WO2009000420A1 - Piston for an internal combustion engine, and method for producing it - Google Patents

Abstract

The invention relates to a piston for an internal combustion engine having a piston basic body (18) which is connected non-releasably to a further component (16) which faces an associated combustion chamber (14), wherein the further component is configured as a lining part (16) which completely forms that piston surface (12) of the piston which faces the combustion chamber (14).

Description

 Piston for an internal combustion engine and method for its

manufacturing

The invention relates to a piston for an internal combustion engine specified in the preamble of claim 1. Art. Furthermore, the invention relates to a method for producing such a piston specified in the preamble of claim 7 Art.

Since about 10 years ago, especially in commercial vehicle engines, the reduction of NOx limits was increasingly discussed, the so-called exhaust gas recirculation rates have been significantly increased. The increase in these exhaust gas recirculation rates means, for example for turbochargers a demand for ever higher boost pressures in order not to have to accept too large losses of specific power of the engines. Parallel to the increasing exhaust gas recirculation rates and supercharging levels, therefore, in order to keep the specific power, the maximum cylinder pressures must be increased. Meanwhile, these are for example in internal combustion engines for commercial vehicles well above 200 bar, in the next step, cylinder pressures should be possible to above 250 bar.

In addition to the highly stressed parts of the crank mechanism, the characteristics of the pistons are therefore also the focal point of development activities, especially the future ones To provide motor properties from the side of thermodynamics and mechanics.

In order to cope with the high piston stresses, it is already known, for example from EP 1 466 383 A1, to permanently connect a piston main body to another component in the form of an insert, which faces an associated combustion chamber. This insert is reflowed by a welding process, in particular a deep welding process, and thus permanently integrated into the piston body.

Moreover, it is already known from EP 1 386 687 A1 that the piston is subjected to a melting treatment in order thus to improve the thermal stability in a bowl rim region facing the combustion chamber.

Finally, it is already known from DE 102 44 513 Al to design the piston in several parts. In this case, the piston crown and the piston skirt are assigned to one of the components, which is connected in a welding or soldering process to a second component, which in turn assumes the bearing of the piston pin or of the connecting rod.

A disadvantage of this multi-part piston, however, is the fact that this is extremely expensive to manufacture.

The object of the present invention is therefore to improve a piston and a method for the production thereof so that, on the one hand, a particularly high resistance and, on the other hand, a particularly simple production of the piston can be realized. This object is achieved by a piston and a method for its preparation with the features of claims 1 and 7, respectively. Advantageous embodiments with expedient and non-trivial developments of the invention are specified in the respective dependent claims.

In order to create a piston which, for example, is particularly thermally resistant and relatively easy to produce, it is inventively provided that the further component is formed as a covering part, which completely forms the combustion chamber facing the piston surface of the piston. In other words, it is thus provided according to the invention to use a lining part which completely covers or forms at least the piston surface facing the combustion chamber. The complete coverage thus ensures that the combustion chamber resulting thermal and mechanical stress can be absorbed by the piston accordingly. Here, the lining part - as will be explained in more detail below - be made relatively thin relative to the piston diameter of the piston, so that a total of both a simple production of the lining part itself as well as the piston can be realized in total.

In a further embodiment of the invention, the covering part and the piston body is made of a same base alloy, wherein the covering part is subjected to a tempering process - for example, a thermal and possibly also chemical and material-technical tempering. The advantage of a same base alloy consists in particular in the fact that both parts have an approximately equal thermal expansion, so that in the planned insoluble connection of the two components no unwanted voltages result.

In a further embodiment of the invention, it has also proven to be advantageous if the covering part is provided on its side facing the piston main body with connecting means - for example in the form of a surface structure or in the form of anchors. In this way, a particularly reliable connection of the lining part to the piston main body can be achieved.

In a further embodiment of the invention, it has also proven to be advantageous if the lining part has a shell thickness, which is based on a piston diameter according to the formula 1% <S / D <10%. If the shell thickness of the lining part lies in the specified value range, then on the one hand a particularly simple production of the lining part itself can be realized and on the other hand a good and reliable connection to the piston main body.

As a further advantage, it has been shown when a moderator is provided between the lining part and the piston diameter. Thus, the two components can perform within certain limits, a thermal relative expansion to each other.

Finally, it has proven to be advantageous if the outer peripheral side of the piston is formed at least partially by the lining part. Thus, it is possible, for example, to easily map piston ring grooves of the piston in the region of the covering part.

The advantages described above in connection with the piston according to the invention apply equally to the method for producing a piston according to Claim 7. This method is further characterized by the fact that the covering part can be connected in a simple manner during casting of the piston body with this. This results in a simple way the desired permanent connection.

The production of the lining part itself is preferably carried out in a casting or ümformverfahren, depending on how complex, for example, the intended on the piston body facing side connecting means should be formed.

Further advantages, features and details of the invention will become apparent from the following description of three preferred embodiments and from the drawings; these show in:

Figure 1 is a partial sectional and partial side view of a piston for an internal combustion engine, which consists of a piston body and a completely forming the combustion chamber facing the piston surface forming part.

2 shows a partial sectional and partial side view of the piston according to FIG. 1, wherein the covering part is shown in an alternative embodiment and at least partially also forms the outer peripheral side of the piston; and in

Fig. 3 is a partial sectional and partial side view of the piston according to FIGS. 1 and 2, wherein the covering part is shown in a third embodiment, which mediates a Moderator layer is connected to the piston body.

FIGS. 1 to 3 each show a piston for an internal combustion engine, which is shown in a partial side view to the left of a central axis m of the piston in a partial sectional view and to the right of the central axis m. In the present embodiments, the piston is provided for a truck diesel engine. As included in the scope of the invention, however, it should be considered that the piston could also be used in other internal combustion engines.

The piston in particular comprises a piston head 10, the piston surface 12 of which faces a combustion chamber 14, not shown, of the internal combustion engine. It is common to all three embodiments according to FIGS. 1 to 3 that the piston surface 12 of the piston facing the combustion chamber is formed by a component in the form of a lining part 16 whose shape and specific embodiment will be explained in more detail below. The lining part 16 is inseparably connected to or carried by a piston main body 18, which in turn has on its side facing away from the piston surface 12 and the combustion chamber 14 a non-recognizable piston pin bearing for connecting the piston with an associated connecting rod.

In order to meet the thermal and mechanical stresses at cylinder pressures up to, for example, over 250 bar, the lining part 16 is adapted to the increasing thermal and mechanical stresses. For this purpose, formed as a piston cup lining part 16 is a thermal and possibly also chemical and material engineering Annealing process has been suspended, which leads to an adapted and possibly very fine structure with the highest strength. The lining part 16 is made in the present embodiments, due to the desirable same thermal expansion almost from the same base material or from the same base alloy as the piston body 18.

The lining part 16 is cast in the present embodiments in the casting process of the piston main body 18 directly or molded. For this reason, the covering part 16 has connecting means 22, which in the embodiment according to FIG. 1 form a surface structure 24. In other words, the covering part 16 at the connecting surface to the piston main body 18 has a very high accessible surface, for example, by the surface structure 24 or by a specific porosity. From Fig. 1 it is also apparent that a further connection means 22 is provided in the form of a central anchorage 26 which is provided in the region of the central axis m of the piston and via the casting process to a positive connection between the lining part 16 and the piston body 18 ,

In the embodiment according to FIG. 2, a region 28, in which a piston ring groove 30 of the piston is formed, is additionally used as connecting means. In other words, Fig. 2 shows an embodiment in which an outer peripheral side of the piston or piston crown at least partially - namely over a certain height - is formed by the lining part 16.

In addition, in the embodiments according to FIGS. 1 to 3 it can be seen that the formed as a piston cup Covering part 16 over a predominant area has a shell thickness S, which is based on a piston diameter D according to the formula 1% <S / D <10%. This usually results in a shell thickness S of the lining part 16 of less than one millimeter to more than 10 millimeters in the present interest car or truck pistons. It can also be seen from FIGS. 1 to 3 that the shell thickness S of the covering part 16 is provided at least where not directly a connecting means 22 for connection to the piston main body 18 or a radius or corner region is arranged. It can also be seen from FIGS. 1 to 3 that the covering part 16 is not flat, but at least one combustion recess 32 is formed, inter alia.

It can be seen in particular from FIG. 3 that in the case of piston optimization with regard to low overall densities and maximum material utilization, combinations of materials (eg aluminum, steel, titanium, carbon, composite material with reinforcements) are also conceivable which have certain thermal relative expansions to one another. If here - as indicated in FIG. 3 - a maximum expansion limit of the lining part 16 and of the piston main body 18 is exceeded, a moderator layer 34 can be provided between the two parts, which ensures a crack-free distortion of the two partners of the piston shell or lining part 16 and the piston main body 18 allowed each other at the desired strength.

In the method for producing the above-described piston, the lining part 16 is thus initially produced. The production of the shells or lining parts, which may extend into the piston eye, z. B. also take place with a lost wax process, in which the lining parts 16 are manufactured as precision castings with little Nachbearbeitungsaufwand. In shell shapes of the covering member 16 without undercut, as shown for example in Fig. 1, however, also forming techniques by means of forging and pressing can be used very inexpensively and ensuring maximum strength.

Subsequent to the prefabrication of the respective lining part 16, this is connected or cast on or cast when casting the piston main body 18. Thus, the desired permanent connection between the lining part 16 and the piston body 18 is created.

Overall, it can thus be seen from FIGS. 1 to 3 that the piston surface 12 of the piston, which faces the combustion chamber 14, is completely formed by the lining part 16 by the lining part 16 in the form of the piston shell. As a result, in particular the increasing thermal and mechanical stresses within the combustion chamber 14 can be met.

Claims

claims 1. Piston for an internal combustion engine having a piston main body (18) which is inextricably connected to an associated combustion chamber (14) facing another component (16), characterized in that the further component is formed as a covering part (16) which completely the piston chamber (12) facing the combustion chamber (14). 2. Piston according to claim 1, characterized in that the covering part (16) and the piston base body (18) are made of the same basic alloy, wherein the covering part (16) is subjected to a tempering process. 3. Piston according to claim 1 or 2, characterized in that the covering part (16) is provided on its the piston base body (18) facing side with connecting means (22). 4. Piston according to one of claims 1 to 3, characterized in that the lining part (16) has a shell thickness (S), which is based on a piston diameter (D) according to the formula 1% <S / D <10%. 5. Piston according to one of claims 1 to 4, characterized in that between the lining part (16) and the piston main body (18) is provided a moderator layer (34). 6. Piston according to one of claims 1 to 5, characterized in that an outer peripheral side of the piston is at least partially formed by the lining part (16). 7. A method for producing a piston for an internal combustion engine, in which a piston main body (18) with an associated combustion chamber (14) facing another component (16) is inextricably linked, characterized in that the piston body (18) with a lining part (16 ), which completely forms the piston surface (12) of the piston facing the combustion chamber (14). 8. The method according to claim 7, characterized in that the covering part (16) during casting of the piston main body (18) is connected thereto. 9. Piston according to claim 7 or 8, characterized in that the covering part (16) is prefabricated as a semi-finished part in a casting or forming process.