The "no arrow" display

Its called 'gliding' It means you are just coasting without using or regenerating any energy. Do a search on "pulse and glide"

 

<div class='quotetop'>QUOTE(bcmarks @ May 10 2006, 01:15 PM) [snapback]252870[/snapback]</div>

Something called momentum? The car will eventually slow down due to surface friction (between tires and road, between bearings in the car, etc.) and air friction.

 

<div class='quotetop'>QUOTE(bcmarks @ May 10 2006, 01:15 PM) [snapback]252870[/snapback]</div>

It took me a while to realize that unless you are going down a not-insignificant downgrade, you can't maintain speed while gliding. In their enthusiasm, some of the posts imply that you can maintain a steady state indefinately. You do slow down and have to "pulse" the car back up to speed. It's great if you're on a fairly flat road and no traffic behind you. I've read (and empirically verified through experience) that you can't glide at speeds over approx. 40mph because the engine turns at that speed even when no gas is being expended.

I've only had the car for two weeks, so I'm no expert, but I do understand your confusion.

 

Prius nirvana???

You must be joking. I can reach that state anytime I want with my manual transmission Volvo, by just pressing down the clutch pedal and not touching the throttle. The Prius is a fancy car with all kinds of neat innovations, but torque-free rolling ("freewheeling") isn't one of them.

 

<div class='quotetop'>QUOTE(vtie @ May 10 2006, 02:13 PM) [snapback]252925[/snapback]</div>

Don't forget to turn off the engine too.

Tom

 

<div class='quotetop'>QUOTE(qbee42 @ May 10 2006, 08:19 PM) [snapback]252932[/snapback]</div>

That's almost irrelevant actually, as soon as you have some speed. 0.4 liter / hour is a reasonable consumption for an idling diesel engine. Suppose that I am driving at 60 km/h. This means that I'm consuming 0.6 liter/100 km at that time. Even for a Prius, this means virtually no fuel consumption.

 

<div class='quotetop'>QUOTE(vtie @ May 10 2006, 03:10 PM) [snapback]252995[/snapback]</div>

True. Even my Durango, which has an instant fuel usage display reads 99MPG when I take my foot off the gas and coast. When I'm accelerating it drops to about 5MPG though.

 

<div class='quotetop'>QUOTE(efusco @ May 10 2006, 10:38 PM) [snapback]253055[/snapback]</div>

Apparently, you don't do much highway driving!

But I would be careful with that calculation. Conventional wisdom says that a combustion engine consumes an extra amount of fuel when initiated. A rule of thumb sometimes applied is that you need a shutoff time of at least one minute to reach the break-even.
Most likely, this will not be that bad for the Prius, because of the different way the engine starts. But there might still be some overhead that could have a big impact on this estimate.

 

No-arrows means neutral, as near as makes no difference. The Energy screen does not show the amperage drawn from the battery to run the car's electrical systems. With the engine off and the car stopped this seems to be between 1 and 1.5 amps. It's easy to give the pedal just enough pressure that you coast (slowing gradually, depending on the incline of the road) and you see no arrows. Now that some of us have the CAN-View, we know that there is virtually always some current flowing into or out of the battery.

 

on level ground I've been able to maintain the glide at about 40 mph !

 

<div class='quotetop'>QUOTE(vtie @ May 10 2006, 01:53 PM) [snapback]253068[/snapback]</div>

That's the beauty of hybrids! They turn conventional wisdom on it's ear. Because of the variable compression ratio, pre-heated engine, 12 hole injectors etc etc it is actually very clean (also read as lean) and light on gas for restarts. Much better than "most likely...not that bad". Most prius owners have "learned" how to drive the prius to optimize the light load, ICE off scenario. No mater how efficient the other engine is it can't beat off. The prius has a useable driving window at the 60% SOC, MG2 driving, ICE Off, MG1 "idling" to make enough hi/lo volts condition. It's hard to get anywhere coasting in a gas/dsl car. They use fuel in the idle cycle and can't regain speed like a prius without significant fuel economy loss. Gas cars still pollute in decel because fuel that was collected on the manifold wall vaporizes as manifold pressure drops. Low manifold pressure also creates crankcase blow-by pollutants even if the injectors are in fuel cut. It starts to look like apples and oranges.
Regards, Mike

 

<div class='quotetop'>QUOTE(IFixEm @ May 11 2006, 08:35 AM) [snapback]253348[/snapback]</div>

Interesting discussion, let me throw in one more consideration. You say that the mode where the Prius is running entirely on MG1 for an extended distance at the same speed is more efficient then on a conventional car. I am actually wondering why. After all, the energy being consumed by MG1 has been generated by the gas engine itself, and has suffered from several partial losses during its long path: "gas engine -> MG1/MG2 -> batteries -> MG1 -> wheels". I understand that one of the advantages of the Prius is that it has more freedom to use its gas engine in its most efficient regime, but still I am wondering how this complicated path could beat the direct path "gas engine -> wheels".

As a matter of fact, if I drive my diesel car at a constant speed of say 60km/h for an extended time, I can easily beat the mpg of my Prius under the same conditions, engine shutdown or not.

I would rather say that time prime advantage of the Prius is the regenerative braking and the fact that it can have a smaller gas engine than an equivalent conventional car. It's my current impression that, in normal traffic conditions, the automatic engine shutdown feature is more important as a fun factor than for the influence on the mpg. But of course I might be wrong.

 

<div class='quotetop'>QUOTE(efusco @ May 10 2006, 02:29 PM) [snapback]252943[/snapback]</div>

Why not simply shift the Prius into neutral? I recently started experimenting with P&G and realized that shifting into neutral seemingly accomplished the same thing, but more consistently (you don't have to concentrate on keeping the gas pedal in just the right spot), at any speed, and without the potential distraction of watching for the "no arrow" state on the MFD. I don't recall seeing this option mentioned in any P&G discussion here or elsewhere. Am I missing something?

Jim

 

"gas engine -> MG1/MG2 -> batteries -> MG1 -> wheels".
When you are above 60% and approaching 80% soc the car thinks about load conditions differently. The prius tries to use the closest thing to free energy we can get...rergen braking. The HVecu likes to be able to capture regen braking whenever possible so the HV batt is held artificially low to a 80% celing so you have room for regen. If load is low enough, <30 calc load, to not require the ICE then the MG 2 is in a near idle condition because it take alot of volts to increase or decrease speed with MG2 but little to hold a constand rpm. Mg2 magnet is big and heavy...once it gets going and has only minimal drag from the fields under light load. since the batt is full and we don't need the ice for power demand we use MG1 to feed Mg2 directly and to the heck with the batt. By driving Mg1 sungear and Mg2 sun gear but holding the carrier with ICE Off, we get the equivilent to 1:1 ratio in the "trany". Crowd the throtle a bit more and we need a lower gear ratio so the ICE MG relationship changes. If you can accelerate slow enough to not burn up to much juice and require long recharge time, AND cruise at the 30-38 range on reasonably flat ground you will find the sweet spot.
Regards, Mike

 

<div class='quotetop'>QUOTE(JimboK @ May 11 2006, 09:50 AM) [snapback]253550[/snapback]</div>

Shifting into neutral is unsafe. For one thing, you then cannot accelerate should it be necessary to do so, and you may lose other safety features. Use neutral only when the wheels have to be able to rotate freely, as when being towed, or in a car wash where the machinery pulls the car through. Neutral may also defeat the car's ability to recharge the battery from the engine (not sure on this) and thereby risk allowing the HV battery to run down.

 

<div class='quotetop'>QUOTE(daniel @ May 12 2006, 02:31 AM) [snapback]253612[/snapback]</div>

That's right. Both MG1 & MG2 are disconnected by the inverters in [N] so ICE can't recharge it thru' MG1 and there is also no regen from MG2 to recharge it.

Another point to add, if the ICE were running prior to shifting to [N], it will continue to run (may slow down gradually to idle rpm but cannot be stopped completely because MG1 was off) even the speed fall below 42 mph. There is no clutch or any other kind of stopper to stop ICE, MG1 is the only control. ICE in idle still consume some fuel.

Unless you know ICE is already stopped, then shifting to [N] will be of benefit.

IMHO, "no arrow" P&G should be limited to road conditions where there are less traffic. You can P&G with arrrows and also get good FE because HSD will manage the most efficient energy flow for you.

 

<div class='quotetop'>QUOTE(vtie @ May 11 2006, 05:13 AM) [snapback]253390[/snapback]</div>

It is true that there are conversions losses going from gas to battery charging to MG1 consumption. But don't forget that an electric motor is far more efficient at converting energy to traction power than an ICE can ever hope to be. If the batteries are charged with regeneration or when the engine would otherwise run at a less efficient RPM or load, then charging the batteries and using electric power for traction can still be significantly more efficient than using the ICE alone. It it were not the case, the Prius would likely see about 10mpg less on average.

<div class='quotetop'>QUOTE(efusco @ May 10 2006, 11:29 AM) [snapback]252943[/snapback]</div>

Wow. Is this known from the CAN-view? 6A actually seems quite big. What all is going on to consume that kind of power? The production EVs consume on the order of 1-2A when "coasting." The power all goes to just keeping the computers awake. And this assumes no AC or heated windshield, etc...