JPS5948861B2 - differential pinion shaft - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement of pinion shafts used in vehicle differentials, and in particular, the surface is coated with a ferromolybdenum alloy by plasma spraying to form a sliding surface with excellent wear resistance. Regarding the pinion shaft.

FIG. 1 shows a differential gear 1, in which a pinion shaft 3 is horizontally suspended in a differential case 2, and pinions 4, 4 are attached to both ends inside the case.
is rotatably fitted, and the pinions 4, 4 are connected to the left and right drive shafts 5.
, 5, and the case 2 is driven by a gear 7 attached to a part of the outer circumference, and the case itself rotates, causing the gears 6, 6 to rotate via pinions 4, 4, Output to axes 5 and 5.

By the way, an extremely high extreme pressure acts on the surface of the pinion shaft 3 of the differential device as the pinion gear 4 rotates during the differential operation.

However, in differential gears, especially in front-wheel drive cars, the differential gear's lubricating oil is shared with transmission oil, and as is known, transmission oil has a low viscosity, and as a result of being lubricated with this low-viscosity oil, the oil film on the pinion shaft surface is cut off. , wear, scuffing (galling), seizure, etc. occur. Therefore, in order to deal with this problem, surface hardening has conventionally been performed on at least the friction sliding surface 3a of the pinion shaft 3 that contacts the pinion gear, and soft nitriding, carburizing, molybdenum spraying, etc. have been adopted as the surface hardening treatment method. ing.

Such conventional pinion gear surface hardening treatment methods include soft nitriding,
The surface hardening layer created by the carburizing method may cause scuffing when the oil film breaks, which may cause seizure.

In addition, the surface treatment layer formed by molybdenum spraying has a weak bond strength between the molybdenum spray particles, so the strength of the sprayed layer as a whole is low.
There is a drawback in that abrasion, a phenomenon in which highly hard particles in the sprayed layer fall off and abrade the mating material, occurs. In other words, since molybdenum has a high melting point of 2620°C, the molybdenum metal is not sufficiently dissolved during thermal spraying, and the bond strength between the sprayed particles is weak, causing abrasion phenomenon during differential application, resulting in the hardness of the molybdenum particles falling off. Since the voltage is extremely high at 600 to 650 HV, scuffs occur on the sliding surface of the pinion gear, and peeling occurs in the sprayed coating on the pinion shaft side, and as this phenomenon progresses, seizure occurs.

Furthermore, molybdenum sprayed material is an expensive alloy and is not commonly used for surface treatment of pinion shafts. However, metal thermal spraying, especially molybdenum thermal spraying, has the property of the sprayed layer that the voids formed between metal particles have the function of retaining lubricating oil, possessing self-lubricating properties, and increasing wear resistance. It has advantages. In view of the above-mentioned problems with surface-treated pinion shafts of differential gears, the present inventors have devised the present invention to solve the problem. By taking advantage of the above advantages and further promoting them, we have effectively solved the above problems.

An object of the present invention is to provide a pinion shaft that rotatably fits and supports a pinion of a differential device, by spraying a ferromolybdenum alloy on at least the fitting sliding surface of the pinion using a plasma spraying method to prevent frictional sliding. A planar coating is formed, specifically, molybdenum (MO) 50 to 70%, carbon C 6% or less, silicon Si 3% or less, phosphorus PO. 1% or less, sulfur SO. 2% or less, copper CuO. A pinion is made by plasma spraying of a ferromolybdenum alloy powder consisting of an α solid solution of iron in molybdenum, an ε phase of iron and molybdenum, and a compound of molybdenum, with the balance being iron (Fe) and a molybdenum compound. The purpose of the present invention is to provide a pinion shaft having a coating that is thermally sprayed on the shaft surface to form a sliding surface with the pinion and has a surface that slides with the pinion gear and has excellent wear resistance.

Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional view of the differential device 1, in which 2 is a differential case, 3 is a pinion shaft, 4 is a pinion gear, and 5 is a longitudinal sectional view of a differential device 1.
is a drive shaft, 6 is a gear, and 7 is a drive gear.

In the present invention, ferromolybdenum alloy powder is thermally sprayed on the sliding surface 3a of the pinion shaft 3 with respect to the pinion gear 4 by plasma spraying, thereby forming the sliding surface 3a having a coating made of the ferromolybdenum alloy.

The composition of the ferromolybdenum alloy is MO5O~70%, C
6% or less, Si3% or less, PO. 1% or less, SO. 2%
Below, CUO. Ferromolybdenum alloy powder consisting of 5% or less and the balance being Fe is sprayed by plasma spraying onto the sliding surface 3a of the pinion shaft 3 against the pinion gear 4 to form a coating.

The melting point of this ferromolybdenum alloy is lower than that of molybdenum, with a liquidus line of 1850°C and a solidus line of 1540°C, so that the sprayed particles are completely melted.

Therefore, the welding between the sprayed particles is large, the strength of the entire sprayed coating layer is high, and a strong coating is formed, resulting in the so-called abrasion phenomenon in which the particles fall off and abrade the mating material even when differential pressure is high. does not occur. By the way, the composition of this thermal spray material consists of an α solid solution in which iron is dissolved in molybdenum, an ε phase (Fe3MO2) consisting of iron and molybdenum, and a trace amount of a molybdenum compound.

The content of molybdenum is 50-70%, which is 50-70%.
Since it is an alloy containing 0% molybdenum, the self-lubricating property of molybdenum is lost, and the wear resistance can be sufficiently satisfied. The porosity in the sprayed layer formed with this sprayed material is 5 to 12%, which is about the same as that of molybdenum, and the synergistic effect with these materials provides excellent wear resistance, abrasion resistance, scuff resistance, and seizure resistance. A coating with excellent properties can be obtained, and a pinion shaft for a differential device with excellent properties can be obtained. Next, a specific example of the pinion shaft of the present invention will be described.

First, the surface of the aforementioned pinion shaft 3 made of talom molybdenum steel is blasted to form a matte rough surface, and then degreased.

And the ferromolybdenum alloy powder (250-400
A mesh) is thermally sprayed onto at least the pinion gear sliding surface 3a of the pinion shaft 3 by plasma spraying to form a coating that forms the sliding surface. A characteristic of plasma spraying is that it uses an inert gas such as argon, so the sprayed coating is difficult to oxidize, unlike methods that use a general gas flame. This can prevent the formation of an oxide intermediate layer that significantly weakens adhesion. Therefore, it has the effect of stabilizing the adhesion strength to the material of the coating, that is, the surface of the pinion shaft, and further increasing the strength of the entire thermal sprayed coating. Next, the outer periphery of the portion of the pinion shaft on which the thermally sprayed coating has been formed is ground to a predetermined size using a diamond grindstone to obtain a pinion shaft formed to the final size.

In addition, the wear resistance and scuff resistance of the mating pinion gear (carburized and quenched chromium molybdenum steel)
When seizure resistance is taken into account, it has been found from test data that the hardness of the sprayed coating and its hardness are determined by the content of molybdenum as the optimum conditions for satisfying this.

In the case of the pinion shaft according to the present invention, the hardness is preferably 450 to 500 HV, and in order to obtain this hardness, the molybdenum content is 50 to 70%.
If the hardness is 0% or less, the hardness distribution of the obtained coating will be 450 HV or less, and the amount of wear on the pinion shaft will be greater than the amount of wear on the pinion gear. Moreover, when the content of molybdenum exceeds 70%, the hardness of the obtained film is 50%.
The hardness distribution of 0HV or more increases, causing scuffs on the pinion gear surface. Therefore, the content of molybdenum is preferably 50 to 70% from the viewpoint of compatibility with the mating pinion gear. Next, the results of a test conducted to compare the pinion shaft of the present invention obtained above with a pinion shaft coated with a sprayed coating using a molybdenum spraying method will be shown.

The pinion gear is made of tarom molybdenum steel SCM-22
Tests were conducted under the same conditions using carburized and fired materials.

Pliers durability test conditions Differential device: Differential device for FF cars with a displacement of 1500 cc Engine Speed: 1600 rpm Load: 10 kg-m Lubricating oil: Oil for automatic transmission Operating time: Test results of 15 minutes or more are the second results. As shown in the graphs of FIG. 3 and FIG. 3, FIG. 2 shows a pinion shaft according to the present invention, and FIG. 3 shows a pinion shaft coated with a molybdenum spray coating. While the shaft has low frictional resistance and does not cause seizure, the frictional resistance of the pinion shaft coated with a molybdenum spray coating increased over time, and seizure occurred within 10 minutes, making it inoperable.

In other words, the pinion shaft coated with molybdenum thermal spraying showed a scuffing phenomenon after the start of operation, and seizure occurred within 10 minutes.
Peeling occurred in the coating.

The amount of wear on the pinion gear reached 10 to 13μ.
On the other hand, the pinion shaft of the present invention was in good condition with no scuffing phenomenon or seizure occurring after 15 minutes of operation, and the wear amount of the pinion gear was 1 to 2 microns. As is clear from the above, according to the present invention, a powder is obtained from a ferromolybdenum alloy that is inexpensive and easily available, and this is thermally sprayed onto the surface of a pinion shaft by plasma spraying to form a coating. In order to obtain wear resistance as described above,
A pinion shaft having a coating with excellent abrasion resistance, scuff resistance, and seizure resistance can be obtained, and the oil film will not break even under extreme pressure conditions using low viscosity oil, and a good pinion shaft can be obtained. Furthermore, the compatibility with the pinion gear, which is the mating member, is optimal, and in addition to obtaining a pinion shaft that is very preferable for the pinion gear, the hardness of the pinion shaft side in relation to the pinion gear,
It also has many advantages such as the strength can be easily adjusted arbitrarily by changing the molybdenum content.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, in which Fig. 1 is a longitudinal sectional view of a differential, Fig. 2 is a graph of test results of the pinion shaft of the invention, and Fig. 3 is a similar graph of a molybdenum sprayed pinion shaft. This is a graph of In the drawing] is a differential device, 3 is a pinion shaft, and 4 is a pinion gear.

Claims (1)

[Claims] 1. In a pinion shaft that rotatably fits and supports a pinion gear of a differential device, at least the fitting sliding surface of the pinion gear of the pinion shaft is coated with 50 to 70 molybdenum.
%, carbon 6% or less, silicon 3% or less, phosphorus 0.1% or less, sulfur 0.2% or less, copper 0.5% or less, the balance is iron, and its composition is α solid solution in which iron is dissolved in molybdenum. A pinion shaft for a differential device, characterized in that it has a coating coated by plasma spraying with ferromolybdenum alloy powder consisting of an ε phase consisting of iron and molybdenum, and a compound of molybdenum.