Cast piston for an internal combustion engine, consisting of an iron-based material

Abstract

A cast piston for an internal combustion engine is made of an iron-based material and has windows in at least one side wall carrying a piston pin boss. The windows are asymmetric relative to one another on the side of the skirt walls.

Claims

1. A cast piston for an internal combustion engine, comprising a piston body having a longitudinal axis made of an iron-based material and having a plurality of piston lands separated by a plurality of piston ring grooves, and at least one skirt wall, and including windows in at least one side wall of the piston, the at least one side wall including a piston pin boss having an axis that is perpendicular to the longitudinal axis, and wherein the windows are asymmetric relative to one another and wherein at a bottom, the windows run diagonally upward in a direction of a piston pin axis, all transitions in the windows are rounded, lower edges of the side walls are at least concavely rounded, and the concave rounding has a smaller curvature radius on a pressure side than on a counter-pressure side of the piston body, and wherein the windows have flat top portions that lie in a common plane perpendicular to the longitudinal axis and in line with a bottom edge of a ring belt portion of the piston.

2. The piston according to claim 1, wherein the skirt wall is cut out in a concave manner when viewed perpendicular to the axis of the piston pin boss.

3. The piston according to claim 1 wherein a width of the skirt wall in the circumferential direction is reduced by at least 30% due to the windows.

4. The piston according to claim 1, wherein the windows are formed primarily in a half of the side wall that is closer to a piston crown.

5. The piston according to claim 1, wherein one of the windows has an extension of at least 40% of the height of the side wall in a direction of a piston stroke axis.

6. The piston according to claim 1, wherein the windows begin at an end of the side wall located in a direction of a piston crown.

7. The piston according to claim 1, wherein the piston is made from spheroidal graphite cast iron or cast steel.

8. The piston according to claim 1, wherein the material of the piston has a lower thermal conductivity than steel.

9. The piston according to claim 1, wherein the windows have flat bottom portions.

10. The piston according to claim 9, wherein the flat bottom portions are inclined away from each other.

11. The piston according to claim 9, wherein the flat bottom portions of the windows are non-parallel with respect to their respective flat top portions of the windows.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention will be described in more detail on the basis of an embodiment example as shown in the drawings. In the drawings:

(2) FIG. 1 is a side view of the piston according to the invention in the direction of the piston pin axis; and

(3) FIG. 2 is a side view of the piston in FIG. 1 from a direction perpendicular thereto.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

(4) As can be seen in FIG. 1, the piston 10 according to the invention firstly comprises a ring zone 12 and secondly skirt walls 14 which are connected by side walls 16 that carry the piston pin bosses 22. In the case shown, both side walls 16, i.e. also the side wall facing away from the viewer according to FIG. 1, are provided with two windows 18, 20, which are formed on both sides of the piston pin boss 22 in each case in the upper region of the side wall 16. The top of the windows 18, 20 is directly adjacent to the lower groove cheek of the lowermost annular groove, and the boundary thereof runs substantially in a plane perpendicular to the piston stroke axis. At the bottom, the boundaries of the windows 18, 20 run diagonally upward in the direction of the piston pin axis, and the lateral boundary on the side of the piston pin boss 22 runs (according to the depiction in FIG. 1) from the bottom to the top in an outwardly inclined manner. On the other side, i.e. the side of the skirt wall 14, the smaller window 18 has a boundary running substantially in the direction of the piston stroke axis, and all of the transitions between the boundaries described are rounded, in order to ensure stress optimization, and to reduce susceptibility to cracks.

(5) Particularly on the right-hand side of FIG. 1, which could typically be the counter-pressure side, the window 20 shows the distinctive feature of the piston according to the invention. Here, the window 20 is clearly formed so as to be asymmetric to the window 18 and extends, in particular, into the region of the skirt wall 14.

(6) As is revealed by FIG. 2 in particular, the skirt wall 14 is therefore cut concavely in this region, and the bearing region thereof is considerably reduced, particularly in the top half thereof. As a result, the effects described above can be achieved. In the viewing direction according to FIG. 2, i.e. perpendicular to the piston pin axis, the shape of the window can be described in the lower region thereof as being parallel to a plane perpendicular to the piston stroke axis, and further on as having a comparatively large curvature radius and parallel to the piston stroke axis at least in sections. All transitions are rounded, for the reasons given. In the lower region, the skirt wall 14 is designed with side edges parallel to the piston stroke axis. This preferably also applies to the other side wall, which is not cut in the embodiment example shown. The lower edges thereof are preferably parallel to a plane perpendicular to the piston stroke axis, and the lower edges of the side walls 16 are at least slightly concavely rounded, wherein in the example shown this concave rounding is more extensive on the pressure side, i.e. it is provided with a smaller curvature radius, than on the counter-pressure side. It should also be noted with respect to the piston according to the invention that it may comprise a combustion-chamber bowl and/or a cooling channel.