Auto Service World
News   January 8, 2015   by Auto Service World

New DCTs Aim To Restore Appeal

Honda and Volkswagen have fired the opening salvos in a gearbox war which aims to restore the customer appeal of dual clutch transmissions. This move is especially timely in North America, where a new generation of super-smooth eight- and nine-speed planetary units from suppliers such as ZF have eroded the perceived advantages of DCTs in terms of sophisticated shifting. DCTs have also suffered from bad press and negative customer feedback, with drivers accustomed to silky-smooth torque converter automatics complaining that DCTs are unacceptably jerky in low-speed maneuvering and slow off the line when accelerating from rest.

Volkswagen, with less of a strict focus on the North American market, has chosen to stay with its established dual wet clutch formula and add a further three speeds to its DQ500 DCT to bring the total ratio count to ten — the first production passenger car transmission of any kind to feature so many ratios. Cleverly, the new DQ511 retains the same dimensions and practically the same weight as its seven-speed companion — essential if it is to fit into VW’s modular component matrix — and, remarkably, the extra ratios have been achieved without having to increase the number of gear pairs.

“Reversing the power flow within the gearbox was enabled without additional pairs of gearwheels by employing an entirely new shifting strategy and adding two shifting elements and a reversing wheel,” says VW’s briefing. “This enables the implementation of ten progressively stepped gears.”

Volkswagen group’s ten-speed DCT is an enhancement of the seven-speed unit, also handling 550 Nm torque.

Significantly, in view of Honda’s similar comments on DCT launch performance, VW has taken the opportunity to make the first three gears low (short) to further improve drive-off, and the “finely graduated” steps right up to ninth gear enable efficiency gains. Tenth is a long gear, significantly reducing rpm and thus CO2 emissions during cruise. VW also points to the possibility of gears for special functions, such as an ultra-low crawler ratio for off-road work, or a special super-overdrive.

Like Honda, VW has developed a special oil for this transmission, and special coatings on the gearwheels and low-friction bearings help further improve efficiency. As with all of VW’s latest DCTs, the DQ511 is equipped to permit engine-off coasting, fully decoupling the engine.

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