Piston ring having a stepped running surface

Abstract

A stepped piston ring (2) includes a ring outer side (5), an upper ring flank (6), and a lower ring flank (8). The ring outer side (5) on the upper edge has a notch (10, so that only a lower portion of the ring outer side (5) forms a contact surface (4).

Claims

1. A stepped piston ring, comprising a ring outer side, an upper ring flank, and a lower ring flank, wherein the ring outer side on an upper edge has a notch that is disposed between the ring outer side and the upper ring flank, wherein the notch forms a step that includes a re-entrant edge and a projecting edge on the ring outer side in an axial direction of the ring so that only a lower portion of the ring outer side forms a contact surface, and wherein the stepped piston ring extends in a circumferential direction and includes a ring gap, and wherein the notch extends in the circumferential direction and terminates at each end thereof short of the ring gap; and wherein the notch has a conicity with an angle of between 0.50 to 5° between the re-entrant edge and the upper flank.

2. The stepped piston ring as set forth in claim 1, wherein the notch has a radial height (Hr) of at least 0.03 mm.

3. The stepped piston ring as set forth in claim 1, wherein the step has a flank angle (α) of between 10° and 70° with respect to a radial plane.

4. The stepped piston ring of claim 3, wherein the flank angle is between 20° and 60°.

5. The stepped piston ring of claim 3, wherein the flank angle is between 35° and 55°.

6. The stepped piston ring as set forth in claim 1, wherein the projecting edge of the step has a blend radius (Ru) of between 0.05 mm and 0.2 mm.

7. The stepped piston ring as set forth in claim 1, wherein the re-entrant edge of the step has a blend radius (Ro) of between 0.05 mm and 0.2 mm.

8. The stepped piston ring as set forth in claim 1, further comprising an inner chamfer or an internal angle between the upper ring flank and an inner surface of the piston ring.

9. The stepped piston ring as set forth in claim 1, further comprising wear protection on the ring outer side and/or on the contact surface.

10. A stepped piston ring as set forth in claim 9, wherein the wear protection comprises a wear protection layer forming said step.

11. The stepped piston ring as set forth in claim 1, wherein the upper ring flank is provided with wear protection and/or wherein the lower ring flank (8) is provided with wear protection.

12. The stepped piston ring (2) as set forth in claim 1, wherein the contact surface (4) has a convexity with two equal or different radii of curvature (R.sub.bo, R.sub.bu) of between 1 mm and 25 mm.

13. The stepped piston ring of claim 12 wherein the two equal or different radii of curvature is between 5 mm and 20 mm.

14. The stepped piston ring (2) as set forth in claim 1, wherein the upper ring flank (6) is marked with the letters “TOP” (30) in order to denote a top side, and/or the piston ring is designated as an upper compression ring by the letters “TOP” (32).

15. The stepped piston ring (2) as set forth in claim 1, wherein the notch (10) has a conicity with an angle (β) of between 0.5° and 5°.

16. The stepped piston ring as set forth in claim 1, wherein the lower edge of the contact surface has an angle of between 30° and 60° and an axial dimension (Hk) of between 0.03 mm and 0.12 mm.

17. The stepped piston ring as set forth in claim 1 the notch extends over an axial range of 10% to 50% of the total axial height of the piston ring.

18. The stepped piston ring of claim 17, wherein the axial range is between 30% and 50% of the total axial height of the piston ring.

Description

THE DRAWINGS

(1) In the following, the present invention is illustrated in greater detail with reference to the drawing of schematically illustrated figures.

(2) FIGS. 1 to 3 show sectional views and enlarged details of a stepped piston ring according to the invention.

(3) FIG. 4 shows a plan view of a stepped piston ring according to the invention that illustrates the course of the step in the circumferential direction.

DETAILED DESCRIPTION

(4) Both in the description and in the figures, same or similar reference symbols are used to refer to same or similar elements and components.

(5) FIG. 1 shows a sectional view through a stepped piston ring 2 according to the invention, with two detailed enlargements of the step regions being shown on the left side. The step piston ring comprises a ring outer surface or outer side 5 of the ring that forms a contact surface 4 in a lower region. In an upper region, the outer side 5 of the ring comprises a notch 10, so that a step 12 is formed between the contact surface 4 and the outer side 5 of the ring. The height of the step is determined by the radial height of the step Hr. Combustion gases can press from the outside through the notch against the piston ring and thus exert a force on the piston ring that counteracts a force generated by combustion gases, which act on an inner surface 34 of the piston ring and press the piston ring against an inner wall of the piston (not shown). The stepped piston ring 2 comprises an upper piston ring flank 6 that faces toward a combustion chamber and a lower piston ring flank 8 that faces away from a combustion chamber. The piston ring is bounded on the inside by an inner surface 34 of the piston ring. The step 12 is shown in the enlargement. The step comprises a projecting edge 16 on the upper side of the contact surface 4. The projecting edge 16 can be rounded with a blend radius Ru. The dimension of the blend radius Ru substantially determines an oil scraping characteristic and/or the characteristic of how easily the piston ring can float on an existing oil film. Another factor that influences the friction and the floating and/or scraping characteristic is the flank steepness or flank slope or the flank angle α. The flank angle is measured in an area in which the axial axis of symmetry is located and measured with respect to an area that extends perpendicular to the axial direction. A flank angle of 0° corresponds to a vertical step, and a flank angle of 60° corresponds to a rather gentle transition from the lower step to the contact surface.

(6) The re-entrant edge 14 can be rounded with a blend radius Ro. The dimension of the blend radius Ro substantially determines how strongly the pressure of the combustion gases acts on the lower edge. In the case of a high flank angle, the effect of the combustion gases diminishes slowly from top to bottom.

(7) The lower contact surface chamfer 38 is shown in the lower detailed enlargement. The contact surface chamfer 38 clearly determines an oil scraping characteristic of the piston ring 2 upon downward movement of the piston. The lower contact surface chamfer 38 has an axial height Hk, which should be about 0.08 mm here. Here, the lower contact surface chamfer 38 has a chamfer angle of about 40° relative to the axial direction. The lower contact surface chamfer tends to influence the oil scraping characteristics more readily than a twisting of the piston ring in the piston ring groove.

(8) The stepped piston ring 2 shown in FIG. 2 has a convexity of the outer surface 5, more particularly of the outer step surface of the piston ring with two different radii of curvature. The maximum diameter of the piston ring is shown by the dotdashed line. Above the maximum diameter 4, the contact surface has an upper convexity R.sub.bo having a radius of curvature that is at least 50% less than a lower convexity R.sub.bu of the contact surface 4 below the maximum diameter.

(9) FIG. 2 also shows a notch 10 with the radial step height Hr. A lateral surface of the notch of the stepped piston ring 4 substantially forms a conical surface here (the deviation from the conical surface lies within the measuring and manufacturing tolerances and applies with the exception of the gap ends of the piston ring).

(10) In the embodiment of FIG. 2, the step height or the radial height of the step Hr is determined by the difference of the radii R.sub.bo and the radius of the lower frustoconical surface, which defines the lateral surface of the notch 10.

(11) FIG. 3 shows an embodiment of a stepped piston ring in which an outer surface of the ring is protected by an applied wear protection layer 24. In FIG. 3 as well, the contact surface is convex with two different blend radii. Furthermore, instead of the upper inner chamfer, an upper internal angle 22 is provided that influences the twist characteristics of the piston ring.

(12) The upper piston ring flank 6 is provided with an upper wear protection layer 26. The lower piston ring flank 8 is provided with a lower wear protection layer 28.

(13) FIG. 4 shows a plan view of a stepped piston ring according to the invention having a joint region with two gap ends 18, with the notch 10 and hence the visible step flank 36 ending right before the gap ends 18 in each case. The orientation of the piston ring is defined by the designation 32, and “top” designates the upper ring flank 6 that faces toward the combustion chamber. The piston ring is denoted as the upper compression ring or “top ring” by the designation 30 “Top.”

(14) It also bears mentioning that the piston ring is preferably embodied as a compression ring or “top ring.”

(15) The effects of the notch 10 would be far less evident in a middle piston ring or even in an oil scraping ring, since the compression ring already absorbs the majority of the pressure in the gap between the piston and the cylinder. It is therefore preferred for the middle and lower piston ring as well if the effects of hot combustion gases that press the piston ring outward from the inner surface of the piston ring against an inner surface of the cylinder are also not diminished so effectively.