Internal combustion engine

Abstract

To suppress abrasion of a crank journal resulting from deformation of a crankshaft while maintaining lubricating performance in a bearing portion of the crank journal.SOLUTION: An engine 1 includes an engine body 10 having a cylinder 2 and a piston 21, a crankshaft 3, and a main bearing 4 pivotally supporting the crankshaft 3 via lubricating oil. The crankshaft 3 includes a crank journal 31 pivotally supported by a journal metal 43 of the main bearing 4, and a counter weight 33 extending from an axial end of the crank journal 31 to a radial outer side. The crank journal 31 includes a recession 5 formed in a portion corresponding to the extension position of the counter weight 33 and recessed to a radial inner side. The recession 5 is deeper in the axial end than in an axial center side of the crank journal 31.SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] The internal combustion engine includes a crankshaft that converts the reciprocating motion of a piston slidably accommodated in a cylinder into rotational motion. The crank journal of the crankshaft is supported by a sliding bearing via lubricating oil. Patent Document 1 discloses an internal combustion engine in which a plurality of recesses are provided on the outer surface of the crank journal to enhance the retention of 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] To improve the fuel efficiency of an internal combustion engine, it is necessary to reduce various mechanical losses. With regard to the above-mentioned lubricating oil, it is desirable to use a low-viscosity oil from the viewpoint of suppressing friction loss on the sliding surface. However, if a low-viscosity oil is used, there is a concern that poor lubrication will occur at the bearing portion of the crank journal, causing wear on the crank journal. In addition, when the piston is subjected to combustion pressure, it is pressed in a direction that intersects with the axial direction, so a deformation force acts on the crankshaft. For this reason, wear caused by deformation of the crank journal itself is also a problem.

[0005] An object of the present invention is to provide an internal combustion engine that can suppress wear of the crank journal due to deformation of the crankshaft while maintaining lubrication at the bearing portion of the crank journal. [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 having cylinders and pistons housed in the cylinders for reciprocating sliding motion; a crankshaft for converting the reciprocating motion of the pistons into rotational motion; and a bearing member for supporting the crankshaft via lubricating oil, wherein the crankshaft includes a crank journal supported by the bearing member and a counterweight extending radially outward from an axial end of the crank journal, the crank journal having a recess formed in a portion corresponding to the extending position of the counterweight and recessed radially inward, the recess being deeper at the axial end of the crank journal than at the axial center side.

[0007] When the piston is subjected to the combustion pressure, a pressing force acts on the crankshaft in a direction intersecting the axial direction. On the other hand, the counterweight is a heavy object and is generally placed at the opposite end of the connection between the piston and the crankshaft to reduce inertial forces. Therefore, when a pressing force from the piston is applied to the crankshaft, a deformation force (load) is generated that causes the counterweight to fall toward the crank journal. This deformation force acts in a direction that brings the circumferential surface of the crank journal corresponding to the extended position of the counterweight closer to the bearing member. In other words, when the counterweight is in the extended position, it creates a state in which the circumferential surface of the crank journal is more likely to come into contact with the bearing member.

[0008] According to the above internal combustion engine, a recess is formed in a portion corresponding to the extension position of the counterweight, and the recess is deeper at the axial end of the crank journal than at the axial center. Therefore, even if a pressing force is applied from the piston, the recess ensures a clearance between the peripheral surface of the crank journal corresponding to the extension position of the counterweight and the bearing member, and contact between the two can be avoided. On the other hand, in an area where the recess is not provided, it is possible to set the clearance between the peripheral surface of the crank journal and the bearing member to be small. Therefore, even if a low-viscosity oil is used as a lubricating oil, oil leakage is unlikely to occur, and lubricity can be ensured. Therefore, it is possible to maintain lubricity at the bearing portion of the crank journal and prevent wear of the crank journal at the same time.

[0009] In the above internal combustion engine, it is preferable that the recess has a depth that gradually increases from an axial center side to an axial end side of the crank journal.

[0010] When a pressing force from the piston is applied to the crankshaft, the axial end of the crank journal deforms in a direction closest to the bearing member at the extended position of the counterweight, and the amount of deformation decreases toward the axial center. According to the above internal combustion engine, the recesses can be formed with a depth distribution that matches the deformation mode of the crank journal, and it is possible to more appropriately ensure lubrication and prevent wear.

[0011] In the above internal combustion engine, it is desirable that the recess has a predetermined axial width and circumferential width in the axial and circumferential directions of the crank journal, and that the axial width of the recess is wider on the upstream side in the rotational direction of the crankshaft than on the downstream side.

[0012] In particular, it is more desirable that the planar shape of the recess in the planar shape of the crank journal expanded in the circumferential direction has a shape having a bulging portion that bulges toward the axial center in a steep curve near the upstream end of the circumferential width, and a gently curved portion that extends from the bulging portion to the downstream end of the circumferential width in a gentle curve.

[0013] According to the analysis by the inventors, it was found that the load acting on the crank journal due to the collapse of the counterweight tends to be larger at the upstream portion in the rotational direction than at the downstream portion at the extended position of the counterweight. More specifically, it was found that the largest load is applied near the upstream end in the rotational direction, and the load gradually decreases toward the downstream end in the rotational direction. According to the above internal combustion engine, the recess can be formed with an axial width that follows this load tendency, and it is possible to more reliably prevent the crank journal from contacting the bearing member.

[0014] In the above internal combustion engine, it is preferable that the recess has a greater depth at the axial end portion as the axial width of the recess increases.

[0015] According to this internal combustion engine, the clearance between the bearing member and the recess can be increased in the portion where the axial width of the recess is large. By locating such a portion where the axial width is large and the recess is deep in the portion of the crank journal that receives the most collapsing load from the counterweight, contact wear of the crank journal can be effectively avoided.

[0016] In the above internal combustion engine, it is desirable that the recess has a predetermined axial width and circumferential width in the axial and circumferential directions of the crank journal, the depth of the recess increases from an upstream end of the circumferential width in the rotational direction toward the downstream side at a first gradient, the deepest part is formed upstream of a central part in the rotational direction, and the depth of the recess has a profile that decreases from the deepest part to the downstream end in the rotational direction at a second gradient, and the first gradient is greater than the second gradient.

[0017] According to the inventors' analysis, the energy loss caused by the direct contact between the crank journal and the bearing member due to the deformation of the crankshaft shows a characteristic that rises relatively steeply in the first half of the contact period and falls relatively slowly in the second half of the contact period. The direct contact causes wear of the crank journal, so the amount of wear is large in the first half of the contact period and small in the second half of the contact period. Therefore, by providing the crank journal with a recess having the above-mentioned depth profile, a contact wear avoidance measure that is in line with the above-mentioned energy loss characteristic can be implemented.

[0018] In the above internal combustion engine, the engine body has a plurality of cylinders aligned in a row in a predetermined arrangement direction, and the crank journal located between two cylinders can be configured to include a first counterweight extending radially outward from one axial end, a second counterweight extending radially outward from the other axial end at a position circumferentially opposite to the first counterweight or at the same circumferential position as the first counterweight, a first recess formed in a portion corresponding to the extension position of the first counterweight and recessed from the one axial end toward the center in the axial direction, and a second recess formed in a portion corresponding to the extension position of the second counterweight and recessed from the other axial end toward the center in the axial direction.

[0019] According to this internal combustion engine, it is possible to maintain lubrication and prevent wear of the crank journal of the crankshaft having a full counter-type counterweight. In the above embodiment, when combustion pressure is applied to the piston, a deformation behavior occurs in which the distance between the first and second counterweights standing on either side of the crank journal narrows. The contact between the crank journal and the bearing member due to such a deformation behavior can be prevented by forming the first recess and the second recess.

[0020] In the above internal combustion engine, the engine body has a plurality of cylinders lined up in a row in a predetermined arrangement direction, and the crank journal located axially outward of the cylinders at one or the other end of the arrangement direction can be configured to include an end counterweight extending radially outward from an axial inner end, and an arrangement end recess formed in a portion corresponding to the extending position of the end counterweight, and recessed from the inner end toward the outside in the axial direction.

[0021] Even in a crankshaft having a full counter type counterweight, the crank journal located axially outward of the cylinders at one or the other end of the arrangement direction only has an end counterweight extending from the inner end in the axial direction. According to this internal combustion engine, the crank journal located at the end of the crankshaft only has an arrangement end recess corresponding to the end counterweight. Therefore, no unnecessary clearance is formed between the crank journal and the bearing member, and it is possible to ensure lubrication and prevent wear of the crank journal at the same time. Effect of the Invention

[0022] According to the present invention, it is possible to provide an internal combustion engine that can suppress wear of the crank journal due to deformation of the crankshaft while maintaining lubrication at the bearing portion of the crank journal. [Brief description of the drawings]

[0023] [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. [Diagram 2] FIG. 2 is a vertical cross-sectional view taken along the direction in which the cylinders are aligned in the engine. [Diagram 3] FIG. 3 is a side view of a crankshaft of a four-cylinder engine. [Figure 4] FIG. 4 is a schematic diagram for explaining deformation of the crank journal. [Diagram 5] FIG. 5 is a diagram showing the load applied to the crank journal due to the combustion pressure. [Figure 6] FIG. 6(A) is a simplified cross-sectional view showing an example of a recess provided in a crank journal, and FIG. 6(B) is a view showing the function of the recess. [Figure 7] FIG. 7 is a side view of the crankshaft with the locations of the recesses noted. [Figure 8] 8(A) to 8(C) are side views showing specific examples of the crank journal having the recessed portion. [Figure 9] FIG. 9 is a development of the crank journal surface showing the axial profile of the recess. [Figure 10] FIG. 10 is a side view of a crank journal showing the depth profile of the recess. [Figure 11] FIG. 11 is a side view of a crankshaft of a six-cylinder engine. [Figure 12] 12(A) to 12(C) are schematic cross-sectional views showing modified examples of the recess. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, an internal combustion engine according to an embodiment of the present invention will be described in detail 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.

[0025] [Engine structure] Fig. 1 is a perspective view showing the exterior of an engine 1 according to this embodiment. Fig. 2 is a longitudinal cross-sectional view taken along the cylinder row direction of the engine 1. The engine 1 is a four-stroke in-line four-cylinder engine. Fig. 1 and several other figures are marked with directional symbols F and R indicating the front and rear sides, respectively, of the engine 1. The engine 1 includes an engine body 10, a crankshaft 3 incorporated in the engine body 10, and a main bearing 4 that supports the crankshaft 3.

[0026] The engine body 10 includes a cylinder block 11, a cylinder head 12, and a lower cylinder block 13. The cylinder block 11 has four cylinders 2 aligned in a line along the engine front-rear direction FR (a predetermined arrangement direction). A piston 21 is accommodated inside each cylinder 2 so as to be capable of reciprocating motion. The cylinder block 11 may include more cylinders 2, and may be for use in an in-line six-cylinder engine, for example.

[0027] The cylinder head 12 is attached to the upper surface of the cylinder block 11 and closes the upper opening of the cylinder 2. The cylinder head 12 is formed with an intake port 14 that takes in intake air into the cylinder 2 and an exhaust port that is not shown in Figs. 1 and 2. Each cylinder 2 is connected to the intake system and the exhaust system in a four-valve format of 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 cylinder arrangement direction. Furthermore, the cylinder head 12 is assembled with an intake valve camshaft 15 that operates the intake valve and an exhaust valve camshaft 16 that operates the exhaust valve. A cylinder head cover (not shown) is attached to the upper surface of the cylinder head 12.

[0028] The lower cylinder block 13 is attached to the lower surface of the cylinder block 11 and supports the crankshaft 3. The lower cylinder block 13 has a ladder frame structure in which the portions supporting the crankshaft 3 are aligned in the front-rear direction of the engine.

[0029] The crankshaft 3 is a rotary output shaft of the engine 1 that converts the reciprocating motion of the pistons 21 into rotary motion. Fig. 3 is a side view of the crankshaft 3, and the phase of the rotational direction shown is the same as that of the cross-sectional view of Fig. 2. The crankshaft 3 includes a crank journal 31, a crank pin 32, a counterweight 33, and a crank arm 34. The crankshaft 3 illustrated here is of a full counterweight type.

[0030] The crank journal 31 is the part that serves as the rotation axis of the crankshaft 3, and is supported by the main bearing 4. The crank pin 32 is the part that is connected to the piston 21 via the connecting rod 22. The connecting rod 22 has a small end 23 at its upper end and a big end 24 at its lower end. The small end 23 is connected to the piston 21 via a piston pin 25. The big end 24 is connected to the crank pin 32. The crank arm 34 is the part that connects the crank journal 31 and the crank pin 32.

[0031] The counterweight 33 is a member that reduces the inertial force caused by the movement of the piston 21 and the connecting rod 22. The counterweight 33 is arranged so as to extend radially outward from the axial end (FR direction) of the crank journal 31. The circumferential position at which the counterweight 33 is arranged is opposite the crank pin 32. In other words, the counterweight 33 extends radially outward from a portion of the crank arm 34 opposite to the portion connected to the crank pin 32.

[0032] The crankshaft 3 corresponds to the in-line four-cylinder engine 1. The arrows #1, #2, #3, and #4 in Fig. 3 indicate the positions where the connecting rods 22 of the four cylinders 2 are arranged. The #1 cylinder 2 is the leading end (one end) cylinder in the axial direction (cylinder arrangement direction), and the #4 cylinder 2 is the rear end (other end) cylinder in the cylinder arrangement direction. The crankshaft 3 has first, second, third, and fourth crankpins 32A, 32B, 32C, and 32D as crankpins 32 corresponding to the #1 to #4 cylinders 2, respectively.

[0033] The crank journals 31 include a first crank journal 31A located on the F side of the #1 cylinder 2 in the axial direction, second, third and fourth crank journals 31B, 31C and 31D located between the first to fourth crank pins 32A to 32D, and a fifth crank journal 31E located on the R side of the #4 cylinder 2 in the axial direction. The counterweights 33 include first and second counterweights 33A and 33B arranged to sandwich the first crank pin 32A, third and fourth counterweights 33C and 33D arranged to sandwich the second crank pin 32B, fifth and sixth counterweights 33E and 33F arranged to sandwich the third crank pin 32C, and seventh and eighth counterweights 33G and 33H arranged to sandwich the fourth crank pin 32D.

[0034] The main bearing 4 includes a journal support portion 41 and a cap 42. The journal support portion 41 is a semicircular cavity portion formed in a plurality of frames arranged in a ladder shape in the lower cylinder block 13, and supports the crank journal 31 from below. The cap 42 is a semicircular recess attached to each journal support portion 41 so as to cover it from above. The crank journal 31 is held by a journal support body formed by the engagement between the journal support portion 41 and the cap 42.

[0035] A journal metal 43 (bearing member) is interposed between the journal support portion 41 and the cap 42 and the crank journal 31. The journal metal 43 is a sliding bearing, and is a bearing member that directly supports the outer circumferential surface of the crank journal 31 via lubricating oil. The journal metal 43 is made of a ring formed by combining two split annular metal pieces. Lubricating oil is supplied between the inner circumferential surface of the journal metal 43 and the outer circumferential surface of the crank journal 31. When the crankshaft 3 (crank journal 31) rotates around its axis, an oil film pressure of the lubricating oil is generated, and the rotation of the crank journal 31 is supported by the oil film.

[0036] A connecting rod metal 44, which is a sliding bearing similar to the journal metal 43, is also interposed between the big end 24 of the connecting rod 22 and the crank pin 32. Lubricating oil is also supplied between the inner circumferential surface of the connecting rod metal 44 and the outer circumferential surface of the crank pin 32.

[0037] [Load applied to crank journal] Next, a load applied to the crank journal 31 during rotation of the crankshaft 3 will be described. Fig. 4 is an enlarged schematic diagram of the first crank pin 32A (crank pin 32) and the second crank journal 31B (crank journal 31) in Fig. 3, with a cross section of the journal metal 43 added. As described above, the state in which an oil film LB of lubricating oil is formed between the journal metals 43 is shown.

[0038] The second crank journal 31B is a crank journal located between the #1 cylinder 2 and the #2 cylinder 2 (FIG. 3). From the F-side end 31f (one end in the axial direction) of the second crank journal 31B, the second counterweight 33B extends downward in the radially outward direction. Meanwhile, at a position 180° opposite to the second counterweight 33B in the circumferential direction, the third counterweight 33C extends upward in the radially outward direction from the R-side end 31r (the other end in the axial direction) of the second crank journal 31B. The fourth and fifth counterweights 33D and 33E extending radially outward from the F-side end 31f and the R-side end 31r of the third crank journal 31C are an example of a pair of counterweights arranged at the same circumferential position.

[0039] The combustion pressure received by the piston 21 of the #1 cylinder 2 is input to the first crank pin 32A from the big end 24 of the connecting rod 22. The arrows in FIG. 4 show a schematic line of force F when the combustion pressure is applied to the first crank pin 32A. The line of force F passes from the first crank pin 32A through the crank arm 34 toward the second crank journal 31B. When the combustion pressure is applied to the second crank journal 31B along the line of force F, a deformation force (load) is generated that causes the second counterweight 33B, which is located opposite the first crank pin 32A, to collapse toward the second crank journal 31B. In other words, a deformation force is generated that causes the gap between the first counterweight 33A (FIG. 3) and the second counterweight 33B, which are arranged on either side of the first crank pin 32A, to expand. In FIG. 4, such deformation of the second counterweight 33B is exaggerated and shown by a dotted line.

[0040] The above-mentioned deformation force acts in a direction that brings the outer circumferential surface of the second crank journal 31B corresponding to the extended position of the second counterweight 33B, i.e., the outer circumferential surface in the vicinity of the F-side end 31f, closer to the inner circumferential surface of the journal metal 43. In other words, a state is created in which the F-side end 31f of the second crank journal 31B is likely to come into contact with the journal metal 43 at the extended position of the second counterweight 33B.

[0041] To suppress mechanical resistance, it is desirable to make the gap between the crank journal 31 and the journal metal 43 as small as possible, thereby making the oil film LB as thin as possible. However, if the gap is made small, the crank journal 31 will deform due to the load of the combustion pressure being applied, causing contact between the crank journal 31 and the journal metal 43, which may actually increase mechanical resistance and promote wear.

[0042] FIG. 5 is a graph showing a measurement example of the load applied to the crank journal 31 by the combustion pressure. The graph shows the outer peripheral surface of the crank journal 31 in a developed form, and the load applied to the outer peripheral surface is shown as a concentration distribution. The higher the concentration, the higher the load acting on the outer peripheral surface. The horizontal axis of the graph corresponds to the axial width of the crank journal 31, and the vertical axis corresponds to the circumferential width. The vertical axis also indicates the rotation direction of the crank journal 31. The crank journal 31 shown in FIG. 5 is assumed to be the third crank journal 31C from which the fourth and fifth counterweights 33D and 33E extend from the same circumferential position.

[0043] The high load point PA where the load is high occurs near 180 degrees in the rotation direction. When the rotation direction is near 180 degrees, the fourth and fifth counterweights 33D and 33E are located downward, and combustion pressure is applied to the second and third crank pins 32B and 32C. It can be seen from FIG. 5 that a high load is applied from the fourth and fifth counterweights 33D and 33E to the third crank journal 31C at such a timing in the rotation direction.

[0044] The high load area PA does not have a load distribution that draws a simple semicircular ripple, but has a drop-shaped load distribution with the center of gravity eccentric to the upstream side in the rotation direction. This is considered to be due to the fact that the large combustion pressure generated by the combustion that mainly occurs near the compression top dead center in the cylinder 2 is suddenly applied to the third crank journal 31C via the piston 21 and the connecting rod 22. That is, the load applied to the third crank journal 31C is relatively large on the upstream side in the rotation direction of the high load area PA where the combustion pressure is suddenly applied. Then, as the rotation progresses toward the downstream side in the rotation direction, the load gradually becomes smaller. Naturally, the deformation amount of the third crank journal 31C is larger on the upstream side in the rotation direction where a larger load is applied at the high load area PA. That is, the third crank journal 31C is more likely to approach the journal metal 43 on the upstream side in the rotation direction.

[0045] [Crank journal of this embodiment] In this embodiment, a specific example of the crank journal 31 is shown, which can avoid contact between the crank journal 31 and the journal metal 43 and does not impair the maintenance of the lubricating oil even if the high load spot PA as described above occurs. Referring to Fig. 6, the crank journal 31 of this embodiment has a recess 5 recessed radially inward. The recess 5 is formed in a portion corresponding to the extension position of the counterweight 33. The recess 5 is deeper at the axial end of the crank journal 31 than at the axial center.

[0046] Fig. 6(A) is a simplified cross-sectional view showing an example of a recess 5 provided in the second crank journal 31B (crank journal 31), and Fig. 6(B) is a diagram showing the function of the recess 5. In the second crank journal 31B, as shown in Fig. 4, a high load spot PA as shown in Fig. 5 occurs near the extension position of the second counterweight 33B at the F-side end 31f. The recess 5 is provided so as to recess a portion of the second crank journal 31B corresponding to the extension position.

[0047] The recess 5 has a cross-sectional shape with a gradient that gradually deepens from the axial center side of the second crank journal 31B toward the F-side end 31f (axial end). That is, the recess 5 is recessed deepest toward the radial inside at the F-side end 31f. As explained in the load distribution of FIG. 5, when the combustion pressure is applied, the load near the extension position of the second counterweight 33B at the F-side end 31f becomes the largest, that is, the deformation amount near the F-side end 31f becomes the largest. Note that the depth of the recess 5 is exaggerated in FIG. 6, and the actual depth of the deepest part of the recess 5 is about several microns to several tens of microns.

[0048] 6(A) shows clearances G1 and G2 between the inner peripheral surface of the journal metal 43 and the outer peripheral surface of the second crank journal 31B. The clearance G1 at a location near the R-side end 31r where the recess 5 is not formed is set to a standard clearance that is set in consideration of the viscosity of the lubricating oil for the sliding bearing. On the other hand, the clearance G2 at a location near the F-side end 31f where the recess 5 is formed is larger than G1 and is largest near the F-side end 31f.

[0049] 6(B), the deformation of the second counterweight 33B and the second crank journal 31B when the combustion pressure is applied is shown by dotted lines. When the combustion pressure is applied to the first crank pin 32A, the second counterweight 33B is deformed so as to fall toward the R-side end 31r of the second crank journal 31B. In response to this, the portion of the second crank journal 31B near the F-side end 31f is deformed in a direction approaching the journal metal 43.

[0050] When such deformation occurs, if the recess 5 does not exist, the vicinity of the F-side end 31f of the second crank journal 31B may come into contact with the journal metal 43. However, when the recess 5 exists, even if the deformation occurs, the clearance G3 between the second crank journal 31B and the journal metal 43 is secured, and it is possible to prevent contact between the two.

[0051] The recess 5 is not provided around the entire circumference of the second crank journal 31B near the F-side end 31f, but is provided so as to recess only the portion corresponding to the high load point PA. Forming the recess 5 on the second crank journal 31B expands the clearance between the journal metal 43 facing it, causing oil leakage in which the lubricating oil escapes from the clearance. In this embodiment, the recess 5 is provided only at the portion corresponding to the high load point PA, and in the region where the recess 5 is not provided, the clearance between the circumferential surface of the second crank journal 31B and the journal metal 43 is set to the standard clearance G1. Therefore, the oil leakage is suppressed to a minimum.

[0052] Also, as shown by the dotted line in FIG. 4, when the combustion pressure is applied to the first crank pin 32A, the F-side end 31f deforms in a direction closest to the journal metal 43, and the amount of deformation decreases toward the axial center. In order to match this deformation tendency, the recess 5 has a profile in which the depth gradually increases from the axial center side of the second crank journal 31B toward the F-side end 31f. In this respect, too, a design is made to prevent the clearance from expanding unnecessarily. For this reason, even if a low-viscosity oil of 0W20 class is used as the lubricating oil, the oil leakage is unlikely to occur, and lubricity can be ensured. Therefore, it is possible to maintain the lubricity of the journal metal 43 and prevent wear of the crank journal 31 at the same time.

[0053] [Location and specific shape of recesses] Next, the position of the recessed portion 5 relative to the crankshaft 3 and the specific shape of the recessed portion 5 will be described. Fig. 7 is a side view of a full counter type crankshaft 3 for an in-line 4-cylinder engine, with the position of the recessed portion 5 relative to the crank journal 31 noted. Figs. 8(A) to (C) are side views showing specific examples of the crank journal 31 having the recessed portion 5.

[0054] Each of the first to fifth crank journals 31A to 31E of the crankshaft 3 is provided with one or two recesses 5. More specifically, for the first crank journal 31A located axially outward (F side) from the arrangement position of the #1 cylinder 2 at the F side end in the cylinder arrangement direction, a first counterweight 33A (end counterweight) extends radially outward from an inner end (R side end 31r) in the axial direction. FIG. 8(A) is a side view of the first crank journal 31A alone. The first crank journal 31A is provided with one recess 5 (arrangement end recess) in a portion corresponding to the extending position of the first counterweight 33A. The recess 5 is recessed from the R side end 31r toward the center side (F side) in the axial direction. The recess 5 has a shape that is deepest at the R side end 31r and gradually becomes shallower toward the F side.

[0055] The fifth crank journal 31E, which is located axially outward (on the R side) of the position of the #4 cylinder 2 at the R side end in the cylinder arrangement direction, has a recess 5 arranged symmetrically to the first crank journal 31A. The fifth crank journal 31E has an eighth counterweight 33H (end counterweight) extending radially outward from the axially inner end (F side end 31f). The fifth crank journal 31A has one recess 5 (arrangement end recess) formed in a portion corresponding to the extending position of the eighth counterweight 33H.

[0056] In this way, for the first and fifth crank journals 31A, 31E each having only one counterweight 33A, 33H, only one recess 5 corresponding to the counterweight 33A, 33H is formed. Therefore, no unnecessary large clearance is formed between the crank journals 31A, 31E and the journal metal 43, so that lubrication can be ensured and wear of the crank journals 31A, 31E can be prevented.

[0057] The second crank journal 31B has a second counterweight 33B extending from its F-side end 31f and a third counterweight 33C extending from its R-side end 31r, with the second counterweight 33B and the third counterweight 33C extending outward in the radial direction, with the second counterweight 33B and the third counterweight 33C extending outward in the circumferential direction, with the second counterweight 33B and the third counterweight 33C extending outward in the radial direction. FIG. 8B is a side view of the second crank journal 31B. The second crank journal 31B has two recesses 5. That is, one recess 5 (first recess) is recessed from the F-side end 31f toward the center in the axial direction, corresponding to the extending position of the second counterweight 33B. In addition, another recess 5 (second recess) is recessed from the R-side end 31r toward the center in the axial direction, corresponding to the extending position of the third counterweight 33C. The fourth crank journal 31D also has two recesses 5 similar to those of the second crank journal 31B.

[0058] The third crank journal 31C has a fourth counterweight 33D extending from its F-side end 31f and a fifth counterweight 33E extending from its R-side end 31r at the same circumferential position, extending radially outward. FIG. 8(C) is a side view of the third crank journal 31C alone. The third crank journal 31C also has two recesses 5. That is, one recess 5 (first recess) is recessed from the F-side end 31f toward the center in the axial direction, corresponding to the extending position of the fourth counterweight 33D. In addition, the other recess 5 (second recess) is recessed from the R-side end 31r toward the center in the axial direction, corresponding to the extending position of the fifth counterweight 33E.

[0059] Next, a specific shape of the recessed portion 5 will be described. Fig. 9 is a development of the surface of the crank journal 31, showing the axial profile of the recessed portion 5, i.e., a diagram showing the planar shape of the crank journal 31 developed in the circumferential direction. The crank journal 31 shown here is a type in which two recessed portions 5 are arranged with a phase difference of 180 degrees, corresponding to the second crank journal 31B or the fourth crank journal 31D shown in Fig. 7.

[0060] The recess 5 has a predetermined axial width and circumferential width in the axial direction (width direction) and circumferential direction (rotation direction) of the crank journal 31. The axial width of the recess 5 is wider on the upstream side in the rotation direction of the crankshaft 3 than on the downstream side. In other words, when the shape of the recess 5 in a plan view is divided into two parts, the upstream side and the downstream side (synonymous with the first half side and the second half side in the rotation direction), the recess 5 has an axial width that is relatively wider on the upstream side than on the downstream side. The axial width is the length from the F-side end 31f or the R-side end 31r of the crank journal 31 to the edge on the axial center side of the recess 5. The circumferential width is the width of the recess along the rotation direction.

[0061] More specifically, in a plan view of the crank journal 31 developed in the circumferential direction, the recess 5 has a teardrop shape including a bulging portion 51 on the upstream side in the rotational direction and a gently curved portion 52 on the downstream side in the rotational direction. The bulging portion 51 is a portion that bulges toward the axial center in a steep curve near the upstream end of the circumferential width of the recess 5. The gently curved portion 52 is a portion that reaches the downstream end of the circumferential width in the rotational direction in a gentle curve from the bulging portion 51. In other words, the edge on the axial center side of the recess 5 has a curved shape that rises steeply from the upstream end in the rotational direction toward the F-side end 31f or the R-side end 31r, reaches a peak position where the width is maximum in the upstream region in the rotational direction, and then approaches the F-side end 31f or the R-side end 31r gently.

[0062] The planar shape of the recess 5 corresponds to the planar shape of the high load area PA of the crank journal 31 shown in FIG. 5. As described above, the load acting on the crank journal 31 due to the collapse of the counterweight 33 tends to be larger in the upstream part in the rotation direction than in the downstream part at the extended position of the counterweight 33. In detail, the largest load is applied near the upstream end in the rotation direction, and the load tends to gradually decrease toward the downstream end in the rotation direction. Therefore, the high load area PA has a teardrop-shaped distribution with the load center of gravity eccentric to the upstream side in the rotation direction. In accordance with the load tendency of the high load area PA, the axial profile of the recess 5 also has a teardrop-shaped shape that is wider on the upstream side in the rotation direction. This can reliably prevent the crank journal 31 from contacting the journal metal 43.

[0063] The recess depth of the recess 5 is also set to follow the load tendency of the high load area PA. That is, the deeper the recess 5 is set in the portion of the crank journal 31 to which a larger load is applied. FIG. 10 is a side view of the crank journal 31 showing the depth profile of the recess 5 along the rotation direction. This profile is the depth profile of the recess 5 at the F-side end 31f or the R-side end 31r. Note that the size of this profile in the depth direction is also exaggerated.

[0064] The recess 5 has an upstream inclined portion 53 on the upstream side in the rotation direction and a downstream inclined portion 54 on the downstream side in the rotation direction in the shape of a recess. The upstream inclined portion 53 has an inclined surface that deepens at a first inclination L1 in a direction from the upstream end of the circumferential width of the recess 5 in the rotation direction toward the central portion LC in the rotation direction. The deepest portion MD of the recess 5 is located upstream of the central portion LC in the rotation direction. The downstream inclined portion 54 has an inclined surface that becomes shallow at a second inclination L2 from the deepest portion MD toward the downstream end in the rotation direction. The relationship between the first inclination L1 and the second inclination L2 is L1>L2 when the inclination directions of both are aligned. That is, the recess 5 has a shape that becomes steeply deeper on the upstream side in the rotation direction and gradually shallower downstream of the deepest portion MD. For example, when comparing L1 and L2 in terms of the angle formed with a tangent to the circumferential surface of the crank journal 31, L1 can be set to about 1.2 to 3 times L2.

[0065] According to the analysis by the inventors, the energy loss due to the direct contact between the crank journal 31 and the journal metal 43 accompanying the deformation of the crankshaft 3 shows a characteristic that rises relatively steeply in the first half of the contact period and drops relatively gently in the second half of the contact period. The direct contact causes wear of the crank journal 31, so that the amount of wear is large in the first half of the contact period and small in the second half of the contact period. Therefore, by providing the crank journal 31 with the recess 5 having a depth profile with the first gradient L1 and the second gradient L2, a contact wear avoidance measure that is in line with the above energy loss characteristic can be implemented.

[0066] 9, the rotational depth profile of the recess 5 is related to the axial profile shown in Fig. 9 in that the longer the axial width of the recess 5, the deeper the axial end (F-side end 31f or R-side end 31r) of the recess 5. Note that the axial depth profile of the recess 5 is similar to the basic example shown in Fig. 6 in that the depth gradually increases from the axial center (the teardrop-shaped edge) toward the F-side end 31f or R-side end 31r.

[0067] That is, the depth profile of the recess 5 is set so that the recess 5 is relatively deep where the load is large and relatively shallow where the load is small, according to the load distribution of the high load portion PA. According to this embodiment, the portion of the recess 5 that has a long axial width and a deep recess is disposed in the portion of the crank journal 31 that receives the most collapsing load from the counterweight 33. Therefore, wear of the crank journal 31 due to contact with the journal metal 43 can be reliably avoided.

[0068] [Variations] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment, and can take the following modified embodiments, for example.

[0069] (1) In the above embodiment, the crankshaft 3 having the full counter-type counterweight 33 is exemplified. The crankshaft 3 may be of a half counter-type. When the crankshaft 3 shown in FIG. 7 is modified to a half counter-type, for example, the third, fifth, and seventh counterweights 33C, 33E, and 33G are omitted. In such a half counter-type crankshaft 3, the first to fifth crank journals 31A to 31E may also be provided with recesses 5 at the same locations as those in FIG. 7. In addition, in the locations where the counterweights are omitted, the axial width, circumferential width, and recess depth of the recesses 5 may be set small, or the formation of the recesses 5 itself may be omitted.

[0070] (2) In the above embodiment, the crankshaft 3 corresponding to the in-line four-cylinder engine 1 has been exemplified. Fig. 11 is a side view showing a full counter type crankshaft 3A corresponding to the in-line six-cylinder engine 1. The concept of arranging the recesses 5 in the in-line six-cylinder crankshaft 3A is the same as that of the above-mentioned crankshaft 3. The recesses 5 are formed in the portions of the crank journals 31 corresponding to the positions at which the counterweights 33 extend. Note that the recesses 5 indicated by dotted lines in Fig. 11 are arranged on the rear side of the exposed portion of the crank journals 31.

[0071] (3) In the above embodiment, the recess 5 is gradually deeper from the axial center of the crank journal 31 toward the axial end (F-side end 31f or R-side end 31r). Various modified embodiments of the recess 5 are possible as long as the recess 5 is deeper at the axial end than at the axial center of the crank journal 31. FIGS. 12(A) to 12(C) show modified recesses 5A, 5B, and 5C.

[0072] FIG. 12(A) is a schematic cross-sectional view of the second crank journal 31B showing a recess 5A having a stepped recess shape. The recess 5A has a recess shape in which horizontal portions 55 with no inclination and downwardly inclined portions 56 inclined downward are alternately connected, and the recess depth is deeper at the axial end portion than at the axial center portion of the second crank journal 31B. FIG. 12(B) shows a recess 5B consisting of one horizontal portion 57 and one downward inclined portion 58. The downward inclined portion 58 is disposed at the axial center portion of the second crank journal 31B, and the horizontal portion 57 extends from the deepest end of the downward inclined portion 58 to the axial end portion. FIG. 12(C) shows a recess 5C having an uneven inclined portion 59. The uneven inclined portion 59 is an inclined portion that becomes deeper overall from the axial center portion to the axial end portion of the second crank journal 31B while repeatedly appearing and disappearing. Even such recesses 5A, 5B, and 5C have the same effect as the recess 5 described above. [Explanation of symbols]

[0073] 1. Engine (internal combustion engine) 10 Engine body 2-cylinder 21 Piston 22 Connecting rod 3. Crankshaft 31, 31A~31E Crank journal 31f F side end (one end in the axial direction) 31b R side end (other end in the axial direction) 33 Counterweight 33A First counterweight (end counterweight) 33E 4th counterweight (end counterweight) 4 Main bearing 43 Journal metal (bearing material) 5, 5A, 5B, 5C recess 51 Bulge 52 Gentle bend section 53 Upstream slope 54 Downstream slope 55 Horizontal section 56 Downhill section 57 Horizontal section 58 Downhill section 59 Uneven slope

Claims

1. An engine body including a cylinder and a piston reciprocally slidably accommodated in the cylinder, a crankshaft that converts the reciprocating motion of the piston into a rotational motion, and a bearing member that pivotally supports the crankshaft via lubricating oil. The crankshaft includes a crank journal pivotally supported by the bearing member and a counterweight extending radially outward from an axial end of the crank journal. The crank journal is formed at a portion corresponding to the extending position of the counterweight and has a recess that is recessed radially inward. In an internal combustion engine in which the recess is deeper at the axial end than at the axially central side of the crank journal, the recess has a predetermined axial width and circumferential width in the axial and circumferential directions of the crank journal. An internal combustion engine in which the axial width of the recess is wider on the upstream side in the rotational direction of the crankshaft than on the downstream side.

2. In the internal combustion engine according to Claim 1, the recess is a recess that gradually becomes deeper from the axially central side of the crank journal toward the axial end.

3. In the internal combustion engine according to Claim 1, in a planar shape obtained by developing the crank journal in the circumferential direction, the shape of the recess in plan view is a bulging portion that bulges axially inward in a steep curve near the upstream end in the rotational direction of the circumferential width, and a gentle curved portion that reaches the downstream end in the rotational direction of the circumferential width from the bulging portion in a gentle curve. An internal combustion engine having such a shape.

4. In the internal combustion engine according to Claim 3, the deeper the depth at the axial end of the recess, the longer the axial width of the recess.

5. An engine body including a cylinder and a piston reciprocally slidably accommodated in the cylinder, a crankshaft that converts the reciprocating motion of the piston into a rotational motion, and a bearing member that pivotally supports the crankshaft via lubricating oil. The crankshaft includes a crank journal pivotally supported by the bearing member and a counterweight extending radially outward from an axial end of the crank journal. The crank journal is formed at a portion corresponding to the extending position of the counterweight and has a recess that is recessed radially inward. In an internal combustion engine in which the recess is deeper at the axial end than at the axially central side of the crank journal, The concave portion has a predetermined axial width and circumferential width in the axial direction and circumferential direction of the crank journal, The depth of the concave portion has a profile that becomes deeper with a first inclination from the upstream end in the rotational direction of the circumferential width toward the downstream side, a deepest portion is formed upstream of the central portion in the rotational direction, and becomes shallower with a second inclination from the deepest portion toward the downstream end in the rotational direction, The first inclination is larger than the second inclination, an internal combustion engine.

6. In the internal combustion engine according to any one of Claims 1 to 5, The engine body has a plurality of cylinders arranged in a row in a predetermined arrangement direction, The crank journal located between two cylinders, A first counterweight extending radially outward from one end side end in the axial direction, A second counterweight extending radially outward from the other end side end in the axial direction at a position facing the first counterweight in the circumferential direction or at the same position in the circumferential direction, A first concave portion formed in a portion corresponding to the extending position of the first counterweight and recessed from the one end side end in the axial direction toward the center in the axial direction, A second concave portion formed in a portion corresponding to the extending position of the second counterweight and recessed from the other end side end in the axial direction toward the center in the axial direction, An internal combustion engine comprising.

7. In the internal combustion engine according to any one of Claims 1 to 5, The engine body has a plurality of cylinders arranged in a row in a predetermined arrangement direction, The crank journal located axially outside the cylinder on one end side or the other end side in the arrangement direction, An end counterweight extending radially outward from the inner end in the axial direction, An arrangement end concave portion formed in a portion corresponding to the extending position of the end counterweight and recessed from the inner end toward the outside in the axial direction, An internal combustion engine comprising.

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