transmission "B"

Welcome to PC fikey,

OMG! It never ceases to amaze me how little correct information comes out of some dealer's mouths. If you want correct answers to your questions forget the dealer - ask them here.

#1 "B" is for engine braking on steep hills, the purpose being so you don't ride your brakes all the way down overheating them.

#2 There is no regen going on while in "B" mode, thus a decrease in mileage.

#3 The friction brakes are only used at speeds of less than 7 mph - there is no need to "save on the brakes".

So the answer to the cruise control to "B" is a "don't bother with "B" anyway.

One point I might add is that you may get better mileage not using cruise control, especially if you're driving hills, since cruise control cannot predict when you are coming up to a hill. If you keep a steady pressure on the gas pedal, or just increase it slightly, you will slowly lose speed going up the hill, but on the down side you can take advantage of a good glide and your speed will increase back to or even more than where you started.

Read this from a very knowledgeable senior PC member:

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

This article explains it well. In the meantime just have fun driving your new car - it knows how to take care of itself very well.

 

I agree, use B only on LONG down hill runs. You really don't need to use it at all, use gentle brake pedal pressure to maintain speed, that will increase regen recharging. When the battery is 80% full (as full as the computer will let it get) the computer will use excess energy turning the petrol engine with one of the 2 electric motors while the other keeps generating electricity.

Selecting B uses the petrol engine in the same way so the computer looks after it all.

I think you need to experiment yourself with cruise control, I find using cruise even in metropolitan traffic, I get slightly better consumption. I think because I have a lead foot so on cruise I travel a little slower, like at the speed limit.

When you are coming to an exit ramp, try to disengage cruise control soon enough that you don't need to use the brakes to slow down to exit.

In trying to get good economy I believe the brake pedal is your biggest enemy, drive to avoid using it but if you have to use it, use it early and soft and long. Racing up to red lights and stop signs is the biggest killer of economy.

I find acceleration rates are less critical up to about half throttle, more right foot than half will bump up consumption some.

Experiment and work out what works for you, there is tons of good information on this site.

 

I hate to disagree with my fellow Baystater (Neicy), but I'm pretty sure there is regen that goes on when the car is in "B" mode. However, I believe it is less efficient regeneration than you get if you just step on the brake.

The B mode is meant to simulate downshifting in a more conventional car; it uses the engine to slow down the car so that you don't overheat the brakes. However, since the Prius uses regen braking until the battery is full, there's way less use of the friction brakes when you're going down a hill. So, most people (especially on the East Coast of the US) will quite literally NEVER need to use B mode. Some examples where using B mode might be useful include driving down Mt. Washington or driving in parts of the Rocky Mountains. It's probably unnecessary (and less efficient) to use B mode in any other situation. Moreover, you may not need to use B mode even in those situations!

So, don't worry about it too much. If you ever downshifted in a previous car, then you could consider using B mode there. However, since the Prius uses the friction brakes way less than a normal car, you probably don't need to worry about it except in the most extreme downshifting conditions.

 

<div class='quotetop'>QUOTE(Neicy @ Oct 13 2007, 06:49 AM) [snapback]525044[/snapback]</div>

Not true. B mode does include regenerative braking, until the battery becomes as full as it can.

<div class='quotetop'>QUOTE(Neicy @ Oct 13 2007, 06:49 AM) [snapback]525044[/snapback]</div>

Unless you apply the brakes at high speed, in cases of "panic braking" - in fact, even braking out of cruise control mode at high speed can get the hydraulic brake system engaged.

 

I can just hear the dealers, "Come to us with your questions. We just can't believe all the inconsistent answers given on PriusChat!"

PA P

 

Thank you Betelgeuse and JimboJones for correcting me. That is what makes this board so great - there is always someone who can correct misinformation. I always learn something new here.

 

Living where you do, you have some opportunity to use "B", unlike us flatlanders. But it's a waste of gas to use it at stop lights and off ramps and the like. Save it for the mountains to avoid riding the brake.

 

Hi !

thanks for all the great posts on this thread.. I have been also being using the "B" setting often.. and I noticed that the Engine does not shutoff when the car is stopped while still in "B".

Could somebody also enlighten me on the "N" setting.. I am used to driving a stick shift, and it feels funny the car lurches forward, soon as I let go off the brakes feels a little annoying.. so I usually put the transmission in "N' position, whenever the car is stopped at a stoplight..

Will this have any effect on the transmission ?

TIA

-PB

 

<div class='quotetop'>QUOTE(pbsriniv @ Oct 30 2007, 01:49 AM) [snapback]532323[/snapback]</div>

No, using N will not hurt the transmission, but the Prius can't charge the battery when it is in N. Leave it in D and keep your foot on the brake, or press the Park button. Either of those will allow the battery to charge without wasting energy. The Prius transmission is unlike any other: It's not a normal automatic, and it's not a manual.

Tom

 

First, we all have to remember there is no "transmission" with movable gears in the Prius. What the "shifting" between "D", "N", "B", and "R" does is tell the computers to operate the various components a certain way.

"D" is "drive". The system operates "normally", giving "creep" while stopped if you release the brake pedal (artificially generated to simulate automatic transmission creep), drag while moving if you release the gas pedal, simulating engine drag, and using both the ICE and electric components as appropriate while controlling the RPM of all components to prevent damage while you drive. Forward motion. The system will also not allow the car to roll backwards while in "D". At least as much as it can.

"N" is "neutral". Battery charging from the ICE is disabled while in "N". Use in car washes or when you want to push the car for some reason. Don't leave the car in "N" for extended periods, particularly in hot weather with the A/C on, as you will drain the HV battery, though again, the car will protect itself from damage (will not allow the battery to be discharged too far). "N" also allows you to control the ICE - you can force it to stay on or off while in "N" - just shift to "N" when the ICE is in the state you want and it will stay in that state. It is very difficult to have "N" engaged while the car is "off".

"B" is intended to enhance drag on the car by the power components. If you drive in the mountains you will notice the car will gain speed much more easily on downhill portions of the road than most other cars. This is due to the lack of mechanical drag and the low Cd. So the engineers included "B" for use while descending long hills for example. It uses the engine to enhance drag and changes the settings re regenerative braking to give more of it. Note that regenerative braking will cease once the HV battery is fully charged (80%) and you will be relying on engine braking only. Unless you use the brake pedal, in which case friction braking will be used to enhance drag. You can easily tell when this happens, as you can feel the "loss of drag" and hear the engine RPM increase to compensate. It happens in just a few seconds once "full charge" is reached. Note that when in this mode, if you depress the accelerator pedal the engine speed will -decrease-. Very odd. But normal.

"R" is used to reverse the car. There is no "reverse gear" in the Prius, so they drive the electric motor in reverse. The ICE may or may not run while in "R". It does not provide mechanical power to reverse motion, though it -may- generate electrical power (not sure about this point). At any rate, while in "R" the Prius power is limited (electric motor only), so you may find a steep enough hill that the car cannot climb in "R".

I can't see any way you or I or anyone else could "damage" the car by operating the "transmission selection lever" in an inappropriate manner. The internal computers control what is happening, not you or I. The position of the lever is just a "request" to the computers.

 

I love this website for all the information that is available! It should mandatory for all dealers to inform customers who buy Hybrids from Toyota of the priuschat.com address and get people to sign something proving they informed the customer. It would really stop a lot of angst while learning the car!