Transmission Design
Porsche Doppelkupplung (PDK) Design
The Porsche Doppelkupplung (PDK) features two multiple-disc clutches operating in oil. Compared to a system with dry clutches, the design of the wet-running multiple-disc clutches increases thermal stability.
Advantages of wet-running multiple-disc clutches compared to dry clutches:
- Good mechanical load capacity for high torques in a compact design
- Good thermal load capacity even under extreme loads
- Better clutch engagement response
- Long service life due to less friction plate wear
- Greater comfort and driving dynamics
The two transmissions in the Porsche Doppelkupplung (PDK) each comprise a multiple-disc clutch and a drive shaft. Each transmission thus has the functional design of a manual transmission and an extremely compact construction. The drive shafts of the transmission act on a common countershaft and from there on the output shaft via a constant. The output shaft is connected via the drive flange to the cardan shaft, which drives the wheels via the rear axle differential. In the all-wheel version, the downforce is provided by the hang-on all-wheel clutch, the beveloid gear wheel set and the connecting shaft directly onto the front-axle final drive and therefore onto the drive shafts of the wheels. The clutches and the shift functions of the individual transmissions are controlled by way of a hydraulic control unit in the bottom part of the transmission.
The oil injection lubrication feature in the Porsche Doppelkupplung (PDK) is another factor in the increased efficiency. This is a type of circulation lubrication in which the oil is injected into the friction point. The gear wheels therefore no longer have to turn in the oil bath, as they do with splash lubrication. Churning losses can therefore be avoided.
The Porsche Doppelkupplung (PDK) has one oil chamber that serves the gear wheels and clutch via a shared oil circuit. Compared to a solution that has two separate oil chambers between the clutch and the gear housing, the advantage of this design is that an extra oil chamber division is not required. This not only reduces the weight of the transmission but also ensures a more compact construction. The weight aspect is also a consideration in the plastic design of the oil pan with integrated oil filter.
The function of the vibration-balancing damping mass is performed by a new dual-mass flywheel in the Porsche Doppelkupplung (PDK). This new dual-mass flywheel is integrated between the engine and the transmission and absorbs engine vibrations. By filtering noise and vibrations, the dual-mass flywheel also ensures comfortable driving in the lower rpm range. This helps to further reduce fuel consumption.
Gear Wheel Lubrication
Since the countershaft (yellow) is positioned on the top of the transmission due to its design, it does not churn the oil. While churning losses are reduced, adequate lubrication of the transmission is still not guaranteed. To ensure that optimum lubrication of the gear wheels is achieved, additional oil splash tubes (arrow) are installed in the transmission.