EP2864617A2

EP2864617A2 - Piston and crankcase assembly for an internal combustion engine

Info

Publication number: EP2864617A2
Application number: EP13744418.8A
Authority: EP
Inventors: Ulrich Bischofberger
Original assignee: Mahle International GmbH
Current assignee: Mahle International GmbH
Priority date: 2012-05-05
Filing date: 2013-05-03
Publication date: 2015-04-29
Anticipated expiration: 2033-05-03
Also published as: DE102012009030A1; JP2015522738A; JP6246187B2; WO2013167102A3; WO2013167102A2; EP2864617B1

Abstract

The invention relates to an assembly (100, 200) consisting of a piston (10, 110, 210) made of a steel-based material, and a crankcase (140, 240) made of an aluminum-based material, for an internal combustion engine. Said piston (10, 110, 210) comprises a piston head (11) and a piston skirt (16), said piston head (11) having a peripheral annular part (15) and in the region of said annular part (15), a peripheral cooling channel (23). The piston skirt (16) comprises piston bores (17) provided with hub bores (18), which are arranged over the hub connections (19) on the underside (11a) of the piston head (11). Said piston hubs (17) are interconnected over the running surfaces (21, 22). According to the invention, at least one bore (24a, 24b, 24c, 24d) which is closed towards the outside is arranged between a running surface (21, 22) and a hub bore (18) such that the at least one bore (24a, 24b, 24c, 24d) leads into the cooling channel (23), and that the cooling channel (23) and the at least one bore (24a, 24b, 24c, 24d) contain a coolant (127, 227) in the form of a metal or a metal alloy which have a low-melting point.

Description

Arrangement of a piston and a crankcase

for an internal combustion engine

The present invention relates to an arrangement of a piston made of a material based on steel and a crankcase made of an aluminum-based material for an internal combustion engine, wherein the piston has a piston head and a piston skirt, wherein the piston head has a circumferential ring portion and in the Area of the ring portion has a circumferential cooling passage, wherein the piston skirt has hub bores provided with piston bosses, which are arranged via hub connections on the underside of the piston head, wherein the piston hubs are connected to each other via running surfaces.

In modern internal combustion engines, the pistons in the region of the piston crowns are exposed to increasingly higher mechanical and thermal loads. Pistons made of a material based on aluminum are increasingly no longer able to cope with these loads. Above all, premature cracks on aluminum pistons are observed at higher loads, starting from the hot spots on the piston crown or in the region of the nabenzene. Such cracks can lead to failure of the engine. Therefore, the use of pistons based on a steel material is desired. Despite the relatively high specific weight of such materials in comparison with aluminum-based materials, it is possible to produce approximately equal-weight pistons with significantly higher load capacity. A disadvantage, however, proves in a generic arrangement, compared to an aluminum-based material smaller coefficient of expansion of steel-based materials. As a result, larger running clearances between the piston and the crankcase occur during engine operation. This effect is observed under different operating conditions of the internal combustion engine. This can lead to annoying engine noise as well as increased oil consumption and blow-by effects.

| Confirmation copy | DE 10 2009 018 981 A1 discloses a piston made of a material based on steel, which is suitable for use in a crankcase made of a material based on aluminum. In this piston, the piston hubs are spaced from the treads, ie the mechanical connection of the piston hubs to the treads is interrupted, so that the piston shank expands more strongly with the hotter piston head, so that the increase of the running play in the engine operation is reduced. The disadvantage of this is that such a piston can absorb only limited lateral forces, since a mechanical support of the running surfaces to the piston hubs is not or only insufficiently available. In addition, more deformations in the region of the annular grooves may occur, which affect the function of the piston rings to seal against the combustion pressure and the combustion gases from the piston head side combustion chamber.

The object of the present invention is to develop a generic arrangement so that it has the lowest possible engine noise during operation and the oil consumption and the blow-by effect are not excessively increased.

The solution is that the piston is made of a material based on steel and that the crankcase is made of an aluminum-based material, that in the piston at least one outwardly closed bore is provided between a tread and a hub bore is arranged, that the at least one bore opens into the cooling channel, and that the cooling channel and the at least one bore contain a coolant in the form of a low-melting metal or a low-melting metal alloy.

The arrangement according to the invention is characterized in that the heat generated in the region of the piston crown is directed via the piston head in a targeted manner into the environment of the at least one bore. As a result, the area between the piston hub and the piston shaft is heated comparatively strongly. Also, the treads are at least partially heated more than in pistons in the prior art. This increased heating causes an additional thermal expansion of the piston in the region of the piston shaft during engine operation. corresponds to the thermal expansion of the crankcase substantially. This reduces the warm play between piston and cylinder. It has been found that an acceptable over the entire load range running clearance between the piston and the crankcase adjusts. The arrangement according to the invention ensures that in the finished engine, the pistons can still move freely even at low temperatures down to -30 ° C. In operational warm condition, the running clearance between the piston and crankcase increases only slightly, so that increased secondary movements of the piston and thus increased engine noise can be avoided. Furthermore, the seal to the piston head side combustion chamber is improved, so that the oil consumption and the blow-by effect are reduced.

For the purposes of the present invention, the term "clearance" (installation play, warm play, running play, cold play) is understood to be the difference between the diameter of the cylinder bore or the cylinder liner on the one hand and the diameter of the piston on the other hand, whereby the diameter of the piston is measured at its largest point.

Advantageous developments emerge from the subclaims.

In a particularly advantageous manner, the thermal expansion coefficient W _{Ko of} the material of the piston and the effective thermal expansion coefficient W _{Ku of} the material of the crankcase form a ratio of W _Ko / W _Ku = 0.4 to 0.7. This is a particularly good compensation of the different thermal expansion of the piston and crankcase in the inventive arrangement is possible. This also applies in conjunction with an optionally cast in the crankcase cylinder liner.

Preferably, the piston is made of a material selected from the group consisting of precipitation-hardening ferritic-pearlitic steels (so-called AFP steels) and martensitic hardening steels with carbon contents of between 0.3 and 0.8% by weight. These materials differ mainly in their hardness, strength and manufacturability, but have approximately the same coefficients of thermal expansion between 11 and 13 E-6 1 / K. The crankcase is advantageously made of an aluminum-silicon casting material. Particularly preferred is a material which is selected from the group comprising hypoeutectic aluminum-silicon alloys (AISi7 to Al-Si9) having a thermal expansion coefficient between 22 E-6 1 / K - 24 E-6 1 / K and aluminum-silicon Alloys with a silicon content up to AISM7 and with a coefficient of expansion between 19 E-6 1 / K and 22 E-6 1 / K.

The crankcase may, for example, be provided with at least one cylinder liner made of a cast iron material. The cylinder liners serve to reduce wear in the cylinder and are cast in a conventional manner in the crankcase. The resulting effective coefficient of expansion W _{Zy of} the cylinder is typically between 17 E-6 1 / K and 20 E-6 1 / K. This depends in a conventional manner on the ratio of the wall thickness of the cylinder liner to the total thickness of the cylinder wall and the material used in each case of the crankcase.

However, the crankcase can also be provided with at least one cylinder bore, which is provided with a coating on the basis of a ferrous material.

Low melting metals suitable for use as coolant in the flask are especially sodium or potassium. In particular, Galinstan® alloys, low melting bismuth alloys and sodium-potassium alloys can be used as the low-melting metal alloys.

Galinstan® alloys are gallium, indium and tin alloy systems that are liquid at room temperature. These alloys consist of 65 wt% to 95 wt% gallium, 5 wt% to 26 wt% indium and 0 wt% to 16 wt% tin. Preferred alloys are, for example, those with 68% by weight to 69% by weight of gallium, 21% by weight to 22% by weight of indium and 9.5% by weight to 10.5% by weight of tin ( Mp -19 ° C), 62% by weight of gallium, 22% by weight of indium and 16% by weight of tin (mp 10.7 ° C.) and 59.6% by weight of gallium, 26% by weight. % Indium and 14.4% by weight tin (ternary eutectic, mp 11 ° C). Low melting bismuth alloys are well known. These include, for example, LBE (eutectic bismuth-lead alloy, mp. 124 ° C), Roses metal (50 wt .-% bismuth, 28 wt .-% lead and 22 wt .-% tin, mp. 98 ° C) Orion metal (42 wt% bismuth, 42 wt% lead and 16 wt% tin, mp 108 ° C); Quick solder (52 weight percent bismuth, 32 weight percent lead and 16 weight percent tin, mp 96 ° C), d'Arcets metal (50 weight percent bismuth, 25 weight percent lead and 25 wt% tin), Wood's metal (50 wt% bismuth, 25 wt% lead, 12.5 wt% tin and 12.5 wt% cadmium, mp 71 ° C), Lipowitz metal (50 wt% bismuth, 27 wt% lead, 13 wt% tin and 10 wt% cadmium, mp 70 ° C), Harper's metal (44 wt% bismuth, 25 wt%). -% lead, 25 wt .-% tin and 6 wt .-% cadmium, mp. 75 ° C), Cerrolow 117 (44.7 wt .-% bismuth, 22.6 wt .-% lead, 19.1 wt Indium, 8.3 wt% tin, and 5.3 wt% cadmium, mp 47 ° C); Cerrolow 174 (57 wt% bismuth, 26 wt% indium, 17 wt% tin, mp 78.9 ° C), Fields metal (32 wt% bismuth, 51 wt% indium, 17 wt .-% tin, mp 62 ° C) and the Walker alloy (45 wt .-% bismuth, 28 wt .-% lead, 22 wt .-% tin and 5 wt .-% antimony).

Suitable sodium-potassium alloys may contain from 40% to 90% by weight of potassium. Particularly suitable is the eutectic alloy NaK with 78 wt .-% potassium and 22% by weight of sodium (mp. -12.6 ° C).

The coolant may additionally contain lithium and / or lithium nitride. If nitrogen is used as a protective gas during filling, this can react with the lithium to lithium nitride and be removed in this way from the cooling channel.

The coolant may further contain sodium oxides and / or potassium oxides if, during filling, any existing dry air has reacted with the coolant.

Preferably, four holes are provided, which are arranged between a running surface and a hub bore in order to achieve a particularly uniform temperature distribution in the piston.

The amount of coolant received in the cooling channel or in the at least one bore depends on its thermal conductivity and the degree of the desired Temperature control off. Preferably, the coolant has a filling level up to half the height of the cooling channel in order to achieve a shaker effect and thus a particularly effective heat distribution in the piston.

The heating of the piston and thus its thermal expansion can also be controlled with the amount of filled coolant. It has been shown that sometimes even a filling of 3% to 10% of the cooling passage volume with the coolant is sufficient to ensure the function of the piston provided according to the invention in cooperation with the inventively provided crankcase.

Embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. In a schematic, not to scale representation:

1 shows an embodiment of a piston for an inventive arrangement, partly in section.

Figure 2 is a section along the line II - II in Figure 1.

Fig. 3 shows a first embodiment of an inventive arrangement in

Cut;

Fig. 4 is an enlarged partial view of Figure 3;

Fig. 5 shows another embodiment of an inventive arrangement in section.

Figures 1 and 2 show an embodiment of a piston 10 for an inventive arrangement. The piston 10 may be a one-piece or multi-piece piston. The piston 10 is made of a steel-based material. Figures 1 and 2 show an example of a piston 10 in the form of a one-piece box piston. The piston 10 has a piston head 11 with a combustion tion recess 13 having the piston head 12, a peripheral land 14 and a ring portion 15 for receiving piston rings (not shown). In the amount of the ring section 15, a circumferential cooling channel 23 is provided. The piston 10 further includes a piston stem 16 with piston bosses 17 and hub bores 18 for receiving a piston pin (not shown). The piston hubs 17 are connected via hub connections 19 with the underside 11 a of the piston head 11. The piston hubs 17 are connected to one another via running surfaces 21, 22 (cf., in particular, FIG. In the exemplary embodiment, the contour of the running surfaces 21, 22 is straight in the axial direction. But there are also arched contours conceivable. The piston diameter for determining the clearance is always measured at its largest point.

The piston shaft 16 has four holes 24a, 24b, 24c, 24d in the exemplary embodiment. The bores 24a-d in the exemplary embodiment extend approximately axially and parallel to the piston center axis M. The bores 24a-d may, however, also extend inclined at an angle to the piston center axis M. The bores 24a-d are arranged between a running surface 21, 22 and a hub bore 18. The bores 24a-d open into the cooling channel 23rd

In the exemplary embodiment, the piston 10 may for example be cast in a conventional manner, wherein the cooling channel 23 and the bores 24a-d can be introduced in a conventional manner by means of a salt core.

The cooling channel 23 and the bores 24a-d are filled with a coolant. On the representation of the coolant was omitted in Figures 1 and 2 for reasons of clarity. Reference is made to FIGS. 3 to 5.

Figure 3 shows a first embodiment of an inventive arrangement 100 with a piston 110 made of a martensitic hardening steel with the name 42CrMo4 with a thermal expansion coefficient of 12 E-6 1 / K. The piston 110 is received in this embodiment in a cylinder liner 130, which in turn is accommodated in a crankcase 140. The cylinder liner 130 can be made of a cast iron material in a manner known per se. stand. The crankcase 140 is in the embodiment of an aluminum-silicon alloy of the type AISi9 with a thermal expansion coefficient of 23 E-6 1 / K.

The piston 110 is substantially similar in construction to the piston 10 according to Figures 1 and 2, so that the same structural elements are provided with the same reference numerals and reference is made to the description of Figures 1 and 2. In the cooling channel 23 and in the bores 24a-d of the piston 110 according to FIG. 3, a coolant 127 is also accommodated.

Figure 4 shows an enlarged partial view of Figure 3, which illustrates a detail of the bores 24a-d in the lower region of the piston bosses 17 on the example of the bore 24a. At least one of the holes 24a-d, in the embodiment, the bore 24a, has an opening 125 to the outside. The coolant 127, namely a low-melting metal or a low-melting metal alloy, as exemplified above, is filled through the opening 125 in the bore 24 a. From there, the coolant 127 is distributed in the cooling channel 23 and in the further holes 24b-d. The opening 125 is then sealed, in the embodiment by means of a pressed-steel ball 126. The opening 125 can also be closed, for example, by welding a lid or pressing a cap (not shown).

The size of the bores 24a-d and the filling amount of the coolant 127 depend essentially on the size of the piston 110 and the desired cooling capacity. On average, about. 10 g to 40 g coolant 127 per piston 110 required. The cooling capacity can be controlled by the amount of added refrigerant 127 taking into account its thermal conductivity coefficient. For example. is a level in the cooling channel 23 suitable, which corresponds approximately to half the height of the cooling channel 23. In this case, during operation, the known sha ker effect can additionally be used for a particularly effective heat distribution in favor of the running surfaces 21, 22. For sodium as coolant 127 with a temperature in operation of 220 ° C results in a cooling capacity of 350kW / m ^2, a maximum surface temperature of the piston 110 of about 260 ° C. In addition, the underside 11a of the piston head 11 can be cooled by injection with cooling oil.

To fill the bore 24a, a lance is inserted through the opening 125 and purged by nitrogen or other suitable inert gas or by dry air. To introduce the coolant 127, it is passed through the opening 125 under protective gas (for example nitrogen, inert gas or dry air), so that the coolant 127 is received in the bore 24a or the cooling channel 23.

Another method for filling the bore 24a is characterized in that after flushing with nitrogen, inert gas or dry air, the bores 24a-d and the cooling channel 23 are evacuated and the coolant 127 is introduced in a vacuum. Thus, the coolant 127 can more easily move in and out of the cooling channel 23 and into and out of the holes 24a-d since it is not hindered by the presence of shielding gas.

Another possibility for removing the protective gas from the cooling channel 23 or the bores 24a-d is to use nitrogen or dry air (ie essentially a mixture of nitrogen and oxygen) as protective gas and a small amount of the coolant 127 Lithium, according to experience about 1.8 mg to 2.0 mg of lithium per cubic centimeter gas space (ie volume of the cooling channel 23 plus volume of the holes 24a-d). While, for example, sodium and potassium react with oxygen to form oxides, the lithium reacts with nitrogen to form lithium nitride. The protective gas is thus almost completely bound as a solid in the coolant 127.

FIG. 5 shows a further exemplary embodiment of an arrangement 200 according to the invention with a martensitic hardening steel piston 210 with the designation 42CrMo4 with a thermal expansion coefficient of 12 E-6 1 / K. The piston 210 is received in this embodiment in a cylinder bore 241 of a crankcase 240. The cylinder bore 241 is in a conventional manner with a coating 242 based on a ferrous material with a Thermal expansion coefficient of 20 E-6 1 / K provided. The coating 242 typically has a thickness of 100 μητι to 200 μητι. The crankcase 240 is in the embodiment of an aluminum-silicon alloy of the type Al-Si9 with a thermal expansion coefficient of 23 E-6 1 / K.

The piston 210 is substantially similar in construction to the piston 10 according to FIGS. 1 and 2, so that identical structural elements are given the same reference numerals and reference is made to FIGS. 1 and 2 for the description. In the cooling channel 23 and in the bores 24a-d of the piston 210 according to FIG. 3, a coolant 227 is also received.

Table 1 shows by way of example the two embodiments of an inventive arrangement according to Figures 3 to 5 (numbers 1 and 2) compared to embodiments of the prior art (numbers 3 to 8). In the arrangement according to the invention, the piston used was filled with pure sodium with a thermal conductivity of 140W / (mK). The filling amount was 5% of the added volume of the cooling channel 23 and the bores 24a-d. It can be clearly seen that the respective piston clearance, ie the change of the same in all cases installation clearance of 50 μητι both at low temperatures and at the highest loads in the inventive arrangement is the lowest.

Table 1

Claims

claims

An assembly (100, 200) of a piston (10, 110, 210) made of a steel-based material and a crankcase (140, 240) for an internal combustion engine made of a material based on aluminum, wherein the piston ( 10, 110, 210) has a piston head (11) and a piston shaft (16), the piston head (11) having a circumferential annular portion (15) and in the region of the annular portion (15) a circumferential cooling channel (23), wherein the piston shaft (16) with hub bores (18) provided with piston hubs (17) which are arranged via hub connections (19) on the underside (11 a) of the piston head (11), wherein the piston hubs (17) via running surfaces (21, 22) with each other are connected, characterized in that in the piston (10, 110, 210) at least one outwardly closed bore (24a, 24b, 24c, 24d) is provided, which arranged between a running surface (21, 22) and a hub bore (18) is that the at least one bore (24a, 24b, 24c, 24d) in the Cooling channel (23) opens, and that the cooling channel (23) and the at least one bore (24 a, 24 b, 24 c, 24 d) containing a coolant (127, 227) in the form of a low-melting metal or a low-melting metal alloy.

2. Arrangement according to claim 1, characterized in that the coefficient of thermal expansion WK _{O of} the material of the piston (10, 110, 210) and the thermal expansion coefficient WK _{u of} the material of the crankcase (140, 240) has a ratio of W _Ko / W _Ku = 0 , 4 - 0.7 form.

3. Arrangement according to claim 1, characterized in that the piston (10, 1 10, 210) consists of a material which is selected from the group consisting of precipitation-hardening ferritic-pearlitic steels and martensitic hardening steels with carbon contents between 0.3 and 0 , 8% by weight.

4. Arrangement according to claim 1, characterized in that the crankcase (140, 240) consists of an aluminum-silicon casting material.

5. Arrangement according to claim 1, characterized in that the crankcase (140, 240) consists of a material which is selected from the group comprising hypoeutectic aluminum-silicon alloys (AISi7 to AISi9) and aluminum-silicon alloys having a silicon content up to AISM7.

6. Arrangement according to claim 1, characterized in that the crankcase (140) is provided with at least one cylinder liner (130) made of a cast iron material.

7. Arrangement according to claim 1, characterized in that the crankcase (240) has at least one cylinder bore (241) which is provided with a coating (242) on the basis of a ferrous material.

8. Arrangement according to claim 1, characterized in that the piston (10, 110, 210) as coolant (27, 127, 227) contains sodium or potassium.

9. Arrangement according to claim 1, characterized in that the piston (10, 110, 210) as coolant (127, 227) a melting metal alloy from the group comprising Galinstan® alloys, low melting bismuth alloys and sodium-potassium alloys contains.

10. Arrangement according to claim 1, characterized in that the coolant (127, 227) in the piston (10, 110, 210) contains lithium and / or lithium nitride.

11. Arrangement according to claim 1, characterized in that the coolant (127, 227) in the piston (10, 110, 210) contains sodium oxides and / or potassium oxides.

12. Arrangement according to claim 1, characterized in that the piston (10, 110, 210) has a filling level of the coolant (127, 227) to half the height of the cooling channel (23).

13. Arrangement according to claim 1, characterized in that the piston (10, 110, 210) has a filling amount of the coolant (127, 227) of 3% to 10% of the volume of the cooling channel (23).

14. Arrangement according to claim 1, characterized in that the piston (10, 110, 210) has four bores (24a, 24b, 24c, 24d) which are arranged between a running surface (21, 22) and a hub bore (18) ,