JP6037017B2 - Assembly camshaft - Google Patents

Description

  The present invention relates to an assembly camshaft that rotates in conjunction with a crankshaft of an internal combustion engine.

  An assembly camshaft is a hollow shaft member that is assembled by combining a plurality of cam lobes (cams) at a predetermined position at a predetermined phase by a method such as shrink fitting or caulking. Part of the valve mechanism of the engine). For example, Patent Document 1 discloses an assembly in which a predetermined number of cam lobes are inserted and positioned in a shaft member, and a mandrel is inserted into the shaft member to expand the shaft member and crimp, thereby fastening the cam lobe to the shaft member. A camshaft is described.

  When a cam lobe is fastened and integrated with the shaft member, it is necessary to accurately assemble the position of the cam lobe relative to the shaft member and the phase difference between the plurality of cam lobes. For example, if there is a variation in phase between a pair of intake valves or a pair of exhaust valves used in the same cylinder, the engine control may be affected, and desired output and exhaust performance may not be obtained. However, it is difficult to ensure the assembly accuracy of the cam lobe, and usually finishing is performed after assembly as described in Patent Document 1.

  By the way, in recent years, there has been proposed one in which a roller is rotatably attached to the distal end portion of the cam body, and the roller rotates while contacting the tappet (see, for example, Patent Document 2). In the case of such a cam lobe with a roller, since the roller rolls and moves on the tappet at the cam tip where the contact stress between the cam lobe and the tappet is highest, the friction can be effectively reduced.

JP 2004-190715 A JP 2011-80372 A

  However, in the case of the cam lobe with a roller as in the above-mentioned Patent Document 2, after the roller is assembled to the cam body, the cam lobe with the roller is assembled to the shaft member. Is difficult. On the other hand, if it is attempted to assemble a plurality of cam lobes with respect to the shaft member at a predetermined position with a predetermined phase with high accuracy in order to omit the finishing process, the manufacturing cost may be increased. Such a problem is not limited to a cam lobe with a roller, but also applies to a general assembly camshaft. That is, in order to omit finishing after assembly, it is necessary to assemble a plurality of cam lobes with respect to the shaft member in advance with high accuracy.

  Also, when the cam lobe is fixed to the shaft member by shrink fitting, the larger the tightening allowance, the greater the tightening force of the cam lobe against the shaft member. Is done. In particular, in the case of a cam lobe with a roller, if it is heated to a temperature higher than the tempering temperature of the roller, the roller is annealed and the hardness of the roller is lowered. It is.

  One of the purposes of the present invention was devised in view of the above-mentioned problems, and by providing an assembly camshaft that can ensure assembly accuracy while reducing costs and can suppress a decrease in hardness. is there. The present invention is not limited to this purpose, and is a function and effect derived from each configuration shown in the embodiments for carrying out the invention described later, and other effects of the present invention are to obtain a function and effect that cannot be obtained by conventional techniques. Can be positioned.

An assembly camshaft disclosed herein includes a shaft member that rotates in conjunction with a crankshaft of an internal combustion engine, a pair of cam lobes that drive a pair of intake valves or a pair of exhaust valves used in the same cylinder of the internal combustion engine, and An assembly camshaft comprising a coupling cam lobe having a mounting hole through which the shaft member is inserted, wherein a journal portion provided between the pair of cam lobes is integrally formed, and each of the pair of cam lobes includes a base circular portion and A cam lobe with a roller having a base cam formed of a valve lift portion and a roller provided at a tip portion of the valve lift portion and rotatable with respect to the base cam, and an outer peripheral surface of the shaft member and an inner peripheral surface of the mounting hole A key extending in the axial direction of the shaft member is inserted at least in the journal portion. It is.
The shaft member has a shaft-side key groove formed along the axial direction of the shaft member and having a length equivalent to the total axial length of the coupling cam lobe, and the coupling cam lobe is formed in the mounting hole. A circumferential surface has a lobe-side key groove formed over the entire axial length of the coupling cam lobe, and the key has a length equivalent to the axial total length of the coupling cam lobe, and the shaft-side key groove And is fitted into the lobe-side keyway. Furthermore, the depth of the lobe side keyway is deeper than the depth of the shaft side keyway .

  It is preferable that the shaft member is pivotally supported by being sandwiched between a bearing portion and a cam cap provided at an upper portion of the cylinder head in the journal portion. The coupling cam lobe is assembled by being externally fitted to the shaft member, and has a key groove (lobe side key groove) provided in the base circle portion and formed along the axial direction on the inner peripheral surface of the mounting hole. Is preferred. It is preferable that the key protrudes outwardly on the outer peripheral surface of the shaft member and is fitted into the key groove at least in the journal portion.

It is preferable that the key is provided between the outer peripheral surface of the shaft member and the inner peripheral surface of the mounting hole at a position facing the roller across the axis of the shaft member.
The key groove is preferably formed on a surface opposite to the valve lift portion of the inner peripheral surface of the mounting hole, and on a straight line connecting the shaft center of the mounting hole and the shaft center of the roller. It is more preferable that the valve lift part is recessed in a straight line along the axial direction on the surface far from the tip part.

The depth of the pre SL lobe side keyway, the key is the is preferably set larger than the amount projecting from the outer circumferential surface of the shaft member in a state fitted to the shaft member.
The coupling cam lobe preferably has a lobe-side key groove formed along the axial direction of the coupling cam lobe on the inner peripheral surface of the mounting hole. In this case, it is preferable that the key is integrally formed with the shaft member and fitted into the lobe-side key groove.

  According to the disclosed assembly camshaft, the variation in the same cylinder can be minimized by the coupling cam lobe, and the assembly cam lobe is assembled using the key, so that the assembly accuracy can be ensured. Thereby, the finishing process after an assembly is not required and cost can be reduced. Further, since the key bears the rotational torque of the combined cam lobe, the tightening margin of the combined cam lobe can be reduced. Therefore, the temperature of the coupling cam lobe at the time of shrink fitting can be suppressed to a relatively low temperature, thereby preventing the coupling cam lobe from being annealed and suppressing a decrease in hardness.

  Further, since the pair of cam lobes are cam lobes with rollers, friction can be reduced compared to cam lobes without rollers, and fuel efficiency can be improved. Furthermore, since the roller itself rotates on the tappet, the cam driving torque in the low rotation range can be reduced.

It is a perspective view of the one end side of the assembly cam shaft which concerns on one Embodiment. It is a longitudinal cross-sectional view in alignment with the axial direction of the part to which the coupling cam lobe of the assembly cam shaft which concerns on one Embodiment was fastened. It is sectional drawing (AA arrow sectional drawing of FIG. 2) of the direction orthogonal to the axial direction of the coupling cam lobe of the assembly cam shaft which concerns on one Embodiment. It is sectional drawing (BB arrow sectional drawing of FIG. 2) of the direction orthogonal to the axial direction of the journal part of the assembly cam shaft which concerns on one Embodiment.

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

[1. Assembly camshaft structure]
The structure of the assembly cam shaft according to the present embodiment will be described with reference to FIGS. FIG. 1 is a perspective view of one end side of the assembly camshaft 10, and FIG. 2 is a longitudinal sectional view along the axial direction of the assembly camshaft 10 shown in FIG. Indicates the state that has been performed. 3 is a cross-sectional view taken along the line AA in FIG. 2, and FIG. 4 is a cross-sectional view taken along the line BB in FIG.

  As shown in FIGS. 1 and 2, the assembly camshaft 10 is a hollow pipe-shaped shaft member 20 that is integrally assembled with a plurality of coupling cam lobes 30 that are externally fitted, and is an engine (not shown). Part of the valve mechanism. Although only one coupling cam lobe 30 is illustrated in FIG. 1, a plurality of coupling cam lobes 30 are provided in the axial direction of the shaft member 20 according to the number of cylinders.

  The shaft member 20 is pivotally supported by an upper end edge (not shown) of an end wall that is erected at both ends in the axial direction of the crankshaft of the cylinder head. A cam sprocket (not shown) is coupled to one end 20 a of the shaft member 20. The rotation of the crankshaft is transmitted to the shaft member 20 via a timing chain and a timing belt (both not shown) spanned between a crank sprocket coupled to one end of the crankshaft of the engine and a cam sprocket. As a result, the shaft member 20 rotates in unison with the coupling cam lobe 30 in conjunction with the crankshaft. Engine oil (lubricating oil) pumped by an oil pump (not shown) flows through the hollow interior of the shaft member 20.

  The coupling cam lobe 30 is formed by integrally forming a pair of cam lobes 30A and 30A and a cylindrical journal portion 30B provided between the pair of cam lobes 30A and 30A. The term “integral molding” as used herein means making a shape as an integral one. That is, the combined cam lobe 30 is not formed by combining two cam lobes of the same shape that are separately formed via the journal part, but has a shape having a pair of cam lobes 30A, 30A and a journal part 30B from the beginning. Molded.

The pair of cam lobes 30A, 30A drives a pair of intake valves or a pair of exhaust valves (hereinafter also simply referred to as valves) used in the same cylinder of the engine. The pair of cam lobes 30A and 30A have the same shape and are formed so that the phase difference is zero or substantially zero.
As shown in FIGS. 2 and 4, the coupling cam lobe 30 is sandwiched between a bearing portion 40 and a cam cap 41 provided at an upper portion of the cylinder head at a substantially axial center of the journal portion 30 </ b> B. As a result, the assembly camshaft 10 is pivotally supported by the bearing portion 40 and the cam cap 41.

  The cam cap 41 is fastened by a bolt 42 with the assembly cam shaft 10 sandwiched between the upper surface of the bearing portion 40. A small gap (not shown) is provided on the sliding surface between the cam cap 41 and the bearing portion 40 and the assembly camshaft 10, and engine oil for lubrication is supplied to the gap from an oil supply passage (not shown). Is done.

  Next, the structure of the coupling cam lobe 30 will be described. As shown in FIG. 3, the cam lobe 30 </ b> A is a cam lobe with a roller including a plate-shaped base cam 31 that is a cam body and a cylindrical roller 32 attached to the base cam 31. The cam lobe 30A drives a tappet (a driven part, also called a valve lifter, not shown) connected to the base end of the valve in each cylinder of the engine to open and close the valve.

The base cam 31 has a base circle portion 31a and a valve lift portion 31b, and the outer peripheral surface (cam surface) is continuous over the entire circumferential direction. A boundary line between the base circle portion 31a and the valve lift portion 31b is indicated by a two-dot chain line in FIG.
The base circular portion 31a is a circular portion of the base cam 31, and a circular hole portion 31h (hereinafter referred to as a cam shaft hole portion 31h) through which the shaft member 20 is inserted is drilled in the center. In other words, the base circle portion 31a corresponds to a portion where the distance from the axis S of the camshaft hole portion 31h is constant.

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

  A pair of opposing yoke portions 31y and 31y are formed on both sides in the width direction of the notch portion 31n formed in the base cam 31. In the pair of yoke portions 31y, 31y, holes 31m, 31m penetrating in the width direction are provided on a straight line. The hole 31m is formed such that its axis T is parallel to the axis S of the camshaft hole 31h formed in the base circle 31a. A roller shaft 33 for attaching the roller 32 to the base cam 31 is inserted through the holes 31m and 31m. Hereinafter, the hole 31m is referred to as a roller shaft hole 31m. A claw portion (not shown) projecting to the outer diameter side is provided on the peripheral edge of the roller shaft 33, and this claw portion is struck against the end surface of the yoke portion 31y of the base cam 31 to be caulked. A roller shaft 33 is fixed to 31.

  As shown in FIGS. 2 and 3, the roller 32 is rotatably assembled to the base cam 31 via a roller shaft 33 inserted through the center thereof. The inner peripheral surface 32 h of the roller 32 functions as a sliding bearing for the roller shaft 33. The roller 32 is attached such that a part of its outer peripheral surface protrudes outside the outer peripheral surface of the tip end portion 31c of the valve lift portion 31b. The amount of protrusion of the roller 32 from the tip portion 31 c is determined by the shape of the base cam 31 and the outer diameter of the roller 32.

  In the cam lobe 30A with a roller, when the assembly cam shaft 10 rotates, first, the valve lift portion 31b of the base cam 31 comes into contact with the tappet and presses the tappet. The valve lift 31b pushes down the tappet as the assembly camshaft 10 rotates. Then, at a certain rotation angle, the position of contact with the tappet moves from the valve lift 31b to the roller 32, and this time the roller 32 presses the tappet. The roller 32 moves while rolling on the tappet to push down the tappet, and finally the valve lift amount is maximized.

  Thereafter, the valve lift amount decreases, the contact position with the tappet changes from the roller 32 to the valve lift portion 31b, and the valve lift portion 31b presses the tappet again. When the valve lift part 31b moves away from the tappet and the base circle part 31a faces the tappet, the valve lift amount becomes zero. Thus, the cam lobe 30A with a roller can reduce friction compared to a cam lobe without the roller 32 because the roller 32 moves while rolling on the tappet and presses the tappet. Further, since the roller 32 itself rotates on the tappet, an excellent effect can be obtained, such as reduction of cam driving torque in a low rotation range.

  Here, the pair of cam lobes 30A and 30A of the coupling cam lobe 30 have the same shape as described above, and the phase difference is formed to be zero or substantially zero. That is, the base cams 31 and 31 of the pair of cam lobes 30A and 30A are provided with valve lift portions 31b and 31b at the same position (angle) in the circumferential direction so that the same rollers 32 and 32 have the same protruding amount. 31 and 31. Therefore, the variation between a pair of intake valves or a pair of exhaust valves used in the same cylinder is minimized.

  On the other hand, as shown in FIG. 2, the journal portion 30B is a cylindrical portion formed integrally with the pair of cam lobes 30A and 30A so as to connect the opposing end surfaces of the base circular portions 31a of the pair of cam lobes 30A and 30A. It is. The journal portion 30B is a portion that is supported by the bearing portion 40 and the cam cap 41 as described above.

  The coupling cam lobe 30 has a mounting hole 30h (that is, the cam shaft hole portions 31h and 31h and the inner peripheral surface of the journal portion 30B) through which the shaft member 20 is inserted. The diameter (inner diameter) of the mounting hole 30 h is smaller than the outer diameter of the shaft member 20. That is, a fastening margin is provided between the coupling cam lobe 30 and the shaft member 20, and the coupling cam lobe 30 is fitted into the shaft member 20 by shrink fitting. In other words, the coupling cam lobe 30 is heated to a predetermined temperature at the time of assembly, and the attachment hole 30h expands and is fitted onto the shaft member 20 when it is wider than the outer diameter of the shaft member 20.

  In addition, the predetermined temperature at this time is set to a temperature lower than a tempering temperature of a roller 32 to be described later, thereby preventing the roller 32 from being annealed during assembly. In other words, the tightening allowance is set to such a size that the coupling cam lobe 30 can be assembled to the shaft member 20 even when the temperature during shrink fitting is set to a temperature lower than the tempering temperature of the roller 32.

  As shown in FIGS. 2 to 4, an axially extending key 34 is fitted between the coupling cam lobe 30 and the shaft member 20. The key 34 is a member for transmitting the rotational motion and rotational torque of the shaft member 20 to the coupling cam lobe 30 and bearing the rotational torque of the coupling cam lobe 30 and is formed in an elongated rectangular parallelepiped shape. Here, the key 34 is formed to have the same length as the axial length of the coupling cam lobe 30.

  Since the rotational torque of the coupling cam lobe 30 is held by the key 34 (that is, the key 34 receives the rotational torque), the coupling cam lobe 30 can be connected to the shaft even if the tightening force of the coupling cam lobe 30 on the shaft member 20 is not increased so much. The member 20 is not shifted in the circumferential direction. For this reason, it is possible to set a small fastening margin when the coupling cam lobe 30 is fixed to the shaft member 20 by shrink fitting. In other words, the coupling cam lobe 30 can be reliably fixed to the shaft member 20 by providing the key 34 even with a small allowance.

  A key groove 20k into which the key 34 is press-fitted (hereinafter referred to as a shaft side key groove 20k) is formed on the outer peripheral surface of the shaft member 20. The shaft-side keyway 20k is located in the axial direction of the shaft member 20 at a position (a position shifted by 180 degrees) on the opposite side of the outer peripheral surface of the shaft member 20 from the surface located on the cam top 31c side of the coupling cam lobe 30. It is recessed along a straight line. The shaft side keyway 20 k is formed in a shape corresponding to the shape of the key 34. For example, it is formed to have a length and width equivalent to the length and width of the key 34, and is formed to a depth that is approximately half the height of the key 34.

  On the other hand, a key groove 30k (hereinafter referred to as a lobe-side key groove 30k) into which the key 34 is fitted is formed in the mounting hole 30h of the coupling cam lobe 30 on the inner peripheral surface opposite to the valve lift portion 31b. Here, the lobe side keyway 30k is a straight line connecting the axis S of the camshaft hole 31h and the axis T of the roller shaft hole 31m on the inner peripheral surface of the mounting hole 30h. On the surface far from the top 31c, it is recessed in a straight line along the axial direction of the coupling cam lobe 30. The lobe-side key groove 30k is provided at a position overlapping the shaft-side key groove 20k when the coupling cam lobe 30 is assembled to the shaft member 20.

  The lobe side keyway 30k extends from the end surface of the one cam lobe 30A opposite to the journal portion 30B to the end surface of the other cam lobe 30A opposite to the journal portion 30B. That is, the lobe-side key groove 30k is formed so as to penetrate the coupling cam lobe 30 in the axial direction (over the entire length in the axial direction). Further, the width of the lobe-side key groove 30k is formed to be equal to the width of the key 34, and the depth of the lobe-side key groove 30k is formed to be equal to or slightly larger than the protruding amount of the key 34 from the outer peripheral surface of the shaft member 20. ing.

  In other words, the depth of the lobe-side keyway 30k is set larger than the amount protruding from the outer peripheral surface of the shaft member 20 in a state where the key 34 is fitted into the shaft member 20. Accordingly, when the coupling cam lobe 30 is fitted into the shaft member 20, a gap is formed between the key 34 and the lobe-side key groove 30k, so that the deformation of the cam surface of the coupling cam lobe 30 when the key is fitted is avoided. The

  The key 34 is press-fitted into the shaft-side key groove 20 k and protrudes outward from the outer peripheral surface of the shaft member 20. When the coupling cam lobe 30 is assembled, the coupling cam lobe 30 is fitted from the axial direction of the shaft member 20 such that the lobe-side key groove 30k is fitted to the protruding key 34. Here, the key 34 is fitted into the lobe-side key groove 30 k over the entire axial length of the coupling cam lobe 30. The coupling cam lobe 30 is an interference fit with respect to the shaft member 20, while the key 34 is an intermediate fit with respect to the lobe side key groove 30k.

[2. Production method]
Next, an example of a method for manufacturing the assembly camshaft 10 according to the present embodiment will be described. The assembly camshaft 10 is fitted into the shaft member 20 in a state where the rollers 32, 32 are assembled to the base cams 31, 31 of the pair of cam lobes 30A, 30A, respectively, and the combined cam lobe 30 is completed. A plurality of coupled cam lobes 30 are manufactured according to the number of cylinders of the engine. Details will be described below.

  In this manufacturing method, a protrusion amount setting process, a selection process, and a surface treatment process for the roller 32, and a roughing process, a finishing process, a grinding process, and a surface for the base cams 31, 31 and the journal portion 30B of the pair of cam lobes 30A, 30A are provided. Processing steps. Furthermore, it has an assembling process for assembling the rollers 32, 32 to the base cams 31, 31, respectively, and an assembling process for fitting the coupling cam lobe 30 into the shaft member 20 for assembly.

  First, each process for the roller 32 will be described. First, the protrusion amount of the roller 32 from the outer peripheral surface of the base cam 31 is set (setting step), and the rollers 32 having the outer diameters corresponding to the protrusion amount are prepared for the number of cam lobes 30A (selection step). Next, before the roller 32 and the roller shaft 33 are assembled, a surface hardening process is performed on the roller 32 and the roller shaft 33, respectively. Here, general induction hardening and tempering are performed as the surface hardening treatment. Thereby, a relatively thick hardened layer is formed on each surface of the roller 32 and the roller shaft 33 (surface treatment process).

  Next, each process with respect to the base cams 31 and 31 and the journal part 30B of a pair of cam lobe 30A, 30A is demonstrated. As a pre-stage of each process of the base cams 31 and 31 and the journal part 30B, the parts that form the basis of the base cams 31 and 31 and the journal part 30B are integrally formed by forging. Next, the forged product is roughly processed to form a portion that becomes the notch 31n, and a portion that becomes the mounting hole 30h of the shaft member 20 and the roller shaft hole 31m is drilled.

  Further, the outer peripheral surface of the forged product is rough processed to form a shape close to the final cam profile of the base cam 31 (rough processing step). The shape close to the final cam profile here refers to a shape that becomes a desired cam profile only by finishing (that is, grinding) the outer peripheral surface. The rough machining step is omitted, and at the stage of forming the forged product, the notch 31n, the mounting hole 30h, and the roller shaft hole 31m are formed, and the outer peripheral surface becomes the final cam profile of the base cam 31. You may form in a near shape.

  The forged product after the roughing process is formed into the final shape of the base cam 31 in the finishing process. The finishing process may be performed using a device capable of performing numerical control, such as an NC lathe, or may be performed manually. For the forged product after the roughing process, first, the mounting hole 30h of the shaft member 20 is finished, and then the roller shaft hole 31m is positioned and finished with reference to the mounting hole 30h.

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

  The outer peripheral surface of the forged product in which the mounting hole 30h and the roller shaft hole 31m are formed is subsequently ground (grinding step). For example, the mounting hole 30h and the roller shaft hole 31m are each fixed by a chuck to support the forged product, and forging is performed for a predetermined feed amount (cutting amount) while contacting a grinding wheel rotating at high speed on the outer peripheral surface. Proceed to the product side and grind the outer peripheral surface of the forged product. Thereby, the base cam 31 having a desired cam profile is completed.

  The completed pair of base cams 31 and 31 and the journal portion 30B are subjected to, for example, general gas nitriding treatment or quenching and tempering treatment in the surface treatment process. Note that the surface treatment of the journal portion 30B may be omitted.

  The rollers 32 are assembled to the pair of base cams 31, 31 that have undergone the above-described processes via the roller shaft 33 in an assembling process. Specifically, the roller 32 has a central through hole overlapped with the roller shaft hole portions 31m and 31m formed in the yoke portions 31y and 31y of the base cam 31, and the gap between the two yoke portions 31y and 31y is substantially omitted. It arrange | positions in the center part of the width direction of the notch part 31n so that it may become equivalent. In this state, the roller shaft 33 is inserted into the roller shaft hole 31m of the one yoke portion 31y, subsequently inserted into the through hole of the roller 32, and further into the roller shaft hole 31m of the other yoke portion 31y. It is inserted. And it fixes to the base cam 31 by expanding the both ends of the roller shaft 33 by caulking.

  Thus, the coupling cam lobe 30 is manufactured by attaching the rollers 32 and 32 to the base cams 31 and 31 of the pair of cam lobes 30A and 30A, respectively. Any of the steps for the roller 32 and the steps for the base cams 31 and 31 and the journal portion 30B may be performed first or simultaneously.

  In the assembly process, first, the key 34 is press-fitted into the shaft-side key groove 20 k of the shaft member 20. Then, the coupling cam lobe 30 heated to a predetermined temperature is inserted into the shaft member 20 from the axial direction so that the lobe-side key groove 30k is fitted to the key 34 protruding from the outer peripheral surface of the shaft member 20. Thus, when the temperature of the coupling cam lobe 30 is lowered, the assembly camshaft 10 in which the coupling cam lobe 30 is firmly fixed to the shaft member 20 is completed.

[3. effect]
Therefore, according to the assembly camshaft 10 according to the present embodiment, the variation in the same cylinder can be minimized by integrally forming the coupling cam lobe 30 and the coupling cam lobe 30 is assembled using the key 34. Can be secured. Thereby, since the finishing process after an assembly process can be omitted, the manufacturing cost can be reduced. In addition, since variations within the same cylinder can be minimized, the accuracy of engine control can be increased, and as a result, output and exhaust performance can be improved.

  Further, since the key 34 is used when the coupling cam lobe 30 is fitted on the shaft member 20, the rotational torque of the coupling cam lobe 30 can be borne by the key 34. That is, since the rotational torque received by the inner peripheral surface of the coupling cam lobe 30 is reduced, it is possible to reduce the tightening margin when the coupling cam lobe 30 is externally fitted to the shaft member 20. For example, when assembling the coupling cam lobe 30 to the shaft member 20, the tightening allowance can be set to such a small extent that the temperature during shrink fitting can be made lower than the tempering temperature of the coupling cam lobe 30. Thereby, it can prevent that the joint cam lobe 30 is annealed, and can suppress a hardness fall. In other words, since the tightening margin can be reduced by providing the key 34, the heating temperature at the time of shrink fitting of the coupling cam lobe 30 can be lowered, and the decrease in hardness can be suppressed.

  Furthermore, since the key 34 is fitted into the lobe-side key groove 30k in the journal portion 30B held between the bearing portion 40 and the cam cap 41, the bearing portion 40 and the cam cap can be used even if a slight deformation occurs in the journal portion 30B. The deformation can be absorbed by the gap set on the sliding surface between 41 and the journal portion 30B.

  Further, in the assembly camshaft 10, the pair of cam lobes 30A and 30A are cam lobes with rollers, so that friction can be reduced and fuel consumption can be improved compared to cam lobes without the rollers 32. . Further, since the roller 32 itself rotates on the tappet, the cam driving torque in the low rotation range can be reduced. In particular, in this embodiment, since the pair of cam lobes 30A and 30A have the same shape and the phase difference is formed to be zero or substantially zero, the variation between the pair of intake valves or the pair of exhaust valves used in the same cylinder is minimized. Can be

  In the assembly camshaft 10, the lobe-side key groove 30k is formed on the surface of the inner peripheral surface of the mounting hole 30h opposite to the valve lift portion 31b. In other words, the key 34 is provided between the outer peripheral surface of the shaft member 20 and the inner peripheral surface of the mounting hole 30h of the coupling cam lobe 30 at a position facing the roller 32 with the axis of the shaft member 20 interposed therebetween. For this reason, it is possible to prevent the lobe side keyway 30k and the key 34 from affecting the driving of the valve by the cam lobe 30A. That is, since the valve lift portion 31b and the roller 32 make contact with the tappet in the cam lobe 30A, the key 34 is provided at a position facing the roller 32 with the shaft center of the shaft member 20 interposed therebetween, so that a slight deformation is caused. Even if this occurs, the valve lift 31b and the roller 32 can drive the valve without being affected by deformation.

  Further, since the key 34 is fitted in the lobe-side key groove 30k over the entire axial length of the coupling cam lobe 30, it is possible to bear the maximum rotational torque of the coupling cam lobe 30. In other words, since the rotational torque (rotational force) that can be held by the key 34 can be maximized, the tightening force between the inner peripheral surface of the mounting hole 30h and the outer peripheral surface of the shaft member 20 can be reduced. The tightening allowance can be further reduced. Further, since the key 34 is fitted into the entire lobe side key groove 30k, no space is formed in the lobe side key groove 30k, and stress concentration can be prevented. Thereby, high intensity | strength is securable in the assembly cam shaft 10 whole.

  Further, the depth of the lobe-side key groove 30k is set larger than the amount protruding from the outer peripheral surface of the shaft member 20 in a state where the key 34 is fitted in the shaft member 20. Thus, when the coupling cam lobe 30 is fitted into the shaft member 20, a gap is formed between the key 34 and the lobe-side key groove 30k, so that deformation of the cam surface of the coupling cam lobe 30 when the key is fitted is avoided. be able to.

[4. Others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
In the above embodiment, the key 34 is fitted into the lobe-side key groove 30k over the entire axial length of the coupling cam lobe 30, but the key 34 may be formed shorter, and at least the lobe-side key in the journal portion 30B. It only has to be fitted in the groove 30k.

  The lobe-side keyway 30k is formed so as to penetrate the coupling cam lobe 30 in the axial direction, but may have any shape as long as the coupling cam lobe 30 can be fitted into the shaft member 20 from the axial direction. For example, when the key 34 is provided only in the journal portion 30B, the lobe-side key groove 30k may be formed in one cam lobe 30A and the journal portion 30B. Further, the position of the lobe-side key groove 30k is not limited to the above embodiment, and may be any inner peripheral surface of the mounting hole 30h, and is preferably separated from the valve lift portion 31b.

  In the above embodiment, the shaft member 20 is also provided with the shaft-side key groove 20k, and the key 34 is press-fitted into the key groove 20k. However, the shaft member 20 and the key are integrally formed, and the shaft member 20 A key may protrude from the outer peripheral surface. Thereby, the number of parts can be reduced. Further, the strength of the shaft member 20 can be kept higher than when the shaft-side keyway 20k is provided in the shaft member 20.

  Further, in the above embodiment, the case where the mounting hole 30h is finished after rough machining and the roller shaft hole 31m is finished after that is illustrated, but the order of finishing may be reversed. In other words, the roller shaft hole 31m is accurately positioned using a jig so that the roller shaft hole 31m is finished first, and the mounting hole 30h is finished using the roller shaft hole 31m as a reference. May be.

Further, the surface hardening process of the roller 32 and the roller shaft 33 is not limited to the induction hardening and tempering process, but may be other surface hardening process. Moreover, as long as high surface hardness can be given, surface hardening processing other than surface hardening processing may be given to the roller 32 and the roller shaft 33. FIG.
Moreover, although the parts used as the base cam 31 and the journal part 30B are demonstrated as a forged product, the parts used as the base cam 31 and the journal part 30B are not limited to the parts formed by forging, but are parts formed by other methods. There may be.

  In the above embodiment, the cam lobe 30 </ b> A in which the roller 32 rotates with respect to the roller shaft 33 fixed to the base cam 31 has been described. However, the roller 32 and the roller shaft 33 are fixed, and the roller shaft 33 is fixed to the base cam 31. It may be a cam lobe that rotates. Further, the roller 32 may be rotatable with respect to the roller shaft 33, and the roller shaft 33 may also be rotatable with respect to the base cam 31.

The method for fixing the roller shaft 33 is not limited to caulking, and the roller shaft 33 may be fixed to the base cam 31 by press-fitting. The method of fixing the coupling cam lobe 30 is not limited to shrink fitting, and may be fixed by press fitting.
The shaft member 20 may be a solid pipe shape or may not be provided with an oil flow path or the like.

10 Assembly cam shaft 20 Shaft member 20k Shaft side key groove 30 Coupling cam lobe 30A Cam lobe 30B Journal part 30h Mounting hole 30k Robe side key groove
31 Base cam 31a Base circle part 31b Valve lift part 31h Cam shaft hole 31m Roller shaft hole 32 Roller 33 Roller shaft 34 Key 40 Bearing part 41 Cam cap

Claims (4)

A shaft member that rotates in conjunction with the crankshaft of the internal combustion engine;
Said pair of driving the pair of intake valves or a pair of exhaust valve used in the same cylinder of an internal combustion engine cam lobe, and, a journal portion provided between the pair of cam lobes are integrally molded, Ru said shaft member is inserted An assembly camshaft comprising a coupling cam lobe having a mounting hole;
Each of the pair of cam lobes is a cam lobe with a roller having a base cam composed of a base circle portion and a valve lift portion, and a roller provided at a tip portion of the valve lift portion and rotatable with respect to the base cam.
A key extending in the axial direction of the shaft member at least in the journal portion is fitted between the outer peripheral surface of the shaft member and the inner peripheral surface of the mounting hole ,
The shaft member has a shaft side keyway formed along the axial direction of the shaft member and having a length equivalent to the total axial length of the coupling cam lobe,
The coupling cam lobe has a lobe-side key groove formed on the inner peripheral surface of the mounting hole over the entire axial length of the coupling cam lobe,
The key has a length equivalent to the total axial length of the coupling cam lobe, and is fitted into the shaft side key groove and the lobe side key groove,
The assembly camshaft characterized in that a depth of the lobe side keyway is deeper than a depth of the shaft side keyway . The key is provided between the outer peripheral surface of the shaft member and the inner peripheral surface of the mounting hole at a position facing the roller across the axis of the shaft member. Assembly camshaft as described . The depth of the lobe side keyway, characterized in that the key is set larger than the amount projecting from the outer peripheral surface of the shaft member in a state fitted to the shaft member, according to claim 1 or 2 Assembly camshaft as described . The coupling cam lobe has a lobe-side key groove formed along the axial direction of the coupling cam lobe on the inner peripheral surface of the mounting hole,
The assembly camshaft according to any one of claims 1 to 3, wherein the key is integrally formed with the shaft member and fitted into the lobe-side key groove .

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