PISTON RING WITH VARIABLE PRESSURE RELIEF

Description

Field of the invention

[0001] The present invention relates to a piston ring that provides variable pressure relief. The basis is a pressure relief bevel formed on the outer surface of the ring. State of the art

[0002] Radial pressures from piston rings, which act between the running surfaces of the cylinder and ring and are amplified by the combustion pressure, do not act evenly across the circumference of the sealing system. Due to the differences in thermal expansion between the inner and outer ring surfaces, radial pressures are higher at the ring joint, which creates a higher surface pressure in this area and reduces the oil film thickness. In addition, near the ring joint, the oil pressures drop to ambient level due to the interruption in the running surface, resulting in extensive lubricating oil flow into the ring joint recess. This leads to further oil film reductions and ultimately to considerable solid body contact or friction, resulting in increased wear, scuffing and reinforcement layer disruption with cracking and cobblestone formation on the running surface, especially in the joint areas of the piston ring.

[0003] Known mitigations, preferably for piston rings with larger axial heights, include ground chamfers on the running surface above the pivot point. These serve as a gas pressure contact surface and generate a force component toward the inner piston groove area. This force component therefore radially counteracts the gas pressure at the inner diameter of the ring, thus relieving the load-bearing area of ​​the running profile to prevent tribological damage to the usually present reinforcement layers, especially on rings in the first piston ring groove, which are directly exposed to the combustion pressure. However, these known pressure relief devices are uniformly positioned around the entire circumference and thus have the effect of evenly counteracting the radial pressure of the ring on the cylinder wall.

[0004] Such piston rings are described in the publication of the European patent with the number EP3421846 B1, wherein this document describes a contact surface that widens at a ring joint.

[0005] From the Japanese utility model JP S56-15437 (U) a clamp ring is also known whose thickness in the radial direction changes in the circumferential direction. #

[0006] A piston ring with improved oil scraping properties is known from Japanese patent application JP 2011-169388 (A).

[0007] The object of the present invention is to take into account the extensive variability of the radial pressures. Summary the invention

[0008] The invention relates to a piston ring having the features of claim 1, preferred embodiments being provided by the dependent claims.

[0009] A piston ring, according to one aspect, comprises a ring outer side, an upper ring flank and a lower ring flank, wherein the ring outer side has a pressure relief bevel on an upper edge, so that only a lower part of the ring outer side forms a contact surface, characterized in that an axial dimension of the contact surface varies in the circumferential direction.

[0010] The advantage of the piston ring according to the invention is that a specifically defined axial dimension of the contact surface around the circumference of the ring compensates for the circumferentially varying radial pressures or effective radial pressures. This occurs through the associated change in the height of the gas attack surface on the running surface, which counteracts the gas pressure at the ring's inner diameter.

[0011] It is preferred that the axial dimension of the contact surface includes a radially outermost point or pivot point of the contact surface.

[0012] It is preferred that the axial dimension of the contact surface extends to the radially outermost point of the tread.

[0013] It is preferred that an axial position of the radially outermost point of the contact surface varies in the circumferential direction.

[0014] It is preferred that an axial distance between the upper edge and the contact surface is maximum in the region of the joint and tapers uniformly over the circumference to a minimum value which is in the range of 2.5% to 30%, preferably 5% to 15% of a piston ring height.

[0015] It is preferred that the axial dimension of the contact surface has a minimum in a region extending over 5% to 35%, preferably 10% to 30%, particularly preferably 10% to 25% of the total circumference of the piston ring on both sides of the ring joint.

[0016] It is preferred that the axial dimension of the contact area increases in the circumferential direction from the minimum to the ring joint and in the opposite direction.

[0017] According to the invention, the axial dimension of the contact surface at the ring joint is minimum.

[0018] It is preferred that the axial dimension of the contact surface increases in the circumferential direction starting from the ring joint.

[0019] It is preferred that the axial dimension of the contact surface is constant on both sides of the ring joint over the area extending over 5% to 35%, preferably 10% to 30%, particularly preferably 10% to 25% of the total circumference of the piston ring on both sides of the ring joint.

[0020] It is preferred that the axial dimension of the contact surface over the area extending over 5% to 35%, preferably 10% to 30%, particularly preferably 10% to 25% of the total circumference of the piston ring, is first constant on both sides of the ring joint and then increases.

[0021] It is preferred that the axial dimension of the contact surface is constant in at least one region in the circumferential direction.

[0022] According to the invention, the axial dimension of the contact surface in partial areas of the circumference is between 60% and 100% of the piston ring height.

[0023] It is preferred that the axial dimension of the contact surface in a region opposite the ring joint is 60% of the piston ring height.

[0024] It is preferred that an angle between the pressure relief slope and the upper edge is in the range of 93° to 160°, preferably in the range of 100° to 150°, particularly preferably in the range of 105° to 140°. Short description of the drawings

[0025] In the following, exemplary embodiments of the invention are described in more detail with reference to the figures, wherein Fig. 1 a cross section of the piston ring according to the invention and Fig. 2 a plan view of the ring outer side in the joint area of ​​the piston ring according to the invention. Detailed description of the drawings

[0026] Fig. 1shows a cross-section of a piston ring 2 with a ring outer side 4, an upper ring flank 6 facing a combustion chamber, and a lower ring flank 8 facing away from the combustion chamber. Visible on the ring outer side 4 is a pressure relief bevel 12, which has an axial dimension in the axial direction 16, starting from an upper edge 10 and extending to approximately 35% to 45% of the axial piston ring height. A radial dimension of the pressure relief bevel 12 is approximately 10% to 15% of the radial dimension of the piston ring cross-section. In this case, a straight line connection of the end of the contact surface 14 which is closest to the upper edge 10 with a point on the upper edge 10 which is offset inwards in the radial direction forms the pressure relief bevel 12. Through this, combustion gases from the outside can press against the piston ring 2 and thus exert a force which counteracts a force which is generated by combustion gases which act on the inside of the piston ring.In the lower area of ​​the ring outer side 4 there is a contact surface 14 or running surface with a radially outermost point 20.

[0027] The pressure relief slope is defined by an angle between the pressure relief slope 12 and the upper edge 10. The minimum angle, which is preferably located at the ring joint 12, is approximately 93° to 110°. The maximum angle is approximately 135° to 140°, whereby this Fig. 1 between the dashed line, which indicates the variation of the pressure relief slope 12 in the circumferential direction 18, and the upper edge 10.

[0028] Fig. 2 shows a top view of the outside of the piston ring 2 in the area of ​​the ring joint 22. The pressure relief bevel 12 is as in Fig. 1 facing the combustion chamber and the contact surface 14 facing away from the combustion chamber. An axial dimension of the pressure relief slope 12 or contact surface 14 varies in the circumferential direction 18.

[0029] The axial dimension in the axial direction 16 of the contact surface 14 has a minimum at the ring joint 22 and amounts to approximately 55% to 65% of the axial piston ring height. In the area of ​​the ring joint 22, the axial dimension of the contact surface 14 is preferably minimal because this is where the oil pressure drop is most severe due to the interruption of the contact surface 14. In the circumferential direction 18, the axial dimension of the contact surface 14 then continuously expands until it amounts to approximately 80% to 85% of the axial piston ring height, with the transitions being rounded. In the further visible circumferential course, the axial dimension of the contact surface 14 is constant. The design of the pressure relief bevel 12 or contact surface 14 is symmetrical to the ring joint 22. List of reference symbols

[0030] 2Piston ring 4Ring outer side 6Upper ring flank 8Lower ring flank 10Top edge 12Pressure relief bevel 14Contact surface 16Axial direction 18Circumferential direction 20Radial outermost point or pivot point 22Ring joint

Claims

1. A piston ring (2), comprising: a ring outer side (4), an upper ring flank (6) and a lower ring flank (8), wherein the ring outer side (4) has a pressure relief chamfer (12) at an upper edge (10), so that only a lower part of the ring outer side has a contact surface (14), which forms a running surface, wherein an axial dimension of the contact surface (14) varies in a circumferential direction (18), wherein the axial dimension of the contact surface (14) has a minimum at a ring end gap (22), characterized in that an axial distance between the upper edge (10) and the contact surface (14) is maximum in the region of the end gap and tapers at an even progression over the circumference (18) to a minimum value, which lies in the range from 2.5 % to 40 % of a piston ring height, and that the axial dimension of the contact surface (14) in subregions of the circumference is more than 60 % and less than 100 % of the piston ring height.

2. The piston ring (2) according to claim 1, wherein the axial dimension of the contact surface (14) includes a radially outermost point (20) of the running surface.

3. The piston ring (2) according to claim 1, wherein the axial dimension of the contact surface (14) extends to the radially outermost point (20) of the running surface.

4. The piston ring (2) according to one of the preceding claims, wherein an axial position of the radially outermost point (20) of the contact surface (14) varies in the circumferential direction (18).

5. The piston ring (2) according to one of the preceding claims, wherein an axial distance between the upper edge (10) and the contact surface (14) is maximum in the region of the end gap and tapers at an even progression over the circumference (18) to a minimum value, which lies in the range from 2.5 % to 30 %, preferably from 5 % to 15 % of a piston ring height.

6. The piston ring (2) according to one of the preceding claims, wherein the axial dimension of the contact surface (14) has the minimum in a region which extends over 5 % to 35 %, preferably 10 % to 30 %, more preferably 10 % to 25 % of the total circumference of the piston ring on both sides of the ring end gap (22).

7. The piston ring (2) according to claim 6, wherein the axial dimension of the contact surface (14) increases in circumferential direction (18) from the minimum to the ring end gap (22) and in opposite direction.

8. The piston ring (2) according to claim 1, wherein the axial dimension of the contact surface (14) increases in circumferential direction (18) starting at the ring end gap (22).

9. The piston ring according to one of claims 1 to 5, wherein the axial dimension of the contact surface (14) is constant over the region, which extends over 5 % to 35 %, preferably 10 % to 30 %, more preferably 10 % to 25 % of the total circumference of the piston ring on both sides of the ring end gap (22).

10. The piston ring (2) according to one of claims 1 to 5, wherein the axial dimension of the contact surface (14) is constant at first and then increases over the region, which extends over 5 % to 35 %, preferably 10 % to 30 %, more preferably 10 % to 25 % of the total circumference of the piston ring on both sides of the ring end gap (22).

11. The piston ring (2) according to one of the preceding claims, wherein the axial dimension of the contact surface (14) is constant in at least one region in circumferential direction (18).

12. The piston ring according to one of the preceding claims, wherein an angle between the pressure relief chamfer (12) and the upper edge (10) lies in the range from 93° to 160°, preferably in the range from 100 ° to 150°, more preferably in the range from 105° to 140 °.