JP6838296B2 - Internal combustion engine - Google Patents

Description

The present invention relates to a reciprocating internal combustion engine in which a piston reciprocates in a cylinder bore.

As is well known, a reciprocating internal combustion engine has a cylinder block, a cylinder head, and a piston. The cylinder block has at least one cylinder bore extending along the axis, and the cylinder head is fixed to one end of the cylinder block by a plurality of bolts. The piston is fitted to the cylinder bore so as to be able to reciprocate along the axis, and can slide with the wall surface of the cylinder bore at the skirt portion.

In order to improve the operating efficiency of the internal combustion engine by smoothly reciprocating the piston in the cylinder bore and reducing blow-by gas, the roundness of the cylinder bore is adjusted over the entire range in which the piston reciprocates. High is important. Therefore, in the present technical field, various proposals for increasing the roundness of the cylinder bore have been conventionally made.

For example, in Patent Document 1 below, the predicted value of the amount of deformation of the cylinder bore due to the cylinder head being fixed to one end of the cylinder block by a plurality of bolts is obtained, and when the predicted value is deformed, it becomes a perfect circle. The technique for processing the cylinder bore into the shape is described. According to this technique, the roundness of the cylinder bore after the cylinder head is fixed to one end of the cylinder block can be increased as compared with the case where the cylinder bore is machined without predicting the amount of deformation of the cylinder bore. it can.

International Publication No. 2011/152216

Generally, in an internal combustion engine, engine oil is supplied between the various movable members so that the friction between the members and the members in contact with the various movable members is reduced, so that the members are lubricated. .. For example, between the piston and the wall surface of the cylinder bore, engine oil is supplied from the crankroom side by flipping up by an oil jet or a crankshaft, so that the space between the piston and the wall surface of the cylinder bore is lubricated.

Even if the roundness of the cylinder bore is high, if the clearance between the skirt of the piston and the wall surface of the cylinder bore is small, the amount of engine oil that can exist between them is small, so the wall surface of the skirt and cylinder bore The degree of friction increases and the friction loss increases. On the contrary, when the clearance between the skirt and the wall surface of the cylinder bore is large, the amount of engine oil that can exist between them is large, so that the engine oil that moves to the combustion chamber as the piston reciprocates. The amount will also increase. The engine oil that has moved to the combustion chamber becomes a gas due to evaporation, combustion, etc. and is discharged to the outside of the internal combustion engine together with the exhaust gas. Therefore, if the amount of engine oil that moves to the combustion chamber increases, the consumption of engine oil increases. Become.

Therefore, the inventors of the present application examined the configuration of the following internal combustion engine.
The part of the minimum diameter of the cylinder bore in the movement range of the skirt part due to the reciprocating movement of the piston is within the axial range facing the skirt part when the piston is at bottom dead center, and when the piston is at bottom dead center. The radial clearance between the skirt portion and the minimum diameter portion in the above is the minimum value of the radial clearance between the skirt portion and the wall surface of the cylinder bore in the movement range of the skirt portion (hereinafter, "" It may be referred to as "the cylinder bore shape").

According to the cylinder bore shape described above, when the piston is at or near the bottom dead center, the amount of engine oil supplied from the crank chamber to the skirt portion and the wall surface of the cylinder bore is reduced, and the compression stroke of the piston is reduced. The amount of engine oil that adheres to and moves on the outer surface of the skirt portion in the radial direction can be reduced. Therefore, the amount of engine oil that moves to the combustion chamber via the skirt portion and the wall surface of the cylinder bore due to the reciprocating movement of the piston (hereinafter, may be referred to as "oil rise amount") is reduced, thereby reducing the amount of engine oil. The amount of consumption can be reduced.

Further, the clearance between the skirt portion and the wall surface of the cylinder bore becomes larger than the minimum value in the compression stroke of the piston, and is maintained at a value larger than the minimum value in the expansion stroke of the piston. Therefore, it is possible to avoid high friction between the skirt portion and the wall surface of the cylinder bore when the piston is in a stroke region other than the bottom dead center and its vicinity.

However, in the internal combustion engine having the cylinder bore shape described above, the tension of each piston ring of the first compression ring, the second compression ring, and the oil ring, which are sequentially attached to the land portion of the piston in the direction away from the top surface of the piston, is , No consideration has been made. That is, each of these piston rings has a tension toward the wall surface of the cylinder bore, and no study has been made on how to set the magnitude of the tension of each piston ring.

The piston ring has an oil control function and a function of ensuring the airtightness of the combustion chamber as the main functions. To ensure these functions, set the tension of the piston ring to an appropriate size. The greater the tension of the piston ring, the higher the airtightness of the combustion chamber and the less the consumption of engine oil. On the other hand, if the tension of the piston ring is too large, the friction loss becomes high.

The conventional oil ring, the first compression ring, and the second compression ring are preferably configured to have the following functions, and tensions corresponding to the functions are set for each piston ring. ..
Oil ring: Oil control function 1st compression ring: A function to ensure the airtightness of the combustion chamber and an auxiliary oil control function as needed 2nd compression ring: Auxiliary oil control function and land pressure Pressure regulation function The land pressure regulation function is the following function.
A function to adjust the pressure of the second land part and the pressure of the third land part (that is, the pressure of the space between the cylinder bore wall surface and the piston wall surface between the second compression ring and the oil ring) by each land volume and the ring.

In order to secure the functions required for the piston ring and further reduce the friction loss, it is not necessary to set the tension for the auxiliary function for the first compression ring and the second compression ring, and the tension is low. It is preferable to make it. That is, it is preferable to set the tension for each piston ring only for the function of each of the following piston rings to reduce the tension.
Oil ring: Oil control function 1st compression ring: Function to ensure the airtightness of the combustion chamber 2nd compression ring: Land pressure adjustment function

However, in an internal combustion engine having a conventional cylinder bore shape (for example, a cylinder bore shape having a large clearance between the skirt portion and the wall surface of the cylinder bore), the amount of oil rising is large, so at least the above-mentioned auxiliary oil is added to the second compression ring. Without the control function, it is unlikely that the oil control function of the piston ring is sufficient.

On the other hand, in the internal combustion engine having the cylinder bore shape described above, the amount of oil rising can be reduced, and thus the amount of oil control required for the piston ring can be reduced. Therefore, the tension of the oil ring can be made smaller, and the need for the first compression ring and the second compression ring to have an auxiliary oil control function can be almost eliminated. That is, the tension of the oil ring can be made smaller, and the tension of the auxiliary oil control function can be hardly set with respect to the first compression ring and the second compression ring. Further, if the airtightness of the combustion chamber is ensured only by the first compression ring, the second compression ring may be provided with a land pressure adjusting function as almost all the functions thereof.

Then, in order to reduce the tension of the piston ring by doing so and thereby further reduce the friction loss, the tension set for each piston ring in the internal combustion engine having the cylinder bore shape described above is increased. It is necessary to specify the size relationship.

The present invention has been made to address the above-mentioned problems. That is, one of the objects of the present invention is to reduce the consumption of engine oil while avoiding an increase in the degree of friction between the skirt portion of the piston and the wall surface of the cylinder bore, and friction. It is to provide an improved internal combustion engine so that the loss can be further reduced.

The present invention includes a cylinder block (12) having a cylinder bore (20) extending along an axis (22), a cylinder head (14) fixed to one end (12T) of the cylinder block (12), and the above. It has a piston (18) housed in the cylinder bore (20) that can reciprocate along an axis, and the pistons include a first compression ring (41), a second compression ring (43), and an oil ring ( In an internal combustion engine having a land portion (36) in which 45) are sequentially mounted in a direction away from the top surface of the piston (18), and a skirt portion (38) slidable with the wall surface of the cylinder bore (20). At the minimum diameter (Dcmin) portion (48) of the cylinder bore (20) in the movement range (Ls) of the skirt portion (38) accompanying the reciprocating movement of the piston (18), the piston is at the bottom dead point. Between the skirt portion (38) and the minimum diameter portion (48) when the piston (18) is at the bottom dead point, facing the lower end (38B) of the skirt portion (38). The radial clearance ((Dcmin-Ds) / 2) is the radial clearance between the skirt portion and the wall surface of the cylinder bore in the moving range (Ls) of the skirt portion ((Dc-Ds) / 2). The region above the minimum diameter portion (48) of the cylinder bore (20) has a diameter larger than the diameter of the minimum diameter portion (48), which is the minimum value of the above. The tension of the oil ring (45) is set to be larger than the tension of the first compression ring (41), and the tension of the first compression ring (41) is set to be larger than the tension of the second compression ring (43). It is an internal combustion engine.
The present invention includes a cylinder block (12) having a cylinder bore (20) extending along an axis (22), a cylinder head (14) fixed to one end (12T) of the cylinder block (12), and the above. It has a piston (18) housed in the cylinder bore (20) that can reciprocate along an axis, and the pistons include a first compression ring (41), a second compression ring (43), and an oil ring ( In an internal combustion engine having a land portion (36) in which 45) are sequentially mounted in a direction away from the top surface of the piston (18), and a skirt portion (38) slidable with the wall surface of the cylinder bore (20). At the minimum diameter (Dcmin) portion (48) of the cylinder bore (20) in the movement range (Ls) of the skirt portion (38) accompanying the reciprocating movement of the piston (18), the piston is at the bottom dead point. The skirt portion (38) and the minimum diameter portion (48) when the piston (18) is in the range (Rs) in the axial direction facing the skirt portion and the piston (18) is at the bottom dead point. The radial clearance between the skirt ((Dcmin-Ds) / 2) is the radial clearance between the skirt and the wall surface of the cylinder bore in the moving range (Ls) of the skirt ((Dc-Ds) / 2). The minimum value of 2), and the sliding portion surface pressure of the oil ring (45) obtained by dividing the tension of the oil ring (45) by the area of the sliding portion of the oil ring is the said. The tension of the first compression ring (41) is larger than the surface pressure of the sliding portion of the first compression ring (41), which is obtained by dividing the tension of the sliding portion of the first compression ring (41) by the area of the sliding portion of the first compression ring (41). The surface pressure of the sliding portion of the first compression ring (41) is obtained by dividing the tension of the second compression ring (43) by the area of the sliding portion of the second compression ring (43). The minimum diameter portion (48) is set to be larger than the sliding portion surface pressure of the second compression ring (43), and the portion (48) of the skirt portion (38) when the piston (18) is at the bottom dead point. The region facing the lower end (38B) and above the minimum diameter portion (48) of the cylinder bore (20) has a diameter larger than the diameter of the minimum diameter portion (48). It is an institution .

According to the present invention, a cylinder block (12) having at least one cylinder bore (20) extending along the axis (22) and a plurality of bolts (24) are fixed to one end (12T) of the cylinder block. An internal combustion engine (14) having a cylinder head (14) and a piston (18) housed in a cylinder bore reciprocating along an axis, the piston having a slidable skirt portion (38) with a wall surface of the cylinder bore. 10) is provided.

The portion (48) of the minimum diameter (Dcmin) of the cylinder bore (20) in the movement range (Ls) of the skirt portion (38) accompanying the reciprocating movement of the piston (18) is the skirt portion (48) when the piston is at bottom dead center. The radial clearance (48) between the skirt portion (38) and the smallest diameter portion (48) when the piston (18) is at bottom dead center within the axial range (Rs) facing 38). (Dcmin-Ds) / 2) is the radial clearance ((Dc-Ds) / 2) between the skirt portion (38) and the wall surface of the cylinder bore (20) in the movement range (Ls) of the skirt portion (38). ) Is the minimum value.

According to the above configuration, the portion having the minimum diameter of the cylinder bore in the movement range of the skirt portion due to the reciprocating movement of the piston faces the skirt portion when the piston is at bottom dead center. Further, the clearance between the skirt portion and the minimum diameter portion when the piston is at bottom dead center is the smallest of the clearances between the skirt portion and the wall surface of the cylinder bore in the movement range of the skirt portion.

Therefore, when the piston is at or near bottom dead center, the amount of engine oil supplied from the crank chamber between the skirt and the wall surface of the cylinder bore is reduced, and the radial outside of the skirt in the compression stroke of the piston. It is possible to reduce the amount of engine oil that adheres to and moves on the surface of the piston. Therefore, it is possible to reduce the amount of engine oil that moves to the combustion chamber via the skirt portion and the wall surface of the cylinder bore due to the reciprocating movement of the piston, thereby reducing the consumption of engine oil.

Further, according to the present invention, the tension of the oil ring (45) is larger than the tension of the first compression ring (41), and the tension of the first compression ring (41) is the tension of the second compression ring (43). ) Is set larger than the tension.

According to the above configuration, the tension of the oil ring can be made smaller, and it is almost unnecessary to set the tension of the auxiliary function for the first compression ring and the second compression ring. The tension of the piston ring can be further reduced. As a result, the friction loss can be further reduced.

FIG. 1 is a schematic configuration diagram showing a first embodiment of an internal combustion engine according to the present invention. FIG. 2A is a front view of the piston shown in FIG. 1 as viewed in a direction perpendicular to the axis. FIG. 2B is a bottom view of the piston shown in FIG. 1A as viewed along the axis from the side of the crankshaft. FIG. 3 is a front view showing the configuration of the piston ring. FIG. 4 is an enlarged partial vertical sectional view showing a first embodiment of an internal combustion engine according to the present invention. FIG. 5 is an enlarged vertical sectional view showing a main part of the first embodiment. FIG. 6 is an explanatory view showing various internal combustion engines in which the diameter of the cylinder bore differs depending on the upper part, the central part, and the lower part along the axis. FIG. 7 is an enlarged vertical sectional view showing a main part of the third embodiment of the internal combustion engine according to the present invention. FIG. 8 is an enlarged vertical sectional view showing a main part of the fourth embodiment of the internal combustion engine according to the present invention. FIG. 9 is an enlarged vertical sectional view showing a main part of the fifth embodiment of the internal combustion engine according to the present invention. FIG. 10 is an enlarged vertical sectional view showing a main part of the sixth embodiment of the internal combustion engine according to the present invention.

Hereinafter, the internal combustion engine according to each embodiment of the present invention will be described with reference to the drawings. In all the drawings of the embodiment, the same or corresponding parts are designated by the same reference numerals. The embodiments described below are suitable specific examples of the present invention, and the contents of the present invention are not limited to these embodiments.

<First Embodiment>
(Constitution)
In FIG. 1, an internal combustion engine according to a first embodiment of the present invention (hereinafter, may be referred to as a “first internal combustion engine”) is indicated by reference numeral 10. The first internal combustion engine 10 has a cylinder block 12, a cylinder head 14, a crank cap 16, and a piston 18. The cylinder block 12 has cylinder bores 20 having a number of cylinders arranged in a direction perpendicular to the paper surface of FIG. 1, and each cylinder bore 20 extends along an axis 22. The cylinder block 12 and the cylinder head 14 are provided with a cooling water passage, but the illustration of the cooling water passage is omitted. The cylinder head 14 is fixed to one end 12T of the cylinder block 12 by bolts 24 at a plurality of positions spaced apart from each other in the direction perpendicular to the paper surface of FIG. 1 on both sides of the cylinder bore 20 as seen in FIG. In the following description, the upper end of each member will be referred to as the "upper end" as seen in FIG. 1 and the like, and the lower other end of each member will be referred to as the "lower end" as seen in FIG. 1 and the like. Further, the upper side and the upper side as seen in FIG. 1 and the like are simply described as "upper side" and "upper side", respectively, and the lower side and the lower side as seen in FIG. 1 and the like are simply described as "lower side" and "lower side", respectively.

The crank cap 16 is fixed to the lower end 12B of the crankcase portion 12C of the cylinder block 12 by a plurality of bolts (not shown in FIG. 1). The crankcase portion 12C and the crank cap 16 cooperate with each other to rotatably support the crankshaft 28 around the rotation axis 26 perpendicular to the axis 22, and form the crank chamber 30. The piston 18 is fitted to the cylinder bore 20 so as to be reciprocating along the axis 22, and cooperates with the cylinder block 12 and the cylinder head 14 to form the combustion chamber 21. As is well known, the reciprocating motion of the piston 18 is transmitted to the crankshaft 28 by a piston pin and a connecting rod (not shown in FIG. 1), and is converted into a rotational motion of the crankshaft 28 by the cooperation of these members. ..

The lower portion of the crank cap 16 forms an oil pan 34 for storing the engine oil 32. The engine oil 32 is bounced up by the crankshaft 28 or by a forced lubrication device not shown in FIG. 1, as shown simply by the arrow A, from the crank chamber 30 to the lower end of the cylinder bore 20 and the piston. It is supplied as an oil jet to the inside of 18. The engine oil 32 supplied to the lower end of the cylinder bore 20 lubricates the members by interposing between the cylinder block 12 and the piston 18. The engine oil 32 is lubricated by being circulated and supplied to other moving parts such as a camshaft, an intake valve and an exhaust valve by a forced lubrication device.

A part of the engine oil 32 that lubricates between the cylinder block 12 and the piston 18 moves to the combustion chamber 21 as the piston 18 reciprocates. The engine oil 32 that has moved to the combustion chamber 21 becomes a gas by evaporation and combustion, and is discharged to the outside of the first internal combustion engine 10 together with the exhaust gas. Therefore, in order to reduce the consumption of the engine oil 32 that lubricates between the cylinder block 12 and the piston 18, the engine oil 32 supplied from the crank chamber 30 and interposed between the cylinder block 12 and the piston 18 It is effective not to make the amount excessive.

As shown in FIGS. 2A and 2B, the piston 18 is integrated with a cylindrical portion 36 (also referred to as a “land portion”) extending along the axis 22 and the cylindrical portion 36. It has two skirt portions 38. The skirt portion 38 is radially spaced from the axis 22 on both sides of the axis 54 of the piston pin (not shown) when viewed from below along the axis 22, but at least in the vicinity of the cylindrical portion 36. It may extend all around the axis 22.

The cylindrical portion 36 has three ring grooves 40, 42, and 44 that receive the first compression ring 41, the second compression ring 43, and the oil ring 45 shown in FIG. 3, respectively. The three ring grooves 40, 42, and 44 are arranged downward from the top surface of the piston 18 in this order.

The ring groove 40 is fitted with a first compression ring 41, the ring groove 42 is fitted with a second compression ring 43, and the ring groove 44 is fitted with an oil ring 45. The first compression ring 41, the second compression ring 43, and the oil ring 45 mounted on the ring grooves 40, 42, and 44, respectively, are arranged downward from the top surface of the piston 18 in this order.

The first compression ring 41, the second compression ring 43, and the oil ring 45 have tension toward the wall surface of the cylinder bore 20. In the first internal combustion engine 10, the tension of the first compression ring 41, the tension of the second compression ring 43, and the magnitude of the tension of the oil ring 45 have a predetermined relationship. Specifically, in the first internal combustion engine, the tension of the oil ring 45 is set to be larger than the tension of the first compression ring 41, and the tension of the first compression ring 41 is set to be larger than the tension of the second compression ring 43. Has been done. That is, in the first internal combustion engine, the magnitudes of the tension of the first compression ring 41, the tension of the second compression ring 43, and the tension of the oil ring 45 are "tension of the oil ring 45> tension of the first compression ring 41> first. 2 It has a relationship of "tension of compression ring 43".

The skirt portion 38 has an arc plate shape centered on the axis 22 and extends along the axis 22. The skirt portion 38 has an outer diameter larger than that of the cylindrical portion 36, and the main portion 46 (cross-hatched region) of the outer surface of the skirt portion 38 that slides on the wall surface of the cylinder bore 20 is subjected to anti-friction treatment.

The cylinder bore 20 in the first internal combustion engine 10 has the form shown in FIGS. 4 and 5 when viewed in a radial cross section passing through the axis 22.

In FIGS. 4 and 5, the alternate long and short dash line and the alternate long and short dash line roughly indicate the positions of the piston 18 when they are at the bottom dead center and the top dead center, respectively. The range of the skirt portion 38 is shown schematically. The arrow Lpt indicates the movement range of the upper end of the piston 18 due to the reciprocating movement, and the arrow Ls indicates the moving range of the skirt portion 38 accompanying the reciprocating movement of the piston 18.

Further, in the illustrated situation in which the cylinder head 14 is fixed to one end 12T of the cylinder block 12 by a bolt 24, the cylinder bore 20 is substantially centered on the axis 22 at any position from the upper end 20T to the lower end 20B. It has a perfect circular cross-sectional shape. In FIGS. 4 and 5, the difference in diameter is exaggerated so as to clarify the magnitude relationship of the diameter at each portion of the cylinder bore 20. These things are the same in the figures shown in FIGS. 6 and below, which will be described later.

As shown in FIGS. 4 and 5, the cylinder bore 20 has a portion 48 having the smallest diameter in the movement range Ls of the skirt portion 38. The diameter Dc of the cylinder bore 20 above the minimum diameter portion 48 in the movement range Ls of the skirt portion 38, that is, on the side of the upper end 12T of the cylinder block 12, is larger than the minimum diameter Dcmin which is the diameter of the minimum diameter portion 48. large. Specifically, the actual difference between the maximum value of the diameter Dc of the cylinder bore 20 and the minimum diameter Dcmin is about 0.015 to 0.2 mm.

In particular, in the first internal combustion engine 10, the lower end 38B of the skirt portion 38 when the piston 18 is at the bottom dead center is located slightly above the lower end 20B of the cylinder bore 20. The minimum diameter portion 48 is provided at an axial position facing the lower end 38B of the skirt portion 38 when the piston 18 is at bottom dead center. Therefore, the portion 48 having the minimum diameter is located within the range Rs facing the region from the upper end 38T to the lower end 38B of the skirt portion 38 when the piston 18 is at the bottom dead center. The outer diameter Ds of the skirt portion 38 is substantially constant from the upper end 38T to the lower end 38B, as shown in FIGS. 4 and 5.

Therefore, the radial clearance (Dc—Ds) / 2 between the skirt portion 38 and the wall surface of the cylinder bore 20 is the smallest at the lower end 38B of the skirt portion 38, and is (Dcmin—Ds) / 2. The diameter Dc of the region from the position facing the lower end 38B to the lower end 20B of the cylinder bore 20 is a constant value of the minimum diameter Dcmin.

As seen in the cross sections of FIGS. 4 and 5, the wall surface of the cylinder bore 20 has a curved surface 20 in a region adjacent to the minimum diameter portion 48 and above the minimum diameter portion 48. That is, in the region, the curved surface 20C convex toward the axis 22 from the conical surface connecting the portion 48 having the minimum diameter and the portion having a diameter larger than the minimum diameter on the upper end 12T side of the portion having the minimum diameter. Is doing. Therefore, the inclination angle of the curved surface 20C with respect to the axis 22 is smaller as it is closer to the minimum diameter portion 48, that is, as it is downward.

Further, in the first internal combustion engine 10, the diameter Dc of the cylinder bore 20 in the region facing the skirt portion 38 when the piston 18 is at the top dead center is smaller as it is closer to the upper end 12T of the cylinder block 12. The diameter Dc of the cylinder bore 20 in the region above the upper end 38T of the skirt portion 38 when the piston 18 is at top dead center is constant, and this region forms the upper end small diameter portion 50 of the cylinder bore 20. The diameter Dc of the upper end small diameter portion 50 is preferably equal to or larger than the diameter Dcmin of the minimum diameter portion 48. The form of the region near the upper end 12T of the cylinder bore 20 described above is the same in other embodiments described later.

Next, as shown in FIG. 6, experimentally confirmed advantages and disadvantages of various internal combustion engines 10a to 10i in which the diameter Dc of the cylinder bore 20 differs depending on the upper part, the central part, and the lower part along the axis 22 will be described. To do. In FIG. 6 and Table 1 described later, “large” indicates a diameter set large so as to reduce friction between the piston 18 and the wall surface of the cylinder bore 20. "Small" indicates a diameter set as small as possible within a range where friction with the wall surface of the cylinder bore 20 is not excessive, and "Medium" indicates a diameter between "Large" and "Small". There is.

The diameter Dc of the cylinder bore 20 at the upper part, the central part and the lower part of the internal combustion engines 10a to 10i is shown in FIG. 6 and Table 1 below. The evaluation item "BBG / NV" of interests and disadvantages in Table 1 indicates blow-by gas and vibration noise, and the smaller the amount of blow-by gas and the lower the vibration noise, the better the performance. “Friction” indicates the friction between the piston 18 and the wall surface of the cylinder bore 20, and the lower the degree of friction, the better the performance. "Oil" indicates the amount of engine oil consumed, and the smaller the amount consumed, the better the performance. "Comprehensive" indicates a comprehensive evaluation based on the performance of the above evaluation items. Further, "◎" and "○" mean that the evaluations are "very good" and "good", respectively, and "Δ" and "×" mean that the evaluations are "normal" and "bad", respectively. Since the diameter Dc at the lower part of each internal combustion engine is "small", the evaluation of "oil" is "◯".

In the internal combustion engine 10a, the diameter Dc at the upper part and the central part is “large”. The performance of "friction" is ○, but the performance of "blow-by gas and vibration noise" is poor. The overall evaluation is ○. In the internal combustion engine 10b, the diameters Dc at the upper part and the central part are "large" and "medium", respectively. The performance of "friction" is Δ, and the performance of "blow-by gas and vibration noise" is poor. Therefore, the overall evaluation is Δ.

In the internal combustion engine 10c, the diameter Dc at the upper part is "large" and the diameter Dc at the central part is "small". Both the performance of "blow-by gas and vibration noise" and the performance of "friction" are poor. Therefore, the overall evaluation is Δ. In the internal combustion engine 10d, the diameter Dc at the upper part is "medium" and the diameter Dc at the central part is "large". Both the performance of "blow-by gas and vibration noise" and the performance of "friction" are Δ. Therefore, the overall evaluation is ○.

In the internal combustion engine 10e, the diameter Dc at the upper portion and the central portion is "medium", and in the internal combustion engine 10f, the diameter Dc at the upper portion is "medium" and the diameter Dc at the central portion is "small". In these internal combustion engines 10e and 10f, the performance of "blow-by gas and vibration noise" is Δ, but the performance of “friction” is poor. Therefore, the overall evaluation is Δ.

In the internal combustion engine 10h, the diameter Dc in the upper part is "small", the diameter Dc in the central part is "medium", and in the internal combustion engine 10i, the diameter Dc in the upper part and the central part is "small". In these internal combustion engines 10h and 10i, the performance of "blow-by gas and vibration noise" is good, but the performance of "friction" is poor. Therefore, the overall evaluation is ○.

Unlike the above internal combustion engine, in the internal combustion engine 10g configured according to the present invention, the diameter Dc at the upper portion is “small” and the diameter Dc at the central portion is “large”. In this internal combustion engine 10 g, the performance of "blow-by gas and vibration noise" is good, and the performance of "friction" is Δ. Therefore, the overall evaluation is ⊚, and 10 g of the internal combustion engine has superior performance to any of the above internal combustion engines.

As described above, the first internal combustion engine 10 has a structure belonging to the basic structure of the internal combustion engine 10g. Therefore, according to the first internal combustion engine 10, the engine oil 32 is maintained while ensuring good performance of blow-by gas and vibration noise and preventing excessive friction between the piston 18 and the wall surface of the cylinder bore 20. The consumption of the engine can be reduced. It should be noted that this basic action and effect can also be obtained in the second to sixth embodiments described later.

In particular, according to the first internal combustion engine 10, the minimum diameter portion 48 of the cylinder bore 20 faces the lower end 38B of the skirt portion 38 when the piston 18 is at bottom dead center, and is above the minimum diameter portion 48. The region has a diameter Dc greater than the diameter Dcmin of the smallest diameter portion 48. Therefore, the cylinder bore 20 and the skirt portion 38 when the piston 18 is near the bottom dead center, as compared with the structure in which the minimum diameter portion 48 extends above the lower end 38B (for example, the third embodiment described later). Friction between and can be reduced.

Further, a structure in which the minimum diameter portion 48 faces the region above the lower end 38B of the skirt portion 38, and the region below the minimum diameter portion 48 has a diameter Dc larger than the minimum diameter Dcmin (for example). Compared with the fourth embodiment described later), it is possible to reduce the amount of engine oil existing between the lower end 38B and its vicinity and the wall surface of the cylinder bore 20 when the piston 18 is at or near the bottom dead center. it can.

Further, in the first internal combustion engine 10, the tension of the oil ring 45 is set to be larger than the tension of the first compression ring 41, and the tension of the first compression ring 41 is set to be larger than the tension of the second compression ring 43. .. As a result, the tension of the oil ring 45 can be made smaller, and it is almost unnecessary to set the tension of the auxiliary function with respect to the first compression ring 41 and the second compression ring 43, and thus the piston. The tension of the ring can be reduced. As a result, the friction loss can be further reduced.

<Second Embodiment>
An internal combustion engine according to a second embodiment of the present invention (hereinafter, may be referred to as a “second internal combustion engine”) will be described.
This second internal combustion engine differs from the first internal combustion engine only in the following points.
-Instead of the relationship between the tension of the first compression ring, the tension of the second compression ring, and the tension of the oil ring, the sliding part surface pressure of the first compression ring, the sliding part surface pressure of the second compression ring, and Points that define the relationship between the magnitudes of the surface pressure of the sliding parts of the oil ring The following will focus on these differences.
The "sliding portion surface pressure of the first compression ring 41" is a surface pressure obtained by " tension of the first compression ring 41" ÷ "area of the sliding portion of the first compression ring 41" (the first). 2 The same applies to the sliding portion surface pressure of the compression ring 43 and the sliding portion surface pressure of the oil ring 45). The sliding portion of the first compression ring 41 means a sliding portion of the first compression ring 41 that slides on the wall surface of the cylinder bore 20 (sliding portion of the second compression ring 43 and the sliding portion of the oil ring 45). The same applies to the department.)

In the second internal combustion engine, the magnitudes of the sliding portion surface pressure of the first compression ring 41, the sliding portion surface pressure of the second compression ring 43, and the sliding portion surface pressure of the oil ring 45 are "sliding of the oil ring 45. There is a relationship of "moving part surface pressure> sliding part surface pressure of the first compression ring 41> sliding part surface pressure of the second compression ring 43".

Therefore, almost all of the functions of the second compression ring 43 are responsible for adjusting the land pressure, so that the surface pressure of the sliding portion of the second compression ring 43 can be minimized. Therefore, the surface pressure of the sliding portion of the second compression ring 43 can be minimized. As a result, the friction loss can be further reduced. The other effects are the same as those in the first embodiment.

<Third Embodiment>
An internal combustion engine according to a third embodiment of the present invention (hereinafter, may be referred to as a “third internal combustion engine”) will be described. This third internal combustion engine is different from the first internal combustion engine only in that the shape of the cylinder bore is different.
Hereinafter, this difference will be mainly described.

The third internal combustion engine is shown in FIG. In the third internal combustion engine, the minimum diameter portion 48 of the cylinder bore 20 is from a position facing the middle between the upper end 38T and the lower end 38B of the skirt portion 38 when the piston 18 is at bottom dead center to the lower end 20B of the cylinder bore 20. Is the range of. The wall surface of the cylinder bore 20 forms a cylindrical region having a constant diameter Dmin and extending along the axis 22 in the range of the minimum diameter portion. Therefore, the radial clearance (Dc—Ds) / 2 between the skirt portion 38 and the wall surface of the cylinder bore 20 is the smallest in the above range of the minimum diameter portion 48, and is (Dcmin—Ds) / 2.

The length of the curved surface 20C of the cylinder bore 20 in the direction along the axis 22 is smaller than the same length in the first internal combustion engine. The other points of the third internal combustion engine are configured in the same manner as the first internal combustion engine described above.

According to the third embodiment, the radial portion between the skirt portion 38 and the wall surface of the cylinder bore 20 is compared with the case where the minimum diameter portion 48 does not extend along the axis 22 at a constant diameter. The stroke range of the piston 18 where the clearance is maintained at the minimum value (Dcmin-Ds) / 2 can be increased. Therefore, as compared with the case of the first embodiment, not only when the piston 18 is at the bottom dead center but also when it is near the bottom dead center, the skirt extends from the crank chamber 30 beyond the minimum diameter portion 48. The amount of engine oil supplied between the portion 38 and the wall surface of the cylinder bore 20 can be effectively reduced. It should be noted that this effect can also be obtained in the fourth and fifth embodiments described later.

<Fourth Embodiment>
An internal combustion engine according to a fourth embodiment of the present invention (hereinafter, may be referred to as a “fourth internal combustion engine”) will be described. This fourth internal combustion engine is different from the first internal combustion engine only in that the shape of the cylinder bore and the shape of the skirt portion are different.
Hereinafter, this difference will be mainly described.

In the fourth internal combustion engine shown in FIG. 8, the skirt portion 38 of the piston 18 has a barrel shape, and the portion 52 having the maximum diameter of the skirt portion 38 is the axis 54 of the piston pin (not shown in FIG. 8). It is located closer to the lower end 38B. The diameter Dsmax of the maximum diameter portion 52 is smaller than the diameter Dcmin of the minimum diameter portion 48 of the cylinder bore 20. The minimum diameter portion 48 is a region facing the maximum diameter portion 52 of the skirt portion 38 and the regions above and below the skirt portion 38 when the piston 18 is at bottom dead center. The upper end 48T of the minimum diameter portion 48 is located at an axial position between the upper end 38T of the skirt portion 38 and the maximum diameter portion 52, and the lower end 48B of the minimum diameter portion 48 is the lower end 38B of the skirt portion 38. It is located at an axial position with the portion 52 having the maximum diameter.

The diameter Dc of the minimum diameter portion 48 is a constant value of the minimum diameter Dmin from the upper end 48T to the lower end 48B. Therefore, the clearance (Dc-Ds) / 2 between the skirt portion 38 and the wall surface of the cylinder bore 20 is the smallest at the portion 52 having the maximum diameter, and is (Dcmin-Dsmax) / 2. In the illustrated embodiment, the diameter Dc of the cylinder bore 20 below the lower end 48B increases toward the lower end 20B. The other points of the fourth internal combustion engine are configured in the same manner as the first internal combustion engine described above.

According to the fourth embodiment, in an internal combustion engine in which the skirt portion 38 of the piston 18 has a barrel shape, the clearance (Dc—Ds) / 2 between the skirt portion 38 and the wall surface of the cylinder bore 20 has a maximum diameter. The minimum value (Dcmin-Dsmax) / 2 can be set at the site 52. Therefore, when the piston 18 is at the bottom dead center, the amount of engine oil supplied upward from the side of the crank chamber 30 beyond the maximum diameter portion 52 can be reduced.

<Fifth Embodiment>
An internal combustion engine according to a fifth embodiment of the present invention (hereinafter, may be referred to as a "fifth internal combustion engine") will be described. This fifth internal combustion engine is different from the third internal combustion engine only in that the shape of the cylinder bore and the shape of the skirt portion are different.
Hereinafter, this difference will be mainly described.

In the fifth internal combustion engine shown in FIG. 9, the diameter Ds of the skirt portion 38 of the piston 18 is the largest in the ridge portion 38M near the upper end 38T, and the ridge portion 38M has an arc shape around the axis 22 of the piston 18. It extends to. The maximum diameter of the ridge 38M is Dsmax, and the diameter Ds of the region on the lower end 30B side of the ridge 38M is substantially constant.

The minimum diameter portion 48 of the cylinder bore 20 is a range from a position facing the middle between the ridge 38M of the skirt portion 38 and the lower end 38B when the piston 18 is at bottom dead center to the lower end 20B of the cylinder bore 20. Therefore, the radial clearance (Dc-Ds) / 2 between the skirt portion 38 and the wall surface of the cylinder bore 20 is the smallest in the above range corresponding to the minimum diameter portion 48, and is (Dcmin-Ds) / 2. ..

In the illustrated embodiment, the curved surface 20C is at least one of the lower slopes of the ridge 38M so that the distance between the ridge 38M and the curved surface 20C is substantially the same as the minimum clearance (Dcmin-Ds) / 2. It extends parallel to the part. The other points of the fifth internal combustion engine are configured in the same manner as the third internal combustion engine described above.

According to the fifth embodiment, in an internal combustion engine in which the skirt portion 38 of the piston 18 has a ridge portion 38M in the vicinity of the upper end 38T, a clearance (Dc—Ds) / 2 between the skirt portion 38 and the wall surface of the cylinder bore 20 is provided. , The minimum value (Dcmin-Dsmax) / 2 can be set below the ridge 38M. Therefore, when the piston 18 is at the bottom dead center, the amount of engine oil supplied upward beyond the region where the clearance is the minimum value (Dcmin-Dsmax) / 2 from the side of the crank chamber 30 can be reduced. ..

<Sixth Embodiment>
An internal combustion engine according to a sixth embodiment of the present invention (hereinafter, may be referred to as a “sixth internal combustion engine”) will be described. This sixth internal combustion engine differs from the first internal combustion engine only in that the lower end of the skirt portion 38 projects downward from the cylinder bore 20 when the piston 18 is at bottom dead center.
Hereinafter, this difference will be mainly described.

In the sixth internal combustion engine shown in FIG. 10, when the piston 18 is at bottom dead center, the lower end 38B of the skirt portion 38 having a cylindrical shape similar to that of the first internal combustion engine is lower than the lower end 20B of the cylinder bore 20. The lower end of the skirt portion 38 projects downward from the cylinder bore 20. Therefore, when the piston 18 is at bottom dead center, the skirt portion 38 faces the wall surface of the cylinder bore 20 in the range Rs from the upper end 38T to the position corresponding to the lower end 20B of the cylinder bore 20, and is below the range Rs. , Exposed to the crank chamber 30.

The diameter Dc of the cylinder bore 20 becomes smaller as it approaches the lower end 20B of the cylinder bore 20 at least in the region facing the piston 18 at the bottom dead center. Therefore, the minimum diameter portion 48 is the lower end 20B of the cylinder bore 20, and the minimum diameter is Dcmin. Further, the radial clearance (Dc-Ds) / 2 between the skirt portion 38 and the wall surface of the cylinder bore 20 is the smallest at the lower end 20B, and is (Dcmin-Ds) / 2. The other points of the sixth internal combustion engine are configured in the same manner as the first internal combustion engine described above.

The structure of the sixth internal combustion engine is the same as the structure of the first internal combustion engine described above, except that the lower end of the skirt portion 38 projects downward from the cylinder bore 20 when the piston 18 is at bottom dead center. Therefore, according to the sixth internal combustion engine, in the internal combustion engine in which the lower end portion of the skirt portion 38 projects downward from the cylinder bore 20 when the piston 18 is at the bottom dead center, the same as in the case of the first internal combustion engine described above. The action effect is obtained.

Further, the lower end 20B of the cylinder bore 20 forms a portion 48 having the minimum diameter, and the clearance between the skirt portion 38 and the wall surface of the cylinder bore 20 becomes the minimum value (Dcmin-Ds) / 2 at the lower end. Therefore, when the piston 18 moves from the bottom dead center to the top dead center, the engine oil adhering to the radial outer surface of the portion exposed to the crank chamber 30 of the skirt portion 38 is scraped off by the lower end 20B. be able to.

According to each of the above-described embodiments, the wall surface of the cylinder bore 20 has an axis line in a region adjacent to the minimum diameter portion 48 and on the upper end 12T side of the minimum diameter portion 48 when viewed in cross section passing through the axis line 22. It has a convex curved surface 20C toward 22. Therefore, as compared with the case where the wall surface of the cylinder bore 20 has a conical shape or a concave curved surface in a direction away from the axis 22 (for example, the broken line in FIG. 5), the skirt portion 38 above the minimum diameter portion 48 The clearance between the cylinder bore 20 and the wall surface can be reduced. Therefore, it is possible to reduce the amount of engine oil existing between the skirt portion 38 and the wall surface of the cylinder bore 20 in the region adjacent to the minimum diameter portion 48 and above the minimum diameter portion.

Further, the skirt portion 38 when the piston 18 moves away from the bottom dead center and toward the top dead center as compared with the case where the wall surface of the cylinder bore 20 has a conical shape or a concave curved surface in a direction away from the axis. The clearance (Dc—Ds) / 2 between the lower end 38B of the cylinder and the wall surface of the cylinder bore 20 can be reduced. Therefore, when the piston 18 leaves the bottom dead center and moves toward the top dead center, the amount of engine oil supplied from the side of the crank chamber 30 between the skirt portion 38 and the wall surface of the cylinder bore 20 is reduced. be able to.

Further, according to each of the above-described embodiments, the diameter Dc of the cylinder bore 20 in the region facing the skirt portion 38 when the piston 18 is at the top dead center is smaller as it is closer to the upper end 12T of the cylinder block 12. Therefore, as the piston 18 approaches the top dead center, the distance between the compression ring and the wall surface of the cylinder bore 20 becomes smaller, and the gas flow path becomes narrower. Therefore, the blow-by gas in the situation where the piston 18 is at or near the top dead center can be reduced. Further, it reduces the possibility that the friction between the skirt portion and the wall surface of the cylinder bore increases due to the engine oil existing between the skirt portion 38 and the wall surface of the cylinder bore 20 being moved to the side of the crank chamber by the blow-by gas. be able to.

Further, according to the third and fifth embodiments described above, the radial clearance (Dc-Ds) / 2 between the skirt portion 38 and the wall surface of the cylinder bore 20 is the minimum value (Dcmin-Ds) / 2. The region not only extends along the axis 22 but also extends to the lower end 20B of the cylinder bore 20. Therefore, as compared with the case where the clearance (Dc—Ds) / 2 at the lower end 20B is larger than the minimum value as in the fourth embodiment, when the piston 18 is at the bottom dead center, the skirt portion 38 is radially outside. The amount of engine oil adhering to the surface can be reduced. Therefore, in the compression stroke of the piston 18, the amount of engine oil that adheres to the surface of the skirt portion 38 and moves upward can be effectively reduced.

Further, according to the third to fifth embodiments described above, in the axial range of the cylindrical region having a constant diameter Dmin and extending along the axis 22, the skirt portion 38 faces the wall surface of the cylinder bore 20. It is smaller than the range Rs. Therefore, the wall surface of the skirt portion 38 and the cylinder bore 20 has a constant diameter Dmin and the axial range of the cylindrical region extending along the axis 22 is equal to or larger than the range Rs. Friction between and can be reduced, and friction loss can be reduced.

<Modification example>
The present invention is not limited to the above-described embodiment, and various modifications can be adopted within the scope of the present invention.

For example, in each embodiment, the internal combustion engine may be either a gasoline engine or a diesel engine.

10 ... Internal combustion engine, 12 ... Cylinder block, 14 ... Cylinder head, 18 ... Piston, 20 ... Cylinder bore, 22 ... Axis, 24 ... Bolt, 28 ... Crankshaft, 32 ... Engine oil, 38 ... Skirt, 41 ... First Compression ring, 43 ... 2nd compression ring, 45 ... Oil ring, 48 ... Minimum diameter part

Claims (2)

It has a cylinder block having a cylinder bore extending along an axis, a cylinder head fixed to one end of the cylinder block, and a piston housed in the cylinder bore so as to be reciprocating along the axis.
The piston
A land portion in which the first compression ring, the second compression ring, and the oil ring are sequentially mounted in the direction away from the top surface of the piston, and
A skirt that can slide with the wall surface of the cylinder bore,
In an internal combustion engine with
The portion of the minimum diameter of the cylinder bore in the movement range of the skirt portion accompanying the reciprocating movement of the piston faces the lower end of the skirt portion when the piston is at bottom dead center, and the piston reaches the bottom dead center. The radial clearance between the skirt portion and the minimum diameter portion at a certain time is the minimum value of the radial clearance between the skirt portion and the wall surface of the cylinder bore in the movement range of the skirt portion. The region above the minimum diameter portion of the cylinder bore has a diameter larger than the diameter of the minimum diameter portion.
An internal combustion engine in which the tension of the oil ring is set to be larger than the tension of the first compression ring, and the tension of the first compression ring is set to be larger than the tension of the second compression ring. It has a cylinder block having a cylinder bore extending along an axis, a cylinder head fixed to one end of the cylinder block, and a piston housed in the cylinder bore so as to be reciprocating along the axis.
The piston
A land portion in which the first compression ring, the second compression ring, and the oil ring are sequentially mounted in the direction away from the top surface of the piston, and
A skirt that can slide with the wall surface of the cylinder bore,
In an internal combustion engine with
The minimum diameter portion of the cylinder bore in the movement range of the skirt portion accompanying the reciprocating movement of the piston is within the axial range facing the skirt portion when the piston is at bottom dead center, and the piston is located. The radial clearance between the skirt portion and the minimum diameter portion at the bottom dead center is the radial clearance between the skirt portion and the wall surface of the cylinder bore in the movement range of the skirt portion. Is the minimum value of
The surface pressure of the sliding portion of the oil ring, which is obtained by dividing the tension of the oil ring by the area of the sliding portion of the oil ring, reduces the tension of the first compression ring to the sliding portion of the first compression ring. The sliding portion surface pressure of the first compression ring is larger than the sliding portion surface pressure of the first compression ring obtained by dividing by the area of the first compression ring, and the sliding portion surface pressure of the first compression ring reduces the tension of the second compression ring to the second. It is set to be larger than the sliding portion surface pressure of the second compression ring, which is obtained by dividing by the area of the sliding portion of the compression ring .
The minimum diameter portion faces the lower end of the skirt portion when the piston is at the bottom dead center, and the region above the minimum diameter portion of the cylinder bore is larger than the diameter of the minimum diameter portion. An internal combustion engine that also has a large diameter.

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