DE19813430A1 - Lightweight piston for use in diesel engines - Google Patents

Abstract

The lightweight piston has reinforcing applied to the crown and to the upper sides of the piston to prevent thermal distortion and hence damage to the engine. The reinforcing comprises steel, nickel, monel or other metals and is applied as a layer onto the base metal of the piston. The piston is pressed by hydro forming using inner pressure. The forming uses a sheet or a tube as a base material and is formed in steps.

Description

The invention relates to a composite casting piston and a method for producing a Composite casting piston with a head part and at least partially over the head part covering reinforcement part.

Highly loaded pistons, for example made of aluminum alloys, occur due to thermal and mechanical stresses due to aging behavior, notch effects of the surface and structural changes, which in connection with high mecha niche loads can cause cracks in the piston crown area. These cracks have a very high rate of progress and lead to the destruction of the component and thus mostly to a total destruction of the engine. Because of the working process Pistons for direct-injection diesel engines are often indispensable combustion chamber troughs particularly badly affected.

From DE-OS 25 13 272 and DE-OS 36 02 241 pistons for internal combustion engines known, wherein a casing of the piston head part with a reinforcement part in one Casting process takes place or is formed. Here have improvements in aging keeping the piston alloy and increasing the heat resistance the area of application for aluminum die-cast pistons opened up in more highly loaded internal combustion engines. Further increasing However, requirements mainly arise due to the structure of the casting process Homogeneities and oxides in the casting limits.

As a remedy, for example, in racing and with supercharged gasoline engines Forged pistons used, however, because of the lack of a ring carrier in diesel motors cannot be used. Such plungers are in production more complex than cast iron and therefore also more expensive.  

This is used to solve diesel engines with a correspondingly high load Problems built pistons, pendulum-shaft pistons or pistons made of ferrous materials can withstand higher temperatures and ignition pressures than Al materials. The disadvantage is that high surface temperatures occur during combustion, which the Raise the temperature level of the entire combustion chamber. This creates in ver combustion increases nitrogen oxides, which means a high level of exhaust gas aftertreatment required. In addition, the filling of the combustion chamber in the intake stroke is significantly worse and the overall efficiency of the engine decreases. All pistons are made of ferrous materials relatively massive, which negatively affects the mass balance especially with fast-moving Engines.

In the case of further proposed solutions, for example according to EP 0 295 481 A2 partial reinforcements in the area of the highest voltages provided or switched on pour, e.g. B. Gray cast iron rings on the edge of the trough. These have the disadvantage that either the Strength of the connecting layer, for example Alfin, is insufficient or the required Connection struts through the casting are strongly promoting cracking.

There are also attempts to squeeze cast in the aluminum fiber reinforced areas to manufacture. However, this has the disadvantage that unavoidable, sporadically occurring Defects or defects in the fiber composite act as a crack starter.

From DE-OS 24 32 990 a piston for internal combustion engines is known, wherein a jacket section covers the piston in predetermined sections.

EP 0 118 204 B1 describes a piston for an internal combustion engine, wherein a reinforcement made of ferrous material is placed over an aluminum piston and has openings for a firm connection with the aluminum connection.

From the essay "Expanding pipes by internal high pressure forming" by Dr.-Ing. Friedrich Klaas, Blech Rohr Profile 35 (1988) 3, pages 175 to 180, and from the Article "Processes and machines for the cold forming of pipes" by Dr.-Wirtsch.-Ing. Fritz-J. Neff, Blech Rohr Profile 28 (1981) 2, pages 54 to 57 is also the internal high pressure forming pipes, known for example for exhaust pipes.  

The present invention has for its object a method of the above Art to provide, the above disadvantages are overcome and thermal-mechanical damage to highly loaded areas of aluminum pistons to prevent reinforcement parts with higher heat resistance from being installed locally.

This object is achieved by a method of the above. Kind with the in claim 1 marked features solved.

For this purpose, it is provided according to the invention that the reinforcement part from an output Work piece by means of hydroforming according to the contours of a workpiece Section of the headboard is made.

Advantageously, this provides ready-made contours that have a high dimensional have accuracy and make subsequent processing unnecessary. Of Another is an inexpensive manufacture of the reinforcement parts, in spite of being more complex in some cases Contours guaranteed. The hydroformed reinforcements can be comparatively thin be walled and thus contribute to a reduction in the total piston weight at.

A reinforcement part produced by hydroforming can simply be made in one step following Alfin process can be cast without post-processing is required.

The hydraulic forming is expediently carried out by means of internal high-pressure forming.

In a particularly advantageous embodiment, a flat workpiece is used as the starting workpiece Sheet or tube used.

A simple and inexpensive method results from the fact that the reinforcement part by partially bulging an original workpiece, by means of rotationally symmetrical Widening a starting workpiece or by means of rotationally symmetrical widening upsetting an original workpiece.

Advantageously, at least two of the above three reshaping types combined.  

Post-processing of the composite casting piston is due to the high dimensional accuracy of the Reinforcement part unnecessary.

Especially, but not exclusively, for pistons for direct injection diesel engines an undercut trough shape also gives a positive connection dung that is supported by the alfin compound.

In a particularly preferred manner, the positive connection is improved in that a piston ring field is molded in the casting or reinforcement part.

Heat-resistant steel is expediently used as the material for the cast-in or reinforcing part with coefficients of thermal expansion similar to the Al material used. Because of the poorer thermal conductivity compared to this Al material After a cold start of an internal combustion engine equipped with this, Stahles becomes its Operating temperature reached faster, which benefits in terms of cold start emissions and the light-off behavior of a downstream catalytic converter.

The manufacturing process using hydroforming or hydroforming leaves material thicknesses from about 0.4 mm to about 3 mm, in particular on the composite casting or reinforcement part, so that a very thin shell with high accuracy of fit can be applied to the piston. Because of this high accuracy of fit of the casting or reinforcement part, a Bear Processing of the piston crown and a ring section are omitted if the entire processing starts from this area.

Furthermore, according to the invention, a piston for an internal combustion engine with an armature tion part proposed, which at least partially covers a head part of the piston, wherein the armoring part is manufactured according to the above method.

Further features, advantages and advantageous configurations of the invention result from the dependent claims, as well as from the following description of an embodiment Example of the invention with reference to the accompanying drawings. This shows in  

Fig. 1 shows a partial section of a Verbundgußkolbens according to a first preferred embodiment,

Fig. 2 is a sectional view taken along line AA of Fig. 1,

Fig. 3 is a partial section of a Verbundgußkolbens according to a second preferred embodiment of the invention, and

FIGS. 4 to 6 more partial sections according to the invention Verbundgußkolben according to further preferred embodiments.

The first embodiment shown in FIG. 1 of a composite casting piston 14 for a turbodiesel engine with direct injection has a reinforcing part 10 and a piston surface 12 . The reinforcing part 10 is connected to the piston 14 in such a way that the reinforcing part delimits a combustion chamber (not shown in more detail) and shields the material of the piston 14 from high temperatures and pressures in the combustion chamber.

Fig. 2 shows the structure of the different layers of the composite casting piston. From above, that is seen from the piston top 12 , the following layer is provided: the reinforcing part 10 , which was preformed by means of hydroforming, and a connecting layer 16 , which produces a material bond between the reinforcing part 10 and a base material 18 according to the following from a gravity casting. A positive connection between reinforcement 10 and piston 14 is formed at points 20 .

Fig. 3 shows a second embodiment of a composite cast piston for a gasoline engine.

Partial reinforcements 10 are also possible. This is shown in FIGS. 4 to 6. These partial reinforcements 10 extend, for example, only to the highly loaded area or to the trough area up to an upper flank of a first annular groove 22 . In FIG. 4, a ring carrier 24 is additionally provided, which can also be hydroformed. These variants are more or less partial tillage measures before geous.

In addition to steel materials, essentially all types of material that can be financed can be used be applied. Nickel-containing or copper-nickel-containing, heat-resistant are particularly preferred Materials such as Monel or the like. For the use of these materials advantageously modified the composition of the Alfinbad suitably. Basically all materials soluble in liquid aluminum are suitable.

The known Alfin method in gravity casting has hitherto been carried out in the case of composite casting of aluminum with iron materials and has proven to be particularly reliable when casting in a ring carrier. By means of this Alfin method, it is now proposed to cast in a piston upper part or a reinforcing part 10 , which either reinforces a narrowly restricted area of high tension or encompasses the entire piston head 14 including the ring section. This reinforcement part 10 is prefabricated using a hydroforming process and therefore requires little or no further processing.

The reinforcing part 10 is preferably cast in using the alfin process, the subsequent piston surface 12 being passivated before the alfinizing, so that a one-sided alfin layer can be applied. The passivation can be generated by any type of surface layer that is not wetted by the melt of the Alfin bath, e.g. B. by ceramic or graphite-containing layers, or by vapor deposition or spraying on layers of suitable materials.

Heat-resistant aluminum alloys can continue to be used as a casting material. In addition, reinforcement of crack-prone areas is obtained with high-temperature steel materials that have up to 4 times higher heat resistance. The thin steel jacket produces a faster heating of the piston surface 12 in the warm-up phase of the engine. This results in fewer emissions of unburned hydrocarbons, particles and carbon monoxide.

The reinforcement material consists of homogeneous rolled material with the finest, flawless Structure without casting inhomogeneities.

Machining of the piston crown can be omitted, since the casting or reinforcement part 10 can be manufactured within the required tolerance range.

The ring carrier of conventional construction can be replaced by a corresponding shaping of the armoring part 10 .

Compared to steel pistons, built pistons and pendulum-shaft pistons, weight results advantages through only a thin steel reinforcement. This improves the vibration level keep the engines especially with 3 and 4 cylinder engines. There are also higher speeds possible. Thanks to improved heat dissipation thanks to the thin sheathing of the Al core lower nitrogen oxide emissions occur at operating temperature. Furthermore, the Her service costs significantly lower.

In comparison with compacts, the ring groove is now reinforced to reduce wear possible, which brings price advantages.

Compared to earlier composite cast pistons with bowl edge inserts and spiders, this results in an improvement of the positive and frictional connection through larger coherent Surfaces. There are no notch effects due to connecting webs between troughs edge and ring bearer. The pouring of a ring carrier is during partial machining of the piston still possible.

In contrast to fiber reinforcement infiltrated with Squeeze Gast (liquid presses) use results in the highest homogeneity in the surface layer of the Ver cast part, which is practically notch effect. Furthermore, a higher one is achieved Heat resistance to fiber-reinforced aluminum.

Instead of the Alfin process or similar immersion release processes, the sprue can be used procedure with connection layers for aluminum from z. B. tin, zinc or copper which are preferably applied galvanically or sprayed. So that can Cast-in part in gravity casting is cast in a force-fitting manner.

Another preferred variant consists in the pouring part by flame or plasma spray coating on one side, creating a porous surface. When pouring a liquid diffusion bond forms the alfine bond to Zugfe stability still surpasses.  

It is also possible to dispense with the binding layer 16 between the reinforcement 10 and the base material 18 ( FIG. 2) in the case of very thin reinforcement parts. Here, the reinforcement part is forged into the die and is held in place by positive locking.

Claims (13)

1. A method for producing a composite casting piston with a head part and a reinforcing part at least partially covering the head part, characterized in that the reinforcing part is produced from an initial workpiece by means of hydroforming accordingly contours of a portion of the head part to be covered. 2. The method according to claim 1, characterized in that the hydroforming takes place by means of hydroforming. 3. The method according to claim 1 or 2, characterized in that a flat sheet or tube is used as the starting workpiece. 4. The method according to any one of the preceding claims, characterized in that the reinforcement part by partially bulging an original workpiece is provided. 5. The method according to any one of claims 1 to 3, characterized in that the reinforcement part by means of a rotationally symmetrical expansion of an initial work piece is produced. 6. The method according to any one of claims 1 to 3, characterized in that  the reinforcement part by means of rotationally symmetrical expansion dipping Starting workpiece is produced. 7. The method according to any one of claims 1 to 3, characterized in that at least two of the types of forming can be combined according to claims 4 to 6. 8. The method according to any one of the preceding claims, characterized in that in a subsequent step, the reinforcement part using an Alfin process is integrally cast in a known casting process. 9. The method according to any one of the preceding claims, characterized in that an undercut trough shape of the piston is formed. 10. The method according to any one of the preceding claims, characterized in that a piston ring field is formed in the reinforcement part. 11. The method according to any one of the preceding claims, characterized in that A heat-resistant steel is used as the material for the reinforcement part. 12. The method according to any one of the preceding claims, characterized in that a material thickness of 0.4 mm to 3 mm is molded into the reinforcement part. 13. Piston for an internal combustion engine with a reinforcement part, which is a head part of the piston at least partially covered, characterized in that the reinforcement part according to a method according to at least one of the above going claims is made.