JP2018145887A - Reciprocation piston engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reciprocation piston engine capable of reducing a mechanical loss as less as possible.SOLUTION: A projection-shaped part 31S projecting toward a first sliding face 2A is provided on a second sliding face 31S. When a gap between the first sliding face 2A and the second sliding face 31S at a peak part Ps that is a portion of the projection-shaped part 31S projecting the most is designated as a minimum gap h1 and a gap at the skirt part Qs that is positioned the most away from the first sliding face 2A 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. Air is interposed between the sliding faces in a low rotation number region, and lubricating liquid is interposed in a high rotation number region A2.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a reciprocating piston engine including a piston that reciprocates in a cylinder and a crank mechanism.

  Conventionally, it has been studied to reduce the mechanical loss in order to improve the fuel efficiency of the engine.

  For example, in Patent Document 1, in a reciprocating piston engine having a piston that reciprocates in a cylinder, the frictional resistance generated between the outer peripheral wall of the piston and the inner peripheral wall of the cylinder is reduced, thereby reducing mechanical loss. The thing which aimed at is disclosed.

  Specifically, in the engine of Patent Document 1, in order to reduce the frictional resistance, a coating layer having a plurality of minute recesses is provided on the outer peripheral wall of the piston in order to lift the piston from the inner peripheral wall of the cylinder. It is comprised so that dynamic pressure may arise in a recessed part.

Japanese Patent Laid-Open No. 2006-121597

  However, only the dynamic pressure generated in each of the recesses makes it difficult to properly lift the piston from the inner peripheral wall of the cylinder when the load on the piston is high. For this reason, there is a limit in reducing the mechanical loss.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a reciprocating piston engine capable of reducing mechanical loss as much as possible with a simple configuration.

In order to solve the above-described problems, the present invention provides a reciprocating piston engine including a piston that reciprocates in a cylinder and a crank mechanism, a first member having a first sliding surface, the first sliding surface, A second sliding surface facing each other with a gap, and a second member that moves relative to the first member in a predetermined sliding direction when the piston reciprocates; the first sliding surface; A lubricating liquid supply device for supplying a lubricating liquid having a viscosity higher than that of air between the second sliding surface and the second sliding surface in the cross section along the sliding direction, An overhanging shape portion projecting toward the first sliding surface, the overhanging shape portion being disposed at least on the downstream side in the sliding direction of the apex that is the most projecting portion, and Including a skirt that is located farthest from one sliding surface, There are, the gap in the top and the minimum gap h1, when the maximum gap h2 of the gap in the skirt,
h1 = 0.5 μm to 40 μm,
h2 / h1 = 1.5-5.0,
The lubricating liquid supply device is configured to supply the lubricating liquid to the first sliding surface and the second sliding surface when the engine rotational speed is equal to or lower than a preset reference rotational speed. On the other hand, when the engine speed is higher than the reference speed, the lubricating layer is formed so that an air layer is formed between the first sliding surface and the second sliding surface. A reciprocating piston engine characterized by stopping the supply of liquid is provided.

  According to this engine, the liquid for lubrication interposed between the second sliding surface and the first sliding surface is transferred to the skirt portion by a simple configuration in which the protruding shape portion is provided on the second sliding surface. It is possible to apply a force in the direction of separating both the sliding surfaces by the lubricating liquid. In addition, since the size of the minimum gap h1 and the ratio between the minimum gap h1 and the maximum gap h2 are set within the above range, the coefficient of friction between both sliding surfaces can be reduced, and the above-mentioned both sliding areas can be reduced. The force in the direction of separating the surfaces can be increased. Therefore, the second sliding surface can be lifted more reliably from the first sliding surface, and the frictional resistance and the mechanical loss generated when the second member slides can be significantly reduced.

  Further, according to this engine, in a low rotational speed region where the engine rotational speed is equal to or lower than the reference rotational speed and in a region where the sliding levitation force obtained with air having a low viscosity is likely to be small, for lubrication having a higher viscosity than air. By supplying the liquid between both sliding surfaces, it is possible to suppress the contact between the sliding surfaces, thereby reducing the frictional resistance, and in other high rotational speed regions, both sliding surfaces having low viscosity Friction resistance can be kept small by using low-viscosity air as the intervening fluid. Therefore, it is possible to reliably reduce the frictional resistance and the mechanical loss accompanying the sliding of the second member in the entire operation region of the engine.

  In the above configuration, it is preferable that the lubricating liquid is at least one of water and low-viscosity oil.

  According to this configuration, water having a relatively low viscosity or oil having a low viscosity is used as the lubricating liquid, so that the frictional resistance generated between the sliding surfaces can be more reliably reduced. Here, oil of about 0 W-20, that is, oil having a viscosity of about 6.8 × 10 −3 [Pa · s] or less is referred to as low viscosity oil.

  In the above configuration, it is preferable that the material of the first member and the material of the second member are the same.

  In this way, fluctuations in the minimum gap h1 and the maximum gap h2 due to the difference in thermal expansion can be suppressed, and these gaps can be more reliably contained in the appropriate range.

  In the above configuration, the first member is the cylinder, and the second member is a skirt portion of a piston that reciprocates in the cylinder, and the outer periphery of the skirt portion that faces the inner peripheral wall of the cylinder It is preferable that the protruding shape portion is provided on the wall.

  In this way, it is possible to reduce the frictional resistance generated between the piston skirt and the inner peripheral wall of the cylinder during the reciprocating motion of the piston, thereby effectively reducing the mechanical loss generated in the entire engine.

  Further, in the above configuration, the crankshaft is coupled to the piston and rotates in accordance with the reciprocating movement of the piston, and a crank bearing that rotatably supports the crankshaft, wherein the first member is the crank It is a shaft, and the second member is the crank bearing, and it is preferable that the projecting shape portion is provided on an inner peripheral wall of the crank bearing facing the outer peripheral wall of the crank shaft. 5).

  By doing so, it is possible to reduce the frictional resistance generated between the crankshaft and the crankshaft when the crankshaft rotates.

  Further, in the above configuration, a connecting rod that connects the piston and the crankshaft is provided, and the connecting rod includes a crankpin bearing that rotates relative to the crankpin in a state in which a crankpin constituting a part of the crankshaft is inserted. The first member is the crank pin, and the second member is the crank pin bearing, and the overhang is formed on an inner peripheral wall of the crank pin bearing facing the outer peripheral wall of the crank pin. A shape portion is preferably provided (claim 6).

  In this way, the frictional resistance generated between the connecting rod and the crankpin bearing when the connecting rod rotates can be reduced.

  As described above, according to the present invention, the mechanical loss of the engine can be reduced as much as possible with a simple configuration.

FIG. 1 is a schematic view showing a reciprocating piston engine according to the present invention. It is the schematic of the cross section which follows the II-II line | wire of FIG. It is the schematic of the cross section which follows the III-III line of FIG. It is a figure which shows the relationship between a connecting rod and a crankshaft. It is a figure which shows the relationship between a connecting rod and a crankshaft. It is the figure which expanded and showed the piston periphery. It is the schematic of the cross section which follows the VII-VII line of FIG. It is the figure which showed the skirt sliding surface typically. It is a figure for demonstrating the profile of an optimal sliding surface. It is the graph which showed the relationship between gap ratio and a levitation capacity coefficient. It is the graph which showed the relationship between the minimum clearance and a friction coefficient. It is a figure for demonstrating the neck swing motion of a piston. It is a schematic sectional drawing of a crank journal part periphery. It is a schematic diagram of the periphery of the connecting rod large end. It is a block diagram which shows the control system of an engine. It is the figure which showed the control area | region of the liquid pump for lubrication. FIG. 17A is a front view of a piston according to the second embodiment, and FIG. 17B is a side view of the piston. It is the XVII-XVII sectional view taken on the line of FIG. It is the XVIII-XVIII sectional view taken on the line of FIG. FIG. 20A is a schematic view of a skirt portion in a neutral state, and FIG. 20B is a schematic view of a skirt portion when a neck swing occurs. FIGS. 21A to 21C are diagrams for explaining the swinging state of the skirt portion accompanying the reciprocating motion of the piston.

(1) Overall Structure Hereinafter, a reciprocating piston engine according to an embodiment of the present invention will be described based on the drawings. A reciprocating piston engine 100 (hereinafter sometimes simply referred to as an engine) is an engine including a piston 5 that reciprocates in a cylinder 2 and a crank mechanism. The reciprocating piston engine 100 is mounted on a vehicle as a power source for driving and driving a vehicle such as an automobile, and as a device for assisting a motor and the like used as a drive source of the vehicle.

  FIG. 1 is a schematic sectional view of a reciprocating piston engine 100. FIG. 2 is a schematic view of a cross section taken along line II-II in FIG. The engine body 1 includes a cylinder block 3 in which a cylinder 2 is formed and a cylinder head 4 attached to the cylinder block 3. In the following description, the center axis direction of the cylinder 2 in the vertical direction in FIG.

  As shown in FIG. 2, in the present embodiment, the engine body 1 is an in-line four-cylinder engine, and the cylinder block 3 is formed with four cylinders 2 arranged in a line. For example, a fuel mainly composed of gasoline is supplied into the cylinder 2, and an air-fuel mixture of the fuel and air is combusted in the cylinder 2.

  In each cylinder 2, a piston 5 is housed so as to be able to reciprocate in the vertical direction. In the cylinder 2, a combustion chamber 6 in which the air-fuel mixture burns is defined by a crown surface 5A of the piston 5, an inner peripheral wall 2A of the cylinder 2, and a lower surface of the cylinder head 4.

  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 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 100 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.

  A spark plug 18 that supplies ignition energy to the air-fuel mixture in the combustion chamber 6 is attached to the cylinder head 4, one for each cylinder 2. Further, one injector 17 for injecting fuel into the combustion chamber 6 is attached to the cylinder head 4, one for each cylinder 2.

  Each piston 5 is connected to an upper end portion 82 of a connecting rod 8. A crankshaft 7 extending in the arrangement direction of the cylinders 2 is connected to the lower end portion 81 of each connecting rod 8. When the fuel / air mixture burns in the combustion chamber 6, the piston 5 and the connecting rod 8 reciprocate in the vertical direction, and the crankshaft 7 rotates about its central axis. The crankshaft 7 and the connecting rod 8 are members that constitute an engine crank mechanism.

(2) Structure of Crank Mechanism FIG. 3 is a schematic view of a cross section taken along line III-III in FIG. 4 and 5 are enlarged schematic views showing the vicinity of the lower end of the connecting rod 8 in order to explain the relationship between the connecting rod 8 and the crankshaft 7.

  As shown in FIG. 2, the crankshaft 7 is provided between a plurality of substantially cylindrical crank journal portions 71 centering on the rotation axis thereof, and between the crank journal portions 71, and is inserted into the lower end portion 81 of the connecting rod 8. The crankpin 72 is provided. Hereinafter, the lower end portion 81 of the connecting rod 8 is referred to as a connecting rod large end portion 81 as appropriate.

  In the cylinder block 3, a plurality of through holes 3 a (five through holes 3 a in the illustrated example) arranged in the arrangement direction of the cylinders 2 are formed at positions below the piston 5. A substantially annular crank bearing (second member) 40 is fitted in each of the through holes 3a. As shown in FIG. 3 and the like, the crank journal part (first member) 71 is inserted into the crank bearing 40 and is rotatably supported by the crank journal part. Surface) 71A slides along the inner peripheral wall (second sliding surface) 40A of the crank bearing 40. In the example of FIG. 4, the crank journal portion 71 rotates in the direction of the arrow Y31.

  The connecting rod large end 81 has a substantially circular through hole 81a. A substantially annular crankpin bearing 83 that rotates integrally with the connecting rod large end 81 is fitted into the through hole 81a. The crankpin 72 of the crankshaft 7 is inserted into a crankpin bearing 83 and is rotatably supported by the crankpin bearing 83.

  As shown in FIGS. 4 and 5, the connecting rod 8 including the crankpin bearing 83 and the crankshaft 7 including the crankpin 72 rotate relatively. Specifically, when the piston 5 is lowered from the state shown in FIG. 4, the connecting rod 8 is lowered while rotating in the direction of the arrow Y21 (counterclockwise in FIG. 5), as shown in FIG. On the other hand, the crankpin 72 revolves in the direction of the arrow Y22 (clockwise in FIG. 5) with respect to the central axis of the crank journal portion 71. The crankpin bearing 83 rotates relative to the crankpin 72 in the direction indicated by the arrow Y21 (counterclockwise in FIG. 5). Thus, with the reciprocation of the piston 5, the outer peripheral wall 72A (first sliding surface) of the crankpin 72 (first member) is moved to the inner peripheral wall 83A (second second) of the crankpin bearing (second member) 83. Slide in the direction of arrow Y21 relative to the sliding surface.

(3) Lubricating liquid supply system As shown in FIG. 2, a lubricating liquid for supplying a lubricating liquid (hereinafter referred to as “lubricating liquid” as appropriate) to the sliding portion of the engine body 1 in the engine 100. A supply system 200 is provided. In the present embodiment, as will be described later, in the low rotational speed region A1, between the inner peripheral wall 2A of the cylinder 2 and the outer peripheral wall of the piston 5, between the crank journal portion 71 and the crank bearing 40, and the crank pin 72. And the crankpin bearing 83 are supplied with lubricating liquid, respectively. Hereinafter, as appropriate, a portion between the inner peripheral wall 2A of the cylinder 2 and the outer peripheral wall of the piston 5, a portion between the crank journal portion 71 and the crank bearing 40, and a portion between the crank pin 72 and the crank pin bearing 83. These parts are collectively referred to as a sliding part of the engine body 1.

  In the present embodiment, water (hereinafter referred to as lubricating water) is used as the lubricating liquid. In particular, water to which a rust inhibitor is added is used as the lubricating water. For example, one of rust preventives for alkyl morpholines such as methylmorpholine and ethylmorpholine, rust preventives for organic amines such as triethanolamine and N-methyldiethanolamine, and rust preventives such as alkali metal carboxylates Or two or more rust inhibitors are added. In the present embodiment, a substance such as ethylene glycol that lowers the freezing point is also added to the lubricating water, and the lubricating water is adjusted so as not to freeze at 0 degrees.

  The lubrication water supply system 200 includes a strainer 201 provided in a pan 209 that is disposed below the engine body 1 and stores a lubrication liquid (lubricating water), a lubrication liquid lubrication liquid pump 202, and a pressure adjustment unit 203. And a filter 204, a lubricating liquid path 210, and a plurality of lubricating liquid ejecting apparatuses 210. The lubricating liquid injection device 210 is a device that injects a lubricating liquid (lubricating water) toward the lower surface of the piston 5, and is arranged in a posture that faces the lower surface of the piston 5 one by one below each piston 5. Yes. The lubricating liquid pump 202 draws up the lubricating liquid (lubricating water) from the pan 209 via the strainer 201. The pumped lubricating liquid (lubricating water) is adjusted to an appropriate pressure by the pressure adjusting unit 203, filtered by the filter 204, and then supplied to each part through the lubricating liquid path 210.

  The lubricating liquid path 210 includes a main passage 211 connected to the filter 204 and a plurality of piston-side passages 212 branched from the main passage 211 and connected to the respective lubricating liquid ejecting apparatuses 210. The lubricating liquid ejecting apparatus 210 is supplied with a lubricating liquid (lubricating water) through the main passage 211 and the piston side passage 212. The lubricating liquid ejecting apparatus 210 injects the supplied lubricating liquid (lubricating water) toward the lower surface of the piston 5, and thereby lubricates between the outer peripheral wall of the piston 5 and the inner peripheral wall 2 </ b> A of the cylinder 2. Liquid (lubricating water) is supplied.

  The lubricating liquid passage 210 includes a plurality of crank-side passages 213 branched from the main passage 211 and directed to the respective crank journal portions 71. In the example of FIG. 2, five crank-side passages 213 are formed corresponding to the five crank journal portions 71. The crank-side passages 213 are formed in the cylinder head 3 and open to the inner peripheral walls of the through holes 3A through which the crank journal portions 71 are respectively inserted. The lubricating liquid (lubricating water) in the crank-side passage 213 is introduced into the through hole 3A from these openings. The lubricating liquid (lubricating water) introduced into the through hole 3 </ b> A spreads between the crank journal portion 71 and the crank bearing 40.

  The lubricating liquid path 210 includes an in-shaft passage 214 formed in the crankshaft 7. Specifically, a plurality of crank journal passages 214a respectively formed in the crank journal portion 71 and opened to the outer peripheral wall 71A, and a plurality of crank pin inner passages 214a formed in the crank pin 72 and opened to the outer peripheral wall 72A. A passage 214c and a communication passage 214b that connects these passages are formed in the crankshaft 7.

  The number of crank journal portions 71 is larger than the number of crank pins 72, and some of the crank journal passages 214a are formed independently without being connected to the crank pin passages 214c. In the example of FIG. 2, the two right crankpin passages 214c are in communication with the crank journal passage 214a adjacent to the right side, and the two left crankpin passages 214c are in the crank journal adjacent to the left side. It communicates with the passage 214a, and the left and right crank journal interior 214a is independent.

  The lubricating liquid (lubricating water) led out to the through hole 3A as described above flows into the crank journal inner passage 214a, and the outer peripheral wall 72A of the crank pin 72 via the communication passage 214b and the crank pin inner passage 214c. Derived outside. The derived lubricating liquid (lubricating water) spreads between the outer peripheral wall 72 A of the crankpin 72 and the crankpin bearing 83.

(4) Piston Structure FIG. 6 is an enlarged schematic cross-sectional view showing the periphery of the piston 5. FIG. 7 is a schematic view of a cross section taken along line VII-VII in FIG. The piston 5 includes a piston head portion 20 that forms an upper portion thereof and has a crown surface 5 </ b> A, and a skirt portion 30 that is disposed below the piston head portion 20. In the present embodiment, the piston head portion 20 and the skirt portion 30 are formed as a single body.

  The skirt portion 30 has a pair of skirt body portions 31 extending on an arc along the inner peripheral wall 2 </ b> A of the cylinder 2 in a cross section perpendicular to the vertical direction, and a substantially flat outer periphery located between the skirt body portions 31. And a pair of flat plate portions 32 having a surface. The skirt body 31 has a shape symmetrical to each other with respect to the surface along the central axis X1 of the piston 5, and one skirt body 31 will be described below.

  The skirt body (second member) 31 is formed along the inner peripheral wall 2A as the piston 5 reciprocates on the surface facing the inner peripheral wall (first sliding surface) 2A of the cylinder 2 (first member). The outer peripheral wall 31S (second sliding surface) slides upward and downward. Hereinafter, the outer peripheral wall 31S of the skirt body 31 is referred to as a skirt sliding surface 31S.

  FIG. 8 is a diagram schematically showing the skirt sliding surface 31S by enlarging a part of FIG.

  The skirt body 31 is configured such that a gap G is formed between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2. That is, the skirt sliding surface 31 </ b> S is levitated from the inner peripheral wall 2 </ b> A of the cylinder 2.

  The skirt sliding surface 31S has an arcuate shape projecting toward the inner peripheral wall 2A of the cylinder 2 in a cross section along the central axis X1 of the cylinder 2, and is located in the center in the vertical direction and is located inside the cylinder 2. The apex Ps that protrudes most toward the peripheral wall 2A side, and the skirt that is located at both ends in the vertical direction and has the smallest protrusion amount toward the inner peripheral wall 2A of the cylinder 2, that is, the skirt that is the farthest away from the inner peripheral wall 2A of the cylinder 2 Part Qs (Qs1, Qs2).

  The upper skirt portion Qs1 is a portion that becomes the downstream end in the sliding direction when the piston 5 moves upward and the skirt sliding surface 31S slides upward. In this case, the skirt sliding portion is more than the top portion Ps. It arrange | positions in the downstream of the sliding direction of the moving surface 31S. Further, the lower skirt Qs2 is a portion which becomes a downstream end in the sliding direction when the piston 5 moves downward and the skirt sliding surface 31S slides downward. In this case, the lower skirt Qs2 is more than the top Ps. It arrange | positions in the downstream of the sliding direction of the skirt sliding surface 31S.

  In the present embodiment, the protruding amount of the skirt sliding surface 31S gradually decreases from the skirt portion Qs (Qs1, Qs2) toward the top portion Ps.

  In the present embodiment, the entire skirt sliding surface 31S protrudes toward the inner peripheral wall 2A side of the cylinder 2 in a cross section along the sliding direction, and the entire skirt sliding surface 31S constitutes the protruding shape portion. ing. In the present embodiment, the skirt sliding surface 31S has a shape that is substantially symmetrical with respect to the top portion Ps in the vertical direction.

  6 and 8, the skirt sliding surface 31S is depicted with a greatly exaggerated shape for easy understanding. Actually, as will be described later, the skirt sliding surface 31S is visually observed. Is an arcuate shape with a micron-order overhang that is difficult to distinguish.

  The skirt sliding surface 31S is formed in an arcuate shape in this way because the skirt sliding surface 31S slides between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2 when sliding upward and downward. This is to keep the resistance small.

  More specifically, when the speed u is given to the skirt portion 30 due to the reciprocation of the piston 5 due to the existence of the gap G, as shown by arrows Y1 and Y2 in FIG. F is drawn between the sliding surfaces (between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2) from the downstream side in the sliding direction. At this time, if the protruding amount of the skirt sliding surface 31S decreases from the skirt portion Qs toward the top portion Ps as described above, the fluid F that has entered between the sliding surfaces is blocked and loses its destination. As a result, the fluid F applies a force in the direction of expanding the gap between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2, and this force causes the skirt sliding surface 31S to move from the inner peripheral wall 2A. Acts to float. Hereinafter, the force that expands the gap by the fluid F is referred to as a sliding levitation force, and the action by the sliding levitation force is referred to as a sliding levitation action.

  Specifically, when the piston 5 is lifted and a speed u1 is given to the skirt portion 30 upward, as shown by an arrow Y1, the fluid F moves toward the top portion Ps from the upper skirt portion Qs1 to the gap G. Thus, a sliding levitation force is applied to the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2. On the other hand, while the piston 5 is descending, as shown by the arrow Y2, the fluid F enters the gap G from the lower skirt portion Qs2 toward the top portion Ps. A sliding levitation force is applied to the peripheral wall 2A.

  Therefore, if the skirt sliding surface 31S is formed in an arcuate shape as described above, the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2 are prevented from coming into contact with each other when the piston 5 reciprocates. The resistance can be reduced and the mechanical loss can be reduced. That is, even when the piston 5 performs a so-called swing motion during the reciprocating motion and is tilted with respect to the center axis X1 of the cylinder 2, the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2 are prevented from contacting each other. can do.

  However, the inventors of the present application cannot obtain sufficient sliding levitation by simply making the skirt sliding surface 31S into an arcuate shape, and can optimally obtain the sliding levitation effectively. As a result, it was found that a profile of the skirt sliding surface 31S exists.

(5) Sliding Surface Profile FIG. 9 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. Here, first, this FIG. 9 is used, not only for the skirt sliding surface 31S, but also for the entire sliding surface Sa of the sliding member C1 that is provided in the engine body 1 and slides as the piston 5 reciprocates. The possible profiles will be described.

  As shown in FIG. 9, the sliding surface Sa has a protruding shape that protrudes toward the sliding surface Sb, and the top portion Pa that is the most protruding portion and the sliding direction of the top portion Pa (arrow Y10). And a skirt portion Qa that is arranged farthest from the sliding surface Sb and is gradually separated from the sliding surface Sb toward the downstream side in the sliding direction. have.

  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. 9). 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. 9), 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 a 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 defined as the maximum gap h2. Is the ratio between the minimum gap h1 and the maximum gap h2, and is expressed as m = h2 / h1.

In equation (1), if the second item is the load capacity coefficient Kw (Kw = 6 / (m−1) ² {lnm−2 (m−1) / (m + 1)}), the sliding levitation force W is the load It is proportional to the capacity coefficient Kw.

  FIG. 10 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.

  Accordingly, a high sliding levitation force W can be obtained if the gap ratio m is set in the vicinity of 2.2. Specifically, if the gap ratio m is 1.5 or more and 5.0 or less, the sliding levitation force W is set to the line L_Kw40 or more in FIG. 10, and the maximum value (when the gap ratio m is 2.2) is set. Value) of 60% or more.

  Note that the sliding levitation force W decreases when the gap ratio m is greater than the appropriate value (m = 2.2). The effect is that the fluid F is blocked by the relatively small minimum gap h1. It is considered that the ratio of the fluid F that becomes excessively large and cannot flow between the sliding surface Sb and the sliding surface Sa increases. In addition, when the clearance ratio m is smaller than an appropriate value (m = 2.2), the sliding levitation force W is reduced because the sliding surface Sa approaches the flat plate and the damming effect of the fluid F is reduced. This is probably because of this.

  Here, based on Formula (1), the sliding levitation force W 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 inventors of the present application 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. 11 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. In addition, the viscosity of air illustrated 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 6.8 × 10 ⁻³ [Pa · s].

  Specifically, FIG. 11 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 equation (1). It is a graph of the minimum clearance h1 and the friction coefficient μ when the required sliding levitation force W is balanced and the sliding surface Sa floats. In FIG. 11, the gap ratio m also changes with the change in the minimum gap h1.

  More specifically, in Equation (1), the average moving speed of the sliding surface Sa that is symmetrical 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. 11, lines L1, L2, and L3 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 added to each of the fluids F. 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.

Here, this range is a range of the minimum gap h1 that should be ensured when the engine body 1 is in operation. When the engine main body 1 is operated, the sliding surface that slides along with the engine main body 1 and the sliding member including the sliding surface are heated and expand thermally. Even if the sliding member and the sliding member on which it slides are made of the same material, the thermal distribution of the two is different and a difference in thermal expansion occurs between them. Accordingly, it is appropriate to set the upper limit value larger as a design value based on normal temperature so that the range can be secured during engine operation. In view of this point, in this embodiment, the range of the minimum gap h1 at room temperature is
For air: 0.5 to 1.5 μm For water: 3 to 15 μm For 0W-20: Set to 15 to 40 μm.

  From the above results, in the category of the fluid F (air, water, low-viscosity oil) that can be used at present to achieve sliding levitation, the range of the minimum gap h1 that can realize good sliding levitation is 0. It can be set to 5 μm to 40 μm.

  Here, looking only at FIG. 11, it seems preferable to use air as the fluid F in order to obtain better sliding levitation. However, as described above, the graph of FIG. 11 is a graph when the engine speed is a typical speed. As shown in the equation (1), the sliding levitation force W is proportional to the speed U corresponding to the engine speed and the viscosity η of the fluid F. Therefore, when the minimum clearance h1 is set as described above, and when the fluid F is air and a fluid having a small viscosity η is used, the engine speed is very small compared to the representative engine speed. As a result, the resulting sliding levitation force W becomes small, which causes a problem that the sliding surface Sa cannot be lifted with respect to the sliding surface Sb. In other words, if the engine speed is low and the sliding speed of the sliding surface Sa is low, and if the viscosity η of the fluid F is small, the amount of the fluid F that enters the gap G of the fluid F and is blocked becomes small. The resulting sliding levitation force W is reduced.

  Therefore, under conditions where the engine speed is low, the use of water or oil having a relatively high viscosity η as the fluid F can ensure a higher sliding levitation force W than when air is used. In other words, under conditions where the engine speed is low, using water or oil rather than air makes it easier to avoid contact with water or oil having high viscosity between the sliding surfaces.

(6) Profile of Skirt Sliding Surface From the above knowledge, in this embodiment, when the engine F is low, the viscosity of the fluid F interposed between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2 is low. Use relatively high water for lubrication, and air when the engine speed is high. A specific procedure for controlling the fluid F will be described later. The minimum gap h1 between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2 is set to a predetermined value of 0.5 μm or more and 40 μm or less.

  In the present embodiment, the smoothness of the skirt sliding surface 31S is set high in order to ensure the accuracy of the minimum gap h1. That is, as described above, since the minimum gap h1 is set within a minute length range, if the skirt sliding surface 31S is a rough surface, the accuracy of the minimum gap h1 decreases. Therefore, in this embodiment, as the minimum gap h1 of the skirt sliding surface 31S is set to 0.5 μm or more and 40 μm or less, the surface roughness of the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2 is Each is set to be 0.4 μm or less.

  In the present embodiment, the skirt sliding surface 31S (the skirt portion 30 and the piston 5) and the constituent member (the cylinder block 3 or the cylinder liner) of the inner peripheral wall 2A of the cylinder 2 are made of the same material. This is to suppress fluctuations in the length of the gap G due to the difference in thermal expansion, that is, fluctuations in the minimum gap h1 and the maximum gap h2. In this embodiment, both are formed of stainless steel (stainless steel, forged product) having a small thermal expansion coefficient.

  Here, in the above description, as shown in FIG. 6, the skirt sliding surface 31S has the profile in a state where the central axis of the piston 5 substantially coincides with the central axis X1 of the cylinder 2 (hereinafter, referred to as neutral state as appropriate). The case where it has was explained. However, when the piston 5 swings in the middle of its reciprocation, that is, when the central axis of the piston 5 is inclined with respect to the central axis of the cylinder 2, the skirt sliding surface 31S is also in this swung state. Configure to maintain the profile.

  Specifically, as shown in FIG. 12, in the state where the piston 5 swings to the left as shown by the solid line from the neutral state of the broken line, the left skirt sliding surface 31S has a skirt sliding surface 31S. Among these, the portion where the dimension of the gap with the inner peripheral wall 2A of the cylinder 2 is the smallest, that is, the top portion Ps2 is located above the vertical center, and the top portion Ps3 is below the vertical center in the right skirt sliding surface 31S. Position. Accordingly, the minimum gap h1 in the skirt sliding surfaces 31S on the left and right sides is different from the minimum gap h1 in the neutral state shown in FIG. Further, the maximum gap (the maximum dimension of the separation distance between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2 on the downstream side in the sliding direction from the tops Ps2 and Ps3) h2 is also in the neutral state shown in FIG. The size is different from the maximum gap h2.

  Further, the maximum gap (the maximum dimension of the separation distance between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2 on the downstream side in the sliding direction from the tops Ps2 and Ps3) h2 is also in the neutral state shown in FIG. The size is different from the maximum gap h2. Specifically, if the state shown by the solid line in FIG. 12 is a state in which the piston 5 is moving upward, the gap dimension at the upper end of the left and right skirt sliding surfaces 31S becomes the maximum gap h2. . On the other hand, if the state shown in FIG. 12 is a state in which the piston 5 is moving downward, the gap size at the lower end of the left and right skirt sliding surfaces 31S becomes the maximum gap h2.

  As described above, when the piston 5 swings, the values of the minimum clearance h1 and the maximum clearance h2 are different between the neutral state and the swinging state. In either state, the minimum clearance h1 is the minimum clearance. The skirt sliding surface S31 is configured so as to be in an appropriate range of h1, and the gap ratio m (h2 / h1) is in the appropriate range.

(7) Sliding surface structure of the crank mechanism In this embodiment, the optimum profile of the sliding surface Sa described in (5) is also applied to the sliding portion of the crank mechanism. This will be described next.

<Crank bearing>
As described above, the inner peripheral wall 40 </ b> A of the crank bearing 40 slides relative to the outer peripheral wall 71 </ b> A of the crank journal portion 71 as the piston 5 reciprocates. Correspondingly, the profile of the sliding surface Sa is applied to the inner peripheral wall 40 </ b> A of the crank bearing 40.

  FIG. 13 is a schematic sectional view around the crank journal portion in FIG.

  The crank bearing 40 has such a size that a gap G is formed between the crank bearing 40 and the crank journal portion 71 over the entire circumference. The cross-sectional shape of the crank journal portion 71 is almost a perfect circle. On the other hand, the inner peripheral wall 40 </ b> A of the crank bearing 40 has a shape protruding toward the outer peripheral wall 71 </ b> A of the crank journal portion 71. Specifically, in the rotation direction Y31 of the crank journal part 71, that is, the direction opposite to the sliding direction Y32 of the crank bearing 40 (the direction opposite to the rotation direction Y32 relative to the crank journal part 71 of the crank bearing 40). In addition, the size of the gap G is gradually reduced. In the present embodiment, the entire inner peripheral wall 40A of the crank bearing 40 is an overhanging portion having this overhanging shape, and the top portion P10 in which the dimension of the gap G is minimized, and the sliding of the crank bearing 40 from the top portion P10. Located on the downstream side in the direction Y32 is the skirt Q10 where the size of the gap G is maximum. In the example of FIG. 13, the inner peripheral wall 40 </ b> A of the crank bearing 40 is expanded in a spiral shape from the top portion P <b> 10 toward the bottom portion Q <b> 10 along the sliding direction Y <b> 32 in the cross section. Is changing.

  Accordingly, when the crank journal portion 71 rotates, that is, when the crank bearing 40 rotates relative to this and slides with respect to the outer peripheral wall 71A of the crank journal portion 71, as shown by an arrow Y30 in FIG. The fluid F flows from the Q10 side toward the top portion P10, and the sliding acts between the outer peripheral wall 71A of the crank journal portion 71 and the inner peripheral wall 40A of the crank bearing 40 in a direction to separate these walls 71A and 40A. Levitation force is generated.

  In the present embodiment, the sliding is applied to the inner peripheral wall 40A of the crank bearing 40 so that a high sliding levitation force can be obtained also between the outer peripheral wall 71A of the crank journal portion 71 and the inner peripheral wall 40A of the crank bearing 40. The optimum profile of the surface Sa is applied.

  Specifically, the gap ratio m = h2 / h1, and the minimum gap h1 that is the minimum value among the dimensions of the gap G between the outer peripheral wall 71A of the crank journal portion 71 and the inner peripheral wall 40A of the crank bearing 40, that is, The separation distance h1 between the top portion P10 and the outer peripheral wall 71A of the crank journal portion 71, and the maximum gap h2 that is the maximum value among the dimensions of the gap G, that is, the separation distance h2 between the bottom portion Q10 and the outer peripheral wall 71A of the crank journal portion 71 Is set to a predetermined value in the range of 1.5 to 5.0.

  Then, between the outer peripheral wall 71A of the crank journal portion 71 and the inner peripheral wall 40A of the crank bearing 40, air or water for lubrication is provided in the same manner as the portion between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2. The air and lubricating water are switched according to the engine speed.

  In the present embodiment, the minimum gap h1 is a predetermined value of not less than 0.5 μm and not more than 40 μm so that the friction coefficient μ between the outer peripheral wall 71A of the crank journal portion 71 and the inner peripheral wall 40A of the crank bearing 40 becomes small. In addition, the surface roughness of the outer peripheral wall 71A of the crank journal portion 71 and the inner peripheral wall 40A of the crank bearing 40 is set to be 0.4 μm or less.

<Crank pin bearing>
As described above, the inner peripheral wall 83 </ b> A of the crankpin bearing 83 slides relative to the outer peripheral wall 72 </ b> A of the crankpin 72 as the piston 5 reciprocates. Correspondingly, the profile of the sliding surface Sa is applied to the inner peripheral wall 83 </ b> A of the crankpin bearing 83.

  14 is a schematic cross-sectional view when the periphery of the connecting rod large end portion 81 is cut along a cross section taken along line XIV-XIV in FIG.

  The crankpin bearing 83 has such a size that a gap G is formed between the inner peripheral wall 83A thereof and the outer peripheral wall 72A of the crankpin 72. The cross-sectional shape of the crankpin 72 is almost a perfect circle. On the other hand, the inner peripheral wall 83 </ b> A of the crankpin bearing 83 has a shape protruding toward the outer peripheral wall 72 </ b> A of the crankpin 72. Specifically, the dimension of the gap G gradually decreases in the direction opposite to the sliding direction Y21 of the crankpin bearing 83 with respect to the crankpin 72. In the present embodiment, the entire inner peripheral wall 83A of the crankpin bearing 83 is a projecting shape portion having this projecting shape, and the top portion P20 where the dimension of the gap G is the smallest, and the crankpin bearing 83 is more than the top portion P20. A skirt Q20 where the dimension of the gap G is the maximum is located adjacent to the downstream side in the sliding direction Y21. In the example of FIG. 14, the inner peripheral wall 83 </ b> A of the crankpin bearing 83 expands in a spiral shape from the top portion P <b> 20 along the sliding direction Y <b> 21 toward the skirt portion Q <b> 20. The dimensions change.

  Like the portion between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2, air or lubricating water is supplied between the gap G, that is, the crankpin bearing 83A and the crankpin 72, and the engine speed is increased. The air and the lubricating water are switched according to In addition, arrow Y20 of FIG. 14 has shown the moving direction of the fluid F accompanying the crankpin bearing 83A.

  A gap ratio m = h2 / h1, which is a ratio of the minimum gap h1 that is the dimension of the gap G at the top P20 and the maximum gap h2 that is the dimension of the gap G at the skirt Q20, is 1.5 or more and 5.0 or less. Is set to a predetermined value. The minimum gap h1 is set to a predetermined value of 0.5 μm or more and 40 μm or less, and the surface roughness between the inner peripheral wall 83A of the crankpin bearing 83 and the outer peripheral wall 72A of the crankpin 72 is 0. It is set to be 4 μm or less.

(8) Switching control of fluid F Next, the sliding part of the engine body 1 (the part between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2, the outer peripheral wall 71A of the crank journal part 71 and the crank bearing 40). The control for switching the fluid F supplied to the portion between the inner peripheral wall 40A and the portion between the inner peripheral wall 83A of the crankpin bearing 83 and the outer peripheral wall 72A of the crankpin 72 to air and lubricating water will be described.

  FIG. 15 is a block diagram showing a control system of the present embodiment. The vehicle is equipped with a PCM (control means) 500 for controlling each part of the engine body 1. As is well known, the PCM 500 is a microprocessor including a CPU, a ROM, a RAM, and the like.

  The PCM 500 is electrically connected to various sensors for detecting the operating state of the engine, and controls various parts of the engine by executing various determinations and calculations based on input signals from these sensors. For example, the PCM 500 includes an engine speed sensor SN1 that detects the engine speed, an airflow sensor SN2 that detects the amount of intake air introduced into the engine body 1, and an accelerator opening that detects the opening of an accelerator pedal provided in the vehicle. In addition to being connected to the sensor SN3 and the like, it is also connected to the spark plug 17 and the injector 18. PCM 500 controls the amount of fuel injected from injector 18 and the ignition timing of spark plug 17 based on the detected engine speed, accelerator opening, intake air amount, and the like.

  Further, the lubricating liquid pump 202 is connected to the PCM 500, and the PCM 500 controls the driving state of the lubricating liquid pump 202. Specifically, the PCM 500 performs switching control between driving and stopping of the lubricating liquid pump 202. Thereby, supply and stop of the lubricating water to the sliding part of the engine body 1 are switched.

  Specifically, as shown in FIG. 16, in the present embodiment, as a control region of the lubricating liquid pump 202, a low rotational speed region A1 in which the engine rotational speed is equal to or lower than a preset reference rotational speed N1, and the engine rotational speed Is set to a high rotational speed region A2 that is greater than the reference rotational speed N1.

  The PCM 500 determines whether the current operating region is the low rotational speed region A1 or the high rotational speed region A2 according to the engine rotational speed detected by the engine rotational speed sensor SN1. When it is determined that the current operation region is the high rotation speed region A2, the driving of the lubricating liquid pump 202 is stopped, and the supply of the lubricating water to the sliding portion of the engine body 1 is stopped. When the supply of lubricating water is stopped in this way, only air exists in the sliding portion of the engine body 1, and an air layer is formed in the sliding portion. On the other hand, when the PCM 500 determines that the current operation range is the low rotation speed range A1, the lubrication liquid pump 202 is driven to supply lubricating water to the sliding portion of the engine body 1. In this way, in the present embodiment, lubricating water is supplied to the sliding portion of the engine body 1 only when the engine speed is equal to or less than the reference speed N1.

  In the present embodiment, the reference rotational speed N1 is set near the idle rotational speed, and the lubricating water is supplied to the sliding portion of the engine body 1 only when the engine rotational speed is very low at the time of starting or the like.

(9) Operation, etc. As described above, in this embodiment, the skirt sliding surface 31S of the skirt body 31 of the piston 5 is shaped to protrude toward the inner peripheral wall 2A side of the cylinder 2, and the cylinder 2 The gap ratio m is configured to be 1.5 or more and 5.0 or less with respect to the inner peripheral wall 2A. Further, while the lubricating water or air layer is formed in the gap G between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2, the minimum gap h1 is set to 0.5 μm or more and 40 μm or less. Yes. Accordingly, a high sliding levitation force can be imparted to the skirt sliding surface 31S with respect to the inner peripheral wall 2A of the cylinder 2, thereby making it possible to more reliably avoid contact between the two and keep the frictional resistance small. In addition, the friction coefficient μ between them can be reduced, and the frictional resistance and mechanical loss generated when the skirt sliding surface 31S slides can be significantly reduced. As a result, fuel efficiency can be improved. In particular, this effect can be obtained with a simple configuration in which the profile of the skirt sliding surface 31S is set as described above, which is advantageous in terms of cost.

  Moreover, in the high rotation speed region A2 where the engine speed is high and the viscosity of the fluid F can be reduced while securing the levitation sliding force as the engine speed is high, the skirt sliding surface 31S and the cylinder 2 The supply of lubricating water to and from the peripheral wall 2A is stopped, and a low-viscosity air layer is formed between them. Therefore, the frictional resistance μ between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2 can be reduced in the high rotation speed region A2 to effectively reduce the frictional resistance.

  On the other hand, if the fluid F is air having a low viscosity in the low engine speed region A1 where the engine speed is low and the engine speed is low, sufficient levitation sliding force cannot be secured and the sliding surfaces are in contact with each other. In a region where the frictional resistance is likely to increase very close, lubricating water having a viscosity higher than that of air is supplied between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2. Therefore, even in the low rotation speed region A1, the contact between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2 can be suppressed, or they can be separated (floated), and the frictional resistance can be suppressed small. Therefore, in this embodiment, the frictional resistance generated when the skirt sliding surface 31S slides can be reliably reduced in the entire engine speed range.

  Further, in the present embodiment, the profile of the sliding surface capable of realizing this high sliding levitation force and reducing the friction coefficient μ is the inner peripheral wall 40A of the crank bearing 40 and the inner peripheral wall of the crank pin bearing 83. This is also applied to 83A. Therefore, the frictional resistance generated during these sliding operations can be reduced, and the mechanical loss can be greatly reduced.

  Further, similarly to the portion between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2, in the high speed region A2, it is between the outer peripheral wall 71A of the crank journal portion 71 and the inner peripheral wall 40A of the crank bearing 40. The supply of lubricating water to the portion and the portion between the inner peripheral wall 83A of the crankpin bearing 83 and the outer peripheral wall 72A of the crankpin 72 is stopped to form a low-viscosity air layer therebetween. On the other hand, in the low rotation speed region A1, lubricating water having a viscosity higher than that of air is supplied to the respective portions. Therefore, also in these portions, the frictional resistance can be reliably reduced in the entire engine speed range.

  Further, in the low rotational speed region A1, a portion between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2, a portion between the outer peripheral wall 71A of the crank journal portion 71 and the inner peripheral wall 40A of the crank bearing 40, and The fluid F supplied to the portion between the inner peripheral wall 83A of the crankpin bearing 83 and the outer peripheral wall 72A of the crankpin 72 is water (lubricating water). For this reason, when shifting from the low rotational speed region A1 to the high rotational speed region A2, the water can be evaporated and removed from each part, and an air layer can be appropriately formed in each part. Therefore, the friction coefficient μ and the frictional resistance of each part can be reliably reduced in the high rotation speed region A2.

  The skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2 are formed of the same stainless steel. Therefore, these thermal expansion differences can be kept small, and the accuracy of the minimum gap h1 and the accuracy of the gap ratio m can be maintained high. Furthermore, while supplying lubricating water between the skirt sliding surface 31 </ b> S and the inner peripheral wall 2 </ b> A of the cylinder 2, it is possible to more reliably suppress rusting of these.

  For the same reason, the outer peripheral wall 71A (crank journal portion 71 and crankshaft 7) of the crank journal portion 71 and the inner peripheral wall 40A (cylinder block 3) of the crank bearing 40 are also the inner peripheral wall of the crankpin bearing 83. 83A (crankpin bearing 83) and outer peripheral wall 72A of crankpin 72 (crankpin 72 and crankshaft 7) are preferably formed of the same material. In particular, it is preferably formed of stainless steel that can suppress rust.

(10) Second Embodiment According to Piston Structure In the above embodiment, the case where the piston head and the skirt portion are integrally formed has been described. However, these may be configured separately. Furthermore, when these are comprised separately, you may comprise a skirt part so that the swing of the skirt part accompanying the swing of a piston head may be suppressed.

  FIG. 17A is a front view of the piston 205 according to the second embodiment in which the piston head portion 220 and the skirt portion 230 are separated, FIG. 17B is a side view of the piston 205, and FIG. FIG. 17A is a cross-sectional view taken along line XVIII-XVIII, and FIG. 19 is a cross-sectional view taken along line XIX-XIX in FIG. In the following description of the second embodiment, the left-right direction in FIG.

  In the second embodiment, the skirt portion 230 is composed of two members, and the piston 205 has a pair of left and right skirt portions 230 and 230.

  As shown in FIG. 18, the piston head portion 220 has a pair of piston bosses 224 extending downward. Piston pin holes 225 are formed in the piston bosses 224. The connecting rod 8 is rotatably supported by the piston head portion 220 by inserting the piston pin 241 through the through hole 282a and the piston pin hole 225 formed in the upper end portion 282 thereof. As shown in FIG. 19 and the like, two skirt pin holes 226 are formed in the pair of piston bosses 224, respectively. The pair of skirt pin holes 226 are disposed at the same height as the piston pin hole 225.

  Each of the pair of skirt portions 230 includes a skirt main body portion 231 and a pair of arm portions 232.

  Each skirt main body 231 is an arc-shaped flat plate member that follows the shape of the inner peripheral wall 2A of the cylinder 2, and includes a skirt sliding surface 231S on the surface facing the inner peripheral wall 2A. Each skirt sliding surface 231S has an arcuate shape projecting toward the inner peripheral wall 2A side of the cylinder 2 as in the first embodiment. The pair of skirt portions 230 are arranged such that the skirt sliding surfaces 231 </ b> S face in opposite directions.

  In each skirt portion 230, the pair of arm portions 232 are directed radially inward of the cylinder 2 from both ends in the circumferential direction of the skirt body portion 231 on the back surface opposite to the skirt sliding surface 231S of the skirt body portion 231. It extends.

  These arm portions 232 are adjacent to one arm portion 232 of the right skirt portion 230 and one arm portion 232 of the left skirt portion 230, and the other arm portion 232 of the right skirt portion 230 and the left skirt portion. The other arm part 232 of 230 is arrange | positioned so that it may adjoin. In the vicinity of the tip of each arm portion 232, a pin through hole 233 is formed.

  The right skirt portion 230 has a skirt pin 242 inserted through a pin passage hole 233 provided at the tip of the two arm portions 232 and a left skirt pin hole 226 formed in the piston boss 224. The piston boss 224 is coupled to the skirt pin 242 so as to be swingable about the axis of the skirt pin 242. Further, the left skirt portion 230 has the skirt pin 242 inserted through a pin through hole 233 provided at the tip of the two arm portions 232 and a right skirt pin hole 226 formed in the piston boss 224. Thus, the piston boss 224 is coupled with the skirt pin 242 so as to be swingable about the axis. In this way, in this embodiment, the piston 205 is configured with a tilt mechanism that allows each skirt portion 230 to swing up and down within a predetermined range.

  As shown in FIG. 17A, an opening 232a is formed at the center of each arm portion 232 in the vertical direction, and the skirt pin 242 of one skirt portion 230 is the arm of the other skirt portion 230. It passes through the opening 232 a of the part 232 and is coupled to the arm part 232 of one skirt part 230. Accordingly, the swing of one skirt portion 230 is restricted to a predetermined range by the skirt pin 242 of the other skirt portion 230.

<Operation of the skirt>
By being configured as described above, in the second embodiment, the neck of the skirt portion 230 is suppressed when the piston 205 is swung. This will be described with reference to FIGS. 20 (A) and 20 (B). FIG. 20A is a schematic view of the skirt portion 230 in a neutral state, and FIG. 20B is a schematic view of the skirt portion 230 when a neck swing occurs.

  In the second embodiment, as shown in FIG. 20 (B), when the neck of the piston 205 is tilted to the left, the piston boss 224 is tilted to the left, so that the right skirt pin hole 226 and the skirt pin hole 226 are inserted therethrough. The right skirt pin 242 is positioned above the left skirt pin hole 226 and the left skirt pin 242 inserted therethrough.

  Here, if the skirt portion 230 cannot swing with respect to the skirt pin 242, the skirt portion 230 is inclined together with the piston head portion 220 as shown by a broken line in FIG.

  On the other hand, in this embodiment, as shown by the solid line in FIG. 20B, the skirt portion 230 swings with respect to the skirt pin 242, so that the skirt portion 230 is the same as or in the neutral state. A close posture can be achieved. That is, swinging of the skirt portion 230 can be suppressed. Therefore, by swinging the profile of the skirt sliding surface 231S of the skirt portion 230 (the size of the minimum gap h1 and the range of the gap ratio m = h1 / h2) to the optimum profile in the neutral state, the piston 5 swings. Even in this case, the profile of the skirt sliding surface 231S can be more reliably maintained in an optimum state.

  On the other hand, in the second embodiment, when acceleration (deceleration) acts on the piston 205, the skirt portion 230 may swing from the neutral state.

  FIGS. 21A to 21C are views for explaining the swinging state of the skirt portion 230 accompanying the acceleration / deceleration of the piston 205. In FIG. 20A, the piston 205 is in a neutral state, and either the acceleration in the downward direction (direction from TDC to BDC) or the acceleration in the upward direction (direction from BDC to TDC) acts on the piston 205. The posture of the skirt portion 230 in a state where the skirt portion 230 is not in the state (for example, a state where the crank angle is 90 ° or 270 °) is shown.

  FIG. 21B shows the posture of the skirt portion 230 in a state where a downward acceleration or an upward deceleration is acting on the piston 5. As shown in FIG. 21B, when a downward acceleration or an upward deceleration acts on the piston 5, the skirt portion 230 continues to stop in place due to inertia. Then, the swinging state of the posture tilted upward is obtained.

  Therefore, in the second embodiment, it is preferable that the profile (minimum gap and gap ratio) of the skirt sliding surface 231S of the skirt portion 230 is the optimum profile even in this upward swing state.

  In the case shown in FIG. 21B, the gap between the skirt sliding surface 231S and the inner peripheral wall 2A of the cylinder 2 is narrower on the lower end side than on the upper end side (however, it is considerably exaggerated). Drawn). When downward acceleration is applied to the piston 5, the fluid F flows into the gap exclusively from the lower end side. Therefore, it is desirable to set the maximum gap at the lower end so that the gap ratio m at the lower end is near the gap ratio m = 2.2 at which the greatest levitation force is obtained.

  FIG. 21C shows the posture of the skirt portion 230 in a state where an upward acceleration or a downward deceleration acts on the piston 5. In this case, contrary to FIG. 20B, the skirt portions 230 are in a swinging state in a posture inclined downward.

  Therefore, in the second embodiment, it is preferable that the profile (minimum gap and gap ratio) of the skirt sliding surface 231S of the skirt portion 230 is the optimum profile even in the downward swing state.

  In this case, the gap between the skirt sliding surface 231S and the inner peripheral wall 2A of the cylinder 2 is narrower on the upper end side than on the lower end side. When upward acceleration is applied to the piston 5, the fluid F flows into the gap exclusively from the upper end side. Therefore, it is desirable to set the maximum gap at the upper end so that the gap ratio m at the upper end becomes close to the gap ratio m = 2.2 at which the greatest levitation force can be obtained.

(11) Other Modifications In the above embodiment, in the low rotation speed region A1, the outer peripheral wall 71A of the crank journal portion 71 and the inner peripheral wall of the crank bearing 40 are provided between the skirt sliding surface 31S and the inner peripheral wall 2A of the cylinder 2. 40A, between the inner peripheral wall 83A of the crankpin bearing 83 and the outer peripheral wall 72A of the crankpin 72, that is, the lubricating water supplied to the sliding portion of the engine body 1 is water to which a rust inhibitor is added. Although some cases have been described, the lubricating water interposed in these gaps G is not limited to this.

  However, if a rust inhibitor is added to the lubricating water, it is possible to prevent the respective parts to which the lubricating water is supplied from being rusted.

  Further, oil may be supplied to the sliding portion of the engine body 1 in the low rotation speed region A1 instead of the lubricating water. Specifically, oil is stored in the pan 209 instead of the lubricating water, and the lubricating liquid supplied to each part by the lubricating liquid supply system 201 is oil. Even in this case, since the viscosity of the oil is higher than the viscosity of the air, a high sliding levitation force is applied to the sliding portion of the engine body 1 in the low rotational speed region A1 to keep the frictional resistance small. Can do.

Here, the oil used is preferably a low viscosity oil. Here, oil of about 0 W-20, that is, oil having a viscosity of about 6.8 × 10 −3 [Pa · s] or less is referred to as low viscosity oil. That is, it is preferable to use an oil having a viscosity of about 6.8 × 10 ⁻³ [Pa · s] or less. In this way, it is possible to suppress an increase in frictional resistance due to a high viscosity while obtaining a high sliding levitation force using oil having a higher viscosity than air in the low rotational speed region A1. The frictional resistance can be appropriately reduced.

  In addition, if oil is used instead of the lubricating water, it is possible to prevent the portion to which the oil is supplied from being rusted.

  On the other hand, if the lubricating water is used, as described above, it is removed early from the sliding portion of the engine body 1 when the low rotational speed region A1 is shifted to the high rotational speed region A2. Therefore, in the high rotation speed region A2, the ratio of air in the sliding portion of the engine body 1 can be increased, and the frictional resistance of the sliding portion can be more reliably suppressed to a small value.

  Moreover, in the said embodiment, the skirt sliding surface 31S has shown the example which is arcuate shape. However, as long as the skirt sliding surface 31S has a projecting shape that projects toward the inner peripheral wall 2A in the cross section along the central axis X1 of the cylinder 2, the skirt sliding surface 31S does not matter. That is, if a portion (top portion Ps) that forms the minimum gap h1 and a portion (hem portion Qs) that forms the maximum gap h2 are included, the shape between these two portions is not necessarily an arcuate curved shape. In addition, various shapes may be provided. For example, a part or the whole between the top portion P and the bottom portion Q may be a surface that is linearly inclined in a cross section along the central axis X1 of the cylinder 2 or a surface that is inclined stepwise.

  Similarly, the outer peripheral wall 71A of the crank journal portion 71 and the inner peripheral wall 83A of the crankpin bearing 83 are also formed with a portion that forms the minimum gap h1 (top portions P10 and P20) and a portion that forms the maximum gap h2 (the skirt portions Q10 and P10). Q20) and other shapes may be provided.

  Moreover, although the said embodiment demonstrated the case where the skirt sliding surface S31 and 2 A of inner peripheral walls of the cylinder 2 were formed with stainless steel, these materials are not restricted to stainless steel. For example, you may form these with cast steel etc. However, since stainless steel has a small coefficient of thermal expansion as described above, the use of stainless steel can suppress the deviation from the appropriate range of the minimum gap h1 and the gap ratio m due to thermal expansion. For the same reason, it is preferable to use stainless steel for the crankshaft 7 and the connecting rod 8 as well.

  Further, the skirt sliding surface S31, the inner peripheral wall 2A of the cylinder 2, the outer peripheral wall 71A of the crank journal portion 71, the inner peripheral wall 40A of the crank bearing 40, the outer peripheral wall 72A of the crank pin 72, and the inner peripheral wall 83A of the crank pin bearing 83 are provided. These may be formed of different materials. However, as described above, if these are made of the same material, the influence of the difference in thermal expansion on the minimum gap h1 and the gap ratio m can be suppressed to be small, and the accuracy thereof can be increased.

1 Engine body 2 Cylinder (first member)
2A Cylinder inner wall (first sliding surface)
5 Piston 7 Crankshaft 8 Connecting rod 30 Skirt 31 Skirt body 31 (second member)
31S Skirt sliding surface (second sliding surface, projecting shape)
40 Crank bearing (second member)
Inner wall of the 40A crank bearing (second sliding surface, overhanging portion)
71 Crank journal (first member)
71A Outer wall of crank journal (first sliding surface)
72 Crankpin (first member)
72A Inner peripheral wall of crank pin (first sliding surface)
83 Crank pin bearing (second member)
83A Inner peripheral wall of crank pin bearing (second sliding surface, projecting shape)
P10 Top part P20 Top part Ps Top part Q10 Bottom part Q20 Bottom part Qs (Qs1, Qs2) Bottom part h1 Minimum gap h2 Maximum gap m Gap ratio

Claims (6)

In a reciprocating piston engine having a piston that reciprocates in a cylinder and a crank mechanism,
A first member having a first sliding surface;
A second sliding surface facing the first sliding surface with a gap, and a second member that moves relative to the first member in a predetermined sliding direction when the piston reciprocates;
A lubricating liquid supply device for supplying a lubricating liquid having a viscosity higher than air between the first sliding surface and the second sliding surface;
The second sliding surface has an overhang-shaped portion projecting toward the first sliding surface in a cross section along the sliding direction,
The projecting shape portion includes a top portion which is the most projecting portion and a skirt portion which is disposed at least downstream of the top portion in the sliding direction and which is located farthest from the first 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 lubricating liquid supply device supplies the lubricating liquid between the first sliding surface and the second sliding surface when the engine rotational speed is equal to or lower than a preset reference rotational speed. When the rotational speed is higher than the reference rotational speed, the supply of the lubricating liquid is stopped so that an air layer is formed between the first sliding surface and the second sliding surface. Features a reciprocating piston engine. The reciprocating piston engine according to claim 1,
The reciprocating piston engine, wherein the lubricating liquid is at least one of water and low viscosity oil. The reciprocating piston engine according to claim 1 or 2,
A reciprocating piston engine, wherein the material of the first member and the material of the second member are the same. The reciprocating piston engine according to any one of claims 1 to 3,
The first member is the cylinder;
The second member is a piston skirt that reciprocates in the cylinder,
A reciprocating piston engine, wherein the projecting shape portion is provided on an outer peripheral wall of the skirt portion facing an inner peripheral wall of the cylinder. The reciprocating piston engine according to any one of claims 1 to 4,
A crankshaft connected to the piston and rotating in accordance with the reciprocation of the piston; and a crank bearing for rotatably supporting the crankshaft;
The first member is the crankshaft;
The second member is the crank bearing,
The reciprocating piston engine according to claim 1, wherein the protruding portion is provided on an inner peripheral wall of the crank bearing facing the outer peripheral wall of the crankshaft. The reciprocating piston engine according to any one of claims 1 to 5,
A connecting rod for connecting the piston and the crankshaft;
The connecting rod includes a crank pin bearing that rotates relative to the crank pin in a state in which a crank pin constituting a part of the crank shaft is inserted;
The first member is the crankpin;
The second member is the crank pin bearing;
The reciprocating piston engine, wherein the projecting shape portion is provided on an inner peripheral wall of the crankpin bearing facing the outer peripheral wall of the crankpin.

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