Question about B Mode

Using the B mode for long downhill grades is recommended. Other than not
riding the brakes, does this gain you anything? Does it generate more juice
for the battery like braking? If not, it seems counter productive.

G-Man

On Wed, 30 Jan 2008 08:31:57 -0500, "G-Man" <g_foremanm> wrote:

>Using the B mode for long downhill grades is recommended. Other than not
>riding the brakes, does this gain you anything? Does it generate more juice
>for the battery like braking? If not, it seems counter productive.

You can't tell when the brakes are actually in use in a Prius, since
regenerative braking is used as much as possible. However, if
regenerative braking is insufficient for the amount of braking being
asked for, the mechanical brakes are engaged. B mode does something
else: it gives the same effect that use of a lower gear in a standard
automatic gearbox does, by spinning the engine and using engine braking.
I live in an area where engine braking is virtually never needed, so I
have only engaged B mode a couple of times, just to see what it does. I
don't know if it engages the brakes, too--but I think not. It will
definitely reduce the demand for braking.

It's only needed for long, steep downhill runs--the kind where a traffic
sign "Use lower gear" probably appears.

In article <13q0v50f5atjr70@news..com>,
"G-Man" <g_foremanm> wrote:

> Using the B mode for long downhill grades is recommended. Other than not
> riding the brakes, does this gain you anything? Does it generate more juice
> for the battery like braking? If not, it seems counter productive.

No, it does not regenerate electricity.

B mode is to get the added drag from the engine pumping air.

On Wed, 30 Jan 2008 12:18:50 -0700, Michelle Steiner
<michelle@michelle.org> wrote:

>In article <rkh1q35br14k0g1faegkl2u290m165fr56@>,
> Pete Granzeau <pgranzeau@cox.net> wrote:
>
>> You can't tell when the brakes are actually in use in a Prius, since
>> regenerative braking is used as much as possible.
>
>Friction brakes on the front wheels are generally used only under two
>conditions:
>
>1. When the vehicle is traveling under six miles per hour.
>2. In panic stops.
>
>The rear wheels, though, have only friction brakes, and no regenerative
>braking.

Yes, but are the rear brakes used when regenerative braking can handle
the load, or are they, too, used only when etc.?

Diako wrote:

> Consider what happens going on a long downhill: after some time the
> battery will get to 'Full' thanks to regenerative braking. At this point
> regenerative braking will stop and the mechanical brakes will do all the
> job.

....according to one who has obviously never driven a Prius under those
conditions. I have. When the battery is as full as the battery can be
the Prius ECU automatically starts "pumping air" to make up the minor
drag which was being produced by regeneration.

Having been in that situation and wondering why the heck my ICE had
started running going down a long steep grade, I tried B and found no
difference between B and D in that situation. Then I thought to look at
the other Info MFD screen and saw my battery was pegged at solid green.

By Diako's description if the battery filled then one would start going
faster when the ECU halted regeneration. As if one had pressed on the
throttle until all the arrows blanked on the energy flow animation.
Toyota is smarter than that. I was shocked when my ICE started "running"
but would have been really surprised had it started accelerating when
the battery was full.

In article
<a188832e-72f6-4054-99d4-6b2c522de0e5@i29g2000prf..com>,
The Tramp <the.tramp@infinito.it> wrote:

> > Having been in that situation and wondering why the heck my ICE had
> > started running going down a long steep grade, I tried B and found no
> > difference betweenbB and D in that situation. Then I thought to look at
> > the other Info MFD screen and saw my battery was pegged at solid green.
>
> Oh boy... you must be deaf.
>
> In these conditions (downhill, green batteries, no acceleration) the
> REV of the ICE is doubled in respect to D.
> I know: I have a Prius, a rev Counter and the Alpes. :D
>
> if under 40 mph:
> Batteries < 80% (and not too hot, otherwise threshold lowers)
> In D RPM = 0 charge = +10 Amp.
> In B RPM = 1300 charge +20 Amp.

Not here.

There's no feed to the batteries from the wheels if the car is in B mode.

On Sat, 2 Feb 2008 15:05:45 -0800 (PST), The Tramp
<the.tramp@infinito.it> wrote:

>One curiosity: a slight pressure on the accelerator while in B = RPM
>does down (and the car goes downhill faster)

Except for the rpm thing, any car would go downhill a bit faster if the
accelerator had some pressure on it, even when a lower gear.

I had a 1971 Chevrolet once which automatically opened the throttle when
the gas pedal wasn't being pressed at speed, so the car wouldn't suck
gas through the carburetor. The result was that the car would run
around at 30 mph without slowing down. If I applied a bit of brake or
lower gear, it would slow down some and the open throttle would go
finally close, permitting a slowdown to 2 or 3 mph, just like any gas
car with auto trans.