Bunch of new fuel saving tech coming

puntmeister · Nov 18, 2014

40X40 said:
You might want to get a mechanic to look at your car. They will likely find a leak somewhere after the MAF.

Bill

I know I need to do a leak test - short of testing, there's no obvious leak.

Still - if there were a leak, why would it only cause a CEL during engine braking? Just seems odd to me, cause that's the one time it really doesn't matter what the airflow is.

Steve Addy · Nov 18, 2014

puntmeister said:
Yeah, there are a host of flaws to the stop/start concept.

Fuel efficiency: not sure about gasoline cars, but, for diesels, idle consumption is very low - about 1/8'th gallon/hour in a BEW. On a commute with a net 10 minutes of idle, stop start results in 1/48'th gallon savings.....and that's assuming no extra fuel is used to generate the electricity to crank start the engine over and over again. I'd have to time it, but I'd guess my daily commute averages no more than 3 minutes of idle time (although it certainly feels much longer...). Some situations would make sense for stop/start - taxis in Manhattan, for example - but on average, I don't think the savings would be significant.

Safety: Situations arise where a rapid start is needed from a stand-still (need to get out of the way of an ambulance, police, drunk-driver, etc). Although I respect the fact that these stop/start vehicles will likely have start profiles much more reliable than today's cars, the issue remains - if an engine isn't already running, there's no guarantee it will start.

Engine wear: My understanding is the bulk of engine friction wear occurs during starting - because the oil is sitting in the pan. Gotta think exponentially increasing the number of stop/starts will reduce engine life.

It just isn't a viable option for diesel, you've pointed out a lot of the justification for why it isn't a good idea.

To further this point, the system may be fully viable when the car is built but how well does it work after years of regular use? What's a tolerable start time at a traffic light for these things? What happens when it takes 5 seconds to get the stupid thing started.

GM had a start / stop truck not all that long ago, it faded into the wilderness pretty quickly, maybe even with that model year. I didn't pay that much attention to it but there's a reason that it disappeared fast, people wouldn't buy it and it risked sending customers to other makes.

A lot of this stuff is idiotically mandated by buffoons who have zero comprehension of how things need to work for regular life. That or their support of such devices / technology comes only after lobbyists fill their coffers.

my .02

[486] · Nov 18, 2014

Steve Addy said:
It just isn't a viable option for diesel, you've pointed out a lot of the justification for why it isn't a good idea.

It very well could, modern electronic diesels start just as well as conventional gasoline engines when warm. With some more attention to the starting maps it could probably even be improved.
Maybe even a well overspecced starter (4kw motor rather than the normal 2), and then to get that initial sensation of movement, get it while the starter drive's still engaged. Your starter motor will move your car around if you defeat the NSS, takes a moment for hydraulic pressure to build up if it is an automatic, though. An accumulator holding a quart of fluid behind a solenoid valve would allow for it to apply clutches before the pump picks up fluid, though.

On the oil pressure issue, have an accumulator on that system as well. Starter engages, solenoid opens the valve, and 20PSI of oil is released into the system under spring pressure. Oil pump catches up half a second later.

Steve Addy · Nov 19, 2014

[486] said:
It very well could, modern electronic diesels start just as well as conventional gasoline engines when warm. With some more attention to the starting maps it could probably even be improved.
Maybe even a well overspecced starter (4kw motor rather than the normal 2), and then to get that initial sensation of movement, get it while the starter drive's still engaged. Your starter motor will move your car around if you defeat the NSS, takes a moment for hydraulic pressure to build up if it is an automatic, though. An accumulator holding a quart of fluid behind a solenoid valve would allow for it to apply clutches before the pump picks up fluid, though.

On the oil pressure issue, have an accumulator on that system as well. Starter engages, solenoid opens the valve, and 20PSI of oil is released into the system under spring pressure. Oil pump catches up half a second later.

Yes, I saw a lady drive her Ford Fiesta (not the new ones) years ago with the starter motor.

Sounds like a lot of added costs to save what?

[486] · Nov 19, 2014

Steve Addy said:
Sounds like a lot of added costs to save what?

Law doesn't say it has to be cheaper, just more MPGs.

Who cares if it needs a new starter every other year. Production and installation of starter motors doesn't have any impact on the environment, that meaningless MPG number sure as hell does.

jhinsc · Nov 19, 2014

puntmeister said:
Coasting to a stop versus engine braking - this has been discussed and analyzed quite a bit.

I used to engine brake a good deal - but kept getting a CEL, related to MAF signal too low, whenever engine braking. I couldn't find anything wrong causing the code, and was so annoyed by it, I stopped engine braking, and reverted to coasting.

In any event - back on point - ultimately, the best mpg will be achieved by coasting to a stop, with no braking of any kind - no brakes, no engine braking, glide to a stop at the exact intended stopping point.

Yes, fuel is consumed while coasting (versus no fuel during engine braking) - but coasting in neutral is ultimately more fuel efficient, as a car will coast farther in neutral than it will in gear, and TDIs use minimal fuel to idle (around .5 liters/hour).

How this works: with the coasting in neutral strategy, you can begin to coast much further from an intended stopping point than you would need if you were to engine brake. ie - with engine braking, full-load driving is necessary for a greater distance. The extra fuel during that needed extra full-load stretch just prior to engine braking is greater than the fuel consumed during the idle/coast.

There are times when engine braking makes sense - like going down a steep hill, or whenever you would need to use your brakes.

This may work in a perfect world, where coasting to a stop in neutral with no brakes is most ideal, however most people don't live there (a perfect world). There is traffic all around us, stop lights, stop signs, turns, traffic congestion, etc. Most people don't have the time to coast to a stop from just rolling momentum in neutral - talk about a long and boring commute! Plus you have people passing you because you're going too slow. So the next best thing in new vehicles is the fuel shutoff while coasting in gear. I use this whenever possible when I anticipate I have to slow down or come to a stop to save on brake use and fuel. However, you defeat this purpose if you shift to neutral because you negate the fuel cut off.

Bunch of new fuel saving tech coming

puntmeister

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Steve Addy

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[486]

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