Regenerative braking

Regenerative braking is important so that you can rack up those cute little green leaf cars on your Consumption screen

 

OK, so what happens in the Prius when the battery pack is fully charged (i.e after going down a long hill) where does all the regenerated energy go to? Is it dissipated off in a heat exchanger or something?

 

<div class='quotetop'>QUOTE(PriusOwner004 @ Oct 3 2007, 02:19 PM) [snapback]520722[/snapback]</div>

On the contrary... It's been a long day at the office, and I needed to regenerate, so I took a break to read priuschat!!! I love regenerative breaking!

(Oh, and that thing the Prius does when you slow down is cool too)

 

<div class='quotetop'>QUOTE(Vince31 @ Oct 3 2007, 05:15 PM) [snapback]520840[/snapback]</div>

when the pack is full it quits regenerating, and uses more friction braking which is why the Prius still comes with a B as a gear selection to give engine braking. If you were going down a mountain you don't want to use the friction brakes in any car because when they get hot they become ineffective at stopping the vehicle and wear much faster.

 

Don't let that new moderator's power go to your head TP :lol:

 

<div class='quotetop'>QUOTE(qbee42 @ Oct 3 2007, 01:46 PM) [snapback]520690[/snapback]</div>

Let me rephrase: How does the prius offer different levels of regenerative braking?


In another thread someone has posted that 60 amp braking is the most efficient. FireEngineer has mentioned that it is the amps that flow in and out of the battery that is important... The normal "drag" regen is only 10 amps. "B" Mode is supposedly 15 amps... This sorta leads me to the line of thinking that it is best to build up speed on a hill instead of leaving it in "drag-regen" mode and then using 60 amp braking when enough speed is built up...

 

Er yeah... but does anyone know how 60amp braking works.

For example. I'm gliding at 40mph. I let my foot off the gas and enter "drag-regen" mode. the ICE is stopped, mg2 is spinning, mg1 is spinning. I don't see where more energy can be recovered or how changing one of the MGs by adding charge will increase braking efficiency.

So whats the difference between "drag-regen" and "60amp" mode in terms of the changes between the MGs?

Or mebbie I need a tutorial on how electric motors generate electricity... As far as I know, the faster it spins, the more electricity it generates (= more amps?) But how does one generate more amps when the wheel that MG2 is attached to spins at 40mph?.

Is there a post/site that explains it? Sure, I have a rough idea about how the HSD works, but I have no idea how it factors regeneration when braking.

 

<div class='quotetop'>QUOTE(Danny Hamilton @ Oct 3 2007, 03:41 PM) [snapback]520780[/snapback]</div>

This is correct. You can call it regeneration if you wish, or just plain dynamic braking. Usually the term regeneration is reserved for when the energy is reused, but that's just a custom.

Tom

 

<div class='quotetop'>QUOTE(qbee42 @ Oct 3 2007, 08:32 PM) [snapback]521006[/snapback]</div>

Check out This site. General Electric now has a hybrid locomotive that recovers some of the wasted dynamic braking.

 

<div class='quotetop'>QUOTE(Tideland Prius @ Oct 4 2007, 01:30 PM) [snapback]521255[/snapback]</div>

MG1 gets into the act controlling whether and how fast the ICE spins, which is an issue with compression braking.

Tom


<div class='quotetop'>QUOTE(Chris Robson @ Oct 4 2007, 12:01 AM) [snapback]521013[/snapback]</div>

Pretty cool. Those will be some big batteries.

Tom

 

It was stated above that Regen Braking stops and Friction Braking takes over if the Brake Pedel is pressed Hard. Is this true?

Why wouldn't both be used when the car is going more than 7 mph?

KR

 

While generally agreeing with most of the comments here on regenerative braking, I have to agree with Scientific American that it is a significant contributor to the improved fuel consumption characteristics of the Prius. Even if the overall efficiency of energy re-capture is of the order of 30 -35%, that is to be compared with zero for a conventional automobile, where all of the kinetic energy destroyed in friction braking is in the form of heat.

Likewise, the key to future gains in hybrid drive efficiency lies in battery technology, and the ability to store more electrical energy at higher densities. It will never achieve the energy density of gasoline however, which compared to NiMH batteries is over 210 times the energy density by weight, or 96 times the energy density by volume. So really the Prius is still predominantly a gas powered vehicle.

Ron.

 

You get different levels of regenerative breaking by changing the load on the motor-generator. If you have a simple DC generator (or motor) and it's disconnected, you can turn it freely - it offers no resistance except friction. If you stick a load across its terminals (a resistor or light bulb, or whatever), it gets harder to turn, as the moving coils send current through the circuit. If you keep lowering the resistance of the circuit, the current flows get larger - the mechanical motion gets turned into electrical power more quickly, and you have to put in more power to keep the motor turning.

It's a bit more complex in an AC motor like the Prius, but that's the idea.

 

<div class='quotetop'>QUOTE(Vince31 @ Oct 4 2007, 06:45 AM) [snapback]520840[/snapback]</div>

Yes in a fashion.
When the traction battery is at 80% charge the controling computer will load MG1 making the ICE spin agains compression. This is the same as a conventional vehicle using the gears to drive the engine to retard forward motion. When air is compressed it gets hot, so kinetic energy is converted into heat and sent out through the exhaust system and cooling system to the atmosphere. There is also an increase in friction braking. Sometimes when a Prius stops at the bottom of a long down hill run the ICE will continue to be spun by MG1 to discharge the battery down to 80% charged. During this process there is also heat generated within the HSD by friction and electrical resistance.

I should point out there is no need to put a capital A in the middle of the word brAke, it's fine to write it brake.

 

so - what is the best prius technique to maximise regenerative braking and reduce wear on the brake pads ?

Is it to brake firmly and quickly, or brake very gently ? Or doesnt it matter ?