JP2001141011A - Rolling element for transmitting torque - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling element for transmitting torque which has an excellent traction coefficient and an excellent durability. SOLUTION: This rolling element for torque transmitting has a main body made of metal and a membrane made of a high extension metal material whose extension is more than 30% which is formed on the rolling surface of the main body beforehand. By forming the membrane which consists of a metal material with a high extension whose extension is more than 30%, to the rolling surface, the aggulatination areas of the metal material membranes are increased to increase the frictional force, and at the same time, since a high extension of metal material is used, the metal material is hardly removed from the rolling surface by the aggulatination friction, so as to improve the durability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rolling element for transmitting torque. More specifically, the present invention relates to a traction drive system, particularly to a torque transmitting rolling element used in a toroidal type continuously variable transmission.

[0002]

2. Description of the Related Art A rolling element for transmitting torque (hereinafter referred to as "rolling element" as appropriate) is a power roller which is a component of a toroidal type continuously variable transmission using a traction drive system.
Used for input disks, output disks, etc.

The traction drive method is a method in which a so-called solidified thin film of lubricating oil exists between the rolling elements due to the pressure between the rolling elements, and torque is transmitted between the rolling elements by the shearing force of the solidified thin film.

In a toroidal type continuously variable transmission, a thin film of lubricating oil called traction fluid exists between an input disk and a power roller and between a power roller and an output disk. In this case, a high pressure of generally 1 GPa or more is applied between the input disk and the power roller and between the power roller and the output disk, so that the traction fluid thin film is solidified. It is considered that the torque is transmitted from the general rolling element to the other rolling element by the shearing force of the thin film of the traction fluid in the solidified state. For example, by rotating the input disk, the power roller is rotated to transmit torque from the input disk to the power roller. Therefore, in a toroidal type continuously variable transmission, a rolling element that efficiently transmits torque has been required.

In order to transmit torque efficiently, it is necessary to increase the frictional force of the rolling elements. The frictional force (F) of a rolling element is generally defined by the product of the traction coefficient (μ) of the rolling element and the load (N) applied to the rolling element. That is, it is expressed by the equation F = μN. That is, when the same load is applied to the rolling elements, the higher the traction coefficient, the greater the frictional force. The higher the frictional force, the more torque can be transmitted to the other rolling element.

Therefore, it has been conventionally required to improve the traction coefficient of the rolling element.

[0007]

In order to improve the traction coefficient of the rolling element, a method of making the rolling surface of the rolling element rough is generally adopted.

However, as described above, in the toroidal type continuously variable transmission, a high surface pressure such as 1 GPa or more at which the traction fluid thin film solidifies between the input disk and the power roller and between the power roller and the output disk. Under the traction fluid, torque is transmitted by the shear force of the thin film. In such a traction drive mechanism, when the rolling surface of a rolling element such as a power roller is roughened, there arises a problem that the rolling surface of the rolling element is rather worn due to a shearing force under a high surface pressure. When the rolling surface of the rolling element is worn, the traction coefficient is reduced, and the life of the rolling element is exhausted. Therefore, from the viewpoint of durability, a rolling element having excellent surface fatigue strength of the rolling surface is required.

An object of the present invention is to provide a rolling element having an excellent traction coefficient and an excellent durability.

[0010]

In the traction drive system, the present inventor has found that a thin film of lubricating oil allows the rolling surfaces of rolling elements to be completely in non-contact state, as generally considered. Instead, the inventors paid attention to the fact that the projections of the unevenness existing on the surface of the rolling surface of the rolling element actually contact each other.

The inventor of the present invention concludes that, in the traction drive system, if the projections of the concavities and convexities are in contact with each other, the same can be said in the traction drive system as in the case of normal sliding friction between solids. Thought. That is, in normal sliding friction in which two solid surfaces are in contact with each other, since the solid contact surface has irregularities, a portion of the contact surface that is actually in contact is a part thereof. Some parts are plastically deformed and adhered by the pressure acting between the solids. The friction force is the force required to shear this adhered portion. The inventor of the present invention is also concerned with the traction drive system. We thought that the force needed to do so was friction.

The inventor of the present invention considered that in the traction drive system as well, the larger the area of the adhered portion on the surface of the rolling surface, the greater the frictional force and the higher the traction coefficient. Further, since friction occurs when the adhered portion is sheared, it is considered that if the rolling surface is not broken even if the adhered portion is sheared, the fatigue strength is excellent and the durability of the rolling element is improved.

The inventor of the present invention has developed a metal body and a coating made of a highly ductile metal material having an elongation of 30% or more formed on a rolling surface of the body, which operates in a lubricating oil. The invention has invented a rolling element for transmitting torque, characterized by having a rolling element.

Here, the elongation means a breaking elongation in a tensile test specified in JISZ2241. That is, it is the percentage of the difference (increase) between the gauge length before tension and the gauge length after breakage of the test piece with respect to the gauge length before tension.

That is, as a result of repeated studies, the present inventors have solved the above-mentioned problem by forming a coating of a highly ductile metal material on the rolling surface of the rolling element. The reason why the elongation was set to 30% or more was that, as a result of research, it was recognized that a coating material was difficult to fall off due to cohesive wear in a metal material having an elongation of 30% or more.

As described above, in the traction drive system, the rolling surfaces of the rolling elements are not completely out of contact with each other, but the protruding portions on the surfaces of the rolling surfaces are in contact with and adhere to each other. . Therefore, the rolling surface of the rolling element has an elongation of 30.
% Or more, the rolling surfaces made of the coating come into contact with each other in a wide range. Due to the contact between the coatings in a wide range, adhesion between the coatings occurs, and the friction coefficient, that is, the traction coefficient of the contact portion can be improved.

The metal material used for the coating has an elongation of 3
Since the metal material is highly ductile such as 0% or more, even if the metal material is stretched when the adhered portion is sheared, the metal material may be broken or fall off from the rolling elements. Few. Therefore, a coating made of a metal material having an elongation of 30% or more is hardly worn, has excellent fatigue strength, and improves the durability of the rolling elements.

Further, since a coating made of a metal material having an elongation of 30% or more is formed on the rolling surface, the rolling surface can be protected. As a result, the durability is improved.

In the traction drive system, high pressure is applied to the rolling surface of the rolling element, but the pressure on the rolling surface of the rolling element can be supported by the metal body of the rolling element.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a rolling element for transmitting torque according to the present invention will be described below.

The rolling element for torque transmission of the present invention is operated in lubricating oil, and is composed of a metal main body and a highly ductile metal material having an elongation of 30% or more formed on the rolling surface of the main body. And a coating.

The rolling element of the present invention operates in lubricating oil and can be used in a torque transmission device or the like employed in a traction drive system using lubricating oil.

For example, when the traction drive system is employed in a continuously variable transmission of a vehicle, the rolling elements are used as an input disk, a power roller, an output disk and the like as described above. In this case, a lubricating oil generally called traction fluid can be used,
Commercially available traction fluid can be used.

The metal body of the rolling element of the present invention is made of a metal having high strength and excellent fatigue strength in consideration of the high pressure applied to the rolling surface of the rolling element and the durability of the rolling element. Can be used. Generally, an iron-based metal can be used, and preferably high carbon chromium bearing steel, immersion single bearing steel, such as SUJ4 (JISG4805) and SUJ2
(JIS G4805) or the like may be used.

The surface roughness of the rolling surface of the metal body may be about 0.01 to 0.2 μm in terms of center line average roughness (Ra), preferably 0.01 to 0.05 μm. Good. If the thickness exceeds 0.05 μm, even if a coating is present on the rolling surface, metal contact between the metal bodies is likely to occur, and the surface of the metal body will be worn. 0.01 μm
If the thickness is less than this, if a film is formed on the rolling surface, the irregularities on the surface of the rolling surface will be too small, and adhesion will not easily occur when a film made of a highly ductile metal is formed.

As a highly ductile metal material having an elongation of 30% or more, for example, gold (45%), silver (48%), copper (5%)
0%), lead (40%), tin (96%), and the like. Also, an alloy having an elongation of 30% or more can be used. If a highly ductile metal material having an elongation of 30% or more is used, falling off due to cohesive wear can be reduced.

In this case, it is preferable to use gold or copper. It is hard to be worn and the traction coefficient can be improved. Particularly, copper is preferable. This is because the traction coefficient is clearly improved as compared with a rolling element having no copper coating as in the examples described later. In this case, the purity of copper is preferably 99% or more. The higher the purity, the more the falling off due to adhesive wear is reduced, and the traction coefficient can be improved.

It is to be noted that the thickness of the film formed on the rolling surface should be set to an appropriate thickness in consideration of the pressure applied to the rolling elements of the rolling elements, the highly ductile metal material used for the coatings, and the like. it can. Generally, it is preferably 0.03 μm or more, and more preferably 0.06 to 0.3 μm. If the thickness of the coating is too small, the rate of friction with the highly ductile metal material decreases, and the traction coefficient cannot be improved. Conversely, if the thickness of the coating is too thick, the metal material forming the coating due to cohesive wear will undergo large plastic flow when high pressure is applied to the rolling surface, and the metal material will often fall off due to wear. .

A known method can be used to form a coating of a highly ductile metal material on the rolling surface. For example, a coating of a highly ductile metal material can be formed by a vacuum evaporation method, an ion plating method, a sputtering method, or the like.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The rolling element of the present invention will be described below based on an embodiment. In order to confirm the traction coefficient of the rolling element of the present invention, three outer cylinders located outside and one located at the center
The rolling element of the present invention was tested using a four-cylinder testing machine having two central cylinders. The four-cylinder testing machine used was a rolling-sliding friction and wear testing machine manufactured by Shinko Zoki Co., Ltd. The result is shown in FIG.

In this test, a load was applied to the upper one of the three outer cylinders, and a slip speed was applied between the three outer cylinders and one central cylinder to measure a traction coefficient. That is, the three outer cylinders were rotated at the same speed, and one central cylinder was given a sliding speed. The outline of the test is described below.

As the rolling element of the embodiment, a rolling element composed of a metal body and a copper film formed on the rolling surface was used as four cylinders of a four-cylinder testing machine. As a comparative example, a rolling element having only the same metal body and having no coating was used as four cylinders.

A cylindrical rolling element having a diameter of 40 mm and a width of 12 mm was used as the three outer cylinders of the four-cylinder testing machine. A cylindrical rolling element having a diameter of 40 mm and a width of 6 mm was used as a central cylinder.

The metal body of these rolling elements was formed of SUJ4 (JIS G4805) which is a high carbon chromium bearing steel. The surface roughness of the outer peripheral surface of the metal body, that is, the rolling surface, was 0.03 μm in center line average roughness (Ra).

In the rolling element used in the examples, a coating made of copper (Cu) having a purity of 99% or more was formed on the rolling surface of the metal main body. The thickness of this coating was 0.2 μm.
In this embodiment, a vacuum deposition method was used as a method for forming a copper film.

As the rolling element of the comparative example, the above-mentioned metal main body on which no coating was formed was used as a rolling element as it was.

In this test, 0.79 GPa, 1.1
The traction coefficient was measured while changing the load applied such as 1 GPa and 1.37 GPa.
The speed of the three outer cylinders was 6.28 m / s, and the speed of the center cylinder was set so that the slip ratio was 2.2%. Traction fluid is Santotra
c) The temperature of the traction fluid was set to 110 ° C. using Santotrac 50 manufactured by the company.

The test results were as follows.

At a pressure of 0.79 GPa, the traction coefficient of the comparative example was 0.0644, whereas the traction coefficient of the comparative example was 0.0656. 1.11G
At a pressure of Pa, the traction coefficient of the comparative example was 0.0775, whereas the traction coefficient of the example was 0.175.
0802. Under a pressure of 1.37 GPa, the traction coefficient of the comparative example was 0.0810 and the traction coefficient of the example was 0.0826.

It can be seen that the traction coefficient of the rolling element of the example is higher than that of the comparative example under any pressure.

Although not shown in the figure, the surface of the rolling element after the test was observed with an electron microscope. As a result, it was confirmed that copper remained on the rolling surface of the rolling element. This indicates that the durability of the rolling elements is also improved.

[0042]

The rolling element for transmitting torque according to the present invention has excellent traction coefficient and excellent durability. Further, since a coating made of a highly ductile metal material having an elongation of 30% or more is formed on the rolling surface of the metal body, there is also an effect of protecting the rolling surface of the metal body.

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of a four-cylinder testing machine.

Claims (5)

[Claims] The invention is characterized in that it has a main body made of metal and a coating made of a highly ductile metal material having an elongation of 30% or more formed on a rolling surface of the main body, which operates in a lubricating oil. Rolling element for transmitting torque. 2. The metal material is at least one of gold and copper.
2. The rolling element for torque transmission according to claim 1, wherein the rolling element comprises a seed. 3. The torque transmitting rolling element according to claim 2, wherein said copper has a purity of 99% or more. 4. The torque transmitting rolling element according to claim 1, wherein the thickness of the coating is 0.03 μm or more. 5. The thickness of the coating is 0.06 to 0.3 μm.
5. The rolling element for torque transmission according to claim 4, wherein