Do rear brakes activate always, despite regenerative braking?

Discussion in 'Gen 4 Prius Technical Discussion' started by Hanzou, Sep 12, 2022.

  1. Hanzou

    Hanzou New Member

    Joined:
    Sep 11, 2022
    2
    0
    0
    Location:
    Australia
    Vehicle:
    2015 Prius
    Model:
    ----Australia----
    Thank you very much for all your answers!
     
  2. RGeB

    RGeB Junior Member

    Joined:
    Apr 18, 2021
    79
    15
    0
    Location:
    Australia
    Vehicle:
    Other Hybrid
    Model:
    N/A
    So (if I have understood correctly) in terms of the OP’s opening question:

    The short answer is no, the rear friction brakes in a FWD HV with regenerative braking (like a gen4 prius) will not necessarily operate each time the brake pedal is pushed.

    The long answer is something like: the outcome from the Electronically Controlled Brake System is affected by lots of variables; things like load distribution in the car, whether the road is rough or slippery, whether you are driving around a corner, your speed, the slope, the traction battery SOC, the drive mode selected, and how hard you press the brake pedal. The car computers are intended to integrate all of this through input of many sensors into interconnected TRC, VSC, EBD, ABS, and Hybrid Control systems, then control the hydraulic (friction) brakes as appropriate through a combination of hydraulic pressure from several pumps and the solenoids that send or relieve hydraulic pressure in each wheel cylinder, controlling each brake caliper. If you don’t mind Russian websites you can go here to get an idea of the interactions in a rav4 (or see specific models, probably copied from TIS).

    In a gen4 prius, the control system no longer includes sensors of pressure in each wheel cylinder or position of each caliper. Some models have no obvious PID for brake pedal position or pressure (sometimes Toyota calls it ‘regulator pressure sensor’). It may be possible to ‘see’ some of what is going on with the friction brakes by logging a combination of hydraulic pressure and solenoid PIDs. The system details, and therefore the best methods to monitor them, vary between models. It may be necessary to use Techstream as not all OBD programs handle ‘status’ PIDs.

    At the level of the ‘brake actuator assembly’ the following table is helpful (but in normal braking all of these are off, other solenoids control the amount of friction braking):

    4.jpg

    At some level of brake pedal pressure, depending on the other variables mentioned above, friction braking will be activated on one or (more often) several wheels. As observed above, this happens, at last to a slight extent, at quite low brake pedal pressure under some circumstances. The fail-safe mode for braking typically uses friction brakes (but it may need a lot of pedal pressure, and not provide much feedback through the pedal).

    This may elaborate the many helpful contributions early in this thread.
     
  3. RGeB

    RGeB Junior Member

    Joined:
    Apr 18, 2021
    79
    15
    0
    Location:
    Australia
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Here is part of a (1 sec interval) log from today in my rav4 HV that shows (among other things):
    (a) regen without friction while pedal is pressed.
    (b) engine braking without regen or friction at high SOC (no pedal press)
    (c) friction followed by regen, with gentle engine braking and without pedal press (who would have guessed?)
    (c) various ratios of regen to friction depending on SOC, pitch etc.

    All un-noticed while driving; the car computers take care of it all without fuss.
    5.jpg
     
    Elektroingenieur likes this.
Loading...