COVER You STORY Diesel Engine will find the5-Cylinder figures mentioned in this article in the German issue of MTZ 1/2004 beginning on page 8.

Der neue FünfzylinderDieselmotor von Volkswagen

The New 5-Cylinder Diesel Engine from Volkswagen Volkswagen has developed a completely new, very compact, 5-cylinder pump-nozzle TDI drive unit with 2.5 l displacement, which permits longitudinal and transverse installation even in narrow engine compartments. For the first time in this engine class, both camshaft and the auxiliary assemblies are driven via helical gear spur wheels. The crankshaft damper was arranged inside the engine. For reasons of weight, an aluminium cylinder crankcase with a plasma-sprayed running layer was developed, which integrates many component functions. First, the engine will be available in two versions (96 and 128 kW) and will be used in the new Multivan / Transporter and the Touareg.

By Jens Hadler, Klaus Blumensaat, Walter Nederkorn, Andreas Kracke and Peter Urban

2

1 Introduction

2 Design Features

As a successor to the successful 2.5-l-TDI with distributor injection pump, of which millions were produced – the first TDI in a passenger car – a completely new drive unit was developed. The most important element of the concept was the required length dimension of the engine of 510 mm, which, in comparison with the predecessor, meant a reduction in engine length of 58 mm. Further development goals included: ■ High economy ■ Favourable fuel consumption through pump injector technology ■ Lightweight design with aluminium cylinder crankcase ■ Minimal maintenance requirements ■ Maintenance-free central drive ■ Suitable for rough terrain (fording depth up to 500 mm and 45° climbing ability and lateral inclination ) ■ Emission safety for EU3 / EU4 ■ Potential for performance gain.

With the engine described in this paper and taking the prescribed engine installation length for the central drive and the drive for auxiliary assemblies into consideration, only 25 mm axial construction space remained. Furthermore, the camshaft drive had to be able to transmit peak torques which occur when the pump injector elements are driven. For this reason, a space saving, helical gear drive was developed to drive the camshaft, oil pump, coolant pump and all auxiliary assemblies. The gear drive is meshed in the area of the engine gearbox flange; the camshaft gear ratio is implemented by an auxiliary gearbox positioned outside the flange with a backlash adjustment option. The drive was positioned at the rear of the crankshaft near the crankshaft vibration nodes. As the torsional vibration damper, which is usually located at the front crankshaft butt, has been positioned as a functional unit with a crank-

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COVER STORY

shaft cheek in the oil chamber, the front crankshaft passage could be omitted. The engine design was carried out carried in PRO/Engineer, Figure 1. 3 Cylinder Crankcase

For reasons of weight, the crankcase, with cylinder spacing of 88 mm, was made of a high-strength aluminium alloy. The “closed deck” concept was implemented in a gravity die casting process and, in conjunction with heat treatment, offers low porosity in the base material as well as sufficient hardness and strength. The development goals, lightweight construction and component reduction, was achieved through the integration of many functions. Coolant pump, thermostat, coolant channel, exhaust turbocharger support, including oil supply and return lines are integrated in the crankcase. The consequence of this is that the number of sealing faces have been reduced to a minimum. Because of the high ignition pressures of 170 bar and intrinsic frequencies, the structure of the crankcase was optimised using an FEM calculation, Figure 2. An innovation in volume cars with a supercharged diesel engine are the plasmacoated cylinder liners. The plasma spray layer consists of an iron-molybdenum layer with a thickness of approx. 120 μm. Following precision turning of the cylinder tube, which is previously roughened by sandblasting, the plasma is applied by means of a rotating plasma torch. Numerous trials for oil consumption and wear strength of the layer confirm that use is possible in a highly stressed diesel engine. Oil consumption is as low as the conventional predecessor engine with a grey castiron cylinder crankcase. Compared to grey cast-iron running surfaces, the cylinder tube wear is less and there is hardly any tendency to creation of a mirror surface. A comparison of surface structures makes this clear, Figure 3. As aluminium is not as strong a material as grey cast iron, a tension bolt concept was selected. Critical tensile stress no longer exists in the cylinder tube area. The tension bolts guarantee an optimised cylinder shape. The cylinder bore, crankshaft bore and gear bearings are clamped prior to machining. In production, a hydraulic tensioning device was developed for this purpose which made the use of circulating material such as honing goggles and screws unnecessary. Figure 4 demonstrates the tension bolt principle. In production and customer service, for assembly/handling reasons the tension bolt group is divided in the parting plane head/block. The connection is by

MTZ worldwide 1/2004 Volume 65

means of a high-strength sliding sleeve, which can be moved in the direction of the screw and is secured in the block against twisting. Special attention had to be paid to the main bearing block because high ignition pressures mean that the area is subject to high changing loads. Potential cracks were dealt with effectively by means of a relief groove optimised by FEM calculation. The main bearing covers are made of grey castiron. 4 Crankshaft Drive

The torsional damper had to be integrated into the crankshaft because installation space was restricted. The new spring-mass damper is no longer rotationally symmetrical and is secured by four screws to the crankshaft instead of the first counterweight. Plastic friction bearings in the damper guarantee the necessary damping effect over the entire speed and load range, whereby the characteristic curve is narrow band as expected. Figure 5 shows the torsional vibration damper as single part and when installed. For cost reasons, the gear for driving the drive is fitted on the output side of the crankshaft. The transmitter wheel is integrated in the counterweight of the outer crank cheek; a screw-fitted transmitter wheel is no longer necessary. Apart from the cost benefits, improved signal accuracy for the high-resolution engine speed measurement and TDC recognition was achieved. The crankshaft journal diameter was specified at 50.9 mm. The pistons are full cooling channel pistons with the proven eccentric VW TDI_ recess. The conrods have been taken over from the 4-cylinder pump nozzle engine. 5 Cylinder Head

The aluminium cylinder head, Figure 6, is a crossflow cylinder head and can therefore be used for reverse installation in the V10 TDI pump nozzle engine. The material used – aluminium alloy – is the same material used in the VW Group for all supercharging diesel engines. All control elements such as valves, tappets, rocker arms and the pump-nozzle elements are from the VW diesel engine modules. The integrally cast gear case guarantees an optimised structural connection. In the course of development, the geometry of the cylinder head was optimised with regard to acoustics. As a further noise measure, the cylinder head cover was optimised acoustically by a moulded-on gasket and a mechanically isolated screw system. It is an aluminium die-

5-Cylinder Diesel Engine

cast part with integrated oil separation. As opposed to the DC cylinder heads in the 2V3- and 4-cylinder series, fuel supply and draining is via an external fuel rail. The crossflow concept means that the throughflow values were improved by approx. 5% compared to the 4-cylinder pump-nozzle engine with DC head. 6 Gear Drive

Development goal for the 5-cylinder pumpnozzle engine was a short engine installation length in order to ensure that the power pack could be installed in the various platforms of the VW Group. The camshaft drive and the drive for the auxiliary components are designed as non-wear and thus maintenance-free components, whereby particular attention must be paid to the input torques of the pump-nozzle drive. These requirements are fulfilled by a gear drive which, ideally, is located in the vibration nodes of the crankshaft between engine and gearbox, Figure 7. The installation restriction for the gear drive of 25 mm specific to this package and the high loads in the camshaft drive make a helical-cut and over-mounted and frictionmounted gear with a width of 20 mm necessary. The gear design, construction, calculation and production is in-house at Volkswagen. As input data, the dynamic gear forces were calculated using a complex multi-body mechanical system simulation model. By means of dynamic measurements of the loads and dynamics in the toothed belt drive, a good comparison between measurement and calculation model was achieved. The gearing has a module of 2.85 and a helix angle of 15°. The gears are supported on steel journals. Particular attention had to be paid to the connection between the steel journals and the aluminium cylinder crankcase. The various levels of thermal expansion between the aluminium cylinder crankcase and the steel journals are particularly critical, as well as the high loads in the gear drive. Above the gearbox flange, the wheel width was increased to 24 mm because the 1:2 ratio meant that the camshaft drive had higher torques. A helix angle of 15 degrees was selected to increase the width of the load-bearing tooth profile, Figure 8. The crankshaft drives an intermediate wheel which is over-mounted in the crankcase. The transmission jump takes place above the gearbox by means of a level jump and therefore does not determine construction length. Tolerance compensation between cylinder head, crankcase and gears is by means of an adjustment wheel in the cylinder head. During assembly, it is set to

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COVER STORY

5-Cylinder Diesel Engine

the specified backlash via its double eccentric axis, Figure 9. Due to the constraints on construction space, all auxiliary assemblies are driven from the main level. The oil pump is driven directly from the crankshaft gear. A stop located on the crankcase for the mating face of the oil pump guarantees specified backlash between oil pump gear and crankshaft gear. Complex setting work is not required. The coolant pump is a plug-in pump and is driven via the auxiliary gear. The alternator and power steering pump are driven via two intermediate gears that are overmounted in the crankcase. In through-drive, the power steering pump drives the air conditioner compressor located axially behind it. To minimise backlash in the auxiliary drive, the second intermediate gear serves as a spring loaded split wheel. The use of the split wheel led to a significant reduction of the maximum acoustic capacity and considerably improved acoustics in idling, Figure 10. The input shaft for the alternator is mounted on a friction bearing in the crankcase. The power steering pump is a plug-in pump and is centred in the crankcase. Particular care was taken in the design and production phase to ensure low tolerance levels in the axle inside calipers. To minimise backlash, all bearings are machined in a clamping device with a drilling head unit. The position tolerance of the axles is below 0.03 mm.

This means that the distance from the main oil passage to the exhaust gas turbocharger mounting is very short and the turbocharger oil supply is guaranteed a very short while after engine start. As is usually the case with turbocharged passenger car engines, the engine has piston cooling nozzles which, in conjunction with the full cooling channel piston, maintain the temperatures in the ring and groove area within the permissible limits. The oil return lines of the cylinder head are design to permit installation inclinations to both transverse sides. The timing gear shaft also serves as a return channel with a large cross-section. The valve cover is equipped with a combined woven and labyrinth separator for the blow-by gases. During development of the oil pan versions and intake lines, attention was paid to the intake ratios during pivot movements in longitudinal and transverse direction. For use in the Touareg, an intake certainty of minimum 45 degrees was achieved in all directions. A thermal oil level sensor monitors the filling level and also indicates the oil temperature. The sensor is an integral part of the flexible service interval display and, in conjunction with the 100 % synthetic 0W30 oils as per VW standard, makes usage-dependent replacement intervals of up to two years, or approx. 30,000 km, possible. 8 Coolant Circuit

7 Oil Circuit

The oil circuit is designed as wet-sump lubrication system. The gear-driven duocentric oil pump has an integrated pressure regulating piston made of plastic and its delivery rate is tuned to the absorption line of the engine with as little drive output as possible. An oil filter module is flange-mounted on the cylinder crankcase; the oil cooler which admits coolant is also accommodated in the oil filter module. The oil filter is a fully incinerable, replaceable filter which can be exchanged from above. Oil is drawn from the oil module into the central oil passage. A special feature of this engine is the incorporation of the tension bolt bores into the oil circuit for distributing the oil to the various bearings, particularly in the toothed belt drive area. The cylinder head is supplied via an inclined channel with integrated oil return block which prevents the hydraulic bucket tappets from running empty when stationary. The development goal was to have as few sealing points and external lines as possible. The oil supply and drain is via a bracket on the cylinder crankcase; external lines that are usually used are completely omitted.

4

The coolant circuit through the cylinder crankcase has a diagonal throughflow design. By means of 3D flow calculations (CFD), the coolant circuit was optimised in the design stage so that no further tuning of the coolant distribution via the cylinder head gasket hole pattern was necessary. The good basic distribution of the coolant flow was optimised simply by adding a few ribs in the coolant jacket space. The coolant pump is a gear-driven plugin pump integrated in the crankcase. Cyclic irregularities in the central drive act on the coolant pump. This required an adaptation of the pump mounting dimensions. 9 Charge Cycle

Because of the cross-flow concept of the package and more stringent power and emission requirements, the charge cycle components had to be redesigned. The intake manifold was optimised carefully by means of CFD and flow trials to ensure high flow rate and good equal distribution of swirl. The exhaust gas recirculation inlet is also favourably positioned and permits good, even distribution of the recirculating exhaust gas.

The inlet swirl channel has better correction values than the previous DC cylinder heads at the same swirl level. Swirl has been optimised in conjunction with piston recess and injection equipment. The valve timing was adapted to the R5 requirements with the help of the charge cycle program PROMO and experimental examinations. Cold starting tests with 5 mm extended glow plugs revealed that time was almost halved up to starting cutout, while the engine smoothness is improved directly after starting cutout. With a warm engine, no disadvantage with regard to consumption and emissions as compared to conventional glow plugs were discovered over the map. The exhaust manifold, Figure 11, is designed as a metal elbow with gas-tight inner shell, which not only guarantees fast heating, but also means that additional heat shielding measures are no longer necessary. This makes better use of construction space in the exhaust-carrying section possible. The flange to the turbocharger is fitted with a corrugated bellows for tolerance compensation. Depending on the drive version, a heat exchanger is flange-mounted at the exhaust manifold for exhaust gas recirculation if necessary. The exhaust gas turbocharger with variable turbine geometry ensures a good response, high charge pressure at low engine speeds and good specific consumption at rated output. The exhaust gas turbocharger bearing housing is screw-fitted directly on the cylinder crankcase. This means that less unbalance vibrations from the running equipment reach the exhaust system. This is controlled by a pneumatic vacuum unit, Figure 12. 10 Auxiliary Drives

The assemblies are driven directly by the gear drive via shafts, whereby with both the alternator and air conditioner compressor the shaft offset, shaft angular deviation and shaft distance deviation are controlled by a torsionally flexible elastomer coupling. Righting moments of the auxiliary assembly masses are eliminated at both auxiliary assemblies by means of a freewheel. The spring effect of the toothed belt coupling ensures that strain caused by cyclic irregularities from the toothed belt drive is reduced considerably. In this manner, for auxiliary assemblies it was possible to revert to assemblies in use at Volkswagen which usually rely on the damping effect of the ribbed V-belt. In numerous simulations and measurements, the dynamic behaviour of the drivelines was examined in depth, Figure 13.

MTZ worldwide 1/2004 Volume 65

IMPRINT In order that the existing screw-on points of the large-series alternator and air conditioner compressor assemblies can be used, both assemblies are screwed onto the crankcase by means of intermediate brackets. Only the power steering pump had to be modified because it is used to drive the air conditioner compressor by means of through-drive, which made an extension of the pump shaft necessary. Through the omission of the ribbed Vbelt drive, functional safety when driving on rough terrain and in dusty countries is considerably higher. Extensive dust tests revealed that dust only has no influence on service life. Figure 14 shows the compact layout of the auxiliary assemblies on the engine. 11 Engine Control Unit, Functional Values

Second-generation pump-nozzle elements are used for mixture formation as in the 3- and 4-cylinder engines. They are fitted with five-hole nozzles, whereby the spraying holes are conical and hydro-erosive rounded. The new EDC-16 control unit is used for engine control. It has a torque-oriented software structure so that engine control is drive-management-oriented. The engine power is rated at 128 kW at 3500 rpm, Figure 15. A soft breakaway characteristic ensures good handling of the car. The maximum torque is 400 Nm, which is a significant increase in comparison with the previous series engine at 295 Nm. The specific power output is 52 kW/l. The maximum useful mean pressure is just below 21 bar. Typical for the pump nozzle, the specific consumption is favourable with a minimum value of 198 g/kWh, Figure 16. In spite of a high exhaust gas recirculation rate over the complete mapping range, the smoke spot number remains very low. In a few vehicle versions, the EGR cooler is not necessary. A power-reduced version with 96 kW at 3500 rpm and 340 Nm is available mainly for use in light commercial vehicles.

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To obtain a unit which would be reliable in the future, after extensive concept studies a completely new unit for longitudinal and transverse installation was developed as a successor for the proven 2.5 l TDI_ with distributor injection pump. The reduction in installation length of 58 mm to 510 mm was put into practice with a meshed gear drive. Both camshaft and auxiliary assemblies are driven via helical gear spur wheels. The torsional damper was integrated in the engine in the crankshaft. For reasons of weight, an aluminium cylinder crankcase with a plasma running layer was developed, which integrates many component functions. The turbocharging is by means of an exhaust gas turbocharger with variable turbine geometry, which is mounted on the cylinder crankcase via its bearing housing and has an oil supply and drain line integrated in the flange. The exhaust manifold is a twinshelled insulated metal elbow. The air conditioner compressor is driven axially in through-drive via the power steering pump by means of a torsionally flexible coupling, which is also used for the alternator drive. During development, synergetic effects were observed by the Volkswagen diesel engine module, particularly with regard to the V10 and R4 TDI pump nozzle engine. With a power output of 128 kW at 3500 rpm and a torque of 400 Nm at 2000 rpm it also ensures that vehicles such as the VW T5 Multivan and the VW Touareg perform excellently and economically, Table 2. ■

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