Are manufacturers ditching dual clutch for torque converters

[TonyTony]

I have just been reading some random reviews recently and noticed quite a few new performance cars coming out are single clutch torque converter gearboxes.

The new S5 Sportback has an 8 speed torque converter, Lexus LC500 has a 10 speed and there's the ZF gearboxes in quite a few others.

The reviews seem to praise the better developed gearbox and say they pretty much are on par for speed/smoothness and economy with dual clutch but I guess they are cheaper to develop/maintain and more reliable.

[wemorgan]

Rather than 'on par' I'd say the latest ZF gearboxes are significantly better than any DSG I've drive so far.

[GroundEffect]

DCTs were always a middle ground. They are very expensive and have disadvantages in launch performance and weight. With the latest hydraulics and locking torque converters, you can recover most of the fuel economy losses of a true auto so many companies are going that way.

[Magic919]

TonyTony said:

single clutch torque converter gearboxes.

What part does the single clutch play?

[TonyTony]

Magic919 said:

What part does the single clutch play?

or

[cptsideways]

I would agree, the Torque converter boxes have become way more efficient, rather than a massive slush heat pump that they always were.

Once the clutch is locked up it's no longer wasting energy through the torque converter (a propeller in a bath of oil) & now most are locked up unless stationary, pulling away or changing gear.

With some clever control of the solenoids you can also have two gears providing torque for a brief moment so technically there is no loss of drive during a gearchange. The Planetary gears are always meshed & just change direction for a ratio change.

It's also a lot easier to get multiple gearing through multiple sets of planetary gears to keep the engine at peak BSFC etc. Obvious advantages with smooth drive-ability too. The Mazda Skyactiv autobox was one of the first to do this, it's also almost half the size of a normal auto. with ZF & Aisin etc now following suit in the mainstream.

[PositronicRay]

cptsideways said:

With some clever control of the solenoids you can also have two gears providing torque for a brief moment

Wow, I did not know that.

[cptsideways]

PositronicRay said:

cptsideways said:

With some clever control of the solenoids you can also have two gears providing torque for a brief moment

Wow, I did not know that.

As the gears are always meshed its actually rather simple, the outer planet gears are held stationary by the friction brake bands (think brake drum) or released to change the ratio. The inner shafts are held by clucth packs much the same. Slippage of two of these friction surfaces means the difference in speeds whilst changing ratios can be absorbed.

Planet gears are wonderful things, you can also think of them like a differential & a traction control system using the brakes to slow the wheel speed, its exactly the same principle!

Just don't take one apart & expect it to go back together the same way autoboxes though simple in the mechanics have hundreds of valves, ports, pressure valves, springs etc all controlled by a few solenoids & loads of horrid little things that you WILL loose.

An Aisin three/four speed is the epitomy of simplicity though, simple pressure makes it all work rather well even to this day still one of the nicest changing boxes ever & autolockup above 40mph.

[Gerber1]

Good news I suppose.

I have a 7 speed PDK but would much prefer the ZF alternative as found in a new BMW.

[saaby93]

cptsideways said:

An Aisin three/four speed is the epitomy of simplicity though, simple pressure makes it all work rather well even to this day still one of the nicest changing boxes ever & autolockup above 40mph.

Whats got that ?

[angels95]

Torque converters are much better!

[cptsideways]

saaby93 said:

cptsideways said:

An Aisin three/four speed is the epitomy of simplicity though, simple pressure makes it all work rather well even to this day still one of the nicest changing boxes ever & autolockup above 40mph.

Whats got that ?

Landcruisers had them & lots of old Toyota's quite a few Volvo estates too.

[liner33]

I had heard the same, the only thing the dsg in my Skoda has over a conventional auto is shift speed and even then its tenths of a second .

In stop start traffic I far prefer a conventional box, in fact I cant think of any time i prefer the dsg although they do make a nice noise at full throttle upshifts, I'm certainly not a hater of the dsg but the reliability and bork factor does worry me slightly

I have a ZF8 in my Jag and it really is an excellent gearbox