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Automotive Could a 100% hydraulic system as a vehicle prime mover work?

  1. May 25, 2012 #1
    Given: I understand that there would have to be the equivalent energy source to drive the pump. That I will look to later (my gut says the real issue), but for the purposes of this discussion, assume endless power from a source of electricity or hydraulic pressure/flow, and you have to build a system and integrate it into a demonstrable vehicle asap.

    Two initial questions:

    1. In a perfect world, between an electric prime mover and a hydraulic, which would (in your view) be better vis-a-vis: off the shelf components, performance, longevity, and simplicity.

    2. If a hydraulic prime mover is indeed better, could you not simply mount up the motor to the yoke of the differential and achieve the same performance (thereby by-passing the need for a transmission)?

    I have been thinking about this for a couple of weeks and am trying to get a handle on this.

    Thanks in advance
  2. jcsd
  3. May 25, 2012 #2


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    Staff: Mentor

    Welcome to the PF.

    I don't know if it helps, but 2-wheel drive motorcycles have been using hydraulic drive for a number of years now:


  4. May 25, 2012 #3


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    Science Advisor
    Gold Member

    Hydrostatic drive vehicles are very common although I haven't heard of it for regular passenger automotive vehicles. Do you have something different in mind or can I assume you are thinking powering a hydraulic pump with some type of engine (gasoline, diesel, etc.) and then controlling the flow to one or more hydraulic motors (wheel motors, single motor at differential input shaft, etc.)?
  5. May 25, 2012 #4
    Yes, driving the hydraulic pump with another source of energy (diesel, gas, etc.).
  6. May 25, 2012 #5
    Lots and lots of special designed vehicles do all that you propose already. I've worked with and around them for decades. With recent improvements in pump and motor technology, it now seems reasonable for a very large variety of vehicle sizes. The trouble is that for smaller vehicles, like passenger cars, the fluid power is much more expensive than conventional options. But if I have to design a thousand ton crane to lift a load and roll down a rail, I'd have no other reasonable options than fluid power.
  7. Jun 8, 2012 #6
    Its not 100% but close enough



    actually I looked into this for my car with these specs,

    Speed: 400-4000 rpm (67 rev/sec)
    Disp Size: 2pcs 378 cm/rev (29 in^3/rev)
    Pressure: 0-276 Bar (0-27Mpa) (0-4000psi) max 5000psi
    Flow rate: 809l/min (13.5 L/s)(213gpm) or 1pc 1618 L/min (27 L/sec)(427gpm)
    Power: 300kW working (402 Hp working) or 1 pc 745 kw (theoretical) (600kW working)
    Torque: 1424Nm (12605 in-lb)(1050 ft-lb)
    direction: Bi-directional
    material: steel/iron preferred, others optional
    type: internal gear positive displacement preferred, others optional
    shaft: axial or radial, splined
    QTY: 1 or 2
    Fluid: Hyd, normal vis.
    flange/port: code 62 preferred or at providers discretion
    Mounting: suitable
    Noise: N/A
    Temp: 15-100 degrees C

    the quote was $9000-$12000 for each pump
    Last edited: Jun 8, 2012
  8. Jun 18, 2012 #7
    A lot of care would need to be taken to optimize the flow of the fluid or you will just generate heat.
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