B mode

Well then, I take everything back! Just kidding... ...sort of.

Generally when you talk about re-configuring the poles (electrically, or otherwise), your are talking about the stators, so when you said they use permanent magnets, it surprised me because it sounded like that's what you were referring to (which, of course, doesn't make sense for an AC motor to have permanent magnet stators!).

So basically, the stators ARE electronically controlled. As such, saying that they use the same MG circuits becomes meaningless. I.e. if you electronically control the stators, you can do just about anything you want - change the number of poles, change impedance, whatever). As you say, "the computers control it all" - including the augmentation of braking torque - and using big switch transistors is exactly how it would be done. We call them SCRs (Silicon Controlled Rectifiers).

Now whether they actually DO control the MGs to augment braking torque is another matter. The literature suggests they don't, but I have my doubts. And after viewing jerry's videos, I expect that it's not nearly so simple.

 

Well, it'd be hard to electronically change the number of poles and such. The stators are still copper wound around structural forms. They pretty much sit there. They are conventional, delta-wound, three-phase AC stators, used with permanent-magnet rotors.

Right, that's the one and only, necessary and sufficient thing, that the computers control: exactly when and for how long each of the three phase legs is switched on and to which power rail. IGBTs (Insulated Gate Bipolar Transistors) are the type of switch Toyota is using, but you've got the idea.

They generate electric power, and that can mildly or strongly augment braking torque, depending on how much power the computer lets them generate. Again, it controls that simply by the timing of the switches, which can shift the current waveform ahead or behind the voltage waveform, allowing their AC product (power) to be either positive (motoring) or negative (generating).

If you've ever been (as I was as a kid) to a hands-on science museum (dad took me to Toronto), and you got to spin a generator while changing the amount of electric load it is powering, you never forget that the more watts it is allowed to generate, the harder that sucker is to turn. (A teacher lecturing about conservation of energy in front of a chalkboard just isn't the same.)

If you watch the computer with Techstream, you can even see it calculating the amount of braking torque it is going to ask the friction brakes for, and the amount it is going to do with regeneration. It's all done out in the open.

 

Yes, I did all that and then went on to retire as an RF and Systems Engineer (large Radar systems) so I do have some experience with 3 phase systems. But motors? Not so much. Most of what I know about motors is what I picked up in college, and most of that is obsolete.

I can believe that. And that's the type of information that I'm looking for.

When operating B-Mode, with the regular brake, viewing the hybrid system monitor, I noticed that braking torque momentarily surges and then decreases as the brake is applied - almost as if there is a reaction time. Also, what you are saying seems to suggest that the mechanical brakes are applied electronically. If so, that might explain any reaction time as a servo-mechanism delay.

As you can see, I still have a lot to learn about hybrid systems, but it's fascinating stuff.

 

The details vary with the generations. In all generations, there is an accumulator filled with brake fluid under high pressure (chamber containing nitrogen gas), and solenoid valves to allow the pressurized fluid out to the brake cylinders, and others to release that fluid back to the reservoir. (An electric pump eventually stuffs it back into the accumulator.)

There are independent pairs of solenoid valves for all four wheels, so the ABS and VSC can do their things. So far, not much of this is hybrid-specific, pretty much any car with ABS will have most of the same pieces. And the valves are electronically controlled. The Gen 1 Prius did not brake all four wheels independently, but left and right front independently, with both rears controlled together.

The ABS actuator also has a fancy linear solenoid valve, not just on/off but controllable through a range, so the computer has fine control over pressure. At times, if you have replaced the actuator or the computer, it will say it has to learn the linear solenoid parameters, which is kind of fun. You tell it "ok, learn" and it sits there for about a minute making different pressures in the brake system and remembering what solenoid currents it took, just making a bunch of clicks and louder and louder squirty noises, and then it blinks the ABS light fast and it's done learning.

Gen 2 has a pretty much pure brake-by-wire system. Your pedal effort pushes fluid into a stroke simulator, the computer monitors that, and you feel like you have power assist because the computer is pretty much running the real brakes for you via the valves.

Other generations (both Gen 1 originally, and coming back again in Gen 3) also have the stroke simulator, but have slightly more conventional plumbing where you feel like you have power assist because some of the pressurized fluid from the accumulator is mechanically valved into a chamber behind the master cylinder piston, where it pushes in the same direction you do.

 

As long as I've participated in Prius Chat, there has always been a recurring conversation about "B" mode, and exactly what it does, means, and when/how to use it. With people inventing and applying "new" ways of using it.

My feeling is, why? And why not just use "B" mode as it is presented in the owners manual. Which is pretty exclusive to just when the Prius is being driven down steep inclines.

As far as I know, there is nothing in the owners manual about using "B" for any other application. Nothing about a benefit at low speeds around town, nothing about mimicking a down shift in a manual transmission.

What is this allure to want to experiment with it? Make it into something more than what it is recommended to be used as?

My opinion is, if you're driving down a big hill or mountain/steeper incline....use "B".
Otherwise, Toyota has kindly provided an option they call "D"-which is designed to be used in nearly every other driving situation to great efficiency.

But my opinion won't change anything. No doubt the experimentation will continue. As people for some reason desire to think they have found a new magical application for "B" mode, that grasps some nearly non-perceptible ounce of efficiency from HSD as it is designed to be operated. This will forever be coupled with the moments of momentary doubt, as in..."I wonder if this is hurting anything?".

To escape this doubt...you can use "D" at speeds around town at 25-35 mph, and rest assured that you are doing nothing out of the ordinary to your Prius.
Which was my choice in operation.

 

Which is a use for downshifting with other cars. B mode is just there to provide that feature.
But people have been downshifting for other reasons besides slopes long before the Prius arrived. With paddle shifters, I've been using it for general braking.
Now B mode doesn't provide more power to the wheels like using a lower gear in another car does, but it can be used whenever a driver wants more off the accelerator braking.

 

...Because geeks like to tinker.

 

Your whole reply seems to be written from a Classic Prius viewpoint, with no acknowledgement that the Prime's B mode goes beyond the Classic Prii version.

This thread is specific to the Prime.

 

Oh god help me...
So now there is regular Prius "B" mode...and Prime "B" mode?

Does Toyota recommend or acknowledge any further usage for B mode with a Prime? I'll retract if Toyota says "Use B Mode around town and at speeds between 25-35 mph" and/or " B mode is great for simulating a manual transmission downshift! Enjoy! "...otherwise...
If not?
I'm sticking with my opinion....Prime or otherwise. Just use "B" as described in the owners manual. Everything else is just playing a game.

 

Prime owners here (I don't have one) have reported distinct HV and EV modes.

The Owner's Manual is exceedingly sparse on B mode. It contains 1 case of when to use it, and 0 cases of when not to use it.

I take these wordings as so lacking in discouragement or recommendations against it, that it effectively acknowledges that other usages exist.



In particular, the last sentence is an offhand or indirect acknowledgement of other cases.

 

We're just going to disagree. Except for the part about Toyota being exceedingly sparse in their explanation of "B" mode.

That exceedingly sparse passage, I don't think should be translated as complicit or subliminal acknowledgement that other usages exist, especially when that same passage ends with....Usually Select The "D" Mode.

I don't take a "lack of discouragement" as to mean that it's acknowledging or encouraging other usages.

Over the years, I've grown so tired of this recurring debate, that I really wish that Toyota would devote a good full page or so, to EXACTLY how "B" mode should be used. Don't be so sparse on the information.
All you have to do is google the terms Toyota Prius B Mode, and you'll find that there is far too much ambiguous discussion about "B" mode. There are a lot of people out there that think they know what "B" mode is all about, and how best to use it, but a lot of these same people aren't agreeing with each other.

When you reach this level of debate, and also disagreement about usage, I think you have to ultimately pin it as a failure to communicate by Toyota.

 

i tried to explain it many time to my friends with the help the App Hybrid assistant so this is my opinion : In the App HA when the engine icon ( piston shaped thingy ) is Grey : the engine is not spinning , Yellow : Spinning but no fuel injected , Green : Spinning with fuel.

When using B mode in Hybrid mode , you give to the engine the permission to spin ( kind of .. ) ... so yeah the B mode will work as everyone seem to say : Engine braking ...So in Hybrid assistant App you will see the engine icon turn yellow with numbers inside ( RPMs)

However when using the B mode while in EV mode the engine icon stay grey , meaning that the engine is NOT spinning AT ALL. In fact it's the electric motor that slow you down by applying regenerative braking , exactly the same way as when you press gently on the brake to not engage the hydraulic brakes , same way as when the adaptive cruise control slow you down gently when a car slower than you is in front.
So the B mode while in EV DOES NOT produce more regeneration , you can achieve the same behaviour if you are really good with the brake pedal without engaging the hydraulic brakes. Using B mode in EV mode in cities only help you to stop faster if you can't anticipate the traffic.

Finally , the engine never spin while using B mode in EV but it can start unexpectedly for many reasons , like when the Hybrid battery is full and you engage B mode in EV while driving down a huge slope the engine may start to eat the extra energy because the traction battery can't take it ... . well this is my conclusion after i used the app Hybrid assistant and tried different things with the B mode.

 

I think from now on, with any question about "B" mode I'm just going to say....

" Never B sharp, Never B flat, always B natural " .

I had a great music teacher that put that in my grade school year book 3 years in a row. If it was a good enough reply then...it will do today.

 

Toyota has changed the manual, or you have misremembered bits.

2019 Prius on B shift position, "Applying engine braking or strong braking when the accelerator pedal has been released on steep down-ward slopes etc." The etc. acknowledges that there are other uses for engine braking beyond downslopes.

2019 Prius c, "Position for engine braking." That is literally all it says about B gear.

2019 Camry hybrid doesn't even use B anymore; it uses the same labels as the ICE Camry shifter. B is now S(equential), which allows you select what max gear the ICE car uses.
"Shift ranges and their functions●You can choose from 6 levels of accelerating force and engine braking force.●A lower shift range will provide greater accelerating force and engine braking force than a higher shift range, and the engine revolutions will also increase."
It is basically B, but with selectable amounts of braking.

Why? B is just the increased engine braking L gave on past automatic cars. It can be used for the same situations as you downshift to L for braking, which extend beyond downslopes. When to downshift for braking is something that should have been covered in driver's ed. It is a standard technique available to any transmission with selectable gear ratios. With the easy reach of paddle shifters, I've been using it to slow down on level roads.

The confusion around B is because hybrids add regenerative braking to the mix. Which wasn't helped by ignorant dealers. For most people, all they need know is that you use B whenever you would have used a lower gear when driving other cars.

 

Returning to the OP, the main downside to using B all the time is the possible reduced fuel efficiency. The car could purposely waste energy with spinning the engine, or there is more conversion losses with more regen braking.

 

But at least with the Prime's EV-B mode, that engine spinning portion of the wastage is eliminated.

 

By increasing the conversion loses of recharging and discharging the battery.

Comes down to the driver. Using B could help, but, like EV mode on the regular Prius, it has the potential to hurt.

The downsides of B in most cases are minor. I think the real question for the OP is why do they want to use it?

 

At least that conversion loss is less than the 100% loss of engine braking.

The earlier descriptions I read about using Prime's EV-B mode on the regular street were for drivability preferences, not for absolute energy efficiency. They came from drivers wanting greater one-pedal speed control before having to switch to two-pedal mode.

Yep.

 

EV Regenerative Braking using the "B" drive in EV Mode | PriusChat