JP4807146B2 - Method for manufacturing pinion shaft and method for manufacturing planetary gear device - Google Patents

Description

The present invention relates to a manufacturing method of preparation and the planetary gear device of the pinion shaft.

  For example, a planetary gear device 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. And the oil path is provided so that lubricating oil may be supplied to each rotation element with the centrifugal force of each rotation.

  However, since the planetary gear device has a complicated structure in which the pinion gear revolves while rotating, it is difficult to supply sufficient lubricating oil to the pinion shaft and the bearing rollers. Moreover, since the rotation speed of the pinion gear is the highest among the rotating elements, there is a tendency that a large load is applied to the pinion shaft that supports the pinion gear in order to support the centrifugal force acting on the pinion gear.

  Therefore, in the conventional planetary gear device, the pinion shaft is made of JIS steel grade SK5 or the like, and is hardened to give the necessary hardness (Hv650 or more) as a rolling member. And, by adopting induction hardening as the hardening method, induction hardening is applied only to the part (rolling surface) where the roller for rolling is rolled, and pinion is formed by caulking the end portion where induction hardening is not applied. The shaft was fixed to the carrier.

In recent years, there has been an increasing demand for lower fuel consumption in automobiles, and transmissions have been made smaller and more efficient for the purpose of reducing fuel consumption. Therefore, since the rotational speed of the pinion gear is increasing, the load applied to the pinion shaft increases, the temperature rises, and the amount of lubricating oil tends to decrease.
As a result, in the conventional pinion shaft as described above, the peeling life due to poor lubrication may be a problem. In such a case, the pinion shaft is made of JIS steel type SUJ2 and subjected to carbonitriding and the like to ensure the service life. However, since the pinion shaft cannot be fixed to the carrier by caulking, Since it is necessary to process the screw hole and fix the pinion shaft with a screw, there is a problem that the cost of the planetary gear device increases.

In addition, due to the increase in load and temperature described above, deformation and early peeling (wear occurs with increased slippage, causing early peeling due to surface roughness due to wear), and the service life is insufficient. There was a problem of becoming.
Patent Documents 1 and 2 disclose that the austenite retained in the core is decomposed by cooling after carbonitriding, or by tempering at a high temperature after quenching. A method of manufacturing a pinion shaft by subjecting a portion to be a rolling surface to induction hardening treatment is disclosed.

The pinion shaft manufactured in this way is not hardened because it has not been induction hardened at the end in the longitudinal direction, so that the end can be caulked and fixed to the carrier, and residual austenite It has sufficient durability. Further, according to this method, the planetary gear device can be manufactured at low cost. Furthermore, since the retained austenite in the core is completely decomposed, the amount of deformation of the pinion shaft during use is suppressed to a small level.
Japanese Patent Laid-Open No. 2002-4003 JP 2004-340221 A

However, the pinion shaft has become smaller in diameter as the volume of the space is reduced due to the multistage transmission. And considering the presence of oil holes, the effective thickness is very thin and the rigidity is reduced. Therefore, it is necessary to consider the decomposition of retained austenite near the surface where the bending stress acting on the pinion shaft becomes larger.
Therefore, the present invention solves the problems of the prior art as described above, a method for manufacturing a pinion shaft that has a long life even when used at high speeds at high temperatures, and is used at high speeds at high temperatures. Another object of the present invention is to provide a method for producing a planetary gear device that is long-lived and inexpensive.

In order to solve the above-described problems, the present invention has the following configuration. That is, the manufacturing method of the pinion shaft according to claim 1 according to the present invention is used in the planetary gear device, in the manufacturing method of a bearing steel of the pinion shaft for rotatably supporting the pinion gears meshing with the disposed the sun gear and the ring gear concentrically Then , carbonitriding treatment and annealing treatment are performed on the steel material, and then only the portion that becomes the rolling surface of the outer peripheral surface is subjected to induction hardening treatment, and then tempering treatment, whereby the amount of retained austenite is 15 A surface layer portion having a volume percent of 30% to 30% and a residual compressive stress of 500 MPa to 1200 MPa and a core portion having a residual austenite amount of 0% by volume, and a method defined in Japanese Industrial Standard JIS G0551 The measured prior austenite grain size of the surface layer part is 8 or more in grain size number , and the longitudinal direction A pinion shaft having an end surface hardness of Hv300 or less is obtained .

According to a second aspect of the present invention, there is provided a planetary gear device manufacturing method comprising: a sun gear; a ring gear concentrically arranged with the sun gear; one or more pinion gears meshed with the sun gear and the ring gear; and the pinion gear rotatable. a pinion shaft supporting a, a carrier in which the pinion gear disposed in the sun gear and the ring gear concentric is fixed, in the manufacturing method of the planetary gear device including a method of manufacturing a pinion shaft according to the pinion shaft to claim 1 and those obtained by, characterized in that fixed by caulking the pinion shaft to the carrier.

The pinion shaft manufacturing method of the present invention can obtain a pinion shaft having a long life even when used at high speed rotation at high temperatures. The planetary gear device manufacturing method of the present invention can provide a planetary gear device that has a long life and is inexpensive even when used at high speeds at high temperatures.

An embodiment of the manufacturing method of the production method and the planetary gear device of the pinion shaft according to the present invention will be described in detail with reference to the drawings. The planetary gear device shown in FIG. 1 includes a sun gear 1 through which a shaft (not shown) is inserted, a ring gear 2 arranged concentrically with the sun gear 1, and one or more (three in FIG. 1) meshing with the sun gear 1 and the ring gear 2. The pinion gear 3 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 are provided.

A pinion shaft 5 fixed to the carrier 4 by caulking is inserted in the center of the pinion gear 3, and a plurality of needle-like shapes (not shown) are provided between the outer peripheral surface of the pinion shaft 5 and the inner peripheral surface of the pinion gear 3. Rollers are arranged, and thereby the pinion gear 3 is rotatable about the pinion shaft 5.
The pinion shaft 5 is made of high carbon chromium bearing steel (SUJ2). Then, following the carbonitriding process and the annealing process, the induction hardening process is performed only on the part (rolling surface) where the needle rollers roll on the outer peripheral surface of the pinion shaft 5.

When manufacturing the pinion shaft 5, after turning a steel material made of high carbon chromium bearing steel to a predetermined dimension (for example, an outer diameter of 8 mm, a length of 35 mm), the heat treatment as described above is performed, Further, finish grinding may be performed.
As a result of such heat treatment, a surface layer portion and a core portion are formed on the pinion shaft 5. The amount of retained austenite in the core is 0% by volume. The amount of retained austenite in the surface layer portion is 15% by volume or more and 30% by volume or less, and the residual compressive stress in the surface layer portion is 500 MPa or more and 1200 MPa or less. Furthermore, the prior austenite grain size (measured by the method defined in Japanese Industrial Standard JIS G0551) in the surface layer portion is preferably 10 or more in terms of grain size number.

Note that the surface layer portion in the present invention means that the diameter of the needle roller disposed between the outer peripheral surface of the pinion shaft and the inner peripheral surface of the pinion gear is Da, and the depth of Da is 2% from the surface of the pinion shaft. It means the part up to the position.
As described above, the longitudinal end portion of the pinion shaft 5 is not subjected to induction hardening, remains as a physical property after annealing, and is not cured (hardness is Hv300 or less). The pinion shaft 5 can be fixed to the carrier 4 by caulking its end. Therefore, this planetary gear device can be manufactured at low cost.

  On the other hand, as a result of examining the decomposition behavior of austenite in the stress load state, it was found that the decomposition of austenite accelerates in the tensile stress load state. Further, it was found that the decomposition of austenite is delayed when it has a compressive residual stress even in the tensile stress load state. Therefore, when the residual compressive stress is applied to the rolling surface, in addition to the effect of delaying crack generation during rolling by the residual compressive stress and improving the life of the pinion shaft 5, the decomposition of the residual austenite is suppressed and at the time of rolling. By suppressing the bending of the pinion shaft 5 and suppressing the occurrence of edge loading, the effect of improving the life can be obtained.

  Furthermore, the finer the prior austenite crystal grains, the more the retained austenite tends to decompose. This is because with the refinement of the prior austenite crystal grains, the internal structure of the packets, blocks, etc. is also refined and the retained austenite is also dispersed, so that the dispersed retained austenite is constrained by the surrounding martensite structure. Conceivable. Therefore, by controlling the residual stress and crystal grain size of the surface layer portion of the pinion shaft 5, it is possible to suppress deformation due to decomposition of residual austenite at the time of rolling, and high durability can be achieved. According to such a method, a small-diameter pinion shaft excellent in durability and caulking can be manufactured using general bearing steel.

Next, the critical significance of the numerical values such as the amount of retained austenite, the residual compressive stress, and the prior austenite grain size will be described.
[About the amount of retained austenite in the surface layer]
Residual austenite is softer than the martensite of the fabric, so if there is a large amount of retained austenite in the surface layer of the pinion shaft, it effectively absorbs deformation energy under load conditions that cause surface damage and damages the rolling surface. It has the effect of suppressing the above and imparting high durability. In order to obtain sufficient durability, the amount of retained austenite in the surface layer portion needs to be 15% by volume or more. However, if the amount of retained austenite in the surface layer portion exceeds 30% by volume, not only the effect is saturated, but also the dimensional stability at high temperature may be lowered. Therefore, the amount of retained austenite in the surface layer portion needs to be 30% by volume or less.

[About the amount of retained austenite in the core]
When residual austenite is present, plastic deformation occurs due to transformation to martensite. Although the amount of retained austenite in the surface layer is somewhat affected, since the core occupies most of the volume of the pinion shaft, if there is residual austenite in the core, plastic deformation is likely to occur in the pinion shaft, and the pinion shaft Bending increases. Therefore, if the amount of retained austenite in the core part is 0% by volume, even if retained austenite is present in the surface layer part, the plastic deformation of the pinion shaft hardly occurs.

[Residual compressive stress in the surface layer]
If the residual compressive stress of the surface layer is less than 500 MPa, there is a possibility that an effective effect of suppressing the retained austenite decomposition against the stress applied during rolling may not be obtained. On the other hand, if the pressure exceeds 1200 MPa, the stress exceeds the elastic limit in the surface layer portion, so plastic deformation of austenite occurs and processing-induced transformation occurs, and on the contrary, decomposition of residual austenite accelerates. Furthermore, in the induction hardening process exceeding 1200 MPa, the curing depth is inevitably difficult to obtain.

The residual stress is determined by the balance between the hardened layer and the non-hardened layer. Further, the volume expansion of the hardened layer by the induction hardening process is pulled by the internal non-hardened layer, and compressive stress is applied to the surface and tensile stress is applied to the inside. Since the residual compressive stress increases as the hardened layer depth decreases, induction hardening in a higher frequency band is preferable after obtaining the required hardened layer depth.
[About the former austenite grain size of the surface layer]
If the old austenite grain size measured by the method specified in Japanese Industrial Standard JIS G0551 is less than 10 (grain size is coarse) in the grain size number, the internal structure of packets, blocks, etc. will not be sufficiently refined, There is a possibility that the effect of suppressing the decomposition of austenite cannot be obtained sufficiently.

[About the average nitrogen concentration in the surface layer]
Nitrogen in steel has a strong effect of lowering the Ms point and increasing the amount of retained austenite. When the nitrogen concentration is less than 0.05% by mass, the above-described action becomes insufficient, and it becomes difficult to stably obtain retained austenite, which may cause a decrease in durability. However, even if it exceeds 0.6 mass%, the above-mentioned action is saturated.

[Surface hardness of the part to be the rolling surface]
In order to ensure sufficient durability of the pinion shaft, it is preferable that the surface hardness of the portion serving as the rolling surface is Hv 700 or more.

[Surface hardness at the end in the longitudinal direction]
In addition to the pro-eutectoid carbide, the surface hardness at the end in the longitudinal direction is an element that affects the caulking properties of the pinion shaft. If the surface hardness of the end portion in the longitudinal direction exceeds Hv300, not only ductility but also deformation resistance increases, so the upper limit is preferably set to Hv300. If the pinion shaft is manufactured by the heat treatment in the present invention, the surface hardness of the end portion in the longitudinal direction is the same hardness as the region (core portion) other than the portion (cured layer) that becomes the rolling surface subjected to induction hardening treatment. It becomes.

[About bearing steel]
In order to reduce the amount of non-metallic inclusions, the carbon content in the bearing steel is preferably 0.5% by mass or more and 1.2% by mass or less. Examples of such bearing steel include high carbon chromium bearing steel and high cleanness carbon alloy steel. The oxygen content in the bearing steel is preferably 12 ppm or less, and more preferably 9 ppm. Furthermore, the sulfur content in the bearing steel is preferably 150 ppm or less, and more preferably 80 ppm.

〔Example〕
Hereinafter, the present invention will be described with reference to more specific examples. After turning a steel made of high carbon chromium bearing steel (SUJ2) to a predetermined size, it is subjected to the heat treatment described later (see also Tables 1 and 2), and further subjected to finish grinding, so that various pinion shafts (outer diameters) 8 mm, length 35 mm). And the durability test of these pinion shafts was done.

  The contents of the heat treatment are as follows. The turned steel material was subjected to a carbonitriding treatment at 850 ° C. for 1 hour or 3 hours, allowed to cool and then annealed. Carbonitriding is preferable because it can be processed at low cost. Then, after performing induction hardening processing only to the part used as a rolling surface among outer peripheral surfaces, the tempering process was performed. In this induction hardening treatment, heating is performed at 800 to 950 ° C. for 3 to 10 seconds by high frequency induction heating (frequency 30 to 200 kHz), and then cooling is performed. Further, the tempering treatment is to cool the sample after holding it at 180 ° C. for 2 hours.

  In Comparative Example 1, after carbonitriding for 3 hours at 850 ° C., normal quenching (heating time is 30 minutes) and annealing by furnace heating were performed without performing induction hardening. In Comparative Example 3, the carbonitriding process was performed at 950 ° C. for 4 hours. Further, Comparative Examples 4 and 5 were subjected to induction hardening as they were after turning without performing carbonitriding and annealing.

  Next, an endurance test method will be described with reference to FIG. A pinion shaft 10 fixed by caulking to a member (not shown) corresponding to a carrier is inserted into the outer ring 11, and is freely rollable between the outer peripheral surface of the pinion shaft 10 and the inner peripheral surface of the outer ring 11. The pinion shaft 10 can be rotated by a plurality of needle rollers 12 (outer diameter 2 mm, length 15 mm). The pinion shaft 10 is provided with a lubricating oil supply hole 10a as shown in the figure, and the lubricating oil injected into the opening 10b on the end face is supplied to the rolling surface from the oil supply hole 10a that opens to the cylindrical surface. It has become.

The pinion shaft 10 was rotated under the conditions of a radial load of 5000 N, a rotational speed of 8000 min ⁻¹ , and a lubricating oil temperature of 130 ° C., and the time until peeling occurred on the pinion shaft 10 was evaluated as a lifetime. The radial load was applied to the outer ring 11 via a support bearing (not shown).
The results of the durability test are shown in Tables 1 and 2. In addition, the numerical value of the lifetime in Tables 1 and 2 is shown as a relative value when the lifetime of Comparative Example 2 is 1. The amount of retained austenite (γ _R amount) in the surface layer portion and the core portion and the residual compressive stress in the surface layer portion are values obtained by measuring the rolling surface with an X-ray diffractometer. Further, the former austenite grain size of the surface layer part is observed by a metallographic microscope after corroding with a solution containing picric acid and ferric chloride, followed by the provisions of Japanese Industrial Standard JIS G0551. Asked.

As can be seen from Tables 1 and 2, the pinion shafts of Examples 1 to 9 had excellent durability even under such a high temperature. In particular, Examples 2 to 5, 8, and 9 in which the surface austenite crystal grain size was 10 or more in terms of grain number number and the residual compressive stress was 500 MPa or more had more excellent durability.
On the other hand, in Comparative Example 1, since the amount of retained austenite at the core portion was large, edge loading due to bending occurred and sufficient durability could not be obtained. Further, Comparative Example 2 has insufficient residual compressive stress in the surface layer portion, Comparative Example 3 has a large amount of residual austenite in the surface layer portion, and Comparative Examples 4 and 5 have insufficient residual austenite amounts in the surface layer portion. Durability was not obtained.

  The present invention is applicable to reduction gears and transmissions of automobiles and machine tools.

It is a disassembled perspective view of the planetary gear apparatus which is one Embodiment of this invention. It is sectional drawing explaining the method of the endurance test of a pinion shaft.

Explanation of symbols

1 Sun Gear 2 Ring Gear 3 Pinion Gear 4 Carrier 5,10 Pinion Shaft 12 Needle Roller

Claims (2)

A method of manufacturing a pinion shaft made of bearing steel that is used in a planetary gear device and rotatably supports a pinion gear meshing with a sun gear and a ring gear arranged concentrically, and carbonitriding and annealing are performed on the steel material, followed by In addition, after subjecting only the portion of the outer peripheral surface that becomes the rolling surface to induction hardening, tempering is performed, whereby the amount of retained austenite is 15% by volume to 30% by volume and the residual compressive stress is 500 MPa to 1200 MPa. And a core portion having a residual austenite amount of 0% by volume, and the former austenite crystal grain size of the surface layer portion measured by the method defined in Japanese Industrial Standard JIS G0551 is 8 in terms of particle size number. Thus, a pinion shaft having a surface hardness at the end in the longitudinal direction of Hv300 or less is obtained. A method of manufacturing a pinion shaft characterized by the above. A sun gear, a ring gear concentrically arranged with the sun gear, one or more pinion gears meshing with the sun gear and the ring gear, a pinion shaft rotatably supporting the pinion gear, and the sun gear and the ring gear. In a method of manufacturing a planetary gear device comprising a carrier to which the pinion gear is fixed,
A method for manufacturing a planetary gear device , wherein the pinion shaft is obtained by the method for manufacturing a pinion shaft according to claim 1, and the pinion shaft is fixed to the carrier by caulking.

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