Any - Stop/Start Systems - ianhad2

I keep reading about cars being fitted with the Stop/Start system, the latest Jag has it.

Then I think of driving through the Blackwall Tunnel, London, every day, in the winter, it can take an hour. Does the system turn the headlights down?

Because I can't see how the battery can survive in the real world.

Any - Stop/Start Systems - injection doc

S S now becoming quite common even on Landrover, there are many sensors on the engine to detect whether it should shut down or not ! for instance if its been stonking along a motorway and you suddenly stop in a traffic jam the system wont allow the SS to come into effect untill its started cooling down and battery voltage is monitered as well.SS can also be overidden by the driver.

Time will tell and will be very interested to see what heppens to some of these cars at 4-5 years old ! There are a few out there as i came across a diesel lupo from Germany must of been in 2006 ish that had SS, was well weird to drive at the time.

Any - Stop/Start Systems - unthrottled

It's a bit of a gimmick. The NEDC has quite a few stationary components to the cycle so it helps bump the official figures up. In practice it's a lot of mechanical faffing for a very small gain. If you're stuck in a traffic jam, you know where the ignition key is....

If facing downhill in a jam, I often turn the engine off-and switch the ignition back to 'on', so the brake lights work. When I need to restart, just drop into 2nd and tickle the engine with the clutch-warm engine starts easily and avoids unnecessary wear to the starter motor. As usual a mechanical gimmick to carry out an operation a dilligent driver can do perfectly well themselves. Bit like automatic transmissions.

Any - Stop/Start Systems - bathtub tom

It's been many years since I've seen a car with the brake lights wired through the ignition switch. Most seem to be permanently live.

Every car I've owned that's been fitted with a catalytic converter, expressly warns not to bump start. I presume it's to do with the starter circuit being energised giving the ECU a message to prevent over-fuelling damaging the cat.

Any - Stop/Start Systems - ohsoslow

Unthrottled,

I was once told that leaving the ignition on without the engine running risks burning out the coil packs.

Edited by ohsoslow on 24/05/2011 at 19:20

Any - Stop/Start Systems - unthrottled

15 years and still going from coil packs...

No problems from cat either. I bump it to avoid the rich starting sequence. It's nonsense that bump starting damages the cat. Bumping from cold can be hard on the engine thoug if you do it frequently.

Any - Stop/Start Systems - Roly93

It is a complete gimmic, I have it on my A4. I always push the disable button when I set off because I cannot see the logic behind stopping the engine because I have been at the lights for 60 seconds. To answer some of your questions, these cars have a huge battery compared to a standard car, but there are various criteria when the system won't allow the engine to be stopped, eg , engine still cold, engine very hot, high power drain causing battery state to be sensed as dropping. For instance I was using an Audi A1 recently, and it stopped stopping as I was driving through town, because I had lights, wipers and demister all on.

On the plus side though, it does help the car to have low emissions on paper so less road TAX.

Any - Stop/Start Systems - barney100

I think stop start will stop me considering any car with it. I can't see how switching the engine on and off do a car anything but harm, seems just a gimmick to me.

'

Any - Stop/Start Systems - unthrottled

Idle fuel consumption is ~0.2-0.3 gallons/hour for a modest sized automotive engine. So if you sat in a traffic jam for an agonising 3.5-5 hours without turning a wheel, you'd only use 1 gallon of fuel. So you're not looking at much fuel just sitting in traffic lights for 30 seconds!

Hardly worth the hassle of the beefed up starter motor and electronics required.

Any - Stop/Start Systems - bathtub tom

If it comes to a court of law, who do I believe, you, unthrottled, or the vehicle handbook?

Any - Stop/Start Systems - John F

.... who do I believe, you, unthrottled, or the vehicle handbook?

It's not a question of belief! It's establishing matters of fact, weighing them up and arriving at an opinion.

In my opinion unthrottled has it right. It must take several years of tiny petrol savings to offset the extra cost of the heavy duty battery and gadgetry for a driver who uses the ignition key and clutch in an intelligent manner.

Any - Stop/Start Systems - WellKnownSid

They make a big difference to CO2 figures... it's not just about fuel.

I travel back and forth a lot to the UK, so I get to hire lots of cars, and have some experience of most of the different mainstream stop-start systems.

Firstly, it takes about a day to get used to the system working... in fact going back to a non stop-start car takes more getting used to!

In general they are all intelligent enough to cope with real-world driving, so they don't just keep tabs on aircon load, and keep the PAS running, etc - but also monitor the important things like brake servo vacuum, so you don't find yourself stranded at the top of a steep hill without powered brakes!

The VAG system that I've used in Audi A3s and A4s along with the VW Passat Greenline is the most intuitive I've used, and becomes second nature in no time. The engine stops in a logical way, without any fuss, it's a consistent experience, and can work out from gear position, clutch, brakes and general timing the occasions when you don't want it to kick in such as parking up.

The other extreme are systems like the Hyundai / Kia... the system is eager to kick in when you are still doing about 3mph, the engine then dies with a chug which makes you think you've stalled it (not intuitive), and takes a fraction of a second longer than the VAG system to restart (the VAG cars seem to be running before you've 50% dipped the clutch vs already selecting a gear with the others).

Of course, yes, these are all hire cars with <10k on the clock. How well they work with a duff battery, low compression and stagnant oil in 8-10 years time after 5 owners may be entirely different. But the theory is good! ;)

Any - Stop/Start Systems - Andy P

The Italians have a new version of this....it's called Stop.

Any - Stop/Start Systems - dieseldogg

Having nerdishly sought max mpg from the Galaxy, I was astounded at the difference killing the engine when stationary made.

This from simply observing the trip computer displayed mpg figures,and I would add...... not instanteanous figures................. but the journey average figures.

Any - Stop/Start Systems - daveyjp

My B class has it - it stops when I'm stationary and starts when I dip the clutch. Easy, unobtrusive and causes me no problems. The system works very well and nothing electrical is put out of action when it stops - steering, lights, wipers, radio etc all continue to work.

If the battery starts losing power the car restarts, like a lot of MBs it has a smaller secondary battery.

I understand the car doesn't use the starter motor to restart so wear on this component is not an issue.

Many may not be in favour, but give it a few years and all cars will have it.

Any - Stop/Start Systems - Neiltoo

So what starts it then?

Any - Stop/Start Systems - daveyjp

So what starts it then?

Courtesy of Mercedes:

And it's all down to the starter-generator which Mercedes fit rather than just relying on the conventional starter motor.

Connected to the crankshaft via the belt drive the starter-generator allows the engine to start much faster and far more quietly than with the conventional starter making it very easy to live with.

During the journey, the starter-generator feeds the electrical system on board the B-Class with energy. An intelligent control system ensures that the battery is only charged when needed, and that charging mainly takes place when the engine is on the overrun to convert braking energy into electrical energy by recuperation.

Using a key involves the starter motor, stop start doesn't and you can tell the difference as it is quick and quiet.

Any - Stop/Start Systems - unthrottled

They make a big difference to CO2 figures... it's not just about fuel.

CO2 and fuel consumption are the same thing expressed in different ways.

It's a bit more complicated when comparing petrol and diesel because of the idiotic way in which fuel is sold on a volumetric basis rather than gravimetric basis.

It is convenient for governments to imply that CO2 is somehow dfferent to fuel economy because it isa nice excuse to impose another tax.

Be careful when looking at fuel economy-it is inversely proportional to the fuel consumption-and this is what matters to your wallet. By this I mean that when fuel economy gets into the 50-60mpg range, it is easy to get a big change in fuel economy but this only correlates to a small change in consumption.

100 miles@a whopping 64mpg=1.56 gallons of fuel

100 miles@only 58mpg =1.72 " " "

The difference being 0.16gallons-or about £1.

Edited by unthrottled on 25/05/2011 at 15:54

Any - Stop/Start Systems - WellKnownSid

CO2 and fuel consumption are the same thing expressed in different ways.

True, but the issue is that drops in CO2 as a result of "small" changes in consumption can result in big swings in vehicle and registration taxes depending where you are in Europe.

Going from 120g/km to 119g/km, for example, means saving 4.75% in registration taxes in Spain... €1,000 on a family car.

The coincidence, of course, is how many cars here now offer 119g/km emissions...

Edited by WellKnownSid on 25/05/2011 at 16:37

Any - Stop/Start Systems - unthrottled

But that's a political decision, not a scientific or engineering one. Politics changes on a whim. It's like the old UK road tax system of having a rate for <1565cc and another one for >1565cc. Of course the most popular size of engine was 1600cc. If manufacturers had shaved 100cc off their engines then you can bet that the threshold would change to 1465cc and so on. It's a dishonest, government distraction from the goal of reducing fuel consumption.

Any - Stop/Start Systems - WellKnownSid

But that's a political decision, not a scientific or engineering one. Politics changes on a whim. It's like the old UK road tax system of having a rate for <1565cc and another one for >1565cc. Of course the most popular size of engine was 1600cc. If manufacturers had shaved 100cc off their engines then you can bet that the threshold would change to 1465cc and so on. It's a dishonest, government distraction from the goal of reducing fuel consumption.

Who are being the most dishonest, though? The politicians for setting "impossible to meet" CO2 targets, or the manufacturers who then magically manage to "just" meet the threshold by a whisker?

The scientific / engineering know-how has always been there... it was just no-one wanted to go first without the political pressure to do so.

Any - Stop/Start Systems - unthrottled

The scientific / engineering know-how has always been there... it was just no-one wanted to go first without the political pressure to do so.

Any - Stop/Start Systems - WellKnownSid

A good example is the Euro 6 standard for diesels. A direct quote from the director of the European Federation for Transport and the Environment:

"An American consumer can buy a super-clean Mercedes diesel today in their local dealer, while a German will have to wait until 2015 to buy something even remotely similar."

No political pressure means the technology is suddenly not available. Except in countries where it is ;)

Any - Stop/Start Systems - unthrottled

The scientific / engineering know-how has always been there... it was just no-one wanted to go first without the political pressure to do so.

Well, when I dig out my old SAE papers from the 80s I find that the brake efficiency of Heavy Duty diesels hasn't improved by much. If you take a car from 1990 rated at 40mpg in the combined cycle, you probably won't have any difficulty achieving that figure in the real world. Compare that to a modern car rated at 60 mpg-you'll do well to get anywhere near that figure.The car on paper appears to have improved by 50%, the reality is a lot less.

Modern cars are cycle tuned to the NEDC-nothing wrong with that except that it doesn't really reflect real world driving. Fuel economy figures are like GCSE results; they improve year on year. But the actual improvement is of course massaged.

The thermodynamics of engines is poorly understood by the public. They think that a brake efficiency of 40% is 'not good enough in this day in age' because their condensing boiler has an efficiency of 90%. But this just shows ignorance of the 2nd law. This leads to ignoramuses clamouring for silly things like diesel hybrids and 8 speed transmissions.

Any - Stop/Start Systems - WellKnownSid

This is true in any field. No matter how the targets are set, a manufacturer will chase the numbers - but not necessarily achieve the underlying objective.

2nd law? Wasn't that about entropy always increasing? IIRC from the Diesel and Otto cycles, that meant optimal efficiency came at 0K...

Any - Stop/Start Systems - unthrottled

I don't know what you're referring to by the 0K thing-the Carnot Cycle? Yes, entropy always does increase-which means that it is impossible to convert chemical energy entirely into mechanical work. Modern small diesels have a peak efficiency of ~40% which gives a gross efficiency of about ~45ish%. That's not far off the theoretical limit so I don't expect it to increase by much-ever.

Any - Stop/Start Systems - unthrottled

"An American consumer can buy a super-clean Mercedes diesel today in their local dealer, while a German will have to wait until 2015 to buy something even remotely similar."

Sid, I design HD diesels for a living. Clearly you do not. You think Euro VI is going to be fun, right? It'll be clean, but not fun-or efficient. Look at European diesels for sale in the USA. Take the VW Jetta 2.0 TDI

Fuel economy:31/41US Miles per US gallon city/highway

so that's 37/49 Miles per UK gallon.

Not exciting is it? Oh, and it only develops 140hp-less than it's European equivalent.

And it requires a NOx trap in addition to the unloved particulate trap you find on European diesels.

Take your Mercedes example. Merc couldn't get their cars to meet the standard with a NOx trap-so they have to use exhaust fluid-which is of course consumable. If you run the exhaust fluid dry and don't refill it, your car won't start. BMWs 335D is exactly the same.

That has been what has holding back economy for years-the trade-off between emissions and economy. In Europe the balance is tipped in favour of economy (for diesels anyway). In the US the balance is tipped in favour of emissions.

Take your pick-which one do you want? You can't have both.





Edited by unthrottled on 25/05/2011 at 20:15

Any - Stop/Start Systems - WellKnownSid

The truth is, most of us just want a reliable and cheap to own motor car - i.e. total cost of ownership over the vehicle's life, no expensive emission-control components to replace once out of warranty.

Which do you think has the brightest future over the next, say, 5 - 10 years... diesel or petrol or something else? There is supposedly a surplus of petrol in Europe, due to the demand of diesels. Do small CC turbo petrols offer a viable alternative, or are they a gimmick with their own problems?

Any - Stop/Start Systems - unthrottled

Small turbo petrols are very promising-but they won't beat diesel in sheer efficiency.

The big gains have already been been exploited in automotive engines. Government needs to put put bigger incentives on domestic CO2 emissions which are way bigger and full of easy pickings. But that is a political hot potato...!

 

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