I am no science expert but I know the basics of physics. and the laws of energy transfer.
Put simply if the engine cuts out at each lights surely it will need at least all the energy it saved if not more to turn over the engine again? I am missing something?
Edited by Rattle on 20/08/2009 at 02:03
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Put simply if the engine cuts out at each lights surely it will need at least all the energy it saved if not more to turn over the engine again?
Does turning over the engine take that much energy?
There must be a time T over which an idling engine uses as much petrol as it uses (indirectly) when starting, and if you are waiting at the lights for less than T then you don't save anything. But I'm guessing T is pretty short.
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I wouldn't be suprissed if these cars with stop / start technology need the car batteries replaced more often.
Less wear and tear on one part means more wear and tear on another !
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I wouldn't be suprissed if these cars with stop / start technology need the car batteries replaced more often.
...and/or starter motors, you'd think.
VWs (and others?) have offered this system in the past - did they have problems?
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VW tried this years ago with the Formel e (Golf?)
I think the benefit then started at around 15 seconds - with modern fuel injection and ignition systems it may be less now.
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I am missing something?
It all comes down to how long the car is stopped at the lights.
Probably takes more energy than it saves if they're red for 10 seconds. Probably the other way around if its a minute.
Most of the systems seem to keep a close eye on battery levels and don't turn the engine off if the battery is low.
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AFAIK, they don't use traditional alternators and starter motors, they have a much more radial one mounted on the crankshaft so there are no belts of meshing of pinions etc. They also have newer battery technology. They were about 9 years in development.
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The reason often quoted in the past why users of diesel engines tended to leave them idling for long periods was that idling required such minute quantities of injected fuel that it was not worth the wear and tear on other components caused by stopping.
On the other hand a carburetted petrol engine needed a richer mixture to maintain idle, so prolonged idling was costly.
So T would have been about half an hour for a traditional diesel and about 10 seconds for a carburetted petrol. For a modern petrol injected engine, perhaps 20 seconds?
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The big downside to me on this system on the Insight was it only worked when you held the car on the footbrake, not something I do for extended periods of time.
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So T would have been about half an hour for a traditional diesel and about 10 seconds for a carburetted petrol.
Thanks Cliff - and presumably the higher compression ratio of diesels means they need more energy to (re-)start as well?
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If it takes half a second to start, that's only going to take the same energy as running for half a second. If you factor in the inefficiencies, maybe a second or two at very worst.
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If it takes half a second to start that's only going to take the same energy as running for half a second.
What sort of 'running'? Idling, or climbing a hill? Half a second of climbing a hill might be a lot of seconds of idling.
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Doesn't turning the camshaft and lifting the valves takes more energy at low speed because there is no inertia?
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If it takes half a second to start that's only going to take the same energy as running for half a second. If you factor in the inefficiencies maybe a second or two at very worst.
BMW say 2 seconds.
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My understanding is that the main reason this is done is because the official CO2 tests include an idling period - I don't know how long - but it improves the figure if there is Stop/Start. I can't complain cos it helps give my BMW118d a laughably low road tax of £35. It may help in real life but it needs the aircon switched off, otherwise the engine comes back on to maintain in-car temperature. As for BMW's execution of it,I have had no faults at all.
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As for BMW's execution of it I have had no faults at all.
Don't you have to put the gear lever in neutral and apply the handbrake for it to operate?
Bearing in mind the very vast majority of people seem to sit at lights with their foot on the brake pedal then it will never operate.
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No handbrake necessary. Brake pedal doesn't matter. Clutch pedal down does stop it working, cos pushing the clutch reactivates engine. It's difficult to describe really but it does feel quite natural after a while
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Maybe 'mild hybrids' will replace stop-start technology - I mean where the car can travel short distances under electric power, e.g. in traffic queues or when travelling only a mile or two. On a front-drive car with normal mechanical driveline, a mild hybrid system could be fitted to the rear wheels - with wheel-hub motor/generators and a small battery pack. Possibly this could be arranged through an 'E' position of the gearlever in addition to the 5 or 6 mechanical gears.
Edited by Sofa Spud on 20/08/2009 at 12:51
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In answer to Rattles question, yes, you are missing something - the energy required to start an already hot modern engine is tiny - as has been said, comparable to mere seconds of idling. IMO, the system should be compulsory on new cars.
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IMO the system should be compulsory on new cars.
IMO it shouldn't. There are far too many rules and regulations already.
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Broadly, I agree about rules and regs - but, it seems crazy to be peeing fuel away in traffic jams, while also complaining about air quality in cities.
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A properly engineered system with an alternator/motor in the flywheel or something similar should be OK, 0mpg in a traffic jam does not make sense.
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Going just a little further ON, the flywheel mounted electrical machine you mention could also be used to smooth the output from the engine - giving and taking kinetic energy like a large heavy flywheel, so, either a 3 cylinder could be made to feel more like a 4, or, the DMF could be deleted - it could even be used to supply extra power during demands for maximum acceleration, allowing the base engine size to be reduced.
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used to supply extra power during demands for maximum acceleration
KERS, eh?
Steady on NC.
'Simplicate and add more lightness', as the American aeronautical tycoon is said to have said...
Cars are too heavy and complicated already.
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>>'Simplicate and add more lightness',
Yes, that's exactly what I'm suggesting!
Do away with seperate starter & alternator, and replace with a flywheel mounted device and incorporate its control into the engine management ECU, saving the mass and cost, and packaging of their seperate housings and bracketry and wiring. Use the device to allow a lighter flywheel than you would otherwise need for a given level of smoothness. Use the controller wisely to obtain benefits you could not get from the old fashioned seperate devices.
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Do away with seperate starter & alternator and replace with a flywheel mounted device and incorporate its control into the engine management ECU saving the mass and cost and packaging of their seperate housings and bracketry and wiring. Use the device to allow a lighter flywheel than you would otherwise need for a given level of smoothness. Use the controller wisely to obtain benefits you could not get from the old fashioned seperate devices.
But you drive an aging spanner friendly Merc to avoid this type of complication?
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>>But you drive an aging spanner friendly Merc to avoid this type of complication?
It has its own special areas of fiendish complication. The heater and AC control, and the wiring for the electric windows is ridiculously complex!
However, a flywheel mounted starter / alternator would be removing complication, not adding it!
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It has its own special areas of fiendish complication. The heater and AC control and the wiring for the electric windows is ridiculously complex!
A car will get you to your destination without those things..........
However a flywheel mounted starter / alternator would be removing complication not adding it!
If that fails you're being towed to your destination.
All this gimmickry is pricing people off the road (maybe your parents or your children)
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Dox, it's an alternator re-packaged, not a flux capacitor!
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'Simplicate and add more lightness' as the American aeronautical tycoon is said to have said...
I thought that British Tommy Sopwith said that.Cars are too heavy and complicated already.
Couldn't agree more.
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IIRC didn't someone do just this on a family car in recent years.
I remember reading it and thinking it sounded similar to the dynastart system I had on a bubble car back in the '60s (except that couldn't provide extra drive power).
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Obviously it's good and ought to be widespread for several very good reasons.
Now that cars are more or less self-tuning and allow their spark plugs to last a long time they usually start very promptly. But in the old days with worn plugs and a maladjusted carburettor, any such system would just have run the starter motor into the ground before its time.
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Presumably they (BMW) use the same system on this - 137mph 3 series under 110g/km
www.honestjohn.co.uk/news/item.htm?id=6731
Edited by Focus {P} on 21/08/2009 at 10:29
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I don't totally agree with us being penalised with a system based on CO 2 , especially when it isn't (a) the main cause of global warming and (b) there are other natural sources that produce more.
So when the manufacturer's figure out ways of beating the system and getting the official figures down I'm all for it. I believe on some cars it's possible to disable this too.
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Some drivers are slow enough at starting off from rest as it is. Stop their engine and it will compound the problem. In congested traffic the system will simply lead to an even slower flow of traffic. No thanks.
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>>No thanks.
By the time you've pushed the clutch and selected the gear, the engine is running and ready for off. If a driver is following the highway code, and is in neutral, there's no difference in terms of time delay. At a junction, to keep the engine running, you just hold the clutch down.
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What i fear the most, is if it didnt start again, at least with a engine running you can listen and detect that its going to cut out, and in most cases apply a little revs to get you away from the lights (for example) and out the way of other traffic
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I recall driving the Golf with the stop/start system in London on its launch around 1994.
VW only used the 64bhp diesel engined model and fitted a heavy duty battery and starter motor to compensate for the need to restart the engine so often.
I remember at the time that it was very eerie realising that the engine had stopped soon after coming to a halt, but gradually became used to it and the fact that it restarted so readily.
But such a feature never really took off and doesn't seem to have do so since as far as motorists are concerned.
Certainly I never felt at ease, especially in heavy London traffic, constantly expecting that the Golf wouldn't start at an inopportune moment.
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The first car I remember with this technology was the FIAT Regata 70ES (Energy Saving) in around 1983. Were they the first?
Of course, everyone routinely ignores this car as it was only a crappy FIAT after all, eh?
;-)
Edited by Alanovich on 20/08/2009 at 17:07
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the obvious flaw ?
lets take the current fiat 500 as an example?
stop start petrol version has worse economy and emissions than the non stop start diesel version
quite why anyone would buy one rather than just getting the diesel version is beyond me
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stop start petrol version has worse economy and emissions than the non stop start diesel version quite why anyone would buy one rather than just getting the diesel version is beyond me
Err, because the diesel is £1400 more expensive and at that price and the MPG difference of 9mpg will mean the extra cost will most likely never be repaid in the cars life time.
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Err because the diesel is £1400 more expensive ...
Agreed.
And also because not everybody likes diesel engines. SWMBO hates them.
See: every diesel vs petrol thread there's ever been... ;)
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..as it was only a crappy FIAT after all, eh?>>
Appreciate the irony...:-)
I had a secondhand Regata 1.6S for more than three years in the late 1980s/early 1990s; it never missed a beat, never revealed a spot of rust and the only problem I had with it (prevalent in the Regata range) centred around the braking system.
Either On or Off. Absolutely nothing in between in the form of progressive slowing down...:-)
Edited by Stuartli on 20/08/2009 at 17:47
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The first car I remember with this technology was the FIAT Regata 70ES (Energy Saving) in around 1983. Were they the first?
Interestingly no they were not. I cannot remember the manufacturer who introduced it, but there was a system called "Startex" (at least that what I believe) introduced around the late 1930s. My father told me about it many years ago as he actually owned a car with this system and it was definitely pre WW2..
It would stop the car when in neutral, but as soon as the clutch was engaged and 1st gear selected the engine would start. I guess i'ts like many so called new inventions, most of them had either been tried or developed a lot longer ago than people realise. I remember someone boasting about all the new features on his car some 30 years ago, who was completely unaware that they had been developed nearly 40 years before that in the wartime Merlin engines.
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This is the next biggest con.
It just gets the CO2 down during the official CO2 test which includes a period of idling.
I certainly would not want my engine cutting out on a diesel car after coming off the m-way at 70mph and getting stuck in a traffic jam. Baking hot oil not being cooled or dissipated, no thanks.
Not to mention more stress on components with things like the battery, starter motor, oil, fuel pumps and not to mention the dual mass flywheel which has to work hardest during start up and shut down.
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OldSkoOL, don't forget that some diesels (like mine) also have to pre-heat using the glow plugs to start again.
Even if the engine on my car is hot and I turn the engine off and then turn the ignition back on, the pre-heat coil light comes on for a couple of seconds.
So if the engine needs a quick pre-heat before starting, this stop start technology may not work for all diesel engines.
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diddy isnt the problem with stop start diesels going to be the turbo bearings etc
most diesels these days are turbo to get the best engine attributes, mostly these and associated components need an oil supply from the running engine
stopping and starting the oil supply to the bearings is surely a bad idea
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thats a good point.
Never thought of that.
When I stop driving I always leave the engine running for 15 - 30 seconds to let the bearings cool down (I also do not blip the accelerator and then turn the ignition off).
The car manual says that this is not needed unless the engine has been working hard (hill climbing or towing)
Maybe the engine does not need it, but I can live with 30 seconds of my life sitting in the car compared to an expensive bill for a new turbo.
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Diddy, no diesel needs glow plugs to start a hot engine, in fact, I am not aware of any current diesel engine which requires them in the UK even from a cold start.
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Try a Kia Rio.
Still has a coil light that goes off after 10 - 15 seconds on a warm day
I cannot comment on the coil light in winter as I have not had the car long enough yet.
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What happens if you ignore the coil light and just try to start the car straight off?
On the subject of stop-start, my biggest gripe is that it won't work when the air-con or demister is on (or anything else that draws big currents), so most of the time it probably won't work anyway - i.e. useless!
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If I start the engine with the coil light on, it starts straight away.
My problem is that I am still getting used to having a diesel engined car.
Once I forgot about the coil preheating and just turned the key.
The engine started straight away.
but I do wonder what damage could be done if the coil preheat is on and the engine is started.
So what fun will I be in for this winter with a diesel engine ?
Do common rail engines start better than previous types of diesel engines ?
(I have vague memories of people sitting in their cars on cold winter mornings, turning the engine over and over for minutes until the car started)
I hope modern diesels are not like that.
Edited by diddy1234 on 20/08/2009 at 17:54
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If I start the engine with the coil light on it starts straight away.
Aha! There you go... :)
but I do wonder what damage could be done if the coil preheat is on and the engine is started.
None at all, unless anyone knows better? The glow-plugs are there to help get the combustion chambers up to temp so the engine can start, if the engine will start without them, then no problem eh?
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I was wondering if starting the engine while the coil packs were on would burn then out quicker.
I would imagine that the coils would heat up the cylinders to a predetermined temperature but under normal engine running the cylinder temperatures are more hotter.
Hence my wondering what damage could be done starting the engine while the coil packs are on.
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If I start the engine with the coil light on it starts straight away.
Direct injection diesel engines will start without preheating with glow plugs in all but the most extreme UK conditions. The glow plugs stay on after engine start for a short period to improve the combustion during the first few seconds, reducing smoke and other emmisions.
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Just how would this work with an automatic transmission car?
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Not sure whether these stop/stop systems cut down CO2 or not. My life as a city dweller would, however, be a lot more pleasant if all cars were fitted with them. Just think of the silence and the additional fresh air replacing the clatter and smell of diesel engines idling at traffic lights.
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I think this is a great technology that will help reduce pollution in built-up areas.
I'm sure in 10 years time all cars will have it - it will become as normal and expected as ABS, AC etc
MVP
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>>I'm sure in 10 years time all cars will have it - it will become as normal.....>>
I'll lay you a pound to a penny that this just doesn't happen...:-)
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If the start stop technology is fitted, can it be turned off?
Please say yes!
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