PISTON FOR AN ENGINE

Description

[0001] The invention relates to a piston for an internal combustion engine.

[0002] In conventional internal combustion engines, the pistons are made of aluminum or steel. Although these two materials differ significantly in thermal conductivity, the effective heat dissipation is very similar in a direct comparison between the two materials. One explanation for this phenomenon may be that the heat transfer coefficient from the flame to the combustion chamber surface depends on the respective wall temperature. Thus, while the steel piston has a higher wall temperature than the aluminum piston, the heat transfer coefficient and heat flow also increase.

[0003] DE 38 14 427 A1 discloses a reciprocating piston internal combustion engine with compression ignition, in which, for at least some of the walls defining the combustion chamber, heat is dissipated to the material surrounding the walls via thermal bridges provided between the walls and the surrounding material. The thermal bridges are at least partially interrupted by the formation of air gaps during the warm-up phase and during partial load operation of the internal combustion engine in order to increase the temperature.

[0004] US 4,018,194 A discloses a piston for an internal combustion engine having a top surface forming part of a combustion chamber. The piston is provided with a cavity or deep recess in the top surface to promote fuel-air mixing and improve the combustion process in the combustion chamber. The cavity is formed in a cup-shaped insert positioned in the piston body such that the cup-shaped insert is substantially spaced or insulated from the piston body, thereby avoiding or minimizing heat losses at the piston walls.

[0005] US 2008 / 0041333 A1 discloses a piston for an internal combustion engine, comprising an upper crown with an upper and a lower surface, and a lower crown with an upper and a lower surface. The upper crown and the lower crown are firmly connected by welds, with the underside of the upper crown and the upper side of the lower crown forming a mating surface. The piston also has at least one air gap formed centrally on the mating surface. The air gap is sealed to prevent airflow into or out of the air gap.

[0006] DE 19 39 435 A1 discloses a bowl-shaped piston for internal combustion engines, particularly made of aluminum or an aluminum alloy, which has gaps in the area of ​​its bowl to reduce heat dissipation. The bowl is lined with a highly heat-resistant sheet metal, which leaves the gap open opposite the bowl wall.

[0007] For further relevant prior art, reference is made to DE 25 45 589 A1, WO 85 / 01314 A1, WO 2017 / 146598 A2 and US 1 506 252 A.

[0008] The invention is based on the object of creating an alternative and / or improved piston for an internal combustion engine.

[0009] The problem is solved by the features according to independent claim 1. Advantageous further developments are specified in the dependent claims and the description.

[0010] The invention provides a piston for an internal combustion engine (e.g., a diesel direct-injection internal combustion engine and / or a reciprocating piston internal combustion engine). The piston has a piston crown, preferably for defining a combustion chamber of the internal combustion engine on the piston side. The piston has a cover that at least partially covers the piston crown (e.g., a piston recess of the piston crown), preferably on the combustion chamber side. A heat-insulating gap, preferably an air gap, is formed between the cover and the piston crown and is in (e.g., direct and / or indirect) fluid communication with the combustion chamber and / or an upper side of the cover facing away from the heat-insulating gap.

[0011] The cover prevents a flame front from at least partially touching the piston crown during combustion in the combustion chamber. The heat-insulating gap forms a barrier that reduces heat conduction from the combustion chamber to the piston crown. This means that the surface temperature of the piston crown does not increase as much as in conventional pistons without a cover. Due to the reduced surface temperature of the piston crown, there is also a reduced heat transfer coefficient from the combustion chamber to the piston. Consequently, the piston does not need to be cooled as much. The fluid connection to the heat-insulating gap also enables fluid exchange between the heat-insulating gap and the combustion chamber. This can reduce the pressure gradient between the combustion chamber and the heat-insulated gap.This allows the cover to be designed to be thin without deforming during combustion. This has the advantage that the thinner the cover, the less heat it can absorb during combustion. The less heat the cover absorbs during combustion, the less heat it releases to the charge air during the charge cycle. This reduces the engine's delivery efficiency to a lesser extent.

[0012] The piston crown can expediently be a region of a main body of the piston, for example a cast or printed one.

[0013] Preferably, the cover may be formed separately from a main body of the piston.

[0014] It is possible that the piston crown of the piston is cooled by cooling channels in the piston below the piston crown.

[0015] In one embodiment, the fluid connection is designed to enable pressure approximation and / or pressure equalization between the combustion chamber and the heat-insulating gap.

[0016] In a further embodiment, a pressure on the top side of the cover and a pressure on a back side of the cover facing the heat-insulating gap are approximated and / or substantially equalized by the fluid connection during operation of the internal combustion engine.

[0017] In a further embodiment, the cover is arranged such that it separates a flame front from the piston crown, preferably a piston recess of the piston crown, during combustion in the combustion chamber.

[0018] In a further embodiment, the fluid connection is arranged at a distance from a fuel injection jet impact area of ​​the cover.

[0019] The fuel injection jet impact area of ​​the cover can expediently be formed by a peripheral edge of an annular shoulder of a piston recess of the piston crown.

[0020] For example, the fluid connection can be arranged above and / or below the fuel injection jet impact area.

[0021] In a further embodiment, the fluid connection is at least partially formed by at least one annular gap between the piston crown and the cover.

[0022] Preferably, the at least one annular gap can have a width between greater than or equal to 0.5 mm and / or less than or equal to 2 mm, preferably approximately 1 mm.

[0023] In one embodiment, the fluid connection is formed at least partially by an annular gap between an outer peripheral edge of the cover and the piston crown.

[0024] For example, the annular gap between the outer peripheral edge of the cover and the piston crown can be arranged above a fuel injection jet impact area of ​​the cover.

[0025] The annular gap between the outer peripheral edge of the cover and the piston crown can expediently be arranged in a radial direction spaced outwards from a fuel injection jet impact area of ​​the cover, preferably coaxial to the fuel injection jet impact area.

[0026] It is possible that the annular gap between the outer peripheral edge of the cover and the piston crown is arranged on an upper side of the piston.

[0027] In a further embodiment, the fluid connection is formed at least partially by an annular gap between an inner peripheral edge of the cover and the piston crown.

[0028] For example, the annular gap between the inner peripheral edge of the cover and the piston crown can be arranged below a fuel injection jet impact area of ​​the cover.

[0029] The annular gap between the inner peripheral edge of the cover and the piston crown can expediently be arranged in a radial direction spaced inwards from a fuel injection jet impact area of ​​the cover, preferably coaxial to the fuel injection jet impact area.

[0030] In a further embodiment, the fluid connection is formed at least partially by at least one through-hole and / or at least one through-slot of the cover.

[0031] Advantageously, several through holes and / or several through slots can be arranged, preferably symmetrically, distributed in the cover.

[0032] In a further development, a plurality of through holes and / or through slots are included, which are preferably arranged at a distance from a fuel injection jet impact area of ​​the cover, preferably above and / or below the fuel injection jet impact area of ​​the cover.

[0033] For example, the at least one through-hole may have a diameter between 0.5 mm and 5 mm or more.

[0034] In one embodiment, the heat-insulating gap has a height greater than or equal to 0.5 mm and / or less than or equal to 2 mm, preferably approximately 1 mm.

[0035] In a further embodiment, the heat-insulating gap has a substantially constant height.

[0036] According to the invention, the piston crown has a piston bowl, and the cover is arranged at least partially in the piston bowl, preferably to at least partially cover the piston bowl, and / or is adapted to the piston bowl. The cover can expediently be designed as a piston liner and / or a piston bowl insert.

[0037] According to the invention, the piston recess has a central elevation and the cover extends annularly around the central elevation or the cover covers the central elevation.

[0038] In a further embodiment, the fluid connection is formed at least partially by an annular gap between an outer peripheral edge of the piston bowl and an outer peripheral edge of the cover. According to the invention, the fluid connection is formed at least partially by an annular gap between an inner peripheral edge of the cover and a central elevation of the piston bowl.

[0039] In one embodiment, a cross-sectional contour of the cover follows a cross-sectional contour of the piston recess, preferably at a substantially constant distance.

[0040] In a further embodiment, the piston recess is designed as an omega recess and / or a stepped recess, preferably with a central elevation, and the cover has at least partially an omega-shaped and / or stepped cross-section.

[0041] In one embodiment, the cover is formed as a sheet metal. The sheet metal can preferably have a substantially constant thickness. Alternatively or additionally, the sheet metal can have a thickness greater than or equal to 0.5 mm and / or less than or equal to 2 mm, preferably approximately 1 mm.

[0042] In a further embodiment, the cover is welded to the piston crown, preferably a piston recess of the piston crown, preferably by means of spot welding and / or friction welding.

[0043] The invention also relates to a motor vehicle, preferably a commercial vehicle (for example a truck or bus), comprising a piston as disclosed herein.

[0044] It is also possible to use the device as disclosed herein for passenger cars, large engines, off-road vehicles, stationary engines, marine engines, etc.

[0045] The above-described preferred embodiments and features of the invention can be combined with one another as desired. Further details and advantages of the invention are described below with reference to the accompanying drawings. They show: Figure 1a cross section through a piston top of a piston according to an embodiment of the present disclosure; and Figure 2 a cross section through a piston top part of a piston according to a non-inventive example of the present disclosure

[0046] The embodiments shown in the figures correspond at least partially, so that similar or identical parts are provided with the same reference numerals and for their explanation reference is also made to the description of the other embodiments or figures in order to avoid repetition.

[0047] The Figure 1shows an upper part of a piston 10. The piston 10 can be incorporated in an internal combustion engine. The internal combustion engine can be, for example, a diesel, gasoline, and / or gas-fuel internal combustion engine. Preferably, the internal combustion engine can be a diesel internal combustion engine with direct injection. The internal combustion engine can be incorporated in a vehicle, e.g., a motor vehicle, rail vehicle, or watercraft, or a stationary system, e.g., for driving a generator or other unit. Preferably, the internal combustion engine can be incorporated in a commercial vehicle, e.g., a truck or a bus.

[0048] The piston 10 is arranged in a manner not shown in detail so as to be movable back and forth within a cylinder of the internal combustion engine, preferably by means of a connecting rod that connects the piston 10 to a crankshaft in an articulated manner. The piston 10 defines a combustion chamber 12 of the cylinder.

[0049] The piston 10 has a piston crown (also called a piston top) 14. The piston crown 14 forms a combustion chamber-side upper surface of a main body 16 of the piston 10, for example, a cast or printed one.

[0050] The piston 10 can have one or more cooling channels 18 for cooling the piston crown 14. A cooling fluid, for example, oil, can be guided within the cooling channels 18 to absorb and dissipate heat from the piston crown 14. The cooling channels 18 can be arranged below the piston crown 14. A material thickness of the main body 16 between an upper side of the piston crown 14 and the cooling channels 18 can be, for example, at least 5 mm.

[0051] As in Figures 1 and 2As shown, the piston crown 14 can have a piston bowl 20. The piston bowl 20 can have any known shape. For example, the piston bowl 20 can be designed as a stepped piston bowl having a central elevation 22, as shown. Stepped piston bowls can be particularly suitable for diesel operation with direct injection. The diesel fuel can, for example, be divided by a central injector, preferably symmetrically, into several injection jets, which are directed onto a circumferential upper edge or a shoulder of the stepped piston bowl (see arrow A in Figure 1 ). The injection jets can then be split upon impact, so that the fuel is directed partly into the piston bowl 20 and partly away from the piston bowl 20. It is also possible, for example, for the piston bowl 20 to have a different shape, e.g., as an omega piston bowl.

[0052] The piston 10 has a cover 24. The cover 24 is formed separately from the main body 16. Preferably, the cover 24 is formed as a thin sheet metal. For example, the cover 24 can have a sheet metal thickness in a range between 0.5 mm and 2 mm, preferably approximately 1 mm. The sheet metal thickness can be substantially constant.

[0053] The cover 24 may be configured such that it is disposed within the piston recess 20 and expediently does not protrude beyond the piston recess 20 and / or is flush with an upper surface of the main body 16.

[0054] The cover 24 is arranged at a distance from the piston crown 14. As shown, a cross-sectional contour of the cover 24 can follow a contour of the piston bowl 20, preferably at a substantially constant distance. For example, the cover 24 can at least partially have a stepped and / or omega-shaped cross-section, like the piston bowl 20. However, it is also possible for the cover 24 and / or the piston crown 14 to have any other shape, up to and including a flat piston crown and a flat cover.

[0055] A gap L is formed between the cover 24 and the piston crown 14. The gap L acts as thermal insulation between the cover 24 and the piston crown 14. The gap is preferably designed as an air gap. During operation of the internal combustion engine, the cover 24 heats up very strongly. The cover 24 keeps the flame front away from the piston bowl 20 during combustion. The piston bowl 20 is not heated by the flame during combustion. In addition, the gap L hinders heat conduction from the highly heated cover 24 to the piston bowl 20. In this way, a heat flow from the cover 24 to the piston crown 14 can be expediently minimized.

[0056] The gap L can, for example, have a height between 0.5 mm and 2 mm, preferably approximately 1 mm. The gap L can have a substantially constant height.

[0057] During combustion, the cover 24 absorbs heat, which it transfers to the intake air, for example, during charge cycles. The thinner the cover 24 is, the less the charge air is heated and the less the engine's efficiency is reduced.

[0058] During the ignition of a fuel-air mixture in the combustion chamber, high ignition pressures can occur, for example in a range between 200 bar and 250 bar. In order to prevent a thin cover 24 from bending, for example during the ignition of the fuel-air mixture, the gap L is in fluid communication with the combustion chamber 12. Fluid can thus be exchanged between the combustion chamber 12 and the gap L. Via the fluid connection, a pressure increase in the combustion chamber, for example during the ignition and combustion of fuel, can also act on a rear side of the cover 24. This enables pressure equalization between the combustion chamber 12 and the gap L. A pressure on a front side or top side of the cover 24 can essentially correspond to a pressure on a rear side or bottom side of the cover 24.At least the fluid connection can approximate a pressure on the back of the cover 24 to a pressure on the front of the cover 24.

[0059] This prevents bending of the cover 24 due to an increase in pressure in the combustion chamber 12 without the cover 24 having a great material thickness for this purpose.

[0060] The fluid connection between the combustion chamber 12 and the gap L can be designed in different ways.

[0061] In the example of Figure 1The cover 24 is designed as an annular insert for insertion into the piston bowl 20. The central elevation 22 extends through a central through-hole in the cover 24. The cover 24 and the piston bowl 20 are connected to one another in such a way that an annular gap R1 is formed between an outer peripheral edge 26 of the cover 24 and an outer peripheral edge 28 of the piston bowl 20. In addition, an annular gap R2 is formed between an inner peripheral edge 30 of the cover 24, i.e., the peripheral edge of a central through-hole in the cover 24, and a peripheral surface of the central elevation 22. The annular gaps R1, R2 form a direct fluid connection between the combustion chamber 12 and the gap L.

[0062] The fluid connection between the combustion chamber 12 and the gap L is preferably arranged such that it is spaced apart from a fuel injection jet impingement area 32 of the cover 24. This prevents a flame formed by the fuel injection jets from directly impinging on the fluid connection and penetrating the gap L, thereby heating the piston crown 14. This spaced arrangement between the fluid connection and the fuel injection jet impingement area 32 can be advantageously implemented, for example, by the annular gaps R1 and R2.

[0063] Figure 2 shows further additional or alternative possibilities for establishing, for example, a direct fluid connection between the combustion chamber 12 and the gap L. For example, the cover 24 can have several through holes 34. For the sake of clarity, Figure 2only some of the through holes are provided with the reference number 34.

[0064] The through-holes 34 connect a front side of the cover 24 to a rear side of the cover 24, and thus the combustion chamber 12 to the gap L. The through-holes 34 can be distributed throughout the cover 24. Preferably, the through-holes 34 are spaced apart from the fuel injection jet impingement area 32, for example, above and below the annular fuel injection jet impingement area 32.

[0065] It is also possible for the cover 24 to have, for example, through-slots or another internal or external structure for establishing the fluid connection between the combustion chamber 12 and the gap L.

[0066] The cover 24 can be fixedly connected to the piston bowl 20. Preferably, the cover 24 and the piston bowl 20 are welded together, for example, by spot welding or friction welding. Using friction welding to attach the cover 24 to the piston bowl 20 can result in separate regions for the gap L. Here, a fluid connection is expediently provided for each region of the gap L for connection to the combustion chamber 12, for example, in the form of the through holes 34, as shown. List of reference symbols

[0067] 10Piston 12Combustion chamber 14Piston crown 16Main body 18Cooling channels 20Piston bowl 22Central boss 24Cover 26Outer peripheral edge 28Outer peripheral edge 30Inner peripheral edge 32Fuel injection spray impact area 34Through hole A Fuel injection spray direction LSap (e.g. air gap) R1 Annular gap R2 Annular gap

Claims

1. A piston (10) for an internal combustion engine, comprising a piston crown (14) for delimiting a combustion chamber (12) of the internal combustion engine on a piston side; and a cover (24), which at least partially covers the piston crown (14), wherein a heat-insulating gap, preferably an air gap (L), is formed between the cover (24) and the piston crown (14), the gap being in fluid connection with the combustion chamber (12) and / or with an upper side of the cover (24) facing away from the heat-insulating gap (L), wherein the piston crown (14) comprises a piston recess (20) and the cover (24) is arranged at least partially in the piston recess (20) and / or is adapted to the piston recess (20), and characterised in that: the piston recess (20) is configured as an omega-shaped recess and / or a stepped recess, and the cover (24) comprises at least partially an omega-shaped and / or a stepped cross-section; and the fluid connection is at least partially formed by an annular gap (R2) between an inner circumferential edge (30) of the cover (24) and a central elevation (22) of the piston recess (20).

2. The piston (10) according to claim 1, wherein: the fluid connection is configured to allow pressure approximation and / or pressure compensation between the combustion chamber (12) and the heat-insulating gap (L); and / or a pressure on the upper side of the cover (24) and a pressure on a rear side of the cover (24) facing the heat-insulating gap (L) is approximated and / or substantially compensated by the fluid connection during operation of the internal combustion engine.

3. The piston (10) according to claim 1 or claim 2, wherein: the cover (24) is arranged to separate a flame front from the piston crown (14), preferably from a piston recess (20) of the piston crown (14), during combustion in the combustion chamber (12); and / or the fluid connection is arranged distant from a fuel injection jet impingement area (32) of the cover (24).

4. The piston (10) according to any one of the preceding claims, wherein: the fluid connection is at least partially formed by at least one annular gap (R1, R2) between the piston crown (14) and the cover (24)5. The piston (10) according to any one of the preceding claims, wherein: the fluid connection is at least partially formed by an annular gap (R1) between an outer circumferential edge (26) of the cover (24) and the piston crown (14); and / or the fluid connection is at least partially formed by an annular gap (R2) between an inner circumferential edge (30) of the cover (24) and the piston crown (14).

6. The piston (10) according to any one of the preceding claims, wherein: the fluid connection is at least partially formed by at least one through-hole (34) and / or at least one through-slit of the cover (24).

7. The piston (10) according to claim 6, wherein: a plurality of through-holes (34) and / or a plurality of through-slits are comprised, which are preferably arranged at a distance from a fuel injection jet impingement area (32) of the cover (24).

8. The piston (10) according to any one of the preceding claims, wherein: the heat-insulating gap (L) has a height greater than or equal to 0.5 mm and / or less than or equal to 2 mm, preferably about 1 mm; and / or the heat-insulating gap (L) has a substantially constant height.

9. The piston (10) according to any one of the preceding claims, wherein: the cover (24) extends annularly around the central elevation (22).

10. The piston (10) according to any one of the preceding claims, wherein: the fluid connection is at least partially formed by an annular gap (R1) between an outer circumferential edge (28) of the piston recess (20) and an outer circumferential edge (26) of the cover (24).

11. The piston (10) according to any one of the preceding claims, wherein: a cross-sectional contour of the cover (24) follows a cross-sectional contour of the piston recess (20), preferably at a substantially constant distance.

12. The piston (10) according to any one of the preceding claims, wherein the cover (24) is formed as a sheet metal, wherein preferably: the sheet metal has a substantially constant sheet thickness; and / or the sheet metal has a sheet thickness greater than or equal to 0.5 mm and / or less than or equal to 2 mm, preferably about 1 mm.

13. The piston (10) according to any one of the preceding claims, wherein: the cover (24) is welded to the piston crown (14), preferably to a piston recess (20) of the piston crown (14), preferably by means of spot welding and / or friction welding.

14. A motor vehicle, preferably a commercial vehicle, comprising a piston (10) according to one of the preceding claims.