STEEL PISTON FOR AN INTERNAL COMBUSTION ENGINE

Abstract

A steel piston (10) for an internal combustion engine includes a cooling cavity (20) extending in a rotationally symmetrical manner about the piston axis and at least three annular grooves (12, 14, 16), wherein the third annular groove (16), as viewed from the piston crown (18), has a greater depth (T3) than the depth (T2) of a second annular groove (14).

Claims

1. A steel piston for an internal combustion engine comprising a cooling cavity extending in a rotationally symmetrical manner about the piston axis and at least a first annular groove, a second annular groove, and a third annular groove, wherein the third annular groove, as viewed from the piston crown, has a greater depth than a depth of the second annular groove.

2. The steel piston according to claim 1, wherein a minimum wall thickness between the third annular groove and the cooling cavity is smaller than a minimum wall thickness between the second annular groove and the cooling cavity due to a local increase in the cross-section of the cooling cavity.

3. The steel piston according to claim 1, wherein a welding bead is present between the first annular groove and the third annular groove.

4. The steel piston according to the third annular groove has at least one groove base radius that is larger than a largest groove base radius of the second annular groove.

5. The steel piston according to claim 4, wherein the third annular groove base radius is at each of a lower flank and an upper flank of the third annular groove and which are each larger than the groove base radii of the second annular groove.

6. The steel piston claim 5, wherein the third annular groove has at least one groove base radius that is elliptical in cross-section or composed of two radii.

7. The steel piston according to claim 6, wherein the cross-section of the groove base of the third annular groove consists of an elliptical curve that tangentially transitions into the lower flank and the upper flank.

8. The steel piston according to claim 5, wherein the groove base of the third annular groove consists of a tangentially continuous transition of at least two radii at the lower flank, a straight section and at least two radii at the upper flank.

9. The steel piston according to claim 5, wherein the groove bottom of the third annular groove consists of a curvature-continuous transition of a convex cubic spline curve at the lower flank, a straight section and a convex cubic spline curve at the upper flank.

10. The steel piston according to claim 1, wherein the third annular groove does not comprise oil drainage holes.

11. The steel piston according to claim 1, wherein the depth of the third annular groove is at least 5% greater than the depth of the second annular groove.

Description

THE DRAWINGS

[0019] In the following, the invention will be explained in more detail in reference to embodiments shown in the drawing in which:

[0020] FIG. 1 is a cross-sectional view of an upper part of a piston.

[0021] FIG. 2a is an enlarged cross-sectional view of one side of a piston according to a first embodiment.

[0022] FIG. 2b is an enlarged cross-sectional view of first, second and third annular grooves of the piston of the first embodiment.

[0023] FIG. 3 is an enlarged cross-sectional view of one side of a piston according to a second embodiment.

[0024] FIG. 4 is an enlarged cross-sectional view of one side of a piston according to a third embodiment.

DETAILED DESCRIPTION

[0025] A steel piston 10 comprises a piston crown 28 with a combustion chamber bowl 26 and a cooling cavity extending in a rotationally symmetrical manner about the piston axis, which is configured as an annular cooling channel 20. Three annular grooves 12, 14, 16 are formed in the region of a ring zone, as viewed from the piston crown. As is apparent in particular in FIG. 2b, the third annular groove 16 has a greater depth T3 than a depth T2 of the second annular groove 14.

[0026] Furthermore, the wall thickness D3 between the third annular groove 16 and the cooling channel 20 is less than the wall thickness D2 between the second annular groove 14 and the cooling channel 20. In contrast to the other figures, FIG. 4 shows an embodiment with a local increase in the cross-section of the cooling channel 20, which further reduces the wall thickness D3 between the third annular groove 16 and the cooling channel 20.

[0027] In the embodiment according to FIGS. 1 and 2, the groove base radii R31, R32 of the third annular groove 16 are larger than the groove base radii R21, R22 of the second annular groove 14. However, it is also possible that only the upper groove base radius R31 of the third annular groove 16 is larger than the upper groove base radius R21 of the second annular groove 14, or that the lower groove base radius R32 of the third annular groove 16 is larger than the lower groove base radius R22 of the second annular groove 14. Alternatively, as shown in FIGS. 3 and 4, the third annular groove 16 may also be configured with a groove base in the shape of an elliptical curve that transitions tangentially into the lower flank 22 and the upper flank 24.

[0028] In addition, an outer weld bead 18 is apparent in the figures, which leads to a stiffening of the material in the shown position in the region of the second annular groove 14, the stress on which can be reduced in an advantageous manner also in the event of thermal deformation by the design of the third annular groove 16 according to the invention. There is furthermore an inner weld bead 19. It should be understood that the outer weld bead 18 shown in the figures does not have to be arranged in the center of the second annular groove 14.