Diesel Air Intake and Exhaust System

8/10/2019 Diesel Air Intake and Exhaust System

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BMW Service

Aftersales Training -Product information.Air Intake and Exhaust System -

Diesel.


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The information contained in the Product Information and the Workbook form an integral part ofthe training literature of BMW Aftersales Training.

Refer to the latest relevant BMW Service information for any changes/supplements to thetechnical data.

Information status: July 2007

Contact: [email protected]

2007 BMW AGMnchen, GermanyReprints of this publication or its parts require the written approval ofBMW AG, MnchenVS-12 Aftersales Training


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Product InformationAir Intake and Exhaust System -Diesel.

Peakperformancewithoptimizedfreshairsupply

Minimum pollutants

Perfect sound


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Notes on this Product Information

Symbols used

The following symbols are used in this Product Information to improveunderstanding and to highlight important information:

3 contains information to improve understanding of the systemsdescribed and their function.

1identifies the end of a note.

Information status and national variants

BMW vehicles satisfy the highest requirements of safety and quality.Changes in terms of environmental protection, customer benefits anddesign render necessary continuous development of systems andcomponents. Discrepancies may therefore arise between specific detailsprovided in this Product Information and the vehicles available during thetraining course.

This document relates exclusively to left-hand drive vehicles withEuropean specifications. On right-hand drive vehicles, some controls orcomponents are arranged differently from the illustrations in this Product

Information. Further differences may arise as the result of the equipmentvariants used in specific markets or countries.

Additional sources of information

Further information on the individual subjects can be found in thefollowing:

- Owner's Handbook

- BMW diagnosis system

- Workshop systems documentation

- BMW Service Technology


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Contents.Air Intake and ExhaustSystem - Diesel

Objectives 1Product Information and reference material forpractical applications 1

Introduction 3General requirements 3

System overview 9Overview 9System overviews of current engines 15

System components 27Unfiltered air duct 27Intake silencer 28Exhaust turbocharger 29Intercooler 35

Sensors - air intake system 38Throttle valve 41Intake air manifold 42Exhaust manifold 44Exhaust gas recirculation 45Exhaust turbocharger 53Sensors - exhaust system 61Oxidation catalytic converter 70Diesel particulate filter 74

Particulate trap catalytic converter 79Silencer 81Vacuum system 89

Service information 101System overview 101System components 102

Summary 103Points to remember 103


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Test questions 109Questions 109Answers to questions 113


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Objectives.Air Intake and Exhaust System - Diesel.

Product Information and reference material for practicalapplications

This Product Information provides detailedinformation on the design and function of thevarious air intake and exhaust systems used inBMW diesel vehicles.

TheProduct Information is designed as a workof reference and supplements the contents ofthe BMW Aftersales Training course. TheProduct Information is also suitable for privatestudy.

As a preparation for the technical trainingcourse, this publication provides an insightinto the air intake and exhaust systems of thecurrent BMW diesel models. In conjunctionwith practical exercises carried out in thetraining course, its aim is to enable courseparticipants to carry out servicing work on theair intake and exhaust systems in BMW dieselvehicles.

Technical and practical backgroundknowledge of the current BMW diesel modelswill simplify your understanding of thesystemsdescribed here and their functions.

Please remember to work throughthe SIP (training and informationprogram) on this topic.Basic knowledge ensuresconfidence in theory and practice.


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Introduction.Air Intake and Exhaust System - Diesel.

General requirements

The air intake system supports the chargecycleprocess. Thehigher thedeliveryrate, themore effective the charge cycle. The termdelivery rate refers to the ratio between theactual and theoretically possible cylindercharge. A large volume of air additionallymeans a higher oxygen content in the cylindercharge. The oxygen content is also higher inair that has been compressed to some extentthus shortening the combustion paths.

The introduction of the transverse flowcylinder head was key in achieving animproved cylinder charge. In this cylinderhead, the intake and exhaust are not arrangedon one side (counterflow cylinder head) butrather on different sides of the displacementengine. The incoming fresh gasses are able toexit the combustion chamber in virtually thesame direction with no flow-back. This designlayout also made possible the use of multi-valve technology with optimum crosssectionsfor the valves and ideal central arrangement ofthe injection nozzles.

Formerly, the counterflow cylinder head stillhad the advantage of effective mixturepreheating for cold start by the exhaustmanifold arranged below it. However, thisadvantage proved to be a disadvantage oncethe engine reached operating temperature.For this reason, intake air preheating(subsequently also thermostaticallycontrolled) has become less and lessprevalent. Theonly remainingdisadvantage ofthe cross-flow cylinder head is the division ofthe engine into a warm exhaust side and a coldintake side. Design measures andcorresponding material selection are requiredto compensate for this disadvantage.

Ever greater significance is being attached tothe typical sound a specific model makes. Inrecent years, the significance of the soundmade by the different models can bemeasured by the attention paid to this topic inthe motor press.

Exhaust emission legislation

Pollutants

Many countries limit the levels of emittedpollutants by way of corresponding exhaustemission legislation. The regulationsstipulated by the respective countries arebased on test procedures, measuringtechnologies and limits that may vary forecological, economic, climatic and politicalreasons.

Limits are specified for following exhaustemissions:

Hydrocarbons (HC), country-specific

Non-methane hydrocarbon compounds(NMHC), country-specific

Carbon monoxide (CO)

Nitrogen oxides (NOx)

Particles (PM)

These pollutants are the result of:

Combustion in the engine

Sulphur content in fuel

Crankcase ventilation

Fuel evaporation

Sulphur compoundsin theexhaust gasaretheresult of the sulphur contained in the fuel. Thelimits for the sulphur content in diesel fuelhave therefore been reduced throughout theworld.

The pollutant emissions from the crankcaseare relatively low as only clean filtered air iscompressed in the diesel engine. The gassesthat enter the crankcase during expansion(combustion stroke) contain only approx. 10%of the pollutant mass that occurs in petrolengines. Nevertheless, a sealed crankcaseventilation system is required by law.

There is no need to monitor evaporativeemissions on diesel engines as the diesel fuelcontains no volatile components.

It is necessary to implementappropriatedesign measureson theair intake and exhaust system inorder to be able to meet theemission limitsspecifiedthroughout

the world. The design of the airintakeand exhaust systemdiffersfordifferent types of engine.


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The particles (PM) consist of: Carbon

Hydrocarbons

Metal abrasion

Sulphur compounds

Water

Type approval testing

Exhaust emission inspections are theprerequisite for granting the general typeapproval for a specific type of vehicle and/orengine. For this purpose, test cycles must berun under defined marginal conditions andemission limits met. The test cycles andemission limits are specific to the respectivecountry.

The following graphics show the differentexhaust emission limits based on the exampleof the EURO specification, US specificationand Japan specification. The tables are notdirectly comparable as the corresponding testconditions for determining the pollutantemissions differ in part quite significantly fromeach other.

Consequently, this means that an engine andtherefore also the air intake and exhaustsystem need to be adapted to the respectiveconditions.

The pollutants hydrocarbon (HC), carbonmonoxide (CO), nitrogen oxides (NOx) andparticle emissions (PM) are measured as partof the EURO type approval test procedure.The vehicle to be tested must have covered arunning-in distance of 3000 km.

In the USA, the Federal State of Californialimits the emission of non-methane

hydrocarbon compounds (NMHC) to theaverage model range of a vehiclemanufacturer. The vehicle manufacturer canusedifferentvehicleconcepts thatdivided intothe following categories depending on theiremission values for NMHC, CO, NOxandparticle emissions:

TLEV (Transitional Low Emission Vehicle)

LEV (Low Emission Vehicle)

ULEV (Ultra-Low Emission Vehicle)

SULEV (Super Ultra-Low Emission Vehicle)

ZEV (Zero Emission Vehicle)For the type approval of a vehicle model, themanufacturer must verify that the pollutantsHC (or NMHC), CO, NOx, particles and smokeemission (turbidity) do not exceed theemission limits over a distance of 50,000 and/or 100,000 miles. The vehicle manufacturermust make available two vehicle fleets fromproduction for this type approval test.

1 - Exhaust gas composition of a diesel engine before exhaust treatment


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Type approval test values, EUROspecification

2 - Exhaust emission limits, EURO specification

Valid from Regulation COin mg/km

NOxin mg/km

HC + NOxin mg/km

Particles(PM) in mg/

km

01.07.1992 EURO 1 2720 970 970 140

01.07.1996 EURO 2 1000 700 700 80

01.01.2000 EURO 3 640 500 560 50

01.01.2005 EURO 4 500 250 300 25

planned

01.09.2009

EURO 5 500 180 230 3

planned01.09.2014

EURO 6 500 80 170 3


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Type approval test values, Japan

3 - Exhaust emission limits, Japan

Valid from Regulation

COin mg/km

NOxin mg/km

HC + NOxin mg/km

Particles(PM) in mg/

km

01.10.1998 - 2100 400 400 80

01.09.2000 - 2100 400 400 80

01.09.2004 - 630 300 120 56

01.09.2007 LEV 2005 630 150 24 14

planned01.09.2010

- 630 80 24 5


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Type approval test values, USspecification in comparison with EUROspecification and Japan specification

4 - Exhaust emission limits, comparison of EURO specification, US specification and Japan specification

Valid from Regulation COin mg/km

NOxin mg/km

HC+NOxin mg/km

Particles (PM)in mg/km

planned01.09.2009

EURO 5 500 180 230 3

01.09.2007 LEV 2005Japan

630 150 24* 14

Model year 2005 LEV II,Tier 2 Bin5

2110 31 47* 6

* NMHC is regulated in the USA. NMHC = Non-methane hydrocarbon


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Preconditions

Intake system

The task of the intake system is to supply theengine with as much cool fresh air as possible.The lower the flow losses, the higher theoutput yield and torque.

The intake system consists of the followingindividual components:

Unfiltered air duct

Intake silencer

Hot-film air mass meter

Filtered air duct

Blow-by gas connection

Exhaust turbocharger

Intercooler

Charge air temperature sensor

Throttle valve

Inlet for exhaust gas recirculation

Intake air manifold

Boost pressure sensor

Swirl flaps

Swirl flap actuator

In the meantime, the intake system is madefrom aluminium or plastic. The plastic materialis heat resistant up to a temperature of 140 Cand, compared to aluminium, provides afurther weight saving of up to one third. On theinside, the intake system should exhibitsmooth surfaces and no steps. The firstsection of the air system and the transition to

the air cleaner also require particularmeticulous design.

The average flow rate in the intake pipe isapprox. 50-200 m/s.

Exhaust system

The task of the exhaust system is to providethe necessary noise damping, low exhaustbackpressure and the necessary exhaust gastreatment.

The exhaust system consists of the followingcomponents:

Exhaust manifold

Exhaust gas recirculation

Exhaust gas recirculation valve

Exhaust gas recirculation cooler

Exhaust gas recirculation bypassactuator


Sensors

Exhaust temperature sensor

Oxygen sensor

Exhaust backpressure sensor

Oxidation catalytic converter

Diesel particulate filter

Primary silencer

Intermediate silencer

Rear silencer

Tail pipe

Exhaust flap


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System overview.Air Intake and Exhaust System - Diesel.

Overview

Air intake system

In addition to reducing the intake noise, the airintake system ensures an optimum supply offresh air to the combustion chamber. A waveof negative pressure acting against thedirection of flow of the fresh air intake iscreated by the movement of the piston afteropening the intake valve. The resultingpressure fluctuations are radiated in the form

of sound via the mouth of the intake system. Inaddition, the pulsation that occurs inside theair intake system causes the walls of thecomponents to vibrate, thus also radiatingnoise. The air intake system is thereforeoptimized in such a way that no disturbing orannoying vibration can occur thus conformingto the noise emission limits applicableworldwide.

The intake system can be dividedintotwosection. Theintake snorkel,intercoolerand, with exceptions,theintake silencer are specificallyassigned to the vehicle and differeven in connection with the sametype of engine due to the differentcharacteristics of the vehiclemodels. The exhaust turbochargerand the intake system with swirlflaps, throttle valve and varioussensors are assigned to the engine.Apartfrom theexhaust turbochargerand exhaust manifold, the exhaustsystem is designed vehicle-specificanddiffersdepending onthe type ofvehicle and specification.


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N47D20T0 Engine

1 - Air intake system, N47D20T0 engine

Index Explanation Index Explanation

A Unfiltered air 7 Charge-air pipe

B Filtered air 8 Intercooler

C Heated charge air 9 Charge air pipe

D Cooled charge air 10 Charge air temperature sensor

1 Unfiltered air pipe 11 Throttle valve

2 Intake silencer 12 Inlet for exhaust gas recirculation

3 Hot-film air mass meter 13 Boost pressure sensor

4 Filtered air pipe 14 Intake air manifold

5 Blow-by gas connection 15 Swirl flap actuator

6 Exhaust turbocharger


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The unfiltered air (A) that is drawn in reachesintake silencer (2) through the intake snorkel(not shown) and unfiltered air pipe (1). In theintake silencer, the unfiltered air is filtered tobecomefiltered air (B). Thefiltered air flows viahot-film air mass meter (3) and filtered air pipe(4) to exhaust turbocharger (6). At the sametime, blow-by gases are fed into the filtered airpipe through blow-by gas connection (5). Inthe exhaust turbocharger, the filtered air iscompressed and thereby heated. Thecompressed, heated charge air (C) isconveyed in charge air pipe (7) to intercooler

(8).

From the intercooler, the now cooled chargeair (D) flows via charge air pipe (9) past chargeair temperature sensor (10) to throttle valve(11). Depending on the position of the throttlevalve more or less cooled charge air (D) flowsinto intake manifold (14). The inlet for therecirculated exhaust gas (12) also joins theintake manifold.

3 If the filtered air pipe downstream of theblow-by gas connection is heavily oiled, thiscould imply increased blow-by gas levels. Thecause of this isusually a leak in the engine (e.g.crankshaft seal) or surplus air taken in through

the vacuum lines. A consequential symptomwould then be an oily exhaust turbocharger,which does not mean that there is a fault withthe exhaust turbocharger itself.1


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M57D30T2 Engine

2 - Air intake system, M57D30T2 engine


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Exhaust system


A Unfiltered air 5 Exhaust turbocharger

B Filtered air 6 Charge-air pipe

C Heated charge air 7 Intercooler

D Cooled charge air 8 Charge air pipe

1 Unfiltered air snorkel 9 Throttle valve

2 Intake silencer 10 Intake air manifold

3 Hot-film air mass meter 11 Valve cover with swirl ports

4 Filtered air pipe

3 - E81/E87 Exhaust system, N47D20O0 engine


1 Rear silencer 7 EGR bypass actuator

2 Intermediate silencer 8 Exhaust turbocharger

3 Exhaust backpressure sensor 9 VNT actuator

4 Exhaust manifold 10 Oxidation catalytic converter anddiesel particulate filter (DPF)

5 EGR valve 11 Oxygen sensor

6 EGR cooler 12 Exhaust temperature sensor


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The task of the exhaust system is to directcombustion gasses into the atmosphere withas little noise and as environmentallyacceptable as possible. In order to fulfil theserequirements, while also producing a definedsound, the individual components such assilencer, catalytic converter, diesel particulatefilter, exhaust turbocharger, exhaust manifoldand various sensors are mutually matched.

3 Theexhaust systemis designedsuch thatthe vibrations corresponding to the enginetiming (intake and pressure waves) optimizethe charge cycle and therefore the engine

output. Consequently, in the event of a defectin the exhaust system, the vibration-coordinated charge cycle is influencednegatively, thus consequently reducingengine output while increasing fuelconsumption. 1

The notion that an engine with reduced noisedamping has a greater power output isincorrect and proven by the previousinformation. The design layout of the exhaustsystem positively influences the flow ofexhaust gasses. Thepressure reductionat thepoint of valve intersection is specifically usedfor the purpose of initiating the inductionstroke and increasing power output.

The power output can be influenced by thepipe length and position of the silencers(catalytic converter/diesel particulate filter).

Current exhaust systems are equipped withone catalytic converter, one diesel particulatefilter and two silencers.


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System overviews of current engines

Using the N47D20O0 engine, N47D20T2engine, M57D30O2 engine, M57D30T1engine, M57D30T2 engine and theM67D44O1 engine as examples,the followingsystem overviews illustrate the air intake andexhaust systems. The graphics demonstratethe differences between the various types ofengine (4-cylinder engine, 6-cylinder engineand 8-cylinder engine) together with theirspecific characteristics.

The air intake and exhaust systemsdiffer depending on the type ofengine and exhaust emissionlegislation. The system overviewsprovide an initial insight into thecomplexity and differences of theindividual engine series.


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N47D20O0 Engine

4 - Air intake and exhaust system, N47D20O0 engine


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1 N47D20O0 Engine 11 Rear silencer

2 Intake silencer (air cleaner) 12 Digital diesel electronics (DDE)

3 Hot-film air mass meter (HFM) 13 EGR (exhaust gas recirculation)valve and position sensor

4 Exhaust turbocharger with VNT 14 Boost pressure sensor

5 Exhaust temperature sensor 15 Throttle valve

6 Oxygen sensor 16 EGR bypass valve

7 Exhaust backpressure sensor 17 EGR cooler

8 Oxidation catalytic converter 18 Intercooler

9 Diesel particulate filter (DPF) 19 Charge air temperature sensor

10 Intermediate silencer


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N47D20T0 Engine

5 - Air intake and exhaust system, N47D20T0 engine


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1 Charge air temperature sensor 12 Oxidation catalytic converter anddiesel particulate filter (DPF)

2 Intercooler 13 Wastegate

3 Intake silencer 14 Exhaust turbocharger, low pressurestage

4 Hot-film air mass meter (HFM) 15 Turbine control valve

5 Compressor bypass valve 16 Exhaust turbocharger, high pressurestage

6 EGR cooler with bypass valve 17 N47D20T0 Engine

7 Exhaust temperature sensor 18 Boost pressure sensor

8 Oxygen sensor 19 EGR valve

9 Exhaust backpressure sensor 20 Throttle valve

10 Primary silencer 21 Digital diesel electronics (DDE)

11 Intermediate silencer


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M57D30O2 Engine



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1 M57D30O2 Engine 10 Intermediate silencer

2 Intake silencer (air cleaner) 11 Rear silencer

3 Hot-film air mass meter (HFM) 12 Digital diesel electronics (DDE)

4 Exhaust turbocharger with VNT 13 EGR valve

5 Exhaust temperature sensor 14 Boost pressure sensor

6 Oxygen sensor 15 Throttle valve

7 Exhaust backpressure sensor 16 EGR cooler

8 Oxidation catalytic converter 17 Intercooler

9 Diesel particulate filter (DPF) 18 Charge air temperature sensor


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M57D30T1/M57D30T2 Engine

7 - Air intake and exhaust system, M57D30T1/M57D30T2 engine


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1 M57D30T1/M57D30T2 Engine 12 Oxidation catalytic converter

2 Intake silencer (air cleaner) 13 Exhaust temperature sensor

3 Hot-film air mass meter (HFM) 14 Diesel particulate filter (DPF)

4 Compressor bypass valve 15 Rear silencer

5 Small exhaust turbocharger 16 Digital diesel electronics (DDE)

6 Large exhaust turbocharger 17 Throttle valve

7 Turbine control valve 18 EGR valve

8 Wastegate 19 Boost pressure sensor

9 Exhaust temperature sensor 20 EGR cooler

10 Oxygen sensor 21 Intercooler

11 Exhaust backpressure sensor 22 Intake air temperature sensor


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M67D44O1 Engine



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1 Charge air temperature sensor 11 Diesel particulate filter

2 Intercooler 12 Oxidation catalytic converter

3 Throttle valve 13 Oxygen sensor

4 EGR cooler 14 Exhaust temperature sensor

5 EGR valve 15 Exhaust backpressure sensor

6 Intake silencer (air cleaner) 16 Digital diesel electronics (DDE)master

7 Hot-film air mass meter (HFM) 17 Intermediate silencer

8 Exhaust turbocharger with VNT 18 Rear silencer

9 Swirl flaps 19 DDE Slave

10 Boost pressure sensor


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System components.Air Intake and Exhaust System - Diesel.

Unfiltered air duct

The unfiltered air duct consists of theunfiltered airsnorkel, pipe andtheunfiltered airarea of the intake silencer. The unfiltered airsnorkel and pipe are designed with the crash

safety of pedestrians in mind. This entails theuse of especially soft materials and yieldingconnections.

M57D30T2 Engine

The M57D30T2 engine draws in theunfiltered air laterally behind the bumperahead of thecooling module. Theunfiltered air

is routed via coarse-mesh screen (1) viaunfiltered air snorkel (2) and unfiltered air pipe(3) into the unfiltered air area of intake silencer(4). The coarse-mesh screen prevents largeparticles such as leaves from being drawn in.

The unfiltered air snorkel in the N47 engine isdesigned as an unfiltered air intake shroud.This has a large surface area, but isexceptionally flat. The air is drawn in by thecooling module.

Theunfilteredfreshair is directedviatheunfiltered airduct intothe intakesystem of the respective engine.

1 - Unfiltered air duct, M57D30T2 engine

Index Explanation

1 Coarse-mesh screen

2 Unfiltered air snorkel

3 Unfiltered air pipe

4 Unfiltered air area of intake silencer

5 Filter element

6 Filtered air area of intake silencer


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Intake silencer

The intake silencer houses the filter elementand is designed such that the filter elementhas as long a service life as possible. Thelarger the filter element, the longer the servicelife and also the greater the space

requirement. The housing of the intakesilencer is also designed to deform in theevent of impact from above (pedestriancollision). This means that it compresses byseveral centimetres.

M57D30O2 Engine

In order to optimally utilize the available spaceand not to have to develop a new intakesilencer for each type of vehicle, the intakesilencer is mounted on the engine and part ofthe cylinder head cover.

M57TU2 TOP engine

Since the combustion chamber is required forboth turbochargers on twin turbo engines, theintake silencer is not fitted directly on theengine. In this case, the intake silencer ispositioned laterally on the wheel well.

The intake silencer reduces theintake noise and houses the filterelement.

2 - Intake silencer with filter element, M57D30O2 engine

Index Explanation

1 Filter element2 Housing

3 - Intake silencer, M57TU2 TOP engine

Index Explanation

1 Filter element2 Housing cover

3 Bottom section of housing


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In 1925 Alfred Bchi produced the firstexhaust turbocharging system with a 40 %increase in power output. This developmentheralded the step-by-step introduction ofexhaust turbocharging.

In exhaust turbocharging a part of the exhaustenergy is used to drive a turbine. The exhaustenergy would simply be wasted without

exhaust turbocharging.

Mounted on the turbine shaft, an impeller(pump wheel) draws in the air and directs itcompressed to the engine.

Compared to a naturally aspirated engine ofthe same size, the engine supercharged withan exhaust turbocharger has lower fuelconsumption as a part of the exhaust energythat would otherwise not be utilized is used toincrease the engine output.

The torque progression of an engine chargedwith an exhaust turbocharger can be laid out

more favourably. Due to the sharp rise intorque at low engine speed, almost the fullpower output is made available below therated engine speed (speed at which theengine reaches its maximum power output).This means it is not necessary to shift so oftenwhen driving uphill.

Compared to naturally aspirated engines, theturbocharged engine looses virtuallyno powereven at great altitude.

The turbocharged engine can be operatedwith a larger air surplus. This is the basis for

low consumption operation of current dieselengines.

The exhaust turbocharger compresses theintake air. In this way, significantly moreoxygen can be delivered to the combustionchamber.

The operation of the exhaust turbocharger isdescribed in the Exhaust system section.

Design

An exhaust turbocharger consists of a turbineand a compressor that are connected by acommon shaft. Driven by the exhaust gasses,the turbine provides the drive energy for thecompressor.

The compressors used in BMW engines are

radial-flow compressors. A compressorconsists of the impeller and the turbinehousing. The speed of the turbine andtherefore of the impeller draws in air axiallywhich is accelerated to high speeds in theimpeller. The air leaves the impeller in radialdirection. The speed of the air is reducedvirtuallywithout loss in thediffuser, resulting inan increase in pressure and air temperature.The diffuser consists of the sealing plate and apart of the compressor housing. The air iscollected in the compressor housing and thespeed is further reduced up to the outlet to theintercooler.

Operation of the exhaust turbocharger isdocumented under .

The exhaust turbocharger uses apart of the exhaust energy tocompress the intake air, thusincreasing the efficiency of theengine. A swirl element is used tooptimize the effect on the fresh air

side.


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4 - Exhaust turbocharger


1 Turbine housing 11 Vacuum unit

2 Turbine wheel 12 Impeller3 Heat shield 13 Piston ring seal

4 Bearing housing 14 Main bearing

5 Outlet to intercooler 15 Bearing bush

6 Oil inlet 16 Oil return

7 Safety plate 17 Inlet from exhaust manifold

8 Sealing plate 18 Wastegate

9 Compressor housing 19 Outlet to catalytic converter

10 Inlet from intake silencer


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Functional principle

The functional principle of an exhaustturbocharger is described based on itscharacteristic map. It shows the pressureconditions as a function of volumetric flow.

The effective characteristic map range of theexhaust turbocharger is limited by

Surge line

Choke line

Maximum permissible turbine speed

The graphic shows an example of the limits fordifferent design layouts of the exhaustturbocharger. For instance, the exhaustturbocharger reaches the surge limit (1) at acompressor efficiency of 0.60. At the samecompressor efficiency of 0.60, the choke lineforms the right marking of the limitation V=0.60 (13).

5 - Compressor characteristic map

Index Explanation

1 Surge line

2 Turbine speed 60,000 rpm







9 V= 0.75

10 V= 0.70

11 V= 0.68

12 V= 0.65

13 V= 0.60

V= Compressor efficiency, limit on theright-hand side corresponds to the chokeline


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Surge line

The flow detaches from the compressorblades (3) at too low a volumetric flow and toohigh a pressure, thus interrupting the delivery.Due to the vacuum on the intake side, the airflows backwards through the compressor (2)until stable pressure conditions are re-established and the air flows in forwarddirection again.

The pressure builds up again and theprocedure is repeated in rapid sequence. Theterm "search" is derived from the resultingnoise.

Choke line

The maximum volumetric flow (2) of theexhaust turbocharger is limited by the crosssection at the compressor inlet. No matterhow much the speed is raised, the throughputcannot be increased beyond a certain value.This value is reached when the air in the wheelinlet reaches the speed of sound (3).

6 - Surge line

Index Explanation

1 Impeller

2 Air flow

3 Flow stall

7 - Choke line

Index Explanation

1 Impeller

2 Volumetric flow

3 Flow at the speed of sound


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Swirler

The swirler improves the flow at thecompressor blades. The swirler shifts thesurge line thus improving pressure build-up.

The angle at which the air flowhits the impelleris changed so that the flow adapts moreeffectively to the compressor blades. Thismeans flow stall (surge line) occurs later.

The graphic shows that the air flow (2) hits thecompressor blade (1)at angle of incidence (3).Flow stall (4) can occur under certainconditions.

The following graphic shows the effect of theswirler under the same operating conditions.

The swirler changes the angle of incidence (3)causing the flow (5) to pass close against theturbine blade.

The swirler isbased ona flexibledesign sothatthis function is achieved under variousoperating conditions. The following graphicsshow the swirler in operation in the rangeclose to idle speed and under full load.

8 - Exhaust turbocharger without swirler

Index Explanation

1 Compressor blade

2 Air flow

3 Flow angle of incidence

4 Flow stall

9 - Exhaust turbocharger with swirler

Index Explanation

1 Compressor blade

2 Air flow

3 Flow angle of incidence

5 Flow


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The swirler increases efficiency and reducesflow noise. The reason for this is that theswirler rotates the intake air into the impellerthus reducing the resistance of the intake air.This gives rise to the advantage of theturbocharging responding earlier from idlespeed. The air resistance through the swirlerwould increase substantially at higher speeds,however, this is avoided by the flexibledeformation of the swirler.

10 - Swirler at idle speed

11 - Swirler at full load


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Intercooler

Overview

The temperature of the air increases as the airis compressed in the exhaust turbocharger.This causes the air to expand. This effectundermines the benefits of the exhaustturbocharger because less oxygen can bedelivered to the combustion chamber. Theintercooler cools the compressed air, the air'sdensity increases and thus more oxygen can

be delivered to the combustion chamber.On BMW diesel engines, charge air is cooledexclusively by fresh air with an air-to-air heatexchanger. The charge air cooling rate greatlydepends on thevehicle speed, temperature ofthe incoming fresh air and the design of theintercooler.

The main purpose of turbocharging in a dieselengine is to boost output. Since more air isdelivered to the combustion chamber as aconsequence of "forced aspiration", it is alsopossible to have more fuel injected, whichleads to high output yields.

However, the air density and therefore themass of oxygen that can be delivered to thecombustion chamber is reduced because theair heats up, and thus expands, as it iscompressed.

The intercooler counteracts this effectbecause the cooling process increases the

density of the compressed air, i.e. so too theoxygen content per volume.

As a result, a larger volume of fuel-air mixturecan be combusted and converted intomechanical energy.

The intercooler is responsible forreduced intake air temperaturescompared to a vehicle with nointercooler. This means the poweroutputcan be additionallyincreasedas a larger mass of air can beconveyed into the combustionchamber.

12 - Intercooler

Index Explanation

1 Heated charge air

2 Cooled charge air

3 Cool fresh air

4 Heated fresh air


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Examples

Using two examples of the M57D30T2engine, the following table shows the extent

the air is cooled under defined operatingconditions.

Taking the N47D20O0 engine as an example,the following table shows the cooling capacity

at various operating points.

The intercooler is located in the coolingmodule underneath the coolant radiator.Compressed air flows parallel through theintercooler in several plates, around whichcooling air is circulated.

Intercooler, N47D20O0 engine

The entire volume of fresh air that is deliveredto the engine and heated as part of the

turbocharging process is directed through theintercooler.

The intercooler transfers the thermal energyof the charge air to the ambient air thuscooling the charge air.

Mass air flow Charge airtemperature beforeintercooler

Cooling airtemperature

Charge airtemperature afterintercooler

0.17 kg/s 130C 25C 68C

0.18 kg/s 155C 35C 66C

Operating point Mass cooling airflow

Charge air volume Cooling capacity

Driving uphill 4 kg/m2s 300 kg/h approx. 5.8 kW

Vmax 8 kg/m2s 700 kg/h approx. 11.9 kW


A Unfiltered air 6 Boost pressure sensor

B Filtered air 7 Throttle valve

C Heated charge air 8 Charge air temperature sensor

D Cooled charge air 9 EGR in-feed line

1 Intake silencer 10 Charge-air pipe

2 Blow-by gas connection 11 Intercooler

3 Exhaust turbocharger 12 Charge-air pipe

4 Swirl flap actuator 13 Unfiltered air pipe

5 Intake air manifold


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13 - Intake system, N47D20O0 engine


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38

Sensors - air intake system


The hot-film air mass meter is located directlydownstream of the intake silencer. It issecured to its housing. The digital HFM 6 is

used on the current engines.The HFM signal is used as a basis for fuelapportioning and for determining the EGRrate.

A labyrinth (6) makes sure that only the actualair mass is recorded. Thanks to the labyrinth,backflow and pulsation are not registered. Inthis way, the HFM determines the actual airmass irrespective of the air pressure andbackflow.

An electrically heated sensor measuring cell

(7) protrudes into the air flow (4). The sensormeasuring cell is always kept at a constanttemperature. The air flow absorbs air from themeasuring cell. The greater the mass air flow,

the more energy is required to keep thetemperature of the measuring cell constant.

Various sensors are used in the airintake system. These include thehot-film air mass meter, charge airtemperature sensor and the boostpressure sensor. Thesesensors arerequired for the purpose ofcalculatingthe EGRrate,fuel volumeapportioning and for controlling theboost pressure.

14 - Hot-film air mass meter

Index Explanation

1 HFM

2 Measurement tube housing

15 - Sectional view of hot-filmair mass meter


1 Electric connections 5 Partial flow for measurement,

exhaust2 Measurement tube housing 6 Labyrinth

3 Electronic evaluator 7 Sensor measuring cell

4 Mass air flow 8 Sensor housing


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The evaluator electronics (3) digitizes thesensor signals. This digitized sensor signal isthen transferred frequency-modulated to theDDE. In order to be able to compensate for

temperature influences, the air mass signal isreferred to the variable temperature signal.

The HFM is supplied with on-board voltageand connected to earth by the DDE.

16 - HFG signal progression

Index ExplanationA Air mass signal

B Air mass

C Temperature signal

1 Air mass signal (A) as a function of air mass (B) and temperature signal (C)

2 The period duration of the air mass signal (A) decreases as the air mass (B)increases

3 The period duration of the air mass signal (A) is extended as the air mass (B)reduces

4 When the temperature increases (C) and air mass (B) remains constant, the period

duration of the air mass signal (A) is extended in order to compensate fortemperature influences

5 When air mass (B) increases, the period duration of the air mass signal decreaseswhile taking the temperature signal (C) into account


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Charge air temperature sensor

The charge-air temperature sensor recordsthetemperature of thecompressed fresh air. Itis located in the boost-pressure pipe, directlyupstream of the throttle valve.

The charge-air temperature is used as asubstitute value for calculating the air mass.This is used to check the plausibility of thevalue of the HFM. If the HFM fails, thesubstitute value is used to calculate the fuelflow measurement and the EGR rate.

The DDE connects the intake temperaturesensor to earth. A further connection isconnected to a voltage divider circuit in theDDE.

The intake temperature sensor contains atemperature-dependent resistor thatprotrudes into the flow of intake air andassumes the temperature of the intake air.

The resistor has a negative temperaturecoefficient (NTC). This means that the

resistance decreases as temperatureincreases.

The resistor is part of a voltage divider circuitthat receives a 5 V voltage from the DDE. Theelectrical voltage at the resistor is dependenton the air temperature. There is a table storedin the DDE that specifies the correspondingtemperature foreach voltage value;thetable istherefore a solution to compensate for thenon-linear relationship between voltage andtemperature.

The resistance changes in relation to

temperature from approx. 75 kto 87,corresponding to a temperature of -40C to120C.

Boost pressure sensor

The boost pressure sensor is required forboost pressure control. The boost pressuresensor monitors and controls the boostpressure in accordance with a characteristicmap resident in the DDE.

Theboost pressure is also used forcalculatingthe volume of fuel.

The sensor is supplied with a 5 V voltage andconnected to earth by the DDE. The

information is sent to the DDE on a signal line.The evaluation signal fluctuatesdependingonthe pressure. On the M57D30T2 engine, themeasuring range from approx. 0.1 - 0.74 Vcorresponds to an absolute pressure from 50kPa (0.5 bar) to 330 kPa (3.3 bar).

17 - Charge air temperature sensor

18 - Boost pressure sensor


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Throttle valve

Overview

A throttle valve is required in all diesel enginesequipped with a diesel particulate filter. Bythrottling the intake air, the throttle valveensures that the elevated exhaust gastemperatures required for diesel particulatefilter regeneration are achieved.

The throttle valve is closed when the engine isshut down to avoid engine judder. After the

engine has stopped, the throttle valve isreopened.

The throttle valves also serves the additionalfunction of effectively preventing overrevvingof the engine. If the DDE detects overrevvingwithout an increase in the injection volume,the throttle valve will close in order to limit theengine speed. This situation can occur as theresult of combustible substances entering thecombustion chamber. Substances may beengine oil from an exhaust turbocharger withbearing damage. This function can effectivelyprevent major damage to the engine.

The throttle valve is located directly upstreamof the intake manifold.

TheDDEcalculates theposition of thethrottlevalve from theposition of theaccelerator pedaland from the torque requirement of othercontrol units. The DDE controls actuation ofthe throttle valve by means of a PWM signalwith a pulse duty factor of 5 to 95 %.

To achieve optimum control of the throttlevalve, its exact position must be recorded on acontinual basis. The throttle valve position ismonitored contactlessly in the throttle valve

actuator by 2 Hall sensors. The sensor issupplied with a 5 V voltage and connected toearth by the DDE. Two data lines guaranteeredundant feedback of the throttle valveposition to the DDE. The second signal isoutput as the inverse of the first. The DDEevaluates the plausibility of the signal throughsubtraction.

The actuator motor for operating the throttlevalve is designed as a DC motor. It is driven bythe DDE on demand. An H-bridge is used foractivation which makes it possible to drive themotor in the opposite direction. The H-bridge

in the DDE is monitored by the diagnosticssystem.

When no power is applied to the drive unit, thethrottle valve is set, spring-loaded, to anemergency operation position.

The throttle valve is required forregenerating the diesel particulatefilterin orderto increasethe exhausttemperature by intervening in theair-fuel mixture. In addition, thethrottle valve is closed when theengine is shut down in order toreduce shut-down judder.The throttle valve also effectivelyprevents overrevving of the engine.

19 - Throttle valve, M57TU2 engine

Index Explanation

1 Housing

2 Vacuum unit

3 Electric motor with electronics

4 Intake air

5 Connection from intercooler

6 EGR connection


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Intake air manifold

Design

In most cases, the intake manifold is made ofplastic. Inside it, the air is branched off theindividual cylinders. In addition, the ports toeach individual cylinder branch off further intoswirl ports and tangential ports. In the N47engines, both ports are routed along the sideof the cylinder head.

The swirl port ensures reliable swirl in the

combustion chamber, and the tangential port

ensures optimum cylinder charge, which iswhy the tangential port is also referred to as acharge port. The swirl flaps are located in thetangential ports.

The swirl port is identifiable by its almostrectangular cross section, while the tangentialport is round.

The intake manifold distributes thefiltered air coming from the intakesilencer to the individual cylinders.The filtered air per cylinder isadditionally divided in a swirl andtangential port in order to moreeffectively mix the injected fuel withthe fresh air located in thecombustion chamber. Additionalswirl flaps are fitted in eachtangential port for this purpose.

20 - Intake manifold, M67TU engine


1 Intake manifold 5 Actuator motor for swirl flaps

2 EGR port 6 Linkage for swirl flaps

3 Swirl port 7 Swirl flaps

4 Tangential port


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Swirl flaps

Swirl flap (4) closes tangential port (3) toachieve greater turbulence of the air via swirlport (2) in the combustion chamber at lowenginespeeds. With increasing enginespeed,it opens to facilitate charging through thetangential ports.

The following table shows the type ofactivation used for the different engines.

To increase the swirl effect, swirl flaps thatclose tight are used on the M57TU engines.

Electrical actuation makes it possible toassume intermediate positions, thus furtheroptimizing internal mixture formation.

The DDE activates the electric motor bymeans of a pulse width modulated signal.Pulse width modulation enables infinitelyvariable adjustment of the swirl flaps. Theposition of the swirl flaps is defined by acharacteristic map. The position is based onthe driver's load choice, engine speed and thecoolant temperature.

The swirl flaps are varied by a linkage (1) thatis operatedby a DCmotor ora vacuumunit(3).

21 - Intake and exhaust ports

Index Explanation

1 Exhaust port

2 Swirl port

3 Tangential port

4 Swirl flap

Engine Electrical Pneumatic

M67D44O1 X -

M57D30T2 - X

M57TU2 - X

N47D20T0 X -

N47 X -

M47TU2 - X

22 - Swirl flap, M57D30T2 engine

Index Explanation

A Swirl flap, opened

B Swirl flap, closed

1 Linkage

2 Swirl flap

3 Vacuum unit

4 Swirl port

5 Tangential port


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Exhaust manifold

The exhaust manifold conjoins the exhaustopenings in the cylinder head into one orseveral ports and transfers the exhaustgasses. The design layout of the exhaust

manifold has an influence on the output yield.Current exhaust manifolds are made of castiron and sheet steel.

Cast exhaust manifold

The spheroidal graphite cast iron exhaustmanifold (GGG) bundles the exhaust gassescoming from the cylinder head and transfers

them to the exhaust turbocharger. As theexhaust gasses can reach extremely hightemperatures, it is important that the exhaustmanifold is designed correspondinglytemperature-resistant. The exhaustturbocharger is mounted at the outlet of theexhaust manifold. An important advantage of

the cast exhaust manifold is its cost-effectiveproduction and high stability as a support forthe exhaust turbocharger.

Air gap insulated exhaust manifold

An air gap insulated exhaust manifold is usedon the M57TU engines.

Advantages:

Lower weight

Lower heat absorption and thereforequicker response of underfloor catalyticconverter

Favourable exhaust gas flow

Lower heat input in engine compartment

The air gap insulated exhaust manifold ismade up of individual parts (see graphic). Theinner exhaust pipes carry the exhaust gasses.The outer sleeve (second shell) shields heatradiation by means of an air gap between theshells. Due to the thin material used for theinner exhaust pipes, the heat absorptioncapacity is very low. Consequently, the hotexhaust gas reaches the catalytic converterand the diesel particulate filter more quickly.

However, a cast exhaust manifold was againused on the successor engine as it waspossible to eliminate the disadvantage of theslower response of the catalytic converter byarranging it directly downstream of theexhaust turbocharger.

On current diesel engines, theexhaust manifold is made fromspherical graphite cast iron. An airgap insulated exhaust manifold isused on the M57TU engines.

23 - Cast exhaust manifold, M67D44O0 engine

24 - Air gap insulated exhaust manifold, M57TU engine

Index Explanation

A Assembly

B Exploded view


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Exhaust gas recirculation

Overview

The diesel engine normally operates withoutthrottling the intake air. The load is controlledby the injected quantity of fuel. Only a slightfuel surplus is available at full load, ensuringrelatively "clean" combustion. There is anoxygen surplus when the full power output isnot required. Nitrogen oxides (NOx) areproduced in the combustion process at an

increased rate in connection with a surplus ofoxygen. Exhaust gas recirculation is used toreduce these nitrogen oxides.

The average combustion temperature isreduced by adding exhaust gas to the intakeair and therefore to the combustion chamber.This has a positive effect on pollutantemissions.

The following pollutant emissions increase asthe result of air deficiency in connection with alarge volume of recirculated exhaust gas:

Soot

Carbon monoxide

Hydrocarbon

To substantially reduce the nitrogen oxideemissions by means of exhaust gasrecirculation, exact adaptation of the fuelquantity to the available air mass is requiredalso in the partial load range. The recirculatedquantity of exhaust gas must be limited suchthat a sufficient quantity of oxygen is availableto ensure effective combustion of the injectedfuel.

Nitrogen oxides are produced in large

amounts if combustion takes place with an airsurplus andat very high temperatures. Oxygencombines with the nitrogen in the combustionair to form nitrogen monoxide (NO) andnitrogen dioxide (NO2).

The exhaust gas recirculation is occasionallyrequired at idling speed but always in thepartial load range because this is where theengine works with a particularly high airsurplus.

The recirculated exhaust gas, which is mixedwith the fresh air and acts as an inert gas,

serves to achieve the following: A lower oxygen and nitrogen content in the

cylinder,

A reduction in the maximum combustiontemperature of up to 500C. This effect isincreased still further if the recirculatedexhaust gases are cooled.

M57TU2 Engines

Exhaust gas recirculation is used toreduce NOxemissions. The oxygencontent inthe cylinder is reduced by

mixing exhaust gas with the intakeair.Adding exhaust gas meansthereis less oxygen available forcombustion thus reducing thecombustion temperature.

25 - EGR system, M57D30O2 engine

Index Explanation

1 Exhaust manifold

2 EGR cooler

3 EGR valve


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M67D44O1 Engine

The EGR system of the M67D44O2 enginefeatures EGRportscast into thecylinder head.From a flange cast on the exhaust manifold,the exhaust gas is routed via a port integratedin the cylinder head to the EGR valve. Fromthe EGR valve, the exhaust gas is directedthrough a further port integrated in thecylinderhead to the EGR cooler and from here via aport integrated in the cylinder head and a

connecting pipe into the intake system.The EGR cooler is located in the V-space ofthe engine. The EGR valves are mounted onthe cylinder head and the valve seats areintegrated in the cylinder head.

26 - EGR system, M67D44O2 engine


1 Cylinder head 4 Coolant connection2 EGR valve 5 EGR port

3 EGR cooler


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N47D20O0 engine and N47D20T0engine

On the N47 engines, the exhaust gasrecirculation system begins at the exhaustmanifold. There is a connection at the frontend for this purpose. Connected here is the

EGR valve, which controls the volume ofrecirculated exhaust gas.

Located downstream of the EGR valve is theEGR cooler. Its design differs depending onthe power class and equipment. The EGRvalve and the EGR cooler are contained in theEGR module.

The EGR port from the EGR cooler to theintake manifold is cast into the cylinder head.At the intake manifold, the exhaust gas isultimately mixed with the fresh air.

27 - EGR module, N47D20O0 engine


1 EGR cooler 5 EGR bypass actuator

2 EGR path sensor 6 Coolant supply3 EGR valve 7 Coolant return

4 Hot exhaust gas 8 Cooled exhaust gas


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EGR valve

The required quantity of exhaust gas isdirected via the EGR valve to the intakesystem. The EGR valve is operated eitherpneumatically or electrically.

M57 Engines

The EGR valve opens by applying vacuum atvacuum connection (9). The vacuum pressesdiaphragm(1) against spring (10) andtheEGRvalve head is lifted from blade-type sleeve (4).

Exhaust gas (5) can now flow past the EGR

valve head into the intake port. The exhaustgas now mixes with the intake air from throttlevalve (2) and is directed in the form of a freshair-exhaust gas-air mixture (6) to the engine.Theblade-type sleevehastheadvantagethat,when the EGR valve is closed, any depositsformed on the sleeve are removed by theblade shape, ensuring the EGR valve alwayscloses reliably. In this way, a coking ring isprevented from forming on the surface of thevalve seat.

28 - EGR valve, M57 engine


1 Diaphragm 6 Fresh air-exhaust gas-air mixture

2 Intake air from throttle valve 7 Guide sleeve

3 EGR valve head 8 EGR housing

4 Blade-type sleeve 9 Vacuum connection

5 Exhaust gas 10 Spring


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M67D44O1 Engine

The EGR valve of the M67D44O1 engine isoperated by an electric motor. Electricactuation enables extremely precise meteringof the exhaust gas recirculation rate. Since theelectronics cannot withstand the same hightemperatures as the vacuum-controlled EGRvalves, the EGR valves of the M67D44O1

engine are cooled.

Coolant enters cooling channel (2) of the EGRvalve via socket (1). Ball (4) closes off the holenecessary to produce the cooling channel.Stem (3) is moved by the electric motor.

The following graphic shows the design of theEGR valve. Cam disc (2) is moved by electricmotor shaft (10). A springpushesthe cam discback into its initial position. A roller (1) restsagainst the cam disc. The roller transfers themovement of the cam disc to stem (8), thuslifting valve (7) from valve seat (6). The valve istherefore opened and exhaust gas can flowpast the valve into the port to the EGR cooler.Plain bearing (4) provides an adequate seal tothe electric motor and ensures the necessarysmooth movement under various operatingconditions. The electric motor is connected to

the DDE via plug connection (9).

29 - EGR valve, M67D44O1 engine

30 - EGR valve, M67TU engine

Index Explanation

1 Socket

2 Cooling channel

3 Stem

4 Ball

31 - EGR valve, M67TU engine

Index Explanation

1 Roller

2 Cam disc3 Cooling channel

4 Plain bearing

5 Exhaust port

6 Valve seat

7 Valve

8 Stem

9 Plug connection

10 Electric motor shaft


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EGR Bypass valve

The EGR cooler for vehicles with manualtransmission offers a new feature. It isequipped with a bypass valve, which allowsthe exhaust gas to bypass the EGR coolerwhen required.

This is useful in the engine warm-up phase forbringing the catalytic converter up to itsoperating temperature more rapidly.

The bypassvalve isadjustedby a vacuumunit.There are two states only: open and closed.

The vacuum canister is controlled by anelectric changeover valve, which in turn iscontrolled by the DDE.

With no negative pressure, the bypass valve isclosed, i.e. the exhaust gas flows through theEGRcooler. If no negative pressure is present,the bypass valve opens the bypass (locatedinside the housing of the EGR cooler) and atthe same time closes the supply to the EGRcooler.

M57D30O2 in X3

The X3has an exhaust valve (flap) upstream ofthe EGR cooler. This flap is closed when theengine is cold to avoid particles clogging theEGR cooler.

35 - Bypass valve closed andopen


A Bypass valve closed B Bypass valve open


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The turbocharger is driven by the engine'sexhaust gases. The hot, pressurized exhaustgases are directed through the turbine of theexhaust turbocharger, thus producing thedrive force for the compressor.

The intake air is precompressed so that ahigher air mass enters the combustionchamber in the engine. In this way, it ispossible to inject and combust a greaterquantity of fuel, which increases the engine's

power output and torque.

The speeds of the turbine are between100,000 rpm and 200,000 rpm. The exhaustinlet temperature may be up to approx. 900C.

The performance of a turbocharged enginecan reach the levels achieved by a naturallyaspirated engine with significantly morecapacity. However, the boost effect can alsobe used in a small engine to achieve a certainoutput with comparatively reduced

consumption.

Exhaust turbocharger with wastegate

Wastegate

The simplest form of controlling the boostpressure is the bypass on the turbine sidewhich is also known as the wastegate.

The turbine is selected small enough to meetthe requirements in terms of torque at lowengine speeds. Smooth engine operation isthe prerequisite for this system. In this set-up,more exhaust gas than is required fordeveloping the boost pressure is fed to theturbine just before reaching the maximumtorque.

Thewastegateallows exhaust gasto flow pastthe exhaust turbocharger thus limiting theboost pressure.

The wastegate is operated by a diaphragmunit. On the first exhaust turbochargers, thisdiaphragm unit was connected to the intakemanifold. The wastegate was opened onexceeding the boost pressure set at the

control rod and the boost air wascorrespondingly limited.

The exhaust turbocharger consistsof a turbine and compressormounted on a common shaft. Itdevelops speeds of up to 200,000rpm and operates at exhausttemperatures of approx. 900C.Up

to 3 different basic designs ofexhaust turbocharger are used.Theseare the exhaust turbochargerwith wastegate, exhaustturbocharger with VNT and twinturbocharging with twoturbochargers connected in series.


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Since its introduction, the digital dieselelectronics DDE has been responsible formonitoring and controlling the boost pressure.

The layout of the exhaust turbochargers hasnow been redesigned such that the maximumboost pressure is already reached at lowerengine speeds. This now makes it possible to

regulate the boost pressure and adapt it torespective operating conditions over a largerengine speed range.

Comparedto pure pneumaticcontrol that onlylimited the boost pressure at full load, flexibleboost pressure control also makes it possibleto set the optimum boost pressure in thepartial load range.

The boost pressure is optimally set as afunction of various parameters such as thecharge air temperature and start of injection.

The wastegate is operated by a diaphragm

unit. Modulated vacuum is applied to thisdiaphragm unit, ensuring infinitely variablecontrol of the wastegate. The vacuum ismodulated by the electropneumatic pressureconverter (EPDW). The electropneumaticpressure converter is actuated by the DDE.

3 Theoretically, varying the control rod in"wastegate opens later" direction wouldincrease the boost pressure. However, sincethe boost pressure is monitored by the DDEwith the aid of a boost pressure sensor, thischange is detected. A characteristic mapstored in the DDE permits deviations in a

defined range in order to compensate forchanges in operation. If this range is exceededas the result of manual intervention, a fault willbe detected as the result of evaluating thereceived sensor signals in the DDE. Thisstatus is indicated by the emission warninglamp in the instrument cluster. This will resultin a reduction in the boost pressure andtherefore in the engine output. 1

36 - Engine operation line in compressor characteristic map

Index Explanation

A Engine operation line

1 Surge line








9 V= 0.75

10 V= 0.70

11 V= 0.6812 V= 0.65

13 V= 0.60

14 Exhaust turbocharger operationline

V = Throughput/efficiency rate yield limit ontheright-hand side corresponds to thechokeline


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VNT

Variable nozzle turbine(VNT)

In contrast to boost pressure control with thewastegate where the exhaust gas bypassesthe turbine, with the variable nozzle turbinesystem, the entire flow of exhaust gas isalways directed through the turbine.

This is made possible by the variablegeometry of the nozzle turbine, which allowsthe flow cross section to be adapted to theturbine depending on the engine operatingpoint. This variable configuration enableseffective utilization of the entire exhaustenergy, thus improving the efficiency of theexhaust turbocharger and therefore of theengine compared to the wastegate controlsystem.

The position of the guide vanes is varied bytheboostpressure actuator (diaphragm unit orelectricactuator). Theadjustment of thevanesreduces the flow cross section ("s", seefollowinggraphic).Theflow rate of theexhaustgas and thus the exhaust gas pressure actingon the turbine wheel increases. The exhaustgas now additionally acts on the end of theturbine blades thus additionally boosting theefficiency by increasing the leverage.

The transfer of power (efficiencyimprovement) to the turbine wheel andcompressor is therefore increased, particularlyat low engine speeds. The boost pressureincreases and a higher injection rate can beauthorized by the DDE.

As the engine speed increases, the vanes aregradually opened so that the power transfer

always remains in equilibrium at the desiredcharger speed and required boost pressurelevel.

The boost pressure actuator is controlled bythe DDE by means of a pulse width modulatedsignal.

Control rod (1) turns shaft (2) and thereforedisplacement ring (3) which in turn movesguide vanes (4). The position of the vanesaffects the size of the flow cross section to theturbine wheel.

37 - VNT vane mechanism, "closed"

38 - Vane adjustment mechanism

Index Explanation

1 Control rod

2 Shaft

3 Displacement ring

4 Guide vane


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The guide vanes are wide open when a largevolume of exhaust gas now flows through theturbine at high engine speed. The leverage atwhich the exhaust gas hits the turbines is

reduced.

This means that there is an additional degreeof freedom in the optimization ofthermodynamicbehaviourby comparison witha conventional exhaust turbocharger (ATL),which has a permanently constant flow crosssection. Furthermore, the exhaustturbocharger with VNT does not need awastegate valve.

39 - VNT vane mechanism, "open"

40 - Vane adjustment mechanism


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Twin turbocharging

Due to the operating principle as previouslymentioned, the design of a turbochargeralways involves a conflict of objectives.

A small exhaust turbocharger respondsquickly and provides ample torque at lowengine speeds. However, its power output islimited as it quickly reaches the surge andchoke line. Although it can generate highpressures, thevolumetric flow is limited duetoits size.

A large exhaust turbocharger is capable ofproducing high power output levels at highengine speeds. However, it respondssluggishly and is not capable of generating ahigh boost pressure at low engine speeds.

One solution to elevate this conflict ofobjectives is the use of variable nozzle turbinetechnology as implemented in the majority ofBMW dieselengines.Theflow cross section isadapted to the engine operating point byadjusting the vanes of the turbine wheel.Nevertheless, the effect of this system islimited so that the entire operating range of

the engine cannot be optimally covered.The ideal solution would be to have twoexhaust turbochargers. One smallturbocharger forquick response andonelargeturbocharger for maximum output yield.

Precisely this configuration has now beendevelopedforBMWtwin turbo dieselengines.Two series-connected exhaust turbochargersare used. A small turbocharger for the highpressure stage and a larger turbocharger forthe low pressure stage. The twoturbochargers do not have variable vanes.

The two turbochargers can be variablycombined providing an optimum for the entireoperating range. This interplay is madepossible by various flaps and valves.

These are:

Turbine control valve (exhaust side)

Compressor bypass valve (air side)

Wastegate (exhaust side)

41 - Advantages of two-stage exhaust turbocharging

Index Explanation

P Engine output

t Response characteristic

Engine Boost pressure(absolute) [bar]

N47D20T0 3.0

N47 2.6

M57D30T1 2.85

M57D30T2 2.95


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Design in 3D animation

To aid understanding, the design and the flapposition are replicated by means of thefollowing animation.

The animation is started by clicking on thegraphic with your mouse.

The buttons underneath the graphic can beused to control the flap position as a functionof the engine speed range.

The animation is supported by Adobe Readerversion 7.08 or more recent versions.


1 High-pressure stage 5 Compressor bypass valve

2 Low-pressure stage 6 Vacuum canister for thecompressor bypass valve

3 Turbine control valve 7 Wastegate valve

4 Vacuum canister for theturbine control valve

8 Vacuum canister for thewastegate valve


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High pressure stage

The high pressure stage is the smaller of thetwo exhaust turbochargers. This is designedas a so-called "integral manifold" as thehousing for the exhaust turbocharger and theexhaust manifold are one single cast unit.

The high pressure stage is not connected by avalve.

The oil inlet and outlet provides the necessarylubrication of the bearing.

Low pressure stage

The large exhaust turbocharger houses theturbine control valve and wastegate. It ismounted on the exhaust manifold and isadditionally supported against the crankcase.The low pressure stage also has a separate oilsupply for the bearing.

Turbine control valve

The turbine control valve opens a bypasschannel on the exhaust side to the lowpressure stage (past the high pressure stage).It is operated pneumatically by a vacuum unitand can be variably adjusted.

An electropneumatic pressure converter(EPDW) applies vacuum to the vacuum unit.

In development, the turbine control valve isreferred to as the main control valve.

42 - High pressure stage, N47D20T0 engine

43 - Low pressure stage, N47D20T0 engine

44 - Turbine control valve, N47D20T0 engine


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Compressor bypass valve

The compressor bypass valve controls thebypass of the high pressure stage on the airintake side. It is operated pneumatically by avacuum unit. The compressor bypass valve iseither fully opened or completely closed.

An electric changeover valve (EUV) appliesvacuum to the vacuum unit.

Wastegate

On reaching the nominal engine output, thewastegate opens to avoid high boost andturbine pressures. A part of the exhaust gasflows via the tailgate past the turbine of the lowpressure stage. It is operated pneumatically bya vacuum unit. The wastegate can be variableadjusted.

An electropneumatic pressure converter(EPDW) applies vacuum to the vacuum unit.

45 - Compressor bypass valve, N47D20T0 engine46 - Wastegate, N47D20T0 engine


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Sensors - exhaust system

Exhaust temperature sensor

TheDDE requires theexhaust temperature forcontrolling regeneration of the dieselparticulate filter. The exhaust temperaturesensor is designed as an NTC resistor sensor(the resistance decreases as temperatureincreases).

3 The electrical supply line must not besubjected to a pulling force of more than 80 N.Sensors that have been dropped must not beused again. 1

Version with 2 exhaust temperaturesensors (EURO3 + EURO4)

One exhaust temperature sensor is locatedupstream of the oxidation catalytic converterand the other upstream of the dieselparticulate filter.

An exhaust temperature in excessof 240 C is

required for regenerating the filter. Initiatingthe filter generation procedure attemperatures below 240C would producewhite smoke caused by excess hydrocarbon(HC). The exhaust temperature sensorupstream of the oxidation catalytic converterensures the regeneration procedure is onlyenabled at temperatures above 240C.

The exhaust temperature upstream of thediesel particulate filter is registered in order tocontrol post-injection and therefore theexhaust temperature itself ahead of the dieselparticulate filter. Depending on the type of

vehicle, the exhaust temperature sensorupstream of the diesel particulate filter sets atemperature between 580C - 610C basedon the post-injection volume.

Three different types of sensor areused in the exhaust system. Thesesensors detect the exhausttemperature, exhaust backpressureand exhaust composition (oxygensensor). The location and numberofexhaust temperature sensors varydepending on the type of vehicle.

Temperatur

e

Resistance Voltage

-40C approx. 96 k approx.4.95V

0C approx. 30 k approx.4.84V

+100C approx. 2.79 k approx.3.68V

+800C approx. 31.7 k approx.0.15V


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47 - E60 Exhaust system with M57D30O1 engine


1 Exhaust temperature sensor 5 Exhaust temperature sensor

2 Oxygen sensor 6 Oxidation catalytic converter

3 Connecting pipe, exhaustbackpressure sensor

7 Diesel particulate filter

4 Exhaust backpressure sensor

48 - Catalytic converter and DPF with sensors, M67D44O1 engine

Index Explanation

1 Exhaust backpressure connection

2 Oxygen sensor

3 Exhaust temperature sensor


5 Oxidation catalytic converter



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Exhaust system with one exhausttemperature sensor (EURO4)

In line with the introduction of the oxidationcatalytic converter and the diesel particulatefilter in one housing, only one exhausttemperature sensor upstream of the oxidationcatalytic converter was used. The sensor

upstream of the diesel particulate filter isreplaced by a characteristic map in the DDE.Currently, however, a second exhausttemperature sensor is again used upstream ofthe dieselparticulate filteras thecharacteristicmap cannot provide the required degree ofaccuracy.

Oxygen sensor

More stringent exhaust emission limits haverendered necessary more accurate control of

the exhaust gasses. The mean quantityadaptation (MMA) makes it possible to complywith the specified limits with a correspondingsafety margin. This is necessary as theemission limits must still be maintaineddespite component tolerances and operatinginfluences.

With mean quantity value adaptation the fuel-air ration (lambda) is adjusted bycorresponding adaptation of the exhaust gasrecirculation. This feature compensates forany inaccuracies relating to manufacturingtolerances of the hot-film air mass meter or of

the fuel injectors. This function was used forthe first time on the E83 with the M57TUengine.

An injection volume averaged across allcylinders is calculated from the fuel-air rationmeasured by the oxygen sensor and the airmass measured by the HFM. This value iscompared with the injection volume specifiedby the DDE. If a discrepancy is detected, thefresh air mass is adapted to match the actual

injection volume by correspondingly adjustingthe EGR valve, thus establishing the correct

fuel-air ratio.TheMMA is notan "instantaneous" regulationbut an adaptive learning process. In otherwords, the injection volume error is taught intoan adaptive characteristic map that ispermanently stored in the control unit.

3 The MMA characteristic map must bereset with the aid of the BMW diagnosissystem after replacing one of the followingcomponents:


Fuel injector(s)

Rail-pressure sensor1

For optimum combustion, a diesel engine isoperated with a fuel-air ratio of> 1, i.e. richinoxygen.= 1 signifies a mixture of 1 kg fuelwith 14.5 kg air.

The oxygen sensor is located at the inlet to theshared housing of the diesel particulate filter(DPF) and oxidation catalytic converter.


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Control sensor with rising characteristic

The control sensor with rising characteristic isa type LSU 4.9 broadband oxygen sensorsupplied by Bosch. This broadband oxygensensor is installed upstream of the catalyticconverter close to the engine.

The oxygen concentration in the exhaust gascan be determined over a large range with thebroadband oxygen sensor. This makes itpossible to determine the fuel-air ratio in thecombustion chamber.

The broadband oxygen sensor is capable ofproviding accurate measurements not only at= 1 but also at< 1 (rich) and> 1 (lean).The broadband oxygen sensor supplies adistinct, steady-state electrical signal from =0.7 to=( = air).

The oxygen sensor is connected by 5 lines tothe connector housing. The followingconnections lead into the housing:

Pump current, positive

Pump current and Nernst voltage, negative

Heating, negative

Heating, positive

Nernst voltage, positive

3 A compensating resistor thatcompensates for production tolerances isintegrated in the oxygen sensor connector.This resistor is connected to a free contact.1

The measuring cell of the broadband oxygensensor is a zirconium dioxide ceramic materialZrO2. It is designed as the combination of aNernst concentration cell (sensor cell with the

function of an oxygen sensor with erraticcharacteristic) and an oxygen pump cell thattransports oxygen ions.

The oxygen pump cell (items 7, 11 and 12)and the Nernst concentration cell (items 4, 5and 6) are arranged such that there is adiffusion gap (8) of about 10 to 50mbetween them. The diffusion gap isconnected via an exhaust inlet hole (9) to theexhaust gas. On the one side, the Nernstconcentration cell is connectedviaa referenceair channel (3) and opening to the surroundingatmosphere. On theother side, it is exposed tothe exhaust gas over a diffusion gap (8).

The exhaust gas passes through the gas inlethole and enters the diffusion gap of the Nernst

concentration cell. Initially, the same oxygenconcentration as in the exhaust gas isestablished in the diffusion gap. In order toachieve= 1 in the diffusion gap, the Nernstconcentration cell compares the exhaust gasin the diffusion gap with the ambient air in thereference air channel.

3 It is extremely importantto ensure that thecable connection to the oxygen sensor is freeof soiling so that the ambient air can enter thereference air channel. It is therefore necessaryto protect the plug connection from soiling,washing agents, preservatives etc.1

49 - Control sensor with rising characteristic


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50 - Design of broadbandoxygen sensor


1 Insulation layer 8 Diffusion gap

2 Heating element 9 Porous diffusion barrier

3 Reference air channel 10 Exhaust inlet hole

4 Inner electrode, reference cell 11 Ceramic layer made of ZrO2

5 Ceramic layer made of ZrO2 12 Outer electrode, oxygen pump cell

6 Outer electrode reference cell 13 Protective layer

7 Inner electrode, oxygen pump cell


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By applying a pump voltage to the outerelectrode (2) and inner electrode (3) of theoxygen pump cell, oxygen can be pumped inor out from the exhaust gas through theporous diffusion barrier into the diffusion gap.An evaluator circuit (9) in theDDE controls thisvoltage applied at the pump cell with the aid ofthe Nernst concentration cell such that thecomposition of the gas in the diffusion gap isalways at a constant= 1. In the case ofexhaust gasfrom lean combustion, theoxygenpump cell pumps the oxygen ions out of the

diffusion gap. Conversely, in the case ofexhaust gas from rich combustion, the oxygenions, resulting from catalytic decomposition ofCO2and H2O at the outer electrode of thepump cell, are pumped out of the surroundingexhaust gas into the diffusion gap. No oxygenions need to be transported at= 1. Thepump current is zero. The pump current isproportional to theoxygen ionconcentration inthe exhaust air and therefore a measure for thefuel-air ratio.

51 - Broadband oxygen sensor with lean mixture


1 Exhaust pipe 7 Connection, oxygen sensorheater, negative

2 Connection, outer electrode of oxygen pump cell, positive

8 Pump current in mA(red = positive)

3 Connection, inner electrode of oxygen pump cell, negative

9 Evaluator circuit

4 Connection, outer electrode of reference cell, negative

10 Reference voltage in V (< 450 mV= blue)

5 Connection, inner electrode of reference cell, positive

11 Oxygen ion flow initiated by pumpcurrent

6 Connection, oxygen sensorheater, positive

O2 Oxygen ions


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52 - Broadband oxygen sensor with rich mixture


1 Exhaust pipe 7 Connection, oxygen sensorheater, negative

2 Connection, outer electrode of oxygen pump cell, positive

8 Pump current in mA(blue = negative)

3 Connection, outer electrode of oxygen pump cell, negative

9 Evaluator circuit

4 Connection, outer electrode of reference cell, negative

10 Reference voltage in V(> 450 mV = red)

5 Connection, inner electrode of reference cell, positive

11 Oxygen ion flow initiated by pumpcurrent

6 Connection, oxygen sensorheater, positive

O2 Oxygen ions


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Exhaust backpressure sensor

The DDE requires the exhaust backpressuresensor for controlling regeneration of thediesel particulate filter.

The exhaust backpressure sensor isconnected by means of a hose to the exhaustsystem after the oxidation catalytic converterand before the diesel particulate filter. Thereason for the distance from the exhaustsystem is the high temperatures radiated bythe exhaust system and impurities that couldotherwise affect the sensor element. Thehose connection must face downward. Thesensor is mounted on the engine.

The exhaust back pressure sensor measuresthe pressure ahead of the diesel particulatefilter. The DDE will initiate regeneration of thediesel particulate filter if the pressure risesabove a permissible value.

The exhaust backpressure is applied to thediaphragm with the sensor element (piezo-element). Ambient pressure acts on the otherside of the diaphragm. The deflection of thediaphragmis convertedby thesensorelementinto an electrical signal. The evaluator circuitprocesses the signal and sends an analoguevoltage signal to the DDE. The voltage signalis applied in linear form as the exhaustbackpressure increases.

3 If the sensor fails, the DDE initiates filterregeneration every 500 km and a fault codeentry is stored in the DDE.1

54 - Pump current/fuel-air ratio diagram

Index Explanation

A Characteristic curve

1 Fuel-air ratio

2 Pump current

Absolute pressure Voltage

0.6 bar approx. 1.9 V

1.0 bar approx. 2.65 V2.0 bar approx. 4.5 V


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Oxidation catalytic converter

Design and function

The oxidation catalytic converter isaccommodated in a stainless steel housingand is firmly embedded in a damping mat.

A monolith (ceramic body) or metal substrateserves as the carrier.

An important factor is to ensure as large asurface as possible so that large quantities of

exhaust gas can be processed. The substrateis made up of thousands of channels (pores)through which the exhaust gas flows. Thechannels are approx. 1 mm wide.

Ceramic substrate

The walls of the monolith are extremely thin tominimize resistance to flow. The walls are onlyapprox. 0.3 mm thick.

The advantages of the ceramic substrate arethe improved recovery of the precious metals,

the cost-effective manufacture and the moreconstant operating temperature.

The ceramic substrate is made of magnesiumaluminium silicate with low thermal expansionand high heat resistance. The melting point isabove 1400C.

The oxidation catalytic converterreduces hydrocarbons and carbonmonoxide under all operatingconditions. An importantcharacteristic is its rapid response.Its location varies depending on thetype of vehicle and version.

55 - Catalytic converter and DPF with sensors, M67D44O1 engine

Index Explanation

1 Exhaust backpressure connection

2 Oxygen sensor3 Exhaust temperature sensor


5 Oxidation catalytic converter


56 - Ceramic substrate


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Metal substrate

The risk of mechanical damage or burn-through is lower with the metal substrate andthe wall thickness can be reduced to approx.0.05 mm. The metal substrate is made fromextremely thin steel foil.

The advantages of the metal substrate can befound in its impact resistance, heat resistance,short heating-up phase and the lowerbackpressure.

Design

An intermediate layer (2), consisting ofaluminium oxide (Al2O3) with promoters, isapplied on the ceramic substrate (1) or metal

substrate (1) to increase the available surface.This intermediate layer increases the effectivesurface of the monolith by a factor of 700. Theoxygen storage capability is also increased.Thepromotersboost thecatalyticeffectof theactive noble metal layer.This noble metal layer(3) is vaporized microscopically thin onto theintermediate layer. The noble metal used forthis purpose in oxidation catalytic convertersfor diesel engines is platinum and possiblypalladium which enhance the

Documents

Diesel Air Intake and Exhaust System