JP2018146044A - Reciprocation piston engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce friction resistance regardless of an operating state of an engine without requiring labors for processing a sliding face at a bearing structure part for reducing friction using a floating effect.SOLUTION: At a bearing structure part of a big end 8B of a connection rod 8 and a crank pin 72, bearing metal 20 is fitted with a bearing hole 8C of the big end 8B. An inner peripheral face 20A of the bearing metal 20 and an outer peripheral face 72A of the crank pin 72 are opposed to each other at a gap G. The inner peripheral face 20A has a projection-shaped part M1 projecting in an opposing direction to the outer peripheral face 72A. When a gap of the projection-shaped part M1 at the peak part P is designated as a minimum gap h1 and a gap at a skirt part Q is designated as a maximum gap h2, a range of h1=0.5 μm to 40 μm and h2/h1=1.5 to 5.0 is set. The inner peripheral face 20A slides and floats to the outer peripheral face 72A. When a rotation number of an engine reaches to a high rotation region where it is difficult to slide and float, lubricating fluid is supplied to the gap G.SELECTED DRAWING: Figure 4A

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 shaft support portion by a lower cylinder block of a crank journal. In these bearing structures, the inner peripheral surface of the bearing member (for example, the inner peripheral surface of the connecting rod large end) and the outer peripheral surface of the shaft member (the outer peripheral surface of the crank pin) 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

  However, depending on the operating state of the engine, the above levitation performance may be reduced. For example, when the engine has a high rotational speed, the bearing load in the bearing structure increases, which may cause a reduction or disappearance of the levitation effect. 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.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a reciprocating piston engine having a bearing structure portion that reduces friction by utilizing a levitation effect, and does not require labor to process a sliding surface, and provides friction resistance regardless of the operating state of the engine. It is to reduce.

A reciprocating piston engine according to one aspect of the present invention is a reciprocating piston engine including a piston and a crank mechanism, and serves as a bearing member in the crank mechanism, and a first member having a first sliding surface on an inner periphery thereof. 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, and the first sliding surface and the second sliding surface, A fluid supply part that supplies a lubricating fluid to a gap between the fluid supply part and a control part that controls a supply operation of the lubricating fluid by the fluid supply part, and by relative rotation of the second member with respect to the first member The first sliding surface and the second sliding surface move relative to each other in a predetermined sliding direction, and at least one of the first sliding surface and the second sliding surface is orthogonal to the axial direction. In the cross-section The projecting shape portion has a projecting shape portion, and the projecting shape portion is located at the most projecting portion, and at the most distant position relative to the mating sliding surface, at least on the downstream side in the sliding direction. And 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,
The control unit controls the fluid supply unit so that the lubricating fluid is supplied to the gap when the rotational speed of the reciprocating piston engine reaches a predetermined high rotation range. It is characterized by.

  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, during the relative movement of the second member, one sliding surface can be levitated from the other sliding surface by the fluid flowing between the first sliding surface and the second sliding surface. Become. That is, the levitation effect can be obtained by the shape feature (profile) of at least one of the first sliding surface and the second sliding surface.

  Further, in a high engine speed region where the inertial force of each part of the crank mechanism increases, that is, in an operation region where it is difficult to obtain a levitation effect, the control unit is provided between the first sliding surface and the second sliding surface. Supply lubricating fluid to the gap. This makes it possible to maintain a low frictional resistance between the first sliding surface and the second sliding surface by the presence of the lubricating fluid even when a good levitation effect cannot be obtained in the high rotation region. Become.

  In the above-described reciprocating piston engine, the crank mechanism includes a crankshaft including a crankpin and a crank journal, and a connecting rod that connects the crankpin and the piston, and the first member is a large end of the connecting rod. In addition, the second member may be the crank pin.

  The connecting rod increases the inertial force as the engine speed increases. A load based on this inertial force, particularly an explosion load applied from the piston during the combustion process, is transmitted to a bearing structure portion comprising a connecting rod large end as a bearing member and a crank pin as a shaft member. For this reason, the above-mentioned levitation effect is likely to be hindered in a high engine speed region. However, according to the above-described reciprocating piston engine, the above-described levitation effect and the low frictional resistance maintaining effect can be obtained in the bearing structure portion including the connecting rod large end portion and the crankpin.

  In the above-described reciprocating piston engine, the crank mechanism includes a crankshaft including a crankpin and a crank journal, and a connecting rod that connects the crankpin and the piston, and the first member is a bearing portion of the crankshaft. And the second member may be the crank journal.

  According to this reciprocating piston engine, the above-described levitation effect and the above-described levitation effect can be achieved in a high rotation region of the engine with respect to a bearing structure portion including a bearing portion of a crank shaft (crank journal) as a bearing member and a crank journal as a shaft member. A maintenance effect of low frictional resistance can be obtained.

  In this case, the control unit supplies the lubricating fluid to the gap when the rotation speed reaches a predetermined high rotation region and the load of the reciprocating piston engine reaches a predetermined high load region. It is desirable to control the fluid supply unit.

  When the engine reaches a high load region, the crankshaft tends to bend and deform. In the bearing structure portion of the crankshaft, the levitation effect is likely to be hindered by the bending deformation. Therefore, when the engine reaches a high rotation and high load region, the above-described levitation effect and a low frictional resistance maintenance effect can be efficiently obtained by supplying the lubricating fluid to the gap.

  In the above-described reciprocating piston engine, it is preferable that the minimum gap h1 is set in a range of 0.5 μm to 1.5 μm, and the fluid supply unit supplies low-viscosity oil as the lubricating fluid to the gap. .

  According to this sliding structure, it is possible to generate a large levitation force with the fluid flowing between the first sliding surface and the second sliding surface being the air that can flow in the most easily. It becomes. In addition, by supplying low-viscosity oil to the gap, it is possible to obtain good lubricity in an operation scene in which the above-described levitation effect of the engine is difficult to be obtained.

  In the above-described reciprocating piston engine, it is desirable that the first member and the second member are made of the same material. As a result, the variation in the length of the gap due to the difference in thermal expansion, that is, the variation in the minimum gap h1 and the maximum gap h2 can be suppressed.

  According to the present invention, in a reciprocating piston engine provided with a bearing structure portion for reducing friction by utilizing a levitation effect, it is not necessary to process a sliding surface in the bearing structure portion, and the operating state of the engine Regardless of this, the frictional resistance between the sliding surfaces can be reduced.

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 diagram illustrating a state in which a load associated with the in-cylinder combustion pressure is applied from the connecting rod to the piston pin. FIG. 12 is a schematic diagram for explaining bending of the crankshaft. FIG. 13 is a graph showing the relationship between in-cylinder combustion pressure and engine speed. FIG. 14 is a block diagram showing a control system of the reciprocating piston engine of the present embodiment. FIG. 15 is a flowchart showing the operation of the control system.

[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 serving as a rotating shaft of the crankshaft 7 and is supported by a bearing metal 21 (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 81 (FIG. 14). 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 strip-shaped metal piece 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. 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 at a predetermined timing.

  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 21 (first member) is fitted into the bearing portion 3C. The bearing metal 21 is a sliding bearing in which a band-shaped metal circle is formed in an annular shape, similar to the bearing metal 20 described above. In the bearing structure portion, the bearing metal 21 is a bearing member, and the crank journal 71 (second member) is a shaft member.

  The bearing metal 21 has a cylindrical inner peripheral surface 21A (first sliding surface) through which the crank journal 71 is inserted. The crank journal 71 is a cylindrical member having a perfect cross section, and has an outer peripheral surface 71A (second sliding surface) facing the inner peripheral surface 21A with a predetermined gap G in the radial direction on the outer periphery. Yes. And 21 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 overhanging shape portion M2 forms one overhang on the circumference of the inner circumferential surface 21A 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 21A and the outer peripheral surface 71A, or may be provided on the outer peripheral surface 71A, or both the inner peripheral surface 21A 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 overhanging 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 21A. 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 21A 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 at a predetermined timing.

  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 21, and the inner peripheral surface 21A 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 peripheral surface 21A (bearing metal 21) is a sliding direction C2 that goes counterclockwise, and the sliding direction of the outer peripheral 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 protruding shape portions M1 and M2 are provided on the bearing metal 20 and 21 sides, respectively. That is, it is provided on the inner peripheral surfaces 20A and 21A 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 21A 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 and 21A, the inner peripheral surfaces 20A and 21A are levitated (sliding levitated) with respect to the outer peripheral surfaces 72A and 71A. By this sliding levitation, the sliding resistance between the inner peripheral surfaces 20A, 21A 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 21A of the bearing metal 21 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 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]
Depending on the operating state of the engine, the sliding levitation performance may be reduced. For example, when the engine reaches a high rotational speed, the bearing load increases in the bearing structure portion of the crankshaft 7, which may reduce or eliminate the levitation effect. This point will be described with reference to FIGS.

  FIG. 11 is a view showing a state in which a load W accompanying the in-cylinder combustion pressure is applied from the connecting rod 8 to the piston pin 72. A high load W is applied 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. When the engine reaches the high rotational speed, the load W is further increased because the inertial force of the connecting rod 8 is increased.

  The load W is directed from the connecting rod 8 to the piston pin 72 mainly along the line segment A. Specifically, in the region HW1 in the vicinity of the portion where the bearing metal 20 integrally attached to the big end 8B intersects the line segment A (the intersection portion on the side close to the small end 8A), the bearing W is loaded by the load W. The inner peripheral surface 20 </ b> A of the metal 20 is directed toward the outer peripheral surface 72 </ b> A of the crankpin 72. If the load W is large, the sliding levitation state is canceled, and the inner peripheral surface 20A may come into contact with the outer peripheral surface 72A and the load W may be transmitted. In this case, the crank pin 72 to which the load W is transmitted moves downward due to inertia, and a region HW2 in the vicinity of the other portion (the intersecting portion far from the small end 8A) intersecting the line segment A of the bearing metal 20 The outer peripheral surface 72A can contact the inner peripheral surface 20A. As a result, the levitation effect that reduces the frictional resistance between the inner peripheral surface 20A and the outer peripheral surface 72A disappears.

  Further, the load W transmitted to the crank pin 72 is also transmitted to the crank journal 71 via the crank arm 73. The sliding levitation is canceled by the load W in the same manner as described above between the inner peripheral surface 20A of the bearing metal 21 and the outer peripheral surface 71A of the crank journal 71 that are integrally attached to the bearing portion 3C. There is. From the above, there is a concern that the frictional resistance increases in the bearing structure portion of the crank mechanism in a high engine speed range.

  Further, when the load on the engine main body 1 becomes high as during uphill running, sliding levitation may be canceled due to the bending of the crankshaft 7. FIG. 12 is a schematic diagram for explaining the bending of the crankshaft 7. When the engine main body 1 is in a high rotation and high load state, a large force is applied to the crankshaft 7 and the crankshaft 7 may be bent and deformed. In the figure, the crankshaft 7A is bent and deformed by a dotted line. Here, a crankshaft 7A that is curved between the bearing portions 3C at both ends of the crankshaft 7 is shown. Since heavy objects such as a crankshaft pulley 75 and a flywheel 76 are attached to the end portion of the crankshaft 7, bending deformation as shown in the figure is likely to occur when a high load state is reached. Due to this bending deformation, the inner peripheral surface 21A of the bearing metal 21 assembled to the bearing portion 3C may come into contact with the outer peripheral surface 71A of the crank journal 71, and the sliding levitation may be canceled.

[Oil supply control]
In view of the above sliding levitation inhibiting factors, in this embodiment, when the sliding levitation can be canceled during the operation of the engine body 1, the lubricating fluid is supplied to the gap G. FIG. 13 is a graph showing the relationship between in-cylinder combustion pressure and engine speed. Here, when the sliding levitation is manifested, the fluid F that flows into the gap G is air (air levitation). The lubricating fluid supplied by the oil supply mechanism 60 is low viscosity oil (0W-20). FIG. 13 is also a graph that divides a region where air levitation is executed and a region where lubrication assist with oil is performed.

  Until the engine speed reaches a predetermined high-speed region, the region is a region where air levitation is executed. In a high speed region where the engine speed exceeds a predetermined threshold, lubrication assist is set as the execution region. The lubrication assist is an operation in which oil is discharged from the discharge port 67A of the crank journal 71 and the discharge port 69A of the crank pin 72 to the gaps G by the operation of the oil pump 61.

  The lubrication assist can take various control modes. The simplest control is to perform lubrication assist on both the crank journal 71 and the crankpin 72 when the engine speed reaches a predetermined high speed region. In this case, whether or not oil is to be discharged from the discharge port 67A and the discharge port 69A is determined depending on whether or not the engine speed has exceeded a threshold value.

  Instead, lubrication assist may be performed only on the crankpin 72 side that receives the load W primarily from the piston 5 when the threshold rotational speed is exceeded. Further, with respect to the crank journal 71 (crankshaft 7), bending deformation becomes a problem when a high load is applied (FIG. 12). Therefore, when the engine speed reaches a predetermined high rotation range and the load of the engine body 1 reaches a predetermined high load range (high rotation / high load range in FIG. 13), the crank journal 71 is lubricated. May be performed. Note that the low rotation / high load region shown in FIG. 13 is also a region where it is difficult to realize sliding levitation. Therefore, lubrication assist may be performed even in this low rotation / high load region.

  FIG. 14 is a block diagram showing a control system of the reciprocating piston engine of the present embodiment. The control system includes a control unit 81 that controls an oil supply operation (lubrication assist) by the oil supply mechanism 60 (oil pump 61). The reciprocating piston engine is provided with an engine rotation sensor 82, an in-cylinder pressure sensor 83, and an accelerator opening sensor 84, and the control unit 81 acquires state information of the engine body 1 from these sensors.

  The engine rotation sensor 82 detects the number of rotations of the crankshaft 7. The in-cylinder pressure sensor 83 detects the combustion pressure in the cylinder 2. The accelerator opening sensor 84 detects the opening of an unillustrated accelerator pedal (the opening of a throttle valve). The control unit 81 determines whether or not the engine body 1 is in a predetermined high rotation region based on the detection result of the engine rotation sensor 82. When the engine body 1 reaches the high rotation region, the oil pump 61 is operated to discharge oil into the gap G from the discharge port 67A and the discharge port 69A. On the other hand, when the high rotation area has not been reached, the oil discharge is stopped.

  The controller 81 determines whether or not the engine body 1 is in a predetermined high load region based on the detection results of the in-cylinder pressure sensor 83 and the accelerator opening sensor 84. This determination process is executed, for example, when lubrication assist is performed on the crank journal 71 only when the condition that the engine body 1 is in a high rotation and high load state is satisfied. In this case, the control unit 81 discharges oil only from the crankpin 72 (discharge port 69A) in a high rotation / low load state. On the other hand, the control unit 81 causes oil to be discharged from both the crank pin 72 (discharge port 69A) and the crank journal 71 (discharge port 67A) in a state of high rotation and high load. In this embodiment, an on-off valve that switches between oil supply and stop is provided at an appropriate position of the oil supply line 65 shown in FIG.

  FIG. 15 is a flowchart showing an oil supply operation by the control unit 81. Here, a control example is shown in which whether or not the engine body 1 has reached the high rotation region is a condition for executing the lubrication assist. The controller 81 acquires data related to the rotation speed (engine rotation speed) of the crankshaft 7 from the engine rotation sensor 82 at a predetermined sampling timing during the operation in which the above air levitation (sliding levitation) is realized. (Step S1). Next, the control unit 81 compares a predetermined threshold rotational speed with the acquired engine rotational speed, and determines whether or not the current rotational speed is in a high rotational speed region (step S2).

  When it is the high rotation region (YES in step S2), the control unit 81 checks whether or not the oil pump 61 is currently operating (step S3). If the oil pump 61 is not operating (NO in step S3), the control unit 81 gives an operation signal to the oil pump 61 to start the operation, and discharges a predetermined amount of oil from the discharge port 67A and the discharge port 69A. (Step S4). On the other hand, if the oil pump 61 is already operating (YES in step S3), step S4 is skipped.

  On the other hand, when the engine speed has not reached the high speed region (NO in step S2), the control unit 81 maintains the oil pump 61 in a stopped state. Alternatively, when the oil pump 61 is operating, the control unit 81 stops the operation of the oil pump 61 (step S5). Thereafter, it is determined whether or not a stop instruction is given to the engine body 1 (step S6). If there is no stop instruction (NO in step S6), the process returns to step S1 and the process is repeated. If there is a stop instruction (YES in step S6), the process ends.

[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 21. The inner peripheral surface 21A (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 21A 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 and 21A can be levitated from the outer peripheral surfaces 72A and 71A by the fluid flowing into the gap G when the inner peripheral surfaces 20A and 21A facing each other and the outer peripheral surfaces 72A and 71A move relative to each other. Become. That is, the levitation effect can be obtained by the shape features (profiles) of the overhanging portions M1 and M2 of the inner peripheral surfaces 20A and 21A. Therefore, the sliding resistance between the inner peripheral surfaces 20A and 21A and the outer peripheral surfaces 72A and 71A can be significantly reduced.

  Further, in the high engine speed region where the inertial force of each part of the crank mechanism increases, that is, in the operation region where it is difficult to obtain the levitation effect, the control unit 81 controls the oil pump 61 to connect the inner peripheral surfaces 20A and 21A. Low viscosity oil is supplied to the gap G between the outer peripheral surfaces 72A and 71A. Thereby, even when a favorable levitation effect cannot be obtained in the high rotation region, the state in which the frictional resistance between the first sliding surface and the second sliding surface is low is maintained by the interposition of the oil pump 61 in the gap G. It becomes possible.

  The overhanging shape portion M1 is applied to the bearing structure portion of the big end 8B of the connecting rod 8 and the crank pin 72. The connecting rod 8 increases in inertial force as the engine body 1 rotates at a higher speed. A load based on this inertial force, particularly an explosion load applied from the piston during the combustion process, is transmitted to the bearing structure portion including the big end 8B and the crankpin 72. For this reason, the effect of sliding levitation tends to be hindered in a high engine speed region. However, in the present embodiment, the control unit 81 supplies the low-viscosity oil to the gap G when the engine body 1 rotates at high speed, so that the state of low frictional resistance can be maintained even when the sliding levitation is canceled.

  The projecting shape portion M2 is also applied to the bearing structure portion of the bearing portion 3C and the crank journal 71. The explosion load is also transmitted secondarily to the bearing structure, but the controller 81 supplies low-viscosity oil to the gap G when the engine body 1 rotates at a high speed, thereby maintaining a low frictional resistance state. To do. In particular, when the engine reaches a high load region, the crankshaft 7 tends to be bent and deformed, and the sliding levitation effect is easily hindered by the bent deformation. However, when the engine reaches a high rotation and high load region, the low-viscosity oil is supplied to the gap G, so that the state of low frictional resistance can be maintained even when sliding levitation is canceled.

  Further, if the minimum gap h1 is set in a range of 0.5 μm to 1.5 μm and air levitation that causes air to flow into the gap G is expressed, the frictional resistance between the sliding surfaces can be minimized. Further, by supplying the low-viscosity oil to the gap G, good lubricity can be obtained in an engine operation scene in which the sliding levitation effect is difficult to be obtained.

[Description of Other Modified Embodiments]
As mentioned above, although embodiment of this invention was described, this invention is not limited to this. For example, in the above-described 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.

  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 Bearing metal (first member)
21A Inner peripheral surface (first sliding surface)
3 Cylinder block 3
3C Bearing part 5 Piston 60 Oil supply mechanism (fluid supply part)
61 Oil pump 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)
81 Control part h1 Minimum gap h2 Maximum gap C1, C2 Sliding direction M1, M2 Overhang shape part P Top part Q Bottom part

Claims (6)

A reciprocating piston engine having a piston and a crank mechanism,
A first member that becomes a bearing member in the crank mechanism and has a first sliding surface on the inner periphery;
A second member that is a shaft member in the crank mechanism and has a second sliding surface on the outer periphery facing the first sliding surface with a gap;
A fluid supply unit for supplying a lubricating fluid to a gap between the first sliding surface and the second sliding surface;
A control unit for controlling the supply operation of the lubricating fluid by the fluid supply unit,
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
The control unit is a reciprocating piston engine that controls the fluid supply unit so that the lubricating fluid is supplied to the gap when the rotation speed of the reciprocating piston engine reaches a predetermined high rotation region. The reciprocating piston engine according to claim 1,
The crank mechanism includes a crankshaft including a crankpin and a crank journal; and a connecting rod for connecting the crankpin and the piston;
The first member is a large end of the connecting rod;
A reciprocating piston engine, wherein the second member is the crank pin. The reciprocating piston engine according to claim 1,
The crank mechanism includes a crankshaft including a crankpin and a crank journal; and a connecting rod for connecting the crankpin and the piston;
The first member is a bearing portion of the crankshaft;
A reciprocating piston engine, wherein the second member is the crank journal. The reciprocating piston engine according to claim 3,
The control unit is configured to supply the lubricating fluid to the gap when the rotation speed reaches a predetermined high rotation region and the load of the reciprocating piston engine reaches a predetermined high load region. A reciprocating piston engine that controls the fluid supply. The reciprocating piston engine according to any one of claims 1 to 4,
The minimum gap h1 is set in a range of 0.5 μm to 1.5 μm,
The fluid supply unit is a reciprocating piston engine that supplies low-viscosity oil as the lubricating fluid to the gap. The reciprocating piston engine according to any one of claims 1 to 5,
A reciprocating piston engine, wherein the first member and the second member are made of the same material.

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