Author Topic: Start Stop on New Jazz  (Read 21120 times)

csp

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Start Stop on New Jazz
« on: December 28, 2015, 12:18:44 PM »
The Automatic Start / Stop on the new Jazz CVT stops the engine when the car comes to a rest and the foot brake pedal is depressed, if the brake pedal is released then the engine restarts.

When in in traffic jam if neutral is selected and the hand brake applied the car will still restart as soon the brake pedal is released. So for the engine to remain stopped the brake pedal has to be kept depressed and the brake lights then remain on which is not ideal, especially for the driver of car behind the Jazz.

I am not sure what happens with Start / Stop on the manual Jazz or other cars with Auto Start / Stop but it would be good if the Start / Stop also was also linked to the hand brake so that it could be applied instead of the driver having to keep the brake pedal depressed. There is already a switch that senses when the hand brake is applied, since  a warning is given if the car is driven off with the hand brake applied.

John Ratsey

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Re: Start Stop on New Jazz
« Reply #1 on: December 28, 2015, 06:23:59 PM »
Needing to keep foot on the brake (at least for the automatic version) is a feature that is shared with the Mk 2 versions with the auto idle stop (my Jazz hybrid had it). I used to get annoyed because, when I got home I would put my foot on the brake and the engine would stop, but moving the gear leave from D to P would start the engine running again.

Your suggestion of linking the behaviour to the handbrake is a good one. The engine can then be woken up by a light touch of the accelerator before wanting to pull away. This method could be applied restrospectively using a software update at no cost to Honda. My alternative suggestion, of a rear-looking sensor to detect a stationary vehicle close behind snd then turn off the brake lights would need extra equipment.

ColinB

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Re: Start Stop on New Jazz
« Reply #2 on: December 28, 2015, 06:29:25 PM »
So for the engine to remain stopped the brake pedal has to be kept depressed and the brake lights then remain on which is not ideal, especially for the driver of car behind the Jazz.
I am astonished. At least it explains why so many drivers seem ignorant about the handbrake when stopped at traffic lights !
With a manual transmission, the procedure is:
- car stationary
- handbrake on
- gear stick in neutral
- foot off clutch
- engine stops (unless one of the many inhibiting factors is in play).
The engine restarts when you depress the clutch. If you don't want the engine to stop (eg if you know it's only going to be a short delay) then just keep your foot on the clutch. None of that involves keeping your foot on the brake pedal.

harry22673

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Re: Start Stop on New Jazz
« Reply #3 on: December 28, 2015, 09:10:51 PM »
Changing the topic slightly but the thing I don't understand is how it uses less fuel than keeping the engine on

Rory

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Re: Start Stop on New Jazz
« Reply #4 on: December 28, 2015, 10:57:36 PM »
errr...an engine that is idling doesn't use much fuel, but a stopped engine doesn't use ANY fuel at all.

culzean

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Re: Start Stop on New Jazz
« Reply #5 on: December 29, 2015, 11:12:29 AM »
I can see start stop working best in city traffic jams,  but very little if any saving in normal motoring.  I would also be worried about wear and tear on battery (more expensive battery needed because of more frequent starting of engine),  wear on starter motor.   When an engine stops the oil drains out of bearings and metal surfaces touch, and when the engine is started again it takes a few seconds to re-establish the hydrodynamic oil film (when bearing surfaces are actually floating on a film of oil) - most engine wear takes place with a cold engine and during startup - I gather that car makers have developed special bearings to resist this lack of oil, but no long term results available on wear.   Some fuel will be required to power the alternator and replace current drawn from battery by restarting, this also puts extra load on alternator,  also with cars increasingly using a turbo to increase efficiency we all know a turbo should be left to 'cool down' by idling the engine before shutoff.   When aircon is used on hot days I guess engine will not shut down if cabin temperature requires aircon to be on,  so I would hope aircon (or auto temperature control as its now called) would inhibit engine shutoff.

Would be interesting if members with auto stop-start could conduct their own experiments on fuel saving and whether using aircon affects engine shut-off.  Will be good to see if this technology is useful or just pandering to climate change lobbyists by marginally reducing fuel used  but increasing the cost of making cars - or maybe just smoke and mirrors like 'clean diesels a-la mode VW.

I wonder if increased purchase cost of cars fitted with stop-start (I don't think motor manufacturers are charities) and increased cost of replacing larger battery (and fuel used to carry weight of larger battery) and maybe the odd starter motor here and there will nullify any savings for most drivers.
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

John Ratsey

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Re: Start Stop on New Jazz
« Reply #6 on: December 29, 2015, 12:55:35 PM »
There is a long list of situations when the auto idle stop won't activate in which case it should show a symbol on the multi-function display. These are explained in the handbook. Having the aircon running is one reason (but subject to "and the difference between the set temperature and actual interior temperature becomes significant." Also having the air ventilation control at, or near, the demist setting also stops the idle stop from working. However, the system isn't infalliable. On a couple of longer journeys I have been stopped at traffic lights or similar and the auto idle stop has not activated nor has there been any symbol explaining why not. Once it has got into this mode then it will continue until after a stop (ie engine turned off). My dealer offered to look at this but I declined because they could take a long time and lots of miles to encounter it and then be none the wiser about the cause.

harry22673

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Re: Start Stop on New Jazz
« Reply #7 on: December 29, 2015, 01:52:01 PM »
errr...an engine that is idling doesn't use much fuel, but a stopped engine doesn't use ANY fuel at all.
But if its off for a few seconds
Starting it back up again would use more fuel

hybridjazz

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Re: Start Stop on New Jazz
« Reply #8 on: December 29, 2015, 04:36:10 PM »
on cars i have had in the past the stop start has always been a bit hit and miss ,sometimes it would work other
times not,in my experience you dont put the battery / starter motor under any more use as the systems i've used have a stop/start generator this motor stores energy to restart the engine in effect its like bump starting the car,
as the cylinders have a full charge of fuel & air all thats required is for the engine to turn and this is the job
of the generator as all other systems are at the ready.

Rory

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Re: Start Stop on New Jazz
« Reply #9 on: December 29, 2015, 04:58:00 PM »
Will be good to see if this technology is useful or just pandering to climate change lobbyists by marginally reducing fuel used  but increasing the cost of making cars - or maybe just smoke and mirrors like 'clean diesels a-la mode VW.

It's been "invented" because the emissons/ fuel consumption test cycle has pauses in it - so stopping the engine makes the car's figures better.

Same reason you can't turn it off permanently - the car has to start in the default condition it was tested in.
« Last Edit: December 29, 2015, 05:05:47 PM by Rory »

Rory

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Re: Start Stop on New Jazz
« Reply #10 on: December 29, 2015, 05:04:42 PM »
But if its off for a few seconds
Starting it back up again would use more fuel

No it wouldn't - these days you don't put your foot on the gas and rev the bollocks off the engine to start it.  You just twist the key or press the button and it starts.  No drama.

BMW say it saves fuel is the engine is stopped for 2 seconds.  Figures probably vary for other manufacturers, but that's the scale of it.

Having said that, we have it on our Tiguan and while it works very well (apparently on some cars it's almost random whether the engine stops or not) we always turn it off.

ColinB

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Re: Start Stop on New Jazz
« Reply #11 on: December 30, 2015, 10:23:00 AM »
It's been "invented" because the emissons/ fuel consumption test cycle has pauses in it - so stopping the engine makes the car's figures better.
Not sure that is quite correct. This link ...
http://www.dft.gov.uk/vca/fcb/the-fuel-consumption-testing-scheme.asp
... describes the official testing, and it's clear that the requirement includes periods with the car stopped but the engine still idling, so if some wily engineer decided he would outfox that by stopping the engine then the test wouldn't be compliant. That's completely different to the VW case.

Nor do I buy the "it'll wear the engine out" argument. The powertrain components affected by start-stop have been designed for it, and the technology has been around for long enough for the engineers to have got it right.

I've always thought the stop-start thing has more to do with reducing pollution than improving fuel consumption. Traffic queues tend to create pollution & noise hot-spots so if everyone turned their engines off surely that's a Good Thing for the poor folks who live or work near there ?


culzean

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Re: Start Stop on New Jazz
« Reply #12 on: December 30, 2015, 11:02:23 AM »
Nor do I buy the "it'll wear the engine out" argument. The powertrain components affected by start-stop have been designed for it, and the technology has been around for long enough for the engineers to have got it right.

I've always thought the stop-start thing has more to do with reducing pollution than improving fuel consumption. Traffic queues tend to create pollution & noise hot-spots so if everyone turned their engines off surely that's a Good Thing for the poor folks who live or work near there ?

You are right that stop-start is more about cutting emissions in traffic jams than reducing consumption,  but if you are paying extra for a car fitted with it (and you will be) what benefit can you expect as a 'pay-back' if not a reduction in your fuel bill.

You may say that 'it has been around long enough for engineers to have got it right'  but the diesel engine has been around a lot longer and the truth has only just come out about how things were hidden and we were lied to.

No one really knows about stop-start on engines life in the real world,  most engines without stop-start will be expected cover at least 200K without engine wear problems and this is well documented,  but is enough data available on stop-start at this point as cars that use stop start a lot probably don't do many miles as they will be stuck in urban traffic most of the time, and high mileage cars won't use stop start very much.

My point was that environmentalists jump up and down to get these technologies and don't mind car prices rising because of new technology with limited gains - they probably see it as a big plus if people can't afford a car and have to ride a bicycle.   
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

Rory

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Re: Start Stop on New Jazz
« Reply #13 on: December 30, 2015, 04:57:23 PM »
Not sure that is quite correct. This link ...
http://www.dft.gov.uk/vca/fcb/the-fuel-consumption-testing-scheme.asp
... describes the official testing, and it's clear that the requirement includes periods with the car stopped but the engine still idling, so if some wily engineer decided he would outfox that by stopping the engine then the test wouldn't be compliant.

Stop start definitely is used during the tests.  It's very worthwhile to manufacturers as they live and die by the emissions test results and a larger proprotion of the test is spent stopped than in normal driving.  That stop/start can't by default to off is due to it being used in the tests - same as cars with auto gearboxes defaulting to eco mode where fitted, which many drivers hate.

ColinB

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Re: Start Stop on New Jazz
« Reply #14 on: December 31, 2015, 09:46:54 AM »
Stop start definitely is used during the tests.  ... a larger proprotion of the test is spent stopped than in normal driving.
Guess we're going to have to agree to differ here !
My reading of both the link I posted to the VCA site, and the more detailed description of the ECE-15 test cycle (here: https://en.wikipedia.org/wiki/New_European_Driving_Cycle) is that the engine should remain idling, not be stopped; one of the many criticisms of this testing is that the official cycle is so old (1970) that no-one had thought of stop-start at the time so the test doesn't permit it. Even if it is permitted, the test specifies that the engine is started from cold so the stop-start wouldn't kick in anyway during the short urban test cycle. Happy to be corrected if anyone can provide a reference proving otherwise.

Also, if you add up the numbers in the wiki article you find that a car under test would be stopped for 240 sec during the urban cycle, but moving for 540 sec; the extra-urban cycle adds a further 400 secs moving.

... if you are paying extra for a car fitted with it (and you will be) what benefit can you expect as a 'pay-back' if not a reduction in your fuel bill.

My point was that environmentalists jump up and down to get these technologies and don't mind car prices rising because of new technology with limited gains - they probably see it as a big plus if people can't afford a car and have to ride a bicycle.   
I wouldn't consider myself a rabid environmentalist, but if I can contribute in a small way that's great, and if it costs me slightly more then so be it. After all, I bought a Jazz, didn't I ?

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