internal combustion engine

Abstract

To provide an internal combustion engine for executing an Atkinson cycle, which can ensure its strength and reduce its weight for power transmission of an eccentric shaft.SOLUTION: In an internal combustion engine comprising an internal gear 60 and an eccentric shaft 30 and executing an Atkinson cycle, the eccentric shaft 30 has a big end connection part 40 that rotatably connects a big end part 16a of a connecting rod 16, and an external gear part 50 that rotates in mesh with the internal gear 60. The external gear part 50 has a hole part 53 whose area gradually increases from an eccentric side R where the big-end connection part 40 is eccentric relative to the external gear part 50, so that the weight of the eccentric shaft is reduced while maintaining strength for power transmission.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an internal combustion engine that operates in the Atkinson cycle, which improves thermal efficiency by making the expansion ratio larger than the compression ratio. [Background technology]

[0002] Efforts aimed at mitigating or reducing the impact of climate change have been ongoing for some time, and research and development into reducing carbon dioxide emissions has been carried out to achieve this. In the field of technology related to reducing carbon dioxide emissions, various internal combustion engines have been proposed that operate in the Atkinson cycle to improve the thermal efficiency by making the expansion ratio larger than the compression ratio in order to improve the combustion efficiency of the internal combustion engine (see, for example, Patent Document 1).

[0003] For example, as disclosed in Prior Art Document 1, there is an internal combustion engine that operates in the Atkinson cycle, in which an eccentric shaft is interposed between the crankpin and the big end of the connecting rod, an internal gear held in the crankcase meshes with an external gear portion formed integrally with the big end connecting portion of this eccentric shaft, and the external gear portion rotates in a cycle of three or more odd-numbered revolutions for every two revolutions of the crankshaft, and the position of the piston at bottom dead center on the expansion stroke is higher than the position of the piston at bottom dead center on the compression stroke. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-241740 Summary of the Invention [Problem to be solved by the invention]

[0005] In such internal combustion engines, the external gear portion of the eccentric shaft is disposed inside the internal gear and rotates in mesh with it, while the external gear portion is disposed outside the big end connector, making the eccentric shaft itself relatively large. Furthermore, the big end connector of the eccentric shaft must be strong enough to transmit power from the crankshaft to the connecting rod, which increases the weight of the eccentric shaft itself. The high-speed rotation of the area around the big end of the connecting rod increases vibration, and the centrifugal force of the eccentric shaft itself generates a load between the eccentric shaft and the crankpin, which increases frictional resistance in the bearings. Therefore, the eccentric shaft must be lightweight while also being strong enough to transmit power. Furthermore, because the eccentric shaft rotates relative to the crank weight, axial rotational resistance is also an issue.

[0006] The present invention has been made in consideration of the above circumstances, and has as its object to provide an internal combustion engine that implements the Atkinson cycle, which is lightweight while ensuring the strength required for power transmission of the eccentric shaft, and which improves combustion efficiency. [Means for solving the problem]

[0007] The present invention provides an internal combustion engine that is equipped with an internal gear and an eccentric shaft and operates using an Atkinson cycle, the eccentric shaft has a big end coupling portion that rotatably couples a big end of a connecting rod, and an external gear portion that rotates while meshing with the internal gear, The internal combustion engine is characterized in that the external gear portion has a hole portion whose area gradually increases from the eccentric side where the big end connecting portion is eccentric with respect to the external gear portion.

[0008] Since the present invention is configured as described above, it is possible to achieve a reduction in weight while ensuring the strength required for power transmission of the eccentric shaft, and to improve combustion efficiency.

[0009] In the above configuration, one side surface of the external gear portion has a low surface roughness region in a contact surface with the big end of the connecting rod, the low surface roughness region being finer than other regions of the one side surface of the external gear portion, All of the plurality of holes may be configured to partially overlap the fine surface roughness region.

[0010] According to the above configuration, lubricating oil flows from the non-contact surface of one side of the external gear portion with the big end of the connecting rod to the contact surface between one side of the external gear portion and the big end of the connecting rod, thereby achieving a lubricating effect between the external gear portion and the big end.

[0011] In the above configuration, the big end connecting portion of the eccentric shaft has a crankpin insertion hole, through which a crankpin is inserted, coaxially with the external gear portion, A first recessed portion and a second recessed portion may be formed on both sides of the big end connecting portion in a region opposite to the eccentric portion between the crankpin insertion hole and the big end connecting portion.

[0012] According to the above configuration, the weight of the big end connecting portion is reduced, and the weight of the eccentric shaft can be further reduced.

[0013] In the above configuration, an outer edge of the first hollowed-out portion may form an outer peripheral wall portion of the big end connecting portion.

[0014] According to the above-described configuration, even if the eccentric shaft is light in weight, it is possible to ensure sufficient strength corresponding to the load even when the eccentric shaft receives the load from the piston.

[0015] In the above-described configuration, the first recessed portion may form a rib portion that extends radially toward an outer periphery of the big end connecting portion.

[0016] According to the above configuration, even if a load from the piston is received, a sufficient strength corresponding to the load can be ensured.

[0017] In the above-described configuration, the first recessed portion may be located between the rib portions and may have a through-hole that penetrates to a rear surface of the big end connecting portion.

[0018] According to the above-described configuration, the weight of the eccentric shaft can be further reduced, and the lubricating oil can flow on both surfaces of the eccentric shaft, thereby improving the lubrication.

[0019] In the above configuration, a washer may be disposed between one side surface of the external gear portion of the eccentric shaft and the big end of the connecting rod.

[0020] According to the above configuration, the relative speed between the big end of the connecting rod and the eccentric shaft can be reduced by the washer, thereby reducing frictional resistance. [Effects of the Invention]

[0021] The present invention can reduce the weight of an internal combustion engine that operates using an Atkinson cycle and is equipped with an internal gear and an eccentric shaft, while ensuring the strength of the eccentric shaft for power transmission, and improve combustion efficiency. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram showing an internal structure of a power unit of an internal combustion engine according to an embodiment of the present invention. [Figure 2] 2 is a cross-sectional view taken along the line II-II in FIG. 1 at the compression top dead center. [Figure 3] FIG. 2 is a left side view of the integrated eccentric shaft and external gear portion as viewed from the left side. [Figure 4] FIG. 2 is a right side view of the integrated eccentric shaft and external gear portion as viewed from the right side. [Figure 5] FIG. 4 is a view taken along the line VV in FIG. 3. [Figure 6] FIG. 6 is a view taken along the line VI-VI in FIG. [Figure 7] FIG. 7 is a view taken along the line VII-VII in FIG. 3. [Figure 8] FIG. [Figure 9] FIG. 2 is an enlarged view of a main part of FIG. 1, showing the flow of lubricating oil. [Figure 10]FIG. 2 is a diagram showing the trajectory of the center of the big end of a connecting rod and the trajectory of the center of a crank pin. [Figure 11] FIG. 4 is a diagram showing the relationship between crank rotation angle and piston displacement. DETAILED DESCRIPTION OF THE INVENTION

[0023] An embodiment of the present invention will be described below with reference to the drawings. In the description, directions such as front, rear, left, right, and up and down are the same as directions relative to the vehicle body unless otherwise specified, and the rotation direction of the crankshaft of the internal combustion engine is clockwise as viewed from the right side of the vehicle body. Also, the symbol FR in each drawing indicates the front of the vehicle body, and the symbol LH indicates the left side of the vehicle body.

[0024] 1 is a diagram showing the internal structure of a power unit P equipped with an internal combustion engine 10 according to a first embodiment of the present invention. This power unit P is a power unit to be mounted on a motorcycle, and is equipped with an internal combustion engine 10. This power unit P is not limited to motorcycles, and may be a power unit to be mounted on various saddle-ride vehicles, including three-wheeled and four-wheeled types. 1 shows an internal combustion engine 10 that is a horizontal engine in which a cylinder portion (not shown) protrudes horizontally forward from a crankcase 11. Although this embodiment is applied to a horizontal engine, it is also possible to apply it to an engine in which the cylinder portion protrudes upward.

[0025] 1, the symbol L indicates a crank axis that passes through the axis of the crankshaft 20 supported in the crankcase 11. The symbol C1 indicates a crankpin center that passes through the axis of the crankpin 24. The crank axis L and the axis of the crankpin center C1 are parallel to each other.

[0026] The internal combustion engine 10 includes a crankshaft 20. The crankshaft 20 is made up of a right crankshaft 20R and a left crankshaft 20L. The right crankshaft 20R and the left crankshaft 20L are connected to each other via a crank web 22. 24 are connected by The crankshaft 20 is rotatably supported by the crankcase 11 via bearings 18, 18 at the crank journal portion 21. Referring also to Figure 8, the right crankshaft 20R and the left crankshaft 20L are provided with crank weights 23 facing the crank webs 22 across the crank axis L.

[0027] Referring also to FIG. 2, the internal combustion engine 10 includes a connecting rod 16 that transmits the power of a piston 15 that slides in a cylinder (not shown) to a crankshaft 20. The connecting rod 16 has a small end 16 b at one end thereof rotatably connected to the piston 15 and a large end 16 a at the other end thereof rotatably connected to the eccentric shaft 30 . As the mixture of intake air and fuel in the cylinder burns, the power generated by the piston 15 sliding up and down inside the cylinder is transmitted to the crankshaft 20 via the connecting rod 16, then to the primary gear 28 supported by the crankshaft 20, and output to the output shaft (not shown) via a driven gear (not shown) that meshes with the primary gear 28.

[0028] The eccentric shaft 30, which is disposed between the big end 16a of the connecting rod 16 and the crankshaft 20, includes a roughly cylindrical big end coupling portion 40 that is coupled to the big end 16a, and an external gear portion 50 that has a larger diameter than the big end coupling portion 40, the big end coupling portion 40 and the external gear portion 50 being integral with each other. The external gear portion 50 is formed on one side surface of the big end coupling portion 40 so as to protrude radially. 2, the external gear portion 50 of the eccentric shaft 30 meshes with a ring-shaped internal gear 60 fixed to the crankcase 11, and moves while rotating along the inside of the internal gear 60. In the internal combustion engine of this embodiment, the internal gear 60 is fixed to the crankcase 11, but it may be fixed to any member of the internal combustion engine 10 other than the crankcase 11 so as not to move.

[0029] 3 to 6, the eccentric shaft 30 has a crank pin passing through the big end connecting portion 40 and the external gear portion 50. 24The eccentric shaft 30 has a crankpin insertion hole 41 through which the crankpin 24 is inserted. A plurality of needle bearings 26 are disposed between the crankpin insertion hole 41 of the eccentric shaft 30 and the crankpin 24. The center of rotation of the external gear portion 50 is coaxial with the crankpin insertion hole 41, i.e., the crankpin center C1 of the crankpin 24, and the center of rotation of the big end coupling portion 40, i.e., the connecting rod big end center C2, is eccentric to the crankpin center C1.

[0030] The number of teeth of the internal gear 60 is set to 72, and the number of teeth of the external gear portion 50 is set to 48. In other words, the ratio of the number of teeth of the internal gear 60 to that of the external gear portion 50 is set to 3:2. Therefore, while the crankshaft 20 rotates twice, the external gear portion 50 rotates three times. The internal gear 60 is arranged so that, at the exhaust bottom dead center, the eccentric side R, on the side where the connecting rod big end center C2 is most eccentric with respect to the crank pin center C1, is positioned below. Intake bottom dead center The cylinder head is fixed to the crankcase 11 so that it is on the upper side at top dead center of the compression stroke, on the rear side at top dead center of the intake stroke, and on the front side at top dead center of the intake stroke.

[0031] In Figure 10, the trajectory of the crank pin center C1 is shown by a solid line and the trajectory of the connecting rod big end center C2 is shown by a dashed line as the crank angle changes from 0 to 720 degrees. Figure 11 also shows the piston displacement from top dead center as the crank angle changes from 0 to 720 degrees. While the crankshaft 20 rotates twice, the external gear portion 50 rotates eccentrically three times, and the internal gear and the eccentric shaft are arranged to have the relationship described above. As a result, as shown in FIG. 11, the bottom dead center position on the intake stroke is lower than the bottom dead center position on the exhaust stroke, and the internal combustion engine 10 operates in the Atkinson cycle. In the internal combustion engine of this embodiment, the external gear portion 50 is set to rotate three times for every two rotations of the crankshaft 20, but it is acceptable as long as the external gear portion 50 rotates an odd number of times, three or more times, for every two rotations of the crankshaft 20.

[0032] The eccentric shaft 30 will be described with reference to Figures 3 to 7. As shown in Figures 3 and 4, a base 51 of the external gear portion 50 of the eccentric shaft 30 is provided with a plurality of circular holes 53 that penetrate the base 51. The plurality of holes 53 have the smallest diameter closest to the eccentric side R on the side where the big end connecting portion 40 is most eccentric with respect to the external gear portion 50, and the diameter gradually increases with increasing distance, i.e., the opening area gradually increases. In this embodiment, the holes 53 are formed in a perfect circle, but they are not limited to a perfect circle and may be formed so as to have a gradually increasing area.

[0033] 3, of the base portion 51 of the external gear part 50, on one side surface 51a on the side from which the big end coupling part 40 protrudes, a region surrounding the big end coupling part 40 has a lower surface roughness than other regions and is subjected to, for example, surface polishing to reduce the roughness, thereby forming a low-surface-roughness region 54. In this way, friction on the surface that comes into contact with the big end 16a of the connecting rod 16 is reduced. Furthermore, all of the hole portions 53 partially overlap with the low surface roughness regions 54, and lubricating oil flows from the non-contact surface of the side surface 51 of the external gear portion 50 with the big end 16a of the connecting rod 16 to the contact surface between the side surface 51 of the external gear portion 50 and the big end 16a of the connecting rod 16, improving lubrication between the external gear portion and the big end. 1 and 9, a washer 70 is disposed between the big end coupling portion 40 and the big end 16a of the connecting rod 16 to further reduce friction between the eccentric shaft 30 and the connecting rod 16.

[0034] 3 to 6, the eccentric side R between the crank pin insertion hole 41 of the big end connecting portion 40 and the big end connecting portion 40 is same In the side region, a first cutout portion 42 and a second cutout portion 47 are formed on both sides.

[0035] 3 and 6, multiple first lightening holes 42 are provided at a predetermined depth in a region on the eccentric side R of one side surface of the big end coupling part 40. The outer edge of each of the first lightening holes 42 forms part of an outer peripheral wall 43 of the big end coupling part 40 to which the big end 16a of the connecting rod 16 is rotatably coupled. The inner edge of each of the first lightening holes 42 forms part of the crankpin insertion hole 41 through which the crankpin 24 is inserted, i.e., part of an inner peripheral wall 44 of the big end coupling part 40. Furthermore, radial ribs 45 are formed between adjacent first recessed portions 42 , and the ribs 45 connect the outer peripheral wall portion 43 and the inner peripheral wall portion 44 of the big end connecting portion 40 . The first hollowed-out portion 42 is provided to reduce weight, and even after hollowing out, the outer peripheral wall portion 43 and the inner peripheral wall portion 44 are kept sufficiently thick. Radial rib portions 45 are provided to connect the outer peripheral wall portion 43 and the inner peripheral wall portion 44, ensuring the strength to withstand the load from the connecting rod 16.

[0036] Referring also to Figure 5, holes 40a are drilled to a predetermined depth but do not penetrate all the way through on both sides of the multiple first lightening holes 42 provided in the big end connecting portion 40, thereby reducing the weight while avoiding a decrease in the strength of the base portion 51 of the external gear portion 50.

[0037] As shown in Figures 4 and 6, a recess 55 is provided on the other side surface 51b of the base portion 51 of the external gear portion 50 at a predetermined depth from the surface of the other side surface 51b so as to surround the periphery of the crankpin insertion hole 41, thereby ensuring the strength of the external gear portion 50 and reducing its weight. 6, a crescent-shaped second lightening portion 47 is provided on the other side surface near the eccentric side R along the crankpin insertion hole 41 so as to be deeper from the bottom surface of the recess 55. The second lightening portion 47 achieves a reduction in weight while ensuring the strength of the big end connecting portion 40. The first cutout portion 42 and the second cutout portion 47 are located between adjacent rib portions 45 and are connected to each other by a through hole 46 that penetrates to the back surface of the big end connecting portion 40, allowing lubricating oil to flow between the two side surfaces of the eccentric shaft 30.

[0038] A first hole 24a is drilled from one side end of the crankpin 24 to a length slightly shorter than the length of the crankpin 24, and second hole portions 24b, which have a smaller diameter and shorter length than the first hole 24a, are drilled from both left and right ends, thereby reducing the weight of the crankpin 24.

[0039] 9 is an enlarged view of the portion of FIG. 1 where the crank web 22 and the big end 16a of the connecting rod 16 are connected by the crankpin 24, with the flow of lubricating oil indicated by arrows. An oil passage 11a is provided in the crankcase 11, which supports the right crankshaft 20R via a bearing 18, and lubricating oil is supplied from an oil supply mechanism (not shown) into a first hole 24a drilled in the crankpin 24. The lubricating oil flows from the first hole 24a through a through-hole 24c formed to communicate with the surface of the crankpin 24, onto the surface of the crankpin 24, and is supplied to a needle bearing 25 disposed between the crankpin 24 and the eccentric shaft 30, thereby reducing friction between the crankpin 24 and the eccentric shaft 30.

[0040] 5 and 6, a groove 48 is formed in the crankpin insertion hole 41 of the big end connecting portion 40 of the eccentric shaft 30. As shown in Figure 7, a through hole 49 that communicates with the surface of the eccentric shaft 30 is formed in the groove 48. The lubricating oil supplied to the groove 48 of the eccentric shaft 30 by the needle bearing 25 flows onto the surface of the eccentric shaft 30 and is supplied to the needle bearing 26 that is arranged between the big end connecting portion 40 and the big end 16a of the connecting rod 16, thereby reducing friction between the big end connecting portion 40 and the big end 16a of the connecting rod 16.

[0041] The internal combustion engine 10 according to one embodiment of the present invention is configured as described above, and therefore provides the following effects.

[0042] An internal combustion engine 10 according to one embodiment of the present invention includes an internal gear 60 and an eccentric shaft 30. The internal combustion engine operates under the Atkinson cycle. The eccentric shaft 30 has a big-end coupling portion 40 that rotatably couples the big end 16 a of the connecting rod 16, and an external gear portion 50 that rotates in mesh with the internal gear 60. The external gear portion 50 has a base 51 that has a hole 53 whose area gradually increases from the eccentric side R where the big-end coupling portion 40 is eccentric with respect to the external gear portion 50. This makes it possible to reduce the weight of the eccentric shaft 30 while ensuring the strength required for power transmission.

[0043] Furthermore, on one side surface 51a of the external gear portion 50, the contact surface with the big end 16a of the connecting rod 16 has a low surface roughness that is lower than the surface roughness in other areas of the one side surface 51a of the external gear portion 50. region 54, and all of the plurality of hole portions 53 partially overlap with the low surface roughness region 54, so that lubricating oil flows into the contact surface between the side surface 51 of the external gear portion 50 and the big end 16a of the connecting rod 16, thereby achieving a lubricating effect between the external gear portion 50 and the big end 16a.

[0044] Furthermore, the big end connecting portion 40 of the eccentric shaft 30 has a crankpin insertion hole 41, through which the crankpin 24 is inserted, that is coaxial with the external gear portion 50, and a first lightening portion 42 and a second lightening portion 47 are provided on both sides in an area of ​​the big end connecting portion 40 opposite the eccentric portion between the crankpin insertion hole 41 and the big end connecting portion 40. Therefore, the lightening of both side surfaces reduces the weight of the big end connecting portion 40, thereby further reducing the weight of the eccentric shaft 30 and, ultimately, enabling to reduce vibration and frictional resistance of the bearings due to centrifugal loads.

[0045] Furthermore, the outer edge of the first hollowed-out portion 42 constitutes the outer peripheral wall portion 43 of the big-end connecting portion 40. 、 Even if the eccentric shaft 30 is made lighter, it is possible to ensure sufficient strength corresponding to the load from the piston 15.

[0046] Furthermore, the first lightening portion 42 forms ribs 45 that radiate outward from the outer periphery of the big end connecting portion 40, and therefore, even when subjected to a load from the piston 15, sufficient strength corresponding to the load can be ensured.

[0047] Furthermore, the first lightening portion 42 is located between the rib portions 45 and has a through-hole 46 that penetrates to the back surface of the big-end connecting portion 40, thereby further reducing the weight of the eccentric shaft 30 and allowing the flow of lubricating oil on both surfaces of the eccentric shaft 30, thereby improving lubrication.

[0048] Furthermore, since a washer 70 is disposed between one side surface 50a of the external gear portion 50 of the eccentric shaft 30 and the big end 16a of the connecting rod 16, the relative speed between the big end 16a of the connecting rod 16 and the eccentric shaft 30 can be reduced by the washer 70, thereby reducing frictional resistance.

[0049] The first, second and third embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various design modifications are possible without departing from the spirit of the present invention. It goes without saying that the present invention includes vehicles, internal combustion engines and the like implemented in various forms within the spirit of the present invention. For the sake of convenience, the illustrated embodiment has been described as being arranged on the left and right, but other arrangements may also be included in the present invention as long as they fall within the scope of the gist of the invention. [Explanation of symbols]

[0050] 16...connecting rod, 16a...big end, 24...crank pin, 30...eccentric shaft, 40...big end connecting portion, 41...crank pin insertion hole, 42...first lightening portion, 43...outer peripheral wall portion, 45...rib portion, 46...through hole, 47...second lightening portion, 50...external gear portion, 51a...one side surface, 53...hole portion, 54...low surface roughness region, 60...internal gear, 70...washer, R...Eccentric side.

Claims

1. An eccentric shaft (30) is disposed between a big end (16a) of a connecting rod (16) and a crank pin (24) of a crankshaft (20), and the eccentric shaft (30) has a big end coupling portion (40) that rotatably couples the big end (16a) of the connecting rod (16) and an external gear portion (50) that rotates in mesh with an internal gear (60) held in a crankcase (11), In an internal combustion engine, the ratio of the number of teeth of the internal gear (60) and the external gear portion (50) is set so that the external gear portion (50) rotates in a cycle of an odd number of rotations, that is, three or more rotations, for every two rotations of the crankshaft (20), and the position of the piston at bottom dead center of the expansion stroke is located lower than the position of the piston at bottom dead center of the intake stroke, The external gear portion (50) has a hole portion (53) whose area gradually increases from the eccentric side (R) where the big end connecting portion (40) is eccentric with respect to the external gear portion (50), an internal combustion engine, characterized in that one side surface (51 a) of the external gear portion (50) has a low surface roughness region (54) that has a lower surface roughness than other regions of the one side surface (51 a) of the external gear portion (50) on a contact surface with the big end (16 a) of the connecting rod (16), and all of the plurality of hole portions (53) respectively partially overlap the low surface roughness region (54).

2. the big end connecting portion (40) of the eccentric shaft (30) has a crank pin insertion hole (41) coaxial with the external gear portion (50), through which a crank pin (24) is inserted; 2. The internal combustion engine according to claim 1, wherein the big end connecting portion (40) has a first lightening portion (42) and a second lightening portion (47) on both sides in a region on the same side as the eccentric side (R) on which the big end connecting portion (40) is eccentric with respect to the external gear portion (50).

3. 3. The internal combustion engine according to claim 2, wherein an outer edge of the first hollowed-out portion (42) forms an outer peripheral wall portion (43) of the big-end connecting portion (40).

4. 3. The internal combustion engine according to claim 2, wherein the first recessed portion (42) forms a rib portion (45) extending radially toward the outer periphery of the big end connecting portion (40).

5. 5. The internal combustion engine according to claim 4, wherein the first hollowed-out portion (42) has a through-hole (46) positioned between the rib portions (45) and penetrating to a rear surface of the big-end connecting portion (40).

6. 3. The internal combustion engine according to claim 2, wherein a washer is disposed between one side surface of the external gear portion of the eccentric shaft and the big end of the connecting rod.

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