JP4270064B2 - Engine camshaft structure - Google Patents

Description

  The present invention relates to a camshaft structure for an engine having a hollow portion formed by casting using a core, and belongs to the technical field of engines for automobiles and the like.

  Conventionally, a hollow portion is formed in the camshaft for opening and closing the intake and exhaust valves of the engine to reduce the weight, or to supply lubricating oil to the bearing portion of the camshaft. It may be used as an oil passage.

  As the camshaft having such a hollow portion, for example, there are those described in Patent Document 1 and Patent Document 2, and in particular, Patent Document 2 discloses a mold comprising upper and lower molds A1 and A2, as shown in FIG. A camshaft-shaped cavity C is formed by A and the core B formed in the shape of the cavity, and the core B is held at a predetermined position in the mold A between the mold A and the core B. A method of manufacturing a camshaft in which a wire-shaped kelen D is provided is disclosed.

JP 2001-105100 A Japanese Utility Model Publication No. 3-8602

  By the way, in the camshaft having such a configuration, it is important that the cavity is correctly formed at a predetermined position in the camshaft. That is, if the hollow portion is formed out of a predetermined position, when this camshaft is incorporated in an engine, shaft vibration is generated due to poor rotation balance, resulting in poor lubrication in the bearing portion of the camshaft, etc. May cause problems.

  For this reason, for example, it is conceivable that some of the cast camshaft materials are extracted and a destructive inspection is performed to investigate the internal state. In this case, however, there is a problem that the yield is surely lowered.

  Also, instead of the above-described destructive inspection, it is conceivable to inspect the rotational balance by rotating the camshaft material, but in that case, if cast burr or the like remains in the material, the effect will be included in the inspection result. This may be reflected, and there is a problem in terms of inspection accuracy.

  Then, after post-processing such as grinding on the material and finishing it into a camshaft product, it is sufficient to inspect the rotational balance described above. In this case, if a defective inspection occurs in the finished product, There is a problem that post-processing is wasted.

  Therefore, the present invention simply checks whether a cavity is correctly formed at a predetermined position when manufacturing a camshaft of an engine having a cavity formed in the axial direction by casting using a core. It is an object of the present invention to provide a camshaft structure for an engine that can be used.

  In order to solve the above problems, the present invention is configured as follows.

First, the invention according to claim 1 is provided with a cam portion and a plurality of bearing portions for opening and closing the intake and exhaust valves of a plurality of cylinders on the shaft, and a cavity extending in the axial direction formed using a core. And a camshaft structure of an engine that is integrally molded by casting, and has an inner peripheral surface that forms a cavity at a predetermined position in the axial direction of the camshaft, and an outer peripheral surface that corresponds to the inner peripheral surface. a pair of flat portions parallel to each other perpendicular to the radial direction is provided on the flat portion of the inner and outer pair is provided respectively for the two radial intersecting with each other in the predetermined position of the axis direction, The flat portion on the outer peripheral surface side of the pair of inner and outer flat portions serves as a contact surface of the inspection probe .

  Next, the invention according to claim 2 is the camshaft structure according to claim 1, wherein two to one set of flat portions are provided at a plurality of locations in the axial direction, and each set of flat portions is flat. The portions are provided so as to have the same phase.

  According to a third aspect of the present invention, in the camshaft structure according to the first or second aspect, the flat portion is set at a place excluding the cam portion and the bearing portion.

  According to a fourth aspect of the present invention, in the camshaft structure according to any one of the first to third aspects, kelen disposed between the mold and the core at the time of casting is cast. The flat portion is set in the vicinity of the cast-in portion of the keren.

First, according to the first aspect of the present invention, a pair of flat surfaces parallel to each other perpendicular to the inner peripheral surface and the outer peripheral surface corresponding to the inner peripheral surface are provided at predetermined locations in the axial direction of the camshaft. Since the portion is provided, when ultrasonic inspection is performed by pressing the inspection probe against the flat portion on the outer peripheral surface side, since the curved surface portion is not interposed, irregular reflection of ultrasonic waves is suppressed, and the inspection accuracy is reliably improved.

  Further, since the pair of inner and outer flat portions are respectively provided in the two radial directions intersecting each other at the predetermined location in the axial direction, the degree of deviation of the hollow portion at the location, that is, the degree of thickness deviation is determined by the ultrasonic inspection described above. It can be accurately inspected.

  In this way, the cast camshaft material is not subjected to post-processing such as grinding to finish the camshaft product and then inspected, and the cast camshaft material is not subjected to the destructive inspection described above. Non-destructive inspection such as sonic inspection can be applied, and as a result, an engine camshaft structure that can easily inspect whether a cavity is correctly formed at a predetermined position at the camshaft material stage is provided. Is done.

  Next, according to the invention described in claim 2, since the two-to-one set of flat portions are provided at a plurality of locations in the axial direction, a wide range of inspection is possible, and the reliability of the inspection is improved.

  Moreover, since the flat portions at a plurality of locations are provided in the same phase, for example, when performing an ultrasonic inspection, the inspection can be performed without changing the phase of the camshaft, or the setting of the inspection apparatus can be easily changed. Thus, the inspection efficiency is improved.

  According to the invention described in claim 3, since the flat portion is set at a place excluding the cam portion and the bearing portion that are normally ground during post-processing, the flat portion is impaired in the rotational balance of the camshaft. If the setting is made so that there is no need to perform post-processing such as grinding, manufacturing efficiency can be maintained. In addition, since a flat part exists also in the product stage after general post-processing, reinspection is attained.

  According to the fourth aspect of the present invention, since kelen was used during casting, and the flat portion was set near the cast-in portion of the keren, in this case, particularly the arrangement effect of kelen was accurately determined. can do.

  Hereinafter, an engine camshaft according to an embodiment of the present invention will be described.

  This camshaft is mounted on a 4-cylinder 16-valve DOHC engine. First, as shown in FIG. 1, an exhaust camshaft 1 for opening and closing an exhaust valve includes a shaft portion 11 and a shaft portion 11 on the shaft portion 11. A pair of left and right first cams 12, 12, second cams 13, 13, third cams 14, 14, and fourth cams 15, 15 formed at four locations corresponding to a cylinder (not shown), and a cylinder head (not shown) The first bearing part 16, the second bearing part 17, the third bearing part 18, and the fourth bearing part 19 are supported by bearings J. Further, another bearing portion 20 is provided on the left side of the exhaust camshaft 1 in the illustrated example. The cams 12, 12, 13, 13, 14, 14, 15, 15 and the bearing parts 16, 17, 18, 19, 20 are formed integrally with the shaft part 11.

  The shaft portion 11 has a hollow portion 11a extending in the axial direction. The hollow portion 11a is provided over the right end portion and the vicinity of the left end portion in the illustrated example, and its cross section is basically circular. A bolt hole 11 b and a knock pin hole 11 c are formed in the left end portion of the shaft portion 11. A cam pulley (not shown) for rotationally driving the exhaust camshaft 1 is assembled to the left end portion of the shaft portion 11.

  The exhaust camshaft 1 is disposed at two locations between the left side of the left first cam 12 and the right side second cam 13 and the left side third cam 14 in the axial direction between the mold and the core during casting, which will be described later. Keren 21 is casted. And the flat part which is the characteristic part of this invention mentioned later in the location shown by the arrows a and b near the cast-in portions of these kerens 21 and 21, that is, the locations excluding the cams 12 to 15 and the bearing portions 16 to 20. Is provided.

  As shown in FIG. 2, the third cam 14 has a nose 14 a that protrudes in one direction from the shaft portion 11, and the cavity 11 aa where the third cam 14 is disposed is indicated by an arrow c. Unlike the circular hollow portion 11a in the normal shaft portion 11, it bulges toward the protruding direction of the nose 14a and the direction orthogonal to the direction. As a result, the exhaust camshaft 1 can be further reduced in weight.

  As shown in FIG. 3, the third bearing portion 18 in the vicinity of the third cam 14 has a slightly larger diameter than the shaft portion 11, and the cavity portion 11ab at the place where the third bearing portion 18 is disposed is a circular shape. It is made into a shape and is made somewhat thicker than the hollow part 11a in the normal shaft part 11. The third bearing portion 18 is provided with a passage 18a communicating from the cavity portion 11a to the outside.

  In addition, although the 3rd cam 14 and the 3rd bearing part 18 were demonstrated as an example, the structure is the same also in the other cams 12, 13, 15 and the bearing parts 16, 17, and 19. FIG. Each of the pair of left and right cams 12, 12, 13, 13, 14, 14, 15, and 15 is set to have the same shape and the same phase. In each pair of cams 12, 12, 13, 13, 14, 14, 15, 15, the noses protruding from the shaft portion 11 to the outer peripheral side are shifted in phase by 90 ° in the rotational direction of the exhaust camshaft 1. Is provided.

  Next, a case where the exhaust camshaft 1 is manufactured by casting will be described.

  That is, as shown in FIGS. 4 to 6, the cavity forming portions K <b> 1 and L <b> 1 are respectively formed on the upper mold K and the lower mold L constituting the shell mold so that the outer peripheral surface of the exhaust camshaft 1 is formed. It is depressed. Further, as shown in FIG. 4, a runner L2 is provided on the right side of the lower mold L, while a feeder part L3 is provided on the left side. In addition, in order to avoid complication of description, the upper mold | type K is abbreviate | omitted in FIG.

  In the center of the space surrounded by the upper mold K and the lower mold L, a shell core M formed in the shape of the hollow portion 11a of the exhaust camshaft 1 is lowered via a baseboard M1 connected to the right end. The mold L is supported and arranged. The core M has a hollow portion M2 extending in the axial direction, and the gas generated during casting of the exhaust camshaft 1 is discharged to the outside through the hollow portion M2.

  In the molds K and L at two locations in the axial direction of the core M, that is, at the locations corresponding to the left side of the left first cam 12 and between the right second cam 13 and the left third cam 14 in FIG. Kelens 21 and 21 made of iron wires for providing a predetermined thickness to the exhaust camshaft 1 having the hollow portion 11a by stably holding the elongated core M are disposed. . In that case, a groove part M3 is formed in the circumferential direction on the outer peripheral surface of the core M, and the kelen 21 is disposed in the groove part M3 so as to be held like a snap ring. By doing so, a cavity N corresponding to the shape of the exhaust camshaft 1 is formed. The exhaust camshaft material obtained by casting is of length d.

Then, the outer peripheral portion of the core M in the vicinity where the kelen 21 indicated by the arrow b is disposed is cut out at two locations, and the flat portions M4 and M5 for forming a flat portion on the inner peripheral surface side of the exhaust camshaft 1 are formed. Is provided. On the other hand, flat portions M4 and M5 for forming a flat portion on the inner peripheral surface side of the exhaust camshaft 1 are also provided in the outer peripheral portion of the core M in the vicinity where the kelen 21 indicated by the arrow a is disposed. It has been.

  Further, a predetermined portion of the cavity forming portion K1 in the upper mold K is further recessed, and a flat surface portion K2 for forming one flat portion on the outer peripheral surface side of the exhaust camshaft 1 is provided. In the vicinity of the mating surface with the lower mold L in K, a flat surface portion K3 for forming approximately half of the other flat portion on the outer peripheral surface side of the exhaust camshaft 1 is provided. On the other hand, in the vicinity of the mating surface of the lower mold L with the upper mold K, a flat surface portion L4 for forming approximately half of the other flat portion on the outer peripheral surface side of the exhaust camshaft 1 is provided. That is, the flat part K3 on the upper mold K side and the flat part L4 on the lower mold L side cooperate to generate a flat part having a dimension corresponding to the flat part K2 on the upper mold K side. Unlike the above configuration, a configuration in which a plane portion is not set on the mating surfaces of the upper and lower molds K and L may be adopted.

  In that case, one flat surface portion K2 on the mold K, L side and one flat surface portion M4 on the core M side are orthogonal to and parallel to the radial direction of the cavity N, and the other on the mold K, L side. These flat portions K3 and L4 and the other flat portion M5 on the core M side are set to be orthogonal to the radial direction of the cavity N and to be parallel to each other. And a pair of plane part K2, M4 and a pair of plane part K3, L4, M5 are each formed about two radial directions which mutually cross | intersect. Note that the intersection angle α is approximately 110 ° in the figure, and an angle of approximately 90 ° is applied.

  The upper mold K and the lower mold L as described above are closed with the core M interposed therebetween, and the molten iron for cast iron is supplied to the cavity N via the runner L2 and is filled. When solidification is completed, the mold is opened, and an exhaust camshaft material in which kelen 21 and 21 are cast is obtained.

  As shown in FIG. 7, the exhaust camshaft material 1 ′ thus formed corresponds to the inner peripheral surface that forms the cavity 11 a and the inner peripheral surface at a position corresponding to the position indicated by the arrow b in FIG. 1. A pair of flat portions 22a, 22b indicated by arrows b1 perpendicular to the radial direction and the outer peripheral surface are provided with a pair of flat portions 23a, 23b, also indicated by arrows b2, and Flat portions 22a, 22b, 23a, and 23b are formed in two radial directions that intersect each other at the predetermined location in the axial direction. In that case, the pair of flat portions 22a and 22b and the pair of flat portions 23a and 23b are formed in two radial directions intersecting each other at an angle α. In particular, the flat portions 22b and 23b on the outer peripheral surface side are set to dimensions that can provide a seat for pressing a probe at the time of ultrasonic inspection, which will be described later, so as not to spoil the rotation balance and impair the rotational balance. ing.

  In addition, although it demonstrated taking the example of the location corresponded to the location shown by the arrow b, the situation is the same also in the location equivalent to the location shown by the arrow a, and two-to-one set flat part 22a, 22b, 23a. , 23b are provided, and the flat portions 22a, 22b, 23a, 23b of the respective sets are provided in phase with each other at locations corresponding to the locations indicated by the arrows a and b. ing.

  The thickness of the exhaust camshaft material 1 ′ is then measured by ultrasonic inspection, and quality is determined based on this thickness. In that case, the probe P is pressed against the flat portion 22b on the outer peripheral surface side, and an ultrasonic wave is projected, and an echo wave reflected by the flat portion 22a on the inner peripheral surface side is detected, so that between the flat portions 22a and 22b. The thickness is measured. The thickness between the other flat portions 23a and 23b is also measured in the same manner.

  After the inspection, the exhaust camshaft material 1 ′ determined to be a non-defective product is subjected to predetermined post-processing such as grinding for the portions corresponding to the cams 12 to 15 and the bearing portions 16 to 20, thereby obtaining the exhaust camshaft 1. Will be.

  With the above configuration, first, as shown in FIG. 7, at a predetermined position in the axial center direction of the exhaust camshaft material 1 ′, the inner peripheral surface and the outer peripheral surface corresponding to the inner peripheral surface are orthogonal to the radial direction. Since a pair of flat portions 22a, 22b, 23a, and 23b that are parallel to each other are provided, for example, when ultrasonic inspection is performed by pressing the probe P against the flat portions 22b and 23b on the outer peripheral surface side, the surface portion is not interposed. The irregular reflection of sound waves is suppressed, and the inspection accuracy is reliably improved.

  Further, since the pair of inner and outer flat portions 22a, 22b, 23a, and 23b are respectively provided in two radial directions intersecting each other at the predetermined location in the axial direction, the cavity portion 11a at the location is determined by the ultrasonic inspection described above. It is possible to accurately inspect the degree of deviation, that is, the degree of thickness deviation.

  That is, as shown in FIG. 8, when only a pair of flat portions 22a and 22b parallel to each other are provided at predetermined positions in the axial direction, the flat portions 22a and 22b are formed from the predetermined position indicated by the chain line of the hollow portion 11a. Even if it is formed as shown by the solid line in the direction of the arrow e along the line E, the reflection process of the ultrasonic wave projected from the probe P during the ultrasonic inspection is not different from that in FIG. There is a problem that it may be inspected as appropriate. On the other hand, according to the configuration shown in FIG. 7, since ultrasonic inspection from two directions is possible at a predetermined location, such a problem is effectively solved.

  In this way, after the exhaust camshaft material 1 'is subjected to post-processing such as grinding to finish the exhaust camshaft 1 and then inspected, the cast exhaust camshaft material 1' is not inspected. Non-destructive inspection such as ultrasonic inspection can be applied instead of the above-described destructive inspection, and as a result, it is easily inspected whether or not the cavity 11a is correctly formed at a predetermined position at the exhaust camshaft material 1 ′ stage. An engine camshaft structure is provided.

  Next, since two pairs of flat portions 22a, 22b, 23a, and 23b are provided at locations corresponding to the two locations indicated by the arrows a and b in the axial direction, a wide range of inspection is possible, and the reliability of the inspection Improves.

  Moreover, since the two flat portions 22a, 22b, 23a, and 23b are provided in the same phase, for example, when performing an ultrasonic inspection, the inspection is performed without changing the phase of the exhaust camshaft material 1 '. Or the setting of the inspection apparatus can be easily changed, and the inspection efficiency is improved.

  Further, since the flat portions 22a, 22b, 23a, and 23b are set at locations other than the cams 12 to 15 and the bearing portions 16 to 20 that are normally ground during post-processing, the flat portions 22a, 22b, 23a, and 23b are set. Is set so as not to impair the rotational balance of the exhaust camshaft 1, it is not necessary to perform post-processing such as grinding, and manufacturing efficiency can be maintained. It should be noted that since the flat portions 22a, 22b, 23a, and 23b exist at the stage of the exhaust camshaft 1 after general post-processing, reinspection is possible.

  Since the kelens 21 and 21 are used at the time of casting, and the flat portions 22a, 22b, 23a and 23b are set in the vicinity of the cast-in portions of the kelens 21 and 21, in this case, especially the arrangement of the kelens 21 and 21 is provided. The effect can be accurately determined.

Next, as shown in FIG. 9, the intake camshaft 2 for driving the intake valve is often similar to the exhaust camshaft 1 described above, and corresponds to the shaft portion 31 and a cylinder (not shown) on the shaft portion 31. A pair of first to fourth cams 32, 32, 33, 33, 34, 34, 35, 35 formed at four locations and bearings J ... J provided on a cylinder head (not shown) are supported. 1 to 4th bearing part 36,37,38,39. Further, another bearing portion 40 is provided on the left side of the intake camshaft 2 in the illustrated example. The cams 32, 32, 33, 33, 34, 34, 35, 35 and the bearing portions 36, 37, 38, 39, 40 are formed integrally with the shaft portion 31.

  The shaft portion 31 has a hollow portion 31a extending in the axial direction. The hollow portion 31a is provided over the right end portion and the vicinity of the left end portion in the illustrated example, and its cross section is basically circular.

  A bolt hole 31 b and a knock pin hole 31 c are formed in the left end portion of the shaft portion 31. In the vicinity of the left end portion of the shaft portion 31, a cam pulley Q for rotationally driving the intake camshaft 2, a valve timing variable mechanism R for changing the rotational phase of the intake camshaft 2 relative to the crankshaft, and A sensor rotor S for detecting the cam angle is assembled. The rotation of the sensor rotor S is detected by an electromagnetic pickup sensor (not shown) arranged close to the sensor rotor S, and the current phase angle of the intake camshaft 2 can be known.

  Keren 41 used during casting is cast in two predetermined locations of the intake camshaft 2, that is, between the left side of the left first cam 32 and the right side second cam 33 and the left side third cam 34, respectively. And the flat part which is the characterizing part of this invention mentioned later is provided in the location shown by the arrows f and g near the cast-in part of these kerens 41, 41.

  The intake camshaft 2 is also manufactured by casting as described above, but the description thereof is omitted because it overlaps.

  Next, the structure of the portion corresponding to the portion indicated by arrows f and g in FIG. 9 in the intake camshaft material obtained by casting will be described. First, the portion corresponding to the portion indicated by arrow g is shown in FIG. Since the configuration is the same as that of the exhaust camshaft material 1 ', the description thereof is omitted.

  As shown in FIG. 10, the intake camshaft material 2 ′ corresponds to the inner peripheral surface that forms the hollow portion 31 a at the position corresponding to the position indicated by the arrow f in the axial direction and the inner peripheral surface. A pair of flat portions 42a and 42b indicated by arrows f1 parallel to each other perpendicular to the radial direction and a pair of flat portions 43a and 43b also indicated by arrows f2 are provided on the outer peripheral surface. Flat portions 42a, 42b, 43a, 43b are respectively formed in two radial directions intersecting each other at the predetermined location in the axial direction. In that case, the pair of flat portions 42a and 42b and the pair of flat portions 43a and 43b are formed in two radial directions intersecting each other at an angle β. Further, the flat portions 42a, 42b, 43a, 43b of the respective sets provided at locations corresponding to the locations indicated by the arrows f, g are provided so as to be in phase with each other.

  Since the sensor rotor S is assembled by, for example, press-fitting at a location corresponding to the location indicated by the arrow f of the intake camshaft material 2 ′, the outer peripheral surface of the location is ground. Therefore, both the flat portions 42b and 43b on the outer peripheral surface side are removed by this grinding, and as shown in FIG. 11, the portions indicated by arrows f1 and f2 in the obtained intake camshaft 2 are located on the inner peripheral surface side. Only the flat portions 42a and 43a remain. The portion f2 is particularly thick, and a screw hole 31d for fixing the sensor rotor S to the shaft portion 31 is formed.

  With the above-described configuration, substantially the same operational effects as those of the exhaust camshaft 1 or the exhaust camshaft material 1 'described above can be obtained. Particularly in this case, the flat portions 42a, 42b, 43a, 43b are provided with arrows in addition to the portions corresponding to the portions indicated by the arrows g where the post-processing such as grinding is not performed on the intake camshaft material 2 'after casting. It is also provided at a location corresponding to the location indicated by f. In other words, since the flat portions 42b and 43b on the outer peripheral surface side are provided in places where they are surely removed by regular post-processing, extra post-processing is required because the flat portions 42b and 43b are provided. Absent. Therefore, in this case, the number of places where the flat portion can be provided is increased, and as a result, the degree of freedom in design is increased. For the same reason, for example, two to one set of flat portions 42a, 42b, 43a, and 43b may be provided at locations where the first to fourth bearing portions 36 to 39 are subjected to post-processing.

  In the above embodiment, in the exhaust camshaft material 1 ′, two pairs of flat portions 22a, 22b, 23a, and 23b are provided at two locations in the axial direction, and also in the intake camshaft material 2 ′. Although the two-to-one set of flat portions 42a, 42b, 43a, and 43b are provided at two locations in the axial direction, the number of the flat portions 42a, 42b, 43a, and 43b may be further increased to further improve the inspection reliability.

  As described above, according to the present invention, when manufacturing a camshaft of an engine having a cavity formed in the axial direction by casting using a core, is the cavity formed correctly at a predetermined position? There is provided a camshaft structure of an engine that can easily check whether or not. That is, the present invention relates to a camshaft structure of an engine having a hollow portion formed by casting using a core, and is widely suitable for the technical field of engines for automobiles and the like.

It is a partially broken top view of the exhaust camshaft which concerns on embodiment of this invention. It is an expanded sectional view by the II-II line of FIG. It is an expanded sectional view by the III-III line of FIG. It is a top view for demonstrating manufacture of the exhaust camshaft by casting. It is an expanded sectional view by the IV-IV line of FIG. It is an expanded sectional view by the VI-VI line of FIG. It is sectional drawing of the location in which the flat part in the exhaust camshaft material was provided. FIG. 8 is a cross-sectional view corresponding to FIG. 7 for explaining a problem when only a pair of flat portions is provided. It is a partially broken plan view of the intake camshaft according to the embodiment of the present invention. It is sectional drawing of the sensor rotor assembly | attachment scheduled part in an intake camshaft raw material. It is sectional drawing of the sensor rotor attachment scheduled part similarly post-processed. It is principal part sectional drawing in the case of manufacturing the camshaft which has a cavity part in a predetermined position using a core and keren at the time of the conventional casting.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust cam shaft 1 'Exhaust cam shaft material 2 Intake cam shaft 2' Intake cam shaft material 11, 31 Shaft part 11a, 31a Cavity part 12-15, 32-35 Cam 16-20, 36-40 Bearing part 21,41 Keren 22a, 22b, 23a, 23b, 42a, 42b, 43a, 43b Flat part K Upper mold (mold)
L Lower mold (mold)
M core

Claims (4)

The shaft has a cam portion for opening and closing the intake and exhaust valves of a plurality of cylinders and a plurality of bearing portions, and has a hollow portion extending in the axial direction formed using a core, and is integrally formed by casting. A camshaft structure for an engine, wherein a pair of parallel shafts perpendicular to each other in a radial direction are formed at predetermined locations in the axial direction of the camshaft, and an inner peripheral surface forming a cavity and an outer peripheral surface corresponding to the inner peripheral surface with the flat portions are provided, the flat portions of the inner and outer pair is provided respectively for the two radial intersecting with each other in the predetermined position of the axis direction, and, of the above pair of inner and outer flat portions A camshaft structure for an engine, characterized in that a flat portion on the outer peripheral surface side serves as a contact surface of an inspection probe .   2. The engine according to claim 1, wherein two to one sets of flat portions are provided at a plurality of locations in the axial direction, and the flat portions of each set are provided in the same phase. Camshaft structure.   The camshaft structure for an engine according to claim 1 or 2, wherein the flat portion is set at a place excluding the cam portion and the bearing portion. 4. The kelen disposed between the mold and the core at the time of casting is cast, and the flat portion is set near the cast-in portion of the keren. An engine camshaft structure according to any one of the above.

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