BMW - auto start stop.

[Black Sheep]

just wondering if its still true that a car uses more fuel to start it than to drive it for a mile

in which case its a waste of fuel unless your stood for a while, no?

 

[briank]

You beat me to it on that one.
Not sure whether the mile figure is right for a well warmed up engine, but it does take a good deal of juice to spin that starter against engine compression.
It must be hard work for the battery. Presumably they can handle it and the electronics that control the charging system ensures that in intensive stop-start driving enough power is sent to the battery to keep it charged up. But of course that power is generated by burning fuel in the engine.
Sometimes, for sure, stuck for minute after minute in a jam on the motorway, the system will be effective.
But there must also be a city driving scenario with lots and lots of very brief stops in which the automatic shut down uses more fuel/emits more pollution than keeping the engine running.
So a gimmick to appeal to the consumer who's green but not very mechanically literate?

 

[mr_hippo]

Are you sure?

No, I am not sure - I'm positive!
http://www.italiaspeed.com/2009/cars/fiat/02/regatta_es/1602.html

Start/stop technologies saw daylight in 1980 when German manufacturer Volkswagen developed such a feature and installed it on Volkswagen Polo, also known as Formel E. The same system was improved and re-used in 1990 on Golf Ecomatic and Lupo 3L, being then adopted and slightly modified by many other carmakers.
Source
http://http://www.autoevolution.com/news/stopstart-helps-mahindra-reduces-fuel-consumption-1725.html

 

[thomas]

Company car drivers are using the technology because they change company cars every year or two on most leasing schemes.

Your post makes no sense. Why would the type of finance or length of lease affect the usage of technology?

A lot of leasing schemes will change their cars every few years for newer models. The newer models have newer technologies. Therefore company cars will benefit from newer technology more frequently....understand?

When I was looking at second had cars at auction there were so many ex-company cars which were only a few years old, if that. They can be a really good buy second hand.

 

[Black Sheep]

You beat me to it on that one.
Not sure whether the mile figure is right for a well warmed up engine, but it does take a good deal of juice to spin that starter against engine compression.
It must be hard work for the battery. Presumably they can handle it and the electronics that control the charging system ensures that in intensive stop-start driving enough power is sent to the battery to keep it charged up. But of course that power is generated by burning fuel in the engine.
Sometimes, for sure, stuck for minute after minute in a jam on the motorway, the system will be effective.
But there must also be a city driving scenario with lots and lots of very brief stops in which the automatic shut down uses more fuel/emits more pollution than keeping the engine running.
So a gimmick to appeal to the consumer who's green but not very mechanically literate?

my assumption is that it will save fuel and emissions when in a traffic jam somewhere, however it does appear to be more like catalytic converters that don't save emissions (its well known that they produce more in producing the unit than it will ever save in its lifetime) but what it does do is move all the horid crap out of a city centre to wherever the units are produced a bit like electric cars and emissions from a power station.

with regards to charging the battery back up, the alternator is charging most of the time anyway keeping the battery topped up so it makes little difference, provided things are in good working order

however, in a few years when the battery has aged, we may well see some cars with this technology stranded at traffic lights.

 

[zaid]

my assumption is that it will save fuel and emissions when in a traffic jam somewhere, however it does appear to be more like catalytic converters that don't save emissions (its well known that they produce more in producing the unit than it will ever save in its lifetime) but what it does do is move all the horid crap out of a city centre to wherever the units are produced a bit like electric cars and emissions from a power station.

with regards to charging the battery back up, the alternator is charging most of the time anyway keeping the battery topped up so it makes little difference, provided things are in good working order

however, in a few years when the battery has aged, we may well see some cars with this technology stranded at traffic lights.

I'm not right up to date with new technology,but, charging of the battery whilst the engine is running is not "free", it increases load on the engine, hence higher CO2. The inner city driving scenario would possibly make these systems counter productive, possibly?

 

[domd1979]

BMW have also developed a system where the energy from braking goes into charging the battery. When accelerating the alternator gets disconnected from the engine and so doesn't place a load on it. Auto start/stop doesn't work until the engine is warm (same with Honda Hybrid) which should mean less starting power required to start the engine I would imagine.

 

[Black Sheep]

I'm not right up to date with new technology,but, charging of the battery whilst the engine is running is not "free", it increases load on the engine, hence higher CO2. The inner city driving scenario would possibly make these systems counter productive, possibly?

I didn't say free, but i wasn't clear.

Most cars alternators are always charging the battery and so the car being run charges the battery up, provided it is run for some minutes between each re-start.

 

[Ivan Ardon]

There can't be many modern cars that need churning away on the starter motor to get them going from warm. Even my runaround 15 year old Fiat will spring to life within half a second.

Assuming a 350 amp current for half a second, it doesn't take an alternator long to put that back into a battery.

If you're churning away on the starter for ten seconds every time you start your car, then there's something seriously wrong with it.

 

[tdr1nka]

If you're churning away on the starter for ten seconds every time you start your car, then there's something seriously wrong with it.

Or you just need to check your fuel line/inline filter and make sure the HT leads and spark plugs aren't loose or coked up.

 

[zaid]

OK, I didn't mean to start anything, if you excuse the pun!

 

[Wigsie]

BMW have also developed a system where the energy from braking goes into charging the battery. When accelerating the alternator gets disconnected from the engine and so doesn't place a load on it. Auto start/stop doesn't work until the engine is warm (same with Honda Hybrid) which should mean less starting power required to start the engine I would imagine.

This is true, its part of their "Efficient Dynamics" the alternator actually kicks in as soon as you take your foot off the accelerator to charge the battery. The Air con, power steering etc runs directly from the battery so the fuel consumption is not affected and you actually get better fuel consumption and around 35bhp more from the same engine.

For every driving style (other than sub 30mph urban driving) these cars are better on the environment than the so called eco friendly hybrids, which cane fuel once the petrol engine kicks in.

 

[Fixedwheelnut]

must be fun if it gets stuck in gridlock in winter or does the heating work without the engine?

There are a load of reasons when the system will shut off the stop start system and prevent the engine stopping, if the heating or rear window is on de-mist , if the engine temperature is too low, if battery voltage is too low.

Of course non of these are explained to the customer by the salesmen and as yet none of the complaints we have had have actually been faults in the system yet.

The VW system was out when I worked for VW and there biggest problem was eating starter motors but technology has improved since then.

 

[twowheelsgood]

Are you sure?

In 1991 I was offered a Phd to research on this technology and sponsored fully by Ford. I didn't take the project but I always wondered what happened to the idea As I remember the project was to reduce fuel consumption at traffic lights and one of the areas of research was to keep the car running in only 2 cylinders, however, I guess batteries have improved sufficiently to implement a technology that kills off the engine completely.

Mk II Golf definitely had this stop/start technology in the 80s, it had an absolutely huge starter motor and and battery IIRC. I believe the Routemaster buses had the "turn a couple of cyclinders off while idling" trick in the 1950s (or was it fire every other cycle?), which is why the sounded and vibrated like they did ät the lights - this was before they received the new engines designed for modern, heavier buses and became the (extremely unlikely) GTi of the bus world! Cadillac also had something they called the modular displacement engine in the 80s which run on 8, 6 or 4 cyclinders as needed.

Ultimately a big and workable with current technology improvement in urban fuel consumption will come from a KERS like system as it would only need to store the energy from a single braking/accelerating cycle and hence wouldn't need a huge battery.