ok, Prius Prime going downhill in the rocky mountains

Depleted battery, Ev mode, B mode on the hills would be my guess from doing smaller hills.

 

Yes. What Lee Jay said. EV mode with B drive mode and apply brakes when it in needed.

#1 in Easley,SC

 

like @Lee Jay and @dalcon95 said ... on my recent trip, going down a 5+mile 6% grade i gained ~11EV miles, freeway with DRCC set @ 65

 

B Mode is engine braking mode. If you will be "full" at the bottom of the hill, then it is in your best interest to use B mode to WASTE energy spinning the gas engine as an air pump as well as putting a little bit back into the battery. There are some mountains where you will definitely fill up the battery, and B mode should be used even on a Prime. In general though, just keep it in D mode. When you use the brakes lightly it will still be regen and fill the battery.

 

The engine is not used as a brake on the Prime when in EV mode and B mode until regenerating EV range has been exhausted. When in EV mode and B mode, the regenerative braking is increased which requires less foot pedal braking and is all regenerative unless you press the foot pedal brake to hard to cause the hydraulic brakes to work. In this situation, the engine does the same as it does at any other time the engine is in EV mode until the regenerating EV range is exhausted and you have a full EV designated portion of the battery. After that, energy is wasted because it has no place to go, which engine braking doesn't matter at that point other than to prevent less use of the hydraulic brakes. Prime operates differently than the liftback Prius in this regard because of the EV mode perimeters set on the Prime versus the liftback limitations. I personal experienced this myself.

#1 in Easley,SC

 

Can EV mode be activated with depleted battery? With the PiP you cannot switch to EV until some regeneration is completed and EV estimated miles appear.
With the PiP, in the situation described by the O/P you better start the downhill in HV with brakes (no B) until you can switch to EV+B, somehow I suspect it is the same with the Prime?

 

If you can't switch to EV mode right away, that will work. Soon as you are in EV mode, put it in B mode.

#1 in Easley,SC

 

When I said "depleted battery", I meant a battery with sufficient remaining capacity to absorb the expected regeneration from the descent.

 

Sounds to me same as what I said.

O/P was specific: he was in HV mode on the top with battery depleted long ago.

 

Which is no problem because as soon as you start the descent regeneration will put you over the 0.1 mile limit for starting Ev mode.

 

That depends on the battery SOC when on top and can be quite longer than 'as soon as you start descent'. As I said, until you can switch to EV, brakes with no B is your best coice.
With the PiP, there is a SOC threshold above it the system reverts to EV mode automatically (about 2 EV miles on the estimate if I remember correctly), what about the Prime?

 

I took a long trip around the Rocky Mountains last year in my PiP. Filled up the battery pack several times on various descents. You Prime guys will be able to take advantage of even more.

 

I can attest that it will recharge to 80% capacity. You won't end up with the same amount as if you'd charge at the wall. Done this several times and while in EV mode but going downhill it will start the ICE to burn off the excess regeneration.

 

I guess I don't understand. How is their excess regeneration if it only charges to 80%?

 

my assumption is that it its a safety for the battery. Unlike wall charge where it trickle charges the final several minutes, brake regeneration is like a slam when it comes to charging.

 

Plus, Charge Mode charging rate is considerably higher than wall charging (it is about 1C rate) so battery is considerably hotter at the end.

 

[Beginning of rant] Lots of opinion here, and some deductive logic (which has proven flawed at times. Brain fart ? )

You will hear about the 80% charge in a lot of different cars that store energy in batteries.

Batteries get hot while charging.

The capacity of a battery varies with temperature. Charging batteries can get very hot.

It's not that batteries are limited to 80%, it's that at very hot temperature levels, the charge level is full at that temperature.

If you look at the charging current graphs in this forum, you will set that at ~80% the charging takes little pauses. This allows the battery to cool, off, increasing charge capacity, allowing more charge shortly later.

Some cars don't have that. It's usually due to liquid cooling of the battery.
Liquid cooling results in a very heavy battery system.
Heavy car results in bigger wheel bearings, ...more loss.

I'm glad that toyota has chose to keep the weight down, == lower capacity bearings == better rolling resistance.

Bear in mind, just because a car is electric, does not mean that it is more efficient.
AAE (as an example) tesla. Good size battery pack (super heavy). Oversize motors( heavy). Crazy with style., big tires, options.....
Does not mean that it is an efficient car.

[end of rant]

In the prius, charging mode increases the temperature of the prius batteries.
Any charge mode braking causes an increase of temperature.
You cannot allow charge mode to use up all of your temperature budget in charging batteries, because that will reduce your regen capacity from braking. Reduces efficiency, good choice toyota.

Even if the batteries cool down, how can the car predict your braking in the future? It doesn't, it just reserves capacity.

It's too bad we don't have the obd codes for the batteries for the prime, we have no way to observe this.

On the 1012 prius, we had all the codes, and I had a scanguage to monitor the batteries.

On one trip up 495 in ma, the traffic was in one of it's crazy modes.
Everybody going 70+, then to standstill in a few minutes, the back to 70+, over and over.
My prius batteries went to a very high temperature, per scan guage. (I dont' recall the temperature).
At that time, there was no more regen, no more electric drive, I was a full fledged gasser !
Toyota fully protected the batteries.

So... when it comes to charging think thermal.
Unfortunately, we have have no way to measure (no OBD codes) battery thermals.

jp