Bmode and better regen

I'll take a stab at this one. B mode probably can help put more regen back into the pack. But B mode alone is not going to make a significant difference in the overall performance of the cars EV capabilities. Not sure which year/model you're asking about and/or if I have any experience with that model/year car. B mode is definitively more useful in no / low traffic driving when the driver can pay much more attention to how the car behaves thus giving the driver more clues how the cars regen works most effectively. Than the driver can drive that way more often and raise the ECO score.

 

Why would B mode improve regen? It's specifically designed to convert energy into heat by moving the engine pistons without any fuel. It does help to extend brakes liffespan (which do the same thing, convert energy to heat) on long/steep downhills, but I have not seen any hard data on B mode attempting to put more electricity into batteries than regular braking.

When braking mildly, the car kinetic energy gets converted to electricity (with some losses of course). When B mode is engaged, this kinetic electricity is partly converted into heat (in the engine) and if anything is left over, it goes to batteries.

 

B mode has less to do with MG1 and MG2 in model/year prii with less EV capability. So you're probably right when referencing 2008 and 2010 prii. As prii got more EV capabilities B mode also changed, especially in EV only mode.
I only have experience with prii plugins so I tried to be as general as possible seeing the OP has a 2010 listed in the profile.

 

B-mode is different between EV operation and HV operation. In HV it engages engine braking like on a traditional Prius, whereas in EV, it adds a little more regenerative braking.

The braking effect in either case is modest, but not insignificant. It’s not nearly as “whoah!” as taking your foot off the gas on a Tesla, for example.

Engaging B mode also prevents you kicking in cruise control, so if you like the extra regen, it’s probably not realistic to drive all the time in that mode.

 

On Prius Plug-in, the B gear, when engaged during EV mode, brings some flavour of One Pedal driving.
But no more than a reinforced coasting, not able to stop the car or even to tackle descents of quite sensitive slopes.
In this case, when the action of B gear is not sufficient and the brake pedal must be pressed, all the additional braking action is carried out hydraulically.
So in a steep descent, driving in EV with the B gear and brakes pressed, leads to a substantial reduction of regeneration power compared with that you could get using the D gear and the brakes.
This can easily be observed using an OBD app such as Hybrid Assistant.

 

EV only regen is different on differing slope angles,,
also at different speeds on the same downhill stretch of road, but I get your point about B mode and Brake Pedal on a steep decline being less effective than using brake pedal only instead of combining B mode than having to press the brake pedal too.
Prime has the default regen dialed in very well. So good that there is not much that can be gained in EV performance with available controls at the drivers disposal.

Holding at one speed on a declining slope using cruise adds another variable to the amount of regen the car pulls from any one slope angle and any one speed.

I like B mode because it's another tool that make driving the Prime in EV mode more fun and offers a surprise or two when the pack is cold.

With Tesla Model S and I'd guess the others as well, regen is driver adjustable. At it's max setting the driver can feel the drag during acceleration, The Primes B mode is barely noticeable during acceleration. If I can't set cruise, after a few tries, I now realize I've forgotten to shift from B mode back to normal D drive.

 

B mode is an instruction to the hybrid ECU to use the hybrid system to reduce speed. When able, it will do so via regen. If unable it will divert torque into freewheeling the gas engine. Either way it's going to actively do something to exert braking influence on the front wheels without heating up the service brakes. Braking is the priority; not energy recovery.

Leaving it in D lets you keep more control over the process. With proper pedal modulation you can get great regen recovery, and the computer has no authority to divert that torque into the gas engine. Energy recovery can potentially be the priority in this mode, if the driver chooses to operate the pedal the right way.

When you're driving in rolling hills, don't forget that you can bank up a bit of inertia on the downhills to reduce power demand on the uphills. This is much more energy-efficient than banking the power in the battery. Granted, there will be traffic and speed limits to manage while doing so, but it is your most powerful tool for saving energy, by a wide margin. Regen capture to the battery for later motive power is a great second chance, but that's all it is.

 

The technology that would help your situation the most would be topographically-coherent navigation. Kia recently debuted something like this on the Niro, though I can't say if it's actually optimized for this exact scenario. @John321 has one, could guide you better than I.

The theory is that if the car knows your destination is a hilltop, it won't bother burning as much gas to raise the state of charge close to arrival. That way there's more capacity available to capture energy upon the next departure.

 

But we're still discussing the 2010? Assuming yes:

The only time I'd use B is if I wanted to reduce charging; that's basically what it does, employing engine braking. A typical scenario would be a protracted downhill run, say multiple miles.

If you don't switch to B, there's a danger of topping up the battery charge as much as the car's willing to do, and having it switch to friction braking only. If this occurs when there's still a long ways to the bottom, you might overheat the brakes.

Again, I'd only use this on extremely long downhills.

Other'n that, I would just leave it in D, all the time. When you need to slow use the brake. That will give you more regen than B.

 

I am speaking about a 2019 Prius Prime (named PHV in EU).

I noticed that in EV mode the B gear, if used when braking, greatly reduces regen power.
I did a test on a short downhill ramp, covered in EV using once D gear, the other time B gear .

The ramp:


Left in D, right in B:




In D regen is quite the double: 180Wh in D, 95Wh in B.

Other tests in more consistent descents have confirmed this observation: braking in B gear is carried out mainly through the hydraulic way.

 

There are some specifics with the Prime others have posted about, specifically Primes gas engine starting on a sizable downhill if the pack has been fully charged while plugged in.

The other part of your scenario that is an important part if you want to drive the entire trip in EV is how long is the entire trip and how much of the trip is uphill if any?

I'm no expert at driving the Prime on hills like there are in your area. I like to find the flattest route I can find to get where I'm going and drive at the steadiest speed traffic allows.

So your downhill. 3 suggestions to try
Don't charge all the way while plugged in. stop charging at about 50 minutes to go if using 120 volt or if charging with 240 volt stop charging with about 30 minutes until full. Adjust as you notice how much charge the downhill adds to the traction pack.

Try using B mode on the hill
Try using Normal D on the hill
Try setting cruise on the hill
and see which you like better and / or adds the desired amount of charge to the traction pack.

If the Prime is in B mode the cruise will not set. I'll have to check what happens if the cruise is set and than Prime is switched to B mode. It will probably drop out of cruise. but I've never done that.

If you are going to use the gas engine on your trip, use the hill to run the Primes gas engine through it's warmup cycle.

 

I think you mean pneumatic, the primary force involved is the compression of air in the engine after it's been drawn past a closed throttle plate.

Either way, thanks for sharing the graphs! Good stuff.

 

I mean through discs and pads.
I also want to emphasize that I'm talking about Braking in B, not Coasting.

 

Ah the B mode confusion rears it's typical head. lol

 

Okay I think that needs clarification. Obviously the braking force applied by the selection of B mode won't be effected by the discs and pads; everyone would have overheated their brakes.

If you mean the braking force applied by depressing the brake pedal while coincidentally in B mode, I'd believe that.

 

Don't forget about the possibly some have asserted that B mode can overspin MG1 or MG2 at higher speeds when the engine is on / running?

Never bother testing to see or even use B mode to often when the gas engine is running.

I really like being able to hear when the pads touch the rotors whenever possible, it helps me get a fell for the pedal.

 

Exactly.
And Coasting is the application of no action on the pedals.

I stated that, driving in EV, coasting in B is great if you need a small-medium advancing resistance, totally made by electric regen (MG2).

But if you need more resistance, and you apply the foot on brake pedal, further resistance is obtained in large part through hydraulic braking on the discs, not with an increment of regen force.

Braking when in D can get the same resistance but with a substantial increment of global energy recovery.

So I avoid using B when I need to press the brake pedal.

I have no explanation for this behavior (no matter of MG1/MG2 because I don't see any reason why something that works in D couldn't do the same in B).