You will find the figures mentioned in this article in the German issue of MTZ 05I2007 beginning on page 346.

Das Zylinderkurbelgehäuse der neuen R4-TFSI-Motorengeneration von Audi

The Crankcase of the New R4-TFSI Engine Generation from Audi The market launch of Audi’s new 1.8-l-4V-TFSI engine from its EA888 engine series in early 2007 marked the start of a comprehensive renewal of its R4 petrol engines over the 1.8 l to 2.0 l capacity range. Over the coming years, the new EA888 engine series will gradually replace the highly successful EA113 series throughout the whole of the VW Group. In June 2007 a new 2.0-l-4V-TFSI engine will be added to the EA888 series. This paper deals with the development of the completely new crankcase for the EA888 engines, which was the result of an intensive collaboration with Eisenwerk Brühl.

1 Introduction

Authors: Frank Grunow, Wim Görtz, Rolf Weber, Joachim Böhme, Joachim Doerr and Achim Lembach

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To achieve the objectives Audi had set out for the new EA888 engine generation in terms of increased power output potential, better comfort, improved robustness and greater maintainability, the development of a completely new base engine and ancillary components was required [1, 2]. Considerable effort was invested in the development of the crankcase, since the overall engine concept is largely determined by the crankcase design.

2 Development Objectives and Concept for the EA888 Crankcase The main objectives for the development of the EA888 engine series, which are especially applicable to the crankcase, were the following: – to increase driving comfort – to reduce manufacturing costs – to improve maintainability – to increase robustness by the integration of functions – to reduce engine weight

Crankcase

– compact dimensions for use as a platform engine – suitability for production worldwide within the Group joint production system – improved fuel economy and increased operating efficiency. To implement these objectives, the EA888 crankcase has the following characteristics: To improve driving comfort, the new EA888 engine series has a second order balance system, in which the balance shafts are positioned at different heights and located directly within the crankcase – the first configuration of this kind to be implemented in the VW Group. This engine concept dispenses with the elaborate and costly add-on solution of a balance shaft module in the area of the oil sump. The balance shaft tunnels on each side of the crankcase also increase its overall rigidity. Thanks to the optimisation of the overall engine concept for function and cost (function integration) and the use of lamellar graphite grey cast iron (GJL) for the crankcase, manufacturing costs have been reduced considerably in comparison to the predecessor engines of the EA113 series. Further cost savings will result from the synergy effects of the engine’s high production numbers, due to the strategic role of the EA888 as a platform unit (global engine). The timing drive system’s chain drives, the balance shaft drive and the oil pump drive are designed for lifetime operation and thus represent major improvements in engine maintainability. The chain drives are all located on the front end of the crankcase, where the chains are largely enclosed by a cast-on housing. This design eliminates the critical point where the timing cover, engine block and cylinder head surfaces meet. The integration of various functions into the crankcase (balance shaft locations, timing chain housing, additional pressurised oil, oil return, blowby and water channels) has reduced the total number of components, thus increasing the engine’s overall maintainability and robustness. In spite of the additional functional surfaces to be machined, the volume of metal removed from the unmachined EA888 crankcase casting has been reduced by over 25 % compared to its predecessor (EA1132.0-l-TFSI). To reduce the weight of the crankcase, its nominal wall thickness was also lowered to 3.5 mm (predecessor engine > 4.0 mm) resulting in a weight saving on the finished crankcase of over 2,0 kg. For

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Figure 8: Precision in core handling, assembly and insertion

weight-saving and functional reasons, areas with no structural purpose, such as the water pump and thermostat housings, are no longer integrated into the crankcase, but are manufactured as separate components in plastic. These measures have brought down the overall weight of the 2.0-l-EA888 engine to 3.2 kg less than that of its predecessor (DIN 70020GZ). As is customary for all Audi engines, the crankcase and the complete engine were designed to extremely compact dimensions. By locating the balance shaft drive directly below the water jacket, instead of in front of it (to do so, the first bearing panel was moved inwards by 10 mm), the engine’s overall length has been reduced to approx. 12 mm less than that of its predecessor (2.0-l-EA113-TFSI). This makes the EA888 series engines ideally suited for use in the VW Group’s transverse and longitudinal platforms. By retaining the previous bore pitch (88 mm) and block height (220 mm) and adopting most of the existing locating and mounting points, the design also ensures that the crankcase can be produced worldwide within the Group’s joint production system. Special structural features in the areas of the bearing blocks and cylinder tubes ensure that the engines can further exploit the potential of the TFSI combustion process in the future [3]. The crankcase’s ability

to accommodate greater loads allows the implementation of higher-efficiency engine concepts, which effectively exploit potential fuel economy gains.

3 Crankcase Design The crankcase for the EA888-T-FSI engine generation is designed as a uniform component for the 1.8 l and 2.0 l versions. The greater displacement in the 2.0 l engine is achieved by an increase in crankshaft stroke. Both units have the same bore diameter of 82.5 mm. The crankcase is made from the proven material GJL-250, which was also the crankcase material of the predecessor EA1113 series turbocharged engines [4]. The crankcase has a classic deep skirt design with a closed-deck construction. The crankshaft bearing caps on bearing blocks 2, 3 and 4 are additionally bolted at the side. This increases the strength of the bearing blocks and improves engine acoustics. A major feature of the top deck design is the fact that the exhaust-side webs between the cylinder tubes and the head plate are offset 6 mm downwards for an optimum flow of coolant water to the cylinder head. This also has the advantage that it provides better support to resist lateral piston force on the exhaust side (pressure MTZ 05I2007 Volume 68

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Crankcase

Figure 9: Robot handling, adjustment, measuring and leak testing

side), which reaches its maximum a few millimetres below TDC. The core package for production of the crankcases is composed of 4 crank cavity cores, 6 cores for internal fluid channels (2 water, 1 pressurised oil, 2 oil return and 1 blowby), 2 cores for the front and rear ends, and the cope and drag boxes for the side walls (moulded in green sand). The cores for fluid channels are shown in colour in Figure 1.

3.1 Fluid Channels As described in [1], the coolant pump, which is flanged onto the intake side of the crankcase, first pumps the coolant water into the water jacket (blue) and then via the cylinder head back into a collection chamber (light green). From there it passes the thermostat and flows into the main radiator or back to the water pump. The pressurised oil passes from the oil pump via the upper section of the oil sump, Figure 1, into a pre-cast oil channel in the intake side of the crankcase (yellow). The oil is conducted out of the crankcase for cooling and filtering (the oil cooler and filter are mounted on an ancillaries bracket) and then re-enters the crankcase and is supplied to the oil consumers via a drilled main oil gallery. Oil is delivered to the crankshaft drive and the intake-side balance shaft directly from the main oil gallery via drilled passages. The exhaust-side balancer shaft is supplied with oil via grooves cut into the bearing blocks. The balancer shafts are vertically offset by 42.9 mm and their bearings are in line with the centres of bearing blocks 1, 2, and 4. The positioning of the shafts at different heights serves to absorb torque fluctuations about the engine’s longitudinal axis to a large degree. The integrated blowby channel on the intake side close to the gearbox flange (shown in brown in Figure 1) is an element 8

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of the first evolution stage (EVO1) of the EA888 series with the introduction of the new 2.0-l-engine. From June 2007 this precast channel will replace in both engines (1.8 l and 2.0 l) the external blowby line used in the 1.8-l-engine already presented in [1]. The integration of the blowby channel into the crankcase structure (the channel exits the crankcase at the top deck and continues in the cylinder head) results in a lower temperature gradient from the blowby gas outlet on the outer wall of the crankcase to the oil mist separator in the cylinder head. This helps to prevent the crankcase breather from freezing up when the vehicle is used for short journeys in very cold regions and it further increases the robustness and compactness of the engine. The oil return channels from the cylinder head are located on the exhaust side of the crankcase (dark red). The oil separated out in the oil mist separator in the cylinder head drains back through a separate channel with its outlet below the oil level in the sump (light red). The Table gives a summary of all the crankcase’s design features and its main dimensions and weights.

4 CAE Development Due to the increased demands specified for the engine, the development of the EA888 crankcase had to meet extensive challenges with regard to acoustic characteristics and component strength. Thanks to the comprehensive use of FEM calculation methods, both the development times and costs were considerably reduced.

4.1 Acoustics Optimisation Right from the early conceptual design phase, extensive optimisations of the crankcase’s NVH characteristics were carried out. The objective pursued was to identify, by means of sensitivity studies,

areas of the crankcase where acoustic modifications would be effective and to optimise these with appropriate design modifications. At this stage the wall thickness patterns and rib design were evaluated and optimised by calculation in accordance with the objectives. These optimisations achieved a significant improvement in airborne and structure-borne noise emission in the medium to high frequency range. Figure 2 shows the improvement in the calculated particle velocity distribution on the surface of the crankcase between the initial status and today’s optimised series production status. As the figure also shows, major improvements in crankcase acoustics across wide frequency ranges have been achieved in the EA888 engine compared with the crankcase of the EA113 predecessor engine (see third octave band spectrum).

4.2 Structural Analyses in the Example of the Bearing Block The structural design of the crankcase bearing tunnels was influenced by the consideration that the engine block is to be used as a common component for the complete EA888 petrol engine family. As a consequence, the crankcase was designed for continued future development of engines with mean pressures up to 25 bar, so as to be capable of accommodating specific power ratings of > 100 kW/l and torques of > 175 Nm/l. For the analysis of the bearing tunnel, a calculation model was set up for the crankcase with which each individual bearing panel area could be evaluated and optimised by calculation methods. The submodel technique was used for the detailed optimisation of individual areas. This radically reduces the calculation time, while providing high fidelity to detail. In order to represent the loads on the bearing panels as realistically as possible, bearing loads were used in the form of a pressure distribution from an elastohydrodynamic analysis of the crankshaft. This is necessary to achieve a design of the individual bearing panels that provides suitable load capacity and high rigidity combined with low weight. The suitability of GJL-250 as the crankcase material was verified by sufficiently high calculated fatigue strengths and tested in component tests and endurance runs.

4.3 Thermomechanical Analysis in the Example of the Block/Head Assembly To verify the behaviour of the crankcase in its assembled state with the cylinder head

Crankcase

and in real engine operation, a model of the crankcase was created with all relevant components and loads and its vehicle-specific mountings. This complex FEM model provided the basis for block/head assembly calculations, Figure 3 (left). The objective of these analyses was to examine the crankcase alongside the cylinder head with regard to its thermomechanical behaviour. The specific results were the calculation of the temperature distribution in the crankcase, Figure 3 (right), and the evaluation and optimisation of component distortions, especially in the areas of the cylinder bores and the crankshaft bearing tunnel. It was possible to optimise the stresses induced by the cylinder head bolts and deformations in the cylinder tubes caused by the bolt loads and by thermal expansion, Figure 4. The pressure of the cylinder head gasket on the liner was also optimised in coordination with the design of the cylinder head, in order to achieve a pressure distribution that is as uniform as possible during engine operation. Overall, by use of this closed calculation scheme, an optimum was achieved with regard to the conflicting goals of acoustics, component strength and rigidity, weight and cost.

5 Material Selection The objective of the development work by Eisenwerk Brühl was to find an innovative way of implementing lightweight construction designs in the instance of a cast iron crankcase in the light of constantly increasing specific power ratings [4, 5, 6].

5.1 Tribological Properties of the Cylinder Bore A major point in favour of GJL as a crankcase material is the functional reliability of the tribosystem of the cylinder face and pistons/piston rings with a high cylinder bore dimensional stability and good running-in characteristics. The material’s excellent antifriction properties, due to its good oil retention and good emergency running properties, ensure minimal friction losses and good fuel economy and in addition provide favourable conditions for continuing increases in lifetime mileages with extended service intervals.

5.2 Mechanical Material Properties The local strengths are dependent on the graphite type and the alloy composition. One advantage is the material’s microstruc-

ture stability in the range from room temperature (RT) to approx. 400°C with the result that its dynamic and static strengths show no significant decline.

5.3 NVH Influence A durable crankshaft bearing arrangement with good acoustic properties requires a rigid bearing tunnel with low distortion (temperature influence). This in turn demands a bearing block design that provides dimensional stability. The material’s high creep strengths also guarantee a high resistance to creep deformation of the bolted main bearing assembly, thus avoiding gradual deformation of the main bearing bores. Its high modulus of elasticity in comparison to aluminium crankcases provides the basis for good acoustic and vibration properties from room temperature to the engine operating temperature. The modulus of elasticity of GJL is essentially dependent on its graphite content. The graphite structure has virtually no influence. The NVH characteristics are also improved by the optimum engineering design of the crankcase and the excellent damping capacity of the material, which has a loss factor of LF > 800*10-6. A further favourable aspect is the fact that the crankcase and crankshaft materials have almost the same thermal expansion coefficient (BRT-200°C _ 13.17 - 13.26 μm/(m*K)). As a result, the main bearing clearance remains constantly low, thus helping to improve NVH characteristics.

5.4 Thermal Material Properties The relatively low thermal conductivity of GJL compared to aluminium materials of M RT-100°C _ 48.7 W/(m*K) means that the cylinder faces are considerably hotter during engine operation than in an aluminium alloy crankcase. This is a very favourable feature with regard to the antifriction properties of a hot cylinder wall (low piston group friction). If the crankcase design consistently takes the properties of cast iron into consideration, possible overheating problems, due to the low thermal conductivity, (e.g. knocking) can be avoided through modifications to the wall thickness and/or modified engine cooling concepts. Due to its ability to withstand high temperatures, the use of cast iron has made it possible to produce a very compact EA888 crankcase. Since there is no need for the additional cylinder liners required in a costeffective aluminium solution, a sufficiently robust construction even for very high-rated engines can be implemented with a cylinder bridge width of 5.5 mm.

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6 Development Process The development process was characterised by a close collaboration between Eisenwerk Brühl GmbH (EB) and the end customer, Audi AG. All departments involved in the development and series production process, from engineering design to calculation, machining etc., took part in regular simultaneous engineering meetings. EB maintained a part CV and a development “what to do list” throughout the development process. Over time these took on an important role as information and planning documents. They provided and still provide a record of all current changes and each status reached up to the present day. The distribution of these documents to all partners in the development process ensured that all parties had access to the same development status. This tool particularly enhanced the consistency and coordination of operations within the EB process in collaboration with all departments and model builders involved. At this point a complete set of CAD master data for the fabrication of all relevant core and model tooling was also available. These data not only provide the unambiguous geometry of the tooling, but at the same time form the basis for offline programming for 100 % product sampling by CMM measuring equipment.

6.1 Casting Simulation The use of mathematical advance-simulation for designing the construction of the gating, feeder and casting systems was an integral part of the development work by EB, Figure 5. The pouring system is dependent on the mould construction and the gates and metal stream are largely determined by the core prints. The final result achieved was an optimum distribution of local mechanical properties in the casting.

7 Casting Technology

7.1 Precision and Reproducible Production With rising costs for input materials, energy and personnel, high production process automation and innovations are essential in order to stay ahead in terms of technology and costs. EB implements continuous improvements to fulfil clients’ requirements in aspects such as low wall-thickness with closer tolerances, more robust materials, consistent high quality and low part prices. MTZ 05I2007 Volume 68

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High-strength steels are playing an increasing role on the market with their use as a metallic component in the charge make-up. Consequently it is critical that the concentrations of subversive trace elements and companion elements in the steel and their limit concentrations in the cast iron are observed and controlled. The casting operation must avoid scatter in the chemical composition of the molten metal, resulting from the characteristics of the metal stream and treatment of the melt, which may lead to scatter in the properties of the casting. The examples of change in absolute standard deviation, Figure 6, demonstrate the scale of technological improvement achieved through innovation. Thanks to modified process engineering, concentration spread of carbon and silicon, for instance, have been reduced by almost half. The same applies to changes in the foundry engineering with regard to the pouring temperature and pouring time. The measuring and monitoring systems along the process chain have an important role in evaluating the fused state of the metal. The assessment of the melt’s nucleation state, the determination of undercooling and the use of an inoculation treatment that is suitable for the fusion state and the casting are measures which determine in advance the casting’s microstructure constituents, graphite type, mechanical properties and defect tendency. The improved and reproducible control of the pouring temperature and pouring time during mould filling, Figure 7, leads to lower reject rates. The online transmission and visualisation of instrument data and the implementation of static control algorithms provide foundry personnel with tools to intervene for independent process control loops.

tions with just-in-time delivery to the mould line – use of improved mould material quality, core materials and core binders to control thermal expansion characteristics – consideration of shrinkage/swell of the casting material in the moulds, which is dependent on the alloy composition and inoculation. Despite complex geometrical specifications, the core structure with a twin configuration represents an economical solution, Figure 8, as it allows four raw castings to be produced in one casting operation. The cores’ contour accuracy and assembly tolerances are important factors affecting the dimensional accuracy of the end product. The tolerances are determined by the mould tools’ NC fabrication process, the evenness of wash coating, a defined core storage time and stable core storage throughout the logistics process up to mould making.

7.2 Moulds and Cores The overall effect of numerous small individual steps along the process chain in the production of the casting ensures that tolerances are met and can be reliably narrowed: – improvement in the dimensional accuracy of core tooling and model equipment thanks to a closed CAD process chain – high uniformity in core moulding due to high-pressure compaction applied as a function of the sand properties – creation of pre-assembled core packages from individual cores in automated assembly, insertion and bonding opera-

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7.3 Machining A suitable procedure was designed in the development process, which completely defines the cleaning, and premachining operations in closely linked process steps. The cleaning methods, such as shaking, vibration and abrasive blasting were adapted to the complex geometry of the raw casting, and cleaning effectiveness was improved with the use of injection blasting equipment for all pre-cast oil channels. Sand and wash residue levels of ≤ 500 mgr/crankcase are guaranteed. All subsequent steps are carried out in an integrated cleaning and premachining chain. The premachining of the side surfaces of the crankcase represents an increase in the range of vertical production with economic advantages for both parties. The subsequent operations of painting, adjusting, leak testing and measuring are fully automated by robot handling of the raw castings with defined positioning and clamping, Figure 9.

8 Summary and Outlook The crankcase of the new EA888 engine generation fulfils all the requirements specified in the early conceptual design stage. With the positive properties achieved, the crankcase’s functional integration and the fact it is designed for mean pressures up to 25 bar, it offers an excellent basis for further EA888 engine derivatives, Figure 10.

The engines will be used throughout the VW Group in transverse and longitudinal installations. With its development competence and outstanding manufacturing and material concept, Eisenwerk Brühl has proven the effectiveness of cast iron as the crankcase material for a modern, high-performance and cost-effective turbocharged petrol engine.

References [1] Böhme, J.; Jung, M.; Fröhlich, G.; Pfannerer, D.; Märkle, T.; Felsmann, C.: Der neue 1,8-l-VierzylinderTFSI-Motor von Audi (Teil 1: Konstruktion und Mechanik). In: MTZ 10/2006, Jahrgang 67, S. 734 - 748 [2] Helbig, J.; Höfner, D.; Grigo, M.; Kuhn, M.; Senft, P.: Der neue 1,8-l-Vierzylinder-TFSI-Motor von Audi (Teil 2: Konstruktion Anbauteile und Thermodynamik). In: MTZ 11/2006, Jahrgang 67, S. 884 - 892 [3] Krebs, R.; Böhme, J.; Dornhöfer, R.; Wurms, R.; Friedmann, K.; Helbig, J.; Hatz, W.; Der neue Audi 2-l-TFSIMotor – Der erste direkteinspritzende Turbo-Ottomotor bei Audi. 25. Internationales Wiener Motorensymposium, April 2004 [4] Böhme, J.; Fröhlich, A.; Doerr, J.: Motorblöcke aus Gusseisen oder Aluminium? In: Gießtechnik im Motorenbau – Anforderungen der Automobilindustrie, VDI-Bericht Nr. 1718, Audi Sonderbeilage, 2003 [5] Martin, T.; Weber, R.: Grauguss: Ein moderner Werkstoff für Kurbelgehäuse. In: Hochleistungsbauteile für Verbrennungsmotoren 30/2004, S. 43-57 [6] Martin, T.; Weber, R.: Leichtbau-Zylinderkurbelgehäuse für die Großserie. In: Gießerei-Praxis 2/2004, S. 19-26