JP3733992B2 - Thrust ball bearing - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thrust ball bearing that supports a thrust load. In particular, the present invention relates to a thrust ball bearing used for parts such as automobile parts (for example, a power roller of a continuously variable transmission (CVT) for automobiles), electrical information equipment, steel, or construction machinery. More specifically, the present invention relates to a thrust ball bearing used for a toroidal type continuously variable transmission.
[0002]
[Prior art]
The use of a toroidal type continuously variable transmission as schematically shown in FIG. 3 has been studied as a transmission for an automobile (see, for example, Japanese Patent Application Laid-Open No. 7-208569). This toroidal continuously variable transmission supports an input side disk 2 concentrically with the input shaft 1 and is disposed concentrically with the input shaft 1 as disclosed in, for example, Japanese Utility Model Publication No. 62-71465. An output side disk 4 is fixed to the end of the output shaft 3. A trunnion 6 that swings around a pivot 5 that is in a twisted position with respect to the input shaft 1 and the output shaft 3 is provided inside the casing that houses the toroidal-type continuously variable transmission. FIG. 3 is a side view showing the basic configuration of the toroidal-type continuously variable transmission in a state at the time of maximum deceleration, and FIG. 4 is a side view similarly shown in a state at the time of maximum acceleration.
[0003]
FIG. 5 is a cross-sectional view of the toroidal type continuously variable transmission. FIG. 6 is a perspective view showing the inner side surface portion of the trunnion 6. Each trunnion 6 is provided with the pivot 5 on the outer surface of both ends. In addition, the base end portion of the displacement shaft 7 is supported at the center of each trunnion 6, and the tilt angle of each displacement shaft 7 is freely adjustable by swinging each trunnion 6 about the pivot shaft 5. . Around the displacement shaft 7 supported by each trunnion 6, a power roller 8 is rotatably supported. Each power roller 8 is sandwiched between the input side and output side disks 2 and 4.
[0004]
Inner side surfaces 2a and 4a of the input side and output side discs 2 and 4 facing each other have a concave surface obtained by rotating a circular arc with the pivot axis 5 as the center. And the peripheral surface 8a of each power roller 8 formed in the spherical convex surface is made to contact | abut to the said inner surface 2a, 4a.
[0005]
A loading cam type pressing device 9 is provided between the input shaft 1 and the input side disc 2, and the pressing device 9 elastically presses the input side disc 2 toward the output side disc 4. Yes. The pressing device 9 includes a cam plate 10 that rotates together with the input shaft 1, and a plurality of (for example, four) rollers 12 that are held by a cage 11. A cam surface 13 that is an uneven surface extending in the circumferential direction is formed on one side surface (left surface in FIGS. 3 and 4) of the cam plate 10, and the outer surface (FIGS. 3 and 4) of the input side disk 2 is formed. The same cam surface 14 is also formed on the right surface in FIG. The plurality of rollers 12 are supported so as to be rotatable about a radial axis with respect to the center of the input shaft 1.
[0006]
When the toroidal type continuously variable transmission configured as described above is used, when the cam plate 10 rotates as the input shaft 1 rotates, the cam surface 13 causes the plurality of rollers 12 to move to the outer surface of the input side disk 2. The cam surface 14 is pressed. As a result, the input disk 2 is pressed by the plurality of power rollers 8, and at the same time, the input disk 2 rotates based on the engagement of the pair of cam surfaces 13, 14 and the plurality of rollers 12. To do. Then, the rotation of the input side disk 2 is transmitted to the output side disk 4 via the plurality of power rollers 8, and the output shaft 3 fixed to the output side disk 4 rotates.
[0007]
When the rotational speeds of the input shaft 1 and the output shaft 3 are changed, and when the deceleration is first performed between the input shaft 1 and the output shaft 3, each trunnion 6 is swung around the pivot 5 and each power As shown in FIG. 3, each of the displacements of the roller 8 so that the peripheral surface 8 a abuts on a portion near the center of the inner surface 2 a of the input side disk 2 and a portion near the outer periphery of the inner surface 4 a of the output side disk 4. The shaft 7 is tilted.
[0008]
On the contrary, when the speed is increased, the trunnion 6 is swung, and the peripheral surface 8a of each power roller 8 is located near the outer peripheral portion of the inner surface 2a of the input side disk 2 and the output side as shown in FIG. Each displacement shaft 7 is inclined so as to abut against the center portion of the inner side surface 4a of the disk 4 respectively. If the inclination angle of each displacement shaft 7 is set intermediate between FIGS. 3 and 4, an intermediate speed ratio can be obtained between the input shaft 1 and the output shaft 3.
[0009]
In FIG. 3, when the torque transmitted from the input side to the output side is large, the roller 12 sandwiched between the cam surface 13 and the cam surface 14 moves to the side where the upper (or lower) gap is smaller, and the torque is increased. When it is small, it moves toward the center with a large gap (a kind of clutch mechanism). When the power of the input shaft 1 is transmitted to the input side disk 2, when the torque is large, the input side disk 2 moves in the right direction in FIG. 3, and when the torque is small, it moves in the left direction. . At this time, if the trunnion 6 is at the same position, the contact between the power roller 8 and the input side and output side disks 2 and 4 becomes uneven. In particular, the contact between the input side disk 2 and the power roller 8 is not stable.
[0010]
Therefore, a support shaft 15 that is parallel to and eccentric from the displacement shaft 7 is provided on the displacement shaft 7, and the support shaft 15 is rotatably supported in a hole 16 formed in the intermediate portion of the trunnion 6. On the other hand, the displacement shaft 7 rotates and automatically aligns so that the input side disk 2 and the peripheral surface 8a of the power roller 8 are in uniform contact.
[0011]
As shown in FIGS. 3 and 4, the trunnions 6 are swung in directions opposite to each other about the pivot 5, so that the peripheral surfaces 8a of the power rollers 8 and the inner surfaces 2a, 4a Changes the rotational speed ratio between the input shaft 1 and the output shaft 3.
[0012]
As described above, when the inclination angle of the displacement shaft 7 is changed in order to change the rotation speed ratio between the input shaft 1 and the output shaft 3, the displacement shafts 7 move the support shaft portions 15. It pivots slightly as the center. As a result of this rotation, the outer surface of the outer ring 18 of each thrust ball bearing 17 and the inner surface of each trunnion 6 are relatively displaced. Thrust needle bearings 19, 20, and 21 are provided between the outer surface and the inner surface to reduce the force required for this relative displacement. Therefore, the force for changing the inclination angle of each displacement shaft 7 can be small.
[0013]
[Problems to be solved by the invention]
Since the thrust ball bearing 17 receives the same load in design for both the power roller (inner ring) 8 and the outer ring 18, the material and bearing design specifications (groove radius, groove roughness, etc.) are designed with the same specifications for the inner and outer rings. In view of the idea that the raceway surface roughness should be as small as possible in order to improve oil film formation, it has not been considered to provide a difference in the roughness of the raceway surfaces of the inner and outer rings.
[0014]
However, under actual conditions of use, for example, a thrust-side ball bearing 17 of a power roller 8 used in an automotive half-toroidal continuously variable transmission (CVT), an inner ring on the rotating side (power roller 8) and an outer ring on the fixed side. 18, the shape, its mounting / supporting structure and the load distribution are different. If the rigidity of the outer ring 18 is small, the deformation of the outer ring 18 causes warpage of the bearing ring, and the rolling element load distribution is not uniform at each point on the circumference of the raceway surface. , A place with a large load and a place with a small load are generated.
[0015]
The thrust needle bearings 19, 20, and 21 incorporated in the toroidal continuously variable transmission have the purpose of facilitating relative displacement between the outer ring 18 and the trunnion 6, and back up the outer ring 18 against the thrust load. Did not consider. For this reason, when the thrust needle bearings 19, 20, 21 and the outer ring 18 as shown in FIG. 6 are overlapped, a part of the outer ring 18 is separated from the edge of the thrust needle bearings 19, 20, 21 in FIG. Projects outward in the horizontal direction indicated by x. A part of the outer ring 18 protruding in this way cannot be supported by the thrust needle bearings 19, 20, 21.
[0016]
On the other hand, a thrust load is applied to the outer ring 18 over the entire circumference by a plurality of balls 22 that constitute a thrust ball bearing 17 together with the outer ring 18. For this reason, the outer ring 18 has a bending stress centered on the boundary between the part and the remaining part due to a thrust load applied to a part of the outer ring 18 protruding outward in the horizontal direction x and a thrust load applied to the remaining part. Added. In the case of a toroidal type continuously variable transmission used as an automobile transmission, such a bending stress is considerably large, and is repeatedly applied along with the revolution movement of the balls 22. For this reason, the outer ring 18 is likely to be damaged in a relatively short time, such as cracking of the outer ring raceway surface, and surface separation of the outer ring raceway surface, resulting in insufficient durability of the toroidal continuously variable transmission.
[0017]
FIG. 7 is a diagram showing the deformation amount of the inner ring (power roller) and the outer ring when a thrust load is received. FIG. 7 shows the shape of the bearing after the test when the outer ring support structure is tested under the condition that the rigidity is high in the vertical position (direction indicated by y in FIG. 6) and the rigidity is low in the horizontal position (direction indicated by x in FIG. 6). It is a measurement result. FIG. 7A is a diagram showing the measurement position of the inner ring (power roller) 8. FIG. 7B is a diagram showing a measurement result of the deformation amount on the raceway surface side of the inner ring. (C) of FIG. 7 is a figure which shows the measurement result of the deformation | transformation amount by the side of the attachment surface of an inner ring | wheel. FIG. 7D is a diagram showing the measurement position in the vertical direction of the outer ring 18 (the direction indicated by y in FIG. 6). (E) of FIG. 7 is a figure which shows the measurement result of the deformation | transformation amount by the side of the track surface in the orthogonal | vertical direction of an outer ring. FIG. 7F is a diagram showing the measurement result of the deformation amount on the bearing mounting surface side in the vertical direction of the outer ring. (G) of FIG. 7 is a figure which shows the measurement position in the horizontal direction (direction shown by x in FIG. 6) of the outer ring | wheel 18. FIG. (H) of Drawing 7 is a figure showing the measurement result of the amount of deformation of the raceway side in the horizontal direction of an outer ring. (I) of FIG. 7 is a figure which shows the measurement result of the deformation | transformation amount of the bearing attachment surface side in the orthogonal | vertical direction of an outer ring | wheel.
[0018]
As can be seen from (d), (e) and (f) of FIG. 7, the outer ring undergoes little deformation at a vertical position where the rigidity of the support structure is high. On the other hand, as can be seen from (g), (h) and (i) of FIG. 7, the outer ring is warped in a convex shape at the horizontal position where the rigidity of the support structure is low. Note that the measurement example shown in FIG. 7 is for the case where the rigidity at the two positions in the vertical position is high and the rigidity at the two positions in the horizontal position is low. The same phenomenon occurs when the rigidity is different at symmetrical positions or when the rigidity is different at three or more divisions, and the same problem is caused by imbalance of the load of the rolling elements.
[0019]
On the other hand, as can be seen from (a), (b) and (c) of FIG. 7, the inner ring (power roller 8) is thicker than the outer ring, so deformation is small.
[0020]
FIG. 8 is a view showing a balance of loads in a state where the outer ring is deformed. When the outer ring is deformed as shown in FIG. 7, the load is balanced in the state shown in FIG. 8, and in the horizontal position where the outer ring is warped, the load escapes and the rolling element load Qb is small, and the outer ring is warped. The rolling element load Qa becomes large at the vertical position where there is no. This also appears in the contact width of the raceway surface of the outer ring in FIG. 9, where the contact width a is wide at the position in the vertical direction y where the load Qa received from the rolling element is large, whereas the load Qb received from the rolling element is The contact width b is narrow at a small position in the horizontal direction x.
[0021]
Therefore, at the position in the vertical direction y where the deformation of the outer ring is small, the traction force is large because the rolling element load Qa is large. At the position in the horizontal direction x where the deformation of the outer ring is large, the traction force is small because the rolling element load Qb is small. Become.
[0022]
Furthermore, when the unevenness | corrugation was measured in the circumferential direction on the groove bottom of the raceway surface of an outer ring and an inner ring, the result as shown in FIG. 10 was obtained. The groove bottoms of the raceways of the outer ring and the inner ring were machined almost horizontally in the circumferential direction before the test. However, due to the warp of the outer ring during the test, as shown in FIG. Then, the raceway surface of the outer ring is concave from the position in the vertical direction y where the deformation is small. In addition, the inner ring having a thick bearing ring and a uniform support rigidity on the circumference has a small deformation and the raceway surface remains substantially horizontal over the entire circumference.
[0023]
When considering the unevenness of the groove bottom of the raceway surface and the change in rolling element load, when the rolling element moves from the vertical position where the deformation of the raceway ring is small to the horizontal position where the deformation of the raceway ring is large, the load and traction force When the movement of the bearing ring from a horizontal position where the deformation of the raceway ring is large to a vertical position where the deformation of the raceway ring is small, the load and the traction force are abruptly increased and the rotation torque is increased. That is, at each point on the circumference of the raceway surface of the bearing, the rolling element rotates in contact with the raceway surface so that torque fluctuation (torque unevenness) always occurs.
[0024]
Furthermore, as shown in FIG. 10, since the outer ring raceway surface is uneven, the horizontal pitch circle diameter (PCD) with a large warp is smaller than the vertical pitch circle diameter (PCD) with a small warp. The contact position of the moving body and the race changes such that the contact position is outside the groove at the horizontal position where the PCD is small, and the contact position is inside the groove at the vertical position where the PCD is large.
[0025]
If such irregular load, traction force, torque, or change in contact point position acts on the rolling element, slippage occurs between the rolling element and the raceway, resulting in significant heat generation or metal contact due to a decrease in oil film. Wear, flaking, etc. occur in a much shorter time than when the rolling elements are evenly loaded and regularly move, making the bearing unusable.
[0026]
The damage at this time occurs in the outer ring on the side of the race ring having a small rigidity. This is because the raceway surface is uneven due to the deformation of the outer ring, and the PCD changes at each position on the circumference, so this raceway surface has irregular load, traction force, torque, and contact point position. This is because slipping easily occurs between the rolling elements as a factor of change.
[0027]
Therefore, an object of the present invention is to suppress slippage between the raceway surface of the outer ring and the rolling element by making the control surface of the rolling element an outer ring that is easily damaged. In other words, in a thrust rolling bearing, the rolling element rotates with either raceway surface of the inner or outer ring as a control surface, but when the rolling element is an inner ring control, unevenness of the outer ring or PCD change accelerates the sliding of the rolling element. This is because, in the case of the outer ring control, the unevenness of the raceway surface of the inner ring and the change in the PCD are small, so that the slip can be suppressed to be small.
[0028]
Further, in the thrust rolling bearing, the inner ring on the drive side and the outer ring that supports the thrust ring bearing may not necessarily have the same size and shape due to restrictions such as the design purpose and the mounting structure. When heat treatment for surface hardening such as carburizing, carbonitriding, induction hardening, etc. is applied to the inner ring and outer ring having different dimensions and shapes, the cracks and decarburization of the smaller ring (thinner wall thickness) In order to prevent the heat treatment failure, the depth of the effective hardened layer having a smaller dimension is made shallower.
[0029]
This is not a problem in terms of heat treatment. To increase fracture toughness even when bending resistance and impact strength are required by the load application method and bearing ring support method regardless of size and shape. On the other hand, the depth of the hardened layer, such as carburizing, carbonitriding, induction hardening, etc., of one raceway ring is reduced.
[0030]
FIG. 11 is a diagram showing a difference in hardness gradient due to a difference in heat treatment. FIG. 12 is a graph showing the relationship between the effective hardened layer depth and the rolling fatigue life. In FIG. 11, Yo represents the carburized hardened layer depth. The carburization depth is determined based on the depth from the surface until the hardness reaches Hv550. As shown in FIG. 12, as can be seen from the rolling fatigue life test results until the occurrence of flaking of the bearing with the carburized depth of the raceway surface changed, the shorter the carburized depth, the shorter the life. This leads to the fact that a raceway ring having a shallow hardened layer depth is easily damaged if there is a difference in the hardened layer depth such as the carburized depth between the inner ring and the outer ring.
[0031]
As a countermeasure in such a case, in order to extend the life of the bearing ring having the shorter life, the groove radius is reduced to reduce the surface pressure, or the raceway surface roughness is reduced to improve oil film formation. Has been considered effective.
[0032]
However, even though the rolling element can only go straight in the case of pure rolling motion, in the case of a thrust bearing, it is necessary to cause the rolling element to make a circular motion, so a force is applied to cause the rolling element to make a circular motion, Spin (for ball bearings) and skew (for roller bearings) occur on the rolling elements. For this reason, the above countermeasures may have an adverse effect depending on which raceway is used as a control surface for applying a force for causing the rolling element to perform a circular motion (revolution).
[0033]
In other words, the countermeasure for reducing the surface roughness of the raceway surface with a short life due to the shallow carburizing effective hardening depth reduces the friction coefficient between the raceway and the rolling element, and the raceway with low roughness of spin slip and skew slip. It occurs only on the surface, and the adverse effect of the slip appears more than the effect of improving the roughness, resulting in a shorter life.
[0034]
Therefore, in the present invention, contrary to the conventional idea, since the effective hardened layer depth is shallow, the surface roughness of the raceway surface of the bearing ring, which is likely to be damaged, is increased to increase the control surface (ball) of the rolling element. The object is to suppress the slip between the raceway surface and the rolling element by using the surface to be revolved, that is, the raceway surface that gives the ball a force to revolve (spin) the ball. That is, in the thrust bearing, the rolling element rotates with the raceway of either the inner or outer ring as the control surface, but since the rolling element uses the raceway with the larger roughness as the control surface, the hardened layer depth is reduced. This is because if the roughness of the raceway surface of the shallower raceway is increased, the slip on this raceway surface can be kept small, and slipping will occur on the raceway side where the hardened layer depth is long and the life is long.
[0035]
[Means for Solving the Problems]
The present invention is a thrust ball bearing supported by a thrust needle bearing and incorporated in a toroidal-type continuously variable transmission, an inner ring having a raceway surface, an outer ring having a raceway surface and having a wall thickness smaller than that of the inner ring. A plurality of balls that are rotatably arranged between the raceway surface of the inner ring and the raceway surface of the outer ring, and an annular retainer that holds the plurality of balls in a freely rollable manner. In the thrust ball bearing that receives a thrust load, the center line average roughness of the surface of the raceway surface of the outer ring having a small wall thickness is defined as the centerline average roughness of the surface of the raceway surface of the inner ring having a large wall thickness. It was bigger than that.
Since the outer ring of the thrust ball bearing is susceptible to damage such as flaking, the center line average roughness Ra (hereinafter referred to as “average roughness”) of the raceway surface of the outer ring having a small wall thickness is the wall thickness dimension. By making it larger than the centerline average roughness of the raceway surface of the large inner ring, the raceway surface of the outer ring with a small wall thickness becomes a control surface that gives the ball the force to revolve the ball along the raceway surface, thereby The slip between the raceway surface of the outer ring and the ball can be suppressed to prevent the outer ring from being damaged.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes an input disk, an output disk, a trunnion that swings about a pivot line that is twisted with respect to the rotation axis of each of the input disk and the output disk, and a trunnion that is rotatably supported by the trunnion. A thrust rolling bearing for use in a toroidal type continuously variable transmission comprising a power roller engaged with the input disk and the output disk, and an outer ring supported by the trunnion;
A thrust rolling bearing comprising a plurality of rolling elements disposed between a raceway surface provided on the outer ring and a raceway surface provided on the trunnion, wherein the average roughness of the surface of the raceway surface of the outer ring is determined. The average roughness of the surface of the raceway surface of the power roller, that is, the inner ring was made larger.
As a result, the raceway surface of the outer ring can be used as a control surface, thereby preventing flaking that occurs on the raceway surface of the outer ring.
[0037]
The average roughness of the raceway surface of the outer ring may be about twice the average roughness of the raceway surface of the power roller.
[0038]
The wall thickness of the outer ring may be smaller than the wall thickness of the power roller. Further, the bending rigidity of the outer ring may be smaller than the bending rigidity of the power roller.
[0039]
The cross section of the groove on the raceway surface of the outer ring and the power roller has an arc shape, and the radius of the groove on the raceway surface of the outer ring may be smaller than the radius of the groove on the raceway surface of the power roller. The radius of the groove on the raceway surface of the outer ring may be about 0 to 6% smaller than the radius of the groove on the raceway surface of the power roller.
[0040]
The raceway surfaces of the outer ring and the power roller are preferably subjected to surface hardening treatment by carburizing, carbonitriding, induction hardening, or the like. The effective hardened layer depth of the raceway surface of the outer ring may be shallower than the effective hardened layer depth of the raceway surface of the power roller.
[0041]
FIG. 1 is a diagram showing the relationship between the surface roughness of the raceway surface and the occurrence of flaking in a thrust ball bearing. Flaking occurs on which raceway surface due to the magnitude relationship between the raceway surface roughness of the inner and outer rings. This is an arrangement. In FIG. 1, the horizontal axis represents the center line average roughness (Ra) of the inner raceway surface of the thrust ball bearing, and the vertical axis represents the centerline average roughness (Ra) of the outer raceway surface of the thrust ball bearing. ). The surface roughness is expressed as a relative value with a predetermined value of 1. In FIG. 1, the point indicated by a circle symbol indicates that flaking has occurred on the raceway surface of the inner ring, and the point indicated by a square symbol indicates that flaking has occurred on the raceway surface of the outer ring. Yes. From FIG. 1, it can be seen that all flaking occurs on the raceway having the smaller surface roughness. The number attached to the symbol is the temperature rise relative to the oiling temperature when the outer ring outer diameter surface is measured with a thermocouple, but the inner ring flaking is about 22-25 ° C, whereas the outer ring flaking is Is about 28-32 ° C. and about 6-7 ° C. higher.
That is, when the surface roughness of the raceway surface of the outer ring is smaller than the surface roughness of the raceway surface of the inner ring, the rolling element control is the inner ring control with a large surface roughness of the raceway surface and a large friction coefficient. Slip occurs in the outer ring having a small surface roughness, the temperature of the outer ring bearing increases, and flaking tends to occur on the raceway surface of the outer ring.
[0042]
The same principle holds true when the outer ring raceway surface roughness is greater than the inner ring raceway surface roughness, and the outer ring raceway surface roughness is determined by the inner ring raceway surface roughness. It can be seen from FIG. 1 that the outer ring flaking can be prevented by increasing the diameter of the outer ring.
[0043]
When this principle is applied as a measure to prevent the phenomenon of easy wear and flaking due to sliding on the outer ring, which is a raceway with low bending rigidity, the surface roughness of the raceway surface of the outer ring with low bending rigidity is set to the other. By making it larger than the surface roughness of the raceway surface of the inner ring, the friction coefficient between the outer ring having the smaller bending rigidity and the rolling element can be made larger than the friction coefficient between the other inner ring and the rolling element.
By doing so, the rolling element rotates with the raceway surface of the outer ring having a large friction coefficient and a small bending rigidity as the control surface. Thereby, the slip between a rolling element and a raceway ring arises between inner rings with small deformation. However, the slip amount between the inner ring and the inner ring can be suppressed to be smaller than the slip amount generated between the inner ring and the outer ring that is largely deformed.
[0044]
In addition, when applying the above principle as a measure to prevent the phenomenon that flaking is likely to occur in a raceway with a shallow effective hardened layer depth of carburizing, the surface roughness of the raceway surface of the raceway with a shallow effective hardened layer depth. Is made larger than the surface roughness of the raceway surface of the raceway with the other effective hardened layer depth, the friction coefficient between the raceway and the rolling element with the shallower effective hardened layer depth is reduced. The friction coefficient between the raceway and the rolling element having a deep layer depth can be made larger.
By doing so, the rolling element rotates with the raceway surface of the raceway having a large friction coefficient and a shallow effective hardened layer depth as a control surface. For this reason, the slip between the rolling element and the raceway surface occurs between the raceway with a deep effective hardened layer depth, and the slip that occurs on the raceway surface of the raceway with a shallow effective hardened layer depth is kept small. be able to.
[0045]
【Example】
Embodiments will be described with reference to the drawings.
FIG. 2 is a sectional view of a thrust ball bearing 17 used in the toroidal type continuously variable transmission. The thrust ball bearing 17 is disposed between an annular outer ring 18 supported by the trunnion 6, a power roller 8 that engages with the input side disk 2 and the output side disk 4, that is, an inner ring, and the outer ring 18 and the inner ring 8. A plurality of balls 22 and a ring-shaped retainer 23 that holds the plurality of balls 22 in a rollable manner. The outer ring 18 is provided with a circular raceway surface 18 a on one side surface of the outer ring 18. The inner ring 8 is provided with a circular raceway surface 8 a on one side surface of the inner ring 8. The raceway surfaces 18a and 8a are formed in a groove shape having a circular cross section. The radii of the arc-shaped grooves on the raceway surfaces 18a and 8a are represented by ro and ri, respectively. The thickness to of the outer ring 18 is smaller than the thickness ti of the inner ring 8. The surface roughness of the raceway surfaces 18a and 8a is expressed using the center line average roughness Ra.
[0046]
(First embodiment)
The radii ro and ri of the grooves on the raceway surfaces 18a and 8a of the outer ring 18 and the inner ring 8 are formed identically in design. The average roughness Rao of the raceway surface 18a of the fixed-side outer ring 18 is 0.044 μm, and the average roughness Rai of the raceway surface 8a of the rotation-side inner ring 8 is 0.022 μm. That is, the average roughness Rao of the raceway surface 18 a of the outer ring 18 is formed to be larger than the average roughness Rai of the raceway surface 8 a of the inner ring 8.
In order to provide a difference in roughness, in the finishing process, the processing time of the outer ring 18 is shortened from the processing time of the inner ring 8, thereby reducing the roughness of the raceway surface 18 a of the outer ring 18 to about 2 of the roughness of the track surface 8 a of the inner ring 8. Doubled.
[0047]
Other methods for providing a difference in the surface roughness of the raceway surface include different grinding wheels in the super finishing process for the inner ring and outer ring, changing the rotation speed and the grinding wheel feed speed, and final finishing. The surface roughness of the raceway surface of the outer ring is made larger than the surface roughness of the raceway surface of the inner ring by changing the combination of these processing methods between the inner ring and the outer ring. Can do.
[0048]
Furthermore, the grindability can be changed by changing the material and heat treatment of the inner ring and the outer ring so that the outer ring becomes rougher than the inner ring when processed in the same process. In other words, when changing the material, the additive amount for improving heat resistance such as Cr, Mo, Si, etc. is larger in the outer ring than in the inner ring, or when changing the heat treatment, the inner ring is carburized. It is effective to carbonitriding only the outer ring.
[0049]
The first embodiment is a general case where superfinishing is performed after grinding both the inner ring and the outer ring. The difference in surface roughness between the raceway surface of the inner ring and the raceway surface of the outer ring is not necessarily about twice. If there is a difference in the surface roughness of the raceway surface, the raceway surface with the larger average roughness Ra is the rolling element. That is, it becomes the control surface of the ball.
[0050]
(Second embodiment)
In the second embodiment, the surface roughness of the raceway surface 18a of the outer ring 18 on the fixed side is made larger than the surface roughness of the raceway surface 8a of the inner ring 8 on the rotation side, and the radius ro of the raceway surface 18a of the outer ring 18 is set. It was made smaller than the radius ri of the groove of the raceway surface 8a of the inner ring 8.
The average roughness Rao of the raceway surface 18a of the fixed-side outer ring 18 is 0.044 μm, and the average roughness Rai of the raceway surface 8a of the rotation-side inner ring 8 is 0.022 μm.
The radius of the groove on the raceway surface is designed in the range of (0.51 to 0.60) da (da: ball diameter), including the case where the radius of the groove on the raceway surface of the inner and outer rings is the same. Specifically, the radius ri of the groove on the raceway surface 8a of the inner ring 8 may be larger by about (0 to 0.03) da than the radius r of the groove on the raceway surface 18a of the outer ring 18.
[0051]
In this way, the surface roughness of the outer ring raceway surface is controlled by making the radius ro of the raceway surface of the outer ring smaller than the radius ri of the groove of the raceway surface of the inner ring. The increase in the frictional force due to the increase in the contact ellipse area is combined with the increase in the frictional force due to the increase in the contact ellipse area.
[0052]
(Third embodiment)
In the third embodiment, the carburizing depth of the outer ring 18 having a small thickness to is shallower than the carburizing depth of the inner ring 8 having a large thickness ti.
The surface roughness Rao of the raceway surface 18a of the outer ring 18 is made larger than the surface roughness Rai of the raceway surface 8a of the inner ring 8 on the rotation side so that the outer ring 18 on the fixed side becomes a control surface of the ball 22 that is a rolling element. is there. The average roughness Rao of the raceway surface 18a of the fixed-side outer ring 18 is 0.044 μm, and the average roughness Rai of the raceway surface 8a of the rotation-side inner ring 8 is 0.022 μm.
[0053]
Note that the third example is a general case where both the inner ring and the outer ring are superfinished after grinding. The difference in surface roughness between the raceway surface of the inner ring and the raceway surface of the outer ring is not necessarily about twice. If there is a difference in the surface roughness of the raceway surface, the raceway surface with the larger average roughness Ra is the rolling element. That is, it becomes the control surface of the ball.
[0054]
In the third embodiment, the case where the effective hardened layer depth of the bearing ring having the smaller thickness (dimension) is shallow is shown. However, when the impact resistance strength is required, the thickness (dimension) is In some cases, a larger raceway reduces the effective hardened layer depth. In such a case, the surface roughness of the raceway surface of the raceway having a large thickness is increased.
[0055]
Further, the third embodiment shows the case of carburizing as the surface effect method, but the present invention can be similarly applied to other heat treatment methods such as carbonitriding and induction hardening.
[0056]
In the above embodiment, the case where a thrust ball bearing is used has been described as an example, but the present invention is not limited to a thrust ball bearing, in addition to the case where a ball is used as a rolling element, a cylindrical roller, For any thrust rolling bearing such as a tapered roller or needle roller, if there is a difference in the surface hardening layer depth between the inner ring and the outer ring, the surface roughness of the raceway surface of the bearing ring with the shallower hardening layer depth. The same effect can be obtained by increasing.
[0057]
【The invention's effect】
The present invention is implemented in the form as described above, and has the following effects.
[0058]
By making the control surface of the rolling element an outer ring whose bearing ring rigidity is small, the sliding between the outer ring raceway surface and the rolling element is suppressed compared to the case of inner ring control, so the wear resistance and flaking resistance are improved and the service life is increased. become.
[0059]
By making the control surface of the rolling element into a raceway with a shallow carburization depth, the slip between the raceway surface of the raceway with a shallow carburization depth and the rolling element is less than when the raceway with a deep carburization depth becomes the control surface. Since it is suppressed, the wear resistance and flaking resistance are improved and the service life is extended.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between the surface roughness of a raceway surface and a flaking occurrence site.
FIG. 2 is a sectional view of a thrust ball bearing used in a toroidal type continuously variable transmission.
FIG. 3 is a side view showing a basic configuration of a conventionally known toroidal continuously variable transmission in a state at the time of maximum deceleration.
FIG. 4 is a side view showing the same state at the maximum speed increase.
FIG. 5 is a cross-sectional view of a toroidal-type continuously variable transmission.
FIG. 6 is a perspective view showing an inner side surface portion of the trunnion.
FIG. 7 is a diagram showing deformation amounts of an inner ring and an outer ring when receiving a thrust load.
FIG. 8 is a diagram showing a balance of loads in a state where the outer ring is deformed.
FIG. 9 is a diagram showing a contact width of a raceway surface of an outer ring.
FIG. 10 is a diagram showing the result of measuring the shape of the groove bottoms on the raceways of the outer ring and the inner ring in the circumferential direction.
FIG. 11 is a diagram showing a difference in hardness gradient due to a difference in heat treatment.
FIG. 12 is a graph showing the relationship between effective hardened layer depth and rolling fatigue life.
[Explanation of symbols]
8 inner ring
8a Track surface
17 Thrust rolling bearing
18 Outer ring
18a Track surface
22 Rolling elements
Rai inner ring average roughness
Rao Average outer ring roughness

Claims (4)

A thrust ball bearing supported by a thrust needle bearing and incorporated in a toroidal continuously variable transmission,
An inner ring having a raceway surface;
An outer ring having a raceway surface and having a smaller wall thickness than the inner ring;
A plurality of balls arranged in a freely rolling manner between the raceway surface of the inner ring and the raceway surface of the outer ring;
A thrust ball bearing comprising a ring-shaped cage that holds the plurality of balls in a freely rolling manner, and receives a thrust load.
A thrust ball bearing characterized in that the center line average roughness of the raceway surface of the outer ring having a small wall thickness is greater than the centerline average roughness of the raceway surface of the inner ring having a large wall thickness. .   The outer ring and the inner ring are surface hardened by carburizing, carbonitriding, or induction hardening, and the effective hardened layer depth of the raceway surface of the outer ring is the effective hardened layer depth of the raceway surface of the inner ring. The thrust ball bearing according to claim 1, wherein the thrust ball bearing is smaller than that.   The thrust ball bearing according to claim 1 or 2, wherein a support rigidity of the outer ring is different between a vertical direction and a horizontal direction.   The cross section of the groove on the raceway surface of the outer ring and the inner ring has an arc shape, and the radius of the groove of the outer ring is smaller than the radius of the groove of the inner ring. The thrust ball bearing described.

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