You will find the figures mentioned in this article in the German issue of MTZ 11I2007 beginning on page 914.

Der neue 2,0-l-4V-TDI mit Common-Rail – Moderne Dieseltechnologie von Volkswagen

The New 2.0-l-4V-TDI Engine with Common Rail Modern Diesel Technology from Volkswagen

Authors: Jens Hadler, Falko Rudolph, Hermann-Josef Engler and Sven Röpke

2

MTZ 11I2007 Volume 68

As a reaction to the challenges of the coming decade in the form of stricter emission limit values, the concerns of pedestrian protection and the increasing demand for comfort with regard to internal and external acoustics, Volkswagen has developed a new generation of diesel engines. The 2.0-l-4V-TDI engine with common rail injection presented here and used for the first time in the new Volkswagen Tiguan, represents the start of a series of dynamic and efficient diesel engines. The combination of the successful 2.0-l-TDI engine with the common rail technology has resulted in an engine that already complies with the limit values of the Euro 5 emission standard and that is characterised by its smooth running and comfort in addition to the driving pleasure and economic efficiency that it provides.

1 Introduction For more than 15 years, Volkswagen has been a pioneer in diesel technology with direct injection and sets standards in the fields of dynamics, driving pleasure and economy. With regard to the increasing competition by improved petrol engines, the classic strengths of the diesel engine, such as fuel consumption and torque development, need to be maximised.

2 Development Objectives The target specifications for the new 2.0-l4V-TDI engine therefore define an engine concept that operates with very high precision, that safely achieves the exhaust emission limit values of the Euro 5 specifications and that is on its way to complying with the Euro 6 limit values. The negative relationship between falling emission values and increasing fuel consumption was to be solved by the improvement of the efficiency of the engines. The focus was also on a high degree of comfort for the customer, particularly in terms of the acoustics. In addition, the aspect of vehicle safety required a reduction of the engine height within the scope of pedestrian protection.

3 Engine and Engine Concept

Diesel Engines

COV E R S T OR Y

axis; the valves are arranged upright around the central injection nozzle and are actuated via roller cam followers. The intake side consists of a tangential duct and a spiral duct. The exhaust duct combines to two partial ducts in the cylinder head to a joint exhaust cross-section in the shape of a “Y-pipe”. The oil reservoir has blow-by holes for pressure compensation between cylinder crankcase and cylinder head. A new oil core has been designed for the ventilation of the crankcase and integrated into the structure of the cylinder head.

seal between vacuum pump and cylinder head is used to seal both the oil hole and the flow of air from the pump into the cylinder head as well as the camshaft holes. Compared to the predecessor model, a more robust, new metal crimp seal with “sponge” coating is used. The new vacuum pump is also characterised by reduced friction.

3.4 Oil Separation

The exhaust camshaft is driven by a toothed belt and transfers the torque to the intake shaft by means of a straight-toothed spur gear unit with compensation for play. The selected compensation for play for the reduction of noise is established by means of a two-part spur wheel on the exhaust shaft. The intake shaft, on the other hand, drives the newly designed, optimised vacuum pump via an Oldham coupling.

The increased environmental and emission requirements place the highest demands on the engine in terms of effective oil separation. It has been possible to significantly improve the efficiency of oil separation despite reduced construction space. This separation takes place in three stages: – via impact plate separator – using switched cyclones (two or four cyclones are used, depending on the vacuum pressure) – in a connected damper volume (the flow is calmed and more oil is separated).

3.3 Vacuum Pump

3.5 Injection System

The newly designed vacuum pump is characterised by a higher vacuum output and reduced power consumption. Despite the increased vacuum output, the oil requirement of the pump has been reduced. The pump‘s oil supply is secured via a central hole in the cylinder head. The flat

The main modification of the 2.0-l-4V-TDI engine concerns the conversion of the injection system to the common rail technology. Established components were able to be used for the new TDI engine that were, however, further developed according to specific requirements.

3.2 Valve Train

The engine concept of the new 2.0-l-4V-TDI engine is based on the established 2.0-l-TDI engine that is equipped with a common rail injection system of the newest CRS 3.2 generation and has also been optimised in other areas. The new injection system uses an injection pressure of 1800 bar, which, combined with other measures such as an entirely new combustion process, has significantly reduced the emission values. The specific reduction of friction contributes towards the improved efficiency of the unit. Furthermore, the engine is characterised by a very low construction height which represents yet another contribution towards more pedestrian safety.

3.1 Cylinder Head The cylinder head of the new 2.0-l-4V-TDI engine has four valves per cylinder that are driven by two camshafts. The cylinder head is characterised by a camshaft axle spacing of 54.6 mm, a construction height of 125 mm and a cylinder spacing of 88 mm, Figure 1. The valve star is rotated by about 9° to the longitudinal engine

Figure 1: Cylinder head MTZ 11I2007 Volume 68

3

C O VER S T O R Y

Diesel Engines

3.6 Pump/Injectors

3.8 Controlled Intake Manifold and Low-temperature EGR

4 Method of Operation

The injection system CRS 3.2 by Bosch is used for the fuel supply of the 2.0-l-4V-TDI engine, Figure 2. The system, which has been further developed in cooperation with the manufacturer, injects the fuel with up to 1800 bar. The main objectives of the development were a pressure increase in the partial load and the precise dosage of the fuel, since the specifications for the exhaust gas treatment result in up to seven injections per combustion cycle. For this reason, the injection operates as a double-actuator system with volumetric dosage and pressure regulation at the rail. More progress for the precision of the injection was achieved by the 1:1 transmission between crankshaft and the drive of the single stamp high-pressure pump with double cam. The pressure curves in the rail and the injections are now synchronised with each other. The injection takes place with the falling edge of the pressure curve. The newly designed highpressure pump CP 4.1 is characterised by friction reduced by 20 % compared to similar multi-piston pumps. The injector with 8-hole nozzle and adapted flow as well as a hole diameter of 0.123 mm was specially developed for the new TDI engine. The nozzle module sets standards due to the optimised position of the jet in terms of the quality of atomisation and hydraulic efficiency.

Higher demands in terms of the emission values also mean higher demands on the carburetion. The swirl of fresh air in the combustion chamber plays a major role. In the 2.0-l-4V-TDI engine, swirl and flow are set by continuously adjustable swirl flaps in the intake manifold according to the operating point, Figure 4. An electric actuator with a contact-free position sensor is responsible for adjusting the swirl flaps. During the production process, the position sensor is programmed together with the intake manifold. A pretensioned system between actuator and intake manifold has been installed as an additional measure to increase the precision. The sum of all measures enables the setting of individual speeds within a wide range according to the engine operating point and thus allows the optimum control of the carburetion. An important measure for the reduction of NOx emissions, without increasing the emission of soot particles or the fuel consumption, is the introduction of the low-temperature exhaust gas recirculation (LT-EGR). A highly efficient EGR cooling with a cooling output of up to 8 kW is required for this purpose. An additional electric pump pumps the water required for this through the main water cooler and the EGR cooler.

The aim of the development of the 2.0-l-4VTDI engine was to comply with the future Euro 5 emission standard, with the increased demands in terms of the emission of nitrogen oxides and the simultaneous minimisation of the emission of CO2. This is achieved with the new 2.0-l-4V-TDI engine, in addition to the reduction of compression to 16.5:1, by the detailed modification of the carburetion of both gas and fuel. The focus of the development was on redesigning the combustion chamber and the charge motion that was mainly achieved by the geometry of the intake duct. Another important development aspect was the precision of the internal engine processes. Numerous detailed technical solutions ensure that these processes are registered and managed with high precision. Special emphasis was placed on the reproducibility within the series and the service life of the engines. The various parameters and components that are decisive for the combustion process were designed with the support of DOE.

3.7 Timing and Auxiliary Drives

3.9 Exhaust Turbocharger

The numerous modifications to the 2.0-l4V-TDI engine meant that the timing and auxiliary drives needed to be redesigned. The established arrangement of the EA 188 series has been retained to a large extent, Figure 3. The drive of the high-pressure fuel pump is a new addition to the drive of the 30 mm wide toothed belt. Shock-resistant hubs, elongated holes and pins are used to ensure the correct position during the assembly process. The developers emphasise this measure, as it allows the improved compensation of production tolerances and the good emission values of the engine to be reproduced in the series. The new design of the complex drive results in less power peaks and both belt drives were able to be designed to the benefit of the engine‘s service life. A particularly low-noise ribbed belt is used for the auxiliary drive for the first time. The ribs on the surface are rounded off by an elastomer film with a high fibre content.

The exhaust turbocharger of the new 2.0-l4V-TDI engine has a pneumatically operated guide vane adjustment on the turbine. An integrated position sensor determines the current position of the guide vanes. A new feature is the pulsation damper that is flanged on to the compressor casing near the compressor wheel. The damping of the pressure pulsations now takes place right next to the source of noise. The improved efficiency of the damper results in a significantly improved behaviour in terms of flow noises, Figure 5.

4

MTZ 11I2007 Volume 68

4.1 Piston Bowl Various combustion chamber geometries were examined within the course of developing the combustion process. The development of the optimum piston bowl geometry at the beginning of the development phase was supported by CFD simulations, Figure 6. The conventional Omega bowl was developed to a significantly broader and flatter geometry. The new bowl shape without distinct bowl collar enables a significantly longer free injection jet, which results in the noticeable reduction of the application of liquid fuel on the bowl collar (wall film). The development of local greasy zones in this area is thus further reduced and the formation of a more homogeneous mixture is enabled. The soot formation is reduced during the combustion process, which results in the reduced emission of particles. As a result, higher EGR rates for the minimisation of NOx are possible and the residual gas compatibility is increased.

3.10 Engine Management In addition to the new injection system, a new engine management system was developed in cooperation with Bosch that ideally supports the multi-injection concept of the 2.0-l-4V-TDI engine. The positional accuracy of the injections enables the optimisation of the operation of the TDI engine in terms of emissions and acoustics.

4.2 Duct Concept – Cylinder Head and Intake Manifold A duct concept was used that forms a mixture that is as homogeneous as possible with flat lambda gradient, which is achieved by a high bowl swirl in the TDC in addition to the good fuel distribution. To compensate the reduction of the bowl swirl by the extended bowl, the basic swirl level

needed to be increased. For this purpose, a newly designed intake duct concept was used that is characterised by a high, continuously adjustable swirl spread and that, in addition to the increased swirl, enables sufficiently high throughput rates that are decisive for achieving the rated power. The duct concept includes a tangential duct, which serves as a swirl-generating duct, and a spiral duct, which serves as filling duct, Figure 7. The variably adjustable swirl flap in the intake manifold is used to close the spiral duct according to the load and speed, so that there is only flow through the tangential duct. Various variants with the shaping of the tangential duct in combination with different swirl chamfers were examined for the further optimisation of the duct concept. The result is a further swirl increase with the same cylinder filling.

4.3 Nozzle Design The injectors were equipped with new 8hole nozzle elements that inject the fuel specifically and very evenly into the combustion chamber. The number of holes, the opening angle and the flow of the nozzles were adapted to the new combustion chamber geometry.

4.4 Exhaust Gas Treatment Within the scope of the exhaust gas treatment, the established integrated component consisting of catalytic converter and diesel particulate filter was consistently further developed for use in the 2.0-l-4V-TDI engine. Instead of a conventional ceramic substrate, a metal substrate with special cell structure is used to enable early starting at a high turnover rate. The existing OxiCat function in the diesel particulate filter has been retained and optimised in terms of its thermal consistency: the filter has a special zone coating made of a platinum-palladium mixture, which ensures early catalytic starting and low thermal ageing.

4.5 Cold Start Due to the increased requirements as a result of the reduced compression, the diesel starters were modified in such a way as to be able to continue to ensure a secure runup in cold condition. The aim was to support the starting common rail TDI engine up to a speed of 450 rpm. For the new 2.0l-4V-TDI engine, starters with permanent excitation as used as well as starters with field excitation. With both designs, the transmission was achieved by an increase in the number of teeth of the pinion and therefore a higher crankshaft speed.

Diesel Engines

COV E R S T OR Y

A fast glowing system with metal glow plugs reduces the preheating time and improves cold starts.

the improved utilisation of the air due to the package of measures. This is achieved by a high number of holes, the length of the free injection jet, the good mixture of the fuel with the air in the combustion chamber, a piston bowl with a larger diameter and the resulting reduced compression of 16.5:1. As a result, higher EGR rates can be achieved and less nitrogen oxides are produced. The mentioned measures for the cylinder head and cylinder head seal, the piston, the nozzles and the intake manifold, the exhaust turbocharger, the treatment of the exhaust gas and the injection system thus contribute significantly towards complying with the Euro 5 emission standard. The ability to manage numerous parameters precisely and reproducibly, enable the 2.0-l-4V-TDI engine to achieve optimum emission values throughout its entire service life.

5 Results The sum of all developments on the 2.0-l4V-TDI present an engine that is not only characterised by high driving pleasure and comfort during driving. Various measures for the reduction of emissions were coordinated very well, resulting in a lower consumption level, despite higher demands in terms of emissions. The aim was to comply with the Euro 5 emission standard safely in an SUV with automatic gearbox and four-wheel drive. Practical driving tests with the Tiguan have confirmed this. With this engine concept, the Tiguan is the trendsetter in the SUV segment. It is the first vehicle to meet the strict Euro 5 emission standard. The engine is characterised by its excellent specific consumption of 196 g/kWh (best value), thus ensuring that the Tiguan has favourable CO2 values, Figure 8. It was even possible to extend the utilisable range of engine speeds, so that the engine now has a rated speed of 4,200 rpm and an adjustable engine speed of 5,400 rpm. In addition, due to the good utilisation of the air, the full load values are improved at small speeds, Figure 9. The set values required for minimal consumption and emissions and good power output at each operating point, were determined in test series and stored in map structures that are new in parts. Due to the improved reaction, the driver experiences significantly increased dynamics of this TDI engine, Table.

5.1 Acoustics In addition to the emission reduction measures, noise comfort was another objective during the development of the 2.0-l-4V-TDI engine. The acoustic power was an important reference value, since the internal specification was 3 dB stricter than the 2.0-l-TDI engine. The main noise measure has to do with the method of operation itself: specific multiple injections reduce the pressure gradient and thus the production of noise. Insulation and damping measures for the engine, such as the newly designed bonnet and the pulsation damper significantly improve the engine‘s acoustics.

5.2 Euro 5

6 Summary The new 2.0-l-4V-TDI engine continues Volkswagen‘s tradition of successful diesel engines. It was possible to significantly reduce the noise level due to various improvements and the use of a highly modern common rail technology so that the new engine meets the specified objectives and sets the standard for 4V diesel vehicles in terms of noise comfort. In addition, the engine concept complies with the strict Euro 5 emission standard so that it is best prepared for stricter emission requirements, in particular for the important target markets in Europe. The typical TDI virtues such as driving pleasure and economic efficiency are fully retained. A new development stage has been reached in terms of the development of performance and dynamics.

References 1] Krebs, R.; Hadler, J.; Blumensaat, K.; Franke, J.-E.; Paehr, G.; Vollmers, E.; Hahne, B.: „Die neue 5-Zylinder-Dieselmotoren-Generation für leichte Nutzfahrzeuge von Volkswagen“; 27. Internationales Wiener Motorensymposium, 2006 [2] Endres, H. ;Hadler, J.; Engler, H.-J.; Dorenkamp, R.; Jelden, H.; Stehr H.: „Der neue 125 kW 4-ZylinderDieselmotor mit Piezo-Pumpe-Düse von Volkswagen; 26. Internationales Wiener Motorensymposium, 2005 [3] Bauder R.; Pölzl, H.-W.; Reuss, T,; Hatz, W.: „Der neue V6-TDI-Motor von Audi“; 25. Internationales Wiener Motorensymposium, 2004

A robust Euro 5 process was developed within the framework of the further development of common rail. Decisive for this is MTZ 11I2007 Volume 68

5