When to use the B drive mode.

[carboncat]

I recently got a Yaris 4Gen 2020. I was wondering when anyone would use the B drive selector/mode ? What is the value of this?

[forkingabout]

Its for descending steep hills as it provides maximum regenerative braking force from the hybrid system - its to stop the normal friction brakes from over heating. 

This video will help explain it. 

 

 

[TonyHSD]

Best places to try it are when you see the road sign Low gear now. It’s actually an engine braking as mentioned above. You can do without it too if you want to use the brakes only as they barely gets hot because of the regenerative braking of the hybrid system. 

[Cyker]

Basically anywhere where you might downshift a manual car into e.g. 2nd/3rd gear to descent a hill. So hardly ever, unless you travel around places with super steep roads like bath or the peak district or wales or something like that regularly  

I pass by Alexandra Palace in London semi-frequently and I don't even use B-mode going down that hill!

So far I've only used B-mode just to see what it does and how the car reacts, but for 99% of driving it is much worse than D-mode as you can't coast in B-mode and (Unlike what a lot of car journalists say) it DOESN'T regen more than braking, esp. on the newer hybrids.

 

[TonyHSD]

1 hour ago, Cyker said:

Basically anywhere where you might downshift a manual car into e.g. 2nd/3rd gear to descent a hill. So hardly ever, unless you travel around places with super steep roads like bath or the peak district or wales or something like that regularly  

I pass by Alexandra Palace in London semi-frequently and I don't even use B-mode going down that hill!

So far I've only used B-mode just to see what it does and how the car reacts, but for 99% of driving it is much worse than D-mode as you can't coast in B-mode and (Unlike what a lot of car journalists say) it DOESN'T regen more than braking, esp. on the newer hybrids.

 

Haha, I actually use B mode exactly at Alexandra palace going from the roundabout down the hill but B mode only its not enough to hold the car and  I have to use brakes too but less often. 

[Sidrat]

In my Corolla I use it anytime you want to deccellerate quicker than just lifting your foot off the accelerator but not applying the breaks, coming up to roundabouts, junctions etc. 

[Cyker]

Yes! This is a weird/interesting difference we noticed when comparing cars:

If my colleague (Who also has a Mk1 Auris HSD!) went down the hill without touching the brakes he'd probably be doing 70+mph at the bottom  

If I don't, I reckon I'd be doing maybe 40-50mph?

(I should clarify these are estimations and we don't actually let the cars get anywhere near such speeds, esp. given there is a tight turn right at the bottom which would be impossible to take at such speeds  )

He has to use light-medium braking all the way down, but like you usually just uses B-mode, whereas I occasionally brake to bring the speed down, but then lift off and let it slowly build again because the car picks up speed down the hill more slowly. I tried the Mk4's B-mode down there once and felt like I was being catapulted through the windscreen   

It's interesting how they've changed how the car responds through the generations, esp. the base-level of regen; It's much higher in the Mk4 than the Auris, so he can coast off-pedal for ages whereas I can't.

This does mean I don't have to touch the brake pedal as much, but not sure if that's a good thing or a bad thing with all the tailgaters around!

[CPN]

59 minutes ago, Sidrat said:

In my Corolla I use it anytime you want to deccellerate quicker than just lifting your foot off the accelerator but not applying the breaks, coming up to roundabouts, junctions etc. 

Though it is rare, that's very much how I use it.

[FROSTYBALLS]

Extract from https://mag.toyota.co.uk/hybrid-driving-tips-for-best-fuel-economy/

 "The shift lever offers four positions: R (Reverse), N (neutral), B (engine braking) and D (drive). For normal driving, D (drive) is absolutely fine, but should you need it, position B has the effect of engine-braking handy when descending a steep hill, for example. It’s not recommended to leave the car in position B for normal driving, mainly because you’d end up using more fuel than necessary!"

[carboncat]

Seems you need to be in a relatively hilly area to use B mode on the hybrids at all. 

[Sidrat]

53 minutes ago, carboncat said:

Seems you need to be in a relatively hilly area to use B mode on the hybrids at all. 

Use it any time you want to decelerate quicker than coasting but not as fast as breaking, roundabouts,  junctions, it's not just for hills, just don't drive around in B mode all the time, treat it as shifting down a gear.

[Stopeter44]

36 minutes ago, Sidrat said:

Use it any time you want to decelerate quicker than coasting but not as fast as breaking, roundabouts,  junctions, it's not just for hills, just don't drive around in B mode all the time, treat it as shifting down a gear.

Given that on a Toyota hybrid the disk brakes don't bite until you really need to stop, or stop quickly, I really don't see the point of using "B" mode like that. The same result is achieved by using the "regen" braking, and this won't start up the ICE.

Each to his/her own.

[RickyC]

Moreover IMHO it's a nonsense to buy a car with automatic gear and continue to shift the lever between D and B.  

If you like to hear the engine scream at roundabouts probably a car with manual gear fits better to you.

[TonyHSD]

B mode could be there as back up when going long downhill more than anything else. If you a new to the hybrids you can experiment and use it to try and see how it works, but in general use after that best to leave it alone. My recommendation when going downhill instead of B switch to N neutral and use the brakes only for couple of minutes to rise the temperature of the brake system a bit and to clean the brake discs surfaces, then switch back to D and continue your drive.
Toyota hybrids get rust issues with brakes when not used daily, driven ultra slow and B mode been used more often. I had to change twice all brake discs and pads because of lack of use previously and my third set is over 60k miles now with minimal brake wear on the components. 
12 months from new and your brake parts may require cleaning procedure if you are not using the car much or the car it’s not garaged. 
Two important things in hybrids different from standard ice cars that require slightly different approach: 

1. Brakes 

2. 12V battery 

👍

 

[Spo2]

9 minutes ago, TonyHSD said:

B mode could be there as back up when going long downhill more than anything else. If you a new to the hybrids you can experiment and use it to try and see how it works, but in general use after that best to leave it alone. My recommendation when going downhill instead of B switch to N neutral and use the brakes only for couple of minutes to rise the temperature of the brake system a bit and to clean the brake discs surfaces, then switch back to D and continue your drive.
Toyota hybrids get rust issues with brakes when not used daily, driven ultra slow and B mode been used more often. I had to change twice all brake discs and pads because of lack of use previously and my third set is over 60k miles now with minimal brake wear on the components. 
12 months from new and your brake parts may require cleaning procedure if you are not using the car much or the car it’s not garaged. 
Two important things in hybrids different from standard ice cars that require slightly different approach: 

1. Brakes 

2. 12V battery 

👍

 

Thanks Tony. Is it safe to let a Toyota hybrid roll in 'N' and use brakes (perfectly okay in manual ICE vehicles)?

[Gray86]

I used B mode last weekend (well, manual mode with the paddles on the 2.0) when driving through the Peak District. The regen alone wasn’t enough to slow the car, and for fear of overheating the brakes, and filling the Battery I pulled the paddle for a simulated 3rd gear. Worked really well 

[TonyHSD]

Just now, Spo2 said:

Thanks Tony. Is it safe to let a Toyota hybrid roll in 'N' and use brakes (perfectly okay in manual ICE vehicles)?

Yes for a short period of time only, 1-2 minutes max just to clean the brakes from rust. Also you can try that when the car is brand new to accelerate the bed in process of the brake parts, but remember No heavy braking, just continues slowing down and free rolling. Important not to keep the car rolling in N for longer or in any other circumstances except short time for cleaning your brake discs surfaces because of lubricating of the transmission bearings, there is an oil pump connected to the engine crankshaft, not sure this is operational when the car is in N and the lubricating of the transmission will only be done via differential gear splash. 👍

[preperationlaunch]

2 hours ago, TonyHSD said:

Yes for a short period of time only, 1-2 minutes max just to clean the brakes from rust. Also you can try that when the car is brand new to accelerate the bed in process of the brake parts, but remember No heavy braking, just continues slowing down and free rolling. Important not to keep the car rolling in N for longer or in any other circumstances except short time for cleaning your brake discs surfaces because of lubricating of the transmission bearings, there is an oil pump connected to the engine crankshaft, not sure this is operational when the car is in N and the lubricating of the transmission will only be done via differential gear splash. 👍

I'd be incredibly careful doing this at any speed, especially in anything Gen3 (Yaris/Auris hybrids, prius Gen3 etc.) or earlier.

I'm not clear on how the mechanism works in Gen4 to allow the higher speeds. In the Prius prime, the ICE has a one-way sprag clutch, so MG1 can be spun to help propel without spinning the ICE. I suspect this is the same in the Gen4 Yaris.

In neutral, there is no power sent to the motors. That means the computers can't do their wizardry to keep the motors at the right speeds.

When the car is going above a certain speed in the Gen3s (approx 42mph where EV mode cuts out), MG1 must be spun backwards by the Battery to turn the ICE, or the ICE must be running, otherwise the motor will overspeed. The car won't be able to protect against that in N.

[TonyHSD]

2 hours ago, preperationlaunch said:

I'd be incredibly careful doing this at any speed, especially in anything Gen3 (Yaris/Auris hybrids, prius Gen3 etc.) or earlier.

I'm not clear on how the mechanism works in Gen4 to allow the higher speeds. In the Prius prime, the ICE has a one-way sprag clutch, so MG1 can be spun to help propel without spinning the ICE. I suspect this is the same in the Gen4 Yaris.

In neutral, there is no power sent to the motors. That means the computers can't do their wizardry to keep the motors at the right speeds.

When the car is going above a certain speed in the Gen3s (approx 42mph where EV mode cuts out), MG1 must be spun backwards by the battery to turn the ICE, or the ICE must be running, otherwise the motor will overspeed. The car won't be able to protect against that in N.

No need to worry about that as the system is designed to protect  itself and also N is selectable even over 70mph and you can easily switch back to D without any issues, you won’t even notice. I have done that many times. The only issue may arise with lubrication of the bearings as they need the oil pump to be spun by the crank shaft, in speeds over 40mph even while in ev mode crankshaft rotates at 1000rpm. It is safe to select N almost in any speeds but it is not advisable to drive in N for long periods of time. 👍

[ToyotaRocker]

You also can't engage cruise control while in B-mode. Found this while trying to engage cruise control on motorway, I panicked thinking the system has malfunctioned and needed service. But noticed I was in B, switched to D and all was working fine.

[preperationlaunch]

7 hours ago, TonyHSD said:

No need to worry about that as the system is designed to protect  itself and also N is selectable even over 70mph and you can easily switch back to D without any issues, you won’t even notice. I have done that many times. The only issue may arise with lubrication of the bearings as they need the oil pump to be spun by the crank shaft, in speeds over 40mph even while in ev mode crankshaft rotates at 1000rpm. It is safe to select N almost in any speeds but it is not advisable to drive in N for long periods of time. 👍

The system can't protect itself in neutral, that's the key issue. The law requiring neutral positions means that the car can't apply any power to the electric motors. Cutting power to the electric motors means the engine can't spin the wheels, it'll just spin MG1 instead. It means the car can't stop or start the engine either. A Hybrid will sit and drain the Battery until it shuts off in neutral. It'll bong angrily and ask to be put into park, but that's it. If it's running, it'll keep running but drain the Battery.

N has to be selectable at any time, in case you're in a situation where the throttle is stuck. Protecting life comes over protecting a gearbox. Even the PRNDL order of gears is in legislation in the US.

But, the car needs to power the motors to control how fast the engine and MG1 spin. MG2 spins at a fixed ratio to the wheels, but, that factors into the equation too.

There is some clever maths behind the speed reasoning, but essentially, the limitation of EV mode top speed is from the speed at which MG1 can spin. MG1 has to spin faster backwards if the engine isn't running, because of the way the planetary geubikt works.

What this actually means in practice is that, if you go above the EV mode speed limit in neutral, either with the ICE off, or the engine at low revs, you risk spinning MG1 far too fast.

 

[TonyHSD]

34 minutes ago, preperationlaunch said:

The system can't protect itself in neutral, that's the key issue. The law requiring neutral positions means that the car can't apply any power to the electric motors. Cutting power to the electric motors means the engine can't spin the wheels, it'll just spin MG1 instead. It means the car can't stop or start the engine either. A Hybrid will sit and drain the battery until it shuts off in neutral. It'll bong angrily and ask to be put into park, but that's it. If it's running, it'll keep running but drain the battery.

N has to be selectable at any time, in case you're in a situation where the throttle is stuck. Protecting life comes over protecting a gearbox. Even the PRNDL order of gears is in legislation in the US.

But, the car needs to power the motors to control how fast the engine and MG1 spin. MG2 spins at a fixed ratio to the wheels, but, that factors into the equation too.

There is some clever maths behind the speed reasoning, but essentially, the limitation of EV mode top speed is from the speed at which MG1 can spin. MG1 has to spin faster backwards if the engine isn't running, because of the way the planetary geubikt works.

What this actually means in practice is that, if you go above the EV mode speed limit in neutral, either with the ICE off, or the engine at low revs, you risk spinning MG1 far too fast.

 

As I said if you select N at any speed nothing wrong will happen to the car, it will simply continue to free rolling. Select D and the car will drive as usual, if you off the gas the regenerative braking will kick in immediately or if you press accelerator the car will accelerate. If you select N at speeds over the maximum allowed 115 mph then you may have an issue as you described, because you will pass the maximum safe speed mg1 can rotate, any other speeds below are safe. I have done over 70mph and selected N then D and no problems at all. 

[preperationlaunch]

30 minutes ago, TonyHSD said:

As I said if you select N at any speed nothing wrong will happen to the car, it will simply continue to free rolling. Select D and the car will drive as usual, if you off the gas the regenerative braking will kick in immediately or if you press accelerator the car will accelerate. If you select N at speeds over the maximum allowed 115 mph then you may have an issue as you described, because you will pass the maximum safe speed mg1 can rotate, any other speeds below are safe. I have done over 70mph and selected N then D and no problems at all. 

You’re forgetting that MG1’s speed isn’t just based on wheel speed. That’s MG2. MG1 spins to essentially absorb the difference between the ICE and the wheels. If MG1 resists turning when the ICE turns, then the wheels must turn. If MG1 spins freely, no power from the ICE goes to the wheels. 

The car will spin the ICE using MG1 at any speed above approx 45mph. The only reason it does that is to reduce the speed at which MG1 spins. This stops MG1 overspeeding when in B or D. 

Coasting in neutral overrides almost all protections. If the engine isn’t running and you coast above the max speed of MG1, the car cannot do anything to prevent damage. 

The engine stays running if already running when shifted to N to try and stop you from ending up in exactly that state. But it isn’t foolproof, especially on a downhill. If you’re coasting beyond the EV mode limit with the engine still off, you’re going over what Toyota have set as the MG1 RPM limit. 

It is less bad if the engine is running, because you have the speed of MG1 reduced because the engine is spinning it. Remember the speed of the ICE and MG1 in combination is tied to the speed of the wheels. 

The 112mph limit will be a limit of MG2, whose speed is directly tied to the wheels at all times.

Whilst you may have gotten away with it, it’s clear why it isn’t a good idea for the longevity of a transmission to be encouraged to go well outside design parameters.

If Toyota thought MG1 would be reliable spinning backwards at those high RPMs, the car would stay in EV mode up to them. The newer cars get around it by having a sprag clutch on the flywheel, which means the shaft for the ICE can spin backwards whilst MG1 and MG2 can both act as propulsion motors at the same time. 

[TonyHSD]

8 hours ago, preperationlaunch said:

You’re forgetting that MG1’s speed isn’t just based on wheel speed. That’s MG2. MG1 spins to essentially absorb the difference between the ICE and the wheels. If MG1 resists turning when the ICE turns, then the wheels must turn. If MG1 spins freely, no power from the ICE goes to the wheels. 

The car will spin the ICE using MG1 at any speed above approx 45mph. The only reason it does that is to reduce the speed at which MG1 spins. This stops MG1 overspeeding when in B or D. 

Coasting in neutral overrides almost all protections. If the engine isn’t running and you coast above the max speed of MG1, the car cannot do anything to prevent damage. 

The engine stays running if already running when shifted to N to try and stop you from ending up in exactly that state. But it isn’t foolproof, especially on a downhill. If you’re coasting beyond the EV mode limit with the engine still off, you’re going over what Toyota have set as the MG1 RPM limit. 

It is less bad if the engine is running, because you have the speed of MG1 reduced because the engine is spinning it. Remember the speed of the ICE and MG1 in combination is tied to the speed of the wheels. 

The 112mph limit will be a limit of MG2, whose speed is directly tied to the wheels at all times.

Whilst you may have gotten away with it, it’s clear why it isn’t a good idea for the longevity of a transmission to be encouraged to go well outside design parameters.

If Toyota thought MG1 would be reliable spinning backwards at those high RPMs, the car would stay in EV mode up to them. The newer cars get around it by having a sprag clutch on the flywheel, which means the shaft for the ICE can spin backwards whilst MG1 and MG2 can both act as propulsion motors at the same time. 

I respect your knowledge of the Toyota hybrids and how they work. 
I also read, watch and learned something about these cars but I drive them a lot, I mean a lot and have been learning practically ever since and done many experiments and put the car in different situations. 
It is not a problem to let the car rolling in N up to the max allowed speed and then switch back to D without even notice anything, no shift shocks, no sound, no jerky action, nothing, it’s smooth and damage less experience., the whole point of having a reliable drive train is to have all possible scenarios thought by the engineers and solved mechanically and electronically before the car went into production. I never got away with selecting N while driving, I have done it many times and also the car has done it by herself, my one once but others some more times when the car detects issue with the hybrid system either been from the electric motor, (clutch damper) or the engine problems the car will set itself into N at any speeds and will display hybrid system malfunction. Once you stop and restart the car if nothing mechanical has been broken you may be able to continue your journey. 
Thanks for all your experience shared. 👍

[Kental]

22 hours ago, ToyotaRocker said:

You also can't engage cruise control while in B-mode. Found this while trying to engage cruise control on motorway, I panicked thinking the system has malfunctioned and needed service. But noticed I was in B, switched to D and all was working fine.

The wife did exactly the same in hers!