Author Topic: Test Drive: 2014 Toyota Prius  (Read 7956 times)

Offline Autos_Editor

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Test Drive: 2014 Toyota Prius
« on: July 24, 2014, 06:28:27 am »


Even though it's been over five years since the Prius hatchback was last redesigned, it still compares favourably with newer competitors.

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Offline JohnM

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Re: Test Drive: 2014 Toyota Prius
« Reply #1 on: July 24, 2014, 07:25:26 am »
The Prius does feel slightly ponderous and unathletic in static turns.  However, I was quite amazed when I took a roller coaster twisty through cottage country at speed.  The Prius was very composed, tight and, well, fast.   A definite transformation from its highway / city feel.

Also, midrange passing power is just fine and a departure from its off-the-line umph.   So under certain circumstances, the Prius will perform beyond expectations.

Cheers,
John M.


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Re: Test Drive: 2014 Toyota Prius
« Reply #2 on: July 24, 2014, 07:36:37 am »
The times I use the power mode is usually on the 401 in the GTA when you a fast response in the gas pedal
I Never use the EV mode, easier just to use the gas pedal to stay in EV mode

I believe your statement about the b mode is wrong
Here is a long draw out explanation

Using "B" Shift Position
The Prius uses an electronic transmission mode selector, similar to a gear shift on a conventional car. Unlike a conventional vehicle with modes P R N D 2 1 (park, reverse, neutral, drive, 2nd gear, 1st gear) the Prius has a power button, a park button, and a selector for modes R N D and B (reverse, neutral, drive, and engine-Braking).

In the course of normal driving, the driver NEVER needs to use 'B' mode (engine Brake mode). The techniques below are optional. 'B' mode is appropriate when descending long grades (i.e. descending down a mountain road), where if the driver uses the brake pedal to control the vehicle's speed, the vehicle's brake pads will overheat and fail.

In a normal vehicle, the driver handles that condition by slowing to an appropriate speed and shifting to a lower gear (2nd or 1st). This forces the vehicle to spin the engine faster than needed, "wasting" energy through vacuum losses but helping maintain a safe vehicle speed without overheating the brake pads.

In a Prius, the driver handles that condition by selecting "B" mode. This tells the Prius to attempt to emulate "engine braking" in a conventional vehicle. Depending on the vehicle's speed and the battery SOC (state of charge), the Prius will do this using regenerative braking and/or high-RPM zero-fuel-flow engine braking.

Engine braking is inefficient because it uses the engine as an air pump, converting kinetic energy into heat. Unnecessary regenerative braking is also inefficient because of energy conversion losses. (Regenerative braking is good when it replaces friction braking, but it's not as efficient as coasting at a constant speed.) Because of this, "B" mode will not recharge your batteries more efficiently than just braking and is not recommended for general driving. Just as you might downshift into 2nd gear when going down a long, steep hill to prevent brake damage, you can "downshift" into "B" mode on a Prius. "Shifting" is all electronic, so the system won't let you shift in a harmful way. (Even if you try to shift into reverse when moving quickly forward, you'll just end up in neutral.)

Offline hemusbull

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Re: Test Drive: 2014 Toyota Prius
« Reply #3 on: July 24, 2014, 09:24:54 am »
"it still compares favourably with newer competitors"...I don't think there are REAL competitors!

Offline ArticSteve

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Re: Test Drive: 2014 Toyota Prius
« Reply #4 on: July 24, 2014, 01:07:11 pm »
I believe your statement about the b mode is wrong

Reviewers on this site ALWAYS get this part wrong.  They don't really understand the Toyota Hybrid system.  They just write about it.  :rofl2:    It's an AIR BRAKE!   Moreover, the "CVTe" is named as such because if Toyota referred to it as a PSD then it would scare buyers off.  :rofl2:   

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Re: Test Drive: 2014 Toyota Prius
« Reply #5 on: July 24, 2014, 01:09:23 pm »
The Prius does feel slightly ponderous and unathletic in static turns

Because the factory tires are sh*t.

Offline ArticSteve

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Re: Test Drive: 2014 Toyota Prius
« Reply #6 on: July 24, 2014, 01:10:04 pm »
"it still compares favourably with newer competitors"...I don't think there are REAL competitors!

BINGO!

Offline ArticSteve

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Re: Test Drive: 2014 Toyota Prius
« Reply #7 on: July 24, 2014, 01:14:14 pm »
Toyota Canada should have these units back down to 0%/60 before the new model rolls in probably @ 4.9%

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Re: Test Drive: 2014 Toyota Prius
« Reply #8 on: July 24, 2014, 02:19:31 pm »
The times I use the power mode is usually on the 401 in the GTA when you a fast response in the gas pedal
I Never use the EV mode, easier just to use the gas pedal to stay in EV mode

I believe your statement about the b mode is wrong
Here is a long draw out explanation

Using "B" Shift Position
The Prius uses an electronic transmission mode selector, similar to a gear shift on a conventional car. Unlike a conventional vehicle with modes P R N D 2 1 (park, reverse, neutral, drive, 2nd gear, 1st gear) the Prius has a power button, a park button, and a selector for modes R N D and B (reverse, neutral, drive, and engine-Braking).

In the course of normal driving, the driver NEVER needs to use 'B' mode (engine Brake mode). The techniques below are optional. 'B' mode is appropriate when descending long grades (i.e. descending down a mountain road), where if the driver uses the brake pedal to control the vehicle's speed, the vehicle's brake pads will overheat and fail.

In a normal vehicle, the driver handles that condition by slowing to an appropriate speed and shifting to a lower gear (2nd or 1st). This forces the vehicle to spin the engine faster than needed, "wasting" energy through vacuum losses but helping maintain a safe vehicle speed without overheating the brake pads.

In a Prius, the driver handles that condition by selecting "B" mode. This tells the Prius to attempt to emulate "engine braking" in a conventional vehicle. Depending on the vehicle's speed and the battery SOC (state of charge), the Prius will do this using regenerative braking and/or high-RPM zero-fuel-flow engine braking.

Engine braking is inefficient because it uses the engine as an air pump, converting kinetic energy into heat. Unnecessary regenerative braking is also inefficient because of energy conversion losses. (Regenerative braking is good when it replaces friction braking, but it's not as efficient as coasting at a constant speed.) Because of this, "B" mode will not recharge your batteries more efficiently than just braking and is not recommended for general driving. Just as you might downshift into 2nd gear when going down a long, steep hill to prevent brake damage, you can "downshift" into "B" mode on a Prius. "Shifting" is all electronic, so the system won't let you shift in a harmful way. (Even if you try to shift into reverse when moving quickly forward, you'll just end up in neutral.)

Thanks for the detailed explanation.  I'm going to talk to Toyota directly about the difference in regeneration between B and D modes.

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Re: Test Drive: 2014 Toyota Prius
« Reply #9 on: July 24, 2014, 03:09:31 pm »
The times I use the power mode is usually on the 401 in the GTA when you a fast response in the gas pedal
I Never use the EV mode, easier just to use the gas pedal to stay in EV mode

I believe your statement about the b mode is wrong
Here is a long draw out explanation

Using "B" Shift Position
The Prius uses an electronic transmission mode selector, similar to a gear shift on a conventional car. Unlike a conventional vehicle with modes P R N D 2 1 (park, reverse, neutral, drive, 2nd gear, 1st gear) the Prius has a power button, a park button, and a selector for modes R N D and B (reverse, neutral, drive, and engine-Braking).

In the course of normal driving, the driver NEVER needs to use 'B' mode (engine Brake mode). The techniques below are optional. 'B' mode is appropriate when descending long grades (i.e. descending down a mountain road), where if the driver uses the brake pedal to control the vehicle's speed, the vehicle's brake pads will overheat and fail.

In a normal vehicle, the driver handles that condition by slowing to an appropriate speed and shifting to a lower gear (2nd or 1st). This forces the vehicle to spin the engine faster than needed, "wasting" energy through vacuum losses but helping maintain a safe vehicle speed without overheating the brake pads.

In a Prius, the driver handles that condition by selecting "B" mode. This tells the Prius to attempt to emulate "engine braking" in a conventional vehicle. Depending on the vehicle's speed and the battery SOC (state of charge), the Prius will do this using regenerative braking and/or high-RPM zero-fuel-flow engine braking.

Engine braking is inefficient because it uses the engine as an air pump, converting kinetic energy into heat. Unnecessary regenerative braking is also inefficient because of energy conversion losses. (Regenerative braking is good when it replaces friction braking, but it's not as efficient as coasting at a constant speed.) Because of this, "B" mode will not recharge your batteries more efficiently than just braking and is not recommended for general driving. Just as you might downshift into 2nd gear when going down a long, steep hill to prevent brake damage, you can "downshift" into "B" mode on a Prius. "Shifting" is all electronic, so the system won't let you shift in a harmful way. (Even if you try to shift into reverse when moving quickly forward, you'll just end up in neutral.)

Thanks for the detailed explanation.  I'm going to talk to Toyota directly about the difference in regeneration between B and D modes.

What makes you think they will know lol
I also know what you mean about the temperature read out it sucks in that colour ,it makes me think of my first computer screen, before there was colour   :rofl2:

Offline ArticSteve

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Re: Test Drive: 2014 Toyota Prius
« Reply #10 on: July 24, 2014, 09:26:04 pm »
Thanks for the detailed explanation.  I'm going to talk to Toyota directly about the difference in regeneration between B and D modes.

http://techno-fandom.org/~hobbit/cars/b-mode.html

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Re: Test Drive: 2014 Toyota Prius
« Reply #11 on: July 24, 2014, 09:36:25 pm »
Thanks for the detailed explanation.  I'm going to talk to Toyota directly about the difference in regeneration between B and D modes.

http://techno-fandom.org/~hobbit/cars/b-mode.html
That is what I posted earlier

Offline ArticSteve

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Re: Test Drive: 2014 Toyota Prius
« Reply #12 on: July 24, 2014, 09:43:13 pm »
Last year?  :)


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Re: Test Drive: 2014 Toyota Prius
« Reply #13 on: July 24, 2014, 10:01:50 pm »

Offline ArticSteve

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Re: Test Drive: 2014 Toyota Prius
« Reply #14 on: July 24, 2014, 10:23:44 pm »
Last year?  :)
Probably. 
Post 2

Please don't tell me you and Rob have been doing the pipe.  ;D 

B-mode made clearer
There is a lot of mystery about the "B" shift selector position in the
Prius.  The official name for it -- Engine Braking -- should provide a
first hint as to what it is really for.  Page 137 in the '04 owners' manual
spells it out fairly clearly, in fact.  But somehow a whole body of mythology
about "more regeneration" and extra battery-charge magically appearing from
nowhere has sprung up since, and really needs to be permanently debunked.
In the smallest possible nutshell, "B" mode is designed to WASTE some energy
that the car cannot recover and store.  But to fully understand "B" mode one
must also take numerous other running conditions into account -- speed,
temperature, battery state of charge [SOC], brake pedal pressure, etc.

A preliminary to this was originally posted at Priuschat on Sep 20 2005,
but was subsequently lost in the Great Database Fire.  In recreating the
information, several other posts and bits of mail were pulled together and
rewritten.  This is long and detailed and hopefully not *too* technical,
but tries to cover everything known and verified about "B" mode.  It is
also worth reading Graham Davies' explanation, at

  http://prius.ecrostech.com/QandA/BMode.htm

A few basics must be understood up front:

   The job of "B" mode is to help stop the car, not to save or
   recover energy.  In fact, it largely throws energy away.

   The difference betwen "D" and "B" only appears during
   decelerative coasting [no pedals pressed at all] or actual
   braking.  When accelerating or just maintaining speed,
   "D" and "B" produce the same behavior.

   All shift positions, with the exception of "P", are simply
   electrical states within the control computers.  In "P", a
   locking pawl engages gear teeth to lock the front wheels
   against turning, but that's the ONLY mechanical change.

   Regenerative braking really has nothing to do with the
   physical wheel brakes on the car -- the regenerative and
   friction systems certainly cooperate closely, but they are
   separate systems.  "B" mode has nothing to do with the
   physical hydraulic brakes at all, other than that the two
   systems can combine forces to help slow the car.

Nonetheless, hydraulic braking, regeneration, and "B" mode are really all
parts of the *overall* braking functionality.  A good overview of the
braking systems in both the '04+ and earlier "classic" Prius is in the
technician-training material on hybrids available from Toyota's Techinfo
site, in section "T072 Chapter 6 Brake system" and in the file
ileaf/techtrg/techtpdf/techtrg/techtrg/cours/section6.pdf ...
which is mirrored temporarily at
  http://techno-fandom.org/~hobbit/cars/cours-section6.pdf for
reference.  It does not really explain "B" mode well either, and in fact
this document may be one of the sources of confusion -- where it says

   selecting "B" ... will maximize regenerative efficiency
   and is useful for controlling speeds downhill.  In "B"
   mode about 30% of the energy is recovered.

This is very misleading, because what it does *not* say is that in normal
"D" mode with proper braking technique, considerably *more* than 30% of
stopping energy is recovered!  I think they meant "30% of the possible
energy recovery" that would otherwise happen in "D" mode, but something
got lost in translation.

Going back to the original definition of "B" mode -- it takes energy to
turn a car engine that is otherwise not running.  Friction in bearings
and pistons and cams can be significant, as anyone who tries to turn
an engine by hand is aware.  But more significant is that it takes energy
to pump air through the engine -- without fuel and spark, an engine is
really nothing more than a big air compressor.  The amount of energy
needed to keep all that turning and pumping is what causes the "engine
drag" felt in conventional cars when the accelerator is released.  And
if the transmission is geared down, the drag effect is more pronounced
because the engine must then spin [i.e. be pulled around against air
and mechanical resistance] that much faster.

In the Prius, however, under most normal conditions when the accelerator is
released the engine shuts down entirely and leaves the car in electric-only
mode.  This would provide no engine-drag, so the Prius fakes a drag feeling
electrically by having the main electric motor-generator [MG2] generate some
current and thus present an energy load against the turning wheels.  Above
41 mph, the engine does still spin, but it is not fed any fuel or spark and
the valve-timing is changed so that the air-pumping loss through the engine
is minimized.  Electrical energy is still drawn from the wheels by MG2
regardless of the car's speed -- and the most useful place to send that
energy is to store it in the battery.  This is a regenerative stopping
force, but in "D" with no brake pedal applied it is a fairly weak force --
not one you could really consider as "braking".  It is not enough to prevent
the car going faster and faster down an appreciable hill, for example.
Regeneration current into the battery in this state is between 10 and 20
amps [out of a possible 100] depending somewhat on speed -- at 200 battery
volts that's still 2000 or 3000 watts or more, which is quite a bit of
energy from just gently resisting the car coasting along!

Gently applying the brake pedal increases that regeneration current, up to
a maximum of 100 amps -- 20 kilowatts -- and in the '04 and up Prius, does
not use the physical friction brakes at all until they are needed.  That's
like the motion of your car powering four electric dryers at once, and
it's *all* going into the battery pack!  But even 20 kilowatts cannot always
provide enough stopping power, especially at higher speeds, so anything over
and above that must be supplied by the friction brakes.  The rest of that
energy then gets wasted as heat in the rotors and pads.  But what if you're
driving down a long, steep mountainside?  Maybe that 20 kilowatts of
battery-charging energy is enough to hold your speed back -- for a while.
But eventually the battery gets full -- actually, to the 80% charged limit
enforced by the computers -- and to protect the system, charging current is
eventually reduced to zero, and the only thing now holding the car back
from disaster is the hydraulic brake system -- which is now rapidly getting
hotter and hotter and reaching its own limits on how well it can continue
stopping the car.  Brake fade, when the parts cannot absorb or dissipate
any more energy, is a very real problem on mountain roads.

Enter "B" mode.  As in, "trucks use lower gear".  By forcing the wheels
to spin the engine and pump air, a good deal of that energy can be turned
to heating the air going through the engine instead of heating the brake
parts.  Since fresh air is always coming into the engine, having it leave
as much warmer air provides a convenient place to dump excess energy.
In a conventional car the wheels push the engine around through the
transmission, but the Prius needs to help that process out a little bit
by actually having its combination of electric motors spin the engine.
In this case, the valve-timing in the Prius engine is advanced to increase
the amount of air taken in and the suction against the throttle flap -- which
uses much more energy than the coasting-in-"D" scenario above.  Either way,
stopping power now comes from a combination of things and the burden on the
friction brakes is greatly reduced, allowing the hill to be descended safely.

"B" mode also increases regeneration current to 30 - 40 amps with no feet on
the pedals, so the part about "more regeneration" is somewhat true.  That
is one of several mechanisms used to increase the "drag" feeling.  That
level also varies with the car's speed.  However, the car's movement is
often supplying much more energy than that, so what isn't captured in the
battery is wasted by flailing the engine around.  This is *not* more
efficient usage -- it is almost always better to gently brake in "D" for
maximum energy recapture, if you have room ahead to do it.  This is one of
the common misconceptions about "B" mode -- it does not create more energy
from nowhere, despite how much it may feel like traditional "gearing down"
and using the brakes less.  In fact, for those times when the rolling *car*
has too much energy for the battery, "B" helps get rid of it.  In addition,
using the brake pedal while in "B" mode behaves exactly the same as in
"D" -- if there's any capacity left in the battery, the system tries to
regenerate up to the same limit of 100 amps, above which the friction brakes
are brought in to help -- the only difference in "B" that the engine is also
spinning away against air pressure.  Again, the hydraulic brake system does
not care if you're in "D" or "B" -- it just supplies what the rest of the
systems cannot.

The only time the physical brakes are used *by preference* is during a
panic stop, when the pedal is suddenly slammed down.  The system senses
this fast rate of change and immediately brings in the hydraulic brakes
for faster and safer stopping with all four wheels.  "B" mode makes no
difference there, either.  And of course all regeneration quits at less
than 6 or 7 mph, when the motors aren't turning fast enough to provide
useful power -- the physical brakes handle the last part of stopping.
Many people can feel a sort of braking "sag" at the transition, although
Toyota has managed to make that fairly smooth and seamless.

If one thing must be understood here, it is the distinction between the
BRAKES and the total BRAKING SYSTEM.  The hydraulic friction brakes in each
wheel cannot supply energy -- they can only waste it, throwing it away as
heat to the air around them.  Parts of the braking SYSTEM -- that one could
consider as including the driveline and electric motors, the hybrid and
braking computers, the battery -- can work together to recover energy and
direct it around to where it needs to go.  But when someone naively says
"the brakes charge the battery", that's really rather wrong.

Now with all of that said, there are a few funny quirks and factoids to
know about "B" mode, none of which really help increase fuel efficiency
but are interesting to know about regardless.  In general, the amount of
extra resistance given by "B" mode is sort of staged upward depending on
the car's speed and how charged the battery is.  Some of these conditions
can be utilized in entertaining ways.

Under 20 mph, if the engine is not already running and your foot comes
off the accelerator, B mode simply regenerates reasonably heavily [30A or
so] into the battery.  This drops off around 12 mph to a lower current,
and is then similar to being in D until regen capability kicks out entirely
around 7 mph.  So between 19 and maybe 10 miles per hour, you can use "B"
to slow down in an energy-productive way, and essentially drive around in
electric-only mode with one pedal -- but be careful to not do something the
person behind you doesn't expect without showing brake lights!  As soon
as you crest 20 mph, however, the engine begins spinning -- to enable the
system to dissipate more energy at the higher speed.

If the engine is running and you come to a standstill while in "B" mode, the
engine *stays* running -- just idling.  The reason for this is not really
known, but it is a way to continue warming the engine when it's cold out and
you're stopped in traffic.  Driving around in "B" during warmup also tends
to charge the battery a little faster, since electric-only mode is avoided,
but again at the expense of burning more fuel to do it.  Engine start/stop
transitions are avoided.  Sometimes this state feels more surefooted and
responsive in snow and other tricky conditions.  People who have autocrossed
the Prius have recommended staying in "B" for better and quicker control --
having the driveline "fall on its face" the instant your foot comes off
the accelerator pedal may be desireable behavior at times.  This may feel
familiar to some EV drivers, where regeneration control all comes from
releasing the go-pedal in controllers without integrated braking features.

Fuel usage in "B" is somewhat mitigated by the fact that when decelerating
above some nominal speed, somewhere around 17 mph, no fuel is sent to the
engine and it just spins "dry".  It's still wasting energy and slowing the
car, but there's no reason to throw away gas along with that.  This is
sometimes called "fuel-starve" mode, and is also used in some conventional
cars during high-speed coasting conditions.

It is difficult to tell when that 100 amp battery-charge limit is exceeded
without extra instrumentation.  When the battery pack is cold, that limit
is actually lower -- down around 50 amps, until cabin heat begins to
circulate through the battery pack ventilation ducts and the pack self-
heats a little from being used.  The system is quite good at protecting
the battery against things like overcurrents, and sometimes that gets in
the way.  Slowing over bumps often confuses the regen mechanism, which can
sometimes be felt by the seat of the pants as that same little braking "sag"
right after the bump.  The system has given up on regen at that point, and
is now only collecting the "coasting" baseline 10 amps of battery current,
and using the physical brakes almost entirely to stop you.  Recovery from
this situation appears to be time-based, so your best bet at that point is
to slap it down into "B" for the duration of that stop since while you may
spin off some energy in the engine, regen current *will* be a bit heavier
than in your now pathological D-but-confused braking state and you might
recover a tiny bit more energy.  But don't get into the habit of using "B"
to slow down unless you really need it -- that's sometimes hard to get used
to if you come from ingrained years of "gearing down" in conventional cars.

Many strange things happen when the battery pack gets up to "eight green
bars" full level.  The hybrid system begins doing several things to pull
a little energy back out of the pack -- the engine will tend to spin in "D"
mode even at low-speed, low-demand conditions, in fact just about in the
same way as "B" mode does when the charge state is more normal.  If "B"
mode is selected in the full state during coasting, then the engine *really*
screams and even more energy is pumped away.  So while all the energy of a
long descent cannot be captured, speed can be controlled in some interesting
ways by creative shifting between "D" and "B" even after the pack is topped
out.  When the car is stopped, the engine may randomly start and stop several
times -- the theory is that the system is ridding itself of excess battery
charge to get it back within safe limits.  You only really get 600 watt-hours
full range to play with, which isn't a whole lot.   Still, the car really
goes out of its way to make sure there's plenty of stopping-power reserve
on tap if the driver needs it.  And there's no question that larger battery
packs would give a much wider range of energy-recovery -- possibly enough
to hold an entire mountain descent's worth.  Some of the extra-battery
experimenters have successfully done that, in fact.

It is said that the early Japanese "hypermilers" used B mode to gain fuel
efficiency.  There is no advantage to be achieved by this with the current
generation of Prius, but in the earliest Japanese models and the "Classic"
imported to the US for 2000-2003 the regenerative braking system is a bit
more crude and brings in the physical brakes much earlier in the game even
when they're not necessarily needed.  With higher-power-capable motors and
the reworked "by wire" brake system in the '04 and since, this is no longer
relevant since little or no pressure is sent to the wheel brakes until the
system has extracted as much regeneration as possible.  However, those early
and somewhat vague stories could be another source of myth and misinformation.

Help clear up some of the confusion about B mode.  Tell other owners [and
dealers!] who don't necessarily read this stuff why "B" is NOT saving
them any gas.


Offline X-Traction

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Re: Test Drive: 2014 Toyota Prius
« Reply #15 on: July 25, 2014, 02:06:37 am »
Last year?  :)
Probably. 
Post 2

Please don't tell me you and Rob have been doing the pipe.  ;D 

B-mode made clearer

(see above)
Great information.  The Ford Escape Hybrid has an "L" transmission position that equates the Prius' "B".

I used to use this to decelerate a lot, believing that slowing without using the brakes was a sign of driver skill and to avoid wasting energy lighting up the brake lights.  But now I know this is nonsense.  In "L" mode, the Escape Hybrid runs the engine in a no-fuel, elevated rpm mode to provide engine braking.  It does not provide any more energy regeneration than using the brakes in "D".  In fact, it wastes energy otherwise recaptured because of all those engine parts flailing around.

There are a couple of interesting aspects to this.  Vancouver has some paved roads that climb/descend so much vertical that they exceed the battery pack's storage capacity.  Such as the Cypress Bowl and Mt. Seymore roads.  After a few trips up and down them, I realized the battery was full within one quarter of the descents, and that keeping the speed under control after that, and in "D", was completely done by the mechanical brakes.  The solution was to use "L" almost all the way down.  Using "L" dissipated energy by running the engine, delaying the fillup of the hybrid battery.  In this mode, the engine uses no fuel, and resetting the mileage readout shows zero gas consumed on the descent.  The Cypress road, especially, has a few turns where power is needed.  I switch to "D" for these corners, and try to have the Escape in EV mode for as long as possible.  (It won't go into EV mode in "L".) This frees up capacity in the battery, so it's longer before the battery is again full to capacity and I have to use the brakes. This approach minimizes load on the mechanical brakes, while the battery is going to be full to capacity at the bottom anyway.  Where the Cypress road goes flat at the bottom, I can then use EV mode all the way to the onramp to the highway.

The second interesting matter is the mechanical brakes. In '08 or '09, Ford changed the Escape Hybrid's rear brakes from discs to drums.  This was universally seen as a dumb idea.  However, rear disc brakes also require small drum brakes to act as parking brakes, since disc brakes don't seem to work as parking brakes.

There are a lot of big hills in BC.  Some people tow trailers with Escape Hybrids.  Some people like me do 4000' descents creeping down rough old logging roads.  These descents quickly fill up the hybrid battery, and even if there is battery capacity, the speed in "L" is far to fast for the roughness of the roads.  As the discussion ArcticSteve posted, there is large potential to overheat the brakes and get into a runaway situation.  This may be why towing is discouraged for hybrids.

If you overheat a hybrid's mechanical brakes in this situation, the ONLY option left is the parking brake.  The larger standard drum brakes on the more recent Escape Hybrid will be more likely to save your bacon than the tiny parking drum brakes provided with rear disc brakes.  Not that this scenario is likely, but it's something to consider.

I should add that on such descents, the front discs warm up before the rear drums, and you can get down any hill using the brakes as long as you're going slow enough to allow the brakes time to dissipate heat.  It takes some experimenting before you learn how fast you can come down what steepness of hill with what load while keeping the brakes from overheating.  So far this has never been a problem at highway speeds because of air resistance.

Just another note about the article. It says the Prius sits at stops with the engine off, and starts the engine when you release the brake pedal.  Perhaps other Prius owners could confirm this.  The Escape Hybrid does not start the engine when the brake is released.  It waits until it can tell how much throttle you're applying, and starts the engine if necessary (which is most of the time). But you can go up surprisingly steep hills in EV mode from a stop, as long as the speed is low enough.
And some cretins think I hate cars.

Offline Ex-airbalancer

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Re: Test Drive: 2014 Toyota Prius
« Reply #16 on: July 25, 2014, 06:25:14 am »
Just another note about the article. It says the Prius sits at stops with the engine off, and starts the engine when you release the brake pedal.  Perhaps other Prius owners could confirm this.  The Escape Hybrid does not start the engine when the brake is released.  It waits until it can tell how much throttle you're applying, and starts the engine if necessary (which is most of the time)

This is also true in a Prius

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Re: Test Drive: 2014 Toyota Prius
« Reply #17 on: July 25, 2014, 08:31:58 am »
In the '07 Prius and in the '13 C, the ICE comes on when either the battery charge or the power demand calls for it.  Starting off or releasing the brake has nothing to do with it.

Cheers,
John M.


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Re: Test Drive: 2014 Toyota Prius
« Reply #18 on: July 25, 2014, 01:30:03 pm »
Few auto reviewers are familiar with the Toyota hybrid system.  Like anything, extended seat time is required.  :)

What's always missed by these ppl is the real nuts and bolts.  For example, the brakes' hydraulic system is artificially created via the brake accumulator which is first activated by the driver's door.  PPl stress about the battery replacement costs if it ever happens.  I stress about a broken brake accumulator.   :rofl2:

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Re: Test Drive: 2014 Toyota Prius
« Reply #19 on: July 25, 2014, 03:28:26 pm »
Last year?  :)
Probably. 
Post 2

Please don't tell me you and Rob have been doing the pipe.  ;D 

B-mode made clearer
There is a lot of mystery about the "B" shift selector position in the
Prius.  The official name for it -- Engine Braking -- should provide a
first hint as to what it is really for.  Page 137 in the '04 owners' manual
spells it out fairly clearly, in fact.  But somehow a whole body of mythology
about "more regeneration" and extra battery-charge magically appearing from
nowhere has sprung up since, and really needs to be permanently debunked.
In the smallest possible nutshell, "B" mode is designed to WASTE some energy
that the car cannot recover and store.  But to fully understand "B" mode one
must also take numerous other running conditions into account -- speed,
temperature, battery state of charge [SOC], brake pedal pressure, etc.

A preliminary to this was originally posted at Priuschat on Sep 20 2005,
but was subsequently lost in the Great Database Fire.  In recreating the
information, several other posts and bits of mail were pulled together and
rewritten.  This is long and detailed and hopefully not *too* technical,
but tries to cover everything known and verified about "B" mode.  It is
also worth reading Graham Davies' explanation, at

  http://prius.ecrostech.com/QandA/BMode.htm

A few basics must be understood up front:

   The job of "B" mode is to help stop the car, not to save or
   recover energy.  In fact, it largely throws energy away.

   The difference betwen "D" and "B" only appears during
   decelerative coasting [no pedals pressed at all] or actual
   braking.  When accelerating or just maintaining speed,
   "D" and "B" produce the same behavior.

   All shift positions, with the exception of "P", are simply
   electrical states within the control computers.  In "P", a
   locking pawl engages gear teeth to lock the front wheels
   against turning, but that's the ONLY mechanical change.

   Regenerative braking really has nothing to do with the
   physical wheel brakes on the car -- the regenerative and
   friction systems certainly cooperate closely, but they are
   separate systems.  "B" mode has nothing to do with the
   physical hydraulic brakes at all, other than that the two
   systems can combine forces to help slow the car.

Nonetheless, hydraulic braking, regeneration, and "B" mode are really all
parts of the *overall* braking functionality.  A good overview of the
braking systems in both the '04+ and earlier "classic" Prius is in the
technician-training material on hybrids available from Toyota's Techinfo
site, in section "T072 Chapter 6 Brake system" and in the file
ileaf/techtrg/techtpdf/techtrg/techtrg/cours/section6.pdf ...
which is mirrored temporarily at
  http://techno-fandom.org/~hobbit/cars/cours-section6.pdf for
reference.  It does not really explain "B" mode well either, and in fact
this document may be one of the sources of confusion -- where it says

   selecting "B" ... will maximize regenerative efficiency
   and is useful for controlling speeds downhill.  In "B"
   mode about 30% of the energy is recovered.

This is very misleading, because what it does *not* say is that in normal
"D" mode with proper braking technique, considerably *more* than 30% of
stopping energy is recovered!  I think they meant "30% of the possible
energy recovery" that would otherwise happen in "D" mode, but something
got lost in translation.

Going back to the original definition of "B" mode -- it takes energy to
turn a car engine that is otherwise not running.  Friction in bearings
and pistons and cams can be significant, as anyone who tries to turn
an engine by hand is aware.  But more significant is that it takes energy
to pump air through the engine -- without fuel and spark, an engine is
really nothing more than a big air compressor.  The amount of energy
needed to keep all that turning and pumping is what causes the "engine
drag" felt in conventional cars when the accelerator is released.  And
if the transmission is geared down, the drag effect is more pronounced
because the engine must then spin [i.e. be pulled around against air
and mechanical resistance] that much faster.

In the Prius, however, under most normal conditions when the accelerator is
released the engine shuts down entirely and leaves the car in electric-only
mode.  This would provide no engine-drag, so the Prius fakes a drag feeling
electrically by having the main electric motor-generator [MG2] generate some
current and thus present an energy load against the turning wheels.  Above
41 mph, the engine does still spin, but it is not fed any fuel or spark and
the valve-timing is changed so that the air-pumping loss through the engine
is minimized.  Electrical energy is still drawn from the wheels by MG2
regardless of the car's speed -- and the most useful place to send that
energy is to store it in the battery.  This is a regenerative stopping
force, but in "D" with no brake pedal applied it is a fairly weak force --
not one you could really consider as "braking".  It is not enough to prevent
the car going faster and faster down an appreciable hill, for example.
Regeneration current into the battery in this state is between 10 and 20
amps [out of a possible 100] depending somewhat on speed -- at 200 battery
volts that's still 2000 or 3000 watts or more, which is quite a bit of
energy from just gently resisting the car coasting along!

Gently applying the brake pedal increases that regeneration current, up to
a maximum of 100 amps -- 20 kilowatts -- and in the '04 and up Prius, does
not use the physical friction brakes at all until they are needed.  That's
like the motion of your car powering four electric dryers at once, and
it's *all* going into the battery pack!  But even 20 kilowatts cannot always
provide enough stopping power, especially at higher speeds, so anything over
and above that must be supplied by the friction brakes.  The rest of that
energy then gets wasted as heat in the rotors and pads.  But what if you're
driving down a long, steep mountainside?  Maybe that 20 kilowatts of
battery-charging energy is enough to hold your speed back -- for a while.
But eventually the battery gets full -- actually, to the 80% charged limit
enforced by the computers -- and to protect the system, charging current is
eventually reduced to zero, and the only thing now holding the car back
from disaster is the hydraulic brake system -- which is now rapidly getting
hotter and hotter and reaching its own limits on how well it can continue
stopping the car.  Brake fade, when the parts cannot absorb or dissipate
any more energy, is a very real problem on mountain roads.

Enter "B" mode.  As in, "trucks use lower gear".  By forcing the wheels
to spin the engine and pump air, a good deal of that energy can be turned
to heating the air going through the engine instead of heating the brake
parts.  Since fresh air is always coming into the engine, having it leave
as much warmer air provides a convenient place to dump excess energy.
In a conventional car the wheels push the engine around through the
transmission, but the Prius needs to help that process out a little bit
by actually having its combination of electric motors spin the engine.
In this case, the valve-timing in the Prius engine is advanced to increase
the amount of air taken in and the suction against the throttle flap -- which
uses much more energy than the coasting-in-"D" scenario above.  Either way,
stopping power now comes from a combination of things and the burden on the
friction brakes is greatly reduced, allowing the hill to be descended safely.

"B" mode also increases regeneration current to 30 - 40 amps with no feet on
the pedals, so the part about "more regeneration" is somewhat true.  That
is one of several mechanisms used to increase the "drag" feeling.  That
level also varies with the car's speed.  However, the car's movement is
often supplying much more energy than that, so what isn't captured in the
battery is wasted by flailing the engine around.  This is *not* more
efficient usage -- it is almost always better to gently brake in "D" for
maximum energy recapture, if you have room ahead to do it.  This is one of
the common misconceptions about "B" mode -- it does not create more energy
from nowhere, despite how much it may feel like traditional "gearing down"
and using the brakes less.  In fact, for those times when the rolling *car*
has too much energy for the battery, "B" helps get rid of it.  In addition,
using the brake pedal while in "B" mode behaves exactly the same as in
"D" -- if there's any capacity left in the battery, the system tries to
regenerate up to the same limit of 100 amps, above which the friction brakes
are brought in to help -- the only difference in "B" that the engine is also
spinning away against air pressure.  Again, the hydraulic brake system does
not care if you're in "D" or "B" -- it just supplies what the rest of the
systems cannot.

The only time the physical brakes are used *by preference* is during a
panic stop, when the pedal is suddenly slammed down.  The system senses
this fast rate of change and immediately brings in the hydraulic brakes
for faster and safer stopping with all four wheels.  "B" mode makes no
difference there, either.  And of course all regeneration quits at less
than 6 or 7 mph, when the motors aren't turning fast enough to provide
useful power -- the physical brakes handle the last part of stopping.
Many people can feel a sort of braking "sag" at the transition, although
Toyota has managed to make that fairly smooth and seamless.

If one thing must be understood here, it is the distinction between the
BRAKES and the total BRAKING SYSTEM.  The hydraulic friction brakes in each
wheel cannot supply energy -- they can only waste it, throwing it away as
heat to the air around them.  Parts of the braking SYSTEM -- that one could
consider as including the driveline and electric motors, the hybrid and
braking computers, the battery -- can work together to recover energy and
direct it around to where it needs to go.  But when someone naively says
"the brakes charge the battery", that's really rather wrong.

Now with all of that said, there are a few funny quirks and factoids to
know about "B" mode, none of which really help increase fuel efficiency
but are interesting to know about regardless.  In general, the amount of
extra resistance given by "B" mode is sort of staged upward depending on
the car's speed and how charged the battery is.  Some of these conditions
can be utilized in entertaining ways.

Under 20 mph, if the engine is not already running and your foot comes
off the accelerator, B mode simply regenerates reasonably heavily [30A or
so] into the battery.  This drops off around 12 mph to a lower current,
and is then similar to being in D until regen capability kicks out entirely
around 7 mph.  So between 19 and maybe 10 miles per hour, you can use "B"
to slow down in an energy-productive way, and essentially drive around in
electric-only mode with one pedal -- but be careful to not do something the
person behind you doesn't expect without showing brake lights!  As soon
as you crest 20 mph, however, the engine begins spinning -- to enable the
system to dissipate more energy at the higher speed.

If the engine is running and you come to a standstill while in "B" mode, the
engine *stays* running -- just idling.  The reason for this is not really
known, but it is a way to continue warming the engine when it's cold out and
you're stopped in traffic.  Driving around in "B" during warmup also tends
to charge the battery a little faster, since electric-only mode is avoided,
but again at the expense of burning more fuel to do it.  Engine start/stop
transitions are avoided.  Sometimes this state feels more surefooted and
responsive in snow and other tricky conditions.  People who have autocrossed
the Prius have recommended staying in "B" for better and quicker control --
having the driveline "fall on its face" the instant your foot comes off
the accelerator pedal may be desireable behavior at times.  This may feel
familiar to some EV drivers, where regeneration control all comes from
releasing the go-pedal in controllers without integrated braking features.

Fuel usage in "B" is somewhat mitigated by the fact that when decelerating
above some nominal speed, somewhere around 17 mph, no fuel is sent to the
engine and it just spins "dry".  It's still wasting energy and slowing the
car, but there's no reason to throw away gas along with that.  This is
sometimes called "fuel-starve" mode, and is also used in some conventional
cars during high-speed coasting conditions.

It is difficult to tell when that 100 amp battery-charge limit is exceeded
without extra instrumentation.  When the battery pack is cold, that limit
is actually lower -- down around 50 amps, until cabin heat begins to
circulate through the battery pack ventilation ducts and the pack self-
heats a little from being used.  The system is quite good at protecting
the battery against things like overcurrents, and sometimes that gets in
the way.  Slowing over bumps often confuses the regen mechanism, which can
sometimes be felt by the seat of the pants as that same little braking "sag"
right after the bump.  The system has given up on regen at that point, and
is now only collecting the "coasting" baseline 10 amps of battery current,
and using the physical brakes almost entirely to stop you.  Recovery from
this situation appears to be time-based, so your best bet at that point is
to slap it down into "B" for the duration of that stop since while you may
spin off some energy in the engine, regen current *will* be a bit heavier
than in your now pathological D-but-confused braking state and you might
recover a tiny bit more energy.  But don't get into the habit of using "B"
to slow down unless you really need it -- that's sometimes hard to get used
to if you come from ingrained years of "gearing down" in conventional cars.

Many strange things happen when the battery pack gets up to "eight green
bars" full level.  The hybrid system begins doing several things to pull
a little energy back out of the pack -- the engine will tend to spin in "D"
mode even at low-speed, low-demand conditions, in fact just about in the
same way as "B" mode does when the charge state is more normal.  If "B"
mode is selected in the full state during coasting, then the engine *really*
screams and even more energy is pumped away.  So while all the energy of a
long descent cannot be captured, speed can be controlled in some interesting
ways by creative shifting between "D" and "B" even after the pack is topped
out.  When the car is stopped, the engine may randomly start and stop several
times -- the theory is that the system is ridding itself of excess battery
charge to get it back within safe limits.  You only really get 600 watt-hours
full range to play with, which isn't a whole lot.   Still, the car really
goes out of its way to make sure there's plenty of stopping-power reserve
on tap if the driver needs it.  And there's no question that larger battery
packs would give a much wider range of energy-recovery -- possibly enough
to hold an entire mountain descent's worth.  Some of the extra-battery
experimenters have successfully done that, in fact.

It is said that the early Japanese "hypermilers" used B mode to gain fuel
efficiency.  There is no advantage to be achieved by this with the current
generation of Prius, but in the earliest Japanese models and the "Classic"
imported to the US for 2000-2003 the regenerative braking system is a bit
more crude and brings in the physical brakes much earlier in the game even
when they're not necessarily needed.  With higher-power-capable motors and
the reworked "by wire" brake system in the '04 and since, this is no longer
relevant since little or no pressure is sent to the wheel brakes until the
system has extracted as much regeneration as possible.  However, those early
and somewhat vague stories could be another source of myth and misinformation.

Help clear up some of the confusion about B mode.  Tell other owners [and
dealers!] who don't necessarily read this stuff why "B" is NOT saving
them any gas.


Steve , can you give the Colesnote Version  :rofl: