I'm in a FB discussion where I'm defending auto start / stop systems.
Can our resident automotive systems engineer please TL;DR summarize the data for me showing the break even on reduced emissions versus letting the car idle?
Thanks!
I'm in a FB discussion where I'm defending auto start / stop systems.
Can our resident automotive systems engineer please TL;DR summarize the data for me showing the break even on reduced emissions versus letting the car idle?
Thanks!
Most of the start / stop systems out there only engage with the engine fully warm, so they do not need to add extra fuel to compensate for fuel puddling in cold intake ports (the main reason for emissions spikes on startup). Some even keep track of the next cylinder due to fire and are able to kick the engine over with a spark instead of the starter.
There are a lot of valid reasons to hate start / stop systems. I have some bad memories of an Escape that would lose its air conditioning at Red lights on scorching Georgia summers. But emissions aren't one of the reasons.
I have that system on both of my newer cars, and I don't have the empirical data to compare the cost/benefit/breakeven numbers, but I havea few observations based on my experiences with it....
1st is I can see the benefit to society in general if you consider the positive effects of not having millions of cars idling and spewing emissions into the air.
However, from a car owner point if view, I question the cost benefit of the increased sized battery it takes to be able to make this system work, and the heavier starter, wiring etc. (The battery in my cars is freakin huge!) and the costs to replace those items when they fail.
Sometimes doesn't work the way I would like it to....for example, when in heavy traffic in town with long stops at a light, I can see it. But once in a while I roll up to a stop and it shuts off just as I get an opening in traffic and want to go. It starts immediately as soon as you let off the brake, but what if it doesn't? And what of that extra second it takes to start and engage the gears again.....
Lastly, I found that if I engage "S" mode, it not only provides sharper initial throttle response and moar powah but it also keeps the start/stop from working.......or I can simply push the button on the dash.
So, no sure answers to your initial question, but maybe some other considerations?
Argonne national lab found that start/stop can begin reducing emissions after as little as 10 seconds of stop time:
To keep catalytic converter heat up and avoid discharging the battery too much and killing AC/heat for too long, start/stop systems will only shut the engine down for a maximum of 45-90sec, so the breakeven point is at least 10sec but well under 45sec.
Stats on average fuel consumption and emissions reductions are easy enough to find that I'm guessing that's not part of the question.
Check out the Youtube channel Engineering Explained. There's a video about idling and the amount of fuel consumed showing it more advantageous to shut down after only about 7 seconds if I remember correctly.
I always felt as if the engine was 'forced' into load when restarting via a start stop system. Under a "normal" start the engine has time to build oil pressure before you put it in gear (unless you shove it in and gas it right away) . Even when fully warmed, by the time you reach for your seat belt and shift into gear, the engine (and transmission) have a few seconds to get fluid moving.
How much does a starter cost?
In reply to VolvoHeretic :
Many systems are using spark or the alternator.
One thing that always blows me away is the start/stop doesnt "stop" when I put the engine in neutral or park.
I have to say implementation is key. Our 23 odyssey is a pita and rough and the 25 vw is smoooth coming back on and off.
vwcorvette (Forum Supporter) said:Check out the Youtube channel Engineering Explained. There's a video about idling and the amount of fuel consumed showing it more advantageous to shut down after only about 7 seconds if I remember correctly.
Interestingly, my van display will switch from MPG to GPH when you come to a stop. Its not a big number.
Its not nothing, but I was surprised at how low.
Im curious how much time the average driver spends idling.
In reply to vwcorvette (Forum Supporter) :
The referenced studies don't appear to be based on direct injected engines either... Which should make the break-even time shorter yet on newer cars.
No good answer but I did find on my Buick shifting into low and them manually shifting in to 6th with the button defeats the autostart. It has direct injection and a normal starter, I defeat it to save on starter life. I would be more concerned with timing chain guides wearing from the constant starting. I do shut off my other cars rather than letting them idle when picking up kids etc. It always blows me away to see several cars just idling for 20 minutes or more for heat or AC on a mild day.
MiniDave said:I have that system on both of my newer cars, and I don't have the empirical data to compare the cost/benefit/breakeven numbers, but I havea few observations based on my experiences with it....
1st is I can see the benefit to society in general if you consider the positive effects of not having millions of cars idling and spewing emissions into the air.
However, from a car owner point if view, I question the cost benefit of the increased sized battery...
Your point about taking a societal/system level view is how I like to think about it. I don't know the numbers (or honestly even the units), but surely if every car on the road is stopped idling, even for a bit, at every stop...that has to add up to something meaningful, right?
And I can't say as the battery on either of my trucks that have had it were any larger than I'd have expected to see. Must vary by car. I do wish the input to restart was standardized. My F-150 was either turn the steering wheel, or tap the gas. My Silverado that replaced the F-150 is when you come off the brake.
MadScientistMatt said:Most of the start / stop systems out there only engage with the engine fully warm, so they do not need to add extra fuel to compensate for fuel puddling in cold intake ports (the main reason for emissions spikes on startup). Some even keep track of the next cylinder due to fire and are able to kick the engine over with a spark instead of the starter.
I had no idea this was the case. It may explain why our 2022 Subaru Outback sometimes sounds different when it restarts. It sounds like a weakening battery - but if it's merely being sparked back to life then it actually sounds "just right"!
Gonna have to google this one to see if my car is restarting via spark.
The favorite feature of my fleet Equinox is the button that allows me to turn that annoying technical marvel off.
I was reading that somebody's system(toyota?) counts how many times the starter has been engaged and will trigger a no start when it hits a certain number. Not sure how true that is, but I would wonder.
I have start/stop in my Jeep which was wild to me. It's the only manual I've ever seen with start/stop. I don't drive in stop-n-go traffic enough for it to really be noticeable for fuel economy but I'm all for the emissions savings.
In reply to ddavidv :
I can't speak to an Equinox but on both of our Volvos it is 100% unobtrusive.
After about 4 days with the first car I barely even noticed it in operation. In fact I notice more if it decides to stay running.
Thanks for the discussion but I was hoping for engineering data. Guess I'll have to dig.
Start/stop is right up there with eliminating spare tires. Creative CAFE accounting that has very little real world benefit with lots of downsides.
Some vehicles like my Ridgeline, have a button to shut that feature off.
The Toyota system works great in my new-to-me '17 Highlander. If you hold the gas pedal lightly the engine stays on, while a firmer press shuts it off. It's hard to accidentally trigger it. If you anticipate needing to go again you just subtly adjust pressure on the pedal and the engine springs back to life. It even has a little timer so when you're like "this light is taking forever!" you can look down and be gently reminded that only 46 seconds have passed.
It doesn't bother me. I let it do it's thing, if it saves a little fuel, bonus.
On idling fuel usage - my VW (EA888) seems to idle with remarkable efficiency. There's almost no point starting it up in the cold to 'warm up' (just so I don't have to get in a cold car - I know it's not helping anything) because it takes forever if not under load. It also has the least engine braking of anything I've ever driven. I assume there is very little parasitic drag.
On topic: my wife's MINI has a switch, which I turned off on day 1. My concern was that she makes a lot of short trips. Her office is 1.5 miles away. I want the car running as much as possible to (hopefully) fully warm up and keep the battery at a high state of charge.
Just yesterday, I installed an "auto start/stop eliminator" in the dash, behind the button of my 2024 F150. Worth every bit of the $30 and 15 minute install.
Speaking with a traffic engineer years ago, emissions were highest at idle and deceleration, so the idea was to keep cars moving. That requires either synchronization of traffic lights or more roads/lanes.
I remember being frustrated at the morons who thought it was bad to have more roads/lanes because there'd be more "traffic".
I wonder that's the benefit is not so much the individual car, but in aggregate.
That said, I more often than not shut off the car when waiting in drive throughs or similar situations.
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