What exactly happens when you brake?

actually that isnt true. the brakes do engage at first when the brakes are touched. but then the "urgency" is gauged and then the primary stopping force is switched over to the regen motor. (the biggest reason for this is the regen doesnt react quite fast enough therefore in case emergency braking is neccessary, the hydraulics work first.)

here is a chart of what happens during braking.

http://priuschat.com/forums/album_pic.php?pic_id=718

as you can see; initially, the main braking force is friction, but that quickly drops off as the power rises to the regen braking. as you can see very light braking will be all regen. (but we already knew that)

 

as simple as I can explain it is that MG2 (main drive motor) is a permanent magnet motor which means it's also a permanent magnet generator. When your going down the road and you apply light pressure on the brake pedal the computer see's that as a command to generate electricity and send it to the battery, which it does in increasing amount the more you press on the brake pedal, at a certain point your request for slowing the car down exceeds the amount of torque the motor can generate so the brakes now are assisted with friction braking. That's the clearest I can submit.

 

http://priuschat.com/forums/album_pic.php?pic_id=718

as you can see in this diagram, friction braking to some degree is present most of the time in all but the lightest braking situation.

 

gee.. rather complicated explanation considering the chart i posted says the same thing but much simpler.

 

well thank you!!

actually now that i look at it, i realize that our posts were practically simultaneous.

sooo you take care of the high tech crowd and ill aim for the picture and illustration crowd.

 

I realise that the expanded range exists, never questioned it. The difference is really very small in a practical sense. The major increase comes as a result of the difference of the HV battery terminal voltage I suspect. 500 verses 273 and the increased torque it'll apply to the MG's to get more braking effect. Brake (regen is still limited to 80%BSOC) useage depends on pedal pressure, so I guess I'll have to cut a line and install a pressure switch to see what all is going on.

 

Evan's pretty picture suggests that in the 2004 models, the hydraulics are NOT used initially as they seem to be in the prior model.

 

my understand is that it's speed of application dependent. The faster the brake pedal is depressed the sooner the hydraulic side come into effect. Slow pedal depression and regen, fast and friction brakes then regen to assist.

 

brake pads?

So will prius brake pads last longer than other cars? Assuming normal brake usage.

 

the Vancouver Yellow Cab Prius Taxi used two sets of front pads in 230,000 Km's.

 

I still think those diagrams make no sense. Is braking behavior really time-dependent, rather than velocity-dependent? If you are travelling downhill, and applying steady brake pressure to maintain a constant speed, will braking characteristics change over time???

Or is the time to maximum on that graph so small that we can effectively ignore it and look at the steady-state portion of the graph, showing that in fact, there is no friction braking on the '04 unless you apply a lot of pedal pressure? (And in the '03, there is only a very brief momentary application of friction braking.)

Evan's pdf really doesn't say anything about this, but reading farther along, about how the VSC works, I'm really glad I have it! Once I made a left turn at an icy intersection and heard the VSC alarm. My car slowed down slightly, but otherwise maintained a perfect turning arc. Cool car!

 

Daniel asks, If you are travelling downhill, and applying steady brake pressure to maintain a constant speed, will braking characteristics change over time???

it will change over time because the battery charge acceptance rate does change. You will have to slowly apply more pedal pressure to keep the same rate of regen. Now whether you will find a hill long enough to see this is another thing.

 

Why can't I display Evan's picture? I get the title, description, size, etc. all within horizontal margins, but no image. The "priuschat" cookies are allowed, are there other cookies that need to be allowed?
Thanks, Hank

 

That was it, thanks Evan.

 

Daniel you are right, the braking is time dependent in a sense as there are two different mechanisms for braking , a preferred method (regen) and friction. however, friction works faster and therefore will when needed be the bulk of the braking. and in the new 04's even under emergency conditions, the bulk of the braking will go to the regen side as soon as the regen builds up. it s just that will all things considered equal, the computer will stop the car with whatever is available and friction is simply available first.