BACKGROUND

1. Technical Field

The invention relates to a method for producing a piston for an internal combustion engine, a piston for an internal combustion engine, a piston blank for producing the piston, and a casting mold or forging die for producing a piston blank.

In the field of pistons for internal combustion engines, it is customary for the purposes of cooling the piston to form a largely ring-shaped cooling channel which is supplied with cooling oil by means of at least one inlet proceeding largely parallel to the piston axis, said cooling oil leaving the cooling channel at at least one outlet which likewise proceeds substantially parallel to the piston axis.

2. Related Art

JP 58190538 A relates to a forged piston in which the coolant inlets and outlets are formed directly in the area of the piston pin bosses. The same applies for the piston according to CN 205297761 U.

Finally, DE 10 2014 222 416 A1 reveals an aluminium piston in which the coolant inlets and outlets are formed on the outside on the so-called box walls, which extend between the (load-bearing) shaft walls and receive the piston bin bosses.

SUMMARY OF THE INVENTION

Against this background, the object of the invention is firstly to create a method for producing a piston with the aid of which a piston which is improved with respect to the so-called retention rate, in other words the proportion of the cooling oil actually reaching the cooling channel, can be produced in an efficient manner. Furthermore, a corresponding piston, piston blank and casting mold or forging die are to be created for it.

Accordingly, already as part of the production of a piston blank, a thickened portion is formed in at least one box wall in the direction of thickness approximately in the center thereof, which is at least partly flush with a cooling channel. The thickened portion described can be used to form the coolant inlets and outlets in that an opening leading to the cooling channel, in particular a bore, is created. Thus, only a few production steps are required, and no additional components, so that simple and cost-efficient production is enabled. At the same time, it can be ensured that a sufficient quantity of cooling oil reaches the cooling channel during operation.

Furthermore, since the thickened portion is formed in a box wall and not directly adjacent to a piston pin boss, an undesirable mass of material is thereby avoided. Moreover, a sufficiently great distance from moving parts such as a connecting rod can be kept in an advantageous manner.

Measures preferred for this purpose and preferred further developments are described in the further claims.

At least in certain applications there are advantages if at least one box wall is formed on the outside on a piston pin boss since sufficient space for the bores is thereby created in an advantageous manner, and at the same time the necessary distance from the connecting rod as a moving part is kept.

Although as part of the method according to the invention the production of a light metal, in particular aluminium, piston and/or through casting is also possible, the current preference is, according to the invention, to make the piston blank by forging and/or from iron or steel. Steel or iron casting, in particular ductile iron, is preferred as the casting method.

The retention rate can be further increased in an advantageous manner by reworking at least one thickened portion mechanically such that at least one coolant inlet or outlet bore is formed at least partially in a funnel shape.

In certain applications it has further proved to be advantageous if two thickened portions are formed in each of both box walls, so that a total of four inlet or outlet bores are present.

It also offers advantages in certain situations if the cooling channel is filled with a coolant such as sodium, and is subsequently sealed.

In accordance with the method described above, the piston according to the invention is provided with at least one thickened portion which advantageously is not mechanically reworked, with the exception of a bore possibly formed therein. The piston blank according to the invention that is used for this purpose and the casting mold or forging die according to the invention correspond to the fore-mentioned features of the method according to the invention. This equally applies to the preferred embodiments, and it should be mentioned that all features mentioned in connection with the method, the piston, the piston blank, the casting mold and/or the forging die can equally be applied to the respective other subject matters of this application and vice versa.

