Tito F. Hermoso / Porsche AG | October 02, 2009 16:28
More than just letters in your alphabet soupStrange but true: by adding another clutch, you can take away the clutch pedal. To engineers, the logic is rather simple: split the function of one clutch into two - one for odd number gears and another for even number gears - and Viola!
And the benefits are legion. With the twin or dual clutch system, one can drive a manual gearbox like a 2-pedal automatic. You never have to live with losing the high performance advantages of a manual transmission. Two pedal motoring without the frictional loses and slippage inherent in all that hydraulic fluid shearing and sloshing in an automatic gearbox.
There's more. Compared to Formula 1 style single clutch automatic sequential gearboxes like the early BMW M3 SMG and early Ferrari clutch pedal-less manuals, the shift quality doesn't have the shift lag that "rocks" your head to and fro. The disadvantage is that twin clutch systems are heavier than a comparable conventional manual transmission (75 kg. vs. 47.5 kg). And for fans of after market-tuning, the design specification tolerances and torque capacity limits constrains after-market engine tuning potential.
As a matter of principle, there are already several off-the-shelf cars with dual clutch systems running on our streets. Three years ago, PGA Audi introduced the S-tronic/DSG to the Audi A3 turbo diesel and the Audi TT direct injection turbo. Last year, Ford introduced its 6-speed Power Shift Focus TDCi, while on the higher end of the power spectrum, BMW came up with the DTC option for the powerful M3. More recently, the Mitsubishi's EVO X and Nissan's GT-R come in twin clutch gearbox. And now the latest 911 with direct fuel injection comes with dual clutch 7-speed PDK.
But this is where the similarities end. Doubtless that many more car makers will make their own dual clutch systems, but it takes a lot more engineering expertise to make twin clutch systems work with the high power to weight ratios and extreme horsepower of a typical Porsche. With Porsche's PDK dual clutch system, the shift times are consistently within 500 milliseconds of the already quick 8 milliseconds for up shifts to the next preselected gear.
Consider the following: Maximum output of the 911 Carrera with its 3.6-liter power is already 345 bhp (254 kW) while output on the 911 Carrera S, with its 3.8-liter power unit is a way out 385 bhp (283 kW). At 1,400kgs of light weight muscular aerodynamic sculpture, a top speed of slightly over 300 km/h is attainable in a very short distance, thanks to the 911's high power to weight ratio. Amazingly, legal highway speed consumption is a responsible 10 km/liter, better than conventional hydraulic automatic transmissions like Porsche's own ZF manual-shift Tiptronic. CO2 emissions is down by 15%.
Credit where credit is due, Porsche practically invented the twin clutch system for the seminal Porsche 959 of 1986. That car was a mildly gentrified Group B racer for the street. More than mere bells and whistles, it was, to a Porsche 911 in 1986, what an EVO X is to a Lancer EL. The 959 established the DNA pool of a modern Porsche's alphabet soup of acronyms for sophisticated high tech variable suspension [PASM], braking, damping, stability and traction control [PSM], that one finds in the latest Porsche.
PGA Porsche's luxuriously appointed Carrera S Coupé accelerates from 0-100 in 4.5 seconds, 0.2 seconds faster than with a manual six-speed gearbox. Order Porsche's optional Sport Chrono Plus with F-1 style Launch Control and full bore acceleration becomes free of slip from a standstill, cutting the 0-100 km/h time to 4.3 seconds.
But the true test of twin clutch systems is at mid-range rpm. Which means, busy, cut-n-thrust, stop n' go city traffic, as this is where SMG's and "ordinary" Formula 1 based automatic clutches make even good drivers look clumsy and amateurish. Porsche's PDK system manages the magical feat of shifting faster than M. Schumacher while matching the smoothness of a veteran limo chauffeur. With PDK's 2 clutches, one gains performance, enhances economy, cuts acceleration time and makes one look like a really refined driver.