Is there a legitimate use for charge mode in the Prime?

Others here had it all figured and located before I bought my first Prius fifteen years ago. And posted instructions and ScanGauge codes for how to cut it to just a single beep, not the factory-default repeating beep.

But ... but ... but ... one of the advantage of PHEVs over hybrids is that we can stop this energy-wasting engine braking, instead reclaiming the energy by regeneration into the battery. All the way down the hill, not just the a few hundred vertical feet. PHEVs have enough battery capacity to capture all the regeneration down any mountain descent I've ever driven, so engine braking ought to be needed only when the driver has a charge management or planning failure before a long descent. (Though has anyone tried Mauna Kea?) Or if the battery gets too warm.

Monday, driving home after a mountain hike on the other side of the Cascades, I captured 30 miles of added EV range via downhill regeneration without engine braking, across multiple descents. One pitch produced 9 added EV miles, a couple others gave 4 and 5 miles, the rest gave just 1 or 2 upticks each. And this doesn't count the many smaller pitches that greatly extended EV range without displaying any upticks. My prior non-plugin Prii would have wasted most of that as engine braking.

BTW, my Prime has replaced that old Prius 'B' label with D1 through D6, accessed through paddle shifters instead of the 'gear' shifter. Regular driving is still in D, without any numeric suffix.

No, B mode is not like the Jake Brake of commercial trucks, the Prius has no compression release when the piston is up. While valve timing is adjusted, it is still much more like downshifting a regular passenger car. This is better described as a vacuum pump than as an air compressor.

 

So what happens when your hybrid battery is at full charge? You can't get any more energy from regenerative braking, and using the friction brakes will eventually burn them up, so what do you think the "B" is for? Baked salmon? It is an engine brake, that dissipates energy when coasting downhill.

I don't mind being proved wrong, but when some of you guys just tell me I'm wrong, and then call me a troll for not going along, it gives me the impression that some of you are idiots.

Prius Shifter B Mode: Everything You Need To Know.

 

From: Toyota Prius/Driving tricks - Wikibooks, open books for an open world.

"In a Prius, the driver handles that condition by selecting "B" mode. This tells the Prius to attempt to emulate "engine braking" in a conventional vehicle. Depending on the vehicle's speed and the battery SOC (state of charge), the Prius will do this using regenerative braking and/or high-RPM zero-fuel-flow engine braking.

Engine braking is inefficient because it uses the engine as an air pump, converting kinetic energy into heat. Unnecessary regenerative braking is also inefficient because of energy conversion losses. (Regenerative braking is good when it replaces friction braking, but it's not as efficient as coasting at a constant speed.) Because of this, "B" mode will not recharge your batteries more efficiently than just braking and is not recommended for general driving. Just as you might downshift into 2nd gear when going down a long, steep hill to prevent brake damage, you can "downshift" into "B" mode on a Prius. "Shifting" is all electronic, so the system won't let you shift in a harmful way. (Even if you try to shift into reverse when moving quickly forward, you'll just end up in neutral.)"

 

READ THE MANUAL. B mode is for Regeneration Boost. The system will not operate if the battery is fully charged. Page 261. The side affect is slowing the car down when it is operating.

Please stop posting stuff from Wiki when the manual is there to explain what is happening. Also, when posting a video pertaining to the Gen 5, you should make sure the video contains the Gen 5.

 

I don't know where you learned to read, but here's what my manual says:
●Use engine braking (downshift)
to maintain a safe speed when
driving down a steep hill.
Using the brakes continuously
may cause the brakes to over-
heat and lose effectiveness.
(P.256)

Nothing at all about trying to force a charge into a full battery by using regeneration. The principle hasn't changed since the Gen 3 or maybe before that. The only way the engine can brake the car is by compressing air, and releasing the energy as heat. It's just basic physics.

 

Why are you trying so hard to misread my posts, change topic, and drag me into something else I wasn't addressing?

I wasn't calling you a troll. But if your responses to me don't quickly show better reading comprehension, then I will.

 

B is not for regeneration boost. It's not in the manual or anywhere else. It's for engine Braking.
Are you just making things up?

HacksawMark said: ↑
READ THE MANUAL. B mode is for Regeneration Boost. The system will not operate if the battery is fully charged. Page 261. The side affect is slowing the car down when it is operating.

Please stop posting stuff from Wiki when the manual is there to explain what is happening. Also, when posting a video pertaining to the Gen 5, you should make sure the video contains the Gen 5.

 

Unlike you, some other Prius Prime owners have carefully distinguished between B-HV and B-EV. Regular Prii effectively have only B-HV (outside some infrequent corner cases), while plug-ins additionally have B-EV. The later can be entirely regeneration, no engine braking, until the battery is near full, a situation that can be entirely avoided with reasonable EV charge management. E.g. use enough EV range before or during the mountain climb, to have sufficient regeneration capacity for the entire descent, very unlike a non-plugin Prius that fills its tiny battery quickly and screams like a banshee the rest of the way down the mountain.

I have a RAV4 Prime. It doesn't use the "B" label at all, instead using D1-6 labels, an expansion of the same concept. I have used it frequently in regeneration-only mode, successfully avoiding engine braking most of the time, and still learning how to do better.

Are you intentionally misreading?

I never claimed or implied it was for 'regeneration boost'. But in my 15 years of Gen3 (non-Prime) driving, it was not exclusively engine braking either. It was mixed regeneration and engine braking, until the former became unavailable.

The Prime has much greater capability than the non-Prime.

 

B mode has always been and will probably always be misunderstood.
Primes B mode has at least two functions. Engine braking - when the engine is running or gets turned on due to shifting into B mode
and
Motor braking when in EV mode and shifting into B mode doesn't start the engine.

The two are very different animals.

 

I'm trying to decipher what you mean. The manual doesn't mention two functions. As I already said, if you find yourself descending a hill with a full battery, there's nothing holding back the car from picking up dangerous speeds. Regeneration won't work, because there's no place for the energy to go, and using the friction brakes would cause excessive wear. So the only way to slow down the car is to dissipate the energy in some way, by using the piston engine. The only function of the B position mentioned is to use the engine to create drag by compressing air and releasing it as heat. That's the only way that engine braking can work, and that's what it does in 18-wheelers, as well.

 

That's why in both my cars I have a Lithium battery booster. I used to have booster cables in my ICE cars but not with EV/PHEV. If my 12V battery dies, I can still start my cars. If someone needs a boost, I don't risk damaging my cars.

 

I don't think I could boost another car from my Prius anyhow. The contact pad where the booster is attached is a thin piece of metal in the fuse box. It's obviously not designed to handle high amperage.

I wouldn't fret over damaging any electronics from boosting, unless you are using jumper cables and are prone to get the polarity wrong. That can produce massive voltage spikes and showers of sparks. Fortunately, most booster packs have wrong polarity protection, and will likely only give you a "wrong polarity" warning.

 

Prime owners would have to use B mode to understand it, and not just once or twice before thinking they understand how it works.
No amount of reading about how it works in a regular Prius is going to describe how motor braking in the Prime works while in EV mode and the systems don't trigger the engine to switch on.

 

This is starting to sound obtuse. Selecting "B" won't fire up the engine to produce power, but it does run in an engine braking mode. Which means that the car turns the engine, and the engine pumps air to create drag and dissipate energy. This is necessary when you are coasting downhill, and the hybrid battery is at full charge and will not take any more energy from regenerative braking. Applying the friction brakes for long periods will destroy them, so the only option left is engine braking.
What's so hard to understand about that?

 

Toyota Owner's Manuals have always been deficient on this topic. But experts here had it all figured out and explained for hybrids before I joined. When the plug-in came along, they quickly figured out its expanded capabilities also.

In a normal hybrid, this is just a fact of life of mountain driving. Because the battery is tiny, some gravitational energy cannot be captured, so must be wasted via engine braking.

But in a PHEV, this can be a learning experience: Don't fill up the battery at the top of the mountain! If you do, some 'free' energy must be wasted just as in a non-plug-in!

The PHEV's bigger battery is big enough to not completely fill up and spill over on the way down the mountain -- any mountain in this country -- if the driver manages battery level well. It does take some experience to figure out how much regeneration can be captured on any given hill, so the driver knows how much battery capacity to have open (not filled) at the top of the hill.

Numerous others have long been doing it, mostly successfully. But the unsuccessful cases give me pause.

 

That depends on the reader. Before getting a Prime, there were several good descriptions here from previous owners that explained it well enough for me, and matched up with my experiences after purchase.

No kidding.

The very obvious response: Quit having a full battery on descent! Leave or make some battery room before the descent, so that it can't quite fill on the way down. This will save either some gasoline on the ascent side, or some electric recharging expense while parked at the top, either way improving overall energy efficiency.

This is one of the big-battery PHEV advantages over tiny-battery regular hybrids that quickly fill the battery even on short descents.

No kidding.

 

Do you ever plan to know how long a hill is when you go on a trip? It sounds a bit silly to make sure your battery is low enough capacity to take all the regenerative braking you might require descending a long hill,
just to avoid pressing the shift lever into B mode.

What if you've never been there before, and you find yourself unexpectedly descending down a slope for 20 miles, and your regen braking has charged your battery to full capacity, and your car has nothing to hold it back from accelerating to dangerous speeds going downhill? Are you seriously saying that to avoid using the "B" you must drain your hybrid battery beforehand? This takes the cake for dumbest things ever said on here.

 

If the mountain is symmetric, the First Law of Thermodynamics says that descending regenerated energy cannot exceed the climbing energy. Between these systems being significantly short of 100% efficient, plus air drag and rolling resistance, the climb always leaves plenty of room for the descent. Unless one climbed mostly on gasoline instead of EV.

And in a Prime, you don't need to avoid shifting into B (or in my RAV, D[n]) in order to avoid engine braking. In fact, you likely do want to go into B. Just make sure it is B-EV, not B-HV.

For places where the mountains are not anywhere close to symmetric, I'm generally sufficiently aware of the geography and topography to adjust as needed. If any adjustment is needed at all. This battery is big enough that if I've used half of it before the top, no downslope anywhere near here can fill it.

A few people do lack similar geographic awareness.

The 20 horizontal miles of that descent slope don't matter. (In fact, the longer it is, the less battery space is needed.) It is the vertical component that really matters.

Hybrid "B" mode and its battery regeneration plus engine braking are ancient regular-hybrid subject matters that the old-timers here well understood long ago.

This thread is about PHEV-specific matters. Are you unable to move forward to the newer big-battery PHEV / Prime matters and capabilities?

Then quit saying it.

 

It appears that there is some over exaggeration going on. The disk brakes are quite capable of stopping the car, but that's not the most efficient way to do it IF you have space in the battery to store the extra energy created when slowing by regeneration.

 

You're so far out of it, that I won't talk to you anymore.