JP2006292026A - Supporting shaft for planetary gear - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a supporting shaft for a planetary gear preventing the occurrence of serious damage leading to breakage even in the case of having a part liable to fall in strength like the opening peripheral edge parts of an axial center hole 14 and branch holes 15, 15 for feeding lubricating oil. <P>SOLUTION: A surface hardened layer 17 with a hardness of Hv550 or more is formed at a surface layer part including an outer peripheral surface 16 by high frequency heat treatment. The effective hardened layer depth h of the surface hardened layer 17 is regulated to ≤0.75 times as long as a distance H from the inner peripheral surface 18 of the axial center hole 14 to the outer peripheral surface 16. With this constitution, cracks initiated at the opening peripheral edge parts of the respective branch holes 15, 15 are prevented from propagating to the inner peripheral surface 18 of the axial center hole 14 to solve the problem. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The planetary gear support shaft of the present invention is an improvement of the planetary gear support shaft for rotatably supporting a planetary gear incorporated in a planetary gear device that constitutes, for example, an automatic transmission for automobiles or a trans-askicle with respect to a carrier. About.

  BACKGROUND ART Conventionally, planetary gear devices constituting an automatic transmission for automobiles are widely known and widely implemented as described in many publications such as Patent Documents 1 to 4, for example. As shown in FIGS. 2 to 4, for example, this conventionally known planetary gear device includes a sun gear 1 having teeth 1 a formed on the outer peripheral surface thereof and a concentric arrangement with the sun gear 1, and teeth 2 a on the inner peripheral surface thereof. A plurality (generally 3 to 4) of planetary gears 3 and 3 are arranged at equal intervals in the circumferential direction between the ring gear 2 and the ring gear 2. The teeth 3a formed on the outer peripheral surfaces of the plurality of planetary gears 3 and 3 are meshed with the teeth 1a and 2a.

  The plurality of planetary gears 3 and 3 are rotatably supported around the support shaft 4 via a plurality of needles 5 and 5, respectively. The base end portion (the right end portion in FIGS. 3 to 4) of each support shaft 4 is supported and fixed to a carrier 6 that is rotatable around the sun gear 1. In the illustrated example, the base end portion of each of the support shafts 4 is fitted into a through hole 7 a formed in the carrier 6 by an interference fit, and a locking pin 8 is provided between the support shaft 4 and the carrier 6. The support shafts 4 are prevented from falling off from the through holes 7a.

  In the illustrated example, the sun gear 1 is formed in a cylindrical shape, and the carrier 6 is formed in an annular shape with an L-shaped cross section. As shown in FIG. 3, the cylindrical portion 9 formed on the inner peripheral edge of the carrier 6 is spline-engaged with the outer peripheral surface of the rotating shaft 10. The sun gear 1 freely supports relative rotation with respect to the rotary shaft 10 around the rotary shaft 10. The ring gear 2 is supported around the members 1, 6, 10 so as to be rotatable relative to the members 1, 6, 10.

  Further, the tip end portions (left end portions in FIGS. 3 to 4) of the respective support shafts 4 are fitted and fixed in through holes 7b formed in the connecting plate 11 formed in an annular shape, and the tip portions of the respective support shafts 4 are fixed. They are linked together. A portion between the carrier 6 and the coupling plate 11 on the outer peripheral surface of the intermediate portion of the plurality of support shafts 4 is a cylindrical inner ring raceway 12. On the other hand, the inner peripheral surface of the planetary gear 3 is a cylindrical outer ring raceway 13. The needles 5, 5 are provided between the inner ring raceway 12 and the outer ring raceway 13, and the planetary gear 3 is placed around the intermediate portion of the support shaft 4 between the connecting plate 11 and the carrier 6. In addition, it is supported rotatably. In addition, as shown in FIG. 4, an axial center hole 14 and a branch hole 15 functioning as oil passage holes are provided inside each support shaft 4, and lubricating oil is applied to the installation portions of the needles 5 and 5. It can be sent freely. That is, the upstream end of the axial center hole 14 communicates with a lubricating oil supply passage 16 provided in the carrier 6, and both ends of the branch hole 15 are connected to the inner peripheral surface of the axial center hole 14. Open to the outer peripheral surface. Then, during operation of the planetary gear type transmission, the lubricating oil can be fed freely into the installation portions of the needles 5 and 5.

  In the planetary gear device configured to include the planetary gear 3 and the support shaft 4 as described above, for example, the rotary shaft 10 is a drive shaft or a driven shaft, and the center of the sun gear 1 or the ring gear 2 is a driven shaft. Or it couple | bonds with a drive shaft. Then, by switching which gears 1, 2, and 3 are rotatable and which gears 1, 2, and 3 are non-rotatable, the shift between the drive shaft and the driven shaft and the conversion of the rotation direction are switched. To do. Since the configuration and operation of such a planetary gear device itself are conventionally well known and are not related to the gist of the present invention, illustration and detailed description of the entire structure are omitted.

  Incidentally, during operation of the planetary gear device as described above, the outer peripheral surface of the support shaft 4 (inner ring raceway 12 of the radial needle bearing) or the surface layer portion is in rolling contact with the rolling surfaces of the needles 5 and 5. Based on this, a large surface pressure (high surface pressure) is applied, and a large contact stress reaching several GPa is generated in this surface layer portion. For this reason, conventionally, as the metal material constituting the support shaft 4, a material that is hard and can withstand a large load, has a long rolling fatigue life, and has good wear resistance against slipping has been selected and used. Specifically, case-hardened steel such as SCM420, induction-hardened steel such as SK5, and high carbon chrome bearing steel such as SUJ2 and SUJ3 are used.

  Further, since the outer peripheral surface or the surface layer portion of the support shaft 4 is repeatedly subjected to shear stress under high surface pressure based on the revolving motion of the needles 5 and 5, severe use conditions from the viewpoint of securing the rolling fatigue life. It becomes. For this reason, the surface layer portion of the support shaft 4 made of the metal material as described above is subjected to surface heat treatment such as carburizing treatment or carbonitriding treatment, regardless of the shear stress repeatedly applied. Endured) to ensure the rolling fatigue life of the surface layer portion. Further, the surface layer portion is subjected to high-frequency heat treatment in addition to the surface heat treatment (following the surface heat treatment) to ensure surface hardness and further improve the rolling fatigue life.

  However, in the case of the support shaft 4 incorporated in the planetary gear device, the following problems occur due to the unique shape and structure. That is, an axial center hole 14 is provided inside the support shaft 4 in order to supply lubricating oil to rolling contact portions between the rolling surfaces of the needles 5 and 5 and the inner ring raceway 12 and the outer ring raceway 13. And the branch hole 15 is formed. On the other hand, in order to improve the hardness of the surface layer portion of the support shaft 4, when the support shaft 4 is quenched with the high-frequency heat treatment, the surface of the support shaft 4 whose temperature has been raised by high-frequency heating is rapidly cooled. Therefore, cooling water is sprayed toward the surface of the support shaft 4. Therefore, at the time of the quenching operation, the surface of the support shaft 4 is cooled first and then is cooled toward the core. For this reason, heat treatment transformation stress and thermal internal stress are generated in the support shaft 4 in a temperature range where martensitic transformation starts on the surface of the support shaft 4 (for example, 200 to 300 ° C. in the case of SUJ2). Of these, the thermal internal stress is generated due to the difference in thermal expansion between the surface and the core portion based on the temperature difference between the surface of the support shaft 4 and the core portion.

  Such heat treatment transformation stress and thermal internal stress may be applied to a part of the support shaft 4 as a large tensile stress that leads to a crack. In particular, the edge portion of the axial center hole 14 and the branch hole 15 is thin and has a heat capacity such as an edge portion present at the peripheral edge portion of the opening existing on the surface (axial end surface or outer peripheral surface) of the support hole 4. When cooling water is sprayed directly on a small part, the temperature of this part drops rapidly, and this part may induce a thermal stress instantaneously and reduce the material strength of this part. If damage such as a crack occurs in this portion, this damage propagates to the core portion of the support shaft 4 and the entire support shaft 4 may be broken. Conventionally, since the force applied to the support shaft 4 during operation of the planetary gear type transmission is limited, there has been no failure such as breakage of the support shaft 4 as described above. On the other hand, in recent years, the force applied to the support shaft 4 tends to increase due to an increase in the output of an automobile engine, and the realization of a technique that can reliably prevent the above-described breakage is demanded.

JP 7-317885 A JP 11-270661 A JP 2002-235841 A Japanese Utility Model Publication No. 63-125254

  In view of the circumstances as described above, the present invention causes serious damage that leads to breakage even when it has a portion whose strength tends to decrease, such as the opening peripheral portion of the axial center hole for supplying lubricating oil. This invention was invented to realize a planetary gear support shaft that does not occur.

The planetary gear support shaft of the present invention has an axial center hole 14 at the center as shown in FIG. 1, for example, like the conventionally known planetary gear support shaft. Moreover, it has the branch holes 15 and 15 which penetrate the inner peripheral surface and outer peripheral surface of this axial direction center hole 14 as needed. And it uses in order to support the planetary gear 3 which comprises a planetary gear type transmission rotatably with respect to the carrier 6 (refer FIGS. 3-4).
In particular, in the planetary gear support shaft of the present invention, the surface layer portion including the outer peripheral surface 16 is formed by high-frequency heat treatment, and the hardness shown in FIG. 2, the effective hardened layer depth h of the hardened surface layer 17 is 0.75 times the distance H from the inner peripheral surface 18 of the axial center hole 14 to the outer peripheral surface 16. The following is regulated (h ≦ 0.75H).

  Note that the hardness of the surface hardened layer 17 formed by high-frequency heat treatment is highest at the outer peripheral surface 16 portion, and decreases as it goes from the outer peripheral surface 16 toward the core portion 19. Accordingly, the effective hardened layer depth h of the surface hardened layer 17 having a hardness of Hv550 or more is a radial distance from the outer peripheral surface 16 to a portion having a hardness of Hv550. In the case of the invention described in claim 2, it is a radial distance from the outer peripheral surface 16 to a portion having a hardness of Hv500. Incidentally, when viewed from the same sample, the value of the effective hardened layer depth h is larger when the hardness is Hv500 than when the hardness is Hv550. Therefore, the upper limit of the effective hardened layer depth h is smaller in claim 2 than in claim 1. The distance H from the inner peripheral surface 18 of the axial center hole 14 to the outer peripheral surface 16 is the distance between the outer diameter D of the planetary gear support shaft 4a and the inner diameter d of the axial center hole 14. The difference is 1/2 {H = (D−d) / 2}.

According to the present invention configured as described above, for a planetary gear having a required rolling fatigue life and having a portion whose strength tends to decrease, such as the opening peripheral edge of a hole for supplying lubricating oil. Even the support shaft 4a can effectively prevent a serious failure such as breakage.
First, since it has a surface hardened layer having a hardness Hv550 (or Hv500) at the effective hardened layer depth h and a hardness near the outer peripheral surface 16 larger than this, a rolling fatigue life of the surface can be secured.

  Further, since the effective hardened layer depth h of the surface hardened layer 17 is restricted to 0.75 times or less of the distance H from the inner peripheral surface 18 of the axial center hole 14 to the outer peripheral surface 16, the surface hardened At the time of induction hardening (high frequency heat treatment) for forming the layer 17, the strength of the metal material is reduced due to internal stress generated in the metal material constituting the support shaft 4 a for the planetary gear, and particularly the axial center hole 14. Even if the material strength of the peripheral edge of the opening of the (further holes 15, 15) is reduced, it is possible to prevent the occurrence of a serious failure based on this reduction. The reason for this is as follows.

  That is, by limiting the effective hardened layer depth h of the surface hardened layer 17 to the above range, a portion having excellent toughness is sufficiently provided on the inner diameter side of the surface hardened layer 17 (a portion closer to the core portion 19). It is left in a state where the radial thickness is secured. In other words, with respect to the radial direction of the support shaft 4a, a portion that supports the surface hardened layer 17 having a martensite structure by high-frequency heat treatment is sufficiently between the surface hardened layer 17 and the axial center hole 14. It exists in the state which secured the thickness dimension.

  Conversely, the effective hardened layer depth h of the surface hardened layer 17 is larger than 0.75 times the distance H from the inner peripheral surface 18 of the axial center hole 14 to the outer peripheral surface 16 (h > 0.75H), the radial thickness of the portion having excellent toughness that should support the surface hardened layer 17 becomes insufficient. And the crack which generate | occur | produced in a part of this surface hardening layer 17 (for example, opening peripheral part of the branch holes 15 and 15) propagates to the radial direction of the said support shaft 4a, and becomes easy to reach the said axial direction center hole 14. FIG. When this crack reaches the axial center hole 14, it becomes easy to lead to a serious failure such as breakage of the support shaft 4a.

  On the other hand, in the case of the present invention, cracks generated in a part of the surface hardened layer 17 by suppressing the effective hardened layer depth h of the surface hardened layer 17 to be small (h ≦ 0.75H). However, it is difficult to reach the axial center hole 14 so that a serious failure such as breakage of the support shaft 4a is difficult to occur.

An experiment conducted for confirming the effect of the present invention will be described. In this experiment, a support shaft 4a as schematically shown in FIG. 1 was used. Such a support shaft 4a was incorporated in a testing machine for a planetary gear type transmission manufactured by the applicant company, and a durability test was performed under the following conditions.
Outer diameter D of support shaft 4a = 16.7mm
Outer diameter of each needle 5, 5 (see FIGS. 3-4) = 3.5mm (total needle type)
Basic dynamic load rating of radial needle bearing C = 23000N
Same basic static load rating C ₀ = 24000N
Radial load applied during operation = 9000N
Rotational speed of planetary gear 3 (see FIGS. 3 to 4) = 6000 min ⁻¹
Calculated life of radial needle bearing L ₁₀ = 56 hours Lubricating oil type and oil temperature = ATF, 100 ° C

  In the durability test, the inner diameter d of the axial center hole 14 of the support shaft 4a and the effective hardened layer depth h of the surface hardened layer 17 were varied (three examples belonging to the technical scope of the present invention and the present invention). Comparative examples that deviate from the technical scope of the above were made different in three types (three types in total). Then, when at least one of the support shaft 4a, the needles 5, 5 and the planetary gear 3 (see FIGS. 2 to 4) is broken, the operation is stopped. Including the rolling fatigue life of the radial needle bearing. The results are shown in Table 1 below.

  As is apparent from Table 1 above, which shows the results of the durability test performed under the above-described conditions, the radial needle bearing incorporating the support shaft 4a belonging to the technical scope of the present invention has an excellent rolling fatigue life. In addition, it is possible to prevent the occurrence of cracks that lead to a serious failure such as breakage. On the other hand, in all of Comparative Examples 1 to 3, the effective hardened layer depth h of the surface hardened layer 17 is too large (h> 0.75H), and cracks reaching the axial center hole 14 occur. Not only did it occur, but the rolling fatigue life was also short. In the case of Comparative Examples 1 and 3, h> H, but in this state, the surface hardened layer 17 is located at a position where the surface center layer 14 is displaced from the axial center hole 14 in the axial direction. A state in which the inner circumferential surface 18 is reached inward in the radial direction.

  In order to perform the durability test described above, the high carbon chromium bearing steel type 2 (SUJ2) was used as the metal material constituting the support shaft 4a. However, when carrying out the present invention, other high carbon chrome bearing steels such as 3 or 4 types of high carbon chrome bearing steel (SUJ3, SUJ4), and case-hardened steel such as SCM420 as described above, Induction hardened steel such as SK5 can also be used.

Sectional drawing of the support shaft for planetary gears which shows the Example of this invention. The schematic side view which shows the 1st example of the planetary gear apparatus of a conventional structure. AA sectional drawing of FIG. Similarly partial expanded sectional view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sun gear 1a Tooth 2 Ring gear 2a Tooth 3 Planetary gear 3a Tooth 4, 4a Support shaft 5 Needle 6 Carrier 7a, 7b Through-hole 8 Locking pin 9 Cylindrical part 10 Rotating shaft 11 Connecting plate 12 Inner ring track 13 Outer ring track 14 Axis Direction center hole 15 Branch hole 16 Outer peripheral surface 17 Surface hardened layer 18 Inner peripheral surface 19 Core

Claims (2)

  A planetary opening that opens at one end surface in the axial direction and has an axial center hole that reaches the middle in the axial direction at the center, and supports the planetary gear constituting the planetary gear type transmission rotatably with respect to the carrier. In the gear support shaft, the effective hardened layer depth of the hardened surface layer having a hardness of Hv550 or higher formed by high frequency heat treatment on the surface layer portion including the outer peripheral surface is from the inner peripheral surface of the axial center hole. A planetary gear support shaft, wherein the distance to the outer peripheral surface is 0.75 times or less. The planetary gear support shaft according to claim 1, wherein the effective hardened layer depth is regulated by setting the hardness of the hardened surface layer to Hv500 or more.

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