"B" Range...What's Really Going On...

Never use B, I don't even think about it, it just causes the engine to worker harder.

 

In some places, it is actually needed.

 

Needed? Most new transmissions CVT know when you are going down hill and as you brake the CVT will adjust without making any gear section change, so I don't know if B range is needed.

 

I forget -- about where do you live? What are the maximum highway grades and elevation changes in your driving area?

Last year, a newbie here took that type of mis-advice to heart. That required repair of heat damaged brakes twice before learning that in some situations, B really is essential.

 

Prius does NOT have a true CVT like other modern non-Hybrid cars w/ a true CVT.
Continuously Variable Transmission

Have you not driven North (San Fran) over the Grape Vine? What about to Vegas? B mode is very useful on the long, and at times, steep, descents. Remaining in D, will cause the car to continuously pick-up speed, causing you to use the brakes more frequently/excessively, possibly to the point of damage (warped rotors, scorched pads/shoes) or failure.

B mode uses the engine to help slow the car, specifically on descents that are long and/or steep.
Use of B on long/steep descents is a prudent move.

 

I have never needed to use B and never have ever needed to use a low gear in any car. Brakes have never failed me, but I can see your reasoning. But what affect will that have on the CVT and engine if you are using B on a daily basis....

 

I can not say with absoulte certainity, but I can't imagine any harm occuring to engine or transaxle from daily or appropriate use of B. A person who has to use B daily, probably lines in a mountainous area. We do know, anecdotally, that HV Batteries in desert and mountainous areas do not have the same long life span due to the extrme heat and big SOC swings, from climbing a hill.

We do know, driving in B, when it should be in D, will adversely affect MPG. Reason due to Regen being limited upto 30%. D has a Rgen limit upto 80%. B will cause the gas engine to be on more.

 

This helps explain your response. A very significant fraction of the country's population lives and drives in conditions where downshifting is never required, but that is far from universal.

In places where low gear is needed for safe descents, the extra wear is simply a cost of having safe mechanical transportation. The alternative shows up in the form of scars on the jersey barriers or along the roadside near the bottom of the hills, marking where equipment (and sometimes life) was destroyed in a vehicle runaway.

The Pikes Peak road in Colorado has a mandatory brake checkpoint half way down. The attendant has a remote IR thermometer to measure brake temperature, directing serious overheat cases into a 30 minute cooling off zone. While my spouse was perusing the adjacent gift shop, an F150 with Florida plates was ordered to cool off. It had the most awful stench of baked brake I have ever witnessed on a passenger car. (I have been exposed to worse from a tractor-trailer that just barely saved itself.)

 

This will sound very stupid, but I cannot seem to shift gears while I'm driving. In other words, the gear shift is locked into D. Is there some kind of trick to moving it to B?

 

While I have no idea why you can't shift to B, while you are in IL, you never need to. (The high point of IL is less than 1000 feet higher than the low point in IL)
If you commute to CO, this will be serious.

 

Um, what does your definition of a "true CVT" require? Something besides Transmitting power and torque in ratios that are Continuously Variable? Prius checks all those boxes....

Well, it makes the engine crankshaft spin and the pistons and valves move. They're built to do that, for hundreds of thousands of miles, running in filtered circulated oil and cooled by clean circulating coolant. It's spinning without combustion in that case, so under less stress than it sees normally while powering the car, and the control logic won't let it overrev.

The transaxle is also spinning and transmitting torque, as it is also built to do, also in circulated oil and coolant, under control of an ECU. It's very good at that.

Meanwhile, excess energy is being kept away from the brakes and the battery, both of which really can be at risk of overheat and loss of effectiveness during a long steep descent.

-Chap

 

Dang. When I first learned of "B" it was described as an alternative to "1st". Then I read somewhere here that it is for downhills. I have used it in downhills and it did well for me. It assisted optimum car control in braking and speed. But some people here also say it is not necessary. When I do not want to perform a tiny enactment of Harry Chapin's "30,000 Pounds Of Bananas" it seems necessary to me. But when this little gem of a gear shines for me is when I am low on gas.

It maximizes the use of the battery and minimizes the use of gas. When conditions allow it conserves the energy of the battery by both using it less and regenerating more. Maybe I am just strange. But I have used it a lot.

 

Almost all of this is wrong.
It diverts energy from recharging the battery to spin the engine as an air pump when coasting and braking.
This can be very helpful on long downhills; but it never saves gas. (It may save you)

 

In Florida, Illinois, and other flat states, it truly isn't necessary. But neither California nor any other state out West is that flat.

Jimbo beat me to it -- this portion is all wrong.

 

Yeah. Personally, the only time I use B is coming down Mount Seymour. Other'n that, if you need to slow: step on the brake.

 

You might have a technology edge on me, but this does the opposite of diverting from the battery. It does not spin the engine as an air pump unless this is a process for slowing the engine and I think it may not be. I started figuring this out when learning about a different car altogether. The BMW i3 was on display at work and my supervisor was driving it around from pillar to post for shelter and charging. He described to me what it is like to drive and I found the exact behavior in my B gear on my C. I did not do formal tests or read any graphs but did use my eco score screen. I asked random drivers of the BMW i3 about the gear action and they all described the same thing. Except on the C we switch it on or off so to say and the BMW uses the mode altogether on the fully electric car.

Accelerate on the pedal with foot, and of course the forward motion. Take the pressure off the accelerator and the engine slows almost to a stop. It is regenerative braking.

I hope I am not breaking a rule but I found a 2012 post in Toyota Nation. I think this helps to clarify it.

Copy the link.

B mode - Toyota Nation Forum : Toyota Car and Truck Forums

 

It diverts energy from charging the battery. The engine races, scaring a fair number of new owners the first time. The harder you press the brake in B, the louder the engine sounds.

 

Read the link. The value of B is what happens when removing pressure from the accelerator. After all who among us accelerates down hills, of course. Removing pressure from the accelerator at a low enough speed performs regen braking without using the brake pedal, but when combined with the brake pedal conforms to that action until the brake is lifted. Constant regen is desirable if you are running so low on gas that you are praying.

 

I suggest you try Donner summit (I-80) to Reno in both in B and in D. I bet you understand, then.

 

Sorry you do not want to read.