Regen while coasting -- why?

<div class='quotetop'>QUOTE(Washington1788 @ Aug 16 2007, 11:29 AM) [snapback]496951[/snapback]</div>

No "correction" here, but a bit more of a question from a rookie.

Having found out that "B" does nothing for my in the recapture of energy (regen), I've found absolutely no use for it in the Midwest. I've only seen green bars twice, and then only for a minute at most, so I can't even imagine being on a steep enough hill where I need to bleed off that much energy. I'm much more interested in learning how to glide or coast better.

It seems that a real glide does not happen for me unless I've been driving for awhile and I have at least 4 or 5 bars showing. Can I simply glide in Neutral? I know it isn't always safe to be out of gear, but I used to shift to neutral in previous cars in order to glide and avoid the slow-down forced by the engine/transmission friction. How does Neutral work in the Prius?

 

<div class='quotetop'>QUOTE(Justifyd @ Aug 21 2007, 06:08 PM) [snapback]500053[/snapback]</div>

I think this explaination makes the most sense, and is the one I personally subscribe to. Well said Jusrifyd.

 

<div class='quotetop'>QUOTE(Justifyd @ Aug 21 2007, 09:08 PM) [snapback]500053[/snapback]</div>

Those are excellent points Justifyd.

Years ago I wrote an engineering term paper on ergonomic automotive design. One of the things I read about in my research was regarding a new transmission design, which was basically a fluid-drive torque converter that didn't require mechanical gearing. One problem with it was that power could only be transferred in one direction, allowing the drive train to freewheel, without any engine drag. When the system was tested, drivers found the lack of engine braking to be extremely unsettling, so the setup was deemed impractical.

 

<div class='quotetop'>QUOTE(a priori @ Aug 21 2007, 11:00 PM) [snapback]500107[/snapback]</div>

As I am sure you have found you can force a glide by using lite throttle but I think there are times when neutral is of use if you are taking FE as far as you can.

The objective is to use any energy stored in the momentum of the vehicle to travel as far a possible without having to use petrol. If you go down a hill you will build up speed but at 41mph the ICE will engage which will use energy so in this case if the glide will exceed 41mph you could use Neutral.

If at the end of a fast glide you have to stop such as at a junction I toggle between Glide, Regen, and Brake to end up stopping at the junction but not exceeding 41mph, this uses no Petrol, gets max regen and you do not get any drag from the ICE free wheeling above 41.

Thats is my current strategy for going down hills.

 

Folks, all of this is well documented, in many previous threads here
and in other fora, and this document from the NHTSA. Drivers pay
more attention to "butt-cues" than you think, and which way the car
drifts at the moment of letting off the brake pedal instantly tells
the driver if everything's okay or not.
.
Braking is easily one of the most complex aspects of how the car
works. Every effort is made to stay off the physical brakes and
collect all the regen possible, but there are plenty of circumstances
that hit limits [100A battery charge current primarily]. There's
a pedal swing-speed sensor the system uses to interpret sudden
movement as a panic stop situation; since it takes time for the
braking computer and the motor-control hybrid computer to decide
about regeneration, that time is bypassed when you just need to stop
the car NOW.
.
You can certain use neutral for lower-speed gliding under 42 mph if
you've made sure the engine has shut down first [it doesn't make much
sense to leave it idling, does it..]. Above 41 the engine spins and
if you go to neutral, idles [burning gas] at about 1000 rpm. If you
use neutral be prepared to jump back into D on very short notice if
you need to slow down and still want to do it regeneratively!
.
_H*

 

<div class='quotetop'>QUOTE(hobbit @ Aug 22 2007, 07:31 AM) [snapback]500205[/snapback]</div>

Thanks, Hobbit.

I've noticed that when I've got a good charge and am on an incline I'll be able to keep a clear or blank on the MFD (sorry, I can't come up with a better description), even if the speed is above 41. By all appearances, the gas engine is not running and no juice is being drawn from the battery. I thought this was a version of the warp steath discussed elsewhere. Are my instruments not telling the truth?

 

<div class='quotetop'>QUOTE(Justifyd @ Aug 21 2007, 09:08 PM) [snapback]500053[/snapback]</div>

True, they are useful, but mostly because we are accustomed to them. The pedal switching you describe is an artifact from standard automotive controls. If we all started from scratch with no previous bias, the controls on a Prius could be quite a bit different and potentially more efficient. Same thing with this silly QWERTY keyboard that I am using.

Tom

 

<div class='quotetop'>QUOTE(Justifyd @ Aug 22 2007, 03:08 AM) [snapback]500053[/snapback]</div>

Another practical thing with the creeping action is when you have to start driving in an uphill situation. The car will not start to roll backwards down the hill. Those of you who have driven a manual transmission will probably know what I'm talking about. You have to balance all three pedals (clutch, brake and throttle) more or less at the same time to be able to start driving without rolling backwards, possibly into the car behind you. Of course you can normally make this start easier using the parking brake instead of the brake pedal, thus being able to hold the car still with the parking brake using one hand and balancing the clutch/trottle with your feet.


Stein

 

Toyota's Hybrid engineers went to a lot of trouble to make the Prius and other hybrids drive like conventional cars. The regen allows the backlash in the drive train to be taken up ready for brake and increased regen application.

The creep function when you take your foot of the brake reduces shock load on the transmission again by taking up any backlash in the gears, making for smoother launch. Drag racers use this same technique although more severe. It also makes your hybrid feel more like the automatic you are used to.