Modern car engine stop/start systems

[Halcyon]

I'm not a car expert but this bloke answered a lot of questions I had. Very well presented.

[sokoloff]

The guy argues that starting the engine takes the same fuel as 10 minutes of idling and then a few minutes later says that manufacturers are gaming the urban drive cycle by taking advantage of shutting down the engine. It doesn't seem like both statements could be true. If they're "gaming" the urban drive cycle, they're doing it to save fuel. If it saves fuel on that cycle (which doesn't have any particularly long stopped periods), then it seems likely to save fuel on the typical urban use pattern.

[CJay]

Starting an engine from cold then getting the engine and  CAT/DPF up to temperature takes some significant percentage more fuel than a hot start, I do not know how much more but it seems intuitively possible that the stop/start eco systems could well save fuel if the CAT/DPF doesn't cool below operating temperature, if cooled too much then there could well also be a spike in emissions which could be the reason all the new VW group cars I've driven recently (and I assume others) will automatically restart the engine after some short period of time after an 'ECO' stop.

[bob225]

Many stop start systems are flawed, imho it causes excessive wear and tear including the rather expensive AGM or EFB batteries and custom charging systems its fine on new cars but on the used car they can be very hit and miss, batteries are 4 times the cost, starters and alternators a 2 times as expensive and not many places keep them in stock

If you have a electronics issue its usually only the Main dealer that can diagnose the issues, the cost could write off a 7-8 year old car, A lot of Nissan owners disable the system by disconnecting the bonnet switch what inhibits the stop/start

Some of these system have such a high threshold I'm surprised they even work, eg. 97% battery level, AC/climate turned off as well as the rear/front defroster being off



 

[jmelson]

The Honda Civic hybrid and the Toyota Prius use these systems with the high voltage hybrid battery.  The engine is started via the traction motor on both of these.  I love it!  Now, some of the semi-hybrid US-brand cars use a giant belt-driven alternator to accomplish this, and that seems like a pretty crazy system. 

I've been driving a Honda Civic hybrid for almost 10 years now, and it has been a great car.  The only thing wrong with it is the horrible hybrid battery.  120 Ni-Mh D-cells in series, no balancing system, 100 A charge and discharge currents on what are essentially flashlight D-cells!  Who would have ever thought there could be a problem with that?

Jon

[james_s]

The start-stop systems in non-hybrid cars are stupid and annoying. I worked with a guy who had one and he was going through batteries once a year. It produced a noticeable lurch each time the engine would start too, it's not like a hybrid where the electric motor can get the car moving before the ICE catches.

It's just a gimmick to game the emissions ratings. I've seen a number of tests where it was found the actual fuel saved was something like a couple of gallons per tens of thousands of miles driven.

[hans]

I've had such a system in my learner car. It's only purpose was on my driving exam to show that I care about driving. It's one of those bonus points that can offset a sloppy maneuver somewhere.

Other than that I doubt they will be saving tons of fuel. I'm not sure about exact L/hr ratings for small petrol/diesel engines, but I cannot imagine it to be much more than 1-2L/hr in idle & warmed up. If you can use start/stop for 10 minutes in 1 trip, you have saved 0.1-0.3L of fuel. That would be a lot of trips before it pays off.. (I don't think I've ever used start/stop >3 minutes in my 2 hr city driving lessons).

I think the engine automatically restarting could also because a modern car may have climate control and exterior lights set on. I'm unsure if airconditioner compressors (or heater for that matter..) stay on when "stopped", nonetheless draining a few hunderd (lights) to kWs out of a regular battery won't last for long.

I doubt that all the oil, water and metal in a typical engine cool down that much (i.e. it's so cold that it reengages the "choke valve" again) in 5-10 minutes.

[jmelson]

I think the engine automatically restarting could also because a modern car may have climate control and exterior lights set on. I'm unsure if airconditioner compressors (or heater for that matter..) stay on when "stopped", nonetheless draining a few hunderd (lights) to kWs out of a regular battery won't last for long.

I doubt that all the oil, water and metal in a typical engine cool down that much (i.e. it's so cold that it reengages the "choke valve" again) in 5-10 minutes.

The Honda Civic hybrid has a dual scroll compressor attached to the engine.  One half is the classic auto air conditioning system, the other half is electrically powered from the hybrid battery.  At mid speeds, it runs the A/C off the mechanically-driven compressor.  At highway speeds, that would be too fast, and I think it runs off the electrical compressor.  And, when you stop at a light, the engine is shut down, and it turns on the electrically-driven compressor.  (It makes a faint "growl" noise when this is running, so I can tell what it is doing.)


CHOKE valve??  Cars have not had chokes since the 1980's.  The Honda Civic hybrid doesn't even have a throttle plate!  It cuts off a varying number of cylinders by switching the cam followers off of the valves, and then adjusts intake cam timing to reduce the effective displacement of the engine.  They only use this technology on the hybrid, as the hydraulic timing adjuster takes time to change power output, so the hybrid system makes this appear seamless (by adding or extracting power as the engine adjusts to the demand).

Jon

[BrianHG]

Actual test done:

It's not what you expect...

[james_s]

The Honda Civic hybrid has a dual scroll compressor attached to the engine.  One half is the classic auto air conditioning system, the other half is electrically powered from the hybrid battery.  At mid speeds, it runs the A/C off the mechanically-driven compressor.  At highway speeds, that would be too fast, and I think it runs off the electrical compressor.  And, when you stop at a light, the engine is shut down, and it turns on the electrically-driven compressor.  (It makes a faint "growl" noise when this is running, so I can tell what it is doing.)

I would have thought using a purely electrical compressor would make more sense from a simplicity standpoint. When you figure that modern brushless motors can be very compact and efficient, is there really enough gain in being able to directly drive the compressor from the engine to be worth it?

[hans]

CHOKE valve??  Cars have not had chokes since the 1980's.  The Honda Civic hybrid doesn't even have a throttle plate!  It cuts off a varying number of cylinders by switching the cam followers off of the valves, and then adjusts intake cam timing to reduce the effective displacement of the engine.  They only use this technology on the hybrid, as the hydraulic timing adjuster takes time to change power output, so the hybrid system makes this appear seamless (by adding or extracting power as the engine adjusts to the demand).

Jon

Ha yes sorry for my nostalgic influences. Only since 3 years I've been driving a car that's not mostly mechanical. The '98 1.2L Opel/Vauxhall Corsa  still had a choke valve, I think.

Sounds like a clever idea. Many engines also shut down cilinders when possible, even in a 4-cyl petrol VW engine (not sure which type). For example, the power demand to hold 80 or 100km/h is so low, the engine can do by shutting down 2 cylinders, and the other 2 work at double power (for those cylinders, e.g. from 1/3 throttle to 2/3)

Formula 1 engines also are doing this for years, especially during idle. I don't think so much because of fuel saving, but also the heat output is reduced while idling, and these cars have no radiator fans.
For those interested; here some very peculiar differences in idling tones of a F1 2018 Honda vs Mercedes 1.6L power trains:
https://www.reddit.com/r/formula1/comments/81ckch/amazing_2018_honda_idle_sound/

[schmitt trigger]

I've been driving a Honda Civic hybrid for almost 10 years now, and it has been a great car.  The only thing wrong with it is the horrible hybrid battery.  120 Ni-Mh D-cells in series, no balancing system, 100 A charge and discharge currents on what are essentially flashlight D-cells!  Who would have ever thought there could be a problem with that?

I also drove a HCH for 8 years. Loved the little car and would have driven it longer, but I live in south Texas where the high ambient heat caused the battery pack to fail, with fewer than 1,000 miles before the warranty would have expired. Lucky me! But Honda did not want to provide any sort of warranty on the replacement pack, so I traded the car a few months later.

Speaking of auto start/stop: At least where I live, when arriving at a red-light intersection with heavy traffic (which in theory is a situation where one would get the most benefit from such a system), the long line of vehicles would slowly inch forward to remove the slack in the vehicle queue. Therefore, less than half a minute after I had arrived at the queue, I would have truck-length gap between me and the front vehicle. The vehicles behind would honk hysterically or some would overtake me. So I had to restart the engine.

Same scenario on the freeway, with rush hour stop-and-go traffic.

So, at least for me, this feature was pretty useless and consider it only a gimmick. The fuel savings were negligible.

[jmelson]

I would have thought using a purely electrical compressor would make more sense from a simplicity standpoint. When you figure that modern brushless motors can be very compact and efficient, is there really enough gain in being able to directly drive the compressor from the engine to be worth it?

Well, you'd have to ask the Honda engineers, of course.  Yes, it is MORE complicated, involves a shaft seal, clutch and belts, and adds weight.  So, they must have had a pretty strong reason to go that way instead of electric-only.

I haven't run the calculations, I just DRIVE the thing, but am interested enough to find out how a lot of the systems work.

Jon

[IanMacdonald]

Same here, most heavy traffic situations involve creeping forward so it would either have to be disabled or would impose heavy wear on the starter.

A local bus company bought some hybrid buses for a trial, and without exception the drivers turn the auto engine shutdown off, saying it is just a PITA and saves nothing. I don't know if they return a better fuel economy than a straight diesel, but they end up being basically a diesel with an electric transmission.  One advantage they do have is much smoother pulling away, none of the sickening gearchange lurch the mechanical auto transmission buses can give.

[CJay]

Weirdly my bus is often a hybrid (Stagecoach) but they definitely don't turn off the stop/start, it's rather unnerving when they move off and there's no engine rumble.

[G7PSK]

Actual test done:

It's not what you expect...

Save a hundred pounds a year on fuel, but how long will the battery last let alone the starter motor, it could cost you the hundred pounds a year plus.

[Bill158]

I have "ECO" on my latest car and I HATE it with a PASSION only reserved for a star going super-nova.  So every time I start the car I have trained myself to turnoff the "ECO".  I had one passenger who said "What is the matter with this car?  Every time you start out from a stop sign or traffic light this super expensive car "shudders"".  I said it is just the "ECO" which is supposed to save gas (petrol for you AU and BRIT types).  There is no permanent way to program it to stay off the way I would like it done.  I am sure that if I had the manufacturer supplied computer that hooks up through the underdash onboard computer access " OBD II " connector it could be done easily.  I see that there are several "adapters" on the market to make this "ECO" stay off but that would involved modifying the car and might void parts of the warranty?  I am not sure.  One involves hooking a module to the car's internal communication buss system.  I agree with the wear and tear on the starter.  The battery isn't a concern.
I do notice that the "ECO" won't engage if the car is cold and it waits until the car reaches some operating temperature to avoid the mechanical wear and tear.  Also the power steering is electric so I can turn the steering while the engine is in "ECO" off.  Also if the interior needs Air Conditioning and the AC compressor needs to keep turning to keep cold air coming in from the vents while cooling the car interior on a very hot day after sitting in the sun for hours!  It also restarts if I have been sitting in traffic too long and the interior is getting hot.  But the ON/OFF cycling when you are "inching" through a traffic jam is just completely unnerving to me.  I can't quite tell when I might suddenly go forward without warning.  All in all it is a stupid way to save fuel.  If you are an "ECO FREAK" and want to save the planet then you should have the option to have it ON all the time.  But I should have the same option to turn it OFF permanently!
IMHO
Bill

[Monkeh]

I can't quite tell when I might suddenly go forward without warning.

If that is occuring from a standstill you are not maintaining control of the car. And it's not the fault of the car.

[BrianHG]

Actual test done:

It's not what you expect...

Save a hundred pounds a year on fuel, but how long will the battery last let alone the starter motor, it could cost you the hundred pounds a year plus.

The Starter & alternator on these cars supposed to be a set of magnets & coils and electronic switched 3 phase control around the shaft of the motor at the transmission.  There is supposed to be 0 wear, no gears, no brushes, or cheap diodes.  Anyways, does it really matter?

[james_s]

The starter is a brushless unit essentially identical to that used in hybrid cars so wear on the starter is not an issue, but wear on the battery most certainly is. The biggest issue is it's just irritating for negligible savings, and I absolutely loathe systems that try to be smarter than me and won't let me set something a certain way and keep it that way. Anyone who has driven one of these start-stop systems in heavy traffic will immediately see how annoying it is. Lurch lurch lurch lurch, it feels like the car is broken.

[Monkeh]

The starter is a brushless unit essentially identical to that used in hybrid cars so wear on the starter is not an issue, but wear on the battery most certainly is. The biggest issue is it's just irritating for negligible savings, and I absolutely loathe systems that try to be smarter than me and won't let me set something a certain way and keep it that way. Anyone who has driven one of these start-stop systems in heavy traffic will immediately see how annoying it is. Lurch lurch lurch lurch, it feels like the car is broken.

Can't say I ever had that problem.

Now, the stupid thing not actually restarting the engine, that happened.

[bob225]

Some of the early system that are 10+ years old now used standard starters - The wear points are on the solenoid, Pinion gear and flywheel - with most eco cars using DMF (dual mass flywheel) your looking up to £1000 ($1400 usd) to replace it let alone the internal wear from restarting a engine with very little oil pressure to lubricate a already hot metal surfaces


Welcome to the world of 5-7 year throw away car

[Jeroen3]

...
The Honda Civic hybrid has a dual scroll compressor attached to the engine.  One half is the classic auto air conditioning system, the other half is electrically powered from the hybrid battery.

I drive an Civic Hybrid, and I did not know this. Had to check the workshop manual to see there is indeed an "A/C Compressor Driver".

It cuts off a varying number of cylinders by switching the cam followers off of the valves, and then adjusts intake cam timing to reduce the effective displacement of the engine.  They only use this technology on the hybrid, as the hydraulic timing adjuster takes time to change power output, so the hybrid system makes this appear seamless (by adding or extracting power as the engine adjusts to the demand).

Yeah, not very seamless in the 2009. But it can drive electric below 48kmh... if you do not move the pedal at all. It also turns off the engine if you brake and go below 11 kmh. Which was strange at first.

However, improvements have been made. You won't even notice the Start/Stop on my dads Mercedes GLE 2017 Diesel. But the previous 2010 E-station did fail both batteries. Yes, two batteries. One for cranking and one to prevent all the electronics and radio from glitching.

[schmitt trigger]

I absolutely loathe systems that try to be smarter than me and won't let me set something a certain way and keep it that way.

Wise and true words, indeed.

The problem with many smart automobiles, appliances and many more "smart "things is that they assume the lowest IQ common denominator.
I guess that MOST people don't like to go thru a bunch of menus and submenus to access a particular feature, but still should be available on some sort of advanced menu.

Perhaps the dealer may disable it properly and without messing the warranty. Have you asked?

[AndyC_772]

The NEDC test cycle includes a disproportionate amount of sitting at idle. Since this cycle was (until Sept 2017) the standard used for cars sold in Europe, switching the engine off while idling has a similarly disproportionate effect on the official carbon dioxide and other emissions figures for the car.

New cars are tested using the WLTP test process, which is much more up-to-date (though not universally agreed to be representative of real world driving in all countries). It doesn't include as much time at idle, so the benefit of start-stop on a vehicle's rated emissions and tax class should be much less.

https://www.lowcvp.org.uk/initiatives/fuel-economy/wltp.htm