ALUSIL® Cylinder Blocks Kolbenschmidt Pierburg Group

Kolbenschmidt Pierburg Group ALUSIL® cylinder blocks for the new AUDI V6 and V8 SI engines 1. Audi setting standards in lightweight design 2. Reasons in favor of ALUSIL® from the viewpoint of Audi: With its vehicle model series, Audi is setting new standards in lightweight design. So it is only logical for the carmaker again There are many technical reasons which induced the car- to count on aluminium in developing the cylinder blocks for maker Audi to adhere to the proven ALUSIL® concept: its new spark-ignition V-engines (Fig. 1). On account of the reduced wall thickness (cylinder land width of only 5.5 mm ALUSIL® makes a minimum weight at a high degree of in- (Fig. 2) between cylinder bores), Audi relies on the hypereu- tegration of engine functions like lubricant, coolant and tectic aluminium-silicon alloy AlSi17Cu4Mg registered for KS engine venting circuits. ATAG under the brand name of ALUSIL®. This concept allows the pistons to move directly along the honed cylinder bore ALUSIL® enables minimum overall cylinder block lengths surfaces of the aluminium casting – an ideal condition for to be implemented because the engines can be operated high-performing engines. without inserted cylinder liners. To achieve the shortest possible engine length at a specified swept volume and stroke, the cylinder bore diameter should be kept as large V6 cylinder block V8 cylinder block (fuel stratified injection [FSI]) V8 cylinder block cylinder block of the (multi-point injection) existing Audi V8 engine Fig. 1: ALUSIL® cylinder block of the new Audi V6 and V8 SI engine generation. 2 as possible, at minimum land width. In such cases, the land width of the jointly cast cylinders is determined in practice by the safe and reliable performance of the cylinder head gasket, by the cutting pressure applied for machining and the cylinder distortion in engine operation. ALUSIL® boasts excellent tribological characteristics. As the pistons and piston rings slide along the exposed sili- 5.5 mm con crystals, their susceptibility to seizing is minimized (Fig. 3). ALUSIL® displays optimum thermal conductivity; Audi is thus in a position to achieve a high specific engine performance. ALUSIL® does not imply any recycling problems because Fig. 2: Cylinder head flange surface with a land width of only the cylinder block does not contain extraneous materials 5.5 mm – such as cast-in cylinder liners made of grey cast iron. ALUSIL® allows cylinder blocks to be cast monolithically without cylinder liners or subsequent coating of the cylinder bores. This makes it possible to achieve: components of optimum structural rigidity through the benefit of a by 12 % higher Young’s modulus of the ALUSIL® alloy compared to a hypoeutectic standard alloy, as well as process reliability in machining without having to interrupt the process flow for costly addi- tional working steps specifically for the cylinder bore surfaces. A decisive milestone in this area was the mechanical exposure of the silicon crystals by means of a third honing step (Fig. 4) as a substitute for the chemical laying bare (etching) after the two-step hon- Fig. 3: Material structure of the alloy AlSi17Cu4Mg / ALUSIL® ing process which was a must before. Laying bare the with primarily precipitated silicon crystals (dark areas in the picture) silicon grains by mechanical means allows perfect on- line production. The above described assets of the ALUSIL® alloy are certain- ly significant arguments in favor of the use of this material. But also the low-pressure die casting method (Fig. 5) which has since then proven to be the best by far is an important prerequisite for process reliability in making mass-produced cylinder block castings of ALUSIL®. Fig. 4: Mechanically exposed ALUSIL® cylinder bore surface 3 3. Reasons in favor of low-pressure die casting from the viewpoint of Audi: Low-pressure die casting, LPDC (Figs. 5 – 6) allows to use sand cores where necessary, e.g. for water jackets (Fig. 7). Sleeve yoke with In this way, structurally rigid closed-deck cylinder blocks movable die half can be produced, a prerequisite for high specific engine Hydraulic cylinder outputs. sleeve lifters LPDC allows controlled, low-turbulence die filling, and what is even more important, controlled cooling of the die to ensure component-specific, virtually ideal directional solidification. The compilation of all casting-relevant data and the resulting control of the casting process are implemented today computer-assisted. Especially a purpose- Cylinder designed cylinder sleeve cooling system is an indispens- sleevers able prerequisite for uniform precipitation of the silicon Open die Casting crystals in the cylinder area (criteria: distribution, grain size range (Fig. 8) and number of crystals per cm²), low Stationary die half Hydraulic lateral shifters porosity and minimizing casting flaws like blowholes, pores, cold fusion, etc. This process control ensures con- Riser stant quality of the castings. LPDC permits unrestricted heat treatment of the casting. Holding furnace It is already possible to achieve a certain increase in hard- with melt ness and strength by applying controlled cooling of the cylinder blocks from the casting temperature by means of customary T5 heat treatment. The subsequent artificial aging not only serves to enhance hardness and strength, Lifting table, but primarily also to stabilize the volume, i.e. avoid an stroke about 2 m irreversible expansion in length and volume (distortion) referred to as “growth” when the casting is exposed to the operating temperature of the engine. Fig. 5: Low-pressure die casting, illustrated principle of a cast- For still higher thermal stresses in engine operation, a modi- ing cell with opened die (movable die half in lifted position) fied T5 heat treatment method is available by which the components of casting temperature are chilled locally, for example in the cylinder deck or bearing bulkhead areas by means of water showers, and their hardness and strength are raised through precipitation hardening. The heat treatment is additionally utilized for stabilizing the alloy. For absolute high-performance engines, Audi will in the fu- ture apply full heat treatment (T6) comprising homogenizing, chilling and artificial aging. This method contributes to a further distinct improvement in terms of static and dynamic strength. As “mere” T6 heat treatment without specific artificial aging only leads to a low degree of volume stabili- zation and involves the risk of distortion at operating temperature of the engine, the artificial aging time is frequently even extended. This extension of the aging time improves the expansion characteristics. Fig. 6: Design of a low-pressure die for aluminium cylinder block 4 4. Audi’s new V-engine generation: 5. The Audi V6 and V8 engine concept: The new V-engine generation of Audi – both petrol and die- The new V6 in the large displacement version of 3.2 l and the sel engines – is setting standards with respect to compact- new V8 with a swept volume of 4.2 l originate from the new ness and overall length. Customers’ requests for more pow- Audi V-engine family with a stroke of 92.8 mm (Fig. 9), a V erful engines even in smaller vehicle model series implied angle of the cylinder banks of 90° and a central division of the need for shorter overall engine lengths and for reducing the cylinder block (bedplate concept). The distance between the vehicle front-part weight. As a result a new V-engine gen- cylinders is 90 mm, the cylinder bank offset being 18.5 mm. eration has been created. For the V6 of 3.2 l as well as the V8 of 4.2 l swept volume, the cylinder bore is 84.5 mm. For the smaller V6 engine of 2.4 l Audi is the market leader in lightweight design, specifically swept volume, it is 81 mm. The cylinders are cast jointly at in the premium segment. The lightweight strategy is impres- a land width of 5.5 mm and of 9 mm, respectively for the V6 sively implemented in the car body through the Audi space with the smaller swept volume. frame aluminium technology. It was a logical consequence therefore to rely on a weight-optimizing all-aluminium solu- The V6 of the large swept volume version operates with fuel tion for the petrol V engines – i.e. ALUSIL® cylinder blocks. stratified injection (FSI), and in the small version, with multi- Thanks to its high competence as the European market lead- point injection (MPI). The different cylinder bore diameters er KS ATAG was able to convince the market with ALUSIL® for do not require an adjustment on the water-jacket side. The cylinder blocks of passenger-car SI engines in the respective V8 SI engines are available in three versions. To the existing market segment. Attractive contracts from Audi are contrib- two engine versions with MPI, a new version with FSI was uting to the further strengthening of KS ATAG’s location in added which also distinguishes itself by its cylinder block Neckarsulm and its market leadership. design. Fig. 7: View of a water-jacket core box in the core shooter: water-jacket sand cores for Audi V6 cylinder block (left) and V8 cylinder block (right) 5 6. Description of the cylinder block top: front, above the V space but connected with it. Water supply to the jackets of the two cylinder banks is accomplished by As mentioned above, the Audi cylinder blocks (Fig. 10) are means of a manifold, flange-mounted in the V space. made of the hypereutectic alloy AlSi17Cu4Mg. The low-pressure die casting method is applied, with controlled cooling The oil circuit ducts are partly pre-cast, partly drilled. The from the casting temperature.

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