RE: PH Blog: freewheeling
Discussion
loudlashadjuster said:
Why not? If it's an electro-magnetic battery recharge then the engine being off will have no effect.
Because thats not how they work, they work by on overrun, then wheels turn the engine, which turns the alternator... Basically brake engergy regeneration is a fancy name for glass mat battery and an intelligent alternator that only turns kicks in when on overrun or when the battery charge is below a certain level..Electromagnets on the brakes would increase unsprung weight which I doubt Porsche would like.
thewheelman said:
This Decoupling idea, I really hope it doesn't catch on. It sounds terrible.
I think this is the next big thing for cars with automatic/DTC gearboxes. I'm sure it will give a very low CO2 value for the EU cycle test and add another nail in the coffin of the manual gearbox. 
loomx said:
loudlashadjuster said:
Why not? If it's an electro-magnetic battery recharge then the engine being off will have no effect.
Because thats not how they work, they work by on overrun, then wheels turn the engine, which turns the alternator... Basically brake engergy regeneration is a fancy name for glass mat battery and an intelligent alternator that only turns kicks in when on overrun or when the battery charge is below a certain level..Electromagnets on the brakes would increase unsprung weight which I doubt Porsche would like.
You have to wonder how much saving you make vs just having the driver drive more sensibly in a much lighter car, much lighter because the money saved on all this stuff could go into a generally lighter car design/materials.
Seems clutching (hoho) at straws in this case I think.
It seems that the fleet average co2 stuff is actually doing more damage to sports cars now because they have to do crackers stuff to get fleet average down.
Porsche, just make a cheap super-light super-frugal hybrid diesel thing like a VX220 that can do 150mpg and then you can forget this bonkers stuff on Boxsters
Dave
McSam said:
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.
true, this is a good point. As long as it does remain an option.A guy on the Porsche forum is giving a running report on his new 911 and has also mentioned this decoupling.
What I don't understand is why this has been introduced.
I have been told in the past that on modern engines due to the electronic ignition control that "coasting" is less fuel efficient than simply running with no throttle since the engine will turn over and use no fuel if the car is rolling in gear but in neutral or with the clutch depressed the engine will burn fuel to turn over.
Presumably what I have seen and been told (above) is utter rubbish if the likes of Porsche are introducing decoupling for energy efficiency reasons.
What I don't understand is why this has been introduced.
I have been told in the past that on modern engines due to the electronic ignition control that "coasting" is less fuel efficient than simply running with no throttle since the engine will turn over and use no fuel if the car is rolling in gear but in neutral or with the clutch depressed the engine will burn fuel to turn over.
Presumably what I have seen and been told (above) is utter rubbish if the likes of Porsche are introducing decoupling for energy efficiency reasons.
just had a new Box S on loan for 24 hrs
200 plus miles and it didn't upset me;
yes, I noticed it; I also noticed a difference in sport / plus
maybe it's because I'm used to a hybrid KN
maybe I can just adjust to cars easily
I don't know
when jumping back in my mk1 996GT3 straight after dropping off the Box I certainly didn't feel I was all excited about being able to use engine braking again.
I could always quote the mantra of certain organisations...throttle to go, brakes to slow....
200 plus miles and it didn't upset me;
yes, I noticed it; I also noticed a difference in sport / plus
maybe it's because I'm used to a hybrid KN
maybe I can just adjust to cars easily
I don't know
when jumping back in my mk1 996GT3 straight after dropping off the Box I certainly didn't feel I was all excited about being able to use engine braking again.
I could always quote the mantra of certain organisations...throttle to go, brakes to slow....
I wonder if the EU test takes into consideration the weight and drag of the vehicle. So its possible that the increase in weight of an autobox/multi-clutch setup may harm the real world mpg in a test it makes no difference (and indeed shows an 'improvement' due to the greater number of gears)
I know having seen the test requirements that stop-start makes a massive difference even with little real world saving for those outside of a specific set of circumstances.
I know having seen the test requirements that stop-start makes a massive difference even with little real world saving for those outside of a specific set of circumstances.
Everyone seems to have forgotten the days when “freewheeling” was commonplace; several manufacturers fitted FW Units as optional extras prior to WW2 .I can remember driving Riley, Rover and others with this feature. There was normally a turn- wheel type control to engage and disengage the FW function. It was generally accepted that it was not a good idea to let the wife drive with the FW engaged , but back then there were very few women drivers therefore I always disconnected the unit when someone else was liable to drive , just in case they were not familiar with the correct driving procedure. The bigger and heavier the car the more pronounced the over-run effect ,so there was a major incentive to fit this unit to bigger more leisurely saloons in order to improve the MPG return.
I seem to remember owning a couple of big Rover limo’s in the 50’s that were so equipped but we used to leave the FW locked because it removed all the engine braking and placed much more reliance on the brakes causing premature and expensive wear and maintenance costs.
This system calls for a complete reappraisal of your driving technique. If you are driving in a relaxed, no hurry mode then there is not much to concern yourself about, but if you want to drive with any sort of urgency then the changes start to occur pretty rapidly and it is very easy to get caught out in moments of panic as your automatic reflexes come into play and make matters worse. I would think that a rear engine car (Porsche) with a high polar- moment of inertia would be the worst possible type of vehicle to start getting to grips with this driving technique.
One of the worst situations is , if you are in the habit of changing regularly (possibly daily )from one type of sporting vehicle to a different make, your balance suffers when driving in a spirited fashion causing moments of indecision and confusion .
In the 1970’s I had an EX-police Austin Westminster 6 cylinder fitted with Healey H-performance engine parts and an overdrive with the freewheel function that created a real problem. The car was very big and heavy but also extremely fast ( for the period) unfortunately with no engine braking all retardation was limited to the brakes which constantly got cooked (overheated) and cost a fortune in replacement parts. Any saving in fuel costs was completely absorbed by the cost of brake repair, over and over again.
At some point in the last 30 years it seems that some form of legislation was introduced to make “freewheeling” illegal because as the price of fuel started to escalate, high mileage drivers got into the habit of knocking the tranny into neutral and coasting on long down hill gradients to extend their gas mileage. After a couple of serious accidents at the bottom of steep hills the police claimed this was considered an “out of control “situation and in future would be rated as a dangerous practice.
I have no idea how this would stack-up in today’s traffic court but it sure is worth thinking about if you get rear-ended by a freewheeler?
While I am aware that all the European manufacturers today have very extensive legal departments in order to protect themselves from the ridiculous and unscrupulous EU committee of “industrial destruction” It would not be a surprise if another screw-up slipped though to plague the motorist of UK.
I seem to remember owning a couple of big Rover limo’s in the 50’s that were so equipped but we used to leave the FW locked because it removed all the engine braking and placed much more reliance on the brakes causing premature and expensive wear and maintenance costs.
This system calls for a complete reappraisal of your driving technique. If you are driving in a relaxed, no hurry mode then there is not much to concern yourself about, but if you want to drive with any sort of urgency then the changes start to occur pretty rapidly and it is very easy to get caught out in moments of panic as your automatic reflexes come into play and make matters worse. I would think that a rear engine car (Porsche) with a high polar- moment of inertia would be the worst possible type of vehicle to start getting to grips with this driving technique.
One of the worst situations is , if you are in the habit of changing regularly (possibly daily )from one type of sporting vehicle to a different make, your balance suffers when driving in a spirited fashion causing moments of indecision and confusion .
In the 1970’s I had an EX-police Austin Westminster 6 cylinder fitted with Healey H-performance engine parts and an overdrive with the freewheel function that created a real problem. The car was very big and heavy but also extremely fast ( for the period) unfortunately with no engine braking all retardation was limited to the brakes which constantly got cooked (overheated) and cost a fortune in replacement parts. Any saving in fuel costs was completely absorbed by the cost of brake repair, over and over again.
At some point in the last 30 years it seems that some form of legislation was introduced to make “freewheeling” illegal because as the price of fuel started to escalate, high mileage drivers got into the habit of knocking the tranny into neutral and coasting on long down hill gradients to extend their gas mileage. After a couple of serious accidents at the bottom of steep hills the police claimed this was considered an “out of control “situation and in future would be rated as a dangerous practice.
I have no idea how this would stack-up in today’s traffic court but it sure is worth thinking about if you get rear-ended by a freewheeler?
While I am aware that all the European manufacturers today have very extensive legal departments in order to protect themselves from the ridiculous and unscrupulous EU committee of “industrial destruction” It would not be a surprise if another screw-up slipped though to plague the motorist of UK.
In terms of the highway code and legal aspect it is not illegal to coast.
Highway code rules that are law include (in bold) "MUST" or "MUST NOT" along with the specific legisaltion.
Coasting is simply not advised because:
It can reduce driver control because
•engine braking is eliminated
•vehicle speed downhill will increase quickly
•increased use of the footbrake can reduce its effectiveness
•steering response will be affected, particularly on bends and corners
•it may be more difficult to select the appropriate gear when needed
My guess this is carefully controlled from the ecu.
In terms of adding complexity - surely it's just a software change that controls the two clutches? They are already computer controlled in the PDK box so making both clutches open is just software.
As for the fueling on overrun... My guess is that cars have become more and more advanced/efficient that the amount of fuel required (esp on a direct injection motor) is much smaller than what it once was and it's very possible that the fuel saved when shutdown on the overrun is less than that you can get coasting (as you'll go further coasting).
Highway code rules that are law include (in bold) "MUST" or "MUST NOT" along with the specific legisaltion.
Coasting is simply not advised because:
It can reduce driver control because
•engine braking is eliminated
•vehicle speed downhill will increase quickly
•increased use of the footbrake can reduce its effectiveness
•steering response will be affected, particularly on bends and corners
•it may be more difficult to select the appropriate gear when needed
My guess this is carefully controlled from the ecu.
In terms of adding complexity - surely it's just a software change that controls the two clutches? They are already computer controlled in the PDK box so making both clutches open is just software.
As for the fueling on overrun... My guess is that cars have become more and more advanced/efficient that the amount of fuel required (esp on a direct injection motor) is much smaller than what it once was and it's very possible that the fuel saved when shutdown on the overrun is less than that you can get coasting (as you'll go further coasting).
- However* - My true feeling it that it's simply a test beater. The only reason PDK/DSG boxes are getting everywhere is that they can make a substantial difference to the CO2 tests. It's probably the same here that the decoupling aspect scores more lab points than fuel cut off on the overrun.
Just swapped my A4 FSI Petrol for a 986 Tiptronic Boxster S.
As a direct comparison this Boxster has considerably more engine braking than the manual FSI A4 did.
If fact a friend who drove my 986 said how NICE it was to have some engine braking in an automatic.
The Audi FSI has a very efficient 2 litre petrol engine setup (over 44mpg avg if I wanted it to) and on overrun the electronics that control the fly-by-wire throttle does something to reduce the pumping losses of the engine.
So not only does it cut the fuel completly on the overrun, it reduces the drag from the engine considerably.
This was a pain at first and still was on hills where I would close up to the car in front quite quickly. But you get used to it.
As a direct comparison this Boxster has considerably more engine braking than the manual FSI A4 did.
If fact a friend who drove my 986 said how NICE it was to have some engine braking in an automatic.
The Audi FSI has a very efficient 2 litre petrol engine setup (over 44mpg avg if I wanted it to) and on overrun the electronics that control the fly-by-wire throttle does something to reduce the pumping losses of the engine.
So not only does it cut the fuel completly on the overrun, it reduces the drag from the engine considerably.
This was a pain at first and still was on hills where I would close up to the car in front quite quickly. But you get used to it.
kambites said:
Didn't some old Saabs used to do this; although I think they actually called it "free-wheeling".
Indeed - also Wartburgs! An ex GF many moons ago had one of these eastern bloc 3 pot strokers and usual problem with 2T premix coasting - if no throttle at high engine rpm, insufficient lube and seizures common... hence freewheel, allowing tick-over and a minimum of carburetion when lifting off. Horrible horrible
ing thing it was too!Edited by KimZ on Friday 27th July 00:18
loudlashadjuster said:
That was my impression also.
I know what Mr Harris means though, my C-Class sheds speed at a very slow rate compared to any other car I've driven. It might be eco-gubbins, it might just be the 7-speed 'box, but whatever the cause it is disconcerting and I'm still adjusting after 8 weeks in it.
Same with my 8 speed ZF auto, lift off on the motorway and it just rolls and rolls leaving you no choice but to hit the brakes, very annoying. I know what Mr Harris means though, my C-Class sheds speed at a very slow rate compared to any other car I've driven. It might be eco-gubbins, it might just be the 7-speed 'box, but whatever the cause it is disconcerting and I'm still adjusting after 8 weeks in it.
I think it is a great idea, I had a polo bluemotion once and averaged about 60mpg from it in everyday driving but found that if I dip the clutch on stretches of road where I could just roll at the same speed as traffic I could easily reach high 70's and even low 90's on the motorway but it made driving quite hard work so I gave up. To me this is just something that makes a fun car better everyday if sport mode dissengages it for when you want your fun what's the problem this isn't the sort of car you'd buy for a weekend toy is it? Atleast for me it wouldn't be my money would be going on a caterham/secondhand gt3 if that were the case so 80% of the time it'll make the car better to live with and the other 20% of the time you have the inconvenince of pressing another button.
As for it being not in full control of a vehicle it isn't as you can still put your foot down and go at any time which is the issue with coasting in a manual.
For anyone who wants to try it just dip the clutch whenever you think you could roll with traffic you'll notice the improvment in fuel consumption and be supprised by how often you can go for miles without using either of the other 2 pedals.
As for it being not in full control of a vehicle it isn't as you can still put your foot down and go at any time which is the issue with coasting in a manual.
For anyone who wants to try it just dip the clutch whenever you think you could roll with traffic you'll notice the improvment in fuel consumption and be supprised by how often you can go for miles without using either of the other 2 pedals.
Gassing Station | General Gassing | Top of Page | What's New | My Stuff