The new generation 911 is available for the first time with the new Porsche Doppelkupplungsgetriebe (PDK), literally Porsche double-clutch gearbox. Offering no less than seven forward gears, the new gearbox combines the driving comfort of a torque converter-equipped automatic transmission with the dynamic manual gearshift functionality of a sequential racing gearbox. PDK also boasts an entirely automatic gearshift function, and replaces the Porsche Tiptronic S automatic transmission previously offered on the Carrera and Carrera S. Through its optimised and adaptive gearshift programmes, PDK improves the acceleration of the 911 and reduces fuel consumption to a level even lower than before.
In principle, the PDK consists of a conventional manual gearbox and a hydraulic control system divided into two separate transmission units. Two wet clutches in radial arrangement, controlled hydraulically, and using oil for both cooling and lubrication, form the heart of the transmission. One clutch is for the first transmission unit with the uneven gear ratios (1,3,5,7) and reverse, and the other clutch is for the second transmission unit with the even gears (2,4,6). Via a number of pressure valves, the hydraulic control unit masterminds both the wet clutches and the shift cylinders activating the transmission ratio required.
The gearshift perceived by the driver comes not from the gears actually changing, but from the change of positive clutch engagement. In this case, the clutch on one transmission opens or disengages while the clutch on the other transmission closes or engages in a simultaneous process. The big advantage is an even faster gearshift than with a conventional manual gearbox or torque converter automatic transmission. The gears are already ‘in mesh’ when shifting and the power of the engine need not be interrupted in the process.
PDK also reduces to a minimum transmission power losses courtesy of the high standard of mechanical efficiency in the double-clutch, and this manifests itself in fuel economy improvements of approximately 13 per cent compared with a conventional Tiptronic S transmission. PDK also offers an advantage in terms of weight – despite two additional gears, it weighs 10kg less than Tiptronic S.
This PDK gearshift principle was first developed by Porsche for motor sport 25 years ago. Porsche works drivers benefiting from this technology were able to accelerate faster than their competitors and keep both hands on the steering wheel while changing gears, thus avoiding even the slightest distraction while shifting.
The seven-speed PDK shifts gears up to 60 per cent faster than a conventional automatic transmission, and naturally, gives the new 911 Carrera models even better performance: when equipped with PDK, the Carrera S Coupé accelerates in 4.5 seconds from 0-62mph, another 0.2 seconds faster than with a manual six-speed gearbox – and 0.8 seconds quicker than its predecessor with Tiptronic S.
And those customers in search of optimum driving dynamics have the option to combine PDK with Sport Chrono Package Plus, now featuring Launch Control. The result is high speed acceleration from rest free of wheel slip, combined with race-style gear shifting, enabling the car to accelerate to 62mph (100 km/h) in a truly outstanding 4.3 seconds.
To use the various functions of the double-clutch transmission, the driver can either shift gears by means of toggles on the spokes of the new steering wheel, or via the new gear selector lever. The driver can press forwards to shift the gears up, and press them from behind to shift downwards. Alternatively, pushing the gear selector lever forwards shifts up a gear, and pulling it back shifts down. The option of PDK costs £2,338, and the Sport Chrono Package Plus upgrade costs £729.Published 6 June 2008