EV mode @ 40 MPH

Howdy, I have a 17 mile one-way commute, most of it on the freeway, but the last 3 miles on city streets/boulevards with limited traffic light in Fremont, CA. I can set the speed control at 40 MPH and do almost all of it in EV mode. I do the same thing in the afternoon after i get off the freeway the last 2-3 miles home.

 

<div class='quotetop'>QUOTE(efusco @ May 13 2007, 04:13 PM) [snapback]441166[/snapback]</div>

I have read that "fact" many times, but my experience is much different. In my 2007, I consistently go to 53-53 mph on battery-only power with no ICE engagement. It takes a very steady foot, but it isn't difficult.

 

<div class='quotetop'>QUOTE(efusco @ May 13 2007, 04:22 PM) [snapback]441171[/snapback]</div>

So, if no fuel is burned then IT IS battery only (EV mode), so what do I care if the ICE is spinning?

 

<div class='quotetop'>QUOTE(efusco @ May 13 2007, 04:52 PM) [snapback]441187[/snapback]</div>

So, if I am reading between the lines correctly, it is impossible to fully optimize mpg using the MFD alone, which means that something like the ScanGauge is a necessity?

 

<div class='quotetop'>QUOTE(mpgFanatic @ May 13 2007, 04:57 PM) [snapback]441191[/snapback]</div>

I would say so, they you can see what is going on. The MFD doesn't always tell the whole story.

 

So I though I was geeting EV at 65, but if you say the ICE is spinning & not using gas I'll take you're word for it, can't tell the difference at that speed & noise level. Hyperstealth should add more to your average I would think.

 

<div class='quotetop'>QUOTE(mpgFanatic @ May 13 2007, 04:57 PM) [snapback]441191[/snapback]</div>

Maybe not. To optimize fuel economy, one should learn first how to pulse and glide (for speeds of 40 MPH and below) and warp stealth (for >40 MPH). Either can be done using the MFD alone.

Part of the ScanGauge's value is that it can display RPM (among other engine parameters), thus allowing the driver to keep RPM within its efficiency range during pulses or other acceleration and while cruising. In another thread, I floated an idea for a rule of thumb for the masses who choose not to buy added instrumentation, using the relationship of the instantaneous MPG and vehicle speed to optimize MPG. The rule is pretty simple if you can do some simple math on the fly: Keep instantaneous MPG > speed x 0.5 and < speed x 1.2.

 

<div class='quotetop'>QUOTE(mpgFanatic @ May 13 2007, 01:18 PM) [snapback]441169[/snapback]</div>

[Emphasis mine.]

The ICE is ALWAYS engaged. In the Prius nothing is ever disengaged. The car can run without power input from the ICE at any speed, if conditions are right. But the rpm limits of MG1, combined with the geometry of the Power-Split Device, require the ICE to spin at speeds over 42 (41???) mph. The Energy screen does not show whether the ICE is spinning, only whether it is supplying energy.

However, at higher speeds it requires more energy to move the car, so on battery power the battery will go down quickly and the car will start the ICE.

Also, electric mode is efficient only under a very narrow range of conditions, and at freeway speed, it is very rarely efficient for the ICE to be off, which is why it seldom happens on level terrain and constant speed.

<div class='quotetop'>QUOTE(AndreJ @ May 13 2007, 02:36 PM) [snapback]441215[/snapback]</div>

The EV switch allows for more aggressive acceleration than the electric mode the car itself initiates. However, this is still very light acceleration. I think my little Xebra can accelerate harder than a Prius in EV mode. This is because it is very inefficient to accelerate on battery power, so the computer starts the ICE in order to improve efficiency.

 

<div class='quotetop'>QUOTE(AndreJ @ May 13 2007, 03:57 PM) [snapback]441164[/snapback]</div>

I'm only able to get into hyperstealth when the weather is warm or the car is hot. Normally, once I hit 33 mph the ice kicks on automatically.

 

<div class='quotetop'>QUOTE(efusco @ May 14 2007, 06:54 AM) [snapback]441586[/snapback]</div>

Regarding your statement above, I'm curious why it's not a good idea. Does it not allow the ICE to warm up? I thought trying to use the battery more offers better FE. Does this damage by baby?

 

<div class='quotetop'>QUOTE(GottaGetOne @ Jun 4 2007, 08:49 PM) [snapback]455348[/snapback]</div>

Very much to the contrary!

The battery is usually the enemy of efficiency. The reasoning has to do with the second law of thermodynamics, the rule of entropy. In a nutshell, any time matter or energy changes states, some is wasted.

All energy in the battery comes from the ICE. Converting it from fuel to motion causes one step of entropy. Converting motion to electricity, then convering electricity to chemistry (charging the battery) then converting chemistry back to electricity, then convering electricity back to motion adds four additional steps. These steps are very inneficient.

You may be thinking, why does the Prius have a battery if this conversion process is so inneficient? There are two answers to this question that I am aware of. One is that the super-efficient engine that the Prius uses is TINY by our standards, and lacks the poweer to accelerate decently. The battery gives us the boost we need to get going. Also, the Prius is able to capture a small portion of energy that would otherwise be used in braking, and re-use it to accelerate again.

There are thousands of other details which contribute to the marvelous efficiency of the elegent masterpiece of engineering that you are driving, but the most important thing to remember, is that electric mode is not your friend. Typically the greatest efficiency happens with no yellow on the energy screen, one red & one green, or nothing at all are the goal.

The first thing to learn, IMO when you are imroving your mileage is to pay attention to the light ahead of you. If it's red, you can probably save energy by braking way early. The hope here is that you will slow down so much while you are far away from the light that it will turn green before you lose all of your speed and have to accelerate again. This is the most efficient, because the energy of your motion does not have to change states at all.

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If anyone has stats on the efficency of regenerative braking in the Prius, I'd love to have them, it would really help educate new drivers.