Compression piston ring with improved oil retention

Abstract

The present invention relates to a compression piston ring (2) having an upper ring flank (8), a lower ring flank (10), an inner surface (6), at least part of which is substantially cylindrical, and an outer surface (4), at least part of the profile of which is convex, wherein the outer surface (4) is provided with a groove (14), which runs externally in the circumferential direction, and wherein this groove is located in the profile of the piston ring at a height (HR) between 1 / 5 and 3 / 5 of the height (HG) of the compression piston ring, and wherein the compression piston ring is also provided with an encircling recess (16) at the location at which the convex outer surface (4) and the lower ring flank (10) meet.

Description

[0001] Compression piston ring with improved oil retention

[0002] The present invention relates to piston rings. Piston rings always have the problem that oil can overflow from the crankcase past the piston rings into the combustion chamber, particularly during load changes. Various attempts to solve this problem are already known. At present, the known solution consisting of a compression piston ring, a split ring and a three-part oil control ring appears to be the best solution. If large quantities of oil overflow from the ring on the cylinder wall, the oil can get into the combustion chamber. This can be in the form of drops or a generally very large oversupply, for example due to a load change. It is therefore desirable to have a piston ring or a piston ring system that allows local oversupplies to be distributed and also prevents short-term surge-like flooding.It is also desirable to build a stable piston ring system that shows stable particle and blow-by behavior even in load change situations.

[0003] According to the present invention, a compression piston ring is provided which comprises an upper ring flank, a lower ring flank, an inner surface which is at least partially substantially shaped like a cylinder jacket, and a convex outer surface which is at least partially convex in profile. The profile of the compression piston ring is provided on the outer surface with a groove which runs outwardly in the circumferential direction, wherein this groove is located in the profile of the piston ring at a height between 1 / 5 and 3 / 5 of the height of the compression piston ring. Furthermore, the compression piston ring is provided with a circumferential recess at the point or region where the at least partially convex outer surface and the lower ring flank meet.

[0004] The profile of the compression piston ring is defined in a plane extending in the axial direction and perpendicular to a tangent circumferentially applied to the outer surface. The cutting plane can also be perpendicular to the ring flanks, in which a center point of the installed piston ring lies. The term outer surface here refers to the part of the piston ring that is radially outward and is usually referred to as the running surface. Here, the term outer surface was chosen because the piston ring is not in contact with the cylinder inner surface with its entire radial outer surface. The height of the groove is measured from a lower ring flank and refers to the arithmetic

[0005] Mean of the upper and lower limits of the groove. The height of the groove is considered as the distance of the lower ring flank, which is closer to the crankcase. The upper

[0006] The ring flank is positioned toward the combustion chamber. The convexity of the outer surface is disrupted by the groove and the circumferential recess. The circumferential recess is located at the point or area where the convex outer surface and the lower ring flank would meet.

[0007] The groove forms an oil chamber that allows small amounts of oil located on the inner cylinder surface to be collected and distributed circumferentially. The circumferential recess, on the other hand, is designed to "cut" larger amounts of oil back to a thinner oil film, similar to a blade or plane. However, unlike oil control rings, there are no oil channels here that can drain the excess oil towards the inside of the piston. The circumferential recess is only intended to temporarily store the oil, although small amounts of oil can also be transported towards the base of the piston ring groove, where they are then expelled downwards out of the piston ring groove by the combustion gases.

[0008] In a further embodiment of the compression piston ring, the outer surface, which is at least partially convex in profile, forms an enveloping circular surface in profile.

[0009] In a preferred embodiment, the outer surface, which is convex in profile, forms a circular surface, which is provided with a groove in the direction of rotation and a circumferential recess. The running surface of the piston ring is crowned.

[0010] According to another exemplary embodiment of the compression piston ring, the profile of the convex outer surface includes a pivot area to maintain contact with the cylinder's inner surface when the piston ring is twisted in the piston ring groove. The pivot area is located above the groove. The pivot area includes a pivot point whose position on the outer surface changes, albeit only slightly, depending on the twist angle. The pivot point, if referenced, always refers to a non-twisted piston ring. In a non-worn piston ring, the entire pivot area is located above the groove.

[0011] In a further embodiment of the compression piston ring, the circumferential recess in the profile is essentially delimited by two straight sections, an outer surface section and a flank section, or by an outer surface section and a tangent of a fillet. Furthermore, it is possible for the circumferential recess in the profile to be delimited by the outer surface section and the flank section, with a fillet present between the outer surface section and the flank section. Furthermore, it is provided that the circumferential recess in the profile is delimited by the outer surface section and the flank section, with a chamfer present between the outer surface section and the flank section. Here, the outer surface section forms an edge with the outer surface. Furthermore, the flank section or, preferably, the tangent of the fillet forms an edge with the lower ring flank.

[0012] If the circumferential recess in the profile comprises an outer surface section and a flank section, these can meet at a corner or in a corner area, or merge into one another through a rounding or a chamfer.

[0013] In an exemplary additional design of the compression piston ring, a

[0014] The edge between the outer surface section has a height (HA) in the axial direction of 0 to 30% of the axial height, preferably 0 to 15% of the axial height, and more preferably 0 to 5% of the axial height relative to a plane spanned by the lower ring flank. This corresponds to the axial distance of the nose tip from the lower ring flank.

[0015] In another exemplary embodiment of the compression piston ring, the outer surface section has a profile angle between -30° and 30°, preferably between -15° and 15°, and more preferably between -10° and 10°, to a radial plane. This corresponds to a truncated cone surface spanned by the outer surface section with a cone angle, more precisely half the cone's opening angle, between 85° and 93°, preferably between 86° and 91°, and more preferably between 87° and 90°.

[0016] An exemplary further embodiment of the compression piston ring is provided with the flank section which has an angle of between 45° and 95°, preferably between 60° and 92° and more preferably between 90° and 70° to the lower ring flank, or wherein a tangent of a rounding to the lower ring flank has an angle of between 45° and 95°, preferably between 60° and 92° and more preferably between 90° and 70°.

[0017] In an additional exemplary embodiment of the compression piston ring, the ring is provided with a recess on its inner surface, which preferably extends in profile between the inner surface and the lower ring flank. The recess further preferably comprises a chamfer or a concave rounding in profile. The recess serves to compensate for a twisting tendency of the piston ring. The recess can also be designed as a chamfer between an edge between the inner surface and the lower ring flank. The recess is to be understood as being relative to an imaginary rectangular envelope of the profile or cross-section of the respectively extended inner surface and lower ring flank.In a further additional embodiment of the compression piston ring, a recess is arranged in the profile on the inner surface at a distance from an edge between the inner surface and the lower ring flank, wherein the recess is preferably designed as a V-shaped recess in a lower half of the inner surface. The recess can be applied internally by turning or grinding. The recess is intended to reduce any effects of the recess and the groove on a tendency to twist. Because the recess is arranged on the inner surface, the width of the piston ring is not reduced in the radial direction. A wider lower contact surface can further limit the possibility of the piston ring twisting compared to a conventional chamfer.A further embodiment of the compression piston ring is additionally provided with an outer chamfer on the edge of the upper ring flank to the outer surface, which has a profile angle of between 5° and 30°, preferably between 10° and 25°, and more preferably between 15° and 20° to the upper ring flank (8) or to a radial plane. This upper chamfer is intended to help the compression piston ring better overflow small amounts of residual oil.

[0018] According to an additional embodiment of the compression piston ring, the circumferential recess has a width in the axial direction of between 0.2 mm and 1.0 mm, preferably between 0.3 mm and 0.8 mm and more preferably between 0.4 mm and 0.6 mm. The axial width is measured from the radially deepest point to the edge between the outer surface section and the outer surface. The radially deepest point can have a smaller radius than the edge between the flank section and the lower ring flank. This is particularly desirable when the piston ring is to provide the widest possible contact surface on the lower piston ring groove flank. According to an additional embodiment of the compression piston ring, the circumferential recess has an axial height of between 0.2 mm and 1.0 mm, preferably between 0.3 mm and 0.8 mm and more preferably between 0.4 mm and 0.6 mm.The height is measured from the edge between the flank section or a tangent of a fillet and the lower ring flank to the highest point of the circumferential recess. Here, too, the highest point of the circumferential recess can be higher in the axial direction than the edge between the outer surface and the outer section. In a further embodiment of the compression piston ring, the groove has a constant width that is less than 1 / 5, preferably less than 1 / 8, and more preferably less than 1 / 10 of the total height (HG) of the compression piston ring. The groove preferably has a rectangular, preferably a square, cross-section.

[0019] In an additional embodiment, the compression piston ring comprises a joint with two contact surfaces, wherein the groove ends in front of the joint or in the circumferential direction in front of the respective contact surface. In another additional embodiment, the circumferential recess ends in the circumferential direction in front of the joint or in front of the respective

[0020] Butt joint. In another additional embodiment, the circumferential recess ends before the joint or before the respective butt joint. In another embodiment, the outer chamfer ends before the joint or before the respective butt joint.

[0021] In the following, the present invention is illustrated in more detail using schematic and non-scale representations.

[0022] Figures 1 and 2 show profile views and cross-sectional views of conventional piston rings, respectively.

[0023] Figures 3 and 8 show profile views and cross-sectional views of piston rings according to the invention. In both the figures and the description, identical or similar

[0024] Reference symbols are used to refer to the same or similar components and elements.

[0025] Figure 1 shows a cross-section through a conventional compression piston ring 50 with a spherical running surface or radial outer surface 4, an inner ring surface 6, and an upper ring flank 8 and a lower ring flank 10. The conventional compression piston ring 50 is essentially circular in plan view and has a gap or joint. In the illustrated sectional view with the convex profile on the outer surface, an axis of rotation running parallel to the long side is located on the right-hand side outside the ring. The shape of piston rings is known to those skilled in the art, which is why a separate plan view is omitted. In Figure 1, the piston ring rests with its left side against a cylinder inner surface a (not shown), and is supported downwards and upwards with the lower ring flank 10 and the upper ring flank 8, respectively, on the corresponding piston ring groove flanks of a piston (also not shown).During operation, the piston ring can twist slightly or tilt up or down, which results from the necessary axial play of the piston ring in the piston ring groove. The compression piston ring is designed with a contact surface that allows high radial forces to be absorbed in order to seal a combustion chamber located at the top in the figures against a crankcase located below. The uppermost compression piston ring makes the greatest contribution to sealing. When operating a conventional compression piston ring 52, the problem arises that an oil film for wear reduction must, on the one hand, be large enough to ensure effective lubrication and thus minimize wear, and on the other hand, as little oil as possible should adhere to the inner cylinder wall, since burning oil has a detrimental effect on the environment.

[0026] Figure 2 shows a conventional nose-faced Napier ring, which is usually used as a second piston ring below a compression piston ring. Since the compression piston ring already seals off a large portion of the combustion gases from the combustion chamber, the second ring must fulfill this function far less effectively. Therefore, the second piston ring, as here in the form of a so-called nose-faced Napier ring, can also fulfill an additional task, namely to create an oil film of a certain thickness. The cone angle, or half the opening angle of the truncated cone surface, which forms the radial outer side of the nose-faced Napier ring, is only a few angular minutes. This illustration makes it clear how schematic a representation of a piston ring must be in order to even begin to depict the inventive aspects. In Figure 1, the curvature of the outer surface is also greatly exaggerated. A nose-faced Napier ring is also called a "taper-faced Napier ring."The conical shape allows the minute ring to float on a film of oil during an upward movement and push it forward like a dozer blade during a downward movement. Oil scraped off during a downward movement is collected in or under the nose until the piston moves upwards again, and the oil is redistributed over the inner surface of the cylinder.

[0027] The combination of compression piston ring and nose minute ring works quite reliably under uniform operation, only in the case of load changes can larger amounts of oil occur on the inner cylinder wall and thus in the combustion chamber.

[0028] Figure 3 shows a sectional view of a first embodiment of an inventive

[0029] Piston ring 2. The piston ring has, like the conventional piston ring 50 of Figure 1, a radial outer surface 4, an inner ring surface 6, as well as an upper ring flank 8, as well as a lower ring flank 10. Here, too, the axis of rotation of the piston ring is located to the right outside the drawing sheet, with the axis of rotation parallel to the intersection line of the

[0030] inner ring surface. In the basic design shown in Figure 3, the compression piston ring 2 is provided with a groove 14 which is located below a center or half the total height HG of the piston ring. In all designs, the compression piston rings are provided with flat flanks which lie in parallel planes. The center of the piston ring is referred to here as a plane which is located exactly between the lower and the upper flank. The center is located at the height HG / 2. In the designs shown, a radially outermost point of the outer (upper) surface of the piston ring lies exactly at the height HG / 2. However, it is also possible for a radially outermost point or a radially outermost region to lie further up towards the upper ring flank. This point or region can also be referred to as the pivot point or pivot region.

[0031] In contrast to the conventional piston ring of Figure 1, the present piston ring is provided with a groove 14 which extends at a constant height in the circumferential direction around the piston ring 2. The groove 14 should have a substantially constant cross-section and a constant height. This groove 14 can absorb small amounts of excess oil present on the inner cylinder wall. However, the relatively small groove 14 is not able to absorb larger amounts of oil on the inner cylinder wall, so that in the case of larger quantities of oil, a considerable portion will enter the combustion chamber. To prevent this situation from occurring, the piston ring 2 is provided with a circumferential recess 16. The circumferential recess 16 is located in the area where the outer surface 4 meets the lower ring flank 10. In Figure 3, the circumferential recess 16 replaces this edge.The circumferential recess 16 is formed here in profile by an outer surface section 40 and a flank section 42, which are each connected to one another by a fillet 44 or merge into one another. The outer surface section 40 forms an edge with the outer surface 4, and the flank section or lower flank section 42 forms an edge with the lower ring flank 10. The edge between the outer surface section 40 and the outer surface 4 forms a type of blade, which is intended to remove higher oil deposits on the inner cylinder wall like a plane, and the removed amount of oil is intended to be absorbed in the circumferential recess 16. The amount or volume of oil adhering to the inner cylinder wall is intended to be reduced to such an extent that the groove 14 can absorb it.It should be noted that the initial situation is not aimed at a cylinder inner wall that is completely wetted with too much oil, but at local, drop-shaped amounts of oil that have only a relatively small extent in both the circumferential and axial directions. The present design is aimed at removing a local amount of oil on the cylinder inner wall through the edge between the outer surface section 40 and the outer surface 4 to such an extent that it can be distributed in the groove 14 in the axial and circumferential directions that there is no longer any significant burning of engine oil in the combustion chamber. Figure 4 shows that the edge between the outer surface section 40 and the outer surface 4 is located at a height above the plane of the lower ring flank 10. This makes it possible to increase the volume of the circumferential recess 16 without changing the width of the circumferential recess.

[0032] 16 in the radial direction, which would increase a width of the lower ring flank 10 and thus a twist tendency. A width of the circumferential recess 16 can be viewed as a distance between the edge between the outer surface section 40 and the outer surface 4 and the radially smallest dimension of the circumferential recess (preferably viewed in a sectional view). Here, the width of the circumferential recess is clearly visible, since both the edge between the outer surface section 40 and the outer surface 4 and the radially deepest point, which here coincides with the edge between the lower flank section 42 and the lower ring flank 10. The term height of the circumferential recess 16 is used to designate a total height of the recess from the lower ring flank 10 to the highest point of the recess in the axial direction. In the following, the term axial edge distance is used for a height difference oran axial distance between the lower ring flank and the edge between the outer surface section 40 and the outer surface 4 is selected.

[0033] The term width of the circumferential recess 16 refers to a total width of the recess 16 from the edge between the outer surface portion 40 and the outer surface 4 to the radially innermost point of the circumferential recess 16 (viewed in a sectional view of the ring).

[0034] Furthermore, the term radial edge distance is used for a difference or a radial distance between the edge between the outer surface section 40 and the outer surface 4 and the outer edge of the lower ring flank 10, wherein the outer edge of the lower ring flank 10 is formed by the lower ring flank 10 and the flank section 42 or by the lower ring flank 10 and a tangent of a fillet 44. This is determined by the angle α at which the outer surface section 40 is inclined outwards towards the lower ring flank. In the analogy to a cutting tool, the angle α corresponds to the rake angle, which here is in a range between 5° and 15°. The analogy to the cutting tool is somewhat flawed here, since the edge between the outer surface section 40 and the outer surface 4, which is considered the cutting edge, has a negative clearance angle, which would not be possible with cutting.

[0035] The flank section 42, or the tangent of the fillet 44, forms an angle ß with the axial direction, which determines how stable or wear-resistant the lower ring flank is. The angle ß largely determines the tendency of oil to penetrate between the lower ring flank and the lower piston ring groove flank.

[0036] In Figure 3, the height of the circumferential recess 16 exceeds the axial edge distance, while the width of the circumferential recess 16 coincides with the radial edge distance.

[0037] In Figure 3, the piston ring is further provided with an outer chamfer 48 in the area where the outer surface 4 meets the upper ring flank 8. This is intended to reduce wear and simplify oil overflow during an upward movement of the piston.

[0038] The angle of the outer chamfer to the radial plane y is here between 2° and 20°, preferably between 3° and 15° and more preferably between 5° and 10°. Figure 4 corresponds largely to Figure 3, although the axial edge distance between the edge of the lower ring flank 10 to a tangent of a fillet 44 and the edge between the outer surface section 40 and the outer surface 4 is zero. The circumferential recess 16 thus extends substantially within the lower ring flank 10. The angle α essentially determines the volume or the cross-sectional area of ​​the circumferential recess 16 and is somewhat smaller here than in the embodiment of Figure 3. The other aspects of the piston ring have not been changed compared to the embodiment of Figure 3.

[0039] Figure 5 largely corresponds to Figure 3. Figure 5 uses the same axial edge distance between the edge of the lower ring flank 10 with the flank section 42 and the edge between the outer surface section 40 and the outer surface 4 as in the embodiment of Figure 3. In contrast to Figure 3, the angle α in the embodiment of Figure 5 is zero. The volume or the cross-sectional area of ​​the circumferential recess 16 is approximately the height of the circumferential recess 16 times the width of the circumferential recess, each multiplied by the circumferential length of the piston ring. Here, the angle α is zero, which means a lower "cutting performance" against oil droplets on the inner cylinder wall. The other aspects of the piston ring have not been changed compared to the embodiment of Figure 3.

[0040] Figure 6 shows the embodiment of Figure 4, wherein a piston ring, different from Figure 4, is provided with a recess 20 which is intended to compensate for the effects of the groove 14, the circumferential recess 16 and the outer chamfer 48 with regard to twisting behavior.

[0041] Figure 7, unlike the other figures, does not represent a sectional view, but a plan view of a butt surface of another embodiment of a piston ring according to the invention. This view shows that the groove 14, the circumferential recess 16, the outer bevel 48 and the recess 20 in this embodiment each end in the circumferential direction before the butt ends 30. This can prevent oil that is in the

[0042] Groove 14 or in the circumferential recess 16 or on the outer chamfer 48 can flow out via the ring joint and be burned in the combustion chamber.

[0043] Figure 8 shows a further embodiment of a compression piston ring according to the invention. Here, minor changes have been made compared to the embodiment in Figure 3. Here, the groove 14 is designed with a rectangular or trapezoidal cross-section. As a result, oil in the groove 14 is distributed more in the axial direction than in the circumferential direction. This shape of the groove 14 easily makes it possible to accommodate a larger volume of oil in the groove. The upper flank and / or the lower flank can be inclined upwards or downwards, respectively, in order to achieve favorable oil distribution and return behavior. In Figure 8, the circumferential recess has been redesigned in order to change the oil absorption. Oil cut off by the edge between the outer surface section 40 and the outer surface 4 is deflected towards the groove base and then redirected back towards the inner cylinder surface by the rounding.Here, a larger amount of oil can be held by a circular flow.

[0044] Here, both the height of the circumferential recess 16 exceeds the axial edge distance, and the width of the circumferential recess 16 exceeds the radial edge distance. Due to the shape of the circumferential recess 16 and the cutout, the piston ring of Figure 8 has a very wide lower ring flank 10. Due to the shortened outer chamfer 48, the upper ring flank 8 is also wider. Overall, these dimensions allow twisting to be kept within limited limits, even under wear. Individual embodiments with different elements, components, and dimensions were shown in Figures 3 to 8; it is clear to the person skilled in the art that all combinations of outer surface shapes, grooves, recesses, cutouts, fillets, and chamfers can be combined here, some of which may end before the abutting surfaces and may have different dimensions. List of reference symbols

[0045] 2 compression piston ring

[0046] 4 Outer surface 6 Inner surface

[0047] 8 upper ring flank

[0048] 10 lower ring flank,

[0049] 14 grooves

[0050] 16 circumferential recess 18 pivot area

[0051] 20 recess

[0052] 30 shots

[0053] 40 outer surface section

[0054] 42 Flank section 44 Fillet

[0055] 46 - Chamfer

[0056] 48 outer bevel

[0057] 50 Conventional compression ring

[0058] 52 Conventional nose minute ring

[0059] BA Width of the recess

[0060] BR Width of the groove

[0061] H Height of the groove

[0062] HA height of the recess

[0063] HG total height

[0064] HR groove height

[0065] P Pivot point a Angle of the outer surface section to the radial plane ß Angle of the flank section to the axial direction y Angle of the outer chamfer to the radial plane

Claims

Claims 1. Compression piston ring (2) comprising: an upper ring flank (8) and a lower ring flank (10), an inner surface (6) which is at least partially substantially cylindrical, an outer surface (4) which is at least partially convex in profile, characterized in that the outer surface (4) is provided with a groove (14) which runs outwards in the circumferential direction, and wherein this groove is located in the profile of the piston ring at a height (H) between 1 / 5 and 3 / 5 of the height of the compression piston ring, and that the compression piston ring is further provided with a circumferential recess (16) at the point or region at which the convex outer surface (4) and the lower ring flank (10) meet.

2. The compression piston ring (2) according to claim 1, wherein the outer surface, which is convex in profile, forms an enveloping circular surface in profile, which has the groove in the direction of rotation.

3. The compression piston ring (2) according to claim 1 or 2, wherein the outer surface, which is convex in profile, comprises a pivot region (18) or a pivot point (P) around which the piston ring can twist, and wherein the pivot region (18) or the pivot point (P) is arranged above the groove (14).

4. Compression piston ring (2) according to claim 1, 2 or 3, wherein the circumferential recess (16) is essentially delimited in profile by two straight sections, an outer surface section (40) and a flank section (42) (or lower flank section) or a tangent of a fillet (44), wherein preferably the outer surface section (40) is connected to the flank section (42) by a fillet (44) or a chamfer. 5 Compression piston ring (2) according to claim 4, wherein an edge between the outer surface portion (40) in the axial direction has a height (HA) of 0 to 30% of the axial height, preferably of 0 to 15% of the axial height and more preferably of 0 to 5% of the axial height relative to a plane which is spanned by the lower ring flank (10).

6. Compression piston ring (2) according to claim 4 or 5, wherein the outer surface portion (40) has an angle between -30° and 30°, preferably between -15° and 15° and more preferably between -10° and 10° to a radial plane.

7. Compression piston ring (2) according to claim 4, 5 or 6, wherein the flank section (42) to the lower ring flank (10) or the tangent of a rounding (44) has an angle between 45° and 95°, preferably between 60° and 92° and more preferably between 90° and 70° of the lower ring flank (10).

8. Compression piston ring (2) according to one of the preceding claims, wherein the compression piston ring (2) has a recess (20) on the inner surface (6) in the profile, which recess is preferably arranged between the inner surface (6) and the lower ring flank (10).

9. Compression piston ring (2) according to claim 8, wherein the recess (20) ends in front of an edge between the inner surface (6) and the lower ring flank (10), wherein the recess (20) is preferably designed as a V-shaped recess in a lower half of the inner surface.

10. Compression piston ring (2) according to one of claims 1 to 9, wherein the compression piston ring (2) is further provided on the upper ring flank (8) to the outer surface (4) with an outer chamfer (48) which in profile has an angle between 5° and 30°, preferably between 10° and 25° and more preferably between 15° and 20° to the upper ring flank (8).

11. Compression piston ring (2) according to one of claims 1 to 10, wherein the recess (16) has a width in the axial direction between 0.2 mm and 1.0 mm, preferably between 0.3 mm and 0.8 mm and more preferably between 0.4 mm and 0.6 mm, wherein the axial width is measured from the radially deepest point to the edge between the outer surface portion (40) and the outer surface (4).

12. Compression piston ring (2) according to one of claims 1 to 11, wherein the recess (16) has an axial height between 0.2 mm and 1.0 mm, preferably between 0.3 mm and 0.8 mm and more preferably between 0.4 mm and 0.6 mm, wherein the height (HA) from a highest point in the axial direction and the lower ring flank is measured.

13. Compression piston ring (2) according to one of claims 1 to 11, wherein the constant width (BR) of the groove (14) is less than 1 / 5, preferably less than 1 / 8 and more preferably less than 1 / 10 of a total thickness of the minute piston ring (2), furthermore it is preferred that the groove has a rectangular cross-section.

14. Compression piston ring (2) according to one of claims 1 to 13, wherein the compression piston ring (2) has a joint with two abutting surfaces, wherein the groove ends before the joint (or the respective abutting surface), and / or wherein the circumferential recess (16) ends before the joint (or the respective abutting surface), and / or wherein the circumferential recess (20) ends before the joint (or the respective abutting surface).

Images