Geeks With Blogs

News
Jason Coyne Jason Coyne's blog

A reader Shawn asks :

Hi, My mother just bought a new Camry '07 as well and we both had a question and we cant seem to find an answer anywhere. We were wondering what the differnce is in the gears on the shifter, like what is different about using "D" vs. "B" like what is differnt about them and when should we use them?

The Short Answer : Use the B mode when you are driving downhill for long distances (like down a mountain for more than 30 minutes). The “B“ mode is NOT a lower gear, like you would use for more traction, or towing or something like that. At almost all times you should be in “D“ mode.

The Long Answer :

A normal car has multiple gears, and as you shift (either manually or on automatic) the gears are swapped out, and the gearing ratio changed, to provide efficiency and torque at different speeds.

A CVT (Continually Variable Transmission) has an effective infinite number of gears, and using a complicated system of belts and pulleys will give you any arbitrary gearing ratio.

The Prius and Camry use the “Hybrid Synergy Drive”, which is often considered a CVT, but it really isn't. The Prius and Camry only have one gear. As more power is needed, the gear spins faster. But the gearing ratio never changes. However, Power is split from this gear to either to drive the car, or charge the battery system. The ratio of power to wheels vs battery is dynamic, and so the car acts like a CVT most of the time.

One of the tricks used by the Hybrid drive to get maximum efficiency, is changing the timing on the engine. When you are coasting, The engine is still turning over, even though no (or minimal) gas is being used. The car changes the timing of the air intakes on the pistons. This is done so you aren't pushing around a lot of air, which makes the car more efficient.

The braking system in the hybrid is also different. The hybrids have a smaller, less powerful set of brakes than would be typical for a car of their size and weight. This is because the hybrid uses regenerative braking to charge the battery, which added to the normal brake system provides all the braking you need.

Now that we have the background, the actual answer!

When you are driving down a mountain, you have the brakes on constantly. In the hybrid system, eventually the battery will get full, which means you are using just the normal brake pads. As the brake pads heat up from the friction, eventually you get to a point of brake failure (brake fade), where they cannot absorb any more heat. This can happen in a normal car too, but its easier to do in the hybrid because of the smaller brakes.

So just like the car can be more efficient by changing how the engine works, it can also be LESS efficient. When you go into B mode, it stars opening the air intake valves at the least efficient time. This causes the engine to push around a lot of air, which uses up energy, and helps slow you down, taking work off of the brakes. I believe the system also starts using the electic motor and gas motor at inefficient times, to try and keep a buffer in the battery system to absorb power.

So essentially, you should ignore B mode, unless you are driving down a mountain. It is not used for towing, snow, up hills, or any other time when you would use the low gear in a normal car.

Here is another article that goes into depth on the B mode, and may explain it better than I have http://techno-fandom.org/~hobbit/cars/b-mode.html

More info on how the Hybrid Synergy Drive works is at Wikipedia : http://en.wikipedia.org/wiki/Hybrid_Synergy_Drive

 

Posted on Thursday, October 12, 2006 5:47 AM gadgets | Back to top


Comments on this post: What is the difference between D mode and B mode on the Toyota Camry Hybrid and Toyota Prius?

# re: What is the difference between D mode and B mode on the Toyota Camry Hybrid and Toyota Prius?
Requesting Gravatar...
b is for engine braking.going down hills.engine braking will help slow the car down with out using the brakes
Left by tim silva on Mar 25, 2007 1:57 PM

# re: What is the difference between D mode and B mode on the Toyota Camry Hybrid and Toyota Prius?
Requesting Gravatar...
One update :

B mode may be useful for breaking in the winter, on icy roads, because it slows the car down by using up kinetic energy, not by friction breaking. Therefore a combination of b mode + regular breaking may lead to faster breaking on ice, without as many slides.
Left by Jason Coyne on Apr 03, 2007 8:30 AM

# re: What is the difference between D mode and B mode on the Toyota Camry Hybrid and Toyota Prius?
Requesting Gravatar...
Wow! I didn't know that and honestly I wasn't interested. I own a Toyota Camry hybrid and I don't any problem with it. I don't need B mode because in my region is not snowing and other things.
Left by cheap car insurance on Mar 25, 2011 7:34 AM

# re: What is the difference between D mode and B mode on the Toyota Camry Hybrid and Toyota Prius?
Requesting Gravatar...
This is quite an interesting article. Toyota is a very creative company and my opinion is that any car they put on the market, it deserves to be there. About the gear issue, I think that few people actually worry about that anyways and they drive their cars as they normally do. The question is: is there a really big difference between B and D?
Left by donate a car on Apr 18, 2011 10:26 PM

# re: What is the difference between D mode and B mode on the Toyota Camry Hybrid and Toyota Prius?
Requesting Gravatar...
Thanks for sharing this information.. I search lot of using string for this option but can not get me but thanks to you, share a good & helpful information.
Left by Monster trucks on Apr 21, 2011 9:09 PM

# re: What is the difference between D mode and B mode on the Toyota Camry Hybrid and Toyota Prius?
Requesting Gravatar...
thank u u been so helpfull
Left by jordan f1rst on Oct 17, 2011 7:54 AM

# re: What is the difference between D mode and B mode on the Toyota Camry Hybrid and Toyota Prius?
Requesting Gravatar...
Everyone, everywhere (including my Toyota dealer) agrees that B gear is used only in long downhills. BUT in the instruction materials supplied with Prius now (I just bought one, Sept 2012) one gets owners manuals for the car, display audio system, and others--including a CD for people driving a hybrid for the first time. In the "Shifter" chapter, one is told that the B gear is to used going UP or DOWN long hills! Who can clarify this one??
Left by Richard on Oct 24, 2012 9:34 AM

# re: What is the difference between D mode and B mode on the Toyota Camry Hybrid and Toyota Prius?
Requesting Gravatar...
My dealer says you can use is anytime you want to slow down with out really having to use your brakes to get even better fuel mileage out of your car. It isn't really any different than a Jake Brake on a semi. You can use them for more than just steep downhill grades or icy conditions.
Left by Mike on Jan 07, 2013 1:58 AM

# re: What is the difference between D mode and B mode on the Toyota Camry Hybrid and Toyota Prius?
Requesting Gravatar...
I use the b gear when slowing to an intersection and find slightly better fuel economy than when braking. I'm likely saving my brakes too.
Left by tired on Dec 09, 2013 4:32 AM

Your comment:
 (will show your gravatar)


Copyright © Jason Coyne | Powered by: GeeksWithBlogs.net | Join free