How do the power brakes work in our Claritys?

Discussion in 'Clarity' started by KentuckyKen, Aug 5, 2018.

  1. KentuckyKen

    KentuckyKen Well-Known Member

    OK, I know we have a fantastic braking system that seemlessly blends regen with friction on all 4 disc brakes. I think Honda does this better than anyone. You can’t even feel it in the pedal when it apportions between the two.

    My question is more technical. How do we get power brakes when there is no ICE and engine vacuum to power the master cylinder like in my old gasmobile? Obviously it must be electrically driven, but does anyone know exactly how?
    I don’t see a master cylinder attached to the brake reservoir; in fact it looks fairly naked. I see the assumed ABS module in front of it and I see one low presssure hose running off the back of it and across the firewall down to what looks kind of like a large master cylinder low down on the left rear of the engine bay. It looks like it’s electrified. So is it electric vacuum pump powered or hydraulic pump powered or something else?
    Inquiring minds want to know.
     
  2. insightman

    insightman Well-Known Member

    Honda's Clarity PHEV press kit says, "An electric-servo brake system is deployed for regenerative braking..." So no vacuum, no hydraulics--it's brake-by-wire.
     
  3. KentuckyKen

    KentuckyKen Well-Known Member

    There are hydraulic lines going from ABS and going to all four calipers, so the final transmission of force is hydraulic like regular brakes. I was curious to know how the hydraulic system was powered.
     
  4. insightman

    insightman Well-Known Member

    You peeked! I just googled. I guess the electric servo must activate the hydraulic system. The servo must be strong enough not to need a vacuum-powered master cylinder? I hope there's not a fuse between the brake pedal and the servo!
     
  5. KentuckyKen

    KentuckyKen Well-Known Member

    Thanks. Trying to figure this car out is like trying to assemble a puzzle that’s still in the box in the dark with mittens on and your hands tied behind your back! I curse Honda regularly for not allowing us to buy the Clarity specific shop/service manual.

    And I'm sure that whatever powers the power brakes is set up like a regular engine vacuum master cylinder so that if the powered side fails, you’ve still got unpowered brakes but you just need way more pedal effort.
     
    Numbernine likes this.
  6. insightman

    insightman Well-Known Member

    I kept googling. Here's a video about the electric-servo brakes in the Fit EV. Here's a diagram from the video:
    upload_2018-8-5_18-47-13.png
     
    Viking79, Johnhaydev and KentuckyKen like this.
  7. KentuckyKen

    KentuckyKen Well-Known Member

    @insightman, you are my hero! So the servo motor is what magnifies our pedal effort when pure regen is not enough to slow us down.
    I watched the video and it has a very interesting graph on how Honda maximizes regen when we brake better than most other EVs. Also interesting is how we get a simulated brake pedal feel even when it’s all regen and no caliper pressure is applied. A beautiful piece of engineering all the way around.
    Thanks for finding the answer.
     
  8. insightman

    insightman Well-Known Member

    After 19 years of driving Honda's first take at integrating regen and mechanical braking, I'm amazed every time I feel the smooth, seamless operation of of our Clarity's brakes. I absolutely cannot tell when the discs take over--which I must admit is a little frustrating. My dreamed-for technical info display on the head unit would include an indicator signaling when the electric servo is activated so I could learn to brake using mostly regen.
     
  9. KentuckyKen

    KentuckyKen Well-Known Member

    I’d like more info too but I think we can do that by noticing on the power meter how far down into the green you go when you brake. I think as long as we don’t bottom out on the display, then it’s all regen until the last low speed part of the stop.
     
    Last edited: Aug 5, 2018
  10. weave

    weave Active Member

    So if it's brake by wire, what happens if the power is cut off. For example, the car fails or you emergency shut it down by holding the power button down. Is braking still possible?
     
  11. neal adkins

    neal adkins Active Member

    In the owners manual on pages 434 and 438, and 439 it goes in-depth about the braking system. Ebd electronic brake distribution system and bas brake assist system in addition to abs. It gives a brief description of each system.
     
  12. neal adkins

    neal adkins Active Member

    on my camry hybrid all the regen is done by the cvt wich actually a generator sitting in oil. The brakes bring the car to a smooth stop and kick in when speed js below 10mph approx. So the clarity regen is probably the same design. Therefore the disc brakes don't regen the car at all. So as long as you see the regen charge level in the green it is all regen braking. I would also think that when you tap the regen paddle al your doing is lightly applying the brake system.
     
  13. insightman

    insightman Well-Known Member

    This text from page 434 seems to imply the disc brakes are activated by any contact with the brake pedal:
    Do not rest your foot on the brake pedal while driving, as it will lightly apply the brakes and cause
    them to lose effectiveness over time and reduce pad life. It will also confuse drivers behind you.
     
  14. Sandroad

    Sandroad Well-Known Member Subscriber

    Toyota has been using the hydraulic booster pump type system for years. The pump supplies the extra pressure needed to stop the vehicle and if the servo motor fails, it's really hard to activate the brakes! You have to push really hard; harder than many folks are strong enough to do. But that type of system allows for the very sophisticated ABS/traction control/stability control systems that use the brakes in vehicles today. I think KentuckyKen may be a generation behind in thinking any vehicle now uses vacuum brake boost, but I could be wrong.
     
  15. KentuckyKen

    KentuckyKen Well-Known Member

    @Sandroad, are my old school roots showing?
    The Clarity definitely uses a servo motor to assist the braking as @insightman showed on the video with his great find on the Fit’s system.
    So the servo motor is magnifying the hydraulic pressure like the old engine vacuum used to do in my 08 CR-V???

    What’s really neat is how Honda figured out how to get more regen than other cars and keep the regen going longer into the stop.
    Check out this graph from the video:
    B17D83DB-46AD-4C7E-A167-39FBCF4C4438.png
    I find it’s possible to slow by regen 100% except for the final 5 mph or so if you don’t run up to the next stop and brake at the last minute and his graph shows why.
     
  16. KentuckyKen

    KentuckyKen Well-Known Member

    It’s definitely hydraulic. Just look under the hood and see diagram posted by @insightman. It’s assisted by a servo motor to give us power brakes. So just like old school engine vacuum assisted power brakes, you still have manual brakes even if all else fails. And as in all cars there are two separate fluid paths for front and back so a leak in either line wont leave you with no brakes.
    So I think it’s just like the “old timey” brakes except the power is from an electric servo motor instead of engine vacuum.
    I assume the brake hold and parking brake work by actuating the servo motor?? Can we tell if that is so?
     
  17. jdonalds

    jdonalds Well-Known Member

    Yes and
    I'm sure the extra hard unnecessary breaking by the ACC is wearing out the brakes prematurely.

    Our 2008 Prius is still on the original brakes with almost 200,000 miles on the car.
     
  18. insightman

    insightman Well-Known Member

    I would expect the brake hold button to actuate the servo motor because brake hold is used only when the car is being driven. However, the electronic parking brake must perform its job when the car is off, so I doubt it could use the servo motor.

    Honda of Ocala's tutorial on brakes says Honda's light trucks use an electric motor to tighten the emergency brake cable (which I assume pulls the rear brake pads into contact with the rear discs). Don't ask me why you can't buy a Ridgeline and a Pilot in the same place:
    Electronic parking brakes like the kind you’ll find the new 2017 Honda Ridgeline for sale near Ocala and the 2017 Honda Pilot for sale near Marion County, FL use an electric motor to tighten the emergency brake cable instead of doing so manually.
     
  19. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    Did anyone think they did?

    All regeneration happens in the motor, not the mechanical brake system. Regen is similar to engine braking in a gasmobile or diesel truck. An EV turns the electric motor into a generator, generating power in the motor while slowing the car.

     
    neal adkins likes this.
  20. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    I hope the system will provide power from the 12v starter battery as an emergency backup?

     

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