JP5760480B2 - Toroidal type continuously variable transmission disk and manufacturing method thereof - Google Patents

Description

  The present invention relates to a toroidal-type continuously variable transmission disk that can be used in transmissions of automobiles and various industrial machines, and a manufacturing method thereof.

  For example, a double-cavity toroidal continuously variable transmission used as a transmission for an automobile is configured as shown in FIGS. As shown in FIG. 7, an input shaft (center shaft) 1 is rotatably supported inside the casing 50, and two input side disks 2, 2 and two outputs are provided on the outer periphery of the input shaft 1. Side disks 3 and 3 are attached. An output gear 4 is rotatably supported on the outer periphery of the intermediate portion of the input shaft 1. Output side disks 3 and 3 are connected to cylindrical flange portions 4a and 4a provided at the center of the output gear 4 by spline coupling.

  The input shaft 1 is rotationally driven by a drive shaft 22 via a loading cam type pressing device 12 provided between an input side disk 2 and a cam plate 7 located on the left side in the drawing. . The output gear 4 is supported in the casing 50 via a partition wall 13 formed by coupling two members, so that the output gear 4 can rotate around the axis O of the input shaft 1 while the axis O. Directional displacement is prevented.

  The output side disks 3 and 3 are supported by needle bearings 5 and 5 interposed between the input shaft 1 so as to be rotatable about the axis O of the input shaft 1. Further, the left input side disk 2 in the figure is supported on the input shaft 1 via a ball spline 6, and the right side input disk 2 in the figure is splined to the input shaft 1. Rotates with the input shaft 1. Further, the power roller 11 (see FIG. 8) is freely rotatable between the inner side surfaces (concave surfaces) 2a, 2a of the input side discs 2, 2 and the inner side surfaces (concave surfaces) 3a, 3a of the output side discs 3, 3. Is sandwiched between.

  A step 2b is provided on the inner peripheral surface 2c of the input side disk 2 located on the right side in FIG. 7, and the step 1b provided on the outer peripheral surface 1a of the input shaft 1 is abutted against the step 2b. At the same time, the back surface (the right surface in FIG. 7) of the input side disk 2 is abutted against the loading nut 9. Thereby, the displacement of the input side disk 2 in the direction of the axis O with respect to the input shaft 1 is substantially prevented. Further, a disc spring 8 is provided between the cam plate 7 and the flange 1d of the input shaft 1, and this disc spring 8 is a concave surface 2a, 2a, 3a of each disk 2, 2, 3, 3. , 3a and the contact surface between the peripheral surfaces 11a and 11a of the power rollers 11 and 11 are applied with a pressing force.

  8 is a cross-sectional view taken along line AA in FIG. As shown in FIG. 8, a pair of trunnions 15, 15 that swing about a pair of pivots 14, 14 that are twisted with respect to the input shaft 1 are provided inside the casing 50. In addition, illustration of the input shaft 1 is abbreviate | omitted in FIG. Each trunnion 15, 15 is a pair of bent portions formed on the inner surface side of the support plate 16 at both ends in the longitudinal direction (vertical direction in FIG. 8) of the support plate 16 that supports the power roller 11. It has the bent wall parts 20 and 20. The bent wall portions 20 and 20 form concave pocket portions P for accommodating the power rollers 11 in the trunnions 15 and 15. Further, the pivot shafts 14 and 14 are concentrically provided on the outer side surfaces of the bent wall portions 20 and 20, respectively.

  A circular hole 21 is formed in the central portion of the support plate portion 16, and the base end portion 23 a of the displacement shaft 23 is supported in the circular hole 21. Then, by swinging each trunnion 15, 15 about each pivot 14, 14, the inclination angle of the displacement shaft (shaft) 23 supported at the center of each trunnion 15, 15 can be adjusted. It has become. In addition, each power roller 11 is rotatably supported via a radial needle bearing 99 around the distal end portion 23b of the displacement shaft 23 protruding from the inner surface of each trunnion 15, 15. 11 is sandwiched between the input disks 2 and 2 and the output disks 3 and 3. In addition, the base end part 23a and the front-end | tip part 23b of each displacement shaft 23 and 23 are mutually eccentric.

  Further, the pivot shafts 14 and 14 of the trunnions 15 and 15 are supported so as to be swingable with respect to the pair of yokes 23A and 23B and to be displaceable in the axial direction (vertical direction in FIG. 8). The horizontal movement of the trunnions 15 and 15 is restricted by 23B. Each yoke 23A, 23B is formed in a rectangular shape by pressing or forging a metal such as steel. Four circular support holes 18 are provided at the four corners of each of the yokes 23 </ b> A and 23 </ b> B, and the pivot shafts 14 provided at both ends of the trunnion 15 swing through the radial needle bearings 30. It is supported freely. In addition, a circular locking hole 19 is provided in the central portion of the yokes 23A and 23B in the width direction (the left-right direction in FIG. 7). 64 and 68 are fitted inside. That is, the upper yoke 23A is swingably supported by the spherical post 64 supported by the casing 50 via the fixing member 52, and the lower yoke 23B is supported by the spherical post 68 and the drive for supporting the same. The upper cylinder body 61 of the cylinder 31 is swingably supported.

  The displacement shafts 23 and 23 provided in the trunnions 15 and 15 are provided at positions 180 degrees opposite to the input shaft 1. Further, the direction in which the distal end portion 23b of each of the displacement shafts 23, 23 is eccentric with respect to the base end portion 23a is the same direction as the rotational direction of the both disks 2, 2, 3, 3 (up and down in FIG. 8). (Reverse direction). Further, the eccentric direction is a direction substantially orthogonal to the direction in which the input shaft 1 is disposed. Accordingly, the power rollers 11 and 11 are supported so that they can be slightly displaced in the longitudinal direction of the input shaft 1. As a result, even if each power roller 11, 11 tends to be displaced in the axial direction of the input shaft 1 due to elastic deformation of each component member based on the thrust load generated by the pressing device 12, each component This displacement is absorbed without applying an excessive force to the member.

  Further, between the outer surface of the power roller 11 and the inner surface of the support plate portion 16 of the trunnion 15, a thrust ball bearing 24 that is a thrust rolling bearing, and a thrust needle bearing, in order from the outer surface side of the power roller 11. 25. Among these, the thrust ball bearing 24 supports the rotation of each power roller 11 while supporting the load in the thrust direction applied to each power roller 11. Each of such thrust ball bearings 24 includes a plurality of balls (hereinafter referred to as rolling elements) 26, 26, an annular retainer 27 that holds the rolling elements 26, 26 in a freely rolling manner, And an annular outer ring 28. Further, the inner ring raceway of each thrust ball bearing 24 is formed on the outer side surface (large end surface) of each power roller 11, and the outer ring raceway is formed on the inner side surface of each outer ring 28.

  The thrust needle bearing 25 is sandwiched between the inner surface of the support plate portion 16 of the trunnion 15 and the outer surface of the outer ring 28. Such a thrust needle bearing 25 supports the thrust load applied to each outer ring 28 from the power roller 11, while the power roller 11 and the outer ring 28 swing around the base end portion 23 a of each displacement shaft 23. Allow.

  Further, driving rods (trunnion shafts) 29 and 29 are provided at one end portions (lower end portions in FIG. 8) of the trunnions 15 and 15, respectively, and a driving piston ( Hydraulic pistons) 33, 33 are fixed. Each of these drive pistons 33 and 33 is oil-tightly fitted in a drive cylinder 31 constituted by an upper cylinder body 61 and a lower cylinder body 62. The drive pistons 33 and 33 and the drive cylinder 31 constitute a drive device 32 that displaces the trunnions 15 and 15 in the axial direction of the pivots 14 and 14 of the trunnions 15 and 15.

  In the case of the toroidal continuously variable transmission configured as described above, the rotation of the input shaft 1 is transmitted to the input side disks 2 and 2 via the pressing device 12. Then, the rotation of the input side disks 2 and 2 is transmitted to the output side disks 3 and 3 via the pair of power rollers 11 and 11, and the rotation of the output side disks 3 and 3 is further transmitted to the output gear 4. Is taken out more.

  When changing the rotational speed ratio between the input shaft 1 and the output gear 4, the pair of drive pistons 33, 33 are displaced in opposite directions. As the drive pistons 33 and 33 are displaced, the pair of trunnions 15 and 15 are displaced in directions opposite to each other. For example, the power roller 11 on the left side in FIG. 8 is displaced to the lower side in the figure, and the power roller 11 on the right side in the figure is displaced to the upper side in the figure. As a result, the peripheral surfaces 11a and 11a of the power rollers 11 and 11 act on contact portions of the input side disks 2 and 2 and the inner side surfaces 2a, 2a, 3a and 3a of the output side disks 3 and 3, respectively. The direction of the tangential force changes. As the force changes, the trunnions 15 and 15 swing (tilt) in opposite directions around the pivots 14 and 14 pivotally supported by the yokes 23A and 23B.

  As a result, the contact position between the peripheral surfaces 11a and 11a of the power rollers 11 and 11 and the inner surfaces 2a and 3a changes, and the gear ratio between the input shaft 1 and the output gear 4 changes. Further, when the torque transmitted between the input shaft 1 and the output gear 4 fluctuates and the amount of elastic deformation of each component changes, the power rollers 11 and 11 and the outer rings attached to the power rollers 11 and 11 will be described. 28 and 28 slightly rotate around the base end portions 23a and 23a of the displacement shafts 23 and 23, respectively. Since the thrust needle bearings 25 and 25 exist between the outer side surfaces of the outer rings 28 and 28 and the inner side surfaces of the support plate portions 16 constituting the trunnions 15 and 15, respectively, the rotation is performed smoothly. Is called. Therefore, as described above, the force for changing the inclination angle of each displacement shaft 23, 23 can be small.

  Incidentally, since the input side disk 2 and the output side disk 3 described above are portions subjected to stress, heat treatment for curing the surface is required. When the carburizing process is performed as the curing heat treatment for the disks 2 and 3, unlike a normal bearing, it is necessary to increase the depth of the cured layer, and thus a long-time process is required. On the other hand, in the case of induction hardening, since the treatment can be performed in a short time, the heat treatment cost can be reduced (for example, see Patent Documents 1 to 4).

JP-A-9-79339 Japanese Patent Laid-Open No. 2005-226753 JP 2002-257206 A JP-A-8-283863

  As for the range of the hardened layer depth of the disks 2 and 3, it is ideal to have a hardened layer depth of a predetermined level or more over the entire surface of the disk. It is necessary to attach the discs 2 and 3 to the induction hardening device (for this reason, the discs 2 and 3 need to be attached to the device side). And the coil shape is technically difficult.

  In addition, since it is difficult to simultaneously cure the entire surfaces of the disks 2 and 3 by induction hardening as described above, induction hardening is performed in two steps, or a portion that is not to be cured is set as a support for attaching to the induction hardening apparatus. Then, several methods are performed, for example, induction hardening is completed once. In these methods, a boundary portion is inevitably generated between the hardened layers. However, since this boundary portion is not quenched, there is a problem that the hardness is low and a residual tensile stress is generated.

  The present invention has been made in view of the above circumstances, and a toroidal continuously variable transmission having an appropriate hardness distribution without residual tensile stress formed by reliably quenching a portion to be induction-hardened. It is an object of the present invention to provide a disk and a manufacturing method thereof.

In order to achieve the above object, the present invention provides a toroidal continuously variable transmission disk that transmits a rotational force at a predetermined speed ratio via power rollers interposed between each other, and the operation of the transmission. The boundary between the hardened layers generated on the disk by at least two induction hardenings has a low stress part where the stress generated on the disk surface is sometimes relatively low and a high stress part where the stress is relatively high. A hardened layer is formed so as to be set at a low stress site.

  According to the above configuration, since the hardened layer is formed so that the boundary between the hardened layers generated in the disk by induction hardening is set at the low stress part of the disk, the high stress part of the disk is insufficiently hardened (hardened) It is possible to avoid situations such as insufficient processing) or quenching (not cured). That is, the high stress portion of the disk to be induction hardened is surely hardened, and an appropriate hardness distribution without residual tensile stress can be realized.

  In the above configuration, the outermost circumferential surface of the disk in the radial direction or the innermost circumferential surface of the disk in the radial direction is located in the vicinity of the back surface on the side opposite to the force transmission surface involved in the transmission of rotational force. It is preferable that the boundary portion exists in at least one of the rear side portions. In this case, after the induction hardening is first applied to the force transmission surface of the disc and the inner peripheral surface excluding the back side portion, the induction back is applied to the back surface of the disc, and the back surface It is preferable that the hardened layer is formed by cooling the force-transmitting surface that has been quenched and the inner peripheral surface excluding the back side portion during quenching. Alternatively, after first induction hardening is performed on the back surface of the disk, induction hardening is performed on the force transmission surface of the disk and the inner peripheral surface excluding the back side portion, and the force transmission surface The hardened layer may be formed by cooling the quenched back surface while the inner peripheral surface excluding the back side portion is quenched. In addition, in this invention, a hardened layer means the site | part more than Hv550.

  The present invention also relates to a method of manufacturing a disk of a toroidal type continuously variable transmission that transmits a rotational force at a predetermined speed ratio via power rollers interposed between each other, and induction-hardened on the surface of the disk. In the manufacturing method of forming a hardened layer having a predetermined depth by the outer peripheral surface of the outermost radial direction of the disk, or the force transmission surface involved in the transmission of rotational force among the innermost inner peripheral surface of the disk radial direction, The hardened layer is formed so that a boundary portion between the hardened layers exists in at least one of the back side portions located in the vicinity of the back side on the opposite side.

  According to this manufacturing method, it is possible to provide a toroidal-type continuously variable transmission disk having an appropriate hardness distribution that does not involve residual tensile stress in which a portion to be induction-hardened is securely quenched.

  In the above method, after first subjecting the force transmission surface of the disc and the inner peripheral surface excluding the back side portion to induction hardening, subjecting the back side of the disc to induction hardening, It is preferable that the force-transmitting surface that has been quenched and the inner peripheral surface excluding the back-side portion are cooled while the material is being quenched.

  According to the present invention, since the hardened layer is formed so that the boundary between the hardened layers generated in the disk by induction hardening is set at the low stress part of the disk, the part to be subjected to induction hardening is sure. It is possible to provide a disk for a toroidal type continuously variable transmission and a method for manufacturing the same having a proper hardness distribution without residual tensile stress.

It is a schematic side view which shows the low stress site | part at the time of the transmission driving | running | working of the output side disk, and a high stress site | part. It is a schematic side view which shows the formation form of the hardened layer of the output side disk which concerns on embodiment of this invention. FIG. 3 is a schematic diagram showing a first processing step of the first manufacturing method of the output side disk of FIG. 2. FIG. 4 is a schematic diagram showing a second processing step of the first manufacturing method of the output side disk of FIG. 2. It is the schematic which shows the 1st process process of the 2nd manufacturing method of the output side disk of FIG. It is the schematic which shows the 2nd process process of the 2nd manufacturing method of the output side disk of FIG. It is sectional drawing which shows an example of the specific structure of the half toroidal type continuously variable transmission conventionally known. It is sectional drawing which follows the AA line of FIG.

Embodiments of the present invention will be described below with reference to the drawings.
The feature of the present invention lies in the induction hardening mode of the disc, and other configurations and operations are the same as the conventional configuration and operations described above. Therefore, only the features of the present invention will be referred to below, and The other parts are simply described with the same reference numerals as those in FIGS.

  FIG. 1 shows an output-side disk 3 which is an example of a toroidal-type continuously variable transmission disk (note that the output-side disk 3 will be described below as an example, but the following description will be applied to the input-side disk 2). Needless to say the same applies). As shown in the figure, the output-side disk 3 includes a low-stress part 100 (100a, 100b) where the stress generated on the disk surface during operation of the transmission is relatively low and a high-stress part 102 (102a, 102b) where the stress is relatively high. 102b). In the present embodiment, the low-stress portion 100 is an inner surface that is a concave surface involved in transmission of rotational force among the radially outermost outer peripheral surface 100a of the disk 3 and the radially innermost inner peripheral surface of the disk 3. (Force transmitting surface) This is a back side portion 100b located in the vicinity of the back surface 3b opposite to the 3a. On the other hand, the high-stress part 102 is involved in the transmission of the rotational force among the inner side surface (force transmission surface) 3a (102a) that is a concave surface involved in the transmission of the rotational force and the radially innermost inner peripheral surface of the disk 3. A portion 102b located in the vicinity of the concave inner surface (force transmission surface) 3a and a back surface 3b (102c). Note that the low-stress part 100 and the high-stress part 102 differ depending on the place (input side, output side, front and rear of the cavity, etc.) and the type (separate type or integrated type) of the disc. It is preferable to set by calculating the stress of time.

  Here, as shown in FIG. 2, the output side disk 3 of the present embodiment forms hardened layers (Hv550 or higher) 130A, 130B, 130C having a predetermined depth in the high stress portions 102a, 102b, 102c by induction hardening. As a result, a hardened layer is not formed in the low stress portions 100a and 100b. That is, in the output side disk 3 of the present embodiment, the boundary portions 120A, 120B between the hardened layers 130A, 130B, 130C are set to the low stress portions 100a, 100b by the manufacturing method shown in FIGS. Thus, the hardened layers 130A, 130B, and 130C are formed. In addition, it is preferable that the space | interval of the hardened layers mutually separated by boundary part 120A, 120B is 1 mm or more.

  3 and 4 show the processing steps for forming a hardened layer on the output side disk 3 step by step. In order to obtain the hardened layer form shown in FIG. 2, first, as shown in FIG. 3, the high frequency is first applied to the inner side surface 3a of the output side disk 3 and the inner peripheral surface 102b excluding the rear side portion 100b. Quenching is performed (first quenching). In this case, induction hardening is performed in a state where the heating coil 160 is opposed to the inner side surface 3 a and the inner peripheral surface 102 b of the disk 3. Thereafter, induction hardening is performed on the back surface 3b of the disk 3 (second hardening). Also in this case, induction hardening is performed with the heating coil 160 facing the back surface 3 b of the disk 3. At this time, that is, during the induction hardening of the back surface 3b, the inner surface 3a and the inner peripheral surface 102b of the hardened disc 3 are simultaneously cooled. This cooling is performed, for example, by spraying the cooling liquid 171 in a state where the cooling nozzle 170 is opposed to the inner side surface 3 a and the inner peripheral surface 102 b of the disk 3. The purpose of cooling the first quenching simultaneously with the second quenching is to prevent the first quenching portion from being heated and tempered. In addition, if the first quenching range and the second quenching range overlap, there is a possibility that cracks may occur in the overlapping part. Therefore, it is preferable to cool at least the vicinity of the overlapping part. In addition, for the cooling of the first quenching range at the time of the second quenching, a cooling device that also serves as the heating coil 160 used at the first quenching may be used as it is, but a cooling device is separately prepared. It doesn't matter. In this way, a cured layer forming form as shown in FIG. 2 is obtained.

5 and 6 show stepwise other processing steps for forming a hardened layer on the output side disk 3 (performed in the reverse order of the processing steps of FIGS. 3 and 4). In order to obtain the hardened layer form shown in FIG. 2, first, as shown in FIG. 5, the back surface 3b of the output side disk 3 is first subjected to induction hardening (first hardening). In this case, induction hardening is performed with the heating coil 160 facing the back surface 3 b of the disk 3. Thereafter, induction hardening is performed on the inner side surface 3a of the output side disk 3 and the inner peripheral surface 102b excluding the back side portion 100b (second quenching). Also in this case, induction hardening is performed in a state where the heating coil 160 is opposed to the inner side surface 3 a and the inner peripheral surface 102 b of the disk 3. At this time, that is, while the induction hardening is performed on the inner surface 3a of the disk 3 and the inner peripheral surface 102b excluding the back surface portion 100b, the back surface 3b of the hardened disk 3 is simultaneously cooled. To do. This cooling is performed, for example, by spraying the cooling liquid 171 with the cooling nozzle 170 facing the back surface 3 b of the disk 3. The purpose of cooling the first quenching simultaneously with the second quenching is to prevent the first quenching site from being heated and tempered as described above. In addition, for the cooling of the first quenching range at the time of the second quenching, a cooling device that also serves as the heating coil 160 used at the first quenching may be used as it is, but a cooling device is separately prepared. It doesn't matter. In this way, a cured layer forming form as shown in FIG. 2 is obtained.
In the case of an integrated disc, basically, the same hardened layer form is adopted.

  As described above, according to the present embodiment, the boundary portions 120A, 120B between the hardened layers 130A, 130B, 130C generated in the disk 3 by induction hardening are set at the low stress portions 100a, 100b of the disk 3. Since the hardened layers 130A, 130B, and 130C are formed as described above, it is possible to avoid a situation in which the high stress portions 102a, 102b, and 102c of the disk 3 are insufficiently quenched (hardening treatment is insufficient) or not hardened (not hardened). In other words, the high stress portions 102a, 102b, 102c of the disk 3 to be induction hardened are surely quenched, and an appropriate hardness distribution without residual tensile stress can be realized.

  The present invention can be applied to disks of full toroidal type continuously variable transmissions without trunnions in addition to various half toroidal type continuously variable transmission disks such as single cavity type and double cavity type.

2 Input side disk 3 Output side disk 3a Inner surface (force transmission surface)
3b Back surface 11 Power roller 100a, 100b Low stress part 102a, 102b, 102c High stress part 120A, 120B Boundary part 130A, 130B, 130C Hardened layer

Claims (5)

A toroidal-type continuously variable transmission disk that transmits a rotational force at a predetermined speed ratio via power rollers interposed between them, and the stress generated on the disk surface during operation of the transmission is relatively low. The hardened layer has a low stress portion and a relatively high stress portion, and the boundary between the hardened layers generated in the disk by at least two induction hardenings is set to the low stress portion. Ri is formed formed,
The boundary portion is located on the rear side portion located in the vicinity of the back surface on the opposite side of the force transmission surface involved in the transmission of rotational force among the radially outermost outer peripheral surface of the disk and the innermost inner surface in the radial direction of the disk. A toroidal-type continuously variable transmission disc characterized by the presence of A toroidal-type continuously variable transmission disk that transmits a rotational force at a predetermined speed ratio via power rollers interposed between them, and the stress generated on the disk surface during operation of the transmission is relatively low. The hardened layer has a low stress portion and a relatively high stress portion, and the boundary between the hardened layers generated in the disk by at least two induction hardenings is set to the low stress portion. Formed, and
The outermost circumferential surface of the disk in the radial direction, or the rear side portion located in the vicinity of the rear surface opposite to the force transmission surface involved in the transmission of rotational force among the innermost circumferential surface of the disk in the radial direction, At least one of the boundaries is present,
After induction hardening is first applied to the force transmission surface of the disc and the inner peripheral surface excluding the rear side portion, induction hardening is applied to the back surface of the disc, and the back surface is quenched. the inner peripheral surface and the features and to belt toroidal type continuously variable transmission that the hardened layer by being cooled is formed, excluding the hardening already said force transmitting surface the back side portion while you're disk. A toroidal-type continuously variable transmission disk that transmits a rotational force at a predetermined speed ratio via power rollers interposed between them, and the stress generated on the disk surface during operation of the transmission is relatively low. The hardened layer has a low stress portion and a relatively high stress portion, and the boundary between the hardened layers generated in the disk by at least two induction hardenings is set to the low stress portion. Formed, and
Of the outermost peripheral surface in the radial direction of the disk or the rear side portion located in the vicinity of the rear surface on the opposite side of the force transmission surface involved in the transmission of rotational force among the innermost peripheral surface in the radial direction of the disc The boundary exists in at least one of
After induction hardening is initially performed on the back surface of the disk, induction hardening is performed on the force transmission surface of the disk and the inner peripheral surface excluding the back side portion, and the force transmission surface and the the inner peripheral surface of hardening already said characteristics and to belt toroidal type that the back is the hardened layer is formed by being cooled continuously variable transmission while being hardened, except the back side portion disk. A method of manufacturing a toroidal-type continuously variable transmission disk in which rotational force is transmitted at a predetermined speed ratio via a power roller interposed between each other, and having a predetermined depth by induction hardening on the surface of the disk. In the manufacturing method for forming the cured layer,
The outer peripheral surface of the radially outermost of the disc, and the hardened layer on the back side position located near the back of the opposite side of the force transmitting surfaces involved in the transmission of the rotational force of the inner peripheral surface of the most radial direction of the disk inner The manufacturing method characterized by forming a hardened layer so that the boundary part may exist between each other. A method of manufacturing a toroidal-type continuously variable transmission disk in which rotational force is transmitted at a predetermined speed ratio via a power roller interposed between each other, and having a predetermined depth by induction hardening on the surface of the disk. In the manufacturing method for forming the cured layer,
Of the outermost peripheral surface in the radial direction of the disk or the rear side portion located in the vicinity of the rear surface on the opposite side of the force transmission surface involved in the transmission of rotational force among the innermost peripheral surface in the radial direction of the disc Forming a cured layer so that there is a boundary between the cured layers on at least one of the
First, induction hardening is performed on the force transmission surface of the disc and the inner peripheral surface excluding the back side portion, and then induction hardening is performed on the back surface of the disc, and the back surface is hardened. production method made you characterized in that cooling and said inner peripheral surface excluding the hardening already said force transmitting surface the rear side portion in.

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