Regenerative braking

[trashman1965]

37 minutes ago, newtalg said:

Why does the hybrid waste energy churning the engine, when the battery could be charged?

This happens in normal drive when braking and on the overrun.

Sounds like I have battery problems that the Toyota dealership don't want to admit to.

Not good on a car not three years old yet.

Occasionally I will see/hear engine turning on braking and overrun but this is either when engine temp has not reached normal or the Battery has reached its safe maximum and excess is being dumped.

If you are seeing this consistently when in D and only D and Battery shows less than max when engine is at temp (and the temp gauge is not a reliable indicator - the ECU will decide when it needs more heat or dump energy). To be absolutely certain you would need diagnosis kit in the OBD to see what is going on at any given time.

If you see it occasionally or in B, that's not an issue.

[preperationlaunch]

2 hours ago, newtalg said:

Why does the hybrid waste energy churning the engine, when the battery could be charged?

This happens in normal drive when braking and on the overrun.

Sounds like I have battery problems that the Toyota dealership don't want to admit to.

Not good on a car not three years old yet.

Toyota's software priorities Battery lifespan over a lot of things.

Depending on how much charge it has, the temperature of the Battery etc. it will change what the Battery can accept within Toyota's design decisions.

There's a maximum rate at which the battery can safely be charged, this varies depending on how much it is already charged. The rate at which the battery can be charged may well be less than the amount of power that MG2 can regenerate. That's as well as the limit to which the car will charge, which varies depending on various factors even on a day to day basis.

The excess power has to go somewhere, so the car sends it out via MG1, which turns over the engine.

Edit to add: the car will also run the engine to generate heat in winter. Even when it seems 'warm', it can cool down quite quickly. So it'll run the motor to warm it up again. There are various cycles and thresholds the car works to as it warms up.

[TonyHSD]

The car maybe is running its engine as mentioned above for heating purposes or when on its warm up stages but also when using AC in hot days to help the Battery as AC uses the high voltage from traction Battery, basically that’s why is called a hybrid the engine can run as petrol generator. The op question is somewhat not viable because Toyota hybrids never waste energy if that energy can be stored or used for propulsion or heating/cooling.
 

For the B mode, you can simply use that to top up your Battery going downhill without touching the brakes and then switch to D without any petrol been used, or energy wasted, it might not be designed for that purpose but it is how it works and how can be used in real life. Again , I am not comparing B vs Brakes for accumulating electricity, only compare B vs free rolling in D while going downhill.
When I am travelling downhill on A road 40mph and I have half + battery soc for example to maintain that speed I need to use the brakes otherwise the car will accelerate over 40mph, if I switch to B the car will start to slow down and engine will be turning but not consuming any fuel since it’s slowing down the car and it will top up the battery and not discharge it. Just before I reach the level ground and the junction I switch back to D and ice turns itself off and I have full battery to use ahead. If I switched to B earlier or if I was using the brakes harder (higher speeds) and battery has reached its designed capacity levels the ice would have started to discharge the battery no matter if the car was in D or B mode beforehand. Therefore B mode can be used for topping up your battery and slow down the car  in short period of time, just like you would have used 4th or 3rd gear on your petrol manual car while going downhill. That’s why many people get confused about B mode and used more often than necessary adding extra heat to the system and unnecessary running of the ice if you are using B instead of D for your regular driving. If you only used the way I explained you can actually get extra energy into your battery, but in hybrids this is not needed since these are small batteries that gets very fast charge and discharge, no need to worry and to top up your battery, plus when battery is full EV mode will be not available.  There are 3 modes that you may not use them at all but it is a good that the car has them: 

1. EV button 

2. B mode

3. N neutral 

Best to drive your car as normal auto and let it do whatever the car needs to. 
 

[preperationlaunch]

Cruise control captures more energy whilst holding speed than B-mode over the same distance.

Going down the same steep and prolonged hill at 40mph yields the following results:

- B mode at ~40mph - the car slows down more, but regeneration is capped at about 25 amps. The rest of the power is being wasted by the ICE spinning.

- Cruise control set at ~40mph - the car holds speed and puts around 50-60 amps sustained into the Battery, the ICE remains off for as long as possible. As it starts to near the full limit, the engine will be spun to burn off the excess power whilst providing braking force. The cruise control slowly ramps up the revs as the rate at which the Battery can charge reduces.

 

[Stopeter44]

1 hour ago, TonyHSD said:

Best to drive your car as normal auto and let it do whatever the car needs to. 

Yes, best to do that. The rest is overthinking, methinks.

[Kental]

On our mk4 Yaris, in B mode, the adaptive cruise will not activate, is this the same in the Corolla?

[trashman1965]

Pretty sure it is.

Logically, B overrides the ECU normal control of the eCVT. Also if you have DRCC/ normal CC or speed limiter it should use regenerative and/or engine braking to reduce the speed. 

[RzrAzr]

Glad there’s no B mode on 2.0. I’ve been coasting down a very long hill today at 90 kph on cruise, pretty much the whole trip was in EV mode. After Battery got fully charged, I could see ICE kick in, probably to slow the car down or at least to waste some energy not to overcharge the batteries. 

[TonyHSD]

What happens when we have Battery full and we don’t have B mode or ice to waste the energy but we are continuing long downhill, let say with a full ev or electric scooter and we have reached the 100%🔋? Will the regenerative braking stop and only actual brakes slow down the vehicle or saved energy can leave the Battery (inverter) into the air via some sort of fuse? Like what happens when a lightning ⚡️ hit an airplane ✈️ ? 

[clix]

1 hour ago, TonyHSD said:

What happens when we have battery full and we don’t have B mode or ice to waste the energy but we are continuing long downhill, let say with a full ev or electric scooter and we have reached the 100%🔋? Will the regenerative braking stop and only actual brakes slow down the vehicle or saved energy can leave the battery (inverter) into the air via some sort of fuse? Like what happens when a lightning ⚡️ hit an airplane ✈️ ? 

Pretty sure, you just loose a regen, so you have to rellay on normal brakes to slow down. It doesn't make sense to waste the Battery charge via some sort of "electric heater"(whitch would have to be quite big or cooled efficienty, to actually make a difference) just to fill it up again. This is what brakes were designed to do and also you are not wasting Battery cycles.

Also, I think that in my corolla, I noticed engine braking being activated during longer descents, even in D mode, if Battery was full, but not 100% sure about that.

[AndrueC]

21 minutes ago, clix said:

Also, I think that in my corolla, I noticed engine braking being activated during longer descents, even in D mode, if battery was full, but not 100% sure about that.

That was my experience last year of descending a very long hilly stretch in North Wales. The first sign was that the ICE began to spin while I was braking and the dash stopped showing as much charging going on. Then the  charging stopped completely and the disc brakes began to take over (you can tell because braking becomes more 'grabby'). The ICE continued spinning so at that point I was presumably getting brake discs and engine braking working together. That makes sense because hybrids have smaller discs and thus need to be protected.

Being aware of the risks of brake fade at that point I slowed the car a lot and continued to crawl down the road (it was a country road so little traffic).

I also noticed when I finally reached flat ground that the car had much more pep when I used the accelerator and it would drop into EV running at every opportunity. It was clearly eager to get the Battery charge back down to normal and was discharging it at every opportunity.

[Cyker]

Yeah if an EV reaches full charge it looses all regen braking; It's partly why they still have such massive brake discs! Reaching that point would be rare except in exceptional circumstances tho' - There is usually quote a lot of headroom for the regen as, like toyota hybrids, they normally leave some extra room as 100% for Battery longevity, and unless you charged to 100% at the top of a mountain before going down, chances are enough charge would have been used that the Battery would have more than enough room for regen charge (Regen charge is not super efficient; a significant fraction gets dissipated as heat and conversion losses in the power electronics).

B-mode is virtually useless for economical driving on the TNGA hybrids; On the older ones they apparently used maximum regen, but on the TNGAs it only does minimal regen, and uses the ICE much more. You're much better off using D and the brakes.

3 minutes ago, AndrueC said:

That was my experience last year of descending a very long hilly stretch in North Wales. The first sign was that the ICE began to spin while I was braking and the dash stopped showing as much charging going on. Then the  charging stopped completely and the disc brakes began to take over (you can tell because braking becomes more 'grabby'). The ICE continued spinning so at that point I was presumably getting brake discs and engine braking working together. That makes sense because hybrids have smaller discs and thus need to be protected.

Being aware of the risks of brake fade at that point I slowed the car a lot and continued to crawl down the road (it was a country road so little traffic).

I also noticed when I finally reached flat ground that the car had much more pep when I used the accelerator and it would drop into EV running at every opportunity. It was clearly eager to get the battery charge back down to normal and was discharging it at every opportunity.

Yeah, I've mentioned a few times that mine is almost fanatical about sticking near 50% SoC and the more I go over it the more it wants to use MG2. I also had the same experience that if you off-accelerator on a downhill, as the SoC goes up it starts to blend in engine braking more and more.

You can see the continuing development and evolution of the HSD with subtle improvements like this!