Patent Grant
11473184
This application is based upon and claims the benefit of priority from Japanese patent application No. 2020-021463, filed on Feb. 12, 2020, the disclosure of which is incorporated herein in its entirety by reference.
The present disclosure relates to a method for manufacturing a metal ring laminate.
A continuously variable transmission (CVT) of a steel belt-type in which an input-side pulley and an output-side pulley are connected to each other by a steel transmission belt is used in, for instance, automobiles. The transmission belt of the steel belt-type CVT has a structure in which a plurality of elements that are aligned without any gaps therebetween are attached to a metal ring laminate formed of a plurality of thin metal rings laminated in a nested manner. The elements are pressed against the input-side pulley and the output-side pulley by the tensile stress of the metal ring laminate, and therefore power is transmitted from the input-side pulley to the output-side pulley.
In order to ensure frictional force between the elements and the input-side and the output-side pulleys, high tensile stress is applied to each metal ring forming the metal ring laminate. Therefore, maraging steel, which is ultra-high strength steel hardened by precipitation, is used for the metal rings. Further, repeated flexural stress is applied to the metal rings under a high tensile stress state. Therefore, in order to enhance the fatigue strength, a nitriding treatment for imparting compressive residual stress to the surface of the metal rings is performed.
In general, the nitriding treatment is performed on each of the plurality of the metal rings, and then the plurality of the nitrided metal rings are laminated. Accordingly, there has been a problem that the size of the nitriding treatment apparatus becomes large. Published Japanese Translation of PCT International Publication for Patent Application, No. 2016-505092 discloses a technique in which a plurality of metal rings are laminated to form the metal ring laminate described above and then a nitriding treatment is performed on the metal ring laminate.
The inventors have found the following problem as regards a method for manufacturing a metal ring laminate in which an aging treatment is performed on the metal ring laminate obtained by laminating a plurality of metal rings made of maraging steel and then a nitriding treatment is performed on the metal ring laminate.
As disclosed in Published Japanese Translation of PCT International Publication for Patent Application, No. 2016-505092, when the nitriding treatment is performed on the metal ring laminate, hardly any nitrogen gas such as ammonia enters the metal rings disposed in the middle of the metal ring laminate, and thus these metal rings are hardly nitrided. Therefore, there has been a problem that the difference between the surface hardness of the metal rings disposed on the surface side of the metal ring laminate and the surface hardness of the metal rings disposed in the middle of the metal ring laminate becomes large.
The present disclosure has been made in view of the problem mentioned above, and the present disclosure is to make the difference between the surface hardness of the metal rings disposed on the surface side of the metal ring laminate and the surface hardness of the metal rings disposed in the middle of the metal ring laminate small while maintaining a desired strength of the metal rings.
A method for manufacturing a metal ring laminate according to an aspect of the present disclosure includes:
performing an aging treatment on a metal ring laminate in which a plurality of metal rings made of maraging steel are laminated; and
performing a nitriding treatment on the metal ring laminate on which the aging treatment has been performed, in which
an oxidizing treatment is performed after the aging treatment but before the nitriding treatment at a temperature equal to or higher than 350° C. and lower than an aging treatment temperature.
In the method for manufacturing the metal ring laminate according to the aforementioned aspect of the present disclosure, the oxidizing treatment is performed on the metal ring laminate after the aging treatment but before the nitriding treatment at a temperature equal to or higher than 350° C. and equal to or lower than an aging treatment temperature. Therefore, the difference between the surface hardness of the metal rings disposed on the surface side of the metal ring laminate and the surface hardness of the metal rings disposed in the middle of the metal ring laminate can be made small while maintaining a desired strength of the metal rings.
The aging treatment temperature may fall in a range of 450° C. to 500° C. In addition, the metal ring laminate may be used for a transmission belt of a continuously variable transmission.
According to the present disclosure, the difference between the surface hardness of the metal rings disposed on the surface side of the metal ring laminate and the surface hardness of the metal rings disposed in the middle of the metal ring laminate can be made small while maintaining a desired strength of the metal rings.
The above and other objects, features and advantages of the present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present disclosure.
Hereinafter, the present disclosure will be described through specific embodiments to which the present disclosure is applied with reference to the drawings. However, the present disclosure is not to be limited to the embodiments described below. Note that the following description and the attached drawings are appropriately shortened and simplified where appropriate to clarify the explanation.
<Structure of Metal Ring>
First, a metal ring that constitutes a metal ring laminate manufactured by a method for manufacturing a metal ring laminate according to a first embodiment is described with reference to
The metal ring 11 is a belt-like thin plate member made of maraging steel. The metal ring 11 has a thickness of, for example, around 0.150 mm to 0.200 mm, and a width of, for example, around 10 mm. As shown in
Note that the metal ring 11 is gently curved such that a widthwise center part thereof protrudes slightly more toward the outer circumferential surface 11a side compared to both widthwise end parts thereof.
The metal ring 11 is made of maraging steel. The maraging steel is a ultra-high strength steel hardened by precipitation and having a carbon concentration equal to or lower than 0.03% by mass and doped with, for instance, nickel (Ni), cobalt (Co), molybdenum (Mo), titanium (Ti), and aluminum (Al), and can exhibit high strength and toughness when the aging treatment is performed. The composition of the maraging steel is, for example, 17% to 19% by mass of Ni, 7% to 13% by mass of Co, 3% to 6% by mass of Mo, 0.3% to 1.0% by mass of Ti, and 0.05% to 0.15% by mass of Al, the rest of the parts of the composition being Fe and inevitable impurities. Further, small amounts of, for instance, Cr and Cu may also be contained in the composition.
To be more specific, as described later with reference to
<Configuration of Belt-Type Continuously Variable Transmission to which Metal Ring is Applied>
Next, a belt-type continuously variable transmission 1 that employs the metal ring laminate manufactured by the method for manufacturing the metal ring laminate according to the first embodiment is described with reference to
As shown in
An enlarged diagram of the transmission belt 2 is shown in a circle indicated by the dashed lines in
As shown in
Here, as shown in
As shown in
The compression coil spring 7 energizes the moveable-side sheave member 5b in a downshifting direction which is a direction toward which the groove width W of the output-side pulley 5 is reduced.
The hydraulic actuator 8 displaces the moveable-side sheave member 5b in the axial direction by causing hydraulic pressure to act on a back side of the moveable sheave member 5b.
By this configuration, a winding radius r of the transmission belt 2 with respect to the output-side pulley 5 can be varied within a range of the minimum radius rmin to the maximum radius rmax.
Note that except that an energizing member such as the compression coil spring 7 is not included in the input-side pulley 4 while it is included in the output-side pulley 5, the input-side pulley 4 and the output-side pulley 5 have substantially the same configuration. Although not illustrated in detail, the input-side pulley 4 includes the fixed-side sheave member fixed to the input shaft 3 and the moveable-side sheave member supported by the input shaft 3 in a moveable manner in the axial direction so as to form a roughly V-shaped groove with the fixed-side sheave member. The input-side pulley 4 further includes a hydraulic actuator that is capable of energizing the moveable-side sheave member in an upshifting direction.
<Method for Manufacturing Metal Ring>
Next, the method for manufacturing the metal ring laminate according to the first embodiment is described with reference to
Prior to performing the steps shown in
First, as shown in the upper half of
Next, as shown in the lower half of
Next, although not illustrated, the thickness of the metal ring 11 is reduced to a prescribed value and the perimeter thereof is lengthened to a prescribed length.
Then, in order to remove distortion, annealing is performed in a nitrogen atmosphere or a reducing atmosphere at a temperature around 800° C. to 900° C. for about 5 to 30 minutes.
Further, tensile stress is applied to the sintered metal ring 11 so that the perimeter of the metal ring is precisely adjusted to the prescribed length thereof, and then a plurality of the metal rings 11 are laminated to form the metal ring laminate 10.
Thereafter, the steps shown in
First, as shown in
Next, the oxidizing treatment is performed on the metal ring laminate 10 (Step ST2). The oxidizing treatment is a pretreatment process for promoting the nitriding treatment. The oxidizing treatment is performed at a temperature equal to or higher than 350° C. and equal to or lower than the aging treatment temperature. The oxidizing treatment time is, for example, 15 to 60 minutes. Details of the oxidizing treatment temperature are described later.
Finally, the nitriding treatment is performed on the metal ring laminate 10 (Step ST3). The nitriding treatment is performed, for example, under an atmosphere of 5% to 15% by volume of ammonia gas, 1% to 3% by volume of hydrogen gas, and the rest being nitrogen gas, at a temperature of around 400° C. to 450° C. for about 40 to 120 minutes.
Note that the hydrogen gas contained within the atmosphere is generated by pyrolysis reaction of ammonia gas shown below.
2NH3→2(N)+3H2
Here, (N) denotes nitrogen atoms that are generated due to contact with the surface of the metal ring 11. Due to entry of these nitrogen atoms inside the metal ring 11, nitride is generated, and the nitrided layer 12 shown in
As described above, in the method for manufacturing the metal ring laminate according to the present embodiment, the nitriding treatment is performed on the metal ring laminate 10 instead of performing the nitriding treatment on each of the plurality of the metal rings 11. Accordingly, the nitriding treatment apparatus can be reduced in size.
On the other hand, when performing the nitriding treatment on the metal ring laminate 10, the difference between the surface hardness of the metal rings disposed on the surface side of the metal ring laminate and the surface hardness of the metal rings disposed in the middle of the metal ring laminate is prone to occur compared to the case where the nitriding treatment is performed on each of the plurality of the metal rings 11.
Specifically, since the outer circumferential surface 11a of the metal ring 11 on the outermost periphery of the metal ring laminate and the inner circumferential surface 11b of the metal ring 11 on the innermost periphery of the metal ring laminate are exposed, these metal rings are easily nitrided. On the other hand, the outer circumferential surface 11a and the inner circumferential surface 11b of the metal ring 11 disposed in the middle of the metal ring laminate 10 are in close contact with the outer circumferential surface 11a or the inner circumferential surface 11b of the adjacent metal ring 11, and hence hardly any ammonia gas enters the metal rings 11 that are disposed in the middle of the metal ring laminate, and thus these metal rings are hardly nitrided.
Therefore, the nitrided layer 12 is thinner on the outer circumferential surface 11a and the inner circumferential surface 11b of the metal ring 11 disposed in the middle of the metal ring laminate 10 compared to the nitrided layer 12 on the outer circumferential surface 11a of the metal ring 11 on the outermost periphery of the metal ring laminate 10 and on the inner circumferential surface 11b of the metal ring 11 on the innermost periphery of the metal ring laminate 10, and thus the surface hardness of the metal ring 11 disposed in the middle of the metal ring laminate 10 is prone to be small.
Further, the surface hardness of the inner circumferential surface 11b of the metal ring 11 on the outermost periphery of the metal ring laminate 10 and the surface hardness of the outer circumferential surface 11a of the metal ring 11 on the innermost periphery of the metal ring laminate 10 are also prone to be small. Note that the thickness of the nitride layer 12 can be measured through, for example, microstructure observation performed after performing the natal etching. Further, the surface hardness of the metal ring 11 can be measured by, for example, performing the micro-Vickers hardness test.
In the method for manufacturing the metal ring laminate according to the present embodiment, the oxidizing treatment for promoting the nitriding treatment is performed at a temperature equal to or higher than 350° C. and equal to or lower than the aging treatment temperature. By setting the oxidizing treatment temperature at a temperature equal to or higher than 350° C., the difference between the surface hardness of the metal rings 11 of the metal ring laminate 10 can be made small. On the other hand, by setting the oxidizing treatment temperature equal to or lower than the aging treatment temperature, excessive aging can be suppressed, and the strength of the bulk (the non-nitrided part 11d) of the metal ring 11 can be maintained at a desired strength.
<Regarding Oxidizing Treatment Temperature>
As described above, in the method for manufacturing the metal ring laminate according to the present embodiment, the oxidizing treatment is performed at a temperature equal to or higher than 350° C. in order to make the difference between the surface hardness of the metal rings 11 of the metal ring laminate 10 small. Hereinbelow, the oxidizing treatment temperature is described.
As shown in
After the oxidizing treatment was performed on the metal rings 11 on which the aging treatment has been performed, the nitriding treatment was performed in the same manner as in the method for manufacturing the metal ring laminate according to the present embodiment.
The aging treatment was performed under an atmosphere of 90% of N2 gas+10% of H2 gas at a temperature of 470° C. for 120 minutes.
The oxidizing treatment was performed under the atmospheric condition for 30 minutes at respective temperatures.
The nitriding treatment was performed under an atmosphere of 90% of N2 gas+10% of NH3 gas at a temperature of 420° C. for 70 minutes.
The surface hardness (HV) of the metal rings 11 of the metal ring laminate that has been nitrided can be measured by performing the micro-Vickers hardness test.
As shown in
As shown in
Next, the surface hardness of the metal rings of the metal ring laminate 10 formed by laminating nine metal rings 11 composed of 12% by mass of Co shown in
Here, the metal ring laminates 10 that were oxidized at oxidizing treatment temperatures 300° C. and 330° C., respectively, are comparative examples and the metal ring laminates 10 that were oxidized at oxidizing treatment temperatures 360° C. and 400° C., respectively, are embodiments.
In
On the uppers side of each of the graphs shown in
As shown in
On the other hand, as shown in
Further, as shown in
On the other hand, as shown in
Further, as shown in
That is, although the surface hardness of the metal rings of the metal ring laminate 10 according to each of the embodiments in which the oxidizing treatment temperatures were 360° C. and 400° C., respectively, decreased, the difference between the surface hardness of the metal rings 11 according to the comparative example could be decreased dramatically to be as small as approximately equal to or lower than 30 HV.
It is considered that in the metal ring laminate 10, the oxygen concentration at the time of the oxidizing treatment and the ammonia gas concentration at the time of the nitriding treatment are lower in the center rings in the widthwise center part of the metal ring laminate than in the surface rings in the widthwise center part of the metal ring laminate. Therefore, oxidizing that promotes nitriding is less likely to occur in the center rings in the widthwise center part of the metal ring laminate compared to the surface rings in the widthwise center part of the metal ring laminate, and thus it is considered that nitriding is unlikely to occur in the center rings thereafter. Therefore, as shown in
Further, since the oxygen concentration is low in the center rings in the widthwise center part of the metal ring laminate compared to the surface rings in the widthwise center part of the metal ring laminate, the oxidizing treatment temperature at which the surface hardness indicates the peak value shifts to a temperature near 330° C. Further, as shown in
Therefore, the difference between the surface hardness of the surface rings and the surface hardness of the center rings decreased sharply. Thus, as shown by the dotted area in
From the disclosure thus described, it will be obvious that the embodiments of the disclosure may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2020-021463 | Feb 2020 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20160059288 | Koga | Mar 2016 | A1 |
| 20160290437 | Serizawa | Oct 2016 | A1 |
| Number | Date | Country |
|---|---|---|
| 106051046 | Oct 2016 | CN |
| 2004-43962 | Feb 2004 | JP |
| 2016-505092 | Feb 2016 | JP |
| 2014102214 | Jul 2014 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20210246540 A1 | Aug 2021 | US |
