Brake Assist

I have question related to the brake assist:
Can the engine be over-sped by using the brake assist in a down hill situation?

 

Jen:
Do you have a Prius v wagon?

 

Would that make a difference?

 

Not necessarily. I'm trying to figure out if this post is in the wrong area.

 

Assuming you are referring to B mode, no.

Actual Brake Assist has nothing to do with the engine at all.
Brake Assist – Vehicle Safety

 

I posted the question based on the subject matter. It's not like I posted it on a BMW forum.

 

My Mistake. I meant B-mode. Thanks for the link.

 

here is another link to my best B mode explanation

B under the D in the Drive gears? | PriusChat

 

Yes, B mode is hard on the engine. Given a choice, it's better to use the brakes to slow down. But, on a long downhill mountain road the traction battery will fill up with energy from the regenerative brakes and then friction brakes take over. On a long downhill, the brakes can then overheat and you can end up with no brakes at all. So, when you need B mode, use it, even if it's a bit hard on the engine. When I was doing some mountain driving, I usually had the car on cruise control and, on a downhill, the car automatically used the regenerative brakes to try to keep the car at the cruise control speed. When the tracktion battery filled up, the car automatically put itself in B mode. The engine was really screaming (couldn't be good for it) but at least it kept me at a safer speed. There's probably no reason to ever put the car in B mode yourself as the car will switch into and out of it on its own when it needs to.

 

If you know the decent will fill the battery, put it in B mode from the top, your friction brakes will stay cooler longer.

 

Is the 'v' different from the regular Liftback in this regard? I'll respond from the Liftback perspective, on the understanding that the 'v' is not different.

When descending in Cruise Control, the car will use engine braking when the battery is full, but I don't believe it is quite as strong as that provided by B mode.

Without Cruise Control, it will still use a little engine braking when the battery is full. But this version is quite weak, not anywhere close to B mode. On most of the hills I travel, it is insufficient to hold speed down to a safe level.

Without Cruise Control, this is quite false, as the provided braking is simply too weak. With CC, well, most long steep hills I descend are not safely negotiated in CC. Deliberate B mode becomes a necessity.

 

+1
Those durned flatlanders are convinced the entire Earth is flat.

 

I have to get use to using the term "B-mode". In any event, when I was going down hill in B-mode the drive train sounded as if it was going to start centrifuging parts out through the hood. Maybe the engine isn't over spinning but what about MG1 and MG2 and the planetary unit. I just don't quite understand where all the inertia is being bled off. Something is spinning... fast. I think!

 

Yes, the ICE (gas engine) is spinning fast, but the RPM on my ScanGauge has never hit redline. MG2 is locked to the wheels, so it should not overspeed as long as you don't exceed the ground speed where the engine would cut out on flat land (~112 ? MPH for the Gen3 Liftback, possibly less for the 'v').

MG1 should not overspeed if the ICE is spinning. Just don't ever put the car into Neutral when the engine is not spinning, then roll downhill to high speed. That leaves MG1 unprotected.

 

Thanks for the clarification.

 

Just drove through the Tahoe hills/mountains. Used the bmode and the dmode. I must say that I prefer using the 4 disc brakes as opposed to tolerating the increased engine drone of the bmode. I could not distinguish any change in the charging state/rate of the battery in b vs. d mode. I'm in a 12 v; gotta change my id....