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

That's my point; it won't be done away with.

 

Was there any point to that point? Has anyone here ever suggested it would?

 

Is there a point to you raising that point?

 

Well, yes, as it happens, just because it has taken some effort over the length of this thread to keep track of what point you were trying to make. Ranked roughly by the number of your posts in this thread where you have made each claim, your claims have included:

• that there is no engine braking unless you select B on the shifter
  #39 #42 #54 #70 #81 #89 #95 #101 #110
• that there is some meaningful distinction between "engine drag" and "engine braking", or B mode "does more than rotate the gas engine."
  #139 #142 #149 #154
• that HacksawMark somehow wasn't quoting directly from the owners' manual when he pointed out that the gen 5 Prime assigned an additional "regeneration boost" effect to the shifter B selection
  #45 #47 #50
• that HacksawMark was going "beyond the absurd to chase the illusion of winning" when he attached PDF of what you had insisted wasn't in the owners' manual
  #65
• that Prius engine braking works (like diesel Jacobs brakes) by manipulating the valves
  #39
• that fuzzy1's explanation to you of when the car employs engine braking was "a made up story"
  #83

There hadn't been anybody in 8 pages of thread talking about whether Toyota would ever "do away with" engine braking, until it became a red herring you raised just this morning in #154.

So I wasn't sure whether "engine braking won't be done away with" is now, as of today, the sum and essence of the point you'd like to make.

If so, that's great—I think we can all agree that engine braking won't be done away with.

 

You forgot a reason, the battery is cold and can't accept anymore current to slow down the car. I've seen it a few times.

 

If simple engine manifold vacuum were enough to hold a car from accelerating out of control on a long, steep slope, they wouldn't have designed an engine brake.

 

Bravo for cataloguing.

It's now back to the sullen non-reply non-sequitur stage it reaches when it refuses to concede a point, won't address arguments or evidence being presented, and doesn't want to go back to writing detailed nonsense of its own. It's done this cycle a number of times now.

I do hope it is a bot, and not actual brain damage or senility.

But as much as I can glean, I think this thread is now at:

• "B" is magic and has a special purpose - "engine braking". That's the starting premise which cannot be conceded.
• Having apparently (but not explicitly?) conceded that the engine will produce drag in D, B remains special because it does "engine braking", while the D can only give you "engine drag".
• Despite one getting up to 13kW of braking/drag from the engine in either B or D - measurements provided.
• No longer any attempt to claim a specific technical difference between "braking" and "drag" (or between the Prius and other cars) and even reluctant to admit it's still suggesting they're different, but the non-sequiturs are based on that.
• B="special engine braking" seems to be the fundamental "prompt" and everything else just follows without proper logic, like a typical AI wordstream. But its had enough negative feedback on what it has produced that it's struggling to produce anything new or concrete.

AI natural language models treat counter-arguments just like additional rules on what the wordstream should contain - an extension of the original prompt. They don't really do logic. But there's not a lot of output space containing both "argue why the special engine braking mode of P in the Prius is required" and all the counter-arguments presented here, so you could end up with something like we're getting now.

(Mind you, ChatGPT and others do tend to concede quite easily, normally - if asked a question, you can point out why an answer's wrong, and they will generally back down and agree. Even wrongly! This one is not working like that, maybe because it wasn't starting from a question like "what does B do in a Prius?")

 

No need to call bots stupid. They are easy to train.
ChatGPT responded as follows.

"In a Toyota Prius, the "B" mode stands for "Engine Braking." When you shift the transmission into "B," it increases the regenerative braking effect of the electric motor, which helps to slow down the vehicle more efficiently when going downhill or during deceleration. This can help recharge the hybrid battery while providing additional control and stability on steep grades. It's particularly useful in situations where you want to maintain a lower speed without relying solely on the brake pedal. However, it's not necessary for regular driving conditions, as the standard "D" (Drive) mode is typically sufficient."

 

Unfortunately, AI bots aren't good at filtering out false information. If a lot of people claim that the "B" mode is some sort of "super regeneration," the bot swallows it, hook, line and sinker.

 

If the people making that claim are talking about HEV Prii, or early PiPs and Primes, they're wrong. If they're talking about gen 5 Primes, they're just reading from the "Regeneration Boost" sections in their owners' manuals, and they're not wrong. Such model and year differences can be very hard for a chatbot to keep straight as it ingests a whole lot of text.

 

Whatever it says in print, the car must follow the laws of physics. When the battery is full and can not absorb any more charge, the energy must be dissipated somewhere. This can either be as heat in the friction brakes, or through the gasoline engine by engine braking. You may never find yourself on a long steep hill with no regen, but if you do, be glad to have the "B" mode.

 

Which no one disputes. The reason the print in the manual is correct is that it is not at odds with physics.

Toyota added the "regeneration boost" language only to the Prime owners' manual. A Prime has such a large battery capacity that "full and can not absorb any more charge" is a very difficult condition to reach (as you learned from both of your attempts to test it last summer).

The regeneration boost function Toyota added naturally operates only when the large battery can absorb more charge. Which, in a Prime, is nearly all of the time. In rare conditions when no more charge can be accepted, the ECU will of course fall back to engine braking, just as it does in D.

I don't have a Prime, just an HEV Prius with the much smaller battery, so I often find myself on steep hills long enough to run out of regen. I am glad to have engine braking at those times, whether I manually ask for it with B on the shifter or just let the car automatically apply it in D.

 

Oh, physics!
Let's calculate the problem of how much energy can be regenerated into the high-voltage battery of a 3365 lb car moving down a 1000 foot hill at a constant speed of 60 mph for 10 miles.

 

That's not the question. Every battery has a maximum charge level, and if it's full while you are coasting down a long, steep hill, how do you dissipate the excess kinetic energy? You can't make it disappear; if you could, you'd win the Nobel Prize.

 

You can dissipate it, up to a rate of 13 kW anyway, by twirling the engine against a closed throttle valve with no fuel or spark.

A clever idea and exactly what the car does, whether you request it early with a B selection on the shifter or just wait for the car to do it when the battery has reached 80% SoC.

 

Good luck with that. I was on such a hill in my VW, and no amount of engine braking would slow my rate of acceleration. I had to apply short, hard braking to keep it at a safe speed. I was trying to keep them from burning up.

 

Without your VW's engine braking, you would have had to use the friction brakes even more. It's no surprise that the engine braking has a limit. If your hill descent is gaining you energy faster than engine braking can dissipate it, you'll need to use some friction too for the rest.

I don't know what the limit of your VW's engine-braking dissipation was. If it had a 4-cylinder gas engine around the same size as in the Prius, it may have been around the same 13 kW that gen 3 Prius engine braking can dissipate.

I've never measured the limit of the larger M20A engine in your gen 5 Prime. If we assume it's proportional to displacement then it might be around 14½ kW for you.

You could measure and report the number, which would be useful new data to contribute to PriusChat. You can see the methodology here. You just have to find a good-enough hill, have instruments, and make sure your battery is close enough to full charge when starting the run. (That, of course, is the hard condition to satisfy in a Prime, as you learned last summer.)

 

I've had many vehicles over the years, and none of them could manage a hill like that with engine drag alone. My cousin, who lived there, had an engine brake installed on his pickup truck.

 

No matter what amount of power your engine is able to dissipate through engine braking, you can always find a hill steep enough, or take the hill fast enough, or load the car heavily enough, to need to use friction braking as well.

On the bright side, you only need to use friction braking to dissipate what remains after engine braking.

What kind of engine did your cousin's pickup truck have? What product did he install?

 

Cummins diesel is all I know. He said it was designed for bigger rigs.