2 MTZ 01/2006 Volume 67

Authors:Joachim Schommers, Mario Mürwald,Erich Arbeiter, Hermann Büter, UlrichHoltmann and Stefan Laulies

Der neue 4,0-l-V8-Dieselmotor von Mercedes-Benz

You will find the figures mentioned in this article in the German issue of MTZ 01/2006 beginning on page 8.

The New Mercedes-Benz 4.0 l V8 Diesel Engine

With the new V8 diesel engine of the E420CDI, Mercedes-Benz is introducing anengine that is a balanced, powerful over-all motor. Its consistent optimizations andexcellent specific values reached in itsclass, more than make up for its lowerdisplacement of 4.0 l, compared with itscompetitors. It will be offered exclusivelyas the Euro 4 model with a particulate fil-ter. Starting with the E-Class, this engine,a basic though enhanced development ofthe familiar V8 diesel engine, will replaceits predecessors in the S-Class, as wellas in the M-Class and G-Class. The pro-duction location at Motorenwerk Berlinwas kept.

1 Introduction and Objective

In 2000, Mercedes-Benz unveiled its first V8diesel engine, which was initially offered inthe S-Class. It was subsequently introducedinto the E-Class as well as the M-Class and G-Class SUV’s, a move that contributed greatlyto its success in this particular market seg-ment. Therefore, it was clear that the con-ceptual design of a successor to the V8 dieselmust incorporate the requirements of thesevehicle model series.

In addition, the following developmentgoals were defined:

– remarkable driving performancethrough increased power and torque

– compliance with the Euro 4 emissionsstandard

– Diesel particulate filter (DPF) as standardequipment

– regeneration of the particulate filterwithout use of additives

– improved fuel economy compared withpredecessor

– better acoustic properties (NVH). Of course, these goals had to be achievedwhile maintaining the trend-setting light-weight concept in this segment.

COVER STORYMercedes-Benz V8 Diesel Engine

3MTZ 01/2006 Volume 67

2 Engine Parameters

The Table summarizes the main engine datafor the E-Class model. At 4.0 l, the displace-ment is the same as its predecessor; it wasnot increased in order to rule out negativeimpacts on weight, installation space, andfuel consumption. The power and torquevalues, Figure 1, are particularly noteworthywith respect to the displacement becausethe highest specific value of an 8-cylinderengine is reached at a mean pressure of 23bar. These demanding objectives could onlybe achieved by steadily developing all thecomponents in the predecessor engine.

3 Engine Description

3.1 Air Ducting, Turbocharging andExhaust Gas SystemParticularly characteristic of this further de-velopment is the unthrottling of the entireair and exhaust gas section, which results ina higher turbocharging level, Figure 2.

The proven basic version of the predeces-sor including engine-mounted air filter, en-gine-mounted water/charge air cooler andtwin turbocharging is highly compact andwas therefore retained.

Supported by extensive flow calcula-tions, the design solution found for air duct-ing reduces pressure loss by 30 % before thecompressor and 62 % after the compressorcompared with the predecessor, while si-multaneously increasing the air flow rate at.

The air is guided to the engine-mountedair filter through clean air intakes aroundthe radiator seal. The air filter contains twofilter cartridges, which are separated fromthe clean air side by a partition wall withswitchover valve. The size and position ofthe switchover valve were fully optimizedwith regard to full load and acoustics.

The cleaned air is guided to the two massair flow sensors (MAF) through two guideribs. This prevents deviations of the air flowsensor signal as a function of the air filtercharge. Precise measuring of the air mass isa prerequisite for exact exhaust gas regula-tion in order to comply with the Euro 4 ex-haust gas limits.

Upstream volumes located right beforethe exhaust gas turbocharger compressorunit contribute considerably to the highertorque curve in the lower rpm range, asshown in Figure 3.

The compressed air is then guided to thejoint water charge air cooler, which was alsounthrottled and its cooling performance im-proved.

The electrically operated intake air throt-tle is located directly downstream the

The vehicle interface, exhaust gas af-tertreatment, and T3 regulation in the CR5engine control represent an improvementover the familiar CR4 engine control.

Unlike its predecessor, the engine doesnot need a valve block to distribute the fuelto the rails of the two cylinder banks. A re-designed rail pressure regulation allows thefuel to feed from the high-pressure pump di-rectly to the left-hand rails, where the pres-sure regulating valve is located, and fromthere to continue to the right-hand rail,where the pressure is measured.

The injectors, which allow up to 5 injec-tions per duty cycle, are equipped with hy-draulically optimized 7-hole nozzles.

Piezo technology reduces the amount ofleaking oil in the return section of the com-mon rail system to almost 0 mm3. The in-take-regulated high pressure pump and thecoupled pressure control (CPC) significantlycontribute to the favourable fuel economy ofthe OM 629. The hydraulic componentseliminate the need for a fuel cooler.

3.3 CoolingThe coolant guide system is very similar tothat of the predecessor. Various customiza-tions and optimizations were performedwith the goal of meeting the increased re-quirements due to the higher loads and toboost EGR cooling to stay safely below theEuro 4 emissions limits.

The water pump is mounted on the faceof the crankcase. A capped impeller increas-es efficiency and power for the necessaryflow rate.

The 10 % reduction in resistance can beattributed primarily to optimized waterflow in the cylinder heads, as well as un-throttling in the crankcase and thermostat.

The design of the ducts in the crankcaseensures even distribution of water to bothcylinder banks. The flow around the wetcylinder liners in the crankcase is opti-mized, which results in little thermal distor-tion.

After that, the cooling water enters thecylinder heads through the passageways inthe cylinder head gaskets. These arematched so that the water cools all cylindersevenly; the flow can be directed to the criti-cal areas within each cylinder. The

two-part design of the cylinder head wa-ter jackets does a good job of cooling thevalve lands and the areas around the injec-tor shafts. The water first flows through thebottom water jacket, which lowers the tem-perature by 30 K in the critical area betweenthe exhaust valves.

The top water jacket then guides the wa-ter flow to the thermostat, which is located

charge air cooler upstream the EGR inletarea. This component, similar to an elec-tronic accelerator actuator, regulates thenecessary pressure drop in EGR mode, aswell as the charge pressure during DPF re-generation.

The charge air manifold, which is con-nected to the cylinder heads via rubber ele-ments, distributes charge air to the twocylinder banks. The rubber elements allowfor better tolerance offset between the cylin-der heads and reduce noise emission of theair manifold.

The exhaust gas temperature resistanceand the maximum wheel assembly rpmwere enhanced in both VNT turbochargers.Additional supports reduce the vibrationstress of the turbochargers in all operatingranges.

The cambered vanes further enhance tur-bine efficiency. The vane bearings as well asthe nozzle ring together with the insert im-prove the heat expansion properties.

An electric actuator motor changes theposition of the guide vanes. The high posi-tional accuracy and adjustment speed thatcan be achieved with the electric actuatorare a prerequisite for exact and fast chargepressure regulation, positively influencingagility and exhaust gas emissions.

The exhaust manifolds also providedpotential for reducing pressure losses,which actually were lowered by more than65 % despite difficult installation condi-tions.

Another development goal was reducingcomponent weight, so that lower thermalcapacities would assist the catalysts close tothe engine to start faster. As an alternative toa cast-iron manifold, an air-gap isolatedsheet metal manifold was examined. Since asheet metal manifold has improved theheating properties of the catalytic convert-ers only slightly without achieving the de-sign possibilities and cost advantages of thecast version, this development was not pur-sued further.

Like the predecessor, the exhaust gas isreturned via two EGR valves (controlled bythe engine map). To improve combustionstability and reduce HC+CO emissions dur-ing warm-up, the exhaust gas is guided pastthe EGR cooler through a switchable bypass.The entire exhaust gas recirculation isshown in Figure 4.

3.2 Injection System and Engine Control As in the new Mercedes-Benz OM 642 V6 en-gine, this one uses a third generation com-mon rail injection system with a maximumrail pressure of 1,600 bar and Piezo injec-tors.

COVER STORY Mercedes-Benz V8 Diesel Engine

4 MTZ 01/2006 Volume 67

on the water-outlet in the front of thecrankcase.

After the cylinder heads, cooling water isdirected to the EGR cooler, the water coolingjacket of the EGR valves, and the heater core.

The oil/water heat exchanger, which ismounted on the inner V of the crankcase, issupplied by the line between water pumpand cylinder space. Figure 5 shows the en-gine coolant circle.

3.4 Cylinder Head / Valve TrainExcept for the split water jacket, the designof the cylinder heads is based on the famil-iar 4-cylinder inline engine OM 646, Figure 6.

During the engine planning phase, nu-merous simulations showed that the advo-cated increase in peak pressure would meanadapting the rigidity of the cylinder head.The intermediate cover in the water jacketsignificantly contributes to this.

The cylinder heads are die cast from ahigh-temperature aluminium alloy. Toachieve the required material propertiesand to keep them highly consistent, thecylinder heads are heat-treated with thesame process that was also used on the newMercedes-Benz V6 diesel engine.

The valve train is familiar from the OM646, with bucket tappets and hydraulicvalve clearance compensation.

The camshaft is driven by the provendouble-bush timing chain, Figure 7. To ex-tend the service life of the chain, the high-pressure pump was moved to the left cylin-der bank, where it is driven by the intakecamshaft gear.

3.5 Crankcase and Drive UnitAll components subject to combustion pres-sure are designed for a peak pressure of 180bar.

The crankcase, Figure 8, uses the familiarbedplate concept of its predecessor, featur-ing cylinder banks arranged at a 75° angleand inserted wet cylinder liners. The toppart is a sand-cast, high-strength aluminiumalloy, AlSi7Mg0.3.

Unlike traditional gravity die-casting,this process guarantees reproducibility and,by applying pressure dwell from the timethe mould is filled to solidification, it en-sures a cavity-free cast.

The gate takes place from both cylinder-head flanges of the crankcase. In the high-stress areas of the thrust bearings and thecylinder head bolts, the solidificationprocess is influenced with cooling irons, inorder to achieve high strength and suffi-cient ductile yield.

Subsequent T7 heat treatment of theblank (annealing, chilling, artificial aging)

achieves the thermal structural stabilitythat is necessary to make the material prop-erties permanent.

When designing the top part, special at-tention was paid to achieving a rigid struc-ture. This goal was reached with ribs on theouter sides and between the cylinder banks.

As is the case with all high-stress V-en-gine crankcases, the design of the main oilchannel was a true challenge. Intensive FEManalysis during the development process al-lowed a significant reduction in stress levelaround the die-cast channel. Parallel to that,material properties have been consistentlyimproved, Figure 9.

Additional structural rigidity is achievedwith the integral gas exchange ducts, whichenable pressure compensation between thechambers of the crankcase, thereby reduc-ing pump losses.

The base section, made of AlSi9Cu3 withintegral GGG60 inlays in the five thrustbearings, is gravity sand-cast. Besides variousother functions, the base section is fittedwith an integral oil catch tray, a stripperedge that removes the engine oil from thebearings and oil nozzles, thus separating itfrom the drive unit roller, and guide ribsthat direct it into the oil pan.

The crankcase with a crankpin offset of15° is forged from 46MnVS6. The propertiesof this steel are similar to heat-treated steel,yet it has the advantage of being easier tomachine.

For acoustic reasons, the rigidity of thecrankcase was improved using larger mainbearing diameters. Further emphasis wasplaced on a dynamically optimized oil sup-ply of the con-rod bearings, since the largebore in combination with a 180 bar peakpressure subjects them to extremely highloads.

The top half of the main bearing is a ter-nary bearing with a groove; the bottom halfis a sputter bearing.

The 70 MnVS4 forged connecting rodwith a cracked large eye is supported by asputter bearing on its high-stress end and aternary bearing on its cover end.

The pistons with a 3mm higher headland are made from an optimized alumini-um alloy 174+. By integrating a sealed cool-ing duct in the reinforced ring groove, it waspossible to further improve the of the piston.

A balancer shaft, which rotates at enginespeed against the rotating direction of theengine, offsets the unbalanced torques ofthe first order, which occur at a 75° cylinderbank angle. The shaft bearing in the mainoil channel optimizes the space in thecrankcase. The timing chain drives the bal-ancer shaft through a guide sprocket.

4 Friction Loss

Since the demanding power, torque, and ex-haust gas emission requirements on the en-gine had to be met while at the same timeimproving fuel economy, there was no wayaround reducing friction loss.

It was possible to reduce the mean fric-tion pressure of the drive unit includingventilation losses by 35 % compared to thepredecessor, despite the increase in bear-ing bore. These improvements wereachieved primarily using the followingmeasures: – optimization of piston with ring package– introduction of gas exchange ducts on

the sides– optimization of the timing chain drive. It was possible to keep the friction loss of thevalve train at the level of the predecessor en-gine, despite increased requirements result-ing from higher exhaust gas counter-pres-sure due to the particulate filter.

5 Measures for Acoustic Optimization

Optimizing acoustics at low loads and rpmin a large displacement diesel engine is al-ways a challenge. Customers drive dispro-portionately often in this operating range.Therefore, the new V8 diesel engine was de-signed to appear pleasant and unobtrusiveunder partial load and sound powerful un-der full load without being loud. TheCampbell diagrams in Figure 10 show thatat a partial load point at 1,700 rpm, thenew engine has a much more harmoniousacoustic pattern compared with the prede-cessor.

The best values in acoustics and smooth-ness are achieved by the following meas-ures:– especially rigid crankcase with bedplate

for additional stiffness– crankcase with larger main bearing bore– balancer shaft– considerably more rigid engine mount

and connection to crankcase– rigid, charge air lines made of alumini-

um with low volume, due to the locationof the charge air cooler on the engine

– decoupling of the charge air manifold– optimized chain guides with rubberized

crankshaft wheel– closed inner V due to EGR valve holders

with optimized acoustic insert– decoupling of the intake pipe fastening

before the exhaust gas turbocharger– decoupled securing of the low pressure

fuel lines– fuel injection at 1,600 bar with dual-pilot

injection

5MTZ 01/2006 Volume 67

– covering of entire motor, in particular injector shaftareas, with sound-absorbing foams under the air filterand the design cover.

Because of theses measures and the optimization of eachcomponent in terms of NVH behaviour, the new E 420CDI claims a top position in its class.

6 Exhaust Gas Results and Exhaust Gas Aftertreatment

In the E-Class, the new 8-cylinder 420 CDI comes standardwith a diesel particulate filter as the Euro 4 model.

After the catalytic converter, the exhaust gas from thetwo cylinder banks is directed towards a joint diesel par-ticulate filter (DPF) located in the under-floor area, Figure11. To reduce heat losses, pipes with insulated air gaps areused between catalytic converters and the DPF.

As in all Mercedes-Benz passenger car diesel engines,the DPF are purged without additives to aid regeneration.With the filter being positioned "far away from the en-gine” and the large displacement engine, which is oper-ated mainly in the low load range, a specially matchedheating strategy was necessary to quickly provide thetemperatures necessary for carbon black regeneration.Up to five injections are deposited; the exhaust gas tem-perature values before the exhaust gas turbocharger andafter the catalytic converter are used as control variablesfor the double post injections. This helped optimize theduration of regeneration and carbon black conversionrates significantly.

7 Fuel Consumption, Driving Performance

At 9.3 l per 100 km, the fuel consumption of the new E420 CDI is 0.1 l / 100 km below the fuel consumption ofthe predecessor model E 400 CDI– despite noticeably better driving performance– despite superior engine acoustics – while complying with much tougher Euro 4 emissions

standards. This could only be achieved through consistent unthrot-tling of air passageways, friction loss reductions in the en-tire drive unit, optimized fuel stream preparation, anduse of a 7-speed automatic transmission.

Its performance figures include a 0 to 100 km time of6.1 s; 60 to 120 km in 4.8 s, which is an improvement of12 % and 28 %, respectively, compared with the predeces-sor model, Figure 12. The top speed is electronically limit-ed to 250 km/h.

8 Summary

Consistent focus on features that the customer can expe-rience helped this new V8 diesel engine rise to the top po-sition in its class. During its design, special emphasis wasplaced on specific power and torque values, in order to re-alize advantages under high absolute full load values,even though displacement had been kept the same.

Despite drastic boosts in performance and torque, theengine acoustics and fuel economy are superior to thoseof the predecessor model.

Naturally, the Euro 4 model of new E 420 CDI will beoffered exclusively with particulate filter. ■

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