Double-VANOS - but with low instead of high pressure.
Focusing on the engine concept, the engineers at BMW M sought from the start to increase engine output through an optimum charge cycle at high engine speeds. Quite simply, this is because reduced charged cycle losses offer not only more power, but also an improved torque curve and optimum engine response as well as a further reduction of fuel consumption and lower emissions. And precisely these are the benefits offered by variable double-VANOS camshaft control introduced in the BMW M3 for the first time worldwide back in 1995.
With its extremely short adjustment times, double-VANOS now also perfects the cylinder charge cycle in the eight-cylinder power unit of the new BMW M3. Under low loads and at low engine speeds, for example, double-VANOS ensures a higher valve overlap and, as a result, better internal recirculation of exhaust gasses. This, in turn, reduces charge cycle losses and helps to minimise fuel consumption.
The level of power delivered by the engine depends on the position of the gas pedal and engine speed. So double-VANOS adjusts the precision and angle spread on the camshafts infinitely to these two parameters with precise management by a control map. Unlike the ten-cylinder power unit featured on the BMW M5 and BMW M6, the eight-cylinder uses a double (and not a single) chain to connect the crankshaft and sprocket. The sprocket, in turn, is connected to the camshaft by a step motor/actuator, and not by a helical gearing.
The advantage is that the low-pressure M double-VANOS developed for the eight-cylinder is able, unlike the high-pressure VANOS featured on the V10, to run with regular engine oil pressure acting on the step motor. In other words, there is no need for a separate high-pressure system of pipes to turn the crankshaft versus the sprocket in a relative motion at maximum speed and with utmost precision. This means that the angle on the intake camshaft may be varied by up to 58, the angle on the exhaust camshaft by up to 48. Maximum angle adjustment speed, in turn, is 360 per second crank angle, low-pressure adjustment thus ensuring very short adjustment times and providing the optimum adjustment angle synchronised to ignition timing and injection volume as a function of load and engine speed.
Reliable oil supply even under extremely dynamic conditions.The high standard of driving dynamics offered by the BMW M3 obviously calls for a sophisticated supply of oil to and within the engine. Indeed, the engine oil supply is conceived for longitudinal and lateral acceleration of up to 1.4 g - far more than the forces acting on a passenger's body when taking off and landing in a jet aircraft. ...next page >>