Secret history of the Porsche PDK
"I sat at home and nearly gave up," says the man who developed the Doppelkupplungsgetriebe...
I love a compound German word, and Doppelkupplungsgetriebe is a cracker. Double-clutch gearbox. That’s what it means, or PDK for short when talking about the Porsche one. And the story of the PDK began more than 40 years ago. Rainer Wüst was the man at the helm of its development programme, and at the time he was the tender age of 35. “The idea,” he says, “was to combine the best of two worlds – the advantages in the degree of efficiency of a manual transmission and the potential for performance of full automation, which still had many weaknesses at the time. It was a huge challenge for a small department such as ours. Maybe it was naivety that helped us, but certainly our pragmatism in dealing with the challenges did – as well as our passion for this subject.”
Let’s start with the principles of the PDK. The gearbox is split in to two sub-transmissions, and each has its own clutch. Only one of the clutches is ever engaged at any one time, meaning next gear can already be selected in the second sub-transmission. To change gear, the control unit simply opens the clutch that was transmitting drive, while simultaneously closing the one that wasn’t. That’s all that’s needed for a quick and seamless shift. Sounds simple, doesn’t it? Well, the journey was anything but.
The starting point was when Wüst discovered some old prototype development transmissions languishing in storage. These were the work of engineer Imre Szodfridt, who, late in the ‘60s, had pitched the idea of a dual-clutch transmission to the Head of Development at Porsche. He was a fella called Ferdinand Piëch. “Szodfridt was a very clever man, so this preliminary work helped us,” Wüst recalls. This was a welcome spring board, then, but Wüst still had a sizeable hurdle to surmount: early ‘80s technology.
“There were neither powerful control electronics nor vehicle-compatible electrohydraulic valves in series production. We got the Szodfridt transmission from storage and worked with pneumatic valves, which we converted to work hydraulically. It was complicated pioneering work from the ground up, but the result already had pre-series status,” he says.
The testbed for this wonder ‘box was the Porsche 944 Turbo, but the Porsche philosophy of testing in motorsport meant the new PDK was soon out on track in a 956. The racing drivers weren’t slow to recognise its potential. Hans-Joachim Stuck points out, “We were able to change gears and drive significantly faster without interrupting the engine’s drive.” And it was Stuck who came up with the novel idea of putting paddle shifters on the steering wheel. “Being able to keep my hands on the steering wheel when changing gears at full throttle felt great right from the start.”
Meanwhile, Jacky Ickx discovered another advantage: being able to left-foot brake while accelerating with his right foot to keep the turbo boosting. “This made him significantly faster coming out of a corner,” says Wüst. Of course, there were also the obvious benefits of being able to shift up quicker for improved acceleration and maximising the speed down the straights. Quicker downshifts also meant shorter braking distances. It minimised human error, too; the PDK wouldn’t miss shift and risk popping the engine.
Still, there were some issues to solve. The smoothness of the gearchanges for one, which was unsettling the racing car during changes. The clutch control wasn’t very smooth, so every time the driver shifted a gear there was ‘a hefty jerk.’ And according to Wüst, those jerks also “put great stress on the transmission – and the entire driveshaft. On a few occasions, this excess torque sent everything flying around us, and I sat at home in the evenings and nearly gave up on the whole thing.”
He didn’t give up, of course. He tested a development PDK in the 962 with reduced transmission inertia. This was the first racing car with a PDK, and, in 1986, Derek Bell broke its winning duck with victory in the 360-kilometre race at Monza. In the same year, Bell and Stuck went on to win the World Sports-Prototype Championship, too. There was rallying success as well. An Audi Sport-Quattro S1, complete with a PDK and one Walter Röhrl at the wheel, grabbed top honours in the 1985 Semperit-Rallye.
These successes proved the technical advantages of the PDK in motorsport, but what about series production? Wüst says, “We were at least 20 years ahead of our time. Along with the development of valves and electronics, which were not sufficiently advanced for series production, the conditions were not in place yet for the deployment of the necessary wet clutch.”
So we jump to the 2000s, by which time Ferdinand Piëch was the boss of Volkswagen and, according to Wüst, a man who “never forgot anything.” And having recalled the test programme at Porsche all those years ago, he facilitated what was now a perfected racing technology through to road cars. In 2008, Porsche replaced the 911’s optional Tiptronic torque converter auto with the option of a PDK. A year later it was fitted it as standard to variants of the Panamera.
Wüst is now Porsche’s Chassis Head of Development, but he gets quite emotional about the PDK years. “PDK is definitely a highlight of my 38 years at Porsche. There were many lovely projects, and this was one of the loveliest. A lot of what you work on ends up in the bin. But this is here to stay, I can feel it. This makes me proud. When I see a car with PDK on the road today, I know: a piece of me is inside that. And this is a wonderful development.”
Porsche achieved success with PDK by selling cars with a high enough price to pay for the fancy engineering and enough power to hide the additional weight.
Edit to add that they built four Club Sport prototypes according to Rennlist.
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