DE102010054831A1 - Design of combustion bowls in pistons for internal combustion engines - Google Patents

Abstract

The invention relates to a piston (1) for an internal combustion engine, comprising a piston head (2), in which a combustion chamber bowl (3) is integrated, which comprises a bowl bottom (4) which extends over a bowl edge (5) with an associated bowl edge radius (6). is connected to the piston crown (2). The combustion bowl (3) includes at least one bowl bottom (4) of any geometrical design, which has a matching or different geometric shape compared to the bowl edge (5) and / or the bowl edge radius (6).

Description

The invention relates to a piston for an internal combustion engine, comprising a piston head, in which a combustion bowl is integrated, which comprises a trough bottom, which is connected via a trough edge with associated Muldenrandradius with the piston head. Furthermore, the invention relates to a method for producing a piston with integrated combustion bowl.

State of the art

The combustion bowl of a piston is thermally stressed in the operating state. So far, the combustion chamber trough was introduced predominantly symmetrically in the piston crown, the wall thickness was compensated for a cooling channel in a liquid-cooled piston by an off-center positioning.

The design of the combustion bowl influences in particular for pistons of diesel internal combustion engines significantly the operating and exhaust behavior. The different requirements between the part-load and the full-load operation of an internal combustion engine require a compromise in the design of the combustion chamber trough.

In particular, the trough edge of the combustion chamber trough is subject to a critical state of stress, since the accelerated gas flow enhances the heat transfer in this zone. As a result, the temperature of the trough edge, which leads to an increased stress load, increases due to a non-uniform temperature distribution. For the trough edge of the combustion bowl there is therefore an increased risk of cracking. The fatigue cracks extending in particular perpendicularly to the combustion chamber depression edge are caused during the heating process by a plastic deformation of the hot edge region of the combustion chamber recess. The trough edge expands due to high temperature, while the underlying structure with a lower temperature level blocks a material expansion, with the result of plasticization. In the cooling process of the piston crown, the edge region of the combustion chamber trough retreats to its original shape, which sets high tensile stresses in the material structure. Exceeding permissible limits of the material can increase cracking.

As a measure to prevent cracking, it is known to change the radius of the trough edge if necessary by a mechanical method, in particular milling. The geometries on pistons to be produced by mechanical machining of surfaces have hitherto extended to rotationally symmetrical measures such as turning and drilling or plane milling operations. Regardless of the mechanical measures used, these require an additional time-consuming deburring.

Another measure provides to refine the trough edge of the combustion bowl by a targeted remelting. This example, from the DE 21 245 595 Known method is based on the fact that a charge carrier beam penetrating into the material melts a small amount of material lying directly in its area, while the environment of the molten zone remains cold and the molten material cools down immediately after removal of the charge carrier and immediately solidifies again. The remelting improves the surface strength and the surface toughness, disadvantageously affecting only a small material zone located directly in the region of the charge carrier jet.

task

The invention has for its object to cost for a piston combustion chamber trough to optimize the combustion, which further reduces the stress in the piston crown.

This problem is solved by the features of claims 1 and 9.

According to the first invention according to claim 1 it is provided that the combustion bowl includes at least one arbitrarily geometrically shaped trough bottom. Advantageously, the invention further includes a combustion chamber, in which both the trough bottom and the trough edge are designed arbitrarily geometrically. In addition, according to the invention, the trough bottom opposite the trough edge have a matching or deviating geometric shape, wherein preferably the trough edge includes a trough rim radius. With a variable design of the trough bottom and / or the Muldenrands the combustion chamber trough can be designed optimized combustion optimized.

In the operating state of a piston with a combustion chamber trough designed according to the invention, advantageously lower stress loads occur in zones subjected to high thermal stress, in particular in the trough edge including the trough rim radius. At the same time a thermal fatigue strength of the material in the edge region of the combustion bowl can be significantly improved by the inventive measure.

Advantageously, the economically feasible measure according to the invention for pistons of Leistungsgesteigerten internal combustion engines are used. In particular, in these pistons, the combustion bowl is subjected to increased stress from the mechanical stress of the gas pressure and an elevated temperature level as well as the stresses from the temperature gradients. The inventively designed piston can withstand these stresses and continue to meet the increased demands in terms of reliability and service life. The inventive design of the burner cavity creates geometric asymmetries that interfere with the formation of acoustic resonance frequencies, which has an advantageous effect on the noise. With the constructive concept according to the invention, an optimum combustion can be achieved in the operating state of the piston. In addition, set up an improved cooling, reduced noise and a voltage reduction at the trough edge.

Further embodiments of the invention are the subject of the dependent, explained below claims 2 to 8.

In a preferred embodiment of the invention, the trough bottom and / or the trough edge including the trough rim radius form a shape deviating from a circular shape geometric shape. A preferred first constructive design provides that the piston comprises a centric or eccentric introduced into the piston crown combustion bowl with a symmetrically shaped trough bottom and a running, preferably oval shaped trough edge including trough rim radius. Another inventive concept also provides a centric or eccentric introduced into the piston crown combustion bowl, which includes an asymmetric trough bottom and a trough edge, including trough rim radius with a consistent, in particular round shape. Another centric or eccentric introduced into the piston crown combustion bowl according to the invention comprises an asymmetrical or oval shaped trough bottom and a trough edge, including trough rim radius with an approximately coincident or extending, for example, oval shape. Depending on requirements, it is advisable that the trough bottom and / or the trough edge is designed asymmetrically on one side or up to a free shape. In addition, the invention offers the possibility of providing the combustion bowl with an arbitrarily geometrically designed free-form trough bottom, which is associated with a trough edge with a likewise free-form or any geometrically shaped shape. Advantageously, the profile or the shape of the trough bottom and / or the trough edge can be freely programmed. If necessary, an approximate geometric profile match between the bowl rim and the tray bottom can be created.

Preferably, the inventive concept of Brennraumpuldengestaltung in conjunction with a liquid-cooled, at least one cooling duct enclosing piston can be used. The invention offers the possibility to optimize the wall thickness between the combustion bowl and the cooling channel with the aim to improve the cooling of the piston. To achieve effective piston cooling, the wall thicknesses between the combustion chamber recess and the cooling channel can thus be advantageously optimized without limiting the piston strength. The inventive concept is applicable to pistons made by a casting, forging or extrusion process or a combination thereof.

The invention according to claim 9 comprises a method for producing the combustion bowl, by means of a cutting, mechanical processing, the combustion bowl can be introduced into the piston crown in different geometrically shaped shapes. For this purpose, a machine tool is preferably used with which, in conjunction with a special tool, the trough bottom and / or the trough edge of the combustion chamber trough can be produced in different or matching shapes. To realize the geometric shape of the trough bottom, the trough edge and / or the Muldenrandradius is set with a machine tool in a single clamping with the special tool at a defined transition point on the combustion bowl and as needed with the angle-dependent tool, for example, the trough opening or other areas of the Brennrummulde produced.

With the method used advantageously any geometrically shaped, in particular deviating from a circular shape or profiles for the trough bottom and the trough edge can be realized. This manufacturing method makes it possible to introduce a combustion chamber trough, whose trough geometry ensures optimal combustion in conjunction with a stress-reduced trough edge, which has an advantageous effect on the component safety of the piston. In addition, the machining process used allows a more flexible, cost-optimized production of the piston. Another cost advantage compared to previously used methods for piston production turns out, since neither milling nor related intersection edges are required at the trough edge.

As a preferred machine tool for producing the design of the combustion bowl according to the invention a Innenovaldreheinheit is used with the advantageous in a clamping the Geometry of the trough bottom and the trough edge including the trough rim radius with matching or divergent geometric configurations can be introduced into the piston head. A first embodiment provides a centric or eccentric introduced into the piston crown combustion bowl, which includes a symmetrical or round-shaped well bottom and a running, preferably oval shaped well edge and Muldenrandradius. Furthermore, an embodiment is suitable, which comprises a centric or eccentric introduced into the piston crown combustion bowl, which is associated with an asymmetrical well bottom and a trough edge including Muldenrandradius with a constant circular shape. The invention comprises as a further embodiment a centric or eccentric introduced into the piston crown combustion bowl with an asymmetric trough bottom, which is associated with a trough edge and Muldenrandradius with a running, preferably oval shaped trough edge and Muldenrandradius. In addition, the combustion bowl according to the invention, a trough bottom and a trough edge with a running, oval or shaped as a freeform, freely programmable form include.

Advantageously, the use of Innenovaldreheinheit allows an embodiment of combustion bowls with well bottoms and / or Muldenrändern, including Muldenrandradien in arbitrarily shaped free-form surfaces, shapes or free-form contours with three-dimensional shape and with and without undercut.

Furthermore, by means of a freely programmable machine tool with CNC control, in particular a Innenovaldreheinheit with associated cutting tool any shapes can be made within the combustion bowl. The controller allows by appropriate free programming the introduction of almost arbitrarily geometrically shaped courses, contours or profiles for the trough bottom and / or the trough edge, for producing an optimally designed combustion bowl. In order to realize the combustion bowl designed according to the invention, advantageously only one clamping of the piston in the machine tool or the machining device is required in order to be able to inexpensively produce, for example, the profile of the well base and the bowl edge in compliance with the lowest manufacturing tolerances. Compared to previous solutions, a considerable time and cost advantage arises with the method according to the invention.

The machining of the piston with integrated, inventively designed combustion bowl is carried out in the following steps: after producing a piston blank by a primary molding process such as a casting, - forging or extrusion process, the machining of the piston blank by mechanical operations. Subsequently, the combustion chamber trough is preferably introduced into the piston head in conjunction with the inner turret unit before the piston is cleaned of cooling lubricant and / or lubricants and adhering chips.

embodiments

In the following, the invention will be explained in more detail by means of preferred embodiments with reference to the drawing, wherein the present invention is not limited to these embodiments. Show it:

1 a partial side view and a partial sectional view of a piston with integrated in the piston crown combustion bowl;

2 a piston in a plan view with a first embodiment of a combustion chamber according to the invention formed;

3 according to the piston 2 with a second embodiment of an inventively designed combustion bowl;

4 according to the piston 2 with a third embodiment of an inventive combustion chamber trough;

5 according to the piston 2 with a fourth embodiment of an inventively designed combustion bowl.

Detailed description of the drawings

The 1 shows a liquid-cooled piston 1 in which in a piston bottom 2 a combustion bowl 3 is introduced. The centrically arranged combustion bowl 3 forms a trough bottom 4 , which is centered in the direction of the piston crown 2 is executed curved. The trough bottom 4 is on the outside of a rounded, in particular convex executed Muldenrand 5 enclosed, a circumferential undercut 7 forms. Over a concave section, a trough rim radius 6 is the trough edge 5 with the piston bottom 2 connected. For cooling the piston 1 is preferably a circumferential, acted upon by a cooling medium cooling channel 8th in the piston 1 integrated. Due to a relatively small wall thickness to the thermally heavily stressed bowl edge 5 the combustion chamber trough 3 An effective piston cooling can be achieved.

The piston 1 according to 2 includes a centric in the piston crown 2 introduced Combustion bowl 13 with a round, symmetrical trough bottom 14 , the one running, oval shaped trough edge 15 assigned.

The 3 shows a combustion bowl 23 with a centric in the piston crown 2 introduced round, symmetrically shaped trough bottom 24 and an eccentric, oval trained trough edge 25 ,

According to 4 closes the combustion bowl 33 of the piston 1 an oval or asymmetrical trough bottom 34 one as well as an oval shaped trough edge 35 ,

In 5 is in the piston crown 2 of the piston 1 a freeform burner trough 43 integrated, which has an irregularly shaped trough bottom 44 and an irregularly shaped bowl rim 45 includes.

LIST OF REFERENCE NUMBERS

1

piston

2

piston crown

3

Combustion bowl

4

depression base

5

bowl edge

6

Bowl edge radius

7

undercut

8th

cooling channel

13

Combustion bowl

14

depression base

15

bowl edge

23

Combustion bowl

24

depression base

25

bowl edge

33

Combustion bowl

34

depression base

35

bowl edge

43

Combustion bowl

44

depression base

45

bowl edge

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 21245595 [0006]

Claims (13)

Piston ( 1 ) for an internal combustion engine, comprising a piston head ( 2 ), in which a combustion bowl ( 3 . 13 . 23 . 33 . 43 ), which is a trough bottom ( 4 . 14 . 24 . 34 . 44 ), which over a Muldenrand ( 5 . 15 . 25 . 35 . 45 ) via an associated bowl rim radius ( 6 . 16 . 26 . 36 . 46 ) with the piston head ( 2 ), characterized in that at least the combustion chamber trough ( 13 . 23 . 33 . 43 ) an arbitrarily geometrically shaped trough bottom ( 14 . 24 . 34 . 44 ), which is opposite the trough edge ( 15 . 25 . 35 . 45 ) and / or the trough rim radius ( 16 . 26 . 36 . 46 ) has a matching or deviating geometric shape. Piston according to claim 1, characterized in that the well bottom ( 34 . 44 ) and / or the trough edge ( 35 . 45 ) including the trough rim radius ( 36 . 46 ) has a shape deviating from a circular shape geometric shape. Piston according to claim 1 or claim 2, characterized in that a centric or eccentric in the piston head ( 2 ) introduced combustion chamber trough ( 13 ) a round or symmetrical trough bottom ( 14 ) as well as a running, or oval shaped trough edge ( 15 ). Piston according to claim 1 or claim 2, characterized in that a centric or eccentric in the piston head ( 1 ) introduced combustion chamber trough ( 23 ) an asymmetrical trough bottom ( 24 ) and a trough edge ( 25 ) with a consistent, especially round shape. Piston according to claim 1 or claim 2, characterized in that a centric or eccentric in the piston head ( 2 ) introduced combustion chamber trough ( 33 ) an asymmetrical or oval shaped trough bottom ( 34 ), which has a trough edge ( 35 ) associated with an approximately coincident or running shape. Piston according to claim 1 or claim 2, characterized in that a free-form or any geometrically designed combustion bowl ( 43 ) in the piston head ( 1 ) is introduced, which a trough bottom ( 44 ) and / or a trough edge ( 45 ) is associated with a free-form or any geometrically shaped form. Piston according to at least one of claims 1 to 6, characterized in that the liquid-cooled piston ( 1 ) at least one cooling channel ( 8th ) includes. Piston according to at least one of claims 1 to 7, characterized in that the piston ( 1 ) can be produced by means of a casting, forging or extrusion process made of steel or a light metal. Method for producing a combustion bowl ( 13 . 23 . 33 . 43 ) in a flask ( 1 ) according to one of claims 1 to 8, characterized in that by means of a cutting, mechanical machining, the combustion chamber trough ( 13 . 23 . 33 . 43 ) in the piston head ( 2 ) is introduced, wherein with a special tool of a machine tool used the trough bottom ( 14 . 24 . 34 . 44 ) and / or the trough edge ( 15 . 25 . 35 . 45 ) of the combustion chamber trough ( 13 . 23 . 33 . 43 ) can be realized in different or matching, any geometrically shaped forms. A method according to claim 9, characterized in that for the design of the trough bottom ( 14 . 24 . 34 . 44 ) and the Muldenrands ( 15 . 25 . 35 . 45 ) of the combustion chamber trough ( 13 . 23 . 33 . 43 ) a Innenovaldreheinheit is used as a machine tool, wherein with a clamping a matching or divergent geometry of the trough bottom ( 14 . 24 . 34 . 44 ) and the Muldenrands ( 15 . 25 . 35 . 45 ) can be produced. A method according to claim 10, characterized in that by means of the inner oval turning unit a trough bottom ( 14 . 24 . 34 . 44 ) and / or a trough edge ( 15 . 25 . 35 . 45 ) can be realized with an arbitrarily geometrically shaped free-form surface, shape or free-form contour, wherein the contour produced includes a three-dimensional shape with and without an undercut. A method according to claim 11, characterized in that by means of Innenovaldreheinheit at least one trough edge ( 15 . 25 . 35 . 45 ) in an arbitrarily designed freely programmable waveform can be produced. Method according to at least one of claims 9 to 12, characterized in that the machining of the piston ( 1 ) in the following steps: - producing a piston blank by a primary molding process such as a forging or casting process or an extrusion process; - machining of the piston blank by mechanical operations; - introducing the combustion chamber trough ( 13 . 23 . 33 . 43 ) in the piston head ( 2 ) in conjunction with the inner-oval-rotation unit; - Cleaning the piston of cooling lubricants and / or lubricants and adhering chips.

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