oh, also, the quick acceleration sucks. I tried that crap out. You have to learn what's best on your own and look at the distance you have your mpg at a given amount and adjust accordingly. No magic formula. Different techniques for different situations you may encounter. I tried the quicker acceleration this morning and found that it killed my mpg while I was doing that by about 25 percent from what I normally can get.

 

UTAlumnus — If you accelerate starting from rest, the instantaneous-FE reading does not stay constant, but rather will start at 0 mpg, and steadily rise as the car's speed increases. It's not possible to start from rest and not have this happen. The instantaneous-FE reading does not reflect your acceleration in any simple way, and in any event, your acceleration does not itself appear in the trip-FE calculation. There's no simple, useful relationship between the constantly-varying instantaneous-FE while you drive, and the overall FE of your complete "trip" — in this regard, the word "trip" should be interpreted to mean the process of accelerating from rest until you reach cruising speed, if that's what you have in mind. I have been attempting to clarify this issue to the best of my ability, but apparently with only limited success. I cannot force you to accept that what I say is true. All I can point out is that the mathematical logic tells us that this must be the case. You are free to disbelieve it if you so wish.

In your post #48 you talk about comparing two different accelerations from rest to the same final speed 'v.' If the acceleration 'a' is constant during each acceleration, then the distance 'x' travelled to reach speed 'v' is given by
x = (v^2)/(2a)
So, if 'a1' and 'a2' are the two accelerations you're comparing, and 'x1' and 'x2' the corresponding distances travelled, we have
x1/x2 = a2/a1
That is, the distances travelled are inversely related to the accelerations. But, the instantaneous-FE varies all over the show during the accelerations; and in any event, the trip-FE is related to the instantaneous-FE by an integral with respect to volume (and not distance — distance is for trip-FC in L/100 km), and so you can't draw any direct conclusion regarding how the two trip-FEs might compare anyhow.

Regarding your post #49, the engine's fuel efficiency (ICE's mechanical energy out vs fuel's chemical energy in) is not affected by tire rolling resistance or air resistance, but these variables do, of course, affect the car's fuel efficiency.

freefiber — I agree with many of your statements. The ECUs have been programmed to always try to operate the ICE near its most efficient operating point for the total amount of power currently required. In any event, there's very little the driver can do to alter this. Without sophisticated instrumentation there's no easy way to monitor ICE efficiency.

mlarma — You say that "quicker acceleration ... killed my mpg." Yes, it may have killed your instantaneous-mpg, but did it kill your trip-mpg? Did you mean the former or the latter? The latter might actually have been improved!

Stan

 

Yes, it killed my avg mpg. If I start REALLY slowly, I can get it to stay in all electric mode for quite a while. I try not to **** those off behind me, so this technique is less annoying at 11PM than it is at 5PM :-) Seriously, though, I know that if I get the electric to get me up to say 20-30, that helps a ton. Then I can accelerate with the mpg going between 15 and 35 before dropping the needle further so that it looks like 60mpg on the gauge (or goes into electric mode).

Mark

 

That's not necessarily true. If you can pop up to 35 or 40 in a couple of seconds then lighten up on the accelerator for a second or two you can then get into E_mode. You'll be spending more time in E-Mode then and thus getting greater MPG longer.

 

I agree but it's the only measure we've got w/o adding instrumentation to the vehicle. The only time there would be a correlation would be under controlled conditions (i.e. closed track w/ consistent starting points. Anywhere else there will be other variables such as grade & wind speed effecting the power required.

Doubling the acceleration will reduce by half the distance traveled to reach a speed.

constant Accel.=feet per second per second or meters per second per second.
Velocity is the first integral of acceleration w/respect to time = feet per second.
Distance is the second integral of acceleration w/ respect to time.

X=(A*t*t)/2

for 40 miles per hour = 58.67 ft/s

accelerating @ 15 ft/s/s
=> t=3.91s => x=114.7'

accelerating @ 6ft/s/s
=> t=9.78s => x=286.82'

X1/X2 = A1/A2

I agree if you limit the model to only looking at forces internal to the ICE. Once you include the rest of the drive train you include the rolling resistance and air resistance.

 

mlarma and coolshock1 — Don't be misled into believing that, just because you are in EV mode, you're necessarily saving gas overall. The electrical energy you're using from the NiMH battery depletes its charge, and it needs to be recharged back to its original state of charge before you can draw any legitimate conclusions about any overall FE benefits. Don't forget that all the electrical energy stored in the battery, including all the regenerated braking energy, ultimately came from the gasoline, and so can't be regained any more efficiently than what's possible at the ICE's best efficiency. Unless you can ensure that you recharge the battery when the ICE is operating at a higher efficiency than when Toyota's ECU tries to recharge the battery, you actually lose overall. Any meaningful measurement must be made on a round trip back to the starting point, and have the NiMH battery at the same charge level at the end as at the beginning. See the thread "An Unpalatable Fact (with apologies to Al Gore!)" for much more discussion on this topic.

Stan

 

UTAlumnus — In your post #55 you say: "X1/X2 = A1/A2." Actually, as I showed in my post #52: "x1/x2 = a2/a1."

Stan

 

What about the regeneration from breaking? On my normal routes I know the areas that I can break for a fair amount of distance to regain some of the lost energy.

Which method of regeneration yields the greatest amount of energy if you don't mind me asking?

 

SPL - I disagree somewhat as it isn't just energy being generated from gasoline, but we're looking at the efficiency in applying that energy, recapturing it, etc. Where the gas engine is efficient at x speed, running off of electricity as much as possible at lower speeds WILL save you gas. Regen is very inefficient I've noticed, but when it is able to charge the battery when the ICE is running, it is quite efficient. I'd love to see the math behind it as to when one is better than the other. Some of these things to gain mpg border on an art. It's tough to get it just right to get the biggest bang/buck. Also, if hybrids were just a less efficient car than one with just an ICE, why would they have them? SPL, in all due respect, there's more to the story of the energy generation, capture, storage and creation of motion from it....

I personally have not seen much gain from regen. Slowing to a stop is the better option. The ICE will run and charge the NiMH batteries when needed and if you are already using the ICE to move the car, a little of that kinetic power turning the generator and charging the batteries isn't too bad at all. The computer manages what part does what when so it just kinda all works together (mostly).

Thanks,

Mark

 

You're right. I reversed the numbers while typing it. Trying to type & answer questions on another topic don't work too well done at the same time.