EP1636473B2 - Piston for a combustion engine and casting method for the production thereof - Google Patents

Description

The invention relates to a piston for an internal combustion engine according to the preamble of claim 1 and a method for its production according to the preamble of claim 2.

From the publication DE 199 22 809 A1 a piston is known whose formed on a cylindrically shaped, upper portion of the piston pin bosses are set back relative to the edge of the upper region, so that when pouring the piston in the bottom of the overhang formed thereby near the pin bosses recesses can be formed. For this purpose, a mold is used which contains a pivotable window insert with a casting core per recess, but which can only produce those recesses from which the casting core can be easily removed after casting. This has the disadvantage that as a result the weight of the upper portion of the piston can not be reduced so much that the center of mass of the piston for smooth engine operation can be displaced as far as possible in the lower region of the piston.

From the publication DE 101 42 980 A1 It is known aufzustecken on a slidable obliquely to the piston axis casting mold a molding with the help of which when casting a piston under the bottom of the piston behind its ring field a recess can be produced, which has a pointing in the direction of the piston axis, nose-shaped undercut. After the casting of the piston, the casting tool is pulled away from the piston obliquely downwards, wherein the shaped body briefly remains in the piston before it is washed out.

The disadvantage here is that a very expensive mechanism is required to keep the casting mold during casting of the piston exactly in the space provided and move away obliquely downwards from the piston after casting and pull out of the molding. In addition, the known from the prior art molding no incisions, which allows a production of ribs in the recess, which brings about the further disadvantage that the piston known from the latter prior art has only a low mechanical strength.

From the European patent application EP 0 364 810 A2 a piston with a combustion bowl in the piston head is known, the underside of which is connected via webs with pin bosses. In the region of the piston head and radially outside, the piston also has a downwardly open recess in the form of a cooling channel, whose radially inner region is divided by the webs. However, since the webs do not extend to the belt, which limits the recess radially outward, there is the disadvantage that the mechanical strength of the piston bottom side region of the piston known from the EP application is very small radially outward.

On this basis, the invention has the object to avoid the disadvantages of the cited prior art. The problem is solved with the features in the characteristics of the main claim and the dependent claim. An expedient embodiment of the invention is the subject of the dependent claim.

The subject matter of the second claim combines the advantages of a hinged window insert, which can be produced on casting technology simple way recesses for which linearly movable slide are unsuitable, with the advantages of a salt core, the unlimited potential for possibilities of shaping cavities in the piston offers.

Fig. 1

einen teilweise geschnittenen Kolben nach dem Guss mit eingesetztem Salzformteil, befestigt auf einem schwenkbaren Fenstereinsatz,

Fig. 2

den Kolben mit eingesetztem Salzformteil und auswärts geschwenktem Fenstereinsatz, der sich vom Salzformteil gelöst hat,

Fig. 3

den teilweise geschnittenen Kolben, nachdem das Salzformteil ausgewaschen ist, und

Fig. 4

eine Untersicht des Kolbens gemäß der Erfindung.

An embodiment of the invention will be described below with reference to the drawings. Show it

Fig. 1

a partially cut piston after casting with inserted salt molding, mounted on a pivoting window insert,

Fig. 2

the piston with inserted salt molding and outwardly pivoted window insert, which has detached from the salt molding,

Fig. 3

the partially cut piston after the salt molding is washed out, and

Fig. 4

a bottom view of the piston according to the invention.

In Fig. 1 a piston 1 is shown in half section, the left half of which lies on the longitudinal axis 2 of a piston pin, not shown, section of the piston and the right half of a side view of the piston 1, in which a coated portion 3 of a piston shaft 4 can be seen. The piston 1 is designed as a box piston, ie, below a circular cylindrical and the piston rings receiving, upper portion 5 is a lower portion 6, which has an approximately box-shaped cross-section, in which the hubs 7 and the box walls in the region of the hubs 7 to the piston center axis are drawn in, and in which only the lying in the region of the pressure and the counterpressure side skirt wall sections in section have the shape of segments of a circle whose diameter corresponds to the piston diameter.

The piston 1 has two elevations 9 and 10, which are arranged on both sides of a combustion chamber trough 11 formed in the piston crown. Thus, by these elevations 9 and 10 of the center of gravity of the piston 1 is not shifted too far upwards in the direction of the combustion bowl 11, are during casting of the piston 1 in the combustion chamber troughs 9, 10 to the lower portion 6 of the piston 1 open recesses 12 and also in formed under the region between the hubs 7 and the upper region 5 undercuts 13, which in the present embodiment in cross-section nose-shaped and in each case to the piston central axis 8 are aligned, but may also have any other shape that is adapted to reduce the weight of the piston. In addition, the mass center of gravity of the piston 1 in the direction of the hubs 7 is displaced by the material saved thereby.

In this case, the casting mold for casting the piston 1 has a pivotable window insert 14 for each of the recesses 12 to be produced in the two elevations 9 and 10. In order hereby to be able to mold the undercuts 13 in the upper region 5 of the piston 1, a prefabricated salt mold part 15 is applied before the casting of the piston 1 on the window insert 14, the shape of which is identical to the shape of the recess 12 including the undercut 13. Das Salt mold part 15 is secured against rotation on the window insert 14 via two conical projections 16 arranged on the window insert 14, onto which the salt mold part 15 is slipped. In the Figures 1 and 2 the window insert 14 is shown in section, which is why only one of the two extensions 16 can be seen. With pivoted-in window insert 14 and salt molding 15 mounted thereon, the piston blank 1 is poured.

Following the casting process is in accordance with FIG. 2 pivoted together with the opening of the other mold, not shown in the figures, the window insert 14 in a clockwise direction, wherein the salt mold part 15 detaches from the window insert 14 and remains in the piston blank 1 to be washed out subsequently.

This results in the FIG. 3 illustrated piston blank 1, which has the recesses 12 with the undercuts 13, wherein these recesses 12, as well as in FIG. 4 are divided by ribs 17,17 ', which serve to improve the dimensional stability of the walls 18 of the elevations 9 and 10. This allows to make the walls 18 very thin, thereby achieving improved cooling of the upper portion 5 of the piston 1 by spraying with cooling oil.

The bottom view of the piston according to FIG. 4 shows the kidney-shaped configuration of the recesses 12, 12 'with the dashed lines undercuts 13, 13', which are divided in the present embodiment of two ribs 17, 17 '. In the preparation of the salt mold part 15 used in this case, the shape and the arrangement of the ribs 17, 17 'in a simple manner by a corresponding design of the salt-molded part 15 are taken into account. In the illustrated embodiment, the shape of the salt mold part 15 corresponds to the negative shape shown in the figures of the recesses 12, 12 'and undercuts 13, 13'. This show the Figures 1 and 2 Sectional views of the salt-molded part 15, which is integrally formed and to form the in the FIGS. 3 and 4 illustrated ribs 17, 17 'has incisions in the shape and depth of the shape of the ribs 17 according to FIG. 3 correspond, and their arrangement of the arrangement of the ribs 17, 17 'in accordance with FIG. 4 equivalent.

LIST OF REFERENCE NUMBERS

1

Piston, piston blank

2

pin axis

3

coated area

4

piston shaft

5

upper area

6

lower area

7

hub

8th

Piston central axis

9

lateral elevation

10

lateral elevation

11

Combustion bowl

12, 12 '

recess

13, 13 '

undercut

14

Fenstereinsatz

15

Salt form part

16

cone-shaped extension

17, 17 '

ribs

18

wall

Claims (3)

1. A piston (1) for an internal combustion engine, said piston consisting of

   - an approximately circular cylindrical upper area (5) for receiving annular grooves and

   - a lower area (6) having two hubs (7) for receiving a piston pin, which hubs are set back toward the piston central axis (8),

   - wherein in the upper area (5), recesses (12, 12') are arranged in the area of the hubs (7), which recesses are open toward the lower area (6) and have molded undercuts (13, 13') in the area between the hubs (7) and the upper area (5),

   characterized in that the recesses (12, 12') are subdivided in each case by at least one rib (17, 17') which is arranged in the radial direction.
2. A casting method for producing a piston, wherein a casting mold having respective pivotable window inserts (14) is used for producing respective recesses (12, 12'), comprising the following method steps:

   - producing salt mold parts (15) by means of which, when casting the piston (1), the recesses (12, 12') and also undercuts (13, 13') projecting into the area between the hubs (7) and the upper area (5) of the piston (1) can be generated,

   - introducing notches into the salt mold parts (15) for producing ribs (17, 17') arranged in the recesses (12, 12') and in the undercuts (13, 13') when casting the piston (1),

   - securing the salt mold parts (15) on the respective window inserts (14),

   - casting the piston (1),

   - pivoting the window inserts (14) away from the finished casted piston (1), wherein the salt mold parts disengage from the window inserts and remain within the piston, and

   - washing the salt mold parts (15) out of the piston (1).
3. The casting method according to claim 2, characterized in that the window inserts (14) have in each case at least two conical extensions (16) onto which the respective salt mold parts (15) are attached.

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