PISTON FOR AN INTERNAL COMBUSTION ENGINE AND METHOD OF MANUFACTURING THE PISTON

Abstract

A piston for an internal combustion engine with a piston crown having an outer surface and with a thermal management layer. The thermal management layer contains a functional layer. The functional layer in turn contains a functional layer matrix, wherein the functional layer matrix includes polysiloxane and hollow spheres embedded in the functional layer matrix. The thermal conductivity of the functional layer is in the range of 0.2 to 2 W/(m*K) and the heat penetration coefficient of the functional layer is in the range of 400 to 1200 J/(K*m2*s).

Claims

1. A piston for an internal combustion engine, comprising: a piston crown having an outer surface; and a thermal management layer, containing a functional layer, wherein the functional layer contains a functional layer matrix including polysiloxane and hollow spheres embedded in the functional layer matrix; wherein a thermal conductivity of the functional layer is in the range of 0.2 to 2 W/(m*K); and wherein a heat penetration coefficient of the functional layer is in the range of 400 to 1200 J/(K*m.sup.2*s.sup.1/2).

2. The piston according to claim 1, wherein the piston includes a piston material with an aluminum alloy or an iron alloy and the thermal management layer is arranged at least in some areas on the outer surface of the piston crown.

3. The piston according to claim 1, wherein the polysiloxane exhibits a temperature resistance up to at least 500 C., preferably the polysiloxane exhibits a temperature resistance up to at least 650 C.

4. The piston according to claim 1, wherein a proportion of hollow spheres in relation to a total volume of the functional layer is 5 to 40 vol-%, preferably the proportion of hollow spheres in relation to the total volume of the functional layer is 10 to 20 vol-%, and more preferably the proportion of hollow spheres in relation to the total volume of the functional layer is 11 to 16 vol-%.

5. The piston according to claim 1, wherein the hollow spheres consist of SiO.sub.2 and are embedded in the functional layer as a filler.

6. The piston according to claim 1, wherein the hollow spheres consist of soda-lime borosilicate glass and are embedded in the functional layer as a filler.

7. The piston according to claim 1, wherein the hollow spheres have a diameter of 5 to 50 m, preferably the hollow spheres have a diameter of 15 to 25 m, and more preferably the hollow spheres have a diameter of 19 to 21 m.

8. The piston according to claim 1, wherein the functional layer includes TiO.sub.2, ZrO.sub.2, and WO.sub.3.

9. The piston according to claim 1, wherein the thermal conductivity of the functional layer is in the range of 0.2 to 1.8 W/(m*K), preferably the thermal conductivity of the functional layer is in the range of 0.3 to 0.4 W/(m*K).

10. The piston according to of claim 1, wherein the heat penetration coefficient of the functional layer is in the range of 500 to 900 J/(K*m.sup.2*s.sup.1/2), preferably the heat penetration coefficient of the functional layer is in the range of 600 to 760 J/(K*m.sup.2*s.sup.1/2).

11. The piston according to claim 1, wherein a specific heat capacity of the functional layer is in the range of 450 to 1000 J/(kg*K).

12. The piston according to claim 1, wherein the functional layer has a thickness of 50 to 250 m, preferably of 80 to 110 m, measured perpendicular to the outer surface of the piston crown.

13. The piston according to claim 1, wherein the functional layer has a thickness of 50 to 110 m, measured perpendicular to the outer surface of the piston crown.

14. The piston according to claim 1, wherein the functional layer has a thickness of 50 to 110 m, measured perpendicular to the outer surface of the piston crown, and the heat penetration coefficient of the functional layer is in the range of 500 to 900 J/(K*m.sup.2*s.sup.1/2).

15. The piston according to claim 1, wherein the thermal management layer further includes a cover layer, wherein the cover layer is attached to the functional layer facing away from the piston crown and consists of a polysiloxane.

16. The piston according to claim 15, wherein the cover layer has a thickness of 4 to 20 m, preferably of 4.5 to 5.5 m, measured perpendicular to the outer surface of the piston crown.

17. The piston according to claim 1, wherein a surface roughness of the thermal management layer is in the range2 m.

18. A method of manufacturing a piston, comprising: cleaning an area of the piston to which a functional layer is to be applied; dispersing hollow spheres (9) into a polysiloxane resin coating to obtain a suspension; applying the suspension to the piston by atmospheric spraying; and curing the suspension obtaining the functional layer.

19. The method according to claim 18, further comprising: roughening the area of the piston during the step of cleaning the area of the piston; applying a second layer by atmospheric spraying a polysiloxane resin coating onto the functional layer; and curing the second layer to obtain a cover layer.

20. A piston, comprising: a piston crown having an outer surface; and a thermal management layer including a functional layer and a cover layer, wherein the functional layer includes a functional layer matrix including polysiloxane and embedded hollow spheres; wherein the cover layer is attached to the functional layer facing away from the piston crown and includes polysiloxane; wherein a thermal conductivity of the functional layer is in the range of 0.3 to 0.4 W/(m*K); wherein a heat penetration coefficient of the functional layer is in the range of 600 to 760 J/(K*m.sup.2*s.sup.1/2); and wherein a specific heat capacity of the functional layer is in the range of 450 to 1000 J/(kg*K).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] FIG. 1: Rough schematic representation of an example of an internal combustion engine, which can be used in a motor vehicle, for example.

[0077] FIG. 2a: Flow diagram of the method according to the invention

[0078] FIG. 2b: Flow diagram of an advantageous further development of the method according to the invention

DETAILED DESCRIPTION

[0079] FIG. 1 shows an example of an embodiment of an internal combustion engine 10 according to the invention. The internal combustion engine comprises a cylinder 11. In the cylinder 11 of the internal combustion engine 10, the piston 1 according to the invention is shown as an example and roughly schematically. Piston 1 partially delimits a combustion chamber of the internal combustion engine 10 with an outer surface 2 of the piston 1, for example on the end face, together with the cylinder 11. FIG. 1 shows a piston 1 with a piston crown 3, which has an outer surface 2. In addition, the piston 1 comprises a thermal management layer 4. This is arranged at least in some areas on the outer surface 2 of the piston crown. FIG. 1 shows one aspect of the invention, in which the thermal management layer 4 comprises a functional layer 5 and a cover layer 6. The functional layer 5 is arranged in contact with the outer surface 2 of the piston crown 3 between the piston crown 3 and the cover layer 6. According to the invention, it is also conceivable for the thermal management layer 4 to comprise only a functional layer 5, but no cover layer 6, which is not shown in FIG. 1. The functional layer 5 comprises a functional layer matrix made of polysiloxane and hollow spheres 9 embedded in the functional layer matrix.

[0080] As can also be seen in FIG. 1, the functional layer 5 has a thickness 7 measured perpendicular to the outer surface 2 of the piston crown 3. According to the invention, the thickness 7 of the functional layer 5 is from 50 to 250 m, preferably from 80 to 110 m. Alternatively, the thickness 7 of the functional layer 5 is preferably 50 to 110 m.

[0081] The cover layer 6 has a thickness 8 of the cover layer 6 measured perpendicular to the outer surface 2 of the piston crown 3. According to the invention, the thickness 8 of the covering layer 6 is 4 to 20 m, preferably 4.5 to 5.5 m, measured perpendicular to the outer surface of the piston head. The functional layer 5 comprises hollow spheres 9. It goes without saying that such hollow spheres may have a geometry that deviates slightly from the ideal sphere due to the manufacturing process. The hollow spheres preferably comprise or consist of SiO.sub.2.

[0082] Alternatively, the hollow spheres are advantageously made of soda-lime borosilicate glass. According to the invention, the functional layer 5 is preferably temperature-stable up to at least 500 C., more preferably up to at least 650 C. The top layer 6, also shown in FIG. 1, is preferably non-porous or closed-porous, according to the invention. This means that the top layer 6 preferably has no pores or only closed pores. This protects the underlying functional layer 5 from the gases in the combustion chamber. It is also provided according to the invention that the top layer 6 is preferably temperature-stable up to at least 500 C., more preferably up to at least 650 C.

[0083] According to the invention, the piston crown 3 shown in FIG. 1 comprises, for example, a piston material made of an aluminum alloy or consists of a piston material with such an aluminum alloy. Alternatively, the piston crown 3 comprises a piston material with an iron alloy or consists of a piston material with such an iron alloy.

[0084] In process step 200, FIG. 2a shows the cleaning and optional roughening of the area of the piston 1 to which the functional layer is subsequently to be applied after cleaning and optional roughening. This is followed by process step 201, in which hollow spheres 9 are introduced into a polysiloxane resin coating and dispersed. A suspension is obtained as a result. In the subsequent process step 202, the previously obtained suspension is applied to the piston 1 by atmospheric spraying. This is followed by process step 203, in which the previously applied layer of suspension is cured. This creates a functional layer 5.

[0085] FIG. 2b also initially shows the process steps 200 to 203 already explained in FIG. 2a. However, in the advantageous further development of the invention shown in FIG. 2b, process step 203 is followed by a further process step 204. In process step 204, a second layer is applied to the resulting functional layer 5 by atmospheric spraying of a polysiloxane resin coating. This second layer is cured in the subsequent process step 205, whereby a top layer 6 is obtained.

[0086] In the following, the invention is described in detail by means of examples, without limiting the scope of the invention to this:

Materials Used:

[0087] Cerakote V-136 [0088] 3M Glass Bubbles IM16K

Inventive Example EB1a

[0089] 21 g of 3M Glass Bubbles IM16K hollow spheres, corresponding to 14% by volume, are dispersed in 400 g of Cerakote V-136. The piston, consisting of an aluminum alloy with a previously cleaned surface to be coated, is then preheated to 80 C. for 30 minutes. The suspension is applied with a spray gun at a pressure of 1 bar from a distance of 17.5 cm. A total of 10 clicks are emitted from the spray gun. The piston is then cured for 1 hour at 150 C. A layer thickness of 80 to 110 m is obtained, measured non-destructively using XRF spectrometry. A crack-free surface is obtained. The specification 80 to 110 m means that the layer thickness obtained is at least 80 m at the thinnest point and a maximum of 110 m at the thickest point.

Inventive Example EB1b

[0090] The pistons coated according to example EB1a were tested in the engine test for 250 hours in continuous operation. Visual inspection of the coating before and after the engine test revealed no changes; the coating adhered stably.

Inventive Example EB1c

[0091] To investigate the thermophysical parameters of the material, 21 g 3M Glass Bubbles IM16K hollow spheres were dispersed in 400 g Cerakote V-136, corresponding to 14% by volume. Subsequently, aluminum foils with previously cleaned surfaces were preheated to 80 C. for 30 min. The suspension is applied using a spray gun. The material including the aluminum foil is then cured for 1 hour at 150 C. and then scraped off the aluminum foil. Layers of about 5 mm thickness and about 12.9 mm diameter were obtained. These layers were then adjusted by hand grinding to a thickness of approximately 2.4 mm and a diameter of approximately 12.7 mm.

[0092] The thermal diffusivity a [mm.sup.2/s] was determined by the laser flash method using a NETZSCH LFA 467 Hyperflash apparatus.

[0093] Furthermore, a determination of the specific heat capacity c.sub.p [J/(g*K)] was carried out by means of heat flow differential calorimetry using a NETZSCH-DSC 204 Phoenix apparatus.

[0094] In addition, a determination of the density [g/cm.sup.3] of the sample was carried out at 23 C. by means of the buoyancy method using the ME235 Sartorius balance together with the YDK 01 density determination set.

[0095] From this, the thermal conductivity [W/(m*K)] was calculated using the following formula:

[00002]$=*c_p*a\mathrm{with}a\left[m^2/s\right]\left[\mathrm{kg}/m^3\right]c_p\left[J/(\mathrm{kg}*K\right]$

There was no temperature-dependent density correction.

TABLE-US-00001 TABLE 1 Temperature C. 25 50 75 100 150 200 g/cm.sup.3 1.244 1.244 1.244 1.244 1.244 1.244 a mm.sup.2/s 0.280 0.272 0.266 0.260 0.252 0.243 c.sub.p J/(g*K) 0.831 0.880 0.926 0.969 1.047 1.110 W/(m*K) 0.29 0.30 0.31 0.31 0.33 0.34 Temperature C. 250 300 350 400 450 500 g/cm.sup.3 1.244 1.244 1.244 1.244 1.244 1.244 a mm.sup.2/s 0.236 0.232 0.228 0.225 0.224 0.224 c.sub.p J/(g*K) 1.163 1.205 1.242 1.273 1.298 1.301 W/(m*K) 0.34 0.35 0.35 0.36 0.36 0.36