Charging EV portion of the battery going down mountains

I am not sure, when driving downhill in HV mode, the ICE is not spinning (up to max. speed allowed) so I believe B position operates the same as in EV mode.

 

The OM says this about B mode:

Applying engine braking or strong braking when the
accelerator pedal has been released on steep downward
slopes etc.

I think the "or strong braking" refers to regen. An owner reported that switching in B mode on a slope didn't engage the ICE.

 

The FAQ is wrong. B mode engages engine braking, which consumes gasoline instead of regenerating electricity. You're giving the wrong advice. B mode really doesn't ever need to be used, because in D mode, if the battery fills, the car will use engine braking anyway. Whether B is more aggressive or not, I don't know, because I've never filled my Plug-in battery to full by coasting down a mountain. And I don't think there's a mountain big enough to charge a Prime battery, but I haven't tried.

 

why have b? i thought for the alps?

 

First of all, using engine braking doesn't use gasoline. The wheels spin the engine.

Second, a Prime owner said that putting it in B mode didn't rev the ICE.

Third, I regularly come down a hill big enough to fully change a completely dead Prime battery, at least in theory (it's a decent of almost 6,000 feet).

 

I am not giving advices, simply describing my experience with the PiP.
@Rebound , have you ever tried B position on downhill? or is it just an 'idea fix'?

 

i think we need to cite some data or official toyota statements with our opinions.

 

You mean, like quoting the Owner's Manual?

 

I agree with your message, but I thought B mode constricts airflow to the manifold, thereby increasing the work of ICE rotation. I'm not aware of any active fuel consumption.

 

I'm done. I cited the page numbers in the owner's manual and no, I'm not going to instrument my car with a scangauge and test it for you.

 

the o/m is good, but can often be confusing with the japamerican translations.

 

■Regenerative braking
In the following situations, kinetic energy is converted to electric energy and deceleration force can be obtained in conjunction with the recharging of the hybrid battery (traction battery).
●The accelerator pedal is released while driving with the shift position in D or B.
●The brake pedal is depressed while driving with the shift position in D or B.

Page 86 of the Prime on-line manual.

I found similar statement in my (Euro) PiP manual.

 

but do we need a distinction of d and b, or are they redundant?

 

Based on this ?

A reduction in fuel efficiency from B mode use does not imply gasoline consumption any more than say, a flat tire. I agree with you that both are best avoided.

 

we need a scan gauge or such to see engine rpm's and fuel use.

 

True, I don't honestly know if the engine vacuum draws in any fuel from the injectors. But either way, you consume more fuel because the engine braking reduces the amount of regenerative braking, so your battery charges less, if at all.

 

Yes; I meant that while going down the hill in B mode, I would not expect to see fuel consumption.

 

This is Graham Davies explaining B mode in a regular Prius.
Understanding the mechanics aside, it is non-intuitive that an intent to slow the car down on a descent would be accompanied by fuel consumption.

And even better, the hobbit has his say.

 

Yes, if no fuel is spritzed into the engine, no fuel is consumed. But if you aren't charging the battery when you could be, fuel consumption increases. IOW, B Mode is not the recommended way to coast downhill and charge up your battery; D Mode is.