 22. The upper mold 21 and the lower mold 22 are opened/closed by a mold clamping mechanism (not shown) to interpose the shaft member 11 from above and below to thereby hold an outer circumference of the shaft member 11. A tooth forming die 23 is detachably mounted in the upper mold 21. The tooth forming die 23 is fixed in contact with an outer surface of the flattened portion 15. A plurality of tooth grooves 25 for forming the rack teeth 13 are provided in a molding surface 24 of the tooth forming die 23 brought into contact with the flattened portion 15.
In the state in which the tooth forming die 23 has brought into contact with the outer surface of the flattened portion 15, a mandrel 30 is inserted into the shaft member 11 through an opening formed in the side of the end portion 11a of the shaft member 11 to be press-fitted into an inside of the flattened portion 15 by a push bar 31. The press-fitted mandrel 30 is pushed back by a push bar 32 inserted from an opening formed in the side of the end portion 11b of the shaft member 11 so that the mandrel 30 can be discharged from the shaft member 11. In a process of moving the mandrel 30 back and forth over the entire length of the flattened portion 15, the material of the flattened portion 15 is forged by the mandrel 30 to thereby plastically deform toward the tooth forming die 23.
The mandrel 30 is replaced with one which is gradually larger, and the press-fitting of the mandrel 30 is repeated. In this manner, the material of the flattened portion 15 gradually enters into the tooth grooves 25 of the tooth forming die 23. The shape of the molding surface 24 of the tooth forming die 23 is transferred to the flattened portion 15. As a result, a plurality of rack teeth 13 are formed on the flattened portion 15. The preliminary rack bar 16 is manufactured via the aforementioned methods.
Next, the rack portion 12 and the shaft portion 14 are quenched in order to increase harness of the rack portion 12 and increase hardness of the shaft portion 14. The preliminary rack bar 16 including the rack portion 12 and the shaft portion 14 may be entirely quenched. Heating during the quenching can be applied, for example, by high frequency induction heating but is not limited to the high frequency induction heating.
Torsional deformation is generated in the rack portion 12 caused by the quenching. A heat distribution in the rack teeth during the quenching is considered as a cause of the torsional deformation. The torsional deformation caused by the heat distribution is generated in a fixed direction. In addition, transformation stress during the quenching is considered as another cause of the torsional deformation. The torsional deformation caused by the transformation stress is determined by the shape of the rack teeth 13. When tooth traces TT of the rack teeth 13 are set to be inclined with respect to a direction perpendicular to the axial direction of the shaft member 11, the torsional deformation caused by the transformation stress is generated in a direction to narrow the pitch of the rack teeth 13.
Here, the pitch surface PS of the preliminary rack bar 16 is twisted in a direction A (see Fig. 3) of widening the pitch of the rack teeth 13. Due to quenching applied to the preliminary rack bar 16, the torsional deformation is caused to the rack portion 12 in a direction (an opposite direction to the direction A) to narrow the pitch of the rack teeth 13. Thus, the pitch surface PS is twisted back to a plane parallel to the axial direction of the shaft member 11. A torsional deformation amount (a torsion angle) generated in the rack portion 12 due to the quenching and a torsion angle of the pitch surface PS of the preliminary rack bar 16 cancelling the deformation amount are experimentally predetermined to be, for example, about 0.05°to 0.1°in the rack portion 12 having a standard length.
Thus, the pitch surface PS of the rack teeth 13 of the preliminary rack bar 16 is twisted around a central axis of the shaft member 11. The pitch surface PS is twisted back to a planar shape caused by the quenching applied to the preliminary rack bar 16. Accordingly, it is possible to easily reduce torsion of the rack bar 10 which is formed by quenching the preliminary rack bar 16.
Fig. 6 illustrates an example of the tooth forming die 23 used for manufacturing the rack bar 10.
Assuming that columnar pins 26 are disposed respectively in the tooth grooves 25 of the tooth forming die 23, a tangential line TL between each of side surfaces of the tooth grooves 25 and a corresponding one of the pins 26 is inclined gradually in a direction in which the tooth grooves 25 arrange from one end side toward the other end side. Rack teeth 13 are molded by the tooth grooves 25. The tangential lines TL between the side surfaces of the tooth grooves 25 and the pins 26 correspond to tooth traces TT of the rack teeth 13 respectively. Since the tangential lines TL between the side surfaces of the tooth grooves 25 and the pins 26 are inclined gradually, the tooth traces TT of the molded rack teeth 13 thus are also inclined gradually. Thus, the pitch surface PS where the tooth traces TT of the rack teeth 13 of the preliminary rack bar 16 exist is twisted around the central axis of the shaft member 11.
Each of bottom surfaces 25a of the tooth grooves 25 can be formed so as to be parallel to a central axis of the pin 26 disposed in the tooth groove 25. In this case, the bottom surfaces 25a are inclined gradually in the direction in which the tooth grooves 25 arrange from one end side toward the other end side. Preferably, the bottom surfaces 25a are formed within the same plane. Thus, manufacturing of the tooth forming die 23 becomes easy. When the bottom surfaces 25a are formed within the same plane, top lands 13a of the rack teeth 13 of the preliminary rack bar 16 are provided within the same plane parallel to the axial direction of the shaft member 11 respectively.
A top face 25b of a protrusion between adjacent two of the tooth groves 25 can be formed so as to be parallel to the central axis of the pin 26 disposed in one of the two tooth grooves 25. In this case, the top faces 25b are gradually inclined in the direction in which the tooth grooves 25 from one end side toward the other end side. Preferably, the top faces25b are formed on the same plane respectively. Thus, the manufacturing of the tooth forming die 23 becomes easy. When the top faces 25b are formed within the same plane, bottom lands 13b of the rack teeth 13 of the preliminary rack bar 16 are provided within the same plane parallel to the axial direction of the shaft member 11.
Fig. 7 and Fig. 8 illustrate a rack bar 110 according to another embodiment of the present invention. Fig. 9 shows illustrates the rack bar of Fig. 7 and Fig. 8 before it is being quenched, i.e., preliminary rack bar 116. Elements that are same as or similar to those of the rack bar 10 and the preliminary rack bar 16 described above will be denoted by the same reference signs, and description thereof will be omitted or simplified.
The rack bar 110 has a solid cylindrical shaft member 111. The shaft member 111 has a rack portion 112 having a plurality of rack teeth 113. The rack portion 112 is provided on one side of the shaft member 111 having an end portion 111a of. The shaft member 111 has a solid cylindrical shaft portion 114. The solid cylindrical shaft portion 114 is provided on the other side of the shaft member 111 having the other end portion 111b. In the present example, tooth traces TT of the rack teeth 113 are perpendicular to an axial direction of the shaft member 111.
The preliminary rack bar 116 illustrated in Fig. 9 is, in other words, the rack bar 100 with the rack portion 112 and the shaft portion 114 being not quenched yet. The preliminary rack bar 116 is configured in a similar manner as the rack bar 110. The pitch surface PS of the rack teeth 113 of the preliminary rack bar 116 is twisted around a central axis of the shaft member 111.
The preliminary rack bar 116 is formed by, for example, forging using a metal mold including a tooth forming die. The rack bar 110 is manufactured by quenching the preliminary rack bar 116. Torsional deformation is generated in the rack portion 112 caused by the quenching. A heat distribution in the rack teeth during the quenching is considered as a cause of the torsional deformation. The torsional deformation caused by the heat distribution is generated in a fixed direction. The torsion angle can be experimentally predetermined. The pitch surface PS of the preliminary rack bar 116 is twisted in an opposite direction to the twist direction caused by the heat distribution of the rack teeth. Thus, the pitch surface PS is twisted back so as to be parallel to the axial direction of the shaft member 111 during the quenching.
Illustrative aspects of the present invention have been described so far with a single pinion type rack bar 10, 110 as an example. However, the present invention may be also applied to a dual pinion type rack bar provided with two rack portions. In addition, the present invention may be also applied to a rack bar in which another linear motion element such as a ball screw is formed on the shaft portion 14, 114 of the rack bar 10, 110.
As described above, according to an illustrative aspect of the present invention, an preliminary rack bar includes a shaft member having a plurality of rack teeth arranged side by side in an axial direction of the shaft member, and the pitch surface of the rack teeth is twisted around a central axis of the shaft member.
The top lands of the rack teeth may be provided within the same plane parallel to the central axis of the shaft member. The bottom lands may be provided within another plane parallel to the central axis of the shaft member.
Tooth traces of the rack teeth may be inclined with respect to a direction perpendicular to the axial direction, and the pitch surface may be twisted in a direction of widening the pitch of the rack teeth.
The shaft member may be a hollow shaft member.
According to another illustrative aspect of the present invention, a method for manufacturing a rack bar includes forming a plurality of rack teeth in a shaft member side by side in an axial direction of the shaft member such that the pitch surface of the rack teeth is twisted around a central axis of the shaft member, and quenching the shaft member having the rack teeth such that the pitch surface is twisted back by the quenching.
The rack teeth may be formed such that the top lands of the rack teeth are provided within the same plane parallel to the central axis of the shaft member. The rack teeth may be formed such that the bottom lands of the rack teeth are provided within another plane parallel to the central axis of the shaft member.
The rack teeth may be formed such that the pitch surface is twisted in a direction of widening the pitch of the rack teeth.
The shaft member may be a hollow shaft member.
This application claims priority to Japanese Patent Application No. 2018-106843 filed on June 4, 2018, the entire content of which is incorporated herein by reference.

Claims (12)

  1. A rack bar in a preliminary form before quenching, the rack bar comprising:
    a shaft member having a plurality of rack teeth arranged side by side in an axial direction of the shaft member,
    wherein a pitch surface of the plurality of rack teeth is twisted around a central axis of the shaft member.
  2. The rack bar according to Claim 1, wherein top lands of the plurality of rack teeth are provided within a plane parallel to the central axis of the shaft member.
  3. The rack bar according to Claim 1, wherein bottom lands of the plurality of rack teeth are provided within a plane parallel to the central axis of the shaft member.
  4. The rack bar according to Claim 2, wherein bottom lands of the plurality of rack teeth are provided within another plane parallel to the central axis of the shaft member.
  5. The rack bar according to Claim 1 or 2, wherein tooth traces of the plurality of rack teeth are inclined with respect to a direction perpendicular to the axial direction, the tooth traces being lines of intersection between tooth surfaces of the plurality of rack teeth and the pitch surface, and
    wherein the pitch surface is twisted in a direction of widening a pitch of the rack teeth.
  6. The rack bar according to any one of Claims 1 to 5, wherein
    the shaft member is a hollow shaft member.
  7. A method for manufacturing a rack bar, the method comprising:
    forming a plurality of rack teeth on a shaft member side by side in an axial direction of the shaft member such that a pitch surface of the plurality of rack teeth is twisted around a central axis of the shaft member; and
    quenching the shaft member having the plurality of rack teeth such that the pitch surface is twisted back by the quenching.
  8. The method according to Claim 7, wherein the forming the plurality of rack teeth comprises forming top lands of the plurality of rack teeth within a plane parallel to the central axis of the shaft member.
  9. The method according to Claim 7, wherein the forming the plurality of rack teeth comprises forming bottom lands of the plurality of rack teeth within a plane parallel to the central axis of the shaft member.
  10. The method according to Claim 8, wherein the forming the plurality of rack teeth comprises forming bottom lands of the plurality of rack teeth within another plane parallel to the central axis of the shaft member.
  11. The method according to any one of Claims 7 to 10, wherein the plurality of rack teeth is formed such that the pitch surface is twisted in a direction of widening a pitch of the plurality of rack teeth.
  12. The method according to any one of Claims 7 to 11, wherein
    the shaft member is a hollow shaft member.

PCT/JP2019/020489 2018-06-04 2019-05-23 Rack bar in preliminary form before quenching and rack bar manufacturing method WO2019235239A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2018106843A JP7086729B2 (en) 2018-06-04 2018-06-04 Manufacturing method of rack bar preformed body and rack bar
JP2018-106843 2018-06-04

Publications (1)

Publication Number Publication Date
WO2019235239A1 true WO2019235239A1 (en) 2019-12-12

Family

ID=66776824

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2019/020489 WO2019235239A1 (en) 2018-06-04 2019-05-23 Rack bar in preliminary form before quenching and rack bar manufacturing method

Country Status (2)

Country Link
JP (1) JP7086729B2 (en)
WO (1) WO2019235239A1 (en)

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS62180018A (en) * 1986-01-31 1987-08-07 Yamada Seisakusho:Kk High frequency quenching method for steering rack
JPS63297524A (en) * 1987-05-28 1988-12-05 High Frequency Heattreat Co Ltd Quenching method for rack bar composed of rack part and pipe part
EP0993881A2 (en) * 1998-10-12 2000-04-19 Neturen Co., Ltd. Constrained hardening method and apparatus for deformed bar workpieces
JP2001011536A (en) 1999-06-28 2001-01-16 High Frequency Heattreat Co Ltd Method and device for hardening rack bar
JP2014133924A (en) 2013-01-10 2014-07-24 Fuji Electronics Industry Co Ltd Rack production method
JP2018106843A (en) 2016-12-22 2018-07-05 パナソニックＩｐマネジメント株式会社 Lighting device and luminaire equipment
WO2018168938A1 (en) * 2017-03-16 2018-09-20 Neturen Co., Ltd. Method for manufacturing rack bar

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS62180018A (en) * 1986-01-31 1987-08-07 Yamada Seisakusho:Kk High frequency quenching method for steering rack
JPS63297524A (en) * 1987-05-28 1988-12-05 High Frequency Heattreat Co Ltd Quenching method for rack bar composed of rack part and pipe part
EP0993881A2 (en) * 1998-10-12 2000-04-19 Neturen Co., Ltd. Constrained hardening method and apparatus for deformed bar workpieces
JP2001011536A (en) 1999-06-28 2001-01-16 High Frequency Heattreat Co Ltd Method and device for hardening rack bar
JP2014133924A (en) 2013-01-10 2014-07-24 Fuji Electronics Industry Co Ltd Rack production method
JP2018106843A (en) 2016-12-22 2018-07-05 パナソニックＩｐマネジメント株式会社 Lighting device and luminaire equipment
WO2018168938A1 (en) * 2017-03-16 2018-09-20 Neturen Co., Ltd. Method for manufacturing rack bar

Also Published As

Publication number Publication date
JP7086729B2 (en) 2022-06-20
JP2019210993A (en) 2019-12-12

Similar Documents

Publication Publication Date Title
US20200039571A1 (en) Hollow rack bar and method of manufacturing the hollow rack bar
US10562138B2 (en) Method for manufacturing rack bar
US6038771A (en) Method of manufacturing tie rod bar for steering linkage of motor vehicle
US20090317181A1 (en) Assembly member and method of manufacturing assembly member
EP2676865B1 (en) Rack bar and rack bar teeth forming die
KR20070110364A (en) Method for producing a joint connection and corresponding joint connection
US9518627B2 (en) Changes enabling the elimination of processes for a torsion bar
DE102005033188A1 (en) Method for production of hollow cylinder precision metal parts with external teeth useful in vehicle production, e.g. steering wheel spindles production of a rough part by cutting the bar material to the required length
EP3475147A1 (en) Ball screw of an electromechanical power steering system having an integrated angular-contact ball bearing
US9975163B2 (en) Method of making shaft
WO2019049477A1 (en) Rack and manufacturing method for same, steering device, vehicle and preforming mold for rack
WO2019235239A1 (en) Rack bar in preliminary form before quenching and rack bar manufacturing method
EP3837065A1 (en) Two-part high-strength screw
KR100843363B1 (en) Method for producing a housing for a ball joint
JP6259210B2 (en) Koma type ball screw
JP4352243B2 (en) Mold for molding hollow parts and manufacturing method
EP1717470B1 (en) Bearing arrangement with two-part bearing housing
WO2006029691A1 (en) Method for shaping an assembling element and assembling element
EP3163123A2 (en) Sprocket and method and device for producing the same
JP6393599B2 (en) Helical gear and manufacturing method thereof
WO2020158616A1 (en) Rack bar
US10967549B2 (en) Pull or push rod or locking nut for a molding machine
EP1507983B1 (en) Housing for receiving a bearing component and method for producing the same
JP5549331B2 (en) Ball screw manufacturing method
JPH11115772A (en) Shaft with gear and steering device

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 19729098

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 19729098

Country of ref document: EP

Kind code of ref document: A1