I have read countless hours of info about the Prius but nowhere have I seen it described what actually happens when I apply my brakes to control the amount of braking force exerted by the generator. I would guess that it has something to do with how MG2 is electronically syncronized with respect to the magnets. Can anyone here verify this and explain it in a way that is easy to understand? Can you explain a little about how MG1 and MG2 work? Do they ever both generate at the same time? I love a car that takes time to understand. What a gift we have been given. I can't wait to see what comes next.
For the brakes portion, the brake pedal has a travel sensor attached to it. The amount of travel, as well as the rate of travel change is measured by the brake control ECU. A target deceleration level has been determined for each millimeter of travel, and load, via regeneration, is applied to the motor to generate negative torque to achieve the target deceleration. This is simply loading a generator to create more output, and thus more negative torque, as the level of desired negative torque increases. Once the brake pedal travel has reached a certain point, or the rate of travel exceeds a programmed limit, or the vehicle is below 8 mph, solenoids are opened by the brake controller which allow hydraulic fluid to generate brake torque via the hydraulic brakes. The failsafe, as I understand it, is such that the brake control ECU is shut down if a problem is detected, and is off by default if the power fails. This results in hydraulic brakes being available in the event of a loss of power to the brake control ECU for any reason. There may also be a redundant travel sensor or a brake pressure sensor to ensure safe operation, however I have not dug into this yet to be sure. Other similar systems have multiple sensors for diagnostic and control purposes. I will post a revision if I find this to be incorrect.
That all makes sense, but what is happening in the generator to apply negative torque or to vary the amount of negative torque?
One of the threads here on Priuschat pointed me to this document: http://www.toyota.co.jp/en/tech/environmen...lReports_12.pdf On about page 9, it talks about regen braking, and page 16 shows how regen braking is different between the 2003(THS) and 2004(THS II) Prius.
