JP2003278768A - Rolling bearing for belt type continuously variable transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the efficiency of a belt type continuously variable transmission, while assuring durability by using a CVT fluid of low viscosity, and by providing sufficient durability even if the flow of the fluid is kept small. <P>SOLUTION: Rings including an outer ring 4 are made from an iron type alloy containing C of 0.15 to 0.5 wt.%, Si of 0.1 to 1.5 wt.%, Mn of 0.1 to 1.5 wt.%, and Cr of 0.5 to 3.0 wt.%. This material is subjected to carbonitriding, quenching, tempering, and finish grinding processes and a surface layer containing C of 0.8 to 1.2 wt.% and N of 0.05 to 0.50 wt.% is provided on the surface part of an outer raceway 6 provided on the inner peripheral surface of the outer ring 4. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a rolling bearing for supporting a rotary shaft of a belt type continuously variable transmission of an automobile. Specifically, in order to stabilize the friction coefficient of the frictional engagement portion between the belt and the pulley and realize low fuel consumption, C
Even if a low viscosity VT fluid (ATF combined oil) is used, a structure that can secure sufficient durability is realized.

[0002]

2. Description of the Related Art A belt type continuously variable transmission is used as a transmission unit for an automatic transmission for an automobile, for example, in Japanese Utility Model No. 8-305.
As described in Japanese Laid-Open Patent Publication No. 26, etc., various kinds have been conventionally considered, and some of them are actually used. FIG. 1 schematically shows the basic structure of such a belt type continuously variable transmission. This belt type continuously variable transmission has an input side rotary shaft 1 and an output side rotary shaft 2 which are arranged in parallel with each other. Each of these rotary shafts 1 and 2 is rotatably supported by a pair of rolling bearings 3 and 3 inside a transmission case (not shown), which is a fixed portion described in the claims. .

As shown in detail in FIG. 2, each of these rolling bearings 3 and 3 has an outer ring 4 and an inner ring 5 which are concentrically provided with each other. The outer ring 4 has an outer ring raceway 6 on the inner peripheral surface thereof, and the inner ring 5 has an inner ring raceway 7 on the outer peripheral surface thereof. Then, in a state where a plurality of rolling elements 8, 8 are held by the cage 9 between the outer ring raceway 6 and the inner ring raceway 7,
It is provided so that it can roll freely. In each of the rolling bearings 3 and 3 configured as described above, the outer ring 4 is fitted in and fixed to a part of the transmission case, and the inner ring 5 is formed.
Is externally fitted and fixed to the input side rotary shaft 1 or the output side rotary shaft 2. With this configuration, both rotary shafts 1 and 2 are rotatably supported inside the transmission case. Conventionally, as each of the rolling bearings 3 and 3, the outer ring 4, the inner ring 5, and the rolling elements 8 and 8 made of general bearing steel type 2 (SUJ2) were used.

The input side rotary shaft 1 of the two rotary shafts 1 and 2 is rotationally driven by a drive source 10 such as an engine via a starting clutch 18 such as a torque converter or an electromagnetic clutch. In addition, the drive-side pulley 1 is provided at a portion located between the pair of rolling bearings 3 and 3 in the intermediate portion of the input-side rotating shaft 1.
1, the drive side pulley 11 and the input side rotary shaft 1 are provided.
It is designed so that and rotate in synchronization. The distance between the pair of drive-side pulley plates 12a and 12b forming the drive-side pulley 11 is set by axially displacing one drive-side pulley plate 12a (left side in FIG. 1) by the drive-side actuator 13. It is adjustable. That is, the groove width of the drive pulley 11 can be expanded and contracted by the drive actuator 13.

On the other hand, a driven pulley 14 is provided at a portion located between the pair of rolling bearings 3 and 3 at an intermediate portion of the output rotary shaft 2, and the driven pulley 14 and the output rotary shaft 2 are connected to each other. Are designed to rotate synchronously. A pair of driven-side pulley plates 15a and 15b forming the driven-side pulley 14.
The space between them is set to one side (see FIG.
It is adjustable by displacing the driven pulley plate 15a (on the right side of FIG. 4) in the axial direction. That is, the driven pulley 14
The groove width can be expanded and contracted by the driven side actuator 16. An endless belt 17 is stretched around the driven pulley 14 and the drive pulley 11. The endless belt 17 is made of metal.

In the belt type continuously variable transmission configured as described above, the power transmitted from the drive source 10 to the input side rotary shaft 1 via the starting clutch 18 is transmitted from the drive side pulley 11 to the endless belt. It is transmitted to the driven pulley 14 via the belt 17. As the endless belt 17, conventionally, one that transmits power in the pressing direction and one that transmits power in the pulling direction are known. In any case, the power transmitted to the driven pulley 14 is transmitted from the output rotary shaft 2 to the drive wheels 21 and 21 via the reduction gear train 19 and the differential gear 20. When changing the gear ratio between the input-side rotary shaft 1 and the output-side rotary shaft 2, the groove widths of the pulleys 11 and 14 are expanded and contracted in association with each other.

For example, when the reduction ratio between the input-side rotary shaft 1 and the output-side rotary shaft 2 is increased, the groove width of the drive-side pulley 11 is increased and the groove width of the driven-side pulley 14 is increased. Reduce the width. As a result, the diameter of the part of the endless belt 17 which is stretched over the pulleys 11 and 14 is small at the drive side pulley 11 part and large at the driven side pulley 14 part, and the input side rotation is increased. Deceleration is performed between the shaft 1 and the output side rotating shaft 2. On the contrary, when the speed increasing ratio between the input side rotating shaft 1 and the output side rotating shaft 2 is increased (the reduction ratio is decreased), the groove width of the drive side pulley 11 is reduced and the driven side is driven. The groove width of the side pulley 14 is increased. As a result, the endless belt 1
The diameter of the part of the pulley 7 that is stretched over both the pulleys 11 and 14 is large in the drive pulley 11 part and small in the driven pulley 14 part.
And the output side rotary shaft 2 is accelerated.

During operation of the belt type continuously variable transmission constructed and operated as described above, lubricating oil is supplied to each movable portion to lubricate each movable portion. As the lubricating oil used in the case of the belt type continuously variable transmission, CVT fluid (ATF combined oil) is used. The reason for this is to increase and stabilize the friction coefficient of the frictional engagement portion between the endless belt 17 made of metal and the drive side and driven side pulleys 11 and 14. Then, the CVT fluid is circulated to the friction portion at a flow rate of 300 cc / min or more to lubricate the friction portion. In addition, a part of the CVT fluid is inside the rolling bearings 3 and 3 (for example, at a flow rate of 20 cc / min or more).
After passing through, the rolling contact portions of these rolling bearings 3 are lubricated. Therefore, inside each of the rolling bearings 3 and 3, abrasion dust generated by friction between the endless belt 17 and the pulleys 11 and 14 and friction at the reduction gear train 19 are generated. Foreign matter such as gear powder is CVT
There is a high possibility that it will get mixed in with the fluid. Such foreign matter causes damage to the rolling contact portions of the rolling bearings 3 and 3 and reduces durability thereof. Therefore, conventionally, by increasing the bearing size of each of the rolling bearings 3 and 3 or by increasing the diameter (ball diameter) of each of the rolling elements 8 and 8 or the like, the basic motion of each of the rolling bearings 3 and 3 is increased. The rated load was increased to allow the rolling bearings 3 and 3 to have a sufficient life.

[0009]

In recent years, the efficiency of a belt type continuously variable transmission is ensured, noise generated during operation is suppressed to a low level, and wear of both drive side and driven side pulleys 11 and 14 and endless belt 17 is prevented. For the purpose of suppressing, it is considered to use CVT fluid having a lower viscosity. In such a case, if standard ones are used as the rolling bearings 3 and 3 for supporting the rotary shafts 1 and 2 on the input side and the output side, the oil film is not sufficiently formed due to the indentation origin type peeling due to the inclusion of foreign matter. It is considered that the possibility of early peeling increases. That is, when a CVT fluid having a low viscosity is used, the outer ring raceway 6 and the inner ring raceway 7 are brought into rolling contact with the rolling surfaces of the rolling elements 8 by the action of vibration in the radial direction and the axial direction due to the belt fluctuation. There is a high possibility that the oil film formation state of the part will be insufficient. It is considered that the possibility of early peeling due to slippage at the rolling contact portion increases.

That is, in the case of the rolling bearing 3 composed of the outer ring 4, the inner ring 5 and the rolling elements 8 made of a general bearing steel such as SUJ2, for example, the kinematic viscosity of the base oil is 40.degree.
40 mm ² / sec (40 × 10 ^-6 m ² / s) or less per hour, 1
CV of low viscosity, said to be 10 mm ² / sec or less at 00 ° C
The use of T-fluid is considered to increase the possibility of premature peeling due to the slip. What if
The temperature of the rolling bearing 3 may exceed 100 ° C. during operation of the belt type continuously variable transmission, and the viscosity of the CVT fluid that enters the inside of the rolling bearing 3 to lubricate the rolling contact portion of the rolling bearing 3 is Less than 10 mm ² / sec,
It is a fairly low value. As a result, the strength of the oil film existing at the rolling contact portion becomes low, and the oil film is easily broken at the rolling contact portion due to the influence of differential, revolution, spin and the like. When the oil film breaks, metal contact occurs at the rolling contact portion, fatigue of the surface layer portion is promoted, and early peeling occurs. Of course, the rolling bearing 3
Although it is possible to secure the required durability by increasing the basic dynamic load rating and increasing the life of the rolling bearing 3, it is possible to increase the weight and rolling resistance with the increase in size. It is not preferable because it invites. In addition, the rolling bearing 3
It is possible to prevent the occurrence of the oil film breakage and improve the durability by increasing the flow rate of the CVT fluid passing through. However, such a method is not preferable because it causes a decrease in the efficiency of the entire belt type continuously variable transmission due to an increase in pump loss caused by circulating a large amount of CVT fluid.

By the way, most of the load applied to the rolling bearing 3 incorporated in the belt type continuously variable transmission is the radial load applied from the endless belt 17, and the acting direction of this radial load is always constant. In the rolling contact portion of the rolling bearing 3, the inner ring raceway 7 and the rolling surfaces of the rolling elements 8, 8 rotate, but the outer ring raceway 6 does not rotate. Therefore, the fatigue of the surface layer portion is caused by the outer ring raceway 6
Part of the above (part supporting the above radial load)
The most advanced. In other words, the outer ring raceway 6 is exposed to the most severe conditions regarding rolling fatigue life. Therefore, ensuring the rolling fatigue life of the outer ring raceway 6 is important from the viewpoint of ensuring the durability of the rolling bearing 3 as a whole.

For example, FIG. 3 shows the fatigue degree of the rolling contact portion when the above-mentioned low-viscosity CVT fluid is used as a lubricating oil in a general gear type transmission and a belt type continuously variable transmission. The results obtained by fatigue analysis are shown below. In addition, the fatigue analysis is Japanese Patent Publication No. 63-3442.
The method of measuring the fatigue degree due to rolling fatigue described in Japanese Patent No. 3 is called Fatigue degree F = ΔB + K · ΔR (ΔB; X-ray diffraction half-width reduction amount of martensite phase, K; depends on the material. Constant, ΔR; decrease in retained austenite). That is, in order to obtain the degree of fatigue F, the X-ray diffraction half width of the martensite phase before and after rolling fatigue of the rolling contact portion of the metal material and the amount of retained austenite (volume%) are measured. Then, a constant determined by the type of metal member is set to K, and a difference between the retained austenite amount (capacity%) in the non-fatigue state and the retained austenite amount in the fatigued state is set to ΔR. Further, the difference between the X-ray diffraction half width of the mantensite phase in the non-fatigue state and the X-ray diffraction half width in the fatigued state is ΔB. And
Substituting the decrease amount ΔR of the X-ray diffraction half width and the decrease amount ΔR of the retained austenite amount of the martensite phase based on the above measured values into the expression F = K · ΔR + ΔB The fatigue degree F is calculated. Then, the degree of fatigue F is evaluated in correspondence with a reference value prepared in advance corresponding to each part of each rolling contact portion, and the degree of fatigue of each part is measured.

In FIG. 3 showing the results of the fatigue analysis conducted under such conditions, (A) is the outer ring raceway of a rolling bearing incorporated in a general gear type transmission, and (B) is a belt type stepless. The fatigue levels of the outer ring raceways of rolling bearings installed in the transmission are shown. The higher the value of the degree of fatigue, the more the fatigue progresses and the shorter the peeling life. The fatigue of the outer ring raceway surface of the rolling bearing incorporated in the general gear type transmission shown in FIG. 3 (A) was about 1.4, while that shown in FIG. 3 (B). The fatigue level of the belt type continuously variable transmission was about 2.8, which was twice as high.

As is clear from FIG. 3, when a CVT fluid having a low viscosity is used, premature peeling occurs in the outer ring raceway of the rolling bearing which constitutes the rotation supporting portion of the belt type continuously variable transmission. Easier to do. In view of such circumstances, the present invention has a low viscosity CV in order to realize a belt type continuously variable transmission having excellent transmission efficiency and sufficient durability.
Even if T-fluid is used, the invention is to realize a rolling bearing for a belt type continuously variable transmission in which the outer ring raceways 6 of the rolling bearings 3 and 3 for rotatably supporting the pulley are less likely to be damaged such as premature peeling. It was done.

[0015]

The rolling bearing for a belt type continuously variable transmission according to the present invention has an outer ring, an inner ring, and the same as the previously known rolling bearing for a belt type continuously variable transmission. And a plurality of rolling elements. The outer ring of these has an outer ring raceway on its inner peripheral surface. Further, the inner ring has an inner ring raceway on the outer peripheral surface. The rolling elements are rollably provided between the outer ring raceway and the inner ring raceway. And
The outer ring is fitted in and supported by a fixed portion such as a transmission case,
The inner ring is externally fitted and supported on a portion that rotates together with a pulley that constitutes the belt type continuously variable transmission, such as an end portion or an intermediate portion of each of the input side and output side rotary shafts, and the pulley is rotated to the fixed portion. Support freely.

Particularly, in the rolling bearing for a belt type continuously variable transmission according to the present invention, at least the outer ring has a thickness of 0.15 to 0.15.
0.5 wt% C, 0.1 to 1.5 wt% Si,
0.1 to 1.5% by weight Mn and 0.5 to 3.0% by weight
It is made by carbonitriding, quenching, tempering, and polishing finishing of an iron-based alloy material containing Cr. The outer raceway surface has a surface layer containing 0.8 to 1.2% by weight of C and 0.05 to 0.50% by weight of N.

Also, preferably, as described in claim 2,
The surface hardness of the surface layer is Hv 720 to 900, and a carbide or carbonitride (M ₃ C, M) having an average particle diameter of 50 to 500 nm is present in the portion from the surface of the outer ring raceway to the maximum shear stress generation position depth. ₇ C ₃ ) is dispersed and precipitated. Further, preferably, as described in claim 3, the subsurface 50 of the outer ring raceway is
The residual austenite amount at μm is 20 to 45% by volume, and the residual compressive stress at 50 μm below the surface of the outer ring raceway is 15
0 to 500 MPa. Further, preferably, as described in claim 4, 0.1 to 3.0% by weight of Mo and 0.1 to 3.
At least one of V and 0% by weight is included.
The residual oxygen concentration is preferably 9 ppm or less, the P content is 0.02% by weight or less, and the S content is preferably 0.02% by weight or less. Further, the present invention is premised on being applied to the outer ring raceway, which has the most severe conditions for rolling fatigue life, for the reasons described above. However, in addition to the outer ring raceway, it is free to apply to the inner ring raceway and the rolling surface of each rolling element.

[0018]

In the case of the rolling bearing for a belt type continuously variable transmission of the present invention constructed as described above, the strength of the oil film interposed in the rolling contact portion cannot be sufficiently secured by using CVT fluid having a low viscosity. Even in this case, the peeling life can be sufficiently secured. First, as described in claim 1, if a material having an appropriate composition is subjected to an appropriate surface treatment to form an appropriate surface layer, the rolling fatigue life of the outer ring raceway exposed to particularly severe conditions during use. Can be secured.

Particularly, as described in claim 2, the surface hardness of the surface layer is set to Hv 720 to 900, and a carbide or carbonitride having an average particle diameter of 50 to 500 nm is dispersed and precipitated in a predetermined portion. In such a case, the rolling fatigue life can be secured more effectively. That is, by using CVT fluid having a low original viscosity and operating under high temperature conditions of 100 ° C or higher, the viscosity of this CVT fluid is further reduced, and the strength of the oil film existing at the rolling contact portion is reduced, resulting in local loss. Even if a specific metal contact occurs, the progress of the surface fatigue of the rolling contact portion can be delayed.

Further, as described in claim 3, by setting the amount of retained austenite in a predetermined portion to an appropriate value, the surface of the rolling contact portion is not affected by the local metal contact generated as described above. It is possible to alleviate the minute peeling and line scratches that occur. Further, by setting the residual compressive stress of the predetermined portion to an appropriate value, even if minute cracks or peeling occur on the surface of the rolling contact portion, it is possible to suppress the propagation of these cracks or peeling and prevent early peeling. It is possible to further improve the effect.

Further, as described in claim 4, 0.1 to
If at least one of 3.0% by weight of Mo and 0.1 to 3.0% by weight of V is contained, the grain size of the above-mentioned carbide or carbonitride is controlled, and these carbides or carbonitrides are controlled. It is possible to make fine deposits. Then, the amount of C in the matrix can be reduced.

The rolling bearing for a belt type continuously variable transmission according to the present invention, due to the above-described action, has a low strength of the oil film existing in the rolling contact portion, which causes local metal contact. The rolling fatigue life can be secured. Therefore, in order to secure the required durability, it is not necessary to use a large-sized rolling bearing having a large basic dynamic load rating. For this reason, the rotation supporting portions of the input-side rotary shaft and the output-side rotary shaft can be made small and lightweight, and the structure with low rotation resistance can ensure sufficient durability. In this case, it is not necessary to increase the amount of lubricating oil that circulates inside the rolling bearing (for example, much higher than 20 cc / min). As a result, it is possible to secure the rolling fatigue life of the rolling bearing that is small and lightweight and has low rolling resistance, and to reduce the size and weight of the belt type continuously variable transmission and improve the transmission efficiency.

Next, the present invention will be described including the reason why each element was added to the raw material made of an iron-based alloy for producing the rolling bearing for a belt type continuously variable transmission of the present invention, and the content of each of these elements. The reason for limiting each specified numerical value will be explained. Of the elements contained in the above materials, first, C is carbonitrided to increase the hardness of the raceway surface to a required value (for example, Hv720-900) in order to ensure rolling fatigue life. It is included for the purpose. In order not to make the treatment time of this carbonitriding treatment unnecessarily long, it is necessary to contain 0.15% by weight or more of C. On the other hand, 0.50% by weight of C
If it is contained in excess of 10%, the toughness of the above-mentioned material is lowered, the cracking strength of the bearing ring made of this material is lowered, and it becomes difficult to secure the dimensional stability at high temperature. Therefore,
The C content was 0.15 to 0.50% by weight.

Next, Si is added to improve the hardenability as well as having the effect of delaying the white microstructure change observed under rolling fatigue. However, the amount of Si added is 0.1% by weight.
If less than, temper softening resistance is insufficient,
It becomes difficult to secure sufficient hardness of the outer ring raceway surface after the heat treatment. On the other hand, if Si is contained in an amount of more than 1.5% by weight, the workability of the material is significantly reduced. Therefore, the Si content is set to 0.1 to 1.5% by weight.

Next, Mn is added to improve the hardenability of steel (iron-based alloy). However, the amount of Mn added is 0.1
If it is less than wt%, it is difficult to secure sufficient hardenability. On the other hand, if the content is more than 1.5% by weight, the workability of the raw material is lowered. Therefore, the content of Mn is set to 0.1 to 1.5% by weight.

Next, Cr is added in order to improve the hardenability and accelerate the spheroidization of the carbide. In order to obtain these effects, it is necessary to contain Cr in an amount of 0.5% by weight or more. On the other hand, if the content is more than 3.0% by weight, the machinability of the material (easiness of cutting) may be deteriorated and the machining of the outer ring raceway may be troublesome. Therefore, the content of Cr is set to 0.5 to 3.0% by weight.

Mo is selectively contained (though not essential for carrying out the present invention). When it is contained, in addition to improving the resistance to temper softening, the hardness of the raw material and the outer ring obtained from this raw material can be increased and the high temperature strength can be improved by the dispersing effect of fine carbide. When adding with the expectation of such effects, 0.1
An amount of addition of at least wt% is necessary. The reason for this is that the addition of Mo reduces the amount of C that dissolves in the matrix and precipitates fine Mo-based carbides. On the other hand, if the addition amount of Mo exceeds 3.0% by weight, solution treatment becomes insufficient and the carbide is not refined, and further workability may be deteriorated. Therefore, when Mo is contained,
Its content is 0.1 to 3.0% by weight.

Further, V is also selectively contained (though not essential for carrying out the present invention). When it is contained, it precipitates at the grain boundaries to suppress the coarsening of the crystal grains, and also binds to carbon in the steel to form fine carbides. The addition improves the hardness of the surface layer of the outer ring and improves the wear resistance. In addition, the effect of delaying the change in white structure due to the hydrogen trap effect can be expected. Such an effect becomes remarkable when the V content is 0.1% by weight or more. On the other hand, when the content of V exceeds 3.0% by weight, huge carbides of V are precipitated at the grain boundaries, the pinning effect is reduced, and further the workability and various mechanical properties are deteriorated. Let Therefore, when V is added, its content is set to 0.1 to 3.0% by weight.

By subjecting Mo and V to solution treatment, Mo
It is possible to control the particle size of the system and V system carbides (M ₃ C, M ₇ C ₃ system) and disperse and precipitate fine carbides, and as a result, reduce the amount of C in the matrix. For this reason, it has an effect of delaying the occurrence of the microstructural change due to C diffusion in matrix fatigue, and consequently improving the rolling fatigue life. Moreover, such a dispersed precipitation effect is an effect of suppressing crack propagation and an effect of improving wear resistance,
Has a hydrogen trap effect for suppressing hydrogen embrittlement resistance.

That is, iron having the composition described in claim 1.
10μ by applying appropriate heat treatment to the material made of system alloy
m² More than 10 carbides or carbonitrides (M₃ C, M
₇ C ₃ ) Can be dispersed and precipitated. Furthermore, above
As shown in the figure, by subjecting Mo and V to solution treatment, Mo-based and V-based
Carbide (M₃ C, M₇ C₃ If you control the particle size of
0 μm² It is possible to disperse and deposit more than 40 carbides per
It is possible to obtain a better durability improving effect.

Next, C and N in the surface layer provided on the surface portion of the raceway surface will be described. First, C is contained in order to obtain the hardness required to secure the rolling fatigue life of this raceway after carbonitriding the raceway and polishing the surface of the raceway surface. . On the surface layer,
In order to provide the hardness (for example, Hv 720 or higher) required to secure a sufficient rolling fatigue life, it is necessary to contain 0.8% by weight or more of C. On the other hand, if the content is more than 1.2% by weight, a large carbide is likely to be generated in the surface layer portion, which easily becomes a starting point of damage such as cracking. Therefore, the content of C in the surface layer portion is
It was regulated to 0.8 to 1.2% by weight.

N is contained in order to improve the tempering resistance of the surface layer portion and to disperse and precipitate fine carbon / nitride to improve the strength. In order to obtain such an effect, the N content needs to be 0.05% by weight or more. On the other hand, when the content of N exceeds 0.50% by weight, the abrasion resistance is excessively improved, and not only the polishing work performed as the finishing work of the outer ring raceway becomes difficult, but also the brittleness of the surface layer is caused. The crack strength also decreases. Therefore, the content of N is
It was regulated to 0.05 to 0.50% by weight. The above explanation is
Although the present invention was applied to only the outer ring,
Even when it is applied to the inner ring or the rolling element added to the outer ring, the rolling fatigue life can be improved by the same action of the member.

Regarding O, P and S, addition of any of them is an unfavorable element from the viewpoint of attaining the object of the present invention, so it is preferable to suppress all of them as much as possible. . First, O forms oxide-based inclusions in steel, and serves as a starting point of damage such as cracks during bending stress fatigue (fish eyes), and may also be non-metallic inclusions that reduce rolling fatigue life. It is an element. Therefore, it is preferable that the O content is as small as possible (as close to 0 as possible). From this viewpoint, it is preferable that the content of O is 9 ppm or less. Next, P is an element that reduces rolling fatigue life and toughness. Therefore, it is preferable that the content of P is as small as possible.
From this aspect, it is preferable to suppress the P content to 0.02% by weight or less. Further, S is an element that improves machinability, but forms a sulfide-based inclusion that reduces the rolling fatigue life by combining with Mn. Also, improving machinability is
Other than adding S, it can be achieved. Therefore, from the viewpoint of ensuring the rolling fatigue life of the outer ring, it is preferable that the content of S is as small as possible. From this aspect, the S content is 0.02% by weight.
It is preferable to suppress it to the following.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION One of the features of the present invention is to provide an outer ring, an inner ring and a plurality of rolling elements which form a rolling bearing for supporting both input and output rotating shafts for a belt type continuously variable transmission. ,
At least by improving the properties of the outer ring, it is possible to improve the durability of the rolling bearing as a whole. Regarding the structure appearing in the drawing, including the structure schematically shown in FIG.
This is the same as a conventionally known rolling bearing for a belt type continuously variable transmission. Therefore, the description of the specific structure of the rolling bearing for a belt type continuously variable transmission will be omitted.

[0035]

EXAMPLES Next, experiments conducted to confirm the effects of the present invention will be described. In the experiment, as shown in the following Table 1, 10 kinds of samples belonging to the technical scope of the present invention (Examples 1 to 10) and 8 kinds of samples deviating from the technical scope of the present invention (Comparative Example 1) .About.8), a total of 18 types of samples were subjected to the heat treatments shown in the same table, and the durability (fatigue degree and L ₁₀ life) of each was measured.

[0036]

[Table 1]

In Table 1 above, the unit of the numerical value indicating the content of the chemical element is% by weight. Also, except for the elements shown in Table 1,
Fe and inevitable impurities. The surfaces C and N are the contents of C and N contained in the surface layer. Further, the heat treatment is performed in the steps as shown in FIGS. 4 (A) and 4 (B).

First, in the case of heat treatment, as shown in FIG. 4 (A), first, for 5 to 10 hours in a state of being heated to 920 to 960 ° C. in an atmosphere of endothermic gas, enriched gas and ammonia gas. Then, heat treatment (carbonitriding) is performed. After that, oil quench (quenching) is performed in oil at 50 to 150 ° C. Next, in an endothermic gas atmosphere,
After heating (soaking) to 0 to 870 ° C for 0.5 to 3 hours, oil quenching (quenching) is performed again in oil at 50 to 150 ° C. Then, after washing, the temperature of this is 160-
After heating in an atmosphere of 200 ° C. for 1 to 5 hours, it is cooled (tempering).

Further, in the case of heat treatment, as shown in FIG. 4 (B), when the heat treatment is performed at 920 to 960 ° C. in an atmosphere of endothermic gas, enriched gas and ammonia gas,
Heat treatment (carbonitriding treatment) is performed for 10 hours. After that, oil quench (quenching) is performed in oil at 50 to 150 ° C. Then, after washing, primary tempering is performed at 180 to 220 ° C. Then, in an endothermic gas atmosphere,
Heat to 0-870 ° C for 0.5-3 hours and then 5
Oil quench in oil at 0-150 ° C. Then, after washing, in the air at 180 to 220 ° C.,
After heating for 1 to 5 hours, it is cooled (secondary tempering).

The outer ring having the composition shown in Table 1 and obtained by subjecting it to predetermined heat treatment and finishing is combined with an inner ring and a plurality of rolling elements to form a rolling bearing unit, as shown in FIG. Built in a simple belt type continuously variable transmission,
It was used to rotatably support the input side rotating shaft 1 with respect to the transmission case. Bearing size is JIS name 6208
(Inner diameter = 40 mm, outer diameter = 80 mm, width = 18 mm).
The roughness of each surface that constitutes the rolling contact portion is 0.01 to 0.03 μ in terms of arithmetic average roughness Ra, as in a normal rolling bearing.
m. As the cage 9, an iron corrugated press cage was used.

The durability of the outer ring raceway was measured under the conditions described below. In the experiment conducted this time, in order to determine the durability of the rolling bearings 3 and 3 incorporated in the rotation supporting portion of the input side rotating shaft 1, the rolling bearings 3 and 3 incorporated in the rotating supporting portion of the output side rotating shaft 2 will be described. , Sufficient amount (200cc
/ Min) of lubricating oil (CVT fluid) was supplied. or,
Rolling elements (balls) that make up rolling bearings 3 and 3 that are not tested
As for Nos. 8 and 8, SUJ2 carbonitrided was used. Then, the rolling bearings 3 and 3 which are not tested are not damaged before the rolling bearings 3 and 3 which are tested. The test conditions are as follows.

Test device: Number of samples of belt type continuously variable transmission shown in FIG. 1: Six for each sample (one for fatigue analysis) Judgment method: Each rolling bearing was disassembled and damaged as the test progressed Check the presence or absence of input torque from the engine to the input side rotary shaft 1: 20
0 N ・ m Rotational speed of input side rotary shaft 1: 6000 min ^-1 Lubricating oil: CVT fluid {Viscosity at 40 ° C = 35 x
10 ⁻⁶ m ² / s (35 cSt), viscosity at 100 ° C. = 7 ×
10 ^-6 m ² / s (7 cSt)} Lubricating oil flow rate: 10 cc / min Bearing temperature: 120 ° C Test duration: 1500 hours Target time: 1000 hours Fatigue analysis: After the lapse of 100 hours, the above 6 pieces were prepared. One of the samples is analyzed to determine fatigue.

As a result of the experiment carried out under the above-mentioned conditions, the following can be understood. First, in Examples 4 and 6, peeling occurred in two samples each by the end of the test duration. However, the L ₁₀ life is 10
I was able to achieve the target of 1000 hours, 15 hours and 1100 hours. The reason why Examples 4 and 6 could secure sufficient durability is that the residual austenite amount γ _R and the residual compressive stress σ _R were properly regulated. This means that the degree of fatigue of the outer ring raceway surface after 100 hours was 1.
This is also clear from the fact that the values are 8 and 1.7, which are lower than those of the comparative examples.

Furthermore, regarding Examples 1 to 3, 5, and 7 to 150, which is longer than the target life of 1000 hours, is 150.
Even after 0 hour, no damage such as peeling occurred in any of the samples, and the degree of fatigue of the outer ring raceway surface was all 1.5 or less. From this, the amount of retained austenite γ _{R is set} to 2
5 to 45% by volume, or the residual compressive stress σ _R is 200 to
It can be seen that by setting the pressure to 500 MPa, superior durability can be ensured.

On the other hand, the standard bearing steel SU
In Comparative Example 1 in which the outer ring was made of J2, peeling occurred in all five samples, the fatigue degree was 2.8 and the L ₁₀ life was 158 hours. Further, in Comparative Examples 2 and 6, the surface hardness of the outer ring raceway surface layer was as low as Hv 615 and 680, so the fatigue level was high at 2.6 and the L ₁₀ life was also short at 105 and 125 hours. Furthermore, in Comparative Examples 3 to 5, 7, and 8, since the residual austenite amount γ _R and the residual compressive stress σ _R are both small, the fatigue degree of the outer ring raceway surface is higher than 2.0, and all five samples are Peeling occurred and the L ₁₀ life was 255, 13
5, 185, 215, 295 hours and a target of 100
It was less than 1/3 of 0 hours.

In the above experiment, a single row deep groove type ball bearing having no seal ring was used. However, in the case of a unit in which a large amount of wear powder is generated at the frictional engagement portion between the pulley and the belt, if there is a margin in the widthwise dimension of the rolling bearing,
A sealing mechanism can be provided. As the seal mechanism used in this case, a TM seal, a non-contact type shield ring of a metal plate, or a contact type seal ring made of acrylic or fluororubber can be used. When installing a seal mechanism, select and use an appropriate structure according to the operating temperature.

The structure and material of the cage are not particularly limited. However, when the rotational speed during use is particularly high, it is preferable to use a crown type cage made of a synthetic resin. It is preferable from the viewpoint of reducing the friction between and, and suppressing the generation of hard abrasion powder to prolong the life.

Further, in the above-mentioned experiment, the internal clearances of the rolling bearings of the respective samples were made normal clearances, and the radius of curvature of the cross-sectional shape of the outer ring raceway 6 and the inner ring raceway 7 was set to the diameter of each rolling element 8, 8. 52%. On the other hand, if the internal gaps and the radii of curvature of the cross-sectional shapes of the orbits 6 and 7 are properly regulated (reduced to be small), rattling in the radial direction and rattling in the axial direction can be suppressed. It is also possible to further improve the performance centered on durability.
Further, the rolling bearing is not limited to the single row deep groove type ball bearing as shown in the figure, but other types of ball bearings such as angular type, cylindrical roller bearings, tapered roller bearings, needle bearings, etc. In the case of, the same action and effect can be obtained.

[0049]

Since the rolling bearing for a belt type continuously variable transmission according to the present invention is constructed and operates as described above, it is sufficient even when a CVT fluid having a low viscosity is used and the flow rate thereof is suppressed to a low level. You can get durability. Therefore, it is possible to improve the efficiency of the belt type continuously variable transmission while ensuring the durability.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a drive system of a vehicle incorporating a belt type continuously variable transmission including a rolling bearing which is an object of the present invention.

FIG. 2 is an enlarged sectional view showing a rolling bearing taken out.

FIG. 3 is a diagram showing the degree of fatigue due to rolling fatigue in a general gear type transmission and a belt type continuously variable transmission.

FIG. 4 is a process chart showing two examples of a heat treatment process for an outer ring.

[Explanation of symbols]

1 Input side rotary shaft 2 Output side rotating shaft 3 Rolling bearing 4 outer ring 5 inner ring 6 Outer ring track 7 Inner ring track 8 rolling elements 9 cage 10 drive source 11 Drive side pulley 12a, 12b Drive side pulley plate 13 Drive side actuator 14 Driven pulley 15a, 15b Driven pulley plate 16 Driven side actuator 17 endless belt 18 Starting clutch 19 Reduction gear train 20 differential gear 21 drive wheels

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) C22C 38/24 C22C 38/24 F16C 19/02 F16C 19/02 33/66 33/66 Z F16H 9/18 F16H 9/18 ZF term (reference) 3J050 AA02 BA03 CE05 DA02 3J101 AA02 AA32 AA42 AA62 BA53 BA54 BA70 DA02 DA03 DA05 EA03 EA04 EA66 EA78 FA32 FA41 GA01 GA11 4K042 AA22 BA03 CA06 CA08 CA13 DA01 DA02 DA06

Claims (4)

[Claims] 1. An outer ring having an outer ring raceway on an inner peripheral surface, an inner ring having an inner ring raceway on an outer peripheral surface, and a plurality of rolling elements rotatably provided between the outer ring raceway and the inner ring raceway. The outer ring is internally fitted and supported on a fixed portion, and the inner ring is externally fitted and supported on a portion that rotates together with a pulley constituting a belt type continuously variable transmission, and the pulley is rotatably supported on the fixed portion. In a rolling bearing for a belt type continuously variable transmission, at least the outer ring contains 0.15 to 0.5% by weight of C, 0.1 to 1.5% by weight of Si, and 0.1 to 1%. It is produced by carbonitriding, quenching, tempering, and polishing a material made of an iron-based alloy containing 0.5 wt% Mn and 0.5 to 3.0 wt% Cr. 0.8 to 1.2 wt% C and 0.05 to 0.50 on the surface of the outer ring raceway
A rolling bearing for a belt type continuously variable transmission, characterized in that it has a surface layer containing N by weight. 2. The surface layer has a surface hardness of Hv 720 to 900, and a carbide or carbonitride having an average particle diameter of 50 to 500 nm is dispersed in the portion from the surface of the outer ring raceway to the depth of maximum shear stress generation position. The rolling bearing for a belt type continuously variable transmission according to claim 1, which is deposited. 3. The residual austenite amount at 50 μm below the surface of the outer ring raceway is set to 20 to 45% by volume, and the residual compressive stress at 50 μm below the surface of the outer ring raceway is set to 150 to 500 MPa. A rolling bearing for a belt type continuously variable transmission as described in. 4. 0.1 to 3.0% by weight of Mo and 0.1 to
The rolling bearing for a belt type continuously variable transmission according to claim 2, wherein at least one of V and 3.0% by weight is contained.