JP5122420B2 - Piston sliding part lubrication structure - Google Patents

Description

  The present invention relates to a lubricating structure for a piston sliding portion.

  As shown in FIG. 4, in a general engine in an automobile or the like, a piston 2 accommodated in a cylinder 1 is supported by a small end portion 4 a of a connecting rod 4 via a piston pin 3 so as to be swingable. Is connected to the crankshaft 6 via the crankpin 5.

  The crankpin 5 is supported at a position shifted from the center of the crankshaft 6 by the crank arm 6a, and the crankpin 5 draws a circular orbit (see the chain line in FIG. 4) around the center of the crankshaft 6. Therefore, the connecting rod 4 swings around the piston pin 3 and the piston 2 moves up and down in the cylinder 1.

  In general, when the piston 2 is made of aluminum, the difference in thermal expansion with respect to the steel cylinder liner 1a becomes large. It is necessary to secure a large amount of piston clearance so as to obtain, but if a large amount of piston clearance is secured, there is a problem that a hitting sound is generated at the time of piston slap.

  For this reason, conventionally, a low friction coating having seizure resistance and low friction characteristics is applied to the outer peripheral surface of the skirt 7 of the piston 2 (portion below the piston ring mounting portion of the piston 2) to fill the piston clearance. Therefore, the hitting sound at the time of piston slap is reduced and the friction of the piston 2 is reduced.

Incidentally, as prior art document information related to this type of piston sliding portion lubrication structure, there is the following Patent Document 1 and the like.
Special table 2007-509279 gazette

  However, the piston 2 pushed down by the explosion pressure A is strongly pressed against the inner wall of the cylinder 1 due to the inclination of the connecting rod 4, and metal contact occurs on the thrust side that receives such a side pressure. The state of mixed lubrication becomes dominant, and on the anti-thrust side, the state of fluid lubrication in which the friction surfaces slip apart with the oil film sandwiched is dominant, but it is low throughout the area to the anti-thrust side where fluid lubrication is dominant. By applying the friction coating, the sliding resistance is increased, thereby finding the fact that room for further improvement in fuel consumption is impaired.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a novel piston sliding portion lubrication structure capable of significantly reducing frictional force and improving fuel efficiency as compared with the prior art. Yes.

The present invention relates to a lubrication structure of a piston sliding portion subjected to low-friction coating on the skirt surface of the piston reciprocating in a cylinder of the engine, the outer peripheral surface of the anti-thrust side that put the piston skirt, said skirt subjecting a low friction coating to form a striped pattern extending toward the sliding direction of, and the remaining uncoated portion releasing the lubricating oil to the sliding direction of the skirt between each other of the coating unit, the thrust of the piston skirt it is characterized in that it has facilities for low friction coating on the outer peripheral surface entire side.

  Thus, in this way, a step corresponding to the coating thickness occurs at the boundary between the coating part and the non-coating part, and the substantial lubrication surface with the cylinder liner side is limited only to the area where each coating part exists. As a result, the lubrication area in the piston skirt is reduced, and the frictional force is greatly reduced.

  That is, the non-coating parts remaining between the coating parts are open in the sliding direction of the skirt so that the lubricating oil can be released freely. It is not even the viscosity of the lubricating oil, and it has a very low frictional resistance, so the actual lubrication surface with the cylinder liner side is limited only to the area where each coating part exists. .

  Moreover, between each coating part and the cylinder liner, fluid lubrication occurs with the friction surfaces slipping apart with an oil film in between, but the piston clearance is clogged in the area where each coating part exists. The oil film thickness when the piston is slid is reduced, which reduces the friction coefficient and reduces the friction force.

  In addition, the piston clearance is clogged because there are coating parts at multiple locations in the circumferential direction of the skirt, so if you ensure the appropriate coating thickness as before, the hitting sound at the time of piston slap will be reduced to the same level as before It becomes possible.

Also, since the facilities a low friction coating on the entire area of outer peripheral surface of the thrust side of the skirt of the piston, the thrust side of said skirt state of mixed lubrication metal contact occurs is dominant, the entire area is low By being coated with the friction coating, it is possible to exhibit seizure resistance and low friction characteristics as usual.

  According to the above-described lubricating structure of the piston sliding portion of the present invention, various excellent effects as described below can be obtained.

  (I) According to the invention described in claim 1 of the present invention, the low friction coating is formed on the outer peripheral surface of the piston skirt on the side opposite to the thrust side so as to form a stripe pattern extending in the sliding direction of the skirt. Since the non-coating part that allows the lubricating oil to escape in the sliding direction of the skirt is left between the coating parts, the lubricating area in the piston skirt can be reduced and the frictional force can be greatly reduced. Thus, it is possible to significantly improve fuel efficiency by reducing friction loss compared to the conventional case.

(II) According to the first aspect of the present invention, on the thrust side of the piston skirt where the state of mixed lubrication in which metal contact occurs is dominant, the entire region is covered with a low friction coating. The seizure resistance and the low friction characteristic can be exhibited.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 to 3 show an example of an embodiment for carrying out the present invention, and the portions denoted by the same reference numerals as those in FIG. 4 represent the same items.

  As shown in FIGS. 1 and 2, in this embodiment, a low friction coating is formed on the outer peripheral surface of the piston 2 on the anti-thrust side of the skirt 7 so as to form a stripe pattern extending in the sliding direction of the skirt 7. And a non-coating portion 9 that allows the lubricating oil to escape in the sliding direction of the skirt 7 is left between the coating portions 8, while a low friction coating is applied to the entire outer peripheral surface on the thrust side of the skirt 7 of the piston 2. ing.

  Thus, in this way, a step g (see FIG. 2) corresponding to the coating thickness is generated at the boundary between the coating portion 8 and the non-coating portion 9, and the substantial lubrication surface with respect to the cylinder liner 1a is provided on each side. This is limited to the region where the coating portion 8 exists, and this reduces the lubrication area in the skirt 7 of the piston 2 and greatly reduces the frictional force.

  That is, the non-coating portions 9 remaining between the coating portions 8 are opened in the sliding direction of the skirt 7 so that the lubricating oil can be released freely. Since the state of lubrication is not so much and the viscosity of the lubricating oil is hardly affected, the frictional resistance is very small. Therefore, the substantial lubrication surface with the cylinder liner 1a side is only in the region where each coating portion 8 exists. It will be limited.

  Moreover, on the anti-thrust side of the skirt 7 of the piston 2, each of the coating portions 8 and the cylinder liner 1 a is in a fluid lubrication state in which the friction surfaces are slipping apart with an oil film interposed therebetween. In the region where the coating portion 8 is present, the piston clearance is clogged and the oil film thickness when the piston 2 is slid is reduced, whereby the friction coefficient is kept small and the frictional force is further reduced.

  That is, as shown in the Stribeck diagram in FIG. 3 where the vertical axis represents the friction coefficient and the horizontal axis represents the oil film thickness, the friction coefficient μ decreases as the oil film thickness decreases in the fluid lubrication region. If the piston clearance becomes clogged due to the presence of oil and the oil film thickness becomes thin, the friction coefficient μ decreases and the frictional force decreases.

  In addition, since each coating part 8 exists in a plurality of locations in the circumferential direction of the skirt 7 and the piston clearance is clogged, if the appropriate coating thickness is ensured as before, the hitting sound at the time of piston slap becomes the same level as before. It becomes possible to reduce.

  Therefore, according to the above embodiment, the low friction coating is applied to the outer peripheral surface of at least the anti-thrust side of the skirt 7 of the piston 2 so as to form a stripe pattern extending in the sliding direction of the skirt 7, and the coating portion By leaving the non-coating portion 9 that allows the lubricating oil to escape in the sliding direction of the skirt 7 between the two, the lubricating area in the skirt 7 of the piston 2 can be reduced and the frictional force can be greatly reduced. Thus, it is possible to significantly improve fuel efficiency by reducing friction loss compared to the conventional case.

  In the present embodiment, since the low friction coating is applied to the entire outer peripheral surface on the thrust side of the skirt 7 of the piston 2, the mixed lubrication state in which metal contact occurs is dominant. In this case, the entire region can be covered with a low friction coating to exhibit conventional seizure resistance and low friction characteristics.

  That is, as shown in the Stribeck diagram of FIG. 3, in the fluid lubrication region, the friction coefficient μ decreases as the oil film thickness decreases, but the mixed lubrication in which metal contact occurs beyond a predetermined oil film thickness. , The friction coefficient μ increases rapidly as the oil film thickness decreases.

  For this reason, on the thrust side where mixed lubrication is dominant, leaving the non-coated portion 9 causes the non-coated portion 9 to make metal contact with the cylinder liner 1a side, resulting in seizure and wear loss. Disadvantages are considered to be greater, and priority is given to avoiding such disadvantages.

  It should be noted that the piston sliding portion lubrication structure of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the scope of the present invention.

It is a side view which shows an example of the form which implements this invention. It is sectional drawing of the II-II arrow of FIG. It is a Stribeck diagram in which the vertical axis represents the friction coefficient and the horizontal axis represents the oil film thickness. It is the schematic which shows a prior art example.

Explanation of symbols

1 Cylinder 2 Piston 7 Skirt 8 Coated part 9 Uncoated part

Claims (1)

A lubricating structure of a piston sliding portion subjected to low-friction coating on the skirt surface of the piston reciprocating in a cylinder of the engine, the outer peripheral surface of the anti-thrust side that put the piston skirt sliding direction of said skirt subjecting a low friction coating to form a striped pattern extending toward the, and the remaining uncoated portion releasing the lubricating oil to the sliding direction of the skirt between each other of the coating portion, the outer peripheral surface of the thrust side of the piston skirt lubrication structure of a piston sliding portion, characterized in that it has facilities for low friction coating throughout.

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