The blueprints of a dual-clutch transmission are 84 years old and go back to 1935. Unfortunately, the transmission never made it into production, but the idea was born and documented on paper.
Porsche Motorsport picked up on the idea in the early ’80s and used their Porsche-DoppelKupplung PDK (Porsche-dual clutch) technology in the Porsche 956 and 962 Le Mans race cars from 1983. The benefit of the PDK transmission of that time was that the driver “could not damage” the transmission by grinding the gears during the endurance races. The extra weight and the inconsistent functionality played a big role in the balance of gaining advantages to its disadvantages. The PDK was obsolete after just a couple of years even though Porsche won the 1986 World Championship with a Porsche 962 equipped with PDK!
The first Porsche 64 was introduced in 1938 with a manual transmission, and it took till 1990 for Porsche to introduce their Steptronic equipped with a ZF 5HP19 automatic transmission. At the time, it was revolutionary, and tests showed that 8 out of 10 people were able to accelerate faster driving the sporty automatic vs. the stick shift transmission. Thank you, ZF!
In the mid-2000s, Porsche returned to ZF Friedrichshafen to develop a transmission that has the best of both worlds. Quicker response time, high performance, and lower production cost vs. the automatic as the end goal.
The best of both worlds means using two hydraulic and electronic controlled clutches, similarly used in automatic transmissions. These clutches are connected as two manual transmissions in one housing. Modern machining and material hardening allowed them to have two input shafts merged by sliding one over the other and transferring high engine torque, especially over the hollow secondary input shaft. An output shaft with end pinions connects to the ring gear to transmit the energy to the final drive. By replacing the stick in the cabin with electronically controlled shift forks, the transmission can engage and disengage the gears via a signal through the controlled solenoid and converted to hydraulic pressure so the transmission can be pre-shifted into the next upcoming gear.
By controlling the clutches via the computer, they are applied at the optimal time to make the shift and optimal pressure depending on engine load. This saves fuel and clutch wear. The transmission upshifts by toggling between clutches. These clutches are connected to the input shafts in the transmission. The 1st, 3rd, 5th, 7th, and reverse gears are available on one shaft, and 2nd, 4th, and 6th gears are available on the other. By having two transmissions in one, we can pre-shift the second transmission in 2nd gear when the transmission is driving in 1st gear. The clutch is not closed, so there is no connection between the second transmission and the engine. Shifts can be accomplished without interrupting torque distribution to the driven road wheels. By applying the engine’s torque to one clutch at the same time as it is being disconnected from the other clutch. Since alternate gear ratios can preselect an odd gear on one gear shaft while the vehicle is being driven in an even gear (and vice versa), DCTs are the fastest-shifting road car transmission available and can shift faster than a professional racing driver. Full throttle upshifts can happen in 80 milliseconds.
Join me at ATRA’s upcoming Powertrain Expo, where I’ll discuss the principles of operation of this revolutionary merge of automatic and manual transmission technology manufactured to the highest industry standards.