JP2017180405A - Cam shaft for multi-cylinder engine and its process of manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cam shaft for multi-cylinder engine capable of restricting a deformation of a shaft part even if its weight is light.SOLUTION: This invention relates to a cam shaft for a multi-cylinder engine comprising a shaft part extending in a direction of row of cylinders of the engine having several cylinders and several cam parts arranged at an outer periphery of the shaft part, the cam parts are arranged at positions corresponding to cylinders present more inside than both ends of the shaft part, the shaft part comprises a first removed wall part formed at a first segment that is a segment between an end part of at least one side of the shaft part and a cam part nearest to the end part and a second removed wall part formed in a second segment that is a segment between a cam part corresponding to one cylinder of adjoining two cylinders and a cam part corresponding to the other cylinder, the first removed wall part and the second removed wall part are formed in such a way that a strength of the shaft part in the second segment may become larger than a strength of the shaft part of the first segment.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a camshaft for a multi-cylinder engine and a manufacturing method thereof.

  Conventionally, camshafts that drive engine intake valves and exhaust valves have solid camshaft shafts (solid type), and camshaft shafts are hollow throughout their length. (Patent Document 1) discloses an example of a manufacturing method of a hollow type camshaft.

  The camshaft manufacturing method described in Patent Document 1 includes a step of manufacturing a mold by disposing a collapsible core made of sand or the like in a collapsible main die made of sand or the like, A step of pouring the molten metal into a cavity formed between the molten metal and a step of disintegrating and removing the mold after the molten metal is cooled. The core is provided with a plurality of positioning pins protruding radially from the outer peripheral surface thereof, and the core is positioned in the main mold by the plurality of pins.

JP 2014-18833 A

  According to the camshaft described in Patent Document 1, although the weight can be reduced as compared with a solid type camshaft, there are the following problems.

  More specifically, stress generated in the shaft portion when the shaft portion of the cam shaft described in Patent Document 1 receives a force from the cam portion (stress to twist the shaft portion and stress to bend the shaft portion). Is different depending on the position in the axial direction (length direction). That is, in the shaft portion of the camshaft in the in-line four-cylinder engine in which the first cylinder, the second cylinder, the third cylinder, and the fourth cylinder are sequentially arranged from one end side to the other end side in the cylinder row direction of the engine, the first cylinder A portion outside the cam portion for the first cylinder (hereinafter referred to as “outer portion”) and a portion between the cam portion for the first cylinder and the cam portion for the second cylinder (hereinafter referred to as “inter-cylinder portion”). The stress generated in the portion between the cylinders is greater than the stress generated in the outer portion. For this reason, the inter-cylinder part of the camshaft tends to be deformed more easily than the outer part.

  However, in the shaft portion of the camshaft described in Patent Document 1, the diameter of the hollow portion formed in the inter-cylinder portion is larger than the diameter of the hollow portion formed in the outer portion. It is considered that the strength of the portion between the cylinders is smaller than the strength of the outer portion. For this reason, the inter-cylinder portion is more easily deformed than the outer portion, and when such deformation occurs, there is a possibility that inconveniences such as variation in valve lift amount among cylinders may occur.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a camshaft for a multi-cylinder engine that can suppress deformation of a shaft portion while being lightweight, and a manufacturing method thereof.

  In order to solve the above problems, the present invention provides a cam for a multi-cylinder engine comprising a shaft portion extending in the cylinder row direction of an engine having a plurality of cylinders and a plurality of cam portions provided on the outer periphery of the shaft portion. The cam portion is provided at a position corresponding to the cylinder on the inner side of both end portions of the shaft portion, and the shaft portion is located at least at one end of the shaft portion and the end portion. A first thinning portion formed in a first section which is a section between the cam section and a cam section corresponding to one cylinder of two adjacent cylinders and a cam section corresponding to the other cylinder; A second gradually-thickening portion formed in a second section that is a section between the first and second thinning portions, and the strength of the shaft portion in the second section is , Formed so as to be larger than the strength of the shaft portion in the first section. Providing a cam shaft for a multi-cylinder engine, it characterized.

  Here, the “thickening part” in the present invention is a part of the shaft part having the same outer diameter so that a part of the cross-sectional area in the length direction is smaller than a cross-sectional area of a part other than the part. The hole part (a recessed part and a through-hole are included) formed in the outer peripheral surface of this, or a notch part is said.

  ADVANTAGE OF THE INVENTION According to this invention, the camshaft for multicylinder engines which can suppress a deformation | transformation of a shaft part while being lightweight can be provided.

  More specifically, in the present invention, since the shaft portion has the first and second thinning portions, the thinning portion is compared with the case where the first and second thinning portions are not provided. The camshaft can be reduced in weight by the weight corresponding to the volume of the part.

  Moreover, the deformation of the shaft portion can be effectively suppressed for the following reasons. That is, the stress generated in the shaft portion when the shaft portion receives a force from the cam portion (stress to twist the shaft portion and stress to bend the shaft portion) is in the axial direction (length direction). Specifically, the stress generated in the second section is larger than the stress generated in the first section. This is because the force transmitted from the cam portion increases as the distance from the cam portion in the shaft portion increases. Further, in the first section, the force is transmitted only from one side in the axial direction. This is because the above-mentioned force is transmitted from both axial sides in the two sections.

  On the other hand, in the present invention, the first thinning portion and the second thinning portion are formed such that the strength of the shaft portion in the second section is greater than the strength of the shaft portion in the first section. Therefore, even if a larger stress is generated in the second section than in the first section, deformation of the shaft portion in the second section can be suppressed. Thereby, it is possible to effectively suppress the occurrence of inconveniences such as variations in the valve lift amount among the cylinders.

  In the present invention, each of the first thinning portion and the second thinning portion is a non-through hole that opens to an outer peripheral surface of the shaft portion, and the depth of the second thinning portion is the first thickness. It is preferable that it is shallower than the depth of one thinning part.

  According to this configuration, each of the first thinning portion and the second thinning portion is a non-through hole that opens to the outer peripheral surface of the shaft portion, and therefore, these thinning portions can be easily formed. Moreover, since the depth of the second thinned portion is shallower than the depth of the first thinned portion, the strength of the shaft portion in the second section is easier and more reliable than the strength of the shaft portion in the first section. Can be bigger.

  In the present invention, each of the first thinning portion and the second thinning portion is a non-through hole that opens to the outer peripheral surface of the shaft portion, and extends in the length direction of the shaft portion, The depth of the first thinned portion is constant in the length direction, and the depth of the second thinned portion gradually decreases from the central portion in the length direction toward both ends in the length direction. Preferably it is.

  According to this configuration, each of the first thinning portion and the second thinning portion is a non-through hole that opens to the outer peripheral surface of the shaft portion, and therefore, these thinning portions can be easily formed. Moreover, the first and second thinning portions extend in the length direction of the shaft portion, and the first thinning portion has a constant depth in the length direction, and the second thinning portion Since the depth gradually decreases from the central portion in the length direction toward both ends in the length direction, the strength of the shaft portion in the second section can be made easier than the strength of the shaft portion in the first section. Can be bigger. More specifically, since the depth of the first thinned portion is constant in the length direction, the strength of the shaft portion in the section where the first thinned portion is formed in the first section is substantially constant. can do. On the other hand, since the depth of the second thinned portion is shallow at the position close to the cam portion, the strength of the shaft portion at the position where the stress is relatively large (position close to the cam portion) in the second section. , The strength of the shaft portion at a position where the stress is relatively small (position far from the cam portion) can be made larger, and thereby the strength of the shaft portion in the second section can be made larger than the strength of the shaft section in the first section. Can be easily enlarged.

  In the present invention, the first thinning portion may be a through hole that penetrates the shaft portion in the radial direction, and the second thinning portion may be a non-through hole that opens on an outer peripheral surface of the shaft portion. preferable.

  According to this configuration, the strength of the shaft portion in the second section can be easily and reliably increased than the strength of the shaft portion in the first section.

  In this invention, the said shaft part has a hollow part extended in the length direction of the said shaft part by the radial direction center part, and the said 1st thinning part and the said 2nd thinning part are respectively said hollow parts It is preferable to communicate with.

  According to this configuration, since the shaft portion has a hollow portion extending in the length direction of the shaft portion at the radial center portion, the volume of the hollow portion is smaller than when the hollow portion is not provided. Thus, the camshaft can be further reduced in weight by the weight corresponding to.

  Further, since the first and second thinning portions are respectively communicated with the hollow portion, when the hollow portion is formed using a rotary cutting tool, the solid shaft portion is cut. The facets that are generated in the process can be quickly discharged to the outside through the first and second thinning portions, and as a result, the efficiency of cutting can be increased.

  In this invention, the said shaft part has a hollow part extended in the length direction of the said shaft part by the radial direction center part, and among the said 1st thinning part and the said 2nd thinning part, it is the said 1st removal. It is preferable that only the meat part communicates with the hollow part.

  According to this configuration, since the shaft portion has a hollow portion extending in the length direction of the shaft portion at the radial center portion, the volume of the hollow portion is smaller than when the hollow portion is not provided. Thus, the camshaft can be further reduced in weight by the weight corresponding to.

  Further, since the first thinned portion communicates with the hollow portion, when the hollow portion is formed using a rotary cutting tool, the facets generated when the solid shaft portion is cut are removed. It can be quickly discharged to the outside through the meat removal part, and as a result, the efficiency of cutting can be increased. And among the 1st thinning part and the 2nd thinning part, since only the 1st thinning part is connected with the above-mentioned hollow part, in the above-mentioned 2nd section, the 2nd thinning part and the hollow part are connected. By doing so, it is possible to suppress a decrease in the strength of the shaft portion, and thereby it is possible to more effectively suppress the deformation of the shaft portion in the second section.

  The present invention is a method for manufacturing a camshaft for a multi-cylinder engine, wherein a solid camshaft having a solid shaft portion in which a central portion in a radial direction is formed solidly and the plurality of cam portions are provided on an outer periphery. A multi-cylinder engine comprising: a casting step of casting, and a hollow portion forming step of forming the hollow portion by cutting a radial center portion of the solid shaft portion using a rotary cutting tool. A method for manufacturing a camshaft for use is provided.

  According to the present invention, the hollow portion is formed by cutting the radial center portion of the solid shaft portion using a rotary cutting tool. Therefore, it is necessary to use a core in the casting process to form the hollow portion. The hollow portion can be easily formed at a relatively low cost.

  In the present invention, of the first thinned portion and the second thinned portion cast in the casting step, the thinned portion that communicates with the hollow portion in the hollow portion forming step is determined by the rotary cutting tool. It is preferable to have a size that allows the facets generated during cutting to be discharged to the outside.

  According to this configuration, the thinned portion communicating with the hollow portion in the hollow portion forming step has a size capable of discharging the face generated when cutting by the rotary cutting tool to the outside. Can be quickly discharged to the outside through the above-mentioned thickness removal portion, and the efficiency of cutting can be effectively increased.

  As described above, according to the present invention, it is possible to provide a camshaft for a multi-cylinder engine capable of suppressing deformation of the shaft portion while being lightweight, and a manufacturing method thereof.

It is a top view which shows a cylinder head provided with the camshaft (exhaust camshaft and intake camshaft) for engines which concerns on embodiment of this invention. It is a perspective view which shows the exhaust camshaft shown by FIG. It is a top view which shows the exhaust camshaft shown by FIG. It is a side view which shows the exhaust camshaft shown by FIG. FIG. 4 is a cross-sectional view of the exhaust camshaft shown in FIG. 3 taken along line AA. FIG. 3 is a cross-sectional view of the intake camshaft shown in FIG. 1 taken along the line BB. (A) is CC sectional view taken on the line of the exhaust camshaft shown by FIG. 3, (b) is DD sectional view taken on the line of the exhaust camshaft shown in FIG. It is sectional drawing which shows a mode that the 1st sand type | mold which comprises a casting_mold | template is manufactured. It is sectional drawing which shows a mode that the 2nd sand type | mold which comprises a casting_mold | template is manufactured. It is sectional drawing which shows the casting_mold | template comprised combining a 1st sand mold and a 2nd sand mold. It is sectional drawing which shows the 1st modification of the hole of an intake camshaft. FIG. 6 is a cross-sectional view showing an intake camshaft when a hollow portion is formed in the radial center portion of the shaft portion of the intake camshaft and all the hole portions opened to the outer peripheral surface of the shaft portion communicate with the hollow portion. is there. (A) is the EE sectional view taken on the line of the intake camshaft shown by FIG. 12, (b) is the FF sectional view taken on the line of the intake camshaft shown in FIG. A hollow portion is formed at the radial center portion of the shaft portion of the intake camshaft, and among the hole portions opened on the outer peripheral surface of the shaft portion, between the end portions on both sides of the shaft portion and the cam portion closest to the end portion. It is sectional drawing which shows an intake camshaft in case the hole formed in this area and the said hollow part are connecting. It is the GG sectional view taken on the line of the intake camshaft shown in FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Engine structure with camshaft>
An engine including a camshaft according to an embodiment of the present invention is an in-line four-cylinder four-cycle diesel engine, and is assembled on a cylinder block (not shown) and the cylinder block as shown in FIG. And a cylinder head 72. In the engine shown in FIG. 1, although not shown, four cylinders of a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder are arranged in order from the left side.

  The cylinder head 72 has, for each cylinder, two exhaust ports and two intake ports communicating with the combustion chamber, an exhaust valve for shutting off each exhaust port from the combustion chamber, and shutting each intake port from the combustion chamber. An exhaust valve drive mechanism 78 for driving each exhaust valve to open and close each exhaust port at a predetermined timing, and each intake valve for driving each intake valve. An intake valve drive mechanism 73 that opens and closes the intake port at a predetermined timing, four bearing portions 24 to 27 that rotatably support an exhaust camshaft 2 described later, and 4 that rotatably supports an intake camshaft 3 described later. And two bearing portions 74 to 77.

  The exhaust valve drive mechanism 78 and the intake valve drive mechanism 73 include an exhaust camshaft 2 and an intake camshaft 3, respectively. The exhaust camshaft 2 and the intake camshaft 3 are well-known configured from a chain, a sprocket, and the like. It is connected to the crankshaft via a power transmission mechanism. Further, the exhaust valve drive mechanism 78 and the intake valve drive mechanism 73 each include a return spring (not shown) that biases the exhaust valve in the closing direction and a return spring (not shown) that biases the intake valve in the closing direction. ing. The exhaust camshaft 2 and the intake camshaft 3 respectively open the exhaust valve and the intake valve against the urging force of the return spring by the driving force of the crankshaft. The exhaust camshaft 2 and the intake camshaft 3 correspond to the “camshaft for a multi-cylinder engine” of the present invention.

<Exhaust camshaft structure>
As shown in FIGS. 1 to 3, the exhaust camshaft 2 includes a columnar shaft portion 5 extending in the cylinder row direction, and eight cam portions integrally provided on the outer periphery of the shaft portion 5 (see FIG. 1). In order from the left side, the first cam portion 6, the second cam portion 7, the third cam portion 8, the fourth cam portion 9, the fifth cam portion 10, the sixth cam portion 11, the seventh cam portion 12, and the eighth cam. Part 13), journal parts 20 to 23 (see FIG. 2) which are integrally provided on the outer periphery of the shaft part 5 and are rotatably supported by the bearing parts 24 to 27, respectively, and a sprocket around which a timing chain is wound (Not shown) is attached, and the sprocket mounting portion 4 provided integrally at one end portion of the shaft portion 5 is integrally provided at the other end portion of the shaft portion 5, and is a drive shaft of the fuel pump. And an Oldham coupling part 15 to which (not shown) is connected. . In the example shown in FIG. 1, the exhaust camshaft 2 rotates in the clockwise direction (clockwise direction) when viewed from the left side.

  In the exhaust camshaft 2, the first cam portion 6 and the second cam portion 7 are eccentric cams provided corresponding to the first cylinders, and these are adjacent to each other via the journal portion 20. (See FIGS. 2 to 4). The first cam portion 6, the second cam portion 7, and the journal portion 20 are located above the first cylinder and on the exhaust side. Similarly, the third cam portion 8 and the fourth cam portion 9 are eccentric cams provided corresponding to the second cylinder, respectively, and are adjacent to each other via the journal portion 21. The third cam portion 8, the fourth cam portion 9, and the journal portion 21 are located above the second cylinder and on the exhaust side. Each of the fifth cam portion 10 and the sixth cam portion 11 is an eccentric cam provided corresponding to the third cylinder, and these are adjacent to each other via the journal portion 22. The fifth cam portion 10, the sixth cam portion 11, and the journal portion 22 are located above the third cylinder and on the exhaust side. Each of the seventh cam portion 12 and the eighth cam portion 13 is an eccentric cam provided corresponding to the fourth cylinder, and these are adjacent to each other via the journal portion 23. The seventh cam portion 12, the eighth cam portion 13, and the journal portion 23 are located above the fourth cylinder and on the exhaust side. Each of the cam portions 6 to 13 includes one nose portion 6a to 13a (see FIG. 2) that protrudes radially outward from the base circle.

  In the engine according to the present embodiment, the explosion order of each cylinder is set as follows: first cylinder → third cylinder → fourth cylinder → second cylinder, and accordingly, the cam portions 6 to 13 of the exhaust camshaft 2. Are provided with a phase difference from each other so that the exhaust valves are opened in the order of explosion described above every 90 ° rotation of the exhaust camshaft 2 (see FIG. 2).

  The shaft portion 5 of the exhaust camshaft 2 corresponds to a section between the sprocket mounting section 4 and the first cam section 6 (corresponding to a “first section” of the present invention. And the section between the second cam section 7 and the third cam section 8 (corresponding to the “second section” of the present invention. In the following description, the “second section”). The rotation angle adjusting portion 18 between the fourth cam portion 9 and the fifth cam portion 10, and between the sixth cam portion 11 and the seventh cam portion 12. (Corresponding to a “second section” of the present invention, which may be referred to as a “second section” in the following description) has a hole 19 and a camshaft identification ring 14.

  As shown in FIG. 5, the hole portion 16 has a first hole portion 16 a that opens at a predetermined position on one radial side of the shaft portion 5, and a first hole portion that opens at a predetermined position on the other radial side of the shaft portion 5. 2 holes 16b. The first hole portion 16a and the second hole portion 16b each extend in the length direction of the shaft portion 5, and are formed so as to gradually narrow toward the center from the radially outer side of the shaft portion 5. (See FIG. 7 (a)).

  More specifically, each of the hole portion 16a and the hole portion 16b is an opening portion that opens in a shape in which a semicircle is combined with both ends of a rectangle extending in the length direction of the shaft portion 5 on the outer peripheral surface of the shaft portion 5. 16e (see FIG. 7 (a)), a substantially flat bottom portion 16d having substantially the same shape as the opening portion 16e and having an area smaller than the opening area of the opening portion 16e, the opening portion 16e and the bottom portion 16d. It has the surrounding wall part 16c to connect. The bottom portion 16d has substantially the same depth over the entire length direction, and a boundary portion between the peripheral wall portion 16c and the bottom portion 16d is formed in a curved surface shape.

  The first hole portion 16a is formed in the same shape and the same size as the second hole portion 16b at a position symmetrical to the second hole portion 16b with respect to the center line of the shaft portion 5. Further, as shown in FIG. 7A, the first hole portion 16a is formed at the apex side of the nose portion 6a of the first cam portion 6, specifically, at the position where the phase (rotation phase) is the same as the apex. The second hole portion 16b is formed at a position opposite to the nose portion 6a of the first cam portion 6, specifically at a position that is approximately 180 ° out of phase with the apex of the nose portion 6a. The first hole portion 16a and the second hole portion 16b correspond to the “first wall removal portion” of the present invention. In the following description, these holes 16a and 16b may be referred to as “first wall removal portions”.

  As shown in FIG. 5, the hole 17 has a first hole 17 a that opens at a predetermined position on one side in the radial direction of the shaft 5 and a first hole that opens at a predetermined position on the other side in the radial direction of the shaft 5. 2 holes 17b. The first hole portion 17a and the second hole portion 17b each extend in the length direction of the shaft portion 5, and are formed so as to gradually narrow from the radially outer side of the shaft portion 5 toward the center. (Refer FIG.7 (b)).

  More specifically, each of the first hole portion 17a and the second hole portion 17b has a shape in which a semicircle is combined with both ends of a rectangle extending in the length direction of the shaft portion 5 on the outer peripheral surface of the shaft portion 5. An opening 17e (see FIG. 7B) and a width narrower than the opening 17e, extending in the length direction of the shaft portion 5, and gradually deeper from both ends in the length direction to the center portion (center in the radial direction) In other words, the shaft portion 5 is formed so as to gradually become shallower from the center in the length direction to both ends in the length direction, and the both ends in the length direction have a substantially V-shaped cross section continuous with the opening 17e. It has a slope portion 17d (see FIG. 5) and a side wall portion 17c that rises from both end portions in the width direction of the slope portion 17d and continues to the end portion in the width direction of the opening portion 17e. The bottom portion of the slope portion 17d (the lower end portion of the V shape) is formed in a curved shape, and the depth of the bottom portion (the depth of the deepest portion of each of the first hole portion 17a and the second hole portion 17b) is It is set to be substantially the same as the depth of the first hole portion 16a and the second hole portion 16b. That is, the diameter (diameter) of the shaft portion 5 in the section between the second cam portion 7 and the third cam portion 8 is the diameter of the shaft portion 5 in the section between the sprocket mounting portion 4 and the first cam portion 6. In addition, the bottom of the slope portion 17d in the first hole portion 17a and the second hole portion 17b is formed in a curved shape, and stress concentration is unlikely to occur in the bottom portion. For this reason, the strength of the shaft portion 5 in the section between the second cam portion 7 and the third cam portion 8 is greater than the strength of the shaft portion 5 in the section between the sprocket mounting portion 4 and the first cam portion 6. It is getting bigger.

  The first hole portion 17a is formed in the same shape and the same size as the second hole portion 17b at a position symmetrical to the second hole portion 17b with respect to the center line of the shaft portion 5. Further, as shown in FIG. 7B, the first hole portion 17a is formed at a position delayed in phase by approximately 90 ° with respect to the apex of the nose portion 8a of the third cam portion 8, and the second hole portion 17 b is formed at a position where the phase is advanced by approximately 90 ° with respect to the apex of the nose portion 8 a of the third cam portion 8. The first hole portion 17a and the second hole portion 17b correspond to the “second wall removal portion” of the present invention. In the following description, these holes 17a and 17b may be referred to as “second thinning portions”.

  The rotation angle adjusting portion 18 is a portion protruding in a hexagonal cross section (regular hexagon) from the outer periphery of the shaft portion 5 to the radially outer side. The rotation angle adjusting unit 18 is used by being engaged with a spanner during engine inspection or the like. That is, at the time of engine inspection or the like, by rotating the spanner by engaging the rotation angle adjusting portion 18 with the opening portion of the spanner, the shaft portion 5 can be rotated and the exhaust port can be closed by the exhaust valve. Thereby, it is possible to prevent foreign matters such as dust from entering from the exhaust port during engine inspection or the like.

  As shown in FIG. 5, the hole 19 has a first hole 19 a that opens at a predetermined position on one side in the radial direction of the shaft portion 5, and a first hole that opens at a predetermined position on the other side in the radial direction of the shaft portion 5. 2 holes 19b. The first hole portion 19a and the second hole portion 19b are formed so as to gradually narrow toward the center from the radially outer side of the shaft portion 5, and more specifically, the hole portion 17a and the hole portion 17b Similarly, it is formed in a substantially V-shaped cross section, but in order to avoid interference with the camshaft identification ring 14, it is formed shorter in the length direction of the shaft portion 5 than the hole portion 17a and the hole portion 17b. . The first hole portion 19a is formed at a position where the phase is advanced by approximately 90 ° with respect to the apex of the nose portion 11a (see FIG. 2) of the sixth cam portion 11, and the second hole portion 19b is formed at the sixth cam portion. It is formed at a position where the phase is delayed by approximately 90 ° with respect to the apex of the nose portion 11a of the portion 11.

  Similar to the section between the second cam section 7 and the third cam section 8, the diameter (diameter) of the shaft section 5 in the section between the sixth cam section 11 and the seventh cam section 12 is the sprocket. The diameter is set larger than the diameter of the shaft portion 5 in the section between the mounting portion 4 and the first cam portion 6, and the bottoms of the slope portions in the first hole portion 19a and the second hole portion 19b are curved. As a result, stress concentration is less likely to occur at the bottom. For this reason, the strength of the shaft portion 5 in the section between the sixth cam portion 11 and the seventh cam portion 12 is greater than the strength of the shaft portion 5 in the section between the sprocket mounting portion 4 and the first cam portion 6. It is getting bigger. The first hole portion 19a and the second hole portion 19b correspond to the “second wall removal portion” of the present invention. In the following description, these holes 19a and 19b may be referred to as “second thinning portions”.

  The camshaft identification ring 14 is a portion protruding in a ring shape radially outward from the outer periphery of the shaft portion 5. The arrangement position of the camshaft identification ring 14 in the length direction of the shaft portion 5 differs depending on the vehicle type. When the engine is assembled, the camshaft identification sensor reads the position of the camshaft identification ring 14, so that the engine assembly apparatus The corresponding vehicle type of the exhaust camshaft 2 can be identified.

  As shown in FIG. 5, a hole 45 extending in the axial direction (length direction) is formed in the central portion in the radial direction of the sprocket mounting portion 4. Further, the Oldham coupling portion 15 is formed with a hole portion 43 penetrating the inside thereof in the axial direction (length direction). Further, the journal portion 23 extends from the end portion of the shaft portion 5 on the Oldham coupling portion 15 side. A hole 44 extending in the length direction thereof and communicating with the hole 43 is formed over the portion corresponding to.

<Structure of intake camshaft>
As shown in FIG. 1, the intake camshaft 3 includes a columnar shaft portion 48 extending in the cylinder row direction, and eight cam portions integrally provided on the outer periphery of the shaft portion 48 (from the left side in FIG. 1). In order, the first cam portion 30, the second cam portion 31, the third cam portion 32, the fourth cam portion 33, the fifth cam portion 34, the sixth cam portion 35, the seventh cam portion 36, and the eighth cam portion 37. ), Journal portions 49 to 52 (see FIG. 6) that are integrally provided on the outer periphery of the shaft portion 48 and are rotatably supported by the bearing portions 74 to 77, respectively, and a sprocket (not shown) around which a timing chain is wound. The sprocket mounting portion 28 provided integrally with one end portion of the shaft portion 48 is connected to the drive shaft (not shown) of the fuel pump, and the other end portion of the shaft portion 48 is attached. Oldham coupling unit Has a 0 and. In the example shown in FIG. 1, the intake camshaft 3 rotates counterclockwise (counterclockwise) as viewed from the left.

  In the intake camshaft 3, the first cam portion 30 and the second cam portion 31 are eccentric cams provided corresponding to the first cylinders, respectively, and these journal portions 49 (see FIG. 6). Are adjacent to each other. The first cam portion 30, the second cam portion 31, and the journal portion 49 are located above the first cylinder and on the intake side. The third cam portion 32 and the fourth cam portion 33 are eccentric cams provided corresponding to the second cylinder, respectively, and these are adjacent to each other via the journal portion 50. The third cam portion 33, the fourth cam portion 34, and the journal portion 50 are located above the second cylinder and on the intake side. The fifth cam portion 34 and the sixth cam portion 35 are eccentric cams provided in correspondence with the third cylinder, respectively, and are adjacent to each other via the journal portion 51. The fifth cam portion 34, the sixth cam portion 35, and the journal portion 51 are located above the third cylinder and on the intake side. The seventh cam portion 36 and the eighth cam portion 37 are eccentric cams provided corresponding to the fourth cylinder, respectively, and these are adjacent to each other via the journal portion 52. The seventh cam portion 36, the eighth cam portion 37, and the journal portion 52 are located above the fourth cylinder and on the intake side. Each of the cam portions 30 to 37 includes one nose portion 30a to 37a (see FIGS. 1 and 6) that protrudes radially outward from the base circle.

  As described above, the cam parts 30 to 37 of the intake camshaft 3 take in the intake air as the explosion order of each cylinder changes from the first cylinder → the third cylinder → the fourth cylinder → the second cylinder. The camshaft 3 is provided with a phase difference from each other so that the intake valve is opened in the above-described explosion order every 90 ° rotation of the camshaft 3.

  The shaft portion 48 of the intake camshaft 3 corresponds to a section between the sprocket mounting portion 28 and the first cam section 30 (corresponding to a “first section” of the present invention. The section between the second cam section 31 and the third cam section 32 (corresponding to the "second section" of the present invention. In the following description, the "second section"). The camshaft identification ring 53 and the hole 39, and between the fourth cam portion 33 and the fifth cam portion 34, the rotation angle adjusting portion 40, the sixth cam portion 35 and the seventh cam portion. A hole 41, the eighth cam portion 37, and the Oldham in a section (corresponding to a “second section” of the present invention, which may be referred to as a “second section” in the following description) between the cam section 36. Section between the coupling unit 90 (corresponding to the “first section” of the present invention) That. The following in the description may be referred to as "first period") has a hole portion 42.

  As shown in FIG. 6, the hole 38 has a first hole 38a that opens at a predetermined position on one side in the radial direction of the shaft 48 and a second hole that opens at a predetermined position on the other side in the radial direction of the shaft 48. And a hole 38b. The first hole 38 a and the second hole 38 b extend in the length direction of the shaft portion 48, respectively, and from the radially outer side of the shaft portion 48, similar to the hole portion 16 of the exhaust camshaft 2. It is formed so as to gradually narrow toward the center. The first hole portion 38a is formed at the apex side of the nose portion 30a of the first cam portion 30, specifically, at a position substantially in phase with the apex, and the second hole portion 38b is formed at the first cam portion 30. Is formed at a position opposite to the nose portion 30a, specifically, at a position that is approximately 180 ° out of phase with the apex of the nose portion 30a. The first hole 38a and the second hole 38b correspond to the “first wall removal portion” of the present invention. In the following description, these holes 38a and 38b may be referred to as “first wall removal portions”.

  As shown in FIG. 6, the hole 39 has a first hole 39 a that opens at a predetermined position on one side in the radial direction of the shaft 48, and a first hole that opens at a predetermined position on the other side in the radial direction of the shaft 48. 2 holes 39b. The first hole portion 39a and the second hole portion 39b each extend in the length direction of the shaft portion 48, and from the radially outer side of the shaft portion 48, like the hole portion 17 of the exhaust camshaft 2. It is formed so as to gradually narrow toward the center. The first hole 39a and the second hole 39b are formed shorter than the hole 17a and the hole 17b of the exhaust camshaft 2 in order to avoid interference with the camshaft identification ring 53. The first hole 39a is formed at a position delayed in phase by about 90 ° with respect to the apex of the nose portion 32a (see FIG. 1) of the third cam portion 32, and the second hole 39b The phase is formed at a position where the phase is advanced by approximately 90 ° with respect to the apex of the nose portion 32 a of the portion 32. The first hole 39a and the second hole 39b correspond to the “second wall removal portion” of the present invention. In the following description, these holes 39a and 39b may be referred to as “second thinning portions”.

  As shown in FIG. 6, the hole 41 has a first hole 41 a that opens at a predetermined position on one side in the radial direction of the shaft portion 48, and a first hole that opens at a predetermined position on the other side in the radial direction of the shaft portion 48. 2 holes 41b. The first hole portion 41a and the second hole portion 41b each extend in the length direction of the shaft portion 48, and, like the hole portion 19 of the exhaust camshaft 2, center from the radially outer side of the shaft portion 48. It is formed so as to gradually narrow toward the front. The first hole portion 41a is formed at a position where the phase is advanced by approximately 90 ° with respect to the apex of the nose portion 35a (see FIG. 1) of the sixth cam portion 35, and the second hole portion 41b is the sixth cam portion. The phase is formed at a position delayed by about 90 ° with respect to the apex of the nose portion 35 a of the portion 35. The first hole 41a and the second hole 41b correspond to the “second wall removal portion” of the present invention. In the following description, these hole portions 41a and 41b may be referred to as “second thinning portions”.

  As shown in FIG. 6, the hole 42 has a first hole 42 a that opens at a predetermined position on one side in the radial direction of the shaft 48, and a first hole 42 a that opens at a predetermined position on the other side in the radial direction of the shaft 48. 2 holes 42b. Each of the first hole portion 42a and the second hole portion 42b extends in the length direction of the shaft portion 48 and, like the hole portion 41, gradually narrows from the radially outer side of the shaft portion 48 toward the center. It is formed as follows. The first hole portion 42a and the second hole portion 42b are formed shorter in the length direction of the shaft portion 48 than the hole portion 41a and the hole portion 41b. Further, the first hole portion 42 a is formed at a position that is approximately 180 ° out of phase with the apex of the nose portion 37 a of the eighth cam portion 37, and the second hole portion 42 b is formed of the nose portion 37 a of the eighth cam portion 37. The vertex is formed at a position where the phase is substantially the same. The first hole portion 42a and the second hole portion 42b correspond to the “first wall removal portion” of the present invention. In the following description, these hole portions 42a and 42b may be referred to as “first wall removal portions”.

  In addition, the hole portions indicated by reference numerals 61, 60, and 62 in FIG. 1 are respectively a hole portion through which the shaft portion of the intake valve corresponding to the first cylinder is inserted, a hole portion through which the shaft portion of the exhaust valve is inserted, It is a hole provided with a fuel injection valve. Similarly, holes indicated by reference numerals 64, 63, and 65 are holes through which the shaft portion of the intake valve corresponding to the second cylinder is inserted, holes through which the shaft portion of the exhaust valve is inserted, and fuel injection, respectively. It is a hole provided with a valve. In addition, holes indicated by reference numerals 67, 66, and 68 are a hole through which the shaft of the intake valve corresponding to the third cylinder is inserted, a hole through which the shaft of the exhaust valve is inserted, and a fuel injection valve, respectively. Is a hole provided. The holes denoted by reference numerals 91, 69, 71 are provided with a hole portion through which the shaft portion of the intake valve corresponding to the fourth cylinder is inserted, a hole portion through which the shaft portion of the exhaust valve is inserted, and a fuel injection valve. Hole.

  As shown in FIG. 6, a hole 46 extending in the axial direction (length direction) is formed in the central portion in the radial direction of the sprocket mounting portion 28. Further, the Oldham coupling portion 90 is formed with a hole portion 47 penetrating the inside thereof in the axial direction (length direction).

<Manufacturing method of exhaust camshaft>
Next, a method for manufacturing the exhaust camshaft 2 will be described with reference to FIGS. Note that the manufacturing method of the intake camshaft 3 is the same as the manufacturing method of the exhaust camshaft 2, and thus the description thereof is omitted.

  The method of manufacturing the exhaust camshaft 2 can be roughly divided into a radial one-side portion 80a (see FIG. 8) and a radial other-side portion 80b (see FIG. 9). A prototype 83 having a camshaft prototype 80 (see FIGS. 8 and 9) having the same shape as the exhaust camshaft 2 is prepared, and a casting mold 84 (see FIG. 10) is prepared using the prototype 83 and casting sand. A series of processes of manufacturing and casting the exhaust camshaft 2 using the mold 84 is provided.

  Hereinafter, each process of the manufacturing method of the exhaust camshaft 2 will be described in detail.

(Prototype preparation process)
First, the camshaft prototype 80 (see FIGS. 8 and 9) and the feeder portion 57 (see FIG. 10) of the mold 84 are provided to form the radial one side portion 81a (see FIG. 8) and the diameter. Provided to form a hot-water supply portion forming portion 81 (see FIGS. 8 and 9) that can be divided into the other side portion 81b (see FIG. 9) and a pouring portion 92 (see FIG. 10) of the mold 84; It has a pouring part forming portion 82 (see FIGS. 8 and 9) that can be divided into a radial one side portion 82a (see FIG. 8) and a radial other side portion 82b (see FIG. 9). A prototype 83 that can be divided into a portion 83a (see FIG. 8) and a second prototype component 83b (see FIG. 9) is prepared. The shaft portion 85 of the prototype 83 has holes 57a, 57b, 57c (see FIG. 8), 59a, 59b, 59c (see FIG. 9) that open at predetermined positions on the outer peripheral surface of the shaft 85. . The holes 57a, 57b, 57c, 59a, 59b, 59c are formed so as to gradually narrow from the radially outer side of the shaft portion 85 of the prototype 83 toward the center. The holes 57a, 57b, 57c, 59a, 59b, 59c of the prototype 83 correspond to the holes 16a, 17a, 19a, 16b, 17b, 19b of the exhaust camshaft 2, respectively.

  In the example shown in FIG. 8, the first prototype component 83 a of the prototype 83 includes a radial one-side portion 80 a of the camshaft prototype 80, a radial one-side portion 81 a of the feeder portion forming portion 81, and pouring It has a radial direction one side part 82a of the part forming part 82. The shaft portion 85a of the radial one side portion 80a of the camshaft prototype 80 has the holes 57a, 57b, and 57c. The first prototype component 83a is arranged in a first casting frame 56 to be described later with its dividing surface Pa facing down so that each hole 57a, 57b, 57c opens upward. Is formed.

  Further, in the example shown in FIG. 9, the second prototype component 83b of the prototype 83 includes the radial other side portion 80b of the camshaft prototype 80, the radial other side portion 81b of the feeder portion forming portion 81, It has the other radial side part 82b of the pouring part forming part 82. The shaft portion 85b of the other radial portion 80b of the camshaft prototype 80 has the holes 59a, 59b, and 59c. The second prototype component 83b is arranged in a second cast frame 58, which will be described later, with its dividing surface Pb facing down so that the holes 59a, 59b, 59c open upward. Is formed.

(First sand mold manufacturing process)
After the prototype 83 is prepared, the first prototype component 83a of the prototype 83 is placed in the first casting frame 56 as shown in FIG. At that time, the first prototype component 83a is arranged in the first casting frame 56 with its dividing surface Pa facing downward so that each of the holes 57a, 57b, 57c opens directly upward. . Then, casting sand is put into the first casting frame 56. This casting sand is a self-hardening casting sand that is hardened by heating, and is constituted by blending a binder made of a thermosetting resin and various additives into sand as an aggregate. .

  After the casting sand is introduced, the casting sand is cured by heating. Then, the first prototype component 83a of the prototype 83 is extracted from the hardened cast sand, and the first cast frame 56 is removed from the hardened cast sand, whereby the first sand mold 84a made of the hardened cast sand is manufactured. To do. In addition, the order which removes the 1st prototype structure part 83a and the 1st casting frame 56 from the hardening casting sand may be simultaneous, and which may be first.

  Here, the holes 57a, 57b, 57c of the first prototype component 83a of the prototype 83 are formed so as to gradually narrow from the radially outer side of the shaft portion 85 toward the center, and the first prototype component described above. 83a is disposed in the first casting frame 56 so that the holes 57a, 57b, and 57c open upward, so that the cast sand hardened in the holes 57a, 57b, and 57c is formed in these holes. Without being caught by 57a, 57b, 57c, the first prototype component 83a of the prototype 83 can be extracted from the cured cast sand, and the first sand mold 84a made of the cured cast sand can be manufactured.

(Second sand mold manufacturing process)
Similar to the first prototype component 83a, the second prototype component 83b of the prototype 83 is placed in the second cast frame 58 and cast sand is poured into the second cast frame 58, as shown in FIG. Then, the second mold component 83b is extracted from the cured casting sand, and the second casting frame 58 is removed from the cured casting sand, whereby the second sand mold made of the cured casting sand is removed. 84b is manufactured. Even when the second sand mold 84b is manufactured, the cast sand hardened in the holes 59a, 59b, 59c is not caught in the holes 59a, 59b, 59c, as in the case of manufacturing the first sand mold 84a. The second prototype component 83b can be extracted from the hardened cast sand to produce the second sand mold 84b made of hardened cast sand. In addition, the order which removes the 2nd prototype structure part 83b and the 2nd casting frame 58 from the hardening casting sand may be simultaneous, and which may be first.

(Mold manufacturing process)
After the first sand mold 84a and the second sand mold 84b are manufactured, they are combined with each other to manufacture the mold 84 having the cavity 56 (see FIG. 10) in which the exhaust camshaft 2 is cast.

(Pouring process)
Next, by pouring a molten metal that is a material of the exhaust camshaft 2 into the pouring part 92 (see FIG. 10), the molten metal is poured into the cavity 56 through the feeder part 57, and the molten metal is cooled and cured. Let

(Camshaft removal process)
Next, the exhaust camshaft 2 is taken out from the mold 84 by collapsing and removing the mold 84 to manufacture the exhaust camshaft 2.

<Operational effects of this embodiment>
According to the exhaust camshaft 2 and the manufacturing method thereof according to the present embodiment, the following operational effects can be achieved. The intake camshaft 3 and the method for manufacturing the intake camshaft 3 have the same effects, but are not described here because they overlap.

  That is, according to this embodiment, as shown in FIG. 5, the shaft portion 5 of the exhaust camshaft 2 has holes 16 a, 17 a, 19 a, 16 b, and 17 b that open at predetermined positions on the outer peripheral surface of the shaft portion 5. 19b, the exhaust camshaft 2 can be reduced in weight by a weight corresponding to the volume of the hole 16a and the like, compared to the case where these holes 16a and the like are not provided.

  Moreover, the deformation of the shaft portion 5 of the exhaust camshaft 2 can be effectively suppressed for the following reasons. That is, when the shaft portion 5 receives a force from the cam portions 6 to 13, the stress generated in the shaft portion 5 (stress to twist the shaft portion 5 and stress to bend the shaft portion 5) is Specifically, in the second section (between the cam portion 7 and the cam portion 8 and between the cam portion 11 and the cam portion 12). The generated stress is larger than the stress generated in the first section (between the sprocket mounting portion 4 and the cam portion 6). This is because the force transmitted from the cam portions 6 to 13 increases as the distance from the cam portions 6 to 13 in the shaft portion 5 increases. Further, in the first section, the above force is applied only from one side in the axial direction. This is because, in the second section, the force is transmitted from both sides in the axial direction.

  On the other hand, in the present embodiment, the first thinned portion (holes 16a and 16b) and the second thinned portion (holes 17a, 17b, 19a and 19b) are arranged in the second section (second cam). The strength of the shaft portion 5 (between the portion 7 and the third cam portion 8) is greater than the strength of the shaft portion 5 in the first section (between the sprocket mounting portion 4 and the first cam portion 6). Therefore, even if a larger stress is generated in the second section than in the first section, the deformation of the shaft portion 5 in the second section can be suppressed. Thereby, it is possible to effectively suppress the occurrence of inconveniences such as variations in the valve lift amount among the cylinders.

  In the present embodiment, the first thinning portion (holes 16a, 16b) and the second thinning portion (holes 17a, 17b, 19a, 19b) are respectively provided on the outer peripheral surface of the shaft portion 5. Since the opening is a non-through hole, these thinned portions can be easily formed. Moreover, since the depth of the second thinning portion is shallower than the depth of the first thinning portion, the shaft portion 5 in the second section (between the second cam portion 7 and the third cam portion 8). The strength of the shaft portion 5 can be easily and reliably increased more than the strength of the shaft portion 5 in the first section (between the sprocket mounting portion 4 and the first cam portion 6).

  In addition, since the depth of the first thinning portion is constant in the length direction, the strength of the shaft portion 5 in the section where the first thinning section is formed in the first section is substantially constant. Can be. On the other hand, since the depth of the second thinning portion is shallow at the position close to the cam portions 7 and 8, the second section (between the second cam portion 7 and the third cam portion 8). Among them, the strength of the shaft portion 5 at a position where the stress is relatively large (position close to the cam portions 7 and 8) is greater than the strength of the shaft portion 5 at a position where the stress is relatively small (position far from the cam portions 7 and 8). Accordingly, the strength of the shaft portion 5 in the second section can be easily made larger than the strength of the shaft portion 5 in the first section.

  Further, the holes 16a, 17a, 19a, 16b, 17b, 19b of the exhaust camshaft 2 are formed so as to gradually narrow from the radially outer side of the shaft portion 5 of the exhaust camshaft 2 toward the center. Accordingly, the holes 57a, 57b, 57c, 59a, 59b, and 59c of the prototype 83 are also formed so as to gradually narrow from the radially outer side of the shaft portion 85 toward the center. Since the constricted shape of the holes 57a, 57b, 57c, 59a, 59b, 59c of the master 83 serves as a draft, in the process of manufacturing the first sand mold 84a, the first master is made from the hardened cast sand. The first sand mold 84a can be manufactured by easily removing the component 83a. The same applies to the production of the second sand mold 84b. Therefore, the exhaust camshaft 2 having the holes 16a, 17a, 19a, 16b, 17b, and 19b can be reliably cast using the first sand mold and the second sand mold. In addition, when casting the exhaust camshaft 2, it is not necessary to use a core for reducing the weight of the camshaft as described in Patent Document 1, and the core is accurate with respect to the main mold. Therefore, the number of mold parts can be reduced and the exhaust camshaft 2 can be easily manufactured.

  Further, according to the present embodiment, the first hole portion 16a of the exhaust camshaft 2 is located at a position symmetrical to the second hole portion 16b with respect to the axial center line of the exhaust camshaft 2, and the second hole portion. Since it is formed in the same shape as 16b, the holes 16a and 16b can be arranged in a well-balanced manner on the one radial side and the other radial side of the exhaust camshaft 2, and as a result, the strength of the shaft 5 Can be ensured with good balance between the one radial side and the other radial side.

<Other embodiments>
Although the embodiments of the exhaust camshaft 2, the intake camshaft 3, and the manufacturing method thereof have been described above, the embodiments can be changed as follows.

  For example, the embodiment of the intake camshaft 3 can be changed as follows, and the same change can be made for the exhaust camshaft 2.

  That is, in the intake camshaft 3 according to the above embodiment, the depth of the first hole 38a and the depth of the second hole 38b are set to be the same (see FIG. 6), but the depth of the second hole 38a. May be set shallower than the depth of the first hole 38b. In this case, the holes 38 a and 38 b can be formed at an appropriate depth according to the stress generated in the shaft portion 48, and deformation of the shaft portion 5 can be suppressed.

  Moreover, in the said embodiment, although the hole 38 (1st hole 38a and 2nd hole 38b) of the intake camshaft 3 is made into the non-through-hole, like the hole 380 shown in FIG. It is good also as a hole which penetrates the axial part 48 to radial direction, and the same change is possible also about the hole 42 of the intake camshaft 3. FIG. Also in this case, the one radial side portion and the other radial side portion of the hole 380 are formed so as to gradually narrow from the radially outer side toward the center. In this case, it is possible to further reduce the weight of the intake camshaft 3 by increasing the volume of the hole as compared with the case where the hole is a non-through hole. Further, by forming a hole portion 380 that penetrates the shaft portion 48, the strength of the shaft portion 48 in the first section (between the sprocket mounting portion 28 and the first cam portion 30) can be increased. 2) (between the two cam portions 31 and the third cam portion 32), the strength of the shaft portion 48 is surely reduced, whereby the strength of the shaft portion 48 in the second section is reduced. It is possible to easily and reliably increase the strength of 48.

  Further, in the above embodiment, the shaft portion 48 of the intake camshaft 3 is formed with a solid central portion in the radial direction. However, as shown in FIG. May be. In the example shown in FIG. 12, the shaft portion 48 extends in the longitudinal direction of the shaft portion 48 in the length direction, and both end portions thereof are the holes 46 of the sprocket mounting portion 28 and the Oldham coupling portion 90. A hollow portion 91 having a circular cross section communicating with the hole 47 is formed. And this hollow part 91 is connected with the said hole part 38a, 38b, 39a, 39b, 41a, 41b, 42a, 42b (refer FIG. 12, 13 (a), (b)).

  In this case, it is possible to further reduce the weight of the intake camshaft 3 by a weight corresponding to the volume of the hollow portion 91 compared to the case where the hollow portion 91 is not formed.

  Here, a method of manufacturing the intake camshaft 3 shown in FIG. 12 will be described.

  The manufacturing method includes a casting step of casting a solid cam shaft (not shown) having a solid shaft portion in which a radial center portion is solid and a plurality of cam portions 30 to 37 are provided on the outer periphery, and A hollow portion forming step of forming the hollow portion 91 by cutting the radial center portion of the solid shaft portion using a rotary cutting tool (for example, a gun drill). These steps will be described below.

(Casting process)
The casting process includes the prototype preparation process, the first sand mold manufacturing process, the second sand mold manufacturing process, the mold manufacturing process, the pouring process, and the camshaft removing process in the method of manufacturing the exhaust camshaft 2. It is comprised from the process similar to each process. In the casting process, the first thinned portions (holes 38a, 38b, 42a, 42b) and the second thinned portions (holes 39a, 39b, 41a, 41b) are formed. Each of the meat portions has a size capable of discharging the facet generated at the time of cutting with the rotary cutting tool to the outside. Specifically, the opening width, the opening area, and the like of each thinning portion are set to sizes that allow the facets to pass.

(Hollow part forming process)
In the hollow portion forming step, using a long rotary cutting tool, for example, from the one end side to the other end side of the solid camshaft, the sprocket mounting portion 28, the solid shaft portion, and the Oldham Cutting is performed so as to penetrate the coupling portion 90 in the axial direction, and the hole portion 46, the hollow portion 91, and the hole portion 47 are formed by the cutting processing. Moreover, in the cutting process, the hollow portion 91 communicates with the first thinned portion (holes 38a, 38b, 42a, 42b) and the second thinned portion (holes 39a, 39b, 41a, 41b). To be done.

  According to the method for manufacturing the intake camshaft 3, the hollow portion 91 is formed by cutting the radial center portion of the solid shaft portion using a rotary cutting tool. It is not necessary to use a core in the casting process, and the hollow portion 91 can be easily formed at a relatively low cost.

  In addition, the facets generated during the cutting process can be quickly discharged to the outside through the first and second thinning parts, and the efficiency of the cutting process can be effectively increased.

  The intake camshaft 3 shown in FIG. 12 can be further modified as follows. In the example shown in FIGS. 14 and 15, the first removal part (holes 38a, 38b, 42a, 42b) and the second removal part (holes 390a, 390b, 410a, 410b) are the first removal parts. Only the meat part (holes 38a, 38b, 42a, 42b) communicates with the hollow part 91, and the second thinned part (holes 390a, 390b, 410a, 410b) communicates with the hollow part 91. Absent. Specifically, the depth of each of the first hole 390a and the second hole 390b constituting the hole 390 and the first hole 410a and the second hole 410b constituting the hole 410 is determined by the hole 38a. , 38b and the hole 42a and the hole 42b are set to a depth which is shallower than the respective depths and does not reach the hollow portion 91.

  In this case, the facets generated when the solid shaft portion is cut can be quickly discharged to the outside through the first wall removal portions (hole portions 38a, 38b, 42a, 42b). The processing efficiency can be increased. In the second section (between the second cam portion 31 and the third cam portion 32 and between the sixth cam portion 35 and the seventh cam portion 36), the second thinning portion (hole portion). 39a, 39b, 41a, 41b) and the hollow portion 91 can be communicated with each other, so that a reduction in the strength of the shaft portion 48 due to the communication can be suppressed, thereby suppressing the deformation of the shaft portion 48 in the second section more effectively. can do.

  Moreover, in each said embodiment, in order to make the intensity | strength of the axial part in a 2nd area larger than the intensity | strength of the axial part in a 1st area, the depth of a 2nd thinning part is mainly set to the depth of a 1st thinning part. Although it is shallower than this, it is not limited to this. For example, the width of the second thinned portion is made smaller than the width of the first thinned portion, or the number of the second thinned portions is smaller than the number of the first thinned portions (of the first thinned portion). The number can be larger than the number of the second thinned portions), or both of them can be employed. As an example in which the number of first thinning portions is larger than the number of second thinning portions, for example, a plurality of spline-like grooves may be formed on the outer peripheral surface of the shaft portion.

  The exhaust camshaft 2 and the intake camshaft 3 according to the above embodiment are applied to an in-line 4-cylinder diesel engine. However, the exhaust camshaft 2 and the intake camshaft 3 may be applied to a diesel engine having another number of cylinders. May be applied.

1 Engine 2 Exhaust Cam Shaft 3 Intake Cam Shaft 5 Exhaust Cam Shaft Shaft 6-13 Exhaust Cam Shaft Cam 6a-13a Exhaust Cam Shaft Nose 16, 17, 19 Exhaust Cam Shaft Hole 16a , 17a, 19a Exhaust camshaft first holes 16b, 17b, 19b Exhaust camshaft second holes 30-37 Intake camshaft cam portions 30a-37a Intake camshaft cam nose portions 38, 39, 41, 42, 390 Intake camshaft hole 38a, 39a, 41a, 42a, 390a Intake camshaft first hole 38b, 39b, 41b, 42b, 390b Intake camshaft second hole 48 Intake camshaft Shaft part 91 Hollow part

Claims (8)

A multi-cylinder engine camshaft comprising a shaft portion extending in a cylinder row direction of an engine having a plurality of cylinders and a plurality of cam portions provided on an outer periphery of the shaft portion,
The cam portion is provided at a position corresponding to the cylinder inside the both end portions of the shaft portion,
The shaft portion includes two adjacent ones of a first thinning portion formed in a first section that is a section between an end portion on at least one side of the shaft portion and the cam portion closest to the end portion. A second slow-thickness portion formed in a second section that is a section between a cam portion corresponding to one of the cylinders and a cam portion corresponding to the other cylinder;
The first thinning portion and the second thinning portion are formed such that the strength of the shaft portion in the second section is greater than the strength of the shaft portion in the first section. Camshaft for multi-cylinder engine. Each of the first thinning portion and the second thinning portion is a non-through hole that opens to the outer peripheral surface of the shaft portion,
2. The camshaft for a multi-cylinder engine according to claim 1, wherein a depth of the second thinning portion is shallower than a depth of the first thinning portion. Each of the first thinning portion and the second thinning portion is a non-through hole that opens in the outer peripheral surface of the shaft portion, and extends in the length direction of the shaft portion,
The first thinned portion has a constant depth in its length direction,
2. The camshaft for a multi-cylinder engine according to claim 1, wherein the second thinning portion has a depth that gradually decreases from the central portion in the length direction toward both ends in the length direction. The first thinned portion is a through-hole penetrating the shaft portion in the radial direction,
2. The multi-cylinder engine camshaft according to claim 1, wherein the second thinning portion is a non-through hole that opens in an outer peripheral surface of the shaft portion. The shaft portion has a hollow portion extending in a length direction of the shaft portion at a radial center portion;
5. The multi-cylinder engine camshaft according to claim 1, wherein each of the first and second thinning portions communicates with the hollow portion. 6. The shaft portion has a hollow portion extending in a length direction of the shaft portion at a radial center portion;
The multiplicity according to any one of claims 2 to 4, wherein, of the first thinning portion and the second thinning portion, only the first thinning portion communicates with the hollow portion. Camshaft for cylinder engine. A method of manufacturing a camshaft for a multi-cylinder engine according to claim 5 or 6,
A casting step of casting a solid camshaft having a solid shaft portion in which a radially central portion is formed solidly and the plurality of cam portions are provided on an outer periphery;
A method of manufacturing a camshaft for a multi-cylinder engine, comprising: a hollow portion forming step of forming the hollow portion by cutting a radial center portion of the solid shaft portion using a rotary cutting tool. .   Of the first thinned portion and the second thinned portion cast in the casting step, the thinned portion that communicates with the hollow portion in the hollow portion forming step is cut by the rotary cutting tool. The method of manufacturing a camshaft for a multi-cylinder engine according to claim 7, wherein the generated facets are large enough to be discharged to the outside.

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