EP2214850B1 - Method for producing cylinder liners for insert casting use of a motor block - Google Patents

Description

The invention relates to a method for producing a cylinder liner for pouring into a light metal engine block, wherein the cylinder liner has at least two different material layers of light metal.

With increasing power density of modern internal combustion engines, the demands on the cylinder running surfaces in the cylinders, which require highly wear-resistant materials, are steadily increasing. At the same time, the internal combustion engines must meet the increasingly stringent requirements for weight savings, which makes the production of lightweight materials required.

A common way to meet the material side conflicting requirements is to pour wear-resistant cylinder liners in light metal cylinder blocks. The cylinder liners often consist of cast iron or hypereutectic Al alloys, which are cast in an aluminum cylinder block.

For a further increase in the engine power density in terms of lightweight construction, such Al cylinder liners are no longer suitable because they do not have the required strength with good running properties. This is particularly evident in cylinder crankcases made of Al or Mg die-cast alloys, where due to the lower strength of the die-cast alloys, the cylinder liners in turn must have high strength. Used for the cylinder liners solid light metal used deficiencies occur in the required wear resistance.

A further improvement of the wear resistance is achieved, for example, by additionally providing the running surface of cylinder liners with a wear-resistant coating. For example, are from the DE 103 08 562 B3 Cylinder liners for internal combustion engines with a main body with a wear protection coating on the body of the cylinder liner known. This coating consists of at least one layer layer based on a high-strength iron alloy with carbon and oxygen or based on TiO ₂ , wherein the wear protection layer has martensitic phases and forms oxides. The preferred coating method is high speed flame spraying (HVOF).

From the DE10135618 A1 Another method for producing cylinder liners made of Al-Si raceways, with increased wear resistance is known. In this case, at least one process step of a fine machining is provided, during which a mechanical edge layer solidification is carried out.
The WO 2004/014584 A1 discloses a method for producing a cast composite of cylindrical hollow profiles and pouring the cast composite into a cylinder block or crankcase of an internal combustion engine. First, a cylindrical hollow section is made by spray compacting, hot extrusion and hot forming, which consists of a light metal alloy with embedded hard phases. This hollow section is then encapsulated by a light metal alloy without embedded hard phases. Then this cast composite is positioned in a mold forming the cylinder block and cast around with light metal material. The DE 100 09 135 A1 provides liners for pouring into cylinder blocks, with at least one outer roughcast surface in the region of their gate into the cylinder block. The roughcast surface is provided with a thin zinc coating on the surfaces to be infiltrated.

DE 196 21 264 A1 discloses a method of manufacturing a cylinder liner made of an aluminum-silicon alloy for an internal combustion engine. In the area of the running surface of the cylinder liner is an increased silicon content. For this purpose, a core with a cylindrical shape is immersed in a silicon-containing hypereutectic aluminum-based alloy melt and generates a relative movement between the core and the melt to produce a high-silicon-containing edge shell on the core

From the EP 1 281 459 A2 For example, a thixotropic injection molding process is known for making parts such as a cylinder liner having a hard wear resistant inner race with graded alloy composition.

The US 3,536,123 , the JP 590 166 62 A1 and the JP 2008 221 308 A1 envisage centrifugal processes for the production of a cylinder liner. In this case, either a high-silicon-containing aluminum alloy or an Al alloy is treated with reinforcing material in a centrifuge, whereby a cylinder liner is formed, the inside of which has a higher silicon content or content of reinforcing material than the outside.

The EP 1 110 644 A1 describes a cylinder block with a cast-iron cylinder liner cast in aluminum or an aluminum alloy. The surface roughness of the cylinder liner is adjusted in a controlled manner.

The DE 10 2005 004 486 A1 discloses a bushing having a lower portion and an upper portion, wherein the bushing is fixed in an engine block by pouring. The lower portion of the bushing is fixed by the engine block, and the upper portion at least partially disposed circumferentially of the engine block.

The DE 19918229 A1 discloses a continuous casting process in which a cylinder liner is cast while the melt is fine-grained and globulitically solidified due to shear introduced into the melt.

In the JP 58 015 741 A1 A production process for cylinder liners is proposed, in which an inner layer of high-silicon-containing hypereutectoidal aluminum is encapsulated with a further aluminum alloy.

Another possibility is to produce the cylinder liner from hypereutectic Al alloys with a high content of Si precipitates and post-treat the tread after the completion of the engine block, or the cylinder crankcase in such a way that the silicon grains are exposed to the tread.

The known methods have the disadvantage that they are sometimes complex, require several post-processing steps of the treads, cost-intensive coating process for the cylinder interior and sometimes expensive materials.

The object of the invention is therefore to show cost-effective method for producing cylinder liners for pouring into the crankcase or cylinder blocks, wherein the cylinder blocks have improved strength with high wear resistance of the tread.

• Überziehen der Innenseite von Aluminium-Rohren aus Al-Legierungen mit einer Materiallage aus einer lauffähigen AlSi-Legierung zur Bildung von einseitig beschichteten Rohren
• Extrudieren der Rohre unter Reduzierung der Wanddicke und Bildung roher Zylinderlaufbuchsen
• mechanische Nachbearbeitung der rohen Zylinderlaufbuchsen auf Endmaß.

The solution of the object according to the invention is a method for producing a cylinder liner for pouring into a light metal engine block, wherein the cylinder liner has at least two different material layers of light metal with different strength, comprising the steps:

• Coating the inside of aluminum tubes made of Al alloys with a material layer made of an AlSi alloy that can be processed on one side to form tubes coated on one side
• Extrude the tubes reducing wall thickness and forming raw cylinder liners
• mechanical reworking of the raw cylinder liners to final dimension.

The cylinder liner according to the invention can be used for an engine block or cylinder crankcase with a cast-in cylinder liner, which consists of at least two layers of material, which have the two functions of high strength and high wear resistance or good runnability. It is essential that the liner is constructed in one piece. The one-piece cylinder liners consist of a bushing made of a high-strength aluminum alloy or an aluminum alloy reinforced by reinforcing agent and the raceway made of an Al-Si alloy which can be run.

The invention is based on the principle in a bushing to connect the properties Hochfest with wear resistant. As a continuous material occurs while an Al alloy whose composition and additives change over the radial extent of the socket. The change in composition takes place more or less continuously, or can take place with different substance gradients. Outside the transition or penetration areas, the compositions are substantially constant, so that these areas are expediently defined as material layers. The Cylinder bushing has at least two layers of material, which correspond to the cylinder surface and the socket body.

The integral nature of the cylinder liner has the advantage that there are no interruptions of form or material bond, as this can occur for example in coatings of any kind. In addition, a continuous Al phase is formed. This leads in particular to a high thermal conductivity of the socket and a maximum of physical compatibility of the different material layers with each other. This is a big advantage compared to coated cylinder liners.

The engine block in closed or open-deck design is particularly preferably made of Al or Mg die-cast alloys. The existing aluminum alloy cylinder liner, in particular the socket body made of aluminum shows due to the very similar materials a very good connection or fabric and positive engagement with Umgusslegierung.

After pouring into the cylinder crankcase, the track already carries the required workable or wear-resistant material layer and no additional coating is required. The aftertreatment may be limited to a fine turning of the tread. Preferably, however, the raceways in the engine block are honed smooth, with the Si particles remaining in the alloy so that the surface of the raceway is covered with a thin Al layer above the Si grains. Preferably, the thickness of the Al coating is in the range of 2-10 μm.

The cylinder liner has a high stability due to the use of a high-strength Al alloy for the bushing body, which also allows highest combustion pressures in the cylinder, without high-strength Al alloys for the cylinder Envelope must be used. Thus, inexpensive die-cast alloys for the cylinder crankcase are applicable.

Wrought alloys (also called extruded alloys) or cast alloys are preferably used for the bushing body.

The aluminum wrought alloys for the bushing body are typically produced by plate and strip production by hot and cold forming (rolling, extrusion, forging). Typical "hardwrought" aluminum wrought alloys are: AlMg, AlMn, AlMgMn, AlSi Curing Alloys Typical curable aluminum wrought alloys or extruded alloys are the systems AlMgSi, AlCuMg, AlZnMg, AlZnMgCu, collectively Al (Mg, Si, Mn, Cu and / or Zn). Especially suitable are the alloy types 6100 (AlSi1MgMnCu), 4032 (AlSi12.5MgCuNi), 2016 (AlCu9SiMg), 2219 (AlCu6Mn), 2014 · AlCu4SiMg, or 2024 (AlCu4Mg) Furthermore, the Zn-containing alloys of type 7000 are important In addition, the Zn content results in a reduced melting temperature, which makes it easier to bond to the die-cast alloy when casting around the cylinder bore, in particular wrought alloys with tensile strengths of 500-600 MPa and yield strengths of 400-500 MPa Alloy series from AlZn4.5Mg1 to AlZn8MgCu interesting.

The cylinder liner can be singulated or as a cylinder liner package, i. contiguous cylinder liners are used.

Among the suitable casting alloys for the socket body of the cylinder liner are particularly interesting alloys based on AlCu4Ti or AlCu4MgTi, which can reach a yield strength of 240-350 MPa and a tensile strength of 350-420 MPa. Furthermore, the alloy type AlCu4MgAgTi with achievable yield strengths of 410-450 MPa and tensile strengths of 460-510 MPa.
Due to the comparatively low material costs, AlMg5 or AlMg5Si2Mn with a yield strength of 150-200 MPa and a tensile strength of 250-300 MPa are of great interest to the socket body. The classic low-cost Al casting alloys, such as AlSi8Cu3, AlSi9Mg, AlSi11Mg, or AlSi12CuNiMg can also be used. In these less strong Al-cast alloys, the disadvantage of lower strength can optionally be made up for by the structural design. For example, comparatively higher wall thicknesses of the socket body can be realized.
The inner material layer corresponds to the cylinder liner. For these an executable Al-Si alloy is provided. These are in particular hypereutectic Al-Si alloys, in which Si precipitates lead to increased wear resistance. The preferred alloys for forming the cylinder bore include the alloys based on AlSi12CuMgNi, AlSi12Cu4Ni2Mg, AlSi18CuMgNi, or AlSi25CuMgNi. Further preferred is an AlSi9-13 alloy, in particular with additions of Cu, Mn, Fe, Ni and / or Ti in an amount of less than 3% by weight.
A further embodiment provides to provide the cylinder liner with bound in the alloys additional material. The cylinder liner can be further reinforced by reinforcing material of fibers or particles. The additional materials have the tasks to strengthen the bush body or to improve the wear resistance and running properties of the cylinder liner.
By introducing reinforcing particles or reinforcing fibers, with a significantly higher modulus of elasticity, such as SiC, the modulus of elasticity in the supporting bushing can be significantly increased. This has advantages with respect to the delay in operation and thus has an advantageous effect on fuel and oil consumption. By constructing the one-piece bushing with a plurality of material layers or material gradients, it can be ensured that the reinforcing material materials, for example the SiC particles for increasing the E-modulus, are not present in the raceway area. There would otherwise be problems regarding machinability of the raceway and wear of the friction partners, ie piston ring or piston.

Different additive materials can be used simultaneously to achieve both effects at the same time.

As a reinforcing material of the female body, the reinforcing materials Si ₃ N ₄ , TiC, ZrO ₂ and / or SiC are preferable. These can be used as particles, in particular as reinforcing fibers.
In particular Si particles are important as additional material for the improvement of the raceway.

Within the cylinder liner, the different Al alloys with filler material from liner body and race or tread merge into one another as the alloy compositions change in a gradient, leaving the Al as a continuous phase.

The engine block may have a more or less thick intermediate layer between the socket body and the Umgussmaterial. This is a mixing zone of cylinder liner material and the casting material. Such an intermediate layer is observed in particular when the cylinder liner has an outer coating or an outer material layer prior to pouring. This layer or layer are applied for the purpose of better connection or improved material bond between the cylinder liner and the encapsulation material. in this connection For example, coatings of Zn or Sn alloys are known.
The cylinder liner for pouring into a light metal engine block has at least two different layers of material of different strength and wear resistance, the cylinder liner being integrally formed from a female member of a high strength aluminum alloy or reinforcing agent reinforced aluminum alloy and a raceway of a less strong Al-Si alloy ,
The construction of a cylinder liner in cross section is schematically in Fig. 1 demonstrated. The proportions are changed for clarity.
It shows the Fig.1 a cylinder liner (1), a cylinder liner (2), a bushing body (3) and a material outer layer (4).
The layers of material merge into one another in a gradient. In this case, the gradients are preferably very steep, so that a pronounced layer-like or layer-like structure results with a cylinder bore (2) and a bushing body (3). The thickness of the non-graded layer of the high-strength aluminum alloy is preferably above 3 mm.
A preferred embodiment provides a bushing body (3) made of particle-reinforced or unreinforced AlSi12, AlCu4Ti, AlCu4MgTi or AlZn4.5Mg1 to AlZn8MgCu and an inner material layer forming the cylinder bore (2) from one of the cast alloy AlSi17, AlSi18CuMgNi or AlSi25CuMgNi.
Another variant of the cylinder liner provides a material outer layer (4). These can be coatings to improve the encapsulation process.

In a preferred embodiment of the invention, the cylinder bore (2) and the outer material layer of the same alloy.

In one possible method for manufacturing a cylinder liner for pouring into a light metal engine block, wherein the cylinder liner has at least two different layers of material of light metal with different strength, the centrifugal casting technique is used. It is envisaged to carry out the centrifugal casting of an Al alloy with Si particles in such a way that the Si particles accumulate indoors to form an Al-Si alloy which can be processed and depleted in the outer region to form a solid aluminum alloy. This phase separation and formation of a Si gradient is possible because Si and the Al alloy differ significantly in terms of their density. Due to the centrifugal forces during spinning, the specifically lighter Si particles can float upwards or accumulate.

This principle of density-dependent gradient formation can also be used for further filler material in particles and / or fiber form. Preferably, the Al alloy to be spun additionally has ceramic reinforcing particles with a higher density than the Al alloy, which accumulate in the outer area during centrifugal casting. Preferred reinforcing particles include SiC, TiC, Si ₃ N ₄ and / or ZrO ₂ .

A suitable combination of specific lighter and heavier particles is given for example by Si and SiC. Due to the density differences, the Si particles preferentially accumulate on the inside and the SiC particles on the outside of the hypereutectic AlSi alloy with SiC particles. That means the Si as a career improvement can be used, while the SiC content increases to the outer edge, thus increasing the rigidity of the socket body.

In centrifugal casting, a roughening of the outer surface of the cylinder liner can be achieved by introducing a suitable size or tool geometry. This has the advantage that, analogous to the known gray cast-roughcasting bushes, a roughcast surface can be constructed on the bush outer skin, which is very advantageous for connection to the die-casting, since in addition to a metallic connection, a high degree of mechanical clamping of the bushing to the diecasting material can be achieved ,

• Überziehen der Innenseite von Aluminium-Rohren aus festen Al-Legierungen mit einer Materiallage aus einer lauffähigen AlSi-Legierung zur Bildung von einseitig beschichteten Rohren
• Extrudieren der Rohre unter Reduzierung der Wanddicke und Bildung roher Zylinderlaufbuchsen
• mechanische Nachbearbeitung der rohen Zylinderlaufbuchsen auf Endmaß.

An embodiment of the method according to the invention provides a casting method with at least the following steps:

• Coating of the inside of aluminum Al-alloy pipes with a material layer of AlSi alloy capable of forming single-sided coated pipes
• Extrude the tubes reducing wall thickness and forming raw cylinder liners
• mechanical reworking of the raw cylinder liners to final dimension.

The coating of the Al tube is preferably carried out by casting aluminum alloy. Likewise, other methods are suitable. This process step can rely on cost-effective and simple processes, since it does not have to be made to measure. Even the connection between the two layers can be incomplete, since the subsequent step of coextrusion causes a mechanical alloying or a firm connection of the material layers with each other.

The aluminum tubes can be additionally provided on the outside with a material layer (material outer layer (4)) made of an Al alloy. Preferably, this is essentially the same composition as the aluminum or magnesium die casting alloy for the engine block.

The coating of the Al tube can also be done by immersion in an AlSi alloy melt, so that the socket body is covered on both sides with an AlSi alloy.

In the next process step, the coated tube is extruded, whereby the wall thickness is reduced. Due to the high pressure, a firm mechanical connection and welding of the different material layers takes place.

The coarse cylinder liner formed by coextrusion with at least two layers of material is then mechanically post-processed to adjust the final dimension.

The aluminum tubes are preferably formed from wrought alloys, in particular extruded wrought alloy or from Al casting alloys with particle reinforcement.

Another possibility for producing a cylinder liner for pouring into a light metal engine block, with an inner material layer of a running AlSi alloy and an outer material layer of a solid Al alloy are composite casting, in which different cast melts are cast simultaneously.
The cylinder liner can be made by stratified or graded co-thixocasting in strand form or co-continuous with the various Al alloys.

The workable AlSi alloys are characterized by the fact that they contain crystalline and relatively coarse Si precipitates in the microstructure. The Si crystals are of great importance for increasing the wear resistance.

A preferred embodiment of the invention provides, after pouring the cylinder liner into a light metal engine block structure Honing the tread perform. The structuring should represent as possible the finishing of the surface.

Ideally, in comparison to today's technology, this finely turned raceway is honed as smoothly as possible, i. the supporting Si particles or intermetallic phases are not exposed mechanically or chemically but remain with a very thin coating of aluminum (2-10 μm). This allows a significant reduction in the coefficients of friction and thus the friction loss. To avoid seizing the piston / piston rings on such a track, a fine structure, e.g. a spiral honing introduced (fine grooves in Siralform introduced), which provide the required oil retention volume. Structure honing is thus used to form oil retention pockets or oil reservoirs for the engine oil. These are in particular formed as fine grooves or grooves, which typically run helically.

The engine blocks with textured treads are preferably used in combination with pistons having slide-coated piston rings. Particularly preferred is the combination of structure-matched treads with pistons having DLC-coated piston rings. DLC is understood to mean diamond-like-carbon coatings, ie, diamond-like layers deposited in particular from the gas phase. The advantage of this combination is that the feared at high piston stresses material welding between the piston rings and the Al of the tread is significantly reduced. In particular, it is thus harmless that the Si crystals are not particularly exposed. While so far smeared or distributed Al had to be removed again after honing in a further process step over the Si crystals, it can be dispensed with in the preferred combination with DLC-coated piston rings.

The use of coated piston rings, in particular DLC-coated, ensures that seizing is avoided. It has been shown that DLC coated piston rings, the seizure safety of the structurally sound AlSi raceways, in which the Si particles were not exposed by about 100% have been improved.

Claims (4)

1. Method for producing a cylinder liner (1) for casting into a light alloy engine block, the cylinder liner (1) having at least two different material layers made of light alloys of different strength,
   the method comprising the characterising steps of:

   - coating the inside of aluminium tubes made of aluminium alloys with a material layer made of an AlSi alloy capable of running to form tubes coated on one side,

   - extruding the tubes while reducing their wall thickness and securely joining the material layers,

   - mechanical reworking of the unfinished cylinder liners (1) to final dimensions.
2. Method according to claim 1,
   characterised in that
   the aluminium tubes are in addition externally coated with a material layer made of an Al alloy which has the same composition as the aluminium or magnesium die-casting alloy for the engine block.
3. Method according to claim 1 or 2,
   characterised in that
   at least one of the material layers is applied by casting around or onto the aluminium tube.
4. Method according to any of claims 1 to 3,
   characterised in that
   the aluminium tubes are selected from wrought alloys or extruded wrought alloys or from Al casting alloys with particle reinforcement.

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