BMW M3 · the new BMW M3, which is a sport coupe absolutely tuned for everyday driving and at the same time performing like a thorough- bred sports car. BMW M GmbH, a company within

The Exhaust SystemThe Exhaust SystemThe Exhaust SystemThe Exhaust SystemThe Exhaust Systemfor the Newfor the Newfor the Newfor the Newfor the NewBMW M3

Development Exhaust System

By Christian Eichmueller, Gerhard Hofstetter,By Christian Eichmueller, Gerhard Hofstetter,By Christian Eichmueller, Gerhard Hofstetter,By Christian Eichmueller, Gerhard Hofstetter,By Christian Eichmueller, Gerhard Hofstetter,Winfried Willeke and Peter GaucheclWinfried Willeke and Peter GaucheclWinfried Willeke and Peter GaucheclWinfried Willeke and Peter GaucheclWinfried Willeke and Peter Gauchecl

In connection with BMW, the letter M has stood for exceptionalIn connection with BMW, the letter M has stood for exceptionalIn connection with BMW, the letter M has stood for exceptionalIn connection with BMW, the letter M has stood for exceptionalIn connection with BMW, the letter M has stood for exceptionalsports vehicles since 1978. This tradition is being continued withsports vehicles since 1978. This tradition is being continued withsports vehicles since 1978. This tradition is being continued withsports vehicles since 1978. This tradition is being continued withsports vehicles since 1978. This tradition is being continued withthe new BMW M3, which is a sport coupe absolutely tuned forthe new BMW M3, which is a sport coupe absolutely tuned forthe new BMW M3, which is a sport coupe absolutely tuned forthe new BMW M3, which is a sport coupe absolutely tuned forthe new BMW M3, which is a sport coupe absolutely tuned foreveryday driving and at the same time performing like a thorough-everyday driving and at the same time performing like a thorough-everyday driving and at the same time performing like a thorough-everyday driving and at the same time performing like a thorough-everyday driving and at the same time performing like a thorough-bred sports car. BMW M GmbH, a company within the BMWbred sports car. BMW M GmbH, a company within the BMWbred sports car. BMW M GmbH, a company within the BMWbred sports car. BMW M GmbH, a company within the BMWbred sports car. BMW M GmbH, a company within the BMWGROUP, has developed the M3. At the heart of the M3 is theGROUP, has developed the M3. At the heart of the M3 is theGROUP, has developed the M3. At the heart of the M3 is theGROUP, has developed the M3. At the heart of the M3 is theGROUP, has developed the M3. At the heart of the M3 is theequally new, high-revving inline six cylinder naturally aspiratedequally new, high-revving inline six cylinder naturally aspiratedequally new, high-revving inline six cylinder naturally aspiratedequally new, high-revving inline six cylinder naturally aspiratedequally new, high-revving inline six cylinder naturally aspiratedengine. From a displacement of 3,246 cc, the engine achieves aengine. From a displacement of 3,246 cc, the engine achieves aengine. From a displacement of 3,246 cc, the engine achieves aengine. From a displacement of 3,246 cc, the engine achieves aengine. From a displacement of 3,246 cc, the engine achieves apower output of 252 kW (343 bhp) at 7,900 rpm. With a specificpower output of 252 kW (343 bhp) at 7,900 rpm. With a specificpower output of 252 kW (343 bhp) at 7,900 rpm. With a specificpower output of 252 kW (343 bhp) at 7,900 rpm. With a specificpower output of 252 kW (343 bhp) at 7,900 rpm. With a specificoutput of 105.7 bhp/litre and a broad usable speed range, thisoutput of 105.7 bhp/litre and a broad usable speed range, thisoutput of 105.7 bhp/litre and a broad usable speed range, thisoutput of 105.7 bhp/litre and a broad usable speed range, thisoutput of 105.7 bhp/litre and a broad usable speed range, thishigh-speed engine represents the very best in naturally aspiratedhigh-speed engine represents the very best in naturally aspiratedhigh-speed engine represents the very best in naturally aspiratedhigh-speed engine represents the very best in naturally aspiratedhigh-speed engine represents the very best in naturally aspiratedengine design. The realization of the high engine-speed conceptengine design. The realization of the high engine-speed conceptengine design. The realization of the high engine-speed conceptengine design. The realization of the high engine-speed conceptengine design. The realization of the high engine-speed conceptrequired highly innovative development of the engine’s specificrequired highly innovative development of the engine’s specificrequired highly innovative development of the engine’s specificrequired highly innovative development of the engine’s specificrequired highly innovative development of the engine’s specificfunctional elements. The design of the new exhaust system wasfunctional elements. The design of the new exhaust system wasfunctional elements. The design of the new exhaust system wasfunctional elements. The design of the new exhaust system wasfunctional elements. The design of the new exhaust system wastherefore perceived as a special challenge.therefore perceived as a special challenge.therefore perceived as a special challenge.therefore perceived as a special challenge.therefore perceived as a special challenge.

The new BMW M3’s exhaust systembegan with the premise of justifyingthe special vehicle concept. The newBMW M3’s dynamic road perfor-

mance and the high-speed design ofthe engine represent a major stressfactor with regard to the strength ofthe exhaust system. The exhaustsystem’s necessary lightweight con-struction and the confined assemblysituation on the vehicle (Figure 1)(Figure 1)(Figure 1)(Figure 1)(Figure 1) also

complicate the design. The engineerstherefore set themselves the task ofmitigating conflicts of objectives anddeveloping technical solutions thatmatch the vehicle concept, as well asappeal to customers. Developmentof the new M3 exhaust system wasdefined by BMW M and brought toseries-production readiness in coop-eration with the manufacturerArvinMeritor. ArvinMeritor developsand manufactures exhaust systemsfor the automotive industry at its pro-duction center in Finnentrop (North-Rhine Westphalia, Germany).

11111 IntroductionIntroductionIntroductionIntroductionIntroductionThe Exhaust System for the NewThe Exhaust System for the NewThe Exhaust System for the NewThe Exhaust System for the NewThe Exhaust System for the NewBMW M3BMW M3BMW M3BMW M3BMW M3

The Exhaust Systemfor the New BMW M3The Exhaust Systemfor the New BMW M3

Rear end view of BMW M3Rear end view of BMW M3Rear end view of BMW M3Rear end view of BMW M3Rear end view of BMW M3

DevelopmentExhaust System

The following development aimswere defined for the new exhaustsystem:

• Optimizing the gas exchange withthe exhaust system

• Consistent lightweight construction(target weight < 50 kg)

• Limitation of the heat capacity inthe manifold, down pipe andcatalytic converter areas

• Compliance with emissionregulations (exhaust, noise)

• Characteristic sporting exhaustsound

• Restrained, but sporting interioracoustics

• Crash-optimized exhaust tailpipesin BMW M look

• Long-term BMW quality• Economical manufacture• Exhaust manifold and catalytic

converter usable as identical partson the BMW M3, BMW M Roadsterand M Coupe

22222 Development AimsDevelopment AimsDevelopment AimsDevelopment AimsDevelopment Aims

33333 DesignDesignDesignDesignDesignTo achieve these development aims,the exhaust manifold and exhaust

44444 Component DesignComponent DesignComponent DesignComponent DesignComponent Design

4.1 Exhaust Manifold4.1 Exhaust Manifold4.1 Exhaust Manifold4.1 Exhaust Manifold4.1 Exhaust Manifold

system as well as all the mountingand attachment elements werenewly designed. The 3D datacreated at BMW M with the CATIACAD system is used throughout theprocess chain (analysis, DMU,manufacturing, quality assurance).The direct further application ofCAD data served as a basis for ashort, effective developmentperiod.

The design of the exhaust manifoldwas consistent with calculated gasexchange requirements. The M3engine therefore has tubular ex-haust manifolds, such as are nor-mally only to be found on racingengines. (Figure 2)(Figure 2)(Figure 2)(Figure 2)(Figure 2)

The exhaust gas flow from theexhaust ports to the collector pipesis in six individual primary pipes ofidentical length. A succession ofpressure and induction waves in theexhaust pipe correctly phased to thevalve timing is the precondition forgood gas exchange. Exhaust from

Figure 1: Platform with exhaust systemFigure 1: Platform with exhaust systemFigure 1: Platform with exhaust systemFigure 1: Platform with exhaust systemFigure 1: Platform with exhaust system

Figure 2: Exhaust manifold (ECE)Figure 2: Exhaust manifold (ECE)Figure 2: Exhaust manifold (ECE)Figure 2: Exhaust manifold (ECE)Figure 2: Exhaust manifold (ECE)


cylinders or primary pipes is there-fore only led to common collectorpipes if the relevant exhaust valveopening times do not overlap at allor only slightly. Because of theengine’s firing order (1-5-3-6-2-4),the three cylinders 1-2-3 and 4-5-6,respectively, were therefore led to acommon collector pipe.

The exhaust manifold pipes aremanufactured by internalhigh-pressure molding (IHU). Incooperation with ArvinMeritor, theworld’s first tubular manifold wasproduced by this process back in1992 for the M3 model then beingmanufactured.

This prior knowledge was drawn onand further refined for the new BMWM3’s exhaust manifolds. All primaryand secondary pipes are in onepiece, despite the complex molding,so that many sockets and their weldseams disappear, and, conversely,fewer obstructions arise in theexhaust flow. In addition, a cross-sectional reduction in the pipes isavoided, since nether folds norflattened bends occur in manufac-ture.

The considerable cold hardening inthe IHU process yields a stable,lightweight construction. A wallthickness of only 1 mm is sufficientfor the exhaust manifold. The thin-walled design limits thermal inertia

when heated up. This was a majorprecondition to improve the light-offperformance of the catalytic con-verter.

To avoid further heat reduction andreduce component weight, allconnecting flanges were of new,lightweight design. The flanges areformed in such a way that thelowest amount of mass is directlycoupled to the piping. The patentedflanges for attachment to the cylin-der head were, in contrast to theprevious model, converted fromprecision castings to sheet metal,and the number of mounting screwsfor each reduced from four to three.(Figure 3)(Figure 3)(Figure 3)(Figure 3)(Figure 3) This results in a weightsaving in detail of more than 66%,as well as better pressure distribu-tion at the sealing face.

Sheet metal flanges instead of

forged flanges are also used at theconnection to the exhaust system.Here, a weight saving of 50 percentis achieved. By integrating linearand angular compensation for theabsorption of heat expansion andassembly tolerances an expensivecorrugated pipe compensator canthus be avoided.

As the sheet metal flanges repre-sent a completely new development,they first had to prove their worthwith regard to strength, distortionand sealing.

Despite its complex shape, theexhaust manifold is suitable for usein both left-hand and right-handdrive vehicles. As the BMW M3’snew engine will also be installed inthe future in the BMW M Roadsterand M Coupe, the installationconditions for these vehicles alsohad to be taken into account.

For the U.S. model, a differentexhaust manifold was developed.Because of the position of thecatalytic converter next to theengine, a different pipe layout fromthe ECE model has been devel-oped, but the design featuresresemble the ECE version.

4.2 Exhaust System and Silencer

The twin-pipe exhaust flow wasmaintained up to the rear silencers,

Figure 3: Mounting flanges (old / new)Figure 3: Mounting flanges (old / new)Figure 3: Mounting flanges (old / new)Figure 3: Mounting flanges (old / new)Figure 3: Mounting flanges (old / new)

Christian Eichmueller Winfried Willeke

Peter GauchelGerhard Hofstetter

The AuthorsThe AuthorsThe AuthorsThe AuthorsThe Authors


in view of the resulting gas ex-change benefits. In order to reduceexhaust backpressure, the compo-nents were designed to be as freeof throttling effects as possible.

4.2.1. Front Pipes with Catalytic4.2.1. Front Pipes with Catalytic4.2.1. Front Pipes with Catalytic4.2.1. Front Pipes with Catalytic4.2.1. Front Pipes with CatalyticConverterConverterConverterConverterConverter

A closed-loop, three-way catalyticconverter is integrated into each ofthe two pipe runs for the purificationof exhaust emissions. Two cylindri-cal metal monoliths from the com-pany EMITEC are arranged insequence for each catalytic con-verter. The main design prioritieswere the conversion rate, rapid lightoff and limitation of pressure losses.These requirements were met witha low number of cells (200 persquare inch), reduced foil gauge(40µm) and a three-metal coatingfrom the Engelhard Company.

In order to permit a reduction in foilthickness without affecting strength,the winding of the metal monolith(SM design) was improved. Thecatalytic converter’s endurance isconsiderably higher as a result of a

higher natural frequency, a greateraxial secondary moment of inertia,more homogeneous radial rigidityand the larger brazing surfacebetween the matrix and the jacket.

IHU pipes are used for the flow tothe catalytic converters. Thistechnology enabled the requiredcross-section for the twin-flowexhaust system and free-flowingtransitions (diffusers) to be realized.

After the catalytic converters, aninterference pipe connects the twopipe runs. This cross-coupling pointleads to an increase in torque atmedium engine speeds.

4.2.2. Exhaust Pipe with Interme-4.2.2. Exhaust Pipe with Interme-4.2.2. Exhaust Pipe with Interme-4.2.2. Exhaust Pipe with Interme-4.2.2. Exhaust Pipe with Interme-diate Silencerdiate Silencerdiate Silencerdiate Silencerdiate Silencer

The required cross-sections in therear axle area could only be ob-tained by means of special IHmolded pipes. Because of the highdegree of cold hardening duringmanufacture, there is no reductionin strength despite the thin walls. Afurther step in the direction oflightweight construction can thus beachieved. The intermediate silencerhas a volume of 1.8 dm3. The one-piece outer casing is double-walled.

4.2.3. Rear Silencer4.2.3. Rear Silencer4.2.3. Rear Silencer4.2.3. Rear Silencer4.2.3. Rear Silencer

To improve the gas flow, gas col-umn oscillations of broad amplitudeare necessary, whereas, the silenc-ing requires the smoothing out ofthese vibration in the exhaust flow tobe as uniform as possible. TheM3’s rear silencer was thereforemainly designed as an absorptionsilencer, since this construction bestunites both requirements. Selectionof the silencer volume is coupled tothe swept volume (VSD=VHUB) andthe engine’s target values. Foreffective silencing without loss ofperformance, the facto “X” shouldnot be less than 12 times the sweptvolume.

Only be means of a modification ofthe floor pan specific to the M3could a large-volume rear silencer(40 dm3) be located across andbehind the differential at the rear ofthe car.

The rear silencer housing consistsof two deep-drawn sheet metal half-shells. These are welded togetherafter the internal components havebeen installed. In order to avoidstructure-borne noise, curved, butrelatively large, boundary surfacesare strengthened by swage-linesand panels. Only glass (Advantex)is used as an absorption material forthe M3. This material combineshigh acoustic silencing propertieswith lasting quality at low weight. Toattenuate the ignition frequencies,one chamber of the rear silenceracts as a resonator. The twinexhaust flows are divided to obtainthe four tailpipes in this chamber. Itwas necessary in particular to testthe new form and installation of thelarge-volume, transverse rearsilencer. (Figure 4)(Figure 4)(Figure 4)(Figure 4)(Figure 4)

4.2.4. Exhaust Tailpipes4.2.4. Exhaust Tailpipes4.2.4. Exhaust Tailpipes4.2.4. Exhaust Tailpipes4.2.4. Exhaust Tailpipes

Two pairs of cylindrical, chrome-plated exhaust tailpipes in twocutouts of the bumper trim empha-size the car’s sporting character.

In a rear-end collision, the exhausttailpipes almost inevitably sufferdamage due to their exposedposition. In order to avoid damageto the exhaust system, new tailpipeswere therefore designed and pat-ented especially for the BMW M3.In a rear-end crash at up to 15 km/h, the new tailpipes are preventedfrom retracting towards the exhaustsystem and causing further dam-age. This is achieved by a crumplezone of suitable length inside thetailpipes. (Figure 5 and Figure 6)(Figure 5 and Figure 6)(Figure 5 and Figure 6)(Figure 5 and Figure 6)(Figure 5 and Figure 6)If necessary, the tailpipes can beeasily replaced individually. Thanks

Figure 4: Entire exhaust systemFigure 4: Entire exhaust systemFigure 4: Entire exhaust systemFigure 4: Entire exhaust systemFigure 4: Entire exhaust system


to this customer-friendly solution,the new BMW M3 qualifies for aless expensive insurance category.The new tailpipes were additionallytested in corrosion and crash tests,as well as in thermal shock tests.

4.2.5. Mountings4.2.5. Mountings4.2.5. Mountings4.2.5. Mountings4.2.5. Mountings

The load is distributed throughseveral points, namely two rubbermountings located at the center ofthe exhaust system and three at therear silencer. The combination ofhigh temperatures and transverseacceleration forces, in connectionwith the confined installation condi-tions, requires the rubber mountingsto be very durable. The mountingsin the central area of the exhaustsystem are particularly exposed tohigh dynamic and thermal stresses.

In order to reduce transverse dis-placement, these rubber mountingsare equipped with a metal insert.These mountings not only give theexhaust system the necessarytransverse rigidity, but also preventirritating vibration in the passengerarea. Because of their relativeproximity to the exhaust pipe, therubber mix for the central mountings

was also optimized for greaterresistance to high temperatures. Atconstant stress and maximumvelocity, temperatures of up to 200degrees C are reached at themounting.

Definition of the Shore hardness incombination with the spring steelsheet-metal insert and the contourof the rubber mountings were partlycarried out mathematically (FEMcalculation) and also empirically incooperation with the WEGU Com-pany. The conflict of objectivesbetween strength and acoustics wasideally solved.

4.2.6. Material and Weight4.2.6. Material and Weight4.2.6. Material and Weight4.2.6. Material and Weight4.2.6. Material and Weight

With the exception of the metalmonoliths in the catalytic converter,all metal components in the entireexhaust system are made of high-temperature resistant austeniticstainless steel. Thanks to its highcorrosion and acid resistance, thedurability of the exhaust system hasbeen extended to match the car’slife expectancy.

Although the volume of the silencerhas been increased by over 50

Figure 6: Comparison of exhaust tailFigure 6: Comparison of exhaust tailFigure 6: Comparison of exhaust tailFigure 6: Comparison of exhaust tailFigure 6: Comparison of exhaust tailpipes (new / after crash)pipes (new / after crash)pipes (new / after crash)pipes (new / after crash)pipes (new / after crash)

Figure 5: Section viewFigure 5: Section viewFigure 5: Section viewFigure 5: Section viewFigure 5: Section viewof exhaust tail pipesof exhaust tail pipesof exhaust tail pipesof exhaust tail pipesof exhaust tail pipes

55555 Exhaust Back-pressureExhaust Back-pressureExhaust Back-pressureExhaust Back-pressureExhaust Back-pressure

Due to the largely throttle-freeexhaust pipes and generous dimen-sioning of the catalytic convertersand silencers, pressure loss hasbeen kept down to 300 mbar at8000 rpm (in standard operatingconditions), which is actually 40percent better than on the previousmodel (E36 M3).

66666 Exhaust EmissionsExhaust EmissionsExhaust EmissionsExhaust EmissionsExhaust Emissions

With the measures described hereapplied to the new BMW M3, amajor contribution has been madeto exhaust emission control. TheBMW M3 is well below the EU3exhaust emission limits. (Figure 7) (Figure 7) (Figure 7) (Figure 7) (Figure 7)

percent compared with the previousmodel (E36 M3), the weight of theexhaust system (including theexhaust manifold) has been keepdown to the previous level, i.e.under 50 kg, by systematic weight-saving design.

HCHCHCHCHC COCOCOCOCO NoxNoxNoxNoxNoxBMW M3 Emissions (g/km)BMW M3 Emissions (g/km)BMW M3 Emissions (g/km)BMW M3 Emissions (g/km)BMW M3 Emissions (g/km) 0.0950.0950.0950.0950.095 0.7170.7170.7170.7170.717 0.0260.0260.0260.0260.026Emission Limit for EUSEmission Limit for EUSEmission Limit for EUSEmission Limit for EUSEmission Limit for EUS 0.200.200.200.200.20 2.302.302.302.302.30 0.150.150.150.150.15% of Limit% of Limit% of Limit% of Limit% of Limit 47.747.747.747.747.7 31.231.231.231.231.2 17.417.417.417.417.4

Figure 7: Chart of certificated emissionsFigure 7: Chart of certificated emissionsFigure 7: Chart of certificated emissionsFigure 7: Chart of certificated emissionsFigure 7: Chart of certificated emissions

Blind RivetBlind RivetBlind RivetBlind RivetBlind Rivet

DiffuserDiffuserDiffuserDiffuserDiffuser

StrengtheningStrengtheningStrengtheningStrengtheningStrengtheningRingRingRingRingRing

Crush ZoneCrush ZoneCrush ZoneCrush ZoneCrush Zone


For the USA, placing the catalyticconverters near to the engine en-ables it to meet LEV I compliance.

Figure 8: Test bedFigure 8: Test bedFigure 8: Test bedFigure 8: Test bedFigure 8: Test bed

77777 Endurance TestingEndurance TestingEndurance TestingEndurance TestingEndurance Testing

The new M3’s exhaust system withall its new features had to proveitself time and time again in specialBMW M-specific long-term testingprofiles, both installed on the vehicleas well as in complex rig testing.(Figure 8)(Figure 8)(Figure 8)(Figure 8)(Figure 8)

Heavy-load testing at the BMWproving ground in Miramas in South-ern France, (corresponding to about200,000 km of motorway) and 8,000km under racing conditions on thenorthern loop of the Nuremburgringhad to be completed successfullyseveral times. Acceleration anddeceleration values of up to 1.1 goccur in the longitudinal or trans-

verse directions. Nuremburgringtesting represents 20 times thestress encountered in normal roaduse.

The suitability of the exhaust systemfor day-to-day use, as well as for therequirements specific to eachcountry were tested and validated innumerous long-distance road tests,in situations likely to be encounteredby a customer. After endurancetesting, the function of individualcomponents of the exhaust systemwas tested. The weld seams,sliding fits, the fit of the partitions,the volume of the absorption mate-rial in the rear silencer and thenewly developed flange seals werescrutinized.

By means of operational vibrationanalysis, a statement on the ex-haust system’s resistance to fatiguevibration could be made even at anearly stage of development and anydeficiencies removed.

88888 AcousticsAcousticsAcousticsAcousticsAcoustics

The new BMW M3 was required topossess and indeed enhance thespecific features of its predecessorwith regard to exhaust systemacoustics, i.e.: a fairly robust, sport-ing sound, without sacrificing com-fort.

The following development aimswere set up from this standpoint andknown requirements taken intoaccount:

• Compliance with an external noiselimit of 75 dB(A)

• Lower outlet noise level• Minimizing structure-borne noise• Restrained, but sporting interior

acoustics


8.1 External Noise8.1 External Noise8.1 External Noise8.1 External Noise8.1 External Noise

An added difficulty regarding theexternal noise pattern on the newBMW M3 was the additional re-quirement for performance opti-mized gearbox/axle ratios. The highengine speed in the drive-by mea-surement is generally reflected inthe results as a higher drive-bynoise level. To comply with theexternal noise limit valued accord-ing to Lex Ferrari of 75 dB (A), itwas therefore necessary to optimizeall noise sources on the BMW M3and aim for a balanced distributionbetween them.

The silencing volumes necessaryfor exhaust system acoustics weremade possible by adopting a trans-verse rear silencer. Through spe-cific division into reflection andadsorption sections, the advantagesof broadband and narrow-bandsilencing were combined.

With the aid of the reflection cham-ber, it was possible in particular tooptimize the outlet noise level, i.e.to adapt it in the best possible wayto the firing frequency for the accel-erated drive-by. (Figure 9) (Figure 9) (Figure 9) (Figure 9) (Figure 9) Tuning

of the resonance chamber tookplace empirically in several develop-ment stages.

The motor-sport type of exhaustsound that is a feature of the newBMW M3 was obtained at theintermediate silencer within theframework of the regulations cur-rently in force. The size and posi-tion of the intermediate silencerwere ascertained with close-fieldnoise level measurements. Thelack of adsorption wool makes anadditional contribution to the robustsound.

Radiated noise from the componentsurfaces was reduced considerablyby careful location of swage-lines.Elliptical or circular componentgeometries increase the inherentstability of these components. Withthe exception of the intermediatesilencer, all pipes and silencer unitsare single-walled.

8.2. Interior Acoustics8.2. Interior Acoustics8.2. Interior Acoustics8.2. Interior Acoustics8.2. Interior Acoustics

A sports car like the new BMW M3does not claim to have the quietinterior acoustics of a family car.However, clearly sensed vibration

and unpleasant resonance in theinterior are undesirable. By match-ing the effective tailpipe length tothe rear silencer volume, low fre-quency drumming (< 100Hz), whichmainly irritates rear-seat passen-gers, was considerably reduced.This measure resulted in a synthe-sis of sound and comfort require-ments.

Under load, the exhaust system’sacoustics provide the driver withpowerful, sporting feedback. Thisclear acoustic feedback of theengine’s load and speed status isbacked by full-bodied air intakenoise.

However, the new M3’s exhaustsystem displays its acoustic suitabil-ity for everyday driving in all otheroperating conditions. The M3 canthus be driven comfortably withoutunpleasant noise levels for longerdistances, when necessary.

The mountings have been designedso that no undesirable vibration andnoise reach the interior.

99999 ProductionProductionProductionProductionProduction

In order to meet structural require-ments, to attain the lowest possibleexhaust back pressure and to makemaximum use of the availableunderfloor space, all the pipes fromthe manifold to the rear silencerhave had to be produced by hydro-forming. This technology is cur-rently the only method of ensuringthat the high qualitative demands ona sports-tuned exhaust system canbe met. As well as fulfilling designspecifications, hydro-forming tech-nology ensures that the pipe cross-section can, for example, bematched to the available installationspace and that very fine toleranceare adhered to. These can beguaranteed by robot welding, evenwith low wall thicknesses.Figure 4: Entire exhaust systemFigure 4: Entire exhaust systemFigure 4: Entire exhaust systemFigure 4: Entire exhaust systemFigure 4: Entire exhaust system

Vechicle Tested: BMW E46/2 M3Vechicle Tested: BMW E46/2 M3Vechicle Tested: BMW E46/2 M3Vechicle Tested: BMW E46/2 M3Vechicle Tested: BMW E46/2 M3Measure point: Tailpipe right of 50cm/45 degreesMeasure point: Tailpipe right of 50cm/45 degreesMeasure point: Tailpipe right of 50cm/45 degreesMeasure point: Tailpipe right of 50cm/45 degreesMeasure point: Tailpipe right of 50cm/45 degrees

Total Noise LevelTotal Noise LevelTotal Noise LevelTotal Noise LevelTotal Noise Level

10001000100010001000 20002000200020002000 30003000300030003000 40004000400040004000 50005000500050005000

RPMRPMRPMRPMRPM

10 d

b10

db

10 d

b10

db

10 d

b


9.1. Bending Technology9.1. Bending Technology9.1. Bending Technology9.1. Bending Technology9.1. Bending Technology

In the first production stage, thepipes must be bent before hydro-forming, Low radii and very thinwalls necessitated the developmentof electric bending machinery with aCNC-controlled tool changer.These machines were developed inclose cooperation with ArvinMeritorand Addison, and brought to series-production maturity.

A total of 21 different bent compo-nents with the smallest of radii andprecision dimensions are needed forthe ECE and U.S. versions. This isachieved by using a fully electriccompression/bending machine. Themachine is equipped with 13 CNC-controlled shafts and a tool maga-zine with 16 sets of contour tools.Each shaft can be programmedindividually. The bending process isthe preparatory production stepbefore hydro-forming and plays akey role in it.

9.2. Internal High-Pressure Mold-9.2. Internal High-Pressure Mold-9.2. Internal High-Pressure Mold-9.2. Internal High-Pressure Mold-9.2. Internal High-Pressure Mold-inginginginging

In this process, the pipes aremolded from within by hydraulicpressure in the tool. Dependingupon the material and wall thick-ness, the pressure is between 2000and 2800 bar. Two types areprincipally used for the M3 exhaustsystem:

Calibration:Calibration:Calibration:Calibration:Calibration:Pre-formed pipes are forced againstthe tool wall in a closed tool by innerpressure (e.g. 2500 bar), (Figure(Figure(Figure(Figure(Figure10)10)10)10)10) to reach the required forminglevel, the pre-formed pipes arenormally annealed before reshap-ing.

Flaring:Flaring:Flaring:Flaring:Flaring:In this process, additional material isbrought into the remolding zone byaxial compression, and very largeamounts of expansion can beachieved. (Figure 11)(Figure 11)(Figure 11)(Figure 11)(Figure 11)

Combination of calibration/Combination of calibration/Combination of calibration/Combination of calibration/Combination of calibration/flaring:flaring:flaring:flaring:flaring:Combination of the two methodsenables complex components to beproduced, partly with a calibratedpipe section, but with greater flaringat one or both ends. This processhas been used successfully, forexample, on the cones of the cata-lytic converters. In this way, weldedshells with a welded-on pipe havebeen replaced by a single compo-nent.

All 21 pipes are given their final formby internal high-pressure molding.Internal high-pressure presses witha locking pressure of 2,500 tons and10 CNC axes are used. All compo-nents are transferred to the internalhigh-pressure molding process byrobots. The expansion levelsachieved are 80 percent more thanin catalytic converter cones. (Figure(Figure(Figure(Figure(Figure12)12)12)12)12)

From an economic point of view, theuse of IHU is equally successful.Costs have been optimized by

minimizing the number of weldseams necessary and by the inte-gration of the required shapingprocess. Thus, there is a consider-able cost benefit compared toconventional construction from splitshells or multi-stage processes.

An example of an integrated compo-nent is the collector for the ECEmanifold. The two collectors arepre-bent as one header pipe, an-nealed and subjected to internalhigh-pressure molding. After re-shaping, the component is sawedinto the two separate parts required.

In conventional production, thiscomponent would consist of at least6 separate parts joined together bywelding. As well as the high numberof separate parts to be manufac-tured, the many weld seams wouldpresent a high risk factor for thecomponent’s lifespan.

9.3. Assembly9.3. Assembly9.3. Assembly9.3. Assembly9.3. Assembly

For further processing of what arenow high precision, internal high-pressure molded pipes and shapedparts, only the latest welding robotsand special welding machines areused. All weld seams are carriedout by machine to ensure consistenthigh quality. The welding processesused are pulsed TIG and MAG. Ahighlight of the whole process is thewelding of the rear silencer. All

Section ViewSection ViewSection ViewSection ViewSection View

CalibrateCalibrateCalibrateCalibrateCalibrate

Figure 11: Flaring prinzipleFigure 11: Flaring prinzipleFigure 11: Flaring prinzipleFigure 11: Flaring prinzipleFigure 11: Flaring prinziple

Figure 10:Figure 10:Figure 10:Figure 10:Figure 10:CalibrationCalibrationCalibrationCalibrationCalibrationprinzipleprinzipleprinzipleprinzipleprinziple

Figure 12:Figure 12:Figure 12:Figure 12:Figure 12:Internal high-pressure componentInternal high-pressure componentInternal high-pressure componentInternal high-pressure componentInternal high-pressure component

of the exhaust manifold (US)of the exhaust manifold (US)of the exhaust manifold (US)of the exhaust manifold (US)of the exhaust manifold (US)


outer seams in this component arewelded in a single clamping. Thesurrounding seal seam of the twoshells is welded without removal in alocking press modified to serve as amanipulator (10 tons clampingforce). In order to ensure freedomfrom slip and torsion on the stillloose shells at the start of thewelding, both tool halves are drivenseparately by a CNC controlledmotor. The motors are digitallyconnected here as an “electricalaxis” and synchronized by the robotcontrols.

The requirements imposed by thevery confined space in the car’sfloor pan could thus be met. Thetailpipes, as an important design

1010101010 SummarySummarySummarySummarySummary

The perfect combination of a power-ful engine and the newly developedexhaust system on the BMW M3creates an extremely spontaneousflow of power, accompanied by asporty, robust sound. As well asoffering the enjoyment of driving asports car such as the M3, the cartakes environmental protectionrequirements fully into account.

Compared with the exhaust systemof the previous model, several basicchanges were made to achieve themain goals of low exhaustbackpressure and lightweightconstruction. Special attention wasdevoted to the major new features,such as sheet metal flanges andseals, thin-walled IHU components,metal catalytic converter monolithswith a foil thickness of 40µm, rearsilencer and tailpipes, and therubber mountings.

Thanks to innovative productionmethods, economical manufacturingwith a high level of quality wasachieved.

feature, must be aligned with therear body apron and follow the lineof the bumper. All these pointsproved practicable with the methoddescribed.


NOTESNOTESNOTESNOTESNOTES

Documents

BMW M3 · the new BMW M3, which is a sport coupe absolutely tuned for everyday driving and at the same time performing like a thorough- bred sports car. BMW M GmbH, a company within