Regenerative Braking - how does it work?
 

I'm looking for a more detailed link on how Regenerative Breaking works.
I know they use generators at the wheels, but how do they engage/disengage them so that there isn't an extra energy load during driving?

Also, while i'm at it, some of the EV Cars I've seen on the news use more than one motor located at the wheels to reduce mechanical energy loss. How do they ensure that both motors turn at the same rate?
(EG: i've once had 2 exact same computers with cloned hard drives. one would boot up in 4 mins, the other would boot up in 2 mins even though they were "Exactly the same")

Thanks. :thumbup:

Physics and electronics help.
The car is going to keep trying to go in a straight line, thereby dictating that both hub motors will have to keep spinning at the same RPM. If one motor were to try to spin slower or faster the car would begin to deviate from it's trajectory, something it does not want to do.

Electronics may help with the acceleration side, controllers can keep track of a motors RPM, and would ensure that they are perfectly matched unless of course you're accelerating around a curve, in which case the motors won't be matched, mimicking the action of a differential in a traditional car.

^ Thanks :) (in short english - onboard computers. :D )

Just use a throw switch like on an old bike generator.

So basically a hydrolic or cable system that swings (engages) the generator against a wheel gear when the brake is pushed. Gotcha.

No no - throw the electrical switch ;) Unless the motor has a load on it (closed circuit + load) - it's not going to have any resistance (well, a tiny tiny tiny bit). No load (open circuit) - throw a switch to complete the circuit - and current will flow ;)

That being said - cars like the Prius, for example, do not have motors at the wheel (in fact, most cars - EV/hybrid/etc. are like that due to the huge amount of unsprung weight that adds). Instead - it's just wherever the drive motor is...

The new Prius uses boost converters so they can have a lower pack voltage - this means they can regen brake at lower speeds....

GM-Allison's bolt-on hybrid transmission has the motors located inside the transmission itself and those handle the regen braking.

Ahhhhhhhhhh.......... Thanks trebuchet

As i understand it, the regen part is where it gets expensive. just a dc drive probably wouldn't cost more than 8 or 9 K$.

but couldn't you use starter motors as regenerative motors?
(isn't that what makes a generator? running a motor to make the charge? would that
work? i wonder....)

The tricky part about regen in EV's is the controller. More expensive controllers are needed to enable regen. Any motor will work to make regen happen, so long as you have the right controller.

andy is right, probably 10hp to make a difference, the controller is key. a good driver can almost do as good as regen, maybe better if you count the weight saving.

I've seen layouts for hybrids where there's one motor, mounted concentric with the engine. It's used as a starter motor and for braking regen and for propulsion when running electric+combustion simultaneously.

I confess to not knowing whether any production hybrids are using this or not. But it makes a lot of sense to me. A relatively simple design in that there's no additional clutching or belt drives etc. needed to make the parts spin. The down side would be that you're spinning both engine and elec. motor/gen whenever either is needed.

I believe that is how the Insight and 1st gen Civic hybrid work brucepick. I'm not sure about the 2nd gen Civic hybrid.

This is interesting stuff.
But it leads me to asking another question on the same font:
which would work better: Regen braking or windmills? (the windmills could be covered when driving and could popup or get uncovered when breaking - such as covered radiator air intakes) I'm thinking that they would work about the same. any input?

I have a windmill that pumps air to the bottom of my pond 24/7, it weights over 300 pounds. cars have to be much lighter, but the windmill could be at home compressing air or charging batteries.
some of the hybrids have the motor built in to the engine flywheel, but engine doesn't turn until started.

"waxy" in WWII they had DC generators that were about 10hp the generator would start the 1 cyl. engine as a motor and then become a generator to make a power supply for their 24vdc equipment. back in the 60's I used one for several years as a motor on farm equipment. no controller it was either full on or off. so it has been done. if the motor/generator was small enough so it wouldn't fry the tires, it could used with just an on/off contactor and clutch, it would be rather jerky, but if hooked directly to a rear wheel it would be to bad, like a golf cart. Also I had an 8 hp lawn tractor and the generator had real heavy windings, it actually was used to as a starter to start the engine with its 12vdc battery.

pedestrian right will definitely improve as more and more of us become them.

One day pedestrian safety will also be a factor on this side of the Atlantic like it is in Europe. I can't see that as being particularly pedestrian friendly... :D

I'm not sure about the civic hybrid, but I know for sure that the insight hybrid uses the hybrid drive motor as a motor, generator, and fly wheel, thus saving the weight of the fly wheel, and helping to smooth out the imballence in speed of the engine as it rotates.
It shouldn't even cost that much, I was thinking $3,000-4,000 $700 or so for a really nice electric motor, $1,000-1,200 for lead acid battery pack, more for other chemistry, $1,000 for speed controler, wiring, and other electronics, and of course any of those parts can be upgraded for better, this is of course figuring that you are doing a pure electric vehicle, not a hybrid.

windmills on a car is just a bad idea, it's almost as good as useing boat ankers as a brake, they are going to do a lousey job of slowing you down in a comfertable way, and when you want yoru vehicle to move they are only going to slow you down, and if you are dreaming of powering your electric vehicle with on board wind... remember that to get reliable wind, you need to be no less than 30 feet higher then anything within 500 feet, this includes the roof of your car and people standing around, to do any less is a waste of money.

i was referring to windmills not as a breaking system but as a recapture system.
EG:
1 - start hitting the breaks
2a - breaks engage and at the same time
2b - air intake on the nose of the car opens up allowing air to pass over the windmills to recapture electricity from wind. (or maybe uncover windmills under the spoiler.)

Think on that some more.

An enthusiastic hypermiler in a car without regen will almost always go further on a given amount of energy than someone driving normally & using regen to recapture some energy slowing the vehicle down.

The hypermiler will only use as much energy as necessary to get the vehicle to the point where they can start coasting to reduce speed, where the "normal" driver will keep burning energy until they apply regen to slow the vehicle (more rapidly). The extra energy input + the conversion losses in regen = less efficiency.

Of course not everyone can drive without braking. So for the times you do have to press the pedal to the left of the accelerator, regen would be more efficient than friction brakes.