internal combustion engine

Abstract

To suppress the wear of a crank journal caused by a deformation of a crankshaft while maintaining the lubrication performance of a bearing portion of the crank journal.SOLUTION: An engine 1 comprises an engine main body 10 having an intake valve 25A and an exhaust valve 25B for opening and closing a suction / exhaustion opening, camshafts 21A, 21B having cam noses 231 for pressing the intake valve 25A and the exhaust valve 25B downward, and a bearing member 30 for pivoting the camshafts via a lubricant. The camshafts include a cam journal 24 arranged in a region approximate to the cam noses 231, and pivoted by the bearing member 30, and a hollow hole 22H extending in an axial direction of the camshafts. When setting a thickness of a side at which the cam noses 231 protrude as X1, and setting a thickness of a side opposite to the cam noses 231 in a circumferential direction as X2 when viewing a thickness of the periphery of the hollow hole 22H in the region of the cam journal 24 in a cross sectional view which is orthogonal to the axial direction, the cam noses include portions which satisfy a relationship of X1>X2.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an internal combustion engine having a structure in which a cam journal of a camshaft is journaled by a bearing member via lubricating oil. [Background technology]

[0002] An internal combustion engine is equipped with a camshaft that operates intake valves that open and close intake ports of cylinders and exhaust valves that open and close exhaust ports. The camshaft has cam lobes that press down the stem ends of the intake valves or exhaust valves, and a cam journal that is journaled on a bearing member of the cylinder head. The cam journal is journaled on a plain bearing via lubricating oil. Patent Document 1 discloses an internal combustion engine in which the crank journal, which is the journal-supported part of the crankshaft, is provided with multiple recesses on its outer surface to enhance its ability to retain lubricating oil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-25653 Summary of the Invention [Problem to be solved by the invention]

[0004] Improving the fuel efficiency of internal combustion engines requires reducing various mechanical losses. Regarding the above-mentioned lubricating oil, it is desirable to use low-viscosity oil from the perspective of suppressing friction loss on the sliding surfaces. However, using low-viscosity oil can cause poor lubrication at the bearing portion of the cam journal, raising concerns about wear on the cam journal. Furthermore, when the cam lobe presses the intake or exhaust valve, a load is applied to the camshaft in a direction intersecting the axial direction, causing deformation forces. Therefore, wear due to deformation of the cam journal itself can also be a problem.

[0005] An object of the present invention is to provide an internal combustion engine that can suppress wear of cam journals that accompanies deformation of a camshaft. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided an internal combustion engine comprising: an engine body including a cylinder having an intake and exhaust opening; and a valve body that opens and closes the opening; a camshaft having a cam lobe that presses down on the valve body to open the opening; and a bearing member that supports the camshaft via lubricating oil, wherein the camshaft includes a cam journal supported by the bearing member and a hollow hole extending in the axial direction of the camshaft; and when viewing a wall thickness around the hollow hole in the region of the cam journal in a cross section perpendicular to the axial direction, the wall thickness on the side from which the cam lobe protrudes is defined as X1 and the wall thickness on the side circumferentially opposite the cam lobe is defined as X2, X1>X2 The present invention is characterized in that the part satisfies the relationship:

[0007] When the cam lobe presses the valve disc, a pressing load from the valve disc acts on the camshaft. The pressing load is a load in a direction intersecting the axial direction of the camshaft, and is a load that deforms the cam lobe in the direction opposite to the pressing direction of the valve disc. The camshaft includes a cam journal that supports the camshaft. Therefore, the deformation force based on the pressing load acts in a direction that moves the circumferential surface of the cam journal closer to the bearing member. In other words, a state is created in which the circumferential surface of the cam journal is likely to come into contact with the bearing member at a position circumferentially opposite the cam lobe.

[0008] In the above-described internal combustion engine, the thickness of the periphery of the hollow hole in the cam journal region is set to be thinner at the side circumferentially facing the cam lobe (X2) than at the side where the cam lobe protrudes (X1). This means that the cam journal region is more susceptible to deformation on the side facing the cam lobe than on the side where the cam lobe protrudes. Therefore, even if the camshaft deforms due to the pressing load of the valve disc and the circumferential surface of the cam journal contacts the bearing member, the cam journal can deform at the thin portion of thickness X2. This deformation can dissipate the force of the cam journal colliding with the bearing member. In other words, it can reduce the contact force between the cam journal and the bearing member. Therefore, wear of the cam journal due to deformation of the camshaft can be suppressed. Therefore, even when a low-viscosity oil is used as a lubricant, it is possible to maintain lubrication at the bearing portion of the cam journal and prevent wear of the cam journal.

[0009] In the above-described internal combustion engine, the hollow hole has a circular shape in a cross section perpendicular to the axial direction, and the axis of the hollow hole is offset from the axis of the camshaft to a side circumferentially opposite the cam lobe, whereby the relationship X1>X2 can be satisfied.

[0010] In this internal combustion engine, a camshaft that satisfies the X1 > X2 relationship can be obtained simply by eccentrically positioning the circular cross-section hollow hole relative to the camshaft axis. For example, if a camshaft has a rectangular cross-section hollow hole, it is difficult to adjust the wall thickness around the hole. However, a circular cross-section hollow hole satisfies the X1 > X2 relationship and makes it easier to deform the cam journal as intended at the location of thickness X2.

[0011] In the above internal combustion engine, it is desirable that the portions that satisfy the relationship X1>X2 are disposed at least at both ends in the axial direction of the cam journal.

[0012] When a pressing load from the valve disc is applied to the camshaft, both axial ends of the cam journal deform most significantly toward the bearing member at positions circumferentially opposite the cam lobes, and the amount of deformation decreases toward the axial center. The internal combustion engine described above can provide a thickness distribution that matches this type of deformation of the cam journal. This means that both axial ends of the cam journal are more likely to deform, effectively reducing the contact force between the cam journal and the bearing member.

[0013] In the above internal combustion engine, it is desirable that the portion that satisfies the relationship X1>X2 be disposed over the entire axial length of the cam journal.

[0014] According to this internal combustion engine, the cam journal can be made to be easily deformable over the entire axial length on the side circumferentially opposing the cam lobe.

[0015] In the above internal combustion engine, each cylinder may be provided with two intake and two exhaust openings, and as the valve bodies, an intake camshaft and an exhaust camshaft each may be provided with a first valve body and a second valve body that respectively open and close the two openings, the camshafts may include a first cam lobe and a second cam lobe that press down the first valve body and the second valve body, respectively, and the cam journal may be arranged at a position sandwiched between the first cam lobe and the second cam lobe.

[0016] In this internal combustion engine, the cam journal is positioned between the first cam lobe and the second cam lobe. Therefore, when a downward load from the first cam lobe is applied to one axial end of the cam journal and a downward load from the second cam lobe is applied to the other axial end, the high-load locations are located at the same circumferential location on the cam journal. Therefore, it is sufficient to form the thin-walled portion with thickness X2 at the same circumferential location on both the axial ends of a single cam journal. This facilitates the machining of a hollow hole in the camshaft. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an internal combustion engine that can suppress wear of the cam journals that accompanies deformation of the camshaft. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a perspective view showing the appearance of an engine, which is an example of an internal combustion engine according to the present invention. [Figure 2] FIG. 2 is a longitudinal cross-sectional view of the engine taken along the direction of cylinder alignment, including a cross-section of a valve mechanism provided in the engine. [Figure 3] FIG. 3 is a perspective view of the valve mechanism. [Figure 4] FIG. 4 is a schematic diagram for explaining the pressing action of the valve body by the cam. [Figure 5] 5(A) to 5(C) are diagrams showing the pressing action of the cam on the valve disc over time, and FIG. 5(D) is a graph showing the pressing load applied to the cam. [Figure 6] FIG. 6 is a diagram showing an example of a camshaft, and is a diagram showing the relationship between the rotation phase of the cam and the position of the pressing load of the valve disc applied to the cam journal. [Figure 7] FIG. 7 is a schematic diagram showing the deformation of the cam journal when a pressing load is applied to the valve disc. [Figure 8] FIG. 8 is a schematic diagram showing an uneven thickness portion of a hollow hole provided in a cam journal. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. [Figure 10] FIG. 10(A) is a cross-sectional view of a cam journal according to this embodiment, and FIG. 10(B) is a schematic diagram showing the deformation operation of the cam journal. [Figure 11] FIG. 11(A) is a cross-sectional view of a cam journal according to a comparative example, and FIG. 11(B) is a schematic diagram showing the deformation operation of the cam journal. [Figure 12] 12(A) to 12(C) are cross-sectional views taken along the axial direction, showing various aspects of the uneven thickness portion of the hollow hole provided in the cam journal. [Figure 13]FIG. 13 is a diagram showing an example of the formation of hollow holes relative to the entire length of a camshaft, and is a cross-sectional view showing the relationship between the rotation phase of the cam and the position of the uneven thickness portion of the hollow hole in the cam journal. [Figure 14] 14(A) to 14(C) are schematic cross-sectional views showing modified examples of the hollow hole. DETAILED DESCRIPTION OF THE INVENTION

[0019] An internal combustion engine according to an embodiment of the present invention will be described in detail below with reference to the drawings. In this embodiment, an engine mounted on a vehicle such as an automobile as a power source for driving the vehicle will be described as an example of the internal combustion engine.

[0020] [Engine structure] FIG. 1 is a perspective view showing the exterior of an engine 1 according to this embodiment. The engine 1 is a four-stroke inline four-cylinder engine. FIG. 1 and several other figures are marked with directional symbols F and R, indicating the front and rear of the engine 1, respectively. The engine 1 includes an engine body 10 and a valve train 20 incorporated into an upper portion of the engine body 10. FIG. 2 is a longitudinal cross-sectional view of the engine 1 taken along the cylinder row direction, including a cross-section of the valve train 20. FIG. 3 is a perspective view of the valve train 20.

[0021] The engine body 10 includes a cylinder block 11 and a cylinder head 12. The cylinder block 11 has four cylinders 2 aligned in a line along the longitudinal direction FR of the engine (a predetermined arrangement direction). A piston is housed inside each cylinder 2 so that it can slide back and forth. The cylinder block 11 may include more cylinders 2, and may be for an in-line six-cylinder engine 1, for example. A crankshaft 16 is disposed inside and below the engine body 10, converting the reciprocating motion of the pistons into rotational motion.

[0022] The cylinder head 12 is attached to the top surface of the cylinder block 11 and closes the upper openings of the cylinders 2. The cylinder head 12 is formed with intake ports 14, which are openings for taking intake air into the cylinders 2, and exhaust ports, which are exhaust openings not shown in FIGS. 1 and 2. Each cylinder 2 is connected to the intake system and exhaust system in a four-valve configuration (two intake valves and two exhaust valves). FIGS. 1 and 2 show four sets of intake ports 14, each consisting of a pair of a first intake port 14A and a second intake port 14B, lined up in the direction of cylinder arrangement.

[0023] The cylinder head 12 is equipped with an intake valve 25A (valve body) that opens and closes the intake port 14, and an exhaust valve 25B (valve body) that opens and closes the exhaust port. The valve mechanism 20 is mounted on the top surface of the cylinder head 12. A cylinder head cover (not shown) is attached to the top surface of the cylinder head 12 so as to cover the valve mechanism 20.

[0024] The valve mechanism 20 is a mechanism that drives the intake valve 25A and the exhaust valve 25B to open and close the intake port 14 and the exhaust port. The intake valve 25A and the exhaust valve 25B are driven by the valve mechanism 20 so as to be linked to the rotation of the crankshaft. This drive causes the valve head 251 of the intake valve 25A to open and close the port opening 14H (Figure 4) of the intake port 14. The same is true for the exhaust valve 25B.

[0025] The intake valve 25A and the exhaust valve 25B are poppet-type valves and include a valve head 251 that actually opens and closes the intake port 14 and the exhaust port, a stem 252 that extends upward from the valve head 251, and a stem end 253 that is the upper end of the stem 252 and receives a pressing force from the valve mechanism 20. A valve spring 254 is inserted into the stem 252. One end of the valve spring 254 abuts against a spring seat 255 that is fixed to the stem 252.

[0026] [Valve train details] Next, we will explain the detailed structure and operation of the valve train 20. The valve train 20 includes an intake valve camshaft 21A and an exhaust valve camshaft 21B, a roller rocker arm 26, a lash adjuster 27, and a bearing member 30 that supports the camshafts 21A and 21B via lubricating oil. The intake valve camshaft 21A and the exhaust valve camshaft 21B are connected to the crankshaft 16 by a chain or belt, and are driven to rotate about their own axes in conjunction with the rotation of the crankshaft 16.

[0027] The intake valve camshaft 21A is disposed above eight intake valves 25A arranged in series. Similarly, the exhaust valve camshaft 21B is disposed above eight exhaust valves 25B arranged in series. Each of the intake valve camshaft 21A and the exhaust valve camshaft 21B includes a shaft body 22, a cam 23, and a cam journal 24. The shaft body 22 extends linearly in the longitudinal direction FR of the engine, with a length corresponding to the arrangement length of the intake valves 25A or the exhaust valves 25B. A hollow hole 22H extending in the axial direction of the camshafts 21A and 21B is formed inside the shaft body 22 for purposes such as circulating cooling oil and reducing weight. This embodiment is characterized in that the hollow hole 22H is formed in a special way to make the cam journal 24 portion easily deformable. This point will be described in detail later.

[0028] The cam 23 is disposed on the shaft body 22 at locations corresponding to the positions of the eight intake valves 25A or the eight exhaust valves 25B. The cam 23 includes a cam lobe 231 and a base circle 232. The cam lobe 231 is the long diameter portion of the cam 23 and presses down the intake valve 25A or the exhaust valve 25B via the roller rocker arm 26 to open the intake port 14 or the exhaust port. Note that a direct acting configuration may be used in which the cam lobe 231 directly presses down the intake valve 25A or the exhaust valve 25B without using the roller rocker arm 26. The base circle 232 is the short diameter portion of the cam 23 and has a diameter larger than that of the shaft body 22.

[0029] The cam journals 24 are portions where the camshafts 21A, 21B are journaled by the bearing members 30. The cam journals 24 are formed to have a diameter slightly larger than that of the shaft body 22, and are disposed in an area close to the cams 23. In this embodiment, one cam journal 24 is disposed between a pair of cams 23 disposed for one cylinder 13.

[0030] The roller rocker arm 26 is a member that transmits the pressing force of the cam 23 to the intake valve 25A or the exhaust valve 25B by using the action of a lever, and is disposed for each of the eight cams 23. The roller rocker arm 26 includes a roller 261 that contacts the peripheral surface of the cam 23, and a swing arm 262 that pivotally supports the roller 261. A contact portion 263 that presses down on the stem end 253 of the intake valve 25A or the exhaust valve 25B is formed on one end of the swing arm 262. A pivot portion 264 that serves as a pivot point for the swing arm 262 to swing is formed on the other end of the swing arm 262.

[0031] The lash adjuster 27 automatically adjusts the valve clearance between the stem end 253 and the contact portion 263. A hydraulic lash adjuster that uses the hydraulic pressure of engine oil can be used as the lash adjuster 27. If the valve clearance increases due to wear or the like, the lash adjuster 27 increases the amount of oil stored inside to reduce the valve clearance.

[0032] The bearing member 30 supports each cam journal 24 of the camshafts 21A and 21B via lubricating oil. The bearing member 30 includes a head-side bearing 31 and a cam cap 32. The cam journal 24 is held by a support body formed by the engagement of the head-side bearing 31 and the cam cap 32. The head-side bearing 31 is a bearing portion formed integrally with the cylinder head 12 and supports the annular circumferential surface of the lower half of the cam journal 24. The cam cap 32 is a member with a semicircular bearing portion that supports the annular circumferential surface of the upper half of the cam journal 24 and is fixed to the head-side bearing 31 by screws or the like. Lubricating oil is supplied between the inner circumferential surfaces of the head-side bearing 31 and cam cap 32 and the outer circumferential surface of the cam journal 24. When the camshafts 21A and 21B rotate about their axes, oil film pressure of the lubricating oil is generated, and this oil film supports the rotation of the cam journal 24.

[0033] FIG. 4 is a schematic diagram illustrating the pressing action of the cam 23 on the intake valve 25A. Note that the same action is performed on the exhaust valve 25B as described below. The circumferential surface of the cam 23 is constantly in contact with the circumferential surface of the roller 261 of the roller rocker arm 26 due to the spring force of a valve spring 254 (not shown in FIG. 4). In FIG. 4, the solid line shows the state in which the base circle 232 of the cam 23 is in contact with the roller 261. In this state, the contact portion 263 of the swing arm 262 does not substantially press down on the stem end 253 of the intake valve 25A. Therefore, the valve head 251 of the intake valve 25A is in contact with the valve seat 15, and the port opening 14H of the intake port 14 is closed.

[0034] As the cam 23 continues to rotate clockwise from the state shown in FIG. 4, the cam lobe 231 of the cam 23 comes into contact with the roller 261, as indicated by the dotted line in the figure. In this state, the roller 261 is pressed downward by the amount of cam lift, and the swing arm 262 tilts downward with the pivot portion 264 as the swing point. This tilting motion causes the contact portion 263 to press the stem end 253 downward. As a result, the valve head 251 moves downward away from the valve seat 15 and enters the cylinder 13, opening the port opening 14H. At this time, a pressing load F of the intake valve 25A acts on the cam 23 at a position circumferentially facing the cam lobe 231, as indicated by the dotted arrow in FIG. 4. This pressing load F will now be further explained.

[0035] [Valve body pressing load and its effects] 5(A) to 5(C) are diagrams showing the pressing action of intake valve 25A by cam lobe 231 of cam 23 over time, and FIG. 5(D) is a graph showing the pressing load F applied to cam 23. FIG. 5(A) shows the state at the initial stage of contact when cam lobe 231 begins to contact roller 261 (phase in the rotational direction of camshaft 21A=θ1). Pressing load F acts from the contact position between cam lobe 231 and roller 261 toward the opposite radial side of cam 23. At this initial stage of contact, as shown in FIG. 5(D), pressing load F increases rapidly. This is because cam 23 requires a relatively large pressing force when it starts to press intake valve 25A.

[0036] 5(B) shows the state in the first half of the middle contact period (rotational phase=θ2) when the contact of cam lobe 231 with roller 261 has progressed. Swing arm 262 swings downward relatively significantly with pivot portion 264 as the swing fulcrum, and contact portion 263 presses down intake valve 25A. In this state, the apex of cam lobe 231 has not yet come into contact with roller 261, but the pressing load F is at its maximum as shown in FIG. 5(D).

[0037] FIG. 5(C) shows a state in the latter stage of contact (rotational phase = θ3) when the contact between the cam lobe 231 and the roller 261 is nearing the end. After phase = θ2, the pressure load F gradually decreases. After passing the peak of the cam lobe 231, the intake valve 25A may move upward, causing the pressure load F to decrease more gradually. As the rotation progresses further and the cam lobe 231 and the roller 261 disengage, the pressure load F disappears.

[0038] 5(A) to 5(C) show cam high load points PA where a pressure load F acts on the cam 23 due to contact between the cam lobe 231 and the roller 261. The cam high load points PA occur at points on the cam 23 that face the cam lobe 231 in the circumferential direction, in other words, at points on the cam 23 on the opposite side of the axial center of the camshaft 21A from the cam lobe 231. In the drawings, the cam high load points PA are depicted as crescent-shaped. This is because, in order to schematically show the distribution of the pressure load F, the positions where the pressure load F is greater are depicted as having a greater radial thickness. However, the cam high load points PA do not actually have a load distribution that forms a simple crescent shape, but rather have a load distribution in which the center of gravity of the load is eccentric upstream in the direction of rotation, as shown in FIG. 5(D).

[0039] FIG. 6 is a simplified diagram of the intake valve camshaft 21A (exhaust valve camshaft 21B) shown in FIGS. 1 to 3, illustrating the relationship between the rotational phase of the cam 23 and the position of the pressure load on the intake valve 25A (exhaust valve 25B) applied to the cam journal 24. The reference numerals #1 to #4 in the diagram indicate the four cylinders 13 aligned in the longitudinal direction FR of the engine. As described above, the intake valve camshaft 21A has two cams 23 arranged for each of the four-valve cylinders #1 to #4, and the cam journal 24 is located midway between the two cams 23.

[0040] As a result of this positional relationship, the cam journal 24 is disposed in a region of the shaft body 22 that is close to the cam 23 (cam lobe 231). Here, the "close region" refers to a region where a deforming force acts on the shaft body 22 due to the pressing load F that the cam 23 receives. For example, as shown in FIG. 2, a typical example of a "close region" is when the axial distance between the cam journal 24 and the cam 23 is approximately the axial width of one cam 23.

[0041] 6 shows a state in which intake valve 25A corresponding to cylinder #4 is pressed down by cam lobe 231 via roller rocker arm 26, and cam lobes 231 for cylinders #1 to #3 are in a phase where they do not engage with roller 261. For cam 23 of cylinder #4, pressing load F is actually acting on the cam high load point PA described above. On the other hand, for cams 23 of cylinders #1 to #3, pressing load F is not acting on the cam high load point PA.

[0042] When a pressing load F acts on a cam high load point PA in the cam 23, a high load is also applied to the cam journal 24, resulting in a journal high load point PB. Like the cam high load point PA, the position at which the journal high load point PB occurs is a position circumferentially opposite the cam lobe 231. At this journal high load point PB, deformation of the cam journal 24 occurs due to the pressing load F applied to the cam 23. Figure 7 is a schematic diagram showing the deformation of the cam journal 24 when a pressing load F from the intake valve 25A is applied.

[0043] The cam journal 24 is rotatably supported by a sliding bearing support formed by the engagement between the head-side bearing 31 and the cam cap 32. A lubricating oil film LB is formed between the inner peripheral surfaces of the head-side bearing 31 and the cam cap 32 and the outer peripheral surface of the cam journal 24. When the cam lobe 231 presses down on the roller 261 of the roller rocker arm 26, a pressing load F acts toward the cam high load area PA circumferentially facing the cam lobe 231. This pressing load F generates a deformation force Fw that deforms the camshaft 21A (shaft main body 22) so as to lift the cam 23 upward, as shown by the dotted line in FIG. 7. Note that the deformation of the cam 23 is exaggerated in FIG. 7.

[0044] When the cam 23 deforms in this manner, a high journal load point PB is also generated in the cam journal 24 adjacent to the cam 23, causing the cam journal 24 to deform. In this embodiment, the cam journal 24 is positioned between a pair of cams 23, and the shaft body 22 deforms so that the pair of cams 23 are lifted upward. As a result, the cam journal 24 deforms in a bow shape, lifting both axial ends. This deformation brings the outer peripheral surface of the cam journal 24 near the F-side and R-side ends closer to the inner peripheral surface of the cam cap 32, which supports the annular peripheral surface of the upper half of the cam journal 24. In other words, a condition is created in which the cam journal 24 is likely to come into contact with the cam cap 32. For the #1 to #3 cylinders, when the rotational phase of the cam 23 is the same as that of the #4 cylinder, deformation occurs in the journal high load point PB of the cam journal 24.

[0045] To suppress mechanical resistance, it is desirable to reduce the gap between the inner peripheral surfaces of the head-side bearing 31 and cam cap 32 and the cam journal 24, thereby making the oil film LB as thin as possible. However, if the gap is reduced, the application of the pressing load F to the cam 23 may cause deformation of the cam journal 24, which may result in contact between the cam journal 24 and the cam cap 32, which may actually increase mechanical resistance and accelerate wear. In consideration of this problem, in this embodiment, the camshaft 21A (21B) is designed in a shape that can dissipate the impact force even if contact occurs between the cam journal 24 and the cam cap 32. This design is described below.

[0046] [Cam journal of this embodiment] In the camshaft 21A (21B) of this embodiment, the hollow hole 22H of the shaft body 22 is formed eccentrically, thereby intentionally making the journal high load point PB of the cam journal 24 easily deformable. When the cam journal 24 comes into contact with the cam cap 32, the deformation of the cam journal 24 dissipates the force of the collision between them. This prevents an increase in mechanical resistance and wear.

[0047] Fig. 8 is a schematic diagram showing a camshaft 21A (21B) according to this embodiment. Fig. 9 is a cross-sectional view taken along line IX-IX in Fig. 8. Fig. 8 shows the cam journal 24 and its bearing member 30 corresponding to the #4 cylinder in Fig. 6, the cam 23 adjacent thereto, and the formation mode of the hollow hole 22H. For the #1 to #3 cylinders, the hollow hole 22H is formed in a similar manner at the journal high load point PB.

[0048] The cam journal 24 of the intake valve camshaft 21A shown in Figure 8 is positioned so as to be sandwiched between a pair of cams 23 that press down on the intake valve 25A of the #4 cylinder. The F-side cam lobe 231 (first cam lobe) presses down on the intake valve 25A (first valve body) that opens and closes the first intake port 14A (Figure 2), and the R-side cam lobe 231 (second cam lobe) presses down on the intake valve 25A (second valve body) that opens and closes the second intake port 14B. The same is true for the exhaust valve camshaft 21B. The cam journal 24 is positioned so as to be sandwiched between and close to both the F-side cam lobe 231 and the R-side cam lobe 231.

[0049] In this arrangement, journal high load points PB are generated at positions on the cam journal 24 circumferentially opposing the F-side cam lobe 231 and the R-side cam lobe 231. The hollow hole 22H drilled in the camshaft 21A is eccentrically provided so that the journal high load points PB are thin-walled. The camshaft 21A has a uniform thickness portion 41, a non-uniform thickness portion 42, and a transition portion 43 according to the drilling position of the hollow hole 22H.

[0050] The uniform thickness portion 41 is a portion where the axis C1 of the camshaft 21A and the axis C2 of the hollow hole 22H are coaxial. The uneven thickness portion 42 is a portion where the axis C2 of the hollow hole 22H is eccentric to the axis C1 of the camshaft 21A on the opposite side to the cam lobe 231. The transition portion 43 is a portion that connects the hollow hole 22H of the uniform thickness portion 41, whose axis C2 is misaligned, with the hollow hole 22H of the uneven thickness portion 42. The uneven thickness portion 42 is located at the position of the cam journal 24 and in the vicinity thereof. The uniform thickness portion 41 is located on the shaft body 22 excluding the area of the cam journal 24.

[0051] 9 shows a cross-sectional view perpendicular to the axial direction of the camshaft 21A, showing the thickness of the periphery of the hollow hole 22H in the area of the cam journal 24. In this cross-sectional view, when the thickness on the side where the cam lobe 231 protrudes is X1 and the thickness on the side circumferentially opposite the cam lobe 231 is X2, the thickness deviation portion 42 is X1>X2 Hollow hole 22H is formed so as to satisfy the relationship. In other words, uneven thickness portion 42 has thick portion 44 on the side where cam lobe 231 protrudes, and thin portion 45 on the side circumferentially opposite cam lobe 231. The thickness around hollow hole 22H gradually increases from thick portion 44 to thin portion 45.

[0052] In this embodiment, the hollow hole 22H has a circular shape in a cross section perpendicular to the axial direction. Therefore, the thickness-eccentric portion 42 satisfies the relationship X1>X2 by offsetting the axis C2 of the hollow hole 22H from the axis C1 of the camshaft 21A by the eccentric length d toward the side circumferentially facing the cam lobe 231 (upward in FIG. 9 ). According to this embodiment, the thickness X1 of the thick-walled portion 44 and the thickness X2 of the thin-walled portion 45 can be easily set simply by selecting the eccentric length d. When the hollow hole 22H has a circular cross section, the ratio X1:X2 can be set, for example, in a range of approximately 1:0.4 to 0.9. X1 is the radial length of the thickest portion of the thick-walled portion 44, and X2 is the radial length of the thinnest portion of the thin-walled portion 45.

[0053] Providing the uneven thickness portion 42 as described above means that the cam journal 24 is made more susceptible to deformation on the side opposite the cam lobe 231 than on the protruding side of the cam lobe 231. In other words, the formation of the thick-walled portion 44 and the thin-walled portion 45 results in a rigidity gradient in the circumferential direction of the cam journal 24. Due to the difference in rigidity between the thick-walled portion 44 and the thin-walled portion 45, the thin-walled portion 45 becomes an easily deformed portion that is relatively easily deformed. In other words, when a high load is applied, the thin-walled portion 45 deforms. Furthermore, the easily deformable thin-walled portion 45 suppresses wear on the cam journal 24.

[0054] FIG. 10(A) is a cross-sectional view of the cam journal 24 according to this embodiment, and FIG. 10(B) is a schematic diagram showing the deformation of the cam journal 24. FIG. 10(A) shows a cross-sectional view of the cam journal 24 alone, as previously shown in FIG. 9. FIG. 10(B) shows a state in which the cam lobe 231 presses down on the roller 261 of the roller rocker arm 26, causing a pressing load F to act on the cam 23. In this state, as described with reference to FIG. 7, a deformation force Fw is generated that deforms the camshaft 21A so as to lift the cam 23 upward. This deformation force Fw may bring the circumferential surface of the cam journal 24 closer to the bearing member 30 (cam cap 32), and eventually into contact with it.

[0055] However, the cam journal 24 has an easily deformable thin-walled portion 45. Therefore, even if the pressing load F causes the camshaft 21A to deform and the circumferential surface of the cam journal 24 to come into contact with the cam cap 32, the cam journal 24 can deform at the thin-walled portion 45. The cushioning effect of this deformation can dissipate the force of the cam journal 24 colliding with the cam cap 32. In other words, the contact force between the cam journal 24 and the cam cap 32 can be alleviated. Therefore, wear on the cam journal 24 due to the deformation of the camshaft 21A caused by the pressing load F can be suppressed.

[0056] FIG. 11(A) is a cross-sectional view of a cam journal 24 according to a comparative example, and FIG. 11(B) is a schematic diagram showing the deformation behavior of the cam journal 24. The cam journal 24 of the comparative example has a wall thickness of X3 on the side from which the cam lobe 231 protrudes, and a wall thickness of X3 on the side circumferentially facing the cam lobe 231. That is, the axis C1 of the camshaft 21A and the axis C2 of the hollow hole 22H are coaxial, and the wall thickness around the hollow hole 22H is constant. In this comparative example, there is no circumferential rigidity gradient, and the ease of deformation is constant along the circumferential direction of the cam journal 24. That is, the region circumferentially facing the cam lobe 231 is not easily deformable.

[0057] As shown in Figure 11(B), suppose that a downward load F acts on the cam journal 24 of the comparative example, generating a deformation force Fw that deforms the camshaft 21A so as to lift the cam 23 upward. In this case, the circumferential surface of the cam journal 24 may come into contact with the cam cap 32. However, even if contact occurs between the two, the cam journal 24 of the comparative example is not easily deformed, so no shock absorbing effect is achieved, and the circumferential surface of the cam journal 24 comes into contact with the cam cap 32 with high rigidity. Therefore, the cam journal 24 is more likely to wear.

[0058] [Various aspects and arrangements of uneven thickness parts] Figures 12(A) to 12(C) are cross-sectional views taken along the axial direction of the cam journal 24, showing various embodiments of the uneven thickness portion 42 in the cam journal 24. Figure 12(A) shows an example in which the uneven thickness portion 42 that satisfies the relationship X1 > X2 is formed over the entire axial length of the cam journal 24. This example is substantially the same as the uneven thickness portion 42 shown in Figure 8. Transition portions 43 are connected to both axial ends of the uneven thickness portion 42, and uniform thickness portions 41 are also connected to them.

[0059] 12(A), the eccentric length d of the axis C2 of the hollow hole 22H relative to the axis C1 of the camshaft 21A is constant in the axial direction (constant eccentricity) in the area of the cam journal 24. The axial length L1 of the uneven thickness portion 42 is set longer than the axial width of the bearing member 30 (cam cap 32). Therefore, the uneven thickness portion 42 has a length that is longer by a margin L2 from each of the axial ends of the bearing member 30. Setting the margin L2 makes it easier for the thin-walled portion 45 to deform even when the peripheral surface of the cam journal 24 collides with the axial edge of the cam cap 32.

[0060] 12(B) shows an example in which thickness-varying portions 42 that satisfy the relationship X1>X2 are formed at both axial ends of the cam journal 24. In this thickness-varying portion 42, the eccentricity of the axis C2 of the hollow hole 22H relative to the axis C1 of the camshaft 21A varies axially within the cam journal 24. That is, thickness-varying portions 42 with an axial length L3 that straddle one and the other axial ends of the bearing member 30 are disposed at both axial ends of the cam journal 24. The axial central region of the cam journal 24 is a uniform thickness portion 41 where the axes C1 and C2 are coaxially aligned. This uniform thickness portion 41 and the thickness-varying portions 42 located at both axial ends are connected by transition portions 43.

[0061] When a pressing load F is applied to the camshaft 21A, both axial ends of the cam journal 24 deform closest to the bearing member 30 at positions circumferentially opposite the cam lobes 231, with the amount of deformation decreasing toward the axial center (see FIG. 7). In other words, by making at least the regions at both axial ends of the cam journal 24 easily deformable, it is possible to accommodate the above-mentioned deformation modes of the cam journal 24. The arrangement of the uneven thickness portion 42 in FIG. 12(B) is designed to match this deformation mode of the cam journal 24. In other words, the example in FIG. 12(B) makes it easy for both axial ends of the cam journal 24 to deform, effectively reducing the contact force between the cam journal 24 and the cam cap 32.

[0062] The uneven thickness portion 42 shown in Figure 12(C) is another example in which the eccentricity of the axial center C2 of the hollow hole 22H is changed. Similar to the uneven thickness portion 42 in Figure 12(B), the uneven thickness portions 42 having an axial length L4 are arranged so as to straddle one axial end and the other axial end of the bearing member 30, and are arranged at both axial ends of the cam journal 24. However, it differs from the uneven thickness portion 42 in Figure 12(B) in that the thickness deviation ratio between the thick-walled portion 44 and the thin-walled portion 45 gradually changes toward the axial center of the cam journal 24.

[0063] FIG. 13 is a cross-sectional view showing an example of the formation of the hollow hole 22H relative to the entire length of the camshaft, illustrating the relationship between the rotational phase of the cam 23 and the position of the uneven-walled portion 42 on the cam journal 24. In this example, the rotational phase of the cam 23 for the #1 cylinder is 0° (the cam lobe 231 points upward), and the rotational phase of the cam 23 for the #4 cylinder is 180° (the cam lobe 231 points downward and contacts the roller 261). The cross section of FIG. 13 exposes the uneven-walled portions 42 corresponding to the #1 and #4 cylinders. That is, for the #1 cylinder, the uneven-walled portion 42 is offset downward with respect to the camshaft axis C1, and the thin-walled portion 45 is located below the axis C1. On the other hand, for the #4 cylinder, the uneven-walled portion 42 is offset upward with respect to the camshaft axis C1, and the thin-walled portion 45 is located above the axis C1.

[0064] On the other hand, the uneven thickness portions 42 corresponding to the #2 and #3 cylinders are not visible in the cross section of Figure 13. The phase of rotation of the cam 23 for the #2 cylinder is 90°, and the phase of rotation of the cam 23 for the #3 cylinder is 270°. These uneven thickness portions 42 are offset in the front-to-rear direction of the page in Figure 13 with respect to the axis C1 of the camshaft. The thin-walled portion 45 for the #2 cylinder is located on the rear side of the page, and the thin-walled portion 45 for the #3 cylinder is located on the front side of the page.

[0065] The hollow holes 22H in the transition portion 43 smoothly connect the hollow holes 22H in the uneven-walled portions 42 of the #1 to #4 cylinders, which are offset in different directions from each other with respect to the camshaft axis C1, to the hollow holes 22H in the uniform-walled portion 41. As long as this smooth connection is achieved, the cross-sectional shape of the hollow holes 22H in the transition portion 43 does not necessarily have to be circular, and may be a cross-sectional shape including a plurality of arcs of different diameters, such as an ellipse. Such a camshaft 21A (21B) can be manufactured, for example, by casting using a core.

[0066] [Variations] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and the following modified embodiments can be adopted, for example.

[0067] (1) In the above embodiment, the camshafts 21A, 21B are illustrated as being compatible with the in-line four-cylinder engine 1. The camshafts 21A, 21B may be camshafts for other multi-cylinder engines, for example, an in-line six-cylinder engine.

[0068] (2) In the above embodiment, an example was shown in which the axis C2 of the hollow hole 22H having a circular cross section is offset from the axis C1 of the camshaft to satisfy the relationship X1>X2 in the uneven thickness portion 42. The hollow hole 22H does not necessarily have to be formed with a circular cross section. Figures 14(A) to 14(C) show cam journals 24A, 24B, and 24C having hollow holes 22H1, 22H2, and 22H3 according to modified examples.

[0069] 14(A) is a cross-sectional view of a cam journal 24A having a hollow hole 22H1 with a substantially square cross-section. The hollow hole 22H1 is disposed eccentrically upward relative to the axis C1 of the camshaft. As a result, the cam journal 24A has a thick-walled portion 44 and a thin-walled portion 45 such that the thickness X1 on the side from which the cam lobe 231 protrudes is greater than the thickness X2 on the side circumferentially opposite the cam lobe 231.

[0070] FIG. 14(B) is a cross-sectional view of cam journal 24B having hollow hole 22H2 with a hexagonal cross-section. In this example, too, the eccentric arrangement of hollow hole 22H2 satisfies the relationship X1 > X2. FIG. 14(C) is a cross-sectional view of cam journal 24C having hollow hole 22H3 with an elliptical cross-section. By eccentrically arranging hollow hole 22H3 and aligning the minor axis of the ellipse with the protruding direction of cam lobe 231, the relationship X1 > X2 is satisfied. Even with these hollow holes 22H1, 22H2, and 22H3, cam journals 24A, 24B, and 24C can be deformed at thin-walled portion 45 in response to pressing load F. [Explanation of symbols]

[0071] 1. Engine (internal combustion engine) 10 Engine body 13 cylinders 14 Intake port 14H port opening (opening for intake and exhaust) 21A Intake valve camshaft (camshaft) 21B Exhaust valve camshaft (camshaft) 22 Shaft body 22H hollow hole 23 Cam 231 Mount Kam 24 Cam Journal 25A, 25B Intake valve, exhaust valve (valve body) 30 Bearing material 31 Head side bearing 32 Cam cap (bearing part) 41 Uniform thickness part 42 Uneven thickness part 43 Transition section 44 Thick section (cam lobe protruding side) 45 Thin-walled section (side facing the cam lobe in the circumferential direction) C1 Camshaft axis C2 Axis of the hollow hole X1 Thickness of thick part X2 Thin-walled part thickness

Claims

1. an engine body including a cylinder having an intake / exhaust opening and a valve body for opening and closing the opening; a camshaft having a cam lobe that presses the valve body to open the opening; a bearing member that supports the camshaft via lubricating oil, The camshaft is a cam journal journal journaled by the bearing member; a hollow hole extending in the axial direction of the camshaft, When viewing the thickness of the periphery of the hollow hole in the region of the cam journal in a cross section perpendicular to the axial direction, the thickness on the side from which the cam lobe protrudes is defined as X1, and the thickness on the side circumferentially opposite the cam lobe is defined as X2, X1>X2 In an internal combustion engine including a part that satisfies the relationship an internal combustion engine, wherein the portion satisfying the relationship X1>X2 is disposed at least at both ends of the cam journal in the axial direction.

2. 2. The internal combustion engine according to claim 1, the hollow hole has a circular shape in a cross section perpendicular to the axial direction, an axis of the hollow hole being offset from an axis of the camshaft to a side circumferentially opposing the cam lobe, thereby satisfying the relationship X1>X2.

3. 3. The internal combustion engine according to claim 1 or 2, an internal combustion engine, wherein the portion satisfying the relationship X1>X2 is arranged over the entire axial length of the cam journal.

4. In the internal combustion engine according to any one of claims 1 to 3, Each cylinder has two intake and two exhaust openings. As the valve bodies, the intake camshaft and the exhaust camshaft each include a first valve body and a second valve body that open and close the two openings, respectively; the camshaft includes a first cam lobe and a second cam lobe that press down the first valve body and the second valve body, respectively; The cam journal is disposed at a position sandwiched between the first cam lobe and the second cam lobe.

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