JP2017207185A - Method of manufacturing pinion shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a pinion shaft having excellent durability and excellent plastic workability resulting from caulking.SOLUTION: A method of manufacturing a pinion shaft 4 includes: a working step of cutting an axial end surface of a substantially columnar raw material composed of alloy steel containing chromium so as to form a work-affected layer, and grinding a columnar surface of the raw material; a passive film forming step of executing heating treatment to the raw material worked in the working step, and forming a passive film 21 containing chromium oxide, on a portion where the work-affected layer is formed; and a heating treatment step of executing heating treatment, including carburization treatment, to the raw film on which the passive film 21 is formed in the passive film forming step, and executing surface hardening to a ground portion where the work-affected layer is not formed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a pinion shaft.

  For example, in a planetary gear device used in an automatic transmission of an automobile, a planetary gear that meshes with a sun gear and a ring gear is freely rotatable via a needle roller on a pinion shaft whose axial end is crimped and fixed to a carrier. It is supported. Therefore, the outer peripheral surface of the pinion shaft needs to have strength against shear stress as an inner ring of a rolling bearing, and the axial end portion thereof needs to have plastic workability that can be caulked.

  As a method of manufacturing a pinion shaft having such contradictory characteristics, a high carbon chromium bearing steel is used as a material, and after nitrocarburizing, it is tempered (tempered) at a high temperature to harden the axial end portion (clamped portion). A method of induction hardening the outer peripheral surface (rolling surface) after reducing the thickness is disclosed. In addition, a method is disclosed in which case-hardened steel with an increased chromium content is used as a material, and the structural stability of the outer peripheral surface (rolling surface) is enhanced by carbonitriding.

  However, when an ordinary carbonitriding treatment is performed on an alloy steel having a high chromium content, pro-eutectoid carbide may be selectively deposited at grain boundaries in the subsequent cooling process. As a result, even if the hardness of the pinion shaft end portion (caulking portion) is lowered to such an extent that it can be caulked, ductility may be lowered due to the influence of pro-eutectoid carbide. In the above-mentioned prior art, it is not considered about the reduction of the caulking property (plastic workability) due to the pro-eutectoid carbide of the alloy steel having a high chromium content, and regarding the caulking property of the axial end portion of the pinion shaft, There was room for further improvement.

JP 2004-340221 A JP 2008-223104 A JP 2013-228032 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a method for producing a pinion shaft having both excellent durability and excellent plastic workability due to caulking properties. .

  In order to solve the above-described problem, a method for manufacturing a pinion shaft according to one aspect of the present invention is such that a work-affected layer is formed on an axial end surface of a substantially columnar material composed of alloy steel containing chromium. In addition, the processing process of grinding the cylindrical surface of the material and the heat-treated material processed in the processing process, a passive film containing chromium oxide is formed on the part where the work-affected layer is formed. Passive film formation process to be formed and the material on which the passive film was formed in the passive film formation process are subjected to heat treatment including carburizing treatment to surface-harden the ground part where the work-affected layer is not formed And a heat treatment step.

In the method of manufacturing a pinion shaft according to one aspect of the present invention, the heat treatment in the passive film forming step is performed in the temperature raising process of the heat treatment in the heat treatment step, and the temperature rise rate during the heat treatment is increased. It is good to control at such a speed. For example, the temperature increase rate during the heat treatment may be controlled to 5 ° C./min or more and 25 ° C./min or less.
Moreover, in the manufacturing method of the pinion shaft which concerns on 1 aspect of this invention, the thickness of a passive film is good also as 0.1 micrometer or more and 30 micrometers or less.

  Furthermore, in the manufacturing method of the pinion shaft which concerns on 1 aspect of this invention, alloy steel is carbon 0.1 mass% or more and 0.29 mass% or less, and chromium is 2.0 mass% or more and 5.0 mass% or less. 0.1 to 1.5% by mass of molybdenum, 0.1 to 1.5% by mass of manganese, 0.1 to 1.5% by mass of silicon, and The balance may be iron and inevitable impurities.

  Furthermore, the method for manufacturing a pinion shaft according to one embodiment of the present invention can be applied as a method for manufacturing a component of a planetary gear device. That is, the method for manufacturing a planetary gear device may include the method for manufacturing a pinion shaft according to one aspect of the present invention. Further, the method for manufacturing a pinion shaft according to one embodiment of the present invention can be applied as a method for manufacturing a component of a vehicle such as an automobile. That is, the manufacturing method of vehicles, such as a motor vehicle, may be provided with the manufacturing method of the pinion shaft which concerns on 1 aspect of this invention.

  According to the present invention, it is possible to manufacture a pinion shaft that has both excellent durability and excellent plastic workability due to caulking properties.

It is sectional drawing which shows the structure of the pinion shaft which concerns on 1st embodiment of this invention. It is the front view which looked at the planetary gear apparatus using the pinion shaft of FIG. 1 from the axial direction end side. FIG. 3 is a sectional view taken along line III-III in FIG. 2. It is a typical fragmentary sectional view of the pinion shaft by which the base end part was crimped. It is sectional drawing which shows the structure of the pinion shaft which concerns on 2nd embodiment of this invention.

The pinion shaft of this embodiment is made of alloy steel containing chromium and has a substantially cylindrical shape. The cylindrical surface is a grinding surface, and both axial end surfaces are cutting surfaces. Both axial end faces have a passive film containing chromium oxide.
Moreover, while providing the high hardness part which has a hardened surface layer in an axial direction intermediate part, the low hardness part whose surface hardness is lower than the surface hardness of a high hardness part is provided in the axial direction both end surface. This low hardness part has a passive film containing chromium oxide on the surface, and the amount of carbide present inside the passive film is more than the amount of carbide present in the hardened surface layer of the high hardness part. Few.

  The pinion shaft of the present embodiment is made of alloy steel containing chromium in order to improve durability (for example, rolling fatigue life), but a passive film is formed on the surface of the low hardness portion. The carburizing amount during carburizing or carbonitriding is controlled. Therefore, since the amount of carbide in the low hardness part is suppressed, the low hardness part has more plastic workability that can be caulked. Therefore, the pinion shaft of this embodiment has both excellent durability and more plastic workability that can be caulked.

  In the pinion shaft of this embodiment, the amount of carbide existing inside the passive film is preferably 15% or less in terms of area ratio and the surface hardness of the low hardness portion is preferably HV350 or less. More preferably, the amount of carbide existing inside the film is 1.0% or more and 12% or less in terms of area ratio, and the surface hardness of the low hardness portion is HV150 or more and HV350 or less, and exists inside the passive film. More preferably, the amount of carbide is 1.0% or more and 12% or less in terms of area ratio, and the surface hardness of the low hardness portion is HV150 or more and HV320 or less. If it is such a structure, the plastic workability of a low-hardness part will become more excellent.

  Further, the alloy steel constituting the pinion shaft of the present embodiment has a carbon content of 0.1% to 0.29% by mass, chromium of 2.0% to 5.0% by mass, and molybdenum of 0.1%. Contains from 0.1% to 1.5% by mass of manganese, from 0.1% to 1.5% by mass of manganese, from 0.1% to 1.5% by mass of silicon, and the balance being iron and inevitable It may be an impurity. The surface hardness of the high hardness portion may be HV700 or more and HV850 or less. Further, the amount of retained austenite of the surface hardened layer is 20% by volume or more and 50% by volume or less, and the amount of retained austenite of the inner core portion of the surface hardened layer is 0% by volume (or 0% by volume exceeding 2.0% by volume or less). ). Further, the thickness of the passive film may be not less than 0.1 μm and not more than 30 μm. With such a configuration, the durability of the high hardness portion is more excellent, and the plastic workability of the low hardness portion is more excellent.

Hereinafter, as an example of the pinion shaft of the present embodiment, a pinion shaft that rotatably supports a planetary gear in a planetary gear device used in an automatic transmission of an automobile will be described in detail with reference to the drawings. In the drawings referred to in the description of each embodiment below, the same or corresponding parts are denoted by the same reference numerals.
[First embodiment]
The pinion shaft 4 of FIG. 1 is made of alloy steel containing chromium and has a substantially cylindrical shape (round bar shape), and includes an axial hole 15 and a plurality of (three in this example) radial holes. 16, 16, 16 and a pair of circular recesses 18a, 18b. The circular recesses 18 a and 18 b have a truncated cone shape and are formed by cutting on both end surfaces in the axial direction of the pinion shaft 4. That is, the inner surfaces of the circular recesses 18a and 18b (both axial end surfaces of the pinion shaft 4) are cutting surfaces.

The axial hole 15 extending in the axial direction of the pinion shaft 4 is formed in the radial center portion of the pinion shaft 4, and one axial end portion (the left end portion in FIG. 1) is opened at the bottom of one circular recess 18a. In addition, the other end portion in the axial direction (the right end portion in FIG. 1) is located near the other end of the intermediate portion X in the axial direction of the pinion shaft 4.
In addition, a pair of radial holes 16 and 16 are formed at substantially the center in the axial direction of the pinion shaft 4 so as to penetrate the pinion shaft 4 in the radial direction, and the other axial end of the pinion shaft 4 is formed. One radial hole 16 extending in the radial direction of the pinion shaft 4 is formed in the side portion. Each of these radial holes 16, 16, 16 has a radially inner end opening on the inner peripheral surface of the axial hole 15, and each radial outer end on the outer peripheral surface of the pinion shaft 4. It is open.

  Of the pinion shaft 4, the outer peripheral surface (that is, the cylindrical surface) of the axial intermediate portion X excluding the axial end portions Y and Y is ground, and the outer peripheral surface is a ground surface. The intermediate portion X of the pinion shaft 4 is subjected to a carbonitriding process (or carburizing process), a tempering process, an induction hardening process, and a tempering process in this order. A hardened surface layer 19 is formed on the outer peripheral surface of the portion X. In addition, at the axial end portions Y and Y of the pinion shaft 4, the portions that are aligned in the axial direction with the circular concave portions 18 a and 18 b (the peripheral portions of the circular concave portions 18 a and 18 b) remain raw without being hardened by hardening. .

The hardened surface layer 19 of the pinion shaft 4 corresponds to the “high hardness portion” described above. Further, a passive film 21 described later in the pinion shaft 4 corresponds to the above-mentioned “low hardness portion”. A portion of the pinion shaft 4 that does not correspond to the surface hardened layer 19 or the passive film 21 (for example, the outer peripheral surface of the axial end Y) is lower in hardness than the surface hardened layer 19 and is passive. It is a medium hardness part that is harder than the film 21.
Passive films 21 and 21 containing chromium oxide are formed on the surfaces of the bottoms of the circular recesses 18a and 18b at both axial ends Y and Y. Since the passive film 21 (having a thickness of, for example, 0.1 μm or more and 30 μm or less) is formed on the surface, the carbonitriding process is performed on both the axial ends Y and Y simultaneously with the axial intermediate portion X. Nevertheless, the amount of carbide existing inside the passive film 21 is 15% or less in terms of area ratio, which is smaller than the amount of carbide present in the surface hardened layer 19.

  Moreover, the surface hardness of the axial direction intermediate part X (surface hardened layer 19) is HV700 or more and HV850 or less, the amount of retained austenite of the surface hardened layer 19 is 20% by volume or more and 50% by volume or less, and the surface hardened layer 19 The amount of retained austenite of the inner core part 20 is 0% by volume. Furthermore, the surface hardness of axial both ends Y and Y (particularly where the passive films 21 and 21 are formed) is HV350 or less.

Since such a pinion shaft 4 has the toughness of the axial end Y, the axial end Y when crimping the axial end Y and fixing it to a member such as a carrier of a planetary gear device. Damages such as cracks and cracks are unlikely to occur. Therefore, when the pinion shaft 4 is fixed to a member such as a carrier, plastic working such as caulking can be preferably used. Further, since the strength of the axial intermediate portion X is ensured, the axial intermediate portion X (rolling surface) is hardly damaged during operation of the planetary gear device.
Here, the critical significance such as the content of alloy components contained in the alloy steel, the surface hardness, the amount of retained austenite, etc. will be described in detail.

[Carbon content]
Carbon (C) dissolves in the base and quenches, improves the hardness after tempering and improves strength, and combines with carbide-forming elements such as iron, chromium, molybdenum, vanadium to form carbides and resists carbon. It is an element that has the effect of increasing wear. If the time for carburizing treatment and carbonitriding treatment to obtain the hardness required for rolling fatigue resistance is increased, the cost increases, so the carbon content is 0.1 mass for shortening the treatment time. % Or more is preferable.

  However, if it exceeds 0.29% by mass, coarse eutectic carbides are likely to be produced during steelmaking, and the rolling fatigue life and strength may decrease. On the other hand, if it exceeds 0.29% by mass, forgeability, cold workability, and machinability may be deteriorated, resulting in an increase in processing cost. Furthermore, if it exceeds 0.29% by mass, the formability to a rod-shaped member is low, and if it is attempted to mold to a rod-shaped member having a diameter of 15 mm or less, plastic processing is difficult and cracks and cracks may occur during molding. .

[Chromium content]
Chromium (Cr) is an element having an effect of increasing the hardenability, temper softening resistance, corrosion resistance, and rolling fatigue life by dissolving in a matrix. In addition, the interstitial solid solution elements such as carbon and nitrogen are substantially prevented from moving to stabilize the base structure, and have a function of greatly suppressing a decrease in life at the time of hydrogen intrusion. Furthermore, since the carbide finely distributed in the alloy steel is composed of carbides such as (Fe, Cr) ₃ C, (Fe, Cr) ₇ C ₃ , (Fe, Cr) ₂₃ C _{6 and the} like having higher hardness, It also has the effect of increasing wear resistance. Further, the retained austenite is not easily decomposed by heat, and as a result, plastic deformation is difficult.
When the content of chromium in the alloy steel is less than 2% by mass, the above-mentioned action may not be sufficiently obtained. When the content exceeds 5% by mass, cold workability, machinability, carbonitriding ( (Or carburizing properties) may be reduced, leading to an increase in cost. Furthermore, coarse eutectic carbides are likely to be generated during steelmaking, and the rolling life and strength may be reduced.

[Molybdenum content]
Molybdenum (Mo) is an element having the effect of increasing the hardenability, temper softening resistance, corrosion resistance, and rolling life by solid solution in the base like chromium. In addition, like chromium, interstitial solid solution elements such as carbon and nitrogen are substantially prevented from moving to stabilize the base structure, and have a function of greatly suppressing a decrease in life at the time of hydrogen intrusion. Furthermore, since the carbide finely distributed in the alloy steel is made of a carbide of molybdenum having a higher hardness, it also has an effect of improving wear resistance.
If the molybdenum content in the alloy steel is less than 0.1% by mass, the above-mentioned action may not be sufficiently obtained. If the content exceeds 1.5% by mass, cold workability and machinability are obtained. There is a risk of lowering and increasing costs. Furthermore, coarse eutectic carbides are likely to be generated during steelmaking, and the rolling life and strength may be reduced.

[About manganese content]
Manganese (Mn) is an element that acts as a deoxidizer during steelmaking, and is preferably added in an amount of 0.1 mass or more. Moreover, it has the effect | action which solid-dissolves to a base | substrate similarly to chromium, and lowers Ms point, ensures a large amount of retained austenite, or improves hardenability. However, if added over 1.5% by mass, not only the cold workability and machinability are lowered, but also the martensitic transformation start temperature is lowered, and a large amount of residual carbonitriding (or after carburizing) is left. Austenite may remain and sufficient hardness may not be obtained.

[About silicon content]
Silicon (Si) is an element that acts as a deoxidizing agent during steel making, like manganese, and is preferably added in an amount of 0.1 mass or more. Moreover, it is an element effective for improving the bearing life by improving the hardenability as well as chromium and manganese, and promoting the martensitic transformation of the base and the stabilization of retained austenite. Furthermore, it has the effect | action which raises temper softening resistance. However, if added over 1.5% by mass, forgeability, cold workability, machinability, and carbonitridability (or carburizability) may deteriorate.

[About surface hardness of rolling surface]
The decrease in the rolling life of the planetary gear device in the foreign matter lubrication environment is caused by stress concentration at the rising edge of the indentation formed by the biting of the foreign matter. If the surface hardness of the rolling surface of the pinion shaft 4 (surface hardness of the axial intermediate portion X (surface hardened layer 19)) is HV700 or more and HV850 or less, indentation is difficult to form, so that the planetary gear device is mixed with foreign matter. Long life even when used in. If the surface hardness of the rolling surface of the pinion shaft 4 is less than HV700, there is a risk that indentation will be formed because the hardness is insufficient, and if it exceeds HV850, it is necessary to increase the quenching temperature. The toughness may be reduced due to the coarsening of the crystal grain size.

[Residual austenite amount of the hardened surface layer 19]
When the amount of retained austenite of the surface hardened layer 19 is 20% by volume or more and 50% by volume or less, the stress concentration as described above hardly occurs. If it is less than 20% by volume, the effect of reducing the stress concentration that relieves surface fatigue is poor, and the fatigue life is reduced. On the other hand, if it exceeds 50% by volume, the surface hardness becomes insufficient and the wear resistance and surface fatigue resistance may be impaired. In order to prevent such inconvenience and to obtain an excellent fatigue life stably, the amount of retained austenite of the surface hardened layer 19 is preferably in the range of 20% by volume to 50% by volume, more preferably 30% by volume. % To 40% by volume or less.

[Residual austenite content of core 20]
By ensuring the amount of retained austenite on the surface of the rolling surface to be 20% by volume or more and 50% by volume or less, it is possible to improve the rolling fatigue life in a foreign matter lubrication environment. On the other hand, retained austenite decomposes and changes to a mixture of ferrite and cementite or martensite when stress such as a load or heat is applied, so that plastic deformation occurs in the pinion shaft. Therefore, in order to suppress the plastic bending of the pinion shaft 4 as much as possible, the amount of retained austenite of the inner core portion 20 of the surface hardened layer 19 is preferably more than 0% by volume and not more than 2.0% by volume, and 0% by volume. More preferably.

[Surface hardness of axial end Y]
In the pinion shaft 4, a high hardness is required for the rolling surface in order to ensure a rolling fatigue life. However, since the axial end Y is fixed by caulking, the hardness should be plastically deformable. There must be. The surface hardness of the axial end Y (particularly where the passive films 21 and 21 are formed) is preferably HV350 or less, more preferably HV150 or more and HV350 or less, and HV150 or more and HV320 or less. More preferably it is. If the surface hardness of the axial end Y exceeds HV350, cracking may occur during caulking, and if it is less than HV150, rigidity after caulking may not be maintained.

[About the thickness of the passive film 21]
By providing the passivation film 21 containing chromium oxide on the surface of the axial end Y of the pinion shaft 4 (the bottom of the circular recess 18a), carbon is applied to the axial end Y during carburizing and carbonitriding. The penetration can be restricted, and the surface hardness of the axial end Y and the generation of proeutectoid carbide can be suppressed. The thickness of the passive film is preferably 0.1 μm or more and 30 μm or less. If the thickness of the passive film 21 is less than 0.1 μm, carbon intrusion may not be sufficiently suppressed. If the thickness is more than 30 μm, it may be peeled off during use in an actual machine as a harmful scale, resulting in adverse effects. There is a risk of getting out.

[About the amount of carbide at the axial end Y]
For example, when normal carbonitriding is performed on case-hardened steel with increased chromium content, pro-eutectoid carbides are likely to selectively precipitate at the grain boundaries in the subsequent cooling process, and the surface of the end Y in the axial direction Even when the hardness is low, the precipitated carbide may be a starting point of cracking during caulking. Therefore, the amount of carbide at the axial end Y, that is, the amount of carbide existing inside the passive film 21 is preferably 15% or less in terms of area ratio, and is 1.0% or more and 12% or less. It is more preferable. If the amount of carbide at the axial end Y is more than 15%, the carbides are easily bonded to each other, and caulking cracks are likely to occur when caulking.

  Next, a method for manufacturing such a pinion shaft 4 will be described. First, a material made of alloy steel containing chromium (for example, high-carbon chromium bearing steel, case-hardened steel) is processed into a substantially cylindrical shape (round bar shape) to form a pinion shaft-shaped member (processing step). During this processing, the outer peripheral surface (cylindrical surface) of the substantially cylindrical material is ground, and both axial end surfaces of the substantially cylindrical material are cut so that a work-affected layer is formed. A work-affected layer is generated on the surface of both end portions in the axial direction of the member (the bottom portion of the circular recess 18a). The thickness of the work-affected layer may be controlled to 3 μm or more and 40 μm or less, for example, by adjusting conditions such as the processing speed.

  Subsequently, the member having the work-affected layer is subjected to heat treatment including carburization or carbonitriding (heat treatment step). As a result, since the member having the work-affected layer is subjected to heat treatment in the temperature rising process of the heat treatment process, the passive film containing chromium oxide is formed on both end surfaces in the axial direction where the work-affected layer is formed. 21 is formed (passive film forming step). On the other hand, a surface hardening by a carburizing process or a carbonitriding process is performed on the axially intermediate part (that is, the ground part) where the work-affected layer is not formed after the temperature raising process. That is, formation of the passive film 21 and surface hardening by carburizing or carbonitriding are achieved by a single treatment.

However, the formation of the passive film 21 and the surface hardening by the carburizing process or the carbonitriding process may be performed separately (two processes may be performed). That is, the member having the work-affected layer is subjected to heat treatment to form the passive film 21 on both end surfaces in the axial direction where the work-affected layer is formed (passive film forming step), and then the passive film 21 is formed. The member may be subjected to heat treatment including carburizing or carbonitriding.
Note that the temperature increase during the heat treatment including the carburizing process or the carbonitriding process is preferably performed gradually so that the passive film 21 is easily formed, and the temperature increasing rate is, for example, 5 ° C./min to 25 ° C./min. It is preferable to control.

  Following heat treatment including carburizing or carbonitriding, annealing is performed at 700 ° C. or higher and 770 ° C. or lower in the air or nitrogen atmosphere (tempering treatment), and then the axial intermediate portion (heat treatment in the heat treatment step). The surface hardening layer 19 is formed by subjecting only the surface of the material subjected to the induction hardening to induction hardening only on the portion different from the portion where the work-affected layer is formed (induction hardening step). Then, a tempering process is further performed. By such a treatment, the surface hardness layer 19 having a surface hardness of HV700 or more and HV850 or less is provided in the axial intermediate portion X, the surface hardness of both axial ends Y and Y is HV150 or more and HV350 or less, and the axial direction The pinion shaft 4 having the passive film 21 on both end faces is obtained. Further, the amount of carbide existing inside the passive film 21 is set to 15% or less by area ratio. Furthermore, the amount of retained austenite of the surface hardened layer 19 is set to 20% by volume or more and 50% by volume or less, and the amount of retained austenite of the core 20 inside the surface hardened layer 19 is set to 0% by volume.

  Thus, the passive film 21 is formed by defining the thickness of the work-affected layer and the temperature increase rate during the heat treatment including the carburizing process or the carbonitriding process, and the axial end Y (the passive film 21 of the passive film 21) is formed. Since the amount of carbides present on the inner side is suppressed, niobium (Nb), which is an element for preventing the formation of coarse grains, is used in spite of using alloy steel with an increased chromium content for improving rolling fatigue life. ) Is not required.

Here, the work-affected layer at the axial end Y and the heating rate during carburizing or carbonitriding will be described in detail.
The formation of the passive film 21 is related to the work-affected layer on the surface and the rate of temperature increase at the time of temperature increase. The presence of a work-affected layer on the surface promotes the diffusion of chromium to the surface, so that no chromium oxide is contained before the start of carburizing or carbonitriding (ie, at the elevated temperature of carburizing or carbonitriding). A dynamic film 21 is formed.

If the thickness of the work-affected layer is less than 3 μm, the generation of the passive film 21 may be insufficient. On the other hand, in order to obtain a work-affected layer deeper than 40 μm (that is, when the work-affected layer has a thickness exceeding 40 μm), processing under severe cutting conditions is required. It is not realistic considering the load.
In addition, the passive film 21 is not formed when processing is performed at room temperature, but is formed under a certain temperature environment during temperature rise. Therefore, when the temperature is increased at a rate faster than 25 ° C./min, there is a possibility that the passive film 21 having a sufficient thickness cannot be formed. On the other hand, at a speed slower than 5 ° C./min, it takes too much time to raise the temperature to the carburizing temperature or the carbonitriding temperature, which is not realistic from the viewpoint of productivity.

  The pinion shaft 4 of FIG. 1 includes a passive film 21, but the passive film 21 is intended to limit carbon intrusion into the axial end Y during carburizing and carbonitriding. It is unnecessary after carburizing and carbonitriding. Therefore, after the carburizing and carbonitriding, the passive film 21 may be removed by a process of removing the passive film by cutting or the like. If the passive film 21 is removed, the end Y in the axial direction is composed of only a layer having a lower hardness, so that the caulking process becomes easier.

  Next, a planetary gear device using the pinion shaft 4 will be described with reference to FIGS. The planetary gear device includes a sun gear 1 having teeth 1a formed on the outer peripheral surface, a ring gear 2 disposed concentrically with the sun gear 1 and having teeth 2a formed on the inner peripheral surface, the sun gear 1 and the ring gear 2 And a plurality (generally 3 to 4) of planetary gears 3, 3, and 3 arranged at equal intervals in the circumferential direction. The teeth 3a formed on the outer peripheral surfaces of the plurality of planetary gears 3, 3 and 3 mesh with both teeth 1a and 2a.

  The plurality of planetary gears 3, 3, and 3 are rotatably supported around the pinion shaft 4 via a plurality of needle rollers 5 and 5, respectively. That is, the planetary gear 3, the pinion shaft 4, and the needle rollers 5, 5 constitute a rolling bearing (radial needle bearing), and the pinion shaft 4 of these corresponds to the inner ring of the rolling bearing.

A base end portion (right end portion in FIG. 3) of each pinion shaft 4 is fixed to a substrate 7 of a carrier 6 that is rotatable around the sun gear 1. More specifically, the base end portion of each pinion shaft 4 is crimped and fitted into a through hole 8a formed in the substrate 7 by an interference fit. FIG. 4 shows the pinion shaft 4 whose base end portion is crimped. A part of the base end portion of the pinion shaft 4 or the entire circumferential direction is fixed to the substrate 7 of the carrier 6 by being caulked and spread radially outward.
In the illustrated example, the sun gear 1 is formed in a cylindrical shape, and the substrate 7 is formed in an annular shape with an L-shaped cross section. As shown in FIG. 3, the cylindrical portion 10 formed on the inner peripheral edge of the substrate 7 is spline-engaged with the outer peripheral surface of the rotating shaft 11. The sun gear 1 is supported around the rotary shaft 11 so as to be rotatable relative to the rotary shaft 11. The ring gear 2 is supported around the sun gear 1, the carrier 6, and the rotation shaft 11 so as to be rotatable relative to the sun gear 1, the carrier 6, and the rotation shaft 11.

Further, the tip end portion (left end portion in FIG. 3) of each pinion shaft 4 is fitted into a through-hole 8b formed in a connecting plate 12 formed in an annular shape that constitutes the carrier 6 together with the substrate 7, and is fixed by crimping. The tip portions of the pinion shafts 4 are connected to each other. The caulking of the tip end portion of the pinion shaft 4 is also the same as the case of the base end portion of the pinion shaft 4 described above, and as shown in FIG. It is fixed to the connecting plate 12 by being caulked and spread outward in the radial direction.
An outer peripheral surface (a portion between the substrate 7 and the connecting plate 12) of the axially intermediate portion of the plurality of pinion shafts 4 is a cylindrical surface-shaped inner ring raceway 13. On the other hand, the inner peripheral surface of the planetary gear 3 is a cylindrical outer ring raceway 14. The needle rollers 5, 5 are arranged between the inner ring raceway 13 and the outer ring raceway 14, and the planetary gear 3 is rotatably supported around the axial intermediate portion of the pinion shaft 4.

  In such a planetary gear device including the planetary gear 3 and the pinion shaft 4, for example, the rotation shaft 11 is used as a drive shaft or a driven shaft, and the center of the sun gear 1 or the ring gear 2 is coupled to the driven shaft or the drive shaft. ing. Then, any one of the sun gear 1, the ring gear 2, and the planetary gear 3 is rotatable, and the drive shaft is switched by switching whether the sun gear 1, the ring gear 2, or the planetary gear 3 is non-rotatable. Speed change and rotation direction conversion between the motor and the driven shaft.

[Second Embodiment]
Next, the pinion shaft 4 of the second embodiment will be described with reference to FIG. In addition, since the structure and manufacturing method of the pinion shaft 4 of 2nd embodiment are substantially the same as the structure and manufacturing method of the pinion shaft 4 of 1st embodiment, only a different part is demonstrated and description of the same part is abbreviate | omitted. To do.
In the case of the pinion shaft 4 of the first embodiment, both end faces in the axial direction are recessed by cutting to form the circular recesses 18a and 18b, and thus the passive films 21 and 21 are formed only on the inner surfaces of the circular recesses 18a and 18b. It was. On the other hand, in the case of the pinion shaft 4 of the second embodiment, both end surfaces in the axial direction are recessed by cutting to form circular recesses 18a and 18b, and corners on the outer periphery of the axial end portions Y and Y are formed. Since chamfering is performed by cutting (thus, the inner surfaces of the circular recesses 18a and 18b, the outer peripheral portions of both axial end surfaces, and the chamfered portions are cutting surfaces), as shown in FIG. 5, the circular recesses 18a and 18b Passive films 21 and 21 are formed not only on the inner surface but also on the outer peripheral side portion and the chamfered portion of both axial end surfaces. The shape of the chamfered portion may be flat (so-called C chamfering) as shown in FIG. 5, or may be curved (so-called R chamfering (round chamfering)).

  In the case of the pinion shaft 4 of the second embodiment, as described above, the axial length of the material is shortened by cutting when the pinion shaft 4 is manufactured. decide. That is, if a material having a larger axial length than the pinion shaft 4 of the finished product is prepared and both end portions in the axial direction of the material are cut as described above to obtain the normal axial length of the pinion shaft 4, Even when such a manufacturing method is employed, the pinion shaft 4 having a desired axial length can be manufactured. In addition, when the passive film 21 is removed by cutting or the like after carburizing or carbonitriding, the axial length of the material may be determined in consideration of the fact that the axial length is shortened accordingly. .

  In the case of the pinion shaft 4 of the first embodiment, the axial intermediate portion X having the hardened surface layer 19 and the axial end portion Y having the passive film 21 are in contact with each other and aligned in the axial direction. On the other hand, in the case of the pinion shaft 4 of the second embodiment, as shown in FIG. 5, both the passive film 21 and the surface hardened layer 19 are interposed between the axial intermediate portion X and the axial end portion Y. A medium hardness portion Z of medium hardness that is not present is interposed. Since neither the passive film 21 nor the surface hardened layer 19 is formed on the surface of the medium hardness portion Z, the surface hardness of the medium hardness portion Z is the surface hardness of the passive film 21 and the surface hardness of the surface hardened layer 19. It is the hardness between.

In addition, said 1st and 2nd embodiment showed an example of this invention, Comprising: This invention is not limited to 1st and 2nd embodiment. Various changes or improvements can be added to the first and second embodiments, and forms to which such changes or improvements are added can also be included in the present invention.
For example, in the first and second embodiments, as an example of a pinion shaft, a pinion shaft as a part used in a planetary gear device or the like has been described. However, the pinion shaft of the present invention is used as a component in a planetary gear device or the like. It is not limited to a pinion shaft. Another example to which the pinion shaft of the present invention can be applied is a shaft component such as a tappet roller shaft.

4 Pinion shaft 13 Inner ring raceway 19 Surface hardened layer 20 Core part 21 Passive film X Axial intermediate part (high hardness part)
Y-axis direction end (low hardness part)

Claims (3)

Cutting the axial end surface of the substantially cylindrical material composed of alloy steel containing chromium, so as to form a work-affected layer, and grinding the cylindrical surface of the material,
Passive film forming step of forming a passive film containing chromium oxide on the portion where the work-affected layer is formed by subjecting the material processed in the processing step to heat treatment;
A heat treatment step of subjecting the material on which the passive film has been formed in the passive film formation step to a heat treatment including a carburizing treatment to harden the ground portion where the work-affected layer is not formed, and
A method of manufacturing a pinion shaft comprising: The heat treatment of the passive film forming step is performed in the temperature rising process of the heat treatment of the heat treatment step,
The method for manufacturing a pinion shaft according to claim 1, wherein a temperature rising rate during the heat treatment is controlled to a rate at which the passive film is formed.   The alloy steel includes carbon in an amount of 0.1 mass% to 0.29 mass%, chromium in an amount of 2.0 mass% to 5.0 mass%, molybdenum in an amount of 0.1 mass% to 1.5 mass%, 3. Manganese is contained in an amount of 0.1 to 1.5 mass%, silicon is contained in an amount of 0.1 to 1.5 mass%, and the balance is iron and inevitable impurities. A method for manufacturing a pinion shaft according to claim 1.

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