RE: PH Blog: freewheeling

[loomx]

But the point is, using engine braking, and on a gradient and new effecient autos there is very little internal resistance anyway, this method uses no fuel..

Decoupling does use fuel, and if you wanted to use a slight amount of throttle to keep a constant speed then its not like the injectors are at a massive duration.

The hill senario is the only senario that I could actually see this remotely working though, any other time, how is the car going to know if I want to engine brake or not... it isnt (hence this artical) and at the points when I want engine braking, when it coasts, I will be using more fuel.

The annoying thing, is the car will know if its on an incline from the rate of deceleration vs throttle position, so they could have implimented it in a way that would benifit you when you actually could make use of it.

Edited by loomx on Thursday 26th July 14:03

[collateral]

I drive up and down a 16% hill most days, and it seems like I'm the only one who just chucks it in 2nd instead of riding the brakes the whole way down. I figure that even if my car is dumb enough to keep fuelling I prefer the price of new oil over new pads and disks.

That being said, I was driving a slushmatic Grand Cherokee the other day and was quite surprised how much more braking I needed to do compared to my Puma - 2 tonnes doesn't slow down much on it's own, even with the added friction of AWD and aerodynamics of a small house

[McSam]

paranoid airbag said:

McSam said:

My main point, though, is that under no circumstance should you have the engine decoupled and be braking, because any resistance benefit you might have gained from decoupling is irrelevant anyway so why waste the idling fuel?

It's a very good argument for the manual version imo

Well, with the Porsche, as soon as you go near the brakes it kicks the engine back into life! I don't think the system is detrimental, I just think it's a rather pointless exercise.

[Dave Hedgehog]

simple answer man the fk up and keep your right foot planted

if you want to save money, buy a shed, any extra fuel used will be insignificant compared to the depreciation on a 60k porker

[Ten Ninety]

Presumably for de-coupling to yield the maximum effect, one would have to adopt a 'pulse and glide' approach on the motorway? Somehow I can't see many Boxster owners doing that so it seems a bit pointless, although doubtless it lowers the official CO2 figures.

Given that it can be switched off though, it seems like a bit of a non-issue to be fussing over.

[kambites]

Ten Ninety said:

Presumably for de-coupling to yield the maximum effect, one would have to adopt a 'pulse and glide' approach on the motorway? Somehow I can't see many Boxster owners doing that so it seems a bit pointless, although doubtless it lowers the official CO2 figures.

Given that it can be switched off though, it seems like a bit of a non-issue to be fussing over.

Next time you drive on the motorway, see how much of the time you're off the throttle completely. It's a surprisingly large proportion of it (and of course would be a greater proportion of the time if you weren't engine braking). I'd be interested to know how the system interacts with cruise control; they were worth together to optimise fuel economy, or just work independently.

[loomx]

kambites said:

Ten Ninety said:

Presumably for de-coupling to yield the maximum effect, one would have to adopt a 'pulse and glide' approach on the motorway? Somehow I can't see many Boxster owners doing that so it seems a bit pointless, although doubtless it lowers the official CO2 figures.

Given that it can be switched off though, it seems like a bit of a non-issue to be fussing over.

Next time you drive on the motorway, see how much of the time you're off the throttle completely. It's a surprisingly large proportion of it (and of course would be a greater proportion of the time if you weren't engine braking). I'd be interested to know how the system interacts with cruise control; they were worth together to optimise fuel economy, or just work independently.

The times you are off throttle on the motorway is because traffic has slowed down or pulled out in front of you. In these situations you will want engine braking. This system just means you have the brake instead now. If there is no traffic, you wouldnt be off throttle at all unless maybe on a steep down hill section.

[filski666]

Ten Ninety said:

Presumably for de-coupling to yield the maximum effect, one would have to adopt a 'pulse and glide' approach on the motorway? Somehow I can't see many Boxster owners doing that so it seems a bit pointless, although doubtless it lowers the official CO2 figures.

Given that it can be switched off though, it seems like a bit of a non-issue to be fussing over.

I don't think the fact it can be switched off makes the discussion null

The article said it couldn't be switched off in isolation - only when you press the sport button? - you might not want the Sport button pressed but want to turn the stupid de-coupling and start/stop off

If you don't want the system - you are stil paying for it. Why pay for something yor don't want? That would annoy me. Can't it be an option?


actually this discussion IS pretty null and void for me, as my youngest vehicle is a 1995MY and I don't plan on buying anything newer than a 2001 vehicle in the near future as they are all too cluttered with stupid technology I don't want

[anniesdad]

ghibbett said:

I have driven the new Boxster (2.7) with the manual. Whilst the gear change is fantastic, there's one massive failing that was enough to put me off considering a manual 2.7: the gear ratios - they're ridiculous! Country lane blats use only 2nd and 3rd. It completely ruined the experience for me. Shame as it was brilliant otherwise.

You want to try a GT3! You're well into very naughty figures at the top of 3rd.

[anniesdad]

filski666 said:

Because on long steep descents - extreme example - coming down the Alpine roads from France into Switzerland - if you were using just your brakes to stop the car accelerating out of control you would overheat them and they will start smoking.

I know - my parents did it when was little - they had to stop and let the brakes cool down before carrying on with the journey.

and your point about the system re-engaging when you press the brake - yes, fine, and as soon as you come off the brakes again it disconnects again - so you shoot forward as you have no engine retardation.....so you have to go back on the brakes again.......so (as I said) you will be on the brakes the whole way down the hill - which WILL cause then to overheat on suitably long and steep gradients.

Edited by filski666 on Thursday 26th July 13:45

I hear you, but you would put the car in a lower gear (higher revs) as per your picture, in which case the coasting would not cut in. It mentions that the coasting is useful on gentle descents, not steep alpine passes!

[405dogvan]

I used to work with a chap who was obsessive about fuel economy and a terrible driver as a result.

He used to drive as slowly as he could and choose routes which featured loads of steep hills so he could drive, not only with the engine decoupled but with it OFF!!

He used cars from the company car pool but had to fuel them himself so he'd bemoan the day when there were none which lacked PAS because that meant he couldn't coast anymore (the unassisted steering being FAR heavier than his previous car's was) - and he'd bemoan when there were only bigger cars in the pool because they used more fuel and so on.

He ignored arguments that choosing a hilly route was pointless because everything he saved 'freewheeling' down one side, he used driving up the other (given that his home and work were roughly the same altitude).

He finally got some of the message when he was stopped, by Plod, for driving down a local hill decoupled. They'd actually stopped him because they suspected he was drunk - as the car was accelerating when they thought it shouldn't be - but when he told them what he was doing (and passed a breathalyser) then charged him with "failing to be in control of a motor vehicle" - it went to court and he lost.

So - decoupling then - have Porsche made a car likely to get you busted?

[philmots]

Same system has been used on Volvo trucks for years...

Once you get used to it you drive around it and the benefits are great. Although, if you're in a hurry it's not too helpful.

For example I can be doing 50mph on a flat DC approaching a roundabout. I'll lift off/switch off cruise abouy a mile before the roundabout and it'll coast all the way to the roundabout. Ending up at around 30mph. That and it de coupling on slight undulations can mean free wheeling for 1 in 10 miles easily.

Around towns if it's used correctly it's great.. Just need plenty of practice.

[loudlashadjuster]

loomx said:

What I dont get, is in Porsches blurb, it says it has brake engery regeneration... which wont work if the engine is decoupled... So I guess this now only works when the engine is running and you are breaking

Why not? If it's an electro-magnetic battery recharge then the engine being off will have no effect.

[Adam2k90]

Can we please have some news from other car manufacturers apart from Porsche!

[Numeric]

is this another of those dubious things that in the real world has little effect but in the ever more obscure economy tests produces a great result, perhaps there is an off the power section that lasts for 10 mins solid or something in the spec of the test regime?

Bit like stop start where on the test they just walk away from the thing for a set amount of time I have heard (I could well be wrong) - is great in the lab but hardly much use to anyone outside of a big city and likely not even to them.

[Great Pretender]

anniesdad said:

filski666 said:

so what do you do on a steep descent - ie when you see this sign?

Your decoupling system disconnects you from your engine braking - you set fire to your brakes and you crash into a pile of children and kittens?

Why would you set fire to your brakes? As soon as you touch the brake or throttle. PDK re-engages the gear in a few milliseconds and you have drive and braking. I put a link in a previous post to Porsche's description of how coasting works.

And for the benefit of the blind:

It is also worth remembering that the function does not activate on any sort of 'descent' as such. So no kittens need be killed. Some of the posters on this thread however...

[Ten Ninety]

filski666 said:

The article said it couldn't be switched off in isolation - only when you press the sport button? - you might not want the Sport button pressed but want to turn the stupid de-coupling and start/stop off

If you don't want the system - you are stil paying for it. Why pay for something yor don't want? That would annoy me. Can't it be an option?

Presumably if it was an option then it couldn't be used to lower the CO2 figures on the official test? I presume this is what's driving the adoption of these kinds of technologies, more than what customers actually want.

[SimonOcean]

One word: "manual".
Nuff said.

[paranoid airbag]

McSam said:

Well, with the Porsche, as soon as you go near the brakes it kicks the engine back into life! I don't think the system is detrimental, I just think it's a rather pointless exercise.

So, in order to get something I previously got automatically (i.e. engine braking), I now have to use a different control (the brake pedal) to select. In return, something I'd previously have to do myself (knock it out of gear, or hold it on the clutch - I'd do the former most of the time, the latter at very low speeds), I now get automatically.

I'd far rather have engine braking as the automatic option, thanks, so from a user point of view it's detrimental for me.

[McSam]

paranoid airbag said:

McSam said:

Well, with the Porsche, as soon as you go near the brakes it kicks the engine back into life! I don't think the system is detrimental, I just think it's a rather pointless exercise.

So, in order to get something I previously got automatically (i.e. engine braking), I now have to use a different control (the brake pedal) to select. In return, something I'd previously have to do myself (knock it out of gear, or hold it on the clutch - I'd do the former most of the time, the latter at very low speeds), I now get automatically.

I'd far rather have engine braking as the automatic option, thanks, so from a user point of view it's detrimental for me.

But then you can turn the whole system off and leave it off! I quite agree with you, as should be clear from my other posts, but what I meant was that they have at least thought it through and it isn't going to decouple you down a big hill or in a high-speed corner.