Piston for an internal combustion engine

Abstract

A piston for an internal combustion engine may include an encircling ring section in a region of a piston crown. The piston may include a convection region, which has at least one cavity containing a heat transfer medium for dissipation of heat from the piston crown to an underside of the piston. The piston may include a heat insulating region, which is arranged between the ring section and the convection region and thermally insulates the ring section.

Claims

1. A piston for an internal combustion engine, comprising: an encircling ring section in a region of a piston crown; a convection region having at least one cavity with an inner duct and configured to contain a heat transfer medium including liquid metal for dissipation of heat from the piston crown to an underside of the piston; and a heat insulation region with an outer duct radially outward and fluidically separated from the inner duct for liquid metal and arranged between the ring section and the convection region to thermally insulate the ring section, wherein the inner duct for liquid metal is arranged is radially inside the outer duct.

2. The piston according to claim 1, wherein the inner duct for liquid metal is concentric to the outer duct.

3. The piston according to claim 2, wherein the outer duct and the inner duct for liquid metal are fluidically separated from one another by a dividing wall, wherein the dividing wall is constructed an integral component of the piston.

4. The piston according to claim 3, wherein the dividing wall, with a separate construction fluidically separating the outer duct and the inner duct for liquid metal, includes at least one of spring steel and plastic.

5. The piston according to claim 3, wherein: the piston is a composite piston and includes a piston upper part, a piston lower part and the dividing wall, or the piston is a composite piston and includes a piston upper part, a piston lower part and a ring section part.

6. The piston according to claim 5, wherein the dividing wall is fixed by clamping.

7. The piston according to claim 6, wherein the dividing wall is arranged obliquely to a piston axis.

8. The piston according to claim 7, wherein the dividing wall has a cross-section of a plate spring and has a smaller diameter in a region of the piston crown than in a region of the underside.

9. The piston according to claim 6, wherein the dividing wall has angled edge regions via which the dividing wall rests on the piston.

10. The piston according to claim 3, wherein the dividing wall is arranged obliquely to a piston axis.

11. The piston according to claim 10, wherein the dividing wall has a cross-section of a plate spring and has a smaller diameter in a region of the piston crown than in a region of the underside.

12. The piston according to claim 3, wherein the dividing wall has angled edge regions, via which the dividing wall rests on the piston.

13. The piston according to claim 3, wherein the dividing wall is formed from at least one of a spring plate, a polyimide and polyetheretherketone (PEEK).

14. The piston according to claim 1, wherein the piston is at least one of steel and a light metal.

15. The piston according to claim 1, wherein the piston is produced by a casting process, and the dividing wall is constructed as an insert part.

16. The piston according to claim 1, wherein the liquid metal is introduced into the inner duct as a paste or solid material.

17. The piston according to claim 16, wherein the liquid metal includes at least one of sodium, potassium and an alloy containing at least one of sodium and potassium.

18. A piston for an internal combustion engine, comprising: a piston crown having an encircling ring section for receiving piston rings, the piston crown having an outer duct in a region of the ring section and an inner duct arranged radially inside the outer duct and concentric to the outer duct; a heat-insulating material arranged in the outer duct for thermally insulating the ring section; a heat transfer medium including liquid metal enclosed in the inner duct for dissipation of heat from the piston crown to an underside of the piston by convection; and a dividing wall fluidically separating the outer duct from the inner duct for liquid metal, wherein the dividing wall is arranged obliquely to a piston axis such that the dividing wall has a smaller diameter in the region of the piston crown than in a region of the underside.

19. The piston according to claim 18, wherein the heat-insulating material includes at least one of air and a metal foam.

20. The piston according to claim 18, wherein in the dividing wall is at least one of a spring steel, a polyimide and polyetheretherketone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) There are shown, respectively diagrammatically,

(2) FIG. 1 a sectional illustration through a piston according to the invention with a dividing wall between an outer and an inner duct, which forms an integral component of the piston,

(3) FIG. 2 an illustration as in FIG. 1, but with a dividing wall as a separate structural part,

(4) FIG. 3 an illustration as in FIG. 2, but with an obliquely positioned dividing wall,

(5) FIG. 4 an illustration as in FIG. 3, but with a composite piston.

DETAILED DESCRIPTION

(6) According to FIGS. 1 to 4, a piston 1 according to the invention for an internal combustion engine which is otherwise not illustrated has an encircling ring section 2 in the region of a piston crown 3 and an encircling outer duct 4 in the region of the ring section 2, and an inner duct 5 arranged coaxially thereto. According to the invention, the outer duct 4 is now constructed as a heat insulator and insulates accordingly the ring section 2 thermally from the inner duct 5 and a piston bowl 6, also designated combustion chamber bowl, whereas the inner duct 5 is constructed as a cooling duct and contains a heat transfer medium for the dissipation of heat from the piston crown 3 to the piston underside 7 of the piston 1.

(7) The outer duct 4 and the inner duct 5 are separated from one another here by a dividing wall 8, wherein this dividing wall can be constructed as a separate structural part, as is illustrated in particular in FIGS. 2 to 4, or wherein this dividing wall 8 forms an integral component of the piston 1, as is illustrated according to FIG. 1. In the case of a separate construction of the dividing wall 8, the latter can be constructed for example from spring steel, in particular from spring plate, or from plastic, in particular from polyimide (PI) or polyetheretherketone (PEEK). Especially the construction from plastic offers a weight advantage, which is not to be underestimated, and the advantage of the low thermal conductivity, which in addition contributes to thermally uncoupling the ring section 2 from the piston bowl 6 or respectively from the piston crown 3.

(8) Generally, the piston 1 can be constructed for example as a single-piece piston 1, wherein in this case the outer duct 4 and the inner duct 5 are formed by corresponding salt- or respectively sand cores, wherein alternatively it is also conceivable that the dividing wall 8 is introduced as an insert part in these salt or respectively sand cores. Alternatively hereto, the piston 1 can also be constructed as a composite piston and can comprise a piston upper part 9, a piston lower part 10 and the dividing wall 8 (cf. FIG. 4). The piston upper part 9 and the piston lower part 10 are welded to one another here, for example via welding points 11, wherein the dividing wall 8 is likewise fixed by a welded connection or else by a simple clamping.

(9) Alternatively hereto, the piston 1 can likewise be constructed as a composite piston and can comprise a piston upper part 9, a piston lower part 10 and a ring section part 12, as is illustrated for example according to FIG. 1. In this case, the piston upper part 9 and the piston lower part 10 are now welded to one another via first welding points 11, and the ring section part 12 with the piston upper part 9 and with the piston lower part 10 via second welding points 11′, wherein the dividing wall 8 forms an integral component of the piston lower part 10.

(10) The piston 1 can generally be produced as a steel piston or as a light metal piston, in this case in particular from aluminium. In this case, the piston 1 is produced by a casting process, wherein the dividing wall 8 can be constructed either as a separate insert part or else as an integral component of the piston 1.

(11) Preferably a heat-insulating material, in particular air or, for example, a metal foam, is arranged in the outer duct 4, whereas a heat transfer medium, for example a liquid metal, in particular sodium, potassium or an alloy containing sodium and/or potassium, is enclosed in the inner duct 5. The sodium- or potassium alloy in the inner duct 5 can be introduced for example as a paste or solid material and can become liquid owing to the lower melting point during the operation of the internal combustion engine. Here, in particular, the eutectic alloy with a potassium component of 78% and a melting point of −11° C. is favourable for an optimum heat transfer. NaK alloys are liquid in a wide range of their mixture ratio at room temperature and in any case at conventional operating temperatures of the piston of an internal combustion engine. A liquid heat transfer medium can be filled into the cooling duct through an opening provided for this, which opening can subsequently be closed e.g. by welding or pressing in of a steel ball with an interference fit. A heat transfer medium which is solid at room temperature but liquid at operating temperature can advantageously be introduced into the cooling duct already during the manufacture of the piston e.g. by friction welding and enclosed there, whereby a subsequent filling and closing of the cooling duct is avoided.

(12) The dividing wall 8 can be aligned, furthermore, parallel to the piston axis 13, as is illustrated for example according to FIGS. 1 and 2, or else obliquely thereto, as is illustrated for example according to FIGS. 3 and 4. In the case of a dividing wall 8 aligned obliquely to the piston axis 13, this dividing wall has a cross-section in the manner of a plate spring and has a smaller diameter in the region of the piston crown 3 than in the region of the underside 7. On a downward movement of the piston 1, therefore, the heat transfer medium, for example sodium or potassium, is directed along the dividing wall 8, whereby the latter is cooled and therefore the thermal uncoupling of the ring section 2 is promoted. On an upward movement of the piston 1, on the other hand, the heat transfer medium, which has now received heat from the piston crown 3 and the piston bowl 6, arrives in a direct path to the piston underside 7, where it is cooled by a spray cooling, for example by oil. This brings about a particularly effective cooling.

(13) The dividing wall 8 can have, moreover, angled edge regions 14, 14′, via which it rests on the piston 1 (cf. in particular FIGS. 2 to 4). The dividing wall 8 therefore forms a heat barrier, which in particular prevents the ring section 2, and hence also the piston rings 15 arranged thereon (cf. FIG. 2), from becoming too hot, which would bring about, for example, a carbonisation of the oil and hence, in turn, a poorer heat transfer between the cylinder wall and the ring section 2. A poor heat transfer between the cylinder wall and the piston rings 15, and therefore the piston 1, brings about an excessive thermal stress in particular of the ring section 2 and can lead, in so doing, to an overheating of the piston rings 15. A welding of the individual parts 9, 10 and 12 of the piston 1 can take place for example by means of laser welding or friction welding.

(14) With the piston 1 according to the invention, and in particular with the thermally separated ring section 2, a particularly effective cooling and hence a high efficiency and a high durability of the piston 1 can be achieved.