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DSG Transmission for Dummies
OK, now that we’ve reviewed TDI technology, let’s take a look at what it directly relates to and what still raises a few questions, i.e. DSG transmission.
A Short History
Since the invention of the automobile and until very recently, two types of transmission were available on the market: manual, and torque converter automatic. Manual transmission (also known as “standard”) is the most fuel-efficient because it operates without outside help, and without absorbing energy from the engine, like other types of transmission. Indeed, it’s the only one that doesn’t need a gear-case oil cooler, which just goes to show how efficient it is – it doesn’t need to dissipate heat since using it produces almost none in the first place.
The traditional automatic transmission with torque converter works differently. A big energy user with its powerful hydraulic pump, it makes use of the engine’s power to operate. Furthermore, even if the car is idling and the transmission is in “Drive”, it still uses the engine’s power. That’s why fuel economy figures are generally less favourable to an automatic than to a manual.
However, since the early 2000s, original equipment manufacturers (or OEMs as they’re called in the trade) have developed two new types of transmission: the Continuously Variable Transmission (or CVT) available from Ford, Nissan, Chrysler, Audi, Mitsubishi and Subaru, and the Dual Clutch Transmission (or DCT) from Volkswagen, Mitsubishi, Audi, Nissan, Porsche, Bugatti and BMW.
The first of these can operate using a metal belt or, in the case of hybrids from Ford and Toyota, two electric motors. This is an interesting transmission that’s more efficient than the automatic with torque converter, but still not as efficient as a manual. However, its performance isn’t to everyone’s liking.
Dual Clutch Transmission
The DCT is completely different. It can be classified as an automatic or a sequential transmission, depending on the manufacturer or the journalist writing the article. It’s almost as efficient as a manual from a fuel-efficiency point of view. The principle behind DCT is the brainchild of a Citroën engineer, Adolphe Kégresse, who developed the idea in the 1930s. But its commercial application had to wait 50 years: Porsche and Audi first used it, and then VW began using it for standard models in 2003.
Its efficiency comes from the fact that it uses gear pairs and a friction clutch, just like a manual. It’s called automatic because it’s an automat, a robot that chooses and changes the speeds. There’s no clutch pedal. It’s also a sequential transmission in that you can’t “skip” speeds. It has to go through all of them sequentially, i.e. in order. What makes this transmission unique is its double design: two clutches each driving three gears shift alternately. Each does half the work: while one is working, the automat prepares the next gear shift, whence the name “direct transmission gearbox.” There’s almost no interruption in power between shifting, except when the driver requests something the system can’t anticipate.
Automatic mode is perfect for daily use, given its smoothness and efficiency. It is well suited to the TDI engine: its greater torque means it can benefit from shifting offering fuel-efficiency and low engine speed, something that manual drivers won’t naturally do. That’s why, under certain conditions, the DSG can sometimes be more efficient than a manual.
Despite these qualities, the DCT is heavier and more complex than a manual, and more costly to manufacture. But VW offers it at the same price as a traditional automatic, no matter what the mode, i.e. $1,400.
A few links
If you’re visually inclined, you might like this video of the new 7-speed dual clutch transmission, which provides a good explanation of how it works.
For those who are still kids at heart, there’s this DSG transmission made using … a Meccano kit! No kidding. A Londoner has managed to build a completely functional Meccano DSG transmission. Furthermore, it simulates the electronic control system thanks to actuator motors and a PC. I’m always astounded by the determination of some model builders who manage to create such wonders. This one is exceptional. He deserves an award!
Personally, I’ve always preferred three-pedal transmissions, even if the DSG is faster, but then I’m the nostalgic type. Take a look at this British video comparing two TTs on a racetrack.Which do you prefer? Manual or DSG? Let’s talk.
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