EP1483493B1 - Multi-part, cooled piston for an internal combustion engine - Google Patents

Description

The invention relates to a multi-part cooled piston for a Internal combustion engine, consisting of an integrally formed piston upper part, comprising a combustion bowl and a ring wall with ring portion, and an integrally formed piston lower part, which is a box-shaped Piston shaft, hubs for receiving the piston connecting the piston with the connecting rod Piston pins and hub supports connected to the piston skirt, comprising, wherein a cooling channel through the piston upper part and piston lower part is formed and limited in its cross section by this.

Such generic pistons are for example from DE-PS 800 350, DE-OS 2 212 922, EP 0 604 223 A1, Jp 60-143148, Jp 60-178345 known. These Pistons have essentially central screw connections and thus have the known disadvantages of so-called built piston, in which by punctiform connection of piston upper and lower part under the Combustion pressure a relative movement causing the wear between arises two piston components. To the advantage of this piston, in particular by the connection wear-resistant piston upper parts made of light metal existing piston bottoms arises without the aforementioned disadvantage in purchase In the past, the glands were in the outer Flange edge area laid, such as from FR 753,615 or US 2,159,989. Generally, these are known from the 30's Constructions are not comparable with the concepts of modern pistons, as these are for significantly lower combustion chamber pressures were designed. In addition, you can Combustion wells are not possible in such constructions.

From the DD123 962 a piston is further known in which a wear-resistant Piston ring field is generated by a piston body with a Flank and the ring field or part of the ring field forming Annular ring element made of any suitable material mechanically connected - screwed here - and secured against loosening. The disadvantage, however, is that only the ring field consists of seal-proof material and high Compression pressures are not feasible with low piston height.

In addition to the central or decentralized screw connection as a combination of Piston parts, which are made of different materials, are also Welding known, such as the friction welding method from the WO 00/06882. Piston top and bottom parts can thus relatively easily welded become. However, the disadvantages are the changes caused by the weld in the material structure, which lead to stress cracks and even more disadvantageous but by the limitation in the choice of materials for the parts to be joined.

The invention therefore deals with the problem of a piston concept for a multi-piece cooled piston for an internal combustion engine to be found at increasing engine power a reduction in compression height and a Increasing the heat load allowed and that one assembly of the piston without structural change allows.

This problem is solved in the generic piston by the features of claim 1. According to this solution, the piston upper part and the Piston base support means with bearing surfaces on which a first and second edition form, wherein the first edition comprehensive support means of Kolbenober- and Unterteilils thread for screwing both piston parts have. in the bolted state of the piston upper part with the piston lower part are both Piston parts supported only on the first and second edition. The result achieved mechanical stability is due to a welded piston part joint superior to avoiding internal tensions. In particular, this stability by the arrangement of the supports with respect to the piston diameter thereby achieved that the first edition arranged radially inward and the second radially outward is and that these requirements in different planes with respect to the piston height are arranged so that an effective inner and outer support is achieved. According to the invention, a part of the support means, as ring and annular Support rib are formed, a thread for screwing the piston parts, wherein the annular rib is designed in its wall construction such that this elastic deformation due to the force exerted on the piston crown Combustion chamber pressure is possible without the stability of the screw connection too Reduce. In particular, it is advantageous by the positional arrangement of the support means, the over the piston longitudinal axis in the radial direction to the piston skirt surface Outgoing radii are defined, the power flow from the piston crown over the Support means on the hub supports or piston pin effectively without Overload of the piston material derived. Damage due to mechanical Stress, such as stress cracks, are thus effectively avoidable. Of Furthermore, the inventive construction has the advantage that the centering the upper piston part to the lower piston part is not performed by the screw, but by wall portions of a stepped formation of the support means, which forms the second, ie outer, support. By the solution according to the invention are piston tops made of heat-resistant steel and piston bases, consisting of Forged AFP steel, particularly easy and inexpensive connectable.

Fig. 1 einen erfindungsgemäßen Kolben im Querschnitt, geschnitten in Bolzenrichtung;

Fi. 2 einen erfindungsgemäßen Kolben im Querschnitt, geschnitten in Druck-Gegendruck-Richtung;

Fig. 3 einen vergrößerten mittels Kreis gekennzeichneten Ausschnitt aus Fig.1.

Advantageous developments are the subject of the dependent claims. The invention will be explained in more detail below with reference to an embodiment. It shows:

1 shows a piston according to the invention in cross-section, cut in the bolt direction.

Fi. FIG. 2 shows a piston according to the invention in cross-section, cut in the pressure-backpressure direction; FIG.

3 shows an enlarged section marked by a circle from FIG.

The multi-part cooled piston 20, as shown in FIG. 1, consists of a Piston upper part 1, which has a combustion bowl 3 and an annular wall 4 with Ring part 11 comprises, and a piston lower part 2, comprising a box-shaped piston shaft 9, hubs for receiving the piston with the Connecting rod connecting piston pin (not shown) and hub supports 6, the are connected to the piston shaft 9. A cooling channel 7 is through the Upper piston part 1 and piston lower part 2 formed and in its cross section through these are limited.

The piston upper part 1 has support means, which consists of one of the combustion bowl. 3 facing away from the bottom side annular bearing surface 10a, a part the horizontal cross-sectional area 12a of the annular wall 4 and of an annular rib fifth consists. At the lower piston part 2 support means are also provided which consist of a annular support rib 13, the cross-sectional area 10b of the support rib 13 and a annular support web 14 consist. To form a first level and horizontal support 10 for both piston parts 1, 2 serve the annular Support surface 10 a and the cross-sectional area 10 b of the annular support rib 13, wherein the Auflage10 relative to the piston diameter D radially inward is arranged and forms an inner support. A second, level and horizontal arranged support 12 for both piston parts consists of the horizontal part of the Cross-sectional area 12a of the annular wall 4 and the cross-sectional area 12b of the annular support web 14, so that a step-shaped design of the support web 14th arises, through which the piston upper part is centered. Essentially serves for Centering of the wall portion 4a (Figure 2) of the annular wall 4, with its Cross-sectional area in the axial direction to the piston shaft 9 forms an air gap, such as from Fig. 1 and Fig. 2 can be seen. The first and second edition is related to Piston height in each case different horizontal planes E1 and E2 arranged, which are characterized by the height H.

A thread 8 for screwing piston upper part 1 and lower piston part 2 is on the radially outward circumferential side relative to the piston diameter the annular rib 5 as an external thread and at the radially inward Peripheral side of the annular support rib 13 designed as an internal thread. As can be seen from Fig. 3, the pin boss facing annular rib 5 in axial Piston direction an at least partially cylindrical or conical shaped Section 13a, which carries the thread and runs parallel to the piston axis (K), wherein the cylindrical or conical shaped portion 13a of the annular rib a Section 13b in the direction of combustion chamber 3 with reduced wall thickness follows. Thus, an elastic region is generated, which by the combustion chamber pressure absorb generated mechanical stresses and on the piston pin can derive.

The thread-bearing peripheral side of the annular rib 5 has a radius R _sheath (R _M ), which is in a range R coat <R Center of the hub support (R MN ) and R coat > R Inner end of the hub support (R IEM ) is arranged, wherein all radii are defined from the piston longitudinal axis (K) in the radial direction to the piston skirt surface and the radii "center of the hub support" and "inner end of the hub support" to the zenith of the hub bore (N _Z ) are related, as shown in FIG 1 and 2 are shown.

The assembly of both piston parts is carried out in the means of relating to Supporting rib 13 projecting wall portion 4a, the piston upper part 1 to Centered piston lower part 2 and then screwed onto the piston lower part becomes. The height H (distance of the planes E1, E2) of the first to the second edition 10, 12th is designed so that by a height difference of about 50 microns first the outer bearing surfaces 12a, 12b touch and after another rotational movement to overcome the height difference, the inner bearing surfaces 10a, 10b, so in the fully bolted state of the piston upper part 1 with the Piston lower part 2 resulting cooling channel 7 only by the support surfaces 10a, 10b, 12a, 12b is sealed. Due to the large diameter is the thread self-locking. In addition, however, a clamping sleeve below the 3rd groove, the radial is attached, be provided.

The piston upper part 1 may be made of an oxidation-resistant and / or heat-resistant Material exist. Typically, steels with chromium contents are used ≥ 4% from the material groups of chemically resistant steels acc. din EN 10027-2 (steel group numbers 1.4x xx) such as stainless, heat resistant or heat-resistant steels, as well as from the material group of alloyed Tool steels, such as alloyed hot-work tool steels.

The piston lower part consists of a precipitation-hardening ferritic-pearlitic Steel or tempered steel, typically steel grades 38MnVS6 or 42CrMo4 be used (according to German steel-iron material sheet 101).

reference numeral

Multi-piece cooled piston

20

Piston crown

1

Piston part

2

combustion bowl

3

ring wall

4

Wall area of the ring wall

4a

annular rib

5

boss support

6

cooling channel

7

thread

8th

piston shaft

9

first edition

10

Support surface piston upper part

10a

Support surface piston lower part

10b

ring belt

11

ring groove

11 a

second edition

12

Support surface piston upper part

12a

Support surface piston lower part

12b

supporting rib

13

Cylindrical section of the support rib

13a

not cylindrical. Section of the support rib

13b

carrying web

14

levels

E1, E2

Height difference from the first to the second support plane

H

piston longitudinal axis

K

boss zenith

N _Z

Claims (11)

1. A multi-part cooled piston for an internal combustion engine, comprising a piston upper part having a combustion bowl and an annular wall with a piston-ring part, a piston lower part having a box-like piston shank, bosses to receive piston pins joining the piston to a connecting rod and boss supports, which are joined to the piston shank, a cooling channel being formed by the piston upper part and the piston lower part and being limited thereby in cross section, the piston upper part (1) and piston lower part (2) comprising support elements (4, 5, 8, 13, 14), having seating faces (10a, 10b, 12a, 12b) which form a first and a second seat (10, 12), characterised in that the support elements (5, 8, 13), comprising the first seat (10), of the piston upper and piston lower part are provided with threads (8) for screwing the piston upper and lower parts together, so that in a screwed together condition of the piston upper part and piston lower part, the two piston parts are supported exclusively via the first and second seats (10, 12), in that the first seat (10) is arranged approximately centrally relative to the annular part (11) and the second seat (12) is arranged below the annular part (11) and in that the screw connection is arranged approximately centrally within a region defined by R_{outer surface} < R_{centre of boss support} (R_MN) and R_{outer surface} > R_{inner end of boss support} (R_IEM), all radii being defined as starting from the axis of the piston (K) in a radial direction relative to the circumferential face and the "centre of boss support" and "inner end of boss support" radii corresponding to the zenith of the boss bores (N_Z).
2. A multi-part cooled piston according to claim 1, characterised in that the first and second seats (10, 12) are disposed in respectively different horizontal planes (E1, E2) relative to the piston height.
3. A multi-part cooled piston according to claim 1 and claim 2, characterised in that the first seat (10) is disposed radially inward relative to the piston diameter and forms an inner support for the piston upper part, and the second seat (12) is disposed radially outward relative to the piston diameter and forms an outer support for the piston upper part.
4. A multi-part cooled piston according to claim 1, characterised in that the support elements of the piston upper part (1) comprise the seating face (10a) disposed on a bottom side remote from the combustion bowl, a part of a horizontal cross-sectional face (12a) of the annular wall (4) and an annular rib (5), and in that the support elements of the piston lower part (2) comprise an annular load-bearing rib (13), the cross-sectional face (10b) of the load-bearing rib (13) as well as an annular load-bearing ridge (14) with its cross-sectional face.
5. A multi-part cooled piston according to claim 1 and claim 4, characterised in that the thread (8) for screwing the piston upper part and piston lower part together is configured as a male thread on the circumferential side of the annular rib (5) disposed radially outward relative to the piston diameter and is configured as a female thread on the circumferential side of the annular load-bearing rib (13) disposed radially inward.
6. A multi-part cooled piston according to claim 4, characterised in that the annular rib (5), extending toward the pin boss in an axial piston direction, comprises an at least partly cylindrical or conical portion (13a), which is threaded and oriented parallel to a piston axis (K).
7. A multi-part cooled piston according to claim 6, characterised in that the cylindrical or conical portion (13a) of the annular rib (5) follows a portion in the direction of the combustion bowl having reduced wall thickness.
8. A multi-part cooled piston according to claim 4, characterised in that the seating faces of the first seat (10) comprise the seating face (10a) disposed on a bottom side remote from the combustion bowl (3) and the cross-sectional face (10b) of the annular load-bearing rib.
9. A multi-part cooled piston according to claim 1, characterised in that the second seat (12) consists of a part of the entire cross-sectional face of the annular wall and of the cross-sectional face (12b) of the annular load bearing ridge (14), so that a stepped configuration of the load-bearing ridge (14) is obtained, by which the piston upper part (1) is centred.
10. A multi-part cooled piston according to claim 1, characterised in that the cooling channel (7), which is formed when the piston upper part (1) is screwed to the piston lower part (2), is sealed exclusively by the seating faces (10a, 10b, 12a, 12b).
11. A multi-part cooled piston according to claim 1, characterised in that the piston upper part (1) consists of an oxidation-resistant and/or heat-resistant material and in that the piston lower part (2) consists of a precipitation-hardening ferritic-perlitic steel or tempering steel.

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