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Can hydraulic systems replace ebikes in power assisted cycle

  1. Jul 26, 2017 #1
    Instead of an electric motor, can it be substituted with an hydraulic force / power amplifying system instead?

    If yes, how would it work? Could chains still be used?

    Instead of an electric motor powering the hydraulic system, could the rider power the hydraulic system through force / power application whilst pedaling?
     
  2. jcsd
  3. Jul 26, 2017 #2

    JBA

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    A hydraulic pump plus motor combination is less efficient than a chain and sprocket drive and therefore of no benefit to the rider. An electric motor assists the rider by delivering energy stored in the battery and therefore reduces the riders energy requirement.
     
  4. Jul 26, 2017 #3

    Baluncore

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    Variable ratio hydraulic motors and pumps are expensive and inefficient compared to roller chain drives.
    Electrical DC to DC converters are light weight and efficient.

    The storage of energy in a hydraulic accumulator is bulky and heavy compared to electric batteries.
     
  5. Jul 26, 2017 #4

    russ_watters

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    Staff: Mentor

    There is no such thing as a "power amplifying system". That would violate conservation of energy.
     
  6. Jul 26, 2017 #5
    I was referring to a system where the motor multiplies the force exerted by the user on the pedals, thus multiplying input speed too.
     
  7. Jul 26, 2017 #6

    Baluncore

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    True. Power is torque * RPM. Gears are equivalent to a transformer that adjusts the ratio of torque to RPM, while maintaining power, = energy flow. What is really needed is an impedance matching system that efficiently optimises power generation by the cyclist and delivery to the drive wheel.

    A cyclist operates most efficiently at a particular cadence and pedal force. With hydraulics, a fixed volume per revolution pump could be used. The hydraulic fluid would then drive a variable ratio motor. By controlling the motor ratio, the hydraulic pressure would be regulated at a point set by the cyclist. That maintains optimum power generation and transfer, while adjusting for road speed and slope. Power variation would be by quickly adjusted by changing cadence or more slowly by changing the pressure setting.

    The requirement that the system be efficient really precludes hydraulics. An electrical system would be more efficient than hydraulics. But roller chain with selectable sprockets and a derailleur is simple, and more efficient than electricity.
     
  8. Jul 27, 2017 #7

    russ_watters

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    Power is torque (force) times speed. If you get more out than you put in, that's a violation of conservation of energy.
     
  9. Jul 27, 2017 #8

    anorlunda

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    I don't dispute what you say, but I can't help thinking of the video of this year's America's Cup Races. They replaced the old direct drive winches with hydraulics. They must have given up some efficiency. What benefit could they gain in return?
    1. Energy storage: Crew members (when they get the chance) manually crank the hand wheels to store energy in the hydraulic accumulator. The energy is used later when needed. With a direct drive, power must be supplied in real time.
    2. Multi-station generators. Multiple hand cranks allow multiple crew members to generate energy to be stored.
    3. Centralized command and push-button application of power. The helmsman had buttons on the steering wheel that commanded sail and other boat adjustments utilizing the previously stored energy.
    It is hard, but not impossible, to imagine similar benefits on a bicycle. Perhaps a multi-rider bicycle could be closer to a yacht. Instead of coasting downhill, the cyclist could store energy to help going up the next hill.

    It would be a fun project to design a car for city traffic that uses a more-or-less constant power engine plus accumulator. Power generation could be levelized while the vehicle goes up/down/accelerate/decelerate. The accumulator and drive motors could be hydraulic or electric.

    It would be even more fun to watch a Tour de France where the cyclists could store/release energy on command. They could use their own stored energy to put on a burst of speed to pass the pack. If that existed for all competitors, how would race tactics evolve? Of course, the accumulator+motor must not be very heavy if used in racing.
     
  10. Jul 27, 2017 #9

    JBA

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    The new Renault EV cruise control uses its regenerative braking system in just such manner, no added system(s) required.
     
  11. Jul 27, 2017 #10

    russ_watters

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    I meant to look into the rules, but 8m going to guess they used hand and pedal power for "purity" reasons; a sailboat should be powered by wind and controlled by people, period.

    Or do you mean why hydraulics instead of having people crank to charge batteries and then use servo motors? Probably the same reason you use hydraulics anywhere; massive force at low actuation speed.
     
  12. Jul 27, 2017 #11

    anorlunda

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    Sure, regenerative braking has been around for decades. But regenerative brakes can't store energy while waiting at a red light. Think of a hybrid vehicle like the Prius. Think of a non-conventional source like a Stirling engine.

     
  13. Jul 27, 2017 #12

    anorlunda

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    No it's not propulsion. Below is a picture of a conventional sheet winch used to pull the ropes that control sail shape. It is those (plus raise/lower the hydrofoil fins) that they converted to hydraulic.

    images?q=tbn:ANd9GcRv_dOgQp87JYVU_3aHGXJv3EbqnJVa2VxoGJtqvspNUudPkqBQ.jpg
     
  14. Jul 27, 2017 #13

    russ_watters

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    I chose my words carefully: powered by wind and controlled by people. If you have a generator or large battery bank, that violates the "powered by wind" philosophy. Admittedly though, they are softening up on the "controlled by people" part a bit, at least in terms of information if not direct fly by wire.
    [Edit]
    I was speculating, but that is indeed the logic:
    https://www.quora.com/Why-are-they-constantly-grinding-on-America’s-cup-racing-yachts
     
  15. Jul 27, 2017 #14

    russ_watters

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    ...Not to get too far off track, but it looked to me like the hydrofoil lift and trim was not fly by wire (I saw a lot of forward drooping), which seems a bit scary to me. I kept expecting to see one dolphin-dive and cartwheel.
     
  16. Jul 27, 2017 #15

    anorlunda

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    No, not if the battery is used to adjust the controls, and does not power propulsion. The phrase "wind powered" refers to propulsion. To say otherwise would make it illegal to have a spring loaded button, push/push to release. And the way those guys run on the edge, nobody could get away with "small" battery is OK, but "big" is illegal.
     
  17. Jul 27, 2017 #16

    anorlunda

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    I agree, it looks scary. And the helmsman can certainly control them incorrectly.

    But I saw a close up of the steering wheel (sorry, I can't find a picture right now). It had buttons to raise/lower those fins, and if you watch the videos, you can see them going up and down when nobody is near them. They are remote controlled.
     
  18. Jul 27, 2017 #17

    russ_watters

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    They do make compromises, but clearly this is not one of them. If electrically actuated controls were allowed, they would have stopped hand (and foot) cranking decades ago and switched to electric motorized winches and big battery packs or gas generators. They hand and foot crank because they felt a line would have been crossed otherwise.
     
  19. Jul 27, 2017 #18

    russ_watters

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    Yes, I know the activation is push-button, but when I say "fly by wire", I mean full fledged fly by wire, which includes computer control. I don't think there is any computer control of the wings. I think the front to back trim is by the same set of buttons on the helm.
     
  20. Jul 27, 2017 #19

    RonL

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    In line with what you are saying, a method to have weight transformed into forward motion is something I tried to get patent coverage in 1978 (no success) :frown:

    SCAN0096.JPG
     

    Attached Files:

  21. Jul 27, 2017 #20

    anorlunda

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    Bummer on the no success.

    Sounds interesting, but you need to learn to use math to express yourself. I got these words from your drawing, "Piston in front of power position might carry a small ..." That's not the right kind of language for a patent application. You need to calculate what the piston will definitely do based on first principles.
     
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