Porsche, vivendo e aprendendo
For my money, the best thing at Geneva was on Ferrari’s stand. Not the intriguing FF, but the FF’s amazing four wheel drive system.
Designing an all-wheel drive system for a car with a transaxle gearbox is a very complex, probably thankless, task.
In fact, the only other car with such a layout is the Nissan GT-R, and Nissan’s solution is mighty complicated. Because the propshaft of a transaxle car is driven directly by the engine, it spins at very high speed. You can’t drive the front wheels of a car from a propshaft turning at 4000rpm. You need a gearbox to slow the rotation so you can use the twist action to turn the wheels.
So the GT-R gets a set-up that uses a second propshaft, driven by the rear-mounted gearbox and running to the front of the car to drive the front wheels. If you ever see the running gear of a GT-R you can’t help but admire the effort that went into engineering, but you also boggle at the complexity and the madness of a car with two propshafts, running in opposite directions.
Even conventional longitudinally-engined, all-wheel drive cars have to use a clunky transfer case on the side of the transmission, with a propshaft running forward to the front of the car, where another gearbox splits the drive to the front wheels. Porsche’s version of this layout actually sees the driveshaft for the front left wheel running through the engine’s sump in order to allow the motor to be mounted low in the nose.
Ferrari’s solution, by contrast, is brilliant in its simplicity. Because the FF’s engine sits so far back in the nose, Ferrari engineers have been able to mount a second gearbox on the front of the crankshaft. This ‘box allows the front wheels to driven directly by conventional driveshafts. The mini-transmission also gets a pair of multi-plate clutches (one for each wheel) to allow engine torque to be divided across the front wheels. A tilt sensor has been incorporated so that the transmission can predict rear wheel slip when the car is starting on an incline. The windscreen’s rain sensor probably even tells the transmission when its raining.
Apparently, the set-up dates back to 2002 when it was designed for the transaxle-equipped Maserati Quattroporte. However, it was felt that the Maser’s V8 wasn’t so torquey as to need all-wheel traction. Engineers from Bentley and Porsche were spotted on the Ferrari stand admiring the FF transmission. And admire it is all they can do because, understandably, Ferrari has patented this brilliant piece of lateral thinking.
http://www.autocar.co.uk/blogs/autoc...wd-system.aspx
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