DE VELO PMENT DIESEL ENGINES
NEW GENERATION OF THE AUDI V6 TDI ENGINE PART 1: DESIGN AND MECHANICS
25 YEARS OF TDI ENGINE FROM AUDI
MAIN DIMENSIONS AND CHARACTERISTIC DATA OF THE ENGINE
Feature
In 1989 car diesel engines underwent a revolution: the TDI from Audi. This direct-injection turbodiesel unit set a new benchmark, being sporty, comfortable and economical [1]. 25 years ago, Audi put into production the world’s first TDI engine for a car – a 2.5-l five-cylinder inline (R5) TDI unit with direct injection, turbocharger and charge air cooling, setting the trend for a fuel injection method that has now become the basis of all modern-day diesel engines [2]. The world’s first V6 TDI engine for cars followed in 1997. The 2.5-l unit featuring a distributor-type injection pump was the first four-valve TDI engine. This was followed by further evolutionary steps [3]. Today the V6 TDI engine is a market success not only for Audi but also throughout the VW Group. More than 2.3 million V6 TDI engines have been produced to date. The next generation of the 3.0-l V6 TDI engine described here represents a systematic enhancement of
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Layout
Unit –
V6 engine with 90° V angle
Capacity
cm 3
2967
Stroke
mm
91.4
Bore
mm
83.0
Stroke/bore
–
1.10
Compression ratio
–
16.0:1 (Euro 6)
Distance between
mm
90
–
Forged, four-bearing mounted
Cylinders crankshaft Main bearing diameter
mm
65.0
Con-rod bearing diameter
mm
60.0
Con-rod length
mm
160.5
Inlet valve diameter
mm
27.5 (2x)
Exhaust valve diameter
mm
25.5 (2x)
–
Common rail, 2000 bar (Bosch CRS 3.20) with piezo-injector and high-pressure pump CP4.2
Fuel injection system Turbocharger Ingnition sequence
GTD 2060 VZ with variable turbine geometry, electronic adjuster –
1, 4, 3, 6, 2, 5
Nominal power output
kW
up to 200 kW at 4000 rpm
Torque
Nm
up to 600 Nm from 1500 – 3000 rpm
Emission standard
–
Euro 5 / Euro 6 / ULEV125
Weight as per
kg
192
mm
437.0
DIN 70020 GZ Motor length
❶ Technical data of the new V6 TDI engine generation
The newly developed Audi’s next generation 3.0-l V6 TDI engine combines extremely low fuel consumption and emissions with outstanding performance, backed by the systematic application of lightweight construction techniques.
the successful V-TDI engine family in terms of power output, emissions and fuel efficiency. The market launch is scheduled for the third quarter of 2014 with the 200 kW Euro 6 version in the new Audi A6/A7 model range.
Efficiency has been improved by optimising the thermal management system, internal friction and the combustion
DEVELOPMENT GOALS
process. The integration of a close-coupled exhaust gas
Highlights alongside the main development objectives : low fuel consumption : low emissions meeting the Euro 6, Euro 5 and ULEV125 standards : engine power output up to 200 kW : high torque : design of the basic engine for ignition pressures up to 200 bar : integration of close-coupled exhaust gas aftertreatment : spontaneous response : high comfort are the requirements for the modular construction of the newly developed engine range. This includes a large number of common/synergy components for all engine derivatives, irrespective of power/ emissions class and vehicle installation.
aftertreatment system was a key design requirement, resulting in further comprehensive modifications to the basic engine. The development of the new-generation engine is presented in two reports. This first part describes design and mechanics, while the second part in MTZ 10 deals with thermodynamics, application and exhaust gas aftertreatment.
DESCRIPTION OF THE ENGINE / ENGINE BLOCK AND POWERTRAIN ❶ shows the main dimensions and characteristic data of the new V6 TDI engine family. The crankcase made of GJV450 compacted graphite iron is manufactured using the core package process and split at the centre of the crankshaft. It has been comprehensively revised for the new V6 TDI, ❷. It has been made another 1.1 kg lighter than its predecessor as a result of the systematic reduction of wall thickness, as well as a shorter bores in the BDC zone.
❷ Engine block and powertrain
AUTHORS
DR.-ING. STEFAN KNIRSCH is Head of Development Powertrain at the Audi AG in Ingolstadt (Germany).
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DIPL.-ING. ULRICH WEISS is Head of Development Diesel Engines at the Audi AG in Neckarsulm (Germany).
DIPL.-ING. (BA) ANDREAS FRÖHLICH is Head of Design V-Diesel Engines at the Audi AG in Neckarsulm (Germany).
DIPL.-ING. JAN HELBIG is Head of Mechanics V-Diesel Engines at the Audi AG in Neckarsulm (Germany).
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100 % Tangential force [% compared to V6 TDI gen 1]
-34 %
-52 %
Groove 1 Groove 2 Groove 3
100 % -17 %
Frictional forces [% compared to V6 TDI gen 1]
-10 %
V6 TDI gen 1 2007
V6 TDI gen 2 2010
1500 rpm, 35 °C
V6 TDI new generation
❸ Comparison of piston ring pre-tensioning and powertrain friction
The capacity of the water jackets has been reduced by 0.4 l by means of reduced lengths and thicknesses. In combination with the separate head/block cooling system with standing coolant in the engine block, this results in an even faster warm-up phase after a cold start. Other improvements in the thermal
management system are described in detail in the related chapter below. The cylinder bores are plate-honed in order to attain an optimum cylinder shape when the engine is running. This technique is key to achieving substantially optimised friction losses by means of a reduction in piston ring pre-tensioning.
The crankshaft forged from 42CrMoS4 features a 30° split pin in order to attain equal ignition intervals. The main bearing and crank pins are inductively hardened to improve strength. The omission of the centre counterweights and weightsaving holes drilled in all the crank pins lead to a further weight reduction. The eight-bolt attachment of the elastomer oscillation damper of the predecessor engine has been replaced by a Hirth coupling with just one central bolt. To reduce friction and improve strength, the aluminium pistons with a salt-core cooling duct are designed as a bush piston with a DLC(Diamond-Like Carbon)-coated gudgeon pin for the 200 kW version. The new development of the ring package has resulted in significant reduction in powertrain friction. ❸ (top) shows the reduction in ring pre-tensioning compared to predecessor engines. Together with a considerably reduced ring height, the powertrain friction (crankshaft, shaft seals, connecting rods and pistons, including rings) has been reduced by 17 % compared to the first-generation engine and approximately 10 % compared to the immediate predecessor (1500 rpm, 35 °C oil temperature). The use of combined piston ring coating processes (Physical Vapour Deposition (PVD) and DLC) enables an optimum compromise between wear, oil consumption and blow-by.
❹ Valve timing drive, high-pressure pump and oil pump drive
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CHAIN DRIVE
A key design requirement for the new V6 TDI engine family was to integrate a close-coupled exhaust gas aftertreatment unit to improve its light-off performance by means of fast warm-up. For the oxidation catalyst, which has increased in volume by 60 % and is now flanged coaxially onto the turbine outlet of the turbocharger, room had to be created at the rear of the space inside the inner-V of the engine. This was achieved by means of a compact valve timing layout with intermediate idler wheels mounted in the cylinder head and a downstream double gear-wheel stage, ❹. For acoustic reasons, tooth play compensation is provided in each case. The intermediate idler wheels are mounted on needle bearings to minimise friction. On the predecessor engine, the oil pump and the high-pressure pump were both driven by one of the chains. These have now been separated with a view to greater requirements arising from increasing injection pressures. The chain drive for the high-pressure pump, which is subject to dynamically high stress, is now designed as a torsionally rigid twoshaft drive, avoiding resonance and consequently high chain forces over the entire engine speed range. The drive for the oil/vacuum tandem pump, which is flanged into the oil sump, is now provided by means of a dedicated
chain, directly from the front end of the crankshaft. Thanks to the greater robustness in terms of oil quality and low oil viscosities (0W30), the Audi V-configuration diesel engines use exclusively bush chains with chromalised pins. CYLINDER HEAD AND VALVE GEAR
The increased demands imposed on the cylinder head in terms of power output and maximum cylinder pressure have been met by a complete redesign. Key features include a valve layout arranged on a parallel axis, as well as the two-part water jacket. The two-part water jacket design already tried and tested in the V6 TDI biturbo [4] has been systematically enhanced and is now employed in all engine variants, ❺. The lower water jacket ensures intensive cooling of the combustion chamber plate and the highly stressed valve bridge thanks to very fast flow rates. Despite the increase in performance, bridge temperatures have been reduced by 25 K compared to the predecessor engine with a single-part water jacket. The homogeneous temperature distribution means no cooling of the inlet valve bridge is required. In order to eliminate micro-notching effects in high loading zones, the geometry of the cooling ducts has been optimised with regard to the separation burr
characteristics, as has that of the inlet ducts. Mould separation burrs have been relocated to zones with lower loading. Automated deburring of the sand cores has also been implemented as an additional strength-enhancing measure. A further feature of the new cylinder head is its extremely compact design, resulting among other factors from the omission of the previously cast-on inlet duct flange. In the new V6 TDI, the inlet duct flange is replaced by a separate, lightweight component in PA6-GF35, ⑤. Together with other structural improvements, this makes both cylinder heads 2.5 kg lighter than in the predecessor engine. The ultra-light camshafts take the form of constructed hollow shafts and are mounted on separate double bearing covers. The bearing diameter has been reduced by 27 % in order to cut down on friction. The valves are actuated by newly designed, rigid rocker arms with larger rocker diameters than the predecessor model. Revolving rocker pins provide the necessary robustness which is a requirement for the use of low oil viscosities (0W30). AIR INTAKE
The electrically operated throttle valve, to which the charge air pipe made of PA6.6GF35 is connected, serves as the interface between the vehicle and engine air duct-
❺ Cylinder head with two-part water jacket and valve timing gear
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❻ Air intake
ing, ❻. The recirculated exhaust gas is fed in via a thermally decoupled stainless steel pipe. The geometric design of the feed guarantees the homogeneous mixing of fresh air and exhaust gas at every point in the operation of the engine, and prevents the deposition of the exhaust gas on the wall of the plastic intake manifold. The electrically operated swirl flap, which is centrally located for both banks
of cylinders, splits the intake manifold into an open swirl duct and a continuously closable fill duct. The intake manifold located inside the V accordingly takes the form of a multi-flow duct to each of the two cylinder banks. To implement this complex geometry, the intake manifold made of PA6-GF35 comprises three individual frictionwelded shells. CFD simulation was used
to optimise the cross-sections and the geometry of the EGR intake with regard to gas flow and even distribution. EXHAUST MANIFOLDS AND TURBOCHARGER
The exhaust manifolds take the form of air gap-insulated sheet steel manifolds, the inner pipes of which are produced
❼ Exhaust manifolds, turbocharger and EGR system
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❽ Map for fully variable oil pump
using the IHU-called hydroforming process. Weight has been reduced by 20 % compared to the predecessor engine, thanks to a weight-optimised flange to the cylinder head, with seven bolting points instead of eight, and by using V-band clamps to fasten to the turbocharger, ❼. The new V6 TDI engine range marks the launch of a new turbocharger generation. Its key features include a reduction in the play of the variable turbine geometry (VTG) and a riveted VTG cartridge in place of the casting of the predecessor generation. The cartridge concept permits the flow-optimised design of the turbine intake cross sections, ⑦. In conjunction with a lowfriction bearing, a high level of efficiency is achieved at low revs, as well as improved transient behaviour by means of more dynamic response. EXHAUST GAS RECIRCULATION (EGR)
The main component of the high-pressure exhaust gas recirculation system is the EGR module, which combines the following functional elements: EGR valve, EGR cooler and bypass valve, ⑦. The electrically operated stroke valve for regulating the EGR rate is located on the hot side of the module. The rising flow speeds as the gas temperature increases and the resulting pressure losses at the valve seat make the flow-optimised layout of the gas flow to the valve especially important. For that reason the geometry 09I2014
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of the housing ahead of the valve seat has been designed with the aid of CFD simulation and produced as a stainless steel precision casting. The cooling-enhanced, U-flow tube cooler made of stainless steel is flangemounted onto the two water-cooled valve housings made of die-cast aluminium. The pneumatically operated stroke valve familiar from the predecessor unit is used to bypass the EGR cooler. The combination of die-cast aluminium and sheet stainless steel constructions has allowed the weight of the EGR module to be reduced by 16 % compared to the predecessor module, with increased cooling capacity. For the ULEV125 application, a precooler with an additional pneumatic bypass valve is added in place of the pipe between the turbocharger and the EGR module. Using the two module versions with single or two-stage exhaust cooler, it is possible to resolve the conflict between cooling capacity and pressure loss in the EGR system to optimum effect for each application. In addition to the even greater maximum cooling capacity, up to four different EGR by-pass circuit states with different cooling capacities and gas pressure losses can be achieved in this way. OIL CIRCUIT
A fully variable oil pump is employed for the first time in an Audi V-configuration TDI engine. The vane pump, continu-
ously controlled by way of an eccentric ring, permits optimum adaptation of the pressure/volume flow depending on factors such as load and engine speed. ❽ shows the oil pressure in the engine’s operating map at an oil temperature of 90 °C. A large part of the engine map is fully variably demand-regulated. The throughput of the piston injectors is also influenced by means of the pressure map. In comparison with the two-stage oil pump of the predecessor engine, this results in a CO2 emissions improvement of 2 g/km in the NEDC. An oil thermostat, consisting of a wax expansion element with a sliding sleeve, integrated into the pressurised oil gallery of the engine block, provides a thermostatically controlled oil cooler bypass, thus ensuring rapid warm-up of the oil after a cold start, ❾. COOLANT CIRCUIT AND THERMAL MANAGEMENT
The proven design concept of the predecessor engine with separate head/block cooling (split cooling) has been retained and optimised with regard to pressure loss reduction and faster block warm-up after a cold start, ❿. The two parallel coolant circuits for the engine block and the cylinder head enable the independent supply of heated coolant to the interior and transmission oil heaters via the cylinder head circuit, regardless of the coolant standing in the engine block. In
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this way innovative thermal management delivers improved fuel consumption in all the engine operating modes of relevance to the customer. The water pump located in the inner-V has a covered impeller with three-dimensionally curved blades, and continuously supplies the two sub-circuits. CYLINDER HEAD CIRCUIT
The continuous-flow cylinder head circuit consists of the water chambers of the two cylinder heads and the oil and EGR coolers, as well as the vehicles heating and transmission oil heat exchangers and the main radiator. Downstream of the water-cooled turbocharger and the AdBlue metering module there is also an electric water pump, which enables cooling to be continued if required after the engine stops. The temperature level of this circuit is regulated by a newly developed mapped thermostat with a ball valve, ⑩. Thanks to its virtually free cross-section, the ball valve reduces pressure losses by approximately 70 % when fully open compared to a conventional disc thermostat. ENGINE BLOCK CIRCUIT
❾ Thermostatically controlled oil cooler bypass
After a cold start the block circuit is initially operated with standing coolant. A vacuum-controlled rotary slide valve
❿ Coolant circuit
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located inside the V prevents any coolant flow when closed, and hence any associated unwanted heat dissipation. When operating temperature has been reached, the coolant temperature in the engine block circuit is regulated by way of the rotary slide valve up to 105 °C in order to reduce friction losses in the part-load range. SUMMARY
The new generation of V6 TDI engine represents a systematic advance in terms of efficiency, performance potential, emissions and lightweight construction. To improve efficiency, improvements have been made in the areas of internal friction, thermal management and charging. The exhaust gas aftertreatment system was a key component of the engine design from the outset. Wideranging modifications to the basic engine, in particular an extremely compact valve timing system, have enabled a highly effective, close-coupled exhaust gas aftertreatment system to be integrated. Together with the modular highpressure EGR system, this ensures compliance with the strict limits of global emissions standards. A new-generation turbocharger ensures outstanding dynamic charge pressure build-up, guaranteeing spontaneous responsiveness. The new generation of V6 TDI engine demonstrates that efficiency and excel-
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lent driving dynamics do not have to be mutually exclusive. The performance and fuel consumption results will be presented in detail in the second part “Thermodynamics, Application and Exhaust Gas Aftertreatment” in MTZ 10. REFERENCES [1] Pölzl, H.-W.; Bauder, R.: The History of the Audi TDI Engine. In: ATZ/MTZ special “10 Years of Audi TDI Engines”, 1999 [2] Siebenpfeiffer, W.: Editorial. In: ATZ/MTZ special “10 Years of Audi TDI Engines”, 1999 [3] Bauder, R.; Bach, M.; Fröhlich, A.; Helbig, J.; Ortwein, J.; Rossi, D.; Seifried, G.: The New-Generation Audi 3.0-l V6-TDI. In: MTZ 71 (2010), No. 10 [4] Bauder, R.; Helbig, J.; Marckwardt, H.; Genc, H.: The New 3.0-l TDI Biturbo Engine from Audi. In: MTZ 73 (2012), No. 1
THANKS The authors would like to thank Dipl.-Ing. (FH) Matthias Honzen, Head of Design V-TDI AddOn Parts, Dr.-Ing. Henning Marckwardt, Head of Engine Mechanics V6-TDI, Dipl.-Ing. Jens Ortwein, Senior Developer Engine Mechanics V6-TDI, Dipl.-Ing. Gerd Seifried, Senior Design Engineer V6-TDI, and Dr.-Ing. Jürgen Trümper, Head of Design V-TDI Basic Engine, all Audi AG, for their assistance.
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