JPS62113918A - Universal coupling - Google Patents

Abstract

PURPOSE:To improve fatigue resistant strength without change of design items by applying low-temperature sulphurizing treatment to a shaft to which a needle bearing is fitted in a universal joint for a vehicle. CONSTITUTION:A tripod shaft 2 is made by SCM420H or SCr420H. Standard cementation hardening treatment is applied to the tripod shaft, and after the shaft is subjected to polishing, the shaft is subjected to low-temperature sulphurizing dipping treatment. The low-temperature sulphurizing dipping treatment is conducted by adding sodium sulfide to an alkali metal salt bath, maintaining same at 180 deg.C, dipping the tripod shaft 2 therein, and applying an electric current for ten minutes with the tripod shaft 2 as an anode, and the treatment bath as a cathode. Thus, coating of iron sulfide is formed on the contact surface of the tripod shaft 2 and a needle roller bearing 3. When high load is applied to the coating, plastic flow is caused to increase the contact area, so that the fatigue resistant strength can be improved remarkably.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in universal joints installed in vehicles and the like, and particularly to universal joints that use needle roller bearings as assembly elements.

(Prior Art) Universal joints that use needle roller bearings as assembly elements include tri-board joints and cruciform joints. For example, a tri-board joint, as shown in Figures 3 and 4,
A plurality (usually three) of tri-board shafts 2 are installed at one end in a direction perpendicular to the axis of rotation 1, and a needle roller bearing 3t- is attached to each of the tri-board shafts 2.
An inboard roller 4 is attached through the inboard roller 4, and this roller 4 is engaged with the groove 6 of the cherry lip 5. Note that the 7,7ij needle roller bearing S t is a retainer for positioning and holding on the tripod shaft 2.

Conventionally, the above-mentioned tri-board shaft 2 has generally been manufactured using low-alloy case hardened steel through the following steps: forging, machining, carburizing or carburizing, nitriding, quenching, arm restoring, and polishing.

(Problem to be Solved by the Invention) Recently, there has been a tendency for vehicles, especially automobile engines, to have higher outputs (turbo devices, 4 valves, etc.), and with this, the load applied to the universal joint of the drive system has increased. The stress becomes severe and fatigue damage such as pitting or flaking occurs early, especially in the tri-board shaft 2 or inboard roller 4 that contacts the 21-dollar roller bearing 3, which has become a problem.

As a countermeasure against this fatigue, for example, as shown in FIG. 5, crowning 3a may be attached to the contact surface of the needle roller bearing 3 with the tri-board shaft 2, or the inboard roller 4. A rounded part 4a with a relatively large curvature is provided at the end of the contact side with the needle roller bearing 6, or the distance t between the start point of the crowning 3a and the end point of the rounded part 4a is varied. I am doing something to help.

However, even with the above measures, it was still difficult to stably increase fatigue strength.

Incidentally, some attempts have been made to apply a phosphate film treatment to the surface of the tri-board shaft 2 or the inner circumferential surface of the inboard roller 4 (Japanese Patent Laid-Open No. 58-200819), but although the initial conformability is good, There was a problem in that it could not withstand long-term use under the above-mentioned harsh conditions.

The present invention has been made in view of the above-mentioned conventional problems.
The purpose of this invention is to provide a universal joint that improves fatigue strength as much as possible without changing design specifications, materials, or heat treatment conditions by devising surface treatment after the finishing process.

(Means for Solving the Problems) Therefore, the present invention provides that, among the members that come into contact with the needle roller bearing, at least the shaft to which the needle roller bearing is fitted is subjected to low-temperature sulfurization treatment. The gist is:

The universal joint according to the present invention uses a needle roller bearing as an assembly element, and includes tri-board joints and cruciform joints. In this case, the shaft to which the low-temperature sulfurizing treatment is applied is the tri-board shaft in the case of a tri-board joint, and the spider in the case of a cruciform joint.

On the other hand, other members that come into contact with the needle roller bearing are an inboard roller in the case of a tri-board bearing, and a flange yoke (cup spider and shell cup) fixed to the shaft end in the case of a cruciform joint.

Low-temperature sulfurization treatment involves adding sodium sulfide (
Na, 5Os) was added and heated to 165-195℃.
A two-pent method can be employed in which the object to be treated (for example, the tri-board shaft) is held as an anode and the treatment tank is used as a cathode and electricity is applied for 10 to 20 minutes.

(Function) In the universal joint having the above configuration, by performing the low temperature sulfurization treatment, an iron sulfide film is formed on the contact surface with the needle roller bear IJ7. This iron sulfide has a largely cubic crystal structure, has a small coefficient of friction, and is rich in plastic fluidity. In particular, plastic flow makes it possible to suppress local surface pressure increases that occur due to metal contact such as edge contact. That is, the distribution pattern of the contact force that is abnormally high at the edge portion is evened out toward the inside, and as a result, the fatigue strength of the entire universal joint is significantly improved.

Since low-temperature sulfurizing treatment can be carried out at a relatively low temperature range of 165 to 195°C, another major feature is that it hardly affects the surface hardness, quenching depth, or internal hardness of the base material. .

(Example) Hereinafter, an example of the present invention will be described based on the accompanying drawings.

The universal joints targeted in this example are shown in Figures 3 and 4 above.
This is the tri-board joint shown in the figure, and the explanation of its structure will be omitted here. In this embodiment, the tri-board axis 2
i It was manufactured using 8CM420H or 5Cr420H case-hardened steel, subjected to standard carburizing and quenching treatment, polished and then subjected to low-temperature sulfurization treatment. Low-temperature sulfurization treatment involves adding sodium sulfide to an alkali metal salt bath, keeping it at 180°C, and immersing the triboard shaft in it.
Electricity was applied for 10 minutes using the tri-board shaft as an anode and the treatment tank as a cathode.

The tri-board joint configured as described above was incorporated into the drive system of an automobile and subjected to a bench durability test simulating the mode of use in the market. For comparison, a conventional tri-board joint with the same material, processing, and heat treatment as the product of this example, but with only the low-temperature sulfurization treatment omitted, was also subjected to the bench durability test.

FIG. 1 shows the results of a bench durability test conducted on eight tri-board joints, plotted on Weibull probability paper. This example product, represented by line A, is I
Compared to the comparative product (conventional product) represented by sB, the L60 life was approximately twice as long, confirming that the low-temperature sulfurization treatment has a large fatigue strength improvement effect.

This improvement in fatigue strength is due to the iron sulfide coating 1 formed on the surface of the tri-board shaft 2, as shown in Fig. 2(a), Φ).
This is thought to be because when No. 1 was subjected to a high load, plastic flow occurred as shown in (a) to (b), increasing the actual contact area.

The spider in the cruciform joint was subjected to the same low-temperature sulfurization treatment as in the above example, and the cruciform joint was assembled into an automobile propeller shaft and a bench durability test was conducted. Improvement was confirmed.

(Effects of the Invention) As explained above in detail, the universal joint according to the present invention is made by subjecting the contact surface with the needle roller bearing to low-temperature sulfurization treatment, so that it can withstand abnormal light stains. The iron sulfide formed on the contact surface has a relaxing effect, and this has resulted in the effect of greatly improving the fatigue strength of the entire adjustable joint.

In addition, the fatigue strength was improved without changing the design specifications such as increasing the shaft diameter or adding crowning, or without changing the material, making it possible to create a small, lightweight, and compact universal joint.

[Brief explanation of drawings]

Figure 1 is a graph showing the fatigue test results of the tri-board joint according to the present invention in comparison with conventional products, and Figures 2 (a) and (b)
is a conceptual diagram showing the mechanism of fatigue strength improvement by low-temperature sulfurization treatment, and Figures 3 and 4 show the structure of the tri-board joint that is the subject of the present invention. 4
The figure is a sectional view of a main part, and FIG. 5 is a sectional view showing an example of measures to improve the fatigue strength of a conventional tri-board joint. 2... Tri-board shaft 3... Needle roller bearing 11... Low-temperature sulfurized coating patent applicant Toyota Motor Corporation Figure 1 Figure 2

Claims (3)

[Claims] (1) A universal joint having a needle roller bearing as an assembly element, in which at least a shaft to which the needle roller bearing is fitted, among the members that come into contact with the needle roller bearing, is subjected to a low-temperature sulfurization treatment. (2) The universal joint according to claim 1, wherein the shaft is a tri-board shaft in a tri-board joint. (3) The universal joint according to claim 1, wherein the shaft is a spider in a cruciform joint.