Wet Clutch or Dry Clutch?
The starting point for any transmission designer is knowing the amount of torque the system needs to handle.
Nowhere does this apply more clearly than in the design of dual clutch gearboxes, where applications
for lower-cost vehicles are already showing a different clutch-design approach to those for
higher-powered models. As technologies at both ends of the spectrum improve, the differences
can be expected to become even more pronounced.
Wet clutches running in an oil bath or mist are used for higher torque applications where there is more energy to handle and more heat to dissipate. All but a few of the DCT systems on the market today are wet-clutch units, but their relatively high cost has until now limited their application to medium-sized vehicles with torque outputs of 250Nm and upwards.
BorgWarner, key developer of roadgoing DCTs with its wet-clutch DualTronic system in the Volkswagen Golf and other VW group models, as developed a lighter, more compact and less expensive dry-clutch DCT for smaller vehicles, especially gasoline models, which do not have to handle such high torque throughputs.
This differentiation has clear consequences not just for the car designer but for the companies which develop transmission lubricants, too. Incorporating clutches into the system means the oil has to handle an additional set of demands compared with a standard gear oil.
BorgWarner is working on two further initiatives: a so-called moist clutch development of its existing technology, in which reduced energy wastage in oil pumping helps save a further 2 percent in fuel, and an innovative micro-DCT architecture to serve emerging markets at lower cost.