JPH11270657A - Rack shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the impact strength of a rack tooth while securing the abrasion resistance and toughness of the rack tooth by providing a rack tooth formed in a shaft with a hardening layer at both ends thereof in the tooth cross direction except for a central part. SOLUTION: A shaft 1 is formed with a rack tooth 2. Hardening layers 3a, 3b are provided in the rack tooth 2 at both ends in the tooth cross direction except for a central part 4. The hardening layers 3a, 3b are formed in a range over from a tooth tip 2a to a tooth bottom 2b oft the rack tooth 2. The hardening layers 3a, 3b are partially hardened by high frequency hardening. A contact element provided with a high frequency induction coil is made to contact with both ends of the rack tooth 2 in the tooth cross direction except for the central part 4, and energized for high frequency hardening. Abrasion resistance of the whole of the rack tooth 2 in the tooth cross direction is thereby secured, and toughness of the central part, which is not hardened, is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rack shaft having improved strength by impact and static strength.

[0002]

2. Description of the Related Art In a rack shaft used in a rack and pinion type steering device of an automobile, as shown in FIG. 4, a high frequency is applied to a rack tooth 2 formed on the shaft 1 in order to secure wear resistance of the rack teeth. A rack shaft provided with a hardened layer 3 by quenching is provided in Japanese Patent Publication No. Hei 5-47426.

[0003]

In the above-mentioned conventional rack shaft, since the hardened layer 3 is provided by performing induction hardening on the entire rack teeth 2, the hardness of the rack teeth 2 is increased, and the wear resistance is secured. However, lack of toughness results in reduced impact and static strength. Thus, for example, when an impact is applied to the rack shaft from the tire side, the rack shaft is hardly deformed, the shock cannot be absorbed, and the steering feeling may be affected.

[0004] It is an object of the present invention to provide a rack shaft in which the wear resistance of the rack teeth is ensured, the toughness is ensured, and the strength by impact is improved.

[0005]

In order to achieve the above object, the present invention provides a structure in which hardened layers are provided at both ends of a rack except for a center portion in a width direction of a rack tooth formed on a shaft. It is a feature.

Further, the hardened layer is formed in a range from the tooth tip of the rack tooth to the tooth bottom.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross section showing a rack shaft according to the present invention. That is, 1 is a shaft, which is a round shaft in the drawing, but is not limited to the round shaft and may be a square shaft. 2
Is a rack tooth formed on the shaft 1, 2a is a tooth tip,
2b is a tooth bottom.

In the present invention, hardened layers 3a and 3b are provided at both ends except for a central portion 4 of the rack teeth 2 in the face width direction. The hardened layers 3a and 3b are provided at the tip 2a of the rack teeth 2.
To the tooth bottom 2b.

The hardened layers 3a and 3b are partially hardened by induction hardening. As shown in FIG. 2 and FIG. 3, the specific means is as follows. By this, induction hardening is performed.

Since the present invention has the structure as described above, the hardened layers 3a and 3b at both ends in the width direction of the rack teeth 2 ensure the overall wear resistance of the rack teeth 2 in the width direction, and the sintering is performed. The toughness is maintained in the central portion 4 where no insertion is performed.

That is, the rack teeth 2 meshing with the pinion
Are in contact with the entire tooth surface, but the hardened layers 3a, 3
Since the abrasion resistance is ensured by b, the central portion 4 not subjected to quenching does not wear unless both ends are worn. Then, the flexibility of the shaft 1 is maintained by the toughness of the central portion 4 not subjected to quenching.

Thus, the wear resistance of the rack teeth 2 is ensured, and the strength of the rack teeth 2 due to impact is improved. Therefore, when this is used for the rack shaft of a rack-and-pinion type steering device for automobiles, when a shock is applied to the rack shaft from the tire side, the shock can be absorbed and affect the steering feeling. Disappears.

[0013]

As described above, according to the present invention, since the hardened layers are provided at both ends except for the central portion in the width direction of the rack teeth, the wear resistance of the rack teeth and the rack shaft are reduced. There is an advantage that the toughness is secured and the strength by impact can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a rack shaft according to the present invention.

FIG. 2 is a sectional view showing induction hardening of a rack shaft of the present invention.

FIG. 3 is a side view showing induction hardening of the rack shaft of the present invention.

FIG. 4 is a cross-sectional view of a conventional rack shaft subjected to induction hardening.

[Explanation of symbols]

 1 shaft 2 rack tooth 2a tooth tip 2b tooth bottom 3a hardened layer 3b hardened layer 4 central part

Claims (2)

[Claims] 1. A rack shaft, wherein hardened layers are provided at both ends of a rack tooth formed on the shaft except for a central portion in a width direction of the rack teeth. 2. The rack shaft according to claim 1, wherein the hardened layer is formed in a range from a tooth tip of the rack tooth to a tooth bottom.