Dual Clutch/Direct Shift Gearbox (DSG)

Dual Clutch Transmission (DCT) was invented by Frenchman Adolphe Kégresse just prior to World War II, but he never developed a working model. The first actual DCTs arrived from Porsche in-house development, for Porsche racing cars in the 1980s. The first series production road car to be fitted with a DCT was the Direct-Shift Gearbox (DSG) in the 2003 Volkswagen Golf Mk4 R32.

Sectional view of the Volkswagen Group dual clutch Direct-Shift Gearbox (DSG) transmission
IMG Ref: http://en.wikipedia.org/wiki/File:VW_DSG_transmission_DTMB.jpg

The revolutionary direct shift gearbox (DSG) combines the advantages of a conventional six-speed manual-shift gearbox with the qualities possessed by a modern automatic transmission. The driver enjoys immense agility and driving pleasure with, at the same time, smooth, dynamic acceleration with no interruption to the power flow.

The technical basis of the direct shift gearbox (DSG) is a double clutch. This consists of two wet plate-type clutches with hydraulically regulated contact pressure. One of the two clutches engages the odd-numbered, the other the even-numbered gears. This principle enables gear shifts to be made without interrupting the power flow and keeps the shift times extremely short. While the first clutch is transmitting the power, the second clutch is ready to engage the next gear, which is preselected. When the driver makes the gear shift, the first clutch is released and the second engages, so that the gear shift takes place in a fraction of a second.

A dual clutch transmission eliminates the torque converter as used in conventional epicyclic-geared automatic transmissions. Instead, dual clutch transmissions that are currently on the market primarily use two oil-bathed wet multi-plate clutches, similar to the clutches used in most motorcycles, though dry clutch versions are also available.

Clutch Types

There are TWO fundamental types of clutches utilised in dual clutch transmissions: either two wet multi-plate clutches which are bathed in oil (for cooling), or two dry single-plate clutches. The wet clutch design is generally used for higher torque engines which can generate 350 newton metres (258 ft·lbf) and more (the wet multi-plate clutch DCT in the Bugatti Veyron is designed to cope with 1,250 N·m (922 ft·lbf)), whereas the dry clutch design is generally suitable for smaller vehicles with lower torque outputs up to 250 N·m (184 ft·lbf). However, whilst the dry clutch variants may be limited in torque compared to their wet clutch counterparts, the dry clutch variants offer an increase in fuel efficiency, due to the lack of pumping losses of the transmission fluid in the clutch housing.

Clutch Installation

There are now three variations of clutch installation. The original design used a concentric arrangement, where both clutches shared the same plane when viewed perpendicularly from the transmission input shaft, along the same centre line as the engine crankshaft; when viewed head-on along the length of the input shaft, this makes one clutch noticeably larger than the other.

The second implementation utilized two single-plate dry clutches which are side-by-side from the perpendicular view, but again sharing the centre line of the crankshaft.

A latest variation uses two separate but identical sized clutches; these are arranged side-by-side when viewed head-on (along the length of the input shaft and crankshaft centre line), and also share the same plane when viewed perpendicularly. This latter clutch arrangement (unlike the other two variations) is driven via a gear from the engine crankshaft.

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The driver can operate the DSG manually or allow changes to take place automatically. In the automatic mode there is a choice between the well-balanced, comfortable standard shift settings and a program with greater sports emphasis. Manual shifts are made either at the gear lever or at shift paddles behind the steering wheel.

Reference:
http://en.wikipedia.org
Audi Glossary

Audi quattro® permanent all wheel drive

IMG Ref: www.audi.com (Click on the picture for a high resolution image)

Permanent all-wheel drive offers an unusually high level of active safety. In terms of tractive force, acceleration and hill-climbing ability on a poor surface it is unbeatable. By distributing the power input from the engine between two axles, higher lateral locating forces can be absorbed when cornering. This enhances lateral acceleration and at the same time ensures the highest possible level of safety.

Asymmetric/dynamic torque distribution, with a rear-biased split, allows the exceptional driving forces produced by powerful engines to reach the road even more efficiently. It reacts to conditions on the road more responsively. And with more agility on tight bends, it delivers a more exhilarating performance than ever.

Better Traction

State 1: Ideal driving conditions

If more traction is required – when towing a trailer, for example – quattro offers real advantages by offering greater tractive force in proportion to the vehicle’s weight.

State 2: Only 50 percent grip

In conditions where tyres experience reduced grip – as on a wet road – the advantages of quattro immediately become apparent. Whenever one wheel loses traction the others can compensate, so the car remains stable and continues to grip the road.

State 3: Only the front wheels have grip

quattro continually adjusts to road conditions to permanently distribute power between the front and rear wheels precisely where and when required. It means the vehicle stays responsive even if only one axle has enough grip. By contrast, if front- or rear-wheel drive vehicles lose grip at the driven axle, they can no longer transmit the engine’s power onto the road.

The self locking centre differential

The self locking centre differential sits at the heart of quattro on models with the engine positioned lengthwise along the car’s centreline.

Operating entirely mechanically, it continually reacts to road conditions and responds to any differences in the rotational speeds between the wheels. This ensures more power is always transmitted to the wheels with a better grip.

In addition, the Electronic Differential Lock (EDL) can act when needed to prevent the wheels from spinning. Excess power at one wheel is diverted to the other wheels that have more grip, maintaining traction in virtually every situation.

IMG Ref: http://www.automobilesreview.com/uploads/2009/05/audi-quattro.jpg

quattro for cars with transverse engines

To ensure the optimal distribution of engine power for each model, Audi uses specially configured all-wheel drive systems that vary in design.

The Haldex clutch is an electronically-controlled multi-plate clutch. It performs the function of the Torsen centre differential in cars with transverse engines, such as the Audi A3, A3 Sportback and Audi TT.

It ensures that engine power is permanently distributed between the front and rear wheels as and when required.

The Haldex clutch works by reacting to differences in the rotating speed between the front and rear wheels. This causes variations in the system’s hydraulic pressure, which in turn compress the clutch plates together to balance the distribution of power between the front and rear wheels. So if the front wheels begin to lose traction, the Haldex clutch channels power to the rear. And the greater the difference in rotational speed, the higher the pressure applied to the plates – which means that more engine power can be transmitted to the rear wheel.

There are six generations (unofficial) of quattro Evolutions.

The latest one is the 6th generation of quattro in the 2010 RS5. The key change in generation VI is the replacement of the Torsen Type "C" centre differential with an Audi-developed "Crown Gear" differential. The net result of this advance in quattro is the ability of the vehicle electronics to fully manage the vehicle dynamics in all traction situations, whether in cornering, acceleration or braking or in any combination of these.

Self-locking crown-gear centre differential

IMG Ref: www.awdwiki.com

Reference:
http://www.audi.co.uk/home.html
http://www.awdwiki.com/quattro.html

Audi S tronic Gearbox

IMG Ref: www.audi.com (Click on the picture for a larger image)

Faster gearshifts, sportier driving: the S tronic combines the sporty characteristics of a manual gearbox with the advantages of an automatic. Gear-changes with the dual-clutch gearbox are performed easily and with no appreciable delay. Depending on the driver’s preference, the gears may be shifted in fully automatic mode or in manual mode using the gearshift paddles on the steering wheel.

This new S tronic transmission can also handle up to 550 Nm of torque, meaning it can be coupled to engines such as the 3.0 V6 TDI or the 4.2 V8 engine of the S5. Or the 4.2 V8 of the RS4, for that matter, since it can handle engines revving up to 9,000 rpm!

Double act: the dual clutch forms the technical basis of the S tronic. One of the two clutches engages the odd-numbered gears and reverse, the other engages the even-numbered gears. The benefit: a gearbox that shifts from one gear to the next in less than 0.2 seconds and with no interruption in power flow.

When in operation, one gear is always engaged and another is pre-selected: while the first clutch is transmitting power in one gear, the second clutch has the next gear selected and ready to engage as shown in the following figures.

Operating principle, acceleration in 1st gear

IMG Ref: www.audi.com (Click on the picture for a larger image)

Operating principle, acceleration in 2nd gear

IMG Ref: www.audi.com (Click on the picture for a larger image)

When the gearshift point is reached, one clutch segment opens in a flash while the other closes. The driver therefore hardly notices the gearshift process.

Highly precise management of both multidisk clutches was one of the most important development goals. This was achieved in part with a compact pressure cylinder, electronically controlled rotation speed compensation and the use of an optimized coil spring package. This package of technology provides maximum precision and comfort at startup and shifting.

The transmission is managed by the so-called mechatronic module. This module involves a compact group of control units and hydraulic control valves that is integrated on the left of the transmission when facing the direction of travel. Its control concept allows the speed of the gear shifting process to vary and extremely precise control of the power necessary for the process.

The required control pressure is provided by an efficiently operating oil pump that is located next to the mechatronic module and is driven by a gear section. The oil pump is supported by a vacuum booster for cooling the twin clutch during starting. This allows the amount of oil pumped to be roughly doubled as needed without increasing power.

A unique feature of the seven-speed S tronic is its two separate oil systems. While the twin clutch, mechatronic module and oil pump are supplied by their own oil circuit with seven liters of automatic transmission fluid (ATF) oil, the wheel sets and the central and front-axle differential are lubricated with about 4.5 liters of hypoid gear oil. This separation allowed the development engineers to position all of the components ideally, without being forced to compromise by using a single lubricant.

The consistently efficient power transmission ideally supports a sporty driving style – both in automatic mode and with manual shifting:

• The flexible automatic mode allows the driver to vary the gearshift behaviour between the sporty character of the shift programme S (Sport) and the comfort-oriented shift programme D (Drive).
• If the driver prefers manual gearshift, the gears can be changed in sporty style with the gearshift paddles on the steering wheel or with the selector lever.

Other advantages of S tronic: the gearbox’s high efficiency leads to low fuel consumption and reduced emissions.

Reference:
http://www.audiusa.com/us/brand/en/tools/advice/glossary/s_tronic.browser.html
http://www.eurocarblog.com/post/677/the-new-audi-s-tronic-7-speed-gearbox