What is a dSG and how do they work?

dsg1

With the DSG (direct-shift gearbox) transmission, a dual-clutch automatic, Volkswagen and Audi made one of the biggest impacts in the industry in 2003, providing an efficient option that offers reliability and great power. And, it has the least downsides of all transmissions.

The German automotive group has released two variants: a 6-speed DSG gearbox (DSG6) and a 7-speed DSG gearbox (DSG7). Despite the fact that various technical improvements have been applied to both gearboxes over the years, the basic principles remain the same.

 

dsg6
DSG6 (6 SPEED)

The main difference between the DSG6 and the DSG7 is the Clutch System. Where the DSG6 uses wet multi-plate clutches, the DSG7 gearbox uses two dry plate clutches. In addition, the DSG7 has an extra output shaft to which the reverse gear is linked.

dsg7
DSG7 (7 SPEED)

The DSG is effectively two separates electronically controlled manual transmissions built into one, where it is operated in a fully automatically mode and the computer decides when and how to shift the next gear. But it can also be operated in semi-automatic mode where the driver uses a gearshift lever to select gears.

 

Volkswagen DSG transmissions uses a transaxle design, which means that the same transmission case houses both the gears, using a torque-splitting differential so the axle shafts can operate at different speeds. A DSG-equipped vehicle has a flywheel, which fits into the input shaft of the transmission, and is engaged by a clutch. This causes the transfer of power from the engine to the drive wheel, through the transmission.

DC1
DSG TRANSMISSION WITH DUAL-CLUTCH

The word “dual-clutch transmission”, means that the DSG has two clutch packs, as well as two separate input shafts. Both are a concentric design, which means that one fits over the top of the other. The first clutch pack engages the odd gears of 1, 3, and 5, while the other engages the even gears of 2, 4, and 6. The two clutch packs are designated as K1 and K2. 

 

 

A mechatronic unit is the control centre of the gearbox and is only found in DSG transmissions. The Mechatronic unit is able to pre-select the next gear that you need before engaging the clutch and performing the shift, since it is working with two transmissions. This unit causes the DSG to shift gears at a very fast speed by simultaneously disengage one gear as it engages the next to deliver more power. The DSG makes driving in traffic, to hitting back roads or race tracks much more convenient.

The Controller Area Network (CAN) bus is a message-based protocol designed to allow the Electronic Control Units (ECUs) found in today’s automobiles, as well as other devices, to communicate with each other. The Mechatronic unit works with other control units in the vehicle, such as the ECU (Engine control unit) and the ABS braking system. A variety of factors contribute to the “decision” of the Mechatronic unit of how and when to select gears. This includes factors such as vehicle speed, engine speed, throttle position, brake pressure, and g-force measurements from the accelerometers in the car. Thus, the Mechatronic unit knows exactly which gear you’re going to want next, whether you are accelerating, braking, or cornering

The components of a mechatronic unit are:

  • Control unit
  • Valve body
  • Solenoids

The control unit collects an analyse the information or data about the current condition of the Mechatronic unit and fluid via the speed, – temperature, – and pressure sensors. From this information, the Mechatronic unit knows exactly when to change to the next gear.

The solenoids are the executive elements of the control unit and its electrohydraulic valves. They allow transmission fluid to flow under a high pressure and they manage the hydraulic valves. The solenoids can work on a higher frequency, and this can help in faster gear changing.

The valve body manage the fluid flow to the various sections of the transmission and is responsible for hydraulic control in the automatic transmission. The valve body consists of the following components:

  • Plates with fluid pad and valve seat
  • Gasket with gaps in specific places
  • Hydraulic valves
  • Springs
  • Plastic and metal balls
  • Manual valves (on the upper plate) – it determines whether the car is in parking, drive or neutral or reverse position.
MECH 1
DSG TRANSMISSION MECHATRONIC UNIT
CU
MECHATRNOIC CONTROL UNIT
VB
MECHATRONIC VALVE BODY
SO
MECHATRONIC SOLENOIDS

So basically, if you’re just driving along in traffic and not accelerating or braking with a lot of force, the transmission will work its way up or down through the gears easily, ensuring smooth performance. The shifting of gears at low revs also contributes to maximum fuel efficiency. When stepping on the accelerator to drive at a higher speed, the Mechatronic unit hold the gear longer due to the increase of power from the engine. It shifts to the next gear faster. A DSG transmission can perform a complete shift in about 200 milliseconds.

 

Most DSG-equipped models also feature a ‘Sport’ mode in addition to ‘drive’ or ‘manual’ modes. Sport mode changes the programming to be a bit more powerful and not as focused on maximum efficiency and miles per litre of fuel. In Sport mode the transmission changes gears faster, hold gears longer, and downshifts to make use of engine-braking. On many vehicles, Sport mode may also cause changes to the responsiveness or power of the engine, firmness of the suspension, or make other changes to enhance the driving experience.

"DSG FART" COMPLAINT

There is one issue that some people have with the fast-shifting of the DSG vehicles, namely the “DSG fart”. If you own a DSG-equipped vehicle, you’ve probably heard a loud ‘crack’ sound coming from the exhaust between hard acceleration.

The sound is simply because of the engine computer pulling timing from the ignition cycle when the shift occurs. This contributes to the smooth changing to the next gear. A small amount of unburned fuel passes into the exhaust on this process and ignites, creating this sound.

In the newer Volkswagen and Audi DSG-equipped vehicles this sound tends not be so clear and loud, because of the changes in transmission design, engine specifications, and programming.

AD1
French engineer Adolphe Kégresse

HISTORY OF THE DSG TRANSMISSION

The first dual-clutch (DSG) transmission was invented in 1935 by French engineer Adolphe Kégresse. Although it has been rejected for a few years, his idea contributed to the invention we know today.

The 2004 Audi TT 3.2 Quattro was the first DSG-equipped vehicle. Volkswagen only decided to provide the DSG as an option for their own vehicles until mid-2005, in the then-new Type 1K PQ35 Mk5 Jetta TDI.

Volkswagen and Audi have typically used DSG and S Tronic DCT transmissions in their sportier models, such as GTI, GLI, CC, and select R models from VW, most S and RS models from Audi, and nearly all TDI-powered vehicles from 2006 on.

The majority DSG transmissions have proved to be extremely reliable, but like any other vehicle component, they are not completely without faults or problems. It is necessary to do proper service and maintenance on this transmission, using high-quality parts and fluids. 

COMMON DSG TRANSMISSION PROBLEMS

The majority DSG transmissions have proved to be extremely reliable, but like any other vehicle component, they are not completely without faults or problems. It is necessary to do proper service and maintenance on this transmission, using high-quality parts and fluids.

Transmission Mount Wear

Like many other parts, the transmission and engine mountings can wear over time. This may cause hard clunking noises coming from the position of the transmission. Your specialists should always check the condition of the mountings when performing a gearbox service. Driving a lot of bumpy or gravel roads causes the engine and gearbox to vibrate and then leads to quicker mounting-wear.

M1
TRANSMISSION MOUNT DIAGRAM
FLYG
WORN FLYWHEEL

Mass Flywheel Wear

The most common wear-related issue of the DSG transmission is probably the failure of the mass flywheel. When the vehicle is failing to select gears, especially from a stop, it may indicate flywheel wear. You may also experience vibration and clear noises when driving. TDI models are most affected by flywheel failure due to the excessive vibration of a diesel engine.

When you fail to replace a bad flywheel, it can damage the bellhousing (part of the transmission that covers the flywheel) and other parts of the transmission. It is best that you immediately stop driving the vehicle or get it inspected should you suspect, there might be flywheel issues.

Dual-Clutch Wear

Another DSG transmission problem can be caused by the clutches. The clutch packs themselves can eventually wear and require replacement. The wear of the clutch might be to an underfilled transmission, which fails to proper lubricate the clutches. Thus, it is important to service your DSG transmission regularly to replace the transmission fluid. With factory power levels and programming, it is unlikely that the clutches will ever need to be replaced if the car is serviced properly. One of the great benefits of the ‘wet clutch’ is that it can last very long, sometimes lifelong, when vehicles are being service regularly and properly.

CLH
WORN CLUTCH
eru5swfmf0901
GEARBOX MALFUNCTION WARNING

Mechatronic Unit Failure

The most expensive and serious issue with DSG transmission is the failure of the Mechatronic unit. Usually, the first sign of a failing Mechatronic unit would be the “gearbox malfunction” warning that appears on the dashboard. Thereafter you might find that the transmission is struggling to select gears or it won’t select gears at all. Another sign of a faulty Mechatronic unit is the shaking and jerking of the vehicle when gears are selected. Many drivers would find that the transmission goes into ‘limp mode’ and there is a limited number of gears available to use. The best way to determine if the Mechatronic unit is faulty, would be with an electronic scan tool. In most cases with failing Mechatronics, other transmission parts like the clutches, flywheel and gears are not physically damaged itself.

Like any other production of goods, there is something like a bad batch. It has come to the industry’s attention that Volkswagen DSG-equipped models between September 2008 and August 2009 were manufactured with a bad batch of Mechatronic units. There was specifically a problem with the transmission temperature sensor, resulting in the transmission going into neutral, even when a different gear is selected.  Most of these faulty Mechatronic units should have been repaired by now, by the Volkswagen dealer themselves.

MAINTENANCE ON YOUR DSG TRANSMISSION

It is very important to perform regular services on any DSG transmission with the best quality fluids and filters.

Make sure that the transmission fluid is filled with the correct quantity for it is possible that when it’s hot, the fluid might be pushed out of the overflow vent on top of the transmission case.

Except for the fluid service, DSG transmissions don’t have any other regular maintenance requirements. Clutches and flywheels are service-free as long as they are functioning correctly and will benefit from regular fluid changes. Related components such as engine and transmission mounts, should be checked and replaced as needed, as well as the CV drive axles. 

S1

DSG TRANSMISSION SERVICE INTERVALS

The exact service intervals will vary depending on the exact vehicle year, model, and transmission code. Every Volkswagen and Audi model include a recommended service interval in the owner’s manual. On the vast majority of models, a DSG transmission oil service is required every 40 000 to 60 000 kilometres. The older the model of the vehicle, the shorter the service intervals become.

When using your DSG vehicle on-track, it is wise to do the transmission service as often as from 30000 kilometres.

A DSG transmission that is low on fluid will not function properly, and continuing to drive a transmission that is low on oil may result in damage to the clutches, gear sets, or other internal components.

At VAG Spec Centre, we have qualified DSG specialists that can service or repair you DSG transmission. Contact us today for any queries or quotations.

CONTACT US