DSG 7 vs 6 speed and GPF?

[dubber36]

Now here's the thing that I don't understand about the DSG coasting function. My understanding is that under normal circumstances, when you are off the throttle, momentum keeps the vehicle moving, which in turn spins the gear box, which keeps the engine turning. No fuel is needed to keep the engine running. With the coasting function, when you are off the throttle, the clutch pack disengages the gearbox from the engine, so in order to keep the engine at tickover speed, fuel is required. Just like when you are idling and stationary. Where does the so called fuel saving come from?

[Watts]

Now here's the thing that I don't understand about the DSG coasting function. My understanding is that under normal circumstances, when you are off the throttle, momentum keeps the vehicle moving, which in turn spins the gear box, which keeps the engine turning. No fuel is needed to keep the engine running. With the coasting function, when you are off the throttle, the clutch pack disengages the gearbox from the engine, so in order to keep the engine at tickover speed, fuel is required. Just like when you are idling and stationary. Where does the so called fuel saving come from?

Now I asked exactly this as I thought the same as you but someone gave an excellent well explained response that convinced me that the coasting function was better. Thing is, I just can't remember what it was! And I do not use the hateful eco mode.

[Watts]

Here you go, reply no.23.

http://www.golfgtiforum.co.uk/index.php?topic=284736.msg2602741#msg2602741

[fredgroves]

It's all energy and energy is created by burning petrol and lost by all sorts of ways other than driving the wheels. The easiest way of trying to stop fuel turning into Co2 is to stop pointless energy loss. Things like led lights make a big difference but the elephant in the room that nobody seems to care about is weight and drag coefficient....

[monkeyhanger]

It's all energy and energy is created by burning petrol and lost by all sorts of ways other than driving the wheels. The easiest way of trying to stop fuel turning into Co2 is to stop pointless energy loss. Things like led lights make a big difference but the elephant in the room that nobody seems to care about is weight and drag coefficient....

The new ugly front end of the MK8 - is that pedestrian safety or drag coefficient, or something else? VW care about weight saving when it goes hand in hand with money saving - make doors out of Aluminium? Accountants say no. Make them from much thinner steel? Accountants say yes.

[Adam T7]

Aluminium is more expensive than steel but is a nightmare for dents and a swine to repair.

[monkeyhanger]

Now here's the thing that I don't understand about the DSG coasting function. My understanding is that under normal circumstances, when you are off the throttle, momentum keeps the vehicle moving, which in turn spins the gear box, which keeps the engine turning. No fuel is needed to keep the engine running. With the coasting function, when you are off the throttle, the clutch pack disengages the gearbox from the engine, so in order to keep the engine at tickover speed, fuel is required. Just like when you are idling and stationary. Where does the so called fuel saving come from?

Coasting allows the whole car can freewheel, much lower frictional losses running the engine on idle with drivetrain disconnected via disengage clutch than pushing the engine and whole drivetrain to run without fuel.

If you want to remain at the same speed on a slight downhill gradient,  pick coasting. If you want to slow down and grab back some of that kinetic energy rather than heating the brake pads up, battery regeneration charging kicks in to a degree, the motor slowing the car down (like a dyno on a bike for keeping the lights on takes more effort to pedal).

In my A4, there's a variant of the instant mpg display - it's a bar with a scale. Increments of scale are 0, 10, 20, 30, 40, max (mpg) and at the end of the scale is a battery charging symbo.

As you drive along, the bar varies to show your real instant mpg. When the car switches to coasting, the scale moves to a high value (roughly corresponding with around 55mpg on the flat).

However, when you come off the accelerator, the instant mpg goes off the end of the scale and well into battery charging mode.

If you're looking to slow down, the process of engine braking with battery charging/energy recuperation is more efficient than coasting.

I do think that if the "dyno effect" recuperation cane on a little stronger, you'd get more energy back (through battery charging) and be putting less wear on the brake pads. There must be a reason they don't make it any stronger - maybe too strenuous on the drivetrain, like doing 50 in 6th/7th and jamming it into 2nd for some severe engine braking?

At the big VW place in Berlin, they had a demo crank of the recuperation unit. You could crank it to the point it was outputting to the same extent as the car to light a bulb - it took some serious cranking!

[monkeyhanger]

Aluminium is more expensive than steel but is a nightmare for dents and a swine to repair.

Not sure about the A3 in general, but I'm sure the pre-facelift S3 has aluminium doors, bonnet and boot lid, as dud the old Lupo GTI.

There's an old Triumph Roadster at the end of my street from 1947, built pretty much completely from Aluminium due to the post WW2 shortage of steel. It looks like new!

If renewable electricity projects expand to bring us ever cheaper electricity, Aluminium could be the material of choice in future. It's the most abundant metal in the Earth's crust, easy to get in Bauxite form and easy (but expensive at current electricity prices) to extract and purify the Aluminum from it's oxide. With breakthrough low electricity prices, aluminium could become cheaper than steel.

[fredgroves]

The new ugly front end of the MK8 - is that pedestrian safety or drag coefficient, or something else?

I found this:

There’s real substance in the Golf 8th gen’s sleeker body. Each body section was reshaped and refined in the wind tunnel. And by lowering the end face of the new model, the Golf 8 is the most aerodynamic Golf in history with a drag coefficient of Cd 0.275.

Having the ability to slice the wind in the most efficient way possible yields a ton of dividends. For starters, reducing drag means lesser mechanical force is required to move the vehicle, resulting in higher fuel savings. Also, having a slippery shape significantly reduces wind noise for better refinement.

From here: https://dlmag.com/2020-volkswagen-golf-8th-gen-top-5-reasons-why-its-the-best-golf-ever/

[monkeyhanger]

The new ugly front end of the MK8 - is that pedestrian safety or drag coefficient, or something else?

I found this:

There’s real substance in the Golf 8th gen’s sleeker body. Each body section was reshaped and refined in the wind tunnel. And by lowering the end face of the new model, the Golf 8 is the most aerodynamic Golf in history with a drag coefficient of Cd 0.275.

Having the ability to slice the wind in the most efficient way possible yields a ton of dividends. For starters, reducing drag means lesser mechanical force is required to move the vehicle, resulting in higher fuel savings. Also, having a slippery shape significantly reduces wind noise for better refinement.

From here: https://dlmag.com/2020-volkswagen-golf-8th-gen-top-5-reasons-why-its-the-best-golf-ever/

Ugly cars will save the world! Not only because they will save a small amount of fuel per trip, but you'll make fewer trips because you won't like to be seen out in it. 

I wonder what the real mpg savings are in % terms?

Any news on energy saving tech, like EA888 3b with budack cycle tech (like Arteon/Tiguan/Polo GTI) or cylinder deactivation.