RE: What is a start-stop system? PH Explains

RE: What is a start-stop system? PH Explains

Tuesday 23rd October

What is a start-stop system? PH Explains

How shutting off an idling engine does more than just save fuel



Billions of gallons of fuel are wasted each year by idling engines. Be it in traffic, at junctions, on or peoples' driveways, these engines that aren't otherwise doing anything useful continue to consume fuel and produce emissions. Idling engines cause several key issues. Besides costing the driver money by burning fuel in a wasteful fashion, they also generate unnecessary pollution and noise. This can be a significant headache for many, particularly in urban areas that suffer from congestion.

Consequently, many manufacturers now use so-called 'start-stop' systems to alleviate these problems. These systems can automatically shut the engine off when the vehicle has come to a stop, preventing wasteful idling. When the driver is ready to set off again, the engine will be automatically restarted and the car can continue onwards. This means that, while the car isn't going anywhere, the engine won't burn any fuel, make any noise or emit unnecessary emissions - greatly reducing carbon dioxide and particulate emissions in congested areas and saving the driver money.

Start-stop systems are not a new development, that said, with early versions arriving the 1980s - but they are now far more commonplace and, in many cases, increasingly unobtrusive in their operation.


How do start-stop systems work?

A start-stop system will monitor various parameters, such as wheel speed and the driver's inputs, in order to decide whether the engine should be shut down or restarted. In a car with a manual transmission, shutting down the engine automatically in a safe fashion typically requires three conditions to be met - the car needs to be stopped, the transmission in neutral and the clutch to be released.

In that situation, the start-stop set-up can shut off the engine when it would otherwise be unnecessarily idling. When the driver intends to set off again, and begins to press the clutch pedal, the engine will be promptly restarted to allow the car to continue on.

Start-stop functions in a similar fashion in automatic cars, although the transmission can often be in drive or neutral - with the car being held in position, enabling the shutdown of the engine, by the driver keeping their foot on the brake. Alternatively, an auto-hold feature may secure the car.


Modern start-stop systems will often account for several other variables in order to ensure the best functionality, too. For example, most 'auto-stop' setups will only shut down the engine when it is up to temperature, once the climate control has met its interior temperature targets and if the battery has reached a sufficient state of charge.

In order to ensure durability and proper operation, manufacturers may also fit uprated components that can endure the repeated on/off cycling and higher electrical loads. Bosch, for example, supplies starter motors with upgraded bearings and pinion assemblies, batteries that are designed to withstand the heavier electrical loads and more efficient alternators.

Many may make further changes to ensure smooth operation. Mercedes-Benz, among others, equips its automatic cars with an electrically operated transmission oil pump for start-stop applications. This allows pressure to be built in the transmission prior to the engine restarting, so that first gear can be engaged quickly; this allows for a much swifter response and less hesitation off the line.


Just how beneficial can a start-stop system be?

During NEDC fuel economy trials, according to manufacturer Bosch, a start-stop system reduced fuel consumption and emissions by eight per cent. It also claims that, in real-world traffic, a start-stop system can offer improvements of up to 15 per cent on both the economy and emissions fronts.

Other reports, such as those published by the technology firm Schaeffler, state a saving of around five per cent in NEDC tests - and more in urban traffic. Reportedly, the amount of fuel necessary for a warm start is equivalent to that consumed when the engine is idle for just 0.7 sec; as a result, the start-stop system does not have to shut the engine down for long for there to be a benefit.

In any case, the potential economy and emissions advantages are notable. As a result, the system is of great use to manufacturers attempting to meet increasingly stringent emissions regulations - including ever-lower CO2 emissions targets. That aside, the reduction of noise from traffic is of considerable benefit to those living alongside the roads.

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Author
Discussion

scarble

Original Poster:

5,158 posts

93 months

Tuesday 23rd October
quotequote all
But, during a stop phase is the cool down of aftertreatment sufficient that emissions of other pollutants is worsened? Is this another case of the CO2 crusades negatively impacting local emissions?
Would stop-start be a better name?
Also modern systems are increasingly able to stop the engine juuust before the car stops and if the driver then tips in before fully stopped can restart an engine while it's still running down, or with 48v systems maybe even just drag the car along under electrical power while the engine runs up, in theory.
And full on coasting, stopping the engine at speed (even at 70), might be along soon.

Gary C

4,373 posts

115 months

Tuesday 23rd October
quotequote all
Christ, I'm suprised PH thought that this needed explanation.

Next, fuel, makes your car go. pH explains smile

Anyway, I notice that on my commute, having ss turned on saves me a few mpg, so it must do something.

buggalugs

8,391 posts

173 months

Tuesday 23rd October
quotequote all
In before some codger goes on about starter motors and batteries as if there the first person ever to think of that...

techguyone

1,151 posts

78 months

Tuesday 23rd October
quotequote all
buggalugs said:
In before some codger goes on about starter motors and batteries as if there the first person ever to think of that...
haha yes, every time SS is mentioned that's the first thing 'I'm not doing that, it'll wreck my... battery/alternator/starter motor....'

Lancashire Lad

8 posts

127 months

Tuesday 23rd October
quotequote all
I simply can't be doing with it. I've an SL63 which has it fitted. It means theres no such thing as a "Smart" getaway. The car has to think about starting then it decides to go. Its so frustrating.
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Lancashire Lad

8 posts

127 months

Tuesday 23rd October
quotequote all
I simply can't be doing with it. I've an SL63 which has it fitted. It means theres no such thing as a "Smart" getaway. The car has to think about starting then it decides to go. Its so frustrating.

Evilex

448 posts

40 months

Tuesday 23rd October
quotequote all
techguyone said:
buggalugs said:
In before some codger goes on about starter motors and batteries as if there the first person ever to think of that...
haha yes, every time SS is mentioned that's the first thing 'I'm not doing that, it'll wreck my... battery/alternator/starter motor....'
Wait until your battery is wrecked. The replacement cost for the appropriate stop/start battery is.....

Eye-watering.

996TT02

2,773 posts

76 months

Tuesday 23rd October
quotequote all
I don't have the figures here. But OH's Qashqai gives a cumulative "CO2 Saved" figure for the stop-start. And there is a lot of stop-start in mostly traffic choked urban trips. The figure is pitiably small, again don't ask, but the respective fuel quantity saved / not consumed over 4 years is close to meaningless, certainly a battery replacement will pummel the savings into oblivion. I feel that this measure was one for the test cycle more than anything else.

Christmassss

449 posts

25 months

Tuesday 23rd October
quotequote all
I find the SS system a bit disconcerting, being sat in the car with the engine off just feels odd. So i turn the system off every time i get in the car.

Chrismawa

152 posts

36 months

Tuesday 23rd October
quotequote all
Christmassss said:
I find the SS system a bit disconcerting, being sat in the car with the engine off just feels odd. So i turn the system off every time i get in the car.
+1

I do it now without even thinking about it.

Baldchap

528 posts

28 months

Tuesday 23rd October
quotequote all
I have recoded my car to permanently disable Start/Stop as well as disable pretend exhaust noises. I'll buy a diesel if I want to save fuel.

Durzel

6,743 posts

104 months

Tuesday 23rd October
quotequote all
Lancashire Lad said:
I simply can't be doing with it. I've an SL63 which has it fitted. It means theres no such thing as a "Smart" getaway. The car has to think about starting then it decides to go. Its so frustrating.
What's a "smart" getaway? Traffic light GPs?

underphil

977 posts

146 months

Tuesday 23rd October
quotequote all
techguyone said:
buggalugs said:
In before some codger goes on about starter motors and batteries as if there the first person ever to think of that...
haha yes, every time SS is mentioned that's the first thing 'I'm not doing that, it'll wreck my... battery/alternator/starter motor....'
Depends on the system, some are better than others

The article doesn't mention this, but the Mazda Skyactiv-G engines stop the crank in a specific position that allows it to be re-started using spark

http://www.mazda.com/en/innovation/technology/env/...

Shiv_P

1,430 posts

41 months

Tuesday 23rd October
quotequote all
Lancashire Lad said:
I simply can't be doing with it. I've an SL63 which has it fitted. It means theres no such thing as a "Smart" getaway. The car has to think about starting then it decides to go. Its so frustrating.
It's probably a st implementation then, the cars I have driven with it have been pretty seamless

underphil

977 posts

146 months

Tuesday 23rd October
quotequote all
Lancashire Lad said:
I simply can't be doing with it. I've an SL63 which has it fitted. It means theres no such thing as a "Smart" getaway. The car has to think about starting then it decides to go. Its so frustrating.
Maybe the system on the SL63 isn't very good? - on mine I can reduce the pressure on the brake pedal (car still stationary) and the engine will start up ready for whenever I want to move off

Red 4

5,158 posts

123 months

Tuesday 23rd October
quotequote all
It's a cynical system to help manufacturers cheat emission figures.

In the real world that reduction amounts to the square root of fk all.

It is, however, just another thing to go wrong with associated repair costs and the Increased costs of stop/ start batteries.

I always turn mine off. I drive the car and decide what it does. I don't need the car to decide what it wants to do (my car is very sensitive to the clearly very complex parameters that control the system - sometimes stop/ start works, sometimes it doesn't).
God knows how many additional sensors are fitted to provide information to the car's brain.
I suspect it's quite a few.
The system monitors steering angle, air con, ambient temperature, whether a door is open, has reverse been engaged recently, etc etc etc
It's just another thing I don't need.
I'm sure the polar bears will be OK if I don't use the system.
The increase in pollution caused by manufacturing the system probably outweighs the benefits of using it !

Edited by Red 4 on Tuesday 23 October 12:05

steveb8189

188 posts

127 months

Tuesday 23rd October
quotequote all
Lancashire Lad said:
I simply can't be doing with it. I've an SL63 which has it fitted. It means theres no such thing as a "Smart" getaway. The car has to think about starting then it decides to go. Its so frustrating.
I presume yours is an auto otherwise it would start upon clutch depression. I just sit there with my foot on the brake and then when I see the traffic starting to move in front or the traffic lights start to change I just blip the throttle to get the engine going. I do wish clicking one of the gear shift paddles would have the same effect though

Ninja59

1,937 posts

48 months

Tuesday 23rd October
quotequote all
I must admit the system on the BMW N57 is fine and smooth unless it is completely hoofed from a stop.

But, I turn it off nearly all the time as I just find it makes no real "meaningful" difference. What does is using the throttle and brakes sensibly and equally I find using eco mode over comfort does allow the car to coast far better on the speed gathered than other modes which ultimately does make in general a more relaxing environment to be in.

Uncle John

1,822 posts

127 months

Tuesday 23rd October
quotequote all
I find the pregnant pause before it fires up quite dangerous particularly at junctions where you are looking for a gap. So I turn it off.

I’ve also managed to stall the car a few times when I’ve caught it out with a ‘I’m going to stop, oh no I’m not!’ as the traffic moves off sequence.

In a genuine traffic jam I’ll turn it off though.

TheTyreAbuser

160 posts

34 months

Tuesday 23rd October
quotequote all
Can't say it bothers me in my Golf, though it is a manual so it makes it a bit more responsive.

Just clutch down when you think it's about time to move off, or if I'm a bit slow on the uptake, the radar system in the car starts the engine when the car in front starts moving.

Though obviously in some automatic cars I've driven it can be quite poorly implemented.
The Discovery Sport is one that's particularly poor, especially as I've never found any way to get it to auto-hold on the electric handbrake (like almost every other e-handbrake system). The stop start only comes on if you have your foot on the brake and it's in drive, press the e-handbrake and it starts the engine. With no auto-hold it just feels like it's a very poorly thought out system.