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Recently purchased a Prius and have a question on the braking system. When going down hill if you just take your foot off the gas do you get full regenerative braking or are you only using MG1? Do you actually have to slightly touch the brake pedal to engage MG2 and get the full reclaim of energy? If the latter how do you know when MG1 is generating versus when MG2 is doing it?
 

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You get regenerative action any time your foot of off the throttle petal.
That comes from the wheel driving one of the motors as a generator.
I don't remember which motor is which, but one drives the wheels and one charges the battery and starts the engine.
 

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MG1 is not involved in regeneration for either simulated engine drag or for braking. If you just let your foot off the accelerator pedal, you get a small amount of resistance from MG2 to simulate engine drag, thus a small amount of regeneration. (This only applies if you're going faster than 7 MPH.) If you push on the brake pedal, you get proportionally higher resistance from MG2 as you push harder. This gives more regeneration. At some point, MG2 is regenerating as much as the system is willing to push into the battery. Any more pressure on the brake pedal results in proportionally higher resistance from the brake pads.

Activation of the ABS and/or vehicle stability control will turn off regenerative braking but not regenerative simulated engine drag. In this case, regenerative braking will be immediately replaced with braking via the brake pads.

All completely under computer control, so you don't have to worry about it.
 

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I hate to display my ignorance so publically, but what are MG1 and 2? Mechanical Gremlins, something like Thing 1 and Thing 2?
 

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Astrowoman said:
I hate to display my ignorance so publically, but what are MG1 and 2? Mechanical Gremlins, something like Thing 1 and Thing 2?
That's actually a pretty good way to think of them until you're ready to understand the inner workings of the Prius. Thanks for the suggestions.

Anyway, the Prius drive train includes two "things" called motor/generators. They are labelled Thing1 and Thing2 ... I mean MG1 and MG2. MG2 is bigger than MG1. Both are able to convert electric power into rotational power or rotational power into electric power. They are located at different places in the drive train. MG2's spin is always proportional to the average of the front wheel spins. MG1 is free to spin as fast as it wants and directly controls the spin of the engine. Both can operate in either forward or reverse directions. The wheels can operate in both forward and reverse directions, but the engine can only operate in the forward direction. So MG1 must be careful to never spin backward so fast that it causes the engine to spin backward. Fortunately computers are on the job full time to make sure MG1 and MG2 are doing the right thing at all times.

To get a good, detailed description of the Prius drive train, including Thing 1 and Thing 2, see Graham's Site. Click on "Understanding the Prius".
 

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I just bought a Pride Scooter, like we old folks & disabled use to get around easier when there is lot of walking involved. It is electric/battery driven, weighs about 90+ lbs.

AND it has REGENERATIVE BRAKING :!: When you release either the forward or reverse lever, regen braking automatically kicks in, to slow it to a stop quickly & smoothly. I dont know whether it recovers power, but it is definitely called regenerative braking.

I did not know that until I got home with it & read the manual. I'm going to post the story with some pics, cause it fits great into the Prius, which was a big reason I got this particular model.
 

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An04Prius said:
I just bought a Pride Scooter, like we old folks & disabled use to get around easier when there is lot of walking involved. It is electric/battery driven, weighs about 90+ lbs.

AND it has REGENERATIVE BRAKING :!: When you release either the forward or reverse lever, regen braking automatically kicks in, to slow it to a stop quickly & smoothly, and recover power.
Now if someone would just add a pedal-driven generator to that bike (no sprockets, chain or derailleur), we'd have something that allows the user to exercise as desired and be easy to use.
 

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Wow, it actually has regeneration? I have heard of electromechanical braking by placing a diode across the motor so that it fights itself, but that is good that they are stepping up.
 

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DanMan32 said:
Wow, it actually has regeneration? I have heard of electromechanical braking by placing a diode across the motor so that it fights itself, but that is good that they are stepping up.
The manual says "Dual Braking System: Electronic, regenerative, and electromechanical" but does not describe it any further...except to say "Regenerative: Uses electricity to rapidly slow the vehicle.." and then the mechanical part kicks in at full stop.

It is all automatic, there is no brake pedal or hand brake.
 

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How do you know when the regeneration max's out and the friction brakes start working? I'd like to avoid using friction brakes as much as possible.
 

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OverTork said:
How do you know when the regeneration max's out and the friction brakes start working? I'd like to avoid using friction brakes as much as possible.
Driver does not have any control over braking. :shock: Sounds scary, I know. That is what I first thought. Since there is no foot or handbrake, braking starts automatically when you release either the forward or reverse throttle...and it stops quickly.

Works just like the electric carts in stores like Target, Wal-mart, Sam's club I've used.
 

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I think he is talking about the Prius.

Some have been able to feel the changeover, I haven't. Sometimes I think I do, but I can attribute it to other conditions, including the brakeforce I requested.

Some say regen quits at 4MPH, I believe it is closer to 7MPH. The car can do both, regen and friction braking if needed. You request the braking force based on the distance and speed of your foot travel, the skid ECU (brake computer) asks the hybrid system how much braking force the regen could deliver, the hybrid gives its answer, and the skid ECU will add friction braking to make up any difference.
In the new generation, it is possible to have strictly regen braking, no friction braking, over a certain speed. In the classic, some friction braking was always applied during brake requests.

When the brake system is working normally (no power loss, no brake pressure loss), the system isolates the master cylinders from the wheel cylinders, so you do not have any direct hydraulic control of the friction brakes. If any failure occurs, then the system will connect the master cylinder to the front wheel cylinders so you can manually apply them.
 
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