Not using the battery

<div class='quotetop'>QUOTE(wkramer @ Jul 27 2007, 08:27 AM) [snapback]486055[/snapback]</div>

Yes this is true. The Prius gets great MPG because it has a small 1.4L atkinson cycle engine. Unfortunately if that was all it had you wouldn't be able to sell very many of them because it is only 76hp at 5000 RPM and only 82 ft.-lb. of torque at 4200 rpm. (very poor excelleration in a 2900 lb car)

They make up for this by putting in the electric motor/generators. Using a bit of the torque when the engine is running and using regenerative braking, they store up excess energy in the battery when it isn't needed. Then when you need/want to accellerate hard, the motor generator can add in another 67hp at 1200 - 1540 rpm and another 295 ft.-lb. of torque at 0 - 1200 rpm for short periods of time.

This allows them to size the ICE for average use rather than for the peak use that a non-hybrid ICE is sized for. The significantly smaller more efficeint atkinson cycle is where most of the MPG improvement comes from.

Additionally, since they have these nice powerfull motor/generators along with some sophisticated computer power, they can shut the engine off entirely when it isn't needed (coasting/gliding/stopped/downhill) and use no fule at all while non-hybrids would be chugging away. The electric motors can provide instantaneous thrust while starting the ICE back up any time the driver requests it by pushing down a bit harder on the accellerator.

Finally, the PSD in combination with the ICE and MGs make it possible to precisely control the RPM of the engine for any given velocity/accelleration (eCVT) this aloows the ICE to more frequently run in its optimpal most efficient RPM range.

Small amounts of battery are used by the hypermilers to do things like start the engine back up after they have been gliding for a while, or control the ICE rpm. However, everytime the brakes are used to regen electricity you are converting distance that could have been traveled into electrical energy for storage in the battery, and due to energy conversion losses you'll never get that same distance travelled back out. Therefore, it is always more efficient to not use the brakes if you can avoid it (don't go as fast, and start coasting to a stop sooner).

Same thing for accelleration. Everytime you draw off the battery for accelleration, that energy will eventually need to be replaced in the battery by use of the ICE. You'll always use more gas to replace the energy in the battery than you would have used if you had just used the ICE directly for the accelleration in the first place.

The most efficient use of the HSD system anyone has found so far is to use the highly efficient ICE for accelleration up to some chosen speed, then allow the momentum to carry the car fuel free with the ICE shut off while you coast without regen for extended distances down to some lower target speed. Then repeat the process. Don't touch the brakes, don't regen, don't used the electric motors for anything accept getting the ICE restarted and controlling the ICE RPM.

 

<div class='quotetop'>QUOTE(wkramer @ Jul 27 2007, 12:13 PM) [snapback]486183[/snapback]</div>

As compared to what?

Without the battery, you can't start your engine, and your transmission won't work.

Are you trying to figure out how much loss of MPG is attributable to the use of the battery as compared to the 100 mpg hypermilers?

The battery doesn't contribute to mpg outside of the cars design. It contributes to the marketability of the car by boosting horsepower and torque over the ICE.

As a part of the cars design through the eCVT the battery contributes by making it possible to more frequently run the ICE in its optimal rpm range. Also as part of the cars design it contributes by making it possible to conveniently shut the engine off when coasting, gliding, stopping or going downhill.

If you could create a CVT that weighed the same amount as the PSD and worked as well but didn't need the battery and MGs to function, and you could create some way to start and stop the engine without the use of the battery and MGs, and you removed the MGs and the battery and replaced them with an identical amount of weight distributed the same, you should see the MPG of the car increase due to the reduced amount of energy lost in conversion from fuel to kinetic to electrical to chemical to electrical to kinetic. Of course the acceleration would be pretty bad and most drivers would therefore not want to drive it.

Use of the battery for thrust doesn't increase efficiency, it reduces it. Regen increases MPG as compared to using friction brakes, but it reduces MPG as compared to gliding to a stop and getting your foot off the accelerator when it isn't needed.

 

The previous posters have covered this quite well, so I will add only a simple thought: The very best mileage for an engine powered car will occur if the car is driven at only one speed, never stops, never starts, never accelerates, never brakes, and only drives on level roads. In this situation you can size the engine to run at its most efficient point, and avoid other power wasting devices such as variable gearing. Obviously this is impossible to do in the real world, but hyper-milers try to drive this way as much as possible. With the Prius, the battery, electric motors, and control system let us drive in a normal fashion, while still keeping the engine running near the ideal. It's a good compromise.

Tom

 

All great responses!

To which I'll add...

The folks getting the super mileage do not drive these like we are typically forced to on normal roads. The battery is there for all the things described above - mostly to allow the car to operate well when driven *normally.* It gets spectacular mileage when you don't have to use the battery for much traction power. It would get infinitely BETTER gas mileage if it had no ICE at all, and more batteries. But I digress...

 

<div class='quotetop'>QUOTE(darelldd @ Jul 27 2007, 12:57 PM) [snapback]486210[/snapback]</div>

Only because it wouldn't go anywhere.

Oh wait you probably want to add a plug and charger for those batteries too don't you?

Even then it would depend a bit on your source of electricity. Mileage would probably be worse if I had to run a gasoline generator to charge up my car regularly. <_<

Still at that point it is probably fairer to compare total cost of ownership than MPG. If we are looking at costs.
The batteries might need to be replaced more frequently, the resale value of the car might be different, you'd have to pay for your source of electricity, I'm sure there are other costs I'm not thinking of.

If we are talking about environmental impact there are so many variables to consider.

Still I'm willing to take your side and believe that even comparing total cost of ownership, for the average driver a well designed affordable mass produced EV would be cheaper than the Prius and better for the environment.

 

<div class='quotetop'>QUOTE(Danny Hamilton @ Jul 27 2007, 02:12 PM) [snapback]486226[/snapback]</div>

I suppose that we could start an argument about how all the electrical energy generated at non-peak times by any electrical power generator is wasted, and I suppose we could also argue that the Pacific Northwest National Laboratory did not conclude in a scientific study that the current electrical generation capability in the US is enough energy to power 80 % of all the cars in the nation.

 

<div class='quotetop'>QUOTE(Wiyosaya @ Jul 27 2007, 01:33 PM) [snapback]486242[/snapback]</div>

A bit confused here. <_<

Why exactly would we want to argue either of these things if they aren't true? :huh:

 

I think Wiyosaya was commenting on all your ways of viewing EVs as NOT cleaner than gasoline cars - when in fact it is quite a bit of work to make an EV dirtier than a gasoline car, and WAY the heck easier to make it cleaner - like by plugging it into the grid.

Fact of the matter is, electricity is the ULTIMATE flex fuel. It can be made from anything - including astonishingly green things like the sun and wind, and can be made at home. Gasoline? Not so much.

Didn't mean to drag this one off so far... thought I guess it is mildly on-topic for this thread...

I just find it ironic that the Prius gets better gas mileage when you use the battery the least - while a battery car is WAY more efficient than any car that uses an internal combustion engine at all.

 

<div class='quotetop'>QUOTE(darelldd @ Jul 27 2007, 06:55 PM) [snapback]486431[/snapback]</div>

Definitely ironic, but of course a prius isn't an EV nor is it designed to be. The design doesn't really use the battery to improve efficiency much, mostly it's just there to improve acceleration because the efficient ICE provides such poor accel.

I wasn't seriously suggesting that the Prius is cleaner than an EV.

You had joked that the Prius would get better milage if it didn't have an ICE.

I joked back that the Prius wouldn't move without the ICE, and teased a bit about how if I still used an ICE to power my EV, it wouldn't help. The emoticons were supposed to make this clear.

Even then I figured that I'd mention that I truely agreed with you, just in case the jesting didn't come across right in my typing.

"Still I'm willing to take your side and believe that even comparing total cost of ownership, for the average driver a well designed affordable mass produced EV would be cheaper than the Prius and better for the environment"

 

As I mentioned in my talk at Hybridfest and had observed on my way

out there, that Atkinson plant is good for over 50 mpg by itself
without the hybrid stuff wrapped around it. Park that sucker at
1800 RPM steady-state across the flatlands of Ohio and Indiana and
it will continue to deliver the goods all day. 62 MPG average
seemed to be about the settling point for that long-haul experiment.
Even the old EPA guesstimate of 51 highway was way off from what
this li'l guy is capable of. Add the hybrid worx to help with
stop/start energy recapture, and you've really got something.
.
_H*