How to use "B" gear?

It shouldn't be detrimental to either. Might even offer a benefit to the battery. Not sure how we could be certain.

 

No known detriment, except to mpg when the battery would not otherwise fill, such as the highway exit ramps.

 

The manual says the b hear is when drivin down steep hills.


iPhone ?

 

Brake mode (B) on the shift lever isn't often used or discussed - so thx for this thread. I'm wondering though if a newbie or unaware driver can shift into B at higher-than-desirable speeds and potentially damage the engine/trans? I believe.... I have shifted to B a few times and could feel the engine revving a bit higher than I would like - nothing serious thought but it did beg the question: What happens if you are going like 35-40+ mph and do this? I'm a bit too scared to really try it out. Anyone have experience with accidentally shifting to B-brake at a higher speed? Any ill effects? What speeds have you used B at and felt comfortable? What happens if you are doing like 50+mph and shift to B on a steep 7%+ grade? Will the engine go high RPM's on you, or sense it needs to restrain itself so as not to "blow up" anything?

 

There is no maximum speed for B mode, it does not alter any gearing, just uses engine braking. While the engine may spin to redline, the computer will not exceed redline.

B mode is often a poor choice,u it is not a dangerous choice. Use it in a non PHEV Prius on hills where you drop ovr 600 feet vertically.

 

I use the "B" all the time. I've used it at 65mph. And I've had no problems.
Of course, I've only been doing this for about 150,000 + plus miles.
I've also use it a LOT at 45mph and under.
From what I've read about "B", the computer cuts the fuel off and power to the coils.
So there is resistance from the engine to slow the vehicle down. It as uses
mg1 and 2 which prvides more resistance to help slow the vehicle dow, and which also
charges the battery faster. I've noticed this on MY Prius. I cannot say what it does with
any other Prius.

If my hybrid battery shows only 3 bars, I will use "B" the last tenth of a mile. And this will get the
battery to 4 bars about 98% of the time. If I forget and don't use it, it MIGHT get to 4 bars.

I'm certain there will be at least one "person" that will likely attack and say I'm wrong.
But I don't care. I can only report on how MY Prius performs.

Bottom line, it won't hurt to use the "B" at any time. It won't hurt the transmission.

 

Everything that happens in B mode is under control of the car's computer, which will never use the engine at a higher RPM than it would like. Whether or not that's higher than you would like, that's something you know and the computer doesn't . The RPM you hear might not be to your taste, but it is always within the limits programmed into the car.

I don't think I would use the term 'redline' there. The only published figure we have for the engine is the peak of its power curve, which happens at 5300 RPM, and the computer never goes above that (why would it ever want to go higher and get less power?).

When engine braking, I've never seen the computer pick a speed much above 4900.

Toyota hasn't published what redline is for this engine ... there isn't anybody who would need to know, since there's no way to make the car rev that high. We can ask questions like "what's a typical redline for a small inline-four Japanese auto engine?" 7000-ish? I haven't been keeping up with such things for a while.

Safe to say, the car goes nowhere near it.

 

Never mind accidentally, I've done it deliberately at full highway speed many more times than I can count. No ill effects.

Have you tried shifting into Reverse or Park at highway speed? As Chapman mentions, the computers won't do something that damages the engine or transaxle. When I try R or P at speed, it chooses Neutral instead, with a double beep warning, and without the delay imposed when deliberately shifting to Neutral.

I tested these back during the Toyota Sudden Unintended Acceleration scare, to make sure power could be disengaged in case of the alleged runaway engine. Still being a regular driver of manual transmissions, this disengagement would be my first reflexive reaction to engine runaway.

At a certain low parking lot speed, it really will go into Park with a big jolt.

I have several 7% highway speed hills on my routes. The engine howl has variously been described as a giant vacuum cleaner, jet engine, or howling banshee, but I've never seen the RPM (as displayed on an OBDII-port engine monitor) reach 5000. At 7%, I don't get enough engine drag to maintain a steady 60 mph, speed slowly creeps higher, requiring some occasional minor brake pedal. It can hold steady at 52-ish mph in my usual conditions.

With no fuel burning, and no combustion-level pressures in the cylinders, the engine is under less stress than when climbing those same hills at similar RPMs.

That happens from engine compression braking, regardless of gear, B or D, though is easier to get to in B. I believe it is called DFCO, deceleration fuel cutoff, and happens in most modern cars, hybrid or not.

Note that this car drives and accelerates just fine in B mode, demonstrating that B mode does not automatically cut fuel and spark. When accelerating or climbing hills, B feels the same as D -- because it really is the same in those circumstances.

 

I have a question - while having in `B`, sometimes I see motor/engine is becoming louder (heavier sound) more and more, like as if you are putting Break & Gas together. what does "like very much loaded" engine sound means at that moment?

 

Since you don't have exhaust noise, you hear the other noises.
And you're getting the noise from the air being pushed out the exhaust, a different noise.

 

Many thx to all those that chimed in! this greatly helps understand "the B"