Engines New Engines for Even Greater Driving Enjoyment and Comfort

ATZ | MTZ Volkswagen PASSAT The authors: Rüdiger Szengel Uwe Kirsch Bern Ebel Silvio Kuhn Stefan Lieske Frank Reschke Figure 0 - Opening image Engines New engines for even greater driving enjoyment and comfort 1. The new V6 engine generation with direct injection technology In order to meet increasing demands to the highest possible standard, the Volkswagen V engine series has been thoroughly redeveloped. The emphases during the development phase were the introduction of petrol direct injection and an increase in the displacement to 3.6 dm³ specially for the US market. The direct injection technology offers a wider range of opportunities for meeting future exhaust limit values and to reduce fuel consumption. The redevelopment was made without changing the vehicle package. The new engine has a maximum torque of 360 Nm and achieves the rated power of 206 kW at 6200 rpm. For the European market, a 3.2 dm³ variant with 330 Nm and 184 kW power is available. 1.1 Introduction In 1991, production was started on the first VR6 Volkswagen engine, with a displacement of 2.8 dm³ and 128 kW power. In 1999, the conversion was made to four-valve technology and in 2000, the displacement was increased to 3.2 dm³ with up to 184 kW power [Reference 1, 2]. In order to meet increasing demands, the engine was thoroughly redeveloped. The displacement has been increased to 3.597 dm³ with the US market particularly in mind. For the European market, a version with 3.168 dm³ is available. The displacement was increased without changing the external measurements for the vehicle Page 1 of 17 package. A further development focus was the introduction of direct petrol injection. The new engine has a maximum torque of 360 Nm and achieves the rated power of 206 kW at 6200 rpm. The 3.2 dm³ variant has a torque of 330 Nm and 184 kW power. 1.2 The basic engine The concept for this new engine generation model is based on its predecessor [Figure 1]. Figure 1 - FSI engine components Extended four-valve cylinder head with roller cam follower valve train Single-section overhead plastic variable intake manifold Weight-reduced grey cast-iron cylinder crankcase Belt drive assigned to the gears with integrated drive for the fuel pump Continuous intake and outlet cam shaft adjustment Thanks to the targeted use of calculation methods, an engine weight of 173 kg was achieved, in conformity with DIN 70020 GZ. Despite the additional FSI technology injection components, this weight is significantly less than the weight of the previous engine. The power-weight ratio of the 3.6 dm³ engine is 0.84 kg/kW. The main components (crankcase, cylinder head, connecting rods, crank and cam shafts) were produced and installed at the same time as the intake manifold injection engine, and in the same production lines. The most important technical data is compiled in [Figure 2]. Figure 2 - Technical data 1.2.1 Crankcase The cylinder diameter has been increased from 84.0 mm to 89.0 mm, and the stroke from 95.9 mm to 96.4 mm. With the VR concept, the drill holes cut through both rows of cylinders at the bottom end. The maintenance of sufficient residual wall thicknesses in this area and on the cover plate to the cylinder head screws required that the V- angle be reduced from 15.0° to 10.6°. The pitching angle of the crankshaft drive was increased from ± 12.5 mm to ± 22.0 mm. Extensive finite element calculations enabled the stress on the components to be reduced with improved rigidity and an increase in load. The cause of the high stress in the deflection of the fuel flow between the cylinder head screws and the crankshaft bearing cap lies in the area of the ventilation gap below the cylinders which is typical of the VR. From the first structural draft design through to the finished model, Page 2 of 17 protection against fatigue fracture was nearly doubled in critical areas, and in some places, exceeds the values of the previous engine [Figure 3]. Figure 3 - Improvement in fatigue fracture protection of the series design compared to the initial starting point The improvement in local rigidity of the crankshaft housing cover plate made it possible to reduce the preliminary installation tension force of the cylinder head screws by approx. 30%, resulting in lower cylinder warpage. During the working cycle, the effect of the combustion pressure is compensated by the load reduction from the component elasticity, and no contact power is lost. On the stopper of the cylinder head seal, the line compression remains above the minimum limit value under all operating conditions [Figure 4]. Figure 4 - Line compression on the cylinder head seal The line compression on the critical combustion chamber channel is also high enough to secure the sealing function. The weight of the crankshaft case has been reduced by approx. 8 kg, or 15%, compared to the previous model, while rigidity was improved. The weight is therefore very low in comparison with other grey cast-iron crankshaft cases. 1.2.2 Cylinder head The tried and tested valve train arrangement and geometry was retained for the cylinder head. The injection valves are housed directly in the cylinder head. The injection nozzles in cylinders 1, 3 and 5 penetrate the inlet channel [Figure 5]. Figure 5 - Arrangement of the injection valves and inlet channels The injection nozzles in cylinders 2, 4 and 6 are arranged underneath the inlet channel, however [Figure 5]. The valve distance to the inlet side has been increased by 2 mm to 36.5 mm, in order to reduce the flow deflection from the injection valves in the channel for the long inlet channels. Both inlet channels exceed the already high flow level of the intake manifold injection engine. When designing the plenum chamber, extensive improvements were made using calculations and supplementary component tests, in order to achieve an even coolant throughput with high flow speeds [Figure 6]. Page 3 of 17 Figure 6 - Improvement in coolant flow of the series design compared to the initial starting point Guide fins and co-ordinated cross-sections enable targeted cooling in the knuckle area between the outlet channels. Typically, the flow around the cylinder head of the first cylinder and the last cylinder in the crankshaft case is weaker for the longitudinal flow. The co-ordination of the cross-sections in the water cooling jacket and the overflow cross- sections in the cylinder head seal means that an even temperature can be maintained for the components. The temperature differences between cylinders 1 and 6 in the crankshaft case remain below 5 °C. 1.2.3 The engine The pitching angle of the crankshaft, which has been increased to 22.0 mm, influences the effective lateral piston forces considerably. The increase in lateral forces occurs during high piston speeds, and therefore under good hydrodynamic external conditions. Compared to the previous engine, loss through friction is practically neutral. Unlike the flat pistons used to date, the combustion process with direct injection requires a pit which generally leads to an increase in mass. At the same time, the piston absorbs stronger lateral forces due to the larger pitching angle of the crankshaft drive. For this reason, importance has been placed on reducing the oscillating masses, while retaining sufficient shaft rigidity. The weight-optimised pistons with retracted hubs and a shortened ring section, the shortened piston pins with funnel-shaped ends and the trapezoid connecting rod compensate for the increase in mass of the piston by 55 g. 1.2.4 The oil pump In the previous engine, the oil pump is installed in the oil pan, and is driven by a diagonally interlocking auxiliary shaft using a complex procedure [Reference 3]. For the new construction, a compact oil pump has been developed, which is installed in the space previously used for the auxiliary shaft [Figure 7]. Figure 7 - Oil pump drive of the previous (left) and new (right) engine generation Taking into account the broad range of applications for the engine, this new development offers above all greater freedom of design when defining the oil pan contour for areas of use with special requirements, such as offroad capability. The removal of the drive shafts leads to a reduction in friction agent pressure, and a weight saving of approx. 2 kg. The degree of effectiveness of the oil pump has been improved by approx. 14% with the conversion from external interlocking to Page 4 of 17 duocentric internal interlocking. The removal of the friction losses in the oil pump drive results in a power gain of approx. 1.5 kW at the nominal speed. 1.2.5 Injection system In the new FSI engine, an injection system is used with two high-pressure rails. This enables the fuel to be supplied to the injection valves, which are positioned on two different levels. The pressure can only build-up in both high-pressure rails and the fuel can only be supplied using a high-pressure pump, since the two rails are connected via a covered transfer line [Figure 5]. The screw fitting on the lower high-pressure rail is also used to attach the intake manifold. This makes it possible to achieve the goal of creating a compact structure, while securing production processes and ease of installation. The high-pressure pump has an integrated quantity control valve to reduce the drive power with low fuel consumption by the engine. The basic pump body is also used in other engine series. Due to its positioning on the gearbox end, the high-pressure pump is installed in a safe place for both the longitudinal and transverse installation of the engine should a crash occur.

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