RE: PH Blog: freewheeling
Discussion
tank slapper said:
In a normal car where the engine constantly engaged, every time you take your foot off the accelerator, energy is being wasted in turning the engine.
If you are looking ahead then I can't see where the benefit is.If you take your foot OFF the accelerator you are asking for some engine braking because you want to slow down. A good driver will lift to partial throttle to maintain speed if that is the intention.
Or if the intention is to slow down but gradually then you lift off a bit more, or all the way.
The throttle just combines as a brake in motorway work which is actually more preferable to having to swap feet from throttle to brake all the time to moderate speed.
In my view I'm not missing the point. I think anything automatic is for the lowest common denominator and clearly this is another dumbass feature for dumbass drivers who can't drive properly for efficiency so the car will do it for them.
You can achieve the same as above in any car just by clutching and coasting but I'm certain if I go try use this technique vs just looking ahead and not being a dick on the motorway, there will be no difference at all.
Dave
Engine braking is only there because that is the way car transmissions have been made up until now, so you are used to it being there. It is certainly not the optimal way to do things, since you are wasting energy every time you use it.
Regardless of how well you look ahead, there are always times when you will be on and off the throttle and each of those times you will gain. There are specific instances where it is desirable to have a method of dissipating energy over a long period, such as descending a steep hill. Engine braking is used because prolonged use of normal brakes tends to overheat them, however it is still energy that is irretrievably lost.
From an efficiency point of view, having an inbuilt waste of energy where one isn't needed is nuts. It would be far better to reduce such losses to a minimum, and then if an additional method of braking is required, add one that is only active when required. As I said above, some form of regenerative braking would be ideal since it allows you to reuse the energy.
Just because something has always been done a certain way and you are used it, doesn't mean it is the best way to do it. I think that people are often reluctant to try new things purely because they are different to what they know. Think back to when ABS first started to become common, and how many people moaned about it ruining braking and the way cars drove and a whole list of other excuses. Some even make the same points today, but ABS is fitted to pretty much every new vehicle now because it is a better solution for the vast majority of drivers. I imagine this type of technology is going to become increasingly commonplace, and people will moan about it for whatever reason, but eventually will accept it and 10 years later won't think twice about it.
There are still cars without ABS if you really don't want it, as there are still steam engines and sailing boats. Just because mainstream technology moves on, it doesn't mean that previous technology has to disappear completely, it just moves to those who want it for a different reason.
Regardless of how well you look ahead, there are always times when you will be on and off the throttle and each of those times you will gain. There are specific instances where it is desirable to have a method of dissipating energy over a long period, such as descending a steep hill. Engine braking is used because prolonged use of normal brakes tends to overheat them, however it is still energy that is irretrievably lost.
From an efficiency point of view, having an inbuilt waste of energy where one isn't needed is nuts. It would be far better to reduce such losses to a minimum, and then if an additional method of braking is required, add one that is only active when required. As I said above, some form of regenerative braking would be ideal since it allows you to reuse the energy.
Just because something has always been done a certain way and you are used it, doesn't mean it is the best way to do it. I think that people are often reluctant to try new things purely because they are different to what they know. Think back to when ABS first started to become common, and how many people moaned about it ruining braking and the way cars drove and a whole list of other excuses. Some even make the same points today, but ABS is fitted to pretty much every new vehicle now because it is a better solution for the vast majority of drivers. I imagine this type of technology is going to become increasingly commonplace, and people will moan about it for whatever reason, but eventually will accept it and 10 years later won't think twice about it.
There are still cars without ABS if you really don't want it, as there are still steam engines and sailing boats. Just because mainstream technology moves on, it doesn't mean that previous technology has to disappear completely, it just moves to those who want it for a different reason.
Lots have cars now harvest the energy from braking inputs, my F10 5 series for a start.
Efficiency is all well and good but I can't help thinking that current legislation is pushing manufacturers down paths in an attempt to lower C02 levels that don't increase the pleasure of driving and actually make it more of chore.
My manual 911 sheds speed nicely at motorway speeds when I lift off in 6th so I hardly ever use the brakes in the F10 auto I'm constantly on them with all the issues that causes in flowing traffic.
My next daily driver may well be a manual.
"Freewheeling" is nothing new. Several German cars during the 1950's had this as a feature. I seem to recall that the Goliath small passenger car (they also manufacturered the infamous Goggomobil and were subsequently taken over by Borgward if I recall) championed this freewheel feature as a way of maximising economy. Several "Mobil Economy Runs" attest to quite remarkable fuel consumption figures at the time but which are now regularly exceeded by small efficient diesels.
Maybe slightly off topic, but if de-coupling is such a good option to reduce 'parasitic losses' is that not at odds with the cylinder deactivation technology shown here recently (where both valve sets were closed)? Was it not mentioned that the pumping losses evened out?
Anyway in the real world while you are merrily freewheeling down a hill your momentum is bound to be haulted by someone doing 35-40, braking at every deviation in the road. So will you pass in nuetral? PS. yes I'm a technophobe - just give me a light, simple, uncomplicated car (nothing electric / powered / no climate control) please and let me just drive it smoothly if I want to save fuel...
Anyway in the real world while you are merrily freewheeling down a hill your momentum is bound to be haulted by someone doing 35-40, braking at every deviation in the road. So will you pass in nuetral? PS. yes I'm a technophobe - just give me a light, simple, uncomplicated car (nothing electric / powered / no climate control) please and let me just drive it smoothly if I want to save fuel...
KimZ said:
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!It sounded just like three motorbikes starting up at the same time. Oil mix was an issue and you had to mix it in with the petrol when filling but later versions had an automix system.
tank slapper said:
Engine braking is only there because that is the way car transmissions have been made up until now, so you are used to it being there. It is certainly not the optimal way to do things, since you are wasting energy every time you use it.
Regardless of how well you look ahead, there are always times when you will be on and off the throttle and each of those times you will gain. There are specific instances where it is desirable to have a method of dissipating energy over a long period, such as descending a steep hill. Engine braking is used because prolonged use of normal brakes tends to overheat them, however it is still energy that is irretrievably lost.
From an efficiency point of view, having an inbuilt waste of energy where one isn't needed is nuts. It would be far better to reduce such losses to a minimum, and then if an additional method of braking is required, add one that is only active when required. As I said above, some form of regenerative braking would be ideal since it allows you to reuse the energy.
Just because something has always been done a certain way and you are used it, doesn't mean it is the best way to do it. I think that people are often reluctant to try new things purely because they are different to what they know. Think back to when ABS first started to become common, and how many people moaned about it ruining braking and the way cars drove and a whole list of other excuses. Some even make the same points today, but ABS is fitted to pretty much every new vehicle now because it is a better solution for the vast majority of drivers. I imagine this type of technology is going to become increasingly commonplace, and people will moan about it for whatever reason, but eventually will accept it and 10 years later won't think twice about it.
There are still cars without ABS if you really don't want it, as there are still steam engines and sailing boats. Just because mainstream technology moves on, it doesn't mean that previous technology has to disappear completely, it just moves to those who want it for a different reason.
I totally agree with everything you have said, but you haven't shown any evidence to say that a very good driver who looks ahead already will gain anything from this system at all.Regardless of how well you look ahead, there are always times when you will be on and off the throttle and each of those times you will gain. There are specific instances where it is desirable to have a method of dissipating energy over a long period, such as descending a steep hill. Engine braking is used because prolonged use of normal brakes tends to overheat them, however it is still energy that is irretrievably lost.
From an efficiency point of view, having an inbuilt waste of energy where one isn't needed is nuts. It would be far better to reduce such losses to a minimum, and then if an additional method of braking is required, add one that is only active when required. As I said above, some form of regenerative braking would be ideal since it allows you to reuse the energy.
Just because something has always been done a certain way and you are used it, doesn't mean it is the best way to do it. I think that people are often reluctant to try new things purely because they are different to what they know. Think back to when ABS first started to become common, and how many people moaned about it ruining braking and the way cars drove and a whole list of other excuses. Some even make the same points today, but ABS is fitted to pretty much every new vehicle now because it is a better solution for the vast majority of drivers. I imagine this type of technology is going to become increasingly commonplace, and people will moan about it for whatever reason, but eventually will accept it and 10 years later won't think twice about it.
There are still cars without ABS if you really don't want it, as there are still steam engines and sailing boats. Just because mainstream technology moves on, it doesn't mean that previous technology has to disappear completely, it just moves to those who want it for a different reason.
I'd argue that if there was anything significant in this then the hypermiler club would have been doing it a decade ago...
There are a LOT of new technologies and advances being made to improve efficiency on the combined cycle test. I do wonder though over a 5 year ownership period how well they stack up in the long run!
ABS is a great point. I'd consider myself a good driver and I've managed to stop in an emergency with and without abs but I'd certainly say I'm safer with ABS in the long run, rather than just lucky without it I think.
Perhaps this new technology will find even a good efficient driver another few percentage points on their mpg simply for the addition of some software to the DSG gearbox... BUT, I think the main attraction is simply that on a euro cycle test and fleet average co2 concerns there is a benefit to be found here.
There may well be even better systems out there for economy that don't even get a look in because on the current co2 test cycle they wouldn't stand out for example.
Lets not mistake the euro cycle co2/mpg tests which motivate the manufacturers for other reasons, the same ones that might benefit us in the real world.
I bet for most people who drive around with half flat tyres, cars covered in mud, junk in their boot etc, that they would still make more difference than clutching in when you found the top-gear engine braking too significant. To be honest I've never lifted off my throttle on the motorway and felt that I was slowing down so fast I'd best clutch in...
But hey, different strokes for different folks. It obviously works for the computer driving the car on a dyno in the test-cell for the combined figure testing
Dave
Sorry if someone else has brought this point up, but I’m talking from direct experience here. Whilst using my girlfriends Audi TT (she needed my A6 for the seating that day) The TT suffered complete brake failure (Burst brake line) whilst traveling at 70mph on the M69.
Thankfully it was the 6 speed manual, so by dropping it from 6th to 2nd; I considerably slowed the car down to a speed where the handbrake was able to finally stop it. It was a worrying 10 seconds or so, no real time to think, just act.
However if I was driving a “Trip-tronic” car with this decoupling technology, I don’t think 10 seconds would have been enough to figure out what to do, and I would have ploughed straight into the stationary traffic ahead of me.
Ok, suffering a complete brake failure is rare, but on that day I was glad I was driving a manual!
I understand why this discussion is based around the possible few pounds a year you may save in fuel, but let’s not forget two things; firstly Fuel is ONLY so expensive in this country because of the unjust and criminal taxation applied to the relatively cheap true cost. Remove the TAX, and this technology, including this discussion wouldn’t even exist.
And secondly; yes you may save a few pounds at the pumps, but when this overly complicated gearbox fails, you’ll lose what you've saved, plus more to have it fixed.
Thankfully it was the 6 speed manual, so by dropping it from 6th to 2nd; I considerably slowed the car down to a speed where the handbrake was able to finally stop it. It was a worrying 10 seconds or so, no real time to think, just act.
However if I was driving a “Trip-tronic” car with this decoupling technology, I don’t think 10 seconds would have been enough to figure out what to do, and I would have ploughed straight into the stationary traffic ahead of me.
Ok, suffering a complete brake failure is rare, but on that day I was glad I was driving a manual!
I understand why this discussion is based around the possible few pounds a year you may save in fuel, but let’s not forget two things; firstly Fuel is ONLY so expensive in this country because of the unjust and criminal taxation applied to the relatively cheap true cost. Remove the TAX, and this technology, including this discussion wouldn’t even exist.
And secondly; yes you may save a few pounds at the pumps, but when this overly complicated gearbox fails, you’ll lose what you've saved, plus more to have it fixed.
here's a few points:
1) it's amazing how many people on PH seem to know better than a major OEM with access to the finest engineering brains in the world wrt fuel economy
2) it's no more "complicated" than a normal autobox (because all it does is unlock the TC and put the system into neutral, just like it does every time you move the lever to N/P etc. It's just a software addition)
3) The argument "it wouldn't be needed if fuel was cheaper" is not valid. Fuel isnt cheaper. If i could fly then i wouldn't need to take a plane to go on holiday..............
4) HAving a brake failure in a manual is just like having a brake failure in an auto. In both you need to down change and then select neutral and use the handbrake to stop. if you can do that in a panic in a manual, you can do that in an auto (in reality in most cases, the average driver who is "asleep at the wheel" will have crashed before they even realise the brake pedal isn't working ;-)
1) it's amazing how many people on PH seem to know better than a major OEM with access to the finest engineering brains in the world wrt fuel economy
2) it's no more "complicated" than a normal autobox (because all it does is unlock the TC and put the system into neutral, just like it does every time you move the lever to N/P etc. It's just a software addition)
3) The argument "it wouldn't be needed if fuel was cheaper" is not valid. Fuel isnt cheaper. If i could fly then i wouldn't need to take a plane to go on holiday..............
4) HAving a brake failure in a manual is just like having a brake failure in an auto. In both you need to down change and then select neutral and use the handbrake to stop. if you can do that in a panic in a manual, you can do that in an auto (in reality in most cases, the average driver who is "asleep at the wheel" will have crashed before they even realise the brake pedal isn't working ;-)
I'm still finding it difficult to adjust to my F30 3 series which seems to have much less engine braking when you lift off than any of the other BMW's I have driven. I don't think it is the sailing as mentioned in the article, more to do with the engine management, but I still find instances when I lift off the accelerator but then have to dab the brakes as the car is not slowing down as much as I expected.
I can understand the resaon for it as it makes better use of the momentum in the car, but it takes a while to get used to.
I can understand the resaon for it as it makes better use of the momentum in the car, but it takes a while to get used to.
3,500 miles into a 991 C2S with PDK and I think I've got to grips with what Porsche actually call their 'gliding' feature.
Chris mentions that you can turn this feature off by pressing the 'sport' button - absolutely correct. There is another way, turn the auto stop/start feature off. Achieves the same goal however, doesn't affect the throttle response or suspension setup.
I tend to disable stop/start when I'm around town (hate this feature on a 911 !) and when I'm travelling on motorways re-enable stop/start to activate the gliding feature.....which does seem to 'learn' your driving style and gets better with age
Chris mentions that you can turn this feature off by pressing the 'sport' button - absolutely correct. There is another way, turn the auto stop/start feature off. Achieves the same goal however, doesn't affect the throttle response or suspension setup.
I tend to disable stop/start when I'm around town (hate this feature on a 911 !) and when I'm travelling on motorways re-enable stop/start to activate the gliding feature.....which does seem to 'learn' your driving style and gets better with age
ads_green said:
Not sure I agree here. Taking the tech away for a moment (as I would expect it to be able to cope with certain unfavourable conditions) coasting is more unstable than driving.
Simple reasons are:
- suspension geometry esp toe is set based on the driven wheels having power. For example, FWD cars will have toe out on the front to compensate for the wheels natural tendancy to toe in when power is applied.
- Brake balance is set with the driven wheels taken into account. So a FWD car will have proportionately less front bias as it would be assumed that a degree of engine braking was occurring. Sure ABS can help here but even the best systems work better when designed for the car as a whole and not a "get out of jail free" card.
From a wheel grip point of view, surely a wheel with no axle torque (either positive or negative) will have more available cornering grip. In most rwd drive cars I have owned, its easier to bring the tail around by lifting off and using the engine braking to tuck the back end in. With a disconnected drive (and assuming geo set to work) it should be less likely to spinSimple reasons are:
- suspension geometry esp toe is set based on the driven wheels having power. For example, FWD cars will have toe out on the front to compensate for the wheels natural tendancy to toe in when power is applied.
- Brake balance is set with the driven wheels taken into account. So a FWD car will have proportionately less front bias as it would be assumed that a degree of engine braking was occurring. Sure ABS can help here but even the best systems work better when designed for the car as a whole and not a "get out of jail free" card.
Gary C said:
ads_green said:
Not sure I agree here. Taking the tech away for a moment (as I would expect it to be able to cope with certain unfavourable conditions) coasting is more unstable than driving.
Simple reasons are:
- suspension geometry esp toe is set based on the driven wheels having power. For example, FWD cars will have toe out on the front to compensate for the wheels natural tendancy to toe in when power is applied.
- Brake balance is set with the driven wheels taken into account. So a FWD car will have proportionately less front bias as it would be assumed that a degree of engine braking was occurring. Sure ABS can help here but even the best systems work better when designed for the car as a whole and not a "get out of jail free" card.
From a wheel grip point of view, surely a wheel with no axle torque (either positive or negative) will have more available cornering grip. In most rwd drive cars I have owned, its easier to bring the tail around by lifting off and using the engine braking to tuck the back end in. With a disconnected drive (and assuming geo set to work) it should be less likely to spinSimple reasons are:
- suspension geometry esp toe is set based on the driven wheels having power. For example, FWD cars will have toe out on the front to compensate for the wheels natural tendancy to toe in when power is applied.
- Brake balance is set with the driven wheels taken into account. So a FWD car will have proportionately less front bias as it would be assumed that a degree of engine braking was occurring. Sure ABS can help here but even the best systems work better when designed for the car as a whole and not a "get out of jail free" card.
My fwd seems to tuck in more when the rear tyre pressures are a couple of psi lower than the front, but that's probably a whole other kettle of cats...
Gassing Station | General Gassing | Top of Page | What's New | My Stuff