JP2005265163A - Bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bearing capable of restraining peeling-off of a surface-damaged type in the bearing including a rotary shaft subjected to high-frequency hardening and caulking and exposed to high temperature. <P>SOLUTION: This bearing comprises the rotary shaft 1, an outer ring 2 and a roller 3 rolling in contact with the outer ring. The rotary shaft has a surface-hardened layer 1a by high-frequency hardening and is within 10 x 10<SP>-5</SP>to 50 x 10<SP>-5</SP>in a dimensional change rate of a central diameter before and after a heating process of 230 °C x 2h. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bearing, and more specifically to a bearing used in a high temperature atmosphere (100 to 200 ° C.) such as an automobile engine or transmission.

  In order to obtain high surface hardness (HRC 58 or higher), steel used for the bearing (especially bearing steel or the like) is heated at a temperature equal to or higher than the A1 transformation point and then quenched into oil or the like to obtain a martensite structure. Next, low temperature tempering at 200 ° C. or lower is performed to remove internal stress. At this time, not all of the austenite generated by the heating before quenching is transformed into martensite, and a part of the austenite phase remains as retained austenite in the martensite. Since this retained austenite is thermally unstable, when left at room temperature for a long time, it gradually transforms into martensite and the volume expands. As a result, the dimensions of the bearing parts change with time. This dimensional change over time becomes a factor that deteriorates the function as a bearing.

  As a typical example of the function deterioration, there is a case where the dimensions are out of specification, particularly the inner diameter of the inner ring which is an inner member is increased, and creep is generated between the inner ring and the shaft. In addition, the bearing clearance (radial clearance, circumferential clearance) is reduced, and there is a possibility of promoting temperature rise and contact between metals in the bearing.

  In order to suppress the secular change of the above dimensions, a method of cooling to below the freezing point after quenching (sub-zero treatment) and transforming residual austenite to martensite is actually performed. (Refer nonpatent literature 1).

In a roller bearing in which a part (roller raceway surface) of an inner member such as a shaft or an inner ring is hardened by high-frequency heat treatment and the end face of the inner member is caulked and fixed, only the surface can be hardened because high-frequency heat treatment is used. For this reason, the amount of retained austenite is small and the secular change is small as compared with the bearing subjected to the bright heat treatment. As a result, even if the inner member is used in a high temperature atmosphere (100 to 200 ° C.) such as an automobile engine or transmission, there is almost no problem with aging, and conventionally, the surface hardness of the rolling shaft and It was only necessary to manage the depth of the hardened layer. For example, in order to caulk the end surface of an inner member such as a rolling shaft, it has been proposed to perform hardness management along the longitudinal direction of the shaft (see Patent Document 1).
JP-A-5-321616 Fujikoshi Heat Treatment Study Group: New heat treatment (Japan Machinist Co.), pages 140-142

  In high-temperature atmospheres (100 to 200 ° C.) such as automobile engines and transmissions, a bearing is used that includes a part in which a hardened layer is formed by high-frequency heat treatment on a part of the bearing part and the end part that is not hardened is caulked. Since high-frequency heat treatment is used, only the surface can be hardened, and the amount of retained austenite is small as described above and the secular change is small as compared with the bearing subjected to the bright heat treatment. It never happened.

  However, with the recent enhancement of functions (higher speed and higher load) and lighter and more compact engines and transmissions, bearings are also required to have higher functions and longer life. Recent bearing failure modes include functional degradation due to the increase in local surface pressure due to the above-mentioned dimensional change, especially bearing clearance (radial clearance) is reduced, and temperature rise in the bearing and contact between metals are reduced. There is a possibility that surface damage type peeling will occur.

  For this reason, it is necessary to take measures to suppress secular change even in bearings in which a part of the inner member of the bearing, for example, the surface layer (orbital surface) of the rolling shaft is hardened by high-frequency heat treatment and the end of the non-hardened part is caulked and fixed. It has become.

  The present invention provides a bearing that includes an induction-hardened hardened layer, includes an inner member that is caulked, and is capable of suppressing surface damage-type peeling in a bearing that is exposed to high temperatures such as an automobile mission. The purpose is to do.

The bearing of the present invention has an inner member and an outer member located around the outer side of the inner member and relatively free to rotate relative to the inner member. The inner member has a surface hardened layer formed by induction hardening. Bearing. In this bearing, the inner member has a dimensional change rate of the center diameter in the range of 10 × 10 ⁻⁵ to 50 × 10 ⁻⁵ before and after the heat treatment of 230 ° C. × 2 h.

  With this configuration, in a bearing in which a part of an inner member such as a shaft or an inner ring is hardened by high-frequency heat treatment and the end portion of the non-hardened portion is caulked, the part that changes over time is limited to the part affected by high-frequency heat treatment. be able to. Deterioration of function due to local increase in surface pressure, especially to prevent surface damage-type peeling promoted by contact between metal and temperature rise due to decrease in bearing clearance (radial clearance) It becomes possible. Moreover, by effectively utilizing the aging change in the limited portion, for example, the edge load of the roller is eliminated by the dimensional change in the above range, and the shape of the inner member is convex with time and temperature ( It is possible to form a gentle crowning shape. As a result, the contact stress with the edge portion of the roller can be relaxed.

(Embodiment 1)
FIGS. 1-3 is sectional drawing which shows the bearing 10 for rocker arms which is a bearing in Embodiment 1 of this invention. 1 to 3, any of the rocker arm bearings 10 includes an outer member (outer ring) 2 that contacts a cam (not shown), a roller 3, a rocker arm portion 5, and a rocker arm portion. And an inner member (inner ring or rolling shaft) 1 fixed by caulking.

  In the rolling shaft 1, induction hardening is applied to the rolling surface in contact with the roller, 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. For this reason, the caulking portion 1b has a hardness significantly lower than that of the induction hardening layer. The rolling shaft 1 is composed of JIS G4805 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 wt% or less, Cr: 1.30 to 1.60 wt%).

  In the induction hardened layer 1a of the rolling shaft of the bearing shown in FIG. 1, the induction hardened layer is formed with a substantially constant depth, and the depth is higher than that of the induction hardened layer shown in FIGS. shallow. 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.

The rolling shaft 1 of the rocker arm bearing 10 according to the embodiment of the present invention has a dimensional change rate of the center diameter of 10 × 10 ⁻⁵ to 50 × 10 before and after the heat treatment of 230 ° C. × 2 h. ^{Be in} the range of ^-5 . In order to achieve the above dimensional change rate, the induction hardening layer 1a of the rolling shaft 1 of the bearing 10 is subjected to induction hardening (including tempering), and then the surface has a hardness of HRC 59 to 65. It is desirable that the amount of retained austenite is adjusted to 30% or less. Since the retained austenite is effective for improving rolling fatigue resistance, it is desirable to contain 10% or more.

4-6 is a figure which shows the shape after use of the rolling shaft 1 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. Do represents the diameter before heat treatment at 230 ° C. for 2 hours, and is approximately equal to the diameter at the end of the rolling shaft. D1 is the diameter at the center of the rolling shaft after the heat treatment. The rolling axis of FIGS. 4 to 6, the dimensional change rate in the process before and after heat treatment 230 ° C. × 2 hours is in a range of ^{10 × 10 -5 ~50 × 10 -5} .

  The shape of the induction hardening layer 1a of the rolling shaft shown in FIGS. 1 to 3 can be freely changed in the hardened layer pattern (heat-affected layer) by setting the conditions for the induction heat treatment. Induction hardening conditions are determined by frequency, heating time, electric energy, and heat pattern. Furthermore, requirements such as coil shape (which may be accompanied by changes in the high frequency coil), type of coolant, cooling time, sub-zero treatment, pre-tempering temperature of the product, tempering temperature, etc. are important. In addition, by controlling the components of the steel material, the distribution shape of the surface hardened layer, etc., it is possible to suppress the above-mentioned aging change to a certain range.

  In the rolling shaft shown in FIG. 3 having the largest heat-affected range, the amount of retained austenite tends to be large, and the dimensional change rate also increases. In the induction hardened layer, the amount of retained austenite decreases in order from FIG. 3 to FIG. 2 to FIG. 1, and the dimensional change rate also decreases. Therefore, as a bearing used in a high-temperature atmosphere (100 to 200 ° C.) such as an automobile engine or transmission, the cured layer pattern shown in FIG. 1 is desirable when the dimensional change rate is to be suppressed within the low range. . However, even in the induction-hardened layer pattern shown in FIGS. 2 and 3, the amount of retained austenite can be reduced by controlling the heat treatment conditions, and the dimensional change rate can be reduced. In the case of the induction hardened layer pattern shown in FIGS. 2 and 3, since the volume of retained austenite is larger in the center portion of the raceway surface than in the end portion of the raceway surface, it can be deformed into a gentle shape in which the center portion of the raceway surface swells. Therefore, the edge stress can be avoided efficiently as in the crowning effect of the roller.

  It is understood from the calculation of the bearing surface pressure that the secular change for eliminating the roller edge load is, for example, when the shaft diameter or the inner ring outer diameter is φ10 mm, the secular variation at the center of the raceway surface is +2 to +6 μm. ing. In order to control the aging change of the inner member, it is necessary to control the induction hardening conditions in the induction heat treatment as described above.

  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. Tempering may or may not be performed after induction hardening. Both cases are called induction hardening. In the case of FIG. By increasing the tempering temperature, the amount of residual austenite decomposed can be increased, but the amount of residual austenite can be adjusted.

  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.

  Aging dimension change is determined by the above factors affecting each other. In addition, since the aging change varies depending on the shape of the shaft, induction heat treatment equipment, etc., it is difficult to set induction hardening conditions a priori. For this reason, adjustment is made by trial error based on the finished product.

  FIG. 9 shows the dimensional change rate of the roller before and after the heat treatment at 230 ° C. for 2 hours, which is an accelerated test of dimensional change, and the dimensional change of the roller before and after holding for 2500 hours at 150 ° C., 120 ° C. and 100 ° C. It is a figure which shows the relationship with a rate. The dimensional change rate on the vertical axis after holding at 150 ° C., 120 ° C. and 100 ° C. for 2500 hours can be interpreted as the dimensional change rate when the bearing is used for a long time. Further, the heat treatment at 230 ° C. × 2 hours can be interpreted as an accelerated test (short-term evaluation test of aging dimensional change) in which retained austenite is almost decomposed into martensite and ε carbide. These are all bright heat-treated products.

  From FIG. 9, it is possible to easily and easily estimate the secular change when the bearing is used for a long time. The bearing according to the embodiment of the present invention is managed as follows from the calculation of the bearing surface pressure and FIG.

230 ° C. × 2 h dimensional change rate at center of raceway surface before and after heat treatment ((size after heat treatment−size before heat treatment) / size before heat treatment): 10 × 10 ⁻⁵ to 50 × 10 ⁻⁵
By producing an inner member (shaft or inner ring) managed as described above, a bearing that eliminates the edge load of the roller and can be used under a rolling surface pressure appropriate for the bearing is provided. Moreover, as a hardening layer pattern (heat influence layer) of induction hardening processing, the hardening layer of the center part is made deep rather than the hardening layer pattern of uniform depth along the longitudinal direction of a rolling shaft. By using such a deep hardened layer pattern at the center, a more gentle crowning shape can be obtained. As a result, the stress at the roller edge portion can be relieved, the crowning of the roller can be eliminated and a small amount of drop can be achieved, and the cost can be reduced. However, since the shaft raceway surface is straight at the beginning, the occurrence of edge stress is predicted. In order to avoid this, it is also possible to incorporate a product that has been aged under the influence of heat before being used as a bearing.

  FIG. 10 is a diagram showing a bearing according to a modification of the first embodiment of the present invention. FIG. 10 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 rocker arm bearing shown in FIG. 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. 11 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. 11, the 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. 11 is JISG4805 SUJ2 (C: 0.95 to 1.10 wt%, Si: 0.15 to 0.35 wt%, Mn: 0.50 wt%, P: 0.025 wt%). %, S: 0.025% by weight or less, Cr: 1.30 to 1.60% by weight).

In the induction hardening layer of the rolling shaft 48 of the planetary gear described above, induction hardening treatment (including tempering) is performed as described above. In this rolling shaft 48, the dimensional change rate before and after the heat treatment at 230 ° C. for 2 hours is in the range of 10 × 10 ⁻⁵ to 50 × 10 ⁻⁵ . For induction hardening for realizing the above dimensional change rate, the method described in the first embodiment of the present invention can be used.

  7 and 8 was used as the induction heat treatment heat pattern, and the induction shaft was induction hardened, and an induction hardening hardened layer was provided on the rolling shaft 1 of the bearing shown in FIGS. The above-mentioned SUJ2 was used as the steel material. The high-frequency heat treatment conditions vary depending on the high-frequency heat treatment equipment (especially frequency, coil shape, etc.), so that the high-frequency output, heating time, etc. vary greatly. Therefore, only typical conditions have been described, but the present invention is judged based on how the product is finished. Therefore, the high-frequency heat treatment conditions are not limited. Similarly, for tempering, conditions such as the number of tempering, tempering temperature, and tempering time are not limited. Further, in order to suppress the secular change, it is possible to insert a sub-zero treatment after the high-frequency heat treatment. The results are shown in Table 1.

  According to Table 1, it is clear that the temperature rise is smaller than that of the comparative example and the temperature rise is suppressed in the bearing having a aging rate of change within the range of the present invention. As for the shape of the induction hardening layer, the retained austenite phase decreases in the order of FIG. 3 → FIG. 2 → FIG. 1, and the dimensional change rate also decreases. A rolling shaft shown in FIG. 1 is desirable as a bearing used in a high temperature atmosphere of 100 ° C. to 200 ° C. such as an automobile engine or transmission.

  However, even with the hardened layer shape of FIGS. 2 and 3, the amount of retained austenite can be reduced by controlling the heat treatment conditions, and the dimensional change rate can be reduced. In the case of the rolling shafts shown in FIGS. 2 and 3, since the amount of retained austenite is larger in the central portion of the rolling shaft than in the end portion, the central portion can be deformed into a shape that gently swells. As a result, the edge stress can be efficiently avoided similarly to the crowning effect of the roller.

  Next, embodiments of the present invention will be enumerated, including those exemplified in the embodiments of the present invention.

You may have a nitrogen enriched layer in the surface layer part of the said inner member. Stable retained austenite is formed by forming a nitrogen-enriched layer on the surface layer, and the crowning shape is adjusted by adjusting the aging change while suppressing surface damage type peeling, facilitating stress adjustment at the edge As described above, the bearing may be a roller follower bearing for a rocker arm, and the end of the inner member may be caulked and fixed to the rocker arm.

  Further, the bearing may be a planetary bearing for a transmission, and the inner member may be caulked and fixed to the carrier.

  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, the dimensional change rate at the center of the diameter of the inner member is within the range of 10 × 10 ⁻⁵ to 50 × 10 ⁻⁵ , eliminating the edge load of the roller, and suitable for the bearing It is possible to provide a bearing that can be used under various rolling contact pressures.

It is a figure which shows the bearing in Embodiment 1 of this invention. It is a figure which shows the other bearing in Embodiment 1 of this invention. It is a figure which shows another bearing in Embodiment 1 of this invention. It is a figure which shows the rolling shaft after use of the bearing of FIG. It is a figure which shows the rolling shaft after use of the bearing of FIG. It is a figure which shows the rolling shaft after use of the bearing of FIG. It is a figure which shows the induction hardening conditions to the rolling shaft in Embodiment 1 of this invention. It is a figure which shows the other induction hardening conditions to the rolling shaft in Embodiment 1 of this invention. It is a figure which shows the relationship between the dimensional change rate in heat processing 230 degreeC x 2 hours, and the dimensional change rate in 100, 120, 150 degreeC x 2500 hours. It is a figure which shows the modification in Embodiment 1 of this invention. It is a figure which shows the bearing in Embodiment 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Rolling shaft (inner member), 1a Induction hardening hardening layer, 1b Caulking part, 2 Outer ring (outer member), 3 Roller (rolling element), 5 Rocker arm, 10 Rocker arm bearing.

Claims (4)

In a bearing having an inner member and an outer member positioned around the outer side of the inner member and in a freely rotatable relationship with the inner member, the inner member has a surface hardened layer by induction hardening.
The inner member is a bearing having a dimensional change rate of a center diameter in a range of 10 × 10 ⁻⁵ to 50 × 10 ⁻⁵ before and after heat treatment at 230 ° C. × 2 h.   The bearing according to claim 1, further comprising a nitrogen-enriched layer in a surface layer portion of the inner member.   The bearing according to claim 1, wherein the bearing is a roller follower bearing for a rocker arm, and an end portion of the inner member is caulked and fixed to the rocker arm.   The bearing according to claim 1, wherein the bearing is a planetary bearing for a transmission, and the inner member is caulked and fixed to a carrier.

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