Driving in B mode

[FreshAndClean]

I've been playing around and shifting into "B" to slow down on downhills, offramps, stop signs, stop and go traffic, etc... To increase regen.

Anyone else playing around with this?

Also, is accelerating in B mode inefficient and/or bad for the traction system? Or would this be akin to driving in aggressive regen mode on a tesla or activ-e?

 

[Dsinned]

I use "B" as much as possible to decelerate to obtain the maximum benefit of regenerative braking. As soon as I get back up to speed, unless I'm going down a steep hill, I shift back to "D". I usually shift "early" to D, but I'm not sure if staying in B all the time in city driving is better for optimizing battery efficiency or not.

Here's a related question I have not yet seen commented on here . . . is regenerative braking in Sport mode more or less effective, or exactly the same as driving in the Normal mode? Anybody have any idea?

 

[SeaMonster]

I believe that B mode, when you are braking, has no added effect. I look at B mode as the EV equivalent of shifting into 2nd. It uses the engine to slow you down, but in this case it generates power too. I use it on long downhills when I don't want to apply the brakes. Applying the brakes lightly should only engage the regenerative brakes. Pressing harder causes more and more of the "regular" brakes to take over. The beauty of B mode is that you don't have to guess if you are crossing the threshold into "regular" brakes or not.

I don't think Sport Mode effects B mode or braking. Just as Sport Mode doesn't effect mellow driving. It just raises the limits of how much you can accelerate. You can drive just as efficiently in sport mode as you do in regular mode if you have self control.

 

[jspearman]

Driving in B is lame compared to driving the Volt's L mode, which is truly 1-pedal driving and sort of fun. Acceleration is normal, but regen is turned up to 11! The only bad part of this setup is that the brake lights don't turn on, and they really should.

I look forward to all EV's having user-adjustable regen, but until then I'll use B and L.

 

[yblaser]

Driving in B is lame compared to driving the Volt's L mode, which is truly 1-pedal driving and sort of fun. Acceleration is normal, but regen is turned up to 11! The only bad part of this setup is that the brake lights don't turn on, and they really should.

I look forward to all EV's having user-adjustable regen, but until then I'll use B and L.

I actually prefer the Rav4 B mode to the Volt L mode. The Volt is not my primary car, so I imagine I could get used to the aggressive regen, but as an occasional driver of the Volt I find it needs much more fine muscle control to maintain my speed. Like learning clutch control, I'm sure muscle memory helps, but from a beginner perspective it is a bit difficult.

What I don't like is that the Rav4 won't engage cruise control with B engaged. With the Volt in L and cruise control engaged the Volt does a great job maintaining the set speed in hilly terrain.

In regard to the previous posts, I find comparing B (or L in the Volt) to a lower gear is inaccurate and misleading. There is no loss in efficiency in driving in B no matter the speed, just increased regenerative braking when the accelerator peddle is released. In addition you can get just as good efficiency in D, as long as you are gentle with the brakes. As others have pointed out, B has the advantage that you can be completely sure that no friction braking is being used.

 

[TonyWilliams]

You can drive around in B mode continuously if you like. If in cruise control, a simple pull back to B mode will disengage the cruise control and increase regenerative braking.

"B" is simply "brake assist" by increasing regen. Obviously, there are limitations with a fully charged battery or a cold battery.

 

[cwerdna]

What I don't like is that the Rav4 won't engage cruise control with B engaged.

I suspect this is a carryover quirk from the Prius. Gen 2 Prius has this behavior and I believe all subsequent generations and members of the Prius family do this too.

 

[TeCKis300]

In regards to normal driving, B mode is indeed LESS efficient, if you do not need to decelerate.

You'll note that the 'eco' light automatically disappears on the dash when B mode is engaged.

That is because the momentum is better utilized letting it ride than to recapture it. To recapturing momentum has some translational losses going from kinetic energy -> electrical energy -> and back to kinetic energy.

As noted a few posts earlier, B mode gives no additional effect vs. using the brake pedal to the same level of braking capacity, other than guaranteeing that you are not engaging the physical brake pads, and is handy for long downhill sections to maintain speed. If you can modulate the brakes well, using the B mode is superfluous for regular braking events.

Waidy had shared a hypermilling strategy which is to use 'N' when letting it ride. It indeed works, but I came across a note in the manual discouraging the use of N in this way.

 

[yblaser]

In regards to normal driving, B mode is indeed LESS efficient, if you do not need to decelerate.

I would say that B mode is not inherently less efficient, but if you use it incorrectly it can be. As you say braking unnecessarily wastes energy, but with proper accelerator control unnecessary braking can be eliminated and or at least minimized in both B and D mode.

 

[SeaMonster]

In regard to the previous posts, I find comparing B (or L in the Volt) to a lower gear is inaccurate and misleading. There is no loss in efficiency in driving in B no matter the speed, just increased regenerative braking when the accelerator peddle is released. In addition you can get just as good efficiency in D, as long as you are gentle with the brakes. As others have pointed out, B has the advantage that you can be completely sure that no friction braking is being used.

Sorry, I didn't mean to imply that B is completely like 2nd gear. Obviously it is not. I just think of it that way when I want to slow my decent on a long and/or steep downhill. I use it like down-shifting. But clearly, once you touch the accelerator, all similarities to 2nd gear are gone.

 

[TeCKis300]

I was giving this topic some thought. It’s interesting that even though there is no ICE motor, the controls on the RAV4 are still very much influenced by our entrenched experience with ICE cars. And likewise, it helps us relate functions on our cars to gas motor concepts to better understand our cars.

In regular drive mode, along with the idle creeping function that mimics an ICE car, there is also some regen dialed in when lifting off the accelerator to mimic an ICE car engine braking. The ‘B’ mode further dials up that regen to some equivalent of ‘2nd gear engine braking’. Though we have the benefit in both modes of actually recapturing the energy instead of translating it to heat and sending it out the tailpipe.

As I said, it’s always better to let the momentum ride than to recapture it, when not needing to decelerate. While I agree that it’s even more efficient to modulate the accelerator, we all do have places to go with some amount of expedience, lest we piss everyone else off.

So it’s too bad we don’t have a true ‘sail’ mode. Waidy’s N approach does approximate this, but I worry that it may prematurely wear something. I don’t think there’s a clutch involved, but there’s definitely a relay involved. Besides, it’s not terribly safe to be coasting in N without having immediate acceleration on demand.

I tried this morning to modulate the throttle at a neutral level, without the power meter showing any accel or decel. It’s very hard to keep it there.

So we’re stuck with D and B for efficiency. Both really are just changing the neutral point that the motor control operates at when no pedals are depressed, which is 2 levels into regen, rather than the true more efficient neutral ‘sail’ point.

 

[TonyWilliams]

... So it’s too bad we don’t have a true ‘sail’ mode. Waidy’s N approach does approximate this, but I worry that it may prematurely wear something. I don’t think there’s a clutch involved, but there’s definitely a relay involved. Besides, it’s not terribly safe to be coasting in N without having immediate acceleration on demand.

I tried this morning to modulate the throttle at a neutral level, without the power meter showing any accel or decel. It’s very hard to keep it there.

So we’re stuck with D and B for efficiency. Both really are just changing the neutral point that the motor control operates at when no pedals are depressed, which is 2 levels into regen, rather than the true more efficient neutral ‘sail’ point.

You were doing great until this part!!! I think this just falls into the "too little info" department. There are no clutches or mechanical switches. The "gear shift" is a Hall effect switch (no mechanical switches or moving parts). I have no idea why you feel you need acceleration on demand for safety, but it's literally a pull of the gear shift into "D" away. It couldn't be simpler.

You're not going to prematurely wear anything out except your mind from worry!!! Yes, Virginia, there is a "sail" mode by just putting the car in Neutral. You don't have to reinvent the wheel for something so basic as coasting.

The brakes are designed to handle the weight of the car with zero regen (when the battery is cold or at too high of an SOC%), but I would recommend pulling the gear shift into D/B anytime you need to brake while in Neutral. It's more efficient and saves brake pad wear.

 

[Richard C.]

I have to agree with TeCKis300 - that coasting in N is not safe when you cannot instantaneously accelerate if needed. Sure, you can flip the gear shift to D, but could see a case where you see someone running a stop sign or red light (headed right for you) and you instinctively hit the accelerator but no response. Not good in my humble opinion.

 

[yblaser]

Sorry, I didn't mean to imply that B is completely like 2nd gear. Obviously it is not. I just think of it that way when I want to slow my decent on a long and/or steep downhill. I use it like down-shifting. But clearly, once you touch the accelerator, all similarities to 2nd gear are gone.

Sorry, despite my wording I wasn't trying to call out your particular post and I think your post was pretty clear in what you meant. It was just my experience with other people outside this forum that seem to think it is indeed a lower gear (e.g. some of the sales people), so I prefer not to use that language.

 

[TeCKis300]

You were doing great until this part!!! I think this just falls into the "too little info" department. There are no clutches or mechanical switches. The "gear shift" is a Hall effect switch (no mechanical switches or moving parts). I have no idea why you feel you need acceleration on demand for safety, but it's literally a pull of the gear shift into "D" away. It couldn't be simpler.

You're not going to prematurely wear anything out except your mind from worry!!! Yes, Virginia, there is a "sail" mode by just putting the car in Neutral. You don't have to reinvent the wheel for something so basic as coasting.

The brakes are designed to handle the weight of the car with zero regen (when the battery is cold or at too high of an SOC%), but I would recommend pulling the gear shift into D/B anytime you need to brake while in Neutral. It's more efficient and saves brake pad wear.

Surely I was not concerned about the little hand toggle lever. I might be wrong and you may be able to offer some more insight, but there may likely be a mechanical relay/contact involved somewhere in the high voltage traction motor circuit when selecting between N and D. My concern would be the arcing across this contact when the car is in motion vs. at a standstill. There should be no appreciable current when at a standstill, but there may be very significant current across this contact when the motor is actively spinning/driven. I have to assume Toyota knows something more when specifically recommending guidance against this.

From a safety standpoint, it is one’s prerogative to use N while the car is in motion. But you can’t deny that there is some risk, especially when recommending this practice to the masses. In fact, it is unlawful in most states, though likely due to the increased risk of an ICE vehicle stalling, which in turn affects the vehicles ability to stop due to loss of vacuum. I agree that the RAV would have no issue stopping without active assistance from the regen system.

 

[TonyWilliams]

... My concern would be the arcing across this contact when the car is in motion vs. at a standstill. There should be no appreciable current when at a standstill, but there may be very significant current across this contact when the motor is actively spinning/driven. I have to assume Toyota knows something more when specifically recommending guidance against this.

I don't know why you think that there is "arcing" going on in there. Sorry, but you've decided for whatever reasons that Neutral is bad, and therefore I don't recommend that you use it. But, dropping little hints of "problems" in the design of the car is just not proper.

If you know that there is some issue with the Tesla design, I'm all ears. Otherwise, you're just throwing mud on the wall to see what sticks.

 

[TeCKis300]

I don't know why you think that there is "arcing" going on in there. Sorry, but you've decided for whatever reasons that Neutral is bad, and therefore I don't recommend that you use it. But, dropping little hints of "problems" in the design of the car is just not proper.

If you know that there is some issue with the Tesla design, I'm all ears. Otherwise, you're just throwing mud on the wall to see what sticks.

I thought there was an audible click when going from N to D, but I was wrong on that so it may be all solid state as you're suggesting. No need to get in a tissy. I'm just trying to understand why Toyota would suggest against it.

 

[SeattleRav4]

I apreciate the discussion on D, B and N modes. I have been experimenting a bit myself to understand. I don't think there is anything wrong with the design but I think some undertanding will go a long way.
What we do know is:
1 )Toyota does not recommend towing.
2) Hypermiling by using N mode, especially to coast down one hill and up the next is much more efficient than regen/accel in D.

My guess, and this is just a guess, is that if the car shuts down due to low charge, it puts the circutry in either a high regen mode or even automatically engages PARK. If that happens, towing would be a bad idea. Toyota likely did not want to get into the comlication of saying "If there is enough charge to engage N mode, than it is safe to tow." In addition to the "It depends" problems, free towing a vehicle, if you have never done it, can be far from safe, especially for the car.

My take away unless someone comes up with new data is that N mode is fine for getting a little extra efficiency. N mode is also fine for towing IF THERE IS ENOUGH CHARGE TO ENGAGE IT.

 

[scooter]

pure speculation - perhaps toyota recommends against using N simply to limit liability in case someone has an accident and dies while in N mode and absentmindedly flooring the accelerator to gun it across the tracks before the train reaches. Another pure speculation, if shifting to N did anything to the motor, I suspect it would have either a noise or a transient jerk in momentum, but it seems very smooth and quiet both into and out of N, at any speed.

 

[TonyWilliams]

I don't know why you think that there is "arcing" going on in there. Sorry, but you've decided for whatever reasons that Neutral is bad, and therefore I don't recommend that you use it. But, dropping little hints of "problems" in the design of the car is just not proper.

If you know that there is some issue with the Tesla design, I'm all ears. Otherwise, you're just throwing mud on the wall to see what sticks.

I thought there was an audible click when going from N to D, but I was wrong on that so it may be all solid state as you're suggesting. No need to get in a tissy. I'm just trying to understand why Toyota would suggest against it.

Tissy? I'm merely pointing out the obvious; you're guessing, and using those guesses as the basis for your actions.

I don't know why Toyota recommends against Neutral, but I think you mentioned that it's actually ILLEGAL in some areas. For a company that is currently paying millions in lawsuits in the USA, they probably want to attempt to limit their liability whenever possible. Of course, I'm guessing, too, but I'm also basing my guess on facts, not fiction.