JP2005273697A - Toroidal type continuously variable transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve durability of a toroidal type continuously variable transmission. <P>SOLUTION: A ball 10 is formed by machining steel which has 0.4-1.2% C content, 0.01% or less S content, 0.02% or less P content, 9 ppm or less O content, and at least one of 0.05-1.5% Si content and 0.05-1.0% Mo content into a predetermined shape. Thereafter, heat treatment including carbonizing and carbonitriding is performed to make C+N content of a surface layer part 0.8-1.3%. At least one of an input disk 2, an output disk 3, a power roller 5 and an outer ring 9 is formed by machining steel which has C content of 0.15% or more and less than that of the ball 10, 9 ppm or less O content, and at least one of 0.05-1.5% Si content and 0.05-1.0% Mo content into a predetermined shape. Thereafter, heat treatment including carbonizing and carbonitriding is performed to make C+N content of a surface layer part 0.8-1.3% and to make γ<SB>R</SB>same as γ<SB>R</SB>of the surface layer part of the ball 10 or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a toroidal-type continuously variable transmission.

  A toroidal-type continuously variable transmission used as a transmission of an automobile is provided on an input disk that rotates in conjunction with an input shaft, an output disk that rotates in conjunction with an output shaft, and the inner surfaces of these disks facing each other. A power roller that has a power transmission surface that is in sliding contact with both of the power transmission surfaces, and is tilted by a trunnion, and an inner ring raceway surface is formed on the power roller to support a thrust load acting on the power roller. And a continuously variable transmission mechanism. Moreover, lubricating oil (traction oil) with a large friction coefficient is supplied to each of these power transmission surfaces.

In this toroidal-type continuously variable transmission, the power applied to the input disk is transmitted to the output disk via the traction oil and the power roller, and the power roller is tilted by the trunnion so that the power roller By changing the contact radius between the input disk and the output disk, the gear ratio can be changed steplessly.
When driving such a toroidal-type continuously variable transmission, high torque is transmitted from the input disk to the output disk. Therefore, a high contact pressure is generated on each power transmission surface serving as a torque transmission surface. Receives high thrust loads.

In particular, when the power roller bearing is a ball bearing, if the ball is rotated at a high speed while receiving a high thrust load as described above, a spin slip is likely to occur in the ball. When spin slip occurs on the ball, the temperature of the rolling surface of the power roller bearing (the inner ring raceway surface of the power roller, the outer ring raceway surface of the outer ring, and the surface of the ball) increases and the hardness decreases, or the rolling surface It is anticipated that micro cracks will be generated due to the tangential tensile stress, which will cause early peeling and breakage. Such a phenomenon appears more prominently in the ball having a smaller volume than the raceway (power roller or outer ring) of the power roller bearing, and the ball is required to have higher fatigue strength than the raceway.
As techniques for improving the fatigue strength of each component constituting such a toroidal-type continuously variable transmission, techniques described in Patent Documents 1 and 2 shown below have been proposed.

  In Patent Document 1, an input disk, an output disk, and a power roller are, in mass ratio, C content of 0.6% to 1.3%, Si content of 0.3% to 3.0%, Ni Formed from a material made of steel with a content of 0.1% to 3.0%, a Mn content of 0.2% to 1.5%, and a Cr content of 0.3% to 5.0% In addition, the fatigue strength at high temperature is improved by setting the surface hardness to HRC58 or higher.

In Patent Document 2, the ball of the power roller bearing is formed of a material made of steel having a Cr content of 2% by mass or more, and the carbon content of the surface layer portion is 0.7% by mass or more, so that fatigue at a high temperature is achieved. The strength is improved.
JP 2001-181784 A JP 2002-213556 A

However, even if the techniques described in Patent Documents 1 and 2 described above are combined, there is room for further improvement in terms of durability of the toroidal type continuously variable transmission.
The present invention improves the fatigue strength of the input disk, the output disk, the power roller, the outer ring of the power roller bearing, and the rolling elements of the toroidal-type continuously variable transmission in consideration of the mutual balance. An object is to improve the durability of the continuously variable transmission.

  In order to solve such a problem, the present invention provides an input disc and an output disc each having a cross-section arc-shaped power transmission surface on the opposing inner surface, and is disposed between the two discs, A power roller having a power transmission surface in sliding contact and tilted by a trunnion; and a power roller bearing for supporting a thrust load acting on the power roller. The power roller bearing has an inner ring raceway surface on the power roller. In the toroidal continuously variable transmission that is formed and includes a trunnion-side outer ring and a rolling element, the rolling element has a mass ratio of C content of 0.4% to 1.2%, S Si with a content of 0.01% or less, a P content of 0.02% or less, an O content of 9 ppm or less, a content of 0.05% or more and 1.5% or less, and a content of 0.05 % Or more A surface layer that forms a rolling surface obtained by processing a material made of steel containing at least one of Mo that is 1.0% or less into a predetermined shape, followed by carburizing or carbonitriding, quenching, and tempering. The total content of C and N is 0.8 mass% or more and 1.3 mass% or less, and at least one of the input disk, the output disk, the power roller, and the outer ring is a mass ratio, and the C content is Is 0.15% or more and less than the C content of the rolling element, the O content is 9 ppm or less, the content is 0.05% or more and 1.5% or less, and the content is 0.05. % And 1.0% or less of a material made of steel containing at least one Mo is processed into a predetermined shape and then subjected to carburizing or carbonitriding treatment, quenching treatment and tempering treatment. The surface layer part is C And N is a total content of 0.8 mass% or more and 1.3 mass% or less, and residual austenite in the surface layer portion forming at least one rolling surface of the input disk, the output disk, the power roller, and the outer ring. The amount is the same as or less than the amount of retained austenite of the surface layer portion forming the rolling surface of the rolling element, and the toroidal continuously variable transmission is provided.

  The rolling surface means a surface that is in rolling contact with other components. Each power transmission surface of the input disk, the output disk, and the power roller, and the inner ring raceway surface of the power roller bearing (formed on the power roller). Refers to the outer ring raceway surface and rolling surface. The surface layer portion refers to a range from the surface to a predetermined depth (for example, 50 μm).

Hereinafter, the critical significance of the numerical limitation of the present invention will be described in detail.
[About C content]
C (carbon) is an element effective for improving the wear resistance by forming a carbonitride while improving the strength after quenching and tempering treatment by solid solution in the matrix.
The C (carbon) content of steel constituting the rolling elements of the power roller bearing needs to be 0.4% by mass or more in order to obtain the above-described effect even with a relatively short carburizing or carbonitriding time. However, if the C content is too high, a difference in hardness between the surface layer and the core due to carburizing or carbonitriding is difficult to occur, so the upper limit was set to 1.2% by mass.

  Further, the C content of steel constituting at least one of the outer ring of the input disk, output disk, power roller, and power roller bearing (hereinafter collectively referred to as “parts other than rolling elements”) is: The C content needs to be lower than that of the rolling element. This is because the toughness of the core is higher than that of the rolling element in “parts other than the rolling element” having a larger volume than the rolling element. This makes the structure resistant to vibration. On the other hand, if the C content of steel constituting at least one of the components other than the rolling elements is too small, the core hardness cannot be obtained sufficiently, so the lower limit was made 0.15% by mass.

[Si content]
Si (silicon) is an effective element for improving the temper softening resistance. In order to acquire this effect, it is necessary to make Si content rate into 0.05 mass% or more. However, if the Si content is too high, diffusion of C and N during carburizing or carbonitriding is likely to be inhibited, and a predetermined effective carburizing depth or effective carbonitriding depth cannot be obtained, or workability is reduced. Therefore, the upper limit was set to 1.5% by mass.

[About Mo content]
Mo (molybdenum) is an element effective for improving the hardenability of steel and the temper softening resistance due to the formation of carbonitrides. In order to acquire this effect, it is necessary to make Mo content into 0.05 mass% or more. However, if the Mo content is too high, the workability deteriorates, so the upper limit was made 1.0 mass%.
Si and Mo are both elements necessary for improving the temper softening resistance, and therefore, at least one of them may be contained.

[Contents of other elements]
O (oxygen) and S (sulfur) generate non-metallic inclusions in steel and cause cracks starting from this, or cause a decrease in fatigue strength. For this reason, it is necessary to reduce these contents as much as possible, but it is acceptable if the O content is 9 ppm or less and the S content is 0.01 mass% or less.
P (phosphorus) segregates at the grain boundaries of steel and causes a decrease in strength. For this reason, it is necessary to reduce the P content as much as possible, but 0.02% by mass or less is acceptable.

[Carburization or carbonitriding]
By performing carburizing or carbonitriding treatment, C and N are dissolved in martensite, which is a steel matrix, so that temper softening resistance is improved, and a decrease in hardness at high temperatures can be suppressed. Further, the martensitic transformation point is shifted between the surface layer portion and the core portion of each component, and residual compressive stress is generated in the surface layer portion of each component after quenching and tempering treatment. Thereby, since it becomes difficult to produce tensile stress in the tangential direction of the surface of each component, generation | occurrence | production of a microcrack is suppressed.

[About the total content of C and N in the surface layer]
In order to obtain the effect of the carburizing or carbonitriding process described above, the total content of C and N in the surface layer portion that forms the rolling surface of the rolling element and the surface layer portion that forms at least one rolling surface among components other than the rolling element The total content of C and N was both 0.8% by mass or more.
On the other hand, if the total content of C and N in the surface layer portion is too large, precipitates such as carbides, carbonitrides and nitrides are coarsened to reduce the rolling fatigue life, so the surface layer portion forming the rolling surface of the rolling element The total content of C and N and the total content of C and N in the surface layer part forming at least one rolling surface among the components other than the rolling elements were both 1.3% by mass or less.

[About the amount of retained austenite in the surface layer]
By generating an appropriate amount of retained austenite in the surface layer portion forming the rolling surface, rolling fatigue is reduced. In the present invention, the amount of retained austenite in the surface layer portion forming the rolling surface of at least one of the parts other than the rolling elements is made to be the same as or less than the amount of retained austenite in the surface layer portion forming the rolling surface of the rolling element. Thereby, the fatigue strength of the rolling element which is small in volume and easily affected by the heat generation of the rolling surface can be made higher than the fatigue strength of at least one of the parts other than the rolling element.
The amount of retained austenite in the surface layer part forming the rolling surface of the rolling element and the amount of retained austenite in the surface layer part forming at least one rolling surface among the parts other than the rolling element are both 20% by volume or more and 40% by volume or less. It is preferable to do.

  According to the present invention, the fatigue strength of the rolling element of the power roller bearing constituting the toroidal-type continuously variable transmission is set to at least one of the components other than the rolling element (input disk, output disk, power roller, outer ring of the power roller bearing). By making it higher than one fatigue strength, the durability of the toroidal type continuously variable transmission can be improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of a toroidal continuously variable transmission according to the present invention. FIG. 1 is a cross-sectional view taken along the axial direction of the input shaft of the toroidal-type continuously variable transmission.
As shown in FIG. 1, the toroidal continuously variable transmission according to the present embodiment includes an input disk 2 that rotates in conjunction with the input shaft 1, an output disk 3 that rotates in conjunction with the output shaft, and both the disks 2. , 3 are disposed between the power rollers 5. Power transmission surfaces 2a and 3a having arcuate cross-sections (half toroids) are formed on the opposing inner side surfaces of both disks 2 and 3, respectively. The power roller 5 has a power transmission surface 5 a that is in sliding contact with the power transmission surfaces 2 a and 3 a of both disks 2 and 3. And traction oil is supplied to each power transmission surface 2a, 3a, 5a.

The toroidal continuously variable transmission also includes a trunnion 7 that can swing in the axial direction of the input shaft 1 (left and right in FIG. 1) about the pivot 6 and a trunnion while rotatably supporting the power roller 5. And a displacement shaft 8 whose inclination angle changes with the swinging motion of 7.
The toroidal continuously variable transmission further includes a power roller bearing 20 that supports a load in the thrust direction applied to the power roller 5.
The inner ring raceway surface 5b of the power roller bearing 20 is formed on the power roller 5, and the outer ring 9 is attached to the trunnion 7 side. The power roller bearing 20 includes a plurality of balls (rolling elements) 10 that are rotatably disposed between the inner ring raceway surface 5b and the outer ring raceway surface 9a, and a cage that holds the balls 10 in a rollable manner. 11 is provided.
In this toroidal-type continuously variable transmission, the rotation of the input shaft 1 is transmitted to the output shaft via the loading cam 1A, the input disk 2, the power roller 5, the output disk 3, and the output gear 4.

Then, when the trunnion 7 is swung around the pivot 6 and the power transmission surface 5a of the power roller 5 is displaced toward the center of the input disk 2 and the outer periphery of the output disk 3, the rotation of the input shaft 1 is caused. When the power transmission surface 5a of the power roller 5 is decelerated to the output shaft and is transferred to the outer peripheral portion of the input disk 2 and the central portion of the output disk 3, the rotation of the input shaft 1 increases to the output shaft. It is transmitted at high speed.
In this embodiment, first, a material made of steel having each composition shown in Table 1 is used as an outer ring of an input disk 2, an output disk 3, a power roller 5, and a power roller bearing 20 of the toroidal type continuously variable transmission shown in FIG. 9 and ball 10 were cut into shapes.

Next, after heat-treating them by the methods shown in Table 1, surface finishing such as grinding was performed. The heat treatment shown in Table 1 as “carbonitriding → quenching → tempering” was performed under the conditions shown in FIG. In addition, the heat treatment indicated by “Carburization → Hardening → Tempering” in Table 1 was performed under the conditions shown in FIG. Furthermore, the heat treatment shown in Table 1 as “quenching → tempering” was performed under the following conditions. First, RX gas was introduced and held at 820 to 860 ° C. for 1 hour, and then an oil quench was performed. Next, the tempering process was performed by hold | maintaining at 160-200 degreeC for 2 hours in air | atmosphere.
Then, the input disk 2, the output disk 3, the power roller 5, and the outer ring 9 (hereinafter referred to as “parts other than the ball 10”) obtained by the production methods A to H shown in Table 1 and the production methods B to E were obtained. As shown in Table 2, No. 10 1 to 14 toroidal continuously variable transmissions were assembled.

Table 2 shows the total content of C and N (content of C + N), hardness, and amount of retained austenite (γ _R ) in the surface layer portion of each part obtained by each manufacturing method. The total content (mass ratio) of C and N in the surface layer portion was measured with an emission spectroscopic analyzer at a portion from the surface to a depth of 50 μm. Further, the hardness (Hv) of the surface layer portion was measured by a Vickers hardness test method defined in JIS Z 2244. Furthermore, the amount of retained austenite (volume ratio) of the surface layer portion was measured by an X-ray diffractometer at a portion from the surface to a depth of 50 μm.

Next, these toroidal continuously variable transmissions were assembled in a test housing, and durability tests were performed under the test conditions shown below. In this durability test, the power transmission surface 2 a of the input disk 2, the power transmission surface 3 a of the output disk 3, the power transmission surface 5 a and the inner ring raceway surface 5 b of the power roller 5, and the outer ring raceway surface 9 a of the outer ring 9 are limited to 500 hours. , And any of the surfaces of the balls 10 until damage (peeling or cracking) that can be confirmed with the naked eye occurs, and the time until the damage occurs was measured. Then, from the test results of a plurality of toroidal-type continuously variable transmission having the same structure were examined L ₁₀ life. When no damage occurred until 500 hours, the L ₁₀ life was set to 500 hours. The results are also shown in Table 2.
(Test conditions)
Rotational speed of input shaft: 4500 min ^-1
Input torque: 300 N · m
Oil used: Synthetic lubricating oil supply temperature: 120 ° C

As can be seen from Table 2, all the parts other than the balls 10 and the balls 10 satisfy the scope of the present invention (steel composition, heat treatment method, total content of C and N in the surface layer, and amount of retained austenite). 1-9 of the toroidal type continuously variable transmission, both not occur breakage up to 500 hours (beyond the L ₁₀ life of 500 hours) was longer life.
On the other hand, no. 10, the C content of the steel constituting the parts other than the ball 10 was less than the range of the present invention, and sufficient hardness was not obtained in the core part. Therefore, the deformation amount of the parts other than the ball 10 was large.

No. 11, since the Si and Mo contents of the steel constituting the parts other than the ball 10 were both zero and the O content was higher than the range of the present invention, a large number of non-metallic inclusions existed. Peeling occurred.
No. In No. 12, parts other than the ball 10 were formed by the manufacturing method H that was not subjected to carburizing or carbonitriding, so that the hardness of the surface layer portion was not sufficiently obtained and peeling occurred in the surface layer portion.
No. 13, because the C content of the steel forming the ball 10 is less than the C content of the steel forming the part other than the ball 10, the toughness of the core part of the part other than the ball 10 is lower than the core part of the ball 10. , Parts other than the ball 10 could not withstand repeated tensile stress.

No. 14, the amount of retained austenite of the parts other than the ball 10 was larger than that of the ball 10, and the amount of expansion of the parts other than the ball 10 was large, so the load applied to the ball 10 increased.
From the above results, the input disk 2, output disk 3, power roller 5, outer ring 9 of the power roller bearing 20 and ball 10 constituting the toroidal continuously variable transmission are configured as the present invention, so that the toroidal continuously variable It was found that the durability of the transmission can be improved.

It is sectional drawing which shows an example of the toroidal type continuously variable transmission of this invention. It is explanatory drawing which shows the heat processing containing a carbonitriding process. It is explanatory drawing which shows the heat processing containing a carburizing process.

Explanation of symbols

2 Input disk 3 Output disk 5 Power roller (inner ring of power roller bearing)
9 Outer ring (outer ring of power roller bearing)
10 balls (rolling element of power roller bearing)
20 Power roller bearings 2a, 3a, 5a Power transmission surface (rolling surface)
5b, 9a Raceway surface (rolling surface)

Claims (1)

An input disc and an output disc each having an arc-shaped power transmission surface on the inner surface facing each other, and a power transmission surface which is disposed between the two discs and slidably contacts the power transmission surface, and is tilted by a trunnion. A power roller, and a power roller bearing that supports a thrust load acting on the power roller. The power roller bearing has an inner ring raceway surface formed on the power roller, a trunnion side outer ring, and a rolling element. In the toroidal type continuously variable transmission provided,
The rolling elements have a mass ratio of C content of 0.4% to 1.2%, S content of 0.01% or less, P content of 0.02% or less, and O content of 9 ppm or less. A material made of steel containing at least one of Si having a content of 0.05% to 1.5% and Mo having a content of 0.05% to 1.0% is processed into a predetermined shape. Then, carburizing or carbonitriding treatment, quenching treatment and tempering treatment are carried out, and the surface layer portion forming the rolling surface has a total content of C and N of 0.8% by mass to 1.3% by mass so,
At least one of the input disk, output disk, power roller, and outer ring has a mass ratio of C content of 0.15% or more and less than the C content of the rolling element, and O content of 9 ppm or less. A material made of steel containing at least one of Si having a content of 0.05% to 1.5% and Mo having a content of 0.05% to 1.0% is processed into a predetermined shape. Then, carburizing or carbonitriding treatment, quenching treatment and tempering treatment are carried out, and the surface layer portion forming the rolling surface has a total content of C and N of 0.8% by mass to 1.3% by mass And
The amount of retained austenite in the surface layer portion that forms at least one rolling surface of the input disk, output disk, power roller, and outer ring is equal to or less than the amount of retained austenite in the surface layer portion that forms the rolling surface of the rolling element. A toroidal-type continuously variable transmission.

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