JP2010138711A - Cylinder liner structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylinder liner structure reducing friction coefficient under a mixed lubrication condition between a piston ring and the cylinder liner, and improving fuel economy. <P>SOLUTION: Surface roughness of an upper inner surface of a cylinder liner 1a at an upper side of a lower surface of an oil ring groove 10a at a top dead center position of a piston ring 2 is maintain finer than surface roughness of an inner surface of the cylinder liner 1a at a lower side of the lower surface of the oil ring groove 10a at the top dead center position of the piston ring 2 so as to reduce friction coefficient under the mixed lubrication condition. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a cylinder liner structure.

  Generally, in an engine in an automobile or the like, as shown in FIG. 3, 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. 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 a crank arm 6a, and the crankpin 5 draws a circular orbit (see the chain line in FIG. 3) 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.

  Here, a piston ring is fitted to the piston 2, and the piston ring slides while lubricating the inner surface of the cylinder liner 1a via lubricating oil, and has a sliding range excluding the vicinity of the top and bottom dead center. In the middle part, lubrication is performed in a so-called fluid lubrication state in which the friction surfaces slide apart with an oil film interposed therebetween, but the sliding speed of the piston 2 decreases near the top and bottom dead center that is the turning position. The lubrication is performed under a so-called mixed lubrication state involving metal contact.

  In particular, among the piston rings near the top dead center, the top ring is seated on the lower surface of the top ring groove by the internal pressure of the cylinder 1 so that the internal pressure of the cylinder 1 pushes the inner peripheral surface of the top ring from the upper surface side of the top ring. The friction loss due to the top ring is maximized.

For example, Patent Document 1 shows a general technical level related to an engine cylinder.
JP-A-8-200135

  However, in the conventional cylinder liner 1a as described above, no consideration is given to the lubrication state with the piston ring, and the inner surface of the cylinder liner 1a is manufactured with a uniform surface roughness. It has been difficult to reduce the coefficient of friction under the mixed lubrication condition between the cylinder liner 1a and the cylinder liner 1a, and there is still room for improvement in terms of fuel consumption.

  In view of such circumstances, the present invention intends to provide a cylinder liner structure that can reduce the coefficient of friction under a mixed lubrication state between a piston ring and a cylinder liner and can improve fuel consumption.

The present invention provides a cylinder liner structure in which a piston having a top ring fitted in a top ring groove and an oil ring fitted in an oil ring groove located below the top ring groove is slidably fitted in an axial direction. There,
The surface roughness of the cylinder liner upper inner surface above the lower surface of the oil ring groove at the piston top dead center position is set below the lower surface of the oil ring groove at the piston top dead center position so that the friction coefficient under the mixed lubrication state is reduced. The present invention relates to a cylinder liner structure characterized in that it is finer than the surface roughness of the inner surface of the cylinder liner.

  According to the above means, the following operation can be obtained.

  As described above, the surface roughness of the cylinder liner upper inner surface above the lower surface of the oil ring groove at the piston top dead center position is reduced so that the friction coefficient under the mixed lubrication state is reduced. If it is finer than the surface roughness of the inner surface of the cylinder liner on the lower side, the sliding speed of the piston decreases near the top dead center, which is the return position of the piston. Lubrication is performed, and among the piston rings near the top dead center, the cylinder internal pressure pushes the top ring inner peripheral surface from the top ring upper surface side against the top ring seated on the lower surface of the top ring groove by the cylinder internal pressure. Even if it acts as described above, the friction loss due to the top ring is reduced, and the fuel efficiency can be improved.

  Here, since the upper inner surface of the cylinder liner is exposed to a flame due to combustion, even if an attempt is made to reduce the friction coefficient by coating the upper inner surface of the cylinder liner, the coating peels off due to the heat of the flame. Therefore, it is difficult to cope with the coating, but if the surface roughness is made fine as in the present invention, there is no fear of being affected by the heat of the flame, and the mixed lubrication between the piston ring and the cylinder liner is performed. It becomes possible to reliably reduce the friction coefficient under the state.

  The piston ring such as the top ring or oil ring slides while lubricating the inner surface of the cylinder liner via lubricating oil, and a friction surface with an oil film sandwiched in the middle of the sliding range except near the top and bottom dead center. Lubrication is performed under a so-called fluid lubrication state in which they slide apart from each other, but in the case of the present invention, since the surface roughness of the cylinder liner inner surface below the oil ring groove lower surface at the piston top dead center position is not fine, There is no concern that the oil film thickness does not increase, and that the increase in the coefficient of friction due to the increase in the oil film thickness and the accompanying deterioration in fuel consumption are not caused.

  In the cylinder liner structure, the range in which the surface roughness is made fine can be the cylinder liner upper inner surface above the oil ring groove lower surface and below the top ring groove upper surface at the piston top dead center position, In this way, it is possible to minimize the range in which the surface roughness is fine.

  According to the cylinder liner structure of the present invention, the friction coefficient under the mixed lubrication state between the piston ring and the cylinder liner can be reduced, and an excellent effect that fuel efficiency can be improved can be achieved.

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

  1 and 2 show an example of an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 3 denote the same components, and the basic configuration is the conventional configuration shown in FIG. As shown in FIGS. 1 and 2, the feature of this example is that the surface roughness of the upper inner surface of the cylinder liner 1a above the lower surface of the oil ring groove 10a at the top dead center position of the piston 2 as shown in FIGS. Is made finer than the surface roughness of the inner surface of the cylinder liner 1a below the lower surface of the oil ring groove 10a at the top dead center position of the piston 2 so that the friction coefficient in the mixed lubrication state is reduced.

  In the case of this illustrated example, a top ring groove 8a, a second ring groove 9a, and an oil ring groove 10a are formed in order from the top on the outer peripheral surface of the piston 2, and the top ring groove 8a, second ring groove 9a, oil A top ring 8, a second ring 9, and an oil ring 10 are fitted as piston rings in the ring grooves 10a, respectively, and the range in which the surface roughness is made fine is the oil ring groove 10a at the top dead center position of the piston 2. The upper inner surface of the cylinder liner 1a is above the lower surface and below the upper surface of the top ring groove 8a.

  Further, the surface roughness of the inner surface of the cylinder liner 1a below the lower surface of the oil ring groove 10a at the top dead center position of the piston 2 is not made fine, but is the same as the current one.

  The surface roughness of the inner surface of the cylinder liner 1a at present is generally about 1 [μm], but the surface of the upper inner surface of the cylinder liner 1a above the lower surface of the oil ring groove 10a at the top dead center position of the piston 2 is approximately. The roughness may be about 0.2 [μm], which is about 1/5 of the current surface roughness of the inner surface of the cylinder liner 1a.

  Next, the operation of the illustrated example will be described.

  As described above, the surface roughness of the upper inner surface of the cylinder liner 1a above the lower surface of the oil ring groove 10a at the piston 2 top dead center position is set so that the friction coefficient in the mixed lubrication state is reduced. If the surface roughness of the inner surface of the cylinder liner 1a is lower than the lower surface of the oil ring groove 10a, the sliding speed of the piston 2 decreases near the top dead center, which is the position where the piston 2 is folded back. Of the piston ring near the top dead center, the cylinder 1 internal pressure is higher than the top ring 8 seated on the lower surface of the top ring groove 8a by the cylinder 1 internal pressure. 8 Even if it acts to spread the inner peripheral surface of the top ring 8 from the upper surface side, the friction loss due to the top ring 8 is reduced, and the fuel It is possible to improve.

  Here, since the upper inner surface of the cylinder liner 1a is exposed to a flame due to combustion, even if an attempt is made to reduce the friction coefficient by coating the upper inner surface of the cylinder liner 1a, the coating is peeled off by the heat of the flame. Therefore, it is difficult to cope with the coating. However, if the surface roughness is made fine as in the illustrated example, there is no fear of being affected by the heat of the flame, and the top ring 8, the second ring 9, In addition, it is possible to reliably reduce the friction coefficient under the mixed lubrication state between the piston ring such as the oil ring 10 and the cylinder liner 1a.

  Further, the piston rings such as the top ring 8, the second ring 9, and the oil ring 10 slide while lubricating the inner surface of the cylinder liner 1a through the lubricating oil, and the middle part of the sliding range excluding the vicinity of the vertical dead center. Then, lubrication is performed under a so-called fluid lubrication state in which the friction surfaces slide apart with an oil film interposed therebetween. However, in the illustrated example, the cylinder liner 1a below the lower surface of the oil ring groove 10a at the top dead center position of the piston 2 is used. Since the surface roughness of the inner surface is not made fine, the oil film thickness is not increased, and there is no concern that the increase in the coefficient of friction and the accompanying deterioration in fuel consumption caused by the increased oil film thickness. Incidentally, as shown in the illustrated example of the present invention, the surface roughness of the upper inner surface of the cylinder liner 1a above the lower surface of the oil ring groove 10a at the top dead center position of the piston 2 is changed so that the friction coefficient in the mixed lubrication state is reduced. 2 When the surface roughness of the inner surface of the cylinder liner 1a is lower than the lower surface of the oil ring groove 10a at the top dead center position, as shown in the Stribeck diagram of FIG. As the thickness decreases, the friction coefficient decreases as in the conventional case, but in a state where the oil film thickness is less than a predetermined value and shifts to mixed lubrication where metal contact occurs, as the oil film thickness decreases. It is possible to reduce the increasing friction coefficient compared to the conventional case (see the broken line in FIG. 2).

  Furthermore, in the illustrated example, the range in which the surface roughness is made fine is the upper inner surface of the cylinder liner 1a above the lower surface of the oil ring groove 10a at the top dead center position of the piston 2 and below the upper surface of the top ring groove 8a. Therefore, the range in which the surface roughness is fine can be minimized.

  In this way, the friction coefficient under the mixed lubrication state between the piston rings such as the top ring 8, the second ring 9, and the oil ring 10 and the cylinder liner 1a can be reduced, and the fuel consumption can be improved.

  Note that the cylinder liner structure of the present invention is not limited to the illustrated example described above, and at least an oil ring groove is provided with a top ring fitted in the top ring groove and positioned below the top ring groove. If the cylinder liner in which the piston fitted with the ring is slidably inserted in the axial direction, the piston without the second ring or the piston with the third ring in addition to the second ring slides in the axial direction. Of course, various modifications can be made without departing from the gist of the present invention, such as being applicable to a movably inserted one.

It is a sectional side view which shows an example of the form which implements this invention. It is a Stribeck diagram which shows the relationship between an oil film thickness and a friction coefficient. It is a schematic diagram showing a general engine.

Explanation of symbols

1a Cylinder liner 2 Piston 3 Piston pin 4 Connecting rod 8 Top ring (piston ring)
8a Top ring groove 10 Oil ring (piston ring)
10a Oil ring groove

Claims (2)

A cylinder liner structure in which a top ring is fitted in a top ring groove and a piston in which an oil ring is fitted in an oil ring groove located below the top ring groove is slidably fitted in an axial direction.
The surface roughness of the cylinder liner upper inner surface above the lower surface of the oil ring groove at the piston top dead center position is set below the lower surface of the oil ring groove at the piston top dead center position so that the friction coefficient under the mixed lubrication state is reduced. A cylinder liner structure characterized by a finer surface roughness than the inner surface of the cylinder liner.   The cylinder liner structure according to claim 1, wherein the range in which the surface roughness is made fine is the cylinder liner upper inner surface above the oil ring groove lower surface and below the top ring groove upper surface at the piston top dead center position.

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