JP2009168164A - Pinion shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pinion shaft suppressing deterioration of material strength accompanied by hardening and hardly causing damage and abrasion. <P>SOLUTION: A planetary gear device is provided with a sun gear 1, a ring gear 2 arranged concentrically with the sun gear 1, and a pinion gear 3 engaged with the sun gear 1 and ring gear 2. Since the pinion shaft 5 is inserted into the center hole 3a of the pinion gear 3 and a needle roller is arranged between the outer peripheral surface of the pinion shaft 5 and the inner peripheral surface of the center hole 3a of the pinion gear 3, the pinion gear 3 can rotate freely with the pinion shaft 5 as an axis. A groove 12 is formed in the axial end surface 5a of the pinion shaft 5, and a surface hardened layer 14 applied with induction hardening is formed on the outer peripheral surface 5b of the pinion shaft. A difference between Vickers hardness of the surface hardened layer 14 and Vickers hardness of an unhardened portion 15 is not less than 350 nor more than 550. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pinion shaft used in a planetary gear device.

For example, a planetary gear set used in an automatic transmission of an automobile includes a sun gear, a ring gear, and a carrier, and these rotating elements are arranged concentrically around an output shaft. Further, a pinion gear meshing with the sun gear and the ring gear is rotatably supported on a pinion shaft fixed to the carrier via bearing rollers.
When the roller rolls on the outer peripheral surface (rolling surface) of the pinion shaft, a high contact stress of several GPa is generated. For this reason, the material used for the pinion shaft is required to be hard and to withstand a load, to have excellent rolling fatigue life, and to have good wear resistance against sliding. Conventionally, for example, bearing steels such as SUJ2 and SUJ3, case-hardening materials such as SCM420, and induction hardening materials such as SK5 are used.

Further, since the pinion shaft is repeatedly subjected to shear stress under a high surface pressure of several GPa on the rolling surface, it is required to withstand the shear stress and to have excellent rolling fatigue life. In order to satisfy these requirements, conventionally, for example, SUJ2 and SUJ3 are subjected to heat treatment such as carburizing and carbonitriding, and then subjected to induction hardening to ensure surface hardness and provide rolling fatigue life. It is improving.
Japanese Patent Laid-Open No. 2002-4003

However, in induction hardening, it is rapidly cooled after being heated to a high temperature instantaneously, but during the heating process, a large volume expansion occurs on the surface of the pinion shaft, and heat treatment distortion due to martensitic transformation occurs on both axial ends and inside. There was a case. Further, in the rapid cooling process, excessive internal stress may be generated in the material due to the occurrence of thermal distortion (due to thermal expansion) due to the temperature difference between the quenched portion and the non-quenched portion. And since the intensity | strength of material itself falls by such heat processing distortion and internal stress, there existed a tendency for a pinion shaft to generate | occur | produce a breakage and abrasion easily. In particular, in the case of a pinion shaft having a groove on the end face in the axial direction, stress tends to concentrate on the edge portion of the groove, so that the strength of the material of the stress concentration portion may be greatly reduced.
Therefore, an object of the present invention is to solve the above-described problems of the prior art and to provide a pinion shaft in which a decrease in material strength due to quenching is suppressed and damage and wear are unlikely to occur.

In order to solve the above-described problems, the present invention has the following configuration. That is, the pinion shaft according to claim 1 of the present invention is a pinion shaft that is used in a planetary gear device and is inserted into a center hole of a pinion gear that meshes with a sun gear and a ring gear that are concentrically arranged to rotatably support the pinion gear. Thus, the following three conditions are satisfied.
Condition A: A groove is provided on at least one of both axial end faces.
Condition B: A surface hardened layer by induction hardening is formed on the outer peripheral surface.
Condition C: The difference between the Vickers hardness of the surface hardened layer and the Vickers hardness of the non-hardened portion other than the surface hardened layer is 350 or more and 550 or less.

The pinion shaft according to claim 2 of the present invention is characterized in that, in the pinion shaft according to claim 1, the following two conditions are further satisfied.
Condition D: The axial length is not less than 5 times the diameter.
Condition E: The hardened surface layer is formed at the axial center portion of the outer peripheral surface and is not formed at both axial end portions, and the axial distance from the axial end surface to the hardened surface layer is 5 mm or more. It is.

  In the pinion shaft of the present invention, since the decrease in material strength accompanying quenching is suppressed, even if the pinion shaft has a portion where stress generated by quenching tends to concentrate, breakage and wear hardly occur.

  An embodiment of a pinion shaft according to the present invention will be described in detail with reference to the drawings. 1 includes a sun gear 1 through which a shaft (not shown) is inserted, a ring gear 2 disposed concentrically with the sun gear 1, and one or more meshing with the sun gear 1 and the ring gear 2 (three in FIG. 1). ) And a carrier 4 that is arranged concentrically with the sun gear 1 and the ring gear 2 and rotatably supports the pinion gear 3.

  A pinion shaft 5 fixed to the carrier 4 by conventional fixing means such as caulking is inserted into the center hole 3a formed in the pinion gear 3, and the outer peripheral surface of the pinion shaft 5 and the center hole 3a of the pinion gear 3 are inserted. A plurality of needle rollers (not shown) are disposed between the inner peripheral surface and the pinion gear 3 so as to be rotatable about the pinion shaft 5.

Next, the pinion shaft 5 will be described in detail with reference to FIG. The pinion shaft 5 is made of a steel material such as high carbon chromium bearing steel (SUJ2). However, the type of steel material is not limited to SUJ2, and other types of bearing steel such as SUJ3, case-hardened materials such as SCM420, and induction-hardened materials such as SK5 may be used.
The pinion shaft 5 is provided with a lubricating oil supply passage 10, and the lubricating oil injected into the opening 10 a that opens in one of the axial end faces 5 a, 5 a opens to the outer peripheral surface 5 b (cylindrical surface). The oil supply port 10b is supplied to the rolling surface (the portion of the outer peripheral surface 5b where the needle rollers roll).

  Moreover, the groove | channel 12 for alignment of the oil filler opening 10b is formed in the other of axial direction both end surface 5a, 5a. That is, since the lubrication is controlled by the position of the oil supply port 10b, the groove 12 is arranged so that the oil supply port 10b has a predetermined positional relationship with respect to the center of the carrier 4 when the pinion shaft 5 is fixed to the carrier 4. (For example, so that the fuel filler opening 10b faces the center of the carrier 4). In addition, the groove | channel 12 may be formed in the axial direction both end surfaces 5a and 5a.

  Further, the pinion shaft 5 is subjected to carburizing or carbonitriding and annealing, and subsequently, only the rolling surface of the outer peripheral surface 5 b of the pinion shaft 5 is subjected to induction hardening. The surface hardening layer 14 is formed on the rolling surface by this induction hardening. The portions other than the surface hardened layer 14, that is, the inner portion of the surface hardened layer 14 (the central portion in the radial direction of the pinion shaft 5) and both axial end portions are not hardened and are not hardened. Induction hardening is performed so that the difference in Vickers hardness between the surface hardened layer 14 and the non-hardened portion 15 is 350 or more and 550 or less.

  As described above, during induction hardening, the strength of the material itself may decrease due to heat treatment distortion or internal stress. Particularly, in the case of a pinion shaft having a groove on the axial end surface, stress is applied to the edge of the groove. Since it tends to concentrate, the strength of the material of the stress concentration portion may be greatly reduced. As a result, the pinion shaft tended to be easily broken and worn, such as cracks and cracks.

  However, in the pinion shaft 5 of the present embodiment, since the hardness of the surface hardened layer 14 is defined as described above, the heat treatment distortion and internal stress described above are unlikely to occur during induction hardening. Therefore, a decrease in material strength due to heat treatment distortion and internal stress is suppressed, and even when the axial end surface 5a has the groove 12 and a stress concentration portion exists, a decrease in material strength of the stress concentration portion is suppressed. Therefore, the pinion shaft 5 of the present embodiment is not easily damaged or worn. The planetary gear device of this embodiment including such a pinion shaft 5 can be suitably used for an automatic transmission of an automobile.

  When the difference between the Vickers hardness of the surface hardened layer 14 and the Vickers hardness of the non-cured portion 15 is less than 350 (that is, when the difference between the two hardnesses is small), the toughness of the axial end portion becomes low. There is a risk that the strength of the material itself may be reduced by the heat treatment distortion and internal stress. In particular, when the groove 12 is provided on the axial end face 5a and a stress concentration portion exists, the strength of the material itself of the stress concentration portion tends to decrease.

On the other hand, if the difference between the two hardnesses exceeds 550, the Vickers hardness of the non-cured portion 15 may be insufficient, so it is necessary when fixing the axial end of the pinion shaft 5 to the carrier 4. May not be satisfactory, and the axial end portion may be worn.
The dimension of the pinion shaft 5 is not particularly limited, but the axial length L is preferably 5 times or more the diameter d. If it is less than 5 times, heat treatment distortion and internal stress generated during induction quenching increase, and therefore, when the axial end surface 5a has the groove 12 and there is a stress concentration portion, the stress concentration portion The strength of the material itself may be reduced.

  Further, since the hardened surface layer 14 is formed only on the rolling surface (axially central portion) of the outer peripheral surface 5b of the pinion shaft 5, it is not formed at both axial end portions of the outer peripheral surface 5b. The axial distance A between the portion of the hardened layer 14 (effective hardened layer) closest to the axial end surface 5a and the axial end surface 5a is preferably 5 mm or more. If it does so, the impact resistance at the time of an impact etc. being applied from the outside to the stress concentration part of the groove | channel 12 of the axial direction end surface 5a will become high.

〔Example〕
Hereinafter, the present invention will be described with reference to more specific examples. A pinion shaft was manufactured by turning a steel material made of SUJ2 or SUJ3 to a predetermined size, then subjecting to a heat treatment to be described later, and further performing a finish grinding process. Table 1 shows the diameter d and length L of the pinion shaft obtained, the Vickers hardness H1 of the surface hardened layer, the Vickers hardness H2 of the non-cured portion, and the difference H1−H2 between the two hardnesses. A linear groove passing through the center of the end face is formed on the end face in the axial direction of the pinion shaft. The width of this groove is 1 mm, the depth is 1 mm, and the length is the same as the diameter d.

The contents of the heat treatment are as follows. The turned steel material was carbonitrided and then subjected to high temperature tempering. Subsequently, induction quenching was performed only on the portion of the outer peripheral surface that would be the rolling surface, followed by low temperature tempering.
When the heat treatment was completed, the end surfaces in the axial direction of these pinion shafts were observed with an optical microscope to investigate whether the grooves were damaged. The results are shown in Table 1. In the pinion shafts of Examples 1 to 4, the difference in both hardnesses H1 to H2 was in the range of 350 to 550, and no breakage was observed in the grooves. On the other hand, the pinion shafts of Comparative Examples 1 and 3 had a difference in hardness between H1 and H2 of less than 350, so that the grooves were damaged.

Furthermore, the abrasion test of these pinion shafts was performed using a planetary needle testing machine manufactured by NSK Ltd. That is, the range within 5 mm of both axial ends of the pinion shaft was fixed with S45C material, and a load of 0 to 1000 N was repeatedly applied for 20 hours. And the presence or absence of abrasion of an axial direction end surface was investigated by measuring the shape of an axial direction end surface using a surf comb shape measuring device. The results are shown in Table 1.
In the pinion shafts of Examples 1 to 4, since the difference H1-H2 in both hardnesses was in the range of 350 to 550, no abrasion was observed on the axial end face. In contrast, in the pinion shafts of Comparative Examples 2 and 4, since the difference H1-H2 between the two hardnesses exceeded 550, wear was observed on the axial end surface.

  Next, a pinion shaft was manufactured in the same manner as described above, and a strength test was performed. Table 2 shows the diameter d, the length L, and the ratio L / d of the obtained pinion shaft. Table 2 also shows the Vickers hardness H1 of the surface hardened layer, the Vickers hardness H2 of the non-cured portion, and the difference H1−H2 between the two hardnesses. Further, Table 2 shows the axial distance A between the portion of the surface hardened layer (effective hardened layer) closest to the axial end face and the axial end face. A linear groove passing through the center of the end face is formed on the end face in the axial direction of the pinion shaft. The width of this groove is 1 mm, the depth is 1.5 mm, and the length is the same as the diameter d.

The strength tests of these pinion shafts were performed using a planetary needle tester manufactured by NSK Ltd. That is, the time until the axial end surface of the pinion shaft is damaged within 5 mm is fixed with S45C material, a load of 0 to 5000 N is repeatedly applied to the axial central portion of the pinion shaft, and the groove on the axial end surface is damaged. Was measured. The results are shown in Table 2.
Since the pinion shafts of Examples 12, 13, 15, and 16 have an axial distance A of 5 mm or more, compared to Examples 11 and 14 in which the axial distance A is less than 5 mm, a repeated load is applied. Also, it was difficult for the groove to break.

It is a disassembled perspective view of the planetary gear apparatus provided with the pinion shaft which is one Embodiment of this invention. It is sectional drawing of a pinion shaft.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sun gear 2 Ring gear 3 Pinion gear 3a Center hole 4 Carrier 5 Pinion shaft 5a Axial end surface 5b Outer peripheral surface 12 Groove 14 Surface hardening layer 15 Non-hardening part

Claims (2)

A pinion shaft that is used in a planetary gear device and is inserted through a central hole of a pinion gear that meshes with a sun gear and a ring gear that are concentrically arranged to rotatably support the pinion gear, and satisfies the following three conditions: And pinion shaft.
Condition A: A groove is provided on at least one of both axial end faces.
Condition B: A surface hardened layer by induction hardening is formed on the outer peripheral surface.
Condition C: The difference between the Vickers hardness of the surface hardened layer and the Vickers hardness of the non-hardened portion other than the surface hardened layer is 350 or more and 550 or less. Furthermore, the following two conditions are satisfied, The pinion shaft of Claim 1 characterized by the above-mentioned.
Condition D: The axial length is not less than 5 times the diameter.
Condition E: The hardened surface layer is formed at the axial center portion of the outer peripheral surface and is not formed at both axial end portions, and the axial distance from the axial end surface to the hardened surface layer is 5 mm or more. It is.

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