Piston for a reciprocating piston machine, and reciprocating piston machine for a motor vehicle

1. A piston for a reciprocating piston machine, comprising:

a piston crown;

a piston recess; and

an annular groove formed in the piston crown, wherein the annular groove extends in a radial direction of the piston outwards and wherein a cross-section of the annular groove has a half-teardrop shape;

wherein the half-teardrop shape has a contouring formed exclusively by a first radius and a second radius, wherein the second radius is directly contiguous with the first radius outwards in the radial direction of the piston, and wherein the second radius is greater than the first radius such that a flow in the annular groove is deflected towards a center of the piston, so that essentially a ricocheting of the flow in all directions is prevented by the annular groove, so that flow turbulence essentially in a form of a torus forms in the annular groove;

wherein the annular groove has interruptions such that the annular groove extends in the piston crown in a corresponding number of segments about a central axis of the piston.

2. The piston according to claim 1 , wherein a mid-point of the first radius lies in a plane of the piston crown extending in an outermost axial direction of the piston and perpendicular to the axial direction of the piston.

3. The piston according to claim 1 , wherein the first radius is 1% to 5% of an outside diameter of the piston and wherein the second radius is 5% to 20% of the outside diameter of the piston.

4. The piston according to claim 1 , wherein the annular groove has an inside diameter which is 70% to 90% of an outside diameter of the piston.

5. The piston according to claim 1 , wherein the half-teardrop shape, in the radial direction of the piston inwards, ends on a separation edge.

6. The piston according to claim 5 , wherein the separation edge has a radius of at most 1 mm.

7. The piston according to claim 5 , wherein a distance extending in the radial direction of the piston between the separation edge and an edge of the piston outermost in the radial direction is in a range from 6% to 10% inclusive of an outside diameter of the piston.

8. The piston according to claim 1 , wherein a width of the annular groove is 3% to 12% of an outside diameter of the piston.

9. The piston according to claim 1 , wherein the piston is configured as a stepped piston such that the piston recess has at least or exactly one step.

10. A reciprocating piston machine for a motor vehicle, comprising:

a cylinder; and

the piston according to claim 1 disposed in the cylinder.

11. A piston for a reciprocating piston machine, comprising:

a piston crown;

a piston recess; and

an annular groove formed in the piston crown, wherein the annular groove extends in a radial direction of the piston outwards and wherein a cross-section of the annular groove has a half-teardrop shape;

wherein the half-teardrop shape has a contouring formed exclusively by a first radius and a second radius, wherein the second radius is directly contiguous with the first radius outwards in the radial direction of the piston, and wherein the second radius is greater than the first radius;

wherein the first radius is 1% to 5% of an outside diameter of the piston and wherein the second radius is 5% to 20% of the outside diameter of the piston;

wherein the annular groove has an inside diameter which is 70% to 90% of an outside diameter of the piston;

wherein a width of the annular groove is 3% to 12% of an outside diameter of the piston;

wherein the half-teardrop shape, in the radial direction of the piston inwards, ends on a separation edge;

wherein the separation edge has a radius of at most 1 mm;

wherein a distance extending in the radial direction of the piston between the separation edge and an edge of the piston outermost in the radial direction is in a range from 6% to 10% inclusive of an outside diameter of the piston;

wherein a flow in the annular groove is deflected towards a center of the piston, so that essentially a ricocheting of the flow in all directions is prevented by the annular groove, so that flow turbulence essentially in a form of a torus forms in the annular groove;

wherein the annular groove has interruptions such that the annular groove extends in the piston crown in a corresponding number of segments about a central axis of the piston.