JP2008240120A - Method for manufacturing hollow rack bar, and hollow rack bar - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the hardness of an end-part while maintaining working precision of an outer-peripheral screw and an inner-peripheral screw formed at the end-part, and preventing delayed breakage. <P>SOLUTION: A method for manufacturing a hollow rack bar is provided with; a tooth part forming process in which the tooth part 12 is formed on a shaft part 11; an end-part hardening process in which a high-frequency induction-hardening is performed to the tooth side end-part 13; a first temperature end-part tempering process in which a high-frequency induction-tempering is performed at 1000°C to the tooth side end-part 13; a screw-working process in which the screw-working for forming the screw 15 on the inner periphery of the tooth side end-part 13 is performed; a shaft part hardening process in which a high-frequency induction-hardening is performed to the shaft part 1 and tooth part 12; and a second tempering process in which the high-frequency induction-tempering is performed at 200°C to the tooth side end-part 13, the shaft part 11 and the tooth part 12. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a hollow rack bar used for a rack and pinion gear used in a power steering device of an automobile and the like, and particularly to a hollow rack bar that can reinforce an end portion on which a screw portion is formed. About.

  A solid rack bar used in a power steering device of an automobile has a tooth portion meshed with a pinion gear at an intermediate portion, and a screw portion used for connection with a ball joint is formed at an end portion thereof. .

  The solid rack bar is formed from a solid material made of a tempered material such as S45C, for example. In S45C, the material hardness is Hv 240 to 285, but the shaft portion located in the middle portion is formed with teeth by cutting and then heat-treated, so that the hardness is Hv 600 or more. On the other hand, since the screw portion located at the end is processed, the material hardness is maintained.

  FIG. 21 is a view showing an example of a hollow rack bar developed in recent years in place of the solid rack bar. The hollow rack bar 100 has a hollow shaft portion 101, and a tooth portion 102 that is engaged with a pinion (not shown) is formed at an intermediate portion of the shaft portion 101. An inner peripheral screw 104 used for connection with the ball joint is provided. In FIG. 21, reference numeral 110 denotes a ball joint, and 111 denotes a socket for connecting the ball joint 110 to the end portion 103 via an outer peripheral screw 112.

In addition, the technique of high-frequency heating the hollow rack bar and the technique of partially changing the heat treatment conditions are generally known (see Patent Documents 1 and 2).
JP-A 63-297524 JP-A-6-264147

  The hollow rack bar described above has the following problems. That is, the input load from the tire to the rack and pinion gear tends to increase due to the recent increase in size of automobiles. However, although the shaft portion 101 can be increased in hardness by heat treatment, the end portion 103 cannot be increased in hardness because it is threaded. Therefore, when a strength test (arrow K in FIG. 21) for inputting a load from the ball joint 110 arranged on the tire side is performed, the screws loosen due to insufficient strength of the end portion 103 or the inner peripheral screw, or as shown in FIG. In some cases, the ball joint 110 may fall off.

  Therefore, the present invention provides a method for manufacturing a hollow rack bar and a hollow rack bar that increase the strength of the end while maintaining the machining accuracy of the inner peripheral screw formed at the end and preventing delayed fracture. It is aimed.

  In order to solve the above-described problems and achieve the object, the method for manufacturing a hollow rack bar and the hollow rack bar of the present invention are configured as follows.

  In the method of manufacturing a hollow rack bar having a tooth portion meshed with a pinion gear in the shaft portion and a screw portion provided for connection to a ball joint on the inner peripheral surface of the end portion, the shaft portion includes A tooth part forming step for forming a tooth part, an end quenching step for induction hardening at the end, a first temperature end tempering step for induction tempering at a first temperature at the end, and the first After the temperature tempering step, a screw machining step for forming the screw portion on the inner periphery of the end portion, a tooth portion quenching step for induction hardening the tooth portion, and an induction hardening for the shaft portion A shaft portion quenching step and a second temperature tempering step of performing induction tempering on the end portion, the tooth portion, and the shaft portion at a second temperature lower than the first temperature are provided.

  In the method of manufacturing a hollow rack bar, the shaft portion has a tooth portion meshed with the pinion gear, and an inner peripheral thread portion provided for connection to a ball joint is formed on an inner peripheral surface of the end portion. A tooth portion forming step for forming a tooth portion on the portion, an end quenching step for performing induction hardening on the outer peripheral surface of the end portion, and a first temperature tempering step for performing induction tempering at a first temperature on the outer peripheral surface of the end portion; , After the first temperature tempering step, a screw processing step for performing screw processing for forming the screw portion on the inner periphery of the end portion, a tooth portion quenching step for performing induction hardening on the tooth portion, and a shaft portion A shaft quenching step for induction hardening, and a second temperature tempering step for induction tempering the end portion, the tooth portion, and the shaft portion at a second temperature lower than the first temperature. Features.

  In the method of manufacturing a hollow rack bar, the shaft portion has a tooth portion meshed with the pinion gear, and an inner peripheral thread portion provided for connection to a ball joint is formed on an inner peripheral surface of the end portion. A tooth part forming step for forming a tooth part on the part, a sumi process step for forming a recess by carrying out a stencil process on the inner periphery of the end part from the opening side, and an inner periphery of the end part and deeper than the recess A screw processing step for performing screw processing for forming the screw portion on the side, an end quenching step for performing induction hardening on the opening end of the end portion, and a first step for performing induction tempering at a first temperature on the end portion. A one-temperature tempering step, a tooth-quenching step for induction-quenching the tooth portion, a shaft-quenching step for induction-quenching the shaft portion, a first temperature lower than the first temperature at the end portion and the shaft portion. Induction tempering at a temperature of 2 Characterized in that it comprises a second temperature tempering process.

  A tooth portion meshed with the pinion gear is provided on a hollow shaft portion, and an end portion provided with an inner peripheral surface of at least one end of the shaft portion and provided with a screw portion used for connection with a ball joint; The hardness of the shaft portion is higher than the hardness of the end portion.

  According to the present invention, it is possible to increase the strength of the end portion while maintaining the machining accuracy of the screw portion formed at the end portion and preventing delayed fracture.

  FIG. 1 is a longitudinal sectional view showing a main part of a rack and pinion gear in which a hollow rack bar 10 according to an embodiment of the present invention is incorporated. The hollow rack bar 10 has a tubular shaft portion 11, and a tooth portion 12 meshed with the pinion 30 is formed at an intermediate portion of the shaft portion 11, and a tooth side end portion 13 positioned at both ends. A screw 15 provided for connection to the ball joint is provided on the inner peripheral surface of the shaft end 14. The hollow rack bar 10 is made of a material such as SMn433, and has an initial hardness of Hv155 to 200.

  On the other hand, a ball joint 20 is attached to the tooth side end portion 13 via a socket 21. The socket 21 is provided with an outer peripheral screw 22 that is screwed onto the screw 15. The socket 21 has a structure that supports the ball joint 20 in a swingable manner, and is provided with a resin sheet 23. In FIG. 1, reference numeral 40 denotes a casing, and 50 denotes a bellows type boot.

  The hollow rack bar 10 described above is formed as follows. That is, the tooth portion 12 is formed on the shaft portion 11 by cold transfer forging. Specifically, by pressing the pipe material with a cold forging die, the upper surface is formed flat together with the tooth profile primary molding, and the core metal is press-fitted into the cavity of the pipe material in the next step. The cored bar is formed in a rod shape, and has a tapered projection on the flat portion side of the pipe material, and the projection portion engages with the flat portion of the pipe material on the inner peripheral side, so that the meat of the flat portion is Is projected by plastic deformation toward the teeth of the mold, and linear teeth 12 having a shape corresponding to the teeth of the mold are applied to the outer peripheral flat portion of the pipe material by the transfer method. Is done.

  Next, the hardness of the hollow rack bar 10 is increased, and screws are formed on the tooth side end portion 13 and the shaft side end portion 14. For example, there are the following three processing methods for increasing the hardness and forming the screw.

  The first processing method is performed as follows. That is, as shown in FIGS. 3A and 3B, the tooth side end portion 13 on which the tooth portion 12 is formed is subjected to induction hardening at, for example, 1000 ° C. to increase the hardness to Hv 620 (end hardening step). Next, induction tempering at 600 ° C. (first temperature) is performed on the tooth side end portion 13 (first temperature tempering step), and the hardness is set to, for example, Hv 250 to 450. Similarly, as shown in FIGS. 4A and 4B, induction hardening and induction tempering are performed on the shaft side end portion 14 to set the hardness to Hv 250 to 450.

  Next, as shown in FIG. 5, screw processing for forming the screw 15 on the inner periphery of the tooth side end portion 13 and the shaft side end portion 14 is performed (screw processing step).

  Next, as shown in FIG. 6A, the tooth portion 12 is induction-hardened at 1000 ° C., for example, to increase the hardness to Hv 620, and similarly to the shaft portion 11 on the shaft side end portion 14 side as shown in FIG. 6B. Induction hardening is performed to raise the Hv620 (shaft hardening process). Next, as shown in FIG. 7, the entire hollow rack bar 10 is subjected to induction tempering at 200 ° C. (second temperature) (second temperature tempering step).

  Thereby, in the 1st processing method, it will be in a hardness state as shown in FIG. That is, the hardness of the shaft portions 11a and 11b is Hv450 to 650, and the hardness of the tooth side end portion 13 is Hv250 to 450. Therefore, it is possible to increase the strength of the tooth side end portion 13 against the external force and at the same time maintain the machining accuracy of the screw 15 and prevent delayed fracture.

  The second processing method is performed as follows. That is, as shown in FIGS. 9A and 9B, induction hardening at, for example, 1000 ° C. is performed at a depth t1 (about 0.5 to 1 mm) of the outer peripheral surface 13a of the tooth side end portion 13 where the tooth portion 12 is formed. The hardness is increased to Hv620 (end quenching process). Next, induction tempering at 600 ° C. (first temperature) is performed on the outer peripheral surface 13a of the tooth side end portion 13 (first temperature tempering step), and the hardness is set to, for example, HvHv 250 to 450. Similarly, as shown in FIGS. 10A and 10B, induction hardening and induction tempering are performed on the outer peripheral surface 14 a of the shaft-side end portion 14 to set the hardness to HvHv 250 to 450.

  Next, as shown in FIG. 11, screw processing for forming the screw 15 on the inner periphery of the tooth side end portion 13 and the shaft side end portion 14 is performed (screw processing step).

  Next, as shown in FIG. 12A, the tooth portion 12 is induction-hardened at 1000 ° C., for example, to increase the hardness to Hv620, and similarly to the shaft portion 11 on the shaft side end portion 14 side as shown in FIG. 12B. Induction hardening is performed to raise the Hv620 (shaft hardening process). Next, as shown in FIG. 13, the entire hollow rack bar 10 is subjected to induction tempering at 200 ° C. (second temperature) (second temperature tempering step).

  Thereby, in the 2nd processing method, it will be in a hardness state as shown in FIG. That is, the hardness of the shaft portion 11 is Hv450 to 650, and the hardness of the tooth side end portion 13 is Hv250 to 450. Therefore, it is possible to increase the strength of the tooth side end portion 13 against the external force and at the same time maintain the machining accuracy of the screw 15 and prevent delayed fracture.

  The third processing method is performed as follows. In other words, the inside of the tooth side end portion 13 and the shaft side end portion 14 is crushed from the opening side to form the concave portion 16 having a depth of about 5 mm (the punishment step). Next, screw processing for forming the screw 15 on the inner side of the tooth side end portion 13 on the back side of the recess 16 is performed (screw processing step). Next, as shown in FIGS. 16A and 16B, induction hardening at 1000 ° C., for example, is performed at a depth t2 (within 5 mm) from the opening end 13b of the tooth side end portion 13 where the tooth portion 12 is formed, and the hardness is set to Hv620. Raise (end quenching process). Next, induction tempering at 600 ° C. (first temperature) is performed on the opening end 13b of the tooth side end portion 13 (first temperature tempering step), and the hardness is set to, for example, Hv 250 to 450. Similarly, as shown in FIGS. 17A and 17B, induction hardening and induction tempering are performed on the opening end 14 b of the shaft side end portion 14 so that the hardness is Hv 250 to 450. In this heat treatment step, since the recess 16 is provided, heat is not transmitted to the screw 15 and the machining accuracy is maintained.

  Next, as shown in FIG. 18A, the tooth portion 12 is induction-hardened at, for example, 1000 ° C. to increase the hardness to Hv 620, and similarly to the shaft portion 11 on the shaft side end portion 14 side as shown in FIG. 18B. Induction hardening is performed to raise the Hv620 (shaft hardening process). Next, as shown in FIG. 19, the entire hollow rack bar 10 is subjected to induction tempering at 200 ° C. (second temperature) (second temperature tempering step).

  Thereby, in the 3rd processing method, it will be in a hardness state as shown in FIG. That is, the hardness of the shaft portion 11 and the tooth portion 12 on the shaft side end portion 14 side is Hv 450 to 650, and the hardness of the opening end 13b of the tooth side end portion 13 is Hv 250 to 450. Therefore, it is possible to increase the strength of the tooth side end portion 13 against the external force and at the same time maintain the machining accuracy of the screw 15 and prevent delayed fracture.

  As described above, according to the method for manufacturing a hollow rack bar according to the embodiment of the present invention, it is possible to maintain the machining accuracy of the screw 15 formed on the tooth side end portion 13 and the shaft side end portion 14 and prevent delayed fracture. While performing, the intensity | strength of the tooth side edge part 13 can be increased.

  The present invention is not limited to the above embodiment. For example, the material of the hollow rack bar 10 is not limited to Smn433, and other materials may be used. The heat treatment conditions (quenching temperature and tempering temperature) are set to obtain a desired hardness and are determined by the material, shape, etc., and are not limited to the temperature in this embodiment. Of course, various modifications can be made without departing from the scope of the present invention.

The longitudinal cross-sectional view which shows the principal part of the rack & pinion gear in which the hollow rack bar which concerns on one embodiment of this invention was integrated. The longitudinal cross-sectional view which shows the principal part of the same hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (induction hardening) of the tooth side edge part of the hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency tempering) of the tooth side edge part of the hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency hardening) of the axial side edge part of the same hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency tempering) of the axial side edge part of the hollow rack bar. The longitudinal cross-sectional view which shows the threading process of the tooth side edge part and axial side edge part of the same hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency hardening) of the tooth | gear part of the hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency hardening) of the axial part of the same hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency tempering) of the same hollow rack bar. The longitudinal cross-sectional view which shows the hardness of the same hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (induction hardening) of the tooth side edge part of the hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency tempering) of the tooth side edge part of the hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency hardening) of the axial side edge part of the same hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency tempering) of the axial side edge part of the hollow rack bar. The longitudinal cross-sectional view which shows the threading process of the tooth side edge part and axial side edge part of the same hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency hardening) of the tooth | gear part of the hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency hardening) of the axial part of the same hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency tempering) of the same hollow rack bar. The longitudinal cross-sectional view which shows the hardness of the same hollow rack bar. The longitudinal cross-sectional view which shows the threading process of the tooth side edge part and axial side edge part of the same hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (induction hardening) of the tooth side edge part of the hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency tempering) of the tooth side edge part of the hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency hardening) of the axial side edge part of the same hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency tempering) of the axial side edge part of the hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency hardening) of the tooth | gear part of the hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency hardening) of the axial part of the same hollow rack bar. The longitudinal cross-sectional view which shows the heat processing process (high frequency tempering) of the same hollow rack bar. The longitudinal cross-sectional view which shows the hardness of the same hollow rack bar. The side view which shows the conventional hollow rack bar and a ball joint. The side view which shows the problem of the conventional hollow rack bar and a ball joint.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Hollow rack bar, 11 ... Shaft part, 12 ... Tooth part, 13 ... Tooth side edge part, 14 ... Shaft side edge part, 15 ... Screw, 16 ... Recessed part

Claims (5)

In the manufacturing method of the hollow rack bar having a tooth portion meshed with the pinion gear in the shaft portion, and a screw portion provided for connection to the ball joint on the inner peripheral surface of the end portion thereof,
A tooth part forming step of forming a tooth part on the shaft part;
An end quenching step of induction hardening to the end;
A first temperature end tempering step for performing induction tempering at a first temperature on the end;
A screw processing step for performing screw processing for forming the screw portion on the inner periphery of the end portion after the first temperature tempering step;
Tooth part quenching step of induction hardening to the tooth part;
A shaft quenching step of induction hardening the shaft,
A method of manufacturing a hollow rack bar, comprising: a second temperature tempering step of performing induction tempering on the end portion, the tooth portion, and the shaft portion by a second temperature lower than the first temperature. In the manufacturing method of the hollow rack bar having a tooth portion meshed with the pinion gear in the shaft portion, and an inner peripheral thread portion provided for connection to the ball joint on the inner peripheral surface of the end portion,
A tooth part forming step of forming a tooth part on the shaft part;
An end quenching step of induction hardening the outer peripheral surface of the end;
A first temperature tempering step of performing induction tempering on the outer peripheral surface of the end portion at a first temperature;
A screw processing step for performing screw processing for forming the screw portion on the inner periphery of the end portion after the first temperature tempering step;
Tooth part quenching step of induction hardening to the tooth part;
A shaft quenching step of induction hardening the shaft,
A method of manufacturing a hollow rack bar, comprising: a second temperature tempering step of performing induction tempering on the end portion, the tooth portion, and the shaft portion by a second temperature lower than the first temperature. In the manufacturing method of the hollow rack bar having a tooth portion meshed with the pinion gear in the shaft portion, and an inner peripheral thread portion provided for connection to the ball joint on the inner peripheral surface of the end portion,
A tooth part forming step of forming a tooth part on the shaft part;
A step of forming a recess by carrying out a process from the opening side on the inner periphery of the end part; and
A screw processing step for performing screw processing for forming the screw portion on the inner side of the end portion and deeper than the concave portion;
An end quenching step of performing induction quenching on the open end of the end; and
Tooth part quenching step of induction hardening to the tooth part;
A first temperature tempering step of performing induction tempering at a first temperature on the end portion;
A shaft quenching step of induction hardening the shaft,
A method of manufacturing a hollow rack bar, comprising: a second temperature tempering step of performing induction tempering on the end portion, the tooth portion, and the shaft portion by a second temperature lower than the first temperature. The tooth part meshed with the pinion gear is a hollow shaft part,
Provided on the inner peripheral surface of at least one end of the shaft portion, and provided with an end portion on which a screw portion provided for connection with the ball joint is formed,
The hollow rack bar is characterized in that a hardness of the shaft portion is higher than a hardness of the end portion.   The hollow rack bar according to claim 4, wherein the shaft portion and the end portion are formed by using the method for manufacturing a hollow rack bar according to claim 1.

Images