Using the Brake

[montego1964]

I'm curious about the braking system on my prius.

Does regeneration occur steadily throughout the entire braking operation, or does it vary according to the pressure applied to the pedal? How can you capitalize by altering your own braking habits?

[hobbit]

There are numerous threads on the subject. Use "search".
.
Both regeneration and physical braking are applied over a smooth
continuum whose parameters are dictated by many inputs. You can
definitely learn to play this for best results.
.
_H*

[donee]

Hi Montego,

We have been having this discussion on PriusOnline. Check out http://www.priusonline.com/viewtopic.php?t...bd5c533fe16695b .

For short, using Attila's data at http://www.vassfamily.net/ToyotaPrius/CAN/eveffindex it seems that about 81.5 percent of the motion energy is regenerated into the battery. And about 66.6 percent of battery energy gets converted into energy of motion for an acceleration. So, this works out to 54.3 percent times the battery losses. A lowball value for the battery efficiency is about 85 percent (I read someplace that 90 percent is more typical), and at that value a conservative total efficiency of reuse estimate is then about 46 percent. This is only one data point (from and to 50 km/hr - 31 mph) however. Actual driving conditions will be more variable.

The amount of energy regenerated is variable too. Check out http://www.vassfamily.net/ToyotaPrius/CAN/brindex.html for more details.

[daniel]

<div class='quotetop'>QUOTE(donee @ Jun 27 2006, 10:06 PM) [snapback]277900[/snapback]</div>

... about 81.5 percent of the motion energy is regenerated into the battery. And about 66.6 percent of battery energy gets converted into energy of motion for an acceleration. ...
[/b]

This seems reasonable, based on the amperage numbers I see on CAN-View when braking. The harder I press on the pedal, the higher the amperage. Pressing fairly hard, it's easy to see around 100 amps. Just letting off the accelerator, where the car emulates an automatic transmission by applying a small amount of regenerative braking, seems to generally produce around 15 or 20 amps.

[MarinJohn]

Daniel I'm really in the dark on this subject. From your post it seems like your experience with CAN is that just letting off the gas gives a little re-gen. Then I think I get from your post the harder you brake the more re-gen you get. Question: do they combine? That is is 1+2=3? or does 2 cancel out 1 thereby=2? Next question is how does selecting B fit into the equasion according to CAN?

[Dithermaster]

<div class='quotetop'>QUOTE(daniel @ Jul 2 2006, 08:26 AM) [snapback]280079[/snapback]</div>

This seems reasonable, based on the amperage numbers I see on CAN-View when braking. The harder I press on the pedal, the higher the amperage. Pressing fairly hard, it's easy to see around 100 amps. Just letting off the accelerator, where the car emulates an automatic transmission by applying a small amount of regenerative braking, seems to generally produce around 15 or 20 amps.
[/b]

That is in line with what I've read. However, 100 amps is max; based on bat. temp and other factors, it might max out at 80 amps. Any braking past the charge max uses the mechanical brakes, which means that energy is wasted as heat. You're better off braking at 50 amps over twice the time as your 100 amp stops, or risk wasting energy. Of course, that requires looking further ahead on the road, which is a good mileage trick in any car.

///d@

[qbee42]

<div class='quotetop'>QUOTE(MarinJohn @ Jul 2 2006, 11:40 AM) [snapback]280100[/snapback]</div>

Daniel I'm really in the dark on this subject. From your post it seems like your experience with CAN is that just letting off the gas gives a little re-gen. Then I think I get from your post the harder you brake the more re-gen you get. Question: do they combine? That is is 1+2=3? or does 2 cancel out 1 thereby=2? Next question is how does selecting B fit into the equasion according to CAN?
[/b]

Yes, the regen from letting off the gas is the same as pressing the brake. Let off the gas, get a little regen. Press lightly on the brake and get a little more regen. Push harder and you get more, up to the limit of the MG sets and the battery. The brake peddle is also rate sensitive: if you mash on the brakes, the computer figures you are panic stopping and worries less about regen and more about stopping in a hurry. The friction brakes are applied early in a panic stop, instead of waiting for around 7 mph.

B mode shifts the engine into a high drag mode for engine braking, like downshifting for a big downhill. The rest of the braking system still works the same.

Tom

[hobbit]

Regenning at very high currents is also likely to cause more ohmic
heating in the battery and wiring, thus more loss. Parts get warmer,
resistance increases, more and more losses.
.
_H*

[MarinJohn]

Thanks Tom.

[daniel]

John: Sorry. I don't often open the Tech Discussion forum. But I agree with all three of the replies above.

I have seen it go just over 100 amps, but I think it likely, as Dithermaster says, that the actual max probably depends on various factors, including battery temp. A lot seems to depend on battery temp.

I don't generally stomp on the brakes. As hobbit says, it's probably less efficient. But I'm not a high-mpg guru either. And I've had my share of sudden stops. Doing 45 on a main drag and a light turns yellow just as you're close upon it, and it can take a 100-amp deceleration to stop. I'd rather waste a wee bit of energy than go through a yellow light if I can safely stop. Safety first. Then conservation.