JP2013019366A - Lubrication structure of piston slide part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubrication structure of a piston slide part which can largely be reduced in friction force without forming a string-shaped fine step at the internal face of a cylinder liner.SOLUTION: The lubrication structure of the piston slide part is constituted in such a manner that a low-friction coating is applied to the external peripheral face at the anti-thrust side of a skirt 7 of a piston 2 which reciprocates in a cylinder 1 of an engine so that there may be formed a striped pattern extending to the slide direction of the piston 2, and a non-coated part 9 for making a lubrication fluid escape to the slide direction of the piston 2 is left between the coated parts 8. Each coated part 8 is formed so that a slide point of each coated part 8 may be changed to the circumferential direction of the cylinder liner 1a according to slide of the piston 2 at the same level as that of the internal face of the cylinder liner 1a, and ranges in which the respective coated parts 8 slide with respect to the internal face of the cylinder liner 1a may be overlapped with each other.

Description

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

  As shown in FIG. 3, 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 4a of a connecting rod 4 via a piston pin 3 so as to be swingable. Is connected to the crankshaft 6 via a 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 track around the center of the crankshaft 6 (see the one-dot chain line in FIG. 3). 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.

  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 slide 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.

  Therefore, as shown in FIGS. 4 and 5, the present inventor has a low friction coating so that a striped pattern extending in the sliding direction of the piston 2 is formed on the outer peripheral surface of the skirt 7 of the piston 2 on the anti-thrust side. And a non-coating portion 9 that allows the lubricating oil to escape in the sliding direction of the piston 2 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. A configuration was created, and this has already been filed as Patent Document 1 below.

  In this way, a gap g (see FIG. 5) 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 the cylinder liner 1a side is provided on each coating portion 8 side. This is limited to the existing region, which 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 piston 2 so that the lubricating oil can be freely released. 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. 6 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.

JP 2010-106724 A

  However, in such a conventional structure, since the vertical stripe pattern coating portions 8 extending in parallel with the sliding direction of the piston 2 are employed, the coating portions 8 are slid by being pressed against the same place on the inner surface of the cylinder liner 1a. Therefore, as shown in FIG. 7, a streak-like slight step 10 (a slight hit caused by the reduced surface roughness) is formed at the position where the coating portion 8 on the inner surface of the cylinder liner 1a hits. There was concern that the durability of the cylinder liner 1a could be adversely affected.

  The present invention has been made in view of the above circumstances, and provides a lubricating structure for a piston sliding portion capable of significantly reducing the frictional force without causing a streak-like slight step on the inner surface of a cylinder liner. The purpose is that.

  The present invention provides a low friction coating on the outer surface of the piston skirt that reciprocates in the cylinder of the engine on the anti-thrust side so as to form a striped pattern extending in the sliding direction of the piston. The piston sliding portion lubrication structure leaves an uncoated portion that allows lubricating oil to escape in the sliding direction of the piston, and the sliding portion of each coating portion is at the same level on the inner surface of the cylinder liner as the piston slides. The coating portions are formed such that the ranges of the coating portions that change in the circumferential direction of the cylinder liner and the sliding portions of the coating portions slide on the inner surface of the cylinder liner overlap each other. .

  Thus, in this way, the sliding portion of each coating portion changes in the circumferential direction of the cylinder liner at the same level on the inner surface of the cylinder liner as the piston slides. While the non-coating portion remains between the portions, the range in which each coating portion slides with respect to the inner surface of the cylinder liner is expanded, and the range in which each coating portion slides overlaps each other. As a result, the entire area of the inner surface of the cylinder liner within the range facing the anti-thrust side of the piston skirt is slid by each coating portion, and there is a possibility that a slight streaky step will occur in this area. To be avoided.

  Further, even in the case of such a coating portion, a gap corresponding to the coating thickness is generated at the boundary between the coating portion and the non-coating portion, and a substantial lubrication surface with the cylinder liner side is provided on each coating portion. Since it is limited only to the existing region, 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 opened in the sliding direction of the piston so that the lubricating oil can be released freely. In other words, the frictional resistance is hardly affected by the viscosity of the lubricating oil, so that the substantial frictional surface with the cylinder liner side is limited only to the region where each coating portion exists.

  In addition, on the anti-thrust side of the piston skirt, the fluid lubrication state occurs between the coating parts and the cylinder liner, with the friction surfaces sliding apart with the oil film in between. In this area, the piston clearance is clogged and the oil film thickness when the piston is slid is thinned. As a result, the friction coefficient is kept small and the frictional force is reduced.

  Further, when carrying out the present invention more specifically, each coating portion is formed in a teardrop shape and the teardrop shapes are arranged next to each other so that the top and bottom are alternately reversed, or each coating It is possible to make the part into a band shape inclined by a required angle in the same direction with respect to the sliding direction of the piston.

  Furthermore, in the present invention, it is preferable to apply a low friction coating to the entire outer peripheral surface on the thrust side of the skirt of the piston. By doing so, the state of mixed lubrication in which metal contact occurs is dominant. On the thrust side, the entire region is covered with the low friction coating, so that the seizure resistance and the low friction characteristics as usual can be exhibited.

  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 first to third aspects of the present invention, a range in which each of the coating portions slides with respect to the inner surface of the cylinder liner while leaving an uncoated portion between the coating portions. The range in which each coating portion slides overlaps each other, and the entire area of the cylinder liner inner surface in the range facing the anti-thrust side of the piston skirt can be slid by each coating portion. Since the frictional force can be greatly reduced without causing a streak-like slight step on the inner surface of the cylinder liner, the possibility that the streak-like step may adversely affect the durability of the cylinder liner is eliminated. be able to.

  (II) According to the invention described in claim 4 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.

It is a side view which shows an example of the form which implements this invention. It is a side view which shows another form example of this invention. It is the schematic which shows the mechanism of a general engine. It is a side view which shows a prior art example. It is sectional drawing of the VV 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 the slight level | step difference which can be made in a cylinder liner inner surface.

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

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

  As shown in FIG. 1, in this embodiment, as in the conventional example of FIG. 4 described above, the outer peripheral surface of the skirt 7 of the piston 2 on the side opposite to the thrust extends in the sliding direction of the piston 2. A low-friction coating is applied so as to form a striped pattern, and an uncoated portion 9 that allows the lubricating oil to escape in the sliding direction of the piston 2 is left between the coating portions 8, while an outer periphery on the thrust side of the skirt 7 of the piston 2 A low friction coating is applied to the entire surface, but each coating portion 8 is replaced with a vertical stripe pattern extending parallel to the sliding direction of the piston 2 as in the conventional example of FIG. In addition, the teardrop shapes are arranged adjacent to each other so that the top and bottom are alternately reversed.

  That is, in this embodiment, a tear drop shape is adopted as a shape in which the sliding portion of each coating portion 8 changes in the circumferential direction of the cylinder liner 1a at the same level on the inner surface of the cylinder liner 1a as the piston 2 slides. For example, when the level L in FIG. 1 is used as a reference, the teardrop-shaped coating portion 8 (the first coating portion 8 from the left in FIG. 1 etc.) that widens downward is the The sliding portion at level L expands in the circumferential direction of the cylinder liner 1a as it rises, and the inverted teardrop-shaped coating portion 8 (the second coating portion 8 from the left in FIG. ), The sliding portion at the level L is reduced in the circumferential direction of the cylinder liner 1a as the piston 2 rises.

  In addition, by arranging such tear-drop-shaped coating portions 8 so that the top and bottom are alternately reversed, between the coating portions 8 are alternately reversed with respect to the sliding direction of the piston 2. Thus, a straight uncoated portion 9 that is inclined by a required angle is left.

  In addition, the protruding position of the maximum width portion of each coating portion 8 in the circumferential direction of the piston 2 extends beyond the protruding position of the maximum width portion of the adjacent counterpart coating portion 8. The maximum width portions of the left and right coating portions 8 are arranged in the projecting range x of the maximum width portion of the coating portion 8 illustrated second from the left in FIG.

  That is, the overhanging range x of the maximum width portion of the coating portion 8 having a teardrop shape indicates a range in which the coating portion 8 slides with respect to the inner surface of the cylinder liner 1a, in other words, the cylinder liner 1a. The range in which each coating portion 8 slides on the inner surface overlaps with each other.

  Thus, if such a teardrop-shaped coating portion 8 is used, the sliding position of each coating portion 8 with respect to the same level of the inner surface of the cylinder liner 1a is changed in the circumferential direction of the cylinder liner 1a according to the sliding of the piston 2. Therefore, the range in which each of the coating portions 8 slides relative to the inner surface of the cylinder liner 1a is expanded while leaving the uncoated portion 9 between the coating portions 8. In addition, since the ranges in which the respective coating portions 8 slide are overlapped with each other, the entire inner surface of the cylinder liner 1a within the range facing the anti-thrust side of the skirt 7 of the piston 2 is covered with each coating portion. Thus, it is avoided that a slight streaky streak is generated here.

  Even in the case of such a coating portion 8, a gap 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 the cylinder liner 1a side is obtained. Since it is limited only to the area where each coating portion 8 exists, the effect of reducing the lubricating area in the skirt 7 of the piston 2 and greatly reducing the frictional force can be obtained as usual.

  That is, the non-coating portions 9 remaining between the coating portions 8 are opened in the sliding direction of the piston 2 so that the lubricating oil can be freely released. 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. 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.

  Therefore, according to the above-described embodiment, while leaving the non-coated portion 9 between the coating portions 8, the range in which each of the coating portions 8 slides with respect to the inner surface of the cylinder liner 1a is expanded. The areas where the coating portion 8 slides are overlapped with each other, and the entire area of the inner surface of the cylinder liner 1a within the range facing the non-thrust side of the skirt 7 of the piston 2 can be slid by each coating portion 8. Since the frictional force can be greatly reduced without generating a streak-like slight step on the inner surface of the liner 1a, the possibility that the durability of the cylinder liner 1a may be adversely affected by the streak-like step is eliminated. can do.

  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. 6, in the fluid lubrication region, the friction coefficient μ decreases as the oil film thickness decreases, but the mixed lubrication where 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.

  Further, FIG. 2 shows another embodiment of the present invention. In the coating portion 8 in this embodiment, the sliding portion of each coating portion 8 is at the same level on the inner surface of the cylinder liner 1a as the piston 2 slides. In this case, it is sufficient that the range in which the coating portions 8 change in the circumferential direction of the cylinder liner 1a and the coating portions 8 slide on the inner surface of the cylinder liner 1a overlap each other. 8 shows an example in which a belt shape 8 is inclined in the same direction with respect to the sliding direction of the piston 2 by a required angle.

  Even in this case, the sliding portion of each coating portion 8 moves in the circumferential direction of the cylinder liner 1a according to the sliding of the piston 2 with respect to the same level of the inner surface of the cylinder liner 1a. While leaving the non-coating portion 9 between the coating portions 8, the range in which each coating portion 8 slides relative to the inner surface of the cylinder liner 1a is expanded as compared with the prior art, and the coating portions 8 slide. Since the ranges to be overlapped with each other, the entire area of the inner surface of the cylinder liner 1a in the range facing the non-thrust side of the skirt 7 of the piston 2 is slid by the respective coating portions 8, and there It is possible to avoid the occurrence of a step difference.

  In addition, the lubricating structure of the piston sliding portion of the present invention is not limited to the above-described embodiment, and the shape of each coating portion is determined by the sliding portion of each coating portion according to the piston sliding. It is only necessary to change the circumferential direction of the cylinder liner at the same level on the inner surface of the cylinder liner and to allow the ranges where the coating portions slide relative to the inner surface of the cylinder liner to overlap each other. Of course, the invention is not limited to the shape of a slanted belt, and various modifications can be made without departing from the scope of the present invention.

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

Claims (4)

  A low friction coating is applied to the outer peripheral surface of the piston skirt that reciprocates in the cylinder of the engine on the anti-thrust side so as to form a stripe pattern extending in the sliding direction of the piston. A piston sliding portion lubrication structure that leaves an uncoated portion that allows lubricating oil to escape in the sliding direction, wherein the sliding portion of each coating portion is at the same level on the inner surface of the cylinder liner as the piston slides. The piston sliding portion lubrication structure is characterized in that the coating portions are formed so that the ranges in which the coating portions slide relative to the inner surface of the cylinder liner overlap each other. .   2. The piston sliding portion lubrication structure according to claim 1, wherein each coating portion has a tear drop shape, and the tear drop shapes are arranged adjacent to each other so that the top and bottom are alternately reversed.   2. The lubricating structure for a piston sliding portion according to claim 1, wherein each coating portion has a band shape inclined at a required angle in the same direction with respect to the sliding direction of the piston.   4. The lubricating structure for a piston sliding portion according to claim 1, wherein a low friction coating is applied to the entire outer peripheral surface on the thrust side of the skirt of the piston.

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