PLANET GEAR SUPPORT SHAFT, METHOD FOR MANUFACTURING PLANET GEAR SUPPORT SHAFT, AND PLANETARY GEAR UNIT

A planet gear support shaft includes a cylindrical body that is open at both ends in a central axis direction. The cylindrical body has an inlet port through which lubricating oil is introduced into a hollow portion of the cylindrical body, and a discharge port through which the lubricating oil introduced into the hollow portion is discharged, the inlet port and the discharge port being open to an inner peripheral surface of the hollow portion at different positions in the central axis direction. An oil guide groove is provided between a first opening of the inlet port and a second opening of the discharge port in the inner peripheral surface. The oil guide groove is configured to guide the lubricating oil between the first opening and the second opening.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2019-033707 filed on Feb. 27, 2019, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The disclosure relates to planet gear support shafts that supports a planet gear, methods for manufacturing a planet gear support shaft, and planetary gear units.

2. Description of Related Art

There is a planetary gear unit that is used for, for example, shifting in a drive system of a vehicle (see, for example, Japanese Unexamined Patent Application Publication No. 2005-321026 (JP 2005-321026 A)). This planetary gear unit includes: an internal gear and an external gear (sun gear) that are supported such that the internal and external gears are coaxially rotatable relative to each other; a plurality of planet gears arranged between the internal gear and the external gear; a carrier that supports the planet gears such that the planet gears are rotatable and revolvable; and roller bearings that make rotation of the planet gears smooth.

The carrier of the planetary gear unit described in JP 2005-321026 has a pair of annular plates interposing the planet gears in the axial direction therebetween, and a plurality of support shafts inserted through the centers of the planet gears. The roller bearing having a plurality of needle rollers is disposed between the planet gear and the support shaft. The support shaft has both ends fitted in through holes formed in the pair of annular plates and is restrained from rotating. The support shaft is made of a cylindrical steel material and has a hollow hole drilled from a one axial end face of the support shaft. The hollow hole is a blind hole that does not extend through the support shaft. An opening at one end of the hollow hole is closed by a plug.

The plug is molded by drawing as follows. A flat sheet of a plug material is placed on the end face of the opening of the hollow hole of the support shaft and is press-fitted into the hollow hole with a punch so as to have a bottomed cylindrical shape. The support shaft has a lubricating oil supply inlet port and a lubricating oil supply outlet port. Lubricating oil is introduced into the hollow hole through the lubricating oil supply inlet port, and the lubricating oil introduced into the hollow hole is supplied to the roller bearing through the lubricating oil supply outlet port. One of the pair of annular plates has an oil groove in a side surface of the annular plate, and the oil groove communicates with the lubricating oil support inlet port. Lubricating oil is introduced from the oil groove into the hollow hole through the lubricating oil supply inlet port due to the centrifugal force generated by rotation of the carrier. The plug inhibits leakage of the lubricating oil introduced into the hollow hole.

SUMMARY

When manufacturing this support shaft, a lot of material is wasted as the hollow hole is drilled. It is also difficult to reduce cost as the process of molding the plug by drawing is required. Moreover, in a method in which the hollow hole is drilled and the plug is press-fitted therein, metal powder tends to be produced during drilling. When such metal powder remains in the hollow hole, it affects smooth rotation of the planet gear. Accordingly, a process of sufficiently cleaning the hollow hole after attaching the plug may be required, and this cleaning process may also contribute to an increase in cost.

The disclosure provides a planet gear support shaft, a method for manufacturing the planet gear support shaft, and a planetary gear unit that achieve reduction in cost.

A first aspect of the disclosure provides a planet gear support shaft that is inserted through a shaft hole of a planet gear to support the planet gear. The planet gear is disposed between an internal gear and an external gear that are supported such that the internal gear and the external gear are coaxially rotatable relative to each other. The planet gear support shaft includes a cylindrical body that is open at both ends in a central axis direction. The cylindrical body has an inlet port through which lubricating oil is introduced into a hollow portion of the cylindrical body, and a discharge port through which the lubricating oil introduced into the hollow portion is discharged. The inlet port and the discharge port are open to an inner peripheral surface of the hollow portion at different positions in the central axis direction. An oil guide groove is provided between a first opening of the inlet port and a second opening of the discharge port in the inner peripheral surface. The oil guide groove is configured to guide the lubricating oil between the first opening and the second opening.

A second aspect of the disclosure provides a method for manufacturing a planet gear support shaft that is inserted through a shaft hole of a planet gear to support the planet gear, the planet gear being disposed between an internal gear and an external gear that are supported such that the internal gear and the external gear are coaxially rotatable relative to each other. The method includes: cutting a steel pipe to a predetermined length to obtain a cylindrical pipe; drilling an inlet port and a discharge port at different positions of the cylindrical pipe in a central axis direction such that the inlet port and the discharge port extend from an inner peripheral surface to an outer peripheral surface of the cylindrical pipe; and cutting an inner peripheral surface of the cylindrical pipe to form between a first opening of the inlet port and a second opening of the discharge port an oil guide groove that guides lubricating oil between the first opening and the second opening.

A third aspect of the disclosure provides a planetary gear unit. The planetary gear unit includes: an internal gear and an external gear that are supported such that the internal gear and the external gear are coaxially rotatable relative to each other; a planet gear disposed between the internal gear and the external gear; and a carrier that supports the planet gear such that the planet gear is rotatable and revolvable. The carrier includes a frame that is coaxially rotatable relative to the internal gear and the external gear, and the support shaft attached to the frame to support the planet gear.

The above configuration achieves reduction in cost for the planet gear support shaft and the planet gear unit.

DETAILED DESCRIPTION OF EMBODIMENTS

First Embodiment

An embodiment of the disclosure will be described with reference toFIGS. 1 to 4D. The embodiments described below are intended to show specific examples that are suitable for carrying out the disclosure. Although various technical matters that are technically preferable are described specifically in some parts of the embodiments, the technical scope of the disclosure is not limited by the specific embodiments.

Overall Configuration of Planetary Gear Unit

FIG. 1is an exploded perspective view of a planetary gear unit using planet gear support shafts (hereinafter referred to as the “support shafts”) according to the present embodiment.FIGS. 2A and 2Billustrate a planet gear and the support shaft.FIG. 2Ais a sectional view taken in the axial direction, andFIG. 2Bis a sectional view taken along line IIB-IIB inFIG. 2A, namely taken in a direction perpendicular to the axial direction.

A planetary gear unit1includes an external gear2, an internal gear3, a plurality of (in the present embodiment, three) planet gears4, a carrier6, and roller bearings7. The external gear2has external teeth21on an outer peripheral surface of the external gear2. The internal gear3has internal teeth31on an inner peripheral surface of the internal gear3. The planet gears4are arranged between the external gear2and the internal gear3and have external teeth41meshing with the external teeth21and the internal teeth31. The carrier6includes a plurality of (three) support shafts5supporting the respective planet gears4. Each of the roller bearings7is disposed between a corresponding one of the planet gears4and a corresponding one of the support shafts5. The external gear2, the internal gear3, and the carrier6are supported such that the external gear2, the internal gear3, and the carrier6are coaxially rotatable relative to each other. The carrier6supports the planet gears4such that the planet gears4are rotatable and revolvable.

For example, the planetary gear unit1is used for a transmission for changing the speed of rotation of a rotary shaft (crankshaft) of an engine that is a driving source for an automobile. When one of the three elements of the planetary gear unit1, namely one of the external gear2, the internal gear3, and the carrier6, is held stationary and torque is input to another one of the three elements, the input torque is reduced or increased in speed and transmitted to the remaining one element. Sliding of each part of the planetary gear unit1is made smooth by lubricating oil (e.g., transmission oil). InFIG. 1, the rotation direction in the case where the carrier6is rotated is indicated by an arrow A.

The external gear2has a shaft20fixed in the center of the external gear2such that the external gear2and the shaft20are not rotatable relative to each other. The external gear2is disposed concentrically with the internal gear3and the carrier6. Each planet gear4has a shaft hole40extending through the center of the planet gear4and has the support shaft5inserted through the shaft hole40. Each planet gear4is thus supported by the support shaft5via the roller bearing7. Each roller bearing7has a plurality of needle rollers71and a cage72holding the needle rollers71. The needle rollers71roll on an inner peripheral surface40aof the shaft hole40of the planet gear4and an outer peripheral surface5aof the support shaft5.

For example, when the internal gear3is held stationary and the shaft20is rotated, rotation of the external gear2that rotates with the shaft20is reduced in speed and output to an output shaft, not shown, that rotates with the carrier6. At this time, the planet gears4revolve around the rotation axis O of the shaft20, and each planet gear4rotates about a central axis C of the support shaft5. A direction parallel to the central axis C is hereinafter referred to as a central axis direction.

Configuration of Carrier6

the carrier6is comprised of a frame60and the plurality of (in the present embodiment, three) support shafts5attached to the frame60. The frame60is coaxially rotatable relative to the external gear2and the internal gear3about the rotation axis O. The frame60includes a first annular plate61, a second annular plate62, a connection wall63, and a fitting cylinder64. The first and second annular plates61,62are a pair of plates interposing the planet gears4in the axial direction therebetween. The connection wall63connects radial outer ends of the first and second annular plates61,62. The fitting cylinder64is fixed to a radial inner end of the first annular plate61. The fitting cylinder64has a plurality of spline ridges641on an inner periphery of the fitting cylinder64. For example, the output shaft is inserted through the fitting cylinder64and is spline-fitted therein.

Configuration of Support Shaft5

Each support shaft5has a one axial end fitted in a fitting hole610provided in the first annular plate61and the other axial end fitted in a fitting hole620provided in the second annular plate62. The support shaft5is a cylindrical body obtained by cutting a steel pipe to a predetermined length and is open at both ends in the central axis direction. The steel pipe is a material formed in a tubular shape in advance, and examples of the steel pipe include a seamless steel pipe produced by a rolling mill and a straight seam steel pipe produced by forming a plate material into a tubular shape by a tube mill.

the support shaft5has an inlet port501and a discharge port502. Lubricating oil is introduced into a hollow portion50of the support shaft5through the inlet port501, and the lubricating oil introduced into the hollow portion50is discharged from the hollow portion50through the discharge port502. In the present embodiment, the support shaft5has a single inlet port501and a single discharge port502. However, the support shaft5may have a plurality of inlet port501or a plurality of discharge ports502. The inlet port501and the discharge port502are open to an inner peripheral surface50aof the hollow portion50at different positions in the central axis direction. More specifically, the inlet port501is open to the inner peripheral surface50aat a position near one end of the hollow portion50in the central axis direction, and the discharge port502is open to the inner peripheral surface50aat a position near the center of the hollow portion50in the central axis direction.

The second annular plate62has an oil supply passage621communicating with the inlet port501. One end621aof the oil supply passage621is open to an inner peripheral surface62aof the second annular plate62, and the other end621bthereof is open to the fitting hole620. Lubricating oil having entered the oil supply passage621through the one end621aflows due to the centrifugal force generated by rotation of the carrier6and thus flows into the inlet port501through the other end621b. The inlet port501is open to the outer peripheral surface5aof the support shaft5and the inner peripheral surface50aof the hollow portion50, and the lubricating oil having entered the inlet port501from the oil supply passage621is supplied to the hollow portion50through the inlet port501. In the present embodiment, the inlet port501is tilted with respect to the radial direction of the support shaft5such that the inlet port501is open on the hollow portion50side at a position located closer to the center of the support shaft5in the central axial direction than a position at which the inlet port501is open on the oil supply passage621side.

The lubricating oil supplied to the hollow portion50flows in the hollow portion50and is discharged from the hollow portion50through the discharge port502. The discharge port502is formed in the support shaft5at the outermost position in the radial direction of the frame60and is open to the inner peripheral surface50aof the hollow portion50and the outer peripheral surface5aof the support shaft5. The lubricating oil discharged through the discharge port502is supplied to the roller bearing7and smoothens, for example, sliding between the needle rollers71and the cage72.

The support shaft5further has a positioning fitting hole503at an end on the first annular plate61side. A positioning pin65is fitted in the positioning fitting hole503. The positioning pin65is press-fitted in a pin hole611provided in the first annular plate61, and the tip end of the positioning pin65is fitted in the positioning fitting hole503. The positioning pin65restrains the support shaft5from rotating with respect to the frame60and positions the support shaft5in the axial direction.

The support shaft5is a cylindrical body that is open at both ends in the central axis direction as described above. Lubricating oil introduced into the hollow portion50through the inlet port501is therefore more likely to flow out through openings5b,5cat respective ends of the support shaft5in the central axis direction, as compared to a support shaft having an end closed by a plug as in the conventional example. Accordingly, in the present embodiment, first and second oil guide grooves51,52are formed between the opening of the inlet port501and the opening of the discharge port502in the inner peripheral surface50aof the hollow portion50. The first and second oil guide grooves51,52guide lubricating oil between the opening of the inlet port501and the opening of the discharge port502. The first and second oil guide grooves51,52will be described in detail below.

FIGS. 3A and 3Bshow the support shaft5.FIG. 3Ais a sectional view of the support shaft5taken along the central axis C, andFIG. 3Bis a sectional perspective view of the support shaft5in the section ofFIG. 3A. InFIGS. 3A and 3B, reference character501adenotes the opening of the inlet port501in the inner peripheral surface50aof the hollow portion50, and reference character502adenotes the opening of the discharge port502in the inner peripheral surface50aof the hollow portion50. The first and second oil guide grooves51,52are formed between the openings501a,502ain the central axis direction.

The first oil guide groove51is formed in an annular shape of the inner peripheral surface50ain the circumferential direction. An inside diameter D1of the first oil guide groove51is larger than a minimum inside diameter D2of a part of the hollow portion50located on one side (inlet port501side) in the central axis direction with respect to the first oil guide groove51and is larger than a minimum inside diameter D3of a part of the hollow portion50located on the other side in the central axis direction with respect to the first oil guide groove51. In the present embodiment, since the support shaft5is produced by cutting a steel pipe to a predetermined length, the minimum inside diameters D2, D3are equal to the inside diameter of the steel pipe.

At an end on the one side of the first oil guide groove51in the central axis direction, a stepped surface51bis formed between an inner peripheral surface51aof the first oil guide groove51and a part of the inner peripheral surface50aof the hollow portion50in which the first oil guide groove51is not formed. At an end on the other side of the first oil guide groove51in the central axis direction, a stepped surface51cis formed between the inner peripheral surface51aof the first oil guide groove51and a part of the inner peripheral surface50aof the hollow portion50in which the first oil guide groove51is not formed. These stepped surfaces51b,51crestrain lubricating oil introduced into the first oil guide groove51through the inlet port501from flowing out through the openings5b,5cat respective ends of the support shaft5.

The second oil guide groove52is helically formed so as to extend in a tilted manner with respect to the central axis direction. In the present embodiment, the entire second oil guide groove52is formed in the inner peripheral surface51aof the first oil guide groove51. The second oil guide groove52has one end communicating with the opening501aof the inlet port501and the other end communicating with the opening502aof the discharge port502. The second oil guide groove52extends in such a direction that, when the carrier6is rotated in the direction of arrow A (seeFIG. 1), lubricating oil in the second oil guide groove52flows from the opening501aof the inlet port501toward the opening502aof the discharge port502due to the centrifugal force and gravity.

Method for Manufacturing Support Shaft5

Next, a method for manufacturing the support shaft5will be described. The support shaft5is manufactured by a cutting process of cutting a steel pipe to a predetermined length to obtain a cylindrical pipe, a drilling process of drilling the inlet port501and the discharge port502, and a cutting process of forming the first and second oil guide grooves51,52. Each process will be described in detail below with reference toFIGS. 4A to 4D.

FIG. 4Aillustrates the cutting process. In the cutting process, a steel pipe (pipe P) is cut to a predetermined length using, for example, a circular saw81to obtain a short cylindrical pipe500. The cylindrical pipe500has a cylindrical shape having inside diameter that is D2and D3shown inFIG. 3Aand having inside and outside diameters that are constant along the entire length in a longitudinal direction.

FIG. 4Billustrates a first cutting process of cutting an inner peripheral surface500aof the cylindrical pipe500obtained by the cutting process to form the first oil guide groove51. The inner peripheral surface500ais cut using a cutting tip82by a turning process. The inside diameter of a part of the cylindrical pipe500in the longitudinal direction is increased to D1shown inFIG. 3Aby the first cutting process.

FIG. 4Cillustrates a second cutting process of forming the helical second oil guide groove52in the inner peripheral surface51aof the first oil guide groove51formed in the first cutting process. In the second cutting process, the second oil guide groove52is formed by using, for example, a ball end mill83.

FIG. 4Dillustrates the drilling process of forming the inlet port501and the discharge port502with drills84,85. The support shaft5is thus finished. The drilling process may be performed either before the first and second cutting processes or between the first and second cutting processes.

Functions and Effects of First Embodiment

According to the first embodiment described above, lubricating oil introduced into the hollow portion50through the inlet port501is guided to the discharge port502by the first and second oil guide grooves51,52, and the lubricating oil is restrained from flowing out through the openings5b,5cat respective ends of the support shaft5without closing both ends of the cylindrical pipe500. Even if chips are produced in the first and second cutting process or the drilling process, the hollow portion50can be easily and reliably cleaned. Reduction in cost for the support shaft5and the planetary gear unit1is thus achieved.

Second Embodiment

A second embodiment of the disclosure will be described with reference toFIGS. 5A and 5B.FIGS. 5A and 5Bshow a support shaft5A according to the second embodiment.FIG. 5Ais a sectional view of the support shaft5A taken along the central axis C, andFIG. 5Bis a sectional perspective view of the support shaft5A in the section ofFIG. 5A. InFIGS. 5A and 5B, components corresponding to those described in the first embodiment are denoted by the same reference characters, and description thereof will not be repeated.

The first embodiment is described with respect to the case where the annular first oil guide groove51extending in the circumferential direction and the helical second oil guide groove52are formed in the inner peripheral surface50aof the hollow portion50. However, the support shaft5A according to the present embodiment only has the annular first oil guide groove51.

This support shaft5A also has functions and effects similar to those of the first embodiment. Moreover, since the second cutting process is not necessary in the second embodiment, further reduction in cost is achieved.

Third Embodiment

A third embodiment of the disclosure will be described with reference toFIGS. 6A and 6B.FIGS. 6A and 6Bshow a support shaft5B according to the third embodiment.FIG. 6Ais a sectional view of the support shaft5B taken along the central axis C, andFIG. 6Bis a sectional perspective view of the support shaft5B in the section ofFIG. 6A. InFIGS. 6A and 6B, components corresponding to those described in the first embodiment are denoted by the same reference characters, and description thereof will not be repeated.

The support shaft5B according to the third embodiment is a modification of the support shaft5A according to the second embodiment. The inner peripheral surface51a, which is the bottom surface of the first oil guide groove51, is tilted such that a radial distance from the inner peripheral surface51ato the central axis C of the hollow portion50is larger on the opening502aside than on the opening501aside. That is, in the present embodiment, the first oil guide groove51has such a tapered shape that the inside diameter is larger on the discharge port502side than on the inlet port501side, and the inside diameter D4at the larger diameter end of the first oil guide groove51is larger than the inside diameter D1at the smaller diameter end of the first oil guide groove51.

This support shaft5B also has functions and effects similar to those of the first embodiment. Moreover, lubricating oil flows more easily toward the discharge port502due to the centrifugal force generated by revolution of the carrier6, as compared to the case where the inner peripheral surface51aof the first oil guide groove51is parallel to the central axis C. A larger amount of lubricating oil can thus be supplied to the roller bearing7.

In the example illustrated inFIGS. 6A and 6B, the entire first oil guide groove51has a tapered shape. However, the support shaft5B has the above effect, namely lubricating oil flows more easily toward the discharge port502, as long as at least a part of the first oil guide groove51has a tapered shape. In other words, it is only necessary that at least a part of the inner peripheral surface51aof the first oil guide groove51be tilted such that the radial distance from the inner peripheral surface51ato the central axis C of the hollow portion50is larger on the opening502aside than on the opening501aside. The helical second oil guide groove52may be formed in the inner peripheral surface51aof the tapered first oil guide groove51.

Fourth Embodiment

A fourth embodiment of the disclosure will be described with reference toFIGS. 7A and 7B.FIGS. 7A and 7Bshow a support shaft5C according to the fourth embodiment.FIG. 7Ais a sectional view of the support shaft5C taken along the central axis C, andFIG. 7Bis a sectional perspective view of the support shaft5C in the section ofFIG. 7A. InFIGS. 7A and 7B, components corresponding to those described in the first embodiment are denoted by the same reference characters, and description thereof will not be repeated.

The support shaft5of the first embodiment is described with respect to the case where the second oil guide groove52is formed in the inner peripheral surface51aof the first oil guide groove51. However, the support shaft5C of the present embodiment does not have the first oil guide groove51and has the helical second oil guide groove52in the inner peripheral surface50aof the hollow portion50that is the inner peripheral surface of a steel pipe as a material.

The support shaft5C also has functions and effects similar to those of the first embodiment. Moreover, since the first cutting process is not necessary in the fourth embodiment, further reduction in cost is achieved.

Fifth Embodiment

A fifth embodiment of the disclosure will be described with reference toFIGS. 8A and 8B.FIGS. 8A and 8Bshow a support shaft5D according to the fifth embodiment.FIG. 8Ais a sectional view of the support shaft5D taken along the central axis C, andFIG. 8Bis a sectional perspective view of the support shaft5D in the section ofFIG. 8A. InFIGS. 8A and 8B, components corresponding to those described in the first embodiment are denoted by the same reference characters, and description thereof will not be repeated.

The support shaft5D has an oil guide groove53in the inner peripheral surface50aof the hollow portion50that is the inner peripheral surface of a steel pipe as a material. The oil guide groove53has a circumferential groove531and an axial groove532that communicate with each other. The circumferential groove531extends in the circumferential direction of the inner peripheral surface50aof the hollow portion50from the opening501aof the inlet port501. The axial groove532extends from the circumferential groove531toward the opening502aof the discharge port502. In the example illustrated inFIGS. 8A and 8B, the axial groove532is parallel to the central axis C, and the axial groove532and the circumferential groove531meet at right angles. However, the axial groove532may be tilted with respect to the central axis direction, and the circumferential groove531and the axial groove532may meet at an obtuse angle or an acute angle.

In the support shaft5D, lubricating oil introduced through the inlet port501flows through the circumferential groove531toward the axial groove532and further flows through the axial groove532toward the discharge port502due to the centrifugal force or gravity. The support shaft5D thus has functions and effects similar to those of the first embodiment. The oil guide groove53may be formed in the inner peripheral surface51aof the first oil guide groove51according to the second or third embodiment.

Although the embodiments of the disclosure are described above, these embodiments are not intended to limit the disclosure according to the claims. It should be understood that not all of the combinations of the features described in the embodiments are essential to solve the problems of the disclosure. The disclosure can be modified as appropriate without departing from the spirit and scope of the disclosure.