Regenerative Brakes? Really?

My take here is that more resistance is applied to the electric motor when u step on the brake, thus it slows the car (more friction inthe electric motor itself, NOT the actual friction of brake pads/rotors), and basically instead of driving the wheel using electricity, it uses the wheel turning as a generator and the electricity goes toward the battery, charging it.
Friction brakes (pads on rotors/drums) engage below 8 or so MPH or if you REALLY stomp on the brake pedal during an emergancy stop. Anyone else?

 

The regeneration is not done by heat capture/conversion. It is done by using one of the motors as a generator, which puts a load resisting the coasting vehicle. That harder you press the brake, the more resistance is used. At some pedal point it starts to use the friction brakes themselves, and at low speed, uses them solely.

 

Click on this link for the best discussion I've seen on the subject. It's all in the H-bridge.

http://www.priusonline.com/viewtopic.php?t...1749&highlight=

 

The best place is Graham's web site. You can get the address from the files. Study in particular motor generator (MG) 2. That's the one that does the regeneration. Another source is Oak Ridge National Laboratory report # ORNL/TM-2004/247, also available on the internet. The term "regenerative braking" is misleading. A better term would be regenerative deceleration. Think of the brake as the regen regulator--the more you press on the brake pedal the higher the regen charge rate and the car decelerates quicker; at some point the friction brakes take over.

 

Manny, et al:

I cannot give you a technical discussion regarding regenerative braking that will speak of voltages, resistance, actuation of energy recovery, control systems, etc.

During driving the motor/generators are used to create and regulate forward motive force in conjunction with the ICE. During braking, and coasting the m/gs are used to recover the kinetic energy from the vehicle's forward movement. This is part of where the term generator comes into the equation (the other part being when a portion of all of the ICE output is turning one of the m/gs and generating electricity, this can happen at a standstill and during cruising).

So, when you apply the brake, the system determines, based on brake position and the force used to depress the brake, what kind of combination of regeneration and friction should be used. In conservative driving situations it is likely that until you are almost at a stop that all braking force will be provided by electrical resistance created by one of the m/gs I believe that at about 7mph the m/gs are no longer effective at braking and friction brakes operate alone. However, in panic braking, quick normal braking, friction brakes will play a greater role than in average braking situations.

When you take you foot off the accelerator the system places an electrical load on the m/g thus simulating auto tranny drag. If this were not part of the programming the vehicle would coast much more like a manual with the clutch engaged. This electrical load is also regenerative in nature. By using electrical loads on the m/gs the vehicle is able to recover some kinetic energy to be reused in propulsing the vehicle.

No energy recovery is loss less, however this method does reduce brake wear and heat and produces something useful for the car to use again when accelerating away from the stop.

Regenerative braking is real and works every time you drive the car.

 

If we can believe Toyota, yes, they are. Don't be misled by the observation that the little arrows in the multi-function display don't move any faster when you touch the brakes. They don't move faster in the other direction when you stamp harder on the gas, either.

 

<div class='quotetop'>QUOTE(jtmhog\";p=\"77696)</div>

I thought the Oak Ridge report was interesting, until I got to the part where they described the turbocharger in the Prius. They kind of took a credibility hit at that point.

 

Yes, the brakes do indeed regen. I've taken it down the mountain for over 20 miles and with no engine running, I got 8 green bars, while running the A/C. The engine did not start even once.

Nate

 

If I understand an earlier post, when I am coasting down hill in "B" on a full battery the computer, in order to not overcharge the battery, will "lose charge" by running the ICE. I also understood that if I use the foot brake with a full battery it by-passes the regen and goes directly to friction. My question is this: Is it better to wear the engine or wear the brakes? This is significant to me as I daily descend 3000 feet.

I would really appreciate an answer to this as it will determine my driving habits.

 

once the BSOC is at the top there is no more regen only friction brakes, by putting it in B the ICE is operating as an air pump and the load it applies to the planet carrier is used as the load on MG1 to force it to draw down the HV battery. Without using the friction brakes. Just watch the BSOC come down as your in B coasting down hill it will slowly drop. Once down a couple of bars put it back in D and watch the BSOC climb back up. We really need a Mini Scanner for the 2k4-5 Prius so people can actually see what happens with current draw and HV battery voltage.

 

Frank
I can always count on you to give informative and accurate input. Keep up the good work.

 

From a technical standpoint, when you press on the brake pedal, you send a request to the Skid (AKA Brake) ECU on how you intend to stop. It sends a request to the HV ECU on how much regen braking force it needs. The HV ECU returns how much force it can deliver, and the Skid handles the excess via friction braking. If any specialized braking is needed, such as TC, VSC or ABS, that has to be done via friction basis on an individual wheel basis.

Attila has done some analyzing on brake pedal force versus energy recovery through regen braking:
http://www.vassfamily.net/ToyotaPrius/CAN/brindex.html

 

Frank Hudon, You're the Prius man!!! Driving around with a mini scanner plugged in. I wouldn't be surprised if Toyota contacts you for data!!!!

 

<div class='quotetop'>QUOTE(jtmhog\";p=\"78346)</div>

That gives me an idea. As long as we are wishing for a G3 mini scanner why not one with memory. Collects all the data then down loads it to your PC for further analysis and perment log. We can wish can't we? 8)

 

Locomotives have long used "dynamic" brakes: these are not regenerative because the energy is dissipated as heat in large resistor banks. It's not feasible to store a useful fraction of the energy from a ten-thousand ton train in batteries, so they don't bother.

The situation with a relatively small switcher locomotive moving a relatively small numbers of cars is more amenable to regeneration, hence the recent introduction of the "Green Goat": http://www.railpower.com/products_hl_ggseries.html

 

Actually, I do believe they are designing locos that will be using batteries.

In the past though, I believe diesel generators were directly coupled to motors, known as a series hybrid configuration. Modern ships do that too, though they I believe have batteries.