Regenerative braking

[newtalg]

Having previously owned an Auris Hybrid Sports Estate (FA16XFV) the only thing I could fault it on was the position of the satellite navigation screen and the beam lighting, which showed the road in the distance well, but not the immediate road. Fuel economy was fantastic, sometimes averaging almost 80 mpg. The engine only cutting in on overrun braking when the Battery showed full. When going down a long hill the Battery would charge until it showed full and then you could hear the engine start churning to take over braking from the electric motor so that the Battery did not overcharge.
When the new Corolla Hybrid Sports Estate arrived on the scene I jumped at the opportunity to get a satellite navigation screen in the right place and lights that allowed you to drive in the dark (GP19UJU). I was also pleased to find that the car would drive electric up to 70 mph.
What did upset me was to find that fuel economy had disappeared, averaging only just over 50 mpg.
The rubbish fuel economy would appear to be because the battery does not recharge to the same extent as my previous hybrid. Energy is wasted on spinning the engine, sometimes to 4000 rpm and above, in B mode, when it could be charging the battery which is only carrying a half charge. the same thing happens when braking and on overrun.
This has been mentioned as a fault when the car was serviced, but I was told this was normal with the new Mark IV version of the synergy drive. Not what I call progress.
Your comments on this would be much appreciated.

[forkingabout]

B mode is there for descending steep hills - using it in everyday normal driving wastes fuel & impacts your fuel economy. 

[TonyHSD]

Hi and welcome. Do you usually drive the car in D or B mode? 

[Woofwoof]

Is this the 1.8 or the 2.0

[Rosgoe]

I must admit I do find the fuel economy worse in the corolla than when I had the auris.

I managed 74.6 once in the auris but generally it was in the low 60s in the summer on the corolla last summer I couldn’t get it over 60mpg even using E5 petrol. Currently in this cold weather I am getting 54.5 that was with a tank full of E10 have filled up now with E5 so will see if it improves.

 

[Cyker]

That is surprising... my colleague had the opposite; He got 10-15mpg more in the Corolla estate rental he had while his Auris was being re-cat'd.

It may be yours still needs loosening up or something? You might need to drive it a bit different to the Auris too - The newer ones tend to keep the engine running once you touch the Eco+ zone, even if you drop back into the Eco zone, and you have to lift off completely and re-engage the pedal at the same place to make it shut off the engine and run off the electrics.

I find my Mk4 gets worse mpg with a constant accelerator input, but does much better when it's being varied all the time; Pulse and glide is particularly effective as the car can hold electric mode at much higher speeds than the previous gen. My Mk4 is currently bouncing between 71 and 75 mpg driving this way, which is pretty damned good for a hybrid in winter, albeit in what stopeater has called frozen-balls mode (i.e. HVAC off, so no heating)  

But definitely DO NOT use B-mode in the newer hybrids; I don't know if it's different in the previous hybrids, but in the newer ones it does NOT maximize regen braking like a lot of car reviewers have incorrectly said - It gives only minimal regen, instead dumping the vast majority of the energy into spinning the ICE, so you waste huge amounts of energy and tank your mpg for no reason.

I consider B-mode only useful for emergencies in the new hybrids, like if the Battery is full so your regen braking disappears and you need to slow down quickly without frying your brakes. 99.999% of the time you should never use B-mode. I so far have never found a use for it, even going down the longest steep hill in my area, using the regen brakes was more than adequate.

D-mode is the optimal mode to be in!

[TonyHSD]

B mode does regenerate more energy into the Battery, you can try in lower speeds below 20mph and even the ice when off you are still getting one pedal drive like feeling and the car dive it’s nose every time u lift off the accelerator.  It is wrong to be used all the time but when you engage going down hill the car slows down more than if you in D. Engine is not consuming any fuel meanwhile., just provides engine braking  like in non hybrid petrol car. Even the Battery is topped up completely regenerative braking is still working., it’s not like will stop working and you are only left with disc brakes. 👍

[Cyker]

It might do on the older gen hybrids but it DOES NOT on the newer ones!! The newer gen hybrids work subtly different to the older ones in a few areas, and this is definitely one of them.

I think B-mode in your car goes to maximum regen as well as spinning up the ICE, but in the newer ones it just spins up the ICE.

It generates far *far* less energy than just using the foot brake in the newer ones, for the same braking force. B-mode has never shown more than 1 block of regen on mine, vs the 3 you can get with pedal braking, and it checks out - If I B-mode my way down e.g. Muswell Hill I get no charge recovery at all, whereas if I am braking with my foot I can get 1, maybe 2 blocks.

Do NOT use B-mode on the newer hybrids - You will just waste loads of mpg!!

 

[AndrueC]

Some'at wrong there for a 1.8. I have one and it doesn't drop much below 60mpg even in winter. In summer it's usually knocking on for 70mpg and that's in normal run about travelling. On a long journey it can get close to 80mpg.

[preperationlaunch]

39 minutes ago, TonyHSD said:

B mode does regenerate more energy into the battery, you can try in lower speeds below 20mph and even the ice when off you are still getting one pedal drive like feeling and the car dive it’s nose every time u lift off the accelerator.  It is wrong to be used all the time but when you engage going down hill the car slows down more than if you in D. Engine is not consuming any fuel meanwhile., just provides engine braking  like in non hybrid petrol car. Even the battery is topped up completely regenerative braking is still working., it’s not like will stop working and you are only left with disc brakes. 👍

Even on the older hybrids, B mode is mainly there to spin the engine using MG1 to waste energy, this energy comes from MG2 which is running as a generator instead of as the main motor. Low speeds are a bit of an exception, but, B-mode still won't regen as much as just using the brakes will.

The spark and fuel are cut, and it's basically having the engine acting as a big compressor. The whole premise being to avoid filling the Battery excessively so that it can continue to provide regenerative braking on long descents. You can notice this, because as soon as you engage B with your foot off the accelerator and the Battery is at a normal state of charge (somewhere between 50-60% or 4-6 bars), you'll notice the engine revs up, even if you were in EV mode.

Otherwise, when you get to near a full Battery, regen braking cuts out and you're left only with friction braking. The transition is a strange one, but it happens gradually. The threshold seems to vary slightly depending on things like battery temperature. It's usually somewhere around 70-75%. The last few percent to 80% charge very slowly by comparison.

Coming down a big hill, B mode charges the battery at approx 25 amps on the Yaris, but the braking force is slowing the car down. Most of the power is being wasted by MG1 with the motor spinning at anything up to the max of approx 4500rpm. The steeper the hill, the more the engine revs, but that charge figure rarely goes far above 25A in B mode.

If you put cruise control on to hold speed, it'll put about 60 amps into the battery from about 40% SoC to 70%, at which point the ICE starts spinning to use the power as the battery nears the hard limit of approx 80%. The closer to 80% it gets, the more the cruise control relies on revving the engine to burn off excess electricity.

Braking on the other hand will go anywhere up to about 100A going into the battery.

Most of my commute in my Hybrid is going up and down big hills, so it gets a full charge and 8 bars quite often. Often to the point where it'll be running the ICE to burn off the excess charge without even being in B mode. I've also got a Scangauge 2 on the dash, so get a good idea of what all the clever electronics are doing at any given stage.

[newtalg]

None of this answers my question.

Why does the hybrid waste energy churning the engine, when the Battery could be taking a charge?

[Hardy888]

Do you mean this is happening when you are driving in B mode? As in the shifter set to B?

Edited January 25, 2022 by Hardy888
Follow-up

[TonyHSD]

B mode adds energy to the Battery more than if the car is coasting in D that was my only point and comparison, I agree when you apply the brakes you can recover more energy., no argument about that. Engine is turning to waste energy when Battery is fully charged and there is no more room for energy storage, otherwise it will not. Toyota hybrids batteries are small and they top up and drain down very quickly. I do often get ice to kick in to discharge Battery. Perhaps Toyota engineer or technician can enlighten us more about this matter with back up of some official information if permitted to share, perhaps a question to the car care nut. 👍

[trashman1965]

19 minutes ago, newtalg said:

None of this answers my question.

Why does the hybrid waste energy churning the engine, when the battery could be taking a charge?

Because B is for slowing the car primarily. 

To slow and maximise charge, gently apply brakes.

Once Battery is full, then it will use the energy to spin the engine to prevent overcharging. 

[TonyHSD]

4 minutes ago, Hardy888 said:

Do you mean this is happening when you are driving in B mode? As in the shifter set to B?

If you mean engine turning to waste energy, this happens in either D or B modes but only when the hybrid Battery is full. Usually drive in D and use B only in specific situations like going long step down hills after  then shift back to D for best efficiency and energy management. B is like shifting to a lower gear for engine braking, in uk we have some road signs “ shift to lower gear” and here is the perfect places to try how B works . 👍

[Hardy888]

Yeah that sounds right from my understanding.

[TonyHSD]

One more thing to note. When Battery shows full or almost full on older gen 3 hybrids actually it’s a way off full 100% although the dash may show exactly that it’s more like 65-75% realistically. Perhaps the newer models has more accurate Battery level readings. There are some interesting apps on iOS and android and all you need is to buy a one 2 adapter like Carista or obdink lx and you can monitor live data on the Battery, engine etc, these are really cool toys and can also help you do some settings like seat belts beep, reverse beeping delete etc 👍 

[preperationlaunch]

58 minutes ago, TonyHSD said:

B mode adds energy to the battery more than if the car is coasting in D that was my only point and comparison, I agree when you apply the brakes you can recover more energy., no argument about that. Engine is turning to waste energy when battery is fully charged and there is no more room for energy storage, otherwise it will not. Toyota hybrids batteries are small and they top up and drain down very quickly. I do often get ice to kick in to discharge battery. Perhaps Toyota engineer or technician can enlighten us more about this matter with back up of some official information if permitted to share, perhaps a question to the car care nut. 👍

B mode will start wasting energy long before the Battery is full. It’s gentler on the Battery and gives a much longer period before the Battery is full. You can test this by trying it at say, 40-50mph and 6 bars full (60% charge, the usual figure it likes to stay around for Ni-Mh models). The EV light will go out and the engine speed will start increasing. 

It’ll only start revving in D if it is absolutely desperate to waste the energy, long after the 8 bars have filled up. This is approx 75% or more of the hard limit at 80% SoC. The only other time it’ll rev in D if you’ve got cruise control on and regen to the battery can’t offer adequate braking anymore. 

[preperationlaunch]

1 hour ago, newtalg said:

None of this answers my question.

Why does the hybrid waste energy churning the engine, when the battery could be taking a charge?

The Battery only has a finite capacity to take a charge. On a really long downhill, you can actually fill the Battery to the limit. At that stage, you’ll only have friction braking.

Friction brakes can get hot and eventually overheat. B mode essentially guarantees you engine braking, no matter how much charge is or isn’t in the Battery. It’ll rev the engine to try and give you a consistent amount of engine braking, even as the battery gets full. 

Even in B mode, as the battery gets more full, the revs will climb as the car uses the motors to slow the car down, and burn off the excess power by spinning the engine. 

[forkingabout]

6 hours ago, newtalg said:

None of this answers my question.

Why does the hybrid waste energy churning the engine, when the battery could be taking a charge?

Because the driver has selected B mode ( for maximum engine braking )

So the hybrid system then uses the traction Battery energy to spin up the engine as an air pump to provide maximum engine braking effort to reduce the load on the normal hydraulic friction braking system.

Unless your descending a steep hill, leave the gear selector in D for maximum fuel  efficiency, the hybrid system is smart enough to look after itself.

Remember B = BRAKING mode.

B isn't there for generating extra energy for the hybrid Battery, it actually takes energy away from the Battery to spin up the engine.

 

 

[TonyHSD]

B - braking , and how the hybrids are braking actually:

 1. Regenerative braking 

2. Standard brake system 

when switching to B the car first uses regenerative braking and topping up the Battery, then spin the engine to deplete the Battery, so basically B mode does accelerate the whole process that happens normally when drive in D. Since it uses more energy to regenerate electricity and then energy including fuel to waste the previously generated Battery charge  it is not as efficient as driving in D , however serve it’s purpose as “engine braking “ something that otherwise does not exist in Toyota hybrid drive trains. 

[Stopeter44]

9 hours ago, TonyHSD said:

B mode does regenerate more energy into the battery, you can try in lower speeds below 20mph and even the ice when off you are still getting one pedal drive like feeling and the car dive it’s nose every time u lift off the accelerator.

That would appear to be in contradiction to what the Car Care Nut has to say about "B" mode.

[newtalg]

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.

[Popama]

Engine braking assumes you need to brake for a significant amount of time and want to protect the disc brakes as much as possible.
When coming down multiple slopes for example. As you should know from driving school, relying on brakes alone for increased periods of time during a significant descent will overheat the brakes and you will eventually run out of brakes. In a manual car you are advised to select a low gear and descent at an increased RPM to apply engine braking. B mode achieves this for the 1.8 hybrid, S mode achieves this for the 2.0 hybrid.

On Toyota hybrids regenerative braking is applied whenever you hit the brake pedal ( up to a point, once the applied force indicates you need more braking power the actual disc brakes are engaged ).

[Stopeter44]

22 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.

With all respect, you haven't indicated if you use "B" mode or standard "D" mode on the shift selector. If you are using "B" mode, the car is behaving as designed. That is, the energy that could be used to charge the traction Battery is being evacuated by turning the engine, but without consuming any fuel, the car does this to protect the traction Battery from overcharge. The Traction Battery operates within a safe band and is neither fully charged or fully discharged*.

Now if you are using "D" mode, then that's a different story and then it would appear something is wrong.

* The traction battery can become fully discharged after leaving the car a long time without use.