JPH07268481A - High-frequency hardening method of rack shaft - Google Patents

Abstract

PURPOSE:To provide a high-frequency hardening method of a rack shaft which decreases hardening strains, improves the bending fatigue strength of teeth and improves productivity. CONSTITUTION:Hardened layers are simultaneously formed on the tooth faces and rear surfaces of the tooth parts of the rack shaft by high-frequency hardening, by which the hardening volume on the tooth face side and the hardening volume on the rear surface side facing the tooth faces are nearly equaled. The range from the tooth parts to the shaft part on the tooth surface side of the rack shaft to the range from the rear surfaces of the tooth parts on the rear surface side to the shaft part are simultaneously subjected to the high-frequency hardening. The hardened layers of the equal volume are simultaneously formed on the tooth faces and rear surfaces of the tooth parts of the rack shaft are formed and, therefore, the rack shaft having the good accuracy and decreased hardening strains is obtd. The uncured parts at the boundaries of the tooth parts and the shaft part are eliminated by executing integral hardening and, therefore, the accuracy is improved. Since the strength is imparted to the tooth surfaces and the wear resistance to the shaft part by one time of stage, the productivity is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction hardening method for a rack shaft used as a part of a steering device of a vehicle such as an automobile.

[0002]

2. Description of the Related Art A rack shaft is a shaft having, at one end of a shaft portion, a pinion having a toothed line which is attached to the tip of a steering shaft in an oblique direction, and a rack portion (tooth portion) which is meshed with a plane.

For example, in JP-A-59-9124, a high frequency current is applied to the tooth surface and the back surface of the rack shaft, and a proximity conductor capable of injecting cooling water is arranged on the tooth surface and the back surface of the rack shaft. There is disclosed a quenching device for a steering rack bar that improves the bending strength of the rack shaft by simultaneously quenching and tempering the tooth surface and the back surface of the rack shaft by energizing. Further, in order to give strength to the shaft, the teeth may be heat treated and then the shaft may be hardened again.

[0004]

However, in the above-mentioned proposal in which the tooth surface and the back surface of the rack shaft are simultaneously induction hardened and tempered, since the tooth surface side and the back surface side have different quenching volumes, the rack shaft is There is a problem that it warps in the axial direction. In addition, when the quenching and tempering treatment is separately performed to give strength to the shaft portion, the number of steps is increased, and further, an uncured portion may be formed at the boundary portion between the tooth portion and the shaft portion.

The present invention has been made to solve the above problems in the quenching and tempering of a rack shaft. The rack shaft has little quenching strain, is excellent in tooth bending fatigue strength, and can shorten the heat treatment time. The purpose of the present invention is to provide an induction hardening method.

[0006]

SUMMARY OF THE INVENTION The inventors of the present invention have considered that the cause of quenching distortion in a rack shaft is that the quenching volume is unbalanced between the tooth flank and the back of the tooth portion. When the clearance between the rack shaft, which is the object to be processed, and the high frequency coil was adjusted, and the quenching volume on the tooth flank side of the tooth and the quenching volume on the back side were almost the same, the quenching strain was remarkable. The present invention has been completed by newly finding that it decreases. Also, by quenching the range from the tooth surface side of the rack shaft to the shaft portion to the shaft portion and the back surface tooth portion from the back surface to the shaft portion at the same time, quenching distortion The present invention was completed by succeeding in reducing the heat treatment time as well as the heat treatment time.

In the induction hardening method for a rack shaft according to claim 1 of the present invention, a hardening layer is simultaneously formed on the tooth surface and the back surface of the tooth portion of the rack shaft by induction hardening to obtain a hardening volume on the tooth surface side. The gist is to make the quenching volume on the back surface side approximately equal to the tooth surface.

Further, the induction hardening method for the rack shaft according to claim 2 of the present invention is the range from the tooth portion on the tooth flank side of the rack shaft to the shaft portion in the rack shaft quenching method according to claim 1. And the range from the back side of the tooth portion to the shaft portion is induction hardened at the same time.

[0009]

According to the first aspect of the present invention, since the hardened layer having the same volume is formed on the tooth surface and the back surface of the tooth portion of the rack shaft at the same time, a rack shaft having high accuracy and less quenching distortion can be obtained. Further, in the invention of claim 2, since the tooth portion and the shaft portion are conventionally hardened in separate steps, there is an uncured portion between the shaft portion and the tooth portion. The precision is improved because the parts are eliminated, and the productivity is improved because strength can be imparted to the tooth surface and wear resistance can be imparted to the shaft portion in one step.

[0010]

EXAMPLES Examples of the present invention will be described in comparison with conventional examples,
The effect of the present invention will be clarified. Using the induction hardening apparatus shown in FIGS. 4 to 6, an upper high frequency coil 3 and a lower high frequency coil 4 are used.
The rack shaft 1 made of the material S45C was arranged between the two. At that time, as shown in FIG. 4 to FIG.
The gap between the tooth surface and the convex portion 3b of the upper high-frequency coil 3 and the gap between the rear surface and the convex portion 4b of the lower high-frequency coil 4 are:
The gap between the shaft portion 1b and the upper and lower high-frequency coils 3 and 4 is narrower than the gaps c and d, and the hardened volume on the tooth surface side and the back surface side of the tooth portion 1a are equalized. The gap B on the side was narrowed.

Next, the high-frequency coil is energized and the frequency 4
After heating at 0 kHz and 250 kw for 5 seconds, the quenching liquid is injected from the cooling water injection holes 2 of the upper and lower high frequency coils 3 and 4 immediately after reaching the required temperature (950 ° C.), and the quenching layer 2 is cooled. Was formed. Then, power of the same equipment is 25
The quenching layer 2 was tempered by heating at kW for a heating time of 10 seconds to complete the heat treatment of the rack shaft.

Then, the induction hardening and tempering rack shaft in this example and the conventional rack shaft heat-treated with the gap between the rack shaft and the induction coil being equal to each other at the upper and lower sides, the hardening strain, the tooth bending fatigue strength and the total strength. The heat treatment time was compared. Regarding the quenching strain, both ends of the rack shaft were received by V blocks, and the quenching strain at the center was measured with a dial gauge. Regarding the tooth bending fatigue strength, it was set so that it was sandwiched from both rack shafts, leaving four teeth out of a plurality of engraved rack teeth, until it was repeatedly loaded with an arbitrary load and destroyed. It was evaluated by the number of times.

Regarding quenching strain, as shown in FIG.
In contrast to the conventional product having a thickness of 1.0 to 3.0 mm, this embodiment has a thickness of 0.3 to 0.7 mm, and it has been found that the quenching strain is significantly reduced according to the method of the present invention. . Regarding the tooth bending fatigue strength, as shown in FIG. 2, the rack shaft broke at 0.9 × 10 ⁷ times in the conventional product, whereas it was 1.6 × 10 ^{7 in the} example of the present invention. The number has improved significantly. As for the total heat treatment processing time including the heat treatment time up to the shaft portion, as shown in FIG.
When it was set to 0, the processing time of the example of the present invention was 0.5, which was half the processing time, and it was confirmed that the productivity was remarkably improved.

The high frequency coil used in this embodiment was used to heat the rack shaft under the above-mentioned heating conditions, move it to another station, cool it while restraining it without rotating it, and burn it. By performing the quenching, the quenching distortion of the rack shaft becomes smaller, and a highly accurate rack shaft can be obtained.

[0015]

As described above in detail, the induction hardening method for the rack shaft of the present invention forms a hardening layer on the tooth surface and the back surface of the tooth portion of the rack shaft by induction hardening at the same time. The volume of quenching and the volume of quenching on the back side relative to the tooth surface are made approximately equal, and the range from the tooth portion on the tooth surface side of the rack shaft to the shaft portion and from the tooth surface on the rear surface side to the shaft portion are reached. Induction hardening at the same time,
Since a hardened layer of the same volume is formed on the tooth surface and back surface of the rack shaft teeth at the same time, the rack shaft is highly accurate and has less quenching distortion and can be hardened to the root of the rack shaft. can get. In addition, by integrally quenching, the uncured portion at the boundary between the tooth part and the shaft part is eliminated, so accuracy is improved, and in one process, the tooth surface is given strength and the shaft part is given wear resistance. Therefore, productivity is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing quenching strains of an example of the present invention and a conventional example.

FIG. 2 is a diagram showing tooth bending fatigue strength of an example of the present invention and a conventional example.

FIG. 3 is a diagram showing a total heat treatment processing time of an example of the present invention and a conventional example.

FIG. 4 is a side sectional view of an induction hardening apparatus used for carrying out the present invention.

5 is a cross-sectional view taken along the line AA in FIG.

6 is a cross-sectional view taken along the line BB in FIG.

[Explanation of symbols]

 1 Rack Shaft 1a Rack Shaft Teeth 1b Rack Shaft Shaft 2 Hardened Layer 3 Upper High Frequency Coil 3a Upper High Frequency Coil Sprinkler 3b Upper High Frequency Coil Convex 4 Lower High Frequency Coil 4a Lower High Frequency Coil Sprinkler 4b Lower High Frequency Coil Convex

Claims (2)

[Claims] 1. A quenching layer is simultaneously formed on a tooth surface and a back surface of a tooth portion of a rack shaft by induction hardening, so that a quenching volume on the tooth surface side and a quenching volume on the back surface side with respect to the tooth surface are substantially equalized. Induction hardening method for rack shafts. 2. The induction hardening is performed simultaneously on a range from a tooth portion on a tooth surface side of a rack shaft to a shaft portion and a range from a back surface of a tooth portion on a back surface side to a shaft portion. The induction hardening method for a rack shaft according to claim 1.