Cast inlet and outlet openings on cast steel and cast iron pistons

Description

[0001] The invention relates to a method for manufacturing a piston having a cooling channel created by means of a lost core, wherein a piston blank is cast using a casting process in which the core is inserted before casting, a piston blank is cast using a casting molten metal, and after the casting molten metal has solidified, the piston blank is removed from the casting mold, the core is then rinsed out, and subsequently the piston blank is finished to produce the piston, according to the features of the preamble of claim 1.

[0002] Such a method for manufacturing a piston, also called a cooling channel piston, is known from US 4,559,685. A expendable core, e.g., a sand core, is fitted at its ends with a metallic retaining piece. A permanent magnet is present in the mold, onto which this metallic retaining piece is placed and thus held. The underside of the expendable core surrounding the metallic retaining piece rests on the retaining device containing the permanent magnet, thus creating a cylindrical end for the core. Consequently, after the core is purged from the finished piston blank, a relatively sharp-edged transition is created in the material area of ​​the piston blank surrounding the cooling channel. This can induce stresses in the microstructure of the piston material, which can lead to cracks when the finished piston operates in the cylinder of the internal combustion engine.

[0003] EP 2 113 319 A2 describes a soluble casting core for forming a cooling channel in a casting-manufactured piston, comprising a molded portion for forming an oil inlet of the cooling channel and a molded portion for forming an oil outlet of the cooling channel. To improve the mechanical strength of the piston, the arrangement of the first and fourth molded portions is chosen such that the oil inlet formed by the fourth molded portion and the first oil outlet formed by the first molded portion each lie in different hub supports of the piston pin hubs.

[0004] DE 10 2007 044 105 A1 shows a soluble and essentially ring-shaped casting core for forming a cooling channel, which transitions via a quarter-circle core bend into two areas arranged approximately parallel to the piston axis and pointing away from the piston base, wherein the second area transitions into a part of the casting core that forms the inlet opening of the cooling channel, and the first area transitions into a part of the casting core that forms the outlet opening of the cooling channel.

[0005] The invention is therefore based on the objective of avoiding the disadvantages described at the outset.

[0006] This problem is solved by the features of claim 1.

[0007] According to the invention, the core extends into a region of the mold that forms an interior area of ​​the piston blank and forms at least one opening with a rounded profile for the cooling channel after purging. Furthermore, according to the invention, at least one inlet opening with a circumferential bead is formed by means of the core, and / or at least one outlet opening with a circumferential bead is formed by means of the core. By extending the core into a region of the mold that forms an interior area of ​​the piston blank, a seamless transition around the opening to the cooling channel can be achieved. This opening then extends not only from the opening itself towards the cooling channel, but also in the opposite direction from the opening towards the interior area.Not only the length of the opening, but also its rounded shape for the cooling channel, offers the advantage of eliminating sharp edges, thus effectively preventing cracking. A further advantage is that any desired opening shape can be achieved using a lost core, such as a salt or sand core. The opening's cross-section no longer needs to be round, but can also be oval or any other rounded shape. Furthermore, a crucial advantage is that the lost core completely forms the opening for accessing the cooling channel, including from the piston's interior, meaning it only needs to be purged after casting and solidification. Machining operations, such as...Drilling (especially for creating the opening itself) or post-processing by machining processes are completely eliminated, so that according to the invention there is no risk that smaller particles generated during machining can penetrate the cooling circuit of the internal combustion engine.

[0008] According to the invention, at least one inlet opening with a circumferential bead is formed by means of the core, supplemented by the formation of at least one outlet opening with a circumferential bead, also formed by means of the lost core. Thus, according to the invention, an opening is not simply created from the inner area of ​​the piston towards the cooling channel, but is also advantageously designed. By means of the circumferential bead, at least around the inlet opening, this area is not only reinforced, but also given a shape that effectively prevents cracks in the material structure around the opening. Here, too, the cross-section of the opening need not be circular, but can also be oval in cross-section or have several changes in the shape of an arc.

[0009] In a further development of the invention, it is also provided that a jet splitter is formed by means of the core, at least in the region of the inlet opening. This jet splitter is located, for example, at the apex of the cooling channel, so that, when viewed from the piston stroke axis, it projects downwards into the free area of ​​the cooling channel. This allows an oil jet, which is injected through the at least one inlet opening towards the cooling channel, to be directed in a specific direction or even in two different directions.

[0010] The invention is described in more detail below with reference to a piston manufactured according to the inventive method and explained with reference to the figures.

[0011] In Figure 1Figure 1 shows a piston blank 1, which, after its manufacture, has an outer contour designated 2. The piston blank 1 is manufactured using a suitable casting process with a mold, the mold having the inner contour of the outer contour 2 of the piston blank 1. The mold can be designed in one or more parts. A lost core 3 is provided as part of the mold and is arranged in a suitable manner on or attached to the mold, e.g., the inner insert of the mold. It is also conceivable to provide more than one lost core 3. After the at least one core 3 has been arranged and attached to the mold, the mold is filled with molten metal and left until it has solidified. The mold is then removed, with the lost core 3 initially remaining in the manufactured piston blank 1.This is rinsed out in the usual way, creating an inner area in the piston blank 1 that corresponds to the outer shape of the core 3 and forms a cooling channel 4. The in the . Figure 1 The contour shown or the course of the cooling channel 4 is exemplary and not limited to this.

[0012] The dashed line 5 indicates a finished contour after the piston blank 1 has been further processed. Specifically, this finishing is achieved by machining the outer area of ​​the piston blank 1. This finishing takes place either after or, if applicable, before the core 3 is rinsed.

[0013] The finished piston has elements that are known in themselves, such as a ring field, a pin bore 6, a piston skirt 7 and other common elements (such as an optional combustion chamber recess).

[0014] In Figure 2is a view into an interior area of ​​a finished piston 8, which is mounted on the piston blank 1 according to Figure 1 The design is based on the following principles. In this exemplary design, it can be seen that connecting walls extend from the bolt bores 6 towards the supporting piston stems 7. These are arranged on the underside of the upper part of the finished piston 8, where at least one inlet opening 9 is also located. In this embodiment, a circumferential bead 10 is arranged around the inlet opening 9. The cross-section of the inlet opening 9 is circular, but can deviate from this geometric shape. The same applies to the circumferential bead 10.

[0015] Looking through the inlet opening 9 towards the underside of the upper part of the piston 8, an optional jet splitter 11 is shown in the cooling channel 4 (more precisely at its apex, projecting downwards towards the inlet opening 9).

[0016] In the case of piston 8 according to Figure 2 Cooling oil is injected via (at least one) inlet opening 9, allowing the cooling oil to circulate in the cooling channel 4. To allow it to exit the cooling channel 4 again, according to... Figure 2 At least one drain opening 12 is present, which is also provided with a circumferential bead 13, but this is not mandatory. According to the invention, the openings 9, 12 (and possibly further openings) are produced by means of the lost core 3, wherein the rounded shape of the opening 9, 12, for example realized with the circumferential bead 10, 13 serving to reinforce the respective area, is also produced by means of the lost core, which extends into a region of the casting mold that forms an inner region of the piston blank 1. REFERENCE MARK LIST

[0017] 1. Piston blank 2. Outer contour 3. Lost core 4. Cooling channel 5. Finished contour 6. Pin bore 7. Piston shaft 8. Finished piston 9. Inlet opening 10. Circumferential bead 11. Jet splitter 12. Outlet opening 13. Circumferential bead

Claims

1. Method for manufacturing a piston (8) which comprises a cooling canal (4) produced by means of a lost core (3), wherein in a casting process using a casting mold into which the core (3) is inserted before casting, a piston blank (1) is cast using a molten casting alloy, and after the molten casting alloy has solidified, the piston blank (1) is removed from the casting mold and the core (3) is then flushed out, followed by finishing of the piston blank (1) to produce the piston (8), wherein the core (3) extends into an area of the casting mold which forms an inner region of the piston blank (1) and at least one opening with a rounded contour for the cooling canal (4) is formed with the core (3) after flushing, characterized in that at least one inlet opening (9) with a circumferential bead (10) is formed by means of the core (3) and / or at least one outlet opening (12) with a circumferential bead (13) is formed by means of the core (3).