JP2005249112A - Bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the durability by adjusting a high frequency hardened layer of a component treated by high-frequency hardening in a bearing receiving thermal influence during its use. <P>SOLUTION: In this bearing including a rolling shaft 1 as an inner ring and manufactured by performing high-frequency hardening treatment on the rolling shaft 1, a hardness of a surface of the high-frequency hardening layer 1a of the rolling shaft is HRC59-65, and the quantity of austenite remaining on the surface is 30% or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bearing, and more specifically to a bearing that is used in a high temperature environment and has high durability.

  There is a type that uses a bearing in a rocker arm that is one of engine valve mechanisms. The bearing in such a type of rocker arm is used in a high-temperature atmosphere (about 130 to 140 ° C.), and the bearing may sometimes undergo a dimensional change due to the influence of heat. The same applies to the planetary gear bearings of transmissions such as CVT (Continuous Variable Transmission) and AT (Automatic Transmission) missions in addition to the rocker arm bearings described above.

There are a press-fit type and a shaft end caulking type as a method of fixing the bearing to the rocker arm. In the press-fit type, the steel constituting the rolling shaft is brightly quenched (submerged quenching) and tempered. In the shaft end caulking type, high-frequency heat treatment is performed to harden only the rolling surface of the rolling shaft. In the type that performs caulking, it is necessary to perform caulking, and in order to facilitate caulking at the end, a method of performing hardness control along the axial direction in the induction hardening process has been proposed (for example, Patent Document 1).
JP-A-5-321616

  However, when the rolling shaft of the rocker arm bearing is subjected to induction hardening, there are no explanations regarding residual austenite control or problems due to dimensional changes during use, although this is an important issue. Not done. Since the steel part subjected to the above-mentioned induction heat treatment is heated at a high temperature in order to ensure hardness, a larger amount of retained austenite tends to be generated as compared with the case of bright quenching (subduction quenching) and tempering. Since the retained austenite is thermally unstable, it is transformed into martensite under the influence of heat. It is a well-known fact that a dimensional change (expansion) is involved in the transformation to martensite.

  The bearing for the rocker arm is manufactured by bright quenching and tempering of the outer ring and the rollers (rolling elements) of the bearing steel, and the rolling shaft corresponding to the inner ring is induction-hardened and then tempered. . All parts of the outer ring, roller and rolling shaft are made of the same material, but the heat treatment conditions are different, so the amount of retained austenite of the product is different, and as a result, it is affected by heat during use. The amount of dimensional change also varies depending on the part.

  As described above, the rolling shaft that has been subjected to induction hardening and tempering produces a larger amount of retained austenite than bright quenching and tempering. For this reason, a dimensional change arises larger than other components by the influence of the heat | fever generate | occur | produced on severe use conditions. For this reason, an appropriate radial gap or circumferential gap is insufficient before use, which may cause wear or seizure.

  Since the above rolling shaft is not induction hardened by caulking both end portions, the retained austenite does not exist at both end portions, so that a dimensional change is likely to occur in the central portion. In particular, in a sliding type bearing, if the surface pressure is locally increased due to a change in the dimension of the shaft, galling, wear, and the like are generated.

  An object of the present invention is to provide a bearing which is improved in durability by adjusting an induction hardening layer of a component subjected to induction hardening in a bearing placed in a high temperature environment during use.

  The bearing of the present invention includes a rolling shaft that is an inner ring, and the hardness of the surface of the induction hardening layer of the rolling shaft is HRC 59 to 65 in the bearing that performs induction hardening on the rolling shaft. The amount of retained austenite is 30% or less.

  With the above configuration, the amount of deformation can be suppressed in a high-temperature environment, and performance such as rolling fatigue resistance can be improved. Residual austenite can be measured by X-ray diffraction or the like.

Another bearing according to the present invention includes a rolling shaft that is an inner ring, and in the bearing that performs induction hardening on the rolling shaft, the hardness of the surface of the induction hardening layer of the rolling shaft is HRC 59 to 65. And the dimensional change rate after maintaining the rolling shaft at 230 ° C. for 2 hours is set to 5 × 10 ⁻⁴ or less.

  By adjusting the induction heat treatment conditions as described above, the dimensional change in the high temperature environment in the induction hardening layer of the rolling shaft can be suppressed, and as a result, an excessive gap can be prevented. Further, in a sliding type roller follower or the like, it is possible to prevent a local increase in surface pressure and to prevent wear, galling, and the like.

(Embodiment 1)
1 to 3 are cross-sectional views showing a rocker arm bearing according to an embodiment of the present invention. 1 to 3, any bearing 10 includes an outer ring 2 that contacts a cam (not shown), a roller 3, a rocker arm portion 5, and an inner ring 1 that is fixed to the rocker arm portion by caulking. And. In the inner ring 1, induction hardening is applied to the rolling contact surface in contact with the rollers, and an induction hardening layer 1 a in which the amount of retained austenite is adjusted is formed. The hardened layer by induction hardening does not reach the caulking portion 1b, and therefore the caulking portion has a hardness that is significantly lower than that of the induction hardening layer. The rolling shaft was JISG4805 SUJ2 (C: 0.95 to 1.10 wt%, Si: 0.15 to 0.35 wt%, Mn: 0.50 wt%, P: 0.025 wt% or less, S : 0.025% by weight or less, Cr: 1.30 to 1.60% by weight). The steel material for the rolling shaft is not limited to SUJ2, and for example, S53C or SK5 may be used.

  In the induction hardening layer 1a of the rolling shaft of the bearing shown in FIG. 1, the induction hardening layer is formed with a substantially constant depth, and the fixed depth is the induction hardening layer shown in FIGS. Shallower than. The induction hardening layer 1a of the rolling shaft shown in FIG. 2 has a shape that becomes deep at the center. The induction hardening layer 1a of the rolling shaft shown in FIG. 3 extends to the central axis of the rolling shaft and extends over the entire cross section of the rolling shaft.

  In the induction hardened layer 1a of the rolling shaft 1 of the bearing 10 described above, after the induction hardening process (including tempering), the hardness is adjusted to a range of HRC59 to 65 on the surface, and the surface remains on the surface. The amount of austenite is 30% or less.

  4-6 is a figure which shows the shape after use of the rolling shaft shown in FIGS. 1-3. As can be seen with reference to FIGS. 4 to 6, generally, the deeper the induction-hardened layer and the larger the volume ratio, the greater the dimensional change rate after use. Although the definition formula of the dimensional change rate is shown only for the rolling shaft shown in FIG. 6, it goes without saying that the same defining formula is applied to the rolling shaft shown in FIGS. 4 and 5. The rolling shaft diameter in the derivation of the dimensional change rate of the rolling shaft is measured at the center.

The rolling shaft 1 of the bearing 10 shown in FIGS. 1 to 3 has a hardness HRC of 59 to 65 on the surface of the induction-hardened layer regardless of the amount of retained austenite, and the rolling shaft is heated to 230 ° C. for 2 hours. The rate of dimensional change before and after the test is 5 × 10 ⁻⁴ or less. The heat treatment is an acceleration process for checking the dimensional change rate, and the measurement of the dimensional change rate is applied to an unused rolling shaft.

  The bearing used in a high-temperature atmosphere preferably has the shape of the induction-hardened layer of FIGS. 1 and 2 rather than FIG. 3 in terms of suppressing the dimensional change rate. This is because, as the induction hardened layer becomes deeper as shown in FIG. 1 → FIG. 2 → FIG. 3, the quenching temperature increases, and as a result, the amount of retained austenite tends to increase. However, even with the shape of the induction-hardened layer shown in FIG. 3, the retained austenite on the surface can be reduced to 30% or less.

  In the induction hardening, conditions are set so that the amount of retained austenite is obtained. At this time, the high-frequency coil may be changed.

  7 and 8 show the conditions of the induction hardening process. In the condition shown in FIG. 7, since a relatively low frequency of 50 kHz is used, the electric power is input to a relatively deep position without being shielded by the surface current. For this reason, it is suitable for forming the induction hardening layer shown in FIG. 2 or FIG. By lowering the heating temperature to 850 to 900 ° C., the amount of undissolved carbide can be increased and the amount of retained austenite after quenching can be suppressed. Since the heating time to the maximum temperature is as short as 1.2 seconds, the austenite grain size can be made relatively fine. Tempering is performed after induction hardening. In the case of FIG. 7, the temperature is set to a slightly high temperature of 180.degree. By increasing the tempering temperature, the amount of residual austenite can be increased and the amount of residual austenite can be reduced.

  In FIG. 8, since a high frequency of 150 kHz is used, the penetration depth of the electric power is shallower than that in the case of FIG. 7, which is suitable for forming the induction hardening layer shown in FIG. In this case, heating is performed in a short time of 1.0 seconds up to the maximum temperature. The tempering temperature is set to a low temperature of 160 ° C. because induction hardening is a condition for suppressing retained austenite.

  As described above, by adjusting the induction hardening conditions including the tempering conditions, an induction hardening layer having any shape and any amount of retained austenite can be formed. Such production conditions are set so as to be the amount of retained austenite, hardness or dimensional change rate, and hardness. As a result, it is possible to provide a bearing that exhibits high durability when used in a high temperature environment.

  FIG. 9 is a view showing a slide bearing of a type in which the outer ring and the rolling shaft as the inner ring are in contact with each other in the above-described rocker arm bearing. In such a bearing 10, by setting the induction hardening layer of the rolling shaft 1 in the above range, a bearing that can ensure high durability in a high temperature environment can be provided.

(Embodiment 2)
FIG. 10 is a diagram showing a bearing in the second embodiment of the present invention. This is a planetary gear bearing used in the AT mission 50. In FIG. 10, this bearing includes an outer ring 42 that is a planetary gear, a rolling shaft 48 that is an inner ring, and rollers 46 that are interposed between the outer ring and the rolling shaft. Gear teeth provided on the outer ring 42 are arranged so as to mesh with a sun gear fixed to the sun gear shaft 41 and interlocking with the sun gear shaft. The inner ring 48 is caulked at its end and is fixed to the carrier 44.

  The rolling shaft shown in FIG. 10 is JISG4805 SUJ2 (C: 0.95 to 1.10% by weight, Si: 0.15 to 0.35% by weight, Mn: 0.50% by weight, P: 0.025% by weight). %, S: 0.025% by weight or less, Cr: 1.30 to 1.60% by weight). The steel material for the rolling shaft is not limited to SUJ2, and for example, S53C or SK5 may be used.

  In the induction hardening layer of the rolling shaft 48 of the planetary gear described above, after the induction hardening treatment (including tempering), the hardness on the surface is adjusted to the range of HRC59 to 65, and the amount of retained austenite on the surface Is 30% or less.

Regardless of the amount of retained austenite, the rolling shaft 48 of the planetary gear has a dimensional change rate after maintaining the hardness of the induction hardened layer at HRC 59 to 65 and maintaining the rolling shaft at 230 ° C. for 2 hours. It can be 5 × 10 ⁻⁴ or less. This dimensional change rate is applied to unused rolling shafts.

  By using the above-mentioned rolling shaft, it is possible to secure a planetary gear bearing having durability even under severe use conditions in a high temperature environment.

  Modification examples of the embodiment of the present invention will be enumerated including the above-described embodiment.

  In the above-described rolling shaft, an end portion to be fixed to a member other than the bearing by caulking is not included in the induction hardening layer.

  Since the end portion has low hardness, it can be easily caulked.

  In the roller follower bearing for the rocker arm, both ends of the rolling shaft for fixing to the rocker arm by caulking may not be included in the induction hardening layer.

  With this configuration, it is possible to provide a rocker arm bearing that is excellent in durability at high temperatures and that is easily caulked.

  It is a bearing for planetary gears of transmissions such as CVT and AT missions, and both end portions for fixing to the carrier by caulking on the rolling shaft can be excluded from the induction hardening layer.

  With this configuration, it is possible to provide an AT mission planetary gear bearing that has excellent durability at high temperatures and is easy to be caulked.

  The rolling shaft can further have a nitrogen-enriched layer.

  With this configuration, the retained austenite on the surface can be stabilized so as not to be easily transformed into martensite, which helps prevent deformation. In addition, when martensitic transformation is performed under extremely severe stress conditions, durability against rolling fatigue is improved.

  In the above-described bearing, the rolling shaft that is an inner ring may be a sliding bearing that is in contact with the outer ring without a rolling element interposed between the inner ring and the outer ring.

  As described above, the sliding type roller follower can prevent a local increase in surface pressure and can prevent wear, galling, and the like.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  By using the bearing of the present invention, it is possible to provide a highly reliable bearing including a rolling shaft with a small dimensional change even under severe use conditions in a high temperature environment. It is expected to be widely used around planetary gear bearings for transmissions such as CVT and AT missions.

It is a figure which shows an example of the bearing for rocker arms in Embodiment 1 of this invention. It is a figure which shows the other example of the rocker arm bearing in Embodiment 1 of this invention. It is a figure which shows another example of the bearing for rocker arms in Embodiment 1 of this invention. It is a figure which shows the shape after use of the rolling shaft shown in FIG. It is a figure which shows the shape after use of the rolling shaft shown in FIG. It is a figure which shows the shape after use of the rolling shaft shown in FIG. It is a figure which shows an example of the heat pattern of induction hardening and the heat pattern of tempering in Embodiment 1 of this invention. It is a figure which shows the other example of the heat pattern of induction hardening and the heat pattern of tempering in Embodiment 1 of this invention. It is a figure which shows the sliding bearing which is a modification of the bearing for rocker arms in Embodiment 1 of this invention. It is a figure which shows the bearing of the planetary gear of AT mission in Embodiment 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Rolling shaft (inner ring), 1a Induction hardening layer, 1b Caulking process part, 3 Roller (rolling element), 5 Rocker arm part, 10 Rocker arm bearing, 41 Sun gear shaft, 42 Outer ring, 44 Carrier, 46 Roller (Rolling elements), 48 Rolling shaft (inner ring), 50 AT mission.

Claims (7)

  In a bearing that includes a rolling shaft that is an inner ring and that is induction hardened on the rolling shaft, the hardness of the surface of the induction hardening layer of the rolling shaft is HRC 59 to 65, and the amount of retained austenite on the surface is 30. % Or less. In a bearing that includes a rolling shaft that is an inner ring and performs induction hardening treatment on the rolling shaft, the hardness of the surface of the induction hardening layer of the rolling shaft is HRC 59 to 65, and the rolling shaft has a temperature of 230 ° C., A bearing whose dimensional change rate after holding for 2 hours is 5 × 10 ⁻⁴ or less.   The bearing according to claim 1 or 2, wherein an end portion for fixing the rolling shaft to a member other than the bearing by caulking is not included in the induction hardening layer.   The roller follower bearing for a rocker arm according to claim 3, wherein both ends of the rolling shaft for fixing to the rocker arm by caulking are not included in the induction hardening layer.   The bearing for a planetary gear of a transmission, wherein both ends for fixing to a carrier on the rolling shaft by caulking are not included in the induction hardened layer.   The bearing according to claim 1, wherein the rolling shaft further has a nitrogen-enriched layer.   7. The bearing according to claim 1, wherein the rolling shaft that is the inner ring is a sliding bearing that is in contact with the outer ring without a rolling element interposed between the inner ring and the outer ring.

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