The [B] gear??

[senectus]

When we test drove our new Prius, we noticed that there is a [b] gear... the sales guy reckons that's for forcing the car to charge the battery using the ICE.

But if the Computer in the car can tell when it needs to recharge and do so automatically, why bother with this gear at all?

[john1701a]

After so many years now, any salesperson that makes up an answer when you ask them about Prius is a clear warning sign. If they don't know, they should either admit it or *finally* look it up.

[b] has absolutely nothing to do with charging.

It's purpose is to provide engine-braking, a benefit to your brakes when driving down a steep decline.

[senectus]

once again john your a fantastic source of info.. thanks :-)

when you say engine do you mean it's using a "changing down a gear" type effect ?

I'm still not sure of the point of this, as the regen brake system should be enough when combined with the normal four disc bake system shouldn't it?
Especially since you can't tow anything on these cars..

[efusco]

once again john your a fantastic source of info.. thanks :-)

when you say engine do you mean it's using a "changing down a gear" type effect ?

I'm still not sure of the point of this, as the regen brake system should be enough when combined with the normal four disc bake system shouldn't it?
Especially since you can't tow anything on these cars..

You could definately drive the Prius and never once use B mode. The advantage is that on long steep downhill grades you can drop into B and both regen braking will be maximized (without the need for you to touch the brake pedal) AND some amount of engine braking (due to back-pressure) will be applied. It allows you to keep your foot off of the brake, for the most part, and enjoy the ride rather than have to ride the brake the whole time.


There is little other need or use for B.

[john1701a]

[b] forces the engine to remain active (even though no fuel is being consumed).

Normally, it would stop entirely. But when you shift into [b], it keeps pumping the pistons. That causes some deceleration even without having to step on the brake-pedal. (By the way, the effect is so smooth, you'll find it helpful on ice.) This additional force helps to reduce the load on the brake shoes & pads.

Using [b] all the time will cause lower MPG, since charging opportunities without using the brake-pedal are reduced.

[senectus]

hmm interesting..
Heh.. I doubt I'll ever get the oppertunity to use it.. because Where I live is mostly flat, and the only time I ever see ice is when I open the freezer door ;-)

Thanks though... I might take the time to educate the sales guy when I pick the car up

[jeepien]

By the way, the effect [of B mode] is so smooth, you'll find it helpful on ice.

I would NOT recommend B mode on ice.

In the first place, its decellerating effect is applied only to the front wheels, which is a destablilzing force.

In the second place, if engine braking should cause a wheel to slip, it won't be under the control of the ABS system. In fact, if wheel slip is detected, the car will respond by cutting off ALL regenerative braking instantly, giving the effect of the car lunging forward. This is done to ensure that the ABS can work properly, but it also has the effect of momentarily upsetting the equilibrium and leaving you in an off-balance condition.

The best course of action on ice is not to brake at all unless absolutely necessary, and then to use the foot brake (which has ABS) as gingerly as possible until you can get down to a safe speed. I'm not sure what a "safe" speed on ice is, because it would depend on the conditions, but it would not be much above a walk.

[andyprius]

Hello John: Your doing a great job! you and the other moderators as well. My question is on a comment you made awhile back: "Lightly touching the brake pedal will improve regeneration", upon releasing the accelerator regen automatically occurs anyway, why should it be more with the brake pedal pressed (lightly or not) Can you offer any proof of this? and what sort of feedback might show the Prius driver that INCREASED regeneration was occuring? I tend to do this anyway as I want the driver behind me to know that I'm slowing. Your comment on freewheeling was excellent, I have put that to use. ty Andy.

[john1701a]

Recovery from an unexpected slip on ice works great. You just drop the Prius into [b] the moment you discover you are going too fast for the curve.

It works great. I've tried it many times. Real-World driving has demonstrated that the engine-braking will not cause the wheels to slip.

In other words, when you detect that braking is too high of a risk, try [b].

[john1701a]

While you are driving, electricity is generated using the 10Kw motor. The source of the power for that doesn't matter, either the engine or simply slowing down a little will do.

When you step on the brake-pedal, the job of generating electricity is taken on by the 50Kw motor instead. That larger size makes a big difference.