Prius 4th GEN Brake diagram

Discussion in 'Gen 4 Prius Technical Discussion' started by Dorin Abeaboeru, Jul 26, 2019.

  1. Dorin Abeaboeru

    Dorin Abeaboeru New Member

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    Hello guys,

    Could anyone help me with a brake fluid diagram for the last generation of Prius? I am particularly interested in the paths the fluid takes and the valves involved. As far as I know, this last version of Prius has the Skid Control ECU bundled with the Brake Booster and the Master cylinder (driver's side) and the Brake actuator and Accumulator with pump on the right side.
    What I don't understand is how the fluid travels, there is the suction tube from the MC reservoir going to the Pump and accumulator, then the high pressure tube going back to the Master Cylinder (MC) and the two brake circuits exiting the MC and going to the Brake Actuator (which has a motor too, just like the non-hybrid ABS brakes). The ABS Actuator should have the well known 8 valves (Hold and Release for each wheel) and the motor (which is different from the pump motor used to maintain accumulator pressure).
    For the Master Cylinder with Booster, on the GTS data list I saw SLR and SLA (linear valves), SSA and SGH as switching valves, but I have no idea how they work.

    Thanks.
     
  2. ChapmanF

    ChapmanF Senior Member

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    Hi ,

    Those exact diagrams are found in a manual called the New Car Features manual (its name in English anyway); here is some information on how to obtain it, in different regions of the world.
     
  3. Dorin Abeaboeru

    Dorin Abeaboeru New Member

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    Thank you very much, I went on Toyota TME (Europe) page and found the diagrams. I am assembling a .doc now. Is it OK if I post it here?
    Dorin
     
  4. bisco

    bisco cookie crumbler

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    sure, why not?
     
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  5. Dorin Abeaboeru

    Dorin Abeaboeru New Member

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  6. Dorin Abeaboeru

    Dorin Abeaboeru New Member

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    This is the Brake Fluid Circuit for Prius Gen4, Corolla HEV 2019 (EU), CH-R 2016 (EU). It is very, very complicated, I haven't yet figured all out, but I am in the process of.

    Dorin
     
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  7. alanclarkeau

    alanclarkeau Senior Member

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    What are you wanting to do with it? Yes, seems very complicated, but we ask more and more of our brakes these days.
     
  8. Elektroingenieur

    Elektroingenieur Senior Member

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    Here’s the same diagram (from New Car Features, under Brake: Brake Control/Dynamic Control Systems: Brake Control System: Brake Control), in which I’ve replaced the reference numbers *1–*32 with text labels for easier reading:
    BrakeFluidCircuitDiagram.png
    The same section of New Car Features has text, tables, and twelve other versions of the diagram, which explain how the brake system and its valves operate under various conditions. I highly recommend it.
     
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  9. bisco

    bisco cookie crumbler

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    i only ask one thing of my brakes, the rest is icing...
     
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  10. alanclarkeau

    alanclarkeau Senior Member

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    It's actually got 3 "normal" functions - plus about 7 others which are happening from time to time, possibly without you knowing, as well as 2 emergency functions (if one brake circuit malfunctions, plus if there's a Power Supply malfunction.
     
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  11. ChapmanF

    ChapmanF Senior Member

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    Goodness gracious, what's with the new small pumps and reservoirs inside the actuator, and what's a gap hold valve, and why does the stroke simulator cut valve look like it's normally-open and in the wrong place to cut the stroke simulator? :confused:
     
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  12. bisco

    bisco cookie crumbler

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    must be why there's a recall :rolleyes:
     
  13. Elektroingenieur

    Elektroingenieur Senior Member

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    I believe they are return pumps. New Car Features doesn’t explain, but see, for example, U.S. patent 6,079,799 to Sawada et al., reference numbers 9, 10, 39, and 40, and Bosch’s book Brakes, Brake Control and Driver Assistance Systems: Function, Regulation and Components (2014), page 75:

    If the degree of slip of any of the wheels increases further despite [switching the solenoid valves to the ‘maintain pressure’ setting], the pressure in the brake(s) concerned must be reduced. To achieve this, the solenoid valves are switched to the “pressure release” setting. The inlet [S__H] valve is still closed, and in addition, the outlet [S__R] valve opens to allow the return pump integrated in the hydraulic modulator [brake actuator assembly] to draw brake fluid from the brake(s) concerned in a controlled manner. The pressure in the relevant brake(s) is thus reduced so that wheel lock-up does not occur.​
    The gap hold valve SGH (to its designers, 離間室カットバルブ, separation chamber cut valve) is open during normal operation, so pressure from the gap hold chamber behind the input piston in the master cylinder can reach the stroke simulator. If the brake actuator or power supply fails, SGH is de-energized and closes.
    Similarly, the stroke simulator cut valve SSA is closed during normal operation, but if the brake actuator or power supply fails, it is de-energized and opens.
     
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  14. Dorin Abeaboeru

    Dorin Abeaboeru New Member

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    Indeed, the pump inside the brake actuator is used for ABS related functions, just like the classic braking system.
     
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