LuK, a specialist in clutch and gear systems, said on Thursday it had developed a dedicated dry double clutch for the new Volkswagen group seven-speed direct-shift (DSG) gearbox.
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Fuel savings of up to 10% are claimed for the new ‘box, when compared with the current wet-clutch six-speed double clutch transmission, and up to 6% compared to a manual transmission.
Buhl, Germany-based LuK said its double clutch, at the heart of the new DSG gearbox, makes the ‘jolting’ that passengers experienced when the driver shifted gear a thing of the past.
As with the older, wet-clucth six-speeder (which just-auto understands uses BorgWarner technology and components), the underlying principle is simple: the double clutch is made up of two clutches located on two drive shafts. One clutch operates the odd-numbered gears – first, third, fifth and seventh – while the second controls the engagement and disengagement of the even gears – second, fourth and sixth – as well as reverse.
The changes are virtually instant as the next gear up or down is already pre-selected and ready for use when automatically activated, reviving a principle used decades ago on the manually-operated pre-selector geaboxes available for some commercial vehicles and large cars.
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By GlobalDataWhen accelerating in second gear, for example, third is already pre-selected in the other sub-gearbox, so that changing gear now becomes a speedy movement that does not involve loss of traction. The gear change is triggered electronically and implemented by means of hydraulic actuators. Torque superimpositions on gear changing, and the fact that the individual clutches open and close within a fraction of a second, mean that the driver is hardly aware of the gear change process, Luk claimed.
By contrast to the wet clutch in the DSG six-speed gearbox, which the Volkswagen group has offered in many VW, Audi, Seat and Skoda models since 2004, the LuK double clutch is a ‘dry’ type. With wet double clutches, torque is transmitted via plates submerged in oil. In the case of dry dual clutches, power is transmitted via friction facings on the clutch plates.
The absence of hydraulic support systems and the high degree of efficiency of the dry clutch enable major fuel savings to be achieved, LuK said. Thus, the combined fuel consumption of the DSG six-speed gearbox is more than 10% higher than that of the new seven-speed DSG gearbox when combined with VW’s popular 105hp/77kW 1.9TDI turbodiesel.
A dual mass flywheel, also supplied by LuK, acts as a torsion damper for the new gearbox.
The clutch specialist worked closely with Volkswagen on the development of the new components from mid-2004 and began shipments last month to the automaker’s plant in Kassel, Germany, where the gearbox is made.
The new seven-speed DSG ‘box is available for the Golf, Golf Plus, Golf Variant and Jetta models in conjunction with the 122hp/90kW 1.4TSI turbo- and supercharged petrol engine and the 1.9TDI.
The seven-speeder in combination with the 1.4TSI engine in the Golf has CO2 emissions of just 139 g/km, or just 137g/km combined with a diesel particulate filter, LuK said.
Luk is part of the Schaeffler Group, whose other brands are INA and FAG and operates at 180 locations in 50 countries. It had group sales of about EUR8.9bn last year.
