BMW allies its new turbo V12 to ZF’s eight-speed automatic for 760i/Li

  • 12-Aug-2009 02:37 EDT
BMW hi res 760i eng 8-09.jpg
This is the first application of BMW’s TwinPower Turbo technology and High Precision Injection (HPI) on a 12-cylinder engine.

The new BMW 760i is very much about numbers: twelve cylinders, 6.0 L, 400 kW (536 hp), 750 N·m (553 lb·ft), eight speeds, 0-100 km/h (0-62 mph) in 4.6 s. And for good measure there is a long-wheelbase version, the Li, that is stretched by 140 mm (5.5 in).

The result is a luxury car that is, in the words of Wolfgang Stadler, Managing Director of the company’s Dingolfing plant, "everything that BMW stands for."

The Li version leads the fifth-generation 7 Series family and is BMW’s flagship.

While both versions of the car come with a plethora of equipment and technologies, what really matters is its new all-aluminum V12 and the first application of ZF’s new eight-speed torque converter gearbox. This combination helps toward achieving an EU combined cycle fuel consumption of 12.9 L/100 km (18.2 mpg) for the 760i and 13.0 L/100 km (18.1 mpg) for the Li. Respective curb weights are 2105 kg (4640 lb DIN) and 2175 kg (4795 lb DIN).

Low vibration and noise levels were major design criteria, and the engine, in 6.6-L form, will be used in the new Rolls-Royce Ghost, due to be seen at the Frankfurt Motor Show in September.

The engine has a closed-deck structure combined with bolts securing the cylinder heads directly to the floor-plate of the crankcase to provide optimum stability. Double bolts on the main bearings with an additional connection to the side panels via threaded support bushes and bolts reduce the influence of lateral forces from the crankdrive on the crankcase. Iron-coated aluminum pistons are used.

This is the first application of BMW’s TwinPower Turbo technology and High Precision Injection (HPI) on a 12-cylinder engine and extrapolates a system used on the company’s six- and eight-cylinder units. The two Garrett turbochargers, one for each bank of cylinders, help the engine to achieve maximum torque at 1500 rpm, which it maintains to 5000 rpm. Compared to BMW’s previous-generation V12 (which had an identical capacity to the new unit), this represents a 25% improvement at an engine speed 2300 rpm lower.

Maximum horsepower of 400 kW is achieved at 5250 rpm and is 22% higher than that of the previous V12. CO2 emissions are 299 g/km for the 760i and 303 g/km for the 760Li. The engine meets EU5 and ULEV II standards.

Piezo-type injectors are fitted in the cylinder head between the valves and directly adjacent to the spark plugs. The system pressure—200 bar (2900 psi)—is generated by single-plunge fuel pumps on each row of cylinders. Camshaft timing is via BMW’s dual-VANOS system. This allows the engine to run efficiently under part load with a high share of residual gas and reduced pumping loss. BMW also claims the double-VANOS gives the engine more direct throttle response.

Oil supply to the engine is via a flow-controlled pump operating on demand. It is a six-chamber, pendulum slide type. Compression ratio is 10:1.

The identical, three-into-one exhaust manifolds are configured to the engine’s firing sequence. In combination with the catalytic converters optimized for minimum counter-pressure, the configuration of the exhaust gas manifolds also helps improve throttle response.

BMW has applied its EfficientDynamics philosophy to the V12, including Brake Energy Regeneration and on-demand operation of the electrical water pumps, plus the oil pump.

The ZF eight-speed transmission is expected to be used in other BMW models including the forthcoming 7 Series hybrid, 5 Series-based GT, and some 3 Series versions. It replaces a six-speed within similar packaging and weight parameters. The new transmission has only a slightly greater parts count than that of the six-speed.

The eight forward, one reverse gear configuration incorporates four simple gearsets and five gearshift elements. The system can change down by more than two gears; the downshift from eighth to second is achieved as a direct change requiring only one clutch to open. When shifting up or down by one or two gears, only one clutch is opened. The transmission design helps improve shifting speed, claims BMW. 

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