JP6102407B2 - Cam manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing a cam constituting an engine valve mechanism.

  A valve operating mechanism of an engine opens and closes an intake valve and an exhaust valve (hereinafter simply referred to as a valve) provided at ends of an intake port and an exhaust port on the combustion chamber side. For example, a direct acting type that does not use a rocker arm A valve operating mechanism is known. The direct-acting valve mechanism includes a driven part called a tappet or a valve lifter connected to the base end of the valve, a valve spring for maintaining the valve in a closed state, and a cam that presses the driven part. And. The driven portion is pressed against the urging force of the valve spring as the cam rotates, and the valve closes when the urging force of the valve spring exceeds the urging force.

  Since the cam slides and presses the driven part while being in contact with the driven part, it is important to reduce friction at the contact point between the cam and the driven part and to suppress the cam wear. Yes. On the other hand, conventionally, a surface hardening process is performed at the time of manufacturing the cam to improve the surface hardness, wear resistance, and the like of the outer peripheral surface (cam surface) of the cam. For example, Patent Document 1 discloses a method of adjusting the peripheral surface of the cam to a required surface hardness by performing induction hardening after brazing the cam (cam piece) to the camshaft and then immediately cooling with water. . Induction hardening (also referred to as induction hardening and tempering) has been conventionally employed as a cam surface hardening treatment because a hardened layer produced is relatively thick and can be applied to a portion with high friction.

  Also, as a structure that reduces the friction at the contact point between the cam and the driven part, a roller is rotatably attached to the tip of the cam body in recent years, and this roller rotates while contacting the driven part. Has been proposed (see, for example, Patent Documents 2 and 3). In the case of such a cam with a roller, since the roller moves while rolling on the tappet at the tip of the cam where the contact stress between the cam and the tappet is highest, friction can be effectively reduced.

JP-A-6-193708 JP 2011-80372 A JP 2012-202355 A

  However, when a hardened layer is generated on the surface of the cam by induction hardening, distortion occurs during the processing, and thus it is necessary to process the surface again after performing the surface hardening treatment. For this reason, the number of manufacturing steps for reprocessing increases, the manufacturing time increases, and the cost may increase. In particular, the above-described cam with a roller requires accuracy of the assembly position between the cam body and the roller. Therefore, if distortion occurs in the surface hardening process, it is necessary to perform processing after the process with high accuracy. Therefore, the cost may increase further.

  One of the objects of the present invention was invented in view of the above problems, and is to provide a cam manufacturing method capable of reducing manufacturing time and costs. The present invention is not limited to this purpose, and is a function and effect derived from each configuration shown in the embodiments for carrying out the invention described later, and other effects of the present invention are to obtain a function and effect that cannot be obtained by conventional techniques. Can be positioned.

(1) The cam manufacturing method disclosed herein includes a roller shaft mounting hole for inserting a roller shaft drilled in a valve lift portion and a notch portion formed in a middle portion in the plate thickness direction of a tip portion of the valve lift portion. And a plate-like base cam having an outer peripheral surface, and a part of the outer peripheral surface is provided in the notch portion so as to protrude outward from the outer peripheral surface of the tip portion of the valve lift portion, and is assembled to the base cam via the roller shaft. And a cylindrical roller. The manufacturing method includes a surface hardening treatment step for performing surface quenching on each of the roller and the roller shaft, a nitriding treatment step for nitriding the base cam, the surface hardening treatment step, and the nitriding treatment. after step, so that the roller which has been subjected to the surface hardening is rotatable relative to the roller shaft subjected to said surface hardening, by fixing the roller shaft relative to the base cam subjected to the nitriding treatment An assembling step for assembling the roller . In the surface hardening treatment step, it is more preferable to perform induction hardening and tempering treatment as the surface hardening.

(2) Further, in the assembling step, the roller is disposed at a center portion in the width direction of the notch portion of the base cam, and the roller shaft is inserted into a through hole formed in the roller and the roller shaft mounting hole. Are preferably fixed .

(3) Further, before the nitriding step, a masking step of masking a camshaft mounting hole for inserting a camshaft drilled in the base cam, and after the assembly step, the cam is press-fitted into the camshaft. And an assembling step for fixing. In this case, it is preferable that the roller shaft mounting hole is not masked in the masking step, and the roller shaft is assembled to the base cam by caulking in the assembly step.
(4) Further, in the nitriding treatment step, it is preferable to perform a gas nitriding treatment as the nitriding treatment.

  According to the disclosed cam manufacturing method, nitriding treatment can be adopted as the surface hardening treatment of the base cam, so that high surface hardness, fatigue strength, wear resistance, and the like can be imparted to the base cam. Further, since the distortion generated in the nitriding process is small, it is not necessary to process again after the process, and the manufacturing process can be simplified. In other words, the shape of the base cam is first completed, and finally the nitriding treatment for hardening the surface is performed, so that the base cam can be processed with one chuck (as it is once fixed). Thereby, the processing accuracy of the base cam can be increased, and the manufacturing time can be shortened to reduce the cost.

  Note that the thickness of the hardened layer on the surface of the nitriding treatment is thinner than that of the induction hardening and tempering treatment, but this cam has a roller attached to the tip of the outer peripheral surface of the base cam where the Hertz stress is highest. The tip of the base cam is not in contact with the tappet. Therefore, even if the nitriding treatment is adopted, there is no fear that the hardened layer is consumed, and wear of the base cam can be appropriately suppressed.

  Further, since the nitriding treatment is performed before the roller is assembled to the base cam, it is possible to prevent the surface having the hardened layer from being formed on the surface where the roller and the roller shaft are in sliding contact with each other. That is, it is possible to prevent a hardened layer from being partially formed on the roller shaft and to prevent the progress of wear on the inner peripheral surface of the roller.

It is a flowchart which shows the manufacturing method of the cam which concerns on one Embodiment. It is a schematic diagram which shows the structure of the cam manufactured by the manufacturing method of the cam which concerns on one Embodiment, (a) is a front view of a base cam, (b) is a side view of the state which assembled | attached the cam to the cam shaft. It is the schematic diagram illustrated about the grinding process of the manufacturing method of the cam which concerns on one Embodiment. It is an expanded sectional view of the assembly | attachment part of the base cam and roller shaft of the cam manufactured by the manufacturing method of the cam which concerns on one Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. Note that the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described in the following embodiment.

[1. Cam structure]
First, the structure of the cam manufactured by the manufacturing method according to the present embodiment will be described with reference to FIGS. 2 (a), 2 (b) and FIG. 2A is a front view of the base cam 31, and FIG. 2B is a side view of the cam lobe (cam) 30 assembled to the camshaft 20. In FIG. 2A, the roller 32 is indicated by a two-dot chain line. FIG. 4 is an enlarged cross-sectional view of a portion where the base cam 31 and the roller shaft 33 are assembled.

  The cam lobe 30 manufactured by the manufacturing method according to this embodiment is fixed by press-fitting to the camshaft 20 that rotates in conjunction with an engine crankshaft (not shown), and rotates together with the camshaft 20. The cam structure 10 including the camshaft 20 and the cam lobe 30 drives a tappet (both not shown) to which a base end portion of an intake valve or an exhaust valve (hereinafter referred to as a valve) is connected in each cylinder of the engine. Open and close.

  As shown in FIG. 2 (b), the camshaft 20 is constituted by a hollow pipe, and the rotation is transmitted from the crankshaft of the engine via a timing chain and a timing belt (both not shown). In the axial direction of the camshaft 20, a plurality of cam lobes 30 for opening and closing the valves are fixed according to the number of valves. Since all the cam lobes 30 have the same configuration, only one cam lobe 30 is shown here and the structure thereof will be described.

  As shown in FIGS. 2A and 2B, the cam lobe 30 includes a plate-like base cam 31 that is a cam body, and a cylindrical roller 32 that is attached to the base cam 31. The base cam 31 has a base circle portion 31a and a valve lift portion 31b, and the outer peripheral surface (cam surface) is continuous over the entire circumferential direction. A boundary line between the base circle portion 31a and the valve lift portion 31b is indicated by a two-dot chain line in FIG. The base circular portion 31a is a circular portion of the base cam 31, and a circular hole portion 31h (hereinafter referred to as a camshaft mounting hole 31h) through which the camshaft 20 is inserted is drilled in the center. In other words, the base circle portion 31a corresponds to a portion where the distance from the axis S of the camshaft mounting hole 31h is constant.

  The valve lift part 31b is a part formed by partially bulging the outer edge of the base circle part 31a in the diameter increasing direction, and is a part that presses the top surface of the tappet to open and close the valve. The valve lift portion 31b has an intermediate portion in the width direction of the base cam 31 (the direction in which the camshaft 20 is inserted, the plate thickness direction), and the outer peripheral surface from the tip portion (cam top portion) 31c toward the base circle portion 31a. And has a notch 31n formed by notching. A roller 32 described later is provided in the notch 31n so as to be rotatable with respect to the base cam 31.

  A pair of opposing yoke portions 31y and 31y are formed on both sides in the width direction of the notch portion 31n formed in the base cam 31. The yoke portions 31y, 31y are provided with holes 31m, 31m penetrating in the width direction on a straight line. The hole 31m is formed such that its axis T is parallel to the axis S of the camshaft mounting hole 31h formed in the base circle 31a. As shown in FIG. 4, a roller shaft 33 for attaching the roller 32 to the base cam 31 is inserted through the hole 31m. Hereinafter, the hole 31m is referred to as a roller shaft mounting hole 31m. A claw portion 33a projecting to the outer diameter side is provided on the peripheral edge of the roller shaft 33, and the claw portion 33a is struck against the end surface of the yoke portion 31y of the base cam 31 to be caulked, thereby being attached to the base cam 31. The roller shaft 33 is fixed.

  As shown in FIGS. 2B and 4, the roller 32 is rotatably assembled to the base cam 31 via a roller shaft 33 inserted through the center thereof. The inner peripheral surface 32 h of the roller 32 functions as a sliding bearing for the roller shaft 33. The roller 32 is attached such that a part of its outer peripheral surface protrudes outside the outer peripheral surface of the tip end portion 31c of the valve lift portion 31b.

  As shown in FIG. 2A, the protrusion amount x of the roller 32 from the tip portion 31c is the outer diameter r of the roller 32 and the length B from the center T of the roller shaft mounting hole 31m to the tip portion 31c. Difference (x = r−B). The length B is a linear direction connecting the center S of the camshaft mounting hole 31h and the center T of the roller shaft mounting hole 31m, and extends from the center T of the roller shaft mounting hole 31m to the tip portion 31c (edge) of the valve lift portion 31b. Part). In other words, it is the distance from the intersection of the straight line passing through the two centers S and T and the contour line of the valve lift 31b to the center T of the roller shaft mounting hole 31m.

[2. Production method]
Next, the manufacturing method according to this embodiment will be described with reference to FIG. FIG. 3 conceptually shows the grinding process. In the figure, the solid line indicates the final shape of the base cam 31 (completed base cam 31), and the alternate long and short dash line indicates the base cam 31 before the outer peripheral surface is ground in the finishing process. The shape of is shown. For the sake of clarity, the space between the solid line and the alternate long and short dash line is shown greatly.

  This manufacturing method includes a roughing process, a finishing process, a masking process, a nitriding process for the base cam 31, a process for setting the protrusion amount x for the roller 32, a surface hardening process, and an assembly process for the base cam 31 and the roller 32. And an assembly process of the cam lobe 30 and the camshaft 20. A plurality of cam lobes 30 are manufactured according to the number of valves of the engine.

  First, each process for the roller 32 will be described. Here, first, the protrusion amount x that the roller 32 protrudes from the outer peripheral surface of the base cam 31 is set, and the roller 32 is prepared. This protrusion amount x is determined by the timing at which the tappet changes between the base cam 31 and the roller 32 (rotation angle of the camshaft 20) and the length that the roller 32 rolls on the tappet (that is, the contact between the roller 32 and the tappet). Length).

  The timing of the transfer affects the magnitude of vibration generated when the base cam 31 and the roller 32 are switched, and the contact length between the roller 32 and the tappet contributes to friction reduction. Therefore, the protrusion amount x is set so that vibration is not generated as much as possible at the time of transfer (even if vibration is generated, the vibration is reduced) and the contact length is as long as possible. Further, as many rollers 32 as the number of cam lobes 30 are prepared with the same outer diameter r (that is, one type of roller 32).

  Next, before the roller 32 and the roller shaft 33 are assembled, a surface hardening process is performed on the roller 32 and the roller shaft 33, respectively. Here, general induction hardening and tempering is performed as the surface hardening treatment. For example, a high-frequency current is passed through a coil provided around the roller 32 to heat the surface of the roller 32 and then rapidly cool. The same process is performed on the roller shaft 33. Thereby, a relatively thick hardened layer is formed on each surface of the roller 32 and the roller shaft 33. In addition, after performing a surface hardening process, you may provide the finishing process process which grinds the surface of the roller 32 and the roller shaft 33. FIG.

  Here, the reason why the induction hardening and tempering process is adopted as the surface hardening process of the roller 32 and the roller shaft 33 will be described. In the case of a conventional cam without a roller, Hertz stress (contact stress) when the cam presses the tappet is highest at the cam top of the valve lift portion. On the other hand, in this cam lobe 30, a roller 32 is assembled to the tip portion 31c of the valve lift portion 31b, and a part of the outer peripheral surface of the roller 32 protrudes outside the outer peripheral surface of the valve lift portion 31b. . Therefore, at the tip 31c of the cam lobe 30, the roller 32 presses the tappet instead of the valve lift 31b of the base cam 31. That is, the Hertz stress when the roller 32 and the tappet are in contact with each other is higher than the Hertz stress when the valve lift portion 31b is in contact with the tappet.

  Therefore, the roller 32 is induction-hardened and tempered to generate a relatively thick hardened layer on the surface of the roller 32, thereby increasing the surface hardness of the roller 32 and improving the wear resistance and the like. The amount is suppressed. In addition, since the roller shaft 33 is a portion that is in sliding contact with the inner peripheral surface 32h of the roller 32, the roller shaft 33 is subjected to the same surface hardening treatment as the roller 32 to give the same surface hardness as the roller 32. Thus, wear at the contact portion between the roller 32 and the roller shaft 33 is suppressed.

  Next, each process for the base cam 31 will be described. As a pre-stage of each process of the base cam 31, a component that is the basis of the base cam 31 is formed by forging. The molded forged product is egg-shaped at least in a front view and has a certain thickness. Further, in the following roughing process and finishing process, forged products for each cylinder of the engine are stacked and processed together. For example, in the case of an engine having four valves per cylinder, four forgings are stacked and processed together. In addition, when it is difficult to process four forged products in piles, the forged products may be stacked for each intake valve and exhaust valve (that is, two forged products).

  First, in the roughing process, the forged product is roughed to form a portion that becomes the notch 31n, and a portion that becomes the camshaft mounting hole 31h and the roller shaft mounting hole 31m is drilled. Further, the outer peripheral surface of the forged product is roughly processed to form a shape close to the final cam profile of the base cam 31. The shape close to the final cam profile here refers to a shape that becomes a desired cam profile only by finishing (that is, grinding) the outer peripheral surface. The rough machining step is omitted, and at the stage of forming the forged product, the notch 31n, the camshaft mounting hole 31h, and the roller shaft mounting hole 31m are formed, and the outer peripheral surface is the final cam profile of the base cam 31. You may form in the shape near.

  The forged product after the roughing process is formed into the final shape of the base cam 31 in the finishing process. The finishing process may be performed using a device capable of performing numerical control, such as an NC lathe, or may be performed manually. For the forged product after the roughing process, first, the camshaft mounting hole 31h and the roller shaft mounting hole 31m are finished one by one. Since the camshaft mounting hole 31h is located at the center of the base circle portion 31a, it is easy to position. Therefore, the camshaft mounting hole 31h is finished first, and then the roller shaft mounting hole 31m is positioned and finished with reference to the camshaft mounting hole 31h. Thus, two holes 31h and 31m are formed in the egg-shaped forged product.

  The camshaft mounting hole 31 h is formed with a diameter slightly smaller than the diameter of the camshaft 20, and the roller shaft mounting hole 31 m is formed with a diameter slightly larger than the diameter of the roller shaft 33. This is because the cam lobe 30 is fixed to the camshaft 20 by press fitting while the roller shaft 33 is fixed to the base cam 31 by caulking.

  The forged product in which the two hole portions 31h and 31m are formed is subsequently ground to finish the outer peripheral surface. The finishing process (grinding process) of the outer peripheral surface is illustrated in FIG. In this grinding process, the forged product indicated by the alternate long and short dash line is supported by fixing the camshaft mounting hole 31h and the roller shaft mounting hole 31m by the chuck (fixing device) 2, and the grinding wheel 3 is fastened on the outer peripheral surface thereof. Contact while rotating. The grinding wheel 3 moves the outer periphery of the forged product while being advanced toward the forged product by a preset feed amount (cut amount) C, and grinds the outer peripheral surface of the forged product. Thereby, the base cam 31 having a desired cam profile is completed.

  The completed base cam 31 masks the camshaft mounting hole 31h of the base cam 31 in the next masking step. In the masking step, the camshaft mounting hole 31h of the base cam 31 is masked by chemical application, plating, or the like to prevent a hardened layer from being generated in the camshaft mounting hole 31h in the next nitriding process. This is because the camshaft 20 and the cam lobe 30 are fixed by press-fitting, so it is important to appropriately manage the press-fitting allowance. When a hardened layer is generated, the press-fitting allowance is reduced by the thickness. It is because it ends. That is, it is possible to appropriately manage the press-fitting allowance by masking the camshaft mounting hole 31h in the masking process.

  In the masking step, the roller shaft mounting hole 31m of the base cam 31 is not masked. This is because the base cam 31 and the roller shaft 33 are fixed by caulking, so that it is not necessary to manage the press-fitting allowance unlike the camshaft mounting hole 31h. That is, as shown in FIG. 4, since a slight gap is formed between the inner peripheral surface of the roller shaft mounting hole 31m of the base cam 31 and the outer peripheral surface of the roller shaft 33, the roller shaft mounting hole 31m is nitrided. This is because the assembly of the roller 32 is not affected even if the above is applied.

The masked base cam 31 is finally nitrided in a nitriding process. The base cam 31 is subjected to a general gas nitriding process as a nitriding process. For example, after the base cam 31 is washed to remove oil and dirt, it is stored in a sealable case and heated to a predetermined temperature for a predetermined time while blowing ammonia gas (NH ₃ ). Thereby, a hardened layer (nitrided layer) is generated on the surface of the base cam 31. As a specific method of gas nitriding treatment, a well-known method can be adopted.

  Here, the reason why the nitriding process is adopted as the surface hardening process of the base cam 31 will be described. Since the nitriding treatment is not hardening by martensite formation, there are advantages that the treatment temperature is relatively low and the strain is small. Therefore, nitriding treatment can be performed after finishing processing is completed, and there is no need to process again after nitriding treatment. Also, high surface hardness and fatigue strength can be obtained by nitriding treatment. On the other hand, the hardened layer produced by the nitriding treatment has a demerit that it is thinner than the thickness of the hardened layer produced by the induction hardening and tempering treatment.

  On the other hand, since the roller 32 is assembled | attached to the front-end | tip part 31c of the valve lift part 31b as mentioned above, the valve lift part 31b does not contact the tappet in the front-end | tip part 31c. In other words, the base cam 31 and the tappet are in contact with the rising portion and the falling portion of the valve lift portion 31b excluding the tip portion 31c, and these have lower Hertz stress than the tip portion 31c. That is, in the case of the cam lobe 30, the amount of wear of the base cam 31 is smaller than that of the conventional cam, and therefore the wear can be sufficiently resisted even with the thickness of the hardened layer generated by nitriding. Accordingly, it is possible to employ a nitriding process as the surface hardening process of the base cam 31.

  In the assembling process, the roller 32 is rotatably assembled to the base cam 31 that has undergone the above processes via the roller shaft 33. Specifically, the roller 32 has a central through hole overlapping roller shaft mounting holes 31m and 31m formed in the yoke portions 31y and 31y of the base cam 31, and the gaps between the two yoke portions 31y and 31y are substantially equal. It arrange | positions in the width direction center part of the notch part 31n so that it may become. In this state, the roller shaft 33 is inserted into the roller shaft mounting hole 31m of one yoke portion 31y, subsequently inserted into the through hole of the roller 32, and further inserted into the roller shaft mounting hole 31m of the other yoke portion 31y. The Then, the claw portions 33 a at both ends of the roller shaft 33 are crushed by being hit and fixed to the base cam 31.

Thus, the cam lobe 30 is manufactured by attaching the roller 32 to the base cam 31. Any of the steps for the base cam 31 and the steps for the roller 32 may be performed first or simultaneously.
In the assembly process, the plurality of cam lobes 30 are assembled and fixed to the camshaft 20 by press-fitting at predetermined angles at predetermined positions. Thereby, the cam structure 10 is completed.

[3. flowchart]
The cam manufacturing method according to the present embodiment is summarized as follows. As shown in FIG. 1, a forged product serving as a base of the base cam 31 is formed (step S10), and a cam shaft mounting hole 31h and a roller shaft mounting hole 31m are formed in the forged product by roughing, and the outer peripheral surface is also roughened. A shape close to the final cam profile is processed (rough machining step, step S20). Next, a finishing process is performed (finishing process, step S30). That is, the camshaft mounting hole 31h is finished, and then the roller shaft mounting hole 31m is finished using the camshaft mounting hole 31h as a reference. Then, a grinding process is performed on the outer peripheral surface. Thereby, the base cam 31 having a desired cam profile is completed.

  Next, only the camshaft mounting hole 31h of the base cam 31 is masked (masking step, step S40). The base cam 31 is subjected to nitriding treatment (nitriding treatment step, step S50), and a hardened layer is generated on the surface of the base cam 31.

  On the other hand, the projection amount x of the roller 32 from the outer peripheral surface of the base cam 31 is set, and a plurality of rollers 32 having an outer diameter r are prepared (step S15). Then, induction hardening and tempering processing is performed on the roller 32 and the roller shaft 33 to generate a hardened layer on the surface (surface hardening processing step, step S25). In FIG. 1, the steps S10 to S50 for the base cam 31 and the steps S15 and S25 for the roller 32 are expressed in parallel. However, the surface hardening process of the roller 32 is finished first. After that, the base cam 31 may be processed or vice versa.

Next, the roller 32 is assembled to the completed base cam 31 (assembly process, step S60). That is, the roller 32 is disposed in the notch 31n of the base cam 31, and the roller shaft 33 is inserted through the roller shaft mounting hole 31m and the central through hole of the roller 32. Then, the roller shaft 33 is fixed to the base cam 31 by hitting the claw portions 33 a at both ends of the roller shaft 33. Thereby, the cam lobe 30 is completed.
Finally, a plurality of cam lobes 30 are assembled and fixed to the camshaft 20 by press fitting, and the cam structure 10 is completed (assembly process, step S70).

[4. effect]
Therefore, according to the cam manufacturing method according to the present embodiment, nitriding can be employed as the surface hardening treatment of the base cam 31, so that high surface hardness, fatigue strength, wear resistance, and the like can be imparted to the base cam 31. it can. Further, since the distortion generated in the nitriding process is small, it is not necessary to process again after the process, and the manufacturing process can be simplified. That is, the shape of the base cam 31 is first completed, and finally the nitriding treatment for hardening the surface is performed. Therefore, the base cam 31 can be processed with one chuck (once fixed, as it is). . Thereby, the processing accuracy of the base cam 31 can be increased, and the manufacturing time can be shortened to reduce the cost.

  In the nitriding process, the thickness of the hardened layer on the surface is reduced as compared with the induction hardening and tempering process. However, the cam lobe 30 has a roller 32 at the tip 31c where the Hertz stress is highest among the outer peripheral surfaces of the base cam 31. Is attached, and the tip 31c of the base cam 31 is not in contact with the tappet. Therefore, even if the nitriding treatment is adopted, there is no possibility that the hardened layer is consumed, and wear of the base cam 31 can be appropriately suppressed.

Further, since the nitriding treatment is performed before the roller 32 is assembled to the base cam 31, it is possible to prevent the surface having the hardened layer and the surface having no hardened layer from being formed on the surface where the roller 32 and the roller shaft 33 are in sliding contact. . If the nitriding process is performed with the roller 32 assembled to the base cam 31, a hardened layer is formed on the outer peripheral surface of the roller shaft 33 located in the gap between the yoke portion 31y and the end surface of the roller 32 as shown in FIG. Is generated. On the other hand, no hardened layer is generated on the inner peripheral surface 32h of the roller 32 or on the outer peripheral surface of the roller shaft 33 facing the inner peripheral surface 32h.

  By the way, the roller 32 is rotatably provided with respect to the roller shaft 33 fixed to the base cam 31, and can move in the axial direction of the roller shaft 33 in the notch 31n. Therefore, if the hardened layer is generated only on the outer peripheral surface of the roller shaft 33 located in the gap between the yoke portion 31y and the end surface of the roller 32, the inner peripheral surface 32h of the roller 32 is moved when the roller 32 moves in the axial direction. Wear progresses. Therefore, in this manufacturing method, the base cam 31 is subjected to nitriding before the roller 32 is assembled to the base cam 31, thereby preventing a partially cured layer from being generated on the roller shaft 33. The progress of wear on the surface 32h can be prevented.

  Moreover, since the roller 32 and the roller shaft 33 are induction-hardened and tempered in the surface hardening process, a hardened layer having a relatively large thickness can be generated. Thereby, the cam lobe 30 provided with the roller 32 which can endure the high Hertz stress at the time of contact with a tappet can be manufactured. Further, by subjecting the roller shaft 33 to the same surface hardening treatment as that of the roller 32, it is possible to prevent wear at the contact point between the roller 32 and the roller shaft 33. Furthermore, after the induction hardening and tempering treatment is performed on the roller 32 and the roller shaft 33, the surface hardness of the roller 32 and the roller shaft 33 can be prevented from being lowered by assembling the roller 32 and the roller shaft 33 with the nitriding base cam 31.

  Further, since the camshaft mounting hole 31h is masked in the masking process before the base cam 31 is nitrided, the press-fitting allowance between the cam lobe 30 and the camshaft 20 can be appropriately managed. Furthermore, since the roller shaft mounting hole 31m is not masked in this masking step, the time for the masking step can be shortened, and the manufacturing time of the cam lobe 30 can be shortened. Since the roller shaft 33 is fixed to the base cam 31 by caulking, it is not necessary to manage the press-fitting allowance, and the manufacturing process can be simplified.

  Further, in the nitriding process of the present embodiment, since the gas nitriding process using ammonia gas is performed, the nitriding process can be performed at a low cost, and the environment is compared with the case where the salt bath nitriding process is performed. The load of can be reduced. Further, when performing the salt bath soft nitriding treatment, it is necessary to mask the roller shaft mounting hole 31m in order to prevent the oxide scale from adhering, but in the case of the gas nitriding treatment, the oxide scale does not adhere. Therefore, masking is not necessary, and the manufacturing time can be shortened.

[5. Others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
For example, the surface hardening process of the roller 32 and the roller shaft 33 is not limited to the induction hardening and tempering process, but may be other surface hardening process. Moreover, as long as high surface hardness can be given, surface hardening processing other than surface hardening processing may be given to the roller 32 and the roller shaft 33. FIG.

The nitriding performed in the nitriding process is not limited to gas nitriding, and liquid nitriding (salt bath nitriding) may be performed instead of gas nitriding. According to the liquid nitriding treatment, the time of the nitriding treatment step can be shortened as compared with the gas nitriding treatment. Further, soft nitriding treatment may be performed to improve wear resistance and fatigue resistance.
Further, a method and a process for managing the press-fitting allowance between the camshaft 20 and the cam lobe 30 may be prepared separately, and masking of the camshaft mounting hole 31h may be omitted. The method for fixing the roller shaft 33 is not limited to caulking, and the roller shaft 33 may be fixed to the base cam 31 by press-fitting. In this case, it is preferable to mask the roller shaft mounting hole 31m in the masking step.

  In the above embodiment, the case where the camshaft mounting hole 31h is finished after rough machining and then the rollershaft mounting hole 31m is finished is illustrated, but the order of finishing may be reversed. That is, by positioning the roller shaft mounting hole 31m with high accuracy using a jig, the roller shaft mounting hole 31m may be finished first, and the camshaft mounting hole 31h may be finished using the roller shaft 31m as a reference. .

  Moreover, in the said embodiment, in the roughing process and finishing process with respect to the base cam 31, the case where the forged product for every cylinder of an engine is piled up and processed together is illustrated, However, Forged products of all the cylinders are piled up. You may process together. Also, in the roughing process, forged products of all cylinders may be stacked and processed together, and in the finishing process, forged products for each cylinder of the engine may be stacked and processed together. They may be processed without being overlapped, and forged products for each cylinder of the engine or forged products of all cylinders may be stacked and processed together in the finishing process.

In addition, although the component used as the base cam 31 is demonstrated as a forged product, the component used as the base cam 31 is not restricted to the component shape | molded by forge, The component shape | molded by the other method may be sufficient.
In the above embodiment, the cam structure 10 in which the roller 32 rotates with respect to the roller shaft 33 fixed to the base cam 31 has been described. However, the roller 32 and the roller shaft 33 are fixed, and the roller shaft 33 is attached to the base cam 31. It may be a cam structure that rotates relative to it. Further, the roller 32 may be rotatable with respect to the roller shaft 33, and the roller shaft 33 may also be rotatable with respect to the base cam 31.

10 Cam structure 20 Camshaft 30 Cam lobe (cam)
31 Base cam 31a Base circle part 31b Valve lift part 31c Tip part 31h Cam shaft attachment hole 31m Roller shaft attachment hole 31n Notch part 31y Yoke part 32 Roller 33 Roller shaft r Roller outer diameter x Projection amount S Center of cam shaft attachment hole T Center of roller shaft mounting hole

Claims (4)

A plate-like base cam having a roller shaft mounting hole for inserting a roller shaft bored in the valve lift portion and a notch portion formed in the middle portion in the plate thickness direction of the tip portion of the valve lift portion; A cam having a cylindrical roller provided at the notch so that the portion protrudes outward from the outer peripheral surface of the tip of the valve lift portion and assembled to the base cam via the roller shaft A method,
A surface hardening treatment step of performing surface hardening for each of the roller and the roller shaft;
A nitriding step for nitriding the base cam;
After the surface hardening process and the nitriding process, so that the roller which has been subjected to the surface hardening is rotatable relative to the roller shaft subjected to said surface hardening, to said base cam subjected to the nitriding treatment And an assembly step of assembling the roller by fixing the roller shaft . In the assembling step, the roller is disposed in the center in the width direction of the notch portion of the base cam, and the roller shaft is inserted and fixed to a through hole formed in the roller and the roller shaft mounting hole. The method of manufacturing a cam according to claim 1, wherein Before the nitriding step, a masking step of masking a camshaft mounting hole for inserting a camshaft drilled in the base cam;
An assembly step of fixing the cam to the camshaft by press-fitting after the assembly step;
In the masking step, the roller shaft mounting hole is not masked,
3. The cam manufacturing method according to claim 1, wherein in the assembling step, the roller shaft is assembled to the base cam by caulking. The cam manufacturing method according to claim 1, wherein in the nitriding step, gas nitriding is performed as the nitriding.

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