JP2014214731A - Structure for lubricating piston sliding part - Google Patents

Abstract

Lubricating structure for a piston sliding portion that significantly reduces frictional force without causing a streak-like minor step on the inner peripheral surface of a cylinder and also reduces fluid friction due to lubricating oil flowing through a gap in a coating portion The purpose is to provide. A coating portion 21 has a pair of sharpened portions 21a and 21b projecting in an axial direction AD of a piston 2 so that the overall shape is axisymmetric and a symmetrical axis AS is along the axial direction AD of the piston 2. Is formed. A branch passage 22 through which lubricating oil flows is formed by one sharp portion 21a of the coating portion 21 and the other sharp portion 21b of the coating portion 21 in the adjacent row. The branch channel 22 has a channel width that is at least half of the gap 2S. [Selection] Figure 1

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 housed in a cylinder 1 is supported by a small end 4a of a connecting rod 4 via a piston pin 3 so as to be swingable. 4 is connected to a crankshaft 6 through 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 follows a circular orbit (see the one-dot chain line in FIG. 3) around the center of the crankshaft 6. Since the connecting rod 4 swings around the piston pin 3, the piston 2 moves up and down in the cylinder 1 up and down in FIG.

  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. However, if a large amount of piston clearance is ensured, there is a problem that a hitting sound is generated during 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.

  The piston 2 pushed downward by the explosion pressure A is strongly pressed against the inner wall of the cylinder 1 on the left side of the piston 2 due to the inclination of the connecting rod 4. Hereinafter, the side that receives the lateral pressure (Side-Thrust) immediately after top dead center is referred to as the thrust side.

  On the thrust side that receives such a side pressure, the state of mixed lubrication in which metal contact occurs is dominant. On the anti-thrust side, the state of fluid lubrication in which the friction surfaces slide with the oil film interposed therebetween is dominant.

  However, the low friction coating is applied to the entire anti-thrust side where fluid lubrication is dominant, which increases the sliding resistance, thereby impairing the room for further improvement in fuel consumption.

  Therefore, as shown in FIGS. 4A and 4B, a low friction coating is formed on the outer surface of the skirt 7 of the piston 2 on the anti-thrust side so as to form a striped pattern extending in the sliding direction of the piston 2. 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 is proposed in Patent Document 1.

  In this way, a gap g corresponding to the coating thickness is generated at the boundary between the coating portion 8 and the non-coating portion 9 (see FIG. 4B), and the lubrication surface substantially on the cylinder liner 1a side is each coating. This is limited to the region where the 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 piston 2 so that the lubricating oil can be released freely. Even the state of lubrication does not occur, and the viscosity of the lubricating oil hardly affects the state of friction resistance. For this reason, the substantial lubrication surface with the cylinder liner 1a side is limited only to the region where each coating portion 8 exists.

  In addition, on the anti-thrust side of the skirt 7 of the piston 2, the fluid lubrication is performed between the coating portions 8 and the cylinder liner 1 a with the friction surfaces sliding apart with the oil film interposed therebetween. On the other hand, in the area where each coating portion 8 exists, the piston clearance is clogged, and the oil film thickness when the piston 2 slides is thinned. As a result, the friction coefficient is kept small and the frictional force is further reduced.

  That is, as shown in the Stribeck diagram in FIG. 5 where the vertical axis represents the friction coefficient and the horizontal axis represents the oil film thickness, in the fluid lubrication region, the friction coefficient μ decreases as the oil film thickness decreases. For this reason, if the piston clearance is clogged due to the presence of each coating portion 8 and the oil film thickness becomes thin, the friction coefficient μ decreases and the frictional force decreases.

  However, since the coating pattern disclosed in Patent Document 1 employs a coating portion 8 having a vertical stripe pattern extending in parallel with the sliding direction of the piston 2, each coating portion 8 is an inner peripheral surface of the cylinder liner 1a. As shown in FIG. 6, the streak-like slight step 10 (the surface roughness is reduced) at the position where the coating portion 8 on the inner peripheral surface of the cylinder liner 1a hits. (The slight hit caused by the above) may occur, and the durability of the cylinder liner 1a may be adversely affected.

  Therefore, as shown in FIGS. 7A and 7B, a lubricating structure of a piston sliding portion in which a skirt 7 is provided with a polka-dot-shaped coating portion 8 in a staggered arrangement has been proposed. That is, the coating portions 8 are arranged with a gap D along the circumferential direction CD of the piston 2 to form a plurality of rows along the circumferential direction CD of the piston 2 and stagger the coating portions 8 in adjacent rows. It is arranged. The diameter of the polka dots is formed to be the same size as the gap D.

  The piston 2 to which such a coating pattern is applied is pressed against the inner peripheral surface of the cylinder liner 1a without any gaps and slides, thereby producing a slight streaky step 10 on the inner peripheral surface of the cylinder liner 1a. The frictional force can be greatly reduced without any problems.

JP 2010-106724 A

  However, the piston 2 having the coating portion 8 arranged in a polka dot staggered arrangement has room for further improvement.

  When the piston 2 having the coating portions 8 arranged in a polka dot staggered arrangement is reciprocated in the cylinder 1 via the lubricating oil, the lubricating oil flows through the gaps between the coating portions 8. Here, when the gap between the coating portions 8 arranged in the direction along the circumferential direction of the piston 2 is D, and the gap between the coating portion 8 and the nearest coating portion 8 ′ in the adjacent row is d, D> 2d It has become. Further, U represents the flow rate of the lubricating oil flowing through the gap D, and u1 represents the flow rate of the lubricating oil in the branch channel flowing through the gap d.

  The lubricating oil flowing in the gap D collides with the circumference of the coating portion 8 in the adjacent row, and is divided into two and flows between the gaps d. At this time, the lubricating oil flowing through the gap D collided with the circumference of the rounded coating portion 8 and thus received a large fluid friction.

  Further, since the size of the gap d is smaller than half of the size of the gap D, the flow rate u1 of the divided oil flowing through the gap d is higher than the flow rate U of the lubricant oil flowing through the gap D. Get faster. That is, a portion where the flow rate of the lubricating oil is different between the coating portions 8 is generated, and the fluid friction of the lubricating oil is received.

  Therefore, the present invention aims to greatly reduce the frictional force without causing a streak-like slight step on the inner peripheral surface of the cylinder, and to reduce the fluid friction due to the lubricating oil flowing through the gap between the coating parts. An object of the present invention is to provide a lubricating structure.

  The present invention provides a coating portion formed by a coating for reducing frictional force on the anti-thrust side of a sliding portion of a piston that reciprocates via lubricating oil in a cylinder of an internal combustion engine along the circumferential direction of the piston. Forming a plurality of rows in which the coating portions of rows adjacent to each other along the circumferential direction of the piston are alternately arranged, and in the circumferential direction of the piston in the coating portion The present invention relates to a lubrication structure for a piston sliding portion that is formed so that the length along the gap is equal to or larger than the size of the gap, and in which lubricating oil flows between coating portions as the piston reciprocates. The coating portion has a pair of pointed portions protruding in the axial direction of the piston, the overall shape is line-symmetrical, and the symmetrical axis is formed along the axial direction of the piston. A branch channel through which the lubricating oil flows is formed by the other sharpened portion of the coating portion in the row adjacent to the sharpened portion, and a branch channel through which the lubricating oil flows is formed. It is characterized by being one-half or more of the gap.

  In the lubricating structure of the piston sliding portion, it is preferable that the coating portion has a rounded portion with rounded corners protruding from the rhombus in the circumferential direction of the piston.

  In the lubricating structure of the piston sliding portion, the entire outer peripheral surface on the thrust side in the sliding portion of the piston can be coated.

  According to the lubricating structure of the piston sliding portion of the present invention, the frictional force is greatly reduced without causing a streak-like slight step on the inner peripheral surface of the cylinder, and the fluid by the lubricating oil flowing through the gap of the coating portion. Friction can also be reduced.

(A) is a side view of a piston showing a lubricating structure of a piston sliding portion of the present invention. (B) is an enlarged view showing a part of the lubricating structure of the piston sliding portion of (A). It is a figure which shows other embodiment in the lubrication structure of the piston sliding part of this invention. It is a figure which shows the mechanism of a general engine. (A) is a side view which shows the lubrication structure of the conventional piston sliding part. (B) is an IV (B) -IV (B) arrow view of (A). 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 generate | occur | produces on the internal peripheral surface of a cylinder liner. (A) is a side view showing a lubricating structure of a piston sliding portion in which a polka dot coating portion is arranged in a staggered arrangement. (B) is an enlarged view showing a part of the lubricating structure of the piston sliding portion in which the polka-dot-shaped coating portions are arranged in a staggered arrangement.

  Hereinafter, the form for implementing this invention is demonstrated with reference to FIG. FIG. 1A is a side view of a piston showing a lubricating structure of a piston sliding portion of the present invention. FIG. 1B is an enlarged view showing a part of the piston sliding portion of FIG. In FIG. 1, the same reference numerals as those in FIG. 3 denote the same parts. The basic configuration is the same as the conventional one shown in FIG.

  In the present invention, a plurality of coating portions 21 are formed on the anti-thrust side of the sliding portion of the piston 2 that reciprocates in the cylinder 1 of the engine (internal combustion engine) through the lubricating oil by a coating that reduces the frictional force. It is formed.

  A plurality of coating portions 21 are formed along the circumferential direction CD of the piston 2 by forming a plurality of coating portions 21 with a gap 2 </ b> S along the circumferential direction CD of the piston 2. In this row, adjacent (adjacent) rows of coating portions 21 ′ are alternately arranged. That is, the coating portion 21 is applied to the skirt 7 in a staggered arrangement. For convenience of explanation, although the coating portions in adjacent rows are indicated by 21 ′, they are the same coating portion 21.

  The coating portion 21 has a shape in which a pair of diagonals are rounded out of four corners of the rhombus. The coating portion 21 has a line-symmetric shape, and is formed so that the axis of symmetry AS is along the axial direction AD of the piston 2. And the part which protrudes in the direction in alignment with circumferential direction CD of piston 2 is rounded. The coating part 21 has a pair of sharp corners 21a, 21b protruding in the axial direction AD of the piston 2 and a pair of rounded corners 21c, 21c.

  The coating portion 21 has the same length 2r in the direction along the circumferential direction CD of the piston 2 as the size of the gap 2S. Here, the rounded corner portion 21c coincides with a part of an inscribed circle 21d inscribed in the coating portion 21 with a radius r.

  In the embodiment for carrying out the present invention, the gravity center position of the coating portion 21 is the same as the gravity center position of the coating portion 21 ′ in the adjacent row, the distance L along the axial direction AD of the piston 2 is 3r, and the circumferential direction of the piston 2. The distance M along the CD is 2r.

  A branch channel 22 through which lubricating oil flows is formed by the other sharpened portion 21b of the coating portion 21 and the sharpened portion 21a of the adjacent coating portion 21 ′ of the row. A constant gap S is provided between the other sharpened portion 21b and the sharpened portion 21a of the coating portion 21 ′ in the adjacent row. Therefore, the branch channel 22 has the same channel width as the gap S and is half the size of the gap 2S between the adjacent coating portions 21 and 21 (21 ′, 21 ′). Is formed.

  The piston sliding portion lubrication structure of the present invention is formed by forming a plurality of coating portions 21 on the anti-thrust side of the sliding portion of the piston with a gap 2S along the circumferential direction CD of the piston 2. A coating pattern is formed which forms a plurality of rows in which the coating portions 21 of rows adjacent to each other along the circumferential direction CD are alternately arranged, and the length along the circumferential direction CD of the piston 2 in the coating portion 21 is It is formed in the same size as the gap 2S.

  As a result, as the piston 2 reciprocates in the cylinder 1, the entire region is slid by the respective coating portions 21 in a range where the portion provided with the coating portion 21 slides on the inner peripheral surface of the cylinder liner 1 a. Thus, it is possible to prevent the occurrence of a slight streak-like step on the inner surface of the cylinder liner 1a.

  Further, the coating portion 21 has a pair of sharp portions 21 a and 21 b that protrude in the axial direction AD of the piston 2. As a result, the lubricating oil flowing through the gap 2S can be divided into two parts with a small fluid friction because the contacting portion is smaller than when the lubricating oil collides with the arc and is divided into two parts.

  A branch channel 22 through which lubricating oil flows is formed by the other sharpened portion 21b of the coating portion 21 and the sharpened portion 21a of the adjacent coating portion 21 ′ of the row. The branch channel 22 has a channel width that is half the size of the gap 2S. As a result, the lubricating oil flowing through the gap 2S is equally divided by the pointed portion 21a (or 21b) and flows through the branch channel 22 having a channel width that is half the interval 2S. Therefore, the flow rate of the lubricating oil flowing through the interval 2S and the flow rate of the lubricating oil flowing through the branch channel 22 are the same flow rate.

  Then, the lubricating oil that has flowed through the branch flow path 22 merges in the merge flow path 23 where the two split flow paths 22 merge to double the flow rate, and flows twice as wide as the branch flow path 22. Therefore, the flow rate of the lubricating oil flowing through the combined flow path 23 is the same as the flow speed of the lubricating oil flowing through the branch flow path 23.

  Further, the coating portion 21 has a rounded corner portion 21 c having rounded corners that protrude in the circumferential direction CD of the piston 2. As a result, the lubricating oil that has flowed through the two split flow paths 22 smoothly merges in the merge path 23.

Therefore, the fluid friction which generate | occur | produces since the flow velocity of the lubricating oil which flows between the coating parts 21 differs can be suppressed.
As described above, a further fuel consumption reduction effect can be obtained.

  Moreover, in the form for implementing this invention, the low friction coating is given to the outer peripheral surface area of the thrust side in the skirt 7 of the piston 2. For this reason, on the thrust side of the skirt 7 where the state of mixed lubrication in which metal contact occurs is dominant, the entire region can be covered with a low friction coating to exhibit conventional seizure resistance and low friction characteristics. it can.

  That is, as shown in the Stribeck diagram of FIG. 5, in the fluid lubrication region, the friction coefficient μ decreases as the oil film thickness decreases, but 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 part causes the non-coated part to cause metal contact with the cylinder liner 1a side, resulting in seizure and wear loss. Is considered to be larger, and priority is given to avoiding such disadvantages.

  With reference to FIG. 2, other embodiment of a piston sliding part is described. FIG. 2 is a view showing another embodiment of the piston sliding portion lubrication structure of the present invention. The piston sliding portion lubrication structure according to another embodiment has the same basic configuration as that of the above embodiment except for the distance between the gravity center position of the coating portion 21 and the gravity center position of the coating portion 21 'in the adjacent row. For this reason, the same components as those in the above-described embodiment are denoted by the same reference numerals, and the description that overlaps the description of the above-described embodiment is omitted.

  The gravity center position of the coating portion 21 is such that the gravity center position of the coating portion 21 ′ in the adjacent row is equal to the distance L along the axial direction AD of the piston 2 and the distance L along the circumferential direction CD of the piston 2. Has been placed.

  The lubricating structure of the piston sliding portion of the present invention is not limited to the above-described embodiment. For example, the coating portion 21 is described using an example in which the length in the direction along the circumferential direction CD of the piston 2 is the same as the length of the gap 2S between the coating portions 21 adjacent in the circumferential direction CD of the piston 2. However, it is not limited to this. The coating part 21 can make the length of the direction along the circumferential direction CD of the piston 2 larger than the magnitude | size of the space | interval 2S with the coating part 21 adjacent along the circumferential direction CD of the piston 2. As shown in FIG.

  Further, the flow path width of the branch flow path 22 has been described as being half the gap 2S between the coating portion 21 adjacent to the adjacent gap along the circumferential direction CD of the piston 2, but the present invention is not limited to this. . The flow path width of the branch flow path 22 can be set to one half or more of the gap with the coating portion 21 adjacent to the gap S of the flow path width along the circumferential direction CD of the piston 2.

  The lubricating structure of the piston sliding portion of the present invention can be variously modified without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Cylinder 1a Cylinder liner 2 Piston 7 Skirt 21 Coating part 21a Sharp part 21b Sharp part 21c Round part 22 Split flow path 2S Gap AD Axial direction CD Circumferential direction AS Symmetric axis

Claims (3)

On the anti-thrust side of the sliding part of the piston that reciprocates through the lubricating oil in the cylinder of the internal combustion engine, a coating portion formed by a coating that reduces the frictional force is spaced along the circumferential direction of the piston. Forming a plurality of rows in which the coating portions of rows adjacent to each other along the circumferential direction of the piston are alternately arranged, and a length along the circumferential direction of the piston in the coating portion. Is a lubricating structure of a piston sliding portion in which the lubricating oil flows so as to flow between coating portions as the piston reciprocates,
The coating portion has a pair of pointed portions that protrude in the axial direction of the piston, and the overall shape is axisymmetric, and the symmetrical axis is formed along the axial direction of the piston.
The one sharpened portion of the coating portion and the other sharpened portion in the coating portion of the adjacent row form a branch channel through which lubricating oil flows,
The lubrication structure for a piston sliding portion, wherein the branch channel has a channel width that is at least one half of the gap.   2. The lubricating structure for a piston sliding portion according to claim 1, wherein the coating portion has a rounded portion with rounded corners protruding from a rhombus in the circumferential direction of the piston.   The lubricating structure for a piston sliding portion according to claim 1 or 2, wherein a coating is applied to the entire outer peripheral surface on the thrust side in the sliding portion of the piston.

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