ENGINE / DRIVE
FOUR CYLINDER INLINE ENGINE 1000 CC.
The high performance four cylinder inline engine with a displacement of 999 cc is a unique solution combining the maximum of riding dynamics and sporting character with the maximum of ridability. Its particularly large bore-stroke ratio of 0.621 provides the basis for extraordinary performance. Its rated power output is 142 kW (193 hp) at 13,000 rpm, and its max torque of 112 Nm is available at 9750 rpm. This engine therefore delivers the best values for series production in the 1000 cc supersports class.
Weighing in at only 59.8 kg, the engine is one of the lightest 1000 cc four cylinder units on the market. Like all BMW motorcycle drives, this engine too is based on an elaborate overall concept and the space saving arrangement of all auxiliary units and the integrated constant mesh six speed gearbox.
The overriding objective of creating a purebred supersports drive gave rise to a particularly compact engine with the ideal concentration of mass around the motorcycle's centre of gravity. Despite the large bore of 80 mm, the installed width at the height of the crankshaft is solely 463 mm. And at 558 mm, also the installed height is very small.
The cylinder's vertical axis was inclined to the front through 32°. This results in the optimal centre of gravity and a distribution of weight towards the front wheels (indispensable for supersports motorcycles) for a ride feel of absolute precision and the best possible feedback from the front section.
The crankshaft of the S 1000 RR engine is a single forged piece of quenched and tempered steel on friction bearings and features the traditional 180° offset for equal ignition intervals. The connecting rods on friction bearings are designed as particularly lightweight forged parts of quenched and tempered steel. Only 103 mm in length, they take up the minimum of space in the engine that benefits the centre of gravity, exerts acceptable forces on the sides of the pistons, and yet maintains smooth engine running. Arranged at 45° to the connecting rod's vertical axis, two lubricating bores in the
connecting rod's upper eye safeguard the supply of oil to the piston pin bearing. The connecting rods are split horizontally by means of so called cracking, allowing high precision assemblies without the need for additional centring.
Lined with Nikasil, the bores house the lightweight forged pistons of 80 mm diameter with very short slipper skirts. They are fitted with two narrow piston rings with optimised friction properties and a three part oil scraper ring.
The flat design of the combustion chamber, piston head, and valve recesses promote good thermodynamic properties during the combustion process and help to optimise the weight of the piston head. The weight of the piston, complete with pin and rings, is only 253 g. Special oil spray nozzles in the crankcase reduce the buildup of heat by cooling the high temperatures on the piston heads. This safeguards reliable operations even under extreme conditions and enhances the service life.
The cylinder crankcase split horizontally into two sections at the height of the crankshaft axis
is made of high strength aluminium alloys. The compact top section of gravity diecast forms a highly rigid construction together with the four cylinders and the top bearing block for the crankshaft. In addition, the top half of the housing takes the lightweight and compact six speed gearbox. The cylinder block with the water jacket is designed for the maximum of rigidity as a so called closed deck structure.
This affects decisively the performance, characteristics, combustion quality, and also the fuel consumption of the cylinder head and VTC. The four valve cylinder head was designed with an eye to the ideal duct geometry, compactness, the optimal thermodynamics, and efficient heat balance. Owing to the small valve angle, the inlet ducts present the ideal linear design and the combustion chamber compact dimensions for high compression and the optimal efficiency.
Featuring a cam follower controller with double overhead camshafts, the four cylinder engine delivers the maximum possible power and torque, at the same time fulfilling the criteria for rigidity, min moving masses, and optimal timing cross sections at the valves. It presents the perfect combination of max rigidity and min weight of moving valve components with a highly compact cylinder head design at the same time. Valve clearance compensation takes the form of very small and light shims installed in the spring plates. On the inlet side, the spring plates are made of lightweight high performance aluminium. The moving masses of the cam follower controller are smaller than a comparable solution with bucket tappets. The small oscillating masses boost valve acceleration for beefy cam profiles and high free valve cross sections.
The speed threshold set down for the series motorcycle is 14,200 rpm, yet the purely mechanical speed capacity is far higher. The large cylinder bore of 80 mm allowed the installation of valve heads with the largest possible diameter for the greatest possible power delivery. The valve head diameters are 33.5 mm on the inlet side and 27.2 mm on the exhaust side for an impressive performance with the greatest possible utilisation of engine capacity on the 1000 cc supersports segment.
The lubricating system in the engine takes the form of a wet sump with Eaton pump, a tried and tested solution on this segment. Instead of a heat exchanger, a separate oil cooler is used that is integrated in the bottom cladding under the radiator for the optimal flow properties. This cooler prevents the additional introduction of undesired heat to the coolant, so a smaller and lighter radiator can be installed with the corresponding reduction in the quantity of coolant needed.
Small installed widths and a compact but above all lightweight design were also prioritised in the arrangement of the electrical auxiliary units and their drives. For instance, the three phase alternator fitted with a permanent magnet sits on the left tail shaft. It delivers 434 W at 6000 rpm and is designed for a max speed of 16,000 rpm. Arranged behind the cylinders in the top half of the engine casing on the left, the intermediate starter motor delivers 800 W and weighs 1050 g. It is coupled via a freewheel
and presents a reduction ratio of 1:24.61 to the left outer crank web designed as a spur gear. For weight saving reasons, the left side cap for the alternator and starter motor is made of lightweight magnesium.
The injection process is fully sequential, i.e. the fuel is introduced to the intake duct individually and in sync with the intake stroke of each cylinder. For better torque curves, the engine features the complex technology of variable intake manifolds. Depending on the engine speed, a servomotor attached to the air box varies the length of the bellmouths over two stages according to program maps. The optimal charge is obtained when the appropriate fuel quantity is supplied through each of the four injector nozzles at the throttle flap strip and above the intake pipe. The injector nozzles are actuated either individually or together depending on the engine speed and power requirements.