Patent Application
20210301874
The present invention relates to roller and cage assemblies and planetary gear support structures.
There is a technique that improves oil flow capability by forming oil flow grooves in the outer peripheral surface of a cage as a structure for lubricating a roller and cage assembly, as described in Japanese Unexamined Patent Publication No. 2015-078742 (Patent Literature 1). In a roller and cage assembly described in Japanese Utility Model No. 2584225 (Patent Literature 2), swaged grooves serving as oil reservoirs are formed in the outer and inner peripheral surfaces of a cage. There is also a technique that improves oil flow capability by forming oil flow grooves in the inner peripheral surface of a cage, as described in Japanese Unexamined Patent Publication No. 2007-255494 (Patent Literature 3).
Patent Literature 1: Japanese Unexamined Patent Publication No. 2015-078742
Patent Literature 2: Japanese Utility Model No. 2584225
Patent Literature 3: Japanese Unexamined Patent Publication No. 2007-255494
For example, roller and cage assemblies are used as bearings that support gears on gear shafts in automobile transmissions. Especially, recent transmissions have more gears for better fuel efficiency of automobiles, and there is a growing demand for planetary gear support structures using roller and cage assemblies. For better fuel efficiency of automobiles, there is also a trend to use less lubricating oil in transmissions and to use lubricating oil with low kinematic viscosity. In this case, less lubricating oil is supplied to roller and cage assemblies, and an oil film is less likely to be formed. Accordingly, at least outer retaining protrusions and rollers may directly contact each other with no oil film therebetween, and the outer retaining protrusions and the rollers may wear each other out.
One possible solution to this problem is to use the roller and cage assembly described in Patent Literature 3. However, the roller and cage assembly described in Patent Literature 3 is configured to supply lubricating oil from an oil supply hole formed in a support shaft for a planetary gear into a region between the cage and the support shaft, and is not intended for a configuration in which lubricating oil is supplied to the sliding contact portions between the rollers and the outer retaining protrusions.
In view of the above circumstances, it is an object of the present invention to provide a roller and cage assembly whose life can be prolonged even in a harsh lubrication environment.
In order to achieve the above object, a roller and cage assembly according to the present invention includes: a cage including a pair of rings and a plurality of cage bars extending in an axial direction and connecting the rings to each other; and rollers disposed in pockets between the cage bars adjacent to each other in a circumferential direction. The cage bar of the cage includes an end portion located on an outer side in the axial direction and a middle portion located radially inward from the end portion. The end portion of the cage bar has an outer retaining protrusion formed therein, the outer retaining protrusion protruding into the pocket and configured to contact the roller to restrict radially outer movement of the roller. The end portion of the cage bar has an oil groove formed in an inner peripheral surface thereof, the oil groove extending in the circumferential direction and connecting to the outer retaining protrusion.
According to the present invention, lubricating oil flows through the oil groove formed in the inner peripheral surface of the end portion of each cage bar of the cage and is supplied to a contact portion between the outer retaining protrusion and the roller. An oil film is therefore formed on the contact portion, and direct contact between the outer retaining protrusion and a rolling surface is avoided. Wear of the outer retaining protrusion and the rolling surface of the roller is thus prevented. Even when the roller and cage assembly revolves around a central axis offset from an axis of the roller and cage assembly and the lubricating oil that lubricates the roller and cage assembly is subjected to a centrifugal force, the revolving motion and rotating motion of the roller and cage assembly cooperate to cause the lubricating oil to flow into the oil groove. This improves oil flow capability of the roller and cage assembly. Since the end portion of each cage bar is located radially outward from the middle portion thereof, the inner peripheral surface of the end portion of each cage bar does not contact an outer peripheral surface of a shaft and need not be ground. The groove depth is therefore not reduced like the conventional oil flow grooves. The present invention requires no oil retaining member and can be produced at low cost. Either only one oil groove or a plurality of oil grooves may be formed in one end portion. The oil groove extending in the circumferential direction may extend parallel to the circumferential direction or may extend obliquely with respect to the circumferential direction.
The depth and width of the oil groove are not limited. In one aspect of the present invention, the end portion of the cage bar has a recessed oil reservoir formed in the inner peripheral surface thereof, the oil reservoir connecting to the oil groove. According to this aspect, the lubricating oil is temporarily stored in the oil reservoir. Accordingly, even when the lubricating oil tends to flow out of the roller and cage assembly due to the centrifugal force, the oil flow capability of the roller and cage assembly is not reduced. The shape and number of oil reservoirs are not particularly limited. In another aspect, the end portion of the cage bar may have only the oil groove formed in the inner peripheral surface thereof.
In a preferred aspect of the present invention, the oil groove has a circumferential end formed in the outer retaining protrusion, the circumferential end extending in a radial direction. According to this aspect, the lubricating oil is supplied to the entire contact portion between the outer retaining protrusion and the rolling surface of the roller.
In another preferred aspect of the present invention, the circumferential end of the oil groove extends in the radial direction so as to extend through the outer retaining protrusion and connects to an outer peripheral surface of the end portion facing outward in the radial direction. In still another aspect, the circumferential end of the oil groove may be formed in the outer retaining protrusion but not connect to the outer peripheral surface of the end portion.
In one aspect, the roller and cage assembly of the present invention is disposed at a center of a planetary gear of a planetary gear support structure. The planetary gear support structure of the present invention is a planetary gear support structure including a ring gear, a sun gear disposed at a center of the ring gear, a plurality of planetary gears meshing with the ring gear and the sun gear, and a carrier supporting the planetary gears, the planetary gears being rotatably supported on support shafts provided on the carrier via rolling bearings. The rolling bearing for the support shaft is the roller and cage assembly described above.
As described above, the present invention provides a roller and cage assembly whose life can be prolonged even in a harsh lubrication environment and a planetary gear support structure including the roller and cage assembly.
Embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, an overview of a planetary gear support structure 100 using needle roller and cage assemblies (hereinafter simply referred to as the roller and cage assemblies) 10 of an embodiment will be given with reference to
The sun gear 102 is disposed coaxially inside the ring gear 101. The planetary gears 103 are disposed radially inward from the ring gear 101 and radially outward from the sun gear 102 and mesh with the ring gear 101 and the sun gear 102. The plurality of support shafts 105 is fixed to the carrier 104. Each support shaft 105 is inserted through a center hole of the planetary gear 103. Each roller and cage assembly 10 of the present embodiment is disposed between the inner peripheral surface of the planetary gear 103 and the outer peripheral surface of the support shaft 105. Each roller and cage assembly 10 serves as a rolling bearing and rotatably supports the planetary gear 103.
The planetary gears 103 can revolve around the sun gear 102 while rotating. The carrier 104 is disposed coaxially with the sun gear 102 and can rotate. The carrier 104 is rotated by the revolution of the planetary gears 103 or causes the planetary gears 103 to revolve around the sun gear 102. The planetary gears 103 and the roller and cage assemblies 10 are subjected to a centrifugal force about the sun gear 102.
Referring to
An oil flow hole 106 for supplying lubricating oil is formed in the support shaft 105. The roller and cage assembly 10 is lubricated by guiding the lubricating oil to the outer peripheral surface of the support shaft 105 through the oil flow hole 106 formed in the support shaft 105. Specifically, the oil flow hole 106 includes a first oil flow hole 106a extending in the axial direction from the right side of the paper of
When the planetary gear support structure 100 is used for automobile transmissions having more gears, less lubricating oil is supplied to the roller and cage assemblies 10 or lubricating oil with lower viscosity is supplied to the roller and cage assemblies 10 in some cases in order to further improve fuel efficiency of automobiles. The kinematic viscosity of the lubricating oil that is used to improve fuel efficiency of automobiles is, e.g., 2 centistokes (cSt) to 8 centistokes (cSt) at 100° C.
Referring to
The pair of rings 11, 11 and the cage bars 21, 21 adjacent to each other in the circumferential direction define the pocket 13. Since each side surface of the cage bar 21 defines the pocket 13, the side surfaces of the cage bars 21 are also referred to as pocket wall surfaces 28.
The support shaft 105 is passed through the center of the roller and cage assembly 10. The roller and cage assembly 10 is disposed inside a housing (planetary gear 103) (see
Referring to
Referring to
The middle portion 23 extends straight and parallel to the axis O and connects at both ends to the inner ends in the axis O direction of the tilted portions 24. Each tilted portion 24 is tilted such that its outer end in the axis O direction is located radially outward from its inner end in the axis O direction. The outer end in the axis O direction of each tilted portion 24 connects to the end portion 22. Each end portion 22 extends straight and parallel to the axis O. When looking at one cage bar 21 shown in
The distance between the outer retaining protrusions 25, 25 facing each other with the pocket 13 therebetween is smaller than the diameter of the needle roller 14 (
In the cage 12 of the type that is guided by its outer peripheral surface, outer peripheral surfaces 27 of the end portions 22 and/or outer peripheral surfaces of the rings 11 of the cage 12 are ground. This improves wear resistance of the outer peripheral surface of the cage 12. Inner peripheral surfaces 26 of the end portions 22 of the cage 12 need not be ground.
An oil groove 31 is formed in the inner peripheral surface 26 of each end portion 22. The width of the oil groove 31 is smaller than the dimension in the axis O direction of the outer retaining protrusion 25 and is constant. The width of the oil groove 31 is preferably in the range of 10% or more and 50% or less of the dimension in the axis O direction of the outer retaining protrusion 25 in view of the capability of holding the lubricating oil and supply of the lubricating oil to the outer retaining protrusions 25.
The oil groove 31 extends in the circumferential direction of the cage 12 and connects to the outer retaining protrusions 25. The depth of the oil groove 31 is constant. The depth of the oil groove 31 is preferably in the range of 5% or more and 50% or less of the thickness dimension of the end portion 22. The thickness dimension of the end portion 22 is the thickness from the inner peripheral surface 26 to the outer peripheral surface 27 of the end portion 22 shown in
The oil groove 31 is located inward from the recesses 15 in the axis O direction and outward from the tilted portion 24 (
Referring back to
According to the present embodiment, the cage 12 has the oil grooves 31 in the inner peripheral surfaces 26. When the roller and cage assembly 10 placed in annular clearance between the housing and the shaft is in use, the lubricating oil flows through the oil grooves 31 to lubricate the caged roller and cage assembly 10. The oil grooves 31 provide sufficient oil flow capability along the entire circumference of the roller and cage assembly 10. The oil grooves 31 connect at their circumferential ends to the contact surfaces 29 of the outer retaining protrusions 25. An oil film is therefore formed on each contact surface 29, and the oil film on each contact surface 29 will not break. Direct contact between the outer retaining protrusions 25 and the rolling surfaces of the needle rollers 14 is thus avoided, and wear of the outer retaining protrusions 25 and the rolling surfaces of the needle rollers 14 is prevented.
As described above, according to the roller and cage assembly 10 of the present embodiment, the lubricating oil is easily supplied to the outer retaining protrusions 25 and the life of the roller and cage assembly 10 is prolonged. The roller and cage assembly 10 of the present embodiment is therefore very effective when applied to planetary gear support structures of automobile transmissions where the lubrication environment for bearings is becoming harsh with improvement in fuel efficiency of automobiles.
If no oil film is formed on the surface of the cage, the cage wears due to direct contact with the rollers. The worn portions of the cage, such as the outer retaining protrusions and the inner retaining protrusions of the cage, have increased surface roughness, and the rolling surfaces of the rollers contact very small protrusions on the worn portions. When this happens, the rolling surfaces of the rollers are repeatedly subjected to high pressures from the roughened portions, specifically from, e.g., the very small protrusions on the surfaces of the outer retaining protrusions and the inner retaining protrusions. As a result, very small spalls develop on the rolling surfaces of the rollers. This phenomenon is called peeling. Peeling tends to occur on the inner raceway surface that is the outer peripheral surface of the shaft and those parts of the rolling surfaces of the rollers which contact the outer retaining protrusions as the inner raceway surface and these parts of the rolling surfaces of the rollers are subjected to high contact surface pressures. Such very small spalls develop into large spalls on the rolling surfaces of the rollers. As a result, noise and vibration are generated by the planetary gear support structure.
According to the present embodiment, when the cage 12 is of the type that is guided by its outer peripheral surface, the outer peripheral surfaces 27 of the end portions 22 are ground, but the inner peripheral surfaces 26 of the end portions 22 in which the oil grooves 31 are formed are not ground. Accordingly, the depth of the oil grooves 31 is not reduced. Grinding the outer peripheral surface of the cage 12 is less costly than grinding the inner peripheral surface of the cage 12 and is also applicable to a cage 12 with a small diameter.
Referring to
Referring to
A method for manufacturing the cage 12 is as follows.
First, strip steel is prepared. Next, a reduced diameter portion is formed in the middle in the lateral direction of the strip steel with a forming roll. The resultant strip steel is then punched in the thickness direction with a press machine to form the pockets 13. Thereafter, the outer retaining protrusions 25 and the contact surfaces 29 are formed with the press machine. Subsequently, the resultant strip steel is cut into strips. Each strip is bent into a cylindrical shape, and the ends of the strip are joined by welding. The reduced diameter portion forms the middle portions 23 of the cage bars 21. The oil grooves 31 can be formed simultaneously with the reduced diameter portion. Oil reservoirs 32 can be formed simultaneously with the outer retaining protrusions 25 and the contact surfaces 29. Circumferential ends 34 can be formed simultaneously with the outer retaining protrusions 25 and the contact surfaces 29. Circumferential ends 33 can be formed simultaneously with the pockets 13. In each of the embodiments of the present invention, the process of forming the outer retaining protrusions 25 and the process of forming the oil grooves 31 are separate processes. Design flexibility of both the outer retaining protrusions 25 and the oil grooves 31 is therefore increased, and the shape and dimensions of the oil grooves 31 can be set according to the supply flow rate of the lubricating oil.
Next, a roller and cage assembly according to another embodiment of the present invention will be described with reference to
According to this embodiment, lubricating oil can be held in the oil reservoir 32. The roller and cage assembly 10 is therefore lubricated even when supply of the lubricating oil from the outside of the roller and cage assembly 10 to the roller and cage assembly 10 is reduced for some reason.
Next, a roller and cage assembly according to still another embodiment of the present invention will be described with reference to
Each outer retaining protrusion 25 is divided into an axial inner portion and an axial outer portion by the circumferential end 33. The groove depth of the circumferential end 33 is small on the inner side in the radial direction and increases as it gets closer to the outer side in the radial direction. The circumferential end 33 has such a groove depth because the amount by which the outer retaining protrusion 25 protrudes is small on the inner side in the radial direction and increases as it gets closer to the outer side in the radial direction.
According to this embodiment, since the circumferential ends 33 of the oil groove 31 extend through the outer retaining protrusions 25, more lubricating oil is supplied to the contact surfaces 29 of the outer retaining protrusions 25.
Next, a roller and cage assembly, which is a modification of the embodiment of
According to the modification, since the circumferential ends 34 have a constant groove depth, the lubricating oil is stably supplied to the contact surfaces 29 of the outer retaining protrusions 25.
Although the embodiments of the present invention are described above with reference to the drawings, the present invention is not limited to the illustrated embodiments. Various alterations and modifications can be made to the illustrated embodiments without departing from the spirit and scope of the present invention. For example, a part of the configurations of one of the above embodiments and another part of the configurations of another one of the above embodiments may be combined.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-153455 | Aug 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/030240 | 8/1/2019 | WO | 00 |
