My random thoughts after 1 week of ownership

<div class='quotetop'>QUOTE(Wiyosaya @ Jul 27 2007, 01:18 PM) [snapback]486231[/snapback]</div>

Sure they do.

He's comparing normal driving to EV driving, and you are comparing normal driving to driving with significant amounts of gliding.

EV uses more fuel in the long run than "just driving it", and that uses more fuel than extensive use of gliding.

Of course I'm assuming that when using the term gliding you mean coasting without use of ICE or MGs for propulsion or regen.

<div class='quotetop'>QUOTE(Wiyosaya @ Jul 27 2007, 12:58 PM) [snapback]486212[/snapback]</div>

Keep in mind that there are means of driving any car that are more efficient than others, and that many of the techniques that are used by Prius hypermilers to get great MPG numbers would also generate great MPG numbers in non-hybrid cars (not as great as in a hybrid, but I wouldn't be surprised by double the EPA numbers).

 

<div class='quotetop'>QUOTE(chogan @ Jul 27 2007, 09:31 AM) [snapback]486086[/snapback]</div>

OK, after reading this post I think *I* need a PhD for all this. Maybe not a PhD, but OCD?? ;-) I do just fine driving "normally." 52 mpg average without making MPG an obsession is good in my book!

 

<div class='quotetop'>QUOTE(Danny Hamilton @ Jul 27 2007, 02:34 PM) [snapback]486238[/snapback]</div>

Unfortunately, the Prius is a rather technical car, so we have to get technical about it, don't we.

Here's what I do:

Try to get up to speed using ICE moderately. When up to speed, try to keep it in electric as much as possible. When possible, try to glide without any energy exchange. Simple as that. Oh, I forgot to add, get angry when it cannot be kept in EV mode. :lol:

 

<div class='quotetop'>QUOTE(Wiyosaya @ Jul 27 2007, 12:58 PM) [snapback]486212[/snapback]</div>

Gotta be careful how this is phrased. Many will read this and see "electricity is more efficient than gasoline". Then they will conclude that avoiding the use of the ICE and using electric propulsion in their Prius as much as possible will gain them the best MPG. What they fail to realize is that the Prius always uses gasoline for it's energy whether it is driving in electric mode or not. Using electricity for propulsion in a Prius that hasn't been converted into a PHEV is always less efficient than using the ICE. Electricity is only more efficient when it is created efficiently (hydroelectric? photovoltaic? geothermal?)

 

<div class='quotetop'>QUOTE(ZA_Andy @ Jul 27 2007, 06:36 AM) [snapback]486017[/snapback]</div>

Because, as I pointed out at the end of my previous post, the ICE of the Prius is very bad at providing low-speed torque. Basically, if you only had the ICE, it would take you forever to accelerate to a reasonable speed from a dead stop.

<div class='quotetop'>QUOTE(ZA_Andy @ Jul 27 2007, 06:36 AM) [snapback]486017[/snapback]</div>

So, basically, you are trying to "smartly" use the car; that's great and it's exactly what you should be trying to do. However, every bit of energy that went into your driving had to have come from the ICE; you can't get energy for free. Your point about charging the battery with a "more efficient" ICE is a good one. However, I I don't know if it makes any difference. Remember that the Prius is optimized for minimizing emissions, not maximizing mileage. This means that the engine must run at some time to heat up the catalytic converter. Obviously, you can help this along if you have a block heater or if it's warm outside, but I don't know if gentle driving at the beginning (i.e. using the stored battery power from the more-efficient ICE usage earlier on) helps; you've still got to warm up the catalytic converter at some point. . .

<div class='quotetop'>QUOTE(ZA_Andy @ Jul 27 2007, 06:36 AM) [snapback]486017[/snapback]</div>

Again, the main way the battery helps is allowing the car to have a more-efficient ICE with minimal low-speed torque. The reality of most driving is that you lose most of your energy to air resistance and tire friction, so there's just not that much energy to reclaim at the end. Moreover, I read somewhere that the generators are only 10% efficient, even AFTER all of the air resistance and friction losses. Charging and discharging a battery is quite inefficient, as well. These losses really add up; note that each little green "car" on the MFD is 50 Wh of energy; that means it's enough to power one 50W light bulb for 1 hour. That's a small amount of energy and during normal driving it's very rare to see even 3 of these little cars in any 5 minute segment.

<div class='quotetop'>QUOTE(ZA_Andy @ Jul 27 2007, 09:28 AM) [snapback]486084[/snapback]</div>

Smart driving definitely helps, although that's true for anyone. Basically, coasting and using the engine when it's most efficient (i.e. at moderate RPMs) is ALWAYS a good thing, no matter what kind of car you have. Using the battery in a smart way is clearly a good idea, too, but making an effort to always use the battery (as opposed to the ICE) is not a good strategy.

<div class='quotetop'>QUOTE(Wiyosaya @ Jul 27 2007, 12:58 PM) [snapback]486212[/snapback]</div>

Prii definitely make better use of the energy in gasoline than most cars, but it's in ways that have little to do with the electric motor and batteries. The car has a very efficient ICE, low rolling resistance tires, and very good aerodynamics. If you've read stories on here about people changing their tires or putting bikes on top of their car, you know that this dramatically affects mileage, even if they keep their driving style the same.

While what you say about the efficiency of electric motors vs. ICEs definitely has some truth to it, all of the losses that you encounter elsewhere in the system outweigh the benefits. On the other hand, if/when Toyota comes out with a Plug-in hybrid, you'll be able to skip a lot of those losses and take (more) advantage of the efficient electric motors.

 

<div class='quotetop'>QUOTE(Wiyosaya @ Jul 27 2007, 01:38 PM) [snapback]486245[/snapback]</div>

Nah, the Prius is just a car, and nobody needs to get technical about it to get better MPG then they would in just about any other gasoline powered production car. Anyone can just buy one, and just drive it.

Now attempting to maximize your MPG, that is a technical endeavor. So many variables, so many places to eek out another fraction of an MPG. Learn as many of them as you can and take advantage of them whenever you can and they all accumulate to the point where you can blow away the EPA numbers.

This is true of most vehicles, not just the Prius. The Prius just seems to make it a bit easier to do and for many of us it makes it a lot more fun.

 

<div class='quotetop'>QUOTE(Danny Hamilton @ Jul 27 2007, 02:41 PM) [snapback]486247[/snapback]</div>

I agree. Words must be chosen carefully; however, as I stated in my previous post I specifically try to use EV with no-energy-transfer glide whenever possible and doing so is getting me 59+ MPG. (Incidentally, my tires are at recommended pressure.)

Also, I think that we need to be careful when saying that the Prius always uses gasoline to generate electricity. Technically, it does not. There are times, gliding to a stop, downhill, etc., when it is generating electricity with no use of gasoline whatsoever. Think a body in motion tends to stay in motion (yes I understand friction) and think flywheel think the mass of the Prius is an energy storage medium.

As I indicated previously, what the Prius does is make the most efficient use of the energy available to it.

To your list of hydro, PV geothermal, I'll add use of off-peak electricity which, according to the best of my knowledge, is all wasted.

 

<div class='quotetop'>QUOTE(Betelgeuse @ Jul 27 2007, 01:45 PM) [snapback]486249[/snapback]</div>

There are 2 important functions of the battery/MG that contribute to the efficiency of the Prius that you are leaving out.

First the MG and battery make possible for the Prius to conveniently shut off the engine when no propulsion is needed and restart it later, such as when gliding to a stop, when stopped, and when going downhill. Most cars would be chugging away unnecessarily burning up fuel in these situations.

Second, the PSD makes use of the MG to create the eCVT functionality that allows the ICE to run in it's optimal RPM range much of the time allowing for more efficient running of the ICE than would otherwise be possible with a traditional transmission.

 

<div class='quotetop'>QUOTE(Betelgeuse @ Jul 27 2007, 02:45 PM) [snapback]486249[/snapback]</div>

Yes, exactly - which was my whole point. Smart driving DOES help, because it's not a simple matter of the amount of energy available to expend, but the manner in which it is used which determines the resultant fuel efficiency. The same techniques that work in a Prius will render fuel savings to some degree in other vehicles too, though not as great in the absence of the ability to collect and reuse some of the energy which in other vehicles would be lost, but which in the Prius can be reclaimed and stored in the battery.

The bland supposition that running on electric is bad for fuel efficiency is not however valid, since as much as the energy in there had to come from the petrol in the tank, used intelligently it can, as you say, make overall energy usage more efficient.

 

<div class='quotetop'>QUOTE(Wiyosaya @ Jul 27 2007, 01:50 PM) [snapback]486252[/snapback]</div>

I disagree here. When you are coasting to a stop, using regen brakes, or going downhill, the electricity still came from gasoline. It was gasoline that was used to get the car moving or get it to the top of the hill. Without the gasoline the car wouldn't be moving and you wouldn't be able to generate the electricity.

There are two situations I can think of where you don't get your electricity exclusively from gasoline.

1) A really stiff tailwind.

2) The car is dragged up a hill by something that didn't use gasoline to do it (EV? Hand winch? waterwheel?)

Now I realize I'm splitting hairs here a bit.

If you have to stop the car anyhow, certainly using regen allows you to avoid wasting (as friction brakes do) the energy that was generated by way of the ICE's use of gasoline. However, you will get better efficiency by starting your stop sooner and gliding to a stop with no power transfer to or from the battery at all then you will by using regen. The battery and MGs make it possible to drive the car in the real world without seriously annoying the drivers around us and still maintaining much of the efficiency inherent to the ICE. This includes both a reasonable acceleration and a reasonable deceleration.

 

<div class='quotetop'>QUOTE(ZA_Andy @ Jul 27 2007, 02:03 PM) [snapback]486265[/snapback]</div>

Depends on the technique. One hypermiling technique involves shutting off the engine and coasting to a stop without using the brakes. In this situation there is nothing to reclaim and nothing to reuse.

Same for the Prius. One hypermiling technique is to use the acceleration pedal to shut the ICE off and glide to a stop with no energy transfer to or from the battery. This is more efficient than trying to recapture the energy and reuse it later, and leaves nothing to recapture or reuse.

<div class='quotetop'>QUOTE(ZA_Andy @ Jul 27 2007, 02:03 PM) [snapback]486265[/snapback]</div>

True, if we want to get really technical about it driving the car is what is bad for fuel efficiency. Once we decide we are going to drive the car and we decide we are going to try to maximize our MPG, it isn't a matter of what is bad for fuel efficiency or good for fuel efficiency. It is a matter of comparing choices and figuring out which choice is better for fuel efficiency.

Regen is better then friction brakes, gliding is better than regen.

Acceleration that doesn't use the battery/MG is better than acceleration that does.
Acceleration that uses the battery/MG and ICE together to maintain optimal RPM is better than acceleration using the ICE alone in non-optimal RPM ranges
Depending on the particular situation acceleration that uses only the battery/MG without the ICE may or may not be better than acceleration that uses the ISE in non-optimal RPM ranges.

Coasting without transfer to or from the battery is better than coasting with regen or coasting with power drawn from the battery.

Lots more variables, lots more to learn, lots more ways to squeeze out that extra 0.1 MPG if you enjoy working for it.

 

<div class='quotetop'>QUOTE(Rae Vynn @ Jul 27 2007, 10:37 AM) [snapback]486196[/snapback]</div>

Prius is not a verb. It's an adjective (before, in front, etc).

 

<div class='quotetop'>QUOTE(chogan @ Jul 27 2007, 10:31 AM) [snapback]486086[/snapback]</div>

do you have any proof or technical data to support this? specifically the rpm range you quote.


(dont worry about being too technical im an aerospace engineer)

 

<div class='quotetop'>QUOTE(AXavier @ Jul 26 2007, 06:44 PM) [snapback]485872[/snapback]</div>

Lol. My other vehicle is a 97 Ford Explorer. I am forcing myself to drive it to work 1 day/week to keep the battery charged. My realization is that I use the same amount of fuel on that one day in the Explorer as I do the other four days when I drive my Prius.

 

<div class='quotetop'>QUOTE(dogfriend @ Jul 27 2007, 06:00 PM) [snapback]486450[/snapback]</div>

Unless the Explorer is odd that way, 1 day/month should be ok. My Acclaim often went much longer than that without running..

 

<div class='quotetop'>QUOTE(Phoenix-D @ Jul 27 2007, 06:09 PM) [snapback]486456[/snapback]</div>

It has an alarm system that will run the battery down. I actually had to buy a new battery for it because I didn't drive it for about 3 mos. and when I put the battery on the charger, it wouldn't accept a charge. Lead Acid batteries don't like being discharged for long periods of time.

Point taken, I could probably go every other week, but I also need to put enough miles on to complete all of the OBD 2 checks so that I can get it smogged by the end of August.

 

Might be a good job for a battery tender. You can get them for about $19... hey then you can call your Explorer a Plug in!

 

All the comments about the ICE being more efficient than the electric seem to ignore one of the basic reasons as to why the hybrid concept is so efficient. Many have stated that all of the energy in the battery came from the ICE, and I certainly don't dispute that fact (nobody has yet disproved Newton's theory.) But reading many of the posts makes it sound as if the Prius is efficient because of its ICE, aerodynamics, etc., and that the electric is only there because the ICE sometimes needs a little help. But that misses a big piece of the picture.

It's the regen that makes it all worthwhile. If the battery was only recharged by the ICE providing the energy to a generator (which it does do at times) then the points about the losses from converting that energy to electricity, and then back into motion would indeed make the electric half of the hybrid system quite ineffective.

It is absolutely true that the energy captured by regen was created by the ICE. But the important point is that if it were it not captured by regen, it would instead be converted to heat energy by the friction brakes, like nearly every other car on the road does. And it's that recaptured energy that makes hybrids so much more efficient than an ICE-only vehicle.

So while the hybrid system isn't creating energy from nothing, what it is doing is reclaiming, and using, much of the energy that other cars lose through heat. And the only way to make use of that recaptured energy is by using the electricity stored in the battery.

If the SOC is low, then it is wasteful to try and pull additional energy from the battery, unless you know you can get it back from regen, like if you have a downhill stretch coming-up. But when the SOC is high, it might as well be used. Fortunately, the Prius knows all this, which is why the 'Just Drive It' concept works.

 

Finally picked ours up TODAY in Hermitage PA and drove home to Indy. area.....374 miles, ave 49.6 mpg..easy trip, great ride. ooh~ that mileage feels so good. I am 6'2" and made the trip comfortably...it really is a different and enjoyable feel....glad we made the switch~~