ALUSIL®-Cylinder Blocks for the New AUDI V6 and V8 SI Engines 2 ALUSIL®-Cylinder Blocks

ALUSIL®-Cylinder Blocks for the new AUDI V6 and V8 SI Engines 2 ALUSIL®-cylinder blocks V8 cylinder block V6 cylinder block (fuel stratified injection [FSI]) Fig. 1: ALUSIL® cylinder block of the new Audi V6 and V8 SI engine generation: V8 cylinder block cylinder block of the (multi-point injection) existing Audi V8 engine 1. Audi setting standards in lightweight design With its vehicle model series, Audi is setting new standards in lightweight design. So it is only logical for the carmaker again to count on aluminium in developing the cylinder blocks for its new spark-ignition V-engines (Fig. 1). On account of the reduced wall thickness (cylinder land width of only 5.5 mm (Fig. 2) between cylinder bores), Audi relies on the hypereu- tectic aluminium-silicon alloy AlSi17Cu4Mg registered for KS ATAG under the brand name of ALUSIL®. This concept al- 5.5 mm lows the pistons to move directly along the honed cylinder bore surfaces of the aluminium casting – an ideal condition for high-performing engines. Fig. 2: Cylinder head flange surface with a land width of only 5.5 mm KS Aluminium-Technologie AG 3 2. Reasons in favor of ALUSIL® from the viewpoint of The above described assets of the ALUSIL® alloy are cer- Audi: tainly significant arguments in favor of the use of this material. But also the low-pressure die casting method (Fig. 5) which There are many technical reasons which induced the car- has since then proven to be the best by far is an important maker Audi to adhere to the proven ALUSIL® concept: prerequisite for process reliability in making mass-produced cylinder block castings of ALUSIL® . • ALUSIL® makes a minimum weight at a high degree of in- tegration of engine functions like lubricant, coolant and engine venting circuits. • ALUSIL® enables minimum overall cylinder block lengths to be implemented because the engines can be operated 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 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 silicon crystals, their susceptibility to seizing is minimized Fig. 3: Material structure of the alloy AlSi17Cu4Mg / ALUSIL® with (Fig. 3). primarily precipitated silicon crystals (dark areas in the picture) • 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 the cylinder block does not contain extraneous materials – 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 hav- Fig. 4: Mechanically exposed ALUSIL® cylinder bore surface ing to interrupt the process flow for costly additional working steps specifically for the cylinder bore surfaces. A decisive milestone in this area was the mechanical ex- posure 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 honing process which was a must before. Laying bare the silicon grains by mechanical means allows perfect on-line production. KS Aluminium-Technologie AG 4 ALUSIL®-cylinder blocks 3. Reasons in favor of low-pressure die casting from crystals in the cylinder area (criteria: distribution, grain the viewpoint of Audi: size range (Fig. 8) and number of crystals per cm²), low porosity and minimizing casting flaws like blowholes, • Low-pressure die casting, LPDC (Figs. 5 + 6) allows the use pores, cold fusion, etc. This process control ensures con- sand cores where necessary, e.g. for water jackets (Fig. 7). stant quality of the castings. In this way, structurally rigid closed-deck cylinder blocks can be produced, a prerequisite for high specific engine • LPDC permits unrestricted heat treatment of the casting. outputs. It is already possible to achieve a certain increase in hardness and strength by applying controlled cooling of the • LPDC allows controlled, low-turbulence die filling, and cylinder blocks from the casting temperature by means what is even more important, controlled cooling of the die of customary T5 heat treatment. The subsequent artificial to ensure component-specific, virtually ideal directional aging not only serves to enhance hardness and strength, solidification. The compilation of all casting-relevant data but primarily also to stabilize the volume, i.e. avoid an and the resulting control of the casting process are imple- irreversible expansion in length and volume (distortion) mented today computer-assisted. Especially a purpose- referred to as “growth” when the casting is exposed to the designed cylinder sleeve cooling system is an indispen- operating temperature of the engine. sable prerequisite for uniform precipitation of the silicon For still higher thermal stresses in engine operation, a modified 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 sleeve yoke with raised through precipitation hardening. The heat treatment is movable die half additionally utilized for stabilizing the alloy. hydraulic cylinder sleeve lifters cylinder sleevers open die casting stationary die half hydraulic lateral shifters riser holding furnace with melt Fig. 6: Design of a low-pressure die for aluminium cylinder block lifting table, stroke about 2m Fig. 5: Low-pressure die casting, illustrated principle of a casting cell with opened die (movable die half in lifted position) KS Aluminium-Technologie AG 5 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) For absolute high-performance engines, Audi will in the the engine, the artificial aging time is frequently even extend- future apply full heat treatment (T6) comprising homogeniz- ed. This extension of the aging time improves the expansion ing, chilling and artificial aging. This method contributes to a characteristics. 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 stabilization and involves the risk of distortion at operating temperature of 25.0 20.0 15.0 10.0 5.0 100.2 micron 0 10 20 30 40 50 60 70 80 Number of grains in the area measured in the area grains Number of Grain size [µm] Area measured Fig. 8: Representative grain distribution of the primarily precipitated silicon crystals KS Aluminium-Technologie AG 6 ALUSIL®-cylinder blocks 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 The new V6 in the large displacement version of 3.2 l and diesel engines – is setting standards with respect to compact- the new V8 with a swept volume of 4.2 l originate from the ness and overall length. Customers’ requests for more power- new Audi V-engine family with a stroke of 92.8 mm (Fig. 9), a ful engines even in smaller vehicle model series implied the V angle of the cylinder banks of 90° and a central division of need for shorter overall engine lengths and for reducing the the cylinder block (bedplate concept). The distance between vehicle front-part weight. As a result a new V-engine genera- cylinders is 90 mm, the cylinder bank offset being 18.5 mm. tion 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, specifi- swept volume, it is 81 mm. The cylinders are cast jointly at cally in the premium segment. The lightweight strategy is a land width of 5.5 mm and of 9 mm, respectively for the V6 impressively implemented in the car body through the Audi with the smaller swept volume. space frame aluminium technology. It was a logical conse- quence therefore to rely on a weight-optimizing all-aluminium The V6 of the large swept volume version operates with solution for the petrol V engines – i.e. ALUSIL® cylinder blocks. fuel stratified injection (FSI), and in the small version, with Thanks to its high competence as the European market leader multi-point injection (MPI). The different cylinder bore diam- KS ATAG was able to convince the market with ALUSIL® for cyl- eters do not require an adjustment on the water-jacket side. inder blocks of passenger-car SI engines in the respective mar- The V8 SI engines are available in three versions. To the ex- ket segment. Attractive contracts from Audi are contributing to isting two engine versions with MPI, a new version with FSI the further strengthening of KS ATAG’s location in Neckarsulm was added which also distinguishes itself by its cylinder and its market leadership. block design. Fig. 9 : The new Audi V6 (left) and V8 (right) SI engines KS Aluminium-Technologie AG 7 6.

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