How does regen braking work in the Prius?

I’ve read about several models of pure-electric car that have a way to control how strongly the electric motor reclaims power. This will cause the car to slow down rapidly whenever the driver releases the throttle pedal.

Anyways, while most mechanically inclined SDers probably haven’t gotten to take apart a Volt/Model S or the new Cadillac version of the Volt, the Prius has been around a lot longer.

When you press on the brake pedal in a Prius, have they tuned it so that it uses regen only for the first part of the pedal?

If I were designing it, the way it would function would be :

0 -> a small pedal travel distance : dead zone
small distance -> about an inch : a sensor connected to the pedal (probably a variable resistor/wiper) tells the car’s onboard electronics to switch the motor circuitry around to reclaim energy. The current goes to charge up the batteries, capacitors, or even a bank of big resistors if there is nowhere else.

Point of maximum regen -> floor : this would connect to a conventional brake system, booster/master cylinder, connected to drum or disk brakes. Like on a conventional car, but with a much bigger dead zone before it activates.

The big problem with this setup is that this is a lot of additional parts and complexity. It raises manufacturing costs and the resources that need to be consumed to build the car.

I could be wrong here, but I believe it is speed based. Prius above x (believe 8) mph - and brakes are pressed - it goes to regenerative braking. If the brakes are still applied and speed falls below 8 mph then it is conventional brakes.

Also - below a certain speed the torque produced by a “electrical generator” will deteriorate significantly - and hence I believe an electrical generator may not be best for braking to a complete stop (Unless you start using Series DC motors where the torque is higher at lower speeds).

I’ve owned Prius and Prius C and have translated extensively for a competitor that begins with H, including for recent hybrid models.

A selling point of H’s electric servo braking system is that it regenerates more electricity than previous H and T hybrids.

Link (I translated this): http://world.honda.com/news/2013/4130905New-Fit-and-Fit-Hybrid/

OK, so the way these braking systems work is that they brake a little bit when you are pressing neither the accelerator nor the brake. If they were to brake too much, you’d take your foot off the accelerator on the freeway, and you’d stop right there. You regenerate a little bit under those conditions, but not a lot.

When you brake, the car uses a combination of rotors and traditional brakes. The rotors are literally little generators that turn the force of stopping the car into electricity that goes back into the battery. But then traditional brakes finish the job and make sure that the car comes to a complete stop. The algorithm for how much rotor and brake to apply when is complex and executed electronically.

Needless to say, the rotors can turn the energy of deceleration into electricity to charge the battery. The brakes waste any such energy.

H’s new and improved braking system is able to use the rotors more during braking, allowing more of the energy of deceleration to be recovered.

What are the “rotors”, though. The simplest system would be to just use the same electric motor(s) that are providing the drive power.

Also, per this question:

You can’t say it is only one or the other, since if you slam on the brakes it will definitely use (only?) the conventional brakes to ensure that you can stop quickly.

Although I think it is safe to say the following:

• Coasting: Rotors only

• Very light braking: Rotors only (not sure if and when conventional brakes kick in)

• Medium braking: ?

• Heavy braking: Conventional brakes definitely kick in right away, not sure if rotors are used at all

Of course T and H will have different systems.

I have a 2010 Prius, also had a 2004, if I watch the power/charge display while braking at moderate speeds I can notice the following:

Foot off “gas” and display shows very slight charge rate
Light braking and display shows higher charge rate
Heavier braking and display shows max charge rate
Hard braking and perhaps it’s subjective but it seems that I can feel the mechanical brakes come into action.