You will find the figures mentioned in this article in the German issue of MTZ 11/2005 beginning on page 844.

Neuer Ottomotor mit Direkteinspritzung und Doppelaufladung von Volkswagen Teil 1: Konstruktive Gestaltung

The New Dual-Charged FSI Petrol Engine by Volkswagen Part 1: Design The new 125 kW engine from Volkswagen in the Golf GT represents a milestone in the development of direct-injection spark-ignition engines. Its performance far surpasses that of conventional engines with the same capacity while at the same time offering substantially improved fuel economy. This result has been achieved by a combination of downsizing, direct fuel injection and double supercharging.

1 Introduction

Authors: Rudolf Krebs, Rüdiger Szengel, Hermann Middendorf, Michael Fleiß, Alfons Laumann and Stefan Voeltz

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The new TSI engine, Title Figure and Figure 1, achieves a mean pressure of 21.7 bar with a torque of 240 Nm. Dual supercharging combines an additionally activated compressor with an exhaust gas turbocharger. As a result, maximum torque is already developed at very low engine speeds and remains available over a very broad engine speed range. The use of gasoline direct injection allowed a compression ratio of 10:1 to be achieved at charging pressures of 2.5bar absolute. The

efficiency of the new 125 kW engine in the Golf GT sets new standards in spark-ignition engine development.

2 Concept and Development Objectives For Volkswagen, there are two reasons for developing highly supercharged downsized engines: – meeting the customers’ demand for economical FSI engines combined with a high degree of driving pleasure – making available a further technological

Spark Ignition Engines

component for reducing the CO2 emissions of the Volkswagen fleet. The basic engine in this development is the FSI engine from the Golf V, in the 1.4-litre 66 kW and 1.6-litre 85 kW power output versions, Table. The following specifications defined the tasks and challenges facing the engineers at the beginning of the development: – low fuel consumption – generous torque characteristics – high quality standard – unrestricted durability – low production costs – production-compatible construction – compact design. The 1.4-litre 125 kW TSI engine develops an impressive torque of more than 200 Nm at 1250 rpm to 6000 rpm, Figure 2. This generous amount of torque is achieved by using two supercharger units, a fast-running mechanical compressor and an exhaust gas turbocharger. The boost pressure control system developed by Volkswagen constantly measures the torque demanded by the driver at any one time and decides whether the boost pressure provided by the turbocharger is sufficient or whether the compressor needs to be activated, Figure 3. Above a certain minimum torque requirement, the compressor operates continuously up to engine speeds of a maximum of 2400 rpm. The turbocharger is specifically designed to operate at maximum efficiency and is therefore unable to supply sufficient boost pressure in the low speed range. The compressor is deactivated at a speed of 3500 rpm at the latest. Above this speed, the turbocharger is able to provide the required boost pressure by itself, and to do so dynamically during the transition from overrun to full-load operation. Up to this speed, the compressor ensures that there is no “turbo lag”, thus guaranteeing spontaneous torque response in any situation. The compressor is activated via a magnetic coupling that is integrated into the water pump drive unit. The control valve ensures that the turbocharger receives the amount of air required for each operating point. In pure turbocharger operation, the control valve is open. In this case, the air takes the usual path for conventional turbocharged engines, flowing through the front intercooler and the throttle valve into the intake manifold, Figure 4. The fuel consumption of 7.2 litres per 100 km (MVEG cycle) – an exceptionally low value for a 125 kW engine – is achieved in the Golf GT by the following measures: – systematic downsizing (shifting the oper-

Number of cylinders

COVER STORY

4

Table: Technical data

Cylinder spacing

82 mm

Displacement

1390 cc

Stroke

75.6 mm

Bore

76.5 mm

Compression ratio

10:1

Output

125 kW 6000 rpm

Torque

240 Nm 1750 rpm – 4500 rpm

Mean eff. pressure

21.7 bar

Max. boost pressure

2.5 bar (absolute)

Fuel consumption in Golf GT

7.2 l/100 km (MVEG cycle)

ating points into the range of higher mean pressures and therefore into ranges with lower specific fuel consumption) – high compression ratio by using FSI direct injection – no enrichment to ensure component protection for the turbocharger and exhaust manifold (exhaust temperatures up to 1,050 °C are permissible) . As a result of this technology, the TSI engine sets new standards for the fuel consumption of spark-ignition engines compared to competitors with conventional engines with the same output. The new 1.4-litre 125 kW TSI engine has its premiere in the Golf GT at the end of 2005. A version with 103 kW designed for ROZ95 fuel is already planned for the Touran in the first quarter of 2006. Further derivatives in the A-segment will follow in mid-2006, and will also include the DSG sequential gearbox.

3 Design 3.1 Engine Components In designing the components for the new engine, the engineers at Volkswagen were able to fall back on the proven 1.4-litre unit. The engines of this series have a largely modular design. The main areas of focus for the TSI engine were in designing the new crankcase and the water pump with an integrated magnetic coupling.

3.1.1 Cast Iron Crankcase As in the 1.4-litre 66 kW and 1.6-litre 85 kW FSI engines, the new crankcase has an opendeck design, Figure 5. The deep-skirt crankcase is made of the grey cast iron material GJL. The decision to use this material also guarantees full operating reliability at all times even at the high mean pressure of 21.7 bar. In order to optimise the production costs, the thin-wall

crankcase is cast in a horizontal casting position. The average wall thickness is 3 mm ± 0.5 mm. At certain places, the wall thickness was increased to withstand the expected loads. The grey cast iron crankcase has a weight of only 29 kg (without the bearing cover), which is an exceptionally low weight in this power class. This low weight was achieved by: – the early use of FEM calculations – the design of the crankcase with embossed walls to ensure high rigidity – the load-dependent design of minimal transverse and longitudinal ribs. The open-deck design has dual-circuit cooling with separate circuits for the cylinder head and crankcase, thus effectively ruling out ventilation and cooling problems caused by air pockets. The cooling circuit within the crankcase and the entire engine was tested and optimised using CFD calculations. When the cylinder head is screwed to the crankcase, forces are introduced through the cylinder head screws. This causes distortions to the cylinders, making them deviate from the ideal circular shape. The result is increased oil consumption, as piston rings have only a limited capacity to adapt to the new shape. Figure 6 shows the cylinder distortion for a closed-deck design (clover leaf). Figure 7 shows the distortion for an open-deck design. The deviation from the ideal shape as well as the absolute amount of distortion is much lower.

3.1.2 Steel Crankshaft In order to improve the overall acoustics of the TSI engine, a steel crankshaft is used. This has a more rigid design than the cast crankshaft from the 1.4-litre 66 kW FSI engine. The steel crankshaft generally improves the sound quality of the engine by providing MTZ 11/2005 Volume 66

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COVER STORY

Spark Ignition Engines

more rigidity due to its higher modulus of elasticity. The use of steel as a material achieves a 23 % increase in rigidity. This value was determined by comparative calculations and verified by subsequent measurements. What is more, the objective measurements are confirmed by the subjective improvement in engine sound. An example of the FFT sound pressure analysis at an engine speed of 4000 rpm is shown in Figure 8. The graph shows the measurements for a cast crankshaft compared to those for a steel crankshaft. The secondary harmonics are substantially reduced in the steel crankshaft.

cooled. At an opening pressure of 2.0 bar, nozzles screwed into the main oil gallery spray oil directly onto the hot exhaust side of the pistons. This also cools the piston hubs.

3.1.3 Lightweight Pistons Systematic application of state-of-the-art calculation and development methods made it possible to use a cast piston with a specific output of 90 kW/litre (2.72 kW/cm3 piston surface) in a supercharged engine, thus allowing a considerable cost benefit to be exploited. This represents a new standard in piston development. The piston bowl is machined and has a distinct edge to guide the flow, Figure 9. The piston is a lightweight piston with a cast recess behind the ring zone for material displacement. The piston system has been optimised with regard to fuel consumption. For this purpose, the following measures were taken to reduce friction: – application of an anti-friction coating – piston running clearance reduced to 55 μm – piston rings with heights of 1.2/1.5/2.0 mm and low tangential forces – fire land height of 5.8 mm. The fire land height of 5.8 mm achieves the objectives of minimising HC emissions with the lowest possible temperature in the first piston ring groove. The groove is hard anodised to prevent micro-welding, while the first ring is nitrided. To make the piston suitable for an ignition pressure of 120 bar, the pin diameter was increased to 19 mm. By comparison, a diameter of 17 mm is sufficient in other engines of this series that use FSI technology (ignition pressure = 85 bar). The piston pin boring is designed as a moulded bore in order to optimise its bearing behaviour under bending stress. The piston pin is supplied with lubricant from the big end bearing through a longitudinal bore in the connecting rod. In order to ensure that the temperature of the pistons is kept sufficiently low under all operating conditions, the pistons are 4

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3.1.4 Timing and Oil Pump Drive The toothed chain drive for the camshafts of the TSI engine has been optimised to withstand the higher load. The chain has hardened pins and stronger links that have been adapted to the chain forces. Due to the additional lubrication points, for example the piston cooling nozzles and the turbocharger, the TSI engine has a higher oil throughput than the 1.4-litre 66 kW and 1.6-litre 85 kW FSI engines. The oil pump has been taken over from the FSI engines and adapted to the required higher pumping rate by changing the gear ratio. In order to optimise the acoustics, the oil pump drive is a toothed chain with 8 mm pitch, which is tensioned by a leg spring.

3.1.5 High-Pressure Pump Drive The high-pressure pump, which is also used in the 1.4-litre 66 kW and 1.6-litre 85 kW FSI engines, has been adapted to the larger fuel quantity required by modifying the contour of the cam operating the high-pressure pump. In the TSI engine, the maximum cam lift is 5.7 mm instead of 5 mm. This increase in the amount of fuel being pumped as well as the rise in pressure in the high-pressure fuel rail from 120 to 150 bar result in considerably higher stress at the contact between the pump cam follower and the pump cam. The use of a roller cam follower provides the necessary durability, Figure 10. In addition, the increase in pressure meant that the high-pressure pump housing is now made of forged aluminium rather than cast aluminium. This approximately doubles the mechanical strength of the pump. The use of a roller cam follower also made it possible to halve the driving torque of the pump, Figure 11.

3.1.6 Sturdy and Low-Cost Crankcase Ventilation Crankcase ventilation was decisively influenced by the development of the oil separator. The oil is continuously returned by a siphon. The optimisation of the oil separator led to excellent results for oil tear resistance (up to 140 rpm) and oil separation (< 1.0 g/h). The oil separator achieves optimum results with low pressure losses, and the degrees of oil separation are comparable to systems with additional fine oil separators. The

risk of deposits forming on downstream components is therefore minimised, Figure 12. The system has one entry point in front of the compressor and one in the intake manifold, Figure 13. A throttle in the pipe to the intake manifold limits the throughflow at high intake manifold underpressure. As a result, a complex and expensive pressure control valve was not necessary. The switching functions are integrated into a valve module that closes the ventilation pipes depending on the charge state. The non-return valve used to open the pipe in front of the turbocharger is designed as a shuttle valve with a precisely defined leakage quantity to make sure that the underpressure in the crankcase is maintained. The flow guidance and the large cross-sections minimise the pressure differences in the ventilation components. The introduction of fresh air into the engine is a further feature of the system. This provides engine scavenging over wide map areas, thus removing condensate.

3.1.7 Coolant Regulator with Two-Stage Thermostat The coolant circuit inside the engine is a dual-circuit system that has already proven itself in the FSI engines of this series. In addition, it integrates the cooling of the exhaust gas turbocharger. A coolant afterrun pump provides cooling for the turbocharger after the engine has been switched off. The water pump ensures an adequate flow of coolant to provide sufficient heating performance when the engine is idling. At nominal engine speed, high flow rates occur in the cooling circuit, resulting in high system pressures. In order to guarantee the temperature-controlled opening of the thermostat and to improve its function in regulating the coolant inlet temperature, a twostage system is used, Figure 14. The small diameter of the first stage opens the thermostat in accordance with the temperature. If the first stage opens further, it starts to move the second, larger diameter stage. As the thermostat closes again, the different cross-sections caused by the difference in diameter of the plates ensure that the thermostat closes securely. As a result, high pressure peaks in the coolant circuit can be safely dealt with.

3.1.8 Water Pump with Magnetic Coupling In addition to pumping the coolant, the water pump module also integrates the function of a switchable drive for the air compressor.

For the first time in this engine series, a VR seal (dual-lip sealing ring) is used, Figure 15. It replaces the familiar axial face seal. The VR seal works on the same principle as a spring-less radial shaft sealing ring. The initial tension of the seal, which is a rubberelastic membrane body, is provided by specially designed support elements. Its main features are the scraper lip on the side towards the coolant and the sealing lip behind it. Between these two seals there is a grease reservoir. The sealing lips run on a hardened stainless steel sleeve that has been pressed onto the shaft of the water pump. The water pump is driven by the main belt drive of the auxiliary drive, while the air compressor is driven by the water pump via a second belt drive. The air compressor is activated by an electromagnetic dry coupling located on the shaft of the water pump. This coupling is a double flux-linked single-disk magnetic dry coupling. The drive wheel has a friction lining with lifetime durability, Figure 16. When a current is applied to the magnet coil the magnetic flux links with the armature via the belt drive of the water pump (friction disk). The maximum power consumption of the magnet coil is 35 W. The 60 Nm of torque that is occasionally required at the coupling is achieved in this compact design by a double flux linkage, with the magnetic flux flowing twice from the rotor into the armature. The armature is fixed to the drive belt wheel and is free to move axially but is torsion-resistant. When the current is switched off, the armature is returned by three leaf springs. Lifetime wear minimisation makes the coupling maintenance-free.

3.1.9 Auxiliary Drive with Two Poly V-Belts The main feature of the auxiliary drive is its two poly V-belt drive lines, Figure 17. The sixgroove main belt line drives the water pump, the generator and the air conditioning compressor. The five-groove secondary belt drives the air compressor, which is geared to run at 4.95 times the crankshaft speed, from the water pump. The magnetic coupling described above is integrated into the drive pulley of the water pump. Both belt lines are fitted with belt tensioners, making them maintenance-free. The speed range close to idling at full load represents a critical state for the belt drive. In this operating range, the combination of a dual-mass flywheel and the driving force for the compressor results in very high loads. Crankshaft vibration angles of up to 7° occur at 850 rpm.

With the aid of the design programme Simdrive, the belt drive was simulated and possible solutions were evaluated. The result was a system with two belt tensioners, and their successful functioning was confirmed in subsequent experimental tests, Figure 18. The first belt tensioner is located in the idler pulley between the water pump and the crankshaft and damps the entire system by means of a double damping system. The second belt tensioner is in the driven pulley between the generator and the water pump. It is highly damped and decouples most of the mass inertia of the compressor.

3.1.10 Design Cover with Integrated Vacuum Reservoir The area between the exhaust gas turbocharger and the air line of the TSI engine has a cover with an integrated vacuum reservoir with a volume of 1000 cc. This reservoir is used to operate the charge motion flaps independently of the engine load.

3.2 Mixture Formation Components 3.2.1 Compressor with Internal Reduction Gear The characteristic feature of the TSI engine is the dual supercharger system. Apart from the exhaust gas turbocharger, it consists of a compressor and an air circulation circuit controlled by a regulator valve. The compressor is a mechanical supercharger based on the Roots principle. It is map-controlled and activated by a magnetic coupling at the water pump. The maximum engine speed at which the compressor operates is 3500 rpm. A special feature of the compressor is its internal gearing upstream of the synchronisation gear wheel pair, Figure 19. The internal reduction gear provides an increase in engine torque when pulling away and in the lower engine speed range compared to conventional designs with an equally compact compressor. The total gear ratio for the auxiliary drive and the internal gearing is itotal=0.20 to the crankshaft. Charge control during compressor operation is provided by an electronic control valve in the air circulation circuit. The valve allows an infinite variation between compressor supercharging alone and turbocharging alone. The compressor is fixed by four screws directly to the crankcase, together with the pressure-side noise damper. The compressor housing is designed to ensure that the minimum gap between the walls and the rotor is guaranteed. The gap is independent of the position within the tolerances of the joined components. Also screwed to the compressor housing

are the intake-side dampers and the belt tensioner of the poly V-belt.

3.2.2 Acoustic Design of the Compressor Acoustic design was one of the central tasks in the development of the compressor system. In the TSI engine, the compressor is located in the direction of the vehicle interior. As a result, any residual noise from the mechanical compressor can be directly heard by the vehicle occupants. Mechanical noise from the compressor and noise due to air pulsation as well as the transfer of residual pulsation noise was therefore minimised. Acoustic optimisation of the compressor mechanics and the pulsations in the intake and pressure lines was achieved by the following measures: – modification of the gear engagement parameters, e.g. crowning, angle of pressure and torsional backlash – reinforcement of the shafts inside the compressor – stronger ribbing of the housing at specific points. The optimisation of the compressor to reduce air pulsation excitation was achieved by the following measures: – repositioning and shape optimisation of the return flow ports – shape optimisation of the inlet and outlet ports. In order to further reduce pulsation noise from the compressor, broadband dampers were installed on the intake and pressure sides, Figure 20. The noise damper on the intake side, which is made of glass fibre reinforced polyamide, is flanged directly to the compressor. The friction-welded shell design consists of nine resonance dampers arranged in series and operating according to the Helmholtz principle. With a total volume of 840 cc, this achieves effective damping of the air pulsation over a wide frequency range. The damper on the pressure side is made of the same material as that on the intake side and is located between the turbocharger and the crankcase at the compressor outlet. Even though installation space was limited, the friction-welded multi-shell design allowed an effective damper to be fitted. To simplify assembly, the pressure pipe was designed as a plug-in solution. The pressure damper also works according to the Helmholtz principle and also has nine chambers with a total resonance volume of 850 cc. It achieves a noise attenuation of up to 30 dB. In order to further reduce noise, the compressor and the dampers are encapsulated MTZ 11/2005 Volume 66

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www.all4engineers.com 11|2005 · November 2005 · Volume 66 Vieweg Verlag | GWV Fachverlage GmbH P.O. Box 15 46, D-65173 Wiesbaden, Germany Abraham-Lincoln-Straße 46, D-65189 Wiesbaden, Germany Managing Director Andreas Kösters Publishing Director Dr. Heinz Weinheimer Senior Advertising Executive Thomas Werner Senior Sales Executive Gabriel Göttlinger Senior Production Executive Bernhard Laquai

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and the shells are lined with absorption foam. The foam increases the damping effect and provides complete sealing without gaps. Figure 21 shows the noise radiation from the engine during compressor operation and run-up between 2,000 and 2,500 rpm. When the engine was measured in its original state on the acoustic test bench, the tonal components of the compressor orders were dominant and were also perceived as disturbing in the vehicle interior. The measures described above allowed both the tonal components and the total noise radiation of the compressor assembly to be effectively attenuated, with the exception of a certain component that has been deliberately maintained in the dynamic activation range.

3.2.3 Exhaust Gas Turbocharger and Heat Shield The second supercharger unit in the TSI engine is an exhaust gas turbocharger, Figure 23, with a wastegate. Its dimensions are as follows: – neck cross-section: 2.8 cm2 – turbine wheel diameter: 45 mm – compressor wheel diameter: 51 mm. The turbine housing and the exhaust manifold are designed as an integral component. The flange for the electric blow-off valve is integrated into the compressor housing. In order to ensure that the customer can exploit the fuel consumption potential of the TSI concept to its maximum extent, component temperature-dependent enrichment has been avoided as far as possible. For this reason, the turbocharger must remain fully functional even at exhaust gas temperatures of up to 1050 °C. The turbocharger was therefore modified as described in the following. The turbine housing is made of heat-resistant cast steel similar to 1.4848. During the course of its development, the housing was crack-optimised by carrying out thermal stress calculations and the results were verified in endurance tests, Figure 23. The turbine wheel is made of the highly heat-resistant nickel-based alloy MAR 246. To increase its efficiency and to shield against heat to the bearing housing, the turbine wheel has a closed back. To ensure adequate component reliability, the shaft is made of the material X45CrSi9.3. The shaft and the turbine wheel are joined by arc welding. The shaft has a reduced heat throttle to ensure sufficient strength over the larger wall thickness. The flap lever of the wastegate is made of the nickel-based alloy INCO 713C to provide the required temperature stability.

Spark Ignition Engines

The bearing housing is water-cooled for better cooling. The water core has a large cross-section and is located close to the piston ring seat. A heat shield between the turbine and bearing housing prevents overheating and coking of the bearing system. The increase in the maximum exhaust temperature to 1050 °C has a considerable influence on the peripheral components of the turbocharger. For this reason, a threelayer heat shield was developed. In addition to the insulation properties of the intermediate layer, the component also has an acoustic effect in that it reduces intrinsic vibration. The geometry of the heat shield was optimised in vehicle tests with regard to its heat shielding effect and its prevention of hot air flows. At the same time, it also serves as a design element of the TSI engine.

3.2.4 Intake Manifold The intake manifold is a two-shell injection moulded part made of the plastic material PA6 GF30. To allow the series temperature behaviour of the component to be represented at an early stage in the development work, PA cast parts from silicone tools were already used in the early concept phase. Extensive CFD calculations with the aim of achieving equal flow into all branches of the manifold resulted in a triangular connection geometry of the 90° pipe bend and to the guide ribs arranged in the collector. The lower part of the intake manifold pipe contains the air guidance with the tumble flap control and the function of the high-pressure fuel rail. The basic concept was adopted from the 1.6-litre 85 kW FSI engine. The high-pressure sensor and the pressure limiter valve were redeveloped for the higher rail pressure of the TSI engine, and the charge motion flaps were reinforced to withstand the higher load.

COVER STORY

Meeting the joining and sealing requirements to the pressure pipe in front of the turbocharger proved to be a particularly difficult task. The tolerances of the entire engine charge air circuit, the turbocharger, the intake manifold and the cylinder head as well as the heat expansion of the components all had to be compensated for. The solution was to use a half-moon-shaped connection shell that can be screwed on at several set positions, thus making it insensitive towards angular and longitudinal tolerances.

References [1] Szengel, R.; Middendorf, H.; Wiedmann, M.; Wietholt, B.; Laumann, A.; Voeltz, S.; Stiebels, B.; Damminger, L.: Die Ottomotoren des neuen Volkswagen Golf. In: Der neue VW Golf, Sonderausgabe der ATZ und MTZ, Oktober 2003 [2] Krebs, R.; Spiegel, L.; Stiebels, B.: Ottomotoren mit Direkteinspritzung von Volkswagen. 8. Aachener Kolloquium, Aachen, 1999 [3] Middendorf, H.; Voeltz, S.: Kurbelgehäuseentlüftung und Ölkreislauf des 1,6-l-85-kW-FSI-Motors. Ölkreislauf von Verbrennungsmotoren, Essen 2005 [4] Golloch, R.; Merker, P.: Downsizing bei Verbrennungsmotoren Grundlagen, Stand der Technik und zukünftige Konzepte. In: MTZ 66 (2005), Nr. 2

3.2.5 Charge Air Circuit The air-guiding components of the engine include the following: – intake connection pipe between the clean air pipe, the intake damper and the control flap – control connection pipe between the control flap, compressor pressure pipe and turbocharger pressure pipe – pressure pipe between the control connection pipe and the turbocharger. In order to achieve low noise radiation as well as free design of the connection geometries, secure connections and ease of assembly, these components are injection moulded in the plastic material PA6 GF30, Figure 24. MTZ 11/2005 Volume 66

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