S Tronic transmission
Reinvigorating this engaging thread with some information on yet another member of the DSG family: the
S Tronic.
And the reason why I wish to do so is because, my association with the DSG family continues for the foreseeable future, courtesy the super Audi A4 (
sneak peek to the initial review).
As some of you might be aware, my Vento kept excellent company for close to 6.5 years/87,000+ km and the DSG experience was nothing short of top class! Well, I could actually write a few words in this thread as a testament to that fantastic experience.
The S Tronic, a term designed by Audi for differentiation within the VAG, is essentially part of the DSG family. Which means, it is the same dual-clutch configuration found in other DSG variants.
Speaking of DSG variants, here is the line-up with some details:
In this post, let me try to pen down whatever I have understood so far. By no means, do I claim my understanding to be exhaustive. So, please treat this post as an endeavor of my humble effort to share what I have learnt so far.
The S Tronic, in my Audi A4, is given the name
DL 382 - 7F. Codename: 0CK. (it's the number '0', not the alphabet 'O')
D = DSG
L = Longitudinal engine
382 = evolution of the nomenclature related to estimated max torque
7 = seven speeds or gears
F = front wheel drive
There's also the DL382-7Q ('Q' for quattro). And the DL382-7A ('A' for All wheel drive).
While the smaller DQ200's (in my Vento) torque handling capacity was 250 Nm, the larger DL382 can handle technically upto 500-550 Nm. One of the fundamental difference is the usage of larger and separate oil 'chambers' or circuits in the S Tronic, giving it flexibility to dissipate a lot of heat under high loads during starting and instant acceleration etc.
By the way, the S Tronic is not the same as a Multitronic or Tiptronic. While the S Tronic is a dual clutch setup, the Multitronic is a continuously variable transmission (CVT) (
details) and the Tiptronic is a more traditional automatic gearbox featuring a torque converter (
details).
Going back to how it operates, the S Tronic has exactly the same principle like other DSGs.
The S Tronic comprises two subunits and integrates two multi-plate clutches that control the various gears. The large K1 clutch located on the outside directs the torque via a solid shaft to the gear wheels for the odd-numbered gears 1, 3, 5 and 7. A hollow shaft rotates around the solid shaft. It is connected to the smaller K2 clutch, which is integrated into the inside of its larger sibling, and which controls the gear wheels for the even-numbered gears 2, 4 and 6, as well as the reverse gear.
Both transmission structures are continuously active, but only one is connected to the engine at any one time. For example, when the driver accelerates in third gear, the fourth gear is already engaged in the second transmission structure. The shifting process takes place as the clutch changes – K1 opens and K2 closes.
For longitudinally installed engines, Audi has developed a special version of the seven-speed S Tronic in which the gear wheels for all gears are situated one behind the other on an output shaft. The three versions for transversely installed engines are configured in a single layout with two output shafts, allowing a compact design. The S Tronic for transverse engines is available with six or seven gears.
The seven-gear S Tronic itself has three sub-versions. Which sub-version is used with which engine depends on the amount of torque to be transmitted. Per Audi, the S Tronic for longitudinal engines can handle engine speeds of up to 9,000 rpm.
Below are some diagrams extracted from public domain sources.
Firstly, the overall schematic of the S Tronic assembly:-
When seen from the car underbody, this is how it looks:-
Given its strategic importance, the box is protected underneath.
A slightly closer look at the 7F (0CK) front wheel drive variant, explaining some of the parts:-
As per certain sources, the DL382 is the redesigned avatar of the DL501 gearbox.
The linear architecture of the 7-speed gearbox:-
The selector lever assembly:-
And the component-by-component view:-
To make things slightly interesting, here is the function diagram of the selector mechanism:-
Here is a diagram showing some of the special features of the newly developed S Tronic:-
One of the key features, talked about highly in various forums is the shift-by-wire/park-by-wire technology.
The A4 (B8 gen onwards) uses the latest 'Audi selector' mechanism with full shift-by-wire capability (SBW). This means that parking lock operation is also fully automatic. The term used for this is "park-by-wire" (PBW). There is no selector cable connecting the selector mechanism to the transmission.
The parking lock is not solely controlled by the mechatronics unit. the selector mechanism is also actively involved.
Coming to speed, Audi says that the 0CK gearbox's top speed is in the 6th gear. In the 7th gear, the engine speed is reduced for better fuel efficiency.
Now, in addition to the above diagrams, I came across some beautiful videos as well. Specially, there's a site which has this technical illustrations all nicely done up, please do check out this website -
Digital Media Technik
They have a variety of technical animations covering multiple topics. They claim that all the illustrations have been reproduced with permission from the OEM.
Here's a YouTube video with a slightly different take:-
However, any DSG story is not complete without its fair share of warnings or ominous messages. For this one too, Audi has shared a list of what can go possibly wrong along with some specific messages.
These are categorized into 3 types:-
Transmission errors with 'red' colored icon on the MID:-
The 'red' are the serious ones indicating a malfunction or the transmission temperature getting too hot. Advised to stop the car immediately.
Transmission errors with 'yellow' colored icon on the MID:-
The 'yellow' errors are due to a malfunction but you can continue to drive by adapting the driving style: this error could be due to limited functionality of the gearbox (for e.g. only even or odd gears) or problems with the selector lever (then recommended to use only paddle shifters)
Transmission errors with 'white' colored icon on the MID:-
This 'white' error is the least disruptive of the set, and is possibly due to a malfunction in the tiptronic mode.
Summary
Taking into account the above information, it becomes clear that S Tronic characteristics significantly contribute to superior driving convenience, enhanced car dynamics, and fuel saving.
A new car equipped with this transmission can impress the owner with smooth gear shifting and great acceleration characteristics in comparison with cars equipped with classic automatic transmissions and CVTs. It has certainly impressed me, a lot!
However, operation principles of this transmission are based on complex algorithms and its design includes the mechatronics as well as numerous servomechanisms. As a result, this transmission is expensive and complex, and possibly with its own share of problems. Maybe not as frequent as the younger siblings of the DSG family.
All information in this post taken from public sources & owner manuals. Will attempt to update this as I learn more.