7G DCT Transmission

[BenzedUP]

Hi Guys,

My other half pick up her brand new A class last weekend which is equipped with the 7G DCT gearbox.

I've driven it a few times now and the best part of the car is the quick transmission, much better than the 7G Automatic.

Got me thinking... why would Mercedes use that on an A class and not on the C’s?

My C350 has the normal 7-Speed automatic, which is slowish compared to the 7G DCT in the A class?

Why can't Mercedes use the 7G-DCT in all of their cars now or at least most of their cars!

Can only imagine my 204 Coupe with the 7G-DCT transmission!

Cheers,


Jo.

 

[grober]

Seven-speed DCT. The new system is an automated three-shaft manual transmission consisting of two subtransmissions, each with its own clutch. Both actuation of the clutches and gear shifting take place fully automatically and without any interruption in tractive power.
With seven gears, it offers a large spread of up to 7.99. This means that a very short transmission ratio is available when moving off on an uphill slope with a high payload, for example, while during cruising the engine speed can be lowered considerably. This transmission is 9% more efficient than the CVT employed in the B-Class to date and attains the efficiency of a manual transmission for the first time.

At a length of 367 millimeters and a weight of 86 kilograms, the 7G-DCT is more compact and lighter than the transmissions which have been available on the market to date. The clutches take the form of wet multi-disc clutches running in an oil bath. The specially developed hydraulic fluid is actively cooled, thus ensuring correct functioning of the transmission even under extreme conditions, despite the comparatively low filling level of six liters.

For the first time on this type of unit, the transmission is supplied with oil by two oil pumps: one mechanical and one electric. The electric pump maintains the oil pressure when the engine is switched off via the start/stop function. This means that the transmission is immediately operational when the engine is restarted and the vehicle can move off again without any delay. In addition, the electric pump is able to support the mechanical pump when peak loads apply, enabling a more compact and efficient design for the mechanical pump.


Another new feature is electrical activation of the hydraulics for the parking lock, which is locked by mechanical means. This park-by-wire function enables the transmission selector lever to be positioned as desired: it is located in the form of a steering column lever on the right behind the steering wheel in the B-Class. In combination with the electric parking brake, additional space has thus been created in the centre console for additional stowage facilities.

DTC transmissions were developed for their fuel efficiency rather than anything else. Any torque converter slippage losses are effectively eliminated
The A class manual and automatic gearboxes are effectively the same gearbox- the difference being how the engine power is transfered to gearbox and how the gears are selected . I believe the automated twin clutch pack system is made by Getrag but not sure. Its a double wet clutch system but I am unsure whether its a tandem or concentric ofr split system?

 

[BenzedUP]

Why can't they use it on the C class as well?

 

[Ditch999]

My B Class has it!

 

[grober]

PRIMARILY DESIGNED FOR A TRANSVERSE FWD ENGINE SETUP. It would appear it uses a concentric clutch arrangement.
[YOUTUBE]h5Uv2DrYwoU&list=PLs6z93YS571sGczLSKPNzt7b4V-IQ-egN[/YOUTUBE]

 

[V12]

It wouldn't cope with the torque of your motor anyway.

 

[blue gnome123]

Isn't the e63 gearbox a twin clutch unit too? RWD and plenty of torque there!

 

[V12]

Different box though.

 

[blue gnome123]

Ok - of course it's a different box (!) but it doesn't mean that the new C or S or next year's E's couldn't have had a DCT

 

[V12]

Yep, of course they could design and manufacture a dct for any model if they so wished.
The choice was likely made because the brand values of MB have never been about crisp, fast gear changes. More about comfort.

Although the suspension department hasn't been getting that memo for a few years anyway...

 

[BenzedUP]

MB need to move with the time and starting fitting DCT in all their cars and ditch the 7-speed auto, the DCT in the A class is smoother than the 7G auto in my 204.

The best part about my other half's A class is the 7G DCT, other than that my 204 Coupe is alot better and nicer to drive just wish it had a DCT.

 

[boxbrownie]

Test drove the GLA with auto.....wow! So much more responsive but smoother gear changes than the 7G.........make a bigger box MB........

 

[robtt]

Been loads of posts on VW/Audi groups about DSG (same as Merc unit I presume) and not being very reliable. Must admit it has rather put me off buying a VW group car for time being. Hope Merc proves more reliable.

 

[Dryce]

DTC transmissions were developed for their fuel efficiency rather than anything else. Any torque converter slippage losses are effectively eliminated

The robotized single clutch boxes were aimed at economy and smaller cars. They were typically competing with small traditional four speed autos and CVTs.

The dual clutch types were a bit more about performance. The likes of VW/Audi offering them on the likes of the TT as a performance option.

Things seem to have got a bit more blurred now. The traditional autos are more economical and the single clutch setups seem to have largely become extinct (not that they were ever that popular) and the dual clutch units a bit more common.

 

[BenzedUP]

The robotized single clutch boxes were aimed at economy and smaller cars. They were typically competing with small traditional four speed autos and CVTs.

I knew it!

BMW's SMG is rubbish, that was controlled by a drunk robot.

 

[vealige]

Been loads of posts on VW/Audi groups about DSG (same as Merc unit I presume) and not being very reliable. Must admit it has rather put me off buying a VW group car for time being. Hope Merc proves more reliable.

The DSG box can be fixed for about £400 for a new mechatronic unit which includes stripping down etc. They do require an oil change every 40k but considering the cost to repair other types of auto boxes its pretty cheap so don't let it put you off one.

As above I recently drove a mk7 tdi golf with a 7 speed dsg box and it was silky smooth you could not tell when it was changing gear at all and it returned 67mpg on the 120 mile trip up the M5. Impressive bit of kit I must admit made the AMG box feel unrefined.

 

[geraldrobins]

Been loads of posts on VW/Audi groups about DSG (same as Merc unit I presume) and not being very reliable. Must admit it has rather put me off buying a VW group car for time being. Hope Merc proves more reliable.

The VAG 7 speed dsg is only used in engines with less than about 280NM of torgue. Above that they use a 6 speed dsg so the fuel consumption suffers compared to the manual. Interstingly the 220 diesels in the A and B class have less torgue than the 220 diesels in the C and E class and I think are single turbo.
As for the reliability of VAG dsgs as mentioned on the forums, arn't most forums where people and most posts are about problems with their cars. Also autos are generally more complicated in any car.

I may be biased as I have had good VAG experiences.

 

[V12]

280nm?! That's less than my lawn mower!!

 

[geraldrobins]

Its also more than a B or A 180cdi, or a 1.6 blue motion golf, which are around 250NM

 

[ant1]

I hate my wife's cvt box in her b class, much prefer my 7g in my AMG, completely smooth and gives a nice thumb when giving her some stick in manual.