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. It is driven by a drive wheel with dual side cams which is also installed in the chain drive. The cylinder head has been lengthened to hold the chain drive and to provide a rigid connection to the fuel pump.

1.2.6 Intake manifold and channel development

The new intake manifold for the FSI engine is designed in plastic according to the well-known principle used for previous variable intake manifolds on the VR engine [Reference 1], and is produced using a core melt-out procedure. The system includes an integrated underpressure volume, longitudinal shifting and the heated inflow of the crankshaft case ventilation [Figure 8].

Figure 8 - Variable intake manifold

For the engine intake system, the intake manifold cross-section for the increased displacement volume and the direct injection was adapted to the increased throughput. The oscillation lengths in the intake manifold are switched at between 515 mm in the torque position and 246 mm in the power output position.

The longitudinal shifting is created by flaps which are positioned on a steel shaft mounted in rubber elements. The flaps are contoured, in order to achieve minimum pressure loss when opened. The rubber bearing enables the acoustic decoupling of the shift system, and low shift operation forces.

Page 5 of 17 By creating images of the internal cylinder flow, it was possible to achieve the required interaction between the intake system, the intake channel and the direct fuel injection. [Figure 9] shows as an example the results of the laser-optic measurement of the flow configuration in the combustion chamber using the “Doppler global velocimetry technique”. The development focus was on the development and optimisation of the tumble, and the flow areas near the walls. The shallower channel flow with a long inlet channel creates an overflow in the valve head, and subsequently a stronger reflection on the cylinder wall. The steeper, short inlet channel leads to strong flow shadow development behind the inlet valves.

Figure 9 - Internal cylinder flow with opened valve

1.3 Combustion process

The combustion process has been optimised in terms of the flow behaviour of the long and short inlet channels, and the positions of the injection valves. The pitching angle also results in different movement patterns in the pistons, the effects of which on the control times of the inlet valves and the injection have to be taken into account. Following the spray adaptation of the short and long injectors to the carburation conditions, the combustion processes of both cylinder banks have been co-ordinated with each other [Figure 10].

Figure 10 - Development of the combustion process on the VR engine

This co-ordination of the combustion process has enabled the homogeneous split catalytic converter heating process [Reference 4] to be used in a direct injection engine. The effect is caused by the relocation of the combustion focus to a late stage, in order to heat the exhaust gas mass flow. In order to ensure the flammability of the mixture under these conditions, special stratification is required. This removes the need for a secondary air system, while maintaining the exhaust limit values in accordance with EU 4 and LEV 2.

1.4 Characteristic engine values

In the same way as for the V6-3.2 dm³ MPI engine, during the development of the FSI engine, particular importance was placed on the best possible torque and maximum power [Figure 11].

Figure 11 - Power and torque curves of the 3.2 dm³ and 3.6 dm³ engine

Page 6 of 17 At 4500 rpm, the variable intake manifold is switched from torque position with long gas flow lengths to the power output position with short gas flow lengths. This achieves 13.1 bar average useful pressure for the 3.2 km³ FSI engine, and 12.6 bar for the 3.6 dm³ engine.

A comparison of the specific consumption in a competitive field is shown in [Figure 12]. Here, it becomes clear that the V6 FSI generation of engines has succeeded in making a leap in development.

Figure 12 - Specific fuel consumption in a competitive field

References

[1] Szengel, R.; Metzner, F.T.; Kirsch, U.; Lieske, S.; Ebel, B.: Der neue V6-3,2 l- Motor im VW Phaeton. (The new V6-3.2 l engine in the VW Phaeton). In: Sonderheft der Automobiltechnischen Zeitschrift / Motortechnischen Zeitschrift Juli 2002, (special edition of the automobile technology journal / engine technology journal July 2002), p. 42–47.

[2] Kirsch, U.; Reschke, F.; Ebel, B.; Lieske, S.: Der V6-3,2 l-Motor im neuen Audi A3. (The new V6 3.2 l engine in the new Audi A3). In: Sonderheft der Automobil- technischen Zeitschrift / Motortechnischen Zeitschrift April 2003, (special edition of the automobile technology journal / engine technology journal April 2003), p. 92–98.

[3] Naumann, F.; Voigt, D.; Deutsch, H.: Der neue VR6-Motor von Volkswagen. (The new Volkswagen VR6 engine). In: MTZ 52 (1991) no. 3, p. 100-105.

[4] Szengel, R.; Middendorf, H.; Wiedmann, M.; Wietholt, B.; Laumann, A.; Voeltz, S.; Stiebels, B.; Damminger, L.: Die Ottomotoren des neuen VW Golf. (The otto engines in the new VW Golf). In: Sonderheft der Automobiltechnischen Zeitschrift / Motortechnischen Zeitschrift Oktober 2003, (special edition of the automobile technology journal / engine technology journal October 2003), p. 42–54.

Page 7 of 17 2. The diesel engines in the new PASSAT

Figure 13 - Opening image

The 6th generation PASSAT is offered with three TDI engines, which include some interesting new developments:

1.9 l with 77 kW 2.0 l with 103 kW 2.0 l with 125 kW

All engines have been thoroughly modernised, above all in terms of emission reducetion, and have been redeveloped in a wide range of other ways. The most important change relates to the standard installation of a diesel particle filter. Here, Volkswagen has used the concept of integrating the oxidation catalytic converter and the diesel particle filter.

All engines already fulfil the strict EU IV exhaust emission standards due to developments made inside the engine. In response to market demands, the diesel particle filter also reduces particle emissions to a minimum. The installation of a new generation of ceramic glow plugs also contributes to reducing the particles, and ensures excellent cold-starting and high tensile strength.

Another key requirement for the new PASSAT is to further increase comfort. For this reason, improving comfort also took priority during the development of the TDI. The new compensating shaft modules of the 2.0 l engines are of particular interest here.

With these innovative TDI engines, Volkswagen has succeeded in underscoring its place as a technological standard bearer in terms of the development and production of modern diesel engines. Increased comfort, greater driving enjoyment and higher performance with reduced consumption and even lower emissions are clear proof of this.

2.1 The 1.9 l with 77 kW

Figure 14 - 1.9 l 77 kW TDI with DPF

The 1.9 l 77 kW TDI, which has been successfully used by Volkswagen in many different models, also offers a balanced relationship between very good driving performance, high efficiency and ideal environmental characteristics in the new PASSAT. With a torque of 250 Nm at 1,900 R/min and an output of 77 kW at 4.000 rpm, it ensures the well-known smooth, harmonious TDI driving dynamics. In the new PASSAT, this engine also conforms to the strict EU IV limit values. The engine is available with a diesel particle filter near the engine on request.

A series of components have been improved for the installation of the particle filter:

Page 8 of 17

The exhaust gas turbocharger has been designed in such a way as to enable the diesel particle filter to be installed as close to the engine as possible with maximum volume. The related high performance of the charge air cooling path has been adapted. The diesel particle filter combines a filter and an oxidation catalytic converter into one component. The pump-jet injection system now injects the fuel precisely into a slightly modified combustion chamber with injection pressures of up to 2,400 bar. The operating range is extended by a modified supply characteristic in the pump-jet. High quality additional injection processes, e.g. for thermic regeneration, are now possible. A newly developed cylinder head cap with improved oil separation reduces the consumption of oil in the engine, and therefore the entry of oil ash into the diesel particle filter.

Figure 15 - Power and torque curves of the 1.9 l 77 kW

2.2 The 2.0 l with 103 kW

The 2.0 l is based on the 2.0 l TDI drive used in the Golf class. The unit already reaches an impressive torque of 320 Nm between 1,750 and 2,500 rpm. This TDI engine type is therefore recommended for particularly comfortable driving in the new PASSAT.

A wide range of structural changes for the installation of the diesel particle filter have also been made to this unit. The modifications, which have been made to the 1.9 l, have in general also been adopted for the 2.0 l.

A further significant measure designed to increase comfort relates to the reduction in vibration. Here, a completely new compensation shaft module has been developed. The compensation shafts are integrated into one separate element together with the oil pump, and are positioned below the cylinder crankshaft case.

The two rotating compensation shafts which run counter to each other with a double engine torque achieve a compensation for the freely oscillating, 2nd engine level forces typical in four-cycle, four-cylinder engines. This creates a significant reduction in vibration stimulation in the vehicle body via the engine bearing, and therefore makes a significant contribution to increasing comfort in the vehicle interior.

Figure 16 - Power and torque curves of the 2.0 l 103 kW

2.3 The 2.0 l with 125 kW

Page 9 of 17

Figure 17 - 2.0 l 125 kW TDI

The higher performance 2.0 l four-valve TDI with 125 kW is making its debut as a top engine type in the new PASSAT. With its new Piezo pump-jet high pressure injection system, the maintenance-free diesel particle filter and a compensation shaft module, the unit ensures maximum driving enjoyment, with the customary low consumption, while creating a high level of comfort with minimum emission levels.

The new 125 kW engine is a further development of the 2.0 l four-valve engine with 103 kW already used in the Golf platform. The specific power output of 63.5 kw/l also marks a peak value for passenger car diesel engines. The maximum torque has been increased from 320 to 350 Nm compared to the 103 kW engine [Figure 18].

Figure 18 - Power and torque curves of the 2.0 l 125 kW

Figure 19 - Technical data

Aims

After the 1.9 l two-valve TDI with 110 kW, and the 118 kW engine in the Seat Cupra became the record holders with regard to specific engine power, the aim was to achieve a power output of 125 kW (170 PS). To date, this value has only been achieved in five or six-cylinder engines. The aim with regard to the torque was to use the limit of the gears, currently at 350 Nm in as large a torque range as possible.

The comfort levels were also designed to come as close to a six-cylinder engine as possible, while achieving an increase in idling acoustics and vibration comfort. The task was also to further improve the specific consumption and exhaust values of the new TDI.

Piezo pump-jet

The current demands for greater engine power, lower pollutant emissions, further reductions in consumption and in particular, reduced injection noise, led Siemens to develop the new, innovative Piezo pump-jet injection system [Figure 20].

Figure 20 - Piezo pump-jet

The use of a Piezo actuator to trigger the high-pressure valve in the pump-jet make it possible to synthesise the known pump-jet advantages:

Maximum injection pressure for the best emissions and high specific power Top hydraulic effectiveness through a very low high-pressure volume

Page 10 of 17 Ideal injection rate process Very precise, low-level preliminary injection under high pressure

With the current advantages of the common rail systems:

Flexible selection of preliminary and subsequent injection quantities and injection intervals Low injection noise (through partial stroke regulation of the shift valve)

The Piezo pump-jet (PPJ) has been specially constructed for the limited installation space in the four-valve TDI engine, while the external conditions such as fuel supply, attachment and contact could to a large extent be adapted from the current pump-jet system. Despite an increase in injection pressure, with a maximum of 2,200 bar instead of the 2,050 bar to date, the drive is not placed under additional stress, since the plunger diameter in the PPJ could be reduced thanks to the low high-pressure volume. This has a positive effect on the noise stimulation during partial load.

An important functional feature of the current pump-jet elements are the different pressure levels for preliminary and main injection. This feature could also be included in the PPJ, despite the removal of the “mechanical alternate piston system” used to date. Variable suction manifold for swirl control

As a further emission measure, and specifically for the heavy vehicle designs with critical emission levels, a variable suction manifold has been developed to control the swirl. In order to increase the inlet swirl in the operating areas with low air throughflow, and therefore to increase the carburetion energy, one of the two inlet channels can be shut down using throttle valves in the intake manifold. The variable shaft is activated from controls in the characteristic map via a pneumatic actuator [Figure 21]. The variable intake manifold is installed in the same space as the “fixed” intake manifold to date, and has identical connection dimensions.

Figure 21 - Variable intake manifold

The compensatory shaft module

A very effective measure introduced to improve comfort levels was the compensatory shaft module (CSM) which was also installed in the 125 kW engine. This mass compensation system consists on its own housing with two compensatory shafts rotating counter to each other with double crankshaft speed – the “Lancaster compensation” – which are driven together with the engine oil pump via diagonally interlocking, acoustically improved spur pinions [Figure 22, 23].

Figure 22 - FEM model of the compensatory shaft module and crankshaft case (view from below)

Figure 23 - Spur pinion drive of the compensatory shaft module

Page 11 of 17

The compensatory shaft module is installed inside the oil pan in such a way as to save space. The oil pan has a new look with additional dents in order to compensate for the volume of oil. [Figure 24] shows the effectiveness of the compensatory shaft module. The 2nd level vibration travel, and therefore the discharge of force into the unit bearing arrangement, could be reduced by up to 80%, particularly during high rotational speeds. The increase in weight of the compensatory shaft module created by the principle could be compensated for by a newly constructed crankshaft with four instead of eight counterweights.

Figure 24 - Minimisation of the 2nd level vibration paths by the compensatory shaft module

Engine developments

Increased crankshaft with 4 counterweights Material: 42CrMoS4

The use of a four-cylinder with such high levels of driving performance results in fuel savings due to the “downsizing effect” alone. These savings have been even further improved through the targeted further development of the combustion process. Deleted: The use of a four-cylinder with such high levels of driving performance results in fuel savings Figure 25 - Piston without valve pockets due to the “downsizing effect” alone. ¶ Durch die gezielte Weiterentwicklung des Brennverfahrens konnte diese Einsparung noch weiter verbessert Figure 26 - New water tank with ring channels werden.¶ ¶ even greater savings could be madehrough the targeted further development of the combustion Development status of the 2.0 l 125 kW process.¶

It has been possible to improve the new 2.0 l engines for the PASSAT with 103 and 125 kW even further in terms of consumption. When the engine is working at full throttle, it remains below the 200 g/kWh mark. The best result has been 129 g/kWh, the best yet for passenger car series engines. In terms of specific consumption, these new TDI engines are therefore “best in class” once again. The increase in efficiency during the combustion process, with pistons without valve pockets, together with the new Piezo pump-jet system with its improved efficiency, are responsible for this success. In the PASSAT with six-speed manual gears, the 125 kW engine shows a test consumption of just 5.9 l/100 km (current value).

The very high torque, together with a dynamic load pressure build-up and the optimum gradation of the six-speed manual gears make for vehicle performance levels which to date were only thought possible with a four-cylinder engineer in this vehicle class. The saloon achieves a spurt from 0 to 100 km/h in just 8.7 seconds, and needs just 8.9 seconds to move up from 80 to 120 km/h in fifth gear. Thanks to the optimum flow-shaped body, a top speed of 223 km/h is possible (current values).

Page 12 of 17 Figure 27 - A comparison of technical data

2.4 Summary and prospects

During their successful ten-year history, the Volkswagen TDI engines have proved that driving enjoyment, efficiency and environmental sensitivity can be combined in diesel units. The new diesel engines for the PASSAT mark a consistent development in the TDI. The additional qualities stand out for their increased comfort, while at the same time reducing consumption and emission levels. “Best in class” for specific consumption and a maintenance-free diesel particle filter concept, which also integrates the catalytic converter, are further milestones in the development of TDI engines.

3. Diesel particle filter close to the engine

3.1 Introduction

The four-cylinder engines in the new PASSAT conform to the EU IV legislation on exhaust fumes. Following requests by customers, these vehicles can now be fitted with the latest generation particle filters, in which the oxidation catalytic converter and the particle filter are combined into a single component.

The first generation of uncoated SiC particle filters has already been offered in the current PASSAT model since 2003. In order to guarantee maximum reliability with this filter regeneration, it has also been necessary to use a fuel additive for the filter system in the vehicle underbody. Although the filter volume is 4.1 l, the filter has to be replaced after 120,000 km due to the accumulated additive ash.

In the new PASSAT, a particle filter system has been developed in which the focus was on a significant increase in filter run times as well as a significant reduction in complexity.

3.2 The particle filter with integrated oxidation catalytic converter

The position of the highly porous SiC particle filter with a volume of 3.0 l close to the engine, and the integration of a new type of oxidation coating in the filter remove the necessity for an oxidation catalytic converter and the use of a fuel additive with the related peripheral system equipment. It has been possible to design of the filter to match the service life of the vehicle thanks to the significant reduction of ash entering the filter through the use of a new engine oil with reduced sulphate ash content.

Figure 28 - Particle filter with sensors near the engine

Page 13 of 17

The filter is mounted in the canning on a non-swelling hybrid mat, which is invisibly screwed to the exhaust gas turbocharger immediately above the inlet funnel. The temperature and lambda sensors and the pipes to measure the pressure for the differential pressure sensor are positioned in the funnels of the canning.

The filter type used has porosity levels of over 50%, in order to be able to coat large quantities of washcoat with a suitably active catalytic converter. The position near the engine plays an important role, together with the catalytic converter coating, in ensuring that soot is continuously oxidised by NO2 during normal driving mode. Thermic regenerations are only necessary after long distances in light load mode.

The catalytic coating of the filter in zones is reflected in the reduction in platinum content over the length of the filter. The large quantities of precious metals used in the front, warmer section of the filter ensure good catalytic starting characteristics. With the lower quantities of platinum in the rear section, the filter can cope with the temperature stress during the soot regeneration and the accumulation of ash over the running time. Ageing influences in the catalytic converter through thermic stress can therefore be kept largely to a minimum.

3.3 Load recognition

The thermic regenerations of the particle filter system, which are required at cyclical intervals, are controlled largely by a DPF soot load model, which is derived from the flow resistance of the DPF. In order to determine the resistance of the DPF flow, the state quantities of the exhaust fumes are recorded by sensors and further processed in a model which takes into account all relevant thermal and aerodynamic influences.

Figure 29 - Adaptive ash compensation model

The core element of this model is a calculation of the differential pressure based on the non-dimensioned similarity figures by Euler and Reynolds, and on both unloaded particle filters and filters with defined loads. The differential pressure currently measured is set in relation to these values, thus defining the current soot load as a percentage. The soot loading model is made plausible by the fact that the operating time, fuel consumption and distance travelled are monitored.

The influences on working life as a result of the ash intake in the DPF are effectively tackled by an adaptive compensation model. The ash deposition mechanism in the filter can be described using two limit cases, which contribute to the increased loss of pressure in very different ways. The particle filters in low and medium-load operation, whose soot loads are thermically regenerated, show ash blockages in the rear section of the channels after a certain period of time. An extreme situation which contributes in a far greater way to the loss of pressure occurs when the filter is kept free of soot during very heavy operation over long distances. Here, a homogeneous ash deposit

Page 14 of 17 can be observed on the channel wall over the entire length of the filter. The majority of filters show a mixture of the phenomena described above when in “normal driving mode”. The adaptive compensation model takes the worst case scenario for increased pressure loss through ash, and corrects this increase following soot regeneration as required. This function guarantees the maximum driving distances between two filter regenerations, even when filter run times are high.

3.4 Regeneration operation

The temperature of the exhaust fumes can be increased in a way unaffected by torque during the DPF regeneration by adjusting the air and injection-specific parameters. In addition to the main injection, which is adapted in relation to the start and duration of supply, the pump-jet system also enables a subsequent injection to be made, which plays a key role in bringing energy to the exhaust fumes. Since the subsequent injection burns almost completely in the cylinder, both fuel entries into the engine oil and catalytic converter loads from extremely high hydrocarbon emissions can be minimised.

Figure 30 - Injection and cylinder pressure path in normal and regeneration mode

The load pressure reduction commonly used to increase temperature does not work in all operating areas. In order to add quantities of energy to the exhaust fumes, thus achieving shorter filter regeneration times, the load pressure was lifted in comparison with normal operation within certain ranges of the characteristic map. The fresh air mass was adjusted via a throttle valve when the exhaust gas reverse flow was switched off.

Using a cascaded lambda temperature control, an exhaust fume temperature of 630 °C can be provided at the entrance to the filter regardless of the ambient conditions, and maintaining a certain lambda value in the characteristic map range. In the inner control circuit, a lambda controller enables the required lambda values to be precisely set, even during highly-dynamic operation. The external circuit of the control cascade consists of a temperature controller which intervenes by linearising the lambda set values.

Figure 31 - DPF regeneration in driving mode

In heavily transient driving mode with a large use of shove mode, such as in urban traffic, special measures are required to heat the filter. During these phases, small fuel quantities are injected which do not burn in the combustion chamber, but are exothermically oxidised on the filter as HC steam. This is controlled after the particle filter by temperature sensor.

Page 15 of 17 The particle filter system must fulfil the requirements set out in the OBD legislation. The same sensors are electrically monitored and made physically plausible. After the engine is switched off, the zero value of the differential pressure sensor is recalibrated, for example. When the filter is dismantled from the exhaust system, this is recognised as a matter of course.

3.5 Summary

The four-cylinder engines in the new PASSAT can be equipped with the latest generation particle filter system if required. The catalytic coating on the filter removes the need for both a separate oxidation catalytic converter and the use of a regeneration additive. Due to its position close to the engine, with correspondingly high exhaust fume temperatures, a large proportion of the soot particles emitted are continuously burned in the filter during normal driving mode. Thermic regenerations are only seldom required due to the low soot emissions from the engine, which already conform to the EU IV exhaust gas norm even without a filter.

This system provides an innovative solution to the diesel particle filter problem with regard to its complexity, increased fuel consumption, costs and maintenance.

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