JP5471493B2 - Manufacturing method of rack and pinion type steering device - Google Patents

Description

  The present invention relates to a method of manufacturing a rack and pinion type steering device used in an automobile or the like.

  In passenger cars, a rack and pinion mechanism is mainly used as a mechanism for converting the rotation of the steering shaft into the motion of the left and right steered wheels because of its high rigidity and light weight. The rack of the rack-and-pinion type steering device is made of a medium carbon steel material (for example, a steel material corresponding to S35 to S55C defined in Japanese Industrial Standard JIS G4051), and is usually manufactured as follows. That is, after quenching and tempering a rod-shaped material obtained by rolling a medium carbon steel material, teeth that mesh with the teeth of the pinion are formed by cutting, and induction hardening is performed on the teeth. As described above, since the rack is formed by cutting, there is a problem in that the manufacturing requires a lot of labor and time and is expensive.

  Therefore, there is a method of forming the rack by plastic working such as cold forging (see Patent Document 1). According to the plastic working, the manufacturing cost is reduced because much labor and time are not required for the manufacturing as compared with the cutting. In recent years, it has been proposed to form a rack by plastic working using a tubular material such as a pipe instead of a rod-shaped material. By manufacturing the rack from a tubular material, the weight of the automobile can be reduced.

JP 2007-144433 A

In recent years, the usage conditions of automobiles have become stricter, and the performance required for rack and pinion type steering devices has been increasing year by year. For example, the rack is required to have excellent impact resistance and static strength so that no damage occurs even when an impact or stress is input by an automobile riding on a curb or the like.
However, racks manufactured by induction hardening after cold forging have a case where the core portion, which is a non-quenched portion, is work-hardened by cold forging, so that the impact resistance may be insufficient. . For this reason, when an impact or stress is input to the rack when the automobile rides on a curb or the like, there is a possibility that a brittle fracture occurs and breaks.
Accordingly, the present invention provides a method for manufacturing a rack-and-pinion type steering device that solves the problems of the prior art as described above and that is unlikely to cause damage to the rack even when an impact or stress is input during use. Let it be an issue.

  In order to solve the above problems, the present invention has the following configuration. That is, the manufacturing method of the rack and pinion type steering apparatus according to the present invention includes a steering shaft that is rotated by a driver's steering, a pinion that is connected to the steering shaft and rotates as the steering shaft rotates, and the pinion When manufacturing a rack and pinion type steering apparatus including a rack that meshes and is connected to a wheel, the rack is manufactured so as to satisfy the following four conditions.

Condition A) A steel material that has been subjected to soft annealing is formed into a predetermined shape by cold forging, and then subjected to recrystallization treatment and further subjected to induction hardening to produce the rack.
Condition B) By the soft annealing, the Vickers hardness of the material before the cold forging is set to HV200 or less, and a structure containing spherical cementite, acicular cementite, and ferrite is included.

Condition C) By the induction hardening, a hardened and hardened surface layer part is formed on the surface, and a non-quenched part not hardened is formed in the core part.
Condition D) By the recrystallization treatment, the Vickers hardness HVh and the softening annealing of the core portion that becomes the non-quenched portion were performed while maintaining the structure containing spherical cementite, acicular cementite, and ferrite. The ratio HVh / HVs to Vickers hardness HVs of the material is set to 1.2 or less.

The steel is preferably one of S35C to S55C defined in Japanese Industrial Standard JIS G4051 and 1035 to 1055 defined in SAE Standard, and is 0.35 mass% or more and 0.55 mass% or less. It preferably contains carbon.
The rack core portion (non-quenched portion) is work hardened by cold forging and has insufficient toughness, but is adjusted to an appropriate hardness by recrystallization treatment after cold forging. The rack of the rack and pinion type steering device obtained by the method of manufacturing the rack and pinion type steering device has excellent impact resistance and static strength. Large shocks and stresses may be input to the rack of a rack and pinion type steering device, but large shocks and stresses are input because the rack has excellent impact resistance and static strength (especially bending strength). However, the rack is not easily damaged.
Here, the critical significance of each numerical value under each condition will be described.

[Condition B]
In forming a material into a rack shape by cold forging, sufficient plastic workability is required. Therefore, it is necessary to first soften and anneal the material. In order to have sufficient plastic workability, the Vickers hardness of the raw material used for cold forging needs to be HV200 or less. Also, if soft annealing is insufficient, deformation resistance may increase during cold forging or cracking may occur. It is considered that the conversion is insufficient. Therefore, it is necessary to make the structure of the material used for cold forging have a structure containing spherical cementite, acicular cementite, and ferrite.

[Condition D]
The core of the rack (non-quenched part) is work hardened by cold forging and its toughness is insufficient, but the toughness is cold because it is adjusted to an appropriate hardness by recrystallization treatment after cold forging. It is almost the same level as the material before forging. Thus, the rack has excellent impact resistance and static strength. In order to ensure sufficient impact resistance and static strength of the rack, the Vickers hardness of the core (non-quenched portion) is set as follows while the structure is soft annealed and maintained in the state before cold forging. It is necessary to reduce like this. That is, the core part (non-quenched part) is made to have a ratio HVh / HVs of 1.2 or less between the Vickers hardness HVh of the core (non-quenched part) and the Vickers hardness HVs of the material after soft annealing and before cold forging. It is necessary to reduce the Vickers hardness of the non-quenched part.
[About the carbon content in steel]
If the carbon content is less than 0.35% by mass, the surface hardness of the teeth formed on the rack may be insufficient. On the other hand, if it exceeds 0.55 mass%, the workability of steel may be insufficient.

  According to the method for manufacturing a rack and pinion type steering apparatus of the present invention, it is possible to manufacture a rack and pinion type steering apparatus that is unlikely to cause damage to the rack even when an impact or stress is input during use.

It is a figure explaining the structure of a rack and pinion type steering device. It is a figure explaining the process of giving cold forging to a rod-shaped raw material, and shape | molding in the shape of a rack. It is a figure explaining the process of giving cold forging to a tubular raw material and shape | molding in the shape of a rack.

An embodiment of a method for manufacturing a rack and pinion type steering device according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a view for explaining the structure of a rack and pinion type steering device manufactured by the method for manufacturing a rack and pinion type steering device according to the present invention.
A steering shaft 11 having a steering wheel 10 fixed to the upper end portion is supported inside a steering shaft housing 12 so as to be rotatable about an axis. Further, the steering shaft housing 12 is fixed at a predetermined position in the vehicle interior in a posture in which the lower portion is inclined toward the front of the vehicle.

  The rack and pinion mechanism that converts the rotation of the steering shaft 11 into the movement of the left and right steered wheels 15 and 15 is supported by the rack 21 that is movable in the axial direction and the rack 21 teeth that are supported obliquely with respect to the axis of the rack 21. And a pinion 22 having teeth meshing with each other, and a rack 21 and a cylindrical rack housing 23 that supports the pinion 22. The rack and pinion mechanism is arranged substantially horizontally in the engine room at the front of the vehicle so that the longitudinal direction thereof is along the width direction of the vehicle.

Further, the upper end portion of the pinion 22 and the lower end portion of the steering shaft 11 are connected via two universal joints 25 and 26. Further, steered wheels 15 and 15 are connected to both ends of the rack 21.
When a steering torque (rotational force) is applied to the steering wheel 10 by the driver, the steering shaft 11 rotates, and the pinion 22 rotates as the steering shaft 11 rotates. Then, the rotation of the pinion 22 is converted into a slide motion in the left-right direction of the rack 21 by the rack and pinion mechanism, and the steered wheels 15 and 15 are driven to steer the automobile.

  The rack and pinion type steering device of the present embodiment may be provided with a so-called power steering mechanism. That is, the steering torque is detected by a torsion bar (not shown) attached to the steering shaft 11, and the output of the electric motor 13 (rotational force assisting steering) is controlled based on the detected steering torque. The output of the electric motor 13 is supplied to an intermediate portion of the steering shaft 11 (may be supplied to the pinion 22), and is combined with the steering torque to drive the steered wheels 15 and 15 by a rack and pinion mechanism. Converted into movement.

In this rack and pinion type steering device, the rack 21 is made of steel. The type of steel is not particularly limited, but is one of S35C to S55C defined in Japanese Industrial Standard JIS G4051 and 1035 to 1055 defined in SAE Standard, and 0.35% by mass or more and 0 It is preferable to use steel containing carbon of .55% by mass or less.
For example, S35C, S38C, S40C, S43C, S45C, S48C, S50C, S53C, S55C specified in Japanese Industrial Standard JIS G4051 and 1035, 1037, 1038, 1039, 1040, 1042, 1043, specified in SAE standard. 1044, 1045, 1046, 1049, 1050, 1053, 1055 are preferable.

The rack 21 is subjected to soft annealing on a rod-like material or tubular material (hereinafter also referred to as a material) made of steel as described above, and then formed into a rack shape by cold forging, and further recrystallized. It is manufactured by performing treatment, induction hardening, and tempering in this order. By induction hardening, a hardened and hardened surface layer portion is formed on the surface, and a non-quenched portion that has not been quenched is formed in the core portion.
Below, the manufacturing method of the rack 21 is demonstrated in detail. First, soft annealing is performed on a rod-like material or tubular material made of steel. An example of the conditions of softening annealing is shown. After holding the material at 740 to 860 ° C. above the A1 transformation point for 0.1 h or more, the temperature is lowered to 680 to 720 ° C. at a cooling rate of 20 to 70 ° C./h and held at the temperature for 1 to 5 hours. Subsequently, the temperature is lowered to 620 to 680 ° C. at a cooling rate of 10 to 100 ° C./h, and further lowered to 500 to 560 ° C. at a cooling rate of 10 to 150 ° C./h.

  By such soft annealing, the material has a Vickers hardness of HV200 or less. Therefore, since the raw material has sufficient plastic workability, the subsequent cold forging can be performed without any problem. In addition, by such soft annealing, the structure of the material used for cold forging is made a structure containing spherical cementite, acicular cementite, and ferrite. Therefore, in the subsequent cold forging, it is possible to suppress deformation resistance from increasing or cracking.

Next, the material subjected to soft annealing is subjected to cold forging as shown in FIGS. 2 and 3 and formed into a predetermined shape. First, an example in which a solid bar material having a circular cross section is formed by cold forging will be described with reference to FIG.
First, the solid bar-shaped material 31 is placed on the die 32 in which the groove 32a having an arcuate cross section is formed. The curvature radius of the groove 32a is set larger than the radius of the solid rod-shaped material 31, and the solid rod-shaped material 31 is disposed in the groove 32a (see FIG. 2A). Then, by pressing the punch 33 against the solid rod-shaped material 31 from above and pressing the punch 33 downward, the solid rod-shaped material 31 is brought into close contact with the groove 32a and deformed. Since the contact surface of the punch 33 with the solid rod-shaped material 31 is flat, a flat portion 31a is formed on the solid rod-shaped material 31 (see FIG. 2B). Thereby, the solid rod-shaped material 31 becomes a shape having the flat surface portion 31a and the cylindrical surface portion 31b. In addition, the contact surface with the solid rod-shaped material 31 of the punch 33 is not limited to a planar shape, and may have a taper.

  Next, a die 34 having a groove 34a deeper than the above-described groove 32a is prepared, and the solid bar-shaped material 31 is disposed in the groove 34a with the cylindrical surface portion 31b facing downward (bottom side of the groove 34a). . At this time, since the width of the groove 34a is designed to be slightly smaller than the diameter of the solid rod-shaped material 31, the solid rod-shaped material 31 is not completely accommodated in the groove 34a ((c) in FIG. 2). See). Then, when the punch 35 having the tooth groove 35 a is pressed against the flat portion 31 a of the solid bar-shaped material 31 and the punch 35 is pressed downward, the solid bar-shaped material 31 is pushed into the groove 34 a of the die 34. At that time, both sides of the solid bar-shaped material 31 (the portions contacting the side walls of the grooves 34a of the die 34) are squeezed and deformed to become parallel planes, and the teeth 31c corresponding to the tooth grooves 35a are formed. It is formed on the flat portion 31a of the solid rod-shaped material 31 (see (d) of FIG. 2). And the meat for the squeezed portions on both sides of the solid rod-shaped material 31 is supplied to the teeth 31c, and the shape of the teeth 31c becomes larger.

  Next, a die 36 in which a groove 36a having a substantially rectangular cross section is formed and a punch 37 in which a groove 37a having a circular arc cross section is prepared. On the bottom surface of the groove 36a formed in the die 36, a tooth groove 36b corresponding to the tooth 31c formed in the flat portion 31a of the solid rod-shaped material 31 is formed. On the other hand, the groove 37 a formed in the punch 37 has a shape corresponding to the cylindrical surface portion 31 b of the solid rod-shaped material 31.

  When the solid rod-shaped material 31 is disposed in the groove 36a formed in the die 36, the width of the groove 36a is slightly smaller than the diameter of the solid rod-shaped material 31, so that the solid rod-shaped material 31 is completely in the groove 36a. Is not accommodated (see FIG. 2E), but when the punch 37 is pressed against the solid bar material 31 from above and pressed downward, the solid bar material 31 is pushed into the groove 36a of the die 36, The shape of the actual bar-shaped material 31 is adjusted. Since both sides of the solid bar-shaped material 31 (parts contacting the side wall of the groove 36a of the die 36) are flat, no surplus is produced when the solid bar-shaped material 31 is pushed into the groove 36a of the die 36. (See (f) in FIG. 2).

  Next, an example in which a tubular material 41 having a circular cross section is formed by cold forging will be described with reference to FIG. In FIG. 3, the same or corresponding parts as those in FIG. 2 are denoted by the same reference numerals as those in FIG. Since the forming method is exactly the same as that of the solid rod-shaped material 31, detailed description is omitted. However, when the tubular material 41 is formed by cold forging, the diameter of the hollow hole 42 is set in the hollow hole 42. It is preferable to put another member 43 having substantially the same diameter. At the stage of first deformation (see FIG. 3B), the hollow member 42 is filled with the separate member 43, and the tubular material 41 and the separate member 43 are integrated.

  Next, a recrystallization process is performed on the material thus formed into a rack shape. The recrystallization treatment is preferably a treatment of heating to a temperature of 500 ° C. or higher and then cooling. The hardness of the rack core that has been hardened by cold forging is adjusted by this recrystallization process, and the toughness of the core is improved and softened and annealed to the same level as the material before cold forging. The impact resistance and static strength of the finished product rack will be sufficient.

  In order to ensure sufficient impact resistance and static strength of the finished product rack, the Vickers hardness HVh and softening annealing of the core are performed while maintaining the structure of the material after softening annealing and before cold forging. Then, the recrystallization treatment is performed so that the ratio HVh / HVs to the Vickers hardness HVs of the raw material before and after cold forging becomes 1.2 or less. The recrystallization treatment condition is that after quenching by holding at 800 to 900 ° C. for 0.1 to 1.5 hours, tempering is performed by holding at 600 to 720 ° C. for 2 to 3 hours.

Furthermore, when induction-quenching is applied to the recrystallized material, a hardened and hardened surface layer portion is formed on the surface, and a non-quenched portion that is not quenched is formed in the core portion. The conditions for induction hardening are not particularly limited, and examples include conditions such as an output current of 220 to 270 A, a frequency of 100 kHz, a heating time of 3 to 5 seconds, and a cooling time of 10 to 15 seconds. Finally, after tempering, the rack 21 was completed by grinding or superfinishing. Induction hardening and tempering are performed after the recrystallization treatment, but the Vickers hardness of the structure and the core is maintained in the state before induction hardening and tempering.
In the rack and pinion type steering apparatus including the rack 21 manufactured in this manner, the rack 21 has excellent impact resistance and static strength, so that even if a large impact or stress is input during use, the rack 21 is not easily damaged.

〔Example〕
Hereinafter, the present invention will be described more specifically with reference to examples. Soft round annealing under the same conditions as in the above example was performed on a 26.5 mm diameter round bar material made of S35C, S45C, or S55C defined in Japanese Industrial Standards JIS. And by this softening annealing, while making the Vickers hardness of the raw material into HV200 or less, the structure | tissue of the raw material was made into the structure | tissue containing spherical cementite, acicular cementite, and a ferrite. Tables 1 to 3 show the Vickers hardness HVs of materials subjected to soft annealing.

  Such a material was cold forged as shown in FIG. 2 and formed into a rack shape. And the crystallization process was performed on the said conditions, and the hardness of the core part work-hardened by cold forging was adjusted, maintaining the said structure containing spherical cementite, acicular cementite, and a ferrite. The crystallization treatment was performed by putting a material into a solenoid coil and heating it.

  Tables 1 to 3 show the Vickers hardness HVh and the hardness ratio HVh / HVs of the core of the material after the crystallization treatment. The Vickers hardness HVh of the core portion was measured for a portion several mm inward from the valley portion between the teeth of the rack, and the highest value among the measured values obtained by measuring a plurality of times was adopted as HVh. The Vickers hardness HVh of the core portion is maintained even if induction hardening and tempering are performed thereafter. Therefore, the Vickers hardness HVh of the core part is also the Vickers hardness of the core part of the finished product rack.

Next, induction hardening was performed. By this induction quenching, a hardened and hardened surface layer portion is formed on the surface, and a non-quenched portion not quenched is formed in the core portion. The conditions of induction hardening are as follows.
Quenching method: Current heating method Output current: 250A
Frequency: 100kHz
Heating time: 4.5 seconds Cooling time: 10 seconds Refrigerant: Soluble oil and water mixed solvent Finally, tempering was performed to complete the rack.

The rack thus obtained was loaded with bending stress to test whether brittle fracture occurred. That is, the rack was incorporated into a rack and pinion type steering device, the steering wheel was rotated to move the rack to the full stroke, and a bending load was applied to the end of the rack farthest from the rack support member.
The results are shown in Tables 1-3. In Tables 1 to 3, when a crack generated in the surface layer part extends to the inside and the rack breaks, it is indicated by x, and when the crack stops halfway and does not break, it is indicated by ○. .
As can be seen from Tables 1 to 3, since the rack of the example had a hardness ratio HVh / HVs of 1.2 or less, the rack did not break.

11 Steering shaft 21 Rack 22 Pinion 31 Bar material 41 Tubular material

Claims (2)

A rack-and-pinion type steering comprising: a steering shaft that is rotated by a driver's steering; a pinion that is coupled to the steering shaft and that rotates as the steering shaft rotates; and a rack that meshes with the pinion and is coupled to a wheel. A manufacturing method of a rack and pinion type steering device, wherein the rack is manufactured so as to satisfy the following four conditions when manufacturing the device.
Condition A) A steel material that has been subjected to soft annealing is formed into a predetermined shape by cold forging, and then subjected to recrystallization treatment and further subjected to induction hardening to produce the rack.
Condition B) By the soft annealing, the Vickers hardness of the material before the cold forging is set to HV200 or less, and a structure containing spherical cementite, acicular cementite, and ferrite is included.
Condition C) By the induction hardening, a hardened and hardened surface layer part is formed on the surface, and a non-quenched part not hardened is formed in the core part.
Condition D) By the recrystallization treatment, the Vickers hardness HVh and the softening annealing of the core portion that becomes the non-quenched portion were performed while maintaining the structure containing spherical cementite, acicular cementite, and ferrite. The ratio HVh / HVs to Vickers hardness HVs of the material is set to 1.2 or less.   The steel is one of S35C to S55C defined in Japanese Industrial Standard JIS G4051 and 1035 to 1055 defined in SAE Standard, and contains 0.35 mass% or more and 0.55 mass% or less of carbon. The method of manufacturing a rack and pinion type steering device according to claim 1, wherein:

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