Putting the "W" in VW and audi: KS Aluminium-Technologie AG is the master at making ALUSIL low-pressure diecast engine blocks

Automotive Industries, Oct, 2003 by Rich Wilson

In the late 1970s, ALUSIL engine blocks made by low pressure die casting (LPDC) had found a place in SI engines for passenger cars in Germany. Aluminum was chosen as a substitute for grey castings to achieve weight reduction.

Since then KS Aluminum-Technologie AG, a division of Kolbenschmidt-Pierburg, has been a supplier of aluminum engine blocks in V arrangement, namely those made from the hypereutectic aluminum-silicon alloy ALUSIL.

The following are current engine block customers with KS Aluminum-Technologie AG: 4.0L V-8 (Jaguar), 4.0L V-8 Supercharged (Jaguar), 3.6L V-8 (BMW 735i), 4.4L V-8 (BMW 745i), 6.0L V-12 (BMW 760i), 6.0L W-12 (VW & Audi), 4.0L W-8 (VW), 2.5L R5 TDI (VW), 5.0L V-10 TDI Biturbo (VW Phaeton/Touareg), 4.5L V8 (Porsche Cayenne), 4.5L V.8 Turbo (Porsche Cayenne), 3.4L Boxer 6-cyl. (Porsche 911 Cabriolet & 911 Carrera Coupe), 1.4L inline 4 (A-Class), 1.6L inline-4, (A-Class), 1.9L inline 4 (A-Class) 1.6L Diesel (A-Class), 1.9L Diesel (A-Class). They also supply for the Volvo S60 and S80 as well as the BWM 5-series. Applying this technology, to the VW "W" series engines was particularly challenging.

ALUSIL engine blocks feature a lowered weight and their monolithic character is engineered to enhance engine performance due to the properties inherent to the alloy.

ALUSIL technology produces monolithic aluminum blocks without requiting the additional reinforcement of the cylinder bores. The tribological properties can be attributed to the hypereutectic alloy AlSi17Cu4Mg and the precipitation of primary silicon which protects the cylinder bore surfaces by means of wear-resistant grains. The VW W8 and VW/AUDI W12 engines represent the latest evolution of the ALUSIL concept.

To implement the fundamental design of the compact W engine concept in an appropriate method, a total of six sand cores were used. In the V section, this led to a primarily vertical layering of cores due to the two through-type horizontal decks. The LPDC method had to be adjusted to make use of its qualitative assets--the quasilaminar mold filling and directional solidification.

The directional solidification aspect can react extremely sensitively to the constraints in active cooling prevailing in the central area of the component. However, it is the contention of the company that the engine blocks of VW/AUDI with W arrangement of the cylinders prove that ultimately a compromise exists between high functional integration, cost-effective product ion and casting quality.

The aluminum engine blocks in W8 and W12 arrange the cylinders in a two part design, the interface between the top part of the engine block made of ALUSIL and the bottom part of conventional alloy (referred to as the bed plate) at fire level of the crankshaft center line.

The bed plate is a high pressure die casting made of secondary alloy Alsi9Cu3 with integrally cast-in "bearing caps" made of spheroidal graphite cast iron. They were engineered to control the main bearing clearance in the service temperature range (acoustic, oil pump delivery rate) and stiffen the bulkhead system.

The inserts consist of two double bosses with a bow-shaped connector. To the sides of the bosses and between them, underneath the bow, undercut and open-worked anchors are arranged to provide for positive coupling with the adjoining aluminum The inserts are cut free in large areas to allow for the free wheeling of the crankshaft as the main bearings are narrow. That is why a solid anchoring system is needed.

The oil separator wall is integrated with the bed plates of the engines with wet-sump lubrication. The wall will route the oil selectively to the oil sump, simultaneously separating it from the crankcase to minimize oil foaming. This design is meant to provide additional rigidity for both the lower part of the engine block, bulkheads and side walls, as well as the overall component.

A challenge for W engine blocks was in areas where the bottom of the cylinders meets the bulkheads. There is an intersection of adjoining cylinders in that area where the crankshaft freewheeling would collide with the outlet for the honing tool. A central link of the bulkheads with the cylinder area calls for a short outlet (cut tree area) for the honing tool and requires special machining techniques for the finishing work.

The cylinder wall tapering down to the point of intersection is straightened out by means of two longitudinal bores. The main oil duct is located in the top part of the oil pan. The bed plate with its plane surface seals on its bottom side (the interface between bed plate and oil pan top).

From the main oil duct, the main bearings are directly supplied with lubricating oil. A riser leads to a central oil gallery in the V above the bulkheads The gallery is pre-cast on both sides using sled cores and subsequently pierced through by drilling and closed from the outside with threaded plugs.

The other lubricating points and the splash oil cooling system for the pistons are supplied with off from the central oil gallery. The unpressurized oil drain ducts from the cylinder heads are arranged on the outer sides, as in the case of V engines.