Engine development for the 7 Series: New six-cylinder from BMW shuts down all valves

IBMW wants to bring the new six-cylinder petrol engine, which will power the 7 Series and the X7 from the beginning of next year, within striking distance of the diesel. It is said to consume up to a liter less fuel than its predecessor, while at the same time the performance increases to a solid 380 horsepower. The manufacturer is showing what engineers can coax out of modern combustion engines if they are allowed to.

The reduced consumption is mainly due to the combination of two technology components. The first building block is to reduce the tiresome drag losses that always occur when the driver takes his foot off the accelerator. A new system then switches the roller rocker arms to a position in which the exhaust valves no longer open. At the same time, the well-known Valvetronic, which is responsible for the lift of the intake valves, also moves to a zero position so that the pistons work against the gas trapped in the cylinder. This in turn acts like a gas pressure spring. During the rebound, BMW uses the mechanical energy to drive a power generator, the second technology component, which is firmly connected to the crankshaft.

contribution to saving fuel

The electricity generated with a voltage of 48 volts in turn supports the combustion engine in those low load ranges in which specific consumption would be particularly high. The electric machine then provides up to 17 kilowatts of drive power.

Another contribution to saving fuel is the renunciation of any “greasing”. This means that even at high speeds, only as much fuel gets into the engine as can actually be burned. In order to nevertheless achieve high specific outputs of up to 100 kilowatts per liter displacement, the coolant flows through the cylinder head twice. According to Roland Welzmüller, who is responsible for the development of petrol engines at BMW, the dormant performance potential should also be used in the future.

Lower emissions

Additional technology is used to make the engine fit for future emissions legislation. The camshaft is no longer actuated hydraulically on both the intake and exhaust sides, but electrically. This system, called E-Vanos, shifts gears twice as fast and is immediately ready for use even after a cold start at low outside temperatures. Particulate emissions are said to be reduced by up to 95 percent through the consistent use of a dual injection system. Each cylinder has two injectors, one of which feeds the fuel directly into the cylinder, the other in front of the intake valve.

Overall, the raw engine emissions should be reduced by half. The exhaust system, which has also been revised, does the rest, combining a three-way catalytic converter with a finer particle filter close to the engine. A second catalytic converter in the underbody, which has long been standard for BMW in Europe, supports the cleaning effect. Welzmüller is confident that the engine will be suitable for the EU7 emissions standard without major modifications. “We have everything in there that money can buy,” says the expert.

During the presentation of the engine at the Aachen Colloquium, Welzmüller announced that in future the four-cylinder engines would also be equipped with their big brother’s technology package. After a thorough examination of the energy balances, the decision was taken against cylinder deactivation. Shutting down all valves beats switching off individual cylinders.