JP6572925B2 - Reciprocating piston engine - Google Patents

Description

  The present invention relates to a reciprocating piston engine having a piston and a crank mechanism.

  The reciprocating piston engine includes a piston that reciprocates in a cylinder and a crank mechanism that converts the reciprocating motion of the piston into a rotational motion. The crank mechanism includes a crankshaft including a crankpin and a crank journal (main shaft), and a connecting rod that connects the crankshaft and a piston, and includes a plurality of types of bearing structures. Specifically, examples of the bearing structure portion include a connecting portion between a large end portion of a connecting rod and a crank pin, and a bearing portion by a lower cylinder block of a crank shaft (crank journal). In these bearing structures, the inner peripheral surface of the bearing member and the outer peripheral surface of the shaft member are sliding surfaces that face each other.

  By reducing the frictional resistance of the sliding surface as much as possible, the fuel efficiency and output performance of the engine can be further improved. As a means for reducing frictional resistance, Patent Document 1 discloses that friction surfaces such as a coating process such as CVD diamond and a mirror polishing process are applied to sliding surfaces facing each other, and the relative speed of the shaft member or the bearing member is a predetermined value. A method for levitation of one of the two with respect to the other is disclosed. In this case, since the sliding surfaces are not in contact with each other due to the levitation, the frictional resistance is reduced.

JP, 2006-121600, A

  A high load acts on the bearing structure portion of the crank mechanism when an explosion load in the combustion process is applied to the piston. This high load causes the inner peripheral surface of the shaft support of the crankshaft and the outer peripheral surface of the crank journal, or the inner peripheral surface of the connecting rod large end and the outer peripheral surface of the crankpin to approach or collide, leading to a reduction or disappearance of the levitation effect. Sometimes. In this case, since the sliding surfaces are in contact with each other, the effect of reducing the frictional resistance is diminished. In addition, the method of Patent Document 1 requires a coating process and a polishing process on the sliding surface, which requires labor.

  An object of the present invention is to provide a reciprocating piston engine having a bearing structure part of a crank mechanism designed to reduce friction by utilizing a levitation effect. The purpose is to reduce the frictional resistance even in a situation where a high load is applied.

A reciprocating piston engine according to one aspect of the present invention is a reciprocating piston engine including a piston and a crank mechanism including a connecting rod and a crankshaft, and serves as a bearing member in the crank mechanism, and has a first sliding surface. A first member having an inner periphery, and a second member having a second sliding surface on the outer periphery which is a shaft member in the crank mechanism and faces the first sliding surface with a gap. Due to the relative rotation of the second member with respect to the member, the first sliding surface and the second sliding surface move relative to each other in a predetermined sliding direction, and the first sliding surface and the second sliding surface are moved. At least one of the surfaces has a projecting shape portion that projects in the facing direction in a cross section orthogonal to the axial direction, and the projecting shape portion includes a top portion that is the most projecting portion, and at least the top portion of the top portion. Sliding direction A skirt that is disposed on the downstream side and is located farthest from the other sliding surface, and in the projecting shape portion, the gap at the top is the minimum gap h1, and the gap at the skirt is the maximum. When the gap is h2,
h1 = 0.5 μm to 40 μm,
h2 / h1 = 1.5-5.0,
A first region serving as a transmission path of a load associated with the in-cylinder maximum combustion pressure received by the connecting rod from the piston on at least one of the first sliding surface and the second sliding surface. The second region other than the first region has a non-affinity with respect to the lubricating fluid, and air flows into the gap, so that the lubricity is improved. The fluid is a low-viscosity oil, and the low-viscosity oil is an oil having a viscosity larger than that of air and not more than 6.8 × 10 ⁻³ [Pa · s] .

  According to this reciprocating piston engine, the minimum gap h1 at the top provided in the projecting shape portion is set to the above numerical range, and the gap ratio h2 / h1 between the minimum gap h1 and the maximum gap h2 is as described above. Set to a numeric range. For this reason, when the first sliding surface and the second sliding surface move relative to each other, one sliding surface can be lifted from the other sliding surface by the fluid flowing into the gap. That is, a levitation effect can be obtained by the shape feature (profile) of the sliding surface.

  Furthermore, the sliding surface is divided into a first region serving as a transmission path of a load accompanying the maximum in-cylinder combustion pressure received by the connecting rod from the piston, and a second region other than that. The first region is a region having affinity with the lubricating fluid, while the second region is a region having non-affinity. Thereby, the lubricating fluid can be held in the first region. Therefore, even if a high load accompanying the in-cylinder maximum combustion pressure acts on the connecting rod, an increase in frictional resistance is suppressed by the lubricating fluid present in the first region.

Further, as the fluid, by flowing the air in the gap, one of the first sliding surface and the second sliding surface can Rukoto is airborne from the other. Furthermore, by using low-viscosity oil as the lubricating fluid, low-viscosity oil can be retained in the first region, and frictional resistance can be effectively reduced.

  In this case, it is desirable that the first region has a surface layer made of a lipophilic substance, and the second region has a surface layer made of an oil repellent material. Thereby, when low-viscosity oil is supplied to the gap, the low-viscosity oil is not held in the second region, and the low-viscosity oil can be held only in the first region.

  In the above-described reciprocating piston engine, it is desirable that the first region has an oil-impregnated surface layer. Thereby, the first region can be kept wet with the low-viscosity oil at all times.

  In the reciprocating piston engine, the crankshaft includes a crankpin and a crank journal, the connecting rod connects the crankpin and the piston, and the first member is attached to a bearing portion of the crankshaft. The bearing metal is fitted, wherein the first sliding surface is an inner peripheral surface of the bearing metal, the second member is the crank journal, and the second sliding surface is the crank journal. An outer peripheral surface is desirable.

  According to this reciprocating piston engine, at the timing at which the in-cylinder maximum combustion pressure acts on the bearing structure portion composed of the bearing portion of the crankshaft (crank journal) as the bearing member and the crank journal as the shaft member, The above-mentioned levitation effect and low friction resistance maintaining effect can be obtained.

  In this case, it is desirable that the reciprocating piston engine is a compression self-ignition type engine, and the first region is disposed in a region serving as a load transmission path when the crank angle is 0 ° to 20 °. .

  In the compression self-ignition engine, the combustion center of gravity, that is, the timing at which the in-cylinder maximum combustion pressure occurs is in the range of crank angle = 0 ° to 20 °. Therefore, by setting the region serving as the load transmission path in the crank angle range as the first region, it is possible to suppress an increase in frictional resistance in the crank mechanism of the compression self-ignition engine.

  In the above-described reciprocating piston engine, the crankshaft includes a crankpin and a crank journal, the connecting rod connects the crankpin and the piston, and the first member is at a large end of the connecting rod. The bearing metal is fitted, wherein the first sliding surface is an inner peripheral surface of the bearing metal, the second member is the crank pin, and the second sliding surface is the crank pin. An outer peripheral surface is desirable.

  According to this reciprocating piston engine, the above-described levitation effect and the low level can be achieved even at the timing at which the in-cylinder maximum combustion pressure acts on the bearing structure portion including the connecting rod large end portion as the bearing member and the crankpin as the shaft member. The effect of maintaining frictional resistance can be obtained.

  According to the present invention, in the reciprocating piston engine having the bearing structure portion of the crank mechanism designed to reduce the friction by utilizing the levitation effect, it is not necessary to process the sliding surface in the bearing structure portion, Further, the frictional resistance between the sliding surfaces can be reduced even in a situation where a high load is applied to the bearing structure.

FIG. 1 is a schematic view showing an example of an engine body to which a reciprocating piston engine according to the present invention is applied. FIG. 2 is a cross-sectional view of the reciprocating piston engine in the crankshaft direction. 3 is a cross-sectional view taken along line III-III in FIG. 4A is an enlarged view of the bearing structure portion of the big end of the connecting rod and the crank pin shown in FIG. 3, and is an exaggerated drawing of the protruding shape portion of the sliding surface of the bearing metal. FIG. 4B is an enlarged view of the bearing portion of the crankshaft shown in FIG. 3, in which the protruding shape portion of the sliding surface of the bearing metal is exaggerated. FIG. 5 is a cross-sectional view showing the state of the crankshaft when the piston is at top dead center. FIG. 6 is a cross-sectional view showing the state of the crankshaft when the crank angle advances from the top dead center. FIG. 7A is an explanatory diagram of the profile of the sliding surface, in which the annular sliding surface and the outer peripheral surface of the crank pin are developed in a planar shape. FIG. 7B is a schematic diagram for explaining an optimal sliding surface profile. FIG. 8 is a graph showing the relationship between the load capacity coefficient and the clearance ratio, which is the ratio between the minimum clearance and the maximum clearance between the sliding surface and the cylinder inner peripheral wall. FIG. 9 is a graph showing the relationship between the minimum clearance between the sliding surface and the outer peripheral surface and the friction coefficient. FIG. 10A is a diagram showing the floating state of the sliding surface when the gap ratio is appropriate, and FIG. 10B is a diagram showing the floating state of the skirt when the gap ratio is inappropriate. is there. FIG. 11 is a graph showing the relationship between in-cylinder combustion pressure (P) and crank angle of a compression self-ignition engine. FIG. 12 is a view showing a state in which a load corresponding to the in-cylinder maximum combustion pressure Pmax is applied from the connecting rod to the crankshaft 7. FIG. 13A is a perspective view showing an example of a lipophilic treatment for a bearing metal for a crankpin, and FIG. 13B is a perspective view showing an example of a lipophilic treatment for a crankpin. FIG. 14A is a perspective view showing an example of a lipophilic treatment for a bearing metal for a crank journal, and FIG. 14B is a perspective view showing an example of a lipophilic treatment for a crank journal.

[Engine structure]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, an engine body 1 to which a reciprocating piston engine according to the present invention is applied will be described with reference to FIG. The engine body 1 shown here is an engine mounted on the vehicle as a power source for driving the vehicle such as an automobile, and is a reciprocating piston type equipped with a piston that reciprocates in a cylinder and a crank mechanism. It is a multi-cylinder engine. In the present embodiment, the fuel supplied to the engine body 1 is mainly composed of gasoline.

  The engine body 1 includes a cylinder block 3, a cylinder head 4, and a piston 5. The cylinder block 3 has a plurality of cylinders 2 (a four-cylinder engine is shown in FIGS. 2 and 3 described later) arranged in a direction perpendicular to the paper surface of FIG. In the cylinder 2, the fuel / air mixture burns. The cylinder head 4 is attached to the upper surface of the cylinder block 3 and closes the upper opening of the cylinder 2.

  The piston 5 is accommodated in each cylinder 2 so as to be slidable back and forth, and is connected to the crankshaft 7 via a connecting rod 8. In response to the reciprocating motion of the piston 5, the crankshaft 7 rotates about its central axis. The structure of the piston 5 will be described in detail later. In FIG. 1, it is assumed that the crankshaft 7 rotates in the clockwise direction, and the thrust side inner peripheral wall 2A and the anti-thrust side inner peripheral wall 2B are shown as inner peripheral walls of the cylinder 2 on which the piston 5 slides.

  A combustion chamber 6 is formed above the piston 5. An intake port 9 and an exhaust port 10 communicating with the combustion chamber 6 are formed in the cylinder head 4. On the bottom surface of the cylinder head 4, an intake side opening 4 </ b> A that is a downstream end of the intake port 9 and an exhaust side opening 4 </ b> B that is an upstream end of the exhaust port 10 are formed. The upstream end of the intake port 9 is connected to the intake passage 9A, and the downstream end of the exhaust port 10 is connected to the exhaust passage 10A. The cylinder head 4 is assembled with an intake valve 11 for opening / closing the intake side opening 4A and an exhaust valve 12 for opening / closing the exhaust side opening 4B. The engine of this embodiment is a double overhead camshaft (DOHC) engine. Two intake side openings 4A and two exhaust side openings 4B are provided for each cylinder 2, and two intake valves 11 and two exhaust valves 12 are also provided.

  The intake valve 11 and the exhaust valve 12 are so-called poppet valves, and each include an umbrella-shaped valve body that opens and closes the openings 4A and 4B, and a stem that extends vertically from the valve body. The valve body has a valve surface facing the combustion chamber 6. In the present embodiment, the combustion chamber 6 is defined by the inner wall surface of the cylinder 2, the crown surface of the piston 5, the bottom surface of the cylinder head 4, and the valve surfaces of the intake valve 11 and the exhaust valve 12.

  The cylinder head 4 is provided with an intake side valve mechanism 13 and an exhaust side valve mechanism 14 for driving the intake valve 11 and the exhaust valve 12, respectively. The valve mechanisms 13 and 14 drive the stems of the intake valve 11 and the exhaust valve 12 in conjunction with the rotation of the crankshaft 7. By driving these stems, the valve body of the intake valve 11 opens and closes the intake side opening 4A, and the valve body of the exhaust valve 12 opens and closes the exhaust side opening 4B.

  An intake side variable valve timing mechanism (intake side VVT) 15 is incorporated in the intake side valve mechanism 13. The intake side VVT 15 is an electric VVT provided on the intake camshaft, and the intake valve 11 is opened and closed by continuously changing the rotation phase of the intake camshaft with respect to the crankshaft 7 within a predetermined angle range. To change. Similarly, an exhaust side variable valve timing mechanism (exhaust side VVT) 16 is incorporated in the exhaust side valve mechanism 14. The exhaust side VVT 16 is an electric VVT provided on the exhaust camshaft, and the exhaust valve 12 is opened and closed by continuously changing the rotational phase of the exhaust camshaft with respect to the crankshaft 7 within a predetermined angular range. To change.

  One ignition plug 17 for supplying ignition energy to the air-fuel mixture in the combustion chamber 6 is attached to the cylinder head 4, one for each cylinder 2. The spark plug 17 is attached to the cylinder head 4 so that the ignition point faces the combustion chamber 6. The spark plug 17 discharges a spark from its tip in response to power supply from an ignition circuit (not shown), and ignites the air-fuel mixture in the combustion chamber 6.

  The cylinder head 4 is provided with one injector 18 for each cylinder 2 for injecting fuel mainly composed of gasoline into the combustion chamber 6 from the tip. The injector 18 injects fuel supplied through a fuel supply pipe (not shown). Connected to the upstream side of the fuel supply pipe is a high-pressure fuel pump (not shown) composed of a plunger-type pump or the like interlocked with the crankshaft 7. A common rail (not shown) for accumulating pressure common to all the cylinders 2 is provided between the high-pressure fuel pump and the fuel supply pipe. The fuel accumulated in the common rail is supplied to the injectors 18 of the respective cylinders 2, whereby high pressure fuel is injected from the injectors 18 into the combustion chamber 6.

[Details of crankshaft]
A more specific example of the above-described crankshaft 7 will be shown. 2 is a cross-sectional view of the reciprocating piston engine in the crankshaft direction, and FIG. 3 is a cross-sectional view taken along the line III-III of FIG. In FIG. 2 and FIG. 3, descriptions of accessories (intake, exhaust valves 11, 12, etc.) attached to the cylinder head 4 are omitted. Here, a four-cylinder engine is illustrated, and pistons 5 are accommodated in four cylinders 2 so as to be able to reciprocate, respectively. Each piston 5 is connected to the crankshaft 7 by a connecting rod 8. That is, the small end 8 </ b> A at the upper end of the connecting rod 8 and the piston 5 are connected via the piston pin 40. Below the cylinder block 3, a lower cylinder block 3A that supports the crankshaft 7 and an oil pan 3B are disposed.

  The crankshaft 7 includes a crank journal 71 (second member), a crank pin 72 (second member), and a crank arm 73. The crank journal 71 is a portion that serves as a rotating shaft of the crankshaft 7 and is supported by a bearing metal 30 (FIG. 4B; first member) fitted in the bearing portion 3C of the lower cylinder block 3A. The crank pin 72 is a portion connected to the big end 8B (large end portion) at the lower end of the connecting rod 8, and is supported by the bearing metal 20 (FIG. 4A; first member) fitted into the inner peripheral surface of the big end 8B. It is supported. The crank arm 73 is a portion that connects the crank journal 71 and the crank pin 72. A balance weight 74 is provided at the end of the crank arm 73 opposite to the end on the connection side with the crank pin 72. The reciprocating motion of the piston 5 is transmitted to the crankshaft 7 by the connecting rod 8 and rotates the crankshaft 7 around the crank journal 71. A crankshaft pulley 75 is attached to one end side of the crankshaft 7, and a flywheel 76 is attached to the other end side.

The cylinder block 3 is provided with an oil supply mechanism 60 (fluid supply unit). The oil supply mechanism 60 supplies low-viscosity oil (lubricating fluid) to the bearing structure portion of the crankshaft 7, that is, the shaft support portions of the crank journal 71 and the crankpin 72. The oil supply mechanism 60 includes an oil pump 61, an oil filter 62, a pressure adjustment valve 63, a filter 64, and an oil supply line 65. For example, 0W-20 (viscosity = 6.8 × 10 ⁻³ [Pa · s]) can be used as the low viscosity oil.

  The oil pump 61 sends low-viscosity oil stored in an unillustrated oil tank (for example, the oil pan 3B) to the oil supply line 65. The oil supply operation by the oil pump 61 is controlled by the control unit 80. The oil filter 62 is connected to the suction port side of the oil pump 61, and removes relatively large foreign matters in the sucked oil. The pressure adjustment valve 63 is connected to the discharge port side of the oil pump 61 and is an adjustment valve for keeping the hydraulic pressure in the oil supply pipeline 65 constant. The filter 64 removes relatively small foreign matters such as fine metal powder contained in the oil sent from the oil pump 61 to the oil supply pipe 65.

  The oil supply line 65 has an oil gallery 66 in the cylinder block 3. The oil supply pipe 65 includes a journal channel 67, an arm channel 68, and a pin channel 69 in the crankshaft 7. The oil gallery 66 is an oil passage provided inside the cylinder block 3, and one end side is connected to the discharge port side (filter 64) of the oil pump 61, and the other end side faces the five bearing portions 3 </ b> C of the crankshaft 7. Branched.

  The journal flow path 67 is an oil passage provided in the crank journal 71 of the crankshaft 7. The journal channel 67 has a discharge port 67A for supplying oil to the outer peripheral surface 71A on the outer peripheral surface 71A (FIG. 4B) of the crank journal 71. The in-arm channel 68 is an oil passage that is connected to the journal channel 67 and is provided in the crank arm 73. The in-pin passage 69 is an oil passage that is connected to the in-arm passage 68 and is provided inside the crankpin 72. The in-pin flow passage 69 has a discharge port 69A for supplying oil to the outer peripheral surface 72A on the outer peripheral surface 72A (FIG. 4A) of the crankpin 72.

[Structure of sliding surface]
The crank mechanism including the connecting rod 8 and the crankshaft 7 has two bearing structures. The bearing structure part constituted by the big end 8B of the connecting rod 8 and the crank pin 72 that relatively rotates in the hole of the big end 8B, and the bearing part 3C of the lower cylinder block 3A and the bearing part 3 rotate relatively. This is a bearing structure portion constituted by the crank journal 71. In these bearing structures, the two opposing sliding surfaces move (rotate) relatively in a predetermined sliding direction. Hereinafter, this sliding surface will be described in detail.

  4A is an enlarged view of a bearing structure portion between the big end 8B of the connecting rod 8 and the crank pin 72 shown in FIG. The big end 8B has a circular bearing hole 8C, and a bearing metal 20 (first member) is fitted into the bearing hole 8C. The bearing metal 20 is a sliding bearing in which a band-shaped metal circle is formed in an annular shape. Usually, the annular bearing metal 20 is formed by abutting the semicircular halves. In the bearing structure portion, the bearing metal 20 is a bearing member, and the crank pin 72 (second member) is a shaft member.

  The bearing metal 20 has a cylindrical inner peripheral surface 20A (first sliding surface) through which the crank pin 72 is inserted. The crankpin 72 is a cylindrical member having a perfect cross section, and has an outer peripheral surface 72A (second sliding surface) facing the inner peripheral surface 20A with a predetermined gap G in the radial direction on the outer periphery. Yes. The crank pin 72 is provided with the above-described in-pin flow passage 69 for circulating the low-viscosity oil, and the oil discharge port 69A is opened on the outer peripheral surface 72A. And 20 A of inner peripheral surfaces are provided with the overhang | projection shape part M1 which protrudes in the crossing direction orthogonal to the axial direction of the crankpin 72 (cross section of FIG. 4A) with 72 A of outer peripheral surfaces. In FIG. 4A, the overhanging shape portion M1 is exaggeratedly drawn, but it is actually a shape having an overhang on the micron order that is difficult to distinguish visually.

  The overhang shape portion M1 forms one overhang on the circumference of the inner peripheral surface 20A in the circumferential direction, and has a top portion P and a skirt portion Q. The top portion P is the portion that protrudes most toward the outer peripheral surface 72A. The skirt portion Q is a portion that is located farthest from the outer peripheral surface 62A (the counterpart sliding surface). The width of the gap G at the top P is the minimum gap h1, and the width of the gap G at the skirt Q is the maximum gap h2. In the present embodiment, an example is shown in which the apex P is disposed in the vicinity of a point where a line segment A connecting the axis of the small end 8A of the connecting rod 8 and the axis of the big end 8B intersects the bearing metal 20. Yes. The overhanging shape portion M1 only needs to be present on at least one of the inner peripheral surface 20A and the outer peripheral surface 72A, or may be provided on the outer peripheral surface 72A, or both the inner peripheral surface 20A and the outer peripheral surface 72A. May be provided. Moreover, it is good also as a structure where the some overhang | projection shape part M1 is provided in series by the circumferential direction.

  The overhanging shape portion M1 has a shape in which the overhang toward the outer peripheral surface 72A gradually increases from the skirt portion Q to the apex portion P in the clockwise direction of FIG. 4A. That is, the cross-sectional shape orthogonal to the axial direction of the overhanging shape portion M1 has a spiral shape that gradually decreases in diameter toward the center of the bearing hole 8C during one round of the inner peripheral surface 20A. The cross-sectional shape protrudes most at the top portion P, and then retreats rapidly outward in the radial direction, and is connected to the skirt portion Q. In other words, the gap G between the inner peripheral surface 20A and the outer peripheral surface 72A becomes narrower as it goes around in the clockwise direction from the maximum gap h2 of the skirt Q, and becomes the minimum gap h1 at the top P. . Further, when it goes around in the clockwise direction, the gap G widens rapidly and becomes the maximum gap h2. The oil supply mechanism 60 described above supplies low-viscosity oil to the gap G from the discharge port 69A at a predetermined timing.

  A part of the inner peripheral surface 20 </ b> A is provided with a lipophilic treatment section 21 (affinity region) having lipophilicity with respect to the low viscosity oil supplied from the oil supply mechanism 60. A region (second region) other than the formation region of the lipophilic treatment portion 21 on the inner peripheral surface 20A is a non-lipophilic portion 22 (region having non-affinity) that does not exhibit lipophilicity to the low-viscosity oil. Has been. The region in which the oleophilic treatment unit 21 is provided is a region (first region) serving as a transmission path for a load accompanying the in-cylinder maximum combustion pressure Pmax received by the connecting rod 8 from the piston 5. This will be described in detail later.

  4B is an enlarged view of the bearing structure portion of the bearing portion 3C and the crankshaft 7 (crank journal 71) of the lower cylinder block 3A shown in FIG. A bearing metal 30 (first member) is fitted into the bearing portion 3C. The bearing metal 30 is a sliding bearing in which a strip-shaped metal piece is formed in an annular shape, similar to the bearing metal 20 described above. In the bearing structure portion, the bearing metal 30 is a bearing member, and the crank journal 71 (second member) is a shaft member.

  The bearing metal 30 has a cylindrical inner peripheral surface 30A (first sliding surface) through which the crank journal 71 is inserted. The crank journal 71 is a cylindrical member whose cross section is a perfect circle, and has an outer peripheral surface 71A (second sliding surface) facing the inner peripheral surface 30A with a predetermined gap G in the radial direction on the outer periphery. Yes. The crank journal 71 is provided with the above-described journal flow passage 67 for circulating low-viscosity oil, and the oil discharge port 67A is opened on the outer peripheral surface 71A. And 30 A of inner peripheral surfaces are provided with the overhang | projection shape part M2 which protrudes in the crossing direction orthogonal to the axial direction of the crank journal 71 (cross section of FIG. 4B) with 71 A of outer peripheral surfaces. In FIG. 4B, the overhanging shape portion M2 is exaggeratedly drawn, but in actuality, it is a shape having a micron-order overhang that is difficult to visually distinguish.

  The overhang shape portion M2 has the same shape as the overhang shape portion M1 described above. That is, the overhang shape portion M2 forms one overhang on the circumference of the inner peripheral surface 30A in the circumferential direction, and has a top portion P and a skirt portion Q. The width of the gap G at the top P is the minimum gap h1, and the width of the gap G at the skirt Q is the maximum gap h2. The overhanging shape portion M2 only needs to be present on at least one of the inner peripheral surface 30A and the outer peripheral surface 71A, or may be provided on the outer peripheral surface 71A, or both the inner peripheral surface 30A and the outer peripheral surface 71A. May be provided. Moreover, it is good also as a structure where the some overhang | projection shape part M2 is provided in a line by the circumferential direction.

  The overhanging shape portion M2 has a shape in which the overhang toward the outer peripheral surface 71A gradually increases from the skirt portion Q to the top portion P in the clockwise direction of FIG. 4B. That is, the cross-sectional shape orthogonal to the axial direction of the projecting shape portion M2 has a spiral shape that gradually decreases in diameter toward the hole center of the bearing portion 3C during one round of the inner peripheral surface 30A. The cross-sectional shape protrudes most at the top portion P, and then retreats rapidly outward in the radial direction, and is connected to the skirt portion Q. In other words, the gap G between the inner peripheral surface 30A and the outer peripheral surface 71A becomes narrower as it circulates clockwise from the maximum gap h2 of the skirt Q, and becomes the minimum gap h1 at the top P. . Further, when it goes around in the clockwise direction, the gap G widens rapidly and becomes the maximum gap h2. The oil supply mechanism 60 described above supplies low-viscosity oil to the gap G from the discharge port 67A at a predetermined timing.

  As in the case of the bearing metal 20 for the crankpin 72, a part of the inner peripheral surface 30A has an oleophilic treatment part 31 (affinity) having oleophilicity with respect to the low-viscosity oil supplied from the oil supply mechanism 60. Region) is provided. The region (second region) other than the region where the lipophilic treatment part 31 is formed on the inner peripheral surface 30A is a non-lipophilic part 32 (region having non-affinity) that does not exhibit lipophilicity to the low-viscosity oil. Has been. The region where the oleophilic treatment unit 31 is provided is a region (first region) serving as a transmission path of a load accompanying the in-cylinder maximum combustion pressure Pmax received by the connecting rod 8 from the piston 5. This will be described in detail later.

  FIG. 5 is a cross-sectional view showing the state of the crankshaft 7 when the piston 5 is at top dead center, and FIG. 6 is a cross-sectional view showing the state of the crankshaft 7 when the crank angle is advanced from the top dead center. It is. When the piston 5 is at top dead center, a line segment A connecting the axis of the small end 8A of the connecting rod 8 and the axis of the big end 8B, and an arm extending from the axis of the crank journal 71 to the axis of the crank pin 72 Axis B is aligned on the same line.

  As shown in FIG. 6, when the crank angle advances, the line segment A and the arm axis B intersect at an angle corresponding to the crank angle. Then, at the big end 8B of the connecting rod 8, the crank pin 72 rotates relative to the bearing metal 20, and the inner peripheral surface 20A and the outer peripheral surface 72A, which are the respective sliding surfaces, relatively move in the respective sliding directions. Moving. In this case, the sliding direction of the inner circumferential surface 20A (bearing metal 20) is a sliding direction C1 that goes counterclockwise, and the sliding direction of the outer circumferential surface 72A (crank pin 72) is the revolution direction of the crank pin 72. It is the sliding direction D1 which goes to the clockwise direction which is.

  In the bearing portion 3C, the crank journal 71 rotates relative to the bearing metal 30, and the inner peripheral surface 30A and the outer peripheral surface 71A, which are the respective sliding surfaces, move relatively in the respective sliding directions. In this case, the sliding direction of the inner circumferential surface 30A (bearing metal 30) is a sliding direction C2 that goes counterclockwise, and the sliding direction of the outer circumferential surface 71A (crank journal 71) is the rotation direction of the crank journal 71. It is the sliding direction D2 which goes to the clockwise direction which is.

  In the present embodiment, the overhanging portions M1 and M2 are provided on the bearing metal 20 and 30 sides, respectively. That is, it is provided on the inner peripheral surfaces 20A and 30A that move in the sliding directions C1 and C2. In this case, the skirt portions Q of the projecting shape portions M1 and M2 are provided on the downstream side of the sliding directions C1 and C2, respectively. That is, in the sliding directions C1 and C2, the top portion P is located on the most upstream side, and the skirt portion Q is located on the most downstream side by making a round in the circumferential direction.

  When the inner peripheral surfaces 20A and 30A slide relative to the outer peripheral surfaces 72A and 71A by the projecting shape portions M1 and M2, the sliding direction of the fluid existing in the gap G is different. Flows in the directions of arrows E1 and E2 (fluid inflow directions E1 and E2) opposite to C1 and C2 occur. That is, the fluid flows from the skirt Q toward the top P. Here, by optimizing the profiles of the inner peripheral surfaces 20A, 30A, the inner peripheral surfaces 20A, 30A are levitated (sliding levitated) with respect to the outer peripheral surfaces 72A, 71A. By this sliding levitation, the sliding resistance between the inner peripheral surfaces 20A, 30A and the outer peripheral surfaces 72A, 71A can be significantly reduced. Hereinafter, the profiles of the overhanging portions M1 and M2 that realize sliding levitation will be described.

[Sliding surface profile]
FIG. 7A is an explanatory diagram of the profile of the sliding surface, and the annular inner peripheral surface 20A (first sliding surface) of the bearing metal 20 and the outer peripheral surface 72A of the cylindrical crankpin 72 are planarized. It is the expanded schematic diagram. This development view also applies to the relationship between the inner peripheral surface 30A of the bearing metal 30 and the outer peripheral surface 71A of the crank journal 71.

  As described above, the inner circumferential surface 20 </ b> A and the outer circumferential surface 72 </ b> A are opposed to each other through the gap G. The protruding shape portion M1 of the inner peripheral surface 20A has a top portion P that protrudes to the outermost peripheral surface 72A side, and has a skirt portion Q that has the smallest protrusion to the outer peripheral surface 72A side at the downstream end in the sliding direction C1. doing. When the velocity u is given to the inner peripheral surface 20A in the sliding direction C1 by the relative movement of the bearing metal 20, the fluid F existing in the vicinity is moved from the skirt Q side to the gap G as shown by the fluid inflow direction E1 in the figure. Be drawn. The fluid F that has lost its destination generates a drag in a direction in which the space between the inner peripheral surface 20A and the outer peripheral surface 72A is enlarged. This drag acts to float the inner peripheral surface 20A from the outer peripheral surface 72A (sliding levitation). The inner peripheral surface 20A is set to a profile in which such sliding levitation is well expressed. The fluid F is, for example, air, water, or low viscosity oil of 0W-20 class, and particularly preferably air.

  As shown in FIG. 7A, the gap between the apex P of the overhanging portion M1 and the outer peripheral surface 72A is the minimum gap h1, and the gap between the skirt Q and the outer peripheral surface 72A is the maximum gap h2. Let h2 / h1 be the gap ratio m (corresponding to h2-h1). In order to achieve good sliding levitation, it is important to set the minimum gap h1 according to the nature of the fluid F and to set the gap ratio m according to the minimum gap h1. The maximum gap h2 is naturally determined by setting h1 and m.

  Here, the profile of the inner peripheral surface 20A that can effectively obtain the action of sliding levitation will be described with reference to FIG. 7B. FIG. 7B is a schematic diagram showing that the sliding member C1 having the sliding surface Sa slides in the direction indicated by the arrow Y10 along the sliding surface Sb. The sliding surface Sa has a protruding shape that protrudes toward the sliding surface Sb, and is the top portion Pa that is the most protruding portion and the downstream side of the sliding direction of the top portion Pa (the direction indicated by the arrow Y10). And a skirt portion Qa that is most separated from the sliding surface Sb, and has a shape that gradually separates from the sliding surface Sb toward the downstream side in the sliding direction.

When the sliding member C1 slides at the speed U, the sliding levitation force W generated between the sliding surface Sa and the sliding surface Sb can be obtained by the following equation (1).

  In Equation (1), η is the viscosity of the fluid F interposed between the sliding surface Sa and the sliding surface Sb, and B is the length of the sliding surface in the sliding direction (from the top Pa in FIG. 7B). C is the length in the direction perpendicular to the sliding direction of the sliding surface (the length in the direction perpendicular to the paper surface of FIG. 7B), and U is the length of the sliding surface Sa. The sliding speed. h1 is the minimum gap, which is the separation distance between the top portion Pa and the sliding surface Sb, that is, the minimum value of the gap dimension between the sliding surface Sa and the sliding surface Sb. m is the above-mentioned gap ratio, and the separation distance between the skirt Qa and the sliding surface Sb, that is, the maximum value of the gap dimension between the sliding surface Sa and the sliding surface Sb is the maximum gap h2. The ratio between the minimum gap h1 and the maximum gap h2 is expressed as m = h2 / h1.

In the formula (1), when the second item is the load capacity coefficient Kw (Kw = 6 / (m−1) ² {lnm−2 (m−1) / (m + 1)}), the buoyancy W is the load capacity It is proportional to the coefficient Kw.

  FIG. 8 is a graph showing the relationship between the load capacity coefficient Kw and the gap ratio m. As shown in this graph, the sliding levitation force W becomes maximum when the gap ratio m is 2.2, and becomes smaller as the gap ratio m is separated from this value. From this finding, a high sliding levitation force W can be obtained if the gap ratio m is set in the vicinity of 2.2. Specifically, by setting the gap ratio m to 1.5 or more and 5.0 or less, the sliding levitation force W can be set to the line L1 or more in FIG. In this case, as the sliding levitation force W, a high value that is 60% or more of the maximum value (value when the gap ratio m is 2.2) can be obtained.

  Here, based on Formula (1), sliding levitation force becomes large, so that the minimum clearance h1 is small. Therefore, it seems that a smaller minimum gap h1 is preferable. On the other hand, the present inventors have found that there exists an optimum range in which the friction coefficient μ generated between the sliding surface Sa and the sliding surface Sb can be kept small for the minimum gap h1. . The magnitude of the friction coefficient μ corresponds to the magnitude of friction when the sliding surface Sa slides and floats, and the smaller the friction coefficient μ, the better the sliding lift can be realized.

FIG. 9 is a graph showing the relationship between the friction coefficient μ and the minimum gap h1 when the fluid F is air, water, or oil. The viscosity of air exemplified as the fluid F is 1.8 × 10 ⁻⁵ [Pa · s], the viscosity of water is 8.9 × 10 ⁻⁴ [Pa · s], and the viscosity of the low-viscosity oil 0W-20 is 6. It is 8 × 10 ⁻³ [Pa · s]. The graph of FIG. 9 shows the maximum value of the load applied to the sliding surface Sa that slides along a predetermined sliding surface with the reciprocation of the piston 5 when the engine is operating, and the sliding calculated by the equation (1). The relationship between the minimum clearance h1 and the friction coefficient μ when the dynamic levitation force W is balanced and the sliding surface Sa floats is shown. In addition, the graph of FIG. 9 has shown that the clearance ratio m also changes with the change of the minimum clearance h1.

  More specifically, in Equation (1), the average moving speed of the sliding surface Sa to be used when the engine speed is a typical predetermined speed is substituted for U, and the viscosity of the fluid F is substituted for η. And the maximum value of the load is substituted for the sliding levitation force W. The value of the minimum gap h1 when the difference (h2−h1) between the maximum gap h2 and the minimum gap h1 is set to a predetermined value is calculated from the formula (1) substituted with these values, and the minimum gap h1 is calculated. Is used to calculate the friction coefficient μ. Further, the value of the predetermined value is changed to change the value of the minimum gap h1, and the friction coefficient μ corresponding to each value is obtained. For example, when driving in an urban area, 1350 rpm can be used as the engine speed corresponding to the U, and the input load applied to the sliding surface Sa can be 1175N.

In FIG. 9, lines L2, L3, and L4 in which the friction coefficient μ is increased by + 20% as compared with the friction coefficient μ in the optimum minimum gap h1, that is, the lowest friction coefficient μ, are respectively added to FIG. doing. The range up to + 20% is a range in which extremely good sliding levitation can be realized. Specifically, when the fluid F is air, the minimum gap h1 is 0.7 μm to 1.3 μm, when water is 4.9 μm to 8.9 μm, and when 0 W-20, 18 μm to 26 μm. Although these are ideal ranges, good sliding levitation can be obtained even if slightly deviated from the range, so the preferable range of the minimum gap h1 is respectively
In the case of air: 0.5 μm to 1.5 μm
In the case of water: 3 μm to 11 μm
In the case of 0W-20: 15 μm to 30 μm
Can be set.

  From the above results, the range of the minimum gap h1 in which good sliding levitation can be realized in the category of the fluid F currently available for achieving sliding levitation (air, water, low viscosity oil) is 0. It can be set to 5 μm to 30 μm. This range is a range of the minimum gap h1 that should be ensured during operation of the engine body 1 (when the crankshaft 7 rotates). When the engine main body 1 is operated, the bearing metal 20 and the crankpin 72 may be hot and expand thermally. Accordingly, it is appropriate to set the upper limit value larger as a design value based on the normal temperature so that the upper limit value of the minimum gap h1 = 30 μm can be secured during operation. In view of this point, in this embodiment, the range of the minimum gap h1 at room temperature is set to 0.5 μm to 40 μm.

  In sliding levitation, the most desirable fluid F from the viewpoint of reducing sliding resistance is air. This is because if air is allowed to flow into the gap G (air levitation), as is clear from FIG. 9, the friction between the inner peripheral surface 20A and the outer peripheral surface 72A can be minimized. When air levitation is adopted, the minimum clearance at room temperature is taken into consideration in consideration of the thermal expansion of the bearing metal 20 and the crank pin 72 so that the minimum clearance h1 = 0.5 μm to 1.5 μm is secured during operation of the engine body 1. It is desirable to determine the design value of h1.

  Here, the inner peripheral surface 20A is desirably a surface having high smoothness. Since the minimum gap h1 is selected within a minute length range of 0.5 μm to 40 μm, if the inner peripheral surface 20A is a rough surface, the accuracy of the minimum gap h1 decreases. Therefore, the inner peripheral surface 20A is desirably a smooth surface having a surface roughness (arithmetic average roughness Ra) of 0.4 μm or less.

  The bearing metal 20 having the inner peripheral surface 20A and the crank pin 72 are preferably made of the same material. Similarly, the bearing metal 21 and the crank journal 71 are preferably made of the same material. Thereby, the fluctuation | variation of the length of the clearance gap G resulting from a thermal expansion difference, ie, the fluctuation | variation of the minimum clearance gap h1, and the maximum clearance gap h2, can be suppressed. For example, it is desirable to form both with cast steel formed by casting steel hot water into a mold. Alternatively, it is preferable that at least the bearing metal 20 is formed of a metal having a small linear expansion coefficient, for example, stainless steel (forged product), because the length variation of the gap G can be suppressed.

  FIG. 7A illustrates an example in which the protruding shape portion M1 of the inner peripheral surface 20A has a protruding height that increases from the skirt portion Q toward the top portion P at a certain rate. However, the projecting shape portion M1 has an essential part in the sliding direction C1 that forms the minimum gap h1 (top portion P) and a portion that forms the maximum gap h2 (hem portion Q). About a shape, the aspect is not ask | required. An overhanging shape portion M1 having a loose bulge and a depression between the top portion P and the bottom portion Q, or an overhanging shape portion M1 in which the projecting height changes in a stepped manner between the top portion P and the bottom portion Q. It is also good.

  FIG. 10A is a diagram illustrating a floating state of the inner peripheral surface 20A when the gap ratio m is an appropriate value (m = 2.2), and FIG. 10B is a diagram in which the gap ratio m is less than the appropriate value. It is a figure which shows the floating state of 20 A of internal peripheral surfaces in the case of being large. When the minimum gap h1 is set in the above range according to the type of the fluid F, the gap ratio m is set to an appropriate value, and the speed u is given to the inner peripheral surface 20A, the state shown in FIG. As a result, the surrounding fluid F flows into the gap G between the inner peripheral surface 20A and the outer peripheral surface 72A. The inflowing fluid F loses its destination (damming effect). Due to the blocking effect of the fluid F, a drag force (levitation force) that separates the inner peripheral surface 20A from the outer peripheral surface 72A is generated, and the inner peripheral surface 20A floats from the outer peripheral surface 72A.

  On the other hand, when the gap ratio m is larger than an appropriate value, that is, when the maximum gap h2 is excessively large, the surrounding fluid F flows into the gap G as shown in FIG. The ratio of the fluid FA that cannot flow into the gap G due to excessive damming effect increases. For this reason, the inflow amount of the fluid F into the gap G is reduced, and the levitation force is also reduced accordingly. Therefore, good sliding levitation cannot be realized. On the other hand, when the gap ratio m is larger than an appropriate value, the inner peripheral surface 20A approaches the flat plate. For this reason, the inflow amount of the fluid F into the gap G is similarly reduced, and the levitation force is also reduced.

[Inhibiting factors of sliding levitation]
A high load is transmitted to the bearing structure portion of the crank mechanism via the connecting rod 8 when an explosion load (in-cylinder combustion pressure) in the combustion process is applied to the piston 5. In particular, at the timing when the in-cylinder maximum combustion pressure Pmax is generated, a high load is transmitted to the bearing structure. Such a high load causes the inner peripheral surface 20A of the bearing metal 20 and the outer peripheral surface 72A of the crank pin 72 that face each other with a gap G during sliding levitation, and the inner peripheral surface 30A of the bearing metal 30 and the crank journal 71. The outer peripheral surface 71A may be approached or collided to reduce or eliminate the levitation effect. This point will be described with reference to FIGS.

  FIG. 11 is a graph showing the relationship between in-cylinder combustion pressure (P) and crank angle of a compression self-ignition engine. As the engine main body 1 of the present embodiment, a compression self-ignition engine such as an HCCI combustion (premixed compression ignition combustion) system can be suitably used. As shown in FIG. 11, in a compression self-ignition engine, the in-cylinder maximum combustion pressure Pmax often occurs at a timing when the crank angle advances about 10 ° from the compression top dead center TDC. Further, the in-cylinder combustion pressure is high in a range of ± 10 ° centered on Pmax, that is, in a range of crank angle = 0 ° to 20 °.

  FIG. 12 is a diagram showing a state in which a load corresponding to the in-cylinder maximum combustion pressure Pmax is applied from the connecting rod 8 to the crankshaft 7 when the engine body 1 has the combustion pressure characteristics as shown in FIG. It is. In FIG. 12, it is assumed that the inclination angle α of the connecting rod 8 is around 10 ° (crank angle = 10 °). However, in order to facilitate understanding, the connecting rod 8 is larger than the actual inclination angle α. It is drawn as if it is tilted.

  Also, the points y1, y2, y3, y4 entered in FIG. 12 indicate the positions of the points y1, y2, y3, y4 shown in FIG. Points y1 and y2 in FIG. 5 are points on the inner peripheral surface 20A of the bearing metal 20 and the outer peripheral surface 72A of the crank pin 72 (the side closer to the small end 8A) that intersects the line segment A when the crank angle = 0 °. Intersection). Further, the points y3 and y4 in FIG. 5 are the inner peripheral surface 30A of the bearing metal 30 and the outer peripheral surface 71A of the crank journal 71 (from the crank pin 72) that intersect the extended line of the line segment A when the crank angle = 0 °. (The intersection on the far side). Since the point y1 is a point on the inner peripheral surface 20A of the bearing metal 20 fixed to the connecting rod 8, it is always located on the line segment A. The point y2 moves in the clockwise direction by the revolution of the crankpin 72. Since the point y3 is a point on the bearing metal 30 fixed to the bearing portion 3C of the lower cylinder block 3A, it does not move. The point y4 moves clockwise according to the rotation of the crankshaft 7.

  When a load W of the in-cylinder maximum combustion pressure Pmax is applied to the crankshaft 7, in the bearing structure portion of the bearing metal 20 of the connecting rod 8 and the crankpin 72, the area around the point y1 is a high load region HW1 where a high load acts. It becomes. Further, when the in-cylinder maximum combustion pressure Pmax is applied to the crankpin 72, it is transmitted to the crank journal 71 via the crank arm 73. That is, in the bearing structure portion of the bearing metal 30 and the crank journal 71, since the load W is transmitted from the shaft member side to the bearing member side, the outer peripheral surface 71A far from the arm shaft B and the crank pin 72 The vicinity of the point y4, which is the intersection of, becomes a high load region HW2 where a high load acts. These high load areas HW1 and HW2 are areas that serve as a transmission path for the load W of the in-cylinder maximum combustion pressure Pmax.

  When a load W is applied to the high load region HW1, the region on the opposite side of the center point between the high load region HW1 and the bearing metal 20 may become the high load region HW1R due to the inertial force of the crank pin 72. . Similarly, the region on the opposite side across the center point of the high load region HW2 and the bearing metal 30 may be the high load region HW2R.

[Formation of lipophilic area]
As described above, at least in the high load regions HW1 and HW2 to which the in-cylinder maximum combustion pressure Pmax is directly applied, there is a possibility that the load W becomes excessive and sliding levitation may not be established. Therefore, in the present embodiment, a lubricating fluid (for example, low-viscosity oil 0W-20 or the like) always exists in the high load areas HW1 and HW2, and between the inner peripheral surface 20A and the outer peripheral surface 72A, or the inner periphery. Even when contact occurs between the surface 30A and the outer peripheral surface 71A, the frictional resistance is not increased. Here, it is assumed that the fluid F flowing into the gap G between the inner peripheral surface 20A and the outer peripheral surface 72A and between the inner peripheral surface 30A and the outer peripheral surface 71A is air (air levitation). Yes.

  In the example shown in FIG. 4A, the lipophilic treatment part 21 is provided on the inner peripheral surface 20A of the bearing metal 20 in the range corresponding to the high load area HW1, while the areas other than the formation area of the lipophilic treatment part 21 are non-lipophilic. An example of the unit 22 is shown. When the low-viscosity oil 0W-20 is used as the lubricating fluid, the oleophilic treatment part 21 is a part that has been subjected to a treatment showing oleophilicity to 0W-20, and the non-lipophilic part 22 is 0W-20. On the other hand, it is a part that does not show lipophilicity. Therefore, in the inner peripheral surface 20A, only the region of the lipophilic treatment section 21 can be always wetted at 0W-20.

  In the example shown in FIG. 4B, the lipophilic treatment part 31 is provided on the inner peripheral surface 30A of the bearing metal 30 in the range corresponding to the high load area HW2, while the areas other than the formation area of the lipophilic treatment part 31 are non-lipophilic. An example of the unit 32 is shown. When low-viscosity oil 0W-20 is used as the lubricating fluid, similarly, the lipophilic treatment part 31 is a part that has been subjected to a treatment that exhibits lipophilicity to 0W-20, and the non-lipophilic part 32 is 0W- 20 is a part that does not exhibit lipophilicity. Therefore, in the inner peripheral surface 30A, only the region of the lipophilic treatment section 31 can be always wetted at 0W-20.

  The low-viscosity oil 0W-20 is supplied to the lipophilic processing units 21 and 31 from the discharge ports 69A and 67A by the oil supply mechanism 60. The discharge ports 69A and 67A are arranged immediately downstream in the relative sliding directions C1 and C2 of the bearing metals 20 and 30 (FIG. 6). For this reason, the low-viscosity oil 0W-20 discharged from the discharge ports 69A and 67A is immediately carried on the lipophilic treatment units 21 and 31. The oil is discharged from the discharge ports 69A and 67A by the controller 80 (FIG. 2) driving the oil pump 61 at a predetermined timing.

  The oleophilic treatment parts 21 and 31 can be formed by applying, evaporating, coating, or adhering oleophilic material pieces to the high-load areas HW1 and HW2 of the inner peripheral surfaces 20A and 30A of the oleophilic material. For example, the lipophilic treatment parts 21 and 31 formed by applying Teflon (registered trademark) as a lipophilic material to the inner peripheral surfaces 20A and 30A is one of the preferred embodiments. On the other hand, when the inner peripheral surfaces 20A and 30A themselves have oil repellency that repels oil, the non-lipophilic portions 22 and 32 are formed by not performing special treatment on the inner peripheral surfaces 20A and 30A. Can do. When the oil repellency is weak, it is desirable to perform a process such as applying an oil repellant material to the regions corresponding to the non-lipophilic portions 22 and 32.

  The oleophilic treatment parts 21 and 31 can also be formed by forming the high load areas HW1 and HW2 of the inner peripheral surfaces 20A and 30A with an oil-impregnated surface layer. For example, in the high load areas HW1 and HW2, a groove is formed on the inner peripheral surfaces 20A and 30A, and a porous member capable of retaining oil is fitted into the groove, thereby providing a lipophilic oil composed of an oil-impregnated surface layer. The processing units 21 and 31 can be formed. Examples of the porous member include foamed metal obtained by foam molding of a metal material kneaded with a foaming agent, and a porous body of ceramics such as silicon carbide, alumina, or zirconia.

  4A and 4B show an example in which the lipophilic treatment portions 21 and 31 are provided on the bearing member side, that is, the inner peripheral surfaces 20A and 30A of the bearing metals 20 and 30, but these are the shafts of the high load regions HW1 and HW2. It may be provided on the member side (the outer peripheral surface 72A of the crank pin 72 and the outer peripheral surface 71A of the crank journal 71) or may be provided on both the bearing member side and the shaft member side. Also in the high load areas HW1R and HW2R where a high load is applied by inertial force, the lipophilic treatment parts 21 and 31 may be provided on at least one of the bearing member side and the shaft member side.

  FIG. 13 and FIG. 14 show a preferred lipophilic treatment when the engine body 1 is a compression self-ignition engine in which the timing at which the in-cylinder maximum combustion pressure Pmax is generated is a crank angle = 0 ° to 20 °. An example of forming the portions 21 and 31 is shown. In FIG.13 and FIG.14, the lipophilic process parts 21 and 31 are the application parts 23, 25, 33, and 35 which apply | coat lipophilic materials, such as Teflon (trademark), and the non-lipophilic parts 22 and 32 are shown. The example which is the oil-repellent part 24,26,34,36 to which the said lipophilic material is not apply | coated is shown.

  FIG. 13A is a perspective view showing an example of a lipophilic treatment for the bearing metal 20 for the crankpin 72. On the inner peripheral surface 20A of the bearing metal 20, an arc portion of θ1 = TDC ± 10 ° centering on a line connecting the center point of the bearing metal 20 and the point y1 serves as a transmission path of the in-cylinder maximum combustion pressure Pmax. It is the 1st field K1 corresponding to high load field HW1. The other area of the inner peripheral surface 20A excluding the first area K1 is the second area K2. The first region K1 is the application part 23, and the second region K2 is the oil repellent part 24.

  FIG. 13B is a perspective view showing an example of a lipophilic treatment on the outer peripheral surface 72A of the crankpin 72. FIG. In this outer peripheral surface 72A, a range of 20 ° in the direction opposite to the sliding direction D1 from the line connecting the center point of the crank pin 72 and the point y2 is the first region K1 corresponding to the high load region HW1. That is, the arc portion of θ2 = TDC to −20 ° is the first region K1. The other area of the outer peripheral surface 72A excluding the first area K1 is the second area K2. The first region K1 is the application part 25, and the second region K2 is the oil repellent part 26.

  FIG. 14A is a perspective view showing an example of a lipophilic treatment for the bearing metal 30 for the crank journal 71. On the inner peripheral surface 30A of the bearing metal 30, the first region K1 corresponding to the high load region HW2 is a range of 20 ° in the direction opposite to the sliding direction C2 from the line connecting the center point of the bearing metal 30 and the point y3. It becomes. That is, the arc portion of θ3 = TDC to + 20 ° is the first region K1. The other region of the inner peripheral surface 30A excluding the first region K1 is the second region K2. The first region K1 is the application part 33, and the second region K2 is the oil repellent part 34.

  FIG. 14B is a perspective view showing an example of a lipophilic treatment on the outer peripheral surface 71 </ b> A of the crank journal 71. In this outer peripheral surface 71A, a circular arc portion of ± 10 ° centering on a line connecting the center point of the crank journal 71 and the point y4 becomes a first region K1 corresponding to the high load region HW2. The other area of the outer peripheral surface 71A excluding the first area K1 is the second area K2. The first region K1 is the application part 35, and the second region K2 is the oil repellent part 36.

[Function and effect]
According to the reciprocating piston engine which concerns on this embodiment demonstrated above, there exist the following effects. The crank mechanism of the present embodiment includes a bearing structure portion in which the inner peripheral surface 20A (first sliding surface) of the bearing metal 20 and the outer peripheral surface 72A (second sliding surface) of the crank pin 72 face each other, and the bearing metal 30. The inner peripheral surface 30A (first sliding surface) and the outer peripheral surface 71A (second sliding surface) of the crank journal 71 are opposed to each other. The inner peripheral surfaces 20A and 30A have projecting shape portions M1 and M2 projecting in the facing direction in a cross section orthogonal to the axial direction. In the projecting shape portions M1 and M2, the minimum gap h1 at the apex P is set in the range of 0.5 μm to 40 μm, and the gap ratio h2 / h1 between the minimum gap h1 and the maximum gap h2 is 1.5 to 5. Set to a range of zero. For this reason, the inner peripheral surfaces 20A, 30A can be levitated from the outer peripheral surfaces 72A, 71A by the fluid flowing into the gap G when the inner peripheral surfaces 20A, 30A and the outer peripheral surfaces 72A, 71A face each other. Become. That is, the levitation effect can be obtained by the shape features (profiles) of the projecting shape portions M1 and M2 of the inner peripheral surfaces 20A and 30A. Therefore, the sliding resistance between the inner peripheral surfaces 20A and 30A and the outer peripheral surfaces 72A and 71A can be significantly reduced.

  Further, the inner peripheral surfaces 20A and 30A serving as the sliding surfaces and the outer peripheral surfaces 72A and 71A serve as a transmission path for the load W accompanying the in-cylinder maximum combustion pressure Pmax received by the connecting rod 8 from the piston 5 (first load K1 (high load)). Region HW) and the other second region K2. The first region K1 is set as the lipophilic treatment unit 21 (region having affinity), while the second region K2 is set as the non-lipophilic portion 22 (region having non-affinity). As a result, a lubricating fluid such as low-viscosity oil is held in the first region K1. Therefore, even when a high load associated with the in-cylinder maximum combustion pressure Pmax acts on the crankshaft 7 from the connecting rod 8 and a good levitation effect cannot be obtained, the lubricating fluid existing in the first region K1 causes the gap between the sliding surfaces. The increase in frictional resistance is suppressed.

  In addition, air flows as a fluid F into a gap G between the inner peripheral surfaces 20A, 30A and the outer peripheral surfaces 72A, 71A, and low viscosity oil is used as the lubricating fluid. As a result, one of the inner peripheral surfaces 20A and 30A and the outer peripheral surfaces 72A and 71A is allowed to float from the other, and the frictional resistance between the sliding surfaces can be minimized. In addition, by retaining low-viscosity oil in the first region K1, the frictional resistance can be reduced even at a timing when air levitation does not occur due to the in-cylinder maximum combustion pressure Pmax.

[Description of Modified Embodiment]
As mentioned above, although embodiment of this invention was described, this invention is not limited to this. For example, in the above-described embodiment, the example in which the lipophilic treatment units 21 and 31 are arranged in the vicinity of the top portion P is shown. However, if there is a difference between the positions of the high load areas HW1 and HW2 and the position of the apex P, the lipophilic treatment sections 21 and 31 may be provided at positions corresponding to the positions of the high load areas HW1 and HW2.

  In the above embodiment, an example in which low viscosity oil is used as the lubricating fluid and the oil supply mechanism 60 supplies oil to the gap G has been described. Instead of this, water may be used as the lubricating fluid, and water may be supplied to the gap G by a water supply mechanism similar to the oil supply mechanism 60. In this case, a hydrophilic treatment part having affinity for water is applied instead of the lipophilic treatment parts 21 and 31, and a water repellent treatment part that repels water is applied instead of the non-lipophilic parts 22 and 32. The

  Moreover, in the said embodiment, although air was illustrated as the fluid F which flows in into the clearance gap G and expresses sliding levitation, you may use water as the fluid F (water levitation). Even in this case, low-viscosity oil can be used as the lubricating fluid. In addition, when water is used as the fluid F, it is desirable to add a rust inhibitor. Furthermore, a low-viscosity oil such as 0W-20 can be used as the fluid F (oil levitation). In this case, oil having a viscosity higher than 0W-20 can be used as the lubricating fluid.

1 Engine body 2 Cylinder 20 Bearing metal (first member)
20A Inner peripheral surface (first sliding surface)
21 Lipophilic treatment part (affinity area)
22 Non-lipophilic part (area with non-affinity)
30 Bearing metal (first member)
30A Inner peripheral surface (first sliding surface)
3 Cylinder block 3
31 Lipophilic treatment part (affinity area)
32 Non-lipophilic part (region having non-affinity)
3C Bearing section 5 Piston 7 Crankshaft 71 Crank journal (second member)
71A Outer peripheral surface (second sliding surface)
72 Crankpin (second member)
72A Outer peripheral surface (second sliding surface)
8 Connecting rod 8B Big end (big end)
h1 Minimum gap h2 Maximum gap C1, C2 Sliding direction M1, M2 Overhanging shape part P Top part Q Bottom part

Claims (6)

A reciprocating piston engine comprising a piston and a crank mechanism including a connecting rod and a crankshaft,
A first member that becomes a bearing member in the crank mechanism and has a first sliding surface on the inner periphery;
A shaft member in the crank mechanism, and a second member having a second sliding surface on the outer periphery facing the first sliding surface with a gap,
By the relative rotation of the second member with respect to the first member, the first sliding surface and the second sliding surface each move relatively in a predetermined sliding direction,
At least one of the first sliding surface and the second sliding surface has a protruding shape portion that projects in the facing direction in a cross section orthogonal to the axial direction,
The projecting shape portion includes a top portion that is the most projecting portion, and a skirt portion that is disposed at least on the downstream side in the sliding direction of the top portion and is positioned farthest from the counterpart sliding surface,
In the projecting shape portion, when the gap at the top is the minimum gap h1, and the gap at the skirt is the maximum gap h2,
h1 = 0.5 μm to 40 μm,
h2 / h1 = 1.5-5.0,
Is set to the range of
In at least one of the first sliding surface and the second sliding surface,
A first region that is a transmission path of a load associated with the in-cylinder maximum combustion pressure received by the connecting rod from the piston is a region having affinity with a predetermined lubricating fluid;
The second region other than the first region is a region having non-affinity with the lubricating fluid ,
Air flows into the gap,
The lubricating fluid is a low viscosity oil;
The low-viscosity oil is an oil having a viscosity larger than that of air and not more than 6.8 × 10 ⁻³ [Pa · s].
A reciprocating piston engine. The reciprocating piston engine according to claim 1 ,
The first region has a surface layer made of a lipophilic substance,
A reciprocating piston engine, wherein the second region has a surface layer made of an oil repellent material. The reciprocating piston engine according to claim 1 ,
A reciprocating piston engine, wherein the first region has an oil-impregnated surface layer. The reciprocating piston engine according to any one of claims 1 to 3 ,
The crankshaft includes a crankpin and a crank journal, and the connecting rod connects the crankpin and the piston;
The first member is a bearing metal fitted in a bearing portion of the crankshaft, and the first sliding surface is an inner peripheral surface of the bearing metal;
A reciprocating piston engine, wherein the second member is the crank journal, and the second sliding surface is an outer peripheral surface of the crank journal. The reciprocating piston engine according to claim 4 ,
The reciprocating piston engine is a compression self-ignition engine;
A reciprocating piston engine, wherein the first region is disposed in a region serving as a load transmission path between a crank angle of 0 ° and 20 °. The reciprocating piston engine according to any one of claims 1 to 3 ,
The crankshaft includes a crankpin and a crank journal, and the connecting rod connects the crankpin and the piston;
The first member is a bearing metal fitted into the large end of the connecting rod, and the first sliding surface is an inner peripheral surface of the bearing metal;
A reciprocating piston engine, wherein the second member is the crank pin, and the second sliding surface is an outer peripheral surface of the crank pin.

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