DE19813430B4 - Composite cast piston and method for its production - Google Patents

Abstract

Method for producing a composite cast piston (14) having a head part and a reinforcing part (10) at least partially covering the head part, characterized in that the arming part (10) is produced from an initial workpiece by hydro-forming according to contours of a section of the head part to be covered and both positively and materially after a dipping-release process or by means of connecting layer (16) is connected to the head part.

Description

The The invention relates to a composite cast piston and a method for Making a composite cast piston with a head part and a head part at least partially covering Reinforcing part.

at highly loaded piston, for example, Al alloys occur due to thermal and mechanical stresses caused by the aging behavior, notch effects on the surface and structural changes which, in conjunction with high mechanical loads cracks may result in the piston crown area. These cracks have one very high speed of progress and lead to the destruction of the Component and thus usually to a total destruction of the engine. Because of the for the Working process often indispensable Burner trough are pistons for directly injecting diesel engines particularly affected.

From the DE 25 13 272 A1 and the DE 36 02 241 A1 Pistons for internal combustion engines are known, wherein a casing of the piston head part takes place or is formed with a reinforcing part in a casting process. Here, improvements in the aging behavior of the piston alloy and increasing the heat resistance have opened up the area of application for Al die-cast pistons in combustion engines subject to higher loads. However, further increasing requirements set limits mainly because of the casting process-related structural inhomogeneities and oxides in the casting.

When Remedy for example in racing and highly charged Gasoline engines forged pistons used, however, because of the absence a ring bearer can not be used in diesel engines. Such plunger are more expensive than cast pistons and thus more expensive to produce.

at Diesel engines with correspondingly high load are used for solution Built this problem piston, pendulum piston or piston Ferrous materials that are significantly higher Temperature loads and ignition pressures as Al materials can endure. The disadvantage is that at burning high surface temperatures arise, raise the temperature level of the entire combustion chamber. As a result, more nitrogen oxides are produced during combustion, resulting in a high effort in the exhaust aftertreatment requires. In addition, the filling the combustion chamber in the intake stroke significantly worse and the overall efficiency of the engine decreases. All pistons of iron materials are relative massive, which has a negative impact on the mass balance especially at high-speed engines.

For further solutions, for example according to the EP 0 295 481 A2 , partial gains in the range of highest voltages are provided or cast in, for. B. gray cast rings on the trough edge. These have the disadvantage that either the strength of the compound layer, such as Alfin, is insufficient or the necessary connecting struts are strongly crack-promoting by the casting.

It There are also attempts to squeeze fiber reinforced areas in aluminum Cast manufacture. However, this has the disadvantage that unavoidable, Sporadically occurring defects or defects in the fiber composite as Rißstarter Act.

From the DE 24 32 990 A1 a piston for internal combustion engines is known, wherein a jacket portion covers the piston in predetermined sections.

In the EP 0 118 204 B1 For example, a piston for an internal combustion engine is described wherein a reinforcement of ferrous material is disposed over a piston of aluminum and has openings for a firm connection with the aluminum connection.

Out the essay "Aufweitabtuchen of tubes by hydroforming "by Dr.-Ing. Friedrich Klaas, sheet metal tubes profiles 35 (1988) 3, pages 175 to 180, and from the article "method and machines for the cold forming of tubes "by Dr.-Wirtsch.-Ing. Fritz-J. Neff, sheet metal tubes profiles 28 (1981) 2, pages 54 to 57 is also the hydroforming of pipes, for example for exhaust pipes known.

With regard to this are also from the DE 42 16 111 A1 a piston-rack unit for a hydraulic power steering and a method for the production thereof. It is proposed here to carry out the piston-rack unit with piston, piston rods and toothed section in one piece by means of the internal high-pressure method of a tube.

Of the The present invention is based on the object, a method of the above type available to provide, with the above-mentioned disadvantages are overcome and thermo-mechanical damage heavily loaded areas of aluminum pistons by a local Installation of reinforcing parts higher To prevent heat resistance.

These The object is achieved by a Method of o. Type having the features characterized in claim 1 solved.

To It is inventively provided that the reinforcing part from an initial workpiece by means of hydro-forming according to contours of a to be covered Section of the head part made and both form-fitting as also cohesive after a dipping-dissolving process or is connected by means of connecting layer with the head part.

advantageously, be prepared by this Fertigkonturen which a high dimensional accuracy have and make subsequent processing dispensable. Furthermore, it is a low cost Production of armouring parts despite partly complex contours guaranteed. The hydroformed reinforcements can comparatively thin-walled be formed and thus contribute to a reduction of the total piston weight at.

One Hydro-formed reinforcement can be simple can be cast in a subsequent Alfin process, without a post-processing is required.

Conveniently, Hydroforming takes place by hydroforming.

In In a particularly advantageous embodiment, the starting workpiece is a flat sheet metal or pipe used.

One simple and inexpensive Method results from the fact that the reinforcement part by means of partial Bulging of a starting workpiece, by means of rotationally symmetrical expansion of a starting workpiece or produced by means of rotationally symmetrical expansion dipping an initial workpiece becomes.

In Advantageously, at least two of the above are three types of transformation combined.

A Post-processing of composite cast piston is due to the high dimensional accuracy of the reinforcing part dispensable.

Especially, but not exclusively at piston for directly injecting diesel engines are obtained by an undercut Trough shape in addition a form-fitting Compound that is cohesively supported by the Alfin compound.

In Particularly preferably, the positive engagement is improved by a piston ring field in the pouring Arming part is formed with.

When Material for the sprue or reinforcing part is expediently heat-resistant steel with coefficients of thermal expansion similar to those used Al material used. Because of compared to this Al material poorer thermal conductivity This steel will be equipped with a cold start Internal combustion engine whose operating temperature reaches faster, which Advantages regarding the cold start emissions and the starting behavior of a downstream catalytic converter brings.

The Manufacturing process by hydroforming or hydro-forming leaves material thicknesses from approx. 0.4 mm to approx. 3 mm, in particular on composite casting or Arming part, so that a very thin shell high accuracy of fit can be applied to the piston. Because of this high accuracy of fit of the pouring Arming parts or a machining of the piston crown and a ring part omitted, if the entire processing of this Area goes out.

Further is inventively a piston for one Internal combustion engine proposed with a reinforcing part, which a head portion of the piston at least partially covered, wherein the reinforcing part is manufactured according to the above method.

Further Features, advantages and advantageous embodiments of the invention arise from the dependent ones claims, as well as from the following description of an embodiment the invention with reference to the attached Drawing. This shows in

1 a partial section of a composite cast piston according to the invention according to a first preferred embodiment,

2 a sectional view taken along the line AA of 1 .

3 a partial section of a composite cast piston according to the invention according to a second preferred embodiment and

4 to 6 further partial sections of composite cast piston according to the invention according to further preferred embodiments.

In the 1 illustrated first embodiment of a composite cast piston 14 for a turbo diesel engine with direct injection has a reinforcing part 10 and a piston surface 12 , The reinforcement part 10 is doing so with the piston 14 connected, that the reinforcing part defines a combustion chamber, not shown, and the material of the piston 14 shielded from high temperatures and pressures in the combustion chamber.

2 shows the structure of the different Layers of composite cast piston. From above, so from the piston top 12 The following layer is provided: The reinforcing part 10 , which was preformed by hydroforming and a tie layer 16 , which a material connection between the Armierungsteil 10 and a subsequent basic material 18 produced from a gravity casting. At the points 20 is a positive connection between reinforcement 10 and pistons 14 educated.

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

There are also partial reinforcements 10 possible. This is in the 4 to 6 shown. These partial reinforcements 10 For example, they expand only on the highly loaded or on the trough area up to an upper flank of a first annular groove 22 out. In 4 is additionally a ring bearer 24 provided, which may also be hydroformed. In these variants, more or less partial tillage operations are advantageous.

Except steel materials can essentially all alfinierbaren material types are used. Particularly preferred are nickel-containing or copper-nickel-containing, heat-resistant materials, such as Monel or the like. For the Use of these materials is advantageously the composition the Alfin bath modified suitably. In principle, all are suitable in the liquid Aluminum dissolvable Materials.

The known Alfin process in gravity casting has hitherto been carried out in composite casting of aluminum with iron materials and has proven to be reliable especially when casting a ring carrier. By means of this Alfin method is now proposed, a piston upper part or a reinforcing part 10 to infuse, which either amplifies a narrow range of high voltage or the entire piston head 14 including the ring section. This armouring part 10 is prefabricated in register by means of a hydroforming process and therefore requires little or no further processing.

The reinforcing part is poured in 10 preferably in the Alfinverfahren, wherein the later piston surface 12 is passivated before Alfinieren, so that a one-sided Alfinschicht can be applied. The passivation can be generated by any type of surface layer which is not wetted by the melt of the alpen bath, e.g. As by ceramic or graphite-containing layers, or by vapor deposition or spraying of layers of suitable materials.

Heat-resistant Al alloys can continue to be used here as a casting material. In addition, a reinforcement of areas susceptible to cracking with heat-resistant steel materials is obtained, which have up to four times higher thermal stability. The thin steel jacket produces a faster heating of the piston surface during the warm-up phase of the engine 12 , This results in less emissions of unburned hydrocarbons, particulates and carbon monoxide.

Of the Reinforcing material consists of homogenous rolled material with finest, faultless structure without Gußinhomogenitäten.

A machining of the piston head can be omitted, since the sprue or reinforcing part 10 can be produced in the required tolerance range.

The ring carrier of conventional construction can by a corresponding shaping of Armungssteiles 10 be replaced.

Opposite steel pistons, Built-piston and pendulum piston results in weight advantages by only a thin one Steel reinforcement. This especially improves the vibration behavior of the motors for 3- and 4-cylinder engines. Furthermore, higher speeds are possible. By an improved heat dissipation through thin ones Cladding of the Al core results in lower operating temperatures Nitrogen oxide emissions. Furthermore, the production costs are clear lower.

in the Comparison with compacts is now a reinforcement of the annular groove for wear reduction possible, which brings price advantages.

Compared to earlier composite cast piston with trough edge inserts Spinning results in an improvement of the form and adhesion through larger connected surfaces. It comes to no notch effects by connecting webs between trough edge and ring bearer. The sprue of a ring bearer is during partial machining of the piston crown still possible.

in the Contrary to using squeeze cast (liquid presses) infiltrated Faserarmierungseinsätzen results in a highest homogeneity in the surface layer the composite casting, which is practically not kerbwirkungsfrei. Furthermore, one achieves a higher heat resistance across from fiber reinforced aluminum.

Instead of the Alfin process or similar dipping-dissolving processes, the sprue with bonding layers for aluminum from z. As tin, zinc or copper are provided, which are preferably applied galvanically or sprayed. Thus, the casting in the gravity casting be poured positively.

A Another preferred variant is the casting by Flame or plasma spraying unilaterally to coat, with a produced porous surface becomes. When pouring means liquid presses Diffusion bonding occurs, which affects the almin bond to tensile strength even better.

It is also possible with very thin reinforcing parts on the bonding layer 16 between reinforcement 10 and base material 18 ( 2 ) to renounce. Here, the reinforcing part is forged in the die and finds over positive engagement stop.

Claims (13)

Method for producing a composite cast piston ( 14 ) with a head part and a head part at least partially covering Armungssteil ( 10 ), characterized in that the reinforcing part ( 10 ) produced from an initial workpiece by means of hydro-forming according to contours of a portion of the head part to be covered and both positive and cohesive after a dipping-release process or by means of bonding layer ( 16 ) is connected to the headboard. Method according to claim 1, characterized in that that the Hydro-forming by hydroforming takes place. Method according to claim 1 or 2, characterized that as Starting workpiece a flat sheet or tube is used. Method according to one of the preceding claims, characterized characterized in that Reinforcing part produced by partial bulging of a starting workpiece becomes. Method according to one of claims 1 to 3, characterized that this Arming made by means of rotationally symmetrical expansion of an initial workpiece becomes. Method according to one of claims 1 to 3, characterized that this Reinforcing part by means of rotationally symmetrical Aufweitstauchens a Output workpiece will be produced. Method according to one of claims 1 to 3, characterized that at least two of the transformation types according to claims 4 to 6 are combined. Method according to one of the preceding claims, characterized characterized in that a subsequent step, the reinforcing member by means of an Alfin method cohesively in a known casting process is poured. Method according to one of the preceding claims, characterized characterized in that a undercut trough shape of the piston is formed. Method according to one of the preceding claims, characterized characterized in that a Piston ring field in the reinforcing part is formed with. Method according to one of the preceding claims, characterized characterized in that as Material for the reinforcing part is a heat-resistant steel is used. Method according to one of the preceding claims, characterized characterized in that Arming molded a material thickness of 0.4 mm to 3 mm becomes. Piston for an internal combustion engine with a reinforcing part, which is a head part the piston is at least partially covered, characterized that this Arming part according to a method according to at least one of the preceding claims is made.