Dual clutch systems, such as that recently introduced on the Audi TT 3.2, are set to take a significant share of the European market over the next few years, as drivers opt for automatic – or automated manual – transmissions in far greater numbers.
Audi recently launched its twin-clutch transmission, which it claims is the only one of its kind in the world. The system uses electronic controls to allow two gears to be engaged at the same time, eliminating the loss of power experienced during gear changes.
Analysis by automotive consultant Ricardo predicts that by the end of the decade, manual gearboxes will account for just under half the market, down from their dominant 86 per cent now. Europe will become more like the US and Japan, where automatics already dominate.
The growth of automatics will be fuelled by pressure on manufacturers to improve economy, safety issues, and the fact that as congestion grows drivers will increasingly see automatics as more convenient.
But torque converter boxes, the original automatic gearbox and the norm in the US, are too big for Europe’s predominantly front-wheel drive cars, especially as forthcoming pedestrian safety regulations will put even more demands on underbonnet space.
Moreover, European manufacturing capacity is set up to produce manual boxes, so automated manuals will find favour. First generation automated manual boxes, such as Alfa Romeo’s Selespeed, are essentially a standard manual box in which the gearshift and clutch are operated by electric or electro-hydraulic actuators. The only packaging issue is finding room for the actuators.
The efficiency of an automated manual is close to an ordinary manual and better than a torque converter type. Fuel consumption can be around five per cent better than a manual for electrically actuated boxes as used on the Smart. ‘For small city cars, high mechanical efficiency gives the best possible fuel consumption on the standard cycle,’ said Ricardo Driveline and Transmission Systems engineer Tony O’Neill.
However, there are problems with perceptions regarding shift quality, achieving consistently smooth launches from rest, introducing creep to aid manoeuvres, and controlling hill starts. ‘Controlling an actuator to keep a normal dry clutch slipping is difficult,’ said O’Neill.
Dual clutch systems, such as Audi’s Direct Shift Gearbox (DSG) solve most of these problems. They are effectively two manual transmissions in parallel, with one shaft and clutch for odd-numbered gears and another for even ones, all under electro- hydraulic control. This arrangement allows two ratios to be selected simultaneously.
During driving, one gear is engaged. Electronic sensors detect throttle opening, braking and lateral acceleration, amongst other information, to decide which gear will be needed next. The appropriate gear is pre-selected but its clutch remains disengaged. The shift process opens the clutch of the currently-activated gear and closes the other clutch simultaneously, all under power. The result is shift quality on a par with a good modern torque converter box.
‘There’s much less reduction in acceleration and a smoother change in engine speed. In gentle driving the transition between gears is completely seamless,’ said O’Neill.