JP2011148403A - Method for manufacturing rack-and-pinion type steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a rack-and-pinion type steering device hardly damaging a rack even when an impact or stress is inputted in use. <P>SOLUTION: The rack 21 of the rack-and-pinion type steering device is molded by cold forging after a material made of steel is softened and annealed, and is further subjected to tempering processing, induction hardening, and tempering. The material before cold forging has a structure containing spherical cementite, acicular cementite, and ferrite by being softened and annealed. Also, a tempered part having a tempered structure and hardness of HV 200-300 is formed on an outer layer portion of an unhardened portion by the tempering processing with induction heating. The length of the tempered part in the depth direction is 2-10 mm. <P>COPYRIGHT: (C)2011,JPO&INPIT

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, a manufacturing method of a 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 In manufacturing a rack and pinion type steering apparatus including a rack that meshes with and is connected to a wheel, the rack is manufactured so as to satisfy the following five conditions.

Condition A) A steel material subjected to soft annealing is formed into a predetermined shape by cold forging, then subjected to a tempering treatment by induction heating, and further subjected to induction hardening to manufacture the rack.
Condition B) By the soft annealing, the material before the cold forging has a structure containing spherical cementite, acicular cementite, and ferrite.

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 tempering treatment, a tempered part having a tempered structure and a hardness of HV200 or more and 300 or less is formed in the outer layer part of the non-quenched part.
Condition E) The length of the tempered portion in the depth direction is 2 mm or more and 10 mm 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 (non-quenched part) is work hardened by cold forging and its toughness is insufficient, but it has a tempered structure and an appropriate hardness by tempering treatment by induction heating after cold forging. Since the tempered portion is formed in the outer layer portion of the non-quenched portion, the rack of the rack and pinion type steering device obtained by the method of manufacturing a rack and pinion type steering device according to the present invention has excellent impact resistance. And has 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, each said condition is demonstrated.
[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. If soft annealing is insufficient, deformation resistance may increase during cold forging, and cracking may occur, but the cause of this is pearlite in the structure or carbide spheroidization. It may be 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]
If the hardness of the tempered part is less than HV200, the tempered structure is unsuitable and the toughness of the non-quenched part becomes insufficient, so that the impact resistance and static strength of the rack are insufficient. As a result, the rack may be damaged when a large impact or stress is input to the rack. On the other hand, if the hardness of the tempered portion is over HV300, the toughness of the non-quenched portion becomes insufficient because it is too hard. Therefore, the rack may be damaged when a large impact or stress is input to the rack.

[Condition E]
If the length of the tempered part in the depth direction is less than 2 mm, cracks generated by loads such as bending stress easily penetrate the tempered part and propagate through the tempered part. If this happens, the rack may be damaged. On the other hand, if the tempering treatment is performed such that the length of the tempered portion in the depth direction exceeds 10 mm, the heat treatment deformation of the entire rack may become a problem.
[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. It is sectional drawing 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 defined in Japanese Industrial Standard JIS G4051, and 1035, 1037, 1038, 1039, defined in SAE Standard (Society of Automotive Engineers) 1040, 1042, 1043, 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 is then formed into a rack shape by cold forging. It is manufactured by performing treatment, induction hardening, and tempering in this order.
The tempering treatment is performed by quenching and tempering by induction heating. And the tempering part which has a tempered structure is formed by this tempering process. By induction hardening after tempering treatment, a hardened and hardened surface layer part is formed on the surface, and a non-quenched part that has not been quenched is formed in the core part, but this tempered part is a non-quenched part It is formed in the outer layer 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 the softening annealing as described above, the Vickers hardness of the material becomes, for example, HV200 or less. Therefore, since the raw material has sufficient plastic workability, the subsequent cold forging can be performed without any problem. Moreover, the structure | tissue of the raw material used for cold forging by the softening annealing as mentioned above is made into the structure | tissue containing spherical cementite, acicular cementite, and a 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 tempering treatment is performed by induction heating on the surface of the material formed in the shape of the rack as described above where the teeth are formed. The condition of the tempering treatment is not particularly limited. For example, after tempering at 800 ° C. or higher and 900 ° C. or lower, tempering at 600 ° C. or higher and 720 ° C. or lower is performed. By such a tempering treatment, a heat treatment is performed on a portion from the surface of the material to a predetermined depth position, the portion has a tempered structure (truthite or sorbite), and the hardness is HV200 or more and 300 or less. A tempered part is formed.

  Furthermore, when induction hardening is performed on the surface where the teeth are formed and the opposite surface of the tempered material, a hardened and hardened surface layer portion is formed on the surface, and quenching is performed. A non-quenched part that is not applied is formed in the core part. 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.

  By this induction quenching, the surface side portion of the tempered portion formed on the surface of the material is quenched, and the tempered structure is denatured by quenching, so the surface side portion of the tempered portion is the surface layer portion. Become. On the other hand, the inner part of the tempered part is not quenched and the tempered structure and hardness are maintained, so the inner part of the tempered part is a non-quenched part. Therefore, the tempered portion is formed in the outer layer portion of the non-quenched portion (see FIG. 4). The length Dc in the depth direction of the tempered portion is 2 mm or more and 10 mm or less.

Finally, after tempering, the rack 21 was completed by grinding or superfinishing. Although induction hardening and tempering are performed after the tempering treatment, the structure and Vickers hardness of the tempered portion are 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 the structure | tissue of the raw material was made into the structure | tissue containing spherical cementite, acicular cementite, and a ferrite by this softening annealing.
Such a material was cold forged as shown in FIG. 2 and formed into a rack shape. And the tempering process was given to the surface in which the tooth | gear is formed among raw materials. The tempering treatment was performed as follows. First, a material is inserted into a ring-shaped coil, heated to 800 ° C. or higher and 900 ° C. or lower by induction heating, and then quenched by cooling with an aqueous solution. Tempered.

  Next, induction hardening was performed on the surface of the material on which the teeth are formed and on the opposite surface. 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. As a result, as shown in FIG. 4, a tempered portion having a tempered structure is formed in the outer layer portion of the non-quenched 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.

  Tables 1 to 6 show the length in the depth direction of the tempered portion and the Vickers hardness HV of the tempered portion. The length of the tempered portion in the depth direction was measured by cutting a rack at a valley between teeth and mirror-finishing the cut surface, corroding with 5% nital, and observing with a metal microscope. Further, the Vickers hardness HV of the tempered portion was measured by cutting the rack at the valley between the teeth and exposing the tempered portion to the cut surface. The measurement location was the central portion in the depth direction of the tempered portion. These measurements were performed after induction hardening.

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 1-6. In Tables 1 to 6, when the 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 midway and does not break, it is indicated by ○. .
As can be seen from Tables 1 to 6, in the rack of the example, the length in the depth direction of the tempered part is 2 mm or more and 10 mm or less, and the Vickers hardness HV of the tempered part is 200 or more and 300 or less. It had excellent impact resistance and static strength and 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 five conditions when manufacturing the device.
Condition A) A steel material subjected to soft annealing is formed into a predetermined shape by cold forging, then subjected to a tempering treatment by induction heating, and further subjected to induction hardening to manufacture the rack.
Condition B) By the soft annealing, the material before the cold forging has a structure containing spherical cementite, acicular cementite, and ferrite.
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 tempering treatment, a tempered part having a tempered structure and a hardness of HV200 or more and 300 or less is formed in the outer layer part of the non-quenched part.
Condition E) The length of the tempered portion in the depth direction is 2 mm or more and 10 mm 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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