JP2015152092A - Yoke of steering universal joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a yoke of a steering universal joint which is further enhanced in mechanical rigidity.SOLUTION: In a yoke 1 of a steering universal joint, nitriding treatment for oil-cooling or water-cooling a root of an arm part 3 at cooling is applied to a fitting hole 2A of a base part 2, and a dimension D in a radial direction of a region 10 in which residual stress at the other end part 2b of the base part 2 is -100 MPa or less, and an inside diameter d of the fitting hole 2A satisfy a relationship of D-d≥1.0(mm). It is preferable that the surface hardness Hv of a nitrogen diffusion layer of the fitting hole 2A is 300 or higher, and also a thickness of a compound layer of the fitting hole 2A is 30 μm or less, and the dimension D and the inside dimension d of the fitting hole 2A satisfy a relationship of D-d≥2(mm).

Description

  The present invention relates to a yoke for a steering universal joint used in a steering device of an automobile.

  2. Description of the Related Art Conventionally, a steering shaft used in an automobile steering device or the like is configured by connecting a plurality of shafts such as an upper shaft, an intermediate shaft, and a lower shaft by universal joints. There are various types of universal joints. For example, universal joints generally called cardan joints are configured by rotatably attaching each axis of a cross shaft called a cross spider crossing two axes to a shaft. (Some have two axes in twisted position). A bifurcated member that rotatably supports each axis of the cross shaft is called a yoke. That is, a yoke is attached to the end of each shaft constituting the steering shaft, and one of the cross shafts is rotatably attached to each yoke.

  In recent years, a steering apparatus having an electric power steering function for transmitting a steering assist force to a steering gear has been developed. In such a steering apparatus having an electric power steering function, a steering shaft that has been subjected to gas soft nitriding in order to improve the mechanical strength of the steering shaft is disclosed (Patent Document). 1-4).

International Publication No. 2003/031250 Japanese Patent No. 5158419 JP 2007-308057 A JP 2007-131088 A

However, the load acting on a universal joint incorporated in a steering apparatus having a power steering function tends to increase, and the universal joint disclosed in Patent Documents 1 to 4 has a further improvement in mechanical strength especially against torsion. Is required. In particular, when the universal joint is an expandable universal joint that is slidably fitted to each other via a ball or the like, the requirement is remarkable.
Accordingly, the present invention has been made paying attention to the above requirements, and an object of the present invention is to provide a yoke for a steering universal joint in which the mechanical strength against twisting is further improved.

A certain aspect of the yoke of the universal joint for steering to achieve the above object has a base portion and an arm portion,
The base is provided with a fitting hole through which the shaft is fitted and fixed from one end thereof,
A pair of arms that extend in the axial direction of the fitting hole at the other end of the base and face each other in a direction orthogonal to the axial direction, and concentric bearing holes formed in that direction. And
A soft nitriding treatment that oil-cools or water-cools the base of the arm portion during cooling is performed on the fitting hole,
The dimension D in the radial direction of the region where the residual stress at the other end is −100 MPa or less and the inner diameter d of the fitting hole satisfy Dd ≧ 1.0 (mm).
Preferably, the surface hardness Hv of the nitrogen diffusion layer of the fitting hole is 300 or more,
The thickness of the compound layer of the fitting hole is 30 μm or less, and the dimension D and the inner diameter d of the fitting hole satisfy Dd ≧ 2 (mm).

Here, in the yoke of the universal joint for steering, it is preferable that the base of the arm portion is water-cooled during cooling of the soft nitriding treatment applied to the fitting hole.
The yoke of the universal joint for steering may be a telescopic shaft on which the base and the shaft slide.

  ADVANTAGE OF THE INVENTION According to this invention, the yoke of the universal joint for steering which improved the mechanical strength with respect to twist can be provided.

It is a side view which shows the structure of the steering mechanism part of a motor vehicle. It is a figure which shows the structure in embodiment with the yoke of the universal joint for steering, (a) is sectional drawing which follows an axial direction, (b) is a front view.

Hereinafter, embodiments of a yoke for a steering universal joint according to the present invention will be described with reference to the drawings. In this specification, the side of the base of the yoke where the arm portion is provided is the front, and the direction perpendicular to the axial direction of the base (or its fitting hole) is the radial direction.
FIG. 1 is a side view illustrating a configuration of a steering mechanism portion of an automobile provided with a vehicle steering shaft to which a yoke of a steering universal joint according to an embodiment is applied. 2A and 2B are diagrams showing the configuration of an embodiment of the yoke of the universal joint for steering, where FIG. 2A is a sectional view along the axial direction, and FIG. 2B is a front view.

<Configuration of steering mechanism of automobile>
FIG. 1 is a side view showing a configuration of a steering mechanism portion of an automobile provided with a vehicle steering shaft to which a yoke of a steering universal joint according to this embodiment is applied.
As shown in FIG. 1, the steering mechanism portion of the automobile includes an upper steering shaft portion 120, a steering wheel 105, a lower steering shaft portion 107, a pinion shaft 109, a steering rack shaft 112, and a steering rack support member 113. Have Among these, the upper steering shaft portion 120 and the lower steering shaft portion 107 constitute a telescopic shaft for vehicle steering (hereinafter, also referred to as a telescopic shaft).

Upper steering shaft portion 120 is attached to member 100 on the vehicle body side via upper bracket 101 and lower bracket 102. The upper steering shaft portion 120 includes a steering column 103 and a steering shaft 104 that is rotatably held by the steering column 103.
The steering wheel 105 is attached to the upper end of the steering shaft 104. On the other hand, the lower steering shaft portion 107 includes a female shaft 107A and a male shaft 107B that can slide on the female shaft 107A. The male shaft 107 </ b> B is connected to the lower end of the upper steering shaft 120 via a universal joint (universal joint) 106.

The pinion shaft 109 is connected to the female shaft 107A of the lower steering shaft portion 107 via a steering shaft joint 108. A steering rack shaft 112 is connected to the pinion shaft 109.
The steering rack support member 113 supports the steering rack shaft 112 and is fixed to another frame 110 of the vehicle body via an elastic body 111.
Here, the yoke 1 (see FIG. 2) of the present embodiment is not particularly limited as long as it constitutes a joint used in the steering mechanism portion of the automobile shown in FIG. 1, for example, the universal joint 106 and the steering joint. What constitutes at least one of 108 may be used.

The lower steering shaft portion 107 is obtained by fitting a female shaft 107A and a male shaft 107B. Such a lower steering shaft portion 107 is required to have a performance that absorbs axial displacement generated when the automobile travels and does not transmit the displacement or vibration on the steering wheel 105.
In such a performance, the vehicle body has a sub-frame structure, and the member 100 that fixes the upper part of the steering mechanism and the frame 110 to which the steering rack support member 113 is fixed are separated. That is, it is required in the case of a structure in which the steering rack support member 113 is fastened and fixed to the frame 110 via an elastic body 111 such as rubber.

In another case, when the steering shaft joint 108 is fastened to the pinion shaft 109, an operator needs to have a telescopic function so that the telescopic shaft is once contracted and then fitted to the pinion shaft 109 for fastening. There is.
Further, the upper steering shaft portion 120 at the upper part of the steering mechanism also has a male shaft and a female shaft fitted to each other. Such an upper steering shaft portion 120 is required to have a function of moving the position of the steering wheel 105 in the axial direction and adjusting the position in order to obtain an optimal position for the driver to drive the automobile. The function of expanding and contracting in the axial direction is required. In all the cases described above, it is possible to reduce the rattling noise of the fitting portion on the telescopic shaft, to reduce the backlash on the steering wheel 105, and to reduce the sliding resistance when sliding in the axial direction. Required.

<York>
2A and 2B are diagrams showing a configuration of an embodiment of a yoke of a steering universal joint, in which FIG. 2A is a cross-sectional view along the axial direction, and FIG. 2B is a front view.
As shown in FIG. 2, a yoke (hereinafter, sometimes referred to as a yoke) 1 of the universal joint for steering according to the present embodiment has a base portion 2 and an arm portion 3 provided on the base portion 2. The base portion 2 corresponds to the female shaft 107A in the lower steering shaft portion 107 (see FIG. 1).

The base 2 has, for example, a cylindrical shape in which the fitting hole 2A penetrates in the axial direction. A shaft (male shaft 107 </ b> B in FIG. 1) is fitted to one end 2 a of the base 2 so that the outer peripheral surface and the inner peripheral surface 2 c of the fitting hole 2 </ b> A of the base 2 are in sliding contact.
The base 2 and the shaft are fitted so as not to rotate and to slide with each other. Illustrated in FIG. 1, the female shaft 107A corresponding to the base 2 is connected to the yoke 108A of the cardan shaft coupling 108 on the steering gear side. On the other hand, the male shaft 107B corresponding to the shaft is connected to the yoke 106A of the cardan shaft coupling 106 on the steering wheel side.

[Groove]
Here, as shown in FIG. 2, the yoke 1 of the present embodiment has six grooves 2 d, each having a substantially arcuate cross section equally distributed on the inner peripheral surface 2 c of the base 2 at intervals of, for example, 60 degrees in the circumferential direction. 2d,... Extend in the axial direction. On the other hand, although not shown in the drawing, a groove that is paired with the grooves 2d, 2d,... Having a substantially arcuate cross section equally distributed at intervals of 60 degrees in the circumferential direction also extends in the axial direction on the outer peripheral surface of the shaft. Is formed.

In addition, between the grooves 2d, 2d... And the grooves on the outer peripheral surface of the shaft, a plurality of balls or needle rollers can roll or slide into the grooves 2d, 2d. It is movably fitted. Note that a preload corrugated leaf spring (not shown) may be interposed between one of the plurality of balls or needle rollers and the groove 2d. When the steering torque is not transmitted, this leaf spring preloads the ball or needle roller to the extent that it does not rattle against the shaft, while when the steering torque is transmitted, the leaf spring elastically deforms to move the ball or needle roller between the shafts in the circumferential direction. It works to restrain you. As a result, backlash between the shaft and the base 2 can be reliably prevented, and the shaft and the base 2 can slide in the axial direction with a stable sliding load without backlash.
Instead of these torque transmission members, a ball or needle roller, a plurality of grooves formed in the axial direction of the shaft that accommodates them, and a plurality of grooves 2d, 2d,. A serration may be formed.

[Yoke material]
The material of the yoke 1 of the present embodiment is preferably a low carbon steel that can be cold forged and has carbon of 0.2% by mass or less. For example, carbon steel equivalent to S15C, which is carbon steel for machine structure, is preferable.

[Yoke hardness]
Further, the inner peripheral surface 2c of the fitting hole 2A of the base 2 of the yoke 1 of the present embodiment is hardened by soft nitriding so that the hardness (Hv) of the nitrogen diffusion layer becomes 300 or more.
Here, examples of the soft nitriding treatment include gas soft nitriding treatment (Nv nitriding and the like) and salt bath nitriding treatment (isonite and the like).
The gas soft nitriding treatment is performed by adding 30 to 50% of NH ₃ gas in a carburizing gas such as a rapid heating-type modified gas, a pyrolysis gas of an organic solvent, or a nitrogen gas atmosphere, and in a temperature range of 550 to 600 ° C. It is preserved by heating for up to 5 hours, and nitrogen and carbon are simultaneously penetrated and diffused to form a compound layer (compound layer of iron and nitrogen) on the surface to be treated. In the yoke 1 of the present embodiment, the thickness of this compound layer is 30 μm or less.
According to this gas soft nitriding treatment, it can be applied to low-grade steel, and the processing time is 90 to 150 minutes, which is much shorter than the normal gas nitriding treatment time 25 to 100 hours, and mass production is possible at low cost. It becomes.

[Residual stress of yoke]
Here, in the soft nitriding treatment, the base portion of the arm portion 3 is cooled to form a region (residual stress specifying region 10) having a residual stress of −100 MPa or less. In addition, the cooling method of the base part of the arm part 3 in soft nitriding is oil cooling or water cooling. This cooling is preferably 50 ° C./s or more from 570 ° C. to around 100 ° C.
The yoke 1 of the present embodiment has a dimension (diameter) in the radial direction of the residual stress specifying region 10 of “D (mm)” and an inner diameter of the fitting hole 2A of “d (mm)”. −d ≧ 1.0 (mm) is satisfied, and preferably D−d ≧ 2 (mm) is satisfied. The surface residual stress on the inner peripheral surface of the residual stress specific region 10 is preferably −100 MPa or less.

  As described above, the yoke 1 of the present embodiment includes the “cooling method of the root portion of the arm portion 3 in soft nitriding”, “the radial dimension D of the residual stress specific region”, and “the inner diameter of the fitting hole 2A”. By defining the difference from “d”, “the hardness of the nitrogen diffusion layer”, and “the thickness of the compound layer”, the mechanical strength against twisting is improved.

Embodiments of the yoke according to the present invention will be described below.
Example 1
In this example, S15C, which is a carbon steel for machine structure, was used as a material constituting the yoke 1. After forming S15C into the base part 2 and the desired bifurcated arm part 3 by cold forging, gas soft nitriding treatment was performed at 570 ° C. for 3 to 5 hours to cool the base part of the arm part 3. In addition, the cooling method of the base part of the arm part 3 in gas soft nitriding was oil cooling.
For the yoke 1 thus manufactured, “residual stress”, “Dd”, “surface hardness of the nitrogen diffusion layer”, and “thickness of the compound layer” are measured in the following manner. "Durability time ratio" was measured. The results are shown in Table 1.

[Measurement of “residual stress”, “D”, and “d”]
The measurement of the residual stress of the yoke 1 was performed on the residual stress specific region 10 by the X-ray method, and the stress direction was measured as the circumferential direction. In the residual stress distribution thus measured, the residual stress specifying region 10 in which the residual stress is −100 MPa or less was specified. And the diameter of the residual stress specific area | region 10 was measured as "D", and "D-d" was computed from the internal diameter "d" of the fitting hole measured separately. The results are shown in Table 1. Table 1 also shows the residual stress on the inner peripheral surface.

[Measurement of surface hardness of nitrogen diffusion layer]
The surface hardness of the nitrogen diffusion layer was measured at 0.49 N using a Vickers hardness meter after the compound layer was removed by polishing. The results are shown in Table 1.
[Measurement of thickness of compound layer]
The thickness of the compound layer was measured by cutting the yoke 1 in a direction perpendicular to the axial direction, polishing the cut surface, etching with nital, and observing the cross section. The results are shown in Table 1.

[Measurement of endurance time ratio]
In this embodiment, the time from when the yoke 1 is fixed with a jig using a durability test apparatus and a torsion torque is input under the following test conditions until breakage such as cracks occurs on the surface of the yoke 1 (endurance time) Was measured. The results are shown in Table 1. The durability time is shown as a ratio when the durability time of Comparative Example 1 is 1.0.
[Test conditions]
・ Canceling: 1 million times ・ Frequency: 6 Hz
・ Input torsion torque: 130 Nm
(Examples 2 to 16, Comparative Examples 1 and 2)
The conditions of Example 1 are as shown in Table 1. In the case of oil cooling, the oil temperature was adjusted, and in the case of water cooling, the water temperature was adjusted between 25 to 100 ° C., respectively, except that the gas soft nitriding time was adjusted. In the same manner as Example 1, yokes of Examples 2 to 16 and Comparative Examples 1 and 2 were produced. The results are shown in Table 1.

  As shown in Table 1, since the yokes of Examples 9 to 16 satisfy “Dd is 1.0 mm or more”, the durability time ratio is larger than that of the yokes of Comparative Examples 1 and 2. In addition, the yokes of Examples 1 to 8 are “the cooling method of the base portion of the arm portion during soft nitriding is oil cooling or water cooling”, “Dd is 2 mm or more”, “residual stress is −100 MPa or less”. The durability time ratio is large by satisfying that “the surface hardness Hv of the nitrogen diffusion layer is 300 or more” and “the thickness of the compound layer is 30 μm or less”. In particular, the yokes of Examples 5 to 8 in which “the cooling method of the base portion of the arm portion during soft nitriding treatment is water-cooled” are cracked on the surface of the yoke even when the number of times of the endurance test is exceeded (1 million times). It was found that the yoke had particularly excellent durability.

On the other hand, the yokes of Comparative Examples 1 and 2 that did not satisfy even one of the above conditions had a small (equivalent or equal) durability time ratio. In particular, it can be seen that in Comparative Example 1, the residual stress was reduced because the “cooling method of the root portion of the arm during soft nitriding” was “air cooling”.
As described above, according to the present embodiment, it is possible to provide a yoke for a steering universal joint that has improved mechanical strength against twisting of the yoke 1 and has sufficient strength for use in an electric power steering apparatus. Can do.

  The yoke of the steering universal joint according to the present invention has been described above. However, the yoke of the steering universal joint according to the present invention is not limited to the above-described embodiment, and various types can be used without departing from the gist of the present invention. Can be modified. For example, the yoke of the steering universal joint according to the present invention is preferably used as a fixed-side yoke, not an input-side, in a universal joint constituted by a pair of yokes and a cross joint.

DESCRIPTION OF SYMBOLS 1 Yoke 2 Base part 2a One end part 2b Other end part 2c Inner peripheral surface 2d Groove part 3 Arm part 3A Bearing hole 3B Bearing hole 10 Residual stress specific area | region

Claims (3)

Having a base and an arm,
The base is provided with a fitting hole through which the shaft is fitted and fixed from one end thereof,
A pair of arms that extend in the axial direction of the fitting hole at the other end of the base and face each other in a direction perpendicular to the axial direction, and concentric bearing holes formed in that direction. And
A soft nitriding treatment that oil-cools or water-cools the base of the arm portion during cooling is performed on the fitting hole,
For steering, wherein the dimension D in the radial direction of the region where the residual stress at the other end is −100 MPa or less and the inner diameter d of the fitting hole satisfy Dd ≧ 1.0 (mm). Universal joint yoke. The surface hardness Hv of the nitrogen diffusion layer of the fitting hole is 300 or more,
The dimension D in the radial direction of the region where the compound layer thickness of the fitting hole is 30 μm or less and the residual stress at the other end is −100 MPa or less and the inner diameter d of the fitting hole are D−d. The yoke for a steering universal joint according to claim 1, wherein ≧ 2 (mm) is satisfied.   The yoke of the universal joint for steering according to claim 1 or 2, wherein a root portion of the arm portion is water-cooled during the cooling.

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