B - Mode

[ToddR]

Is there any reason not to always use B mode over Drive? I know you can't shift directly to B and can use cruise control in B, but isn't B mode simply more efficient while reducing the need to brake?

I noticed Tesla owners talking about 1 pedal driving - Isn't this B-mode?

 

[doug401]

I use B mode most of the time. I prefer one peddle driving too, just like the Tesla guys. It's common for me to commute to work while only touching the brake peddle for anything under 15 mph, or pulling into my parking space.

 

[SeaMonster]

You have to balance two different inefficiencies. It is inefficient to use friction braking to slow down, IF you could have slowed down with regen. Also it is inefficient to convert kinetic energy to electricity and then back to kinetic.

So if you know that you have to slow down, B-mode can help you convert more kinetic energy to electricity instead of friction heat. However, you can do the same thing by applying the brake lightly.

If you want to coast, but don't need to slow down, then B-mode will slow you down more than you need and is inefficient. You convert extra kinetic energy to electricity and then you have to hit the "gas" to convert electricity to kinetic to speed back up. However, you can counteract that by applying the gas pedal lightly to keep the regen from kicking in.

So it really depends on how you like to drive. I don't like one-pedal driving, because no matter how much you try, you still need that brake pedal (eventually). And I like moving my foot over the brake (without pressing) whenever I am not on the gas. That's just a personal safety habit. YMMV. For me, I only use B when going down steep, long hills where coasting would take me faster than I like. For short hills, I use the brake and try to use only a little when I can to avoid friction braking. On the Waldo Grade, I'd be going over 80 if I coasted so I engage B-Mode. But I disengage before the bottom so that I maximize kinetic energy (within my personal safety limits) for the non-coasting I will do ahead. Sometimes in traffic I see a light turn red ahead and I flip into B-mode to slow me down gradually without pressing the brake, but I find that's just a fun game and usually I just press the brake lightly.

 

[snoltor]

In the Prius there is a charge meter in the Hybrid System Indicator and as long as you don't fill the charge meter (CHG in the attached image) while braking then you are only using regenerative brakes and have not engaged the friction brakes. Nice feedback and helps the interested driver to brake easily. Not yet sure if the charge meter works the same in the Rav4 EV. Anybody know?

http://www.blogcdn.com/green.autoblog.com/media/2010/04/phev-prius-drive-2010-scrn-1.jpg

I use the brake and try to use only a little when I can to avoid friction braking.

 

[SeaMonster]

In the Prius there is a charge meter in the Hybrid System Indicator and as long as you don't fill the charge meter (CHG in the attached image) while braking then you are only using regenerative brakes and have not engaged the friction brakes. Nice feedback and helps the interested driver to brake easily. Not yet sure if the charge meter works the same in the Rav4 EV. Anybody know?

I'm pretty sure that the Power meter in the Rav4 does NOT give any indication of whether friction braking is engaged. While going reasonable speeds, it feels like friction engages before the lower purple portion hits full. Plus as the vehicle slows, the purple levels shrinks (as you would expect) and friction definitely engages as the vehicle gets close to stopping. I think it is only showing what level of power is being regenerated.

I would really love to have an indication of when friction engages.

 

[snoltor]

Breaking does feel very different in the Rav4 to me. Not surprising I guess since it has a 1000 pounds on the Prius

 

[doug401]

I use B mode most of the time.

Yes.. although I use B mode most of the time, I don't use it at all if hyper mile'ing, unless I've misjudged my coasting distance. Then I'll drop it into B to brake for the regen. But as most know, "pulse and glide" is the best practice for max distance. Since the Rav is so great with range, I find myself not hyper mile'ing as much as I used to do with the Prius or Leaf.

Pulse and Glide was an old Prius technique... it's soooo 2005

 

[robertk925]

Doug, does pulse and glide work (i.e. increase range) for BEV vehicles? I thought it was only effective with hybrids.

 

[yblaser]

Doug, does pulse and glide work (i.e. increase range) for BEV vehicles? I thought it was only effective with hybrids.

+1. I thought that technique works because ICEs are more efficient under load which I don't think is true for EV motors (edit - It is true but not as dramatic as with ICEs).

 

[doug401]

Yes you're both right... It's an outdated term. Pulse and Glide was an old Prius technique... it's soooo 2005 It's for hybrids... Pulse the engine up to speed, usually 45mph, then glide down to 30 mph. Repeat as necessary. I went from Seattle to Portland and back and got 65mpg.

But drafting... now you can't get me on that one. I can still draft semi's on the freeway right? I just can't pass up a hi-velocity wind break.

***Disclaimer... I do not condone tail gating, or following too closely as the law allows.***

Back to the action. I prefer Canadian tour buses, meth fueled Arizona long haulers, and RV's that know the camp ground is filling up fast.

 

[TonyWilliams]

Is there any reason not to always use B mode over Drive? I know you can't shift directly to B and can use cruise control in B, but isn't B mode simply more efficient while reducing the need to brake?

I noticed Tesla owners talking about 1 pedal driving - Isn't this B-mode?

Not sure you said what you meant... Cruise control does not work in B, just like a Prius.

 

[ToddR]

Oops - mean't you CAN'T use cruise control in 'B' - for some reason - who knows?

Also it seems like slight pressure on the accelerator in B acts like D

 

[alflash]

Take a look how much energy is returned to the HV battery when braking is RAV4EV and when B mode is ON (355V and 125A)

 

[miimura]

Check out my response above... you are likely significantly reducing your efficiency by doing this.

Your video is about hybrids. The EV is not a hybrid, so it doesn't apply at all.

 

[Hybridsarebetter]

Your video is about hybrids. The EV is not a hybrid, so it doesn't apply at all.

So B mode is different in EV's versus hybrids? I'm asking because I really don't know, but it would seem odd to me for Toyota to use the same name "b-mode" if it the function was considerably different between models.

 

[davewill]

So B mode is different in EV's versus hybrids? I'm asking because I really don't know, but it would seem odd to me for Toyota to use the same name "b-mode" if it the function was considerably different between models.

B Mode in a Toyota hybrid is similar to the EV. They both use more regen braking when you let off the accelerator in B mode, and they both disable cruise control. I think one of the differences is that when the battery is full, the hybrid can still use the gas engine to brake, but the EV can't. B Mode will just coast in that case.

 

[miimura]

So B mode is different in EV's versus hybrids? I'm asking because I really don't know, but it would seem odd to me for Toyota to use the same name "b-mode" if it the function was considerably different between models.

My main point was about efficiency. If you have to slow down anyway, using B mode in the EV will capture as much energy as possible back into the traction battery. If you slow down with the same deceleration in D mode, you will be blending regen and the friction brakes. As long as the B mode deceleration is sufficient for your driving needs, it will be more efficient than D mode. Like any EV with good regenerative braking, you should always use the accelerator to smoothly control your speed of acceleration and deceleration according to the traffic conditions. The brake pedal is only for complete stops or slowing down faster than the regen allows.

The other thing you need to know about the RAV4 EV is that it was a compliance car. They used as many common parts as they could from the RAV4 and Prius as they could. The gear selector lever is clearly one of these parts that came straight from the Prius parts bin. Since the lever had a B mode, they chose to implement it on the EV in a similar manner as the hybrid.

Now, if you're talking about the bad habit people develop in gas cars of just blindly lifting completely off the accelerator to coast and continuing to use that approach in a hybrid or EV, then sure, B mode will be less efficient because the driver didn't really intend to decelerate that much and really wanted to coast.

 

[Hybridsarebetter]

My main point was about efficiency. If you have to slow down anyway, using B mode in the EV will capture as much energy as possible back into the traction battery. If you slow down with the same deceleration in D mode, you will be blending regen and the friction brakes. As long as the B mode deceleration is sufficient for your driving needs, it will be more efficient than D mode. Like any EV with good regenerative braking, you should always use the accelerator to smoothly control your speed of acceleration and deceleration according to the traffic conditions. The brake pedal is only for complete stops or slowing down faster than the regen allows.

The other thing you need to know about the RAV4 EV is that it was a compliance car. They used as many common parts as they could from the RAV4 and Prius as they could. The gear selector lever is clearly one of these parts that came straight from the Prius parts bin. Since the lever had a B mode, they chose to implement it on the EV in a similar manner as the hybrid.

Now, if you're talking about the bad habit people develop in gas cars of just blindly lifting completely off the accelerator to coast and continuing to use that approach in a hybrid or EV, then sure, B mode will be less efficient because the driver didn't really intend to decelerate that much and really wanted to coast.

I agree with you for the most part. I think I would just simply say that anytime that you slow your forward momentum to generate electricity to charge your battery, there is overall lost efficiency. Coasting, on the other hand, uses zero energy. That is precisely why B mode is designed for most efficient energy generation when you would otherwise be braking, not coasting. The average person that drives around in B mode all the time is not realizing the highest efficiency. That's why that video that I posted a link to is so good... Seems to be the only Toyota tech that did a really good job explaining how B mode functions. Principle is the same whether EV or hybrid. Energy can neither be created nor destroyed, and every transfer has efficiency losses in the form of heat.

 

[davewill]

I agree with you for the most part. I think I would just simply say that anytime that you slow your forward momentum to generate electricity to charge your battery, there is overall lost efficiency. Coasting, on the other hand, uses zero energy. That is precisely why B mode is designed for most efficient energy generation when you would otherwise be braking, not coasting. The average person that drives around in B mode all the time is not realizing the highest efficiency. That's why that video that I posted a link to is so good... Seems to be the only Toyota tech that did a really good job explaining how B mode functions. Principle is the same whether EV or hybrid. Energy can neither be created nor destroyed, and every transfer has efficiency losses in the form of heat.

It depends on their driving style. If they are using B Mode to do one-pedal driving like a Tesla, and keeping consistent pressure on the accelerator when they want to maintain speed, rather cycling between slowing and accelerating, then there's no reason for it to be less efficient, it might even be more efficient if it allows them to more consistently use regen to brake when they have to.