A u di A 4
Aggregates | Diesel Engines
The New TDI Generation The 2.0-litre TDI Engine with Common-rail Injection The abbreviation TDI stands for impressive power and exemplary efficiency. With the new A4, Audi makes the driving experience even more enjoyable: for the first time, the four-valve 2.0-litre TDI engine will be equipped with a common-rail injection system, which ensures superior refinement thanks to rapid-action piezo injectors. Elaborate fine-tuning ensures that the new TDI engine already fulfils the limits of the expected EU 5 emissions standard.
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Audi A4
The Authors Dipl.-Ing. Falko Rudolph is Head of Diesel Engine Devevelopment at Volkswagen AG.
Dipl.-Ing. Hermann-Josef Engler is Head of EADK 3- and 4-cylinder Diesel Engine Development at Volkswagen AG.
1 Introduction
2 High-pressure Injection Technology
The 2.0-litre TDI CR 4V with an output of 105 kW (143 bhp) and common-rail (CR) injection marks the beginning of a new generation of dynamic and efficient diesel engines from Volkswagen and Audi. It reinterprets the qualities of the TDI concept and focuses on the challenges of the future, particularly those presented by environmental protection requirements. The combination of the 2.0-litre TDI powerplant and common-rail technology sets new standards. The engine already meets the strict requirements of the EU 5 emissions standard, which is expected to come into effect in 2010. The typical strengths of TDI technology such as dynamic handling, driving enjoyment, economy and reliability have been enhanced yet further. The 2.0-litre TDI engine produced at Audi Hungaria Motor in Györ makes its debut in the new Audi A4.
By employing common-rail technology, the 2.0-litre TDI CR 4V achieves significant benefits in terms of emissions, acoustics, weight and overall height. The mixture formation is undertaken by a latest-generation common-rail system, consisting of four injectors and a single-piston high-pressure pump as well as the rail with pressure control and pressure-maintaining valve. Injection pressure of up to 1800 bar ensures particularly fine atomisation of the fuel. This results in optimised mixture preparation and particularly efficient combustion. The eight-hole injectors with adapted flow are activated by state-of-the-art piezo inline injectors, Figure 1. Electrically operated piezo actuators trigger the injection process, assisted by a hydraulic element. Compared with conventional solenoid valves, piezo technology – thanks to the higher speed of the injector needles – per-
Figure 1: Piezo inline injector Special Edition ATZ and MTZ I September 2007
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A u di A 4
Aggregates | Diesel Engines
control to adapt the air movement to the respective engine speed and load. The piston recess, the spray position of the jets, the valve seat chamfer in the cylinder head and the intake ports are precisely coordinated with each other, Figure 4.
4 Driving Enjoyment by Propulsive Power
Figure 2: Full-load curve
mits more f lexible injection processes with smaller and more precisely controlled injection quantities at low tolerances, from injection to injection and from injector to injector. This variability is the basis for an effective combustion process combined with pleasant engine acoustics.
3 Successful Technology Effectively Optimised
DOI: 10.1365/s40111-007-0016-z
The 2.0-litre TDI CR 4V is based on the successful 2.0-litre TDI engine with pump/nozzle injection. From a displacement of 1968 cc, the new four-cylinder inline engine with common-rail technology achieves an output of 105 kW (143 bhp) at 4200 rpm, Figure 2.
Figure 3: Cylinder head 84
Audi A4
The stroke-to-bore ratio is 1.18 : 1 with a stroke of 95.5 mm and a bore of 81.0 mm. The compression ratio is 16.5:1. The compact engine in the new Audi A4 is tilted 20° to the right. Individual components come from the group’s modular system and details have been optimised with a view to the specific challenges. These include the tried-and-tested crankcase, crankshaft drive and oil sump adapted to particular vehicle factors. The cylinder head, Figure 3, represents a new development that takes into account experience gained with Audi’s successful V6/V8 diesel units. Two overhead, five-bearing camshafts control the four valves for each cylinder. They are driven by a toothed belt. Further features include the vane-controlled turbocharger and the intake manifold with electronic continuous swirl flap
The TDI engines offer superior power even at low engine speeds. The aim in developing the 2.0-litre TDI CR 4V was to enhance this quality even further. This was achieved by a further optimised application and coordinated control software, which benefits in particular from improved sensor technology. As from this engine generation a wide engine speed range will be used; the engine is governed only at 5400 rpm. This makes it possible to utilise its potential to an even greater extent. The new turbocharger generation ensures superior response.
Figure 4: Intake and exhaust ports
Figure 5: Turbocharger
Figure 6: Complete system: mixture formation
5 Acoustic Comfort thanks to Smooth-running Properties The smooth-running properties of the 2.0litre TDI engine have been decisively enhanced following the decision to employ the common-rail injection system. Additional measures carried out on engine and vehicle lower acoustic emissions. The turbocharger was fitted with a pulsation damper located near the compressor to achieve good damping characteristics, Figure 5. The toothed-belt drive has been updated in terms of acoustic behaviour and the engine compartment lid has received other acoustic treatment. Smooth operation calls for less vibration and for this reason the balancing-shaft module familiar from predecessor engines is also being employed.
Table: Primary dimensions and characteristics of the 2.0-litre TDI engine
6 Exhaust Emissions It is anticipated that the EU 5 emissions standard will come into effect in 2010 with more stringent emission limits for diesel and petrol engines. Engineers focussed on optimised mixture preparation of the CR and exhaust gas recirculation (EGR) system during the development phase, as well as the aspect of exhaust treatment. The anticipated high standards of the EU 5 emissions specification are fulfilled by the latest-generation TDI engine thanks to a variety of measures. These include the
low-temperature EGR, which contributes towards improved cooling power to optimise untreated engine emissions. Air management was particularly enhanced by continuous swirl flap control, Figure 6. The new geometry of the piston and other measures led to improved combustion and thus high EGR compatibility. With these in-engine measures it was possible,
for instance, to substantially reduce NOx values. The under-bonnet diesel particulate filter with further enhanced primary oxidising catalytic converter is characterised by its maintenance-free operation. The Table shows the primary dimensions and characteristics of the 2.0-litre TDI engine. The technical data of fuel consumption are shown in the Table on page 25. n Special Edition ATZ and MTZ I September 2007
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