PISTON OF TWO-PIECE CONSTRUCTION FOR AN INTERNAL COMBUSTION ENGINE

Abstract

A piston for an internal combustion engine, configured as a gallery-cooled piston of two-piece construction includes a main body and a ring element. The ring element which has a ring zone and a fire land encloses a cooling gallery on the outside, which cooling gallery is delimited on the inside by an intermediate wall which separates the cooling gallery from a combustion chamber recess which is made in a piston head of the main body. The main body and the ring element together form two circumferential dividing planes which are offset with respect to one another, to which end in each case two interacting joining webs of the ring element and of the main body are connected with a material-to-material bond.

Description

BACKGROUND

The disclosure relates to a piston for an internal combustion engine, configured as a two-piece gallery-cooled piston that comprises a main body and a ring element.

A piston for internal combustion engines is exposed to high thermal stresses and high alternating mechanical stresses caused by gas and mass forces that require suitable dimensioning and design. Severely stressed zones of the piston, for example, the combustion bowl in the piston crown and the ring zone, require effective cooling. To this end it is known to integrate a cooling gallery in the piston. A cooling medium, such as the lubricating oil for the internal combustion engine, circulates through the cooling gallery cavity. The efficacy of piston cooling is determined. in particular, by the volume of cooling medium exchanged in the cooling gallery.

A two-piece piston is known from DD 123 962 A1 which includes a main body and a ring element. The separate, circular ring element, which includes comprises the top land and the ring zone of the piston and delimits the cooling gallery to the outside, is attached to the main body by means of a screw thread. The ring element is fixed in position in the installed state by means of dowels or threaded pins that are used between the main body and the ring element. U.S. Pat. No. 6,155,157 discloses a cooling gallery piston with two components that can be produced separately and then joined in a material-to-material bond using friction welding.

It would be desirable to create a two-piece cooling-gallery piston that includes a permanent connection of the individual components.

SUMMARY

A piston has the ring element and the main body jointly forming two circumferential dividing planes offset to each other to which end two respective corresponding interacting joining webs of the ring element and of the main body are joined in a material-to-material bond. The ring element is supported on dedicated joining webs of the main body through two joining webs positioned in different locations and offset in height. This design principle permits a piston construction with which a permanent joining of the individual piston components can be realized. At the same time, the concept has the advantage of optimizing the cooling gallery through appropriate design of the ring element to improve piston cooling and to realize a piston that can tolerate higher thermal loads.

Additionally, using this design, the construction or the design of the separate ring element, in particular with respect to wall thicknesses of individual piston sections, can be manipulated to reduce piston weight, for example. The possibility further exists of optimizing the top land, the ring zone or the ring carrier of the ring element. This construction offers the possibility of locating the dividing planes between the main body and the ring element in such a way that an optimal location results with respect to component strength and/or welding.

The piston design further offers the possibility of specially configuring the thermally and mechanically highly stressed ring element. The ring element including the top land and the ring zone for the piston rings can be optimized with respect to durability and wear resistance.

In accordance with one aspect of the piston, no defined position for the dividing planes is provided. The interacting, circumferential dividing planes can be advantageously configured in such a way that the dividing planes are both offset to each other and aligned diverging from each other.

Depending on the layout criteria, for example, optimal cooling gallery design, an optimized location for welding or taking strength into consideration, a piston can have matching or differently shaped dividing planes. Accordingly, the piston offers the opportunity of providing two dividing planes between the ring element and the main body, offset in height, of which one can run vertically and the other horizontally.

A piston, in another aspect, has at least one of the two dividing planes is aligned obliquely, or inclined. With two inclined dividing planes the dividing planes can run in the same direction or counter to each other. Advantageously there is no specification for the direction for the respective dividing plane. With dividing planes inclined in opposite directions, a centering effect of these components can continue to be used when the ring element and the main body are joined.

For a piston design with one vertical and one horizontal dividing plane, a vertically aligned dividing plane can be provided in the piston crown between the ring element and the main body and a horizontally aligned dividing plane can be provided below the ring zone of the ring element. A maximum vertical offset results between the two dividing planes with this piston construction.

In accordance with another aspect, the main body forms a circumferential step on the outside whose joining web running concentric to a longitudinal axis of the piston is enclosed by the joining web of the ring element to form a vertical dividing plane. In this aspect, the length of the dividing plane can be advantageously affected by the axial length of the step, or ledge, wherein this concept simultaneously brings about a centering effect on the components when they are joined.

Another aspect further provides for the matching, interacting joining webs of the ring element and of the main body to have constant wall thicknesses. The effect of joining webs with at least approximately identically dimensioned wall thicknesses is a desirable optimal equalization of tension, or distribution of tension in the piston upper part.

The piston furthermore offers the advantage of producing the ring element and the main body from an identical material or from different materials. A multi-piece piston provides this advantage, wherein the choice of material can be made with respect to the particular thermal and/or mechanical stress. The ring element can be produced from a hard wearing, specifically thermally stable material. In order to save weight, a less hard wearing material, a light alloy for example, can be chosen as the material for the main body.

A method is additionally proposed to produce a piston that includes the following steps. First of all, a main body and a ring element are produced separately as blanks. These components can be produced as forged or cast blanks, by stamping or pressing, from a semi-finished material of a steel material. As an alternative, extrusion, forging or casting is suitable for producing the main body and the ring element. The production process for the main body and the ring element includes forming the joining webs without reworking. The main body and the ring element can be produced from a matching material or from different materials. With the subsequent pre-machining, the combustion bowl and a piston pin bore can be introduced into the main body along with piston ring grooves in the ring belt of the ring element.

Then the main body and the ring element are joined until two respective matching joining webs abut and form two dividing planes offset to each other. The main body is joined to the ring element in a material-to-material bond by subsequent welding of the joining webs.

Different methods can be employed for the material-to-material bond of the main body and the ring element. Friction welding, or multi-orbital or multi-linear friction welding is can be used. Alternatively, electron beam welding, resistance press welding, condenser discharge welding or laser welding is suitable. Soldering can be used, in addition, for material-to-material joining of the matching joining webs. After the welding process is complete, the weld seams that have formed externally are removed. Final machining and cleaning of the piston follows as the last step.

BRIEF DESCRIPTION OF THE DRAWING

Additional features can be found in the following description and the drawings which show aspects of the present piston. Unless otherwise stated, identical or functionally identical components are given the same reference numerals.

FIG. 1 shows a first aspect of a piston in a sectional view;

FIG. 2 shows a second aspect of a piston in a sectional view;

FIG. 3 shows a third aspect of a piston in a sectional view;

FIG. 4 shows a fourth aspect of a piston in a sectional view.

DETAILED DESCRIPTION

FIG. 1 shows a sectional view of a piston 1 produced as one piece comprising a main body 2 and a ring element 3 that are connected by joining webs 6a, 6b; 7a, 7b forming dividing planes 4a, 5a. The joining webs 6a, 6b; 7a, 7b are joined in a material-to-material bond in the area of the dividing planes 4a, 5a by means of friction welding.

For example, multi-orbital friction welding is employed in which, because of the extremely small, circular orbital movements, no, or only minor, weld beads 8, 9 are formed in the area of the dividing planes 4a, 5a that require no, or only minor, reworking. The wall thickness S1, S2 of the joining webs 6a, 6b and the joining webs 7a, 7b is can be constant as far as possible. A maximum height offset H results between the vertically aligned dividing plane 5a and the horizontally running dividing plane 4a. The main body 2 of the piston 1 includes a combustion bowl 12 introduced into a piston crown 10 eccentric or rotationally symmetrical to a longitudinal axis 11. A piston skirt 13 of the main body 2 includes two diametrically opposed piston pin bores 4 that are intended to receive a piston pin (not shown). An intermediate wall 16 surrounding the combustion bowl 12 delimits a cooling gallery 15 on the inside that is enclosed on the outside by the ring element 3. The cooling gallery 15 is closed circumferentially by the main body 2 with the ring element 3 after welding has been performed. When the engine is operating, a cooling medium can be selectively applied to the cooling gallery 15 through at least one inlet and one outlet (not shown). The ring element 3 has a top land 17 on the piston crown side to which a ring belt 18 is attached with ring grooves 19 that are intended to receive piston rings (not shown).

FIGS. 2 to 4 show alternative aspects of the piston 1, wherein matching reference numerals are used for identical or identically functioning components. The following descriptions of FIGS. 2 to 4 are largely limited to differences in features compared with FIG. 1.

In accordance with FIG. 2, the piston 1 includes two vertically aligned dividing planes 4b, 5a between the main body 2 and the ring element 3. Dividing plane 4b is formed by a step 20 of the main body 2 that is enclosed on the outside by an end section of the ring element 3. An overlapping area of the joining webs 7a, 7b of the interacting components, the main body 2 and the ring element 3, defines the dividing plane 4b.

FIG. 3 illustrates shows the piston 1, the construction of which largely matches the illustration in FIG. 2. The piston 1 in FIG. 3 shows, in addition to the dividing plane 4b from FIG. 2, the horizontally running dividing plane 5b assigned to the intermediate wall 16 said planes being formed by the joining webs 21a, 21b. If the components forming the piston 1 are joined axially, the step 20 of the main body 2 can be used to center the ring element 3.

The piston 1 in FIG. 4 comprises two inclined, or oblique, dividing planes 4c, 5c between the main body 2 and the ring element 3. As an alternative to dividing planes 4c, 5c from FIG. 4 that run on a matching incline, it is possible that the dividing planes 4c, 5c run counter to each other.

Claims

1. A piston for an internal combustion engine configured as a cooling-gallery piston of two-piece construction that includes a main body and a ring element, wherein the ring element with a ring belt and a top land encloses on the outside a cooling gallery delimited on the inside by an intermediate wall dividing the cooling gallery from a combustion bowl introduced into a piston crown of the main body and the ring element is joined in a material-to-material bond to the main body characterized in that the main body and the ring element jointly form two circumferential dividing planes offset to each other, to which end two matching, interacting joining webs of the ring element and the main body are joined in a material-to-material bond.

2. The piston from claim 1, wherein the dividing planes run between the ring element and the main body diverging from one another or matching vertically or horizontally.

3. The piston from claim 1, wherein the dividing planes are aligned obliquely or inclined.

4. The piston from claim 1 wherein a vertically aligned dividing plane and a horizontally aligned dividing plane are provided between the ring element and the main body.

5. The piston from claim 4, wherein a height offset H results between the vertically aligned dividing plane assigned to the piston crown and the horizontally aligned dividing plane.

6. The piston from claim 1, wherein the main body forms a circumferential step on the outside whose joining web running concentric to the longitudinal axis of the piston is enclosed at least in sections by the joining web of the ring element.

7. The piston from claim 1, wherein the matching joining webs of the ring element and the main body are dimensioned at least approximately equal.

8. The piston from claim 1, wherein the main body and the ring element are produced from a matching material or from different materials.

9. A method for producing a piston for an internal combustion engine, configured as a cooling-gallery piston of two-piece construction including a main body and a ring element , characterized by producing a main body and a ring element as blanks by forging or casting or by stamping from a semi-finished material from a steel material; pre-machining the main body and the ring element including introducing a combustion bowl into the main body and creating a ring belt;joining two matching joining webs of the main body and the ring element, which respectively form a dividing plane, by a material-to-material bond; andfinal finish machining of the piston.