THE NEW BMW THREE- AND FOUR-CYLINDER GASOLINE ENGINESBMW has developed a new modular inline engine system that includes both gasoline and diesel units

and ensures a high level of commonality. The following report describes the development of the

three- and four-cylinder gasoline engines. The new power units will be used for the fi rst time in the

Mini and the BMW i8. A report on the new diesel engines will follow in MTZ 7-8.

14

DEVELOPMENT GASOLINE ENGINES

Gasoline Engines

ONE BASIC CONCEPT FOR ALL IN-LINE-ENGINES

With the market launch of the new Mini, BMW has evoked a completely new en -gine family which eventually will com-prise of three-, for-, and six-cylinder gaso-line and diesel engines. The objective isto build all in-line engines on the basis of the same engine concept and uniform engine peripherals.

On the gasoline engine side, the new generation of engines will start with three three-cylinder engines and a four-cylinder derivative. The three-cylinder engines will be available with two en -gine capacities, 1.2 and 1.5l. The 1.2-l version starts with a power of 75kW, thus covering the Mini One positioning. The 1.5-l engine is available with 100kW for the Mini Cooper and in a specific high-performance variant with 170kW for the new electrified BMW i8 sports car. The initial launch of the new four-cylinder engine is with a 140kW version for the Mini Cooper S. Subsequently, engines with significantly higher power output will in future be used in other BMW and Mini derivatives [1].

OBJECTIVE

More efficient, lightweight design, higher performance and conceptionally aligned with future more stringent legal require-ments worldwide. This summarises the major objectives for the new units in simple terms. Accordingly, the following functional objectives were laid down in the requirements specification: : high specific power output of up to

115kW/l for the top applications : high low-end torque at speeds just

above idle speed : response characteristics comparable

with naturally aspirated engines with the same power output

: low fuel consumption during customer operation and also in certification drive cycles

: potential for compliance with the stringent exhaust emission regulations worldwide

: lightweight construction with alumin-ium crankcase

: minimum friction losses as a result of optimised base engine configuration

: greatest possible refinement as a result of mass balance systems on both the three- and four-cylinder engine.

The common gasoline/diesel family approach also resulted in the specifications: : production flexibility (gasoline and

diesel, three, four and six cylinders) across a number of production facilities

: simple and rapid implementation of different technology variants on the same base engine platform

: simple and rapid construction of derivatives

: uniform vehicle interfaces for all variants.

Despite the maximum degrees of com-monality, another requirement and chal-lenge was to design at the same time the individual derivatives with optimised functions to ensure in each case top positioning among the competition.

CONCEPT

The basic engine dimensions of the new three-/four-cylinder engines, , include continued use of the cylinder spacing of 91mm for in-line engines that has been standard at BMW for many years. The individual cylinder displacement volume is 0.5l, with the exception of an entry-level version of the three-cylinder engine for the Mini One which has 0.4l individ-ual cylinder displacement volume to pro-duce a total engine capacity of 1.2l. As a general principle, the engines have been conceived as turbocharged engines with regard to configuration and peripherals. In order to create the best possible condi-tions for optimised functionality and vehicle integration, the gas exchange takes place according to the crossflow principle with the air supply on the left and the exhaust manifold on the right side of the engine. The arrangement of the chain drive on the back of the en -gineenables concentration of all aux-iliary components on the intake side, which means that the right side of the engine is completely available for turbo-charging and close coupled exhaust after-treatment. shows the longitudi-nal and cross-sectional views of the engine.

DESIGN BASE ENGINE

The crankcase, , is made of solid alu-minium on all derivatives. The camshaft chain drive system is on the flywheel end. The cylinder surface technology

AUTHORS

ING. FRITZ STEINPARZERis Head of the Diesel Engine Development Program of the

BMW AG in Steyr (Austria).

DIPL.-ING. THOMAS BRNERis Department Manager Development Mechanics at the BMW AG in Munich

(Germany).

PROF. DR. CHRISTIAN SCHWARZ is General Manager Process

Powertrain Product Line Small and Midsize Series at the BMW AG

in Munich (Germany).

DIPL.-ING. MARKUS RLICKE is Department Manager of Gasoline

Engines Communality Projects in Powertrain Development at the

BMW AG in Munich (Germany).

06I2014 Volume 75 15

Gasoline Engines

uses an innovative coating system created by wire arc spraying. Only 0.3mm thick, this coating is extremely wear-resistant and achieves much better heat transfer from the cylinder to the coolant than conventional cast iron liners. The steel crankshafts are forged and induction

hardened on the bearing faces. The counterbalance shafts integrated in the crankcase are driven by the forward end of the crankshaft on the three-cylinder engines, whereas on the four-cylinder versions the drive mechanism is inte-grated in the rear crankshaft arm. The

main bearings are an aluminium com-posite design using two materials. The big-end bearings are triple-material com-posites with a polymer coating. The con-rods are of forged construction and a graduated design. The conrod small end has an inserted solid bronze rolled bush.

To balance the engines first-order inertial forces, a forged counterbalance shaft mounted in the crankcase with two diametrically opposite counterbalance weights is used on all three-cylinder engines. One of these counterbalance weights is forged onto the shaft. The counterbalance shaft is driven by a gear integrated on the crankshaft to directly drive the gear arranged on the front face of the counterbalance shaft. The second counterbalance weight, made using sin-tering technology and decoupled with an elastomeric groove, is integrated in this drive gear. To reduce the drive power, the counterbalance shaft is mounted on anti-friction bearings.

This arrangement, which is identical on all gasoline/diesel three-cylinder engines, enables a low-vibration crank-shaft drive. The different combustion processes and moving gasoline/diesel drive unit masses are taken into account by means of the specific adaptation of the imbalances and of the drive.

On the four-cylinder engine, two forged balancing shafts mounted on bearings in the crankcase, which run in opposite di -rections at double crankshaft speed, are used to eliminate the engines oscillating inertial forces of the second order. To reduce drive power, all counterbalance shafts on four-cylinder engines are mount- ed on anti-friction bearings in the same way as on the three-cylinder engines.

The height offset of the two identically designed counterbalance shafts addition-ally balances out the moments of inertia of the second order. The slightly smaller height offset compared to the previous four-cylinder engine shifts the generated alternating torque towards low speed, which particularly benefits comfort in the range close to low-end torque.

The oil is supplied by means of a map-regulated pendulum-slider pump with variable volumetric flow that is identical for the three- and four-cylinder engines. The oil pump is integrated in the same housing of the vacuum pump, creating a chain drive tandem pump which is posi-tioned in the oil pan sump. The map controlled continuously variable engine Longitudinal and cross-sectional views of the four-cylinder engine

THREE-CYLINDER FOUR-CYLINDER

KEY SPECIFICATION UNIT MIN MAX

Maximum power (corresponding rpm) kW at rpm 100 at 4500 170 at 5800 141 at 4700

Maximum torque (corresponding rpm) Nm at rpm 220 at 1250 320 at 3500 280 at 1250

Maximum engine speed rpm 6500 6500 6500

Specific power kW/I 66.7 113.3 70.5

Specific torque Nm/I 146.6 213.3 140

Maximum specific work kJ/I 1.82 2.35 1.7

KEY SPECIFICATION UNIT THREE-CYLINDER FOUR-CYLINDER

BASIC MEASUREMENTS

Piston displacement cm3 1498.8 1998.3

Bore mm 82 82

Stroke mm 94.6 94.6

Stroke-bore-ratio 1.15 1.15

Volume per cylinder cm3 499.6 499.6

Connecting rod length mm 148.2 148.2

Connecting rod ratio 0.319 0.319

Cylinder distance mm 91 91

PISTON

Compression height mm 33.2 33.2

Top ring land mm 7 7

PISTON PIN

Diameter mm 22 22

Length mm 55 55

VALVE

Diameter, inlet/exhaust mm 30/28.5 30/28.5

Valve lift, inlet/exhaust mm 9.9/9.7 9.9/9.7

Stem diameter, inlet/exhaust mm 5.0/5.0 5.0/5.0

Compression ratio 11.0 11.0

Technical data and main dimen-sions of the three- and four-cylinder engines

DEVELOPMENT GASOLINE ENGINES

16

oil pressure is provided by means of a proportional solenoid valve and in accord-ance with a characteristic map stored in the ECU. A combined oil pressure and temperature sensor is fi tted in the main oil gallery. Its signals are used for the map controlled oil pump and engine heat management. An oil level sensor in the oil pan permanently monitors the oil level. The oil fi lter module is made of plastic and designed with an integrated oil/water heat exchanger.

The valvetrain is the 4th generation of Valvetronic familiar from the previous engines. The actuator for adjusting the eccentric shaft is positioned at the front of the intake side of the cylinder head and is integrated into the package of the intake system. The further development of the intake valvetrain above all ena-bled a signifi cant reduction in the instal-lation requirement. Exchanging the posi-

tion of the intake camshaft with the eccentric shaft has enabled a signifi cant reduction in height, .

The new location of the intermediate lever and guide block simplify the appli-cation forces into the cylinder head. The guide block is mounted onto the bearing block by only a single bolt and is posi-tioned by two precise contact surfaces inthe cylinder head. The return spring for the intermediate lever is supported be tween the cylinder head and bearing bridge and therefore does not require a separate additional fi xing. The eccentric shaft and the camshafts are of assem-bled design. The exhaust camshaft sim-ultaneously drives the high-pressure pump of the injection system by means of a triple cam.

The power transmission from the chain drive takes place via two hydraulic Vanos units. The three-vane actuators have an

adjustment range of 70CA on the intake shaft and 60CA on the exhaust cam-shaft. A feature of the new BMW gasoline engines is the positioning of the chain drive on the power output side. From the crankshaft downwards, a separate short chain drives the tandem pump (combi-nation of oil and vacuum pump). From the crankshaft upwards, the intermedi-ate chain drive runs to the idler gear. The idler gear with the two chain planes (number of teeth 24/32) ensures the fi nal drive ratio of the crankshaft (24teeth) to the camshaft/Vanos units (36teeth) from 2 to 1. This enables a reduction in the di a-meter of the Vanos units and therefore reduces the total height of the engine. The timing chain assembly above the idler gear drives the camshafts. A guide rail attached to the cylinder head between the Vanos units serves as a chain-skip protection. Both the intermediate chain

Crankcase

Layout Valvetronic in comparison to the previous engine

06I2014 Volume 75 17

drive and the timing chain drive each have a separate chain tensioner. The oil pump drive is designed in such a way that it works without a guide or tension-ing system.

TURBOCHARGING

The new BMW engines incorporate new and worldwide unique innovations in the area of the turbocharging technology. For example, the new four-cylinder engine has a twin-scroll turbo module with an integrated exhaust manifold. This design ensures a reliable separation of the ex -haust gas flow up to the turbine wheel, which results in a higher low-end torque and simultaneously develops further potentials in response characteristics. In order to enable adequate expansion of the manifold and assembly in the very

tight package, the manifold is flanged onto the cylinder head by means of a clamping/sliding bar. With this concept of the integral twin-scroll exhaust turbo-charger, water cooling was not required.

The situation for the new three-cylin-der modular kit engine is completely dif-ferent. For the first time worldwide in passenger vehicles, a water cooled full-aluminium exhaust turbocharger made using lost foam technology is used. This construction, which is also fastened to the cylinder head by means of a clamp-ing/sliding bar, creates extensive degrees of freedom with regard to design. Com-plex CFD simulations were used to opti-mise both the exhaust side and the water side in the interplay with the component strength calculation in such a way that the reduction in the flow of wall heat creates a minimal additional cooling re -

quirement. Despite additional cooling requirements, this design therefore com-bines significant weight savings with a considerable CO2 reduction potential. An -other benefit compared to the non-cooled steel exhaust turbochargers is that the exhaust-gas temperature, before the cat-alytic converter, is substantially below 850C. This ensures that catalytic con-verter aging can be more or less excluded.

The partition area between the turbo module and cylinder head has been de -liberately placed in the cylinder head flange in order to be able to flange a con-ventional steel exhaust turbocharger onto the identical cylinder head for the top variant BMW i8. To standardise the installation situation of the exhaust sys-tems in all vehicles, the location for the catalytic converter flange has been kept identical for the three- and four-cylinder engines, .

THERMODYNAMICS, COMBUSTION AND FUEL INJECTION APPLICATIONS

A further development of the new modu-lar-design gasoline engines is the Twin-Power Turbo combustion process, famil-iar from the predecessor models, with the objective to comply with additional emission standards while simultaneously achieving greater efficiency. In compari-son to the previous gasoline engines, the cylinder bore has been reduced by 2 to 82mm. The result is a considerably larger stroke to bore ratio of 1.15 : 1, representing an optimum in terms of thermodynamics and friction. shows a vertical cross-section through

the combustion chamber illustrating increased piston-crown recess despite

Turbocharger unit of three- and four-cylinder engines

Section view of the combustion chamber

DEVELOPMENT GASOLINE ENGINES

18

the narrower bore compared with the previous design. Combined with a wider spray pattern using multi-jet injectors with reduced flow rates, substantially improved mixture homogenisation has been achieved in conjunction with increased charge motion. The reduction of the nominal flow rate of the multi-jet injectors has also considerably reduced the penetration depth of the spray.

By optimising the spray pattern using individual nozzle jet injection volumes and directions, it has also been possible to achieve an excellent compromise between the demands of catalytic con-verter heating (stratified injection) and normal engine operating temperature. Atthe same time it has been possible to reduce wetting of the piston, cylinder liner walls and the inlet valves to a mini-mum. The second generation so-called CVO (Controlled Valve Operation) func-tionality provides even greater scope in terms of fuel injection, enabling a wider range of the injector regulation to be used for micro-volume injection. Both measures have an extremely positive effect in terms of further substantial reduction of the particulate count across the entire engine map.

As seen in the fuel to air ratio dis-tribution, at the firing top dead centre point, has been substantially improved in comparison with the predecessor engine. It has also been possible to with-draw the position of the sparkplug ap -proximately 2mm out of the combustion chamber, thereby substantially reducing the stress on the sparkplug. shows the progression of the indi-

cated specific fuel consumption plotted against indicated load at a speed of 2000rpm. It can clearly be seen that, due to the improvements in the combustion process development, a reduction in fuel consumption of as much as 5 % over an extensive range has been achieved. In the rated power range, the new modular-design engine operates under normal operating conditions at a stoichiometric air to fuel ratio.

HEAT MANAGEMENT

Optimum heat management plays a vital role for modern engines in achieving low-ermost fuel consumption for customer real-life driving cycles. In this re spect, BMW is treading new ground in particu-lar with the three-cylinder engine. The

central element of the new heat manage-ment concept is a water cooled hot end with not only a cooled manifoldbut also a cooled turbine. In combination with an appropriately dimensioned oil/water heat exchanger, the extra heat recovered is used to heat the oil more quickly during the warm-up phase. The resulting temper-ature in crease amounts up to 19C in NEFZ. The units cooling system is inte-grated inthe overall coolant circulation system and receives its supply of coolant from the cylinder head.

The coolant flows via a flange mounted pump on the crankcase into the engines coolant jacket. For reasons of commonal-ity with the diesel engines and in order to efficiently utilise the advantages of the cooled hot end, the coolant pump is a

belt driven, mechanical, constant-deliv-ery type. Inside the same housing there is also an electrically heated map-con-trolled thermostat which regulates the engine inlet temperature. The coolant first flows lengthways through the exhaust side of the crankcase and then enters the cylinder head where it is selec-tively distributed to parts of the cylinder head subject to high thermal stresses and to the cooled hot end. Some of the coolant entering the cylinder head is diverted directly for cooling the exhaust zone and the exhaust port bridge. The main coolant stream passes via the cyl-inder head into the hot end where it cools the manifold and the turbocharger turbine before being fed back into the cylinder head. The coolant passes through

0

2

4

6

8

10

12

14

16

0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4Fr

eque

ncy

[%]

Air/fuel ratio [-]

Air/fuel ratio distribution at ignition timing

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8

Prev. engine

New enginen = 2000 rpm

ISFC

[g/

kWh]

IMEP [kJ/dm]

Prev. engine

New enginen = 2000 rp

= 20 g/kWh

Specific fuel consumption at 2000 rpm

06I2014 Volume 75 19

the cylinder head and the hot end in a crossfl ow pattern and re-enters the crank-case on the inlet side, from where it re -turns to the radiator fl ow pipe. shows the internal coolant circulation in the engine as illustrated by the three-cylin-der engine with water cooled hot end.

VEHICLE INTEGRATION

Another key point of focus in the design of the new modular engine design was the standardisation of the interfaces for integration in the similarly new vehicle platform design with front transverse engines. The result is a modular concept with the modular engine system as an integral component. The engine design has standardised interfaces with the modular cooling system, the air intake system and the exhaust system. As a consequence, the complexity of the pro-duction systems is reduced, forming the basis for exploiting the economies of scale with the peripheral components. Furthermore, the design concept for the new engine family has also taken ac -count of compliance with the new pedes-trian impact regulation requirements and optimisation of engine compartment heat management.

FUEL CONSUMPTION

Consistent and rigorous refi nement of the combustion process and the turbo-

charging systems, improved warm-up characteristics, the use of a water cool- edmanifold, the reductions in friction, optimisation of the air intake system, charge air cooling and the exhaust sys-tem, the CO2 emissions of the new three-cylinder engine have been lowered by 16 % with a manual gearbox and as

much as 28 % with an automatic trans-mission. At the same time, the top speed has been in creased by 7 and 13km/h, respectively. The new three-cylinder engine also shows signifi cant improve-ments for the customer fuel consump-tion since it can be operated with a stoi-chiometric air to fuel ratio right across the engine data map because of its water cooled turbocharger. The CO2 emissions of the new four-cylinder engine with a manual gearbox have been maintained at the same level as the previous model while the engine response characteris-tics are substantially improved due to the new en gines greater induction torque. With the new automatic trans-mission family the CO2 levels are as much as 18 % lower.

POWER AND TORQUE

shows the full-power curves for the new three- and four-cylinder gasoline engines. The 1.5-l three-cylinder engine offers an output range of up to 100kW for the new Mini and up to 170kW when used in the BMW i8 sports car, corre-sponding to a specifi c power output range of 67 to 113kW/l. A similar spread is evident in the torque fi gures for the three-cylinder power unit. They range

Torq

ue [

Nm

]

360

300

240

180

120

60

0

Torq

ue [

Nm

]

420

360

300

240

180

120

60

0

180

150

120

90

60

30

00 1000 2000 3000 4000 5000 6000 7000

Three-cyl. 170 kW

Three-cyl. 100 kW

Four-cyl. 141 kW

Engine speed [rpm]

0 1000 2000 3000 4000 5000 6000 7000

Engine speed [rpm]

Pow

er [

kW]

210

180

150

120

90

60

30

0

Pow

er [

kW]

Powe

r

Torque

Torque

Power

Torque

Power

Coolant fl ow in three-cylinder engine with water-cooled hot end

Full-load curves for the three- and four-cylinder engines

DEVELOPMENT GASOLINE ENGINES

20

from 220Nm for the new Mini to 320Nm for the BMW i8. The lowend torque point is 1250rpm in the new Mini and, in combination with the new gearbox design, provides for a further reduction of fuel consumption in the range relevant to customer use together with a high level of driveability.

The fourcylinder engine will initiallybe rated at 141kW for transverse installation in the new Mini. The torque figure is 280Nm and, as with the threecylinder engine, is achieved from only 1250rpm upwards. A higher power and higher torque version will follow at a later date without significant hardware modifications.

As a result of the higher torque and power output compared with the previous Mini engines and a new automatic transmission family, the CooperS will achieve substantially better performance figures. Thus the acceleration time from 0 to 100km/h is 0.2s faster with a manual gearbox and 0.5s better with an automatic transmission, while the acceleration from 80 to 120km/h is 0.6s faster with a manual gearbox. The top speed has also been increased by 8 and 10km/h respectively. Due to the combustion process optimisation and charge cycle improvements in the air intake and exhaust system, charge air cooling, a minimum air to fuel ratio of 0.94 can be achieved. In all other operating conditions, the new fourcylinder engine operates almost entirely at a stoichiometric air to fuel ratio.

Significant improvements in terms of the new Mini Cooper position have also been achieved in all disciplines. Thus, due to the changeover to the new threecylinder engines, the acceleration figuresfrom 0 to 100km/h have been improved by 1.2s for the manual gearbox model and 2.6s for the automatic. Equally impressive is the 2.8s reduction achieved in the acceleration time from 80to 120km/h for the manual gearbox version.

EMISSIONS

Further development of the combustion process has achieved substantial improvements in the raw emissions compared with the predecessor engines. In conjunction with optimised air induction and positioning of the closecoupled catalytic converter, the introduction of an electric wastegate actuator and the re finement of the warmup strategy, the stringent emission regulations worldwide (Euro6, ULEV, SULEV) are easily complied to without engine hardware modifications. The use of the water cool ed manifold on the new threecylinder engine also provides for substantial re duction of the thermal stresses on the closecoupled catalytic converter, resulting in significantly reduced catalytic converter aging.

SUMMARY

With the market introduction of the new three and fourcylinder engines BMW has started a completely new modular engine family. As well as the established BMW TwinPower Turbo technology, di rect injection, fully variable valvetrain and exhaust turbocharger, the introduction of completely new technologies are also being introduced, for example on the threecylinder engine the water cool ed aluminium hot end. The first application of the new modular engine is with the market introduction of the new Mini. The top version of the threecylinder engine with 170kW is introduced in the new BMW i8 sports car. In the near future the modular engine family will also incorporate a conceptually similar sixcylinder engine and will find applications within all of the BMW vehicles.

REFERENCE[1] Steinparzer, F.; Schwarz, C.; Brner, T.; Mattes, W.: The new BMW 3- and 4-cylinder Petrol Engines with TwinPower Turbo Technology; 35. International Vienna Motor Symposium, 2014

06I2014 Volume 75 21