New gearbox modes dangerous?

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dozypillock

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C209 CLK320
Just spotted in the press release about the new E63 gearboxes. The 9 speed, I believe, and that it has several modes. I am merely questioning one of them.

"Comfort" is the well-balanced drive program with a comfort-oriented suspension and steering set-up, as well as a fuel-efficient powertrain configuration and early upshifts – including smooth gear changes and a discreet engine sound. Cylinder deactivation, ECO start/stop function and gliding mode are on. When the driver releases the accelerator in a speed range between 37 and 99 mph, the clutch of the MCT transmission opens and the engine is decoupled from the powertrain. The electronics reduce the engine speed to idle level, and the motion resistance is reduced by the compression and frictional forces of the engine in overrun mode.

The bit in question is "When the driver releases the accelerator in a speed range between 37 and 99 mph, the clutch of the MCT transmission opens and the engine is decoupled from the powertrain."

I was always taught that the engine must be connected at all times. Even coasting is advised against, if not actually illegal?

Neil
 
You were advised this so that if needs be you could drive out of a situation...something you can do with this 'box.
 
My A45 does this already, you get a little sailboat icon on the dash when it's sailing, as soon as you brake or accelerate the box engages again, you don't really notice it unless looking for it or at the rev counter, very smooth.
 
It decouples and couples within a fraction of a second whereas if you coast in a manual, it can take an undefined time to select and re-engage a gear from the neutral position.

It's like the ECO mode, whereas the engine will shut down while you have your foot on the brake pedal, but as soon as you move your foot from the brake pedal to the accelerator pedal, the engine sparks in to life.

On my old SAAB, it would couple the Direct Drive when cruising, yet engage the torque converter when the speed dropped below a set point.

Technology has left the Highway Code behind.
 
The old Saab 95 2stroke had a selectable freewheel on the over-run. Quite disconcerting if you weren't used to it. A very aerodynamic car for its time it was strange to feel it sail on at the same speed for what seemed like ages after lifting off.
 
Does this too on the 7 speed in the W205.

Though I think it's strange why Mercedes don't allow it to coast below 40mph if the name of the game is eco.

Where on a VW gearbox it does coast at low speeds as well on a rental vehicle I had.
 
Sounds safe enough but two things strike me:

I thought on every modern engine, fuel is already cut on the overrun as an energy saving measure. That saves more fuel than cutting to idle.

They will have had to re-think the smart alternator programming which is usually set to do most of the battery charging on the overrun as minor sort of regenerative braking. It cant do much charging at idle so that means the alternator will need to be consuming power at some other time.

Perhaps the retention of kinetic energy in glide mode exceeds both of those losses.
 
The old Saab 95 2stroke had a selectable freewheel on the over-run. Quite disconcerting if you weren't used to it. A very aerodynamic car for its time it was strange to feel it sail on at the same speed for what seemed like ages after lifting off.

My dad had a couple of Rovers - a 90 and a 105S - I can't remember which but one of them had a freewheel mode too .
 

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