Regenerative Braking - how does it work?

[WaxyChicken]

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.

[AndrewJ]

Originally Posted by WaxyChicken

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?

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.

[WaxyChicken]

^ Thanks (in short english - onboard computers. )

[SVOboy]

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

[WaxyChicken]

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

[trebuchet03]

Originally Posted by WaxyChicken

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.

[WaxyChicken]

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

[diesel_john]

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$.

[WaxyChicken]

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....)

[AndrewJ]

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.