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In a conventional hydraulic transmission, the engine drives a pump which pushes fluid through motors located at the wheels. Because the fluid has to travel long distances throught the lines, there are high viscous losses. Maybe it would be better to trasmit the energy through high pressure pulses.
The displacement of each bit of fluid relative to the line walls would be very small, so viscous losses should be reduced. Also, only one line would be necessary. The engine would be connected to a pulse generator, which would cause plungers at the wheels to oscilate. This oscillation would be converted to rotary motion by a one-way clutch mechanism. When load is high, the plunger oscilation amplitude decreases and torque increases, etc.
Patent for vibrating hydraulic system
http://www.patentst...5665919-claims.html
It seems someone has been trying this. [pashute, Feb 27 2008]
gogu constantinescu
http://fluid.power....pn/const/index.html
see this page about sonics theory and torque converters [blimpyway, Jun 11 2008]
On analagous systems
http://en.wikipedia...i/Hydraulic_analogy
strengths and weaknesses discussed [4whom, Jun 12 2008]
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Would it go "lub-dub...lub-dub..."? |
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Certainly making directional-boring machines more effecient |
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The main loss of efficiency in an automatic transmission is through the torque converter, which is basically a pump, and is relativly inefficient, but there is a simple way to solve that. The biggest problem is that each time you convert one type of motion to another you lose a large portion of the energy involved. This is why rotary engines should be superior to conventional piston engines, no reciprocating motion to deal with. With your idea we still have to deal with inefficiency in the pulse generator, and with the pistons at the wheels. We could simply have one hydraulicly actuated piston drive a conventional driveshaft, but we could accomplish that much more simply with a steam engine. IMHO it would be much easier simply to stick with a clutch and manual transmission. |
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[austere_apathy] - I believe that [gabe] was not referring to automatic gearbox / transmission systems as found in many cars. Rather, we're talking about systems that use hydraulic lines instead of driveshafts. |
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yes, I was talking about conventional hydrostatic transmissions such as the ones used in forklifts or some lawnmowers. |
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oops, sorry. In that case, it makes a little more sense. |
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Well, the engine actuates a diaphragm pump through you standard cam, sends pulses through single line,pulses at the other end are transformed to a steady flow by another diaphragm pum(through a different circuit) that moves a conventional gear motor. You have eliminated the return line and simplified the system. And perhaps, as you said, the
performance will be better. Bun for you. |
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I am assuming this is more than a single sided hydraulic system - such as used to provide lift when gravity is available for lowering (single hose cylinders) like hydraulic jacks....
This is an interesting concept and it would be good to build such a system to gain knowledge - the problem I see is you are making a hydraulic system that is more like an AC electrical system (which alternates current direction - or pulses electricity) now pulsing fluid has some inherant problems that I see.... 1) the entire fluids in the line has to be started and stopped many times per second? Would this not be more like pressure waves in a fluids system - does this not cause reflection of energy and possibly damaging energy spikes when the reflected wave meet the oncoming waves (I believe this is the definition of water hammer in pipes) 2) I believe this may cause a lot of loss in energy because although nearly incompressable the fluid will compress and expand - loosing energy - generating heat? 3) this may be more of a vibration that the fluids will act to adsorb more than pass the energy along and the vibration will be passed to everything (Lines, pumps, and motors) that touch the fluid - also acting to destroying the system? |
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[sklaus], your anno sounds like those anti AC vibes, from Thomas Edison and his friends, when AC electricty was first out. Perhaps with a proper "transformer" you could get back more of the energy on the other side, and probably because of the wavelike pulsing, you would reach some sort of better energy transfer that avoids viscosity and shear loss.
A proper transformer at the end of the line would shield the motors from energy spikes. |
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Move out of car:Transmission and to Product:Energy:Other its about transmitting energy, not about car gears. |
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I'm really not sure you are losing all that much energy to loss in the hoses as you think, the loss also is dictated by the length of the hose so in a pulsed system you would still have losses over the entire length of the hose, just divided over the in pulse and the out pulse, this being the case the losses may actually be greater for a given input of energy as you also need to over come the inertia of the fluid transitioning from forward to reverse flow. |
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I don't know this is very interesting and seems very analogous to converting DC to AC. In that line of thought, it should be better to actually run three lines to the motor to transmit 3 phase AC hydraulic fluid. Go with high pressure/low volume to lower friction. The motor would just convert the 3phase back into DC to drive the motor in a similar fashion that an electrical 3phase current would be converted to DC. Then you create 6 one-way valves (hydraulic diodes) to create reasonably smooth flowing DC for the hydraulic motor. |
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This maybe outside the original design of the idea and I am not completely sure there would be less frictional losses. |
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WOW [masterQED] you just managed to trample on like half the physics textbook. I think you are on VERY shaky ground to make any kind of comparison between electrical Transmission and Hydraulic Systems. While hydraulics is a convenient analog of an electrical distribution system, the principles and realities involved are fundamentally dissimilar and cannot be interchanged. |
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The appropriate analogy with electrical
transmission would be the use of high
voltage lines for long distance, low-loss
transmission. By that analogy, you want
to use a hydraulic line that operates at
very high pressure but moves only a
small volume of liquid. |
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The question of "AC" versus "DC" is
subsidiary. AC is advantageous,
because power transmission is
proportional to the RMS voltage; in
effect, the peaks of your AC wave are
more efficiently transmitted, being
high-voltage compared to the troughs. |
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The analogy holds good for liquids -
system will be slightly more efficient if
power is transmitted by "AC", except
that you'll have new losses caused by
the tubes ballooning. |
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Overall, the most important thing is to
use high pressure and low volume. |
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With [jhomrighaus], I think you'd lose energy accelerating and decelerating the fluid continuously. Also, it would be a perfect fatigue machine and you'd fail pressure lines, fittings etc on a very frequent basis. |
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[jhomrighaus] No, I’ll admit the advantages are dubious, but the physics are sound. First I’ll explain the physics, and then we can debate the existence of any advantage. |
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My analogy to a DC current is a standard vane type hydraulic pump connecting to another vane type hydraulic pump. Fluid flows one way on one hose and back in another, which is analogous to electron flow in DC electrical circuits. My analogy of AC current is a single piston pump on a crank with no valves that is connected to a second identical single piston pump on a crank. Fluid never circulates, only moves back and forth in the single hose. The current of the fluid alternates direction. I suggested three phase to even out the power transmission. The one way valves enable the AC flow to be turned back into DC flow to allow non-identical motors. |
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The dubious advantage is whether this system creates more/less or identical fluid friction. And yes, this would lead to severe fatigue problems and the energy loss from decelerating and accelerating the fluid may be significant. Or the pipe expansion may absorb all pressure changes. |
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i have no objection to the analogy, what I object to is the physics, what works for an electrical distribution system does not work for a hydraulic system, for example, in an electrical system the working medium(electrons) are essentially massless and move at the speed of light, thus AC power does not have to overcome inertia, In a hydraulic system the fluid has considerable mass and thus a considerable inertia that must be overcome if you were to physically move the fluid forward and backward rapidly. |
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Another issue that arises is the speed of propagation of the pressure pulse in the fluid which as mentioned before is limited to roughly the speed of sound in a fluid, thus long distance transmission of fluids is problematic (one of the reasons for water hammer) the pulses will rapidly get jumbled up and lose coherence unless the pulse rate is quite slow. Contrary to many statement fluids can be compressed such that a pulse of pressure is transmitted. If it was not so then if you blew a depth charge all the water in the ocean would move at once which is not the case. |
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For a hydralic system linear flow is normally the most efficient means as the system can reach a static equilibrium and then you extract whatever energy you wan t from the system. Another difference is the conduit itself which is flexible such that you experience small but measurable losses due to expansion of the conduit, thus the more frequently the pressure changes the greater the amount of loss that is incurred by expanding the conduit with the pressure pulse. |
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While it may seem like a an equivalence exists, this is really not the case. |
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// in an electrical system the working
medium(electrons) are essentially
massless and move at the speed of
light,// No, they don't. Honest. |
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Suppose we have a 1 metre long copper
wire with a cross-section of 1 square
millimetre, carrying a current of 1 amp.
How fast do the electrons move? |
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Well, first of all let's assume that there's
one mobile electron for each copper
atom (not true, but roughly). The wire
contains about 10^23 atoms of copper,
and hence 10^23 mobile electrons. |
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Now, in one second, at one amp, one
coulomb of charge passes through the
wire. The charge on an electron is 1.6 x
10^-19 coulombs, so roughly 10^18
electrons pass out of the end of the
wire per second. Dividing 10^18 by
10^23 tells you that, in one second, the
electrons move about 10^-5 metres, or
about a hundredth of a millimetre. |
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So, the electrons in the wire are moving
just over an inch per hour. This is
substantially less than the speed of
light. |
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Look, strip away the confusing stuff and its a really simple idea. |
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Two double acting pistons act to comunicate hydraulic energy without the need for a return line. Oscilation on one end produces occiation on the other and work is communicated. Simple but pointless anywhere where a better sytem could be used. Fluid systems push great, but they hate to pull (suck fluid). A flow regulated loop is more efficient and thus the standard for transmitting power at a distance. |
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What you describe here was developed almost a century ago by George Constantinescu - under the technical field of sonics - that basicaly is using vibrations or pulses in a fluid or solid medium to transmit power. |
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One important aplication was a through-propeller machine gun synchronising fire device, used by british aircraft during WWI . |
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Others applications folowed - like drilling hammers or fluid propelled gun.
Also an inertial infinitely variable torque converter was inspired by his research on sonics.
(see the gogu constantinescu link above for detailed info) |
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What you are describing seems more analogous to a modern switching power supply than a transformer. The general approach doesn't require fluids, though they probably simplify things. A non-fluid analogue would be a pile driver. Each whomp from the falling weight will yield roughly the same amount of energy; the less force is required to move the piling, the further it will travel. I believe an impact wrench is also similar. |
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The problem in all the mechanical situations is that the frictional losses end up being rather huge. To be sure, in a typical pile-driver application, the primary force to be overcome is friction, but if one were using the same approach to compress a spring against a ratchet it would be possible to have a continuously-variable transmission without any fluid. |
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