JP2003130166A - Rolling element for traction drive and troidal-type continuously variable transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling element for traction drive, in which traction coefficient can be kept high under a condition of a thick oil film and durability will not decrease, under condition of thin oil film. SOLUTION: A recesses 11 and 12 with different depth are equipped within a passing range of a Herzian contact ellipse, with at least largest load on the rolling surfaces of the rolling element. Under the condition of a thick oil film, higher traction coefficient can be generated due to the existence of the deep concave 11 and under the condition of thin oil film, a metal contact can be protected effectively and durability can be developed by the existence of the shallow recess 12.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rolling element for a traction drive and a toroidal type continuously variable transmission.

[0002]

2. Description of the Related Art Continuously variable transmissions have been studied in various fields because they have excellent power transmission and there is no shift shock. Among them, for the purpose of transmitting a large amount of power, a method of transmitting power between rolling contact surfaces via a traction oil (traction drive method) has been studied.

As an example of this traction drive type continuously variable transmission, there is a toroidal type continuously variable transmission.

In the toroidal type continuously variable transmission, an input disk whose diameter gradually decreases from the large diameter side to the small diameter side and an output disk whose diameter gradually decreases from the large diameter side to the small diameter side have mutually small diameters. The disks are arranged coaxially with their sides facing each other, and a plurality of power rollers are interposed between both disks. Traction oil is interposed between the rolling surfaces of both discs and the power roller.

Then, the rotation of the input disk is transmitted to the output disk via each power roller, and at this time, each power roller is tilted so that the contact position of the power roller between the large diameter side and the small diameter side of both disks is increased. By changing it, the gear ratio is changed steplessly.

As such a toroidal type continuously variable transmission, generally, as described in JP-A-11-148542, the rolling surface of the power roller is superfinished so that the surface roughness is Ra. The smooth surface having a thickness of 0.05 μm or less prevents a decrease in oil film forming property caused by heat generation due to spin and a decrease in durability due to defective formation of an oil film.

[0007]

However, in the conventional toroidal type continuously variable transmission as described above, an excessively thick oil film is formed between the disc and the power roller, especially under operating conditions where the rolling speed is high. However, there is a problem that the traction coefficient is reduced due to the formation of the ridge. On the contrary, when the oil film becomes thin, there is no problem in the traction coefficient, but there is a problem that the possibility of metal contact with each other increases and durability deteriorates.

Therefore, an object of the present invention is to maintain a high traction coefficient even under a condition where the oil film is thick, and at the same time, to reduce the durability even under a condition where the oil film is thin, and a rolling element for the traction drive. To provide a toroidal type continuously variable transmission.

[0009]

The object of the present invention is achieved by the following constitutions.

(1) In a rolling element for a traction drive which transmits power through traction oil between rolling surfaces, within a range where at least the Hertzian contact ellipse at the maximum load of the rolling surfaces of the rolling element passes. A rolling element for a traction drive having a plurality of recesses having different depths.

(2) The recesses are characterized in that the arrangement density thereof is the same regardless of the depth of the recesses.

(3) The recesses are arranged such that the arrangement density increases as the depth decreases.

(4) The relationship between the depth of the recesses and the arrangement density of the recesses is self-affine fractal.

(5) The recesses are characterized in that those having the same depth are repeatedly formed at predetermined intervals.

(6) The depth of the recesses is 1 to 5 μm in the deepest recesses, and the distance between the deepest recesses is 60 to 120 times the depth of the deepest recesses.

(7) It is characterized in that the heights of the tops of the portions projecting toward the rolling surface relative to the recesses are the same in the sectional curve of the rolling surface.

(8) An input disk and an output disk each having a rolling surface having an annular concave surface shape are arranged in opposition to each other, and a rolling surface having an annular convex surface shape is provided between the input disk and the output disk. In a toroidal type continuously variable transmission in which a power transmission power roller having a surface is tiltably interposed, at least one of the power roller, the input disk, and the output disk is ) To (7), a toroidal type continuously variable transmission characterized by using the rolling element for traction drive described in any one of (1) to (7).

[0018]

The present invention has the following effects.

According to the present invention, since the concave portion is formed in the rolling surface of the rolling element within the range where the Hertz contact ellipse at the maximum load passes, and the concave portions are arranged so that the depths thereof are different. Under high oil film conditions, deep dents can produce a high traction coefficient, and under thin oil films, shallow cavities can effectively prevent metal contact and improve durability. It becomes possible to do.

According to the present invention, the arrangement density of the recesses is the same regardless of the depth of the recesses, and the shallower the recesses are, the larger the arrangement density of the recesses is. It is considered that the ability to prevent the above and to improve the traction coefficient is proportional to the cross-sectional area of the recess per unit length (the cross-sectional area of the recess per unit area). Therefore, when the shape of the recess is similar, The cross-sectional area will be proportional to the square of the depth. Therefore, in a wider oil film range,
It is possible to improve the traction coefficient and prevent deterioration of durability.

According to the present invention, the relationship between the depth of the recesses and the arrangement density of the recesses is such that the self-affine fractal property is exhibited, so that the traction coefficient can be improved and the durability deterioration preventing ability can be improved in a wider range. It is possible to further improve.

According to the present invention, since those having the same depth are repeated at a predetermined interval, deep recesses and shallow recesses are evenly arranged to prevent a local decrease in oil film thickness. It is possible to further improve the durability.

According to the present invention, the depth of the deepest recess is 1
Since the distance (pitch) between the deepest recesses is set to ˜5 μm and 60 to 120 times the depth of the deepest recesses, the traction coefficient improving ability and durability suitable for the toroidal continuously variable transmission for automobiles are improved. It becomes possible to achieve both of the deterioration prevention ability.

According to the present invention, the heights of the tops of the portions projecting toward the rolling surface relative to the recesses are aligned in the cross-section curve of the rolling surface that does not pass through the filter. It becomes possible to prevent contact more effectively.

According to the present invention, at least one of the power roller, the input disc and the output disc of the toroidal type continuously variable transmission, and the traction drive according to any one of claims 1 to 7. Since the rolling element for use is used, it becomes possible to provide a toroidal type continuously variable transmission having a higher traction coefficient and excellent durability.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing one half of a toroidal type continuously variable transmission, and FIG. 2 is a drawing showing a power roller bottom surface of the toroidal type continuously variable transmission.

This toroidal type continuously variable transmission is used for a transmission of an automobile, and has an input disk 1 connected to the engine side via a power transmission system and an axle via another power transmission system. Side output disc 2 and a plurality of power rollers 3 interposed between the discs 1 and 2.
Is equipped with.

The input disk 1 and the output disk 2 are
In both cases, the rolling surface 1 has a substantially conical shape in which the diameter gradually decreases from the large diameter side to the small diameter side, and has an annular concave surface shape.
a and 2a, and are arranged coaxially with the small diameter sides facing each other.

The power roller 3 has a rolling surface 3a having an annular convex shape, and is attached to a support member (not shown) at the position of the central connecting hole 4.

This power roller 3 is provided for each disk 1, 2
Is rotatable about a rotation axis B that intersects with the rotation axis A, and can be tilted in the direction of both disks 1 and 2 (left and right direction in FIG. 1) together with the support member by a tilt center C on the rotation axis B. A tilting operation is performed by a driving unit (not shown).

Both disks 1, 2 and power roller 3
The power roller 3 is brought into contact with both the disks 1 and 2 at a predetermined pressure by means for pressing the disks 1 and 2 in the direction of the rotation axis A and means for pressing the power roller 3 in the direction of the rotation axis B. At this time, the disks 1 and 2 come into contact with the power roller 3 via the traction oil. These disks 1, 2 and the power roller 3 are rolling elements for traction drive.

In such a toroidal type continuously variable transmission,
The logical contact position between the disks 1 and 2 and the power roller 3 is a point contact as shown in E in the figure, but the Hertz contact ellipse at the maximum load passes through the actual contact portion. Within this range, there are ranges D1 and D2 (these are collectively referred to as a contact range D) with the illustrated logical contact position E interposed therebetween.

The power roller 3 has a rolling surface 3a.
A fine uneven shape is formed on the surface of at least the range D through which the Hertzian contact ellipse passes.

This concavo-convex shape is provided only in the contact area D with both discs 1 and 2, and as shown in FIG. 3, the concave portions have different depths (here, deep concave portion 11).
And shallow recesses 12) are regularly formed. On the other hand, the heights of the tops of the protrusions 13 are the same as the heights of the tops of the protrusions in the cross-sectional curve that does not pass the filter on the rolling surface (details will be described later). The pitch shown in FIG. 3 and FIG. 4 is the best in terms of manufacturability.

In the toroidal type continuously variable transmission configured as described above, the rotation of the input disk 1 is transmitted to the output disk 2 via a plurality of power rollers, and at this time, the contact position of the power roller 3 is changed. However, the toroidal type continuously variable transmission is operated at a wide range of rolling speeds from the start to the maximum speed while the vehicle is in operation. For this reason, the oil film thickness on the rolling surface during operation changes greatly.

The change in the oil film thickness can be obtained by the Hamrock-Dowson oil film thickness Hmin calculation formula shown in the following equation (1).

Hmin = 3.63.U0.68.G0.49.W-0.073. {1-ex p (-0.68k)} (1) In the equation (1), U is a speed parameter ( U = η0 / ER),
G is a material parameter (G = αE), W is a load parameter (W = w / ER2, w is a load per unit width). Further, η0: viscosity of oil under atmospheric pressure, α: pressure viscosity index of oil, R: equivalent radius, u: peripheral speed (u1 + u2) /
2, E: Equivalent elastic modulus.

From the equation (1), in the toroidal type continuously variable transmission, the peripheral speed is high and the oil film is formed on the HIGH side of the gear ratio, that is, on the large diameter side for the input disc and the small diameter side for the output disc. An unnecessarily thick oil film will be formed at an easy position.

This is particularly noticeable when the rolling surface of the power roller 3 is a smooth surface as in the conventional case, and under the operating conditions where the rolling speed is high, both the disks 1 and 2 and the power roller 3 are driven. The oil film formed between them may become excessively thick. Then, as the oil film becomes thicker, the traction coefficient decreases. This is because the shearing force generated by the traction oil is simply expressed by (viscosity) × (shearing rate), so increasing the oil film reduces the shearing rate. The traction coefficient is reduced.

In order to prevent such an oil film from becoming thick, it is conceivable to form, for example, recesses having a uniform size.

However, for example, when the depth of the recess 81 is uniform and deep as in Comparative Example 1 shown in FIG. 8, the effect of improving the traction coefficient is obtained when the oil film is thick, but when the oil film is thin, the recess is formed. As a result, the relatively protruding portion (convex portion 82) is easily exposed from the oil film,
There is concern that metal contact may occur and durability may deteriorate.

Further, as in Comparative Example 2 shown in FIG.
When the depth of 1 is uniform and shallow, there is no problem of deterioration in durability when the oil film is thin, but the effect of improving the traction coefficient when the oil film is thick is almost lost.

On the other hand, in the toroidal type continuously variable transmission according to the present embodiment, the recesses 11 and 12 are composed of combinations of different depths, and these combinations are regularly repeated. The traction coefficient can be maintained high under thick conditions, and at the same time, the durability does not decrease even under conditions where the oil film is thin.

Regarding the shape of this recess, the shallower the recess,
The arrangement density (frequency) of the recesses is increased.
This is because the ability to prevent the formation of an excessive oil film and improve the traction coefficient is considered to be proportional to the cross-sectional area of the concave portion per unit length (the cross-sectional area of the concave portion per unit area). For example, if the shape of the recess is similar, the cross-sectional area of the recess will be proportional to the square of the depth. Therefore, by increasing the arrangement density of the shallow recesses as compared with the deep recesses, it is possible to improve the traction coefficient and prevent the durability from deteriorating in a wider oil film thickness range.

Further, the relation between the depth of the recesses and the arrangement density of the recesses is self-affine fractal (Self-affine).
Fractals) is preferable. By providing the self-similarity in this way, it becomes possible to balance the traction coefficient improving margin and the durability deterioration preventing ability in a wider range.

Regarding the depth of the recesses, the depth of the deepest recesses is 1 to 5 μm, and the distance (pitch) between the deepest recesses is 60 to 120 times the depth of the deepest recesses. preferable. This makes it possible to achieve both a traction coefficient improving capability and a durability reduction preventing capability suitable for a toroidal continuously variable transmission for automobiles. It is considered that the traction coefficient is further improved when the depth of the deepest recess is 1 μm or more, while it is considered to be higher when the depth is 5 μm or less.
This is because it seems that the durability is improved.

On the other hand, the shallowest recess is 1 of the deepest recesses.
The depth is preferably / 5 to 1/20. this is,
This is because the ratio of the oil film thickness at the slowest speed to the oil film thickness at the fastest speed is considered to fall within this range.

Further, in the rolling element for traction drive, the height of the top of the convex portion 13 projecting on the rolling surface relative to the concave portions 11 and 12 is the sectional curve (measured by the surface roughness meter ( It is preferable that the heights on the upper side from the cross-section curve which does not pass through the filter are uniform. This makes it possible to prevent metal contact more effectively. Also,
The shape of the convex portion 13 is such that the shape of the convex portion above the center line of the sectional curve measured by the surface roughness meter, that is, the line drawn to the average height obtained by integrating the sectional curve in the longitudinal direction,
A trapezoidal shape, a trapezoidal shape with rounded corners, a trapezoidal shape with chamfered corners, a crowning shape, an elliptic arc shape, a sine wave shape, a triangular shape with rounded apexes, and the like are preferable. With such a shape, it is possible to generate a large traction force while keeping the metal contact small.

Taking these conditions into consideration, in the first embodiment, as shown in FIG. 3, the depth of the recess is two kinds. The two types of recesses are shallow recesses 12
In this case, the formation frequency (arrangement density) is increased.

The depth of the concave portion is 3 μm deeper than that of the deep concave portion 11.
m, the repeating interval is 300 μm, the depth of the shallow recess 12 is 0.5 μm, and the repeating interval is 100 μm.

As a method for regularly forming the recesses having different depths in this way, for example, case hardening steel or bearing steel is used as the material.
Carburizing and tempering or carbonitriding and quenching and tempering are performed. In the case of bearing steel, quenching and tempering, carburizing and quenching and tempering, and carbonitriding and quenching and tempering are performed. Then, after the heat treatment, a recess is formed on the surface to be the rolling surface by grinding and cutting with a c-BN tool. As a result, the portion protruding in the surface direction of the rolling surface relative to the processed recess becomes the protrusion.

The recesses formed at this time are of two types, the deep recess 11 and the shallow recess 12 in the first embodiment. After that, tape wrap and convex portions are sequentially scraped off to form a smooth surface on the surface excluding the concave portions.

Another embodiment having a different concave shape will be described below.

(Second Embodiment) FIG. 4 is a sectional view showing the shape of a recess according to the second embodiment.

In the second embodiment, the depths of the recesses are three types. The depth of the deepest recess 21 is 5 μm, the repeating interval is 300 μm, and the depth of the second deepest recess 22 is 2 μm. The repetition interval is 150 μm, the depth of the shallow recess 23 is 0.5 μm, and the repetition interval is 50 μm. The rest of the configuration is similar to that of the first embodiment described above.

As a result, similar to the first embodiment described above, the traction coefficient can be kept high under the condition of a thick oil film, and at the same time, the durability does not decrease even under the condition of a thin oil film.

Compared with the first embodiment described above, the depths of the recesses are three, so that various oil film thicknesses can be accommodated as compared with the first embodiment described above. This makes it possible to generate a high traction coefficient in good balance with respect to various oil film thicknesses, and also to improve durability.

(Third Embodiment) FIG. 5 is a sectional view showing the shape of a recess according to the third embodiment.

In the third embodiment, the depth of the recess is 2
The type is the same and the arrangement density of the recesses is the same regardless of the depth of the recesses.

The depth of the deep concave portion 31 is 3 μm and the depth of the shallow concave portion 32 is 0.5 μm, and the repeating interval of each of the deep and shallow concave portions is 200 μm.

As a result, similarly to the first embodiment described above, the traction coefficient can be kept high under the condition that the oil film is thick, and at the same time, the durability does not decrease even under the condition that the oil film is thin.

(Fourth Embodiment) FIG. 6 is a sectional view showing the shape of a recess according to the fourth embodiment.

In the fourth embodiment, the depth of the recess is set to 3
The type is the same and the arrangement density of the recesses is the same regardless of the depth of the recesses.

The depth of the deepest recess 41 is 2 μm, the depth of the second deepest recess 42 is 1 μm, the depth of the shallowest recess 43 is 0.5 μm, and the repetition interval of each is 120.
μm.

As a result, similar to the first embodiment described above, the traction coefficient can be kept high under the condition that the oil film is thick, and at the same time, the durability does not decrease even under the condition that the oil film is thin.

(Fifth Embodiment) FIG. 7 is a sectional view showing the shape of a recess according to the fifth embodiment.

In the fifth embodiment, concave portions having various depths are randomly provided.

As described above, the recesses 51, 5 having different depths are formed.
By providing 2, 53, ... Randomly, it is possible to maintain a high traction coefficient under the condition where the oil film is thick, and at the same time, it is possible to prevent the durability from decreasing even under the condition where the oil film is thin.

However, when the recesses having different depths are formed at random as described above, only the recesses having the deep depth are not partially concentrated, and conversely, the shallow recesses are not partially concentrated. There is a need to. This is because, if a portion having many deep recesses or a portion having many shallow recesses is formed, those portions locally become the state as in the above-mentioned Comparative Examples 1 and 2, so that the traction coefficient decreases, or This is because there is a concern that the durability may be locally reduced.

As described above, the rolling element for traction drive and the toroidal type continuously variable transmission using the same according to the present invention have a traction coefficient under a thick oil film by combining concave portions having different depths. It is possible to maintain a high value, and at the same time, it is possible to obtain an excellent effect that durability is not deteriorated even under a condition of a thin oil film.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a toroidal continuously variable transmission according to the present invention with one side omitted.

FIG. 2 is a drawing showing a bottom surface of a power roller of a toroidal type continuously variable transmission according to the present invention.

FIG. 3 is a cross-sectional view for explaining a recess in the first embodiment to which the present invention is applied.

FIG. 4 is a sectional view for explaining a recess in the second embodiment to which the present invention is applied.

FIG. 5 is a cross-sectional view for explaining a concave portion according to a third embodiment of the present invention.

FIG. 6 is a sectional view for explaining a recess in a fourth embodiment to which the present invention is applied.

FIG. 7 is a cross-sectional view for explaining a recess according to a fifth embodiment of the present invention.

FIG. 8 is an explanatory cross-sectional view showing a recess of Comparative Example 1.

FIG. 9 is a cross-sectional explanatory view showing a recess of Comparative Example 2.

[Explanation of symbols]

1 ... Input disc 2 ... Output disc 3 ... Power roller 4 ... Connection hole 11, 12, 31, 32, 41, 42, 43, 51, 5
2, 53, 81, 91, ... Recessed portion 13 ... Convex portion

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshiteru Yasuda             Nissan, Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan             Inside the automobile corporation F term (reference) 3J051 AA01 AA03 BA03 BA10 BB01                       BB04 BE01 BE09 EC02 EC03                       EC07 FA02

Claims (8)

[Claims] 1. A rolling element for a traction drive that transmits power through traction oil between rolling surfaces, within a range in which a Hertzian contact ellipse at least at a maximum load passes on the rolling surface of the rolling element. A rolling element for a traction drive having a plurality of recesses having different depths. 2. The rolling element for a traction drive according to claim 1, wherein the recesses have the same arrangement density regardless of the depth of the recesses. 3. The rolling element for a traction drive according to claim 1, wherein the recesses are arranged such that the arrangement density increases as the depth decreases. 4. The rolling element for a traction drive according to claim 3, wherein the relationship between the depth of the recesses and the arrangement density of the recesses exhibits self-affine fractal property. 5. The rolling element for a traction drive according to claim 1, wherein the recesses are formed to have the same depth repeatedly at predetermined intervals. 6. The depth of the recesses is 1 to 5 μm in the deepest recesses, and the distance between the deepest recesses is 60 to 120 times the depth of the deepest recesses. The rolling element for traction drive described in any one of 1 to 5. 7. The height of the apex of the portion projecting to the rolling surface relative to the recess is equal in the sectional curve of the rolling surface. Rolling element for traction drive. 8. An input disk and an output disk, each of which is provided with a rolling surface having an annular concave surface shape, are arranged in opposition to each other, and a rolling surface having an annular convex surface shape is provided between the input disk and the output disk. A toroidal type continuously variable transmission in which a power transmission roller for rotation transmission is tiltably interposed, wherein at least one of the power roller, the input disc, and the output disc is provided.
A toroidal-type continuously variable transmission characterized by using the rolling element for traction drive described in any one of to.