JPH0547426B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is directed to a rack shaft used in a rack and pinion type steering device for automobiles, etc., in which a rack tooth portion is formed on a part of a rack shaft, particularly a round bar shaft. The present invention relates to a rack shaft for a steering device in which an induction hardened layer is provided on the teeth and the back surface.

[Prior art]

5 and 6 show conventional examples of rack shafts for steering devices. In the drawings, reference numeral 1 denotes a rack shaft, and a rack tooth portion 2 is formed on a part of the round bar-shaped shaft. The rack teeth 2 mesh with a pinion gear connected to the handle shaft, and as the pinion gear rotates, the rack shaft 1 reciprocates left and right. This rack shaft 1 forms part of a steering link, and the reciprocating motion of the rack shaft 1 deflects the steering wheel. As shown in the drawing, the rack tooth part 2 and the back part 3 of the rack shaft 1
It is already known to provide induction hardened layers 4 and 5. By providing the hardened layer on the back surface 3 in addition to the rack teeth 2 in this manner, the axial strength (particularly the bending strength) of the rack shaft 1 can be increased. The quench-hardened layer 5 on the back surface was provided along the arcuate surface of the back surface with substantially the same hardening depth, as in the case of ordinary induction hardening of a round shaft.

[Problem that the invention seeks to solve]

When providing an induction hardened layer on the rack teeth and the tooth surface of the rack shaft in this way, it is necessary to harden the rack teeth and the back surface under different hardening conditions or with an induction hardening machine. Due to the capacity of
It is often necessary to harden the rack teeth and the back surface in two separate steps. In this case, when the hardened layer on the back surface is provided along the arc surface as shown above, the hardened layer formed in the previous step is affected by heat during heating in the later step, and There was a problem that the hardness decreased. In particular, when the back surface is hardened later, the heat effect is concentrated on the edge of the rack tooth in the tooth width direction, resulting in a significant decrease in the hardness of this area and a decrease in both wear resistance and strength. A serious problem arose as a rack shaft for a mobile device. In order to reduce this thermal effect, narrowing the area where the back hardened layer is provided and making the hardening depth shallow may have some effect, but in this case it was difficult to obtain sufficient axial strength. .

An object of the present invention is to provide a back hardened layer pattern that can reduce the thermal effects while ensuring axial strength.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention provides a rack shaft for a steering device in which a rack tooth portion is formed on a part of the round bar-shaped shaft, and an induction hardened layer is provided on the rack tooth portion and the back surface portion. The quenched hardened layer on the back surface has a predetermined hardening depth at approximately the center in the circumferential direction of the back surface,
A substantially arcuate hardened layer pattern was formed in which the hardened depth decreased as it moved away from the center.

[Effect]

If the hardened layer pattern of the back surface is made into a substantially arcuate shape with the deepest hardening depth at the approximately center portion in the circumferential direction of the back surface as described above, the quenched hardened layer of the rack tooth portion (hereinafter simply referred to as the tooth hardened layer) The hardened layer on the back surface (hereinafter referred to simply as the hardened layer on the back surface) is sufficiently separated, and there is no area where the heat effect is concentrated during hardening on the back surface, so that the heat effect acts almost uniformly and the effect is Reduced. Furthermore, since a deep hardened layer is located just behind the rack teeth, sufficient axial strength can be obtained without unnecessarily increasing the hardening depth and width.

〔Example〕

Figure 1 shows an embodiment of the present invention, in which the diameter
This test was carried out on a rack shaft of 21 mm, the tooth thickness of the rack tooth 4 mm, the distance from the bottom surface to the back surface of the tooth 15.16 mm, and the material is S43C (JIS). The tooth hardened layer 4 is formed in an area that slightly exceeds the tooth bottom surface 6, and the back hardened layer 7 extends approximately at the center of the back surface 3 in the circumferential direction.
The hardening depth was 2.5 mm, and the hardened layer pattern was approximately arcuate so that the boundary line between the hardened layer and the non-hardened layer was a straight line. Therefore, the depth of the hardened layer is deepest at the center immediately behind the rack teeth, and decreases as it moves away from there. Incidentally, when hardening the back surface, a flat induction electrode and a relatively narrow contact electrode were used together, and the plate voltage was 100V and the plate current was 9A.
was heated for 3.5 seconds, and immediately thereafter cooling water was applied for 4.5 seconds to form the quenched hardened layer.

Since the back hardened layer is patterned as described above, the distance between the tooth hardened layer and the back hardened layer is averaged, and the heat effect during heating in the post-process is not concentrated locally, making it possible to locally increase the hardness. never deteriorates. In this example, there was almost no difference in hardness between the ends in the tooth width direction and the center of the rack teeth. In addition, since a deep hardened layer is located directly behind the rack teeth 2, the axial strength of the rack shaft is approximately 150% of that without the hardened layer on the back surface with a hardened depth of 2.5 mm at the center.
I was able to obtain something powerful.

By the way, if you increase the hardening depth of the back hardened layer,
The axial strength of the rack shaft increases, but at the same time, the thermal influence on the rack teeth when heating the back surface increases, although it is averaged out. FIG. 4 shows changes in the shaft strength and the hardness of the rack teeth when the hardened layer on the back surface was changed in the above embodiment. As shown in the drawing, when the hardening depth of the back surface exceeds 3 mm, that is, 20% of the distance d from the bottom surface of the rack tooth to the back surface of the shaft, the hardness of the rack tooth decreases rapidly. This is because the thermal effect during heating of the back surface gives an excessive tempering effect to the quenched hardened layer of the rack teeth, and if the hardened layer exceeds 4 mm (26% of distance d), the shaft strength itself will actually decrease. Therefore, the hardening depth of the back surface hardened layer is preferably 20% or less of the distance d from the bottom surface of the rack tooth to the back surface of the shaft.

The quenching pattern of the hardened layer on the back surface may be such that the boundary layer has a substantially linear shape as shown in the above embodiment, a slightly convex curve as shown in FIG. 2, or a quench pattern as shown in FIG. It may be a slightly concave curved shape as shown in FIG. The substantially arcuate hardened layer pattern of the present invention includes such slight deformations, and can be expected to have substantially the same effects as the above-mentioned embodiments.

〔Effect of the invention〕

Since the present invention is as described above, the tooth hardened layer and the back hardened layer are sufficiently separated, and the heat effect during hardening of the back side acts almost equally on the rack teeth, so that Hardness does not decrease locally,
Furthermore, since the deep hardened layer is located directly behind the rack teeth, sufficient axial strength can be obtained without unnecessarily increasing the hardened depth and width.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view at right angles to the axis of a rack shaft according to an embodiment of the present invention, Figs. 2 and 3 are cross-sectional views at right angles to the axis of a rack shaft according to a modified embodiment, and Fig. 4 shows the hardening depth of the back surface and the rack teeth. FIG. 5 is an axial cross-sectional view of a conventional rack shaft, and FIG. 6 is a cross-sectional view perpendicular to the shaft of a conventional rack shaft. Explanation of symbols 1...Rack shaft, 2...Rack teeth,
3... Back part, 4... Hardened hardened layer of rack tooth part, 5,
7, 8, 9... Back side hardened layer.

Claims (1)

[Scope of Claims] 1. A rack shaft for a steering device, in which a rack tooth portion is formed on a part of a round bar-shaped shaft, and an induction hardened layer is provided on the rack tooth portion and the back surface portion, wherein the rear surface portion has a hardened layer. The quenched hardened layer has a substantially arcuate hardened layer pattern with a predetermined hardening depth at approximately the center in the circumferential direction of the back surface, and the hardening depth decreases as it moves away from the center. Rack shaft for steering device. 2 The hardening depth of the approximately central part in the circumferential direction of the back surface is 20% of the distance d from the bottom surface of the rack tooth to the back surface of the shaft.
Claim 1 characterized by the following:
Rack shaft for steering device as described in Section 1.