A lot of people wonder what the deal is with the "B" position on the shifter of the 2004 Toyota Prius (and most other Toyota Hybrids). Some people figure that B increases the level of regenerative braking and plows more juice into the battery.
Not so fast. Turns out the opposite is true.
Compared to coasting in plain-old D, engine speed goes up in B to provide more genuine engine braking. RPMs increase in this mode, just as they would if you had downshifted a regular transmission, with the drag coming from the engine pumping air through itself while the fuel injectors sit dormant. But the Prius planetary transmission's gear ratio regulating element, electric motor-generator MG1, has to expend some battery energy to command the engine's crankshaft speed up to create this extra drag.
It gets worse. Engine braking represents a lost opportunity for the electrical regenerative braking system, the system by which all hybrids collect most (and in some cases all) of the electricity that makes them hybrids in the first place. The mechanical engine pumping losses that are engine braking could and should be avoided so they can go through the regenerative path to the battery instead. But the use of B robs the charging system of this chance and, ultimately, robs your wallet in the form of lost mpg.
In a regular car it would be madness to tell someone they should use the brakes to slow the car when going downhill, but here in the Prius, a so-called "strong" hybrid with sizable electric motors, that's oftentimes better for efficiency and no serious threat to the integrity of your regular friction brakes.
That's because the regenerative braking system in a strong hybrid can develop a significant amount of slowing by using the electric motor as a generator. In the 2010 and 2011 Gen 3 Toyota Prius, for example, the regen system can produce decelerations of up to 0.6g. Our somewhat less-efficient Gen 2 Prius (rated at 46 mpg combined instead of 50 mpg for the Gen 3) doesn't do quite as well in this regard, but the regen braking effect it can produce is still significant.
Need perspective? Most normal stops are made at 0.2 to 0.3g. Impatient folk stop at 0.4g or so. You might touch 0.6g if you get surprised by a yellow light. Unless your license has several points on it, over 90% of your braking occurs below 0.6g.
Unless the grade is very steep or very long, the foot braking mode you'll be in on a downgrade will be an electronic one, with your battery as benefactor. Your brake pads and rotors can't overheat if they're not being asked to do much.
Fun fact: our 2004 Prius has over 85,000 miles on the clock. The original brake pads still have some meat left and the rotors still look good and run true. That's regenerative braking for you.
But you can overdo it. The battery in a Prius can only hold so much, and a long grade can top it fully, at which time the computer begins to rely more heavily on the friction brakes. Keep one eye on your battery monitor and shift into B if there's still grade remaining when the gauge reads full.
Of course fully electric cars have no possibility of engine braking, so this B mode discussion is a moot point. But their batteries and electric motors are so large that they can soak up just about everything the longest grade can throw at them.
Dan Edmunds, Director of Vehicle Testing @ 85,354 miles
konocar400h says:
08:13 AM, 10/19/10
While most of this article is true, I know for a fact that the "B" position in my hybrid (RX400h) does increase the regenerative braking. If you shift into B down a hill and look at the battery meter, it sinks down into regenerative mode. Its quite effective, too.
I have never experienced the ICE "engine braking" from shifting to B. Actually, I don't think I've ever experienced engine braking in that vehicle.
Could the Prius be different? Is this post just from experience or is there a source?
questionlp says:
09:18 AM, 10/19/10
The RX400h uses a slightly different setup than the Prius, which is documented fairly well on Wikipedia:
http://en.wikipedia.org/wiki/Lexus_RX_%28XU30%29
http://en.wikipedia.org/wiki/Lexus_Hybrid_Drive
Also noted on the second page is an explanation of the "B" selection:
"The HSD system has a special transmission setting labelled 'B' (for Brake), that takes the place of a conventional automatic transmission's 'L' setting, providing engine braking on hills. This can be manually selected in place of regenerative braking. During braking when the battery is approaching potentially damaging high charge levels, the electronic control system automatically switches to conventional compression braking, drawing power from MG2 and shunting it to MG1, speeding the engine with throttle closed to absorb energy and decelerate the vehicle."
bodyblue says:
09:27 AM, 10/19/10
"Fun fact: our 2004 Prius has over 85,000 miles on the clock. The original brake pads still have some meat left and the rotors still look good and run true. That's regenerative braking for you. "
But yet some fools continue the myth of "higher cost of ownership" BS. Our Prius has 78,000 on it and still has a lot of brake pad left. Our Prius has been dirt cheap to own, period. Not ONE problem so far so we have spent money on one set of tires and oil changes etc. And with an average of almost 50 MPG. How can anyone complain about that?
konocar400h says:
09:36 AM, 10/19/10
Thank you Question LP! Didn't know they were different. And bodyblue, you are absolutely right for the lower cost of ownership for a hybrid. I've been so pleasantly surprised over the course of 98k miles that I will probably purchase another.
nelsonlu says:
10:02 AM, 10/19/10
I think I observe the same phenomenon on my Ford Fusion Hybrid (which uses "L"). For most downhill drives, the regenerative braking is quite sufficient to slow the car down without going into "L." Another Fusion Hybrid owner recommended going into L if and only if the battery was already full.
lostboyz says:
10:41 AM, 10/19/10
good then will you ask your congressmen to get rid of the tax rebate on them since they are obviously worth so much.
bodyblue says:
11:49 AM, 10/19/10
"good then will you ask your congressmen to get rid of the tax rebate on them since they are obviously worth so much."
I believe that is over for the Prius. Just think how much fuel I am saving for the monster SUV drivers! By keeping demand down for fuel I am helping keeping prices down! If there werent so many hybrid drivers on the road the price of gas would be higher.
And you are welcome.
seppoboy says:
11:55 AM, 10/19/10
I have a 2006 VW Jetta TDI with 125,000 highly reliable miles, and I still have the original brake pads. I've never had a car before that didn't require replacing pads several times and rotors at least once before the 100k mile mark. So diesels also spare the brakes with their high compression ratio and resulting engine braking. I do a lot of mountain driving, too, and 45 mpg. And unlike the Prius drivers, I can actually feel the road through the steering wheel, so for me this is a much better deal than a hybrid Toyota.
How many typical Prius owners know or care about how their transmission shifter control affects the operation of their vehicle?
questionlp says:
12:26 PM, 10/19/10
"How many typical drives know or care about how their transmission shifter control affects the operation of their vehicle?"
TFTFY. If more people knew what compression or engine braking meant and didn't jab at their brake pedals at any hint of slowdown, commuting and traffic would be a touch better.
lostboyz says:
12:52 PM, 10/19/10
@bodyblue, thank you for supporting strip mining and shipping your battery materials around the world. Getting better gas mileage has nothing to do with how much fuel you actually use. You are comparing two things with different units. I wouldn't expect a hybrid owner to actually know these kinds of things though.
cello_one says:
01:09 PM, 10/19/10
Until there is a definitive tech agreed upon for lowering emissions the battles will continue...
firstwagon says:
01:26 PM, 10/19/10
"@bodyblue, thank you for supporting strip mining and shipping your battery materials around the world. Getting better gas mileage has nothing to do with how much fuel you actually use. You are comparing two things with different units. I wouldn't expect a hybrid owner to actually know these kinds of things though."
So what part of the battery comes from strip mining? (and before you say nickle it's deep mined, not stripped mined). Are you as concerned with other things shipped around the world too? Check where most of the stuff in you house is made and get back to us on that.
Most of the evil of Prius batteries you read on the internet is BS but the fact it uses half the fuel of the average mid size car is true.... and that's a savings you see every day.
stwok says:
01:42 PM, 10/19/10
Thanks for the post Dan, I've always wondered what that was but never RTFM.
konocar400h says:
03:12 PM, 10/19/10
+1 firstwagon,
That is a myth that hopefully will be dispelled in the future.
lostboyz says:
03:40 PM, 10/19/10
Its an offset energy savings, and without the tax rebate you don't save any money either. So the end consumer sees a lot of the benefit, in the whole scheme of being 'green' it is by no means a solution.
bodyblue says:
05:32 PM, 10/19/10
"Getting better gas mileage has nothing to do with how much fuel you actually use."
HUH?? Lets see......I went 50 miles and used 1 gallon of fuel. Then I got in my Dodge and went 50 miles and used 2 gallons of fuel to do so........BUT according to your logic I did not use less fuel?
Now I understand the "lost" in lostboyz
bodyblue says:
05:38 PM, 10/19/10
"and without the tax rebate you don't save any money either"
You are indeed completely without a clue as to what you are talking about. A new Prius costs around 24k.....it is pretty well equipped. It gets 50 MPG.....now a Taurus costs about the same and gets 30 on the highway...or a Malibu that gets 25 in town.....
There is no tax rebate I could find. Please tell me you dont save money with a hybrid? When compared to any well equipped midsize car the cost of ownership is less.
wjtinatl says:
07:33 PM, 10/19/10
Wow, brake pad & rotor technology has really improved this decade. My 2004 Navigator went 91k on the original pads before I got nervous and had them replaced. I admit the Prius has me beat on gas mileage however.
stovt001 says:
08:33 PM, 10/19/10
@ bodyblue, firstwagon, and konocar400h:
http://www.leftlanenews.com/study-prius-production-harmful-to-environment.html
And that is from Toyota's own admittance.
And on the issue of cost benefits:
http://www.insideline.com/honda/fit/2008/comparison-test-2008-honda-fit-vs-2008-toyota-prius.html
lostboyz says:
04:25 AM, 10/20/10
@bodyblue, if you have a very fuel efficient car you might be more inclined to drive more, if you have a big SUV you might not drive as much especially when gas prices are high. Fuel rate only correlates to fuel when you determine how much you drive. If you have an 80 mile commute to work in a prius, and I have a 5 mile drive and I drive a big truck, I will use less fuel than you. If they should give tax rebates to anyone its people who work close to home.
wyounger says:
06:00 AM, 10/20/10
The tax credits are mostly gone already- there was a quota per manufacturer- and the last of them expire at the end of 2010. As for those that resent the credits, just consider them a refund on the national defense cost not incurred by being less dependent on foreign oil. Toyota sold the most hybrids, so they used up their quota first, and Toyotas purchased after 9/30/2007 did not get credits. I bought a Prius, despite the lifeless steering, as much because it was the right thing for national security as for actual environmental concern. I don't like buying oil from terrorists.
A gently driven 2004-09 Prius uses its friction brakes so little that rust on the drum surfaces can actually cause minor driveability issues in damp weather- the rear brakes get grabby during the transition from regenerative to friction braking when coming to a stop. When I notice this problem, I either make one hard stop or one gentle stop in Neutral (so no regen braking) to rub off the rust.
P.S. Diesels are getting tax credits too. http://www.fueleconomy.gov/feg/taxLeanburn.shtml
lostboyz says:
06:11 AM, 10/20/10
so you think you drive a hybrid that will somehow stop the war in the middle east?
you aren't saving anything, the prius a smug machine
another article on the 'dirty' prius
http://www.autonews.com/apps/pbcs.dll/article?AID=/20101018/OEM01/310189979
bodyblue says:
07:29 AM, 10/20/10
"http://www.insideline.com/honda/fit/2008/comparison-test-2008-honda-fit-vs-2008-toyota-prius.html"
Nice try.....they compared a Base Fit with roll up windows. That test was hardly fair. And it was two years ago. The Fit has a 98in wheelbase and the Prius has a 106....hardly the same class of car. What I am saying is that when compared apples to apples hybrids are now cheaper to own because of the falling prices.
A 2011 Civic LX with auto is $19305 and a Prius ll is $23560 Hardly the 8k difference........Hell an Insight is only 20K.
Two years is a long time nowdays......so you will have to find another line of reasoning to hate Hybrids....
"so you think you drive a hybrid that will somehow stop the war in the middle east?
you aren't saving anything, the prius a smug machine"
LOL you are so out of your league. Did you actually read the article??
"But it was slightly worse than average in emissions of nonmethane hydrocarbons and particulate matter."
WOW SLIGHTLY worse.....and how much less foreign oil will we need if we used less?
Just give it up.....We can tell you hate hybrids and like most other folks there is no rational reason to do so.
lostboyz says:
07:56 AM, 10/20/10
I don't hate hybrids, by the numbers they are not greener and they are not the cost savings they are made out to be. By the time you do save a lot of money in 7-10 years, you have to replace the battery. You are paying someone else to pollute for you.
wyounger says:
09:48 AM, 10/20/10
I don't think driving a Prius will stop the war- by no means is it that simple. But the country's addiction to oil is related, and the fact that a single step alone won't magically fix things doesn't absolve my conscience of any interest in trying to do something about the problem. It's a first step.
As for smug, is it me that's smug or you that's feeling guilty? I don't tell anybody what they should do. I make my own decisions based on my own personal needs (hatchback), wants (gadgets), and yes, a little conscience. Is that smug?
If so you're REALLY gonna hate me when I buy an electric car and stop buying oil completely.
wyounger says:
10:01 AM, 10/20/10
Oh, and almost no Priuses have undergone battery replacement. The only one I've heard of is at 320k miles. It's the Honda hybrids that are having battery problems, not Toyotas.
As for paying someone else to pollute, like the Chinese nickel mine or (for a future electric car) the American coal mine or the American power plant, they don't hate us, they don't blow up our landmark buildings. Same as with ethanol- it may or may not be environmentally preferable to oil, but I prefer to pay an American farmer to pollute American rivers with fertilizer and pesticides used to grow American corn for ethanol than to pay hostile nations to send us oil (with its well-documented but perhaps no worse environmental consequences). It's better for the American economy and better for our national security interests. I am personally willing to pay a little extra for those things, even if it's no better environmentally. So whether it's cheaper for me personally or not isn't a make or break issue.
As for the Prius and its notoriously smug image, find me a smooth-riding, quiet Honda Fit with bluetooth, keyless operation, and stability control. In 2006. The non-hybrid competition wasn't the same thing minus the hybrid, they didn't really have a comparable package. Even now there isn't really a direct non-hybrid competitor; only the Insight is really similar, and it still doesn't compete on ride, noise, or gadgets.
firstwagon says:
10:47 AM, 10/20/10
"As for paying someone else to pollute, like the Chinese nickel mine or (for a future electric car) the American coal mine or the American power plant, they don't hate us, they don't blow up our landmark buildings."
Ummm, hate to bring this up... don't want to get in the way of the need to hate those that are different but the Taliban is not an oil producing nation. They are not a nation at all. It's just a group of extremists who also hate those that are diferent.
Saudi Arabia did not attack the US. Neither did Iraq for that matter.
I'm all for reducing oil usage but lets not start rewriting history so quickly.
lostboyz says:
02:22 PM, 10/20/10
@wyounger
you know what I did to use less fuel? I moved closer to work. I probably saved a lot more than you did by buying a hybrid.
Between turbo diesels and the higher and higher efficiency inline 4 cylinders, no a hybrid is not worth the extra weight and complexity. It really isn't a step in the right direction, its just different.
Also, I don't know if its racism or ignorance that makes you think that everyone in the middle east both produces oil and supports terrorism.
cocojoe53 says:
08:55 PM, 12/18/10
Really now....I Have a Mustang Bullitt and a Prius. The Prius is my daliy driver. It averages over 50 mpg. I don't care what Toyota had to pollute to build it. It saves me Money. Who cares how much it weighs. As far as complexity, Toyota Prius is about as dependable as you can get. I bought mine from the largest dealer in the State. They have NEVER had to replace a critical component of any Prius they have sold through all 3 generations...