Power trio: a pair of sixes and a 500 hp V-10 add up to a winning hand for BMW powertrain

Automotive Industries, August, 2004 by Michael Scarlett

>From the exhaust viewpoint, the small turbine is upstream of the large one; gas can by-pass either turbine. From the inlet aspect, matters are reverse& with the big turbocharger upstream of the small one; air always passes through the large blower, but can largely by-pass the small one. All of this is controlled by three electro-pneumatic disc valves; the working of these is best understood from the four schematic diagrams.

Much of the remainder of the engine follows comparatively conventional European turbo-diesel practice. A cast-iron cylinder block is use& capable of withstanding up to 2,610 psi combustion pressures. Solenoid fuel injectors are fed at 23,200 psi. To meet Euro 4 emissions requirements, which are strict about particulates but not yet quite as demanding as U.S. regulations about N[O.sub.x], a zero-maintenance particulate catalyst is fitted. Unusually, to counter the usual diesel disadvantage compared to gasoline engines of a narrower working rpm range, this engine will run usefully to 5,000 rpm.

Finally, journalists were introduced to the new 5.0L V-10 M.5 engine. This is a relatively conventional four-valves-per-cylinder design, albeit that it claims to be the first V-10 in a production car, and boasts a very highly specific power output of exactly 100 hp/L--500 hp at 7,750 rpm for a 304.5 cu.in. swept volume derived from a markedly over-square 92 x 75.2 mm bore and stroke.

With a 90 degree bank angle, offset at crankshaft center height by 17 mm, the cylinder block is again a low- pressure gravity die casting in hyper-eutectic aluminum silicon alloy (17 percent silicon) with iron-coated pistons running direct on the machined faces of the precipitated silicon of the aluminum alloy bores. A racing-engine-style aluminum alloy bedplate has grey cast-iron inserts to act as supports for the 60 mm diameter by 28.2 mm wide main bearings. Pairs of connecting rods run on the tire crank pins, which are offset at 72 degrees. Bores are spaced at 98 mm centers, keeping overall crankshaft, and therefore engine length, down as much as possible.

Although power control is conventional, with individual throttle butterflies for each cylinder, both inlet and exhaust camshafts are variably timed using BMW's bi-VANOS system. The engine meets both Euro 4 and U.S. LEV2 emissions demands. This is helped by the highly sophisticated engine control unit, which has three 32-bit microprocessors and "ten times the memory capacity of the previous V8 M5 engine." The lubrication system recognizes that the M5 is capable of very high cornering rates, so it is a "semi-dry sump" design, with four oil pumps, and the sump itself designed to never run dry, to avoid any possibility of oil starvation. Given the unit's maximum speed--8,000 rpm--conventional audio-type knock detectors were not fast enough, so the engine uses ionic current detection via its spark plugs to provide fast enough individual knock detection for each cylinder.

To transmit all this power to the rear wheels, BMW has collaborated with German transmission specialists, Getrag, to design a remarkable seven-speed helical spur gear sequential automatic gearbox with a torque capacity of 405 lb.ft, to cope with the engine's 384 lb.ft, of torque at 6,100 rpm. This can be left to its own devices, of "manually" shifted, according to driver mood. Its electronic control allows the provision of a "climbing assistant," with which, coupled to brake control summoned by a prod of the brake pedal, the car simplifies hill starts by holding automatically until the driver accelerates away.