Remember when enthusiasts all decried the imposition of regulations on emissions, saying that government regulation would make our cars pale shadows of what they had been? And they all believed that, never imagining that we would arrive at the present situation, with luxury limousines like BMW's Active Hybrid 7 - to use the official nomenclature - accelerating to 60 mph in less than five seconds, running to 155 mph, while being both more economical and cleaner.
The 7 Hybrid is a magnificent engineering achievement. It not only attains the "impossible" standards we now demand, but is also a good bit faster, quieter and easier to live with than the basic internal combustion only model. Technologies developed in concert with Mercedes-Benz allow BMW to add features formerly unavailable, like the transparent stop-and-start system. When you come to a stop, the V-8 shuts off, leaving the cabin absolutely silent, and releasing the brake pedal has the engine running in microseconds, the car already moving under the impulsion of the 51-pound three-phase synchronous 20 hp 120 Volt electric motor interposed between the crankshaft of the twin-turbocharged V-8 and the all-new eight-speed automatic transmission when there is the slightest touch on the throttle.
BMW is not new to turbocharging. There was a 2002 Turbo in the Seventies, one of the first applications in series production, and the 745i was essentially just a a turbocharged 733i E-23 sedan, but earlier models were achieved by adding a turbo to an existing engine. The V-8 in the current 750i and 750iL models is completely new, conceived specifically to be blown, with the turbos nestling in the vee of the block, and intake coming through the underside of the heads. in the Hybrid 7 the engine is stripped of most of its accessories. There is no starter; that function is handled by the integrated traction motor. The air conditioning compressor under the hood is electrically driven by the 120V system - which means that it can be remotely activated to cool the cabin down before anyone gets into the car, a very luxurious touch in hot climates.
The whole mild hybrid system, including the 60 pound Lithium-ion battery pack in the trunk, adds some 220 pounds to the already hefty 750i (around two and a quarter tons in the lightest model). In compensation there is a 17% reduction in CO2 and an increase in total power from 407 to 465 bhp. Torque is up 16.7% and the heavier Hybrid gets to 100 kph (62 mph) three-tenths of a second quicker. Any time the brake pedal is activated energy is recovered and fed into the battery, located just behind the rear seats in space that is ordinarily used for a rear A/C unit. The battery is protected by a sturdy shield as a safety measure.
The Active Hybrid 7 is identified by chrome badges on the trunk lid, on both C pillars, and by specific 19-inch wheels carrying 245/45 front tires on 8 inch rims and 275/40 rears on rims a half-inch wider. This means that each lightweight low-rolling-resistance tire on the car is specific to its place. There is special instrumentation to let the driver know how the various systems are interacting, but none of it is of "Tokyo by Night" quality. Like the rest of the interior, it is restrained and slightly understated. Many differences cannot be seen, as for example the use of the 760i's larger differential to cope with the higher torque levels of the hybrid.
Obviously there are substantial costs involved in attaining higher performance and lower emissions, but an owner can reasonably expect to gain much of that cost back at the pump. BMW expects 45% of the hybrid 7s to be sold in the US, 20 % in Germany, 7% in China, with the other third of production dispersed in the rest of the world.
It all works so well, so transparently, to such good effect that we think BMW will spread this mild hybrid approach to almost all its ever-widening range of models - maybe even into its motorcycles. It's that good.
source: automobilemag
