CN111148924A

CN111148924A - Piston ring

Info

Publication number: CN111148924A
Application number: CN201880063649.4A
Authority: CN
Inventors: 伊藤伦浩; 莲见良介
Original assignee: Nippon Piston Ring Co Ltd
Current assignee: Nippon Piston Ring Co Ltd
Priority date: 2017-09-29
Filing date: 2018-09-27
Publication date: 2020-05-12
Also published as: JP7045383B2; WO2019065830A1; JPWO2019065830A1

Abstract

The invention provides a piston ring combined with a low-friction cylinder liner, which can obtain the friction reduction effect of the low-friction cylinder liner even when the rotation speed of an internal combustion engine is below 1000rpm in an idling state. The piston ring is combined with a low-friction cylinder liner with a specified concave part formed on the inner wall surface of the cylinder liner, and the surface pressure of the piston ring is 0.8-2.5 MPa.

Description

Piston ring

Technical Field

The present invention relates to a piston ring for an internal combustion engine, and more particularly, to a piston ring which is combined with a low-friction cylinder liner having a predetermined recess formed in an inner wall surface of the cylinder liner and which can sufficiently exhibit the effect of low friction of the low-friction cylinder liner even when the internal combustion engine is rotating at a low speed.

Background

Conventionally, a piston ring is known which is assembled to a piston of an internal combustion engine and which can achieve low friction and reduction in fuel consumption regardless of the type of cylinder liner to which the piston ring is assembled.

Various shapes of piston rings are known to achieve such low friction and reduction in fuel consumption, and for example, as described in patent document 1 below, a piston ring having a structure including a base material, a hard first layer formed on the base material, and a second layer laminated on the first layer and being softer than the first layer, wherein the surface roughness (Ra) of the first layer is 0.7 μm or less is known.

The surface roughness (Ra) of the first layer of the piston ring configured as described above is 0.7 μm or less, and therefore, friction can be reduced and fuel consumption can be suppressed regardless of the cylinder liner combination.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2017-36823

Disclosure of Invention

Problems to be solved by the invention

However, in recent internal combustion engines, for the purpose of improving fuel consumption and reducing fuel consumption, the contact area between the cylinder liner and the piston ring is reduced to minimize friction between the cylinder liner and the piston ring.

Various methods are known for reducing the contact area, and for example, it is known to use a low-friction cylinder liner provided with a recess at a predetermined position of the inner wall surface of the cylinder liner. By combining the piston ring with the low-friction cylinder liner, it is possible to achieve further friction reduction by the friction reduction effect of the low-friction cylinder liner in addition to the friction reduction effect of the surface roughness (Ra) of the first layer of the piston ring.

However, the present inventors have obtained the following findings: the friction reducing effect described above is confirmed at the rotational speed at which an automobile provided with an internal combustion engine normally travels, but the friction reducing effect by the low-friction cylinder liner cannot be sufficiently obtained in a region of low-speed rotation such as an idling state during parking.

The present invention has been made in view of the above problems, and an object thereof is to provide a piston ring combined with a low-friction cylinder liner, which can obtain a friction reduction effect of the low-friction cylinder liner even when the engine rotates at a low speed of 1000rpm or less, such as in an idling state.

Means for solving the problems

The piston ring of the present invention is a piston ring combined with a low-friction cylinder liner having a predetermined recess formed in an inner wall surface of the cylinder liner, and is characterized in that a surface pressure of the piston ring is 0.8 to 2.5 MPa.

In the piston ring according to the present invention, it is preferable that the piston ring has a follow-up coefficient of 0.1 or more.

In the piston ring according to the present invention, it is preferable that the contact width of the outer circumferential sliding surface of the piston ring is 0.05 to 0.40 mm.

In the piston ring according to the present invention, the piston ring is preferably a two-piece oil ring composed of a spiral expansion ring (coilexpander) and an oil ring main body.

ADVANTAGEOUS EFFECTS OF INVENTION

In the piston ring of the present invention, the surface pressure of the piston ring is set to 0.8 to 2.5MPa, and therefore, the surface pressure is optimized, and the friction force reducing effect by the low-friction cylinder liner can be exhibited even when the internal combustion engine rotates at a low speed.

Further, since the coefficient of follow-up property of the piston ring of the present invention is set to 0.1 or more, fuel consumption can be reduced in addition to the effect of reducing friction.

In addition, the piston ring of the present invention can further optimize the surface pressure because the contact width of the outer peripheral sliding surface of the piston ring is set to 0.05 to 0.40 mm.

The piston ring of the present invention is preferably used in a diesel engine as a two-piece oil ring composed of a helical expansion ring and an oil ring main body.

Drawings

Fig. 1(a) is a cross-sectional view showing an example of a piston ring according to an embodiment of the present invention, and (b) is a cross-sectional view showing another example.

Fig. 2 is an explanatory diagram illustrating an example of a position of formation of a recess in a cylinder liner inner wall surface combined with a piston ring according to an embodiment of the present invention.

Fig. 3 is a schematic expanded view showing an example of the arrangement of the concave portions in the stroke center region.

Fig. 4 is a schematic expanded view and a schematic cross-sectional view illustrating the dimensional position of a recess formed in the cylinder of the present invention.

Fig. 5 shows the results of a test showing the frictional force ratio according to the number of revolutions of the piston ring of the present embodiment.

Fig. 6 shows the results of the FMEP ratio test according to the surface pressure of the piston ring of the present embodiment.

Fig. 7 shows the results of a test for fuel consumption according to the surface pressure of the piston ring of the present embodiment.

Fig. 8 is a graph showing a relationship between the surface pressure and the follow-up coefficient of the piston ring according to the present embodiment.

Detailed Description

Preferred embodiments for carrying out the present invention will be described below with reference to the accompanying drawings. The following embodiments do not limit the inventions according to the respective aspects, and all combinations of the features described in the embodiments are not necessarily essential to the means for solving the inventions.

FIG. 1(a) is a cross-sectional view showing an example of a piston ring according to an embodiment of the present invention, (b) is a cross-sectional view showing another example, FIG. 2 is an explanatory view showing an example of a position of formation of a recess in a cylinder liner inner wall surface combined with a piston ring according to an embodiment of the present invention, FIG. 3 is a schematic development view showing an example of the arrangement of the recess in the stroke center region, FIG. 4 is a schematic development view and a schematic sectional view for explaining the dimensional position of the recess formed in the cylinder of the present invention, FIG. 5 shows the results of a test of the frictional force ratio according to the number of revolutions of the piston ring of the present embodiment, FIG. 6 shows the results of the FMEP ratio test according to the surface pressure of the piston ring of the present embodiment, FIG. 7 shows the results of a test for fuel consumption according to the surface pressure of the piston ring of the present embodiment, fig. 8 is a graph showing a relationship between the surface pressure and the follow-up coefficient of the piston ring according to the present embodiment.

As shown in fig. 1 a, the piston ring 1 of the present embodiment is assembled in a ring groove (not shown) formed in the outer peripheral surface of a piston of an internal combustion engine, and scrapes off excess engine oil adhering to the inner wall of a cylinder by sliding contact with the inner wall of the cylinder, thereby forming an appropriate oil film on the inner wall of the cylinder.

The piston ring 1 is a two-piece combined oil ring, and is composed of an oil ring main body 2 and a helical expansion ring 6. The oil ring main body 2 is formed in a substantially I-shaped cross section by connecting two rails 3, each having an outer peripheral sliding

portion protrusion

4, 4 formed at the tip end thereof, by a pillar portion 5. The helical expansion ring 6 is disposed in an inner circumferential groove formed in the inner circumferential surface of the pillar portion 5 of the oil ring main body 2, and urges the oil ring main body 2 radially outward. In the piston ring 1 of the present embodiment, the post portion 5 is formed with the oil return hole 7.

In the piston ring 1 of the present embodiment, it is preferable that the length (contact width) of the outer circumferential

sliding section protrusions

4, 4 in the axial direction of the two

guide rails

3, 3 formed on the oil ring main body 2 is 0.05 to 0.40 mm.

By setting the contact width to 0.05 to 0.40mm in this way, the sliding area of the oil ring main body 2 with the cylinder inner wall surface can be reduced, whereby the friction force can be reduced and the fuel consumption can be reduced.

As shown in fig. 1(b), the outer peripheral sliding surface may have a stepped shape in which the

convex portions

8 and 8 are formed.

The oil ring main body 2 preferably includes a base material 11 and a surface treatment layer 10 formed on the surface of the base material 11. The surface treatment layer 10 can be applied to various surface treatments used in the piston ring, and for example, a hard carbon coating (DLC), a physical vapor deposition coating (PVD), a nitrided layer, a hard chromium plated layer, or the like is preferably used. The base material 11 is preferably a flat plate-like annular member formed with a seam. The base material 11 is not particularly limited as long as it is made of steel, cast iron, aluminum alloy, or the like and exhibits good wear resistance. As a preferable example of the steel material, 13Cr steel can be used for the oil ring main body 2. The 13Cr steel is characterized in that: 0.6 to 0.7 mass% of carbon, 0.25 to 0.5 mass% of silicon, 0.20 to 0.50 mass% of manganese, 13.0 to 14.0 mass% of chromium, 0.2 to 0.4 mass% of molybdenum, 0.03 mass% or less of phosphorus, 0.03 mass% or less of sulfur, and the balance of iron and inevitable impurities.

In addition, 17Cr steel may be used for the oil ring main body 2 of the oil ring of the present embodiment. The 17Cr steel is characterized in that: 0.80 to 0.95 mass% of carbon, 0.35 to 0.5 mass% of silicon, 0.25 to 0.40 mass% of manganese, 17.0 to 18.0 mass% of chromium, 1.00 to 1.25 mass% of molybdenum, 0.08 to 0.15 mass% of vanadium, 0.04 mass% or less of phosphorus, 0.04 mass% or less of sulfur, and the balance of iron and unavoidable impurities. As other materials, 8Cr steel, SWRH77B equivalent material, or SKD61 equivalent material may be used.

The helical expansion ring 6 can use raw materials corresponding to SWOSC-V materials, and means that: 0.50 to 0.60 mass% of carbon, 1.20 to 1.60 mass% of silicon, 0.50 to 0.80 mass% of manganese, 0.50 to 0.80 mass% of chromium, 0.12 mass% or less of copper, 0.030 mass% or less of phosphorus, 0.030 mass% or less of sulfur, and the balance of iron and inevitable impurities.

Next, referring to fig. 2 to 4, a low friction cylinder liner 20 combined with the piston ring of the present embodiment as appropriate will be described.

Fig. 2 is an explanatory diagram illustrating an example of a position of formation of a recess in a liner inner wall surface of a cylinder liner fixed to an inner wall surface of a cylinder body (not shown).

As illustrated in fig. 2, a plurality of recesses 22 are formed in an inner wall surface 21 of the cylinder liner 20 of the present embodiment. The recess 22 is formed only in the stroke center region 23 of the inner wall surface 21 of the cylinder liner 20, and is not formed in a region other than the stroke center region 23. The stroke center region 23 is a region from a lower surface position of the ring groove of the lowermost piston ring at the top dead center of the piston to an upper surface position of the ring groove of the uppermost piston ring at the bottom dead center of the piston.

In order to improve the energy efficiency of a device using a cylinder, for example, to improve the fuel consumption of an engine, it is effective to reduce the friction loss between the piston ring and the inner wall surface of the cylinder (in this embodiment, the inner wall surface of the cylinder liner). The method of reducing the friction loss differs depending on the sliding condition, and in particular, the piston has a characteristic that the speed is 0 at the top dead center, and therefore, differs depending on the position of the sliding. Therefore, in the cylinder liner constituting the cylinder of the present embodiment, the recess is formed only in the stroke center region 23 of the inner wall surface thereof, and the recesses are formed so that at least one of the plurality of recesses is present in the entire cross section in the cylinder circumferential direction, in other words, the recesses are formed so as to overlap in the cylinder axial direction, whereby the frictional force can be reduced in the entire region of the stroke center region 23.

That is, the reduction of the reciprocating friction can be achieved by reducing the surface roughness of the inner wall surface of the cylinder liner in the vicinity of the top dead center and the vicinity of the bottom dead center where the moving speed of the piston is small. However, in the stroke center region 23, which is a region where the sliding speed between the inner wall surface of the cylinder liner and the piston ring is high, the influence of the shearing resistance of the lubricating oil becomes large. Therefore, in the present embodiment, by forming the recess only in the stroke center portion region 23 in the inner wall surface of the cylinder liner, the contact area between the piston ring and the inner wall surface of the cylinder liner can be reduced, and the influence of the shearing resistance of the lubricating oil can be reduced.

In addition, in the case where a plurality of recesses are formed in the stroke center region 23 without a lot of effort, the contact area between the piston ring and the inner wall surface of the cylinder liner is small in the entire stroke center region 23, but the width of the sliding piston ring (the length in the axial direction of the cylinder) is microscopically very short compared to the stroke center region 23, and therefore, depending on the position, there is a possibility that there is a portion where no recess is formed, and in this portion, the piston ring sliding surface contacts 100% of the inner wall surface of the cylinder liner, and the above-described effects may not be sufficiently exhibited, but in the present aspect, as described above, at least one recess among the plurality of recesses is formed in the entire cross section in the cylinder circumferential direction, in other words, each recess is formed so as to overlap in the cylinder axial direction, and therefore, the sliding piston ring always contacts the recess, and as a result, the contact area between the piston ring and the inner wall surface of the cylinder liner does not become 100%, and the above-described effects can be exhibited all the time.

When a recess is formed in the entire sliding region of the piston ring, that is, in a region other than the stroke center region, the contact area is reduced in the vicinity of the top dead center and the bottom dead center, and the contact surface pressure is increased to cause boundary lubrication, thereby increasing the frictional force. Further, if such a portion has a recess, it becomes an unnecessary oil reservoir, which may cause combustion and increase fuel consumption.

Next, the concave portion 22 formed in the stroke center region 23 of the inner wall surface of the cylinder liner constituting the cylinder of the present embodiment will be described.

In the present embodiment, the shape of the recess 22 formed in the stroke center region 23 is not particularly limited, and may be appropriately adjusted according to the arrangement of the recess, and the like. The concave portion may be formed in a shape of a straight line and/or a curved line. The concave portion may be laterally long, may be vertically long, or may have a substantially equal aspect ratio.

Here, in the cylinder according to the present aspect, at least one of the recessed portions is formed in the entire cross section in the cylinder circumferential direction in the stroke center region. This can effectively and evenly reduce the contact area.

As described above, in consideration of the cross section in the circumferential direction, if one recess is not formed in a certain cross section, the contact area between the piston ring and the inner wall surface of the cylinder liner becomes larger when the piston ring passes through the cross section than when the piston ring passes through the cross section in which a plurality of recesses are formed. Therefore, the influence of the shear resistance of the lubricating oil becomes large, and as a result, the reciprocating friction also becomes large.

In contrast, by forming at least one recess in all the cross-sections in the cylinder circumferential direction in the stroke center region, the contact area can be reduced reliably and evenly regardless of which circumferential cross-section the piston ring passes through in the stroke center region, and therefore, the reciprocating friction can be reduced reliably.

As an example of a state in which "at least one recess of the plurality of recesses is formed in the entire cross section in the cylinder circumferential direction" which is a characteristic of the present embodiment, the cases of fig. 3(a) and (b) can be cited.

Fig. 3(a) is a schematic expanded view showing an example of the arrangement of the concave portions 22 in the stroke center region 23 of fig. 2. In fig. 3(a), the vertical direction of the drawing is the axial direction of the cylinder, and the horizontal direction of the drawing is the circumferential direction of the cylinder. As illustrated in fig. 3(a), the lowest point 5a of the recess 22a is located lower than the uppermost point 6b of the recess 22b closest to the lower side thereof with respect to the line X drawn in the cylinder circumferential direction. Further, with respect to a line Y drawn in the cylinder circumferential direction, the lowest point 5b of the concave portion 22b is located lower than the uppermost point 6c of the concave portion 22c closest to the lower side thereof. In this way, by disposing the vertically adjacent concave portions so as to overlap each other in the cylinder axial direction, at least one of the plurality of concave portions can be formed in the entire cross section in the cylinder circumferential direction. According to the above, when the piston reciprocates, the sliding piston ring can reduce the contact area with the inner wall surface of the cylinder at any position in the cylinder axial direction in the stroke center region, and the effect of reducing the reciprocating friction is obtained.

Here, fig. 3(b) is a schematic expanded view showing an example of the arrangement of the concave portion 22 in the stroke center region 23 of fig. 2, as in fig. 3 (a). In fig. 3(b), the vertical direction in the drawing is the axial direction of the cylinder, and the horizontal direction in the drawing is the circumferential direction of the cylinder. In fig. 3(a), the concave portion 22 is formed with a uniform area in the cylinder axial direction, but the present invention is not limited to this form, and as shown in fig. 3(b), the area of the concave portion 22 may be reduced in the vicinity of the end portion of the stroke center region 23 in the cylinder axial direction, and the area of the concave portion may be increased in the vicinity of the center portion of the stroke center region 23, and may be appropriately adjusted.

In the present embodiment, the size of the recess is not particularly limited, and may be appropriately adjusted according to the size of the cylinder or the piston ring used together. The recessed portion may be formed to penetrate the stroke center region in the cylinder axial direction, but from the viewpoint of maintaining the airtightness of the cylinder, it is preferable that the average length of the recessed portion in the cylinder axial direction is equal to or less than the length of the uppermost piston ring in the piston rings used in the cylinder axial direction. More specifically, the length of the uppermost piston ring of the piston rings to be used is preferably about 5 to 100% of the length in the cylinder axial direction.

In this embodiment, the average length of each concave portion is an average length of each portion illustrated in fig. 4. Fig. 4(a) is a schematic developed view of the inner wall surface of the cylinder liner showing the cylinder axial direction in the vertical direction of the drawing. Fig. 4(b) is a schematic circumferential cross-sectional view of the cylinder liner. As illustrated in fig. 4(a), the average length in the axial direction of the recess is an average of the lengths of the recesses 22 in the cylinder axial direction.

As illustrated in fig. 4(a), the circumferential average length of the recessed portion 22 is an average of the lengths of the recessed portions 22 in the cylinder circumferential direction. As illustrated in fig. 4(b), the average length in the circumferential direction of the recess 22 is an average of lengths on a plane including the inner wall surface 21, and the same applies to the area of the recess.

As illustrated in fig. 4(b), the radial length of the recess 22 is an average of lengths from the bottom surface of the recess 22 to the inner wall surface 21 of the cylinder liner 20. As illustrated in fig. 4(a) and (b), the average length (interval) in the cylinder circumferential direction between the concave portions is an average of the intervals between the adjacent concave portions 22.

The average length of the recess in the cylinder circumferential direction is preferably in the range of 0.1mm to 15mm, and particularly preferably in the range of 0.3mm to 5 mm. If the average length in the cylinder circumferential direction is less than this range, the effect of forming the recessed portion may not be sufficiently obtained. On the other hand, if the average length in the circumferential direction exceeds this range, a part of the piston ring may enter the recess, causing a problem such as deformation of the piston ring.

The average length of the concave portions in the cylinder radial direction is preferably in the range of 0.1 to 1000. mu.m, more preferably in the range of 0.1 to 500. mu.m, and particularly preferably in the range of 0.1 to 50 μm. When the average length of the recess in the cylinder radial direction is less than this range, the effect of forming the recess may not be sufficiently obtained. On the other hand, if the radial average length exceeds this range, the processing becomes difficult, and there may be a case where the radial length of the cylinder liner needs to be increased (thickness of the cylinder liner is increased).

In the present embodiment, the average length (interval) in the cylinder circumferential direction between adjacent recesses is preferably in the range of 0.1 to 15mm, and particularly preferably in the range of 0.3 to 5 mm. When the average length (interval) in the cylinder circumferential direction between adjacent recesses is smaller than this range, the width of the inner wall surface of the cylinder liner on which the piston ring slides is too small, and there is a possibility that the piston ring and the inner wall surface of the cylinder liner cannot slide stably. On the other hand, if the amount exceeds this range, the effect of forming the concave portion may not be sufficiently obtained.

The piston ring 1 of the present embodiment is combined with the low friction cylinder liner described above. In this case, the surface pressure W of the piston ring 1 is preferably set to 0.8 to 2.5 MPa. By setting the surface pressure W in this manner, the friction reduction effect by the low-friction cylinder liner can be sufficiently obtained even at the time of low-speed rotation. The surface pressure can be determined from (2 × piston ring tension)/(cylinder bore diameter × contact width), and the piston ring 1 of the present embodiment has a piston ring tension Ft and a contact width h1 set so as to have a surface pressure lower than the conventional surface pressure.

The piston ring 1 of the present embodiment is set such that the follow-up coefficient Kp of the piston ring is 0.1 or more. The following coefficient Kp is a coefficient representing following properties against cylinder bore deformation caused by thermal expansion of the internal combustion engine, and is expressed by the following equation.

[ formula 1]

d 1: cylinder bore diameter (mm)

h 1: ring width dimension (mm)

Ft: piston ring tension (N)

a 1: ring thickness dimension (mm)

E: coefficient of elasticity (N/mm)²)

k: ratio of sectional coefficients

By setting the follow-up coefficient of the piston ring in this way, it is possible to suppress an increase in fuel consumption due to a decrease in the follow-up coefficient, and to achieve both reduction in friction and suppression of fuel consumption using the low-friction cylinder liner.

Examples

Next, the present invention will be described in more detail with reference to examples and comparative examples.

The friction coefficients of the piston rings and the low-friction cylinder liners having the following structures and the conventional cylinder liners were measured.

Examples, comparative examples 1 and 2 used two-piece oil rings, and 13Cr steel constituting the oil ring main body was made of a material corresponding to the material of SUS410 of JIS standard having a composition of carbon of 0.65 mass%, silicon of 0.38 mass%, manganese of 0.35 mass%, chromium of 13.50 mass%, molybdenum of 0.3 mass%, phosphorus of 0.01 mass%, sulfur of 0.01 mass%, and the balance iron and inevitable impurities, and a nitrided layer was provided over the entire circumference of the oil ring main body, and the contact width of the outer circumferential sliding surface was set to 0.2 mm.

In addition, in the embodiment, the surface pressures are set to 1.2MPa (embodiment 1), 1.8MPa (embodiment 2), and 2.5MPa (embodiment 3), and the combined cylinder liner uses a low friction cylinder liner. In comparative example 1, the surface pressure was set to 2.8MPa, which is equivalent to that of the conventional cylinder, and a low-friction cylinder liner was used as the combined cylinder. The low-friction cylinder liner used was a cylinder liner having a recess area ratio of 50%, a recess cylinder axial length of 0.5mm, a circumferential length of 0.5mm, and a cylinder radial length of 2 μm, assuming that the stroke center region was 100. In comparative example 2, the surface pressure was set to 1.8MPa, and in comparative example 3, the surface pressure was set to 2.5MPa, and a normal cylinder liner was used as the combined cylinder liner. The roughness of the inner wall surface of the low friction cylinder liner is the same as that of the normal cylinder liner.

A known single-body evaluation device was used to measure the friction coefficient between the oil ring and the cylinder. In the single body evaluation device, the oil ring is further attached to the top face of the piston that moves up and down by the crank mechanism via the rod, and the rod is supported also on the upper side, so that the friction coefficient of the oil ring can be measured without being affected by a lateral force. The cylinder liner needs to be consistent with the stroke of the single evaluation device, but the oil ring of a real engine can be directly used as the oil ring. The Strobek indexes are consistent through the adjustment of temperature and sliding speed, so that the sliding environment of the engine is simulated.

Fig. 5 shows a typical friction waveform obtained by the single evaluation device. In this test, the friction coefficient at the fastest point of the piston and the stribeck index at that point are calculated from a friction waveform obtained by changing the rotation speed of the testing machine, and the calculated friction coefficients and stribeck indexes are collected as a stribeck diagram and used for analysis.

As shown in fig. 5, in the case of example 1 in which the surface pressure is set to be low and combined with the low friction cylinder liner, it can be confirmed that the friction coefficient decreases from the low speed rotation region to the high speed rotation region as compared with comparative example 1 in which the surface pressure is set to be high in combination with the same low friction cylinder liner. In addition, when comparative examples 2 and 3, in which the surface pressure is set low and the cylinder liner is combined with a normal cylinder liner, are compared with examples 2 and 3, respectively, it is confirmed that the friction reduction effect cannot be sufficiently exhibited even with the normal cylinder liner combination.

As shown in fig. 6, when the ratio of the surface pressure to FMEP (mechanical loss) at the time of low-speed rotation such as 1000rpm is confirmed, the following can be confirmed: in the case of a piston ring combined with a normal cylinder liner, the friction coefficient does not change greatly even if the surface pressure is changed, but in the case of a piston ring combined with a low-friction cylinder liner, when the surface pressure exceeds 2.5MPa, the friction coefficient becomes larger than that of the normal cylinder liner, and the friction reduction effect cannot be exhibited effectively. In addition, when the cylinder liner is combined with a low-friction cylinder liner, it is confirmed that the friction reduction effect can be effectively exhibited by setting the surface pressure to 0.8 to 2.5 MPa.

In fig. 6, the lower limit of the surface pressure is set to 0.8MPa, and as a result, as shown in fig. 7, fuel consumption is confirmed under normal operating conditions, and as a result, it is confirmed that fuel consumption rapidly deteriorates when the surface pressure is lower than 0.8MPa, and therefore, the surface pressure is set to 0.8 MPa.

As shown in fig. 8, it can be seen that: the following coefficient can be ensured to be 0.10 or more when the surface pressure is 0.5 to 2.5MPa when the contact width of the outer peripheral sliding surface of the piston ring is 0.08 to 0.40mm, and the following coefficient can be ensured to be 0.10 or more when the surface pressure is 0.8 to 2.5MPa when the contact width is 0.05 mm. In addition, when the contact width is less than 0.02mm, the surface pressure needs to be 0.5 to 2.5MPa, but the design cannot be made because the lower limit of the surface pressure is lower, and when the contact width is 0.02 to 0.04mm, the design range is narrowed, so that the lower limit of the contact width is set to 0.05mm, and the upper limit is set to 0.40 mm. Note that, for "contact width: as described in 0.02mm × 2 ", the oil ring has a contact width at each of the upper rail and the lower rail as shown in fig. 1(a) and (b), and the contact width is 2 times as large as the contact width of the entire oil ring, so that the description of" contact width × 2 "is adopted.

The piston ring according to the present embodiment is described above as applied to a two-piece oil ring, but may be applied to a three-piece oil ring, a top ring, and a second ring. In addition, although the piston ring according to the present embodiment has been described above with respect to the case where one surface-treated layer is formed on the oil ring main body, the surface-treated layer may not be provided, or a plurality of surface-treated layers may be stacked. The embodiments modified or improved as described above are also included in the technical scope of the present invention, as is apparent from the description of the scope of the claims.

Description of the reference numerals

1 piston ring

2 oil ring main body

3 guide rail

4 sliding part projection

5 column part

6 spiral expansion ring

7 oil return hole

8 convex part

10 surface treatment layer

11 base material

20 low friction cylinder jacket

21 inner wall surface

22 recess

23 stroke center region

Claims

1. A piston ring to be combined with a low-friction cylinder liner having a predetermined recess formed in an inner wall surface of the cylinder liner,

the surface pressure of the piston ring is 0.8-2.5 MPa.

2. The piston ring of claim 1,

the piston ring has a follow-up coefficient of 0.1 or more.

3. The piston ring as claimed in claim 1 or 2,

the contact width of the outer peripheral sliding surface of the piston ring is 0.05-0.40 mm.

4. The piston ring according to any one of claims 1 to 3,

the piston ring is a two-component oil ring composed of a spiral expansion ring and an oil ring main body.