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2 MTZ 06|2006 Volume 67 Authors: Michael Gumpesberger, Christian Landerl, Josef Miritsch, Ernst Mosmüller, Peter Müller and Gerd Ohrnberger Der Antrieb der neuen BMW F 800 You will find the figures mentioned in this article in the German issue of MTZ 06|2006 beginning on page 420. The Drive of the New BMW F 800 BMW Motorrad continues its model offensive by moving into the medium category with two new models. After a development period of 47 months – in- cluding the phase of detailed concept studies – the sporty F 800 S and the touring bike F 800 ST now close the gap between the F 650 single cylinders and the motorcycles with flat twin engine. The drive is a completely new parallel twin engine with four-valve technology and a capacity of 798 cm 3 developed by BMW Motorrad in co-operation with BRP-Rotax GmbH & Co. KG. The mass balancing sys- tem of the parallel twin is completely unique in seri- al production engine construction: a balancing mechanism compensates the first and second order inertia forces and thus ensures the unusually low level of vibration in this in-line two-cylinder engine. 1 Introduction With the motorcycles F 800 S und F 800 ST, BMW Motorrad launches a new two-cylinder series and thus enters the medium category for the first time. Both models are fitted with the same two-cylinder in-line engine, which has been completely new developed as a parallel twin without crankpin offset. The transversely mounted, liquid-cooled en- gine operates with an even ignition firing order of 360°. The result is a similarity in sound with the flat twin engines – which is certainly intentional – but the even firing order also provides an excellent basis for a balanced charge cycle with high torque effi- ciency and even characteristics. Mass balanc- ing is effected by means of a balancing mechanism consisting of a balancing rod and pinion. This allows the free first and sec- ond order inertia forces and momentum to be significantly reduced or eliminated com- pletely. The four-valve cylinder head with two upper camshafts and cam followers pro- vides an excellent basis for optimum charge exchange and high mean pressures. Carbu- retion is performed by means of induction tube injection, with dosage taken care of by

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Page 1: The drive of the new BMW F 800

2 MTZ 06|2006 Volume 67

Authors:Michael Gumpesberger, Christian Landerl, Josef Miritsch, Ernst Mosmüller, Peter Müller and Gerd Ohrnberger

Der Antrieb der neuen BMW F 800

You will find the figures mentioned in this article in the German issue of MTZ 06|2006 beginning on page 420.

The Drive of the New BMW F 800

BMW Motorrad continues its model offensive bymoving into the medium category with two newmodels. After a development period of 47 months – in-cluding the phase of detailed concept studies – thesporty F 800 S and the touring bike F 800 ST nowclose the gap between the F 650 single cylindersand the motorcycles with flat twin engine. The drive is a completely new parallel twin engine with four-valve technology and a capacity of 798 cm3

developed by BMW Motorrad in co-operation withBRP-Rotax GmbH & Co. KG. The mass balancing sys-tem of the parallel twin is completely unique in seri-al production engine construction: a balancingmechanism compensates the first and second orderinertia forces and thus ensures the unusually lowlevel of vibration in this in-line two-cylinder engine.

1 Introduction

With the motorcycles F 800 S und F 800 ST,BMW Motorrad launches a new two-cylinderseries and thus enters the medium categoryfor the first time. Both models are fittedwith the same two-cylinder in-line engine,which has been completely new developedas a parallel twin without crankpin offset.The transversely mounted, liquid-cooled en-gine operates with an even ignition firingorder of 360°. The result is a similarity insound with the flat twin engines – which iscertainly intentional – but the even firing

order also provides an excellent basis for abalanced charge cycle with high torque effi-ciency and even characteristics. Mass balanc-ing is effected by means of a balancingmechanism consisting of a balancing rodand pinion. This allows the free first and sec-ond order inertia forces and momentum tobe significantly reduced or eliminated com-pletely. The four-valve cylinder head withtwo upper camshafts and cam followers pro-vides an excellent basis for optimum chargeexchange and high mean pressures. Carbu-retion is performed by means of inductiontube injection, with dosage taken care of by

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DEVELOPMENTGasoline Engines

3MTZ 06|2006 Volume 67

an engine control unit which is capable ofprocessing complex information – even con-trolling the oxygen sensor in the three-waycatalytic converter or regulating the fuelpressure in the returnless fuel system, forexample. Power transmission to the rearwheel is via a primary gear drive, a wetmultiplate clutch, a six-speed constant-meshgearbox and finally a low-maintenance andlow-noise toothed-belt drive.

The strongly distinctive in-line two-cylin-der engine has particularly impressivepulling power, spontaneous response andlow fuel consumption. It has a rated outputof 62.5 kW at 8000/min and achieves atorque of 86 Nm at 5800/min.

2 Development Objectives and ConceptDefinition

The motorcycle is unique in that it is the on-ly vehicle with which the overall objectivedetermines the selection of engine concept.In order to create a compact sports/sportstouring bike with excellent riding character-istics, low weight and high agility, an engineis required which is both light and high-torque with low overall width which fitsperfectly into the overall vehicle package.The capacity of 798 cm3 and the outputthus available derives from the strategic ob-jective of filling the gap between the singlecylinder models and the large-volume flattwin models. The requirement of a high lev-el of torque with harmonious characteris-tics in conjunction with general packageconsiderations results in the choice of thetwo-cylinder engine. Concept studies werecarried out and showed a clear preferencefor the in-line engine concept selected, be-ing superior to a V engine in terms of com-pactness, weight and costs. Due to theunique balancing mechanism for mass bal-ancing which was newly developed for thisengine, it was also possible to create a paral-lel twin with 360° firing interval. Thetorque-oriented design is supported by themoderately short-stroke design with 82 mmbore and 75.6 mm stroke in conjunctionwith a four-valve cylinder head, in whichthe valves are activated by two uppercamshafts and the cam followers already fa-miliar from the K 1200 S. The very low levelof moving masses in the valve train due tocam follower activation allow additionalfreedom in terms of control times and valvestroke. In conjunction with aerodynamical-ly optimised inlet passages and the straight-line continuation of the intake funnel intothe large-volume air box, very high meanpressures can be achieved.

balancing pinion, a roughly straight up-and-down movement of the small eye of the bal-ancing rod is achieved. This mechanism isable to completely compensate free first or-der forces and reduce free second orderforces by 70 %. The arrangement of the bal-ancing system at the centre between the twopower cylinders provides the benefit of elim-inating mass momentum.

The two weight-optimised cast pistonsare connected to the crankshaft by means ofcracked forged rods. The piston ring packageconsists of a compression ring, a taper-facednapier ring and a triple section oil controlring.

3.2 Cylinder Head and Valve TrainThe rough section of the cylinder head ismanufactured in chill cast AlSi10MgCu withgravity filling with subsequent heat treat-ment. For aerodynamic optimisation, the in-take channel goes out very steeply from thecylinder head. In conjunction with thesmall intake and outlet angles of 10° and11° to the cylinder axis and the centrallyplaced 12 mm spark plug, a very compactcombustion chamber is created with a com-pression ratio of 12 : 1. Activation of the 4valves per cylinder unit is effected by meansof DLC-coated, friction and wear-optimisedcam followers and two upper camshafts,Figure 3. This weight-optimised arrangementallows very high valve accelerations andthus form the basis for high mean pressures.For the adjustment of the valve play, preci-sion-ground half balls are used which areinserted in the spherical segment in thecam follower. Valve play is not checked atfixed service intervals and adjusted; instead,load data in the engine control unit isanalysed and from this the remainingmileage until the next necessary check isdetermined. The camshafts are driven bymeans of a tooth-type chain, the chain guideuses single-section synthetic guide tracksand tension is created by means of a mainte-nance-free hydraulic chain tensioner.

A dual layer metal cylinder head sealprovides sealing from the cylinder. On thecylinder cover there is the secondary intakesystem membrane valve, via which clean airis phased through bores to the outlet chan-nels of the two cylinders for afterburn.

3.3 Oil and Water CirculationThe engine is supplied with oil by means ofdry sump lubrication, the oil tank is inte-grated in the engine and is located underthe crankcase, separated from the latter bymeans of a pin shaft, Figure 4. The pressureand suction pump are driven by a primarydrive via a shared, through-going drive shaft

3 Basic Engine

The engine casing is horizontally split and ismanufactured in die-cast using the alumini-um alloy Al Si9Cu3Mg. The upper half of thecasing contains the cylinder and is an open-deck construction. Encapsulated, dry andweight-optimised grey cast-iron sockets areused as cylinder barrels. The mounting posi-tions of both the crankshaft and the twogearshafts are located at the mould joint ofthe crankcase, Figure 1. The main bearing ismounted at the outer mounting positionsbetween the upper and lower sections, thetwo inner mounting positions are bolted on-to the crankcase upper section as mountsupports. The crankshaft drive with the bal-ancing system is separated from the oilpan/tank by a cover. This effectively preventsloss due to splashing. The lower half of thecasing contains the oil pumps and gearboxswitch unit. Sealing between the upper andlower section of the crankcase is by means ofliquid sealing from the casing covers and oilpan/tank to a paper seal. The engine is aload-bearing component of the chassis andis mounted distortion-free via two connec-tions at left and right. The engine casing isreinforced at the rear for the attachment ofchassis load. The main frame is connectedby means of two bolts on the left and rightfrom underneath.

3.1 Crankshaft Drive and Mass BalancingThe forged crankshaft with 360° crankpinoffset is mounted transversely and withquadruple plain-bearing mount. The materi-al used here is the highly resilient steel38MnVS5, and the crankshaft is also in-ductively hardened to increase long-termstrength. To the right in the direction oftravel there is a compact generator attachedto the free crankshaft end, and both enginespeed sensors and the free-wheel cog of thestarter are integrated in the generator rotor.The pressed-on primary drive cog and thepinion of the valve train are located at theleft-hand end of the crankshaft.For the balancing mechanism, Figure 2, athird separate eccentric is attached on thecrankshaft at the centre of the cylinder forthe friction-bearing balancing rod, whichforms an articulation system with the bal-ancing pinion mounted at right angles tothe cylinder axis. This is supported in thecrankcase with a coated pin and connectedto the swivel rod by means of a roller bear-ing. The kinematic pattern is designed sothat the balancing rods move in counter-ro-tation to two engine rods. Due to the factthat they are fed through the relatively long

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DEVELOPMENT Gasoline Engines

4 MTZ 06|2006 Volume 67

with cog. These two trochoid pumps supplya total of 3.4 l of lubrication oil through theengine. Oil and blow-by gases are removedfrom the crankcase by means of suctionpump, the latter measuring 50 mm in dia-meter with a width of 25 mm, so that a par-tial vacuum of 0.2 bar is created in thecrankcase. In this way, pump loss of the pis-tons and balancing mechanism is effectivelyreduced. The supply performance of thepressure pump is approximate 20 l/min atmaximum engine speed, average operatingpressure is at around 4.5 bar. From the pres-sure pump, the oil initially reaches the cen-tral pressure oil duct via the heat exchangerand filter. Excess pressure valve allows amaximum of 8 bar in this duct. The connect-ing-rod bearings are supplied with pressureoil fed centrally into the crankshaft. Viabores in the four friction bearings, oil is fedto the four friction bearings and cylinderhead. It feeds the hydraulic chain tensionerand – via a calibrated bore – the two hollow-bore camshafts. The lubrication of the con-tact surface between cam and cam followeris secured intermittently by means of agroove in the camshaft bearings. Two oil jetsalso cool the piston heads with spray oil. Adeactivation channel and a throttling jetsupply the gearbox with oil.

The crankcase ventilation is through thetiming-chain chamber and the cylinderhead and subsequently via a centrifugal sep-arator system. This is integrated in and onthe drive cog of the coolant pump mountedon the intake camshaft.

Coolant circulation, Figure 5, is ideallysuited to function and package require-ments. The coolant pump is integrated inthe right of the cylinder head and is pow-ered by a cylindrical gearing system. The 85°thermostat valve is housed in a cooling-wa-ter reservoir of the U-shaped through-flowradiator. In total, the cooling system has acapacity of 1.5 l of coolant. An electrical fanis activated at a coolant temperature of 105 °C and secures functional reliabilitywhen riding slowly or when stationary. Anoil-water heat exchanger is additionally inte-grated in the water circulation system abovethe easily accessible oil filter. This meansthat the engine operating temperature isreached more quickly in the warm-up phaseand engine cooling is guaranteed under fullthrottle conditions.

3.4 Clutch and GearboxThe wet multidisc clutch is situated on thegearbox-input shaft and is driven by thecrankshaft via an optimised spur gear toothsystem, Figure 6. For moment transmissionbetween the powered clutch cage and the

clutch hub there are nine pairs of ribs. Fordamping abrupt load alteration there is amultistage suspension damper system onthe primary clutch side consisting of a totalof six torsional springs and an axiallyaligned disc spring. The downforce for therib package is produced by means of sixpressure springs, while the defined oil sup-ply for the clutch is provided by means of athrottle bore in the gear in put shaft.

The constant-mesh six-speed gearbox, Figure 7, is integrated in the engine casingand consists of the gearbox input shaft andthe output shaft, the cog pairs and thegearshift mechanism. A grooved ball be-aring is provided for the shafts in thecrankcase. The straight-toothed fixed gearsand movable gears of the individual gearsare arranged on the shafts as per interna-tional standard. Shifting of the various gearsis effected by the sequential displacement ofthe torsion-resistant sliding gears. The shift-ing drum is turned via the foot shift lever,the selector shaft and the shift catch. Thealuminium shift forks and thus the gearboxwheels on the gearbox input and outputshafts are moved by means of curve tracksmachine-cut into the latter, thus shiftingthe relevant gears. The exact gear position-ing is secured by means of a shift star and in-dex lever. The total gearbox stepping is 2.56,the individual gears are narrowly steppedfor a sporty riding style, Figure 8.

3.5 Drive TrainThe secondary drive is a toothed belt drive,Figure 9. This type of drive is particularlylow-maintenance and reliable. Maintenanceand re-tensioning work is limited to serviceintervals of 10,000 km, no lubrication is re-quired. The belt tension is set by means ofthe eccentric rear axle mount in the swingarm. With trouble-free operation, a mileageof over 40,000 km is possible. The toothedbelt secondary drive ensures zero-play loadreversal and is maintains a constant lownoise level even after high mileage. A four-section torque cushion made of mattedhigh-quality steel is integrated in the reartoothed belt cog to damp unwanted load re-versal reactions and to enable jerk-free accel-eration from the very lowest engine speedsas far as possible.

4 Periphery

4.1 Intake System and Exhaust SystemThe intake system consists of an air box, araw air intake snorkel and two harmonisedinner intake tubes, Figure 10. The raw air en-ters the air box by means of the intakesnorkel, which is favourably positioned in

the cool airflow. The filter element has athrough-flow area of approx 0.45 m2. Thelarge volume of 9 l is favourable for torqueand the long straight intake tubes are possi-ble due to the positioning of the fuel tankbelow the seat. The air box is vibration de-coupled and at the same time serves as abearer for electronic components such asthe battery, temperature sensor, idle actua-tor and distributor, the secondary intake sys-tem shift valve and the fuel tank ventilationvalve.

The weight-optimised exhaust system ismade entirely of high-quality steel and divid-ed at the manifold end. The metal suppercatalytic converter with a diameter of 90 mmand a length of 75 mm has a cell density of300 cpsi and a PtTdRh coating of 44 g/ft3. It is positioned at the front end of the rearsilencer.

4.2 Fuel System, Carburetion, Control UnitCarburetion is effected by means of intaketube injection with BMS-K engine manage-ment and two throttle valves measuring 46mm. The fuel system works without returnand only supplies the amount actually re-quired by the engine. This energy-saving sys-tem of fuel feed means that the fuel pres-sure can be altered for optimum carbure-tion across a wide range. In addition to thefamiliar parameters such as load, enginespeed and temperature, the residual oxygencontent of the exhaust gas is also used todose fuel feed quantity. The relevant infor-mation is provided by an oxygen sensor po-sitioned behind the manifold convergencepoint: this is indispensable for effective con-version in the standard three-way catalyticconverter. A secondary air system aeratesthe exhaust gas additionally so as to reducepollutant emissions to a minimum.

5 Functional Properties

The general design of the engine achievesthe desired objective of very harmoniouspower delivery with high torque at compa-rably low engine speeds. For example, 90 %of the maximum torque is available at5000/min. Between 5000 and 8000/min, theengine displays an impressively dynamicpower delivery accompanied by a distinctivesound. The maximum effective mean pres-sure achieved of around 13.5 bar is outsidethe distribution range of comparable en-gines in this category of motorbike. The rat-ed performance figures of the 798 cm3 largetwin, i. e. 62.5 kW at 8000/min and 86 Nm at5800/min, Figure 11, result in a tendency tounderestimate the power available. Agility isfurther enhanced by means of a low inertia

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5MTZ 06|2006 Volume 67

weight and modern carburetion. In conjunc-tion with the low frictional loss and op-timised combustion, this also ensures lowfuel consumption, Figure 12. Constant fuelconsumption levels are achieved of 3.4l/100km at 90 km/h and 4.5 l/100km at 120km/h. When running on country roads, a fu-el consumption level of well under 5 l of pre-mium-grade fuel per 100 km is possible.Adaptation to regular fuel, something cus-tomers may possibly want, can be providedby means of reprogramming the controlunit, though this does result in a reductionof top output by 1.5 kW as well as a slightlyhigher fuel consumption level.

6 Summary

With the new distinctive parallel twin,BMW Motorrad now has a medium categoryconcept which sets a new benchmark with arider-oriented concept which has been care-fully designed and optimised down to thelast detail. The in-line two-cylinder provedthe best solution for realising this perfect in-teraction of all components. The compactparallel twin with its unique mass balanc-ing by means of balancing pinion has an im-pressively low level of vibration, excellentpulling power, spontaneous response and alow fuel consumption level. The rated out-put of the engine is 62.5 kW at 8000/minand a torque of 86 Nm at 5800/min.

However, the performance figures of thisengine with its environment-friendly closed-loop 3-way catalytic converter, secondary airsystem and low-maintenance belt drive donot fully express the impressive power po-tential of the new BMW. In just 3.5 s the S model spurts from 0 to 100 km/h and is also characterised by a high degree of elas-ticity. At high speeds, the slim and aerody-namically optimised trim also comes into itsown. Another important contribution to dynamic performance is made by the lowdry weight of 182 kg. Road-ready and fullyfuelled, the bike weighs 205 kg. ■

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