On cars with this feature, do you actually have to brake in order to be regenerative? Does it regenerate if you're just coasting to a halt?
I tend to try to anticipate the road ahead and conditions and aim to arrive at roundabouts, traffic lights and so on with little braking required.
If I bought something (hybrid?) that featured RB, would I need to start braking more to get the benefit?
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>> Does it regenerate if you're just coasting to a halt?
I doubt it. Bit here about regen braking:
"As I understand it, in a normal car, as soon as the engine is running, the alternator starts charging the battery at its maximum rate until the battery is fully charged, then the alternator outputs only as much electricity as needed to run all the car's systems. This puts a load on the engine, which means it burns more fuel.
In a regenerative system, the battery is not fully charged again after starting. Instead, the car waits until you apply the brakes, then the alternator starts charging the battery. The energy comes from the car's momentum spinning the wheels/engine/alternator. When you accelerate again, the alternator stops charging and the battery is used to power accessories. In this way the battery is rarely "fully" charged, instead maintaining about 50-70% of full charge. Enough to restart the car several times. If the charge starts to get too low, then the alternator will use engine load to charge like an old car".
www.briskoda.net/forums/topic/325688-regenerative-braking/
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You get a nice little meter in an Efficient Dynamics BMW....personally I've de-activated it. Goes on my nerves.
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De- activated the indicators on my BM
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On my Outlander PHEV I can alter the level of regen by using the flappy paddles. Useful on hills, as it means you do not need to use the brakes.
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Yes, you do get regen in my CT200h (and I guess all the other Toyota hybrids)
If you have the energy monitor on you can see the flow of energy and when you lift off and start to coast the monitor shows power flowing from the wheels back into the battery - the same as when you brake
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The answer is probably:
- On hybrids (which will have regen-braking) the electric motor can be used in reverse as a generator.
- On normal cars with regen brakes, they probably do not capture the lost energy as you cost. But coasting will be using less fuel.
In eco mode on my car, if I coast, it will disengage the gearbox and the engine falls to idle. My cars is simply a petrol DSG one.
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"On hybrids (which will have regen-braking) the electric motor can be used in reverse as a generator"
Really? Wouldn't that use as much as or more than it generates? Otherwise we've discovered perpetual motion haven't we? :-)
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In the context of regenerative braking, it doesn't do that when the petrol engine is running. It's used to slow the car down. The electric motor provides resistance and will charge the battery.
Most EVs do have a recharge mode for the batteries that will increase fuel consumption.
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>> "On hybrids (which will have regen-braking) the electric motor can be used in reverse as
>> a generator"
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>> Really? Wouldn't that use as much as or more than it generates? Otherwise we've discovered
>> perpetual motion haven't we? :-)
no because its slowing down the car.
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This suggests it doesn't require the brakes to be activated:
Make use of every watt: by charging the battery only when your BMW is braking, coasting or decelerating, Brake Energy Regeneration improves fuel efficiency by up to three percent and ensures that the full power of your engine is available for acceleration.
www.bmw.com/com/en/insights/technology/technology_guide/articles/mm_brake_energy_regeneration.html
I'd interpret it as the wheels being allowed to drive the alternator when the car is not increasing speed. Not sure if it requires some sort of clutch to control that.
BMW's Brake Energy Regeneration operates differently: the generator is activated only when you take your foot from the accelerator or apply the brake. The kinetic energy that would otherwise go to waste is now used efficiently, converted into electricity by the generator and stored in the battery.
Producing electricity in this highly efficient way delivers an additional advantage: when you apply the accelerator, the generator is deactivated - so the full power of the engine can be directed to the drive wheels.
Last edited by: WillDeBeest on Sun 20 Mar 16 at 12:32
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On the e-tron version of the A3 there seems to be little, if any, charging of the battery when coasting , regardless of mode. It always cuts the petrol engine completely (at least at speeds I've driven at...) but assumes you don't actively want to slow down. Which seems sensible to me, and is presumably how it claims that on a 414 mile mostly motorway journey 31% of those miles were emissions free...
Using the paddles to drop a gear (not that it actually does I don't think) will put it into regen mode, so you slow down as you coast, again engine off. Phyically pressing the brake pedal will also actually use regen braking, unless you need more braking force than that can generate, in which case the disc brakes are activated as well. A useful side effect of this is that there's virtually no brake dust on the wheels even after a month of use!
The other oberservation I have is that on motorways it's quite happy to cut the engine and use the electric motor to maintain speed for quite long stretches of road if they are flat or slightly downhill. It as a 'power' gauge rather than a rev counter, and surprisingly little power is needed to maintain motorway speeds. Interestingly it's one when cruise control does seem to be less efficient - it can't see ahead and so the car coasts much less if CC is operating. The benefit however, is that you don't find the speed creeping up ;)
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... is beautiful, a giant step towards 'perfect efficiency' which may be 90% but can never be 100%.
It works surprisingly well, despite the weight of the electric drive motor and the complexity of the controlling switchgear.
There's a lot to go wrong though. Just as well F1 has the support of industrial giants which use it as an advertising hoarding.
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>> There's a lot to go wrong though. Just as well F1 has the support of industrial giants
but you never know what will become of the industrial giants when there's a huge thrashing about in the shark pool.
I don't really fancy cars with this hi-tech stuff. I don't trust it.
Give me a well-sorted 2.8 litre Capri any day. Slow but sure, and very agreeable in the process unless you're an idiot.
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>> The other oberservation I have is that on motorways it's quite happy to cut the engine and use
>> the electric motor to maintain speed for quite long stretches of road if they are flat or slightly
>> downhill.
Under light load, the engine on these A3 with a COD engine will go into 4 cylinder mode. Because you don't need all four cylinders to maintain speed. Clearly yours has another option - electric mode.
I wonder if the e-Tron uses COD?
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I can see that on a car that has a powerful electric motor it will on overrun work as a powerful generator, so will produce real stopping power.
But the energy absorbed by driving an ordinary alternator is surely minimal? An engine can turn an alternator to produce 50 amps at idling speed without even exerting itself - just try letting the engine idle and then switch on all the lights etc - the engine barely falters as it takes the load.
I just don't see how an ordinary alternator can produce any useful braking effect.
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>> I just don't see how an ordinary alternator can produce any useful braking effect.
Who said cars are using the alternator to produce braking effect? Maybe I jumped a post or two on this thread...
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Who said cars are using the alternator to produce braking effect?
It's implicit in the BMW description that I posted. The converse of engaging the alternator when off throttle is disengaging it when accelerating, and BMW claims (well, it would) some benefit there in terms of dynamic response. The implication is that in any car with a conventional system, the alternator is exerting some braking effect all the time.
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> The implication is that in any car with
>> a conventional system, the alternator is exerting some braking effect all the time.
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Or rather, all the time that it is charging the battery or operating accessories.
Hence the explanation in the second post, by Dog, that the control system can deliberately refrain from using fuel to charge the battery fully, in order to leave a space to mop up energy from regenerative braking.
If the battery were fully charged then that ability would be wasted.
But although theoretically true, I find it very hard to believe the effect is significant or even noticeable.
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>> I wonder if the e-Tron uses COD?
>>
Further playing today shows that when coasting it will regenerate, but only if otherwise the. At would be increasing in speed. So coasting on the flat or a slight downhill incline = no regen. Coast down a steeper hill and the car will start using the electric motor to maintain sped, generating power in return.
I've been unable to ascertain wether the 150PS 1.4T engine in the e-tron is the COD unit or not though. Logically it would be - why have two engines of the same capacity and output that are different? However there's no mention on the web, the brochure or the handbook to indicate that it does have COD technology...
Though I can see that layering the decision for EV/Coast/Generate Power/engine 4 cylinder mode/engine 2 cylinder mode is a layer of complexity that might not be needed! So perhaps it's the same engine with that bit of software disabled or not present?
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I'm interested in case say a Passat GTE on overall monthly rental and BIK grounds saves me some money. I might not bother plugging it in much but I know I should if I got one - I do a lot of short trips. Our garage is at the end of the garden with a gate to the side. There is no open driveway. So parking it on there is actually less secure for the house because the gates would be open to the rear garden.
I'd have to get power to it over the fence or out the front. No idea what the monthly cost might be though. I've got a minimum of 12 months before I need to worry and things could all change.
What I do know is I like the petrol DSG combination in the A3. A smaller, lighter car than a Passat granted.
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Regenerative braking - Dog
