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In my welcome post I have a few things I either don't understand or don't agree with. http://www.cleanmpg.com/forums/showp...7&postcount=15 I was going to add the text later , but will seperate them here for more input. Thanks in advance.
I won't talk about the parts I agree with , only the parts I don't.

Driving with load: If I understand this concept correctly I'm going to submit that it I can do the opposite and get better fe. Maybe not. For simplicity lets stay in the same high gear at all times.

Let's both start out with same identical vehicles and maintain the exact same average speed. DWL describes having a locked pedal (or close to it) where the car goes faster downhill ans slower uphill. OR the throttle is lessened as the load is increased to maintain a light load at all times. Hope I got that right.

I'm going to drive like this: (exaggerated for affect) I'm going to floor it up hill and almost let off going down hill , yet keep a forward torque on my driveline while keeping the exact same average speed as the other guy. I'm going to beat you uphill , but your going to pass me back going down hills.

Pick it apart please. Thanks for reading and dialog.

It really depends on your car, the hills, and the conditions. DWL is just one of many techniques that might make the most sense to minimize waste.

Odds are the Blazer and the Venture in your profile are automatic cars. Those are likely to be most efficient in their top gear, so one good use for DWL is to keep a vehicle from kicking down on the way up a hill. "Flooring it" pretty much guarantees that you will be accelerating in a lower gear and you will never make up for it! Not only are the high revs inefficient, but WOT acceleration dumps even more fuel than needed into the cylinder to keep pinging at bay.

A lot of the time I will use P&G instead of DWL. On gentle hills I can accelerate up them at an efficient RPM and then let the engine shut down for my glide down the back side. On the other hand I might use DWL on a steeper hill because I know if my engine RPMs get above a certain level the valves change profile and I lose efficiency.

Let's stick with a manual trans and For simplicity lets stay in the same high gear at all times.

Actually. if you do this right you are implementing a form of pulse and glide keeping your engine operating in high efficiency territory under "acceleration" while reducing cumulative drag by decreasing speed variance. Just don't floor it all the way and do some engine off coasting downhill and you should beat DWL. Leaving the engine on will likely give mixed results depending in no small part on how well/whether your vehicle does deceleration fuel cutoff. If you have to brake at the bottom of the hill as well as keep up with traffic at the top, it isn't a bad strategy to coast downhill--just try not to crest the hill too fast in any case.

I'm confused about why you want the manual transmissions to stay locked in high gear.

If you floor it going uphill, you're going to murder your gas mileage. If I understand it correctly, DWL uses a minimum amount of fuel going uphill, and uses gravity to get you downhill.

Lets exaggerate this to make it a lot more interesting and fun. Much longer and steeper hills. For comparisons sake I will still want to WOT in high gear going up the hills , yet keep a slight positive twist on the driveline going down.

Actually. if you do this right you are implementing a form of pulse and glide keeping your engine operating in high efficiency territory under "acceleration" while reducing cumulative drag by decreasing speed variance. Just don't floor it all the way and do some engine off coasting downhill and you should beat DWL. Leaving the engine on will likely give mixed results depending in no small part on how well/whether your vehicle does deceleration fuel cutoff. If you have to brake at the bottom of the hill as well as keep up with traffic at the top, it isn't a bad strategy to coast downhill--just try not to crest the hill too fast in any case.

I'm confused about why you want the manual transmissions to stay locked in high gear.

I'd like to compare high gear only because it is the best gear to use for fe and is a fair comparison for both cars to use same gear. It is also why I am not trying to talk about p&g and alos want to use the same average speed. My goal is to eliminate all the other variables and talk about ONLY dwl and then talk about why it works if it works.

DWL beats steady speed.
P&G beats DWL.

DWL is a technique that lets you blend with traffic better than P&G.

I don't think anyone claims DWL will beat P&G, in general. (There are cars than don't respond well to P&G, but DWL like champs.)

Your strategy sounds like P&G with some waste thrown in by keeping light torque on the drive train during the glides.

DWL beats steady speed.
P&G beats DWL.

DWL is a technique that lets you blend with traffic better than P&G.

I don't think anyone claims DWL will beat P&G, in general. (There are cars than don't respond well to P&G, but DWL like champs.)

Your strategy sounds like P&G with some waste thrown in by keeping light torque on the drive train during the glides.

That actually sounds quite accurate , P&G with some waste thrown in. I'm not getting any fuel cut , but I'm also not getting any engine breaking either. But I'm also not slowing down nearly as much either.

Hi Nidly:

___You can compare anything you want but DWL saves a ton of fuel vs. CC or racing up the hill and running fuel cut down. It works for MT, AT's and the eCVT's of a full hybrid.

___Good Luck

___Wayne

Does dwl save fuel when the average speeds are the same as well? I am not surprised that dwl will out do CC , but am very surprised it will out do racing up hill (in high gear) and a FC down the hill. If so, why is that?

Hi Nidly:

___Your average speed over 5-miles with one DWL solution is insignificant as your droop may only be 2 to 5 mph by the time you crest and back to the same speed when you reach the other side. When you are driving a in a very fuel efficient area that your vehicle was designed around, DWL will maintain it up with little to no fuel consumed on the back side during your acceleration back to target.

___FC going down converts your KE into heat with the engine acting as a compressor. That energy loss has to be made up by more fuel being consumed to bring your total KE back up to what it was by DWL.

___Equip your vehicles and you'll see it as plain as day.

___Good Luck

___Wayne

I think I'm starting to get the pic. Please allow me to re-phrase if I may (sorry it's a touch of asperger syndrome)

Are you saying that we are using very close to the same amount of fuel on the downhills (with me using slight less fuel since I am going faster and using less tps ) Yet you are completey blowing me away on the uphills since I am using far higher tps and fuel and you are continuing to use light throttle?

Both average speeds are the same, same gear, only difference is you may use a locked (or close to it) pedal and I am using a lot of throttle going up and very little throttle going down. Your speed is varying far more than mine, in fact I may go up the hill faster than I go down, but our average must stay the same.

Hi Nidly:

___One way for a non iFCD equipped driver to simulate DWL is to lock his accelerator pedal during the climb and fall. I wrote it up that way as well. With an SG-II, you will see the overall difference and the real time difference of climbing at or above EPA and the descent at far above EPA vs. half or less of the EPA while climbing on CC and fuel cut, injector startup and push through some very inefficient regions while the Torque Converter unlocks/locks on the back side.

___Good Luck

___Wayne

What about if you accelerate before you get onto a hill? So speed is higher (depending on the hill's steepness) when you start going up. Would that be worse than speeding ON the hill/as good as DWL?

Actually, a "running start" combined with DWL is an excellent technique which will improve your mileage substantially. Gain momentum while you can do it without fighting gravity too much. In some cases that can actually improve mileage over just DWL at a lower speed.

A running start is especially useful with an automatic transmission. You can get caught in a corner where adding any throttle will make it downshift, but losing any more speed will also make it downshift. Starting the hill 5mph faster can make all the difference in a case like this.

My version of DWL, with the gentle hills here, was to maintain steady throttle pressure (in my SVT Focus, a TPS reading of 33), accelerating down hills and slowly scrubbing that speed going back up them. Netted me 2mpg from my city to Texarkana, about a 130 mile drive one way, from 33mpg to 35. Hardly scientific, but then again I don't get much open road time :)

The other aspect of DWL is keeping the throttle "reasonably"
open and RPM down. Both throttle-plate pumping losses and the
number of times the pistons scrape up and down over any given
distance are major sources of loss in an engine, so the more you
can minimize those the better. You also have more heat loss if
you're firing more times per a given distance by letting RPM
creep up -- remember, two thirds of the energy you're sucking
out of the tank is going away as unrecoverable heat, so the less
heat one produces to get over the hill the better.
.
It sounds like twisted physics, but that's how it works out for
internal-combustion engines. Note carefully that I have not
included *time* as a factor, such as RPM and ignitions per second
and all that -- when one is talking about MILES per GALLON, the
time factor has dropped out of the equations somewhere in the
process. It's sort of deceiving because many people think "well,
if I push up the hill hard I'm getting less FE but for a shorter
time, right?" ... but at that point you've had that interval
of less FE over the same distance, even if the velocity coming
out of it is a little more -- that doesn't seem to compensate.
.
_H*

Hi Nidly:

___You can compare anything you want but DWL saves a ton of fuel vs. CC or racing up the hill and running fuel cut down. It works for MT, AT's and the eCVT's of a full hybrid.

___Good Luck

___Wayne


Wayne, you have to agree, there must be a sweet spot on the speed profile over a hill. Say you DWL up the hill and go over the crest with a small enough speed, the idle consumption will hit you quite hard before the car picks up speed again. (In a prius, or with FAS, however it's another story)

I always end up in a compromise, trying to have enough speed over the top to enter DFCO in top gear and still pick up speed, and when the speed has picked up I go nice-on so as to achieve terminal velocity before the bottom (limited to 55-60 mph which is slightly above the most usual speed limit in my region)

I have to say, the DFCO can be very easy to maintain in some rpm ranges due to the efficiency of my engine.

Hi Nidly:


___FC going down converts your KE into heat with the engine acting as a compressor. That energy loss has to be made up by more fuel being consumed to bring your total KE back up to what it was by DWL.

___Wayne


Wayne, I have to arrest you on that!

Fuel cut can be very efficient, as long as your engine has EGR, either via an EGR valve or thru variable valves (VVT). Basically when you DFCO, the engine's pistons see vacuum on one side and atmosphere (thru the exhaust pipe) on the other side and this causes a loss.

For DFCO to be efficient you want the pistons to see the same pressure on both sides, and that is indeed done by allowing the exhaust gas to flow thru and back into the intake manifold. You equalize the pressure and the pumping loss is reduced dramatically.

I can certainly feel the effect of this on my car, because some times the VVT will suddenly close the valve overlap and the brake effect will increase significantly.

Are you saying that we are using very close to the same amount of fuel on the downhills (with me using slight less fuel since I am going faster and using less tps ) Yet you are completey blowing me away on the uphills since I am using far higher tps and fuel and you are continuing to use light throttle?

.

I think it is very important to separate manual vs automatic here. I can not see why DWL vs WOT will have much difference on the uphill, if you are in top gear with a manual tranny, and while doing this (you are far enough down the rpm range) you do not accelerate uphill (which is not likely in my country, at least where everything above 1.8 litres displacement is taxed to death). If the speed is too large you can nice-on before the crest and still go over the top with low speed.

For an automatic you want to keep your transmission clueless about the hill, so that it stays in lockup. Then I see a big benefit of DWL.

Hi Shrek:

___Engine braking is engine braking and I can only speak from my experiences in EVERY vehicle I have ever driven. DWL and NICE-On (if you are not in a FAS) is far better than the transfer from on the engine to FC and back to on again unless coming to a stop or you will exceed a legal terminal. Beyond the scope but their are periods when brakes are better to use than to reengage in some hybrids as well. Anytime that engine is spinning without fuel, your total sytem energy is reduced at a faster rate than a NICE-On consumes fuel at idle from slower speeds all the way up.

___And never use WOT vs any other technique. Your FE will be shot. There are many here with mountiain, foothills and small hill climbing experience to say otherwise.

___Good Luck

___Wayne